Drum brake

Abstract

Drum brake comprises a revolving drum (1) having a cylindrical inner surface (2), a pair of opposite stationary jaws (3, 4) having respective cylindrical outer surfaces facing the inner surface (2) of the drum and carrying respective friction linings (5, 6), and actuator means (9) for carrying out the opening of the jaws (3, 4) and the engagement between the friction linings (5, 6) and the drum (1). Multilayer elastic damping members (12) are arranged between the actuator means (9) and the corresponding ends (3b, 4b) of both jaws (3, 4).

Description

[0001] “Drum brake”

[0002] ****

[0003] Field of the invention

[0004] The present invention relates to drum brakes for vehicles of the type comprising a revolving drum having a cylindrical inner surface and a pair of stationary and opposite jaws (or brake blocks), having respective cylindrical outer surfaces facing the inner surface of the drum and carrying respective friction linings. Typically, the two jaws have respective first ends resting against a reaction piece and second ends between which there are interposed actuator means for carrying out the opening of the jaws and the engagement between relative friction linings and the drum.

[0005] State of the prior art

[0006] In the drum braking systems during use there may occur annoying noise problems, for example high frequency whistling noise, due to vibrations between the jaws and the drum.

[0007] In order to limit the intensity of these noises there are normally used solutions for the mass or rigidity of modification of one or more components of the drum brake so as to de-couple the frequencies thereof and the vibration modes.

[0008] These solutions for example include changes in the formulation of the material of the friction linings, changes in the mase and / or rigidity of the drum, changes in the mass and / or rigidity of the brake-holder-plate (jaw support), change in the mass and / or rigidity of the jaws by changing the thickness on the edge and / or strip or with grooves on the edge, works on the radius for grinding the friction material and / or jaws, works on the roughness of the brake rotor on the inner surface of the drum.

[0009] All these solutions do not effectively or fully solve the noise-related problem.

[0010] The document US-5,099,967 provides a solution according to which with one of the ends of each jaw there is associated a respective elastic damping member. More particularly, elastic damping members are interposed between the first end of the jaws and the reaction piece. In a variant, wherein instead of the reaction piece there are provided for actuator means both between the first and between the second ends of the jaw, an i elastic damping member is associated with the first end of a jaw and an elastic damping member is associated with the second end of the other jaw.

[0011] These solutions did not show to be fully satisfactory either, in particular considering the fact that the noise generated by the vibrations of the jaws could occur not only in one direction of rotation of the drum (forward motion), but also in the opposite direction of rotation (reverse motion).

[0012] Summary of the invention

[0013] With the aim of overcoming this drawback, the present invention relates to a drum brake of the type specified above, whose peculiar characteristic lies in the fact that first elastic damping members are arranged between the second ends of both jaws and the aforementioned actuator means.

[0014] Thanks to this solution idea, the effectiveness of the damping of the vibrations, and therefore of then elimination of the noise of the drum brake, is ensured in both directions of rotation of the drum of the brake that is in the forward motion and in the reverse motion.

[0015] According to a further characteristic of the invention, second elastic damping members may also be interposed between both first ends of the jaws and the reaction piece.

[0016] Each elastic damping member is conveniently formed by a multilayer body and it may for example comprise a stainless steel layer in contact with the jaw, a first layer of acrylic adhesive, a first layer of nitrile rubber, a layer of galvanised steel, a second layer of nitrile rubber and a second layer of acrylic adhesive, with respective variable thicknesses.

[0017] Brief description of the drawings

[0018] The invention will now be described in detail with reference to the attached drawings, provided purely by way of non-limiting example, wherein:

[0019] - figure 1 is an elevational schematic view of a drum brake according to an embodiment of the invention,

[0020] - figure 2 is an exploded perspective view of one of the multilayer elastic damping members with which the drum brake is provided,

[0021] - figure 3 is a schematic perspective view of a detail of the drum brake, and

[0022] - figure 4 is an exploded view of the detail of figure 3.

[0023] Detailed description of the invention

[0024] Initially with reference to figure 1 , a drum brake according to an embodiment of the invention comprises, in a generally known manner, a revolving drum 1 having a cylindrical inner surface 2, and a pair of brake blocks or stationary opposite jaws 3, 4, or rather not rotatable with respect to the drum 1 , whose cylindrical outer surfaces carry respective friction linings 5, 6 facing the inner surface 2 of the drum 1 .

[0025] The jaws 3, 4 have respective vacant ends 3a, 4a kept resting, the action of a traction spring 7, against a reaction piece 8 fixed to the drum 1 . The opposite ends 3b, 4b of the two jaws 3, 4 cooperate with an actuator device 9 which carries out the mutual opening thereof so as to bring the friction linings 5, 6 to engage with the inner surface 2 of the drum 1 and carry out the braking thereof.

[0026] In the case of the shown example, the actuator device 9 consists of a hydraulic jack 9 from whose cylinder 10 there protrude - on opposite sides - two plungers 11 acting against the ends 3b, 4b of the two jaws 3, 4. A pair of traction springs 13 tend to keep the two jaws 3, 4 in a non-interference position with the inner surface 2 of the drum 1 .

[0027] According to the distinctive characteristic of the invention, between each of the plungers 11 of the actuator 9 and the end 3b - on one side - and the end 4b - on the other side there is interposed a respective first elastic damping member 12.

[0028] Each elastic damping member 12 is conveniently fixed to the respective plunger 11 by gluing and it has a multilayer configuration, for example as exemplified in figure 2. It may include a stainless steel outer layer 12a for the contact with the end 3b or 4b of the respective jaw 3, 4, a first layer 12b of acrylic adhesive (for example with thickness comprised between 0.02 and 0.1 mm), a first layer of nitrile rubber 12c (for example with thickness comprised between 0.2 and 1 mm), a layer 12d of galvanised steel (for example with thickness comprised between 0.4 and 0.8 mm), a second layer 12e of nitrile rubber (for example with thickness comprised between 0.2 and 1 mm), and a second terminal layer 12f of acrylic adhesive. In the operation, the elastic damping members 12 allow to dampen the intensity of the noise which may be generated, due to vibrations, following the contact with the jaws 3, 4 and the drum 1 . They basically allow to efficiently de-couple the relative specific frequencies and the relevant vibration modes. The dampening effect is especially conferred by the layers of nitrile rubber 12c and 12e, and the de-coupling of the critical frequencies and the vibration modes of the components is conferred by the multilayer structure of the elastic members 12.

[0029] In particular, the provision of the elastic members 12 on both plungers 11 of the actuator 9 allows to obtain an effective damping effect in both directions of rotation of the drum (forward motion or reverse motion), therefore guaranteeing a double damping action.

[0030] It should be observed that the thicknesses, the type of material, the number and the sequences of the layers of each damping member 12 may differ from the one indicated by way of example, as a function of the damping level which can be obtained experimentally, of the type of application of the drum brake and of the mechanical stresses to which it can be subjected in use, as well as the standard operating environmental / temperature conditions of the drum brake.

[0031] According to an advantageous characteristic of the invention two second elastic damping members 14 may also be interposed between the first ends 3a, 4a of the jaws 3, 4 and the reaction piece 8. In this case, the configuration of each damping member 14 may be of the multilayer type, similar to that of the damping members 12.

[0032] Obviously, the construction details and the embodiments may widely vary with respect to what has been described and illustrated, without departing from the scope of protection of the present invention.

Claims

CLAIMS1. Drum brake, comprising a revolving drum (1 ) having a cylindrical inner surface (2), a pair of opposite stationary jaws (3, 4) having respective cylindrical outer surfaces facing the inner surface (2) of the drum and carrying respective friction linings (5, 6), said jaws (3, 4) having respective first ends (3a, 4a) resting against a reaction piece (8) of the drum (1 ) and second ends (3b, 4b), and actuator means (9) interposed between said second ends (3b, 4b) for carrying out the opening of the jaws (3, 4) and the engagement between said friction linings (5, 6) and the drum (1 ), characterised in that first elastic damping members (12) are arranged between said actuator means (9) and said second ends (3b, 4b) of both jaws (3, 4).

2. Drum brake according to claim 1 , characterised in that second elastic damping members (14) are also interposed between said reaction piece (8) and said first ends (3a, 4a) of the jaws (3, 4).

3. Drum brake according to claim 1 or claim 2, characterised in that each elastic damping member (12; 14) is multilayered.

4. Drum brake according to claim 3, characterised in that each multilayer elastic damping member (12; 14) comprises a layer of stainless steel (12a) in contact with the respective jaw (3, 4), a first layer of acrylic adhesive (12b), a first layer of nitrile rubber (12c), a layer of galvanized steel (12d), a second layer of nitrile rubber (12e) and a second layer of acrylic adhesive (12f).

5. Drum brake according to claim 4, characterised in that:- the first layer of acrylic adhesive has a thickness comprised between approximately 0.02 and 0.1 mm,- the first layer of nitrile rubber has a thickness comprised between approximately 0.2 and 1 mm,- the layer of galvanized steel has a thickness comprised between approximately 0.4 and 0.8 mm,- the second layer of nitrile rubber has a thickness comprised between approximately 0.2 and 1 mm,- the second layer of acrylic adhesive has a thickness comprised between 0.02 and 0.1 mm.

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