JPS6157503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention maintains the gap between the brake drum and the brake shoe, that is, the braking gap, at an appropriate value at all times, prevents an increase in the stroke of the brake operation pedal, and improves the distance between the brake drum and the brake shoe. The present invention relates to a braking gap adjustment device that prevents an increase in shoe drag torque.

With a typical brake gap adjustment device that automatically adjusts the brake gap in conjunction with brake operation, if an excessive braking force that deforms the brake drum is applied, the brake gap may become excessive. The brake drum and brake shoe may drag when the brake is released.

In order to prevent this kind of dragging, a brake clearance device has been proposed that allows the adjustment amount to be adjusted with a single brake operation to an extremely small value. Many brake operations must be performed before the braking clearance is obtained, and a large amount of time is spent on initial adjustment work.

A braking gap adjustment device has been proposed that allows for easy initial adjustment and also interrupts the adjustment action when the drum deforms. Overregulation cannot be avoided.

The present invention allows the initial adjustment of the braking gap with a single brake operation, and also prevents over-adjustment action based on thermal deformation of the brake drum, which may increase the drag torque between the brake drum and the brake shoe. The purpose of the present invention is to propose a braking gap adjustment device that allows the braking gap to be returned to an appropriate value simply by operating the brake again.

The configuration of the present invention will be explained based on illustrated embodiments. As shown in Fig. 1, a pair of pistons 4, 44 are slidably fitted inside a wheel cylinder 1 fixed to the back plate of a drum brake, and are inserted into grooves provided at their outer ends. The ends of the pair of brake shoes 2, 22 are engaged by the force of a return spring 3 stretched between the brake shoes 2, 22. A dustproof boot 15 is installed between the outer end of each piston 4, 44 and the end of the cylinder 1 to prevent dust from entering the sliding portion of the piston from the outside. Cup seals 18 are installed on the pistons 4 and 44.
are respectively attached to seal the liquid chamber configured inside the cylinder 1.

A cylindrical portion having a small diameter on the left side and a large diameter on the right side from the stepped portion 16 is provided on the inner end side of the piston 4, and the adjusting nut 6 is accommodated in the large diameter cylindrical portion. An annular seat plate 7 serving as a stopper is fitted into the end of the large diameter cylindrical portion and fixed by caulking, etc., and one end of a detent pin 6a passing through this seat plate 7 is fixed to the adjustment nut 6. The adjustment nut 6 does not rotate, but is configured to be able to move axially inside the cylindrical part. The adjusting nut 6 is biased toward the seat plate 7 by a coil spring 14 interposed between the adjusting nut 6 and the end wall of the small diameter cylindrical portion. The adjusting bolt 5 is screwed into the adjusting nut 6 with a reversible thread groove. A flange 5a is integrally provided at the right end of the adjustment bolt 5, and the piston 4
It protrudes into the interior of the cylindrical portion of No. 4, and is supported so that it can move in the axial direction within a certain range and rotate.

A seat plate 11 having a rectangular hole is fixed to the inner end wall of the piston 44, and a bearing 10 is interposed between the seat plate 10 and the right end surface of the flange 5a of the adjustment bolt 5. A seat plate 8 is secured to the outer end of the cylindrical portion of the piston 44, and a coiled leaf spring 9 interposed between the seat plate 8 and the left side surface of the flange 5a causes the flange 5a to be attached to the bearing 10. being pressed against. The piston 44 also includes a cylinder 20, into which an overadjustment release piston 12 equipped with a seal ring is fitted, and a spring 13 interposed between the piston 44 and the inner end wall of the cylinder 20 causes the piston 12 to
The conically pointed tip is the conical surface 2 of the flange 5a.
3 is engaged. The tip end side of the piston 12 has a rectangular stepped surface, and is fitted into the square hole of the rotation stopper plate 11 described above, so that it can move in the axial direction within a certain range but cannot rotate.

Note that the engagement between the flange 5a and the piston 12 is not limited to a conical surface, but may be engaged with teeth such that the two do not rotate relative to each other.

Next, the operation of the brake gap adjusting device according to the present invention will be explained. When pressurized fluid is supplied to the inside of the cylinder 1, the pair of pistons 4, 44 are pushed apart from each other, and the brake shoes 2, 22 are pushed back and expanded against the spring 3, causing the inner periphery of the brake drum (not shown) to expand. It generates braking force by frictionally engaging the surface. The pair of pistons 4, 44 do not rotate because the grooves at their ends are engaged with the brake shoes. Further, the piston 12 is prevented from rotating by the seat plate 11. The adjustment bolt 5 has its conical surface 23 frictionally engaged with the piston 12 by the force of the spring 9, and is prevented from rotating. Therefore, as the piston 4 moves to the left, the adjusting nut 6 moves to the right together with the adjusting bolt 5 (without relative screwing) under the force of the spring 14, and collides with the seat plate 7. Stop in place. When the braking clearance is at a predetermined value, the pair of pistons 4,
44 generates a braking force within the gap between the adjusting nut 6 and the seat plate 7.

Now, if the braking gap exceeds a predetermined value due to wear of the brake shoe, the adjustment nut 6 and the adjustment are adjusted by the seat plate 7 as the piston 4 moves to the left before the brake shoe contacts the brake drum. The bolt 5 is pulled to the left while integrally deflecting the spring 9. At this time, the piston 12 moves to the left following the adjusting bolt 5 under the force of the spring 13, and continues to prevent the adjusting bolt 5 from rotating.

Eventually, the brake shoe comes into contact with the brake drum, and when excessive fluid pressure is applied to the fluid chamber of cylinder 1 that causes deformation of the brake drum, this fluid pressure acts on the left end surface of piston 12, causing it to deform. is moved to the right against the spring 13 to release the frictional engagement with the conical surface 23 of the adjusting bolt 5. As the piston 12 retreats, the adjustment bolt 5 is pushed to the right by the spring 9 and pressed against the bearing 10. When the piston 4 moves further to the left, the adjusting bolt 5 is free to rotate, allowing the adjusting nut 6 to move to the left. In a higher hydraulic pressure state, the adjustment bolt 5 only rotates in response to deformation of each part.

When the brake is released, the force exerted by the hydraulic pressure inside the cylinder 1 on the left end surface of the piston 12 is applied to the spring 13.
, the adjustment nut 6 is pressed against the seat plate 7 by the force of the spring 14 against the return movement of the pistons 4 and 44, and the adjustment bolt 5 is in contact with the bearing 10 and reversed. Rotate in the direction.
The hydraulic pressure inside the cylinder 1 decreases, and the piston 12
is pushed back by the spring 13 and engages the conical surface 23 of the adjusting bolt 5, thereby preventing the adjusting bolt 5 from rotating. However, the adjusting bolt 5 is engaged with the bearing 10 by a spring 9 which is stronger than the spring 13.
When the pistons 4, 44 are returned further by the force of the return spring 3, the adjusting nut 6 is threaded onto the adjusting bolt 5 and cannot be rotated, so it remains in its threaded position and the piston 4 deflects the spring 14 so that the right and stops when the stepped portion 16 comes into contact with the adjusting nut 6.

As is clear from the above explanation, the adjustment nut 6 and the adjustment bolt 5 are integrally moved to the right side with the piston 44 until the brake shoe contacts the brake drum when the brake is applied, and until a predetermined braking gap is filled. , only the piston 4 moves to the left, and when the specified braking gap is exceeded, the adjusting nut 6
and the adjustment bolt 5 bends the spring 9 and the piston 4
and move to the left in unison. After the brake shoe has frictionally engaged with the brake drum, when the hydraulic pressure exceeds a specified pressure, the adjusting bolt 5 is released from its frictional engagement with the piston 12, and the adjusting bolt 5 is moved integrally with the piston 4 to the left. It will be rotated to the right by the amount it has moved towards. In other words, a relative screw movement occurs between the adjusting bolt 5 and the adjusting nut 6 up to the amount of deformation of the drum, but the adjusting bolt 5 and the piston 12 do not move until the hydraulic pressure at the time of brake release falls to the specified hydraulic pressure. Since the frictional engagement of the adjusting bolt 5 is released, the adjusting bolt 5 rotates in the opposite direction, that is, is returned by a relative screw movement with the adjusting nut 6, thereby eliminating the overadjustment amount due to the deformation of the drum.

In this way, the braking gap is always maintained at the value determined by the gap between the adjusting nut 6 and the seat plate 7 in FIG. However, over-adjustment due to heat distortion of the brake drum cannot be eliminated. This is because the thermal deformation of the brake drum does not allow it to return to its normal diameter immediately after the brake is released. If the brake shoe starts to drag on the inner circumferential surface of the brake drum after the brake drum has cooled down, try depressing the brake pedal strongly while the vehicle is stopped to remove the fluid inside cylinder 1. If the pressure is increased and the piston 12 is moved to the right against the spring 13, the adjusting bolt 5 will be in a state where it can freely rotate as described above, and when the brake operation is released, the adjusting bolt 5 will return. A proper braking clearance can be obtained by.

It will be easily understood that the initial adjustment to a predetermined braking gap after the drum brake is assembled can be similarly accomplished with a single brake operation.

In the above-mentioned embodiments, the case of a wheel cylinder device in which a pair of pistons is fitted into a cylinder has been explained, but as shown in FIG. The present invention can also be applied to the wheel cylinder device of the type described above, and exactly the same effects can be obtained. That is, it is sufficient to eliminate one of the pistons and configure the piston to be integral with the cylinder 1. Corresponding components are designated by the same reference numerals as in FIG. 1, and their explanations will be omitted.

Since the present invention is configured as described above, the following effects can be obtained.

(1) Since the braking gap adjustment device is built into the inside of the wheel cylinder device, it is not exposed to dust or muddy water from the outside, so stable performance can always be obtained.

(2) For initial adjustment when a wheel cylinder device is installed on a vehicle, simply press the brake pedal hard once and both pistons will move until the brake shoe engages with the inner circumferential surface of the drum brake. When the brake shoe is strongly engaged with the drum, the over-adjustment release piston 12 moves back due to the hydraulic pressure in the cylinder, and under this hydraulic pressure, the adjustment bolt 5 rotates freely even after the brake is released, and the predetermined position is reached. Adjust to braking clearance.

(3) The adjustment bolt once makes an adjustment movement in response to the deformation of the brake drum, but when the brake is released, it returns by the amount of overadjustment due to the deformation of the brake drum, and does not substantially perform overadjustment.

(4) Over-adjustment due to thermal deformation of the brake drum can be returned to the appropriate braking gap by strongly operating the brake while the brake drum is cooled, as in the case of initial adjustment, to prevent brake shoe dragging. can do.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a braking gap adjusting device for a drum brake according to the present invention, and FIG. 2 is a longitudinal sectional view of a braking gap adjusting device according to a partially modified embodiment of the present invention. 1... Wheel cylinder, 2... Brake shoe, 3... Return spring, 4... Piston, 5... Adjustment bolt, 5a... Flange, 6... Adjustment nut, 9... Spring, 10... Bearing , 11... Anti-rotation seat plate, 12... Over-adjustment release piston, 13...
...Spring, 22...Brake shoe.

Claims (1)

[Claims] 1. An adjustment nut supported movably within a predetermined range in the axial direction on the inner cylindrical portion of the piston that fits into the cylinder; an adjustment bolt screwed into the adjustment nut with a reversible thread groove; a thrust bearing 10 for rotationally supporting an end flange of the adjustment bolt with respect to the cylinder or second piston; a spring biasing the end flange against the thrust bearing; and a spring fixed on the cylinder or second piston side. A braking gap adjustment device for a drum brake, comprising an overadjustment release piston that is supported so as to be axially slidable within a range of 1 and 2 and whose tip end is frictionally engaged with the end flange by a spring.