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 function if a steering actuator fails, particularly in larger vehicles where electric actuators are insufficient and hydraulic systems are inefficient and complex.
Innovation Solution
A steer-by-wire system with two or more steering actuators of different categories (e.g., hydraulic and electric) that can continue to operate if one actuator fails, utilizing a control device to manage the actuators' complementary advantages and compensate for their disadvantages, ensuring fail-operational functionality.
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 in a hybrid system. The electric actuator provides precision and responsiveness for normal operation, while the hydraulic actuator supplements the system during high-power requirements or failure modes, thereby achieving both precision and sufficient power without relying on a single actuator type.
Solution Approach 2:
The system dynamically changes the operational parameters by switching between electric and hydraulic actuators based on power demands. The control device monitors system state and adjusts which actuator is active, allowing the system to operate at optimal parameters for different operating conditions.
2Power
If hydraulic steering actuators are used, then steering power is improved, but the system becomes larger, has higher latency, and greater complexity
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 power when needed while maintaining the precision benefits of electric control. The segmentation allows selective activation based on operational requirements.
Solution Approach 2:
The hybrid system provides multi-functionality by enabling the steering system to perform both precise control (electric actuator) and high-power actuation (hydraulic actuator). The control device manages both actuators to provide universal steering capability across different operating conditions, from normal driving to high-load scenarios.
3Reliability
If two independent hydraulic systems are used for redundancy, then system reliability is improved, but the structural configurations become very extensive
Solution Approach 1:
Instead of copying the entire hydraulic system twice for redundancy, the patent uses one electric actuator and one hydraulic actuator. The electric actuator serves as the redundant backup, providing failover capability without requiring a second complete hydraulic system. This approach maintains reliability while significantly reducing structural complexity.
Solution Approach 2:
The patent replaces the mechanical/hydraulic redundancy approach with an electromechanical solution. The electric actuator, being electronically controlled and simpler in structure, substitutes for the second hydraulic system, thereby reducing mechanical complexity while maintaining the redundancy needed for safe operation.
4Reliability
If steer-by-wire systems are designed redundantly with duplicate components, then safety is improved, but the system becomes more complex
Solution Approach 1:
The patent merges the redundancy function into a hybrid actuator architecture where the electric and hydraulic systems work together. Rather than duplicating entire systems, the control device manages both actuators to provide redundant capability, achieving safety while minimizing the complexity increase through intelligent integration.
Data Source
AI summary
A steer-by-wire system for steering a motor vehicle includes two steering actuators 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 fails, the motor vehicle can still be steered by the other of the steering actuators. The steer-by-wire system further includes a control device for processing steering signals and controlling the steering actuators on the basis of the steering signals. One of the steering actuators is from a first category and the other of the steering actuators is from a second category, which differs from the first category.