Brake System with Fail-Open Wheel Valves
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Solution Overview
Problem
Existing brake systems for highly automated or autonomous vehicles face challenges in maintaining availability and cost-effectiveness, particularly in the event of hydraulic or electrical faults, and often require multiple electrically activated valves and isolating valves that increase complexity and manufacturing costs.
Innovation Solution
A brake system with two electrically activated pressure sources, where one pressure source is connected directly to wheel valves without intermediate valves, and a circuit isolating valve allows demand-based division of brake circuits, reducing the number of required valves and eliminating unnecessary flow resistances, while ensuring high availability through independent electronic devices and energy sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple electrically activated valves and isolating valves are used to ensure availability during faults, then reliability is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent removes the circuit isolating valve from the system by implementing a fail-open design where the wheel valves automatically open in case of electrical failure, allowing pressure medium to flow freely to the wheel brakes. This extraction of the isolating valve reduces device complexity while maintaining reliability through the inherent fail-safe behavior of the wheel valves themselves
Solution Approach 2:
The wheel valves are designed with inherent fail-open behavior that automatically activates during electrical failures without requiring additional control systems or isolating valves. The valves serve their own safety function by defaulting to an open state, eliminating the need for separate protective isolation mechanisms and reducing overall system complexity
2Reliability
If isolating valves are arranged between pressure sources and wheel valves to ensure fault isolation, then reliability is improved, but manufacturing costs and device complexity increase
Solution Approach 1:
The patent eliminates the need for isolating valves between pressure sources and wheel valves by designing the wheel valves with inherent fail-open behavior. This extraction removes unnecessary components, reducing manufacturing costs while the fail-open design itself provides the required fault isolation capability through its default safety state
Solution Approach 2:
The design replaces expensive isolating valves with a simpler, more cost-effective wheel valve design that achieves fault isolation through its fail-open behavior. The wheel valves themselves become the primary isolation mechanism, reducing the need for additional expensive isolation components in the hydraulic circuit
3Reliability
If multiple isolating valves are used to disconnect pressure sources from wheel valves, then availability during faults is improved, but the number of electrically activated valves increases
Solution Approach 1:
The patent removes the need for additional isolating valves by implementing fail-open wheel valves that automatically provide fault isolation through their default open state. This extraction eliminates redundant electrically activated valves while maintaining the same reliability level through the inherent safety behavior of the wheel valves
Solution Approach 2:
The wheel valves are designed to perform multiple functions: normal brake actuation control and automatic fault isolation. By making the wheel valves universal components that handle both operational control and safety isolation, the system eliminates the need for separate isolating valves, reducing the total number of electrically activated valves required
Data Source
AI summary
A brake system for a motor vehicle with at least four hydraulically activated wheel brakes. Each of the wheel brakes has a first electrically activated wheel valve which is open when de-energized and a second electrically activated wheel valve which is closed when de-energized, a first electrically activated pressure source, connected to the first wheel valves via a first brake supply line. Arranged in the first brake supply line is an electrically activated circuit isolating valve by which two of the first wheel valves can be hydraulically disconnected from the first pressure source, a second electrically activated pressure source, and a pressure medium reservoir vessel at atmospheric pressure. The circuit isolating valve is designed to be open when de-energized, and the second electrically activated pressure source is connected to the second wheel valves via a second brake supply line. A method for operating the brake system is also disclosed.