Steering gear comprising a ball screw drive, and steering system comprising the steering gear
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-23
- Publication Date
- 2026-03-04
AI Technical Summary
Insufficient radial support of the ball nut device in steering gears leads to increased wear and reduced service life of the ball screw drive in vehicle steering systems.
The ball nut device is designed with a lateral surface supported in defined contact areas on the inner circumference of the cylinder space, providing stable radial support and a sliding layer to reduce friction, while maintaining a low-friction linear movement, thereby enhancing the radial fit and extending the service life of the steering gear.
This design improves the radial support and reduces wear, leading to a more stable and efficient steering gear operation with extended service life and improved operating behavior.
Smart Images
Figure IB2024053945_31102024_PF_FP_ABST
Abstract
Description
[0001] Steering gear with a ball screw drive 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 one another 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 publication DE 10 2014 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 medium 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 at the outset, 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. The subject matter of the invention is 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.
[0007] 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.
[0008] 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 in terms of drive technology.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.
[0009] The steering gear has a ball nut device which is guided axially with respect to the first axis of rotation and which has a circumferential surface and 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 essentially in two 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 or is incorporated into the circumferential surface. The toothed section is preferably designed as a rack toothing which extends partially or completely over the axial length of the guide sleeve.
[0010] 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 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 the 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.
[0011] Within the scope of the invention, it is proposed that the outer surface is supported in the circumferential direction in sections in at least or precisely one defined contact area on an inner circumference of the cylinder chamber. Put simply, the ball nut device is supported radially with no or little play in the contact area with respect to the first axis of rotation and is guided or slide-mounted in an axially sliding manner. In particular, “low play” is to be understood as meaning that the outer surface is supported in the radial direction with respect to the first axis of rotation in the contact area with a small radial play on the inner circumference of the cylinder chamber. For example, the radial play in the contact area can be less than 50 pm, preferably less than 30 pm, in particular less than 10 pm.In particular, a defined contact area is understood to mean a contact between the outer surface and the inner circumference of the cylinder chamber, which remains unchanged and / or rotationally fixed at least in the circumferential direction during an axial movement of the ball nut. Preferably, the outer surface is arranged at a distance from and / or without contact with the inner circumference outside the contact area. In principle, the outer surface can be supported in the contact area via at least or exactly one point contact on the inner circumference. Alternatively, the outer surface is supported in the contact area via a line contact on the inner circumference. In particular, the line contact is defined by a contact line which extends essentially in the axial direction with respect to the first axis of rotation. In particular, the outer surface has a non-circular outer contour when viewed in cross-section.In particular, "non-circular" is to be understood as meaning that the outer surface has an outer contour that deviates from the cylindrical, in particular round, cross-sectional shape of the cylinder chamber. For example, the outer surface can have an essentially elliptical or polygonal shape.
[0012] 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 by supporting the ball nut assembly in at least one contact area, over-determination of the contact areas is avoided and thus particularly stable radial support of the ball nut assembly is enabled. Thus, the radial support of the ball nut, which is necessary for safe and long-lasting operation, can be improved in a simple manner, particularly taking into account the radial fit design, and thus the service life of the steering gear can be extended.
[0013] In a further development, at least one free area is formed in the circumferential direction between the contact area 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. In particular, the free area is to be understood as a contact-free area of the ball nut device or the outer surface with respect to the inner circumference of the cylinder chamber. Preferably, the outer surface in the free area is spaced from the inner circumference by a distance of more than 0.1 mm, preferably more than 1 mm, in particular more than 5 mm. Preferably, 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 the free area.Preferably, the lateral surface is supported in exactly one contact area on the inner circumference of the cylinder chamber, with two free areas adjoining the contact area on both sides in the circumferential direction. Alternatively, the lateral surface can be supported in at least or exactly two contact areas on the inner circumference of the cylinder chamber, with exactly three free areas being formed in the circumferential direction between the toothed section and the two contact areas. In other words, the contact areas and the free areas alternate in the circumferential direction, or a free area borders each contact area in the circumferential direction. Preferably, the lateral surface outside the contact areas or in the free areas has a different diameter and / or radius of curvature than the contact areas. In other words, the lateral surface has a differently curved surface over the circumference.Specifically, the outer surface, at least in the contact areas, has a radius of curvature that closely matches the radius of the inner circumference. The free areas ensure a contactless arrangement of the ball nut outside the contact areas. The fluidic connection of the cylinder chambers also allows for easy pressure equalization between the two cylinder chambers, thereby improving the operating behavior of the steering gear.
[0014] In a further specification, it is provided that the at least one, preferably exactly one contact region is arranged in the radial direction opposite the toothed section with respect to the first axis of rotation. In particular, the contact region 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 contact region is arranged diametrically with respect to the first axis of rotation and / or offset by 180° in the circumferential direction to the toothed section. Alternatively, the at least one contact region or optionally additionally at least one further contact region is arranged offset in the circumferential direction at an angular range of greater than 90° to the toothed section. In particular, the at least one contact region is in the cross-section orviewed in the axial direction with respect to the first axis of rotation, preferably arranged off-center with respect to the center line of the toothed section. Put simply, the at least one contact region is arranged offset from the toothed section by more than 90° and / or less than 180° with respect to the first axis of rotation in the circumferential direction. In particular, exactly two contact regions can be arranged in a Y-shape with respect to the toothed section, with the vertical leg being defined by the center line of the toothed section. A particularly stable support of the ball nut device in the cylinder space is thus proposed, with the at least one contact region opposite the toothed section being able to reliably support a radial force introduced via the segment shaft or direct it into the gear housing.
[0015] In a further development, it is provided that the ball nut device is slide-mounted or slidably supported at least in the contact area via a sliding layer on the inner circumference of the cylinder chamber. 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 ball nut device or the gear housing. Particularly preferably, the ball nut device is supported on the gear housing over the entire axial length or the entire contact area via the sliding layer. The sliding layer can extend, preferably over the entire linear movement range, on the inner circumference of the cylinder chamber. Alternatively, the sliding layer can extend, preferably over the entire axial length, in the contact area of the ball nut device. The ball nut device orthe gearbox housing 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.
[0016] In a specific implementation, it is provided that the sliding layer is formed by a plain bearing sleeve arranged in the gear housing, in particular in the cylinder chamber. In particular, the plain bearing sleeve is designed to run circumferentially around the first axis of rotation or the worm shaft. The plain bearing sleeve preferably has a radial opening through which the ball nut device engages with the segment shaft. In particular, the plain bearing sleeve is received in the cylinder chamber in a form-fitting and / or force-fitting manner, preferably without play, in the radial and / or axial direction with respect to the first axis of rotation. The ball nut device thus forms a direct friction partner for the plain bearing sleeve. The plain bearing sleeve enables a particularly simple and cost-effective arrangement of the sliding layer in the cylinder chamber.In an alternative implementation, it is provided that the sliding layer is formed by a sliding element arranged at least in the contact area. In principle, the sliding element can be formed by a plain bearing sleeve which is formed circumferentially to the outer surface and is fixed to the ball nut device. Alternatively, the at least one sliding element can be formed by a sliding block or a sliding sleeve section which is arranged at least or exclusively in the one contact area and is fixed to the ball nut device. In particular, the steering gear has a separate, associated sliding element for each contact area. The gear housing thus forms a direct friction partner for the sliding elements.By arranging the sliding elements on the ball nut device, a particularly cost-effective implementation of the sliding layer can be achieved, since these only have to be arranged in the contact areas of the ball nut device.
[0017] 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. In particular, the guide sleeve serves for the linear guidance of the ball nut along the first axis of rotation and for absorbing mechanically induced radial loads of the ball screw drive. In principle, the ball nut can be received within the guide sleeve without any 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 outer surface and the toothed section and is thus supported via the at least one contact area in the cylinder chamber or is in meshing engagement with the segment shaft.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 such that it is optimized with regard to force transmission. By accommodating the ball nut separately in the guide sleeve, these can be optimized and / or selected independently of one another with regard to their function, fit, material, shape, or the like. 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 that of the ball nut on the inside.The guide sleeve preferably has an axial bore into which the ball nut is axially inserted and secured against loss. Particularly preferably, the ball nut has at least one of the raceways on its inside, as previously 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, and especially more than six of the raceways. This proposes a particularly simple and cost-effective production of the ball nut and the guide sleeve.
[0018] In a further specific embodiment, 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. Optionally, the ball nut can be received in the guide sleeve in a force-fitting manner in the axial and / or radial directions with respect to the first axis of rotation. This ensures particularly secure support and thus reliable force transmission from the ball nut to the guide sleeve.
[0019] In one specific embodiment, the guide sleeve has a circumferential support section on an axial end face of the ball nut, wherein the ball nut is supported on the guide sleeve in an axial direction relative to the first axis of rotation via the support section. In other words, the axial bore of the guide sleeve is delimited in the axial direction by the support section. In particular, the guide sleeve is and / or can be supported in a form-fitting manner on the support section in the axial direction. In particular, the support section extends radially inward and / or in a radial plane of the first axis of rotation. Preferably, the support section is formed by a collar, flange, annular shoulder or the like that surrounds the first axis of rotation. This enables particularly stable axial support of the ball nut on the guide sleeve.In a further specific embodiment, the steering gear is provided with a securing element which is mounted on an axial end face of the ball nut in the guide sleeve. The ball nut is supported on the guide sleeve in an axial direction, preferably opposite to the axial direction, via the securing element. In other words, the axial bore of the guide sleeve is delimited by the securing element in the axial opposite direction. In particular, the guide sleeve is and / or can be supported in a form-fitting manner on the securing element in the axial opposite direction. The securing element is preferably fixed in a form-fitting manner, 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 securing ring which runs around the first axis of rotation.This ensures particularly simple and safe assembly of the ball nut in the guide sleeve.
[0020] 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 plain bearing sleeve, 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.
[0021] In a further embodiment, it is provided that an axial length of the guide sleeve is at least 10% longer than an axial length of the ball nut. In particular, the axial length of the guide sleeve is more than 10%, preferably more than 15%, especially more than 20% of the axial length of the ball nut. The extended guide sleeve can further improve the radial support of the guide sleeve in the gearbox housing. In a further development, it is provided that the steering gear has a feather key which is mounted radially between the ball nut and the guide sleeve in a feather key groove, wherein either the ball nut or the guide sleeve has the feather key groove. The ball nut is supported on the guide sleeve in a radial direction with respect to the first axis of rotation via the feather key, without play. In particular, the feather key serves to clamp the support of the ball nut in the receiving section.Preferably, the key is partially recessed and / or captively mounted in the keyway. For this purpose, the keyway can be designed, for example, with an undercut, e.g., a trapezoidal or T-shaped groove, for the key. The key enables backlash-free, preferably friction-locked, installation of the ball nut in the radial direction in the guide sleeve.
[0022] 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 (car), 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 servomotor 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 connected to the threaded spindle, in particular to the input interface, for this purpose.
[0023] Further features, advantages, and effects of the invention will become apparent from the following description of preferred embodiments of the invention. These show: Fig. 1 shows a sectional view of a steering gear for a steering system of a vehicle as an embodiment of the invention;
[0024] Fig. 2 shows a further sectional view of a steering gear for a steering system of a vehicle as an embodiment of the invention;
[0025] Fig. 3 is a schematic representation of an electric steering system with the steering gear from Fig. 1;
[0026] Figure 1 shows a steering gear 1 for a vehicle, which is designed as a so-called recirculating ball gear. 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.
[0027] The steering gear 1 has a gear housing 5, wherein the threaded spindle 2 is mounted in the gear housing 5 for rotation about a 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 as a double-row ball bearing. In a plan view, the first and second axes of rotation 100, 101 are aligned transversely and at right angles to each other, respectively.
[0028] The threaded spindle 2 has an input interface 7 leading from the gear 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 having a form-fitting 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). The threaded spindle 2 has a helical groove 9 on its outer circumference, which serves to guide a row of balls (not shown). To form the ball screw drive, the threaded spindle 2 is in peaceful connection with a ball nut device 3 via the row of balls, whereby a rotational movement of the threaded spindle 2 about the 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 ball nut device 3 can have a further running groove, not shown, on the inside, which together with the running groove 9 forms a ball running channel for guiding the balls in the ball row. The ball nut device 3 is arranged coaxially to the first axis of rotation 100 and is mounted in a cylinder chamber 10 of the gear housing 5 so as to be displaceable in the axial direction.
[0029] The ball nut device 3 is designed in several parts and has a ball nut
[0030] 11 and a guide sleeve 12, which is arranged in the cylinder chamber 10 for the 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.
[0031] The guide sleeve 12 has a toothed section 13 on the outside, via which the guide sleeve 12 meshes with a toothed 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.
[0032] 12 and extends in sections in the circumferential direction on the guide sleeve 12. The toothing 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 axis of rotation 100 thus causes the segment shaft 4 to rotate within the angular range about the second axis of rotation 101, whereby a steering angle of the vehicle is adjusted. The guide sleeve 12 also has a jacket surface 15 which is supported in sections in the circumferential direction in at least or exactly one defined contact area 104 on an inner circumference of the cylinder chamber 10. For example, the contact area 104 can be defined by a non-circular shape of the jacket surface 15 that deviates from the cylindrical shape of the cylinder chamber, so that the guide sleeve 12 is supported oroutside the contact region 104, spaced from the inner circumference of the cylinder chamber 10. In the illustrated embodiment, the contact region 104 can be arranged radially opposite the first axis of rotation 100 or offset in the circumferential direction by at least 180° from the toothed section 13. Thus, radial forces introduced, for example, via the segment shaft 4 can be securely supported via the contact region 104.
[0033] The guide sleeve 12 has a receiving section 18 on its inside, which is designed and / or suitable for positively receiving the ball nut 11, at least in the axial direction. For this purpose, the receiving section 15 is delimited in an axial direction 102 relative to the first axis of rotation 100 by a circumferential support section 16, on which the ball nut 11 is positively supported in the axial direction 102. The support section 16 is formed, for example, by an annular shoulder formed on the inner circumference of the guide sleeve 12.
[0034] Furthermore, the receiving section 15 is delimited in an axially opposite direction 103 by a securing element 17, on which the ball nut 11 is positively supported in the axially opposite direction 103. The securing element 17 is designed as a retaining ring which 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 16 and the securing element 17 without play, in particular in a clamping manner.
[0035] The ball nut 11 also has a keyway 19 on the outer circumference, particularly designed as a trapezoidal groove, into which a key 20 is captively mounted. The ball nut 11 is supported radially within the receiving section 18 on the guide sleeve 12 via the key 20. For example, the key 20 serves to provide clamping and / or play-free support for the ball nut 11 in the receiving section 18. For this purpose, the key 20 is recessed in sections into the receiving groove 10, whereby the key 20 forms a type of clamping contour.
[0036] The steering gear 1 also has a sliding layer 22 formed by a plain bearing sleeve 21, which is arranged within the cylinder chamber 10 in the gear housing 5, wherein the guide sleeve 12 is slidably supported in the radial direction on the plain bearing sleeve 21 in the at least one contact area 104. For example, the sliding layer 22 can be formed from a friction-optimized plastic, such as PTFE. The guide sleeve 12 forms a friction partner for the sliding layer 22 in the contact area 104 and can be made of steel or a steel alloy. The plain bearing sleeve 21 is fixed in the cylinder chamber 10 in the axial and radial directions with respect to the first axis of rotation 100 in a form-fitting and / or force-fitting manner, preferably without play.For this purpose, the plain bearing sleeve 21 can be supported in the axial direction 102 on a radial shoulder of the gear housing 5 and in the axial opposite direction 103 on an outer ring of the second bearing device 6b.
[0037] The guide sleeve 12 is supported with its outer surface 15 in the contact area 104 in the radial direction with little play and / or a precise fit on an inner circumference of the plain bearing sleeve 21. For this purpose, the guide sleeve 12 is received in the plain bearing sleeve 21 at least in the contact area 104 in the radial direction with a clearance fit or a small radial play of less than 30 μm. The plain bearing sleeve 21 has an opening 23 in an engagement area of the toothed section 13 with the toothed geometry 14, via which the toothed geometry 14 engages the toothed section 13.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. By combining a friction-optimized plain bearing sleeve 21 with a design-optimized guide sleeve 12, taking into account the radial fit design, both the radial support of the ball nut device 3 required for safe and long-lasting operation and a low-friction linear movement of the ball nut device 3 can be ensured. This can increase the service life and efficiency of the ball screw drive or the steering gear 1.
[0038] As shown in Figure 2, the ball nut device 3 is supported in the radial direction via the guide sleeve 12 in an angular range of approximately 180° opposite the toothed section 13 on the inner circumference of the plain bearing sleeve 21 in the contact area 104. In the circumferential direction, a free area 105 is formed on both sides of the contact area 104, over which the guide sleeve 12 is arranged at a distance from the inner circumference of the plain bearing sleeve 21.
[0039] For this purpose, the lateral surface 15 has a different radius r1, r2, wherein a radius r1 in the contact region 104 is greater than a radius r2 in the free region 105. For example, the guide sleeve is arranged in the free region 105 at a distance of greater than 1 mm from the plain bearing sleeve 21. 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.
[0040] Figure 3 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 designed, for example, as an electric power steering system.
[0041] 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.
[0042] Furthermore, the steering system 26 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.
[0043] Reference symbol
[0044] 1 steering gear
[0045] 2 threaded spindles
[0046] 3 Ball nut device
[0047] 4 segment shaft
[0048] 5 Gearbox housing
[0049] 6a, b storage facility
[0050] 7 Input interface
[0051] 8 Output interface
[0052] 9 Running groove
[0053] 10 Cylinder chamber
[0054] 10 ball nut
[0055] 12 Guide sleeve
[0056] 13 Gear section
[0057] 14 Gear geometry
[0058] 15 Shell surface
[0059] 16 support section
[0060] 17 Securing element
[0061] 18 Recording section
[0062] 19 keyway
[0063] 20 key
[0064] 21 plain bearing sleeve
[0065] 22 Sliding layer
[0066] 23 Breakthrough
[0067] 24a, b cylinder chamber
[0068] 25 Steering system
[0069] 26 Steering handle
[0070] 27 Steering column
[0071] 28 vehicle wheel
[0072] 29 Steering column lever
[0073] 30 Handlebar
[0074] 31 Track lever 32 Drive motor
[0075] 100 first axis of rotation
[0076] 101 second axis of rotation
[0077] 102 axial direction
[0078] 103 axial opposite direction
[0079] 104 Contact area
[0080] 105 outdoor area
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 has a circumferential surface (15) and 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 circumferential surface (15) is supported in sections in at least one fixed contact area (104) on an inner circumference of the cylinder chamber (10).
2. Steering gear (1) according to claim 1, characterized in that in the circumferential direction between the contact area (104) and the toothed section (13) at least one free area (105) is formed, in which the ball nut device (3) is arranged at a distance from the inner circumference of the cylinder space (10).
3. Steering gear (1) according to claim 1 or 2, characterized in that the at least one contact region (104) is arranged in relation to the first axis of rotation (100) in the radial direction opposite to the toothed section (13) and / or is arranged offset in the circumferential direction in an angular range of greater than 90° to the toothed section (13).
4. Steering gear (1) according to one of the preceding claims, characterized in that the ball nut device (3) is slide-mounted in the cylinder chamber (10) at least in the contact region (104) via a sliding layer (22).
5. Steering gear (1) according to claim 4, characterized in that the sliding layer (22) is formed by a sliding bearing sleeve (21) arranged in the cylinder space (10).
6. Steering gear (1) according to claim 4, characterized in that the sliding layer (22) is formed by at least one sliding element arranged in the contact region (104).
7. 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.
8. Steering gear (1) according to claim 7, 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.
9. Steering gear (1) according to claim 7 or 8, 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).
10. Steering gear (1) according to one of claims 7 to 9, characterized in that the guide sleeve (12) has a circumferential support section (16) on an axial end face of the ball nut (10), wherein the ball nut (10) is supported on the guide sleeve (12) in an axial direction (102) via the support section (16).
11. Steering gear (1) according to one of claims 7 to 10, characterized by a securing element (17), wherein the securing element (17) is mounted on an axial end face of the ball nut (10) in the guide sleeve (12), wherein the ball nut (10) is supported in an axial opposite direction (103) via the securing ring (17) on the guide sleeve (12).
12. Steering gear (1) according to one of claims 7 to 10, characterized in that the ball nut (10) and the guide sleeve (12) are made of a different material and / or have different material properties.
13. Steering gear (1) according to one of claims 7 to 12, characterized in that an axial length of the guide sleeve (12) is at least 10% longer than an axial length of the ball nut (10).
14. Steering gear (1) according to one of claims 7 to 13, characterized by a feather key (20) which is mounted in a feather key groove (19) of the ball nut (10) or the guide sleeve (12), wherein the ball nut (10) is supported in the radial direction via the feather key (20) on the guide sleeve (12) without play.
15. Electric steering system (25) for a vehicle, comprising the steering gear (1) according to one of the preceding claims.