Vehicle Drive Force Control for Adaptive Friction Circle Limiting
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Solution Overview
Problem
Existing vehicle drive force control methods fail to stabilize vehicle behavior on road surfaces with low friction coefficients, such as icy or snowy conditions, where rapid changes in friction coefficient lead to unstable drive force and vehicle behavior.
Innovation Solution
A vehicle drive force control method that calculates an estimated friction coefficient based on longitudinal and lateral accelerations, limits drive force according to the friction coefficient, and adjusts the change rate of the friction coefficient estimation to prevent abrupt changes, allowing for a slower change rate on low-friction surfaces and a faster response on high-friction surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the drive force control rapidly follows the change of friction coefficient, then the control responsiveness is improved, but the vehicle behavior becomes unstable on low-friction surfaces
Solution Approach 1:
The patent applies dynamics by making the change rate limitation adaptive rather than fixed. The limitation value is dynamically adjusted based on the estimated friction coefficient, allowing the system to be responsive on high-friction surfaces while stable on low-friction surfaces. This resolves the contradiction by making the control characteristics variable according to road conditions.
Solution Approach 2:
The patent changes the parameter of change rate limitation based on the friction coefficient. When the friction coefficient is low, the change rate limitation is set to a smaller value, and when the friction coefficient is high, the limitation is increased. This parameter adaptation allows the system to maintain both stability and responsiveness under different operating conditions.
2Measurement precision
If the change rate of estimated friction circle size rapidly follows friction coefficient changes, then the control accuracy is improved, but the drive force changes abruptly causing vehicle instability
Solution Approach 1:
The system dynamically adjusts the change rate limitation based on the current friction coefficient estimation. This allows the estimated friction circle to accurately track actual conditions while preventing abrupt changes that would cause instability. The dynamic adjustment of the limitation parameter resolves the contradiction between accuracy and stability.
Solution Approach 2:
The change rate limitation acts as an intermediary between the friction coefficient estimation and the drive force control. It filters out abrupt changes in the estimated friction circle size, providing a smoothed control signal that maintains accuracy while preventing instability. This intermediary function resolves the contradiction by decoupling the estimation accuracy from the control response.
3Stability of the object's composition
If the drive force control is limited on low-friction surfaces, then the vehicle stability is improved, but the responsiveness to driver acceleration intentions deteriorates
Solution Approach 1:
The patent changes the change rate limitation parameter based on the friction coefficient. On low-friction surfaces, the limitation is set to a smaller value to maintain stability, while on high-friction surfaces, the limitation is increased to improve responsiveness. This parameter adaptation resolves the contradiction by making the control characteristics match the road conditions.
Solution Approach 2:
The system dynamically adjusts the control characteristics based on real-time friction coefficient estimation. This allows the control responsiveness to be optimized for each driving condition, maintaining stability on icy surfaces while preserving responsiveness on dry surfaces. The dynamic adjustment resolves the contradiction between stability and responsiveness.
Data Source
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AI summary
A vehicle drive force control method according to the present invention includes calculating an estimated friction circle on the basis of longitudinal and lateral accelerations of a vehicle, limiting a drive force of the vehicle depending on a size of the estimated friction circle, and limiting a change rate of the size of the estimated friction circle during vehicle traveling on the basis of a tire generation force. The method further the change rate as the tire generation force increases.