Two part shifter shaft

The present invention is a transmission having a two part shift shaft. The spur gear supporting portion of the shift shaft is received by bearings of the housing at its two ends and is made of a relatively strong material for supporting the load of the spur gears. One of the bearings is formed in an internal wall of the housing to support the proximal end of the shift shaft. The shift collar supporting portion of the shift shaft supports the shift collar and is axially aligned with the gear supporting portion. A projection of the shift collar supporting portion engages a recess in the gear supporting portion to axially align and properly position the shift collar for operation of the shifting mechanism. The shift collar supporting portion is made of a less expensive material than the gear supporting portion, thus reducing the overall cost of the transmission.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to small transmissions such as used in riding 
lawn mowers and the like. More specifically, the field of the invention is 
that of shift shafts for such in-line transmissions. 
2. Prior Art 
In-line shift transmissions include a plurality of linked transmission 
shafts, with one of the shafts being a shift shaft supporting a plurality 
of rotatable spur gears. The transmission housing includes bearings which 
support the shift shaft at its opposite ends. The shift shaft includes 
axial channels in which keys are disposed for engaging internal keyways of 
the rotatable spur gears and thereby rotatably connecting the engaged spur 
gear to the output shaft. The key is made of a resilient metal including 
an elongate shaft disposed in the axial channel of the shift shaft and a 
head portion which is biased to extend into one of the keyways. 
An in-line transmission is disclosed in U.S. Pat. No. 4,996,574, assigned 
to assignee of the present invention, the disclosure of which is 
explicitly incorporated by reference. The shifting mechanism of the '574 
transmission includes a pair of axially movable shift keys disposed in the 
longitudinal channels of the shift shaft. The shift keys rotatably couple 
the shift shaft with one of the gears. Each key has a base portion 
engaging a shift collar which is axially slidable on the shift shaft. The 
collar has a peripheral groove receiving a pin of a shift fork, which can 
pivot within the housing and is connected to the shifting mechanism of the 
vehicle. The shift collar may be axially moved along a portion of the 
shift shaft by the pivoting action of the shift fork. The spur gears are 
disposed on a second portion of the shift shaft, and the resilient keys 
extend from the shift collar on the first portion of the shift shaft to 
engage a keyway of a spur gear on the second portion of the shift shaft. 
The shift fork, pin, and annular groove permit the collar, and hence the 
keys, to be moved axially while the keys are at the same time rotating 
with the shift shaft. Each of the spur gears journalled on the shift shaft 
has on its inner circumference four circumferentially spaced keyways which 
may be engaged by the keys to rotatably couple the shift shaft with the 
selected spur gear. Consequently, as the keys are moved axially by the 
shift collar, the key heads successively engage and disengage keyways of 
adjacent spur gears, thereby coupling each spur gear to the shift shaft 
sequentially one at a time. 
In order to provide the several shifting positions in the transmission 
disclosed in the aforementioned U.S. Pat. No. 4,996,574, the shift shaft 
extends across the length of the transmission housing. Further, in order 
to support the loading of the gears, the shift shaft must be made of 
material, for example steel, capable of withstanding the high loading 
forces from the transmission gears. However, the strong material which 
comprises the shift shaft is relatively expensive, thus increasing the 
cost of an in-line transmission. 
In one known transmission, one section of the steel shift shaft has a 
reduced diameter and is fitted with a plastic sleeve which defines the 
axial channel around the reduced diameter portion of the steel shift 
shaft. This arrangement reduces the amount of steel required to make the 
shift shaft while still providing a seating for the collar and an axial 
channel for positioning the keys. However, the shift shaft still must 
extend across the length of the transmission housing which requires almost 
as much steel material as single piece shift shafts. Therefore, further 
reduction in the amount of steel material in the shift shaft is desirable. 
What is needed is a less costly shift shaft for a transmission. 
Also needed is such a shift shaft which reduces the amount of steel 
material without impairing the functionality of the shift shaft. 
SUMMARY OF THE INVENTION 
The present invention is a transmission having a shift shaft made of two 
separate portions, so that one portion of the shaft may be made of less 
expensive material. The spur gear supporting portion of the shift shaft is 
made from conventional material such as steel to support the rotating spur 
gears. However, the shift collar supporting portion of the shift shaft is 
made from less expensive material such as plastic because it is only 
subject to loading from the shift collar. 
The housing of the transmission includes an additional bearing for 
receiving the middle of the shift shaft at one end of the spur gear 
supporting portion. With this arrangement, the loading of the spur gear 
supporting portion is supported by housing bearings at both its ends, 
while the shift collar supporting portion is connected in axial alignment 
with the spur gear supporting portion of the shift shaft to provide 
adequate support for the loading of the shift collar. 
The shift keys of the transmission extend from the shift collar to the gear 
supporting portion of the shift shaft. A base portion at one end of the 
shift key engages the shift collar, and a shaft portion of the shift key 
extends from the base through an axial channel in the shift shaft. The key 
head extends from the other end of the shift key and is adapted to engage 
the keyways of the gears. The shaft portion is made of a resilient metal 
so that the key head is biased into the keyway, while the base portion is 
keyed to the shift collar for axial movement. 
The two largest sections of the shift shaft are the shift collar supporting 
portion and the spur gear supporting portion. The diameter of these 
sections are larger than the remainder of the shift shaft in order to 
provide the axial channel which houses the shift key of the in-line 
shifting mechanism. The axial channel is at least twice as long as the 
shift collar supporting portion, although only about half of the shaft 
defining the axial channel actually supports spur gears. Therefore, the 
application of the invention to an in-line transmission shift shaft 
significantly reduces the material cost of the axial channel defining 
portion of the shift shaft without impairing its utility. 
The present invention, in one form, is a transmission comprising a housing, 
a plurality of shafts rotatably disposed within said housing, a shifting 
mechanism, and a supporting structure. One of the plurality or shafts is a 
shift shaft supporting a plurality of gears. The shifting mechanism 
selectively engages one of the gears disposed on the shift shaft. The 
supporting structure retains the shift shaft within the housing. The shift 
shaft comprises a first and second shift shaft portion. The first 
shift-shaft portion consists essentially of a first material which 
supports the plurality of gears, and the second shift shaft portion 
consists essentially of a second material which supports the shifting 
mechanism. The first material is more expensive than the second material 
so that the cost of the shift shaft is reduced in comparison to prior art 
shift shafts. 
One object of the present invention is to provide a less costly shift shaft 
for a transmission. 
Also an object is to provide such a shift shaft which reduces the amount of 
steel material without impairing the functionality of the shift shaft.

Corresponding reference characters indicate corresponding parts throughout 
the several views. The exemplification set out herein illustrates one 
preferred embodiment of the invention, in one form, and such 
exemplifications are not to be construed as limiting the scope of the 
invention in any manner. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention relates to transaxle 10 as shown in FIG. 1. Lower 
housing 12 together with an upper housing (not shown) rotatably supports 
axles 14 and 16, shift shaft 18, and counter shaft 20. An input shaft (not 
shown) turns input bevel gear 22 which is freely rotatable about shift 
shaft 18 and engaged with gear 24 of counter shaft 20. Companion gears 26 
of counter shaft 20 engage spur gears 28 of shift shaft 18 so that gear 30 
of shift shaft 18 drives ring gear 32 of differential 34 and thereby turns 
axles 14 and 16 in a forward direction. In addition, transaxle 10 may be 
slowed or stopped by operation of brake assembly 36. A reverse gear may be 
provided by stub shaft and gear 38 being disposed between one of companion 
gears 26 and one of spur gears 28. 
The transmission gear ratio of transaxle 10 is determined by shifting 
mechanism 40 which includes shift input shaft 42, shifter fork 44, pin 46, 
collar 48, and keys 50. Shift input shaft 42 is connected in a known 
manner to linkage (not shown) of the vehicle which allows the vehicle 
operator to change gears manually. Shifter fork 44 is pivotally connected 
with shift input shaft 42 and includes pin 46 which extends into annular 
groove 52 of collar 48. Collar 48 is disposed and slidably axially movable 
on shift shaft 18 and is operably engaged with base portions 50.1 of keys 
50. Shafts portions 50.2 of keys 50 are disposed within annual channel 54 
of shift shaft 18 and include outwardly extending head portions 50.3. The 
head portions 50.3 may selectively engage gear keyways 56 which are 
internal recesses in spur gears 28. The selective engagement of heads 50.3 
with keyways 56 provide the operator selectable forward and reverse gear 
ratios of transaxle 10. Neutral sleeve 58 provides an axial position 
within shift shaft 18 wherein keys 50 do not engage any keyway 56. 
Alternatively, neutral sleeve 58 may include an internal recess to provide 
an engagable neutral position. 
In accordance with the present invention, shift shaft 18 includes two 
distinct and independent axial portions 60 and 62 having an axial 
connection 64. Shift collar supporting portion 60 is made of a relatively 
lighter material, for example a plastic material, which is less expensive 
than the material of spur gear supporting portion 62, for example steel. 
Also, the material of spur gear supporting portion 62 is relatively smooth 
to facilitate the axial movement of shift collar 48. Axial connection 64 
may include projection 66 of shift collar supporting portion 60 being 
received in recess 68 of spur gear supporting portion 62 (as shown in 
FIGS. 1-3), or projection 70 of spur gear supporting portion 62' being 
received in a recess (not shown in FIG. 4) of shift collar supporting 
portion 60' (as shown in FIG. 4). Shift shaft 18 is conventionally 
supported by the housing of transaxle 10 at distal ends 72 and 74 of 
portions 60 and 62, respectively, and shift shaft 18 is additionally 
supported at an intermediate position at proximal end 76 of spur gear 
supporting portion 62. 
In order to support spur gears 28, input gear 22, and gear 18, portion 62 
requires bearings which are formed in the transmission housing. Distal end 
74 is supported in bearing 78 of lower housing 12 (and a corresponding 
bearing in the upper housing which is not shown) in a conventional 
arrangement. The housing in transaxle 10 further includes internal wall 80 
in which bearing 82 is formed to receive proximal end 76 of spur gear 
supporting portion 62. Internal wall 80 may extend only partially across 
the transmission housing as shown in FIG. 1, or alternatively wall 80 may 
extend fully across the transmission housing. Bearings 78 and 82 rotatably 
support spur gear supporting portion 62 and are capable of absorbing the 
forces applied to spur gear supporting portion 62. Shift collar supporting 
portion 60 is supported at distal end 72 by bearing 84 in a conventional 
arrangement. Axial connection 64 provides sufficient support for proximal 
end 86 of shift collar supporting portion 60 because shift collar 
supporting portion 60 receives only the loading of shift collar 48, which 
is only a small fraction of the loading on spur gear supporting portion 
62. Thus, bearings 78, 82, and 84 support shift shaft 18; and only bearing 
82 requires additional material, namely the material of the transmission 
housing required to form internal wall 80. 
In the preferred embodiment, shift collar supporting portion 60 is 
comprised of plastic materials such as nylon. Spur gear supporting portion 
62 is preferably comprised of a durable material such as steel or SAE 
1018, SAE 1117, and SAE 86L20H. Also, housing 12 is comprised of a soft 
material such as type 380 aluminum. 
While this invention has been described as having a preferred design, the 
present invention can be further modified within the spirit and scope of 
this disclosure. This application is therefore intended to cover any 
variations, uses, or adaptations of the invention using its general 
principles. Further, this application is intended to cover such departures 
from the present disclosure as come within known or customary practice in 
the art to which this invention pertains and which fall within the limits 
of the appended claims.