Vehicle Steering Torque Control via Non-Linear Proportional Gain
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Solution Overview
Problem
Existing driver assistance systems for vehicles using electric power steering face challenges in preventing rapid changes in steering torque control during driver intervention, which can lead to discomfort, and in maintaining compliance with target steering angles despite disturbances.
Innovation Solution
The system employs different proportional and integral term characteristics based on the presence or absence of driver steering intervention, with non-linear characteristics slowing the increase of the proportional term and a coefficient-based integral term calculation to prevent rapid changes in steering torque, ensuring compliance with the target steering angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the control amount of steering torque is increased to ensure compliance with target steering angle, then the compliance is improved, but rapid change occurs causing driver discomfort
Solution Approach 1:
The patent applies dynamics by making the proportional term characteristics changeable based on driving conditions. The ECU switches between first proportional term characteristics (with larger proportional gain) and second proportional term characteristics (with smaller proportional gain) depending on whether the vehicle is traveling straight or turning. This dynamic adjustment allows the system to maintain high compliance during straight travel while reducing rapid changes and driver discomfort during turning operations.
Solution Approach 2:
The patent implements parameter changes by modifying the proportional gain value based on the steering angle. When the absolute value of the steering angle exceeds a threshold (indicating a turn), the system switches to smaller proportional gain to prevent excessive steering torque changes. This parameter adaptation resolves the contradiction by adjusting the control aggressiveness according to the current maneuver type.
2Speed
If the proportional gain is increased to improve response speed, then the compliance with target steering angle is improved, but the steering torque changes rapidly causing discomfort
Solution Approach 1:
The system dynamically adjusts the proportional gain based on the steering angle magnitude. During straight travel (small steering angle), a larger proportional gain is used to ensure fast response and high compliance. During turning (large steering angle), a smaller proportional gain is applied to prevent rapid torque changes that would discomfort the driver. This conditional parameter switching resolves the speed-comfort contradiction.
Solution Approach 2:
The patent applies local quality by using different control parameters for different operating conditions. Instead of a uniform proportional gain, the system uses first proportional term characteristics for straight travel and second proportional term characteristics for turning. This localized parameter optimization allows high response speed where needed while minimizing discomfort where aggressive control is unnecessary.
3Object-affected harmful factors
If the control amount is limited to prevent rapid change, then driver comfort is improved, but the compliance with target steering angle may decrease
Solution Approach 1:
The system dynamically selects the appropriate control characteristics based on the steering angle. During straight travel, the full compliance-oriented control is applied without artificial limitations. During turning, the system switches to modified characteristics that inherently limit the rate of change. This conditional approach maintains compliance where critical while ensuring comfort where appropriate.
Solution Approach 2:
The patent segments the control strategy into two distinct modes: one for straight travel with high compliance priority, and another for turning with comfort priority. By dividing the operating conditions and applying different control characteristics to each segment, the system achieves both compliance and comfort in their respective contexts without compromise.
Data Source
AI summary
When a steering intervention of the driver is performed during automated steering control, a driver assistance system for a vehicle determines a P control amount based on a non-linear characteristics and calculates an I control amount using a coefficient according to a characteristics (solid line). In an angle difference range R1, the P control amount based on the non-linear characteristics is determined such that the amount of increase of absolute value of the P control amount with respect to the amount of increase of absolute value of the angle difference becomes smaller as compared to a linear characteristics. The coefficient with the characteristics (solid line) indicates 1 in the angle difference range R1, and approaches zero when the absolute value of the angle difference is greater in an angle difference range R2. To calculate the I control amount, the coefficient is multiplied by the current value of the angle difference.