Note: Descriptions are shown in the official language in which they were submitted.
' 2195514
DESCRIPTION
TRANSMISSION BAND WITH ANCHOR BRACKET
HAVING LOCAL COINING AT THE ANCHOR HOLE
RE~ATED APPLICATIONS
This application is a continuation-in-part of co-pending application
Serial No.08/162,495, filed December 3,1993, which is a continuation-
in-part of application Serial No.08/006,324, filed January 19,1993 and
application Serial No. 07/960,994, filed October 14, 1992, now both
abandoned. Application Serial No. 07/960,994 is a continuation of
application Serial No. 07/784,537, filed October 29, 1991, now
abandoned. The subject matter of application Serial Nos. 08/162,495,
08/006,324, 07/960,994 and 07/784,537 are expressly incorporated
herein by reference in their entirety.
TECHNICAL FIELD
This invention relates to a transmission brake band utilized in a
vehicle automatic transmission, wherein the bands encompass one or
more clutch drives and, under the influence of suitable hydraulic controls,
effect ~ear changes and control the direction of rotation of tho output or
drive shaft from the transmission.
BACKGROUNI;) OF THE INVENTION
In conventional vehicle automatic transmissions of the torque
converter type, a driving shaft extends from the torque converter into the
transmission housin~ to a unit havin~ one or more clutch drums around
which are arranged either sin~le wrap or double wrap brake bands. It is
the function of the brake band through the application of suitable
hydraulic controls to effect gear changes and control the direction of the
- 21 9551 4
rotation of the output shaft from the transmission to the differential for
the drivin~ wheels of the vehicle.
Brake band research has recently focused on the provision of
bands which are composed of li~htweight materials of reduced cross-
se~tional thicknesses, thereby optimizin~ wei~ht characteristics while yet
retainin~ desi~n requirements for the fatigue life of the bands. Generally,
the failure of a brake band will occur at either the actuation or apply
bracket or the reaction or anchor bracket. It is a requisite that each
brake band have an actuation or apply bracket for receivin~ an apply
piston and a reaction or anchor bracket which operatively receives a
reaction member located in the transmission. Various types of automatic
transmissions utilize different types of reaction members. Some reaction
members may be of the tan~ential type which comprise a stationary
plun~er or stop member actin~ a~ainst the anchor end of the brake band,
while other reaction members may be the reaction pin type where the pin
is positioned perpendicular to the clutch drum and strap member and
extends into a reaction openin~ located in the anchor bracket of the
brake band.
An improved reaction or anchor bracket intended for use with the
reaction pin type is disclosed in the United States Patent No. 5,381;876,
wherein the anchor bracket includes a dome portion surroundin~ the
reaction openin~ which is formed as a blanked hole by punchin~ or
piercin~ the bracket material. The reaction bracket of the '876 patent is
commonly formed from a double thickness of strap material which is
expanded and prestressed in part to create a dome configuration. The
expansion operation prestresses the strap material at the location where
the strap material is deformed to create the dome, thereby providin~
somewhat enhanced stren~th characteristics to the dome anchor. The
dome is at the same time pierced or punched to form a blanked hole to
produce the reaction hole opening in the non-stressed strap material
which is centered in the dome. The dome portion surroundin~ the
21 ~55t ~
reaction openin~ places is formed from strap material which is in a
~enerally perpendicular relationship to the reaction pin as it is inserted
into the reaction openin~.
Problems have been encountered with the anchor bracket structure
tau~ht by United States Patent No. 5,381,876 when hi~h loads are used
with the band. It has been discovered that current brake bands
manufactured according to the teachin~s of the '876 patent have an
approximately median life of 16,000 cycles when tested per the standard
producticn fati~ue procedure which is 970 pounds of apply force and
140 foot pounds of torque. Failure will almost always occur at the
blanked hole in the reaction member. It has been found that, even
thou~h the domed portion is expanded and prestressed to create a dome
confi~uration, the flattened portion of the band surroundin~ the blanked
hole is not prestressed. The materials from which the hands are
commonly constructed has a characteristic that allow the material to
harden when it is formed or worked. Thus the material characteristics
remain unchan~ed without a si~nificant amount of material flow or
formin~ around the hole. Consequently, the prestress hardenin~
characteristics do not apply until areas are reached where the strap
material has been expanded to create the dome.
Therefore, it is the object of the is invention to provide an
improvement to the domed anchor bracket disclosed in United States
Patent No. S,381,876.
It is yet another object of this invention to provide work hardenin~
of the anchor bracket in the proximity of the anchor or reaction hole to
improve the fati~ue stren~th of the anchor bracket.
It is yet another object of the invention to provide localized
prestressin~ of the bracket material about the anchor hole.
2195514
BRIEF DESCRIPTION OF THE INVENTION
The present invention provides an improved anchor bracket for use
with automatic transmission brake bands. The bracket includes a dome
having hardened or prestressed areas surrounding the reaction opening
5 which is formed as a blanked hole by punching or piercing the bracket
material. The bracket of the invention is herein described generally with
re~ard to its incorporation with a single piece brake band, however, it is
envisioned that the bracket of this invention may be utilized with any
brake band desi~n where prestressed or work-hardened areas
10 surroundin~ the reaction holes are needed. For the purposes of simplicity
in explanation of the invention, the present invention will be described
herein as used with a sin~le strip of suitable metallic band material,
wherein the anchor bracket portion is integrally formed therefrom.
A typical brake band maybe formed in accordance with the
processes tau~ht by United States Patent No. 5,381,876. Once the
domed reaction bracket is formed, the peripheral surface area
surrounding the reaction openin~ is ~enerally aligned in parallel with the
curvilinear surface of the remainder of the band. The dome portion
surrounding the reaction opening places the strap material into a
20 ~enerally perpendicular relationship with the reaction pin as it is inserted
in the reaction opening. There is not a significant amount of rnaterial
flow or working in forming on the hole, consequently the strength
improving characteristic of the band material is usually not utilized at the
locations where most stresses from hand operation are focused. Thus,
25 ~he present invention provides that the ed~e of the anchor hole be coined
or work hardened to prestress the material and improve the material
strength of the anchor bracket and thus, improve its fatigue life.
Typical brake bands of the type of the present invention are
manufactured from SAE grade 980-XF material. One of the beneficial
30 characteristics of the SAE ~rade 980-XF metal is its work hardenin~
capability. Initially, the material is formable, but as the material is
~195514
formed, it ~ains stren~th in the formed areas. Therefore, the present
invention provides for work hardenin~ or ~coinin~ of the perimeter ed~e
surroundin~ the anchor hole to improve the material strength of the
anchor hole and thus, improve its fati~ue life.
The inventii~n will be more readily understood after readin~ the
followin~ best mode for carryin~ out the invention with reference to the
accompanyin~ drawin~s.
BRIEF DESCRIPTION OF THE DRAWINGS
Fi~. 1 is an elevated side view of the transmission brake band of
the present invention.
Fi~. 2 is a partial top plan view of the reaction bracket for the
transmission brake band of Fi~. 1.
Fi~. 3 is a sectional view taken alon~ lines 3-3 of Fi~. 2.
Fi~. 4 is a partial top plan view of a first alternative embodiment
of the reaction bracket of the transmission brake band of Fi~. 1.
Fi~. 5 is a sectional view taken alon~ lines 5-5 of Fi~. 4.
BEST MODF FOR CARRYING OUT THE INVFN~ION
Referrin~ now with particularity to the drawin~s, the present
invention will be described in detail as a one-piece sin~le wrap brake
band. However, it is not intended that this description of the invention
in use with a sin~le wrap one-piece brake band be necessarily limitin~
upon the envisioned ran~e of the embodiments for the present invention.
Referrin~ now to Fi~. 1, a one-piece brake band ~enerally
desi~nated by the reference No. 10 which is formed from an elon~ated
strap of material 12 definin~ an annular band of determinant len~th. In
the embodiment shown in Fi~. 1, the opposed ends 14, 16 of the strap
12 are folded over and rearwardly back upon the strap 12 to create
bracket members 18, 20 desi~ned to en~aye an apply piston (not shown)
and a reaction pin (not shown). The brake band further includes a
~1 955~ 4
friction linin~ (not shown~ suitably secured to the interior circumference
33 by an acceptable method of adhesion.
The apply bracket member 18 rnay be formed in any acceptable
manner. The apply bracket member shown in Fi~. 1 is formed by foldin~
S the end 14 into an upwardly folded rid~e 26 havin~ a stren~thenin~ rib
28 on the side of the fold located below the contact point for an apply
piston or pin. The folded rid~e 26 may or may not include a depressed
area (not shown~ intended to form a pocket in the central area of the side
opposite the stren~thenin~ rib 28. The depressed area is adapted to
10 enga~e the end of the apply piston actin~ in a ~enerally tangential
direction to the clutch drum. The end 14 with rid~e 26 and
stren~thenin~ rib 28 are folded over the strap 12 and secured to the
strap, preferably in a simultaneous manufacturin~ step with the foldin~
and forming operation, by commonly accepted methods such as clinch
15 fastenin~ 30.
Referrin~ now to Fi~s. 2 and 3, the present invention resides in the
end 16 which forrns the reaction bracket 20. The end 16 is formed by
foldin~ the strap member 12 upwardly and rearwardly upon itself. The
double layer of material is then subjected to an expansion and blankin~
20 operation which forms the dome 36 and creates the blanked hole or
reaction openin~ 32. The surface area of the dome 36 surroundin~ the
opening 32 is symrnetrically oriented to be substantially perpendicular to
the axial center line formed by the reaction openin~ 32. Preferably, the
blanked hole or reaction openin~ 32 includes four flats 34 such that the
25 reaction openin~ 32 is of a ~enerally square confi~uration. The flats 34
are ~enerally disposed in a 90~ relationship with one another and are
joined with curved corners 38. Each of the flats 34 includes a work
hardened or coined 40 area that extends the len~th of the flat 34. The
work hardened area 40 is produced by compressin~ or coinin~ the strap
30 material proximate the flat 34, as shown in Fig. 3 by the arrow, to
thereby reduce the cross-sectional thickness of the perimeter ed~e of
21 95~ 1 4
each flat 34. Work-hardenin~ or coinin~ thus stren~thens the strap
material in the work hardened area 40. Preferably, the curvature of the
coined or work hardened areas 40 matches the radial curvature of the
corners 38 which act to join the flats 34 to~ether. The preferably width
5 of the coined area is .020 nches.
Referrin~ now to Fi~s. 4 and 5, an alternative embodiment of the
present invention is disclosed. The alternative reaction bracket member
120 is formed by foldin~ the strap material 112 upwardly and rearwardly
back upon itself. The double layer of strap material is subjected to an
10 expansion and piercin~ operation which forms a dome 136 and creates
a blanked hole or reaction openin~ 132. The blanked hole or reaction
openin~ 132 is circular in shape and the perimeter ed~e of the reaction
openin~ 132 is work hardened or coined 140 about its entire
circumference.
- - 2 1 955 1 4
.
Exam~le
A set of prototype bands built in accordance with the best mode
of the present invention were compared with typical production bands
made simultaneously from the same strip of steel and from the same
5 toolin~ set up so as to eliminate ;~ll variables other than the effects of
work hardenin~ or coinin~. The fati~ue life of the bands, measured as
the rnedian B10 life on the Weibul Distribution Fati~ue Analysis, built in
accordance with the best mode of the present ;nvention and the typical
production bands are shown in the followin~ table.
Table 1
Coined Bands Production Bands
73,900 54,200
68,900 44,000
56,900 33,900
55,300 30,700
47,500 30,000
1st Group 43,600 29,700
42,700 28,800
42,600 28,100
42,400 23,500
41,800 23,400
40,500 21,700
37,200 20,400
57,800 25,000
46,200 24,600
40,200 23,000
2nd Group 39,200 20,100
38,500 19,200
37,000 18,000
19,700 18,000
17,900
- 2 1 955 1 4
The data from the test ~roup shows an 80% increase in median
B10 life by coinin~ or work-hardenin~ the anchor hole in accordance with
the best mode of the present invention. For the coined bands, median
B10 life was 28,424 cycles with a slope of 3.8. For the production
bands, median B10 life was 15,787 ycles with a slope of 3.5. The
slope measurement is indicative of the variability or distribution of
results. The hi~her the slope number, the more narrow the band of
variability or distribution and therefore, the more positive the results.
The work hardened and coined dome reaction bracket of the
present invention provides for ~reater stren~th in retainin~ the reaction
pin in position without premature failure of the brake band. It is intended
that variations of the embodiments disclosed herein may be incorporated
with reaction or apply brackets with transmission bands without the
departin~ from the scope and content of the followin~ claims.
