1. Field of the Invention:
The present invention relates to a damper pulley, and more particularly to a damper pulley for restraining both exerted bending and torsional vibrations.
2. Description of Related Art:
A damper pulley is generally provided with a pulley having a boss portion and a plate portion formed around the boss portion, and a dynamic damper having a resilient rubber member and a damper-mass member which is joined to the plate portion of the pulley through the resilient rubber member.
One example of such a damper pulley is illustrated in FIG. 3. In the drawing, a pulley 1 is composed of a boss portion 11 which is secured to a crankshaft (not shown), a plate portion 12 that projects radially outwardly from the boss portion 11, and a belt retaining portion 13 which is integrally formed with the outer periphery of the plate portion 12 for retaining a belt along the outer surface thereof.
An annular resilient rubber member 21 having a predetermined thickness is provided around the boss portion 11 on an annular surface 12a of the plate portion 12. An annular metallic damper-mass member 22 is joined to the resilient rubber member 21, thereby composing a dynamic damper 2.
When bending vibrations are exerted from the crankshaft, the pulley 1 vibrates in the radial direction thereof so that the resilient rubber member 21 radially deforms. Due to this deformation of the resilient rubber member 21, the dynamic damper 2 resonates with the pulley 1 with a resonance frequency FR which is determined by the radial deformation of the resilient rubber member 21 and the mass of the damper-mass member 22. Thus the bending vibrations are restrained.
When torsional vibrations are exerted from the crankshaft, the pulley 1 vibrates in the circumferential direction thereof so that the resilient rubber member 21 circumferentially deforms. Due to this deformation of the resilient rubber member 21, the dynamic damper 2 resonates with the pulley 1 with a resonance frequency F.THETA. which is determined by the circumferential deformation of the resilient rubber member 21 and the moment of the inertia of the damper-mass member 22. Thus, the torsional vibrations are restrained.
In order to sufficiently restrain both the bending vibrations and torsional vibrations of the crankshaft, it is preferable to set the resonance ratio (FR/F.THETA.) to about 0.7. To achieve this ratio, the moment of the inertia of the damper-mass member 22 has been reduced by tapering the outer surface of the damper-mass member 22, as shown in FIG. 3.
As the moment of inertia decreases, the resonance frequency F.THETA. acting against the torsional vibrations increases, but, the damping effect of the dynamic damper 2 is reduced. Therefore, in order to prevent such a reduction in the damping effect of the dynamic damper 2, the prior art has not decreased the resonance ratio of the conventional damper pulley to more than about 0.88.