DE102017112710A1 - Actuator for a vehicle steering - Google Patents

Abstract

The invention relates to an actuator (1) for a vehicle steering system, comprising a housing element (2) and a relative to this in the direction of an axis (a) movable displacement element (3), in particular a spindle, wherein the movement of the displacement element (3) relative to Housing element (2) by an electric drive with a drive element (4), wherein the displacement movement of the displacement element (3) by a planetary roller screw (5) takes place, a ring gear (6), the displacement element (3) and a number of planets (7 ), which are arranged between the ring gear (6) and the displacement element (3) and which are held by a cage (8). In order to ensure a precise and smooth running of the actuator, the invention provides that the drive element (4) with the cage (8) is rotatably connected and this about the axis (a) rotates.

Description

Field of the invention

The invention relates to an actuator for a vehicle steering system, comprising a housing element and a movable relative to this in the direction of an axis sliding element, in particular a spindle, wherein the movement of the displacement element relative to the housing element by an electric drive with a drive element, wherein the displacement movement of the displacement element is performed by a planetary roller screw, which comprises a ring gear, the displacement element and a number of planets, which are arranged between the ring gear and the displacement element and which are held by a cage.

Background of the invention

A generic actuator is from the DE 10 2012 207 005 A1 known. For an electromechanical vehicle steering system, an actuator is used here, which uses a planetary roller screw drive to convert a rotational movement into a linear movement.

The aim is to ensure in such an actuator that in operation of the planetary roller according to the rotation angle applied by the drive, a precise corresponding linear feed is generated. It is desirable that this is realized in the quietest possible way from the actuator.

Object of the invention

The present invention has for its object to develop a generic actuator so that a precise and smooth running of the same is guaranteed. Furthermore, the aim is a compact design of the arrangement as possible.

Summary of the invention

The solution of this problem by the invention is characterized in that the drive element is rotatably connected to the cage and this rotates about the axis.

The drive element is preferably designed as a pulley and arranged coaxially with the axis.

The drive element can be connected to a sleeve, wherein the sleeve has an axially inwardly directed portion in an axial end region, which is connected to the cage. The drive element can be connected to the sleeve by means of a press fit between the drive element and sleeve.

The drive element may be rotatably mounted on the ring gear by means of a rolling bearing. In this case, it is preferably provided that the rolling bearing is designed as a needle bearing. The needle bearing is preferably designed as a needle sleeve which is pressed into a radially inner cylindrical surface of the sleeve.

In the region of the contact point between the sleeve and the cage, a plastic ring may be arranged.

Between the housing element and the ring gear, a rolling bearing may be arranged, this being designed in particular as a four-point bearing.

The sleeve is preferably connected to the cage by means of a forming process (in particular a beading process) and / or by means of a welding operation.

Thus, the proposed concept is based on the use of a planetary roller screw drive, which is known as such in steering systems, in particular for motor vehicles, wherein the cage drives the cage directly from the drive. Since all planets of Planetwälzgewindetriebes always on the ring gear or on the spindle are engaged, a precise translational feed is ensured upon application of a corresponding rotational movement by the direct drive of the cage, resulting in accordance with the thread pitch of the system. Possible slippage of the planets remains irrelevant. The torque of the drive is thus introduced directly into the planet carrier (ie into the cage).

In the proposed embodiment can be advantageously dispensed with an additional reduction stage of the planetary gear.

However, the advantage is achieved that due to the positive drive no further (safety relevant) redundancies in the electronic control of the steering drive are needed. Furthermore, no large radial bias is needed for the planetary drive within the planetary roller screw, since the system is synchronized in the proposed concept.

A further advantage is a simplified drive reversal, if the electrical supply fails and the vehicle must remain maneuverable only by the steering wheel without steering assistance.

The drive torque of the electric drive comes, for example, from an electric motor, the axis-parallel to the spindle axis (in this case per toothed belt to the drive pulley) or coaxial (to the planetary gear) can be arranged.

In particular in the case of paraxial guidance, the drive belt pulley can be pressed onto the sleeve (preferably made of sheet metal). In the sleeve, a needle sleeve can be pressed, which ensures the radial bearing of the pulley.

Within the sleeve, a plastic disc can be inserted in a form-fitting manner. A connection between the sleeve and the cage can be made by reshaped sections of the cage or the sleeve, by caulking or by welding (eg laser welding).

On the axially opposite side of the cage may equally be arranged a plastic disc which is mounted to the above-mentioned plastic disc in exactly the same orientation. This can be achieved that all the planets are guided in parallel and in the circumference exactly aligned with the spindle axis.

The pitch of the spindle (i.e., the displacement member) is chosen to be large enough so that the planetary roller screw is not self-locking; Thus, even in case of failure of the electric steering actuation of the steering is possible.

A good rolling behavior of the planets is favored when the ring gear (nut ring) is supported by a four-point bearing relative to the housing element. In this case, the tilting stiffness is increased when the storage is designed as an O-bearing.

With the proposed embodiment it is achieved that regardless of a slippage of the planet after a revolution of the planet cage a precise axial relative displacement between the nut and the spindle is forced, which corresponds exactly to the slope.

list of figures

• 1 im Radialschnitt einen Aktuator für die Umwandlung einer Drehbewegung in eine translatorische Vorschubbewegung, um hiermit eine Lenkbewegung auszuführen, und
• 2 in perspektivischer Darstellung einen Käfig, der Bestandteil eines Planetenwälzgewindetriebes ist, der in dem Aktuator eingesetzt wird.

In the figures, an embodiment of the invention is shown. Show it:

• 1 in radial section, an actuator for the conversion of a rotational movement in a translational feed motion, to thereby execute a steering movement, and
• 2 in perspective view of a cage which is part of a Planetenwälzgewindetriebes, which is used in the actuator.

Detailed description of the figures

In 1 is an actuator 1 represented, with the electric motor, a steering movement can be generated. The general structure of such a system is expressly referred to above DE 10 2012 207 005 A1 the applicant referred.

The actuator 1 comprises a housing element 2 , which is firmly installed on or in an attachment, not shown. Relative to the housing element 2 can be a sliding element 3 in the form of a spindle a translational movement in the direction of an axis a and so realize the said steering movement.

For this purpose, a drive is provided, of which only one drive element 4 is shown in the form of a pulley. About the pulley 4 runs a drive belt, which is moved by an electric motor and so the pulley 4 around the axis a rotates.

The conversion of the rotary motion of the pulley 4 in the translational movement of the spindle 3 via a planetary roller screw drive 5 , This essentially comprises a ring gear 6 (Nut ring) and the spindle 3 and several between ring gear 6 and spindle 3 arranged planets 7 , The planets 7 are held by a cage 8, which in 1 only hinted at 2 however, perspective is shown. In 2 can also be seen that the cage 8 receiving pocket 16 for the individual planets 7 Has.

The ring gear 6 is relative to the housing element 2 rotatably mounted, including a rolling bearing 13 is used. This is formed in the embodiment as a four-point bearing. In the embodiment, the outer ring of the rolling bearing acts 13 as a housing element 2 within the meaning of the present nomenclature. Of course, as explained above, the housing member 2 , So in the present case, the outer ring of the bearing 13 , firmly connected to a corresponding attachment.

Advantageously, the ring gear acts 6 at the same time as an inner ring of the rolling bearing 13 as well as an inner ring of a needle bearing 11 (which is explained in more detail below), as it turns out 1 results. Hereby, a very space-saving construction can be realized.

It is essential that the drive element 4 , ie in the present case, the pulley, with the cage 8 is rotatably connected and this about the axis a rotates.

For this purpose, a sleeve in the embodiment 9 made of sheet metal, which in radial section a has substantially U-shaped shape. Accordingly, the sleeve has 9 in its radially outer region a hollow cylindrical design, to which a radially (see. Direction r in 1 ) inwardly extending section 10 followed. The radially inwardly extending portion 10 thus acts as a drive flange for the cage. 8

The radially outer region of the sleeve 9 press-fit the pulley 4 located in the radially outer region of the sleeve 9 is thus fixed. In the radially inner region of the hollow cylindrical portion of the sleeve 9 is the already mentioned needle bearing 11 arranged. The needle bearing 11 is formed as a needle sleeve, which in turn press-fitted in the radially inner region of the hollow cylindrical portion of the sleeve 9 is fixed. This accomplishes that the sleeve 9 , driven by the pulley 4 to the axis a rotatable on a cylindrical outer circumference of the ring gear 6 is arranged.

The radially inward reaching section 10 the sleeve 9 is rotatably connected to the cage 8, as explained. For this purpose, illustrated as a possibility in the illustrated embodiment that the cage 8 in his the section 10 facing end region with axial extensions 15 is provided (s. 2 ), through corresponding recesses or openings in the section 10 pass through and then by forming firmly with the sleeve 9 are connected. Other connection techniques are of course also possible, in particular to a welding of cage 8 and sleeve 9 thought is.

In the area of the transition or the attachment point of cage 8 and sleeve 9 is a plastic ring twelve arranged. This also applies to the other axial end of the cage, where there is a plastic ring 14 located.

When operating the pulley 4 by the (electric) drive motor, not shown, is thus on the sleeve 9 directly the cage 8 with the planets 7 around the axis a rotated so that the rotational movement in a precise manner over the pitch of the threads of the planetary roller screw 5 in the corresponding translational movement of the spindle 3 is implemented. Possible slippage does not matter insofar.

Incidentally, the illustrated construction provides a very compact structure of the arrangement and thus the ability to accommodate the required functionality in a confined space.

LIST OF REFERENCE NUMBERS

1

actuator

2

housing element

3

Sliding element (spindle)

4

Drive element (pulley)

5

Planetwälzgewindetrieb

6

Ring gear (nut ring)

7

planet

8th

Cage

9

shell

10

Section of the sleeve

11

Rolling bearings (needle bearing / needle sleeve)

12

Plastic ring

13

Rolling bearings (four point bearings)

14

Plastic ring

15

axial extension

16

receiving pocket

a

axis

r

radial direction

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012207005 A1 [0002, 0024]

Claims (10)

Actuator (1) for a vehicle steering, comprising a housing element (2) and a relative to this in the direction of an axis (a) movable sliding element (3), in particular a spindle, wherein the movement of the displacement element (3) relative to the housing element (2) by an electric drive with a drive element (4), wherein the displacement movement of the displacement element (3) by a planetary roller screw (5), which comprises a ring gear (6), the displacement element (3) and a number of planets (7) between the ring gear (6) and the displacement element (3) are arranged and which are held by a cage (8), characterized in that the drive element (4) with the cage (8) is rotatably connected and this about the axis (a ) turns. Actuator after Claim 1 , characterized in that the drive element (4) is formed as a pulley and coaxial with the axis (a) is arranged. Actuator after Claim 1 or 2 characterized in that the drive element (4) is connected to a sleeve (9), the sleeve (9) having in an axial end region a radially (r) inwardly directed portion (10) which communicates with the cage (8). connected is. Actuator after Claim 3 , characterized in that the drive element (4) with the sleeve (9) by means of a press fit between the drive element (4) and sleeve (9) is connected. Actuator after one of Claims 1 to 4 , characterized in that the drive element (4) on the ring gear (6) by means of a rolling bearing (11) is rotatably mounted. Actuator after Claim 5 , characterized in that the rolling bearing (11) is designed as a needle bearing. Actuator after Claim 6 , characterized in that the needle bearing (11) is designed as a needle sleeve which is pressed into a radially inner cylindrical surface of the sleeve (9). Actuator after one of Claims 3 to 7 Characterized in that a plastic ring (12) is arranged in the area of contact between the sleeve (9) and the cage (8). Actuator after one of Claims 1 to 8th , characterized in that between the housing element (2) and the ring gear (6) a rolling bearing (13) is arranged, in particular a four-point bearing. Actuator after one of Claims 3 to 9 , characterized in that the sleeve (9) is connected to the cage (8) by means of a forming process and / or by means of a welding operation.

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