Abstract:
The invention concerns a hydraulic steering arrangement ( 1 ) with a supply connection arrangement having at least a high-pressure connection (P) and a low-pressure connection (T), a working connection arrangement having at least two working connections (L, R), a steering unit ( 7 ), which can be activated by a steering transducer ( 2 ), the steering unit having a first load-sensing connection (LS 1 ), and a steering valve ( 8 ) having a second load-sensing connection (LS 2 ), the steering unit ( 7 ) and the steering valve ( 8 ) being arranged in parallel with each other between the supply connection arrangement and the working connection arrangement. It is endeavoured to ensure a good steering behaviour. For this purpose, a priority valve ( 12 ) is connected in series with the high-pressure connection (P), said priority valve ( 12 ) having a third load-sensing connection (LS 3 ), which is connected with the first load-sensing connection (LS 1 ) via a pipe ( 23 ), in which is located a control valve ( 24 ) that can be activated by the second load-sensing connection (LS 2 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Applicant hereby claims foreign priority benefits under U.S.C. § 119 from German Patent Application No. 10 2004 061 077.0 filed on Dec. 18, 2004, the contents of which are incorporated by reference herein.  
       FIELD OF THE INVENTION  
       [0002]     The invention concerns a hydraulic steering arrangement with a supply connection arrangement having at least a high-pressure connection and a low-pressure connection, a working connection arrangement having at least two working connections, a steering unit, which can be activated by a steering transducer, the steering unit having a first load-sensing connection, and a steering valve having a second load-sensing connection, the steering unit and the steering valve being arranged in parallel with each other between the supply connection arrangement and the working connection arrangement.  
       BACKGROUND OF THE INVENTION  
       [0003]     Such a steering arrangement is, for example, known from DE 102 57 130 A1. In common, the steering unit and the steering valve can act upon a steering motor. This has the advantage that the steering unit, which is usually provided with a measuring motor, can have smaller dimensions. The measuring motor, which is used for activating the steering motor on failing supply pressure, can then be activated with smaller force expenditure.  
         [0004]     A similar embodiment of a steering arrangement is known from EP 1 447 307 A2. Also here, the steering motor can be activated by the steering unit or the steering valve or both in common.  
         [0005]     When such a steering arrangement is now used in a vehicle, which additionally has other hydraulic consumers, for example working hydraulics, it is difficult to ensure the “correct” supply for the steering arrangement. Under certain circumstances, this can cause a somewhat problematic steering behaviour.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The invention is based on the task of ensuring a good steering behaviour.  
         [0007]     With a hydraulic steering arrangement as mentioned in the introduction, this task is solved in that a priority valve is connected in series with the high-pressure connection, said priority valve having a third load-sensing connection, which is connected with the first load-sensing connection via a pipe, in which is located a control valve that can be activated by the second load-sensing connection.  
         [0008]     With such an embodiment, it is firstly ensured that the steering arrangement on a whole is supplied with the required pressure via the priority valve. The priority valve has a priority outlet, which is connected with the high-pressure connection of the steering unit. The priority outlet is the outlet, which has higher priority in being supplied with pressurised hydraulic fluid. The working hydraulics, however, is located at an outlet, which has low priority in being supplied with hydraulic fluid. For this purpose, the priority valve often has a slide, which is exposed to a control pressure. This control pressure, for example, corresponds to the pressure at the third load-sensing connection. When, now, the first load-sensing connection, that is, the load-sensing connection at the steering unit, is connected with the third load-sensing connection, that is, the load-sensing connection at the priority valve, the priority valve receives information about the load state at the steering unit. When, then, a control valve is built into this connection, said control valve being controlled via the pressure at the second load-sensing connection, that is, at the load-sensing connection of the steering valve, the priority valve can also receive information about the pressure at the load-sensing connection of the steering valve. Thus, when the steering valve is activated, also the pressure at the third load-sensing connection increases, so that also in this case the priority valve can be activated accordingly.  
         [0009]     Preferably, the control valve forms a throttle, whose resistance can be changed by the pressure at the second load-sensing connection. This is a relatively simple way of reporting a load change at the steering valve to the priority valve. A supply of hydraulic fluid from the second lad-sensing connection into the connection between the first and the third load-sensing connections is not required.  
         [0010]     Preferably, the priority valve has a connection between its priority outlet and the third load-sensing connection, in which a throttle arrangement is located. Thus, the priority valve is a “dynamic” priority valve, which can react relatively fast to load changes. The throttle arrangement prevents an unthrottled outlet of hydraulic fluid from the priority outlet to the load-sensing connection. However, it permits a relatively fast passing on of pressures from the priority outlet to the third load-sensing connection.  
         [0011]     It is preferred that the throttle arrangement has a central outlet, whose pressure acts upon a control slide in a direction, in which the priority outlet is connected with the pressure inlet. Thus, a pressure divider is formed between the priority outlet and the third load-sensing connection, so that the pressure acting upon the control slide of the priority valve is somewhat higher than the pressure at the third load-sensing connection. This further improves the response time of the priority valve without significantly stressing the load-sensing system, which is located at the load-sensing connections.  
         [0012]     Preferably, the second load-sensing connection is connected with the high-pressure connection via a bleed. Thus, it can be ensured that the second load-sensing connection is always supplied with sufficient pressure.  
         [0013]     It is preferred that in the neutral position of the steering valve, the second load-sensing connection is connected with the low-pressure connection. As long as the steering valve is in the neutral position, the pressure at the second load-sensing connection corresponds to the pressure at the low-pressure connection, that is, usually the tank pressure. As soon as the steering valve is displaced from its neutral position, the high-pressure connection immediately supplies pressure via the bleed, which pressure can then be used for controlling the control valve.  
         [0014]     Preferably, the first load-sensing connection is connected with a pressure switch, which changes over, when a predetermined pressure is exceeded. When interventions in the connection between the first load-sensing connection and the third load-sensing connection are made with the control by means of the control valve on the basis of the pressure at the second load-sensing connection, a very stable pressure in the pipe between the control valve and the first load-sensing connection is achieved. Thus, the switching time of the pressure switch is very easily defined. Such a pressure switch can be used for various purposes.  
         [0015]     Particularly preferred, however, is that the pressure switch is connected with a control device, which controls the steering valve. When the pressure switch is activated, the control device “knows” that the steering unit has an increased pressure requirement. The control device can then control the steering valve accordingly.  
         [0016]     In a preferred embodiment, it is ensured that the control device controls the steering valve to its neutral position, when the predetermined pressure is exceeded. Such an embodiment is, for example, advantageous, when the vehicle equipped with the steering arrangement is remote controlled, and the steering valve is used for this purpose. When, now, the user activates the steering unit, for example via the steering handwheel or another steering means, the steering unit shall apparently have priority in the steering of the vehicle. Therefore, the control through the steering valve is postponed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     In the following, the invention is described on the basis of a preferred embodiment in connection with the drawing, showing:  
         [0018]      FIG. 1  is a schematic view of a steering arrangement. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     A steering arrangement  1  exists in the form of a fully hydraulic steering; no active mechanical connection exists between a steering handwheel  2  or another steering means and steered wheels  3 , which can be deflected by a steering motor  4 .  
         [0020]     Such a fully hydraulic steering arrangement  1  is known per se. It has a supply connection arrangement with a high-pressure connection P and a low-pressure connection T. Further, it has a working connection arrangement with two working connections L, R, to which the steering motor  4  is connected.  
         [0021]     Via a directional valve  5 , which can be activated by means of the steering handwheel  2 , the steering motor  4  is supplied with pressurised hydraulic fluid. In a manner known per se, the directional valve  5  consists of two slides, which can be reset to a neutral position by a measuring motor  6 , through which the hydraulic fluid supplied to the steering motor flows, when the wheels  3  have reached a turning angle corresponding to the deflection of the steering handwheel  2 . The directional valve  5  and the measuring motor  6  are essential components in a steering unit  7 .  
         [0022]     Further provided is a steering valve  8  in the form of a proportional valve. The steering valve  8  is located in parallel with the steering unit  7  between the supply connection arrangement P, T and the working connection arrangement L, R. The steering valve  8  has an auxiliary force actuated drive  9 , for example an electric magnet, which can be activated by a control device  10 . In a manner not shown in detail, the control device  10  can be connected to an instruction transmitter, for example a joystick. However, it can also be connected with a sensor at the shaft  11  of the steering handwheel  2  and with a steering angle sensor, not shown in detail, at the steering motor  4 , for example to support the steering unit  7  when steering the wheels.  
         [0023]     In front of the high-pressure inlet P of the steering arrangement  1  is located a priority valve  12 , having a priority outlet CF, which ensures a higher priority supply to the steering arrangement  1  of pressurised hydraulic fluid from an inlet P 0  of the priority valve  12 , when an corresponding demand occurs. Further, the priority valve  12  has an outlet EF, which is connected with a merely schematically shown working hydraulics  13 . The outlet EF receives a lower priority supply of pressurised hydraulic oil, that is, only when the steering arrangement  1  has not corresponding demand.  
         [0024]     The steering unit  7  has a first load-sensing connection LS 1 , which is connected with the low-pressure connection T in the neutral position of the directional valve  5 .  
         [0025]     The steering valve  8  has a second load-sensing connection LS 2 , which is connected with the high-pressure connection P via a bleed  14 . In many cases, the bleed  14  can be avoided. In this case, a “static” steering valve is achieved. In the neutral position of the steering valve  8 , the second load-sensing connection LS 2  is connected with the low-pressure connection T via non-return valves  15 , which are located in the slide  16  of the steering valve  8 . In the neutral position of the steering unit  7 , that is, in the neutral position of the steering valve  5 , the pressure at the low-pressure connection, that is, usually the tank pressure, rules at the first load-sensing connection LS 1 . Accordingly, in the neutral position of the steering valve  8 , the pressure at the low-pressure connection T also rules at the second load-sensing connection LS 2 .  
         [0026]     The priority valve  12  is provided with a third load-sensing connection LS 3 . Via a throttle arrangement comprising two throttles  17 ,  18 , a central outlet  19  of the third load-sensing connection LS 3  is connected with the priority outlet CF of the priority valve  12 .  
         [0027]     The priority valve  12  has a slide  20 , whose one front side is connected with the priority outlet CF via a throttle  21 . Upon the opposite front side of the slide  20  acts the pressure at the central outlet  19  between the two throttles  17 ,  18 . Additionally, a spring  22  acts in the direction of this pressure, said spring positioning the slide  20 so that it connects the pressure inlet P 0  of the priority valve  12  with the priority outlet CF.  
         [0028]     The third load-sensing connection LS 3  is connected with the first load-sensing connection LS 1  via a pipe  23 . In this pipe  23  is located a control valve  24  having a control inlet  25 , which is connected with the second load-sensing connection LS 2 . The control valve  24  can be a valve, whose design is in principle known from the valve PVFC of Sauer-Danfoss ApS, Nordborg, Denmark. This valve throttles the cross-section of the pipe  23  more or less, in dependence of the position of its slide.  
         [0029]     Via a spring  26 , the control valve  24  is prestressed in the closing direction or the throttling direction, via a control pipe  27  that is connected with the third load-sensing connection LS 3 , however, loaded in the opening direction.  
         [0030]     In a preferred embodiment, the control valve  24  and the steering valve  8  are combined in one component, that is, they have, for example, the same housing.  
         [0031]     An overpressure valve  28  in the pipe  23  ensures that excessively high pressures of the third load-sensing connection LS 3  are carried off.  
         [0032]     With the first load-sensing connection LS 1  is connected a pressure switch  29 , which again is connected with the control device  10 . The pressure switch  29  closes, when a predetermined pressure at the first load-sensing connection LS 1  is exceeded. This can, for example, be used to moving the steering valve  8  into the neutral position shown, when the pressure at the first load-sensing connection LS 1  exceeds the predetermined limit.  
         [0033]     It is also possible that the control valve  24  closes completely. In this case, however, the pressure switch is not active.  
         [0034]     The steering arrangement  1  works as follows:  
         [0035]     In the neutral position of the steering unit  7 , the first load-sensing connection LS 1  is, as shown, connected with the low-pressure connection T. Accordingly, a certain, small fluid amount from the pressure inlet P 0  of the priority valve  12  currently flows off to tank via the priority outlet CF and the third load-sensing connection LS 3  of the priority valve  12 . Due to the pressure in the control pipe  27 , the control valve  24  is open, so that practically the same pressures rule at the first load sensing connection LS 1  and the third load-sensing connection LS 3 . Load-sensing pressures from the working hydraulics  13  are disconnected from the pipe  23  via a shuttle valve  30 .  
         [0036]     When, now, the steering unit  7  is activated, the pressure at the first load-sensing connection LS 1  increases, so that the slide  20  of the priority valve  12  is at any rate displaced to the priority position shown, in which the priority outlet CF is preferably supplied with pressure fluid.  
         [0037]     When, now, the steering valve  8  is activated, the pressure at the second load-sensing connection LS 2  increases. This causes that the control valve  24  increasingly throttles the connection between the third load-sensing connection LS 3  and the first load-sensing connection LS 1 , so that the fluid, which should like to flow from the third load-sensing connection LS 3  to the first load-sensing connection LS 1 , is throttled in the control valve  24 . This leads to a corresponding pressure increase at the third load-sensing connection LS 3 , which also causes that the slide  20  of the priority valve  12  is displaced to or retained in the priority position shown. Also when activating the steering valve  8 , it is thus possible in a simple manner to receive the working pressure required at the high-pressure connection P from the priority valve  12 .  
         [0038]     When the steering arrangement  1  is set so that the vehicle can also be controlled merely via the steering valve  8 , for example, by a remote control, a user, however, wishing to interfere manually in the steering by activating the steering unit  7 , the following situation occurs:  
         [0039]     The connection between the third load-sensing connection LS 3  and the first load-sensing connection LS 1  is throttled, but not interrupted, by the control valve  24 . Accordingly, still a small amount of fluid flows to the first load-sensing connection LS 1  and off to the low-pressure connection T via the directional valve  5 . When, now, the directional valve  5  is moved, the connection between the load-sensing connection LS 1  and the low-pressure connection T is interrupted and the pressure at the first load-sensing connection LS 1  increases. This pressure increase is detected by the pressure switch  29 , which switches over and reports this to the control device  10 . The control device  10  is then able to move the control valve  8  back into the neutral position shown.  
         [0040]     With the steering arrangement  1  an internal shuttle valve is not required, which passes on the load-sensing pressures from the steering unit  7  or the steering valve  8 . Additional bleeds or throttles are not required either, except for the bleed  14 . Thus, the steering arrangement has a relatively simple design.  
         [0041]     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.