Reduced size transmission tunnel in an automobile and a method for the same

This invention relates to rear-wheel driven automobiles having an underhung carriage, an engine located at the front end, and a rear passenger compartment having a floor. In particular, the invention relates to a segmented drive shaft for transmitting rotation from the engine to the rear wheels, which is supported substantially below the floor. In this manner, the floor has a transmission tunnel of reduced size so that the floor is relatively flat. In the preferred embodiment the segmented drive shaft comprises three elements, between an output shaft of the transmission of the engine and a pinion of a rear differential. The first element is inclined downwardly from front to back, the second element is substantially parallel to the floor, and the third element may be inclined upwardly from front to back. The second element of the segmented drive shaft may comprise an outer non-rotating tube and an inner rotating tube, and lubrication fluid may also be provided therebetween.

BACKGROUND OF THE INVENTION 
This invention relates to rear wheel driven passenger automobiles having 
underhung carriages (meaning that the body is constructed with some 
portion of the body within the frame structure), an engine located at the 
front end, and a rear passenger compartment having a floor. In particular, 
this invention relates to such a passenger automobile in which a 
transmission tunnel runs centrally along the floor to accommodate a drive 
shaft. 
In general, most modern front-engine rear-wheel drive automobiles, whether 
they are of unibody or frame construction, are designed to provide a 
maximum of internal space in the riding compartment. In addition, 
automobiles are also generally designed within certain height 
restrictions. To accommodate these competing objectives it is typical to 
have an underhung carriage which has the effect of maximizing the internal 
space in the automobile while maintaining an acceptable overall height. 
The underhung carriage results in the external hardware of the car, such 
as the drive shaft and exhaust pipes, being set into recesses in the body. 
An example of such a recess is the transmission tunnel, which is formed in 
the floor panels of the automobile. The recesses provide structural 
reinforcement, because they act as stiffening corrugations. This is 
especially true of the transmission tunnel. 
In automobiles having underhung carriages, a typical transmission tunnel, 
for accommodating a conventional drive shaft, runs front to back centrally 
and results in a raised hump or bump which runs through the passenger 
space along the floor. The drive shaft connects the output shaft of the 
transmission at the rear of the engine with the pinion of the rear wheel 
differential. The rear wheel differential in turn transmits rotation and 
drive to the rear wheels. A splined slip yoke may be used to accommodate 
changes in the overall length of the drive shaft and is usually located on 
the output shaft of the transmission. 
Typically, conventional drive shafts are one piece for automobiles having 
non-independent rear suspensions. In a one piece drive shaft universal 
joints are required at either end of the shaft, because as the rear 
suspension moves up and down to accommodate irregularities in the riding 
surface, so does the rear differential, and the shaft attached thereto. 
The transmission tunnel provided in the floor of the automobile must be 
large enough to accommodate this deflection of the drive shaft. 
There are a few cars that have two piece drive shafts including extended 
wheel base limousines. Extended wheel base automobiles are made by taking 
a conventional full sized automobile, such as a Lincoln Town car, cutting 
the car in half and welding metal panels into the opening to provide the 
desired amount of increased length. In such applications, it is necessary 
to replace the shorter conventional drive shaft member with a longer two 
piece drive shaft assembly which still requires a transmission tunnel in 
the floor to accommodate it. At either end of the second segment of the 
drive shaft is located a universal joint. 
In a two piece drive shaft, in automobiles having a non-independent rear 
suspension, the universal joints are necessary because the rear 
differential moves up and down with the rear suspension. Therefore, the 
rear end of the second segment of the drive shaft tends to ride up and 
down as the rear wheel suspension accommodates irregularities in the 
riding surface. This deflection of the drive shaft must be accommodated in 
the height of the transmission tunnel. To locate the two piece drive shaft 
in place a support is usually provided on the section of the shaft that 
does not move. 
The transmission tunnel or hump that appears in the floor of the passenger 
compartment reduces the riding comfort of passengers, especially in the 
middle portion of the rear seat. Typically, such passengers are forced to 
rest their legs on the raised portion of the hump causing their knees to 
be uncomfortably high relative their seat. Alternatively, they can rest 
one leg on either side of the hump but this tends to impinge upon the foot 
space occupied by occupants on either side of the seat. In an extended 
wheel base car it is also typical to insert an auxiliary rear seat either 
facing forward or more commonly rearward. Typically full width bench 
seats, rather than bucket seats, are used. Two full width seats have 
seating capacity for six people, quite comfortably. However, the presence 
of the hump means that in practice, only four passengers can be 
accommodated comfortably. 
The problem with the hump in the floor of the rear seat or the transmission 
tunnel is exacerbated in the case of such extended wheel base automobiles. 
With female passengers, in an extended wheel base car having opposed rear 
seats a modesty problem can be created by having the knees higher than the 
seat exposing undergarments. 
Clearly it would be desirable, in conventional automobiles, and 
particularly in extended wheel base automobiles if the hump could be 
eliminated or substantially reduced in size or profile, without creating 
other problems, such as excessive vibration, an unacceptably low ground 
clearance or an unacceptable weakness in the body structure. 
SUMMARY OF THE INVENTION 
In accordance with the broad aspect of the present invention there is 
provided a rear wheel driven passenger automobile having an underhung 
carriage, an engine located at a front end, a rear passenger compartment 
having a floor and a rear passenger seat, the automobile including: 
A segmented drive shaft having at least three elements for transmitting 
rotation from the transmission unit tot he rear wheels and including; 
a first element connected between an output shaft of the transmission unit 
and a second element, the first element being inclined downwardly from 
front to back; 
a second element connected between the first element and a third element 
and being generally parallel to and below the floor; 
a third element connected between the second element and a pinion of a rear 
differential, the third element being located substantially below the rear 
passenger seat; 
a substantially flat floor located in front of the rear passenger seat and 
including a transmission tunnel of reduced size, the transmission tunnel 
having a flat upper surface, sloping side surfaces and flat lower 
surfaces; 
means for supporting the segmented drive shaft in placed below the floor, 
the supporting means comprising at least one hanger member fixed to the 
underside of the automobile, and having bearing means therein; and 
reinforcing means for reinforcing the automobile between the front and rear 
wheels, the reinforcing means comprising two reinforced floor panels being 
secured on either side of said transmission tunnel to said flat lower 
surfaces.

PREFERRED EMBODIMENT OF THE INVENTION 
Referring to FIG. 1, an automobile indicated generally at 10 is shown in 
part section. The automobile 10 has front wheels 12 and rear wheels 14. A 
portion of a engine 16 is shown in ghost outline. Extending rearwardly 
from the engine is an output shaft of the transmission 18. Shown in ghost 
outlines as 20 is a rear differential having a pinion 22. 
Located between the engine 16 and the rear differential 20 is a segmented 
drive shaft indicated generally as 24. The segment drive shaft is made up 
of a first element 26, a second element 28 and a third element 30. Located 
between each paid of elements, between the engine 16 and the first element 
26 and between the third element 30 and the pinion 22 are a number of 
universal joints 32. The second element 28 is supported by means of two 
fixed hanger members which extend traversely across the underside of the 
automobile 10. There is a front hanger member 34 and a rear hanger member 
36 which are described in more detail below. 
Referring to FIG. 2 the second element 28 of the segmented drive shaft 24 
is shown in cross sectional view. Reference will now be made to the 
rotating elements of second element 28. Beginning at the left hand side of 
FIG. 2 is shown a yoke 40 which comprises one half of the universal joint 
32 between the first element 26 and the second element 28 of the segmented 
drive shaft 24. The yoke 40 is integrally formed and has a U-shaped 
portion 41 and a tube 46. The tube 46 has on its internal surface splines 
running longitudinally along the length of the tube 46. The inner surface 
of the tube 46 mates with the outside surface of a spline shaft 48. In 
this manner rotational movement is transmitted between the tube 46 and the 
spline shaft 48. By means of a screw 42, inserted through hole 43 and into 
hole 49, and a bearing plate 44, the spline shaft 48 is prevented from 
falling out of the tube 46. The screw 42 merely retains the spline 48 
within yoke 40 and thus can be small gauge. It has been found that 
providing 31 splines at 60 degrees on the spline shaft 48 yields good 
results. Also, the spline shaft 48 is preferably heat-treated to provide a 
Rockwell hardness of 60. 
The spline shaft 48 has a rearwardly extending securing post 50. The 
securing post 50 snuggly fits within an open end of a rotating inner tube 
52. The rotating inner tube 52 is rigidly fastened to the securing post 
50, again preferably by welding or the like. The joint needs to be 
sufficiently strong to withstand the torque applied to the drive shaft 24 
by the engine 16. It will be appreciated that rotating inner tube 52 is 
preferably hollow, to reduce weight, but may also be made solid. The 
foregoing description completes the description of all of the rotating 
parts in the left hand half of the second element 28 of the segmented 
drive shaft 24 as shown in FIG. 2. 
Now reference will be made to the stationary elements also by referring to 
FIGS. 2 and 3. Beginning at the left hand side, is shown a seal 60 which 
fits snuggly around the tube 46. The seal 60 is attached to a bushing 
housing 62. The bushing housing 62 carries on its inner surface an end 
bushing 64, which may be a tri-metal bushing formed from copper, steel and 
aluminum or the like. At the opposite end of bushing housing 62 from the 
seal 60 is located an outer tube 66. The outer tube may be attached to the 
bushing housing 62 by any conventional means such as welding. A bearing 
surface is provided between the end bushing 64 and the tube 46 and is 
indicated generally at 74. The outer surface of tube 46 would have a 
machined finish for this purpose. The bearing surface of end bushing 64 is 
preferably about two inches long. 
Carried inside the outer tube 66 and secured thereto by a set screw 68 is a 
middle bushing 70. The set screw 68 extends through the side of outer tube 
66 and into the bushing 70. In this manner the bearing surface is located 
between the outer surface of rotating inner tube 52 and the inner surface 
of middle bushing 70. This bearing surface is indicated at 72. The outer 
surface of inner tube 52 may also be provided with a machined finish in 
this area. 
To facilitate the smooth running of bearing surfaces 72 and 74 it is 
preferrable to provide some form of lubrication. Satisfactory results have 
been obtained by half filling the outer tube 66 with 10W-30 engine oil or 
type "F" transmission fluid. The middle bushing 70 is preferably located 
approximately half way along the second element and may be made from a 
material such as nylon. A lubricating groove 76 is preferably provided at 
the lower-most point of bearing surface 72. The middle bushing 70 is 
preferably about three inches long. 
While the foregoing description has concentrated on only one end of the 
second element it will be appreciated from the drawings that the ends of 
the second element are identical to each other, and accordingly the 
description of the second end is not repeated. However, while not 
necessary, as drawn the left hand yoke 40 is 90.degree. out of phase with 
right hand yoke 40, which adds to the balancing and smooth running of the 
drive shaft 24. 
The outer tube 66 may be provided with vents 82 and a filling hole 83 and 
drain holes 84. Both the filling hole 83 and the drain hole 84 would be 
resealable, by means of a screw plug 85 or the like. The vents 82 and 
resealable holes 83, 84 would be desirable where the outer tube 66 was 
half filled with lubricating fluid. However, as will be appreciated the 
vents 82 could be removed and instead conduits, 86, shown in ghost 
outline, could be run from the return of the transmission oil cooler to 
the outer tube 66 and back to the transmission. In this manner the need 
for separate shaft service would be eliminated as it would be done when 
the transmission was being serviced. 
In terms of construction, it has been found that mild steel is an 
appropriate material for the inner tube 52 and the outer tube 66. The 
inner tube may be either hollow, or may be in the form of a solid shaft. 
The dimensions of these components depends upon the length of the second 
element 28, but in general, the following dimensions for the rotating 
inner shaft 52 have been found acceptable. 
______________________________________ 
Length Solid Tubular 
______________________________________ 
30" to 50" 1.250" 1.25" .times. .250" 
50" to 70" 1.375" 1.375" .times. .250" 
70" to 100" 1.500" 1.500" .times. .250" 
100" to 140" 1.625" 1.625" .times. .250" 
______________________________________ 
Referring now to FIG. 4 the hanger member 34 is shown in broken section. 
The hanger member 34 is comprised of a first flat rectangular member 90 
and a second flat triangular member 92. Members 90 and 92 are attached at 
right angles and may be formed from separate components welded together or 
may be integrally formed with a 90.degree. bend therebetween. The hanger 
member 34 is isolated from the bearing housing 62 by a resilient 
insulating material shown as 80. The purpose of resilient material 80 is 
to prevent vibration in the second element of the drive shaft from being 
transmitted through the hanger member 34 to the body of the automobile and 
thereby to the occupants riding therein. 
The triangular member 92 has a circular hole 93 cut out of its middle to 
accommodate the resilient material 80 which in turn supports the bushing 
housing 62. Also, shown in part at the break lines are orifices 95, which 
are made for the exhaust pipes of the automobile. The maximum possible 
ground clearance is obtained by having the exhaust pipes pass through 
member 92, as opposed to passing beneath it. The first member 90 is 
somewhat wider than the second member 92 and extends further on each side. 
As shown in FIG. 4 a bolt 94 and a nut 96 may be used to secure the first 
flat member 90 to an angle 98. The angle 98 in turn is attached to a 
portion of the frame 100 of the automobile. The angle 98 may be welded or 
fastened in any suitable manner to the frame 100. Alternatively, the first 
flat member 90 may be bolted directly onto the underside of the frame by 
drilling and tapping. Also, between the angle 98 and the member 90, may be 
located a resilient element 91, as shown, to reduce the vibration 
transmitted there between. The element 91 may be made from any suitable 
rubber or may be a series of stacked spring washers. 
Turning to FIG. 1, the first element 26 of segmented drive shaft 24 is 
inclined downwardly from front to back. The second element 28 is generally 
parallel to the floor or frame of the automobile. The third element 30 may 
be positioned at any suitable angle either up or down within the limits of 
the U-joint. In some applications it may be advantageous to angle the 
third element identically to the first element, either up or down, to 
reduce vibration. In addition the second element 28 is relatively long 
compared to first element 26 and third element 30. It is desirable that 
the first and second elements are of such a length that the third element 
is as short as possible while maintaining its ability to transmit rotation 
smoothly through the universal joints at either end of element 30. 
It has been found that good results are achieved in an extended wheel base 
Lincoln Town car when the first element 26 of the segmented drive shaft 24 
is approximately 293/4" from centerline to centerline of the U-joints at 
either end. The third element 30 is preferably 173/8", but may be slightly 
longer or shorter as described below. The second element 28, as measured 
from outside shoulder to outside shoulder of the bushing housings 62, can 
be made from 36" to 146" as desired. 
When torque is applied to the segmented drive shaft 24 the forces act to 
lift middle or second segment 28 into horizontal alignment between the 
engine 16 and the differential pinion 22. Hanger members 34 and 36 must be 
sufficiently strong to resist this upward thrust. It has been found that 
by using 0.25" thick mild steel plate good results are achieved. The 
member 92 can have a height of 5" and a base of 57.25", with slightly 
squared shoulders as shown. 
The above described segmented drive shaft 24 allows for a relatively flat 
floor in the rear compartment of an automobile by virtue of a number of 
factors. The first factor is that the drive shaft is of smaller diameter, 
along the second element, than typical drive shafts. The second factor is 
the location of the universal joints between the second and third 
elements. In the location shown, under the rear seat of the rear passenger 
compartment, there is no need to extend the transmission hump into the 
floor of the rear passenger compartment to accommodate deflection of the 
drive shaft as a result of the rear suspension moving up and down. Only 
the third segment 30 is subject to the movement of the rear suspension. 
Thus, a relatively shorter transmission tunnel, for only the third segment 
30, can be installed, which is almost entirely located under the rear 
seat. In this manner the relatively flat floor is provided in the rear 
passenger compartment. However, it must be noted that standard -joints, as 
described herein, have a limited ability to transmit rotation through an 
angle, without developing vibration. In general, the greater the angle, 
the greater the vibration. Thus the third element 30 should not be too 
short. On the other hand, if the third element is made too long, then the 
size of the transmission tunnel in the floor of the rear passenger 
compartment will have to be increased. Therefore, while the size of the 
third element can vary, it has been found that 173/8 is satisfactory. 
In the preferred embodiment, it has been found difficult to eliminate the 
bump entirely from the floor of the rear passenger's compartment, partly 
because of the space required by the U-joints. However, it has been found 
that the transmission tunnel above the second element 28 can be reduced in 
height to two inches or less. With such a small hump in the floor, it is 
possible to pad or build up the other portions of the floor so that the 
bump is rendered virtually undetectable. In this manner, the effective 
seating capacity of the rear of the vehicle is increased by one third. 
With the transmission tunnel of reduced size, the automobile will have lost 
some rigidity and strength that was formerly provided by the tunnel. This 
loss of strength can be made up for by increasing the gauge of the frame 
elements, if there are any, or by increasing the strength of other front 
to back components, such as the floor panels. In the extended wheel base 
Lincoln Town car of the present invention, satisfactory results have been 
obtained by reinforcing the floor panels. 
Referring to FIG. 7, a cross section through a portion of a reinforced 
floor is shown. A reduced height transmission tunnel 140 is shown, which 
has a flat upper surface 142 and inclined side surfaces 143. A section 
through the segmented drive shaft, showing inner tube 52 and outer tube 66 
is also illustrated. Flat lower surfaces 144 are provided, to secure the 
tunnel 140 to the floor 146. The floor 146 is comprised of a number of 
elements, sandwiched together. The elements include upper and lower floor 
panels, 150 and 152 respectively, between which is located an expanded 
high strength plastic layer 154. The lower panel 152 may be provided with 
corrugations 156 to prevent "oil canning" when the floor is stepped on. 
The interior may be finished by means of a carpet 157. Preferably, the 
metal components are welded together, and are also bonded to the plastic 
layer 154. However, other forms of fastening may also be used. As 
illustrated in FIG. 7, the flat lower surface 144 would be welded to the 
underside of lower floor panel 152, and the lower floor panel 152, at the 
other side would be welded to rocker panel 100. 
The expanded plastic layer 154 is in the form of a honey comb, with holes 
formed on opposite faces and having common side walls. The holes are 
generally circular at the open end and triangular at the closed end. This 
expanded plastic layer 154 is extremely light weight for its strength, and 
resists flexural displacement. It has been found that the product with the 
trade name NORCOR supplied by Norfield Corporation, is suitable in this 
regard. 
Referring now to FIGS. 5 and 6 a second embodiment of the present invention 
is shown in sectional outline. In reference to FIGS. 5 and 6 like elements 
to the first embodiment are indicated with the same numerals with the 
addition of a prime. As shown in FIG. 5 a bearing yoke 110 is attached to 
one side of a universal joint 32'. The bearing yoke 110 would slide onto 
the output shaft of the transmission from the engine 16. The segmented 
drive shaft 24' consists of a first element 26' a second element 28' and a 
third element 30'. Between third element 30' and the differential pinion 
22' of rear differential 20' is a second universal joint 32'. Unlike 
second element 28, second element 28' comprises a single rotating hollow 
tube. At either end of the hollow tube 28' are attached stub shafts 112. 
Hanger members 34' and 36' are also somewhat different. A hollow 
rectangular tube 114 forms the basic horizontal member for each of hanger 
members 34' and 36'. A hanger bearing 116 as shown in FIGS. 6 is bent to 
form a guide within which is housed a resilient material 118. The hanger 
bearing may be formed out of 18 gauge steel and can be attached to the 
hollow rectangular member 114 by means of bolts and nuts 124 and 126 
respectively. The resilient material 118 absorbs and prevents vibration 
from being transmitted to the frame 100'. The resilient material 118 in 
turn houses a roller bearing 120 which provides the bearing surface 
between the stub shaft 112 and the resilient material 118. A similar 
bearing arrangement is provided for both ends of the second element 28'. 
In addition, there are provided flingers 122 which are secured to the stub 
shaft. One flinger 122 is provided immediately behind hanger member 34', 
whilst another is provided in front at hanger 36'. Others may be provided 
as deemed appropriate. The flinger 122 rotates and insures that dirt, mud 
and other material is not taken into the roller bearing. Because they will 
be rotating rapidly with the drive shaft any material which comes into 
contact with the flingers 122 will tend to be thrown off. 
To accommodate the change in angle between the first shaft 26' and the 
second shaft 28' a Cardan joint indicated generally at 130 is provided. A 
Cardan joint consists essentially of two U-joints which are stacked onto 
each other. In this fashion the phase velocity problem which typically 
arises from a U-joint when it works through an angle is avoided. 
Essentially, the U-joints are balanced and because they are out of phase 
the speed variance due to the ellipse of the U-joint is cancelled. Thus, 
the same phase velocity that goes into the Cardan joint will come out of 
the Cardan joint. This provides a balanced speed of rotation, which 
facilitates the smooth running of the drive shaft 24. While the reference 
to the Cardan joint has been made only in respect of the second 
embodiment, it will be readily appreciated by those skilled in the art 
that a similar joint may also be usefully employed in the first 
embodiment. In certain applications of the present invention, such a 
Cardan joint has been found to provide satisfactory results. 
In a Lincoln Town car that has had its wheel base extended by 54", 
satisfactory results have been obtained where the distance between the 
center line of front hanger member 34 and rear hanger member 36 is 62". 
The overall length of the segmented drive shaft in this case is 121" plus 
or minus approximately 11/2. The length from the differential pinion 22 of 
rear differential 20 to the center of rear hanger member 36 is 
approximately 241/2". 
In addition, good results have been obtained when the downward angle with 
respect to the horizontal of the first element 26 of segmented drive shaft 
24 is 2.degree. to 7.degree.. The second element 28 is preferably parallel 
to the frame or floor of the automobile. In a rest position, the third 
element 30 preferably forms an angle in a range of 2.degree. upwardly or 
downwardly with respect to the frame or floor. However, the third element 
will achieve angles of up to approximately 17.degree. positive (up) or 
15.degree. negative (down) as the rear suspension travels from full bump 
to full rebound. 
As will be known to those skilled in the art, the movement of the rear 
suspension, from full bump to full rebound is not exactly vertical. To 
minimize the change in length of the drive shaft, it is typical to provide 
that the suspension move arcuately, along a portion of a circle having its 
center of rotation located somewhere forwardly along the drive shaft. 
However, even with such arcuate movement, the length of the drive shaft 24 
can change from full bump through to full rebound. To accommodate such 
length changes, it is known to provide a slip yoke (not shown), in which a 
spline post slides freely within a spline tube. 
As in the conventional drive shaft, in the present invention the slip yoke 
would be located on the output shaft of the transmission. Also, the 
segmented drive shaft 24 is preferably free floating, so that changes in 
its length can be accommodated without introducing axial stresses into the 
drive shaft elements. Consequently, inner tube 52 is permitted a limited 
amount of front to back travel within outer tube 66 in the preferred 
embodiment. This requires that the outer surface of the tube portion 46 of 
the yoke member 40, be machine polished along some of its length. In 
addition, it is beneficial to anchor the outer shaft 66 axially, by means 
of a bolt 67 or the like, attached to the hanger member 90. 
It will be appreciated by those skilled in the art that certain 
modifications can be made to the invention, without departing from the 
spirit thereof. For example, while reference has been made throughout the 
specification to specific dimensions, these are provided by way of example 
only, and are not intended to be limiting. For example, it would be 
possible to install the present invention on makes of automobiles other 
than the Lincoln Town car such as on models made by Chrysler and General 
Motors, and in such case it may be necessary to vary certain of the 
dimensions to ones more suitable to such makes. Also, while the invention 
is particularly suited for extended wheel base automobiles, because of the 
premium placed on the available internal space in such automobiles, the 
invention is equally applicable to regular sized car models.