Abstract:
The invention concerns a hydraulic steering ( 1 ) with a supply connection arrangement (P, T), a steering motor ( 2 ) and a steering unit ( 3 ) between the supply connection arrangement and the steering motor ( 2 ), the steering unit ( 3 ) having a directional section ( 4 ) and a measuring section ( 5 ), a steering valve ( 9 ) being arranged in parallel to the steering unit ( 3 ). With such a steering, it is endeavoured to achieve the best possible safety. For this purpose, it is ensured that for each steering direction the directional section ( 4 ) comprises a first outlet (A 1 L, A 1 R), which is connected to the steering motor ( 2 ) by means of a first pipe ( 23, 24 ), and a second outlet (A 2 L, A 2 R), which is connected to the steering motor ( 2 ) by means of a second pipe ( 25, 26 ), the first outlet (A 1 L, A 1 R) being, in the neutral position of the directional section ( 4 ), connected to the measuring section ( 5 ), and the first pipe ( 23, 24 ) being interruptible by means of a valve arrangement ( 27, 27   a ).

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    Applicant hereby claims foreign priority benefits under U.S.C. § 119 from German Patent Application No. 10 2007 053 024.4 filed on Nov. 5, 2007, the contents of which are incorporated by reference herein. 
       FIELD OF THE INVENTION 
       [0002]    The invention concerns a hydraulic steering with a supply connection arrangement, a steering motor and a steering unit between the supply connection arrangement and the steering motor, the steering unit having a directional section and a measuring section, a steering valve being arranged in parallel to the steering unit. 
       BACKGROUND OF THE INVENTION 
       [0003]    Such a hydraulic steering is, for example, known from DE 10 2006 010 695 A1. A vehicle equipped with such a steering can either be steered via the steering unit, the driver then usually activating a steering member, for example a steering handwheel, or via the steering valve. When the driver steers the vehicle by means of the steering unit, in many cases a so-called reaction behaviour is desired, that is, the driver must feel through the steering handwheel that forces are acting upon the steering motor. However, this reaction behaviour causes problems, if the vehicle is steered by means of the steering valve. Thus, in the state of the art a reaction suppression arrangement has been proposed, in which a valve is arranged in one or both pipes between the steering unit and the steering motor, said valve(s) being able to interrupt or release the pipe(s). 
         [0004]    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. In the state of the art this causes problems, if a valve of the reaction suppression arrangement gets stuck. In this case, the pipe between the steering unit and the steering motor is blocked, so that the driver can no longer steer the vehicle via the steering unit. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is based on the task of providing a steering with the highest possible degree of safety. 
         [0006]    With a hydraulic steering as mentioned in the introduction, this task is solved in that 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 outlet being, in the neutral position of the directional section, connected to the measuring section, and the first pipe being interruptible by means of a valve arrangement. 
         [0007]    With this embodiment, a reaction of the steering motor for the steering arrangement is not only achieved, if the directional section is activated, but also in the neutral position of the directional section. 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. If, here, hydraulic pressures are changing, the driver can feel this via the steering member, for example the steering handwheel. This, however, only applies for as long as the valve arrangement has not interrupted the first pipe. When the valve arrangement interrupts the first pipe, the reaction behaviour does no longer exist. The valve arrangement then forms a reaction suppression arrangement. The vehicle can then, for example, be steered via the steering valve. If now, the valve arrangement should remain in the interruption position, for some reason, however, the vehicle should, for example in an emergency situation or during a manoeuvre, require steering via the steering unit, this is possible, because the hydraulic fluid from the measuring section reaches the measuring motor via the steering unit and the second outlet and the second pipe. Thus, the second pipe bypasses the valve arrangement, so that for such cases the actual opening behaviour of the valve arrangement is of inferior importance. A somewhat larger resistance may occur during steering, as only one of two pipes is available for supplying the hydraulic fluid from the steering unit to the steering motor. However, this is usually sufficient. If the valve arrangement is still blocking the first pipe, the fluid flowing back from the steering motor can flow back via the second pipe to the directional section and from there to the supply connection arrangement. Thus, also the low-pressure side offers an opportunity of bypassing the valve arrangement. 
         [0008]    Preferably, the valve arrangement can be activated by a signal that activates the steering valve. This gives an automatic interruption of the first pipes, when the steering valve is used. In this case, the reaction suppression arrangement is, however, desired. The driver does not have to worry about the suppression of the reaction. 
         [0009]    Preferably, the valve arrangement is made as a normally open valve arrangement. The valve arrangement opens the first two pipes, if no additional external forces are acting. Such an embodiment can, for example, be achieved by means of a spring that takes the valve arrangement to the opening position. 
         [0010]    Preferably, the valve arrangement is hydraulically activated. Thus, no additional energy is required for activating the valve arrangement. Pressurised hydraulic fluid is usually available in a hydraulic steering anyway. The pressure required for activating the valve arrangement is merely a control pressure, so that here relatively small pressures can be sufficient. 
         [0011]    In a preferred embodiment it is provided that during activation the two outlets of the directional section are connected to the inlet that is connected to the measuring section. Fluid that flows through the measuring section, for example when turning the steering handwheel, can then reach the steering motor in two ways, namely on the one hand via the first outlet and the first pipe and on the other hand via the second outlet and the second pipe. The hydraulic fluid flowing back from the motor can then flow back via the first and the second outlet of the other direction. If the valve arrangement has opened the first pipe or the first pipes, the hydraulic fluid can flow from the steering unit to the steering motor via two parallel pipes. If the valve arrangement has interrupted the first pipe or the first pipes, the second pipe will still be available for the hydraulic fluid. Otherwise, practically nothing is changed in the steering behaviour, as exactly the amount of fluid supplied by the measuring section will also reach the steering motor. Only, during undisturbed operation it will be supplied to the steering motor via two pipes and during disturbed operation it will be supplied via one pipe. 
         [0012]    Preferably, the steering valve is connectable to the steering motor via the valve arrangement. This means that the valve arrangement does not only interrupt the first pipes, but, during the interruption, it also creates a connection between the steering valve and one first pipe. This also applies in the opposite case: If the valve arrangement connects the first pipes, it interrupts the connection between the steering valve and the steering motor. If, in this case, the directional section of the steering arrangement is in the neutral position, the reaction is blocked, as no hydraulic fluid can flow from the steering motor to the measuring section via the first pipe. The pressures reported to the steering unit via the second pipe do not reach the measuring section, as, in the neutral position, the directional section interrupts a connection from the second outlets to the measuring section. 
         [0013]    Preferably, the valve arrangement connects a load-sensing pipe to a low-pressure connection, when the first pipe is open. Thus, the valve arrangement ensures that a load-sensing system cannot build up a pressure, which could open the steering valve, when the first pipes are open and the vehicle should accordingly be steered via the steering unit. 
         [0014]    Preferably, the valve arrangement has one first valve, which releases or interrupts the first pipe, and a second valve, which releases or interrupts a supply to the steering valve. In a manner of speaking, this provides two opportunities of taking influence on, whether the vehicle is controlled via the steering unit or via the steering valve. The risk that a serious error will occur is therefore kept small. 
         [0015]    It is preferred that the first valve and the second valve have a common activation signal and an opposite interruption behaviour. This means that, when the first valve closes, the second valve opens, and vice versa. Thus, when activating the steering valve, the reaction behaviour can at the same time be suppressed. 
         [0016]    Preferably, the two first pipes can be interrupted by a common valve arrangement. This simplifies the design. Further, this can ensure that the two first pipes are interrupted or opened for both directions at approximately the same time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    In the following, the invention is described on the basis of preferred embodiments with reference to the drawings, showing: 
           [0018]      FIG. 1  is a first embodiment of a hydraulic steering, and 
           [0019]      FIG. 2  is a second embodiment of a hydraulic steering. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    A hydraulic steering  1  is supplied with pressurised hydraulic fluid via a supply connection arrangement. The supply connection arrangement has a high-pressure connection P and a low-pressure connection T. Additionally, also a load-sensing connection LS 1  and an outlet with a low priority EF may be provided. 
         [0021]    The steering  1  serves the purpose of steering a steering motor  2 , which has two connections L, R. 
         [0022]    The 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 “closed-centre” unit. However, also an “open-centre” unit can be used. 
         [0023]    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 position. 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 handwheel  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 per se. 
         [0024]    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  has four, for example electrically activated, valves  12 - 15 . Depending on, which of the valves  12 - 15  are opening, 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 is reported to a control electronic  17  via a sensor  16 . 
         [0025]    The high-pressure connection P is connected to a priority valve  18 , whose priority outlet  19  is connected to the steering unit  3  via a non-return valve  20 . The priority outlet is also connected to an inlet of the steering valve  9 . Further, the priority outlet  19  of the priority valve is connected to a pressure control valve  21 , whose outlet supplies a pressure of, for example, 12 bar. Between the pressure control valve  21  and the bridge circuit  11  is arranged a stop valve  22 , which does, in the switching position shown, prevent pressurised hydraulic fluid from reaching the hydraulic bridge circuit  11 . The lack of a supply to the hydraulic bridge circuit  11  causes that the steering valve  9 , which can be a proportional valve, cannot be activated. 
         [0026]    The directional section  4  has five inlets E 1 , E 2 , E 3 , E 4  and 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. 
         [0027]    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 released (position shown) or interrupted via a 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. 
         [0028]    In the shown neutral position of the directional valve slide  6 , the two first 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 handwheel  7 . In many cases, this is desired. 
         [0029]    When the steering unit  3  is activated, pressurised 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 . 
         [0030]    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. 
         [0031]    If, with a steering unit  3  in the neutral position, the vehicle shall be steered via the steering valve  9 , the stop valve  22  is activated. The hydraulic bridge circuit  11  receives pressurised hydraulic fluid, so that it can displace the steering valve slide  10 . As soon as the hydraulic bridge circuit  11  receives pressure, a corresponding control pressure is lead to the valve arrangement  27 , which is switched to the other position against the force of a spring  28 . This is the position, which is shown in the left box of the valve arrangement  27 . In this position, the two first pipes  23 ,  24  are interrupted. In stead, two outlets  29 ,  30  of the steering valve  9  are connected to the two pipes  25 ,  26 , so that the steering motor  2  is now steered via the steering valve  9 . 
         [0032]    As soon as the stop valve  22  is deactivated, the hydraulic bridge circuit  11  no longer receives a pressure. At the same time, the control pressure on the valve arrangement  27  is reduced, so that the spring  28  again sets the valve arrangement so that the two first pipes  23 ,  24  are open, as shown. 
         [0033]    In this position, the valve arrangement  27  connects a load-sensing pipe  31  to the low-pressure connection T, so that a pressure cannot mistakenly build up, for example because of leakages or the like, which activates the steering valve  9  in an undesired manner. 
         [0034]    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 second pipes  25 ,  26  are interrupted by the directional section  4 . Accordingly, a reaction to the steering handwheel  7  does not take place, if external forces act upon the steering motor. 
         [0035]    If the vehicle is steered via the 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 handwheel  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. 
         [0036]    The two first pipes  23 ,  24  are always controlled in common by the valve arrangement  27 , that is, they are practically released or interrupted at the same time. Any further adaptation measures are not required. 
         [0037]    The valve arrangement  27  does not only disconnect the reaction function, but generally also makes the steering  1  safer. 
         [0038]      FIG. 2  shows a modified embodiment, in which the same elements have the same reference numbers. 
         [0039]    The embodiment of the valve arrangement  27  has been changed. The valve arrangement  27  now has two separate valves  27   a  and  27   b . The valve  27   a  acts upon the first pipes  23 ,  24  from the directional section  4  of the steering unit  3  to the steering motor  2 . The valve  27   b  interrupts a connection from the high-pressure connection P to the steering valve  9  and a connection from the steering valve  9  to the low-pressure connection T. Both valves  27   a ,  27   b  are activated by an activation of the stop valve  22 . For this purpose, the outlet of the stop valve  22  is connected to control pressure surfaces  32   a ,  32   b  of the two valves  27   a ,  27   b . This means that both valves  27   a ,  27   b  switch at the same time. However, the two valves  27   a ,  27   b  have different passage behaviours. In the normal position shown in  FIG. 2 , the valve  27   a  is open, that is, it releases the two pipes  23 ,  24 , whereas the valve  27   b  is closed and interrupts a connection from the high-pressure connection P to the steering valve  9 . After switching, the valve  27   a  interrupts the two first pipes  23 ,  24 , whereas the valve  27   b  releases the connection from the high-pressure connection P to the steering valve  9 . 
         [0040]    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.