Patent Publication Number: US-2013231812-A1

Title: Controller for hybrid vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2012-47709 filed on Mar. 5, 2012, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a controller for a hybrid vehicle equipped with a brake booster of negative-pressure type. 
     BACKGROUND 
     A hybrid vehicle is equipped with an internal combustion engine and a motor-generator (MG). The MG is provided in a power-transmitting system between the engine and a transmission. 
     When a hybrid vehicle is decelerated, a regenerative deceleration (regenerative brake) is conducted. In such a regenerative deceleration, a motive power of wheels drives the MG so that kinetic energy of the vehicle is converted into electric power to be charged in a battery. At this moment, if the engine is rotated along with the MG, an energy recovery amount by the regenerative deceleration may be decreased due to an energy loss, a pumping loss and a friction loss. 
     JP-08-100689A shows a regenerating device for an internal combustion engine. The engine is provided with an EGR apparatus for recirculating a part of exhaust gas to an intake passage. When a vehicle is decelerated, an EGR valve is fully opened to decrease negative pressure in the intake passage, whereby a pumping loss of the engine is reduced. Some kinds of vehicles are provided with a brake booster of negative-pressure type. 
     The brake booster introduces the negative pressure in the intake pipe to the brake booster, and increases a stepping-in force of a brake pedal by utilizing a differential pressure between the negative pressure and the atmospheric pressure, whereby the braking force is increased. 
     JP-10-73039A shows an engine control system in which an EGR valve is closed to reduce the EGR gas quantity when the negative pressure runs shortage, whereby the negative pressure is ensured. 
     However, in the engine control system shown in JP-10-73039A, it is likely that a time period required for the negative pressure to be restored to a target negative pressure may disperse according to the engine speed. The negative pressure may become unstable. For example, when the negative pressure in the brake booster is rapidly decreased due to a pumping braking at the time of deceleration, it is likely that the desired deceleration may not be achieved. 
     SUMMARY 
     It is an object of the present disclosure to provide a controller for a hybrid vehicle equipped with a brake booster of negative-pressure type, which is able to ensure a desired deceleration even if a negative pressure runs shortage at a time of deceleration of a vehicle. 
     According to the present disclosure, a hybrid vehicle which is equipped with an engine; a motor generator disposed in a power transmitting system between the engine and a wheel; a negative-pressure type brake booster amplifying a stepping-in force of a brake pedal in order to increase a braking force of a brake by using of a negative pressure in an intake passage of the engine; an EGR valve adjusting a quantity of an exhaust gas recirculating into the intake passage; and an automatic brake unit electronically controlling the braking force of the brake. 
     A controller for the hybrid vehicle includes: a negative-pressure-determination portion for determining whether the negative pressure is insufficient based on the negative pressure and a decrease amount of the negative pressure at a time of a deceleration of the hybrid vehicle; an EGR-close control portion for performing an EGR-close control in which the EGR valve is driven to a close position when the negative-pressure-determination portion determines that the negative pressure is insufficient; and an automatic brake unit for performing a braking-force assist control to compensate the braking force of the brake when the negative pressure is not restored to a target negative pressure in a specified time after the negative-pressure-determination portion determines that the negative pressure is insufficient. 
     According to the above configuration, when it is determined that the negative pressure is insufficient at a time of deceleration of the vehicle and when the negative pressure is not restored to the target negative pressure in the specified time even though the EGR-close control is executed, the automatic brake unit performs the braking-force assist control to compensate the braking force of the brake. Thereby, the shortage of the braking force due to the insufficient negative pressure is compensated by the braking force generated by the automatic brake unit. Even if the negative pressure becomes insufficient at the time of deceleration of the vehicle, the desired deceleration can be ensured. 
     According to another aspect of the present disclosure, a hybrid vehicle is equipped with an engine; a motor generator and a transmission disposed in a power transmitting system between the engine and a wheel. The hybrid vehicle is further equipped a negative-pressure type brake booster amplifying a stepping-in force of a brake pedal in order to increase a braking force of a brake by using of a negative pressure in an intake passage of the engine; and an EGR valve adjusting a quantity of an exhaust gas recirculating into the intake passage. 
     A controller for the hybrid vehicle includes: a negative-pressure-determination portion for determining whether the negative pressure is insufficient based on the negative pressure and a decrease amount of the negative pressure at a time of a deceleration of the hybrid vehicle; an EGR-close control portion for performing an EGR-close control in which the EGR valve is driven to a close position when the negative-pressure-determination portion determines that the negative pressure is insufficient; and an engine-speed-increase portion for performing an engine-speed increase control in which an engine speed of the engine is increased by using of at least one of the motor-generator and the transmission when the negative-pressure-determination portion determines that the negative pressure is insufficient. 
     According to the above configuration, when it is determined that the negative pressure is insufficient at a time of deceleration of the vehicle the EGR-close control and the engine-speed increase control are performed. Thereby, the negative pressure is promptly restored to the target negative pressure, so that the braking force of the brake never becomes insufficient. Even if the negative pressure becomes insufficient at a time of deceleration of the vehicle, the deceleration required by a driver is certainly ensured. 
     Furthermore, the controller may includes an automatic brake unit electronically controlling the braking force of the brake; and an automatic brake unit for performing a braking-force assist control to compensate the braking force of the brake when the negative pressure is not restored to a target negative pressure in a specified time after the negative-pressure-determination portion determines that the negative pressure is insufficient. When it is determined that the negative pressure is insufficient at the time of deceleration of the vehicle and when the negative pressure is not restored to the target negative pressure in the specified time even though the EGR-close control and the engine-speed increase control are executed, the automatic brake unit performs the braking-force assist control to compensate the braking force of the brake. Thereby, the shortage of the braking force due to the insufficient negative pressure is compensated by the braking force generated by the automatic brake unit  34 . The deceleration required by a driver is certainly ensured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a schematic view of a power transmitting system of a hybrid vehicle according to a first embodiment; 
         FIG. 2  is a schematic view of a control system of the hybrid vehicle according to the first embodiment; 
         FIG. 3  is a chart for explaining an operation characteristic of a brake; 
         FIG. 4  is a chart showing a relationship between a brake pedal stepping-in force and a brake drive oil pressure. 
         FIG. 5  is a time chart for explaining a deceleration-control according to the first embodiment; 
         FIG. 6  is a flow chart showing a processing of a deceleration-control routine according to the first embodiment; 
         FIG. 7  is a chart conceptually showing a negative-pressure-determination map; 
         FIG. 8  is a time chart for explaining a deceleration-control according to a second embodiment; 
         FIG. 9  is a flow chart showing a processing of a deceleration-control routine according to the second embodiment; 
         FIG. 10  is a chart conceptually showing a map of an injection cycle of the reforming-fuel; 
         FIG. 11  is a time chart for explaining a deceleration-control according to a third embodiment; 
         FIG. 12  is a flow chart showing a processing of a deceleration-control routine according to the third embodiment; and 
         FIG. 13  is a schematic view of a power transmitting system of a hybrid vehicle according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described, hereinafter. 
     First Embodiment   
     Referring to  FIGS. 1 to 7 , a first embodiment will be described hereinafter. Based on  FIGS. 1 and 2 , a power transmitting system and a control system of a hybrid vehicle will be explained. 
     The hybrid vehicle is equipped with an internal combustion engine  11  and a motor-generator (MG)  12 . A power of an output shaft (crankshaft) of the engine  11  is transferred to the transmission  13  through the MG  12 . The power of the output shaft of the transmission  13  is transferred to wheels  16  through a differential gear mechanism  14  and axles  15 . The transmission  13  may be a continuously variable transmission (CVT). The MG  12  is disposed between the engine  11  and the transmission  13 . A clutch  17  is disposed between the MG  12  and the transmission  13 . This clutch  17  may be a hydraulic clutch or an electromagnetic clutch. An inverter  18  driving the MG  18  is connected to a battery  19 , so that electric power is delivered between the MG  12  and the battery  19  through the inverter  18 . 
     As shown in  FIG. 2 , a throttle valve  21  driven by a motor is disposed in an intake pipe (intake passage)  20 . A surge tank  22  is provided downstream of the throttle valve  21 . The engine  11  is provided with an exhaust gas recirculation (EGR) apparatus  24  for recirculating a part of exhaust gas from an exhaust pipe  20  into the intake pipe  20 . The EGR apparatus  24  has an EGR pipe  25  connecting the exhaust pipe  23  and the intake pipe  20 . An EGR valve  26  adjusting the EGR gas quantity is provided in the EGR pipe  25 . 
     A negative-pressure-introduction pipe  28  is connected to the surge tank  22  so that the negative pressure in the intake pipe  20  is introduced into the brake booster  27 . The brake booster  27  amplifies the stepping-in force of a brake pedal  29  by utilizing a differential pressure between the negative pressure and the atmospheric pressure. The amplified stepping-in force is transferred to a piston (not shown) of a master cylinder  30 . The hydraulic pressure in the master cylinder  30  is increased to increase the driving hydraulic pressure of the brake  31  provided to each wheel, whereby the braking force of each brake  31  is increased. A pressure sensor  32  which detects the negative pressure introduced into the brake booster  27  is provided to the brake booster  27 . 
     A PT-ECU  33  is a computer which controls the power transmitting system of the hybrid vehicle. Specifically, the PT-ECU  33  controls the engine  11 , the MG  12  and the transmission  13  according to a driving condition of the vehicle. When a hybrid vehicle is decelerated, a regenerative deceleration (regenerative brake) is conducted. In such a regenerative deceleration, a motive power of wheels  16  drives the MG  12  so that kinetic energy of the vehicle is converted into electric power to be charged in a battery  19 . 
     Furthermore, the PT-ECU  33  controls an automatic brake unit  34  according to the driving condition of the vehicle. The automatic brake unit  34  is comprised of a BRK-ECU  35  which controls a hydraulic controller  36  (a hydraulic pump, a pressure regulating valve, etc.) so that the driving hydraulic pressure of the brake  31  is controlled. 
     As shown in  FIGS. 3 and 4 , in a region “A” where the stepping-in force “F” of the brake pedal  29  is not greater than a specified value “a”, the hydraulic pressure by operating the brake pedal  29  is hardly generated. The hydraulic pressure in the master cylinder  30  hardly rises. The PT-ECU  33  controls the torque of the MG  12  so that the braking force is generated according to the stepping-in force “F” in cooperation with the regenerative brake by the MG  12  and the automatic brake unit  34 . Further, the hydraulic controller  36  controls the driving hydraulic pressure of the brake  31 . 
     Meanwhile, in a region “B” where the stepping-in force “F” of the brake pedal  29  is greater than the specified value “a”, the hydraulic pressure in the master cylinder  30  rises according to the stepping-in force “F”. The driving hydraulic pressure of the brake  31  is increased so that the braking force of the brake  31  increases. Moreover, the hydraulic controller  36  controls the driving hydraulic pressure of the brake  31 . 
     For example, when the negative pressure in the brake booster  27  is rapidly decreased due to a pumping braking at the time of deceleration, it is likely that the desired deceleration may not be achieved. 
     According to the first embodiment, the PT-ECU  33  executes a deceleration-control routine shown in  FIG. 6  when the vehicle is decelerated. 
     As shown in a time chart of  FIG. 5 , when the vehicle is decelerated, the computer determines whether the negative pressure is insufficient based on the negative pressure detected by the pressure sensor  32  and a decrease amount of the negative pressure. 
     For example, when the negative pressure in the brake booster  27  is rapidly decreased due to a pumping braking and the computer determines that the negative pressure is insufficient at a time t 1 , an EGR-close control is executed so that the EGR valve  26  is driven toward a close position. In the EGR-close control, the opening degree of the EGR valve  26  is adjusted to a target opening degree which is predetermined or established according to the negative pressure. Alternatively, the EGR valve  26  may be fully closed. Thereby, the EGR gas quantity is reduced or made zero, so that the negative pressure in the intake pipe  20  is increased. That is, the pressure in the intake pipe  20  is decreased toward vacuum. 
     After that, the computer determines whether the negative pressure detected by the pressure sensor  32  is restored to a specified target negative pressure. When the negative pressure is not restored to the target negative pressure even after a specified time period At has elapsed after the time t 1 , the automatic brake unit  34  executes a braking-force assist control to assist the braking force of the brake  31  at a time t 2 . In the braking-force assist control, the braking force of the brake  31  generated by the automatic brake unit  34  is increased by a specified amount which corresponds to the decrease in braking force due to a shortage of negative pressure. Thereby, the shortage of the braking force due to the insufficient negative pressure is compensated by the braking force generated by the automatic brake unit  34 . 
     Then, when the computer determines that the negative pressure detected with the pressure sensor  32  is restored to the target negative pressure, the EGR-close control and the braking-force assist control are terminated at a time t 3 . 
     The above described deceleration-control is executed by the PT-ECU  33  according to the deceleration-control routine shown in  FIG. 6 . The process of this routine will be described hereinafter. 
     The deceleration-control routine is executed at specified intervals while the PT-ECU  33  is ON. In step  101 , the computer determines whether the vehicle is decelerated. When the answer is NO, the procedure ends. 
     When the answer is YES in step  101 , the procedure proceeds to step  102  in which the computer determines whether the negative pressure is insufficient based on the negative pressure detected by the pressure sensor  32  and a decrease amount of the negative pressure. Specifically, in view of a negative-pressure-determination map shown in  FIG. 7 , the computer determines whether the negative pressure is insufficient based on whether the negative pressure and the decrease amount are in a negative-pressure-insufficient region. The negative-pressure-determination map is previously formed based on experimental data and design data, and is stored in the ROM of the PT-ECU  33 . The process in step  102  corresponds to a negative-pressure-determination portion. 
     When the answer is NO in step  102 , the routine is finished without performing the subsequent steps. 
     When the answer is YES in step  102 , the procedure proceeds to step  103  in which the EGR-close control is executed. In the EGR-close control, the opening degree of the EGR valve  26  is adjusted to a target opening degree which is predetermined or established according to the negative pressure. Alternatively, the EGR valve  26  may be fully closed. Thereby, the EGR gas quantity is reduced or made zero, so that the negative pressure in the intake pipe  20  is increased. That is, the pressure in the intake pipe  20  is decreased toward vacuum. The process in step  103  corresponds to an EGR-close control portion. 
     Then, the procedure proceeds to step  104  in which the computer determines whether the negative pressure detected by the pressure sensor  32  has been restored to the specified target negative pressure. The target negative pressure is set as negative pressure required for the brake booster  27  to normally operate. 
     When the answer is NO in step  104 , the procedure proceeds to step  105  in which the computer determines whether a specified time At has elapsed after it was determined the negative pressure is insufficient. When the answer is NO in step  105 , the procedure goes back to step  103 . 
     When the answer is NO in step  104  and the answer is YES in step  105 , the procedure proceeds to step  106 . In step  106 , the computer computes a target braking force of the automatic brake unit  34 . Specifically, the computer computes the target braking force based on the negative pressure detected by the pressure sensor  32  and the target negative pressure so that the braking force of the brake  31  is increased by the amount corresponding to the shortage of barking force of the brake  31  due to the shortage of negative pressure. 
     Then, the procedure proceeds to step  107  in which the automatic brake unit  34  executes the braking-force assist control to assist the braking force of the brake  31 . In the braking-force assist control, the hydraulic controller  36  controls the driving hydraulic pressure of the brake  31  so that the braking force of the brake  31  becomes the target braking force. The braking force of the brake  31  generated by the automatic brake unit  34  is increased by a specified amount which corresponds to the decrease in braking force due to a shortage of negative pressure. Thereby, the shortage of the braking force due to the insufficient negative pressure is compensated by the braking force generated by the automatic brake unit  34 . The process in step  107  corresponds to a braking force correction portion. 
     Then, when the computer determines that the negative pressure detected with the pressure sensor  32  is restored to the target negative pressure in step  104 , the procedure proceeds to step  108  in which the EGR-close control and the braking-force assist control are terminated. 
     According to the above first embodiment, when it is determined that the negative pressure is insufficient at the time of deceleration of the vehicle and when the negative pressure is not restored to the target negative pressure in the specified time Δt even though the EGR-close control is executed, the automatic brake unit  34  performs the braking-force assist control to compensate the braking force of the brake  31 . Thereby, the shortage of the braking force due to the insufficient negative pressure is compensated by the braking force generated by the automatic brake unit  34 . Even if the negative pressure becomes insufficient at the time of deceleration of the vehicle, the desired deceleration can be ensured. 
     Second Embodiment 
     Referring to  FIGS. 8 to 10 , a second embodiment will be described hereinafter. In the second embodiment, the same parts and components as those in the first embodiment are indicated with the same reference numerals and the same descriptions will not be reiterated. 
     According to the second, the PT-ECU  33  executes a deceleration-control routine shown in  FIG. 9  when the vehicle is decelerated. 
     As shown in a time chart of  FIG. 9 , when the vehicle is decelerated, it is determined whether the negative pressure is insufficient based on the negative pressure detected by the pressure sensor  32  and its decrease amount. When it is determined that the negative pressure is insufficient at a time t 4 , the EGR-close control is executed and an engine-speed increase control is executed to increase the engine speed. In the engine-speed increase control, a change gear ratio (reduction ratio) of the transmission  13  is increased to increase the engine speed. Alternatively, the MG  12  drives the engine  11  to increase the engine speed. These operations may be conducted at the same time. Thereby, the negative pressure is promptly restored to the target negative pressure, so that the braking force of the brake  31  never becomes insufficient. 
     Then, the computer determines whether the negative pressure detected by the pressure sensor  32  is restored to the target negative pressure. When the negative pressure is restored to the target negative pressure, the EGR-close control and the engine-speed increase control are terminated at a time t 5 . 
     The above described deceleration-control is executed by the PT-ECU  33  according to the deceleration-control routine shown in  FIG. 9 . 
     In step  201 , the computer determines whether the vehicle is decelerating. When the answer is YES, the procedure proceeds to step  202  in which the computer determines whether the negative pressure is insufficient. Specifically, in view of the negative-pressure-determination map shown in  FIG. 7 , the computer determines whether the negative pressure is insufficient based on whether the negative pressure and the decrease amount are in a negative-pressure-insufficient region. 
     When the answer is YES in step  202 , the procedure proceeds to step  203  in which the EGR-close control is executed. 
     Then, the procedure proceeds to step  204  in which the computer computes a target engine speed which is required to promptly restore the negative pressure to the target negative pressure. Specifically, in view of a target-engine-speed map shown in  FIG. 10 , a target engine speed is computed according to the negative pressure. The target-engine-speed map is previously formed based on experimental data and design data, and is stored in the ROM of the PT-ECU  33 . 
     Then, the procedure proceeds to step  205  in which the engine-speed increase control is performed. In the engine-speed increase control, a change gear ratio (reduction ratio) of the transmission  13  is increased to increase the engine speed. Alternatively, the 
     MG  12  drives the engine  11  to increase the engine speed. These operations may be conducted at the same time. Thereby, the negative pressure is promptly restored to the target negative pressure, so that the braking force of the brake  31  never becomes insufficient. The process in step  205  corresponds to an engine-speed-increase portion. 
     Then, the procedure proceeds to step  206  in which the computer determines whether the negative pressure detected by the pressure sensor  32  is restored to the target negative pressure. When the negative pressure is not restored to the target negative pressure, the procedure goes back to step  203 . 
     When the computer determines that the negative pressure is restored to the target negative pressure in step  206 , the procedure proceeds to step  207  in which the EGR-close control and the engine-speed increase control are terminated. 
     According to the above second embodiment, when it is determined that the negative pressure is insufficient at the time of deceleration of the vehicle, the EGR-close control and the engine-speed increase control are performed. Thereby, the negative pressure is promptly restored to the target negative pressure, so that the braking force of the brake  31  never becomes insufficient. Even if the negative pressure becomes insufficient at the time of deceleration of the vehicle, the desired deceleration can be ensured. 
     Third Embodiment 
     Referring to  FIGS. 11 and 12 , a third embodiment will be described hereinafter. In the third embodiment, the same parts and components as those in the first and the second embodiment are indicated with the same reference numerals and the same descriptions will not be reiterated. 
     According to the third embodiment, the PT-ECU  33  executes a deceleration-control routine shown in  FIG. 12  when the vehicle is decelerated. 
     As shown in a time chart of  FIG. 11 , when the vehicle is decelerated, it is determined whether the negative pressure is insufficient based on the negative pressure detected by the pressure sensor  32  and its decrease amount. When it is determined that the negative pressure is insufficient at a time t 6 , the EGR-close control is executed and the engine-speed increase control is executed to increase the engine speed. 
     After that, the computer determines whether the negative pressure detected by the pressure sensor  32  is restored to the target negative pressure. When the negative pressure is not restored to the target negative pressure even after a specified time period At has elapsed after the time t 6 , the automatic brake unit  34  executes a braking-force assist control to assist the braking force of the brake  31  at a time t 7 . 
     Then, when the computer determines that the negative pressure detected with the pressure sensor  32  is restored to the target negative pressure, the EGR-close control, the engine-speed increase control and the braking-force assist control are terminated at a time t 8 . 
     The above described deceleration-control is executed by the PT-ECU  33  according to the deceleration-control routine shown in  FIG. 12 . 
     In step  301 , the computer determines whether the vehicle is decelerating. When the answer is YES, the procedure proceeds to step  302  in which the computer determines whether the negative pressure is insufficient. Specifically, in view of the negative-pressure-determination map shown in  FIG. 7 , the computer determines whether the negative pressure is insufficient based on whether the negative pressure and the decrease amount are in a negative-pressure-insufficient region. 
     When the answer is YES in step  302 , the procedure proceeds to step  303  in which the EGR-close control is executed. 
     Then, the procedure proceeds to step  304  in which the computer computes a target engine speed which is required to promptly restore the negative pressure to the target negative pressure. Then, the procedure proceeds to step  305  in which the engine-speed increase control is performed. 
     Then, the procedure proceeds to step  306  in which the computer determines whether the negative pressure detected by the pressure sensor  32  has been restored to the specified target negative pressure. When the answer is NO in step  306 , the procedure proceeds to step  307  in which the computer determines whether a specified time At has been elapsed after it was determined the negative pressure is insufficient. When the answer is NO in step  307 , the procedure goes back to step  303 . 
     When the answer is NO in step  306  and the answer is YES in step  307 , the procedure proceeds to step  308 . In step  308 , the computer computes a target braking force of the automatic brake unit  34 . Then, the procedure proceeds to step  309  in which the automatic brake unit  34  executes the braking-force assist control to assist the braking force of the brake  31 . 
     Then, when the computer determines that the negative pressure detected with the pressure sensor  32  is restored to the target negative pressure in step  306 , the procedure proceeds to step  310  in which the EGR-close control, the engine-speed increase control and the braking-force assist control are terminated. 
     According to the above first embodiment, when it is determined that the negative pressure is insufficient at the time of deceleration of the vehicle and when the negative pressure is not restored to the target negative pressure in the specified time At even though the EGR-close control and the engine-speed increase control are executed, the automatic brake unit  34  performs the braking-force assist control to compensate the braking force of the brake  31 . Thereby, the shortage of the braking force due to the insufficient negative pressure is compensated by the braking force generated by the automatic brake unit  34 . The deceleration required by a driver is certainly ensured. 
     The present disclosure can be applied to a hybrid vehicle which is provided with a first clutch  17  between the MG  12  and the transmission  13  and a second clutch  37  between the engine  11  and the MG  12 , as shown in  FIG. 13 .