JPS5814930B2 - Drum brake auto-adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic braking gap adjustment device for a drum brake that brakes a drum by expanding a pair of left and right brake shoes. A piston back chamber is formed with a piston back chamber, a liquid or gas fluid is sealed in the compartment, and either the piston rod tip or the rod tip provided in the cylinder is loosely fitted into the brake shoe web of the piston with a predetermined gap. The other end is fixed to the web of another plate, or the tips of both ronds are loosely fitted into both webs with a predetermined gap, and a passage is provided in the piston that communicates with the above-mentioned compartment, and a passage is provided from the piston front chamber to the piston front chamber. The passage is equipped with a check valve mechanism that allows the sealed fluid to flow only to the piston back chamber, and its purpose is to prevent the rod tip and web from fitting loosely into the web of the brake shoe when the lining wears out. When the piston is operated beyond the predetermined gap set between The fluid sealed in the front chamber of the piston opens the check valve mechanism and flows through the passage to the back chamber of the piston, reducing the return of the piston and cylinder by that amount and automatically adjusting the braking gap. The purpose is to provide a completely new auto-adjust device that is simple and easy to install in narrow spaces.

The illustrated embodiment will be described below.

1 is the back plate of the drum brake that is fixed to the stationary part of the vehicle body, and inside it there are a pair of left and right brake shoes 2,
2', and linings 3, 3' are bonded to the outer peripheries of the shoes 2, 2', and are connected to the inner peripheral surface of a brake drum (not shown) that surrounds the shoes and rotates together with the wheels. There is.

Reference numeral 4 denotes a wheel cylinder provided on the inside upper part of the back plate 1, and pistons 5, 5' connected to the upper ends of the brake shoes 2, 2' are operated by the output hydraulic pressure of the mask cylinder operated by the brake pedal. , the brake shoes 2, 2' are expanded.

Reference numeral 6 denotes an anchor body provided at the inner lower part of the back plate 1, which supports the lower ends of the brake shoes 2, 2' and serves as a fulcrum for expansion and contraction of the shoes 2, 2'.

Reference numerals 7 and 7' indicate return springs that are stretched between the brake shoes 2 and 2' above and below, and always urge the shoes 2 and 2' in the direction of contraction.

8 is a brake shoe 2 adjacent to the wheel cylinder 4;
A link 9 extends between 2' so as to be able to slide on the back plate 1, and 9 is a bell crank-shaped brake lever that passes through an opening in the back plate 1, and is pivotally connected to the left end of the link 8 by a pin 10. The upper arm 9a of the lever 9 engages with a through hole 12 formed in the webbing 11 of the brake shoe 2',
The lower arm 9b is connected to a handbrake operating lever via a wire 13.

Reference numeral 14 denotes an auto adjuster, which includes a cylinder 15, a piston 16 that slides into the cylinder 15, a piston front chamber 17 and a piston back chamber 18 formed in the cylinder 15 by the piston 16, and a fluid, that is, liquid or gas, sealed in both chambers 1718. , the piston rod 19 and the rod 20 provided in the cylinder 15, and both chambers 17 and 18 provided in the piston 16.
A check valve 22 is provided in the passage 21 to allow sealed fluid to flow only from the piston front chamber 17 to the back chamber 18.

23 is a spring of the valve 22;
It is sufficient that the spring force has enough urging force to prevent the sealed fluid from flowing back from the piston back chamber 18 to the front chamber 17.

24 is a passage for communicating the atmosphere with the rear end of the piston rear shaft 25 which passes through the piston back chamber 18 and is slidably inserted into the back surface of the cylinder 15; These ports introduce sealed fluids into the back chambers 18, respectively, and the pressure adjustment of the sealed fluids in the piston front chamber 17 and back chamber 18 during brake adjustment, that is, the positional relationship between the cylinder 15 and the piston 16, is carried out through ports 26 and 27. While introducing fluid into both chambers 17 and 18, the pressure of the fluid and the positional relationship between the cylinder 15 and the piston 16 are adjusted.
6, 27 or close the cylinder 15 as shown in Figure 5.
A passage 28 communicating with the compartment 1718 is formed in the passage 2.
A valve 29 that can be opened and closed from the outside of the cylinder 15 is provided at 8, and the sealed fluid introduced into the cylinder 15 is opened to adjust the pressure difference between the compartments 17 and 18, and the valve 29 is closed to drain the sealed fluid into the passage 28. This is done by means such as blocking the

Reference numeral 30 denotes a mounting hole formed in the web 11 of the brake shoe 2, into which the tip of the piston rod 19 is loosely fitted with a predetermined gap G.

31 is a mounting hole formed in the web 11' of the brake shoe 2', into which the tip of the iron 20 of the cylinder 15 is tightly fitted, and the auto adjuster 14 is installed adjacent to the return spring 7 between the brake shoes 2 and 2'. Installed.

The tip of the rod 20 of the cylinder 5 may be loosely fitted into the mounting hole 31 with a predetermined gap G, and the tip of the piston rod 19 may be tightly fitted into the mounting hole 30.
The tips of 9 and 20 may be loosely fitted into the mounting holes 30 and 31 with a predetermined gap of 1/2 G, respectively.

Further, the check valve mechanism used in the present invention is not limited to the check valve 22 of the above embodiment.

Next, the operation of the above embodiment will be explained. When pressure oil is supplied to the wheel cylinder 4 by operating the brake pedal, the pistons 5 and 5' cause the brake shoes 2 and 2 to
' is operated to expand, and the linings 3, 3' can be brought into pressure contact with the brake drum to brake the wheels.

When the braking gap is normal, the brake shoes 2, 2' operate within the predetermined gap G between the piston rod 19 and the mounting hole 300, so the cylinder 5 and piston rod 16 do not operate, but the linings 3, 3' are worn out. When the brake shoes 2, 2' operate beyond the predetermined gap G, the piston rod 19 is pulled by the web 11, and the cylinder 5 is also pulled by the web 11', so the piston front chamber 17 is pressurized. The pressure in the back chamber 18 becomes negative, and the fluid sealed in the piston front chamber 17 opens the check valve 22 and flows into the back chamber 18 through the passage 21, and the pressures in the compartments 17 and 18 are maintained in balance, preventing brake operation. When released, the return of the cylinder 5 and piston 16 is reduced by the amount that flows into the piston back chamber 18, and the braking gap is automatically adjusted.

As described above, the present invention makes it possible to adjust the braking gap by using the pressure difference of the fluid sealed in the compartments in the cylinder divided by the piston, so that stepless adjustment is possible and the structure is simple. This is a novel invention that can be easily installed even in narrow spaces.

[Brief explanation of the drawing]

Figure 1 is a front view of a drum brake equipped with the auto adjuster of the present invention, Figure 2 is a cross-sectional view of Figure 1, Figure 3 is a cross-sectional view of Figure 1, Figures 4 and 5. The figures are sectional views of essential parts showing respective embodiments of the auto-adjuster. 2, 2' are brake shoes, 11, 11' are webs, 1
4 is an auto adjuster, 15 is a cylinder, 16 is a piston, 17 is a piston front chamber, 18 is a piston back chamber, 1
9 is a piston rod, 20 is a rod, 21 is a passage, 22
is a check valve, and 23 is a spring of the check valve 22.

Claims (1)

[Claims] 1 Expand the left and right pair of brake shoes and open the drum]
In a drum brake that operates, a piston that slides into the cylinder forms a piston front chamber and a poston back chamber in the cylinder, and fluid is sealed in the chambers, and either the piston rod tip or the rod tip provided in the cylinder is Loosely fitting the web of one brake shoe with a predetermined gap and fixing the other to the web of the other brake shoe, or loosely fitting the ends of both rods into both webs with a predetermined gap, An automatic adjustment device for a drum brake, characterized in that the piston is provided with a passage communicating with both chambers, and the passage is provided with a check valve mechanism that allows the sealed fluid to flow only from the piston front chamber to the piston back chamber.