Vehicle disc brake

1. A vehicle disc brake including:

a caliper body;

a caliper bracket which is fixed to a vehicle body, and which has a pair of caliper support arms extending to straddle an outer edge of a disc rotor in an axial direction thereof, each caliper support arm having a pair of pad guide grooves;

a pair of friction pads which is disposed at each side of the disc rotor, each friction pad having a backing plate, the backing plate having a pair of lug pieces extending from side portions thereof, the lug pieces being supported movably in the pad guide grooves; and

a pad return spring which is disposed between the lug pieces and the caliper support arms to bias the friction pad so as to move away from the disc rotor when the brake is released,

wherein an outer surface of each lug piece in a rotating direction of the disc rotor has a stepped shape in which a projecting length on a radially outer side is shorter than a projecting length on a radially inner side, and a space portion is defined between the radially outer side of the lug piece and the pad guide groove,

wherein the space portion is disposed in a position where a first imaginary line passes, the first imaginary line being defined to pass a gravity center of the friction pad and to intersect perpendicularly a center line connecting a center of the disc rotor and a center of a piston, and

wherein the gravity center of the friction pad lies further radially inwards than a center of the piston.

2. The vehicle disc brake of claim 1 ,

wherein the space portion is disposed in the position where a second imaginary line also passes, the second imaginary line being defined to pass the center of the piston and to intersect perpendicularly the center line.

3. The vehicle disc brake of claim 1 ,

wherein, in a first a state, the first imaginary line passes the gravity center of the friction pad and intersects perpendicularly the center line connecting the center of the disc rotor the center of the piston,

wherein, in a second state, the lug pieces are fixed within the pad guide grooves restricting generation of brake noise or squeal, and

wherein, in the second state, the space portion is disposed in a position where a second imaginary line passes the center of the piston and intersects perpendicularly the center line.

4. The vehicle disc brake of claim 1 ,

wherein the pad return spring is a non-linear characteristic spring in which biasing force changes as the friction pads move in the axial direction of the disc rotor.

5. A vehicle disc brake including:

a caliper body;

a caliper bracket which is fixed to a vehicle body, and which has a pair of caliper support arms extending to straddle an outer edge of a disc rotor in an axial direction thereof, each caliper support arm having a pair of pad guide grooves;

a pair of friction pads which is disposed at each side of the disc rotor, each friction pad having a backing plate, the backing plate having a pair of lug pieces extending from side portions thereof, the lug pieces being supported movably in the pad guide grooves; and

a pad return spring which is disposed between the lug pieces and the caliper support arms to bias the friction pad so as to move away from the disc rotor when the brake is released,

wherein an outer surface of each lug piece in a rotating direction of the disc rotor has a stepped shape in which a projecting length on a radially outer side is shorter than a projecting length on a radially inner side, and a space portion is defined between the radially outer side of the lug piece and the pad guide groove,

wherein the space portion is disposed in a position where a first imaginary line passes, the first imaginary line being defined to pass a gravity center of the friction pad and to intersect perpendicularly a center line connecting a center of the disc rotor and a center of a piston, and

wherein the pad return spring includes:

a locking portion which is locked on the lug piece;

a spring portion which is formed by bending back an extending piece which extends from the locking portion so as to move away from the disc rotor towards the disc rotor via a curved portion; and

an abutment portion which is provided at a distal end of the spring portion and which is brought into abutment with a side surface of the caliper support aim which lies opposite to a side surface facing the disc rotor.

6. The vehicle disc brake of claim 5 ,

wherein the locking portion is also disposed in the position where the first imaginary line passes.

7. The vehicle disc brake of claim 5 ,

wherein the locking portion of the pad return portion is disposed in a position where the first imaginary line passes, whereby when the brake is released, the friction pads are pulled back in a horizontal direction by means of the spring force of the pad return spring so that the friction pads can move away from the side surface of the disc rotor.

8. The vehicle disc brake of claim 5 ,

wherein the abutment portion is an arc-like shape whose side facing the caliper bracket is convex.

9. The vehicle disc brake of claim 5 ,

wherein the spring portion of the pad return spring is not disposed in the space portion defined between the lug pieces and the pad guide grooves.

10. A vehicle disc brake including:

a caliper body;

a caliper bracket which is fixed to a vehicle body, and which has a pair of caliper support arms extending to straddle an outer edge of a disc rotor in an axial direction thereof, each caliper support arm having a pair of pad guide portions;

a pair of friction pads which is disposed at each side of the disc rotor, each friction pad having a backing plate, the backing plate having a pair of lug pieces extending from side portions thereof, the lug pieces being supported movably in the pad guide portions; and

a pad return spring which is disposed between the lug pieces and the caliper support arms to bias the friction pad so as to move away from the disc rotor when the brake is released,

wherein the pad return spring includes:

a locking portion which is locked on the lug piece;

a first extending piece which extends from the locking portion so as to move away from the disc rotor via a first curved portion;

a second extending piece which is formed by bending back a distal end portion of the first extending piece towards the disc rotor via a second curved portion; and

an abutment portion which is provided at a distal end of the second extending piece and which is brought into abutment with a side surface of the caliper support arm which lies opposite to a side surface facing the disc rotor,

wherein the first extending piece is provided so as to be inclined gradually outwards of the friction pad from the first curved portion to the second curved portion in a free state in which the locking portion is locked on the lug piece, and

wherein, when the friction pad is assembled to the pad guide portions and the abutment portion is brought into abutment with the side surface of the caliper support arm which lies opposite to the side surface facing the disc rotor, the first extending piece comes near to a state in which the first extending piece is parallel to an axis of the disc rotor, and as the friction pad moves towards the disc rotor, the first extending piece comes nearer to the state in which the first extending piece is parallel to the axis of the disc rotor, thereby decreasing gradually a displacement amount thereof.

11. The vehicle disc brake of claim 10 ,

wherein a sectional area of the second extending piece is smaller than a sectional area of the first extending piece.

12. The vehicle disc brake of claim 10 ,

wherein a width of the second extending piece is narrower than a width of the first extending piece.

13. The vehicle disc brake of claim 10 ,

wherein an elongated hole is formed in the second extending piece.

14. A vehicle disc brake including:

a caliper body;

a caliper bracket which is fixed to a vehicle body, and which has a pair of caliper support arms extending to straddle an outer edge of a disc rotor in an axial direction thereof, each caliper support arm having a pair of pad guide grooves;

a pair of friction pads which is disposed at each side of the disc rotor, each friction pad having a backing plate, the backing plate having a pair of lug pieces extending from side portions thereof, the lug pieces being supported movably in the pad guide grooves; and

a pad return spring which is disposed between the lug pieces and the caliper support arms to bias the friction pad so as to move away from the disc rotor when the brake is released,

wherein an outer surface of each lug piece in a rotating direction of the disc rotor has a stepped shape in which a projecting length on a radially outer side is shorter than a projecting length on a radially inner side, and a space portion is defined between the radially outer side of the lug piece and the pad guide groove,

wherein the space portion is disposed in a position where a first imaginary line passes, the first imaginary line being defined to pass a gravity center of the friction pad and to intersect perpendicularly a center line connecting a center of the disc rotor and a center of a piston, and

wherein the pad return spring includes:

a locking portion which is locked on the lug piece,

a first extending piece which extends from the locking portion away from the disc rotor via a first curved portion,

a second extending piece which is formed by bending back a distal end portion of the first extending piece towards the disc rotor via a second curved portion, and

an abutment portion which is provided at a distal end of the second extending piece and which is brought into abutment with a side surface of the caliper support arm which lies opposite to a side surface facing the disc rotor.

15. The vehicle disc brake of claim 14 ,

wherein a width of the second extending piece is narrower than a width of the first extending piece, and the abutment portion is formed into an arc-like shape whose side facing the caliper bracket becomes convex.

16. The vehicle disc brake of claim 15 ,

wherein when the pad return spring is left free, the first extending piece is inclined outwards of the friction pad from the first curved portion towards the second curved portion,

the lug pieces of the friction pad are inserted into the pad guide grooves to which pad retainers are attached, and the abutment portion is brought into abutment with a side surface of the caliper support arm which lies opposite to the side surfaces facing the disc rotor, and

the first extending piece comes near to a state in which the first extending piece becomes parallel to an axis of the disc rotor from the inclined state.

17. The vehicle disc brake of claim 14 ,

wherein a width of a first extending piece and a width direction of the second extending piece are made identical, and a substantially rectangular elongated hole is formed in the second extending piece.

18. The vehicle disc brake of claim 14 ,

wherein a sectional area of the second extending piece is smaller than a sectional area of the first extending piece.

19. The vehicle disc brake of claim 18 ,

wherein a width of the second extending piece is narrower than the width of the first extending piece, and

wherein an elongated hole is provided in the second extending piece.