Abstract:
In braking/driving force controlling apparatus and method for an automotive vehicle, a state discriminating section discriminates between a parking state in which a manipulation for the vehicle to be parked is carried out and a non-parking state in which no manipulation for the vehicle to be parked is carried out, a controller detects a manipulated variable of a manual input section, generates a constant target vehicle speed corresponding to the detected manipulated variable in a case where the state discriminating section discriminates the parking state, calculates a vehicular braking/driving force for a present vehicle speed to become the target vehicle speed, and controls the vehicular braking/driving force on the basis of the calculated braking/driving force.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to braking/driving force controlling apparatus and method for an automotive vehicle and, more specifically, relates to the braking/driving force controlling apparatus and method suitable for the automotive vehicle to be parked. 
     2. Description of the Related Art 
     A Japanese Patent Application First Publication No. Heisei 10-278825 published on Oct. 28, 1998 which corresponds to a U.S. Pat. No. 5,931,252 issued on Aug. 3, 1999 exemplifies a previously proposed automatic steering system for an automotive vehicle in which the vehicle moves in accordance with a locus predefined at a time of an automatic steering during a vehicular parking. In a case where a vehicle creep speed falls out of a predetermined speed range, the automatic steering system urges a vehicle driver to carry out a brake manipulation or accelerator manipulation through a liquid crystal display or speaker. 
     SUMMARY OF THE INVENTION 
     In the previously proposed automatic steering system disclosed in the above-identified Japanese Patent Application First Publication, the driver is informed to carry out the brake manipulation or accelerator manipulation. 
     Hence, for example, in a case where the vehicle is needed to be parked while ascending a slope, a suitable vehicle creep speed is often not obtained merely by the brake manipulation. In this case, the driver needs to depress an accelerator pedal to once raise the vehicle speed up to a predetermined vehicle speed and, thereafter, needs to depress a brake pedal in accordance with an operation command from the previously proposed automatic steering system. In this way, the driver needs to change the pedal to be depressed to drive the vehicle. The driving operation is troublesome for the driver. 
     It is, hence, an object of the present invention to provide improved braking/driving force control apparatus and method for an automotive vehicle which can achieve an easy driving operation even if the vehicle parking is carried out at any place. 
     According to one aspect of the present invention, there is provided a braking/driving force controlling apparatus for an automotive vehicle, comprising: a state discriminating section that discriminates between a parking state in which a manipulation for the vehicle to be parked is carried out and a non-parking state in which no manipulation for the vehicle to be parked is carried out; a manual input section that is enabled to be manipulated; a manipulated variable detecting section that detects a manipulated variable of the manual input section; a target vehicle speed generating section that generates a constant target vehicle speed corresponding to the manipulated variable detected by the manipulated variable detecting section in a case where the state discriminating section discriminates the parking state; a braking/driving force calculating section that calculates a vehicular braking/driving force for a present vehicle speed to become the target vehicle speed; and a braking/driving force controlling section that controls the vehicular braking/driving force on the basis of the vehicular braking/driving force calculated by the braking/driving force calculating section. 
     According to another aspect of the present invention, there is provided a braking/driving force controlling apparatus for an automotive vehicle, comprising: a state discriminating section that discriminates between a parking state in which a manipulation for the vehicle to be parked is carried out and a non-parking state in which no manipulation for the vehicle to be parked is carried out; a manual input section that is enabled to be manipulated; a manipulated variable detecting section that detects a manipulated variable of the manual input section; a target vehicle speed generating section that generates a target vehicle speed based on the manipulated variable detected by the manipulated variable detecting section; a braking/driving force calculating section that calculates a vehicular braking/driving force for a present vehicle speed to become the target vehicle speed generated by the target vehicle speed generating section; and a braking/driving force controlling section that controls a vehicular braking/driving force on the basis of the vehicular braking/driving force calculated by the braking/driving force calculating section, and wherein the target vehicle speed generating section generates a constant target vehicle speed when the manipulated variable detected by the manipulated variable detecting section is zero and the braking/driving force calculating section calculates a new target braking/driving force by combining the vehicular braking/driving force for the vehicle speed to become the constant target vehicle speed with the vehicular braking/driving force based on the manipulated variable detected by the manipulation detecting section. 
     According to a still another aspect of the present invention, there is provided a braking/driving force controlling method for an automotive vehicle, comprising: discriminating between a parking state in which a manipulation for the vehicle to be parked is carried out and a non-parking state in which no manipulation for the vehicle to be parked is carried out; detecting a manipulated variable of a manual input section that is enabled to be manipulated; generating a constant target vehicle speed corresponding to the detected manipulated variable in a case where the parking state is discriminated; calculating a vehicular braking/driving force for a present vehicle speed to become the target vehicle speed; and controlling the vehicular braking/driving force on the basis of the calculated vehicular braking/driving force. 
     This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic circuit block diagram of a braking/driving force control apparatus in a first preferred embodiment according to the present invention. 
     FIG. 2 is an operational flowchart executed by a controller of the first embodiment shown in FIG.  1 . 
     FIG. 3 is a characteristic graph representing a relationship between a brake manipulated variable and vehicle speed. 
     FIG. 4 is an operational flowchart executed by the controller of a second preferred embodiment according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention. 
     FIG. 1 shows a schematic circuit block diagram of a braking/driving force control apparatus in a first preferred embodiment according to the present invention. 
     In FIG. 1, a mode selection switch  10  is installed on an instrument panel of a passenger compartment of a vehicle (not shown) to be manipulated by a vehicle driver. If a terminal A is contacted with a termina  1 C, a signal indicating a parking mode is outputted to a controller  50 . In addition, if a terminal B is contacted with terminal C (grounded), a signal indicating a non-parking mode is outputted to controller  50 . 
     A brake pedal sensor  30  is disposed on a brake pedal  30 A to detect a manipulated variable of the brake pedal  30 A. It is noted that, in the whole specification, the manipulated variable detected by brake pedal sensor  30  is described in such a way that the manipulated variable is 0[%] in a case where brake pedal  30 A is not depressed (not manipulated), namely, when non-operation of brake pedal  30 A is carried out and in such a way that the manipulated variable corresponding to a full brake is 100[%]. An accelerator pedal sensor  20  is disposed on an accelerator pedal  20 A to detect a manipulated variable of accelerator pedal  20 A. A vehicle speed sensor  40  includes an encoder for detecting a wheel speed of a non-driven wheel of the vehicle. 
     Controller  50  includes, for example, a microcomputer having a CPU (Central Processing Unit)  50   a ; a ROM (Read Only Memory)  50   b ; a RAM (Random Access Memory)  50   c ; a V-RAM (Video-Random Access Memory)  50   d ; an interrupt controller  50   e ; a DMA (Direct Memory Access) controller  50   f ; and Communication Interface  50   g ; an I/O interface  50   h ; and a common bus. 
     An engine controller  60  generally controls an intake-air quantity and so forth of an engine  65  in accordance with predefined arithmetic and logic operations while inputting various sensor signals from accelerator pedal sensor  20 , a coolant temperature sensor (not shown), and so forth. 
     A brake controller  70  controls a brake liquid pressure of a brake  75  in accordance with predefined arithmetic and logic operations while inputting various signals from brake pedal sensor  30 , vehicle speed sensor  40 , and longitudinal and lateral acceleration sensors (not shown). 
     A transmission controller  80  controls a continuously variable transmission (so-called, CVT)  70  in accordance with predefined arithmetic and logic operations while inputting throttle opening angle (engine load) and so forth. 
     A display  90  is connected to controller  50  and is disposed within the passenger compartment to display, for example, a navigation image screen, a vehicular air conditioner image screen, and other vehicular information and display an information to an effect that the driver operates mode selection switch (SW)  10  to the parking mode or that accelerator pedal  20 A depressed in spite of mode selection switch  10  positioned into the parking mode. Furthermore, a buzzer  95  is installed within the passenger compartment to inform the driver that accelerator pedal  20 A is operated in spite of the fact that mode selection switch  10  is placed in the parking mode as described above. 
     Next, FIG. 2 shows an operational flowchart for explaining a control program stored in ROM  50   b  within controller  50 . 
     The control program based on FIG. 2 is started when an ignition switch of the vehicle is turned on (IGN SW ON). 
     At a step S 1 , controller  50  detects the manipulated variable of brake pedal  30 A from brake pedal sensor  30 . 
     At the next step S 2 , controller  50  detects the manipulated variable of accelerator pedal  20 A from accelerator pedal sensor  20 . 
     At the next step S 3 , controller  50  determines to which mode mode selection switch  10  is selected, i.e., whether mode selection switch  10  is selected to the parking mode. 
     If mode selection switch  10  is selected to the parking mode (Yes) at step S 3 , the routine goes to a step S 4 . If not selected to the parking mode (No) at step S 3 , the routine goes to a step S 17 . 
     At step S 4 , controller  50  determines if accelerator pedal  20 A is manipulated. This step S 4  serves to determine whether accelerator pedal  20 A has been manipulated in spite of the fact that mode selection switch  10  is selected to the non-parking mode. If accelerator pedal  20   a  has been manipulated (Yes) at step S 4 , controller  50  determines that the parking mode is cancelled according to an intention of the driver and the routine goes to a step S 15 . If No at step S 4 , the routine goes to a step S 5 . 
     At step S 15 , controller  50  forcefully moves mode selection switch  10  to the non-parking mode. Thereafter, the routine goes to a step S 16 . At step S 16 , controller  50  commands display  90  to display that the driving mode is switched to the non-parking mode and issues an alarm through buzzer  95 . 
     Next, if controller  50  does not determine that accelerator pedal  20 A is manipulated (No) at step S 4 , controller  50  determines that the parking mode is continued and detects a present vehicle speed at step S 5 . 
     At the next step S 6 , controller  50  reads (calculates) a target vehicle speed from a map shown in FIG.  3  and stored in ROM  50   b  on the basis of the manipulated variable of brake pedal  30 A. As shown in the map in FIG. 3, if the manipulated variable of brake pedal  30 A is 0[%], the target vehicle speed is a predetermined vehicle speed (for example, 10 Km/h). As the manipulated variable of brake pedal  30 A becomes large, the target vehicle speed becomes small. At a time point at which the manipulated variable of brake pedal  30 A is larger than a certain value (for example, 80[%]), the target vehicle speed indicates 0 Km/h. The map in FIG. 3 is set in such a way that when the manipulated variable of brake pedal  30 A is 0[%], i.e., during the non-manipulation of brake pedal  30 A, the target vehicle speed is the vehicle speed equal to or larger than the vehicle creep speed at an ordinary run of the vehicle on a flat road. 
     Next, at a step S 7 , controller  50  calculates a vehicle speed deviation ΔV between the target vehicle speed calculated at step S 6  and an actual (present) vehicle speed detected at step S 5 . At a step S 8 , controller  50  integrates vehicle speed deviation ΔV calculated at step S 7  (∫ΔV). 
     At the next step S 8 , controller  50  calculates a differentiation of vehicle speed deviation ΔV((d/dt)·ΔV) calculated at step S 7 . 
     At the next step S 10 , controller  50  calculates a target braking/driving force on the basis of the following equation. Target braking/driving force Te=K p ·ΔV+K I ∫ΔV+K D ((d/dt)·ΔV), K p  denotes a predetermined proportional gain, K I  denotes a predetermined integration gain, and K p  denotes a predetermined differentiation gain. 
     Suppose that the manipulated variable of the brake pedal is 0[%], the target vehicle speed is 10 Km/h, and the present detected vehicle speed is, for example, 7 Km/h. In this case, it is sufficient to obtain the braking/driving force to achieve the deviation of the vehicle speed (namely, 10−7=3 Km/h). These steps S 7  through S 9  calculate such a target braking/driving force as described above. 
     At the next step S 11 , controller  50  compares target braking/driving force Te calculated at step S 10  with a predetermined braking/driving force T. If Te&gt;T at step S 11 , controller  50  sets target braking/driving force Te to a predetermined value of T (Te=T). This means that a limiter is applied to target braking/driving force Te, namely, an upper limit value is provided in target braking/driving force Te. The reason for the provision on the limiter is as follows: for example, in a situation in which the vehicle is contacted against a difference in a road level to be stopped, it is not necessary for the vehicle to be moved more than the difference in the road level even if the parking is appropriately carried out. If the limiter is not provided, the vehicle tries to run at a certain vehicle speed on the basis of the brake manipulation of the vehicle driver in this situation. To prevent such an unnecessary vehicular movement as described above, the upper limit value is provided on the target braking/driving force. It is noted that although, as described above, the upper limit value is provided on the braking/driving force, the upper limit value is provided for the driving force but may not be provided for the braking force. However, to simplify the calculation, the upper limit value is, in this embodiment, present in a combination of the driving force with the braking force. 
     Next, at a step S 12 , controller  50  calculates a target throttle opening angle to achieve a target braking/driving force for which a limier process is executed at step S 11 . The calculated target throttle opening angle is outputted to engine controller  60 . At step S 12 , controller  50  a target liquid pressure of the brake to achieve the target braking/driving force for which the limiter is provided and calculates a target transmission gear ratio (in a case of CVT  85 , the target transmission gear ratio is called a target speed ratio) to achieve target braking/driving force for which the limiter is processed. The calculated target speed ratio is outputted to transmission controller  80 . Then, the routine returns to step S 1  (engine controller  60 , brake controller  70 , and transmission controller  80  control braking force and driving force to achieve target throttle opening angle, target brake liquid pressure, and target speed ratio inputted thereinto, respectively). 
     As described above, in the first embodiment according to the present invention, controller  50  calculates target braking/driving force for the vehicle to provide the constant vehicle speed in accordance with the manipulated variable in a case where mode selection switch  10  is selected to the parking mode. The engine, brake, and transmission (CVT) are controlled to achieve the target braking/driving force. Since the manipulation can be made with only brake pedal  30 A, it is not necessary to change the pedal to be depressed even if any situation of the parking occurs. Consequently, the driving operation is not troublesome but may become easy. 
     In addition, since the constant vehicle speed corresponding to the manipulated variable of brake pedal  30 A is obtained, the vehicle speed can be adjusted by operating brake pedal  30 A the vehicle driver is ordinarily accustomed to use. A burden imposed on a parking operation of the driver can be relieved. Since a relatively high vehicle speed can be obtained when brake pedal  30 A is not manipulated, the vehicle speed is set to a speed (about 5 Km/h to 10 Km/h) such as not to give an unpleasant feeling to the driver during the parking operation. It is, hence, not necessary to manipulate brake pedal  30 A immediately before the vehicle stops. Consequently, the number of times the driver operates brake pedal  30 A can be reduced. 
     Since a maximum value of the target vehicle speed is a vehicle speed equal to or higher than the ordinary vehicle creep speed that the vehicle can obtain during the run on the flat road, an adjustment of the vehicle speed can be made by depressing brake pedal  30 A on which a tiptoe of the driver is rested. In a case where the accelerator pedal is manipulated so that a higher vehicle speed than the expected is resulted, it is not necessary to change the pedal to be depressed and a quick adjustment of the vehicle speed can be made. 
     First Modification of First Embodiment 
     Next, a first modification of the first embodiment will be described below. 
     In the first embodiment, the constant vehicle speed corresponding to the brake pedal manipulated variable if the parking mode is selected. In the first modification, the constant vehicle speed corresponding to the manipulated variable of accelerator pedal  20 A is derived. That is to say, during the parking mode, a certain constant vehicle speed (for example, 10 Km/h) is resulted if the manipulated variable of accelerator pedal  20 A is equal to or larger than a predetermined variable. As the manipulated variable becomes small, the vehicle speed becomes lower. When accelerator pedal  20 A is in the non-operation state (during a full closure of the throttle valve, a stroke variable is zero), controller  50  sets the vehicle speed to zero. In the first modification, the same advantages as those described in the first embodiment can be achieved. 
     Second Modification of First Embodiment 
     A second modification of the first embodiment will be described below. 
     If the parking mode is selected, the vehicle speed is controlled through a dedicated lever  100 A in the second modification although the vehicle speed is controlled on the basis of the brake pedal manipulated variable in the first embodiment and is controlled on the basis of the accelerator pedal manipulated variable in the first modification. In the same way as described in the first embodiment, the constant vehicle speed is resulted during a non-operation of lever  10 A. In addition, the vehicle speed may be lowered as an operation stroke of lever  100 A detected by a lever stroke sensor  100  is increased. When a maximum operation of lever  100 A is resulted, the vehicle speed becomes lowered in accordance with a quantity returned from the maximum operation state to the non-operation state. In a case where lever  100 A is not manipulated, the vehicle speed may be set to 0 Km/h. 
     According to the second modification, the same advantages as the first embodiment can be achieved. Since dedicated lever  100 A is operated, the driver can recognize that the vehicle enters the parking mode which is different from the ordinary run and operates lever  100 A upon the recognition of the parking mode by the driver. Consequently, no unpleasant feeling which does not meet with the driving sense can be relieved. In a case wherein the brake pedal and accelerator pedal manipulations are detected during the operation of lever  10 A, the forceful set from the parking mode to the non-parking mode is made so that the driver makes a quick response to a step of parking motion. 
     In the above-described second modification, dedicated lever  100 A has been used to control the vehicle speed. However, the same advantages as those described in the second modification can be achieved by a use of a joystick or other switches. 
     Second Embodiment 
     Next, a second embodiment of the braking/driving force control apparatus according to the present invention will be described below. 
     An operation of the braking/driving control apparatus according to the present invention will be described below. 
     At a step S 51 , controller  50  detects whether mode selection switch  10  is set at the parking mode. In the case of the parking mode (Yes), the routine goes to a step S 52 . If controller  50  determines that mode selection switch  10  is set to the non-parking mode (No), the routine goes to a step S 82 . If controller  50  determines that mode selection switch  10  is in the parking mode, the routine goes to a step S 52 . At step S 52 , controller  50  detects the manipulated variable of the accelerator pedal from accelerator pedal sensor  20 . At a step S 53 , controller  50  determines if accelerator pedal  20 A is manipulated. If accelerator pedal  20 A is manipulated (Yes) at a step S 53 , the routine goes to a step S 80 . If accelerator pedal  20 A is not manipulated (No) at step S 53 , the routine goes to a step S 64 . 
     At step S 54 , controller  50  detects the manipulated variable of brake pedal  30 A and the routine goes to a step S 55 . At step S 55 , controller  50  determines whether brake pedal  30 A is manipulated from the manipulated variable of brake pedal  30 A detected at step S 54 . If brake pedal  30 A is manipulated (Yes) at step S 55 , the routine goes to a step S 70 . If brake pedal  30 A is not manipulated (No) at step S 55 , the routine goes to a step S 56 . If controller  50  detects the present vehicle speed on the basis of an output signal from vehicle speed sensor  40 . At a step S 57 , controller  50  determines the target vehicle speed. 
     In the case where the routine shown in FIG. 4 goes to step S 57 , controller  50  determines a state in which brake pedal  30 A is not operated. Since brake pedal  30 A is not operated, controller  50  reads the target vehicle speed (for example, 10 Km/h) which indicates the brake manipulated variable of zero [%] from the map previously stored in ROM  50   b  of controller  50  and shown in FIG.  3  and sets the read target vehicle speed as the target vehicle speed. 
     At the next step S 58 , controller  50  calculates the vehicle speed deviation ΔV between the present (actual) vehicle speed detected at step S 56  and a target vehicle speed set at step S 57 . 
     At the step S 59 , controller  50  calculates an integration (∫ΔV) of the vehicle speed deviation ΔV calculated at step S 58  and a differentiation ((d/dt)·ΔV) of the vehicle speed deviation (ΔV). At the next step S 60 , controller  50  calculates the target braking/driving force on the basis of the following equation: 
     
       
         Target Braking/Driving Force Te=K p ·ΔV+K I ∫ΔV+K D ((d/dt)·ΔV) 
       
     
     This is because the manipulated variable of brake pedal  30 A is 0[%], the target vehicle speed is 10 Km/h, the vehicle speed presently detected is, for example, 7 Km/h, the deviation of the vehicle speed (namely, 10−7=3 Km/h) to achieve the braking/driving force may be obtained. Steps S 59  through S 60  calculate such target braking/driving forces as described above. At the step S 61 , controller  50  stores the target braking/driving force calculated at step S 60 . At the next step S 62 , controller  50  compares target braking/driving force Te stored at step S 61  with a predetermined braking/driving force T. If Te&gt;T, the limiter is provided for target braking/driving force calculated at step S 60 . At the next step S 62 , controller  50  compares target braking/driving force Te stored at step S 61  with a predetermined braking/driving force T. If Te&gt;T, the limiter is provided for target braking/driving force. 
     It is noted that, in this embodiment, the upper limit value is provided for the braking/driving force but the upper limit value may be provided for the driving force and may not be provided for the braking force. In order to simplify the calculation, the upper limit value is provided for the combination of the braking force with the driving force. At the next step S 63 , controller  50  calculates the target throttle opening angle of the engine to achieve the limiter provided target braking/driving force at step S 62 . The target liquid pressure of the brake to achieve target braking/driving force is calculated and outputted to brake controller  70 . The target transmission gear ratio (target speed ratio) to achieve the target braking/driving force is outputted to transmission controller  80  and the routine is returned to step S 51 . It is noted that, at step S 63 , each of engine controller  60 , brake controller  70 , and transmission controller  80  performs the control to achieve respectively inputted target throttle opening angle, target liquid pressure, and target speed ratio. 
     In a case where neither accelerator pedal  20 A nor brake pedal  30 A is manipulated, the target driving force is calculated to maintain the vehicle speed constant and a newest value of the calculated target driving force is always stored. 
     On the other hand, if controller  50  determines that brake pedal  30 A is manipulated, controller  50  calculates the braking force corresponding to the manipulated variable of brake pedal  30 A at step S 70 . 
     At step S 71 , controller  50  adds the target braking/driving force stored at step S 61  to the braking force calculated at step S 70  to calculate a new target braking/driving force. 
     At the next step S 72 , controller  50  calculates the throttle opening angle, the brake liquid pressure, and the speed ratio on the basis of the new target braking/driving force calculated at a step S 72 . Each target value described above is outputted to the corresponding one of controllers  60 ,  70 , and  80 . 
     If controller  50  determines that accelerator pedal  20 A is manipulated at step S 53  (Yes), controller  50  force fully moves mode selection switch  10  to the non-parking mode. At the next step S 81 , controller  50  displays that display  90  is entered in the non-parking mode and produces the alarm through buzzer  95 . 
     If the non-parking mode is selected through mode selection switch  10  at step S 51  (No) and if the manipulation of accelerator pedal  20 A is detected at step S 53  (Yes), controller  50  calculates target braking/driving force at a step S 82 . 
     At the next step S 83 , controller  50  calculates target throttle opening angle of engine  65 , calculates target liquid pressure of brake  75 , and calculates target speed ratio of CVT  85 . Each target value described above is outputted to the corresponding one of controllers  60 ,  70 , and  80 . 
     As described hereinabove, during a non-operation of brake pedal  30 A in the second embodiment, the vehicle speed is controlled at the predetermined constant vehicle speed. If brake pedal  30 A is operated, the controller  50  controls the braking/driving force in accordance with the manipulated variable of brake pedal  30 A by the vehicle driver from a time point at which the driver manipulates brake pedal  30 A. 
     It becomes possible for the vehicle to run at a constant vehicle speed irrespective of a situation of a road during the non-operation of brake pedal  30 A. After brake pedal  30 A is manipulated, the driving/braking force can be controlled by carrying out the brake manipulated from the predetermined constant vehicle speed irrespective of the road situation after the brake pedal is manipulated. It is noted that, in the specification, the driving force means a power generated in a positive direction with respect to a forwarding direction of the vehicle, the braking force means the power generated in a reverse direction to the forwarding direction of the vehicle, and the braking/driving force means a power of an addition of both of the driving force and the braking force. 
     Hence, in a case where the parking is carried out while the vehicle is ascending the slope, the power generated by engine  65  and developed in the direction in which the vehicle is ascending the slope is the driving force, the power developed in such a way that the vehicle does not ascend the ascending slope through the brake or engine brake is the braking force. The power combined with the driving force and the braking force is the braking/driving force. On the contrary, in a case where as described in the first embodiment, the parking is carried out while the vehicle is descending the slope, the power developed due to the engine brake to descend the slope according to the brake pedal manipulation is the driving force. The power acted in a direction such that the brake or engine brake is acted in a direction not to descend the slope is the braking force. The power which is the combination of the driving force and the braking force in the braking/driving force. In addition, the driving force is not only developed by the engine or transmission but also includes a power acted in an acceleration direction due to a weak brake liquid pressure by a relief of the brake manipulated variable. Similarly, the braking force is not developed only by means of the brake but also includes the power acted in the deceleration direction by means of the engine brake due to the weakening of the accelerator manipulated variable. 
     The entire contents of a Japanese Patent Application No. 2001-076248 (filed in Japan on Mar. 16, 2001) are herein incorporated by reference. The scope of the invention is defined with reference to the following claims.