Note: Descriptions are shown in the official language in which they were submitted.
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DRIVE TRAIN FOR SELF-PROPELLED MOWERS
FIELD OF THE INVENTION
This invention relates to
self-propelled lawn mower driven trains.
BACKGROUND OF THE IN~ENTIO_
When the clutch is engaged on a
self-propelled rotary mower the torque typically
causes the front wheels to lift off the ground
causing a skip in the mowing. If the drive train
uses drive rollers on the tires, very careful
actuation can permit slippage but from a practical
standpoint even that clutch will cause front wheel
lift when engaged. Since wheel lift causes a skip in
the mowing, the operator learns that he should back
up after stopping so as to avoid the skip when
restarting. That is a nuisance and it is desirable
to avoid wheel lift. Even with a reel-type mower the
jump caused by clutch engagement is troublesome and
desirably avoided.
Attention is directed to Shaw patent
No. 2,947,132, Jones U.S. patent No. 4,117,652 and
Wehner U.S. Patent No. 2,860,473.
SUMMARY OF THE INVENTION
The invention provides a self-propelled
lawn mower having a frame provided with a drive wheel
and supporting an engine, a drive train for
delivering power from the engine to the drive wheel
and including clutch means comprising multiple drive
and driven plates which are separated when the clutch
means is disengaged, means biasing the plates to
separated positions, and manual control means
actuated by an operator for variably applying axial
load to the plates against the action of the biasing
means so as to variably engage the clutch means to
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effect rotation of the drive wheel at selective
speeds within a speed range between zero and
substantially above zero.
The invention also provides a
self-propelled lawn mower having a frame provided
with a drive wheel and supporting an engine, a drive
train for delivering power from the engine to the
drive wheel and including a worm gear driven by the
engine, a worm wheel driven by the worm gear, and
clutch means including multiple drive plates driven
by the worm gear and multiple driven plates which are
operably connected to the drive wheel and which are
separated from the drive plates when the clutch means
is disengaged, means biasing the plates to
non-driving separated positions, and manual control
means actuated by an operator for variably applying
axial load to the plates against the action of the
biasing means so as to continuously variably engage
the clutch means to effect rotation of the drive
wheel at selective speeds within a speed range
between zero and substantially above zero.
The invention also provides a
self-propelled rotary lawn mower comprising a housing
having rear drive wheels and front support wheels, an
engine mounted on the housing, a rotary cutter blade
mounted inside the housing and driven by the engine,
a transmission mounted on the housing and having an
input shaft and an output shaft, a belt drive from
the engine to the input shaft, which output shaft
extends across the housing and has, on each end, a
drive gear, each drive wheel having an internal ring
gear engaged by one of the drive gears, which
transmission includes clutch means between the input
and output shafts, which clutch means includes
multiple drive and driven plate sets immersed in
lubricant, means biasing the plate sets into
non-driving separated positions, and manual ~ontrol
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means actuated by an operator for selectively
applying axial load to the plates so as to move the
plate sets into engagement against the action of the
biasing means to cause lubricant to be expelled from
between the plates and so as to effect continuously
variable operator controlled rotation of the drive
wheels within a speed range from zero to
substantially above zero.
The invention also provides a
self-propelled lawn mower having a frame provided
with a drive wheel and supporting an engine, a drive
train for delivering power from the engine to the
drive wheel and including clutch means for varying
the rate of rotation of the drive wheel and including
multiple drive and driven plates which are separated
when the clutch means is disengaged, means biasing
the plates to separated positions, and manuaI control
means actuated by an operator ~or variably applying
an~axial load to the plates against the action of the
biasing means so as to va~riably engage the clutch
means to effect continuously variable operator
controlled rotation of the drive wheel within a speed
range from zero t~o substantially above zero.
The invention also provides a
self-propelled lawn~mower having a frame provided
with a drive wheel and supporting an engine, a drive
train for delivering power from the engine to the
drive wheel and including a worm gear driven by the
engine, a worm wheel driven by the worm gear, and
clutch means for selectively varying the amount of
power delivered from the engine to the drive wheel
and including multi~le drive plates driven by the
worm gear and multiple driven plates which are
operably connected to the drive wheel and which are
; 35 separated from the drive plates when the clutch means
is disengaged, means biasing the plates to
non-driving separated positions, and manual control
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: means actuated by an operator for variably applying
axial load to the plates against the action of the
~ biasing means so as to~variably engage the clutch
: means to cause continuously variable operator
5~ controlled rotation of the~drive wheel within a speed
:~ range from zero to substantially above zero.
The invention also provides a
: self-propelled rotary lawn mower including a housing
having front support wheels and rear drive wheels
each having an internal ring gear, an engine mounted
on the housing,:a rotary cutter blade mounted inside
the housing and driven by the engine, and~a drive
train for delivering power erom the engine to the
drive wheels and including a drive belt driven by the
: engine, and a transmission mounted on the housing~and
having an input shaft driven by the drive~belt, an
output shaft extending across the housing and having,
at each end, a dr:ive~ gear~engaged with one of the
internal ring gears, a~nd clutch means between the
20 ~: input and output s~hafts for selectively varying the
power level transmitted from the engine to the rear
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drive wheels and including multiple drive plates on
: the input:~shaft,~multiple drlven plates on the output
shaft and:extending intermediate the drive plates,
25 ~: means biasing the plates into non-driving separated
:: positions,~and manual control means actuatable by an
operator: fo~r~vari:ably applying axial:load to the
plates against the action of the biasing means so as
to effect continuously variable operator controlled
30~ ~ rotatlon of the drive wheels within a speed range
from zero to substantially above zero.
The invention also provides a
self-propelled rotary:lawn mower including a housing
;: :~ having front support wheels and rear drive wheels
~ ~ ~ 35 each having an internal ring gear, an engine mounted
: on the housing, a rotary cutter blade mounted inside
: the housing and driven by the engine, and a drive
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5i369~3
train for delivering power from the engine to the
drive wheels and including a drive belt driven by the
engine, and a transmission mounted on the housing and
having a worm driven by the drive belt, a worm wheel
engaged by the worm, an output shaft extending across
the housing and having, at each end, a drive gear
engaged with one of the internal ring gears, and
clutch means between the worm wheel and the output
shaft for selectively varying the power level
transmitted from the engine to the rear drive wheels
and including multiple drive plates on the worm
wheel, multiple driven plates on the output shaft and
extending intermediate the drive plates, means
biasing the plates into non~driving separated
positions, and manual control means actuatable by an
operator for variably appIying axial load on the
plates against the action of the biasing means so as
to effect continuously variable operator controlled
rotation of the drive wheels within a speed range
from zero to substantially above zero.
This invention is not limited to the
details of construction and the arrangement of
components set forth in the following description or
illustrated in the drawings. The invention is
capable of other embodiments and of being practiced
and carried out in various ways. Also, it is to be
understood that the phraseology and terminology
employed herein is for the purpose of description and
should not be regarded as limiting.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side elevation showing the
general orientation of the drive.
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Fig. 2 is a fragmentary perspective view
showing the drive train to the wheels.
Fig. 3 is a plan view of the clutch control.
Fig. 4 is a vertical section on line 4-4 in
Fig. 3.
Fig. 5 is a vertical section on line 5-5 in
Fig. 3.
DETAILED DESCRIPTION OF THE DR~WINGS
The lawn mo~er 10 has a housing ~1~
supporting an engine 12 inside the cover 14. The
engine drives shaft 16 on which the rotary mower
blade 18 i5 moun~ed. The shaft 16 also carries a
pulley 20 which drives a drive belt to pulley 22
mounted on input shaft 24 which projects upwardly
from the transmission case 26. The lower end of
shaft 24 i6 received in beaIing 28 and the hardened
steel worm gear 30 engages bron~e worm wheel 32. The
upper end of shaft 24 lS journaled in bearing 34.
WOLm wheel 3~ is a spur gear keyed at 36 to
drive member 38 which is journaled on the driven
shaft 40 which extends transversely of the lawn mower
and is provided, on each end, with a gear 42 which
engages the internal ring gear 44 carried by each of
the eear drive wheels 46 of the mower. The front of
the mower housing is supported on front wheels 47.
The drive shaft 40 is jouLnaled in a bearing 48 at
one end of the gear case 26 and in bearing 50 at the
other end. Both bearings are provided with packing
52 to prevent los~ of lubricant along the sha~t. The
worm wheel is selec~ively connected to the drive
shaft 40 through a clu~ch.
The clutch includes the axially facing
surface 54 of the drive member 38 which functions as
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a driver plate engageable with the adjacent dLiven
plate 56. The clutch includes four additional driven
plates 56. All the driven plates are shaped with a
configuration such that the driven plates are, in
effect, keyed at 57 to the driven sleeve 58. In a
similar manner, all of the independent driver plates
50 are keyed at 61 to the driver member 3~. When the
clutch is disengaged, there is relative rotation
be~ween the driver plates and the driven plates.
When the collar 62 is moved towards the worm wheel,
it will squeeæe the plates together so the driver
plates engage the driven plates which in turn drive
the sleeve 58 which drives the driven shaft 40
through the drive pin 64. A considerable axial load
must be applied to the collar 62 to engage the
;~ clutch. The axial load is absorbed by the thrust
bearing 66 mounted between the thrust washer 68, 68
on each side of the bearing, the thrust washer
adjacent the inner wall of the casing being pushed
into engagement with the inside axially facing
urface of bearing 50.
; The transmission housing is filled with
lubricant. The driver plates and driven plates are
hardened carbon steel plates and are not the kind of
plates found in a dry clutch. When the clutch is
disengaged, lubricant can get between the various
plates. When the clutch is engaged, the axial
loading first has to squeeze the lubricant out from
between the plates in order for the plates to drive
and the clutch to become fully opera~ive. Therefore,
this clutch with the proper number of plate sets and
proper axial loading can be made to engage relatively
slowly. This permits the speed of the mower to
gradually increase. When the clutch is Eully
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engaged, there is no slippage for all practical
effects, but during the engagement there i8 slippage
and the front wheels will not lift off the ground.
The accelleration is smooth.
S The clutch is actuated ~y means of the shift
arm or yoke 70 mounted on and keyed to shaft 72
projecting from the top of the gear case parallel ~o
ths worm gear shaft. The lower end of the shaft 72
is journaled in a socket 74 molded into the lower
part of the case 26. The shaf~ carries a shif~ing
fork 76 having fingers 78 projecting inwardly to
engage groove 81 in collar 62. One snd of the yoks
70 has a Bowden wire (a push/pull cable) 81 connected
thereto through spring B2. The Bowden wire 80 is
anchored in bracket 84 mounted on the top of the
transmission housing. A coil spring 86 connected
between the bracket 84 and the other end 88 of yoke
70 biases the yoke to the position in which the
clutch is disengaged. The Bowden wire is actuated by
~he manual control 89 carried on the handle 90 and
having an over center action. The control goes over
center and the clutch remains engaged until ~he
manual control is actuated to disengage the clutch.
As soon as the manual control is actuated back over
center, the re~urn spring 86 will ensure that the
collar moves back from the stacked clutch plates and
permits them to resume relative rota~ion between the
plates.
The reduction in the belt drive from the
engine shaft to the WOLm gear is 1.75:1. The
reduction at the point of engagement of the drive
gears with the internal gears of the drive wheels is
4:1. The worm gearset provides only a 4:1 reduction
as opposed to the usual 7:1 reduction necessitated by
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the usual external gear at the wheel providing only
2:1 reducti~n.
Due to the 4:1 reduction at the wheels, the
present clutch operates at higher speed that the
prior design. This has advantages in that the torque
handled by the clutch lS much lower and the
engagemen~ is smoother (softer), both resulting in
less shock to the transmission. Furthermore, the
elutch has more positive lock-up when engaged ~due to
less torque) and slippage is descreased. The 4:1
reduction in the worm gearset reduces loading which
reduces heat generation and reduces the operating
temperature of the transmission. The temperature
reduction is great enough to permit the transmission
I5 gear case to be molded out of plastic as opposed ~o
the metal in the prior art. This is a direct cost
reduction. The greatly reduced operating temperature
results in a very substantial increase in life. The
prior art arrangement generated such high
temperature~ that it caused considerable wear which
in turn caused even higher temperatures and
everything worked towards shortening the useful life
of the transmission.~
The greatIy improved performance of the
gearset by reason of~reducing the gear ratio permits
a very substantial increase in life as noted above.
The presen~ clutch arrangement contributes to the
; increased life with its inheren~ slippage on
engagement. This avoids the high shock loads found
30 in the art. Therefore, the engagement is easy and
avoids the high loads in prior designs.
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This invention has application to reel-type
mowers as well.~ These mowers tend to tilt back on
their rolleLs when the clutch engages. The present
arrangement should avoid that and allow the mower to
accelerate to speed smoothly.
I claim: ~
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