Vehicle gear transmission having an overdrive gear stage

A vehicle gear transmission having an overdrive and reverse gear stages. The counter-overdrive gear and the counter-reverse gear on the countershaft are rotatably mounted on the countershaft and a synchronizing mechanism is provided between the counter-overdrive gear and the counter-reverse gear. The clutch hub sleeve of the synchronizing mechanism is actuated by a manual shift lever through a reversing lever which functions to reverse the direction of movement of the shift lever before the movement is transmitted to the clutch hub sleeve.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a vehicle gear transmission, and more 
particularly to a vehicle gear transmission having an overdrive gear 
stage. 
2. Description of the Prior Art 
A manually operated gear transmission for motor vehicles generally includes 
a countershaft adapted to be driven by an engine drive shaft and an output 
shaft which is located in parallel with the countershaft and adapted to be 
connected with vehicle driven shaft usually through a differential gear 
mechanism. Between the countershaft and the output shaft, there are 
provided a plurality sets of intermeshing gears of different gear ratios, 
one of the gear sets being selected to complete a power transmitting gear 
train of a desired gear ratio. 
In conventional structures, so-called counter gears provided on the 
countershaft are mounted on the countershaft through splines so that they 
rotate together with the countershaft. The driven gears on the output 
shaft are rotatable with respect to the output shaft and mechanisms are 
provided for selectively connecting one of the gears to the output shaft. 
In connecting one of the gears to the output shaft, there usually is a 
difference in rotating speed between the output shaft and the one gear on 
the output shaft so that a synchronizing mechanism is provided for each 
gear on the output shaft. Usually, such synchronizing mechanism is 
provided between two adjacent gears on the output shaft so that one such 
mechanism can be used in common for the two gears at the opposite sides of 
the synchronizing mechanism. For example, in a gear transmission having an 
overdrive gear stage, a first synchronizer is provided between the first 
and second stage driven gears, a second synchronizer is provided between 
the third and fourth stage driven gears, and a third synchronizer is 
provided between the overdrive driven gear and the reverse stage driven 
gear. The arrangement is believed as being effective in making the 
structure simple. 
In a gear transmission having an overdrive gear stage, the gear on the 
countershaft for the overdrive gear stage is of a large diameter in order 
to provide a desired gear ratio. In case where such a counter-overdrive 
gear of a large diameter is provided to rotate with the countershaft, 
there will be a substantial increase in the inertia of the countershaft. 
This will cause inconveniencies in gear shifting operations in that the 
rotating speed of the counter-overdrive gear has to be synchronized with 
that of the output shaft overcoming the inertia of the countershaft. Thus, 
the shifting operations are made difficult and the synchronizing mechanism 
is subjected to an excessive load. 
In order to eliminate the problems, there is proposed, by Japanese patent 
application No. 58-152948 which has been filed on Aug. 22, 1983 and 
disclosed for public inspection under the disclosure No. 60-44640, to 
mount the counter-overdrive gear rotatably on the countershaft and instead 
to connect the overdrive gear with the output shaft to rotate therewith. 
The arrangement is considered as being advantageous in that the inertia of 
the countershaft can be decreased. 
It should however be noted that the arrangement as proposed by the 
aforementioned Japanese patent application is disadvantageous in that an 
additional synchronizer has to be provided between the countershaft and 
the counter-overdrive gear on the countershaft. In order to make it 
possible to actuate the synchronizer between the countershaft and the 
counter-overdrive gear, the shift rod for the overdrive gear stage and the 
reverse gear stage has to be provided with a shift fork for actuating the 
synchronizer for the overdrive gear stage as well as a shift fork for 
actuating the synchronizer for the reverse gear stage. Thus, a complicated 
mechanism is required. It should further be noted that in a conventional 
arrangement, the shift rod is located above the gear mechanism whereas the 
countershaft is in a lower portion of the gear mechanism so that a shift 
fork of a substantial length has to be provided in order to actuate the 
synchronizer on the countershaft. This will cause a further problem 
because there is a possibility that the rigidity of the shift fork is 
decreased to an undesirable extent. In order to increase the rigidity of 
the shift fork, the size of the shift fork is undesirably increased. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a vehicle 
gear transmission having an overdrive gear stage but the inertia of the 
countershaft is not undesirably increased. 
Another object of the present invention is to provide a vehicle gear 
transmission having an overdrive gear stage in which the counter-overdrive 
gear is rotatable on the countershaft but a synchronizer is commonly used 
for the overdrive gear stage and for the reverse gear stage. 
Still further object of the present invention is to provide a novel gear 
shifting mechanism for a vehicle gear transmission. 
According to the present invention, the above and other objects can be 
accomplished by a vehicle gear transmission including a countershaft 
adapted to be driven by an engine drive shaft, a plurality of first gears 
provided on said countershaft, an output shaft carrying a plurality of 
second gears which are paired and in meshing engagement with respective 
ones of the first gears, one of the gears in each pair being mounted on 
one of the countershaft and the output shaft to which said one gear is 
associated for rotation with said one shaft, the other of the gear in the 
pair being mounted on the other shaft for free rotation, connecting means 
for connecting said other gear with said other shaft, shifting means for 
selectively actuating said connecting means so that selected one of said 
other gears is connected with said other shaft to establish a power 
transmitting gear train of a desired gear ratio, said pairs of gears 
including gears for an overdrive gear stage and for a reverse gear stage, 
the first gears for the overdrive and reverse gear stages being adjacent 
to each other and freely rotatable on the countershaft, said connecting 
means being provided in common between said first gears for the overdrive 
and reverse gear stages for alternately connecting said first gears for 
the overdrive and reverse gear stages to said countershaft, shifting means 
including shifting rod means and reversing lever means for reversing 
direction of movement of the shifting rod means and transmitting the 
movement of the shifting rod means to the connecting means to actuate the 
connecting means. The connecting means may include synchronizing means for 
synchronizing rotation of said other gear with rotation of said other 
shaft. 
According to features of the present invention, the counter-overdrive gear 
on the countershaft is rotatable so that the inertia of the countershaft 
can be decreased to a desirable extent. Further, since the counter-reverse 
gear is also rotatable on the countershaft, it is possible to provide a 
connecting means in common between the counter-overdrive gear and the 
counter-reverse gear. Thus, the shifting mechanism can be simplified. In 
the arrangement of the present invention, the connecting means on the 
countershaft is located away from the shifting rod means, however, since 
the movement of the shifting rod means is transmitted through the reverse 
rod means to the connecting means, it is possible to ensure a positive 
shifting operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings, particularly to FIG. 1, there is shown a vehicle 
gear transmission 1 which includes an input shaft 2 adapted to be driven 
by an engine drive shaft (not shown) and an output shaft 3 coaxially 
aligned with respect to the input shaft 2. A countershaft 4 is provided 
beneath the output shaft 3 in parallel with the output shaft 3. These 
shafts 2, 3 and 4 are arranged in a transmission casing 5 for rotation 
about their own axes. 
The countershaft 4 is provided at one end with an input gear 6 which is in 
meshing engagement with a drive gear 7 provided on the input shaft 2 so 
that the countershaft 4 is driven by the input shaft 2 at a predetermined 
gear ratio. The countershaft 4 is provided adjacent to the input gear 6 
with a counter-third gear 13.sub.1 for a third stage. The counter-third 
gear 13.sub.1 is rotatable together with the shaft 4 and in meshing 
engagement with an output third gear 13.sub.2 which is provided for free 
rotation on the output shaft 3. The gears 13.sub.1 and 13.sub.2, 
respectively; provide a third gear stage 13 for the transmission. Adjacent 
to the counter-third gear 13.sub.1, the countershaft 4 is provided with a 
counter-second gear 12.sub.1 which is rotatable together with the 
countershaft 4 and in meshing engagement with a driven second gear 
12.sub.2 provided for free rotation on the input shaft 3 to provide a 
second gear stage 12 of the transmission. Similarly, a first gear stage 11 
is provided by a counter-first gear 11.sub.1 which is provided on the 
countershaft 4 to rotate therewith and engaged with a driven first gear 
11.sub.2 freely rotatable on the input shaft 3. 
Between the driven first gear 11.sub.2 the driven second gear 12.sub.2, 
there is provided a synchronizing mechanism 21 for alternately connecting 
the gears 11.sub.2 and 12.sub.2, respectively; with the output shaft 3. 
The synchronizing mechanism 21 includes a clutch hub 21a which is splined 
to the output shaft 3 and a clutch hub sleeve 21b which is splined to the 
outer surface of the clutch hub 21a for axial sliding movements with 
respect thereto. A synchronizer key is provided between the synchronizer 
hub 21a and the sleeve 21b. At the opposite sides of the hub 21a, the 
gears 11.sub.2 and 12.sub.2, respectively are provided respectively with 
gear splines 21d and 21e which have tapered cones respectively engaged 
with synchronizer rings 21f and 21g. In this mechanism, when the clutch 
hub sleeve 21b is slidably moved in the direction shown by an arrow A, the 
sleeve 21b is at first engaged with the spline formed on the outer surface 
of the synchronizer ring 21f and the ring 21f is then forced through the 
synchronizer key 21c toward the tapered cone on the gear spline 21d so 
that the rotation of the clutch hub 21a is synchronized with the rotation 
of the gear spline 21d. As the sleeve 21b is engaged further deep with the 
gear spline 21d, the driven first gear 11.sub.2 is engaged through the 
gear spline 21d, the sleeve 21b and clutch hub 21a with the output shaft 
3. Similarly, when the clutch hub sleeve 21b is slidably moved in the 
direction shown by an arrow B, the driven second gear 12b is engaged with 
the output shaft 3 through the gear spline 21e, the sleeve 21b and the 
clutch hub 21a. The synchronizing mechanism 21 is well known in the art so 
that detailed description will be omitted. 
A similar synchronizing mechanism 22 is provided between the input shaft 2 
and the counter-third gear 13.sub.2. The mechanism 22 includes a clutch 
hub 22a splined to the output shaft 3, a sleeve 22b provided on the outer 
surface of the clutch hub 22a, a synchronizer key 22c between the hub 22a 
and the sleeve 22b, gear splines 22d and 22e provided at the opposite 
sides of the clutch hub 22a, and synchronizer rings 22f and 22g. As the 
sleeve 22b is slidably moved in the direction shown by an arrow C in FIG. 
1, the driven third gear 13.sub.2 is connected with the output shaft 3 to 
establish the third gear stage 13. When the sleeve 22b is in turn moved in 
the direction shown by an arrow D, the output shaft 3 is connected with 
the input shaft 2 to establish a fourth gear stage or a direct connection. 
The transmission 1 shown in FIG. 1 includes a fifth or overdrive gear stage 
15 and a reverse gear stage 16. The fifth gear stage 15 includes a 
counter-overdrive gear 15.sub.1 mounted on the countershaft 4 for free 
rotation with respect thereto and a driven fifth gear 15.sub.2 provided on 
the output shaft 3 to rotate therewith. The driven fifth gear 15.sub.2 is 
in meshing engagement with the counter-overdrive gear 15.sub.1. For 
providing the reverse gear stage 16, there is an idler shaft 4a which is 
supported on an extension housing 9 provided integrally with the 
transmission casing 5. A counter-reverse gear 16.sub.1 is mounted on the 
countershaft 4 for free rotation with respect thereto. A driven reverse 
gear 16.sub.2 is provide on the output shaft 3 to rotate together with the 
output shaft 3. The counter-reverse gear 16.sub.1 on the countershaft 4 is 
in engagement with an idler gear 16.sub.3 which is in turn engaged with 
the driven reverse gear 16.sub.2 on the output shaft 3. 
There is provided a synchronizing mechanism 23 between the 
counter-overdrive gear 15.sub.1 and the counter-reverse gear 16.sub.1. The 
synchronizing mechanism 23 is identical in structure to the synchronizing 
mechanism 21 so that detailed descriptions will be omitted but reference 
characters are given only to the synchronizing hub 23a, the sleeve 23b and 
the gear splines 23d and 23e. It will be noted that when the clutch hub 
sleeve 23b is slidably moved in the direction shown by an arrow E, the 
counter-overdrive gear 15.sub.1 is connected with the countershaft 4. When 
the sleeve 23b is slidably moved in the direction shown by an arrow F, the 
counter-reverse gear 16.sub.1 is connected with the countershaft 4. 
In order to actuate the clutch hub sleeves 21b, 22b and 23b, there is 
provided a shift lever 30 and shift rods 31, 32 and 33. As shown in FIG. 
2, a gear case cover 8 is attached to the upper portion of the 
transmission casing 5 and the shift rods 31, 32 and 33 are located in the 
space covered by the gear case cover 8 to extend parallel with the shafts 
3 and 4. In FIG. 1, it will be noted that the central shift rod 32 is 
provided at a portion beneath the shift lever 30 with a block 42 which has 
an upwardly opened transversely extending groove 42a. The other rods 31 
and 33 are provided adjacent to the block 42 whith blocks 41 and 43, 
respectively. 
The shift lever 30 has a downwardly extending pawl 30a which is normally 
engaged with the groove 42a in the block 42 when the lever 30 is in the 
neutral position shown in FIG. 2. The shift lever 30 is mounted at a 
vertically intermediate portion on the case cover 8 by means of a 
spherical bearing 30b so that it can be moved from the position a to the 
positions b and c. As shown in FIG. 2, the block 41 has a laterally 
inwardly opened cutout 41a. Similarly, the block 43 has a laterally 
inwardly opened cutout 43a. Thus, it will be understood that the pawl 30a 
on the shift lever 30 is engaged with the cutout 41a in the block 41 when 
the lever 30 is moved to the position b and with the cutout 43a in the 
block 43 when the lever 30 is moved to the position c. In order to return 
the shift lever to the neutral position shown as the position a, the block 
41 is provided with a return spring 41b which forces the pawl 30a of the 
shift lever 30 through a return pin 41c. Similarly, the block 43 is 
provided with a return spring 43b and a pin 43c. 
In the structure described above, it will be understood that when the shift 
rod 30 is moved in the direction shown by an arrow x in FIG. 1 while it is 
held in the neutral position a, the shift rod 32 is moved toward right in 
FIG. 1. When the shift lever 30 is moved in the opposite direction as 
shown by an arrow y, the shift rod 32 is moved toward left in FIG. 1. When 
the shift lever 30 is moved in a similar manner while it is held in the 
positions b and c, the shift rods 31 and 33 are respectively actuated. In 
order to yieldably hold the rod 33 longitudinally in the position shown in 
FIG. 1, a ball detent device 33a is provided as shown in FIG. 1. A similar 
ball detent device is also provided for each of the rods 31 and 32. The 
block 41 is formed integrally with a shift fork 51 which is engaged with 
the clutch hub sleeve 21b of the synchronizing mechanism 21. The block 42 
is integrally formed with a shift fork 52 which is engaged with the clutch 
hub sleeve 22 b in the synchronizing mechanism 22. 
As shown in FIGS. 1 and 3, the shift rod 33 has a shift block 54 which is 
secured thereto at an end portion. A reversing or swingable lever 56 is 
provided and supported at a side wall of the transmission casing 5 by 
means of a pin 55. The shift block 54 has a lug 54a which is engaged with 
an upper end portion 56a of the lever 56 so that the lever 56 is swingably 
moved about the pin 55 as the shift rod 33 is moved in its axial 
direction. A shift fork 53 is supported for slidably movement by a shaft 
57 and has a lug portion 53a which is engaged with a lower end portion 56b 
of the lever 56. It will therefore be understood that the movement of the 
shift rod 33 is transmitted through the shift block 54 and the reversing 
lever 56 to the shift fork 53 to move the shift fork in the direction 
opposite to the direction of movement of the shift rod 33. The shift fork 
53 is engaged with the clutch hub sleeve 23b of the synchronizing 
mechanism 23 so that the clutch hub sleeve 23b is moved as the shift rod 
33 is moved in the direction opposite to the direction of the movement of 
the shift rod 33. In order to retain the shift fork 53 in a neutral 
position, a ball detent device 53b is provided. 
The pin 55 is in the form of an eccentric shaft having a base cylindrical 
portion 55a and an eccentric portion 55b. The base portion 55a is mounted 
on the transmission casing 5 and the eccentric portion 55b supports the 
reversing lever 56 through a sleeve 63. The pin 55 is secured to the 
casing 5 by means of a nut 66. The eccentric portion 55b is radially 
offset from the base portion 55a by a distance 1 as shown in FIG. 3 so 
that it is possible to adjust the position of the shift fork 53 with 
respect to the shift block 54 by simply rotating the pin 55 as shown in 
FIG. 4. 
Referring now to FIGS. 5 and 6, the embodiment shown therein is different 
from the previous embodiment in that the central shift rod 32 has a shift 
block 142 which is similar to the block 42 in the previous embodiment but 
secured to the rod 32 at one end portion. Adjacent to the block 142, the 
shift rods 31 and 33 are provided respectively with shift blocks 141 and 
143. The block 141 is similar in structure to the block 41 in the previous 
embodiment and has a sidewardly opened lug 141a, a return spring 141b and 
a return block 141c. The shift block 143 has a laterally inwardly opened 
lub 143a for engagement with the lower end portion 30a of the shift lever 
30, and a return spring 143b and a return block 143c are provided as in 
the previous embodiment. The block 143 is further provided with a ball 
detent device 143d for retaining the shift lever in the neutral position 
a. At the laterally outer end, the block 143 is formed with a lug 143e 
which is engaged with the upper end 56a of the reversing lever 56. The 
operations of this embodiment are the same as in the previous embodiment 
so that detailed descriptions will not be made. 
The invention has thus been shown and described with reference to 
preferable embodiments which are illustrated in the accompanying drawings, 
however, it should be noted that the invention is in no way limited to the 
details of the illustrated structures but changes and modifications may be 
made without departing from the scope of the appended claims.