Vehicle brake pad

Abstract

A vehicle brake pad includes a back plate layer, an underlayer, an adhesive layer that mediates between the back plate layer and the underlayer, and a friction material layer, wherein the vehicle brake pad does not include a shim and wherein at least one of the back plate layer, the adhesive layer, and the underlayer has a loss factor of 0.2 or higher, calculated according to the following Equation 1, at temperatures from 100 to 300 to damp noise of a frequency range of 200 to 20,000 Hz at temperatures from 100 to 300: (Equation 1) Loss factor =(f.sub.2f.sub.1)/f.sub.0, where is a loss factor, f.sub.0 is a noise frequency, f.sub.1 is a minimum value of amplitude of a noise frequency when a noise level is reduced by 3 dB, and f.sub.2 a maximum value of amplitude when the noise level is reduced by 3 dB.

Claims

1. A vehicle brake pad that generates braking force by coming into contact with a disk of a brake, the vehicle brake pad comprising: a back plate layer; an underlayer disposed on a front surface of the back plate layer; an adhesive layer that mediates between the back plate layer and the underlayer; and a friction material layer combined with a front surface of the underlayer and generating friction by coming into contact with the disk of the brake; wherein the vehicle brake pad does not include a shim and wherein the back plate layer has a loss factor above 0.2 at temperatures from 25 to 300 C. to damp, in combination with the adhesive layer and the underlayer, noise of a frequency range of 200 to 20,000 Hz at temperatures from 100 to 300 C., wherein the loss factor is calculated according to the following Equation 1:
Loss factor =(f.sub.2f.sub.1)/f.sub.0(Equation 1), where is a loss factor, f.sub.0 is a noise frequency, f.sub.1 is a minimum value of amplitude of a noise frequency when a noise level is reduced by 3 dB, and f.sub.2 a maximum value of amplitude when the noise level is reduced by 3 dB, and wherein the back plate layer is made of a FeMn-based damping alloy containing 15 to 25 wt % of Mn.

2. The vehicle brake pad according to claim 1, wherein the adhesive layer is an acryl-based damping adhesive that has a loss factor above 0.2 at temperatures from 0 to 100 C.

3. The vehicle brake pad according to claim 1, wherein the underlayer contains 10 to 20 wt % of binder, 20 to 30 wt % of filler, 5 to 20 wt % of reinforcing agent, 15 to 40 wt % of elastomer, 10 to 30 wt % of inorganic regulator, and inevitable impurities, and wherein the elastomer contains at least one of rubber of NBR, EPDM and SBR, and the reinforcing agent includes an aramid-based organic fiber.

4. The vehicle brake pad according to claim 3, wherein the underlayer has a loss factor above 0.2 at temperatures from 100 to 50 C.

5. The vehicle brake pad according to claim 1, wherein one surface of the back plate layer and one surface of the friction material layer that face each other are uneven surfaces that mesh with each other, and wherein the underlayer and the adhesive layer are bent in accordance with contours of the uneven surfaces.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a cross-sectional view illustrating a conventional vehicle brake pad;

(3) FIG. 2 is a diagram illustrating a method of calculating a loss factor () according to exemplary embodiments of the present disclosure;

(4) FIG. 3 is a diagram illustrating a vehicle brake pad according to exemplary embodiments of the present disclosure;

(5) FIG. 4 is a graph illustrating damping coefficients in accordance with temperatures for a conventional vehicle brake pad and a vehicle brake pad according to exemplary embodiments of the present disclosure;

(6) FIG. 5 is a graph illustrating damping capacities of a back plate layer in accordance with temperatures and materials of the back plate layer according to exemplary embodiments of the present disclosure;

(7) FIG. 6 is a graph illustrating damping capacities of a back plate layer, in accordance with the content of manganese (Mn) according to exemplary embodiments of the present disclosure; and

(8) FIG. 7 is an image illustrating loss factors in accordance with temperatures of an adhesive layer used in the vehicle brake pad according to one exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

(9) Hereinbelow, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings but are not limited to limit the scope of the present disclosure.

(10) Throughout the drawings, the same reference numerals will refer to the same or like parts. Under the rule, a description can be made with reference to a plurality of drawings at the same time, and details that ordinarily skilled persons in the art would think of as being obvious or repetitive may be omitted in the description.

(11) A vehicle brake pad according to one embodiment of the present disclosure features a simplified structure that does not include a shim and a specific structure in which constituent layers have different temperature ranges that ensure a specific damping capacity (SDC) to damp noise of audible frequencies of 20 to 20,000 Hz at temperatures from 100 to 300 C. Thus, the present disclosure increases a temperature range that ensures damping of noise of audible frequencies and simplifies the structure of a vehicle brake pad.

(12) The specific damping capacity (SDC) of the vehicle brake pad is represented by a loss factor.

(13) FIG. 2 is a diagram showing a method of calculating a loss factor according to embodiments of the present disclosure.

(14) As illustrated in FIG. 2, the loss factor can be calculated based on Equation 1, using a noise frequency f.sub.0 of a sound wave regarded as noise, a minimum value f.sub.1, and a maximum value f.sub.2 of the amplitude of the noise frequency f.sub.0 when a noise level of the noise frequency f.sub.0 is reduced by 3 dB.
Loss factor =(f.sub.2f.sub.1)/f.sub.0(Equation 1)
where, is a loss factor, f.sub.0 is a noise frequency, f.sub.1 is a minimum value of the amplitude of the noise frequency when a noise level is reduced by 3 dB and f.sub.2 is a maximum value of the amplitude when the noise level is reduced by 3 dB.

(15) The loss factor calculated according to Equation 1 can be converted into a damping ratio , based on Equation 2.
Damping ratio =Loss factor /2(Equation 2)

(16) FIG. 3 is a cross-sectional view illustrating a vehicle brake pad according to embodiments of the present disclosure, and FIG. 4 is a graph illustrating damping coefficients in accordance with temperatures for a conventional vehicle brake pad and a vehicle brake pad according to embodiments of the present disclosure.

(17) As illustrated in FIG. 3, the vehicle brake pad according to embodiments of the present disclosure includes: a back plate layer 100 that transfers pressure applied by a hydraulic cylinder and emits heat generated during braking; an underlayer 300 bonded onto a front surface of the back plate layer 100 and that transfers heat and vibration generated during braking; an adhesive layer 200 that mediates between the back plate layer 100 and the underlayer 300; and a friction material layer 400 that is disposed on a front surface of the underlayer and generates friction by coming into contact with a disk of a brake.

(18) In the vehicle brake pad according to embodiments of the present disclosure, preferably the loss factor of at least any one of the back plate layer 100, the adhesive layer 200, and the underlayer 300 is 0.2 or higher, as calculated according to Equation 1, at temperatures of from 100 to 300 C. to reduce noise of frequencies of 200 to 20,000 Hz.

(19) As illustrated in FIG. 4, conventional vehicle brake pads exhibit a loss factor of 0.2 or higher at temperatures of from 25 to 200. On the other hand, the vehicle brake pad according to embodiments of the present disclosure exhibits a loss factor of 0.2 or higher at temperatures of from 100 to 300 C., which is a wider temperature range than that of conventional vehicle brake pads. That is, the vehicle brake pad according to the present disclosure improves the noise damping capacity over a wider temperature range than do conventional vehicle brake pads.

(20) The back plate layer 100 may be made of gray cast iron in which precipitates, such as complex microstructures or graphite, occur to obtain as high a vibration damping capacity as a metal. The back plate layer 100 may alternatively be made of a steel sheet for press forming that is excellent in vibration damping because it is provided with an excessive amount of dislocations that effectively damp vibrations by consuming energy. According to embodiments of the present disclosure, the back plate layer may be made of a FeMn-based damping alloy containing 15 to 25 wt % of manganese (Mn).

(21) FIG. 5 is a graph illustrating damping capacities of a back plate layer in accordance with temperatures and materials of the back plate layer according to embodiments of the present disclosure.

(22) As illustrated in FIG. 5, among steel sheets for press forming that were conventionally used to make a back plate layer, a composite sandwich steel has a very narrow temperature range, 10 to 50 C., that ensures a damping capacity of 32% or higher. In addition, as the temperature is increased, the damping capacity of carbon steel is decreased.

(23) On the other hand, a back plate layer made of a FeMn-based damping alloy containing 17 wt % of Mn has a wide damping-ensuring temperature range that ensures a damping capacity of 32% or higher. In addition, when the FeMn-based damping alloy is used, the damping capacity varies little in accordance with changes in temperature. Therefore, the back plate layer made of a FeMn-based damping alloy has an excellent damping capacity over a wider temperature range in comparison with that of carbon steel or composite sandwich steel.

(24) FIG. 6 is a graph illustrating a damping capacity of a back plate layer in accordance with the content of Mn according to embodiments of the present disclosure.

(25) As illustrated in FIG. 6, when the back plate layer 100 according to embodiments of the present disclosure contains 15 to 25 wt % of Mn, the back plate layer 100 exhibits an excellent damping capacity of 20% or higher. On the other hand, when the content of Mn is outside the range, the damping capacity is decreased below 20%.

(26) Accordingly, the back plate layer according to embodiments of the present disclosure preferably contains 15 to 25% of Mn.

(27) As having been described above, in the vehicle brake pad according to the present disclosure, the back plate layer 100 is made of a FeMn-based damping alloy containing 15 to 25 wt % of Mn. In this case, the vehicle brake pad ensures a loss factor of 0.2 or higher at temperatures of from 25 to 300 C. That is, the vehicle brake pad according to embodiments of the present disclosure improves a noise damping capacity at temperatures within a temperature range of 25 to 300 C.

(28) The underlayer 300 may be made of a polymer containing an oxide-based inorganic material having a heat insulating characteristic and an elastomer so as to exhibit a loss factor of 0.2 or higher at temperatures from 100 to 50 C.

(29) Preferably, the underlayer according to one embodiment of the present disclosure may contain 10 to 20 wt % of binder, 20 to 30 wt % of filler, 5 to 20 wt % of reinforcing agent, 15 to 40 wt % of elastomer, 10 to 30 wt % of inorganic regulator, and some inevitable impurities.

(30) TABLE-US-00001 TABLE 1 Constituent materials (wt %) Reinforcing Agent Filler (Aramid Inorganic Binder (Barite + fiber + Regulator (Phenolic Potassium Copper Elas- (Cashew Resin) hydroxide) fiber) tomer Powder) Comparative 20 45 10 10 15 Example Embodiment 1 19 15 18 29 19 Embodiment 2 19 15 18 30 18 Embodiment 3 19 15 18 28 20

(31) Table 1 shows the composition of the underlayer 300 according to one embodiment of the present disclosure and the composition of a conventional underlayer.

(32) As shown in Table 1, the underlayer 300 according to one embodiment of the present disclosure contains 15 to 40 wt % of elastomer to improve a damping capacity at temperatures of from 100 to 50 C.

(33) When the content of elastomer is lower than 15 wt %, the damping capacity is very low at temperatures of from 100 to 50 C. Conversely, when the content of elastomer is higher than wt %, the physical characteristics (compressive strain, density, hardness etc.) of the underlayer 300 are excessively changed, thereby not satisfying the required physical characteristics of an underlayer.

(34) The elastomer may include at least one of NBR, EPDM and SBR. The reinforcing agent may include an aramid-based organic fiber. More preferably, the reinforcing agent may be a material that can be firmly bonded to the friction material layer 400.

(35) The underlayer 300 according to an embodiment of the present disclosure is formed by putting a molded product of a material selected among the above materials on the friction material layer 400 and pressing it under conditions of a pressure of 500 to 700 kgf/cm.sup.2 and a temperature range of 150 to 180 C. Through this process, the underlayer 300 is integrated with the friction material layer 400.

(36) The adhesive layer 200 according to an embodiment of the present disclosure may be made of a highly elastic acryl-based damping adhesive that has a loss factor of 0.2 or higher at temperatures of from 0 to 100 C. The adhesive layer 200 may be formed through a coating or spraying process.

(37) FIG. 7 is an image illustrating loss factors of the adhesive layer of one embodiment of the present disclosure, in accordance with temperatures.

(38) As shown in FIG. 7, the adhesive layer 200 according to the embodiment exhibits an excellent vibration-damping capacity by having a loss factor of 0.2 or higher at temperatures from 0 to 100 C.

(39) In addition, one surface of the friction material layer 400 and one surface the back plate layer 100 that face each other may be uneven surfaces formed to mesh with each other.

(40) This is because it is difficult to perform surface treatments to increase shear strength with respect to the back plate layer 100 due to a high hardness of the back plate layer 100.

(41) Therefore, the present disclosure increases the shear strength of the vehicle brake pad by increasing bonding force between the friction material layer 400 and the back plate layer 100, thereby improving accuracy and stability of braking.

(42) As has been described above, the adhesive layer 200 according to the embodiment of the present disclosure exhibits a loss factor of 0.2 or higher at temperatures from 0 to 100 C., the back plate layer 100 exhibits a loss factor of 0.2 or higher at temperatures of from 25 to 300 C., and the underlayer 300 exhibits a loss factor of 0.2 or higher at temperatures of from 100 to 50 C.

(43) Therefore, the vehicle brake pad according to an embodiment of the present disclosure, including the back plate layer 100, the underlayer 300, and the adhesive layer 200 that are prepared in the manners described above, has an improved noise damping capacity at temperatures within a wide temperature range of from 100 to 300.

(44) TABLE-US-00002 TABLE 2 Items 1st 2nd Total Ave. Comparative 0 C. Freq.(kHz) 2.696 8.744 1.891 Example Damping 0.600 0.755 ratio(%) 25 C. Freq.(kHz) 2.656 8.604 1.826 Damping 0.574 0.978 ratio(%) 100 C. Freq.(kHz) 2.480 8.488 2.100 Damping 0.597 0.838 ratio(%) Embodiment 0 C. Freq.(kHz) 2.524 8.220 2.080 Damping 0.800 1.287 ratio(%) 25 C. v Freq.(kHz) 1.932 8.120 3.043 Damping 3.984 1.550 ratio(%) 100 C. Freq.(kHz) 1.832 8.112 3.009 Damping 2.419 1.176 ratio(%)

(45) Table 2 shows natural frequencies and damping ratios in accordance with temperatures for a brake pad according to a comparative example and a brake pad according to an embodiment of the present disclosure.

(46) As shown in Table 2, the vehicle brake pad according to an embodiment of the present disclosure has an improved noise damping characteristic at temperatures within a wider temperature range than that of conventional vehicle brake pads and maintains a damping capacity of 20% or higher at room temperatures while suppressing a variation in natural frequency in a frequency response function (FRF) to 3% or less. In addition, the vehicle brake pad according to an embodiment of the present disclosure has an improved damping ratio that changes in accordance with temperature, in comparison with conventional vehicle brake pads.

(47) The vehicle brake pad according to embodiments of the present disclosure can not only increase a frequency range of noise that can be damped at temperatures of from 100 to 300 C. to 200 to 20,000 Hz but also improve a damping capacity. That is, it is possible to dramatically increase a frequency range of noise that can be damped and a temperature range that ensures a good damping capacity.

(48) Although embodiments of the present disclosure have been described for illustrative purpose, those skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.