Steering gear comprising a ball screw drive, and steering system comprising the steering gear

Abstract

The invention relates to a steering gear 1 for a steering system 25 of a vehicle, comprising: a gear housing 5, the gear housing 5 having a cylinder chamber 10; a threaded spindle 2 rotatably mounted in the gear housing 5, the threaded spindle 2 having an input interface 7 for connecting a steering drive; a segment shaft 4 rotatably mounted in the gear housing 5, the segment shaft 4 having an output interface 8 for connection to a steering linkage; and a ball nut device 3 which is guided axially in relation to a first axis of rotation 100 of the threaded spindle 2 and has a toothed section 13 for meshing engagement with the segment shaft 4, wherein the ball nut device 3 forms, together with the threaded spindle 2, a ball screw drive. According to the invention, the ball nut device 3 comprises a guide contour 15 on the outer circumference, and the gear housing 5 comprises a mating contour 16 on the inner circumference of the cylinder chamber 10, wherein the ball nut device 3 is supported, via the guide contour 15, against the mating contour 16 in the radial direction and in the circumferential direction in relation to the first axis of rotation 100, and is guided in a straight line along the mating contour 16 in the axial direction in relation to the first axis of rotation 100.

Description

[0001] Steering gear with a ball screw and steering system with the steering gear

[0002] The invention relates to a steering gear for a steering system of a vehicle having the features of the preamble of claim 1. Furthermore, the invention relates to a steering system having the steering gear.

[0003] Ball screw drives, also known as recirculating ball drives, are known for vehicle steering systems. These drive systems convert a steering command from a steering wheel into a rotary motion of the steerable vehicle wheels. Such ball screw drives essentially comprise an input shaft and an output shaft, which are operatively connected to each other via a ball screw drive (KGT). For this purpose, the input shaft is designed as a screw spindle, which forms the ball screw drive with a spindle nut meshing with the output shaft.

[0004] The document DE 102014 106488 A1 discloses a recirculating ball steering system with a steering housing in which a steering piston is mounted between a first working chamber and a second working chamber. The steering piston has a toothed area on its outer wall of the steering piston, into which the teeth of a segment shaft engage, and is displaceable along a longitudinal axis. The working chambers are connected to a control valve via pressure fluid lines for steering assistance. On a side of the steering piston facing away from the toothed area, at least one sliding element is arranged between a steering housing inner wall and a steering piston outer wall.

[0005] The object of the invention is to create a steering gear of the type mentioned above, which is characterized by improved operating behavior.

[0006] This object is achieved according to the invention by a steering gear having the features of claim 1 and a steering system having the features of claim 15. Advantageous embodiments emerge from the subclaims, the drawings and / or the description.

[0007] The invention relates to a steering gear designed and / or suitable for a steering system. In particular, the steering gear serves to transmit a steering movement to one or more vehicle wheels of a vehicle.

[0008] The steering gear has a gear housing with a cylinder chamber, wherein a threaded spindle and a segment shaft are rotatably mounted in the gear housing. In particular, the threaded spindle and the segment shaft are aligned transversely to one another. In other words, the threaded spindle defines a first axis of rotation and the segment shaft a second axis of rotation, wherein the two axes of rotation intersect in a plan view, in particular at right angles. In particular, a threaded spindle is understood to be a shaft which has a helical raceway for guiding at least one row of balls. In particular, a segment shaft is understood to be a shaft which has a toothing geometry designed as a segment toothing. In particular, the toothing geometry extends in the circumferential direction over an angular range of less than 270 degrees, preferably less than 180.Preferably, the threaded spindle is arranged coaxially and / or concentrically in the cylinder chamber with respect to the first axis of rotation. In other words, the cylinder chamber extends axially relative to the first axis of rotation and / or circumferentially relative to the first axis of rotation.

[0009] The threaded spindle has an input interface which is designed and / or suitable for connecting a steering drive. In principle, the input interface can be connected to a steering spindle or a steering column in order to transmit a steering movement applied by a steering handle, in particular a steering wheel, to the threaded spindle. Alternatively or optionally additionally, the input interface can be connected to a drive motor, preferably an electric servomotor, in order to transmit a steering movement generated by the drive motor to the threaded spindle. The input interface can be designed as a shaft journal protruding from the end of the transmission housing, to which the steering column and / or the drive motor are connected for drive purposes.

[0010] The segment shaft has an output interface, which is designed and / or suitable for transmitting a steering movement to one or more, preferably two, vehicle wheels. The output interface can be designed as a further shaft journal protruding from the end of the transmission housing, which is connected to the at least one vehicle wheel via known kinematic connections in order to change a wheel steering angle on the vehicle wheel upon rotation of the output shaft.

[0011] The steering gear has a ball nut device which is guided axially with respect to the first axis of rotation and which has a toothed section for meshing engagement with the segment shaft. In principle, the ball nut device can be made in one piece, in particular from a single piece of material. Alternatively, however, the ball nut device can also be designed in multiple parts. In particular, the toothed section is formed in sections or partially on the outer circumference of the ball nut device in the axial direction and / or circumferential direction with respect to the first axis of rotation and / or is incorporated into said outer circumference. The toothed section is preferably designed as a rack toothing which extends partially or completely over the axial length of the guide sleeve.

[0012] The ball nut device, together with the threaded spindle, forms a ball screw drive. In particular, the ball nut device serves to convert a rotational movement of the threaded spindle about the first axis of rotation into a rotational movement of the segment shaft about the second axis of rotation. For this purpose, the ball nut device is preferably connected to the threaded spindle via at least one row of balls, on the one hand, for driving purposes, and on the other hand, is meshingly engaged with the segment shaft or its toothing geometry via the toothed section. Particularly preferably, the ball nut device also has at least one circumferential and / or helical raceway on its inside, which, together with the raceway of the threaded spindle, forms at least one ball raceway for guiding the balls of the at least one row of balls.When the steering movement is transmitted, the threaded spindle is rotated about the first axis of rotation, whereby the ball nut device moves in the axial direction with respect to the first axis of rotation in the gear housing and thus drives the segment shaft about the second axis of rotation.

[0013] Within the scope of the invention, it is proposed that the ball nut device has a guide contour on the outer circumference and that the gear housing has a mating contour on an inner circumference of the cylinder chamber, wherein the ball nut device is supported on the mating contour in the radial direction and in the circumferential direction via the guide contour and is guided straightly on the mating contour in the axial direction with respect to the axis of rotation. Put simply, the ball nut device is supported on the mating contour in a radially fixed and rotationally fixed manner via the guide contour and is simultaneously guided axially along the mating contour. In the circumferential direction therefore means that the guide contour is supported on the mating contour both in a direction of rotation about the first axis of rotation and in an opposite counter-direction of rotation.In principle, the ball nut device can be supported on the mating contour via the guide contour in the radial direction and in the circumferential direction, each via at least one or exactly one point contact. Alternatively, the guide contour is supported on the mating contour in the radial direction and in the circumferential direction, each via a line contact. In particular, the line contact is defined by a contact line that extends essentially in the axial direction with respect to the first axis of rotation. The guide contour can be partially formed on the outer circumference of the ball nut device and / or molded or incorporated therein. Accordingly, the mating contour can be partially formed on the inner circumference of the gearbox housing and / or molded or incorporated therein.

[0014] The invention is based on the finding that insufficient radial support of the ball nut assembly increases wear on the ball screw and thus reduces its service life. The advantage of the invention is that the axial guidance of the ball nut assembly via the guide contour provides optimized linear guidance and, at the same time, radial support for the ball screw assembly (KGT), while simultaneously transmitting a rolling moment to the gearbox housing to reduce the load on the segment shaft. Thus, the support of the ball nut required for safe and long-lasting operation can be improved in a simple manner, particularly by taking the radial fit design into account, and thus the service life of the steering gear can be extended.

[0015] In a specific embodiment, it is provided that the guide contour is arranged in the radial direction opposite the toothed section with respect to the first axis of rotation. In particular, the guide contour lies in the cross-section or in the axial direction with respect to the first axis of rotation, preferably centrally and / or symmetrically, on a vertical center line of the toothed section, in particular intersecting the first axis of rotation. Put simply, the guide contour is arranged diametrically with respect to the first axis of rotation and / or offset by 180° in the circumferential direction from the toothed section. This proposes particularly stable support for the ball nut device in the cylinder space, wherein the guide contour opposite the toothed section enables a radial force introduced via the segment shaft to be reliably supported or guided into the gear housing.

[0016] In a further development, it is provided that the guide contour and the counter contour are slide-mounted or guided in a sliding manner relative to one another via a sliding layer. In particular, the sliding layer serves to reduce friction during axial movement between the ball nut device and the gear housing. For this purpose, the sliding layer is arranged optionally on the guide contour or the counter contour. Particularly preferably, the ball nut device or the guide contour is supported on the gear housing or the counter contour over the entire axial length, in particular at least over the entire contact area, via the sliding layer. In other words, the sliding layer preferably extends over the entire linear movement range on the counter contour or on the guide contour. Particularly preferably, the sliding layer is arranged exclusively in the contact area of ​​the guide contour with the counter contour. Preferably, the guide contour orthe mating contour has, at least in the contact area, a contact surface and / or contact surface orientation optimized for the sliding layer. In principle, the sliding layer can be formed by a sliding coating. Alternatively, the sliding layer can be formed by a separate component, as described below. For example, the sliding layer can be made from a material with sliding-optimized or self-lubricating properties, in particular a metal alloy, such as a lead, tin, copper and / or zinc alloy, a plastic, such as PTFE, or technical ceramic. By combining a friction-optimized sliding layer with the fit-optimized ball nut device, a low-friction linear movement of the ball nut device can be achieved, thereby increasing the efficiency of the steering gear.

[0017] In one specific embodiment, the sliding layer is formed by a sliding element arranged on the guide contour and / or the counter contour. In particular, the at least one sliding element is formed by a sliding block, a sliding rail or a sliding sleeve section which is arranged at least or exclusively in the contact area of ​​the guide contour or the counter contour. The sliding element can be arranged or fixed on the guide contour, with the counter contour forming a direct friction partner for the sliding element. Alternatively, the sliding element can be arranged or fixed on the counter contour, with the guide contour forming a direct friction partner for the sliding element. By arranging the sliding element on the guide contour or the counter contour, a particularly cost-effective implementation of the sliding layer can be achieved, since it only has to be frictionally applied in the contact areas of the guide contour or the counter contour.the counter contour. This reduces or optimizes the effort required for plain bearing production and assembly.

[0018] In a specific implementation, it is provided that the guide contour has at least or exactly one guide surface extending in the axial direction with respect to the first axis of rotation and the counter contour has at least one counter surface complementary to the guide contour, wherein the guide surface and the counter surface are designed such that they are and / or can be supported against one another in a form-fitting manner in the radial direction and in the circumferential direction. In particular, the guide surface is aligned in the same direction in the axial direction and / or parallel to the counter surface, so that the guide surface is guided along the counter surface in the axial direction. Particularly preferably, the guide surface and the counter surface have a similar geometric shape when viewed in cross-section. Form-fitting is preferably to be understood to mean that the guide surface and the counter surface are supported against one another in the radial direction and in the circumferential direction without or with little play.In particular, “low backlash” is to be understood as meaning that the guide surface is supported on the counter surface with a small amount of play. For example, the play can be less than 50 pm, preferably less than 30 pm, especially less than 10 pm. Particularly preferably, the ball nut device is arranged at a distance outside the guide surface and / or without contact with the gear housing. In particular, the sliding layer or the sliding element is arranged either flatly on the guide surface or the counter surface, preferably over the entire surface. By reducing the contact area between the ball nut device and the gear housing to that of the guide surface and the counter surface, both the friction during axial movement and the mechanical machining effort of the ball nut device and the gear housing can be reduced.

[0019] In a further specific embodiment, the guide contour is formed by a recess running in the axial direction, the guide surface being concave and / or V-shaped in cross-section. The recess is preferably introduced into the outer circumference of the ball nut device in the radial direction with respect to the first axis of rotation. The counter-contour can be formed by an elevation complementary to the recess, so that the counter-contour engages positively in the guide contour in the radial and circumferential directions. For example, the recess is formed by an axially continuous groove with a constant cross-sectional profile. A guide contour is thus proposed which enables both radial and circumferential support of the guide surface and the counter-surface.

[0020] In an alternative embodiment, the guide contour is formed by an elevation running in the axial direction, wherein the guide surface is convex and / or C-shaped in cross-section. The elevation is preferably formed on the outer circumference of the ball nut device in the radial direction with respect to the first axis of rotation. The counter contour can be formed by a recess complementary to the elevation, so that the guide contour engages the counter contour in a form-fitting manner in the radial and circumferential directions. An alternative guide contour is thus proposed which enables both radial and circumferential support of the guide surface and the counter surface.

[0021] In a specific implementation, it is provided that the guide surface and the counter surface are curved to an axis of symmetry running in the radial direction with respect to the first axis of rotation. In other words, a vertex of curvature of the curved guide surface and the curved counter surface lies on the axis of symmetry. Alternatively or optionally additionally, the guide surface and the counter surface are designed at an angle to the axis of symmetry. In other words, the axis of symmetry forms an angle bisector of the guide surface and the counter surface. Preferably, the axis of symmetry is defined by the center line of the toothed section. Preferably, the recess has a larger radius of curvature and / or angle than the elevation, so that tilting of the ball nut device in the axial direction is prevented. In particular, the elevation has at least one radius of curvature and / or angle that conforms to the contour of the recess.

[0022] In a further embodiment, the cylinder chamber is divided by the ball nut device into two separate cylinder chambers, wherein the cylinder chambers are fluidically connected to one another via a free area formed in the circumferential direction between the guide contour and the toothed section, in which free area the ball nut device is arranged at a distance from the inner circumference of the cylinder chamber. Preferably, the guide contour is supported on the counter contour in exactly one contact area, wherein a free area adjoins the contact area on both sides in the circumferential direction. For example, the outer circumference of the ball nut device is spaced from the inner circumference in the free area by a distance of more than 0.1 mm, preferably more than 1 mm, in particular more than 5 mm. The free areas ensure a contact-free arrangement of the ball nut outside the contact area.The fluidic connection of the cylinder chambers also makes it easy to equalize pressure between the two cylinder chambers, thereby improving the operating behavior of the steering gear.

[0023] In a specific embodiment, the ball nut device is designed in several parts, wherein the ball nut device has a ball nut and a guide sleeve, wherein the ball nut is received in the guide sleeve, preferably in a rotationally fixed manner. In particular, the guide sleeve serves to provide linear guidance for the ball nut along the first axis of rotation and to absorb mechanically induced radial loads of the ball screw drive. In principle, the ball nut can be received within the guide sleeve without play. Alternatively, however, the ball nut can also be received in the guide sleeve with little play, at least in the radial direction, in order to compensate for tolerances. The guide sleeve preferably has the guide contour and the toothed section. In particular, the guide sleeve can be designed such that it is optimized with regard to radial fit and / or axial guidance.Accordingly, the ball nut can be designed to optimize its force transmission. By housing the ball nut separately in the guide sleeve, these can be optimized and / or selected independently of each other with regard to their function, fit, material, shape, etc.

[0024] In a specific implementation, it is provided that the ball nut has a round-cylindrical shape and that the guide sleeve has a shape that deliberately deviates from the round-cylindrical shape, preferably is non-circular. In particular, the guide sleeve has the deviating or non-circular shape at least on the outside, whereas the guide sleeve has a shape complementary to the ball nut on the inside. Preferably, the guide sleeve has an axial bore into which the ball nut is axially inserted and secured against loss. Particularly preferably, the ball nut has at least or exactly one of the raceways on the inside, as already described, in which the at least one row of balls is circumferentially guided. In particular, the ball nut has more than two, preferably more than four, especially more than six of the raceways.A particularly simple and cost-effective production of the ball nut and the guide sleeve is thus proposed.

[0025] In a further specific embodiment, it is provided that the ball nut is received in the guide sleeve at least in a form-fitting manner in the axial and radial directions with respect to the first axis of rotation. For this purpose, the guide sleeve can have a circumferential support section on one axial end face of the ball nut, wherein the ball nut is supported on the guide sleeve in an axial direction with respect to the first axis of rotation via the support section. For example, the support section is formed by a collar, flange, annular shoulder or the like surrounding the first axis of rotation. Furthermore, the steering gear can have a securing element which is mounted on the other axial end face of the ball nut in the guide sleeve, wherein the ball nut is supported on the guide sleeve via the securing element in an axial direction, preferably opposite to the axial direction. The securing element is preferably form-fitting, e.g.via a screw connection, and / or non-positively, e.g., via a press fit, within the guide sleeve or the receiving section. For example, the securing element is designed as a retaining ring surrounding the first axis of rotation. Optionally, the ball nut can be non-positively received in the guide sleeve in the axial and / or radial direction with respect to the first axis of rotation. This ensures secure force transmission from the ball nut to the guide sleeve as well as simple and secure assembly of the ball nut in the guide sleeve.

[0026] In a further embodiment, the axial length of the guide sleeve is at least 10% longer than the axial length of the ball nut. In particular, the axial length of the guide sleeve is more than 10%, preferably more than 15%, and especially more than 20% of the axial length of the ball nut. The extended guide sleeve further improves the radial support of the guide sleeve in the gearbox housing.

[0027] In a further specific implementation, it is provided that the ball nut and the guide sleeve are made of a different material and / or have different material properties. In particular, the ball nut and the guide sleeve can have different hardness and / or strength. Preferably, the ball nut is optimized with regard to force transmission and the guide sleeve with regard to fit and / or friction. In other words, the guide sleeve and the sliding layer, in particular the sliding element, have a low-friction material pairing, preferably a low-friction material and surface pairing. Preferably, at least the guide sleeve is made of steel or a steel alloy. This can further increase the efficiency and service life of the steering gear.

[0028] Another subject of the invention relates to an electric steering system for a vehicle, with the steering gear as already described above or according to one of claims 1 to 14. In particular, the electric steering system serves to electrically, in particular electromechanically, implement a steering command generated by a steering handle to at least one steerable vehicle wheel. The vehicle can in principle be a passenger car (PC), an agricultural or construction machine. The vehicle is preferably a commercial vehicle (CV). In particular, the electric steering system is designed as an electric power steering system (EPS). In particular, the electric power steering system has an electric servo motor for steering assistance.During a steering operation, a steering angle is specified by the steering handle as a measure of the desired wheel steering angle for the at least one steerable wheel, with the electric servomotor providing additional torque for steering assistance. In particular, the electric servomotor is drive-connected to the threaded spindle, in particular the input interface.

[0029] Further features, advantages, and effects of the invention will become apparent from the following description of preferred embodiments of the invention. These show:

[0030] Fig. 1 is a sectional view of a steering gear for a steering system of a vehicle as an embodiment of the invention;

[0031] Fig. 2 is a further sectional view of a steering gear for a steering system of a vehicle as an embodiment of the invention;

[0032] Fig. 3 is a perspective view of a ball nut device for the steering gear of Fig. 2;

[0033] Fig. 4 shows an alternative embodiment of the steering gear in the same representation as Fig. 2;

[0034] Fig. 5 is a schematic representation of an electric steering system with the steering gear from Fig. 1;

[0035] Figure 1 shows a steering gear 1 for a vehicle, which is designed as a so-called recirculating ball gear, wherein for this purpose an input shaft designed as a threaded spindle 2 is operatively connected via a ball screw drive to an output shaft designed as a segment shaft 4. For this purpose, the threaded spindle 2, to form the ball screw drive, is drivingly connected via at least one row of balls to a ball nut device 3, whereby a rotational movement of the threaded spindle 2 about a first axis of rotation 100 is converted into a linear movement of the ball nut device 3 along the first axis of rotation 100. The steering gear 1 has a gear housing 5, wherein the threaded spindle 2 is mounted in the gear housing 5 so as to be rotatable about the first axis of rotation 100 and the segment shaft 4 about a second axis of rotation 101. For this purpose, the threaded spindle 2 is rotatably supported in the gear housing 5 via two bearing devices 6a, 6b.For example, the bearing device 6a is designed as a needle bearing, and the second bearing device 6b is designed as a double-row ball bearing. In a plan view, the first and second rotation axes 100, 101 are aligned transversely and perpendicularly to each other, respectively.

[0036] The threaded spindle 2 has an input interface 7 extending from the transmission housing 5, which serves for the mechanical connection of a steering drive (not shown). The input interface 7 is formed, for example, by a shaft journal that carries a positive-locking contour, e.g., a spline. Accordingly, the output shaft 4 has an output interface 8, as shown in Figure 2, which serves for the mechanical connection to a steering linkage (not shown).

[0037] The threaded spindle 2 has a helical groove 9 on its outer circumference, which serves to guide a row of balls (not shown). The ball nut device 3 can have a further groove (not shown) on its inside, which, together with the groove 9, forms a ball raceway for guiding the balls in the row of balls. The ball nut device 3 is arranged coaxially to the first rotational axis 100 and is mounted in a cylindrical chamber 10 of the gear housing 5 for axial displacement.

[0038] The ball nut device 3 is designed in several parts and has a ball nut 11 and a guide sleeve 12, which is arranged in the cylinder chamber 10 for axial guidance and radial support of the ball nut 11. For this purpose, the ball nut 11 is fixed within the guide sleeve 12 at least in the axial direction with respect to the first axis of rotation 100, so that the linear movement generated by the ball nut 11 is directly transmitted to the guide sleeve 12, which also executes the linear movement along the first axis of rotation 100. In simple terms, the ball nut 11 is motion-coupled to the guide sleeve 12 at least in the axial direction with respect to the first axis of rotation 100. The guide sleeve 12 has a toothed section 13 on its outside, via which the guide sleeve 12 meshes with a toothing geometry 14 of the segment shaft 4, designed as a segment toothing.The toothed section 13 is formed, for example, by a rack toothing, which extends in the axial direction over the entire axial length of the guide sleeve 12 and in sections in the circumferential direction on the guide sleeve 12. The toothed geometry 14 of the segment shaft 4 extends over an angular range of approximately 180 degrees. A longitudinal displacement of the guide sleeve 12 along the first rotational axis 100 thus causes the segment shaft 4 to rotate within the angular range about the second rotational axis 101, thereby adjusting the steering angle of the vehicle.

[0039] The guide sleeve 12 has a guide contour 15 on its outer circumference, which is supported in the radial direction and in the circumferential direction in a defined contact area 104 on a mating contour 16 arranged on the inner circumference of the cylinder chamber 10. The guide contour 15 and the mating contour 16 are aligned in the axial direction with respect to the first axis of rotation 100, so that the guide sleeve 12 is guided straightly or linearly in the axial direction via the guide contour 15 on the mating contour 16. The guide sleeve 12 is supported exclusively in the contact area 104 or is arranged outside the contact area 104 at a distance from the inner circumference of the cylinder chamber 10. Thus, radial forces and rolling moments introduced, for example, via the segment shaft 4 can be securely supported on the gearbox housing 5 via the guide contour 15.

[0040] The guide sleeve 12 has a receiving section 17 on its inside, which is designed and / or suitable for the positively receiving of the ball nut 11, at least in the axial direction. For this purpose, the receiving section 17 is delimited in an axial direction 102 relative to the first axis of rotation 100 by a circumferential support section 18, on which the ball nut 11 is positively supported in the axial direction 102. The support section 18 is formed, for example, by an annular shoulder formed on the inner circumference of the guide sleeve 12.

[0041] Furthermore, the receiving section 17 is delimited in an axially opposite direction 103 by a securing element 19, against which the ball nut 11 is positively supported in the axially opposite direction 103. The securing element 19 is designed as a retaining ring that is screwed or pressed into the guide sleeve 12. For example, the ball nut 11 is fixed in the axial direction with respect to the first axis of rotation 100 between the support section 18 and the securing element 19 without play, in particular by clamping.

[0042] The steering gear 1 also has a sliding layer 21 formed by a sliding element 20, which is arranged within the cylinder chamber 10 on the mating contour 16, wherein the guide sleeve 12 is supported on the mating contour 16 in the radial direction and in the circumferential direction with the guide contour 15 via the sliding element 20. For example, the sliding layer 21 can be formed from a friction-optimized plastic, such as PTFE. The guide sleeve 12 thus forms a friction partner for the sliding layer 21 in the contact area 104 and can be made of steel or a steel alloy. The sliding element 20 can, for example, be fixed to the mating contour 16 in a material-to-material manner, e.g., via an adhesive connection. To further improve the radial support, it is provided that, relative to the first axis of rotation 100, an axial length of the guide sleeve 12 is, for example, more than 15% longer than an axial length of the ball nut 11.

[0043] As shown in Figure 2, the guide contour 15 is arranged opposite the toothed section 13 in the radial direction with respect to the first axis of rotation 100 or offset by 180° in the circumferential direction. The guide contour 15 is formed by a recess arranged on the outer circumference of the guide sleeve 12 and having a V-shaped guide surface 22. Correspondingly, the counter contour 16 is formed by an elevation arranged on the inner circumference of the cylinder chamber 10 and having a V-shaped counter surface 23 complementary to the guide surface 22. The guide surface 22 and the counter surface 23 are arranged at an angle with respect to an axis of symmetry 106 running radially with respect to the first axis of rotation 100 and, viewed in cross-section, each have an obtuse angle W. For example, the angle W of the guide surface 22 is greater than the angle of the counter surface 23, with the guide surface 22, for example, having an angle W of approximately 130°.The axis of symmetry 106 forms an angle bisector of the angle W and at the same time a center line of the toothed section 13. The sliding element 20 forms a contour partner to the mating contour 16, so that the sliding layer 21 is preferably arranged over its entire surface on the mating surface 23. The mating contour 16 thus engages with the guide contour 15 via the sliding element 20, so that the guide sleeve 12 is supported on the sliding element 20 in a form-fitting manner in the radial direction and in the circumferential direction, in particular with little play and / or a precise fit. For this purpose, the guide sleeve 12 is supported on the sliding element 20 at least in the contact area 104 in the radial direction and in the circumferential direction with a clearance fit or a slight radial play of less than 30 pm.

[0044] By combining a friction-optimized sliding element 20 with a design-optimized guide sleeve 12, taking into account the radial fit design, both the radial and rotationally fixed support of the ball nut assembly 3 required for safe and long-lasting operation and a low-friction linear movement of the ball nut assembly 3 can be ensured. This can increase the service life and efficiency of the ball screw assembly or the steering gear 1.

[0045] In the circumferential direction, a free area 105 is formed on each side of the contact area 104, over which the guide sleeve 12 is arranged at a distance from the inner circumference of the cylinder chamber 10. For example, the guide sleeve is arranged in the free area 105 at a distance of greater than 1 mm from the inner circumference of the cylinder chamber 10. Through the opening thus formed, a first and a second cylinder chamber 24a, 24b can be fluidically connected to one another, as shown in Figure 1, whereby pressure equalization takes place between the two cylinder chambers 24a, 24b and the axial movement of the ball nut device 3 is not inhibited.

[0046] As shown in Figure 3, the guide contour 15 is formed by a continuous V-groove in the axial direction relative to the first rotational axis 101, which extends over the entire axial length of the guide sleeve with a constant cross-sectional profile. For example, the guide surface 22 can have a friction-optimized surface and / or surface orientation relative to the counter surface 23 or the sliding layer 20. The V-shaped design of the guide contour 15 thus realizes a linear guide for the ball nut device 3 in the cylinder chamber 10, which simultaneously enables radially fixed and rotationally fixed support on the gear housing 5.

[0047] Figure 4 shows an alternative embodiment of the guide contour 15, which is formed by a raised portion arranged on the outer circumference of the guide sleeve 12 with a C-shaped guide surface 22. Correspondingly, the counter-contour 16 is formed by a recess arranged on the inner circumference of the cylinder chamber 10 with a C-shaped counter-surface 23 complementary to the guide surface 22. The guide surface 22 and the counter-surface 23 are curved with respect to the axis of symmetry 106 and, viewed in cross-section, each have a radius R. For example, the radius R of the guide surface 22 is smaller than the radius of the counter-surface 23. A vertex of curvature of the guide surface 22 and the counter-surface 23 lies on the axis of symmetry 106, wherein the axis of symmetry 106 simultaneously forms the center line of the toothed section 13.The guide contour 15 is thus in engagement with the counter contour 16 via the sliding element 20, so that the guide sleeve 12 is supported on the sliding element 20 in a form-fitting manner in the radial direction and in the circumferential direction, in particular with little play and / or a precise fit.

[0048] Figure 4 shows a highly simplified representation of an electric steering system 25 for a vehicle, in particular for a commercial vehicle. The electric steering system 25 is embodied, for example, as an electric power steering system.

[0049] The steering system 25 has a steering handle 26 designed as a steering wheel, which is connected to the steering gear 1 via a steering column 27, as described in Fig. 1. The steering gear 1 serves to adjust a wheel steering angle of at least one steerable vehicle wheel 28 of the vehicle as a function of a rotation of the steering column 27. For this purpose, the steering column 27 is connected to the threaded spindle 2, in particular the input interface 7, and the segment shaft 4, in particular the output interface 8, is connected to a steering rod 30 via a steering column arm 29, wherein a rotational movement of the steering column 27 is translated into a pivoting movement of the steering column arm 29 via the ball screw drive 3. The ball screw drive 3 amplifies the rotational movement of the segment shaft 4 resulting from the actuation of the steering handle 26.The rotary movement of the segment shaft 4 is in turn converted via the steering column lever 29 into a linear movement of the steering rod 30, which is connected via a track lever 31 to the vehicle wheel 28 to be steered in order to adjust the corresponding wheel steering angle on the vehicle wheel 28.

[0050] Furthermore, the steering system 25 can have an electric drive motor 32, which is drive-coupled to the steering gear 1 to apply additional torque. For example, the drive motor 31 and the steering column 27 can jointly act on the threaded spindle 2 of the steering gear 1. Thus, the steering column 27 and the drive motor 32 form a steering drive of the steering system 1. The electric drive motor 32 is designed as an electric servomotor.

[0051] Reference symbol

[0052] Steering gear Threaded spindle Ball nut device Segment shaft Gearbox housing a, b Bearing device Input interface Output interface Raceway groove 0 Cylinder chamber 0 Ball nut 2 Guide sleeve 3 Toothed section 4 Toothed geometry 5 Guide contour 6 Counter contour 7 Receiving section 8 Support section 9 Securing element 0 Sliding element 1 Sliding layer 2 Guide surface 3 Counter surface 4a, b Cylinder chamber 5 Steering system 6 Steering handle 7 Steering column 8 Vehicle wheel 9 Pitman arm 0 Steering rod 1 Track arm 2 Drive motor 100 First axis of rotation

[0053] 101 second axis of rotation

[0054] 102 axial direction

[0055] 103 axial opposite direction

[0056] 104 Contact area

[0057] 105 outdoor area

[0058] 106 axis of symmetry

[0059] R Radius

[0060] W angle

Claims

Patent claims 1. Steering gear (1) for a steering system (25) of a vehicle, - with a gear housing (5), wherein the gear housing (5) has a cylinder chamber (10), - with a threaded spindle (2) rotatably mounted in the gear housing (5), wherein the threaded spindle (2) has an input interface (7) for connecting a steering drive, - with a segment shaft (4) rotatably mounted in the gear housing (5), wherein the segment shaft (4) has an output interface (8) for connection to a steering linkage, - with a ball nut device (3) which is guided axially with respect to a first axis of rotation (100) of the threaded spindle (2), which ball nut device has a toothed section (13) for meshing engagement with the segment shaft (4), wherein the ball nut device (3) together with the threaded spindle (2) forms a ball screw drive, characterized in that the ball nut device (3) has a guide contour (15) on the outer circumference and the gear housing (5) has a counter contour (16) on the inner circumference of the cylinder chamber (10), wherein the ball nut device (3) is supported via the guide contour (15) in the radial direction and in the circumferential direction with respect to the first axis of rotation (100) on the counter contour (16) and is guided in a straight line in the axial direction with respect to the first axis of rotation (100) on the counter contour (16).

2. Steering gear (1) according to claim 1, characterized in that the guide contour (15) is arranged in the radial direction opposite the toothed section (13) with respect to the first axis of rotation (100).

3. Steering gear (1) according to claim 1 or 2, characterized in that the guide contour (15) and the counter contour (16) are slidably mounted relative to one another via a sliding layer (21).

4. Steering gear (1) according to claim 3, characterized in that the sliding layer (21) is formed by a sliding element (20) arranged on the guide contour (15) and / or the counter contour (16).

5. Steering gear (1) according to one of the preceding claims, characterized in that the guide contour (15) has a guide surface (22) extending in the axial direction with respect to the first axis of rotation (100) and the counter contour (16) has a counter surface (23) complementary to the guide contour, wherein the guide surface (22) and the counter surface (23) are designed such that they are and / or can be supported on one another in a form-fitting manner in the radial direction and in the circumferential direction.

6. Steering gear (1) according to claim 5, characterized in that the guide contour (15) is formed by a recess extending in the axial direction, wherein the guide surface (22) is concave and / or V-shaped in cross section.

7. Steering gear (1) according to claim 5, characterized in that the guide contour (15) is formed by an elevation extending in the axial direction, wherein the guide surface (22) is convex and / or C-shaped in cross section.

8. Steering gear (1) according to one of claims 5 to 7, characterized in that the guide surface (22) and the counter surface (23) are curved and / or angled to an axis of symmetry (106) extending in the radial direction with respect to the first axis of rotation (100).

9. Steering gear (1) according to one of the preceding claims, characterized in that the cylinder space (10) is separated by the ball nut device (3) into two separate cylinder chambers (24a, 24b), wherein the cylinder chambers (24a, 24b) are fluidically connected to one another via a free area (105) formed in the circumferential direction between the guide contour (15) and the toothed section (13), in which the ball nut device (3) is arranged at a distance from the inner circumference of the cylinder space (10).

10. Steering gear (1) according to one of the preceding claims, characterized in that the ball nut device (3) is designed in several parts, wherein the ball nut device (3) has a ball nut (10) and a guide sleeve (12), wherein the ball nut (10) is received in the guide sleeve (12) without play.

11. Steering gear (1) according to claim 10, characterized in that the ball nut (10) has a round-cylindrical shape and that the guide sleeve (12) has a shape that deliberately deviates from the round-cylindrical shape.

12. Steering gear (1) according to claim 10 or 11, characterized in that the ball nut (10) is received in the guide sleeve (12) at least in a form-fitting manner in the axial and radial directions with respect to the first axis of rotation (100).

13. Steering gear (1) according to one of claims 10 to 12, characterized in that an axial length of the guide sleeve (12) is greater than an axial length of the ball nut (10).

14. Steering gear (1) according to one of claims 10 to 13, characterized in that the ball nut (10) and the guide sleeve (12) are made of a different material and / or have different material properties.

15. Electric steering system (25) for a vehicle, comprising the steering gear (1) according to one of the preceding claims.

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