JPH0247782Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to an improvement of a dual-servo type drum brake with automatic shoe gap adjustment that automatically adjusts the gap between the brake shoe and the rotating drum (hereinafter referred to as the shoe gap). be.

PRIOR ART A pair of arc-shaped brake shoes has an anchor that receives braking torque transmitted to the brake shoes by abutting one end of the brake shoes, and an adjuster wheel. a coupling mechanism that connects each other end of the brake shoe and adjusts the shoe gap by separating the other ends as the adjustment wheel rotates in one direction; an adjustment lever rotatably provided on the other end side and having a pawl portion that engages with the adjustment wheel in a direction for rotating the adjustment wheel in the direction of reducing the shoe gap; and one longitudinal axis of the brake shoe. A cable guide provided at a direction intermediate portion, and a cable that is spanned between the adjustment lever and the anchor via the cable guide, and rotates the adjustment lever when the brake shoe is expanded. A dual-servo type drum brake with automatic shoe gap adjustment is known.

In such a dual-servo type drum brake, a tension coil spring and a stopper member for preventing the tension coil spring from contracting beyond a certain limit are usually provided between one end of the cable and the adjustment lever. When the tension of the cable exceeds a predetermined limit, the spring is expanded to prevent further increase in cable tension, thereby preventing over-adjustment.

Problems to be Solved by the Invention However, in such dual-servo drum brakes, the spring is usually elastically deformed with a relatively large preload so that it cannot be stretched when the shoe gap needs to be adjusted. A frame-shaped stopper member was provided on the outside of the spring in order to apply a predetermined preload to the spring and prevent the spring from contracting beyond a certain limit.

Since such an overadjustment prevention mechanism consisting of a spring and a stopper member is usually located on the inner circumferential side of the brake shoe, sufficient space must be secured on the inner circumferential side of the brake shoe. The problem was that I couldn't get it. This is particularly noticeable in small-sized dual-servo type drum brakes.

Means for Solving the Problems The present invention was made against the background of the above circumstances, and its gist is that in the above-mentioned type of dual-servo type drum brake,
The cable guide is rotatably or movably attached to one of the brake shoes, and
a spring that is stretched when the tension of the cable exceeds a predetermined limit and prevents over-adjustment by allowing rotation or movement of the cable guide in a direction to reduce the tension; A stopper is provided to apply a predetermined preload to the spring by preventing the spring from contracting beyond a certain limit.

By doing this, the cable guide rotatably or movably attached to one side of the brake shoe is always prevented from rotating or moving when the brake shoe is expanded. It is operated in conjunction with the brake shoe, but when the cable tension exceeds a predetermined limit, the spring is stretched and the cable guide is rotated or moved in a direction that reduces the cable tension. This prevents further rotation of the adjustment lever and prevents overadjustment.

Effects of the invention As a result, an over-adjustment prevention mechanism consisting of a cable guide, a spring, etc. is disposed on the brake shoe, making it possible to secure a larger space on the inner circumferential side of the brake shoe than in the past. .

The spring is preferably mounted such that one end thereof is spaced apart from the center of rotation by a distance greater than the distance between the center of rotation of the cable guide and the point of force exerted on the cable guide by the cable. . In this way, it is possible to ensure a large lever ratio between the distance between the center of rotation of the cable guide and the spring biasing position and the distance between the center of rotation and the force point, so the biasing force of the spring can be compared. The target can be made smaller and relatively small springs can be used.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing the main parts of a dual servo type drum brake equipped with an automatic shoe gap adjustment device to which the present invention is applied, in which a bucking plate 10
A pair of arcuate brake shoes 1 are shown above for sliding contact with the inner circumferential surface of a rotating drum (not shown).
2 and 14 are mutually supported by hold-down devices 16 and 18 so as to be expandable. One ends of the brake shoes 12 and 14 that are close to each other are brought into contact with the outer circumferential surface of an anchor pin (anchor) 20 protruding from the bucking plate 10, respectively. Brake shoe 12, 14
The other ends of the brake shoes 12 and 14 are urged toward each other by a spring 21 so as to come into contact with both ends of the coupling mechanism 22, so that both brake shoes 12 and 14 are brought into contact with the coupling mechanism 22. Therefore, they are connected to each other. The connection mechanism 22 includes a first connection part 24, a second connection part 26, and both connection parts 2.
4 and 26, and in this embodiment, by rotating the adjustment wheel 28 in the direction A in the figure, both connecting portions 24 and 26 are connected.
are moved in a direction away from each other, thereby pushing the brake shoes 12, 14 toward the outer periphery of each other and adjusting the shoe gap.

Anchor pin 20 is placed on bucking plate 10.
A wheel cylinder 30 is fixed on the inner peripheral side of the wheel cylinder 30, and a pair of pistons 32 and 34 are fitted into the inside of the wheel cylinder 30 so as to be able to protrude in the axial direction and away from each other. The tips of the pistons 32, 34 are respectively engaged with the anchor pin 20 sides of the brake shoes 12, 14, and as the pistons 32, 34 are pushed out, the brake shoes 12, 14
are now expanding into each other. A parking brake lever 36 to which a parking cable (not shown) is connected at one end is rotatably attached to one brake shoe 12 by a pin 38 at the other end. A strut 40 is spanned between this parking brake lever 36 and the other brake shoe 14, and when the parking brake lever 36 is rotated counterclockwise in the figure by the parking cable, The brake shoes 12 and 14 are also spread apart from each other via the strut 40.

An adjustment lever 42 is connected to the pin 4 at one end of the brake shoe 12 on the coupling mechanism 22 side.
4, and a claw portion 4 formed at the other end of the adjustment lever 42.
6 is engaged with the outer peripheral tooth of the adjustment wheel 28 in the direction of rotating the adjustment wheel 28 in the direction A. On the other hand, a cable guide 4 is provided at the longitudinally intermediate portion of the brake shoe 12.
8 is rotatably attached at one end by a pin 50. A spring 52 is stretched between the other end of the cable guide 48 and the brake shoe 12, and the spring 52 constantly biases the cable guide 48 clockwise in the figure with a preset preload. An elongated hole 54 is formed near the other end of the guide 48, and a stopper pin 56 that protrudes in the direction away from the bucking plate 10 in the brake shoe 12 is fitted into the elongated hole 54. There is. As a result, the spring 52 is prevented from contracting beyond a certain limit, and the predetermined preload is applied to the spring 52, and the cable guide 48 is always connected to the brake shoe 12 of the elongated hole 54 due to the biasing force of the spring 52. The inner peripheral side (right side in the figure) is located at a position where it abuts against the stopper pin 56. Therefore, in this embodiment, the stopper pin 56 and the elongated hole 54 constitute a stopper. Further, the preload of the spring 52 does not allow rotation of the cable guide 48 within the range of a normal brake device, but overadjustment is performed by elastic deformation of the rotating drum and brake shoes 12 and 14. The value is determined to allow rotation of the cable guide 48 during such an excessive brake operation, that is, when the tension of the cable 60 exceeds a predetermined constant value.

A guide portion 58 having an arcuate shape is provided at the intermediate portion in the longitudinal direction of the cable guide 48. With the intermediate portion in contact with the outer circumferential surface of the guide portion 58, the cable 60 moves between the anchor pin 20 and the adjuster lever 42. It is bridged between the middle part of This adjustment lever 42 has a torsion coil spring 62.
Therefore, the cable 60 is constantly biased clockwise in the figure, that is, in the direction in which the cable 60 is pulled. In addition, 64 and 66 are return springs that always urge the brake shoes 12 and 14 in the direction of diameter reduction, and 68 is the connection mechanism 2 of the brake shoe 12.
This is a spring for positioning both brake shoes 12 and 14 within a rotating drum (not shown) by biasing the end portion on the second side substantially in the inner circumferential direction.

Next, the automatic shoe gap adjustment operation of the dual servo type drum brake configured as above will be explained.

When the wheel is rotating in direction B in the figure, when brake fluid pressure is supplied to the wheel cylinder 30 and the pistons 32, 34 are pushed out to opposite sides, the brake shoes 12, 14 are moved by the return springs 64, 66. The coupling mechanism 22 is expanded outward using both ends as fulcrums and pressed against the inner circumferential surface of the rotating drum, and the braking torque generated in one brake shoe 12 is applied to the coupling mechanism 22. The signal is inputted to the other brake shoe 14 via. As a result, the brake shoes 12 and 14 are both rotated in the B direction (counterclockwise) on the bucking plate 10,
The end of the brake shoe 12 on the wheel cylinder 30 side is separated from the anchor pin 20 until the end of the brake shoe 14 on the wheel cylinder 30 side comes into contact with the anchor pin 20. As the end of the brake shoe 12 on the wheel cylinder 30 side moves away from the anchor pin 20, the cable 6
0 is pulled, and as a result, the adjustment lever 42 is rotated counterclockwise in the figure against the biasing force of the torsion coil spring 62. The rotation angle of this adjustment lever 42 increases with the shoe gap, and each adjustment wheel 28 is rotated slightly accordingly. Next, when the brake fluid pressure is released, the diameter of the brake shoes 12 and 14 is reduced according to the urging force of the return springs 64 and 66 until one end of each comes into contact with the anchor pin 20, and the tension of the cable 60 is reduced. As a result, the adjustment lever 42 is rotated clockwise in the figure according to the biasing force of the torsion coil spring 62 and returned to its original position (the position when braking is not applied).

When the brake shoes 12, 14 are worn and the shoe gap exceeds a predetermined upper limit, the pawl portion 46 of the adjustment lever 42 passes over one outer peripheral tooth of the adjustment wheel 28 when the brake is released, and then When the brake shoes 12 and 14 are expanded when the wheels rotate in direction B, the adjustment wheel 28 moves in the direction of decreasing the shoe gap (direction A) as the adjustment lever 42 rotates counterclockwise in the figure. is rotated by a predetermined amount. This results in
The first connecting portion 24 and the second connecting portion 26 are moved in a direction away from each other, and the brake shoe 12,
14 are pushed toward each other in the circumferential direction, thereby compensating for the increased shoe gap. Note that when the wheels are rotating in the direction opposite to direction B, the adjustment lever 42 is slightly rotated counterclockwise in the figure by the cable 60 when the brake shoe 12 is initially expanded. become. However, since the adjustment wheel 12 is then rotated toward the anchor pin 20, the tension on the cable 60 is reduced and the adjustment lever 42 is rotated clockwise to near its original position.

As a result, the amount of rotation of the adjustment lever 42 counterclockwise in the figure is smaller than when the vehicle is rotating in the B direction, so the shoe gap is adjusted only when the vehicle is rotating in the B direction. Furthermore, the B direction is preferably the backward direction of the vehicle, but may also be the forward direction.

In such a dual-servo type drum brake, when excessive brake fluid pressure is supplied to the wheel cylinder 30 when the wheel rotates in the B direction, the brake shoes 12, 14, the rotating drum, etc. are elastically deformed in the outer circumferential direction. There may be cases where In such a case, adjust the adjustment lever 4.
If the cable 60 is rotated excessively, the claw portion 46 may unnecessarily go over the outer teeth of the adjustment wheel 28, and the claw portion 46 may cause the adjustment wheel 28 to rotate unnecessarily. When the tension exceeds a certain predetermined value, the spring 52 is stretched and the cable 60
The cable guide 48 is rotated in the direction in which the tension of the cable is reduced (toward the left in FIG. 1). As a result, even though the shoe gap does not exceed a predetermined upper limit value, the adjustment wheel 28 is preferably rotated in the direction of decreasing the shoe gap by the adjustment lever 42 to be over-adjusted. Prevented. The operation of the automatic shoe gap adjustment device described above is the same even when the brake shoes 12 and 14 are opened by the parking brake lever 36 when the wheels are rotating in the B direction.

Here, FIG. 3 is a diagram showing a dual servo type drum brake equipped with a conventional shoe gap automatic adjustment device. It should be noted that the same parts as in the previous embodiment are given the same reference numerals and detailed explanations will be omitted.

In the figure, the cable guide 80 is rotatably attached at its longitudinally intermediate portion by a pin 82, and the brake shoe 12 is connected between the intermediate portion of the cable 60 guided by the guide portion 84 and the brake shoe 12. Relative movement in the radial direction is prevented. One end of the cable 60 is fixed to one end of a frame-shaped stopper member 86 located on the inner peripheral side of the brake shoe 12, and
A tension coil spring 88 for preventing overadjustment is tensioned inside the stopper member 86 in a state where contraction beyond a certain limit is prevented, and one end of the spring 88 is attached to the adjustment lever 42. There is. In this way, conventionally, the spring 88 and the stopper member 86 constituting the over-adjustment prevention mechanism are provided on the inner circumferential side of the brake shoe 12, so that the space on the inner circumferential side of the brake shoe 12 is There was a problem that it was not possible to secure a sufficient amount of

This problem was particularly noticeable in small-sized dual-servo type drum brakes.

In contrast, according to this embodiment, the cable guide 48, spring 52, etc. that constitute the over-adjustment prevention mechanism are provided on the brake shoe 12, so that the inner periphery of the brake shoe 12 is This allows for more space on the sides.

Further, according to this embodiment, since the distance between the pin 50 and the biased position of the spring 52 is set to about twice the distance between the pin 50 and the guide portion 58, the spring 52 is This has the advantage that the biasing force is reduced by approximately half compared to the conventional spring 88, and the spring 52 is further miniaturized.

In addition, in the above-mentioned embodiment, the spring 5
2 uses a tension coil spring, but it is also possible to use a compression coil spring.

In this case, for example, as shown in Figure 2,
Casing 70 fixed to brake shoe 12
A compression coil spring 72 is provided with a predetermined preload applied therein, and when the tension of the cable 60 exceeds a predetermined certain limit, it is connected to the end of the cable guide 48 opposite to the pin 50. The coil spring 7 is compressed by the tip of the rod 74.
2, move the cable guide 48 in the direction in which the tension of the cable 60 decreases (counterclockwise in the figure).
It may be made to rotate. In this case, the rod 74 and the like function as a stopper, and the above-mentioned certain limit is determined based on the preload of the compression coil spring 72, the biasing force of the torsion coil spring 62, and the like.

Further, in the above embodiment, the stopper is constituted by the stopper pin 56 and the elongated hole 54, but the cable guide 48 may be brought into direct contact with the brake shoe 12.

Further, in the embodiment described above, the adjustment wheel 28 is configured to be rotated in the direction of decreasing the shoe gap (direction A) as the adjustment lever 42 is rotated in the counterclockwise direction in FIG. However, this is not necessarily necessary, and by rotating the adjustment lever 42 clockwise in FIG.
8 may be rotated in the shoe gap decreasing direction (the opposite direction to the direction A).

Furthermore, the cable guide 48 of the above-described embodiment is
Although it is rotatably attached to the brake shoe 12 by a pin 50, it can be moved in a direction substantially parallel to the radial direction of the bucking plate 10 by providing an elongated guide hole in the brake shoe 12. There is no problem.

In addition, various changes may be made to the present invention without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a front view showing the main parts of a dual-servo type drum brake equipped with an automatic shoe gap adjustment device to which the present invention is applied. FIG. 2 is a diagram showing the main parts of another example of the present invention. FIG. 3 is a diagram showing the main parts of a dual-servo type drum brake equipped with a conventional shoe gap automatic adjustment device, and corresponds to FIG. 1. 12, 14: Brake shoe, 20: Anchor pin, 22: Connection mechanism, 28: Adjustment wheel, 42: Adjustment lever, 46: Claw, 4
8: Cable guide, 50: Pin, 52: Spring, 54: Elongated hole, 56: Stopper pin, 58:
Guide part, 60: Cable, 72: Compression coil spring, 74: Rod.

Claims (1)

[Claims for Utility Model Registration] (1) An anchor that receives braking torque transmitted to a pair of arc-shaped brake shoes when their mutually adjacent ends are brought into contact with each other, and an adjuster. a connection mechanism having a wheel that connects the other ends of the brake shoe and adjusts the shoe gap by separating the other ends as the adjustment wheel rotates in one direction; an adjustment lever that is rotatably provided on the other end side of one of the brake shoes and has a pawl that engages with the adjustment wheel in a direction that rotates the adjustment wheel in a shoe gap decreasing direction; A cable guide provided at an intermediate portion in the longitudinal direction of one of the brake shoes, and a cable guide that is bridged between the adjustment lever and the anchor via the cable guide, and the adjustment lever and the anchor are connected to each other when the brake shoe is expanded. In a dual-servo type drum brake with automatic shoe gap adjustment, the cable guide is rotatably or movably attached to one of the brake shoes, and the tension of the cable is set in advance. a spring that is stretched when a predetermined limit is exceeded and prevents over-adjustment by allowing rotation or movement of the cable guide in a direction that reduces the tension; A dual servo type drum brake with automatic shoe gap adjustment, characterized in that it is provided with a stopper that applies a predetermined preload to the spring by preventing contraction. (2) One end of the spring is mounted at a position away from the center of rotation by a distance greater than the distance between the center of rotation of the cable guide and the point of force applied to the cable guide by the cable. The dual servo type drum brake with automatic shoe gap adjustment according to claim 1, which is a utility model registered as claimed in claim 1.