Method of making a transmission shaft

An elongated shaft (124) for a compound transmission (110) and a method for producing same is provided. The shaft is finish machined from a work piece (200) comprising three segments (204, 206, 208) joined at friction-welded joints (210, 212).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to transmission shafts and a method for 
producing same. In particular, the present invention relates to elongated 
shafts, such as transmission countershafts, and a method of producing same 
involving friction or inertia welding of forged segments which are 
optimized for weight reduction, material cost and/or required strength. 
2. Description of the Prior Art 
Heavy-duty transmissions and the shafts utilized therein are well known in 
the prior art, as may be seen by reference to U.S. Pat. Nos. 3,105,395; 
4,754,665 and 4,944,197, the disclosures of which are incorporated herein 
by reference. Such transmissions typically utilize countershafts machined 
from one-piece solid forgings and define one or more gears, typically the 
gears associated with the low and/or reverse ratios, integral therewith. 
A more recent compound transmission design utilizes an increasingly 
elongated countershaft which extends from the forward to the rear housing 
walls (see U.S. Pat. No. 5,390,561, the disclosure of which is 
incorporated herein by reference). 
The prior art shafts and the method of producing same involved machining of 
a one-piece solid cold forging which, especially for an elongated 
countershaft, was not totally satisfactory, as the shaft was more 
expensive to produce and/or heavier than desired. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the drawbacks of the prior art 
are minimized or overcome by the provision of a structure and 
manufacturing method for an elongated shaft which will result in a less 
expensive and lighter weight shaft as compared to the prior art 
transmission shaft structures and manufacturing methods. 
The foregoing is accomplished by providing a structure for an elongated 
shaft work piece comprising at least one hot forged segment having a 
cup-shaped cavity at one or both of its ends which is welded, preferably 
by inertia or friction welding, to a similar hot forged segment or to a 
bar stock segment. The welded segments define a hollowed-out work piece 
which is then finish machined and/or heat and/or surface treated to 
complete production of the shaft. The hot forged segment (or segments) is 
configured to provide optimized weight reduction and required strength of 
the assembled shaft. As the strength requirements for the various segments 
may differ, the most cost-effective material for each segment may be 
individually selected. 
Accordingly, it is an object of the present invention to provide a new and 
improved structure and manufacturing method for an elongated transmission 
shaft. 
This and other objects and advantages of the present invention will become 
apparent from a reading of the following description of the preferred 
embodiment taken in connection with the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Certain terminology will be used in the following description of the 
preferred embodiment for convenience only and will not be limiting. The 
terms "upwardly," "downwardly," "rightwardly" and "leftwardly" will 
designate directions in the drawings to which reference is made. The terms 
"forward" and "rearward" will refer, respectively, to the front and rear 
ends of the drive train components as conventionally mounted in the 
vehicle, being, respectively, to the left and right sides of the various 
drive train components, as illustrated in FIG. 5. The words "inwardly" and 
"outwardly" will refer, respectively, to directions toward and away from 
the geometric center of the device and designated parts thereof. Said 
terminology includes the words above specifically mentioned, derivatives 
thereof and words of similar import. 
FIG. 5 illustrates a compound heavy-duty vehicular transmission 110 of the 
type advantageously utilizing the increasingly elongated front or main 
section countershaft 124 of the present invention. A detailed description 
of transmission 110 may be seen by reference to aforementioned U.S. Pat. 
No. 5,390,561. 
Transmission 110 includes a mainsection 112 and an auxiliary section 114, 
both contained within housing 116. Housing 116 includes a forward end wall 
116A and a rearward end wall 116B, but not an intermediate wall. 
Input shaft 118 carries input gear 120 fixed for rotation therewith and is 
supported by bearing 118A. The mainshaft 146 carries mainshaft clutches 
148 and 150 and the mainshaft splitter clutch 180 and is supported by the 
input shaft 118 and the output shaft 158. Shift forks 152 and 154 are 
provided for shifting clutches 148 and 150, respectively. Mainshaft 146 is 
independently rotatable relative to input shaft 118 and output shaft 158 
and preferably is free for limited radial movements relative thereto. 
The main section 112 includes two substantially identical main section 
countershaft assemblies 122 each comprising an elongated main section 
countershaft 124 carrying countershaft gears 130, 132, 134, 136 and 138 
fixed thereto. Gear pairs 130, 134, 136 and 138 are constantly meshed with 
input gear 118, mainshaft gears 140 and 142 and idler 157, which is meshed 
with reverse mainshaft gear 144, respectively. It is noted that, in the 
preferred design, countershaft gears 136 and/or 138 are formed integrally 
on shaft 124. 
Mainsection countershaft 124 extends rearwardly into the auxiliary section, 
where its rearward end 124A is supported directly or indirectly in rear 
housing end wall 116B. 
The auxiliary section 114 includes two substantially identical auxiliary 
countershaft assemblies 160, each including an auxiliary countershaft 162 
carrying auxiliary countershaft gears 168, 170 and 172 for rotation 
therewith. Auxiliary countershaft gear pairs 168, 170 and 172 are 
constantly meshed with splitter gear 174, splitter/range gear 176 and 
range gear 178, respectively. Splitter clutch 180 is fixed to mainshaft 
146 for selectively clutching either gear 174 or 176 thereto, while 
synchronized range clutch 182 is fixed to output shaft 158 for selectively 
clutching either gear 176 or gear 178 thereto. 
Auxiliary countershafts 162 are generally tubular in shape defining a 
through bore 162A for receipt of the rearward extensions of the main 
section countershafts 124. Bearings or bushings 162B and 162C are provided 
to rotatably support auxiliary countershaft 162 on main section 
countershaft 124. Bearing 162D directly or indirectly supports the rear 
ends of countershafts 124 and 162 in the rear end wall 116B. 
The use of the elongated front or main section countershaft 124 with the 
auxiliary section countershafts telescopically supported thereon allows 
for the elimination or minimization of intermediate walls and, for a 
comparable capacity, a considerably shorter and/or lighter transmission. 
See aforementioned U.S. Pat. No. 5,390,561 and copending U.S. Pat. 
application Ser. No. 08/345,092, now U.S. Pat. No. 5,546,823 entitled 
HIGH-CAITY COMPOUND TRANSMISSION and assigned to EATON CORPORATION, the 
assignee of this application, the disclosures of which are incorporated 
herein by reference. 
Due to the considerable length (about 18.9 inches or 48.0 centimeters with 
an outer diameter of about 2.6 to 4.5 inches or 7.0 to 11.3 centimeters) 
of elongated main section countershaft 124, producing same in the 
traditional manner (i.e., machining the shaft from a one-piece solid cold 
forged forging) results in a shaft that is heavier and more expensive than 
desired. 
Referring to FIGS. 1A-4, the work piece 200, from which the elongated main 
section countershaft 124 is machined, may be seen. In FIG. 1A, the phantom 
line 202 illustrates the final machined form of countershaft 124. The work 
piece 200 is formed from a first hot forged segment 204, a second hot 
forged segment 206, and a third bar stock segment 208. The segments 204, 
206 and 208 are individually illustrated in FIGS. 2, 3 and 4, 
respectively. 
The first and second segments 204 and 206 are joined at weld joint 210, 
while the second and third segments 206 and 208 are joined at weld joint 
212. The welded joints preferably are done by the so-called "friction 
welding" or "inertia welding" process. In this process, one of the 
segments is caused to rotate rapidly relative to the other segment and 
then the segments are moved axially into sustained forced contact. This 
welding process, and acceptable modifications and alternatives, are well 
known in the art. 
The segments 204, 206 and 208 preferably are of a typical shaft or gear 
grade of steel commonly used in heavy-duty transmissions such as, for 
example, SAE 8620H, SAE 4120RH, SAE 8627H, SAE 4130RH, SAE PS 18, SAE 
4130, SAE 4817H or SAE 4817RH. Segments 204 and 206 preferably are of a 
relatively short length relative to their diameter, allowing production by 
a common hot forging process, which is less expensive than a cold forging 
process required to forge the work piece for shaft 124 as a single 
forging. 
The friction or inertia welding process allows joining of segments of 
different alloys and, thus, each individual segment may be of a material 
selected to maximize the strength and material cost considerations 
thereof. By way of example, the requirements of segments 204 and 208 may 
be less than for segment 206, allowing a more costly alloy to be utilized 
for only segment 206, rather than for the entire shaft, as would be 
required if shaft 124 was of the prior art structure produced by the prior 
art methods. 
Although friction welding is the preferred method of joining the segments, 
other forms of joining the segments are possible within the scope of the 
present invention, such as, by way of non-limiting example, other forms of 
welding or adhesives. 
As may be seen by reference to FIGS. 1A and 1B, work piece 200 and shaft 
124 define two enclosed internal cavities 214 and 216, which considerably 
reduce the weight and material cost of shaft 124 as compared to the prior 
art solid structures. As may be seen, internal cavity 214 is defined by 
rearwardly opening cavity 218 in the first segment 204 and forwardly 
opening cavity 220 in the second segment 206. Internal cavity 216 is 
defined by rearwardly opening cavity 222 in the second segment 206 and a 
shallow forwardly opening cavity 224 in the third segment 208. The 
specific shapes and locations of the cavities are selected in view of 
maximizing weight and material savings while retaining required shaft 
strength and durability and preserving ease of forging and welding. 
First segment 204 is provided with an enlarged flanged area 226 for 
formation of the external gear teeth to define countershaft gear 136, 
while the second segment 206 is provided with an enlarged flanged area 228 
for formation of the external gear teeth to define countershaft gear 138. 
The rib 230 separating the cavities 220 and 222 in the second segment 206 
is axially aligned with flanged area 228. 
The internal and external dimensions of the various segments, and of the 
assembled work piece 200, are symmetrical about the axis of rotation 232 
of the shaft 124. 
After forging of the segments and required intermediate machining, if any, 
the work piece 200 is assembled by welding. After assembly of the work 
piece, the work piece is machined and heat and surface treated to its 
final configuration for assembly as main section countershaft 124 into 
transmission 110. 
Accordingly, it may be seen that a new and improved elongated transmission 
shaft structure and method for producing same is provided which will 
minimize or eliminate the drawbacks of the prior art. 
Although the present invention has been described with a certain degree of 
particularity, it is understood that the description of the preferred 
embodiment is by way of example only and that numerous changes to form and 
detail are possible without departing from the spirit and scope of the 
invention as hereinafter claimed.