Disk brake

#The present invention relates to disk brakes for use in vehicles such as two- and four-wheeled vehicles.

#In a disk brake, a seal member may be thermally expanded by heat generated between a disk rotor and a friction pad during braking, which is transmitted from the friction pad to the seal member through a piston in a caliper. The thermal expansion of the seal member forces the piston to retract toward the bottom of the cylinder bore. To reduce the amount of retracting movement of the piston, a technique has been disclosed in which the bottom surface of a seal groove where the seal member is provided is formed to have a diameter-increasing portion increasing in diameter toward the opening of the cylinder bore in the axial direction of the cylinder bore and a peripheral surface portion positioned closer to the bottom of the cylinder bore in the axial direction thereof than the diameter-increasing portion. The peripheral surface portion has a smaller angle to the axis of the cylinder bore than the diameter-increasing portion (see Japanese Patent Application Publication No. 2004-156651.

#It is desirable for disk brakes to suppress the movement of the piston toward the bottom of the cylinder bore due to thermal expansion of the seal member, and it is demanded to further enhance the effect of suppressing the undesired retracting movement of the piston.

#FIG. 1 is a top view of a caliper of a disk brake according to an embodiment of the present invention.

#FIG. 2 is a sectional view taken along the line A-A in FIG. 1.

#FIG. 3 is a sectional view showing the way in which a piston seal member is disposed in a seal groove according to a first embodiment of the present invention.

#Embodiments of the present invention will be explained below in detail with reference to FIGS. 1 to 6. As shown in FIGS. 1 and 2, a disk brake 1 according to an embodiment of the present invention has a disk rotor 2 rotating together as one unit with a wheel to be braked. The disk brake 1 further has a caliper 3 applying a frictional resistance to the disk rotor 2. The caliper 3 is an opposed 4-piston caliper that has a caliper body 4 extending over the disk rotor 2 in the axial direction of the latter and secured to a non-rotating part of a vehicle (i.e. a stationary member non-rotatable with the wheel, e.g. a front fork of a motorcycle, or a knuckle member of an automobile). The opposed 4-piston caliper further has two pairs of pistons 5 slidably provided in the caliper body 4 such that the pistons 5 of each pair face each other across the disk rotor 2. It should be noted that the sectional view of FIG. 2 shows only one pair of pistons 5.

#The caliper body 4 has, as shown in FIGS. 1 and 2, an outer cylinder portion 7 disposed at the outer side of the disk rotor 2 (i.e. at the side of the disk rotor 2 remote from the wheel) and an inner cylinder portion 8 disposed at the inner side of the disk rotor 2 (i.e. at the side of the disk rotor 2 closer to the wheel). The caliper body 4 further has three bridge portions 9a, 9b and 9c connecting together the outer cylinder portion 7 and the inner cylinder portion 8 at the radially outer side of the disk rotor 2. Further, the caliper body 4 has a pair of pad pins 10 spaced in the disk circumferential direction. The pad pins 10 extend between the outer cylinder portion 7 and the inner cylinder portion 8 along the disk axial direction.

#The outer cylinder portion 7 and the inner cylinder portion 8 are provided with two pairs of cylinder bores 11 spaced from each other in the disk circumferential direction. The cylinder bores 11 of each pair are opposed to each other in the disk axial direction. Cup-shaped pistons 5 are slidably accommodated in the cylinder bores 11, respectively, such that the bottom of each piston 5 faces the bottom of the associated cylinder bore 11. It should be noted that the outer cylinder portion 7 and the inner cylinder portion 8 are provided with two pairs of pistons 5 spaced from each other in the disk circumferential direction such that the pistons 5 of each pair face each other across the disk rotor 2.