Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to shift mechanism for shifting
a clutch collar or the like into engagement with a gear and for
moving the collar out of engagement with the gear even when a
transmission or the like in wllich the mechanism is mounted is
under a heavy load.
It is sometimes difficult to disengage a clutch collar
from a gear in a small transmission of a riding lawn mower, a
garden tractor, or a self-propelled lawn mower. This can par-
ticularly occur when the transmission is under a heavy load, such
as when the mower is travelling uphill, particularly if it is a
self-propelled rear bagger with the load on the rear, driven
wheels, by way of example. A dangerous condition can thereby
result if the mower cannot be stopped, or at least parts of the
shift mechanism can be distorted, bent, or broken.
By forming the lugs or teeth of the clutch collar and
gear with their engagable surfaces at angles, about six degrees,
for example, the clutch collar and gear can be relatively easily
disengaged even when the transmission is under a heavy load. ~ow-
ever, this angle causes the lugs to wear mucil faster and have
severely shortened useful life.
The present invention provides a shift mechanism which
enables a clutch collar or dog to be disengaged from a gear of a
transmission even when it is under a heavy load. The snift mech-
anism includes the clutch collar which is mounted on a shaf-t of
the transmission for rotatable movement therewith and for lineal
movement with respect thereto. The clutch collar has at least
one lug or projection extending toward the gear in tile transmission,
which gear is rotatably mounted on the shaf-t and has at least one
luq or projection facing toward the clutch collar. Tlle clutcn
collar can have a peripheral Elange extending outwardly beyond the
collar lug which is engaged by a shif-ter fork for movin~ the clutch
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collar toward and away from the gear, between an engaged position
in which -the collar is engaged with the gear and a disengaged po-
sition in which the collar is spaced from the gear.
One of the clutch collar and gear has a recess adjacent
its respective lug in which a ball is located in contact with the
respective lu~. A retaining ring is also located on the collar
or gear to further aid in retaining the ball in place in the re-
cess. A shallow groove is located adjacent the recess to receive
the lug of the other one of the collar and gear, witll the ball
preferably extending out of the recess by a distance exceeding
the radius of the ball. The lug of the other one of the collar
and gear then contacts the ball, when the collar and gear are in
the engaqed position, on a point which is on a line parallel to
the shaft and tangential to the surface of the ball. This enables
solid engagemen-t of the collar and gear. At the same time, even
iE the transmission is under a heavy load, the collar can be rela-
tively easily disengaged from the gear with the point contact be-
tween the lugs and the ball and with the ball having the ability
to rotate as the lugs of the collar and gear separate.
It is, therefore, a principal object of the invention
to provide improved shift mechanism for a small transmission or
the li]~e.
Another object of the invention is to provide shift
mechanism for a transmission for disengag~ing a clutch collar
from a gear even w~en the transmission is under a heavy load.
Yet another object of the invention is to provide shift
mechanism including a clutch collar and a gear wi-th lugs facing
each other and with one of the collar and gear having a recess in
which a ball is received with the ball contacting both lugs when
-the collar and ~ear are engaqed.
Many other objects and advantages of the invention will
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be apparent ~rom ~he followin~ detailed description of a pr~E~rr~d
embodimellt ther~of, referance ~in~ mado to the ~acompanying draw-
int7B, in which: .
Fi~. 1 is a viaw in p~rspective of a s~all txansr~ n
embodying shift mechanl sm accGrdin~ to ~he inven~ion;
Fig. 2 is a view in longitudinal, ~ertical cross ~ection,
taken alon~ ~he line 2-2 of Fi~
Fig. 3 i~ a view in perspecti~e o f a clutch collar ~ r~-
taining rin~, and ~ear in accordance with the invention;
Fig . 4 1B an enlarged front view, with parts ~roken away
of ~he clutch collar of Fi~. 3, wi~h lu~ of the gear ~llown in
dotted line~; and
Fi~. 5 is a view in cross section~ taken along the line
5-5 0~ Pi~. 4.
R~ferrinq to the drawings, and particularly to Fig. 1, a
~all transmi~sion embodyin~ the invention i~ indicated at 10 an~
can ~e mo~mted on a dec~ of a ssl~-prQpelled, walkin~ lat~n mower~
hy tYa~ 0~ example. ~itll the tran~mi~sion position~ as in ~i~o 1
the mower ~rould be movin~ ~rom the lower rlght toward the u~per
~0 le~t. ~hs transmission includ~ a main hou~in~ 12 with ~ vartical
~nput shaet 14 ~xtendln~ upwar~lly th~r~:from to rec~3ive a drive
pulley or the like driven by an internal con~u~tioJl ~nyine on tho
mo~wer. 1~ ~rive ~ha~t 16 extend~ outwardly from botll ~ide~ o the
housin~ 12, with the lef~ end baing suitably cosln~cted to a 1~3t
rear whe~l of th~ mower and the right ~nd b~ing ~uitably co~n~3c~d
to ~ riqht rear whe~l oft ~he mow~r. The basic transmi~ion can
be of the type ~ho~n in ~onos ~t al patent no. 4,117,652, is~ued
on ()ctober 3, 1978 ~ in the U.S.
A drive worrn (not shown) i5 affixe~l to th~ drive shaft 14
3(~ wi tlli.n th~ hou!3in~ 12 and m~sh(3~ witll d worm wh~3al or y~ar 1~ or
othar toothed member which is rotatably mounted on th~ out~ut
.~-
shaft 16. The shaft 16 is rotatably supported in bushings 20 and
22 having seals 24 and 26. The shaft is prevented from longitudi-
nal movement by pins 28 and 30 on either side of the bushing 20
and bearing against washers 32 and 34.
The worm gear 18 has a recess 36 at one end to receive
the seal 26 and one end of the bushing 22. The opposite end of
the worm gear has a circular end face 38 cooperating with an up-
wardly-extending flange 40 in the housing 12, which is made in two
halves. The worm gear thereby is restrained from longitudinal move-
ment of the shaft 16 but is free to rotate relative thereto. Thegear has a plurality, three in this instance, of lug5 or projec-
tions 42 extending axially of the shaft 16.
A clutch collar or dog 44 is mounted on the output shaf-t
16 for longitudinal but nonrotatable movemen-t wi-th respect thereto.
The collar 44 has a bora 46 with a groove 48 receiving a key 50
which extends outwardly from a recess 52 in the shaft 16. The
collar 44 has a central hub 54 with a plurality, three in this in-
stance, of lu~s or projections 56 extending radially outwardly
therefrom and extending axially of the shaft 16 toward the worm
gear 18. A re~ar, outer hub 58 e~tends outwardly beyond the cantral
hub 54. I.ocating means in the form of a recess 60 is located ad-
jacent each of the lugs 56 and extends from the periphery of the
central hub 54 to the periphery of the outer hub 58. A member with
opposite rounded surfaces, preferably a ball 62 is located in each
of the recesses 60 with the ball having a diameter about equal to
the length of the recess 60. The radius of the ball preferably
exceeds the depth of the recess 60, as shown in Fig. 5, so that
the adjacent faces of the lugs 42 and 56, rather than edges of
-the lugs, contac-t the ball 62. When the collar 44 and the gear
18 are engaged, -the gear lug A2 then contacts the ball at a point
on a line e~-tending through the center of the ball and through -the
point of contac-t of the ball with the collar lug 56. Stated
another way, each of the lugs 42 and 56 contacts the respective
ball 62 at a point which is on a line tangential to the ball 62
and also parallel to the axis of the shaft 16.
The balls 62 are preferably retained in the recesses 60
by a retaining ring 64 which has one end mounted on the outer hub
58 by a press fit or by other suitable means and has at the other
end an inwardly-curved shoulder 66 which extends over the ball 62
and terminates in the plane of the face of the central hub 54.
The balls 62 are ~hereby retained in the recesses 60 but preferably
can rotate therein. The point contact of the lugs 42 and 56 and
the ball 62 enables the collar 44 to be relatively easily disen-
gaged from the gear 18 even when the transmission 10 is under a
heavy load. Rotation of the ball 62 also tends to facilitate dis-
engagement of the collar and the gear.
` A shallow groove 67 is formed at the face of the outer
hub 58 between the edge o the central hub 54 and the inner sur~ace
of the retaining ring 64 and extends from the recess 60 to the next
one of the lugs 56. The groove 67 provides entry access for the
gear lug 42 to move into po~ition to engage the ball 62.
To move the collar between an engaged positlon in which
the lugs 42 and 56 are in contact with the ball 62, and a disen-
gaged position in which the lugs 42 are spaced from the balls 62,
the clutch collar 44 has an outwardly extending flange 68 on the
outer hub 58. A shifter fork 70 is used to move the collar 44
between the two positions. The fork 70 has an upper, generally
rectangular block 72 (F.ig. 2) located in an upper portion of the
housing 12 and supported on a divider plate 74 which is suitably
mounted in an upper portion of the housing 12~ The shifter fork
has two downwardl~ extending flanges 76 and 78 which engage the
sides of the collar flange 68 when the shifter fork is moved
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parallel to the axle 16.
When the shifter fork 70 is moved toward the worm gear
18, the flange 76 engages the collar flange 68 and moves the
collar toward the worm gear with the gear lugs 42 moving into the
shallow groove 67 and engaging the balls 62. When the shifter
fork 70 is moved away from the worm gear 18, the flange 78 en-
gages the collar flange 68 and moves the collar away from the
worm gear, disengaging the gear lugs 42 from the balls 62. This
occurs even if the transmission is under a heavy load at the time
of the desired disengagement, due to the interaction between th~
lugs and balls.
The shifter fork 70 can be moved between the two posi-
tions by any sultable means. As shown, the fork has a post 80
extending upwardly through the housing 12 and through a slot 82
(Fig. 1) in a shift lever 8~. The shift lever 84 has a portion
spaced from the slot 82, which lever is pivotally mounted on the
housing 12 by a suitable fastener 86. The shifter fork 70 is
moved toward the worm gear when the shift lever 84 is pivoted
through a bowden cable 88 which is connected to the shift lever
2~ and extends to a control lever (not shown) mounted on the opera-
tor's handle of the mower. The shifter fork 70 is urged in -the
opposite direction by coil springs 90 (Fig. 2) located in the
upper portion of the housing and bearing against an end of the
block 72. From one to three of the springs can be employed, with
two being preferred.
~ hile the rounded members 62 are disclosed as be~ng
carried by the collar, they can also be carried by the gear. Fur-
ther, the rounded mem~ers 62 can be of shapes other than balls,
such as rollers with -their axes transverse to the axis of the
shaft 16.
