Abstract:
A hydraulic actuator is provided for controlling relative movement between first and second structures between which the actuator is mounted, for example between a boom and the base frame of an agricultural sprayer, while providing some resilience in the form of suspension. The actuator comprises a piston cylinder having a floating cushion piston supported within the cylinder end to support the piston within the cylinder in a retracted position at a prescribed spacing from the cylinder end. The piston can thus be deflected from the retracted position in either direction using a pressure relief mechanism so as to provide some flexibility to the actuator to accommodate the varying forces between the pair of relatively movable structures between which the actuator is mounted. The cushion piston requires no additional electrical switches or controllers and can be part of the hydraulic circuitry of the actuator so as to provide a simple, low cost actuator with integral suspension.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a hydraulic actuator for controlling relative movement between first and second structures between which the actuator is mounted and more particularly to a hydraulic actuator having some having integral suspension.  
         BACKGROUND  
         [0002]    Elongate structures, for example booms which are commonly used in various applications, are typically subjected to large bending forces, requiring some flexibility in order to prevent failure of the structure. In the agricultural industry for instance, booms are used for various application including spraying crops and the like. When displacing a boom of this type across a field, the boom may be subjected to varying bending forces due to uneven terrain, cornering and acceleration of the vehicle supporting the boom. Suspension of the boom thus must accommodate these varying bending forces to prevent failure of the boom structure.  
           [0003]    Often elongate structures, including booms and the like, however must be collapsible for transport due to the irregular shape of the structures. Collapsing such a structure involves pivotally mounting the structure on a base frame and providing an actuator for displacing the structure between deployed and undeployed positions. Common actuators, such as hydraulic actuators, however are very rigid in both fully extended and retracted positions of the actuator and thus additional suspension is required to accommodate the flexibility needed of the structure.  
           [0004]    In place of additional suspension when using a hydraulic actuator, the use of limit switches are known to prevent the actuator from being fully extended or retracted in normal operation such that some flexibility of the actuator is permitted when an accumulator or pressure relief is provided. The use of limit switches however results in a costly and complex design which is far less reliable than the hydraulic actuator itself.  
         SUMMARY  
         [0005]    According to one aspect of the present invention there is provided a hydraulic actuator for controlling relative movement between first and second structures between which the actuator is mounted, the actuator comprising:  
           [0006]    a cylinder having a mounting end for coupling to one of the structures and an open end opposite the mounting end;  
           [0007]    a cushion piston slidably mounted within the cylinder;  
           [0008]    a stop member arranged to restrict displacement of the cushion piston away from the mounting end of the cylinder beyond a prescribed spacing from the mounting end of the cylinder in a static position of the cushion piston;  
           [0009]    a biasing mechanism urging the cushion piston away from the mounting end of the cylinder towards the static position adjacent the stop member, the cushion piston being movable against the biasing mechanism;  
           [0010]    a rod slidably mounted through the open end of the cylinder with the open end of the cylinder being sealed with respect to the rod, the rod having a piston end slidably mounted in sealing engagement within the cylinder between a retracted position adjacent the cushion piston and an extended position adjacent the open end of the cylinder and having a mounting end for coupling to the other structure; and  
           [0011]    hydraulic fluid supply lines coupled to both a retraction port adjacent the open end of cylinder in communication with a first side of the piston end of the rod to retract the rod into the retracted position and an extension port adjacent the mounting end of the cylinder in communication with a second side of the piston end of the rod to extend the rod into the extended position;  
           [0012]    the rod being movable with the cushion piston towards the mounting end of the cylinder beyond the retracted position when subjected to a force which exceeds a prescribed holding force of the biasing mechanism.  
           [0013]    The cushion piston provides some flexibility to the actuator to accommodate the varying forces between a pair of relatively movable structures between which the actuator is mounted. The cushion piston requires no additional electrical switches or controllers and can be part of the hydraulic circuitry of the actuator so as to provide a simple, low cost actuator with integral suspension which is effective and reliable unlike any prior known device.  
           [0014]    In a preferred embodiment, the cushion piston is sealed with respect to the cylinder and the biasing mechanism comprises a cushion chamber under hydraulic pressure within the cylinder between the cushion piston and the mounting end of the cylinder.  
           [0015]    Pressure of hydraulic fluid within the cushion chamber and at the retraction port are preferably substantially equal in the retracted position. Accordingly, a cross sectional area of the cushion piston in communication with the cushion chamber is preferably greater than a cross sectional area of the first side of the piston end of the rod in communication with the retraction port.  
           [0016]    There may be provided a pressure relief mechanism in communication with the cushion chamber and the retraction port so as to permit the rod to be deflected from the retracted position in either direction. In one embodiment, the pressure relief mechanism includes a hydraulic fluid accumulator in communication with each of the cushion chamber and the retraction port, permitting hydraulic fluid to be received therein when a prescribed holding force of the accumulator is exceeded.  
           [0017]    When the hydraulic fluid lines are coupled in communication with the cushion chamber, a hydraulic switch is preferably arranged to selectively couple the hydraulic fluid lines to an outlet and a return reservoir of a hydraulic fluid pump.  
           [0018]    The cushion chamber and the retraction port may be arranged to communicate with one another at a junction between the hydraulic switch and the cylinder. A flow restrictor is preferably coupled in series with the hydraulic fluid lines between the junction and the retraction port to ensure the cushion chamber is pressurised first.  
           [0019]    There may be provided a check valve coupled in communication with a respective one of the hydraulic fluid supply lines of each of the retraction and extension ports, the check valve of each port being operable when the respective hydraulic fluid supply line of the other port is pressurised.  
           [0020]    The piston end of the rod is preferably engaged upon the cushion piston in the retracted position of the rod. When the stop member is mounted between the piston end of the rod and the cushion piston, the stop member preferably spans only partway into the cylinder to permit communication of the piston end of the rod and the cushion piston across the stop member.  
           [0021]    There may be provided a projection engaged between the cushion piston and the piston end of the rod to displace the cushion piston from the stop member before the piston end of the rod engages the stop member when the rod is deflected from the retracted position towards the mounting end of the cylinder.  
           [0022]    The stop member is preferably fixed in relation to the cylinder.  
           [0023]    The hydraulic actuator may be provided in combination with a boom structure pivotally supported on a base frame structure for movement relative to the base frame structure, the mounting end of the cylinder and the mounting end of the rod each being coupled to a respective one of the structures. Preferably the mounting end of the cylinder is mounted on the base frame structure and the mounting end of the rod is mounted on the boom structure.  
           [0024]    The hydraulic actuator may also be provided in combination with an agricultural sprayer comprising:  
           [0025]    a base frame structure having a tank supported thereon for rolling movement along the ground; and  
           [0026]    a boom structure pivotally supported on the base frame structure for pivotal movement relative to the base frame structure, the boom structure having spraying lines and nozzles supported thereon in communication with the tank on the base frame;  
           [0027]    the mounting end of the cylinder and the mounting end of the rod each being coupled to a respective one of the structures.  
           [0028]    The hydraulic actuator in this instance preferably controls pivotal movement of the boom structure relative to the base frame structure about an upright axis.  
           [0029]    The hydraulic actuator may control pivotal movement of the boom structure relative to the base frame structure between a folded position in which the boom structure extends generally in a direction of travel of the sprayer and a field position in which the boom structure lies transversely to the direction of travel. The rod is preferably oriented so as to be in the retracted position of the rod when the boom structure is in the field position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:  
         [0031]    [0031]FIG. 1 is a partly sectional view of the hydraulic actuator.  
         [0032]    [0032]FIG. 2A is a schematic of the hydraulic circuitry coupled to the actuator of FIG. 1 with the actuator in a static retracted position.  
         [0033]    [0033]FIGS. 2B and 2C are schematics of the actuator as shown in FIG. 2A with the actuator in respective first and second deflected positions from the static retracted position.  
         [0034]    [0034]FIG. 3 is a rear elevational view of an agricultural sprayer upon which the actuator of FIG. 1 is mounted.  
         [0035]    [0035]FIG. 4 is a top plan view of the sprayer according to FIG. 3.  
         [0036]    [0036]FIG. 5 is an isometric view of the sprayer according to FIG. 3. 
     
    
     DETAILED DESCRIPTION  
       [0037]    Referring to the accompanying drawings, there is illustrated a hydraulic actuator generally indicated by reference numeral  10 . The actuator  10  is intended for use in controlling relative movement between a pair of structures when some limited flexibility is required between the two structures. The actuator  10  is particularly useful for controlling the position of a boom for example as in an agricultural boom of a sprayer shown in FIGS. 3 through 5.  
         [0038]    Referring initially to FIGS. 1 and 2A through  2 C, the actuator  10  and the hydraulic circuitry controlling it are shown in greater detail. The actuator  10  generally comprises a cylinder  12  which slidably mounts a rod  14  therein.  
         [0039]    The cylinder  12  includes a pivot mount on a mounting end  16  for pivotally mounting on a supporting structure. The cylinder  12  further includes an open end  18  opposite the mounting end arranged to slidably mount the rod  14  therethrough. A plug  20  is provided in the open end of the cylinder having an aperture for receiving the rod  14  therethrough. The plug  20  is suitably arranged to seal between the rod  14  and the surrounding wall of the cylinder  12  while permitting the rod  14  to remain slidable relative to the cylinder.  
         [0040]    The rod  14  includes a mounting end  22  which projects from the cylinder  12  which similarly includes a pivot mount for pivotally mounting to a supporting structure. Opposite the mounting end  22 , the rod  14  includes a piston end  24  having an annular member  26  mounted thereon for sliding movement within the cylinder  12 . The annular member  26  at the piston end of the rod is arranged to be sealed with respect to the surrounding walls of the cylinder  12  so as to divide the cylinder into a retraction chamber  28  in communication with a first side  30  of the annular member and an extension chamber  32  in communication with a second side  34  of the annular member  26 . A projection extends longitudinally outwardly from the second side  34  of the annular member of the rod in the form of a bolt  36  which is provided for mounting the annular member  26  on the piston end of the rod. The bolt  36  thus acts as a spacer between the piston end of the rod and a cushion piston  38 .  
         [0041]    The cushion piston  38  is provided in the form of a round plug which is slidably mounted within the cylinder in sealing engagement with the walls of the cylinder. The cushion piston  38  is mounted within the cylinder between the piston end of the rod  14  and the mounting end  16  of the cylinder. The cushion piston  38  includes a first end face  40  in communication with the extension chamber and a second end face  42  in communication with a cushion chamber  44  defined between the cushion piston  38  and the mounting end of the cylinder  12 .  
         [0042]    Pressure within the cushion chamber  44  is arranged to bias the cushion piston  38  away from the mounting end of the cylinder  12 . A stop member  46  is mounted within the cylinder walls to restrict displacement of the cushion piston  38  away from the mounting end of the cylinder beyond a prescribed spacing from the mounting end of the cylinder in a static position of the cushion piston in which the piston  38  engages the stop member  46 .  
         [0043]    The stop member  46  generally comprises an annular ring partially embedded into an inner surface of the walls of the cylinder  12  at a fixed spacing from the mounting end of the cylinder for engaging the first end face  40  of the cushion piston  38 . The stop member  46  only spans partway into and across the cylinder to define an opening  48  therein which is suitably sized to receive the bolt  36  at the end of the rod therethrough when the bolt  36  extends across the stop member, engaged between the piston end of the rod and the cushion piston. The first end face  40  of the cushion piston  38  is a generally flat face lying perpendicular to the longitudinal direction of the cylinder for engaging the bolt  36  projecting from the piston end of the rod  14  when the rod is retracted into the cylinder.  
         [0044]    Hydraulic fluid is introduced into the cylinder  12  through a set of ports extending through the walls of the cylinder  12 . These ports include a cushion port  50 , a retraction port  52  and an extension port  54 .  
         [0045]    The cushion port  50  is located adjacent the mounting end  16  of the cylinder and is arranged to communicate with the cushion chamber  44  so as to control the pressure of hydraulic fluid within the cushion chamber.  
         [0046]    The retraction port  52  is located adjacent the open end  18  of the cylinder in communication with the retraction chamber  28  to control the pressure of hydraulic fluid acting on the first side  30  of the annular member at the end of the rod  14  for retracting the rod within the cylinder.  
         [0047]    The extension port  54  is located intermediate the cushion port  50  and the retraction port  52  nearer to the mounting end  16  of the cylinder. The extension port  54  is located adjacent the stop member  46  with the stop member being positioned immediately adjacent the extension port on a side which is closest to the mounting end  16  of the cylinder. The extension port  54  is thus suitably arranged to communicate with the extension chamber  32  of the cylinder for controlling the pressure of hydraulic fluid acting on the second side  34  of the annular member at the piston end of the rod so as to extend the rod from the cylinder.  
         [0048]    The rod  14  is movable from an extended position to a retracted position. In the extended position, the piston end of the rod is located adjacent the open end of the cylinder with pressure in the extension chamber  32  being greater than pressure within the retraction chamber  28 .  
         [0049]    In the retracted position the annular member  26  at the piston end of the rod  14  is located adjacent the cushion piston  38  at the mounting end of the cylinder. In the retracted position pressure in the retraction chamber  28  is greater than pressure within the extension chamber  32  while pressure in the cushion chamber  44  and the retraction chamber  28  are substantially equal.  
         [0050]    The cross sectional area of the cushion piston  38  at the second end face  42  in communication with the cushion chamber  44  is greater than the cross sectional area of the first side  30  of the annular member at the piston end of the rod  14  in communication with the retraction chamber  28  such that the force acting on the cushion piston  38  is greater in the direction which biases the cushion piston  38  against the stop member  46  in the static position thereof than the force of the piston end  24  of the rod acting on the first end face  40  of the cushion piston. The bolt  36  at the piston end of the rod thus holds the annular member  26  at a fixed spacing from the cushion piston  38  in the retracted position of the actuator.  
         [0051]    When the rod  14  is in the retracted position and the cushion piston  38  is in the static position thereof, excess force acting on the rod  14  in either direction allows some limited movement into one of the first and second deflected positions shown in FIGS. 2C and 2B respectively. FIG. 2C illustrates the first deflected position in which the rod is deflected towards the mounting end  16  of the cylinder beyond the retracted position shown in FIG. 2A. This occurs when force acting on the rod  14  exceeds a prescribed holding force of the cushion chamber  44  in the static position thereof. The prescribed holding force is determined by the pressure relief setting for the cushion chamber  44  to be described later herein, as well as the difference in the cross sectional area between the second end face  42  of the cushion piston and the first side  30  of the piston end of the rod.  
         [0052]    The second deflected position is shown in FIG. 2B in which the rod  14  is deflected from the retracted position towards the extended position. The rod is deflected into the second deflected position if force acting on the rod  14  in a direction to extend the rod is greater than a pressure relief setting of the retraction chamber  28  also to be described later herein.  
         [0053]    The hydraulic circuitry operating the actuator  10  is shown in further detail in FIG. 2A in which two actuators  10  are shown coupled in parallel with a pressure supply line  60  in communication with the outlet of a hydraulic fluid pump and a reservoir return line  62  of the pump. The connection of the two actuators  10  to the lines  60  and  62  are similar and thus only one of the actuators will be described herein in detail.  
         [0054]    The actuator  10  includes a retraction line  64  coupled to the retraction port  52 , an extension line  66  coupled to the extension port  54  and a cushion line  68  coupled to the cushion port  50 . The retraction line  64  and the extension line  66  each include a check valve  70  coupled in series therewith between the cylinder and a hydraulic switch in the form of a directional valve  72  selectively coupling the ports to the respective pressure supply and reservoir return lines. The cushion line  68  is coupled in communication with the retraction line  64  at a junction between the valve  72  and the cylinder so as to be pressurised when the retraction line is pressurised.  
         [0055]    Displacing the directional valve  72  as illustrated to the right acts to retract the piston by coupling the retraction line  64  to the pressure supply line  60  and the extension line  66  to the reservoir return line  62 . A pilot line on the check valve  70  of the extension line  66  is coupled to the retraction line  64  to hold the check valve  70  of the extension line  66  open to drain the extension chamber  32  as required when retracting the rod within the cylinder.  
         [0056]    Once in the retracted position as illustrated in FIG. 2A, the directional valve  72  is returned to the neutral position in which the pressure supply line  60  is capped. The check valve  70  in the retraction line  64  hold the pressure in the retraction line so that pressure is maintained on the pilot line of the check valve  70  of the extension line  66  to maintain the extension line  66  draining to the reservoir return line  62  while also draining the pilot line for the check valve  70  of the retraction line  64  to maintain that check valve closed. As long as the check valve  70  of the retraction line  64  is closed pressure will be maintained in the retraction chamber and the pilot on the check valve of the extension line  66  holds that check valve open so that the extension line remains free to draw fluid from or dump fluid to the reservoir return line as needed for deflection of the actuator.  
         [0057]    Deflection of the directional valve  72  to the left as illustrated in FIG. 2A causes the retraction line  64  to be coupled to the reservoir return line  62  and the extension line  66  to be coupled to the pressure supply line  60  to pressurize the extension chamber and drain the retraction chamber through the retraction line  64 . This is permitted because the pilot line of the check valve  70  of the retraction line  64  is held open by pressure in the extension line  66  so that the retraction chamber is free to drain to the reservoir return line  62 .  
         [0058]    The cushion line  68  is coupled to the retraction line  64  after the directional valve  72  so as to be pressurized when the retraction line  64  is pressurized at substantially the same pressure in both. Pressure of hydraulic fluid distributed to the cushion chamber and the retraction chamber is thus substantially equal when in the retracted position. A flow restrictor  74  is located in the retraction line  64  between the junction with the cushion line  68  and the cylinder to optimise flow to the retraction chamber by permitting the cushion chamber to be filled first. In the equilibrium position, flow through the flow restrictor  74  will eventually equalize to a balance pressure within the retraction chamber and the cushion chamber.  
         [0059]    The cushion line  68  includes a first check valve  76  at a point of coupling to the retraction line  64  and a second check valve  78  coupled in series after a pressure relief valve  80  in series with the cushion line  68  between the first and second check valves. A pilot line on the second check valve  78  is coupled to the cushion line  68  immediately after the first check valve  76  to maintain the second check valve  78  open when the directional valve  72  is deflected to the right for retraction of the rod within the cylinder. The cushion line  68  after the first check valve is thus arranged to drain beyond the second check valve  78  at the pressure relief valve  80  as required if excess pressure in the line occurs.  
         [0060]    An accumulator  82  is coupled in communication to both the retraction line  64  and the cushion line  68  adjacent the respective ports coupling the lines to the cylinder to selectively relieve pressure temporarily within the respective lines as required. Each accumulator  82  is a chamber having a diaphragm  84  mounted therein for dividing the chamber into a first side in communication with the respective hydraulic line and a second side which is pressurized with gas.  
         [0061]    Pressure of the gas within the accumulator  82  adjusts the prescribed holding force of the actuator to resist deflection into one of the first and second deflected positions and the volume of the accumulator adjusts the rate of increase in holding force per amount of deflection into the first and second deflected positions. In the respective deflected positions force acting on the rod  14  causes pressure within one of the hydraulic fluid lines to exceed a prescribed holding force of a respective accumulator  82  as determined by the gas pressure thereof so that the diaphragm  84  is deflected to compress the gas and receive hydraulic fluid from the hydraulic lines coupled thereto to relieve pressure in the hydraulic line temporarily. Firmness of the cylinder is controlled by the charge of pressure within the accumulator in conjunction with the setting of the pressure relief valve  80 .  
         [0062]    When mechanical forces cause the rod to retract beyond the retracted position, hydraulic fluid is displaced from the cushion chamber into the accumulator  82  coupled to the cushion line  68  so that the piston end of the rod  14  and the cushion piston  38  move together from the retracted position towards the mounting end  16  of the cylinder. If the cylinder is extended due to the mechanical forces, the hydraulic fluid is pushed out of the retraction chamber into the accumulator  82  coupled to the retraction line  64 . The extension line  66  being coupled to the reservoir return line  62  allows fluid to be drawn into the extension chamber while the cushion piston  38  remains in the static position. In either case the pressure ramps in the respective accumulator  82  until the forces of the hydraulic fluid and the gas are balanced at which point the accumulator then returns the oil back to the cylinder to return the cylinder to the neutral retracted position of FIG. 2A.  
         [0063]    As noted previously in one application of the hydraulic actuator  10 , a pair of the actuators are mounted on an agricultural sprayer  86  as shown in FIGS. 3 through 5. The sprayer  86  includes a base frame  87  supported on wheels  88  for rolling movement across the ground. The base frame  87  may be either a pull-type frame for towing behind a tractor or a self-propelled frame having its own drive system. A tank  89  for containing spraying fluid is arranged to be supported on the base frame  87  for movement across the ground therewith.  
         [0064]    A pair of booms  90  are provided which are pivotally mounted at respective inner ends on the base frame  87  about a generally upright axis so as to be pivotal between a field position in which the booms span laterally outwardly in opposite directions from the base frame, transversely to a direction of travel of the sprayer and a folded position in which the booms  90  are pivoted forwardly so as to be generally parallel to one another along opposing sides of the base frame  87 , extending generally in the direction of travel of the sprayer.  
         [0065]    An actuator  10  according to the present invention is coupled between each boom  90 , at the mounting end of the rod, and the base frame  87 , at the mounting end of the cylinder, for displacing the booms into the field position as the actuators are retracted and for displacing the booms into the folded position when the actuators are extended. When the booms are located in the field position the rod  14  of each actuator  10  is in the retracted position as illustrated in FIG. 2A in which the rod may be deflected in either direction into one of the deflected positions as shown in FIGS. 2B and 2C.  
         [0066]    Due to the elongate structure of the booms  90 , significant forward and rearward bending forces are present when the sprayer travels over the field and either accelerates, rocks forwardly and rearwardly over uneven terrain or turns corners. When turning a corner in the field for instance, the forward speed of the booms  90  may accelerate quickly from low speeds in the order of 3 miles per hour upwards to higher speeds in the order of 16 miles per hour. The use of the actuators  10  provides some flexibility to the boom structure by permitting the booms to be deflected slightly forwardly and rearwardly from the field position by deflecting the rod  14  of each actuator between the respective first and second deflected positions thereof.  
         [0067]    While one embodiment of the present invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. The invention is to be considered limited solely by the scope of the appended claims.