Abstract:
A working machine includes a body and an axle which is mounted so as to be moveable relative to the body, the axle carrying at or towards each end, a ground engaging wheel by means of which the machine can travel over the ground, the machine including a speed sensor sensitive to the machine ground speed, and there being a hydraulic control system including at least one control actuator connected between the body and the axle for controlling movement of the axle relative to the body, and the hydraulic system further including at least one control valve which is operable to restrict fluid flow occurring as a result of the control actuator extending or retracting in response to axle movements relative to the body, depending upon the signal provided by the speed sensor, wherein the control valve is an electrically operated control valve, operated proportionally by a valve controller which responds to changes in machine speed, by adjusting the restriction to fluid flow so as to permit more fluid flow as the machine speed increases.

Description:
BACKGROUND TO THE INVENTION 
       [0001]    This invention relates to a working machine which includes an axle carrying ground engaging wheels, which is moveable relative to a body of the machine. 
         [0002]    More particularly but not exclusively the invention relates to a working machine of the kind which has a working arm which is moveable relative to the body of the machine, the working arm carrying a working implement such as a loading forks or loading or excavating bucket for examples only. 
         [0003]    However the invention may be applied to other working machines such as tractors. The axle may be suspended from the body, or may be fixed to pivot about a pivot axis relative to the body. 
         [0004]    Such working machines are required to be driven over ground which typically will include many surface irregularities. To facilitate machine travel it is well known to mount one of the axles for pivoting movement relative to the body, about a generally horizontal axis which extends longitudinally of the machine. Such pivoting movement permits the wheels carried by the axle to move in response to ground surface irregularities encountered as the machine travels. 
       DESCRIPTION OF THE PRIOR ART 
       [0005]    Various proposals have been made, for example in U.S. Pat. No. 6,179,304 or U.S. Pat. No. 6,082,742 for controlling the axle pivoting depending upon parameters so as to avoid machine instability conditions arising. Such prior proposals permit the machine to operate in distinct operating modes depending upon the control parameters used. For example such prior proposals may permit the free pivoting of the axle in an axle unlocked mode, or may permit no axle pivoting in an axle locked mode, and may permit restricted axle pivoting in so-called cushioned mode. The machine is caused automatically to change operating mode upon a control parameter changing. Such automatic switching between one operating mode and another can be disconcerting for a machine operator. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect of the present invention we provide a working machine which includes a body and an axle which is mounted so as to be moveable relative to the body, the axle carrying at or towards each end, a ground engaging wheel by means of which the machine is moveable on the ground. The machine may include a speed sensor sensitive to the machine ground speed, and there may be a hydraulic control system including at least one control actuator connected between the body and the axle for controlling movement of the axle relative to the body. The hydraulic system may further include at least one control valve which is operable to restrict fluid flow occurring as a result of the control actuator extending or retracting in response to axle movements relative to the body, by an amount depending upon a machine speed signal provided by the speed sensor. The control valve may be an electrically operated control valve, operated proportionally by a valve controller which responds to changes in machine speed, by adjusting the restriction to fluid flow so as to permit more fluid flow as the machine speed increases. 
         [0007]    By virtue of the invention movement of the axle in response to the wheels engaging ground irregularities, is controlled depending on machine speed by restricting the fluid flow e.g. to and/or from the control actuator, and preferably the degree of restriction to fluid flow is continuously varied in response to machine speed variations. Thus there is no switching between operating modes in response to machine ground speed. In one example, the control valve is an electrically operated control valve, operated by a valve controller which responds to changes in machine speed by proportionally or unproportionally, adjusting the restriction to fluid flow. 
         [0008]    In one example, above a threshold speed, the control valve may provide substantially no restriction to fluid flow. 
         [0009]    Desirably, when the machine is stationary, the controller operates the control valve to prevent fluid flow in the hydraulic system so as to prevent axle movement relative to the body, and the controller operates the control valve to permit more fluid flow as the machine speed increases, at least to the threshold speed at which the control valve may provide substantially no restriction to fluid flow so that the axle may freely move as permitted by its mounting. 
         [0010]    However if desired when the machine is stationary, some restricted fluid flow may be permitted upon the controller receiving an auxiliary input from a manual control device, such as for example only, a control lever position sensor, or a switch. 
         [0011]    For example, the working machine may include a pair of stabilisers which are both lowered from the body into engagement with the ground at remote positions preferably at either side of the body, to stabilise the machine when performing a working operation, upon an operator manually operating a stabiliser control lever or a switch. As the stabilisers engage with the ground, the ground surface may be at a different level at one side of the body compared to the other. By permitting restricted fluid flow to and/or from the control valve during stabiliser lowering, the stabilisers may engage with the ground whilst the axle may move so that both wheels on the axle may remain in contact with the ground. 
         [0012]    In another example the machine may include a further axle which is mounted so as to be moveable relative to the body, the further axle carrying at or towards each end, a ground engaging wheel by means of which the machine travels over the ground. The machine may include a further, sway, actuator connected between the body and the further axle for causing movement of the further axle relative to the body. Such a facility which is known as “sway”, is provided to facilitate levelling of the machine body for performing working operations when the machine is stationary. 
         [0013]    The sway actuator is operated by a manually operable sway control lever or switch and desirably, when the sway control lever or switch is operated, with the machine stationary, the auxiliary input is provided to the controller which responds by permitting restricted fluid flow. 
         [0014]    In a preferred embodiment, the hydraulic system includes a pair of control actuators which include pistons in cylinders, one at or towards either end of the axle, and the control valve controls the flow of fluid from the cylinder at one side of the piston of one of the control actuators, to the cylinder at the one side of the piston of the other of the control actuators. In another example though a single control actuator may be provided with the control valve controlling the flow of fluid from the cylinder at one side of the piston, to the cylinder at the other side of the piston. 
         [0015]    The invention has particularly but non-exclusively been developed for a working machine of the kind which includes a loading arm which is pivoted to the body for up and down movement relative to the machine, e.g. at a rear of the body, the loading arm extending beyond a front end of the body and mounting a load handling implement. The loading arm may be telescopically extendible and retractable. The stability of such a machine, particularly when handling loads at great height above and distant from the body of the machine is crucial. The present invention, in which the control valve is operable to prevent or at least maximally restrict fluid flow and hence axle movement, provides for maximum stability during load handling. The control actuator is preferably provided between a rear axle and the body, and the axle with the sway actuator, where provided, is the front axle. 
         [0016]    The invention may though be applied to many other working machines which have working arms, such as for examples only, excavating machines, loading machines and machines which are capable for performing both excavating and loading operations, as well as to tractors and the like working machines. 
         [0017]    In a preferred embodiment, the axle, movement of which is controlled by the hydraulic system in response to machine ground speed, may be pivotable relative to the body about a substantially horizontal pivot axis which extends longitudinally of the machine. 
         [0018]    In another embodiment, the axle may be suspended from the body by suspension control links. 
         [0019]    In each case, the other of the axles may be pivoted relative to, or suspended from, the body. 
         [0020]    According to a second aspect of the invention we provide a method of operating a working machine which includes a body and an axle which is mounted so as to be moveable relative to the body. The axle may carry at or towards each end, a ground engaging wheel by means of which the machine is moveable on the ground, and the machine may include a speed sensor sensitive to the machine ground speed. A hydraulic control system may be provided which includes at least one control actuator connected between the body and the axle for controlling movement of the axle relative to the body, and the hydraulic system may further include at least one control valve which is operable to restrict fluid flow occurring as a result of the control actuator extending or retracting in response to axle movements relative to the body, the method including restricting fluid flow proportionally depending upon a signal provided by the speed sensor. 
         [0021]    According to a third aspect of the invention we provide a method of operating a working machine which includes a body and an axle which is mounted so as to be moveable relative to the body, the axle carrying at or towards each end, a ground engaging wheel by means of which the machine is moveable on the ground. There may be a hydraulic fluid control system including at least one control actuator connected between the body and the axle for controlling movement of the axle relative to the body, and at least one control valve which is operable to at least restrict hydraulic fluid flow in the system occurring as a result of the control actuator extending or retracting in response to axle movements relative to the body. The system may include a controller which provides command signals to the control valve to vary the restriction to fluid flow, depending on a control regime, and the working machine may include an auxiliary hydraulically operated service, and when the auxiliary hydraulically operated service is operated, the restriction to hydraulic fluid otherwise provided by the control valve in accordance with the control regime is at least partially relieved. 
         [0022]    In one example, the auxiliary hydraulically operated service is a service for raising and lowering stabilisers of the machine which may stabilise the machine when performing a working operation, in which case when the stabilisers are lowered towards the ground, the restriction to fluid flow in the hydraulic fluid control system may be at least partially relieved. For example, the movement of a part of a stabiliser control structure may operate a device which provides an auxiliary input to the controller. The stabiliser control device may be manually operable upon an operator manually operating a stabiliser control lever or switch. 
         [0023]    In another example, additionally or alternatively, the auxiliary service is a service for causing movement of a further axle of the machine relative to the body, the service including a sway actuator connected between the body and the further axle, and the restriction to fluid flow in the hydraulic fluid control system may be at least partially relieved when the sway actuator is operated upon a sway control structure being operated. Movement of a part of a sway control structure may operate a device which provides an auxiliary input to the controller which responds by relieving the flow restriction. The sway control device may be manually operable upon an operator manually operating a sway control lever or switch. 
         [0024]    In each case, the control valve may, in the absence of the auxiliary input, be operable to restrict fluid flow in the hydraulic fluid control system occurring as a result of the control actuator extending or retracting in response to axle movements relative to the body, by an amount depending upon a machine speed signal provided by a machine speed sensor. The control valve may thus be an electrically operated control valve, operated proportionally by the controller which responds to changes in machine speed, by adjusting the restriction to fluid flow so as to permit more fluid flow as the machine speed increases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Embodiments of the invention will now be described with reference to the accompanying drawings in which: 
           [0026]      FIG. 1  is a side illustrative view of a working machine in accordance with the present invention; 
           [0027]      FIG. 2  is an illustrative view of part of the machine of  FIG. 1  including a hydraulic circuit thereof. 
           [0028]      FIG. 3  is a diagram showing a controller for use in a machine according to the invention; 
           [0029]      FIG. 4  is an illustrative diagram showing part of an auxiliary hydraulically operated service of the machine of  FIGS. 1 and 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Referring to the drawings a working machine  10  in this example is a load handling machine, which includes a body  12  having a front end  13  and a rear end  14 . Towards a front end of the machine  10  there is a front axle  15  which carries at or near to each end, a front wheel  16 , and towards the rear end  14 , there is a rear axle  18  which carries at or near each end, a rear wheel  20 . 
         [0031]    Each of the front  15  and rear  18  axles in this example are pivotally mounted with respect to the body  12  about respective pivot axes A, B. The pivot axes A, B are generally horizontal and extend longitudinally of the machine  10 , and in this example are substantially co-axial. 
         [0032]    The machine  10  further mounts a loading arm  25  for pivoting up and down movement about a further generally horizontal axis C which is transverse to the pivot axes A, B of the axles  15 ,  18 . The loading arm  25  is mounted on a mounting structure  26  at or toward the rear end  14  of the body  12  and extends forwardly beyond the front end  13  of the body  12 . 
         [0033]    The loading arm  25  includes a plurality of sections  25   a,    25   b  which are telescopically extendible relative to one another by means of internal hydraulic actuators, and at an outermost end of the loading arm  25 , there is a loading implement which in this example is a pair of loading forks  30 . 
         [0034]    The body  12  carries an operator&#39;s cab  32  where an operator sits and controls the machine  10 , and in this example, the cab  32  is at one side of the body  12  whilst the loading arm  25  is side mounted at the other side of the body  12  to the cab  32 . 
         [0035]    An engine E to provide power for the machine  10  is shown mounted towards the rear end  14  of the machine  10 , but in another example could be side mounted. The engine E drives the wheels  16 ,  20  of the machine  10  via a mechanical or hydrostatic or other transmission  38 , and a machine ground speed sensor  39  senses movement of part of the transmission  38 , such as the rotation of a gear wheel or drive shaft, the speed sensor  39  in use providing an input signal to a controller  40  which is indicative of machine ground speed, which signal is used by the controller  40  to control the operation of a hydraulic system  42  of the machine  10  which will be more particularly described below with reference to  FIG. 2 . The speed sensor  39  may for example be a Hall effect sensor. 
         [0036]    The machine  10  in this example, further includes a pair of stabiliser arms  35 ,  36  one being provided at each side of the body  12 , in this example at the front end  13  of the machine  10 . The stabiliser arms  35 ,  36  are in use, lowered into engagement with the ground to stabilise the machine  10  during working operations as described below, and when not in use are raised into a stowed condition. The stabiliser arms  35 ,  36  are preferably raised and lowered by an auxiliary hydraulically operated service which includes respective hydraulic actuators. 
         [0037]    Within the operator&#39;s cab  32  there is provided a manually operated stabiliser arm control lever  43  which when operated causes the stabiliser arms  35 ,  36  to be raised or lowered, there being in this example a stabiliser control lever movement sensor drive  44  to sense movements of the stabiliser arm control lever  43  from a rest position. Also in the cab  32  there is a manually operable sway control lever  45  the purpose of which will be explained below, and there being a sway control lever movement sensor device  46  to sense movements of the sway control lever  45  from a neutral position. 
         [0038]    Each of the stabiliser arm control lever sensor  44  and the sway control lever sensor  46 , upon sensing a movement from a neutral position of the respective control lever  43 ,  45 , provides a signal to the controller  40 . 
         [0039]    Referring to  FIGS. 2 and 3 , between the front axle  15  and the body  12  there is a sway actuator  50  which is in this example a double acting hydraulic actuator of the piston-in-cylinder kind. Under the control of an operator operating the sway control lever  45 , the sway actuator  50  may be extended or retracted to pivot the front axle  15  relative to the body  12 , to change the attitude of the body  12  relative to the ground. Thus in the event that it is required to perform a working operation and the body  12  of the machine  10  and hence the loading arm  25  is not at a level attitude, the sway actuator  50  may be extended or retracted to level the body  12 , to compensate for an unlevelled ground surface. 
         [0040]    Other than when being adjusted, the front axle  15  is rigid relative to the body  12 , particularly when the machine  10  is travelling over the ground surface. 
         [0041]    If desired, the operator&#39;s ability to operate the sway may be prevented at other than very slow speeds and when the machine  10  is stationary. 
         [0042]    Between the rear axle  18  and the body  12  there are in this example, a pair of control actuators  55 ,  56 , of the hydraulic system, one at each side of the pivot axis B. Each control actuator  55 ,  56  is again of the piston-in-cylinder kind and may be double acting as drawn or single acting. 
         [0043]    The cylinders of the control actuators  55 ,  56  at the non-annulus sides of the control actuators  55 ,  56 , are interconnected via a hydraulic system  42  which includes a pair of control valves  58 ,  59 , each control valve  58 ,  58  being provided in a respective hydraulic line  60 ,  61  which extends to and from the respective control actuators  55 ,  56 . 
         [0044]    Each control valve  58 ,  59  is an electrically operated proportional valve, electrical operation being effected by the controller  40 . Each control valve  58 ,  59  permits the substantially unrestricted flow of hydraulic fluid to the non-annulus side of the respective control actuators  55 ,  56  via a poppet  58   a,    59   a,  but the flow of fluid from the non-annulus sides of the respective control actuators  55 ,  56  is controlled depending on the extent of opening of the control valves  58 ,  59  which depends on a control signal received from the controller  40 . The control valves  58 ,  59  may each have a solenoid or other electrical actuator as shown at  58   b,    59   b.    
         [0045]    Operation of the hydraulic system  42  will now be described. 
         [0046]    Upon the rear axle  18  moving in response to ground surface irregularities as the machine  10  travels over the ground, depending on the operating conditions of the control valves  58 ,  59 , pivoting of the rear axle  18  relative to the body  12  may or may not be permitted. 
         [0047]    At ground speeds sensed by the machine speed sensor  39  of greater than a threshold speed, for example 4 kph, the controller  40  signals the respective valve solenoids  58   b,    59   b  fully to open the control valves  58 ,  59  to allow the substantially free flow of fluid through the lines  60 ,  61 . Thus as the machine  10  travels at the threshold speed or higher, the rear axle  18  may pivot about its pivot axis B in response to irregularities in the ground surface as permitted by its mounting, with fluid flowing from one non-annulus control actuator  55 ,  56  piston side to the non-annulus piston side of the other control actuator  56 ,  55  depending upon which side of the axle  18  rises and lowers relative to the body  12 . Thus the machine body  12  may remain more level than if the rear axle  18  was rigidly mounted, despite ground surface irregularities. 
         [0048]    When the machine  10  is stationary or substantially so, the controller  40  will respond to the signal from the speed sensor  39  by signalling the solenoid valves  58 ,  59  to close, for example by removing any electrical power to the solenoids  58   b,    59   b  altogether, so that the control valves  58 ,  59  are closed by respective mechanical springs  58   c,    59   c.  Thus fluid will not be permitted to pass from either non-annulus sides of the control actuators  55 ,  56  to the other and the rear axle  18  will be locked relative to the body  12 . Thus when the machine  10  is performing work operations, when stationary, the locked rear axle  18  will afford maximum stability. 
         [0049]    At speeds between zero and the threshold speed, the controller  30  responds to the signal from the speed sensor  39  according to e.g. a programmed control regime, by allowing a restricted flow of fluid between the non-annulus sides of the control actuators  55 ,  56 . For example the degree of restriction may be proportional to the machine  10  speed up to the threshold speed. This partial restriction to fluid flow is achieved as the controller  40  provides signals to the solenoids  58   b,    59   b  of the control valves  58 ,  59  partially to open the valves  58 ,  59  against the springs  58   c,    59   c  pressures, preferably in proportion to the machine speed signalled by the speed sensor  39 . 
         [0050]    Thus at speeds up to the threshold speed, some, cushioned, rear axle  18  pivoting is permitted relative to the body  12 , the extent of cushioning depending upon machine  10  speed. Thus as machine  10  speed increases from zero, as more accommodation of irregular ground surface conditions is required, the extent of cushioning movement of the rear axle  18  decreases to a minimum as threshold speed is reached. 
         [0051]    Because the control valves  55 ,  56  are proportional valves, there is no sudden change between one discrete operating mode and another, but the degree of change in the amount of cushioning of the rear axle  18  movement as the machine  10  speeds up and slows down, is continuous. 
         [0052]    When the machine  10  is stationary for performing working operations, the stabiliser arms  35 ,  36  may be lowered by a further auxiliary hydraulically operated service. Movement of the stabiliser arm control lever  43  is sensed by the sensor  44  and an auxiliary signal is provided to the controller  40  which responds by relieving the restriction to fluid flow otherwise provided by the control valves  58 ,  59  in accordance with the control regime. In this example, where the valves  58 ,  59  are fully closed when the machine  10  is stationary, the controller  40  responds to the auxiliary input from sensor device  44  by partially opening the control valves  58 ,  59  even though the machine  10  is stationary, the auxiliary input from the stabiliser arm sensor  44  thus overriding. In one example the control valves  58 ,  59  may be opened to restrict the fluid flow by about 50% as a result of the auxiliary input from sensor  44 . Where the control valves  58 ,  59  are proportional valves, this means that the valves  58 ,  59  need to be half opened against the forces of the respective closure springs  58   c,    59   c.    
         [0053]    When the stabiliser arms  35 ,  36  are lowered into engagement with the ground so as to be load bearing, the control lever  43  is released, and this returns under spring control for example to its neutral position, and the controller  40  will again lock-up the rear axle  18  by closing the control  58 ,  59  valves. 
         [0054]    Moreover if it is desired to adjust the level of the front axle  15  by operating the sway actuator  50 , when the machine  10  is stationary or slow moving such that in the example, the control valves  58 ,  59  are fully closed by the control  40  in accordance with the control regime, the sway actuator control lever  45  movement sensor  46  will signal the controller  40 . The controller  40  will respond by partially opening the control valves  58 ,  59 , again by for example, 50% to relieve the restriction to fluid flow between the control actuators  55 ,  56 , to permit cushioned rear axle  18  movements. Again, when the sway control lever  45  is released and is returned for example under spring control, to a neutral position, the rear axle  18  will again be locked-out as the control valves  58 ,  59  close so that fluid cannot pass to and/or from the control actuators  55 ,  56 . 
         [0055]    The provision of the auxiliary inputs from sensor devices  44  and  46  to override the control regime otherwise imposed by the controller  40 , allows the rear wheels  20  to remain in contact with the ground as the machine  10  is levelled ready for performing working operations, using either or both of the stabiliser arms  35 ,  36  or the sway control actuator  50 . Whereas typically the control valves  58 ,  59  will be fully closed when the auxiliary input from one or both of the sensor devices  44 ,  46  is provided, particularly if the machine  10  is still slowly moving over the ground, in the generality, an auxiliary input has the effect of overriding the usual control regime to relieve the restriction to fluid flow which is otherwise imposed. 
         [0056]    In the example described, sensor devices  44 ,  46  have been described as being provided to sense respective movements of parts of respective control structures, namely control lever  43 ,  45  movements. In another example, illustrated in  FIG. 4 , movement of another part of the control structure for either the sway actuator  50  or the stabiliser arm actuator(s) may provide the auxiliary input to the controller  40 . 
         [0057]    In  FIG. 4 , it can be seen that the control structure for the sway actuator  50  includes a hydraulic control valve  79  of the kind having a spool  81  which moves in a valve housing  82 , with an end of the spool  81  extending from the valve housing  82  to an external position. As the spool  81  moves in response to operation of a control such as the control lever  45 , or another control, which may be directly connected to the spool  81  or indirectly operationally connected to the spool  81  e.g. via a hydraulic servo or an electrical actuating circuit, the spool  81  will reach a position as shown in  FIG. 4 . 
         [0058]    In  FIG. 4  it can be seen that the spool has a groove  85  in the end of the spool  81  external to the valve housing  82 , and in the example, the groove  85  is aligned with a detent  76  which may be urged by a resilient device such as a spring, or by gravity, towards the groove  85 . If the detent  76  moves out of groove  85 , this will cause a signal to the controller  40  to be provided by a signalling device  80  to which the detent  86  is coupled, to indicate that the sway actuator  50  is being operated, thus to provide the auxiliary input to the controller  40  which responds by relieving the restriction to fluid flow between the control actuators  55 ,  56  which otherwise the control regime would demand. 
         [0059]    In yet another example, not illustrated, instead of the operation of the auxiliary hydraulically operated service providing an auxiliary input to the controller  40 , at least partially to relieve the restriction to fluid flow between the control actuators  55 ,  56 , operation of the auxiliary service may otherwise at least partially relieve the restriction to fluid flow, by for example a part of a control structure which controls the auxiliary service moving to open a relief valve in a by-pass circuit, or directly acting on the control valves  58 ,  59 , in each case so that the restriction to fluid flow between the control  55 ,  56  actuators is at least partially relieved. 
         [0060]    Further features which are illustrated are as follows. 
         [0061]    In the example illustrated, the control actuators  55 ,  56  are double acting and the annulus sides of the cylinders are interconnected via a flow line  63 , so that upon the control actuators  55 ,  56  being extended and retracted, under the control of the hydraulic system  42 , fluid is exchanged between the annulus sides of the control actuators  55 ,  56 . In another example, the control actuators  55 ,  56  may be single acting. 
         [0062]    In the event that the hydraulic fluid in the hydraulic system  42  becomes heated in use and thus expands, to ensure that this does not result in unwanted control actuator  55 ,  56  extension, there is provided in each hydraulic line  60 ,  61 , a respective one way relief valve  70 ,  71 , which relief valves permit fluid flow between the non-annulus sides of the control actuators  55 ,  56  and a respective low pressure take-up line  73 ,  75  which each extend to a reservoir  74  for hydraulic fluid. 
         [0063]    The line  75  from the relief valve  71  to the reservoir  74  is also connected via line  76 , to each of the annulus sides of the control actuators  55 ,  56 . 
         [0064]    Thus under steady state conditions in which the fluid expands, excess fluid may leak from the hydraulic lines  60 ,  61  in which the control valves  58 ,  59  are provided, via the respective throttled thermal relief valves  70 ,  71  to the supply and take-up lines  73 ,  75 . 
         [0065]    In the event of any loss of volume of hydraulic fluid from the hydraulic system  42  due to leakage or shrinkage, which could result in unwanted control actuator  55 ,  56  movements, fluid may pass from a pressured supply  79 , via a one way valve  78  into the hydraulic lines  60 ,  61  in which the control valves  58 ,  59  are provided. If the control valves  58 ,  59  are closed, the fluid may pass into the lines  60 ,  61  between the valves  58 ,  59  and control actuators  55 ,  56  via check valves  58   d,    59   d.    
         [0066]    Various modifications may be made without departing from the scope of the invention. 
         [0067]    For example, although in the example described, a pair of control actuators  55 ,  56  are provided, one for each side of the rear axle  18 , in another embodiment a single control actuator may be provided at one side of the pivot axis B, with fluid flow between the cylinder at one side of the piston and the cylinder at the other side of the piston being controlled by one or more control valves. 
         [0068]    In another example, where there are two control actuators  55 ,  56  as illustrated, instead of each control actuator  55 ,  56  having in the respective hydraulic line  60 ,  61  its own control valve  58 ,  59 , in another example, fluid flow between the control actuators  55 ,  56  or between the one cylinder side and the other where a single control actuator is provided, may be controlled by a single control valve. 
         [0069]    In the example described, lowering or raising of the stabiliser arms  35 ,  36  is achieved with a manually operable control device being a control lever  43 , but this may be achieved with a switch which not only provides for stabiliser movement but also for providing an auxiliary input indicative of stabiliser arm  35 ,  36  actuator, to the controller  40  such that a separate sensor as shown at  44  need not be required. 
         [0070]    A switch may be provided instead of the sway control lever  45  also so that again, a separate sway control movement sensor as indicated at  46  need not be provided. 
         [0071]    Although the invention has been described in relation to a loading machine  10 , the invention is applicable to a multitude of different working machines. With alternative geometry loading machines and/or other alternative working machines, instead of the rear axle  18  being stabilised as described above, the front axle  15  and/or front and rear axles  15 ,  18 , may be stabilised in the manner described for rear axle  18  in the example. 
         [0072]    In a modified embodiment, if desired other inputs may be provided to the controller  40  which affect the operation of the hydraulic system  42 . For example, the controller  40  may not open the control valves  58 ,  59  in response to the signal from the speed sensor  39  in the event that a parking brake is operational, but subject to either auxiliary input or inputs which indicate stabiliser arm  35 ,  36  lower or raising, or sway actuator  50  operation. 
         [0073]    Of course, if desired, no sway facility or stabilizer arms, need to be provided. An auxiliary signal to the controller  40  to at least partially relieve restriction to fluid flow otherwise provided, may be derived from any appropriate auxiliary service, as desired. 
         [0074]    In another embodiment, the rear axle  18 , or at least the axle movement of which is to be controlled by the hydraulic system  42 , need not be pivoted relative to the body  12  as described, but the axle  18  may be suspended from the body  12  by suspension control links which permit up and down axle  18  movements relative to the body  12 , differentially at either side of the machine  10 . 
         [0075]    Dampers such as mechanical or gas springs, would be required to damp axle movements. 
         [0076]    However, the hydraulic system  42  described may still control axle movements relative to the body  12  in substantially the same way as described for pivoted axle  18  of the illustrated embodiment. 
         [0077]    In each case of pivoted or suspended axle  18 , the other axle, e.g. front axle  15 , may be pivoted too, as described with reference to  FIG. 2 , or suspended from, the body  12  as required although in the case of a suspended axle  15 ,  18 , two control actuators  50 ;  55 ,  56 , one at or towards each of the respective axle ends, would be required. 
         [0078]    Although in each example described above, the hydraulic system  42  is only operational to restrict fluid flow so as to prevent free axle movement as permitted by its mounting, below a threshold speed, in another example, in which the amount of fluid flow restriction may or may not be proportional to the machine  10  ground speed, the hydraulic system  42  may provide resistance to fluid flow by an amount depending on machine ground speed, over the entire machine ground speed range.