Differential Braking for Autonomous Vehicle Direction Control
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Solution Overview
Problem
Autonomous and semi-autonomous vehicles face challenges in maintaining direction control when the electrical power steering (EPS) system fails, as the system's ability to control steering is cut off, potentially leading to vehicle accidents.
Innovation Solution
A method and system that selectively use electrical park brakes (EPBs) and hydraulic brakes to control vehicle direction by determining the total brake force needed and optimizing the fusion of these systems, including determining the appropriate distribution of brake force between front and rear wheels to maintain vehicle stability and alignment with the desired path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the electrical power steering (EPS) system is used for automatic steering control, then the lane centering system can maintain vehicle position in the center of the lane, but the system reliability deteriorates when the EPS system fails
Solution Approach 1:
The system changes the control parameter from steering angle (EPS) to brake force distribution (differential braking). When EPS fails, the lane centering system switches to controlling vehicle direction through differential application of brake force to rear wheels, fundamentally changing the control mechanism to maintain reliability.
Solution Approach 2:
The system prepares a backup control method (differential braking) in advance that can be activated when the primary EPS system fails. This beforehand preparation ensures that the lane centering function remains reliable even when the primary steering system fails.
2Reliability
If the EPS system fails, then the automatic steering control is lost, but the vehicle direction control capability deteriorates
Solution Approach 1:
The brake system is given a dual function: its primary function is to slow or stop the vehicle, and its secondary function is to control vehicle direction through differential braking. This multi-functionality ensures that direction control capability is maintained even when the EPS system fails.
Solution Approach 2:
Instead of using the steering system to control direction (conventional approach), the system inverts the approach by using the brake system to control direction. Differential braking on rear wheels creates a yaw moment that steers the vehicle, fundamentally inverting the control mechanism.
3Reliability
If differential braking is applied to control vehicle direction, then the vehicle can maintain lane centering after EPS failure, but the brake system complexity increases
Solution Approach 1:
The existing brake system components are made multi-functional, serving both their primary braking function and the secondary function of directional control. This avoids adding separate hardware for fail-safe operation, managing complexity while maintaining reliability.
Solution Approach 2:
The brake system serves itself by utilizing its existing capability to generate braking force and applying it differentially to achieve directional control. The same actuator and brake mechanism that slows the vehicle is also used to steer, eliminating the need for additional dedicated fail-safe components.
4Manufacturing precision
If optimal fusion of EPB and hydraulic brake is implemented, then the brake force distribution is optimized for directional control, but the control system complexity increases
Solution Approach 1:
The system optimizes the distribution of brake force as a controllable parameter, dynamically adjusting the ratio of force applied to left versus right rear brakes based on the desired steering angle and vehicle state. This precise parameter control achieves accurate directional control through software algorithms rather than mechanical complexity.
Data Source
AI summary
A method, for controlling direction of a vehicle as desired in connection with operation of an autonomous driving maneuver using selectively, independently and/or in combination, multiple electrical park brakes (EPBs) and multiple hydraulic brakes (HBs). The method includes determining a total brake force needed for redirecting the vehicle in a pre-determined manner, and determining whether an applicable EPB can provide the total brake force needed. The method further includes providing, if it is determined that the applicable EPB can provide the total brake force needed, a brake command instructing the applicable EPB to apply the total brake force. The method also includes determining, if it is determined that the EPB is alone insufficient, an optimal fusion of the EPBs and the HBs, including two front and two rear HBs, two rear EPBs, and in some embodiments, also two front EPBs.