Patent Application
20110278110
The present disclosure generally relates to disc brake systems, and in particular to shims for use with brake calipers of such brake systems.
In general, a disc brake includes a disc, or rotor, that rotates with the wheel, caliper assembly attached to a wheel carrier, or other portion of the vehicle that does not rotate with the wheel, and friction materials, such as brake pads, that are mounted to the caliper assembly. In operation, hydraulic pressure is applied to one or more pistons mounted in cylinders in the caliper which force the piston(s) into contact with the disc. Braking force is generated by friction between the disc pads as they are urged against the disc rotor by the hydraulic pressure in the caliper.
Calipers typically have either a “floating” or a “fixed” configuration. Depending on the application, a floating caliper has one or more pistons with each piston being located on one side of the caliper only. In operation, hydraulic pressure is applied to the piston(s) which for forces the inboard pad into contact with the disc. As the pressure increases, the floating caliper is moved in the opposite direction of the inboard pad which brings the outboard pad into contact with the disc. Braking force is generated by friction between the disc pads as they are urged against the disc rotor. In the fixed caliper design, one or more pistons are located on each side of the caliper on opposing sides of the disc. Hydraulic pressure is applied to the pistons located on each side of the disc which causes the pistons to force the inboard and the outboard brake pads toward each other and into contact with the disc to thereby generate the braking force.
One issue faced in the operation of disc brakes is brake noise. Brake noise is typically caused by high or low frequency vibrations that are transferred to the brake caliper or chassis components leading to audible brake moan or squeal. In addition, excessive friction generated between the piston and brake pad may lead to twisting (tapering) forces on the brake pad. Such twisting forces can cause binding of axially moving components in the caliper, such as the actuator pin that links the force applied to the brake pedal to the piston assembly in the caliper. Twisting forces may also result in uneven brake pad wear, a condition commonly referred to as taper wear. Taper wear can lead to a loss of clearance between the less worn portions of a brake pad and the brake disc which in turn may result in the less worn portions of the brake pad remaining in contact with the disc when the brake piston (brake released). Over time, excessive contact between the brake pad and disc due to taper wear can lead to uneven disc wear which in turn can lead to brake roughness or judder.
To prevent or limit brake noise in disc brakes, metal plates, referred to as shims, may be provided between the brake pad and the piston. Stainless steel clips are used to clip the shims to a backplate of the brake pad or to the head of the piston, and a layer of viscous material is provided at the interface between the plates. The viscous material provides two benefits: 1) viscous dampening between the brake pad and caliper (piston) interface for axial, tangential, and radial directions of movement of the brake pad relative to the piston; and 2) minimization of the twisting forces of the brake pads on the caliper during the application of the brakes. While effective, the viscous material in the interface is exposed to the environment. Therefore, the viscous material may escape the interface, dry up, and/or become contaminated over time which in turn degrades the performance of the shims.
In accordance with one embodiment of the present disclosure, a disc brake system is provided that includes a disc, and a caliper housing defining a bore that faces one side of the disc. A piston is disposed in the bore for translational movement toward the disc, and a brake pad is arranged between the piston and the disc. A shim plate is arranged between the brake pad and the piston. A convolute boot is provided that has a first end portion and a second end portion. The first end portion is sealingly connected to the caliper housing. The second end portion (i) is sealingly connected to the shim plate and (ii) includes an interface area sealing portion that extends between the shim plate and the piston. The interface area sealing portion is sealingly connected to the piston to define an interface area. An anti-vibration material is located in the interface area.
In accordance with another embodiment of the present disclosure, a piston assembly is provided for use in an actuation section of a disc brake. The piston assembly comprises a piston body having an end portion for arrangement in a bore of a caliper housing facing a disc. A shim plate is positioned at the end portion of the piston. A convolute boot is provided that has a first end portion and a second end portion. The first end portion is configured to be sealingly connected to the caliper housing. The second end portion (i) is sealingly connected to the shim plate and (ii) includes an interface area sealing portion that extends between the shim plate and the piston. The interface area sealing portion is sealingly connected to the piston to define an interface area. An anti-vibration material is located in the interface area.
Features of the present invention will become apparent to those of ordinary skill in the art to which this device pertains from the following description with reference to the figures, in which:
For the purpose of promoting an understanding of the principles of the device described herein, reference will now be made to the embodiment(s) illustrated in the figures and described in the following written specification. It is understood that no limitation to the scope of the device is thereby intended. It is further understood that the device includes any alterations and modifications to the illustrated embodiment(s) and includes further applications of the principles of the device as would normally occur to one of ordinary skill in the art to which this device pertains.
A seal ring 38 is provided in an annular recess or groove 40 in the bore. The seal ring 38 is compressed between the bottom of the groove 40 and the axially sliding piston 30 to form a fluid-tight seal. When an operator desires to apply the brakes, pressurized brake fluid is supplied to the bore 28 via an inlet 31 at the rear of the piston 30. The pressurized fluid forces the piston 30 to move in a first direction A in the cylinder and push the first friction member 34 toward the first side of the disc. In a floating caliper design, the pressurized fluid also acts on the caliper housing 22 to force the caliper housing 22 in a second direction B that is opposite the first direction A thereby moving the second friction member 36 toward the second side of the disc. In a fixed caliper design, hydraulic fluid is delivered to the actuation section on the opposite side of the disc to force the second friction member 36 toward the disc 18. In either case, the first friction member 34 and the second friction member 36 compress the disc 18 therebetween and generate a braking force based on the desired level of braking applied by the operator.
To dampen vibrations caused by frictional contact between the friction members 34, 36 and the disc 18, the disc brake 10 is provided with a sealed floating shim 14. As seen in
A piston boot 60 extends between the sidewall portion 44 of the shim plate and the caliper housing 22. As best seen in
The piston boot 60 may be sealingly attached to sidewall portion 44 of the shim plate 14 and to the caliper housing 22 in any suitable manner. In the embodiment of
The second annular gasket portion 54 of the piston boot includes an inner gasket portion 64 that is interposed and sealed between the sidewall 44 of the shim plate and the side 37 of the piston 30 to define the interface area 50. The inner portion 64 of the second annular gasket portion 54 of the boot spaces the sidewall 44 apart from the side surface 37 of the piston 30 to prevent metal on metal contact between the shim plate and the piston to limit the ability of vibrations to be transferred to the piston and caliper. As best seen in
To provide the shim plate 14 with vibration dampening capability, the interface area is provided with a vibration dampening material 100. Any suitable vibration dampening material may be used. In one embodiment, the material 100 comprises a viscous, lubricant material, such as silicone grease or oil. The grease acts to absorb or dampen vibrations as they transfer from the brake pads to the piston 30 or caliber housing 22. In contrast to the previously known disc brake shims, when utilizing the shim arrangement of the present disclosure, the grease used to dampen vibrations for the shim is permanently sealed into the interface area 50 to provide a sealed-for-life vibrational decoupling of the brake pads from the caliper housing 22.
It will be appreciated that various of the above-described features and functions, as well as other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those of ordinary skill in the art which are also intended to be encompassed by the following claims.
