JPS599326A - Disc brake pad - Google Patents

Abstract

PURPOSE:To prevent heat from transmitting from a disc brake pad to a shim or a caliper piston and consequently prevent the temperatures of the shim and the brake fluid from rising by a structure wherein a flexible graphite sheet layer is provided in the disc brake pad. CONSTITUTION:A disc brake pad consists of a friction material 3, a back metal 4 lined with a flexible graphite sheet layer at its back and further, if necessary, a protective layer 12 made of sheet plate. The frictional heat generated between the surface of the friction material 3 and the disc is transmitted to the flexible graphite sheet layer 11. Because the heat conductivity of the flexible graphite sheet in the direction of its face is about three times as large as that of steel and is nearly equal to that of aluminum, the transmitted heat is quickly diffused in the direction of the face of the graphite sheet and radiated to the open air. On the other hand, because the heat conductivity of the flexible graphite sheet in the direction of its thickness is one-thirtieth of that in the direction of its face or about one-tenth of that of steel, the flexible graphite sheet has sufficient heat insulating effect.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a disc brake pad, and more particularly, a flexible graphite layer is used to reduce the transmission of frictional heat generated between a friction material and a disc toward a caliper piston. The present invention relates to a disc brake pad provided with.

A disc brake pad is made of a friction material and a backing metal, and the two are generally bonded together by a phenolic resin which is an inner layer for the friction material.

Fig. 1 shows the configuration of a conventional disc platen and its peripheral parts. In Fig. 1, 1 is a disk,
2 is a disc brake pad, 3.3' is a friction material, 4.
4' is the back metal, 5 is the caliper piston, 6 is the boot, 7
is a seal, 8 is a cylinder, 9 is brake fluid, and lO is a caliper. The friction material 3 of the disc brake pad 2 is manufactured by compression molding asbestos or steel wool, graphite, metal powder, barium sulfate, etc. using a phenol resin as a binder. The back plate 4 is generally made of metal such as stainless steel, and the caliper piston 5 is made of chrome-plated steel. When the disc brake operates, that is, during braking, frictional heat is generated between the disc 1 and the friction material 8. The amount of heat increases as the vehicle speed increases when braking starts; in other words, kinetic energy is converted into thermal energy. As a result, the surface of the friction material generally reaches a temperature of 51)0°C or higher, the phenol resin in that area is decomposed and carbonized, and the friction material is worn out. This heat is transferred from the friction material to the brake fluid 9 via the metal back plate 4 and piston 5. As a result, the temperature of the brake fluid 9 increases and there is no problem during normal driving, but if you use the brakes frequently on steep downhill slopes, the so-called paper lock phenomenon occurs, where the brake fluid no longer functions properly. It is extremely dangerous.

This tendency is higher than that of friction materials using asbestos.
It is strongly rubbed in a friction material using large pieces of steel wool. When a brake with a friction material made of asbestos is tested in extremely frequent use, the temperature of each part is 500°C or more on the surface of the friction material 3, and 850 to 500° at the boundary between the friction material 3 and the back metal 4. The temperature is 300°C to 350°C on the back side of the C1 disc brake pad 2, 150°C to 250°C on the cutter piston 5, and even higher with a friction material made of steel wool. Furthermore, in order to prevent the generation of noise from the disc brake, a shim having a vibration energy absorbing layer made of a viscoelastic material such as synthetic rubber is provided between the disc brake pad 2 and the caliper piston 5. However, since the temperature of the back surface of the disc brake pad rises above F'1ano°C, the temperature of the viscoelastic material is expected to rise above 200°C, and at such high temperatures, the viscoelastic properties of synthetic rubber etc. It must be considered that not only will substances not be able to fully demonstrate their functions, but their physical properties will also be accelerated.

In order to solve these problems, consideration has been given to insulating the back metal and the caliper piston by using resin to prevent the temperature of the shim or brake fluid from rising. However, the backing metal is required to have heat resistance of 300° C. or more and high compression resistance and shear resistance at high temperatures, and it is extremely difficult to achieve this with resin. In addition, caliber pistons are required to have heat resistance of 200'C or higher, stable sliding characteristics at that temperature, strength, and mechanical stability over a wide temperature range, and physical and chemical changes occur with brake fluid. It is difficult to simultaneously satisfy these conditions with a resin.

The present invention was made in view of the problems of the prior art, and by providing a flexible graphite sheet layer on the disc brake pad, heat transfer from the disc brake pad to the shim or caliper piston is improved. prevent,
The purpose is to prevent the temperature of the shim and brake fluid from rising.

The disc brake pad of the present invention is characterized in that a flexible graphite sheet is provided on the back surface of the back metal.

FIG. 2 shows an example of a disc brake pad according to the present invention. A protective layer 12 is provided.

Flexible graphite sheet used in the present invention)

Graphite with highly layered crystals such as natural graphite, Kitssie graphite, and pyrolytic graphite is crushed into foil-like pieces and subjected to an oxidation reaction using an oxidizing agent such as potassium permanganate in concentrated sulfuric acid to form crystals. A glabellar compound is formed between the layers. After the reaction, thoroughly wash with water, dry, and then rapidly heat to 800-1000°C.
When heated to a temperature of
It expands by 200 times to obtain caterpillar-shaped particles (hereinafter referred to as expanded graphite particles). A flexible graphite sheet is obtained by calender roll molding or compression molding of the expanded graphite particles. Nika film (
Known examples include Nippon Carbon Co., Ltd.), Graph Oil (Union Carbide), and Palcaff Oil (Nippon Barca).

This method is suitable for mass production, but it has high density (1,6
Since it is difficult to obtain a product with a diameter of 97cm8 or more, a high-density product can be obtained by first punching out a roll-formed product into the desired shape and then compression-molding it.

In the method of directly compression molding expanded graphite particles, the bulk density of the particles is extremely small and difficult to handle, so a method of granulating them has been proposed.

The first characteristic of flexible graphite sheets with a density of 1.5 is
Shown in the table. The physical properties in Table 1 that are particularly useful for the present invention are anisotropy of thermal conductivity, temperature range of use in air, and compression recovery. The thermal conductivity of the sheet in the in-plane direction is t 20 K
Ca'/m=hr, "c", which is 3 to 4 times thicker than that of copper, and the thermal conductivity in the thickness direction is one-thirtieth of that.Also, the sheet must not contain organic matter. Its initial properties are stable within the operating temperature range of 1200°C to 450'C.The compression properties of the sheet are shown in Figure 8 (initial density 1.
59/cm81°Next, the density of the flexible graphite sheet used in the invention will be explained.

When the brake is applied and the caliper piston pushes the disc brake, the flexible graphite sheet absorbs the pressure. In other words, the flexible graphite sheet is compressively deformed and the distance the friction material moves toward the disc is small. This is not desirable in terms of the original function of the brake. This VC is judged by the amount of strain when a surface pressure (compressive stress) of 300 kg/C, m'' is applied, and the strain is 50
It needs to be less than μ, preferably less than 85 μ.

Table 2 shows the relationship between compressive stress of 800 kg/Cm5t and compressive strain rate of flexible graphite sheets of various densities.

Next, Table 3 shows the relationship between the sheet thickness x1 when the compressive strain is 50μ, the sheet thickness key y and the sheet density when the compressive strain is 35μ. If the thickness of the sheet is thicker than X or y, the strain will be greater than 50μ or 35μ, which is not suitable for practical use.

The one with a density of 1.09/m8 has a tensile strength of 40 kg/m8.
Since the thickness is +2, a thickness Q of 1lfi is extremely weak in terms of strength, and a thickness of 0.1lfi is not suitable for implementing the present invention because a sufficient heat insulation effect cannot be expected. Also density 1
．． Those with a value of 99A+n8 or higher are extremely difficult to manufacture and are therefore not suitable for practical use. For these reasons, the present invention has a density of 1.
．． 2~1.9ri/cm8, thickness 0.08~0.8+m
, preferably 1.4 to 1. It is appropriate to use a flexible graphite sheet of qg/cm8. More preferably density 1
．． 5 to 1.72/crn8 and a thickness of 0.2 to 0.5 mm is preferably used.

In the present invention, adhesion is a suitable method for attaching the flexible graphite sheet to the disc brake pad body.

Since the adhesive needs to have good heat resistance, thermosetting resin-based adhesives are generally suitable. In practice, a liquid phenolic resin adhesive may be uniformly applied to the bonding surface, followed by heat-pressure bonding.

The disc brake pad of the present invention has the flexible graphite sheet attached to the back surface of the metal backing, and in the first preferred embodiment, a protective layer is further provided thereon. The protective layer is made of stainless steel or chrome-plated steel, or a fiber-reinforced synthetic resin plate. There is no problem with heat resistance and strength with stainless steel or chrome-plated steel sheets, but in the case of fiber-reinforced synthetic resin sheets, sufficient attention must be paid to heat resistance and strength. Therefore, it is preferable to use a thermosetting resin reinforced with glass fiber, carbon fiber, metal fiber, alumina fiber, silicon carbide fiber, aromatic polyamide fiber, or boron fiber. As the thermosetting resin, it is appropriate to use a phenol resin in consideration of heat resistance, cost, and adhesiveness. Adhesion is a common method for attaching the protective layer to the flexible graphite sheet. The adhesive used is the same as that used for adhering the flexible graphite sheet layer to the disc brake body. Another method other than gluing is to attach the protective plate to the disc brake pad body using screws, screws, etc. When using this method, there is no need to glue the flexible graphite sheet to the disc brake body. Instead, the IC can be removed between the disc brake pad body and the plate serving as the protective layer, and then the protective layer can be attached to the disc brake pad body.

In a second preferred embodiment of the invention, an eight-layer thermal insulation laminate comprising a flexible graphite sheet with protective layers on both sides is attached to the back side of the backing metal. This heat insulating laminate may be used by adhering to the back metal, but it can also be used without adhesion. Using it without adhesion is more effective as it absorbs vibrations from the disk better. In this three-layer heat insulating laminate, two protective layers are used, and as shown in FIG. 4, the protective layer A1B is on the back metal 4 side, and the protection layer B14 is on the caliper piston 5 side.

Protective layer shell 18, flexible graphite sheet) 11. The protective layers 14 are bonded to each other. In the example shown in FIG. 4, the protective layer 13 is not bonded to the back metal.

Since the disc brake pad of the present invention has a flexible graphite sheet layer on the back surface of its back metal, the frictional heat generated between the surface of the friction material and the disc is transmitted to the flexible graphite sheet layer. The thermal conductivity of this flexible graphite sheet in the plane direction is about three times that of steel, which is close to that of aluminum, and heat quickly diffuses in the plane direction and is radiated into the atmosphere. On the other hand, the thermal conductivity in the thickness direction of a flexible graphite sheet is 1/30 of that in the in-plane direction.
Since it is about 1/10th that of steel, the insulation effect is H. In addition, since flexible graphite sheets do not contain organic substances,
Stable in oxidizing atmosphere from 0Q''C to 450°C)
The characteristics can be stably developed above ano'c, which is the temperature when the brake is used.

For these reasons, the disc brake pad of the present invention diffuses and dissipates heat well in the surface direction, and has heat insulation properties in the thickness direction, so that the friction material force, shim, and heat conduction in the direction of the caliper piston are improved. This has the effect of preventing the rise in temperature of the viscoelastic body of the shim, the caliper piston, the brake fluid, etc.

Next, the present invention will be explained using Example j and Reference Examples.

Reference Example 1 Glass fiber-reinforced ferrule, I'll as a protective layer
A board made of resin (hereinafter referred to as FRP) was manufactured by the method described in F.

Glass chops (O86E401, manufactured by Nitto Boseki Co., Ltd.) surface-treated with silane resin were selected as the reinforcing material, and novolac-type -y-c norl resin (Pryophen J-875, manufactured by Dainippon Ink) was selected as the phenolic resin.
) and calcium stearate was selected as the mold release agent. [Glass Chop] 41g layer was placed in a Henschel mixer and while stirring, 200g of methanol was added to wet the glass surface, and 10kg of Fxnol resin was added,
200 g of calcium stearate was added and the temperature of the mixer was raised to about 90° C. while stirring. Take 18L;I from the resulting mixture and add it to 100#111X10
0mm flat plate mold V-shaped, 180'C, 400kg/
Compression molded with a pressure of cm2, thickness 1 mm, density 1.87
/cm3 thin plate was obtained. This thin plate was heated at 180°C for 2 to 8
After being post-cured for a period of time, it was cut into a predetermined shape to obtain a waist protection layer.

Reference Example 2 Two types of friction materials, an asbestos type (hereinafter referred to as A) and a steel wool type (hereinafter referred to as B), were manufactured using the ingredients (parts by weight) shown in Table 4 below.

Table 4: Thoroughly mix the above ingredients in a Henschel mixer, then mix at 180°C% 500''/cm2 for 10 minutes...
The compression molded pieces were post-cured at 180°C for 10 hours to obtain friction materials A and B. The following table 5 shows the 1 and 1 keys of A and B. The wall thicknesses of A and B were both V-10.

Table 5 Examples Desk brake pads having the structure shown in Table 6 below were prepared. R1 to RIO are examples of the present invention, 01 to 2 are comparative examples, and A and B shown in Reference Example 2 were used as friction materials. The back metal was made of stainless steel, and the flexible graphite sheet manufactured by Nippon Carbon Co., Ltd. was suitably compressed to produce thick and dense sheets as shown in Table 6. The protective layer was made of stainless steel or FRPO as shown in Reference Example 1.

The disk plate kino ζrad (0
1-02, R1-RIO) was placed with the friction material side down on a steel plate kept at 450°C, and 50 kg7 was placed from above.
cm'' pressure was applied and held for 80 seconds, the temperature on the back side of the disc brake pad was measured.The results are shown in Table 6 (l cycle temperature).This experiment was repeated 10 times at 2 minute intervals.
Table 6 also shows the temperature of the surface of the disc brake pad when the cycle was repeated (10 cycle temperature).

Table 6 also shows the total thickness of the disc brake pad and the amount of strain (μ) at a surface pressure of 800 kg//cm.

Next 01, 02. -C using R5, R6, R9, RIO
We conducted an actual vehicle test. The conditions for the actual vehicle test are shown in Table 7 below.

Table 7 Immediately after the experiment, the temperature of the disc, friction material, caliper piston on the back side of the pad, caliper, and brake fluid (°C) was measured.
) are added by 51 and the results are shown in Table 8 below.

As described above, since the disc brake pad of the present invention uses a flexible graphite sheet, it has good heat dissipation and heat insulation properties, and therefore can prevent the temperature of the caliber piston and brake fluid from rising.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional disc brake pad and its peripheral parts, Fig. 2 is a perspective view of an example of the disc brake pad of the present invention, and Fig. 8 is the compression characteristics of a flexible graphite sheet with a density of 1.5. FIG. 4 is a side view of a disc brake pad and a caliper piston according to another example of the present invention. l... Disc 2... Disc brake pad 8... Friction material 4... Back metal 5... Caliper piston 6... Boot 7...
・Seal 8... Cylinder 9... Brake fluid 10... Caliper 11... Flexible graphite layer 1
2...Protective layer 18...In the protective layer 14...Protective layer B Figure 1 Figure 2

Claims (1)

[Claims] ] A disc brake pad comprising a friction material and a backing metal, characterized in that a flexible graphite layer is attached to the back side of the backing metal. The disc brake pad according to claim 1, wherein the flexible graphite layer has a protective layer on its outer surface or both surfaces.