Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~13833
1HYDROSTATIC FRONT WHEEL DRIVE SYSTEM
The present invention relates to an auxiliary front wheel
drive system for a vehicle and more particularly relates to an
auxiliary front wheel drive system for a motor grader.
The prior art includes various types of vehicles having main
or primary drive systems for driving first sets of wheels by
means of engine-driven mechanical transmissions, and auxiliary or
assist drive systems for driving second sets of wheels by means
of engine-driven hydrostatic transmissions when operating condi-
tions are such that additional traction is desired. Representa-
tives of these prior art vehicles are those respectively dis-
closed in U.S. Patent No. 3,458,005 issued to Malm et al on 29 !
July 1969, U.S. Patent No. 3,584,698 issued to Larson et al on 15
June 1971 and U.S. Patent No. 3,997,017 issued to Campbell et al
on 14 December 1976.
The auxiliary drive system disclosed in the above-identified -
Malm et al and Campbell et al patents are similar to each other
in that they both include electrical controls and utilize a
variable displacement, pressure-compensated pump for delivering
working fluid to fixed displacement hydraulic front wheel drive
motors. Because it is a characteristic of such pumps to maintain
the pressure of the working fluid at a preselected pressure and
the pressure necessary for rotating the wheels depends upon the
resistance encountered by them, then the pressure selected for
maintenance by the pump must be high enough to rotate the front
wheels at the highest expected resistance. The result of such
systems has been that the front wheels tend to overspeed anytime
the resistance to their rotation decreases substantially below an
average resistance such as occurs, for example, when the wheels
enter a mud puddle, are raised off the ground or encounter an icy
surface. This overspeeding is undesirable since it results in
undue engine horsepower consumption and working fluid heating and
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1 sometimes results in material such as gravel or mud and the like
being thrown onto the vehicle and on any other thing that may be
in the vicinity of the front wheels.
The auxiliary drive system disclosed in the above-identified
Larson et al system avoids the overspeeding problem inherent in
the Malm et al and Campbell et al auxiliary drive systems by
employing a fixed displacement pump driven by the main drive
transmission input shaft and having its displacement matched to
that of the auxiliary drive motors such that, when the transmis-
sion is in its first speed range, the speed of the main drivewheels is required to be a preselected percentage greater than
the speed of the auxiliary drive wheels before the pump has
; capacity to develop any driving torque in the motors, and, when
the transmission is in its second speed xange, the pump will have
capacity to develop dxiving torque in the motors when the main
and auxiliary drive wheel speeds are equal. However, the auxil-
iary drive system of Larson et al lacks versatility since the
point at which the pump will supply sufficient fluid for develop-
ing driving torque in the auxiliary drive motors is Very much
dependant upon the speed ratios of the main traction drive trans-
mission. In fact, the Larson et al auxiliary drive system
includes a two-speed final drive transmission which is shifted in
response to the main drive transmission being shifted to compen-
sate for speed ratio changes in the main drive transmission.
Summary of the Invention
.
According to the present invention, there is provided a
novel hydrostatic auxiliary drive system for a vehicle and more
particularly there is provided a novel front wheel drive system
for a motor grader.
A primary object of the invention is to provide an auxiliary
hydrostatic drive system including a reversible, variable dis-
placement pump connected to a pair of fixed displacement wheel
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1 motors such as to form a closed loop system and associated with
controls for automatically controlling its displacement for
maintaining a preselected correspondence between the respective
speeds of the main and auxiliary drive wheels.
A more specific object is to provide an auxiliary drive
system including hydraulic circuitry for routing working fluid to
the auxiliary drive wheel motors and to respective pressure-
controlled normally disengaged clutches which are operative when
pressurized to establish respective driving connections between
the motors and the auxiliary drive wheels.
A further object is to provide an auxiliary drive system, as
set forth in the immediately preceding object, wherein disengage- !
ment of the auxiliary drive wheels from the wheel motors is
automatically effected anytime the main traction dxive clutch is
disengaged, or when the main traction drive transmission is
shifted to neutral or to selected speed ratios where the auxil-
iary drive is not required to thus permit free wheeling of the
auxiliary drive wheels.
Yet another object is to provide hydraulic circuitry, as set
forth in the preceding object, which routes the working fluid
pressure to the wheel engagement clutches such that the wheel may
overrun the wheeI motors to thus eliminate torque interferences
between the main and auxiliary drive systems, especially during
turning operations~
Still another object is to provide hydraulic circuitry, as
set forth in the preceding objects, which includes forward and
~;~ reverse valves operable in response to foxward and reverse
shuttle-shifting of the main traction drive transmission such as
~i~
to ensure smooth operation by properly timing the engagement of
the wheel motors with the auxiliary wheels in respect to engage-
ment of the main transmission.
A further object is to provide hydxaulic circuitxy, as set
forth in one or more of the preceding objects, wherein a flow
~i383~ ~
1 divider-combiner valve is connected between the variable displace-
ment pump and first work ports of each of the wheel motors and
wherein a restricted passage joins respective lines connecting
the divider-combiner valve to the first work ports, whereby a
partial differential lock action is established which functions
to reduce scuffing of the tires during turning. The restricted
passage also acts to equalize the pressure between the wheel
motors such as to cause the divider-combiner valve to be reposi-
tioned to a centered unbiased dividing position after a turn has
been completed so that the idling wheel during the turn again
develops torque instead of the flow divider-combiner valve remain-
ing in a position wherein it restricts the flow path to that
wheel.
These and other objects will become apparent from reading
. . .
the ensuing description together with the appended drawings.
::,
Brief Description of the Drawings
- Fig. la is a right side perspective view of the forward
portion of a motor grader embodying the present invention.
Fig. lb is a right side perspective view of the rearward
- 20 portion of the motor grader 8hown in Fig. la.
Fig. 2 is an elevational view of the left front grader wheel
and hydraulic motor for driving the same.
Fig. 3 is a view of the hydraulic motor taken along the line
; 3--3 in Fig. 2.
,~ , .
Fig. 4 is a sectional view taken along the line 4--4 in Fig.
3 and showing a conventional digital magnetic sensor for sensing
the speed of the left front wheel motor.
- Fig. 5 is a perspective view showing a portion of the differ-
ential section of the main transmission and showing a conven-
tional digital magnetic sensor for sensing the speed of the main
traction drive wheels.
Fig. 6 is a schematic of the front wheel drive system.
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1 Description of the Preferred Embodiment
Referring now to Figs. la and lb, therein is shown a motor
grader 10 including front and rear frame sections 12 and 14,
respectively. The forward end of the frame section 12 is sup-
ported on right and left front wheels 16 and 18, respectively,
and the rearward end of the frame section 12 is supported on the
rear frame section 14 to which it is connected by a pivot assem-
bly 20 defining an upright axis about which the frame sections
are selectively articulated by means of a pair of two-way hydrau-
lic steering actuators, a portion of one being shown at 22. The
rear frame section 14 is in tuxn supported on right and left sets
of bogey-mounted main traction drive wheels 24 and 26,
respectively.
An operator's station 28 is located on the rear end of the
frame section 12 within a cab 30 and has a plurality of controls
for the motor grader located thereat, the only controls shown
being main traction drive transmisslon controls including a gear
selector lever 32, a direction selector lever 34 and a clutch
pedal 36.
:: .
The rear frame section 14 supports an engine 40 within a
; compartment 42. Coupled to an output shaft at the rear of the
engine 40 is a set of transfer gears, indicated generally at 44,
which drive an input shaft of a main traction drive transmission
46. The principles of the present invention are applicable to
vehicles having various types of main traction drive transmis-
sions, however, as specifically disclosed herein the invention is
adapted for use with a planetary transmission shiftable to achieve
eight forward and four reverse speeds and including a plurality
of hydraulically actuated clutches and brakes (Fig. 6) including
a main drive clutch 47, which disengages the transmission when-
ever the pedal 36 is depressed, a forward drive clutch 48, which
is actuated whenever the direction selector lever 34 is moved
from neutral to place the transmission in a selected forward
.
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1 driving mode, and a reverse drive brake 49, which is actuated
whenever the direction selector lever is moved from neutral to
place the transmission in the reverse driving mode. An example
of such a transmission is disclosed in U.S. Patent No. 3,298,252
issued to Harris et al on 17 January 1967 and incorporated here-
in, in its entirety, by reference.
In any event, the transmission 46 has an output shaft coupled
to a differential gear set 50 which is in turn coupled to the
rear sets of wheels 24 and 26 by respective final drive gear
trains including respective planetary gear sets (not shown). As
can best be seen in Fig. 5, a parking brake disc 51 is also
coupled to the gear set 50, the coupling including a shaft 52
having the disc 51 fixed to its upper end and a spiral gear 54
integral with its lower end and meshed with a differential ring
gear 56. A plurality of teeth 58 are provided at the periphery
of the disc 51 and a digital magnetic sensor 60 is mounted adja-
cent the path swept by the teeth 58 and is operative for sending
out electrical pulses which corxespond to the speed of rotation
of the disc 51 which in turn corresponds to the average speed of
rotation of the rear sets of wheels 24 and 26. The purpose for
the sensor 60 is described more fully hereinbelow.
An auxiliary front wheel drive syStem 62 (Fig. 6) is pro-
vided for selectively augmenting the main traction drive system
of the grader 10 and includes right and left hydraulic motors 64
and 66 respectively located within housings 68 and 70 (Fig. la),
which are fixed to the rims of the wheels 16 and 18 and which may
be selectively coupled for being driven by the motors through
means of planetary gearing (not shown) upon pressurization of
- normally disengaged right and left clutches 72 and 74 (Fig. 6).
Referring now to Figs. 2 - 4, it can be Seen that the left hous-
,~ ing 70 includes a removable inner member 76 which covers an inner
end of a rotor 78 of the motor 66. Fixed to the rotor 78 is a
toothed member 80 and mounted adjacent the path traced by the
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1 teeth of the member 80 is a digital magnetic sensor 82 which is
` operable for producing an electrical pulse signal that is propor-
tional to the speed of rotation of the rotor 78. The purpose of
the sensor 82 is set forth hereinbelow.
Referring now to Fig. 6, it can be seen that the auxiliary
- front wheel drive system 62 includes a reversible variable dis-
placement pump 84 having an upper port connected to a port at one
side of a conventional flow divider-combiner valve 86 by a supply
return line 88, the valve 86 having a pair of ports at its oppo-
site side respectively connected to respective first work ports
of the wheel motors 64 and 66 by supply-return lines 90 and 92,
which are connected together by a restricted line 93 for a purpose
'~ explained below. Connected between a lower port of the pump 84
and respective second work ports of the motorS 64 and 66 is a
branched supply-return line 94. Thus, it will be appreciated
that a closed loop hydraulic circuit extends between the pump 84
and motors 64 and 66 and that the latter are connected in paral-
lel with one another.
. .
The pump 84 is a conventional axial piston pump having an
angularly adjustable swash plate 96 to which one-way hydraulic
actuators 98 and 100 are respectively linked at lower and upper
locations thereof and are respectively pressure-actuatable to
move the swash plate from a centered position, as shown, so as to
establi~h forward and rearward pumping conditions in the pump 84
respectively resulting in fluid being displaced from the line 94
to the line 88 and vice versa.
,~ A pilot-operated control valve 102 is connected to the
actuators 98 and 100 and to a pump 104 and includes a valve spool
106 selectively shiftable rightwardly and leftwardly, of an
illustrated neutral position, for respectively pressurizing the
; actuators 98 and 100. The movement o the valve spool 106 is in
; turn controlled by a linear electrohydraulic actuator 108 having
a reciprocable output member 110 connected to the spool 106, the
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1 actuator 108 being of a commercially available type which exhibits
the characteristic of displacing the member 110 in direction and
magnitude in accordance with the direction and magnitude of
electrical control signals sent to the actuator 108, in a manner
set forth hereinbelow, to effect automatic control of the actu-
ator 108 and consequently of the magnitude and direction of
displacement of the pump 84. A feedback linkage 112 is connected
between the swash plate 96 and the valve spool 106 and acts in
the usual way to return the spool 106 to its neutral position in
response to the swashplate 96 moving to a new position as com- :
manded by the actuator 108.
A hydraulic circuit is provided for connecting the working
fluid of the motors 64 and 66 to the clutches 72 and 74 for actu-
ating the latter to establish respective driving connections be-
tween the motor 64 and the wheeI 16, and between the motor 66 and . ~ `
the wheel 18. Specifically, working fluid for driving the right
wheel motor 64 forwardly is routed from the supply-return line 90
^~l to the clutch 72 by a line 114 connected between the line 90 and
one side of a right forward drive solenoid-operated valve 116 `
having its opposite side connected to a drain line 118 and to a
port at one end of a shuttle valve 120 by a line 122. The valve
. ~ .
120 has a center port connected to the clutch 72 by a line 124.
; Similarly, working fluid for driving the left wheel motor 66
forwardly is routed from the supplv-return line 92 to the clutch
74 by a line 126 connected between the line 92 and one side of a
.~ left forward drive solenoid-operated valve 128 having its opposite
l side connected to a drain line 130 and to a port at one end of a
.'. shuttle valve 132 by a line 134. The valve 132 has a center port
connected to the clutch 74 by a line 134 and has a port at its
other end connected to a port at the other end of the shuttle
valve 120 by a line 136.
: Working fluid for driving the ri~ht and left wheel motoxs 64
and 66 in reverse is routed from the supply-return line 94 to the
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1 clutches 72 and 74 by a line L38 connected between the line 94
and one side of a reverse drive solenoid-operated valve 140
ha~ing its opposite side connected to the drain line 130 and to
the line 136 between the shuttle valves 120 and 132 by a line
144.
The solenoid-operated valves 116, 128 and 140 are all illus-
trated in de-energized positions wherein they connect the clutches
to sump via the drain lines 118 and 130. In a manner to be de-
scribed hereinafter, the forward drive solenoid-operated valves
116 and 128 will be energized in response to the main traction
drive transmission becoming fully engaged for driving forwardly
at certain speed ratios. Energization of the valve 116 results
in the latter being shifted leftwardly to connect the line 114 to
the line 1220 The check ball in the shuttle valve 120 wlll shift
to block flow to the line 136 while permitting fluid to flow to
the clutch 72 via the line 124. ~imilarly, energization of the
valve 128 results in the latter being shifted leftwardly to
connect the line 126 to the line 134. The check ball in the
shuttle valve 132 will shit to block flow to the line 136 while
permitting fluid to flow to the clutch 74 via the line 134. It
will be appreciated then that the fluid pressure for actuat.ing
the clutch 72 is isolated from that for actuating the clutch 74
: except for the connection Via restricted line 93, this isolation
; being an important feature since it permits the wheels 16 and 18
to overrun the wheel motors 64 and 66 either together, as might ~-
; occur when the grader is travelling straight, or individually, as
occurs when the grader is making a turn. The restricted line 93
functions during such turning to develop a partial differential
. lock action to reduce scuffing of the tires and also functions as
a pressure equalizer between the lines 90 and 92 to return the
~ spool of the flow divider-combiner valve 86 from a position
; wherein it restricts the flow path to the idling wheel during the
turn to a centered unbiased dividing position after the turn has
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1 been completed so that the idling wheel motor during the turn
again develops torque.
Energization of the reverse drive solenoid-operated valve ;
140 is effected, in a manner to be presently descrlbed, in re-
sponse to the main traction drive transmission becoming fully
engaged for reverse driving. Energi~ation of the valve 140
results in the latter being shifted leftwardly to connect the
line 138 to the line 144 to thus connect fluid pressure to the
line 136 and hence to both of the shuttle valves 120 and 132.
` 10 The check balls of the valves 120 and 132 will then seat to
prevent flow to draln via the deenergized valves 116 and 128
while permitting flow to the clutches 72 and 74 via the lines 124
i and 134.
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The operation of that paxt of the front wheel drive system
62 described hereinabove is selectively automatically controlled
by electrical circuitry 150 forming a part of the system 62.
; Specifically, the circuitry 150 includes an electronic control
I box 152 containing control circuitry ~not shown) for processing
various electrical input signals, described hereinafter, and
sending out control signals to the linear electrohydraulic actu-
ator 108 via forward and reVer9e drive signal leads 154 and 156,
respectively, connected between the box 152 and the actuator 108.
It is here noted that while the specifics of the control circui-
try contained in control box 152 forms no part of the invention
claimed herein, specific circuitry for use in the control box 152
~ is described in Can. Patent application Ser. No. 323,120 filed
:l on an even date with and having the same assignee as does the
~ instant application. Power for the signal-processing circui-
,1 . .
try in the control box 152 is provided by a battery l58 connected
to the box 152 by a power supply lead 160 containing an ignition
switch 162 connected in series with a switch 164 positioned to be
closed by a cam (not shown) in response to moving the gear selec-
tor lever 32 to shift the transmission 46 to gears 1-4. The
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1 power lead 160 connects to a lead 166 located within the control
box 152 and containing an on-off switch 168. Thus, it will be
appreciated that no power will be supplied to the box unless all
of the switches 162, 164 and 166 are closed.
A lead 170 is connected to the control box 152 such as to
join the lead 166, the lead 170 branching at a junction 172 into
a forward drive lead 174 connected to the right and left forward
drive solenoid-operated valves 116 and 128 and into a reverse
drive lead 176 connected to the reverse drive solenoid-operated
10 valve 140. Contained in the lead 170 is a pressure-operated
switch 178 which opens when the main clutch pedal 36 is depressed
to release the clutch 47. Respectively contained in the leads
174 and 176 are, normally open, forward and reverse drive switches
180 and 182 that are respectively closed by cams (not shown)
operated in response to the direction control lever 34 of the
transmission being placed in forward and reverse drive effecting
positions. Also contained in the lead 174 is a normally open
pressure-operated switch 184 which is closed when the forward
;` drive effecting clutch 48 of the transmission 46 becomes fully
engaged. Similarly, the lead 176 contains a normally open,
pressure-operated switch 186 which is closed when the reverse
drive effecting brake 49 of the transmission 46 becomes fully
engaged.
The sensorS 60 and 82 are respectively connected, via command
and feedback input signal leads 188 and 190, to the control box
152 for providing signals for processing by the circuitry in the
control box to determine the magnitude of the slgnals outputted
to the linear electrohydraulic actuator 108. The sensors 60 and
82 are not direction sensitive, however, proper polarity of the
; 30 signal outputted to the actuator 108 is ensured as follows. A
forward drive input signal lead 192 is connected to the control
box 152 and to the forward drive lead 174 such as to be energized
only when the forward drive switch 180 is closed. Similarly, a
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1 reverse drive input signal lead 194 is connected to the control
box 152 and to the reverse drive lead 176 such as to be energized
only when reverse drive switch 182 is closed.
The auxiliary drive system 62 has been found to operate most
efficiently when applied to a motor grader equipped as disclosed
by the applicant if the front wheel motors 64 and 66 are con-
trolled to develop torque only after the main traction drive
wheel sets 24 and 26 develop approximately 2-1/2% slip. Accord-
ingly, the circuitry in the control box 152 has been set up to
effect such control of the front wheel motors.
However, under some woxking conditions with the grader 26
working on a slope for example, it may be desirable for the front
wheels to be aggressive to keep the grader tracking properly on
the slope and for these conditions the circuitry in the control
box includes an "aggressive loop" which may be selectively
switched into circuit by a control switch 196 mounted on the
control box 152. When the circuit is in its aggressive mode, the
wheel motors 64 and 66 are controlled to operate at a speed 1
, greater than that of the rear wheel sets 24 and 26.
While the circuitry in the control box 152 is described
herein as being operable to produce only one under speed and one
over speed mode of operation, it is to be understood that the
circuitry could be modified such as to be capable of adjustment
.:.
to effect an infinite number of operating modes with a desired
operating range.
The auxiliary front wheel drive system 62, as applied to the
motor grader 10, operates in the following manner.
In order for the auxiliary drive system 62 to be activated
; for auxiliary drive operation, the battery 158 must be connected
to the control circuitry in the control box 152. The operator
accomplishes such activation by closing the ignition switch 162,
; by shifting the gear selector lever 32 to any one of its posi-
`~ tions for effecting gears 1 - 4 in the transmission, such posi-
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~13~33~
1 tioning effecting the closing of the switch 164, and by moving
the auxiliary drive selector switch 168 to its "on" position.
With power connected to the control box 152, the sensors 60 and
82 are energized for sending signals representative respectively
of the average speed of the rear wheel sets 24 and 26 and of the
: speed of the rotor 78 of the left wheel motor 66.
Assuming that the operator has caused the system 62 to be
energized in the manner just described but that the direction
selector lever 34 is in its neutral position, the motor grader
will be standing still and consequently the sensors 60 and 82
will not be sending any signals for processing by the circuitry
in the control box 152 and no output signals will be sent to
energize the llnear electrohydraulic actuator 108 and the swash -
. plate 96 of the pump 84 will thus remain in its centered posltion
wherein it effects the zero-displacement condition in the pump. ~ :
If the operator should then desire to drive the grader 10
forwardly, he needs only to place the direction selector lever 34
in its forward position for effecting a forw~rd driving condition .
in the transmission 46. Such moVement of the lever 34 immedi-
ately closes the forward drive switch 180 and assuming that the
main traction drive clutch is ully engaged, as it should be with
the main clutch control pedal 36 released, the main clutch pres-
sure-responsive switch 178 will also be closed thus completing a
circuit between the battery 158 and the forward drive lead 174
.. and forward drive input signal lead 192. Then upon the forward
. drive clutch hecoming fully engaged, the forward drive clutch
: pressure-responsive sWitch 184 will close to energize the right
and left forward drive solenoid-operated valves 116 and 128 to
i; shift the latter leftwardly, thus resulting in the supply-return
line 90 being connected for supplying fluid pressure to the
clutch 72 and in the supply-return line 92 being connected for
supplying fluid pressure to clutch 74.
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1 With the transmission 46 thus placed in its forward driving :
condition, forward drive torque will be transmitted therefrom to ; :
the rear traction wheel sets 24 and 26 via the differential
gearing 50, which also drives the park brake disc 51 at a speed
corresponding to the average speed of rotation of the wheel sets
24 and 26. Upon initial rotation of the disc 51, the sensor 60
begins to send electrical pulse command input signals, representa-
tive of the speed of such rotation, to the control box 152 for
processing. It is noted that at this time, the control box 152
will not be receiving any feed back input signals from the sensor
82 as the left wheel motor 66 will not yet be drlving its rotor
78. Assuming that the operator has preselected the condition of
the control circuitry in the control box 152 $or controlling the
left wheel motor 66 to drive at a speed 2-1/2% less than the ~-
speed represented by the signal sent by the sensor 60, the control
, circuitry will process the command and eedback input signals
respectively received from sensors 60 and 82 and send an output
signal to the electrohydraulic lineax actuator 108, via forward
drive lead 154. The output signal has a magn:ltude for energizing
the actuator 108 such that it controls the pilot valve for effect-
ing movement of the swash plate 96 of the pump 84 to a position
corresponding to that for displacing fluid from the line 94 to
the line 86 in a quantity sufficient for causing the rotor 78 of
the wheel motor 66 to rotate at a speed 2-1/2~ less than the
. average speed of the rear wheel sets 24 and 26. Once the valve
spool of the pilot valve has been shifted and the actuator begins
~ to adjust the angular position of the swash plate 96, the feed
;'~! back linkage operates to reposition the valve spool to its neutral
position. The fluid delivered to the line 88 by the pump 84 is
divided by the flow divider-combiner valve to flow to the lines
90 and 92 such as to drive the motors 64 and 66 at equal speeds,
the pressurized fluid in the lines 90 and 92 also being connected
~ to the clutches 72 and 74 by virtue of the fact that the solenoid-
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1 operated valves 116 and 178 are now energized as described
hereinabove.
Of course, once the left wheel motor 66 begins driving, the
sensor 82 begins to send an electrical closed loop feedback input
signal to the control box 152 for processing together with the
command input signal from the sensor 60.
: Assuming that the motor grader 10 is traveling straight
ahead and that the rear wheel sets 24 and 26 are not slipping the
front wheels 16 and 18 will be rotating at the same speed as the
rear wheel sets and this speed will exceed that which the motors
64 and 66 are regulated to drive by 2-1/2%. While the pressure
required in the lines 90 and 92 for overcoming internal resis- :
tances of the motors 64 and 66 and driving their rotors is suffi-
cient for effectlng engagement of the clutches 72 and 74 to
.~ thereby establish driving connections between the motor 64 and
wheel 16 and between the motor 66 and wheel 18, it ~ill be appre-
ciated that, as soon as such connections are established, the
wheels drive the motors resulting in the pressure in the lines 90
, and 92 being reduced below that necessary for engaging the
,: 20 clutches to permit the wheels to oVerrun the motors. Thus, the
pressure in the lines 90 and 92 modulates abo~e and below that
necessary for effecting engagement of the clutches 72 and 74 to
thus permit the wheels 16 and 18 to overrun the motors 64 and 66
and in this way avoid main-to-auxiliary drive torque inter-
ferences.
Next, assuming that the motor grader 10 continues to be
travelling straight ahead as before but now with the rear wheel
sets 24 and 26 developing at least 2-1/2% slip, the wheels 16 and :~ :
. 18 will no longer be operating at speeds which are faster than
.: 30 that developed by the motors 64 and 66 and, consequently, the ~ ~
pressure in the lines 90 and 92 will be sufficient to maintain ~:
the clutches 72 and 74 in engagement. If the motor grader 10 is
~: then caused to turn sharply to the left, for example, the outside
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1 right wheel 16 will be caused to rotate faster than the motor 64
and will consequently drive the motor 64 such as to reduce the
pressure in the line 90 below that required for maintaining
engagement of the clutch 72. The wheel 16 then overruns the
motor 64, to avoid torque interferences, while the motor 66
; drives the left wheel 18. The wheel 18 will similarly overrun
the motor 16 when the motor grader 10 is turned sharply to the
right.
It is to be noted that during turning the divider-combiner
valve 86 will operate to restrict the flow path to the outside
wheel and that once the turn is completed the restricted passage
93 will act to equalize the pressures in the lines 90 and 92 to
ensure that the valve 86 will be repositioned to an unbiased
dividing position. Also, durin~ turnin~ with both motors 64 and
66 driving the wheels 16 and 18, the restricted passage 93 will
act to bleed drive pressure from that one o the lines 90 and 92,
which is connected to the motor driving the inside wheel, to the
other line so that a partial differential lock condition is
; established which results in reduced tire scuffing.
~; 20 The motor grader 10 may be shifted from its forward driving
condition to operate in reverse by moving the direction selector
lever 34 from its forward to its reverse posltion to effect a
reverse drive condition in the main traction drive transmission
46. At the same time, the auxiliary drive system 62 is readied
for reverse drive operation. Specifically, movement of the lever
34 to its reverse position effects opening the forward drive
. .
switch 180 and closing of the reverse drive switch 182. This
connects the battery 158 to the reverse drive lead 176 and to the
reverse drive input signal lead 194. The movement of the lever
34 also effects the disconnection of hydraulic control pressure
from the forward drive clutch 48 and connection of control pres-
sure to the reverse drive brake 49 of the transmission. The
forward drive pressure switch 184 opens, upon the reduction of
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1 forward drive clutch pressure, to de-energize the right and left
forward drive solenoid-operated valves 116 and 128, which results ~:
in the release of clutches 72 and 74. Upon the reverse drive ~ -
brake 49 of the main transmission 46 becoming fully engaged, the
reverse drive pressure switch 186 closes to energize the reverse :
drive solenoid-operated valve 140 which shifts leftwardly to
; connect the supply-return line 94 in fluid communication with the
clutches 72 and 74. At this time, it is possible for the motors .
64 and 66 to drive the wheels 16 and 18 to augment the main
traction drive in the event that the rear wheel sets 24 and 26
develop at least 2-1/2% slip. Thus, it will be appreciated that
the switches 180 and 182, operated by the direction selector
.l lever 34, work in conjunction with the pressure-operated swltches
184 and 186 to immediately disconnect the auxiliary drive motors
. 64 and 66 from the wheels 16 and 18, upon the direction selector
; lever 34 being moved from one to the other of its operating
positions, and then to reconnect the auxiliary drive motors to
the front wheels for driving them in the opposite direction only
after the main traction drive tXansmission i8 dxivin~ the rear
wheel sets 24 and 26 in the opposite direction. In this way, the
engagement and disengagement of the main and auxiliary drive
systems are timed so that one drive system does not work against
the other. This is especially desirable when the direction
selector lever 34 is being shuttled between its forward and
reverse positions so as to cause the motor grader 10 to be rocked -
~for dislodging it from a mud hole, for example.
Upon the gear selector levex 32 being shifted to neutral or
to any one of its positions 5 - 8 for establishing corresponding
gears in the tXansmission 46, the switch 164 will be automat-
ically opened to disconnect the battery 158 from the control box
: 152 to effect deactivation of the auxiliary drive system 62 and
consequently deswashing of the pump 84 so that the motors 64 and
, ~
. 66 are no longer driven and the clutches 72 and 74 are no longer
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~13~3~ ~
1 engaged. Deactivation of the auxiliary drive 62 when the trans-
mission 46 is in neutral is a safety measure while deactivation
of the auxiliary drive when the transmission is shifted to one of
its gears 5 - 8, where need for auxiliary traction is normally
not needed, permits free wheeling of the wheels 16 and 18 and
discontinues unnecessary fluid flow through the hydraulic circui-
try of the auxiliary drive system 62.
During operation o the grader 10, it may become necessary
, to quickly stop. This is usually done by applying the brakes
subsequent to depressing the main clutch pedal 36 to disengage
the clutch 47. Disengagement o the clutch 47, automatlcally de-
activates the front wheel drive system 62 by causing the pressure
switch 178 to open and disconnect the battery 158 from the direc-
tion signal input lines 192 or 194 and rom the solenoid-operated
valves 116 and 128 or 140 to instantly disengage the wheels from
the wheel motors to ensure that the motor grader 10 will be
~, brought to a safe stop.
Another instance when the clutch pedal 36 is depressed such
:.,
as to effect deactivation of the auxiliary drive system 62 is
during inching operation. The pressure at which the switch 178
closes is such that the auxiliary drive system 62 in no way
interferes with the inching operation.
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