Hybrid Vehicle Acceleration Control via Variable Valve Timing
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Solution Overview
Problem
In hybrid vehicles, there is a delay in the increase of drive shaft torque with respect to the increase of engine rotation number, leading to a poor acceleration feeling for the driver due to the synchronization of intake negative pressure and engine valve timing changes.
Innovation Solution
An electronic control unit is used to limit engine power based on drive shaft torque until a torque threshold is reached, then relax the limitation to enhance acceleration, while adjusting the variable valve timing mechanism to improve response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the engine rotation number increases quickly after accelerator pedal is stepped, then the engine can respond faster to driver acceleration request, but the drive shaft torque increase is delayed relative to engine rotation number increase, resulting in poor acceleration feeling
Solution Approach 1:
The control device performs preliminary action by adjusting the variable valve timing mechanism in advance before the throttle valve opens. When acceleration is requested, the intake valve timing is changed to an advanced timing earlier than conventional control, which prepares the intake system to respond more quickly to the subsequent throttle opening, thereby reducing the delay between engine rotation increase and drive shaft torque increase.
Solution Approach 2:
The control device applies dynamics by dynamically changing the valve timing based on operating conditions. The intake valve timing is made variable and is adjusted according to the accelerator opening degree and engine state. During acceleration, the timing transitions to a more advanced position, optimizing the intake flow characteristics dynamically to improve torque response speed.
2Speed
If the opening degree of the throttle valve is corrected to be larger than steady state to improve intake negative pressure response, then the response delay is reduced, but the device complexity increases due to additional control mechanisms
Solution Approach 1:
The control device uses the existing variable valve timing mechanism, originally designed for fuel economy optimization, to also improve acceleration response. By making the valve timing variable and controlling it based on accelerator opening degree, the same hardware component serves dual purposes: fuel efficiency during cruising and rapid torque response during acceleration, avoiding additional dedicated hardware.
Solution Approach 2:
The control device changes operational parameters by adjusting the intake valve timing angle based on accelerator opening degree. Instead of modifying the physical structure or adding components, the solution varies the timing parameter dynamically - using more advanced timing during acceleration and returning to conventional timing during steady-state operation, thereby improving response without increasing device complexity.
Data Source
AI summary
A hybrid vehicle includes an engine, a motor, a battery and an electronic control unit. The electronic control unit is configured to set a running torque based on a required torque of a drive shaft according to an accelerator opening degree. The electronic control unit is configured to control the engine and the motor such that the running torque is output to the drive shaft. The electronic control unit is configured to limit the power of the engine by use of the running torque or a drive-shaft torque output to the drive shaft as a torque for determination until the torque for determination reaches a torque threshold smaller than the required torque, as compared with the power of the engine after the torque for determination has reached the torque threshold, when a predetermined acceleration request is made by a user.