Accumulator piston

An accumulator piston for an automatic transmission. The piston comprises two components, the first and second being cup elements welded together with their closed ends in abutting relation. The lower cup includes a curled back portion with a radial flange having an axially extending bi-directional oil seal thereon, and spaced apart recesses in the curled back portion to permit oil to flow therein. The upper cup includes a radial flange of reduced diameter compared to the lower cup flange. The flange also has a lip seal thereon. The piston is spring-loaded and moves up and down in a bore and counterbore in response to fluid flow on either side of the piston to absorb shifting shocks.

BACKGROUND OF THE INVENTION 
The present invention relates generally to automatic transmissions, and 
more particularly, to an accumulator piston used therein. Specifically, 
the invention relates to an improved so-called 1-2 accumulator piston, 
which is made and assembled into one piece from two pieces, and which 
includes two seals bonded to the piston. This arrangement is advantageous 
from the standpoints of simplicity, reliability, and installation in the 
intended application. 
As currently manufactured, one form of the 1-2 accumulator piston includes 
two O-rings as the seal. By switching to a welded component having two 
deep-drawn cups separately formed and then butt-welded together, with the 
seals being bonded on to the stampings or casings, an improved product is 
made. 
Basically, the 1-2 accumulator piston in prior art transmissions has either 
been an aluminum casting or forging or a plastic piston. In the case of 
the aluminum casting or forging, two loose lip seals or O-rings were used. 
In the case of the plastic piston, two loose lip seals or O-rings were 
also provided. The aluminum casting approach had the disadvantage of being 
more expensive, because of the machining required on several surfaces. The 
aluminum casting, in addition, was heavier and in some cases less 
accurately machined. The loose lip seals were not as durable as bonded 
seals. In addition, the problem of a fit in the bore was presented. A 
machined aluminum casting or forging with loose O-ring seals had the 
further disadvantage of galling in the steel or aluminum bore formed in 
the housing. 
In the case of plastic, the strength was questionable as regards the 
piston. This shortcoming was particularly apparent over the life of the 
product, which could easily exceed 100,000 miles or perhaps, even two or 
three times that amount. Prior art plastic cups simply did not have the 
potential life expectancy of a more substantial piston. The invention does 
away with the need of O-ring or other loose lip seals, replacing them with 
bonded seals having several advantages. 
A one-step assembly process is possible with the design, which includes a 
major diameter flange on one cup and a smaller diameter flange on the 
other cup, with the two cups being deep drawn and welded together at the 
interface. The resulting metal piston is much stronger than prior art 
designs, it is lighter, more durable, and less expensive. 
In view of the failure of the prior art to develop an accumulator piston of 
an advantageous type, it is an object of the present invention to provide 
an improved accumulator piston. 
Another object of the present invention is to provide a one-piece component 
in place of components having O-rings or other loose-fitting seals. 
Yet another object of the present invention is to provide a bonded 
accumulator piston and seal unit requiring no additional assembly 
operations by the end user, that is, the labor force at the automatic 
transmission assembly point. 
Still another object of the invention is to make housekeeping easier for 
the user, in the sense of taking up less warehouse space with separate 
components requiring assembly and subsequent fitting. 
It is a further object of the invention to provide an element which, in 
use, will avoid undue pinching of rubber elements. In this connection, a 
dual molded lip is more durable and less likely to be torn or otherwise 
damaged in use than are O-rings. 
In particular, it is an object of the invention to locate the seals on the 
part where they will not engage the ports or openings in the bores during 
the assembly process. 
A still further object of the invention is to provide a piston wherein 
scoring or galling of the running surfaces can be avoided, particularly 
those where there would be metal-to-metal contact in the event of 
misalignment in either aluminum or steel housings. By way of explanation, 
when a non-bonded O-ring moves in the groove in which it is located, it 
eventually becomes torn or breaks down. Metal-to-metal contact then 
occurs. This occurs with every non-bonded O-ring. When there is 
misalignment, wear is accelerated. 
An additional object of the invention is to provide reduced stresses and 
strains and increased fatigue life over the expected life of the unit. 
Yet another object of the invention is to provide a lower cost assembly 
compared with an aluminum forging or casting. 
Still another object of the invention is to provide easier installation 
than is attainable with constructions containing O-rings. 
More specifically, another object is to avoid the presence of O-rings, 
which, during installation, and thereafter, are more easily cut by the 
passages in the bores, creating questionable installation reliability. 
A further object of the invention is to avoid scuffing and galling of the 
parts relative to each other. 
A still further object of the invention is to do away with scuffing of the 
bore surface by reason of having rubber-to-metal contact rather than 
aluminum-to-steel contact in the area of the bores or, in the alternative, 
with aluminum-to-aluminum to contact in the bore. 
The above advantages of the invention are achieved in practice by providing 
a bonded piston, preferably laser welded and made from two deep draws, 
with the open sides of the draws being directed oppositely and with each 
end portion of the piston having its own associated seal bonded thereto. 
The exact manner in which the foregoing invention is achieved in practice 
will become more clearly apparent when reference is made to the following 
detailed description of the invention set forth by way of example and 
shown in the accompanying drawings, in which like reference numbers 
indicate corresponding parts throughout.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
While the invention may comprise several aspects, and may take on several 
forms in use, several presently preferred embodiments of the invention 
will be discussed below. 
FIG. 1 shows the laser-bonded piston of the invention generally designated 
10 to be contained within an automatic transmission generally designated 
12. FIG. 1 shows the invention to include a housing 14 for the 
transmission generally designated 12, a flex plate 16, a torque converter 
18, a plurality of gear sets 20, 22, and an output shaft 24. In 
particular, the 1-2 accumulator piston is disposed in a bore in a shift 
body generally designated 26, which includes a downwardly biased spring 
28, an upwardly biased spring 30, and a movable piston 10 operating 
between the two. 
Referring in particular to FIG. 2, the composite piston 10 is shown to 
include a reduced diameter cup 32 which includes a radial lip seal 34 
bonded to a flange 35 at the open end thereof, and the spring 28 held 
captive in the cup 32. The second cup generally designated 36, contains a 
captive spring 30, shown compressed in FIG. 2, and this cup includes a 
convoluted wall section 38, having an enlarged diameter, two way seal 40 
bonded to a flange 39, which forms its end portion. 
The cup 36 includes a closed end 42, and plural scallops 44 or the like, 
permitting entry of oil for the purpose of actuating the piston. The bore 
46, which is enlarged to accumulate the larger flange on the piston 10, 
includes a snap-ring 48, and a piston support 49, having a seal 50 on its 
end portion 51. The support 49 includes a well 52 and a surrounding ridge 
54, which engages and supports the bottom cup 36 when the cup 36 is in its 
downwardmost position. 
The bore 46 includes a pair of inlet ports, a lower port 56 and an upper 
port 58. The lower port 56 is serviced by a pressure passage 60, and the 
upper port 58 is serviced by a pressure passage 62. On the opposite side 
of the bore 46 is an exhaust port 64, serviced by a passage 66 which is 
connected in use to a line tap. In use, pressure in the port 56 serves to 
move the piston 10 up, while pressure in the port 58 serves to move the 
piston 10 down. 
Finally, an outlet port 68 and a passage 70 serve the purpose of permitting 
the oil on the upper side of the piston to return by venting to a clutch 
housing area. The seal 34 on the flange 35 is positioned in a counterbore 
72 of somewhat reduced diameter in respect to the first or principal bore 
46. Preferably, a plug 69 in the end of the bore serves as a perch for the 
upper spring 28, and a contoured opening 71 therein leads to the outlet 
port 68. Assembly is aided by a taper 74 formed where the principal bore 
46 meets a shoulder 70 in the counterbore 72. 
The hydraulic accumulator is necessary to modern automatic transmissions. 
Accumulators are used in parallel to cushion the application of servos and 
hydraulic clutches. When hydraulic fluid accelerates or changes direction 
rapidly such as when pressure is applied through a shift valve, it is 
subject to surging. A rapid surge of hydraulic pressure can cause an 
"apply" device to vibrate or to engage harshly. This would cause rough 
shifts and could conceivably damage the transmission. 
An accumulator cushions or damps hydraulic pressure surges. This is done by 
temporarily diverting a part of the fluid in the circuit into a parallel 
circuit or chamber, in this case having a resiliently movable piston. The 
diversion allows pressure to increase in the main circuit more gradually 
(although still in a relatively short time) and provides the desired 
smooth engagement of the band or clutch with which it is associated in 
use. In this case, it is the 1-2 shift mechanism. 
The 1-2 accumulator thus comprises a pair of back-to-back welded cups or 
piston halves or the like that are able to move as a unit from one 
position to another in use. To move the piston upward as shown in FIG. 2, 
the unit operates as described. The overdrive-drive-1 pressure that was 
blocked at the 1-2 shift valve in first gear is shifted so that the 
hydraulic pressure flows through the valve to the intermediate clutch, the 
1-2 accumulator, and to the overdrive-servo regulator valve. 
As a result, the pressure appearing in the oil thus flows through the line 
and appears at the port 56. A scallop or relief on the underside of the 
piston 10 permits oil to fill the cup 36, as well as passing between the 
seals 40 and 50 and exerting a biasing-apart force on them. This urges the 
piston in an upward direction, causing flow out the port 58 and the line 
62, until the piston 10 reaches the top of its travel. This moves fluid 
from the region above the piston to a clutch housing area. Whereas there 
is line pressure in the line 62, the accumulator sees more pressure by 
reason of filling the entire interior 42 of the cup with oil. This causes 
the piston to move to its upwardmost position and compresses the spring 
28, while relieving the pressure on the spring 30. The port 64 and line 66 
are connected to a line tap. 
In another situation, an opposite movement of the accumulator piston takes 
place. In this instance, the line or higher pressure is seen at line 62 
and port 58, while the port 56 and the line 60 see a diminished pressure. 
With this condition, the pressure is greater on the upwardly facing 
surfaces (FIG. 2) than the downward facing surfaces, and the piston 
compresses the spring 30 and descends to its low position as shown in FIG. 
2. 
Referring now to FIGS. 3 and 4, a method of making the unit is shown. Here, 
the upper cup 32 and the lower cup 36 are shown. The deep draw into a cup 
32 is made, following which the radial elastomeric lip seal 34 is bonded 
to the flange 35. In FIG. 3, the bottom surface 42 of the cup 36 is shown, 
as is the curl 38 or return upon itself, and the dual lip seal 40 on the 
flange 39. The scallops 44 are also shown in this illustration. In this 
instance, the side walls 33, 35 of the upper and lower cups 36, 32 are of 
the same diameter. Once the cups are held in aligned relation, a laser 
beam 80 is shown melting the edges of the piston and securing the two 
halves together along the interface 92 shown in the drawings. The laser 
welder is the preferred method of welding, using a highly localized beam 
and little heat outside that concentrated at the welding point. 
In FIG. 5, an embodiment is shown wherein the cup 136 containing the larger 
flange 139 contains, in addition to the convoluted portion 138 and the 
dual lip seal 140, a depressed center section generally designated 182. 
This section 182 is shown to include a wall section 184 and a bottom 
section 186 constituting a further draw in the steel. The scallop 144 is 
illustrated as being in a rounded or out-of-phase position with respect to 
its counterpart in the other embodiments. 
Shown with the cup 136 is the other piston-forming cup 132 having a side 
wall 133 and a bonded seal 134 affixed to a flange 135. This unit also 
includes a second draw 142 in the portion into which the nose 186 will 
protrude. In addition to the bottom wall 138, the cup includes an 
offsetting center wall 140, and a bottom wall portion 142. In addition, an 
optional second wall portion 144 is taken from the portion of metal 
forming the end wall 146. This form of apparatus is used when the 
centering between the two units is in question, or when a stronger bond is 
preferred. A weld at the interface 192 is shown. In use, the piston 100 
operates in the same manner as its counterpart shown in FIG. 2. The weld 
192 is formed on a smaller diameter than in its counterpart in FIG. 2. 
Referring now to FIG. 6, a still further embodiment of the invention is 
shown. Here, the smaller diameter portion 232 of the piston 200 having the 
bonded seal 234 on the flange 235 is shown to include, at the depth of the 
principal draw 246, a stepped or second draw 242. This presents a reduced 
diameter nose portion to be accommodated in a pocket in the upper portion 
of the piston 200. This pocket is generally designated 243, and is shown 
to be defined by a side wall 284, and a bottom wall 286, formed in the 
larger diameter portion of the piston 200. In this case, a somewhat 
different configuration of scallop 244 is shown as being drawn from the 
stack that formed the curl 238 in the side wall 236. 
The dual lip seal 240 is of the same kind as is shown in the other 
illustrations, and is formed in the same way. The circumference of the 
portion at which the weld is made, 292 is also somewhat reduced in size, 
as the opening 243 serves as a pilot diameter for the side wall 246. This 
insures a close fit between parts and does away with any possible 
misalignment. 
Referring to the material from which the components of the invention are 
made, the two cups of the invention are preferably made from a steel 
material. In one respect, the simpler form of the first embodiment is 
preferred, while the interlocking function may be achieved by the other. 
The seals are made from a hydrogenated nitrile rubber preferably or may be 
made from other synthetic elastomers of a suitable type. 
It will thus be seen that the present invention provides a new and improved 
accumulator having a number of advantages and characteristics including 
those pointed out and others which are inherent in the invention. Several 
preferred embodiments of the invention being shown by way of example, it 
is anticipated that several variations may be made from the preferred form 
of the invention and that such modifications and changes may be made 
without departing from the spirit of the invention and the scope of the 
appended claims.