On-Demand Four-Wheel-Drive Torque Control via Axle Speed Differential
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Solution Overview
Problem
Existing on-demand four-wheel-drive systems face challenges with high costs due to the use of expensive steering angle sensors and induce stress and noise during vehicle turns due to abrupt torque transfer and large speed differences between axles.
Innovation Solution
A system that includes a sensor system to detect speed differences between the front and rear drive trains and a controller to manage torque distribution through a transfer case, allowing for smooth and efficient torque transfer without a steering angle sensor, by activating the clutch when the rear drive train exceeds the front drive train speed and limiting torque to the front drive train during turns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If torque is split between front and rear axles during vehicle turns, then vehicle stability is maintained, but the vehicle resists turning and stress is induced in the drive train
Solution Approach 1:
The system dynamically adjusts torque distribution between front and rear axles based on real-time speed differential detection. During turns, when speed differentials are detected, the system limits torque to the front axle, allowing smooth turning without drive train stress. During slip conditions, full torque distribution is activated for stability. This dynamic adaptation resolves the contradiction between maintaining stability and enabling smooth turning.
2Ease of operation
If steering angle sensors are used to detect vehicle turns, then torque distribution can be optimized, but system cost increases
Solution Approach 1:
The invention extracts and eliminates the steering angle sensor from the system by using an alternative detection method. Instead of directly measuring steering angle, the system detects speed differentials between front and rear axles, which indirectly indicates turning conditions. This extraction of the expensive sensor while maintaining the functional capability resolves the contradiction between operational ease and device complexity.
Solution Approach 2:
The speed differential measurement acts as an intermediary indicator for detecting vehicle turns. Rather than directly measuring steering angle with an expensive sensor, the system uses the easily measurable speed difference between axles as a proxy indicator. This intermediary approach provides the necessary control information at lower cost, resolving the contradiction between operational capability and system cost.
3Ease of operation
If large speed differences are allowed between front and rear axles, then vehicle turning is facilitated, but torque transfer becomes abrupt and produces noise
Solution Approach 1:
The system continuously monitors speed differentials between front and rear axles and uses this feedback to dynamically control torque distribution. When speed differentials indicating turns are detected, the system responds by limiting front axle torque, which smooths torque transfer and eliminates noise. This closed-loop feedback control resolves the contradiction between enabling turning and preventing noise.
Data Source
AI summary
An on-demand four wheel drive system for a vehicle having a front drive train, a rear drive train, and a transfer case. The system includes a sensor system operable to detect the speed of the front drive train and the speed of the rear drive train. The system also includes a controller operable to cause the transfer case to supply input torque to the front drive train and the rear drive train when the sensor system detects that the speed of the rear drive train exceeds the speed of the front drive train by a predetermined amount. The controller is further operable to cause the transfer case to limit the amount of input torque supplied to the front drive train when the sensor system detects that the speed of the front drive train exceeds the speed of the rear drive train.