Caliper brake apparatus

1. A caliper brake apparatus that applies a brake to a vehicle wheel by applying frictional force to a disc that rotates together with the vehicle wheel, comprising:

a caliper main body supported by a vehicle body;

a brake shoe capable of applying frictional force to the disc by sliding against the disc;

a guide plate that supports the brake shoe;

an anchor pin that supports the guide plate and is provided in the caliper main body to be free to advance and retreat relative to the caliper main body;

a piston provided in the caliper main body to be free to advance and retreat relative to the caliper main body;

a piston plate that is fixed to a front surface of the piston and supported by the anchor pin;

an elastic membrane that is provided on a back surface of the piston so as to define a pressure chamber in the caliper main body, and that is configured to be deformed elastically by working fluid pressure in the pressure chamber so as to move the brake shoe via the piston, the piston plate, and the guide plate; and

an intermediate member sandwiched between the piston plate and the guide plate,

wherein the intermediate member is interposed between the piston plate and the guide plate such that a gap is located between the piston plate and the guide plate.

2. The caliper brake apparatus as defined in claim 1 , wherein the piston plate comprises a first housing recessed portion housing a part of the intermediate member.

3. The caliper brake apparatus as defined in claim 2 , wherein a depth of the first housing recessed portion is smaller than a thickness of the intermediate member in a depth direction, and

the intermediate member projects from the first housing recessed portion, such that the gap is located between the piston plate and the guide plate.

4. The caliper brake apparatus as defined in claim 2 , wherein the intermediate member is disposed such that an end surface thereof on a side not housed in the first housing recessed portion contacts the guide plate.

5. The caliper brake apparatus as defined in claim 1 , wherein the intermediate member includes a hole portion extending in a thickness direction of the intermediate member.

6. The caliper brake apparatus as defined in claim 1 , wherein the intermediate member is an adiabatic member having a lower thermal conductivity than the piston plate.

7. The caliper brake apparatus as defined in claim 2 , wherein a second housing recessed portion is formed in the back surface of the piston in a position opposing the first housing recessed portion, and

the piston plate and the piston are fastened to each other via a bolt disposed in a bottom portion of one of the first housing recessed portion and the second housing recessed portion, and a nut disposed in a bottom portion of the other.

8. The caliper brake apparatus as defined in claim 7 , wherein the nut is screwed to the bolt via a plate spring.

9. The caliper brake apparatus as defined in claim 7 , wherein the second housing recessed portion is constituted by an air chamber.

10. The caliper brake apparatus as defined in claim 1 , wherein the piston and the piston plate are connected via an adiabatic body having a lower thermal conductivity than the piston plate.

11. The caliper brake apparatus as defined in claim 1 , wherein an air layer is located between the piston and the piston plate.

12. The caliper brake apparatus as defined in claim 1 , further comprising:

a cylinder provided in the caliper main body to house the piston; and

a dust boot provided between the cylinder and the piston,

wherein the dust boot is formed from a tubular member, and

one end of the dust boot is fixed to a tip end outer periphery of the cylinder while another end is fixed to a tip end outer periphery of the piston.