Hybrid Vehicle Braking Transition Control
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Solution Overview
Problem
Hybrid vehicles face inefficiencies in regenerative braking due to the decoupling of powertrain torque from vehicle wheels at low speeds, leading to suboptimal fuel economy and rough deceleration experiences.
Innovation Solution
A control system that transitions from regenerative braking to friction braking by decaying regenerative torque and increasing friction brake resistance when vehicle speed drops below a threshold, ensuring seamless deceleration and maintaining driver braking demand satisfaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If regenerative braking is used at low speeds, then energy recovery is reduced, but fuel economy deteriorates and deceleration smoothness worsens
Solution Approach 1:
The controller predicts the upcoming decoupling event and begins decaying regenerative torque in advance, before the torque converter actually decouples. This preliminary action ensures a smooth transition by gradually reducing regenerative torque while simultaneously increasing friction brake torque, preventing abrupt changes in deceleration force when decoupling occurs.
Solution Approach 2:
The friction brake system serves as an intermediary during the transition from regenerative to mechanical braking. By coordinating friction brake application with regenerative torque decay, the system smoothly transfers the braking function between the two systems, maintaining deceleration smoothness while optimizing energy recovery at low speeds.
2Use of energy by moving object
If regenerative torque is maintained at low speeds, then energy recovery continues, but torque converter decoupling causes abrupt deceleration changes
Solution Approach 1:
The controller predicts the upcoming decoupling event and begins decaying regenerative torque in advance, before the torque converter actually decouples. This preliminary action ensures a smooth transition by gradually reducing regenerative torque while simultaneously increasing friction brake torque, preventing abrupt changes in deceleration force when decoupling occurs.
Solution Approach 2:
The controller continuously monitors vehicle speed, brake pedal demand, and torque converter status to dynamically adjust the blend between regenerative and friction braking. This feedback mechanism ensures that regenerative torque is maintained when beneficial for energy recovery while being reduced when approaching decoupling conditions, maintaining deceleration stability.
3Device complexity
If friction brakes are used exclusively, then deceleration control is simple, but energy recovery opportunity is lost
Solution Approach 1:
The braking system dynamically switches between regenerative and friction braking based on real-time vehicle conditions including speed, brake demand, and torque converter status. At higher speeds, regenerative braking is prioritized for energy recovery; at lower speeds near decoupling, friction braking takes over. This dynamic allocation optimizes energy recovery while maintaining manageable system complexity through automated control.
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 fuel efficiency and smoothness of vehicle deceleration by ensuring that friction brakes take over when regenerative torque is minimal, preventing abrupt changes and optimizing energy recovery.
Implementation Method 1
issue a command for the electric machine to apply a regenerative torque to decelerate the vehicle
Implementation Method 2
cause both a decay in the regenerative torque and a countervailing increase in the resistance of the friction brakes
Data Source
AI summary
A vehicle includes a powertrain having an electric machine, and friction brakes configured to resist rotation of a vehicle wheel. The further includes at least one controller programmed to (i) issue a command for the electric machine to apply a regenerative torque to decelerate the vehicle in response to driver braking demand, and (ii) cause both a decay in the regenerative torque and a countervailing increase in the resistance of the friction brakes when vehicle speed is reduced to less than a first threshold such that braking demand is substantially satisfied by only the friction brakes when the vehicle speed is less than a second threshold.