Key shift transmission

A multi-speed transmission with a shift mechanism which selectively couples at least a forward and a reverse gear operatively positioned on a shaft. The shift mechanism is disposed entirely within the transmission housing and includes a shift key arranged for sliding movement of the key in the shaft. An improved neutral collar is positioned on the shaft between the forward and the reverse gears. The neutral collar has its widest cross section centrally located thereto. From this widest central cross section, the neutral collar profile tapers along the inside surface thereof to relatively narrow cross section at each end thereof.

BACKGROUND OF THE INVENTION 
The present invention relates to transmissions and in particular to a gear 
shifting arrangement for a key shift transmission. 
In key shift transmissions, at least one forward and one reverse gears 
forming a change-speed gear set are assembled side by side on a shift in 
constant running mesh with each other. The shifting arrangement drivingly 
couples either the forward or the reverse gear to the shaft one at a time 
to provide different directional motion. In one known type of shifting 
arrangement for this type of transmission, a key is axially slid into the 
groove of the shaft which both the forward and reverse gear are assembled 
to selectively couple one of the gears to the shaft. Normally, a neutral 
spacer collar is provided between the forward and the reverse gear. 
It is conventional to mount the reverse gear both in close proximity to a 
plurality of forward gears or remote from a plurality of forward gears. 
U.S. Pat. No. 3,812,735 illustrates the technique of mounting the reverse 
gear remote from the forward gear and U.S. Pat. No. 4,480,501 illustrates 
the technique of mounting the reverse gear in close proximity to the 
forward gear so that the biased end of the key is used to engage and 
disengage reverse gear, thereby eliminating double clutching necessitated 
by using the blunt end of the key to engage reverse gear as disclosed by 
U.S. Pat. No. 3,812,735. As disclosed by U.S. Pat. No. 4,480,501, because 
the forward gears and reverse gears are in close proximity with each 
other, a positive neutral position collar is disposed on the shaft between 
the forward gears and reverse gears to give the user a positive indication 
or "feel" of the transmission or transaxle being in a neutral gear 
position. This positive neutral position is provided by a recess radially 
outwardly disposed in the inner surface of the collar which is conformed 
to the shape of the biased end of the key. 
In one embodiment of the transaxle disclosed in U.S. Pat. No. 4,480,501, 
the neutral collar has slot-shaped recess which captures the biased end of 
the key when it is shifted between the forward gears and the reverse 
gears, while in a second embodiment, the collar has a circular recess 
which also captures the biased end of the key when it is positioned 
between the forward gears and reverse gear. 
As shown in FIGS. 1 and 1a of U.S. Pat. No. 4,480,501, a neutral collar or 
spacer is positioned between the single forward and the single reverse 
gear of a belt driven small lawn and garden tractor. While the neutral 
spacer as illustrated was initially satisfactory to provide a means for 
shifting the key from neutral to either forward or reverse or from forward 
through neutral to reverse, or vice versa, problems developed relating to 
the amount of effort required by an operator to push or pull the key out 
of either forward or reverse into the neutral collar area, particularly 
where there was some belt drag to the transmission input, and when the 
operator shifted gears without utilizing the clutch. The prior neutral 
collar design engaged the keys in such a manner that wear areas which 
developed on the key after a period of time caused the key to disengage 
from the gear pockets without the operator moving the control lever. 
As the key shift transmission was repeatedly shifted between forward and 
reverse without engaging the clutch, excessive wear on the key caused the 
key when engaged in the gear pocket to have a tendency to frequently 
disengage. Once this tendency developed, the key required repair which 
could only be accomplished by tearing down the transmission and replacing 
the keys, a rather time consuming and expensive operation. 
Specifically, after a number of shifts without utilization of the clutch, 
laboratory testing indicated that the design of these prior neutral 
collars caused the key tip surface engaging the gear pocket do become so 
severely worn from impact with the gear pocket that the key tended to fly 
out of engagement with the gear pocket for a short period until the next 
pocket rotated into engagement with the key thereby causing a jerking 
action. This tendency for the key tip to disengage appears to result from 
hammering the sides of the key tip into a slope which translates in the 
pocket. When sloped, the key tip cannot carry the torque created by the 
engagement with the pocket because with side loading, the slope acts like 
a ramp and allows the key tip to kick out of the pocket. 
At this point, the transmission must be disassembled and, as a minimum, the 
key replaced. The gear pockets and the shaft must also be reviewed for 
wear resulting of this severe impact and replaced if excessively worn. 
Accordingly, there is a need for an improved key shift transmission having 
a neutral collar designed such that the above mentioned problems are 
overcome. Specifically, an improved neutral collar design should provide 
for a positive neutral feel as well as requiring minimum effort to move 
the key between forward and reverse gears particularly when there is some 
belt drag through the transmission input; and should reduce wear on the 
key such that the key will not disengage from the gear pocket unless 
positively moved by the control lever, despite excessive clutchless 
shifting, thereby significantly reducing the frequency of key, gear and 
shaft replacement thereby enhancing the serviceability and reliability of 
the entire transmission. 
SUMMARY OF THE INVENTION 
The present invention is an improved key shift transmission which greatly 
reduces the effort required to move the key from engagement with the 
forward gear and through the neutral collar into engagement with the 
reverse gear and vice versa particularly where there is some belt drag to 
the transmission input and which eliminates excessive wear on the key 
thereby preventing the key from disengaging the gear pockets without 
control lever movement. 
As disclosed, the present invention provides an improved key shift 
transmission construction having a neutral collar located between a 
forward and a reverse gear. The neutral collar has its widest cross 
section centrally located thereto. From the widest central cross section, 
the neutral collar profile tapers down to relatively narrow cross sections 
at each end thereof. 
Specifically, the key shift transmission of the present invention consists 
of a transmission or transaxle housing, a driving input shaft positioned 
in the housing and having an input drive pinion positioned on one end 
thereof, a driven input shaft having at least one groove formed therein, 
at least one forward and at least one reverse gear each having at least 
one key receiving means formed therein, each gear is operatively 
positioned on one end of the driven shaft, a key positioned in the groove 
for selectively engaging one of the key engaging means, means for shifting 
the key in the groove to engage the key receiving means, and a neutral 
collar having an internal cross section relatively wider at its center and 
sloped internal surfaces from the central wide cross section to each end 
of the collar. 
Therefore, the primary object of this invention is to provide an improved 
key shift transmission which requires relatively little operator effort to 
shift the key between forward and reverse gear through the neutral collar, 
particularly where there is some belt drag to the transmission input; 
which significantly reduces key wear caused by impact between the key and 
the gear pocket particularly wear caused by clutchless shifting; which 
significantly increases the durability of the key thereby increasing 
product reliability; which allows for excessive clutchless shifting 
without undue key wear; which transposes the impact from clutchless 
shifting between the gear pocket and the key tip closer to the base of the 
key tip; which eliminates side sloping of the key from impact between the 
key and the gear pocket during clutchless shifting; and which effectively 
prevents the key from disengaging the gear pocket once shifted thereto 
without positive gear lever movement. 
Other objects and advantages of the invention will be apparent in the 
following description, accompanying drawings and the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A belt driven small lawn tractor 20 is shown in FIG. 1 which incorporates 
the improved key shift transmission, generally designated as 22, of the 
present invention. Since the relative forward speed of such a vehicle is 
normally controlled by the belts and a variator (not shown), only one 
forward gear is required. While only one forward gear is illustrated, it 
should be apparent to those skilled in the art that the present invention 
could be utilized in key shift transmissions having a plurality of forward 
gears such as shown in U.S. Pat. No. 4,480,501 which is hereby 
incorporated by reference. 
A transaxle 24 consisting of a transmission 22 and a differential 25 is 
shown in FIG. 2 for utilization in the lawn tractor 20 of FIG. 1. The 
specific gear mechanism of the transmission 22 of FIG. 2 is illustrated in 
detail in FIG. 3. An input shaft 40 is operatively connected to an engine 
(not shown). The input shaft is positioned inside of the transmission 22 
and has bearings 42 and 44 at each end thereof. One end of the input shaft 
40 receives a drive pinion 46. The drive pinion 46 is conventionally 
operatively connected to the input shaft 40 by O-ring 48 and a thrush 
washer 50 positioned between the bearing 44 and the drive pinion 46. 
Securing the drive pinion 46 to the input shaft 40 is a retainer ring 52. 
A driven shaft 60 having at least one forward 62 and one reverse gear 64 
with a neutral spacer 66 operatively positioned on the shaft 60 
therebetween is assembled transverse to the input shaft 40. The gears 62 
and 64 are assembled on the end of the shaft 60 by flanged bushing 70. A 
washer 72 is positioned between the bushing and the forward gear 62. The 
bushing 70 is sealed on shaft 60 by a square cut seal 74. 
A pair of keys 76 are positioned in a pair of slots 78 in driven shaft 60. 
The slots 78 are preferably formed on opposite sides of in the circular 
shaft 60. Each of the keys 76 has a tip 80 for engagement with one of a 
plurality of pockets 82 located in both the forward 62 and reverse 64 
gears. There are preferably four (4) pockets formed in each gear, it being 
understood that more or less pockets in each gear may be adequate for the 
purposes of the present invention. 
The relative position of the keys are conventionally controlled by a 
mechanism such as a rod and fork assembly 84 having a stud 86. As shown, 
the stud 86 engages a shift collar 88 which is operatively attached to the 
end of the shaft 60 opposite from the gears 62, 64. A gear spur 90 is 
positioned on the shaft 60 proximate the shift collar 88 and is held in 
position thereon by a second flanged bushing 70. A second thrush washer 72 
is positioned between the bushing 70 and the gear 90 and a second square 
cut seal 74 is assembled over the second flange bushing 70 to secure the 
assembly to the shaft 60. 
During operation of the riding mower 20 illustrated in FIG. 1, an operator 
moves gear lever 100 connected to rod and fork assembly 84 to either the 
forward or reverse position. By so doing, keys 76 are moved in grooves 78 
such that tip 80 is moved into engagement with one of the pockets 82 in 
one of the gears 62, 64. When the gear lever 100 is positioned in neutral, 
the key tip 80 is located in the neutral collar 66 positioned between the 
two gears 62, 64. 
As illustrated in FIGS. 6 and 7, the neutral collar 66 of the present 
invention has its relatively widest cross section 190 centrally located 
between its two ends 102, 104. The distance D between the two center 
points 110, 112, of the internal cross section of collar 66 is selected so 
that the driven shaft 60 fits snugly and rotatably therebetween. Keys 76 
are selectively movable from engagement with pocket 82 in forward gear 62. 
As key tip 80 moves between forward gear 62 and reverse gear 64 and vice 
versa, it maintains contact with internal sloped surface 94 of collar 66 
until it reaches cross section 90. When moving from forward gear 62 to 
reverse gear 64, dip 80 continues along internal sloped surface 96 until 
it engages pocket 82 of reverse gear 64. 
It should be pointed out that it appears that by providing sloped internal 
surfaces 94, 96, disengagement of tip 80 from pockets 82 requires 
relatively less effort than with the prior collar 66' of FIGS. 4 and 5. 
The effort required to shift between gears appears to be related to the 
width Wc of the two center points 110, 112 relative the total width Wt of 
the internal cross section of the collar 66. If the width Wc of the two 
center points 110, 112 is only a point, the effort required to shift gears 
is relatively less. As the width Wc of the two center points 110, 112 
increases, the effort required to shift gears increases to the relative 
maximum, as illustrated in FIG. 4. Additionally, by reducing the 
overlapping portion 120 between the gear pocket 82 and the collar 66, 
entrance and exit of the key tip 80 into and out of the pocket diverts the 
point of impact between the key tip 80 and the side of pocket 82 from the 
radially outermost portion 116 of the key tip, especially during 
clutchless shifting, to a location 122 near the base of the tip 80. when 
shifting into reverse gear and at a location 124 when shifting into 
forward gear depending upon the direction of rotation of the gears 62, 64. 
Specifically, with the improved neutral collar 66, it appears that the 
impact between the key tip 80 and the gear pocket 82 takes place on either 
the leading or trailing edge of the key tip 80 at location 122 or 124 
depending upon the direction of rotation of the gears and whether shifting 
into forward or reverse gear. Laboratory tests indicate that these 
locations of impact 122, 124 reduces damage to the radially outer most 
portion 116 of the key tip 80 by shifting the impact between the key tip 
80 and the pockets of the surfaces 81, 83 away from the large key surfaces 
81, 83 to the above mentioned edges 82 at locations 122, 124. This impact 
location shift apparently results in the key tip 80 not becoming 
disengaged from the pocket 82 due to the radially outermost portion 116 of 
surface 81 being beaten to a taper by repeated impact as occured with the 
prior collar 66'. 
Laboratory test results indicate that the improved neutral collar 66 of the 
present invention significantly reduces the wear on both sides 81, 83 of 
the radially outermost corner 116 of tip 80 parallel to the shaft 60, thus 
eliminating the tendency of the key tip 80 from being disengaged from 
pocket 82 without the appropriate movement of the gear lever 84. 
Additionally, the same test results indicate marked improvement in 
durability and increased life cycle for key tip 80, pocket 82, and shaft 
60, when utilizing the neutral collar 66 of the present invention as 
opposed to the prior collar 66'. 
While the form of apparatus herein described constitutes a preferred 
embodiment of this invention, it is to be understood that the invention is 
not limited to this precise form of apparatus, and that changes may be 
made therein without departing from the scope of the invention which is 
defined in the appended claims.