Vehicle drive system for road and railroad track

A vehicle for operation on both road and railroad track (off road) is provided with a wheeled chassis comprising a steered front wheel axle and rear wheel differential axle(s), all with road or rubber tire wheels. A front axle and a rear wheel differential axle(s) are provided with rail wheels, the rear rail wheel axle(s) being suspended horizontally behind the rear most tired axle(s) of the wheel chassis. The rail wheel differential axle(s) are horizontally displaceable to be moved into engagement with the railroad track during the lifting of adjacent road or rubber tire wheels out of engagement with the ground. The rear rail wheel differential axle(s) is located behind the rear most wheel axle(s) for road or rubber tire wheels of the vehicle and is being driven by the rubber tire vehicles differential in front of it. The rail differential axle(s) also incorporates a link suspension system including an engagement mechanism permanently secured to the rear part of the vehicle. In conjunction with this rail drive system a holding device including an anti axle dive system is to be installed on the rear road or rubber tire wheel suspension system so that it holds the suspension system and axle(s) at a fixed dimension when the steel wheel differential axle(s) is engaged with the rail and lifts the road or rubber tired axle(s) and suspension system out of engagement with the ground. The above application may be reversed so that the steel rail wheel axle(s) are in front of the road or rubber tire wheel axle(s).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a vehicle for operation on both road and railroad 
track and more particularly to an improvement in propelling such a vehicle 
over railroad track. 
2. Related Art 
Numerous arrangements of vehicles which operate on both road and railroad 
track are know in the art. Common to many of these arrangements is the use 
of a set of front and rear wheel axles, with road or rubber tires, and 
another set of front and rear wheel axles, with rail wheels. In the 
typical arrangement, the front and rear rail wheels are disposed slightly 
behind the respective front and rear road wheels. During road or highway 
operation, the rail wheels are suspended above the ground from the chassis 
of the vehicle. When the rail mode is desired, the rail wheels are lowered 
into engagement with the railroad track, thereby lifting the road wheels 
off of the ground. This allows for a vehicle which can be used on roads 
and highways, while also being convertible for use on railroad track. 
Vehicles of this kind are previously known as described in U.S. Pat. Nos. 
4,048,925; 4,520,735; 3,134,343; and 3,179,066. 
Because the road wheels are out of engagement with the ground or railroad 
track when vehicles of this type are in the rail mode, the rail wheels 
must be powered in order to propel the vehicle along a railroad track. 
U.S. Pat. Nos. 4,048,925 and 4,520,735 both disclose the use of a 
hydraulic motor and drive system, running off the main engine, to drive 
the rail wheels. In these arrangements, when the rail mode is desired, the 
road mode transmission is disengaged and the vehicle engine is directly 
connected to the hydraulic motor which powers the rail wheels. A 
disadvantage of arrangements of this type is that additional costs are 
incurred through the need for a separate hydraulic drive system. 
An alternative solution to the problem of powering the rail wheels is 
disclosed in U.S. Pat. Nos. 3,134,343 and 3,179,066 which teach the use of 
two separate drive shafts extending from the engine of the vehicle, one 
for transmitting power to the road wheels and the other for transmitting 
power to the rail wheels. In these arrangements, driving power is 
distributed alternatively to either the road wheels or rail wheels, 
depending on the desired mode of operation. The disadvantage of this 
arrangement, however, is that when a highway vehicle is desired which 
requires a tandem rear road wheel arrangement (as is often required by law 
when heavy loads are carried), it becomes difficult to extend the rail 
wheel drive shaft past the tandem wheels to connect with the rear rail 
wheel differential. The crowding that occurs at the rear end of the 
vehicle in such a tandem rear wheel arrangement and the need for the rail 
wheels to be able to raise and lower when switching between road and rail 
modes make the use of a lengthy rail wheel shaft difficult if not 
impossible. 
In the present invention, an improved rail wheel drive system is disclosed 
which overcomes the limitations of the above conventional techniques. 
SUMMARY OF THE INVENTION 
According to the invention there is a more efficient way of propelling a 
vehicle for operation on both road and railroad track. The vehicle is 
provided with a wheeled chassis comprising a steered first front wheel 
axle, a first rear wheel differential axle, a second front wheel axle, and 
a second rear wheel differential axle. Road wheels are rotably mounted on 
the steered first front wheel axle and the first rear wheel differential 
axle, and rail wheels are rotably mounted on the second front wheel axle 
and the second rear wheel differential axle. In the road mode, the vehicle 
chassis is supported by the road wheels disposed on the steered first 
front wheel axle and the first rear differential axle, while the rail 
wheels mounted on the second front wheel axle and the second rear wheel 
axle are horizontally suspended from the chassis. In the rail mode, on the 
other hand, the rail wheels are extended so as to engage with the railroad 
track and the road wheels are lifted off of the ground. A drive shaft is 
disposed between the output of the first rear wheel differential and the 
input of the second rear wheel differential and the second rear wheel 
differential axle is driven by the first rear wheel differential axle 
through the drive shaft when the vehicle is being driven on the railroad 
track. 
Alternatively, the vehicle can be provided with a wheeled chassis 
comprising a steered first front wheel axle, a first rear wheel 
differential axle, a second front wheel axle, a second rear wheel 
differential axle, and a third rear wheel differential axle, where the 
third rear wheel differential axle is disposed between the first rear 
wheel differential axle and the second rear wheel differential axle. Road 
wheels are rotably mounted on the steered first front wheel axle, the 
first rear wheel differential axle and the third rear wheel differential 
axle, and rail wheels are rotably mounted on the second front wheel axle 
and the second rear wheel differential axle. In the road mode, the vehicle 
chassis is supported by the road wheels disposed on the steered front 
wheel axle and the first and third rear wheel differential axles, while 
the rail wheels mounted on the second front wheel axle and the second rear 
wheel axle are horizontally suspended from the chassis. In the rail mode, 
on the other hand, the rail wheels are extended so as to engage with the 
railroad track and the road wheels are lifted off of the ground. A drive 
shaft is disposed between the output of the third rear wheel differential 
and the input of the second rear wheel differential and the second rear 
wheel differential axle is driven by the third rear wheel differential 
axle through the drive shaft when the vehicle is being driven on the 
railroad track. A holding means, such as a spring lock-out hook, must be 
employed at the rear of the vehicle to maintain the first and third rear 
wheel differential axles at a predetermined distance from the chassis 
during the rail mode and thereby minimize the angular movement of the 
universal joint at the output of the third rear wheel differential axle. 
Additionally, a anti-dive spring may be incorporated into the spring stack 
of the suspension system for the rear road wheels, in order to keep the 
rear road wheels horizontally level during heavy breaking and acceleration 
of the vehicle in the rail mode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 both show a vehicle according to the present invention. The 
vehicle could be one designed for bridge work, such as one with an open 
work platform for bridge maintenance as shown in FIG. 1 or with an 
enclosed work platform for underbridge inspection as in FIG. 2, but the 
present invention is not limited to bridge work vehicles. More generally, 
this invention is directed to any vehicle for which operation on roads and 
highways as well as on railroad track is desired. A preexisting road 
vehicle can be converted to a vehicle according to the present invention 
rather easily or a vehicle can be designed specifically in accordance with 
this invention. Additionally, while a vehicle with tandem rear road or 
rubber wheel axles is shown in FIGS. 1 and 2 and described below, this 
invention is also directed to vehicles having only one rear road or rubber 
wheel axle. Similarly, while the road or rubber wheel axles 5a, 6a are 
disposed in front of the adjacent steel rail wheel axle 3a on the vehicle 
shown in FIGS. 1 and 2 and described below, the present application may be 
reversed so that the steel rail wheel axle is disposed in front of the 
adjacent road or rubber wheel axles. 
As can be seen in FIG. 1, in the road mode position, vehicle chassis 1 
rests on front road or rubber wheels 4 and rear road or rubber wheels 5,6. 
Front road or rubber wheels 4 are rotably mounted on front road or rubber 
wheel axle 4a and rear road or rubber wheels 5,6 are rotably mounted on 
rear road or rubber wheel axles 5a, 6a, respectively. Front steel rail 
wheels 2 and rear steel rail wheels 3 are suspended above the ground from 
chassis 1 as discussed below. Front steel rail wheels 2 are rotably 
mounted on front steel rail wheel axle 2a and rear steel rail wheels 3 are 
rotably mounted on rear steel rail wheel axle 3a. 
In the rail mode position, on the other hand, as shown in FIG. 2, vehicle 
chassis 1 rests on front steel rail wheels 2 and rear steel rail wheels 3. 
Front road or rubber wheels 4 and rear road or rubber wheels 5,6 are 
lifted off the ground. Anti-dive spring 29 and spring lock-out hook 14 
(FIG. 4) are used to maintain rear road or rubber wheels 5,6 level and at 
predetermined distance 16 from chassis 1, as discussed below. 
Predetermined distance 16 corresponds to the desired vehicle riding 
height, measured from the bottom of the frame of chassis 1 to the center 
of rear road or rubber wheel 5. In the rail mode position, rear steel rail 
wheels 3 are driven through rear steel rail wheel differential 3b, which 
is driven by rear road or rubber wheel differential 6b, through rail wheel 
drive shaft 12, as discussed below, with reference to FIG. 5. 
As shown in FIGS. 1 and 2, front steel rail wheels 2 are rotably mounted to 
front steel rail wheel axle 2a and are disposed at the front of the 
vehicle by a rail wheel conversion means known in the art, such as that 
disclosed in U.S. Pat. No. 4,488,494, incorporated herein in its entirety 
by reference. According to U.S. Pat. No. 4,488,494, support arm 31 is 
fixed at the front of the vehicle from which front steel rail wheels 2 and 
front steel rail wheel axle 2a are pivotally attached. Through the use of 
a drive mechanism, typically a hydraulic cylinder (not shown), front steel 
rail wheels 2 can be rotated from a raised position, FIG. 1, to a position 
of engagement with the railroad track, FIG. 2. 
As shown in FIGS. 3 and 4, rear steel rail wheels 3 are rotably mounted to 
rear steel rail wheel axle 3a and are disposed at the rear of the vehicle 
through the use of trailing arm 7 and links 9,10. To facilitate the 
addition of rear steel rail wheels 3, trailing arm 7, and links 9,10 to 
the rear of the vehicle, deck 30 can be mounted on top of chassis 1 
through the use of a plurality of attach plates, including attach plates 
21, 25, and 27, as shown in FIGS. 3 and 4. On the other hand, deck 30 may 
not be necessary where equipment has already been mounted to the vehicle 
and a similar deck or platform is already in place on top of chassis 1, to 
which mount blocks 20, 22, 24, and 26 can be fixed. 
Trailing arm 7 is pivotally attached at one end, to trailing arm support 23 
at pivot 7a, and at the other end to rear steel rail wheel axle 3a. Link 9 
is pivotally attached at one end to trailing arm 7 and link 10 is 
pivotally attached at one end to mount block 24. The other ends of link 9 
and link 10 are joined at pivot point 11a. Drive mechanism 11, which may 
be a hydraulic cylinder as shown, is pivotally attached at one end to deck 
30, at mount block 26, and is joined at the other end to links 9,10 at 
pivot point 11a. By extending and retracting drive mechanism 11 in a 
conventional fashion and thereby moving links 9, 10, trailing arm 7 is 
raised and lowered so that rear steel rail wheels 3 can be moved up and 
down. 
FIGS. 3 and 4 show a typical vehicle suspension system for rear road or 
rubber wheels 5,6. Additionally, FIGS. 3 and 4 show spring lock-out hook 
14 according to this invention. Spring lock-out hook 14 is pivotally 
attached to deck 30, at mount block 20, and is driven by drive mechanism 
13, which could be a hydraulic cylinder. Drive mechanism 13 is pivotally 
attached at one end to spring lock-out hook 14, at pivot 13a, and at the 
other end to mount block 22. When spring lock-out hook 14 is engaged to 
bolster 15 (FIG. 4) it holds the vehicle ridding height at a predetermined 
distance 16 from chassis 1. As shown in FIG. 5, this sets the location of 
universal joint 32, holding it in a level horizontal position to keep the 
extreme angular velocities of universal joint 32, which drives rear steel 
rail wheel differential 3b through rail wheel drive shaft 12, at a 
minimum, as discussed below. Additionally, by lifting rear road or rubber 
wheels 5,6 off or out of engagement with the ground, the vertical center 
of gravity is lowered, making the vehicle with this type of equipment more 
stable. This is especially important where the vehicle is used in 
conjunction with a crane or man carrying device, such as would be done for 
overhead or under bridge inspection and maintenance, as this type of 
vehicle usually does not have outriggers for additional stability support. 
During rail mode operation, rear steel rail wheels 3 are driven by the 
vehicle engine through rear steel rail wheel differential 3b. As shown in 
FIG. 5, rear steel rail wheel axle 3a and rear steel rail wheel 
differential 3b are powered by rail wheel drive shaft 12, which is 
drivingly connected to rear road or rubber wheel differential 6b, disposed 
directly in front of rear steel rail wheel differential 3b. In turn, rear 
road or rubber wheel differential 6b is powered by drive shaft 19, which 
is drivingly connected to rear road or rubber wheel differential 5b, 
disposed directly in front of rear road or rubber wheel differential 6b. 
Rear road or rubber wheel differential 5b is powered by drive shaft 33, 
which transfers power from the vehicle engine. When spring lock-out hook 
14 is engaged, universal joint 32 at the output of rear road or rubber 
differential 6b is held in a level horizontal position to keep the extreme 
angular velocities of universal joint 32, which drives rear steel rail 
wheel differential 3b through rail wheel drive shaft 12, at a minimum, 
despite the rotation of rail wheel drive shaft 12 along arc 8 during 
conversion between road and rail modes. By minimizing the angular 
velocities of universal joint 32, wear on universal joint 32 is reduced. 
This arrangement allows rear steel rail wheel differential 3b to be driven 
through a simple connection with rear road or rubber wheel differential 6b 
directly in front of it and avoids the need for separate power units or 
lengthy drive shafts. 
Additionally, this arrangement allows for an existing road vehicle to be 
easily converted for road/rail use according to this invention. Such a 
conversion would simply require removing the preexisting rearmost rear 
road or rubber wheel differential and replacing it with rear road or 
rubber wheel differential 6b, identical to rear road or rubber wheel 
differential 5b, which has both an input and an output shaft, and then 
reconnecting the preexisting rearmost rear road or rubber wheel 
differential, this time to the output shaft of rear road or rubber wheel 
differential 6b, so as to act as rear steel rail wheel differential 3b, as 
shown in FIG., 5. 
If any difference exists between the rolling radius of rear road or rubber 
wheels 5,6 when on the road and the rolling radius of rear steel rail 
wheels 3 when on the railroad track, an adjustment to the ratio of rear 
steel rail wheel differential 3b must be made so that the vehicle's 
speedometer will read correctly. One way this could be done would be to 
pick standard commercially available gears for rear steel rail wheel 
differential 3b and machine the diameter of rear steel rail wheels 3 to 
the required size. Proper working of the vehicle's speedometer is 
necessary in order to keep accurate records of the vehicle's mileage for 
warranty and scheduled periodic maintenance purposes. 
Since rear road or rubber wheel differentials 5b, 6b are powered during the 
rail mode, the braking and acceleration of rear steel rail wheels 3 can be 
accomplished through rear road or rubber wheel axles 5a, 6a and rear road 
or rubber wheel differentials 5b, 6b. On the other hand, if required, an 
independent or additional braking system could be employed for braking 
rear steel rail wheels 3. To help maintain rear road or rubber wheels 5,6 
horizontally level in the rail mode during heavy breaking and 
acceleration, an anti-dive spring 29, which may be a leaf spring as shown, 
can be incorporated in the conventional spring stack of the vehicle's 
suspension. During the rail mode, rear road or rubber wheels 5,6 are 
suspended from chassis 1 as discussed above. In this arrangement, as there 
is nothing beneath rear road or rubber wheels 5,6 to restrict their 
movement, rear road or rubber wheels 5,6 are prone to rock forward and 
backward in response to heavy breaking and acceleration. This rocking 
response causes rear road or rubber wheels 5 to dive, to fall below a 
level horizontal alignment when looked at from the side, in response to 
heavy breaking and causes rear road or rubber wheels 6 to dive, to fall 
below a level horizontal alignment when looked at from the side, in 
response to heavy acceleration. Anti-dive spring 29 provides a balancing 
force acting on rear road or rubber wheel axles 5a, 6a to keep rear road 
or rubber wheels 5 from diving in response to the forces acting on the 
vehicle during heavy breaking and to keep rear road or rubber wheels 6 
from diving in response to heavy acceleration. 
In use, the transfer of the vehicle from road to rail will be done at a 
location where the vehicle can be approximately positioned perpendicular 
to the railroad track. A plate or foot (not shown) liftable and lowerable 
approximately beneath the center of gravity of the vehicle will lift the 
vehicle to permit its turning about a vertical axis. The plate or foot 
which is fastened to a large bearing (not shown) may have locating fingers 
or ears which when approximately located across the center of the railroad 
track can locate the vehicle and align it properly with the railroad 
track. Such a plate or foot is known in the art as described in U.S. Pat. 
No. 4,520,735, incorporated herein in its entirety by reference. 
Encroachment with adjacent railroad track is required should there be more 
than one set of tracks at the chosen location of vehicle transfer to rail. 
Traffic control or collision risks are negligible, however, because when 
this type of equipment is required to enter rail track for bridge 
inspection and maintenance or some other maintenance purpose, dates, 
times, location and train scheduling have been acquired and permission has 
been given. 
In order to transfer from road mode to rail mode, the vehicle is positioned 
approximately perpendicularly over the railroad track with front road or 
rubber wheels 4 on one side of the track and rear road or rubber wheels 
5,6 on the other side of the track and the plate or foot positioned across 
the two rails of the track. When first moved into this position, the rear 
end of the vehicle is as shown in FIG. 3, with rear steel rail wheels 3 in 
their raised position. Before lowering the plate or foot and rotating the 
vehicle into alignment with the railroad track, spring lock-out hook 14 
must be extended by way of drive mechanism 13, so as to engage with 
bolster 15. Spring lock-out hook 14 remains locked in engagement with 
bolster 15 during the rail mode, so as to maintain the level horizontal 
arrangement of rear road or rubber wheels 5,6. Additionally, interlock 
device 18, which may be an electric switch as shown, is disposed on spring 
lock-out hook 14 and allows the actuation of drive mechanism 11 only after 
spring lockout hook 14 is engaged with bolster 15. 
After spring lock-out hook 14 is engaged, the plate or foot is lowered into 
engagement with the rails of the railroad track and the vehicle is rotated 
manually or automatically on the plate or foot until the front steel rail 
wheels 2 and rear steel rail wheels 3 are aligned with the track wheels. 
Front steel rail wheels 2 are lowered by way of a drive mechanism (not 
shown) which swings front steel rail wheels 2 from a raised position to a 
lowered position. At the same time, rear steel rail wheels 3 are lowered 
into place by extending drive mechanism 11 to move links 9,10, thereby 
rotating trailing arm 7 around pivot 7a so that pivot point 11a comes in 
contact with over-center stop 28. At this point, the plate or foot is 
raised off of the rails, thereby lowering the front of the vehicle onto 
front steel rail wheels 2 and the rear of the vehicle onto rear steel rail 
wheels 3, so as to engage front steel rail wheels 2 and rear steel rail 
wheels 3 with the railroad track. Since links 9,10 are rotated into a 
position just past vertical, rear steel rail wheels 3 can be maintained in 
the lowered position and support the rear end of the vehicle. When rear 
steel rail wheels 3 are fully engaged with the railroad track, all loads 
supported at the rear of the vehicle are taken through links 9 and 10 and 
not through drive mechanism 11. 
FIG. 4 shows the vehicle after the transfer from road mode to rail mode is 
complete. Front steel rail wheels 2 and rear steel rail wheels 3 are 
lowered into engagement with the railroad track, while front road or 
rubber wheels 4 and rear road or rubber wheels 5,6 are suspended above the 
ground and maintained at a predetermined distance 16 from chassis 1 by 
spring lock-out hook 14. 
When it is desired to transfer the vehicle from rail mode back to road 
mode, the process described above is done in reverse. The foot or plate is 
lowered into engagement with the rails of the railroad track, lifting 
front steel rail wheels 2 and rear steel rail wheels 3 out of engagement 
with the railroad track. Front steel rail wheels 2 are raised by way of a 
drive mechanism (not shown) which swings front steel rail wheels 2 from a 
lowered position to a raised position. At the same time, rear steel rail 
wheels 3 are raised by retracting drive mechanism 11 to move links 9,10, 
thereby rotating trailing arm 7 around pivot 7a so that rear steel rail 
wheels 3 are raised into the road mode position. Then, the vehicle is 
rotated on the plate or foot into a position perpendicularly over the 
railroad track and the foot or plate is raised, thereby lowering front 
road or rubber wheels 4 and rear road or rubber wheels 5,6 into engagement 
with the ground. Finally, spring lock-out hook 14 is disengaged. 
FIG. 3 shows the vehicle after the transfer from rail mode back to road 
mode is complete. Chassis 1 is supported by front road or rubber wheels 4 
and rear road or rubber wheels 5,6, which are engaged with the ground, 
while front steel rail wheels 2 and rear steel rail wheels 3 are suspended 
above the ground and spring lock-out hook 14 is disengaged. 
Alternatively, the raising and lowering front steel rail wheels 2 and rear 
steel rail wheels 3 can be done while the vehicle is not raised off the 
ground by the foot or plate. For example, when converting to rail mode, 
the plate or foot can be used to turn the vehicle into position over the 
railroad tracks and lower the vehicle onto front road or rubber wheels 4 
and rear road or rubber wheels 5,6. Then front steel rail wheels 2 and 
rear steel rail wheels 3 can be lowered into engagement with the railroad 
track, thereby lifting front road or rubber wheels 4 and rear road or 
rubber wheels 5,6 off of the ground. When switching back to road mode, 
front steel rail wheels 2 and rear steel rail wheels 3 can be raised 
first, thereby lowering front road or rubber wheels 4 and rear road or 
rubber wheels 5,6 into engagement with the ground, and then the foot or 
plate can be lowered, in order to turn the vehicle perpendicular to the 
railroad tracks. 
The plate or foot is not necessary, however, as the vehicle could also be 
driven next to the railroad tracks and then positioned so that front steel 
rail wheels 2 and rear steel rail wheels 3 can be lowered into engagement 
with the railroad tracks. Positioning the vehicle in this manner would 
require a repeated process of driving the vehicle forward and backward 
while steering front road or rubber wheels 4, in a similar manner as is 
used when parallel parking the vehicle. 
In all of the above embodiments, it is important to ensure that spring 
lock-out hook 14 is locked in engagement with bolster 15 before rear steel 
rail wheels 3 are lowered, in order to maintain rear road or rubber wheels 
5,6 at predetermined distance 16 from chassis 1 when raised off the ground 
and to reduce wear on universal joint 32. 
While a number of embodiments of the present invention have been described 
above, it should be understood that they have been presented by way of 
example, and not limitation. It will be apparent to persons skilled in the 
relevant art that various changes in form and detail can be made therein 
without departing from the spirit and scope of the invention. Thus the 
present invention should not be limited by any of the above-described 
exemplary embodiments, but should be defined only in accordance with the 
following claims and their equivalents.