Manifold for reducing or generating pilot pressure of a pilot operated excavator

Abstract

The present invention relates to a manifold for reducing or generating pilot pressure for a pilot operated excavator. A pilot hydraulic system is provided that can include a pilot pressure source, a pilot pressure return tank, a pilot valve, a pilot pressure supply line connecting the pilot pressure source to the pilot valve, and a pilot pressure return line connecting the pilot pressure return tank to the pilot valve. A main control valve can include a pilot chamber. A pilot pressure control line connects the pilot valve to the pilot chamber. A hydraulic subsystem is provided for modifying the pilot pressure provided to the pilot chamber of the main control valve. The hydraulic subsystem can include a variable orifice valve disposed in the pilot pressure control line, a pilot pressure bypass line communicating the pilot pressure control line downstream of the variable orifice valve with the pilot pressure return line, and an electro-hydraulic pressure reducing valve (EHPRV) disposed in the pilot pressure bypass line.

Description

Technical Field

[0001] This disclosure relates to pilot operated control for operating machines. Background Technology

[0002] When implementing automation functions in pilot-operated work machines such as excavators, a system is needed to generate or reduce hydraulic pilot pressure in response to commands from an automatic controller. Summary of the Invention

[0003] In one embodiment, a pilot hydraulic system is provided, which may include: a pilot pressure source, a pilot pressure return tank, a pilot valve, a pilot pressure supply line connecting the pilot pressure source to the pilot valve, and a pilot pressure return line connecting the pilot pressure return tank to the pilot valve. A main control valve may include a pilot chamber. A pilot pressure control line connects the pilot valve to the pilot chamber. A hydraulic subsystem is provided for modifying the pilot pressure supplied to the pilot chamber of the main control valve. This hydraulic subsystem may include: a variable orifice valve disposed in the pilot pressure control line, a pilot pressure bypass line connecting the pilot pressure control line downstream of the variable orifice valve to the pilot pressure return line, and an electro-hydraulic pressure reducing valve (EHPRV) disposed in the pilot pressure bypass line.

[0004] Many objects, features, and advantages of the present invention will be apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings. Attached Figure Description

[0005] Figure 1 This is a left-side view of a working machine (e.g., an excavator) that includes the pilot hydraulic system disclosed herein.

[0006] Figure 2 This is a schematic illustration of the operator's seat and a console including left and right joystick controls.

[0007] Figure 3 This is a schematic illustration of a first embodiment of the pilot hydraulic system disclosed herein.

[0008] Figure 4 This is a schematic diagram illustrating the control system of the machine.

[0009] Figure 5 It is during normal operation. Figure 3 A schematic illustration of a pilot hydraulic system.

[0010] Figure 6 This is during operation in pilot pressure reduction mode. Figure 3A schematic illustration of a pilot hydraulic system.

[0011] Figure 7 This is during operation in the pilot pressure generation mode. Figure 3 A schematic illustration of a pilot hydraulic system.

[0012] Figure 8 This is a schematic illustration of an alternative implementation of a pilot hydraulic system.

[0013] Figure 9 It is during normal operation. Figure 8 A schematic illustration of a pilot hydraulic system.

[0014] Figure 10 It is in the pilot pressure reduction mode. Figure 8 A schematic illustration of a pilot hydraulic system.

[0015] Figure 11 It is in the pilot pressure generation mode. Figure 8 A schematic illustration of a pilot hydraulic system. Detailed Implementation

[0016] The embodiments of this disclosure described below are not intended to be exclusive or to limit this disclosure to the precise forms disclosed in the following detailed description. Rather, these embodiments were chosen and described so that those skilled in the art can conceive of and understand the principles and specific practices of this disclosure.

[0017] Figure 1 An example embodiment of the working machine is shown. This machine is specifically implemented as an excavator 100. However, the invention is not limited to excavators but can be extended to other working machines, such as loaders, tracked towing devices, harvesters, timber harvesters, backhoes, log stackers, motorized graders, or any other working machine. Similarly, while the drawings and the following description may refer to excavators, it is to be understood that the scope of this disclosure extends beyond excavators, and where applicable, the terms "machine" or "working machine" will be used instead. The terms "machine" or "working machine" are intended to be broader and, for the purposes of this disclosure, encompass other vehicles besides excavators.

[0018] Reference Figure 1 The machine 100 includes a chassis comprising an upper frame 102 pivotally mounted to a base frame 104. The upper frame 102 is pivotally mounted on the base frame 104 by means of a swing pivot 108. The upper frame 102 is rotatable approximately 360 degrees relative to the base frame 104 on the swing pivot 108. A hydraulic motor (not shown) can drive a gear train (not shown) to pivot the upper frame 102 about the swing pivot 108.

[0019] The underframe 104 may include a pair of ground engagement mechanisms, such as tracks 106 located on opposite sides of the underframe 104, for movement along the ground. Alternatively, the machine 100 may include more than two tracks or wheels for engaging the ground. The upper frame 102 includes a cab 110 in which a machine operator controls the machine. Figure 2 As schematically shown, the cab 110 may include an operator's seat 128 and a control console 130. The control console 130 may include a left joystick control 228L and a right joystick control 228R, as well as other controls. For the purpose of operating the work machine 100, a human operator may actuate one or more of the controls on the control console 130.

[0020] The machine 100 also includes a boom 114 extending from an upper frame 102 adjacent to the cab 110. The boom 114 can be rotated about a vertical arc by actuation of a pair of boom cylinders 116. A bucket stick or arm 118 is rotatably mounted at one end of the boom 114, and the position of the bucket stick or arm is controlled by a hydraulic boom cylinder 122. At the opposite end of the boom 114, the bucket stick or arm 118 is rotatably connected to an implement or bucket 124, which can be pivoted relative to the arm 118 by means of a hydraulic implement pivot cylinder 120.

[0021] The upper frame 102 of the machine 100 includes a housing located above the engine assembly 112. At the end opposite to the cab 110, the upper frame 102 includes a counterweight body 126. The counterweight body 126 includes a shell filled with material to increase the weight of the machine and counteract the load collected in the bucket 124. This offset weight can improve the lifting or digging performance characteristics of the machine 100.

[0022] The operator of machine 100 can manually control boom cylinder 116, hydraulic boom cylinder 122, hydraulic tool pivot cylinder 120, and hydraulic motor, which causes the upper frame 102 to pivot about the base frame 104 on the slewing pivot 108. Figure 2 As schematically shown, these controls may include a left-hand joystick 228L and a right-hand joystick 228R located on opposite sides of the operator's seat 128. These two joysticks are typically configured to control bidirectional movement of various hydraulic actuators according to either an ISO control mode or a SAE control mode. For example, in ISO control mode, the two joysticks are configured as follows: Left hand to the left = turn to the left Left hand to right = turn right Left hand forward = lever boom (bucket) moves away Left hand backward = lever boom (bucket) moves closer Right hand to left = the bucket rolls up (closes). Right hand to right = bucket unfolds (unloading) Right hand forward = active arm lowered Right hand backward = active arm rises.

[0023] In manually controlled operating machines, the left and right joysticks directly control the spool valve, which directs the operating fluid pressure to the various actuators. In pilot-controlled operating machines, the left and right joysticks control the pilot valve, which directs pilot pressure to the main operating valve, which in turn directs the operating fluid pressure to the various actuators.

[0024] This disclosure aims to improve pilot-controlled working machines by providing interaction with an automated control system to complement pilot pressure control that was originally guided by a human operator. An example of such an automated control system is an automated slope control system, whereby the working machine is configured to automatically control the slope of the working implement, i.e., its height and / or position.

[0025] Another example of such an automated control system features a virtual “fence mode” in which the control system is configured to prevent work tools from moving over virtual fences established within the control system.

[0026] The following description of the pilot hydraulic system of the present invention is set in the context of an automated slope control system for an excavator. It should be understood that the pilot hydraulic system can be applied to other work machines and other automatic control systems.

[0027] Figure 3 This is a schematic illustration of a pilot hydraulic system 200 according to one embodiment of the present invention. The pilot hydraulic system 200 includes: a pilot pressure source 202, a pilot pressure return tank 204, a first pilot valve 206a, a second pilot valve 206b, a pilot pressure supply line 208 connecting the pilot pressure source 202 to the first pilot valve and the second pilot valve, and a pilot pressure return line 210 connecting the pilot pressure return tank 204 to the first pilot valve and the second pilot valve.

[0028] The pilot hydraulic system 200 also includes a main control valve 212, which includes a first pilot chamber 214a and a second pilot chamber 214b. A first pilot pressure control line 216a connects a first pilot valve 206a to the first pilot chamber 214a. A second pilot pressure control line 216b connects a second pilot valve 206b to the second pilot chamber 214b. The main control valve 212 controls the flow of working hydraulic fluid from the working hydraulic fluid source P to any of the aforementioned hydraulic actuators, and the return of hydraulic fluid from the actuator to the working hydraulic fluid tank T. It should be understood that there will be a pilot hydraulic system 200 associated with various hydraulic actuators to be controlled, such as boom cylinder 116, hydraulic boom cylinder 122, hydraulic tool pivot cylinder 120, and a hydraulic motor that causes the upper frame 102 to pivot about the underframe 104 on the slewing pivot 108.

[0029] The manually operable pilot valve control input 226 includes an input handle 228 and at least a first pilot valve 206a and a second pilot valve 206b. The handle 228, which may be a joystick 228, is configured to move the first pilot valve 206a when the handle 228 moves in a first direction, and to move the second pilot valve 206b when the handle 228 moves in a second direction. For example, the handle 228 may represent... Figure 2 The left-hand control lever 228L is shown, and the first and second directions can be the forward and backward directions of the left-hand control lever, so that when the excavator's ISO control mode is used, the hydraulic boom cylinder 122 is controlled to move the boom 118 away from and towards the boom 114.

[0030] The pilot hydraulic system 200 also includes a hydraulic subsystem 218, which is typically included in Figure 3 The features contained within the dashed rectangle indicated by 218. The hydraulic subsystem 218 may also be referred to as manifold 218. The hydraulic subsystem 218 will allow features such as those described below. Figure 4 The automated control system further describes the modification of the pilot pressure, which would otherwise be supplied from pilot valves 206a and 206b to the pilot chambers 214a and 214b of the main control valve 212.

[0031] The hydraulic subsystem 218 includes: a first variable orifice valve 220a disposed in a first pilot pressure control line 216a; and a second variable orifice valve 220b disposed in a second pilot pressure control line 216b.

[0032] The hydraulic subsystem 218 further includes: a first pilot pressure bypass line 222a, which connects a first pilot pressure control line 216a downstream of the first variable orifice valve 220a and a pilot pressure return line 210; and a second pilot pressure bypass line 222b, which connects a second pilot pressure control line 216a downstream of the second variable orifice valve 220a and a pilot pressure return line 210. The variable orifice valves 220a and 220b may be bidirectional proportional variable orifice valves.

[0033] The hydraulic subsystem 218 also includes: a first electro-hydraulic pressure reducing valve (EHPRV) 224a disposed in a first pilot pressure bypass line 222a; and a second EHPRV 224b disposed in a second pilot pressure bypass line 222b.

[0034] The hydraulic subsystem 218 may further include: a first on / off valve 230a disposed in a first pilot pressure bypass line 222a between the first EHPRV 224a and the first pilot pressure control line 216a; and a second on / off valve 230b disposed in a second pilot pressure bypass line 222b between the second EHPRV 224b and the second pilot pressure control line 216b. For example, the first on / off valve 230a and the second on / off valve 230b may be variable orifice / flow control valves, such as the Model PWK10020V or Model PWK06020V available from HYDAC.

[0035] The hydraulic subsystem 218 may further include: a first pressure sensor 232a, which is connected to a first pilot pressure control line 216a between a first pilot valve 206a and a first variable orifice valve 220a; and a second pressure sensor 232b, which is connected to a second pilot pressure control line 216b between a second pilot valve 206b and a second variable orifice valve 220b.

[0036] Figure 4 control system

[0037] like Figure 4 As illustrated schematically, the work machine 100 includes a control system 300, which includes a controller 302. The controller 302 may be part of the machine control system of the work machine 100, or it may be a separate control module. The controller 302 may be installed in the operator's cab 110. The controller 302 is configured to receive input signals from various sensors. Figure 4The dashed lines connecting the sensors and the controller are used to schematically indicate the signals sent from various sensors to the controller 302. The dashed lines have arrows indicating the signal flow from the sensors to the controller 302.

[0038] For example, a pressure signal from a pressure sensor such as 232a will be received so that the controller can monitor the hydraulic pressure from the individual pilot control valves (such as 206a) in the pilot control valves.

[0039] If a slope control system is being implemented on machine 100, input signals can be received from a slope control sensor, schematically shown as 318. The slope control sensor can be a wired sensor. The slope control sensor can be a laser-based system. The slope control system can be based on signals from a global navigation satellite system.

[0040] If a virtual fence mode is being implemented on the work machine 100, input signals can be received from a position sensor, schematically shown as 320. The control system 300 can use an IMU, a rotation sensor, and a GPS as position sensors 320 to monitor the position of the work machine 100 and its various components.

[0041] Similarly, controller 302 will generate control signals for controlling the operation of the various electro-mechanical valves discussed above, these control signals in Figure 4 The diagram uses dashed lines connecting controller 302 to various valves to schematically indicate the flow of command signals from controller 302 to the corresponding valves. For example, Figure 4 Valves 220a, 224a, and 230a are schematically shown.

[0042] Controller 302 includes or may be associated with processor 304, computer-readable medium 306, database 308, and input / output module or control panel 310 having display 312. Input / output devices 314, such as keyboards, joysticks, or other user interfaces, are provided to allow a human operator to input commands to the controller. It should be understood that controller 302 described herein may be a single controller having all the functions described, or it may include multiple controllers, wherein the described functions are distributed among the multiple controllers.

[0043] The various operations, steps, or algorithms described in conjunction with controller 302 can be implemented directly in hardware, as a computer program product 316 such as a software module executed by processor 304, or a combination of both. Computer program product 316 can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, or any other form of computer-readable medium 306 known in the art. Exemplary computer-readable medium 306 can be coupled to processor 304, enabling the processor to read information from and write information to the memory / storage medium. In this alternative, the medium can be integrated with the processor. The processor and medium can reside in an application-specific integrated circuit (ASIC). The ASIC can reside in a user terminal. In this alternative, the processor and medium can reside as discrete components in the user terminal.

[0044] As used herein, the term "processor" can refer to at least general-purpose or special-purpose processing devices and / or logic that can be understood by those skilled in the art, including but not limited to microprocessors, microcontrollers, state machines, etc. A processor can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a combination of multiple microprocessors, a combination of one or more microprocessors combined with a DSP core, or any other such configuration.

[0045] Specifically, the controller 302 can be programmed to have a pilot pressure generation mode and a pilot pressure reduction mode. The pilot pressure generation mode is used to automatically generate a hydraulic pilot pressure signal for the main control valve 212 when the controller determines that the human operator has not sent the necessary hydraulic pilot pressure signal. The pilot pressure reduction mode is used to automatically reduce the hydraulic pilot pressure signal when the controller determines that the main control valve should not be actuated according to the human operator's instructions. The controller 302 can also have a normal operating mode, as further described below. Figure 5 As described, the pilot pressure from the pilot valve is transmitted to the pilot chamber via the hydraulic subsystem without modification.

[0046] In such Figure 1In the context of the automatic slope control system of the excavator 100 shown, the human operator typically only commands the function of the boom 118, while the boom 114 and bucket 124 are controlled by the controller 302 to keep the bucket tip on the desired slope line. If needed, the controller 302 can command a reduction in the pilot pressure line 216a leading to the main control valve 212 associated with the boom hydraulic cylinder 122. For example, a maximum permissible speed of the boom 118 can be set in the control system 300, and if needed, the control system 300 can reduce the boom speed, which would otherwise be guided by the human operator's input to the joystick 228 to slow down the boom 118. The controller 302 can also send pilot pressure signals to the main control valve 212 associated with the boom cylinder 116 and bucket pivot cylinder 120 as needed to control these operations.

[0047] In the context of a virtual fence system, if controller 302 determines that a human operator is turning boom 114 back into a prohibited area, controller 302 may, for example, reduce the hydraulic pilot pressure being sent to the hydraulic motor that is used to rotate the boom to the main control valve 212.

[0048] Normal pilot valve operation mode

[0049] Figure 5 The schematic illustration illustrates the normal operating mode of the pilot lever 228, which directs hydraulic pilot pressure from the first pilot valve 206a to the first pilot chamber 214a of the main control valve 212. For example, if a human operator moves the lever 228 in one direction to direct hydraulic fluid through the first pilot valve 206a, the pilot pressure from the first pilot valve 206a passes through the hydraulic subsystem 218 substantially unmodified. The pilot pressure from the pilot pressure supply line 208 is transmitted to the first pilot chamber 214a via the first pilot valve 206a and then via the first variable orifice valve 220a. Note that the second pilot chamber 214b is connected to the pilot pressure return line 210 via the second variable orifice valve 220b and the second pilot valve 206b to create a pressure difference between the pilot chambers 214a and 214b, causing the spool of the main control valve 212 to shift against a bias spring. The pressure differential quantity control directs the hydraulic working fluid via the main control valve 212 to the rate at which the hydraulic actuator (e.g., boom cylinder 122) is actuated.

[0050] Pilot pressure reduction mode

[0051] Figure 6The pilot pressure reduction mode is illustrated schematically. The human operator is directing the first pilot valve 206a to direct pilot pressure to the first pilot chamber 214a, but the controller 302 has determined that the pilot pressure should be reduced. The first on / off valve 230a is commanded to be "open," allowing pilot oil from the first pilot pressure control line 216a to be discharged via the first EHPRV 224a to the pilot pressure return line 210. The first EHPRV 224a is commanded to regulate the pilot pressure delivered to the first pilot chamber 214a.

[0052] The controller can send a command to the first variable orifice valve 220a to create an orifice that restricts the flow through it, allowing the first EHPRV 224a to control the pilot pressure without saturating. Saturation is a condition that can occur when the EHPRV fails to reduce the pressure to the commanded value, because the pressure source can generate sufficient flow to maintain the pressure in the source line. In other words, in the current situation, unless a restriction is created between the manually operable pilot valve control input 226 and the EHPRV 224a, the manually operable pilot valve control input 226 can generate a flow rate greater than that that the EHPRV 224a can discharge.

[0053] Throughout the pressure reduction operation, the controller 302 monitors the pilot pressure via the first pressure sensor 232a.

[0054] Note that the valve spool of the main control valve 212 is schematically indicated to have moved back to the right due to the reduced pilot pressure, thereby reducing the flow of working hydraulic fluid through the main control valve to the associated hydraulic actuator.

[0055] Pilot pressure generation mode

[0056] Figure 7 The pilot pressure generation mode is illustrated schematically. The lever 228 and the first pilot valve 206a are schematically indicated in a manner that the human operator is not directing pilot pressure to the first pilot chamber 214a. This mode can also be applied to situations where the human operator is directing some pilot pressure to the first pilot chamber 214a, but the controller 302 determines that the pilot pressure is insufficient.

[0057] The controller 302 sends a command to the first on / off valve 230a to command the first on / off valve to the "open" position. The command to the first EHPRV 224a is to transmit pressure from the pilot pressure supply line 208 to the first pilot pressure control line 216a via the first EHPRV 224a and the first pilot pressure bypass line 222a to generate pilot pressure in the first pilot pressure control line 216a.

[0058] The controller 302 can also command the first bidirectional proportional variable orifice valve 220a to create a flow path restriction in the first pilot pressure supply line. The controller 302 can optionally command the first bidirectional proportional variable orifice valve 220a to close the first pilot pressure supply line.

[0059] Throughout the pressure generation operation, the controller 302 monitors the pilot pressure via the first pressure sensor 232a.

[0060] Figures 8 to 11 Alternative implementation methods

[0061] Figures 8 to 11 An alternative embodiment of the pilot hydraulic system 400 with a modified hydraulic subsystem 402 is illustrated, wherein the on / off valves 230a, 230b of the first embodiment have been replaced with mechanical selector valves 404a, 404b.

[0062] Most of the components of the pilot hydraulic system 400 are the same as those of the pilot hydraulic system 200, and... Figures 8 to 11 The same component numbering will be maintained. Components that are substantially the same will not be described further, and it should be understood that their construction and operation are as previously described. Furthermore, Figure 4 The controller 300 can be used to control the pilot hydraulic system 400, the only difference being that there are no on / off valves 230a and 230b.

[0063] Mechanical selector valves 404a and 404b operate in response to pressure in their respective pilot pressure supply lines, which causes the corresponding valve cores 408a and 408b to move against return springs 406a and 406b.

[0064] Figure 9 This illustrative example illustrates the concepts discussed above. Figure 5 The pilot hydraulic system is similar to the normal operating mode of the pilot hydraulic system 400. In the normal operating mode of the pilot hydraulic system 400, the pilot pressure from the first pilot valve 206a operated by the operator's lever 228 is transmitted to the first mechanical selector valve 404a via the first variable orifice valve 220a. This pressure acts on one side of the mechanical selector valve spool 408a of the first mechanical selector valve 404a, causing the spool to shift and allowing pressure to flow to the first pilot chamber 214a of the main control valve 212. Depending on the size of the return spring 406a, the first mechanical selector valve 404a will allow some of the pressure to be discharged via the first bypass line 222a and the first EHPRV 224a to the pilot pressure return line 210, resulting in a small, constant hydraulic fluid flow returning to the pilot pressure return line 210.

[0065] Figure 10 This illustrative example illustrates the concepts discussed above. Figure 6 The pilot hydraulic system is similar to the pressure reduction mode of the pilot hydraulic system 400. In the pressure reduction mode of the pilot hydraulic system 400, the first EHPRV 224a operates in a manner similar to that described above. Figure 6 The described method controls the pressure reaching the first pilot chamber 214a of the main control valve 212 by discharging pressure from the first pilot pressure supply line via the first bypass line 222a. As described above, the first variable orifice valve 220a can create a limit to prevent saturation of the first EHPRV 224a. The first mechanical selector valve 404a allows pressure from the first variable orifice valve 220a (as modified according to the operation of the first EHPRV 224a) to reach the first pilot chamber 214a.

[0066] Figure 11 This is an illustrative example of what has been discussed above. Figure 7 The pilot hydraulic system 400 employs a pressure generation mode similar to that of a pilot hydraulic system. Again, the lever 228 and the first pilot valve 206a are schematically indicated in a manner that the human operator is not directing pilot pressure to the first pilot chamber 214a. This mode can also be applied to situations where the human operator is directing some pilot pressure to the first pilot chamber 214a, but the controller 302 determines that the pilot pressure is insufficient.

[0067] Controller 302 sends a command to the first EHPRV 224a to transmit pressure from the pilot pressure supply line 208 to the first pilot pressure control line 216a via the first EHPRV 224a and the first pilot pressure bypass line 222a, to generate pilot pressure in the first pilot pressure control line 216a. A first mechanical selector valve 404a allows this connection from the first pilot pressure bypass line 222a to the first pilot pressure control line 216a.

[0068] The controller 302 can also command the first bidirectional proportional variable orifice valve 220a to create a flow path restriction in the first pilot pressure supply line. The controller 302 can optionally command the first bidirectional proportional variable orifice valve 220a to close the first pilot pressure supply line. Throughout the pressure generation operation, the controller 302 monitors the pilot pressure via the first pressure sensor 232a.

[0069] Therefore, it can be seen that the apparatus and methods of this disclosure readily achieve the mentioned and inherent purposes and advantages. While certain preferred embodiments of this disclosure have been illustrated and described for these purposes, many changes can be made by those skilled in the art to the arrangement and construction of components and steps, and these changes are covered within the scope and spirit of this disclosure as defined by the appended claims. Features or embodiments of each disclosure can be combined with any of the features or embodiments of other disclosures.

Claims

1. A pilot hydraulic system (200), the pilot hydraulic system comprising: Pilot pressure source (202); Pilot pressure return box (204); Pilot valves (206a, 206b); Pilot pressure supply line (208), the pilot pressure supply line connecting the pilot pressure source to the pilot valve; Pilot pressure return line (210), the pilot pressure return line connecting the pilot pressure return box to the pilot valve; Main control valve (212), the main control valve including pilot chamber (214a); A pilot pressure control line (216a) connects the pilot valve to the pilot chamber (214a). as well as Hydraulic subsystem (218), the hydraulic subsystem being used to modify the pilot pressure supplied to the pilot chamber of the main control valve, the hydraulic subsystem comprising: A variable orifice valve (220a) is disposed in the pilot pressure control line (216a); A pilot pressure bypass line (222a) connecting the pilot pressure control line (216a) downstream of the variable orifice valve (220a) to the pilot pressure return line (210); and An electro-hydraulic pressure reducing valve EHPRV (224a) is provided in the pilot pressure bypass line (222a).

2. The pilot hydraulic system according to claim 1, wherein: The pilot valve is a first pilot valve (206a); and The pilot hydraulic system further includes a manually operable pilot valve control input (226), which includes an input handle (228) and at least a first pilot valve (206a) and a second pilot valve (206b). The input handle is configured to move the first pilot valve when the input handle moves in a first direction and to move the second pilot valve when the input handle moves in a second direction.

3. The pilot hydraulic system according to claim 2, wherein: The input handle (228) is a joystick.

4. The pilot hydraulic system according to claim 1, wherein: The hydraulic subsystem (218) also includes an on / off valve (230a) disposed in the pilot pressure bypass line (222a) between the EHPRV (224a) and the pilot pressure control line (216a).

5. The pilot hydraulic system according to claim 1, wherein: The hydraulic subsystem (218) further includes a selector valve (408a) disposed in the pilot pressure control line (216a) and in communication with the pilot pressure bypass line (222a). The selector valve is configured to allow flow from the pilot pressure control line to the pilot pressure bypass line and to allow flow from the pilot pressure bypass line through the pilot pressure supply line to the pilot chamber (214a).

6. The pilot hydraulic system according to claim 2, wherein: The hydraulic subsystem (218) also includes a pressure sensor (232a) connected to a pilot pressure control line (216a) located between the first pilot valve (206a) and the variable orifice valve (220a).

7. The pilot hydraulic system according to claim 1, wherein: The variable orifice valve (220a) is a bidirectional proportional variable orifice valve.

8. The pilot hydraulic system according to claim 2, wherein: The hydraulic subsystem (218) also includes a pressure sensor (232a) connected to the pilot pressure control line (216a); The pilot hydraulic system further includes a controller (302) connected to the pressure sensor (232a) for monitoring pressure in the pilot pressure control line (216a), and the controller is connected to the EHPRV (224a) and the variable orifice valve (220a) for sending control signals to the EHPRV (224a) and the variable orifice valve (220a). The controller is configured to have a pilot pressure generation mode in which the EHPRV is commanded to generate pilot pressure in the pilot pressure control line by transmitting pressure from the pilot pressure supply line through the EHPRV and the pilot pressure bypass line to the pilot pressure control line.

9. The pilot hydraulic system according to claim 8, wherein: The controller (302) is also configured to employ the pilot pressure generation mode to command the variable orifice valve (220a) to generate flow path restriction in the pilot pressure supply line.

10. The pilot hydraulic system according to claim 8, wherein: The controller (302) is also configured to have a pilot pressure reduction mode, in which the EHPRV (224a) is commanded to regulate the pressure delivered from the first pilot valve (206a) to the pilot chamber (214a) by releasing pressure from the pilot pressure control line (216a).

11. The pilot hydraulic system according to claim 10, wherein: The controller (302) is also configured to employ the pilot pressure reduction mode, such that the variable orifice valve (220a) is commanded to create a flow path restriction in the pilot pressure supply line, enabling the EHPRV (224a) to control the pilot pressure without saturation.

12. The pilot hydraulic system according to claim 10, wherein: The pilot valve is a first pilot valve (206a); The pilot hydraulic system further includes a manually operable pilot valve control input (226), which includes an input handle (228) and at least a first pilot valve (206a) and a second pilot valve (206b). The input handle is configured to move the first pilot valve (206a) when the input handle moves in a first direction, and to move the second pilot valve (206b) when the input handle moves in a second direction. The controller (302) is also configured such that when the controller uses the pilot pressure generation mode or the pilot pressure reduction mode for the first pilot chamber (214a), the second pilot chamber (214b) of the main control valve (212) is connected to the pilot pressure return line (210).

13. The pilot hydraulic system according to claim 10, wherein: The controller (302) is also configured to have a normal operating mode in which the pilot pressure from the first pilot valve (206a) is transmitted to the pilot chamber (214a) via the hydraulic subsystem (218) without modification; and The hydraulic subsystem also includes an on / off valve (230a) disposed in the pilot pressure bypass line (222a) between the EHPRV (224a) and the pilot pressure control line (216a). The on / off valve is closed in the normal operating mode and is open in the pilot pressure generation mode and the pilot pressure reduction mode.

14. The pilot hydraulic system according to claim 10, wherein: The controller (302) is also configured to have a normal operating mode in which pilot pressure from the first pilot valve (206a) is transmitted to the pilot chamber (214a) via the hydraulic subsystem (218); and The hydraulic subsystem (218) further includes a mechanical selector valve (404a) disposed in the pilot pressure control line (216a) and connected to the pilot pressure bypass line (222a), the mechanical selector valve being configured to: In the normal operating mode, pressure is transmitted from the first pilot valve (206a) to the pilot chamber (214a); In the pilot pressure reduction mode, flow is permitted from the pilot pressure control line (216a) to the pilot pressure bypass line (222a); as well as In the pilot pressure generation mode, flow is permitted from the pilot pressure bypass line (222a) to the pilot chamber (214a) via the pilot pressure supply line.

15. The pilot hydraulic system according to claim 12, wherein: The hydraulic subsystem (218) also includes a pressure sensor (232a) connected to the pilot pressure control line (216a); and The pilot hydraulic system further includes a controller (302) connected to the pressure sensor (232a) for monitoring the pressure in the pilot pressure control line (216a), and connected to the EHPRV (224a) and the variable orifice valve (220a) for sending control signals to the EHPRV (224a) and the variable orifice valve (220a). The controller is configured to have a pilot pressure reduction mode in which: The variable orifice valve (220a) is commanded to create flow path restriction in the pilot pressure supply line; and The EHPRV (224a) is commanded to regulate the pressure delivered from the first pilot valve (206a) to the pilot chamber (214a) by relieving pressure from the pilot pressure control line (216a).

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