4WD Vehicle Speed Estimation Under Full-Wheel Slip
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Solution Overview
Problem
In four-wheel drive vehicles, the estimated vehicle body speed based on wheel speeds is higher than the actual speed when all wheels are slipping, leading to decreased accuracy in vehicle control and information processing.
Innovation Solution
A method and apparatus that acquire an estimated vehicle body speed using wheel speeds or longitudinal acceleration, perform torque limitation on specific wheels when the estimated speed exceeds a determination speed, and stop the limitation when the actual speed is recovered, ensuring accurate vehicle body speed estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the estimated vehicle body speed is calculated based on wheel speeds, then the calculation is simple and responsive, but the accuracy deteriorates when all wheels are slipping
Solution Approach 1:
The patent introduces a torque limitation control mechanism as an intermediary to correct the inaccurate speed estimation. When wheel slip is detected (estimated speed exceeds actual speed by a threshold), the system applies torque limitation to the drive wheels, which indirectly corrects the speed estimation by reducing the slip condition. This mediator approach resolves the contradiction by maintaining simple speed calculation while improving accuracy through corrective control action.
Solution Approach 2:
The system implements feedback by continuously monitoring the relationship between estimated vehicle body speed and actual wheel speeds. When the estimated speed deviates from the actual speed beyond a predetermined threshold, the system activates torque limitation control. This feedback loop ensures that speed estimation accuracy is maintained by detecting errors and applying corrective measures, resolving the contradiction between simple calculation and accurate measurement.
2Measurement precision
If torque limitation is applied to reduce wheel slip, then the vehicle body speed estimation accuracy is improved, but unnecessary torque limitation may occur when the slip condition is temporary
Solution Approach 1:
The patent applies preliminary action by requiring that the wheel slip condition persists for a predetermined time period before activating torque limitation control. This preliminary verification ensures that temporary or transient slip conditions do not trigger unnecessary torque limitation, thereby maintaining ease of operation and vehicle acceleration performance while still correcting persistent speed estimation errors.
Solution Approach 2:
The system dynamically adjusts its response based on the duration and severity of the wheel slip condition. By incorporating a time-based threshold and configurable torque limitation levels, the system adapts its control action to the actual driving conditions, applying torque limitation only when necessary and at appropriate intensities, thus balancing accuracy improvement with operational ease.
Data Source
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AI summary
A vehicle body speed estimation method applied to a four-wheel drive vehicle (1) includes: acquiring an estimated vehicle body speed based on wheel speeds or a longitudinal acceleration of the vehicle (1); determining whether an operation condition that includes at least a condition that the estimated vehicle body speed is higher than an operation determination speed is satisfied; performing torque limitation to reduce a torque of a portion of wheels (5) of the vehicle (1) when the operation condition is satisfied; determining whether a stop condition that includes a condition that the estimated vehicle body speed is lower than or equal to a stop determination speed or a condition that a duration of a state where a wheel acceleration of the portion of the wheels (5) is higher than zero is longer than or equal to a set period of time; and stopping the torque limitation when the stop condition is satisfied.