Hybrid EV Creep Torque Control Under Battery Charging Limits
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Solution Overview
Problem
Hybrid electric vehicles face challenges in replicating the creep torque feeling when battery charging is limited, leading to a pushing feeling and fuel consumption due to engine startup, as existing methods rely on engine friction torque which has limitations and causes shift differences during driving.
Innovation Solution
A method for controlling creep torque in hybrid electric vehicles involves determining expected charging power and using the first motor to idle the engine and discharge the battery when the expected charging power exceeds the battery charging limit, allowing the second motor to generate the target creep torque through regenerative braking, thereby avoiding engine startup and maintaining consistent vehicle behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If regenerative braking of the drive motor is used to generate creep torque, then the creep feeling is realized, but when battery charging is limited, the reverse torque cannot be applied and the creep feeling cannot be achieved
Solution Approach 1:
The patent introduces an intermediary system consisting of the first motor, engine, and battery to enable creep torque generation when the drive motor's regenerative braking is limited by battery charging constraints. The first motor acts as a mediator to drive the engine, which then provides friction torque to the drive shaft through the engine clutch, bypassing the battery charging limitation and maintaining creep feeling.
Solution Approach 2:
The patent changes the source of reverse torque from the drive motor's regenerative braking to the engine's friction torque by controlling the first motor to drive the engine. This parameter change in the torque generation mechanism allows the system to adapt to battery charging limitations while maintaining the desired creep feeling.
2Ease of operation
If the engine clutch is engaged to transmit engine friction torque to the drive shaft, then the creep feeling can be achieved, but the engine must be started and speed synchronization is required causing delay and fuel consumption
Solution Approach 1:
The patent applies preliminary action by controlling the first motor to drive the engine to rotate at the target rotational speed before engaging the engine clutch. This pre-synchronization of engine speed with the drive motor speed eliminates the delay that would otherwise occur during clutch engagement and ensures immediate transmission of friction torque for creep feeling.
3Adaptability or versatility
If the engine friction torque is used as the only source of reverse torque, then the creep feeling can be achieved when battery charging is limited, but the friction torque has a magnitude limit and causes shift difference feeling
Solution Approach 1:
The patent merges two torque sources: the drive motor's regenerative braking torque and the engine's friction torque. By combining these torque sources, the system overcomes the magnitude limitation of engine friction torque alone, providing sufficient reverse torque to maintain consistent creep feeling while adapting to battery charging limitations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the realization of creep torque within motor and engine friction torque characteristics, reducing fuel consumption and eliminating shift differences during engine brake mode transitions, ensuring a consistent driving experience.
Implementation Method 1
a first motor configured to drive the engine to rotate
Implementation Method 2
when a target creep torque is generated through regenerative braking of the second motor
Implementation Method 3
a friction torque of the engine when a battery charging is limited
Data Source
AI summary
Disclosed is a hybrid electric vehicle and a method for controlling a creep torque for the hybrid electric vehicle that includes: a first motor connected to an engine, a second motor directly connected to a transmission input terminal, and an engine clutch connected to an engine shaft and the second motor. The method for controlling a creep torque includes: determining an expected charging power that is expected when a target creep torque is generated through a regenerative braking of the second motor; discharging a battery by idling the engine with the first motor while the engine clutch is open when an expected charging power is equal to or greater than a battery charging limit power; and generating the target creep torque via the regenerative braking of the second motor.