Steer-by-Wire Rack Force Determination During Friction
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Solution Overview
Problem
Steer-by-wire steering systems face challenges in generating realistic reaction forces, particularly when no rack movements occur due to internal system friction, leading to inadequate driver feedback.
Innovation Solution
A method to detect frictional operation in the steering system by determining the rack force based on the positioning force of the vehicle wheel actuator, allowing for realistic reaction force generation even without rack movement, using control signals and variables from the actuator to account for internal friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rack force is determined using conventional methods (modeling with vehicle speed or steering handle position), then cost is reduced by avoiding direct measurement, but measurement precision deteriorates because friction effects cannot be adequately accounted for
Solution Approach 1:
The patent introduces the actuating force from the vehicle wheel actuator as an intermediary variable to indirectly determine rack force. Instead of directly measuring rack force (which would be expensive) or using imprecise modeling, the system uses the actuating force signal from the actuator that is already present in the system to represent the rack force, especially during frictional operation when rack movement is zero.
Solution Approach 2:
The system continuously monitors rack movement and steering handle position changes to detect frictional operation states. When friction is detected (rack movement remains zero despite steering input), the system switches to using actuating force as the rack force indicator. This feedback mechanism ensures accurate rack force determination adapts to changing operating conditions.
2Ease of operation
If rack movement is used to determine rack force, then measurement is simplified, but reliability deteriorates during frictional operation when rack movement is zero despite actual rack forces being present
Solution Approach 1:
The patent dynamically adapts the method for determining rack force based on the detected operating state. During normal operation with rack movement, conventional methods can be used. During frictional operation when rack movement is zero, the system switches to using actuating force as the determinant. This dynamic adaptation ensures reliability across all operating conditions.
Solution Approach 2:
The actuating force serves as an intermediary indicator that reliably represents rack force even when rack movement is zero. During frictional operation, the actuating force becomes the proxy measurement for rack force, allowing the system to maintain reliability without directly measuring rack force or relying on rack movement.
3Device complexity
If reaction force is adjusted based on modeled rack force, then direct measurement equipment is avoided, but driver feedback realism deteriorates due to unaccounted friction effects
Solution Approach 1:
The actuating force from the vehicle wheel actuator serves as an intermediary variable that directly reflects the actual rack force being applied, including the effects of friction. By using this intermediary signal instead of simplified models, the system maintains low device complexity while significantly improving the realism of reaction force feedback to the driver.
Data Source
Figure 1~2
AI summary
The invention relates to a method for determining a gear rack force of a steer-by-wire steering system (1), the steering system (1) comprising: a steering handle (2), by means of which a steering angle can be specified as a function of a steering handle position; a vehicle wheel actuator (11), which is designed to set the steering angle by movement of a gear rack (9) of the steering system (1), by applying an actuating force (F), said gear rack being coupled to at least one vehicle wheel; a reaction force actuator (5), by means of which a reaction force on the steering handle (2) can be produced in accordance with a gear rack force, the method comprising: determining friction operation, in which gear rack movement does not occur when the steering handle position is changed; and, if friction operation is present: determining the gear rack force on the basis of the actuating force (F) of the vehicle wheel actuator (11). The invention further relates to a steer-by-wire steering system (1) and to a vehicle having a steer-by-wire steering system (1) of this type.