Torque Coupling Control for Tight Corner Braking in 4WD
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Solution Overview
Problem
Four-wheel-drive vehicles experience tight corner braking phenomena and reduced traction performance due to inadequate torque transmission to auxiliary wheels, especially on low-friction surfaces and when starting from a stopped state, as existing control methods struggle to accurately detect turning radius and wheel speeds at low vehicle speeds.
Innovation Solution
A drive force transmission apparatus with a torque coupling and control device that adjusts torque transmission capacity based on calculated turning radius and wheel speeds, inhibiting tight corner control when skidding is detected, and ensuring sufficient torque is transmitted to auxiliary wheels by considering steering wheel angle and vehicle speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the torque transmission capacity is set to a great value when the four-wheel-drive vehicle turns at a small turning radius, then the traction performance is improved, but the rotation difference between the front wheels and the rear wheels cannot be absorbed, causing tight corner braking phenomenon
Solution Approach 1:
The control device dynamically adjusts the torque transmission capacity based on real-time detection of wheel speeds and calculated turning radius. The torque coupling continuously varies the torque distribution between front and rear wheels to match the actual turning conditions, preventing both tight corner braking and torque deficiency during maneuvers.
Solution Approach 2:
The control device receives feedback from wheel speed sensors and continuously calculates the turning radius based on differential wheel speeds. This feedback loop enables the system to detect turning conditions and adjust torque transmission capacity accordingly, resolving the contradiction between maintaining traction and accommodating rotation differences.
2Ease of operation
If the torque transmission capacity is set to a small value to suppress tight corner braking, then the turning performance is improved, but sufficient torque cannot be transmitted to the auxiliary drive wheels when the vehicle starts on low friction coefficient road surfaces
Solution Approach 1:
The control device monitors wheel speed differences and turning radius to determine when the vehicle is skidding on low-friction surfaces. Based on these parameter changes, the system adjusts the torque transmission capacity to provide sufficient torque for traction while preventing tight corner braking under normal conditions.
Solution Approach 2:
The system replaces fixed mechanical torque distribution with a controllable torque coupling mechanism that can dynamically adjust torque transmission capacity. This substitution enables the system to adapt torque distribution based on detected vehicle state, resolving the contradiction between traction needs and turning performance.
3Measurement precision
If the turning radius is calculated based on the difference between rotational speed of wheels, then the torque transmission capacity can be adjusted appropriately, but a relatively long time elapses from when the vehicle starts to run to when the turning radius can be obtained
Solution Approach 1:
The control device begins calculating the turning radius as soon as the vehicle starts moving, using the differential wheel speeds from the moment motion begins. This preliminary calculation approach reduces the time delay before torque transmission capacity can be adjusted, enabling faster response to turning conditions.
4Measurement precision
If the wheel speed sensors are used to detect rotational speeds, then the turning radius can be calculated, but the sensors may not be capable of accurately detecting the rotational speeds when the vehicle speed is lower than the upper limit value of the vehicle speed range corresponding to the starting state
Solution Approach 1:
The control device uses the detected steering wheel turning angle to predict and compensate for potential detection failures at low speeds. By combining steering angle information with wheel speed data, the system can estimate turning radius even when wheel speed sensors provide unreliable readings during vehicle startup.
Data Source
AI summary
When determining that a vehicle is not skidding, the ECU carries out tight corner control if vehicle speed is smaller than the upper limit value of the vehicle speed range corresponding to the starting state of the vehicle and the steering wheel turning angle of a steering wheel is greater than or equal to the minimum value of the steering wheel turning angle at which the tight corner braking phenomenon may occur. When determining that the vehicle is skidding, the ECU inhibits the tight corner control even if the vehicle speed is smaller than the upper limit value and the steering wheel turning angle is greater than or equal to the minimum value of the steering wheel turning angle at which the tight corner braking phenomenon may occur.