Reverse idler gear operating mechanism

A reverse idler gear is mounted for rotation but against axial movement on a swingable reverse idler shaft and adapted to be moved into mesh with other gears to reverse the drive line or disengaged from same in response to the ocillatory motion of the reverse idler shaft.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a reverse idler gear operating mechanism 
for use in an automobile manual transmission. 
2. Description of the Prior Art 
A reverse idler gear is used in automobile manual transmissions to reverse 
the normal direction of rotation of the main or output shaft so that the 
automobile can be moved backward. The reverse idler gear in a typical 
manual transmission is mounted for both rotation and axial movement on a 
stationary shaft so that it can be selectively moved into two operative 
positions, i.e., a neutral position where disengaged from other gears and 
a shifted position where engaging the gears to reverse the drive line. 
With such sliding reverse idler gear, the transmission is required to have 
an additional axial length by at least the extent corresponding to the 
sliding distance of the reverse idler gear between the above two operative 
positions. Further, the transmission requires additional preventive 
measures against a transmission slipping out of reverse gear since the 
sliding reverse idler gear is subject to axial thrust loads and likely to 
cause the transmission to slip out of reverse gear. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a novel reverse 
idler gear operating mechanism for use in a motor vehicle manual 
transmission. The mechanism comprises a reverse idler gear engageable with 
driving and driven reverse gears to reverse the drive line, and a reverse 
idler shaft pivotally mounted at one end thereof to a transmission case 
and having mounted thereon the reverse idler gear for rotation but against 
axial movement relative thereto. The reverse idler shaft is turnable about 
the aforementioned one end thereof between a first angular position where 
it allows the reverse idler gear to engage the driving and driven reverse 
gears and a second angular position where it allows the former to be 
disengaged from the latter. 
This structure enables the transmission to be compact, particularly with 
respect to the axial length thereof. Further, this structure enables the 
transmission to be positively and assuredly prevented from slipping out of 
reverse gear without requiring additional preventive measures. 
It is accordingly an object of the present invention to provide a novel 
reverse idler gear operating mechanism for use in an automobile manual 
transmission which enables the transmission to be compact, particularly 
with respect to the axial length thereof. 
It is a further object of the present invention to provide a novel reverse 
idler gear operating mechanism of the above described character which 
enables the transmission to be positively and assuredly prevented from 
slipping out of reverse gear without requiring additional preventive 
measures.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 1 and 2, a reverse idler gear operating mechanism 
for use in an automobile manual transmission according to the present 
invention is generally indicated at 10 and shown to comprise a reverse 
idler gear 12, a mainshaft or output shaft 14, a driven reverse gear 16 
integrally formed with the mainshaft 14 and a driving reverse gear 18 
mounted on a shaft 20, a counter shaft or a transmission input shaft for 
instance, parallel with the mainshaft 14. 
In accordance with the present invention, the reverse idler gear 12 is 
mounted for rotation but against axial movement on a reverse idler shaft 
22 which is turnable or swingable about a pivot shaft 24. More 
specifically, the reverse idler gear 12 is rotatably mounted via a bushing 
26 on the reverse idler shaft 22 and placed between a flange 22a 
integrally formed with the reverse idler shaft 22 and a snap ring 28 
fitted in an annular groove 22b in the periphery of the reverse idler 
shaft 22 so that the reverse idler gear 12 is held fixed axially of the 
reverse idler shaft 22. The reverse idler shaft 22 is pivotally mounted at 
one end 22c thereof on the pivot shaft 24 extending to cross the mainshaft 
14 and the shaft 20 at right angles and fixedly attached to a transmission 
case (not shown). 
The reverse idler shaft 22 has at the other end portion 22d thereof a 
radial opening 22e which is elongated axially of the shaft 22 and extends 
radially thoughout the same. Received in the opening 22e is a sliding pin 
30 which is slidingly movable between two extreme positions where engaging 
the longitudinally opposed ends 22f and 22g of the opening 22e. The 
sliding pin 30 is attached to one end 34a of a bellcrank-shaped shifter 34 
whose the other end 334b is received in a notch 32a formed in an axially 
slidable rod 32. In this instance, the notch 32a is adapted to engage at 
the opposed side walls thereof with the end 34b of the shifter 34 and not 
to directly engage at the top wall thereof with the same. The shifter 34 
is pivotally mounted at a location intermediate between the ends 34a and 
34b thereof on a pivot shaft 36 extending in parallel with the pivot shaft 
24 and fixedly attached to the transmission case. 
The above described mechanism of the present invention operates as follows. 
The reverse idler gear 12 as illustrated in full lines in the neutral 
position where it is disengaged from the driving and driven reverse gears 
18 and 16 so that the mainshaft 14 may not revolve or may revolve in the 
normal direction. The reverse idler gear 12 is also illustrated in dash 
and dot lines in the shifted position into which it is moved from the 
neutral position when a shift lever (not shown) is shifted into the 
reverse gear selecting position. That is, in response to the shifting of 
the shift lever into reverse, the rod 32 is cause to move from the 
position illustrated in full lines into the position illustrated in dash 
and dot lines. This in turn causes the shifter 34 to rotate 
counterclockwise about the pivot shaft 36 into the position illustrated in 
dash and dot lines. During such rotation of the shifter 34, the sliding 
pin 30 is caused to move from the position where engaging the end 22f of 
the opening 22e into the position where engaging the end 22g of same, 
causing the reverse idler shaft 22 to turn about the pivot pin 24 from the 
position illustrated in full lines where it is incline relative to the 
shafts 14 and 20 into the position illustrated in dash and dot lines where 
it extends in parallel with the shafts 14 and 20. When this is the case, 
the sliding pin 30 is brought into abutting engagement with the end 22g of 
the opening 22e to prevent the reverse idler shaft 22 to turn further 
beyond the horizontal position. In the above manner, the shifter 34 
imparts oscillatory motion to the reverse idler shaft 22 in response to 
the axial sliding of the rod 32 and as a consequence the reverse idler 
gear 12 is moved into the shifted position illustrated in dash and dot 
lines and brought into mesh with the driving and driven reverse gears 16 
and 18 to cause reverse mainshaft rotation so that the automobile can be 
moved backward. 
Thereafter, when the shift lever is shifted from the reverse gear selecting 
position into the neutral position, the rod 32 is returned from the 
position illustrated in dash and dot lines to the position illustrated in 
full lines, causing the shifter 34 to return to the position illustrated 
in full line. This in turn causes the sliding pin 30 to be moved back into 
the position where it is abuttingly engaged with the end 22f of the 
opening 22e. In response to such movement of the sliding pin 30, the 
reverse idler shaft 22 turns about the pivot shaft 24 and causes the 
reverse idler shaft 12 to be moved from the shifted position illustrated 
in dash and dot lines into the neutral position illustrated in full lines. 
The reverse idler gear 12 is thus disengaged from the driving and driven 
gears 16 and 18 and does not cause reverse mainshaft rotation. 
From the foregoing, it is to be understood that according to the present 
invention the reverse idler gear is adapted to be selectively moved into 
the neutral and shifted positions not by moving the reverse idler gear 
relative to and axially of the reverse idler shaft but by swinging or 
turning the reverse idler shaft about one end thereof. This structure 
enables the transmission to be compact, particularly with respect to the 
axial length thereof. The structure of this invention also provides 
effective preventive measures against a transmission slipping out of 
reverse gear since axial thrust loads on the reverse idler gear 12 is 
transferred to the pivot shaft 24 fixedly attached to the transmission 
case to be sustained thereby and further since radial thrust loads on the 
reverse idler gear is transferred to the pivot shaft 36 fixedly attached 
to the transmission case to be sustained thereby. With the reverse idler 
gear operating mechanism of this invention, the transmission can therefore 
be positively and assuredly prevented from slipping out of reverse gear 
without requiring additional preventive measures. In this connection, the 
reverse idler gear operating mechanism of the present invention can 
provide more positive and assured preventive measures against a 
transmission slipping out of reverse gear when the angle .theta. is set to 
be 90.degree. , where .theta. is the angle formed by the center axis of 
the reverse idler shaft 22 in the shifted position illustrated in full 
lines and the line interconnecting the center 0.sub.1 of the pivot shaft 
36 and the center 0.sub.2 of the sliding pin 30 in the state engaging the 
end 22g of the opening 22. 
Obviously, many variations and modifications of the present invention are 
possible in light of the above teachings. It is, therefore, to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described.