METHOD FOR SETTING AN AXIAL PRELOAD FORCE OF A ROLLER SCREW DRIVE OF AN ACTUATOR OF A STEERING DEVICE OF A MOTOR VEHICLE

Abstract

A method for setting an axial preload force of a roller screw drive (3) which is rotatably mounted in a housing (2) by means of bearings (4, 5) which are axially spaced apart from one another. The housing (2) is split transversely with respect to the thrust rod (7) into a first and a second housing part (8, 9). The roller screw drive (3) is inserted with the two bearings (4, 5) into the second housing part (9). An axial preload force is applied which is transmitted from the first bearing (4) via the roller screw drive (3) to the second bearing (5). An axial load spacing (“X”) between the bearing supporting surface of the first bearing (4) and a second housing edge (31) of the second housing part (9) is measured. An adjusting nut (10) is screwed into the first housing part (8) until an axial adjustable spacing between the end-side adjusting nut supporting surface (12) and the first housing edge (30) of the first housing part (8) is the same size as the measured axial load spacing (“X”). The adjusting nut (10) is then secured in place in the first housing part (8), and the two housing parts (8, 9) are connected to one another, with the result that both bear against one another by their housing edges (30, 31).

Claims

1. A method for setting an axial preload force of a roller screw drive (3) which is rotatably mounted in a housing (2) by means of bearings (4, 5) which are axially spaced apart from one another, the threaded spindle (6) of which is part of a thrust rod (7) penetrating the housing (2), which is split transversely to the thrust rod (7) into a first and a second housing part (8, 9), and the first bearing (4) of which is assigned to the first housing part (8) and the second bearing (5) of which is assigned to the second housing part (9), wherein the first housing part (8) has a first housing edge (30) located transversely to the spindle axis and the second housing part (9) has a second housing edge (31) located transversely to the spindle axis, wherein the two housing edges (30, 31) are designed to rest against one another, and wherein an adjusting nut (10) penetrated by the thrust rod (7) is screwed into the first housing part (8) and is engaged with the end-side adjusting nut supporting surface (12) thereof against a bearing supporting surface (38) of the first bearing (4), according to the following steps: insertion of the roller screw drive (3) with the two bearings (4, 5) into the second housing part (9), application of the axial preload force, which is transmitted from the first bearing (4) via the roller screw drive (3) to the second bearing (5), measuring of an axial load spacing (“X”) between the bearing supporting surface (38) of the first bearing (4) and the second housing edge (31) of the second housing part (9), screwing the adjusting nut (10) into the first housing part (8) until an axial adjustment spacing between the end-side adjusting nut supporting surface (12) to the first housing edge (30) of the first housing part (8) is the same size as the measured axial load spacing (“X”), securing in place of the adjusting nut (10) in the first housing part (8), connecting the two housing parts (8, 9) to one another, with the result that both bear against one another by their housing edges (30, 31).

2. The method according to claim 1, the adjusting nut (10) of which is secured in place on the first housing part (8) by means of a screw lock.

3. The method according to claim 2, the screw lock of which is formed by a material connection (36) or by a thread lock (32) between the first housing part (8) and the adjusting nut (10).

4. The method according to one of claims 1 to 3, the adjusting nut (10) of which is screwed into a threaded bore (13) of the first housing part (8) arranged to be coaxial to the thrust rod (7) and is provided with a radial rim (14) having the supporting surface (12).

5. The method according to one of claims 1 to 4, the bearings (4, 5) of which are formed by axial angular contact roller bearings (15) with tapered raceways (17).

6. The method according to claim 5, the adjusting nut (10) of which has a tapered supporting surface (12) adapted to the tapered raceway (17) as a support for the axial angular contact roller bearing (15).

7. The method according to one of claims 1 to 6, the roller screw drive (3) of which is formed by a planetary roller screw drive (19), the planetary rollers (20) mesh with the groove profiles (21) thereof on the one hand with a groove profile (22) of the nut (23) and on the other hand with a thread (11) of the threaded spindle (6), and the rotationally driven planetary roller carrier (25) thereof accommodates the planetary rollers (20) in the pockets (26) thereof distributed over the circumference, wherein the planetary roller carrier (25) is mounted on the housing (2) on the one hand by means of the axial angular contact roller bearings (15) and on the other hand by means of axial roller bearings (27), which are arranged between the planetary roller carrier (25) and the nut (23).

8. The method according to claim 7, the planetary roller carrier (25) of which has a sleeve element (28) surrounding the nut (23) and flanges (29) which are arranged on both axial sides thereof and which are connected to the sleeve element (28) in a non-rotatable and axially displaceable manner with respect to one another, wherein one of the axial roller bearings (27) each is arranged between the flanges (29) and the nut (23), and wherein one of the axial angular contact roller bearings (15) each is arranged between the flanges (29) and the housing (2).

Description

[0038] The invention is explained in more detail below with reference to an exemplary embodiment shown in a total of seven figures. In the figures:

[0039] FIG. 1 shows an actuator of a rear-wheel steering system of a motor vehicle,

[0040] FIG. 2 shows an enlargement of a section of FIG. 1,

[0041] FIG. 3 shows a detail from FIG. 1,

[0042] FIG. 4 shows further details from FIG. 1,

[0043] FIG. 5 shows a detail from FIG. 1,

[0044] FIG. 6 shows a variant of the detail from FIG. 5; and

[0045] FIG. 7 shows another enlargement of a section of FIG. 1.

[0046] FIG. 1 shows a schematic representation of an actuator for a steering device of a motor vehicle, specifically for a rear-wheel steering system.

[0047] The actuator is provided with an electric motor 1 and has a roller screw drive 3 arranged in a housing 2, which is rotatably mounted in the housing 2 by means of bearings 4, 5 arranged axially spaced apart from one another. An axially displaceable threaded spindle 6 is part of a thrust rod 7 penetrating the housing 2.

[0048] The housing 2 is split transversely to the thrust rod into housing parts 8, 9. The first bearing 4 is associated with the first housing part 8 and the second bearing 5 is associated with the second housing part 9.

[0049] An adjusting nut10 penetrated by the thrust rod 7 is screwed into a thread 11 of the first housing part 8. The first bearing 4 is supported or mounted on an end-side supporting surface 12 of the adjusting nut 10. An axial bearing distance between the two bearings 4, 5 is set by screwing the adjusting nut 10 into the thread 11.

[0050] In the exemplary embodiment, the adjusting nut 10 is screwed into a threaded bore 13 of the first housing part 8 which is arranged coaxially to the thrust rod and forms the thread 11. On the end face thereof facing the first bearing 4, the adjusting nut 10 is provided with a radial rim 14 having the supporting surface 12.

[0051] In the exemplary embodiment, the bearings 4, 5 are formed by axial angular contact roller bearings 15, the tapered raceways 17 of which are inclined to a plane arranged transversely to the spindle axis.

[0052] The adjusting nut 10 has a tapered supporting surface 12 adapted to the axial angular contact roller bearing 15 as a support for the axial angular contact roller bearing.

[0053] The detail enlargements in FIGS. 2 and 7 show an enlarged view of the roller screw drive 3, which is formed by a planetary roller screw drive 19 in the exemplary embodiment. Planetary rollers 20 mesh with the groove profiles 21 thereof on the one hand with groove profiles 22 of a nut 23 and on the other hand with a thread 24 of the threaded spindle 6.

[0054] A rotationally driven planetary roller carrier 25 accommodates the planetary rollers 20 in the pockets 26 thereof distributed over the circumference. The planetary roller carrier 25 is mounted on the housing 2 on the one hand by means of the axial angular contact roller bearings 15, 16 and on the other hand by means of axial roller bearings 27, which are arranged between the planetary roller carrier 25 and the nut 23.

[0055] The planetary roller carrier 25 has a sleeve element 28 that engages around the nut 23 and flanges 29 arranged on both axial sides, which are connected to the sleeve element 28 in a non-rotatable and axially displaceable manner with respect to one another, wherein one of the axial roller bearings 27 each is arranged between the flanges 29 and the nut 23, and one of the axial angular contact roller bearings 15 each is arranged between the flanges 29 and the housing 2.

[0056] The electric motor 1 mentioned at the outset drives the planetary roller carrier 25 of the planetary roller screw drive 19 via a belt drive 37 (FIGS. 1, 2). Under the rotation thereof, the planetary rollers 20 orbit the threaded spindle 6 and roll off the threaded spindle 6 and the nut 23. The rolling of the planetary rollers 20 causes the nut 23 to rotate relative to the threaded spindle 6 and to the planetary roller carrier 25. The thrust rod 7 is displaced axially in this way.

[0057] FIGS. 3 and 4 clearly show the first housing part 8, which has a first housing edge 30 located transversely to the spindle axis and the second housing part 9 thereof has a second housing edge 31 located transversely to the spindle axis, which rest against one another, as can be clearly seen in FIG. 2.

[0058] FIGS. 5 and 6 show two examples of a screw lock, by means of which the adjusting nut 10 is secured in place on the first housing part 8. The screw lock according to FIG. 5 is carried out by a thread lock 32 between the first housing part 8 and the adjusting nut 10, and according to FIG. 6 is formed by a material connection 36 by means of a coating 33 of the screw thread 34 of the adjusting nut 10.

[0059] In the case of the thread lock 32, a special thread 35 is pressed into a longitudinal groove that is made in the screw thread 34.

[0060] In the case of the coating 33, a central thread portion of the screw thread 34 is coated.

[0061] FIG. 7 shows a further enlargement of a section of FIG. 1, specifically in the area of the first bearing 4, that is the axial angular contact roller bearing 15. The running disks 40, 41 thereof and the set of rollers 42 arranged between the running disks can be clearly seen. A mean bearing diameter dL circumscribes a circular path that forms a reference line on an end face 43 of the running disk 40 facing the adjusting nut 10, from which a distance “x” can be measured in the axial direction to the second edge of the housing edge 31, as is explained in more detail below.

[0062] The setting of a desired axial preload of the planetary roller screw drive 19 can be carried out in a simple manner with the proposed actuator. The planetary roller screw drive 19 is inserted with the two axial angular contact roller bearings 15 into the second housing part 9 (FIG. 4). The axial angular contact roller bearing 15 as the second bearing is inserted in the intended bearing point thereof of the second housing part 9. The other axial angular contact roller bearing 15 as the first bearing 4 is also mounted. Both axial angular contact roller bearings 15 are arranged on both sides of the flanges 29 of the planetary roller carrier 25.

[0063] An axial load is now introduced, which is transmitted from the first bearing 4—axial angular contact roller bearing 15—via the planetary roller screw drive 19 to the second bearing 5—thus the other axial angular contact roller bearing 15. This axial load is so great that a desired preload force is set. An axial load distance “X” is now measured (FIG. 4) starting from the reference line, which is formed as a circular path with the mean bearing diameter “d.sub.L” of the axial angular contact roller bearing 15 on the side of the bearing disk 40 thereof facing the adjusting nut 10, up to the second housing edge 31 of the second housing part 9.

[0064] The adjusting nut 10 can now be screwed into the first housing part 8 (FIG. 3) and an axial adjustment distance can be measured, starting from a circular reference line on the tapered supporting surface 12 of the adjusting nut 10, with the mean bearing diameter “d.sub.L” of the axial angular contact roller bearing 15. Starting from this reference line, the axial adjustment distance to the first housing edge 30 of the first housing part 8 is set (see FIG. 3). The adjusting nut 10 is screwed in until the axial adjustment distance has reached the amount “x”.

[0065] A securing in place of the adjusting nut 10 in the first housing part 8 reliably maintains the preload once it has been set during operation of the actuator. Finally, the two housing parts 8, 9 can be assembled and the actuator can be completed.

[0066] The reference lines on the tapered supporting surface 12 and on the bearing disk 40 are in the same place in the axial direction after assembly is complete and coincide. The housing edges 30, 31 of the two housing parts 8, 9 are also in the same place in the axial direction after assembly is complete and coincide. As a result, the adjustment distance and the load distance “X” are of the same amount.

[0067] The two housing parts 8, 9 can now be screwed together.

[0068] After assembly, the desired axial preload force is set on the roller screw drive.

LIST OF REFERENCE SYMBOLS

[0069] 1 Electric motor [0070] 2 Housing [0071] 3 Roller screw drive [0072] 4 First bearing [0073] 5 Second bearing [0074] 6 Threaded spindle [0075] 7 Thrust rod [0076] 8 First housing part [0077] 9 Second housing part [0078] 10 Adjusting nut [0079] 11 Thread [0080] 12 Adjusting nut supporting surface [0081] 13 Threaded bore [0082] 14 Radial rim [0083] 15 Axial angular contact roller bearing [0084] 16 [0085] 17 Tapered raceway [0086] 18 [0087] 19 Planetary roller screw drive [0088] 20 Planetary rollers [0089] 21 Groove profile [0090] 22 Groove profile [0091] 23 Nut [0092] 24 Thread [0093] 25 Planetary roller carrier [0094] 26 Pockets [0095] 27 Axial roller bearings [0096] 28 Sleeve element [0097] 29 Flange [0098] 30 First housing edge [0099] 31 Second housing edge [0100] 32 Thread lock [0101] 33 Coating [0102] 34 Screw thread [0103] 35 Thread [0104] 36 Material connection [0105] 37 Belt drive [0106] 38 Bearing supporting surface [0107] 39 [0108] 40 Running disk [0109] 41 Running disk [0110] 42 Roller set [0111] d.sub.L