Abstract:
A flow control valve for a hydropneumatic suspension comprises a circular valve body including a flow restriction and a plurality of flow relief passages closed at one side by respective leaf springs. Further flow relief is provided by a reciprocal central sleeve which contains the flow restrictor and is movable to unseat one or both leaf springs.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a control valve of a hydraulic duct, the valve being adapted to control hydraulic flow in both directions through the duct. 
       BACKGROUND OF THE INVENTION 
       [0002]    Hydraulic systems rely upon flow of a hydraulic fluid, typically an oil or water based liquid, to achieve a desired effect. One example of such a system is a hydropneumatic suspension of a vehicle, in which road wheels are mounted on respective hydraulic actuators, and springing is provided by a hydropneumatic suspension module containing a springing medium, such as nitrogen gas. Suspension modules are typically in the form of a sphere having a diaphragm separating hydraulic fluid from a suspension gas under pressure. Working of the suspension causes movement of hydraulic fluid to and from the sphere. Such suspension systems are well known and need not be further described here. 
         [0003]    As the hydraulic fluid moves to and from the suspension module, some means of damping must be provided to reduce the amplitude of suspension movement. Orifices and spring loaded relief valves have been proposed to allow suspension characteristics to be tuned for optimized ride and handling of the vehicle. The characteristics for bump and rebound are usually different, so that typically the fluid flow path in the bump (upward) direction of a wheel is different from that of the rebound (downward) direction of a wheel. 
         [0004]    Some kinds of vehicle, particularly agricultural and construction vehicles, are designed to operate both on and off highway. The respective ranges of suspension movement are significantly different, so that a suspension optimized for on-highway use may be too hard for off-highway use. Conversely a suspension capable of accommodating wheel deflections in off-highway use may be uncomfortably soft in on-highway conditions. In either case the speed of travel of a vehicle may be severely limited if used on terrain for which the suspension is not optimized. A driver selectable alternative increases expense and complication, and is preferably avoided. 
       SUMMARY OF THE INVENTION 
       [0005]    It would be desirable to have a simplified bi-directional flow control valve with several integrated features to permit tuning thereof, particularly to accommodate ranges of suspension movement appropriate for both on-highway and off-highway vehicle use. 
         [0006]    According to the invention there is provided a flow control valve for a hydraulic conduit, said valve comprising a valve body having an open through passage defining a flow restriction, and an arcuate array of flow relief passages, each of said relief passages having at one side a closure comprising a leaf spring, and at least one said leaf spring being provided at each side of the valve body, wherein said valve includes a piston reciprocal in said body, said piston having end abutments to limit travel thereof, said piston being resiliently biased in one direction to permit said one end abutment to seat a corresponding leaf spring at one side of said body, and being movable under increasing hydraulic pressure to unseat said corresponding leaf spring, thereby to open a respective relief passage. 
         [0007]    Such a bi-directional valve is substantially symmetrical and relatively straightforward to manufacture whilst being tunable for both bump and rebound. 
         [0008]    The open through passage may be provided in said piston, for example as an axial opening of a substantial annular piston. 
         [0009]    The array of relief passage may be circular and equispaced. The leaf springs may be circular and annular, and the lip thereof may lift under pressure to provide a first relief opening. A second relief opening is provided by sliding motion of the piston within the body. 
         [0010]    In one embodiment a double acting relief valve has two-stage relief available for both directions of hydraulic flow (bump and rebound), both stages on each side being independently tunable. 
         [0011]    Such a valve provides damping and flow relief suitable for on-highway travel, yet can provide for additional suspension travel in off-highway travel whilst maintaining an acceptable ride and handling characteristic at speed. 
         [0012]    Features of the invention will be apparent from the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]    Other features of the invention will be apparent from the following description of a preferred embodiment illustrated by way of example only in the accompanying drawings in which: 
           [0014]      FIG. 1  illustrates a hydropneumatic wheel suspension of a vehicle. 
           [0015]      FIG. 2  illustrates in plan a circular valve element for use in the present invention. 
           [0016]      FIG. 3  is a vertical section (as viewed) through the centre of the element of  FIG. 2 . 
           [0017]      FIG. 4  is a horizontal section (as viewed) through the centre of the element of  FIG. 2 . 
           [0018]      FIG. 5  is a partial section showing one mode of operation of the valve element of  FIGS. 2-4 . 
           [0019]      FIG. 6  is a transverse section through a first embodiment according to the invention. 
           [0020]      FIG. 7  is a transverse section through a second embodiment according to the invention. 
           [0021]      FIG. 8  is a transverse section through a third embodiment according to the invention in a first stage of operation. 
           [0022]      FIG. 9  is a transverse section through a fourth embodiment according to the invention in a second stage of operation. 
           [0023]      FIG. 10  is a transverse section though a fifth embodiment according to the invention in a third stage of operation. 
           [0024]      FIG. 11  shows the graphical relationship between operating speed and internal pressure drop in an embodiment of the invention, for both bounce and rebound. 
           [0025]      FIG. 12  shows inside elevation a sixth embodiment of the invention. 
           [0026]      FIG. 13  is a diametral cross-section on line ‘ 13 - 13 ’ of  FIG. 12 . 
           [0027]      FIGS. 14 and 15  show perspective views of the valve body of  FIG. 12  from above and below. 
           [0028]      FIGS. 16-21  show schematically the stages of operation of the valve of  FIG. 12 , in both bump and rebound. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    With reference to  FIG. 1 , a vehicle  11  has a wheel  12  connected thereto by a pivotable suspension arm  13 . A hydraulic strut  14  permits suspension movement of the wheel and is coupled via a hydraulic line  15  to a suspension sphere  16  having an internal diaphragm  17  confining pressurized gas  18  on one side thereof. A fluid restrictor  19  provides damping of the movement of hydraulic fluid as the suspension is worked.  FIG. 1  illustrates a strut  14  by way of example, but any suitable actuator or motor may be used. 
         [0030]    Although an independent suspension of one wheel is illustrated in  FIG. 1 , this kind of suspension is also fitted to beam axle vehicles. 
         [0031]    One element of the invention for inclusion in a practical valve embodiment is illustrated in  FIGS. 2-4 . A cylindrical body  21  fits closely within a hydraulic duct  22 , and has four equispaced through apertures  23 . The opposite end faces of the body  21  are planar, and at each side two of the apertures open to the outer periphery via respective slots  24 . 
         [0032]    The opposite end faces each have a respective spring disc  25 ,  26  of diameter sufficient to cover the apertures  23 , but less than the internal diameter of the duct  22 , so that a fluid flow passage is formed from either side as illustrated by arrows  27 ,  28 . 
         [0033]    The hydraulic duct is in use part of the hydraulic line  15 , and is connected at one side to the suspension sphere  16 , and at the other side to the strut  14 . 
         [0034]    In use fluid flow passing through the slots  24  enters two of the apertures, depending upon the direction of flow; the other two apertures in the same flow direction are blocked by the respective spring disc. At a predetermined pressure, the respective spring disc lifts in the manner of a leaf spring to uncover the apertures on the downstream side, thus allowing the passage of hydraulic fluid ( FIG. 5 ). On the upstream side fluid pressure holds the other spring disc against the body  21 . Flow in the opposite direction is controlled in the same manner, and is via the other two apertures. 
         [0035]    The valve element of  FIG. 2  is simple, and permits considerable tuning of the opening and flow characteristics, for example by altering the number and/or the diameter and/or the shape of the apertures  23 , the size of the slots  24 , the outside diameter of the discs  25 ,  26 , and the resilience of the discs  25 ,  26 . The characteristics of the flow direction can be adjusted independently of the rebound direction. 
         [0036]    A flow control valve in accordance with one embodiment of the invention is illustrated in  FIG. 6 , and incorporates an element  31  of the kind illustrated in  FIGS. 2-5 . The element  31  consists of a body  32  having a circular array of through passages  33 , some of which allow flow downwards (as illustrated) and some of which allow flow upwards (as illustrated). One slot  34  is shown in  FIG. 6 , and others are out of the plane of the section illustrated. 
         [0037]    The body  32  is retained in a stepped duct  41  by a close-fitting insert  42 , and sealing rings  43 ,  44  are provided in respective grooves to prevent leakage of hydraulic fluid. The duct may form part of an independent hydraulic device, or may be incorporated within the strut  14  or suspension sphere  17  in use. 
         [0038]    The body is provided with a central through bore  35  within which is located a sliding piston in the form of a sleeve  36  having an enlarged head  37 . Axial movement of the sleeve is restricted by an abutment  38  provided on the opposite end to the head  37 . The through passage of the sleeve contains a throat or restrictor  39  which is open but constitutes a restriction to flow of hydraulic fluid therethrough. The restrictor may be quite small, and in one embodiment is a side of the order of 1-2 mm in diameter. 
         [0039]    The sleeve  36  is biased upwardly (as viewed) by a stack of Belleville spring washers  45  between the body  32  and head  37 , and placed back to back so as to exert a pre-load; suitable thrust washers  46  are included, and it will be understood that in consequence the spring discs  47 ,  48  are held tightly over the through passages  33 . 
         [0040]    In practice the sleeve  36  may comprise a screw-threaded bolt having an internal hex head  37  and a self-locking nut as abutment  38 . The nut may be used to adjust the pre-load exerted by the stack of spring washers  45 . 
         [0041]    Operation of the flow control valve of  FIG. 6  is as follows. Free flow of hydraulic fluid is permitted in either direction via the throat  39 , which constitutes a flow restriction. The area of the throat is tuned (for example by drilling a hole of appropriate diameter) to damp the flow of fluid, and thus cause suspension oscillation to diminish. Such a restrictive throat is suitable for optimizing on-road suspension characteristics. 
         [0042]    It is typically desirable to permit greater flow in one direction than the other, for example to give different bounce and rebound characteristics to the invention. Thus, as illustrated, if hydraulic pressure increases at the upper side, by virtue of the flow restriction imposed at the throat  39 , such pressure will act via the slot(s)  34  on the spring disc  48 , and cause it to bend downwardly (as viewed) so as to open the associated through passage. A further increase in hydraulic pressure causes the sleeve  36  to act as a piston and compress the spring stack  45  to move the abutment  38  downwardly. As a result the spring disc  48  disengages the body  32 , and allows additional flow of hydraulic fluid to the downstream side via the respective through passage(s)  33 . As fluid pressure on the upper side falls, the sleeve  36  will return upwardly to re-seat the spring disc  48  on the body  32 , and allow the through passages  33  to be closed. 
         [0043]    This arrangement provides a two-stage relief valve which opens at a predetermined hydraulic pressures, and may provide for the greater suspension movements which are characteristic of off-road travel. It will be understood that the Belleville washers may be arranged in the same or in different directions so as to alter the spring characteristic. 
         [0044]    In this embodiment, a second stage relief valve is also provided in the reverse direction, i.e. upon build-up of hydraulic pressure on the lower side, as viewed. First stage pressure relief is provided by bending of the upper spring disc  47 , and second stage relief by movement of the spring disc  47  upwardly against the effect of the spring stack  45 . 
         [0045]    The arrangement of  FIG. 7  is substantially identical to that of  FIG. 6  save that the spring stack  45  is replaced by a coil spring  51 , and that adjustability provided by the threaded abutment  38  is removed. The sleeve  52  is unthreaded and the lower abutment is provided by a circlip or spring ring  53 , which gives a fixed pre-load to the coil spring  51 . 
         [0046]    Operation of the embodiment of  FIG. 7  is identical to that of  FIG. 6 , but the different spring characteristics of the coil spring  51  and spring stack  45  allow a different relationship between hydraulic pressure and travel of the sleeve. 
         [0047]    The flow control valve may be inserted in the hydraulic line  15  in either direction according to the requirements of use. In use the relief provided by movement of the sleeves  37 ,  52  is typically sequential to relief provided by bending of the spring discs  47 ,  48 , and may be used for example to accommodate very high pressure. These relief stages may however overlap to some extent if desired. 
         [0048]      FIGS. 8-9  illustrate a flow control valve having the characteristics of the valve of  FIGS. 6 and 7 , and with secondary pressure relief in both directions of flow. 
         [0049]    The sleeve  61  floats at a position of mid-travel in the body  62  by virtue of stacks of Belleville spring washers  63 ,  64  on either side thereof. As illustrated in  FIG. 8 , the spring stacks exert a closing force on the spring discs  65 ,  66  so that the through passages  67  are normally closed in both directions. A throat  68  is provided in the sleeve  61 , as before. 
         [0050]    In use flow from one side of the valve to the other is initially damped by the throat  68  (flow from above illustrated in  FIG. 8 ). As the volume of hydraulic fluid to be moved through the valve increases, pressure builds up and the spring disc  66  bends to allow a first stage of pressure relief, as illustrated in  FIG. 9 . 
         [0051]    A further increased in pressure causes the sleeve to move, thus permitting unseating of the respective spring disc  66 , and a second stage of pressure relief, as illustrated in  FIG. 10 . 
         [0052]    In the opposite direction, two-stage pressure relief is also provided, but the relief characteristic may be different, as demonstrated by the different number of spring washers in the spring stacks  65 ,  64 . It will be understood that coil springs may also be used in the embodiment of  FIGS. 8-10 . 
         [0053]    In the embodiments of  FIGS. 8-10 , the bore of the hydraulic duct may be around 36 mm, and the spring disc may be of spring steel, about 0.19 mm thick. 
         [0054]    A typical operating characteristic for the valve of the  FIGS. 8-10  illustrated in  FIG. 11 . 
         [0055]    The normally closed mid-condition of the valve is represented by chain-dot line  71 . 
         [0056]    For slow speed movement of the suspension in either direction, represented by a relatively small pressure drop, hydraulic flow is solely via the valve throat  68 . At intermediate speeds, the volume of fluid is greater and accordingly the first stage of relief is provided via deformation of the respective spring disc  65 ,  66 . At high speeds the second stage of relief is required via unseating to the respective spring disc  65 ,  66 . 
         [0057]    The characteristics for bump (compression) and rebound may be individually tuned so that the response on either side of the mid-condition may be different. 
         [0058]      FIG. 12  illustrates a flow control valve insert in accordance with the invention, and substantially corresponding to the single acting embodiments of  FIGS. 6 and 7 . The body  71 , coil spring  72 , spring discs  73 ,  74 , head  75  and abutment  76  can be clearly seen. 
         [0059]    The cross-section of  FIG. 13  shows one embodiment of through passages  77 ,  78  which are different in the bounce and rebound directions. 
         [0060]      FIGS. 14 and 15  show perspective views of the valve body of  FIG. 12  on an enlarged scale. The central bore  79  is defined for the moving sleeve, and the through passages  77 ,  78  are defined by respective upstanding walls  80 ,  81  which constitute a means of supporting the spring discs above the corresponding openings which correspond to the slots  24 . Additional upstands  82  are provided on one side to support the corresponding spring disc. The valve body  71  may for example comprise an aluminium die casting. 
         [0061]    Stages of operation of the flow control valve of  FIGS. 12-15  are illustrated in  FIGS. 16-21 . 
         [0062]      FIG. 16  shows low speed compression (bump) flow with hydraulic oil passing solely via restrictor  83 . At medium speed, the spring disc  73  lifts at the edge to allow additional flow via the through passages  77 . At high speed the build-up of pressure is sufficient to lift the spring disc  73  fully from the seat formed by wall  80  to allow a further increase in fluid flow. 
         [0063]    During compression flow the spring disc  74  remains seated, thus blocking the corresponding through passages  78 . 
         [0064]    Rebound flow is illustrated in  FIGS. 19-21 , during which time the through passages  77  are blocked by the spring disc  73 . 
         [0065]    At low rebound speed flow is solely via the throat  83 . At medium speed ( FIG. 20 ), the spring disc  74  lifts at the edge to allow additional flow through the passages  78 . At high speed ( FIG. 21 ), the build-up of hydraulic pressure is sufficient to lift spring disc  74  fully from the seat formed by wall  81 , to allow a further increase in fluid flow. 
         [0066]    It will be appreciated that both instances of high flow cause compression of the coil spring  72 , and the second stage relief may thus be identical for both directions of fluid flow. 
         [0067]    In the described embodiments of  FIGS. 6 to 9  and  16  to  21 , an open through passage of a sleeve is depicted. However, this bypass passage may be provided in many other ways. For example, the passage may be around the perimeter of the valve body, for example by providing a “loose” diametral fit or a notch in the circumferential wall of the valve body, or duct in which it is contained. In another alternative a controlled bypass of a normally closed leaf spring may be provided, for example by means of one or more channels in the corresponding valve seat. Other alternatives will occur to a person skilled in the art of hydraulic valve design.