GB1561233A

GB1561233A - Partial disc brake particularly for motor vehicles

Info

Publication number: GB1561233A
Application number: GB398177A
Authority: GB
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1976-02-02
Filing date: 1977-02-01
Publication date: 1980-02-13
Also published as: DE2603795A1; FR2339779A1; FR2339779B3

Description

(54) PARTIAL DISC BRAKE, PARTICULARLY FOR MOTOR VEHICLES (71) We, VOLKSWAGENWERK AKTIENGESELLSCHAFT, a German Company, of 3180 Wolfsburg, Hanover, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a caliper for a partial disc brake and to a disc brake employing the caliper, the disc brake being of the kind having a brake carrier which is located on one side of the disc of the brake and which, in use, is secured to a fixed part of the machine the brake is used with, and the caliper; the caliper being in the form of a floating frame which is axially displaceably mounted on the brake carrier to straddle the edge of the brake disc and transmit the force of an actuating device of the brake acting directly on a first brake pad arranged to face one side of the disc, indirectly of to a second brake pad arranged at the other side of the disc. Such disc brakes are often used in motor vehicles and are known to be provided with a coating to reduce screeching of the brake.

It is common knowledge that a very unpleasant screeching sound frequently occurs when a motor vehicle is braked and is apparently caused in the case of disc brakes by the fact that, when the brake pads are applied to the brake disc, vibrations are caused which, in the case of resonant vibrations, are particularly intense.

Various measures are known for avoiding screeching of brakes. Thus, it is known (for example, from German Auslegeschrift 1,816,256, German Offenlegungsschrift, 2,207,162) to provide the disc of a disc brake with integrally cast containers filled with damping material, or to provide the end face of the brake disc with an annular groove and, if required, to mount a sheet metal ring therein. These measures are intended to damp vibrations induced in the brake disc and thus at least reduce the screeching of the brakes. It is, however, relatively expensive to manufacture brake discs of this type. Furthermore, even these measures do not fully prevent the screeching of the brakes in all cases.

In the case of disc brakes, of the kind described above, screeching does not occur in dry weather, but sudden screeching of the brakes may occur in wet weather or on wet roads, and to avoid this, it is known see (German Offenlegungsschrift 2,335,595) to provide a thin coating of a plastics material adhesive, a few tenths of a centimetre thick, on the outwardly directed surfaces of the brake, apart from the surfaces which engage in frictional or sliding contact with other surfaces of the brake or need to be exposed for assembly purposes in the brake carrier, the floating frame and the actuating device, and any tension springs provided. the notion underlying this coating of the parts was that, during wet weather, so much water is absorbed by the coating that the parts movable against one another slide on these coatings, so that vibration due to friction cannot be manifested as sound.

Manufacturing costs are high, since all the individual parts concerned of this known partial disc brake are coated.

The object of the invention is to provide a caliper for a partial disc brake of the type described- above by which the tendency of the brakes to screech may be avoided, or, at least, greatly reduced without any substantial increase in manufacturing cost.

Based on the realisation that the floating frame forms a particularly powerful sound reflector, this object is achieved, in accordance with the invention, in that only the floating frame is provided with a coating; the coating being a material resistant to heat generated in use of the brake and transmitted to the coating and having a loss factor d between 5 x 10-3 and 3. By "loss factor" is meant the ratio of the energy (Ev) dissipated in a period (T) of one vibration, T being equal to 1/f where f is the frequency of vibration, in the coating, and the energy (Es) absorbed by the floating frame. Thus, d = Ev Es x 2n where 2z is a proportionality factor. This coating preferably surrounds the floating frame on all sides, with the exception of the specified surfaces, and may have a thickness of some 5 to 10 mm.

By virtue of the present invention, the vibration energy of the floating frame is absorbed in statu nascendi, and thus the objectionable screeching sounds are reduced.

In order to reduce the excitation which causes the floating frame to vibrate, and thus, further to reduce the tendency of the brake to screech, in accordance with a preferred feature of the invention, the floating frame has, for the purpose of transmitting the actuating force to the second brake pad, two spaced, projecting bearing surfaces, one of which bearing surfaces acts upon the rear edge of the disc entry end of the brake pad, and the other bearing surface acts upon the rear edge of the disc exit end of the brake pad, the second brake pad preferably having a non-divided brake lining.

An embodiment of the present invention will now be described, by way of exaple only, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a disc brake caliper according to the present invention; and Figure 2 is a section thereof taken on the line II-II of Figure 1.

In the present embodiment, the caliper in the form of a floating frame manufactured from sheet metal in, for example, a punching and pressing operation, is designated 1. It has, in a known manner, a first recess 6 for accommodating a brake carrier (not shown) secured in use to a fixed part of the machine the brake is used with, and an actuating device (not shown), the floating frame 1 being supported on the brake carrier and/or on the actuating device by means of the slide and guide surfaces designated 6.1 and 6.2 and by means of a tongue-shaped guide lug 6.3. A second recess 7 in the floating frame 1 embracing the edge of the brake disc (not shown) acts as an opening for the edge of the brake disc. The force of the actuating device is transmitted in a conventional manner directly to a first brake pad 8 indicated by broken lines, and indirectly by way of the axially displaceable floating frame 1 to a second brake pad 3 arranged on the other side of the brake disc.

In order to avoid or at least reduce the screeching of the brake, and in accordance with the invention, the floating frame 1 is coated with a material 2 having a high intrinsic damping effect. This coating material has a loss factor d which lies between 5 x 10-3 and 3 and surrounds the floating frame on al sides to a thickness of some 5 to 10 mm. Only those parts of the floating frame which perform slide functions guide functions or assembly functions are not provided with the coating. The proposed nature of the coating considerably reduces the Q-factor of the floating frame 1, this Q-factor being of the order of magnitude of Q = 3.000 in conventional floating frames. All materials having a high value of loss factor in the given range, and which have the requisite heat-resistant, are suitable for the coating. By way of example, a synthetic resin, marketed under the name "Bary X" by the firm Stankiewicx, has proved to be particularly suitable. Again, by way of example, barytes, such as barium sulphate, bonded in polymeric resinous material such as thermosetting polyurethane-, polyethylene- or polypropylene resins, has proved to be suitable. A Q-factor of only 54 was ascertained in tests with floating frames made from a sheet metal having a gauge of approximately 8 mm and a coating of "Bary X" also approximately 8 mm thick. The Q-factor is defined as the reciprocal value of the relative half-value width of the velocity resonance curve.

Q = - - wherein AfH fo = resonance frequency fH = width of the resonance curve on a level with the Jr- fold maximum vibration amplitude.

Jr The sound made by the floating frame disc brake is permanently reduced by the proposed type of coating, it being particularly advantageous that only the floating frame is coated and not the brake carrier and/or the actuating device or parts thereof. The floating frame itself is coated in a relatively simple manner. By way of example, the floating frame can be coated by means of an injection mould in which the parts of the floating frame to be coated are placed.

In order to assist the reduction in the screeching sound achieved by the proposed coating by eliminating the vibration energy of the floating frame, it is particularly advantageous to construct the floating frame 1, in its region transmitting the actuating force to the second brake pad 3, and this brake pad itself, such that, from the outset, only minimum vibration can be transmitted to the floating frame by the second brake pad. For this purpose, in the present embodiment, the floating frame 1, is provided with two spaced, projecting bearing surfaces 4 and 5 which in each case come into abutment against a respective edge of the brake pad, i.e. against the disc entry end and the disc exit end on the back of the second brake pad 3, and serve to transmit the actuating force of the actuating device to this second brake pad. In this second brake pad 3, the carrier plate 3.2 of the brake pad carries a continuous brake lining 3.1, i.e. a brake pad which is not sub-divided by rain grooves or the like. Thus, the brake pad is relatively resistant to bending, whereby, in conjunction with the actuating force introduced in the outer edge region of the brake pad, the development of flexural vibration is prevented, and thus the transmission of vibration energy from this brake pad to the floating frame.

WHAT WE CLAIM IS: 1. A caliper for a partial disc brake of the kind comprising a brake carrier which is located on one side of the disc of the brake and which, in use, is secured to a fixed part of the machine the brake is used with, and the caliper; the caliper being in the form of a floating frame which is axially displaceably mounted on the brake carrier to straddle the edge of the disc and transmit the force of an actuating device of the brake acting directly on a first brake pad arranged to face one side of the disc, indirectly of to a second brake pad arranged to face the opposite side of the disc; wherein the caliper bears a coating thereon of a material having a loss factor (as hereinbefore defined) between 5 x 10-3 and 3, and being resistant to heat generated in use of the broke and transmitted to the coating.

2. A caliper according to claim 1, wherein the coating covers the entire surface of the caliper except for the parts thereof which engage in frictional or sliding contact with other surfaces of the brake or need to be exposed for purposes of assembly of the brake.

3. A caliper according to claim 1 or 2, wherein the. coating is from 5 to 10 mm thick.

4. A caliper according to any of the preceding claims, wherein the material of the coating is barium sulphate bonded in a polymeric resinous material.

5. A caliper according to claim 4, wherein the polymeric resonous material is a thermosetting polyurethane-, polyethylene - or polypropylene resin.

6. A caliper according to any of the preceding claims, wherein the caliper comprises two spaced, projecting bearing surfaces one of which bearing surfaces, when the caliper is installed in the brake together with respective brake pads, acts upon the rear edge of the disc entry end of the indirectly-actuated brake pad, and the other of which bearing surfaces acts upon the rear edge of the disc exit end of that pad.

7. A caliper according to claim 6, wherein the indirectly - actuated brake pad is one having an undivided pad lining.

8. A caliper for a partial disc brake, substantially as hereinbefore described with reference to the accompanying drawings.

9. A partial disc brake comprising a caliper according to any of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. In order to assist the reduction in the screeching sound achieved by the proposed coating by eliminating the vibration energy of the floating frame, it is particularly advantageous to construct the floating frame 1, in its region transmitting the actuating force to the second brake pad 3, and this brake pad itself, such that, from the outset, only minimum vibration can be transmitted to the floating frame by the second brake pad. For this purpose, in the present embodiment, the floating frame 1, is provided with two spaced, projecting bearing surfaces 4 and 5 which in each case come into abutment against a respective edge of the brake pad, i.e. against the disc entry end and the disc exit end on the back of the second brake pad 3, and serve to transmit the actuating force of the actuating device to this second brake pad. In this second brake pad 3, the carrier plate 3.2 of the brake pad carries a continuous brake lining 3.1, i.e. a brake pad which is not sub-divided by rain grooves or the like. Thus, the brake pad is relatively resistant to bending, whereby, in conjunction with the actuating force introduced in the outer edge region of the brake pad, the development of flexural vibration is prevented, and thus the transmission of vibration energy from this brake pad to the floating frame. WHAT WE CLAIM IS:

1. A caliper for a partial disc brake of the kind comprising a brake carrier which is located on one side of the disc of the brake and which, in use, is secured to a fixed part of the machine the brake is used with, and the caliper; the caliper being in the form of a floating frame which is axially displaceably mounted on the brake carrier to straddle the edge of the disc and transmit the force of an actuating device of the brake acting directly on a first brake pad arranged to face one side of the disc, indirectly of to a second brake pad arranged to face the opposite side of the disc; wherein the caliper bears a coating thereon of a material having a loss factor (as hereinbefore defined) between 5 x 10-3 and 3, and being resistant to heat generated in use of the broke and transmitted to the coating.