JPS642821B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wheel cylinder of a two-leading type vehicle drum brake incorporating an auto-adjustment mechanism.

As is well known, in a two-leading type vehicle drum brake, a pair of arcuate brake shoes are arranged on a back plate so that they can be expanded in the circumferential direction by the operation of a wheel cylinder, with one end serving as a fulcrum, and the brake shoes are integrated with the wheels. The inner circumferential surface of the rotating brake drum comes into pressure contact with the brake drum to provide braking. When the brake lining wears out due to this braking, the braking gap between the brake lining and the inner circumferential surface of the brake drum increases, so an adjuster mechanism provided separately from the wheel cylinder is activated to expand the brake shoe. The braking gap is adjusted so that it is always constant.

Therefore, an object of the present invention is to incorporate the adjusting mechanism, which is provided separately from the wheel cylinder that expands the brake shoe, into the wheel cylinder, so that the structure is simple and can be manufactured at low cost, and the adjusting mechanism part is To provide a wheel cylinder for a two-leading type vehicle drum brake which can quickly bleed air from a hydraulic pressure chamber.

In accordance with the above object, the present invention forms a cylinder with a large diameter part opening at one end of a cylinder body and a small diameter part connected to the inner part of the large diameter part, and allows a piston to slide into the large diameter part. When inserted, hydraulic pressure chambers are defined in the large diameter section and small diameter section at the rear end of the piston, and a hydraulic pressure introduction hole is provided in the hydraulic pressure chamber of the small diameter section, and a discharge hole is provided in the hydraulic pressure chamber at the bottom of the large diameter section. , the expansion side end of one brake shoe is supported on the front end of the piston protruding from the large diameter part, and the expansion side end of the other brake shoe is supported on the other end of the cylinder body, and the small diameter part An adjusting bolt with a clutch surface is arranged in the axial direction with a backlash equal to the braking gap and is threaded with a multi-thread screw to a nut member fixed to the bolt, and the adjusting bolt is constantly pressed in the direction of the piston by an adjusting spring. The clutch surface of the adjusting bolt is brought into contact with the clutch receiving surface of the piston, and when the piston advances beyond the backlash between the nut member and the adjusting bolt, the adjusting bolt rotates and moves forward following the piston. The reason is that it has a built-in auto-adjustment mechanism.

Hereinafter, an embodiment of a wheel cylinder of a two-leading type vehicle drum brake according to the present invention will be explained with reference to the drawings. Inside a back plate (not shown), a pair of arcuate brake shoes 1 and 1' are arranged on a shoe web. They are disposed so as to be expandable with one end of 1a, 1'a as a fulcrum, and are always urged in the proximal direction by a return spring (not shown).

The wheel cylinder of the present invention is arranged between the shoe web ends 1b, 1b' of the brake shoes 1, 1', and is fixed to the back plate. A cylinder body 2 of this wheel cylinder is open at one end, and a piston 3 is tightly and slidably fitted into a large diameter portion 2a of the cylinder body 2 by means of a piston cup 4. As a result, inside the cylinder body 2, there is an opposing portion 2c of the rear wall of the cylinder that faces the piston 3 and has a small diameter portion 2b;
A hydraulic chamber 5 is defined by the piston 3, and pressure fluid is supplied into the hydraulic chamber 5 through a fluid supply port 6 communicating with a master cylinder (not shown). Opposing part 2
A nut member 7 having a multi-thread internal thread 7a is press-fitted and fixed to the front end of c. The adjustment bolt 8 is composed of a shaft portion having a multi-thread male screw 8a and a conical head having a clutch surface 8b.
The multi-start male thread 8a of the shaft portion is screwed into the multi-start male thread 7a of the nut member 7 with a backlash in the axial direction, and the clutch surface 8b of the head is formed on the rear of the piston 3. It is arranged in contact with the clutch receiving surface 3a of the recessed portion.

The brake shoes include brake shoes 1a,
It is set equal to the braking gap between the brake linings 1c and 1'c of 1'a and the inner circumferential surface of the brake drum (not shown) that rotates integrally with the wheel.

The adjusting bolt 8 is always pressed in the direction of the piston 3 by the adjusting spring 10 via the retainer 9. The rear part 8c of the adjusting bolt 8 is formed to protrude into a spherical shape, and is in point contact with the flat plate-shaped retainer 9 at the axial center. When the piston 3 advances beyond the set braking gap, the adjustment bolt 8 and nut member 7
The forward movement of the adjusting bolt 8 is restricted, and the clutch surface 8b of the adjusting bolt 8 is no longer in contact with the clutch receiving surface 3a of the piston 3. At this time, the adjusting bolt 8 is pushed by the adjusting spring 10. It rotates due to pressure and follows the piston 3, and the clutch bearing surface 3 of the piston 3
The clutch face 8b of the adjuster bolt 8 comes into contact with the bolt 8a and moves forward until its rotation is restricted. In addition, in this embodiment, the rear part 8c of the adjuster bolt 8 is made into a protruding spherical surface, and the retainer 9
However, on the contrary, the rear part 8c of the adjusting bolt 8 may be made flat, and the retainer 9 may be provided with a spherical surface that protrudes toward the adjusting bolt 8. In short, the rear part 8c of the adjusting bolt 8 and the retainer 9 may be in point contact with the adjusting bolt 8 at its rotational axis.

The concave portion of the piston 3 is formed in a conical shape with its center facing the axis of the piston 3, and the conical concave portion of the piston 3 is closer than the conically protruding head of the adjusting bolt 8. The slope is made gentle so that the clutch surface 8b and the clutch receiving surface 3a are in a ring-shaped line contact on the outer side in the radial direction away from the rotation axis of the adjusting bolt 8. Further, contrary to this embodiment, a conical recess may be formed in the head of the adjusting bolt 8, and a conical protrusion may be formed in the rear of the piston 3 correspondingly to the conical protrusion so as to come into contact therewith.

If the clutch surface 8b of the adjusting bolt 8 and the clutch receiving surface 3a of the piston 3 are in line contact at a position further away from the rotational axis of the adjusting bolt 8, the rotation of the adjusting bolt 8 will be reduced. Regulation becomes more certain.

An air vent hole 11 is formed in the large diameter portion 2a of the cylinder body 2 at a position that will be upward when assembled to the vehicle body. It can be removed using the collision with bolt 8. Further, the piston head 12 engages with the shew web end portion 1'b in a rotationally restricted manner, and is rotatably fitted with the piston 3. A gear 13 is fixedly provided at the front end of the piston 3, and when the brake linings 1c, 1'c are caught in the wear grooves on the inner peripheral surface of the brake drum and the brake drum cannot be removed,
It is used to rotate the piston 3 when releasing the adjustment. That is, since the brake shoes 1, 1' are always urged in the proximal direction by the return spring, the clutch receiving surface 3a of the piston 3 and the clutch surface 8b of the adjusting bolt 8 are pressed into contact with each other. The rotation of the adjusting bolt 8 is restricted, and the adjusted piston 3 will not return to its original position. Therefore, this piston 3
When the gear 13 is rotated in the non-adjustment direction, the adjustment bolt 8 also rotates and retreats, allowing the piston 3 to return.

Next, the operation of this embodiment will be explained.

When the pressure fluid from the master cylinder is introduced into the hydraulic pressure chamber 5 from the fluid supply hole 6, the piston 3 moves forward to the right, moving the shoe web end 1'b of the brake shoe 1' toward the brake drum. Move to.
As a result, the brake shoe 1' expands using the fixed portion of the brake cylinder device provided on the other side as a fulcrum. Similarly, the brake shoe 1 expands using the fixed portion 14 of the brake cylinder device as a fulcrum, and presses against the inner circumferential surface of the brake drum that rotates together with the wheel to perform a braking action.

At this time, when the piston 3 moves forward, the adjusting bolt 8 is pushed by the adjusting spring 10, and the clutch surface 8b of the head moves by the amount of backlash while contacting the clutch receiving surface 3a of the piston 3, thereby performing a braking action. Therefore, the adjustment bolt 8 does not rotate and is not adjusted. When the brake is released, the piston 3 and adjustment bolt 8 return to their original positions together.

Brake lining 1 due to repeated braking
When c and 1'c wear out, the braking gap becomes more than the backlash, so the piston 3 moves forward due to the action of the pressure fluid, but the adjustment bolt 8 is regulated by the nut member 7 and does not move forward together with the piston 3. become unable to do so. Therefore, the clutch receiving surface 3a of the piston 3 and the clutch surface 8b of the adjusting bolt 8 are separated from each other. At this time, since the axial center of the adjusting bolt 8 is always pushed in the direction of the piston 3 by the adjusting spring 10, rotational torque is generated at the multi-thread threaded portion with the nut member 7. This rotational torque is applied to the nut member 7.
is fixed, the adjuster bolt 8 rotates and moves forward only by the rotational resistance of the multi-thread thread. This adjusting bolt 8 is attached to the clutch surface 8b.
hits the clutch receiving surface 3a of the piston 3, and rotates until the frictional resistance of the line contact between the clutch surface 8b and the clutch receiving surface 3a becomes greater than the rotational resistance, and follows the forward movement of the piston 3.

When the brake is released, the brake shoes 1, 1' are returned to their original positions by the return spring, but at this time, the adjustment bolt 8 is connected to its clutch surface 8b and the clutch receiving surface 3a of the piston 3.
Since they are in line contact with each other, the piston 3 returns integrally with the piston 3 by the amount of backlash without rotating, and the adjustment is completed. Since this brake stroke is set equal to the braking gap,
Even if the brake linings 1c, 1'c wear out, the braking gap is automatically adjusted to always remain constant.

If the brake drum cannot be removed due to wear grooves caused by the brake lining on the inner peripheral surface of the brake drum, the gear 13 can be rotated in the non-adjustment direction to rotate the piston 3, and the adjustment bolt 8 can be integrated with the piston 3. Since the brake shoes 1, 1' are contracted inward by the return spring, the brake drum can be easily removed.

As described above, the present invention involves screwing an adjusting bolt into a nut member fixed in a cylinder with a multi-start screw with a predetermined backlash in the axial direction, and expanding the clutch surface of the adjusting bolt into a brake shoe. Since it contacts the clutch receiving surface of the piston and is always pressed in the direction of the piston by the adjuster spring, the braking gap can be reliably adjusted with a simple structure, reducing manufacturing costs. Since the adjustment mechanism is built-in, there is no need to assemble the auto-adjustment mechanism to the brake device separately from the cylinder device, and the assembly of the brake parts becomes simple and easy, and workability can be improved. Moreover, a hydraulic pressure introduction hole is provided in the hydraulic pressure chamber in the small diameter part of the cylinder body, and an exhaust hole is provided in the hydraulic pressure chamber at the bottom of the large diameter part, so that the hydraulic fluid passes from the hydraulic pressure introduction hole to the exhaust hole. This has the effect of making it possible to quickly bleed air from the auto-adjustment mechanism.

[Brief explanation of the drawing]

The figure is a sectional front view showing one embodiment of the present invention. 1... Brake shoe, 2... Cylinder body, 3
... Piston, 5... Hydraulic pressure chamber, 7... Nut member, 8...
Adjustment bolt, 10...Adjustment spring.

Claims (1)

[Claims] 1 a large diameter portion opening at one end of the cylinder body;
A cylinder is formed by a small diameter part connected to the back of the large diameter part, and a piston is slidably inserted into the large diameter part to form a hydraulic chamber in the large diameter part and the small diameter part at the rear end of the piston. A hydraulic pressure introduction hole is provided in the hydraulic pressure chamber in the small diameter part, a discharge hole is provided in the hydraulic pressure chamber at the bottom of the large diameter part, and one brake shoe is expanded at the front end of the piston that protrudes from the large diameter part. The side end is supported by the other end of the cylinder body on the expansion fulcrum side of the other brake shoe, and the adjustment bolt, which has a clutch surface on a nut member fixed to the small diameter part, is axially braked. The adjusting bolt is arranged with a back clutch equal to the gap and is screwed with a multi-start screw, and the adjusting bolt is constantly pressed in the direction of the piston by an adjusting spring so that the clutch surface of the adjusting bolt is brought into contact with the clutch receiving surface of the piston, A two-leading type drum brake for a vehicle, characterized in that it incorporates an auto-adjustment mechanism in which when the piston advances beyond the backlash between the nut member and the adjustment bolt, the adjustment bolt rotates and moves forward following the piston. wheel cylinder.