Device for lubricating rear bush in extension housing of automotive transmission

The oil grooves which are formed in the bore of a hollow rear bushing that is disposed adjacent to the rear end of an extension housing of an automotive transmission are provided in such a pattern that upon rotation of the output shaft or sleeve journalled in the bore, lubricating oil is drawn into the grooves from both the front and rear ends of the bushing. The oil drawn in is distributed over the whole inner surface of the bore and discharged into the space behind the rear bushing. The extension housing is provided with a passageway which interconnects the space behind the rear bushing with the space ahead of the rear bushing.

BACKGROUND OF THE INVENTION 
The present invention relates to a system for lubricating a rear bush (i.e. 
a rear bushing) disposed adjacent the rear end of an extension housing of 
an automotive transmission for supporting an output shaft or sleeve yoke 
splined thereto. 
In conventional automotive transmissions, an extension housing is extended 
rearwardly from a transmission case for supporting an output shaft or 
sleeve yoke splined thereto by a rear bush disposed adjacent the rear end 
of the extension housing. The extension housing contains oil for 
lubricating the rear bush. The rear bush is provided with oil grooves so 
that lubricating oil flows through the rear bush forwardly and backwardly 
under the screw pump action produced upon rotation of the output shaft or 
sleeve yoke in the rear bush, and a plurality of axially extended passages 
are formed in a rear bush retainer section of the extension housing for 
intercommunicating the front and rear spaces in front of and behind the 
rear bush so that sufficient lubricating oil may exist in the rear space 
as well as the front space. 
In general, the automotive transmissions of the type described are mounted 
on vehicles of the front-engine and rear-drive type at an angle of 
3.degree. to 4.degree. inclined rearwardly with respect to the horizontal 
because of the construction of the vehicles. Therefore the lubricating oil 
is filled into the extension housing in such a quantity that the inclined 
rear bush may be completely immersed with lubricating oil. In other words, 
the rear bush is below the level of the lubricating oil when a vehicle is 
traveling on a flat road or upgrade slope, but when the vehicle is 
traveling on a down-hill, the lubricating oil flows toward and remains on 
the side of the transmission case, leaving almost no lubricant in the rear 
bush so that seizure of the rear bush results. 
The simplest solution for this problem is to increase the lubricating oil 
in the extension housing so that the rear bush may be kept immersed even 
during the down-hill traveling, but this method is not preferable because 
the transmission efficiency decreases with the increase in resistance 
encountered by the transmission gears from the increased lubricating oil 
and the power required for shifting the transmission is increased. 
To overcome this problem there has been proposed and practised a method for 
disposing in the extension housing a weir extended upwardly from the 
bottom thereof so as to hold back the flow of the lubricating oil toward 
the transmission case during the down-hill traveling, thereby keeping the 
rear bush sufficiently immersed with the lubricating oil. However this 
method must be provided with means for trapping the lubricating oil 
splashed by the transmission gears and feeding the trapped oil to an oil 
sump defined by the weir. As a result, the parts required for the 
lubrication of the rear bush is increased in number, and the fabrication 
of the extension housings by die-casting becomes difficult because the 
existence of the weir, thus resulting in the use of inefficient sandmolds 
with a complex pattern and the decrease in productivity. 
SUMMARY OF THE INVENTION 
The present invention was made to overcome the above problems, and has for 
its object to provide a device for lubricating a rear bush in an extension 
housing of an automotive transmission which device is very simple in 
construction yet capable of ensuring reliable lubrication of the rear bush 
with a small quantity of oil for a certain time interval even when most of 
the lubricating oil has flowed toward the transmission case during the 
down-hill traveling. 
To the above and other ends, the present invention provides a rear bush 
lubrication device for use in an automotive transmission of the type in 
which a cylindrical hollow rear bush is disposed adjacent the rear end of 
an extension housing of the automotive transmission for rotatably 
supporting an output shaft or sleeve rotatable in unison therewith, oil 
grooves are formed on the inner surface of said rear bush in such a way 
that upon rotation of said output shaft, lubricating oil is drawn into 
said oil grooves from the front and rear ends of said rear bush to be 
uniformly distributed over the whole inner surface of said rear bush, and 
an axial passage or passages are formed in said extension housing for 
intercommunicating the front and rear spaces in front of and behind said 
rear bush, characterized in that said oil grooves are arranged in such a 
pattern that said lubricating oil can be discharged only into said rear 
space, and said axial passages for intercommunicating said front and rear 
spaces are formed only in a portion of said extension housing surrounding 
the upper portion of said rear bush. 
According to the present invention, during the travel on a flat road or 
up-hill, the lubricating oil is drawn from the front space into the oil 
grooves of the rear bush so as to lubricate the rear bush and discharged 
into the rear space and the lubricating oil in the rear space is returned 
through the axial passage into the front space, and even when the 
lubricating oil flows away from the rear bush during the down-hill 
traveling, the satisfactory lubrication of the rear bush continues for a 
certain time until all the lubricating oil trapped in the rear space leaks 
through the clearance between the rear bush and the output shaft or sleeve 
splined thereto into the front space. 
In view of actual road circumstances it is observed that the longest 
down-hill travel time is only 20 minutes at the most. The rear bush 
lubrication device in accordance with the present invention ensures the 
satisfactory lubrication of the rear bush for a down-hill travel time of 
the order of 20 minutes. 
The above and other objects, features and advantages of the present 
invention will become more apparent from the following description of some 
preferred embodiments thereof taken in conjunction with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Prior Art, FIGS. 1, 2 and 3 
Prior to the description of the preferred embodiments of the present 
invention, the prior art lubrication system for a rear bush in an 
extension housing of an automotive transmission will be briefly described 
to specially point out the problems thereof with reference to FIGS. 1 
through 3. 
FIG. 1 is a longitudinal sectional view of the prior art automotive 
transmission, illustrating mainly the construction thereof in the vicinity 
of a rear bush 3 force fitted into a cylindrical rear bush retainer 
section 2 of an extension housing 1. A sleeve yoke 5 is fitted over the 
rear portion of an output shaft 4 to be rotatably supported in the rear 
bush 2. The sleeve yoke 5 is splined at 6 to the output shaft for rotation 
therewith and axial movement therealong in order to absorb the axial 
movement of a propeller shaft (not shown) joined to the yoke 5. An oil 
seal 7 is placed at the rear end of the extension housing 1 to seal the 
yoke 5, and collars 8 and 9 are fitted over the extension housing 1 and 
the yoke 5, respectively, to prevent the intrusion of dust into the 
extension housing 1. The rear end opening of the sleeve yoke 5 is closed 
with a plug 10. 
The rear bush 3 is formed into a cylindrical shape from a flat sheet with 
an oil grooving pattern 11 shown in FIG. 2 so that helical grooves 11' and 
11" which have a pitch substantially equal to the length of the rear bush 
3 and intersect with each other at the middle point between the ends of 
the rear bush 3 are provided. Three circumferentially spaced axial grooves 
12, 13 and 14 are formed on the bore of the rear bush retainer section 2 
as shown in FIG. 3 so as to provide passages axially extending along the 
outer periphery of the rear bush 3 and intercommunicating spaces in front 
of and behind the rear bush. 
The transmission with the rear bush 3 is mounted on an automotive vehicle 
in such a manner as to be inclined rearwardly at an angle of 3.degree. to 
4.degree. with respect the horizontal. When the vehicle is running on a 
flat road or upgrade slope, the level of lubricating oil within the 
extension housing 1 is high enough to immerse the rear bush 3, and 
lubricating oil flows through the axial passages 12, 13 and 14 to 
completely fill the space behind the rear bush 3 as well as the space in 
front of the rear bush 3. When the sleeve yoke 5 is rotating in the 
direction indicated by the arrow A in FIG. 2, the lubricating oil in the 
space in front of the rear bush (that is, on the left side in FIG. 2) is 
entrained or drawn into the helical groove 11' under the screw pump action 
of the sleeve yoke 5 and, after lubricating the rear bush, discharged into 
the space behind the rear bush 3 (that is, on the right side in FIG. 2). 
In like manner, the lubricating oil in the space behind the rear bush 3 is 
forced to flow through the helical oil groove 11" into the space in front 
of the rear bush 3. Therefore the sliding contact interface between the 
rear bush 3 and the sleeve yoke 5 may be completely lubricated with oil. 
However when the vehicle starts travelling on a down-hill, the lubricating 
oil flows toward the transmission case (that is, to the left side in FIG. 
1) so that the rear bush 3 is exposed out of the level of lubricating oil 
and the lubricating oil in the space behind of the rear bush 3 flows 
through the axial passages 12, 13 and 14 into the space in front of the 
rear bush 3. As a result, the rear bush 3 is not supplied with lubricating 
oil, and the lubrication of the rear bush 3 is greatly adversely affected, 
resulting in seizure between the rear bush 3 and the sleeve yoke 5. 
The Invention, FIGS. 4 through 8 
The present invention was made to overcome the above problem encountered in 
the prior art systems for lubricating a rear bush in an extension housing 
of an automotive transmission, and will be described in detail with 
reference to FIGS. 4 through 8. 
A first essential feature of the present invention is that the lower axial 
passage 12 of the prior art rear bush lubrication system is eliminated as 
shown in FIG. 5 and the upper axial passages 13 and 14 are located in a 
position as high as possible. In the preferred embodiment of the present 
invention only one axial passage 15 having a relatively large cross 
section is formed in the extension housing 1 immediately above the rear 
bush as shown in FIGS. 4 and 5. Instead of completely eliminating the 
axial passage 12, it may be formed as a blind bore opening only at the 
rear end of the bush 3 as shown in FIG. 4 so that the rear space behind 
the rear bush 3 may be advantageously increased in volumne as will be 
described in detail hereinafter. 
A second essential feature of the present invention is an unique oil 
grooving pattern which is so formed as to prevent the discharge of 
lubricating oil into the front space from the oil grooves of the rear bush 
3. In FIG. 6 there is shown a first embodiment of an oil grooving pattern 
in accordance with the present invention. It should be noted that the 
front end of an oil groove 16 corresponding to the helical oil groove 11" 
shown in FIG. 2 is terminated adjacent the front end of the rear bush 3. 
Therefore upon rotation of the sleeve yoke 5, lubricating oil is forced to 
be drawn into the helical oil groove 11' to flow from the front space to 
the rear space throughout the helical groove 11' but the lubricant which 
has been drawn into the helical groove 16 from the rear space is not 
discharged into the front space. 
In FIG. 7 there is shown a second embodiment of an oil grooving pattern in 
accordance with the present invention. In this embodiment the helical 
groove 11" shown in FIG. 2 is substituted by two helical grooves 16' and 
16" which are interrupted at the middle point between the ends of the rear 
bush without intersecting the helical groove 11'. Since the groove 16" is 
out of communication with the rear space, the lubricating oil is not 
discharged into the front space. 
In FIG. 8 there is shown a modification of the second embodiment shown in 
FIG. 7. Partly extended oil grooves 16' and 16" are inclined at a 
relatively greater angle with respect to the rear and front sides, 
respectively, of the rear bush 3 so that they may be extended over a 
relatively longer distance in the axial direction of the rear bush 3 and 
consequently a wider lubrication distribution may be attained. 
The oil grooving pattern shown in FIGS. 7 and 8 are symmetrical so that 
they have an advantage in that in assembly it is not required to take into 
consideration the direction of the rear bush 3. 
According to the present invention as described above, when the vehicle is 
traveling on a flat road or upgrade slope, the lubricating oil after 
lubrication of the sliding contact surfaces of the rear bush 3 and the 
sleeve yoke 5 is discharged only into the rear space and the lubricant 
discharged into the rear space is returned into the front space through 
the axial passage 15. When the vehicle is traveling on a down-hill, the 
lubricant flows toward the transmission case, leaving almost no lubricant 
just in front of the rear bush 3, but a considerable amount of the 
lubricant remains in the rear space because an axial passage extending 
below the rear bush 3 is not provided in accordance with the present 
invention. The lubricant in the rear space is drawn into the helical 
groove 16 or 16' to lubricate the sliding contact surfaces. These oil 
grooves, however, are not communicated with the front space so that the 
lubricant drawn into them is not discharged into the front space except an 
extremely small amount of oil leaking through the clearance between the 
rear bush 3 and the sleeve yoke 5. Therefore the effective lubrication can 
be attained until all of the lubricant remaining in the rear space leaks 
through the clearance between the rear bush 3 and the sleeve yoke 5 into 
the front space. In general, down-hill traveling continues 20 minutes at 
the maximum, and the lubricating oil trapped in the rear space is 
sufficient in quantity to continue the satisfactory lubrication of the 
rear bush and sleeve yoke during 20 minutes. When the blind bore 12 is 
formed as stated hereinbefore, there is an advantage that the lubricant 
remaining in the rear sapce at the beginning of the down-hill traveling is 
increased in quantity. 
A further arrangement for prolonging the duration of lubrication of the 
rear space during the down-hill traveling is to extend the rear end of the 
bush 3 beyond the rear end 17 of the retainer section 2 of the extension 
housing 1 as shown in FIG. 4. The lubricating oil trapped in the rear 
space is taken by the sleeve yoke during the down-hill drive to swirl 
therewith so that an annular layer of oil with a certain thickness is 
formed around the sleeve yoke. When this swirling lubricant layer extends 
radially beyond the outer periphery of the rear bush, the lubricating oil 
flows into the upper axial passage 15 to be discharged into the front 
space. The lubricating oil splashed upwardly by the sleeve yoke 5 is also 
discharged through the axial groove 15 into the front space. When the 
lubricating oil trapped in the rear space is discharged into the front 
space through the axial passage in the manner described above, the oil for 
lubricating the rear bush 3 and the sleeve yoke 5 is relatively rapidly 
decreased in volume, resulting in a shorter lubrication time during the 
down-hill drive. However when the rear end of the rear bush 3 is extended 
axially backwardly of the rear end 17 of the retainer section 2 as 
described above, the inlet of the axial passage 15 is spaced apart from 
the outer surface of the sleeve 5 by a certain distance so that a 
substantial amount of the lubricating oil drops before it reaches the 
inlet of the axial passage 15 and consequently the loss of the lubricating 
oil discharged through the axial passage 15 may be minimized. 
As described above, according to the present invention, the problem of 
lubrication of a rear bush in an automotive transmission during the 
down-hill traveling may be overcomed only by the minor modifications of 
the prior art lubrication systems so that from the practical viewpoint the 
present invention is very advantageous over the hitherto proposed 
solutions.