Abstract:
A hybrid vehicle provided with a hybrid system that serves as the driving force thereof and has an engine and a motor, wherein: the engine torque is maintained while the output transmitted to the drive wheels is decreased by controlling the motor torque, when the accelerator and the brake pedal are simultaneously depressed, causing the recovery in the driving force of the hybrid vehicle when the decrease in output is released to occur through an increase in the motor torque, which is more responsive than the engine torque.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present invention relates to a hybrid vehicle control device that is applied to a hybrid vehicle including, as a drive source, a hybrid system having an engine and a motor and reduces an output to be transmitted to drive wheels when an accelerator operation and a brake operation are simultaneously performed by a driver. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    As a control system to be applied to a vehicle, there is a brake override system shown in Patent Document 1. The brake override system described in Patent Document 1 is activated when an accelerator operation and a brake operation are simultaneously performed by a driver and throttles a throttle valve and reduces an engine output to lower a drive force of the vehicle. Accordingly, braking of the vehicle based on the brake operation is made to override acceleration of the vehicle based on the accelerator operation. 
       PRIOR ART DOCUMENT 
     Patent Document 
       [0000]    
       
         Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-038051 
       
     
       SUMMARY OF THE INVENTION 
     Problems that the Invention is to Solve 
       [0004]    There is a vehicle driving technique that increases re-acceleration of a vehicle after passing through a curve by reducing the speed of the vehicle without reducing the engine torque by stepping on the brake pedal while also stepping on the accelerator pedal before the curve. In a vehicle using the above-described brake override system, by simultaneously stepping on the accelerator pedal and the brake pedal, the brake override system is activated and reduces the engine torque, so that even if the speed is reduced while stepping on the accelerator pedal, the engine torque is reduced. It takes some time to recover from the reduction in engine torque, so that recovery of the drive force of the vehicle after the brake override system is deactivated takes time. Therefore, in a vehicle using the brake override system, even with the above-described driving technique, sufficient re-acceleration demanded by the driver of the vehicle after passing through a curve cannot be ensured, and drivability deteriorates. 
         [0005]    An objective of the present invention is to provide a hybrid vehicle control device capable of preventing drivability from deteriorating in a favorable manner. 
       Means for Solving the Problems 
       [0006]    To achieve the foregoing objective, a first hybrid vehicle control device according to the present invention is applied to a hybrid vehicle including, as a drive source, a hybrid system having an engine and a motor. The control device reduces an output to be transmitted to drive wheels when an accelerator operation and a brake operation are simultaneously performed by a driver. At the time of reducing the output when an accelerator operation and a brake operation are simultaneously performed, a ratio of an amount of reduction of the output by torque control of the motor to the total amount of reduction of the output is larger than that in the case where similar reduction of the output is performed according to a reduction in an accelerator operation amount. 
         [0007]    The output to be transmitted to the drive wheels is reduced through reduction of the engine torque and torque control of the motor (reduction of the output torque of the motor and an increase in regenerative torque of the motor) when an accelerator operation and a brake operation are simultaneously performed by the driver. With the above-described configuration, the ratio of the amount of reduction of the output by torque control of the motor to the total amount of reduction of the output increases. Accordingly, the amount of reduction of the engine torque decreases. As a result, the amount of increase in engine torque necessary for recovering the output to be transmitted to the drive wheels decreases. Accordingly, the amount of increase in motor torque necessary for the recovery increases. Therefore, when recovering the drive force after the output reduction is canceled, the torque is increased, and the time needed for recovering the drive force is shortened by torque control of the motor with higher responsiveness. Therefore, re-acceleration of the vehicle after the reduction of the output according to simultaneous performance of an accelerator operation and a brake operation is canceled is improved, and drivability is prevented from deteriorating in a favorable manner. 
         [0008]    To achieve the foregoing objective, a second hybrid vehicle control device according to the present invention is applied to a hybrid vehicle including, as a drive source, a hybrid system having an engine and a motor. When an accelerator operation and a brake operation are simultaneously performed by a driver, an output to be transmitted to drive wheels is reduced by torque control of the motor while engine torque is maintained. 
         [0009]    With the above-described configuration, when an accelerator operation and a brake operation are simultaneously performed by a driver, an output to be transmitted to the drive wheels is reduced by motor torque control, that is, a reduction of the output torque of the motor and an increase in regenerative torque of the motor, while the engine torque is maintained. In this case, the drive force after the reduction of the output to be transmitted to the drive wheels is canceled is recovered by increasing the motor torque, the responsiveness of which is higher than that of the engine torque. Therefore, the drive force of the hybrid vehicle can be recovered without waiting for an increase in engine torque the responsiveness of which is low, so that the time taken for recovering the drive force of the vehicle after cancellation of the output reduction is shortened. Therefore, re-acceleration of the vehicle after cancellation of the output reduction is improved, and drivability is prevented from deteriorating in a favorable manner. 
         [0010]    To achieve the foregoing objective, a third hybrid vehicle control device according to the present invention is applied to a hybrid vehicle including, as a drive source, a hybrid system having an engine and a motor. The control device reduces an output to be transmitted to drive wheels when an accelerator operation and a brake operation are simultaneously performed by a driver. At the time of reducing the output, an engine torque is increased and the output is reduced by torque control of the motor by an amount exceeding the amount of increase in the output according to the increase in engine torque. 
         [0011]    With the above-described configuration, when an accelerator operation and a brake operation are simultaneously performed by a driver, the output to be transmitted to the drive wheels is reduced by torque control of the motor with high responsiveness. In addition, in preparation for subsequent re-acceleration of the vehicle, the engine output is increased in advance. Therefore, after cancellation of the output reduction, the output to be transmitted to the drive wheels is quickly increased. Therefore, re-acceleration of the vehicle after the output reduction is canceled is improved, and the drivability is prevented from deteriorating in a favorable manner. 
         [0012]    If the engine is in a stopped state when increasing the output to be transmitted to the drive wheels again by canceling the brake operation, a necessary output cannot be achieved only by the motor output, and it may become necessary to start the engine. In this case, according to the time to be taken for starting the engine, the increase in output to be transmitted to the drive wheels is delayed, so that re-acceleration of the hybrid vehicle, after the brake operation is cancelled, deteriorates. Even in this case, when an accelerator operation and a brake operation are simultaneously performed by a driver while the engine is in a stopped state, the engine is started and torque control of the motor is executed such that the output is reduced by an amount exceeding the amount of increase in output caused by the starting of the engine. Accordingly, the output to be transmitted to the drive wheels at the time of re-acceleration can be increased without delay caused by waiting for engine start. 
         [0013]    When the amount of reduction of the output by torque control of the motor is increased, the loads on the motor and battery increase, so that the motor and battery are required to have high load resistance. Therefore, it is preferable that, after a prescribed time elapses from the start of simultaneous performance of an accelerator operation and a brake operation, the loads on the motor and battery are reduced by reducing the amount of the output reduction to be transmitted to the drive wheels by torque control of the motor and increasing the amount of the output reduction by reducing the engine torque. If the loads on the motor and battery are high, these loads can also be suppressed by reducing the amount of the output reduction by torque control of the motor. 
         [0014]    In a hybrid vehicle capable of switching among a plurality of traveling modes, which are different in traveling characteristics from each other, it is considered that the driver&#39;s demand for re-acceleration performance after cancellation of the output reduction is great when a traveling mode is selected that improves the acceleration performance of the vehicle to a level that is higher than usual and that the driver&#39;s demand is small when a different traveling mode is selected. Therefore, if the traveling mode that increases the acceleration performance of the hybrid vehicle to a level that is higher than usual is not selected, the drivability can be more efficiently prevented from deteriorating by reducing the amount of the output reduction to be transmitted to the drive wheels by torque control of the motor as compared with the case where the mode is selected. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a diagram schematically showing a configuration of a hybrid system of a hybrid vehicle to which a first embodiment of the present invention is applied; 
           [0016]      FIG. 2  is a graph showing a relationship between an accelerator operation amount and a requested output in each traveling mode of the hybrid vehicle to which the same embodiment is applied; 
           [0017]      FIG. 3  is a flowchart showing procedures of a brake override control routine to be applied to the same embodiment; 
           [0018]      FIG. 4  is a time chart showing a control mode in a case where reduction of an HVS output at activation of the brake override system is performed by reduction of the engine torque and torque control of the motor; 
           [0019]      FIG. 5  is a time chart showing an example of control at activation of the brake override system in the same embodiment; 
           [0020]      FIG. 6  is a flowchart showing processing procedures of a brake override control routine to be applied to a second embodiment of the present invention; 
           [0021]      FIG. 7  is a time chart showing an example of control at activation of the brake override system in the same embodiment; 
           [0022]      FIG. 8  is a flowchart showing processing procedures of a brake override control routine to be applied to a third embodiment of the present invention; 
           [0023]      FIG. 9  is a time chart showing an example of control at activation of the brake override system in the same embodiment; 
           [0024]      FIG. 10  is a flowchart showing processing procedures of a brake override control routine to be applied to a fourth embodiment of the present invention; 
           [0025]      FIG. 11  is a time chart showing an example of control at activation of the brake override system in the same embodiment; and 
           [0026]      FIG. 12  is a flowchart showing processing procedures of a brake override control routine to be applied to a fifth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0027]    A hybrid vehicle control device according to a first embodiment of the present invention will now be described with reference to  FIGS. 1 to 5 . 
         [0028]    First, a configuration of a hybrid system for a hybrid vehicle to which the control device of the present embodiment is applied will be described with reference to  FIG. 1 . 
         [0029]    This hybrid system includes an engine  1 , as a heat engine, and two motor generators. Hereinafter, a motor generator to be used mainly to generate electricity of the two motor generators is referred to as a generator  2 , and a motor generator to be used mainly to generate a drive force is referred to as a motor  3 . 
         [0030]    The engine  1 , the generator  2 , and the motor  3  are connected to a power split mechanism  4  formed by a planetary gear. The power split mechanism  4  is connected to drive wheels  6  via a speed reduction mechanism  5 . By this power split mechanism  4 , power of the engine  1  is split into power to drive the generator  2  and power to drive the drive wheels  6 . 
         [0031]    The rotational speeds of the engine  1 , generator  2 , and drive wheels  6  joined via the power split mechanism  4  always have a relationship shown by a straight line on an alignment chart illustrating a rotation state of the planetary gear of the power split mechanism  4 . Therefore, in this hybrid system, by changing the rotational speed of the generator  2 , the change gear ratio between the engine  1  and the drive wheels  6 , that is, the ratio of the rotational speed of the drive wheels  6  to the rotational speed of the engine  1  is changed. 
         [0032]    Further, the hybrid system includes a power control unit  7  having a boost converter and an inverter. The boost converter boosts the voltage of the hybrid battery  8  to a voltage necessary for driving the generator  2  and the motor  3 . The inverter converts a high voltage DC current boosted by the boost converter into an alternating current to be supplied to the generator  2  and the motor  3  and converts alternating currents generated by the generator  2  and the motor  3  into direct currents when they function as power generators. 
         [0033]    This hybrid system is controlled by an electronic control unit  9 . The electronic control unit  9  includes a central processing unit (CPU), which performs arithmetic processing relating to various controls of the hybrid system, a read-only memory (ROM), in which control programs and data are stored, and a random access memory (RAM), which temporarily stores operation results of the CPU and detection results of sensors. 
         [0034]    The electronic control unit  9  receives detection signals of sensors provided at various portions of the hybrid vehicle. The sensors include an accelerator position sensor  10 , a master cylinder pressure sensor  11 , a vehicle speed sensor  12 , a battery temperature sensor  13 , a battery voltage sensor  14 , a battery current sensor  15 , and a motor temperature sensor  16 . The accelerator position sensor  10  detects the amount of stepping on an accelerator pedal  10   a  (accelerator operation amount), and the master cylinder pressure sensor  11  detects a master cylinder pressure generated according to stepping on the brake pedal  11   a . The vehicle speed sensor  12  detects the vehicle speed of the hybrid vehicle. Further, the battery temperature sensor  13 , the battery voltage sensor  14 , and the battery current sensor  15  detect the temperature, voltage, and current value of the hybrid battery  8 , respectively. The motor temperature sensor  16  detects the temperature of the motor  3 . 
         [0035]    The electronic control unit  9  is connected to a traveling mode changeover switch  17  for selecting a traveling mode of the hybrid vehicle. In this hybrid vehicle, according to an operation on the traveling mode changeover switch  17 , one of three traveling modes of an economy traveling mode, which prioritizes fuel efficiency, a sport traveling mode, which prioritizes acceleration, and a normal traveling mode in between is selected. 
         [0036]    The electronic control unit  9  calculates outputs of the engine  1  and the motor  3  corresponding to the driving state of the hybrid vehicle based on detection results of these sensors and transmits output requests to these components to control the drive force of the hybrid vehicle. Next, such drive force control of the hybrid vehicle will be described. 
         [0037]    For drive force control, first, the electronic control unit  9  calculates the magnitude of an output of the hybrid system demanded by the driver as a requested output based on the accelerator operation amount detected by the accelerator position sensor  10  and the vehicle speed detected by the vehicle speed sensor  12 . The relationships between the accelerator operation amounts and requested outputs in the traveling modes of the hybrid vehicle at the same vehicle speed are as shown in  FIG. 2 . As shown in this drawing, in the sport traveling mode, the requested output is larger than in the normal traveling mode and the economy traveling mode at the same accelerator operation amount. 
         [0038]    The electronic control unit  9  calculates the state of charge (SOC) value of the hybrid battery  8  based on detection signals of the battery temperature sensor  13 , the battery voltage sensor  14 , and the battery current sensor  15 . Then, the electronic control unit  9  calculates a requested total output, which is a requested value of an output to be transmitted from the hybrid system, which is a drive source for the drive wheels  6  (hereinafter, referred to as HVS output), based on the requested output and the SOC value. The HVS output is the sum of the output of the engine  1 , the output of the generator  2 , and the output of the motor  3 . When the generator  2  or the motor  3  generates power, these outputs are calculated as negative values by setting the power used for power generation as an absolute value. 
         [0039]    Subsequently, the electronic control unit  9  calculates a target engine speed and a requested engine output based on the requested total output and sends a corresponding command to the engine  1 . In the engine  1 , according to this command, engine control including fuel injection control and ignition time control is performed to obtain an engine output corresponding to the requested engine output and an engine speed corresponding to the target engine speed. 
         [0040]    The electronic control unit  9  calculates a driver&#39;s requested torque corresponding to the traveling state of the hybrid vehicle. This requested torque is an output torque of the hybrid system necessary for obtaining an HVS output corresponding to the requested total output at the current vehicle speed. 
         [0041]    Then, the electronic control unit  9  calculates torque command values of the generator  2  and the motor  3  based on the driver&#39;s requested torque and the engine torque determined by the requested engine output and the target engine speed. Then, the electronic control unit  9  sends a command corresponding to the calculated torque command values of the generator  2  and the motor  3  to the power control unit  7 . The torque command values are set to be positive when the generator  2  and the motor  3  are made to perform powering operation and set to be negative when the generator and the motor are made to perform regenerative operation. According to this command, the power control unit  7  controls the drive alternating currents or power generating alternating currents of the generator  2  and the motor  3  such that torques corresponding to the torque command values are output. 
         [0042]    The hybrid vehicle to which the control device according to the present embodiment is applied employs a brake override system that makes braking of the vehicle based on a brake operation (stepping on the brake pedal  11   a ) override acceleration of the vehicle based on an accelerator operation (stepping on the accelerator pedal  10   a ). Next, this brake override system will be described. 
         [0043]    In the present embodiment, a brake override system is realized through the processing of the brake override control routine shown in  FIG. 3 . The processing of this routine is repeatedly performed by the electronic control unit  9  in each prescribed control cycle during traveling of the hybrid vehicle. 
         [0044]    When the processing of this routine is started, first, in Step S 100 , it is determined whether an accelerator operation and a brake operation are simultaneously performed, that is, it is determined whether the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on. If the accelerator pedal  10   a  and the brake pedal  11   a  are not simultaneously stepped on (S 100 : NO), this processing of this routine is ended. 
         [0045]    If the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on (S 100 : YES), the HVS output is reduced by torque control of the motor  3  in Step S 101 , while the engine torque is maintained. Thereafter, this processing of the routine is ended. 
         [0046]    Specifically, the processing of the electronic control unit  9  in Step S 101  is performed according to the following procedures. That is, at this time, the electronic control unit  9  resets the requested total output to be smaller than the value calculated from the requested output and the SOC value. However, the electronic control unit  9  calculates a requested engine output and a target engine speed based on the requested total output before being reset. The electronic control unit  9  calculates torque command values of the generator  2  and the motor  3  based on an engine torque determined by the requested engine output and the target engine speed calculated herein and a requested torque corresponding to the reset requested total output. 
         [0047]    When the torque command value of the motor  3  calculated herein is negative, the motor  3  is made to perform regenerative operation, and a part of the power that is transmitted from the engine  1  to the drive wheels  6  in normal conditions is used for regenerative power generation. Accordingly, the HVS output is reduced by a necessary amount. 
         [0048]    In the present embodiment, reduction of the HVS output according to activation of the brake override system is performed only by reduction of the motor torque. Therefore, in the present embodiment, when the HVS output is reduced according to simultaneous performance of an accelerator operation and a brake operation, the ratio of the amount of reduction of the HVS output by torque control of the motor  3  to the total amount of reduction of the HVS output becomes larger than in the case where similar reduction of the HVS output is performed by reduction in the accelerator operation amount. 
         [0049]    Next, a control operation at activation of the brake override system in the hybrid vehicle control device according to the present embodiment will be described. 
         [0050]    First, the case where reduction of the HVS output according to activation of the brake override system is performed by both reducing the engine torque and controlling the torque of the motor  3  will now be described. As shown in  FIG. 4 , in this case, when an accelerator operation and a brake operation are simultaneously performed at a point in time t 1 , both engine torque and motor torque are reduced by a corresponding reduction in requested total output. The reduced engine torque and motor torque are recovered according to release of the brake operation at a point in time t 2 . 
         [0051]    The responsiveness of the motor torque is comparatively high, so that the motor torque is recovered in a comparatively short time in this case. However, an increase in engine torque is accompanied by a delay such as a response delay of intake, so that recovery of the engine torque in this case takes time. Therefore, in this case, recovery of the drive force of the hybrid vehicle after the brake override system is deactivated is delayed. 
         [0052]    In contrast, in the present embodiment, as shown in  FIG. 5 , in response to the reduction of the requested total output at the point in time t 1 , at which an accelerator operation and a brake operation are simultaneously performed, the motor torque is reduced. However, the engine torque is maintained as it is. Therefore, in this case, recovery of the drive force of the hybrid vehicle after the point in time t 2 , at which the brake override system is deactivated, is performed by increasing the motor torque with high responsiveness. Therefore, in this case, recovery of the drive force of the hybrid vehicle after the brake override system is deactivated is performed in a comparatively short time. 
         [0053]    The present embodiment as described above has the following advantages. 
         [0054]    (1) In the present embodiment, when activating the brake override system according to simultaneous performance of an accelerator operation and a brake operation, the HVS output is reduced by torque control of the motor  3  while the engine torque is maintained. Specifically, reduction of the HVS output according to activation of the brake override system is performed only by torque control of the motor  3 . Therefore, recovery of the drive force of the hybrid vehicle after the brake override system is deactivated is performed by increasing the motor torque higher in responsiveness than the engine torque, and therefore, the time to be taken for the recovery is shortened. Therefore, re-acceleration performance of the vehicle after the brake override system is deactivated is improved, and the drivability is prevented from deteriorating in a favorable manner. 
       Second Embodiment 
       [0055]    A hybrid vehicle control device according to a second embodiment of the present invention will now be described with reference to  FIGS. 6 and 7 . In the present embodiment and each of the following embodiments, like or the same reference numerals are given to those components that are like or the same as the corresponding components of the above described embodiment and detailed explanations are omitted. 
         [0056]    In the first embodiment, when the brake override system is activated, the engine torque is maintained to prevent re-acceleration performance of the hybrid vehicle from deteriorating after the brake override system is deactivated. In the present embodiment, when the brake override system is activated, the engine torque is increased in advance in preparation for re-acceleration performance of the hybrid vehicle after the brake override system is deactivated, thereby achieving higher re-acceleration performance. 
         [0057]    In the present embodiment, the brake override system is realized through the processing of the brake override control routine shown in  FIG. 6 . The processing of this routine is repeatedly performed in each prescribed control cycle by the electronic control unit  9  during traveling of the hybrid vehicle. 
         [0058]    When the processing of this routine is started, first, in Step S 200 , it is determined whether an accelerator operation and a brake operation are simultaneously performed. If the accelerator pedal  10   a  and the brake pedal  11   a  are not simultaneously stepped on (S 200 : NO), this processing of the routine is ended. 
         [0059]    If the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on (S 200 : YES), the engine torque is increased in Step S 201 . In the subsequent Step S 202 , this processing of the routine is then ended after the HVS output is reduced by torque control of the motor  3 . 
         [0060]    Specifically, the processing of the electronic control unit  9  in Step S 201  and Step S 202  is performed according to the following procedures. Specifically, at this time, the electronic control unit  9  resets the requested total output to be smaller than the value calculated from the requested output and the SOC value. Further, the electronic control unit  9  calculates a requested engine output and a target engine speed such that the engine torque is increased. Further, the electronic control unit  9  calculates torque command values of the generator  2  and the motor  3  based on an engine torque determined by the requested engine output and the target engine speed calculated herein and a requested torque corresponding to the reset requested total output. This torque command value of the motor  3  is set such that reducing the torque of the motor  3  will reduce the HVS output, which is the sum of the amount of the requested total output reduction according to brake override control and the amount of increase in HVS output according to the increase in engine torque. 
         [0061]    Next, a control operation at activation of the brake override system in the hybrid vehicle control device according to the present embodiment will be described with reference to  FIG. 7 . 
         [0062]    When an accelerator operation and a brake operation are simultaneously performed at a point in time t 3  in  FIG. 7 , the requested total output is reduced to lower the HVS output. At this time, in the present embodiment, the engine torque is increased. Then, in response to reducing the motor torque, the HVS output is reduced according to the reduction of the requested total output. 
         [0063]    When stepping on the brake pedal  11   a  is cancelled and the accelerator pedal  10   a  is additionally stepped on, the requested total output is increased at point in time t 4 , and an increase in HVS output for re-acceleration of the hybrid vehicle is started. At this time, in the present embodiment, the engine torque has been increased in advance. Thus, the amount of increase in engine torque necessary for the increase in HVS output is limited. Therefore, the increase in HVS output for re-acceleration is performed mainly by increasing the motor torque with higher responsiveness. 
         [0064]    The present embodiment as described above has the following advantages. 
         [0065]    (2) In the present embodiment, when an accelerator operation and a brake operation are simultaneously performed by the driver, the engine torque is increased, and torque control of the motor  3  is executed such that the HVS output is reduced by an amount exceeding the amount of increase in HVS output caused by the increase in engine torque. Therefore, the amount of increase in engine torque necessary for an increase in HVS output for re-acceleration becomes smaller. This increases the amount of increase in motor torque necessary for the increase in HVS output. As a result, at the time of acceleration, the HVS output is increased to be higher by increasing the motor torque with high responsiveness. Therefore, re-acceleration performance of the vehicle after a reduction of the HVS output is canceled is improved, and the drivability is prevented from deteriorating in a favorable manner. 
       Third Embodiment 
       [0066]    A hybrid vehicle control device according to a third embodiment of the present invention will now be described with reference to  FIGS. 8 and 9 . 
         [0067]    In a case where the brake override system is activated during motor-driven traveling of the hybrid vehicle with the engine  1  stopped, if the accelerator pedal  10   a  is additionally stepped on after stepping on the brake pedal  11   a  is cancelled, it may become impossible to ensure the HVS output requested by the driver only by the output of the motor  3 . In such a case, it becomes necessary to start the engine  1 , and an increase in HVS output is delayed by the time required for starting the engine  1 . This deteriorates the re-acceleration performance of the hybrid vehicle. Therefore, in the present embodiment, by starting the engine  1  in advance before the brake override system is activated, the re-acceleration performance of the hybrid vehicle after the brake override system is deactivated is improved. 
         [0068]    In the present embodiment, the brake override system is realized through the processing of the brake override control routine shown in  FIG. 8 . The processing of this routine is repeatedly performed in each prescribed control cycle by the electronic control unit  9  during traveling of the hybrid vehicle. 
         [0069]    When the processing of this routine is started, first, in Step S 300 , it is determined whether an accelerator operation and a brake operation are simultaneously performed, that is, whether the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on. If the accelerator pedal  10   a  and the brake pedal  11   a  are not simultaneously stepped on (S 300 : NO), the processing of this routine is ended. 
         [0070]    If the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on (S 300 : YES), it is determined, in Step S 301 , whether the engine  1  is in a stopped state. If the engine  1  is not in a stopped state (Step S 301 : NO), the processing is directly advanced to Step S 303 . If the engine  1  is in a stopped state (S 301 : YES), the processing is advanced to Step S 303  after the engine  1  is started in Step S 302 . 
         [0071]    When the processing is advanced to Step S 303 , the HVS output is reduced by torque control of the motor  3 . Thereafter, this processing of the routine is ended. 
         [0072]    Specifically, the processing of the electronic control unit  9  in Step S 303  is performed according to the following procedures. That is, the electronic control unit  9  at this time resets the requested total output to be smaller than the value calculated from the requested output and the SOC value. The electronic control unit  9  calculates torque command values of the generator  2  and the motor  3  in accordance with the reset requested total output. However, when the engine  1  is started in Step S 302 , the HVS output increases according to an engine output generated by this start. Therefore, the torque command value of the motor  3  at this time is set such that reducing the torque of the motor  3  reduces the HVS output, which is the sum of the amount of reduction in the requested total output according to brake override control and the amount of increase in HVS output according to the starting of the engine  1 . 
         [0073]    A control operation at activation of the brake override system in the hybrid vehicle control device according to the present embodiment described above will be described with reference to  FIG. 9 . 
         [0074]    During motor-driven traveling, when an accelerator operation and a brake operation are simultaneously performed at the point in time t 5 , the requested total output is reduced to lower the HVS output. At this time, in the present embodiment, the engine  1  is started, and the motor torque is reduced such that the HVS output is reduced by an amount exceeding the amount of increase in HVS output caused by the start of the motor. 
         [0075]    When stepping on the brake pedal  11   a  is cancelled and the accelerator pedal  10   a  is additionally stepped on at point in time t 6 , the requested total output, which has been reduced at the point in time t 5 , is increased, and an increase in HVS output for re-acceleration of the hybrid vehicle is started. The requested total output at this time is increased to a value over the critical power of the motor  3  allowed according to the SOC value of the present hybrid battery  8 , and the HVS output corresponding to the requested total output cannot be ensured only by the motor  3 . 
         [0076]    However, in the present embodiment, the engine  1  is started in advance at the point in time t 5 , at which the brake override system is activated. Therefore, the HVS output is increased without delay due to waiting for the starting of the engine  1 , and the drive force is quickly increased for re-acceleration. 
         [0077]    The present embodiment has the following advantages in addition to the advantage (1). 
         [0078]    (3) In the present embodiment, when an accelerator operation and a brake operation are simultaneously performed by the driver while the engine  1  is in a stopped state, the engine  1  is started, torque control of the motor  3  is executed such that the HVS output is reduced by an amount exceeding the amount of increase in HVS output caused by the start. Therefore, even in the case where the brake override system is activated while the engine  1  is in a stopped state, the HVS output can be increased to a value requested by the driver after the brake override system is deactivated, without waiting for completion of the starting of the engine  1 . Therefore, the re-acceleration performance of the vehicle is further improved. 
         [0079]    (4) In the case where the brake override system is activated while the engine  1  is in a stopped state, the HVS output can also be recovered by increasing both the engine torque and the motor torque after the system is deactivated. Therefore, in the case where the brake override system is activated while the engine  1  is in a stopped state, recovery of the HVS output after the system is deactivated can be shortened. 
       Fourth Embodiment 
       [0080]    A hybrid vehicle control device according to a fourth embodiment of the present invention will now be described with reference to  FIGS. 10 and 11 . 
         [0081]    In the embodiments described above, the amount of reduction of the HVS output by torque control of the motor  3  is increased when the HVS output is reduced according to activation of the brake override system. This suppresses a reduction of the engine torque and prevents the re-acceleration performance of the hybrid vehicle after deactivation of the system from deteriorating. However, such torque control of the motor  3  increases the loads on the motor  3  and the hybrid battery  8 , so that these components require high load resistance. Therefore, in the present embodiment, after a prescribed time elapses from activation of the brake override system, the amount of the HVS output reduction by torque control of the motor  3  is reduced, and accordingly, the amount of the reduction of the same HVS output by reducing the engine torque is increased to reduce the loads on the motor  3  and the hybrid battery  8 . 
         [0082]    In the present embodiment, the brake override system is realized through the processing of the brake override control routine shown in  FIG. 10 . The processing of this routine is repeatedly performed in each prescribed control cycle by the electronic control unit  9  during traveling of the hybrid vehicle. 
         [0083]    When the processing of this routine is started, first, in Step S 400 , it is determined whether an accelerator operation and a brake operation are simultaneously performed, that is, whether the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on. If the accelerator pedal  10   a  and the brake pedal  11   a  are not simultaneously stepped on (S 400 : NO), this processing of the routine is ended. 
         [0084]    If the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on (S 400 : YES), it is determined, in Step S 401 , whether an elapsed time after the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on is less than a threshold α. If the elapsed time is less than the threshold α (S 401 : YES), the processing is advanced to Step S 402 , and in this Step S 402 , the HVS output is reduced only by torque control of the motor  3 , and then this processing of the routine is ended. When the elapsed time is equal to or more than the threshold α (S 401 : NO), the processing is advanced to Step S 403 . In this Step S 403 , the HVS output is reduced by reducing the engine torque and torque control of the motor  3 , and then this processing of the routine is ended. 
         [0085]    Specifically, the processing of the electronic control unit  9  in Step S 402  is performed according to the following procedures. Specifically, at this time, the electronic control unit  9  resets the requested total output to be smaller than the value calculated from the requested output and the SOC value. However, at this time, the electronic control unit  9  calculates a requested engine output and a target engine speed from the requested total output before being reset. Then, the electronic control unit  9  calculates torque command values of the generator  2  and the motor  3  based on the engine torque determined by the requested engine output and the target engine speed calculated herein and a requested torque corresponding to the reset requested total output. 
         [0086]    The processing of the electronic control unit  9  in Step S 403  is performed according to the following procedures. Specifically, at this time, the electronic control unit  9  resets the requested total output to be smaller than the value calculated from the requested output and the SOC value. Then, the electronic control unit  9  calculates a requested engine output and a target engine speed based on the reset requested total output. Further, the electronic control unit  9  calculates torque command values of the generator  2  and the motor  3  based on an engine torque determined by the requested engine output and the target engine speed calculated herein and the requested torque corresponding to the reset requested total output. 
         [0087]    Next, a control operation at activation of the brake override system in the hybrid vehicle control device according to the present embodiment will be described with reference to  FIG. 11 . 
         [0088]    When an accelerator operation and a brake operation are simultaneously performed at point in time t 7 , the requested total output is reduced. In the present embodiment, the reduction of the HVS output in accordance with this reduction of the requested total output is performed only by torque control of the motor  3 . Therefore, at this time, only the motor torque is lowered, and the engine torque is maintained as it is. 
         [0089]    After the point in time t 8 , at which the time equal to the threshold α has elapsed after the point in time t 7 , a reduction of the HVS output in accordance with a reduction of the requested total output is performed by both reducing the engine torque and controlling the torque of the motor  3 . Therefore, at the point in time t 8 , the engine torque is reduced, and accordingly, the amount of reduction of the motor torque is reduced. As a result, the amount of reduction of the HVS output by torque control of the motor  3  is reduced, and the loads on the motor  3  and the hybrid battery  8  are reduced. 
         [0090]    The present embodiment has the following advantages in addition to the advantage (1). 
         [0091]    (5) In the present embodiment, after the prescribed time elapses from activation of the brake override system, the amount of reduction of the HVS output by torque control of the motor  3  is reduced, and accordingly, the amount of reduction of the HVS output by reducing the engine torque is increased. More specifically, a reduction of the HVS output according to activation of the brake override system is performed only by torque control of the motor  3  until the prescribed time elapses after the start of activation of the brake override system and is performed by both reducing the engine torque and controlling the torque of the motor  3  after the prescribed time elapses. Therefore, the loads on the motor  3  and the hybrid battery  8  can be prevented from being increased by extension of activation of the brake override system. 
       Fifth Embodiment 
       [0092]    Next, a hybrid vehicle control device according to a fifth embodiment of the present invention will be described with reference to  FIG. 12 . 
         [0093]    As described above, by increasing the amount of reduction of the HVS output by torque control of the motor  3  at activation of the brake override system, reduction of the engine torque is suppressed. After the system is deactivated, the re-acceleration performance of the hybrid vehicle is prevented from deteriorating. However, if the amount of reduction of the HVS output by torque control of the motor  3  is increased while the loads on the motor  3  and the hybrid battery  8  are high, these loads become higher. Therefore, when increasing the amount of reduction of the HVS output by torque control of the motor  3 , the motor  3  and the hybrid battery  8  require high load resistance. Therefore, in the present embodiment, only when the loads on the motor  3  and the hybrid battery  8  are not high, the HVS output is reduced only by torque control of the motor  3  according to activation of the brake override system. Accordingly, when the loads on the motor  3  and the hybrid battery  8  are high, the amount of reduction of the HVS output by torque control of the motor  3  is reduced to reduce the loads. 
         [0094]    In contrast, in a hybrid vehicle capable of switching the traveling mode as described above, it is assumed that the driver&#39;s demand for re-acceleration performance after deactivation of the brake override system is great when the sport traveling mode, which increases acceleration performance to be higher than normal, is selected and is small when other traveling modes are selected. Therefore, in the present embodiment, only when the sport traveling mode is selected, the amount of reduction of the HVS output by torque control of the motor  3  according to activation of the brake override system is increased. 
         [0095]    In the present embodiment, the brake override system is realized through the processing of the brake override control routine shown in  FIG. 12 . The processing of this routine is repeatedly performed in each prescribed control cycle by the electronic control unit  9  during traveling of the hybrid vehicle. 
         [0096]    When the processing of this routine is started, first, in Step S 500 , it is determined whether an accelerator operation and a brake operation are simultaneously performed, that is, whether the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on. If the accelerator pedal  10   a  and the brake pedal  11   a  are not simultaneously stepped on (S 500 : NO), this processing of the routine is ended. 
         [0097]    If the accelerator pedal  10   a  and the brake pedal  11   a  are simultaneously stepped on (S 500 : YES), it is determined, in Step S 501 , whether all of the following conditions (A) to (E) are satisfied. The following conditions (A) to (D) are for determining whether or not there are allowances for loads on the motor  3  and the hybrid battery  8 . When one or more of these conditions are not satisfied, at least one of the loads on the motor  3  and the hybrid battery  8  is high. 
         [0098]    (A) The temperature of the hybrid battery  8  is equal to or less than a threshold. 
         [0099]    (B) The voltage of the hybrid battery  8  is equal to or less than a threshold. 
         [0100]    (C) The SOC value of the hybrid battery  8  is equal to or less than a threshold. 
         [0101]    (D) The temperature of the motor  3  is equal to or less than a threshold. 
         [0102]    (E) The sport traveling mode is selected. 
         [0103]    If all of the conditions (A) to (E) are satisfied (S 501 : YES), the HVS output is reduced only by torque control of the motor  3  in Step S 502 , and then this processing of the routine is ended. If any one of the conditions (A) to (E) is not satisfied (S 501 : NO), the HVS output is reduced by reducing the engine torque and by controlling the torque of the motor  3  in Step S 503 , and then this processing of the routine is ended. 
         [0104]    Specifically, the processing of the electronic control unit  9  in Step S 502  is performed according to the following procedures. That is, at this time, the electronic control unit  9  resets the requested total output to be smaller than the value calculated from the requested output and the SOC value. However, the electronic control unit  9  calculates a requested engine output and a target engine speed based on the requested total output before being reset. Then, the electronic control unit  9  calculates torque command values of the generator  2  and the motor  3  based on an engine torque determined by the requested engine output and the target engine speed calculated herein and a requested torque corresponding to the reset requested total output. 
         [0105]    Specifically, the processing of the electronic control unit  9  in Step S 503  is performed according to the following procedures. That is, at this time, the electronic control unit  9  resets the requested total output to be smaller than the value calculated from the requested output and the SOC value. Then, the electronic control unit  9  calculates a requested engine output and a target engine speed based on the reset requested total output. Further, the electronic control unit  9  calculates torque command values of the generator  2  and the motor  3  based on an engine torque determined by the requested engine output and the target engine speed calculated herein and a requested torque corresponding to the reset requested total output. 
         [0106]    The present embodiment has the following advantages in addition to the advantage (1). 
         [0107]    (6) If loads on the motor  3  and the hybrid battery  8  are high, reduction of the HVS at activation of the brake override system is performed by both reducing the engine torque and controlling the torque of the motor  3 , and the amount of reduction of the HVS output by the torque control of the motor  3  is reduced. Therefore, the loads on the motor  3  and the hybrid battery  8  are suppressed. 
         [0108]    (7) In the present embodiment, only when the sport traveling mode, which increases acceleration performance of the hybrid vehicle to be higher than usual, is selected, reducing the HVS output at activation of the brake override system is performed only by controlling the control of the motor  3 . Therefore, the re-acceleration performance after the brake override system is deactivated is made higher only when it is demanded by the driver, so that the drivability is more efficiently prevented from deteriorating. Further, a reduction of the HVS output only by torque control of the motor  3  that leads to increases in load on the motor  3  and the hybrid battery  8  can be limited to only when it is actually demanded, so that these loads are suppressed. 
         [0109]    The above described embodiments may be modified as follows. 
         [0110]    In the above-described embodiment, the acceleration performance of the vehicle in the sport traveling mode is improved by increasing the requested output at the same accelerator operation amount. However, the acceleration performance in the sport traveling mode may be improved by other methods. For example, the acceleration performance of the vehicle can also be made higher than usual by changing the shift map to reduce the change gear ratio between the engine  1  and the drive wheels  6  at the same vehicle speed according to setting of the sport traveling mode. 
         [0111]    In a vehicle using a traction control system, when occurrence of wheel spin is detected from the vehicle speed and the rotation speeds of the wheels, wheel spin is eliminated by reducing the drive force to be transmitted to the drive wheels by reducing the output of the drive source (engine or the like). In a vehicle having such a traction control system, even when a driver strongly steps on the accelerator pedal  10   a , the traction control system is activated and the output does not rise in some cases. Therefore, when a driver needs high acceleration performance, a traction control system deactivation switch may be installed so that the traction control system can be deactivated. In this vehicle, when reduction of the output according to activation of the traction control system does not occur, the acceleration performance of the vehicle accordingly becomes higher, so that the acceleration performance of the vehicle is increased to be higher than usual by deactivating the traction control system. Therefore, such deactivation of the traction control system also corresponds to selecting of a traveling mode that increases the acceleration performance of the hybrid vehicle to be higher than usual in the present invention. 
         [0112]    In the fifth embodiment, whether or not the loads on the motor  3  and the hybrid battery  8  are high is determined from the temperature of the motor  3  and the temperature, voltage, and SOC value of the hybrid battery  8 , however, this determination may be performed by using other parameters. 
         [0113]    In the fifth embodiment, when loads on the motor  3  and the hybrid battery  8  are high, the HVS output is reduced by reducing the engine torque and torque control of the motor  3 . Otherwise, the HVS output is reduced only by controlling the torque of the motor  3 . As a matter of course, by reducing the amount of reduction of the HVS output by controlling the torque of the motor  3 , loads on the motor  3  and the hybrid battery  8  can be suppressed. Therefore, even when the HVS output is reduced in a manner other than the manner described above at the time of activation of the brake override system, the amount of reduction of the HVS output by torque control of the motor  3  may be reduced when the loads on the motor  3  and the hybrid battery  8  are high, so that these loads can be suppressed. 
         [0114]    In the fifth embodiment, the amount the HVS output reduction by torque control of the motor  3  at the time of activation of the brake override system is increased only when both of the following conditions (a) and (b) are satisfied, however, the amount of reduction may be increased when either one of the conditions is satisfied. 
         [0115]    (a) The loads on the motor  3  and the hybrid battery  8  are not high. 
         [0116]    (b) A traveling mode that increases the acceleration performance of the vehicle to be higher than usual is set. 
         [0117]    The processing to reduce the HVS output by torque control of the motor  3  while maintaining the engine torque of Step S 101  in the brake override control routine according to the first embodiment may be performed if either or both of (a) and (b) given above are satisfied. In other cases, by reducing HVS output by reducing the engine torque and by controlling the torque of the motor  3 , the loads on the motor  3  and the hybrid battery  8  are suppressed and the drivability is more efficiently prevented from deteriorating. 
         [0118]    The processing to increase the engine torque of Step S 201  in the brake override control routine and the processing to reduce the HVS output by torque control of the motor  3  of Step S 202  in the second embodiment may be performed on condition that either or both of (a) and (b) given above are satisfied. In other cases, by reducing the HVS output by reducing the engine torque and by controlling the torque of the motor  3 , the loads on the motor  3  and the hybrid battery  8  can be suppressed and the drivability is more efficiently prevented from deteriorating. 
         [0119]    The processing to start the engine  1  of Step S 302  and the processing to reduce the HVS output by torque control of the motor  3  of Step S 303  in the brake override control routine in the third embodiment may be performed on condition that either or both of (a) and (b) given above are satisfied. In other cases, by reducing the HVS output by reducing the engine torque and by controlling the torque of the motor  3 , the loads on the motor  3  and the hybrid battery  8  can be suppressed and the drivability is more efficiently prevented from deteriorating. 
         [0120]    In the brake override control routine in the fourth embodiment, on condition that the elapsed time after the start of activation of the brake override system is less than the threshold α, the HVS output is reduced only by torque control of the motor  3 . As a condition for reducing the HVS output only by controlling the torque of the motor  3 , either or both of (a) and (b) given above may be added. 
         [0121]    In the fourth embodiment, when the elapsed time after the start of activation of the brake override system becomes equal to or more than the threshold α, the amount of reduction of the HVS output by torque control of the motor  3  is reduced. However, the threshold α may be variable according to the loads on the motor  3  and the hybrid battery  8 . Specifically, when these loads are high, a smaller value is set as the threshold α so that the loads are reduced in a shorter time, and accordingly, the loads on the motor  3  and the hybrid battery  8  can be suppressed. 
         [0122]    In the fourth embodiment, the amount of reduction of the HVS output by torque control of the motor  3  is reduced only once when the elapsed time after the start of activation of the brake override system reaches the threshold α. However, the amount of reduction of the HVS output by torque control of the motor  3  may be gradually reduced or reduced in a stepwise manner with the elapsed time. 
         [0123]    In each embodiment described above, by reducing the HVS output by reducing only the motor torque without reducing the engine torque, the re-acceleration performance of the hybrid vehicle after the brake override system is deactivated is prevented from deteriorating. As a matter of course, even if the engine torque is reduced, as long as the amount of reduction is small, deterioration of the re-acceleration performance is limited. Therefore, at the time of the reduction of the HVS output according to activation of the brake override system, re-acceleration performance is prevented from deteriorating by increasing the ratio of the amount of reduction of the HVS output by torque control of the motor  3  to the total amount of reduction of the HVS output to be higher than in the case where similar reduction of the HVS output is performed according to reduction in accelerator operation amount. 
       DESCRIPTION OF THE REFERENCE NUMERALS 
       [0124]      1  . . . engine,  2  . . . generator,  3  . . . motor,  4  . . . power split mechanism,  5  . . . speed reduction mechanism,  6  . . . drive wheel,  7  . . . power control unit,  8  . . . hybrid battery,  9  . . . electronic control unit,  10  . . . accelerator position sensor,  10   a  . . . accelerator pedal,  11  . . . master cylinder pressure sensor,  11   a  . . . brake pedal,  12  . . . vehicle speed sensor,  13  . . . battery temperature sensor,  14  . . . battery voltage sensor,  15  . . . battery current sensor,  16  . . . motor temperature sensor,  17  . . . traveling mode changeover switch