Hybrid Vehicle Torque Modulation During Regenerative Braking Downshifts
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Solution Overview
Problem
Hybrid vehicle powertrains experience shift shock during downshifts in regenerative braking due to variations in total powertrain output torque, which is not effectively addressed by existing solutions that require complex control systems and energy wastage.
Innovation Solution
A controller regulates the powertrain to maintain constant total output torque during downshifts by modulating engine and electric motor torques and adjusting friction braking force, allowing for three modes: modulating engine torque, electric motor torque, or both, and compensating for lag time in friction braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If regenerative braking is applied during downshift in hybrid powertrain, then fuel economy is improved through kinetic energy recovery, but shift shock increases due to negative torque at transmission input
Solution Approach 1:
The controller predicts the upcoming downshift event and proactively modulates the regenerative braking torque before the shift occurs. By anticipating the shift timing based on transmission speed ratio changes, the system reduces negative torque at the transmission input in advance, preventing shift shock while maintaining energy recovery efficiency
Solution Approach 2:
The system dynamically adjusts the regenerative braking torque level in real-time based on transmission operating conditions. During predicted downshift events, the controller modulates the magnitude of regenerative torque to match the dynamic requirements of the shifting transmission, allowing smooth transition between gear ratios while continuing to recover kinetic energy
2Ease of operation
If regenerative braking torque is reduced during downshift, then shift quality is improved, but energy recovery efficiency decreases
Solution Approach 1:
The controller implements periodic modulation of regenerative braking torque that synchronizes with the transmission downshift cycle. During the brief downshift interval, torque is reduced to ensure smooth shifting, then restored to maximum level immediately after the shift completes, creating a rhythmic pattern that maintains both shift quality and overall energy recovery efficiency
Solution Approach 2:
The system temporarily skips regenerative braking torque application during the critical downshift window, allowing the transmission to complete the ratio change without disturbance. This brief interruption is strategically timed to minimize impact on overall energy recovery, as the system rapidly resumes torque modulation after the shift event
Data Source
AI summary
A controller and a control strategy minimizes shift shock in a hybrid electric vehicle during a downshift conducted while the vehicle is in a regenerative braking mode by maintaining total powertrain torque at a desired target during the downshift. The controller has three preferable modes including modulating just engine torque, modulating just electric motor torque or simultaneously modulating both motor and engine torque.