GB2048403A - Internal-expanding shoe brake with a wear-compensating device - Google Patents
Internal-expanding shoe brake with a wear-compensating device Download PDFInfo
- Publication number
- GB2048403A GB2048403A GB7937554A GB7937554A GB2048403A GB 2048403 A GB2048403 A GB 2048403A GB 7937554 A GB7937554 A GB 7937554A GB 7937554 A GB7937554 A GB 7937554A GB 2048403 A GB2048403 A GB 2048403A
- Authority
- GB
- United Kingdom
- Prior art keywords
- brake
- control rod
- shoe
- expansion
- wear
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000008878 coupling Effects 0.000 claims description 11
- 238000010168 coupling process Methods 0.000 claims description 11
- 238000005859 coupling reaction Methods 0.000 claims description 11
- 238000006073 displacement reaction Methods 0.000 claims description 10
- 239000004020 conductor Substances 0.000 claims description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 abstract description 2
- 229910052802 copper Inorganic materials 0.000 abstract description 2
- 239000010949 copper Substances 0.000 abstract description 2
- 239000000463 material Substances 0.000 abstract description 2
- 238000010438 heat treatment Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000007373 indentation Methods 0.000 description 3
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 230000008602 contraction Effects 0.000 description 1
- 230000000994 depressogenic effect Effects 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D65/00—Parts or details
- F16D65/38—Slack adjusters
- F16D65/40—Slack adjusters mechanical
- F16D65/52—Slack adjusters mechanical self-acting in one direction for adjusting excessive play
- F16D65/54—Slack adjusters mechanical self-acting in one direction for adjusting excessive play by means of direct linear adjustment
- F16D65/546—Slack adjusters mechanical self-acting in one direction for adjusting excessive play by means of direct linear adjustment for mounting within the confines of a drum brake
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D65/00—Parts or details
- F16D65/38—Slack adjusters
- F16D65/40—Slack adjusters mechanical
- F16D65/52—Slack adjusters mechanical self-acting in one direction for adjusting excessive play
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Braking Arrangements (AREA)
Abstract
An internal-expanding shoe brake has a wear compensating device which can function efficiently throughout the temperature ranges, and consequent expansion, experienced during severe braking, since the device control rod (9) interconnecting the brake shoe flanges (2a, 3a) is provided with a portion (15) having a substantially higher coefficient of expansion than the other components of the brake, thereby permitting the control rod to expand with these components. In further embodiments (Figs. 3, 4, not shown) the control rod is in the form of telescoping tubes filled with a material with a high thermal coefficient, and (Fig. 5, not shown) a thermal connection is made between brake shoe and the control rod using copper cable. <IMAGE>
Description
SPECIFICATION
Internal-expanding shoe brake with a wearcompensating device
The present invention relates to internal-expanding shoe brakes having wear-compensating devices.
More particularly, the invention is concerned with a shoe brake having a wearcompensating device which automatically ajdusts the position of the brake shoes and comprises a control rod which extends between the shoes, the rod being coupled to one shoe by a coupling having a predetermined clearance, and co-operating with the other shoe in such a way that axial displacement of the rod relative to said other shoe is permitted in one direction, which compensates for wear in the brake, and is prevented in the opposite direction.
A well-known problem in shoe brakes provided witn a wear-compensating device of the aforesaid type is that of achieving the correct functioning of the device even when the brake becomes hot as a result of frictional heating, particularly during severe or sustained braking.
During braking, the friction between the brake shoes and the brake drum causes heating and expansion of the latter, while the control rod remains at a substantially constant temperature which is closely similar to the external ambient temperature, being unaffected by the degree of heating of the drum.
As a result, the control rod is displaced axially relative to the respective shoe until it reaches a position which compensates for the differential expansion of the drum and the control rod. When braking ceases, or is reduced in intensity, the drum cools and contracts in a linear manner, whilst the length of the control rod remains substantially unchanged.
Displacement of the control rod relative to the respective shoe is permitted in the direction which allows the spacing between the shoes to be increased, that is, to allow engagement with the brake drum, but is prevented in the opposite direction. Therefore, since the brake drum has expanded during braking, the shoes are maintained in the braking position as the temperature drops, and, as a result, when the drum contracts is comes into contact with the shoes, resulting in spontaneous braking, and even seizure of the brakes.
The object of the present invention is to provide an internal-expanding shoe brake provided with a wear-compensating device of the aforesaid type which can function efficiently regardless of the temperature differences between the brake drum and the control rod.
According to the present invention there is provided and internal-expanding shoe brake provided with a wear compensating device of the aforesaid type, characterised in that the control rod includes a portion having a substantially higher coefficient of thermal expansion than the brake drum.
The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a side elevational view of an internal-expanding shoe brake according to one embodiment of the present invention;
Figure 2 is a partially-exploded perspective view of the brake of Fig. 1;
Figure 3 is a side elevational view of a seocnd embodiment of the invention;
Figure 4 is an axial section of detail of Fig.
3 on an enlarged scale, and
Figure 5 is a side elevational view of a third embodiment of the invention.
In the drawings similar or corresponding component parts are identified by the same reference numerals.
Referring now to the drawings, there is shown, generally indicated 1, an internalexpanding motor vehicle shoe brake comprising opposing first and second brake shoes 2, 3, respectively, which are housed within a drum 4 and secured, in known manner, to a fixed part of the vehicle, the drum 4 being attached to or forming part of a wheel hub.
Each shoe 2, 3 is pivotally connected at one end to an articulation plate 5 which is also supported by the fixed part of the vehicle.
A hydraulic actuator 6 is interposed between the other ends of the shoes 2, 3 and, during braking, operates to thrust these ends apart by two opposite-acting axial pistons (not shown).
Each shoe 2, 3 has a respective radially inwardly projecting flange 2a, 3a, the flange 2a of the first shoe 2 being provided adjacent its said other end, with an aperture 7. The aperture 7 receives, with clearance, a small coupling plate 8 (Fig. 2), which is attached to one end 9a of a control rod 9 extending parallel to the axis of, and adjacent, the actuator 6. The other end 9b of the control rod 9 is gripped between two cam surfaces 1 0a, 11 a formed, respectively, on adjacent ends of a projection 10, carried by the flange 3a of the second shoe 3, and a lever 11 pivoted centrally on a pivot pin 1 2 projecting perpendicularly of the flange 3a intermediate its ends.The gripping action is caused by biassing of the the lever 11 by a tension spring 1 3 reacting between the first flange 2a and the other end of the lever 11.
The control rod 9 is formed, adjacent the coupling plate 8, into an omega-shaped looped portion 14, and an omega-shaped expansion strip 1 5 is fixed at each end to the control rod 9 and conforms to the looped portion 14. The control rod 9 and the expansion strip 1 5 are both made of metal, the metal of the expansion strip having a greater coefficient of thermal expansion than that of the control rod 9.
The brake shoes 2, 3 are biassed to the rest position, as shown in Fig. 1, by a tension spring 1 6 acting between the shoes and extending parallel to the control rod 9.
The brake 1 operates as follows: when the brake pedal is depressed, a piston in a hydaulic master cylinder (not shown) is displaced, increasing the pressure throughout the brake system. This pressure extends the pistons of the actuator 6 to thrust the brake shoes 2, 3 against the inner surface of the drum 4 by causing the shoes 2, 3 to rotate in opposite directions relative to the articulation plate 5.
The drum-engaging surfaces of the shoes 2, 3 are provided with friction linings which develop the braking force when in engagement with the drum 4.
When the brake shoes 2, 3 are thrust apart, the control rod 9 is displaced. However, the grip of the cam surfaces 1 0a, 1 a on the cooperating end 9b of the control rod 9 causes the coupling plate 8 to take up the clearance in the aperture 7. As the friction linings wear with successive braking operations, the increased rotation of the shoes 2, 3 necessary to effect braking. exceeds the displacement of the control rod 9 permitted by the clearance of the coupling plate 8 in the aperture 7.At the same time, however, the thrusting force of the actuator 6 overcomes the gripping action of the cam surfaces 1 0a, 1 a and the respective end 9b of the control rod 9 slides, relative to the surfaces 1 0a, 11 a, into a position which compensates for the wear of the friction linings.
When the brake pedal is released, the gripping action is reasserted with the control rod 9 in its wear-compensating position so that, as the tension spring 1 6 biasses the shoes 2, 3 to the rest position, the shoes 2, 3 mbve relative to the control rod 9 by a distance corresponding to the clearance allowed by the aperture 7. In this way, for any degree of wear of the friction linings, the amount by which the shoes 2, 3 are displaced from rest position to effect subsequent braking corresponds to the displacement of the control rod 9 permitted by the clearance between the coupling plate 8 and the aperture 7.
During severe or prolonged braking, the increased frictional heating causes excessive expansion of the drum 4, together with the shoes 2, 3, the actuator 6 and articulation plate 5. The control rod 9, having only a small area of contact with the heated parts, is heated to and remains at a substantially lower temperature than the other heated parts.
Without the expansion strip 15, the control rod 9 would undergo no appreciable expansion and the above described sliding between the end 9b of the control rod 9 and the cam surfaces 1 0a, 11 a would occur when the expansion of the heated parts is at a maximum so that, when braking ceased and contraction occurred, the shoes 2, 3 would be prevented from returning completely to their rest position by the control rod 9. An extreme situation can be envisaged where the shoes 2, 3 are maintained in engagement with the drum even when fully contracted.
The expansion strip 1 5 causes expansion of the control rod 9 at a- net rate substantially equal to that of the other components, since the coefficient of expansion of the strip 1 5 is greater than that of the drum 4 and other components, and thereby allows the control rod 9 to function correctly when abnormally high temperatures are reached. Expansion of the control rod 9 is permitted by distortion of the looped portion 14, which tends to open out as the expansion strip 1 5 expands.
In the embodiment shown in Figs. 3 and 4, the shoes 2, 3 are biassed towards their rest position by a tension spring 1 7 arranged adjacent, and parallel to, the articulation plate 5. The flange 2a of the first shoe 2 is provided at its end adjacent the actuator 6, with a perpendicularly projecting pin 1 8 which pivotally mounts a coupling plate 1 9 with a fixed clearance. The coupling plate 1 9 is connected to one end of a control rod 20 extending adjacent, and parallel to, the actuator 6. The other end of the control rod rod 20 carries an arrestor plate 21 which has an indented edge 21 a remote from the rod 20.
The indentations co-operate with a pin 22 carried by a lever 23 which is articulated to the flange 3a of the second shoe 3 about a pin 24 corresponding to the pin 1 8 on the first shoe. In this example, the lever 23 is connected to a hand-operated or parking brake (not shown). The coupling plate 1 9 is biassed towards the flange 3a of the second shoe 3 by a tension spring 25 acting between the plate 29 and the flange 3a.
As the wear of the friction linings increases with successive braking operations, the increased displacement necessary for the shoes
2, 3 to effect braking causes the pin 22 on the lever 23 to disengage from the respective
indentation in the arrestor plate 21. When the shoes 2, 3 are in engagement with the drum
4, that is, the braking position, the biassing
action of the spring 25 causes a displacement
of the control rod 20, allowing the pin 22 to
engage in another indentation of the arrestor
plate 21 and so compensate for the wear of the friction linings prior to the next braking
operation. In the subsequent braking operation the shoes 2, 3 are displaced by an
amount equivalent to the pivoting of the cou
pling plate 1 9 permitted by the spring 25
and, therefore, the displacement remains sub
stantially constant through the lifetime of the
friction linings.
As shown in Fig. 4, the control rod 20
comprises two telescopically-slidable cylindri
cal tubes 29, 30 closed at respective opposite ends to form a sealed chamber 31. The chamber 31 is filled with a material having a higher coefficient of thermal expansion than the other components of the brake. In this example, a wax filling is used which will melt at the high temperatures resulting from severe braking and, by expansion, cause relative displacement of the tubes 29, 30. In this way the control rod 29 expands with the other components and can therefore function correctly.
In a third embodiment, shown in Fig. 5, the flange 2a of the first shoe 2 is provided, adjacent its said other end, with a pin 32 which pivotally mounts a first lever 33. The free end 33a of the lever 33 is formed with a plurality of teeth which mesh with complimentary teeth formed on the adjacent free edge 35a of a toothed pawl 35. The pawl 35 is articulated to the first flange 2a by a pivot pin 34. The teeth are kept in meshing engagement with each other by a biassing spring 40 acting between the pawl 35 and the flange 2a. The flange 3a of the second shoe 3 is provided with a respective lever 23 which is pivoted to the flange 3a about a pin 24 corresponding to the pin 32 of the first flange 2a.
The levers 33, 23 are interconnected by a control rod 36, which is housed at one end 36a, with a predetermined clearance, in an aperture 41 formed in the first lever adjacent the pin 32. The other end of the control rod 36 is articulated, without clearance, to the second lever 23. The control rod 36 includes, intermediate its ends, an enlarged member 37 having a higher coefficient of thermal expansion than the other components of the brake.
The enlarged intermediate member 37 is connected to the second shoe 3 by a flexible conductor member 38 having a higher thermal conductivity than the rod 36, and made, for example, from copper.
When, during braking, the displacement of the shoes 2, 3 and, consequently, the control rod 36 exceeds that permitted by the clearance provided by the aperture 41, the first lever 33 pivots about the pin 32, causing the teeth at its free end 33ato rack along the teeth of the pawl 35 until a wear-compensating position is reached. This position is maintained for a subsequent braking operation by the spring 40, which keeps the teeth interengaged when the shoes 2, 3 are in the rest position. At the same time, heat is conducted to the intermediate member 37 by the conductor 38, causing an expansion of the control rod 36 to correspond to the expansion of the other components of the brake.
Claims (6)
1. An internal-expanding shoe brake having a wear-compensating device which automatically regulates the position of the brake shoe and comprises a control rod which extends between the shoes, the rod being coupled to one shoe by a coupling having a predetermined clearance, and co-operating with the other shoe in such a way that axial displacement of the rod relative to said other shoe is permitted in one direction, which compensates for wear in the brake, and is prevented in the opposite direction, in which the control rod includes a portion having a substantially higher coefficient of thermal expansion than the brake drum.
2. A brake as claimed in Claim 1, in which the control rod has an omega-shaped looped portion, in which the portion having a high coefficient of expansion comprises an expansion strip which is attached at each of its ends to the control rod and conforms to said looped portion.
3. A brake as claimed in Claim 1, in which the control rod comprises two coaxiallyarranged members between which is interposed an intermediate member constituting the portion with a high coefficient of expansion.
4. A brake as claimed in Claim 3, in which the coaxially arranged members comprise telescopically slidable cylinders closed at opposite ends to define a sealed chamber which contains said intermediate member, the latter having a coefficient of thermal expansion substantially greater than that of the cylinders.
5. A brake as claimed in Claim 1, in which the rod portion having a high coefficient of expansion is connected to a part of one shoe, which, in use, reaches a high temperature, by a flexible conductor member having a higher thermal conductivity that the control rod.
6. An internal-expanding shoe brake having a wear-compensating device, substantially as herein described with reference to and as shown in Figs. 1 and 2, Figs. 3 and 4 or Fig.
5 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT67869/79A IT1118962B (en) | 1979-04-24 | 1979-04-24 | INTERNAL SHOE DRUM BRAKE PROVIDED WITH A WEAR COMPENSATION DEVICE |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2048403A true GB2048403A (en) | 1980-12-10 |
| GB2048403B GB2048403B (en) | 1983-04-27 |
Family
ID=11305941
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7937554A Expired GB2048403B (en) | 1979-04-24 | 1979-10-30 | Internalexpanding shoe brake with a wear-compensating device |
Country Status (6)
| Country | Link |
|---|---|
| BR (1) | BR7907802A (en) |
| DE (1) | DE2943596C2 (en) |
| ES (1) | ES486034A1 (en) |
| FR (1) | FR2455219A1 (en) |
| GB (1) | GB2048403B (en) |
| IT (1) | IT1118962B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2132291A (en) * | 1982-12-24 | 1984-07-04 | Teves Gmbh Alfred | Device for the automatic adjustment of brake pads |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2049077A (en) * | 1979-05-21 | 1980-12-17 | Lucas Industries Ltd | Automatic adjuster for drum brakes |
| FR2541740B1 (en) * | 1983-02-25 | 1985-07-05 | Dba | SELF-ADJUSTING DRUM BRAKE |
| DE10325957B4 (en) * | 2002-10-31 | 2007-03-29 | Cherkasky, Yakiv, Dipl.-Ing. | Brake assembly with thermoregulation of the game |
| DE10250682B4 (en) * | 2002-10-31 | 2007-04-12 | Cherkasky, Yakiv, Dipl.-Ing. | Adjustment device, preferably for brakes to achieve a stable game with adaptation to changing temperature |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB487968A (en) * | 1936-02-27 | 1938-06-29 | Hydraulic Brake Co | Improvements in brakes |
| US2301272A (en) * | 1940-06-05 | 1942-11-10 | Bendix Aviat Corp | Brake |
| US2292017A (en) * | 1940-09-26 | 1942-08-04 | Thermo Brakes Corp | Brake adjuster |
| GB1507550A (en) * | 1975-10-13 | 1978-04-19 | Girling Ltd | Internal shoe drum brakes |
| IT1051319B (en) * | 1975-12-01 | 1981-04-21 | Start Spa | DEVICE TO AUTOMATICALLY THINK THE WEAR IN MOTOR VEHICLE BRAKING SYSTEMS |
-
1979
- 1979-04-24 IT IT67869/79A patent/IT1118962B/en active
- 1979-10-29 DE DE2943596A patent/DE2943596C2/en not_active Expired
- 1979-10-30 GB GB7937554A patent/GB2048403B/en not_active Expired
- 1979-11-09 FR FR7927728A patent/FR2455219A1/en active Granted
- 1979-11-16 ES ES486034A patent/ES486034A1/en not_active Expired
- 1979-11-30 BR BR7907802A patent/BR7907802A/en unknown
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2132291A (en) * | 1982-12-24 | 1984-07-04 | Teves Gmbh Alfred | Device for the automatic adjustment of brake pads |
Also Published As
| Publication number | Publication date |
|---|---|
| ES486034A1 (en) | 1980-05-16 |
| FR2455219A1 (en) | 1980-11-21 |
| BR7907802A (en) | 1980-12-09 |
| GB2048403B (en) | 1983-04-27 |
| DE2943596C2 (en) | 1983-12-01 |
| FR2455219B1 (en) | 1984-03-23 |
| IT7967869A0 (en) | 1979-04-24 |
| DE2943596A1 (en) | 1980-10-30 |
| IT1118962B (en) | 1986-03-03 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |