JPH0732239U - Automatic clearance adjuster for drum brakes - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent the gap between the inner peripheral surface of the drum and the outer peripheral surface of the lining from becoming too narrow due to vibration during traveling. [Structure] When the above gap is widened, the piston 3
The adjusting nut 13 is rotated in the circular hole 12 of a.
Based on this rotation, the adjustment bolt 16 is pushed out in the direction of the arrow β to narrow the gap. The O-ring 2 is inserted into the locking groove 27 formed on the outer peripheral surface of the adjusting nut 13.
8 is attached, and the outer peripheral edge of the O-ring 28 is pressed against the inner peripheral surface of the circular hole 12. The O-ring 28 increases the torque required to rotate the adjust nut 13 and prevents the adjust nut 13 from rotating due to vibration during traveling.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The automatic clearance adjusting device for a drum brake according to the present invention is incorporated in a drum brake used for braking an automobile, and regardless of wear of the lining, the gap between the outer peripheral surface of the lining and the inner peripheral surface of the drum is maintained during non-braking. Plays a role in keeping the gaps existing in the space constant.

[0002]

[Prior art]

 The drum brake is configured, for example, as schematically shown in FIG. One or two wheel cylinders 2, 2 are fixed to the front surface (the outer surface in the width direction of the vehicle) of the back plate 1 which is supported by the suspension device and does not rotate. Pressure oil is fed to the wheel cylinders 2 and 2 during braking, and the amount of protrusion of the pistons 3 and 3 is increased in accordance with the feed of the pressure oil. On the other hand, a pair of left and right brake shoes 4, 4 are supported on the front surface of the back plate 1 so as to be freely displaceable in the diametrical direction of the back plate 1. Each of the brake shoes 4, 4 comprises backing plates 6, 6 fixed to the outer peripheral edges of substantially crescent-shaped webs 5, 5, and linings 7, 7 are attached to the outer peripheral surfaces of the backing plates 6, 6.

Both ends of the webs 5 and 5 of the brake shoes 4 and 4 are anchor portions 8 formed at the tips of the pistons 3 and 3 or the end portions of the wheel cylinders 2 and 2, respectively. It is in contact with 8. Return springs 9 and 9 are provided between the webs 5 and 5 to give the brake shoes 4 and 4 an elastic force directed inward in the diametrical direction of the back plate 1. Further, a cylindrical drum 10 having a bottom is put around the brake shoes 4 and 4, and the inner peripheral surface 10a of the drum 10 and the outer peripheral surfaces 7a and 7a of the linings 7 and 7 are opposed to each other. There is.

The inner peripheral surface 10a and the outer peripheral surfaces 7a, 7a are separated from each other through a small gap during non-braking, but contact each other during braking, and friction between these two surfaces 10a, 7a causes Demonstrate the braking force. That is, at the time of braking, the amount of protrusion of the pistons 3, 3 is increased by sending the pressure oil into the wheel cylinders 2, 2 so that the brake shoes 4, 4 are made elastic by the return springs 9, 9. Against this, the back plate 1 is displaced outward in the diametrical direction to bring the both surfaces 10a, 7a into contact.

If the linings 7, 7 wear due to such repeated braking, the thickness of the gap existing between the inner peripheral surface 10a and the outer peripheral surfaces 7a, 7a when not braking increases. This increase in thickness leads to an increase in the amount of pressure oil to be sent to each of the wheel cylinders 2 and 2 during braking, and thus an increase in the amount of depression of the brake pedal, which is not preferable.

For this reason, conventionally, as the linings 7, 7 wear, the brake shoes 4, 4 are extruded outward in the diametrical direction of the back plate 1 to keep the thickness of the gap below a certain value. An automatic clearance adjusting device for a brake is known and actually used, as described in, for example, Japanese Utility Model Publication No. 50-7424.

The structure and operation of such an automatic gap adjusting device for a drum brake will be described with reference to FIGS. 1 and 2 showing an embodiment of the present invention. Pistons 3a and 3b are oil-tightly fitted in a wheel cylinder 2a fixed to the back plate 1 (Fig. 4). Both of these pistons 3a, 3b increase the amount of protrusion from the wheel cylinder 2a as the pressure oil is fed into the wheel cylinder 2a.

One of the pistons 3a and 3b (the right side in FIGS. 1 and 2) has a groove 11 on the outer end surface (the right end surface in FIGS. 1 and 2) of the piston 3b. It is formed over a period of time. At the time of assembling the drum brake, the end of the web 5 engages with the groove 11. Therefore, the piston 3b is held in the wheel cylinder 2a only without any rotation, only the displacement in the axial direction.

A circular hole 12 is formed inside the other piston 3a (on the left side in FIGS. 1 and 2) concentrically with the piston 3a. The end of the circular hole 12 is opened at the center of the outer end surface of the piston 3a. The adjust nut 13 is rotatably inserted in the circular hole 12. The adjusting nut 13 has a female screw on the inner peripheral surface. It should be noted that a ring 15 having a high slidability is provided between the step portion 14 formed in the middle portion of the inner peripheral surface of the circular hole 12 and the inner end surface (right end surface in FIG. 2) of the adjusting nut 13. The thrust load applied to the adjustment nut 13 is freely supported.

Further, the adjusting nut 13 and the circular hole 12 are filled with grease, and then an adjusting bolt 16 is screwed into the adjusting nut 13. A groove 17 is formed on the outer end surface (left end surface in FIGS. 1 to 3) of the adjusting bolt 16 over the diameter direction of the outer end surface. At the time of assembling the drum brake, the end of the web 5 is engaged with the groove 17. Therefore, the adjusting bolt 16 does not rotate regardless of the rotation of the adjusting nut 13, and is displaced in the axial direction when the adjusting nut 13 rotates.

An adjust ring 18 is fixed to the outer end surface of the adjust nut 13. The outer peripheral edge of the adjust ring 18 is concentric with the adjust nut 13, and ratchet tooth-shaped engaging teeth 19, 19 are formed on the outer peripheral edge. A base end portion of the adjust lever 20 is pivotally supported on a pivot shaft 21 provided on the outer surface of the intermediate portion of the wheel cylinder 2a. A claw portion 22 is formed at the tip of the adjust lever 20 made of an L-shaped metal plate, and the claw portion 22 can be engaged with the engaging teeth 19 and 19.

A locking portion 23 is formed on one side surface (a back surface in FIG. 1 and a lower surface in FIG. 2) of a portion of the adjusting lever 20 near the tip of the intermediate portion, and the locking spring 23 is attached to the locking portion 23. The end is locked. The other end of the tension spring 24 is locked to a fixed portion such as the outer surface of the wheel cylinder 2a or the front surface of the back plate 1. The tension spring 24 applies an elastic force to the adjusting lever 20 in a direction to separate the claw portion 22 from the engaging teeth 19 and 19, and at the same time, causes the claw portion 22 to float in a direction to separate from the wheel cylinder 2a. Has a role to prevent.

Further, a mounting plate 25 is fixed to the outer end surface (the left end surface in FIGS. 1 to 3) of the piston 3a. A connecting member 26 is provided between the tip end portion (upper end portion in FIG. 2) of the arm piece 29 protruding from the outer peripheral edge of the mounting plate 25 and the intermediate portion proximal end portion of the adjusting lever 20. There is. The details of the connecting member 26 are disclosed in Japanese Patent Application No. 4-76485, which is not the gist of the present invention, and a detailed description thereof will be omitted.

Due to the presence of the mounting plate 25 and the connecting member 26, as the amount by which the piston 3a projects from the wheel cylinder 2a increases, the adjusting lever 20 moves around the pivot shaft 21 in FIG. Swing counterclockwise. Then, the adjusting lever 20 swings in this way, and the claw portion 22 and any one of the engaging teeth 19 are engaged with each other. As a result, when the adjusting nut 13 is rotated through the adjusting string 18, The directions of the screws formed on the adjusting bolt 16 and the adjusting nut 13 are determined so that the adjusting bolt 16 is pushed outward from the adjusting nut 13.

The operation of the automatic gap adjusting device for a drum brake configured as described above is as follows. The piston 3a reciprocates in the wheel cylinder 2a in the axial direction as the braking and the braking are repeatedly performed. When the thickness of the gap existing between the inner peripheral surface 10a of the drum 10 and the outer peripheral surfaces 7a, 7a of the linings 7, 7 during non-braking is small, the reciprocating movement amount of the piston 3a is also small. Therefore, the swing amount of the adjust lever 20 is also small, and the claw portion 22 only makes sliding contact with the outer peripheral edge of the same engagement tooth 19 and does not engage with any engagement tooth 19. Therefore, the adjusting ring 18 and the adjusting nut 13 do not rotate, the amount of the adjusting bolt 16 protruding from the adjusting nut 13 does not change, and the gap is not adjusted.

When the thickness of the gap increases as the linings 7, 7 wear, the reciprocating movement amount of the piston 3a and the swinging amount of the adjusting lever 20 during the control increase. As a result, the pawl portion 22 engages with the engaging tooth 19 and rotates the adjust string 18 and the adjust nut 13 fixing the adjust string 18 as shown by an arrow α in FIG. As a result, the adjustment bolt 16 screwed into the adjustment nut 13 moves in a direction projecting from the adjust nut 13 as shown by an arrow β in FIG. Then, the brake shoe 4 having its end engaged with the concave groove 17 on the outer end surface of the adjusting bolt 16 is pushed in the direction indicated by the arrow γ in FIG. 1 to narrow the gap.

[0017]

[Problems to be solved by the device]

 However, in the case of a drum brake incorporating the automatic clearance adjusting device for a drum brake configured and acting as described above, the outer surfaces 7a, 7a of the linings 7, 7 and the inner surface 10a of the drum 10 are rarely formed. The gap may become too narrow and the two surfaces 7a, 10a may rub against each other during traveling.

As a result of repeated research by the present inventor on the cause of the gap being too narrow, it is caused by the addition of vibration accompanying the traveling of the automobile to the screwing portion between the adjusting nut 13 and the adjusting bolt 16. I knew I would do it. That is, when vibration of a specific frequency is applied to the screwed portion, a rotational torque due to the action of a kind of ultrasonic motor is applied to the screwed portion to rotate the adjustment nut 13. By rotating the adjusting nut 13 in this manner, the adjusting bolt 16 is displaced in the axial direction, and the size of the gap is changed.

Of course, the displacement of the adjusting bolt 16 due to the vibration may be performed in any of the protruding direction and the retracting direction from the adjusting nut 13. However, in the case of displacement in the retracting direction, this displacement is compensated by the action of the automatic gap adjusting device at the time of the next braking, so there is no particular problem. However, when it is displaced in the protruding direction, the automatic gap adjusting device cannot compensate for this displacement, and as described above, the outer peripheral surfaces 7a and 7a of the linings 7 and 7 and the inner peripheral surface 10a of the drum 10 are separated from each other. It causes rubbing.

The automatic gap adjusting device for a drum brake of the present invention was devised in view of such circumstances.

[0021]

[Means for Solving the Problems]

 The automatic clearance adjusting device for a drum brake according to the present invention is similar to the known automatic clearance adjusting device for a drum brake, and a wheel cylinder 2a fixed to the back plate 1 and an axial direction in the wheel cylinder 2a. A piston 3a, which is fitted in an oil-tight manner so that it can be displaced only freely, and which increases the amount of protrusion from the wheel cylinder 2a as the pressure oil is fed into the wheel cylinder 2a, and the outer end surface of the piston 3a. A circular hole 12 having an end opened at the center, an adjust nut 13 rotatably inserted in the circular hole 12 and having an internal thread on the inner peripheral surface thereof, and the adjust nut 13 are screwed together to form a brake. The adjusting bolt 16 that does not rotate due to the engagement with the end of the shoe 4 and the outer end surface of the adjusting nut 13 are fixed, and are concentric with the adjusting nut 13. An adjust ring 18 having engaging teeth 19, 19 formed on the outer peripheral edge thereof, a base end portion of which is pivotally supported on the outer surface of the intermediate portion of the wheel cylinder 2a, and a claw portion 22 formed at the tip end thereof is provided with the engaging teeth. The adjusting lever 20, which is freely engageable with 19, and the intermediate portion of the adjusting lever 20 and the outer end portion of the piston 3a are coupled to each other, and the adjusting lever 20 is connected to the claw as the protrusion amount increases. The portion 22 and the engaging teeth 19, 19 are provided with a connecting member 26 that is swung in a direction in which the engaging teeth 19 and 19 engage with each other. Then, based on the engagement between the claw portion 22 and the engaging teeth 19 and 19, the adjusting nut 13 pushes the adjusting bolt 16 outward from the adjusting nut 13 via the adjusting ring 18. It is configured to rotate to.

Particularly, in the automatic gap adjusting device for a drum brake of the present invention, the adjusting nut 13 rotates between the inner peripheral surface of the circular hole 12 and the outer peripheral surface of the adjusting nut 13. It features a friction member that increases the required torque.

[0023]

[Action]

 The automatic gap adjusting device for a drum brake according to the present invention, which is constructed as described above, acts itself when the size of the gap between the outer peripheral surface 7a of the liner 7 and the inner peripheral surface 10a of the drum 10 is maintained at an appropriate value. Is as described above.

Particularly, in the case of the automatic gap adjusting device for a drum brake of the present invention, the torque required to rotate the adjusting nut 13 inside the piston 3a becomes large due to the presence of the friction member. As a result, at the drive torque degree generated based on the vibration during traveling, the adjust nut 13 does not rotate and the gap does not become too narrow.

[0025]

【Example】

 1 to 3 show an embodiment of the present invention. The feature of the present invention is that the adjustment nut 13 fitted in the circular hole 12 of the piston 3a prevents the adjustment nut 13 from rotating due to vibration during traveling, and the structure of the other parts. And the action are as described above. Therefore, redundant description will be omitted, and the characteristic part of the present invention will be described below.

A locking concave groove 27 is formed on the outer peripheral surface of the intermediate portion of the adjust nut 13 over the entire circumference. An O-ring 28, which is a friction member, is fitted inside the locking groove 27. The diameter dimension of the cross section of the O-ring 28 is sufficiently larger than the depth dimension of the locking groove 27. Therefore, after the O-ring 28 is fitted in the locking groove 27 and before the adjust nut 13 is inserted into the circular hole 12, the portion of the O-ring 28 near the outer periphery of the adjust nut 13 is located. It projects from the outer peripheral surface.

When the adjusting nut 13 having the O-ring 28 mounted on the outer peripheral surface of the intermediate portion is fitted into the circular hole 12 as described above, the O-ring 28 is elastically crushed and the locking recess is formed. It is pushed into the groove 27. The outer peripheral edge portion of the O-ring 28 is formed on the inner peripheral surface of the circular hole 12, and the outer peripheral edge portion is formed on the bottom surface of the engaging groove 27, which is a part of the outer peripheral surface of the adjust nut 13. It is pressed based on the elastic restoring force of the O-ring 28.

Friction forces act between the inner and outer peripheral portions of the rubber O-ring 28 and the inner peripheral surface of the circular hole 12 and the bottom surface of the locking groove 27, respectively. Therefore, in order to rotate the adjusting nut 13 inside the circular hole 12, a relatively large torque is required. As a result, the adjust nut 13 does not rotate at a torque that is generated based on the vibration during traveling, and the gap between the outer peripheral surfaces 7a, 7a of the linings 7, 7 and the inner peripheral surface 10a of the drum 10 is reduced. It will not be too narrow. Further, the O-ring 28 can prevent foreign matters such as water and dust from entering the circular hole 12 through the gap between the inner peripheral surface of the piston 3a and the outer peripheral surface of the adjust nut 13.

When braking with the gap widened, the rotation torque applied by the claw portion 22 of the adjustment lever 20 to the adjustment nut 13 via the adjustment string 18 is greater than the rotation torque based on the vibration. Is also much larger. Therefore, the provision of the O-ring 28 does not impair the original function of the automatic gap adjusting device.

[0030]

[Effect of device]

 Since the automatic gap adjusting device for the drum brake of the present invention is constructed and operated as described above, it effectively prevents the gap between the outer peripheral surface of the lining and the inner peripheral surface of the drum from becoming too narrow, and at the same time, the external Water and dust can be effectively prevented from entering. Therefore, it can contribute to improving the stability of operation of a vehicle equipped with a drum brake.

[Brief description of drawings]

FIG. 1 is a front view of a wheel cylinder incorporating an automatic gap adjusting device according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an enlarged view of the left part of FIG.

FIG. 4 is a schematic front view showing an example of a drum brake to which the present invention is applied.

[Explanation of symbols]

 1 Back plate 2, 2a Wheel cylinder 3, 3a, 3b Piston 4 Brake shoe 5 Web 6 Back metal 7 Lining 7a Outer peripheral surface 8 Anchor portion 9 Return spring 10 Drum 10a Inner peripheral surface 11 Recessed groove 12 Circular hole 13 Adjust nut 14 Stepped portion 15 ring 16 adjusting bolt 17 concave groove 18 adjusting string 19 engaging tooth 20 adjusting lever 21 pivot 22 claw 23 locking portion 24 tension spring 25 mounting plate 26 connecting member 27 locking concave groove 28 O-ring 29 arm piece

Claims (1)

[Scope of utility model registration request] 1. A wheel cylinder fixed to a back plate, and an oil-tight fit in the wheel cylinder so that only displacement in the axial direction is possible, and when pressure oil is fed into the wheel cylinder. A piston that increases the amount of protrusion from the lever wheel cylinder, a circular hole whose end is opened at the center of the outer end surface of this piston, and a female screw on the inner peripheral surface that is rotatably inserted in this circular hole. An adjusting nut having a screw, an adjusting bolt that is screwed with the adjusting nut and does not rotate due to the engagement with the end of the brake shoe, and the adjusting nut is fixed to the outer end surface of the adjusting nut, and the outer peripheral edge is concentric with the adjusting nut. An adjust ring having engaging teeth formed thereon and a base end portion of which is pivotally supported on an outer surface of an intermediate portion of the wheel cylinder, and a claw portion formed at a tip end thereof is adapted to be engageable with the engaging teeth. By connecting the just lever, the intermediate part of the adjust lever and the outer end of the piston,
With the increase in the amount of protrusion, the adjusting lever is provided with a connecting member that swings in a direction in which the claw portion and the engaging tooth engage with each other, and based on the engagement between the claw portion and the engaging tooth, In the automatic clearance adjusting device for a drum brake, in which the adjusting nut is rotated in a direction of pushing the adjusting bolt outward from the adjusting nut through the adjusting string, the inner peripheral surface of the circular hole and the adjusting nut An automatic clearance adjusting device for a drum brake, characterized in that a friction member for increasing a torque required for rotating the adjusting nut is provided between the outer peripheral surface and the outer peripheral surface.