Driving power transmission

A driving power transmission which is simply changeable of the axis of a counter shaft in order to facilitate a change in a reduction ratio and mountable of a gear train different in the reduction ratio and which inserts a bevel gear to be fitted onto an output shaft at the transmission unit into a mission case prior to coupling of a lower mission case thereof with an upper mission case and places the bevel gear on a mounting table so that the bevel gear can be fitted onto the output shaft only by being later inserted into the bevel gear.

SUMMARY OF THE INVENTION 
A transmission case, divided into two sections at the point where the axis 
of a shaft supporting speed reduction gears is located, is the subject 
matter of Applicant's co-pending U.S. patent application Ser. No. 928,151. 
For manufacturing a large or a light tractor, it is often used to change a 
diameter of a tire only but not other parts. 
Such method is very simple and largely different in appearance, thereby 
being the most effective. 
When the diameter of the tire is changed, the peripheral speed of the tire 
is different for the same driving power transmission, thereby changing the 
running speed. Hence, in order to compensate the running speed, it is 
required that exchange of the tire is anticipated to constitute a driving 
power transmission changeable of a reduction ratio. 
The aforesaid prior application constitutes a reduction gear mechanism with 
a first shaft receiving a driving force from an oil pressure motor at a 
hydrostatic-transmission-type (HST type) transmission, in which wheel 
bases at the three axes are decided during the processing, so that when 
the reduction ratio is intended to change, each wheel base should be 
changed. Hence, a separate mission case must be prepared. 
The present invention has been designed to solve the above problem. 
In the prior application, as shown in FIG. 11 of the present invention, a 
bearing is fixed by shrinkage fitting means or the like to a boss of a 
bevel gear fitted onto an output shaft at a transmission unit and at a 
mission case to which other transmission unit is attached is provided with 
an opening of thickness and a layer diameter enough to support the bevel 
gear through the bearing so that the output shaft fixedly supporting the 
bevel gear is inserted through the opening and journaled by the bearing. 
Accordingly, the assembly process for fixing the bearing to the boss at the 
bevel gear increases, and when the mission case has the aforesaid large 
thickness at the upper surface, the transmission is disposed at a high 
level to that extent to enlarge the entire driving power transmission and 
raise the input shaft thereof, whereby an engine should be disposed at a 
high level. 
An object of the present invention is to provide a driving power 
transmission suitable for a compact light tractor whose transmission unit 
is formed at the attaching surface smaller in thickness to make the engine 
lower in position as much as possible by designing a mounting structure of 
the bevel gear fitted onto the output shaft at the transmission unit. 
The above and further objects and novel features of the invention will more 
fully appear from the following detailed description when the same is read 
in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An object and construction of the invention are as above-mentioned. Next, 
explanation will be given on construction of the embodiment shown in the 
drawings. 
Referring to FIGS. 1 and 2, the entire construction of the tractor will be 
described. 
Power is transmitted through a V-belt from a crank shaft of an engine E to 
a transmission Unit H fixed to a mission or transmission case 1. The 
rotation after changing the speed is transmitted by the transmission unit 
H to a diff or differential gear through a reduction gear train, thereby 
driving therethrough lateral axles 12. 
Front wheels 20 of driving wheel are fixed to the axles 12, rear wheels 21 
of steering wheel being fixed to the rear of the tractor. 
In the present invention, the size of tire is exchanged in order to produce 
various kinds of larger or light tractors. 
Variation in the circumferential speed of the tire caused by a change in 
the size thereof is restored the original by changing a reduction ratio in 
the mission case 1. 
In addition, a mower R is disposed in the front of the tractor. 
Next, explanation will be given on the mission case 1 shown in FIGS. 3, 4, 
5 and 6. 
An upper mission case 1b is loaded on a lower mission case 1c and a diff 
case 1a is placed at an opening provided above the diff gear at the upper 
mission case 1b. 
The driving power transmission unit H is placed on a portion of the upper 
mission case 1b where no diff case is loaded, and an output shaft 16 of 
the driving power transmission unit H projects into the mission case 1 
through an insertion bore of the upper mission case 1b. 
The output shaft 16 is supported by a bearing at a side of the driving 
power transmission unit H, no bearing is provided at an insertion bore at 
the upper mission case 1b side. 
Therefore, at the upper mission case 1b is merely formed the insertion bore 
of a somewhat larger diameter than a diameter of the output shaft 16 and 
of the size enough to insert the output shaft 16 into the mission case 1c. 
Conventionally, as shown in FIG. 11, a bevel 9 is inserted into the mission 
case 1c after coupling the lower mission case 1c with the upper mission 
case 1b. The present invention, however, disposes the bevel gear 9 in 
engagement with a bevel gear 8 within the mission case 1 prior to coupling 
of the lower mission case 1c with the upper mission case 1b, the bevel 
gear 9 being placed on a mounting table or mounting element 17 projecting 
from the lower mission case 1c. 
Hence, the output shaft 16, which is inserted into the upper mission case 
1b, can be fitted into a spline bore 9a at the bevel gear 9. 
The bevel gear 9 is driven by the output shaft 16 so as to be subjected by 
thrust reaction to a force to float the bevel gear 9 above the mounting 
table 17 with respect to the bevel gear 8 as shown in FIG. 10. 
The bevel gear 8 mounted on one end of a first shaft 3 and engageable with 
the bevel gear 9 drives the first shaft 3 to rotate a first gear 7 
thereon. The first shaft 3 projects at the other end thereof into a brake 
chamber 1g at the lower mission case 1c and fixedly supports a brake drum 
18. 
Referring to FIG. 5, a counter gear 6 is freely fitted on a counter shaft 2 
through bearing metal 25 and engages with the first gear 7 and further 
with a larger diameter gear 5 on a third shaft 4. 
A smaller diameter gear 10 thereon engages with a ring gear 11 at the diff 
gear unit. 
The diff gear unit is so constructed that a pinion shaft support 15 is 
fitted into a bore formed at a boss of the ring gear 11, two pinions 13 
and 14 are freely fitted on the pinion shaft support 15, and a boss 
thereof forms a fitting bore through which the lateral axes 12 abut 
against each other and further forms a positioning portion at the inside 
of each lateral diff side gear 26. 
In the above-mentioned constitution, the present invention is directed to 
shifting of the counter shaft 2 so as to change diameters of the counter 
gear 6 and larger diameter gear 5 to cope with variation in the tire 
diameter. 
Namely, the lower mission case 1c and counter shaft 2 are formed in 
configuration shown in FIGS. 7 and 8. 
Generally, the counter shaft 2 is rotatably supported at the shaft into a 
round shaft bore in the state where it is fitted into the bearing metal. 
On the contrary, in the present invention, the counter shaft 2, which is 
round in section, is not supported directly by the bearing metal but 
supported in such a manner that fixedly retaining portions 2a each are 
formed in a rectangular parallelepiped easy to machine and disposed to put 
the center or central axis H2 thereof at the position eccentric only by 
eccentricity .DELTA.H from the axis H1 of counter shaft 2 and fitted into 
retaining recesses or grooves 1e and 1f provided at the lower mission case 
1c and an intermediate mission case 1b, thereby not-rotatably supporting 
the counter shaft 2. 
Bearing metal 25 is coated on the counter shaft 2 and the counter gear 6 is 
rotatably supported thereon. 
Since the center H2 of the fixedly retaining portions 2a shifts only by the 
eccentricity .DELTA.H from the axis of counter shaft 2, the counter shaft 
2, when disposed as shown in FIG. 3, approaches the first shaft 3 only by 
the eccentricity .DELTA.H, whereby the counter gear 6 can use a smaller 
diameter gear and contrary the larger diameter gear 5 can use a larger 
diameter gear, thereby increasing the reduction ratio. 
Also, in a case that the fixedly retaining portions 2a are turned over and 
the counter shaft 2 is disposed as shown in FIG. 5, the axis is changed in 
position and the counter shaft 2 moves away from the first shaft 3 by the 
eccentricity .DELTA.H, whereby it is possible to change the counter gear 6 
to a larger diameter one 6' and contrary the larger diameter gear 5 to a 
slightly smaller diameter gear, so that the reduction ratio is reduced in 
comparison with the state in FIG. 3. 
Thus, the fixedly retaining portions 2a at the counter shaft 2 are turned 
over, whereby one mission case, even when in use, can obtain two kinds of 
reduction ratios. 
In this embodiment, the first gear 7 on the first shaft 3 is equal in 
diameter and used in common. Alternatively, the counter gear 6 and first 
gear 7 may change in diameter so that the larger diameter gear 5 may be 
used in common. 
The present invention constructed as above-mentioned has the following 
effects. 
Firstly, since the fixedly retaining portions 2a at the counter shaft 2 
are turned over to enable the wheel base from the first shaft 3 to the 
counter shaft 2 and that therefrom to the third shaft 4 to be simply 
changed, when the reduction ratio is changed at the steering speed change 
unit side to correspond to a change in specification of the tire diameter, 
one mission case is usable in common. 
Secondly, since the mission case 1 is divided into the upper mission case 
1b above the axis of counter shaft 2 and the lower mission case 1c under 
the same, the reduction ratio, when changed, largely facilitates its 
assembly and reassembly works. 
Thirdly, the counter shaft 2, fixedly retaining portions 2a and retaining 
grooves 1e and 1f at the mission case 1 are simple in configuration, 
thereby being inexpensive to produce. 
Fourthly, since the mission case 1 can be reduced in vertical width, the 
transmission unit is lowered at the mounting position so that the entire 
driving power transmission can be made compact, thereby being suitable for 
the light tractor. 
Although several embodiments have been described, they are merely exemplary 
of the invention and not to be constructed as limiting, the invention 
being defined solely by the appended claims.