JPH0353074Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a dust boot for a wheel cylinder for a drum brake.

Prior Art Generally, in a wheel cylinder for a drum brake, a dust boot has an annular first attachment part and a second attachment part.The first attachment part is attached to the outer peripheral surface of the wheel cylinder, and the second attachment part is attached to the wheel cylinder. The pistons are fitted into annular grooves formed on the outer circumferential surface of a piston that is fitted so as to be able to protrude therein, respectively, by being fitted with a predetermined tightening force. When brake fluid is supplied into such wheel cylinders, the air inside the wheel cylinders is vented by creating a negative pressure in the wheel cylinders prior to supplying the brake fluid.

Problems to be Solved by the Invention However, by creating a negative pressure state inside the wheel cylinder, negative pressure is created inside the dust boot through a small gap between the inner wall of the wheel cylinder and the outer peripheral surface of the piston. In this case, as the dust boot is deformed, a force may be applied to the second attachment portion of the dust boot in the outer circumferential direction, causing the second attachment portion to expand relatively largely in the outer circumferential direction. It was hot. In such a case, there is a risk that outside air will be sucked in between the inner circumferential surface of the second mounting portion and the outer circumferential surface of the piston, making it impossible to bleed air from the wheel cylinder sufficiently.

On the other hand, it is considered that by providing the second attachment part with a metal ring whose diameter cannot be expanded, it is possible to suitably prevent the second attachment part from expanding in the outer circumferential direction. However, even in this case, there are still problems to be solved. That is, when attaching the second attachment part to the annular groove, it is normally necessary to expand the diameter of the second attachment part while elastically deforming it in the outer circumferential direction. If the second mounting part is installed in the annular groove, the diameter of the second mounting part will be prevented from expanding not only when air is removed due to negative pressure but also when the second mounting part is installed. In addition to making the work difficult, in order to make the installation work easier, it is necessary to install the second mounting part in a divided state at the part where the annular groove is formed in the piston, which increases the number of man-hours for the installation work. It is difficult to avoid.

Means for Solving the Problems The present invention was developed against the background of the above-mentioned circumstances, and its purpose is to more reliably bleed air from the negative pressure inside the wheel cylinder, and to To provide a dust boot whose second attachment part can be easily attached to a piston and which does not require a large number of man-hours.
In order to achieve this object, the present invention has a first mounting part and a second mounting part that are annular, the first mounting part being attached to the outer peripheral surface of a drum brake wheel cylinder, and the second mounting part being attached to the wheel cylinder. The dust boot is fitted with a predetermined tightening force into an annular groove formed on the outer circumferential surface of a piston fitted so as to be able to protrude into the cylinder. It is characterized by providing an elastic annular member whose diameter can be expanded by a force that exceeds the force in the outer circumferential direction that acts on the second attachment portion when the inside is brought into a negative pressure state.

Function and Effects of the Invention By doing this, the diameter of the elastic annular member will not expand due to the force in the outer circumferential direction that acts on the second mounting portion when the inside of the dust boot is in a negative pressure state. This elastic annular member can suitably prevent the second mounting portion from expanding in the outer circumferential direction, and can more reliably bleed air due to the negative pressure within the wheel cylinder. When added to the second attachment part, the elastic annular member can be elastically deformed and expanded in diameter together with the second attachment part;
Compared to installing a metal ring that cannot be expanded in diameter,
The work of attaching the second attaching part to the annular groove can be made easier, and there is no need to attach the second attaching part with the piston divided at the part where the annular groove is formed. Man-hours can be reduced.

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

FIG. 2 is a diagram showing an example of a drum brake equipped with a wheel cylinder having a dust boot to which the present invention is applied, and 10 is a packing plate. On the packing plate 10, a pair of brake shoes 12, 14 are supported by shoe hold-down devices 16, 18 so as to be expandable to each other, and one end of the brake shoes 12, 14 facing each other is attached to a packing plate. The other ends of the brake shoes 12 and 14 are in contact with both ends of the wheel cylinder 22 fixed on the packing plate 10. They are engaged with each other. Note that 24 and 26 are shoe return springs, and 27 is a rotating drum.

As shown in FIGS. 1 and 2, the wheel cylinder 22 includes a cylinder body 30 having a cylinder bore 28 extending therethrough;
A pair of piston members 32 and 33 (only 33 is shown in FIG. 1) are fitted into the cylinder bore 28 so as to be able to protrude in opposite directions.
It is composed of: piston member 32,
Reference numeral 33 constitutes the piston of this embodiment, and is composed of a piston body 34 and an engaging portion 36 having a smaller diameter. An annular groove 38 having a predetermined depth and width is formed therebetween, and an engagement groove 40 extending in the radial direction is formed on the distal end surface of the engagement portion 36, and the engagement groove 40 is formed in the cylinder bore 28 in the piston body 34. They are fitted, and are adapted to be engaged with the other ends of the brake shoes 12, 14 within the engagement grooves 40.

At both ends of the wheel cylinder 22 in the axial direction,
As shown in FIG. 2, dust boots 48, 50 are provided which are made of an elastically deformable material such as a rubber material. In addition, these dust boots 48, 50
Since the dust boots 50 are constructed in the same way, the following explanation will be given only for one dust boot 50. As shown in FIG. 1, the dust boot 50 includes a first annular attachment portion 52, a second attachment portion 54 having a smaller diameter, and connects the first attachment portion 52 and the second attachment portion 54 to each other. A state in which the first mounting portion 52 has a predetermined tightening force within an annular groove 58 formed at the end in the axial direction of the wheel cylinder 22. At the same time, the second mounting portion 54
is fitted into the annular groove 38 of the piston member 33 with a predetermined tightening force.

Here, in this embodiment, the dust boots 5
A coil spring 60 curved into an annular shape is buried inside the second mounting portion 54 of No. 0 . This coil spring 60 is embedded in the second mounting portion 54 when the dust boot 50 is molded. The coil spring 60 constitutes the elastic annular member of this embodiment, and is attached to the dust boot 5.
When the inside of 0 is in a negative pressure state, the second mounting part 5
The wire diameter of the wire constituting the coil spring 60 is determined in advance so that the coil spring 60 can be expanded in diameter while being elastically deformed by a force exceeding the force in the outer circumferential direction acting on the coil spring 60 .

In the drum brake configured as described above, before supplying brake fluid to the fluid chamber 62 in the wheel cylinder 22, the air in the fluid chamber 62 is vented by bringing the fluid chamber 62 into a negative pressure state. is being carried out. In this case, by bringing the liquid chamber 62 into a negative pressure state, the cylinder bore 28
When a negative pressure is applied to the inside of the dust boot 50 through a small gap between the inner circumferential surface and the outer circumferential surface of the piston body 34, the connection part 56 of the dust boot 50 deforms and the second attachment A relatively large force may be applied to the portion 54 via the connecting portion 56 in the outer circumferential direction. At this time, in this embodiment, a coil spring 60 is provided inside the second attachment part 54, and when the inside of the dust boot 50 is brought into a negative pressure state, the coil spring 60 acts on the second attachment part 54 in the outer circumferential direction. Because the diameter of the coil spring 60 cannot be expanded depending on the force of the coil spring 6
0, the second mounting portion 54 is preferably prevented from expanding in the outer circumferential direction, and the wheel cylinder 22
On the other hand, when a force exceeding the above-mentioned force is applied to the second attachment part 54, the coil spring 60 is elastically deformed together with the second attachment part 54 and expands in diameter. As a result, the annular groove 3 of the second mounting portion 54 is
8 becomes easier, and there is no need to attach the second attachment part 54 with the piston member 33 divided at the part where the annular groove 38 is formed, which reduces the number of man-hours required for the attachment work of the second attachment part 54. Reduced.

In the above-described embodiment, the coil spring 60 is provided inside the second mounting portion 54, but it is not necessary to do so. For example, as shown in FIG. An annular groove 64 may be formed and the coil spring 60 may be provided within the groove 64. In this case, the groove 64
When the coil spring 60 is fitted into the groove 64 of the shape shown in FIG. 4, for example, the portions of the second mounting portion 54 located on both sides of the groove 64 are pressed in opposite directions. With this configuration, in addition to obtaining the same effects as in the above-described embodiment, it is possible to suitably ensure the adhesion of the second mounting portion 54 to both side walls of the annular groove 38, thereby reducing the negative impact inside the wheel cylinder 22. This has the advantage of further improving air removal properties due to pressure.

Further, in the above-described embodiment, the elastic annular member is constituted by the coil spring 60, but this is not necessarily necessary, and it is also possible to constitute it by, for example, a rubber ring.

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 an enlarged sectional view of section A in FIG. 2. FIG. FIG. 2 is a front view showing the main parts of a drum brake equipped with a wheel cylinder having a dust boot to which the present invention is applied. FIG. 3 is a diagram showing another example of the present invention, and corresponds to FIG. 1. FIG. 4 is a diagram for explaining still another example of the present invention, and is a sectional view of a main part of the dust boot before installation. 22: Wheel cylinder, 32, 33: Piston member (piston), 38: Annular groove, 48, 5
0: dust boot, 52: first attachment part, 54: second attachment part, 60: coil spring (elastic annular member).

Claims (1)

[Claims for Utility Model Registration] (1) A first mounting part and a second mounting part are formed in an annular shape, and the first mounting part is attached to the outer peripheral surface of a wheel cylinder for a drum brake, and the second mounting part is attached to the outer peripheral surface of a wheel cylinder for a drum brake. A dust boot is fitted with a predetermined tightening force into an annular groove formed on an outer circumferential surface of a piston that is fitted so as to be able to protrude into a wheel cylinder, wherein the dust boot is attached to the second mounting portion. A wheel cylinder for a drum brake, characterized in that it is provided with an elastic annular member whose diameter can be expanded by a force exceeding a force in the outer circumferential direction that acts on the second mounting part when the inside of the cylinder is brought into a negative pressure state. dust boots. (2) Utility model registration claim 1, wherein the elastic annular member is an annularly bent coil spring.
Dust boots for drum brake wheel cylinders as described in section.