EV Rear Wheel Torque Control for Steering Stability
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Solution Overview
Problem
Electric vehicles with rear wheels driven by motors face degradation in steering stability due to changes in turning angle, caused by yaw motion and compliance in the rear wheel suspension, leading to reduced ride quality and stability.
Innovation Solution
An electric vehicle with left and right rear wheels capable of independent motor-driven control, using a control device to calculate and correct target driving forces based on relative displacement differences between the rear wheels, reducing the difference in longitudinal displacement and velocity to minimize turning angle changes and maintain steering stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the rear wheel suspension compliance is increased to improve ride quality, then the ride quality is improved, but the steering stability deteriorates due to increased yaw motion and turning angle changes of rear wheels
Solution Approach 1:
The control device calculates target driving forces for the left and right rear wheels in advance based on the difference in relative displacement amounts, and controls the driving forces to reduce the displacement difference before it causes significant steering instability. This proactive control prevents the worsening of steering stability while maintaining suspension compliance for ride quality.
2Productivity
If the vehicle speed is increased to improve productivity, then the productivity is improved, but the steering stability deteriorates due to more conspicuous rear wheel yaw motion
Solution Approach 1:
The control device continuously monitors the relative displacement amounts of the left and right rear wheels and adjusts the target driving forces based on the detected difference. This feedback control ensures that steering stability is maintained across various vehicle speeds by dynamically compensating for yaw motion effects on the rear wheels.
3Speed
If the change speed of steering angle of front wheels is increased to improve responsiveness, then the responsiveness is improved, but the steering stability deteriorates due to more conspicuous rear wheel turning angle changes
Solution Approach 1:
The control device proactively calculates and applies corrective driving forces to the rear wheels based on the detected displacement difference before the steering instability fully develops. This preliminary control action maintains steering stability even when the front wheels undergo rapid steering angle changes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces the change in turning angle of the rear wheels, thereby enhancing steering stability without compromising ride quality or requiring reduced suspension compliance, even under conditions like cross winds.
Implementation Method 1
left and right rear wheels, which are suspended from a vehicle body by suspensions that elastically allow the left and right rear wheels to be displaced in a longitudinal direction of the electric vehicle with respect to the vehicle body
Data Source
AI summary
Provided is an electric vehicle, including: left and right rear wheels, which are suspended from a vehicle body by suspensions that elastically allow displacements in a longitudinal direction of the vehicle with respect to the vehicle body, the rear wheels being capable of being driven by corresponding motors independently of each other; and a control device configured to control driving forces of the rear wheels. Target driving forces Ti for the left and right rear wheels are calculated during traveling, a value ΔG relevant to a difference between relative displacement amounts of the rear wheels in a longitudinal direction of the vehicle with respect to the vehicle body is calculated, and the target driving forces are corrected based on the value relevant to the difference between the relative displacement amounts so that a magnitude of the value relevant to the difference between the relative displacement amounts becomes smaller.