Hybrid Vehicle Braking Downshift Torque Control
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Solution Overview
Problem
Hybrid propulsion systems with fixed-ratio transmissions experience driveline disturbances due to abrupt changes in engine brake torque during downshifts, affecting vehicle drivability, especially during engine compression braking and descending downhill grades.
Innovation Solution
A hybrid propulsion system with a multiple-step fixed-ratio transmission and a control system that increases the negative torque output of electric energy conversion devices during transmission downshifts to maintain smooth wheel braking torque, utilizing regenerative braking capabilities to reduce driveline disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed-ratio transmission is used for torque transmission, then device complexity and manufacturing cost are reduced, but driveline disturbances occur during downshifts due to abrupt engine brake torque changes
Solution Approach 1:
The electric machines serve as an intermediary between the transmission and wheels, absorbing or generating torque to compensate for abrupt brake torque changes during downshifts. This mediator smooths the torque transmission to the wheels, eliminating driveline disturbances while maintaining the simplicity of the fixed-ratio transmission.
Solution Approach 2:
The control system dynamically adjusts the torque output parameters of the electric machines during downshift events. By changing the electrical torque parameter in response to transmission gear changes, the system compensates for abrupt engine brake torque variations and maintains smooth wheel torque delivery.
2Loss of energy
If transmission downshift is performed during deceleration to extend regenerative braking, then energy recovery is improved, but driveline disturbances and torque spikes are generated
Solution Approach 1:
The control system performs preliminary action by adjusting electric machine torque before and during the downshift event. This preemptive torque adjustment compensates for the upcoming abrupt engine brake torque change, allowing the transmission to downshift for extended regenerative braking while preventing torque spikes from reaching the wheels.
Solution Approach 2:
The control system continuously monitors transmission gear state and wheel torque, providing feedback to adjust electric machine torque in real-time. This feedback mechanism ensures that during downshifts, the electric machines compensate for engine brake torque changes, maintaining smooth torque delivery while enabling energy recovery extension.
3Loss of energy
If engine compression braking is used for vehicle deceleration, then energy recovery is improved, but drivability is reduced due to abrupt torque changes during downshifts
Solution Approach 1:
The electric machines act as a torque mediator between the engine compression braking system and the wheels. During downshifts, they smooth out abrupt torque changes while maintaining the beneficial energy recovery effects of engine compression braking, thereby preserving both energy efficiency and drivability.
Solution Approach 2:
The control system dynamically adjusts the torque parameter of the electric machines in response to downshift events during engine braking. This parameter change compensates for abrupt engine brake torque variations, maintaining smooth drivability while allowing engine compression braking to continue providing energy recovery.
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 enhances vehicle drivability by providing smooth driveline braking during engine braking transmission downshifts, reducing torque spikes and improving energy recovery through extended brake torque application.
Implementation Method 1
the electric machines can be used to absorb torque that may be converted into electric energy which may be stored in a battery in what may be referred to as regenerative braking
Implementation Method 2
a hybrid propulsion system for a vehicle may be configured as a hybrid electric vehicle (HEV), wherein one or more electric machines and an internal combustion engine may be selectively operated to provide the requested propulsive effort
Data Source
AI summary
A hybrid propulsion system for a vehicle is disclosed. In one embodiment an energy conversion device compensates for transmission shifting. The system can improve transmission shifting during at least some conditions.