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 wlth a gear or the like
and for foxcing the clutch collar out of engagement.
It is fre~uently difficul-t to disengage a clutcn collar
from a gear in a transmission of a riding lawn mower, a garden
tractor, or even a self-propelled lawn mower. This can 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 bag-
ger with the load on the rear, driven wheels, by way of example.
This can result in a dangerous condition, if tile mower cannot be
stopped, or at least parts of the shif~ mechanism can be distorted,
bent, or broken.
By forming the clutch lugs or -teeth of the clu-tch collar
of the transmission with their engagable surfaces at angles, about
six degrees for example, the clutch collar and gear can be disen-
gaged even when the transmission is under a heavy load. EIowever,
this angle causes the lugs to wear much faster and have severely
shortened useful life.
The present invention provides a shift mechanism which
causes the clutch collar to engage the gear in the usual manner
and then physically forces the clutch collar out of engagement
with the gear, when disengagement is desired. The shift mecnanism
includes the clutch collar or dog which is mounted on a shaft of
the transmission for rotatable movement therewith and for lineal
movement with respect thereto. The clutch collar has at leas-t one
lug or tooth extending toward the gear in the transmission, which
gear is rotatably mounted on the shaft and has at least one ]ug
or tooth facing toward the clutch collar. The clutch collar has
a peripheral flange extending radially outwardly beyond the clutc~
collar lug. The side of the flange facing toward the gear has a
cam surface with at least one thick cam portion or lobe and at
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least one thin cam portion. The opposite side of the flange nas
a planar peripheral surface.
A shifter fork has a flange with a planar surface engag-
able with the planar peripheral surface of the clutch collar flange
to ~ove the clutch collar from a disengaged position in whicn the
lugs are spaced apart to an enyaged position in which the lugs are
in contact, to cause the gear to rotate witn -the shaft through tne
collar. The shifter ork also has a projection or cam follower
spaced from the shifter for]~ flange by a distance exceeding the
thickness of the thick cam portion of the clutch collar flange.
This projection preferably has a convex cam surface engagable witn
the cam surface of the clutch collar to force the clutch collar
from the engaged position to the disengaged position when moved
into engagement with the clutch collar flange. The transmission
can then be disengaged even if under a heavy load.
It is-, therefore, a principal object of the invention to
provide improved shift mechanism for a small transmission or the
like.
Another object of the invention is to provide shift mecn-
anism for a transmission for disengaging a clutch collar from agear even when the transmission is under a heavy load.
A further object of the invention is to provide shift
mechanism in which a clutch collar is disengaged from a gear by a
camming action.
Yet another object of the invention is to provide shift
mechanism including a clutch collar with a peripheral flange hav-
ing a cam configuration on one sur~ace and a shifter fork having a
cam follower engagable with the cam surface of the collar.
~ any other objects and advantages of the invention will
be apparent from the following detailed description of a preferred
embodiment thereof~reference being made to the acco~panying draw_
a~ 3
ings, in which:
Fig. 1 is a view in perspective of a small transmission
embodying shift mechanism according to the invention;
Fig. 2 is a view in longitudinal, vertical cross section,
taken along the line 2-2 of Fig. l;
Fig. 3 is a view in perspective oE a shifter fork, clutch
collar, and a gear in accordance with the invention; and
Fig. 4 is a view in perspective of the shifter fork of
Fig. 3.
Referring to the drawings, and particularly to Fig. 1, a
small transmission embodying the invention is indicated at 10 and
can be mounted on a deck of a self~propelled, walking lawn mower,
for example. With the transmission positioned as in Fig. 1, the
mower would be moving from the lower right toward the upper left.
The transmission includes a main housing 12 with a vertical input
shaft 14 extending upwardly therefrom to receive a drive pulley or
the like. A drive shaft 16 extends outwardly from both sides of
the housing 12, with the left end being suitably connected to a
left rear wheel of the mower and the right end being suitably con-
nected to a right rear wheel of the mower. The basic transmission
can be of the type shown in Jones et al U.S. patent no. 4,117,652,
issued on October 3, 1978.
A drive worm (not shown) is affixed to the drive shaft
14 within the housing 12 and meshes with a worm wheel or gear 18
which is rotatably mounted on the output shaft 16. The shaft 16
is rotatably supported in bushings 20 and 22 having seals 24 and
26. The shaft is prevented from longitudinal movement by pins 2g
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
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the worm gear has a circular end face 38 coo~erating With an up-
wardly-extending flange 40 of the housiny 12, which i5 made in
two halves. The worm gear thereby is restrained from longitudi-
nal movement cn the shaft 16 ~ut is free to rotate relative there-
to. The gear has a plurality, four in this instance, lugs or
teeth 42 extending axially of the shaft 16.
A clutch collar or doy 44 is mounted on -the ou-tput shaft
16 for lonyitudinal but nonrotatable movement with respect there-
to. The collar 44 has a bore 46 with a groove 48 receiving a key
50 which extends outwardly from a recess 52 in the snaft 16. Tlle
collar 44 has a central hub 54 with a plurality, four, in this in-
stance, lugs or projections 56 extending radially ou-twardly from
the bore 46 and extending axially of the shaft 16 toward the worm
gear 18 from the face of the hub 54. These lugs 56 are engagable
with and disengagable frorn the lugs 42 of the worm gear 180 When
the collar 44 is in an engaged position and the lugs are engaged,
the clutch collar 44 causes the worm gear 18 to rotate with the
shaft 16 through the collar. When the luys 56 are spaced from
the lugs 42 and the collar 44 is in a disengaged position, the
worm gear is again free to rotate relative to the shaft 16.
The clutch collar 44 has an annular, peripheral flange
58 extending outwardly beyond the lugs 56. The flange has a
planar surface 59 on the side thereof facing away from the worm
gear 18 and an undulating or cam surface 60 on the side facing
toward the worm gear. The cam surface 60 has at least one thick
cam portion or lobe 62 and at least one -thin cam portion 64, four
of the thick portions 62 and four of the thin portions 64 being
shown. Preferably, there are a sufficient number to enable the
clutch collar 44 to be disengaged when the engine is stopped.
The clutch collar 44 is moved between the disengaged and
engaged positions by a shifter fork 66. The shifter fork has an
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upper, generally rectangular block 68 loca-ted in an upper portion
of the housing 12 and supported on a di~ider plate 70 suitably
mounted in an upper portion of the housing. The shifter fork has
a downwardly extending flange 72 with an arcuate edge, the flange
having a planar surface facing toward the worrn gear 18 and engag-
able with the planar surface 59 of the flange 58 of the clutch
collar 44. The shifter fork also has a downwardly extending pro-
jection or cam follower 74 spaced from the flange 72 toward the
worm gear 18 with the projection 74 having a convex curved cam
surface 76 facing toward the cam surface 60 of the clutch collar
44. The cam surface 76 is spaced from the planar surface of the
flange 72 by a distance which exceeds the thickest portion of the
cam lobe 62 of the cam surface 60.
When tlle shifter fork 66 is moved toward the worm gear
18, the flange 72 engages the planar surface 59 of the collar
flange 58 and moves the collar toward the worm gear with the
collar lugs 56 engaging the gear lugs 42. When the shifter fork
66 is moved away from the worm gear 18, the cam surface 76 of the
projection 74 engages the cam surface 60 of the clutch collar 44
and forces the collar away from the worm gear, disengaging the
collar lugs 56 from the worm gear lugs 42. This occurs even if
the transmission is under a heavy load at the time of the desired
disengagement, aue to the interaction of the cam surfaces.
The shifter fork 66 can be moved between the two positions
by any suitable means. As shown, the shifter fork has a pos-t 78
extending upwardly through the housing and through a slot 80 in a
shift lever 82. The shift lever 82 has a portion spaced from the
slot 80 which is pivotally mounted on the housing 12 by a suitable
fastener 84 (Fig. 1). The shifter fork 66 is moved toward the
worm gear when the shift lever 82 is pivoted through a bowden ca-
ble 86 connected to the shift lever and extending to a control
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lever mounted on the operator's handle of the moT~er. Tile snifter
fork 66 is urged ln tlle opposite directi,on by coil springs 88 (Fig~
2) located in the upper portion of the housin~, wit~ ends received
in notches 90 (Fig. 3) in the shifter fork block 68. From one to
three of the springs 88 can be employed, with two, .in the outer
two notches 90, being preferred.
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