Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BRACKET ASSEMBLY FOR A DOUBLE WRAP BAND
Description
Conventional automatic transmissions transmit
torque through what is commonly called a planetary gear
system. Planetary gears are in constant mesh and
thus cannot clash. They also provide, through arrest of
the various gear carrying members, means for drive ratio
and direction selection. Brake bands under suitable
hydraulic controls are sometimes used to effect these
changes. The bands provide a means of holding gear
carriers and usually act as apply force multipliers. As
the governing equation is exponential in nature, a
so-called double wrap band may have more than twice the
holding power of an otherwise similar single wrap band,
at the expense of increased stroke, to full applied
position.
Conventionally manufactured double wrap brake
bands are formed from -a relatively thick metal strap,
and a forging or casting is secured to the end~ of the
strap to provide the apply bracket portions and a
transverse tie for the band; the apply portions or ears
being engaged by struts and by a hydraulic piston in the
transmission to actuate the band. Once the bracket is
welded to the strap, the band may be heat treated and
the band assembly is expanded to size, the bracket is
transversely~ broached or milled to form the transverse
tie and apply ears, openings are pierced in the bottom
wall of the slots, the interior surface of the band is
prepared for bonding and a friction lini~g ~applied
0 thereto, openlngs are pier~ced ln the llning, the
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interior surface is bored and the lin~ng i9 grooved, and two
circumferential slots are sawed through the lining strap and bracket
except for the transverse tie, to result in the three generally parallel,
radially expansible bands.
In commonly owned Canadian Patent No. 1,182,379 of February 12,
19~5 an improved double wrap band and bracket assembly and its method of
formation is disclosed which obviates the disadvantages of the internal
stresses created in previous bands that lead to distortion of the bands so
they are out of round in the released position, thus creating undesirable
friction drag between the band and clutch drum and uneven engagement of
the band on the drum when actuated. The double wrap band of the above
application utilizes a stamped slotted thin steel band with transverse tie
portions and a stamped bracket with longitudinal tie portions secured
thereto. A preslotted friction lining is applied to the interior of the
band and bracket, and the tie portions are punched out to form the three
parallel band portions having improved roundness in the open position
and providing a uniform engagement thereof with the drum.
The present invention comprehends the provision of a bracket
nssembly for a double wrap brake band which is formed from a stamped one-
piece bracket member; the band and bracket being secured together andsubsequently separated into the bracket portions and three parallel bands.
The bracket assembly includes a central tran3verse bar portion3 an anchor
portion and an apply portion; the anchor portion having a central raised
bridging portion ~oining outer flanges wlth a single
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reaction pocket formed in the bridging portion to
receive a reaction or transmission pin of the transmis-
sion. The apply portion has an upwardly folded apply
ear to receive the end of a hydraulic piston or ~rod and
angled side arms to aid in band orientation.
Further objects are to provide a construction of
maximum simplicity, eficiency, economy, and ease of
assembly, and such further objects, advantages and
capabilities as will later more ful~y appear and are
inherently possessed thereby.
Figure 1 is a top plan view of one form of a
stamped slotted strap for the double wrap brake band.
Figure 2 is a side elevational view of the finished
band and bracket assembly.
Figure 3 is a top elevational view of the finished
band and bracket assembly before removal of the connect-
ing ties.
Figure 4 is a cross sectional view of the bracket
taken on line 4-4 of Figure 3.
Referring more particularly to the disclosure in
the drawings wherein is shown an illustrative embodiment
of the present invention, Figure 1 discloses one form of
a preslotted stamped strap 10, utilized in the formation
of the double wrap brake band, composed of outer bands
11 and 12 and a central band 13 of substantially equal
widths for at least 50~ of the length of the strap. The
strap has parallel longitudinally extending slots 14,14
interrupted by transverse ties~lS,15; with the ~slots
diverging at 16~16 fo~-pproximately 25 to 50%~ ol
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the strap length to provide a tapered central band
portion 17 having an end 18 that is of a greater width
than the normal band portion 13 and correspondingly
narro~er outer band portions 19,19. The ends 21,21 of
the narrow outer band portions extend beyond the center
band end 18 and terminate in a width substantially equal
to the width of the normal band portions. At the
opposite end of the strap, the central band end 22
extends beyond the ends 23,23 of the outer bands.
A stamped one-piece anchor bracket 24 is utilized
to join the opposite ends of the strap to form a circu-
ar brake band 38. The bracket includes a central
transverse bar portion 25 of a width e~ual to the strap
width, an anchor portion 26 of the same width as the bar
portion, and a centrally located apply portion 27; the
apply portion and anchor portion being joined to the bar
portion by longitudina~ly extending ties 280 The
transverse bar portion 25 is suitably secured~ as by
spot welding or brazing, to the ends 21,21 of the outer
20 bands 11,12 and the opposite end 22 of the central band
13.
The anchor portion 26 is secured to the ends 23,23
o~ the outer bands and has a raised bridging portion 29
rece ving thereunder the central band 13 adjacent the
end 22 secured to tAe transverse bar portion; the
bridging portion allowing ~or movement of the central
band when the double wrap band is applied to the clutch
drum or opened. A~so, the anchor portion is provided
with a circular opening forming a self-centering anchor
p~cket or seat 31 in the bridging portion ~9 adapted
to receive a single reaction or transmission pin 34 that
is generally perpendicular to the band. A transverse
raised ridge 32 is formed in the anchor porti~n ~or the
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pocket 31 with the forward edge 33 of the pocket at the
highest point of the ridge to provide more positive
~ contact with the reaction pin. ~his pocket 31 is
positioned substantially in the center of the bridging
portion 29.
The apply portion 27 is secured to the end 18 of
the central band 13 opposite to end 22 and has an
upwardly bent or folded ear or lip 35 cooperating with
the end of a piston or strut (not shown) which is
suitably actuated to engage the band on the clutch drum.
The lip has a concave surface 36 and oppositely angled
side arms 37 to aid in orientation of the band to the
strut.
The one-piece anchor bracket member 24 is formed
into an arcuate member of substantially the same curva-
ture as the curved band 10 and secured to the ends
thereof to form a circular brake band assembly 38. The
assembled unit is heat treated, formed and heat set to
the desired diameter over an expanding fixture. A
preslotted friction lining 39 having longitudinally
extending slots and transverse ties is bonded to the
interior surface of the formed band by a suitable
adhesive, the ties 28 joining the bracket portions are
cut out, and then the ties 15 joining the bands of the
strap and lining are removed by punching or other
suitable operation to form the interconnected three
bands of the final assembly 38.
As well as having better alignment of the bands
and superior roundness for more uniform engagement and
more complete release from the drum, the stamping of the
preslotted band and the anchor bracket provides for
tighter dimensional control of critical fit areas.
Stamping of the preslotted ba~nd and anchor bracket
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allo~s use of materials that, when suitably processed,
result in a higher strength to weight ratio and hence
improved fatigue life over equal weight conventional
double wrap bands. Tight dimensional control of this
higher strength material results in improved fatigue
life over conventional bands for equal space occupied.
Further, the anchor pocket 31 minimizes the effects of
bracket/strap and bandJpin misalignment and allows
design and manufacture of the seat with minimal stress
risers or cracks. The use of the single central pocket
provides a larger surface area for suitably securing the
bracket to the straps and facilitates easy adjustment of
band length by milling or other suitable means. Also,
this design reduces the complexity and cost of the
transmission anchor system and effectively captures the
band. Although shown for a strap 10 having tapered
portions toward one end, this bracket member 24 could
obviously be applied to a strap having substantially
parallel bands for the entire length of the strap.
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