Drive unit with a rotationally fixed bearing element

The invention relates to a drive unit (10) and to a method for producing said drive unit, especially for adjusting mobile parts in a motor vehicle. Said drive unit comprises a drive shaft (12), received in a housing (24) by means of at least one bearing element (22). Said housing comprises a lower housing part (26) and an upper housing part (28) which can be radially assembled in relation to the drive shaft (12). The bearing element (22) is configured as a plain bearing bush (38) that positively engages in a peripheral direction (33) in a corresponding bearing seat (30) of the housing (24) in order to form a rotational lock (42).

RELATED ART

The present invention relates to a drive unit, in particular for adjusting movable parts in a motor vehicle, and a method for manufacturing such a drive unit with a drive shaft that is supported in a housing using at least one bearing element, according to the preamble of the independent claims.

Publication DE 10352240 A1 makes known an electric motor, the housing of which is composed of two half shells, which are installable radially to the armature shaft. The armature shaft and a further transmission shaft are supported in a first housing shell using bearing elements. By installing the shaft in such a radial manner, the bearing elements are typically prevented from rotating via a radial contact force. The radial contact force must be so great that the related friction forces are greater than the initial friction of the bearing element. Given that the level of the contact force is specified by the rotational lock of the bearing element, it is very difficult to bring the shaft into an exact radial position, since the radial positioning is also greatly influenced by the contact force.

DISCLOSURE OF THE INVENTION

The inventive drive unit and the manufacturing method with the characterizing features of the independent claims have the advantage that, by integrally forming a rotational lock with the bearing element, the bearing element engages in a corresponding bearing seat of the housing in a form-fit manner. As a result, the bearing element is prevented from rotating in the circumferential direction by the form-fit connection between the bearing element and the housing. The radial contact force on the bearing element may therefore be adjusted entirely independently of the rotational lock. The shaft may therefore be positioned very exactly via the contact force applied by the second housing part.

Advantageous refinements and improvements of the features indicated in the independent claims are made possible by the measures listed in the subclaims. When, in order to rotationally lock the bearing element, a geometry with a polygonal outline as the outer circumference or a related external profile is integrally formed with the bearing element as the form-fit connection, it is very easy to manufacture a reliable form-fit connection with the bearing seat. The polygonal geometry is preferably designed, e.g., as a square, which engages in a corresponding U-shaped recess in the bearing seat. As a result of this form-fit connection, additional securing elements such as clamping disks may be eliminated entirely, thereby enabling the drive unit to be manufactured more quickly and cost-favorably. By designing the plain bearing bush as a single piece with the polygonal geometry, no additional effort is required to manufacture the bearing element.

When the form-fit rotational lock is integrally formed with the bearing element on its axial end, this does not interfere with the plain bearing bush being accommodated in the bearing seat of the housing. Depending on the torques that act on the bearing element, a polygonal geometry may be integrally formed on the plain bearing bush, on one or both axial ends.

It is advantageous when the bearing element is designed as a calotte bearing, since it may absorb radial forces from various directions, and it compensates for the deflection of the drive shaft during installation and operation. By using sintered metal that can absorb a lubricant, the shaft is supported in a manner such that it may glide easily for the duration of its service life.

To ensure that the functionality of the spherical cap is not impaired, and to ensure that it may continue to compensate for deflections in the drive shaft, the outer diameter of the form-fit rotational lock is designed to be smaller than the minimum outer diameter of the spherical cap. The rotational locking of the bearing element may therefore be decoupled from the actual function of the shaft bearing.

To accommodate the polygonal geometry, the bearing seat includes a rotational lock region, into which the rotational lock may be inserted in a form-fit manner. Very favorably, the rotational lock region, together with the bearing seat, may be designed directly as a single piece with the lower housing part, which may be manufactured, e.g., using a plastic injection-molding method.

To ensure that the bearing element may be inserted very easily in the corresponding bearing seat during installation, the polygonal geometry bears—in the fully installed state—against the rotational lock region of the bearing seat with exactly two surfaces or edges of each rotational lock. The two surfaces form an angle with each other in which two corresponding mating surfaces of the rotational lock region engage in a form-fit manner. The polygonal geometry is preferably designed as a square, which bears against two mating surfaces of the rotational lock region that form an angle with each other of approximately 90°.

When the bearing seat is formed directly in the lower housing part, the bearing element may be pressed easily into the bearing seat when the second housing part is installed. To this end, a projection may be integrally formed, e.g., as one piece with the second housing part, the projection bearing directly against the spherical cap when in the installed state.

To ensure that the bearing element that accommodates the shaft automatically moves into the correct rotational position when it is installed radially, the rotational lock region includes an insertion chamfer. The form-fit rotational lock of the bearing element may glide along the insertion chamfer and be rotated via the radial installation force such that it forms a form-fit connection with the rotational lock region.

Via the inventive method for manufacturing the drive unit, the bearing element may be fixed securely in position radially in one installation process without using any additional components, and it may be simultaneously secured against rotation. Due to the self-finding rotational lock, the bearing element is automatically secured against rotation via its correct radial positioning.

When the bearing element is installed, the contact force used to position it radially may be adjusted entirely independently of frictional forces on the surface of the bearing element. According to the related art, the frictional forces are intended to prevent the bearing element from rotating.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

InFIG. 1, an electric motor10is shown as drive unit10, with which an armature shaft11is designed as drive shaft12. Drive shaft12is driven by an armature14mounted thereon and transfers a torque using a driven element16—which is designed, e.g., as a worm20—to a not-shown, movable part in the motor vehicle. Drive shaft12is supported in a housing24using bearing elements22. Housing24includes a lower housing part26and an upper housing part28. A bearing seat30is formed in lower housing part26, which is made, e.g., of plastic. Bearing element22may be inserted in bearing seat30in radial direction32relative to drive shaft12. Bearing element22includes a spherical cap34, curved surface35of which bears against an inner wall36of bearing seat30. Spherical cap34is designed as a plain bearing bush38made, e.g., of a sintered metal, and rotatably accommodates drive shaft12. A form-fit rotational lock42is located on axial ends40of plain bearing bush42, and is designed with a polygonal geometry44. In this exemplary embodiment, polygonal geometry44is designed as square46, with which four surfaces48form angles of approximately 90° with each other. Surfaces48are interconnected with a radius51that makes it easier to insert bearing element22into bearing seat30. The maximum diameter50of form-fit rotational lock42is smaller than minimum outer diameter52of plain bearing bush38. Bearing seat30includes a rotational lock region54into which its rotational lock42engages in a form-fit manner after bearing element22is installed. Rotational lock region54includes mating surfaces49, against which surfaces48of polygonal geometry44bear after bearing element22has been installed.

Drive unit10is shown in the fully installed state inFIG. 2. Rotational lock42of bearing element22forms a form-fit connection with rotational lock region54of bearing seat30. Exactly—and only—two adjacent surfaces48bear against corresponding mating surfaces49in this case. Using square46as an example, surfaces48and mating surfaces49form an angle47of approximately900. Third and fourth surfaces48′ of square46do not bear against a mating surface49. Instead, they are located at a distance56from mating surface49′, to make it easier to insert rotational lock42into rotational lock region54. For this purpose, rotational lock region54also includes an insertion phase58, along which polygonal geometry44glides, to form a form-fit connection in rotational lock region54. Plain bearing bush38is pressed by an extension60of upper housing part28against inner wall36of bearing seat30.

To install drive unit10, bearing element22is slid onto drive shaft12. Bearing element22and drive shaft12are then inserted into bearing seat30of lower housing part26in radial direction32. Surface35of plain bearing bush38bears against corresponding inner surface36of bearing seat30. When form-fit rotational lock42is inserted, it glides on insertion phase58into rotational lock region54. If surfaces48are not oriented parallel to mating surfaces49upon insertion, rotational lock42rotates with plain bearing bush38in circumferential direction33until surfaces48,49are nearly parallel and bearing element22is inserted fully into receptacle30. The two surfaces48, which form angle47, and mating surfaces49are positioned relative to drive shaft12such that they form a form-fit connection when bearing element22has been pressed in completely. Due to distance56between surface48′ and mating surface49′, rotational lock42is prevented from tilting when it is inserted. An additional assembly step is therefore not required to reliably locate the rotational position of polygonal geometry44. Next, upper housing part28is placed on lower housing part26and is connected therewith. Radial extension60exerts a contact force62on plain bearing bush38, in particular on spherical cap34, and presses it into bearing seat30in order to position drive shaft30radially.

It should be noted that, with regard for the exemplary embodiments presented in the figures and the description, many different combinations of the individual features are possible. For example, the specific design of form-fit rotational lock42may be varied, by designing polygonal geometry44, e.g, as a triangle, a pentagon, or a hexagon. Rotational lock42may also have a curved circumference, e.g., an oval, which also forms a form-fit connection with related rotational lock region54. Surfaces48and mating surfaces49need not be designed as extended surfaces. They may be designed as edges, for example. The form-fit connection is preferably formed by two surfaces48, which are positioned relative to each other at angle47, e.g., of approximately 90°. More than two surfaces48with different angles47may also form a form-fit connection with mating surfaces49of rotational lock region54. The present invention is not limited to the use of calotte bearings34. It may also be used for other sliding bearings or roller bearings.