Brake Torque Compensation During EV Gearshift Deceleration
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Solution Overview
Problem
Existing electric traction machines in vehicles experience torque interruption at the wheel during gear changes in braking, particularly in hybrid architectures where regenerative torque is uncoupled, leading to a poorly received loss of braking torque by the user.
Innovation Solution
A method is proposed to compensate for torque loss by defining a mechanical braking torque setpoint at the wheels, which is a function of the electric machine control type and the gear change request, using a control system that adjusts the vehicle's braking system to maintain consistent deceleration during gear changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the sliding gear passes through an intermediate neutral position during gear change, then the dog clutch can be disengaged and reengaged properly, but torque transmission from the electric traction machine to the wheel is interrupted
Solution Approach 1:
The patent introduces a sliding gear as an intermediary element that physically connects or disconnects the electric traction machine from the wheel during gear changes. This sliding gear passes through a neutral position to enable safe disengagement of the dog clutch, while the control system uses it as a mediator to manage the transition between different gear ratios and braking modes.
Solution Approach 2:
The patent dynamically adjusts the control strategy based on the real-time position of the sliding gear. During the transition phase when the sliding gear is in the neutral position, the system dynamically switches between electric braking, mechanical braking, or combined braking modes to maintain torque continuity. This dynamic adaptation allows the system to respond to the changing mechanical configuration during gear changes.
2Reliability
If the torque supplied by the electric motor is canceled during the initial phase of gear change to reduce torque at the dog clutch, then the gear change can be executed safely, but the braking torque at the wheel is significantly reduced
Solution Approach 1:
The patent applies the counterweight principle by introducing mechanical braking as a compensating force to offset the loss of electric braking torque during gear changes. When the electric motor torque is reduced or canceled to protect the dog clutch during disengagement, the mechanical braking system activates to provide an equalizing braking force, thereby maintaining the overall braking torque at the wheel and preventing the perceived braking interruption by the user.
Solution Approach 2:
The patent merges two different braking mechanisms - electric braking and mechanical braking - into a unified braking system. During normal operation, electric braking is used for regenerative energy recovery. During gear changes, when electric braking torque must be reduced, the system seamlessly combines mechanical braking to compensate, creating a hybrid braking approach that maintains performance throughout the transition.
3Adaptability or versatility
If regenerative torque coupling to the wheel is disabled during gear changes in ZEV mode, then the electric machine can change gears without mechanical interference, but torque loss at the wheel is observed during braking
Solution Approach 1:
The patent changes the operational parameters of the braking system based on the gear change state. When detecting that a gear change is in progress in ZEV mode, the system modifies the torque distribution parameters by reducing electric braking torque and increasing mechanical braking torque. This parameter adjustment allows the electric machine to complete gear changes without mechanical interference while compensating for the perceived torque loss through increased mechanical braking contribution.
Data Source
Figure 1~2
AI summary
A method for compensating for wheel torque interruption in the event of a change in braking ratio in a vehicle provided with an electric traction unit (5) linked to the wheels of the vehicle by a gearbox (1) capable of transmitting, to the wheels, the braking torque of the electric traction unit (5) in the deceleration phase over at least two transmission ratios, and a mechanical braking system acting on the wheels independently of the electric traction unit, characterised in that it involves defining a setpoint for mechanical braking torque at the wheels (BRK Tq sp raw(t)), depending on the type of control of the electric traction unit, and the date (Tf) of the downshift ratio change request to the gearbox. The mechanical braking torque setpoint is equal at the time (t) to the difference between an anticipated torque request to the electric traction unit ME Tq sp whl ant(t) and the estimation of the torque at the wheel ME Tq esti whl (t), before the date of the end of the shift at the gearbox (Tf), if the electric traction unit is torque-controlled.