Abstract:
A steering stop for a steer-by-wire steering system, includes a steering shaft for functionally connecting to a steering wheel, wherein a pressure chamber is provided for each direction of rotation of the steering shaft. A rotation of the steering shaft produces a reduction in the volume of a corresponding pressure chamber, and the steering stop also comprises a hydraulic valve such that resistance against a further rotation of the steering shaft is generated by the operation of said hydraulic valve when predetermined environmental conditions are met.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2014/002228, filed Aug. 13, 2014, which designated the United States and has been published as International Publication No. WO 2015/024643 and which claims the priority of German Patent Application, Serial No. 10 2013 014 121.4, filed Aug. 23, 2013, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a steering stop for use in steer-by-wire steerings, in particular in non track-bound vehicles. 
     In steer-by-wire steerings no direct mechanical coupling between the steering wheel and the steered wheels exists. Instead the steering handle and/or the angular speed steering wheel is measured by sensors and the wheels are correspondingly turned in by actuators. Such arrangements are known from DE 10 2010 041 738A1 or DE 10 2008 021 973.A1. 
     In steer-by-wire steerings the direct feedback between the steering angle input by the driver via the steering wheel and the actually resulting steering angle at the wheel is therefore not available. Correspondingly the driver does not receive any feedback regarding whether the steering transmission is already at the stop in case of a strong steering. In case of a freely rotatable steering wheel infinitely great steering angles can thus be generated without the steering transmission being able to realize these steering angles. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a steering wheel stop for use in steer-by-wire, in which the user receives a haptic feedback when reaching the maximally possible steering angle. In particular it is taken into account that different driving conditions may require different maximal turn-in angles of the wheels and different transmission ratios from the steering wheel position to the wheel turn-in angle may be required. 
     The object is solved with the features of the independent claim. Advantageous refinements are set forth in independent claims. 
     The steering wheel stop for a steer-by-wire steering system includes a steering shaft for functional connection with a steering handle, in particular a steering wheel, wherein a pressure chamber is provided for each direction of rotation of the steering shaft. A rotation of the steering shaft causes, in particular via a coupling with a hydraulic piston, a reduction of the volume of an assigned pressure chamber and the steering stop includes a hydraulic valve in order to generate a resistance against a further turning of the steering shaft by switching a hydraulic valve when predetermined environmental conditions are given. Instead of coupling the steering shaft with a hydraulic piston, which is described in more detail in the following preferred embodiment, the steering wheel can also be coupled with the hydraulic cylinder and the volume reduction can be caused by a stationary and double-acting hydraulic piston. Naturally, the steering shaft can hereby be rotated in two directions. The predetermined environmental conditions are in particular caused by the rotation of the steering shaft. The resistance against the rotation of the steering shaft means in particular that the switched, i.e., closed hydraulic valve, prevents a (further) outflow of the hydraulic fluid from the pressure chamber, thereby preventing rotation in this direction. In a steering wheel that has no stops against a free (endless) rotation, this makes it possible to provide the driver with a feedback regarding when the maximally possible steering or turning-in angle is reached. 
     In a steer-by-wire steering no mechanical coupling or hydraulic coupling via transmission stages or the like to mechanical components that set the wheel turn-in angle, for example a steering rod, is present. Rather the rotation of the steering angle is converted into an electronic signal via which turning-in of the wheels is accomplished. 
     The mentioned environmental conditions can in particular be generated by a defined or definable angular position of the steering shaft or an orientation or position of a component of the steering wheel stop and/or a defined or definable volume of a pressure chamber and/or a defined or definable inflow or outflow into or out of one of the pressure chambers. A determination of the angular position of the steering wheel is advantageous in order to reproducibly generate the same stop for the steering wheel. Generating the stop of the steering wheel in dependence on a position and/or orientation of the piston rod provides the driver with a feedback of the vehicle situation at hand. 
     Further at least a part of the pressure chamber can be a component of the steering shaft or can be directly coupled with the steering shaft. In this way the drive-by-wire function is realized by a spatial separation from the hydraulic system, which is used for turning the wheels and a direct feedback from the pressure increase in the pressure chamber to the driver is improved. 
     In particular a hydraulic system is arranged between the two pressure chambers in order to enable a fluid low from one of the pressure chambers into the other pressure chamber in dependence on the switching position of the at least one hydraulic valve. Because the total volume of both pressure chambers is constant in every position of the hydraulic piston this allows generating a closed hydraulic system in a simple manner. 
     In particular when turning the steering shaft in a first direction, the volume of a first pressure chamber is reduced and the hydraulic valve is configured to prevent a further outflow out of the first pressure chamber when further turning the steering shaft in the first direction. This circumstance also applies correspondingly to the second pressure chamber. 
     Preferably a hydraulic valve function is provided for each pressure chamber, wherein both hydraulic valve functions are in particular arranged in a common hydraulic valve, thereby creating a same stop or end position for the steering wheel in both directions of rotation. 
     Also in particular a one-way function can be provided, so that when the outflow out of one of the pressure chambers and rotation of the steering shaft in a first direction of rotation is limited by switching the hydraulic valve, an inflow into this pressure chamber remains possible in order to not prevent turning of the steering shaft in the direction opposite to the first direction of rotation. The check valve can be part of the hydraulic valve or can be connected in parallel as a separate assembly. 
     In particular a reduction of the volume of the one pressure chamber caused by the rotation of the steering shaft corresponds to an identical increase of the volume of the other pressure chamber. In this way no special fluid compensation reservoir is required because the fluid, which flows out of the one pressure chamber can directly flow into the other pressure chamber. 
     Further a shutoff valve can be arranged in the fluid circuit of the hydraulic system between the pressure chambers, which shutoff valve is functionally separated from the hydraulic valve. The term functionally separated in particular means that the system includes a separate control logic with a separate (electronic) actuating drive and/or a controlled flow section of the fluid is present in the hydraulic circuit between the hydraulic valve and the shutoff valve. This can in particular be an interconnected tube or in the case of design in which the shutoff valve is integrated with the hydraulic valve in one unit, a valve-free flow region can be provided between the valves. 
     In a concrete embodiment the steering shaft can have a threaded section. Hereby a piston element is operatively engaged with the threaded section of the steering shaft and is supported torsion-stiff against a cylinder which includes the two pressure chambers so that a rotation of the steering shaft causes a corresponding volume change of the pressure chambers. 
     Further a hydraulic system, which includes the pressure chambers, is fluidly separated from an optionally present hydraulic system for hydraulic setting of the wheel turn-in angle. Thus the hydraulic system of the turning the wheels includes no further piston/cylinder assemblies beyond the first and second pressure chambers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the following preferred embodiments are described by way of the Figures. 
         FIG. 1  schematic shows a construction of the steering wheel stop together with the region of the turned-in wheels of a non track-bound motor vehicle and 
         FIG. 2  shows a section of  FIG. 1  with an alternative embodiment of the hydraulic cylinder. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A steering handle  10 , or more specifically a steering wheel  10 , is connected with a steering shaft  11 . The steering shaft has threading  19  in a middle section  8 . This threading  19 , which is preferably an outer threading, engages with a corresponding threading of a hydraulic piston  18 . This hydraulic piston  18  is located inside a hydraulic cylinder  12 , which is arranged stationary on a vehicle. The steering shaft  11  passes axially through the hydraulic cylinder  12 . 
     The hydraulic piston  18  is supported torsion stiff and axially displaceable relative to the hydraulic cylinder  12 . This is achieved in that at least one bolt  16 , preferably at least two bolts  16 , is connected with the hydraulic cylinder  12  parallel to the longitudinal axis and in particular off-center, and is hereby guided through a bore inside the hydraulic piston  18 . In alternative embodiments, a longitudinally extending tongue and groove guide can be provided on the inside of the cylinder  12  as connection with the piston  18 . 
     When the steering is actuated, the piston  18  is displaced by the rotation of the steering shaft  11  in the longitudinal direction of the cylinder, so that the volume of a first pressure chamber  14  and a second pressure chamber  15 , which are respectively provided inside the cylinder  12  and which are delimited by the double-acting hydraulic piston, changes. The connecting regions of the hydraulic cylinder  12  with a steering shaft  11  are sealed via ring gaskets. In addition guides are provided between the piston  18  and the bolt  16 , which are dimensions so as to be substantially liquid tight. For this purpose gaskets can be used. Also the threaded connection between the piston  18  and the steering shaft  11  is configured substantially liquid tight. The two pressure chambers  14  and  15  are connected with each other via a hydraulic line  25 , in which a hydraulic valve  30  and a shutoff valve  35  are arranged. The shutoff valve  35  is also a hydraulically operated valve. The hydraulic valve  30  has three switching positions. In the flow through position fluid flow is permitted in both directions. In the two one-way positions fluid flow is permitted in one direction and is blocked in the opposite direction. The shutoff valve  35  has two switching positions, i.e., a flow through position and a closed position in which fluid flow is interrupted. 
     A steering transmission can have a further and separate hydraulic system for setting the steering angles of the wheels  110 . In alternative embodiments an electric drive can be used. In the hydraulic system a hydraulic pump  124  is provided and a three-way control valve  130 , which can be controlled by an electronic control  100 , so that the hydraulic fluid flows into a steering cylinder  111 . In this way a steering piston  118  can selectively be shifted in the steering cylinder  111  in both directions. The steering piston  118  is connected with a piston rod  114  on both sides, to the ends of which a steering rod  112  is coupled, which is respectively connected with the corresponding wheel  110 . In this way the steering angle or turn-in angle of the wheels  110  can be set via the position of the steering piston  118 . When turning of the wheels  110  to the left is desired the control  100  switches the three-way valve  130  into the shifting position shown in  FIG. 1  on the left hand side in which the fluid moves from the pump  124  into the right chamber of the steering cylinder  111  and thus causes the turning of the wheels. In order to cause turning of the wheels in the opposite direction the control valve  130  is caused to assume the opposite shifting position and the fluid is pumped into the left chamber of the steering cylinder  111 . 
     In the present exemplary embodiment of the invention, the steering angle-/wheel turn-in angle ratio is 2.5 to 1. This means that at a rotational angle of the steering wheel  10  of +900°, starting from the center position, in the one direction the one steering angle can be achieved and of −900° in the other direction the other steering angle can be achieved. The angular sensor  20  measures the respective position of the steering wheel  10  and provides the result to the control  100 . At normal driving when no maximal wheel turn-in angle is present, the hydraulic valve  30  is in the flow through position. 
     When the steering wheel  10  is turned to the right, the hydraulic piston  18  moves upwards and reduces the size of the first pressure chamber  14 . When the steering angle of +900° is reached the control  100  switches the hydraulic valve  30  into the first one-way position (right switching symbol of the valve), in which no further fluid can drain from the first pressure chamber  14 . The pressure increase resulting therefrom is perceived by the driver as resistance and he immediately obtains the feedback that a maximal wheel turn-in angle is reached. Due to the one-way function of the hydraulic system the driver can steer in the opposite direction and thus reduce the steering angle of the steering wheel  10 . Thus the check valve function of the hydraulic valve  30  acts as a one-sided stop for the steering wheel  10 . The steering wheel stop is constructed symmetric or identical with regard to both directions of rotation of the steering wheel  10 . 
     Depending on the situation a different steering angle/wheel turn-in angle ratio may be desired. For example the vehicle can have a sporty drive program. In case of a sporty driving the steering is to react more sensitively to the steering angle of the steering wheel. Thus in this case a steering angle of respectively 1.5 rotations, i.e., =+/−540°, can correspond to the maximal wheel turn-in angle. In case of a drive program for off-road drives a different maximal wheel turn-in angle can be predetermined. Also in the case of wheels with different diameters (such as for example summer or winter tires) a changed maximal wheel turn-in angle can be predetermined. Furthermore, the motor control can predetermine a maximally permitted wheel turn-in angle in dependence on the speed. Also in these cases it is desired that the driver receives a changed feedback regarding the maximal steering angle of the steering wheel  10 . In these cases the control  100  can bring the hydraulic valve  30  into the corresponding one-way position already at smaller measured steering angles of the angular sensor  20 , in order to generate a changed stop for the steering wheel  10 . 
     During driving operation of the vehicle the shutoff valve  35  is always in its open position. When the vehicle is turned off, for example for parking, the control  100  ensures that the shutoff valve  25  assumes its closed position. Because as a result no outflow from either of the pressure chambers  14  and  15  is possible, the steering wheel  10  can thus no longer be turned, which corresponds to the function of a steering wheel lock. For safety reasons it must be excluded that the shutoff  35  assumes the described blocking function during driving. For this reason it is configured separate from the hydraulic valve  30 . In alternative embodiments the blocking function can however also be integrated in the hydraulic valve  30  as further switching position. 
     According to  FIG. 1  the hydraulic cylinder  12  is arranged in a center position of the steering shaft  11 . Alternatively it may also be arranged at the end of the steering shaft  11  so that it extends into the cylinder  12  only on one side. In this case one of the two gaskets between the cylinder  12  and the steering shaft  11  is not required. 
       FIG. 2  shows an alternative embodiment of the piston  18 . A nut  50  is coupled with the steering shaft  11  via a threading. On this nut  50  a piston rod  52  is fastened and this fastening ensures an anti-rotation support of the nut  50  so that it rotates in longitudinal direction of the steering shaft when the steering shaft  11  rotates. The cylinder  12  is dual action, so that two pressure chambers  14  and  15  result.  FIG. 2  also shows two connection lines of the pressure chambers, which as described are connected with each other via the hydraulic valve  30  and the shutoff valve  35 . Because in the embodiment of  FIG. 2  the volume-flows into and out of the pressure chambers  14 ,  15  are different when the piston moves, a fluid compensation reservoir (not shown) is required in this case. 
     The features of different embodiments can be freely combined with each other. 
     REFERENCE SIGNS 
     
         
           10  steering handle, steering wheel 
           11  steering shaft 
           12  hydraulic cylinder, cylinder 
           14 ,  15  first and second pressure chamber 
           16  bolt 
           18  hydraulic piston 
           19  threading 
           20  angular sensor 
           25  hydraulic line 
           30  hydraulic valve 
           35  shutoff valve 
           50  nut 
           52  piston rod 
           100  control 
           110  wheel 
           111  steering cylinder 
           112  steering rod 
           114  piston rod 
           118  steering piston 
           124  hydraulic pump 
           130  three-way control valve