Electro-Pneumatic Hand Brake Valve Layout for Power-Fail Hold
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Solution Overview
Problem
The electro-pneumatic hand brake system in commercial vehicles can unintentionally release parking brakes due to the bistable solenoid valve remaining in a travel position, leading to dangerous situations when the electrical system fails or is malfunctioning, causing the vehicle to roll, especially on inclined surfaces.
Innovation Solution
A self-retaining switching valve is introduced upstream of the bistable solenoid valve, which can be moved into a flow-through position with sufficient pressure and retains this position independently, preventing ventilation of the spring brake cylinder, even when the bistable solenoid valve is in the flow-through position, thus ensuring the parking brakes remain engaged.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the bistable solenoid valve is used to control ventilation of spring brake cylinders, then the parking brakes can be released during travel, but the valve may remain in the travel position after power failure causing unintentional vehicle movement
Solution Approach 1:
A self-retaining switching valve is introduced as an intermediary component between the air supply and the bistable solenoid valve. This switching valve has a self-retaining characteristic where it maintains its switching position even when control pressure is removed, thereby preventing unintended ventilation of spring brake cylinders after power failure while still allowing normal operation during travel
2Reliability
If the bistable solenoid valve remains in travel position due to electrical system failure, then the parking brakes are unintentionally released, but adding a self-retaining switching valve increases system complexity
Solution Approach 1:
The self-retaining switching valve is designed to automatically maintain its switching position without requiring continuous external control pressure or electrical power. The valve's inherent self-retaining mechanism allows it to service itself by maintaining the blocked position that prevents air supply to the solenoid valve, thereby enhancing safety without requiring additional active control systems
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 self-retaining switching valve prevents unintended ventilation of the spring brake cylinder, maintaining the engagement of parking brakes even after power failure or malfunction, thereby preventing unintentional vehicle movement and enhancing safety.
Implementation Method 1
the self-retaining switching valve can be moved against the force of a restoring element from a blocking position into an flow-through position when there is sufficient pressure at its control input
Implementation Method 2
the self-retaining switching valve can be moved against the force of a restoring element
Implementation Method 3
an inlet of the bistable solenoid valve is provided for connecting to a line carrying ventilation pressure
Data Source
AI summary
An electro-pneumatic hand brake system is for a vehicle with spring-loaded brakes. The system includes a pneumatic relay valve, a bistable solenoid valve for controlling the relay valve and a control unit for controlling the bistable solenoid valve. An outlet of the relay valve is connected to ports for the spring-loaded brakes. An inlet of the bistable solenoid valve is provided for connecting to a line carrying ventilation pressure. A self-retaining switching valve with a control input is provided before the inlet of the bistable solenoid valve. The self-retaining switching valve can be moved against the force of a restoring element from a blocking position into a flow-through position when there is sufficient pressure at its control input. An outlet of the self-retaining switching valve is connected to the inlet of the bistable solenoid valve.