Secondary Steering via Differential Braking and Scrub Radius
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Solution Overview
Problem
Autonomous vehicles face uncontrollability due to steering actuator faults, leading to potential road departure, and existing redundant steering systems increase complexity and cost.
Innovation Solution
A secondary steering system unit that utilizes differential braking, yaw torque, and scrub radius to control the vehicle's path, eliminating the need for redundant actuators by activating differential braking of at least one wheel brake to steer the vehicle along a generated path when a fault in the main steering system is detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant steering actuators are used to ensure safety, then reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical steering actuator system with a braking system to achieve steering control. When the main steering actuator fails, the secondary steering system uses differential braking forces on the wheels to generate yaw torque and alignment torque, which steers the vehicle without requiring a redundant steering actuator. This substitution of mechanical steering with braking-based steering resolves the contradiction by maintaining reliability through a backup system while avoiding the complexity and cost of redundant steering actuators.
2Reliability
If a steering actuator fault occurs, then reliability deteriorates, but using redundant actuators increases device complexity
Solution Approach 1:
The braking system is designed to perform both its primary function of deceleration and a secondary function of steering control. The wheel brakes are equipped with sensors and control arrangements that enable them to generate differential braking forces for steering purposes when the main steering actuator fails. This multi-functionality allows the same braking components to serve dual purposes, maintaining vehicle controllability without adding dedicated redundant steering actuators.
Solution Approach 2:
The patent substitutes the failed steering actuator's function with the braking system. The control arrangement detects steering actuator faults and activates the secondary steering mode, where differential braking forces replace the overlay torque that would normally be provided by the steering actuator. This substitution maintains vehicle controllability while avoiding the need for complex redundant steering system architecture.
3Device complexity
If differential braking is used for steering, then device complexity is reduced, but control precision must be maintained
Solution Approach 1:
The secondary steering system incorporates sensors (such as yaw rate sensors, steering angle sensors, and wheel speed sensors) that provide feedback to the control arrangement. The control arrangement continuously monitors the vehicle's response to differential braking and adjusts the braking forces accordingly to achieve the desired steering effect. This feedback mechanism ensures that even though the braking system is used for steering rather than a dedicated actuator, the steering control precision is maintained through active control and real-time adjustments.
Solution Approach 2:
The control arrangement dynamically adjusts the braking force parameters (magnitude, distribution, and duration) to achieve precise steering control. By varying the braking force on individual wheels based on real-time vehicle state and desired trajectory, the system can precisely control the vehicle's path despite using a braking system originally designed for deceleration. The parameter changes in braking force allow the system to compensate for the non-ideal characteristics of using brakes for steering.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient and cost-effective vehicle control during steering faults, enhancing safety by allowing the vehicle to follow a safe path without road departure, using a single wheel's differential braking and scrub radius for lateral control.
Implementation Method 1
a vehicle wheel brake arranged to brake the vehicle wheel
Implementation Method 2
a steering angle resulting from a generated alignment torque on a braked steerable wheel caused by the associated wheel suspension scrub radius
Data Source
Figure 1a~2
Figure 3
Figure 4
AI summary
A vehicle (50), a method (100), a secondary steering system unit (40) and a secondary steering system (36) are provided. The secondary steering system unit (40) comprises: a fault determination arrangement (41), arranged to determine the presence of a fault in the main steering system and a path controller (42), arranged to generate an upcoming path (P) for the host vehicle (50). The secondary steering system unit (40) is arranged to steer the host vehicle (50) along the path (P) by differential braking upon determination that a fault is present in the main steering system and is arranged to steer the differential braking in dependence of both a yaw torque (T) acting on the host vehicle (50) as a result of the differential braking and a steering angle resulting from a generated alignment torque on a braked steerable wheel (10) caused by the associated wheel suspension scrub radius (27).