Transmission shift control mechanism

A shift control mechanism particularly adapted for use with a manual transmission having a main control shaft on an axis normal to a single shift fork rail. Both rotational and longitudinal motion is transferred from the main control shaft to the shift fork rail through a single pivoted idler lever. A pair of shift forks and a reverse gear transfer bar are connected to an interlock system which insures that the shift fork rail establishes only one gear ratio at any time as it is rotated for crossover selection and moved longitudinally for gear engagement.

BACKGROUND OF THE INVENTION 
This invention relates generally to the control of an automotive 
transmission or the like. More particularly, it relates to an improved 
shift control mechanism for a manual transmission, the transmission being 
particularly adaptable for use in a front-wheel-drive automotive vehicle 
having a transversely mounted engine. 
In recent years there have been many improvements in automotive drive 
trains, including improvements relating to the shifting of sliding gear 
manual transmissions. One such transmission is disclosed in U.S. Pat. No. 
3,929,029 issued Dec. 30, 1975. As disclosed therein first and second 
shift rails are connected by a link element. A shift stick is connected to 
the first shift rail such that movement in one direction causes rotation 
and movement in another direction causes longitudinal sliding of this 
shift rail. Motion of the first shift rail is transmitted to the other 
shift rail by the link element so as to provide opposite rotational and 
longitudinal sliding thereof. 
One disadvantage of this arrangement is the requirement for two parallel 
shift rails. This results in a complex linkage arrangement, as well as a 
bulky apparatus which in turn requires a large extension housing for the 
transmission. Another disadvantage is that orientation of the shift rails 
is such that it would be difficult to incorporate this control mechanism 
in a front-wheel-drive vehicle having a transversely mounted transmission. 
SUMMARY OF THE INVENTION 
One of the objects of this invention is to overcome the disadvantages noted 
above. To that end, there is provided a shift control mechanism which may 
be incorporated in a multi-speed manual transmission having, for example, 
four fully synchronized forward gear ratios and a reverse gear ratio. Such 
a transmission is adapted for crosswise installation in a 
front-wheel-drive automotive vehicle. 
A control input shaft enters the side of the transmission and is oriented 
transversely to a single shift fork rail. A single idler lever is mounted 
on a fulcrum shaft which is transverse to both the control input shaft and 
the shift fork rail. Rotary motion is imparted to the control input shaft 
for crossover selection of gear ranges. This motion is transferred to the 
idler lever, causing it to slide on its fulcrum shaft. This in turn 
imparts rotary motion to the shift fork rail and to an associated shift 
fork selector head. The head enters one of the associated shift forks or a 
reverse transfer bar. A suitable interlock insures that only one selection 
is obtainable at any time. 
Once proper crossover selection has been completed, the control input shaft 
is moved longitudinally to engage the appropriate gear. Longitudinal 
motion causes the idler lever to rotate about its fulcrum shaft. This 
motion is imparted to the shift fork rail, which is moved longitudinally 
to complete the shift into the desired gear range. 
Engagement in a forward gear ratio is accomplished by selection and 
movement of an appropriate shift fork. Engagement in reverse is 
accomplished by selection of the reverse transfer bar and, upon movement 
thereof, movement of an associated reverse idler lever to engage a reverse 
idler gear. 
The shift control mechanism disclosed herein requires only one idler lever 
and one shift fork rail. Thus, the mechanism requires fewer parts of a 
less complicated nature than mechanisms known heretofore. Some of the 
close dimensional tolerances inherent in prior art mechanisms are 
eliminated, and the overall cost thus is reduced.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawings in greater detail, there is shown generally a 
compact manual transmission 10 adapted for use in an automotive vehicle 
incorporating a transversely mounted engine. Transmission 10 is 
particularly adapted for transverse mounting so as to transmit torque from 
the engine through the drive axle assembly to the front wheels. 
Transmission 10 includes a housing 12 which may be an associated clutch 
housing, and which may include or be adjacent to an associated 
differential. 
An input shaft 14 is journalled in housing 12 and is adapted to receive 
torque from the engine through an appropriate clutch. Similarly, a 
countershaft or output shaft 16 is journalled in housing 12 and is 
oriented adjacent the ring gear 18 of an associated differential. 
Defined by or secured to input shaft 14 are a first ratio input gear 20, a 
reverse ratio input gear 22, a second ratio input gear 24, a third ratio 
input gear 26 and a fourth ratio input gear 28. Journalled on output shaft 
16 are a first ratio output gear 30, a second ratio output gear 32, a 
third ratio output gear 34, and a fourth ratio output gear 36. Gear 20 is 
in mesh with gear 30, gear 24 is in mesh with gear 32, gear 26 is in mesh 
with gear 34, and gear 28 is in mesh with gear 36. An output drive gear 38 
is defined by or secured to output shaft 16 and is in mesh with gear 18. 
A suitable first-second synchronizing clutch mechanism 40 is slidably 
supported by output shaft 16. A reverse ratio output gear 42 is secured to 
the hub of synchronizer 40. A similar third-fourth synchronizing clutch 
mechanism 44 is slidably supported by output shaft 16. As shown in FIG. 5, 
synchronizer 40 may slide rightwardly to engage gear 30 with output shaft 
16, thereby establishing the first forward gear ratio. Synchronizer 40 may 
slide leftwardly to engage gear 32 with output shaft 16, thereby 
establishing the second forward gear ratio. Similarly, synchronizer 44 may 
slide to the right to engage gear 34 with output shaft 16, thereby 
establishing the third forward gear ratio, and to the left to engage gear 
36 with output shaft 16, thereby establishing the fourth forward gear 
ratio. 
A reverse support block 46 is rigidly secured within a housing 11 by 
suitable bolts 48 or the like. As bolts 48 do not extend through the 
exterior wall of housing 11, transmission assembly is facilitated without 
introducing a potential leakage point in this area. A reverse idler shaft 
50 is entered into block 46 and into a suitable bore 52 defined by housing 
12. A reverse idler gear 54 is rotatably supported on shaft 50 and is 
slidable relative thereto. Gear 54 defines a groove 56. Gear 54 is 
slidable from the disengaged position shown in FIG. 4 to the right into 
meshing engagement with gears 22 and 42, thereby establishing the reverse 
gear ratio. 
Turning now to the mechanism for shifting synchronizers 40 and 44 and gear 
54, there is shown a control input shaft 58 received in bores 60 and 62, 
respectively defined by housing 12 and a boss 64 formed by housing 12. 
Control shaft 58 is rotatable on a first axis A, and is axially or 
longitudinally slidable thereon. Control shaft 58 defines spaced notches 
66, 68 and 70. A detent plunger 72 is slidably received in a bore 74 
defined by boss 64. A suitable spring 76 biases detent 72 toward control 
shaft 58. With detent 72 engaged in one of notches 66, 68 or 70, control 
shaft 58 is restrained in one of its longitudinal positions. A control 
head 78 is secured to control shaft 58 for rotational and longitudinal 
movement therewith. Control head 78 defines a socket 80. 
A fulcrum pin 82 is pressed into bores 84 and 86, respectively defined by 
housing 12 and a boss 88 formed by housing 12. Fulcrum pin 82 is thus 
rigidly secured to housing 12 on a second axis B substantially normal to 
first axis A. 
An idler lever 90 is supported on fulcrum pin 82 by suitable bearings 92 or 
the like for pivotal movement about axis B and sliding movement axially or 
longitudinally therealong. Idler lever 90 defines a first lever arm 94, 
from which extends a first ball 96. Ball 96 is received in socket 80 of 
control head 78 to form therewith a first articulated connection. Idler 
lever 90 also defines a second lever arm 98. A second ball 100 is secured 
to lever arm 98 and extends therefrom. 
A shift fork rail 102 is received in bores 104 and 106 defined by housings 
12 and 11 for rotation on a third axis C and for sliding movement axially 
or longitudinally therealong. Axis C is substantially normal to both axes 
A and B, and is substantially parallel to output shaft 16. Shift rail 102 
defines spaced notches 108, 110 and 112. A detent ball 114 is slidably 
received in a bore 116 defined by housing 11. A suitable spring 118 biases 
detent 114 toward shift rail 102. With detent 114 engaged in one of 
notches 108, 110 or 112, shift rail 102 is restrained in one of its 
longitudinal positions. A shift head 120 is secured to shift rail 102 for 
rotational and longitudinal movement therewith. Shift head 120 defines a 
socket 121 in which is received ball 100 of idler lever 90 to form 
therewith a second articulated connection. 
As best shown in FIGS. 1 and 3, rotation of control shaft 58 and control 
head 78 on axis A causes idler lever 90 to slide longitudinally along axis 
B. This in turn causes rotation of shift head 120 and shift rail 102 on 
axis C. The distance from axis A to first connection 96-80 relative to the 
distance from second connection 100-121 to axis C determines a mechanical 
advantage obtained as shift rail 102 is rotated. 
As best shown in FIG. 2, axial or longitudinal movement of control shaft 58 
and control head 78 along axis A causes pivotal movement of idler lever 90 
about axis B. This in turn causes axial or longitudinal movement of shift 
head 120 and shift rail 102 along axis C. The distance from first 
connection 96-80 to axis B relative to the distance from axis B to second 
connection 100-121 determines a mechanical advantage obtained as shift 
rail 102 is moved longitudinally. 
As best shown in FIG. 1, idler lever 90 defines surfaces 122 and 124 
respectively cooperable with surface 126 defined by housing 12 and surface 
128 defined by boss 88. Abutment of surface 122 against surface 126 serves 
to limit clockwise rotation of shift rail 102. Similarly, abutment of 
surface 124 against surface 128 serves to limit counterclockwise rotation 
of shift rail 102. 
In a preferred form of the invention, rotation of control shaft 58 by 12 
degrees in one direction abutts surface 122 against surface 126. This 
results in rotation of shift rail 102 by 20 degrees in one direction. 
Rotation of control shaft 58 by 12 degrees in the opposite direction is 
not sufficient to abutt surface 124 against surface 128. This allows 
rotation of shift rail 102 slightly more than 20 degrees in the opposite 
direction, for a purpose to be explained. Alternatively, surfaces 124 and 
128 could be arranged such that a 12 degree rotation of control shaft 58 
would cause them to abutt, thereby limiting rotation of shift rail 102 to 
20 degrees in either direction, for a purpose to be explained. 
A first shift fork 125 is engaged with synchronizer 40 to effect shifting 
thereof. Shift fork 125 defines a bore 127 in which shift rail 102 is 
slidably received. As best shown in FIGS. 5 and 7, shift fork 125 also 
defines a bar 129 extending along shift rail 102 and defining an inwardly 
facing slot 130. Similarly, a shift fork 132 is engaged with synchronizer 
44 for effecting shifting thereof. Shift fork 132 defines a bore 134 in 
which shift rail 102 is slidably received. Shift fork 132 also defines a 
bar 136 extending along shift rail 102 and defining an inwardly facing 
slot 138 in alignment with slot 130. In a preferred form of the invention, 
bar 136 is spaced from bar 129 by 20 degrees. A pad 140 is secured to bar 
136 on the far side thereof from bar 129. Pad 140 serves as a limit stop 
partially closing slot 138. 
With reference to FIGS. 4, 5, 6 and 7, the reverse gear actuating linkage 
includes a reverse transfer bar 142 extending along shift rail 102 and 
defining an inwardly facing slot 144 in alignment with slots 130 and 138. 
In a preferred form of the invention, transfer bar 142 is spaced from bar 
129 by 20 degrees. As best shown in FIG. 4, transfer bar 142 is slidable 
in a bore 146 defined by housing 11. Transfer bar 142 also defines a slot 
148 and a notch 150. A reverse fulcrum pin 152 is rigidly secured to 
housing 12 and extends through slot 148. Pin 152 and slot 148 guide 
longitudinal movement of transfer bar 142 and limit the extent thereof. A 
reverse idler lever 154 is pivotal about the axis of reverse fulcrum pin 
152. Reverse idler lever 154 defines a pad 156 extending into notch 150 of 
reverse transfer bar 142. Reverse idler lever 154 also defines a pad 158 
extending into groove 56 of gear 54. As shown in FIG. 4, transfer bar 142 
is at its extreme rightward position and reverse idler gear 54 is 
disengaged. Leftward movement of transfer bar 142 causes pivotal movement 
of reverse idler lever 154 clockwise about the axis of reverse fulcrum pin 
152. This causes rightward movement of gear 54 into meshing engagement 
with gears 22 and 42. Movement of reverse idler lever 154 acutates a 
suitable switch 160 to turn on the backup lights of an associated vehicle. 
As best shown in FIG. 7, a selector head 162 is secured to shift rail 102 
for rotational and longitudinal movement therewith. Selector head 162 
defines a finger 164 extending into slot 130 of bar 129. In this position, 
shift rail 102 is engaged with shift fork 125. Counterclockwise rotation 
of shift rail 102 and selector head 162 by 20 degrees moves finger 164 out 
of slot 130 and into slot 138 of bar 136. In this position, shift rail 102 
is engaged with shift fork 132. Similarly, clockwise rotation of shift 
rail 102 and selector head 162 by 20 degrees moves finger 164 out of slot 
130 and into slot 144 of transfer bar 142. In this position, shift rail 
102 is engaged with the reverse gear actuating linkage. Thus crossover 
selection is accomplished by rotation of shift rail 102 such that finger 
164 of selector head 162 is positioned within one of slots 130, 138 or 
144. 
An interlock is provided to insure that only one bar is moved at any given 
time. A guide 168 may be, for example, the inner end of a bolt secured to 
housing 11. An interlock member 170 includes bifurcated end portion 172 
straddling guide 168. Outwardly extending tongues 174 defined by selector 
head 162 fit into inwardly facing grooves 176 defined by interlock member 
170. It is apparent that as shift rail 102 and selector head 162 rotate, 
tongues 174 rotate interlock member 170 relative to guide 168. As finger 
164 is rotated into one of slots 130, 138 or 144, interlock member 170 is 
rotated into the other two slots. Upon longitudinal movement of shift rail 
102 and selector head 162, finger 164 carries the engaged bar, but tongues 
174 slide in grooves 176. Guide 168 prevents longitudinal movement of 
interlock member 170, and this prevents longitudinal movement of the 
remaining two bars in either direction. 
As shown in FIGS. 5 and 7, longitudinal movement of shift rail 102 causes 
finger 164 to slide bar 129 and shift fork 125 along shift rail 102. This 
causes longitudinal sliding movement of synchronizer 40 so as to engage 
either gear 30 or gear 32 with output shaft 16. Interlock member 170 
prevents longitudinal movement of bar 136 and transfer bar 142. With 
finger 164 positioned in slot 138, longitudinal movement of shift rail 102 
causes finger 164 to slide bar 136 and shift fork 132 longitudinally, 
moving synchronizer 44 so as to engage either gear 34 or gear 36 with 
output shaft 16. Interlock member 170 prevents longitudinal movement of 
bar 129 and transfer bar 142. With finger 164 in slot 144, longitudinal 
movement of shift rail 102 operates the reverse gear actuating linkage. 
Transfer bar 142 is moved longitudinally, thereby pivoting reverse idler 
lever 154 about the axis of reverse fulcrum pin 152. Gear 54 is moved 
along shaft 50 into meshing engagement with gears 22 and 42. Interlock 
member 170 prevents longitudinal movement of bars 129 and 136. 
The shift control mechanism and the gears are arranged to give the shift 
pattern shown in FIG. 9, as seen by the vehicle operator. In neutral, 
finger 164 is in notch 130 so as to select shift fork 125. Rightward 
movement of control shaft 58, as shown in FIG. 2, causes counterclockwise 
pivotal movement of idler lever 90 and downward movement of shift rail 
102. This corresponds to rightward movement of shift rail 102, as shown in 
FIG. 5. Shift fork 125 moves synchronizer 40 to the right so as to engage 
gear 30 with output shaft 16, thereby establishing the first forward gear 
ratio. Similarly, leftward movement of control shaft 58, as shown in FIG. 
2, causes clockwise pivotal movement of idler lever 90 and upward movement 
of shift rail 102. This corresponds to leftward movement of shift rail 
102, as shown in FIG. 5. Shift fork 125 moves synchronizer 40 to the left 
so as to engage gear 32 with output shaft 16, thereby establishing the 
second forward gear ratio. 
Rotation of control shaft 58 clockwise from neutral, as shown in FIG. 3, 
causes idler lever 90 to slide rightwardly along the axis of fulcrum pin 
82. This corresponds to upward movement, as shown in FIG. 1. This movement 
causes counterclockwise rotation of shift rail 102, thus moving finger 164 
out of slot 130 of bar 129 and into slot 138 of bar 136. Pad 140 insures 
proper alignment of finger 164 in slot 138 by preventing excessive 
crossover movement. Alternatively, pad 140 could be removed and surfaces 
124 and 128 so oriented that abutment of surface 124 against surface 128 
limits the longitudinal travel of idler lever 90, and thus limits 
counterclockwise rotation of shift rail 102 at a point where finger 164 is 
aligned in slot 138. 
Rightward movement of control shaft 58, as shown in FIG. 2, results in 
rightward movement of shift fork 132, as shown in FIG. 5. Synchronizer 44 
engages gear 34 with output shaft 16 so as to establish the third forward 
gear ratio. Similarly, leftward movement of control shaft 58, as shown in 
FIG. 2, corresponds to leftward movement of shift fork 132, as shown in 
FIG. 5. Synchronizer 44 engages gear 36 with output shaft 16, thereby 
establishing the fourth forward gear ratio. 
Rotation of control shaft 58 counterclockwise from neutral, as shown in 
FIG. 3, slides idler lever 90 to the left until surface 122 abutts surface 
126. This rotates shift rail 102 clockwise, as shown in FIG. 7, so as to 
move finger 164 out of slot 130 and into slot 144 of transfer bar 142. 
Subsequent movement of control shaft 58 to the right, as shown in FIG. 2, 
causes leftward movement of transfer bar 142, as shown in FIG. 4, so as to 
engage the reverse gear ratio. 
It should be apparent that a simple and very compact shift control 
mechanism has been disclosed herein, which mechanism provides for a 
control shaft oriented at 90 degrees relative to a single shift rail. 
Rotation of the control shaft causes rotation of the shift rail to effect 
crossover selection. Thereafter, longitudinal movement of the control 
shaft causes longitudinal movement of the shift rail to effect engagement 
of the selected gear ratio. An interlock prevents inadvertent clashing of 
other gears as the selected gear ratio is being established. Alternative 
limit stops may be provided to insure proper alignment of the shift 
control mechanism with the shift forks and the reverse transfer bar during 
crossover selection. 
Although the shift control mechanism as disclosed herein may be used in 
conjunction with a transmission having four forward speed ratios, it is 
readily adapted for use in other transmissions, with or without overdrive. 
While a preferred embodiment of the invention has been shown and described, 
this should be considered as illustrative and may be modified by those 
skilled in the art. It is intended that the claims herein cover all such 
modifications as may fall within the spirit and scope of the invention.