Vehicle Drive Force Control Using Adaptive Friction Circle Limits
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Solution Overview
Problem
Vehicle behavior becomes unstable on road surfaces with low friction coefficients due to rapid changes in friction coefficient, leading to abrupt changes in drive force, especially on icy or snowy surfaces where friction coefficient variations are significant.
Innovation Solution
A vehicle drive force control method that calculates an estimated friction circle based on longitudinal and lateral accelerations, limits drive force according to the friction circle size, and adjusts the change rate of the friction circle size during travel based on tire generation force, increasing the change rate as the tire generation force increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the change rate of the estimated friction circle rapidly follows the change of the friction coefficient, then the drive force responds quickly to road surface changes, but the drive force abruptly changes causing vehicle behavior instability 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 current friction coefficient and vehicle state, allowing the system to respond quickly on high-friction surfaces while suppressing rapid changes on low-friction surfaces. This resolves the contradiction by making the response characteristics flexible and context-dependent.
Solution Approach 2:
The patent changes the parameter of change rate limitation based on the friction coefficient magnitude. When the friction coefficient is below a threshold, a stricter limitation is applied; when above the threshold, a more permissive limitation is used. This parameter adaptation allows the system to optimize both responsiveness and stability according to road conditions.
2Stability of the object's composition
If the drive force is limited based on the estimated friction circle, then vehicle behavior stability is improved on low-friction surfaces, but the responsiveness to road surface changes is reduced
Solution Approach 1:
The limitation strategy is made dynamic by adjusting the change rate limitation value based on real-time friction coefficient estimation. The system transitions between restrictive and permissive limitation modes according to road conditions, ensuring stability when needed while maintaining responsiveness when safe.
Solution Approach 2:
Different limitation strategies are applied locally based on the friction coefficient magnitude. The system applies strict change rate limitation only in the low-friction regime (below threshold), while allowing faster response in the high-friction regime (above threshold). This localized application of different control qualities resolves the contradiction.
3Measurement precision
If the friction coefficient estimation changes rapidly on icy or snowy road surfaces, then the estimated friction circle accurately reflects road surface variations, but the drive force changes abruptly causing vehicle instability
Solution Approach 1:
The patent introduces a change rate limitation mechanism as an intermediary between the friction coefficient estimation and the drive force control. This intermediary filters out excessive variations in the drive force that would result from rapid friction coefficient changes, while still allowing the estimation to reflect actual road surface conditions. The limitation value acts as a buffer that prevents direct transmission of estimation noise to the drive force.
Data Source
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.