Construction machine

Abstract

A construction machine includes a pump, a pressure sensor measuring pressure, and a working cylinder including a rod operable to extend and retract. The working cylinder has a bore chamber, a rod chamber, a bore chamber pressure sensor, a bore pressure, a rod chamber pressure sensor, and a rod pressure. The machine includes an input movable between an intermediate position, an extended position, and a retracted position, and a sensor that measures the position. The machine includes a controller programmed with an algorithm to control movement of the working cylinder based on a detected position input by an operator. The algorithm is configured to, in response to identification of an operator input in the rod extension position, confirm that the pump pressure exceeds the bore-side chamber pressure as a prerequisite to set a command to control movement of the working cylinder for rod extension.

Description

Background Art

[0001] The present disclosure relates to a hydraulic system for a construction machine. Summary of the invention

[0002] In one aspect, the present disclosure provides a construction machine, which includes a pump, a pressure sensor, a working cylinder, a bore side chamber pressure sensor, an operator input and a controller. The pressure sensor is configured to measure pump pressure. The working cylinder includes a rod operable to extend and retract. The bore side chamber of the working cylinder is configured to supply fluid from the pump during rod extension, while the fluid is removed from the rod side chamber. The rod side chamber of the working cylinder is configured to supply fluid from the pump during rod retraction, while the fluid is removed from the bore side chamber. The bore side chamber pressure sensor is configured to measure the bore side chamber pressure. The operator input can move between an intermediate position, a rod extension position and a rod retract position. The operator input includes a position sensor configured to measure an intermediate position, a rod extension position and a rod retract position. The controller is communicatively coupled to the working cylinder and programmed with an algorithm configured to control the movement of the working cylinder based on the position of the detected operator input. The algorithm is configured to confirm, in response to recognition of an operator input in a rod extended position, that the pump pressure exceeds the bore side chamber pressure as a prerequisite to setting a command controlling movement of the slave cylinder for rod extension.

[0003] In another aspect, the present disclosure relates to a construction machine, which includes a pump, a pressure sensor, a working cylinder, a bore side chamber pressure sensor, an operator input, a main valve core, a pilot control valve and a controller. The pressure sensor is configured to measure pump pressure. The working cylinder includes a rod operable to extend and retract. The bore side chamber of the working cylinder is configured to supply fluid from the pump during rod extension, while the fluid is removed from the rod side chamber. The rod side chamber of the working cylinder is configured to supply fluid from the pump during rod retraction, while the fluid is removed from the bore side chamber. The bore side chamber pressure sensor is configured to measure the bore side chamber pressure. The operator input is movable between an intermediate position, a rod extension position and a rod retract position. The operator input includes a position sensor configured to measure an intermediate position, a rod extension position and a rod retract position. The main valve core is in fluid communication with the working cylinder and the pump. The pilot control valve is in fluid communication with the main valve core and the pump. A controller is communicatively coupled to the slave cylinder and is programmed with an algorithm configured to output a signal to the pilot control valve to control its output based on the position of the detected operator input. The algorithm is configured to confirm that the pump pressure exceeds the bore side chamber pressure as a prerequisite to setting a command to control movement of the pilot control valve for rod extension in response to recognition of the operator input in the rod extended position.

[0004] The present disclosure also relates to a method for controlling a construction machine. The method includes a controller receiving a position signal from a position sensor that measures an intermediate position, a rod extension position, and a rod retracted position input by an operator. The controller receives a pump pressure of a pump from a pressure sensor. The controller receives a bore pressure from a bore pressure sensor on a bore side of a working cylinder, the bore side of the working cylinder increasing in volume during rod extension and decreasing in volume during rod retraction. The controller receives a rod pressure from a rod pressure sensor on a rod side of a working cylinder, the rod side of the working cylinder decreasing in volume during rod extension and increasing in volume during rod retraction. The controller analyzes the position signal, the pump pressure, the bore pressure, and the rod pressure. The controller, in response to recognition of an operator input in a rod extension position, confirms that the pump pressure exceeds the bore pressure as a prerequisite for setting a command to control movement of the working cylinder for rod extension. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 A schematic illustration of a hydraulic system of a construction machine and the associated boom cylinders is shown.

[0006] Figure 2 A flow chart detailing a control algorithm for a hydraulic system is shown.

[0007] Figure 3 An exemplary construction machine is shown.

[0008] Before any embodiments of the invention are explained in detail, it should be understood that the invention is not limited in its application to the details of construction and arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. DETAILED DESCRIPTION

[0009] Figure 1Schematic illustration of a hydraulic system 10 for use in a construction machine 12 with a boom cylinder 14. The hydraulic system 10 may also be used with other working cylinders, such as a bucket cylinder and a stick cylinder. The boom cylinder 14 includes a rod 18 that is operable to extend and retract the boom of the construction machine 12. Examples of retracting machines include skid steers, compact wheel loaders, mini excavators, and dump trucks. The boom cylinder 14 includes a bore-side chamber 22 and a rod-side chamber 26. The bore-side chamber 22 is located in the boom cylinder 14 so that the rod 18 extends outward as the volume of fluid in the bore-side chamber 22 increases and the volume of fluid in the rod-side chamber 26 decreases. The rod-side chamber 26 is located in the boom cylinder 14 around the rod 18 so that the rod 18 retracts into the boom cylinder 14 as the volume of fluid in the rod-side chamber 26 increases and the volume of fluid in the bore-side chamber 22 decreases. The fluid supplied to the bore-side chamber 22 and the rod-side chamber 26 is supplied through a main control valve 106 (e.g., a main spool) controlled by the controller 30. The controller 30 includes a control system 100 for a load holding function (i.e., a load holding function) of a load when the rod 18 of the boom cylinder 14 is extended and retracted. Figure 2 ). In contrast, solutions for holding a load during extension and retraction of the rod 18 utilize additional valves. U.S. Patent No. 10590962 describes the use of a pressure compensating valve and a counterbalance valve to hold a load. U.S. Patent No. 5579642 describes the use of a post-compensating control valve to hold a load. The hydraulic system 10 is capable of holding a load without the use of additional valves through the integrated control system 100. The control system 100 will be discussed in more detail below.

[0010] The controller 30 may include one or more electronic processors and one or more memory devices. The controller 30 may be communicatively connected to one or more sensors or other inputs, such as described herein. The electronic processor may be implemented as a programmable microprocessor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGA), a set of processing components, or implemented as having other suitable electronic processing components. The memory device (e.g., a non-temporary computer-readable medium) includes one or more devices (e.g., RAM, ROM, flash memory, hard disk storage, etc.) for storing data and / or computer code to complete or facilitate the various processes, methods, layers and / or modules described herein. The memory device may include a database component, an object code component, a script component, or other types of code and information for supporting various activities and information structures described in this application. According to an example, the memory device is communicatively connected to the electronic processor and may include computer code for executing one or more processes described herein. The controller 30 may also include an input-output ("I / O") module. The I / O module may be configured to directly interface with one or more devices (such as power supplies, sensors, displays, etc.). In one embodiment, the I / O modules may utilize general purpose I / O (GPIO) ports, analog input / output, digital input / output, etc. As described in further detail below, the controller 30 may be programmed with an algorithm.

[0011] The algorithm of the controller 30 is configured to interpret and analyze a plurality of signals. The plurality of signals include the bore side pressure P A , rod side pressure P B , Pump pressure P P and position signal cmd in Hole side pressure P A The rod side pressure P is measured by the bore side pressure sensor 50 and the rod side pressure P B Measured by the rod side pressure sensor 54. Pump pressure P P Measured by pressure sensor 58. The bore side pressure sensor 50, the rod side pressure sensor 54 and the pressure sensor 58 are pressure transducers. The pressure sensor 58 is connected to the pump line 62, which is connected to the pump 63. The position signal cmd in is measured by position sensor 66 and is dependent upon operator input 70 (i.e., joystick) to a neutral position ( Figure 1 ), the rod extended position 74, and the rod retracted position 78. The controller 30 is in data communication with each of the sensors 50, 54, 58, 66 so that the parameters measured thereby can be provided to the controller 30 periodically or continuously. The algorithm of the controller 30 analyzes the hole side pressure P A , rod side pressure P B , Pump pressure P Pand position signal cmd in , and determines whether to send a signal 82 to the first pilot control valve 86 (in response to the rod extended position 74 of the operator input 70), or whether to send a signal 90 to the second pilot control valve 94 (in response to the rod retracted position 78 of the operator input 70). Depending on the conditions being monitored, the algorithm may instead ignore or override the rod extend or rod retract command from the operator input 70 and default to load holding. Further details of the control system 100 of the algorithm of the controller 30 are discussed below ( Figure 2 ).

[0012] Pump 63 is a variable displacement pump (e.g., an axial piston pump) capable of changing the displacement setting (e.g., via a swash plate angle) and is driven by a drive source 64. Drive source 64 may include an internal combustion engine or an electric motor to drive pump 63. In addition, pump 63 is variable for positive and negative displacement (i.e., reversible flow direction from a "pumping" mode that produces flow to a "motor driven" mode that receives flow) and is referred to as having over-center capability because it can switch between positive and negative displacements during operation. Pump 63 may also be referred to as an eccentric variable displacement pump. In some constructions, pump 63 may be a Bosch Rexroth A10VO (also known as EC4) with eOC control, although other pumps may also be suitable for use. Pump 63 is fluidly connected to pump line 62 and provides a pump pressure P P The pilot control valves 86, 94 are both individually actuable from an inactive state to an active state in response to the signals 82, 90. In the active state, the pilot control valves 86, 94 receive the signals 82, 90, respectively, to allow fluid communication between the control pressure line 104 and the main valve core 106. The control pressure line 104 is maintained at a pressure between 25-30 bar by the pump 63 and actuates the main valve core 106.

[0013] The pilot control valve 86 in the activated state is for stem extension and allows pressurized fluid to flow from the control pressure line 104 into the line 107 to the first end 110 of the main valve core 106. The pressurized fluid supplied by the line 107 actuates the main valve core 106 against the biasing force provided by the spring 114 and actuates the main valve core 106 into the stem extended position. The stem extended position of the main valve core 106 allows fluid communication between the first work port A and the pump line 62, which is in fluid communication with the bore side chamber 22 via the bore line 116. The pump line 62 supplies pressurized fluid to the bore line 116 and thus to the bore side chamber 22 to increase the fluid volume in the bore side chamber 22, thereby extending the rod 18. The stem extended position of the main valve core 106 allows fluid communication between the second work port B and the tank line 112, which is in fluid communication with the rod side chamber 26 via the line 120. The tank line 112 is at atmospheric pressure, and fluid is delivered to the tank line 112 from the rod side chamber 26 during the stem extension period. Since the first pilot control valve 86 is in an activated state, the second pilot control valve 94 must be in an inactive state to allow the main valve core 106 to actuate to the stem extended position. The second pilot control valve 94 enables fluid communication between the tank line 108, which is in fluid communication with the tank line 112, and the second end 118 of the main valve core 106 via the line 121. This allows the fluid at the second end 118 of the main valve core 106 to be dispersed as the main valve core 106 moves to the stem extended position.

[0014] The second pilot control valve 94 in the activated state is used for stem retraction and its operation is similar to the first pilot control valve 86 in the activated state. Instead of the pressurized fluid from the control pressure line 104 being delivered to the first end 110 of the main valve core 106, the pressurized fluid is delivered by the second pilot control valve 94 to the second end 118 of the main valve core 106 via the line 121 to actuate the main valve core 106 to the stem retracted position against the bias of the spring 122. The stem retracted position of the main valve core 106 allows fluid communication between the second workport B and the pump line 62. The pump line 62 supplies pressurized fluid to the rod side chamber 26 via the line 120 to increase the fluid volume in the rod side chamber 26, thereby retracting the rod 18. The stem retracted position of the main valve core 106 allows fluid communication between the first workport A and the tank line 112 via the orifice line 116. During the increase in fluid volume within the rod-side chamber 26, the bore-side chamber 22 delivers fluid to the tank line 112 to allow the stem of the rod 18 to extend. Since the pilot control valve 94 is in the activated state, the pilot control valve 86 must be in the inactive state to allow the main valve core 106 to actuate to the stem retracted position. The pilot control valve 86 allows fluid communication between the tank line 108 and the first end 110 of the main valve core 106 via the line 107. This allows the fluid at the first end 110 of the main valve core 106 to be dispersed as the main valve core 106 moves toward the stem retracted position.

[0015] In addition to the above two states, when the rod 18 is neither extended nor retracted, the two pilot control valves 86, 94 can be in the inactive state at the same time. In the inactive state, both pilot control valves 86, 94 supply the main valve core 106 fluid at atmospheric pressure from the tank line 108. Due to the absence of pressure, the main valve core 106 is biased by the springs 114, 122 to the middle state, in which the first working port A and the second working port B are both blocked by the main valve core 106 from fluid communication with the pump line 62 and the tank line 112.

[0016] The hydraulic system 10 also includes a load sensing line 123, a shuttle valve 124, a port-side pressure reducing valve 126, and a rod-side pressure reducing valve 130. In the example where the pump 63 is a hydraulic mechanical load sensing pump, the load sensing line 123 and the shuttle valve 124 are provided. The port-side pressure reducing valve 126 is disposed between the port line 116 and the tank line 112. If the port-side pressure P A If the pressure threshold is exceeded, the bore-side pressure relief valve 126 enables fluid communication between the bore-side chamber 22 and the tank line 112. The pressure threshold for the bore-side chamber is about 280 bar. In other configurations, the pressure threshold may be less than or greater than 280 bar. The rod-side pressure relief valve 130 is disposed between the line 120 and the tank line 112 and is activated if the rod-side pressure P B Above 320 bar, a reduced pressure is provided. In other configurations, for the pressure reducing valves 126 and 130, the pressure threshold may be less than or greater than 320 bar.

[0017] Figure 2 1 shows the logic of the control system 100 for controlling the volume of fluid in the bore-side chamber 22 and the rod-side chamber 26 and, thus, the movement of the rod 18. The control system 100 begins at box 140 when the construction machine 12 is turned on. At box 144, the algorithm of the controller 30 receives an input signal cmd from the position sensor 66. in , Pump pressure P P , hole side pressure P A and rod side pressure P B At box 148, the algorithm identifies whether the position of the operator input 70 is in the neutral position ( Figure 1 During detection of the intermediate position, the algorithm continues to box 152 and the algorithm controls the cylinder 18 by outputting cmd out Set equal to the input signal cmd in (and cmd out =cmd in=0) to perform the hold function. In other words, neither pilot control valve 86, 94 is activated and main valve spool 106 remains in the neutral position. The algorithm restarts at box 144 and during the hold function, main valve spool 106 remains in the neutral position (i.e., pilot control valves 86 and 94 do not receive a signal of an activated state). As previously described, the algorithm moves from box 144 to box 148 to identify whether operator input 70 is in the neutral position ( Figure 1 ).

[0018] When the operator input 70 is not in the middle position ( Figure 1 ), the algorithm moves from box 148 to box 156. The algorithm identifies whether the position of the operator input 70 is in the extended position 74 (i.e., cmd in >0). Under the condition that the operator input 70 is in the rod extended position 74, the algorithm moves to box 160. At box 160, the algorithm checks the pump pressure P P Is it greater than or equal to the hole side pressure P A and the specified margin P mar The sum (i.e., P P ≥P A +P mar ). This can be summarized as the algorithm confirming the pump pressure P P Exceeds the hole side pressure P A (Because the margin P is specified mar can be any positive value). In some contemplated configurations, the margin P is specified mar It can be in the range of 20-30 bar. In other configurations, the margin P is specified mar Less or more than 20-30 bar. Specified margin P mar The decision at box 160 acts as a trigger for the controller 30 to output cmd at box 164. out Set to equal input cmd in In the illustrated configuration, this results in the actuation of the first pilot control valve 86 (signal 82, Figure 1 ) to move the main spool 106 and achieve stem extension because the operator input 70 is in the stem extended position 74. mar is incorporated into the algorithm to ensure that when the main valve core 106 moves to the command stem extension, no backflow occurs in the pump line 62 toward the pump 63. As described above, the pump pressure P has previously been ensured by utilizing an additional valve. P The load is held at the desired pressure before the rod is extended. In addition to the control system 100, the hydraulic system 10 monitors the position signal cmd in , Pump pressure PP , hole side pressure P A and rod side pressure P B And control the movement of the main valve core 106 for rod extension to achieve load holding. P Less than the hole side pressure P A and the specified margin P mar The sum of the conditions (ie, pump pressure P P Not exceeding the hole side pressure P A ), the algorithm advances from frame 160 to frame 152, and continues to frame 144 as previously described. When moving from frame 160 to frame 152, the algorithm may trigger an alarm to notify the user that the pump pressure P P Less than the hole side pressure P A and the specified margin P mar The sum of the pump pressure P is the sum of the pump pressure P and the load holding function P. P Is it greater than or equal to the hole side pressure P A and the specified margin P mar sum.

[0019] Under the condition that the operator input 70 is not in the rod extended position 74 (ie, cmd in >0, or in other words cmd in <0 and the operator input 70 is in the rod retracted position 78), the algorithm moves from frame 156 to frame 168. At frame 168, the algorithm identifies the pump pressure P P Is it greater than or equal to the rod side pressure P B and the specified margin P mar The sum (i.e., P P ≥P B +P mar ). This can be summarized as confirming the pump pressure P P Exceeding rod side pressure P B The decision at box 168 acts as the controller 30 outputting cmd at box 164 out Set to equal input cmd in In the illustrated configuration, this results in the actuation of the second pilot control valve 94 (signal 90, Figure 1 ) to move the main spool 106 and achieve stem retraction because the operator input 70 is in the stem retracted position 78. mar is incorporated into the algorithm to ensure that when the main valve core 106 moves to the command stem retracted, no backflow occurs in the pump line 62 toward the pump 63. As described above, the pump pressure P has previously been ensured by utilizing an additional valve. P The load is held at the desired pressure before the rod is retracted.P Less than rod side pressure P B and the specified margin P mar The algorithm advances to box 152 and continues to box 144 as previously described. When moving from box 168 to box 152, the algorithm can trigger an alarm to notify the user that the pump pressure P P Less than rod side pressure P B and the specified margin P mar The sum of the two, because the operator will expect the rod to extend. In addition to the specified margin P mar In addition, the algorithm continuously monitors the pump pressure P P Is it greater than the rod side pressure P B .

[0020] Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention described.

Claims

1. A construction machine comprising: Pumps; a pressure sensor configured to measure pump pressure; a slave cylinder including a rod operable to extend and retract, wherein a bore-side chamber of the slave cylinder is configured to supply fluid from a pump while removing fluid from the rod-side chamber during rod extension, wherein the rod-side chamber of the slave cylinder is configured to supply fluid from a pump while removing fluid from the bore-side chamber during rod retraction; an orifice-side chamber pressure sensor configured to measure orifice-side chamber pressure; an operator input movable between a neutral position, a rod extended position, and a rod retracted position, the operator input comprising a position sensor configured to detect the neutral position, the rod extended position, and the rod retracted position; and a controller communicatively coupled to the slave cylinder and programmed with an algorithm configured to control movement of the slave cylinder based on a detected position of an operator input, Wherein the algorithm is configured to, in response to recognition of an operator input in a rod extended position, confirm that the pump pressure exceeds the bore side chamber pressure as a prerequisite to setting a command to control movement of the working cylinder for rod extension.

2. The construction machine of claim 1 further comprising a rod side chamber pressure sensor configured to measure rod side chamber pressure, wherein the algorithm is configured to confirm that the pump pressure exceeds the rod side chamber pressure in response to recognition of an operator input in a rod retracted position as a prerequisite for setting a command to control movement of the working cylinder for rod retraction.

3. A construction machine according to claim 2, wherein the algorithm is configured to, in response to recognition of an operator input in a rod retracted position, confirm that the pump pressure exceeds the rod side chamber pressure by at least a specified margin as a prerequisite for setting a command to control movement of the working cylinder for rod retraction.

4. The construction machine of claim 2, wherein the algorithm is configured to, in response to recognition of an operator input in a rod retracted position, recognize that the pump pressure does not exceed the rod side chamber pressure and respond by performing a load holding function rather than setting a command to control movement of the working cylinder for rod retraction.

5. The construction machine of claim 1 , wherein the algorithm is configured to, in response to recognition of an operator input in a rod extended position, confirm that the pump pressure exceeds the bore side chamber pressure by at least a specified margin as a prerequisite for setting a command to control movement of the working cylinder for rod extension. 6 . The construction machine according to claim 5 , wherein the prescribed margin is configured to match a pressure drop between a pump and a working cylinder.

7. The construction machine of claim 1 , wherein the algorithm is configured to respond to recognition of an operator input in a rod extended position, recognize that the pump pressure does not exceed the bore side chamber pressure, and respond by performing a load holding function rather than setting a command to control movement of the working cylinder for rod extension.

8. The construction machine according to claim 1, further comprising: A main valve core connected to the working cylinder and the pump via a fluid pipeline; and a pilot control valve in fluid communication with the main valve core and the pump, the pilot control valve being configured to direct fluid to the main valve core, which in turn delivers fluid from the pump to the working cylinder, Wherein the algorithm is configured to output a signal to the pilot control valve in response to an operator input in a lever extended position.

9. The construction machine according to claim 8, further comprising: a second pilot control valve in fluid communication with the main valve spool and the pump, the second pilot control valve being configured to direct fluid to the main valve spool, which in turn delivers fluid from the pump to the working cylinder, Wherein the algorithm is configured to output a signal to the second pilot control valve in response to an operator input in a rod retracted position.

10. The construction machine according to claim 8, wherein the pump and the main valve core are directly connected through a pump line without any intermediate hydraulic components.

11. A construction machine comprising: Pump, a pressure sensor configured to measure pump pressure; a slave cylinder including a rod operable to extend and retract, wherein a bore-side chamber of the slave cylinder is configured to supply fluid from a pump while removing fluid from the rod-side chamber during rod extension, wherein the rod-side chamber of the slave cylinder is configured to supply fluid from a pump while removing fluid from the bore-side chamber during rod retraction, a bore-side chamber pressure sensor configured to measure the bore-side chamber pressure, an operator input movable between a neutral position, a rod extended position, and a rod retracted position, the operator input comprising a position sensor configured to measure the neutral position, the rod extended position, and the rod retracted position; A main valve core in fluid communication with the working cylinder and the pump; a pilot control valve in fluid communication with the main valve spool and the pump; and a controller communicatively coupled to the slave cylinder and programmed with an algorithm configured to output a signal to the pilot control valve to control an output thereof based on the sensed position of the operator input, Wherein the algorithm is configured to, in response to recognition of an operator input in a stem extended position, confirm that the pump pressure exceeds the bore side chamber pressure as a prerequisite to setting a command to control movement of the pilot control valve for stem extension.

12. The construction machine according to claim 11, wherein the pump and the main valve core are directly connected through a pump line without any intermediate hydraulic components. 13 . The construction machine according to claim 12 , wherein the main valve core is configured to enable fluid communication between the bore-side chamber and the pump in response to the pilot control valve receiving the signal.

14. The construction machine according to claim 12, further comprising: a rod side chamber pressure sensor configured to measure rod side chamber pressure; and a second pilot control valve, wherein the algorithm is configured to confirm that the pump pressure exceeds the rod side chamber pressure in response to recognition of an operator input in a rod retracted position as a prerequisite for setting a command to control movement of the second pilot control valve for rod retraction. 15 . The construction machine according to claim 14 , wherein the main valve core is configured to enable fluid communication between the rod-side chamber and the pump in response to the second pilot control valve receiving the signal.

16. A method for controlling a construction machine, the method comprising: receiving, with a controller, position signals from a position sensor that measures an operator-input intermediate position, a rod-extended position, and a rod-retracted position; receiving, with a controller, a pump pressure of the pump from a pressure sensor; receiving, with a controller, a bore pressure from a bore pressure sensor on a bore side of a working cylinder that increases in volume during rod extension and decreases in volume during rod retraction; receiving, with a controller, a rod pressure from a rod pressure sensor on a rod side of a working cylinder that decreases in volume during rod extension and increases in volume during rod retraction; Analyze position signals, pump pressure, bore pressure, and rod pressure using a controller; and In response to recognition of the operator input in the rod extended position, the controller confirms that the pump pressure exceeds the bore pressure as a prerequisite for setting a command to control movement of the working cylinder for rod extension.

17. The method of claim 16 further comprising, in response to identification of an operator input in a rod extending position, identifying with a controller that pump pressure does not exceed bore pressure, and the controller responding by performing a load holding function rather than setting a command to control movement of a working cylinder for rod extension.

18. The method of claim 16 further comprising, in response to identification of the operator input in the rod retracted position, confirming with the controller that the pump pressure exceeds the rod pressure as a prerequisite to setting a command to control movement of the working cylinder for rod retraction.

19. The method of claim 18 further comprising, in response to identification of the operator input in the rod retracted position, identifying with the controller that the pump pressure does not exceed the rod pressure, and the controller responding by performing a load holding function rather than setting a command to control movement of the working cylinder for rod retraction.

Images