Note: Descriptions are shown in the official language in which they were submitted.
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VEHICULAR DRIVE SYSTEM WITH FWD-ONLY MODE AND ASSOCIATED
METHOD
[0001]
Field of the Disclosure
[0002] The present disclosure relates to vehicular drive systems and
methods
associated therewith.
Background of the Disclosure
[0003] A variety of drive systems may be used to propel work vehicles. For
example, there are front-and-rear-wheel-drive (FWD-and-RWD) systems (e.g., all-
wheel drive or less than all-wheel drive), front-wheel-drive (FWD) systems,
and rear-
wheel-drive (RWD) systems.
[0004] A typical drive system for motor graders allows operation of the
motor
grader in a FWD-and-RWD mode, a FWD-only mode (may also be referred to as
"precision mode" or "creep mode"), or a RWD-only mode. The drive system may be
switched between these modes.
[0005] The FWD-only mode allows operation of the motor grader at reduced
speeds which may be particularly useful for maneuvering in relatively tight
areas (e.g.,
in a cul-de-sac), fine grading, and miffing through pavement, to name just a
few
possible uses. However, at least in some cases, the motor grader must be
stationary
to engage FWD-only mode. Thus, in such cases, an operator desiring to engage
FWD-only mode must first stop the motor grader before engaging FWD-only mode,
adding to the work load of the operator and decreasing overall productivity.
Summary of the Disclosure
[0006] According to the present disclosure, there is provided a drive
system for a
work vehicle. The drive system comprises a speed ratio setting input device, a
drive-
request input device, and a control unit arranged for communication with the
speed
ratio setting input device and the drive-request input device. The control
unit is
adapted to: monitor output of the speed ratio setting input device for a speed
ratio
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setting request signal and output of the drive-request input device for a FWD-
only
request signal, determine from the speed ratio setting request signal if a
requested
speed ratio setting represented thereby is one of at least one predetermined
speed
ratio setting among a plurality of speed ratio settings possible for the work
vehicle
upon receipt of the FWD-only request signal, and, if so, output at least one
control
signal engaging a FWD-only mode enabling FWD operation of the work vehicle but
disabling RWD operation of the work vehicle.
[0007] In this way, exemplarily, the work vehicle can assume a FWD-only mode
of
operation "on the fly" while the vehicle is moving along a surface (i.e.,
without
requiring the vehicle to stop) simply by switching the drive-request input
device to an
"on" position requesting FWD-only operation and shifting the transmission
shifter of
the vehicle to one of a number of predetermined speed ratio settings (e.g.,
forward
first gear, forward second gear, or forward third gear). Further, the work
vehicle can
be switched back to a FWD-and-RWD mode of operation again "on the fly" simply
by
either switching the drive-request input device to an "off' position or
shifting the
transmission shifter to assume a speed ratio setting other than one of the
predetermined speed ratio settings (e.g., anything but forward first, second,
or third
gear such as, for example, any reverse gear or a forward gear higher than
third
gear).
[0008] An associated method is disclosed. Exemplarily, the method comprises
monitoring for a speed ratio setting request signal and for a FWD-only request
signal, determining from the speed ratio setting request signal if a requested
speed
ratio setting represented thereby is one of at least one predetermined speed
ratio
setting among a plurality of speed ratio settings possible for the work
vehicle upon
receipt of the FWD-only request signal, and, if so, outputting at least one
control
signal engaging a FWD-only mode enabling FWD operation of the work vehicle but
disabling RWD operation of the work vehicle.
[0009] The above and other features will become apparent from the following
description and the attached drawings.
Brief Description of the Drawings
[0010] The detailed description of the drawings refers to the accompanying
figures
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in which:
[0011] FIG. 1 is a side elevational view of a work vehicle in the form of, for
example, a motor grader;
[0012] FIG. 2 is a diagrammatic view showing a drive system for the work
vehicle;
and
[0013] FIG. 3 is a view of a control routine to be performed by a control unit
of the
drive system.
Detailed Description of the Drawings
[0014] Referring to FIG. 1, there is shown a work vehicle 10 which has a drive
system 12 shown in FIG. 2 for controlling whether a FWD-only mode of operation
is
engaged according to a control routine 14 shown in FIG. 3.
[0015] Exemplarily, the work vehicle 10 is illustrated as a motor grader. In
such a
case, the motor grader has a moldboard or blade 16 for grading material. The
moldboard 16 is part of a front section 18 of the motor grader, the front
section 18
being articulated to a rear section 20 for relative movement between the
sections 18,
20 about an articulation axis 22.
[0016] The front section 18 has a pair of front drive wheels 24 (one shown in
FIG.
1). Each front drive wheel 24 is driven, for example, by an associated
hydrostatic
transmission 26. Each hydrostatic transmission 26 has a pump 27 and motor 29.
The pumps 27 are mechanically operated by an engine 74 housed in an engine
compartment 34 on the rear section 20. Such operation of the pumps 27, in
turn,
operate the motors 29 to drive the wheels 24. The two hydrostatic
transmissions 26
cooperate to provide a FWD transmission 28, as shown, for example, in FIG. 2.
In
some embodiments, the transmission 28 may be a single-path hydrostatic
transmission serving both front wheels 24 instead of the illustrated dual-path
hydrostatic transmission. More generally, in some embodiments, the FWD
transmission 28 may take the form of something other than a hydrostatic
transmission such as, for example, a direct drive, a torque converter, or an
electric
drive, to name but a few.
[0017] The rear section 20 has a pair of tandem arrangements, one on each side
of
the rear section 20 as shown with respect to one of the tandem arrangements in
FIG.
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1. Each tandem arrangement has a pair of rear drive wheels 30. The rear drive
wheels 30 are driven by a RWD transmission 32 (e.g., a direct drive
transmission)
operated by the engine 74. The RWD transmission 32 may take the form of
something other than a direct drive transmission such as, for example, a
hydrostatic
transmission, a torque converter, or an electric drive, to name but a few.
[0018] The work vehicle 10 may be operated in a number of different drive
modes.
For example, it may be operated in a FWD-and-RWD mode, a RWD-only mode, or a
FWD-only mode. In the FWD-and-RWD mode, both FWD operation and RWD
operation are enabled (e.g., all-wheel-drive). In the RWD-only mode, RWD
operation is enabled but FWD operation is disabled. In the FWD-only mode, FWD
operation is enabled but RWD operation is disabled. The FWD-only mode may be
engaged and disengaged as discussed below in connection with FIGS. 2 and 3. It
is
to be understood that, in each of these modes, all or less than all of the
wheels of the
applicable enabled section 18, 20 may act as drive wheels.
[0019] Referring to FIG. 2, the drive system 12 comprises a control unit 36
which
receives inputs from a speed ratio setting input device 38 and a drive-request
input
device 40 and generates outputs to the FWD and RWD transmissions 28, 32. In
particular, the control unit 36 is arranged for communication with the speed
ratio
setting input device 38 and the drive-request input device 40 and is adapted
to:
monitor output of the speed ratio setting input device 38 for a speed ratio
setting
request signal and output of the drive-request input device 40 for a FWD-only
request signal, determine from the speed ratio setting request signal if a
requested
speed ratio setting represented thereby is one of at least one predetermined
speed
ratio setting among a plurality of speed ratio settings possible for the work
vehicle 10
upon receipt of the FWD-only request signal, and, if so, output at least one
control
signal engaging a FWD-only mode enabling FWD operation of the work vehicle 10
but disabling RWD operation of the work vehicle 10.
[0020] The control unit 36 may be configured in a variety of ways. For
example, in
some embodiments, the control unit 36 may be a single electronic controller.
In
other embodiments, the control unit 36 may comprise multiple electronic
controllers
interconnected for communication therebetween. Illustratively, the control
unit 36 is
configured as a controller network including an electronic FWD controller 42,
an
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electronic RWD controller 44 (which may also be referred to as the
transmission
controller), and a communications bus 46 [e.g., controller area network (CAN)
bus]
interconnecting the controllers 42 and 44 for communication therebetween. Each
controller 42, 44 includes a processor 48 and a memory 50, the memory 50
having a
plurality of instructions stored therein which, when executed by the processor
48,
cause the processor 48 to perform the various functions of the respective
controller
42, 44.
[0021] The speed ratio setting input device 38 is located, for example, at an
operator's station 52 of the vehicle 10 for actuation by the operator to
establish the
speed ratio setting of the vehicle 10. Exemplarily, the speed ratio setting
input
device 38 includes a transmission shifter 54 and a shifter position sensor 56.
An
operator requests a speed ratio setting for the vehicle 10 by movement of the
shifter
54 to a position corresponding to the requested speed ratio setting. The
sensor 56
senses the position of the shifter 54 and outputs a requested speed ratio
setting
signal representative of the requested speed ratio setting to the RWD
controller 44.
The RWD controller 44 monitors the output of the sensor 56 for the requested
speed
ratio setting signal.
[0022] The drive-request input device 40 may also be located at the operator's
station 52 for actuation by the operator to enable activation of the FWD-only
mode.
The drive-request input device 40 may be configured, for example, as an on-off
rocker switch. Switching to the on position enables activation of the FWD-only
mode
whereas switching to the off position disables activation of the FWD-only
mode. The
FWD controller 42 monitors output of the drive-request input device for the
FWD-only
request signal.
[0023] From time to time, the vehicle operator may request that the speed
ratio
setting change from a reverse speed ratio setting to a predetermined forward
speed
ratio setting to effect a change in direction of the vehicle 10 from reverse
to forward
and, at the same time, request FWD-only mode. However, if the vehicle 10 were
to
engage the FWD-only mode immediately upon such a change request, the FWD
system 71 under the control of the FWD controller 42 may not be able to
generate
sufficient tractive effort through the FWD transmission 28 and front drive
wheel(s) 24
to accomplish the direction change from reverse to forward, possibly resulting
in
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undesirable skidding or spinning of the front drive wheel(s) 24 and/or
excessive
vehicle roll-out in the reverse direction.
[0024] The vehicle 10 may be configured to address this situation. Instead, of
automatically immediately engaging the FWD-only mode, the modified control
routine 114 waits until the RWD 72 starts to operate in the forward direction.
Once
that occurs, the FWD-only mode is engaged.
[0025] In particular, the control unit 36 is adapted to determine if (i) the
FWD-only
mode is requested based on the FWD-only request signal, (ii) the requested
speed
ratio setting is changed from a reverse speed ratio setting to a predetermined
forward speed ratio setting of the at least one predetermined speed ratio
setting
(e.g., first, second, or third forward gears of the RWD transmission 32) based
on the
speed ratio setting request signal, and (iii) the RWD system 72 of the vehicle
10
under the control of the RWD controller 44 is operating in the forward
direction. If
those conditions [i.e., conditions (i), (ii), and (iii)] are met, the control
unit 36 is
adapted to output at least one control signal engaging the FWD-only mode.
[0026] To determine if the requested speed ratio setting is changed from a
reverse
speed ratio setting to a predetermined forward speed ratio setting, the RWD
controller 44 monitors output of the shifter position sensor 56 for a shifter
position
signal representing the position of the transmission shifter 54. The RWD
controller
44 determines from this signal if the shifter 54 has been switched from a
reverse
speed ratio setting to one of the predetermined forward speed ratio settings
(e.g.,
first, second, or third forward gears).
[0027] A direction sensor 74 may be employed to sense a direction 78 of
operation
(i.e., forward or reverse) of the RWD system 72. In such a case, the RWD
controller
44 monitors output of the direction sensor 74 for a direction signal
representative of
the direction in which the RWD system 72 is operating and determines from the
direction signal if the RWD system 72 of the vehicle 10 is operating in the
forward
direction.
[0028] The direction sensor 74 may be associated with a transmission output
shaft
76 of the RWD transmission 32 to sense the direction 78 (i.e., forward or
reverse) of
the shaft 76 and output the direction signal representative thereof to the RWD
controller 44. The direction sensor 74 may be, for example, a shaft speed
sensor
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capable of sensing the direction in which the shaft is rotating. In other
examples, the
direction sensor 74 may include other sensors including, but not limited to,
one or
more of a clutch pressure sensor, front tire speed, and/or the like.
[0029] Once the control unit 36 determines that the RWD system 72 is operating
in
the forward direction (e.g., the transmission output shaft is rotating in the
forward
direction), the RWD controller 44 outputs a control signal to the RWD
transmission
32 causing the RWD transmission 32 to go to neutral, disabling RWD operation.
Further, the FWD controller 42 outputs at least one control signal to the FWD
transmission 28 (e.g., a control signal to each pump 27) engaging FWD
operation.
Such FWD operation may be a continuation of FWD operation in reverse or may be
the commencement of FWD operation. In either case, the FWD-only mode is thus
assumed.
[0030] Referring to FIG. 3, there is shown a control routine 14 performed by
the
control unit 36. In act 60, the control unit 36 monitors output of the speed
ratio
setting input device 38 for the speed ratio setting request signal, output of
the drive-
request input device 40 for the FWD-only request signal, and output of the
direction
sensor 74 for the direction signal. In particular, the RWD controller 44
monitors the
output of the shifter position sensor 56 for the speed ratio setting request
signal, and
the output of the direction sensor 74 for the direction signal. The FWD
controller 42
monitors output of the drive-request input device 40 for the FWD-only request
signal.
[0031] In act 62, the control unit 36 determines if there is a request for FWD-
only
(e.g., the operator has switched the rocker switch to its on position). If no,
the
control routine 14 returns to act 60. In doing so, if the FWD-only mode had
already
been engaged, the control unit 36 disengages the FWD-only mode and engages,
for
example, the FWD-and-RWD mode in act 64 prior to return to act 60. If there is
a
FWD-only request, in response to receipt of the FWD-only request signal, the
FWD
controller 42 broadcasts a FWD-only message to the RWD controller 44 via the
communications bus 48 to inform the RWD controller 44 that there is a FWD-only
request. Upon receipt of this message, the RWD controller 44 determines that
there
is a FWD-only request and the control routine 14 advances to act 66.
[0032] In act 66, the control unit 36 determines from the speed ratio setting
request
signal if a requested speed ratio setting represented thereby is one of at
least one
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predetermined speed ratio setting among a plurality of speed ratio settings
possible
for the work vehicle 10 upon receipt of the FWD-only request signal. If no,
the
control routine 14 returns to act 60, performing act 64 on its way to act 60
if
applicable. If yes, the control routine 14 advances to act 67.
[0033] The at least one predetermined speed ratio setting is, for example, a
plurality of predetermined speed ratio settings, the plurality of
predetermined speed
ratio settings being only a portion of the speed ratio settings possible for
the work
vehicle 10. In some embodiments, the plurality of predetermined speed ratio
settings are the first three forward speed ratio settings of the vehicle 10
(e.g., first,
second, and third forward gears). The number of total speed ratio settings
possible
for the vehicle 10 depends on the type of vehicle at issue. For example, in
the
context of a motor grader, there may be eight forward speed ratio settings and
eight
reverse speed ratio settings, such that movement of the shifter 54 to any of
the first
three forward speed ratio settings is a condition for engagement of the FWD-
only
mode. In some embodiments, the plurality of predetermined speed ratio settings
may include any one or more reverse speed ratio settings in which case the
vehicle
would operate in reverse in the FWD-only mode.
[0034] In act 67, the control unit 36 determines if the requested speed ratio
setting
was changed from a reverse speed ratio setting to a predetermined forward
speed
ratio setting of the at least one predetermined speed ratio setting (e.g.,
from any
reverse gear to one of the first, second, or third forward gears). If no, the
control
routine 14 advances to act 69 for engagement of the FWD-only mode. If yes, the
control routine 14 advances to act 68.
[0035] In act 68, the control unit 36 (e.g., the RWD controller 44) outputs at
least
one control signal operating the RWD system 72 in forward, such that at least
RWD
operation in forward is engaged, whether the FWD system 72 is operated or not
(i.e.,
in FWD-and-RWD mode or in RWD-only mode). Further, in act 68, the control unit
36 (e.g., the RWD controller 44) continues to monitor output of the direction
sensor
74 for the direction signal and thus the direction of operation of the RWD
system 72
(e.g., the transmission output shaft 76). The control routine 14 advances to
act 69.
[0036] In act 69, the control unit 36 determines if the RWD system 72 is
operating
in the forward direction. Exemplarily, the RWD controller 44 determines from
the
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direction signal of the direction sensor 74 if the transmission output shaft
76 (or other
directional component) is rotating in the forward direction. If no, the
control unit 36
loops back to act 68, so as to continue to command RWD operation in the
forward
direction and monitor output of the direction sensor 74 to determine, thus
delaying
engagement of the FWD-only mode until the RWD system 72 begins to operate in
forward. If yes, the control routine 14 advances to act 70. In the motor
grader
context, this means that the rear tandem arrangements will be commanded to
operate in the forward direction until it is detected that they have begun to
operate in
the forward direction by virtue of rotation of the shaft 76 in the forward
direction, after
which they can be disengaged (by putting the transmission in neutral) for
engagement of the FWD-only mode.
[0037] In act 70, the control unit 36 outputs at least one control signal
engaging the
FWD-only mode enabling FWD operation of the work vehicle 10 but disabling RWD
operation of the work vehicle 10. In particular, the FWD controller 42 outputs
control
signals commanding operation of the FWD transmission 28 such that the pumps
27,
which are powered by the engine 74, drive the front wheels 24 through the
motors 29
while the RWD controller 44 outputs a control signal commanding the RWD
transmission to neutral so as to disengage the rear wheels 30 from the engine
74.
[0038] While the FWD-only mode is engaged, the control routine 14 loops back
to
act 60 where the control unit 36 continues to monitor output of the devices 38
and
40. If, at some point, either the drive-request input device 40 ceases to
signal a
FWD-only mode request (act 62) or the speed ratio setting input device 38
ceases to
output a signal representative of any of the predetermined speed ratio
setting(s)
(e.g., first, second, or third forward gears) (act 66), the control unit 36
will in act 64
disengage the FWD-only mode and engage either the FWD-and-RWD mode (e.g.,
six-wheel-drive mode on the motor grader) or the RWD-only mode (e.g., four-
wheel-
drive mode on the motor grader) causing the RWD controller 44 to output a
control
signal commanding the RWD transmission 32 to assume a speed ratio setting
based
on the input from the speed ratio setting input device 38.
[0039] When in the FWD-only mode, ground speed may be adjusted by use of a
trim device 58. In particular, the trim device 58 may be located at the
operator's
station 52 for precision adjustment of the speed ratio setting selected by the
operator
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upon manipulation of the shifter 54. The trim device 58 may be configured, for
example, as a 15-position rotary dial, the output of which is monitored by the
FWD
controller 42. In response to the output of the trim device 58, the FWD
controller 42
may output control signals to the pumps 27 to cause precision adjustment of
the
requested speed ratio setting, resulting in an adjustment of the ground speed.
[0040] In the example of the rotary dial, position 15 of the rotary dial
may be set so
as not to command any adjustment whereas the other positions may be set to
command a corresponding adjustment, position 1 resulting in the greatest
adjustment
(i.e., the minimum speed). Exemplarily, at an engine speed of about 1200 rpm
(revolutions per minute) with the trim device 58 in its lowest speed position
(e.g.,
position 1 in the case of the rotary dial example), the ground speed in first
forward
gear may be about 1.4 mph (miles per hour) in FWD-and-RWD mode but only about
0.4 to about 0.5 mph in FWD-only mode, the ground speed in second forward gear
may be about 1.9 mph in FWD-and-RWD mode but only about 0.75 to about 1.0 mph
in FWD-only mode, and the ground speed in third forward gear may be about 2.5
mph
in FWD-and-RWD mode but only about 1.5 to about 2.0 mph in FWD-only mode.
[0041] Ground speed in the FWD-only mode may also be affected by engine
speed. In such a case, an electronic engine controller 72 included in the
control unit 36
for control of the engine 74 monitors output of an engine speed sensor 70 for
an
engine speed signal representative of the engine speed of the engine 74. The
engine
controller 72 communicates this engine speed over the communications bus 74 to
the
FWD controller 42 which then may output control signals to the pumps 27 to
vary the
displacement setting of the pumps 27 (e.g., swashplate angle) in view of the
engine
speed so as to adjust the ground speed of the vehicle 10.
[0042] While the disclosure has been illustrated and described in detail in
the
drawings and foregoing description, such illustration and description is to be
considered as exemplary and not restrictive in character, it being understood
that
illustrative embodiments have been shown and described and that all changes
and
modifications that come within the scope of the disclosure are desired to be
protected.
It will be noted that alternative embodiments of the present disclosure may
not
include all of the features described yet still benefit from at least some of
the
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advantages of such features. The scope of the claims should not be limited by
particular embodiments set forth herein, but should be construed in a manner
consistent with the specification as a whole.
