Hybrid vehicle control method and device

Abstract

Provided is a hybrid vehicle control device for suppressing a temporary increase / decrease in maximum system torque in a travel mode transition process, thus resolving a jerky feeling.　A vehicle ECU 201 of a hybrid vehicle comprises: a setting unit 210 for setting, as the maximum value of drive-use battery output from a battery 110, a first upper limit battery power for which a discharge time exceeds a predetermined length of time, and a second upper limit battery power for which a discharge time is equal to or less than the predetermined length of time and which is greater than the first upper limit battery power; an alleviation power calculation unit 211 for calculating alleviation power for causing the maximum value of the drive battery output to increase in the direction from the first upper limit battery power to the second upper limit battery power in a travel mode for traveling by using an engine as a power source; and a maximum motor drive shaft torque calculation unit 212 for suppressing a temporary increase / decrease in maximum motor drive shaft torque in a travel mode transition process by using the alleviation power to change the maximum value of the drive battery output between the first upper limit battery power and the second upper limit battery power.

Description

Hybrid vehicle control method and device

[0001] The present invention relates to a control technology for a hybrid vehicle having a parallel driving mode and a series driving mode.

[0002] Generally, hybrid vehicles are equipped with a motor (electric motor), a generator (electric power generator), and an engine (internal combustion engine), and a driving mode such as series driving mode, parallel driving mode, or EV mode is selected as appropriate depending on the driving situation. In series driving mode, the motor is used as the power source for driving the vehicle, and the engine is used as the power source for the generator. In parallel driving mode, the motor and the engine are used as the power sources for driving the vehicle. Patent Document 1 discloses an example of a control technique for the engine and generator in parallel driving mode. Furthermore, Patent Document 2 discloses a control technique for a hybrid vehicle equipped with an engine clutch and a motor clutch, and when it is determined that motor assistance is necessary in parallel driving, the driving force is assisted by power running of the generator until the motor clutch is engaged.

[0003] JP 2023-093777 A Patent No. 7010391 A

[0004] When the accelerator pedal is depressed to about WOT (Wide Open Throttle) during steady-state driving in engine-only parallel driving mode, the control device engages the motor clutch to connect the motor to the drive shaft, and releases the engine clutch to switch to series driving mode, thereby increasing the engine speed, ensuring sufficient power generation by the generator and increasing drive shaft torque in response to the driver's request.

[0005] When the motor clutch is engaged in parallel driving mode, the system transitions to clutch disengagement mode, in which the engine clutch is disengaged. When clutch disengagement mode begins, the maximum battery power (battery upper limit power) supplied to the motor is increased from the maximum long-term dischargeable power (long-term SOP (State of Power)) to the short-term SOP. The long-term SOP is the maximum power applied when discharging for a period longer than a predetermined time, while the short-term SOP is applied when discharging for a period shorter than a predetermined time and is a maximum power greater than the long-term SOP. Therefore, the long-term SOP is applied in parallel driving mode, which is mainly selected for steady-state driving, and the short-term SOP is applied in series driving mode, which requires a good acceleration response.

[0006] However, when the battery upper limit power increases from the long-time SOP to the short-time SOP during a transition from parallel driving mode to clutch disengagement mode, the maximum drive shaft torque generated by the motor increases in a step-like manner. Furthermore, when the engine speed increases during a transition from clutch disengagement mode to series driving mode, the required power generation temporarily decreases. As a result, the system maximum torque, which is the sum of the maximum engine drive shaft torque and the maximum motor drive shaft torque, increases during a transition from parallel driving mode to clutch disengagement mode and decreases during a transition to series driving mode. This temporary increase or decrease in the system maximum torque during a transition between driving modes can be perceived as a sense of pressure if the user's required torque exceeds the system limit, degrading the driving feel. In particular, if the transition from parallel driving mode to clutch disengagement mode takes a long time due to the motor clutch being engaged or disengaged, the time spent in parallel driving mode, which uses the long-time SOP, becomes relatively longer, making fluctuations in the system maximum torque more noticeable.

[0007] The present invention has been devised in consideration of the above circumstances, and an object of the present invention is to provide a control method and device for a hybrid vehicle that can suppress temporary increases and decreases in system maximum torque during the driving mode transition process, thereby eliminating the feeling of being pushed forward.

[0008] According to one embodiment of the present invention, there is provided a control device for a hybrid vehicle having a motor, a generator, an engine, and a battery that exchanges electric power between the motor and the generator, and having a plurality of driving modes including a parallel driving mode in which the motor and the engine are used as a power source for driving the vehicle, and a series driving mode in which the motor is used as a power source for driving the vehicle and the engine is used as a power source for the generator, the control device comprising: a setting unit that sets, as a maximum value of drive battery output from the battery, a first battery upper limit power when the discharge time exceeds a predetermined time, and a second battery upper limit power that is greater than the first battery upper limit power for a discharge time equal to or less than the predetermined time; a relaxation power calculation unit that calculates a relaxation power that increases the maximum value of the drive battery output from the battery from the first battery upper limit power to the second battery upper limit power in the driving mode in which the vehicle is driven using the engine as a power source; and a maximum motor drive shaft torque calculation unit that suppresses temporary increases and decreases in maximum motor drive shaft torque during a driving mode transition process by using the relaxation power to change the maximum value of the drive battery output between the first battery upper limit power and the second battery upper limit power. According to one embodiment of the present invention, in the parallel traveling mode from the start of the traveling mode transition process until the ratio of the engine output to the system maximum torque is reduced, the first relaxation power may be set according to the following formula: First relaxation power = (second battery upper limit power) - (first battery upper limit power) - (rotation synchronization upper limit power). According to one embodiment of the present invention, from the start of the reduction in the ratio of the engine output to the system maximum torque during the traveling mode transition process, the second relaxation power may be set according to the following formula: Second relaxation power = (first relaxation power) + (target generated power) - (generator requested generated power). Furthermore, according to one embodiment of the present invention, the mitigation power can be set using the following formulas: mitigation power = (rotational synchronization output margin) + (required generated power reduction); rotational synchronization output margin = max {0 kW, (second battery upper limit power) - (first battery upper limit power) - (rotational synchronization upper limit output)}; required generated power reduction = max {0 kW, (target generated power) - (generator required generated power)}.According to another embodiment of the present invention, the first relaxation power may be set in the parallel traveling mode in which the motor clutch between the motor and the drive shaft is disengaged from the start of the traveling mode transition process. According to another embodiment of the present invention, the second relaxation power may be set after the motor clutch is engaged and the engine clutch between the engine and the drive shaft begins to be disengaged. According to another embodiment of the present invention, the control unit may start relaxation control of the maximum value of the traction battery output using the relaxation power when it is predicted that the user requested output will exceed the system maximum torque. Furthermore, according to one embodiment of the present invention, there is provided a control method for a hybrid vehicle having a motor, a generator, an engine, and a battery that exchanges electric power between the motor and the generator, and having a plurality of driving modes including a parallel driving mode in which the motor and the engine are used as a power source for driving the vehicle, and a series driving mode in which the motor is used as a power source for driving the vehicle and the engine is used as a power source for the generator, wherein a control device of the hybrid vehicle sets, as maximum values ​​of drive battery output from the battery, a first battery upper limit power when the discharge time exceeds a predetermined time, and a second battery upper limit power that is greater than the first battery upper limit power for a discharge time equal to or less than the predetermined time, and in a driving mode in which the hybrid vehicle runs using the engine as a power source, calculates a relaxation power that increases the maximum value of the drive battery output from the first battery upper limit power toward the second battery upper limit power, and changes the maximum value of the drive battery output between the first battery upper limit power and the second battery upper limit power using the relaxation power, thereby suppressing temporary increases and decreases in maximum motor drive shaft torque during a driving mode transition process.

[0009] According to one embodiment of the present invention, by increasing the maximum value of the traction battery output toward the second battery upper limit power by the relaxation power, it is possible to suppress temporary increases and decreases in the system maximum torque during the traveling mode transition process. Furthermore, according to one embodiment of the present invention, it is possible to calculate the relaxation power in the parallel traveling mode before the engine output ratio is reduced. Furthermore, according to one embodiment of the present invention, it is possible to calculate the relaxation power after the engine output ratio is reduced. Furthermore, according to one embodiment of the present invention, it is possible to calculate the relaxation power regardless of the traveling mode switching. Furthermore, according to one embodiment of the present invention, it is possible to set the first relaxation power and the second relaxation power during the motor clutch engagement process and the engine clutch release process.

[0010] 7A is a block diagram illustrating a schematic configuration of a drive system in a hybrid vehicle according to an embodiment of the present invention; FIG. 7B is a block diagram illustrating a schematic configuration of a control system in a hybrid vehicle according to an embodiment of the present invention; FIG. 7C is a schematic time chart illustrating a breakdown of torque fluctuations in a hybrid vehicle according to an embodiment of the present invention; FIG. 7D is a schematic time chart illustrating a breakdown of torque fluctuations in the background art for comparison with the present embodiment; FIG. 7E is a schematic time chart illustrating fluctuations in maximum motor drive shaft torque in FIGS. 3 and 4; FIG. 7F is a block configuration diagram illustrating a calculation process of relaxation power in a control system of a hybrid vehicle according to the present embodiment; FIG. 7G is a time chart illustrating a portion of the operation of a hybrid vehicle according to an embodiment of the present invention; FIG. 7H is a time chart illustrating another portion of the operation of the hybrid vehicle shown in FIG.

[0011] 1. Vehicle Configuration An example of the configuration and control system of a hybrid vehicle (hereinafter also simply referred to as "vehicle") according to an embodiment of the present invention will be described with reference to FIGS.

[0012] 1, a hybrid vehicle 100 according to one embodiment of the present invention has an engine 101, a motor 102, and a generator 103, which are interconnected with a drive shaft 105 and drive wheels 106 by a power transmission mechanism 104. The power transmission mechanism 104 is made up of an engine clutch 107, a motor clutch 108, a differential gear 109, and other gear mechanisms, and may be a transaxle that integrates these. Note that the engine clutch 107 may be included in a transmission (not shown).

[0013] The engine 101 is an internal combustion engine that uses gasoline or diesel as fuel. The crankshaft of the engine 101 is gear-coupled to the shaft of the generator 103 and to the engine clutch 107. As a result, the torque of the engine 101 is transmitted to the generator 103, and the torque of the generator 103 is transmitted to the engine 102 and the engine clutch 107. By engaging the engine clutch 107, the torque of the engine 101 or the generator 103 can be transmitted to the drive shaft 105. Furthermore, by disengaging the engine clutch 107, the engine 101 can be used exclusively for generating electricity for the generator 103.

[0014] The motor 102 is connected to a differential gear 109 via a motor clutch 108, and the torque of the motor 102 is transmitted to a drive shaft 105. As is well known, the motor 102 functions as a generator during regeneration, and the generator 103 can function as a motor during power running.

[0015] Furthermore, the hybrid vehicle 100 includes a battery 110, a control unit 200 (control device), various operation amount sensors such as an accelerator opening sensor (not shown), a vehicle speed sensor that detects the traveling speed V, and various sensors that detect the engine rotation speed, axle rotation speed, motor rotation speed, etc. The control unit 200 controls the engine 101, the motor 102, the generator 103, the engine clutch 107, and the motor clutch 108, and executes various controls including the traveling control according to this embodiment, which will be described later.

[0016] If hybrid vehicle 100 is a plug-in hybrid (PHEV) type, battery 110 may be charged by an external charging unit (not shown) supplied with power from a commercial household power source or a rapid charging power source at a charging station, or an external power supply unit (not shown) may be provided to supply power from battery 110 to home appliances, etc. The control system will now be described with reference to FIG.

[0017] 2, the control unit 200 includes a vehicle ECU (Electronic Control Unit) 201, an MCU (Motor Control Unit) 202, an engine (ENG) ECU 203, a transmission ECU 204, a GCU (Generator Control Unit) 205, a BMU (Battery Control Unit) 206, and other control units. The vehicle ECU 201 is connected to the MCU 201, the engine ECU 203, the transmission ECU 204, the GCU 205, and the BMU 202, and realizes the control function according to this embodiment.

[0018] Here, it is assumed that the vehicle ECU 201 realizes the functions of a setting unit 210, a relaxation power calculation unit 211, a maximum motor drive shaft torque calculation unit 212, a maximum engine drive shaft torque calculation unit 213, and a system maximum torque calculation unit 214. The setting unit 210 sets a long-term SOP (first battery upper limit power), a short-term SOP (second battery upper limit power), and other data described below, and outputs them to the relaxation power calculation unit 211. As described below, the long-term SOP is a relatively small upper limit battery power that is longer than a predetermined time, and is applied to the parallel running mode. The short-term SOP is a battery upper limit power that is shorter than a predetermined time but greater than the long-term SOP, and is applied to the series running mode and the clutch release mode. Application of the short-term SOP can improve acceleration response.

[0019] As described below, the relaxation power calculation unit 211 calculates the relaxation power to be added to the long-term SOP and outputs it to the maximum motor drive shaft torque calculation unit 212. The maximum motor drive shaft torque calculation unit 212 adds the relaxation power to the long-term SOP and then adds the required power generation to calculate the maximum motor drive shaft torque. The maximum engine drive shaft torque calculation unit 213 calculates the maximum engine drive shaft torque. The system maximum torque calculation unit 214 adds the calculated maximum motor drive shaft torque and maximum engine drive shaft torque to calculate the system maximum torque. According to this embodiment, by changing the magnitude of the relaxation power to be added from the long-term SOP to the short-term SOP, the maximum motor drive shaft torque can be smoothly changed from the start of the clutch release mode, thereby preventing temporary increases and decreases in the system maximum torque. The control operation according to this embodiment will be described in detail below.

[0020] 2. Control Operation The control method according to this embodiment will be described in detail below with reference to Figures 3 to 6. Figure 3 illustrates a sequence according to this embodiment, and Figure 4 illustrates a sequence according to the background art for comparison. These sequences show a driving mode transition process in which the vehicle transitions from parallel driving mode to series driving mode via clutch release mode. This driving mode transition process begins when the vehicle transitions to a driving mode in which the vehicle runs using the engine as a power source. However, it may also begin at time t0 when the accelerator is depressed to approximately wide open throttle (WOT) during parallel driving with the motor clutch disengaged.

[0021] 3 and 4, the maximum system torque T ＳＹＳ＿ＭＡＸ is the maximum engine drive shaft torque T ＥＮＧ＿ＭＡＸ and maximum motor drive shaft torque T ＭＯＴ＿ＭＡＸ That is, T ＳＹＳ＿ＭＡＸ =T ＥＮＧ＿ＭＡＸ +T ＭＯＴ＿ＭＡＸ is.

[0022] Here, the maximum engine drive shaft torque T ＥＮＧ＿ＭＡＸ Is T ＥＮＧ＿ＭＡＸ = Maximum possible torque (MMAX) x reduction ratio x engine output ratio Maximum motor drive shaft torque T ＭＯＴ＿ＭＡＸIs T ＭＯＴ＿ＭＡＸ = (Upper limit battery power + Required power generation - Auxiliary power consumption - Loss power) x Axle angular velocity Therefore, the maximum motor drive shaft torque T ＭＯＴ＿ＭＡＸ increases or decreases depending on the battery power limit and the required power generation.

[0023] The battery upper limit power is the upper limit of the dischargeable power of the battery 110, and in the parallel running mode, a long-term SOP is used, while in the series running mode and the clutch release mode, a short-term SOP is used to improve acceleration response during power generation increase.

[0024] The required power generation steadily coincides with the target power generation. The target power generation at WOT is 0 kW in parallel running mode, and is the vehicle drive power (plus battery charging) in series running mode. In clutch release mode, the target power generation is a value obtained by interpolating the value in parallel running mode and the value in series running mode according to the engine output ratio. However, this value temporarily decreases during power assist by generator 103 (from time t1 to t2 in FIG. 3) and while engine speed Ne is increasing in series running mode (after time t3 in FIG. 3). In addition, an increase in the target power generation may result in a power generation shortage relative to the required power generation.

[0025] According to this embodiment, the temporary decrease or shortage of the required generated power is compensated for by the relaxation power, and the generated power is increased so as to compensate for the decrease in the maximum engine drive shaft torque (decrease in the engine output rate) in the clutch release mode. In other words, the difference between the target generated power and the required generated power is offset by raising the battery upper limit power by the relaxation power, and the target generated power is increased in accordance with the rate of decrease in the engine output. As a result, the maximum motor drive shaft torque T ＭＯＴ＿ＭＡＸ In this way, the system maximum torque T ＳＹＳ＿ＭＡＸ This eliminates the temporary increase or decrease in torque, enabling a smooth transition from parallel to series driving even when the user-requested torque exceeds the system's limited torque.

[0026] According to the background art shown in FIG. 4, the battery upper limit power is increased in a stepwise manner from the long-time SOP to the short-time SOP at time t1, and the maximum motor drive shaft torque TＭＯＴ＿ＭＡＸ 4. Furthermore, the maximum motor drive shaft torque T ＭＯＴ＿ＭＡＸ As a result, the maximum system torque T ＳＹＳ＿ＭＡＸ changes as shown by reference numeral 20 throughout the driving mode transition process, and particularly increases and decreases significantly at time t1 and immediately thereafter at reference numeral 21, and at time t3 after reference numeral 22, causing a so-called pushing sensation.

[0027] In contrast, according to this embodiment, as shown in FIG. 3, the relaxation power PWR is applied to the long-term SOP 301 through the process of transitioning the traveling mode from the parallel traveling mode to the series traveling mode. ＢＳＴ is added. Below, the mitigation power PWR to the long-term SOP301 ＢＳＴ The "addition" will be referred to as "relaxation to the short-term SOP side" as appropriate.

[0028] <Relaxed Power> FIG. 5 illustrates a comparison between the background art and this embodiment regarding the maximum motor drive shaft torque. ＢＳＴ is set between the difference between the long-term SOP and the short-term SOP as follows: From time t0 to time t1 in parallel driving mode, the relaxation value PWR Ｂ (302); Between time t1 and time t2 when the clutch release mode is entered, the relaxation value PWR is set to 11 (302A); Between time t2 and time t3, the relaxation value PWR is set to 11 (302B). Ｂ (302B); After time t3 when the mode is changed to the series traveling mode, the required generated power is increased to compensate for the decrease 12 in the required generated power while the engine speed Ne is increasing (302C).

[0029] As will be described later, even if an increase in the target power generation power causes a power generation shortage between the target power generation power and the required power generation power, the mitigation power PWR is set to compensate for the power generation shortage. ＢＳＴ Increase.

[0030] As shown in FIG. 6, the relaxation power calculation unit 211 calculates the relaxation power PWR, which changes from time t0 in the parallel running mode to the series running mode. ＢＳＴ is calculated using the following formula: Mitigation power PWR ＢＳＴ = rotation-synchronized output margin PWR ＭＲＧ + Required power generation reduction amount PWR ｄＧＥＮ

[0031] Here, the rotation-synchronized output margin PWR ＭＲＧ is PWR ＭＲＧ =max{0 kW, short-time SOP-long-time SOP-rotation synchronization upper limit output}.

[0032] Here, the rotation synchronization upper limit output is the upper limit value of the power used for rotation synchronization when the motor clutch is connected or disconnected, and is set to a fixed value smaller than the difference between the short-term SOP and the long-term SOP. ＭＲＧ (= Short-time SOP - Long-time SOP - Rotation synchronous upper limit output) is the relaxation power PWR ＢＳＴ If a motor clutch is not provided, the power can be set based on the power for adjusting the rotation speed required to increase the engine rotation speed Ne in the series running mode.

[0033] Also, the required power generation reduction amount PWR ｄＧＥＮ is PWR ｄＧＥＮ = max {0 kW, target generated power - generator required generated power}, and target generated power = engine required power output - generator loss power.

[0034] The mitigation power PWR for the long-term SOP described above ＢＳＴ (= rotation-synchronized output margin PWR ＭＲＧ + Required power generation reduction amount PWR ｄＧＥＮ ) is distributed as follows through the parallel driving mode, clutch release mode and series driving mode:

[0035]

[0036] As mentioned above, the mitigation power PWR ＢＳＴBy varying the SOP to relax the SOP for a long time, it is possible to prevent an increase or decrease in the system maximum torque that limits the required drive shaft torque during mode transition, thereby eliminating the push-out feeling that previously occurred.

[0037] 3. Example Hereinafter, the operation of a hybrid vehicle to which a control method according to one example of the present invention is applied will be described with reference to operations (a) to (k) in FIGS. 7A and 7B.

[0038] First, it is assumed that the vehicle is running steadily in parallel running mode (PR) with the motor clutch 108 in a disengaged state (b). During this parallel running, when the accelerator opening AP increases beyond a predetermined value at time t0 and exceeds the system maximum torque (a), the control unit 200 turns off the request to disengage the motor clutch 108 (disengagement prohibited) (c) and starts rotation synchronization of the motor clutch 108 (e). As described above, the control unit 200 calculates the rotation synchronization output margin PWR ＭＲＧ (= Short-time SOP - Long-time SOP - Rotation synchronous upper limit output) is the relaxation power PWR ＢＳＴ , the upper battery power limit can be increased (i) and the maximum motor drive shaft torque can be increased (j).

[0039] When rotation synchronization is completed at time t1, the control unit 200 connects the motor clutch 108 (d) and transitions to a clutch release mode (CLO) (b). In the clutch release mode, the engine 101 output rate and the generator 103 assist rate each decrease from 1 to 0 over a predetermined time period in order to release the engine clutch 107 (g). Here, it is assumed that the generator assist rate becomes 0 between time t1 and time t2.

[0040] As the output rate of engine 101 decreases, the target generated power increases to the target value for series running mode (SR) (h), and together with the engine output rate, maximum engine drive shaft torque 401 decreases to 0 [Nm] (k).

[0041] Furthermore, the generator 103 shifts from power assist to power generation in response to the decrease in the assist rate, and the required power generation begins to increase from time t2 (h). However, there is a period during which the required power generation falls below the target power generation, and the power generation decrease is indicated by the shaded area. Specifically, when the engine 101 reaches the maximum engine output (actual rotation speed Ne) at the maximum possible torque MMAX, the required power generation cannot be generated any more. Therefore, an increase in the target power generation creates a power generation shortage between the target power generation and the required power generation. According to this embodiment, the control unit 200 adjusts the relaxation power PWR to compensate for the power generation shortage. ＢＳＴ is increased by increments 302A, 302B (i).

[0042] Furthermore, when the mode transitions to the series running mode after time t3, the target Ne of the engine 101 increases, causing a difference with the actual Ne, and the required power generation is reduced by adjusting the rotation of the generator 103, resulting in a power generation shortage. According to this embodiment, the control unit 200 adjusts the relaxation power PWR to compensate for the power generation shortage. ＢＳＴ by increment 302C (i).

[0043] In this way, by relaxing the upper battery power limit from the long-time SOP to the short-time SOP by using the relaxation power, the maximum motor drive shaft torque increases accordingly. Therefore, the system maximum torque 407 added to the maximum engine drive shaft torque 401 forms a smooth curve without temporary fluctuations, eliminating the push-up sensation that occurs with the conventional maximum motor drive shaft torque 13 and required drive shaft torque 20.

[0044] The vehicle ECU 201 of the control unit 200 includes a processor such as a CPU (Central Processing Unit), a ROM (Read-only memory) that stores control programs executed by the processor, a RAM (Random access memory) as an operating area for the control programs, an interface with peripheral circuits, etc. The control method according to this embodiment can be implemented by executing a program on the processor of the vehicle ECU 201.

[0045] REFERENCE SIGNS LIST 100 Hybrid vehicle 101 Engine 102 Motor 103 Generator 104 Power transmission mechanism 105 Drive shaft 106 Drive wheels 107 Engine clutch 108 Motor clutch 109 Differential gear 110 Battery 200 Control unit 201 Vehicle ECU 210 Setting unit 211 Relaxation power calculation unit 212 Maximum motor drive shaft torque calculation unit

Claims

1. A control device for a hybrid vehicle having a motor, a generator, an engine, and a battery that supplies and receives power between the motor and the generator, and having multiple driving modes including a parallel driving mode in which the motor and the engine are used as power sources for driving the vehicle, and a series driving mode in which the motor is used as the power source for driving the vehicle and the engine is used as a power source for the generator, the control device comprising: a setting unit that sets, as the maximum value of drive battery output from the battery, a first battery upper limit power when the discharge time exceeds a predetermined time, and a second battery upper limit power that is greater than the first battery upper limit power for a discharge time equal to or less than the predetermined time; a relaxation power calculation unit that calculates a relaxation power that increases the maximum value of drive battery output from the battery from the first battery upper limit power to the second battery upper limit power in a driving mode in which the vehicle is driven using the engine as a power source; and a maximum motor drive shaft torque calculation unit that suppresses temporary increases and decreases in maximum motor drive shaft torque during the driving mode transition process by using the relaxation power to change the maximum value of drive battery output between the first battery upper limit power and the second battery upper limit power.

2. The control device for a hybrid vehicle according to claim 1, wherein in the parallel driving mode from the start of the driving mode transition process until the ratio of engine output to the system maximum torque is reduced, the first relaxation power is set by the following formula: First relaxation power = (Second battery upper limit power) - (First battery upper limit power) - (Rotation synchronization upper limit output).

3. The control device for a hybrid vehicle as described in claim 2, characterized in that, from the start of the decrease in the ratio of engine output to the system maximum torque during the driving mode transition process, the second relaxation power is set using the following formula: second relaxation power = (first relaxation power) + (target generated power) - (generator requested generated power).

4. The control device for a hybrid vehicle according to claim 1, characterized in that the relaxation power is set using the following formulas: Relaxation power = (rotation-synchronized output margin) + (required power generation reduction amount); rotation-synchronized output margin = max {0 kW, (second battery upper limit power) - (first battery upper limit power) - (rotation-synchronized upper limit output)}; required power generation reduction amount = max {0 kW, (target power generation) - (generator-required power generation)}.

5. The control device for a hybrid vehicle according to claim 2, wherein the first relaxation power is set in the parallel running mode in which the motor clutch between the motor and the drive shaft is in a disengaged state from the start of the running mode transition process.

6. The control device for a hybrid vehicle according to claim 3, wherein the second relaxation power is set after the motor clutch is connected and the engine clutch between the engine and the drive shaft starts to be released.

7. A control device for a hybrid vehicle described in any one of claims 1 to 6, characterized in that the control unit starts mitigation control of the maximum value of the drive battery output using the mitigation power when it is predicted that the user requested output will exceed the system maximum torque.

8. A control method for a hybrid vehicle comprising a motor, a generator, an engine, and a battery that supplies and receives power between the motor and the generator, and having multiple driving modes including a parallel driving mode in which the motor and the engine are used as power sources for driving the vehicle, and a series driving mode in which the motor is used as the power source for driving the vehicle and the engine is used as the power source for the generator, wherein the control device of the hybrid vehicle: sets, as the maximum value of drive battery output from the battery, a first battery upper limit power when the discharge time exceeds a predetermined time, and a second battery upper limit power that is greater than the first battery upper limit power for a discharge time equal to or less than the predetermined time; calculates a relaxation power that increases the maximum value of drive battery output from the battery from the first battery upper limit power toward the second battery upper limit power in the driving mode in which the vehicle runs using the engine as a power source; and suppresses temporary increases and decreases in maximum motor drive shaft torque during the driving mode transition process by changing the maximum value of drive battery output between the first battery upper limit power and the second battery upper limit power using the relaxation power.

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