A lightweight pulley is provided which can be produced in a simple manner at low cost. The pulley has a cylindrical boss portion, an annular main portion which extends radially outwardly from the cylindrical boss portion, and a ring-shaped belt retaining portion. The boss portion and the main portion are integrally formed from a thin metal plate by press-forming, thereby reducing the weight of the pulley, and facilitating the production thereof. The peripheral wall of the boss portion is alternately bent inwardly and outwardly in its peripheral direction to form a plurality of ribs, thus increasing the strength of the boss portion. A method of manufacturing the pulley is also provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a pulley, and more particularly to a 
pulley which is lightweight and can be produced in a simple manner. 
2. Description of Related Art 
FIG. 1 illustrates a conventional pulley which acts as a damper pulley. As 
shown, a cylindrical boss portion 10, to be press-fitted onto a rotary 
shaft (not shown), and an annular main portion 12, provided outside the 
cylindrical boss portion 10 are integrally formed by machining a cast 
metal. A metallic ring body 16, acting as a damper mass, is joined to the 
outer periphery of the main portion 12 via rubber body 14. V-shaped 
grooves 18 are formed in the outer periphery of the metallic ring body 16. 
Thus, the metallic ring body 16 also serves as a belt retaining portion of 
the pulley. 
The pulley formed of cast metal is large in thickness, and accordingly has 
substantial weight, and also requires machining work, which increases 
production costs. 
FIG. 2 illustrates another conventional pulley. As shown, in order to 
reduce both the weight and production cost thereof, the main portion 12 
and the belt retaining portion 19 are integrally formed from a thin metal 
plate by press-forming. However, the cylindrical boss portion 10 is formed 
separately, from a thick metal plate and is coupled to the main portion 
12. The boss portion 10 is made thick, since it requires a high strength, 
as compared to the remaining portions. 
The conventional pulley of FIG. 2 requires a troublesome welding process to 
secure the cylindrical boss portion 10 to the main portion 12, thus 
increasing production costs. In addition, with this conventional pulley, 
the weight cannot be sufficiently reduced. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a lightweight pulley 
which can be produced in a simple manner at low cost. 
A pulley in accordance with the present invention has a cylindrical boss 
portion adapted to be press-fitted onto a rotary shaft, a ring-shaped belt 
retaining portion which is concentrically disposed about the boss portion, 
and a plate-shaped main portion which connects the boss portion and the 
belt retaining portion. At least the boss portion and the main portion are 
integrally formed of a thin metal plate by press-forming. The boss portion 
has a plurality of ribs which are formed by alternately bending its 
peripheral wall inwardly and outwardly in the circumferential direction 
thereof. 
The pulley, provided in accordance with the present invention, can be 
manufactured inexpensively and is of reduced weight, since at least the 
boss portion and the main portion are integrally formed from a thin metal 
plate. 
Furthermore, sufficient strength of the boss portion can be obtained by 
virtue of the ribs formed in its peripheral wall. 
Other objects, features and characteristics of the present invention will 
become apparent upon consideration of the following description and the 
appended claims with reference to the accompanying drawings, all of which 
form a part of the specification.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS 
FIGS. 3 and 4 illustrate a first embodiment of a pulley provided in 
accordance with the principles of the present invention, which acts as a 
damper pulley. As shown in the drawings, the entire damper pulley is 
formed of a relatively thin (about 2.8 mm thick) SPCC plate by 
press-forming. The damper pulley includes a cylindrical boss portion 20 
and an annular main portion 22 which extends radially outwardly from one 
axial end of the cylindrical boss portion 20. The outer peripheral part of 
the main portion 22 is bent to be substantially perpendicular to the plane 
surface of the main portion 22, so as to define a ring-shaped belt 
retaining portion 24 which is concentric with the boss portion 20. 
The peripheral wall of the cylindrical boss portion 20 has a substantially 
U-shaped cross-section. The inner peripheral wall of the boss portion 20 
is alternately bent inwardly and outwardly in its circumferential 
direction to form a plurality of ribs 26 having a nearly rectangular 
cross-section, as shown in FIG. 4. 
An axial end of the rotary shaft S is inserted into the boss portion 20, 
and is secured thereto by a nut B. 
V-shaped grooves 241 are formed in the outer peripheral surface of the belt 
retaining portion 24, which is parallel to the rotary shaft S. 
A ring-shaped rubber body 28 of a uniform thickness is concentrically 
joined to the planar surface of the main portion 22. A ring-shaped 
damper-mass member 29 is coupled to the rubber body 28. 
When torsional vibrations are exerted from the rotary shaft S, the 
damper-mass member 29 resonates therewith, thereby absorbing or 
restraining the exerted torsional vibrations. 
With the first embodiment of the pulley having the above-described 
structure, the cylindrical boss portion 20 formed from a thin metal plate 
has sufficient strength due to the ribs 26. Thus, the pulley of the first 
embodiment can be easily produced by press-forming without such 
troublesome steps of preparing a thick cylindrical boss portion, and 
securing the boss portion to the main portion of the pulley by welding, 
which conventionally have been required. Therefore, with the present 
embodiment, production costs can be reduced. 
FIGS. 5 and 6 illustrate a second embodiment of a pulley provided in 
accordance with the principles of the present invention, which acts as a 
damper pulley. As shown in the drawings, a cylindrical boss portion 30 
includes two portions 301 and 302 of different diameters. An axial end of 
the rotary shaft S is inserted into the smaller diameter portion 301, and 
is secured by a nut B which is accommodated within the larger diameter 
portion 302. 
An annular plate-shaped main portion 32 extends radially outwardly from the 
open end of the larger diameter portion 302 of the boss portion 30. The 
outer peripheral part of the main portion 32 is bent to be substantially 
perpendicular to the main portion 32, thereby defining a ring-shaped belt 
retaining portion 32, which is concentric with the boss portion 30. 
V-shaped grooves 341 are formed in the outer peripheral surface of the 
belt-retaining portion 34, which is parallel to the rotary shaft S. 
As shown in FIG. 6, the peripheral wall of the boss portion 30 including 
the smaller diameter portion 301 and the larger diameter portion 302, is 
alternately bent inwardly and outwardly in its circumferential direction 
to form a plurality of ribs 361 and 362. Ribs 362 of the larger diameter 
portion 302 which does not directly receive a load from the rotary shaft S 
are small, and have shallow V-shaped cross-sections, composed of gently 
inclined surfaces. 
In contrast, ribs 361 of the smaller diameter portion 301 which directly 
receives a load from the rotary shaft S are large, and have deep U-shaped 
cross-sections, composed of steeply inclined surfaces. One outwardly bent 
rib of ribs 361 is formed to have a rectangular cross-section, thereby 
defining a key-way 37. 
As shown in FIG. 5, a ring-shaped damper-mass member 39 is bonded to the 
planar surface of the main portion 32 via a ring-shaped rubber body 38 of 
a uniform thickness, which is disposed within a space defined by the boss 
portion 30 and the belt retaining portion 34. 
By virtue of the ribs 361 and 362, the boss portion 30 has sufficient 
strength, although it is made from a thin metal plate. The ribs 361 
respectively have U-shaped cross-sections so that after pressing-forming, 
the obtained product can be smoothly separated from a die, and 
accordingly, efficient production of the pulley can be realized. 
With the present embodiment, if the rubber body 38 is broken during 
operation of the pulley, the broken rubber pieces are prevented from 
scattering outward, because the damper-mass member 39 is directed to a 
main portion of an engine E, from which the rotary shaft S projects. 
In addition, the amount of projection of the pulley in its axial direction 
can be reduced, because the nut B is accommodated within the larger 
diameter portion 302 of the boss portion 30. 
FIGS. 7 and 8 illustrate a third embodiment of a pulley provided in 
accordance with the principles of the present invention, which acts as a 
damper pulley. As shown in the drawings, a cylindrical boss portion 40 and 
an annular plate-shaped main portion 42 are integrally formed from a thin 
metal plate by press-forming. The peripheral wall of the boss portion 40 
is alternately bent inwardly and outwardly in the circumferential 
direction to form ribs 46 having a rectangular cross-section. The outer 
periphery of the main portion 42 is tapered to define a receiving portion 
421. A ring-shaped damper-mass member 49 is bonded to the outer peripheral 
surface of the receiving portion 421 via a rubber body 48, having a 
uniform thickness. The damper-mass member 49 is formed from a ring-shaped 
thin metal plate by press-forming. V-shaped grooves 491 are formed in the 
outer peripheral surface of the damper-mass member 49, which extends in 
parallel to an axial line of boss portion 40. Thus, the damper-mass member 
49 serves as a belt retaining portion. 
When torsional vibrations are exerted from a rotary shaft (not shown), the 
damper-mass member 49 resonates therewith to effectively absorb or 
restrain the torsional vibrations. 
With the present embodiment, a sufficient mass of inertia can be obtained 
because the damper-mass member 49 is positioned outside the main portion 
42, and the weight of the pulley can be significantly reduced, because the 
damper-mass member 49 is also formed of a thin metal plate by 
press-forming. 
As described above, the pulley, provided in accordance with the present 
invention, can be produced in a simple manner at low cost, and the weight 
of the pulley can be significantly reduced. 
While the invention has been described in connection with what is presently 
considered to be the most practical and preferred embodiments, it is to be 
understood that the invention is not limited to the disclosed embodiments, 
but, on the contrary, is intended to cover various modifications and 
equivalent arrangements included within the spirit and scope of the 
appended claims.