JPH0228741B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention automatically compensates for the wear of the brake shoe as a brake element in a hydraulically actuated drum brake, maintains the operating clearance constant, and always maintains the braking force of the brake pedal, etc. The present invention relates to an automatic adjustment device that allows braking to be performed accurately using a predetermined amount of operation of an operator.

In general, in brakes, when strong braking is performed, elastic deformation occurs in each part of the brake, but this elastic deformation causes apparent wear on the brake elements, and when the automatic adjustment device responds to this, it causes excessive adjustment (overadjustment). As a result, when the brake is released, there is no operating gap for the brake element, causing a dragging phenomenon. In order to eliminate such inconveniences, a hydraulically operated disc brake in which an automatic adjustment device with an overadjustment prevention function is disposed in the hydraulic chamber of a hydraulic cylinder is disclosed, for example, in Japanese Patent Laid-Open No. 118956/1983. This is conventionally known, but in that structure, the adjustment rod of the automatic adjustment device and the adjustment nut screwed into it via a quick screw are received in a receiving hole formed inside the piston of the hydraulic cylinder. If applied as is to the wheel cylinder of a hydraulically operated drum brake, the following problems will occur.

In other words, in the wheel cylinder of a hydraulically operated drum brake, an annular seal groove is recessed in the outer circumferential surface of the piston in order to install a seal ring to seal the fitting part between the piston and the cylinder body. The internal accommodation hole has a small diameter, and in order to accommodate the adjustment rod and adjustment nut of the automatic adjustment device in the hole, it is necessary to form them with a small diameter, which poses problems in terms of strength and processing.
Furthermore, if the diameter of the piston itself is increased in order to avoid this problem, there are other disadvantages such as the piston and eventually the wheel cylinder becoming larger.

An object of the present invention is to provide an automatic adjustment device for a hydraulically operated drum brake, which allows the automatic adjustment device to be easily incorporated into a hydraulic chamber in a wheel cylinder of a hydraulically operated drum brake without causing such problems. shall be.

In order to achieve this purpose, the present invention
The hydraulic chamber of the wheel cylinder includes a non-rotatable piston that is slidably fitted to the inner periphery of the cylinder body;
An annular seal groove is defined between the piston and an opposing portion axially opposed to the piston, and an annular seal groove is recessed in the outer peripheral surface of the piston for mounting an annular seal ring that closely contacts the inner periphery of the cylinder body. In the hydraulically operated drum brake, an adjusting rod having one end received in a small diameter hole formed in an inner end surface of the piston and penetrating through the hydraulic chamber so as to be surrounded by the annular seal groove; a clutch body fixedly attached to the other end and cooperating with a clutch surface provided on the opposing part; and a large diameter hole adjacent to the small diameter hole via an annular step, and integral with the inner end surface of the piston. a guide tube that protrudes from the cylinder body and whose outer circumferential portion is slidably supported by the inner circumference of the cylinder body; and a rotating shaft that is received in the large diameter hole and is screwed onto the adjustment rod via a quick screw. a spring having one end engaged with the nut and the other end being locked in the opening of the large diameter hole in order to bias the adjustment nut toward the annular stepped portion; The clutch body is characterized in that the clutch body is frictionally connected to the clutch surface when receiving a thrust toward the clutch surface due to a hydraulic pressure of a certain value or more in the hydraulic chamber.

Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 1 shows a first embodiment in which the present invention is applied to a two-leading shoe type drum brake for an automobile.A pair of upper and lower wheel cylinders 2,
2' and a pair of left and right brake shoes 3, 3' are arranged point-symmetrically around the center of the back plate 1, and a brake drum that surrounds the brake shoes 3, 3' and rotates together with the wheels is not shown. It has not been.

The wheel cylinders 2 and 2' each include a cylinder body 4 having a cylinder hole 4a that is open at only one end, and a hydraulic chamber 5 that gathers in the cylinder hole 4a.
The cylinder body 4 is fixed to the back plate 1 with bolts 7 and nuts 8. Engagement grooves 9 and 9' are formed in the outer ends of the cylinder body 4 and the piston 6, respectively, and the corresponding ends of the brake shoes 3 and 3' are engaged with these grooves 9 and 9'. , and return springs 10, 10' are tensioned between the brake shoes 3, 3' to maintain the engagement and bias the brake shoes 3, 3' in the contraction direction. The engagement between the grooves 9, 9' and the brake shoes 3, 3' prevents relative rotation between the cylinder body 4 and the piston 6. An annular seal groove g is formed in the outer circumferential surface of the piston 6, and a seal ring S that closely contacts the cylinder hole 4a is mounted in this groove g.

The upper wheel cylinder 2 has its hydraulic chamber 5.
A hydraulic pressure introduction port 11 for introducing the output hydraulic pressure of a brake master cylinder (not shown) is provided between the two wheel cylinders 2 and 2', and the hydraulic pressure introduced into the upper wheel cylinder 2 is transferred to the lower wheel cylinder 2'. Communication pipe 1 for supplying
2 is connected.

The automatic adjustment device A of the present invention is provided in the hydraulic chambers 5 of both wheel cylinders 2 and 2', and since these have the same structure, only the automatic adjustment device A in the upper wheel cylinder 2 will be described in detail below. Explain.

The inner end surface of the piston 6 is provided with the annular seal groove g.
A guide cylinder 6a having a large diameter hole 13 adjacent to the small diameter hole 14 via an annular step 15 on its inner periphery is integrated with the inner end of the piston 6. The guide tube 6a protrudes from the
An annular flange portion that is slidably fitted and supported in the cylinder hole 4a is integrally provided on the outer circumferential surface of the cylinder hole 4a.
An adjustment nut 16 that abuts the annular step 15 in a separable manner is slidably fitted into the large diameter hole 13, and a coil spring 17 is applied to bias the adjustment nut 16 toward the annular step 15. The small diameter tip is the nut 1
6, and its large diameter proximal end is integrally locked in the annular groove of the opening of the large diameter hole 13.

Said spring 17 pushes the adjusting nut 16 into the annular step 1
In addition to having the function of pressing and holding the spring 17
It also has a function of preventing the adjustment nut 16 from rotating due to frictional engagement or concave-convex engagement between the adjustment nut 16 and the adjustment nut 16.

An adjustment rod 18 is screwed into the center of the adjustment nut 16 through a quick screw 19 so as to pass through the adjustment nut 16, and one end thereof is received in the small diameter hole 14.
The threaded portion between the adjusting nut 16 and the adjusting rod 18 is provided with an appropriate operating gap for each brake shoe 3, 3', that is, an appropriate gap between each brake shoe 3, 3' and a brake drum (not shown). There is a corresponding axial play through which the large diameter hole 13 and the small diameter hole 1
4 is in constant communication. Therefore, the hydraulic chamber 5
The hydraulic pressure introduced into the small diameter hole 14 acts on the adjustment rod 18 inside the small diameter hole 14.

A clutch body 20 is integrally formed at the other end of the adjustment rod 18, and this clutch body 20 is rotatably fitted into a blind hole 21 provided in the end wall 4b of the cylinder body 4. It faces a conical clutch surface 22 formed on the back wall of 21. Blind hole 21
A sealing member 23 for preventing the hydraulic pressure in the hydraulic chamber 5 from acting on the clutch surface 22 is fitted therein.

Next, to explain the operation of this embodiment, in order to perform braking, if a brake master cylinder (not shown) is operated and its output oil pressure is supplied to the oil pressure chamber 5 of the upper wheel cylinder 2, the oil pressure is transferred to the communication pipe 1.
2 to the lower wheel cylinders 2', these oil pressures cause the pistons 6 of each wheel cylinder 2, 2' to move outward and expand the corresponding brake shoes 3, 3'. By pressing against the inner peripheral surface of a brake drum (not shown), it is possible to apply braking force to the brake drum and therefore to the wheels.

During this braking, the hydraulic pressure in the hydraulic chamber 5 is controlled by the adjusting nut 1.
6, no thrust is exerted on the clutch body 20 because it acts equally on both its left and right end faces, but the clutch surface has a value equal to the cross-sectional area of the clutch body 20 multiplied by the above-mentioned oil pressure. It exerts a thrust toward clutch body 22, and this thrust
0 and the clutch surface 22 is determined.

By the way, under normal braking conditions, the oil pressure in the hydraulic chamber 5 is relatively low, and therefore the frictional coupling force between the clutch body 20 and the clutch surface 22 is relatively small. When the piston 6 moves further outward as a result, the adjusting nut 16 moves together with the piston 6 while maintaining the contact state with the annular stepped portion 15 by the elastic force of the spring 17, and the clutch is engaged via the adjusting rod 18. The body 20 is pulled away from the clutch face 22 against the thrust. When the clutch body 20 separates from the clutch surface 22, the thrust causes the clutch body 20 to move toward the clutch surface 22 while being threadedly engaged with the non-rotatable adjusting nut 16, and to reengage the clutch surface 22. In this way, the brake shoe 3,
A self-adjusting action takes place to compensate for wear of the lining 3'. Here, in order to release the brake, the hydraulic chamber 5
If the internal pressure is reduced, the brake shoes 3, 3' will contract under the return force of the return springs 10, 10'.
The return force of the return springs 10, 10' acts on the clutch body 20 as a thrust toward the clutch surface 22 through the piston 6, the adjusting nut 16, and the adjusting rod 18, so that the clutch body 20 is caused to frictionally slide against the clutch surface 22. Combined and unable to rotate. Therefore, relative rotation between the adjusting nut 16 and the adjusting rod 18 is also disabled, so that the piston 6 and the adjusting nut 1
6 can only retreat by the stroke of the clearance between the screwed part of the adjusting nut 16 and the adjusting rod 18;
As a result, an appropriate gap corresponding to the above-mentioned play is created between the lining of each brake shoe 3, 3' and the inner peripheral surface of the brake drum.

In addition, when strong braking is performed, the above-mentioned process will take place before the hydraulic pressure in the hydraulic chamber 5 rises to a predetermined value that causes elastic deformation in the brake shoes 3, 3', brake drum, etc. When the automatic adjustment action is performed and the oil pressure exceeds the predetermined value, the thrust due to the oil pressure of the clutch body 20 increases to maintain the clutch body 20 in a frictionally connected state with the clutch surface 22, so that the clutch body 20 and Adjustment rod 18
becomes unable to rotate. Therefore, since the adjusting nut 16, which is originally non-rotatable, is fastened on the adjusting rod 18, when the piston 6 moves further outward due to elastic deformation of the brake drum, etc., the annular stepped portion 15 of the piston 6 moves away from the adjusting nut 16. I will be leaving.
In this way, the automatic adjustment effect is stopped.

FIG. 2 shows a second embodiment of the present invention in which the automatic adjustment device A is applied to a type of drum brake equipped with a leading shoe 103 and a trailing shoe 103'.
This shows an example, in which the annular stepped portion 15 is connected to the leading shoe 10 in the wheel cylinder 102.
3 actuating first piston 106, the clutch surface 2
2 is formed on the second piston 106' for operating the trailing shoe 103', and the structure is the same as that of the previous embodiment, and in FIG. It was attached with.

As described above, according to the present invention, the hydraulic chamber of the wheel cylinder is located between the non-rotatable piston that is slidably fitted to the inner periphery of the cylinder body and the opposing portion that opposes the piston in the axial direction. In a hydraulically operated drum brake, an annular seal groove is formed in the outer peripheral surface of the piston for mounting an annular seal ring that is in close contact with an inner periphery of the cylinder body. an adjusting rod having one end received in a small diameter hole recessed in the inner end surface of the piston so as to be surrounded and passing through the hydraulic chamber; a clutch body that cooperates with the clutch surface,
a guide cylinder having a large-diameter hole adjacent to the small-diameter hole via an annular step and integrally protruding from the inner end surface of the piston, and having an outer circumference slidably supported on the inner circumference of the cylinder body; , a non-rotatable adjusting nut received in the large diameter hole and screwed onto the adjusting rod via a quick thread; one end attached to the nut for biasing the adjusting nut toward the annular step; a spring that is engaged and whose other end is locked in the opening of the large diameter hole, and when the clutch body receives thrust toward the clutch surface due to hydraulic pressure of a certain value or more in the hydraulic chamber, Since the clutch is frictionally connected to the clutch surface, during strong braking in which the oil pressure in the hydraulic chamber is increased above the certain value, the thrust acting on the adjustment rod is increased by the oil pressure, causing the clutch body to engage with the clutch surface. Since the rotation of the adjustment rod can be restricted by maintaining the frictional engagement state, even if the piston continues to move forward due to elastic deformation of the brake drum, the adjustment nut remains on the adjustment rod and does not move away from the annular step of the piston. , it is possible to automatically stop the original automatic adjustment function, and therefore it is possible to prevent a dragging phenomenon due to over-adjustment.

In addition, the small diameter hole of the piston, which has a relatively small diameter because it is surrounded by an annular seal groove on the outer periphery of the piston, receives only one end of a relatively small diameter adjustment rod, and an adjustment rod with a larger diameter than that of the adjustment rod can be received. Since the nut is received in the large diameter hole of the guide cylinder protruding from the inner end surface of the piston, these adjustments can be made without increasing the diameter of the piston itself or reducing the overall diameter of the adjustment nut and adjustment rod. The nut and adjustment rod can be placed within the piston or in the vicinity thereof without strain, and the adjustment nut and adjustment rod can be formed relatively large compared to the effective diameter of the piston, and therefore the piston can be formed with a large diameter. Even if you do not do this, the adjustment nut and adjustment rod will not cause any special problems in terms of strength or processing.
This is advantageous in reducing the size of the piston and thus the wheel cylinder. Moreover, since the guide tube is slidably supported on the inner periphery of the cylinder body, it is possible to effectively prevent the piston from falling in the axial direction and to ensure smooth sliding of the piston at all times.

Furthermore, before assembling the piston into the cylinder body, the piston and the adjustment rod, adjustment nut, and spring, which are the main parts of the automatic adjustment device, can be assembled into one small assembly. There is no risk of parts being lost, and the assembly of the actual adjustment device to the wheel cylinder is extremely easy, contributing to improved work efficiency.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional front view of a main part of a brake showing a first embodiment of the present invention, and FIG. 2 is a longitudinal sectional front view of a main part of a brake showing a second embodiment thereof. A...Automatic adjustment device, S...Seal ring, g
...Seal groove, 2,2'...Wheel cylinder,
3, 3'... Brake shoe, 4... Cylinder body, 4b... End wall as opposing part, 5... Hydraulic chamber, 6, 106... Piston, 6a, 106a...
...Guide tube, 10,10'...Return spring, 15...
Annular stepped portion, 16...adjusting nut, 17...spring,
18... Adjustment rod, 19... Quick screw, 20... Clutch body, 22... Clutch surface, 102... Wheel cylinder, 103... Leading brake shoe, 103'... Trailing brake shoe,
106'... Piston as an opposing part.

Claims (1)

[Claims] 1 The hydraulic chamber 5 of the wheel cylinder 2, 102 is
A non-rotatable piston 6, 106 slidably fitted to the inner periphery of the cylinder body 4;
Opposed portions 4b, 106' axially opposed to 106
An annular seal groove g is defined between the pistons 6 and 106, and an annular seal groove g is formed on the outer peripheral surface of the piston 6, 106 for mounting an annular seal ring S that closely contacts the inner periphery of the cylinder body 4.
In the hydraulic drum brake, one end of the piston 6, 106 is received in a small diameter hole 14 recessed in the inner end surface of the piston 6, 106 so as to be surrounded by the annular seal groove g, and the hydraulic chamber 5 is recessed. An adjusting rod 18 penetrating through the inside, a clutch body 20 fixed to the other end of the adjusting rod 18 and cooperating with a clutch surface 22 provided on the opposing portions 4b, 106', and a clutch body 20 extending through the small diameter hole 14. It has a large-diameter hole 13 adjacent to it via an annular step 15, and is integrally provided on the inner end surface of the piston 6, 106, and its outer periphery is connected to the cylinder body 4.
Guide tubes 6a, 10 slidably supported on the inner periphery of
6a, a non-rotatable adjusting nut 16 received in the large diameter hole 13 and screwed onto the adjusting rod 18 via a quick screw 19;
The clutch body 20 includes a spring 17, one end of which engages with the nut 16 and the other end of which is engaged with the opening of the large diameter hole 13 in order to bias the clutch body 20 toward the annular stepped portion 15. An automatic adjustment device for a hydraulically actuated drum brake, which is configured to frictionally connect with the clutch surface 22 when the clutch surface 22 receives a thrust directed toward the clutch surface 22 due to oil pressure of a certain value or more in the hydraulic chamber 5.