Redundant Electrohydraulic Braking System for Autonomous Vehicles
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Solution Overview
Problem
Electrohydraulic vehicle braking systems for autonomous or semiautonomous driving lack redundancy in hydraulic pressure generation, particularly in scenarios where a driver is not present or unable to actuate the brake pedal, necessitating additional safety measures like master cylinders and pushthrough functionality.
Innovation Solution
An electrohydraulic vehicle braking system with two redundantly electrically controllable hydraulic pressure generators and a modular design, featuring valve devices that allow for parallel operation and fail-safe switching, eliminating the need for a master cylinder and pushthrough functionality by ensuring continuous brake pressure generation through redundant hydraulic pressure generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single electrically controllable hydraulic pressure generator is used, then the system complexity is reduced, but the reliability is insufficient for autonomous driving scenarios
Solution Approach 1:
The braking system is segmented into two independent hydraulic pressure generation channels: a first channel with a first hydraulic pressure generator and first valve device, and a second channel with a second hydraulic pressure generator and second valve device. This segmentation allows each channel to operate independently, providing redundancy while maintaining manageable complexity through modular architecture.
Solution Approach 2:
The system changes the operational parameters of the hydraulic pressure generators based on system state. During normal operation, both generators can contribute to brake pressure generation. During failure scenarios, the system automatically adjusts parameters to rely on the functional generator, maintaining reliability without requiring permanent dual-operation complexity.
2Reliability
If a master cylinder with pushthrough functionality is added for emergency braking, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The first and second valve devices are designed with multi-functionality. Each valve device can independently control its associated hydraulic pressure generator during normal operation, and can automatically switch to emergency braking mode by redirecting hydraulic fluid to the fluid reservoir when failure is detected. This eliminates the need for separate master cylinder pushthrough functionality.
Solution Approach 2:
The emergency braking function is merged into the normal braking valve devices. The first valve device and second valve device both incorporate emergency braking capability by being able to connect their respective hydraulic pressure generators to the hydraulic fluid reservoir, combining normal and emergency functions into unified components.
3Reliability
If two electrically controllable hydraulic pressure generators are used for redundancy, then the reliability for autonomous driving is improved, but the system complexity increases
Solution Approach 1:
The hydraulic circuit is segmented into parallel first and second channels, each with its own pressure generator and valve device. This segmentation isolates potential failures to single channels while maintaining overall system functionality, managing complexity through clear modular boundaries.
Solution Approach 2:
The first and second valve devices act as intermediaries between the hydraulic pressure generators and the wheel brakes. They manage the complexity of switching between normal and emergency modes by automatically redirecting hydraulic fluid flow based on system state, without requiring complex control logic in the hydraulic circuit itself.
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
The system provides a highly redundant and efficient braking solution, ensuring reliable brake pressure generation even in the absence of a driver, reducing system complexity and eliminating the need for a master cylinder, while maintaining high fail-safety operations.
Implementation Method 1
an electrically controllable first hydraulic pressure generator and an electrically controllable second hydraulic pressure generator
Implementation Method 2
a first valve device for each wheel brake, having at least one first valve, wherein in an electrically uncontrolled state the first valve device separates its associated wheel brake from an output of the first hydraulic pressure generator
Data Source
AI summary
An electrohydraulic vehicle braking system is provided, comprising an electrically controllable first hydraulic pressure generator and an electrically controllable second hydraulic pressure generator. The braking system further comprises a first valve device for each wheel brake, having at least one first valve, wherein in an electrically uncontrolled state the first valve device separates its associated wheel brake from an output of the first hydraulic pressure generator, and in an electrically controlled state connects it to the output of the first hydraulic pressure generator. In addition, a second valve device for each wheel brake is provided, having a second valve between an output of the second hydraulic pressure generator and its associated wheel brake, as well as a third valve between this wheel brake and a first hydraulic fluid reservoir. The first valve device and the second valve device are arranged in parallel to one another.