Patent Publication Number: US-2022213906-A1

Title: Hydraulic actuator

Description:
FIELD 
     This invention relates to a hydraulic actuator. The invention also relates to a material handling machine having a hydraulic actuator. 
     BACKGROUND 
     Some material handling machines are required to perform two distinct tasks, firstly a loading task where material is moved relatively short distances and loaded into hoppers, trucks or the like. Secondly, in a transport mode a material handling machine is required to transport a single load a significant distance, often over undulating terrain. Driving over undulating terrain can be uncomfortable for an operator. 
     SUMMARY 
     An object of the present invention is to provide a compact hydraulic actuator. 
     An object of the present invention is to provide an improved material handling machine. 
     Thus, according to an aspect of the present invention there is provided a hydraulic actuator having a body defining a bore, the bore having a first end surface, a second end surface and a bore surface, a piston slidable in the bore, the piston, bore surface and first end surface defining a first chamber, the piston, bore surface and second end surface defining a second chamber, a piston rod, connected to the piston, the body further defining an accumulator chamber and a fluid passage between the first chamber and the accumulator chamber, the hydraulic actuator further including an accumulator received in the accumulator chamber and a valve for selectably opening and closing the fluid passage. 
     According to an aspect of the present invention there is provided a material handling machine having a material handling implement configured to move relative to a body of the material handling machine by operation of a hydraulic actuator, the material handling machine having a first mode of operation wherein the valve is closed and having a second mode of operation wherein the valve is open. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a view of a material handling machine according to the present invention including a hydraulic actuator according to the present invention; 
         FIG. 2  is a cross-section view of a hydraulic actuator according to the present invention; and 
         FIG. 3  is an enlarged view of part of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows a material handling machine, in this case a backhoe loader  90  having a backhoe  91  and a loader  92 . 
     The loader  92  includes a loader arm  92 A pivotable about axis E relative to a body or chassis  93  of the back hoe loader. A material handling implement, in this embodiment a loader shovel  92 B, is pivotable about axis F relative to the loader arm  92 A. Pivotable movement of the loader arm  92 A about axis E is controlled by two hydraulic actuators  10 , one mounted on each side of the vehicle and accordingly only one which is visible in  FIG. 1 . Attachment and operation of the two hydraulic actuator  10  is identical and accordingly only operation of the hydraulic actuator  10  visible in  FIG. 1  will be described. 
     The hydraulic actuator  10  shown in  FIG. 1  is pivotally attached to the chassis about axis G via a pivot pin which passes through hole  50  of attachment portion  49  (see  FIG. 2  and description below). The rod eye  59  is pivotally attached to the loader arm  92 A via a pivot pin passing through the rod eye. As will be appreciate, the rod eye  59  of the hydraulic actuator  10  as shown in  FIG. 1  is obscured by the front left wheel of the back hoe loader. 
     Extension of the hydraulic actuator  10  causes the loader arm  92 A to pivot in a clockwise direction about pivot E when viewing  FIG. 1 , thereby raising the loader shovel  92 B and any load contained therein. Retraction of the hydraulic actuator  10  causes the loader arm  92 A to pivot in an anti-clockwise direction about axis E, thereby lowering the loader shovel  92 B and any load contained therein. 
     With reference to  FIGS. 2 and 3 , there is shown the hydraulic actuator  10  having a body  12 , a piston  14 , a piston rod  16 , a rod seal arrangement  25 , a valve  18  and an accumulator  20 . 
     The body  12  includes a first tube  31 , a second tube  32 , an end cap  33 , and a partition wall  34 . 
     The first tube  31  is cylindrical and defines a bore wall  38  having an outer diameter A and an inner diameter B. The inner diameter B defines a bore surface  39  of a bore  40  of the first tube  31 . 
     The first tube  31  includes ports  31 A and  31 B (both shown schematically only on  FIG. 2 ). 
     The second tube  32  is cylindrical and defines an accumulator chamber wall  42  having an outer diameter C and an inner diameter D. The inner diameter defines a bore surface  43  of a bore  44  of the second tube  32 . 
     The end cap  33  includes a cylindrical portion  48  and an attachment portion  49  having a hole  50 . The end cap  33  also defines a passage  51 . 
     The piston is circular and includes a piston seal  54 . The piston includes a central hole  55 . 
     The piston rod is generally elongate and includes a threaded portion  58  at one end and a rod eye  59  at an opposite end. 
     The partition wall  34  is generally circular and includes a passage  60  having a first end  61  and a second end  62 . 
     The rod seal arrangement  35  is generally cylindrical and includes rod seals  64 . 
     The accumulator  20  includes a flexible membrane  66 . 
     The body  12  is assembled as follows:— 
     The accumulator is assembled into the second tube  32  and the end cap  33  is then attached to the second tube  32  (e.g. by welding, screw fitting or the like). The partition wall is attached to an opposite end of the second tube  32  (e.g. by welding, screw fitting or the like). The first tube is attached to the partition wall  34  (e.g. by welding, screw fitting or the like). Note that alternative orders of assembly are possible. 
     The actuator  10  is assembled as follows: 
     The valve  18  is assembled onto the partition wall  34  (e.g. by welding, screw fitting or the like) of the body  12 . 
     The rod seals  64  are assembled into the rod seal arrangement  35  and the rod seal arrangement  35  is slid onto the piston rod  16 . The piston is slid onto the rod and tightened in place by nut  68  engaging threaded portion  58 . The piston seals  54  are assembled onto the piston  14 . Note that alternative orders of assembly are possible. 
     The piston  14  is slid into the bore  40  and the rod seal arrangement  35  is attached to the end of the first tube  31 , e.g. by screw fitting. 
     As assembled, it can be seen that the bore  40  has a first end surface  71  defined by the surface of the partition wall  34  facing the piston  14 . The bore  40  also has a second end surface  72  defined by a surface of the rod seal arrangement facing the piston  14 . 
     The piston  14  is slidable within the bore  40  as will be further described below. 
     The piston  14 , bore  40  and first end surface  71  define a first chamber  81 . The piston  14 , bore  40  and second end surface  72  define a second chamber  82 . 
     An accumulator chamber  83  is defined by the bore surface  43 , a surface  52  of the end cap  33  facing the partition wall  34  and a surface  63  of the partition wall facing the end cap  33 . 
     The flexible membrane  66  of the accumulator  20  divides the accumulator chamber  83  into a first portion  84  proximate to the partition wall  34  and a second portion  85  proximate the end cap  33 . 
     Once assembled, the first chamber  81 , second chamber  82  and first portion  84  are primed with hydraulic fluid via ports  31 A and  31 B and/or via further fill and bleed ports (not shown). The second portion  85  is filled with a pressurized gas via passage  51  which acts as an accumulator charging port. 
     Operation of the actuator  10  is as follows. 
     One task frequently performed by a back hoe loader is that of “loading” whereby the loader shovel is used to move material a relatively short distance, e.g. to pick up loose material from the ground and load it into an adjacent truck. Under these circumstances, the operator is almost constantly raising or lowering the loader arm, e.g. raising the loader arm to pick up the load and raise it to a height where it can be loaded into the truck, and once dumped in the truck, then immediately lowering the arms in order to prepare for picking the next load. Under these circumstances, a loading cycle might take in the order of 30 seconds. Under these circumstances, valve  18  will be closed, as will be further explained below. For the purposes of explanation, this mode will be described hereafter as a loader mode. 
     An alternative mode of operation is that of transporting a single load from one site to another site. Under these circumstances, once the load has been picked up by the loader shovel, then the loader arm will remain at a mid-height and the operator will then drive the back hoe loader from the first site to the second site. Travelling from the first site to the second site may take several minutes or even hours. Under these circumstances, valve  18  will be open as further described below. For the purposes of explanation, this mode will hereafter be described as a transport mode. 
     Operation in the Loader Mode 
     When operating in the loader mode as mentioned above, the valve  18  will be closed. Under these circumstances, the first end  61  of passage  60  is fluidly isolated from the second end  62  by virtue of the valve  18  being closed. Under these circumstances, in order to lift the loader arm, pressurized hydraulic fluid is supplied to the first chamber  81  via the port  31 A which causes the piston  14  and hence piston rod  16  to move in the direction of arrow H of  FIG. 2 . Consequently, hydraulic fluid in the second chamber  82  is allowed to be vented via port  31 B. As will be appreciated, this causes the hydraulic actuator to extend. 
     In order to lower the loader arm, hydraulic fluid from the first chamber  81  is vented via port  31 A (and consequently hydraulic fluid is allowed to enter the second chamber  82  via port  31 B) thereby causing the piston rod to move in the direction of arrow J of  FIG. 2 , i.e. causing the hydraulic actuator  10  to retract. 
     Transport Mode 
     As mentioned above, when in the transport mode, valve  18  is open. With valve  18  open, first end  61  of passage  60  is fluidly connected to second end  62  and consequentially first chamber  81  is fluidly connected to the first portion  84  of the accumulator chamber  83 . Accordingly, hydraulic pressure in the first chamber  81  will be at the same nominal pressure as in the first portion  84  of the accumulator chamber  83 . 
     Since the first portion  84  of the accumulator chamber  83  is separated by the flexible membrane  66  from the second portion  85 , then consequently the hydraulic pressure in the first portion  84  will be the same as the gas pressure in the second portion  85 . 
     Thus consider the scenario where the back hoe loader  90  is in the transport mode and is carrying a load in the loader shovel along an uneven road. As the back hoe loader hits a bump in the road, the inertia of the load in the loader shovel will cause the pressure in the first chamber  81  to increase which in turn will increase the pressure in the first portion  84  of the accumulator chamber. This will cause the flexible membrane  66  to move to the left when viewing  FIG. 2  resulting in the gas in the second portion  84  being compressed in order to match the instantaneous pressure in the first portion  84  and first chamber  81 . This moving of flexible membrane  66  to the left allows the hydraulic actuator  10  to momentarily retract as the back hoe loader goes over the bump thereby allowing the loader arm  92 A to pivot slightly relative to the chassis  93 . As will be appreciated, with the valve  18  open the loader arm  92 A is resiliently mounted relative to the chassis and this resilient mounting improves the ride of the back hoe loader which therefore improves the comfort for the operator. 
     The particular construction of the hydraulic actuator  10  has several advantages. 
     The accumulator is integrated into the body of the hydraulic actuator thereby providing for a compact arrangement. 
     The passage  60  is relatively short (being little more than the thickness of the partition wall  34 ). With a short passage  60 , variations in pressure in the first chamber  81  are quickly seen as variations in pressure in the first portion  84 . As such, the accumulator is capable of responding quickly to any variations in pressure in first chamber  81  caused by the vehicle hitting bumps/undulations and the like and this provides for an improved ride and hence comfort for the operator. 
     The physical positioning of the first chamber  81 , second chamber  82  and accumulator chamber  83 , in alignment between the attachment portion  49  and rod eye  59 , mean that axial loads seen in the bore wall  38  and accumulator chamber wall  42  can all be efficiently transmitted to the attachment portion  49 . Thus, the second tube  32  which partially defines the accumulator chamber is concentric with the first tube  31  which partially defines the first and second chambers. Furthermore, the outer diameter A of the first tube  31  is the same as the outer diameter C of the second tube  32 . Furthermore, the inner diameter B of the first tube is the same as the inner diameter D of the second tube. Accordingly, axial loads in one tube are efficiently transmitted to axial loads in the other tube via the partition wall  34 . 
     In further embodiments, whilst the inner and/or outer diameters of the first and second tubes may not be the same, it is advantageous to have a diameter of one of the tubes overlap a diameter of the other of the tubes, for example, it is advantageous to have an inner diameter of one of the tubes be greater than an inner diameter of the other tube but less than an outer diameter of the other tube. Alternatively, it is advantageous for an outer diameter of one of the tubes to be less than the outer diameter of the other of the tubes but more than the inner diameter of the other of the tubes. 
     In alternative embodiments the body may not be cylindrical and/or the accumulator chamber may not be cylindrical, for example they may have an oval or other non-circular cross-section. Similarly, the partition wall may be non-circular. 
     The actuator may be double or single acting. 
     The valve  18  may be operated in any manner, but advantageously the valve may be a solenoid operated valve. 
     As shown in  FIG. 2 , the accumulator  20  includes a flexible membrane or diaphragm and is gas pressurized. However, any type of accumulator may be used, including an accumulator having a piston slidable within a bore and/or an accumulator having a bias device, such as a spring to react against pressure within the first portion  84 . 
     The material handling machine shown in  FIG. 1  is a backhoe loader, but the hydraulic actuator can be used on any other suitable type of material handling machine, for example a loading shovel, a telehandler or the like.