Hybrid Steer-by-Wire Actuation for Fail-Operational Steering
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Solution Overview
Problem
Conventional steer-by-wire systems lack redundancy and fail to maintain steering functionality in the event of actuator failure, particularly in larger vehicles where electric actuators are insufficient and hydraulic systems are complex and inefficient.
Innovation Solution
A steer-by-wire system incorporating two or more steering actuators of different types, such as electric and hydraulic, with a control device to manage redundancy and switch between them, ensuring continued steering functionality even if one actuator fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electric steering actuators are used in larger vehicles, then steering precision and responsiveness are improved, but the required power becomes so high that suitable actuators are rarely used
Solution Approach 1:
The patent combines electric and hydraulic steering actuators into a hybrid system. The electric actuator provides precision and responsiveness for normal operation, while the hydraulic actuator supplies additional power when needed. This merging resolves the contradiction by allowing the system to achieve high precision without requiring a single overpowered actuator, instead distributing the power requirement across two complementary systems.
2Power
If hydraulic steering actuators are used, then power and actuating force are improved, but the system becomes larger, more complex, and exhibits higher latency
Solution Approach 1:
The patent segments the steering actuation function into two independent systems: an electric actuator subsystem and a hydraulic actuator subsystem. Each subsystem can operate independently, allowing the system to achieve high actuating force through the hydraulic component while maintaining lower complexity in the electric component. The segmentation enables selective activation of each subsystem based on operational requirements.
3Reliability
If two independent hydraulic systems are used for redundancy, then steering reliability is improved, but the design requirements become very complex and all components must be duplicated
Solution Approach 1:
The patent merges the redundancy function across different actuator types rather than duplicating entire hydraulic systems. The electric and hydraulic actuators serve as complementary redundant systems, where the electric actuator can compensate for hydraulic failures and vice versa. This approach achieves high reliability without requiring duplication of all hydraulic components, thereby reducing design complexity.
4Reliability
If steer-by-wire systems are designed with redundancy, then steering safety is improved, but the system complexity and component duplication increase
Solution Approach 1:
The patent changes the fundamental parameter of the actuator system from homogeneous (two identical hydraulic systems) to heterogeneous (electric and hydraulic systems of different types). This parameter change allows redundancy to be achieved through functional complementarity rather than literal duplication, reducing the complexity increase while maintaining safety. The control device manages the complexity by coordinating the different actuator types based on their operational characteristics.
Data Source
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Figure 2
Figure 3a~3c
AI summary
The invention relates to a steer-by-wire system 1 for steering a motor vehicle. The steer-by-wire system 1 comprises two steering actuators 3, 5 for adjusting at least one steering angle of at least one wheel and/or at least one rigid axle of the motor vehicle. If one of the steering actuators 3, 5 fails, the motor vehicle can still be steered by the other of the steering actuators 3, 5. The steer-by-wire system 1 further comprises a control device 7 for processing steering signals LS and controlling the steering actuators 3, 5 based on the steering signals LS. One of the steering actuators 3, 5 belongs to a first type, and the other of the steering actuators 3, 5 belongs to a second type that differs from the first type.