BEV Creep Speed Torque Filtering for Driveline Backlash
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Solution Overview
Problem
Battery electric vehicles (BEVs) lack a creep speed function, leading to potential backlash and driveline damage due to the direct connection of electric motors to wheels, which causes sudden torque changes during gear direction reversals.
Innovation Solution
A creep speed control system that activates when the vehicle speed crosses a predetermined threshold, sending a filtered torque signal to the electric motors to control speed, limiting torque to prevent backlash and allowing gradual torque changes from negative to positive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If electric motors are directly connected to vehicle wheels to provide drive torque, then the vehicle structure is simplified and efficiency is improved, but backlash and driveline damage occur during torque reversal from negative to positive values
Solution Approach 1:
The control system performs preliminary action by detecting when vehicle speed crosses a threshold above the creep speed target value and proactively limiting the torque signal before it can cause backlash. The torque limiter is activated in advance to gradually increase torque from negative to positive values, preventing the sudden torque reversal that would otherwise damage the driveline.
Solution Approach 2:
A torque limiter is introduced as an intermediary component between the creep speed control module and the electric motors. This mediator filters and limits the torque signal, transforming the direct torque connection into a controlled torque transmission path that prevents backlash while maintaining the benefits of direct connection.
2Ease of operation
If creep speed control is activated to simulate conventional vehicle behavior in BEVs, then driver comfort and familiarity are improved, but torque reversal causes backlash and oscillations in the driveline
Solution Approach 1:
The torque limiter serves as an intermediary that allows creep speed control to be activated for driver comfort while preventing the harmful backlash effect. It mediates between the creep speed control module's torque requests and the electric motors, ensuring gradual torque changes that eliminate oscillations.
Solution Approach 2:
The system changes the torque parameter from unfiltered direct control to filtered controlled torque. By limiting the torque signal to a maximum value and filtering it before reaching the motors, the system maintains creep speed functionality while changing the torque delivery characteristics to prevent backlash.
3Reliability
If the creep speed control torque signal is limited to a filtered torque value, then backlash is reduced and driveline damage is prevented, but the response time and speed of torque delivery may be reduced
Solution Approach 1:
The torque limiter applies partial action by limiting the torque signal only when necessary to prevent backlash, rather than continuously reducing torque. The filter allows torque to reach the motors at near-maximum values when safe, providing sufficient response speed while preventing harmful torque reversals.
Data Source
AI summary
The present disclosure relates to a creep speed control system for a vehicle having at least one electric motor for providing torque to at least one vehicle wheel. The system comprises an input configured to receive a current speed signal indicative of a current speed of the vehicle; a creep speed control module that is configured to activate when the current speed of the vehicle crosses a predetermined threshold above a creep speed target value; and, an output configured to, upon activation of the creep speed control module, send a creep speed control torque signal to the at least one electric motor to control the vehicle speed in dependence on the creep speed target value, wherein the creep speed control torque signal is limited to a creep speed control filtered torque value less than a creep speed control maximum torque value.