Abstract:
To improve the drivability of an automobile at the time of transmission which restricts a torque of an engine, a hybrid automobile is structured which performs transmission control for performing control so that an output restriction is temporarily released in a step of restoring a torque that is reduced once in neutral at the time of transmission during the output restriction by an output restriction control unit and a torque by a motor is added to the torque of the engine.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. national stage of application No. PCT/JP2011/074180, filed on Oct. 20, 2011. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Patent Application No. 2010-236612, filed on Oct. 21, 2010, the disclosure of which are also incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a transmission control device, a hybrid vehicle, a transmission control method, and a computer program. 
     BACKGROUND ART 
     The limitation of the torque of the engine in response to the torque required by a driver is a measure for reducing the exhaust gas of a vehicle. This gives a constant limitation on the torque of the engine even though the driver fully depresses the accelerator pedal, so that the vehicle is controlled to output torque less than the maximum torque (for example, see patent literature PTL1). 
     CITATION LIST 
     Patent Literature 
     PTL1: JP 2006-280049 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     When a vehicle shifts the gears, the torque of the engine is temporarily reduced in order to transfer the gear from a gear number before the shift into neutral. After that, the gear is shifted to the gear number after the shift in order to return the torque of the engine that has temporarily been reduced. At that time, if the vehicle is in a mode in which the torque of the engine is limited in response to the request torque from the driver, the torque is limited even when the torque of the engine is returned after the gear has been shifted to the gear number after the shift from neutral. This causes the delay of the return of the torque in the gear shifting and aggravates the drivability. 
     In light of the foregoing, an objective of the present invention is to provide a transmission control device, a hybrid vehicle, a transmission control method, and a computer program that can improve the drivability in the gear shifting in a mode in which the torque of the engine is limited in response to the torque required by the driver. 
     Solution to Problem 
     An aspect of the present invention is directed to a transmission control device. According to the aspect of the present invention, the transmission control device of a hybrid vehicle that includes an engine and an electric motor, that is capable of running by the engine or the electric motor or capable of running by cooperation between the engine and the electric motor, includes: an output limitation means for limiting torque output from the engine and/or the electric motor; and an automatic gear shifting means for shifting a gear number according to a variation in a vehicle speed, in which the automatic gear shifting means performs a control for temporarily reducing the torque output from the engine in neutral while a gear is transferred from a gear number before the shift to a gear number after the shift through neutral once, and, when the gear shifting is performed during output limitation, the output limitation means performs a control for temporarily cancelling the output limitation in a process for returning the torque that has temporarily been reduced in neutral, and adding torque by the electric motor to torque of the engine. 
     Another aspect of the present invention is directed to a hybrid vehicle. The hybrid vehicle includes the transmission control device according to the present invention. 
     Still another aspect of the present invention is directed to a transmission control method. The transmission control method of a hybrid vehicle, that includes an engine and an electric motor, that is capable of running by the engine or the electric motor or capable of running by cooperation between the engine and the electric motor, and that includes an output limitation means for limiting torque output from the engine and/or the electric motor, and an automatic gear shifting means for shifting a gear number according to a variation in a vehicle speed, the automatic gear shifting means performing a control for temporarily reducing the torque output from the engine in neutral while a gear is transferred from a gear number before the shift to a gear number after the shift through neutral once, includes a step in which, when the gear shifting is performed during output limitation, the output limitation means performs a control for temporarily cancelling the output limitation in a process for returning the torque that has temporarily been reduced in neutral, and adding torque by the electric motor to torque of the engine. 
     Still another aspect of the present invention is directed to a computer program. The computer program causes an information processing apparatus to implement a function of the transmission control device according to the present invention. 
     Advantageous Effects of Invention 
     The present invention can improve the drivability in the gear shifting in a mode in which the torque of the engine is limited in response to the torque required by the driver. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       {FIG.  1 } It shows a block diagram for illustrating an exemplary structure of a hybrid vehicle according to an embodiment of the present invention. 
       {FIG.  2 } It shows a block diagram for illustrating an exemplary configuration of a function implemented in a hybrid ECU illustrated in  FIG. 1 . 
       {FIG.  3 } It shows a flowchart for illustrating a process in an output limitation control unit and a transmission control unit illustrated in  FIG. 2 . 
       {FIG.  4 } It shows a view for illustrating the relationship between the limited acceleration and the gear numbers and the variation in the torque in the gear shifting at the output limitation control in the output limitation control unit illustrated in  FIG. 2 . 
       {FIG.  5 } It shows a view for describing the variation in the torque by the transmission control in the transmission control unit illustrated in  FIG. 2 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a hybrid vehicle according to an embodiment of the present invention will be described with reference to  FIGS. 1 to 5 . 
       FIG. 1  is a block diagram for illustrating an exemplary structure of a hybrid vehicle  1 . The hybrid vehicle  1  is an example of a vehicle. The hybrid vehicle  1  is driven by an engine (internal combustion engine)  10  and/or an electric motor  13  through a gear box having an automated mechanical/manual transmission. The hybrid vehicle  1  can performs an output limitation for limiting the torque output from the engine  10  and/or the electric motor  13 . Note that the automated mechanical/manual transmission is a transmission that can automatically shift the gears while having the same structure as a manual transmission. 
     The hybrid vehicle  1  includes the engine  10 , an engine Electronic Control Unit (ECU)  11 , a clutch  12 , the electric motor  13 , an inverter  14 , a battery  15 , a transmission  16 , a motor ECU  17 , a hybrid ECU  18 , a wheel  19 , and a key switch  20 . Note that the transmission  16  includes the above-mentioned automated mechanical/manual transmission and is operated by a shift unit  21  (not shown in the drawings) including a drive range (hereinafter, referred to as a D (Drive) range). 
     The engine  10  is an example of an internal combustion engine, and is controlled by the engine ECU  11 . The engine  10  internally combusts gasoline, light oil, Compressed Natural Gas (CNG), Liquefied Petroleum Gas (LPG), alternative fuel, or the like in order to generate power for rotating a shaft and transfer the generated power to the clutch  12 . 
     The engine ECU  11  is a computer working in coordination with the motor ECU  17  according to the instructions from the hybrid ECU  18 , and controls the engine  10 , for example, the amount of fuel injection and the valve timing. For example, the engine ECU  11  includes a Central Processing Unit (CPU), an Application Specific Integrated Circuit (ASIC), a microprocessor (micro-computer), a Digital Signal Processor (DSP), and the like, and internally has an operation unit, a memory, an Input/Output (I/O) port, and the like. 
     The clutch  12  is controlled by the hybrid ECU  18 , and transfers the shaft output from the engine  10  to the wheel  19  through the electric motor  13  and the transmission  16 . In other words, the clutch  12  mechanically connects the rotating shaft of the engine  10  to the rotating shaft of the electric motor  13  by the control of the hybrid ECU  18  in order to transfer the shaft output of the engine  10  to the electric motor  13 . On the other hand, the clutch  12  cuts the mechanical connection between the rotating shaft of the engine  10  and the rotating shaft of the electric motor  13  so that the shaft of the engine  10  and the rotating shaft of the electric motor  13  can rotate at different rotational speeds from each other. 
     For example, the clutch  12  mechanically connects the rotating shaft of the engine  10  to the rotating shaft of the electric motor  13 , for example, when the hybrid vehicle  1  runs by the power of the engine  10  and this causes the electric motor  13  to generate electric power, when the driving force of the electric motor  13  assists the engine  10 , and when the electric motor  13  starts the engine  10 . 
     Alternatively, for example, the clutch  12  cuts the mechanical connection between the rotating shaft of the engine  10  and the rotating shaft of the electric motor  13  when the engine  10  stops or is in an idling state and the hybrid vehicle  1  runs by the driving force of the electric motor  13 , and when the hybrid vehicle  1  decelerates or runs on the down grade and the electric motor  13  generates electric power (regenerates electric power) while the engine  10  stops or is in an idling state. 
     Note that the clutch  12  differs from the clutch operated by the driver&#39;s operation of a clutch pedal, and is operated by the control of the hybrid ECU  18 . 
     The electric motor  13  is a so-called motor generator that supplies a shaft output to the transmission  16  by generating the power for rotating the shaft using the electric power supplied from the inverter  14 , or that supplies electric power to the inverter  14  by generating the electric power using the power for rotating the shaft supplied from the transmission  16 . For example, when the hybrid vehicle  1  accelerates or runs at a constant speed, the electric motor  13  generates the power for rotating the shaft to supply the shaft output to the transmission  16  in order to cause the hybrid vehicle  1  to run in cooperation with the engine  10 . Further, the electric motor  13  works as an electric generator, for example, when the electric motor  13  is driven by the engine  10 , or when the hybrid vehicle  1  runs without power, for example, the hybrid vehicle  1  decelerates or runs on the down grade. In that case, electric power is generated by the power for rotating the shaft supplied from the transmission  16  and is supplied to the inverter  14  in order to charge the battery  15 . 
     The inverter  14  is controlled by the motor ECU  17 , and converts the direct voltage from the battery  15  into an alternating voltage or converts the alternating voltage from the electric motor  13  into a direct voltage. When the electric motor  13  generates power, the inverter  14  converts the direct voltage of the battery  15  into an alternating voltage and supplies the electric power to the electric motor  13 . When the electric motor  13  generates electric power, the inverter  14  converts the alternating voltage from the electric motor  13  into a direct voltage. In other words, in that case, the inverter  14  works as a rectifier and a voltage regulator for supplying a direct voltage to the battery  15 . 
     The battery  15  is a secondary cell capable of being charged and discharged. The battery  15  supplies electric power to the electric motor  13  through the inverter  14  when the electric motor  13  generates power. Alternatively, the battery  15  is charged with the electric power generated by the electric motor  13  when the electric motor  13  generates electric power. 
     The transmission  16  includes an automated mechanical/manual transmission (not shown in the drawings) that selects one of a plurality of gear ratios (change gear ratios) according to the shift instruction signal from the hybrid ECU  18  in order to shift the change gear ratios and transfer the gear-shifted power of the engine  10  and/or of the electric motor  13  to the wheel  19 . Alternatively, the transmission  16  transfers the power from the wheel  19  to the electric motor  13 , for example, when the vehicle decelerates or runs on the down grade. Note that the automated mechanical/manual transmission can also shift the gear position to a given gear number by the driver&#39;s hand operation. 
     The motor ECU  17  is a computer working in coordination with the engine ECU  11  according to the instructions from the hybrid ECU  18 , and controls the electric motor  13  by controlling the inverter  14 . For example, the motor ECU  17  includes a CPU, an ASIC, a microprocessor (micro-computer), a DSP, and the like, and internally has an operation unit, a memory, an I/O port, and the like. 
     The hybrid ECU  18  is an example of a computer. For hybrid driving, the hybrid ECU  18  obtains accelerator opening level information, brake operation information, vehicle speed information, the gear position information obtained from the transmission  16 , and the engine rotational speed information obtained from the engine ECU  11  in order to refer to the information, control the clutch  12  and supply the shift instruction signal in order to control the transmission  16 . For hybrid driving, the hybrid ECU  18  further gives the control instructions of the electric motor  13  and the inverter  14  to the motor ECU  17  based on the obtained SOC information on the battery  15  and other information, and gives the control instruction of the engine  10  to the engine ECU  11 . For example, the hybrid ECU  18  includes a CPU, an ASIC, a microprocessor (micro-computer), a DSP, and the like, and internally has an operation unit, a memory, an I/O port, and the like. 
     Note that a computer program to be executed by the hybrid ECU  18  can be installed on the hybrid ECU  18  that is a computer in advance by being stored in a non-volatile memory inside the hybrid ECU  18  in advance. 
     The engine ECU  11 , the motor ECU  17 , and the hybrid ECU  18  are connected to each other, for example, through a bus complying with the standard of the Control Area Network (CAN) or the like. 
     The wheel  19  is a drive wheel for transmitting the driving force to the road surface. Note that, although only a wheel  19  is illustrated in  FIG. 1 , the hybrid vehicle  1  actually includes a plurality of the wheels  19 . 
     The key switch  20  is a switch that is turned ON/OFF, for example, by insertion of a key by the user at the start of drive. Turning ON the switch activates each unit of the hybrid vehicle  1 , and turning OFF the key switch  20  stops each unit of the hybrid vehicle  1 . 
       FIG. 2  is a block diagram for illustrating an exemplary configuration of a function implemented in the hybrid ECU  18  that executes a computer program. In other words, once the hybrid ECU  18  executes a computer program, an output limitation control unit  30  and a transmission control unit  31  are implemented. 
     The output limitation control unit  30  performs a control for setting an acceleration that is accepted at each of the gear numbers. This limits the acceleration to a predetermined acceleration according to the gear number and the vehicle speed, for example, even when the driver depresses the accelerator to rapidly accelerate the vehicle. Concretely, a target torque is limited in order to prevent acceleration equal to or more than the predetermined acceleration. This will be described in detail below with reference to  FIG. 4 . 
     The transmission control unit  31  controls the automatic gear shifting of the hybrid vehicle  1 . Note that the transmission control unit  31  controls the automatic gear shifting during output limitation in cooperation with the output limitation control unit  30 . 
     Next, a process for the transmission control during output limitation that is performed in the hybrid ECU  18  executing a computer program will be described with reference to the flowchart illustrated in  FIG. 3 . Note that the flow illustrated in  FIG. 3  is one cycle of the process and the process is repeatedly performed as long as the key switch  20  is in the ON state. 
     At the “Start” of  FIG. 3 , the key switch  20  is in the ON state and the hybrid ECU  18  executes a computer program and the output limitation control unit  30  and the transmission control unit  31  are implemented by the hybrid ECU  18 . The process goes to step S 1 . Note that the hybrid vehicle  1  runs in an output limitation mode at the “Start”. 
     In step S 1 , the transmission control unit  31  determines whether a condition for shifting gears is satisfied. For example, at an acceleration mode in which the vehicle speed of the hybrid vehicle  1  gradually increases or at a deceleration mode in which the vehicle speed of the hybrid vehicle  1  gradually decreases, the gear shifting is performed according to the increase or the decrease in the vehicle speed. When it is determined in step S 1  that the condition for shifting gears is satisfied, the process goes to step S 2 . On the other hand, when it is determined in step S 1  that the condition for shifting gears is not satisfied, step S 1  of the process is repeated. 
     The transmission control unit  31  reduces the torque of the engine  10  in order to shift the gear position into neutral in step S 2 , and shifts the gear position to a gear number according to the vehicle speed in step S 3 . At that time, the transmission control unit  31  temporarily disengages the clutch  12  and then reduces the torque of the engine  10 . After that, the transmission control unit  31  shifts the gear position into neutral in order to shift the gear number and then controls the clutch  12  to be engaged again. 
     In step S 4 , the transmission control unit  31  cancels the limitation of the torque and the process goes to step S 5 . 
     In step S 5 , the transmission control unit  31  causes the electric motor  13  to assist the engine  10  and the process goes to step S 6 . 
     In step S 6 , the transmission control unit  31  determines whether the torque of the engine  10  returns to the state before the gear shifting has been performed. When it is determined in step S 6  that the torque of the engine  10  returns to the state before the gear shifting has been performed, the process goes to step S 7 . On the other hand, when it is determined in step S 6  that the torque of the engine  10  does not return to the state before the gear shifting has been performed, the process goes back to step S 5 . 
     In step S 7 , the transmission control unit  31  causes the electric motor  13  to terminate assisting the engine  10  and terminates a cycle of the process. 
     Next, the relationship between the limited acceleration and the gear numbers and the variation in the torque of the engine  10  when the gear shifting is performed at the output limitation control in the output limitation control unit  30  will be described with reference to  FIG. 4 . At the upper part of  FIG. 4 , the limited accelerations when the gear number is set at a second speed, a third speed, and a fourth speed are illustrated with dashed lines and the acceleration of the hybrid vehicle  1  is illustrated with a solid line. At the lower part of  FIG. 4 , the variation in the torque of the engine  10  of the hybrid vehicle  1  is illustrated while corresponding to the drawing of the upper part. 
     As illustrated at the upper part of  FIG. 4 , the hybrid vehicle  1  accelerates at the second speed that is the starting gear number (a period T 1 ). After the acceleration has reached the limited acceleration of the second speed, the acceleration is regulated along the limited acceleration only while the acceleration reaches the limited acceleration of the second speed (a period T 2 ). When the gear shifting is performed at that time (a period T 3 ), the gear number is shifted into neutral and the torque of the engine  10  is temporarily reduced. After the gear shifting has been completed, the torque of the engine  10  returns and the vehicle accelerates to the limited acceleration of the third speed. 
     After the hybrid vehicle  1  has continued running at the limited acceleration of the third speed and the vehicle speed further has increased (a period T 4 ), the gear shifting is performed again (a period T 5 ). When the gear shifting is performed at that time (the period T 5 ), the gear number is shifted into neutral and the torque of the engine  10  is temporarily reduced. After the gear shifting has been completed, the torque of the engine  10  returns and the vehicle accelerates to the limited acceleration of the fourth speed. After that, the hybrid vehicle  1  runs at the limited acceleration of the fourth speed (a period T 6 ). 
       FIG. 5  enlarges the torque of the engine  10  in detail when the gear shifting is performed in  FIG. 4  (the period T 3  or the period T 5 ).  FIG. 5  illustrates a request torque tr 1  by the driver, a limited torque tr 2  by the output limitation control, a target torque tr 3 , a limited torque at gear shifting tr 4 , and an actual torque tr 5  of the engine  10 , and a normal torque at gear shifting tr 6  as a comparison example.  FIG. 5  further illustrates an assisting region A (shaded region) in which the electric motor  13  assists the engine  10 , an unstable region D of the engine torque, and a return rate r. 
     Note that a knocking possibly occurs at the unstable region D of the engine torque depending on the characteristics of the engine  10 . Thus, the engine torque preferably comes out of the unstable region D as soon as possible. 
     When the output limitation is not performed, the torque of the engine  10  starts to return to the required torque tr 1  as illustrated with the normal torque at gear shifting tr 6  because the required torque tr 1  is equal to the target torque. On the other hand, when the output limitation is performed, the torque of the engine  10  starts to return to the target torque tr 3  that has been set according to the limited acceleration. When the accelerator is depressed for a rapid acceleration, the target torque tr 3  becomes smaller than the required torque tr 1  according to the acceleration control as illustrated in  FIG. 5 . 
     As described above, when the target torque tr 3  becomes smaller than the required torque tr 1 , the difference between the actual torque and the target torque becomes smaller in comparison with the case in which the output limitation is not performed. Thus, a P (proportion) I (integration) control according to the difference is performed, so that the rate until the return is completed becomes small. As a result, the feeling of acceleration decreases and the drivability is aggravated. Accordingly, it takes more time until the torque returns to the target torque in comparison with the case in which the output limitation is not performed. Thus, the time when the actual torque is in the unstable region D of the engine torque becomes long, so that the engine becomes unstable. As described above, the rise of the torque of the engine  10  becomes slower in comparison with the case without limitation so that the actual torque tr 5  of the engine cannot reach the target torque tr 3  within the return rate r. 
     In light of the foregoing, for example, the transmission control unit  31  causes the electric motor  13  to assist the engine  10  in order to enable the torque to return to the target torque in the same time as in the case in which the output limitation is not performed. 
     Here, on the assumption that a T is the actual torque of the engine  10 , a TI is the proportion torque, a TP is the integration torque, a Tref is the target torque, a ΔT is the difference between the target torque and the actual torque, and an I is the gain in the proportion control,
 
 T=TI+TP   (1)
 
 TI=ΔT·I   (2)
 
Δ T=Tref −T   (3)
 
can be expressed. The actual torque T is PI-controlled as shown in the expression (1). The TI is obtained by multiplying the difference ΔT between the actual torque T and the target torque (the expression 3) by the I gain as shown in the (expression 2). Then, the I gain is set as a large value at the timing when the actual torque T returns to the target torque Tref. As a result, to obtain a desired T, the torque of the electric motor  13  is added to the torque of the engine  10  and the electric motor  13  assists the engine  10 . Further, when the gear number is shifted into neutral at that time, the gain I is changed. After that, when the fact that the gear shifting has been completed is notified from the transmission  16 , the gain I returns to the original. As an example of the variations in the gain I, the gain I when the torque returns from neutral is ten times as much as the gain I when the gear shifting is completed.
 
     This enables the torque to reach the target torque tr 3  in the period of the return rate r as described with the limited torque at gear shifting tr 4  even when the output limitation is performed. At that time, the region in which the electric motor  13  assists the engine  10  corresponds to the assisting region A. Note that increasing the torque of the engine  10  also enables the actual torque tr 5  of the engine to reach the target torque tr 3  in the period of the return rate r. As described above, applying the control only by the engine  10  enables the present control to be applied to a vehicle other than a hybrid vehicle. Such a control only by the engine  10  is preferably not applied in the present embodiment because the control is performed for the hybrid vehicle  1  and the control only by the engine  10  causes poor fuel efficiency. 
     (Effect) 
     In the hybrid vehicle  1 , when the gear shifting is performed while the output limitation control unit  30  performs the output limitation, the output limitation is temporarily cancelled during the process for returning the torque that has been reduced in neutral. Further, the assistance is controlled in order to add the torque by the electric motor  13  to the torque of the engine  10 . Thus, the drivability when the gear shifting is performed can be improved. 
     (Other Embodiments) 
     The above-mentioned return rate r can variably be set according to the gross weight of the hybrid vehicle  1  or the degree of the upgrade surface on which the hybrid vehicle  1  runs. For example, when the clutch  12  is temporarily disengaged and the gear position is shifted into neutral for gear shifting while the gross weight of the hybrid vehicle  1  is large, or while the upgrade surface on which the hybrid vehicle  1  runs is steep, the amount of the deceleration is larger in comparison with the case when the gross weight of the hybrid vehicle  1  is small, or when the surface on which the hybrid vehicle  1  runs is flat. In light of the foregoing, the return rate r is shortened when the gross weight of the hybrid vehicle  1  is large, or when the upgrade surface on which the hybrid vehicle  1  runs is steep in comparison with the case when the gross weight of the hybrid vehicle  1  is small, or when the surface on which the hybrid vehicle  1  runs is flat. This causes the rise of the torque to be rapid after the clutch  12  has been engaged again after the gear number has been changed, so that the feeling of decreasing speed with the gear shifting can be reduced. 
     To change the return rate r, it is preferable that a threshold is provided to the gross weight of the hybrid vehicle  1  or to the upgrade surface on which the hybrid vehicle  1  runs and the return rate r is shortened when the gross weight or the upgrade surface exceeds the threshold. Note that it is preferable to monitor both of the gross weight of the hybrid vehicle  1  and the upgrade surface on which the hybrid vehicle  1  runs and change the return rate r when one of the gross weight and the upgrade exceeds the threshold. Alternatively, both of the gross weight of the hybrid vehicle  1  and the upgrade surface on which the hybrid vehicle  1  runs are monitored, and the return rate r can be changed in two stages when one of the gross weight and the upgrade surface exceeds the threshold and when both of the gross weight and the upgrade surface exceed the thresholds. It is preferable in that case that the return rate r when both of the gross weight of the hybrid vehicle  1  and the upgrade surface on which the hybrid vehicle  1  runs exceed the thresholds is further shorter than the return rate r when one of the gross weight and the upgrade exceeds the threshold. 
     Further, although the engine  10  has been described as an internal combustion engine, the engine  10  can also be a heat engine including an external combustion engine. 
     While the computer program executed by the hybrid ECU  18  is installed on the hybrid ECU  18  in advance in the description above, the computer program can be installed on the hybrid ECU  18  as a computer by attaching removable media recording the computer program (storing the computer program), for example, to a drive (not shown in the drawings) and storing the computer program read from the removable media in a non-volatile memory inside the hybrid ECU  18 , or receiving, by a communication unit (not shown in the drawings), a computer program transmitted through a wired or wireless transmission medium and storing the computer program in a non-volatile memory inside the hybrid ECU  18 . 
     Further, each ECU can be implemented by an ECU combining each of the ECUs. Alternatively, an ECU can newly be provided by the subdivision of the function of each ECU. 
     Note that the computer program executed by the computer can be for performing the process in chronological order according to the order described herein or can be for performing the process in parallel or at the necessary timing, for example, when the computer program is invoked. 
     Further, the embodiments of the present invention are not limited to the above-mentioned embodiments, and can be variously modified without departing from the gist of the invention.