Patent Application
20170036656
The present disclosure relates generally to a method and system of releasing a parking brake of a machine, in particular, to a hydraulic control system for the parking brake of the machine.
Machines employ a brake system including a service brake for braking during travelling of the machine. Machines are also provided with a fail-safe parking brake for keeping the machine stationary. The parking brake may be a spring-driven, hydraulic-releasing brake. A hydraulic control system having a plurality of fluid component is used in cooperation for applying and releasing the service brake and the parking brake.
The hydraulic control system includes a hydraulic fluid tank, a pump which is fluidly connected to a first pressure storage means and second pressure storage means, for example a first service braking accumulator and a second service braking accumulator. The pump is configured to withdraw fluid from the hydraulic oil tank and output it into the first and second service braking accumulators. The first and second service braking accumulators are connected, via a service brake valve, with the service brake consisting of a front axle brake and a rear axle brake. The hydraulic system further includes a parking brake accumulator in fluid communication with the pump. The parking brake accumulator is connected, via a parking brake valve, with the parking brake. The parking brake is typically used with a power transmission system of the machine for emergency parking.
In an aspect, the present disclosure is directed to a hydraulic control system for a parking brake of a machine. The hydraulic control system includes a hydraulic fluid tank, a pump configured to withdraw hydraulic fluid from the hydraulic fluid tank, and a first accumulator and a second accumulator fluidly connected to the pump. The first and second accumulators configured to supply the hydraulic fluid to the service brake and the parking brake. Further, a resolver valve fluidly coupled between the first and second accumulators and configured to selectively supply the hydraulic fluid from one of the first and second accumulators to the parking brake.
In another aspect, a method for releasing a parking brake in the machine is provided. The method includes charging the first accumulator and the second accumulator from the hydraulic fluid tank and to supply the hydraulic fluid to the service brake and the parking brake. Determining which of the first and second accumulators is at relatively higher pressure. Further, the method includes supplying hydraulic fluid from the determined higher pressure accumulator to release the parking brake.
According to an embodiment of the present disclosure, the hydraulic control system 206 may include a hydraulic fluid tank 220, a pump 224 configured for withdrawing hydraulic fluid such as, oil, from the hydraulic fluid tank 220 through a pump supply conduit 222. The pump 224 may be a variable positive displacement pump such that movement of a swashplate 226, which is contained within the pump 224, controls the output of the pump 224 from zero to maximum. In an embodiment, a solenoid operated valve 230 is used to provide a pressure feedback via a signal conduit 232 to control the output from the pump 224. As illustrated, the solenoid operated valve 230 can be a two-position, three-way valve. In a first position (as illustrated in
At an end of the main supply conduit 228 an accumulator valve assembly 240 is provided. The output from the pump 224, via the main supply conduit 228, is supplied to at least one of a first accumulator 242 and a second accumulator 244, and the accumulator valve assembly 240 controls pressure at the first accumulator 242 and the second accumulator 244. In one example, two branch conduits 250, 252 in fluid communication with the main supply conduit 228 lead to the first and second accumulators 242, 244 respectively. In on example, each of the branch conduits 250, 252 have a check valve 246, 248 being arranged in an opposing manner in the accumulator valve assembly 240. The accumulator valve assembly 240 may be fluidly connected to the first accumulator 242, that is, e.g., a front braking accumulator, and the second accumulator 244, that is, e.g., a rear braking accumulator, via the respective check valves 246, 248. The check valves 246, 248 are configured to provide one-way flow direction when opened based upon a predetermined pressure as provided with the force setting of respective springs. Further, a check valve 229 can be disposed upstream of the accumulator valve assembly 240 and the connection of the discharge conduit 234. The check valve 229 is configured to provide one-way flow direction when opened based upon a predetermined pressure as provided with the force setting of spring.
The pump 224 can be used for other hydraulic functions in the machine 100, but is mainly used for charging the accumulators 242, 244 when a fluid pressure is determined to be lower than a threshold pressure. In one example, a controller 264 is operatively connected with pressure sensors 263. The pressure sensors 263 are configured to generate accumulator pressure signals indicative of the fluid pressure at the accumulators 242, 244. The controller 264 may control the operation of the pump 224, to maintain the fluid pressure equal to or more than the threshold pressure, by controlling the solenoid operated valve 230 for changing the position of the swashplate 226. The controller 264 may include a processor and a memory component. The processor may include microprocessors or other processors as known in the art. In some embodiments the processor may include multiple processors. The processor may execute instructions for determining the fluid pressure of the accumulators 242, 244 and calculating the position of the swashplate 226 to maintain the threshold pressure at the accumulators 242, 244.
The first accumulator 242 and the second accumulator 244, respectively, may be connected, by means of a service brake valve 258, with the front brake assembly 208 and the rear brake assembly 210. A first braking conduit 254 and a second braking conduit 256 are provided to fluidly couple the first and the second accumulators 242, 244 with the service brake valve 258. Further, an operator input device, such as a brake pedal 262, provided in the operator compartment 104, may be activated by an operator during service braking. As a result, the service brake valve 258 is moved to an open position to permit fluid to be discharged from the first accumulator 242 and the second accumulator 244 for supply to the front brake assembly 208 and the rear brake assembly 210, respectively, and tank ports of the service brake valve 258 are blocked. The pressurized hydraulic fluid urges a brake caliper to engage a corresponding disc to apply brake on the wheels 114, 116, and 118. In a closed position (as illustrated in
According to an embodiment of the present disclosure, the parking brake 204 is also fluidly coupled to the first and second accumulators 242, 244. The first and second accumulators 242, 244 can be discharged to the parking brake actuator 212 via a parking brake conduit 268. Further, a parking brake control valve 270 is coupled to the parking brake conduit 268 and operable to control the supply the hydraulic fluid from one of the first and second accumulators 242, 244 to the parking brake 204. The parking brake control valve 270 may be a two-position, three-way valve, as shown. In a first position (as illustrated in
According to an embodiment of the present disclosure, a resolver valve 266 is fluidly coupled between the branch conduits 250, 252 leading to the first and second accumulators 242, 244. In an embodiment, the resolver valve 266 may be a shuttle valve configured to selectively supply the hydraulic fluid from one of the first and second accumulators 242, 244, whichever is relatively at the higher pressure, into a hydraulic flow path, via the second portion of the parking brake conduit 268 connected to the parking brake control valve 270. A one-way check valve 272 and a flow restriction valve 274 may be included to control the pressure and flow characteristics of the fluid to the parking brake actuator 212. Moreover, a filter 276 may be disposed on the first portion of the parking brake conduit 268 between the parking brake control valve 270 and the parking brake actuator 212. The parking brake control valve 270 may be a solenoid operated valve or manually operated by the operator to selectively supply the pressurized hydraulic fluid into the parking brake actuator 212 and release the parking brake 204. According to an embodiment, in order to release the parking brake 204, the controller 264 may command signal to move the service brake valve 258 in the second position and supply the pressurized hydraulic fluid into the parking brake actuator 212. The pressurized hydraulic fluid acts against the compression spring 218 and move apart the brake shoes 214 via the link rod 216 and releases the parking brake 204.
According to another embodiment of the present disclosure, the resolver valve 266 may a electro-hydraulic valve (EH valve) and can be controlled by the controller 264 to control and to selectively supply the hydraulic fluid from one of the first and second accumulators 242, 244 to the parking brake 204 based on the pressure sensors 263 readings.
The brake system 200 can be used in various machines, such as a loader, a grader, an excavator, and other heavy machinery. The machine may be a tractor or any other type of machine associated with certain operations for industries, such as mining, construction, agriculture, and transportation. The disclosed hydraulic control system 206 may help to reduce parts and save cost by utilizing the service braking accumulators alone for releasing the parking brake 204.
Various benefits are associated with the present disclosure, particularly with the disclosed hydraulic control system 206. First, the hydraulic control system 206 utilizes service braking accumulators (i.e., the accumulators 242, 244), during releasing of the parking brake 204. This not only avoids need for an extra dedicated parking brake accumulator, but also reduces load on the pump 224 of charging and maintaining pressure in that extra dedicated accumulator. Second, use of the shuttle valve as the resolver valve 266 provides an inexpensive and retrofittable solution as compared to other expensive sensor based, electro-mechanical or electro-hydrostatic actuators. The shuttle valve may also reduce complexity and associated cost of the hydraulic control system 206. Third, the disclosed hydraulic control system 206 reduces dependencies in the likelihood of failure of one of the accumulators 242 or 244 and still provides proper working of the parking brake 204.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed hydraulic control system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed hydraulic control system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
