Transmission for self-propelled walking lawn mowers

A transmission for self-propelled walking lawn mowers, comprising: a casing 17; an input shaft 5 vertically inserted into the casing 17; an output shaft 10 extending horizontally through the casing 17; a small gear 20 fixed on the input shaft 5; a large gear 21 meshing with the small gear; a supporting shaft fixedly spporting the large gear; and first and second intermediate gears 24 and 25 mounted on the supporting shaft and the output shaft 10, respectively, wherein the input shaft 5 is arranged on the side of the. large gear facing opposite to the supporting shaft and is supported by the top and bottom walls of the casing. Accordingly, it is possible to reduce the size of the casing for self-propelled walking lawn mowers, thereby making a lawn mower compact.

TECHNICAL FIELD 
The present invention relates to a transmission for transmitting rotation 
of an engine to wheels after the rotational speed having being reduced, 
and more particularly to a transmission for use in self-propelled walking 
lawn mowers. 
BACKGROUND OF THE INVENTION 
One example of this kind of conventional transmission is disclosed in, for 
example, Japanese Unexamined Utility Model Publication No. 98953/1989. In 
this transmission, drive power is transmitted from an engine (not shown) 
to an input shaft 102 via a belt pulley 101 as shown in FIGS. 6 and 7. The 
input shaft 102 is supported by two superimposed bearings 104 and 105 in 
the upper portion of the casing 103. A small gear 106 attached at the 
lower end of the input shaft 102 meshes with a large gear 107. The ends of 
a supporting shaft 108 supporting the large gear 107 are fitted in and 
supported by a pair of recesses 103a, 103a that are formed in the casing 
103. Drive power is transmitted from the supporting shaft 108 to an output 
shaft 111 via a speed change gear mechanism 109 and a clutch 110 after the 
rotational speed having been changed. 
However, the above prior art transmission is too bulky with the two 
bearings being superimposed to stably support the input shaft. Therefore, 
the belt pulley, which is attached at the end of the input shaft to 
transmit drive power from the engine, is located distant from the ground. 
Thus, the prior art transmission could not address the need for a compact 
walking lawn mower. 
In order to solve the above problem, it is an object of the present 
invention to provide a transmission wherein the distance between the belt 
pulley and the ground is reduced by reducing the height dimension of the 
transmission, thereby making a lawn mower compact. 
SUMMARY OF THE INVENTION 
In order to solve the above problem, the transmission for self-propelled 
walking lawn mowers, comprising: 
a casing; 
an input shaft vertically inserted into the casing through an opening 
formed in a wall of the casing; 
an output shaft passing through the casing and extending horizontally; 
a small gear fixedly mounted on the input shaft; 
a large gear meshing with the small gear; 
a supporting shaft fixedly carrying the large gear at one end thereof and 
extending substantially in parallel to the output shaft; and 
first and second intermediate gears mounted on the supporting shaft and the 
output shaft, respectively, and meshing with each other for power 
transmission, 
wherein the input shaft is arranged on the side of the large gear facing 
opposite to the supporting shaft and is supported by the top and bottom 
walls of the casing. 
Preferably, a clutch is arranged between the output shaft and the second 
intermediate gear. 
Preferably, the clutch comprises an power input part connected to the 
second intermediate gear and a power receiving part connected to the 
output shaft. 
Preferably, the supporting member is enclosed in and rotatably supported by 
a holder formed by the peripheral portion of the casing having a generally 
cylindrical shape. 
Preferably, the small gear engages the large gear fixedly attached at one 
end of the supporting shaft and the end face of the large gear bears 
against an internal portion of the casing so that the supporting shaft is 
prevented from moving axially by the small gear and the internal portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The embodiment of the transmission of the present invention will be 
described below with reference to the attached drawings. 
FIG. 1 is a perspective view schematically showing the internal structure 
of a self-propelled walking lawn mower 1. A pulley 4 is fixedly mounted on 
a drive shaft 3 that projects downwardly from a drive unit 2 comprising an 
engine, etc. A pulley 6 is fixedly mounted on an input shaft 5. A belt 7 
is passed through the pulleys 4 and 6. The belt 7 is maintained taut by a 
tension roller 8. The input shaft 5 is vertically inserted into a 
transmission 9 from above. The rotational force of a horizontally 
extending output shaft 10 is transmitted to mower wheels 13 via gears 11 
and 12. Pivotally attached to a handle 15 of the lawn mower 1 is an 
operating arm 16 to which a clutch cable 14 is connected. 
FIGS. 2 and 3 are a horizontal and a vertical cross sections, both showing 
the internal structure of the transmission 9. Mounted below an upper 
opening 18 of the casing 17 and also on the inner bottom wall of the 
casing 17 are bearings 19a and 19b for supporting the input shaft 5. A 
small gear 20 is fixedly mounted on the input shaft 5 and located directly 
below the upper opening 18 of the casing 17. A large gear 21 meshing with 
the small gear 20 is supportedly attached at one end of a supporting shaft 
22. The supporting shaft 22 extends in the direction opposite to the input 
shaft side of the large gear 21. The small gear 20 may also be mounted on 
the inner bottom wall of the casing 17 as indicated by an alternate long 
and short dash line in FIG. 3. In this case, the rotational direction of 
the output shaft 10 is in reverse to that in the case where the small gear 
20 is mounted to the upper casing portion. The bearings 19a and 19b may 
preferably be ball bearings, but roller bearings or slide bearings may 
also be used. 
As shown in FIG. 4, the supporting shaft 22 for the large gear 21 is 
supported by a holder 17a and a collar 23 fitted in the holder 17a, the 
holder 17a being formed by peripheral portions of the upper and lower 
casing halves each having a generally half-cylindrical shape. The collar 
23 and the holder 17a are set to have enough length and thickness to 
stably support the supporting shaft 22. Attached at the opposite end of 
the supporting shaft 22 to the large gear 21 is a first intermediate gear 
24 for transmitting drive power to the later-described clutch. 
To prevent the supporting shaft 22 from moving. towards the input shaft 5, 
face gears, bevel gears, hypoid gears or like gears are used as the large 
gear 21 and the small gear 20. To prevent the supporting shaft 22 from 
moving in the direction opposite to the input shaft 5, the casing is 
integrally provided with a contact portion 17b contacting the large gear 
21 and/or an extension 17c bearing against the first intermediate gear 24. 
The first intermediate gear 24 meshes with a second intermediate gear 25 to 
drive the second intermediate gear 25. The second intermediate gear 25 is 
a large-diameter spur gear having teeth 27 and rotatably mounted on the 
output shaft 10. As shown in FIG. 5, a friction member 29 is fitted in one 
side of the second intermediate gear 25. The second intermediate gear 25 
has a boss 30 at its central portion. A hole 31 for receiving the output 
shaft 10 passes through the boss 30. An annular groove 32 is formed around 
the boss 30. Formed in the groove 32 are three radially extending raised 
portions. 
The friction member 29 is constituted by three circumferentially arranged 
friction pieces 34 that form a ring as a whole. Each friction piece 34 is 
partially wedge-shaped in axial cross section to taper towards a slider 26 
described below. The outer and inner tapering faces of the friction piece 
34 form friction surfaces 35. The friction piece 34 has a recess 36 formed 
on the side opposite to the friction surface 35 to engage one of the 
raised portions 33 of the second intermediate gear 25. The friction pieces 
34 are fitted in the groove 32 with a small radial play. The raised 
portions 33 engage the recesses 36 so that the friction member 29 is fixed 
to the second intermediate gear 25 so as not to move in a circumferential 
direction of the gear 25. Each friction piece 34 has a lug 37 at the end 
portion close to the second intermediate gear 25. The lug 37 projects in 
the direction opposite to a rotational direction of the friction member 29 
and engages a correspondingly positioned complementary recess 38 formed in 
the rearward friction piece 34. With this construction, when the lug 37 of 
the friction piece 34 is forced to float off during rotation, the recess 
38 formed in the rearward friction piece 34 presses down the lug 37, so 
that the friction piece 34 is prevented from partially floating off from 
the groove 32. 
Mounted on the output shaft 10 is an axially slidable slider 26. The slider 
26 is keyed to the output shaft 10 so as not to rotate relative to the 
output shaft 10. Formed on the side of the slider 26 facing towards the 
friction member 29 is a friction surface 39 formed by a generally V-shaped 
annular groove, the friction surface 39 being engageable with the friction 
surface 35 of the friction member 29. 
Thus, a clutch having a power input part and a power receiving part is 
constituted, wherein the power input part of the transmission is formed by 
the second intermediate gear 25 and the friction member 29, and the power 
receiving part of the transmission is formed by the slider 26. This clutch 
is engaged or disengaged respectively by the engagement and disengagement 
between the friction surfaces 35 and 39. According to this clutch, both 
the inner and outer faces of the friction piece 34 form the friction 
surface 35, with which the generally V-shaped friction surface 39 engages, 
so that drive power can be transmitted stably and efficiently due to the 
large frictional engaging area. It is possible, therefore, to reduce the 
radii of the friction piece 34 and the slider 26 to thereby make the 
transmission light and compact. 
Arranged between the second intermediate gear 25 and the slider 26 is a 
clutch spring 40 that forces these components away from each other. 
Further, fitted to the output shaft 10 are thrust bearings 41 and 42 that 
are located adjacent to and bear on the second intermediate gear 25 and 
the slider 26, respectively. The thrust bearings 41 and 42 are axially 
slidable relative to the output shaft 10. 
Disposed on the side of the thrust bearing 42 facing opposite to the slider 
26 is a fork 43 which makes the engagement and disengagement of the clutch 
by external operation. The one end of the fork 43 is supported by the 
casing 17, and the other end projects out of the casing 17. An operating 
rod 46 is attached to the projecting end of the fork 43. The operating rod 
46 is connected to the operating arm 16 and the clutch cable 14 shown in 
FIG. 1. The fork 43 has two fingers between which the output shaft 10 
extends. The fingers contact an intermediate member 44. The intermediate 
member 44 is rotatably mounted on the output shaft 10 and contacts the 
thrust bearing 42. Accordingly, when the operating arm 16 shown in FIG. 1 
is grasped together with the handle 15, the clutch cable 14 tensions to 
rotate the operating rod 46 and therefore rotate the fork 43. Then, the 
slider 26 moves towards the second intermediate gear 25 against the spring 
force of the clutch spring 40. Thereby, the friction surfaces 35 and 39 
engages each other to engage the clutch. By contrast, when the operating 
arm 16 is released to loose the clutch cable 14, the fork 43 is also 
released, so that the slider 26 is moved away from the second intermediate 
gear 25 by the spring force of the clutch spring 40 to thereby disengage 
the clutch. 
In this instance, a boss 48 is attached integrally to the operating arm 46 
so as to receive the top end of the fork 43, the upper end of the boss 48 
being closed and the lower end being opened. The boss 48 is inserted into 
a receiving hole of the casing 17. A sealing ring 49 is fitted between the 
boss 48 and the casing wall. The lower end of the boss 48 spreads 
resiliently in the radial direction so as not to slip off from the fork 
43. 
The internal operation of the thus-constructed transmission 9 is described 
below. When the drive unit 2 is actuated, the input shaft 5 is rotated via 
the belt 7. The small gear 20 is rotated with the rotation of the input 
shaft 5. The rotational speed is reduced at the large gear 21. The first 
intermediate gear 24 coaxial with the large gear 21 is rotated, and then 
the second intermediate gear 25 meshing therewith is rotated after the 
rotational speed being further reduced. 
By grasping the operating arm 16, the fork 43 is operated via the operating 
rod 46 to thereby move the slider 26 towards the second intermediate gear 
25 against the spring force of the clutch spring 40, so that the slider 26 
frictionally engages the friction member 29. Since the slider 26 and the 
intermediate gear 25 are supported by the thrust bearings 41 and 42, 
respectively, they can be readily rotated although pushed towards each 
other. When the slider 26 rotates, the output shaft 10 keyed therewith 
rotates. By the rotation of the output shaft, the wheels 13 rotate. 
According to the transmission 9 employing the above construction, the 
supporting shaft 22 is supported by the casing 17, and the one end thereof 
is connected to the small gear 20 via the large gear 21, while the other 
end of the supporting shaft 22 bears on the projection 17c. Further, the 
supporting shaft 22 contacts the casing at 17b to prevent the supporting 
shaft 22 from moving axially. 
Furthermore, since the input shaft 5 is arranged on the side of the large 
gear facing opposite to the supporting shaft 22, the input shaft 5 can 
extend to the bottom wall of the casing 17, and thus the input shaft 5 can 
be supported by the opening 18 formed in the top wall and the bearing 19b 
formed on the bottom wall. Therefore, the input shaft 5 can be supported 
without two bearings being superimposed at the shaft receiving portion as 
seen in conventional transmissions, so that the height dimension of the 
transmission can be reduced. 
As described above, according to the transmission of the invention for 
self-propelled walking lawn mowers, the large gear to mesh with the small 
gear is supported at one end of the supporting shaft, the small gear being 
fixedly attached to the input shaft, and the input shaft is arranged on 
the side opposite to the large gear. Further, since the input shaft is 
supported by the top and bottom walls of the casing, the height dimension 
of the casing can be reduced, thereby making compact the transmission and 
the resulting lawn mower.