JPS6237263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an automatic shoe gap adjustment device for a drum brake.

Regarding drum brakes, as the linings of the pair of left and right brake shoes that slide into contact with the drum wear out, it is necessary to maintain the gap between the inner peripheral surface of the drum and the brake shoe at a substantially constant value when not braking. Various automatic shoe gap adjustment devices have been provided that gradually expand the return position of the brake shoe and reposition it, and the present invention provides a brake shoe clearance adjustment device that gradually expands and repositions the return position of the brake shoe. A strut installed between a pair of left and right brake shoes to which a spring force is applied, and by engaging with both brake shoes, determines the closed/closed return position of the left and right brake shoes in the span between the two engagement points. This is an automatic shoe gap adjustment device that adjusts and repositions the return dependence by extending the span of the strut. In particular, it utilizes the contracting and closing action of the brake shoe when the brake is released to adjust the ratchet of the strut. This invention relates to an improvement of a negative type shoe gap automatic adjustment device that extends the span of a strut by rotating a vehicle.

As one of the conventional negative type adjustment devices of this type, a strut installed between a pair of left and right brake shoes is used to adjust the strut to one of the brake shoes when the brake shoe is expanded when the brake is applied. The other brake shoe is equipped with an adjuster lever that rotates as the strut and the brake shoe move relative to each other, and when the brake is released, the spring force of the return spring is used to When the brake shoe is pulled back to a stationary state, the spring force of the return spring is transmitted to the adjuster lever via the strut to cause it to rotate back, and the adjuster lever is rotated by the spring force of the return spring. A device is known in which the claw portion rotates the ratchet of the strut.

However, one of the problems with this kind of configuration is that
The amount of rotation of the adjuster lever for gap adjustment is
Although it is determined by the relative movement between the strut and the other brake shoe, the rotational force of the adjuster lever's return rotation ultimately depends on the spring force of the return spring, so the threaded portion of the strut may become rusted and stuck. When rotation becomes impossible due to such reasons, there is a risk that rotation of the adjuster lever will be restricted due to engagement between the ratchet and the pawl of the adjuster lever, and the left and right brake shoes will not be able to contract or close.

In order to solve these difficulties, it is possible to take measures such as preventing rust on the strut screws, but in the present invention, we have taken measures to prevent the possibility of problems caused by such rust. This can be reliably prevented by biasing the adjuster lever.

That is, the present invention includes a pair of left and right brake shoes arranged so that one opposing end side is expanded by a brake actuation mechanism, a return spring that applies a spring force in the direction of contraction and closing to these brake shoes, and a return spring that applies a spring force to these brake shoes in the direction of contraction and closing. A strut is installed between the two to lock the expansion/closing of both at its span, and the span is gradually increased by rotation of a ratchet attached to the shaft. on the other brake shoe so as to press the end to bias it toward the brake shoe, and to rotate the ratchet by swinging a pawl extending on the edge of the ratchet of the strut. and an adjuster lever pivotally mounted on the adjuster lever, and the adjuster lever is provided so as to rotate the ratchet when the return swing increases when the brake is released. The pivot support structure for the brake shoe consists of a pin on the other brake shoe, an elongated hole in the adjuster lever that loosely fits into this pin, and an elongated hole in the adjuster lever that is stretched between these pins and the adjuster lever. This automatic shoe gap adjustment device for a drum brake is characterized by comprising an overload spring that biases a pin so as to provide an extra gap on the one brake shoe side.

The present invention will be described below based on embodiments shown in the drawings.

For convenience of explanation, Figure 1 shows the configuration of an automatic shoe gap adjustment device for drum brakes. A return spring 3 is stretched between one 1 and the other 2 of the pair of brake shoes 1, 2, and a strut 4 resists the spring force of the return spring 3 to connect the brake shoes 1, 2. It is constructed to support the contraction and closing of 2. This strut 4 has one end supported by one brake shoe,
and a nut part 5 having a female thread formed at the other end, a bolt part 6 whose male thread is screwed into the female thread of the nut part, and which is pivoted on the ratchet 7, and one end of which rotates with the head of the bolt part 6. It is composed of a socket part 8 which can be freely fitted and whose other end is supported by the other brake shoe 2, and when the ratchet 7 is rotated by the adjuster lever 9 described below, the bolt part 6 is connected to the nut part. 5 and extends the span of the entire strut.

The adjuster lever 9 is inserted into the elongated hole 1 of the pin 14 fixed on the other brake shoe 2.
0 is fitted and pivotally supported, but the pin 14
The looseness of the elongated hole 10 in the loosely fitted state is absorbed by the spring force of the overload spring 15 stretched between the pin 14 and the adjuster lever 9, and the adjuster lever 9 is moved relative to the pin 14 as shown in the figure. They are engaged at the right end of the opening of the elongated hole 10 as shown in FIG.

Reference numerals 11 and 12 indicate first and second arm portions of the adjuster lever 9 extending in a substantially L-shape, and the first arm portion 11 extends along the generatrix direction of the strut 4 and has a tip claw portion. 3 is provided to mesh with the ratchet 7 of the strut 4, and the other second arm 12 has a compression spring 1 between the brake shoes 2.
6 is stretched, and a clockwise rotating force is applied in the figure. The rotation of the adjuster lever 9 is stopped by a portion thereof engaging with the end of the socket portion 8 of the strut 4. In other words, the strut 4 is connected to the compression spring 16 via the adjuster lever 9. It is biased toward the one brake shoe 1 by the spring force.

Next, to explain the adjustment operation, the brake shoes 1, 2 are operated by the hydraulic actuating mechanism etc. arranged between the pair of brake shoes 1, 2.
When the struts 2 are expanded to the left and right and generate a braking force by coming into contact with the inner periphery of the drum, the strut 4 as a whole follows the expansion of one brake shoe 1,
The pin 14 on the other brake shoe 2 moves in the opposite direction.

Therefore, the adjuster lever 9 is connected to the socket portion 8 of the strut 4 that locks its rotation from the illustrated state.
Since the end has moved to the left, it rotates clockwise, and the claw portion 13 swings to escape upward. When the brakes are released, the pair of left and right brake shoes 1 and 2 are contracted and closed by the spring force of the return spring 3, and the socket portion 8 of the strut 4 is closed.
When one end engages the other brake shoe 2, these brake shoes 1, 2 are stationary. During the process of returning to the rest position, the adjuster lever 9, which is always engaged with the socket portion 8 of the strut 4,
is rotated back by the strut 4 and the claw portion 13
returns from the upper swing position to the lower swing position.

In this case, as the linings of the brake shoes 1 and 2 are progressively worn, the amount of expansion gradually increases, and when a predetermined constant value is exceeded, the adjuster lever pawl 13 swings upward. This allows him to overcome one tooth of Ratchet 7. In this case, the adjuster lever claw 13 rotates the ratchet 7 by returning from the upper swing position to the lower swing position, thereby extending the span of the strut 4. The rotation of the ratchet 7 due to the rotation of the adjuster lever 9 ultimately depends on the spring force of the return spring 3 that contracts and closes the pair of left and right brake shoes. It is understood that the magnitude of the adjustment lever 9 needs to exceed the rotational force of the adjuster lever 9 and the resistance force during rotation of the ratchet 7 of the strut 4.

The feature of the present invention is that in such a configuration, it is possible to mechanically escape the trouble caused by an abnormal increase in the rotational resistance of the ratchet 7. Matching elongated hole 10 and overload spring 15
It is made by a combination of. That is, normally, due to the spring force of the overrot spring 15, the elongated hole 10 of the adjuster lever 9 is engaged with the right end of its opening (in short, there is a margin on the one brake shoe 1 side). When the pawl 13 of the adjuster lever 9 meshes with the teeth of the ratchet 7 and is locked due to high rotational resistance during the contraction/closing of the brake shoes 1, 2, the pin 14 extends the overload spring 15 while adjusting the adjuster. The inside of the long hole 10 of the star lever 9 is moved to the left side in the figure to compensate for the contraction and closing of the brake shoes 1 and 2.

Regarding the parking brake mechanism, for example, if the parking lever is mounted on one of the brake shoes 1 and linked to the other brake shoe 2 via the strut 4, the parking brake mechanism can be used. No adjustment will be made.

FIG. 2 shows another embodiment in which an adjuster lever 9 is mounted on the one side of the brake shoe 1, and a tension spring 16' is tensioned to provide rotational force to the adjuster lever 9. The structure is substantially the same except that the position and the relationship between tension and compression are different from those of the previous embodiment, and when the rotational resistance of the ratchet 7 of the strut 4 becomes abnormally high, the adjuster lever 9 is loaded. Spring 15
The operation is the same in that the long hole 10 moves relative to the pin 14 by expanding the brake shoes 1 and 2 to compensate for the contraction and closing of the brake shoes 1 and 2.

As described above, the drum brake automatic shoe gap adjustment device according to the present invention completely eliminates the drawbacks of negative type devices, and its practical benefits are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a partial front view showing the configuration of an automatic shoe gap adjustment device for a drum brake according to one embodiment of the present invention, and FIG. 2 is a partial front view showing another embodiment of the same. 1, 2...Brake shoe, 3...Return spring, 4...Strut, 5...Nut part, 6...Bolt part, 7...Ratchet, 8...Socket part, 9...Adjuster lever, 10...Elongated hole, 11...No. 1 arm portion, 12... second arm portion, 13... claw portion, 14... pin, 15... overload spring, 16... compression spring, 16'... tension spring.

Claims (1)

[Claims] 1 A pair of left and right brake shoes arranged so that one opposing end side is expanded by the brake operating mechanism, a return spring that applies a spring force in the direction of contraction and closing to these brake shoes, and a spring between these brake shoes. A strut is installed so that the contraction and closing of both struts can be locked at the span thereof, and the span can be gradually increased by rotation of the ratchet attached to the shaft, and the end of the strut is pivoted on said other brake shoe so as to bias it toward said brake shoe and to rotate said ratchet by swinging of a pawl extending on said ratchet edge of said strut; Equipped with an adjuster lever mounted so that
This adjuster lever is provided so as to rotate the ratchet when the return swing increases when the brake is released, and the pivot support structure of the adjuster lever for the other brake shoe is provided on the other brake shoe. a pin, an elongated hole in the adjuster lever that is loosely fitted to this pin, and an elongated hole stretched between these pins and the adjuster lever so as to provide a clearance on the one brake shoe side of the elongated hole. An automatic shoe gap adjustment device for a drum brake, comprising an overload spring that biases a pin.