Note: Descriptions are shown in the official language in which they were submitted.
11~)4~939
This invention relates to a four-wheel drive tractor
and more particularly to an articulated vehicle having articu-
lated steering on the rear wheels and having front-wheel steering
for steering the front wheels relative to a pivoting front axle.
The conventional vehicle, such as an automobile,
employs a rear-wheel drive and a front-wheel steer with a single
main chassis. This type of operation has been used quite
extensively in the tractors as well. With an increase in size of
engines in the tractor-type vehicles, and the advent of the
four-wheel drive wherein the front and rear wheels are essen-
tially the same size, the articulated vehicle has been looked
on more favorably. Various types of articulating joints have-
been used for pivotal relative movement on a horizontal and a
vertical axis. Although the conventional articulated vehicle is
pivoted on a vertical axis, some means must be provided for
oscillation of the one axle relative to the other due to the
uneveness in the terrain. The type of pivoting mechanism on
the front axle and the pivot for the articulation of the vehicle
is critical since this does affect the stability of the vehicle.
An articulation of the vehicles having the articulating joint
of the vehicle centrally located between the front and rear
wheels will cause instability particularly on uphill turns
because tne center of gravity is shifted outside the center
line of the vehicle. Large angles of articulation reduce the
tractive effort of the tractor as well as drawbar pull since
the wheels work in opposition to each other. This interaction
consumes extra power without productive work being done.
Accordingly, this invention is intended to overcome this
instability and inefficiency, and to provide greater maneuver-
ability and improved traction for the vehicle.
1L)4~939
Accordingly, this invention provides for a four-wheel
drive vehicle with articulation between the front and rear
frames of the vehicle chassis. The articulation point is
approximately in the ratio of 3 to 1 between the front and rear
frames of the vehicle chassis. For examp~e, a vehicle with a
llO-inch wheel base would have a front frame of approximately
83 inches from the pivot center to the front axle center line
and a rear frame of 27 inches from the pivot to the rear axle
~center line. The rear wheels are steered by articulation of the
vehicle. The front wheels are mounted on a pivotal axle
pivotally mounted under the front frame of the chassis. The
front wheels are steerable on axes defined by the pivotal
connections between the wheel support and the front axle.
Accordingly, the vehicle can be steered as a conventional
single-frame chassis or as the combined front-wheel steering
and articulated steering of the rear wheels for left or right
turns or crab steering. This in turn will provide conventional
steering, such as the single-framed front-wheel steering-type
rnechanism or articulated steering or a combination of either of
these two types of steerinq, to reduce the angularity between
the center line of the front frame and the center line of the
rear frame with the line of draft of the vehicle if a tractor
or line thrust if a bulldozer or front-end loader vehicle.
This provides greater stability because the center of gravity is
maintained in a more central location on the vehicle. The
steerability of the front wheels relative to the front axle
together with articulated rear-wheel steering provides greater
maneuverability of the vehicle and less side thrust on a rear-
end coupled implernent during corrective steering or during
turning. The constant pull on the implement is not momentarily
interrupted or reduced by corrective steering as is experienced
1~48~39
by center-articulated steering due to interaction between the
front and rear wheels.
It is an object of this invention to provide a four-
wheel drive tractor with steerable front wheels on a front axle
and articulated steering for the rear wheels of the tractor to
provide left-turn or right-turn steering and crab steering for
the vehicle.
It is another object of this invention to provide a
pivotal front axle with steerable wheels on the axle and an
articulated chassis with the front frame being substantially
longer than the rear frame on the vehicle.
It is a further object of.- this invention to provide
a four-wheel drive tractor with steerable front wheels and an
articulated chassis with articulated rear-wheel steering to
reduce the angularity between the longitudinal center lines of
the front and rear frames with the line of draft or forward
thrust of the vehicle while turning.
It is a further object of this invention to provide
a four-wheel drive vehicle with steerable front wheels on a
pivotal front axle and articulated vehicle rear-wheel steering to
provide a three-point hitching arrangement to avoid implement
engagement with the rear wheels or excessive side thrust on the
implement when turning.
It is a futher object of this invention to provide an
articulated vehicle havin~ articulated rear-wheel steering and a
pivotal front axle with steerable front wheels steerable about
essentially vertical pivotal axes to increase the maneuverability
and stability of the vehicle.
It is a further object of this invention to provide a
four-wheel drive tractor having an articulated chassis with a
pivotal front axle having steerable wheels and articulated
, ,~ - 3 -
1~48~39
steering on the rear wheels with a long front bogie for
supporting the operator station and a short rear bogie to
increase stability and maneuverability of the vehicle during
articulation and steering of the vehicle.
It is a further object of this invention to provide a
four-wheel drive tractor with steerable front wheels and
articulated rear-wheel steering having a line of draft which if
projected forward would always lie between the front wheels.
The objects of this invention are accomplished by
providing a four-wheel drive vehicle. The vehicle chassis
includes a front frame and a rear frame with articulation rear-
wardly of the center of the vehicle chassis with a ratio of
about 3 to 1. The rear axle is supported on the rear wheels
and the steering of the rear wheels is controlled by hydraulic
actuators in connection with the articulated joint of the
vehicle chassis.
The front axle of the vehicle pivotally supports the
front frame and allows for the pivoting of the front axle in
response to the unevenness of the terrain. The front wheels
are steerable on the axle and are steered hydraulically in
response to the hydraulic controls by the operator. The drive
for the front and rear wheels may be a mechanical drive through
universal joints running fore and aft from a transmission drop
box centrally located on the vehicle chassis and supported on
the front frame. The articulated joint on the vehicle chassis
pivots on a top and lower bearing to maintain the upright
position of the front frame while the rear wheels maintain the
stability and position of the front and rear frames. Since the
front axle is pivotal relative to the front frame, this does
not control the position of the front frame, but merely allows
for the front wheels to follow the terrain and maintain traction
39
while the vehicle is in operation. ~ith the front-wheel steering
and the articulated steering of the rear wheels, the steerable
angle of the articulated joint can be substantially reduced and,
accordingly, the longitudinal center lines of the front and
rear frames are more parallel with the line of travel and the
stability of the tractor and maneuverability of the tractor is
improved.
In accordance with the invention, a four-wheel drive
tractor comprising a chassis including a front frame and rear
frame, a drawbar for applying a draft load, means pivotally
connecting said drawbar to and carrying the draft load on said
front frame of said chassis, an engine supported on the front
frame of said chassis, an axle pivotally supporting the front
frame of said chassis, front steerable drive wheels rotatably
supporting said front axle and pivotal relative to said front
axle for front-end steering, front wheel steering mechanism for
steering the front wheels, a rear axle supporting said rear frame
of said chassis, a pair of rear drive wheels rotatably supporting
said rear axle, an articulating joint including vertically spaced
pivotal bearings pivotally connecting said front frame with said
rear frame of said chassis, an articulating steering mechanism
for arti.culation of said front and rear frames, front wheel
manual steering control means for steering said front wheels
through said front wheel steering mechanism and rear wheel manual
steering control means for steering said rear wheels of said
tractor through said articulating steering mechanism, said front
frame and said rear frame defining length ratios of approximately
3 to 1 with lengths from the center line of the articulating
joint to the center line of the front axle relative to the center
line of the articulating joint to the center line of the rear
~ ~ - 5 -
1~4~939
axle, means defining an operator station on said front frame of
said chassis for operating said tractor.
Referring to the drawings, the preferred embodiment of
this invention is illustrated:
Fig. 1 shows a partially sectioned side view of the
vehicle;
Fig. 2 illustrates a plan view of the vehicle;
Fig. 3 illustrates a schematic diagram of the hydraulic
system for operating the vehicle;
Fig. 4 shows crab steering of the vehicle and the
limited angularity of the drive line on the vehicle;
Fig. S illustrates front-wheel steering for the
vehicle;
Fig. 6 illustrates front-wheel steering in the right-
hand direction and rear-wheel articulated steering in the left-
hand direction on the vehicle;
Fig. 7 is a plan view of the front axle and front-
end carriage;
Fig. 8 is a front elevation view of Fig. 7;
Fig. 9 illustrates a plan view showing the mounting of
the drawbar on an axis coincidental with the axis of articulation
of the vehicle;
,-~ - 5a -
lr~48939
Fig. 10 is a side elevation view of Fig. 9;
Fig. 11 is a modification of the vehicle shown in
Fig. 10 with the pivotal connection for the drawbar on the
front frame only;
Fig. 12 is a plan view of a schematic illustration of
an articulated vehicle with the drawbar connected to the front
frame; and,
Fig. 13 is a plan view of a schematic illustration
for an articulated vehicle with an articulated joint midway
between the front and rear axles.
Referring to the drawings, Fig. 1 illustrates a
partially sectioned side view of the tractor 1. The tractor
includes a platform 2 supporting the seat 3 at the operator
station 4. The steering wheel 5 is mounted on the control
console 6. The engine hood 7 is mounted between the control
console 6 and the grill 8 mounted in front of the radiator.
The radiator and the grill 8 and engine 9 are mounted on the
frame 10 which is a part of the vehicle chassis.
The engine 9 drives through the transmission 11 which
drives into the drop box 12. The drop box 12 drives forwardly
to the shaft 13, the universal joint 14, the intermediate
shaft 15, and universal joint 16. Universal joint 16 drives
into the shaft 17 and a differential in the front-wheel drive
18. A front-wheel drive shaft 19 drives one of the front wheels.
Front wheels 20 and 70 support the front end of the tractor.
The front-end carriage 21 is connected to the front
axle 22 and is pivotally supported on the pins 23 and 24, which
in turn are mounted in the brackets 25 and 26 of the front
frame end. Accordingly, the front carriage 21 is pivotal on a
longitudinal axis of the tractor 1.
- 6 -
1~)48939
The drop box 12 also drives rearwardly through the
shaft 27, the universal joint 28 and the intermediate shaft 29
and the universal joint 30. The universal joint 30 drives
shaft`31 and through a differential in the rear-axle assembly
32. The rear-drive assembly 32 drives through the rear axle 33
to one of the rear wheels. The rear wheels 88, of which one is
shown in Fig. 1, support the rear frame 34. The rear frame 34
includes the brackets 35 and 36 which are pivotally connected
to the clevises 37 and 38 on the front frame 10. The upper
bearing 39 formed by brackets 35 and clevis 37 is pivotally
connected by the pin 40, while the lower bearing assembly 41
formed by bracket 36 and clevis 38 is pivotally connected by
the pin 42.
The rear-drive housing 43 pivotally supports the rock
shaft 44 and the rock arms 45 are pivotally connected to the
lift links 46. A pair of lift links 46 raise and lower the
lower draft arms 47 in response to movement of the rock shaft
44. The lower draft arms are co~nected through arms 88 on the
rear-drive assembly to a suitable draft movement-sensing
mechanism.
The implement 49 is connected to the upper link 50 by
a pivot pin 51. The implement includes a mast 52 which extends
downwardly and is connected to the lower draft arms 47 by means
of a pivot pin 53. The drawbar 54 is supported by a drawbar
bale 55 and the bracket 56 connected to the rear-drive housing
43.
In Fig. 2, the articulating bearing 39 is shown which
is immediately above the bearing 41. The hydraulic actuators 60
and 61 are supported on the brackets 167 and 168 on the front
frame 10 and pivotally connected to the brackets 58 and 59 on
the rear frame 34. Selective actuation of the hydraulic
1048939
actuators 60 and 61 provides articulated steering of the rear
wheels 88. This steering mechanism is provided through the
hydraulic system shown in Fig. 3.
Figs. 7 and 8 show the steering mechanism for the
front wheels. The carriage 21 is mounted on the housing of the
front-wheel drive 18. The brackets 62 and 63 connect the
carriage to the front axle 22. The hydraulic actuator 64 is
mounted on the bracket 65 on the carriage 21 and selectively
operates the steering arm 66. The steering arm pivots the
right-front wheel 20 on its pivotal axis. The tie rod 67
connects the arm 68 with the arm 69 to steer a left-front
wheel 70 on its pivotal axis. Accordingly, the front wheels
are steered by pivotal movement of the wheels 20 and 70 on
their respective pivotal axis.
Referring to Fig. 3, the pump 72 receives hydraulic
fluid from the reservoir 73 and pressurizes fluid in the
hydraulic line 74. A relief valve 75 is connected on the dis-
charge pump 72 to relieve excess fluid pressure in the conduit
74. The hydraulic actuator 64 is connected through the control
valve 76. The control valve 76 is controlled by the steering
wheel 5. The control valve 76 includes a neutral section 77 as
well as a left-turn and a right-turn section 78 and 79. Also
connected to the high-pressure conduit 74 is conduit 81 which
leads to control valves 76 and 83, respectively. The return
line 80 is connected to conduit 82 which leads from the control
valves 76 and 83 to the reservoir. The control valve 83 controls
the articulated steering through the lever 84 which operates the
control valve 83 between the neutral position 85 and the right-
hand and left-hand turn sections 86 and 87. The articulated
steering selectively operates through the hydraulic actuator
60 and 61 to provide articulated steering of the rear frame 34
relative to the front frame 10.
-- 8
1048~39
Fig. 4 illustrates the crab steering of the vehicle
in which the front wheels 20 and 70 are steering in the right-
hand direction while the articulated steering of the rear wheels
88 are steering in the right-hand direction. The drive line 29
to the rear wheels requires a slight amount of angularity to
provide for crab steering.
Fig. 5 illustrates conventional steering in which the
drive line 29 extends in essentially a straight line between
the rear frame 34 and the front frame 10 of the chassis. When
the vehicle is operated in this manner, it operates as a con-
ventional single-frame chassis in which front-wheel steering
is used to control the movement of the vehicle.
Fig. 6 illustrates steering of the vehicle in which
the front wheels 20 and 70 are being steered by the front-
steering mechanism in the right-hand direction and the rear-
articulated steering provides for steering of the rear wheels
in the left-hand direction. In this manner, the vehicle steers
with a minimum amount of scuffing of the tires as the rear end
of the vehicle is moved in the left-hand direction and the
front end of the vehicle is moved in the right-hand direction.
Fig. 9 is a plan view of a four-wheel drive vehicle.
A drive mechanism is not shown in detail in this view, but the
positioning of the drawbar and its mounting on the vehicle
together with the articulating joint is shown. The drive for
the vehicle may be similar to that shown in Figs. 1 and 2 show-
ing a mechanical drive or the drive may be a hydraulic drive
suitable for driving the front and rear wheels. Such a system
may include one or two pumps which are engine driven and a
motor for each of the four wheels for driving the vehicle
hydraulically. The vehicle may be used for operating a bull-
dozer blade or a front-end loader in which the thrust would be
through the attachment connected on the front end of the vehicle.
1~48939
The vehicle may also be used as a tractor for pulling of an
implement. The coupling between the tractor and the implement
may be a three-point hitch or a drawbar as shown in Figs. 1 and
2. Figs. 9 and 10 show a modification of the connection of
the drawbar and Fig. 11 shows a further modification in connect-
ing the drawbar to the tractor. Fig. 9 shows the four wheels
100, 101, 102 and 103 which drive the vehicle. The front wheels
100 and 101 are rotatably mounted on the front axle 104. A
suitable steering arrangement for the front wheels as shown in
Fig. 7 is provided to steer the front wheels relative to the
front axle. The front axle is also pivotally mounted on a
pivoting axis as shown in Fig. 7 whereby the front axle pivots
about a longitudinal axis.
The rear wheels 102 and 103 as shown are driven by
the rear-drive axle 105 and 106 which are rotatably mounted in
the rear-drive assembly 107. The rear wheels 102 and 103 are
steered by the articulating mechanism for pivoting at the
articulating joint 108.
Fig. 10 illustrates the drawbar 109 which is pivotally
mounted on an axis coincidental with the axis of an articulating
joint 108. Essentially, the drawbar is connected to the front
frame of the vehicle. The drawbar is a swinging drawbar as
shown in Fig. 9 and swings on the pivot 110 between the limits
defined by the stops lll and- 112 shown in Fig. 9. Fig. 11 shows
a modification whereby the drawbar 113 is pivoted on a pin 114
mounted forwardly of the articulating joint 108. The line of
draft 132 of the drawbar, projecting forwardly, will pass
between the two front wheels 100 and 101 as shown in Fig. 12.
The required angle of articulation is substantially less than
shown for a vehicle of the type shown in Fig. 13 because the
-- 10 --
lV48939
front wheels are steerable on the front axle while the rear
wheels are steered by articulation of the vehicle. In this
manner, the vehicle can provide crab steering or it can pro-
vide right-hand and left-hand steering as well. Fig. 12 shows
the vehicle with the front wheels steered to the left and the
articulation steering is also steered in a manner to make a
left turn as shown.
Fig. 13 shows a conventional articulated vehicle in
which the articulating joint is midway between the front axle
and the rear axle. It is noted that the angle of articulation
is greatly increased when there is no front-wheel steerable
wheels and the articulating joint is positioned forwardly com-
pared to the articulated joint shown in the invention covered
in this application. It is also clearly shown that the vehicle
shown in Fig. 13 is not nearly as stable as the vehicle shown
in Fig. 12 and, particularly, when the vehicles shown are
turned uphill. With the articulated steering shown in Fig. 13,
the interaction between the front and rear wheels reduces the
draft load capable of being pulled by the tractor and reduces
the efficiency of the tractor. Corrective steering of the
vehicle as shown in Fig. 13 may momentarily interrupt or vary
the draft loads carried by the vehicle.
The operation of the device will be described in the
following paragraphs:
The vehicle shown in Fig. 1 is an articulated vehicle.
The articulation of the vehicle is on the bearings 39 and 41.
The vehicle is steerable by articulation of the vehicle through
the hydraulic actuators 60 and 61 in the hydraulic circuits
shown in Fig. 3. The vehicle is also steerable by steering the
front wheels 20 and 70 which pivot on their axes in response to
operation of the hydraulic actuator 64. The front-end carriage
~04~939
21 pivots on the pins 23 and 24 to keep the wheels of the
vehicle in traction although the terrain is uneven. Traction
of the vehicle is provided on all four wheels and the drive to
the four wheels is provided through the transmission 11, the
drop box 12 and drive means including universal joints.
Since the front wheels are turned by selective opera-
tion of the steering wheel 5, it turns the vehicle left or right
by selective operation of the section 78 or 79 of the control
valve 76. When the articulation of the vehicle is not used,
the vehicle is used as a conventional front steerable vehicle.
The articulated steering on the rear wheels is accomplished
through selective actuation of the hydraulic actuators 60 and
61. The control lever 84 selectively operates the control
valve 83 for selective operation of the section 86 or 87 to
operate the hydraulic actuators 60 and 61. The rear wheels 88
and the rear frame 34 can be pivoted angularly to the right or
left relative to the front frame 10 to provide steering of the
vehicle in response to movement of the actuators 60 and 61.
The wheels 88 and frame 34 can be pivoted or steered either
right or left regardless of the steering direction of the
front wheels 20 and 70. Accordingly, to pivot the rear frame
and steer the rear wheels of the vehicle in the same direction
as the front wheels are being steered will provide crab steer-
ing. To steer the rear wheels in the opposite direction from
the front wheels will cause the vehicle to turn in the direction
of the steering of the front wheels while the rear end of the
vehicle moves in the opposite direction and steer the vehicle
on a shorter radius than if only the front wheels were used in
steering. It is noted that because the front wheels can be
steered relative to the front axles, a lesser amount of
~48939
angularity is required of the drive line between the drop box
12 and the rear drive assembly 32. Because less angularity is
required of the drive line components, the drive line should
be more reliable and assure longer life of the drive line in
the vehicle. The articulating bearings of the vehicle for
articulation between the front section 10 and the rear section
34 are located between the rear wheels 88 of the rear section
34. The length of the front frame between the front axle and
the articulating joint as compared to the length of the rear
frame 34 is approximately 3 to 1. The level of the vehicle is
controlled by the two rear wheels 88 and the central pivot of
the front-end carriage 21 under the front frame 10. With the
positioning of the pivoting axis for articulation of the
vehicle rearwardly of the center of the chassis, a more stable
vehicle is provided. The pivotal movement of the carriage 21
and a front axle with the front frame provides for the necessary
oscillating movement in response to the-unevenness of the
terrain.
The operation of the vehicle shown in Figs. 9, 10, 11
and 12 will be described in the following paragraphs.
The vehicle shown is illustrative only and not limit-
ing. For example, the vehicle shown may be a vehicle of
approximately llO-inch wheel base with the front frame measur-
ing 83 inches from the center line of the front axle to the
center line of the articulating joint. The rear frame has a
frame which measures 27 inches from the articulating joint to
the center of the rear axle. Roughly, the ratio of the front
frame to the rear frame is 3 to 1. This ratio of articulated
vehicle is used with front axles having steerable wheels having
essentially a standard turn angle. With a turning radius of
approximately that of conventional four-wheel drive tractors,
- 13 -
1~4t~939
the vehicle covered herein is never put in an unfavorable
position as are the center-articulated vehicles. The maximum
steering angle of the front wheels and of the articulated
steering of the rear wheels is approximately 22 degrees.
When a center-articulated tractor goes into a sharp
turn, the pivot ~oint moves outside the line of pull so that
one set of the wheels tends to go straight and the other set
off at 44 degrees. Fig. 13 shows the front wheels 136 and 137
at about 44 degrees to the rear wheels 138 and 139. The line
of traction 140 is approximately at 44 degrees to the line of
propulsion 141. The line of draft 142 is to the right of
both the line of propulsion 141 and the line of traction 140.
The large angle of articulation reduces the tractive effort
since the wheels work in opposition to each other. This
interaction consumes extra power without productive work being
done. The useful draft component is substantially reduced
after side thrust on the implement, interaction of the front
and rear bogies, and large angularity between line of traction
and the line of propulsion with the line of draft is overcome.
Corrective steering constantly varies the effective drawbar
pull, this in turn causes the governor of the engine to be
constantly hunting to accommodate the variations in the engine
output and to provide the relatively constant draft load of
the implement.
The vehicle covered herein never has an angle of
articulation as large as the center-articulated vehicle. The
reduced steering angles and more favorable line of pull improve
tractor performance. The tractor pulls straighter on the load
and does not create the side thrust on the implement. This,
in turn, provides a more efficient and productive tractor.
Since the line of draft of the proposed tractor stays
more parallel with the direction of travel, less nonproductive
1¢)4~3939
side forces are encountered than with a center-articulated
steering tractor. The tractor, as shown, carries a three-point
hitch as well as a drawbar. The three-point hitch is connected
to the rear bogie 116 which trails the front bogie 115. The
longitudinal center line 130 of the front bogie 115 passes
through a midpoint in the front axle 104. The line of pro-
pulsion 131 of the rear bogie is an imaginary line passing
through the center of the rear axle and normal to the rear axle.
Accordingly, the line of traction 131 is generally parallel
with the line of draft 132.
The center line 130 of the front bogie 115 and the
line of propulsion 131 of the rear bogie 116 are theoretically
coincidental when the vehicle is traveling in straight ahead.
With the drawbar 109 pivotally mounted on the vehicle chassis,
the center line of the drawbar defines the line of draft 132
for the vehicle, and this also theoretically is in line with
the line of propulsion 131 of the rear bogie 116 and with the
line of traction of the front bogie 115 when the vehicle is
traveling straight ahead. The implement when connected to the
drawbar trails the front bogie 115. The rear bogie 116 pro-
vides a propelling force through the articulating joint with
the front bogie 115. For small angles of corrective steering,
the front wheels alone may provide steering and articulated
steering for the rear wheels is unnecessary. Also on hillside
work, the rear wheels and front wheels may both be used simul-
taneously for crab steering and corrective steering and gener-
ally keep the vehicle going in the direction desired. The cor-
rective steering for this vehicle does not require articulation
nor produce interacting forces between the front bogie 115 and
rear bogie 116 to vary the efficiency of power transmission to
the drawbar due to the interaction between the two bogies.
1¢)489;~9
Accordingly, this vehicle will provide greater efficiency of
power transmission to the drawbar.
Fig. 11 is a modification of FigO 10 and provides
for a drawbar which is pivotally connected forwardly of the
articulating joint 108. Positioning of the drawbar forwardly
of an articulating joint has some advantage since it produces
less angularity between the line of draft and the line of
travel of the vehicle. The connection of a drawbar in this
manner will provide a line of draft when extended which will
always lie between the two f~ont wheels. Accordingly, it can
be seen that this vehicle is more maneuverable because the
front and rear wheels are steered. Because both front and
rear wheels are steered, the vehicle does not have to articu-
late as much as the vehicle shown in Fig. 13. Because the
vehicle does not articulate as much, the stability of the
vehicle is improved and this is an important factor, parti-
cularly in hilly country. If the center of gravity is shifted
outside of the confines of the wheel, the vehicle may become
very unstable and even upset if the slope of the hillside is
too great. Maximum traction is also provided with the vehicle
shown in Fig. 12 since the interaction is reduced to a minimum
between the front and rear bogies. Maximum traction provides
greater efficiency for the tractor and also a uniform pull on
the drawbar for improved operation of the vehicle under all
load conditions.
~ 16 ~
