Electric Drive Torque Limiting During Differential Lock Engagement
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Solution Overview
Problem
Existing powertrain systems in vehicles face challenges in managing torque distribution to half shafts during differential locking, particularly when one wheel is in a droop condition and the other is in a jounce condition, leading to potential overloading of half shafts beyond their torque capacity.
Innovation Solution
A controller is programmed to truncate the torque of the electric machine when the differential locker is activated and conditions indicate that one half shaft is likely to exceed its torque capacity, based on factors like wheel displacement, steering angle, and torque command, ensuring the torque distribution does not exceed the capacity of either half shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the differential locker is activated to lock the differential, then the first and second half shafts are restricted to rotate in unison, but the torque distribution to the half shafts may exceed their torque capacity
Solution Approach 1:
The controller calculates the torque capacity of each half shaft before the locker engagement based on sensor data (wheel speeds, steering angle, suspension position) and proactively determines a safe torque limit. This preliminary calculation allows the system to prepare torque truncation parameters in advance, preventing torque overload before it occurs during locker engagement.
Solution Approach 2:
The system continuously monitors wheel speeds, steering angle, and suspension position to calculate half shaft torque capacity in real-time. During locker engagement, the controller uses this feedback to dynamically adjust the torque command to the electric machine, ensuring the torque distribution remains within the calculated safe limits while maintaining differential lock functionality.
2Reliability
If the torque of the electric machine is truncated to prevent half shaft overload, then the torque distribution to the half shafts remains within capacity, but the desired torque output is reduced
Solution Approach 1:
The controller applies torque truncation only to the extent necessary to prevent half shaft overload, rather than completely limiting the torque output. By calculating the specific torque capacity of each half shaft and comparing it with the commanded torque distribution, the system truncates torque partially - enough to protect the half shafts while maintaining maximum possible power delivery within safe limits.
3Reliability
If the controller dynamically adjusts torque output based on real-time conditions, then the half shafts are protected from excessive torque, but the control system complexity increases
Solution Approach 1:
The control logic is segmented into distinct functional modules: sensor data acquisition, torque capacity calculation based on geometric relationships, torque distribution analysis, and torque command adjustment. This modular segmentation of the control algorithm makes the complex control system more manageable and implementable by breaking down the overall control task into separate, well-defined computational steps.
Data Source
AI summary
A vehicle having an electric machine, a first half shaft, a second half shaft, a steering wheel, and a controller. The first and second half shafts are configured to deliver torque from the electric machine to first and second wheels, respectively. The controller is programmed to, in response to (i) locking the first half shaft to the second half shaft, (ii) displacement of at least one of the first and second half shafts or the steering wheel, and (iii) a torque command to the electric machine to a desired value resulting in a torque distribution to the first and second half shafts exceeding a torque capacity of at least one of the first and second half shafts, truncate the torque of the electric machine to less than the desired value.