GB2113329A

GB2113329A - Anti-lick device for drum brake

Info

Publication number: GB2113329A
Application number: GB08301142A
Authority: GB
Inventors: Jean Gergele
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 1982-01-18
Filing date: 1983-01-17
Publication date: 1983-08-03
Also published as: BE895630A; BR8300226A; ES518884A0; GB8301142D0; FR2520074A1; IT8352842V0; IT1159958B; FR2520074B1; SE8300206L; AU1056983A; AR230681A1; SE8300206D0; ES8400564A1; IT8367037A0; NL8204976A; DE3301130A1; JPS58124837A; LU84585A1

Abstract

A drum brake having brake tongs 12 comprising arms 121, 122 actuated by a ram 14. Between arms 121, 122 there is arranged device 3 provided with a bore 31 and with a slideway 32 the extent "h" of which makes it possible to select the necessary play between the brake lining 131 and the drum 11. A mobile element 34 connected to one of the arms 122 of the brake tongs slides with friction in the bore 31. Slideable without friction in the slideway 32 is a stud 33 connected to the other arm 121 of the tongs 12. The friction force of the mobile element 34 in the bore 31 is greater than the force produced by the opening spring 15 of the linings 131, 132, but less than the force produced by the ram 14 which closes the linings 131, 132 on the drum 11. The travel "h" of the stud in the slideway determines the play between the linings 131, 132 and the drum 11 in order to obviate licking of the linings on the drum. In an alternative embodiment (Fig. 2, not shown) the friction force is in the arm pivot (123) and a stud (53) and slot (52) provides the travel "h". <IMAGE>

Description

SPECIFICATION Anti-lick device for drum brake The invention relates to improvements in brakes known as drum brakes. Such brakes comprising a brake drum of cylindrical shape coaxial and integral with the rotating assembly, for example a vehicle wheel, which is to be braked, a tongs whose arms support friction linings arranged radially internally of and externally of the braking surfaces of the drum, these arms being actuated by a hydraulic ram.

Despite the advantages over other types of brake, more particularly very small bulk for considerable braking efficacy, this type of brake has the one disadvantage that in order to obtain an acceptable response time, slight but permanent rubbing of the linings on the brake drum is tolerated. This phenomenon, called licking, dissipates energy uselessly and causes local wear on the drum, so that the functioning of the brake is not wholly satisfactory.

One way of eliminating licking of the linings consists in introducing a play of appropriate extent between the linings and their braking surfaces on the drum.

It is an object of the present invention to provide a drum brake having a device associated with the tongs for the purpose of obviating licking of the brake linings.

Therefore according to the present invention there is provided a drum brake for a rotating assembly, e.g. a vehicle wheel, comprising a drum coaxial with the rotating assembly and integral therewith, and a tongs immobilised with respect to the rotation of the rotating assembly and comprising two arms connected by a pivot joint, the tongs being provided with brake linings arranged one externally of and another internally of the drum, and a brake control ram and at least one spring acting in opposition to the action of the ram, in which there is interposed between the arms of the tongs as assembly comprising a member having a bore and a slideway, an element mobile with friction in the bore of the member and fast with one of the arms of the tongs, and a stud capable of sliding freely and about the pivot axis of the tongs in the slideway of the member, the stud being fast with the other arm of the tongs and being in abutment at one of the ends of the slideway when the linings are open and at the other end when the linings are closed, the distance between the two ends of the slideway corresponding to the play provided between the linings and the brake drum, the friction force of the said mobile element in the bore of the member being greater than the tension force of the opposing spring, but less than the force of the ram taken at the level of the element.

The invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a brake assembly according to the invention in which the antilicking device is arranged at the ends of the arms of the brake tongs opposite from those comprising the linings, and Figure 2 illustrates another variant in which the frictionally mobile element of the antilicking device according to the invention is common to the two arms of the tongs.

Fig. 1 illustrates a brake assembly having a drum 11 mounted on a vehicle wheel having an axis of rotation XX'. Only parts of the wheels disc 8 and hub 9 are shown.

The brake assembly 1 comprises a drum 11, a tongs 12, linings 131, 132, a ram 14 and springs 1 5. The drum 11 is cylindrical, coaxial with the axis XX' and secured to the wheel disc 8, for example, by welding. The tongs 12 is formed of two arms 121, 1 22 whose ends disposed one radially externally and the other radial internally of the drum 11, each carry a brake lining 131, 132. The tongs 1 2 has a pivot 1 23 perpendicular to the axis XX' of revolution of the drum 11. Arranged at the other side of the pivot of the tongs 1 2 relative the drum 11 and the linings 131, 132, the ram 14 for closing the linings 131, 1 32 on the drum 11 is connected to each of the arms of the tongs 121, 122 by pivoting joints 141, 142 respectively.

The brake assembly 1 is shown in the braking position. The linings 131, 132 are closed on the drum 11. The springs 1 5 connected to the arms 121, 1 22 of the tongs 1 2 are tensioned, the two springs 1 5 which are substantially identical are connected to one another by means of a part 151 immobilised relative to the rotating assembly. The position of this part 151 is adjustable in the radial direction so as to balance the amounts of play between the radially external lining on the one hand and the radially internal lining on the other hand and the brake drum 11.If an anti-licking device according to the invention is arranged on each of the arms 121, 1 22 of the tongs 1 2 it is possible to dispense with this part 151 for balancing the amounts of play between the linings 131, 1 32 and the brake drum 11.

According to the invention a device 3 is interposed between the ends of the arms of the tongs 121, 122 opposite from those comprising the linings 131, 132. The device 3 is provided with a bore 31 and a slideway 32. The bore 31 is cylindrical and perpendi cular to the axis of pivot 1 23 of the tongs 1 2.

The slideway 32 extends over a distance "h" perpendicular to the axis of the pivot 1 23 of the tongs 1 2. The distance "h" between the two ends of the slideway 32 is adjustable by means of the screw 1 33 disposed in one face of the device 3. The distance "h" corre sponds to the travel of the stud 33 positioned on one end of the arm 121 of the tongs and to the amount of play which it is desired to give to the linings 131, 1 32 relatively to the drum 11 to avoid licking, taking into account the lengths of the arms between the pivot 123 of the tongs 12 and on the one hand the linings 131, 132 and on the other hand the stud on the end of the tongs arm 121.The stud 33 which can slide freely about the axis of the pivot 1 23 of the tongs 1 2 in the slideway 32 of the device 3.

The end of the tongs arm 122, is provided with a cylindrical rod 34 preferably perpendicular to the axis of rotation XX' of the drum 11. The rod 34 is capable of sliding with friction in the bore 31 of the device 3. In this example, the rod 34 positions in the device 3 and, simultaneously, the slideway 32 relative to the movement of the stud 33 integral with the end of the tongs arm 1 21.

The sliding friction force of the rod 34 in the bore 31 of the device 3 is greater than the tension force of the springs 1 5 when the linings are open, that is to say when the brake is in the deactivated state or rest position, taking into account the lever arm existing between the springs 1 5 and the rod 34. In other words, the (working) tension force of the springs 1 5 must be sufficiently high, when the linings 131, 132 are closed on the drum 11, to return the linings 131, 132 to their rest positions, i.e. to re-establish the play which obviates licking between the linings 131, 132 and the drum 11, and also the rest tension force must be less than the friction force of the rod 34 sliding in the bore 31 of the device 3.

Therefore, the working tension force of the springs 1 5 must also be less than the friction force of the rod 34 in the bore 31, still taking into account the lever arm between the springs 1 5 and the rod 34.

When the brake returns to the rest position the stud 33 sliding in the slideway 32 leaves the support of the adjustment screw 1 33 and, at the end of its travel "h", comes to abut against the radially interal end 320 of the slideway, that is to say travels over the distance "h" of the slideway corresponding to the re-establishment of the anti-licking play between the linings 131, 132 and the drum 11. The friction force of the rod 34 in the bore 31 being greater than the tension force of the springs 15, the device 3 does not slide along the rod 34.

The wear on the linings 131, 1 32 is compensated for by the sliding of the rod 34 in the device 3 under the action of the ram 14 during braking. This is because the friction force of the rod 34 in the bore is, according to the invention, greater than the tension force of the springs 15, but markedly less than the force of the ram 14 on the arms 121, 122 of the tongs 12. Thus, it is possible to maintain a constant play sufficient to avoid licking of the linings 131, 131 on the brake drum 11 whatever the degree of wear of the linings 131, 132.

The friction force appropriate for the rod 34 in the bore 31 of the interposed part 3 may be produced by known means, for example by gripping the rod 34 with a spring or a sealing element (not shown) acting in the bore 31.

Fig. 2 shows another construction form for an anti-licking device according to the invention acting about the pivot pin 1 23 common to the two arms 121, 122 of the tongs 12 which is identical to the tongs 1 2 of the assembly shown in Fig. 1 with the exception that the anti-licking device 3 is absent. Only the region of the pivot joint of the tongs 1 2 and the anti-licking device are illustrated in Fig. 2. The device according to the invention comprises a member 5, the pivot pin 1 23 and a stud 53.

The member 5 comprises a bore 51 arranaged in friction contact with the pivot pin 1 23. The pivot pin 1 23 is integeral for example with the arm 1 22 of the tongs 1 2.

The portion of the member 5 comprising the bore 51 is constructed from an elastic metal and is provided with a slot 35. This slot 35 makes it possible to move apart the two elastic arms 511, 512 forming the bore 51 to mount the member 5 on the pivot pin 1 23.

According to the invention, the friction force developed on the pivot pin 1 23 by the elastic clamping of the two arms 511, 512 of the member 5 must be greater that the tension force developed by the (opening) springs of the tongs, but very much less than the (closing) force of the brake ram.

The member 5 also comprises a slideway 52 in the form of an arc of a circle centered on the axis of pivot 123, wherein a stud 53 slides freely. This stud 53 is fast with the tongs arm 121. The angular sector a swept by the stud, i.e. the travel of the stud 53, in the slideway 52 corresponds to the play provided for avoiding licking of the linings 131, 1 32. The length "cow" of this sector, i.e. the travel of the stud 53, may be regulated by a pointed screw (not shown) similar to the pointed screw 1 33 of the anti-licking device of Fig. 1.

The operation of the assembly of Fig. 2 is similar to that of Fig. 1. In proportion as the linings 131, 1 32 of the brake become worn, the member 5 progresses in rotation about the mobile element formed by the pivot pin 123, under the action of the brake ram. Thus the stud 53 is always in abutment at the corresponding end of the slideway 52 before a new braking operation.

Claims

1. A drum brake for a rotating assembly, e.g. a vehicle wheel, comprising a drum coaxial with the rotating assembly and integral therewith, and a tongs immobilised with respect to the rotation of the rotating assembly and comprising two arms connected by a pivot joint, the tongs being provided with brake linings arranged one externally of and another internally of the drum, and a brake control ram and at least one spring acting in opposition to the action of the ram, in which there is interposed between the arms of the tongs an assembly comprising a member having a bore and a slideway, an element mobile with friction in the bore of the member and fast with one of the arms of the tongs, and a stud capable of sliding freely and about the pivot axis of the tongs in the slideway of the member, the stud being fast with the other arm of the tongs and being in abutment at one of the ends of the slideway when the linings are open and at the other end when the linings are closed, the distance between the two ends of the slideway corresponding to the play provided between the linings and the brake drum, the friction force of the said mobile element in the bore of the member being greater than the tension force of the opposing spring, but less than the fore of the ram taken at the level of the element.

2. A drum brake as claimed in Claim 1, in which at the level of its bore the member grips the mobile element elastically to provide the friction force greater than the tension force of the spring but less than the force of the ram.

3. A drum brake as claimed in Claim 1 or Claim 2, in which the member provided with a bore and with a slideway is interposed between the ends of the tongs arms opposite from those comprising the linings, the bore and the slideway being arranged perpendicularly to the pivot axis of the tongs, and the element mobile with friction in the bore of the member is formed of a rod fast with the end of one of the arms, and in that the stud sliding freely in the slideway is integral with the end of the other arm.

4. A drum brake as claimed in Claim 1 or Claim 2, in which the pivot joint of the two tongs arms is forced of a pin common to the two arms, which pin is fast with one of the arms and forms said mobile element in the bore of the said member.

5. A drum brake as claimed in Claim 1, in which the spring which serves for opening the linings includes a device for allowing the amounts of play between the linings and the brake drum to be balanced.

6. A drum brake as claimed in Claim 1 or Claim 2, in which at the end of the slideway corresponding to the opening of the linings there is provided a screw for adjusting the distance between the two ends of the slideway in which the studs slides without friction.

7. A drum brake substantially as herein described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.