Title: Fire-fighting vehicle
Abstract: An airport rescue fire-fighting vehicle comprising a support structure coupled to at least two wheel sets. The support structure has a front end and a back end with one wheel set coupled to the front end of the support structure and one wheel set coupled to the back end of the support structure. A power source is mounted on the support structure and coupled to at least one wheel set. Each wheel of the vehicle is coupled to a modular independent suspension. A mechanical steering apparatus is coupled to the front wheel set and at least one rear wheel set.
Patent Number: 6,883,815 Issued on 04/26/2005 to Archer
| Inventors:
|
Archer; David W. (Hortonville, WI)
|
| Assignee:
|
Oshkosh Truck Corporation (Oshkosh, WI)
|
| Appl. No.:
|
171076 |
| Filed:
|
June 13, 2002 |
| Current U.S. Class: |
280/91.1; 180/24.01 |
| Intern'l Class: |
B60D 007//04 |
| Field of Search: |
280/911,99,103
180/240.1,408-410,412,414
|
References Cited [Referenced By]
U.S. Patent Documents
| 4185712 | Jan., 1980 | Bulger.
| |
| 4582334 | Apr., 1986 | Tashiro et al.
| |
| 4592561 | Jun., 1986 | Furukawa et al.
| |
| 4669744 | Jun., 1987 | Sano et al.
| |
| 4926954 | May., 1990 | Ataka et al.
| |
| 4968080 | Nov., 1990 | Kerry.
| |
| 5010971 | Apr., 1991 | Hamada et al.
| |
| 5076597 | Dec., 1991 | Korekane et al.
| |
| 5111901 | May., 1992 | Bachhuber et al.
| |
| 5137292 | Aug., 1992 | Eisen.
| |
| 5217083 | Jun., 1993 | Bachhuber et al.
| |
| 5225983 | Jul., 1993 | Ohmura et al.
| |
| 5307891 | May., 1994 | Shaw et al.
| |
| 5390945 | Feb., 1995 | Orr.
| |
| 5417299 | May., 1995 | Pillar et al.
| |
| 5501288 | Mar., 1996 | Ducote.
| |
| 5533584 | Jul., 1996 | Johnson.
| |
| 5538274 | Jul., 1996 | Schmitz et al.
| |
| 5607028 | Mar., 1997 | Braun et al.
| |
| 5820150 | Oct., 1998 | Archer et al.
| |
| 6086074 | Jul., 2000 | Braun.
| |
| 6615944 | Sep., 2003 | Horwath et al.
| |
Other References
U.S. Department of Transportation, Federal Aviation Administration, Guide Specification
for Water/Foam Aircraft Rescue and Fire Fighting Vehicles, Feb. 18, 2002.
|
Primary Examiner: Culbreth; Eric
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
1. An airport rescue fire fighting vehicle comprising;
a support structure coupled to at least three wheel sets, and having a front
end and a back end, wherein one of the wheel sets is coupled to the front end of
the support structure and one wheel set is coupled to the back end of the support
structure;
a power source mounted on the support structure and coupled to at least one wheel
set;
a modular independent suspension coupled to each wheel; and
a mechanical steering apparatus coupled to the front wheel set and at least one
rear wheel set, with the mechanical steering apparatus configured to proportionately
move the rear wheel set in linked relationship to the movement of the front wheel
set to minimize tire scrub on the rear wheel set, wherein the mechanical steering
apparatus includes:
a steering wheel;
a first parallel shaft gear box coupled to the steering wheel, a front master/slave
steering gear set and an elongated rotary shaft; and
a second parallel shaft gear box coupled to the elongated rotary shaft and coupled
to a back master/slave steering gear set,
wherein the front master/slave steering gear set is coupled to the front wheel
set and the back master/slave steering gear set is coupled to the rear wheel set
so that when the front wheel set is turned in one direction the rear wheel set
will turn in a proportional opposite direction in response to the steering wheel
movement.
2. The airport rescue fire fighting vehicle of claim 1, including a cab and a
vehicle body mounted on the support structure.
3. The airport rescue fire fighting vehicle of claim 2, wherein the cab is mounted
at the front end of the support structure and the power source is mounted at the
back end of the support structure.
4. The airport rescue fire fighting vehicle of claim 2, wherein the overall width
of the cab and vehicle body does not exceed 120 inches.
5. The airport rescue fire fighting vehicle of claim 4, wherein the vehicle has
a tilt-table capability of more than 30° with fully fire fighting fluid tanks.
6. The airport rescue fire fighting vehicle of claim 1, wherein each master/slave
steering gear set includes a tie rod.
7. The airport rescue fire fighting vehicle of claim 1, wherein the elongated
rotary shaft is segmented.
8. The airport rescue fire-fighting vehicle of claim 1, including an intermediate
wheel set coupled to the support structure.
9. A mechanical steering apparatus for an airport rescue fire fighting vehicle
having a front wheel set, and at least two wheel sets and a modular independent
suspension coupled to each wheel of each wheel set, the mechanical steering apparatus comprising:
a steering wheel mounted on the vehicle;
a first parallel shaft gear box coupled to the steering wheel, a front master/slave
steering gear set and an elongated rotary shaft; and
a second parallel shaft gear box coupled to the elongated rotary shaft and coupled
to a back master/slave steering gear set,
wherein the front master/slave steering gear set is coupled to the front wheel
set and the back master/slave steering gear set is coupled to one of the rear wheel
sets so that when the front wheel set is turned in one direction the rear wheel
set will turn in a proportional opposite direction in response to the steering
wheel movement, and minimize tire scrub on the rear wheel set.
10. The mechanical steering apparatus of claim 9, wherein each master/slave steering
gear set includes a tie rod.
11. The mechanical steering apparatus of claim 9, wherein the elongated rotary
shaft is segmented.
12. The mechanical steering apparatus of claim 9, including an intermediate wheel set.
13. A fire fighting vehicle comprising:
a means for supporting coupled to at least three wheel sets, and having a front
end and a back end, wherein one wheel set is coupled to the front end of the means
for supporting and one wheel set is coupled to the back end of the means for supporting;
a means for powering mounted on the means for supporting and coupled to at least
one wheel set;
a modular independent suspension coupled to each wheel; and
a means for mechanically steering coupled to the front wheel set and at least
one rear wheel set, with the means for mechanically steering configured to minimize
tire scrub on the rear wheel set, wherein the means for mechanically steering includes:
a means for steering;
a first means for transferring torque coupled to the means for steering, a front
means for wheel steering and an elongated rotary shaft; and
a second means for transferring torque coupled to the elongated rotary shaft
and coupled to a back means for wheel steering,
wherein the front means for wheel steering is coupled to the front wheel set
and the back means for wheel steering is coupled to the rear wheel set so that
when the front wheel set is turned in one direction the rear wheel set will turn
in a proportional opposite direction in response to the means for steering movement.
14. The fire fighting vehicle of claim 13, including a cab and a means for shrouding
mounted on the means for supporting.
15. The fire fighting vehicle of claim 14, wherein the cab is mounted at the
front end of the means for supporting and the means for powering is mounted at
the back end of the means for supporting.
16. The fire fighting vehicle of claim 14, wherein the overall width of the cab
and means for supporting does not exceed 120 inches.
17. The fire fighting vehicle of claim 16, wherein the vehicle has a tilt-table
capability of more than 30° with fully loaded fire fighting fluid tanks.
18. Fire fighting vehicle of claim 13, wherein each means for wheel steering
includes a means for connecting.
19. The fire fighting vehicle of claim 13, wherein the elongated rotary shaft
is segmented.
20. The fire-fighting vehicle of claim 13, including an intermediate wheel set
coupled to the means for supporting.
21. The fire fighting vehicle of claim 13, wherein the vehicle is configured
as an airport rescue crash truck.
Description
BACKGROUND OF THE INVENTION
This invention relates to vehicles in general and particularly to fire-fighting
type work vehicles and specifically to an airport rescue fire-fighting vehicle.
Prior art vehicles, specifically fire-fighting type of vehicles have a variety
of equipment and apparatus utilized during fire-fighting and rescue operations.
Typical fire-fighting vehicles provide for only front wheel steer capability. Specialized
vehicles such as extension ladder fire trucks may provide for rear wheel steer;
however, those typically require an operator sitting in a rear cabin to turn the
rear wheel set in an independent linkage from the front wheel steering apparatus.
Other steering configurations include all wheel steer systems such as disclosed
in U.S. Pat. No. 5,607,028 assigned to the present assignee. Such all wheel steering
system utilizes a programmable controller and typically is utilized on heavy-duty
vehicles such as equipment haulers and construction equipment. One problem experienced
by vehicles not being capable of rear steering is excessive tire wear on the rear
set of wheels. There is a need for an apparatus that will minimize or eliminate
excessive tire wear on the rear or back wheel set for fire-fighting vehicle.
Fire-fighting vehicles, and particularly airport rescue fire-fighting
vehicles have to comply with several standards with respect to stability. The Federal
Aviation Administration (FAA) and the National Fire Protection Agency (NFPA) have
published certain documents which set out standards and requirements that must
be met by all airport rescue fire-fighting vehicles. One such requirement is that
a tilt-table capability for fire-fighting vehicles be at least 30°. The agencies
also adopted requirements that the fire-fighting vehicles meet the NATO lane change
test and a dynamic turning circle test at 28 m.p.h. Compliance with such standards
and meeting such tests would, as determined by the FAA and NFPA provide a stable
platform for the fire-fighting vehicle. Thus, there is a need for a fire-fighting
vehicle, and particularly an airport rescue fire-fighting vehicle to comply with
the requirements as established by the FAA and NFPA.
SUMMARY OF THE INVENTION
There is provided an airport rescue fire-fighting vehicle comprising a support
structure coupled to at least three wheel sets. The support structure has a front
end and a back end with one wheel set coupled to the front end of the support structure
and one wheel set coupled to the back end of the support structure. A power source
is mounted on the support structure and coupled to at least one wheel set. Each
wheel of the vehicle is coupled to a modular independent suspension. A mechanical
steering apparatus is coupled to the front wheel set and at least one rear wheel
set, with the mechanical steering apparatus configured to minimize tire scrub on
the rear wheel seat. Another embodiment of the airport rescue fire-fighting vehicle
includes a steering wheel coupled to a first parallel shaft gear box. A front master/slave
steering gear set and an elongated rotary shaft is also coupled to the first parallel
shaft gear box. A second parallel shaft gear box is coupled to the elongated rotary
shaft and is coupled to a back master/slave steering gear set. The front master/slave
steering gear set is coupled to the front wheel set and the back master/slave steering
gear set is coupled to the rear wheel set so that when the front wheel set is turned
in one direction the rear wheel set will turn in a proportional opposite direction
in response to the steering wheel movement.
There is also provided a mechanical steering apparatus for an airport rescue
fire-fighting vehicle. The airport rescue fire-fighting vehicle has a front wheel
set, and at least two wheel sets. A modular independent suspension is coupled to
each wheel of each wheel set. The mechanical steering apparatus comprises a steering
wheel mounted on the vehicle. A first parallel shaft gear box is coupled to the
steering wheel, a front master/slave steering gear set and an elongated rotary
shaft. A second parallel shaft gear box is coupled to the elongated rotary shaft
and is coupled to a back master/slave steering gear set. The front master/slave
steering gear set is coupled to the front wheel set and the back master/slave steering
gear set is coupled to one of the rear wheel sets so that when the front wheel
set is turned in one direction, the rear wheel set will turn in a proportional
opposite direction in response to the steering wheel movement and minimize tire
scub on the rear wheel set. In another embodiment, the elongated rotary shaft can
be segmented.
There is further provided a fire-fighting vehicle comprising a means for supporting
coupled to at least three wheel sets. The means for supporting has a front end
and a back end wherein one wheel set is coupled to the front end of the means for
supporting and one wheel set is coupled to the back end of the means for supporting.
A means for powering is mounted on the means for supporting and is coupled to at
least one wheel set. A modular independent suspension is coupled to each wheel.
A means for mechanically steering is coupled to the front wheel set and at least
one rear wheel set, with the means for mechanically steering configured to minimize
tire scrub on the rear wheel set. Another embodiment includes a means for steering,
a first means for transferring torque coupled to the means for steering, a front
means for wheel steering and an elongated rotary shaft. A second means for transferring
torque is coupled to the elongated rotary shaft and is coupled to a back means
for wheel steering. The front means for wheel steering is coupled to the front
wheel set and the back means for wheel steering is coupled to the rear wheel set
so that when the front wheel set is turned in one direction, the rear wheel set
will turn in a proportional opposite direction in response to movement of the means
for steering.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan side view of an embodiment of an airport rescue fire-fighting
vehicle having a mechanical steering mechanism.
FIG. 2 is a front view of the airport rescue fire-fighting vehicle illustrated
in FIG. 1, illustrating the center of gravity when the vehicle is empty of fire-fighting
fluids and when the vehicle has a full load of fire-fighting fluids.
FIG. 3 is a schematic illustration of a prior art fire-fighting vehicle having
a maximum 28° tilt-bed capability.
FIG. 4 is a schematic illustration of the airport rescue fire-fighting vehicle
illustrated in FIGS. 1 and 2 having at least a 30° tilt-bed capability.
FIG. 5 is a top perspective view of an embodiment of a mechanical steering apparatus
coupling a back wheel set to a front wheel set and a steering wheel of an airport
rescue fire-fighting vehicle, with the back wheel set aligned with the front wheel
set for straight travel.
FIG. 6 is a partial top perspective view of an embodiment of the mechanical
steering apparatus for an airport rescue fire-fighting vehicle mounted on a support
structure of the vehicle, with the front wheel set in a full right turn and the
back wheel set in a proportional opposite direction turn in response to the steering
wheel movement.
FIG. 7A is a schematic view of the prior art fire-fighting vehicle not having
steerable rear wheels making a right turn.
FIG. 7B is a schematic view of an embodiment of a fire-fighting vehicle having
a mechanical steering apparatus with a steerable back wheel set making a right
turn with a shorter radius than the vehicle illustrated in FIG. 7A.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
Before discussing an exemplary embodiment of a fire-fighting vehicle
10,
there are a few preliminary comments. When referring to a work vehicle
10,
it is contemplated that a vehicle
10 can be of several different uses and
it is referred to as a work vehicle, a fire-fighting vehicle
10, a crash
truck
10, a multi-wheel vehicle
10 and the like. It is also contemplated
that articulated tracks mounted on the wheels can be used as support for the support
structure
12 of the vehicle
10. The vehicle
10 also typically
has an area designated as a vehicle body
22, a cab
15, a vehicle
side
22a (typically two sides) and a rear
22b. It is
contemplated that any convenient and conventional materials can be utilized for
such vehicle portions commensurate with the type duty that will be experienced
by the vehicle. For example, the body can be made out of steel, aluminum, or a
composite material. The wheels
19 can be cast or machined. The wheel arrangements
can be four-wheel, six-wheel (two tandem wheel sets at the rear of the vehicle
as illustrated in FIG. 1) and eight-wheel vehicle.
A fluid source can be mounted directly on the fire-fighting vehicle
10,
can be towed on a separate trailer structure or can be a fixed fluid source such
as lake, river or tank. For example if the fire-fighting vehicle
10 is configured
as a airport rescue fire-fighting vehicle, the fluid source is typically mounted
on the vehicle
10, or the vehicle
10 can be brought to an independent
fluid source which then utilizes the vehicle for pumping purposes.
As discussed above, the work vehicle
10 can be a fire truck or crash truck.
For this application, fire truck means a municipal fire truck equipped to fight
structural building fires and typically is not considered an off-road vehicle.
For this application, a crash truck means an airport rescue fire-fighting vehicle
equipped to fight aircraft fires and fuel fires. The crash truck is configured
for off-road use. A typical application for a fire-fighting or crash truck utilized
at an airport is for it to be called upon in the event of an airplane crash at
or near the airport.
Referring now to the Figures, FIG. 1 illustrates an airport rescue fire-fighting
type vehicle. The vehicle is configured with at least two tandem wheel sets
18,
which includes a front wheel set
20, and a rear or back wheel set
24.
The vehicle can also have an intermediate wheel set
23 as shown in FIG.
1. The vehicle includes a support structure
12 having a front end
13 and a back end
14 (see FIGS.
1 and
6). One of the
wheel sets
18 is coupled to the front end
13 of the support structure
12 and at least one wheel set
18 is coupled to the back end
14
of the support structure
12. A power source
16 is mounted on the
support structure
12 and is coupled to at least one of the wheel sets
18.
It should be noted that the power source
16 can be a hybrid-electric system
an internal combustion engine, such as a gasoline or a diesel engine or a turbine
engine or the like. It should also be understood that the power source
16
can be coupled to more than one wheel set
18 and can include an all-wheel
drive vehicle.
Each wheel
19 is coupled to a modular independent suspension
26.
(See FIGS.
2 and
4). The modular independent suspension
26
includes a coil spring suspension for steerable and non-steerable wheel assemblies
and drive and non-drive axles. The modular independent suspension
26 is
coupled to the support structure
12 and to each wheel assembly of the fire-fighting
vehicle
10. An example of such modular independent suspension
26
is more fully described in U.S. Pat. Nos. 5,538,274 and 5,820,150 commonly assigned
to the assignee of the present application. Such disclosures are incorporated herein
by this reference.
The airport rescue fire-fighting vehicle
10 also includes a mechanical
steering apparatus
30 coupled to the front wheel set
20 and at least
one of the rear wheel sets
24, typically the rear-most wheel set
18.
(See FIGS. 5 and 6)
The mechanical steering apparatus
30 includes a steering wheel
32
and a first parallel shaft gear box
34 coupled to the steering wheel, a
front master/slave steering gear set and an elongated rotary shaft
40. A
second parallel shaft gear box
44 is coupled to the elongated rotary shaft
40 and is coupled to a back master/slave steering gear set
46. The
front master/slave steering gear set is
36 is coupled to the front wheel
set
20 and the back master/slave steering gear set
46 is coupled
to the rear wheel set
24 so that when the front wheel set
20 is turned
in one direction the rear wheel set
24 will turn in a proportional opposite
direction in response to the steering wheel
32 movement. (See FIGS. 5 and 6.)
Each master/slave steering gear set
36,
46 consists of a master
steering gear and a slave steering gear which are coupled together by a tie rod
38 and mounted to the support structure
12 by any convenient and
conventional manner such as bolting or welding. Each steering gear is coupled to
a steerable wheel utilizing a toe control linkage in any convenient manner. Likewise,
the rear master gear and slave gear set are coupled together by a tie rod
38
and mounted on the support structure
12 in any convenient manner, such as
bolting or welding. Each gear set is coupled to a steerable wheel by a toe control
arm in any convenient manner.
The front master/slave steering gear set
36 and the back master/slave
steering gear set
46 are coupled together by the elongated rotary shaft
40. As shown in the figures, the elongated rotary shaft
40 can include
several segments
42. The segments
42 are coupled together in any
convenient and conventional manner such as utilizing universal joints. The rotary
shaft
40 is mounted on the support structure
12 with torque being
transferred between the various components by a plurality of parallel shaft gear
boxes
34,
44. The first parallel shaft gear box
34 and a second
parallel shaft gear box
44 are illustrated in the figures. It should be
understood however, that additional parallel shaft gear boxes can be utilized to
transfer torque from one component to another as part of the mechanical steer apparatus
30. The steering wheel
32 is mounted in the cab
15.
As shown in FIGS. 1 and 6, the fire-fighting vehicle
10 is shrouded by
a vehicle body
22. The vehicle body encloses the principal pieces of equipment
of the fire-fighting vehicle
10 such as the power source
16, the
mechanical steer apparatus
30 and the several fluid tanks (not shown) that
are mounted on the support structure
12. Typical fluid tanks include a water
tank and a chemical agent tank. Such tanks are coupled to selected fire-fighting
equipment
68 such as bumper mounted nozzles or boom mounted nozzles.
One advantage of the present fire-fighting vehicle is its stability. The fire-fighting
vehicle
10 is configured to be as low and wide as possible. It has been
determined that due primarily to garage door widths, operator visibility requirements
and maneuverability, the widest width of the vehicle should not exceed 120 inches.
Such 120 inch width is measured on the overall width of the vehicle body
22
from side
22a to side
22a. It should be noted, however,
that extraneous items such as mirrors and door handles were allowed to set out
past the 120 inch width without affecting the stability of the vehicle. Within
the constraint of the 120 inch width, the various components and equipment mounted
on the fire-fighting vehicle
10 was spread out and lowered as much as possible.
For example, the water tank center of gravity was moved down as a result of the
widening of the vehicle. The vehicle was also configured to move large volume,
low density items up and large volume, high density items down within the constraints
of the vehicle overall width. For example, the power source
16 was moved
down within the frame and air reservoirs were moved out of the frame support structure
12. For a hybrid-electric system powered vehicle
10, the power source
16 is proximate each wheel. Such configuration lowers the center of gravity
even further. The net effect of these various design configurations move the overall
center of gravity C.G. of the vehicle down from previous configurations thereby
increasing stability.
FIG. 2 illustrates an airport rescue fire-fighting vehicle
10 which illustrates
a center of gravity C.G. when the vehicle is empty and the center of gravity C.G.
when the vehicle is full. It is noted that the center of gravity when full, is
actually higher than the center of gravity when the vehicle is empty. The reference
to full and empty is to the fire-fighting fluid tanks which account for the largest
variable weight distribution on the fire-fighting vehicle
10. The weight
of the water primarily accounts for the largest shift of the center of gravity
in an upward direction. Notwithstanding that phenomena, the center of gravity of
the present fire-fighting vehicle
10 is lower than the center of gravity
of prior art airport rescue fire-fighting vehicles. It is the relationship of the
width of the vehicle at the ground vs. the height of the center of gravity that
affects the stability of the vehicle during its maneuvers.
To confirm the stability of the vehicle, a tilt-table capability test is typically
required for airport rescue fire-fighting vehicles to comply with the FAA and NFPA
Standards as discussed above. The tilt-table evaluation is a test performed to
quantify the static stability of a vehicle. The test performed is typically done
in accordance with standard SAE J 2180. The point at which a vehicle becomes unstable
is defined as a point in which at least all axles have been lifted off a test table
except the front of the vehicle. At this point, the test table movement is stopped
and the test table angle is recorded. The lateral acceleration required to tip
the vehicle over can then be calculated based on the resulting table angle. This
measurement is only an estimation of the lateral acceleration needed to tip a vehicle
and a dynamic response due to dynamic variables such as road surface, vehicle condition
and pay load variations. However, a benchmark database can be generated and used
as a comprehensive value between vehicles.
Other factors contributing to vehicle roll are lateral and vertical tire stiffness,
suspension roll stiffness, center of gravity height, and overall width of the vehicle.
The relationship of the height and width are the most fundamental and significant
to roll stability of a vehicle. As the vehicle width is increased and the center
of gravity height is lowered, the vehicle naturally becomes more stable with all
other factors being equal. This is due to the fact that the overturning moment
of the vehicle does not generate until the location of the center of gravity, and
the vertical plane is moved outside the pivot point P.P. of the vehicle at the
tire ground interface. At this point, the lateral acceleration will have the ability
to turn the vehicle over.
The suspension system for the vehicle will also deflect as the lateral acceleration
is increased. The downhill suspension will collapse as the uphill suspension extends.
These deflections move the roll center of the vehicle, as well as, causing the
center of gravity C.G. location to move towards the pivot point P.P. of the tire
ground interface. Anti-roll bars are typically installed in an attempt to stiffen
the suspension in roll. However, the modular independent suspension
26 as
described above, also contributes to the stability of the fire-fighting vehicle
10.
FIG. 3 illustrates a typical prior art vehicle illustrating the tilt-table capability
which illustrates a typical tilt-table angle as described above. Lateral acceleration
beyond the 28° will tip the vehicle over. In contrast, FIG. 4 depicts the
tilt-table angle of the present fire-fighting vehicle
10. As can be seen,
the tilt-table angle is 30° which complies with the standards established
by the FAA and NFPA described above. Applicant has determined that the tilt-table
capability angle can be as high as 35° without the vehicle rolling over. The
illustrated three degree tilt table angle difference between prior art and the
present fire-fighting vehicle
10 is significant and is attributable to the
overall configuration of the fire-fighting vehicle
10.
Other factors that must be considered in the overall configuration of the fire-fighting
vehicle can include an increasing in the length of the vehicle which can also reduce
the center of gravity height over the surface, however, design specifications of
break-over clearance and approach and departure angles (which must be at least
30° as established by the FAA and NFPA) significantly limits the vehicle length
designs. It has also been determined that increasing the spring stiffness or using
stiff anti-roll bars are effective only to'the point of lifting the opposite wheel
off the ground. After that point, additional stiffening has no effect and in any
event the stiffer the springs and roll bars the more uncomfortable the ride quality
will be for the operators of the vehicle.
FIGS. 7
a and
7b schematically illustrate the vehicle
10
making a right hand turn with the front wheels
20 turned fully to the right.
FIG. 7
a illustrates a fire-fighting vehicle with a fixed rear wheel set
24. FIG. 7
b illustrates a fire-fighting vehicle
10 with rear
steer wheels coupled proportionately to the front wheels by the mechanical steering
apparatus
30 described above. As can be seen, the vehicle in FIG. 7
b
can turn more sharply than the vehicle in
7a wherein the greater
maneuverability is afforded to the vehicle illustrated in FIG. 7
b. By coupling
the rear wheel set
24 to the front wheel set
20, tire wear on the
rear wheel set
24, wheels
19 is minimized. The tire wear known as
scrub experienced by tires in the configuration as depicted in FIG. 7
a is
a result of the tires sliding as the vehicle turns. As the front wheels turn, the
vehicle pivots on the fixed rear axle wheel set with the rear wheels rolling and
sliding through the turn which causes the tread on the tire to wear faster than
other tires on a vehicle. Tires on an airport rescue fire-fighting vehicle can
exceed $1,500 each and therefore minimizing the wear on a tire is economical not
only because of the cost of the tire, but also the time and expense in taking the
vehicle out of service in order to replace the tire.
As illustrated in FIG. 7
b, the fire-fighting vehicle
10 with the
rear steer capability can make a sharper turn because of the reduced turning radius.
In the illustration, the front wheel set
20 is turned at about 32°
and the back wheel set
24 is turned a proportional opposite direction of
about 6° in response to the steering wheel
32 movement. The mechanical
steering apparatus
30 is balanced to provide enough steering (turn radius)
in the back wheel set
24 for tracking in the turn and without too much steering
angle which would cause the front wheel set
20 to slide sideways. The mechanical
steering apparatus
30 allows the vehicle
10 to pivot about the center
of the radius of the turn, while maintaining control of the vehicle
10 and
minimizing tire scrub, particularly on the tires of the back wheel set
24.
Thus, there is provided a fire-fighting vehicle, and particularly an airport
rescue, fire-fighting vehicle including a mechanical steering apparatus and having
a tilt-bed capability of at least 30°. One of the embodiments illustrated
in the figures and described above, are presently preferred, but it should be understood
that these embodiments are offered by way of example only. The invention is not
intended to be limited to any particular embodiment but is intended to extend to
various modifications that nevertheless fall within the scope of the appended claims.
Additional modifications will be evident to those with ordinary skill in the art.
*
