JP2014105835A - Piston seal member and disc brake using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a piston seal member having excellent brake gap adjustment characteristics; and a disc brake using the piston seal member.SOLUTION: A disc brake piston seal member 8 is made of a rubber composition composed mainly of ethylene-propylene rubber. Fluororesin particles are dispersed in the rubber composition. A disk brake includes: a cylinder 6 having a cylinder hole 6a; a piston 5 to be inserted into the cylinder hole 6a; and a piston seal member 8 to be fitted in an annular groove 7 formed on an inner circumferential wall of the cylinder hole 6a.

Description

  The present invention relates to a piston seal member and a disc brake using the piston seal member.

  The piston seal member is generally molded from a crosslinked rubber composition mainly composed of rubber. For example, a caliper body incorporating a piston and a cylinder is attached to a disc brake for a vehicle, and a piston seal member is attached to an annular groove formed on the inner peripheral surface of the cylinder. In the disc brake, the friction pad is pressed against the disc rotor fixed to each wheel by the brake hydraulic pressure, and the rotation of the wheel is stopped by the frictional force of the friction pad as a friction material. By mounting the piston seal member, the cylinder and the piston inserted into the hole of the cylinder can be brought into close contact with each other in a liquid-tight movable state. Further, the piston advanced by the hydraulic pressure is rolled back by the piston seal member (see, for example, Patent Document 1).

  A piston seal member for a disc brake made of such a rubber composition is required to have a brake clearance adjustment characteristic in addition to prevention of brake fluid leakage between the cylinder and the piston and rollback. The brake clearance adjustment characteristic is a characteristic that suppresses a change in the rollback amount by appropriately sliding the piston and the piston seal member even when the friction pad is worn. In general, the brake clearance adjustment characteristics of the piston seal member may vary depending on the thermal load caused by the friction between the disk rotor and the friction pad.

  Accordingly, a disc brake piston seal member made of a rubber composition mainly composed of ethylene-propylene rubber with improved heat resistance has been proposed (see, for example, Patent Documents 2 and 3).

  Further, in order to improve the brake clearance adjustment characteristics, it has been proposed to reduce the coefficient of friction of the piston seal member with respect to the piston by coating the inner peripheral surface of the piston seal member with a lubricant (for example, Patent Document 4). reference). However, since the adhesive strength between the rubber composition of the piston seal member and the lubricant coating layer is not sufficient, there is a risk of peeling, and the flexibility of the piston seal member is reduced due to the provision of the lubricant coating layer. There was a problem.

Japanese Examined Patent Publication No. 3-59291 JP 2004-316773 A Japanese Patent Laid-Open No. 2004-232786 JP 2001-65614 A

  An object of the present invention is to provide a piston seal member having excellent brake clearance adjustment characteristics and a disc brake using the piston seal member.

The piston seal member according to the present invention is
A piston seal member for a disc brake made of a rubber composition mainly composed of ethylene-propylene rubber,
Fluorine resin particles are dispersed in the rubber composition.

  According to the piston seal member of the present invention, the brake clearance adjustment characteristic for the piston of the piston seal member with respect to the piston is improved by the fluororesin particles contained in the rubber composition without substantially affecting the physical properties as the piston seal member. be able to.

In the piston seal member according to the present invention,
The fluororesin particles may be polytetrafluoroethylene particles.

In the piston seal member according to the present invention,
The polytetrafluoroethylene particles may be included in the rubber composition in an amount of 3 to 5% by weight.

The disc brake according to the present invention is
The piston seal member;
A cylinder having a cylinder hole;
A piston inserted into the cylinder hole,
The piston seal member is fitted into an annular groove formed in the inner peripheral wall of the cylinder hole, and the piston inserted into the cylinder hole is brought into close contact with the liquid-tight movable state and is advanced by hydraulic pressure. The piston is rolled back.

It is sectional drawing which shows typically the piston seal member which concerns on one embodiment of this invention. It is sectional drawing which shows typically the disc brake containing the piston seal member shown in FIG.

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

  FIG. 1 is a cross-sectional view schematically showing a piston seal member 8 according to an embodiment of the present invention. FIG. 2 is a sectional view schematically showing the disc brake 20 including the piston seal member 8 shown in FIG. In the present embodiment, a floating type disk brake for a vehicle will be described as an example.

(Disc brake)
The disc brake 20 according to the present embodiment includes a piston seal member 8, a cylinder 6 having a cylinder hole 6a, and a piston 5 inserted into the cylinder hole 6a. The piston 5 is fitted into an annular groove piston seal groove 7 formed in the inner peripheral wall, and the piston 5 inserted into the cylinder hole 6a is brought into close contact with the liquid-tight movable state. Let me back.

The disc brake 20 includes a bracket 3 fixed to a vehicle body (not shown), and a caliper body 1 supported by the bracket 3 in a slidable state. The caliper body 1 includes an action part 1b and a reaction part 1c, and the piston 5 and the cylinder 6 are formed in the action part 1b. The action part 1b and the reaction part 1c are integrally formed via the bridge part 1a. A pair of friction pads 4b and 4c are arranged facing the friction surfaces on both sides of the disk rotor 2 that rotates integrally with the wheels (not shown). A caliper body 1 that presses the friction pads 4b and 4c against the disc rotor 2 is connected to the bracket 3 via a slide pin (not shown) so as to be able to advance and retract. The caliper body 1 includes an action portion 1b disposed on the back surface of one friction pad 4b, a reaction portion 1c disposed on the back surface of the other friction pad 4c, and the action portion 1b and the reaction portion straddling the outer periphery of the disk rotor 2. It is comprised with the bridge part 1a which connects 1c. The friction pad 4 b is moved by being pushed by the piston 5 inserted into the cylinder hole 6 a and is in contact with one side surface of the disk rotor 2. The friction pad 4 c is moved by being pushed by the reaction portion 1 c and is in contact with the other side surface of the disk rotor 2. Braking is performed by the above operation.

  An annular piston seal groove 7 is provided on the inner peripheral wall of the cylinder hole 6a. An annular piston seal member 8 is fitted in the piston seal groove 7. The material of the piston seal member 8 and the manufacturing method thereof will be described later.

  The hydraulic chamber 9 is provided between the bottom of the piston 5 and the cylinder 6. Brake fluid is supplied to the hydraulic chamber 9 from the supply port 10. The piston seal member 8 has a function of sealing the brake fluid and a function of rolling back the piston 5 that has moved forward when the hydraulic pressure in the hydraulic pressure chamber 9 decreases. The supply port 10 is connected to an output port (not shown) of a master cylinder (not shown), which is a hydraulic pressure source, via a hydraulic pressure path 28.

  As shown in FIG. 1, the piston seal groove 7 has a chamfered corner 7a and a chamfered corner 7b. The piston seal member 8 follows the sliding surface of the piston 5 as the piston 5 slides forward in the direction of the black arrow shown in FIG. 1 (the disk rotor 2 side in FIG. 2). A part enters the chamfer corner 7a. When the hydraulic pressure in the hydraulic chamber 9 decreases, the piston 5 is rolled back in the direction opposite to the arrow by being restored by the elasticity of the piston seal member 8. The type of the disc brake 20 is not limited to the pin slide type as in the present embodiment, but may be an opposed disc brake in which pistons are arranged on both sides of the disc rotor, and the number of pistons and the shape of the piston seal member are also different. The present invention is not limited to this embodiment.

(Piston seal member)
The piston seal member 8 according to the present embodiment is a disc brake piston seal member made of a rubber composition containing ethylene-propylene rubber as a main component, and is made by dispersing fluororesin particles in the rubber composition. The piston seal member 8 can be used, for example, in a caliper body 1 of a disc brake 20 as shown in FIG. 2, and as shown in FIG. 1, a cylinder hole 6a and a piston 5 sliding in the cylinder hole 6a Can be held fluid-tight and slidable.

The piston seal member 8 includes, for example, 20 to 60 parts by weight of first carbon black having an average particle diameter of 35 to 100 nm and a DBP oil absorption of 50 to 200 ml / 100 g with respect to 100 parts by weight of ethylene propylene rubber. The second carbon black having a diameter of 60 to 500 nm and a DBP oil absorption of 5 to 50 ml / 100 g may be molded with a rubber composition containing 70 to 160 parts by weight in total. The first carbon black can give a reinforcing effect to the piston seal member when blended by 20 parts by weight or more, and can maintain the flexibility of the piston seal member by blending 60 parts by weight or less. preferable. The second carbon black can be blended in an amount of 50 parts by weight or more to reduce the rubber polymer fraction in the piston seal member and keep the coefficient of linear expansion low. The member can maintain appropriate flexibility. More preferably, the piston seal member 8 includes 30 to 50 parts by weight of the first carbon black and 60 to 80 parts by weight of the second carbon black with respect to 100 parts by weight of the ethylene propylene rubber. Is molded by. Here, “parts by weight” indicates “phr” unless otherwise specified, and “phr” is an abbreviation of “parts per undred of resin or rubber” and represents the percentage of external additives such as additives to rubber and the like. It is.

  In a state where the piston seal member and the piston are at a high temperature, the adhesion of the piston seal member to the piston 5 is usually high and slipping is difficult, but the piston seal member 8 in the present embodiment disperses the fluororesin particles in the rubber composition. By blending, the ease of slipping of the piston seal member 8 with respect to the piston 5 can be improved, and the brake clearance adjustment characteristics can be stabilized. The brake gap d corresponds to the rollback amount of the piston 5, and as shown in FIG. 2, the friction pads 4b and 4c are spaced from the disc rotor 2, and the friction pads 4b and 4c are disc rotors due to repeated braking. 2 tends to widen when worn in contact. The brake gap adjustment characteristic is to make adjustment so that the brake gap does not become wide even if the friction pads 4b and 4c are worn. Thus, if the brake interval is not widened, the rollback amount of the piston 5 is stabilized, and the driver can hardly feel changes such as the stroke amount of the brake lever.

  When the piston seal member according to the present embodiment is used, even if the friction pads 4b and 4c are worn, the brake gap is widened because the piston seal member 8 appropriately slides against the surface 5a of the piston 5 during braking. Can be prevented. More specifically, when the piston seal member and the piston are at a high temperature, the force for moving the piston 5 forward with respect to the disk rotor 2 during braking exceeds the frictional force between the piston seal member 8 and the piston 5, and the piston 5 This means that the predetermined brake clearance can be maintained by moving forward.

(Ethylene-propylene rubber)
As the ethylene-propylene rubber, it is preferable to use EPDM (ethylene-propylene-diene copolymer). In order to obtain heat resistance, cold resistance and sealability required for the piston seal member, a third component such as ethylidene norbornene is used. In addition, the copolymerization ratio of ethylene and propylene is preferably EPDM having an ethylene content of 45% to 80%.

(Fluorine resin)
The fluororesin particles are thermoplastic particles having a carbon-fluorine bond in the molecule. For example, polytetrafluoroethylene (PTFE), polytrifluorochloroethylene (PTFCE), polyvinylidene fluoride (PVDF), Particles such as tetrafluoroethylene / hexafluoropropylene copolymer (FEP) can be used. Particularly in terms of durability and cost, the fluororesin particles are preferably polytetrafluoroethylene (hereinafter referred to as PTFE) particles. The piston seal member 8 can contain 3 to 5% by weight of PTFE particles in the rubber composition. The blending amount of the PTFE particles is preferably 3% by weight or more in order to reduce the friction coefficient. However, since PTFE is generally difficult to wet with ethylene-propylene rubber, it is 5% by weight or less so that the physical properties of the piston seal member 8 do not deteriorate. Is preferable.

(Carbon black)
Since the first carbon black is used as a reinforcement of the rubber composition, it is preferable that the average particle size is 35 nm to 100 nm and the DBP oil absorption is 50 to 200 ml / 100 g, more preferably the average particle size is 40 to 75 nm. DBP oil absorption is 100 to 160 ml / 100 g. The rubber composition is reinforced with the first carbon black to improve the rigidity and durability by keeping the elastic modulus low, and when used for a piston seal member of a disc brake, a sufficient rollback amount is obtained. Can be obtained. The second carbon black has an average particle size in order to keep the hardness and mechanical strength necessary for the piston seal member, while reducing the rubber polymer fraction in the rubber composition and keeping the coefficient of linear expansion of the rubber composition low. The diameter is preferably 60 to 500 nm and the DBP oil absorption is 5 to 50 ml / 100 g, more preferably 80 to 150 nm and the DBP oil absorption is 30 to 45 ml / 100 g.

(Method for producing rubber composition)
As a method for producing the rubber composition according to the present embodiment, ethylene-propylene rubber, fluororesin particles, first carbon black, second carbon black, and other compounding agents are mixed rolls, It can be supplied to a known mixer such as a single or twin screw extruder, Banbury mixer, kneader and kneaded. Usually, the same amount of process oil as that of carbon black is used in this kneading, but it is desirable not to use it in the production process of the rubber composition of the present invention. This is because when a piston seal member of a disc brake manufactured using process oil is used, the process oil melts into the brake fluid, causing a change in the performance of the brake fluid over time and a change in heat resistance.

  The rubber composition obtained by kneading ethylene-propylene rubber and various compounding agents in this way is molded into the piston seal member 8 by an extrusion molding machine, a compression molding machine, an injection molding machine, a transfer molding machine or the like, and then crosslinked. The The crosslinking conditions are, for example, 150 to 220 ° C. and 1 to 30 minutes. In the method for producing a rubber composition, a compounding agent usually used in the processing of ethylene-propylene rubber can be added. A well-known thing can be used as a compounding agent.

  In addition, this invention is not limited to the said embodiment, In the range of the summary of this invention, it can deform | transform into various forms.

  For example, in the present embodiment, the piston seal member is built in the disc brake for the vehicle, but other piston seal members for the disc brake may be used.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

(1) Preparation of rubber composition sample The first carbon black of SRF-HS grade (average particle size 72 nm, DBP oil absorption 152 ml / 100 g) with respect to 100 parts by weight of EPDM (trade name EP33) manufactured by JSR Corporation 20 parts by weight, MT grade (average particle size 122 nm, DBP oil absorption 41 ml / 100 g) second carbon black 100 parts by weight, organic peroxide 2.5 parts by weight, co-crosslinking agent 1 part by weight and shown in Table 1 An amount of PTFE particles (average particle size 30 μm) was kneaded to obtain a rubber composition. In Comparative Example 1, PTFE particles are not blended as shown in Table 1.

  This rubber composition was used for injection molding, and heated at 175 ° C. for 20 minutes for crosslinking to obtain a piston seal member sample. Further, this rubber composition was similarly heated and crosslinked to obtain a JIS dumbbell-shaped No. 3 test piece.

(2) Measurement of normal state property About each test piece, rubber hardness (JIS-A), tensile strength (TB), cutting elongation (EB), and 100% tensile stress (M100) were measured. The rubber hardness (JIS-A) was measured according to JIS K 6253-1997. TB, EB and M100 were measured according to JIS K 6251-1993. More specifically, the 100% tensile stress (MPa) was determined by stretching the sample at 10 mm / min and determining the stress at 100% deformation (M100: 100% modulus). These results are shown in Table 1.

(3) Measurement of heat aging characteristics Each test piece is hung in a test tank, heated at an aging temperature of 200 ° C. and an aging time of 24 hours, and then taken out from the test tank and allowed to cool to room temperature. Rubber hardness (JIS-A), tensile strength (TB), and elongation at break (EB) were measured according to JIS K 6253, and changes with respect to each measured value of normal physical properties were calculated according to JIS K 6257-1993. These results are shown in Table 1.

(4) Compression set test About each test piece, the compression set was measured by JISK6262. The compression set was performed under the conditions of 200 ° C., 24 hours, and 25% compression. The compression set is an evaluation of the so-called stickiness resistance of the piston seal member at a high temperature. These results are shown in Table 1.

(5) Measurement of friction coefficient For each specimen, (20 mm x 100 mm x 2 mm thickness), using a linear sliding type testing machine (Haydon 14DR) manufactured by Shinto Kagaku Co., Ltd., static and dynamic friction coefficients Was measured.
Measuring jig: SUS ball load weight: 100 gf
Moving table speed: 30mm
Number of repeated measurements: 5 times (measures the fifth static / dynamic frictional resistance)
The friction coefficient was calculated as follows: static / dynamic frictional resistance force / vertical load.
These results are shown in Table 1.

(6) Brake test Next, this piston seal member was fitted into the annular piston seal groove of the disc brake, and an evaluation test of the rollback amount was performed to evaluate its characteristics. The rollback amount was measured at a piston seal member 140 ° C. by applying a hydraulic pressure of 0.9 MPa to the disc brake 10 times and then operating for 5 seconds at a hydraulic pressure of 6.9 MPa. The amount of piston movement when the hydraulic pressure was released was measured. The results of the evaluation test are shown in Table 1.

  From Table 1, according to Examples 1 and 2 of the present invention, the following was confirmed. That is, the piston seal members of Examples 1 and 2 have a smaller rollback amount despite the fact that there are no significant changes in normal properties, heat aging characteristics and compression set characteristics as compared with the piston seal members of Comparative Example 1. I found out.

DESCRIPTION OF SYMBOLS 1 Caliper body, 1a Bridge part, 1b Action part, 1c Reaction part, 2 Disc rotor, 3 Bracket, 4b, 4c Friction pad, 5 Piston, 5a Piston surface, 6 Cylinder, 6a Cylinder hole, 7 Piston seal groove, 7a 7b
Chamfer corner, 8 piston seal member, 9 hydraulic chamber, 20 disc brake

Claims (4)

A piston seal member for a disc brake made of a rubber composition mainly composed of ethylene-propylene rubber,
A piston seal member in which fluororesin particles are dispersed in the rubber composition. In claim 1,
The piston seal member, wherein the fluororesin particles are polytetrafluoroethylene particles. In claim 1 or 2,
A piston seal member comprising 3 to 5% by weight of the polytetrafluoroethylene particles in the rubber composition. The piston seal member according to any one of claims 1 to 3,
A cylinder having a cylinder hole;
A piston inserted into the cylinder hole,
The piston seal member is fitted into an annular groove formed in the inner peripheral wall of the cylinder hole, and the piston inserted into the cylinder hole is brought into close contact with the liquid-tight movable state and is advanced by hydraulic pressure. A disc brake that rolls back the piston.

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