Slip Determination System for Electric Vehicles
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Solution Overview
Problem
Conventional slip determination systems for vehicles with electric motor-driven wheels struggle with accurate slip detection during state switches, leading to erroneous slip determination due to backlash clogging and temporary fluctuations in rotational speeds, which affects drivability and accuracy.
Innovation Solution
A slip determination system that acquires wheel speed parameters and basic speed parameters, sets threshold values based on vehicle and wheel speeds, and adjusts these values when the motor's braking/driving force sign is inverted to prevent erroneous slip detection by accounting for temporary speed changes caused by backlash clogging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the command torque is held at 0 for a predetermined time period when the state of the wheels driven/braked by the motor is switched, then torque shock caused by backlash clogging is prevented, but responsiveness of the motor is insufficient and drivability is adversely affected
Solution Approach 1:
The threshold value for slip determination is dynamically adjusted based on the driving/braking state. When the motor transitions from driving to braking state, the threshold value is set to a higher second threshold value that is more difficult to reach, preventing erroneous slip detection during state transitions while maintaining accurate slip detection during steady-state operation.
2Reliability
If the mechanical connection between the motor and the wheels is released temporarily when the state is switched, then backlash clogging is eliminated, but rotational speeds of the motor and wheels are temporarily fluctuated causing erroneous slip determination
Solution Approach 1:
The determination threshold parameter is changed based on operating conditions. During state transitions when rotational speed fluctuations occur due to backlash elimination, the threshold value is adjusted to a second threshold value that accounts for these temporary fluctuations, preventing false slip detection while maintaining measurement accuracy during normal operation.
3Device complexity
If the wheel speed parameter is compared with a fixed threshold value for slip determination, then simple slip detection is achieved, but erroneous determination occurs when rotational speed fluctuates during state switching
Solution Approach 1:
The threshold value is made dynamic rather than fixed. The system automatically selects between a first threshold value and a second threshold value based on the current driving/braking state, maintaining simple detection logic while improving accuracy during state transitions.
Solution Approach 2:
The threshold parameter is adjusted according to operating conditions. When the motor state transitions, the threshold value changes from the first threshold value to the second threshold value, allowing accurate slip determination across different operating states without complicating the detection mechanism.
Data Source
AI summary
A slip determination system for a vehicle, which is capable of improving the determination accuracy by avoiding erroneous determination of excessive slip of wheels when a state of the wheels, driven/braked by motors, is switched. In the slip determination system according to the present invention, when first and second motor rotational speeds NMOT1 and NMOT2, which are rotational speeds of rear motors which brake/drive rear wheels WRL and WRR, reach a reference rotational speed NMREF set based on wheel rotational speeds NWFL, NWFR, NWRL, and NWRR, it is determined that excessive slip has occurred in the rear wheels WRL and WRR. When the sign of a target torque TROBJ of the rear motors is inverted, the reference rotational speed NMREF is changed to a value more difficult to be reached by the first and second motor rotational speeds NMOT1 and NMOT2, or the excessive slip determination is inhibited.