Multi-speed rear wheel drive transmission with reduced in-neutral gear rattle

A multi-speed rear wheel drive transmission having synchronizers and a plurality of gears rotatable on the input shaft provides for the elimination of neutral roll-over noise and optimization of common reduced size synchronizers. Gear face widths are also reduced along with shaft diameters to further optimize the transmission design. Towing restrictions are no longer required in vehicles utilizing this design. The input shaft is coaxial with the output shaft and may be connected by synchronizer to the output shaft. A countershaft is in continuous meshing contact with the output shaft.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
The present invention relates to transmissions. More particularly, the 
present invention relates to multi-speed rear wheel drive transmissions. 
II. Description of the Prior Art 
Typically, most rear wheel drive transmissions are constructed with a short 
input shaft which transmits driving torque from a source such as an engine 
through a pair of gears known as a headset, to a countershaft. The 
countershaft is located parallel to the input shaft and is positioned amid 
a plurality of driving gears. An output shaft, having a plurality of 
driven output gears surrounding the shaft, is located parallel to the 
countershaft. Each of the driven output gears surrounding the output shaft 
is in mesh with a corresponding driving gear from the plurality of gears 
on the countershaft. Usually the output shaft is coaxial with the input 
shaft. A number of axially reciprocating synchronizers are coupled to the 
output shaft or countershaft to engage one of the speed gears on one side 
and another of the speed gears on its other side. One of the speed gears 
on the output shaft is a reverse gear which is in mesh with the driving 
gear on the countershaft through an idler gear. Most often, the output 
shaft is coaxial with the input shaft with one of the synchronizers 
arranged to engage, in one position, the input shaft directly to the 
output shaft to effect one of the speed changes. 
With the typical headset multi-speed transmission, all of the driving and 
driven speed gears are in continuous motion when the vehicle is 
stationary, the transmission is in neutral, the driving source, or engine 
is running and the clutch is engaged. Invariably, the driving source, or 
engine, generates angular accelerations in the power output 
characteristics that induce rotational harmonics of the drivetrain. The 
rotational harmonics of the rotating gears of the typical headset 
multi-speed transmission cause a considerable noise problem commonly 
referred to as "neutral roll-over noise". 
With the typical headset transmission design, the torque of the driving 
source or engine is multiplied by the headset gear ratio. Hence, all of 
the speed gears that transmit torque in the power flow sequence after the 
headset must have an adequate face width to transmit the multiplied 
torque. Since the torque multiplication is transmitted through a single 
driving gear on the countershaft to an engaged driven gear on the output 
shaft, the countershaft and output shaft have to be sized and supported to 
withstand considerable deflection forces. 
During synchronization, each gear mesh creates a different amount of 
reflected inertia, which, in a headset multi-speed transmission, results 
in the use of different synchronizers sized to effectively handle the 
different reflected inertia values. 
Vehicles equipped with a typical headset multi-speed transmission cannot be 
towed without restrictions and/or the risk of serious damage to the 
transmission, when the rear wheels of the vehicle are in contact with the 
pavement, the transmission is in neutral and the drivetrain clutch is 
engaged to the stationary driving source or engine. Under these 
conditions, the rotation of the output shaft may cause serious damage to 
bearings, journals, or thrust surfaces, since the rest of the transmission 
components are in a stationary state and adequate lubrication of the 
bearings, journals, gear meshes, or thrust surfaces does not occur. To 
avoid such damage, towing under these conditions is typically restricted 
to speeds of no greater than 30 miles per hour and for distances of 50 
miles or less. 
SUMMARY OF THE INVENTION 
The present invention is directed to overcoming the various disadvantages 
outlined relative to the prior art headset transmission. With the 
transmission of the invention, neutral roll-over noise is eliminated. The 
gear face widths are minimized and reduced. Shaft deflections and, thus, 
the diameter of the shafts can be reduced. The required synchronizer 
capacity and size is the same in all positions and, thus, size is 
minimized. Vehicles containing the transmission can be towed with the 
transmission in neutral without restrictions since lubrication of the 
bearings, journals, and thrust surfaces occurs. 
The multi-speed transmission of this invention is particularly designed for 
rear wheel drive vehicles and includes a driven input shaft. A first 
series of driving speed gears surrounds the input shaft. A number of 
single sized synchronizers are coupled to the input shaft and arranged 
operatively to couple with one of two of the series of driving speed 
gears. A countershaft arranged parallel to the input shaft has a series of 
driven speed gears meshing with different ones of the driving speed gears 
on the input shaft. One of the driven speed gears on the countershaft can 
be engaged with the reverse driving speed gear on the input shaft through 
an idler gear. An output shaft is arranged coaxial with the input shaft 
and is parallel with the countershaft. Means for coupling the countershaft 
to the output shaft include a driving output gear fixed to the 
countershaft in mesh with a driven output gear fixed to the output shaft. 
The driving output gear and driven output gear are referred to as a final 
drive set, hence, the arrangement of the invention is referred to as a 
final drive, multi-speed rear wheel drive transmission. A synchronizer on 
the input shaft can be used to selectively engage a gear on the input 
shaft or the output shaft through the driven output gear to provide one of 
the multiple speed changes. 
With the foregoing arrangement of the invention, all of the driving and 
driven gears are stationary when the vehicle is stationary, the 
transmission is in neutral, the driving source or engine is running, and 
the clutch is engaged. Therefore, neutral roll-over noise is eliminated. 
With the foregoing arrangement of the invention, there is no headset torque 
multiplication, therefore, the face widths of the speed gears can be 
reduced. Likewise, shaft deflections are reduced permitting a reduction in 
shaft diameters. 
With the foregoing arrangement of the invention, the inertia of speed 
gears, countershaft, and output shaft is no longer a factor during 
synchronization, therefore, each of the synchronizers can be of the same 
optimum size. 
Vehicles equipped with the transmission of the foregoing arrangement of the 
invention can be towed without restrictions and/or the risk of serious 
damage to the transmission when the vehicle wheels are in contact with the 
pavement, and the transmission is in neutral and the drivetrain clutch is 
engaged to the stationary driving source or engine. This is possible since 
rotation of the transmission output shaft induces rotation of the 
countershaft through the final drive gear mesh and all of the gears within 
the transmission, which results in oil splash and lubrication to bearings, 
journals, gear meshes and thrust surfaces.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing, and particularly to FIG. 1, a prior art six speed 
headset transmission 10 is shown. Input shaft 12 journalled in bearing 14 
carries a driving gear 16 which is in mesh with driven gear 18 coupled to 
countershaft 20 journalled at its ends in bearings 22 and 24. Countershaft 
20 carries a number of driving gears integrally formed with the shaft or 
coupled to the shaft. These driving gears 26, 28, 30, 32, 34, and 38, are 
respectively, the reverse, first, second, third, fourth, and sixth gears 
of the transmission and are in constant mesh with driven speed gears 40, 
42, 44, 46, 48, and 52 surrounding an output shaft 54 journalled at its 
ends in bearings 56 and 58. Bearing 56 can be a bearing internally 
contained in input shaft 12. Synchronizers 60, 62, 64 and 66 are coupled 
to output shaft 54 for reciprocal axial movement to selectively engage 
adjacent gears on either side by the use of inter-engaging splines and 
known principals of synchronizer design. For example, synchronizer 62 can 
be moved to the right as seen in FIG. 1 to engage first gear 42 with the 
output shaft 54, or it can be moved to the left to engage second gear 44 
with the output shaft 54. 
Likewise synchronizer 66 can be moved to the right as viewed in FIG. 1 to 
engage sixth gear 52 with the output shaft 54, or can be moved to the left 
to engage input shaft 12 directly with the output shaft 54 for a 1:1 
ratio, which in this case serves as the fifth gear. 
It can be seen that all of the gears on both the countershaft 20 and output 
shaft 54 are in continuous movement through the gears 16 and 18, 
therefore, when the transmission is in neutral, the complete gearset is 
rotating. This rotation causes neutral roll-over noise. Since there is an 
engine torque multiplication created by the driving input gear 16 and the 
driven countershaft gear 18, the gears on the output shaft 54 and the 
countershaft 20 must have adequate face width to transfer the engine 
torque from the input shaft 12 to the output shaft 54. For this same 
reason, countershaft 20 and the output shaft 54 must be sized and 
supported to withstand considerable deflection forces. Furthermore, during 
synchronization, each of the gear meshes 40-26, 42-28, 44-30, 46-32, 
48-34, 52-38, and 16-18 create different amounts of reflected inertia, 
requiring that the individual synchronizers 60, 62, 64 and 66 be sized to 
best handle the work required to effect the speed changes through the 
gears on either side of the individual synchronizer. 
Referring now to FIGS. 2 and 3, the transmission 70, according to the 
invention, has an input shaft 71 extending through the wall of a front 
housing 75 terminating within a rear housing 120. A series of driving 
speed gears surround the input shaft 71 and are supported for rotation 
about the input shaft 71 by coaxial needle bearings 83 (FIG. 2). The 
driving speed gears 72, 74, 76, 78, 80 and 82 constitute, respectively, 
the reverse, first, second, third, fourth, and sixth gears of the 
transmission. The driving speed gears are in constant mesh with driven 
gears 87, 88, 90, 92, 94, and 96 mounted on the countershaft 100. A final 
drive pinion gear 98 on the countershaft 100 is in constant mesh with the 
driven output gear 84 on an output shaft 86. 
The input shaft 71 is supported by a conventional bearing 112, such as a 
ball bearing or a tapered roller bearing, in the front housing 75 and by 
bearing 114 on the other end at the output shaft 86. The output shaft 86 
is supported by spaced opposed tapered roller bearings 116 and 118 in the 
rear housing 120. Countershaft 100 is supported at its ends by bearing 122 
and bearing 124. 
Synchronizers 102, 104, 106 and 108 are coupled to the input shaft 71 for 
reciprocal axial movement to selectively engage adjacent gears on either 
side by the use of interengaging splines. For example, the synchronizer 
106 can be moved to the right as viewed in FIG. 2 to engage first gear 74, 
or it can be moved to the left to engage second gear 76. Likewise, 
synchronizer 102 can be moved to the left as viewed in FIG. 2 to engage 
sixth gear 82 or to the right to engage the input shaft 71 directly with 
the output shaft 86 for a 1:1 ratio, which in this case serves as the 
fifth gear. The synchronizers 102, 104, 106 and 108 are actuated through 
the shift mechanism 110, not described in this disclosure. 
As shown in FIG. 4, an idler gear 89, mounted on a shaft 91, is in mesh 
with driving gear 72 and driven gear 87 to provide a reverse gearing when 
the synchronizer 104 is moved for engagement with driving gear 72. As is 
known in the art, the shaft 91 is supported by bearings (not shown) in a 
parallel alignment with the input shaft 71 and countershaft 100. 
With the present invention, all gears are idle when the vehicle is 
stationary, the transmission is in neutral, the engine is running and the 
clutch is engaged, neutral roll-over noise is eliminated. This results in 
a cost savings for clutch disc design since a pre-damper stage is no 
longer required. Also, the elimination of the pre-damper stage reduces 
driveline clunk. 
Since in the power flow sequence, there is no engine torque multiplication 
created by a gear mesh ahead of the gear meshes formed by the speed gears 
on the input shaft 71 and the mating gears on the countershaft 100, the 
face widths of the gears on the input shaft 71 and countershaft 100 can be 
reduced compared to the prior art design, thereby, reducing the overall 
length of the transmission. The only gears that will transmit multiplied 
engine torque are the final drive pinion 98 and gear 84. Thus, these are 
the only gears that will have face widths comparable to the prior art 
design. 
With the lower torque load carried by the speed gears along with adequate 
bearing support provided by bearings 112, 114, 116, 118, 122 and 124, the 
deflections of input shaft 71 and countershaft 100 are reduced allowing 
reduction in shaft diameters. 
It can also be seen with the present invention that the inertias of the 
speed gears and the countershaft are no longer a factor during 
synchronization because these inertias are now directly coupled to the 
driveshaft through the final drive gear mesh and become part of the 
vehicle inertia. Therefore, synchronizers 102, 104, 106 and 108 can be of 
the same optimum size since the work they must perform during the 
synchronization of any speed change involves changing the speed of only 
the input shaft, synchronizer assembly and clutch disc inertias. 
Towing restrictions for the vehicle are no longer required, since the final 
drive gear set is in constant mesh and connected to the drive shaft. This 
enables the countershaft and speed gears to turn when the transmission is 
in neutral, the vehicle rear wheels are in contact with the pavement, and 
the clutch is engaged to the stopped engine. The turning countershaft 
gears provide the oil splash required to lubricate the needle bearings, 
support bearings, journals, gear meshes and thrust surfaces. 
Although a six speed transmission is shown herein, it is clearly within the 
scope of the invention to encompass a seven speed transmission.