1.  Field of the Invention
The present invention relates to a disc brake, more particularly to a disc brake in which a caliper is supported by a mounting slidably in the axial direction of the rotor via a pair of pin sliding means. 
2.  Description of Related Art
An example of this kind of disc brake is disclosed in UKP No.  1500907.  According to this example, one of the pin sliding means is mounted in an installation hole in the caliper via a cylindrical elastic member.  This structure enables elastic deformation of the elastic member to absorb dimensional tolerance between the installation hole of the caliper and the installation hole in the mounting and deformation of the mounting generated during braking. 
However, in the aforementioned conventional disc brake, transitional change (i.e. permanent set in fatigue) of the elastic member may make the disc brake unable to obtain the predetermined function.  In addition, when the caliper is pulled in the rotational direction of the rotor in accordance with braking (i.e. when the caliper is deformed in the direction of twist), a large twist is generated on the side where no elastic member is used, inhibiting smooth sliding at the pin sliding means. 
In order to solve the aforementioned problems, the present invention provides a disc brake in which the caliper is supported by the mounting slidably in the axial direction of the rotor via a pair of pin sliding means, characterized in that the pin sliding means is such that the caliper side axial portion mounted in an installation hole in the caliper rotatably and integrally movably in the axial direction is off-centered from the mounting side axial portion fitted into the installation hole in the mounting rotatably and slidably in the axial direction. 
In this case, it is preferable that the eccentric amount at one of the pin sliding means is different from that at another pin sliding means, or that the installation hole in the caliper is brought into contact in a circular line with the caliper side axial portion of the pin sliding means, or that the disc brake further comprises urging means for urging the caliper in the diametrical direction of the rotor. 
In the aforementioned disc brake according to the present invention, rotation of each pin sliding means with respect to the caliper and the mounting enables each pin sliding means to rotatably displace the center of the caliper side axial portion with respect to the center of the mounting side axial portion, whereby the dimensional tolerance between the pitch between both installation holes in the caliper and the pitch between both installation holes in the mounting can be absorbed in the range of eccentric amounts of both pin sliding means.  This allows the clearance at a fitting portion between each installation hole in the mounting and the mounting side axial portion to be set small so as to improve slidability at each fitting portion without having to consider each of the dimensional tolerances above.  In addition, even in the case where the pitch between both installation holes in the mounting changes due to deformation of the mounting during braking , as i n the case where the aforementioned tolerance is absorbed, the pitch between both pin sliding means can be changed accordingly along with the dimensional tolerance. 
In the aforementioned disc brake according to the present invention, the aforementioned effect is achieved by employing each pin sliding means in which the caliper side axial portion mounted in the installation hole in the caliper rotatably and integrally movably in the axial direction is off-centered from the mounting side axial portion fitted into the installation hole in the mounting rotatably and slidably in the axial direction.  Since no transitional change occurs between each sliding means and the caliper and mounting, the initial function can be obtained for a long period of time. 
According to a preferred form of the present invention, an eccentric amount at one pin sliding means is different from that at another pin sliding means.  In this case, the caliper is moved to one side in the diametrical direction of the rotor with respect to the mounting when the pitch between both installation holes in the mounting changes due to deformation of the mounting during braking.  Therefore, behavior of the caliper with respect to the mounting during braking can be properly set by appropriately setting an eccentric amount at each pin sliding means. 
According to another preferred form of the present invention, the installation hole in the caliper is brought into contact, in a circular line, with the caliper side axial portion of the pin sliding means.  In this case, the pin sliding means can be moved to one side at the caliper side axial portion, and dimensional tolerance and deformation due to braking in the direction of twist (i.e. the direction in which the caliper is twisted due to braking force) can also be absorbed.  Therefore, even in the case where the caliper is pulled in the rotational direction of the rotor in accordance with braking (i.e. when the caliper is deformed in the direction of twist), no major twist is generated at each pin sliding means, such that smooth sliding in the pin sliding means is ensured. 
According to yet another preferred form of the present invention, urging means is provided for urging the caliper in the dimensional direction of the rotor.  In this case, it is possible to prescribe the initial position (i.e. a position when no braking is applied) with respect to the mounting, to stabilize behavior of the caliper with respect to the mounting during braking, and thus obtain stable braking force.