Electric Power Steering Torque Control for Rack Movement States
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Solution Overview
Problem
Existing electromechanical steering systems face challenges in providing a natural and direct steering feel, as they often require compromises between sporty and comfortable steering behaviors due to fixed torque relationships that do not account for varying driver inputs and rack movements.
Innovation Solution
A method that dynamically adjusts steering assistance by using different preset functions or characteristic curves based on the presence or absence of rack movement, allowing higher support torques when the rack is stationary and lower torques when in motion, thereby decoupling initial rack movement from subsequent steering states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If high levels of steering assistance are provided with low steering inputs, then driver comfort is improved, but the steering feels less direct and sporty
Solution Approach 1:
The steering assistance system dynamically adjusts the support torque based on the detected rack movement state. When rack movement is detected, the system provides high assistance levels for comfort; when no movement is detected, it reduces assistance to maintain directness. This dynamic adaptation resolves the contradiction by allowing both high comfort and directness at different operational phases.
Solution Approach 2:
The system changes the assistance parameter (support torque level) based on the rack movement state. By detecting whether the rack is moving or stationary, the control unit adjusts the torque ratio between support and hand torque, thereby adapting the steering characteristics to provide either comfort or directness as needed.
2Device complexity
If a linear relationship between driver hand torque and assistance torque is used, then control simplicity is maintained, but steering feel becomes heavy at the beginning of steering maneuvers
Solution Approach 1:
The system performs preliminary detection of rack movement state before determining the assistance torque level. This preliminary action allows the system to prepare the appropriate torque relationship in advance, ensuring responsive steering feel from the beginning of the maneuver without requiring complex real-time calculations.
Solution Approach 2:
The system changes the torque relationship parameter based on rack movement detection. Instead of using a fixed linear relationship, the system selects between different torque ratios depending on whether the rack is moving, thereby improving responsiveness while maintaining relatively simple control logic.
3Reliability
If assistance torque increases proportionally with steering inputs, then consistent support is provided, but initial rack movement is delayed
Solution Approach 1:
The system dynamically adjusts the assistance torque level based on the rack movement state. During the initiation phase (no movement detected), the system provides higher proportional support to overcome static friction and initiate movement quickly. Once movement is detected, it transitions to a different proportional relationship to maintain consistent support during the maneuver.
Solution Approach 2:
The system provides preliminary high-level assistance torque when rack movement is first detected, before transitioning to the standard proportional relationship. This preliminary action ensures that the rack begins moving without delay while still maintaining consistent support throughout the subsequent maneuver.
Data Source
Figure 1~2
AI summary
The invention relates to a method for operating an electric-motor steering system (10) of a vehicle (1), comprising: - monitoring gear rack movements; - sensing a driver steering request; - determining a motor assistance torque (MU) to be produced, on the basis of a specification function (F1, F2) which specifies the assistance torque (MU) to be produced according to the driver steering request; wherein, if there is no gear rack movement when a driver steering request is sensed, the assistance torque (MU) is determined by means of a first specification function (F1); and wherein, if there is a gear rack movement when a driver steering request is sensed, the assistance torque (MU) is determined by means of a second specification function (F2).