Vehicle Braking-Force Control for Oversteer and Understeer Stability
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Solution Overview
Problem
Existing vehicle braking-force control devices face challenges in maintaining vehicle stability during oversteer and understeer conditions, as they often compromise driver intention for acceleration and comfort, and may lose effectiveness when engine torque is adjusted.
Innovation Solution
A vehicle braking-force control device that includes a road-surface friction coefficient estimator, ground-load estimator, lateral-tire-force estimator, permissible-engine-torque calculator, vehicle-behavior detector, brake controller, and engine-torque controller to dynamically adjust braking and engine torque based on real-time conditions, ensuring stability and reflecting driver intent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If brake control is applied to outside turning wheels during oversteer condition, then vehicle stability is improved, but driver's acceleration intention may be compromised
Solution Approach 1:
The system dynamically changes engine torque parameters based on detected vehicle conditions. During oversteer, engine torque is reduced to a value lower than current torque to prevent further instability, while during understeer, torque is limited based on calculated permissible values. This parameter adjustment resolves the contradiction by adapting the torque level to match both stability requirements and driver intent.
Solution Approach 2:
The system continuously monitors vehicle behavior through the vehicle behavior detector and adjusts engine torque accordingly. The feedback loop ensures that torque reduction or limitation is applied only when necessary for stability, otherwise allowing full driver acceleration intention to pass through, thus resolving the contradiction between stability control and driver intent.
2Stability of the object's composition
If engine torque is over-reduced during oversteer prevention, then vehicle stability is improved, but driver comfort and acceleration expectation are compromised
Solution Approach 1:
The system applies partial torque reduction during oversteer conditions rather than complete torque cut-off. By reducing torque to a value lower than current but not eliminating it entirely, the system provides just enough stability correction while maintaining driver comfort and acceleration expectation, avoiding excessive action that would cause discomfort.
3Stability of the object's composition
If brake control is applied to inside turning wheels during understeer condition, then vehicle stability is improved, but engine torque limitation may reduce acceleration performance
Solution Approach 1:
The system dynamically adjusts engine torque based on real-time vehicle conditions and road surface friction. During understeer, torque is limited to calculated permissible values that maintain stability while allowing maximum possible acceleration. The dynamic nature of the control ensures acceleration performance is optimized within stability constraints, resolving the contradiction between stability and productivity.
Data Source
AI summary
A braking-force control device has a brake control function for performing brake control on a front outside wheel when a vehicle is detected to be in an oversteer condition during a turning operation and for performing brake control on a rear inside wheel when the vehicle is detected to be in an understeer condition during a turning operation. For preventing the oversteer condition, a command for reducing the engine torque is output. On the other hand, for preventing the understeer condition, the engine torque is limited in accordance with a permissible engine torque value that is calculated on the basis of a road-surface friction coefficient, and ground loads and lateral tire forces of individual wheels. If it is detected that engine braking is in operation, the engine torque is adjusted to substantially zero.