Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED STRAP CONFIGURATION 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 member, means for drive ratio and
direction selection. Brake bands under suitable hy-
draulic 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
metal forging or casting is secured to the ends of the
strap to provide the apply and anchor bracket portions
and a transverse tie for the band; the anchor and apply
portions or ears being engaged by the struts and 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 assembly expanded to size,
the bracket is transversely broached or milled to form
the transverse tie and apply and anchor ears, openings
are pierced in the bottom wall of the slots, the inte-
rior surface of the band is prepared for bonding
and a friction lining applied thereto, openings zre
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pierced in the lining, the interior surface is bored and the lining is
grooved, and two circumferential slots are sawed through the lining strap
and bracket except for the transverse tie portion to result in the three
radially expansible bands.
In commonly owned Canadian Patent No. 1,182,379 of February 12,
1985 an improved double wrap band 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 band of the above application utili~es a stamped
slotted thin steel band with transverse tie portions and a stamped bracket
with longitudinal tie portions secured thereto. A preslotted friction
lining ls applied to the interior of the band and bracket 9 and the tie
portions are punched ou~ to form the three parallel band portions having
improved roundness in the open position.
The present invention comprehends the provision of an improved
double wrap brake band which is formed from a preformed and preslotted
stamped strap, a preslotted friction liner and a separate stamped one-
piece bracket member; the band and bracket being secured together and the
liner applied to the interior surface. The band configuration provides a
preslotted stamped strap having equal width bands at one end and a wider
central band with narrower outer bands at the opposite end, the wider
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central band forming with the bracket the apply end
which terminates short of the outer bands; the outer
bands having widened ends beyond the wide end of the
central band. The central band tapers from the wider
end to the normal width portion over a substantial
fraction of the strap length. The bracket is appro-
priately sized for the width of the band ends.
Further objects are to provide a construction of
maximum simplicity, efficiency, economy, and ease of
assembly, and such further objects, advantages and
capabilities as will later more fully appear and are
inherently possessed thereby.
Figure 1 is an eleva~ional view of the preslotted
strap utilized in the formation of the improved band.
lS Figure 2 is an elevational view of the band and
bracket before removal of the connecting ties.
Figure 3 is an edge elevational view of the band
and bracket.
Figure 4 is an enlarged perspective view of the
finished double wrap brake band.
Referring more particularly to the disclosure in
the drawings wherein is shown an illustrative embodi-
ment of the present invention, Figure 1 discloses a
preslotted stamped strap 10, utilized in the formation
of the aouble wrap brake iard, co-pused of out-r bands
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11 and 12 and a central band 13 of substantially equal
widths for 50 to 75% of the length of the strap. The
strap has parallel longitudinally extending slots 14,14
interrupted by transverse ties 15,15; with the slots
diverging at 16,16 for 25 to 50~ of 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 having correspondingly narrower 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 o~ the
strap, the central band end 22 extends beyond the ends
23,23 of the outer bands.
lS A suitable stamped one-piece anchor bracket 24
(Figure 2) is utilized to join the opposite ends of the
strap to form a circular brake band 25. The bracket
includes a central transverse bar portion 26 of a width
equal to the strap width, an anchor portion 27 of the
same width as the bar portion, and a centrall~ located
apply portion 28; the apply portion and anchor portion
being joined to the bar portion by longitudinally
extending ties 29. The transverse bar portion 26 is
suitably secured, as by spot welding or brazing, to the
ends 21,21 of the outer bands 11,12 and the opposite end
22 of the central band 13.
The anchor portion 27 is secured to the ends 23,23
of the outer bands and has a raised bridging portion 31
receiving thereunder the central band 13 adjacent the
end 22 secured to the transverse bar portion; the
bridging portion allowing for movement of the central
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band 13 when the double wrap band is applied to the
clutch drum or opened. Also, the anchor portion is
provided with an upwardly bent or folded transverse
ridge 32 extending across the outer bands for app ica-
tion by suitable means in the transmission. Also, the
apply portion 28 has an upwardly bent or fo~ded ear or
lip 33 cooperating with piston means (not shown) in the
transmission to tighten the band onto the clutch drum.
The on~-piece anchor bracket member 24 i5 formed
into an arcuate member of substantially the same curva-
ture as the curved band and secured to the ends thereof
as above noted. The assembled unit is heat treated,
formed and heat set to the desired diameter over an
expanding fixture. ~ preslotted friction lining 34
lS having longitudinally extending slots and transverse
ties is bonded to the interior surface of the formed
band by a suitable adhesive~ the ties 29 joining the
bracket portions are cut out, and then the ties 15
joining the bands of the strap are removed by punching
or other suitable operation to form the interconnected
three bands 36,37,38 of the final assembly 35 (Figure
4~. As well as having better alignment of the bands
and superior roundness for more uniform engagement and
lower open running drag, the tapered portion "A"
of the central band provides increased lining durability
by allowing a more uniform lining pressure distribution
and increased apply end fatigue llfe through reduction
of band end flexure. Also, the stamping of the preslot-
ted band and the anchor bracket allows use of materials
that when suitably processed, result in a higher
strength to weight ratio and hence improved ~atigue life
over equal weight conventional dbuble wrap bands.
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The extent of taper of the central band in the
preslotted stamped strap is over a substantial fraction
of its length and is tailored to the application.
"Substantial fraction", as used herein and in the
appended claims, means a range of approximately one-
fourth to one-half the length of the central band. In
the embodiment shown, which has been successfully built
and tested, the fraction is approximately one-third the
length of the central band.
