Hybrid Vehicle Regenerative Braking Torque Limit Control
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Solution Overview
Problem
Hybrid vehicles face efficiency losses and rough transitions during regenerative braking due to the decoupling of the electric machine from the wheels, particularly at low speeds, which can lead to inefficient energy recovery and discomfort for the driver.
Innovation Solution
A controller is programmed to adjust the regenerative torque limit based on the torque converter's open speed, ensuring a smooth transition by reducing the regenerative torque during transitions into and out of regenerative braking, and applying a replacement limit to maintain stability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the electric machine is decoupled from the wheels during regenerative braking, then energy recovery efficiency is improved, but transition smoothness deteriorates
Solution Approach 1:
The controller anticipates the torque converter clutch open event and proactively reduces the regenerative torque limit before the clutch actually opens. This preliminary action prevents the abrupt transition that would occur if regenerative braking were maintained until the moment of clutch opening, thereby maintaining both energy recovery efficiency and transition smoothness
Solution Approach 2:
The regenerative torque limit is made dynamic rather than static, adjusting in real-time based on the torque converter clutch state and predicted open events. The controller continuously monitors clutch engagement status and modifies the regenerative torque limit accordingly, allowing the system to optimize between energy recovery and transition smoothness under varying operating conditions
2Ease of operation
If the regenerative torque limit is reduced during transitions, then transition smoothness is improved, but energy recovery efficiency deteriorates
Solution Approach 1:
The controller reduces regenerative torque limit in advance of the clutch open event, not after. This timing allows the system to maintain smooth transitions while minimizing the duration and magnitude of regenerative torque reduction, thereby preserving as much energy recovery efficiency as possible during the transition period
Solution Approach 2:
The controller dynamically adjusts the regenerative torque limit parameter based on clutch engagement status and predicted open events. By changing this parameter proactively rather than reactively, the system achieves smooth transitions while minimizing energy loss, as the reduction is timed to coincide with the actual transition needs rather than being applied continuously
3Measurement precision
If multiple controllers are used to manage regenerative braking, then control precision is improved, but system complexity deteriorates
Solution Approach 1:
The patent integrates the regenerative torque limit determination functions across multiple controllers (powertrain control module, transmission control module, and torque converter clutch control) into a unified control strategy. By merging these control functions and having them work cooperatively with a shared understanding of clutch state and regenerative braking requirements, the system achieves high control precision while avoiding the complexity that would arise from multiple independent control systems
Solution Approach 2:
The controllers exchange feedback information about clutch engagement status, regenerative torque application, and predicted open events. This feedback mechanism allows the distributed control system to operate as a coordinated unit, achieving precise control of regenerative braking transitions without the complexity of independent control decisions at each controller level
Data Source
AI summary
A vehicle includes a powertrain having an electric machine configured to selectively apply regenerative torque to cause deceleration in response to braking demand; the powertrain further including a torque converter configured to decouple the electric machine from wheels of the vehicle. The vehicle is also provided with a controller programmed to, during a regenerative braking event, receive a signal defining a regenerative torque limit, and in response to a fault condition associated with the regenerative torque limit, generate a replacement regenerative torque limit based upon a torque converter open speed to decrease roughness during transitions into and out of regenerative braking.