All-Wheel Drive Torque Control via Friction Analysis
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Solution Overview
Problem
All-wheel drive motor vehicles with engageable systems face the risk of axle overload, particularly when the front axle is on asphalt and the rear axle is on ice, leading to potential component damage and limitations in engine performance and hill climbing abilities due to torque distribution imbalances.
Innovation Solution
A control system with an analysis unit adjusts the maximum allowed engine torque by adding a moment of inertia fraction from the rear axle with a low friction coefficient to the front axle with a high friction coefficient, allowing for increased engine torque without risking axle overload, and includes an electronic differential lock to enhance torque distribution during startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the maximum allowed engine torque is limited to prevent front axle overload, then component protection is ensured, but engine performance and hill climbing abilities are reduced
Solution Approach 1:
The control system dynamically adjusts the maximum allowed engine torque based on real-time driving conditions, particularly the friction coefficients of the front and rear axles. When the front axle has high friction and rear axle has low friction, the system increases the allowed torque beyond traditional limits by utilizing the rear axle's moment of inertia, thereby maintaining engine performance while preventing front axle overload through adaptive control
Solution Approach 2:
The system changes the parameter of maximum allowed engine torque based on the friction conditions of different axles. By detecting the friction coefficient difference between front and rear axles, the control instrument adjusts the torque limit parameter dynamically, allowing higher torque when rear axle slip is possible, thus resolving the contradiction between component protection and engine performance
2Stability of the object's composition
If torque is distributed uniformly to front and rear axles via mechanical differential, then torque compensation between axles is achieved, but front axle overload cannot be prevented when front axle has higher friction
Solution Approach 1:
The control instrument continuously monitors the friction coefficients of both axles and uses this feedback to dynamically adjust torque distribution. When the front axle friction coefficient is significantly higher than the rear axle, the system receives feedback that the front axle is at risk of overload and accordingly limits the torque transmitted to the front axle, preventing component damage while maintaining stable torque distribution under normal conditions
Solution Approach 2:
The system transitions from static uniform torque distribution to dynamic adaptive torque distribution. Based on real-time friction condition detection, the control system dynamically adjusts the torque split between axles, allowing non-uniform distribution when friction conditions differ significantly, thus preventing front axle overload while maintaining overall system stability
Data Source
AI summary
A drive device for an all-wheel drive, two-track motor vehicle, in the drive train of which a first motor vehicle axle and, via a center clutch, a second motor vehicle axle are driven permanently by a drive assembly in driving operation. In the closed state of the center clutch, the second vehicle axle is engaged with the drive train, and, in the open state of the clutch, the second vehicle axle is decoupled from the drive train. In a driving situation with engaged all-wheel drive as well as with axle friction coefficients of varying size, a greater wheel torque can be taken up at the vehicle axle with a large axle friction coefficient than at the vehicle axle with a small axle friction coefficient, and a control instrument is provided, which, for engine torque limitation, limits the drive assembly to a maximum allowed engine torque.