Vehicle Force Distribution Control for Split Friction Estimation
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Solution Overview
Problem
Existing methods for estimating road surface friction coefficient have varying error ranges, leading to unstable vehicle behavior due to excessive driving or braking forces on rear wheels, particularly during acceleration and deceleration, as they fail to integrate different estimation principles effectively.
Innovation Solution
A braking and driving force control apparatus that includes independent motors for front and rear wheels, with a control system using two friction coefficient settings: a first estimation based on tire forces and a second based on road surface properties, to dynamically adjust the output allotment ratio between these motors, ensuring stable vehicle behavior by setting lower and upper limits on friction coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single road surface friction coefficient estimation method is used, then the device complexity is reduced, but the measurement precision and reliability of friction coefficient estimation deteriorates due to varying error ranges
Solution Approach 1:
The patent divides the friction coefficient estimation into two separate segments: a first estimation based on tire forces (from vehicle dynamics) and a second estimation based on road surface properties (from sensors). Each estimation method has its own calculation unit, allowing them to operate independently with their respective error characteristics, thereby improving overall measurement precision without excessive complexity increase.
Solution Approach 2:
The patent merges the two different friction coefficient estimation results into a unified control system. The braking and driving force distribution control unit integrates both estimations to determine the actual friction coefficient, combining the advantages of both methods while compensating for their individual limitations and error ranges.
2Adaptability or versatility
If the friction coefficient estimation error range is large, then the adaptability to different road conditions improves, but the vehicle stability deteriorates due to excessive driving or braking forces on rear wheels
Solution Approach 1:
The patent implements a feedback mechanism where the control unit continuously monitors both friction coefficient estimations and adjusts the driving and braking force distribution accordingly. When the estimated friction coefficient indicates low-friction road conditions, the system automatically reduces rear wheel forces to prevent slip or locking, thereby maintaining vehicle stability while adapting to varying road conditions.
Solution Approach 2:
The patent changes the control parameters (driving force and braking force distribution ratios) based on the friction coefficient estimation results. By dynamically adjusting these parameters according to the estimated friction level, the system maintains optimal vehicle stability across different road conditions without excessive forces on rear wheels.
3Productivity
If friction coefficient estimation is performed during acceleration, then the driving force control improves, but the rear wheel slip increases due to excessive driving force
Solution Approach 1:
The patent applies partial action by using only the necessary portion of the estimated friction coefficient information for driving force control. Instead of fully utilizing the maximum possible driving force, the system carefully modulates the rear wheel driving force based on the friction estimation, applying just enough force to maintain traction without causing slip.
4Productivity
If friction coefficient estimation is performed during braking, then the braking force control improves, but the rear wheel locking increases due to excessive braking force
Solution Approach 1:
The patent applies preliminary anti-action by anticipating potential rear wheel locking and taking preventive measures. The control unit calculates the safe braking force limit based on the friction coefficient estimation before excessive braking force is applied, thereby preventing rear wheel locking while maintaining effective braking control.
Data Source
AI summary
A braking and driving force control apparatus to be provided in a vehicle including front-wheel and rear-wheel longitudinal force generators that generate longitudinal forces of front and rear wheels, respectively. The braking and driving force control apparatus includes: first and second road surface friction coefficient setting units that respectively set first and second road surface friction coefficients; and a braking and driving force distribution control unit. The second road surface friction coefficient is larger than the first road surface friction coefficient. When the front-wheel and rear-wheel longitudinal force generators generate a driving force, the braking and driving force distribution control unit controls an output allotment ratio by using the first road surface friction coefficient. When the front-wheel and the rear-wheel longitudinal force generators generate a braking force, the braking and driving force distribution control unit controls the output allotment ratio by using the second road surface friction coefficient.