Systems and methods for using a source of pressurized fluid for actuating a pump to an overcenter state in bidirectional shaft applications

Abstract

An example hydraulic system includes: a pump driven by an input shaft that is bidirectional, wherein the pump has a swashplate, wherein the pump draws fluid through an inlet port and discharges fluid through an outlet port of the pump; a control piston coupled to the swashplate of the pump; a source of pressurized fluid; and one or more valves that control fluid flow from the source of pressurized fluid to the control piston, wherein as a direction of rotation of the input shaft is reversed, the one or more valves control fluid communication from the source of pressurized fluid to cause the control piston to move the swashplate to an overcenter position, causing the pump to continue providing fluid flow through the outlet port of the pump.

Description

Systems and Methods for Using a Source of Pressurized Fluid for Actuating a Pump to an Overcenter State in Bidirectional Shaft ApplicationsCROSS REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to (i) U.S. Provisional Application No. 63 / 657,161 filed on June 7, 2024, (ii) U.S. Provisional Application No. 63 / 705,576 filed on October 10, 2024, and (iii) U.S. Provisional Application No. 63 / 747,409 filed on January 21, 2025, the entire contents of all of which are herein incorporated by reference as if fully set forth in this description.BACKGROUND

[0002] A hydraulic pump is a mechanical device that converts mechanical or electrical energy into fluid pressure or hydraulic energy. For example, a shaft of an internal combustion engine or electric motor can be coupled to a rotating group of a pump such that as the shaft rotates, the pump displaces fluid from an inlet port to an outlet port of the pump. Fluid is then used to perform work, such as operate hydraulic actuators (e.g., hydraulic cylinders or hydraulic motors).

[0003] In some applications (e.g., marine or agricultural applications), the shaft driving the pump may be expected to reverse its direction of rotation. In such examples, it may be desirable to configure the pump in a manner that allows the pump to continue providing fluid flow from the same outlet port regardless of the direction of rotation of the shaft. It is with respect to these and other considerations that the disclosure made herein is presented.SUMMARY

[0004] The present disclosure describes implementations that relate to systems and methods for using a source of pressurized fluid for actuating a pump to an overcenter state in bidirectional shaft applications.

[0005] In a first example implementation, the present disclosure describes a hydraulic system. The hydraulic system includes: a pump driven by an input shaft that is bidirectional, wherein the pump has a swashplate, and wherein an angle of the swashplate determines fluid flow rate from the pump; a control piston coupled to the swashplate of the pump; a source of pressurized fluid; and an electrically-actuated valve that controls fluid flow from the source of pressurized fluid. The electrically-actuated valve is configured to enable fluid flow from the source of pressurized fluid to cause the control piston to move the swashplate to an overcenter position, causing the pump to continue providing fluid flow when the input shaft reverses its rotational direction.

[0006] In a second example implementation, the present disclosure describes a machine (e.g., a tractor) including the hydraulic system of the first example implementation.

[0007] In a third example implementation, the present disclosure describes a method of operating the hydraulic system of the first example implementation or the machine of the second example implementation.

[0008] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, implementations, and features described above, further aspects, implementations, and features will become apparent by reference to the figures and the following detailed description.BRIEF DESCRIPTION OF THE FIGURES

[0009] Figure 1 is a block diagram representing a machine, according to an example implementation.

[0010] Figure 2 illustrates a cross-sectional side view of a pump with a swashplate of the pump in a neutral position, according to an example implementation.

[0011] Figure 3 illustrates a cross-sectional side view of the pump of Figure 2 with the swashplate in a positive stroke position, according to an example implementation.

[0012] Figure 4 illustrates a cross-sectional side view of the pump of Figure 2 with the swashplate in an overcenter position, according to an example implementation.

[0013] Figure 5 illustrates a schematic of a hydraulic system of the machine of Figure 1, according to an example implementation.

[0014] Figure 6 illustrates another schematic of a hydraulic system of the machine of Figure 1, according to an example implementation.

[0015] Figure 7 illustrates another schematic of a hydraulic system of the machine of Figure 1, according to an example implementation.

[0016] Figure 8 illustrates another schematic of a hydraulic system of the machine of Figure 1, according to an example implementation.

[0017] Figure 9 is a graph showing test results for the hydraulic system of Figure 5, according to an example implementation.

[0018] Figure 10 is a flowchart of a method for operating a hydraulic system, according to an example implementation.DETAILED DESCRIPTION

[0019] Disclosed herein are systems and methods for using a source of pressurized fluid to actuate a pump to an overcenter state. This way, the pump can draw fluid from a suction line via a single inlet port and discharge fluid via a single outlet port regardless of a direction of rotation of a shaft driving the pump.

[0020] Figure 1 is a block diagram representing a machine 100, according to an example implementation. The machine 100 can be an agricultural machine, such as a combine header, for example. The machine 100 has actuators 102, which can be hydraulic cylinders or motors, to control operation of various implements of the machine 100.

[0021] The machine 100 has a hydraulic system 103 that controls operation of the actuators 102. The hydraulic system 103 includes a pump 104 configured as a source of fluid flow. Particularly, the pump 104 is configured to draw fluid from a fluid reservoir 106 through an inlet port 108 of the pump 104, then displace the fluid to be discharged via an outlet port 110 of the pump 104.

[0022] Fluid can then be provided to the actuators 102, and fluid discharged from the actuators 102 can then return to the fluid reservoir 106. A fluid connection between the actuators 102 and the fluid reservoir 106 is not shown to reduce visual clutter in the drawing.

[0023] As an example, the pump 104 can be a variable displacement piston pump having a rotating group that is rotatable via a central or input shaft 112, which is driven by a prime mover 114 (e.g., engine or electric motor) of the machine 100. As described in more details below, the pump 104 can have a swashplate, the position of which determines the flow rate of fluid discharged from the pump 104.

[0024] The position of the swashplate of the pump 104 is determined by one or more cylinder actuators as described below. The machine 100 includes one or more valve(s) 116 that control fluid flow to the one or more cylinder actuators that control position of the swashplate of the pump 104.

[0025] In an example, the input shaft 112 is bidirectional. In other words, the input shaft 112 can be rotated by the prime mover 114 in both rotational directions (e.g., clockwise and counterclockwise) to propel the machine forward or in reverse. In such examples, it may be desirable to move the swashplate to an overcenter position when the input shaft 112 rotates in the reverse or opposite direction. This way, the pump 104 continues to draw fluid through the inlet port 108 and discharge fluid through the outlet port 110 to maintain operation of the actuators 102 regardless of the direction of rotation of the input shaft 112.

[0026] Particularly, if the input shaft 112 rotates in a first rotational direction (e.g., clockwise), the swashplate is actuated (via the cylinder actuators) to move in a first direction (e.g., to a positive displacement position). If the input shaft 112 rotates in a second rotational direction (e.g., counterclockwise), opposite the first rotational direction, it may be desirable to actuate the swashplate to move in a second direction (e.g., to the overcenter position). This way, the pump 104 continues providing fluid flow through the outlet port 110.

[0027] Conventional systems include multiple pumps and an extensive logic network (including several valve elements) to operate the pumps and prevent cavitation. The hydraulic system 103, however, enables maintaining flow through the outlet port 110 of the pump 104 via a simplified system architecture, reducing complexity and weight, and increasing reliability of the system or machine.

[0028] Particularly, to enable the swashplate to move to the overcenter position, the machine 100 has a source 118 of pressurized fluid. The source 118 can be referred to as an “external source” of fluid as it is separate from the pump 104.

[0029] In one example, the source 118 can be a separate charge pump. In another example, the source 118 includes an accumulator operating as a source of stored pressurized fluid, as described below with respect to Figures 5-8.

[0030] The valve(s) 116 control fluid flow to and from the source 118. For example, the valve(s) 116 can include an electrically-actuated valve that controls fluid flow between the source 118 and the pump 104. A fluid connection between the valve(s) 116 and the fluid reservoir 106 may exist, but is not shown to reduce visual clutter in the drawing.

[0031] The machine 100 can include a controller 120. The controller 120 can have a microprocessor that can include one or more processors. A processor can include a general purpose processor (e.g., an INTEL® single core microprocessor or an INTEL® multi core microprocessor), or a special purpose processor (e.g., a digital signal processor, a graphics processor, or an application specific integrated circuit (ASIC) processor). A processor can be configured to execute computer-readable program instructions (CRPI) to perform the operations described throughout herein. A processor can be configured to execute hard-coded functionality in addition to or as an alternative to software-coded functionality e.g., via CRPI).

[0032] The controller 120 can receive sensor signals indicating a direction of rotation of the input shaft 112. For example, a rotary sensor may be coupled to the input shaft 112 and such sensor may provide rotary direction information to the controller 120. In another example, the controller 120 may be in communication with an input device (e.g., a joystick), which indicates a direction of travel of the machine 100 as commanded by an operator. In another example, the controller120 may be in communication with a controller of the prime mover 114. As such, the controller 120 can receive information indicating that the rotational direction of the input shaft 112 is about to change or has changed.

[0033] Responsively, the controller 120 can command the valve(s) 116 to provide flow to the cylinder actuators of the pump 104 to position the swashplate in an overcenter position. This way, the pump 104 can maintain drawing fluid through the inlet port 108 and providing fluid through the outlet port 110 to the actuators 102 regardless of the direction of rotation of the input shaft 112.

[0034] Figure 2 illustrates a cross-sectional side view of the pump 104 with a swashplate of the pump 104 in a neutral position, according to an example implementation. The pump 104 includes a housing 200 (e.g., a casting) and a port block 202 coupled to the housing 200 via a plurality of fasteners. Seals can be disposed at the interface between the housing 200 and the port block 202 to prevent leakage.

[0035] The port block 202 includes the inlet port 108 and the outlet port 110 of Figure 1. For example, the inlet port 108 can be fluidly coupled to the fluid reservoir 106, while the outlet port 110 can be fluidly coupled to the actuators 102.

[0036] The pump 104 has the input shaft 112, which is coupled to a rotating group of the pump disposed within the pump 104 as described below. As the input shaft 112 rotates, the pump draws fluid through the inlet port 108 and discharges fluid through the outlet port 110.

[0037] The pump 104 has a swashplate 204 and a rotating group 206 mounted to the input shaft 112 and rotatable therewith. As shown, the input shaft 112 is supported via a first bearing 208 and a second bearing 210 disposed within the housing 200 and the port block 202 to facilitate rotation of the input shaft 112.

[0038] The rotating group 206 includes a cylinder block 212 defining a plurality of cylinders such as cylinder 214 therein. The rotating group 206 further includes a plurality of pistons, such as piston 216, disposed in a circular array within the respective cylinders of the cylinder block 212. For example, the piston 216 is disposed within a chamber 218 formed within the cylinder 214. The pistons (e.g., the piston 216) are each coupled to a slipper 220, which allows the pistons to slip across the surface of the swashplate 204 as the rotating group 206 rotates.

[0039] The pump 104 further includes a valve plate 236 configured as a disk having openings or holes that operate as inlet or low pressure holes fluidly coupled to the inlet port 108 of the pump 104. The inlet port 108 can be fluidly coupled to the fluid reservoir 106 as mentioned above. The valve plate 236 also has openings or holes operating as an outlet or high pressure openings fluidly coupled to the outlet port 110 of the pump 104.

[0040] The input shaft 112 can be coupled to an output shaft of the prime mover 114, which controls rotation of the input shaft 112. As the input shaft 112 rotates, the rotating group 206 rotates therewith. As the rotating group 206 rotates while the swashplate 204 is disposed at a zero angle (a vertical position perpendicular to the input shaft 112) as shown in Figure 2, the pistons (e.g., the piston 216) do not reciprocate and no fluid is drawn from the fluid reservoir 106 or discharged from the pump 104.

[0041] If the swashplate 204 is moved to a particular angle, the pistons reciprocate within their respective cylinders. For example, the piston 216 can reciprocate within the cylinder 214 when the rotating group 206 rotates and the swashplate 204 is angled. By varying the angle of the swashplate 204, a continuous ratio from zero flow to a maximum fluid flow rate can be obtained. The angle of the swashplate 204 relative to the input shaft 112 can be changed via a first cylinder actuator 222 and a second cylinder actuator 224 having a biasing spring 226.

[0042] Particularly, the first cylinder actuator 222 has a control piston 228 movable in a chamber 230 formed in a cylinder of the first cylinder actuator 222. Similarly, the second cylinder actuator 224 has a bias piston 232 movable in a chamber 234 formed in a cylinder of the second cylinder actuator 224. The bias piston 232 may also be referred to as a control piston, similar to the control piston 228. The biasing spring 226 biases the bias piston 232, and thus the swashplate 204 to a positive stroke or on-center position.

[0043] Fluid provided to the chamber 234 also applies a fluid force on the bias piston 232 to extend and move the swashplate 204 to the positive stroke position. On the other hand, fluid provided to the chamber 230 of the first cylinder actuator 222 applies a fluid force on the control piston 228, thereby applying a force on the swashplate 204 to return to a neutral position or move to an overcenter position as described below.

[0044] Thus, the position of the swashplate 204 is determined via a force balance or equilibrium between the fluid force acting on the control piston 228, the fluid force acting on the bias piston 232, and the spring force of the biasing spring 226. Notably, the surface area of the control piston 228 may be larger than a respective surface area of the bias piston 232. With this configuration, if pressure level in the chamber 230 is equal to pressure level in the chamber 234, the fluid force acting on the control piston 228 is larger than the fluid force acting on the bias piston 232.

[0045] Figure 3 illustrates a cross-sectional side view of the pump 104 with the swashplate 204 in a positive stroke position, according to an example implementation. If fluid is provided to the chamber 234 such that the fluid force acting on the bias piston 232 and the biasing force of the biasing spring 226 overcome the fluid force acting on the control piston 228, the bias piston 232 can extend, pushing the swashplate 204 to left in Figure 3 (rotating the swashplate 204 in a clockwise direction) increasing the angle of the swashplate 204 as shown in Figure 3.

[0046] The angle of the swashplate 204 determines respective strokes of the pistons of the rotating group 206, and thus determines the flow rate of fluid discharged from the pump 104. If the angle of the swashplate 204 relative to the input shaft 112 is 90 degrees (e.g., the swashplate 204 is vertical) as shown in Figure 2, the pump 104 does not discharge fluid. However, when the swashplate 204 is actuated to a particular angle as shown in Figure 3, the pistons of the rotating group 206 reciprocate within the cylinder block 212, thereby drawing fluid from the fluid reservoir 106 coupled to the inlet port 108 and discharging fluid through the outlet port 110 of the pump 104.

[0047] By changing the angle of the swashplate 204, the stroke of the pistons of the pump 104 can be varied continuously to vary the amount of fluid flow discharged from the pump 104. In other words, the angular position of the swashplate 204 determines a pump displacement PD of the pump 104, where the pump displacement PD can be expressed in cubic inches per revolution (in3 / rev), for example. The pump displacement PD determines the amount of fluid discharged by the pump 104. The prime mover 114 of the machine 100 rotates the input shaft 112 at a particular speed having units of revolutions per minute (RPM), for example. As such, multiplying the speed of the input shaft 112 by PD determines the fluid flow rate Q in cubic inches per minute (in3 / min) provided by the pump 104.

[0048] As mentioned above, it may be desirable to have the pump 104 continue to provide fluid through the outlet port 110 when the input shaft 112 reverses its rotational direction. As such, when the controller 120 senses, or receives information indicating, that the input shaft 112 reversed its rotational direction, the controller 120 actuates the valve(s) 116 in a manner that causes the source 118 to provide fluid to the chamber 230 such that the fluid force acting on the control piston228 overcomes the fluid force and the spring force acting on the bias piston 232. This way, the swashplate 204 moves to an overcenter position.

[0049] Figure 4 illustrates a cross-sectional side view of the pump 104 with the swashplate 204 in an overcenter position, according to an example implementation. As depicted, the control piston 228 has moved to a fully-extended position, while the bias piston 232 has retracted against the biasing spring 226. In this position of the swashplate 204, as the input shaft 112 rotates in an opposite rotational direction, the pump 104 maintains providing fluid through the outlet port 110 to the actuators 102.

[0050] Implementation of the hydraulic system 103 of the machine 100 as shown in Figure 1 can take several forms. For example, operations of the valve(s) 116 can be accomplished using different types of valves.

[0051] Figure 5 illustrates a schematic of a hydraulic system 300 of the machine 100, according to an example implementation. The hydraulic system 300 is an example implementation of the hydraulic system 103 described in Figure 1. The same components shown in Figures 1-2 and Figure 5 are designated with the same reference numbers. The prime mover 114 and the controller 120 are not shown in Figure 5 to reduce visual clutter in the drawing.

[0052] The hydraulic system 300 includes the pump 104 which is configured to draw fluid from the fluid reservoir 106 through the inlet port 108, then displace the fluid to be discharged via the outlet port 110 to the actuators 102 via fluid line 302. Check valve 304 prevents back flow to the fluid reservoir 106.

[0053] As mentioned above, the fluid forces acting on the control piston 228 and the bias piston 232 are determined based on pressure level of fluid supplied to the chambers 230, 234. The forceequilibrium between the fluid forces and the spring force of the spring 226 determines the position of the swashplate 204. Fluid from the outlet port 110 of the pump 104 is provide via fluid line 306 to the chamber 234. Such fluid applies a fluid force on the bias piston 232 and the swashplate 204, and this fluid force along with the biasing spring 226 tend to move the swashplate 204 to the positive stroke position represented by arrow 308.

[0054] Referring to Figures 1, 5 together, the valve(s) 116 include a proportional valve 310 that controls pressure level of fluid supplied to the chamber 230 of the first cylinder actuator 222. For example, the proportional valve 310 can be a solenoid-actuated valve such that a command signal provided to its solenoid actuator 312 determines a position of a movable element (e.g., piston, spool, or poppet) within the proportional valve 310, which in turn controls pressure level provided to the chamber 230. Particularly, fluid from the outlet port 110 of the pump 104 is provided via a check valve 314 to an inlet port of the proportional valve 310. The controller 120 provides a command signal to the solenoid actuator 312 of the proportional valve 310 to set the position of its movable element, thereby controlling the pressure drop or decrease across the proportional valve 310, thus controlling the pressure level of fluid discharged from the outlet port of the proportional valve 310 to the chamber 230.

[0055] As such, the fluid forces acting on the control piston 228 and the bias piston 232, which in turn act on the swashplate 204, can be controlled via the command signal to the proportional valve 310. This way, the angle of the swashplate 204 is controlled by the command signal to the proportional valve 310.

[0056] In some examples, the pump 104 may include one cylinder actuator rather than two. Such cylinder actuator can have a control piston coupled to the swashplate 204, and a spring can also be coupled to the swashplate 204. The relative magnitudes of the fluid force acting on the controlpiston and the biasing force of the spring determine the angle of the swashplate 204. Thus, a pump may include at least one cylinder actuator in some implementations.

[0057] To enable the swashplate 204 to move to the overcenter position represented by arrow 316 (corresponding to Figure 4), the hydraulic system 300 has the source 118 of pressurized fluid, which is an external source of fluid as mentioned above with respect to Figure 1.

[0058] In one example, the source 118 can be a separate charge pump. In another example, as shown in Figure 5, the source 118 includes an accumulator 318 operating as a source of stored pressurized fluid. Particularly, the accumulator 318 is configured to store pressurized fluid therein at a particular pressure level, e.g., based on a charge pressure of gas within the accumulator 318.

[0059] The valve(s) 116 (see Figure 1) of the hydraulic system 300 can further include an electrically-actuated valve 320 that controls fluid flow to and from the accumulator 318. For example, in an unactuated position or state, the electrically-actuated valve 320 operates as a check valve allowing fluid flow from the outlet port 110 of the pump 104 through the check valve 314 and the electrically-actuated valve 320 to charge the accumulator 318. In this state, the electrically- actuated valve 320 prevents discharging the accumulator 318 when pressure level of fluid at the outlet port 110 is less than pressure level within the accumulator 318.

[0060] On the other hand, when a solenoid actuator 322 of the electrically-actuated valve 320 is energized by receiving a command signal from the controller 120, the electrically-actuated valve 320 switches to an actuated state that allows the accumulator 318 to discharge its fluid through the electrically-actuated valve 320. Fluid can then flow through the proportional valve 310 to the chamber 230 of the first cylinder actuator 222 to apply a fluid force on the control piston 228 and the swashplate 204. The check valve 314 prevents fluid discharged from the accumulator 318 from flowing to the pump 104.

[0061] If the precharge pressure level of the accumulator 318 exceeds a particular threshold value, the fluid force acting on the control piston 228 may overcome the fluid force and the spring force of the biasing spring 226 acting on the bias piston 232, thereby causing the swashplate 204 to move to the overcenter position represented by the arrow 316 and shown in Figure 4. In this position, as the input shaft 112 rotates in the opposite rotational direction, the pump 104 maintains providing fluid through the outlet port 110 to the actuators 102.

[0062] As such, the controller 120 can control both the so electrically-actuated valve 320 and the proportional valve 310 to control the position of the swashplate 204. The pump 104 may include a swashplate position sensor 324 that provides sensor information indicating the angular position of the swashplate 204 to the controller 120. The controller 120 can then implement a closed-loop feedback control system to accurately control the angular position of the swashplate 204 via providing commands to the solenoid actuators 312, 322.

[0063] Notably, the electrically-actuated valve 320 does not need to remain in the actuated state. Rather, it may be actuated only for a particular period of time (e.g., 1-2 seconds) to allow the swashplate 204 to move to the overcenter position, then the electrically-actuated valve 320 is switched back to the unactuated state.

[0064] Thus, in the implementation of Figure 5, the valve(s) 116 include the proportional valve 310 and the electrically-actuated valve 320. In other example implementations, the valve(s) 116 could include other valve types to accomplish control of the fluid forces of the cylinder actuators 222, 224.

[0065] Figure 6 illustrates a schematic of a hydraulic system 400 of the machine 100, according to an example implementation. The hydraulic system 400 is another example implementation of the hydraulic system 103 described in Figure 1. The same components shown in Figures 1-2 andFigures 5-6 are designated with the same reference numbers. The prime mover 114 and the controller 120 are not shown in Figure 6 to reduce visual clutter in the drawing.

[0066] The hydraulic system 400 differs from the hydraulic system 300 in that, rather than using the proportional valve 310 to control flow to the chamber 230 of the first cylinder actuator 222, the hydraulic system 400 has a proportional pressure control valve 402 to control pressure and flow from the accumulator 318 to the chamber 230. The proportional pressure control valve 402 can have (i) an inlet port 404 that is fluidly coupled to the accumulator 318, (ii) an outlet port 406 that is fluidly coupled to the chamber 230 of the first cylinder actuator 222, and (iii) a return port 408 that is fluidly coupled to drain line 410 of the pump 104, which is fluidly coupled to the fluid reservoir 106.

[0067] The proportional pressure control valve 402 can include movable element (e.g., spool, poppet, or piston) disposed therein. The position of the movable element within the valve controls the size of a restriction or flow area through the proportional pressure control valve 402.

[0068] The proportional pressure control valve 402 can be electrically actuated via a solenoid actuator 412. Particularly, the controller 120 of the hydraulic system 400 is configured to send an electric command signal to the solenoid actuator 412 to actuate the proportional pressure control valve 402 and control pressure level downstream therefrom.

[0069] In an example, the proportional pressure control valve 402 can be configured as a proportional pressure reducing valve. Particularly, the solenoid actuator 412 receives a valve command signal from the controller 120, and responsively modulates (e.g., changes the position of) the movable element of the proportional pressure control valve 402 to reduce the pressure level at the outlet port 406 compared to pressure level at the inlet port 404 based on the magnitude of the command signal provided to the solenoid actuator 412. The smaller the magnitude of thecommand, the smaller the flow area of the proportional pressure control valve 402, and the pressure level at the outlet port 406 decreases, for example. Conversely, the larger the magnitude of the valve command signal, the larger the flow area of the proportional pressure control valve 402, and the pressure level at the outlet port 406 increases, for example.

[0070] The outlet port 406 of the proportional pressure control valve 402 is fluidly coupled to the chamber 230, and thus fluid having a particular pressure level at the outlet port 406 applies a force on the control piston 228 as described above with respect to Figures 2-5 to adjust the angular position of the swashplate 204, and place the swashplate 204 in the overcenter position when needed. As mentioned above, the fluid forces acting on the control piston 228 and the bias piston 232 are determined based on pressure level of fluid supplied to the chambers 230, 234. The force equilibrium between the fluid forces and the spring force of the spring 226 determines the position of the swashplate 204.

[0071] Notably, in addition to the proportional pressure control valve 402 operating as a pressure reducer valve, it also operates in a second mode of operation as a pressure relief valve. Particularly, if a pressure spike occurs in the chamber 230 (at the outlet port 406 of the proportional pressure control valve 402), the proportional pressure control valve 402 relieves fluid from the chamber 230 to the return port 408, which is fluidly coupled to the fluid reservoir 106. Thus, the proportional pressure control valve 402 can be referred to as a pressure reducing-relieving valve.

[0072] The pump 104 can charge the accumulator 318 via fluid line 414. The proportional pressure control valve 402 can then be actuated by the controller 120 to control fluid flow from the accumulator 318 to the chamber 230 and maintain a particular pressure level in the chamber 230, thereby controlling the angular position of the swashplate 204. Thus, the controller 120 can enable the swashplate 204 to move to the overcenter position represented by arrow 316(corresponding to Figure 4) when the input shaft 112 changes its rotational direction as mentioned above.

[0073] With the implementation of Figure 6, the valve(s) 1 16 include the proportional pressure control valve 402. Although the hydraulic system 400 does not show the electrically-actuated valve 320, in other examples, the electrically-actuated valve 320 can be included.

[0074] Figure 7 illustrates a schematic of a hydraulic system 416 of the machine 100, according to an example implementation. The hydraulic system 416 is another example implementation of the hydraulic system 103 described in Figure 1. The same components shown in Figures 1-2 and Figures 5-7 are designated with the same reference numbers. The prime mover 114 and the controller 120 are not shown in Figure 7 to reduce visual clutter in the drawing.

[0075] The hydraulic system 416 includes the electrically-actuated valve 320 described above with respect to Figure 5. The electrically-actuated valve 320 can control fluid flow from the accumulator 318 to the proportional pressure control valve 402. For example, in an unactuated position or state, the electrically-actuated valve 320 operates as a check valve that prevents discharging the accumulator 318. On the other hand, when the solenoid actuator 322 of the electrically-actuated valve 320 is energized by receiving a command signal from the controller 120, the electrically-actuated valve 320 switches to an actuated state that allows the accumulator 318 to discharge its fluid through the electrically-actuated valve 320 to the proportional pressure control valve 402, which in turn controls pressure level in the chamber 230 as described above with respect to Figure 6.

[0076] As mentioned above, the electrically-actuated valve 320 does not need to remain in the actuated state. Rather, it may be actuated only for a particular period of time (e.g., 1-2 seconds)to allow the swashplate 204 to move to the overcenter position, then the electrically-actuated valve320 is switched back to the unactuated state.

[0077] Thus, in the implementation of Figure 7, the valve(s) 116 include the proportional pressure control valve 402 and the electrically-actuated valve 320. Other example implementations are contemplated. For example, the hydraulic system 103 may be configured as a load-sensing system where the pump 104 receives a load-sense signal indicative of the highest load pressure the actuators 102 are subjected to, then the pump 104 provides fluid at a pressure level that is higher than such load-sense signal by a pressure margin.

[0078] Figure 8 illustrates a schematic of a hydraulic system 500 of the machine 100, according to an example implementation. The hydraulic system 500 is another example implementation of the hydraulic system 103 described in Figure 1. The same components shown in Figures 1-2 and Figures 5-8 are designated with the same reference numbers. The prime mover 114 and the controller 120 are not shown in Figure 8 to reduce visual clutter in the drawing.

[0079] The hydraulic system 500 is configured as a load-sensing system. Particularly, the hydraulic system 500 can include a valve assembly 502 that is configured as a load-sensing valve.

[0080] The valve assembly 502 controls fluid flow from the pump 104 to the actuators 102 and from the actuators 102 to the fluid reservoir 106. As an example, the valve assembly 502 may include a sectional valve having a plurality of sections such as an inlet section, an outlet section, and a plurality of worksections interposed therebetween. Each worksection of the worksections is configured to control fluid flow to and from an actuator of the actuators 102.

[0081] In an example, each of the worksections can include a respective spool movable in a spool bore within the respective worksection. The spool can be actuated in either direction via varioustypes of mechanisms. As an example for illustration, the spools can be actuated manually where an operator can move a joystick or handle connected to the spool and can thus move the spool manually. In another example, the spool can be actuated via hydraulic pilot fluid signal where an operator moves a joystick, and responsively, a hydraulic fluid signal is provided to one side of the spool to move the spool in a given direction. In yet another example, the spool can be actuated via an electric signal to a pilot valve.

[0082] When the spool moves in a given direction, fluid is provided to the respective actuator to actuate a piston (e.g., if the actuator is a hydraulic cylinder) or rotating group (e.g., if the actuator is a hydraulic motor) in a first direction. When the spool moves in an opposite direction, fluid is provided to the actuator to actuate it in a second direction, opposite the first direction.

[0083] As mentioned above, the valve assembly 502 is configured to be a load-sensing valve. When the actuator applies a force or is subjected to force, fluid pressure level in at least one chamber of the chambers of the actuator increases. The pressure in the chamber can be referred to as load-induced pressure. Such pressure level in the chamber is indicative of the force or load that the actuator applies or is subjected to.

[0084] Each worksection includes a respective load-sense passage, and when a spool of a worksection is actuated to provide fluid to a respective actuator, the load-sense passage is fluidly- coupled to the actuator via a respective workport of the worksection. Thus, the load-sense passage provides or transmits a pressure feedback signal from the workport, wherein the pressure feedback signal indicates the load on the actuator.

[0085] As such, the pressure feedback signal may be referred to as a load-sense fluid pressure signal. Each worksection of the worksections of the valve assembly 502 is configured to produce a respective load-sense fluid pressure signal. The valve assembly 502 can further include a networkof check valves and / or shuttle valves that compares the pressure levels of the different load-sense fluid pressure signals, and then outputs the load-sense fluid pressure signal having the highest pressure level via load-sense fluid line 504. This load-sense fluid pressure signal is a “universal” or “global” load-sense fluid pressure signal indicative of the highest load that the actuators 102 controlled by the valve assembly 502 are subjected to.

[0086] The load-sense fluid pressure signal is provided via the load-sense fluid line 504 to a pressure margin valve 506. The pressure margin valve 506 is configured to facilitate maintaining a pressure differential or pressure margin between the pump 104 (at the outlet port 110) and the load-sense pressure signal in the load-sense fluid line 504.

[0087] In an example implementation, the pressure margin valve 506 has an inlet port 508 that is fluidly-coupled to the outlet port 110 of the pump 104 via fluid line 510 and fluid line 512. The pressure margin valve 506 also has a load-sense port 514 that is fluidly-coupled to the load-sense fluid line 504, and thus receives the load-sense fluid pressure signal indicative of the highest load among the loads of the actuators 102.

[0088] The pressure margin valve 506 further includes an outlet port 516 that is fluidly-coupled to an inlet port of an electrically-actuated valve 518, where an outlet port of the electrically- actuated valve 518 is fluidly coupled to the chamber 230 of the first cylinder actuator 222 as depicted in Figure 8. In an example, the hydraulic system 500 may include a bleed orifice 519 to bleed any trapped fluid between the outlet port 516 and the electrically-actuated valve 518 to the fluid reservoir 106.

[0089] In an example, the pressure margin valve 506 includes a movable element such as a poppet, spool, or piston therein, and also includes a spring 520 applying a biasing force on the movableelement toward a seat. When seated, the movable element blocks fluid flow from the inlet port508 to the outlet port 516.

[0090] The load-sense fluid pressure signal received at the load-sense port 514 applies a first fluid force on the movable element toward the seat. As such, the first fluid force of the load-sense fluid pressure signal and the biasing force of the spring 520 cooperate to drive the movable element toward a seated position. Thus, the combined force or resultant force comprising the first fluid force of the load-sense fluid pressure signal and the biasing force of the spring 520 can be referred to as a closing force.

[0091] On the other hand, fluid received from the pump 104 at the inlet port 508 applies a second fluid force on the movable element that opposes the closing force, i.e., the second fluid force tends to act on the movable element to be unseated. Thus, the second fluid force can be referred to as an opening force.

[0092] With this configuration, if the differential pressure (difference in pressure level) between the pump fluid (provided to the inlet port 508) and the load-sense signal (provided to the loadsense port 514) increases, pressure level of the fluid provided to the outlet port 516 also increases as the movable element moves further off its seat (e.g., the pressure margin valve 506 becomes less restrictive). Conversely, if the differential pressure (difference in pressure level) between the pump fluid and the load-sense signal decreases, pressure level of the fluid provided to the outlet port 516 also decreases as the movable element moves toward its seat (e.g., the pressure margin valve 506 becomes more restrictive).

[0093] As described in more details below, the pressure margin valve 506 and the pump 104 (along with the cylinder actuators 222, 224 thereof) cooperate to maintain substantially constant pressure margin between the pressure level of fluid discharged from the pump 104 via the outlet port 110and the load-sense signal received at the load-sense port 514. The margin pressure is based on the spring force of the spring 520.

[0094] The electrically-actuated valve 518 can have a solenoid actuator 522 that is connected to the controller 120 of the hydraulic system 500, for example. In the unactuated state shown in Figure 8, fluid from the outlet port 516 of the pressure margin valve 506 is communicated via the electrically-actuated valve 518 to the chamber 230 of the first cylinder actuator 222. Such fluid applies a force on the control piston 228, which tends to push the swashplate 204 toward a neutral position.

[0095] At the same time, fluid from the pump 104 is communicated via the fluid lines 510, 512 to the chamber 234 of the second cylinder actuator 224. Such fluid applies a force on the bias piston 232, which tends to push the swashplate 204 toward a positive stroke position. The balance between the fluid forces and the spring force of the biasing spring 226 determines the position of the swashplate 204 as described above.

[0096] If pressure level of the load-sense signal provided to the load-sense port 514 of the pressure margin valve 506 increases, the difference between the pressure level of the pump fluid and the load-sense signal, and thus the pressure level of the signal at the outlet port 516, is reduced. As such, the fluid force acting on the control piston 228 is reduced, and the fluid force acting on the bias piston 232 causes the swashplate 204 to move further in the positive stroke direction, increasing flow and pressure at the inlet port 508 of the pressure margin valve, thus increasing the pressure differential between the pump fluid and the load-sense signal.

[0097] Conversely, if pressure level of the load-sense signal provided to the load-sense port 514 of the pressure margin valve 506 decreases, the difference between the pressure level of the pump fluid and the load-sense signal, and thus the pressure level of the signal at the outlet port 516,increases. As such, the fluid force acting on the control piston 228 increases, causing the swashplate 204 to move further toward the neutral position, reducing flow and pressure at the inlet port 508 of the pressure margin valve, thus reducing the pressure differential between the pump fluid and the load-sense signal.

[0098] With this configuration, the pressure margin valve 506 operates to maintain the pressure differential between the pump fluid and the load-sense signal substantially constant. The pressure differential is based on the spring 520. For example, if the spring 520 is a 200 psi spring, the pressure margin valve 506 operates to maintain the pressure differential between the pump fluid and the load-sense signal as 200 psi.

[0099] As a particular example, if the load-sense signal at the inlet port 514 has a pressure level of 2000 psi, the swashplate 204 is actuated to a position at which the pump 104 provides fluid having a pressure level of 2200 psi to the inlet port 508. If the pressure level of the load-sense signal increases to 2200 psi, the force acting on the control piston 228 decreases, causing the swashplate 204 to move in the positive stroke direction, increasing the pressure level of the pump fluid to 2400 psi. Conversely, if the pressure level of the load-sense signal decreases from 2000 psi to 1800 psi, the force acting on the control piston 228 increases, causing the swashplate 204 to move toward the neutral position, decreasing the pressure level of the pump fluid to 2000 psi.

[0100] When the electrically-actuated valve 518 is in the unactuated state shown in Figure 8, fluid from the accumulator 318 through accumulator fluid line 524 is blocked by the electrically- actuated valve 518. Also, a check valve 526 allows the pump 104 to charge the accumulator 318 via the fluid line 512, while preventing fluid to be discharged from the accumulator 318 back to the pump 104.

[0101] The controller 120 may detect or receive information that the input shaft 112 is about to reverse its rotation direction, e.g., the input shaft 112 has stopped rotating and is about to reverse direction. In this state, the pump 104 may momentarily stop providing fluid to the chambers 230, 234. The controller 120 responsively sends a command signal to the solenoid actuator 522 of the electrically-actuated valve 518 to switch it to an actuated state for a particular period of time (e.g., 1-2 seconds).

[0102] In such actuated state of the electrically-actuated valve 518, fluid from the accumulator 318 is discharged through the accumulator fluid line 524, through the electrically-actuated valve 518 to the chamber 230 of the first cylinder actuator 222, thus forcing the swashplate 204 in the overcenter position as the chamber 234 does not receive pressurized fluid from the pump 104 to resist. Thereafter, the prime mover 114 may rotate the input shaft 112 in the opposite rotational direction, and the pump 104 resumes providing fluid flow to the actuators 102 via the outlet port 110 despite the change in rotational direction of the input shaft 112.

[0103] After the particular period of time in which the electrically-actuated valve 518 is switched to the actuated state, the controller 120 may stop sending a signal to the solenoid actuator 522, and the electrically-actuated valve 518 switches back to the unactuated state. The pump 104 then provides fluid to both the chamber 230 (via the electrically-actuated valve 518) and to the chamber 234 via the fluid lines 510, 512. Due to the difference in surface areas of the control piston 228 and the bias piston 232 as described above, the fluid force acting on the control piston 228 is larger than the fluid force acting on the bias piston 232, and thus the swashplate 204 remains in the overcenter position. In this state where the pump 104 is in the fully-stroked overcenter position, the pump 104 may operate as a fixed displacement pump, rather than a load-sensing pump.

[0104] If the input shaft 112 is stopped again, and is about to return to the first rotational direction, the pump 104 may momentarily stop discharging fluid. The biasing spring 226 may then actuate the swashplate 204 back to the neutral position. As the input shaft 112 begins to rotate again in the first rotational direction, the pump 104 resume operating as a load-sensing pump where the pressure margin valve 506 operates to maintain the pressure differential between the pump and the load-sense signal substantially constant as described above.

[0105] With the implementation of Figure 8, the valve(s) 116 may include the pressure margin valve 506 and the electrically-actuated valve 518.

[0106] Figure 9 is a graph 600 showing test results for the hydraulic system 300, according to an example implementation. The x-axis represents time, while the left and right y-axes represent, pressure level, rotational speed in RPM, percentage angular position of the swashplate 204, and electric current level in milliampere (mA).

[0107] Particularly, line 602 represents the rotational speed of the input shaft 112 in RPM. Line 604 represents pressure level of fluid discharged via the outlet port 110 of the pump 104. Line 606 represents pressure level of fluid in the accumulator 318. Line 608 represents percentage of angular position of the swashplate 204 relative to a maximum angular position. Line 610 represents electric current provided to the solenoid of the electrically-actuated valve 320. Line 612 represents electric current provided to the solenoid of the proportional valve 310.

[0108] As shown by line 602, the rotational speed of the input shaft 112 is ramped up at time T1 (while the swashplate 204 is actuated to maximum positive angular position, 100%, as shown by the line 608). The rotational speed of the input shaft 112 settles at a particular speed for a period of time, then ramps down to a zero speed at time T2. Correspondingly, as the line 604 indicates, pressure level of fluid discharged from the outlet port 110 of the pump 104 also ramps up to aparticular level then returns to a substantially zero value at time T2. Further, while the pump 104 discharges fluid, it charges the accumulator 318 to a particular pressure level as shown by the line 606.

[0109] The controller 120 of the hydraulic system 300 may receive an indication that the rotational direction of the input shaft 112 is about to be reversed. To continue providing fluid through the outlet port 110 of the pump 104, the controller 120 energizes the solenoid of the proportional valve 310 as indicated by the line 612 to open a fluid path fluid to the chamber 230. Then, shortly thereafter at time T3, the controller 120 also energizes the solenoid of the electrically-actuated valve 320, thereby actuating the electrically-actuated valve 320 and causing fluid to flow from the accumulator 318 through the electrically-actuated valve 320 and the proportional valve 310 to the chamber 230. This extends the control piston to move the swashplate 204 to the overcenter (-100%) as shown by the line 608. As a result, pressure level of fluid of the accumulator 318 dips as shown by the line 606.

[0110] In this state, as the input shaft 112 starts rotating in the opposite rotational direction at time T4, fluid is discharged again from the outlet port 110 of the pump 104 as shown by the line 604 rising up again after T4. The line 606 representing pressure of the accumulator fluid also shows pressure level increasing again as the pump 104 recharges the accumulator after the swashplate 204 is moved all the way to the overcenter position.

[0111] Notably, the electrically-actuated valve 320 does not remain in the actuated state. Rather, it is actuated only for a particular period of time (e g., 1-2 seconds) to allow the swashplate 204 to move to the overcenter position, then the electrically-actuated valve 320 is switched back to the unactuated state at T5.

[0112] Figure 10 is a flowchart of a method 700 for operating a hydraulic system, according to an example implementation. The method 700 can, for example, be used for operating any of the hydraulic systems 300, 400, 416, 500 described above. Further, at least some of the operations of the method 700 are performed by the controller 120 described above.

[0113] The method 700 may include one or more operations, or actions as illustrated by one or more of blocks 702-708. Although the blocks are illustrated in a sequential order, these blocks may in some instances be performed in parallel, and / or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and / or removed based upon the desired implementation.

[0114] In addition, for the method 700 and other processes and operations disclosed herein, the flowchart shows operation of one possible implementation of present examples. In this regard, each block may represent a module, a segment, or a portion of program code, which includes one or more instructions executable by a processor (e.g., a processor of the controller 120) for implementing specific logical operations or steps in the process. The program code may be stored on any type of computer readable medium or memory, for example, such as a storage device including a disk or hard drive. The computer readable medium may include a non-transitory computer readable medium or memory, for example, such as computer-readable media that stores data for short periods of time like register memory, processor cache and Random Access Memory (RAM). The computer readable medium may also include non-transitory media or memory, such as secondary or persistent long term storage, like read only memory (ROM), optical or magnetic disks, compact-disc read only memory (CD-ROM), for example. The computer readable media may also be any other volatile or non-volatile storage systems. The computer readable medium may be considered a computer readable storage medium, a tangible storage device, or other articleof manufacture, for example. In addition, for the method 700 and other processes and operations disclosed herein, one or more blocks in Figure 10 may represent circuitry or digital logic that is arranged to perform the specific logical operations in the process.

[0115] At block 702, the method 700 includes operating the pump 104 to draw fluid through the inlet port 108 and discharge fluid through the outlet port 110, wherein the pump 104 is driven by the input shaft 112 that is bidirectional, wherein the pump 104 has the swashplate 204, and wherein an angle of the swashplate 204 determines fluid flow rate from the outlet port 110 of the pump 104.

[0116] At block 704, the method 700 includes receiving, at the controller 120, information indicative of a reversal in a direction of rotation of the input shaft 112.

[0117] At block 706, the method 700 includes, responsively, sending, by the controller, a command signal to at least one valve (e.g., the electrically-actuated valve 320, the proportional valve 310, and / or the proportional pressure control valve 402) to control fluid communication from an external source of pressurized fluid (e.g., the source 118, which can be the accumulator 318) to a control piston (e.g., the control piston 228 and / or the bias piston 232) coupled to the swashplate 204 of the pump 104.

[0118] At block 708, the method 700 includes moving the swashplate 204 to an overcenter position (see Figure 4, and the arrow 316 in Figures 5-7), thereby causing the pump 104 to continue providing fluid flow through the outlet port 110 of the pump 104.

[0119] The method 700 can further include any of the steps or operations described throughout herein.

[0120] The detailed description above describes various features and operations of the disclosed systems with reference to the accompanying figures. The illustrative implementations described herein are not meant to be limiting. Certain aspects of the disclosed systems can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.

[0121] Further, unless context suggests otherwise, the features illustrated in each of the figures may be used in combination with one another. Thus, the figures should be generally viewed as component aspects of one or more overall implementations, with the understanding that not all illustrated features are necessary for each implementation.

[0122] Additionally, any enumeration of elements, blocks, or steps in this specification or the claims is for purposes of clarity. Thus, such enumeration should not be interpreted to require or imply that these elements, blocks, or steps adhere to a particular arrangement or are carried out in a particular order.

[0123] Further, devices or systems may be used or configured to perform functions presented in the figures. In some instances, components of the devices and / or systems may be configured to perform the functions such that the components are actually configured and structured (with hardware and / or software) to enable such performance. In other examples, components of the devices and / or systems may be arranged to be adapted to, capable of, or suited for performing the functions, such as when operated in a specific manner.

[0124] By the term “substantially” or “about” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those with skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0125] The arrangements described herein are for purposes of example only. As such, those skilled in the art will appreciate that other arrangements and other elements (e.g., machines, interfaces, operations, orders, and groupings of operations, etc.) can be used instead, and some elements may be omitted altogether according to the desired results. Further, many of the elements that are described are functional entities that may be implemented as discrete or distributed components or in conjunction with other components, in any suitable combination and location.

[0126] While various aspects and implementations have been disclosed herein, other aspects and implementations will be apparent to those skilled in the art. The various aspects and implementations disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims, along with the full scope of equivalents to which such claims are entitled. Also, the terminology used herein is for the purpose of describing particular implementations only, and is not intended to be limiting.

[0127] Embodiments of the present disclosure can thus relate to one of the enumerated example embodiments (EEEs) listed below.

[0128] EEE 1 is a hydraulic system comprising: a pump driven by an input shaft that is bidirectional, wherein the pump has a swashplate, wherein the pump draws fluid through an inlet port and discharges fluid through an outlet port of the pump, and wherein an angle of the swashplate determines fluid flow rate from the outlet port of the pump; a control piston coupled to the swashplate of the pump; a source of pressurized fluid; and one or more valves that control fluid flow from the source of pressurized fluid to the control piston, wherein as a direction of rotation of the input shaft is reversed from a first rotational direction to a second rotational direction, opposite the first rotational direction, the one or more valves control fluid communication fromthe source of pressurized fluid to cause the control piston to move the swashplate to an overcenter position, causing the pump to continue providing fluid flow through the outlet port of the pump.

[0129] EEE 2 is the hydraulic system of EEE 1, wherein the source of pressurized fluid includes an accumulator storing pressurized fluid therein, and wherein the one or more valves control fluid communication between the accumulator and the control piston.

[0130] EEE 3 is the hydraulic system of any of EEEs 1-2, wherein the one or more valves comprise a proportional valve, and wherein the hydraulic system further comprises a controller performing operations comprising: receiving information indicating reversal in a direction of rotation of the input shaft; and responsively, sending a command signal to the proportional valve to control fluid communication to the control piston and move the swashplate to the overcenter position.

[0131] EEE 4 is the hydraulic system of EEE 3, wherein the one or more valves further comprise: an electrically-actuated valve that controls fluid flow from the source of pressurized fluid, wherein when the electrically-actuated valve operates in a first state, fluid flow from the pump charges the source of pressurized fluid, and wherein when the controller commands the electrically-actuated valve to operate in a second state, the electrically-actuated valve allows pressurized fluid to flow from the source of pressurized fluid through the electrically-actuated valve and the proportional valve to the control piston.

[0132] EEE 5 is the hydraulic system of any of EEEs 1-4, wherein the one or more valves comprise a proportional pressure control valve, and wherein the hydraulic system further comprises a controller performing operations comprising: receiving information indicating reversal in a direction of rotation of the input shaft; and responsively, sending a command signalto the proportional pressure control valve to control pressure level of fluid acting on the control piston, thereby controlling the angle of the swashplate.

[0133] EEE 6 is the hydraulic system of EEE 5, wherein the one or more valves further comprise: an electrically-actuated valve that controls fluid flow from the source of pressurized fluid, wherein the controller commands the electrically-actuated valve to operate in an actuated state, allowing pressurized fluid to flow from the source of pressurized fluid through the electrically-actuated valve and the proportional pressure control valve to the control piston.

[0134] EEE 7 is the hydraulic system of EEE 6, wherein the proportional pressure control valve is a pressure reducing-relieving valve.

[0135] EEE 8 is the hydraulic system of any of EEEs 1-7, further comprising: a bias piston coupled to the swashplate, wherein the one or more valve control fluid communication to the bias piston.

[0136] EEE 9 is the hydraulic system of EEE 8, wherein a surface area of the control piston is different from a respective surface area of the bias piston.

[0137] EEE 10 is the hydraulic system of any of EEEs 8-9, further comprising: a biasing spring applying a biasing force on the bias piston, such that relative magnitudes of fluid forces acting on the control piston and the bias piston, and the biasing force of the biasing spring determine the angle of the swashplate.

[0138] EEE 11 is the hydraulic system of any of EEEs 8-10, wherein the control piston receives fluid via the one or more valves, and wherein the bias piston receives fluid from the outlet port of the pump.

[0139] EEE 12 is a machine comprising the hydraulic system of any of EEEs 1-11. For example, the machine comprises: a prime mover; one or more actuators controlling operation of respective implements of the machine; a fluid reservoir; a pump driven by an input shaft coupled to the prime mover such that the input shaft is bidirectional, wherein the pump has a swashplate, wherein the pump draws fluid from the fluid reservoir through an inlet port and discharges fluid through an outlet port of the pump to the one or more actuators, and wherein an angle of the swashplate determines fluid flow rate from the outlet port of the pump; a control piston coupled to the swashplate of the pump; a source of pressurized fluid; and one or more valves that control fluid flow from the source of pressurized fluid to the control piston, wherein as a direction of rotation of the input shaft is reversed from a first rotational direction to a second rotational direction, opposite the first rotational direction, the one or more valves control fluid communication from the source of pressurized fluid to cause the control piston to move the swashplate to an overcenter position, causing the pump to continue providing fluid flow through the outlet port of the pump.

[0140] EEE 13 is the machine of EEE 12, wherein the source of pressurized fluid includes an accumulator storing pressurized fluid therein, and wherein the one or more valves control fluid communication between the accumulator and the control piston.

[0141] EEE 14 is the machine of any of EEEs 12-13, wherein the one or more valves comprise a proportional valve, and wherein the machine further comprises a controller performing operations comprising: receiving information indicating reversal in a direction of rotation of the input shaft; and responsively, sending a command signal to the proportional valve to control fluid communication to the control piston and move the swashplate to the overcenter position.

[0142] EEE 15 is the machine of EEE 14, wherein the one or more valves further comprise: an electrically-actuated valve that controls fluid flow from the source of pressurized fluid, whereinwhen the electrically-actuated valve operates in a first state, fluid flow from the pump charges the source of pressurized fluid, and wherein when the controller commands the electrically-actuated valve to operate in a second state, the electrically-actuated valve allows pressurized fluid to flow from the source of pressurized fluid through the electrically-actuated valve and the proportional valve to the control piston.

[0143] EEE 16 is the machine of any of EEEs 12-15, wherein the one or more valves comprise a proportional pressure control valve, and wherein the machine further comprises a controller performing operations comprising: receiving information indicating reversal in a direction of rotation of the input shaft; and responsively, sending a command signal to the proportional pressure control valve to control pressure level of fluid acting on the control piston, thereby controlling the angle of the swashplate.

[0144] EEE 17 is amethod for operating the hydraulic system of any ofEEEs 1-11 or the machine of any ofEEEs 12-16. For example, the method comprises: operating a pump to draw fluid through an inlet port and discharge fluid through an outlet port, wherein the pump is driven by an input shaft that is bidirectional, wherein the pump has a swashplate, and wherein an angle of the swashplate determines fluid flow rate from the outlet port of the pump; receiving, at a controller, information indicative of a reversal in a direction of rotation of the input shaft; and responsively, sending, by the controller, a command signal to at least one valve to control fluid communication from an external source of pressurized fluid to a control piston coupled to the swashplate of the pump; and moving the swashplate to an overcenter position, thereby causing the pump to continue providing fluid flow through the outlet port of the pump.

[0145] EEE 18 is the method of EEE 17, wherein the at least one valve comprises a proportional valve, and wherein sending, by the controller, the command signal to at least one valve comprises:sending, by the controller, the command signal to the proportional valve to control fluid communication to the control piston and move the swashplate to the overcenter position.

[0146] EEE 19 is the method of EEE 18, wherein the at least one valve further comprises an electrically-actuated valve that controls fluid flow from the external source of pressurized fluid, wherein when the electrically-actuated valve operates in a first state, fluid flow from the pump charges the external source of pressurized fluid, and wherein the method further comprises: sending, by the controller, a respective command signal to the electrically-actuated valve to operate in a second state, allowing pressurized fluid to flow from the external source of pressurized fluid through the electrically-actuated valve and the proportional valve to the control piston.

[0147] EEE 20 is the method of any of EEEs 17-19, wherein the at least one valve comprises a proportional pressure control valve operating as a pressure reducing valve, and wherein sending, by the controller, the command signal to at least one valve comprises: sending, by the controller, the command signal to the proportional pressure control valve to control pressure level of fluid acting on control piston, thereby controlling the angle of the swashplate.

[0148] EEE 21 is the hydraulic system of any of EEEs 1-11, the machine of EEEs 12-16, or the method of EEEs 17-20, wherein the one or more valves further comprise: a pressure margin valve configured to facilitate maintaining a pressure differential between fluid discharged by the pump and a load-sense signal substantially constant; and an electrically-actuated valve that controls fluid flow (i) between the pressure margin valve and the control piston, and (ii) between the source of pressurized fluid and the control piston, wherein the controller commands the electrically-actuated valve to operate in an actuated state, allowing pressurized fluid to flow from the source of pressurized fluid through the electrically-actuated valve to the control piston.

Claims

CLAIMSWhat is claimed is:1 . A hydraulic system comprising: a pump driven by an input shaft that is bidirectional, wherein the pump has a swashplate, wherein the pump draws fluid through an inlet port and discharges fluid through an outlet port of the pump, and wherein an angle of the swashplate determines fluid flow rate from the outlet port of the pump; a control piston coupled to the swashplate of the pump; a source of pressurized fluid; and one or more valves that control fluid flow from the source of pressurized fluid to the control piston, wherein as a direction of rotation of the input shaft is reversed from a first rotational direction to a second rotational direction, opposite the first rotational direction, the one or more valves control fluid communication from the source of pressurized fluid to cause the control piston to move the swashplate to an overcenter position, causing the pump to continue providing fluid flow through the outlet port of the pump.

2. The hydraulic system of claim 1, wherein the source of pressurized fluid includes an accumulator storing pressurized fluid therein, and wherein the one or more valves control fluid communication between the accumulator and the control piston.

3. The hydraulic system of claim 1, wherein the one or more valves comprise a proportional valve, and wherein the hydraulic system further comprises a controller performing operations comprising:receiving information indicating reversal in a direction of rotation of the input shaft; and responsively, sending a command signal to the proportional valve to control fluid communication to the control piston and move the swashplate to the overcenter position.

4. The hydraulic system of claim 3, wherein the one or more valves further comprise: an electrically-actuated valve that controls fluid flow from the source of pressurized fluid, wherein when the electrically-actuated valve operates in a first state, fluid flow from the pump charges the source of pressurized fluid, and wherein when the controller commands the electrically-actuated valve to operate in a second state, the electrically-actuated valve allows pressurized fluid to flow from the source of pressurized fluid through the electrically-actuated valve and the proportional valve to the control piston.

5. The hydraulic system of claim 1, wherein the one or more valves comprise a proportional pressure control valve, and wherein the hydraulic system further comprises a controller performing operations comprising: receiving information indicating reversal in a direction of rotation of the input shaft; and responsively, sending a command signal to the proportional pressure control valve to control pressure level of fluid acting on the control piston, thereby controlling the angle of the swashplate.

6. The hydraulic system of claim 5, wherein the one or more valves further comprise: an electrically-actuated valve that controls fluid flow from the source of pressurized fluid, wherein the controller commands the electrically-actuated valve to operate in an actuated state,allowing pressurized fluid to flow from the source of pressurized fluid through the electrically- actuated valve and the proportional pressure control valve to the control piston.

7. The hydraulic system of claim 1, wherein the one or more valves further comprise: a pressure margin valve configured to facilitate maintaining a pressure differential between fluid discharged by the pump and a load-sense signal substantially constant; and an electrically-actuated valve that controls fluid flow (i) between the pressure margin valve and the control piston, and (ii) between the source of pressurized fluid and the control piston, wherein the controller commands the electrically-actuated valve to operate in an actuated state, allowing pressurized fluid to flow from the source of pressurized fluid through the electrically- actuated valve to the control piston.

8. The hydraulic system of claim 1, further comprising: a bias piston coupled to the swashplate, wherein the one or more valve control fluid communication to the bias piston.

9. The hydraulic system of claim 8, wherein a surface area of the control piston is different from a respective surface area of the bias piston.

10. The hydraulic system of claim 8, further comprising: a biasing spring applying a biasing force on the bias piston, such that relative magnitudes of fluid forces acting on the control piston and the bias piston, and the biasing force of the biasing spring determine the angle of the swashplate.11 . The hydraulic system of claim 8, wherein the control piston receives fluid via the one or more valves, and wherein the bias piston receives fluid from the outlet port of the pump.

12. A machine comprising: a prime mover; one or more actuators controlling operation of respective implements of the machine; a fluid reservoir; a pump driven by an input shaft coupled to the prime mover such that the input shaft is bidirectional, wherein the pump has a swashplate, wherein the pump draws fluid from the fluid reservoir through an inlet port and discharges fluid through an outlet port of the pump to the one or more actuators, and wherein an angle of the swashplate determines fluid flow rate from the outlet port of the pump; a control piston coupled to the swashplate of the pump; a source of pressurized fluid; and one or more valves that control fluid flow from the source of pressurized fluid to the control piston, wherein as a direction of rotation of the input shaft is reversed from a first rotational direction to a second rotational direction, opposite the first rotational direction, the one or more valves control fluid communication from the source of pressurized fluid to cause the control piston to move the swashplate to an overcenter position, causing the pump to continue providing fluid flow through the outlet port of the pump.

13. The machine of claim 12, wherein the source of pressurized fluid includes an accumulator storing pressurized fluid therein, and wherein the one or more valves control fluid communication between the accumulator and the control piston.

14. The machine of claim 12, wherein the one or more valves comprise a proportional valve, and wherein the machine further comprises a controller performing operations comprising: receiving information indicating reversal in a direction of rotation of the input shaft; and responsively, sending a command signal to the proportional valve to control fluid communication to the control piston and move the swashplate to the overcenter position.

15. The machine of claim 14, wherein the one or more valves further comprise: an electrically-actuated valve that controls fluid flow from the source of pressurized fluid, wherein when the electrically-actuated valve operates in a first state, fluid flow from the pump charges the source of pressurized fluid, and wherein when the controller commands the electrically-actuated valve to operate in a second state, the electrically-actuated valve allows pressurized fluid to flow from the source of pressurized fluid through the electrically-actuated valve and the proportional valve to the control piston.

16. The machine of claim 12, wherein the one or more valves comprise a proportional pressure control valve, and wherein the machine further comprises a controller performing operations comprising: receiving information indicating reversal in a direction of rotation of the input shaft; andresponsively, sending a command signal to the proportional pressure control valve to control pressure level of fluid acting on the control piston, thereby controlling the angle of the swashplate.

17. A method comprising: operating a pump to draw fluid through an inlet port and discharge fluid through an outlet port, wherein the pump is driven by an input shaft that is bidirectional, wherein the pump has a swashplate, and wherein an angle of the swashplate determines fluid flow rate from the outlet port of the pump; receiving, at a controller, information indicative of a reversal in a direction of rotation of the input shaft; and responsively, sending, by the controller, a command signal to at least one valve to control fluid communication from an external source of pressurized fluid to a control piston coupled to the swashplate of the pump; and moving the swashplate to an overcenter position, thereby causing the pump to continue providing fluid flow through the outlet port of the pump.

18. The method of claim 17, wherein the at least one valve comprises a proportional valve, and wherein sending, by the controller, the command signal to at least one valve comprises: sending, by the controller, the command signal to the proportional valve to control fluid communication to the control piston and move the swashplate to the overcenter position.

19. The method of claim 18, wherein the at least one valve further comprises an electrically-actuated valve that controls fluid flow from the external source of pressurized fluid, wherein when the electrically-actuated valve operates in a first state, fluid flow from the pump charges the external source of pressurized fluid, and wherein the method further comprises: sending, by the controller, a respective command signal to the electrically-actuated valve to operate in a second state, allowing pressurized fluid to flow from the external source of pressurized fluid through the electrically-actuated valve and the proportional valve to the control piston.

20. The method of claim 17, wherein the at least one valve comprises a proportional pressure control valve operating as a pressure reducing valve, and wherein sending, by the controller, the command signal to at least one valve comprises: sending, by the controller, the command signal to the proportional pressure control valve to control pressure level of fluid acting on the control piston, thereby controlling the angle of the swashplate.

Images