Abstract:
A hydraulic steering device is disclosed, having a housing in which an inner control slider and an outer control slider are arranged so that they are rotatable relative to one another and which together are arranged as alterable flow path means between a supply connection arrangement and a working connection arrangement. In such a steering device it is desirable to produce a remote control facility of simple construction. To that end, each control slider is connected to a driving slider, and between the two driving sliders there is created at least one pressure chamber which is acted upon by fluid under pressure, and a change in volume of the pressure chamber effects a relative displacement of the two control sliders.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a hydraulic steering device, having a housing in which an inner control slider and an outer control slider are arranged so that they are rotatable relative to one another and which together are arranged as alterable flow path means between a supply connection arrangement and a working connection arrangement. 
     Such a steering device is known, for example, from DE 43 42 933 A1. 
     In steering devices of that kind, the supply connection arrangement generally comprises a pump connection and a tank connection. The working connection arrangement generally comprises two working connections. Depending on which of the two working connections is acted upon by pressure, a connected steering motor is moved in one or the other direction. 
     In most cases the inner control slider is moved by means of a steering handwheel, that is, is rotated with respect to the outer control slider. In this case a flow path between the pump connection and the corresponding working connection, and between the other working connection and the tank connection is unblocked with more or less throttling. Hydraulic fluid therefore flows from the pump by way of the steering motor to the tank again. At the same time, the hydraulic fluid actuates a measuring motor which rotates the outer control slider relative to the inner control slider and thus brings both control sliders into their original aligned position again in which the flow path is closed. 
     In some cases it is desirable to be able to steer a vehicle that is equipped with such a steering device not only from a driver position using the steering handwheel, but also, for example, in the case of self-propelled working machines, from several positions. 
     This has primarily been achieved until now by mounting a drive motor on the steering handwheel shaft, which motor, when suitably actuated, takes on the function of the human hand as drive means for that hand wheel shaft. Additional installation space is required for that motor, however. 
     SUMMARY OF THE INVENTION 
     The invention is based on the problem of providing a remote control facility of simple construction for the steering device. 
     In a hydraulic steering device of the kind mentioned in the introduction, that problem is solved in that each control slider is connected to a driving slider, and between the two driving sliders there is created at least one pressure chamber which is acted upon by fluid under pressure, and a change in volume of the pressure chamber effects a relative displacement of the two control sliders. 
     The customary point of application, namely the steering handwheel shaft, for a remote steering device is therefore abandoned. The remote control now acts directly on the two control sliders and can there effect a relative displacement of the two control sliders. The corresponding generation of torque is effected simply by the pressure loading and the resultant expansion of a pressure chamber, which is formed between the two driving sliders, so that additional external motors can be omitted. The direct intervention in the kinematics of the two control sliders not only enables, as was previously the case, the inner control slider to rotate with respect to the housing, in which case the outer control slider then had to be tracked after it (if the outer control slider was driven the inner control slider had to be tracked); in addition, a relative displacement of the two control sliders in the housing can be effected directly, so that in some cases a movement of the steering handwheel, with the endangering of operating personnel resulting therefrom, can be completely avoided. Moreover, with this kind of remote control other control principles can be pursued. For example, the customary measuring motor can be omitted. Returning of the two control sliders towards their starting position can likewise be effected by the driving sliders, if the associated control signals are made available in a different manner. 
     In that case is it especially preferred for at least one control slider to be formed in one piece with the driving slider associated with it. This simplifies the construction. The one-piece construction of driving slider and control slider means that additional fixing elements are no longer needed. 
     In an advantageous construction, provision is made for the two driving sliders to be arranged concentrically with respect to one another, the pressure chamber being arranged in an annular gap between the two driving sliders and each driving slider having a projection protruding into the annular gap and bearing against the other driving slider, which projection bounds the pressure chamber circumferentially. In this construction the increase in volume, which is effected for example, when fluid under pressure is admitted to the pressure chamber, directly causes a torque and thus a rotation of the two sliders relative to one another. No further measures are required. The size of the projections, that is, the amount they extend radially and axially, determines the available pressure application surface, which in turn, together with the pressure in the pressure chamber, defines the torque generated. Even with a relatively small annular gap, the torque required for displacing the two control sliders relative to one another can nevertheless be produced. 
     It is also preferred for the projections to be rounded at their free end. The free end is the end of the projections with which they lie against the respective other driving slider. This rounding reduces wear and to a certain extent improves the options available for sealing. 
     Preferably, each projection serves as a boundary for two pressure chambers. The possibility of being able to actuate the steering device in both directions is improved with two pressure chambers. The restoring forces are easier to apply. 
     Preferably, more than two pressure chambers are provided. The number of projections, and thus the number of surfaces that are available to receive pressure, also increases accordingly. In this manner, the torque can be multiplied without particular difficulties. From the point of view of the space required, in most cases it is also possible to accommodate more than two pressure chambers, because the relative displacement of the two control sliders is mostly merely less than 20° and the pressure chambers do not need to be very much bigger than that. 
     Preferably, an even number of pressure chambers is provided. The effect of the driving sliders in the two steering directions can thus be made uniform. 
     Advantageously, the fluid under pressure comes from the same pressure source as the hydraulic fluid used for the steering device. An additional pressure source is not therefore needed. The hydraulic fluid is generally available at the necessary pressure anyway. Since only a comparatively small amount of hydraulic fluid is used to operate the driving sliders, an economical operation can be achieved in this manner. 
     Advantageously, a control device is arranged between each pressure chamber and the pressure source. The pressure in the individual pressure chambers can then be set at will to a specific value, so that the desired relative rotation of the two driving sliders and the relative rotation of the two control sliders resulting therefrom can be effected. 
     The control device preferably has pulse-controlled electromagnetic valves. Using the pulse-controlled electromagnetic valves the desired pressure can be set with relatively few problems by means of the pulse duty factor. The pulse duty factor is the ratio of the open time of an electromagnetic valve to the time of a complete period, that is, the sum of the open and the closed time. 
     It is also an advantage that the pressure chambers are divided into two pressure chamber groups, and that for each pressure chamber group an electromagnetic valve is provided in series with a throttle, the pressure chamber group being connected to a tapping-point between the electromagnetic valve and the throttle. Because the pressure chambers are uniformly combined to form a pressure chamber group, in each pressure chamber of a group the pressure is the same, so that the application of torque in the circumferential direction is very uniform. The use of a single electromagnetic valve per group with a throttle enables a relatively simple control system to be created. 
     The pressure chambers together with the throttles are preferably in the form of a damping arrangement. In this manner, damping between the two sliding members is achieved. Any tendency to oscillate can therefore be prevented very easily. This is a significant advantage, in particular in the case of vehicles with centre-pivot steering. 
     It is also an advantage for the common connection of the throttles to be connected to a load-sensing control line. In this manner, the pressure drop across the electromagnetic valves and the throttles can always be kept constant. This facilitates, for example, electronic triggering of the electromagnetic valves. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described hereinafter with reference to a preferred embodiment in conjunction with the drawings, in which: 
     FIG. 1 is a diagrammatic longitudinal section through a steering device and 
     FIG. 2 is a diagrammatic sectional view II—II according to FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows diagrammatically a steering device  101  with a housing  30  that has a housing bore  31 . An outer control slider  32  and in it an inner control slider  33  are rotatably mounted in the housing bore  31 . An articulated shaft  34  connects a measuring motor  116  to the outer control slider  32 . The inner control slider  33  is arranged to be connected by way of a coupling  35  to a steering handwheel shaft, not illustrated. The coupling is here in the form of a multiple-spline shaft into which the steering handwheel shaft can be inserted. 
     The inner control slider  33  and the outer control slider  32  are connected to one another by way of leaf springs  36  which allow the two control sliders  32 ,  33  to rotate relative to one another to a limited extent. 
     The measuring motor  116  is a gearwheel motor which has an outer toothed ring  37  and an inner gearwheel  38 , between which there are displacement chambers  39 ; the entire assembly is covered over by a cover  40 . The two control sliders  32  and  33  form a flow path arrangement  41 . 
     The flow path arrangement  41  connects different connections selectively and with different throttlings. For that purpose there is an annular groove  42  that is connected to a tank connection T, an annular groove  43  that is connected to a left-hand working connection L, an annular groove  44  that is connected to a right-hand working connection R, a series of control openings  45  that are connected by way of axial channels  46  to respective displacement chambers  39 , an annular groove  47  that is connected to a pump connection P, and an annular groove  48  that is connected to a control signal connection LS. 
     Furthermore, there are a number of axial channels, for example,  49 , and a number of control openings, for example,  50 . Together, they all form the flow path arrangement between the supply connection arrangement, which is here formed by the pump connection P and the tank connection T, and the working connection arrangement, which is here formed by the connections L and R. 
     The construction and the mode of operation of such a steering device are known per se. When the inner control slider member  33  is rotated relative to the outer control slider member  32  by means of the steering handwheel shaft, a flow path is opened from the pump connection P to, depending on the direction, one of the two working connections L, R. Another flow path opens correspondingly from the other working connection R, L to the tank connection T. At the same time, hydraulic fluid acts on the measuring motor  116 . The gearwheel  38  then rotates in accordance with the amount of hydraulic fluid fed in and tracks the outer control slider  32  onto the inner control slider  33  until the neutral position is reached again and the individual flow paths have been interrupted again. 
     In addition to the provision made in the steering device  101  for actuating the inner control slider  33  by means of the steering handwheel shaft by way of the coupling  35 , there is also provision for remote control. For that purpose a driver device  10  is arranged in the region of the end of the two control sliders  32 ,  33  on which also the coupling  35  is mounted. 
     The driver device  10  is illustrated diagrammatically in section in FIG.  2 . It has an inner driving slider  11  and an outer driving slider  12 , which are mounted concentrically in the bore  31  in the housing  30 . Rotation of the two driving sliders  11 ,  12  relative to one another and rotation of the driving sliders  11 ,  12  relative to the housing  30  is thus possible. 
     As can be seen from FIG. 1, the inner driving slider  11  is in one piece with the inner control slider  33 . The outer driving slider  12  can likewise be formed in one piece with the outer control slider  32 . In this particular case, however, it is connected by way of a connecting means  13  to the outer control slider  32 . 
     Between the two driving sliders  11 ,  12  there is an annular space  14  which has the form of a circular ring in cross-section. 
     The inner control slider has four radially outwardly projecting projections  15 , which pass through the annular space  14  and bear against the outer control slider  12  or, more accurately, against the inner wall thereof. Similarly, the outer driving slider  12  has four projections  16  which pass radially through the annular space  14  and bear against the inner driving slider  11 . In this manner a total of eight pressure chambers  17   a ,  17   b ,  17   c ,  17   d ,  18   a ,  18   b ,  18   c ,  18   d  are formed. Each pressure chamber can be loaded with pressure by way of a pressure line  19 ,  20 . The pressure lines  19  for the pressure chambers  17   a ,  17   b ,  17   c ,  17   d  are here combined to form a group by a ring line  21 . The pressure lines  20  for the pressure chambers  18   a ,  18   b ,  18   c ,  18   d  are combined to form a group by way of a ring line  22 . 
     A control device, comprising the series connection of a pulse-controlled electromagnetic valve  23  (for the pressure chambers  17 ),  24  (for the pressure chambers  18 ) and a throttle  25 ,  26 , is provided for each group, the pressure chambers  17  being connected with a tapping-point between the electromagnetic valve  23  and the throttle  25  and the pressure chambers  18  being connected with a tapping-point between the electromagnetic valve  24  and the throttle  26 . Both paths  23 ,  25  and  24 ,  26  are arranged parallel to one another between the pump connection P and the tank connection T. 
     The electromagnetic valves  23 ,  24  are pulse-controlled. Within a predetermined period they are therefore in the open position for a variable time and for the rest of the time in that period are in the closed position. A mean opening degree can thus be set which determines the throttling resistance of the electromagnetic valve  23 ,  24 . 
     When the two throttles  25 ,  26  have the same properties, on uniform triggering of the two pulse-controlled electromagnetic valves  23 ,  24  there is a pressure equilibrium between the pressure chambers  17  and the pressure chambers  18 . The position that the inner driving slider  11  has assumed with respect to the outer driving slider  12  is not changed thereby. If, however, the electromagnetic valve  23  is opened more, the pressure in the pressure chambers  17  increases, and the inner driving slider  11  rotates anticlockwise in the illustration according to FIG. 2 relative to the outer driving slider  12 . If, because of some influence or other, the steering handwheel is held in a fixed position, the outer driving slider  12  can also rotate clockwise relative to the inner driving slider  11 . The effect is virtually the same in both cases. The desired relative displacement of inner control slider  33  to outer control slider  32  is achieved, accompanied by the desired actuation of the steering motor connected to the working connections L, R. 
     Even more pressure chambers than the illustrated eight pressure chambers are, of course, possible. Generally speaking, the maximum adjustability between inner and outer control slider is about 15°. Accordingly, the pressure chambers need be no larger circumferentially. The more pressure chambers used, the more pressure application surfaces there are available circumferentially and the larger at the same pressure can the generated torque be made. 
     The projections  15 ,  16  are rounded at their free end, that is, at the end with which they bear against the respective other driving slider  12 ,  11 . This rounding reduces wear and improves the seal.