Vehicle door

A mass transit vehicle having a sliding door, the sliding door being mounted at its lower end, by means of a rider, on a linear bearing rod extending outwardly from a bracket mounted on the lower vehicle frame. At its upper end, the door is guided, through a rider, by a linear bearing rod suspended from a bracket which is mounted to the upper vehicle frame.

TECHNICAL FIELD 
This invention relates to doors, and more particularly this invention 
relates to a sliding door for a mass transit vehicle such as a bus. 
BACKGROUND OF THE INVENTION 
There are presently in use a variety of mass transport vehicles which are 
commonly acknowledged as being energy efficient and relatively inexpensive 
to operate and maintain. These mass transport vehicles can be considered 
to fall within two general categories, namely, trains and buses. Trains 
include long distance passenger trains as well as commuter trains and 
subways. Buses include such vehicles as executive transport vehicles, 
school buses, intra- or inter-city buses, vehicles used at airports or 
train terminals for transporting travelers from one terminal to another or 
for transporting travelers from a remote part of an airport to a passenger 
terminal, vehicles used to transport travelers from an airport or train 
terminal to motels and hotels, vehicles used to transport travelers from a 
city terminal to a remote airport, and vehicles used at airports for 
transporting passengers to auto rental facilities located at a distance 
from the terminal. 
The most obvious common feature of all mass transport vehicles, regardless 
of type or size, is that they include a body enclosing the passenger 
carrying compartment and means for entering and leaving the vehicle, the 
last mentioned means being one or more doorways. The problems encountered 
with the design and operation of the doors in mass transit vehicles are 
common to all types of vehicles, whether trains or buses, whether small or 
large. For ease in the following description, reference will be made to 
buses in particular although it will be immediately recognized by one 
skilled in the art that such reference to buses is illustrative only and 
is equally applicable to any suitable type of mass transit vehicle. 
In designing such buses, consideration must be given to the fact that the 
passengers may be entering and leaving the bus with hand luggage and a 
particularly wide door is necessary. Similarly, the passenger carrying 
hand luggage will be somewhat awkward in entering and leaving the bus and 
safety factors, therefore, must be considered. Most of the buses in common 
use utilize a so-called bi-fold door which is essentially a door having 
two panels which are hingedly joined to each other as well as being 
hingedly mounted on the body of the bus so that when the door is opened, 
it folds back upon itself. Some buses utilize a so-called double bi-fold 
door which is merely two bi-fold doors opening to opposite sides of the 
door opening. 
There are several disadvantages associated with bi-fold doors in buses of 
this type. The main disadvantage is the tendency of the doors to stick due 
to the fact that the bodies of the vehicles have a variety of stresses 
applied to them as they travel on roughly paved surfaces and as the weight 
distribution shifts when passengers enter and leave the vehicle. These 
stresses and the shifting weight cause the body of the vehicle to flex 
and, thereby, cause misalignment of the doors with the tracks and 
associated mechanism. 
DISCLOSURE OF INVENTION 
It is, therefore, the primary object of the present invention to provide a 
door for a passenger carrying vehicle which is free of the aforementioned 
and other such disadvantages. 
It is another object of the present invention to provide a sliding door for 
a passenger carrying vehicle which is simple of construction and reliable 
in use. 
It is a further object of the present invention to provide a sliding door 
for a passenger carrying vehicle which is resistant to binding, sticking, 
or jamming. 
It is yet another object of the present invention to provide a mounting 
system for a sliding door in a passenger carrying vehicle which is 
tolerant of deflections and other stresses caused by over-the-road 
vehicular operations. 
It is still a further object of the present invention to provide a 
passenger carrying vehicle having a sliding door consistent with the 
foregoing objects. 
Consistent with these objects, the present invention, in its most 
significant aspect, comprises a sliding door which is mounted on a lower 
bearing rod which carries most of the weight of the door and an upper 
bearing rod which is primarily a guide. The upper bearing rod is mounted 
on supporting blocks which are suspended from the top frame of the vehicle 
while the lower bearing rod is mounted on supporting blocks extending 
outwardly from a bracket on the lower frame of the vehicle. Furthermore, 
the upper supporting blocks are flexibly mounted to allow for minor rod 
deflections. 
In preferred embodiments, a brake interlock system is used to preclude the 
possibility of the door accidentally opening. Furthermore, the leading 
edge of the door, in a preferred embodiment, is equipped with a sensing 
edge to reverse door travel direction in the event the sensitive edge is 
contacted when the door is closing. At the present time the preferred 
operating mechanism for opening and closing the door is a pneumatic 
system, although any known means for causing selective reciprocal movement 
of the door may be used. 
There are three preferred alternate embodiments for the bearing system used 
to mount the door on the bearing rod. The first is a C-shaped linear 
motion ball bearing bushing which rides on the bearing rod. The second is 
a similar linear motion ball bearing bushing, but of a closed type which 
completely encircles the bearing rod. The third is a series of wheels, 
similar in appearance to pulleys, which are mounted on sealed bearings and 
ride on the bearing rod.

BEST MODE FOR CARRYING OUT THE INVENTION 
As has already been mentioned, the present invention applies to a variety 
of mass transit vehicles such as trains, vehicles commonly called vans, 
and those vehicles commonly called buses which are somewhat larger than 
the vans. In this detailed description of the invention, reference is had, 
for exemplary purposes only and not in a limiting sense, to a particular 
type of bus commonly used at airports which utilizes a basic vehicle known 
as the GMC "Transmode" which is purchased complete with chassis, body, and 
running gear, but in an unfinished form. The interior is then fitted out 
for carrying passengers and door means are installed. This invention can 
be used equally well in vehicles made by other manufacturers. 
Referring first to FIG. 1, there is shown a typical airport bus generally 
designated by the numeral 10 having a front end portion 12 and a rear end 
portion 14. A single sliding door 16 is provided such that it moves 
forwardly when opening. Stair well 18 allows for convenience in entering 
and leaving the bus. 
As will be seen from FIG. 2, door 16 is suspended at the top from upper 
rail 20 and at the bottom from lower rail 22. Movement of the door to its 
forward, open, position and to its rearward, closed, position is through 
linkage means 24 and pneumatic actuating means 26 which will be more fully 
described hereinbelow. 
Turning now to FIG. 3, as has already been described, door 16 is supported 
by, and rides on, upper track 20 and lower track 22. Upper track 20 
comprises linear bearing means 28 mounted on a plurality of suspending 
T-shaped brackets 30 which, in turn, are mounted on upper track support 
32. Upper track support 32 is fixed to the upper portion of the frame of 
the bus 34. The upper portion of door 16 is attached to bracket 38. Fixed 
to bracket 38 are a plurality of ball bushing assemblies 40. It will be 
seen that brackets 30 are mounted in a horizontal plane, that is, the base 
of the brackets 30 is horizontal, while the depending portion to which 
bearing means 28 is attached is vertical. Linear bearing means 28 is an 
elongated polished steel rod which is circular in cross-section. 
The lower end of door 16 is fixed to bracket 44 to which is attached a 
plurality of ball bushing assemblies 46 which ride on linear bearing 48 
which is identical to linear bearing 28. Linear bearing 48 is fixed to 
brackets 50 which, in turn, are fixed to lower support 52. Lower support 
52 is fixed by suitable means such as welding to the lower frame of the 
bus 54. It will be seen that T-shaped lower brackets 50 are mounted with 
their bases in a vertical plane so that the leg of the T-shaped bracket 
extends horizontally outwardly. Door 16 slides in pocket 56 between outer 
wall 58 and inner wall 60 of the bus. 
For a better understanding of the mounting of the door to the bus, 
reference is had to FIGS. 4 and 5 which show the upper mount in greater 
detail, it being appreciated by one skilled in the art that the lower 
mount is similar. Support 32 is fixed to the upper framework of the bus 34 
by any suitable means such as welding. It is preferred that support 32 be 
a single length of any suitable material such as steel. A plurality of 
brackets 30 are fixed to support 32 by means of resilient bushings 62 
having threaded metal inserts 64 into which are screwed bolts 66 thereby 
providing a strong yet resilient, mounting for bracket 30. Linear bearing 
28 is a length of circular rod made of any suitable bearing material such 
as a highly polished steel. A hole 68 is bored and tapped in bearing 28 at 
a location corresponding to each bracket 30. Similarly, a hole 70 is bored 
in each bracket 30 and countersunk. A bolt 72 is then used to attach 
bearing 28 to each support 30. There are preferably from four to six 
brackets 30, depending on the length of bearing 28, with one at each end 
and the others equally spaced along the length of bearing 28, as partially 
shown in FIG. 6. 
Riding on bearing 28 are a plurality of ball bushings 74 which, together 
with bushing mounting blocks 76 make up ball bushing assembly 40. Bushing 
mounting block 76 is fixed to bracket 38 by any suitable means such as 
screws (not shown). Brackets 38 are, in turn, fixed, as by bolts 78, to 
door 16. 
Considering both FIGS. 5 and 6, ball bushing 74 is C-shaped and comprises a 
suitable hard resilient material such as rubber with a plurality of 
channels 80 which have, freely riding therewithin, a plurality of ball 
bearings 82. Bushing 74 is securely held in mounting block 76. It will be 
appreciated that by using a split bushing, the potential problem of the 
ball bushing moving past brackets 30 is solved. 
FIG. 7 shows an alternate embodiment using a pair of sliding doors 84 and 
86 which are shown in the closed position. When opened by means of 
pneumatic cylinders 88 and 90, and pistons 92 and 94, respectively, the 
doors slide in opposite directions into pockets provided therefor. The 
same mounting system is used as in the preferred single door embodiment of 
FIG. 2 wherein the doors ride on upper rail 20 and lower rail 22. 
Returning to FIG. 3, it will be appreciated that, due to the positioning of 
the upper and lower rails 20 and 22, and the way the ball bushing 
assemblies 40 and 46 are suspended therefrom, the door actually primarily 
rides on the lower suspension while the upper suspension primarily serves 
as a guide, which is directly opposite the way prior art sliding door 
mounting arrangements work. 
Turning now to FIG. 8, there is depicted schematically the pneumatic system 
for operating the door of FIG. 2. It is initially pointed out that all the 
components are commercially available and are well-known in the art. 
Accordingly, any detailed description of the individual components is not 
necessary. Free air is compressed in air compressor 96 which is a standard 
12 volt air compressor having a capacity of 28.32 liters (one cubic foot) 
per minute at 6.8 Atm. (100 PSI). After passing through unloader check 
valve 98, the air is stored in air compressor tank 100. Air compressor 
tank 100 is fitted with pressure relief valve 102, pressure gauge 104 and 
automatic drain valve 106. The air is then passed through automatic drain 
filter 108 and automatic drain lubricator 110 to reservoir 112 where it is 
stored at an operating pressure somewhat lower than the pressure in air 
compressor tank 100 after passing through pressure regulator 114. Air 
pressure regulator 114 is set at a pressure corresponding to the desired 
speed of door opening or closing, such setting being apparent to one 
skilled in the art. 
The regulated air for actuating pneumatic cylinder 26 passes through check 
valve 116 and solenoid valve 118. Solenoid valve 118 is a four way-two 
position double solenoid momentary contact maintained position valve which 
operates on a standard 12 volt electrical source. 
If the door is cycled to the "open" position by the sensing edge or the 
"emergency door open" switch, valve 120 directs high pressure air to the 
rod end of cylinder 26 and quick exhaust valve 122 opens to the atmosphere 
to minimize the time required for the door to change direction. Valve 120 
is a three way-two position solenoid maintained contact-spring return 
solenoid valve. 
Emergency door control valve 124 is manually actuated for emergency door 
operation. By exhausting the head end of cylinder 26 to the atmosphere, 
system pressure will open the door if valve 118 is in the "open" position. 
If valve 118 is jammed in the "closed" position, the door may be manually 
pushed open. 
The actual operation of the inventive door system will be better understood 
when consideration is given to the schematic diagram of the electrical 
system depicted in FIG. 9. Power to the electrical system is derived from 
four sources. First, power line 126 is connected to the "accessory" side 
of the vehicle ignition switch and is controlled by fuse 128. Second, 
power line 130 is connected to the switched side of the stop light switch 
and is controlled by fuse 132. If the vehicle stop light switch grounds 
the circuit, an additional relay will be required as will be apparent to 
one skilled in the art. Power line 134 is connected to the battery side of 
the vehicle starter solenoid as is power line 136. Power lines 134 and 136 
are controlled by fuse 138 and circuit breaker 140, respectively. 
In operation, the operator of the vehicle first closes switch 142 to start 
compressor 96. Pilot light 144 indicates that switch 142 is on. Next, door 
master switch 146 is switched on and pilot light 148 lights to indicate 
this. It should be noted that when switch 142 is on, power is provided to 
air compressor solenoid 150 through air pressure control 152. If air 
pressure in the main tank 100 drops below 4.08 Atm. (60 PSI), low pressure 
switch 154 located on tank 100 closes and causes pilot light 156 to light 
thereby warning the operator. Pilot light 158 cycles on and off to 
indicate when the compressor is running. 
In order to open the door, the driver must have the brake pedal depressed 
since the stop lights must be on to energize the door open switch 160 
which is a single pole single throw momentary contact push switch. When 
door open switch 160 is pushed, pilot light 162 which is integral with 
switch 160 momentarily lights. Momentary power through switch 160 to the 
coil of valve 118 maintains the valve in the open position. 
The close cycle is similar to the open cycle. Power for the door switch 160 
comes from the stop light switch. On the other hand, power for the door 
close switch 164 comes from the ignition switch whenever the vehicle key 
switch is in the "ignition" or "accessory" position. Door close switch 164 
is also a single pole, single throw momentary contact push switch. When 
door close switch 164 is pushed, pilot light 166 which is integral 
therewith momentarily lights. In a manner similar to the open cycle, 
momentary power through switch 164 to the coil of valve 118 maintains the 
valve in the close position. When the door opens, it trips limit switch 
168 which causes the inside ceiling lights and the door step lights to go 
on, through relay 170, and also activates sensitive edge 172. Under 
ordinary conditions, when the door is closing, limit switch 174 disables 
sensitive edge 172 when the door is approximately 1.27 cm. (1/2 inch) from 
fully closed to allow full door closing. Limit switch 174 is a single 
pole, single throw normally closed switch. It should also be noted that 
when limit switch 168 is tripped, door open pilot light 176 goes on. 
If there is an obstruction in the doorway as the door closes, sensitive 
edge 172 will contact it and reverse the door direction, powering the door 
to the full open position. This is done through relay 178 which disrupts 
the close door circuit when the sensitive edge 172 is activitated and does 
not allow the close door cycle to activate until the door is fully open. 
When activated by sensitive edge 172, relay 178 accomplishes four 
functions. First, pole A acts as a holding circuit to maintain relay coil 
energy until the door is fully opened. Second, pole B directs power to the 
high-pressure door open valve 120 and sounds buzzer 180 to alert the 
vehicle operator. Third, pole C switches door control valve 118 from the 
close position to the open position. Finally, pole D disables the door 
close button 164. 
Emergency door open switch 182 located near the door is powered from the 
vehicle battery. Actuation of this switch cycles valve 118 and applies 
high-pressure air to the open end of cylinder 26. External door control 
switch 184 allows operation of the door from outside the bus. This switch 
is powered directly by the battery as is relay 170. 
The embodiment shown in FIGS. 3-6 provides a reliable, smoothly working, 
door opening and closing mechanism. Ball bushing assemblies 40 and 46 move 
smoothly along linear bearing means 28 and 48, respectively. Due to the 
fact that the lower suspension system bears most of the weight of the 
door, approximately eighty percent, and the upper suspension system acts 
primarily as a guide, bearing only about twenty percent of the weight of 
the door, and that twenty percent load actually being an outwardly 
directed torque rather than a downward moment of force, the system of the 
invention is able to withstand the rough treatment which these vehicles 
are ordinarily given. It should also be noted that the vehicle frame, both 
top and bottom portions, is additionally braced to withstand a variety of 
stresses encountered in driving along an often uneven roadway, and to 
maintain the vehicle perfectly square. Thus, linear bearing means 28 and 
48 are maintained perfectly parallel to each other. 
But, due to the nature of the C-shaped, or split, ball bushing 40 and 46, 
in some climates which are particularly dusty or humid, dust or moisture 
can enter the bushing 74 and cause wear of the ball bearings 82. 
Accordingly, in a second embodiment which is depicted in FIGS. 10 and 11, 
a ball bushing assembly 188 is used which completely encircles, or 
encapsulates, linear bearing 28. Similarly, a lower ball bushing assembly 
194 is used to completely surround, or encapsulate, lower linear bearing 
48. Ball bushing assembly 188 comprises a hard rubber ball bushing 190 in 
which ball bearings 82 ride. This ball bearing-bushing assembly is held 
securely in mounting block 196. The obvious difference between this ball 
bushing assembly 188 and the ball bushing assembly 40 of the first 
embodiment is that ball bushing assembly 188 completely surrounds linear 
bearing 28. 
Obviously, with ball bushing assembly 188 completely surrounding linear 
bearing 28, linear bearing 28 cannot be suspended from upper track support 
32 by as many supporting brackets 30 since they would interfere with the 
motion of ball bushings 188 along linear bearing 28. It has been found 
that linear bearing 28 can be suspended at its ends only by brackets 30 
with such suspending brackets 30 being made somewhat larger than those 
which would be used in connection with the first embodiment using the 
C-shaped ball bushing assembly. This is shown in phantom at 192 in FIG. 6. 
Then, whereas in the first embodiment using the C-shaped ball bushing 
assembly 40, at least two ball bushing assemblies 40 are used, one at the 
forward edge of the door and one at the rearward edge, with others 
optionally used at other locations along the top of the door, in this 
second embodiment using ball bushing 188 which completely surrounds linear 
bearing 28, only one or two ball bushing assemblies 188 are used. If one 
is used, it is located at the center of the top edge of the door and is 
made wider than would be necessary when more than one ball bushing is 
used. If two ball bushings 188 are used, they are equally spaced to either 
side of the longitudinal axis of the door, perhaps about twelve to fifteen 
centimeters (about 5-6 inches) on either side of said longitudinal axis. 
While the foregoing description of the ball bushing and suspension system 
used in this second embodiment has been by reference to the upper 
suspension system, it should be distinctly understood that the same 
comments apply equally to the lower suspension system. Again, as with the 
first embodiment, it is the lower suspension system that bears most of the 
weight of the door and the upper suspension system that acts primarily as 
a guide. As with the upper suspension system, the lower suspension system 
would have a single mount 50 at each end of rod 48 and either a pair of 
ball bushing assemblies 194 spaced apart equidistant on either side of the 
longitudinal axis of the door, or a single double-or triple-width ball 
bushing assembly 194 centered on the longitudinal axis of the door 
assuming the door is relatively uniform in weight distribution. If it is 
necessary, to maintain the balance of the door, ball bushing assembly 194 
could be shifted to one side or the other, or weights placed in 
appropriate places in the door to equalize the balance about the 
longitudinal axis. Of course, this would be apparent to, and easily 
accomplished by, one skilled in the art. 
Turning now to FIGS. 12-15, there is shown a third preferred embodiment of 
the suspension system using a system of wheels instead of the ball 
bushings. In this embodiment, the same linear bearing rod 28 mounted on 
suspending T-shaped brackets 30 is used. But, instead of ball bushing 
assembly 40 or 188, a wheel assembly 198 is used to mount the door to the 
bearing rod 28. Wheel assembly 198 comprises bracket 206 which is affixed 
to the top of door 16 and a pair of wheels 202 and 204 which ride on a 
sealed ball bearing hub mounted to bracket 206. As illustrated in FIG. 13, 
the wheels have an arcuate bearing surface 207 which fit around linear 
bearing rod 28. As will be appreciated, linear bearing rod 28 is circular 
in cross-section and arcuate bearing surface 207 is of a size and shape to 
mate with the outer circular surface of rod 28 without any interference 
from mounting bracket 30. 
While, as with the previous embodiments, the lower suspension system is 
essentially the same as the upper suspension system, there is a single 
difference. Specifically, this difference is the use of three bearing 
wheels 208, 210 and 212 as shown in FIG. 15. Since it is the lower 
suspension that bears most of the weight, the use of two upper wheels 208 
and 212 provides for better weight distribution of the door and, 
therefore, smoother and more efficient movement. Lower wheel 210 acts to 
keep the wheels from slipping off rod 48, acts as a guide, and also 
provides smoother operation. It will be seen, by reference to wheel 208, 
for example, that it is mounted on hub 214 which comprises a sealed ball 
bearing system which is commercially available. As with previous 
embodiments, T-shaped mounting bracket 50 is fixed to Z-shaped bracket 52 
which is, in turn, fixed to the lower frame 54 of the vehicle, and under 
the interior floor 209. Wheels 208, 210 and 212 are mounted on a T-shaped 
bracket 44 as in the previous embodiments. 
While the wheels 202, 204, 208, 210 and 212, have been described in this 
preferred embodiment as having arcuate bearing surface 207 to mate with 
linear bearing rod 28, one skilled in the art will appreciate that these 
wheels could be V-shaped, like typical pulley wheels, and would then mate 
with a linear bearing rod whose cross-section would be rhombic in shape. 
This is shown in FIGS. 16 and 17 where upper wheels 203 and 205 of 
assembly 199 are V-shaped and linear bearing rod 215 is rhombic, and 
wheels 209 and 211 of assembly 201 are V-shaped and linear bearing rod 217 
is rhombic. The arcuate bearing surface to mate with a circular rod is 
preferred since the circular rod is used in the other embodiments and the 
wheel mounting arrangement 198 and 200 could merely replace the other ball 
bushing mounting arrangements without any modification of the remaining 
suspension system. 
It should be apparent from the foregoing detailed description that the 
objects set forth hereinabove have been successfully achieved. Moreover, 
while there is shown and described a present preferred embodiment of the 
invention, it is to be distinctly understood that the invention is not 
limited thereto but may be otherwise variously embodied and practiced 
within the scope of the following claims. Accordingly,