JPS6224655B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a drum brake in which the braking gap is automatically adjusted during brake application using hydraulic pressure, and the adjustment action is interrupted in response to excessive brake fluid pressure. This invention relates to a braking gap adjustment device.

[Prior Art] A conventional braking gap adjustment device is generally provided outside a wheel cylinder device.
There are various difficulties in arranging this in the limited internal space of the brake drum, and there is also a risk of rust due to muddy water entering from the outside.

[Problems to be Solved by the Invention] An object of the present invention is to provide a braking gap adjustment device for a drum brake incorporated in a wheel cylinder device that does not have the above-mentioned problems.

[Means for Solving the Problem] In order to achieve the above object, the configuration of the present invention includes first and second pistons that are fitted into a hydraulic cylinder and whose outer ends are engaged with a brake shoe; A spring that is fitted into a stepped cylindrical part that opens toward the inner end of the first piston, has a larger diameter on the inner end, and is interposed between the outer end and the first piston at a predetermined hydraulic pressure. a stepped sleeve that moves toward the second piston against the
An adjustment nut is rotatably and slidably fitted between a friction plate fixed to the inner end wall of the cylindrical portion and the stepped sleeve, and an adjustment nut passes through the stepped sleeve and has a reversible screw groove at one end. Screw into the nut, and the other end is the second
and an adjustment bolt that is screwed into the piston, and when the brake is applied, the adjustment nut separates from the friction plate and screws against the stepped sleeve.

[Function] When the brake is applied, the piston 41 as well as the adjustment bolt 20 and the adjustment nut 1 screwed thereto
8 moves to the left, leaves the friction plate 23, and comes into contact with the right end surface of the stepped sleeve 21. When the piston 41 and the adjustment bolt 20 move further to the left, the adjustment nut 18 is prevented from moving in the axial direction by the stepped sleeve 21 and rotates. At this time, the adjustment nut 18 is screwed out from the adjustment bolt 20 to the right.

When excessive hydraulic pressure is applied to the cylinder 14 so as to deform the brake drum, the hydraulic pressure acting on the large diameter end face (right end face) of the stepped sleeve 21 inside the cylindrical portion 29 is applied to the small diameter end face (left end face). The force becomes greater than the resultant force of the acting hydraulic pressure and the disc spring 4, and the stepped sleeve 21 moves to the left and separates from the adjusting nut 18, so that the adjusting nut 18 does not screw, but moves together with the adjusting bolt 20.

When the hydraulic pressure in the cylinder 14 is released, the pistons 41 and 22 are returned inwardly by known return springs, and the stepped sleeve 21 is pressed against the stepped portion 28 by the force of the disc spring 4. The piston 41, adjustment bolt 20, and adjustment nut 18 move to the right together, and the adjustment nut 18 engages with the friction plate 23. When the piston 41 moves further to the right, the adjustment bolt 20 relatively screws to the right and stops when it collides with the friction plate 23. In this way, the amount of rotation (rightward screwing amount) of the adjusting nut 18 that occurs when the brake is applied
Therefore, when the brake is released, the adjustment bolt 20 spirals relative to the piston 41 to the right, and as a result, the mutual distance between the pistons 41 and 22 increases, and the braking gap is reduced.

[Embodiment of the Invention] As shown in FIG. 1, the wheel cylinder device includes seal rings 16 and 17 inside the cylinder 14.
A pair of pistons 4 each mounted on the outer periphery
1 and 22, and known brake shoes 12 and 22 are fitted into the grooves 13 and 8 provided at their outer ends, respectively.
19 webs are engaged to prevent rotation of both pistons.

A threaded hole 15 is provided at the inner end of the piston 41, into which the threaded portion 20a of the adjustment bolt 20 is screwed. The right end of the adjustment bolt 20 is connected to the piston 2
The adjustment nut 18 is projected into the interior of a cylindrical portion 29 provided on the inner end side of the cylindrical portion 2, and is screwed into the adjustment nut 18 rotatably and slidably fitted into the cylindrical portion 29 via a reversible screw groove 20b. A friction plate 23 is fixed to the inner end wall of the cylindrical portion 29 with a pin 24 . A large number of protrusions are provided on the left end surface of the friction plate 23 at intervals in the circumferential direction and extend in the radial direction, and these protrusions engage with grooves cut on the right end surface of the adjustment nut 18 to prevent rotation of the adjustment nut 18. be done. Instead of providing grooves on the surface of the friction plate 23, a friction material having a large friction coefficient may be used.

A stepped sleeve 21 is attached to the open end (left end) of the cylindrical portion 29, and a gap S is provided between the right end surface of the stepped sleeve 21 and the left end surface of the adjustment nut 18. Shaft hole 3 through which adjustment bolt 20 passes
A stepped sleeve 21 having a diameter of 3 is attached to a stepped cylindrical portion adjacent to cylindrical portion 29 as shown in FIG. That is, the stepped portion 28 is formed on the open end side of the cylindrical portion 29.
A large diameter cylindrical portion 27 is formed from the step portion 26.
A cylindrical portion 25 having a larger diameter is formed from this point.
The stepped sleeve 21 includes a large diameter shaft portion that fits into the cylindrical portion 27 via the seal ring 9, and a stepped portion 32.
A small-diameter shaft portion is integrally provided with a small-diameter shaft portion that has a small diameter from a portion thereof and is fitted into the cylindrical portion 25 via a seal ring 6, and a seat fitted with the back-up spring 7 and the left end portion of the stepped sleeve 21. The seal ring 6 is restrained from moving much in the axial direction by the plate 5.

On the other hand, the seat plate 3 is fitted into the cylindrical portion 25, and movement in the axial direction is restricted by a retaining ring 2 that is engaged with the cylindrical portion 25. This seat plate 3 and the seat plate 5 mentioned above
The right end surface of the stepped sleeve 21 is pressed against the stepped portion 28 by the disc spring 4 interposed between the stepped sleeve 21 and the stepped sleeve 21 .
Step portion 32 of stepped sleeve 21 and step portion 26 of cylindrical portion
The space between seal ring 6 and seal ring 9
It is sealed from the liquid chamber by

It is preferable that a low-friction material, a bearing, or the like be interposed between the right end surface of the stepped sleeve 21 and the left end surface of the adjustment nut 18 to reduce rotational resistance as much as possible.

Next, the operation of the braking gap adjusting device for a drum brake according to the present invention will be explained. When pressurized fluid is supplied to the fluid chamber 30 from the brake released state shown in FIG.
9 frictionally engages with the inner peripheral surface of the brake drum to generate braking force.

When the adjustment nut 18 screwed onto the adjustment bolt 20 moves to the left, leaves the friction plate 23 and collides with the right end surface of the stepped sleeve 21, the adjustment nut 18 is prevented from moving in the axial direction and rotates (screws). do.

When excessive hydraulic pressure is applied to the cylinder 14 to the extent that the brake drum is deformed, the hydraulic pressure acting on the right end surface of the stepped sleeve 21 inside the cylindrical portion 29 is
The force becomes greater than the resultant force of the hydraulic pressure acting on the left end surface and the disc spring 4, and the stepped sleeve 21 moves to the left.
Leave the adjustment nut 18. Therefore, the adjusting nut 18 does not screw, but moves to the left together with the adjusting bolt 20.

When the braking gap is at a normal value, the relative movement between the piston 41 and the piston 22 accompanying the brake operation is performed within the range of the gap S.

When the hydraulic pressure in the cylinder 14 is released, the pistons 41 and 22 are returned inward by known return springs stretched between the brake shoes 12 and 19, and the stepped sleeve 21 is moved by the force of the disc spring 4. It is pressed against the stepped portion 28. The adjustment bolt 20 moves to the right together with the piston 41, and the adjustment nut 18 screwed into it also moves to the right together, and the friction plate 2
3. When the piston 41 moves further to the right, the adjustment bolt 20 relatively screws to the right and stops when it collides with the friction plate 23. In this way, when the brake is released, the adjusting bolt 20 is rotated by the amount of rotation of the adjusting nut 18 that occurs when the brake is applied, and is screwed to the right relative to the piston 41, so that the distance between the pistons 41 and 22 is is increased and the braking gap is reduced.

[Effects of the Invention] As described above, in the present invention, the braking gap is automatically adjusted according to the wear of the lining, and is always maintained at an appropriate value, and the adjustment action is interrupted when the braking action is excessive. , the braking gap is not narrowed excessively in response to deformation of the brake drum.

According to the present invention, all the components of the braking gap adjustment device are incorporated inside the wheel cylinder device, so problems such as rust do not occur.
Since the structure is simple, an inexpensive and high-performance braking gap adjustment device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a braking gap adjustment device for a drum brake according to the present invention, and FIG. 2 is an enlarged sectional view of the main part of the device. 4: Belleville spring, 12: Brake shoe, 14: Cylinder, 18: Adjustment nut, 19: Brake shoe, 20: Adjustment bolt, 21: Stepped sleeve, 2
2: Piston, 20b: Reversible screw groove, 23: Friction plate, 29: Cylindrical portion, 41: Piston.

Claims (1)

[Claims] 1. First and second pistons that are fitted into a hydraulic cylinder and whose outer ends are engaged with a brake shoe, and a stepped cylindrical portion that opens at the inner end of the first piston. a stepped sleeve that is fitted into the sleeve, has a large diameter on the inner end side, and moves toward the second piston against a spring interposed between the outer end and the first piston under a predetermined hydraulic pressure; an adjustment nut that is rotatably and slidably fitted between the friction plate fixed to the inner end wall of the cylindrical portion and the stepped sleeve; and an adjustment nut that passes through the stepped sleeve and has a reversible threaded groove at one end. and an adjusting bolt whose other end is screwed into the adjusting nut and whose other end is screwed into the second piston, and when the brake is applied, the adjusting nut separates from the friction plate and abuts against the stepped sleeve and screws. Features a braking gap adjustment device for drum brakes.