Ball return with axially mountable mounting sleeve

Abstract

Power steering (1) for a motor vehicle, comprising a servo motor (14) which drives an axially displaceable rack (6) via a ball nut (11) rotatably mounted in a bearing in a housing, wherein the ball nut (11) engages with a threaded spindle (9) formed on the rack (6) and has a ball thread (17) on its inside for rolling balls (18), and with an external ball return (20) which connects the beginning of the ball thread (17) to the end of the ball thread (18) to enable continuous rotation of the balls (18), and with a deflection body (16) and a sleeve (15), characterized in that a return channel (20') of the ball return (20) is formed by the deflection body (16) and the sleeve (15), wherein the division of the return channel (20') between the deflection body (16) and the sleeve (15) is the outer contact plane of the spheres (18).

Description

[0001] The present invention relates to a power steering system having the features of the preamble of claim 1 and a sleeve for such a power steering system.

[0002] Ball screw drives are used to convert rotary motion into linear motion, or vice versa. In the steering systems of motor vehicles with an electric servo drive that operates via a ball screw drive, the rack has a section designed as a threaded spindle. A ball nut is mounted on the threaded spindle and is rotatably supported on it by means of balls. A servo motor drives the ball nut via a gearbox to provide electric assistance for the longitudinal displacement of the rack. The rack with the threaded spindle section is housed in a casing. The ball nut is rotatably mounted in this casing by means of a rolling bearing. The rolling bearing has an outer ring and an inner ring.

[0003] From DE 10 2010 054 134, a plastic sleeve is known which is slid over the ball nut to radially secure an external ball return system. The sleeve has arcuate and spring-loaded support areas on its inner surface that bear against the ball nut. A disadvantage of such a sleeve is its complex manufacturing process. Furthermore, a tubular deflector is disclosed that guides the balls back into the ball nut.

[0004] This tubular return path requires additional installation space, which is considered a disadvantage.

[0005] EP 1 659 312 B1 discloses a ball screw drive in which the plastic deflection elements are inserted into the base body from the outside. The deflection elements protrude beyond the outer circumference of the metallic base body of the ball nut. Recesses are provided inside the toothed belt pulley for securing the deflection elements in the ball nut. This direct attachment of the deflection elements to the toothed belt pulley has the disadvantage that, in the event of a toothed belt breakage, parts of the pulley can become trapped between the base body and the deflection elements, hindering or blocking the rotation of the ball nut.

[0006] A method for manufacturing a rotary-translational transmission is known from German patent application DE 10 2013 213 957 A1. The return mechanism for recirculating the rolling elements is formed by an inner and an outer return element, the outer return element being a sleeve.

[0007] The invention is based on the objective of creating a power steering system with a ball screw drive in which the ball return requires little installation space and is easy to manufacture, and in which the vehicle should remain steerable even if the timing belt breaks.

[0008] This problem is solved by a power steering system with the features of claim 1.

[0009] The power steering system, intended for a motor vehicle, comprises a servo motor that drives an axially displaceable rack via a ball nut rotatably mounted in a bearing within a housing. The ball nut engages with a threaded spindle formed on the rack and has a ball thread on its inner surface for rolling balls. The system also includes an external ball return system that connects the beginning and end of the ball thread to allow for continuous rotation of the balls, a deflector, and a sleeve. The deflector and sleeve together form a return channel for the ball return system. The sleeve thus performs two functions: partially forming the return channel and securing the deflector. The division of the return channel between the deflector and the sleeve lies in the outer contact plane of the balls.The outer contact plane of the balls is the area that forms the connecting surface between the ball and the sleeve but is not in contact with the adjacent balls or with the return channel.

[0010] The deflecting body preferably has a recess that forms an open return channel. It is advantageous if the sleeve, which slides axially towards the ball nut and the deflecting body, closes the open return channel.

[0011] Preferably, the ball nut has two recesses for the entry and exit of balls for external return to the opposite end of the ball screw.

[0012] In an advantageous embodiment, the deflecting body has pins for positioning it on the ball nut. These pins preferably engage in the recesses of the ball nut, thus positioning and securing the deflecting body on the ball nut.

[0013] The sleeve preferably encompasses the ball nut and the deflecting body placed on the ball nut, thus securing the position of the deflecting body on the ball nut.

[0014] It is advantageous if the deflector body has two further recesses, each arranged laterally to and parallel with the recess of the return channel. These recesses allow for weight savings.

[0015] Preferably, the longitudinal section of the return channel is not circular, but U-shaped. This gives the sleeve a cross-section that allows it to be mounted axially.

[0016] It is advantageous if the sleeve has a cylindrical geometry.

[0017] An embodiment of the invention is described in more detail below with reference to the drawings. Identical or functionally equivalent components are designated with the same reference numerals in all drawings. The drawings show: Fig. 1: A schematic representation of a motor vehicle steering system with an electromechanical servo drive, Fig. 2: a spatial representation of a rack with a ball screw drive and a pulley, Fig. 3: a spatial representation of the rack made of Fig. 2 without pulley, Fig. 4: a spatial representation of a deflecting body arranged on a ball nut, Fig. 5: a spatial representation of the ball nut made of Fig. 4 without sleeve, Fig. 6: an exploded view of the ball screw assembly, as well as Fig. 7: A top view of the deflection body of the Fig. 4.

[0018] In the Fig. Figure 1 schematically depicts an electromechanical motor vehicle steering system 1 with a steering wheel 2, which is non-rotatably coupled to an upper steering shaft 3 and a lower steering shaft 4. The lower steering shaft 4 is non-rotatably connected to a pinion 5. The pinion 5 meshes with a toothed segment of a rack 6 in a known manner. The rack 6 is slidably mounted in a steering housing along its longitudinal axis. At its free end, the rack 6 is connected to tie rods 7 via ball joints (not shown). The tie rods 7 themselves are connected in a known manner via steering knuckles to each steered wheel 8 of the motor vehicle. Rotation of the steering wheel 2, via the connection of the steering shafts 3, 4, and the pinion 5, leads to a longitudinal displacement of the rack 6 and thus to a pivoting of the steered wheels 8.A ball screw 9 is provided on the outer side of the rack 6. This ball screw drive 10 further comprises a ball nut 11 with rotating balls 18 arranged therein. The ball nut 11 is rotationally fixed to a pulley 12, which is positively engaged on its circumferential side by a toothed belt 13. This toothed belt 13 is driven by a servo motor 14. The ball nut 11 is, in turn, rotatably and axially fixedly mounted in the steering housing (not shown) by means of a ball bearing.

[0019] In a manner known per se, the servomotor 14 is controlled by a signal derived from the torque in the steering column to assist the steering movement. The servomotor 14 is set in rotation and, via the toothed belt 13 and the ball nut 11, ultimately drives the rack 6. The required hand torque at the steering wheel 2 is thus reduced.

[0020] In the Fig. 2 and the Fig. Figure 3 shows sections of an electrically driven motor vehicle power steering system according to the invention. The sections show the rack 6 with ball screw 9 and the ball screw drive 10 arranged on it, once with pulley 12 and once without pulley. A sleeve 15 circumferentially encompasses the ball nut 11 and a deflection element 16 mounted on the ball nut 11.

[0021] In the Fig. 4 is the ball nut 11 with attached deflector 16 and in the Fig. Figure 5 shows the ball nut 11 without the deflecting body 16. On its inner surface, the ball nut 11 has a ball thread 17 in which balls 18 roll in a manner known per se. The ball nut 11 has two through-holes 19. One hole 19 is provided for the entry and exit of balls 18 for the external ball return 20 to the opposite end of the ball thread 17. The ball return 20, which connects the two holes 19, is formed at least partially by the deflecting body 16. The ball return 20 is U-shaped. The return channel 20' is formed at least partially by a recess 21 in the deflecting body 16 and two adjoining pins 22. The recess 21 is arranged diagonally across the deflecting body 16, which, as an attachment, is adapted on its inner side to the curvature of the top of the ball nut 11 and extends circumferentially over a limited sector of the ball nut 11. As shown in... Fig. As shown in Figure 6, the deflecting body 16 is inserted into the two recesses 19 of the ball nut 11 by means of the pins 22, so that the ball return 20 is connected to both ends of the ball screw 17.

[0022] The return channel 20' is closed by the sleeve 15. This allows the balls 18 to move along the U-shaped track and be held in the channel. The division of the return channel 20' between the deflector 16 and the sleeve 15 is located in the outer contact plane of the balls 18. During assembly, the deflector 16 is first placed onto the ball nut 11, and then the sleeve 15 is axially slid onto the ball nut 11. The assembly effort is therefore very low.

[0023] In the Fig.Figure 7 shows the deflecting body 16. In addition to the U-shaped return channel 20', the deflecting body 16 has two further U-shaped recesses 23, each arranged laterally to and parallel with the return channel 20'. These recesses 23 serve to optimize weight.

[0024] The ball screw drive according to the invention features a U-shaped ball return system requiring minimal installation space. The ball return system is formed by a deflecting body and a sleeve. The parting line between the deflecting body and the sleeve lies in the outer contact plane of the balls, so that the deflecting body and the sleeve have a particularly simple geometry and the sleeve can be manufactured as a continuous semi-finished product.

Claims

[1] Power steering (1) for a motor vehicle, comprising a servo motor (14) which drives an axially displaceable rack (6) via a ball nut (11) rotatably mounted in a bearing in a housing, the ball nut (11) engaging with a threaded spindle (9) formed on the rack (6) and having on its inside a ball thread (17) for rolling balls (18), and with an external ball return (20) which connects the beginning of the ball thread (17) to the end of the ball thread (17) to enable endless rotation of the balls (18), and with a deflection body (16) and a sleeve (15), characterized by , that a return channel (20') of the ball return (20) is formed by the deflecting body (16) and the sleeve (15), wherein the division of the return channel (20') between the deflecting body (16) and the sleeve (15) runs in the outer contact plane of the balls (18). [2] Power steering according to claim 1, characterized by, that the deflecting body (16) has a recess (21) which forms an open return channel (20'). [3] Power steering according to claim 2, characterized by , that the sleeve (15) which is to be pushed axially onto the ball nut (11) and the deflecting body (16) closes off the open return channel (20'). [4] Power steering according to any one of the preceding claims, characterized by , that the deflecting body (16) has pins (22) for positioning the deflecting body (16) on the ball nut (11). [5] Power steering according to any one of the preceding claims, characterized by , that the ball nut (11) has two recesses (19) for the entry and exit of balls (18) for external return to the opposite end of the ball screw (17). [6] Power steering according to claim 5, characterized by , that the pins (22) of the deflecting body (16) engage in the recesses (19) of the ball nut (11). [7] Power steering according to any one of the preceding claims, characterized by , that the sleeve (15) encompasses the ball nut (11) and the deflecting body (16) placed on the ball nut (11) and thus secures the deflecting body (16) on the ball nut (11). [8] Power steering according to any one of claims 2 to 7, characterized by , that the deflecting body (16) has two further recesses (23) which are arranged laterally to the recess (21) of the return channel (20') and parallel to it. [9] Power steering according to any one of the preceding claims, characterized by , that the ball return (20) is U-shaped. [10] Power steering according to any of the preceding claims, characterized by , that the sleeve (15) has a cylindrical geometry.

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