Abstract:
The invention concerns a hydraulic steering arrangement with a hydraulically actuated steering valve arrangement, steering motor connections (CL, CR), which are connected to supply connections (HP, T) via the steering valve arrangement, and a steering unit. It is endeavoured to equalize in a simple manner the steering behaviour in both directions. For this purpose, it is ensured that the steering valve arrangement has a directional valve and a flow control valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Applicant hereby claims foreign priority benefits under U.S.C. § 119 from German Patent Application No. 10 2005 033 576.4 filed on Jul. 19, 2005, the contents of which are incorporated by reference herein.  
       FIELD OF THE INVENTION  
       [0002]     The invention concerns a hydraulic steering arrangement with a hydraulically actuated steering valve arrangement, steering motor connections, which are connected to supply connections via the steering valve arrangement, and a steering unit.  
       BACKGROUND OF THE INVENTION  
       [0003]     Such steering arrangements are, for example, known from DE 10 2004 027 971 A1. When a driver of a vehicle provided with such a steering arrangement wishes to steer the vehicle, he activates the steering unit. In dependence of the actuation of the steering unit, hydraulic pressures are generated, which activate the steering valve arrangement, thus releasing a flow path from the supply connections to the steering motor.  
         [0004]     It has now been observed that in many cases there are differences in the steering behaviour of such steering arrangements, in dependence of whether steering is made to the left or to the right. Often, the driver finds this unpleasant.  
         [0005]     This phenomenon could be remedied in that the production accuracy is increased and that all areas, channels, pressure admission surfaces etc., which are important for the determination of the flow of the hydraulic fluid, were made as equal as possible. However, the required production efforts would be substantial.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The invention is based on the task of equalising the steering behaviour in a simple manner.  
         [0007]     With a hydraulic steering arrangement as mentioned in the introduction, this task is solved in that the steering valve arrangement has a directional valve and a flow control valve.  
         [0008]     This embodiment provides a simple manner of ensuring a substantially improved equality of the steering behaviour in both steering directions. In many cases, the result will even be exactly equal steering behaviours. The function of the amount setting will be taken over by the flow control valve. Independently of the direction, in which the vehicle is steered, the flow control valve supplies the amount of hydraulic fluid defined by the driver via the actuation of the steering unit. The directional valve only determines the direction, in which the vehicle shall be steered. The influence, which the directional valve takes on the flow amount of hydraulic fluid, can be heavily reduced or even eliminated.  
         [0009]     Preferably, the directional valve is placed after the flow control valve in the direction from the supply connections to the steering motor connections. This gives a substantial simplification of the piping arrangement.  
         [0010]     Preferably, a control inlet arrangement of the directional valve is connected to the steering unit and a control inlet of the flow control valve is connected to the directional valve. Thus, the flow control valve is controlled through the directional valve. This has the advantage that it can be ensured in a simple manner that an actuation of the steering unit will cause the directional valve to respond and be actuated first. The flow control valve is not actuated until the direction has been established. This permits a very simple design of the directional valve. It no longer has to be ensured that here throttling spots open gradually to permit a jerk-free steering. On the contrary, the directional valve can practically be an “on-off” valve. The flow control including a controlled opening of throttling spots can be taken over by the flow control valve.  
         [0011]     Preferably, the flow control valve has a larger activation pressure than the directional valve. Also with this measure it is ensured that the directional valve is actuated earlier, that is, at a lower pressure, than the flow control valve. The directional valve is in any case open in one direction or the other, when the flow control valve starts leading hydraulic fluid to the working connections.  
         [0012]     Preferably, the steering unit has a manually actuated control device, which has a pressure connection and two directional connections, the pressure connection being connected to a pressure source arrangement by means of a pipe path led through the flow control valve. The steering unit can, for example, be a unit of the type “OSP” from Sauer-Danfoss ApS, Nordborg, Denmark. Depending on the actuation of a steering handwheel, such a steering unit measures a certain amount of hydraulic fluid, which is supplied via the pressure connection and leads it on via one of the directional connections to the directional valve. Such a steering unit can also be used as emergency steering pump, when the hydraulic supply pressure fails, for example, when the drive motor of the vehicle fails, which motor also drives a hydraulic pump.  
         [0013]     It is preferred that in the area of an end position of the flow control valve, which permits a maximum supply flow to the steering motor connections, the pipe path is throttled. This throttling can also be so extensive that the pipe path is closed. In this case, the driver receives a signal via the steering handwheel. In this case, the steering handwheel can namely only be turned with an increased torque. The driver then feels that the vehicle is more difficult to steer. Then the driver knows that the flow control valve is in the maximum opening position and that a higher steering speed is not longer possible.  
         [0014]     Preferably, a change-over valve is located between the directional valve and the flow control valve, the outlet of the change-over valve being connected to a supply inlet of the directional valve, the supply inlet being connected to one of the two steering motor connections in dependence of an actuation device of the directional valve, a first inlet of the change-over valve being connected to a pressure outlet of the flow control valve and a second inlet of the change-over valve being connected to the steering unit via the directional valve. This embodiment is particularly advantageous, when the steering unit is used as an emergency steering pump during a failure of the hydraulic pump. The change-over valve then ensures that the hydraulic fluid from the emergency steering pump no longer has to be led via the flow control valve to the steering motor connections, but can be led to the steering motor connections directly via the change-over valve and through the directional valve.  
         [0015]     It is also preferred that the directional valve and the flow control valve each have a slide. The use of slide valves in steering devices has proved to be good. An axial displacement of the slides permits a simple setting of the different positions of the valves.  
         [0016]     Preferably, a supply connection connected to a tank has a pre-set non-return valve opening in the direction of the tank. Thus it is ensured that in the hydraulic system of the steering unit a predetermined minimum pressure is always maintained. This minimum pressure is determined by the presetting of the non-return valve. It can, for example, be in the range from 4 to 5 bar.  
         [0017]     It is also advantageous, when the steering unit has an electrically actuated control valve. This control valve can be provided alternatively or additionally to the mechanically actuated steering unit. The control valve can, for example, be an electrically actuated proportional valve of the type PVE from Sauer-Danfoss ApS, Nordborg, Denmark.  
         [0018]     It is preferred that the steering unit and the control valve are connected to the control inlet of the directional valve via a change-over valve arrangement. Thus, the directional valve always reacts to the higher of the two pressures from control valve and steering unit. When the outlet pressure of the control valve is limited, it can thus be ensured in a simple manner that the steering via a steering handwheel and the steering unit always has priority over the steering with the control valve.  
         [0019]     It is also advantageous that the control valve is connected to the control inlet of the flow control valve, the flow control valve being connected to the control valve via a feed-back unit. Thus, the flow control valve is no longer controlled through the directional valve. However, via the feed-back unit, for example a position sensor, which reacts to the slide of the flow control valve, it can always be ensured that the flow control valve permits the flow of hydraulic fluid to the steering motor connections in the desired manner. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     In the following, the invention is described by means of preferred embodiments in connection with the drawings, showing:  
         [0021]      FIG. 1  is a first embodiment of a hydraulic steering arrangement.  
         [0022]      FIG. 2  is a second embodiment of a hydraulic steering arrangement. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIG. 1  shows a hydraulic steering arrangement  1  with steering motor connections CL, CR and supply connections HP, T. Additionally a load-sensing connection LS is provided at the supply connections HP, T.  
         [0024]     A steering motor can be connected to the steering motor connections CL, CR, said motor being used for steering a vehicle, not shown in detail. A pump  2  is connected to a high-pressure connection HP, the pump  2  being driven by a motor  3 , for example the drive motor of the vehicle. The other supply connection T ends in a tank  4 .  
         [0025]     The steering arrangement  1  has a steering valve arrangement  5 , which both determines a deflection direction and a deflection speed of the steered members of the vehicle.  
         [0026]     The steering valve arrangement has a directional valve  6  with a directional valve slide  7 . In a neutral position, the directional valve slide is loaded by two springs  8 ,  9 . The springs  8 ,  9  define an actuation pressure, which is, for example, in the range from 3 to 5 bar.  
         [0027]     The steering valve arrangement  5  further has a flow control valve  10  with a flow control valve slide  11 , which can be moved against the force of a spring  12 . The force of the spring  12  corresponds to a pressure of approximately 5 to 10 bar. At any rate, the force of the spring  12  is larger than the force of the springs  8 ,  9 .  
         [0028]     The supply connection HP is connected to a priority valve  13 , which has three outlets  14 ,  15 ,  16 , the outlet  16  being connected to an inlet EF, through which further hydraulic consumers can be supplied.  
         [0029]     A hydraulic steering unit  17 , for example a steering unit OSP of Sauer-Danfoss ApS, Nordborg, Denmark, can be actuated via a steering handwheel  18 . The steering unit  17  has a connection PS, through which the steering unit  17  is supplied with pressurised hydraulic fluid, as will be explained overleaf.  
         [0030]     Further, the steering unit has a connection TS, which is connected to the supply connection T, as will also be explained overleaf.  
         [0031]     The steering unit  17  has a first directional connection L and a second directional connection R. The directional connection L is connected twice with the directional valve  6 . Firstly, the directional connection L is connected to a control inlet  19 , through which the pressure from the directional connection L acts upon the slide  7 . Secondly, the directional connection L is connected to a first directional inlet  20  of the directional valve  6 .  
         [0032]     In a similar manner, a second directional inlet R of the steering unit  17  is connected to a control inlet  21 , through which pressure acts upon the slide  7  of the directional valve  6 , und with a second directional inlet  22 .  
         [0033]     The directional valve  6  has a first directional outlet  23 , which is connected to the steering motor connection CL, and a second directional outlet  24 , which is connected to the steering motor connection CR.  
         [0034]     The directional valve  6  has a control outlet  25 , a return flow outlet  26  and a supply inlet  27 .  
         [0035]     The flow control valve  10  has a pressure inlet  28 , which is connected to the second outlet  15  of the priority valve. As soon as the slide  11  of the flow control valve  10  is actuated, the pressure inlet  28  is connected to a pressure outlet  29 , which is connected to a first inlet  30  of a change-over valve  31 , whose outlet is connected to the supply inlet  27  of the directional valve  6 .  
         [0036]     The return flow outlet  26  of the directional valve  6  is connected to a return flow inlet  32  of the flow control valve  10 , which is connected to a return flow connection  33  of the flow control valve  10 , as soon as the slide  11  of the flow control valve  10  is actuated. The return flow connection  33  is connected to the connection TS of the steering unit  17 . This connection TS is connected to the supply connection T and thus with the tank  4  via a prestressed non-return valve  34 . The non-return valve  34  has a prestressing spring  35 , which, for example, ensures a minimum pressure at the connection TS of 4.5 bar.  
         [0037]     The control outlet  25  of the directional valve is firstly connected to the second inlet  36  of the change-over valve  31 . Secondly, it is connected to a control inlet  38  of the flow control valve  10  via a pipe  37 . A pressure at the control inlet  38  acts against the force of the spring  12 . Finally, the control inlet  25  is also connected to an inlet  39  of the flow control valve  10 , which is, on actuation of the slide  11 , connected to an outlet  40 , which is connected to the connection TS via a stop valve  41 , which can be closed by a pressure at the pressure outlet  29  of the flow control valve  10 .  
         [0038]     The first outlet  14  of the priority valve  13 , which is throttled (see throttle  42 ) in the shown position of the priority valve  13 , in which merely the steering arrangement  1  is supplied with hydraulic fluid, is connected to the outlet PS of the steering unit  17  via a pipe path  43 , which is formed in the flow control valve  10 . The pipe path  43  remains open over the largest share of the movement of the slide  11  of the flow control valve  10 . Merely in the area of an end position, in which the flow control valve  10  permits passing of the maximum amount of hydraulic fluid, the pipe path  43  is interrupted, so that hydraulic fluid can no longer be supplied to the connection PS of the steering unit  17  via this pipe path  43 .  
         [0039]     In a manner known per se, the second outlet  15  of the priority valve is connected to the load sensing connection LS.  
         [0040]     Further shown are some anti-cavitation valves, overpressure valves and pressure control valves, which will not be explained in detail, as they are known per se.  
         [0041]     When, now, the steering handwheel  18  is turned, for example to turn the vehicle to the right, the steering motor connection CR must be supplied with pressurised hydraulic fluid. To manage this, the steering unit  17  provides a pressure on the control inlet  21  of the directional valve  6  via the directional outlet R, which displaces the slide  7  to the left (in relation to the view in  FIG. 1 ). Thus, the pressure from the second directional inlet  22  reaches the control outlet  25 . At the same time, the first directional outlet  23 , which is connected to the steering motor connection CL, is connected to the return flow outlet  26 , from which hydraulic fluid can flow off via the flow control valve  10 , as soon as this valve has opened.  
         [0042]     The pressure at the control outlet  25  is led to the control inlet  38  of the flow control valve  10 , where it displaces the slide  11 , also to the left. Thus, the pressure inlet  28  is connected to the pressure outlet  29 , and the hydraulic fluid leaving here reaches the second directional outlet  24  via the change-over valve  31  and the supply inlet  27  of the directional valve  6 , and from here to the steering motor connection CR. In this connection, the position of the slide  11  of the flow control valve  10  determines the amount of hydraulic fluid supplied to the steering motor connection CR.  
         [0043]     As soon as the slide  11  of the flow control valve  10  has been displaced to an end area, in which the maximum flow of hydraulic fluid is released, the pipe path  43  is interrupted and via a non-return valve  44 , the connection PS of the steering unit  17  receives merely the share of the hydraulic fluid returning from the steering motor connection CL. The result of this is that it gets harder to turn the steering handwheel  18  und this signals to the driver that the maximum steering speed has been reached.  
         [0044]     If, on the other hand, the vehicle is steered in the opposite direction, the steering unit  17  supplies a pressure via the directional outlet L, which then acts upon the first control inlet  19  of the directional valve  6  and displaces the slide  7  to the right. Thus, the pressure from the first directional inlet  20  reaches the control outlet  25  of the directional valve and the flow control valve  1   o  is controlled in the same way as before, when steering to the right.  
         [0045]     If the motor  3  should fail, accordingly not being able to supply the pump  2 , the steering unit  17  can be used as emergency steering pump. In this case, the pressure supplied via the directional input  20 ,  22 , which is also distributed via the control outlet  25 , is passed on to the second inlet  36  of the change-over valve  31 . As, at the first inlet  30  of the change-over valve  31  no pressure is available (the pump  2  does not work and the flow control valve  10  is closed), the pressure from the directional outlet L, R of the steering unit  17  is then led on to the corresponding directional outlet  23 ,  24  of the directional valve  6 .  
         [0046]     The stop valve  41  can be used to create a fixed stop for the movement of the steering handwheel  18 , when the corresponding steering cylinder (or another working motor) is in the end position.  
         [0047]     The spring preload of the stop valve  41  is smaller than the spring preload of the priority valve  13 . This causes that during normal operation the stop valve  41  is open. When, however, the steering cylinder is in an end position, the pressure increases. A pilot valve in the LS-pipe opens for the load-sensing pressure to the tank. The non-return valve in the load-sensing pipe prevents a return flow and a pressure difference occurs over this non-return valve, which corresponds to the spring preload of the priority valve  13 . As the stop valve  41  is controlled by the pressure difference over this non-return valve, and as, in the end position of the steering cylinder, this pressure difference exceeds the spring preload of the stop valve  41 , the stop valve  41  goes to the closed position. As now the path of the pilot fluid to the tank  4  is blocked, the steering wheel torque at the steering unit  17  will increase and the driver will feel this as a fixed stop.  
         [0048]      FIG. 2  shows a modified embodiment of a steering arrangement  1 , in which the same elements have the same reference numbers as in  FIG. 1 . As, to a large extent, the steering arrangement  1  according to  FIG. 2  corresponds to the steering arrangement according to  FIG. 1 , merely the differences will be explained here.  
         [0049]     Additionally to the steering unit  17 , the steering arrangement  1  has an electrically actuated control valve  45 , for example an electrically actuated proportional valve of the type PVE from Sauer-Danfoss ApS, Nordborg, Denmark.  
         [0050]     The control valve PVE has a directional outlet ER for steering the vehicle to the right, a directional outlet EL for steering the vehicle to the left, a tank outlet ET and a pump inlet EP. The pump inlet EP is connected to the priority valve  13  by way of the second outlet  15 . The tank outlet ET is connected to the point TS.  
         [0051]     The directional outlet ER is connected to the control inlet  21  of the directional valve  6  via a change-over valve  46 , thus controlling the slide  7  so that a path to the steering motor connection CR is released. Further, the directional connection ER is connected to the control inlet  38  of the flow control valve  10  via a change-over valve  47 .  
         [0052]     In a similar manner, the directional outlet EL of the control valve  45  is connected to the control inlet  19  of the directional valve  6  via a change-over valve  48 . Further, the directional outlet EL is connected to the control inlet  38  of the flow control valve  10  via the change-over valve  47 .  
         [0053]     The mode of operation is like that of the steering arrangement according to  FIG. 1 . Depending on whether the steering unit  17  or the control valve  45  supplies the higher pressure, the directional valve  6  is actuated via the steering unit  17  or the control valve  45 . When the steering unit  17  supplies a higher pressure than the control valve, also the flow control valve  10  is controlled by the steering unit  17 . For this purpose, a non-return valve  49  is provided in the pipe between the control outlet  25  of the directional valve  6  and the control inlet  38 , before a point, in which the outlet of the change-over vale  47  ends in this control pipe  37 .  
         [0054]     Via a position transducer  50 , the slide  11  of the flow control valve  10  is connected to the control valve  45 . Thus, at any time the control valve  45  is able to control a pressure at the directional outlets ER, EL in such a manner that the desired amount of hydraulic fluid flows to the selected steering motor connection CR, CL.  
         [0055]     While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present invention.