JPH0141857B2 - - 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.

In general, a pair of left and right brake shoes are mounted on a bucking plate so that they can be expanded and retracted, and the opposite end of one of the shoes is used as an anchor, and the opposite end of the shoe is expanded. For so-called leading-training type (hereinafter referred to as LT type) drum brakes, an automatic shoe gap adjustment device is installed using a strut that is arranged to determine the shoe compression/closing limit between the expanding sides of the brake shoe. Often configured.

This reduces the gap between the inner peripheral surface of the drum and the brake shoe, which increases as the shoe lining wears.
The system corrects the return contracted/closed position of the brake shoe by gradually expanding it and keeps it constant. Specifically, a screw mechanism for span extension is built into the strut, and the left and right brakes are An adjuster lever is provided that rotates in conjunction with the opening operation of the shoe (when the brakes are applied).As the brake shoe lining becomes worn, the amount of expansion of the brake shoe increases, and as a result, the adjuster lever Usually, when the amount of rotation of the strut exceeds a predetermined value, the screw mechanism is rotated to extend the span of the strut. By the way, in this type of drum brake, a return spring with a relatively large spring force is stretched between a pair of brake shoes in order to ensure that the brake shoes return and close when the brake is released. When the rest position (retracted/closed position) of the left and right brake shoes is gradually expanded due to the extension of the struts, they are stretched by that amount, and the amount of stretching is from when the shoe lining is new (unworn) to the wear limit. The axial force of the strut increases due to a large change in the spring force of the return spring, and the axial force of the strut increases during the shoe expansion operation (during braking).
In addition to problems such as increased input loss, there was a problem that there were large restrictions on the selection range of the set spring load and spring constant in order to obtain stable and reliable spring action over the entire range of changes in the extension of the return spring. .

From this point of view, the present invention provides an automatic shoe gap adjustment device configured such that the spring force of the return spring does not change over the entire range of shoe lining wear. A pair of left and right brake shoes mounted on a bucking plate, an anchor disposed between one opposing end of these brake shoes, and an expansion shoe installed on the other opposing end side. A two-member span consisting of a mechanism, a socket that is rotatably fitted to the head of one end of the screw member and is not removed, and a nut that is threadably screwed into the threaded portion of the other end of the screw member, is used to prevent the screw from collapsing at the limit. A strut that determines the spacing and extends the span by rotating the screw member, a return spring that applies spring force to the brake shoe in the direction of contraction and closure, and a strut that is linked to the expansion and contraction of the brake shoe. In the drum brake shoe gap automatic adjustment device, the drum brake shoe gap automatic adjustment device is equipped with an adjuster lever that rotates to rotate and screw out and rotate the screw member through a gear, and the return spring is arranged between the socket of the strut and the brake shoe on one side. , and one brake shoe on the other side, each of which is tensioned so as to apply a tension spring force between the nut and the brake shoe on the other side.

One of the return springs can be stretched directly between the brake shoe and the socket, or as explained in the example below, the return spring can be stretched between the brake shoe and the adjuster lever that is pivotally connected to the socket. It may be arranged so that it is indirectly stretched between the socket and the brake shoe.

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

Figures 1 and 2 show the hydraulic operating mechanism for the service brake of the LT type drum brake, which performs normal vehicle running braking, and the parking lever that rotates in a plane parallel to the shoe expansion sliding surface. In the figure, 1 is a bucking plate, 2 and 3 are a pair of left and right brake shoes, and 4 is one of these brake shoes 2 and 3. The anchor 5 is a hydraulic actuator placed between the opposite ends, and the hydraulic actuator 5 causes the left and right brake shoes 2 and 3 to actuate the anchor 4. It is expanded to the left and right from the center, and the shoe lining is brought into contact with a drum (not shown) to generate braking force. Reference numeral 6 denotes a tension spring that connects opposite ends of the brake shoes 2 and 3 on the anchor side.

Reference numeral 7 designates a strut installed parallel to the hydraulic actuator 5 between the expansion sides of the left and right brake shoes 2 and 3, and includes a bolt 8 and a nut 9 that are screwed in and out. The socket 11 is comprised of a gear 10 which is pivotally attached to the bolt 8 and has teeth formed on its circumference, and a socket 11 which is rotatably fitted to the head of the bolt 8 and is locked to prevent it from coming off. The nut 9 is non-rotatably engaged with the brake shoe 2 and the other brake shoe 3, respectively. 12 is an adjuster lever pivotally connected to the socket 11 by a pin 15; a first arm 13 extending along the generatrix direction of the strut 7 hits the teeth of the gear 10; The arm 14 is brought into contact with the inner end of the sheave web of one brake shoe 2. A first return spring 16 is connected between this adjuster lever 12 and one brake shoe 5.
is tensioned, pulling the one brake shoe 2 toward the socket 11, and applying a spring force to the adjuster lever 12 in the clockwise direction in FIG. It is engaged with the show web of U2.

Further, a second return spring 17 is stretched between the nut 9 and the other brake shoe 3, and applies a spring force to draw them together. is set to be greater than the spring force of the first return spring 16.

With the above configuration, as shown in FIG.
The adjuster lever 12 has an end 14a of the arm 14 in contact with the inner end of the shoe web of the brake shoe 2.
In this case, the spring force of the first return spring 16 hooked at an intermediate position is applied so that the first return spring 16 approaches the brake shoe 2 relatively, and when the brake is released, the socket 11 engages with the brake shoe 2. By matching, the socket 11, the brake shoe 2, and the adjuster lever 12 are kept stationary (as shown).

18 is the pin 19 attached to the other brake shoe 3.
This parking lever is rotatably assembled in the parking lever, and is provided so that the left and right brake shoes 2 and 3 are opened via the strut 7 by rotation in the clockwise direction in FIG.

Next, to explain its operation, the strut 7 has a bolt 8 and a nut 9 screwed together, and a socket 10 is fitted onto the head of the bolt to prevent it from coming off, so the first and second return springs 16, At 17, a spring force is applied to the left and right brake shoes 2 and 3 in the contracting and closing direction, so that they are in the state shown in the figure when the brakes are not applied. When the hydraulic actuation device 5 is then operated, the left and right brake shoes 2 and 3 are expanded, and at this time, the first return spring 16 is extended due to the relationship between the spring forces of the return springs 16 and 17, and the strut 7 is extended. follows the other brake shoe 3 as a whole. As a result, the pin 15 of the socket 11 and one brake shoe 2 shift in opposite directions,
Therefore, the second arm 14 of the adjuster lever 12
The tip 14a of the strut 7 follows the movement of the brake shoe 2 to the left in the figure while maintaining engagement with the inner end of the web of the brake shoe 2.
Since the second return spring 17 is a stronger spring than the first return spring 16, it moves to the right in the figure as a whole, so the pin 15 on the socket 11 follows this (therefore, the socket 11 moves toward the right side in the figure). You 2
This causes the adjuster lever 12 to rotate in the clockwise direction in FIG. 2, and the pawl of the first arm 13 rotates the gear 10 of the strut 7. As this rotation increases, the pawl passes over one tooth of the gear 10 and engages with a new tooth when returning, and this repetition allows the strut 7 to elongate as the shoe lining wears. become.

In such an arrangement, the amount adjusted by the extension of the strut 7 will only result in an increase in the relative spacing between the socket 11 and the nut 9, which will cause the first or second return spring 16, 17 to Since it is independent of the tensioned position, the spring force of the return springs 16 and 17 is always kept constant regardless of whether the strut is extended, and there is no increase in input loss due to shoe expansion. Further, the axial force of the strut 7 is small and its change can be ignored.
In order to prevent malfunction caused by the gear 10 twisting, for example, as shown in the figure, the first and second return springs 1 are
By making the struts 6 and 17 eccentric, the strut 7
All you have to do is apply a bending moment to the surface and provide rotational resistance. It goes without saying that the first return spring 16 may be directly stretched between the brake shoe 2 and the socket 11, and a spring for rotating the adjuster lever 12 may be provided separately.

Further, when the parking brake is applied, the rotation of the parking lever 18 causes the strut 7 to follow the one brake shoe 2 side, contrary to when the service brake is used, so no adjustment occurs, and therefore, the automatic shoe gap adjustment device of this example is a positive type of service adjust type.

It should be noted that this may naturally be adjusted when the brake is released, as well as the positional relationship between the parking lever 18 and the adjuster lever 12,
It is obvious that by changing the spring force of the first and second return springs 16 and 17, an adjustment type for both service and parking or a parking adjustment type can be used. In this example, it is also possible to add a lightly loaded return spring that spans between both brake shoes as shown in the figure, if necessary.

FIG. 3 shows an example in which the present invention is applied to a drum brake equipped with a so-called crawl pull type parking brake mechanism in which the parking lever rotation surface is perpendicular to the shoe expansion surface, and the strut 7' is A pin 21 is attached to the inner end of the parking lever 20, which is disposed obliquely with respect to the shoe expansion surface, and has a nut 9' inserted into the drum.
The parking lever 20 has substantially the same shape and configuration as that of the previous embodiment, except that the parking lever 20 is configured to engage the other brake shoe 3'. Therefore, the same reference numerals are indicated by adding a dot to the same reference numerals.

Even in such a configuration, adjustment by extension of the strut 7' is performed by the first and second return springs 16',
17', and a constant return spring force is always ensured until the shoe lining reaches its limit wear.

As described above, the automatic drum brake shoe gap adjustment device according to the present invention can always maintain a constant return spring force from the initial stage to the final stage of adjustment, ensuring stability of adjustment, It was extremely useful, as it did not have the disadvantage of increasing external force loss due to the shoe expansion, and it greatly reduced restrictions on the selection of spring force.

[Brief explanation of drawings]

The drawings show embodiments of the present invention.
The figure is a front view of one embodiment, and the second figure is a plane view of the same part.
FIG. 3 is a partial plan view showing another embodiment. 1...Bucking plate, 2, 3, 2',
3'...Brake shoe, 4...Anchor, 5...
...Hydraulic actuator, 6...Tension spring, 7,
7'...Strut, 8,8'...Bolt, 9,
9'...nut, 10,10'...gear, 11,1
1'...Socket, 12, 12'...Adjuster lever, 13, 13'...First arm, 14, 14'...
...Second arm, 15,15'...Pin, 16,1
6'...First return spring, 17, 17'...Second return spring, 18...Parking lever, 19...
Pin, 20... Parking lever, 21... Pin.

Claims (1)

[Scope of Claims] 1. A pair of left and right brake shoes mounted on a bucking plate so as to be expandable left and right, an anchor disposed between opposing ends of one of these brake shoes, and an anchor disposed between opposite ends of the other brake shoe. A shoe expansion mechanism assembled on the opposite end side, a socket rotatably and non-removably fitted to the head of one end of the screw member, and a socket screwed into the threaded part of the other end of the screw member so as to be unscrewable. A strut that determines the distance between the two members of the nut at the limit of contraction and closing of the shoe, and extends the span by rotating the screw member, and a return spring that applies a spring force to the brake shoe in the direction of contraction and closing. In the drum brake shoe gap automatic adjustment device, the drum brake shoe gap automatic adjustment device includes an adjuster lever that rotates in conjunction with the expansion and contraction of the brake shoe and screws out and rotates the screw member via a gear. , a shoe gap of a drum brake characterized in that one tension spring is provided between the strut socket and the brake shoe on one side, and between the nut and the brake shoe on the other side so as to apply a tension spring force respectively. Automatic adjustment device. 2. The adjuster lever is pivotally connected to the socket of the strut, and one of the two return springs is stretched between the socket and one of the brake shoes.
The drum brake shoe gap automatic adjustment device according to claim 1, wherein the other return spring is stretched between the nut and the other brake shoe. 3. The automatic shoe gap adjustment device for a drum brake according to claim 2, wherein the spring force of one return spring is set to be greater than the spring force of the other return spring.