Belt pulley and method for producing it

Abstract

A belt pulley (1) for a belt drive and a plastic injection molding method for producing the belt pulley are provided. The belt pulley (1) includes an anti-friction bearing (2) and a running ring (3) which surrounds the bearing outer ring (7). An end side of the running ring has a multiplicity of molding points (13) which run on the sector radii (R) of circular sectors which have a common center point on the rotational axis (15) of the belt pulley and at least two center point angles (α) of different size. Part of the circular sectors are to have sector radii, on which the molding points have cross sections of different size. Here, the center point angle of the adjacent circular sector on the side of the larger molding cross section is larger than the center point angle of the adjacent circular sector on the side of the smaller molding cross section.

Claims

1. A method for producing a belt pulley for a belt drive comprising: providing an anti-friction bearing with an outer ring; and injection molding a plastic running ring onto the outer ring by end-side injection molding via a plurality of feed channels; wherein one end of the running ring has a plurality of injection molding points that are each located on sector radii (R) of circular sectors that have a common center point on a rotational axis of the belt pulley and at least two different size center angles (α); a part of each of the circular sectors include the sector radii (R) on which the injection molding points are located and the injection molding points each have different size cross sections; and the center angle (α) of an adjacent one of the circular sectors on a side of a larger injection molding point cross section is greater than a center angle (α) of an adjacent circular sector on a side of a smaller injection molding point cross section.

2. The method according to claim 1, wherein the running ring has an inner ring, an outer ring, and a ring web connecting the inner ring to the outer ring, and on both sides of the ring web, a plurality of ribs that extend radially with non-uniform angular distribution and support the outer ring against the inner ring, and the injection molding points each are arranged between two of the ribs on a ring bead rising from the ring web.

3. The method according to claim 2, wherein a number of the ribs is odd.

4. The method according to claim 1, wherein the injection molding points are circular and have different diameters (D) between 0.8 mm and 2.4 mm.

5. A method for producing a belt pulley for a belt drive comprising: providing an anti-friction bearing with an outer ring; and injection molding a plastic running ring onto the outer ring by end-side injection molding via a plurality of feed channels at a plurality of injection molding points that are each located on sector radii (R) of circular sectors of the running ring that have a common center point; wherein the plurality of injection molding points include different size cross sections and a center angle (α) of an adjacent one of the circular sectors on a side of a larger injection molding point cross section is greater than a center angle (α) of an adjacent circular sector on a side of a smaller injection molding point cross section.

6. The method according to claim 5, wherein the running ring has an inner ring, an outer ring, and a ring web connecting the inner ring to the outer ring, and on both sides of the ring web, a plurality of ribs that extend radially with non-uniform angular distribution and support the outer ring against the inner ring, and the injection molding points each are arranged between two of the ribs on a ring bead rising from the ring web.

7. The method according to claim 6, wherein a number of the ribs is odd.

8. The method according to claim 5, wherein the injection molding points are circular and have different diameters (D) between 0.8 mm and 2.4 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional features of the invention result from the following description and from the drawings in which an embodiment of a belt pulley according to the invention is shown for an auxiliary unit belt drive of an internal combustion engine. Shown are:

(2) FIG. 1 the belt pulley in perspective view,

(3) FIG. 2 the belt pulley in longitudinal section,

(4) FIG. 3 the belt pulley in top view of the injection molding side,

(5) FIG. 4 the injection molding geometry of the running ring,

(6) FIG. 5 the value table associated with the injection molding geometry,

(7) FIG. 6 in schematic view, the feed channel of a cold runner of an injection molding machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) The belt pulley 1 shown in FIGS. 1 to 3 comprises an anti-friction bearing 2 in the shape of a one-row ball bearing with seals on two sides, a running ring 3 made from plastic for a poly-V belt, a fastening screw 5 centered in the inner ring 4 of the ball bearing, and a cap 6 snapped onto the running ring for protecting the ball bearing from contaminating particles and spray water. The cap is only indicated in FIG. 2 and omitted in FIG. 3.

(9) The running ring 3 made from polyamide PA66 with 25% glass-fiber reinforcement is produced by injection molding the running ring 3 onto the bearing outer ring 7. The running ring encloses the bearing outer ring on its cylindrical lateral surface and engages in a known way in the teeth of a surrounding groove 8. The running ring is assembled geometrically from an inner ring 9, an outer ring 10, a ring web 11 connecting the two rings, and an odd number of ribs 12 that support the outer ring against the inner ring. On each side of the ring web extend 27 ribs with non-uniform angular distribution in the radial direction. The injection molding of the running ring is realized at injection molding points 13 that run on an end side of the running ring with non-uniform angular distribution each centrally between two adjacent ribs on a ring bead 14 that rises on the ring web and is used as a flow aid for the plastic melt. The outer diameter of the running ring is 90 mm and the partial circular diameter on which the injection molding points are arranged is 61 mm.

(10) FIG. 4 shows an injection molding geometry according to the invention for the running ring 3. The injection molding geometry is the result of a plastic injection molding simulation that has the objective of equalizing the progress of the filling of the circular ring-shaped injection molding cavity in terms of time with the plastic melt injected at the end. As explained above, such an equalized filling process reduces the out-of-roundness deformation of the bearing outer ring 7 due to the pressure increases caused by the process at the end of the filling process and, at the same time, also the undesired orientation of fibers in the pulley revolving direction, which also deforms the bearing outer ring. The simulation takes place by the process simulation program “Autodesk Moldflow,” wherein the parameters of number, circumferential position, and cross section of the injection molding points 13, but not the circumferentially non-uniform arrangement of the ribs 12, would be changed, whose angles are given in the dimensioned FIG. 3. An injection molding geometry optimized for minimal deformation of the bearing outer ring is given in this rib arrangement with twelve injection molding points, whose diameters and circumferential distribution are given from FIG. 4 and from the value table according to FIG. 5.

(11) Additional parameters of the simulation:

(12) approx. 1.2 million elements, 1 mold cavity modeled

(13) Filling time: 1.8 s

(14) Profiled pressure increase: 12 s, 700/500 bar

(15) Mold: 80° C., melt 295° C.

(16) Geometrically, the injection molding points 13 run on the sector radii R of circular sectors no. 1 to no. 12, which have a common center point on the rotational axis 15 of the belt pulley 1 (see FIG. 2) and three different size center angles α with 14.5°, 29°, and 39°. A part of the circular sectors, namely sectors no. 2, no. 4, no. 10, and no. 12, has sector radii on which the injection molding points have different size cross sections. For example, for circular sector no. 2, the diameter D1 of one injection molding point is 1.4 mm and the diameter D2 of the other injection molding point is 2.0 mm. For this part of the circular sectors, it is now applicable that the center angle of one circular sector that runs on the neighboring side of the larger injection molding cross section is greater than the center angle of the other circular sector that runs on the neighboring side of the smaller injection molding cross section. For the circular sector no. 2 explained as an example, the center angle of the circular sector no. 3 adjacent on the side of the larger injection molding cross section with D2=2.0 mm is α(Dmax)=39°, and the center angle of the circular sector no. 1 adjacent on the side of the smaller injection molding cross section with D1=1.4 mm is α(Dmin)=14.5°. Expressed extremely simplified, this means that the injection molding point responsible for the filling of a larger angular region also has a correspondingly larger injection molding cross section. The parameter values of the different circular sectors are to be taken from the table accordingly.

(17) As an alternative to the illustrated embodiment, it is also conceivable for the injection molding points to have a non-circular cross section and/or to divide their cross sections into multiple injection molding points for each sector radius R. The diameters D of circular injection molding points are advantageously between 0.8 mm and 2.4 mm.

(18) The injection molding of the running ring 3 onto the bearing outer ring 7 with plastic takes place via a cold runner with a plurality of feed channels that are arranged on the ends of the cavity adjacent to the running ring 3 corresponding to the circumferential distribution of the injection molding points 13. As shown schematically in FIG. 6, the cross sections and thus the volumes of the feed channels 16 up to a transition cone 17 are identical, wherein the cone angle of each transition cone is dimensioned so that the cross section of the feed channel is reduced to the respective cross section or diameter D of the injection molding point (gate cross section).

REFERENCE NUMBERS

(19) 1 Belt pulley 2 Anti-friction bearing 3 Running ring 4 Bearing inner ring 5 Fastening screw 6 Cap 7 Bearing outer ring 8 Groove 9 Inner ring 10 Outer ring 11 Ring web 12 Rib 13 Injection molding point 14 Ring bead 15 Rotational axis 16 Feed channel 17 Transition cone