JPH0147658B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a device for expanding and contracting the outside diameter of a brake shoe in a drum brake.

In conventional brake drum assembly work, the outer diameter of the pair of brake shoes is usually set in advance to be considerably smaller than the drum inner diameter in order to facilitate mass production. In order to obtain the desired stroke of the brake pedal or hand lever after assembling the drum, if it is equipped with a manual shoe clearance adjustment device, once the adjusting nut or cam, etc. is rotated until the drum is locked, it is reversed by the desired amount. Or, if the vehicle is equipped with an automatic shoe gap adjustment device, the pedal or hand lever must be operated several times to readjust the gap between the drum and the brake shoe to an appropriate amount.

Therefore, this work requires a large amount of man-hours, and
The reality is that this is extremely troublesome. In addition, since these operations are usually performed with the vehicle stationary, brakes with automatic adjustment devices do not have the same clearance gap as brakes with manual adjustment devices, and the disadvantage is that the stroke is large in the initial state, and over-adjustment can occur. When the sliding surfaces of the drum and brake lining are scratched and engaged, it is essential to have a means for reducing the outside diameter of the brake shoe to facilitate removal of the drum.

The present invention enables the brake lever, which is a mechanical actuation device attached to the brake assembly, to
The above-mentioned drawbacks have been solved by making the structure capable of also having the function of returning to the original position.

To describe an example of the structure of the brake in detail, a pair of brake shoes facing the inner peripheral surface of a rotatable brake drum are movably mounted on a fixed back plate, and a pair of brake shoes is movably mounted on a fixed back plate, and a A non-shew gap adjustable or a shoe gap adjustable anchor member, with a hydraulically actuated device disposed between its other adjacent ends, is typically secured to the back plate. The pair of brake shoes are equipped with a shoe holding device to prevent them from lifting up from the back plate, and a return spring is usually installed on the pair of brake shoes to separate the brake lining from the drum when the brake is not working. It is installed between the user.

Next, the mechanical actuating device will be explained with reference to the drawings. The above-mentioned bulk plate 1, a pair of brake shoes 2 and 3 have a T-shaped cross section, and brake linings 2a and 3a are fixed to the outer periphery of the shoes 2 and 3. The mechanical actuator 4 is generally disposed adjacent to the hydraulic actuator described above, and in this example is shown with an automatic shoe gap adjustment device. Therefore, the anchor member may be of the non-shew gap adjustable type. Reference numeral 5 denotes a plate-shaped strut disposed adjacent to the hydraulic actuator, and a bell crank lever 6 is provided at one end of the strut so as to be rotatable and linearly movable in the length direction of the strut 5. It is supported by pin 7. One arm 6a with a cam of the bell crank lever 6 is fitted into the opening of the brake shoe 2 with a clearance δ, and the small teeth on the arcuate outer end surface of the other arm 6b are connected to the corresponding strut 5.
It engages with teeth formed in the middle part of. The intermediate portion of the brake lever 8 is rotatably supported by a pin 9 at the other end of the strut 5, and its inner arm 8a abuts against the inner edge of the brake shoe 3 and penetrates through the back plate 1. The outer arm 8b, which extends in a substantially perpendicular direction, is connected to a control cable (not shown) or the like. 10 is a spring stretched between the strut 5 and the brake shoe 3; 11 is a spring stretched between the strut 5 and the pin 7; the load is set to be weaker than that of the spring 10.
12 is a dust boot, and 13 is a boot clip. As is clear from the above, brake shoe 2,
Due to the action of the return spring, the brake shoe 3 on one side contacts the inner arm 8a of the brake lever 8, and the brake shoe 2 on the other side contacts the one arm 6a of the bell crank lever 6, respectively. This is determined by supporting the movement of the outer arm 8b of the brake lever 8 in the retracting direction. To explain the support device according to the present invention, a generally L-shaped guide member 14, which is a fixed member, is fixed to the back surface of the back plate 1, and a guide groove for guiding the brake lever 8 is provided in the upright piece 14a of the guide member 14. 14b is formed. In addition, a tongue-like portion 14c formed by cutting and bending from the guide groove 14b is attached to the brake lever 8.
The outer arm 8b extends approximately parallel to the end of the outer arm 8b for a suitable length. However, between the tongue portion 14c and the inner edge of the brake lever 8, a pair of coil portions 15a and 15a' of the coil spring 15 are located on substantially the same coil center line.
The brake levers 8 are arranged to face each other in a direction transverse to the operating direction of the brake lever 8. Therefore, under normal conditions, the brake lever 8 is in contact with the outer periphery of the coil portions 15a, 15a' to restrict its backward position, but when the coil portions 15a, 15a' are separated from each other, the brake lever 8 is in contact with the outer periphery of the coil portions 15a, 15a'. The brake lever 8 moves back. The coil spring 15 has one leg 15b and 15b' that continuously extend from the outside of each coil portion 15, 15' and is connected to the outer edge of the coil spring 15 so as to straddle the brake lever 8. , the hooked end portions of the other leg portions 15c, 15c' extending continuously from the inside of each coil portion 15a, 15a' are hooked to the opening of the guide member 14, and thereby the coil portions 15a, 15a' are connected to each other. The brake lever 8 is biased in the approaching direction and the brake lever 8 is biased in the retracting direction while being held in a fixed position. Although the coil spring 15 of this example is in the form of a single piece, one of the connected leg portions 15b and 15b' is separated and each tip is formed into a hook shape that can be hooked to the brake lever 8, It is also possible to use two coil springs.

First, service brake operation in the above configuration will be explained. When pressurized fluid is supplied to the wheel cylinder, the brake shoes 2 and 3 expand around the anchor member, thereby frictionally engaging the rotating drum and braking it. At this time, if the gap between the linings 2a, 3a and the drum is larger than a predetermined amount, the strut 5, brake lever 8, etc. will follow the movement of the brake shoe 3 by the spring 10, and the bell crank lever 6 will move the brake shoe 3. 2, the teeth of the bell crank lever 6 and the strut 5 disengage, and the bell crank lever 6 rotates clockwise in FIG. 1, increasing the length of the mechanical actuating device 4. . Therefore, even when the drum gets grooved, it continues to be adjusted.

Next, the operation of the mechanical actuator 4 will be explained.
When the end of the outer arm 8b of the brake lever 8 is pulled in the direction of arrow F, the inner arm 8a expands the brake shoe 3 using the pin 9 as a fulcrum, and the reaction force is transmitted via the pin 9 to the bell crank lever 6. The brake shoe 2 is spread out and brought into frictional engagement with the drum.

However, in the present invention, before assembling the drum,
A pair of coil parts 15a, 15 of the coil spring 15
a' and move the brake lever 8 backward into this gap, in other words, in a state where it is in contact with the guide member 14 as shown in the dashed line in FIG. 1 and as shown in FIG. Set the diameter to be considerably smaller than the drum diameter. After assembling the drum, when the brake lever 8 is pulled in the direction of arrow F, the lever 8 comes out of the coil portions 15a and 15a'.
The outer diameter of the brake shoes 2 and 3 can be expanded by the distance L between the inner edge of the brake lever 8 and the guide member 14. If the sliding surfaces of the drum and the linings 2a, 3a are scratched and engaged, use a tool such as a screwdriver to separate the pair of coil parts 15a, 15a', and insert the brake lever 8 into this gap. The drum can be easily removed by moving it backwards. As described above, according to the present invention, the brake shoe 2,
3 expansion and small operation can be done with one touch, and by arranging the coil spring 15 symmetrically with respect to the center line of the plate thickness of the brake lever 8, it can also have a function of preventing the brake lever 8 from being biased. I can do it. Although this embodiment has been described in detail for a brake with automatic shoe gap adjustment, it is by no means limited to this type of brake; for example, the bell crank lever 6 may be removed and the strut 5 may be directly connected to the brake shoe 2. It is obvious that the present invention can also be applied to brake types in which the above-mentioned anchor member is of various conventionally known manual adjustment type shoe gaps.

[Brief explanation of drawings]

The drawing shows one embodiment including the device of the present invention,
FIG. 1 is a cross-sectional view showing the mechanical actuating device of a drum brake, and FIGS. 2 and 3 are respectively shown in FIG. 1.
, - sectional view, FIG. 4 is a Y arrow view of FIG. 1,
FIG. 5 is a view corresponding to FIG. 4 when the brake lever is fully retreated. 2, 3... Brake shoe, 4... Mechanical actuating device, 5... Strut, 6... Bell crank lever, 8... Brake lever, 14... Guide member, 15... Coil spring, 15a, 15a '... Coil part, 15b, 15b', 15c, 15c'... Leg part.

Claims (1)

[Claims] 1. A mechanical actuation device consisting of a brake lever that operates one brake shoe and a strut that transmits the reaction force to the other brake shoe, the brake lever being supported in a backward position and a brake drum. In a drum brake that regulates the gap between the brake lever and the brake shoe, the brake lever is normally in a retracted position supported by the outer periphery of a pair of coils facing each other in the direction of the same centerline, and the pair of coils are spaced apart. 1. A brake lever support device, characterized in that the brake lever is configured to retract into the gap when the brake lever is pressed.