The present invention relates to a rotary type hydraulic damper. More particularly, the invention relates to a rotary type hydraulic damper especially adapted for use with a motorcycle suspension.
As one kind of hydraulic damper used for the rear wheel suspension of a motorcycle there is, for example, a rotary type hydraulic damper as disclosed in Japanese Laid-Open Patent Publication No. 56-28008 (No. 28008/1981). Generally, this kind of rotary type hydraulic damper comprises a shaft arranged in a cylindrical housing which is closed at both ends by fixedly providing side cases rotatable with respect to said shaft, and a plurality of oil chambers which are defined in said housing by projecting vanes diametrically oppositely from an inner periphery of the cylindrical housing and from an outer periphery of the shaft, which vanes communicate with each other through the intermediary of damping force generating means.
Also, there is disclosed in a Japanese Patent Application , assigned to the assignee herein, a rotary type damper particularly adapted for motorcycle suspension applications. The described damper apparatus is one wherein one of the end cases is provided with a pair of oil passages that connect the damping force generating means of the apparatus on the one hand with compression side oil chambers and on the other hand with expansion side oil chambers. Obviously, in situations such as in the disclosed arrangement where both of the oil passages are provided in one end case, the problem arises that each of the passages must be limited in its cross-sectional flow area. Consequently, the resistance to flow of hydraulic fluid through the passages is increased and, as a result, the design of the damping force generator is more complicated.
Moreover, in the apparatus disclosed in Japanese Patent Application No. 60-265936, the shaft of the rotary type damper is coaxially arranged with the swing shaft of the swing arm that is pivotally mounted with respect to the vehicle frame and the drive sprocket, that drives the vehicle wheel supported on the swing arm, is mounted on a bearing case provided on the engine. Consequently, because the loading of the driving chain is concentrated on the sprocket, the bearing case provided on the rear of the engine must have sufficient mass to withstand this loading. This results in a bearing case that is thick and heavy.
It is to the amelioration of these problems, therefore, that the present invention is directed.