Patent Publication Number: US-2005125134-A1

Title: Deceleration control apparatus and method for a vehicle

Description:
INCORPORATION BY REFERENCE  
      The disclosure of Japanese Patent Application No. 2003-407782 filed on Dec. 5, 2003 including the specification, drawings and abstract is incorporated herein by reference in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to a deceleration control apparatus and method for a vehicle. More particularly, the invention relates to a deceleration control apparatus and method for a vehicle, which controls deceleration of the vehicle by an operation of a brake system which applies braking force to the vehicle and a shift operation that shifts an automatic transmission into a relatively lower speed or speed ratio.  
      2. Description of the Related Art  
      Technology is known that controls an automatic transmission and a brake in cooperation by operating the brake when the automatic transmission is manually shifted into a speed that will cause the engine brake to engage. One such example of this type of technology is disclosed in U.S. Pat. No. 2,503,426.  
      According to the technology disclosed in U.S. Pat. No. 2,503,426, when an automatic transmission (A/T) has been manually shifted so that the engine brake will engage, the brakes of the vehicle are operated to prevent free running of the vehicle due to the vehicle being in a neutral state between the time that the shift starts and the time that the engine brake engages.  
      According to U.S. Pat. No. 2,503,426, the brakes of the vehicle are operated corresponding to a peak value of an engine negative torque during the shift obtained from the type of shift and the vehicle speed and the like, from the time that a manual downshift command is given either for a predetermined period of time or until the engine brake starts to engage (i.e., until the absolute value of the negative torque of the output shaft of the automatic transmission becomes large). Because the brakes of the vehicle are applied during the manual shift with a braking force that corresponds to the negative torque of the output shaft of the automatic transmission during the shift, a braking force is applied to the vehicle which corresponds to the amount of engine brake during the manual shift. As a result, a steady braking force is applied to the vehicle from the time the manual shift is performed until the shift is complete, such that a highly responsive and steady braking force can be obtained during the manual shift. Fluctuation in braking force is able to be reduced because the engine brake does not suddenly engage due to the brakes of the vehicle being applied while the automatic transmission is in the neutral state.  
      In U.S. Pat. No. 2,503,426, the brake is operated a predetermined amount for a predetermined period of time to reduce (deceleration transitional characteristics) problems in the period of time until the deceleration torque by the manual downshift is stably generated. The problems with the deceleration transitional characteristics during a shift of the automatic transmission in U.S. Pat. No. 2,503,426 include the initial neutral state, and the low torque region and the torque step from the end of the first shift, at which time the second shift is performed, through the start of the second shift.  
      In the foregoing publication, the predetermined period of time for which the brakes are operated is determined based on the detection results of the rotation speed of the output shaft of the automatic transmission and the engine speed. The predetermined amount that the brakes are operated is determined based on the kind of shift and the vehicle speed. However, the following problems and complications arise when putting this method into practice.  
      That is, when the predetermined period of time is determined based on the detection results of the rotation speed of the output shaft of the automatic transmission and the like, detection delays, as well as a dispersion in those delays, may result in the deceleration torque produced by the brakes not matching the deceleration torque produced by the automatic transmission. As a result, good deceleration characteristics may not be achieved. Further, while it is possible to use a timer for timing the period of time that has passed from the shift timing (the start/end timing) when determining the predetermined period of time, dispersion in the shift timing may result in the deceleration torque produced by the brakes not matching the deceleration torque produced by the automatic transmission.  
      Also, with regard to the predetermined amount that the brakes are operated, dispersion (on both the release side and apply side) in the clutch torque of a clutch, which is an apply element of the automatic transmission, may also result in the deceleration torque produced by the brakes not matching the deceleration torque produced by the automatic transmission.  
      In order to solve the foregoing problems, a learning correction or other such measure based on the operating results of the automatic transmission and the brakes is necessary. The foregoing problem arises due to the fact that both the automatic transmission and the brakes are sequence controlled in the foregoing publication.  
      U.S. Pat. No. 2,503,426 only mentions that the brake control generates a braking force by the brakes for the predetermined period of time and of the predetermined amount during the period until the deceleration torque by the shift of the automatic transmission is stably generated. No mention was given to deceleration control required by various other situations.  
      As described above, the technology in U.S. Pat. No. 2,503,426 applies braking force by the brakes until the deceleration torque by the shift of the automatic transmission is stably generated. Accordingly, the braking force by the brakes is a value which is calculated only once for each shift as the predetermined amount based on the type of shift and the vehicle speed, and applied for a predetermined period of time. The amount of braking force applied by the brakes is fixed. Therefore, the technology in U.S. Pat. No. 2,503,426 does not anticipate flexibly controlling an event generated (by something other than a shift) in real time regarding a deceleration required by the vehicle by changing the braking force applied to the brakes.  
      Further, consideration given to the control details of the braking is insufficient. The technology described in U.S. Pat. No. 2,503,426 still leaves room for improvement with respect to deceleration transitional characteristics of the vehicle. Also, U.S. Pat. No. 2,503,426 only discloses deceleration control by a manual downshift and does not mention that the invention can be applied to deceleration control performed when it has been determined on the vehicle side that deceleration is necessary.  
     SUMMARY OF THE INVENTION  
      In view of the foregoing problems, this invention thus provides a deceleration control apparatus and method for a vehicle which can respond to various situations and achieve a good deceleration transitional characteristic for the vehicle.  
      That is, one aspect of this invention relates to a deceleration control apparatus for a vehicle provided with a brake system for generating braking force in the vehicle, and a transmission. This deceleration control apparatus includes a controller that controls the brake system and the transmission such that a deceleration acting on the vehicle matches a target deceleration set as a deceleration to be applied to the vehicle by a brake operation of the brake system and a shift operation which shifts the transmission into a relatively low speed or speed ratio.  
      Another aspect of the invention relates to a deceleration control method for a vehicle provided with a brake system for generating braking force in the vehicle, and a transmission. This deceleration control method includes the steps of setting a target deceleration as a deceleration to be applied to the vehicle by a brake operation of the brake system and a shift operation which shifts the transmission into a relatively low speed or speed ratio; and controlling the brake system and the transmission so that the deceleration acting on the vehicle matches the set target deceleration.  
      According to the deceleration control apparatus and method for a vehicle described above, a target value of the deceleration, which is the sum of the deceleration by the brake system and the deceleration by the shift operation, can be set as the target deceleration. By cooperatively controlling the brake system and the transmission so that the deceleration matches the target deceleration, a smooth shift is made possible. Also, in the deceleration control according to the invention as described above, the operation of the brake system (i.e., brake control) and the shift operation (i.e., shift control) can be executed simultaneously in cooperation with one another. The deceleration here refers to the degree (amount) of vehicle deceleration represented by the deceleration or deceleration torque.  
      Still another aspect of the invention relates to a deceleration control apparatus for a vehicle provided with a brake system for generating braking force in the vehicle, and a transmission. This deceleration control apparatus includes a controller that controls the braking force generated by the brake system so that a target deceleration acts on the vehicle. This control is based on i) the target deceleration which is set as a deceleration to be applied to the vehicle by a brake operation of the brake system and a shift operation which shifts the transmission into a relatively low speed or speed ratio, and ii) a deceleration by the shift operation into a speed or speed ratio selected as a speed or speed ratio appropriate for achieving the target deceleration.  
      Yet another aspect of the invention relates to a deceleration control method for a vehicle provided with a brake system for generating braking force in the vehicle, and a transmission. This deceleration control method includes the steps of setting a target deceleration as a deceleration to be applied to the vehicle by a brake operation of the brake system and a shift operation which shifts the transmission into a relatively low speed or speed ratio; and controlling a braking force generated by the brake system so that the target deceleration acts on the vehicle. This control is based on the set target deceleration and a deceleration by the shift operation into a speed or speed ratio selected as a speed or speed ratio appropriate for achieving the target deceleration.  
      According to the deceleration control apparatus and method for a vehicle described above, when the target deceleration is set and the speed or speed ratio appropriate for achieving that target deceleration is selected, the brake system can be controlled in real time to compensate for the difference between the target deceleration and the deceleration by the shift into the selected speed or speed ratio so that, as an overall result of the cooperative control of the brake system and the transmission, the target deceleration acts on the vehicle.  
      Unlike the control in U.S. Pat. No. 2,503,426, the control of this invention is not a sequence control (e.g., a control in which the stages of the control are proceeded through successively according to a predetermined sequence in which, after the type of shift is determined, the braking force is then determined based on that type of shift and the vehicle speed, and then that determined braking force is applied for a predetermined period of time). Therefore, this invention is able to respond to various situations, and as a result, achieve a good deceleration transitional characteristic of the vehicle.  
      In this invention, as a result of the cooperative control, the brake system performs a final adjustment (correction control) when the target deceleration is applied to the vehicle. Because the brake system has better response as well as a higher degree of freedom in the deceleration it generates than does the transmission, it is suitable for executing the final adjustment when the target deceleration is applied to the vehicle as a result of cooperative control. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above-mentioned objects, features, advantages, technical and industrial significance of this invention will be better understood by reading the following detailed description of exemplary embodiments of the invention, when considered in connection with the accompanying drawings, in which:  
       FIG. 1  is a flowchart illustrating a control by a deceleration control apparatus for a vehicle according to a first exemplary embodiment of the invention;  
       FIG. 2  is a block diagram schematically showing the deceleration control apparatus for a vehicle according to the first exemplary embodiment of the invention;  
       FIG. 3  is a skeleton view of an automatic transmission of the deceleration control apparatus for a vehicle according to the first exemplary embodiment of the invention;  
       FIG. 4  is a table showing engagement/disengagement combinations of the automatic transmission of the deceleration control apparatus for a vehicle according to the first exemplary embodiment of the invention;  
       FIG. 5  is a time chart showing the deceleration transitional characteristics of the deceleration control apparatus for a vehicle according to the first exemplary embodiment of the invention;  
       FIG. 6  is a view illustrating the gradient of the target deceleration of the deceleration control apparatus for a vehicle according to the first exemplary embodiment of the invention;  
       FIG. 7  is a view illustrating how the gradient of the target deceleration of the deceleration control apparatus for a vehicle is determined according to the first exemplary embodiment of the invention;  
       FIG. 8  is a block diagram schematically showing peripheral devices around a control circuit of a deceleration control apparatus for a vehicle according to a second exemplary embodiment of the invention;  
       FIGS. 9A and 9B  are flowcharts illustrating control by the deceleration control apparatus for a vehicle according to the second exemplary embodiment of the invention;  
       FIG. 10  is time chart showing the deceleration transitional characteristics of the deceleration control apparatus for a vehicle according to the second exemplary embodiment of the invention;  
       FIG. 11  is a flowchart illustrating a control by a deceleration control apparatus for a vehicle according to a third exemplary embodiment of the invention;  
       FIG. 12  is a time chart showing the deceleration transitional characteristics of the deceleration control apparatus for a vehicle according to the third exemplary embodiment of the invention;  
       FIGS. 13A and 13B  are flowcharts illustrating a control by a deceleration control apparatus for a vehicle according to a fourth exemplary embodiment of the invention;  
       FIGS. 14A and 14B  are flowcharts illustrating a control by a deceleration control apparatus for a vehicle according to a fifth exemplary embodiment of the invention;  
       FIG. 15  is a time chart showing the deceleration transitional characteristics (a first case) of the deceleration control apparatus for a vehicle according to the fifth exemplary embodiment of the invention;  
       FIG. 16  is a time chart showing the deceleration transitional characteristics (a second case) of the deceleration control apparatus for a vehicle according to the fifth exemplary embodiment of the invention;  
       FIG. 17  is a graph showing the target deceleration (in the second case) of the deceleration control apparatus for a vehicle according to the fifth exemplary embodiment of the invention;  
       FIG. 18A  is a flowchart illustrating a first part of an operation by a deceleration control apparatus for a vehicle according to a sixth exemplary embodiment of the invention;  
       FIG. 18B  is a flowchart illustrating a second part of the operation by the deceleration control apparatus for a vehicle according to the sixth exemplary embodiment of the invention;  
       FIG. 19  is a block diagram schematically showing the deceleration control apparatus for a vehicle according to the sixth exemplary embodiment of the invention;  
       FIG. 20  is a target deceleration map of the deceleration control apparatus for a vehicle according to the sixth exemplary embodiment of the invention;  
       FIG. 21  is a speed target deceleration map of the deceleration control apparatus for a vehicle according to the sixth exemplary embodiment of the invention;  
       FIG. 22  is a chart showing a deceleration produced by an output shaft rotation speed and the speed in the deceleration control apparatus for a vehicle according to the sixth exemplary embodiment of the invention;  
       FIG. 23  is a graph showing the relationship between the speed target deceleration, the current gear speed deceleration, and the maximum target deceleration in the deceleration control apparatus for a vehicle according to the sixth exemplary embodiment of the invention;  
       FIG. 24  is a graph illustrating the deceleration for each vehicle speed in each gear speed in the deceleration control apparatus for a vehicle according to the sixth exemplary embodiment of the invention;  
       FIG. 25  is time chart illustrating the operation of the deceleration control apparatus for a vehicle according to the sixth exemplary embodiment of the invention;  
       FIG. 26A  is a flowchart illustrating a first part of an operation by a deceleration control apparatus for a vehicle according to a seventh exemplary embodiment of the invention;  
       FIG. 26B  is a flowchart illustrating a second part of the operation by the deceleration control apparatus for a vehicle according to the seventh exemplary embodiment of the invention;  
       FIG. 27  is a block diagram schematically showing a control circuit of a deceleration control apparatus for a vehicle according to an eighth exemplary embodiment of the invention;  
       FIG. 28  is a block diagram schematically showing a control circuit of a deceleration control apparatus for a vehicle according to a ninth exemplary embodiment of the invention;  
       FIG. 29  is a chart showing correction quantities for the deceleration for each corner size and output shaft rotation speed in the deceleration control apparatus for the vehicle according to the ninth exemplary embodiment of the invention; and  
       FIG. 30  is a chart showing correction quantities for the deceleration for each road ratio μ and output shaft rotation speed in a deceleration control apparatus for the vehicle according to a tenth exemplary embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In the following description and the accompanying drawings, the present invention will be described in more detail with reference to exemplary embodiments.  
      Hereinafter, ten embodiments according to the invention will be described. All ten embodiments relate to a deceleration control apparatus for a vehicle, which performs cooperative control of a brake system (including brakes and a motor/generator) and an automatic transmission. In addition, all ten embodiments have the following points in common.  
      That is, when a target value (a target deceleration) of a deceleration to be applied to the vehicle is set and a speed or speed ratio of the automatic transmission that is appropriate for achieving that target deceleration selected during cooperative control of the brake system and the automatic transmission, the brake system is controlled to compensate for the difference between the target deceleration and the deceleration produced by the shift into the selected speed or speed ratio so that, as an overall result of cooperative control of the brake system and the automatic transmission, the target deceleration acts on the vehicle.  
      In the exemplary embodiments of the invention, the brake system performs a final adjustment (correction control) when applying the target deceleration to the vehicle as a result of the cooperative control. The brake system has better response than the automatic transmission, which makes it suitable for performing the final adjustment when applying the target deceleration on the vehicle as the result of the cooperative control. That is, in the brake system, the time that it takes to generate a final steady-state value (i.e., the specific deceleration indicated in the control command) as an output, including wasted time and startup time and the like, for a command signal indicative of the specific deceleration to be produced by the brake system and the timing at which that deceleration is to be produced, as well as the time it takes until the output has stabilized at the final steady-state value, is short. Moreover, the difference between the size of the output and the final steady-state value, such as an overshoot, is small.  
      Also, compared with the automatic transmission, the brake system has a high degree of flexibility with respect to the deceleration generated, which means that the desired deceleration is able to be generated. As a result, the brake system is more suitable for performing the final adjustment when applying the target deceleration to the vehicle as a result of the cooperative control.  
      The target deceleration is not limited to being produced by only one of the brake system or the automatic transmission. On the contrary, it may be produced by both an operation of the brake system and a shift of the automatic transmission. That is, the target deceleration corresponds to the sum of the deceleration generated by an operation of the brake system and the deceleration generated a shift of the automatic transmission. In this case, the ratio of the deceleration generated by the operation of the brake system to the deceleration generated by the shift of the automatic transmission in the overall deceleration (i.e., the target deceleration) does not matter.  
      Here, the target deceleration is set as a joint target to be generated by control of both the brake system and the automatic transmission, as described above. This does not mean, however, that when a condition to end the control of one of either the brake system or the automatic transmission is satisfied, the deceleration to be achieved by the other of the brake system or the automatic transmission is excluded from the target deceleration as a result.  
      In the first and the fifth exemplary embodiments, when a manual downshift is performed, the target deceleration is set and the speed appropriate for achieving that target deceleration selected by the driver. A manual downshift in this case is a downshift that is performed manually when the driver wishes to increase the engine braking force.  
      Also in the first to the fifth exemplary embodiments, when a shift by shift point control is performed, the target deceleration is set and the speed appropriate for achieving that target deceleration selected by a control circuit (reference numeral  130  in  FIG. 2 ) mounted in the vehicle based on, for example, the size of a corner ahead of the vehicle or the road surface gradient. A shift by shift point control in this case is a shift that is performed based on various information such as information pertaining to the road on which the vehicle is running, including information about the size of an upcoming corner R and the road gradient, and road traffic information pertaining to traffic on the road on which the vehicle is running, including information about the distance between vehicles.  
      In the sixth to the tenth exemplary embodiments, when a shift by vehicle-to-vehicle distance control (vehicle-following control) is performed, the target deceleration is set and the speed appropriate for achieving that target deceleration selected by a control circuit (reference numeral  130  in  FIG. 19 ) mounted in the vehicle based on the vehicle-to-vehicle distance, the relative vehicle speed, the time between vehicle, or the like.  
      With both shift point control and vehicle-to-vehicle distance control, the target deceleration is set and the speed appropriate for achieving that target deceleration selected automatically on the vehicle side according to the road and traffic conditions.  
      The target deceleration includes a deceleration gradient and a maximum target deceleration, to be described later. Also, the target deceleration can be updated in real time in response to, for example, a change in the size of an upcoming corner or the road surface gradient or the like, a change in the vehicle-to-vehicle distance, the relative vehicle speed, or the time between vehicles (which is calculated by dividing the object-to-vehicle distance by the vehicle speed), or the like, or a change in the engine braking force desired by the driver. That is, the target deceleration may be a value that is fixed until the foregoing control ends, or a value that varies.  
      When the deceleration is referred to in this specification, it is understood to be high when the absolute value of the deceleration is large and low when the absolute value of the deceleration is small.  
      First, a first exemplary embodiment of the invention will be described with reference to FIGS.  1  to  7 . This exemplary embodiment relates to a deceleration control apparatus for a vehicle, which performs a manual shift or a shift by shift point control by cooperative control of a brake system and an automatic transmission. The deceleration control apparatus for a vehicle according to this exemplary embodiment improves the deceleration transitional characteristics of the vehicle.  
      When the deceleration (braking force) is applied to the vehicle, it is possible that the vehicle may become unstable. U.S. Pat. No. 2,503,426 described above does not disclose technology for dealing with this. Another object of this exemplary embodiment is therefore to provide a deceleration control apparatus for a vehicle that can easily control a vehicle in an unstable state.  
      Also, shift point control technology has recently been developed that performs a shift based on the radius of an upcoming corner, the road gradient, and the like. As opposed to a manual shift, a shift by the shift point control has relatively little to do with an intention to shift of driver. This difference between a shift by shift point control and a manual shift must be taken into consideration when applying technology to cooperatively control the automatic transmission and brakes to a shift by shift point control. Still a further object of this exemplary embodiment is thus to provide a deceleration control apparatus for a vehicle that takes this difference into account.  
      According to this exemplary embodiment, in an apparatus for cooperatively controlling a brake system and an automatic transmission, when a manual downshift or a downshift by shift point control is performed, two target decelerations are set: one for an initial period (a first period) during which the target deceleration has at least a gradient, and another for a second period during which the target deceleration is generally level after the first period.  
       FIG. 2  shows an automatic transmission  10 , an engine  40 , and a brake system  200 . The automatic transmission  10  is capable of achieving five speeds (1st speed to 5th speed) by controlling hydraulic pressure, which is done by energizing and de-energizing electromagnetic valves  121   a ,  121   b , and  121   c .  FIG. 2  shows three electromagnetic valves  121   a ,  121   b , and  121   c , but their number is not limited to this. These electromagnetic valves  121   a ,  121   b , and  121   c  are driven by signals sent from a control circuit  130 .  
      A throttle opening amount sensor  114  detects an opening amount of a throttle valve  43  disposed inside an intake passage  41  of the engine  40 . An engine speed sensor  116  detects the speed of the engine  40 . A vehicle speed sensor  122  detects the rotational speed an output shaft  120   c  of the automatic transmission  10  in proportion to the vehicle speed. A shift position sensor  123  detects a shift position of the automatic transmission  10 . A pattern select switch  117  is used when selecting a shift pattern of the automatic transmission  10 .  
      An acceleration sensor  90  detects a deceleration of the vehicle. A manual shift determining portion  95  outputs a signal indicative of a need for a downshift (a manual downshift) or an upshift by a manual operation performed by the driver. A shift point control shift determining portion  100  outputs a signal indicative of a need for a downshift by shift point control. A road ratio μ detecting/estimating portion  115  detects or estimates a friction coefficient of the road surface (hereinafter referred to as “road ratio”) μ.  
      The signals indicative of the various detection results from the throttle opening amount sensor  114 , the engine speed sensor  116 , the vehicle speed sensor  122 , the shift position-sensor  123 , and the acceleration sensor  90  are all input to the control circuit  130 . Also input to the control circuit  130  are a signal indicative of the switching state of the pattern select switch  117 , a signal indicative of the detection or estimation results from the road ratio μ detecting/estimating portion  115 , a signal indicative of the need to shift from the manual shift determining portion  95 , and a signal indicative of the need to shift from the shift point control shift determining portion  100 .  
      The control circuit  130  is a known micro-computer, and includes a CPU  131 , RAM  132 , ROM  133 , an input port  134 , an output port  135 , and a common bus  136 . Signals from the various sensors  114 ,  116 ,  122 ,  123 , and  90 , as well as signals from the pattern select switch  117 , the road ratio μ detecting/estimating portion  115 , the manual shift determining portion  95  and the shift point control shift determining portion  100  are all input to the input port  134 . Electromagnetic valve driving portions  138   a ,  138   b , and  138   c , as well as a brake braking force signal line L 1  leading to a brake control circuit  230  are all connected to the output port  135 . The brake braking force signal line L 1  transmits a brake braking force signal SG 1 .  
      An operation (a control step) illustrated in the flowchart in  FIG. 1 , in addition to a shift map for shifting the speed of the automatic transmission  10  and an operation for shift control (not shown), are stored in the ROM  133  in advance. The control circuit  130  shifts the automatic transmission  10  based on the various control conditions that are input.  
      The brake system  200  is controlled by the brake control circuit  230 , into which the brake braking force signal SG 1  is input from the control circuit  130 , so as to brake the vehicle. The brake system  200  includes a hydraulic pressure control circuit  220  and brake devices  208 ,  209 ,  210 , and  211  provided on vehicle wheels  204 ,  205 ,  206 , and  207 , respectively. Each brake device  208 ,  209 ,  210 , and  211  controls the braking force of the corresponding wheel  204 ,  205 ,  206 , and  207  according to a brake hydraulic pressure which is controlled by the hydraulic pressure control circuit  220 . The hydraulic pressure control circuit  220  is controlled by the brake control circuit  230 .  
      The hydraulic pressure control circuit  220  performs brake control by controlling the brake hydraulic pressure supplied to each brake device  208 ,  209 ,  210 , and  211  based on a brake control signal SG 2  that ultimately determines the braking force to be applied to the vehicle. The brake control signal SG 2  is generated by the brake control circuit  230  based on the brake braking force signal SG 1  that the brake control circuit  230  receives from the control circuit  130  of the automatic transmission  10 .  
      The brake control circuit  230  is a known micro-computer, and includes a CPU  231 , RAM  232 , ROM  233 , an input port  234 , an output port  235 , and a common bus  236 . The hydraulic pressure control circuit  220  is connected to the output port  235 . The operation for generating the brake control signal SG 2  based on the various data included in the brake braking force signal SG 1  is stored in the ROM  233  in advance. The brake control circuit  230  controls the brake system  200  (i.e., performs brake control) based on the various control conditions that are input.  
      The structure of the automatic transmission  10  is shown in  FIG. 3 . In the drawing, output from the engine  40 , i.e., an internal combustion engine which serves as the driving source for running the vehicle, is input to the automatic transmission  10  via an input clutch  12  and a torque converter  14 , which is a hydraulic power transmitting device, and transmitted to driven wheels via a differential gear unit and an axle, not shown. A first motor/generator MG 1  which functions as both an electric motor and a generator is arranged between the input clutch  12  and the torque converter  14 .  
      The torque converter  14  includes a pump impeller  20  which is coupled to the input clutch  12 , a turbine runner  24  which is coupled to an input shaft  22  of the automatic transmission  10 , a lock-up clutch  26  for locking the pump impeller  20  and the turbine runner  24  together, and a stator  30  that is prevented from rotating in one direction by a one-way clutch  28 .  
      The automatic transmission  10  includes a first transmitting portion  32  which switches between a high speed and a low speed, and a second transmitting portion  34  which is capable of switching between a reverse speed and four forward speeds. The first transmitting portion  32  includes an HL planetary gearset  36 , a clutch C 0 , a one-way clutch F 0 , and a brake B 0 . The HL planetary gearset  36  includes a sun gear S 0 , a ring gear R 0 , and planetary gears P 0  that are rotatably supported by a carrier K 0  and in mesh with the sun gear S 0  and the ring gear R 0 . The clutch C 0  and the one-way clutch F 0  are provided between the sun gear S 0  and the carrier K 0 , and the brake B 0  is provided between the sun gear S 0  and a housing  38 .  
      The second transmitting portion  34  includes a first planetary gearset  400 , a second planetary gearset  42 , and a third second planetary gearset  44 . The first planetary gearset  400  includes a sun gear S 1 , a ring gear R 1 , and planetary gears P 1  that are rotatably supported by a carrier K 1  and in mesh with the sun gear S 1  and the ring gear R 1 . The second planetary gearset  42  includes a sun gear S 2 , a ring gear R 2 , and planetary gears P 2  that are rotatably supported by a carrier K 2  and in mesh with the sun gear S 2  and the ring gear R 2 . The third planetary gearset  44  includes a sun gear S 3 , a ring gear R 3 , and planetary gears P 3  that are rotatably supported by a carrier K 3  and in mesh with the sun gear S 3  and the ring gear R 3 .  
      The sun gear S 1  and the sun gear S 2  are integrally coupled together, while the ring gear R 1  and the carrier K 2  and the carrier K 3  are integrally coupled together. The carrier K 3  is coupled to the output shaft  120   c . Similarly, the ring gear R 2  is integrally coupled to the sun gear S 3  and an intermediate shaft  48 . A clutch C 1  is provided between the ring gear R 0  and the intermediate shaft  48 , and a clutch C 2  is provided between the sun gear S 1  and the sun gear S 2 , and the ring gear R 0 . Also, a band brake B 1  is provided on the housing  38  in order to prevent the sun gear S 1  and the sun gear S 2  from rotating. Further, a one-way clutch F 1  and a brake B 2  are provided in series between the sun gear S 1  and the sun gear S 2 , and the housing  38 . The one-way clutch F 1  applies when the sun gear S 1  and the sun gear S 2  try to rotate in the direction opposite that of the input shaft  22 .  
      A brake B 3  is provided between the carrier K 1  and the housing  38 , and a brake B 4  and a one-way clutch F 2  are provided in parallel between the ring gear R 3  and the housing  38 . The one-way clutch F 2  applies when the ring gear R 3  tries to rotate in the direction opposite that of the input shaft  22 .  
      The automatic transmission  10  of the above-described structure is able to switch between any of one reverse speed and five forward speeds (1st to 5th) of different speed ratios, according to the table showing engagement/disengagement combinations of the automatic transmission shown in  FIG. 4 , for example. In the table in  FIG. 4 , the single circle indicates application, a blank space indicates release, a double circle (bulls-eye) indicates application when the engine brake is engaged, and a triangle indicates application but with no power being transmitted. The clutches C 0  to C 2  and the brakes B 0  to B 4  are all hydraulic friction apply devices that are applied by hydraulic actuators.  
      Next, operation of the first exemplary embodiment will be described with reference to  FIGS. 1 and 5 .  
       FIG. 1  is a flowchart showing the control flow of the first exemplary embodiment.  FIG. 5  is a time chart to help explain the exemplary embodiment. The input rotation speed of the automatic transmission  10 , accelerator opening amount, brake control amount, clutch torque, and deceleration (G) acting on the vehicle are all indicated in the drawing.  
      In  FIG. 1 , it is determined by the control circuit  130  in step S 1  whether the accelerator (i.e., the throttle opening amount) is fully closed based on the detection results of the throttle opening amount sensor  114 . If the accelerator is fully closed (i.e., YES in step S 1 ), it is determined, when there is a shift, that the shift is intended to engage the engine brake. Therefore, the brake control of the exemplary embodiment is continued in steps S 2  onward. In  FIG. 5 , the accelerator opening amount is fully closed at time t 1 , as denoted by reference numeral  401 .  
      If, on the other hand, it is determined in step S 1  that the accelerator is not fully closed (i.e., NO in step S 1 ), a command is output to end the brake control of the exemplary embodiment (step S 12 ). When the brake control is not being executed, this state is maintained. Next in step S 13 , a flag F is reset to 0, after which the control flow is reset.  
      In step S 2 , the flag F is checked by the control circuit  130 . Because the flag F is 0 at the start of this control flow, step S 3  is executed. If the flag F were 1, however, step S 8  would be executed instead.  
      In step S 3 , it is determined by the control circuit  130  whether there is a determination to shift (i.e., whether there is a shift command). More specifically, it is determined whether a signal indicative of a need to shift the automatic transmission  10  into a relatively lower speed (i.e., a downshift) has been output from either the manual shift determining portion  95  or the shift point control shift determining portion  100 . Data indicative of the speed into which the transmission is to be downshifted (hereinafter also referred to as the “target downshift speed”) is included in that signal.  
      When a signal indicative of a need to downshift is output from the manual shift determining portion  95 , it means that the driver has set the deceleration obtained by a manual downshift into the target downshift speed that is specified by that signal as the “target deceleration” which is set as the joint target for the brake system  200  and the automatic transmission  10 . It also means that, in this case, the driver has set the speed into target downshift speed specified by that signal as the “speed appropriate for achieving the target deceleration.” 
      When a signal indicative of the need to downshift is output from the shift point control shift determining portion  100 , it means that the shift point control shift determining portion  100  has set the deceleration to be achieved by the downshift into the target downshift speed specified by that signal as the aforementioned “target deceleration” to be set as the joint target of the brake system  200  and the automatic transmission  10 , as described above. In this case it also means that the shift point control shift determining portion  100  has set the target downshift speed specified by that signal as the “speed appropriate for achieving the target deceleration.” 
      In  FIG. 5 , the determination in step S 3  is made at time t 1 . If it is determined in step S 3  that a signal indicative of the need to downshift has been output from either the manual shift determining portion  95  or the shift point control shift determining portion  100  (i.e., YES in step S 3 ), then step S 4  is executed. If not (i.e., NO in step S 3 ), the control flow is reset.  
      In the example described above, the accelerator is fully closed in step S 1  at time t 1 , but it can be closed earlier, as long as it is closed before step S 3  is performed at time t 1 . In regard to the signal indicating a need for a downshift output from the manual shift determining portion  95  or the shift point control shift determining portion  100 , the example in  FIG. 5  shows a case in which it has been determined by the control circuit  130  that there is a need for a downshift at time t 1 . Based on the determination that there is a need to downshift at time t 1 , the control circuit  130  then outputs a downshift command at time t 1  (step S 6 ), as will be described later.  
      In step S 4 , a maximum target deceleration Gt is obtained by the control circuit  130 . The maximum target deceleration Gt is included in the “target deceleration” as the joint target for the brake system  200  and the automatic transmission  10  described above. This maximum target deceleration Gt is made the same (or approximately the same) as a maximum deceleration (to be described later) that is determined by the type of shift (e.g., by the combination of the speed before the shift and the speed after the shift, such as 4th→3rd or 3rd→2nd) and the vehicle speed. The broken line denoted by reference numeral  402  in  FIG. 5  indicates the deceleration corresponding to the negative torque (braking force, engine brake) of the output shaft  120   c  of the automatic transmission  10 , and is determined by the type of shift and the vehicle speed.  
      The maximum target deceleration Gt is determined to be substantially the same as a maximum value (the maximum deceleration mentioned above)  402   max  of a deceleration  402  that acts on the vehicle from the shift of the automatic transmission  10 . The maximum value  402   max  of the deceleration  402  from the shift of the automatic transmission  10  is determined referencing a maximum deceleration map stored in advance in the ROM  133 . In the maximum deceleration map, the value of the maximum deceleration  402   max  is determined based on the type of shift and the vehicle speed. After step S 4 , step S 5  is then executed.  
      In step S 5 , a gradient α of a target deceleration  403  is determined by the control circuit  130 . The target deceleration  403  (including the gradient α) is included in the aforementioned “target deceleration” that is set as the joint target for the brake system  200  and the automatic transmission  10 .  
      When determining this gradient α, an initial gradient minimum value of the target deceleration  403  is first determined based on a time ta from after the downshift command is output (at time t 1  in step S 6 , to be described later) until the shift (actually) starts (time t 3 ), such that the deceleration that actually acts on the vehicle (hereinafter, this deceleration will be referred to as the “actual deceleration of the vehicle”) will reach the maximum target deceleration Gt by time t 3  when the shift starts. The time ta from time t 1  when the downshift command is output until time t 3  when the shift actually starts is determined based on the type of shift.  
      In  FIG. 6 , the chain double-dashed line denoted by reference numeral  404  corresponds to the initial gradient minimum value of the target deceleration. Also, a gradient upper limit value and a gradient lower limit value are set beforehand for the deceleration  403  such that shock accompanying deceleration does not become large and an instability phenomenon of the vehicle is able to be controlled (i.e., avoided). The chain double-dashed line denoted by reference numeral  405  in  FIG. 6  corresponds to the gradient upper limit value.  
      An instability phenomenon of the vehicle refers to an unstable state of the vehicle, such as unstable behavior of the vehicle, a decrease in the degree of grip of the tires, or sliding that occurs for one reason or another such as a change in the road ratio μ or a steering operation when a deceleration (caused by brake control and/or the engine brake engaging due to a shift) acts on the vehicle.  
      In step S 5 , the gradient α of the target deceleration  403  is set larger than the gradient minimum value  404  but smaller than the gradient upper limit value  405 , as shown in  FIG. 6 .  
      The initial gradient α of the target deceleration  403  sets the optimum manner of change for the deceleration in order to change the initial deceleration of the vehicle smoothly and prevent an instability phenomenon of the vehicle. The gradient α can be determined based on, for example, the rate at which the accelerator returned (hereinafter referred to as “accelerator return rate”) (see ΔΔo in  FIG. 5 ) or the road ratio μ detected or estimated by the road ratio μ detecting/estimating portion  115 . The gradient α can also be changed depending on whether the shift is a manual shift or a shift performed by shift point control. A detailed description of these is as follows with reference to  FIG. 7 .  
       FIG. 7  shows one example of a method for setting the gradient α. As shown in the drawing, the gradient α is set smaller the smaller the road ratio μ and larger the larger the accelerator return rate. Also, the gradient α is set smaller for a shift by shift point control than it is for a manual shift. This is because a shift by shift point control is not based directly on the intention of the driver so the rate of deceleration is set to be gradual (the deceleration is set relatively low). In  FIG. 7 , the relationships between the gradient α and the road ratio μ and the accelerator return rate and the like are linear, but they can also be set to be nonlinear.  
      A large portion (shown by the bold line in  FIG. 5 ) of the target deceleration  403  in this exemplary embodiment is determined by steps S 4  and S 5 . That is, as shown in  FIG. 5 , the target deceleration  403  is set to reach the maximum target deceleration Gt at the gradient α obtained in steps S 4  and S 5 . Thereafter, the target deceleration  403  is maintained at the maximum target deceleration Gt until time t 5  when the shift of the automatic transmission  10  ends. This is done in order to achieve a deceleration until the maximum deceleration  402   max  (≈maximum target deceleration Gt) produced by the shift of the automatic transmission  10  is reached, using the brakes, which have good response, while quickly suppressing deceleration shock. Realizing the initial deceleration with the brakes which have good response makes it possible to quickly control an instability phenomenon of the vehicle, should one occur. The setting of the target deceleration  403  after time t 5  when the shift of the automatic transmission  10  ends will be described later. After step S 5 , step S 6  is executed.  
      In step S 6 , the downshift command (shift command) is output from the CPU  131  of the control circuit  130  to the electromagnetic valve driving portions  138   a  to  138   c . In response to this downshift command, the electromagnetic valve driving portions  138   a  to  138   c  energize or de-energize the electromagnetic valves  121   a  to  121   c . As a result, the shift (i.e., the “shift into the speed appropriate for achieving the target deceleration”) indicated by the downshift command is executed in the automatic transmission  10 . If it is determined by the control circuit  130  at time t 1  that there is a need for a downshift (i.e., YES in step S 3 ), the downshift command is output at the same time as that determination (i.e., at time t 1 ).  
      As shown in  FIG. 5 , when a downshift command is output at time t 1  (step S 6 ), the shift of the automatic transmission  10  actually starts at time t 3 , after the time ta determined based on the type of shift has passed after time t 1 . When the shift starts, clutch torque  408  starts to increase, as does the deceleration  402  from the shift of the automatic transmission  10 . After step S 6 , step S 7  is executed.  
      In step S 7 , a brake feedback control is executed by the brake control circuit  230 . As shown by reference numeral  406 , the brake feedback control starts at time t 1  when the downshift command is output.  
      That is, a signal indicative of the target deceleration  403  is output as the brake braking force signal SG 1  at time t 1  from the control circuit  130  to the brake control circuit  230  via the brake braking force signal line L 1 . Then based on the brake braking force signal SG 1  input from the control circuit  130 , the brake control circuit  230  then generates the brake control signal SG 2  and outputs it to the hydraulic pressure control circuit  220 .  
      The hydraulic pressure control circuit  220  then generates a braking force (a brake control amount  406 ) as indicated by the brake control signal SG 2  by controlling the hydraulic pressure supplied to the brake devices  208 ,  209 ,  210 , and  211  based on the brake control signal SG 2 .  
      In the feedback control of the brake system  200  in step S 7 , the target value is the target deceleration  403 , the control amount is the actual deceleration of the vehicle, the objects to be controlled are the brakes (brake devices  208 ,  209 ,  210 , and  211 ), the operating amount is the brake control amount  406 , and the disturbance is mainly the deceleration  402  caused by the shift of the automatic transmission  10 . The actual deceleration of the vehicle is detected by the acceleration sensor  90 .  
      That is, in the brake system  200 , the brake braking force (i.e., brake control amount  406 ) is controlled so that the actual deceleration of the vehicle comes to match the target deceleration  403 . That is, the brake control amount  406  is set to produce a deceleration that makes up for the difference between the deceleration  402  caused by the shift of the automatic transmission  10  and the target deceleration  403  in the vehicle.  
      In the example shown in  FIG. 5 , the deceleration  402  caused by the automatic transmission  10  is zero from time t 1  when the downshift command is output until time t 3  when the automatic transmission actually starts to shift. Therefore, the brake control amount  406  is set such that the deceleration matches the entire target deceleration  403  using the brakes. From time t 3  the automatic transmission  10  starts to shift, and the brake control amount  406  decreases as the deceleration  402  caused by the automatic transmission  10  increases.  
      In this way, the brake system  200  in this exemplary embodiment is feedback controlled to compensate for the difference between the target deceleration ( 403 ) and the deceleration by the shift into a speed that is appropriate for achieving the target deceleration ( 403 ) (i.e., the target downshift speed corresponding to the downshift command) so that, as an overall result of the cooperative control of the brake system  200  and the automatic transmission  10 , the target deceleration ( 403 ) acts on the vehicle.  
      In step S 8 , the control circuit  130  determines whether the shift of the automatic transmission  10  is ending (or close thereto). This determination is made based on the rotation speed of rotating members in the automatic transmission  10  (see input rotation speed in  FIG. 5 ). In this case, it is determined according to whether the following relational expression is satisfied. 
 
 No×If−Nin≦Nin  
 
      Here, No is the rotation speed of the output shaft  120   c  of the automatic transmission  10 , Nin is the input shaft rotation speed (turbine rotation speed etc.), If is the speed ratio after the shift, and ΔNin is a constant value. The control circuit  130  inputs the detection results from a detecting portion (not shown) that detects the input shaft rotation speed Nin of the automatic transmission  10  (i.e., the turbine rotation speed of the turbine runner  24 , etc.).  
      If that relational expression is not satisfied in step S 8 , it is determined that the shift of the automatic transmission  10  is not yet ending and the flag F is set to 1 in step S 14 , after which the control flow is reset. The routine then repeats steps S 1 , S 2 , and S 8  until that relational expression is satisfied. If during that time the accelerator opening amount is anything other than fully closed, the routine proceeds to step S 12  and the brake control according to this exemplary embodiment ends.  
      If, on the other hand, the foregoing relational expression in step S 8  is satisfied, the routine proceeds on to step S 9 . In  FIG. 5 , the shift ends at (right before) time t 5 , whereby the relational expression is satisfied. As can be seen in  FIG. 5 , the deceleration  402  that acts on the vehicle from the shift of the automatic transmission  10  reaches the maximum value  402   max  (≈maximum target deceleration Gt) at time t 5 , indicating that the shift of the automatic transmission  10  has ended.  
      In step S 9 , the brake feedback control that started in step S 7  ends. After step S 9 , the control circuit  130  no longer includes the signal corresponding to the brake feedback control in the brake braking force signal SG 1  that is output to the brake control circuit  230 .  
      That is, the brake feedback control is performed until the shift of the automatic transmission  10  ends. As shown in  FIG. 5 , the brake control amount  406  is zero at time t 5  when the shift of the automatic transmission  10  ends. When the shift of the automatic transmission  10  ends at time t 5 , the deceleration  402  produced by the automatic transmission  10  reaches the maximum value  402   max . At that time t 5 , the deceleration  402  alone produced by the automatic transmission  10  is sufficient to reach the maximum target deceleration Gt of the target deceleration  403  set (in step S 4 ) to be substantially the same as the maximum value  402   max  of the deceleration  402  produced by the automatic transmission  10 , so the brake control amount  406  can be zero. After step S 9 , step S 10  is executed.  
      In step S 10 , the control circuit  130  outputs, and then gradually reduces, the brake torque (deceleration) for the amount of shift inertia to the brakes via the brake braking force signal SG 1  that is output to the brake control circuit  230 . The shift inertia is generated from between times t 5  and t 6  after the shift of the automatic transmission  10  has ended, through time t 7  in  FIG. 5 . The shift inertia (i.e., inertia torque) is determined by a time differential value and an inertia value of a rotation speed of a rotating member of the automatic transmission  10  at time t 5  when the shift of the automatic transmission  10  has ended.  
      In  FIG. 5 , step S 10  is executed between time t 5  and time t 7 . In order to keep shift shock to a minimum, the control circuit  130  sets the target deceleration  403  so its gradient is gradual after time t 5 . The gradient of the target deceleration  403  remains gradual until the target deceleration  403  reaches a final deceleration Ge obtained by a downshift of the automatic transmission  10 . The setting of the target deceleration  403  ends when it reaches the final deceleration Ge. At that point, the final deceleration Ge, which is the engine brake desired by the downshift, acts on the vehicle as the actual deceleration of the vehicle, so from that point on, brake control according to the exemplary embodiment is no longer necessary.  
      In step S 10 , the brake control amount  406  for the shift inertia amount is supplied by the hydraulic pressure control circuit  220  in response to the brake control signal SG 2  generated based on the brake braking force signal SG 1  that was input to the brake control circuit  230 . Then the brake control amount  406  is gradually reduced to correspond to the gradient of the target deceleration  403 . After step S 10 , step S 11  is executed.  
      In step S 11 , the control circuit  130  clears the flag F to 0 and resets the control flow.  
      According to this exemplary embodiment, the brakes are feedback controlled to compensate for the difference between the target deceleration  403  and the deceleration produced by the shift in response to the downshift command so that the sum of the deceleration produced by the shift in response to the downshift command and the deceleration produced by the brake control equals the target deceleration  403 . In this case, feedback control is performed using the brakes which have better response than the automatic transmission, so the desired deceleration is able to be produced by the brakes. Accordingly, the target deceleration  403  can always be produced with good controllability as an overall result of the cooperative control of the automatic transmission and the brakes. As a result, the deceleration characteristics in response to the downshift command are able to be improved.  
      This exemplary embodiment enables ideal deceleration transitional characteristics to be obtained, as shown by the target deceleration  403  in  FIG. 5 . The deceleration smoothly shifts from the driven wheels to the non-driven wheels. Thereafter as well, the deceleration smoothly shifts to the final deceleration Ge obtained by the downshift of the automatic transmission  10 . These ideal deceleration transitional characteristics are further described below.  
      That is, immediately after it is confirmed (i.e., immediately after there has been a determination) that there is a need for a downshift in step S 3  (time t 1 ), the brake control (step S 7 ) that starts upon that confirmation (i.e., at time t 1 ) causes the actual deceleration of the vehicle to gradually increase both at a gradient α that does not produce a large deceleration shock and within a range in which it is still possible to control a vehicle instability phenomenon should one occur. The actual deceleration of the vehicle increases until it reaches the maximum value  402   max  (≈maximum target deceleration Gt) of the deceleration  402  produced by the shift before time t 3  when the shift starts. The actual deceleration of the vehicle then gradually falls, without producing a large shift shock at the end of the shift (after time t 5 ), until it reaches the final deceleration Ge obtained by the shift.  
      As described above, according to this exemplary embodiment, the actual deceleration of the vehicle starts to increase quickly, i.e., immediately after time t 1  when it has been confirmed that there is a need for a downshift. The actual deceleration of the vehicle then gradually increases until it reaches, at time t 2  before time t 3  when the shift starts, the maximum value  402   max  (≈maximum target deceleration Gt) of the deceleration  402  produced by the shift. The actual deceleration of the vehicle is then maintained at the maximum target deceleration Gt until time t 5  when the shift ends.  
      If an instability phenomenon is going to occur in the vehicle from a temporal shift in the actual deceleration of the vehicle, as described above, it is highly likely that it will occur either while the actual deceleration of the vehicle is increasing to the maximum target deceleration Gt (between time t 1  and time t 2 ), or at the latest, by time t 3  before the shift starts immediately after the actual deceleration of the vehicle has reached the maximum target deceleration Gt. During this period when it is highly likely that a vehicle instability phenomenon will occur, only the brakes are used to produce a deceleration (that is, the automatic transmission  10  which has not yet actually started to shift is not used to produce a deceleration). Because the brakes have better response than the automatic transmission, an instability phenomenon in the vehicle, should one occur, can be both quickly and easily controlled by controlling the brakes.  
      That is, the brakes can be quickly and easily controlled to reduce or cancel the brake braking force (i.e., the brake control amount  406 ) in response to an instability phenomenon of the vehicle. On the other hand, if an instability phenomenon occurs in the vehicle after the automatic transmission has started to shift, even if the shift is cancelled at that point, it takes time until the shift is actually cancelled.  
      Further, during the period mentioned above when the likelihood that an instability phenomenon will occur in the vehicle is high (i.e., from time t 1  to time t 2  or from time t 1  to time t 3 ), the automatic transmission  10  does not start to shift and the friction apply devices such as the clutches and brakes of the automatic transmission  10  are not applied, so no problem will result if the shift of the automatic transmission  10  is cancelled in response to the occurrence of an instability phenomenon in the vehicle.  
      A second exemplary embodiment of the invention will now be described with reference to FIGS.  8  to  10 . In the following description of the second exemplary embodiment, only those parts that differ from the first exemplary embodiment will be described; descriptions of parts that are the same as those in the first exemplary embodiment will be omitted.  
      The first exemplary embodiment as described above can be used for both a case of a manual shift and a case of a shift by shift point control. The second exemplary embodiment, however, assumes only a case in which the shift is performed by shift point control.  
       FIG. 8  is a block diagram schematically showing the peripheral devices of the control circuit  130  according to the second exemplary embodiment. In the second exemplary embodiment, a vehicle instability detecting/estimating portion road gradient measuring/estimating portion  118 , which detects when the vehicle is unstable or estimates or anticipates that the vehicle will become unstable, is connected to the control circuit  130 .  
      The vehicle instability detecting/estimating portion  118  detects, estimates, or anticipates an unstable state of the vehicle (a state in which the braking force/deceleration should be reduced), such as a decrease in the degree of grip of the tire, sliding, or unstable behavior, that has occurred or will occur for one reason or another (including a change in the road ratio μ and a steering operation). The following describes an example in which the vehicle instability detecting/estimating portion  118  detects or estimates a decrease in the degree of tire grip and control according to this exemplary embodiment is executed based on those detection or estimation results.  
       FIGS. 9A and 9B  are flowcharts showing the control flow according to the second exemplary embodiment. This operation is stored in advance in the ROM  133 . As shown in the drawing, the control flow of the second exemplary embodiment differs from the control flow ( FIG. 1 ) of the first exemplary embodiment in that steps S 15  to S 17  have been added. Furthermore, step S 3 ′ in  FIG. 9A  differs from step S 3  in  FIG. 1  in that in step S 3 ′ in  FIG. 9A , it is determined whether a command has been output for a downshift by shift point control.  
      A shift according to shift point control is not a downshift based on an intention originating in the driver, as is a manual shift. Therefore, even if a deceleration caused by the downshift (including both a deceleration caused by brake control and a deceleration caused by the shift (engine brake)) is corrected, that correction does not immediately contradict the intention of the driver.  
      Thus, according to this exemplary embodiment, when deceleration control (steps S 3 , S 6 , and S 7 ) is executed in response to a downshift by shift point control, the deceleration is corrected (step S 16 ) so that it is reduced when it is desirable to reduce the braking force/deceleration, such as when the degree of tire grip is low (i.e., YES in step S 15 ).  
      In the case of shift point control, when a signal indicative of the need to downshift is output from the shift point control shift determining portion  100 , it means that the shift point control shift determining portion  100  has set the deceleration to be achieved by the downshift into the target downshift speed specified by that signal as the aforementioned “target deceleration” to be set as the joint target of the brake system  200  and the automatic transmission  10 , as described above. In this case it also means that the shift point control shift determining portion  100  has set the target downshift speed included in that signal as the “speed appropriate for achieving the target deceleration.” 
      However, according to this exemplary embodiment, when it is desirable that the braking force/deceleration be reduced, such as when the degree of tire grip is low, (i.e., YES in step S 15 ), the aforementioned “target deceleration” that is set as the joint target of the brake system  200  and the automatic transmission  10  that was set based on the signal from the shift point control shift determining portion  100  is updated (step S 16 ). The “speed appropriate for achieving the target deceleration” may also need to be reset (step S 16 ) following an update of the “target deceleration” that is set as the joint target.  
      The control flow of the second exemplary embodiment will now be described with reference to  FIGS. 9 and 10 . Steps S 1 , S 2 , S 4 , S 5 , and S 7  to S 14  are the same as in the first exemplary embodiment so a description of these steps will be omitted.  
      In step S 3 ′, the control circuit  130  determines whether a signal indicative of the need to downshift is being output from the shift point control shift determining portion  100 . The  FIG. 10  shows an example similar to that in  FIG. 5 , in which there has been a determination that there is a need to downshift by shift point control at time t 1 . When it has been determined in step S 3 ′ that there is a need to downshift based on the signal from the shift point control shift determining portion  100  (i.e., YES in step S 3 ′), the maximum target deceleration Gt is determined (step S 14 ) and the gradient α of the target deceleration  403  is determined (step S 5 ), after which step S 6  is executed, just as in the first exemplary embodiment.  
      The target deceleration  403  (including the maximum target deceleration Gt and the gradient α) is included in the aforementioned “target deceleration” that is set as the joint target for the brake system  200  and the automatic transmission  10 .  
      In step S 6 , a command for a downshift according to shift point control is output from the CPU  131  of the control circuit  130  to the electromagnetic valve driving portions  138   a  to  138   c  at time t 1 . Thereafter, brake feedback control is executed (step S 7 ) at time t 1 , just as in the first exemplary embodiment. After step S 7 , step S 15  is executed.  
      In step S 7 , the brake system  200  is feedback controlled to compensate for the difference between the target deceleration ( 403 ) and the deceleration produced by the shift into the speed appropriate for achieving the target deceleration ( 403 ) (i.e., into the target downshift speed corresponding to the downshift command), so that, as the overall result of the cooperative control of the brake system  200  and the automatic transmission  10 , the target deceleration ( 403 ) acts on the vehicle, just as in the first exemplary embodiment. After step S 7 , step S 15  is executed.  
      In step S 15 , the vehicle instability detecting/estimating portion  118  determines whether the degree of grip is less than a predetermined value. If it is determined that the degree of grip is less than the predetermined value (i.e., YES in step S 15 ), the control circuit  130  reduces the maximum target deceleration Gt (step S 16 ).  
      In  FIG. 10 , a maximum target deceleration Gt′, which is the maximum target deceleration Gt after being reduced in step S 16 , is shown by an alternate long and short dash line denoted by reference numeral  406 ′. As a result of reducing the maximum target deceleration Gt in step S 16 , the brake control amount  406  according to the brake feedback control that started in step S 7  decreases, as shown by that alternate long and short dash line  406 ′.  
      In step S 16 , the control circuit  130  changes the shift restriction or shift transitional characteristics when necessary at the same time that the maximum target deceleration Gt is being reduced. A shift restriction refers to, for example, canceling the downshift in a case where the shift involves only one speed, and reducing the number of speeds to be shifted into by at least one in a case where a plurality of shifts are to be performed into two or more speeds. The decrease in the maximum target deceleration Gt indicates that the “target deceleration” described above, which is set as the overall target of the cooperative control, changes. As the “target deceleration” changes, it results in the resetting of the “speed that is appropriate for achieving the target deceleration” and the shift restriction mentioned above.  
      A shift can be canceled if necessary when the deceleration  402  caused by the shift of the automatic transmission  10  is larger than the maximum target deceleration Gt′ resulting from step S 16 , as shown in  FIG. 10 . In the case of a plurality of shifts of two or more speeds, only a shift, in which the deceleration is larger than the maximum target deceleration Gt′, can be canceled. Accordingly, the shift transitional characteristics can be changed.  
      In the example in  FIG. 10 , the deceleration  402  caused by the shift of the automatic transmission  10  is larger than the maximum target deceleration Gt′ so the shift of the automatic transmission  10  is cancelled. The deceleration caused by the automatic transmission  10  following that cancellation is shown by the chain double-dashed line denoted by reference numeral  402 ′. When the shift is cancelled, the deceleration  402 ′ caused by the shift of the automatic transmission  10  decreases, returning to the deceleration before the start of the shift. Also, when the shift of the automatic transmission  10  is cancelled, the clutch torque  408  of the automatic transmission  10  decreases, as shown by the chain double-dashed line denoted by reference numeral  408 ′.  
      In step S 17 , the control circuit  130  determines whether a shift restriction has been imposed in step S 16 . If a shift restriction has been imposed (i.e., YES in step S 17 ), brake control following the shift is unnecessary so it ends (step S 18 ) and the flag F is reset to 0 (step S 11 ). If, on the other hand, it is determined in step S 17  that a shift restriction has not been imposed (i.e., NO in step S 17 ), step S 8  is executed. Steps S 8  onward are the same as in the first exemplary embodiment so descriptions thereof will be omitted here.  
      According to the second exemplary embodiment, when an instability phenomenon (such as a reduction in the degree of slip) has been detected, estimated, or anticipated in the vehicle (i.e., YES in step S 15 ) when a downshift by shift point control is performed (step S 6 ) and brake control corresponding to that downshift is performed (step S 7 ), the maximum target deceleration Gt in  FIG. 10  can be changed to a small value Gt′, as shown by the alternate long and short dashed line. As a result, the brake control amount  406  becomes a small value  406 ′, as shown by the alternate long and short dashed line. Also, when the deceleration  402  caused by the automatic transmission  10  exceeds the maximum target deceleration Gt′ following a downshift (step S 6 ) of the automatic transmission  10  by shift point control, that shift can be cancelled if necessary (see the chain double-dashed line  402 ′ that branches off from the line denoted by the reference numeral  402  in  FIG. 10 ).  
      From the description above, according to the second exemplary embodiment, when an instability phenomenon in the vehicle has occurred, or when it is anticipated that an instability phenomenon in the vehicle will occur, the actual deceleration of the vehicle decreases, making it easier to eliminate an instability phenomenon in the vehicle, prevent one from becoming worse, or prevent one from occurring in the first place. In the above description, when a shift restriction is imposed (i.e., YES in step S 17 ), the brake control ends at that point (see brake control amount  406 ′ when the shift is cancelled).  
      Next, a third exemplary embodiment of the invention will be described with reference to  FIGS. 11 and 12 . In the following description of the third exemplary embodiment, only those parts that differ from the foregoing exemplary embodiments will be described; descriptions of parts that are the same as those in the foregoing exemplary embodiments will be omitted.  
      The third exemplary embodiment assumes a downshift by shift point control, just like the second exemplary embodiment. The third exemplary embodiment, however, goes farther into the detail with step S 16  of the second exemplary embodiment.  
       FIG. 11  is a flowchart showing the control flow of the third exemplary embodiment. The operation of the control flow is stored in advance in the ROM  133 .  FIG. 11  differs from  FIGS. 9A and 9B  showing the control flow of the second exemplary embodiment in two ways. First, steps S 100  to S 160  have been added between step S 15  and step S 8 . Second, steps S 17  and S 18  in  FIG. 9B  have been omitted (as they correspond to steps S 150  and S 160 ) in  FIG. 11 . Steps S 1  to S 15  in  FIG. 11  are the same as in the foregoing exemplary embodiment, so descriptions thereof will be omitted.  
      Step S 100  is executed when the degree of grip becomes less than a predetermined value (i.e., YES in step S 15 ) after a downshift by shift point control is performed at time t 1  (step S 6 ) and brake feedback control has started (step S 7 ). In step S 100 , the control circuit  130  determines whether the target deceleration  403  or the actual deceleration of the vehicle has reached the maximum target deceleration Gt at the current point.  
      In the example in  FIG. 12 , before time t 2 , the target deceleration  403  or the actual deceleration of the vehicle is still sweeping down at the gradient α and has not yet reached the maximum target deceleration Gt, so the determination in step S 100  is NO. In this case, step S 110  is then executed. After time t 2 , on the other hand, the target deceleration  403  or the actual deceleration of the vehicle has reached the maximum target deceleration Gt, so the determination in step S 100  is YES. In this case, step S 130  is executed. That is, if the target deceleration  403  or the actual deceleration of the vehicle has reached the maximum target deceleration Gt (i.e., YES in step S 100 ), the target deceleration  403  or the actual deceleration of the vehicle will not increase anymore so the routine proceeds directly on to step S 130  without executing steps S 110  and S 120 , which will be described next.  
      In step S 110 , the control circuit  130  reduces the maximum target deceleration Gt. More specifically, the value of the maximum target deceleration Gt reduced in step S 110  (i.e., the value of the maximum target deceleration Gt′) is determined as follows. That is, because the degree of grip is reduced (step S 15 ) while the target deceleration  403  or the actual deceleration of the vehicle is still increasing over time (i.e., NO in step S 100 ) when step S 110  is executed, the value of the target deceleration  403  or the actual deceleration of the vehicle at the point when step S 110  is executed is made the new maximum target deceleration Gt′. The decrease in the maximum deceleration Gt indicates that the “target deceleration” set as the overall target of the cooperative control changes. After step S 110 , step S 120  is executed.  
      In step S 120 , the control circuit  130  reduces the hydraulic pressure (clutch pressure) operating a clutch of the automatic transmission  10  by a predetermined value. More specifically, the control circuit  130  reduces the clutch pressure by controlling the operating states of the electromagnetic valves  121   a  to  121   c  using the electromagnetic valve driving portions  138   a  to  138   c.    
      The deceleration caused by a shift of the automatic transmission  10  when the clutch pressure is reduced is denoted by reference numeral  402 ′. When the clutch pressure is reduced, the time required for the shift increases (to time t 6 ) and the maximum value  402   max ′ of the deceleration  402 ′ caused by the shift decreases. In step S 120 , the decrease amount of the clutch pressure is a value corresponding to the decrease amount of the maximum target deceleration Gt′. As a result, the maximum target deceleration Gt′ and the deceleration of the maximum value  402   max ′ of the deceleration  402 ′ caused by the shift of the automatic transmission  10  are equal, as shown in  FIG. 12 .  
      Because step S 120  is executed when the target deceleration  403  or the actual deceleration of the vehicle has not yet reached the maximum target deceleration Gt (i.e., before time t 2 ) (i.e., NO in step S 100 ), step S 120  is executed before time t 3  when the automatic transmission  10  actually starts to shift. As a result, the clutch pressure of the automatic transmission  10  can easily be reduced in step S 120 .  
      The brake control amount changes in response to a decrease in the maximum target deceleration Gt′ and a decrease in the clutch pressure (i.e., in response to a change in the deceleration  402 ′ caused by the shift of the automatic transmission  10 ), as shown by reference numeral  406 ′. In this exemplary embodiment, the brake control amount  406 ′ changes as a result of feedback control of the brake system  200  being performed in response to a change in the target deceleration  403  (the maximum target deceleration Gt′) and a change in the deceleration  402 ′ from a shift of the automatic transmission  10 . Also, the clutch torque decreases in response to a decrease in clutch pressure, as shown by reference numeral  408 ′. After step S 120 , step S 130  is executed.  
      In step S 130 , the control circuit  130  determines whether a determination has been made for a second shift while the current shift operation (hereinafter referred to as the “first shift”) is being performed. That is, the control circuit  130  determines whether a signal indicative of a need for a second shift, which is different from the first shift, is being output from either the manual shift determining portion  95  or the shift point control shift determining portion  100 .  
      If it is determined that the signal indicative of a need for the second shift is being output (i.e., YES in step S 130 ), step S 140  is then executed. If, on the other hand, it is determined that the signal indicative of a need for the second shift is not being output (i.e., NO in step S 130 ), step S 8  is executed. Steps S 8  onward are the same as those in the foregoing exemplary embodiment so descriptions thereof will be omitted here.  
      In step S 140 , the control circuit  130  determines whether the second shift is a downshift. If it is a downshift (i.e., YES in step S 140 ), then step S 150  is executed. If not (i.e., NO in step S 140 ), i.e., if it is an upshift, then step S 160  is executed.  
      In step S 150 , the control circuit  130  cancels both the downshift command corresponding to the signal indicating a need for the second shift that was output from either the manual shift determining portion  95  or the shift point control shift determining portion  100 , and the brake control corresponding to the second shift.  
      When the second shift, which is a downshift, is to be performed, there is a possibility that the deceleration will increase as a result. If the degree of grip is low (i.e., YES in step S 15 ) at this time, the vehicle may become even more unstable. In order to prevent this, the second shift command and the brake control corresponding to that second shift are cancelled in step S 150 . After step S 150 , step S 8  is executed. The determination to end the shift in step S 8  is directed towards the first shift.  
      In step S 160 , the control circuit  130  outputs the shift command corresponding to the signal indicating a need for the second shift that was output from either the manual shift determining portion  95  or the shift point control shift determining portion  100  and executes the second shift which is an upshift. At the same time, the control circuit  130  ends the brake control corresponding to the first shift. The fact that the command for the second shift, which is an upshift, was output (i.e., NO in step S 140 ) indicates that the deceleration required by the first shift is no longer necessary. By performing the second shift which is an upshift, the deceleration  402  caused by the shift of the automatic transmission  10  also decreases. That is, when the command for the second shift, which is an upshift, is output (i.e., NO in step S 140 ), there is no longer a need for the deceleration (the overall target deceleration of the cooperative control) required by the first shift, so it is cancelled. Therefore, when the command for the second shift, which is an upshift, has been output (i.e., NO in step S 140 ), the brake control corresponding to the first shift is no longer necessary. The brake control ends when the overall target deceleration of the cooperative control is cancelled.  
      After the brake control has ended in step S 160 , the determination as to whether to end the shift for the first shift (i.e., step S 8 ) is no longer necessary, so after step S 160 , step S 11  is executed.  
      As described above, according to the third exemplary embodiment, when an instability phenomenon such as a decrease in the degree of grip has been detected or estimated in the vehicle (i.e., YES in step S 15 ) when there is a downshift by shift point control, the maximum target deceleration Gt′ is reduced (step S 110 ) which in turn results in the brake control amount  406 ′ being reduced. As a result, the actual deceleration of the vehicle decreases, making it easier to eliminate an instability phenomenon in the vehicle or prevent one from becoming worse.  
      Further, the clutch pressure of the automatic transmission  10  is simultaneously reduced (step S 120 ) when an instability phenomenon such as a decrease in the degree of grip has been detected or estimated in the vehicle (i.e., YES in step S 15 ) when there is a downshift by shift point control. Therefore, the maximum value  402   max ′ of the deceleration  402 ′ caused by the shift of the automatic transmission  10  can be reduced to near the maximum target deceleration Gt′ while the increase gradient of the deceleration  402 ′ caused by the shift can be made smooth (the shift transitional characteristics can be changed) without canceling the shift of the automatic transmission  10 . As a result, it easier to eliminate an instability phenomenon in the vehicle or prevent one from becoming worse.  
      In this exemplary embodiment, the brakes, which have superior response, are feedback controlled in order to achieve the overall target deceleration of the cooperative control. As a result, even if the target deceleration  403  (i.e., the maximum target deceleration Gt′) and the deceleration  402 ′ of the automatic transmission  10  change, the brake control amount  406 ′ is changed in real time so it is able to accurately follow those changes.  
      If an instability phenomenon occurs in the vehicle, it is highly likely that it will occur during the period of increase in the target deceleration  403  or the actual deceleration of the vehicle (i.e., between times t 1  and t 2  in  FIG. 12 ). During this period (i.e., from time t 1  to time t 2  in  FIG. 12 ), only the brakes, which have good response, are used to produce a deceleration so any instability phenomenon in the vehicle can be easily controlled. That is, it is possible to quickly stop or reduce the braking force (brake control amount  406 ) by the brakes. Also during this period (i.e., from time t 1  to time t 2  in  FIG. 12 ), the automatic transmission  10  has not yet started to shift so the clutch pressure can be reduced easily.  
      Next, a fourth exemplary embodiment of the invention will be described with reference to  FIGS. 13A and 13B . In the following description of the fourth exemplary embodiment, only those parts that differ from the foregoing exemplary embodiments will be described; descriptions of parts that are the same as those in the foregoing exemplary embodiments will be omitted.  
      In the first through the third exemplary embodiments, the initial target deceleration  403  is set to increase to the maximum value  402   max  (≈maximum target deceleration Gt) of the deceleration  402  caused by the shift in the automatic transmission  10  at time t 2  before time t 3  when the automatic transmission  10  actually starts to shift (steps S 4  and S 5 ), which makes it easy to control an instability phenomenon in the vehicle should one occur.  
      In contrast, there may be cases where brake control alone is not sufficient to keep up with the target, or where the gradient α of the target deceleration  403  can not be set high due to the fact that it may result in deceleration shock. In such cases, it is thought that it may not be possible for the actual deceleration of the vehicle to reach the maximum value  402   max  (≈maximum target deceleration Gt) of the deceleration  402  caused by the shift of the automatic transmission  10  before time t 3  when the shift starts. The fourth exemplary embodiment is particularly effective for dealing with this kind of situation.  
       FIGS. 13A and 13B  are a flowchart showing the control flow of the fourth exemplary embodiment. The operation for this control flow is stored in advance in the ROM  133 . As shown in  FIGS. 13A and 13B , the control flow of the fourth exemplary embodiment differs from the control flow of the second exemplary embodiment shown in  FIGS. 9A and 9B  in that steps S 210  and S 220  have been added, and the order in which step S 6  and step S 7  are executed has been reversed. The steps in  FIGS. 13A and 13B  that are the same as those in the foregoing exemplary embodiments are denoted by the same reference numerals and descriptions thereof will be omitted.  
      Step S 210  is executed after the brake feedback control has started in step S 7 . In step S 210 , the control circuit  130  determines whether a predetermined period of time has passed after the brake feedback control has started. If the predetermined period of time has passed (i.e., (YES in step S 210 ), the routine proceeds on to step S 6 . If, on the other hand, the predetermined period of time has not passed (i.e., NO in step S 210 ), the routine proceeds on to step S 220 .  
      At first, the predetermined period of time will not have passed (i.e., NO in step S 210 ) so step S 220  is executed. In step S 220 , the control circuit  130  sets the flag F to 1 and then resets the control flow. Then in step S 2 , the flag F is determined to be 1 so step S 210  is then executed. The operation is repeated in this way until the predetermined time passes (i.e., YES in step S 210 ), at which point step S 6  is executed such that a downshift command is output.  
      As described above, in the second exemplary embodiment, both the brake control is started (step S 7 ) and the downshift command is output (step S 6 ) at time t 1 . In the fourth exemplary embodiment, however, the downshift command is output (step S 6 ) a predetermined time after (step S 210 ) the brake control is started (step S 7 ; time t 1 ). As a result, the time at which the shift is started can be delayed for a predetermined period of time. Therefore, the actual deceleration of the vehicle is able to reach the maximum value  402   max  (≈maximum target deceleration Gt) of the deceleration  402  caused by the shift of the automatic transmission  10  before the shift starts.  
      The predetermined time in step S 210  is able to be changed by the control circuit  130  according to the type of shift. This is because the time from the time that the downshift command is output until the time that the shift starts changes depending on the type of shift.  
      In this exemplary embodiment, the time that the automatic transmission  10  starts to shift is delayed, but by performing cooperative control with the brakes (steps S 4 , S 5 , and S 7 ), the vehicle actually starts to decelerate earlier than when it is decelerated by the shift of the automatic transmission  10  alone. Therefore, the driver is not aware that the starting time of the shift of the automatic transmission  10  is late, and any adverse effects from the delayed shift starting time are able to be kept to the minimum.  
      Step S 14 ′ in  FIG. 13B  differs from step S 14  in  FIG. 9B  in that, in step S 14 ′ in  FIG. 13B , the flag F is set to 2 instead of 1 because it is set to 1 in step S 220 .  
      In the fourth exemplary embodiment, the control flow differs from the control flow of the second exemplary embodiment shown in  FIGS. 9A and 9B  in that steps S 210  and S 220  have been added, and the order in which step S 6  and step S 7  are executed has been reversed. Alternatively, however, is also possible to add steps S 210  and S 220  and reverse the order in which step S 6  and step S 7  are executed in the control flow of the first exemplary embodiment ( FIG. 1 ).  
      Moreover, in the above description, operation to avoid an instability phenomenon in the vehicle (such as a reduction in the degree of tire grip) is performed only in the case of a shift by shift point control. This kind of operation may also be performed in the case of a manual shift as well. In this case, the criteria (the degree of slip, in the above description) for performing the operation to avoid an instability phenomenon in the vehicle can be set differently for a manual shift than it is for a shift by shift point control. For example, in the case of a manual shift, the deceleration increases according to the intention of the driver, so it is possible to make the criteria stricter (i.e., make it more difficult for the avoidance operation to be performed) so that the result will not contradict the intention of the driver (i.e., the amount of increase in the deceleration will not be easily reduced).  
      Further, in the example described above, the degree of grip is used as an example of the criteria that is detected or estimated by the vehicle instability detecting/estimating portion  118  and used for performing the operation to avoid an instability phenomenon in the vehicle. Alternatively, however, other indicators, such as an actual occurrence of an instability phenomenon (such as slipping of the tires) (e.g., a detection made by a difference between the rotation speeds of the front and rear tires, etc.), vehicle yaw, or operating signals for VSC (vehicle stability control) may also be used. Furthermore, the criteria for the operation to avoid an instability phenomenon in the vehicle may also use different indicators depending on whether the shift is a shift by shift point control or a manual shift.  
      Next, a fifth exemplary embodiment will be described. Parts in the fifth exemplary embodiment that are the same as parts in the exemplary embodiments described above will be referred to by the same reference numerals, and detailed descriptions thereof will be omitted.  
      According to this exemplary embodiment, in an apparatus for cooperatively controlling a brake system and an automatic transmission when a manual downshift or a downshift by shift point control is performed, a common target deceleration to be achieved by a shift and the brakes is set and the brakes are at least feedback controlled. When commands for multiple shifts have been output and the new shift command is a downshift, control to achieve the target deceleration corresponding to the initial shift command smoothly shifts to control to achieve the new target deceleration corresponding to the new shift command.  
      Next, operation of this exemplary embodiment will be described with reference to  FIGS. 14, 15 , and  16 .  
       FIGS. 14A and 14B  are flowchart illustrating the control flow of this exemplary embodiment.  FIG. 15  is a time chart showing a first case in the exemplary embodiment, while  FIG. 16  is a time chart showing a second case in the exemplary embodiment.  FIGS. 15 and 16  both show the input rotation speed of the automatic transmission  10 , the accelerator opening amount, the brake control amount, the clutch torque, and the deceleration (G) acting on the vehicle.  
      The first case will now be described with reference to  FIGS. 14 and 15 . Steps S 1  to S 5  are basically the same as steps S 1  to S 5  in  FIG. 1  described above so a description thereof will be omitted here. However, time t 4  in  FIG. 15  is earlier than it is (i.e., between time t 3  and time t 4 ) in  FIG. 5 . As a result, time t 5  in  FIG. 15  corresponds to time t 4  in  FIG. 5 , time t 6  in  FIG. 15  corresponds to time t 5  in  FIG. 5 , and so on.  
      In step S 6 , the control circuit  130  sets the target deceleration  403  based on the current actual deceleration of the vehicle or the current target deceleration  403 . In the example in  FIG. 15 , the target deceleration  403  is initially set based on the actual deceleration of the vehicle at time t 1 . The actual deceleration of the vehicle at time t 1  corresponds to the starting point of the target deceleration  403  in  FIG. 15 . After the start (i.e., after the brake control in step S 8  starts) the target deceleration  403  is set based on the either the current actual deceleration of the vehicle or the current target deceleration  403 .  
      If the target following performance (following ability) of the brake feedback control in step S 8 , which will be described later, is good, then either the current actual deceleration of the vehicle or the current target deceleration  403  may be used in step S 6 . After step S 6 , step S 7  is executed.  
      Steps S 7  and S 8  are basically the same as steps S 6  and S 7  in  FIG. 1 .  
      That is, in the brake system  200 , the brake braking force (i.e., brake control amount  406 ) is controlled in step S 8  so that the actual deceleration of the vehicle comes to match the target deceleration  403 . That is, the brake control amount  406  is set so that, when producing the target deceleration  403  in the vehicle, it produces a deceleration that makes up for the difference between the deceleration  402  caused by the shift of the automatic transmission  10  and the target deceleration  403  in the vehicle, so that the target deceleration  403  can be achieved by the vehicle.  
      In step S 9 , it is determined by the control circuit  130  whether there is a determination to shift again (i.e., a new shift) (that is, whether there is new shift command) before the shift corresponding to the downshift command output in step S 7  has ended. More specifically, it is determined whether a signal indicative of a need to shift again has been output from either the manual shift determining portion  95  or the shift point control shift determining portion  100 .  
      If it is determined in step S 9  that a signal indicative of the need to shift again has been output from either the manual shift determining portion  95  or the shift point control shift determining portion  100  (i.e., YES in step S 9 ), then step S 17  is executed. If not (i.e., NO in step S 9 ), then step S 10  is executed.  
      In the first case, step S 9  in  FIG. 15  is executed at time t 4  and it is determined that a signal indicative of the need to shift again has not been output from either the manual shift determining portion  95  or the shift point control shift determining portion  100  (i.e., NO in step S 9 ). Therefore, in the first case, after step S 9  is executed, the process proceeds on to step S 10 .  
      Steps S 10  and S 11  are the same as steps S 8  and S 9  in the  FIG. 1  so a description of these steps will be omitted.  
      In step S 12 , the control circuit  130  and the brake control circuit  230  gradually reduce the brake control amount  406 . A signal indicative of the gradual reduction of the brake amount is output as the brake braking force signal SG 1  from the control circuit  130  to the brake control circuit  230  via the brake braking force signal line L 1 . The brake control circuit  230  then generates the brake control signal SG 2  corresponding to that gradual reduction of the brake amount based on the brake braking force signal SG 1 , and outputs it to the hydraulic pressure control circuit  220 .  
      Step S 12  is executed when it has been determined that the shift of the automatic transmission  10  is ending (or close thereto) (i:e., YES in step S 10 ), after the feedback control of the brake has ended (step S 11 ). Step S 12  ends when the brake control amount  406  becomes zero. After the brake control amount  406  becomes zero, the actual deceleration of the vehicle is maintained at the final deceleration Ge obtained by the downshift of the automatic transmission  10 . After step S 12 , step S 13  is executed. Step S 13  is the same as step S 11  in  FIG. 1 .  
      Operation in the first case described above enables the deceleration transitional characteristics shown in  FIG. 15  to be achieved. Next, a second case will be described with reference to  FIGS. 14 and 16 . A description of the details that are the same as those in the first case will be omitted.  
      The second case is identical to the first case up until right before time t 4 , as shown in  FIGS. 15 and 16 . In the second case, the determination in step S 9  is made at time t 4 , just as in the first case, but the result of that determination is different. That is, in the second case, it is determined that a signal indicative of a need to shift again has been output from the manual shift determining portion  95  or the shift point control shift determining portion  100  (i.e., YES in step S 9 ). As a result, the process proceeds on to a different step in the second case than it does in the first case (i.e., after step S 9 , the process proceeds on to step S 17  instead of step S 10 ). Thus, the following description will start with the determination in step S 9  at time t 4 .  
      In step S 9 , the control circuit  130  determines whether there is a determination (i.e., a command) for new shift before the shift corresponding to the downshift command output in step S 7  has ended, just as described above.  
      In the second case, in regard to the signal indicating a need for a new shift output from the manual shift determining portion  95  or the shift point control shift determining portion  100 , the control circuit  130  determines at time t 4  that there is a need for a new shift (i.e., YES in step S 9 ). In this case, step S 17  is then executed.  
      In step S 17 , it is determined whether the need for the new shift from the manual shift determining portion  95  or the shift point control shift determining portion  100  determined in step S 9  relates to a downshift. If so, i.e., if it does relate to a downshift, then step S 18  is executed. If, on the other hand, it is determined that it does not relate to a downshift but rather an upshift, step S 19  is executed. In the following description, it is assumed that the new shift is a downshift.  
      In step S 18 , the control circuit  130  sets the flag F to 2 and then resets the control flow.  
      When the control flow is reset via step S 18 , the process returns to step S 1 . In the second case, because the accelerator is fully closed at time t 4  (i.e., YES in step S 1 ), the process proceeds on to step S 2 . In step S 2  it is determined that the flag F is 2 so step S 4  is executed.  
      In step S 4 , a maximum target deceleration Gta corresponding to the new shift is determined, just like in step S 4  the first time. The maximum target deceleration Gta is determined so as to be the same (or close) to the maximum deceleration determined from the vehicle speed and the type of new shift that was determined necessary in step S 9 . In  FIG. 16 , the solid line denoted by reference numeral  402   a  indicates the deceleration that corresponds to the negative torque of the output shaft  120   c  of the automatic transmission  10  determined from the type of shift and the vehicle speed. The maximum target deceleration Gta is determined so as to be substantially the same as a maximum value  402   amax  of the deceleration  402   a  that acts on the vehicle from the shift of the automatic transmission  10 . The maximum value  402   amax  of the deceleration  402   a  produced from the shift of the automatic transmission  10  is determined referencing the maximum deceleration map described above. After step S 4 , step S 5  is executed.  
      In step S 5 , a gradient αa of a target deceleration  403   a  is determined just like in step S 5  the first time. That is, when determining this gradient αa, an initial gradient minimum value of the target deceleration  403   a  is first determined based on a time ta′ from after the downshift command is output (at time t 4  in step S 7 ) until the shift actually starts (time t 7 ), such that the actual deceleration of the vehicle reaches the maximum target deceleration Gta by time t 6  when the shift starts. The time ta′ from time t 4  when the downshift command is output until time t 7  when the shift actually starts is determined based on the type of shift, just as described above.  
      In  FIG. 17 , the chain double-dashed line denoted by reference numeral  404   a  corresponds to the initial gradient minimum value of the target deceleration. Also, the chain double-dashed line denoted by reference numeral  405   a  in  FIG. 17  corresponds to the gradient upper limit value. In step S 5 , the gradient αa of the target deceleration  403   a  is set larger than the gradient minimum value  404   a  but smaller than the gradient upper limit value  405   a , as shown in  FIG. 17 . The gradient αa of the target deceleration  403   a  determines the braking shock that acts on the vehicle at time t 4  when the new downshift command is output, so the gradient upper limit value  405   a  is set so as to suppress that braking shock.  
      In steps S 4  and S 5 , the target deceleration  403   a  is determined as indicated by the broken bold line in  FIG. 16 . That is, as shown in  FIG. 16 , the target deceleration  403   a  is set to reach the maximum target deceleration Gta at the gradient αa. Thereafter, the target deceleration  403   a  is maintained at the maximum target deceleration Gta until time t 8  when the shift of the automatic transmission  10  ends. This is done in order to achieve a deceleration until the maximum deceleration  402   amax  (≈maximum target deceleration Gta) produced by the shift of the automatic transmission  10  is reached, using the brakes, which have good response, while quickly suppressing deceleration shock. After step S 5 , step S 6  is executed.  
      In step S 6 , the control circuit  130  sets the target deceleration  403   a  corresponding to the new downshift based on the current actual deceleration of the vehicle or the current target deceleration  403 . In this case, the current actual deceleration of the vehicle or the current target deceleration  403  at time t 4  corresponds to the target deceleration  403  at time t 4 . In step S 6 , the target deceleration  403   a  is set based on this. After step S 6 , step S 7  is executed.  
      In step S 7 , the new downshift command is output from the CPU  131  of the control circuit  130  to the electromagnetic valve driving portions  138   a  to  138   c , as described above. When it is determined by the control circuit  130  at time t 4  that there is a need to downshift (i.e., YES in step S 9 ), the new downshift command is output simultaneously with that determination (i.e., at time t 4 ).  
      As shown in  FIG. 16 , when the new downshift command is output at time t 4  (i.e., step S 7 ), the automatic transmission  10  actually starts to shift at time t 7 , which is after the period of time ta′ determined based on the type of shift has passed from that time (i.e., from when the command was output at time t 4 ). When the automatic transmission  10  actually starts to shift, the clutch torque  408   a  starts to increase, as does the deceleration  402   a  produced by the shift of the automatic transmission  10 .  
      The downshift corresponding to the initial downshift command continues to be executed (as in the first case described above) even after time t 4  when the new downshift command is output, as indicated by the deceleration  402  produced by the shift of the automatic transmission  10 . The shift then ends at time t 6 , after which the deceleration is maintained at the final deceleration Ge produced by the initial downshift. The new downshift then starts at time t 7  and ends at time t 8 , as shown by reference numeral  402   a , after which the deceleration is maintained at the final deceleration Gea produced by the new downshift. After step S 7 , step S 8  is executed.  
      In step S 8 , the brake feedback control which started in response to the initial downshift command continues to be executed. The brake feedback control is performed, as shown by the brake control amount  406   a  in response to the new downshift, so that the deceleration of the vehicle corresponds to the target deceleration  403   a.    
      In the example in  FIG. 16 , the deceleration  402  produced by the automatic transmission  10  according to the initial downshift is generated from time t 4  when the new downshift command is output until time t 6  when the new downshift ends. Therefore, in order to reach the target deceleration  403   a , the brake control amount  406   a  is generated to produce a deceleration that makes up for the difference between the deceleration  402  produced by the automatic transmission  10  and the target deceleration  403   a.    
      In the same way, the final deceleration Ge is produced by the automatic transmission  10  according to the initial downshift from time t 6  to time t 7 . Therefore, in order to reach the target deceleration  403   a , the brake control amount  406   a  is generated to produce a deceleration that makes up for the difference between the final deceleration Ge and the target deceleration  403   a . Similarly, the deceleration  402   a  produced by the automatic transmission  10  according to the new downshift is generated from time t 7  to time t 8 , so in order to reach the target deceleration  403   a , the brake control amount  406   a  is generated to produce a deceleration that makes up for the difference between the deceleration  402   a  and the target deceleration  403   a.    
      In step S 9 , it is determined whether there is a determination to shift again (i.e., a new shift) (that is, whether there is new shift command) before the shift corresponding to the downshift command output in step S 7  has ended, as described above. In regard to the signal indicating a need for a new shift output from the manual shift determining portion  95  or the shift point control shift determining portion  100 , the control circuit  130  determines that there is no need for a new shift (i.e., NO in step S 9 ) between time t 4  and time t 8  in  FIG. 16 . In this case, step S 10  is then executed.  
      In step S 10 , it is determined whether the aforementioned relational expression is satisfied. If the relational expression is not satisfied, the routine is repeated until it is. When the relational expression in step S 10  has been satisfied, step S 11  is then executed. In  FIG. 16 , the shift in response to the new downshift command ends at time t 8 , such that the relational expression is satisfied. As can be seen in  FIG. 16 , the deceleration  402   a  that acts on the vehicle from the new downshift reaches the maximum value  402   amax  (≈maximum target deceleration Gta) at time t 8 , indicating that the shift of the automatic transmission  10  has ended.  
      In step S 11 , the brake feedback control, which started at time  1  in step S 8  the first time in response to the initial downshift command and was then continued by the new downshift command, ends. After step S 11 , the control circuit  130  no longer includes the signal corresponding to the brake feedback control in the brake braking force signal SG 1  that is output to the brake control circuit  230 .  
      That is, the brake feedback control is performed until the shift (i.e., the new downshift) of the automatic transmission  10  ends. As shown in  FIG. 16 , the brake control amount  406   a  is zero at time t 8  when the shift of the automatic transmission  10  ends. When the shift of the automatic transmission  10  ends at time t 8 , the deceleration  402   a  produced by the automatic transmission  10  reaches the maximum value  402   amax . At that time t 8 , the deceleration  402   a  alone produced by the automatic transmission  10  is sufficient to reach the maximum target deceleration Gta of the target deceleration  403   a  set (in step S 4 ) to be substantially the same as the maximum value  402   amax  of the deceleration  402   a  produced by the automatic transmission  10 , so the brake control amount  406   a  can be zero. After step S 11 , step S 12  is executed.  
      In step S 12 , the brake control amount  406   a  is gradually reduced. If, however, the brake control amount  406   a  is already zero at the time step S 12  is executed, as shown in  FIG. 16 , then this step is essentially not executed. After the brake control amount  406   a  reaches zero, the actual deceleration of the vehicle becomes equivalent to the deceleration produced by the new downshift of the automatic transmission  10 , and is thereafter maintained at the final deceleration Gea produced by the new downshift. After step S 12 , step S 13  is executed as described above.  
      Next, the second case, in which the new shift is an upshift (i.e., NO in step S 17 ), will be described.  
      In step S 19 , the brake feedback control that started in step S 8  in response to the initial downshift command ends, just as in step S 11 . After step S 19 , the control circuit  130  no longer includes the signal corresponding to the brake feedback control in the brake braking force signal SG 1  that is output to the brake control circuit  230 .  
      In the example shown in  FIG. 16 , the brake control amount when the new shift that was determined necessary at time t 4  (i.e., YES in step S 9 ) is an upshift (i.e., NO in step S 17 ) is indicated by reference numeral  406   b , shown by the alternate long and short dash line from time t 4 . The brake control amount  406   b  is not generated by feedback control (step S 19 ), but is rather controlled to decrease gradually in step S 20 , as described below.  
      When the new shift is an upshift (i.e., NO in step S 17 ), it means that the deceleration from the initial downshift that was determined necessary in step S 3  the first time (i.e., at time t 1 ) is no longer necessary. Further, by performing the upshift as the new shift, the deceleration from the shift of the automatic transmission  10  would decrease (not shown). Therefore, when the new shift is an upshift (i.e., NO in step S 17 ), the brake feedback control that started in step S 8  at time t 1  ends (i.e., step S 19 ). After step S 19 , step S 20  is executed.  
      In step S 20 , the control circuit  130  and the brake control circuit  230  gradually reduce the brake control amount  406   b , just as in step S 12 . Step S 20  ends when the brake control amount  406   b  becomes zero (at time t 6 ). After the brake control amount  406   b  becomes zero, the actual deceleration of the vehicle becomes a value that corresponds to the engine braking force by the automatic transmission  10 . After step S 20 , step S 13  is executed as described above.  
      In the second case, in regard to the signal indicating a need for a new shift output from the manual shift determining portion  95  or the shift point control shift determining portion  100 , an example is given in which it has been determined by the control circuit  130  that there is a need for a new shift (i.e., YES in step S 9 ) at time t 4  after time t 3  when the initial downshift started. In this exemplary embodiment, however, the timing at which it is determined that there is a need for a new shift (i.e., YES in step S 9 ) may also be before time t 3  when the initial downshift starts, as long as it is after time t 1  when the initial downshift command is output. As long as that timing is after time t 1  when the initial downshift command is output, the target deceleration  403   a  corresponding to the new downshift command is set and deceleration control corresponding to that target deceleration  403   a  takes over from the deceleration control corresponding to the initial downshift command.  
      Similarly, in this exemplary embodiment, the timing at which it is determined that there is a need for a new shift (i.e., YES in step S 9 ) need only be before time t 6  when the initial downshift ends (i.e., YES in step S 10 ). In this case, the target deceleration  403   a  corresponding to the new downshift command is set and deceleration control corresponding to that target deceleration  403   a  takes over from the deceleration control corresponding to the initial downshift command.  
      Next, the effects of this exemplary embodiment will be described. In the second case in this exemplary embodiment, before it has been determined that the initial (nth) downshift has ended (step S 10 ), a new (nth+1) shift determination is made (step S 9 ). A new target deceleration is set (i.e., the target deceleration is updated) every time a new shift is performed.  
      Here, the brakes, which have good response, are feedback controlled in order to achieve the overall target deceleration of the cooperative control. Therefore, even if the target deceleration  403   a  corresponding to the new shift determination changes or the deceleration  402   a  from a new shift of the automatic transmission  10  is produced, the brake control amount  406   a  is changed in real time so it is able to accurately follow those changes.  
      As shown in the second case, it is also possible to handle a shift command for either a downshift or an upshift that is generated before the initial downshift ends. In this exemplary embodiment, the period until the shift ends (step S 10 ) is regarded as one control unit. Alternatively, however, the period up until the braking force becomes zero may be regarded as one control unit.  
      Next, a sixth exemplary embodiment of the invention will be described with reference to  FIGS. 18A  to  29 . Parts in the sixth exemplary embodiment that are the same as parts in the foregoing exemplary embodiments are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.  
      This exemplary embodiment provides a deceleration control that incorporates the advantages of good response and controllability offered by the brakes by performing brake control (automatic brake control), as well as the advantage of increased engine braking offered by a downshift by performing shift control (downshift control by an automatic transmission), in cooperation with one another when it is detected, based on vehicle-to-vehicle distance information, that the distance between vehicles is equal to, or less than, a predetermined value.  
      In terms of the structure of this exemplary embodiment, it is assumed that means capable of measuring the distance between a host vehicle and a preceding vehicle, and a deceleration control apparatus that operates a brake and a shift control of an automatic transmission in cooperation with one another based on that distance information, are provided. These will be described in detail below.  
      As shown in  FIG. 19 , this exemplary embodiment is provided with a relative vehicle speed detecting/estimating portion  95   a  and a vehicle-to-vehicle distance measuring portion  100   a  instead of the manual shift determining portion  95  and the shift point control shift determining portion  100  in  FIG. 2 . The relative vehicle speed detecting/estimating portion  95   a  detects or estimates the relative speed between a host vehicle and a preceding vehicle. The vehicle-to-vehicle distance measuring portion  100   a  has a sensor such as a laser radar sensor or a millimeter wave radar sensor mounted on the front of the vehicle, which is used to measure the distance to the preceding vehicle.  
      The control circuit  130  inputs both a signal indicative of the detection or estimation results from the relative vehicle speed detecting/estimating portion  95   a  and a signal indicative of the measurement results from the vehicle-to-vehicle distance measuring portion  100   a . The operation (control steps) indicated in the flowchart in  FIGS. 18A and 18B  is stored in the ROM  133  beforehand.  
      The operation of this exemplary embodiment will now be described with reference to  FIGS. 18A, 18B ,  19 , and  25 .  FIG. 25  is a time chart illustrating the deceleration control of this exemplary embodiment.  FIG. 25  shows the current gear speed deceleration, the speed target deceleration, the maximum target deceleration, the speed of the automatic transmission  10 , the rotation speed of the input shaft of the automatic transmission  10  (AT), the torque of the output shaft of the AT, the braking force, and the accelerator opening amount. At time T 0 , the current deceleration (i.e., the actual deceleration of the vehicle) is the same as the current gear speed deceleration, shown by reference numeral  303 .  
      First in step S 1  in  FIG. 18A , the control circuit  130  determines whether the distance between the host vehicle and the preceding vehicle is equal to, or less than, a predetermined value based on a signal indicative of the vehicle-to-vehicle distance input from the vehicle-to-vehicle distance measuring portion  100   a . If it is determined that the vehicle-to-vehicle distance is equal to, or less than, the predetermined value, then step S 2  is executed. If, on the other hand, it is determined that the vehicle-to-vehicle distance is not equal to, nor less than, the predetermined value, the control flow ends.  
      Instead of directly determining whether the vehicle-to-vehicle distance is equal to, or less than, the predetermined value, the control circuit  130  may also indirectly determine whether the vehicle-to-vehicle distance is equal to, or less than, the predetermined value by a parameter by which it can be known that the vehicle-to-vehicle distance is equal to, or less than, the predetermined value, such as the time to collision (vehicle-to-vehicle distance/relative vehicle speed), the time between vehicles (vehicle-to-vehicle distance/host vehicle speed), or a combination of the two.  
      In step S 2 , the control circuit  130  determines whether the accelerator is off based on a signal output from the throttle opening amount sensor  114 . If it is determined in step S 2  that the accelerator is off, then step S 3  is executed. Vehicle-following control starts from step S 3 . If, on the other hand, it is determined that the accelerator is not off, the control flow ends.  
      In step S 3 , the control circuit  130  obtains a target deceleration. The target deceleration is obtained as a value (deceleration) with which the relationship with the preceding vehicle comes to equal the target vehicle-to-vehicle distance or relative vehicle speed when deceleration control based on that target deceleration (to be described later) is executed in the host vehicle.  
      The target deceleration is obtained referencing a target deceleration map ( FIG. 20 ) stored in the ROM  133  beforehand. As shown in  FIG. 20 , the target deceleration is obtained based on the relative speed (km/h) and time (sec) between the host vehicle and the preceding vehicle. Here, the time between vehicles is the vehicle-to-vehicle distance divided by the host vehicle speed, as described above.  
      In  FIG. 20 , for example, when the relative vehicle speed (here the relative vehicle speed equals the preceding vehicle speed minus the host vehicle speed) is −20 [km/h] and the time between the vehicles is 1.0 [sec], the target deceleration is −0.20 (G). The absolute value of the target deceleration is set smaller (so that the vehicle will not decelerate) the closer the relationship between the host vehicle and the preceding vehicle is to a safe relative vehicle speed and vehicle-to-vehicle distance. That is, the target deceleration is obtained as a value that has a smaller absolute value on the upper right side of the target deceleration map in  FIG. 20  the greater the distance between the host vehicle and the preceding vehicle. On the other hand, the target deceleration is obtained as a value that has a larger absolute value on the lower left side of the target deceleration map in  FIG. 20  the closer the distance between the host vehicle and the preceding vehicle.  
      The target deceleration obtained in step S 3  is referred to as the target deceleration, or more specifically, the maximum target deceleration, for before the shift control (step S 7 ) and the brake control (step S 8 ) are actually performed (i.e., at the starting point of the deceleration control) after the conditions to start the deceleration control (steps S 1  and S 2 ) have been satisfied. That is, because the target deceleration is set in real time even while the deceleration control is being executed, as will be described later, the target deceleration obtained in step S 3  is referred to specifically as the maximum target deceleration in order to differentiate it from the target deceleration set after the brake control and shift control have actually been executed (i.e., while the brake control and shift control are being executed). After step S 3 , step S 4  is executed.  
      In step S 4 , the target deceleration is set. Here, the target deceleration is set to reach the maximum target deceleration at a predetermined gradient from the current (when the control starts; time T 0  in  FIG. 25 ) deceleration  303  (i.e., the current gear speed deceleration). The predetermined gradient can be changed based on the road ratio μ, the accelerator return rate at the start of the control, or the opening amount of the accelerator before it is returned. For example, the gradient (slope) is set small when the road ratio μ is small and large when the accelerator return rate or the opening amount of the accelerator before it is returned is large. In the example in  FIG. 25 , the target deceleration reaches the maximum target deceleration at time T 1  as a result of the target deceleration being set based on the predetermined gradient. The signal indicative of that set target deceleration is output as the brake braking force signal SG 1  from the control circuit  130  to the brake control circuit  230  via the brake braking force signal line L 1 . Here, the set target deceleration is the overall target deceleration of the cooperative control of the brake system  200  and the automatic transmission  10 .  
      In step S 5 , the control circuit  130  obtains the target deceleration produced by the automatic transmission  10  (hereinafter referred to as “speed target deceleration”), and then determines the speed to be selected for the shift control (downshift) of the automatic transmission  10  based on the speed target deceleration. Here, the speed to be selected that is determined corresponds to the speed selected as the speed appropriate for achieving the overall target deceleration of the cooperative control. The details of step S 5  are described broken down into two parts ((1) and (2)) as follows.  
      (1) First, the speed target deceleration is obtained. The speed target deceleration corresponds to the engine braking force (deceleration) to be obtained by the shift control of the automatic transmission  10 . The speed target deceleration is set to be a value equal to, or less than, the maximum target deceleration. (Note: the degree of deceleration referred to here and throughout this specification refers to the size of the absolute value of the deceleration.) The speed target deceleration can be obtained by any of the following three methods.  
      The first of the three methods for obtaining the speed target deceleration is as follows. The speed target deceleration is set in step S 3  as the product of a coefficient greater than 0 but equal to, or less than, 1 multiplied by the maximum target deceleration obtained from the target deceleration map in  FIG. 20 . For example, when the maximum target deceleration is −0.20 G, as in the case of the example in step S 3 , the speed target deceleration can be set to −0.10 G, which is the product of the maximum target deceleration −0.20 G multiplied by the coefficient 0.5, for example.  
      The second of the three methods for obtaining the speed target deceleration is as follows. A speed target deceleration map ( FIG. 21 ) is stored in the ROM  133  in advance. The speed target deceleration can then be obtained referencing this speed target deceleration map in  FIG. 21 . As shown in  FIG. 21 , the speed target deceleration can be obtained based on the relative vehicle speed [km/h] and time [sec] between the host vehicle and the preceding vehicle, just like the target deceleration in  FIG. 20 . For example, if the relative vehicle speed is −20 [km/h] and the time between vehicles is 1.0 [sec], as in the case of the example in step S 3 , a speed target deceleration of −0.10 G can be obtained. As is evident from  FIGS. 20 and 21 , when i) the relative vehicle speed is high so that the vehicles suddenly come close to one another, ii) the time between vehicles is short, or iii) the vehicle-to-vehicle distance is short, the vehicle-to-vehicle distance must be appropriately established early on, so the deceleration must be made larger. This also results in a lower speed being selected in the above-described situation.  
      The third of the three methods for obtaining the speed target deceleration is as follows. First, the engine braking force (deceleration G) when the accelerator is off in the current gear speed of the automatic transmission  10  is obtained (hereinafter simply referred to as the “current gear speed deceleration”). A current gear speed deceleration map ( FIG. 22 ) is stored in advance in the ROM  133 . The current gear speed deceleration (deceleration) can be obtained referencing this current gear speed deceleration map in  FIG. 22 . As shown in  FIG. 22 , the current gear speed deceleration can be obtained based on the gear speed and the rotation speed No of the output shaft  120   c  of the automatic transmission  10 . For example, when the current gear speed is 5th speed and the output rotation speed is 1000 [rpm], the current gear speed deceleration is −0.04 G.  
      The current gear speed deceleration may also be a value obtained from the current gear speed deceleration map, which is corrected according to the situation, for example, according to whether an air conditioner of the vehicle is being operated, whether there is a fuel cut, and the like. Further, a plurality of current gear speed deceleration maps, one for each situation, may be provided in the ROM  133 , and the current gear speed deceleration map used may be switched according to the situation.  
      Next, the speed target deceleration is set as a value between the current gear speed deceleration and the maximum target deceleration. That is, the speed target deceleration is obtained as a value that is larger than the current gear speed deceleration but equal to, or less than, the maximum target deceleration. One example of the relationship between the speed target deceleration, the current gear speed deceleration, and the maximum target deceleration is shown in  FIG. 23 .  
      The speed target deceleration can be obtained by the following expression. 
 
speed target deceleration=(maximum target deceleration−current gear speed deceleration)×coefficient+current gear speed deceleration 
 
 In the above expression, the coefficient is a value greater than 0 but equal to, or less than, 1. 
 
      In the above example, the maximum target deceleration is −0.20 G and the current gear speed deceleration is −0.04 G. When calculated with a coefficient of 0.5, the speed target deceleration is −0.12 G.  
      As described above, in the first through third methods for obtaining the speed target deceleration, a coefficient is used. The value of this coefficient, however, is not obtained theoretically, but is a suitable value that is able to be set appropriately from the various conditions. That is, in a sports car, for example, a relatively large deceleration is preferable when decelerating, so the coefficient can be set to a large value. Also, in the same vehicle, the value of the coefficient can be variably controlled according to the vehicle speed or the gear speed. In a vehicle in which a sport mode (which aims to increase the vehicle response to an operation by the driver so as to achieve crisp and precise handling), a luxury mode (which aims to achieve a relaxed and easy response to an operation by the driver), and an economy mode (which aims to achieve fuel efficient running) are available, when the sport mode is selected, the speed target deceleration is set so that a larger speed change occurs than would occur in the luxury mode or the economy mode.  
      After being obtained in step S 5 , the speed target deceleration is not reset until the deceleration control ends. That is, the speed target deceleration is set so that, once it is obtained at the starting point of the deceleration control (i.e., the point at which the brake control (step S 8 ) and the shift control (step S 7 ) actually start), it is the same value until the deceleration control ends. As shown in  FIG. 23 , the speed target deceleration (the value shown by the broken line) is a constant value over time.  
      (2) Next, the speed to be selected during the shift control of the automatic transmission  10  is determined based on the speed target deceleration obtained in part (1) above. Vehicle characteristic data indicative of the deceleration G at each speed in each gear speed when the accelerator is off, such as that shown in  FIG. 24 , is stored in advance in the ROM  133 .  
      Here, assuming a case in which the output rotation speed is 1000 [rpm] and the speed target deceleration is −0.12 G, just as in the example given above, the gear speed corresponding to the vehicle speed when the output speed is 1000 [rpm] and the deceleration is closest to the speed target deceleration of −0.12 G is 4th speed, as can be seen in  FIG. 24 . Accordingly, in the case of the above example, it would be determined in step S 5  that the gear speed to be selected is 4th speed.  
      Here, the gear speed that would achieve a deceleration closest to the speed target deceleration is selected as the gear speed to be selected. Alternatively, however, the gear speed to be selected may be a gear speed that would achieve a deceleration which is both equal to, or less than, (or equal to, or greater than,) the speed target deceleration, and closest to the speed target deceleration. After step S 5 , step S 6  is executed.  
      In step S 6 , the control circuit  130  determines whether the accelerator and the brake are off. In step S 6 , when the brake is off, it means that the brake is off because a brake pedal (not shown) is not being operated by the driver. This determination is made based on output from a brake sensor (not shown) that is input via the brake control circuit  230 . If it is determined in step S 6  that both the accelerator and the brake are off, step S 7  is executed. If, on the other hand, it is not determined that both the accelerator and the brake are off, step S 12  is executed.  
      At time T 0  in  FIG. 25 , the brake is off (i.e., braking force equals zero), as shown by reference numeral  302 , and the accelerator is off (i.e., the accelerator opening amount is zero with the accelerator being fully closed), as shown by reference numeral  301 .  
      In step S 7 , the control circuit  130  starts the shift control. That is, automatic transmission  10  is shifted to the selected gear speed (4th speed in this example) that was determined in step S 5 . The automatic transmission  10  is downshifted by the shift control at time T 0  in  FIG. 25 , as shown by reference numeral  304 . As a result, the engine braking force increases, so the current deceleration  303  increases a corresponding amount. After step S 7 , step S 8  is executed.  
      In step S 8 , the brake control circuit  230  starts the brake control. That is, the brakes are feedback controlled so that the current deceleration  303  matches the target deceleration set in step S 4 . As a result of that feedback control, the braking force  302  gradually increases from time T 0  to time T 1  in  FIG. 25 , causing the current deceleration  303  to increase following the target deceleration. The brake feedback control is continued until the current deceleration  303  reaches the end-point deceleration (the maximum target deceleration, in this case) of the set target deceleration at time T 1  (step S 9 ).  
      In step S 7 , the brake control circuit  230  outputs the brake control signal SG 2  to the hydraulic pressure control circuit  220  based on the brake braking force signal SG 1  input from the control circuit  130 . As described above, the hydraulic pressure control circuit  220  generates the braking force  302  as indicated by the brake control signal SG 2  by controlling the hydraulic pressure supplied to the brake devices  208 ,  209 ,  210 , and  211  based on the brake control signal SG 2 .  
      The braking force  302  by the brake control may also be determined taking into account a time differential value of the rotation speed of the input shaft of the automatic transmission  10  and a shift inertia torque amount determined by the inertia.  
      Here, both the target deceleration set in step S 4  and the target deceleration set again in step S 10 , which will be described later, are included in the “target deceleration” in steps S 8  and S 9 . The brake control of step S 8  continues to be executed until it is ended in step S 12 . After step S 8 , step S 9  is executed.  
      In step S 9 , the control circuit  130  determines whether the current deceleration  303  is the end-point deceleration of the set target deceleration. If it is determined that the current deceleration  303  is the end-point deceleration of the set target deceleration, then step S 10  is executed. If, on the other hand, it is determined that the current deceleration  303  is not the end-point deceleration of the set target deceleration, the process returns to step S 8 . Because the current deceleration  303  does not reach the end-point deceleration of the set target deceleration (here, the maximum target deceleration) until time T 1  in  FIG. 25 , the feedback control of the brake is continued in step S 8  until it does.  
      Then in step S 10 , the target deceleration is set again, as shown in  FIG. 18B . The control circuit  130  sets the target deceleration referencing the target deceleration map ( FIG. 20 ), just as in step S 3 . The target deceleration is set based on the relative vehicle speed and the vehicle-to-vehicle distance, as described above. Because the relative vehicle speed and the vehicle-to-vehicle distance change when the deceleration control (i.e., both the shift control and the brake control) starts, the target deceleration is set in real time according to that change.  
      When the target deceleration is set in real time in step S 10 , the braking force  302  is applied to the vehicle such that the current deceleration  303  matches the target deceleration by the brake feedback control that is continuing from when it was started in step S 8  (see steps S 7  and S 8 ).  
      The operation to obtain the target deceleration in step S 10  continues to be performed until the brake control ends in step S 12 . The brake control continues (steps S 11  and S 12 ) until the current deceleration  303  matches the speed target deceleration, as will be described later. Because the current deceleration  303  is controlled to match the target deceleration (steps S 8  and S 9 ), as described above, the operation to set the target deceleration in step S 10  continues until the set target deceleration matches the speed target deceleration.  
      At the time that step S 10  is executed, the vehicle speed of the host vehicle is less, by the amount that the deceleration control has already been performed, than it was at the time that step S 3  was performed before the start of the deceleration control. From this, the target deceleration set in order to achieve the target vehicle-to-vehicle distance and relative vehicle speed usually becomes, in step S 10 , a value smaller than the maximum target deceleration obtained in step S 3 .  
      From time T 1  to time T 7  in  FIG. 25 , the operation of setting the target deceleration in real time and applying the braking force  302  such that the current deceleration  303  matches that target deceleration is repeated. During that time, however, as a result of the brake control being continued, the target deceleration repeatedly set in step S 10  gradually decreases. In response to this decrease in the value of the target deceleration, the braking force  302  applied by the feedback control of the brake control also gradually decreases, such that the current deceleration  303  gradually decreases while substantially matching that target deceleration. After step S 10 , step S 11  is executed.  
      In step S 11 , the control circuit  130  determines whether the current deceleration  303  matches the speed target deceleration. If it is determined that the current deceleration  303  matches the speed target deceleration, the brake control ends (step S 12 ) and this fact is transmitted to the brake control circuit  230  by the brake braking force signal SG 1 . If, on the other hand, the current deceleration  303  does not match the speed target deceleration, the brake control does not end. Since the current deceleration  303  matches the speed target deceleration at time T 7  in  FIG. 25 , the braking force  302  applied to the vehicle becomes zero (i.e., the brake feedback control ends).  
      In step S 13 , the control circuit  130  determines whether the accelerator is on. If the accelerator is on, step S 14  is executed. If not, step S 17  is executed. In the example in  FIG. 25 , it is determined that the accelerator is on at time t 8 .  
      In step S 14 , a return timer is started. In the example in  FIG. 25 , the return timer starts from time T 8 . After step S 14 , step S 15  is executed. The return timer (not shown) is provided in the CPU  131  of the control circuit  130 .  
      In step S 15 , the control circuit  130  determines whether a count value of the return timer is equal to, or greater than, a predetermined value. If the count value is not equal to, nor greater than, the predetermined value, the process returns to step S 13 . If the count value is equal to, or greater than, the process proceeds on to step S 16 . In the example shown in  FIG. 25 , the count value becomes equal to, or greater than, the predetermined value at time T 9 .  
      In step S 16 , the control circuit  130  ends the shift control (downshift control) and returns the automatic transmission  10  to the speed determined based on the accelerator opening amount and the vehicle speed according to a normal shift map (shift line) stored beforehand in the ROM  133 . In the example shown in  FIG. 25 , the shift control ends at time T 9 , at which time an upshift is executed. When step S 16  is executed, the control flow ends.  
      In step S 17 , the control circuit  130  determines whether the vehicle-to-vehicle distance exceeds a predetermined value. Step S 17  corresponds to step S 1 . If it is determined that the vehicle-to-vehicle distance does exceed the predetermined value, step S 16  is then executed. If it is determined that the vehicle-to-vehicle distance does not exceed the predetermined value, the process returns to step S 13 .  
      The foregoing exemplary embodiment enables the following effects to be achieved. According to this exemplary embodiment, the deceleration necessary for the vehicle-to-vehicle distance control is set as the overall target deceleration of the cooperative control, and the brakes, which have good response, are feedback controlled to achieve that set target deceleration. Therefore, the current deceleration is able to accurately follow the overall target deceleration (i.e., the deceleration necessary for the vehicle-to-vehicle distance control) of the cooperative control. As a result, vehicle-following control (i.e., vehicle-to-vehicle distance control) with respect to the distance between vehicles which changes continuously is able to be performed smoothly.  
      According to this exemplary embodiment, the speed target deceleration is set so as to be between the current gear speed deceleration and the maximum target deceleration (step S 4 ). That is, the deceleration caused by the engine braking force obtained from the downshift (shift control) into the selected gear speed is set so as to be between the engine braking force of the speed before the start of the deceleration control (i.e., the current gear speed deceleration) and the maximum target deceleration (step S 5 ). As a result, even when deceleration control in which the brake control and shift control are performed simultaneously in cooperation with one another is executed (steps S 7  and S 8 ), the deceleration is not excessive so no sense of discomfort is imparted to the driver. In addition, even when the vehicle-to-vehicle distance and the relative vehicle speed have reached their respective target values and the brake control has ended (step S 12 ), the engine brake from the downshift continues to be effective so hunting of the brake control due to an increase in vehicle speed (particularly when on a downward slope) following the end of the brake control (step S 12 ) is able to be effectively suppressed.  
      Also according to this exemplary embodiment, from time T 1  to time T 7  in  FIG. 25  after the current deceleration  303  matches the maximum target deceleration (step S 9 ), the current deceleration  303  gradually decreases while substantially matching the target deceleration calculated in real time. Then at the point when the target deceleration (the same as the current deceleration  303  in this case) matches the speed target deceleration, the brake control ends, as shown in steps S 11  and S 12 . That is, the brake control ends when the target deceleration calculated in real time matches the speed target deceleration (i.e., the deceleration after the downshift control). In other words, the brake control does not continue until the target deceleration (the current deceleration  303  in this case) returns to the deceleration that it was at time T 0  when the deceleration control started (i.e., returns to the current gear speed deceleration).  
      If the deceleration control were to be performed by the brake control alone, i.e., without performing the shift control, it would be necessary to continue the brake control until the target deceleration returned to near the current gear speed deceleration and the target vehicle-to-vehicle distance and relative vehicle speed could be realized by the current gear speed deceleration alone. In contrast, because in this exemplary embodiment the shift control and the brake control are performed simultaneously in cooperation with one another, the brake control can be ended when the target deceleration substantially matches the deceleration achieved by the shift control (i.e., the speed target deceleration) and the target vehicle-to-vehicle distance and relative vehicle speed can be achieved by the deceleration achieved by the shift control alone. As a result, in this exemplary embodiment, the brake control can be ended in a shorter period of time, which ensures durability of the brakes (i.e., reduces brake fade and wear on the brake pads and discs.  
      Further in this exemplary embodiment, the brake control ends when the target deceleration (i.e., the current deceleration  303  in this case) matches the speed target deceleration (i.e., the deceleration after the downshift control), and deceleration control by only the shift control is performed from that point (steps S 11  and S 12 ; time T 7  in  FIG. 25 ). As a result, deceleration control is performed with only shift control while the current deceleration  303  substantially matches the deceleration after the shift control (i.e., the deceleration produced by the engine braking force), which enables a smooth transition to the deceleration produced by the engine braking force.  
      As described above, the brake control ends when the target deceleration substantially matches the speed target deceleration (i.e., the deceleration produced by the engine braking force after the shift control). The shift control, on the other hand, ends either after a predetermined period of time has passed after the accelerator has been turned on (steps S 13  and S 14 ) after the brake control ends (step S 12 ) or when the vehicle-to-vehicle distance exceeds a predetermined value after the brake control ends (step S 17 ). In this way, by making the conditions for ending (i.e., returning from) the brake control different from those for ending (i.e., returning from) the shift control, the brake control can be ended in a short period of time, thus helping to ensure durability of the brakes. Also, because the shift control does not end unless the vehicle-to-vehicle distance exceeds the predetermined value, the engine brake continues to be effective.  
      Next, a seventh exemplary embodiment of the invention will be described with reference to  FIGS. 26A and 26B  and  FIG. 25 . Descriptions of parts in the seventh exemplary embodiment that are the same as those in the sixth exemplary embodiment will be omitted; only parts that are different will be described.  
      In the sixth exemplary embodiment, feedback control is performed. In contrast, in the seventh exemplary embodiment, the brake control is performed on the brake as follows. That is, the brake is controlled to compensate for the insufficiency in the deceleration  402  produced by the shift of the automatic transmission  10  (i.e., by the downshift into the selected gear speed) so that the braking force  12  increases by a predetermined gradient until the deceleration that acts on the vehicle reaches the target deceleration.  
       FIGS. 26A and 26B  show the control flow of the seventh exemplary embodiment of the invention.  FIG. 25  is a time chart of the seventh exemplary embodiment (the same as in the sixth exemplary embodiment). As can be seen from  FIGS. 26A, 26B , and  25 , much of the seventh exemplary embodiment is the same as the sixth exemplary embodiment described above. Therefore, only parts that are different will be described here.  
      Step S 4  (setting the target deceleration at a predetermined gradient) in  FIG. 18A  is omitted in  FIG. 26A , as can be seen when comparing  FIG. 26A  with  FIG. 18A  which shows the flow of the sixth exemplary embodiment. In the seventh exemplary embodiment, only the maximum target deceleration is set for the target deceleration in step S 3  until before the brake control starts (step S 7 ). Steps S 1  to S 6  in  FIG. 26A  are the same as steps S 1  to S 3  and S 5  to S 7  in  FIG. 18A , so descriptions thereof will be omitted here.  
      In step S 7 , the brake control circuit  230  starts the brake control. That is, the braking force is gradually increased (sweep control) at a predetermined gradient until the target deceleration. From time T 0  to time T 1  in  FIG. 25 , the braking force  302  increases at a predetermined gradient, which results in an increase in the current deceleration  303 . The braking force  302  continues to increase until the current deceleration  303  reaches the target deceleration at time T 1  (step S 8 ).  
      Just as in the sixth exemplary embodiment, the brake control circuit  230  outputs the brake control signal SG 2  to the hydraulic pressure control circuit  220  based on the brake braking force signal SG 1  input from the control circuit control circuit  130 .  
      The predetermined gradient in step S 7  is determined by the brake braking force signal SG 1  which is referenced when generating the brake control signal SG 2 . The predetermined gradient is indicated by the brake braking force signal SG 1  and can be changed based on the road ratio μ, the accelerator return rate at the start of the control (immediately before time T 0  in  FIG. 25 ), or the opening amount of the accelerator before it is returned. For example, the gradient (slope) is set small when the road ratio μ is small and large when the accelerator return rate or the opening amount of the accelerator before it is returned is large.  
      The braking force  302  by the brake control may be determined taking into account a time differential value of the rotation speed of the input shaft of the automatic transmission  10  and a shift inertia torque amount determined by the inertia.  
      Here, both the maximum target deceleration obtained in step S 3  and the target deceleration obtained again in step S 9 , which will be described later, are included in the “target deceleration” in step S 7 . The brake control of step S 7  continues to be executed until it is ended in step S 11 . After step S 7 , step S 8  is executed.  
      In step S 8 , the control circuit  130  determines whether the current deceleration  303  is the target deceleration. If it is determined that the current deceleration  303  is the target deceleration, step S 9  is executed. If, on the other hand, it is determined that the current deceleration  303  is not the target deceleration, the process returns to step S 7 . Because the current deceleration  303  does not reach the target deceleration until time T 1  in  FIG. 25 , the braking force  302  increases at a predetermined gradient in step S 7  until then.  
      Because steps S 9  to S 15  in  FIG. 26B  are the same as steps S 10  to S 16  in  FIG. 18B , a described thereof will be omitted.  
      Just like the exemplary embodiments described above, the seventh exemplary embodiment also uses the brake, which has superior response and controllability, to compensate for the shortage of deceleration produced by the shift of the automatic transmission  10  so that, as an overall result of the cooperative control, the target deceleration is produced.  
      According to the seventh exemplary embodiment, it is possible to stop (temporarily and with good response) the braking force  12  from being applied to the vehicle (time T 1 ) when the maximum target deceleration is produced as an overall result of the cooperative control due to the braking force  12  being applied to the vehicle. Accordingly, a deceleration exceeding the maximum target deceleration as an overall result of the cooperative control, whether temporary or not, which acts on the vehicle (i.e., overshooting) is able to be minimized.  
      Next, an eighth exemplary embodiment of the invention will be described with reference to  FIG. 27 . Descriptions of parts in the eighth exemplary embodiment that are the same as those in the sixth and seventh exemplary embodiments will be omitted; only parts that are different will be described.  
      The eighth exemplary embodiment relates to the speed target deceleration of the sixth and seventh exemplary embodiments (step S 5  or step S 4 ). In the eighth exemplary embodiment, the speed target deceleration is corrected according to the gradient of the road.  FIG. 27  is a block diagram schematically showing the control circuit  130  according to the eighth exemplary embodiment. In the eighth exemplary embodiment, a road gradient measuring/estimating portion  118  is provided which measures or estimates the road gradient.  
      The road gradient measuring/estimating portion  118  can be provided as a portion of the CPU  131 . The road gradient measuring/estimating portion  118  can measure or estimate the road gradient based on acceleration detected by the acceleration sensor  90 . Further, the road gradient measuring/estimating portion  118  can store acceleration on a level road in the ROM  133  in advance, and obtain the road gradient by comparing that stored acceleration with the actual acceleration detected by the acceleration sensor  90 .  
      In this exemplary embodiment, the speed target deceleration is corrected as follows. First, a gradient correction quantity (deceleration) is obtained. Here, it is obtained as a gradient 1%≈0.01 G (an upward gradient is positive and a downward gradient is negative).  
      Next, the speed target deceleration after the correction can be obtained from the following expression according to the third method for obtaining the speed target deceleration. 
 
speed target deceleration=(maximum target deceleration−current gear speed deceleration)×coefficient+current gear speed deceleration+gradient correction quantity 
 
 In the above expression, the coefficient is a value that is greater than 0 but equal to, or less than, 1. 
 
      Accordingly, on a downward gradient such as a downward slope, the speed target deceleration is corrected to a large value such that the gear speed to be selected, which is determined in step S 5  or step S 4 , is a lower gear speed than a gear speed selected when on a level road. On an upward gradient, the speed target deceleration is corrected to a small value such that the gear speed to be selected, which is determined in step S 5  or step S 4 , is a higher gear speed than a gear speed selected when on a level road.  
      According to the eighth exemplary embodiment, correcting the speed target deceleration according to the gradient of the road on which the vehicle is traveling enables optimum engine braking force to be obtained. As a result, an engine braking amount which matches that expected by the driver (i.e., required by the driver) is able to be obtained.  
      Next, a ninth exemplary embodiment of the invention will be described with reference to  FIG. 28 . Descriptions of parts in the ninth exemplary embodiment that are the same as those in the foregoing exemplary embodiments will be omitted; only parts that are different will be described.  
      The ninth exemplary embodiment relates to the speed target deceleration (step S 5  or step S 4 ) of the sixth or seventh exemplary embodiment, just like the eighth exemplary embodiment. The ninth exemplary embodiment corrects the speed target deceleration according to the shape of the road, such as the size (radius) of an upcoming corner, or any intersections or junctions that might be ahead. One example of a correction according to the size of a corner is as follows.  FIG. 28  is a block view schematically showing the control circuit  130  according to the ninth exemplary embodiment. In the ninth exemplary embodiment, a corner measuring/estimating portion  119  which measures or estimates the size of a corner is connected to the control circuit  130 .  
      The corner measuring/estimating portion  119  determines whether there is a corner ahead of the vehicle, and if so, measures or estimates the size of the corner. The determination and measurement or estimation are made based on, for example, information of the road shape obtained from a car navigation system mounted in the vehicle and an image captured by a camera mounted to the front of the vehicle. In the following example, the corner measuring/estimating portion  119  stores (in advance) the sizes of corners classified into one of three classifications (i.e., gentle, medium, hairpin) based on information indicating the size of the corner obtained by the car navigation system.  
      In this exemplary embodiment, the speed target deceleration is corrected as follows. First, a deceleration correction quantity (deceleration) for the corner is obtained. Here, a map such as that shown in  FIG. 29 , for example, which is stored in the corner measuring/estimating portion  119 , may be used. Correction quantities for the deceleration are stored beforehand in the map. The correction quantities are based on the three different classifications of corner size and the rotation speed (No) of the output shaft  120   c  of the automatic transmission  10  corresponding to the vehicle speed.  
      For example, when a corner ahead of the vehicle is a medium corner and the current rotation speed of the output shaft  120   c  is 2000 [rpm], the deceleration correction quantity for that corner is obtained as 0.007 (G). The corner measuring/estimating portion  119  outputs data indicative of the deceleration correction quantity for that corner (hereinafter referred to as the “corner correction quantity”) to the control circuit  130 .  
      Next, the speed target deceleration after the correction can be obtained from the following expression according to the third method for obtaining the speed target deceleration. 
 
speed target deceleration=(maximum target deceleration−current gear speed deceleration)×coefficient+current gear speed deceleration−corner correction quantity 
 
 In the above expression, the coefficient is a value that is greater than 0 but equal to, or less than, 1. 
 
      Accordingly, on a sharp corner, the speed target deceleration is corrected to a considerably large value such that the gear speed to be selected, which is determined in step S 5 , is a much lower gear speed than a gear speed selected when on a straight road (i.e., not on a corner). On gentle curve, the amount of increase in the speed target deceleration is kept small compared to when on a sharp corner, such that the gear speed to be selected, which is determined in step S 4 , is a somewhat lower gear speed than a gear speed selected when on a straight road.  
      According to the ninth exemplary embodiment, correcting the speed target deceleration according to the shape, such as a corner, of the road on which the vehicle is traveling enables optimum engine braking force to be obtained. As a result, an engine braking amount which matches that expected by the driver (i.e., required by the driver) is able to be obtained.  
      Next, a tenth exemplary embodiment of the invention will be described with reference to  FIG. 30 . Descriptions of parts in the tenth exemplary embodiment that are the same as those in the foregoing exemplary embodiments will be omitted; only parts that are different will be described.  
      The tenth exemplary embodiment relates to the speed target deceleration (step S 5  or step S 4 ) of the sixth or seventh exemplary embodiment, just like the eighth and ninth exemplary embodiments. The tenth exemplary embodiment corrects the speed target deceleration based on the slipperiness of the road surface, such as the road ratio μ of the road on which the vehicle is traveling. The tenth exemplary embodiment uses the detection or estimation results from the road ratio μ detecting/estimating portion  115  that detects or estimates the road ratio μ.  
      The specific method for detecting or estimating the road ratio μ by the road ratio μ detecting/estimating portion  115  is not particularly limited, but can be any known method that is suitable. For example, other than the difference between the wheel speeds of the front and rear wheels, at least one of the change rate in the wheel speed, the operation history of ABS (antilock brake system), TRS (traction control system), or VSC (vehicle stability control), the acceleration of the vehicle, and navigation information can be used to detect/estimate the road ratio μ. Here, navigation information includes information pertaining to the road surface (such as whether the road is paved or not) stored on a storage medium (such as DVD or HDD) beforehand, as with a car navigation system, as well as information (including traffic and weather information) obtained by the vehicle itself through communication (including vehicle-to-vehicle communication and roadside-to-vehicle communication) with vehicles that were actually traveling earlier, other vehicles, or a communication center. This communication also includes road traffic information communication system (VICS) and so-called Telematics.  
      In this exemplary embodiment, the speed target deceleration is corrected as follows. First, a road ratio μ correction quantity (deceleration) is obtained. Here, a map such as that shown in  FIG. 30 , for example, which is stored in the ROM  133 , may be used. Correction quantities for the deceleration are stored beforehand in the map. These correction quantities are based on the road ratio μ and the rotation speed (No) of the output shaft  120   c  of the automatic transmission  10  corresponding to the vehicle speed. For example, when the road ratio μ is 0.5 and the current rotation speed of the output shaft  120   c  is 2000 [rpm], the deceleration correction quantity (road ratio μ correction quantity) for that road ratio μ is obtained as 0.003 (G).  
      Next, the speed target deceleration after the correction can be obtained from the following expression according to the third method for obtaining the speed target deceleration. 
 
speed target deceleration=(maximum target deceleration−current gear speed deceleration)×coefficient+current gear speed deceleration+road ratio μ correction quantity 
 
 In the above expression, the coefficient is a value that is greater than 0 but equal to, or less than, 1. 
 
      Accordingly, the speed target deceleration is corrected to a smaller value the lower the road ratio μ, such that the gear speed to be selected, which is determined in step S 5  or step S 4 , is a higher gear speed than a gear speed selected when the road ratio μ is high.  
      According to the tenth exemplary embodiment, correcting the speed target deceleration according to the slipperiness of the road surface, such as the road ratio A, of the road on which the vehicle is traveling enables optimum engine braking force to be obtained. As a result, an engine braking amount which matches that expected by the driver (i.e., required by the driver) is able to be obtained.  
      The deceleration control apparatus for a vehicle according to this exemplary embodiment thus incorporates the advantages of both control of a brake system that applies braking force to the vehicle and shift control that shifts an automatic transmission into a relatively low speed or speed ratio, when performing deceleration control on the vehicle.  
      Various modifications are also possible with the foregoing first through the tenth exemplary embodiments. For example, in the examples described above, brake control is used. Instead of brake control, however, regenerative control by a MG (motor/generator) apparatus provided in a power train system (as in the case of a hybrid system) can also be used. Further, in the example described above, a stepped automatic transmission  10  is used for the transmission. The invention may of course also be applied, however, to a CVT (continuously variable transmission). In this case, the terms “gear speed” and “speed” may be replaced with the term “speed ratio”, and the term “downshift” may be replaced with the term “CVT adjustment”. Moreover, in the above description, the deceleration (G) is used as the deceleration indicative of the amount of deceleration of the vehicle. Alternatively, however, the control may be performed based on the deceleration torque.  
      While the invention has been described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the exemplary embodiments are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element are also within the spirit and scope of the invention.