Control device for a hybrid electric vehicle

Abstract

A hybrid electric vehicle is arranged such that a driving force of an engine and a driving force of an electric motor can be transmitted to driving wheels through an automatic transmission having a plurality of forward gears. When it is detected that the vehicle is in a predetermined state in which it is difficult for the electric motor to output an upper limit torque predetermined as a generable maximum torque, a vehicle ECU controls the automatic transmission using a gear shift map configured such that the automatic transmission is downshifted earlier in accordance with a change in the operating state of the vehicle and upshifted later in accordance with a change in the operating state of the vehicle in comparison with a gear shift map that is used when it is not detected that the vehicle is in the predetermined state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein:

FIG. 1 is a diagram showing a substantial part of a hybrid electric vehicle having a control device according to one embodiment of the present invention;

FIG. 2 is a flowchart showing a switching control of gear shift maps performed in the hybrid electric vehicle shown in FIG. 1;

FIG. 3 is a diagram showing a gear shift map SU1 for upshift;

FIG. 4 is a diagram showing a gear shift map SU2 for upshift;

FIG. 5 is a diagram showing a gear shift map SD1 for downshift;

FIG. 6 is a diagram showing a gear shift map SD2 for downshift;

FIG. 7 is a diagram showing output power ranges of an engine and an electric motor;

FIG. 8 is a flowchart showing a switching control of a clutch control performed in the hybrid electric vehicle shown in FIG. 1; and

FIG. 9 is a diagram showing a relationship between an upper limit decelerating torque of an electric motor and a required decelerating torque.

Claims

1. A control device for a hybrid electric vehicle arranged such that a driving force of an engine and a driving force of an electric motor can be transmitted to driving wheels through an automatic transmission having a plurality of forward gears, the control device comprising: an output limit detection means for detecting that the vehicle is in a predetermined state in which it is difficult for the electric motor to output an upper limit torque predetermined as a generable maximum torque; anda control means for controlling a gear shift of the automatic transmission according to a change in an operating state of the vehicle based on a predetermined gear shift map; whereinwhen it is detected by the output limit detection means that the vehicle is in the predetermined state, the control means controls the automatic transmission using a gear shift map configured such that the automatic transmission is downshifted earlier in accordance with a change in the operating state of the vehicle and upshifted later in accordance with a change in the operating state of the vehicle in comparison to a gear shift map that is used when the output limit detection means does not detect that the vehicle is in the predetermined state.

2. The control device for a hybrid electric vehicle according to claim 1, wherein: the output limit detection means detects that the vehicle is in the predetermined state when a generable torque of the electric motor is actually limited to a limited torque that is lower than the upper limit torque.

3. The control device for a hybrid electric vehicle according to claim 1, further comprising: a storage rate detection means for detecting a storage rate of a battery that supplies electric power to the electric motor, wherein:the output limit detection means detects that the vehicle is in the predetermined state when the storage rate of the battery detected by the storage rate detection means lowers below a predetermined lower limit storage rate.

4. The control device for a hybrid electric vehicle according to claim 1, wherein: the output limit detection means detects that the vehicle is in the predetermined state when an allowable output value, which is an upper limit of the electric power that the battery can output, lowers below a predetermined output power.

5. The control device for a hybrid electric vehicle according to claim 1, wherein: the control means uses a gear shift map configured such that the gear of the automatic transmission for start-up of the vehicle is set to a first gear when it is detected by the output limit detection means that the vehicle is in the predetermined state, and on the other hand, uses a gear shift map configured such that the gear of the automatic transmission for start-up of the vehicle is set to a second gear that is higher than the first gear when it is not detected by the output limit detection means that the vehicle is in the predetermined state.

6. The control device for a hybrid electric vehicle according to claim 1, further comprising: a failure detection means for detecting a failure of the electric motor, wherein:when the failure of the electric motor is detected by the failure detection means, the control means controls the automatic transmission using a gear shift map configured such that the automatic transmission is downshifted earlier in accordance with a change in the operating state of the vehicle and upshifted later in accordance with a change in the operating state of the vehicle in comparison with a gear shift map that is used when the failure of the electric motor is not detected by the failure detection means.

7. The control device for a hybrid electric vehicle according to claim 6, further comprising: a clutch capable of cutting off the driving force transmitted from the engine to the automatic transmission; anda revolution speed detection means for detecting a revolution speed of the electric motor, wherein:in the event that the failure is not detected by the failure detection means during deceleration of the vehicle, the control means sets a regenerative braking torque that can be generated by the electric motor as an upper limit decelerating torque and a decelerating torque necessary for the deceleration of the vehicle as a required decelerating torque in accordance with the revolution speed detected by the revolution speed detection means, the control means disengages the clutch and controls the electric motor so that the electric motor generates the required decelerating torque when the required decelerating torque is equal to or lower than the upper limit decelerating torque, and on the other hand, engages the clutch and controls the engine and the electric motor so that a sum of a decelerating torque from the engine and a regenerative braking torque from the electric motor is equal to the required decelerating torque when the required decelerating torque is greater than the upper limit decelerating torque; andin the event that the failure is detected by the failure detection means during deceleration of the vehicle, the control means maintains engagement of the clutch at least until the revolution speed of the engine decreases to the vicinity of an idling speed of the engine.