planetary roller screw

Abstract

The invention relates to a planetary roller screw having a nut (2) which is arranged on a threaded spindle (1) and is divided into two nut parts (3) transversely to the spindle axis, planetary rollers (3) which are arranged distributed in a circle between the threaded spindle (1) and the nut (2) and which are in mesh with the nut parts (3) and the threaded spindle (1), a rotationally driven planetary roller carrier (8) which is arranged on the threaded spindle (1), the planetary rollers (4) being mounted in recesses (9) of the planetary roller carrier which are arranged distributed in a circle, the planetary rollers being held at a distance in the circumferential direction in order to be able to rotate about a planetary roller axis, and a housing (13) in which the planetary roller carrier (8) is mounted in a rotatable manner. A preloading device (19) is provided in order to adjust the axial preload between the housing (13) and the planetary rollers (4).

Description

TECHNICAL FIELD

[0001] The invention relates to a planetary roller screw for converting a rotary motion into a translatory motion. The invention further relates to a front axle steering system of a motor vehicle and to an actuator of a rear axle steering system having such a planetary roller screw. BACKGROUND

[0002] A planetary roller screw according to the features of the preamble of claim 1 has already been known from DE 10 2018 116 867 A1. The planetary roller screw is provided with a nut arranged on a threaded spindle, which is divided into two nut parts transversely to the spindle axis, and with planetary rollers arranged between the threaded spindle and the nut, which, with their planetary-side groove profile, are in meshing engagement with the groove profile of the nut on the one hand and with the thread profile of the threaded spindle on the other hand. The planetary roller screw further has a planetary roller carrier, in the recesses of which arranged distributed over the circumference, the planetary rollers are mounted in a manner rotatable about their planetary roller axis.

[0003] The planetary roller carrier is joined around the nut, the nut parts of which are preloaded by means of various technical measures to allow play-free engagement with the planetary rollers. The publication proposes to install spacers between the nut parts. The following alternative is also proposed: The nut parts are inserted into two screw sleeves, the nut parts are axially supported on the screw sleeves and are screwed together until the aforementioned play-free engagement is achieved.

[0004] These measures are complex and require corresponding installation space within the planetary roller carrier. However, particularly in automotive applications, there is often a need for cost-effective, space-saving planetary roller screws, especially when the planetary roller screw is used in an actuator of a rear axle steering system or a front axle steering system. SUMMARY

[0005] The invention is based on the object of providing a planetary roller screw according to the preamble of claim 1, which is easy to manufacture and requires less installation space.

[0006] According to the invention, this object is achieved by a planetary roller screw according to claim 1.

[0007] A planetary roller screw is provided with a nut arranged on a threaded spindle, which is axially divided into two nut parts transverse to the spindle axis. The two nut parts are arranged one axially behind the other. The axial distance between the two nut parts is adjusted according to the shape of the planetary rollers that mesh with the nut parts. The two nut parts do not need to be connected to each other by means other than the planetary rollers that mesh with the nut parts. The nut parts can have sleeve-like extensions facing each other, which are coaxial with the nut parts and are interlocked with a very small radial play, i.e. axially overlap each other. In this case, the interlocked extensions are dimensioned such that the nut parts are radially aligned with each other and have a defined radial play or a defined fit to each other.

[0008] Between the threaded spindle and the nut, planetary rollers are arranged distributed in a circle, which on the one hand mesh with the nut parts and on the other hand mesh with the threaded spindle. The planetary rollers can each have a central groove profile that meshes with the thread profile of the threaded spindle and each have an outer groove profile on both sides of the central groove profile, one of the outer groove profiles meshing with one of the nut parts and the other of the outer groove profiles meshing with the other of the nut parts. The central groove profile is larger in diameter than the adjacent outer groove profiles.

[0009] Furthermore, a rotationally driven planetary roller carrier is provided on the threaded spindle, the planets being held at a distance in a circumferential direction and mounted in a rotationally rotatable manner about their planetary roller axis in recesses of the planetary roller carrier arranged distributed in a circle. The planetary roller carrier can be part of a belt wheel, around which a toothed belt of a belt drive is wound. The toothed belt can be driven by an electric motor. Under rotational drive, the planetary carrier rotates about the threaded spindle and the planets roll off the threaded spindle and the nut and rotate in the recesses of the planetary roller carrier about their longitudinal axis. One complete rotation of the planetary roller carrier corresponds to a spindle feed, the amount of which corresponds to the pitch of the thread of the threaded spindle. Therefore, this type of planetary roller screw is pitch correct.

[0010] The planetary roller carrier can have two carrier flanges arranged axially spaced apart from each other and a drive gear or drive sleeve, e.g. a toothed belt wheel, arranged coaxially to the threaded spindle, which drive gear or drive sleeve, e.g. a toothed belt wheel, engages around the nut and is connected in a non-rotatable manner to the two carrier flanges, wherein the two carrier flanges are arranged to be axially displaceable relative to each other. One of the two carrier flanges can be fixedly connected to the drive gear, the other carrier flange can be connected to the drive gear by means of a sliding fit, which allows an axial relative displacement between this carrier flange and the drive gear and thus between the two carrier flanges. The two carrier flanges are provided with pockets to receive the planetary rollers.

[0011] The planetary roller screw has a housing, in which the above-mentioned components are mounted. The housing can be an actuator housing. If the planetary roller screw is part of an actuator of a rear axle steering system of a motor vehicle, the housing can be provided with two through-holes for a push rod to pass through, wherein the threaded spindle is part of the push rod. The housing can be an open component with a fixed mount, on which the moving components of the planetary roller screw are mounted.

[0012] The planetary roller carrier can be supported by means of inner and outer support bearings. One outer support bearing can be located between one nut component and the housing and another outer support bearing can be located between the other nut component and the housing. In this way, the planetary roller carrier can be mounted in the housing in a rotatable manner without any problems, wherein the carrier flanges arranged to be axially displaceable relative to each other simplify the adjustment of the desired axial bearing play or axial preload.

[0013] One inner support bearing can be located between one nut component and one carrier flange and another inner support bearing can be located between the other nut component and the other carrier flange.

[0014] This bearing arrangement is chosen such that the axial play of the planetary roller carrier in the housing can be adjusted to the desired axial preload by means of a preloading device. In the simplest case, the axial bearing surface in the housing-side bearing seat for one outer support bearing can be adjusted such that, with an axial displacement of this axial bearing surface, the axial play of all components involved can be adjusted between the two outer support bearings to the desired axial preload.

[0015] Preferably, the inner support bearings are formed by axial roller bearings. The nut components can be operated without radial load and only transmit axial forces introduced via the threaded spindle into the housing via the support bearings.

[0016] Preferably, the outer support bearing is formed by an angular contact bearing. In this way, the tensile force transmitted by the toothed belt is transmitted as a radial force via the angular contact bearing into the housing. If an angular contact roller bearing with cylindrical rolling elements is used, the raceways of conical shape of this angular contact bearing can be arranged, for example, at an angle of approximately 15 degrees to a plane arranged transversely to the spindle axis. In this way, large axial forces can be transmitted on the one hand and radial forces on the other hand.

[0017] In the case of an angular contact roller bearing as outer support bearing, it is advantageous if the carrier flange of the planetary roller carrier is each provided on its end face facing away from one another with a conical support surface for the angular contact bearing. This one bearing washer of the angular contact roller bearing can lie flat against this support surface, or this support surface can be used directly as a raceway for the cylindrical or tapered rolling elements of the angular contact roller bearing. As mentioned above, the conical angle can be approximately 15 degrees.

[0018] A preloading device is provided in order to adjust an axial preload between the housing and the planetary roller. This axial preload is transmitted from the housing to the planetary roller via two nut components. The support bearings optionally arranged on both sides of the carrier flange in the described manner transmit this axial preload. Under this preload, the planetary roller is subjected to a compressive load.

[0019] Compared to known preloading devices, no special components are required in the installation space inside the planetary roller carrier to establish this preloading. It is sufficient to install the preloading device between the housing and the planetary roller carrier. In addition to a reduction in the installation space required, this means that the mass of the rotating components can be reduced.

[0020] Preferably, the preloading device can have a screw component screwed into the housing, the end face of which facing the outer support bearing is designed as an axial support surface in the housing-side bearing seat for one outer support bearing. It is sufficient to provide this screw component on only one axial side. The other axial support surface on the opposite housing-side bearing seat for the other outer support bearing can be an integral part of the housing. The screw component can be designed as a threaded ring arranged coaxially to the threaded spindle, which is screwed into a threaded hole of the housing arranged coaxially to the threaded spindle.

[0021] As an alternative to the screw component, it is sufficient to insert a compensation ring into the housing, the end face of which is designed as an axial support surface in the housing-side bearing seat for one outer support bearing. The thicker the compensation ring, the smaller the axial play of the planetary roller screw.

[0022] To adjust the desired axial preload or axial play, the preload device is advanced until the corresponding axial play between the housing and the planetary rollers is set. In the case of a ball screw, it is advanced towards one of the outer bearing supports until the desired play or no play is achieved between the housing and the planetary rollers and is then fixed in this ball screw position.

[0023] The planetary roller screw according to the application is particularly suitable for use in an actuator of a rear axle steering system and of a front axle steering system of a motor vehicle. The actuator is provided with a push rod, the ends of which facing away from one another are designed as steering rear wheels of the motor vehicle. In this case, the threaded spindle can be part of the push rod, the threaded spindle being formed between the ends of the push rod. The push rod can have two push rod parts, between which the threaded spindle is arranged and fixedly connected. The free ends of the push rod facing away from one another extend from the housing of the actuator and are provided with steering heads which engage with wheel carriers of the rear wheels.

[0024] Preferably, the actuator is provided with an electric motor and a belt drive, the toothed belt of which is wound around a motor pinion of the electric motor and a drive sleeve. The belt drive and the motor pinion and the planetary roller screw can be arranged in the actuator housing. The electric motor can be arranged outside the housing. BRIEF DESCRIPTION OF DRAWINGS

[0025] The application is explained in more detail below with reference to exemplary embodiments shown in five drawings. In the drawings:

[0026] Figure 1 The planetary roller screw is shown in a longitudinal section,

[0027] Figure 2 An enlarged portion of Figure 1 is shown,

[0028] Figure 3 A variant of the nut of the planetary roller screw is shown,

[0029] Figure 4 An actuator of a rear axle steering system of a motor vehicle is shown, and

[0030] Figure 5 A section of the actuator of Figure 4 is shown. DETAILED DESCRIPTION

[0031] Figure 1 and Figure 2The planetary roller screw shown in the middle is provided with a nut 2 arranged on a threaded spindle 1. The nut 2 is divided into two nut parts 3 which are arranged one behind the other in the axial direction. Between the threaded spindle 1 and the nut 2, distributed over the circumference of the threaded spindle 1, there are planetary rollers 4. The planetary rollers 4 engage with their outer groove profile 5 with both nut parts 3 and with their central groove profile 6 with the helically wound thread profile 7 of the threaded spindle 1 around the spindle axis. The central groove profile 6 is larger in diameter than the adjacent outer groove profile 5. The threaded spindle 1 is part of a push rod 24. The two axial ends of the threaded spindle are fixedly connected to the push rod part in a releasable or non-releasable manner.

[0032] The planetary roller screw also has a planetary roller carrier 8 in which the planetary rollers 4 are mounted in a rotationally fixed manner around their planetary roller axis in pockets 9 arranged distributed over the circumference. Figure 2 The bearing journal 10 formed at the axial end of the planetary roller 4 is clearly shown, which engages in the pocket 9 of the planetary roller carrier 8.

[0033] The planetary roller carrier 8 has two carrier flanges 11 arranged axially spaced apart from one another and a drive gear 12 arranged coaxially with the threaded spindle 1, which engages around the nut 2 and is connected in a rotationally fixed manner to the two carrier flanges 11. The two carrier flanges 11 are arranged to be axially movable relative to one another. The two carrier flanges 11 are rotationally fixed, but can be axially displaced by means of a sliding fit with the drive gear 12. The two carrier flanges 11 are provided with pockets 9 for receiving the planetary rollers 4.

[0034] The planetary roller screw has a housing 13 in which the planetary roller carrier 8 is mounted in a rotationally fixed manner by means of an outer bearing 14. The two nut parts 3 are mounted in a rotationally fixed manner on their side facing the respective carrier flange 11 by means of an inner bearing 15. The inner bearing 14 is formed by an axial roller bearing 16. The outer bearing 13 is formed by an angular contact bearing 17.

[0035] The carrier flanges 11 are each provided on their end faces facing away from one another with a conical bearing surface 18 for the cylindrical rolling elements of the angular contact bearing 17. The carrier flanges are designed to be flat at their facing end faces to support the axial roller bearing 16.

[0036] Furthermore, a preloading device 19 is provided in order to adjust the axial preload between the housing 13 and the planetary roller 4. The preloading device has a screw member 20 which is screwed into the housing 13, the end face of which which faces the angular contact bearing 17 is designed as a housing-side bearing seat 21 of one of the outer support bearings. The screw member 20 is designed as a threaded ring 22 which is arranged coaxially to the threaded spindle 1 and which is screwed into a threaded hole 23 of the housing 13.

[0037] In order to eliminate the bearing play from the described bearing arrangement, the threaded ring 22 is advanced axially in the direction of the adjacent angular contact bearing 17 by a screwing movement. In this axial advancing movement, Figure 1 The carrier flange 11 shown on the left in the middle is pressed towards the right and the axial bearing play of the axial roller bearing 16 is eliminated. Thus, in the case of the engagement of the two nut members 3 with the planetary roller 4, Figure 1 The nut member 3 shown on the right in the middle is moved to the right in the direction of the axial roller bearing 16 and the angular contact bearing 17 until finally the axial bearing play of these bearings is also eliminated. The force flow described here runs from left to right, from the threaded ring 22 via the angular contact bearing 17, the carrier flange 11, the axial roller bearing 16, the nut member 3, the planetary roller 4 and from the planetary roller via the other nut member 3, the other axial roller bearing 16, the other carrier flange 11, the other angular contact bearing 17 finally into the housing 13.

[0038] Figure 3 A variant of the nut 2 is shown, which has sleeve-shaped protrusions 31, 32 which are provided on the facing end faces of the two nut members 3 and which are interlocked and axially overlap one another. These extensions are arranged coaxially to the nut 2 but have different diameters which match one another for the fitting; the nut members are thus perfectly radially aligned with one another in this way. There is thus only a small radial play between the extensions 31, 32.

[0039] Figure 4 And Figure 5 An actuator of a rear axle steering system of a motor vehicle with the above-described planetary roller screw is shown. The housing 13 has housing openings 25 on the left and right side, through which the push rod 24 passes on both sides. In Figure 4 In the middle, the push rod is concealed outside the housing 13 by a bellows. The push rod 24 is provided at its end with a steering head 26, to which a wheel control arm which is not further shown is connected.

[0040] During operation of the actuator, the planetary roller screw, which is adjusted to be play-free, ensures the reverse movement of the push rod 24 upon reversal of the rotational direction of the planetary roller carrier, during which no axial play is reduced. Under the influence of the preloading force, all bearing components involved are adjusted to such an extent that the planetary rollers 4 are pressed into contact with the nut component 3.

[0041] The actuator has an electric motor 27 and a belt drive 28. A toothed belt 29 is wound around a motor pinion 30 of the electric motor 27 and a drive gear 12, not shown here.

[0042] List of reference signs

[0043] 1 threaded spindle

[0044] 2 nut

[0045] 3 nut component

[0046] 4 planetary roller

[0047] 5 outer groove profile

[0048] 6 central groove profile

[0049] 7 threaded profile

[0050] 8 planetary roller carrier

[0051] 9 pocket

[0052] 10 bearing journal

[0053] 11 carrier flange

[0054] 12 drive gear

[0055] 13 housing

[0056] 14 outer support bearing

[0057] 15 inner support bearing

[0058] 16 axial roller bearing

[0059] 17 angular contact bearing

[0060] 18 raceway

[0061] 19 preloading device

[0062] 20 screw component

[0063] 21 housing-side bearing seat

[0064] 22 threaded ring

[0065] 23 threaded hole

[0066] 24 push rod

[0067] 25 housing opening

[0068] 26 steering head

[0069] 27 electric motor

[0070] 28 belt drive

[0071] 29 toothed belt

[0072] 30 motor pinion

[0073] 31 sleeve-like extension

[0074] 32 sleeve-like extension

Claims

1. A planetary roller screw having a nut (2) which is arranged on a threaded spindle (1) and is divided into two nut parts (3) transversely to the spindle axis, and having planetary rollers (4) which are arranged distributed in a circle between the threaded spindle (1) and the nut (2), which intermesh with the nut parts (3) and the threaded spindle (1), and having a rotationally driven planetary roller carrier (8) which is arranged on the threaded spindle (1), in the recesses (9) of which the planetary rollers (4) are mounted distributed in a circle, which are held at a distance in the circumferential direction in order to be able to rotate about a planetary roller axis, and having a housing (13) in which the planetary roller carrier (8) is mounted in a rotatable manner, which has two carrier flanges (11) which are arranged axially spaced apart from one another, which are arranged axially displaceable relative to one another and are provided with the recesses (9) for receiving the planetary rollers (4), characterized in that A preloading device (19) is provided in order to adjust the axial preloading between the housing (13) and the planetary rollers (4).

2. The planetary roller screw according to claim 1, the planetary rollers (4) of which each have a central groove profile (6) which intermeshes with the thread profile (7) of the threaded spindle (1) and each have an outer groove profile (5) on both sides of the central groove profile (6), one of the outer groove profiles (5) intermeshing with one nut part (3) and the other of the outer groove profiles (5) intermeshing with the other nut part (3).

3. The planetary roller screw according to claim 1, the planetary roller carrier (8) of which further has a drive gear (12) which is arranged coaxially to the threaded spindle (1), engages around the nut (2) and is connected in a rotationally fixed manner to the two carrier flanges (11).

4. The planetary roller screw according to any one of claims 1 to 3, the planetary roller carrier (8) of which is supported by means of inner bearing (15) and outer bearing (14), one of the outer bearings (14) being arranged between one nut part (3) and the housing (13) and the other of the outer bearings (14) being arranged between the other nut part (3) and the housing (13) and one of the inner bearings (15) being arranged between one nut part (3) and one carrier flange (11) and the other of the inner bearings (15) being arranged between the other nut part (3) and the other carrier flange (11).

5. The planetary roller screw according to claim 4, the inner bearings (15) of which are formed by axial roller bearings (16) and the outer bearings (14) of which are formed by angular contact bearings (17).

6. The planetary roller screw according to claim 5, the carrier flanges (11) of which are each provided on their end faces facing away from one another with a conical bearing surface (18) for the angular contact bearings (17).

7. The planetary roller screw according to claim 5 or 6, the preloading device (19) of which has a screw part (20) which is screwed to the housing (13), the end face of the screw part facing the angular contact bearings (17) being designed as a housing-side bearing seat (21) of one of the outer bearings (14).

8. The planetary roller screw according to claim 7, the screw part (20) of which is designed as a threaded ring (22) which is arranged coaxially to the threaded spindle (1) and is screwed into a threaded bore (23) of the housing (13).

9. An actuator for a rear axle steering system of a motor vehicle, having a planetary roller screw according to any one of claims 1 to 8, a push rod (24) being guided in the housing (13) of the planetary roller screw in a longitudinally displaceable manner and being provided at an end thereof with a steering head (26) which engages through a housing opening (25) of the housing (13), the threaded spindle (1) being part of the push rod (24).

10. A method for adjusting the preload of a planetary roller screw according to any one of claims 1 to 8, the method being carried out according to the following steps: - inserting the planetary roller screw into the housing (13) and adjusting the preload device (19) until an axial play is set between the housing (13) and the planetary rollers (4).

Images