WO2007054817A2

WO2007054817A2 - Drum brakes

Info

Publication number: WO2007054817A2
Application number: PCT/IB2006/003406
Authority: WO
Inventors: Ivan Cecchelli; Marco Monopoli
Original assignee: Automotive Products Italia (Sv) S.R.L.
Priority date: 2005-11-11
Filing date: 2006-11-02
Publication date: 2007-05-18
Also published as: WO2007054817A3; GB0523107D0

Abstract

A brake has a pair of brake pads (12) , each pad being moveable generally radially outwardly into contact with a brake drum by a respective operating lever (14) acted on at one end by a brake applying means (15) and pivoted (16) at the other end from a backplate (11) . Each pad is contacted by a portion (14c) of the respective operating lever intermediate the lever ends and moving radially outwardly between a pair of circumf erentially spaced abutments (45) which extend generally perpendicular to the backplate and which react braking torque when the brake is -applied. Each lever (14) is pivoted on the backplate (11) by a pin (16) which extends generally perpendicular to the backplate. The free ends of the pins (14) are connected by a bracing link (50) to help to control the deflection of the pins (16) when the brake is applied.

Description

DRUM BRAKES

This invention relates to drum brakes and in particular to brakes of the type in which a pair of brake pads or shoes are provided, each pad or shoe being rnoveable generally radially outwardly into contact with a brake drum by a respective operating lever acted on at one end by a brake applying means and pivoted at the other end from a backplate, each pad or shoe being contacted by a portion of the respective operating lever intermediate the lever ends and moving radially outwardly between a pair of circumferentially spaced abutments which extend generally perpendicular to the backplate and which react braking torque when the brake is applied.

Such drum brakes are known and are shown, for example, in US 2051088, US 2503489 and US 4350230.

It is an object of the present invention to provide an improved from of the brake described above.

Thus in accordance with the present invention there is provided a brake comprising a pair of brake pads, each pad being moveable generally radially outwardly into contact with a brake drum by a respective operating lever acted on at one end by a brake applying means and pivoted at the other end from a backplate, each pad being contacted by a portion of the respective operating lever intermediate the lever ends and moving radially outwardly between a pair of circumferentially spaced abutments which extend generally perpendicular to the backplate and which react braking torque when the brake is applied, each lever being pivoted on the backplate

by a pin which extends generally perpendicular to the backplate, the free ends of the pins remote from the backplate being connected by a bracing link which helps to control the deflection of the pins relative to the backplate when the brake is applied.

By bracing the lever mounting pins in accordance with the present invention the stiffness of the brake is greatly improved thus significantly improving the response of the brake since the loss of actuating displacement previously caused by the deflection of the mounting pins is reduced. Also the reduction of the deflection of the mounting pins relative to the backplate helps to reduce the likelihood of any failure of the mounting of the pins on the backplate. It is also likely that the improved stiffness of the brake will allow the thickness of the backplate to be reduced (from say typically 2.5mm to 2.0mm) thus significantly reducing the material costs of the brake.

Preferably the bracing link is curved to increase the clearance around the hub of the associated wheel.

The link is also preferably provided with a longitudinally extending stiffening formation. This formation may be a longitudinally extending ridge pressed into the link.

Preferably the brake is also provided with the linked reaction abutments which are the subject of the Applicant's earlier British patent application No. 05 07470.3.

A handbrake lever may be pivoted on one of said operating levers adjacent said one end thereof and a strut may extend between said hand brake lever and said one end of the other operating member so that pivoting of the hand brake lever relative to said one operating lever moves the other operating lever towards its associated pad and thus, by reaction through the strut, also moves said one operating lever towards its associated pad thus applying the brake to provide a hand brake function.

The brake applying means may be hydraulic or electrical.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 shows a side view of a brake in accordance with the present invention with the drum removed;

Figure 2 shows a section on the line X-X of Figure 1 ; Figure 3 shows a section on the line Y1-Y1 of Figure 1;

Figure 4 shows a perspective view of a pad operating lever and associated handbrake lever which form part of the brake of Figure 1 ;

Figure 5 shows a perspective view of a brake pad used in the present invention;

Figure 6 shows a perspective view of an automatic brake clearance adjusting strut used in the present invention;

Figure 7 shows a perspective view of the brake shown in Figure 1;

Figures 8, 9, 10, 11 and 12 show views of a spring clip used to secure a brake pad to an associated operating lever in accordance with the invention;

Figure 13 shows, on a larger scale, details of the brake pad, abutment and operating lever arrangement of the present invention;

Figure 14 shows a section on the line Z-Z of Figure 13;

Figure 15 shows details of an aperture in the back plate to allow easy removal of a brake pad in a brake of the present invention;

Figure 16 and 17 show alternative abutment arrangements for supporting a brake pad in a brake of the present invention; Figure 18 shows a dual-limb type handbrake lever used in a brake in accordance with the present invention;

Figure 19 shows diagrammatically an alternative backplate arrangement for a brake in accordance in the present invention;

Figure 20 shows the bracing link of the present invention;

Figure 21 shows in diagrammatic form the deflection of the lever pivots in a brake which does not have the bracing link of the present invention;

Figure 22 shows details of the operating lever pivot pins of a brake in accordance with the present invention, and

Figure 23 and 24 show details of an alternative pressed metal bracing link of the present invention.

Referring to the drawings, a brake 10 has a backplate 11 on which a pair of brake pads 12 are supported for generally radially outward movement into contact with a ■ associated brake drum (not shown) by abutment structures 13. Each pad is moved radially outward into contact with the drum by an associated operating lever 14 which is acted on at its upper end 14a by a brake applying means in the form of a hydraulic wheel cylinder 15. The lower end 14b of each operating lever is pivoted on the associated abutment structure 13 by a pivot pin 16 which is also used together with a further rivet pin 17 to secure the abutment structure 13 to the backplate 11.

Pivoted on the right-hand operating lever 14 by a rivet 19 is a handbrake lever 18. The handbrake lever has a U-shaped lower portion 18a which engages with a nipple (not shown) on the end of a handbrake operating cable in a conventional manner. Alternatively, any other form of connection of the hand brake operating cable to the lower end 18a of lever 18 can be employed. For example, the quick attach arrangement shown in the Applicants patent EP 917630 is suitable.

The handbrake lever 18 engages one end 22a of an automatic brake pad clearance adjusting strut 22 whose effective length is automatically adjusted as the pads 12 wear to maintain a substantially constant pad to drum clearance throughout the life of the pads. This auto adjuster may, for example, be of the form disclosed in the Applicants European patent EP 388057 to which the reader is directed if further details are required. The other end 22b of strut 22 engages the left-hand operating lever 14. Thus as in well known, when lever 18 is pivoted about rivet 19 in a clockwise sense as indicated by arrow A lever 18 pushes on strut 22 which in turn pivots lever left-hand lever 14 its about pivot 16 to force left-hand pad 12 into contact with the associated drum. The reaction force of left-hand pad 12 contacting the shoe is transmitted to right-hand lever 14b via pivot pin 19 through strut 22 thus also forcing right-hand brake pad 12 to engage the associated drum so that a full handbrake function is generated.

As best seen in Figures 2, 3 and 7, each abutment structure 13 is formed as a generally U-shaped channel structure with one side 30 contacting the backplate 11 and the base of the channel having an aperture 31 through which a portion 14c of the respective operating lever 14 extends.

As shown in Fig 5, each brake pad 12 comprises a friction pad 40 and a metal backing/support member 41. Each support member 41 has a pair of locating rods 42 which extend between ears 43. Locating rods 42 are used to secure pad 12 to its associated operating lever 14 using a removable roll pin 44 as best seen in Fig 2. The ears 43 of the pad supports 41 contact abutment surfaces 45a or 45b on the abutment structures 13 when the brake is applied depending on the direction of rotation of the drum. This contact reacts the braking torque generated.

The abutment surfaces 45a and 45b are provided on abutment portions 45 of each abutment structure 13 and extend across the base of the abutment structure and into the sides of the U-shaped structure adjacent the base to provide a good balanced contact area between the pads 12 and the abutment structure 13. These abutments portions 45 are linked circumferentially by portion 46 of the abutment structure which forms the opposite side 32 of the U-shaped channel structure. This link 46 between the abutment portions 45 (which is the subject of the Applicant's previously referred to British application No. 05 07470.3 braces the abutment portions against relative circumferential deflection when the brake is applied thus better resisting the braking torque generated and providing a more robust and rigid brake structure.

As can be seen from Fig 1 , a retraction spring 22c encircles the adjusting strut 22 and is engaged at opposite ends with holes 14d in the operating levers 14. This retraction spring pivots the levers away from the associated brake drum when the hydraulic wheel cylinder 15 or the handbrake lever 18 is released thus retracting the operating levers and hence the associated brake pads 12 by their connection through pins 44.

In accordance with the present invention the pins 16 which pivotally mount the levers 14 on the backplate are connected by a bracing link 50 (see Figure 20) which extend between the free ends 16a of the pins 16 to help to control the deflection of ^' the pins 16 relative to the backplate when the brake us applied. The bracing link 50 is curved to increase the clearance around the hub of the associated wheel. In certain installation there may be sufficient space for link 50 to be straight in form.

Figure 21 shows diagrammatically the tendency of the free ends 16a of the pins 16 to deflect towards each other when the brake is applied (shown in dotted detail). By providing the bracing link 50 this tendency is significantly reduced and thus the stiffness of the brake is greatly improved. This significantly improves the response of the brake since the loss of actuating displacement which occurs (as a result of the deflection of pins 16) if the bracing link 50 is not used is reduced. Also the reduction of the deflection of the mounting pins 16 relative to the backplate 11 helps to reduce the likelihood of any failure of the mounting of the pins on the backplate. The improved stiffness of the brake also allows the thickness of the backplate to be reduced (e.g. from 2.5mm to 2.0mm) this significantly reduces the materia! costs of the brake.

Figure 22 shows the detail of one of the pins 16. The free end 16a of the pin is riveted over at 16b (see Figure 3) to secure the bracing link 50 against a first shoulder 16c on each pin. When the brake is assembled the other end of each pin 16 is riveted against 16 backplate 11 at 16d to sandwich the side 30 of each abutment structure 13 between the backplate and a second shoulder 16e on each pin. Lever 18 is pivoted on portion 16f of each pin between a spacing washer 51 and a third shoulder 16g of each pin.

Figures 23 and 24 show an alternative form of bracing link 50 which is formed by pressing and which includes a longitudinally extending stiffening formation in the form of a pressed ridge 52.

Figures 8 to 14 show an alternative arrangement in which each brake pad 12 is secured to the associated lever 14 using a spring clip 60. The ends 61 of each clip are arranged to grip around the ears 43 of each pad to secure the clip to the pad. The clip has tongues 62 which extend on either side of the associated operating lever portion 14c to help locate the pad in direction at right angles to the backplate. A further pair of tongues 63 are provided on clip 60which clip into notches 14e provided on the associated operating lever to secure the pad to the operating lever.

Also, as can be seen from Fig 1OA the end portions 61 of the spring clip are spaced a small distance S from the brake pad support member ears 43. The end portions 61 of the spring clip are arranged to contact the abutment surfaces 45a and 45b on the abutment portions 45. Thus a resilient contact is provided between the brake pads and the abutment portions as the small clearance S is closed when the brake pad is moved slightly circumferentially on contacting the associated drum. This resilient contact helps to reduce brake pad vibration/noise.

A brake in accordance with the present invention may be provided with an aperture 70 in the backplate 11 adjacent each brake pad 12 (see Figure 15) to allow the brake pad to be removed through the backplate in the direction generally perpendicular to the backplate for servicing/replacement of the pads. Each of these apertures 70 is preferably provided with a cover 71 of plastics material which can be inserted in position in the aperture 70. Fig 16 and 17 show alternative abutment structures for supporting the pads 12. In Fig 16, the ears 43 of the pads are supported on external abutment surfaces 45a and 45b of the abutment portions 45 of the structure and these abutment portions 45 are again linked by portion 46 of the structure to resist displacements of the abutment portions when the braking torque is reacted.

In the Fig 17 construction the ears 43 of the brake pads 12 are received in slots 47 of the abutment structure which are located in the abutment portions 45 intermediate the slot 31 through which the lever portions 14c extend and the external surfaces 45a, 45b of the abutment portions.

Figure 18 shows an alternative handbrake lever which is of the dual-limb type in which the respective limbs 18b the handbrake lever extend on each side of the associated operating lever 14. The cable 21 and associated cable nipple 20 engaging between the limbs 18b as shown. Again, if required, any suitable form of the quick attach cable arrangement can be used such as that disclosed in the Applicants previously referred to patent EP 917630.

Figure 19 shows in diagrammatic form an alternative backplate arrangement in which the backplate comprises a main strip-like structural portion 80 on each end of which an abutment structure 13 is formed or secured with the bases of the U- shaped abutment structures facing away from each other. The remaining portion 81 of the backplate can be formed from a significantly thinner and less robust material since it is not required to resist the braking torque which is taken by the main strip- like structural support 80. The use of the bracing link 50 in the present invention thus provides a significantly stiffened brake with consequent improved response.

Claims

1. A brake comprising a pair of brake pads, each pad being moveable generally radially outwardly into contact with a brake drum by a respective operating lever acted on at one end by a brake applying means and pivoted at the other end from a backplate, each pad being contacted by a portion of the respective operating lever intermediate the lever ends and moving radially outwardly between a pair of circumferentially spaced abutments which extend generally perpendicular to the backplate and which react braking torque when the brake is applied, each lever being pivoted on the backplate by a pin which extends generally perpendicular to the backplate, the free ends of the pins remote from the backplate being connected by a bracing link which helps to control the deflection of the pins relative to the backplate when the brake is applied.

2. A brake according to claim 1 in which the bracing link is curved to increase the clearance around the hub of the associated wheel.

3. A brake according to claim 1 or 2 in which the bracing piece is provided with a longitudinally extending stiffening formation.

4. A brake according to claim 3 in which the longitudinally extending stiffening formation is a longitudinally extending ridge pressed into the link.

5. A brake according to any one of claims 1 to 4 in which a handbrake lever is pivoted on one of said operating levers adjacent said one end thereof and a strut extends between said hand brake lever and said one end of the other operating

member so that pivoting of the hand brake lever relative to said one operating lever moves the other operating lever towards its associated pad and thus, by reaction through the strut, also moves said one operating lever towards its associated pad thus applying the brake to provide a hand brake function.

6. A brake according to Claim 5 in which the strut is an automatic brake pad clearance adjusting strut

7. A brake according to any one of claims 1 to 6 in which one end of each pair of abutments, between which the pads or shoes move radially outwardly, is supported from the backplate, and the other free ends of each pair of abutments are linked circumferentially to each other to brace each pair of abutments against relative circumferential deflection when the brake is applied.

8. A brake according to any one of claims 1 to 7 in which each pad is connected with its associated operating lever to limit radial movement of the pad relative to the lever.

9. A brake according to any one of claims 1 to 8 in which retraction spring means are provided to retract the operating levers when the brake is released thus retracting the associated pads.

10. A brake according to claim 9 when dependent on claim 5 in which the retraction spring means surrounds the strut.

11. A brake according to any one of claims 8 to 10 in which each pad is connected with its associated operating lever by a spring clip which has first formations which grip the pad and second formations which grip a formation on the associated operating lever.

12. A brake according to any one of claims 8 to 10 in which each pad is connected with its associated operating lever by removable pin means which engage the lever and a formation on the pad.

13. A brake according to claim 11 in which the spring clip is shaped to extend between the pad and the abutments to provide a resilient contact therebetween to help reduce pad vibration/noise.

14. A pad for use in a brake according to claim 11 or 13 having a clip for engagement with the formations on the associated operating lever.

15. A brake constructed and arranged substantially as hereinbefore described with reference to and as shown in Figures 1 to 7 and 20 or 22 or 23 and 24 of the accompanying drawings.