Belt pulley

A belt pulley is described which includes a pulley member and a flanged wheel. The pulley member has a belt-bearing surface and a projection disposed at a position axially adjacent to the belt-bearing surface. The flanged wheel is capable of being assembled separately on the pulley member and includes a spring washer having an inside diameter and an outside diameter. The spring washer is substantially elastically extendable in the area of the inside diameter. The dimensions of the inside diameter are defined such that, upon assembly, the inside diameter elastically extends and touches upon a surface of the projection over at least a portion of the inside diameter such that the flanged wheel is mounted concentrically and non-rotatably in relation to the belt-bearing surface. The inner and outer diameters of the spring washer are defined such that, upon assembly, the flanged wheel projects outwardly in a radial direction beyond the belt-bearing surface, thereby delimiting the belt-bearing surface in the axial direction.

BACKGROUND OF THE INVENTION 
The invention relates generally to belt pulleys and, more particularly, to 
belt pulleys having at least one pulley member with a belt-bearing surface 
that is delimited in the axial direction by at least one separately 
assembled flanged wheel. The separately assembled flanged wheel projects 
outwardly from the belt-bearing surface in a radial direction and is 
mounted concentrically and non-rotatably in relation to the belt-bearing 
surface such that it is movable, together with the belt-bearing surface, 
around an axis of rotation. 
Belt pulleys of this general type are known and are used, for example, to 
drive accessory machine units in the field of internal combustion engines. 
The generally known separately assembled flanged wheels are not very 
desirable from a production engineering standpoint, because such flanged 
wheels typically must be screwed or shrunk onto the belt pulley member 
during installation. 
An object of this invention is to further develop a belt pulley of the 
above-mentioned type which would make use of a separately assembled 
flanged wheel, which can easily and cost-effectively be produced and which 
considerably simplifies assembly. 
SUMMARY OF THE INVENTION 
The invention addresses this need by providing a belt pulley having a 
flanged wheel that is mounted on a projection that is axially adjacent to 
a belt-bearing surface. The projection is integrally formed in a single 
piece with the pulley member, and the flanged wheel is in the form of a 
spring washer, which is elastically widened in the region of its inside 
diameter and which contacts at least a portion of the circumference of the 
projection. 
According to an embodiment of the invention, a belt pulley is provided 
which comprises a pulley member and a flanged wheel. The pulley member 
includes a belt-bearing surface and a projection disposed at a position 
axially adjacent to the belt-bearing surface. The flanged wheel is capable 
of being assembled separately on the pulley member and includes a spring 
washer having an inside diameter and an outside diameter. The spring 
washer is substantially elastically extendable in the area of the inside 
diameter. The dimensions of the inside diameter are defined such that, 
upon assembly, the inside diameter elastically extends and touches upon a 
surface of the projection over at least a portion of the inside diameter 
such that the flanged wheel is mounted concentrically and non-rotatably in 
relation to the belt-bearing surface. The inner and outer diameters of the 
spring washer are defined such that, upon assembly, the flanged wheel 
projects outwardly in a radial direction beyond the belt-bearing surface, 
thereby delimiting the belt-bearing surface in the axial direction. 
One advantage of the invention is that the spring action of the elastically 
widened spring washer enables one to easily assemble the flanged wheel. A 
permanent composite construction is created simply by pressing the flanged 
wheel onto the projection of the belt pulley member. This simple 
construction assures good working properties for the belt pulley over a 
long service life. 
Depending upon the conditions of the particular application at hand, 
according to an embodiment of the invention, the spring washer can be 
provided such that the inside diameter of the spring washer continuously 
contacts the projection along an essentially circular peripheral line. A 
spring washer designed in accordance with this embodiment can be produced 
quite inexpensively. 
According to another embodiment of the invention, a spring washer can be 
provided with flexible tabs that are distributed along the inside 
circumference of the spring washer for contact with the projection. 
Advantages of this embodiment include a comparatively small inertial mass 
for the spring washer, and the ability to compensate for manufacturing 
tolerances of the spring washer itself and of the projection. The working 
properties of such a belt pulley are excellent. 
For most embodiments, radially directed prestressing is sufficient to lock 
the spring washer place, preventing circumferential rotation of the spring 
washer on the projection of the belt pulley. Another measure, comprising 
arranging flexible tabs in axially running grooves along the projection, 
can provide additional means for locking the spring washer in place. In 
such an embodiment, the flexible tabs contact the base of the groove and, 
in this manner, prevent the spring washer from being axially displaced. 
Moreover, by situating the tabs in the grooves, the spring washer and the 
belt pulley member are also prevented from rotating relative to one 
another in the circumferential direction. 
In one embodiment, the spring washer is advantageously made of a metallic 
material, and essentially U-shaped perforations are uniformly distributed 
along its inside diameter in the direction of the projection. This 
embodiment makes it possible t reduce or even to avoid notch stresses. 
This embodiment also prevents hairline cracks from forming in the area of 
the radial transition zone between the flexible tabs and the stop faces of 
the flexible tabs during normal operational use of the belt pulley. 
In the above embodiment, there are preferably at least three flexible tabs 
and perforations. Depending upon the size of the belt pulley, the number 
of flexible tabs/perforations should be selected to securely attach the 
flanged wheel on the belt pulley member, while at the same time ensuring 
the simplest possible production and assembly of the flanged wheel. The 
number of flexible tabs and perforations will also depend upon the size of 
the belt pulley. 
Depending upon the particular application at hand, the radial depth of the 
perforations can, for example, be 0.01 to 0.5 times as great as the radial 
thickness of the flanged wheel. Advantageous radial depths of 1 mm to 10 
mm, for example, are common. Optimization of the flexible 
tabs/perforations influences the radial prestressing of the flexible tabs, 
which are braced against the projection along an essentially circular 
peripheral line. 
According to another embodiment, the flexible tabs formed by the 
perforations can be axially bent in a direction opposed to the direction 
of assembly (which extends parallel to the axis of rotation) such that the 
flexible tabs form an angle of 45.degree. to 89.degree., preferably of 
65.degree. to 85.degree., with respect to the axis of rotation. The radial 
spring action of the flexible tabs in the direction of the projection 
produces a barb-like interaction between these two elements. When the 
flanged wheel is pressed on the projection, the interaction between the 
flexible tabs and the projection forces the flexible tabs to elastically 
expand in a radially outward direction. Once the press-on operation is 
ended, and the flanged wheel forms the axial boundary edge of the 
belt-bearing surface, and a barb-like mechanical interaction is produced 
between the flexible tabs and the projection of the belt pulley member. 
This prevents the flanged wheel from moving in an axial direction contrary 
to the direction of assembly during normal operational use. 
One advantageous embodiment provides for the belt pulley member to be made 
of a polymeric material. Because the material of the belt pulley member 
and, thus, of the projection is comparatively softer than the material of 
the flexible tabs (which are made, for example, of hardened spring steel), 
the barb-like interaction between the flanged wheel and the projection on 
the belt pulley member is further enhanced. 
According to another embodiment, the belt pulley member can consist of 
metallic material. In such a case, however, it is desirable that a 
circumferential grooved indentation be provided on the projection of the 
pulley member so that, when the flanged wheel is installed, the flexible 
tabs are able to be snapped into the grooved indentation to brace them 
against an axial displacement. However, belt pulley members consisting of 
a polymer material have the advantages of being cheaper to produce and 
having smaller inertial mass. 
According to another embodiment, assembly of the flanged wheel can be 
further simplified if the outside diameter of the projection is offset in 
relation to the outside diameter of the belt-bearing surface. This offset 
provides a stop face for the spring washer, so that an unvarying 
predetermined axial width is guaranteed in a simple fashion for the 
belt-bearing surface, facilitating mass production of the component. 
To be able to slide the spring washer in the direction of assembly with 
particular ease and in a concentric fashion onto the projection of the 
pulley member, according to another embodiment, the projection is 
chamfered in the axial direction on the side of the projection facing away 
from the belt-bearing surface. The chamfer forms an angle, for example, of 
5.degree. to 35.degree. with respect to the axis of rotation.

DETAILED DESCRIPTION 
FIG. 1 shows a belt pulley, according to an embodiment of the invention, 
comprising a pulley member 1 of polymer material with a premolded flanged 
wheel 11 premolded in one piece on the pulley member 1 in the axial 
direction. A belt-bearing surface 2 is provided between the premolded 
flanged wheel 11 and a separately assembled flanged wheel 3, which is 
capable of being assembled separately. The premolded flanged wheel and the 
separately assembled flanged wheel 3 project outwardly in the radial 
direction from the belt-bearing surface 2 and the belt (not numbered) 
resting on it, thus preventing axial displacement of the belt during 
normal operational use. The separately assembled flanged wheel 3 is 
mounted on a projection 5, which is axially adjacent to the belt-bearing 
surface 2. The projection 5 is integrally formed with the pulley member 1 
and consists, in this exemplified embodiment, of a polymer material. 
FIGS. 2A and 2B depict an embodiment of a separately assembled flanged 
wheel 3 in the form of a spring washer 6 on an enlarged scale. In the area 
of its inside diameter 6.1, the spring washer 6 has flexible tabs 7, which 
are separated by perforations 8 and which are axially crimped contrary to 
the direction of assembly 9 and which form an angle of about 10.degree. to 
20.degree. with respect to an imaginary radial plane. The abutment surface 
12 of the spring washer 6 which abuts the belt to be used forms an angle 
of about 15.degree. with respect to the radial plane in this example, such 
that the abutment surface 12 tapers away from the belt with increasing 
radial distance from the belt-bearing surface 2. 
Referring now to FIGS. 1 and 2A, the separately assembled flanged wheel 3 
is provided in the form of a spring washer 6, which can be elastically 
extended in the area of its inside diameter 6.1 and which contacts the 
projection 5 with flexible tabs 7 that are uniformly distributed in the 
circumferential direction with radial prestressing. The flexible tabs 7 
are axially crimped in a direction contrary to the direction of assembly 9 
and, in this exemplified embodiment, form an angle of about 70.degree. to 
80.degree. with respect to the axis of rotation 4. The inside diameter 6.1 
of the spring washer 6 is manufactured such that the inside diameter 6.1 
is smaller than the outside diameter of the projection 5. As a result of 
this arrangement, after the spring washer 6 is installed on the projection 
5, the flexible tabs 7 mechanically claw into the surface of the 
projection 5. 
The spring washer 6 can be produced quite easily and inexpensively in large 
piece numbers, and it forms a secure axial boundary edge for the belt on 
the belt-bearing surface 2 due to the barb-like effect of the flexible 
tabs 7 upon the projection 5. 
The assembly operation is carried out by simply pressing the spring washer 
6 in an axial direction 9 onto the projection 5. The spring washer 6 is 
pressed in the axial direction over the surface of the projection 5, until 
it is positioned against an offset, which corresponds to an axial boundary 
of the belt-bearing surface 2. As a result, the assembly operation is 
quite simple. 
Moreover, the projection 5 is chamfered in the axial direction on the side 
of the projection 5 facing away from the belt-bearing surface 2. The 
chamfer 10 forms an angle of about 5.degree. to 35.degree. with respect to 
the axis of rotation 4 and facilitates the pressing of the spring washer 6 
in the direction of assembly 9 onto the projection 5. 
FIG. 3 depicts an exemplified embodiment of a spring washer 6 that has 
flexible tabs 7 uniformly distributed along its inside diameter 6.1 of the 
spring washer 6. The flexible tabs 7 are guided in grooves, which extend 
in the axial direction along the projection 5, locking the spring washer 6 
against axial rotation with respect to the projection 5. In the area of 
the inner diameter 6.1, the flexible tabs 7 extend, with radial 
prestressing, to the bottom of the grooves, contacting the projection 5. 
This provides an excellent protection for the spring washer 6, preventing 
it from being axially displaced and from rotating on the projection 5.