1992-04-01

Reverse Modulating Brake Valves, Circuit Design Considerations and Applications 920908

Spring apply, hydraulic release (SAHR) brake circuits can provide service, emergency, and parking brake functions, requiring less hardware as compared to a conventional hydraulically actuated brake circuit. However, the spring apply, hydraulic release brakes also require unique control circuits.
Brake system components must be selected based on the unique features of spring apply hydraulic release brakes. Each component will affect the overall performance of the brake system. This paper will discuss design prerequisites, circuit design considerations, component selection and brake design considerations.
Spring applied hydraulic release brake systems are becoming increasingly important to off-highway equipment designers and engineers. For this reason it is important to understand the difference between the conventional hydraulic brake actuation system and the spring applied hydraulic release brake actuation system.
To obtain brake performance as recommended by the many accepted brake standards (Ref. 1), a conventional hydraulic brake actuation system may require independent service, secondary, and parking brake circuits to provide braking in the event of any single failure in the service brake system. Service brake actuation systems are commonly split to add redundancy to a system. This method produces 50% service braking with any single brake circuit failure. In addition, parking functions typically require an independent brake and a separate method of actuation. The complexity of such systems will be apparent when you consider the number of valves, switches, hoses and connectors that are involved.
Spring apply, hydraulic release brake systems, on the other hand, may consist of a single circuit, providing service, secondary and parking functions with a common brake(s). The actuation circuit used to control this brake will require limited control hardware and plumbing. Consequently, this brake system will be easy to maintain, troubleshoot and is cost effective.

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