CA1195263A - Double wrap brake band assembly - Google Patents

Abstract

Abstract:

An improved double wrap brake band (43) for an automatic transmission and the method of making the band wherein the band is lightweight and heat set round at the released open position with the utilization of thinner strap material at higher hardness ranges. The band is formed from a preslotted and preformed strap (10) and a stamped one-piece bracket member (21) secured to the strap (10). The band subassembly is heat treated and heat set, the interior surface is acid etched and a preslotted friction lining (36) applied to the interior treated surface, the subassembly is sized, and the connecting ties for both the strap and bracket member are removed to provide the final band assembly.

Description

The p-esent inventlon relates to an improvement in double wrap brake band of the type used in the automatic transmission OL an automotive vehicle. In a conven-~ion~L
automatic transmission ol the torque converter type, a driven shaft extends from the torque conver-ter into the transmission to a unit having one or more clutch drums around which are placed double wrap brake bands; and more specifically, the double wrap bands are used for the 1-2 unit and for the reverse unit. It is the function of the brake bands under suitable hydraulic controls to effect gear change and control of the direction of rotation o~ the output or drive shaEt from -the transmission.
This is a division of copending Canadian Patent Application serial number 396,677, filed February 19, 1982.
Presently manufactured double wrap brake bands are formed from a relatively thick metal strap and a forging or casting forming ears and a transverse tie for the band;
the ears being engaged by the struts and a hydraulic piston in the transmission to actuate the band. The forging or casting is located in the space between the ends of the arcuate strap and the edcJes of the casting and strap are butt welded together. As seen in U.S. Patent No. 2,867,89~, once the bracket is welded to the strap, khe assembly is expanded to size and shape, the bracket is transversely broachecl ;

. ~

to Eorm the transverse tie and ears separa-ted by par~llel slcts and to form "V" slots in the ears to ~ccommodate the struts, openings are pierced in the bottom wall of the broached slots, the interior surface of the assembly is shot peened and the friction lining is bonded to the surEace. AE-ter bonding, openings are pierced in the friction material, -the interior surface is bored, the friction lining is circ~nferentially grooved, and two circumferential slots are formed through the assembly, except the transverse tie, by sawing through the strap and lining to produce the three radially expansible bands.
The double wrap bands made by the above enumerated method have certain disadvantages in operation. The internal stresses created in the bands during manufacture will distort the bands so that they are not round in the released position.
Thus, when assembled in an automatic transmission, there will be a certain amount of drag between the bands and its associated drum. Also, when the bands are actuated to engage the drum, a lack of concentricity of the outer and middle bands results in uneven engagement of the band. The double wrap brake band of the present invention obviates the disadvan-tages of the previously used bands.
The present invention relates to an intermediate assembly in the process of forming a double wrap b~ake band including an elongated curved sheet metal strap having longitudinally extending elongated parallel slots separated ky transverse ties and generally defining three parallel bands.
The slots open into both ends of the strap, and an anchor bracket member is secured to the opposite ends o~ the strap.

- sb/

;2~.3 rrhe bracket member includes a transverse connectin~ bar portion, a transverse anchor portion joined -to the connec~in~
bar portion by parallel ties, and a central apply portion on the opposite side of the connec-ting bar portion and attached thereto by a longitudinally extending tie.
More specifically, the present invention comprehends, therefore, the provision of an improved double wrap brake band which is formed from a preformed and preslotted stamped s-trap and a separate stamped one-piece bracket member. The band and bracket may be formed from thinner gauge sheet metal for improved cost and lighter weight with the material having a higher hardness range. The bracket and strap are secured toyether, and the assembly may then be heat set round in the released position to decrease the drag of the band on the clutch drum when the band is released.
Anillustrated embodiment o-f the present invention also comprehends the provision of an improved double wrap brake band utilizing a preslot-ted non-asbestos friction lining.
Less material is required for the band, and there is better axial alignment of the outside and middle bands in the free position. ~lso, there is a better engaged conformity of the double wrap ban~ with all three bands in substantially uniform engagement with the clutch drum.
In a specific embodiment of the present invention, the preslotted strap is formed into a curved confi~uration and a preslotted metal bracket member is spot wel~ed to the strap; both the strap and bracket having tie portions retaining a unitary assembly. The assembly is heat treated, : sb/ `

i3 hea-t set and the interior surface prepared for bonding. A
preslot-ted friction lining is bonded to the interior surface of the band, and the ties in the strap and bracket are removed to provide the final double wrap band.
Further objects are ~o provide a construction of maximum simplicity, efficiency, economy and ease of operation, and such further objects, advantages and capabilities as will later more fully appear and are inherently possessed thereby.
One way of carrying out the invention is described in detail below with reference to drawings which illustrate only one specific embodiment, in which:
Figure 1 is a top plan vlew of the preslo-tted strap forming the double wrap band.
Figure 2 is a side elevational view of the strap in a curved condition.
Figure 3 is a top plan view of the curved strap.
Figure ~ is a side elevational view of the bracke-t member for the band.

~b/

.g5~6~

Figure 5 is a top plan vle~ o~ t~e hracket mem~er.

~ igure 6 is an enlar~d perspective vi.e~ o~ ~he ~racket me~er.

Figure 7 is a partlal slde elevati.onal view o~ the assem~led strap and ~racket secured toge~her in accordance with this invention.
Figure 8 i5 a top plan vîe~ of the assem~

Fiyure 9 is a top plan vie~ o~ the preslottea friction lining ~or the ~and.

Flgure 1~ is a side elevational v.iew o~ the ~and assemhly with the ~racket ties ~eing removed~

Figure 11 is a cross sectional view taken on the line 11-11 of Figure 10.

Fl~ure 12 is a top plan view of ~he ~and assemfil~ with the bracket tie straps removed.

Figure 13 is a s.ide elevational view of the ~and a5sem~1~ ~ith the strap ties removed.

Fi.~ure 14 i5 a top plan vie~ o~ a portion of the ~and sho~i.n~ the stra~ tie~ removed.

F~gure 15 is a top plan vi.e~ o~ the f.inal - ~md assem~

Figure 16 is a cross sectional view taken on t~e line 16-16 o~ Figure 15~

~ ;gure 17, ~ihich appears on the same sheet oE
dra~ings as Figure 6, is a cross sectional view -taken on -the line 17-17 oE ~igure 15.

Figure 18 is a top plan view or a strap for a reverse ~and.

Figure 19 is a side elevational view of the bracket and strap with the bracket ties removed.

Figure 20 is a top plan view of the assembled bracket and strap.

Referring more particularly to the disclosure in the drawings wherein are shown illustrative embodiments of the present invention, Figure 1 discloses the pre-slotted flat strap 10 which forms the basis for the final double wrap brake band. The strap includes two parallel lines of elongated slots 11 separated by transversely ali~ned ties 12 to form parallel outside bands or band

2~ seyments 13 and 14 and a middle band or band segment 15 One end 16 of the middle band extends beyond the ends . 17,17 of the outside band, while at the opposite end, the ends 18,18 of the outside bands project beyond the end 19 of the middle band. The slotted band is formed , into a cwrved member 33 (Fi~ures 2 and 3).

~ An important aspect of the preSQnt in~ention resides in a one-piece anchor bracket- member 21 (Figures ~, 5 and 6) formed by stamping the bracket member from 30 sheet metal to provide a longitudinally curved member.
The bracket member 21 includes a mab/~ J

., .

central ~ransverse connecting har portion 22 haviIlg a wid-th e~ual to -the width o~ -the stxap 10, an anchor portion 23 extending the ~idth oE the strap and having an upwardly foldecl or crimped rldge 2~ and a raised central ~ridging section or portion 2~ on each side of an extending under the crimp~d, convex ridge 2~; the anchor por-tion being integral with the transverse connecting bar portion 22 throuyh a pair o~ parallel ties 26,26. The anchor portion 23 of bracket member 21 serves the unique purpose of connecting the anchor ends 17,17 of the outer bands 13 and 14 to improve the alignment of the bands 13,14 during engagement. A pair of upwardly bent positioning tabs 27,27 are stamped out of the anchor portion adjacent but rea-wal^dly of the folded ridge 24; the tabs or earC, 27 functioning as locating members. ~xtending from the opposite side of the transverse connecting bar portion 22 is a cen-trally located longitudinally extending apply portion 28 havirlg an upwardly crimped or folded lip 29 with an indented central area 31; the apply portion being attached to the transverse bar portion 22 by a tie 32.

The above described bracket member is also disclosed and is claimed in applicant's copending divisional application serial number , filed Sep-tember 11, 1984.
The anchor bracket member 2:L i9 a one-piece stamping that is located on the ends of the strap 10 when it is Eormed or curved into a generally arcuate member 33 with the central band 15 extending under the raised bridying section 25 of the bracket member. The bracket member is spot welded as at 34 to the ends 16,19 of the middle band and the ends 17,17,18,18 of the outer bands (Figures 7 and 8). After s~ot welding, the bracket and curved strap may be copper brazed to~ether to impxove the reliability over a simple we.~led assembly.

sb/

~' After spot ~elding and~or brazing at a -temperature in the range OL 2Q30 to 2Q50~., the - asse~bly is held for five minutes at the elevated iemperature and then heat treated ~y neating t~ a ~emperature in t~e range o~ 155Q to 17Q0.F~ and quenched in hot or cold ClQQF. - 35~~.1 oil to provide a Rock~ell C scale ~ardness of 54 to 58.
Then the asse~l~ is predrawn at a ternperature of approximately 40Q~ for about 35 minutes to a 1~ Roc~w~ll C scale hardness of 50 to S4. Finally, . t~e assernhly i5 ~eat set to the desired diarneter over an expanding fi~ture at a temperature i.n t~e range of 700 to 740 F. over a time period of 20 to 30 minutes to produce a Rockwell C scale hardness ~5 of 40 -to ~5.

A preslotted non-asbestos friction lining 36 (Figure 9~ is applied to the interior surface 35 of the band assem~ly after the surface is prepared by an acid etch or other suitable surface preparation~
2a The linin~ also is forrned with elongated longituctinal parallel slots 37 separated ~y trans~erse ties 38.
The ends 39 of the bands ~ormed by the slots are also joined by ties ~1 rather than the open slots of the strap 10. The lining is bonded to the sur~ace 35 by a 5ui.table adhesi~e at a temperature in -the range of 400 to 44Q F. at th.e ~ond line for two minutes ~ith ~he tie~ 38 aligned with the ties 12 o the strap ln and po~itioning notches 40 aligned ~ri-th the ties 26 of the bracket rnernberi t~e ends of the lin~ng ~eing positioned su~stantially diame-trically opposite to -the ~racke-t mem~.er 21.

Once the lining is bonded to the hand assemhl~
to form the assembly 42~ the ties 26,26 joini.n~
the portion 23 to t~e connecting ~.ar portion 22 and the tie 32 joining the apply portion 2~ to the ~ar portion are cut out ~igures lQ, 11 and 121-Then tne ties 12 and 38 in t~e trap and liner;
respectivel~, are removed ~ punc~ng or other suita~le operati.on CFigures 13 and 14l to form the interconnected three ~ands 44,45,46 of the final asser~ 43 tFigure 15~.. This a~sembly has a ~etter alignment of the ~ands due to the inter-connection of the anchor ends 17,17 of the outer bands 44 and 46 ~y t~e ~ridging sectlon 25 in the ..ree or released position to provide greater roundness and t~us less drag between -the ~ands and the clutch drum. Also, when the band is applied to the drum~ engagemenk i5 more uniform throughou~
-the three parallel bands 44,45,46. Obviously, ~he -ties 12 and 38 in the band could be initially . 20 removed follo~ed by the bracket ties 26 and 32 -to obtain the same result.
,~
Flgure 18 discloses an elongated strap 51 to form t~e reverse double wrap band which is generally similar ta the strap 10 in having longitudinall~
e~tending slot~ 52 w.~th transverse ties 53; however, the end 55 of the central ~and 54 ex-tends farther ~e~ond the end~ 57 o~ the outside hands 56 ~t the one end and, a-t the opposite end, the ends 5~ of th.e outer hands extend ~arther be~ond the end 58 - of the central band. Like~ise the ~racket member 61 (Figures 19 and 201 of the reverse bznd îs more 9 _ , .

., elon~atecl with a con~e~ a~ 3 ort~on 62, an anchor portion 63 connected to the har portion by a pair o.E eloncJa-ted ties 6~, and an apply poxtion 68 connecLed -to the bar portion 6~ by a sin~le elon-~a-ted tie 69. Tne anchor portion 63 i~
formed with a central circumferentially e~tending raised bridging section 65 having an upwardly bent convex portion 66, and a pair o~ up;~lardly bent ears 67,67 punched out of the mernber aligned with the ou-ter bands 56 of the elongated s~rap 51 to receive anchor struts or pins thereagains-t.
lC) The apply por-tion 68 includes a punched out concave cen-tral upwardly extending lip 71 and a pair of punched out side tabs 72,72 sliyhtly rearwardly and laterally o-f the lip 71 to positively locate the apply piston pin (not sho~n) against the lip 71; the tabs 72,7~ preventing laieral misalignment of the piston. The process of forming he final double wrap band assembly for the reverse band is substan-tially -the same as described and shown in Figures 1 through 17.
The complete double wrap brake band and the method or Eorming the same which are also disclosed and claimed in above-identified paren-t application serial number 396,677.
The double wrap brake band and the method of making the same has sevexal technical advantayes over presently manufactured double wrap bands as follo~.is:
1. Less material is utilized -for the band and bracket to provide a lighter weight unit.

sb/' . , i263 2. Lower running dra~ loss on -the drum ~it~
the ~and in ~he open position.

3. An improved facigue life for -the ~and resulting from u-tilization of a hîg~er hardness range.

4. W~ere the ~racket and strap are brazed together, t~ere is improved relia~ilit~
over a welded only assem~ly.

5~ Better alig~nent of t~e ~ands in open position and better engaged conformity.
5. The assem~ly has a lower unit cost as stampings are used instead of forgings and all machining operations are eliminatea.

7. There is an improved bonding of the friction lining to the band.
8. A more uni~orrn product is achieved.

9. A non-as~e~tos band lining is utilized.

. -- 11 --, .

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An intermediate assembly in the process of forming a double wrap brake band including an elongated curved sheet metal strap having longitudinally extending elongated parallel slots separated by transverse ties and generally defining three parallel bands, said slots opening into both ends of the strap, and an anchor bracket member secured to the opposite ends of the strap, said bracket member including a transverse connecting bar portion, a transverse anchor portion joined to the connecting bar portion by parallel ties, and a central apply portion on the opposite side of the connecting bar portion and attached thereto by a longitudinally extending tie.

2. An intermediate assembly as set forth in claim 1, wherein a friction lining is bonded to the interior surface of said strap, said lining comprising an elongated strip of friction material having longitudinally extending elongated parallel slots therein separated by transverse ties, said slots and ties of the friction material corresponding to the slots and ties of said metal strap.

3. An intermediate assembly as set forth in claim 1, in which the end of said central band extends beyond the ends of the outside bands at one end of said strap, and the ends of the outside bands extend beyond the end of the central band at the opposite end of the strap.

4. An intermediate assembly as set forth in claim 1, in which said anchor portion includes an upwardly folded transversely extending anchor ridge and a pair of laterally spaced upwardly bent tabs rearwardly of said ridge, and said apply portion includes an upwardly folded transverse apply lip having a central indentation facing away from said connecting bar portion.

5. An intermediate assembly as set forth in claim 1, in which said anchor portion includes a pair of upwardly bent ears aligned with said outside bands and a central upwardly bent convex transverse ridge rearwardly of said ears and aligned with said central band, and said apply portion includes an upwardly bent apply ear having a concave surface facing away from said connecting bar portion and a pair of upwardly bent tabs formed outwardly and rearwardly of said apply ear.

6. An intermediate assembly as set forth in claim 1, wherein said connecting bar portion is secured to the ends of the outer bands at one end of the strap and the opposite end of the central band, said anchor portion is secured to the opposite ends of the outer bands, and the apply portion is connected to the one end of the central band.