JP2006275120A - Piston for brake cylinder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To devise a piston structure, so as to extremely stabilize the fitting relationship between a cylinder and a piston base of a seal part even in an overheat state, by minimizing heat transfer to the piston base for a brake cylinder. <P>SOLUTION: In this piston for the brake cylinder, a seal R is fitted in an annular groove of the outer periphery of a piston base side part 2b, and this seal is brought into pressure contact with an inner surface of the cylinder 1. In the piston for the brake cylinder, the piston is divided into a pad side part 2a and the piston base side part 2b, and is formed into a composite structure of joining the pad side part 2a and the piston base side part 2b; the joining of the pad side part 2a and the piston base side part 2b is press-in fitting; the pad side part 2a is composed of a material having high heat resistance and low heat conductivity; and the piston base side part 2b is composed of a material having the same linear expansion coefficient as the cylinder 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piston for a brake cylinder, and relates to a piston for a brake cylinder that is required to exhibit high performance under severe thermal conditions, and is stable even under extremely severe thermal conditions. Thus, high braking performance can be exhibited.

  The brake cylinder piston is provided with a seal between the piston and the cylinder inner surface, and is pushed out by the operating pressure of the brake oil while elastically deforming the seal. The piston is overheated to a high temperature in response to the frictional heat of the brake surface. In order to maintain high braking performance stably even under harsh operating conditions, the friction characteristics of the brake pad should be maintained, but even under such conditions, the sealing function by the seal and the rollback function Must be ensured. For this purpose, a composite structure composed of a metal member having high heat resistance and a synthetic resin material having high heat insulation is known (Japanese Patent Laid-Open No. 7-77230). This has the structure shown in FIGS. 4 and 5, the brake pad side portion is the first member 11 made of a metal member having high heat resistance, and the piston base side portion (the side far from the brake pad) is a highly heat-insulating composite. A second member 12 made of a resin material is used, and a seal 14 fitted in an annular groove on the inner surface of the cylinder 13 is pressed against the sliding portion 11 a of the first member 11.

  Moreover, although not publicly known, an annular groove is provided on the outer periphery of the piston base side, a seal is fitted into the groove, and the brake pad side is made porous to suppress heat transfer to the piston base side. 6 has a structure shown in FIG. 6, and the piston 20 is not a composite structure, and a large number of holes 22 are provided on the brake pad side 21 to make it a porous material (reducing heat conductivity). A seal is fitted into the annular groove 23 on the outer periphery of the base side, and this is pressed against the inner surface of the cylinder. This prevents overheating of the seal due to the heat of the brake pad and significantly reduces the mounting of the seal in the brake cylinder assembly process. Easy and simple.

For pistons in automobile brake cylinders, heat transfer to the brake hydraulic oil side is suppressed, and the fitting relationship between the cylinder and piston is stable and high sealing characteristics are maintained even in an overheated state. Is required. It is difficult for the above-mentioned prior art to meet both of these requirements, and particularly when used under severe thermal conditions. On the other hand, if the stability of the fitting relationship between the piston and cylinder seals in an overheated state is not maintained, the amount of brake fluid and drag characteristics may not be stable, and the brake characteristics may become unstable. Will increase.
JP-A-7-77230

  The object of the present invention is to meet the above-mentioned demands. Heat transfer to the piston base of the brake cylinder piston is suppressed as much as possible, and the fitting relationship between the cylinder and the piston base is extremely stable even in an overheated state. The piston structure should be devised.

Means for solving the above-mentioned problems are constituted by the following (a) to (c) with respect to a brake cylinder piston in which a seal is fitted in an annular groove on the outer periphery of the piston base side part and pressed against the cylinder inner surface. Is.
(A) The piston is divided into a pad side part and a piston base side part, and is a composite structure in which the pad side part and the piston base side part are coupled;
(B) The above-mentioned coupling between the pad side and the piston base side is press-fit.
(C) The pad side portion is made of a material having high heat resistance and low thermal conductivity, and the piston base side portion is made of a material having the same linear expansion coefficient as that of the cylinder.

[Embodiment 1]
Embodiment 1 is that the pad side portion is made of any of stainless steel, titanium alloy, and synthetic resin.
[Embodiment 2]
The second embodiment is that the cylinder is made of an aluminum alloy and the piston base side portion of the piston is made of an aluminum alloy.
[Embodiment 3]
Embodiment 3 is that the pad side portion and the piston base side portion that are joined by press-fitting by tightening allowance are also fixed by a plurality of screws.

The piston is divided into a pad side and a piston base side, and is a composite structure in which the pad side and the piston base side are combined. The pad side and the piston base side are press-fit. Since they are joined together, there is a high degree of freedom in selecting materials for the pad side and piston base side.
Therefore, it is easy to configure the pad side portion with high heat resistance and low heat transfer, and the piston base side portion can be configured with a material having a linear expansion coefficient equivalent to that of the cylinder.

Since the pad side is made of a material with high heat resistance and low thermal conductivity, the strength of the pad side is maintained even in an overheated state, and overheating to the piston base side is suppressed as much as possible. The Since the piston base side portion is made of a material having the same linear expansion coefficient as that of the cylinder, the same amount of the piston base side portion and the fitting portion of the seal portion interposed between the cylinders is the same amount. Because the cylinder only expands, the interference in the radial direction of the cylinder does not change, the thermal influence is suppressed as much as possible, and the fitting relationship is extremely stable without any particular change even in the overheated state. The rollback of the seal having the base side portion interposed in the fitting portion with the cylinder (retraction action for the piston by the seal) is stabilized.
Therefore, even under a severe heat condition, the brake characteristics (fluid amount, drag) are stabilized and a high braking force is exhibited.
Further, according to the third embodiment, the pad side portion and the piston base side portion, which are joined by press-fitting, are also fixed by a plurality of screws, so that the fixing relationship between the pad side portion and the piston base side portion is further increased. Strengthened and the bond is stable.

Next, examples will be described with reference to the drawings.
The caliper of this embodiment is made of an aluminum alloy (A6061), and therefore the cylinder 1 is made of the same aluminum alloy. The piston 2 is of a type in which an elastic seal R is mounted in an annular groove provided on the outer periphery of the piston base side, and includes a cylindrical pad side portion 2a and a cup-type piston base side portion 2b which are separate from each other. It is a composite type. The right end small diameter portion of the pad side portion 2a is press-fitted and fitted inside the piston base side portion 2b (with a fitting length of 4 mm), and a hexagon socket set screw 3 is screwed and fixed in the radial direction. The pad side portion 2a is made of a titanium alloy having extremely low thermal conductivity, and the piston base side portion 2b is made of the same aluminum alloy as the cylinder 1 (A6061). The outer diameter of the piston 2 is 31 mm, its total length is 34 mm, and the length of the pad side portion 2a is 23 mm (see FIG. 1).

Incidentally, the thermal conductivity of the aluminum alloy is 170 W / mK, whereas the thermal conductivity of the titanium alloy is 7.5 W / mK.
The cylinder 1 and the piston base side portion 2b are both made of an aluminum alloy, and their linear expansion coefficients are equal to (19 to 24) × 10 ⁻⁶ .
Further, the material of the pad side portion 2a may be stainless steel, and its thermal conductivity is 16 W / mK.
A seal characteristic comparison test by changing the liquid amount was performed on the titanium piston having the same shape as the above example (comparative example). The result is as shown in FIG.

Data A in FIG. 2 shows seal characteristics in which the brake operating pressure is on the horizontal axis and the piston stroke (fluid amount) is on the vertical axis in Examples and Comparative Examples at normal temperature. Data B shows the sealing characteristics of the example at an operating temperature of 200 ° C., and data C shows the sealing characteristics of a comparative example at an operating temperature of 200 ° C. The liquid volume increase rate in this example is 10% or less, and it is clear that the liquid volume increase rate in the comparative example is a little less than 40%. This example has extremely high sealing characteristics even at an operating temperature of 200 ° C. It turns out that it is stable.
When the cylinder is cast iron, the side of the piston base is made of a material having the same or equivalent linear expansion coefficient. However, the integral coupling means for the pad side and the piston base side is basically press-fit. Therefore, the connection between the pad side portion and the piston base side portion is reliable regardless of the material of both.

FIG. 3 shows another specific example. The pad side portion 2a is made of stainless steel (SUS304), and a plurality of holes 2c are provided at the end of the pad side portion 2a to form a porous material. This is an example in which the thermal suppression effect is enhanced, and the fitting portion between the pad side portion 2a and the piston base side portion 2b is more firmly fixed by a hexagon socket set screw 3.
In addition, although this content has shown the example by which the seal | sticker was fitted by the piston base side part, even if the seal | sticker is fitted by the cylinder side, the pad side part of a cylinder and a piston is comprised with the material of an equivalent linear expansion coefficient. Needless to say, the same effect can be obtained.

These are sectional drawings of an Example. These are the graphs which show the sealing characteristic result of an Example and a comparative example. These are sectional drawings of the modification of an Example. These are sectional drawings of a prior art example. These are sectional drawings of the brake device using a prior art example. (A) is a side view of a piston according to the prior art, and (b) is a sectional view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cylinder 2 ... Piston 2a ... Pad side part 2b ... Piston base side part 3 ... Hexagon socket set screw R ... Seal

Claims (5)

A piston for a brake cylinder in which a seal is fitted in an annular groove on the outer periphery of the piston base side, and this is pressed against the inner surface of the cylinder,
The piston is a composite structure consisting of a pad side and a piston base side,
Piston for brake cylinder, the piston base side is made of a material with the same linear expansion coefficient as the cylinder.   2. The brake cylinder piston according to claim 1, wherein the pad side portion and the piston base side portion are divided, and are joined by press fitting.   The brake cylinder piston according to claim 2, wherein the pad side portion and the piston base side portion joined by press-fitting are also fixed by a plurality of screws.   4. The brake cylinder piston according to claim 1, wherein a pad side portion of the piston is made of stainless steel, titanium alloy, or synthetic resin.   5. The brake cylinder piston according to claim 1, wherein the cylinder is made of an aluminum alloy and the piston base side portion of the piston is made of an aluminum alloy.

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