Left-right wheel drive force distribution control for vehicle stability
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Solution Overview
Problem
Conventional drive force distribution control for four-wheel drive vehicles fails to reliably transmit drive force during over-steering and under-steering states, leading to drive slippage and stability issues, especially on canted road surfaces, as it incorrectly adjusts drive force between inside and outside wheels based on yaw rate comparisons.
Innovation Solution
A control system that determines over-steering and under-steering states and sets the drive force difference between left and right subordinate drive wheels to zero, maintaining equal drive force distribution to prevent drive slippage and maintain vehicle stability, even on canted road surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If drive force difference control is executed based on yaw rate comparison during over-steering, then the actual yaw rate can be decreased toward the target yaw rate, but the turning-direction inside wheel undergoes drive slippage and vehicle turning stability is damaged
Solution Approach 1:
The patent inverts the conventional control logic by determining over-steering and under-steering states based on steering operation and vehicle speed rather than yaw rate comparison. This inversion prevents the system from attempting to correct over-steering by increasing drive force to the inside wheel, thereby avoiding drive slippage while maintaining yaw rate control through equal drive force distribution to both subordinate wheels.
Solution Approach 2:
The patent changes the control parameters from yaw rate-based feedback to steering operation and vehicle speed-based feedforward control. By using steering angle and vehicle speed as input parameters to determine steering state, the system avoids the harmful feedback loop that causes drive slippage during over-steering correction while maintaining effective yaw rate management.
2Measurement precision
If drive force difference control is executed during under-steering on canted road surfaces, then the target yaw rate can be achieved, but a yaw moment tending to cause the vehicle to ride up the canted road surface acts on the vehicle
Solution Approach 1:
The patent inverts the control approach by using steering operation and vehicle speed to determine under-steering state rather than relying on yaw rate comparison. This prevents the system from incorrectly interpreting driver counter-steering on canted surfaces as under-steering that requires correction, thereby avoiding the generation of harmful yaw moments that would cause the vehicle to ride up the canted road surface.
Solution Approach 2:
The patent converts the potentially harmful yaw moment generation into a beneficial outcome by recognizing that equal drive force distribution during determined under-steering states maintains vehicle stability on canted surfaces. The control system accepts the under-steering condition and uses equal drive force to prevent unintended vehicle movement while the driver maintains steering control.
3Reliability
If equal drive force is distributed to both subordinate drive wheels during over-steering, then drive slippage is prevented, but the excessively large actual yaw rate cannot be effectively decreased
Solution Approach 1:
The patent implements feedback control by continuously monitoring steering operation and vehicle speed to determine over-steering and under-steering states. This feedback mechanism allows the system to maintain equal drive force distribution during over-steering (preventing slippage) while dynamically adjusting clutch engagement and drive force allocation based on the determined steering state to achieve effective yaw rate convergence.
Solution Approach 2:
The patent introduces dynamic control by making the drive force distribution adaptive to the determined steering state. The system dynamically switches between equal drive force distribution during over-steering and drive force difference control during under-steering, optimizing both drive force transmission reliability and yaw rate convergence speed according to real-time vehicle conditions.
Data Source
AI summary
Upon determining than an over-steered state exits, a feedback control coefficient for a rear wheel total drive force is set to 0 and a feedback control coefficient for a rear wheel drive force difference is also set to 0 to impose a two-wheel drive state. As a result, it is possible to avoid a turn cruising instability caused by cruising in four-wheel drive in an over-steered state. Upon determining that an under-steered state exists, the feedback control coefficients are set such that four-wheel drive is allowed but a drive force difference is not set between the left and right rear wheels. As a result, when the under-steered state exists, excellent traction can be enjoyed by operating in four-wheel drive and the phenomenon of riding up a canted road surface due to a drive force difference set between the left and right rear wheels can be avoided.