Aerial work platform with linkage damping

Abstract

A lift device and a method of controlling the lift device are provided. The lift device has a linkage assembly supported by a chassis, a work platform supported by the linkage assembly, and a hydraulic system. The hydraulic system has a lift cylinder to move the linkage assembly between a retracted position and an extended position, and a damping cylinder to increase stiffness of a pair of linkages positioned between the distal end of the lift cylinder and the work platform. When the linkage assembly is being extended, the lift cylinder receives pressure from the hydraulic system at a first pressure and the damping cylinder receives fluid from the hydraulic system at a second pressure, the second pressure lower than the first pressure.

Description

AERIAL WORK PLATFORM WITH LINKAGE DAMPINGCROSS-REFERNCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese patent application Serial No. 202311027213.9 filed August 15, 2023, the disclosure of which is hereby incorporated in its entirety by reference herein.TECHNICAL FIELD

[0002] Various embodiments relate to an aerial work platform or a mobile elevated work platform, such as a scissor lift, with a linkage damping system, and a method for damping linkages in such an aerial work platform.BACKGROUND

[0003] Various examples of aerial work platforms are disclosed in Chinese Patent Publication No. CN 115057391 A; Chinese Patent Publication No. CN 208327336 U, Chinese Patent Publication No. CN 112279166 A; Chinese Patent Publication No. CN 112340668 A; and Chinese Patent Publication No. CN 115417352 A.SUMMARY

[0004] A lift device according to the disclosure includes a chassis, and a linkage assembly supported by the chassis, a work platform supported by the linkage assembly, a hydraulic system. The linkage assembly has a series of pairs of linkages, with each pair of linkages rotatably connected to at least one other pair of linkages, and linkages in each pair of linkages are rotatably connected to one another. The hydraulic system has a lift cylinder and a damping cylinder. The lift cylinder has a distal end connected to a first pair of linkages of the series of pair of linkages, with the lift cylinder movable between a retracted position and an extended position to move the linkage assembly between a retracted position and an extended position. The damping cylinder is movable between a retracted position and an extended position to limit movement of a second pairof linkages positioned between the first pair of linkages and the work platform. When the linkage assembly is being extended, the lift cylinder receives pressure from the hydraulic system at a first pressure and the damping cylinder receives fluid from the hydraulic system at a second pressure, the second pressure lower than the first pressure.

[0005] A lift device according to the disclosure includes a chassis, a stack linkage assembly supported by the chassis, a work platform supported by the stack linkage assembly, and a fluid system. The fluid system is provided with a lift cylinder movable between a retracted position and an extended position to move the stack linkage assembly between a retracted position and an extended position, and a damping cylinder movable between a retracted position and an extended position to limit movement of one or more linkages positioned between a distal end of the lift cylinder and the work platform.

[0006] A method according to the disclosure is provided to control a linkage assembly for a lift device. A lift cylinder with a distal end connected to an intermediate linkage in a series of linkages for the linkage assembly is extended to extend the linkage assembly by providing fluid flow to the lift cylinder at a first pressure and in response to a request to extend a linkage assembly. A damping cylinder connected to another linkage in the series of linkages is extended thereby limiting movement in the linkage assembly by providing fluid flow to the damping cylinder at a second pressure lower than the first pressure and in response to the request to extend the linkage assembly, the another linkage positioned between the intermediate linkage and a work platform for the lift device. Movement of the work platform and the linkage assembly is damped when the linkage assembly is in an at least partially extended position via fluid flow through a relief valve associated with the damping cylinder in response to a pressure in the damping cylinder exceeding a pressure threshold of the relief valve.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIGURE 1 illustrates an aerial work platform or lift device with a fluid system according to an embodiment, and in an at least partially extended position;

[0008] FIGURE 2 illustrates a schematic of a fluid system according to an embodiment and for use with the aerial work platform of Figure 1 ; and

[0009] FIGURE 3 illustrates another schematic of a fluid system according to an embodiment and for use with the aerial work platform of Figure 1.DETAILED DESCRIPTION

[0010] As required, detailed embodiments of the present disclosure are provided herein; however, it is to be understood that the disclosed embodiments are merely examples that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure.

[0011] Figure 1 illustrates a lift device 10 such as an aerial work platform or mobile elevated work platform according to an example. In the example shown, the lift device 10 is provided as a scissor lift. The lift device 10 has a chassis 12, a lifting assembly or linkage assembly 14, and a work platform 16. The chassis 12 may be supported on an underlying surface via traction devices 18, such as wheels, tracks or the like. The lift device 10 may be provided with a propulsion system to drive the traction devices to propel the mobile device. The propulsion system may be provided by one or more electric motors connected to a traction battery, and / or an internal combustion engine. In one example, the electric motors and / or the internal combustion engine may be coupled to the traction devices to provide torque thereto, e.g. directly or via a transmission. In another example, the electric motors and / or the internal combustion engine may drive a pump fluidly coupled to a hydraulic drive system, with the wheels driven by hydraulic motors in the hydraulic drive system. In other examples, the device 10 may be stationary, and provided as a stationary support structure. The work platform 16 may be sized to support one or more users or operators, as well as their tools, supplies, or the like.

[0012] The lifting assembly 14 supports the work platform 16 relative to the chassis 12, and is connected to the chassis 12 and the work platform 16. The lifting assembly 14 is movable relative to the chassis 12 between a stowed or retracted position, and a deployed or extended position, shown in Figure 1, as well as to various positions located between the retracted position and the extended position, in order to move the work platform 16 to any one of multiple desired use positions.

[0013] The lifting assembly 14 may be moved using a fluid system with a lift cylinder 20 and a cylinder 22, as described further below. The fluid system may be supported at least partially by the chassis 12and the lifting assembly 14. The fluid system may be fluidly connected to the propulsion hydraulic system, or may be fluidly decoupled and independent therefrom, e.g. where the fluids in the two hydraulic systems do not mix and are maintained separately. For example, a lift device 10 with electric drive motors may have a separate function hydraulic system to operate various functions of the device, such as steering, moving the linkage assembly, and the like.

[0014] The lifting assembly 14 has a series of linkages 30 that are connected to one another. Each linkage 30 may be provided by a member or arm that extends from a distal end to a proximal end. Each linkage 30 may be provided by a bar, rod, tube, or the like, and may be formed from metal or another rigid material. In one example, the linkages 30 are connected to one another, for example, as one or more stack linkages or pantograph mechanisms for the linkage assembly. In the example shown, the linkage assembly 14 has a first pantograph or scissor on one side, and a second pantograph or scissor on the other side. The two pantograph mechanisms are opposed to one another, and cooperate to form the linkage assembly and support the work platform above the chassis.

[0015] For each pantograph, the linkages 30 may be provided in pairs 32, with each pair rotatably linked to one another, e.g. via an intermediate or central pivot pin 34 that is positioned between the distal and proximal ends of each linkage 30. The first, lowermost pair of linkages 40 is supported by the chassis, with the proximal ends of the linkages rotatably and translatably supported by the chassis. The distal ends of the first pair of linkages are rotatably connected to the proximal ends of a second pair of linkages, e.g. via pivot pins. The distal ends of the second pair of linkages are rotatably connected to the proximal ends of a this pair of linkages, and so on.For the uppermost pair of linkages 42, the distal ends are rotatably and translatably supported by the work platform.

[0016] As the linkage assembly 14 is extended, the central pivot pins 34 remain aligned with one another, and the ends of the linkages 0 moved closer to one another and closer to the axis defined by the central pivot pins 34. When the linkage assembly 14 is retracted, the ends of the linkages 30 move farther away from one another.

[0017] The lift cylinder 20, as described below in further detail, is connected to one or more linkages 30 of the linkage assembly 14. The lift cylinder may be a hydraulic cylinder or other fluid cylinder, with fluids including liquids and / or gases. As the lift cylinder 20 is extended, the linkages 30 move relative to one another and the linkage assembly 14 is extended. As the lift cylinder 20 is retracted, the linkages 30 move relative to one another and the linkage assembly 14 is retracted. The lift cylinder 20 may move between a first extended position corresponding to the extended position of the linkage assembly, and a second retracted position corresponding to the retracted position of the linkage assembly. The lift cylinder 20 may also be maintained at a position between the first and second positions to maintain the linkage assembly 14 in an intermediate selected position based on the desired height of the work platform 16.

[0018] The hydraulic lift cylinder 20 is connected to one or more intermediate linkages of the linkage assembly, and as such, there are one or pairs or sets of linkages that are above the uppermost or distal end 20a of the hydraulic lift cylinder. Without a damping cylinder 22, the linkages 30 in the linkage assembly 14 that are above the distal end of the hydraulic lift cylinder 20 may have a lower stiffness than linkages 30 between the two ends 20a, 20b of the hydraulic lift cylinder. The hydraulic lift cylinder 20 supports the overall linkage assembly 14, and may provide increased stiffness for linkages 30 in the assembly 14. One or more damping cylinders 22, or upper damping cylinders, may be provided as described below to further limit movement of linkages and increase the overall stiffness of the linkage assembly, e.g. by reducing or limiting the amount that the associated or upper linkages may move relative to one another to reduce movement or shaking of the work platform 16, and by increasing the vertical stiffness of the linkage assembly 14. The damping cylinder 22 may be a hydraulic cylinder, or other fluid cylinder. The damping cylinder 22 may increase the stiffness of the pairs or sets of linkages 32 that are above the hydrauliclift cylinder 20. The damping cylinder 22 may be operated at a different fluid pressure than the hydraulic lift cylinder 20, or may be fluidly decoupled from the hydraulic lift cylinder, as described below in further detail.

[0019] The damping cylinder(s) 22 may be provided at a location above the hydraulic lift cylinder 20, and generally moves in conjunction with, or in a coordinated fashion with, the hydraulic lift cylinder 20. In one example, the damping cylinder 22 has a first end 22a and a second end 22b. The first end 22a of the damping cylinder is connected to one or more of the linkages 30, e.g. an intermediate linkage at or above an upper distal end 20a of the hydraulic lift cylinder. The second end 22b of the damping cylinder is connected to another one or more of the linkages 30 above the first end of the damping cylinder or to the work platform. In one example, the damping cylinder 20 may be positioned such that it is connected to only linkages 30 at or above the upper end 20a of the hydraulic lift cylinder. In the example shown, the distal end 20a of the lift cylinder 20 is connected to an intermediate pair of linkages 36, the proximal end 20b of the lift cylinder 20 is connected to either the chassis 12 or a pair of linkages 37 positioned between the pair of linkages 36 and the chassis 12. In the example shown, the damping cylinder 22 has one end 22a connected to the pair of linkages 36, and another end connected to an upper pair of linkages 38. In other examples, the cylinders 20, 22 may be connected to other linkages in the linkage assembly,

[0020] By providing a damping cylinder 22 as described herein, various non-limiting advantages may be provided. For example, the damping cylinder 22 may reduce vertical deflection of the linkage assembly 14 and work platform 16 by increasing the stiffness of the linkage assembly 14. By operating the damping cylinder 22 at different pressures than the hydraulic cylinder 20, the linkage assembly 14 pivot forces may be optimized without being restricted by the damping cylinder 22, and the damping cylinder 22 may also be provided with a reduced size compared to the lift cylinder 20 and configured to provide lower forces on the linkage assembly 14.

[0021] Conventionally, a lift device has been provided with a single hydraulic lifting cylinder for the linkage assembly, which may be connected to several bottom pairs or sets of linkages, leaving the upper layers unsupported or above the single lifting cylinder, which may result inreduced vertical stiffness in the linkage assembly, and possible up and down movement of the work platform when users are working on it.

[0022] The function hydraulic system has one or more fluid circuits, as described below with reference to Figures 2 and 3. The function hydraulic system includes a motor, a pump, and a hydraulic lifting cylinder. The function hydraulic system may also operate other functions for the vehicle, such as steering or the like. The function hydraulic system may also contain various valves, filters, and other fluid system components.

[0023] Figure 2 illustrates a schematic of a function hydraulic system 100 according to a first example, and for use with a lift device 10, such as the device described above with respect to Figure 1.

[0024] The function hydraulic system 100 has a fluid circuit 102 with a reservoir 104. A motor 106, such as an electric motor, is used to drive a fluid pump 108 to provide fluid flow from the reservoir 104 to one or more function select valves 110. The electric motor may be in electronic communication with a traction battery. In other examples, the motor 106 may be provided by a conventional internal combustion engine.

[0025] In the example shown, the function select valve 110 is provided as a crossover valve, and may be controlled via a solenoid such as an electrically operated solenoid. A first relief valve 112 may also be provided to fluidly connect the pump 108 outlet to the reservoir 104 as shown, and limit the pressure at the pump outlet and the fluid line immediately downstream therefrom. The fluid circuit 102 provides fluid from the reservoir 104 to various functions, such as steering and lift for the linkage assembly, as described below.

[0026] When the function select valve 110 is in a first position, as shown, the function select valve 110 fluidly connects the pump 108 outlet to a steering manifold 114. In the steering manifold 114, the fluid flows from the pump 108 and function select valve 110, to a steering select valve 116. The steering select valve 116 may be provided by one or more valves to control fluid flow to either (i) a first side of a steering cylinder 118 to move one or more wheels such that the device 10 steers to the left, (ii) a second side of the steering cylinder 118 to move one or more wheels such that the device 10 steers to the right, or (iii) a return line to direct fluid flow back to thereservoir 104 as shown. In other examples, the steering manifold may provide additional and / or non-steering lift device 10 functions other than the position of the linkage assembly 14.

[0027] The function select valve 110 and associated solenoid may be configured such that the function select valve 110 is in the first position when the solenoid is off as shown. When the solenoid for the valve 110 is powered, e.g. when the coil within the solenoid is energized, the solenoid may move the valve element of the function select valve 110 to the second position.

[0028] When the function select valve 110 is in the second position, the pump 108 outlet is fluidly coupled to a fluid passage 132 (or pressure galley) for a lift manifold 130 for the linkage assembly 14, with the lift manifold 130 containing both the hydraulic lift cylinder 20 and the damping cylinder 22. The fluid passage 132 is fluidly coupled to the hydraulic lift cylinder 20 via a first flow control valve 134, also referred to herein as a first directional valve 134.

[0029] The first directional valve 134 may be a two position and two way valve, and may be controlled via a solenoid such as an electrically operated solenoid. When the first directional valve 134 is in a first position, as shown, the first directional valve 134 fluidly connects the fluid passage 132 to the lift cylinder 20 to allow fluid to flow only in one direction from the fluid passage 132 into the lift cylinder 20 with the function select valve 110 in the second position and the pump 108 operating, which would extend the lift cylinder 20 and raise the linkage assembly 14, or maintain the position of the linkage assembly 14 by preventing the linkage assembly from retracting regardless of the position of the function select valve 110. Note that fluid is prevented from exiting the lift cylinder 20 with the first directional valve 134 in the first position based on the internal check valve as shown.

[0030] When the first directional valve 134 is in a second position, the first directional valve 134 fluidly connects the lift cylinder 20 to the fluid passage 132 to allow fluid to flow only in one direction from the lift cylinder 20 and into the fluid passage 132, which would provide for retraction of the lift cylinder 20 and retraction of the linkage assembly 14 with the function select valve 110 in the first position as shown. Note that the function select valve 110 fluidly connects the fluid passage 132 to the return line 120 and reservoir 104 in the first position.

[0031] The first directional valve 134 and associated solenoid may be configured such that the first directional valve 134 is in the first position when the solenoid is off, such that the position of the work platform 16 is maintained. In the event that the solenoid for the first directional valve 134 is off, and a user would like to retract the linkage assembly 14 and lower the lift platform 16, the user may engage a release lever 136 to manually move the first directional valve 134 to the second position (and likewise, stop movement by releasing or returning the lever 136 associated with the first directional valve 134). When the solenoid is powered, e.g. when the coil within the solenoid is energized, the solenoid may move the valve element of the first directional valve 134 to the second position.

[0032] The lift manifold fluid passage 132 is also connected to the damping cylinder 22 via a pressure reduction valve 140, a second flow control valve 142 (also referred to herein as a second directional valve 142), and a second relief valve 144. The hydraulic lift cylinder 20 and the damping cylinder 22 are therefore operated on the same hydraulic circuit 102, but at different pressures.

[0033] The pressure reduction valve 140 reduces the fluid pressure as fluid flows from the fluid passage 132 to the second directional valve 142. In one example, the pressure reduction valve 140 may be provided as a pilot-operated pressure reduction valve, with the outlet pressure pre-selected for the valve. In other examples, the pressure reduction valve 140 may be controlled via a solenoid, e.g. to provide variable pressure at the valve outlet. In one non-limiting example, the fluid passage 132 may be operated on the order of 1500-2500 psi, with the pressure reduction valve 140 reducing the pressure of the fluid to on the order of 500-1500 psi. The pressure reduction valve 140 may be used to reduce the fluid pressure from the fluid passage 132 to a fixed pressure that is lower than a pressure threshold set for the second relief valve 144, and also to provide a lower pressure for use with the damping cylinder 22.

[0034] The pressure reduction valve 140 is connected to the damping cylinder 22 via the second directional valve 142. The second directional valve 142 may be a two position and two way valve, and may be controlled via a solenoid such as an electrically operated solenoid. When the second directional valve 142 is in a first position, as shown, the second directional valve 142 fluidly connects the pressure reduction valve 140 to the damping cylinder 22 to allow fluid to flow onlyin one direction from the pressure reduction valve 140 and into the damping cylinder 22 with the function select valve 110 in the second position and the pump 108 operating, which would extend the damping cylinder 22 and further support the upper linkages of the linkage assembly 14 and increase stiffness, or maintain the position of the damping cylinder 22 by preventing the damping cylinder 22 from retracting regardless of the position of the function select valve 110. Note that the damping cylinder 22 position may be at least partially controlled via external forces applied to the damping cylinder via movement of the associated linkages 30 as the lift cylinder 20 extends the linkage assembly 14.

[0035] When the second directional valve 142 is in a second position, the second directional valve 142 fluidly connects the damping cylinder 22 to the pressure reduction valve 140 and the fluid passage 132 to allow fluid to flow only in one direction from the damping cylinder 22 and into the fluid passage 132, which would provide for retraction of the damping cylinder 22 in conjunction with operation of the first directional valve 134 and retraction of the lift cylinder 20, and with the function select valve 110 in the first position as shown.

[0036] The fluid passage 132 and pressure reduction valve 140 are also connected to the damping cylinder 22 via the second relief valve 144. The second relief valve 144 may be provided as a pilot-operated second relief valve, with the pressure threshold, or pressure within the damping cylinder 22, for opening the valve 144 being pre-selected for the valve. The second relief valve 144 opens to fluidly connect the damping cylinder 22 to the pressure reduction valve 140 when the pressure in the damping cylinder 22 is greater than the pressure threshold set for the second relief valve 144. In one non-limiting example, the pressure threshold may be selected to be at a higher value than the setting for the pressure reduction valve 140, e.g. with the pressure reduction valve 140 reducing the pressure of the fluid to on the order of 500-1500 psi, and the second relief valve 144 having a pressure threshold on the order of 1000-2000 psi. In some examples, the second relief valve 144 may be manually adjusted to change the pressure threshold, e.g. when the device 10 is not in operation; and in other examples, the second relief valve 144 may be provided with a predetermined pressure threshold.

[0037] In operation, the damping cylinder 22 provides additional support for the upper linkages 30 above the distal end of the lift cylinder 20, thereby increasing the stiffness of the linkageassembly 14. The second relief valve 144 permits fluid flow out of the damping cylinder 22 based on loads onto the work platform 16 if the load causes the damping cylinder 22 pressure to exceed the pressure threshold for the second relief valve 144. Likewise, the fluid may flow into the damping cylinder 22 via the second directional valve 142 if the pressure in the damping cylinder 22 falls below the pressure at the outlet of the second pressure reduction valve 140 (with the second pressure reduction valve in the first position).

[0038] The second directional valve 142 and associated solenoid may be configured such that the second directional valve 142 is in the first position when the solenoid is off, such that the position of the damping cylinder 22 is maintained as outlet flow is prevented via a check valve element within the valve 142. In the event that the solenoid for the second directional valve 142 is off, and a user would like to retract the linkage assembly 14 and lower the lift platform 16, the user may engage the release lever 136 to manually move the first directional valve 134 to the second position and retract the lift cylinder 20 (and likewise, stop movement by releasing or return the lever 136 associated with the first directional valve). The fluid in the damping cylinder 22 would flow out through the second relief valve 144 in this instance, as the pressure in the damping cylinder 22 would be greater than the pressure at the outlet of the second relief valve 144 (e.g. between the pressure reduction valve and the second relief valve), due to the forces on the damping cylinder 22 caused by the retracting linkages 30 in the linkage assembly 14.

[0039] A controller 150 may be provided for the system 100 and lift device 10. The controller 150 and control system may include any number of controllers, and may be integrated into a single controller, or have various modules. Some or all of the controllers may be connected by a controller area network (CAN) or other system. It is recognized that any controller, circuit or other electrical device disclosed herein may include any number of microprocessors, integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or other suitable variants thereof) and software which co-act with one another to perform operation(s) disclosed herein. In addition, any one or more of the electrical devices as disclosed herein may be configured to execute a computer-program that is embodied in a non-transitory computer readable medium that is programmed to perform any number of the functions as disclosed herein.

[0040] The controller 150 may be electrically connected to or in communication with the various valves in the lift device 10 and function hydraulic system 100. In the example shown, the controller 150 is connected to the solenoids for the function select valve 110, the steering valve 116, the first directional valve 134 and the second directional valve 142, as well as to the motor 106. The controller 150 is also in communication with one or more control inputs 152 for the lift device 10, e.g. a steering input, a work platform height input, and the like. The control inputs 152 may additionally control the propulsion of the device. In various examples, the control inputs 152 may be provided by at least one of a joystick, buttons or switches, a display screen, or the like. The control inputs 152 may be supported on the work platform 16 of the lift device 10 according to various examples so a user can control functions of the device 10 while the work platform 16 is extended.

[0041] According to one example, and when a user requests the work platform 16 to be raised or lifted via the control input 152, the controller 150 commands the function select valve 110 to the second position to provide fluid flow from the pump 108 to the fluid passage 132, commands the first directional valve 134 to the first position thereby allowing fluid flow into the lift cylinder 20 to extend the lift cylinder 20 and extend the linkage assembly 14, and commands the second directional valve 142 to the first position such that fluid flows from the fluid passage 132 through the pressure reduction valve 140 and second directional valve 142 and into the damping cylinder 22 to extend the damping cylinder 22 and support linkages 30 within the linkage assembly.

[0042] When a user requests the work platform 16 to be lowered via the control input 152, the controller 150 commands the function select valve 110 to the first position to fluidly connect the fluid passage 132 to the return line 120 to the reservoir 104, commands the first directional valve 134 to the second position thereby allowing fluid flow from the lift cylinder 20 and into the fluid passage 132 to retract the lifting cylinder 20 and retract the linkage assembly 14, and commands the second directional valve 142 to the second position such that fluid flows from the damping cylinder 22 through the second directional valve 142 and the pressure reduction valve 140 and into the fluid passage 132 and return line 120 to retract the damping cylinder 22.

[0043] If the user requests that the work platform 16 be stopped and its position maintained using the control input 152 at an intermediate position between the retracted and extended positionswhile raising or lowering the work platform 16, or when the linkage assembly 14 reaches its fully extended position, the controller 150 commands the first and second directional valves 134, 142 to their first positions (e.g. with the solenoids off), respectively, thereby preventing fluid from leaving the lift and damping cylinders 20, 22 via their associated directional valves. The damping cylinder 22 may therefore support associated linkages 30 in the linkage assembly 14, and reduce vertical deflection of these linkages and increase stiffness. In one example, vertical deflection of linkages 30 associated with the damper cylinder 22 was reduced by over half, e.g. from 50-60 mm in a similar device without a damping cylinder to 20-30 mm.

[0044] In the event that the user needs to manually control the lift device 10 and function hydraulic system 100 to lower the work platform 16 when the linkage assembly 14 is at least partially extended, e.g. if one or more of the solenoids are inoperative or there is insufficient power to operate the solenoids, the user manually operates or moves the release lever 136 for the first directional valve 134 to move the first directional valve 134 to the second position to allow fluid to flow from the hydraulic lift cylinder 20 to the fluid passage 132. The solenoid for the function select valve 110 would also be off in this case, with the fluid passage 132 fluidly connected to the return line 120 to the reservoir. The solenoid for the second directional valve 142 is also off, the pressure in the damping cylinder 22 increases as the damping cylinder 22 is retracted based on the retracting linkage assembly 14. When the damping cylinder 22 pressure is above the pressure threshold for the second relief valve 144, fluid flows from the damping cylinder 22, through the relief valve 144 and through the pressure reduction valve 140, and to the fluid passage 132 and reservoir 104. The damping cylinder 22 maintains a fluid pressure at or below the pressure threshold of the relief valve 144 to provide stiffness for the linkage assembly 14 as the linkage assembly is retracted. The fluid from the lift cylinder 20 and the damping cylinder 22 returns to the reservoir 104 as the linkage assembly retracts.

[0045] If the user requests that the work platform 16 be stopped and its position maintained in the manual operation mode, the user manually operates or moves the release lever 136 for the first directional valve 134 to move the first directional valve 134 to the first position to prevent fluid from leaving the lift cylinder 20 to maintain the position of the lift cylinder. The solenoid for the function select valve 110 is also off in this case, with the fluid passage 132 fluidly connected to the return line 120 to the reservoir; however, fluid flow is prevented from leaving the lift cylinder22 via the first directional valve 134 being in the first position. The solenoid for the second directional valve 142 also remains off, preventing fluid from leaving the damping cylinder 22 unless the pressure in the damping cylinder 22 exceeds the threshold pressure of the second relief valve 144, and the damping cylinder 22 continues to provide stiffness for the linkage assembly 14 in the selected position.

[0046] Figure 3 illustrates a function hydraulic system according to a second example. Reference may be made to the prior description for elements that are the same as or similar to those described above, and these elements are given the same reference numbers for simplicity. In the example shown, the hydraulic system 200 has a first hydraulic circuit 102 with a motor 106, pump 108, function select valve 110, steering select valve 116, first directional valve 134 with solenoid and release lever 136, hydraulic lift 20 cylinder, and first reservoir 104. The hydraulic system 200 also has a second hydraulic circuit 202 that is separate and independent from the first hydraulic circuit 102, with the second hydraulic circuit 202 containing one or more damping cylinders 22. In various examples, the hydraulic system 200 may be provided such that the first hydraulic circuit 102 does not have any damping cylinders 22, or in further examples, damping cylinders 22 may be provided in the circuit 202, as well as in circuit 102 as described above with reference to Figure 2.

[0047] The second hydraulic circuit 202 may be generally supported on the linkage assembly 14, e.g. above the lift cylinder 20, or may be at least partially supported by the chassis 12. The second hydraulic circuit 202 may be a closed hydraulic circuit as shown. The second hydraulic circuit 202 has one or more hydraulic damping cylinders 22 as described above.

[0048] The second hydraulic circuit 202 has an associated second reservoir 204 that is fluidly connected to an inlet for a flow control valve 206. The flow control valve 206 may be an on / off valve as shown, or may be provided as a proportional valve, and the flow control valve 206 may be operated via a solenoid, and controlled via a controller 150. The flow control valve 206 is moveable between a first position as shown with the valve 206 closed and the solenoid in an off state as shown, and a second position with the valve 206 open and the solenoid in an energized state.

[0049] The damping cylinder 22 is fluidly coupled to the outlet of the flow control valve 206, and also to an inlet of a third relief valve 208. The outlet of the third relief valve 208 is fluidly coupled to the second reservoir 204 and to the inlet of the flow control valve 206.

[0050] The third relief valve 208 may be provided as a pilot-operated third relief valve, with the pressure threshold, or pressure within the damping cylinder 22, for opening the valve 208 being pre-selected for the valve. The third relief valve 208 opens to fluidly connect the damping cylinder 22 to the reservoir 204 when the pressure in the damping cylinder 22 is greater than the pressure threshold set for the third relief valve 208. In one non-limiting example, the pressure threshold may be selected based on the weight on the work platform 16 and associated load, e.g. to control the damping provided by the damping cylinder 22 and the stiffness in the associated linkages. In some examples, the third relief valve 208 may be manually adjusted to change the pressure threshold, e.g. when the device 10 is not in operation; and in other examples, the third relief valve 208 may be provided with a predetermined pressure threshold.

[0051] The second hydraulic circuit 202 may be operated as a passive system, e.g. without a pump, with fluid flow in the circuit 202 caused by the movement of the damping cylinder 22 and external forces thereon from the linkage assembly 14. The flow control valve 206 may be selectively controlled based on the operating mode for the linkage assembly 14.

[0052] In operation, according to one example, and when a user requests the work platform 16 to be raised or lifted via the control input 152, the controller 150 commands the function select valve 110 to the second position to provide fluid flow from the pump 108 to the fluid passage 132, commands the first directional valve 134 to the first position thereby allowing fluid flow into the lift cylinder 20 to extend the lift cylinder 20 and extend the linkage assembly 14, and commands the flow control valve 206 to the second position such that fluid may flow from the second reservoir 204 and into the damping cylinder 22 as the damping cylinder 22 is extended and to support linkages 30 within the linkage assembly. Note that the damping cylinder 22 is extended due to external forces on the damping cylinder 22 caused by the moving linkages 30 connected to the opposed ends 22a, 22b of the damping cylinder, and the movement of the piston within the damping cylinder 22 draws fluid from the second reservoir 204 into the damping cylinder 22 with the flow control valve 206 open.

[0053] When a user requests the work platform 16 to be lowered via the control input 152, the controller 150 commands the function select valve 110 to the first position to fluidly connect the fluid passage 132 to the return line 120 to the reservoir 104, commands the first directional valve 134 to the second position thereby allowing fluid flow from the lift cylinder 20 and into the fluid passage 132 to retract the lift cylinder 20 and retract the linkage assembly 14, and commands the flow control valve 206 to the second position such that fluid may flow from the damping cylinder 22 into the second reservoir 204 as the damping cylinder 22 is retracted. Note that the damping cylinder 22 is retracted due to external forces from the moving linkages connected to the opposed ends of the damping cylinder, and the movement of the piston within the damping cylinder drives the fluid from the damping cylinder 22 back to the second reservoir 204 via the open valve 206.

[0054] If the user requests that the work platform 26 be stopped and its position maintained using the control input 152 at an intermediate position between the retracted and extended positions while raising or lowering the work platform, or when the linkage assembly 14 reaches its fully extended position, the controller 150 commands the first directional valve 134 to its first position and the flow control valve 110 to its first position (e.g. with their solenoids off), thereby preventing fluid from leaving the lift and damping cylinders 20, 22 via their associated first directional and flow control valves 134, 206. The lift cylinder 20 maintains the position of the linkage assembly overall, while the damping cylinder 22 provides additional support to its associated upper linkages 30 in the linkage assembly 14, and reduces vertical deflection of these linkages and increases stiffness for the linkage assembly 14 overall.

[0055] In the event that the user needs to manually control the lift device 10 and function hydraulic system 200 to lower the work platform 16 when the linkage assembly 14 is at least partially extended, e.g. if one or more of the solenoids are inoperative or there is insufficient power to operate the solenoids, the user manually operates or moves the release lever 136 for the first directional valve 134 to move the first directional valve to the second position to allow fluid to flow from the hydraulic lift cylinder 20 to the fluid passage 132. The solenoid for the first directional valve 134 is off in this case, with the fluid passage 132 fluidly connected to the return line 120 to the reservoir 104 via the function select valve 110 in its off position. The solenoid for the flow control valve 206 is also off, and the pressure in the damping cylinder 22 increases as the damping cylinder 22 is retracted based external forces applied by the associated linkages 30 in theretracting linkage assembly 14. When the damping cylinder 22 pressure is above the pressure threshold for the third relief valve 208, fluid flows from the damping cylinder 22, through the third relief valve 208, and to the second reservoir204. Fluid at a pressure at or below the relief valve 208 threshold pressure is therefore maintained within the damping cylinder 22 such that the damping cylinder 22 continues to provide stiffness for the linkage assembly 14 as the linkage assembly is retracted. The fluid from the lift cylinder 20 and the damping cylinder 22 returns to their respective first and second reservoirs 104, 204 as the linkage assembly 14 retracts.

[0056] If the user requests that the work platform 16 be stopped and its position maintained in the manual operation mode, the user manually operates or moves the release lever 136 for the first directional valve 134 to move the first directional valve to the first position to prevent fluid from leaving the lift cylinder 20 to maintain the position of the lift cylinder. The solenoid for the first directional valve 134 is off in this case, and with the fluid passage 132 fluidly connected to the return line 120 to the reservoir; however, fluid flow is prevented from leaving the lift cylinder 20 via the first directional valve 134 being in the first position. The solenoid for the flow control valve 206 also remains off, preventing fluid from leaving the damping cylinder 22 unless the pressure in the damping cylinder 20 exceeds the threshold pressure of the third relief valve 208, and the damping cylinder 22continues to provide additional stiffness for the linkage assembly 14 in the selected position.

[0057] Although various valves may be described herein as being a single valve element, it is also contemplated that multiple valves may be used as a valve assembly to provide the same or similar functions as the valves described.

[0058] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosure or invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the disclosure.

Claims

WHAT IS CLAIMED IS:

1. A lift device comprising: a chassis; a linkage assembly supported by the chassis, the linkage assembly comprising a series of pairs of linkages, each pair of linkages rotatably connected to at least one other pair of linkages, wherein linkages in each pair of linkages are rotatably connected to one another; a work platform supported by the linkage assembly; and a hydraulic system comprising: a lift cylinder having a distal end connected to a first pair of linkages of the series of pair of linkages, the lift cylinder movable between a retracted position and an extended position to move the linkage assembly between a retracted position and an extended position, and a damping cylinder movable between a retracted position and an extended position to limit movement of a second pair of linkages positioned between the first pair of linkages and the work platform, wherein, when the linkage assembly is being extended, the lift cylinder receives pressure from the hydraulic system at a first pressure and the damping cylinder receives fluid from the hydraulic system at a second pressure, the second pressure lower than the first pressure.

2. The lift device of claim 1 wherein a proximal end of the lift cylinder is connected to one of the chassis and a third pair of linkages positioned between the second pair of linkages and the chassis.

3. The lift device of claim 1 wherein an end of the damping cylinder is connected to the second pair of linkages.

4. The lift device of claim 3 wherein another end of the damping cylinder is connected to the first pair of linkages.

5. The lift device of claim 1 wherein the linkage assembly comprises a stack linkage mechanism.

6. The lift device of claim 1 wherein the hydraulic system comprises a first hydraulic circuit fluidly connecting a first reservoir to a pump, and fluidly connecting the pump to the lift cylinder via a first directional valve, the first directional valve providing a one-way valve for flow into the lift cylinder in a first position, and a one-way valve for flow out of the lift cylinder in a second position.

7. The lift device of claim 6 wherein the hydraulic system further comprises a function manifold and a function select valve, wherein the pump is fluidly connected to one of the function manifold and the first directional valve based on the position of the function select valve.

8. The lift device of claim 7 wherein the function select valve fluidly connects the first directional valve to a first reservoir of the first hydraulic circuit when the function select valve fluidly connects the pump to the function manifold.

9. The lift device of claim 8 wherein the first directional valve is a solenoid valve, and wherein the first directional valve is in the second position with the solenoid energized.

10. The lift device of claim 9 wherein the first directional valve comprises a release for manual control of the first directional valve by a user to the second position.

11. The lift device of claim 6 wherein the pump is fluidly connected to the first directional valve via a fluid passage; and wherein the first hydraulic circuit further comprises a pressure reduction valve, a second directional valve, and a relief valve fluidly connecting the damping cylinder to the fluid passage; wherein the second directional valve provides a one-way valve for flow into the damping cylinder in a first position and a one-way valve for flow out of the damping cylinder in a second position; andwherein the relief valve is configured to open when a pressure in the damping cylinder exceeds a pressure threshold of the relief valve such that fluid may exit the damping cylinder with the second directional valve in the first position.

12. The lift device of claim 11 wherein the pressure reduction valve is positioned to receive fluid from the fluid passage, the second directional valve fluidly connects the pressure reduction valve to the damping cylinder, and the relief valve fluidly connects the pressure reduction valve to the damping cylinder.

13. The lift device of claim 12 wherein the second directional valve is a solenoid valve, and wherein the second directional valve is in the second position with the solenoid energized.

14. The lift device of claim 6 wherein the hydraulic system comprises a second hydraulic circuit independent of the first hydraulic circuit, the second hydraulic circuit comprising the damping cylinder, a flow control valve, a relief valve, and a second reservoir; wherein the flow control valve prevents flow therethrough in a first position, and the flow control valve fluidly connects the second reservoir to the damping cylinder in a second position.

15. The lift device of claim 14 wherein the flow control valve fluidly connects the second reservoir to the damping cylinder, and the relief valve separately fluidly connects the damping cylinder to the second reservoir; and wherein the relief valve is configured to open when a pressure in the damping cylinder exceeds a pressure threshold of the relief valve such that fluid may exit the damping cylinder with the flow control valve in the first position.

16. A lift device comprising: a chassis; a stack linkage assembly supported by the chassis; a work platform supported by the stack linkage assembly; anda fluid system comprising: a lift cylinder movable between a retracted position and an extended position to move the stack linkage assembly between a retracted position and an extended position, and a damping cylinder movable between a retracted position and an extended position to limit movement of one or more linkages positioned between a distal end of the lift cylinder and the work platform.

17. A method of controlling linkage assembly for a lift device, the method comprising: extending a lift cylinder with a distal end connected to an intermediate linkage in a series of linkages for the linkage assembly to extend the linkage assembly by providing fluid flow to the lift cylinder at a first pressure and in response to a request to extend a linkage assembly; extending a damping cylinder connected to another linkage in the series of linkages thereby limiting movement in the linkage assembly by providing fluid flow to the damping cylinder at a second pressure lower than the first pressure and in response to the request to extend the linkage assembly, the another linkage positioned between the intermediate linkage and a work platform for the lift device; and damping movement of the work platform and the linkage assembly when the linkage assembly is in an at least partially extended position via fluid flow through a relief valve associated with the damping cylinder in response to a pressure in the damping cylinder exceeding a pressure threshold of the relief valve.

18. The method of claim 17 further comprising retracting the lift cylinder to retract the linkage assembly by controlling a first directional valve associated with the lift cylinder such that fluid flows out of the lift cylinder in response to a request to retract the linkage assembly; and retracting the damping cylinder by controlling a flow control valve associated with the damping cylinder such that fluid flows out of the damping cylinder in response to the request to retract the linkage assembly.

19. The method of claim 18 further comprising fluidly connecting the lift cylinder to a fluid passage via the first directional control valve, and fluidly connecting the damping cylinder to the fluid passage via a pressure reduction valve and the flow control valve.

20. The method of claim 18 further comprising retracting the lift cylinder to retract the linkage assembly in response to a release associated with the first directional valve being moved by a user such that fluid flows out of the lift cylinder, wherein retracting the lift cylinder causes the linkage assembly to input a force onto the damping cylinder, and the damping cylinder retracts via fluid flow through the relief valve when a pressure in the damping cylinder exceeds the pressure threshold and without fluid flow through the flow control valve.

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