What is in this article?:
- Hydraulics goes off spring brakes
- Hydraulic release
Hydrostatic transmissions are widely used to drive and decelerate just about every type of mobile equipment. But when a machine is at rest, any of several spring-applied brakes can be used to ensure that the machine remains at rest.
Another simple solution to disengage the brake of a disabled vehicle is to use a ball valve and a hand pump. The ball valve serves as a connection between brake valve and brake cylinder. The hand pump can then be used to pressurize the brake’s hydraulic line, thereby releasing the brake. This method saves time because, depending on the hydraulic circuitry, it disengages all brake cylinders simultaneously. Perhaps more importantly, it does not require a mechanic to crawl under the machine. This makes it possible to safely release the parking brake even when the machine is parked on an incline.
The position of the ball valve at a central position of the machine indicates the operating status of the parking brake. Some machine manufacturers fix the control lever in place with a screw in order to prevent the ball valve from being actuated inadvertently. This prevents unintentional disengagement of the parking brake. However, a mechanic could still forget to reset the ball valve once repairs are complete or when the towing procedure is finished. As with the mechanical release, this would leave the vehicle’s parking brake disabled.
Indicating the switching position of the ball valve to the operator requires monitoring pressure in the brake line or position of the valve actuating lever. Because it is rarely necessary to interfere with the parking brake circuit, this type of monitoring is generally not implemented. Therefore, no convenient method is provided to determine whether or not the parking brakes have been disengaged.
The most effective solution would be to provide quick and easy disabling of the brakes, prevent unintentional disabling, and provide feedback so an operator knows if the parking brakes are operational or have been disabled. However, to be practical for machine builders, it cannot add substantially to the cost beyond that of the standard hydraulic solution.
Automatic pressure-dependent resetting of the changeover valve has been developed by Argo-Hytos, Bowling Green, Ohio. The solution is both simple and cost-effective. It does not interfere with the machine‘s control system and can be retrofitted into existing machines or integrated into new designs.
The Argo-Hytos solution works in a fashion similar to the standard hydraulic valve already described. It incorporates a manually actuated 2-port, 2-position (2/2-way) directional control valve fitted with a hydraulic resetting system. Pushing a button causes the 2/2-way directional valve to block flow between the brakes’ cylinders and the main 3/2-way brake valve. A hand pump is then used to pressurize the line to the brake, which has now been isolated from the rest of the hydraulic circuit.
When the towing procedure is finished, the parking brake can be reengaged by pulling out the control button. If the operator forgets to reset the 2/2-way directional valve after repairing the machine, the valve will be reset automatically by the brake supply pressure. This resetting takes place regardless of whether or not the actual brake valve has been actuated or de-energized because the control signal in the pressure line is tapped upstream of the 3/2-way directional valve. This means the machine cannot be operated if the parking brake has been disabled unintentionally. The operator can be confident that the parking brake is operational simply by noticing that the control button is extended. This solution greatly improves the safety, efficiency, and reliability operation of mobile equipment.
An integrated solution
The valves are housed in a manifold block, which can also incorporate the hand pump. Three models are available for different applications. Model 1 consists of a pressure-switched 2/2-way directional control valve and a pressure relief valve. It is intended for machines already equipped with a hand pump. Model 2 is identical to Model 1 but it incorporates a hand pump into the manifold. Model 3 features a hand pump, a 2/2-way directional and relief valve, plus a solenoid actuated 3/2-way directional valve, which serves as the main parking brake control valve. This full-featured assembly is a cost-effective alternative to specifying all the components separately, takes up little additional space, and is easy to install.
This information was provided by Argo-Hytos. For more information, call (419) 353-6070 or visit www.argo-hytos.com.