Auxiliary power transmission having synchronizing mechanism

An automobile auxiliary power transmission having a synchronizer mechanism comprised of a synchronizer hub, a pair of synchronizer rings cooperating respectively with a low speed and high speed gears, and an axially movable synchronizer sleeve. The synchronizer sleeve has spline teeth for engagement with the synchronizer hub and with the synchronizer rings and the gears. The spline tooth on the sleeve has an axial length which is sufficient to engage with both of the synchronizer rings when it is disengaged from both of the gears. The arrangement is effective to make the shifting stroke of the sleeve smaller than that in conventional structures.

The present invention relates to an automobile power transmission and more 
particularly to an auxiliary power transmission adapted to be associated 
with a main power transmission for providing two alternative series of 
gear ratios. More particularly, the present invention pertains to a 
synchronizer mechanism for such auxiliary power transmission. 
Heretofore, it has been known in automobiles to provide an auxiliary power 
transmission associated with a main power transmission so that two 
alternative series of gear ratios are provided. Such auxiliary power 
transmission generally includes axially aligned input and output shafts, a 
low speed gear splined to the output shaft and a high speed gear which is 
rotatably mounted on the input shaft and connected through a gear 
mechanism with the output shaft. The input shaft carries a hub having an 
external gear and a sleeve having an internal gear is provided for 
alternately connecting the external gear of the hub with the low speed or 
high speed gear. The auxiliary transmission further includes a 
synchronizing mechanism which comprises an axially extending hub portion 
provided on each of the low speed and high speed gears and having a 
frustoconical outer surface, and a synchronizer ring having a 
frustoconical inner surface adapted for sliding engagement with the 
frustoconical outer surface of the hub portion on each of the low speed 
and high speed gears. Each synchronizer ring has an external gear adapted 
for engagement with the internal gear of the sleeve, and keys are carried 
on the sleeve. The arrangement is such that, when the sleeve is moved 
axially toward one of the low speed and high speed gears, the internal 
gear in the sleeve is meshed with the external gear in the appropriate one 
of the synchronizer ring and at the same time the keys engage the 
particular synchronizer ring to force it toward the associated gear. Thus, 
the frustoconical inner surface of the synchronizer ring is forced into 
sliding engagement with the frustoconical outer surface of the hub portion 
of the particular gear so that the rotating speed of the synchronizer ring 
and that of the sleeve are synchronized with the gear. A further axial 
movement of the sleeve therefore accomplishes a meshing engagement between 
the internal gear in the sleeve and the particular one of the low speed 
and high speed gears to thereby connect the latter with the input shaft 
through the hub and the sleeve. 
According to the conventional structure, the arrangement is such that the 
sleeve can take a neutral position where the internal gear therein is free 
from either of the external gears on the synchronizer rings, and when the 
sleeve is axially moved toward either one of the low speed and high speed 
gears, the internal gear in the sleeve is meshed with the external gear in 
the appropriate one of the synchronizer rings. It will therefore be 
understood that a relatively large stroke is required for the synchronizer 
sleeve to change the meshing engagement from one to the other of the low 
speed and high speed gears. This will mean that the lever ratio in the 
actuating mechanism cannot be increased and a substantial actuating force 
is accordingly required. 
It is therefore an object of the present invention to provide a 
synchronizing mechanism for an auxiliary power transmission in which the 
stroke of the synchronizer sleeve can be decreased. 
Another object of the present invention is to provide a synchronizing 
mechanism for an auxiliary power transmission in which actuating force can 
be decreased. 
According to the present invention, the above and other objects can be 
accomplished by an auxiliary power transmission comprising axially aligned 
input and intermediate shafts which are rotatable with respect to each 
other, a first gear rotatably mounted on said input shaft and having first 
external teeth, a second gear mounted on said intermediate shaft to rotate 
therewith and having second external teeth, a synchronizer hub disposed 
between said first and second gears and mounted on said input shaft to 
rotate therewith, said synchronizer hub being formed with external teeth, 
a synchronizer sleeve having internal teeth which are in meshing 
engagement with said external teeth on said synchronizer hub and axially 
movable to bring the internal teeth thereon into meshing engagement 
alternatively with said first and second external teeth on said first and 
second gears, first and second synchronizer rings respectively provided 
between said synchronizer hub and said first and second gears, said first 
and second synchronizer rings being formed with external teeth adapted to 
mesh with said internal teeth of the synchronizer sleeve, first friction 
clutch means provided between said first gear and said first synchronizer 
ring for synchronizing said first gear in rotation with said synchronizer 
sleeve when the sleeve is moved axially toward the first gear, second 
friction clutch means provided between said second gear and said second 
synchronizer ring for synchronizing said second gear in rotation with said 
synchronizer sleeve when the sleeve is moved axially toward the second 
gear, said synchronizer sleeve having an axial length so that the internal 
teeth therein engage both the external teeth on the first and second 
synchronizer rings when the sleeve is out of engagement with said first 
and second gears. 
In a preferable aspect of the present invention, means is provided between 
the synchronizer sleeve and the synchronizer hub for alternately forcing 
one of the first and second synchronizer rings toward the gear cooperating 
with said one synchronizer ring when the synchronizer sleeve is axially 
moved toward the gear cooperating with said one synchronizer ring to 
thereby engage the friction clutch means between said one synchronizer 
ring and said cooperating gear. The forcing means may be embodied in the 
form of at least one key disposed between the synchronizer sleeve and the 
synchronizer hub, engagement means being provided between the synchronizer 
sleeve and the key so that the key is forced against one of the 
synchronizer rings by the sleeve as soon as the sleeve is disengaged from 
the gear cooperating with the other synchronizer ring. The key may be 
provided with resilient means for forcing it radially outwardly and formed 
at an intermediate portion with radially outward projection means, the 
synchronizer sleeve being formed with radially inward projection means 
adapted for engagement with said radially outward projection means on the 
key, said resilient means allowing the projection means on the sleeve to 
ride and pass over the projection means on the key when the sleeve is 
further forced axially after the friction clutch means is engaged.

Referring now to the drawings, particularly to FIG. 1, the transmission 
shown therein includes an auxiliary power transmission A and a main power 
transmission B. The auxiliary power transmission A includes an input shaft 
1a and an intermediate shaft 1b which are axially aligned and rotatable 
with each other. The input shaft 1a is connected through a clutch 
mechanism C with an engine drive shaft D. The main power transmission B 
includes a main shaft E which is axially aligned with the intermediate 
shaft 1b. 
Referring also to FIGS. 2 through 4, there is mounted on the intermediate 
shaft 1b a low speed gear 2 having external spline teeth 2a. The gear 2 is 
splined to the shaft 1b to rotate therewith. The input shaft 1a rotatably 
carries a high speed gear 3 which has external spline teeth 3a and 
external gear teeth 3b. On the input shaft 1a, there is further mounted a 
synchronizer hub 7 which is splined to the input shaft 1a to rotate 
therewith. The synchronizer hub 7 has external spline teeth 7a and a 
synchronizer sleeve 14 having internal spline teeth 14a is engaged with 
the synchronizer hub 7. Thus, the rotation of the input shaft 1a is 
transmitted through the hub 7 to the sleeve 14. 
As shown in FIG. 1, the intermediate shaft 1b is formed with a gear F and a 
gear G having external spline teeth which form a part of a synchronizing 
mechanism H in the main power transmission B. The auxiliary power 
transmission A includes a counter-shaft J formed with a gear K having gear 
teeth which are in meshing engagement with the gear teeth 3b formed on the 
high speed gear 3. The counter-shaft J is connected with a second 
counter-shaft L which is formed with a gear M meshing with the gear F on 
the intermediate shaft 1b. The second counter-shaft L is further formed 
with transmission gears which constitute parts of the main power 
transmission. 
Between the low speed gear 2 and the synchronizer hub 7, there is provided 
a synchronizer ring 4 which has external spline teeth 4a adapted for 
engagement with the internal spline teeth 14a on the sleeve 14. The low 
speed gear 2 is formed at a side facing the synchronizer hub 7 with an 
axially extending hub portion 2b having a frustoconical outer surface 2c. 
The synchronizer ring 4 is formed with a frustoconical inner surface 4b 
which is complementary to the surface 2c of the low speed gear 2. 
Similarly, a synchronizer ring 5 is provided between the high speed gear 3 
and the synchronizer hub 7. The high speed gear 3 is formed with an 
axially extending hub portion 3c having a frustoconical outer surface 3d. 
The synchronizer ring 5 has an external spline teeth 5a adapted for 
engagement with the internal spline teeth 14a on the synchronizing sleeve 
14. Further, the synchronizer ring 5 is formed with a frustoconical inner 
surface 5b complementary to the surface 3d on the high speed gear 3. 
As shown in FIG. 2, there are provided three synchronizer keys 12 which are 
located at three angularly equi-distant positions between the synchronizer 
hub 7 and the synchronizer sleeve 14. The synchronizer key 12 has a 
general configuration as shown in FIG. 3(a) and formed at an intermediate 
portion on the radially outer surface 12a with a radially outward 
projection 13. As shown in FIG. 3(b), at each position where the key 12 is 
located, one or more of the spline teeth 14a are cut to form recesses 16 
for receiving the projection 13 on the key 12. Each of the recesses 16 is 
comprised of two axially aligned recess portions 18 and 19 to leave a 
projection 17 therebetween. The projection 13 on the key 12 has axially 
opposite end surfaces which are inclined with respect to a plane 
perpendicular to the axis of the input shaft 1a. Similarly, the projection 
17 on the sleeve 14 has inclined axially opposite end surfaces. The keys 
12 are resiliently forced radially outwardly by means of springs 8 as 
shown in FIGS. 2 and 4. Further, the synchronizer rings 4 and 5 are formed 
at the sides adjacent to the keys 12 with annular surfaces 4c and 5c which 
are adapted to be engaged by the adjacent ends of the keys 12 when the 
keys 12 are moved thereto. 
As shown in FIG. 4(b) and FIG. 5(c), the spline teeth 14a on the 
synchronizer sleeve 14 are of axial lengths which are sufficient to keep 
the spline teeth 14a in engagement simultaneously with both the teeth 4a 
and 5a on the synchronizer rings 4 and 5. Supposing that the synchronizer 
sleeve 14 is shifted toward the high speed gear 3 so that the spline teeth 
14a are engaged with the spline teeth 3a on the gear 3 as shown in FIG. 
5(a), the input shaft 1a is connected through the hub 7 and the sleeve 14 
with the high speed gear 3. Therefore, the rotation of the input shaft 1a 
is transmitted through the gear 3 and further through the gear K to the 
counter-shaft J. In this position, the projection 13 on the key 12 is 
received by the recess portion 19. When it is desired to connect the low 
speed gear 2 with the input shaft 1a, the synchronizer sleeve 14 is 
axially moved toward the gear 2. In the initial stage of such operation, 
the spline teeth 14a on the sleeve 14 are at first disengaged from the 
spline teeth 3a on the gear 3. In this instance, the spline teeth 14a are 
still in engagement with the spline teeth 5a on the synchronizer ring 5 
but not with the spline teeth 4a on the synchronizer ring 4 as shown in 
FIG. 4(a) and FIG. 5(b). 
As the synchronizer sleeve 14 is further moved axially in the same 
direction, the synchronizer keys 12 are forced in the same direction 
through the engagement between the projections 13 and 17 so that the keys 
12 are engaged with the surface 4c. Thus, the rotation of the synchronizer 
ring 4 is synchronized with the rotation of the sleeve 14. Then, the 
spline teeth 14a are meshed with the spline teeth 4a through a further 
axial movement of the sleeve 14. At this position, the spline teeth 14a on 
the sleeve 14 are engaged with both the spline teeth 4a and 5a on the 
rings 4 and 5 as shown in FIG. 4(b) and FIG. 5(c). In order to readily 
bring the spline teeth 14a on the sleeve 14 into meshing engagement with 
either the spline teeth 4a or 5a, each of the teeth 14a is chamfered at 
the opposite axial ends as shown in FIG. 3(b) and FIG. 5 and each of the 
teeth 4a and 5a is correspondingly chamfered at an end adjacent to the 
tooth 14a. In the position shown in FIG. 4(b) and FIG. 5(c), the chamfered 
ends of the spline teeth 14a are in engagement with the chamfered ends of 
the spline teeth 4a and 5a. 
As the synchronizer sleeve 14 is further moved axially, the spline teeth 
14a thereon are disengaged from the spline teeth 5a on the synchronizer 
ring 5 and completely engaged with the spline teeth 4a on the ring 4 as 
shown in FIGS. 4(c) and 5(d). By this time, the frustoconical surface 4b 
of the synchronizer ring 4 is firmly forced against the frustoconical 
surface 2c of the low speed gear 2 by the synchronizer keys 12 so that the 
rotation of the low speed gear 2 is synchronized with the rotation of the 
synchronizer ring 4 and therefore with the rotation of the sleeve due to 
the friction between the surfaces 2c and 4b. Further, the projections 17 
on the sleeve 14 ride over the projections 13 on the keys 12, resiliently 
deflecting the springs 8 as shown in FIGS. 4(b) and (c) so that the 
projections 13 are now received in the recesses 18. 
A further axial movement of the synchronizer sleeve 14 brings the spline 
teeth 14a into engagement with the spline teeth 2a on the low speed gear 2 
as shown in FIG. 4(d) and FIG. 5(e). The teeth 2a are also chamfered at 
the ends adjacent to the synchronizer ring 4 to make the spline teeth 14a 
readily engageable with the spline teeth 2a. Similarly, the teeth 3a on 
the high speed gear 3 are chamfered at the ends adjacent to the 
synchronizer ring 5. The high speed gear 3 can be connected with the input 
shaft 1a in a similar manner by moving the synchronizer sleeve 14 in the 
opposite direction. At this instance, the synchronizer keys 12 are forced 
against the synchronizing ring 5 through the engagement between the 
projections 13 and 17 because the projections 13 are now received in the 
recesses 19. 
FIG. 6 shows another embodiment of the present invention in which selected 
ones of the spline teeth 114a on the synchronizer sleeve 114 are formed at 
their intermediate portions with radially inward projections 117. 
Synchronizer keys 112 are each formed with a pair of recesses 118 and 119 
to leave a radially outward projection 113. In other respects, the 
arrangements are the same as in the previous embodiment. 
FIG. 7 shows how the teeth on the sleeve 14 engage with rings 4 and 5, and 
with hub 7. 
According to the features of the present invention, the axial length N of 
the spline teeth 14a or 114a is larger than the distance or space L 
between the spline teeth 4a and 5a but smaller than the distance or space 
P between the spline teeth 2a and 3a. Thus, the auxiliary power 
transmission does not take a neutral position as in conventional 
arrangements. Therefore, it is possible to decrease the shifting stroke of 
the synchronizing sleeve. In a preferable arrangement, the axial length N 
of the spline tooth 14a is smaller than the distance M between the root of 
the chamfered portion of the spline tooth in one of the synchronizer rings 
and the adjacent end of the spline tooth in the gear at the side opposite 
to the said one synchronizer ring. More preferably, the axial length N of 
the spline tooth 114a should be smaller than the distance or space M.sub.1 
between the spline teeth on one of the synchronizer rings and the spline 
teeth on the gear at the side opposite to the said particular synchronizer 
ring. 
The invention has thus been shown and described with reference to specific 
embodiments, 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.