Abstract:
A hydraulic remote control (HRC) valve including a main spool valve and a pilot pressure control valve. A lever is operatively connected to the pilot valve whereby to provide “finger tip” control of the main spool valve. The HRC has an inverting output, whereby movement of the lever away from a neutral position causes a decrease in hydraulic pressure supplied to a hydraulic clutch. In practice, two HRC&#39;s according to the invention are embodied in a single housing. The HRC of the invention is of use in controlling the hydraulic steering clutches of tracked vehicles.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to hydraulic control means and more especially to a hydraulic remote control (HRC) valve. The invention has particular, but not exclusive, application to the control of hydraulic clutches employed on tracked vehicles such as earth-working equipment (bulldozers, etc) and military tanks. 
     As is well known, a tracked vehicle is steered by reducing or fully interrupting the drive to one or other of the two tracks, according to the change in direction required. This is achieved by reducing or interrupting the hydraulic supply to one or other of the clutches associated with tracks. Typically, this control of the hydraulic supply to the clutches is effected directly by the operation of levers acting on hydraulic valves but the torque involved is relatively high, thus requiring considerable manual effort on the part of the vehicle driver. 
     BRIEF SUMMARY OF THE INVENTION 
     There is a growing requirement for easing the effort required to operate tracked and other vehicles/machinery, especially having regard to the now recognised repetitive strain syndrome. The object of the present invention is to provide a hydraulic control valve requiring low-torque operation. 
     The present invention is defined in the appended claims and may provide a hydraulic control valve comprising a main hydraulic valve and a pilot pressure control valve operable manually to control the output of the main valve, the pilot valve being arranged such that when in operation the operating pressure of the pilot valve is increased, the output pressure of the main valve is decreased. 
     The pilot control valve may be, for example, a pressure-relief valve or a pressure-reducing valve and if the former, may be in the form of a poppet valve. 
     The operating pressure of the pressure-relief valve may be controlled by a manually-operable piston acting on a spring engaging the closure member of the poppet valve, the piston having a return spring, the rate of the return spring being such as to ensure that there is always a net force operable to urge the poppet valve to the open position. 
     The main valve may be a spool valve. 
     The output of the main valve may be fed back to the first end of the spool of that valve over a first portion of the overall cross-section of the spool, wherein pressure fluid controlled by the pilot valve is applied to a second portion of the overall cross-section of the spool at the first end, the forces generated by these pressures being balanced by a spring force acting on a second end of the spool. 
     A spring having a low, and substantially constant rate may act upon the second end of the spool of the main valve. 
     The pressure fluid may be applied to the first end of the spool of the main valve through restrictor means which may comprise two restrictors, one affecting the signal from the output, the other affecting the signal from the pilot valve. 
     In the application of the invention to the control of the two hydraulic clutches of a tracked vehicle, two control valves referred to above may be provided in a common housing and having independent controls. In view of the fact that in each control valve only a pilot valve is being manually controlled involving very small forces, mere finger-tip control has to be applied by the operator to the manually-operable means controlling that valve. 
     The present invention may also provide a method of controlling pressurised fluid comprising the steps of: 
     i) providing a main hydraulic valve; 
     ii) providing a pilot pressure control valve operable manually to control output of the main valve; and 
     iii) arranging the main valve such that an increase in the operating pressure of the pilot valve results in a decrease in the output pressure of the main valve. 
     The present invention may also provide a method of controlling hydraulic clutches associated with respective tracks of a tracked vehicle, comprising the steps of: 
     i) providing for each clutch a main hydraulic valve; 
     ii) providing for each main valve a pilot pressure control valve manually operable to control the associated main valve; 
     iii) providing independent manual controls for the pilot valves; and 
     iv) arranging the main valves such that an increase in the operating pressure of either pilot valve results in a decrease in the output pressure of the associated main valve. 
     This method may comprise the further step of providing the two main valves and two pilot valves in a common housing. 
     The step of providing a common housing may further comprise providing a block of material and drilling that block to provide valve bodies and fluid flow passages. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a hydraulic circuit diagram of part of the embodiment; 
     FIG. 2 is a schematic cross-section of part of the embodiment of FIG. 1; 
     FIG. 3 is one side elevation of the whole of the first embodiment; 
     FIG. 4 is a second side elevation of the whole of the first embodiment; 
     FIG. 5 is a fourth side elevation of the whole of the embodiment; 
     FIG. 6 is a plan view from above of FIG. 4; 
     FIG. 7 is a plan view from below of FIG. 4; and 
     FIGS. 8 and 9 are explanatory graphs of operation of the illustrated embodiment and an alternative embodiment, respectively. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIG. 1, the preferred embodiment of HRC valve in accordance with the present invention comprises a remote supply Ps of pressurised hydraulic fluid, typically emanating from a hydraulic pump, and connected to both a main spool valve  1  and a pilot pressure control valve  2 , the latter via a restrictor  3  to provide a pilot valve pressure supply Pp. The pilot valve  2  is in the form of a pressure-relief valve. 
     The supply pressure Ps is connected directly to the main valve  1  via a connection  4 . The output pressure Px of the main valve  1  is supplied to a hydraulic clutch (not shown) associated with one track of the bulldozer (also not shown) and is also fed back via pipeline  7 , through a restrictor  8 , to the main valve  1 . 
     The pilot valve  2  vents to tank T. The setting of the control pressure of the pilot valve  2  is controlled by a poppet valve  9  operated manually by the driver of the tracked vehicle via a lever  11  pivoted on a fulcrum  12  and having one end  13  engageable by the driver and the other end  14  engageable with a rod  15  of a spring guide  16  forming part of the pilot valve (FIG.  2 ). The control pressure is fed to the main valve  1  via a connection  5  embodying a restrictor  6 . 
     Looking now at FIG. 2, this shows a practical embodiment of the circuit of FIG.  1  and it can be seen that the pilot valve  2  has a body  17 , formed by a drilling in a block of material  20 , in which the spring guide  16  is slidably mounted, the spring guide being provided with a return spring  18  engaging at one end an annulus  19  on the guide. The guide  16  also has a central recess  21 . 
     One end of the pilot valve body  17  is sealed by a plug  22  and sealing ring  23 , the plug having a central through bore through which the rod  15  acts against the guide  16 . The rod  15  is sealed in the plug through bore by a sealing ring  24 . 
     The poppet valve  9  has a poppet  25  engageable with an aperture  26  provided in a closure  27  for the other end of the valve body  17 . The poppet  25  is urged into sealing engagement with the aperture  26  by a spring  28 , the rates of this spring and the return spring  18  being such that there is always a net force acting on the poppet  25  to urge it into engagement with the aperture  26 , during operation of the valve. 
     When no load is applied via the lever  11 , the return spring  18  urges the spring guide  16  upwards against the plug  22 . In the “rest” position of the poppet valve  9 , the downward movement of the poppet  25  is limited by a pin  57  movable in a slot  58  provided in the guide  16 . In this rest position, poppet  25  is not urged into a sealing engagement with the aperture  26 . In this way, fluid can flow freely past the poppet  25  and no pressure is generated by the poppet valve  9 . 
     Downward loading of the spring guide  16  by movement of the lever  11  allows the pin  57  to move away from the end of the slot  57 , thus allowing the poppet  25  to be urged against aperture  26  by the spring  28 , ie. urged into a “valve-closed” position. 
     After a certain further downward movement of guide  16 , the top surface of the recess  21  makes contact with a top face  59  of the poppet  25 . In this position, the force urging the poppet  25  against the aperture  26  is not controlled by  28  but instead by the force applied to the end  13  of the lever  11 . In this way the fluid pressure Pp generated by the poppet valve  9  can be raised to the limiting supply pressure Ps. 
     The above modes of operation of poppet valve  9  allow the outlet pressure characteristic shown in FIG. 8 to have three corresponding modes  100 , 101 , 102 . 
     The poppet valve arrangement may be simplified if only a single mode, linear pressure characteristic is required as illustrated in FIG.  9 . 
     Still referring to FIG. 2, the main valve  1  comprises a spool  29  slidably mounted in a body  31 , formed by a drilling in the block  20 , and having a spring  32  acting between one (second) end and a plug  33  closing one end of the body. The spring  32  has a low, and as constant as possible, rate. The spool  29  is provided with two lands  34  and  35 . A piston  60  is located in the end of the spool  29  opposite that acted upon by the return spring  32 . The piston  60  is held engaged in the spool  29  by a circlip  61 . The separate spool  29  and piston  60  may be replaced by a one-part component. 
     The end of the main valve body  31  opposite that closed by the plug  33  has a reduced diameter and is closed by a plug  41 . There is a gallery  42  between the end of the piston  60  and the plug  41 , which gallery connects with the poppet valve  9  via the restrictor  6  and drilling  43 . The output pressure Px of the main valve is supplied via restrictor  8  and drilling  44 , to a gallery  62  in the valve body  31 . 
     An output port  46  is provided in the block  20  for attachment of a pipeline (not shown) leading to the clutch. A drilling  47  in the block  20  connects respective ends of the valve bodies  17  and  31  to tank T. 
     Supply pressure Ps is supplied to the block  20  via a pressure or input port  51 , the supply being taken to both the main valve spool  29  via a gallery  63  and to the poppet valve  9  via the drilling  52  and  53 , restrictor  3  and further drilling  43 . 
     It will be appreciated that in order to drill the block  20 , to provide the various valve bodies and drillings referred to above, access drillings have to be provided which, after manufacture, are closed by plugs  56 . 
     The piston rod  15  of the relief valve  2  is acted upon by the end  14  of the lever  11 , which is L-shaped and pivotally attached at  54  to the fulcrum  12  supported on the block  20 . 
     The block  20  contains two of the hydraulic circuits shown in FIGS. 1 and 2, one for each of the two clutches associated with the right- and left-hand tracks of the vehicle. The two operating levers  11  are seen in FIGS. 3 to  5 . 
     In operation, the lever  11  is normally in the rest position shown in FIG. 2 in which supply pressure Ps is fully supplied as the output Px to both clutches, via the galleries  62  and  63  around the main valve spool  29 . This output pressure Px is also supplied via drilling  44  and restrictor  8  to a first end  64  of the main valve spool  29  opposite the second end. 
     The supply pressure Ps which is supplied to the poppet valve  9  via the drillings  53  and  55  via the restrictor  3  is vented to tank T. 
     When it is required to steer the tracked vehicle, differential drive to the tracks is required, whereby one clutch has to be partially or fully declutched. The driver pivots the associated lever  11  about the pivot  52  by moving the lever end  13  to the right as seen in FIG.  2 . As already explained above, this action moves the lever end  14  downwardly and eventually moves the rod  15  and spring guide  16  downwardly. This movement compresses spring  28  and hence increases the closing force on the poppet  25 . This in turn means an increase in the pressure Pp which is fed to gallery  42  and acts on the piston  60 . This tends to move the spool  29  against the spring  32  and thus vents Px via an output gallery  65 , and hence the associated clutch is de-pressurised to a certain extent, thereby reducing the drive to the associated track. This reduced Px is of course fed back to the first end of the spool  29  to maintain its balance, the balance of total pressure force acting on one end of the spool  29  against the force of the spring  32  acting on the other end. The spool position modulates to maintain this balance. 
     Clearly, the more the lever  11  is rotated, the greater the reduction in output pressure Px and the greater the de-clutching of the clutch in question. In other words, the greater the torque applied to the lever  11 , the greater the reduction in output pressure Px. Put another way, the clutch control circuit achieves an inverse modulation output. 
     This is illustrated, as already mentioned, in FIG. 8 which is a graph of the pressure ports  46  (Px) of the two circuits against the movement (stroke) of the levers  11 . 
     In as much as the driver only has to control the operating force on the poppet valve  9 , extremely low torque is involved allowing mere finger-tip control which is an important advance in the art. 
     The annulus formed at the first end  64  of the spool by the land  35  and reduced diameter portion  60  of the main valve spool  29  is typically 50% of the overall spool cross-sectional area, and the end of that spool formed in effect by the piston  60  is also typically 50% of the overall spool cross-sectional area but other percentages, ideally adding up to 100%, may be employed ideally totalling approximately 100% of the cross-sectional area. 
     Although in the illustrated embodiment the output pressure Px acts on an outer (annulus) part of the first end  64  of the spool  29 , with the relief valve pressure Pp acting on inner part (piston  60 ), this may be reversed. 
     The supply pressure Ps is typically 25 bar and the diameter of the aperture  26  of the poppet valve  9  may be 2.5 mm.