JPS6231731A - Piston for brake device - Google Patents

Abstract

PURPOSE:To reduce the generation of vapor lock and to increase the thickness of a friction material, by forming a part in the outer peripheral section of a plastic piston, which is arranged to make slidable contact with a piston seal, of materials having a high hardness, such as, for example, metal and ceramic. CONSTITUTION:A piston body 1 made of plastic materials such as, for example, highly heat-resistant phenol resin having a low heat conductivity, is formed therein with a cavity 2 and a hydraulic pressure receiving surface 3 and is molded therein with an annular slidable contact member 4 made of ceramic and having a sliding surface 4a for a piston seal S. In this arrangement, the annular ring 4 is formed therein with a tapered surfaces 4b with which it has a tapered end to prevent from moving relative to the piston body 1 and from coming off, and a flange part 4c.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates in particular to a piston for a disc-type brake device for automobiles.

[Conventional technology]

Generally, in a disc-type brake device, as shown in a partial view in Fig. 1, a disc D, which is interlocked with a rotating body of a wheel, is brought into pressure contact with pads P1 and P2 under the action of a piston Q. , the frictional force with the disc D applies braking force to the rotation of the wheel. In this way, since the braking action is performed by the frictional force when the pads P, P2 are slid in pressure contact with the disc D, a large amount of heat is generated during braking, and this heat is transferred to the entire brake system, especially when The heat from pads P, P2 is on the back metal of the band, M! From piston seal S1 dust seal G
This results in the heating of the brake oil L in the cylinder C that drives the piston Q. According to an example of measuring the temperature rise during the operation of such a brake device, the temperature of the pads P1 and P2 reaches approximately 400°C, and the brake oil L in the cylinder C reaches a high temperature of 120°C, especially the rubber dust seal G and the piston. Seal S may deteriorate significantly, leading to oil leakage due to seal failure, or may cause vapor lock due to oil deterioration, which may lead to serious consequences due to deterioration of brake performance.

In order to avoid such inconveniences, there was a system as shown in FIG. In other words, as shown in the figure (a), the insulation material R is interposed between the pad P and the back metal M, and the figure (b) (
As shown in c), there is a heat insulating material R between the back metal M and the end of the piston Q.
There was something that intervened.

[Problems with conventional technology]

Such conventional brake devices mainly have the following problems.

■ In the limited axial space, the height of the friction material is reduced, resulting in reduced pad life.

■ This results in an increase in the number of parts and higher costs.

■ If the insulation material is installed incorrectly, it may cause vapor lock in the worst case.

■ On the other hand, pistons made of plastic such as phenolic resin have low thermal conductivity and are difficult to cause vapor lock, but the corners of the grooves where the piston seal S and dust seal G provided on the piston Q and cylinder C sides There was a great risk that wear would occur and the airtightness would gradually be lost.

[Means for solving problems]

In view of the above circumstances, the present invention consists of a piston body made of lightweight plastic with excellent heat insulation properties, and only the area on the outer periphery of the piston body where the piston seal makes sliding contact with metal, carbide, or cermet with excellent wear resistance. It is characterized by being made of ceramic material.

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described in detail with reference to the drawings.

Figures 2(a) and 2(b) show central longitudinal sectional views of the piston body l according to the present invention. The piston body 1 is made of plastic such as phenolic resin, which has low thermal conductivity and heat resistance, and has a cavity 2 and a hydraulic receiving surface 3.
An annular sliding member 4 made of a ceramic material and having a sliding surface 4a of a piston seal S on its outer peripheral portion is molded onto a plastic body.

In this case, the annular ring 4 has a tapered surface 4 to prevent it from moving or detaching from the piston body 1.
b and flange part 4c. 1
It is.

Further, as in the embodiment shown in FIG. 4(b), grooves 4d may be formed concentrically in the annular sliding member 4 to increase the connection with the piston body l.

By the way, such a plastic piston body 1
The annular sliding contact body 4 that is integrally molded with the mold may be made of a ceramic material such as alumina, silicon nitride, silicon carbide, forsterite, or mullite, or may be made of metal such as steel or aluminum. In addition, any material such as carbide or cermet may be used as long as it has a harder hardness than at least the plastic material that constitutes the piston body 1. The coefficient of thermal expansion of this plastic material (15 to 30 x 10-'/'c for phenolic fiber-reinforced resin) is higher than that of ceramic material (4.3 x 10-'/'c for mullite).
c, alumina 7. lXl0-6/"C) as well as metal materials (10 to 20 x 10-'/"C for steel materials)
+ Since it is considerably larger than 20X10-'/''C) for aluminum, even if the temperature of the piston body 1 rises due to brake operation, there will be a gap between it and the annular sliding body 4 based on the difference in thermal expansion. There is no risk that this will occur; in fact, a pressing force will act on the annular sliding member 4, but even if the annular sliding member 4 is made of ceramic material, there is no risk of damage. If the surface roughness of the sliding surface 4a, which is the outer surface of the contact body 4, is finished to about 0°2 Ra, there is no risk of premature wear of the piston seal S or loss of airtightness.

By the way, as a result of testing the piston according to the embodiment of the present invention using a dynamometer, no damage was observed on the sliding surface. In addition, when the heat transfer characteristics of the piston according to the embodiment of the present invention shown in FIG. 2 (a) was investigated, the heat transfer characteristics of the piston in which the annular sliding member 4 made of alumina ceramic was molded on the piston body l according to the embodiment of the present invention were as shown in the graph shown in FIG. 4. The temperature rise on the piston surface was low, that is, the temperature rise characteristics were almost similar to those of plastic pistons, which have the highest thermal insulation properties.

As a means of measuring the temperature rise (heat transfer characteristics) on the piston surface shown in Fig. 4, as shown in Fig. 3, a heating plate N (corresponding to a brake disc) with an electric heater H disposed at the bottom is used. On the other hand, a method is used in which the piston body Q is placed on the pad P and the back metal M, and the relationship between the temperature increase at the center point A of the top surface of the piston body Q and the elapsed time after the piston body Q is placed on the hot plate N is investigated. [Effects of the Invention] According to the piston for a brake device of the present invention, the piston body is made of a plastic material with excellent heat insulation properties, and only the portion where the piston seal slides is made of a ceramic material.
Since it is made of a material such as cermet that is harder than the synthetic resin that makes up the piston body, the frictional heat during brake operation is difficult to transfer to the brake oil through the piston, which greatly reduces the occurrence of vapor lock. Since the heat insulating property is good, there is no need to provide a separate heat insulating material, and the thickness of the friction material can be increased by that much, thereby extending the life of the brake device. In addition, only the sliding contact area of the piston seal is made of a large wear-resistant ceramic material, so the airtightness will not deteriorate even after long or harsh use, and the lightweight piston provides stable braking. Performance can be maintained over a long period of time.

[Brief explanation of drawings]

Figure 1 is a sectional view of a conventional brake device, and Figure 2 (
A) and B) are both sectional views of a piston for a brake device according to an embodiment of the present invention. FIG. 3 is a schematic side view of a device for measuring temperature rise characteristics of a piston for a brake device, and FIG. 4 is a graph showing the relationship between temperature rise and elapsed time for a piston for a brake device according to the conventional technology and the present invention. . FIG. 5 is a sectional view showing only the main parts of a conventional brake device. 1: Piston body 2: Cavity 3: Hydraulic pressure receiving surface 4: Annular sliding contact body 4a: Sliding contact surface

Claims (1)

[Claims] The cylindrical piston body with one end open is made of plastic, and the area on the outer periphery of the piston body where the piston seal slides is made of a material harder than plastic, such as metal, carbide, cermet, or ceramic. Features piston for brake equipment.