Conventional fluid control circuits for brakes, including separate parking and retarding valves, include high volume lines and/or complex mechanical linkages to selectively effect the braking functions. This invention provides a relatively non-complex fluid control circuit (10) for closely controlling engagement of brakes (15), including a first valve (25) for controlling engagement of the brakes (15), a pilot line (20), a second valve (47) connected to the pilot line (20), and movable between a closed position and an open position for venting an inlet (28) to the first valve (25), and a third valve (19 or 22) for closing the pilot line (20) and the second valve (47) or for venting the pilot line (20) to open the second valve (47) to vent the inlet (28) to the first valve (25). The third valve (19 or 22) may include interassociated parking (19) and retarder (22) valves adapted for common attachment within a cab of a vehicle for ready access by an operator thereof.
A system suitable for positively holding an earthmover in a fixed position during excavating or loading operation, comprising a first air reservoir in communication with a parking brake via a parking control valve. A second air reservoir communicates with front and rear wheel brake cylinders via a dual brake control valve assembly and pneumatic-to-hydraulic converters. A pilot-operated source selector valve coacts with shuttle valves to normally allow communication between the brake control valve assembly and the converters and, upon application of the parking brake by the parking control valve, to place the first air reservoir in communication with the converters. Thus the actuation of the parking control valve results in the application of not only the parking brake but also the service brakes. Interposed between the converters and the brake cylinders, pilot-operated brake locking valves also respond to the actuation of the parking control valve for holding the service brakes applied by permitting fluid flow only in a direction from the converters to the brake cylinders.
In the braking systems of many vehicles, a parking brake is utilized that is spring applied and fluid pressure released. In the event of a mechanical breakdown, a mechanical device or other specialized tools must be used to bring about the disengagement of the parking brake so that the vehicle may be towed. The present invention overcomes this problem by providing an auxiliary actuating mechanism for a spring applied, fluid pressure released parking brake that includes an auxiliary accumulator that will maintain a preselected amount of pressure upon the loss of the primary source of pressure. An auxiliary actuating valve is positioned between the accumulator and the parking brake to selectively communicate fluid therebetween. The auxiliary actuating mechanism is provided with two remotely located actuators that may be utilized to selectively position the valve to permit the communication of the pressurized fluid within the accumulator with the parking brake assembly to achieve the disengagement thereof.
A log skidding vehicle (10) having a winch (18) controlled by a lever (20) on which is mounted means (50) for simultaneously actuating a transmission neutralizer (46) and a brake apparatus (38). The actuating means (50), when engaged by the operator, causes a winch brake control valve (32) to transmit compressed air to the brake apparatus (38). Simultaneously therewith, the actuating means (50) causes a transmission neutralizer control valve (42) to obstruct air flow to a transmission neutralizer (46) and thus cause a transmission (48) associated therewith and its shift lever (49) to move to a neutral position. By mounting the actuating means (50) on the winch control lever (20) operator visibility of the skidded load is improved and the operator's comfort is enhanced. In moving the transmission (48) and its shift lever (49) to neutral the utilizing vehicle will not, without additional operator action, move subsequent to disengagement of the brake apparatus (38).
