WO2015036823A1

WO2015036823A1 - Control apparatus for hybrid vehicle

Info

Publication number: WO2015036823A1
Application number: PCT/IB2014/001693
Authority: WO
Inventors: Takeshi Hoshiba; Takeshi Aoki
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2013-09-12
Filing date: 2014-09-04
Publication date: 2015-03-19
Anticipated expiration: 2016-03-12
Also published as: JP2015054633A

Abstract

A control apparatus for a hybrid vehicle is provided. The hybrid vehicle includes an engine and an electric motor. The control apparatus includes a clutch and an electronic control unit. The clutch is configured to allow or interrupt transmission of power between the engine and the electric motor. The clutch is configured to be urged in a direction in which the clutch is engaged so as to transmit a predetermined torque smaller than a maximum transmission torque when transmission of power between the engine and the electric motor is neither allowed nor interrupted. The electronic control unit is configured to, when there occurs an abnormality in connecting or disconnecting the clutch, determine an engine torque command value of the engine such that a rotational difference between a rotation speed of the engine and a rotation speed of the electric motor falls within έ predetermined range.

Description

CONTROL APPARATUS FOR HYBRID VEHICLE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a control apparatus for a hybrid vehicle including an engine, an electric motor and a clutch that is able to connect the engine to the electric motor or disconnect the engine from the electric motor and, more particularly, to a technique for allowing retreat traveling while preventing a seizure of the clutch in the event of a failure of the clutch.

2. Description of Related Art

[0002] There is a hybrid vehicle including an engine, an electric motor, and a clutch. The clutch is able to connect the engine to the electric motor or disconnect the engine from the electric motor. Some of the hybrid vehicles employ a so-called normally-closed clutch. In a non-actuated state of the normally-closed clutch, the clutch is constantly placed in an engaged state where the clutch is preliminary urged toward an engaged side by the urging force of an urging member, such as a disc spring, provided in the clutch. Such a hybrid vehicle is, for example, described in Japanese Patent Application Publication No. 2012-97842 (JP 2012-97842 A).

SUMMARY OF THE INVENTION

[0003] Incidentally, because the clutch is constantly placed in an engaged state, the hybrid vehicle described in JP 2012-97842 A is able to carry out retreat traveling, for example, even when the clutch fails and the clutch is placed in a non-actuated state. However, in the above-described hybrid vehicle, there is an inconvenience that, for example, if a torque engagement pressure cannot be controlled in the event of a failure of the clutch and eventual torque is transmitted, the clutch slides to heat up when engine torque is too large and, as a result, a seizure, or the like, occurs. If engine torque is limited so as not to cause a seizure of the clutch, the hybrid vehicle may not be able to sufficiently carry out retreat traveling.

[0004] The invention provides a control apparatus for a hybrid vehicle, which allows the hybrid vehicle to sufficiently carry out retreat traveling while preventing a seizure of a clutch in the event of a failure of the clutch.

[0005] An aspect of the invention provides a Control apparatus for a hybrid vehicle. The hybrid vehicle includes an engine and an electric motor. The control apparatus includes: a clutch configured to allow or interrupt transmission of power between the engine and the electric motor, the clutch being configured to be urged in a direction in which the clutch is engaged so as to transmit a predetermined torque smaller than a maximum transmission torque when the clutch is in a non-actuated state; and an electronic control unit configured to, when there occurs an abnormality in connecting or disconnecting the clutch, determine an engine torque command value of the engine so that a rotational difference between a rotation speed of the engine and a rotation speed of the electric motor falls within a predetermined range.

[0006] With the thus configured control apparatus for a hybrid vehicle, when there occurs the abnormality in connecting or disconnecting the clutch, the engine torque command value is determined so that the rotational difference falls within the predetermined range in which no seizure of the clutch occurs and which is obtained from, for example, a clutch temperature. Therefore, in the event of a failure of the clutch, it is possible to carry out retreat traveling while preventing a seizure of the clutch.

[0007] In the control apparatus according to one aspect of the invention, the electronic control unit may be configured to, when the clutch heats up, determine the engine torque command value so that the rotational difference becomes 0. The electronic control unit may be configured to, when a temperature of the clutch is higher than a predetermined temperature, determine that the clutch heats up. Therefore, when the clutch heats up, the engine torque command value is determined so that the rotational difference becomes 0, that is, no slip occurs in the clutch, so the clutch is preventing from heating up, and it is possible to suitably expand the allowable range of the rotational difference at the time when the user requires toque.

[0008] In the control apparatus according to one aspect of the invention, the electronic control unit may be configured to determine an allowable range of the rotational difference on the basis of a clutch temperature of the clutch. Therefore, the allowable range of the rotational difference is set on the basis of the clutch temperature of the clutch so that no seizure occurs in the clutch. Therefore, in the event of an abnormality of the clutch, a seizure of the clutch is suitably prevented.

[0009] In the control apparatus according to one aspect of the invention, the electronic control unit may be configured to, when there occurs an abnormality in connecting or disconnecting the clutch, set the clutch to the non-actuated state. Therefore, the clutch in the non-actuated state is urged toward the engaged side so as to transmit the predetermined torque smaller than the maximum transmission torque from the engine, so it is possible to suitably carry out retreat traveling in the event of an abnormality of the clutch.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a view that illustrates the schematic configuration of a power transmission path from an engine and an electric motor to drive wheels, which constitute a hybrid vehicle to which the invention is suitably applied, and is a view that illustrates a relevant portion of a control system provided in the hybrid vehicle for, for example, engine torque control over the engine that functions as a driving force source for propelling the hybrid vehicle;

FIG. 2 is a cross-sectional view that shows the detailed structure of a clutch that is able to connect the engine to the electric motor or disconnect the engine from the electric motor where the engine and the electric motor are provided in the hybrid vehicle shown in FIG. 1;

FIG. 3 is a functional block diagram that illustrates a relevant portion of control functions provided in an electronic control unit in the hybrid vehicle shown in FIG. 1;

FIG. 4 is a graph that shows the correlation between an estimated clutch K0 temperature and an allowable rotational difference, the correlation being used by an allowable rotational difference calculation unit shown in FIG. 3 in order to calculate an allowable rotational difference; and

FIG. 5 is a flowchart that illustrates an example of control operations for controlling engine torque in the event of a failure of a clutch in the electronic control unit shown in FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS

[0011] Hereinafter, an embodiment of the invention will be described in detail with reference to the accompanying drawings. In the following embodiment, the drawings are simplified or modified where appropriate for the sake of easy understanding, and the scale ratio, shape, and the like, of each portion are not always accurately drawn.

[0012] FIG. 1 is a view that illustrates the schematic configuration of a power transmission path from an engine 12 and an electric motor MG to drive wheels 14, which constitute a hybrid vehicle 10 (hereinafter, referred to as vehicle 10) to which the invention is suitably applied, and is a view that illustrates a relevant portion of a control system provided in the vehicle 10 for, for example, engine torque control over the engine 12 that functions as a driving force source for propelling the vehicle 10.

[0013] In FIG. 1, a vehicle powertrain 16 (hereinafter, referred to as powertrain 16) includes an engine separation clutch (clutch) K0, the electric motor MG, a torque converter 20, an oil pump 22, an automatic transmission 24, and the like, in order from the engine 12 side inside a transmission case 18. The transmission case 18 serves as a non-rotating member, for example, bolted to a vehicle body. The thus configured powertrain 16 is suitably used in, for example, the front-engine rear-wheel-drive (FR) vehicle 10. In the powertrain 16, when the engine separation clutch K0 is engaged, the power of the engine 12 is transmitted from an engine coupling shaft 26 to the pair of drive wheels 14 via the engine separation clutch KO, the electric motor MG, the torque converter 20, the automatic transmission 24, a propeller shaft 28, a differential gear unit 30, a pair of axles 32, and the like. The engine coupling shaft 26 couples the engine 12 to the engine separation clutch KO.

[0014] As shown in FIG. 2, the engine separation clutch K0 is, for example, a wet multi-disc hydraulic friction engagement device in which a plurality of friction plates 34, 36 stacked on top of each other are pressed by a hydraulic actuator. Engage/release control, that is, control for connecting the engine 12 to the electric motor MG or disconnecting the engine 12 from the electric motor MG, is executed by a hydraulic control circuit 40 (see FIG. 1) by using a hydraulic pressure as a source pressure. The hydraulic pressure is generated from the oil pump 22 or an electric oil pump 38 (see FIG. 1). The hydraulic control circuit 40 is provided in the powertrain 16. In the engage/release control, the transmittable torque capacity of the engine separation clutch K0, that is, the engagement force of the engine separation clutch K0, is, for example, continuously changed by pressure adjustment of a linear solenoid, and the like, in the hydraulic control circuit 40. The engine separation clutch K0 connects or disconnects a power transmission path between the engine 12 and the electric motor MG through the above-described engage/release control.

[0015] As shown in FIG. 2, the engine separation clutch K0 includes a clutch hub

42 and a clutch drum 44. The clutch hub 42 and the clutch drum 44 are relatively rotatable in a released state where the power transmission path between the engine 12 and the electric motor MG is interrupted. The clutch hub 42 is integrally coupled to the engine coupling shaft 26 so as to be relatively non-rotatable. The clutch drum 44 is integrally coupled to a rotor 46 of the electric motor MG and a cover portion 20a of the torque converter 20, that is, a pump impeller 20b, by a first fastening bolt 48 and a second fastening bolt 49 so as to be relatively non-rotatable. As shown in FIG. 2, the engine separation clutch K0 includes a piston 50, a first hydraulic chamber 52, a first oil passage (not shown), a second hydraulic chamber 54, a second oil passage 56, and a disc spring 58. The piston 50 is arranged between the clutch hub 42 and the clutch drum 44 so as to be movable in an axis C direction of the engine coupling shaft 26. The first hydraulic chamber 52 is formed between the piston 50 and the clutch drum 44. The first oil passage supplies hydraulic oil from the hydraulic control circuit 40 to the first hydraulic chamber 52. The second hydraulic chamber 54 is formed between the piston 50 and the clutch hub 42. The second oil passage 56 supplies circulating hydraulic pressure from the hydraulic control circuit 40 to the second hydraulic chamber 54. The disc spring 58 is arranged between the piston 50 and the clutch drum 44. The disc spring 58 is an urging member that applies pressure at a set magnitude in a direction in which the piston 50 is spaced apart from the clutch drum 44, that is, a direction in which the piston 50 approaches the clutch hub 42.

[0016] In the thus configured engine separation clutch K0, when hydraulic oil is supplied to the first hydraulic chamber 52 through the first oil passage and then the piston 50 is moved in the direction to approach the clutch hub 42, an engaged state is established, and the rotor 46 and the pump impeller 20b are integrally rotated with the engine 12 via the engine coupling shaft 26. In the engaged state, the power transmission path between the engine 12 and the electric motor MG is connected. In a state where the inside of the first hydraulic chamber 52 has atmospheric pressure, when circulating hydraulic pressure is applied to the second hydraulic chamber 54 through the second oil passage 56 and then the piston 50 is moved in the direction to approach the engine 12 against the urging force of the disc spring 58, the engine separation clutch K0 enters a released state, with the result that transmission of power is interrupted between both the electric motor MG and the pump impeller 20b and the engine 12.

[0017] When the engine separation clutch K0 is in a non-actuated state where no hydraulic oil is supplied to the first hydraulic chamber 52 or the second hydraulic chamber 54, the insides of the first hydraulic chamber 52 and second hydraulic chamber 54 have atmospheric pressure and the above-described engage/release control, that is, connecting/disconnecting control, is not executed, the piston 50 is constantly urged by the urging force of the disc spring 58 in the direction to approach the clutch hub 42, with the result that the engine separation clutch KO enters an engaged state. That is, when the engine separation clutch KO is in the non-actuated state, the engine separation clutch KO is urged toward the engaged side by the urging force of the disc spring 58 so as to transmit a predetermined torque smaller than a maximum transmission torque that can be transmitted from the engine 12 to the electric motor MG. The engine separation clutch KO is a so-called normally-closed clutch that is constantly placed in an engaged state where the engine separation clutch KO is preliminary urged toward the engaged side by the urging force of, for example, the disc spring 58, or the like, provided in the engine separation clutch KO.

[0018] The vehicle 10 includes a control system illustrated in FIG. 1. An electronic control unit (control apparatus) 60 shown in FIG. 1 includes a so-called microcomputer including, for example, a CPU, a RAM, a ROM, input/output interfaces, and the like. The CPU executes signal processing in accordance with a program prestored in the ROM while utilizing a temporary storage function of the RAM, thus executing various controls over the vehicle 10. For example, the electronic control unit 60 is configured to execute engine torque control over the engine 12, drive control over the electric motor MG, shift control over the automatic transmission 24, engage/release control over the engine separation clutch K0, and the like. The drive control over the electric motor MG includes regenerative control over the electric motor MG. The electronic control unit 60 is, where necessary, separately formed of an engine control electronic control unit, an electric motor control electronic control unit, a hydraulic control (shift control) electronic control unit, and the like.

[0019] As shown in FIG. 1, a signal indicating a rotation speed (the number of revolutions) Ne (rpm) of the engine 12, a signal indicating a rotation speed (the number of revolutions) Nm (rpm) of the electric motor MG a signal indicating a hydraulic pressure P O, a signal indicating an accelerator operation amount Acc, and the like, are supplied to the electronic control unit 60. For example, the rotation speed (the number of revolutions) Ne (rpm) of the engine 12 is detected by an engine rotation speed sensor 62. The rotation speed (the number of revolutions) Nm (rpm) of the electric motor MG is detected by a motor rotation speed sensor 64. The hydraulic pressure P_K0 is supplied from the hydraulic control circuit 40 to the engine separation clutch KO. The hydraulic pressure Ρ ο is detected by a hydraulic pressure sensor 66. The accelerator operation amount Acc is the operation amount of an accelerator pedal 70, and indicates the magnitude of a user required engine torque (user required output) Te, required of the vehicle 10 by the user (driver). The accelerator operation amount Acc is detected by an accelerator operation amount sensor 68.

[0020] For example, an engine torque command value (engine output control command signal) Se, an electric motor control command signal Sm, a hydraulic pressure command signal Sp, and the like, are output from the electronic control unit 60. The engine torque command value (engine output control command signal) Se is used for engine torque control over the engine 12. The electric motor control command signal Sm is used for controlling the operation of the electric motor MG. The hydraulic pressure command signal Sp is used for operating electromagnetic valves (solenoid valves), the electric oil pump 38, and the like. The electromagnetic valves (solenoid valves) are included in the hydraulic control circuit 40 for controlling the engine separation clutch K0 and the hydraulic actuators of clutches and brakes of the automatic transmission 24.

[0021] FIG. 3 is a functional block diagram that illustrates a relevant portion of control functions of the electronic control unit 60. In FIG. 3, a clutch K0 failure determination unit (K0 clutch failure determination means) 72 determines whether the engine separation clutch K0 has a failure because, for example, a torque engagement pressure cannot be controlled in the engine separation clutch K0. The clutch K0 failure determination unit 72, for example, detects the hydraulic pressure P_Ko that is supplied to the engine separation clutch K0 and the hydraulic pressure command signal Sp that is input in order to operate the electromagnetic valves included in the hydraulic control circuit 40, and determines that the engine separation clutch K0 has a failure on the basis of the fact that the difference between those hydraulic pressure Ρκο and hydraulic pressure command signal Sp exceeds a preset abnormality determination value. Alternatively, the clutch K0 failure determination unit 72 determines that the engine separation clutch K0 has a failure on the basis of the fact that there is a rotational difference in the engine separation clutch K0 at the time when the hydraulic pressure command signal Sp indicates a maximum engagement pressure.

[0022] When the clutch KO failure determination unit 72 determines that the engine separation clutch KO has a failure, an allowable rotational difference calculation unit (allowable rotational difference calculation means) 74 calculates an allowable range of rotational difference, that is, an allowable rotational difference Npd (rpm), between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG on the basis of an estimated clutch KO temperature (clutch temperature) T_Ko (°C). The estimated clutch K0 temperature (clutch temperature) T_K0 (°C) is estimated by a clutch K0 temperature estimation unit (clutch K0 temperature estimation means) 76. In the allowable rotational difference Npd (rpm), no seizure occurs in the engine separation clutch K0. The allowable rotational difference calculation unit 74 calculates the above-described allowable rotational difference Npd (rpm) from an estimated temperature of the engine separation clutch K0, that is, the estimated clutch K0 temperature Τ ο (°C). The estimated temperature of the engine separation clutch K0 is estimated by the clutch K0 temperature estimation unit 76 by, for example, using the map shown in FIG. 4.

[0023] The allowable rotational difference Npd shown in FIG. 4 is obtained by an experiment, or the like, in advance when no seizure occurs in the engine separation clutch K0 even when there occurs a slip, that is, rotational difference, in the engine separation clutch K0 within the range of the allowable rotational difference Npd at a predetermined temperature (°C) of the engine separation clutch K0. When the estimated clutch K0 temperature Τ ο estimated by the clutch K0 temperature estimation unit 76 is higher than a high temperature determination value set on the basis of, for example, a predetermined temperature ΤΗ ο (°C) shown in FIG. 4 or a value lower than the predetermined temperature ΤΗ ο (°C), that is, when the engine separation clutch K0 heats up, the allowable rotational difference calculation unit 74 sets the allowable rotational difference Npd to 0 (rpm).

[0024] For example, when the clutch K0 failure determination unit 72 determines that the engine separation clutch KO has a failure, the allowable rotational difference calculation unit 74 sets the engine separation clutch KO to the non-actuated state by stopping engage/release control over the engine separation clutch KO, that is, by stopping hydraulic oil that is supplied to the first hydraulic chamber 52 and second hydraulic chamber 54 of the engine separation clutch KO.

[0025] Because the amount of heat generated by the engine separation clutch K0 is estimated by the product of the rotational difference Nd between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG and a time t , the clutch K0 temperature estimation unit 76 is able to calculate the estimated clutch K0 temperature Τ ο (°C) of the engine separation clutch K0 by integrating the product of the rotational difference Nd and the time t. Therefore, the clutch K0 temperature estimation unit 76, for example, estimates the estimated clutch K0 temperature Τκο (°C) of the engine separation clutch K0 by the following mathematical expression (1). AN(t) in the mathematical expression (1) is a rotational difference (|Nm-Ne|), that is, a slip amount, of the engine separation clutch K0. The coefficient K in the mathematical expression (1) is, for example, an experimental value obtained by an experiment from the urging force of the disc spring 58 of the engine separation clutch K0, the friction coefficient μ of the friction plates 34, 36, the thermal capacity of the engine separation clutch K0, and the like.

T_K0(^oC) = iK^«AN(t)dt (1)

[0026] When the allowable rotational difference Npd is calculated by the allowable rotational difference calculation unit 74, the clutch K0 protection determination unit (clutch K0 protection determination means) 78 determines whether there is a possibility that a seizure occurs in the engine separation clutch K0 and protection of the engine separation clutch K0 is not ensured on the basis of the calculated allowable rotational difference Npd and an actual rotational difference (Ne - Nm ) Nd between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG. For example, when the allowable rotational difference Npd is calculated by the allowable rotational difference calculation unit 74, the clutch K0 protection determination unit 78 determines that protection of the engine separation clutch K0 is not ensured on the basis of the fact that the actual rotational difference Nd is larger than the allowable rotational difference Npd calculated by the allowable rotational difference calculation unit 74, and the clutch KO protection determination unit 78 determines that protection of the engine separation clutch KO is ensured, that is, no seizure occurs in the engine separation clutch KO, on the basis of the fact that the actual rotational difference Nd is smaller than the allowable rotational difference Npd.

[0027] When the clutch KO protection determination unit 78 determines that protection of the engine separation clutch KO is not ensured, an engine torque control unit (engine torque control means) 80, for example, determines the engine torque command value Se on the basis of the user required engine torque Te required by the user (driver) and determined on the basis of the accelerator operation amount Acc such that the actual rotational difference Nd between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG falls within the allowable rotational difference Npd calculated by the allowable rotational difference calculation unit 74, that is, the actual rotational difference Nd becomes lower than or equal to the allowable rotational difference Npd, and controls the rotational difference Nd, that is, a slip, of the engine separation clutch K0 by the engine torque. For example, when the accelerator operation amount Acc is relatively large and the user required engine torque Te is large, the engine torque control unit 80 determines the engine torque command value Se through PI feedback control such that the actual rotational difference Nd between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG becomes the allowable rotational difference Npd. When the estimated clutch K0 temperature Τ ο is higher than the predetermined temperature ΤΗ ο as shown in FIG. 4 in the clutch K0 temperature estimation unit 76, that is, the engine separation clutch K0 heats up, the engine torque control unit 80 determines the engine torque command value Se so that the actual rotational difference Nd between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG becomes 0. That is, when the clutch heats up, the engine torque command value Se is determined so that the engine torque is lower than or equal to a predetermined torque that is allowed to be transmitted from the engine 12 to the electric motor MG via the engine separation clutch KO in the non-actuated state of the engine separation clutch KO.

[0028] When the clutch KO protection determination unit 78 determines that protection of the engine separation clutch KO is ensured or when the clutch KO failure determination unit 72 determines that the engine separation clutch KO has no failure, the engine torque control unit 80, for example, determines the user required engine torque Te required by the user (driver) on the basis of the accelerator operation amount Acc, and determines the engine torque command value Se such that the user required engine torque Te is output.

[0029] FIG. 5 is a flowchart that illustrates a relevant portion of control operations of the electronic control unit 60, that is, an example of control operations for controlling the engine torque in the event of a failure of the engine separation clutch K0. The flowchart is, for example, repeatedly executed at an extremely short cycle time of about several milliseconds to several tens of milliseconds.

[0030] Initially, in step (hereinafter, step is omitted) SI corresponding to the clutch K0 failure determination unit 72, it is determined whether the engine separation clutch K0 has a failure. When negative determination is made in SI, in S2 corresponding to the engine torque control unit 80, the user required engine torque Te is determined on the basis of the accelerator operation amount Acc, and the engine torque command value Se is determined so that the user required engine torque Te is output. The engine torque is controlled on the basis of the determined engine torque command value Se.

[0031] When affirmative determination is made in SI, S3 corresponding to the allowable rotational difference calculation unit 74 and the clutch K0 temperature estimation unit 76 is executed. In S3, the estimated clutch K0 temperature T O(°C) of the engine separation clutch K0 is estimated, and the allowable rotational difference Npd (rpm) is calculated on the basis of the estimated clutch K0 temperature T O(°C). In S3, engage/release control over the engine separation clutch K0 is stopped, and the engine separation clutch K0 is set to the non-actuated state.

[0032] Subsequently, in S4 corresponding to the clutch K0 protection determination unit 78, it is determined whether protection of the engine separation clutch KO is not ensured, that is, whether the actual rotational difference Nd between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG is higher than the allowable rotational difference Npd calculated in S3. When negative determination is made in S4, that is, when there is no possibility that a seizure occurs in the engine separation clutch KO and protection of the engine separation clutch KO is ensured, in S5 corresponding to the engine torque control unit 80, the user required engine torque Te is determined on the basis of the accelerator operation amount Acc, and the engine torque command value Se is determined so that the user required engine torque Te is output. The engine torque is controlled on the basis of the determined engine torque command value Se.

[0033] When affirmative determination is made in S4, that is, when there is a possibility that a seizure occurs in the engine separation clutch K0 and protection of the engine separation clutch K0 is not ensured, S6 corresponding to the engine torque control unit 80 is executed. In S6, the engine torque command value Se is determined on the basis of the user required engine torque Te so that the actual rotational difference Nd between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG falls within the allowable rotational difference Npd calculated in S3, for example, so that the actual rotational difference Nd becomes the allowable rotational difference Npd when the user required engine torque Te is relatively high, and the rotational difference (slip) of the engine separation clutch K0 is controlled on the basis of the determined engine torque command value Se. When the engine separation clutch K0 heats up, the engine torque command value Se is determined so that the actual rotational difference Nd becomes 0 (rpm).

[0034] As described above, with the electronic control unit 60 of the hybrid vehicle 10 according to the present embodiment, the engine separation clutch K0 is urged toward the engaged side by the disc spring 58 so as to transmit the predetermined torque smaller than the maximum transmission torque when control for connecting the engine 12 to the electric motor MG or disconnecting the engine 12 from the electric motor MG is not executed, that is, in the non-actuated state, and, when there occurs an abnormality in control for connecting or disconnecting the engine separation clutch K0, the engine torque command value Se of the engine 12 is determined on the basis of the user required engine torque Te so that the actual rotational difference Nd between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG falls within the allowable rotational difference Npd. Therefore, when there occurs an abnormality in control for connecting or disconnecting the engine separation clutch K0, the engine torque command value Se is determined for the user required engine torque Te so that the actual rotational difference Nd falls within the allowable rotational difference Npd in which no seizure occurs in the engine separation clutch K0 and which is obtained on the basis of the estimated clutch K0 temperature Τκο of the engine separation clutch K0. Therefore, in the event of a failure of the engine separation clutch K0, it is possible to sufficiently allow retreat traveling while preventing a seizure of the engine separation clutch K0.

[0035] With the electronic control unit 60 of the hybrid vehicle 10 according to the present embodiment, when the engine separation clutch K0 heats up where the estimated clutch K0 temperature Τ ο is higher than the predetermined temperature ΤΗ ο, the engine torque command value Se is determined such that the rotational difference Nd becomes 0 (rpm). Therefore, when the engine separation clutch K0 heats up, the engine torque command value Se is determined such that the rotational difference Nd becomes 0 (rpm), that is, no slip occurs in the engine separation clutch K0. Therefore, heat-up of the engine separation clutch K0 is prevented, and it is possible to suitably increase the allowable rotational difference Npd of the rotational difference Nd at the time when the user requires torque. When the engine separation clutch K0 heats up, the engine torque command value Se is determined so that no slip occurs in the engine separation clutch K0. Therefore, by transmitting the engine torque to the electric motor MG, the automatic transmission 24, and the like, downstream of the engine separation clutch K0 while protecting the engine separation clutch K0 from temperature, it is possible to charge a battery and ensure driving torque, so retreat traveling performance is improved even in the event of a failure of the engine separation clutch K0. [0036] With the electronic control unit 60 of the hybrid vehicle 10 according to the present embodiment, the allowable rotational difference Npd of the rotational difference Nd between the rotation speed Ne of the engine 12 and the rotation speed Nm of the electric motor MG is determined on the basis of the estimated clutch K0 temperature T O of the engine separation clutch K0. Therefore, when the allowable rotational difference Npd is set to a value obtained on the basis of the estimated clutch K0 temperature T O of the engine separation clutch K0 so that no seizure occurs in the engine separation clutch K0, a seizure of the engine separation clutch K0 is suitably prevented in the event of a failure of the engine separation clutch K0.

[0037] With the electronic control unit 60 of the hybrid vehicle 10 according to the present embodiment, when there occurs an abnormality in control for connecting or disconnecting the engine separation clutch K0, control for connecting or disconnecting the engine separation clutch K0 is stopped, and the engine separation clutch K0 is set to the non-actuated state. Therefore, the engine separation clutch K0 in the non-actuated state is urged toward the engaged side by the disc spring 58 so as to transmit the predetermined torque smaller than the maximum transmission torque from the engine 12, so it is possible to suitably carry out retreat traveling in the event of an abnormality in control for connecting or disconnecting the engine separation clutch K0.

[0038] The embodiment of the invention is described in detail with reference to the accompanying drawings; however, the invention is also applicable to another alternative embodiment.

[0039] In the electronic control unit 60 according to the present embodiment, in the allowable rotational difference calculation unit 74, the allowable rotational difference Npd (rpm) is calculated on the basis of the estimated temperature of the engine separation clutch K0, that is, the estimated clutch K0 temperature TKO, obtained by the clutch K0 temperature estimation unit 76. Instead, for example, the allowable rotational difference Npd (rpm) may be calculated on the basis of the temperature of the engine separation clutch K0, measured by using a temperature sensor that directly measures the temperature of the engine separation clutch K0. [0040] The above-described embodiment is only illustrative. The invention may be implemented in modes including various modifications or improvements on the basis of the knowledge of persons skilled in the art.

Claims

CLAIMS:

1. A control apparatus for a hybrid vehicle, the hybrid vehicle including an engine and an electric motor, the control apparatus comprising:

a clutch configured to allow or interrupt transmission of power between the engine and the electric motor, the clutch being configured to be urged in a direction in which the clutch is engaged so as to transmit a predetermined torque smaller than a maximum transmission torque when the clutch is in a non-actuated state; and

an electronic control unit configured to, when there occurs an abnormality in connecting or disconnecting the clutch, determine an engine torque command value of the engine so that a rotational difference between a rotation speed of the engine and a rotation speed of the electric motor falls within a predetermined range.

2. The control apparatus according to claim 1, wherein

the electronic control unit is configured to, when the clutch heats up, determine the engine torque command value so that the rotational difference becomes 0.

3. The control apparatus according to claim 1 or 2, wherein

the electronic control unit is configured to determine an allowable range of the rotational difference on the basis of a clutch temperature of the clutch.

4. The control apparatus according to any one of claims 1 to 3, wherein

the electronic control unit is configured to, when there occurs the abnormality in connecting or disconnecting the clutch, set the clutch to the non-actuated state.

5. The control apparatus according to any one of claims 1 to 4, wherein

the electronic control unit is configured to determine the engine torque command value on the basis of an engine output that is required by a user.

6. The control apparatus according to claim 2, wherein

the electronic control unit is configured to, when a temperature of the clutch is higher than a predetermined temperature, determine that the clutch heats up.