Clutch control device for hybrid vehicle

Abstract

A hybrid vehicle clutch control device includes an engine, a motor generator, a first clutch, a second clutch and at least one controller. The first clutch interrupts a torque transmission between the engine and the motor generator. The second clutch interrupts the torque transmission between the motor generator and driving wheels. The controller starts the engine using torque from the motor generator, when switching from an electric vehicle mode to a hybrid mode. When starting the engine accompanying an accelerator depression, the allocation of the transmission torque capacity of the second clutch is increased when the accelerator position opening amount is equal to or less than a predetermined accelerator position opening amount, as compared to when exceeding the predetermined accelerator position opening amount.

Description

This application is a U.S. National stage application of International Application No. PCT/JP2014/059797, filed Apr. 3, 2014, which claims priority to Japanese Patent Application No. 2013-093218 filed in Japan on Apr. 26, 2013.

BACKGROUND

Field of the Invention

The present invention relates to a clutch control device for a hybrid vehicle.

Background Information

Conventionally, a hybrid vehicle comprising a first clutch for interrupting the torque transmission between the engine and the motor generator and a second clutch for interrupting the torque transmission between the motor generator and the driving wheel is known. Japanese Laid-Open Patent Application No. 2009-227277 discloses a technique for preventing motor torque from exceeding an upper limit torque by allocating a first clutch torque capacity, which is the cranking torque, and a second clutch torque capacity, which is the driving torque of the vehicle, within a range of the motor upper limit torque when an engine is started by connecting a first clutch after a driver steps on an accelerator. At this time, acceleration of the vehicle via an early engine start is achieved by increasing the allocation of the first clutch torque capacity as the accelerator depression speed of the driver increases.

SUMMARY

In the conventional technology described above, even when the accelerator position opening amount is small, if the accelerator depression speed is high, the allocation of the first clutch torque capacity is increased; as a result, there was the problem that the acceleration is stagnated and that the acceleration performance that is desired by the driver cannot be obtained immediately after depression until starting the engine has been completed.

An object of the present invention is to provide a clutch control device for a hybrid vehicle that can realize the acceleration performance that is desired by the driver.

In the present invention, when starting the engine following an accelerator being stepped on, the allocation of the transmission torque capacity command value of the second clutch is increased if the accelerator position opening amount is equal to or less than a predetermined accelerator position opening amount, as compared to when exceeding the predetermined accelerator position opening amount.

Therefore, when the required acceleration of the driver is small, a drive torque that matches the required acceleration can be generated immediately after depression by prioritizing the increase in the drive torque over the shortening of the engine start time, and an acceleration performance that is desired by the driver can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of this original disclosure.

FIG. 1 is a system view of the hybrid vehicle to which is applied the clutch control device of a first embodiment.

FIG. 2 is a flowchart illustrating the processing content of the integrated controller 13.

FIG. 3 is a drive torque command calculation map, according to the vehicle speed and the accelerator position opening amount.

FIG. 4 (a) shows the clutch torque capacity—via a clutch hydraulic pressure conversion map and FIG. 4 (b) shows the clutch hydraulic pressure—via a current conversion map.

FIG. 5 is a flowchart illustrating a method for setting the second clutch control mode.

FIG. 6 (a) shows the second clutch slip rotational speed target value calculation map, based on a basic second clutch torque capacity command value, and a second clutch oil temperature, and FIG. 6 (b) shows the second clutch slip rotational speed target value calculation map, based on an allocated motor torque for starting the engine.

FIG. 7 is a block view of a feedback control for the second clutch.

FIG. 8 is a flowchart illustrating the torque capacity command value calculation method for each clutch when starting the engine.

FIG. 9 is an engine start lower limit torque calculation map.

FIG. 10 is a motor upper limit torque calculation map.

FIG. 11 is a characteristic view of the second clutch torque capacity command correction value corresponding to the drive torque command value change rate.

FIG. 12 is a time chart showing when the engine is started by an abrupt operation of the accelerator during EV traveling, as well as when traveling while the depression amount is at a low opening amount (abrupt acceleration).

FIG. 13 is a time chart showing when the engine is started by an abrupt operation of the accelerator during EV traveling, as well as when traveling while the depression amount is at a high opening amount.

FIG. 14 is a time chart showing when the engine is started by an abrupt operation of the accelerator during EV traveling, as well as when traveling while the depression amount is at a medium opening amount.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be explained below, with reference to the appended drawings. The description below does not limit the technical scope or the meanings of the terms described in the Claims.

First Embodiment

FIG. 1 is a system view of the hybrid vehicle to which is applied the clutch control device of the first embodiment. The motor generator (hereinafter referred to as the motor) 1 is an AC synchronous motor, configured to drive the left and right driving wheels 21a, 21b via the drive torque control and to recover the vehicle kinetic energy for the high-voltage battery 9 via the regenerative braking control. The engine 2 is capable of lean combustion, and the engine torque is controlled to match the command value by controlling the intake air amount via a throttle actuator, the fuel injection amount via an injector, and the ignition timing via a spark plug. The first clutch 3 is a dry clutch, which performs the engagement/release between the engine 2 and the motor 1. When the first clutch 3 is in a full engagement state, the motor torque+the engine torque are transmitted to the second clutch 4; when in a released state, only the motor torque is transmitted to the second clutch 4. The second clutch 4 is a wet clutch, in which transmission torque (clutch torque capacity) is generated in accordance with the clutch hydraulic pressure (pressing force). The transmission torque of the second clutch 4 transmits the torque that is output from the motor 1 and the engine 2 (when the first clutch is engaged) to the left and right drive shafts 20a, 20b via the transmission 5 and the final gear 19.

The transmission 5 is a stepped transmission, configured from a plurality of planetary gears. Gear shifting is performed by changing the transmission path of the force by engaging/releasing each of the brake and the clutches inside of the transmission. The second clutch input shaft (motor) rotational speed sensor 6 detects the current input rotational speed of the second clutch 4. The second clutch output shaft rotational speed sensor 7 detects the current rotational speed of the output shaft of the second clutch 4. A high-voltage inverter (hereinafter referred to as an inverter) 8 generates a drive current of the motor 1 by performing DC-AC conversion. A high-voltage battery (hereinafter referred to as the battery) 9 accumulates the regenerative energy from the motor 1. An accelerator position sensor 10 detects the accelerator position opening amount. The engine rotational speed sensor 11 detects the current engine rotational speed. The clutch oil temperature sensor 12 detects the oil temperature of the second clutch 4.

The integrated controller 13 calculates the drive torque command value based on the battery state, the accelerator position opening amount, and the vehicle speed (a value that is synchronous with the transmission output shaft rotational speed). Based on the results thereof, the command value for each actuator (the motor 1, the engine 2, the first clutch 3, and the second clutch 4) is calculated and transmitted to each of the controllers 14-17. The integrated controller 13 (engine starting means) starts the engine 2 by utilizing the torque of the motor generator 1, when switching from an EV (electric vehicle) mode for cutting off the first clutch 3 and traveling with the torque of the motor generator 1, to an HEV (hybrid mode) for connecting the first clutch 3 and traveling with the torque of the engine 2 and the motor generator 1. The transmission controller 14 performs a shift control so as to achieve the gear changing command from the integrated controller 13. The clutch controller 15 controls the current of the solenoid valve so as to realize the clutch hydraulic pressure (current) command value, with respect to each clutch hydraulic pressure command value from the integrated controller 13. The engine controller 16 controls the engine torque so as to achieve the engine torque command value from the integrated controller 13. The motor controller 17 controls the motor torque so as to achieve the motor torque command value from the integrated controller 13. The battery controller 18 manages the charging state of the battery 9 and transmits the information thereof to the integrated controller 13. The communication between each of the controllers 13-18 is performed via a communication line 22.

Control of the Integrated Controller

FIG. 2 is a flowchart illustrating the processing content of the integrated controller 13. The processing content is assumed to have been executed in a set sampling cycle. In step S1, vehicle states measured by other controllers are received, such as the battery charging amount SOC, the shift position of the transmission 5, the input/output shaft rotational speed of the second clutch 4 ω_cl2i, ω₀, the engine rotational speed ω_e, the operating state of the engine E_sts, and the vehicle speed Vsp. In step S2, the accelerator position opening amount Apo is measured from the accelerator position sensor 10. In step S3 (drive torque command value calculation means), the drive torque command value T_d* is calculated from the accelerator position opening amount Apo and the vehicle speed Vsp. In the first embodiment, for example, a calculation is performed with reference to a drive torque command value calculation map, corresponding to the vehicle speed Vsp and the accelerator position opening amount Apo, such as illustrated in FIG. 3. In FIG. 3, the drive torque command value T_d* is set to be larger as the accelerator position opening amount Apo increases, and this value is set to be smaller as the vehicle speed Vsp increases.

In step S4, the first clutch control mode (setting of the first clutch mode flag fCL1) is set from the vehicle states, such as the battery charging amount SOC, the drive torque command value T_d*, and the vehicle speed Vsp. While the details have been omitted here, for example, in a traveling situation in which the efficiency of the engine 2 is relatively poor, such as when starting at a low acceleration, traveling is done by the motor alone (EV mode); therefore, the first clutch 3 is released (fCL1=0). In addition, EV traveling is difficult during rapid acceleration, when the battery charging amount SOC is equal to or less than a predetermined value SOC_th1 or when the vehicle speed Vsp is equal to or greater than a predetermined value Vsp_th1 (the motor rotational speed exceeds the allowable rotational speed); therefore, the first clutch 3 is engaged (fCL1=1) in order to travel with the engine 2 and the motor 1 (HEV mode). In step S5, the second clutch control mode CL2MODE (engage, release, slip) is set from vehicle states, such as the battery charging amount SOC, the drive torque command value T_d*, the first clutch control mode flag fCL1, and the vehicle speed Vsp. The method to set the second clutch control mode will be described below.

In step S6, the drive torque command value T_d* is allocated to a base engine torque command value T_{e base}* and a base motor torque command value T_{m base}*, based on the control mode of each clutch and the vehicle state. Various means can be conceived regarding the allocation method, but the details have been omitted. In step S7 (transmission torque capacity allocating means), the torque capacity command values T_{cl1 ENG START}, T_{cl2 ENG START} for each clutch when starting the engine are calculated based on the control mode of each clutch, the engine rotational speed ω_e, the drive torque command value T_d*, and various vehicle states. The calculation method will be described in detail below. In step S8, whether or not the engine is being started is determined based on the first clutch control mode flag fCL1, the second clutch input rotational speed ωC_l2i, and the engine rotational speed ω_e. In practice, when the first clutch control mode is the engaged mode, and when the engine rotational speed is lower than the second clutch input rotational speed, the engine is determined to be starting, and a starting flag fENG_ST is set; otherwise, the engine is determined to be not starting, and the flag is cleared. In step S9, whether or not a slip rotational speed control of the second clutch 4 should be executed is determined. When the second clutch 4 is set to the slip state in S5 and the absolute value of the actual slip rotational speed (input shaft-output shaft) becomes equal to or greater than a predetermined value, the slip rotational speed control is turned ON, and the operation proceeds to step S10; when set to release or engage, the rotational speed control is turned OFF, and the operation proceeds to step S14.

In step S10, the base second clutch torque capacity command value T_{cl2 base}* is calculated. Here, for example, the same value as the drive torque command value T_d* is assumed. In step S11, the input shaft rotational speed target value ω_cl2i* is calculated based on the first clutch control mode flag fCL1, the base second clutch torque capacity command value T_{cl2 base}*, the second clutch oil temperature Temp_cl2, the battery charging amount SOC, and the output shaft rotational speed measurement value ω₀. The calculation method will be described in detail below. In step S12, a motor torque command value for the rotational speed control T_{m FB ON} is calculated so that the input rotational speed target value ω_cl2i* and the input rotational speed measurement value ω_cl2i match. Various calculation (control) methods can be conceived; for example, the calculation can be done using the following formula (PI control). For the actual calculation, the calculation is done using a recurrence formula that is obtained by discretizing with the Tustin approximation or the like.

$\begin{array}{cc}\mathrm{Formula}1& \\ T_{m\_\mathrm{FB}\_\mathrm{ON}}=\frac{K_{\mathrm{Pm}}S+K_{\mathrm{Im}}}{S}\times \left({\omega }_{\mathrm{cl}2i^{*}}-{\omega }_{\mathrm{cl}2i}\right)& \left(1\right)\end{array}$

Where,

K_Pm: proportional gain for motor control

K_Im: integral gain for motor control

S: differential operator

In step S13, a second clutch torque capacity command value T_{cl FB ON} for the rotational speed control is calculated based on the base second clutch torque capacity command value T_{cl2 base}*, the motor torque command value for the rotational speed control T_{m FB ON}, and the engine torque command value T_{e base}*. The calculation method will be described in detail below. In step S14, an internal state variable for calculating the above-described motor torque command value for the rotational speed control T_{m FB ON} and the second clutch torque capacity command value for the rotational speed control T_{cl FB ON} is initialized. In step S15, a clutch torque capacity command value T_{cl2 FB OFF} when the rotational speed control is not performed, that is, when the rotational speed is controlled (put into a slip state) from an engaged/released state or an engaged state of the second clutch 4.

1. When engaging

• • (1) If T_{cl2 zl}*<T_d*×K_safe T_{cl2 FB OFF}=T_{cl2 zl}*+ΔT_cl2LU  (2)
  • (2) If T_{cl2 zl}*≧T_d*×K_safe T_{cl2 FB OFF}=T_d*×K_safe  (3)

2. When releasingT_{cl2 FB OFF}=0  (4)

3. When the second clutch is engaged→put into a slip stateT_{cl2 FB OFF}=T_{cl2 zl}*T_cl2slp  (5)

• • Where,
    • K_safe: second clutch safety factor coefficient (>1)
    • ΔT_cl2LU: torque capacity change rate when transitioning from slip (or release)→engaged
  • ΔT_cl2slp: torque capacity change rate when transitioning from engaged→slip
  • T_{cl2 zl}*: final second torque command value previous value

In step S16, the final second clutch torque capacity command value T_cl2* is determined using the following conditions.

1. During slip rotational speed control

• • (1) During engine start (fENG STEP=1)T_cl2*=T_{cl2 ENG START}  (6)
  • (2) Cases other than the aboveT_cl2*=T_{cl2 FB ON}  (7)

2. When slip rotational speed control is stoppedT_cl2*=T_{cl2 FB OFF}  (8)

In step S17, a first clutch torque capacity command value T_cl1* is determined based on the first clutch control mode flag fCL1.

1. When the first clutch control mode is in the engaged mode,

• • (1) During engine start (fENG STEP=1)T_CL1*=T_{cl1 ENG START}  (9)
  • (2) Cases other than the aboveT_CL1*=T_{cl1 max}  (10)
  • Where,
  • T_{cl1 max}: first clutch maximum torque capacity

2. When the first clutch control mode is in the released mode,T_CL1*=0  (11)

In step S18, the current command values I_CL1*, I_CL2* are calculated from the clutch torque capacity command values T_CL1*, T_CL2*. In practice, this calculation is performed with reference to the clutch torque capacity—the clutch hydraulic pressure conversion map in FIG. 4(a) and the clutch hydraulic pressure—the current conversion map in FIG. 4(b), which is prepared based on characteristics acquired beforehand. The above-described linear control theory can thereby be applied even when the clutch torque capacity has a non-linear characteristic with respect to the hydraulic pressure and the electric current, since the control target can be considered to be linear. In step S19, the final motor torque command value T_m* is determined based on the following conditions.

1. During slip rotational speed controlT_m*=T_{m FB ON}  (12)

2. When slip rotational speed control is stoppedT_m*=T_{m base}  (13)

• • In step S20, the calculated command value is transmitted to each controller.

Second Clutch Control Mode Setting Operation

FIG. 5 is a flowchart illustrating a method for setting the second clutch control mode. The control mode CL2MODE of the second clutch 4 is set from the vehicle states, such as the battery charging amount SOC, the drive torque command value T_d*, the first clutch control mode flag fCL1, and the vehicle speed Vsp. In step S51, the first clutch control mode is determined. If the first clutch control mode is engaged (engine start) (fCL1=1), the operation proceeds to step S55; if this is in the release mode (engine stop) (fCL1=0), the operation proceeds to step S52. In step S52, whether or not the vehicle speed Vsp is zero (stopped) is determined. If stopped, the operation proceeds to step S53; otherwise, the operation proceeds to step S54. In step S53, the second clutch control mode is set to the engaged mode (CL2MODE=1). In step S54, the second clutch control mode is set to the slip mode (CL2MODE=2). In step S55, whether or not the vehicle speed Vsp is higher than a predetermined value Vth1 (for example, the minimum vehicle speed at which the engine can be started) is determined. If lower, the operation proceeds to step S56, and if higher, the operation proceeds to step S58.

In step S56, the sign of the drive torque command value T_d* is determined; if positive, the operation proceeds to step S54, and if negative, the operation proceeds to step S57. In step S57, the second clutch control mode is set to the release mode (CL2MODE=0). In step S58, whether or not the previous second clutch control mode was the engaged mode is determined. If the mode was the engaged mode, the operation proceeds to step S53; otherwise, the operation proceeds to step S59. In step S59, whether or not a slip continuation condition is satisfied is determined based on the engine rotational speed measurement value ω_e, the second clutch slip rotational speed measurement value ω_cl2slp, and a slip rotational speed threshold value ω_cl2slpth. When the slip continuation condition is established, the operation proceeds to step S54, and slipping is started or continued; if the condition is not established, the operation proceeds to step S53, and slipping ends to transition to the engaged mode. The slip continuation condition is as follows.

ω_e≠ω_cl2i (first clutch released or slip), or, ω_cl2slp>; ω_cl2slpth

Input Rotational Speed Target Value Calculation

Next, the method for calculating the input rotational speed target value ω_cl2i* will be described. First, the second clutch slip rotational speed target value ω_cl2s1p* is calculated based on the following.

1. If in the EV mode (fCL1=0)ω_{cl2 slp}*=f_{cl2 slp cl10P}(T_{cl2 base}*. Temp_cl2)  (14)

Here, f_{cl2slp cl10p} ( ) is a function to which the base second clutch torque capacity command value T_{cl2 base}* and the second clutch oil temperature Temp_cl2 are input. In practice, for example, the above is set from a second clutch slip rotational speed target value calculation map, based on the base second clutch torque capacity command value T_{cl base}* and the second clutch oil temperature Temp_cl2, such as shown in FIG. 6(a). The second clutch slip rotational speed target value ω_{cl2 slp}* in the EV mode is set to decrease as the second clutch oil temperature Temp increases and is set to decrease as the base second clutch torque capacity command value T_{cl base}* increases, as illustrated in FIG. 6(a). When the “oil temperature is high” or when the “clutch capacity command value is large” in the second clutch 4, a rise in the clutch oil temperature can be prevented by decreasing the second clutch slip rotational speed target value ω_{cl2 slp}* specific luminance peak.

2. During engine torque startingω_{cl2 slp}*=f_{cl2 slp cl10P}(T_{cl2 base}*. Temp_cl2)+f_{cl2 Δωslp}(T_{eng start})  (15)

Here, f_{cl2 slp cl10P} ( ) is a function for calculating a slip rotational speed increase amount for starting the engine, to which an engine start allocated motor torque T_{eng start} is input. In practice, for example, a second clutch slip rotational speed target value calculation map, based on the engine start allocated motor torque T_{eng start} as illustrated in FIG. 6(b), is used. The second clutch slip rotational speed target value ω_cl2slp* during engine torque start is set to be higher as the engine start allocated motor torque T_{eng start} decreases, as illustrated in FIG. 6(b). An abrupt engagement can thereby be prevented even if the rotational speed is reduced because disturbance from the first clutch 3 cannot be completely counteracted; as a result, the engine 2 can be started without generating an acceleration variation. If slip control is continued after starting the engine, the slip rotational speed is configured to be the same that as during EV traveling (the increased portion is not added).

Next, an input shaft rotational speed target value ω_cl2i* is calculated based on the slip rotational speed target value ω_{cl2 slp}* and the output shaft rotational speed measurement value ω₀, using the following formula.ω_cl2i*=ω_{cl2 slp}*+ω₀  (16)

Finally, the upper and lower limits are set to the input rotational speed target value ω_cl2i* calculated from the above formula so as to set a final input shaft rotational speed target value. The upper and lower limits are set as the upper and lower limits of the engine rotational speed.

Calculation of the Second Clutch Torque Capacity Command Value for Rotational Speed Control

Next, the method for calculating the second clutch torque capacity command value for rotational speed control T_{clFB ON} will be described in detail. FIG. 7 is a block view of a feedback control for the second clutch. The present control system is designed by a 2-degree-of freedom control method comprising a feed-forward (F/F) compensation and a feedback (F/B) compensation. Various methods of designing the F/B compensation unit can be conceived, but here, a PI control is described as one example. The calculation method thereof is described below. First, a phase compensation is applied to the base second clutch torque capacity command value T_{cl2 base}* based on the phase compensation filter G_FF(s), which is illustrated by the following formula, to calculate the F/F second clutch torque capacity command value T_{cl2 base}*. For the actual calculation, the calculation is done using a recurrence formula obtained by discretizing with Tustin approximation or the like.

$\begin{array}{cc}\mathrm{Formula}2& \\ \frac{T_{\mathrm{cl}2\_\mathrm{FF}}}{T_{\mathrm{cl}2\mathrm{base}}^{*}}=G_{\mathrm{FF}}\left(S\right)=\frac{{\tau }_{\mathrm{cl}2}·S+1}{{\tau }_{\mathrm{cl}2\_\mathrm{ref}}·S+1}& \left(17\right)\end{array}$

Where,

τ_cl2: clutch model time constant

τ_{cl2 ref}: normative response time constant for clutch control

Next, the second clutch torque capacity target value t_{cl2 t} is calculated based on the following.

1. If in the EV modeT_{cl2 t}=T_{cl2 base}*  (18)

2. If in the HEV mode (first clutch is in the engaged state)T_{cl2 t}=T_{cl2 base}*−T_{e est}  (19)

The second clutch torque capacity target value in the HEV mode refers to the capacity of the motor component with respect to the torque capacity of the whole (the engine 2 and the motor 1). T_{e est} is the engine torque estimated value, which is, for example, calculated based on the following formula.

$\begin{array}{cc}\mathrm{Formula}3& \\ T_{e\_\mathrm{est}}=\frac{1}{{\tau }_{e}S+1}{e}^{-\mathrm{Les}}\times T_{e\_\mathrm{base}}^{*}& \left(20\right)\end{array}$

Where,

τ_e: engine first order lag time constant

L_e: engine dead time

Next, the second clutch torque capacity reference value T_{cl2 ref} is calculated based on the following formula.

$\begin{array}{cc}\mathrm{Formula}4& \\ \frac{T_{\mathrm{cl}2\_\mathrm{ref}}}{T_{\mathrm{cl}2\_t}}=G_{\mathrm{cl}2\_\mathrm{REF}}\left(S\right)=\frac{1}{{\tau }_{\mathrm{cl}2\_\mathrm{ref}}·S+1}& \left(21\right)\end{array}$

Next, the F/B second clutch torque capacity command value T_{cl2 FB} is calculated based on the second clutch torque capacity reference value T_{cl2 ref} and the above-described motor torque command value for rotational speed control T_{m FB ON} using the following formula.

$\begin{array}{cc}\mathrm{Formula}5& \\ T_{\mathrm{cl}2\_\mathrm{FB}}=\frac{K_{\mathrm{pcl}2}S+K_{\mathrm{Icl}2}}{S}\times \left(T_{\mathrm{cl}2\_\mathrm{ref}}-T_{m\_\mathrm{FB}\_\mathrm{ON}}\right)& \left(22\right)\end{array}$

Where,

K_pcl2: proportional gain for controlling the second clutch

K_Icl2: integral gain for controlling the second clutch

In addition, by considering the torque that is generated by the change in the input rotational speed (inertia torque) as in the following formula, the torque capacity can be precisely controlled even when the input rotational speed is changing.

$\begin{array}{cc}\mathrm{Formula}6& \\ T_{\mathrm{cl}2\_\mathrm{FB}}=\frac{K_{\mathrm{pcl}2}S+K_{\mathrm{Icl}2}}{S}\times \left(T_{\mathrm{cl}2\_\mathrm{ref}}-T_{m\_\mathrm{FB}\_\mathrm{ON}}-T_{\mathrm{cl}2\_\mathrm{est}}\right)& \left(23\right)\end{array}$ Here, T_{Icl2 est} is an inertia torque estimated value, which is obtained by, for example, multiplying the inertia moment around the input shaft by the input rotational speed change amount (differential value). Then, the F/F second clutch torque capacity command value T_{cl2 FF} and the F/B second clutch torque capacity command value T_{cl2 FB} are added to calculate the final second clutch torque capacity command value for rotational speed control T_{cl2 FB ON}.

Calculation of the Torque Capacity Command Value

Next, the method for calculating the torque capacity command values T_{cl1 ENG START}, T_{cl2 ENG START} of each clutch when starting the engine will be described in detail. FIG. 8 is a flowchart illustrating the torque capacity command value calculation method for each clutch when starting the engine. In step S71, whether or not the first clutch control mode is the release mode is determined. If not the release mode (if in the engaged mode), the operation proceeds to step S72; if in the release mode, the operation ends. In step S72, whether or not the previous first clutch control mode was the engaged mode is determined. If the previous mode was not the engaged mode (if the mode was the release mode), the operation proceeds to step S73; if the mode was the engaged mode, the operation proceeds to step S74.

In step S73 (drive torque command value change rate calculation means), the drive torque command value change rate (differential value) dT_d*/dt is calculated. The drive torque command value change rate (differential value) dT_d*/dt is calculated by, for example, using an approximate differentiation operation according to a bypass filter. In step S74 (engine start lower limit torque calculation means), an engine start lower limit torque T_{ENG START}, which is the minimum amount required for cranking in the current engine rotational speed, is calculated based on the engine rotational speed ω_e and the engine operating state E_sts (whether or not this is after the initial explosion). In practice, if before the initial explosion, the calculation is performed using an engine start lower limit torque calculation map (refer to FIG. 9) that is prepared from a value obtained by adding the engine friction torque for each rotational speed obtained by experimentation or another means beforehand and a portion required for increasing the engine rotation. Additionally, if after the initial explosion, the value is obtained by subtracting the torque that is output by the engine itself from the torque that is necessary for ending the engine start (increased to the second clutch input rotational speed) within a predetermined time.

In step S75 (motor upper limit torque calculation means), the motor upper limit torque Tm HLMT is calculated from the battery charging amount SOC (or the terminal voltage V₈) and the input shaft rotational speed ω_cl2i. In practice, the calculation is performed, for example, by using a motor upper limit torque calculation map, such as that illustrated in FIG. 10. In step S76 (second clutch torque capacity upper limit value calculation means), a second clutch torque capacity upper limit value T_{cl2 ENG START HLMT} is calculated based on the engine start lower limit torque T_{ENG START} and the motor upper limit torque T_{m HLMT}.T_{cl2 ENG START HLMT}=T_{m HLMT}−T_{ENG START}  (24)

In step S77 (second clutch torque capacity maximum value calculation means), a second clutch torque capacity maximum value T_{cl2 ENG START max}, which is the maximum value of the torque that can be allocated to the second clutch when starting the engine is calculated based on the motor upper limit torque T_{m HLMT} and the engine start lower limit torque minimum value T_{ENG START min}) which is calculated in step S74, using the following formula.T_{cl2 ENG START max}=T_{m HLMT}−T_{cl2 ENG START min}  (25)

The engine start lower limit torque minimum value T_{ENG START min} is the minimum value of the engine start lower limit torque T_{ENG START} throughout before and after the initial explosion, and a value obtained beforehand is used therefor.

In step S78, a second clutch torque capacity command base value for starting the engine T_{cl2 ENG START B} is determined based on the second clutch torque capacity upper limit value T_{cl2 ENG START HLMT} and the drive torque command value T_d* using the following.

1. When T_d*>T_{cl2 ENG START HLMT} T_{cl2 ENG START B}=T_{cl2 ENG START HLMT}

2. When T_d*T_{cl2 ENG START HLMT} T_{cl2 ENG START B}=T_d*

In step S79, the calculation is performed based on the drive torque command value T_d* and the change rate thereof dT_d*/dt, using the following.

1. When T_{cl2 ENG START max}≧T_d*K_{cl2 ENG START}=1.0

2. When T_{cl2 ENG START max}<T_d*K_{cl2 ENG START}=f_{cl2 ENG START}(dT_d*/dt)

f_{cl2 ENG START}(dT_d*/dt) is a function to which the drive torque command value change rate dT_d*/dt, which is set to the characteristic illustrated in FIG. 11, is input. FIG. 11 is a characteristic view of the second clutch torque capacity command correction value K_{cl2 ENG START}, corresponding to the drive torque command value change rate dT_d*/dt; K_{cl2 ENG START} is 1.0 when dT_d*/dt is within a range from zero to a first predetermined value and decreases as dT_d*/dt increases when within a range from the first predetermined value to a second predetermined value (>the first predetermined value), and is zero when within a range that exceeds the second predetermined value.

In step S710, a final second clutch torque capacity command value for starting the engine T_{cl2 ENG START} is calculated based on the second clutch torque capacity command base value for starting the engine T_{cl2 ENG START B} and the second clutch torque capacity command correction value K_{cl2 ENG START}, using the following formula.T_{cl2 ENG START}=T_{cl2 ENG START B}×K_{cl2 ENG START}  (26)

In step S711, a first clutch torque capacity command value for starting the engine T_{cl2 ENG START} is calculated based on the motor upper limit torque T_{m HLMT} and the second clutch torque capacity command value for engine start K_{cl2 ENG START}, using the following formula.T_{cl1 ENG START}=T_{m HLMT}−T_{cl2 ENG START}  (27)

Next, the effects are described. FIG. 12 is a time chart showing when the engine is started by an abrupt operation of the accelerator during EV traveling and when traveling while the depression amount is at a low opening amount (abrupt acceleration). In a conventional clutch control device, the allocation of the first clutch torque capacity is increased as the accelerator depression speed is increased; as a result, acceleration is stagnated, and the acceleration performance that is desired by the driver cannot be obtained from immediately after depression until starting the engine is completed. In contrast, in the first embodiment, when the accelerator depression amount is small and the drive torque command value T_d* is equal to or less than the second clutch torque capacity maximum value T_{cl2 ENG START max}, as in the situation illustrated in FIG. 12, the second clutch torque capacity command correction value K_{cl2 ENG START}, which corrects the second clutch torque capacity command base value for engine start T_{cl2 ENG START B}, takes the maximum value (1.0). That is, when the drive torque command value T_d* can be realized by only the motor torque, the allocation of the second clutch torque capacity is maximized, regardless of the drive torque command value change rate dT_d*/dt. Here, since the drive torque command value T_d* will be a larger value as the accelerator position opening amount Apo increases, to paraphrase the above, in the first embodiment, when the accelerator position opening amount Apo is a low opening amount (equal to or less than a predetermined accelerator position opening amount), the allocation of the second clutch torque capacity is maximized, regardless of the accelerator depression speed. That is, when the required acceleration of the driver is small and the drive torque command value T_d* can be realized only by the drive torque command value T_d*, the drive torque can be matched with the drive torque command value T_d* from immediately after depression by prioritizing the increase in the drive torque over the shortening of the engine start time. Therefore, since the acceleration stagnation can be improved with respect to the prior art described above, the desired acceleration performance of the driver can be obtained.

FIG. 13 is a time chart showing when the engine is started by an abrupt operation of the accelerator during EV traveling and when traveling while the depression amount is at a high opening amount. In this case, the drive torque command value T_d* is larger than the second clutch torque capacity maximum value T_{cl2 ENG START max}, and the second clutch torque capacity command correction value K_{cl2 ENG START} becomes f_{cl2 ENG START} (dT_d*/dt), taking a smaller value as the drive torque command value change rate dT_d*/dt increases. That is, when the drive torque command value T_d* cannot be realized by only the motor torque, the allocation of the first clutch torque capacity is increased as the drive torque command value change rate dT_d*/dt increases. Here, since the drive torque command value change rate dT_d*/dt will be a larger value as the accelerator depression speed increases, to paraphrase the above, in the first embodiment, when the accelerator position opening amount Apo is a high opening amount (exceeds the predetermined accelerator position opening amount), the allocation of the first clutch torque capacity is increased as the accelerator depression speed increases. In other words, if the required acceleration of the driver is large, the motor torque does not reach the drive torque command value T_d* even if increased; as a result, engine torque is quickly generated by prioritizing the shortening of the engine start time over the increase in the drive torque. The drive torque can thereby be increased to the drive torque command value T_d* at an early stage, and the desired acceleration performance of the driver can be obtained.

FIG. 14 is a time chart showing when the engine is started by an abrupt operation of the accelerator during EV traveling and when traveling while the depression amount is at a medium opening amount. In this case, the drive torque command value T_d* is less than the second clutch torque capacity maximum value T_{cl2 ENG START max}, and the second clutch torque capacity command correction value K_{cl2 ENG START} takes the maximum value (1.0). Here, the engine start lower limit torque T_{ENG START} becomes smaller as the engine rotational speed ω_e increases, as illustrated in FIG. 9. In particular, after the initial explosion of the engine, the engine itself generates a combustion torque; as a result, the cranking torque required for starting the engine becomes smaller, as compared to before the initial explosion. On the other hand, the motor upper limit torque T_{m HLMT} decreases as the engine rotational speed ω_e increases in a region in which the engine rotational speed ω_e is high but is constant in a region in which the engine rotational speed ω_e is low, such as when starting the engine, as illustrated in FIG. 10. That is, the second clutch torque capacity upper limit value T_{cl2 ENG START HLMT} is increased as the engine rotational speed ω_e is increased. Therefore, in the first embodiment, after removing the engine start lower limit torque T_{ENG START}, all of the remainder required for starting the engine from the motor upper limit torque T_{m HLMT}, which is the torque that the motor 1 is capable of outputting (second clutch torque capacity upper limit value T_{cl2 ENG START HLMT}), is set as the second clutch torque capacity command value for starting the engine T_{cl2 ENG START}; the value obtained by subtracting the second clutch torque capacity command value for starting the engine T_{cl2 ENG START} from the motor upper limit torque T_{m HLMT} is set as the first clutch torque capacity command value for starting the engine T_{cl1 ENG START}. The drive torque of the vehicle can thereby be increased along with a rise in the engine rotational speed ωe while reliably starting the engine 2 within the range of the motor upper limit torque T_{m HLMT}; as a result, the drive torque can be matched with the drive torque command value T_d* after the initial explosion of the engine and before starting the engine has been completed, that is, at a point in time before transitioning to the HEV mode, as illustrated in FIG. 14. Therefore, the stagnation of acceleration can be suppressed, and the desired acceleration can be obtained at an earlier stage.

The effects listed below can be obtained with the first embodiment, as described above.

(1) The embodiment comprises an engine 2, a motor generator 1, a first clutch 3 for interrupting a torque transmission between the engine 2 and the motor generator 1; a second clutch 4 for interrupting the torque transmission between the motor generator 1 and the driving wheels 21a, 21b; an integrated controller 13 for starting the engine 2 by utilizing the torque of the motor generator 1, when switching from an electric vehicle mode that cuts off the first clutch 3 and travels via the torque of the motor generator 1 to a hybrid mode that connects with the first clutch 3 and travels via the torque of the engine 2 and the motor generator 1; a motor upper limit torque calculation means (step S75) for calculating the motor upper limit torque T_{m HLMT}; and a transmission torque capacity allocating means (step S7) for allocating a first clutch torque capacity command value for starting the engine T_{cl1 ENG START} and a second clutch torque capacity command value for starting the engine T_{cl2 ENG START} within the range of the motor upper limit torque T_{m HLMT} when starting the engine accompanying an accelerator depression, wherein the transmission torque capacity allocating means increases the allocation of the second clutch torque capacity command value for starting the engine T_{cl2 ENG START} when the accelerator position opening amount is equal to or less than a predetermined accelerator position opening amount, as compared to when exceeding the predetermined accelerator position opening amount. Therefore, when the required acceleration of the driver is small, the drive torque can be matched with the drive torque command value T_d* from immediately after depression by prioritizing the increase in the drive torque over the shortening of the engine start time, and an acceleration performance that is desired by the driver can be realized.

(2) The transmission torque capacity allocating means increases the allocation of the first clutch torque capacity command value for starting the engine T_{cl1 ENG START} as the accelerator depression speed increases when the accelerator position opening amount exceeds the predetermined accelerator position opening amount. Therefore, when the required acceleration of the driver is large, the engine torque can be quickly generated, and the drive torque can be increased to the drive torque command value T_d* at an earlier stage by prioritizing the shortening of the engine start time over the increase in the drive torque; as a result, the acceleration performance that is desired by the driver can be realized.

(3) The embodiment comprises a drive torque command value calculation means (step S3) for calculating the drive torque command value T_d* based on the accelerator position opening amount; a drive torque command value change rate calculation means (step S73) for calculating the change rate dT_d*/dt of the drive torque command value T_d*; and a second clutch torque capacity maximum value calculation means (step S77) for calculating the second clutch torque capacity maximum value T_{cl2 ENG START max}, which is the maximum value of the torque that can be allocated to the second clutch 4 when starting the engine by subtracting the engine start lower limit torque minimum value T_{ENG START min}, which is the minimum value of the engine start lower limit torque that is minimally required for cranking, from the motor upper limit torque T_{m HLMT}, wherein the transmission torque capacity allocating means maximizes the allocation of the second clutch torque capacity command value for starting the engine T_{cl2 ENG START} when the drive torque command value T_d* is equal to or less than the second clutch torque capacity maximum value T_{cl2 ENG START max}, and increases the allocation of the first clutch torque capacity command value for starting the engine T_{cl1 ENG START} as the drive torque command value change rate dT_d*/dt increases, when the drive torque command value T_d* exceeds the second clutch torque capacity maximum value T_{cl2 ENG START max}. That is, when the drive torque command value T_d* can be realized only by the motor torque, the drive torque can be matched with the drive torque command value T_d* from immediately after depression by prioritizing the increase in the drive torque. On the other hand, when the drive torque command value T_d* cannot be realized by only the motor torque, the engine torque can be quickly generated, and the drive torque can be increased to the drive torque command value T_d* at an earlier stage by prioritizing the shortening of the engine start time as the drive torque command value change rate dT_d*/dt increases.

(4) This comprises an engine start lower limit torque calculation means (S74) for calculating the engine start lower limit torque T_{ENG START} that is minimally required for cranking at the current engine rotational speed, as well as a second clutch torque capacity upper limit value calculation means (S76) for calculating the second clutch torque capacity upper limit value T_{cl2 ENG START HLMT} that can be allocated to the second clutch 4, by subtracting the engine start lower limit torque T_{ENG START} from the motor upper limit torque T_{m HLMT}, wherein the transmission torque capacity allocating means sets a value restricting the upper limit of the drive torque command value T_d* with the second clutch torque capacity upper limit value T_{cl2 ENG START HLMT} as the second clutch torque capacity command value for starting the engine T_{cl2 ENG START} and sets a value obtained by subtracting the second clutch torque capacity command value for starting the engine T_{cl2 ENG START} based on the motor upper limit torque T_{m HLMT} as the first clutch torque capacity command value for starting the engine T_{cl1 ENG START} when the drive torque command value T_d* is equal to or less than the second clutch torque capacity maximum value T_{cl2 ENG START max}; additionally, the transmission torque capacity allocating means sets a value obtained by reducing this to correct a value restricting the upper limit of the drive torque command value T_d* with the second clutch torque capacity upper limit value T_{d2 ENG START HLMT} as the drive torque command value T_d* change rate dT_d*/dt increases, as the second clutch torque capacity command value for starting the engine T_{d2 ENG START}, and sets a value subtracting the second clutch torque capacity command value for starting the engine T_{d2 ENG START} from the motor upper limit torque T_{m HLMT} as the first clutch torque capacity command value for starting the engine T_{cl1 ENG START}, when the drive torque command value T_d* is greater than the second clutch torque capacity maximum value T_{cl2 ENG START max}. Therefore, the drive torque of the vehicle can be increased along with a rise in the engine rotational speed ω_e while reliably starting the engine 2 within the range of the motor upper limit torque T_{m HLMT}; as a result, the stagnation of acceleration can be suppressed, and the desired acceleration can be obtained at an earlier stage.

Other Embodiments

A preferred embodiment of the present invention was described above based on one embodiment, but specific configurations of the present invention are not limited by the embodiment; changes to the design made without departing from the scope of the invention are also included in the present invention.

Claims

1. A clutch control device for a hybrid vehicle comprising: an engine;a motor generator;a first clutch for interrupting a torque transmission between the engine and the motor generator;a second clutch for interrupting the torque transmission between the motor generator and driving wheels; andat least one controller programmed to start the engine by utilizing torque from the motor generator, when switching from an electric vehicle mode that cuts off the first clutch and travels via the torque of the motor generator to a hybrid mode that connects the first clutch and travels via the torque of the engine and the motor generator;calculate a motor upper limit torque,allocate a first clutch transmission torque capacity command value and a second clutch transmission torque capacity command value within the range of the motor upper limit torque when starting the engine accompanying an accelerator depression, the allocating including controlling both the first clutch and the second clutch to be in a power transmission state, and increasing the allocation of the second clutch transmission torque capacity command value when an accelerator position opening amount is equal to or less than a predetermined accelerator position opening amount, as compared to when exceeding the predetermined accelerator position opening amount,increase the allocation of the first clutch transmission torque capacity command value as an accelerator depression speed increases when the accelerator position opening amount exceeds the predetermined accelerator position opening amount,calculate a drive torque command value based on the accelerator position opening amount,calculate a change rate of the drive torque command value,calculate a second clutch torque capacity maximum value, which is the maximum value of the torque that can be allocated to the second clutch when starting the engine by subtracting an engine start lower limit torque minimum value, which is the minimum value of an engine start torque that is required for cranking from the motor upper limit torque, andallocate the second clutch transmission torque capacity command value when the drive torque command value is equal to or less than the second clutch torque capacity maximum value, and increase the allocation of the first clutch transmission torque capacity command value as the drive torque command value change rate increases when the drive torque command value exceeds the second clutch torque capacity maximum value.

2. The clutch control device according to claim 1, wherein the at least one controller is further programmed to calculate the engine start lower limit torque that is minimally required for cranking at a current engine rotational speed based on the engine rotational speed and whether or not an initial explosion has already occurred in the engine,calculate a second clutch torque capacity upper limit value that can be allocated to the second clutch by subtracting the engine start lower limit torque from the motor upper limit torque,set a first value restricting the upper limit of the drive torque command value with the second clutch torque capacity upper limit value as the second clutch transmission torque capacity command value,set a second value obtained by subtracting the second clutch transmission torque capacity command value from the motor upper limit torque as the first clutch transmission torque capacity command value when the drive torque command value is equal to or less than the second clutch torque capacity maximum value,set a third value obtained by reducing this to correct the first value restricting the upper limit of the drive torque command value with the second clutch torque capacity upper limit value as the accelerator depression speed increases, as the second clutch transmission torque capacity command value, andset a fourth value subtracting the second clutch transmission torque capacity command value from the motor upper limit torque as the first clutch transmission torque capacity command value when the drive torque command value is greater than the second clutch torque capacity maximum value.