DE102014109407A1 - Power steering for motor vehicles - Google Patents

Abstract

The invention relates to a power steering system (10) for motor vehicles, comprising a housing (14), a roller bearing (16) having a bearing inner ring (18) and a bearing outer ring (20), a nut (22) secured by means of the roller bearing (16 ) is rotatably mounted about a longitudinal axis (A) in the housing (14), and a rack (24) extending in the axial direction (26) and having a with the nut (22) engaging threaded spindle portion (28), wherein a spring element (36) is provided which engages both the housing (14) or a component fixed to the housing and the nut (22) or a component fastened to the nut (22) and the nut (22) relative to the housing (14). acted upon axially.

Description

The invention relates to a power steering system for motor vehicles, comprising a housing, a rolling bearing having a bearing inner ring and a bearing outer ring, a nut which is rotatably supported by means of the rolling bearing about a longitudinal axis in the housing, and a rack which extends in the axial direction and having a threaded spindle portion engaging with the nut.

Such motor vehicle steering systems are already known in particular from the prior art as electromechanical power steering systems. Such a power steering system comprises a servomotor which is drivingly connected to the nut via a belt and a pulley, for example, and applies a desired steering assist force to the rack of the motor vehicle steering system via a rotation of the nut.

To avoid tension in the screw between the nut and the threaded spindle portion and to ensure a tolerance compensation, is in the generic WO 2013/056770 A1 proposed an electromechanical motor vehicle steering in which the bearing outer ring of the bearing mounted axially displaceably on the housing and axially loaded by corrugated springs and clamped. Through this mounting of the bearing outer ring a tiltable mounting of the mother and thus a tolerance compensation in the screw drive should be achieved. The attachment of the bearing outer ring requires two corrugated springs and usually two thrust washers against which the corrugated springs are supported in order to avoid damage to the housing usually made of light metal by direct contact with the corrugated springs. This leads to a relatively large space requirement in the axial direction. The corrugated springs generally have a high spring rate and act on the bearing outer ring in a defined starting position. In this way, for example, extreme loads can be cushioned by external impacts on the motor vehicle steering and occurring component stresses can be reduced. However, a reduction of the axial play in the motor vehicle steering system as well as noise minimization during steering direction changes under normal load during normal operation of the power steering can not be achieved or only to a very limited extent.

The object of the invention is to provide a compact power steering system for motor vehicles, which in the usual steering operation, a particularly low axial play and thus lower impact noise, especially in steering direction changes has.

This object is achieved by a power steering of the type mentioned, in which a spring element is provided which engages both the housing or a housing-fixed component and on the mother or a nut attached to the component and the nut is axially applied relative to the housing. This axial bias of the nut relative to the housing causes the axial clearance between the nut and the threaded spindle portion is eliminated or at least significantly reduced.

In one embodiment, the power steering is also provided that the spring element and the bearing inner ring is applied axially relative to the bearing outer ring. By this bias of the rolling bearing reduces the axial clearance between the bearing inner ring and the bearing outer ring. Consequently, the spring element reduces both the axial clearance in the screw drive and the axial bearing clearance in the rolling bearing, wherein the respective smaller axial clearance can be even completely eliminated in particular.

Preferably, the bearing inner ring of the rolling bearing are axially fixed to the nut and the bearing outer ring axially on the housing of the power steering.

In a preferred embodiment, the spring element comprises a coaxially arranged to the mother ring and a plurality of spring arms, which each extend from the ring in the radial direction to a free end and are elastically deformable in the axial direction. Such spring elements can provide sufficient axial force and are also compact and easy and inexpensive to produce.

The spring element is preferably mounted in the power steering, that the ring is axially fixed to the housing and attack at least some spring arms on the bearing inner ring of the rolling bearing. Alternatively or additionally, however, at least some spring arms can also engage the nut. If the bearing inner ring is axially fixed to the nut, however, it is preferred for manufacturing and assembly reasons that all spring arms engage either on the bearing inner ring or on the nut.

In a further embodiment of the power steering, the spring arms have a contact region, wherein at least the contact region is coated with a friction-reducing material such as Teflon or grease. Alternatively or additionally, of course, an axially adjacent mating surface, for example, the bearing inner ring or the nut, have such a coating.

The spring arms may further comprise axial contact projections to the contact surface with the axially adjacent component, such as the bearing inner ring or the nut, ideally to reduce to a point-like contact. With a rotation of the nut relative to the housing can be reduced by the friction-reducing coating and / or the reduction of the contact area advantageously the friction between the spring arms and the nut (or a nut attached to the component).

Preferably, the spring arms of the spring element are distributed uniformly over the circumference of the ring and formed integrally with the ring. This ensures in the circumferential direction for a uniform Axialbeaufschlagung the mother and incidentally for easy manufacture and assembly of the spring element.

The spring element preferably has a progressive spring characteristic. Thus, the spring element under normal load in the usual vehicle operation only a small spring force or bias ready to reduce the axial play in the rolling bearing and screw and the resulting noise from the axial play. In the event of exceptional stresses on the power steering, the spring element is axially deflected more strongly and then provides a significantly higher spring force due to the progressive spring characteristic, so that, for example, external shocks to the power steering can be effectively cushioned.

Preferably, the spring element is made of spring steel. Spring steel is easy to process and, moreover, has spring properties that only change insignificantly over time. Alternatively, however, it is also conceivable to manufacture the spring element from another suitable spring-elastic material, for example from plastic, especially a fiber-reinforced plastic.

In particular, the spring element may be produced as a bending stamped part from a steel plate having a plate thickness of not more than 1.5 mm, in particular not more than 1.0 mm. The axial space requirement for the spring element is correspondingly low, which leads to a particularly compact design of the power steering. In addition, such a spring element is particularly inexpensive due to the low material requirements and the ease of manufacture as a bending stamped part in the production.

In a further embodiment of the power steering, the nut is a recirculating ball nut and forms a ball screw drive with the threaded spindle section. In this way, the friction in the screw drive can be significantly reduced.

The rolling bearing is preferably a four-point bearing, which can accommodate axial loads in both axial directions with little axial space requirement and thus also contributes to a particularly compact design of the power steering.

The power steering may in particular be an electromechanical power steering and have an electric motor, which is drivingly connected to the nut via a belt and a pulley and the nut can rotate about the longitudinal axis.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings. In these show:

1 a schematic detail section through a power steering according to a first embodiment of the invention;

2 a perspective detailed view of a spring element of the power steering according to 1 ;

3 a schematic detail section through a power steering according to a second embodiment of the invention;

4 a perspective detailed view of a spring element of the power steering according to 3 ;

5 a schematic detail section through a power steering according to a third embodiment of the invention; and

6 a perspective detailed view of a spring element of the power steering according to 5 ,

The 1 . 3 and 5 each show a schematic detail section of a power steering 10 for motor vehicles in the field of a screw drive 12 ,

The power steering 10 includes a housing 14 , a rolling bearing 16 that has a bearing inner ring 18 and a bearing outer ring 20 has, a mother 22 , by means of the rolling bearing 16 about a longitudinal axis A rotatable in the housing 14 is stored, as well as a rack 24 extending in the axial direction 26 extends and one with the mother 22 engaged threaded spindle section 28 having.

In the present power steering 10 it is in particular an electromechanical power steering with an electric motor 30 , which has a belt (indicated by dashed lines) 32 and a pulley 34 drivingly with the mother 22 is connected and the mother 22 can rotate about the longitudinal axis A. Upon actuation of the reversibly driven electric motor 30 leaves in this way via the screw drive 12 a desired, axial steering assistance force on the rack 24 the power steering 10 muster.

To the friction in the screw drive 12 To keep as low as possible is the mother 22 designed especially as a ball nut and forms with the threaded spindle section 28 a low-friction ball screw.

The rolling bearing 16 is in the illustrated embodiments, respectively, a deep groove ball bearing, in particular a four-point bearing, which axial load in a small axial space requirement in both axial directions 26 can take and thus a particularly compact design of the power steering 10 contributes.

The power steering 10 further comprises a spring element 36 , which both on the housing 14 or a housing-fixed component as well as on the mother 22 or a component attached to the nut.

A housing-fixed component, for example, the bearing outer ring 20 which according to the 1 . 3 and 5 through a fastening ring 38 axially on the housing 14 is fixed. One at the mother 22 attached component is in particular the bearing inner ring 18 which according to the 1 . 3 and 5 through a clamping nut 40 axially on the nut 22 is fixed. The clamping nut 40 itself as well as the pulley 34 are other examples of the mother 22 fastened components.

The power steering 10 is constructively constructed so that the spring element 36 both the mother 22 relative to the housing 14 as well as the bearing inner ring 18 relative to the bearing outer ring 20 acted upon axially. Consequently, by the spring element 36 in a simple way, the axial play in the screw drive 12 and at the same time the axial bearing clearance in the rolling bearing 16 reduced, wherein the smaller axial clearance can even be completely eliminated.

The spring element 36 is made of spring steel. The advantages of the spring steel lie in the ease of processing and over the life of the power steering 10 largely constant spring behavior. Alternatively, the spring element 36 but of course also be made of plastic or other suitable spring-elastic materials.

In the illustrated embodiments, the spring element 36 each produced as a bending stamped part of a steel plate having a plate thickness of not more than 1.5 mm, in particular not more than 1.0 mm and particularly preferably about 0.8 mm. Due to the low material requirements and the simple production in the bending punching process, the spring element can be 36 extremely inexpensive manufacture. Furthermore, the axial space requirement of the spring element 36 extremely low, which in turn leads to a particularly compact design of the power steering 10 contributes.

In the 2 . 4 and 6 are different embodiments of the spring element 36 the power steering 10 shown in perspective detail view.

Regardless of the specific embodiment is thereby clear that the spring element 36 a coaxial with the mother 22 arranged ring 42 and a variety of spring arms 44 includes, each starting from the ring 42 in the radial direction 46 radially inward to a free end 48 extend and in the axial direction 26 are elastically deformable.

The spring arms 44 of the spring element 36 are evenly over the circumference of the ring 42 distributed and integral with the ring 42 educated. In addition, the spring element 36 preferably at least 12 spring arms 44 on to a circumferentially uniform loading of the nut 22 to ensure, in each of the present embodiments 24 spring arms 44 are provided.

Otherwise, the spring element 36 , in concrete terms, every single spring arm 44 of the spring element 36 , a progressive spring characteristic. In other words, this means that the axial spring force starts from a relaxed state of the spring element 36 with increasing axial deformation of the spring arms 44 increases, in particular increases exponentially.

In this way, for the normal load of the power steering 10 be set in the usual driving a small axial spring force, wherein the spring arms 44 are only slightly deformed compared to their relaxed starting position. This small axial preload is sufficient to under normal load both the axial clearance in the rolling bearing 16 as well as the axial play in the screw drive 12 to reduce. This reduced axial clearance then leads in particular to steering direction changes to a significantly reduced noise. In addition, a low axial preload during normal driving contributes to a driver perceived as positive steering feel.

For extraordinary extreme loads of the power steering 10 , For example, by an external impact on the steerable vehicle wheels, the rack can 24 and about the screw drive 12 also the mother 22 in the axial direction 26 jerkily be moved, which ultimately leads to a greater axial deformation of the spring arms 44 of the spring element 36 leads. Due to the progressive spring characteristic of the spring element 36 results from the greater deformation of the spring arms 44 a stronger axial spring force, so that such impact load of the power steering 10 over the spring element 36 can be effectively cushioned.

The 1 and 2 show a section of the power steering 10 according to a first embodiment, wherein the ring 42 of the spring element 36 between the bearing outer ring 20 and a housing extension 50 axially clamped and thus on the housing 14 is fixed. The spring arms 44 extend radially inward and point in the region of their free ends 48 a contact area 52 on, on one end face 54 of the bearing inner ring 18 attacks.

At a twist of the mother 22 relative to the housing 14 the friction between the spring arms 44 and the bearing inner ring 18 To minimize, at least the contact area 52 be coated with a friction-reducing material such as Teflon or grease. Alternatively or additionally, of course, an axially adjacent counter surface, according to 1 So the front page 54 of the bearing inner ring 18 to have such a coating.

The 3 and 4 show a section of the power steering 10 according to a second embodiment, which differs from the first embodiment according to the 1 and 2 but only by the construction of the spring element 36 different.

At a twist of the mother 22 relative to the housing 14 the friction between the spring arms 44 and the bearing inner ring 18 reduce, have the spring arms 44 of the spring element 36 according to the 3 and 4 axial contact projections 56 on, thereby increasing the contact area 52 with the bearing inner ring 18 reduced. The contact projections 56 have in particular a (spherical) curved surface and ideally provide for a punctiform contact with the axially adjacent bearing inner ring 18 so that the frictional resistance in comparison with the first embodiment according to the 1 and 2 is reduced.

If the spring element 36 made of spring steel, are the contact projections 56 the spring arms 44 preferably directly at the bending punching of the spring element 36 formed.

Analogous to the first embodiment, the contact areas 52 that is the contact projections 56 the spring arms 44 , of course, be coated with a friction-reducing material. Alternatively or additionally, it is also conceivable that an axially adjacent mating surface, according to 3 So the front page 54 of the bearing inner ring 18 having such a coating.

The 5 and 6 show a section of the power steering 10 according to a third embodiment, which in turn only by the construction of the spring element 36 different.

The ring 42 of the spring element 36 is as in the previously described embodiments of the power steering 10 axially on the housing 14 fixed. The spring arms 44 of the spring element 36 However, unlike the other embodiments do not engage the bearing inner ring 18 of the rolling bearing 16 but to the mother 22 , in particular on a front side 58 mother 22 , on (see 5 ).

Just as in the second embodiment of the power steering 10 have the spring arms 44 of the spring element 36 in the 5 and 6 axial contact projections 56 on to the friction between the (housing-fixed) spring arms 44 and the mother 22 to reduce at a relative rotation.

Analogous to the other embodiments, the contact areas 52 that is the contact projections 56 the spring arms 44 , of course, be coated with a friction-reducing material. Alternatively or additionally, it is also conceivable that an axially adjacent mating surface, according to 3 So the front page 58 mother 22 having such a coating.

Of course, embodiments are possible in which some spring arms 44 of the spring element 36 on the bearing inner ring 18 and the other spring arms 44 at the mother 22 attack, with the spring arms 44 in particular alternately on the bearing inner ring 18 and at the mother 22 can attack.

In the illustrated embodiments, the bearing inner ring is in each case 18 axially on the nut 22 and the bearing outer ring 20 axially on the housing 14 fixed so that it is functionally irrelevant whether the spring arms 44 of the spring element 36 on the bearing inner ring 18 or at the mother 22 attack. For manufacturing and assembly reasons, embodiments are preferred in these cases, in which all spring arms 44 of the spring element 36 either according to the 1 and 3 on the bearing inner ring 18 or according to 5 at the mother 22 attack.

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

• WO 2013/056770 A1 [0003]

Claims (15)

Power steering for motor vehicles, with a housing ( 14 ), a rolling bearing ( 16 ), which has a bearing inner ring ( 18 ) and a bearing outer ring ( 20 ), a mother ( 22 ), which by means of the rolling bearing ( 16 ) about a longitudinal axis (A) rotatable in the housing ( 14 ) is mounted, and a rack ( 24 ) extending in the axial direction ( 26 ) and one with the mother ( 22 ) engaged threaded spindle section ( 28 ), characterized in that a spring element ( 36 ) is provided which both on the housing ( 14 ) or a housing-fixed component as well as on the nut ( 22 ) or one at the mother ( 22 ) fastened component and the nut ( 22 ) relative to the housing ( 14 ) acted upon axially. Power steering system according to claim 1, characterized in that the spring element ( 36 ) the bearing inner ring ( 18 ) relative to the bearing outer ring ( 20 ) acted upon axially. Power steering system according to claim 1 or 2, characterized in that the bearing inner ring ( 18 ) axially on the nut ( 22 ) and the bearing outer ring ( 20 ) axially on the housing ( 14 ) is fixed. Power steering system according to one of the preceding claims, characterized in that the spring element ( 36 ) one coaxial with the mother ( 22 ) arranged ring ( 42 ) and a plurality of spring arms ( 44 ), each starting from the ring ( 42 ) in the radial direction ( 46 ) to a free end ( 48 ) and in the axial direction ( 26 ) are elastically deformable. Power steering system according to claim 4, characterized in that the ring ( 42 ) of the spring element ( 36 ) axially on the housing ( 14 ) is fixed and at least some spring arms ( 44 ) on the bearing inner ring ( 18 ) of the rolling bearing ( 16 attack). Power steering system according to claim 4 or 5, characterized in that the ring ( 42 ) of the spring element ( 36 ) axially on the housing ( 14 ) is fixed and at least some spring arms ( 44 ) at the mother ( 22 attack). Power steering system according to one of claims 4 to 6, characterized in that the spring arms ( 44 ) a contact area ( 52 ), wherein at least the contact area ( 52 ) is coated with a friction-reducing material. Power steering system according to one of claims 4 to 7, characterized in that the spring arms ( 44 ) of the spring element ( 36 ) axial contact projections ( 56 ) exhibit. Power steering system according to one of claims 4 to 8, characterized in that the spring arms ( 44 ) of the spring element ( 36 ) evenly over the circumference of the ring ( 42 ) and integrally with the ring ( 42 ) are formed. Power steering system according to one of the preceding claims, characterized in that the spring element ( 36 ) has a progressive spring characteristic. Power steering system according to one of the preceding claims, characterized in that the spring element ( 36 ) is made of spring steel. Power steering system according to one of the preceding claims, characterized in that the spring element ( 36 ) is produced as a bending stamped part of a steel plate with a plate thickness of not more than 1.5 mm, in particular not more than 1.0 mm. Power steering system according to one of the preceding claims, characterized in that the nut ( 22 ) is a ball nut and with the threaded spindle section ( 28 ) forms a ball screw. Power steering system according to one of the preceding claims, characterized in that the rolling bearing ( 16 ) is a four-point camp. Power steering system according to one of the preceding claims, characterized in that the power steering ( 10 ) is an electromechanical power steering and an electric motor ( 30 ), which via a belt ( 32 ) and a pulley ( 34 ) drivingly with the mother ( 22 ) and the mother ( 22 ) about the longitudinal axis (A) can rotate.

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