Abstract:
The invention concerns a hydraulic steering ( 1 ) comprising a supply connection arrangement, a steering motor ( 2 ), a high pressure supply (P), and a steering unit ( 3 ) arranged between the supply connection arrangement (S) and the steering motor ( 2 ), the supply connection arrangement comprising a steering valve ( 9 ), and a valve arrangement ( 27 ). The task of the hydraulic steering is to improve the safety and faults detection over the state of the art. For this purpose, the steering valve ( 9 ) is only deflectable if the valve arrangement ( 27 ) is deflected.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     Applicant hereby claims foreign priority benefits under U.S.C. §119 from European Patent Application No. 13000506.9 filed on Feb. 1, 2013, the contents of which are incorporated by reference herein. 
     TECHNICAL FIELD 
     The invention relates to a hydraulic steering comprising a supply connection arrangement, a steering motor, a high pressure supply, and a steering unit between the supply connection arrangement and the steering motor, the supply connection arrangement comprising a steering valve, a stop valve and a valve arrangement. The invention further relates to a method for detecting the position of at least one first valve by activating a second valve. 
     BACKGROUND 
     Such a hydraulic steering is, for example, known from DE 10 2007 053 024 B4. A vehicle equipped with such a steering can either be steered via the steering unit comprising a directional section, or via the steering valve. The driver will then usually activate a steering member, for example a steering hand wheel. When the driver steers the vehicle by means of the steering unit, in many cases a so called reaction behavior is desired, that is, the driver must feel through the steering hand wheel that forces are acting upon the steering motor. 
     However, this reaction behavior causes problems, if the vehicle is steered by means of the steering valve. Thus, in the state of the art for each steering direction the directional section comprises a first outlet, which is connected to the steering motor by means of a first pipe, and a second outlet, which is connected to the steering motor by means of a second pipe, the first pipe being, in the neutral position of the directional section, connected to a measuring section, and the first pipe being interruptible by means of the valve arrangement. 
     With this solution a reaction of the steering motor is achieved both if the directional section is activated and if the directional section is in a neutral position. Forces acting upon the steering motor are transferred via the first pipe to the first outlet and via the directional section to the measuring motor. 
     In some cases it happens that a valve gets stuck, that is, in spite of an activation signal the valve does not change its position as specified by the activation signal. If now, for example, the valve arrangement gets stuck in a closed position and interrupts the first pipe the second pipe will bypass the valve arrangement. This way the hydraulic steering can still be operated via the steering unit. The disadvantage of this solution is that the steering resistance will be higher if the valve arrangement gets stuck. At the same time such a wrong valve position cannot be directly detected during normal operation within a hydraulic steering according to the state of the art. 
     SUMMARY 
     Thus, the underlying task of the invention is to provide a hydraulic steering that allows to detect at least for some of the valves if they are in the correct position. 
     The problem is solved in a hydraulic steering of the above mentioned type in that the steering valve is only deflectable if the valve arrangement is deflected. 
     This way the steering valve can be used to detect if the valve arrangement is stuck in a faulty position. Then one may test if the steering valve is deflectable and will consequently find out if the valve arrangement is deflected or not. This improves the safety of the system without introducing new components and thus at the same time will not increase the production costs compared to the state of the art. 
     Preferably the supply connection arrangement further comprises a stop valve and the steering valve is only deflectable if both the stop valve and the valve arrangement are in a deflected position. This way by testing if the steering valve is deflectable one will detect if there is a faulty position of either one or both of the valve arrangement and the close valve. 
     In a preferred embodiment the hydraulic steering further comprises a hydraulic bridge circuit arranged between the valve arrangement and at least one pilot supply of the steering valve. Such a bridge circuit allows to supply the steering valve with hydraulic pressures that are necessary to displace the steering valve. Thus, if the bridge circuit is arranged between the valve arrangement and the at least one pilot supply of the steering valve the valve arrangement is able to interrupt the pressure supply to the bridge circuit. In the state of the art the bridge circuit is connectable to a high pressure supply by opening a close valve irrespectable of the valve position of the valve arrangement. 
     In a further preferred embodiment the stop valve in the deflected position connects a pilot supply of the valve arrangement to the high pressure supply. This way the valve arrangement can only be displaced if the stop valve has been displaced. 
     In another preferred embodiment the valve arrangement is hydraulically activated by opening the close valve. This way opening the close valve will automatically also activate the valve arrangement. 
     It is preferred if the valve arrangement in the deflected position connects the hydraulic bridge circuit to the high pressure supply. This way the hydraulic bridge circuit can only supply the steering valve with hydraulic pressure differences if the valve arrangement has been displaced. This improves the fault protection of the hydraulic steering. 
     Preferably the steering valve is connectable to the steering motor via the valve arrangement. Preferably in the valve position in which a valve arrangement connects the steering valve to the steering motor the valve arrangement will also connect the hydraulic bridge circuit to the high pressure supply such that the steering valve may be displaced. In its other valve position the valve arrangement may then interrupt the connection between the steering motor and the steering valve. In this valve position the steering valve may then also open additional pipe connections between the steering motor and the steering unit. 
     Preferably the steering valve is deflectable within a dead band without changing the valve position. This way one may check if the steering valve is deflectable without moving the steering valve into a different valve position. This way one may or easily detect an error in the valve position of the close valve or the valve position of the valve arrangement by trying to displace the steering valve within its dead band. 
     In a further preferred embodiment the steering valve is only deflectable if one of the at least one pilot supplies is connected to the high pressure supply. In this embodiment it is rather simple to ensure that the steering valve is only deflectable if the valve arrangement is deflected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention is described on the basis of preferred embodiments with reference to the drawings, showing: 
         FIG. 1  a hydraulic steering according to the invention, 
         FIG. 2  a valve arrangement according to the invention, 
         FIG. 3  a hydraulic steering according to the state of the art. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIGS. 1 and 2  a hydraulic steering  1  according to the invention is disclosed. In  FIG. 2  the valve arrangement as disclosed in  FIG. 1  is shown in more detail. In  FIG. 3  a hydraulic steering according to the state of the art as disclosed in DE 10 2007 053 024 B4 is shown. 
     In  FIG. 1  a hydraulic steering  1  is supplied with pressurized hydraulic fluid via a supply connection arrangement. The supply connection arrangement has a high pressure connection P and a low pressure connection T. 
     The hydraulic steering  1  serves the purpose of steering a steering motor  2 , which has two connections L, R. 
     The hydraulic steering  1  has a steering unit  3  with a directional section  4  and a measuring section  5 , which can, in a manner known per se, be formed by a measuring motor  8 . Here, the steering unit  3  is a “close-center” unit. However, also an “open-center” unit can be used. 
     The directional section  4  has a valve, here simply shown as a directional valve slide  6 , which can be displaced into three different positions, namely the neutral position shown, and two directional positions displaced from the neutral positions. In reality, the directional section  4  will often have two mutually rotatable valve sleeves, which are rotatably supported in a housing. One of these sleeves is connected to a steering hand wheel  7 . The other valve sleeve is connected to the measuring motor  8  of the measuring section  5 . The principle embodiment of such a steering unit  3  is known in the state of the art. 
     Further, the steering  1  has a steering valve  9  with a steering valve slide  10 . The steering valve slide  10  is only shown schematically. It can be displaced from the neutral position shown into two directional positions. The displacement takes place by means of hydraulic pressures, which are supplied via a hydraulic bridge circuit  11 . The hydraulic bridge circuit  11  comprises four, for example electrically activated, valves  12  to  15 . Depending on which of the valves  12  to  15  are opened, the steering valve slide  10  is displaced to the left or to the right (in relation to the view of  FIG. 1 ). The resulting position of the slide  10  is detected by a sensor  16  and reported to a control electronic  17 . 
     The control electronic  17  and the sensor  16  can be used to check the valve position of the steering valve  9 . This may be used to check for faulty valve positions of other valves in the hydraulic steering that do not comprise a sensor. This will be explained in more detail later on. 
     The high-pressure connection P is connected to a priority valve  18 , whose priority outlet  19  is connected to the steering unit via a non-return valve  20 . The priority outlet is also connected to an inlet of the steering valve  9  and an inlet of a pressure control valve  21 . The pressure control valve  21  may supply an adjustable pressure at its outlet. Between the pressure control valve  21  and the bridge circuit is arranged a stop valve  22  and a valve arrangement  27 . When the stop valve  22  is in an open position a pressure supplied by the pressure control valve  21  will be delivered via the stop valve  22  to a pilot supply PS 3  of the valve arrangement  27 . This will activate the valve arrangement  27  and move it out of the neutral position opening a connection between the pressure control valve  21  and the hydraulic bridge circuit  11 . Thus, if the stop valve  22  is closed pressurized hydraulic fluid will be prevented from reaching the hydraulic bridge circuit  11 . In this case due to the lack of supply of hydraulic pressures to the hydraulic bridge circuit  11  the steering valve  9  cannot be activated. The steering valve  9  can be a proportional valve. 
     The directional section  4  has five inlets E 1 , E 2 , E 3 , E 4 , E 5 . Here, the term “inlet” has been chosen for reasons of simplicity. Hydraulic fluid can also flow off from the directional section via an inlet. The inlet E 1  is connected to the priority outlet  19  of the priority valve. The inlets E 2 , E 3  are connected to the measuring section  5 . The inlet E 4  is connected to a load sensing pipe LS, and the inlet E 5  is connected to the low-pressure connection T. 
     The directional section  4  has four outlets A 1 L, A 1 R, A 2 L, A 2 R. Thus, for each steering direction a first outlet A 1 L, A 1 R and a second outlet A 2 L, A 2 R is provided. The first outlets A 1 L, A 1 R are connected via a first pipe  23 ,  24 , respectively, to the steering motor  2 . The second outlets A 2 L, A 2 R are also connected via a second pipe  25 ,  26 , respectively, to the steering motor  2 . The first pipes  23 ,  24  can be opened (shown position) or interrupted via the valve arrangement  27 , when the valve arrangement  27  is switched over. Also here, the term “outlet” has been chosen for reasons of simplicity. Hydraulic fluid can also flow into the directional section via an outlet. 
     In the shown neutral position of the directional valve slide  6 , the first two pipes  23 ,  24  are connected to the measuring motor  8  through the directional valve slide  6 . The two second pipes  25 ,  26  are interrupted by the directional valve slide  6 , that is, they are neither connected to the measuring section  5  nor to the supply connection arrangement. In the shown position of the valve arrangement  27 , this causes that pressure changes occurring on the steering motor  2  because of external forces will result in a reaction on the steering motor  8  and thus on the steering hand wheel  7 . In many cases, this is desired. When the steering unit  3  is activated, pressurized hydraulic fluid gets from the priority outlet  19  through the steering valve slide  6  to the measuring motor  8  and from there (when steering to the left) via the first outlet A 1 L into the first pipe  23  and via the second outlet A 2 L into the second pipe  25 . Here, the two pipes are arranged in parallel to each other. With a steering movement in the opposite direction, the same applies for the outlets A 1 R, A 2 R and the pipes  24 ,  26 . 
     Usually, the steering unit  3  is only activated to move the steered wheels of a vehicle. As soon as they have reached their position, the steering unit  3  is deactivated again. This also applies, if at that time the wheels are set in an angle to the vehicle steering axis. The directional section  4  then returns to the neutral position. 
     If, with a steering unit  3  in the neutral position, the vehicle is steered via the steering valve  9 , the stop valve  22  is activated. Then a pilot supply PS 3  of the valve arrangement  27  will be supplied with a high pressure from the high pressure supply P and will thus be displaced out of the neutral position. In this displaced position a hydraulic path from the pressure control valve  21  to the hydraulic bridge circuit  11  will open in the valve arrangement  27 . Thus a high pressure supplied by the pressure control valve  21  will reach the hydraulic bridge circuit  11 , and thus the steering valve  9  can be displaced in one of the two directions. In the displaced position the valve arrangement  27  will also interrupt the two first pipes  23 ,  24 . Instead, two outlets  29 ,  30  of the steering valve  9  are connected to the two pipes  25 ,  26 , so that the steering motor  2  can now also be steered via the steering valve  9 . 
     As soon as the stop valve  22  is closed the valve arrangement  27  is no longer supplied with a pilot pressure and will thus move back into the neutral position. In the neutral position of the valve arrangement  27  the hydraulic bridge circuit  11  will no longer be supplied with hydraulic pressure differences, thus the steering valve  9  will no longer be deflectable. At the same time, the two first pipes  23 ,  24  are open again. 
     If the vehicle is steered via the steering valve  9 , the two first pipes  23 ,  24  are interrupted by the valve arrangement  27 . The two pipes  25 ,  26  are interrupted by the directional section  4 . Accordingly, a reaction to the steering hand wheel  7  does not take place, if external forces act upon the steering motor. 
     If the vehicle is steered via a steering valve  9 , the hydraulic pressure supplied to the steering motor  2  by the steering valve  9  is always lower than a pressure that would origin from the steering unit  3 . If, in a situation, where the vehicle is steered via the steering valve  9 , the driver activates the steering hand wheel  7 , the steering unit  3  first supplies a somewhat higher pressure than the steering valve  9 . This pressure is passed on to the steering motor  2  through one of the two pipes  25 ,  26 , even though the two first pipes  23 ,  24  are interrupted. Also when the steering valve  9  is still active or blocks the valve arrangement  27 , a steering of the vehicle by means of the steering unit  3  is possible. 
     The two first pipes  23 ,  24  are always controlled in common with the valve arrangement  27 , that is, they are practically released or interrupted at the same time. 
     The valve arrangement  27  does not only disconnect the reaction function, but generally also makes the steering  1  safer. 
     Now there may be situations when the steering mode of the hydraulic steering  1  needs to be changed, but the close valve  22  and/or the valve arrangement  27  get stuck and does not change position. This will either mean that the vehicle cannot be steered by the steering valve  9  (if either of the valves  22 ,  27  are stuck in the neutral position) or that the steering resistance of the manual steering via the steering unit  3  is larger (if either one or both of the valves  22 ,  27  are stuck in a displaced position). 
     With a hydraulic steering according to the invention one may now test for such a faulty position of the stop valve  22  and/or the valve arrangement  27  by means of the steering valve  9 . 
     Such a test can be applied in the following way:
         Activating the control electronic  17  to supply the steering valve  9  with a hydraulic pressure via the hydraulic bridge circuit  11  to displace the steering valve  9  within a dead band;   Measuring the actual displacement of the steering valve  9  using the sensor  16 ;   Comparing if the valve position of the steering valve agrees with the expected position of the steering valve;   Giving an error signal if the actual valve position does not coincide with the expected valve position of the steering valve.       

     By this method if either one of the steering valve  9 , the close valve  12  or the valve arrangement  27  is stuck in a faulty position it can be detected and reported for example to the driver via an alarm signal. 
     Of course this method may be used on a more basic level to detect the position of at least one first valve (in the given embodiment the close valve  22  or the valve arrangement  27 ) by activating a second valve (in the given embodiment the steering valve  9 ), wherein the second valve can only be displaced if all of the at least one first valves are in a displaced position. The method comprises:
         Activating the second valve to displace the valve position of the second valve,   Checking if the second valve is in the expected position.       

     Thus one may detect an error in one of a plurality of valves by only checking if one valve can be displaced. 
     In  FIG. 2  a hydraulic steering according to the state of the art is disclosed, wherein the same components are denoted with the same reference signs. 
     Here the close valve  22  in the open position is directly connected to both the hydraulic bridge circuit  11  and the pilot supply of the valve arrangement  27 . Thus opening the close valve  22  will displace the valve arrangement  27  to connect the steering motor  2  to the steering valve  9  and will supply the bridge circuit  11  with hydraulic pressures. 
     Now if the close valve  22  is open but the valve arrangement  27  is stuck in the neutral position the steering valve can be displaced but there is no connection of the steering valve  9  to the steering motor  2  and thus no steering reaction. Consequently, checking if the steering valve  9  is displaceable would not allow to detect if the valve arrangement  27  is in a faulty position within the state of the art. Thus the improved safety and fault detection of the invention becomes clear. 
     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.