Patent Publication Number: US-2007105689-A1

Title: Vehicle drive control apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority to Japanese Patent Application Nos. 2005-324766, filed on Nov. 9, 2005 and 2006-290026, filed on Oct. 25, 2006. The entire disclosures of Japanese Patent Application Nos. 2005-324766 and 2006-290026 are hereby incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention generally relates to a vehicle drive control for a vehicle. More specifically, the present invention relates to a vehicle drive control apparatus that affords significantly lower fuel consumption during driving.  
      2. Background Information  
      Fuel cutoff control, in which the supply of fuel is interrupted when the driver releases the accelerator pedal, is a commonly employed control method for improving fuel consumption (hereinafter termed mileage) during driving (see for example, Japanese Laid-Open Patent Publication No. 2005-75179). In this publication, it is asserted that improved mileage can be achieved through fuel cutoff control, while performing vehicle drive control in a manner affording acceleration and deceleration feel that is satisfactory for the driver.  
     SUMMARY OF THE INVENTION  
      It has been discovered that typically in a vehicle driving on a downhill slope or the like, when the driver releases the accelerator pedal and simply coasts, the engine itself provides resistance and applies engine braking. Particularly in a vehicle equipped with automatic shift, where the accelerator pedal has been released on a downhill slope, the fuel feed to the engine has been cut, and the vehicle is coasting, the gear is shifted to low gear to automatically increase the engine speed and increase the engine braking force, in order to control the vehicle so as to maintain a constant speed.  
      With the method disclosed in Japanese Laid-Open Patent Publication No. 2005-75179, however, depending on the level of acceleration demand by the driver by depressing the accelerator pedal, it may become necessary to suspend fuel cutoff control and resume fuel feed to accelerate the vehicle, despite the fact that control to increase braking force is ongoing. Under conditions of high engine speed resulting from control to increase braking force, i.e. under conditions requiring more fuel during fuel feed, in the event that fuel is injected and the vehicle accelerated by means of depressing the accelerator pedal in this way, the problem of appreciably lowered mileage occurs.  
      The present invention is proposed in view of problems such as that described above. One object of the present invention is to provide a vehicle drive control apparatus and a vehicle drive control process affording significantly acceleration control with appreciably improved mileage, even in instances where the accelerator pedal is depressed while fuel feed to the engine is cut off.  
      In order to achieve the aforementioned object and other objects, a vehicle drive control apparatus in accordance with the present invention is basically provided with an engine, a transmission, an accelerator depression sensor, a vehicle traveling environment detection device, a vehicle driving environment condition determination section and a controller. The transmission is connected to the engine for transmitting rotary torque generated by the engine to a drive shaft. The accelerator depression sensor is configured and arranged to detect depression of an accelerator pedal. The vehicle traveling environment detection device is configured to detect a traveling environment. The vehicle driving environment condition determination section is configured to determine a current vehicle driving environment condition based on the traveling environment detected by the vehicle traveling environment detection device. The controller configured to: determine if the current vehicle driving environment condition determined by the vehicle driving environment condition determination section indicates a driving environment condition requiring braking power; perform an engine braking force control to apply engine braking by changing a change gear ratio of the transmission from a first gear ratio to a lower gear ratio so that the engine speed shifts to a higher speed than a normal driving speed of the engine upon determining the current driving environment condition outputted by the vehicle driving environment condition determination section requires braking power; change the change gear ratio of the transmission from the lower gear ratio to a higher gear ratio so that the speed of the engine will shift to the normal driving speed of the engine when depression of the accelerator pedal is sensed by the depression sensor during the engine braking force control and performance of a fuel cutting operation to the engine; and perform a fuel injection control to inject fuel into the engine once the change gear ratio of the transmission has shifted to the higher gear ratio.  
      These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Referring now to the attached drawings which form a part of this original disclosure:  
       FIG. 1  is an illustration depicting an arrangement of a vehicle drive control apparatus in accordance with one preferred embodiment of the present invention;  
       FIG. 2  is a schematic diagram of the vehicle drive control apparatus installed in a vehicle in accordance with the illustrated embodiment of the present invention;  
       FIG. 3  is a flowchart showing a control process executed by the vehicle drive control apparatus in accordance with the illustrated embodiment of the present invention; and  
       FIG. 4  is a table stored in memory in the vehicle drive control apparatus for associating accelerator pedal depression rate with CVT shift speed in accordance with the illustrated embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Selected embodiments of the present invention will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.  
      Referring initially to  FIGS. 1 and 2 , a vehicle drive control apparatus is illustrated in accordance with one embodiment of the present invention. As shown in  FIG. 1 , the vehicle drive control apparatus  10  basically includes an accelerator pedal position sensor  12 , an engine rotational speed sensor  13 , a memory or storage device  14 , a camera or imaging device  15 , an image processor  16 , a GPS (global positioning system) receiver  17 , a position information processor  18 , a driving environment condition calculation/output portion  19 , and an electronic control unit (ECU)  20  (hereinafter referred to as “controller  20 ”). As particularly shown in  FIG. 2 , the vehicle drive control apparatus  10  is installed in a vehicle that is equipped with, among other things, a continuously variable transmission (CVT)  30  and an engine  40 . The engine  40  has a fuel injection control device (fuel injector)  41  that is controlled by the controller  20  in response to control signals from the engine rotational speed sensor  13 , as described later. The continuously variable transmission  30  is connected to the engine  40  in a conventional manner such that rotation/torque of the output shaft of the engine  40  is transmitted to the drive wheels via the continuously variable transmission  30 . By executing control of the continuously variable transmission  30  as well as control of the fuel injection controller  41  that injects fuel into the engine  40 , this vehicle drive control apparatus  10  can appreciably improve fuel consumption (hereinafter referred to as “mileage”) during driving.  
      The continuously variable transmission  30  is a belt type or toroidal type transmission that continuously varies its change gear ratio (also called speed change ratio) in response to control signals from the controller  20 , the transmission  30  controls the drive power corresponding to change in change gear ratio.  
      The accelerator pedal position sensor  12  is attached to the accelerator pedal such that it is configured and arranged to detect a depression angle of the accelerator pedal by the driver. The accelerator pedal position sensor  12  outputs the detected accelerator pedal depression angle as an accelerator angle signal to the controller  20 . As will be discussed later, the accelerator angle signal outputted by the accelerator pedal position sensor  12  is also used for the purpose of determining whether the accelerator pedal is being depressed or not being depressed.  
      The engine rotational speed sensor  13  is a sensor that it is configured and arranged to detect an engine rotational engine speed (rpm&#39;s) of the engine  40  of the vehicle. The engine rotational speed sensor  13  outputs the detected engine speed as a speed sensor signal to the controller  20 .  
      The memory device  14  is preferable a ROM (read-only memory) device, that has prestored data and various programs for execution by the controller  20 . The data for controlling the continuously variable transmission  30  are also prestored in a table form in the memory device  14 . The data prestored in table form in the memory device  14  shall be discussed in detail later.  
      As shown in  FIG. 2 , the camera  15  is installed at the front of the vehicle, and is configured and arranged to capture images of the traveling conditions ahead of the vehicle. Image information captured by the camera  15  is outputted to the image processor  16 . By performing image processing using images captured by the camera  15 , the image processor  16  acquires the traveling conditions of the road ahead on which the vehicle is traveling, the running conditions of the vehicle, information regarding preceding obstacles, and so on. The image processor  16  outputs the various kinds of information so acquired to the vehicle driving environment condition determination section  19 .  
      The GPS receiver  17 , using its GPS antenna to receive signals transmitted from GPS satellites, carries out position measurement by GPS navigation and derives the absolute vehicle position (latitude and longitude) of the vehicle. The absolute vehicle position derived in this way is output to the position information processor  18 .  
      The position information processor  18  calculates the current position of the vehicle from the absolute vehicle position information acquired by the GPS receiver  17 , and by using map data or road data read out, for example, from a removable storage medium such as a CD-ROM (compact disk-read only memory) or DVD-ROM (digital versatile disk-read only memory) or from a fixed storage medium such as an HD (hard disk; not shown), acquires road information for the surrounding area of the vehicle, and outputs the information to the vehicle driving environment condition determination section  19 .  
      The vehicle driving environment condition determination section  19  integrates the traveling or environment conditions of the road ahead, the traveling or environment conditions of the vehicle, information regarding obstacles, and other aspects output by the image processor  16 , and the vehicle surrounding area road information output by the position information processor  18 , to derive current vehicle driving environment conditions for the vehicle. Thus, the camera  15 , the image processor  16 , the GPS receiver  17  and the position information processor  18  constitute a vehicle traveling environment detection device that is configured to detect a traveling environment, i.e., at a minimum curvature information for curves on the road and gradient information for hills. The vehicle driving environment condition determination section  19  is configured to determine the current vehicle driving environment condition based on the traveling environment detected by the vehicle traveling environment detection device (components  15  to  18 ). In other words, the current vehicle driving environment condition derived by the vehicle driving environment condition determination section  19  include at a minimum curvature information for curves on the road and gradient information for hills. The vehicle driving environment condition determination section  19  then outputs the vehicle driving environment conditions so derived to the controller  20 . While the vehicle driving environment condition determination section  19  and the controller  20  are illustrated as a separate components, it will be apparent form this disclosure that the vehicle driving environment condition determination section  19  and the controller  20  are constituted preferably integrated into a single calculation and control unit  
      The controller  20  preferably includes a microcomputer with a gear shifting and fuel injection control programs that controls the gear shifting operations and the fuel injection operations as discussed below. The controller  20  can also include other conventional components such as an input interface circuit and an output interface circuit. In other words, the microcomputer of the controller  20  is programmed to control carry out the gear shifting operations and the fuel injection operations in accordance with the present invention. It will be apparent to those skilled in the art from this disclosure that the precise structure and algorithms for the controller  20  can be any combination of hardware and software that will carry out the functions of the present invention. In other words, “means plus function” clauses as utilized in the specification and claims should include any structure or hardware and/or algorithm or software that can be utilized to carry out the function of the “means plus function” clause.  
      The controller  20  is configured to carry out overall control of the vehicle drive control apparatus  10 . On the basis of the various information output by the accelerator pedal position sensor  12 , the engine rotational speed sensor  13 , and the vehicle driving environment condition calculation/output portion  19 , as well as information stored in the memory device  14 , the controller  20  switches drive modes so as to afford optimal driving, and executes control of the change gear ratio of the continuously variable transmission  30  and control of the fuel injection timing to the engine  40  by the fuel injection controller  41 .  
      From the vehicle driving environment conditions outputted by the vehicle driving environment condition determination section  19 , the controller  20  determines whether, for example, the vehicle is driving downhill, or is entering a curve. Then, depending on the result of the decision, the controller  20  controls the change gear ratio of the continuously variable transmission  30  to control engine braking, as well as controlling the fuel injection timing to the engine  40  by the fuel injection controller  41 .  
      Typically, when controlling the engine braking force, the continuously variable transmission  30  is shifted to a low gear ratio to increase the engine speed with the aim of increasing the engine braking force. However, with the engine  40  running at such high speed, the level of air intake to the engine  40  for a given time period is very high. Thus, while driving with the fuel cut off under these conditions, if fuel is being supplied to the engine  40  should resume in association with an acceleration demand produced by the driver depressing the accelerator pedal, fuel will be supplied at a level commensurate with the increased air intake, resulting in extremely high consumption of fuel and poor mileage.  
      Accordingly, under conditions of the increasing engine braking force control carried out in this way and further with the supply of fuel to the engine  40  having been cut off, the controller  20  of the vehicle drive control apparatus  10  will, in the event that the driver should depress the accelerator pedal to make an acceleration demand, perform control of the change gear ratio of the continuously variable transmission  30  and control of the fuel injection controller  41  in such a way as to avoid poor mileage, and to actually improve mileage. The method for doing so shall be described in detail below.  
      The control process of the controller  20  in response to an acceleration demand by the driver during engine braking control shall be described using the flowchart shown in  FIG. 3 . For purposes of discussion the vehicle equipped with the vehicle drive control apparatus  10  is assumed to be entering a downhill slope from a flat stretch of road. However, the invention is not limited to such a case, and can be implemented in any instance where engine braking control takes place, such as when the vehicle enters a curve, for example.  
      In Step S 1 , on the basis of a vehicle driving environment condition output by the vehicle driving environment condition determination section  19 , the controller  20  determines that the vehicle is currently driving on a downhill slope, and changes the driving mode from the normal driving mode (first gear ratio) to a downhill driving mode (second gear ratio) so as to apply a downhill engine brake. Specifically, in response to shifting of the driving mode to downhill driving mode, the controller  20  applies an engine braking force control so as to shift the continuously variable transmission  30  from a first gear ratio serving as a coasting gear ratio for normal driving mode (generally the highest gear ratio that the continuously variable transmission can attain) with the accelerator pedal being released to a lower second gear ratio serving as a coasting gear ratio for downhill driving mode with the accelerator pedal being released, which results in an increase in the engine speed of the engine  40  to a higher speed than during normal driving.  
      In Step S 2 , the controller  20  determines whether the accelerator pedal is being depressed (i.e. the idle switch flag is OFF) or not being depressed (i.e. the idle switch flag is ON) from the accelerator angle signal indicating the depression angle of the accelerator pedal sensed and output by the accelerator pedal position sensor  12 . Then, the controller  20 , on the basis of this decision, now determines whether to cut the fuel being fed to the engine  40 . In the event that the accelerator pedal is not depressed, that is, the idle switch flag is ON, the controller  20  then determines to cut the fuel being fed to the engine  40 , and proceeds to Step S 3 . However, if the accelerator pedal is depressed, i.e., the idle switch flag is OFF, then the controller  20  determines not to cut the fuel to the engine  40 , and terminates the process.  
      In Step S 3 , with the supply of fuel to the engine  40  being cut off, the controller  20  determines whether the accelerator pedal has been depressed so that the idle switch flag has changed from ON to OFF. In the event that the idle switch flag has changed from ON to OFF, then the controller  20  proceeds to Step S 4 , or if the idle switch flag remains ON, returns to Step S 1 .  
      In Step S 4 , in response to the idle switch flag having changed from ON to OFF, the controller  20  halts control in the downhill driving mode, in which control was carried out so as to apply engine braking. Subsequently, the controller  20  changes from the downhill driving mode in which engine braking control was carried out, to the normal driving mode in which braking control is not carried out.  
      In Step S 5 , the controller  20  calculates a rate of depression of the accelerator pedal, from the amount of displacement of the accelerator pedal depression angle during a prescribed unit of time using the accelerator angle signal indicating the depression angle of the accelerator pedal sensed and output by the accelerator pedal position sensor  12 . The rate of depression of the accelerator pedal, rather than being calculated by the controller  20 , could instead be acquired with a sensor that can to directly sense the rate of depression.  
      Using the rate of depression of the accelerator pedal calculated in this way, the controller  20  retrieved from the memory device  14  and reads out an engine speed for shifting the continuously variable transmission  30 . Specifically, a CVT shift speed representing an operating speed for changing the change gear ratio of the continuously variable transmission  30  has been stored in the memory device  14  in table form and associated with corresponding accelerator pedal depression rates of the accelerator pedal as seen in  FIG. 4 .  
      For example, as seen in  FIG. 4 , a table associating the accelerator pedal depression rates with the CVT shift speed is illustrated that is stored in the memory device  14 . As shown in  FIG. 4 , the accelerator pedal depression rate is expressed as an accelerator pedal depression angle per a 10-msec period, while the CVT shift speed is expressed as a speed per this 10-msec period. As shown in  FIG. 4 , it will be apparent that the CVT shift speed varies depending on the accelerator pedal depression rates, with the CVT shift speed becoming faster in association with a faster accelerator pedal depression rate of the accelerator pedal. Since a faster accelerator pedal depression rate indicates that the driver has demanded a greater acceleration speed, in order to improve acceleration response to such an acceleration demand, it is necessary for the CVT shift speed (operating speed for changing the change gear ratio of the continuously variable transmission  30 ) to be faster as well.  
      In Step S 6 , the controller  20  now shifts the continuously variable transmission  30  at the CVT shift speed retrieved from the memory device  14  such that the coasting gear ratio for normal driving mode is obtained. Specifically, in the downhill driving mode, the continuously variable transmission  30  is shifted by the controller  20  to the lower coasting gear ratio for downhill driving mode which results an increase in the rotational engine speed of the engine  40  in order to increase engine braking force. However, in the normal driving mode, the controller  20  performs a shifting control so as to shift the continuously variable transmission  30  to the higher coasting gear ratio, which reduces the rotational engine speed of the engine  40 .  
      By reducing the rotational engine speed of the engine  40  in this way, the kinetic energy of the vehicle that is freed up from consumption by the engine  40  is utilized as driving energy for the vehicle, in response to the acceleration demand produced by depressing the accelerator pedal.  
      In Step S 7 , the controller  20  monitors the rotational engine speed of the engine  40  detected by the engine rotational speed sensor  13 , and the change gear ratio of the continuously variable transmission  30 . Then, the controller  20  determines whether the gear ratio has shifted to the coasting gear ratio for normal driving mode. In the event that the change gear ratio of the continuously variable transmission  30  has transitioned to the coasting gear ratio for normal driving mode, the controller  20  deems that the rotational speed of the engine  40  has decreased to the desired speed and proceeds to the process of Step S 8 . In the event that this transition has not taken place, the control process returns to the process of Step S 6 .  
      In Step S 8 , the controller  20  controls the fuel injection controller  41 , and injects fuel into the engine  40  in an amount commensurate with the air intake level at that time. In this way, the vehicle drive control apparatus  10  of the present invention is such that under prescribed driving environment conditions, the controller  20  carries out increased engine braking control to shift the gear ratio of the continuously variable transmission  30  to the low gear ratio resulting in an increase in the rotational engine speed of the engine  40  to a higher level than during normal driving, and additionally the fuel to the engine  40  is cut off in response to an acceleration demand produced by depression of the accelerator pedal, first, the gear ratio of the continuously variable transmission  30  will be shifted to the high gear ratio to lower the rotational engine speed of the engine  40 . Then, once the rotational engine speed of the engine  40  has dropped to the desired rotational engine speed, fuel in an amount commensurate with the air intake level associated with the lower rotational engine speed will be injected into the engine  40 .  
      Consequently, the amount of injected fuel can be reduced when fuel injection is resumed. Additionally, by lowering the rotational engine speed of the engine  40  while the fuel is cut off, rotation energy equivalent to the drop in speed can be utilized to reaccelerate the vehicle, so reacceleration in response to depression of the accelerator pedal can take place with a lower level of fuel consumption. Mileage can be improved appreciably thereby.  
      In Step S 3  of the flowchart shown in  FIG. 3 , during the time that the accelerator pedal is depressed and the idle switch flag is OFF, the controller  20  performs a fuel cutting operation or control so that fuel is not supplied to the engine  40 , during the interval up to Step S 8 . That is, since fuel is not supplied to the engine  40  during the transition period in which the continuously variable transmission  30  transitions to coasting gear ratio for normal driving mode at the CVT shift speed under the control of the controller  20 , the period of fuel cutoff can be extended, and mileage improved.  
      Additionally, during shifting of the gear ratio of the continuously variable transmission  30  from the low gear ratio to the hi gear ratio, the controller  20  causes the continuously variable transmission  30  to shift at a CVT shift speed that has been determined depending on the depression rate of the accelerator pedal. By so doing, it is possible to attain acceleration control that reflects acceleration demands by the driver, determined by the depression rate of the accelerator pedal.  
      In particular, the controller  20  causes the continuously variable transmission  30  to shift from the low gear ratio to the hi gear ratio at higher CVT shift speed in association with a higher depression rate of the accelerator pedal, and thus the effect of engine braking can be lessened in concert with the depression rate of the accelerator pedal. Consequently, in the event that the driver depresses the accelerator pedal at a faster rate, the extent of deceleration of the vehicle due to engine braking will be perceived as decreasing faster. That is, by executing the control process of the controller  20  in this manner, the difference between the driver&#39;s intention to accelerate by depressing the accelerator pedal on the one hand, and the actual sensation of acceleration experienced by the driver, can be reduced appreciably.  
      While the embodiment of the present invention herein has described the use of a continuously variable transmission  30  as the transmission, the invention is not limited thereto, and can be implemented analogously in vehicles which employ as the transmission a so-called AT (automatic transmission) instead. Also, while the controller  20  and the vehicle driving environment condition determination section  19  herein have been provided as separate computing units, the invention is not limited to this arrangement, it being possible to instead provide a single computing/control unit, with the function of both of the devices being assumed by this single computing/control unit. It is further possible for the functions of the image processor  16  and the position information processor  18  to be integrated into the single computing/control unit.  
     GENERAL INTERPRETATION OF TERMS  
      In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” “portion,” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts. Also as used herein to describe the above embodiment(s), the following directional terms “forward, rearward, above, downward, vertical, horizontal, below and transverse” as well as any other similar directional terms refer to those directions of a vehicle equipped with the present invention. Accordingly, these terms, as utilized to describe the present invention should be interpreted relative to a vehicle equipped with the present invention.  
      The term “detect” as used herein to describe an operation or function carried out by a component, a section, a device or the like includes a component, a section, a device or the like that does not require physical detection, but rather includes determining, measuring, modeling, predicting or computing or the like to carry out the operation or function. The term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function. Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention. The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed.  
      While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, the size, shape, location or orientation of the various components can be changed as needed and/or desired. Components that are shown directly connected or contacting each other can have intermediate structures disposed between them. The functions of one element can be performed by two, and vice versa. The structures and functions of one embodiment can be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.