Abstract:
Hydraulic steering ( 1 ) is disclosed comprising a high pressure port (P), a low pressure port (T), two working ports (CL, CR), a manual steering section ( 3 ), and a steering valve section having a steering valve  5  and a hydraulic driving arrangement ( 6 ) adjusting hydraulically a position of said steering valve. A change from automatic steering to manual steering should be reliably ensured when the manual steering section is directly influenced by a driver. To this end, a switching valve ( 11 ) is provided, which is actuatable between a first position in which said driving arrangement ( 6 ) is supplied with hydraulic fluid under pressure, and a second position in which a supply of hydraulic fluid to said driving arrangement ( 6 ) is interrupted, wherein said switching valve ( 11 ) is hydraulically actuated into said second position by a pressure generated upon actuating of said manual steering section ( 3 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    Applicant hereby claims foreign priority benefits under U.S.C. §119 from German Patent Application No. DE102016106793.8 filed on Apr. 13, 2016, the content of which is incorporated by reference herein. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a hydraulic steering comprising a high pressure port, a low pressure port, two working ports, a manual steering section, and a steering valve section having a steering valve and a hydraulic driving arrangement adjusting hydraulically a position of said steering valve. 
       BACKGROUND 
       [0003]    Such a hydraulic steering is known, for example, from DE 10 2006 010 695 B4. Vehicles equipped with such a hydraulic steering can either be steered via the hydraulic steering valve in an automatic mode or they can be steered via the manual steering section, for example using steering means like a steering wheel. 
         [0004]    When the vehicle is controlled via the hydraulic steering valve, the steering is performed automatically, for example by a control unit using the global positioning system (GPS). Such a functionality is, for example, important for agricultural vehicles. 
         [0005]    The operator or driver of the vehicle is basically free to use the steering valve section or the manual steering section. To this end, a selection valve can be used with which the user can choose the appropriate mode of operation. However, for safety reasons it is important that the driver can also use the manual steering section to steer the wheels, for example, in emergency situations. 
         [0006]    To this end, in DE 10 2006 010 695 B1 a steering wheel sensor is provided that can detect if the steering wheel has been turned by the driver. 
         [0007]    However, the usage of a sensor on the steering wheel has the disadvantage that such a sensor is not always reliable and increases the costs of installation and maintenance of the hydraulic steering. 
       SUMMARY 
       [0008]    The task underlying the present invention is to provide a hydraulic steering in which a change from automatic steering to manual steering can be reliably ensured when the manual steering section is directly influenced by a driver, for example by turning a steering wheel. 
         [0009]    This object is solved with a hydraulic steering as described at the outset in that a switching valve is provided, which is actuatable between a first position in which said driving arrangement is supplied with hydraulic fluid under pressure, and a second position in which a supply of hydraulic fluid to said driving arrangement is interrupted, wherein said switching valve is hydraulically actuated into said second position by a pressure generated upon actuating of said manual steering section. 
         [0010]    When the manual steering section is actuated, for example, by turning a steering wheel, a pressure is automatically generated. This pressure is necessary to actuate a steering motor which is connected to the working ports. This pressure or a pressure derived from this pressure can now be used to automatically change the position of the switching valve from the first position into the second position. In the second position the hydraulic drive arrangement for the steering valve is cut-off from a supply of hydraulic fluid so that the driving arrangement is no longer able to actuate the steering valve. In this situation the steering valve is no longer able to deliver hydraulic fluid under pressure to one of the two working ports, but the hydraulic fluid is delivered from the manual steering section only. Preferably said steering valve has means to move it into a neutral position when there are no external pressures driving the steering valve. 
         [0011]    Preferably in said second position said switching valve connects a high pressure driving port of said hydraulic driving arrangement to said low pressure port. The hydraulic driving means are not only cut-off from a supply of hydraulic fluid. The high pressure driving port of the hydraulic driving arrangement is connected to the low pressure port which leads to the situation that the high pressure driving port and the low pressure driving port of the hydraulic driving arrangement are basically on the same pressure level. Therefore, no pressure difference can be generated over the steering valve. 
         [0012]    Preferably in said second position said switching valve interrupts a connection between said steering valve and said working ports when said pressure is generated. Such an embodiment is of advantage in a case in which the steering valve needs some time to return into a neutral position. The switching valve interrupts a connection between the steering valve and the working ports so that even in this time no hydraulic fluid can reach the working ports from the steering valve. 
         [0013]    Preferably said pressure acts on an auxiliary valve, said auxiliary valve establishes a connection between said manual steering section and said working ports when said pressure is generated. When the steering is performed exclusively by means of the steering valve the manual steering section is separated from the working ports by means of the auxiliary valve. The manual steering section is not loaded by pressure produced by the steering valve. However, when it is necessary to steer the vehicle by means of the manual steering section, the auxiliary valve establishes such a connection automatically. 
         [0014]    In a preferred embodiment said steering valve comprises two driving ports, wherein each of said driving ports is connected to a return line via valve means opening in said second position of said switching valve. The driving ports are connected to the hydraulic driving arrangement as well. The hydraulic driving arrangement can be, for example, in form of a hydraulic bridge. When it is necessary to interrupt the operation of the steering valve, the pressure at the driving ports is automatically released so that the steering valve can return, for example, to a neutral position. 
         [0015]    In this case it is preferred that said return line is connected to said low pressure port by means of said switching valve when said pressure is generated. When the pressure is generated, the switching valve is moved into the second position. In the second position it connects the return line to the low pressure port so that the driving ports of the steering valve are loaded with the pressure at the low pressure port which is usually the lowest pressure in the hydraulic steering. Preferably said valve means comprise for each driving port a check valve opening away from said driving port towards said return line. A check valve automatically assumes the appropriate operating condition. When the pressure at the outlet of the check valve is lower than at the inlet of the check valve, it opens. The check valve closes when the pressure relation is opposite. When the pressure in the return line is lowered to a low pressure, for example the pressure at the low pressure port, hydraulic fluid from the driving port opens the check valve so that it can escape to the return line. 
         [0016]    Preferably said return line opens into a supply line of said driving arrangement, said supply line being connected to said low pressure port in the second position of said switching valve. This means that at least part of a line leading to the low pressure port can be used commonly to reduce the pressure in the return line and the pressure in the supply line. 
         [0017]    Preferably said steering valve is connected to a position sensor, said position sensor being connected to control means, said control means comparing a given set-value and a position value detected by said position sensor. When the control means detect a difference between the set-value and the position value detected by the position sensor, the control means know that there is an “overriding” of the steering pressure by the manual steering section. 
         [0018]    In a preferred embodiment said steering valve comprises means to return a steering valve element to a predetermined position range upon activation of said manual steering section. In this way it is possible that the control means recognize the position of the valve element inside the well-defined or pre-determined position range. In this case the control means can detect that the manual steering section has been activated and automatic steering functionality, for example by a control unit using the Global Positioning System (GPS), can be stopped. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Preferred embodiments of the invention will now be described in more detail with reference to the drawing, wherein: 
           [0020]      FIG. 1  is a schematic hydraulic circuit diagram of a first embodiment of a hydraulic steering and 
           [0021]      FIG. 2  is a schematic hydraulic circuit diagram of a second embodiment of the hydraulic steering. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  schematically shows a hydraulic circuit diagram of a hydraulic steering  1 . 
         [0023]    The hydraulic steering  1  comprises a high pressure port P, a low pressure port T, and two working ports CL, CR, which can be connected to a steering motor  2 . 
         [0024]    The hydraulic steering  1  comprises a manual steering section  3  which is known per se. The manual steering section  3  comprises a steering wheel axis  4  which can be rotated by means of a steering wheel (not shown). Upon rotating of the steering wheel axis  4  the steering motor  2  is actuated. 
         [0025]    Furthermore, the hydraulic steering  1  comprises a steering valve section comprising a steering valve  5  and a hydraulic driving arrangement  6 . The driving arrangement  6  can receive hydraulic fluid under pressure from a supply line  6   a,  as will be described later. The steering valve  5  comprises driving ports  7 ,  8  acting in opposite directions on a valve element  9  of the steering valve  5 . The driving ports  7 ,  8  are connected to the driving arrangement  6 . The driving arrangement  6  is in form of a hydraulic bridge having four branches arranged in form of a rectangle. In each branch a valve is mounted. One diagonal of the rectangle is connected to the driving ports  7 ,  8  and the other diagonal is connected to a high pressure port PE and a low pressure driving port TE. The low pressure driving port TE is connected to the low pressure port T. 
         [0026]    Other forms of a hydraulic driving arrangement  6  are possible. 
         [0027]    A selection valve  10  is provided with which the mode of operation can be selected by a driver. The operation of the selection valve  10  will be explained below. 
         [0028]    A switching valve  11  is connected between the steering valve  5  and the working ports CL, CR. The switching valve  11  can be moved between a first position and a second position.  FIG. 1  shows the second position. 
         [0029]    The steering valve  5  is connected to the high pressure port P and to the low pressure port T. Depending on the position of the valve element  9 , the steering valve  5  connects the high pressure port P to one of the working ports CL, CR and the low pressure port T to the other one of the working ports CL, CR provided that the switching valve  11  is in the first position. 
         [0030]    An auxiliary valve  12  is arranged between the manual steering section  3  and the working ports CL, CR. The auxiliary valve  12  can be moved between a first position and a second position.  FIG. 1  shows the second position of the auxiliary valve  12 . In the second position the auxiliary valve  12  connects the manual steering section  3  to the working ports CL, CR. In the first position the auxiliary valve interrupts this connection between the manual steering section  3  and the working ports CL, CR. 
         [0031]    A shock-and suction valve arrangement  13  is arranged between the two working ports CL, CR, as it is known. 
         [0032]    The switching valve  11  comprises a switching valve spring  14  acting on the switching valve  11  to move it into the second position. The auxiliary valve  12  comprises an auxiliary valve spring  15  acting on the auxiliary valve  12  to move it into the second position. 
         [0033]    The switching valve  11  comprises a first control port  16  connected to the selection valve  10 . The auxiliary valve  12  comprises a first control port  17  connected to the selection valve  10  as well. The pressures at the control ports  16 ,  17  act in a direction opposite to said springs  14 ,  15 . 
         [0034]    The auxiliary valve  12  connects in each of the two positions a load sensing port LS of the manual steering section  3  to a second control port  18  of the switching valve  11  and to a second control port  19  of the auxiliary valve  12 . The pressures at the second control ports  18 ,  19  act in the same directions as the forces of spring  14 ,  15 . 
         [0035]    The high pressure port P is connected to a first supply valve  20  and to a second supply valve  21 . First supply valve  20  comprises an output which is connected to the switching valve  11 . When the switching valve  11  is in the first position it connects the output of the first supply valve  20  to the supply line  6   a  of the high pressure driving port PE of the driving arrangement  6 . When the switching valve  11  is in the second position (shown in  FIG. 1 ) this connection is interrupted so that there is no supply of hydraulic fluid under pressure to the driving arrangement  6 . 
         [0036]    The driving port  7  of the steering valve  6  is connected to a return line  22  via a check valve  23  opening in a direction towards this return line  22 . The other driving port  8  of the steering valve  5  is connected to the return line  22  via another check valve  24  opening towards the return line  22  as well. 
         [0037]    The return line  22  is connected to the high pressure driving port PE of the driving arrangement  6 . The return line  22  is connected to the supply line  6   a.    
         [0038]    This means that the return line  22  is on the pressure level of the output of the first supply valve  20  when the switching valve  11  is in the first position so that the check valves  23 ,  24  are automatically closed, and the return line  22  is on the pressure level at the low pressure port T when the switching valve  11  is in the second position (shown in  FIG. 1 ), so that the check valves  23 ,  24  open automatically. 
         [0039]    The second supply valve  21  connects the pressure port P to an input of the selection valve  11 . 
         [0040]    Both supply valves  20 ,  21  can be used to adjust an appropriate output pressure which is lower than the pressure at the pressure port P, since the pressure at the outputs of the supply valves  20 ,  21  is used for steering purposes only. 
         [0041]    In a way known per se a pump  25  is connected via a priority valve  26  to the high pressure port P and the low pressure port T is connected to a tank  27 . 
         [0042]    The steering valve  5  is connected to a position sensor  28  which is in turn connected to control means  29  controlling the hydraulic driving arrangement  6 . 
         [0043]    The operation of the hydraulic steering  1  can be described as follows: When the selection valve  10  is in the position shown in  FIG. 1  the actuation of the steering motor  2  is performed exclusively by means of the manual steering section  3 . The steering valve  11  and the auxiliary valve  12  are both in their second position. There is no pressure (or only the pressure of the low pressure port T) at the first control ports  16 ,  17  and the force of the springs  14 ,  15  is greater than the force generated by the pressure at the control ports  16 ,  17 . 
         [0044]    When the selection valve  10  is actuated, it connects the output of the second supply valve  21  to the first control ports  16 ,  17  of the switching valve  11  and of the auxiliary valve  12  moving these two valves  11 ,  12  in their first positions. 
         [0045]    As mentioned above, in the first position of the auxiliary valve  12  a connection between the manual steering section  3  and the working ports CL, CR is interrupted. A connection between the steering valve  5  and the working ports CL, CR is established by the steering valve  5 . The control means  29  control the position of the steering valve  5  as desired, for example, in response to data obtained from a Global Positioning System (GPS). 
         [0046]    When the selection valve  10  is in the position just described to select a steering mode performed by the steering valve  5  and the operator nevertheless operates the manual steering section  3 , a pressure is generated at the load sensing port LS. This pressure automatically moves the auxiliary valve  12  in the second position shown in  FIG. 1  and at the same time moves the switching valve  11  in the second position shown in  FIG. 1  as well. This movement or switching of the switching valve  11  has the following effects: 
         [0047]    The connection between the steering valve  5  and the working ports CL, CR is interrupted. Furthermore, a connection between the first supply valve  20  and the high pressure driving port PE of the driving arrangement  6  is interrupted and at the same time a connection between the high pressure driving port PE and the low pressure port T is established. This means that the hydraulic driving arrangement  6  does no longer receive hydraulic fluid under pressure so that the hydraulic driving arrangement  6  is no longer able to move the valve element  9  of the steering valve  5 . The steering valve  5  is equipped with restoring springs moving the valve element  9  of the steering valve  5  into the neutral position. At the same time the pressure in the return line  22  and the pressure at the high pressure driving port PE are lowered to the pressure at the low pressure port T so that the check valves  23 ,  24  open to release the pressure at the drive ports  7 ,  8  of the steering valve  5 . Such a release or “venting” establishes very fast the desired pressure conditions over the steering valve  5 . 
         [0048]    In the embodiment shown in  FIG. 1  the manual steering section  3  comprises a closed center steering unit  30  or any other steering unit having a load sensing port LS. 
         [0049]      FIG. 2  shows an embodiment with a manual steering section  3  having an open center steering unit  31 . 
         [0050]    The same elements as in  FIG. 1  are described with the same reference numerals. 
         [0051]    The pump  25  is connected to the high pressure port P. A priority valve  26  is arranged between the high pressure port P and the steering valve  11 . 
         [0052]    When the open center steering unit  31  is in neutral position, there is a permanent flow from the high pressure port P to the low pressure port T of the manual steering section  3 . When the steering wheel axis  4  is rotated, this flow is throttled so that a pressure at a second output  32  of priority valve  26  increases. The increased pressure reaches the second control ports  18 ,  19  of the switching valve  11  and of the auxiliary valve  12  to move them into the second position. The operation of this embodiment is the same as of the embodiment shown in  FIG. 1 . 
         [0053]    In both embodiments, the steering valve  5  is connected to a position sensor  28 . The position sensor  28  detects the position of the valve element  9  of the steering valve  5  and transmits this position value to control means  29 . Control means  29  compares the position detected by the position sensor  28  with a set-value given by an automatic steering system, for example on basis of GPS-data. The control means controls the hydraulic driving arrangement  6  accordingly. 
         [0054]    When the steering is taken over by the manual steering section  3 , there will be a difference between the value detected by the position sensor  28  and the given set-value. This control means  29  detects that it is not possible to minimize this difference. This is a reliable indication that the steering is performed by the manual steering section  3 . 
         [0055]    The steering valve  5  comprises means  33 ,  34  to return the steering valve element  9  to a predetermined position range upon activation of said manual steering section  3 . By having the control means  29  recognizing the position of the valve element  9  inside the well-defined or predetermined position range, activation of the manual steering section  3  can be said to have happened and automatic steering functionality, for example, by a control unit using the Global Positioning System (GPS), can be stopped. 
         [0056]    The return means  33 ,  34  can be in form of springs, for example. 
         [0057]    To avoid unclear situations, for example that the steering valve element  9  is in the neutral position and the control means  29  cannot decide if the manual steering section  3  has been activated, the steering valve element  9  is controlled to have a position some distance away from neutral position but without outputting any flow to the steering motor  2 . If the steering valve element  9  is then put in real neutral position, the control means knows that the manual steering section has been activated. 
         [0058]    While the present disclosure 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 disclosure may be made without departing from the spirit and scope of the present disclosure.