U.S. patent application number 14/896441 was filed with the patent office on 2017-04-13 for work vehicle and method of controlling work vehicle.
The applicant listed for this patent is KOMATSU LTD.. Invention is credited to Kazunori NISHIMURA.
Application Number | 20170101763 14/896441 |
Document ID | / |
Family ID | 55533382 |
Filed Date | 2017-04-13 |
United States Patent
Application |
20170101763 |
Kind Code |
A1 |
NISHIMURA; Kazunori |
April 13, 2017 |
WORK VEHICLE AND METHOD OF CONTROLLING WORK VEHICLE
Abstract
A work vehicle includes an engine, a variable displacement
hydraulic pump, a hydraulic motor, an exhaust treatment device, and
a controller. The engine drives the variable displacement hydraulic
pump. The variable displacement hydraulic pump is able configured
to change the discharge direction of the hydraulic fluid. Depending
on the discharge direction of the hydraulic oil from the variable
displacement hydraulic pump, the hydraulic motor is configured to
change the driving direction to the forward direction or the
reverse direction. The exhaust treatment device is configured to
treat the exhaust from the engine. The controller is configured to
increase the speed of the engine to a predetermined first speed or
greater and to change the discharge direction of the variable
displacement hydraulic pump to a neutral state during regeneration
of the exhaust treatment device.
Inventors: |
NISHIMURA; Kazunori;
(Komatsu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOMATSU LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
55533382 |
Appl. No.: |
14/896441 |
Filed: |
October 9, 2015 |
PCT Filed: |
October 9, 2015 |
PCT NO: |
PCT/JP2015/078853 |
371 Date: |
December 7, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F15B 2211/30525
20130101; B60W 10/103 20130101; B60W 2710/1066 20130101; E02F
9/2235 20130101; B60W 2710/0644 20130101; E02F 3/34 20130101; B60W
2300/17 20130101; E02F 9/0866 20130101; F01N 3/20 20130101; F15B
2211/85 20130101; B60W 10/06 20130101; F02D 41/027 20130101; F01N
3/103 20130101; E02F 9/20 20130101; B60Y 2200/411 20130101; F01N
3/025 20130101; E02F 9/2253 20130101; E02F 9/2296 20130101; F01N
3/2066 20130101; F15B 9/04 20130101; F01N 3/08 20130101; F15B 9/09
20130101 |
International
Class: |
E02F 9/22 20060101
E02F009/22; B60W 10/06 20060101 B60W010/06; B60W 10/103 20060101
B60W010/103; F02D 41/02 20060101 F02D041/02; F15B 9/09 20060101
F15B009/09; F01N 3/20 20060101 F01N003/20; F01N 3/10 20060101
F01N003/10; E02F 9/08 20060101 E02F009/08; F15B 9/04 20060101
F15B009/04 |
Claims
1. A work vehicle comprising: an engine; a variable displacement
hydraulic pump having a variable discharge direction, and driven by
the engine; a hydraulic motor configured to change a driving
direction to a forward direction or a reverse direction depending
on the discharge direction of the hydraulic oil from the variable
displacement hydraulic pump; an exhaust treatment device configured
to treat exhaust from the engine; and a controller configured to
increase a speed of the engine to a predetermined first speed or
greater and to change the discharge direction of the variable
displacement hydraulic pump to a neutral state during regeneration
of the exhaust treatment device.
2. The work vehicle according to claim 1, further comprising a
forward-reverse travel switching valve for switching the discharge
direction of the hydraulic oil from the variable displacement
hydraulic pump, the controller being configured to switch the
discharge direction of the variable displacement hydraulic pump to
the neutral state by switching the forward-reverse travel switching
valve to a neutral state.
3. The work vehicle according to claim 2, further comprising a pump
capacity control cylinder configured to change the capacity and the
discharge direction from the variable displacement hydraulic pump
in accordance with a supply direction, which is a direction the
hydraulic oil is supplied from the forward-reverse travel switching
valve.
4. The work vehicle according to claim 3, further comprising a
fixed displacement hydraulic pump driven by the engine; and an
engine sensing valve configured to convert a hydraulic pressure of
the hydraulic oil discharged from the fixed displacement hydraulic
pump to a hydraulic pressure corresponding to the engine speed, and
to supply the converted hydraulic oil to the forward-reverse travel
switching valve, the pump capacity control cylinder being
configured to change the capacity of the variable displacement
hydraulic pump to a capacity at a level capable of travelling the
vehicle when the engine speed is a first speed, and the
forward-reverse travel switching valve is in the forward travel
state or the reverse travel state.
5. The work vehicle according to claim 1, wherein the controller is
configured to increase a low idle engine speed during the
regeneration of the exhaust treatment device.
6. The work vehicle according to claim 2, wherein the exhaust
treatment device is a selective catalytic reduction device; and the
regeneration of the exhaust treatment device is started when a
removal efficiency in the exhaust treatment device for a removal
object to be removed becomes less than a predetermined value, or
when a predetermined time or greater has elapsed since the latest
regeneration.
7. The work vehicle according to claim 1, wherein the exhaust
treatment device is a diesel oxidation catalyst (DOC) device; and
the regeneration of the exhaust treatment device is started when a
first predetermined time or greater has elapsed since the
temperature of the exhaust from the exhaust treatment device during
the operation of the engine becomes no greater than a first
predetermined temperature.
8. The work vehicle according to claim 6, wherein p1 the controller
is configured to switch the forward-reverse travel switching valve
to the neutral state when an accelerator operation amount is less
than a predetermined first operation amount, and the vehicle speed
is less than a predetermined speed.
9. The work vehicle according to claim 8, wherein the controller is
configured such that the regeneration of the exhaust treatment
device is finished when a second predetermined time or greater has
elapsed since the temperature of the exhaust from the exhaust
treatment device becomes no less than a second predetermined
temperature.
10. The work vehicle according to claim 7, wherein the controller
is configured such that the regeneration of the exhaust treatment
device is finished when a third predetermined time or greater has
elapsed since the regeneration is started.
11. The work vehicle according to claim 9, wherein the controller
is configured to finish the control switching the forward-reverse
travel switching valve to the neutral state when the regeneration
of the exhaust treatment device is finished, and the engine speed
becomes less than a predetermined second speed which is less than
the first speed.
12. The work vehicle according to claim 8, wherein the controller
is configured to finish the control switching the forward-reverse
travel switching valve to the neutral state when the accelerator
operation amount becomes a first operation amount or greater.
13. A method of controlling a work vehicle, the method comprising
steps of: driving a hydraulic pump having a variable discharge
direction of hydraulic oil by an engine; driving a hydraulic motor
configured to generate driving power for traveling with the
hydraulic oil discharged from the hydraulic pump; regenerating an
exhaust treatment device; and switching the discharge direction of
the hydraulic pump to a neutral state and increasing the speed of
the engine to a predetermined first speed or greater during the
regenerating the exhaust treatment device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. National stage application of
International Application No. PCT/JP2015/078853, filed on Oct. 9,
2015.
FIELD OF THE INVENTION
[0002] A work vehicle and a method of controlling the work vehicle
are disclosed.
BACKGROUND INFORMATION
[0003] Japanese Laid-Open Patent Application Publication No.
2011-052794 discloses a work vehicle provided with a variable
displacement hydraulic pump driven by an engine, and a hydraulic
motor driven by the hydraulic oil discharged from the variable
displacement hydraulic pump. The work vehicle travels on the
driving power from the hydraulic motor.
[0004] The tightening of emission controls in recent years has made
it increasingly necessary to regenerate the exhaust treatment
device mounted in this kind of work vehicle to maintain the
purification performance of the exhaust treatment device.
Regenerating an exhaust treatment device is performed when the
purification performance of the device has deteriorated or when the
device has been operating for over a predetermined time, and
involves increasing the exhaust temperature to remove soot, urea
deposits, or the like that have accumulated in the exhaust
treatment device (refer to Japanese Laid-Open Patent Application
Publication No. 2015-086714).
SUMMARY
[0005] The work vehicle in Japanese Laid-Open Patent Application
Publication No. 2011-052794 requires increasing the engine speed to
regenerate the exhaust treatment device. Once the engine speed has
increased, the hydraulic motor is driven beyond the driving power
corresponding to the accelerator operation amount, which tends to
make it difficult to travel the work vehicle at the speed intended
by the operator.
[0006] The present description discloses a work vehicle capable of
traveling at the speed intended by the operator when regenerating
the exhaust treatment device.
[0007] A work vehicle according to a first aspect of the present
invention includes an engine, a variable displacement hydraulic
pump, a hydraulic motor, an exhaust treatment device, and a
controller. The engine drives the variable displacement hydraulic
pump. The variable displacement hydraulic pump is configured to
change the discharge direction of the hydraulic fluid. Depending on
the discharge direction of the hydraulic oil from the variable
displacement hydraulic pump, the hydraulic motor is configured to
change the driving direction to the forward direction or the
reverse direction. The exhaust treatment device is configured to
treat the exhaust from the engine. The controller is configured to
increase the speed of the engine to a predetermined first speed or
greater and to change the discharge direction of the variable
displacement hydraulic pump to a neutral state during regeneration
of the exhaust treatment device.
[0008] The work vehicle may further include a forward-reverse
travel switching valve for switching the discharge direction of the
hydraulic oil from the variable displacement hydraulic pump. The
controller may be configured to switch the discharge direction of
the variable displacement hydraulic pump to the neutral state by
switching the forward-reverse travel switching valve to a neutral
state.
[0009] The work vehicle may be provided with a pump capacity
control cylinder configured to change the capacity and the
discharge direction from the variable displacement hydraulic pump
in accordance with a supply direction, which is the direction the
hydraulic oil is supplied from the forward-reverse travel switching
valve.
[0010] The work vehicle may be further provided with a fixed
displacement hydraulic pump, and an engine sensing valve. The
engine drives the fixed displacement hydraulic pump. The engine
sensing valve is configured to convert the hydraulic pressure of
the hydraulic oil discharged from the fixed displacement hydraulic
pump to a hydraulic pressure corresponding to the engine speed, and
to supply the converted hydraulic oil to the forward-reverse travel
switching valve. The pump capacity control cylinder may be
configured to change the capacity of the variable displacement
hydraulic pump to a capacity at a level capable of traveling the
vehicle when the engine speed is a first speed, and the
forward-reverse travel switching valve is in a forward travel state
or a reverse travel state.
[0011] The controller may be configured to increase the low idle
engine speed during the regeneration of the exhaust treatment
device.
[0012] The exhaust treatment device may be a selective catalytic
reduction device. The regeneration of the exhaust treatment device
may be started when the removal efficiency in the exhaust treatment
device for a removal object to be removed becomes less than a
predetermined value, or when a predetermined time or greater has
elapsed since the latest regeneration.
[0013] The exhaust treatment device may be a diesel oxidation
catalyst device. The regeneration of the exhaust treatment device
may be started when a first predetermined time or greater has
elapsed since the temperature of the exhaust from the exhaust
treatment device during the operation of the engine becomes no
greater than a first predetermined temperature.
[0014] The controller may be configured to switch the
forward-reverse travel switching valve to the neutral state when an
accelerator operation amount is less than a predetermined first
operation amount, and the vehicle speed is less than a
predetermined speed.
[0015] The regeneration of the exhaust treatment device may be
finished when a second predetermined time or greater has elapsed
since the temperature of the exhaust from the exhaust treatment
device becomes no less than a second predetermined temperature.
[0016] The regeneration of the exhaust treatment device may be
finished when a third predetermined time or greater has elapsed
since the regeneration is started.
[0017] The controller may be configured to finish the control
switching the forward-reverse travel switching valve to the neutral
state when the regeneration of the exhaust treatment device is
finished, and the engine speed becomes less than a predetermined
second speed which is less than the first speed.
[0018] The controller may be configured to finish the control
switching the forward-reverse travel switching valve to the neutral
state when the accelerator operation amount becomes a first
operation amount or greater.
[0019] A method of controlling a work vehicle according to the
second aspect of the present invention involves steps of causing
the engine to drive a hydraulic pump having a variable discharge
direction of hydraulic oil discharged therefrom; driving a
hydraulic motor for travelling a vehicle with the hydraulic oil
discharged from the hydraulic pump; switching the discharge
direction of the hydraulic pump to a neutral state; increasing the
speed of the engine to at or above a predetermined first speed; and
regenerating an exhaust treatment device.
[0020] The work vehicle according to the first aspect, and the
method of controlling a work vehicle according to the second aspect
increases the speed of the engine to a predetermined first speed or
greater and switches the discharge direction of the hydraulic pump
to a neutral state when regenerating the exhaust treatment device.
Therefore, the vehicle speed does not increase even when the engine
speed is increased for the purpose of regenerating the exhaust
treatment device. Consequently, the vehicle may travel at the speed
intended by the operator.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a side view of a work vehicle.
[0022] FIG. 2 is a side view illustrating a configuration of the
inside of the engine compartment.
[0023] FIG. 3 illustrates a configuration of a hydraulic driving
mechanism provided to the work vehicle.
[0024] FIG. 4 is a graph illustrating the relationship between the
engine speed and the pilot pressure in the engine sensing
valve.
[0025] FIG. 5 is a flowchart illustrating operations in the work
vehicle when regenerating a first exhaust treatment device.
[0026] FIG. 6 is a flowchart illustrating operations in the work
vehicle when regenerating a second exhaust treatment device.
[0027] FIG. 7 is a flowchart illustrating operations in the
hydraulic driving mechanism when regenerating the second exhaust
treatment device.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0028] Overall Configuration
[0029] A side view of a work vehicle 1 according to an exemplary
embodiment of the present invention is illustrated in FIG. 1. The
work vehicle 1 is a wheel loader capable of traveling via tires 4a,
4b and carrying out the desired work via a working implement 3. The
work vehicle 1 is provided with a vehicle frame 2, a working
implement 3, tires 4a, 4b, and a cab 5.
[0030] The vehicle frame 2 contains a front frame 2a, and a rear
frame 2b arranged behind the front frame. The front frame 2a and
the rear frame 2b are connected at the center of the vehicle frame
2 and are able to pivot horizontally thereat.
[0031] The working implement 3 and the pair of front tires 4a are
installed on the front frame 2a. The hydraulic oil from a
working-implement hydraulic pump 11 (refer to FIG. 3) drives the
working implement 3 which is provided with a lift arm 3a mounted to
the front of the front frame 2a, a bucket 3b installed on the tip
end of the lift arm 3a, a lift cylinder (not shown) that drives the
lift arm 3a, and a tilt cylinder 3c that drives the bucket 3b. The
pair of front tires 4a is provided on the sides of the front frame
2a.
[0032] The cab 5, an engine compartment 6, and the pair of rear
tires 4b are provided on the rear frame 2b. The cab 5 is installed
on the upper part of the vehicle frame 2. Control units, such as a
steering wheel and an accelerator pedal 61 (refer to FIG. 3); a
display unit (not shown) for displaying various kinds of
information, such as the vehicle speed; an operator seat; and the
like, can be installed within the cab 5. The engine compartment 6
is arranged behind the cab 5. The pair of rear tires 4b is provided
on the sides of the rear frame 2b.
[0033] FIG. 2 is a side view illustrating a configuration of the
inside of the engine compartment 6. As illustrated in FIG. 2, an
engine 8, a first exhaust treatment device 51, and a second exhaust
treatment device 55 are arranged inside the engine compartment
6.
[0034] The engine 8 is a so-called diesel engine. The engine 8
drives the above-described tires 4a, 4b and the hydraulic pumps 9,
11 (refer to FIG. 3). The engine 8 is supported on the rear frame
2b.
[0035] The first exhaust treatment device 51 is arranged above the
engine 8. The first exhaust treatment device 51 treats the exhaust
from the engine 8. The first exhaust treatment device 51 is, for
example, a diesel oxidation catalyst (DOC) device. The DOC device
oxidizes the nitrogen oxide (NO) and nitrogen dioxide (NO2) present
in the exhaust from the engine 8 and facilitates exhaust treatment
in the second exhaust treatment device 55. The DOC device further
removes the hydrocarbon (HC) and the carbon monoxide (CO) in the
exhaust from the engine 8. The first exhaust treatment device 51 is
a roughly circular cylinder. The first exhaust treatment device 51
is arranged such that the lengthwise direction thereof follows the
width of the vehicle. The first exhaust treatment device 51 is
connected to the engine 8 via a first connecting pipe 50.
[0036] The second exhaust treatment device 55 is arranged above the
engine 8 adjacent to the first exhaust treatment device 51. The
second exhaust treatment device 55 treats the exhaust from the
engine 8. The second exhaust treatment device 55 is, for example, a
selective catalytic reduction (SCR) device. The SCR device uses a
reductant to remove the nitrogen oxides (NOx) in the exhaust from
the engine 8. That is, the NOx are the objects to be removed by the
second exhaust treatment device 55. The second exhaust treatment
device 55 is a roughly circular cylinder. The second exhaust
treatment device 55 is arranged such that the lengthwise direction
thereof follows the width of the vehicle. The second exhaust
treatment device 55 is connected to the first exhaust treatment
device 51 via a second connecting pipe 53.
[0037] The second connecting pipe 53 is arranged above the second
exhaust treatment device 55. A reductant injector 54 is installed
on the second connecting pipe 53. The reductant injector 54 injects
the reductant into the second connecting pipe 53. The reductant may
be an aqueous solution of urea. The second connecting pipe 53 mixes
the reductant with the exhaust from the engine 8.
[0038] An exhaust pipe 59 is connected to the second exhaust
treatment device 55. The exhaust pipe 59 is arranged above the
second exhaust treatment device 55. Above the second exhaust
treatment device 55, the exhaust pipe 59 extends along the width of
the vehicle, and bends upward. As illustrated in FIG. 1, the tip
end portion of the exhaust pipe 59 protrudes upward from the upper
surface of the engine compartment 6. The tip end portion of the
exhaust pipe 59 curves rearward.
[0039] Hydraulic Driving Mechanism
[0040] A hydraulic driving mechanism 7 is mounted on the vehicle
frame 2 to drive the tires 4a, 4b and the working implement 3. A
configuration of the hydraulic driving mechanism 7 is described
below based on FIG. 3. The hydraulic driving mechanism 7 contains
primarily, the engine 8, a hydraulic pump for traveling (travel
hydraulic pump) 9, a charge pump 10, a hydraulic pump for actuating
working implement (working-implement hydraulic pump) 11, a
hydraulic motor for traveling (travel hydraulic motor) 12, a drive
shaft IS, and a controller 16, and adopts the so-called
hydro-static transmission (HST) system.
[0041] The output torque generated by the engine 8 is transmitted
to the travel hydraulic pump 9, the charge pump 10, and the
working-implement hydraulic pump 11, and the like. A fuel injector
17 is provided to the engine 8 for controlling the output torque
and the speed of the engine 8. The fuel injector 17 adjusts the
amount of fuel injected on the basis of a commanded speed signal
from the controller 16 to the engine 8; the commanded speed signal
is adjusted depending on an amount the accelerator pedal 61 is
operated (referred to below as an "accelerator operation
amount").
[0042] The accelerator pedal 61 is a means of directing the target
speed of the engine 8, and is provided with an accelerator
operation amount detector 62. The accelerator operation amount
detector 62 is configured from a potentiometer to detect the
accelerator operation amount. The accelerator operation amount
detector 62 sends the controller 16 an operation amount signal
indicative of the accelerator operation amount, and outputs the
command signal from the controller 16 to the fuel injector 17.
Therefore, the operator may control the speed of the engine 8 by
adjusting the operation amount entered via the accelerator pedal
61.
[0043] The engine 8 is also provided with an engine-speed detector
25 configured from a rotation sensor that detects the actual
rotation speed of the engine 8. A detection signal indicative of
the engine speed is sent from the engine-speed detector 25 to the
controller 16.
[0044] The travel hydraulic pump 9 is a variable displacement
hydraulic pump that changes the capacity and the discharge
direction of the hydraulic oil therefrom in accordance with a
change in the tilt angle of the swashplate. The engine 8 drives the
travel hydraulic pump 9. The hydraulic oil discharged from the
travel hydraulic pump 9 is sent to the travel hydraulic motor 12
through hydraulic circuits for traveling (travel circuits) 20, 21.
The travel circuit 20 (referred to below as the "forward travel
circuit 20") is a flow path supplying the travel hydraulic motor 12
with hydraulic oil so that driving the travel hydraulic motor 12
causes the vehicle to move forward. The travel circuit 21 (referred
to below as the "reverse travel circuit 21") is a flow path
supplying the travel hydraulic motor 12 with hydraulic oil so that
driving the travel hydraulic motor 12 causes the vehicle to move in
reverse.
[0045] A pump capacity control cylinder 23 and a forward-reverse
travel switching valve 24 are connected to the travel hydraulic
pump 9; the pump capacity control cylinder 23 is able to change the
tilt angle of the swashplate in the travel hydraulic pump 9.
[0046] The pump capacity control cylinder 23 moves a piston 22 in
accordance with the pressure of the hydraulic oil supplied thereto.
A spring 22a is installed on the piston 22. The pump capacity
control cylinder 23 includes a first hydraulic chamber 23a and a
second hydraulic chamber 23b; the location of the piston 22 changes
depending on the balance between the force of the spring, and a
pressure differential between the hydraulic pressures inside the
first hydraulic chamber 23a and the second hydraulic chamber 23b
respectively. The piston 22 is connected to the swashplate in the
travel hydraulic pump 9, and the movement of the piston 22 changes
the tilt angle of the swashplate in the travel hydraulic pump 9.
Hereby, the pump capacity control cylinder 23 is able to vary the
capacity and the discharge direction of the hydraulic oil from the
travel hydraulic pump 9.
[0047] The forward-reverse travel switching valve 24 is an
electromagnetic control valve that controls the pump capacity
control cylinder 23 on the basis of a command signal from the
controller 16. The forward-reverse travel switching valve 24 is
able to control the direction the hydraulic oil is supplied to the
pump capacity control cylinder 23 on the basis of a command signal
from the controller 16.
[0048] Consequently, the controller 16 may switch the discharge
direction of the hydraulic oil from the travel hydraulic pump 9 by
controlling the forward-reverse travel switching valve 24
electrically. The forward-reverse travel switching valve 24 can
switch between a forward-travel state F, a reverse-travel state R,
and a neutral state N.
[0049] In the forward-travel state F, the forward-reverse travel
switching valve 24 links a later-described first pilot circuit 36
and the main pilot circuit 33, and connects a second pilot circuit
37 and a drain circuit 38. The first pilot circuit 36 is connected
to the first hydraulic chamber 23a in the pump capacity control
cylinder 23. The second pilot circuit 37 is connected to the second
hydraulic chamber 23b in the pump capacity control cylinder 23.
Therefore, when the forward-reverse travel switching valve 24 is in
the forward-travel state F, hydraulic oil is supplied to the first
hydraulic chamber 23a via the main pilot circuit 33 and the first
pilot circuit 36, and discharged from the second hydraulic chamber
23b. Hereby, the tilt angle in the travel hydraulic pump 9 changes
to an orientation that increases the capacity in the forward travel
circuit 20.
[0050] In addition, in the reverse-travel state R, the
forward-reverse travel switching valve 24 links the second pilot
circuit 37 and the main pilot circuit 33, and connects the first
pilot circuit 36 and the drain circuit 38. Therefore, when the
forward-reverse travel switching valve 24 is in the reverse-travel
state R, hydraulic oil is supplied to the second hydraulic chamber
23b via the main pilot circuit 33 and the second pilot circuit 37.
Hereby, the tilt angle in the travel hydraulic pump 9 changes to an
orientation that increases the capacity in the reverse travel
circuit 21.
[0051] The first pilot circuit 36 and the second pilot circuit 37
are connected to the drain circuit 38 in the neutral state N of the
forward-reverse travel switching valve 24. In this case, the travel
hydraulic pump 9 does not discharge hydraulic oil to either of the
forward travel circuit 20 or the reverse travel circuit 21. The
discharge direction of the hydraulic oil from the travel hydraulic
motor 12 at this point is said to be in the neutral state.
[0052] The charge pump 10 is a fixed displacement hydraulic pump
that discharges hydraulic oil when driven by the engine 8. The
hydraulic oil discharged from the charge pump 10 is normally
supplied to the forward-reverse travel switching valve 24 through a
charge circuit 42, an engine sensing valve 32, and the main pilot
circuit 33. The charge pump 10 supplies the forward-reverse travel
switching valve 24 with the hydraulic oil that operates the pump
capacity control cylinder 23.
[0053] The engine sensing valve 32 converts the hydraulic pressure
of the hydraulic oil discharged from the charge pump 10 to a
hydraulic pressure that corresponds to the engine speed, and
supplies the converted hydraulic oil to the forward-reverse travel
switching valve 24. The engine sensing valve 32 changes the
pressure in the main pilot circuit 33 (i.e., the pilot pressure) in
accordance with the engine speed. FIG. 4 is a graph illustrating
the relationship in the engine sensing valve 32 between the engine
speed and the pilot pressure.
[0054] As illustrated in FIG. 4, when the engine speed increases
the engine sensing valve 32 increases the pilot pressure. The
variable Pnoc in FIG. 4 is the minimum required pilot pressure
needed in the pump capacity control cylinder 23 to move the piston
22. In other words, when the pilot pressure is greater than Pnoc,
the pressure differential between the hydraulic pressure inside the
first hydraulic chamber 23a and the hydraulic pressure inside the
second hydraulic chamber 23b is greater than the biasing force of
the spring 22a and the piston 22 moves. The low idle speed of the
engine 8 during normal operation (i.e., the engine speed when no
load is applied to the engine) is smaller than the engine speed NO
corresponding to Pnoc. Consequently, the discharge direction of the
hydraulic oil from the travel hydraulic motor 12 is in the neutral
state when the accelerator operation amount is zero during normal
operation, and the work vehicle does not move.
[0055] When the engine speed is Nx (N0<Nx<Nm) illustrated in
FIG. 4, the piston 22 moves to a location where the pilot pressure
Px corresponding to the engine speed Nx and the spring force of the
spring 22a are balanced thereby setting the capacity of the travel
hydraulic pump 9. When the engine speed is greater than or equal to
Nm illustrated in FIG. 4, a later-described cut-off valve 31
operates to thereby set the pilot pressure at a maximum value Pmax.
At this point, the piston 22 moves up to the location where the
pilot pressure Pmax and the spring force of the spring 22a are
balanced, thereby setting the capacity of the travel hydraulic pump
9. In this manner, the engine sensing valve 32 changes the pilot
pressure, to thereby increase or decrease the capacity of the
travel hydraulic pump 9 as above described.
[0056] In FIG. 3, a cut-off circuit 39, which is connected to the
cut-off valve 31, is connected to the main pilot circuit 33. The
cut-off valve 31 is a pressure reducing valve that reduces the
pilot pressure in the pump capacity control cylinder 23 to an
established pressure by balancing the hydraulic pressure in the
travel circuits 20, 21 (referred to below as the "travel circuit
hydraulic pressure") and the spring force. The cut-off valve 31
limits the pilot pressure to the maximum pilot pressure Pmax in
FIG. 4. The cut-off valve 31 is configured to reduce the pilot
pressure supplied to the pump capacity control cylinder 23 when the
travel circuit hydraulic pressure is at or exceeds an established
cut-off pressure value to thereby ensure that the travel circuit
hydraulic pressure does not exceed the cut-off pressure value.
[0057] The engine 8 drives the working-implement hydraulic pump 11.
The hydraulic oil discharged from the working-implement hydraulic
pump 11 is sent, for instance, to the tilt cylinder 3c via the
work-machine circuit 49 (refer to FIG. 1) to drive the tilt
cylinder 3c.
[0058] The travel hydraulic motor 12 is a variable displacement
hydraulic motor, the capacity of which changes within a range of
values greater than zero in accordance with a change in the tilt
angle of the swashplate. The hydraulic oil supplied to the travel
hydraulic motor 12 from the travel hydraulic pump 9 via the travel
circuits 20, 21 drives the travel hydraulic motor 12. Hereby, the
travel hydraulic motor 12 generates the driving power that causes
the vehicle to move.
[0059] Depending on the discharge direction of the hydraulic oil
from the travel hydraulic pump 9, the travel hydraulic motor 12
changes the driving direction to the forward direction or the
reverse direction. More specifically, the travel hydraulic motor 12
is driven in a direction that causes the vehicle to move forward
when the hydraulic oil is supplied via the forward travel circuit
20. The travel hydraulic motor 12 is driven in a direction that
causes the vehicle to move in reverse when the hydraulic oil is
supplied via the reverse travel circuit 21.
[0060] A motor cylinder 29, and a motor control valve 30 are
provided in the travel hydraulic motor 12; the motor cylinder 29
controls the tilt angle in the travel hydraulic motor 12, and the
motor control valve 30 controls the motor cylinder 29. The motor
control valve 30 is an electromagnetic control valve controlled on
the basis of a control signal from the controller 16. The
controller 16 is capable of changing the capacity of the travel
hydraulic motor 12 as desired by controlling the motor cylinder
29.
[0061] The drive shaft 15 causes the tires 4a, 4b to rotate by
transmitting the driving power from the travel hydraulic motor 12
to the tires 4a, 4b (refer to FIG. 1). The drive shaft 15 is also
provided with an output speed detector 34 configured from a
rotation sensor that detects the rotation speed of the drive shaft
15. The information detected by the output speed detector 34 is
sent to the controller 16 as a detection signal. The controller 16
computes the moving direction and speed of the vehicle on the basis
of the rotation speed of the drive shaft 15 detected by the output
speed detector 34. Note that the vehicle speed in the exemplary
embodiment is a scalar value defined in accordance to magnitude and
is not dependent on the moving direction of the work vehicle 1.
[0062] A parking brake 44, and a parking brake control valve 45 are
further provided on the drive shaft 15. The parking brake 44 can
switch between an engaged state, and a disengaged state. In the
engaged state the parking brake 44 stops the drive shaft 15. In the
disengaged state the parking brake 44 releases the drive shaft
15.
[0063] The parking brake control valve 45 is an electromagnetic
control valve controlled on the basis of a control signal from the
controller 16. The controller 16 controls the parking brake control
valve 45 to thereby switch the parking brake 44 between the engaged
state and the disengaged state. The parking brake 44 can switch
between the engaged state and the disengaged state in accordance
with the operation of a parking brake operation member 68.
[0064] The parking brake 44 contains a brake disc portion 44a, and
a piston portion 44b. When the piston portion 44b is supplied with
hydraulic fluid, the oil pressure causes the piston portion 44b and
the plurality of brake disks in the brake disc portion 44a to come
in contact with each other. The parking brake 44 is thereby in the
engaged state. Switching the parking brake 44 to the engaged state
may also be referred to as operating the parking brake 44.
Additionally, discharging hydraulic oil from the piston portion 44b
causes the piston portion 44b and the brake discs to be held out of
contact with each other due to the elastic force of an elastic
component provided in the piston portion 44b. The parking brake 44
is thereby in the disengaged state.
[0065] The parking brake operation member 68 is provided in the cab
5, and is manipulated to operate the parking brake 44. The parking
brake operation member 68 may be, for instance, a braking switch,
or a parking lever that the operator can manipulate. Finally, an
operation signal is sent to the controller 16 when the parking
brake operation member 68 is operated.
[0066] A forward-reverse switching control unit 64 contains a
forward-reverse switching lever 65 and a lever-operation detector
66 which serve as the forward-reverse travel operation control. The
operator operates the forward-reverse switching lever 65, located
in the cab 5, to direct switching the vehicle between forward
travel and reverse travel. The forward-reverse switching lever 65
may be switched between a forward-travel position, a reverse-travel
position, and a neutral position. The lever-operation detector 66
detects to which of the positions, i.e., the forward-travel
position, the reverse-travel position, and the neutral position
that the forward-reverse switching lever 65 has been switched, and
sends the detection result to the controller 16 as a detection
signal.
[0067] The first connecting pipe 50 connected to the engine 8 is
provided with a first concentration measurement unit 56. The first
concentration measurement unit 56 is configured from a nitrogen
oxide detector or the like for detecting the concentration of the
NOx in the exhaust discharged from the engine 8. The first
concentration measurement unit 56 sends a signal to the controller
16 representing a concentration D1 of the NOx present in the
exhaust discharged from the engine 8.
[0068] A first temperature detector 52 is provided in the first
exhaust treatment device 51. The first temperature detector 52 is
configured from a temperature sensor or the like to detect the
temperature of the exhaust from the first exhaust treatment device
51 (referred to below as the DOC temperature). The first
temperature detector 52 sends a signal to the controller 16
representing the DOC temperature.
[0069] The second exhaust treatment device 55 is provided with a
second temperature detector 57 and a second concentration
measurement unit 58. The second temperature detector 57 is
configured from a temperature sensor or the like to detect the
temperature of the exhaust from the second exhaust treatment device
55 (referred to below as the SCR temperature). The second
temperature detector 57 sends a signal to the controller 16
representing the SCR temperature. The second concentration
measurement unit 58 is configured from a nitrogen oxide detector or
the like for detecting the concentration of the NOx in the exhaust
discharged from the second exhaust treatment device 55. The second
concentration measurement unit 58 sends a signal to the controller
16 representing a concentration D2 of the NOx present in the
exhaust discharged from the second exhaust treatment device 55.
[0070] The controller 16 is any electronic control unit including,
for instance, a CPU and various kinds of memory. The controller 16
is programmed to electrically control the various electromagnetic
valves and the fuel injector 17 on the basis of the signals output
from the detectors. Hereby, the controller 16 controls the engine
speed, the capacity of the motor, and the like. In the work vehicle
1, the traction force and the vehicle speed are continuously varied
so that gear shifting occurs automatically between a vehicle speed
of zero to a maximum speed without a gear shifting operation.
[0071] The controller 16 usually outputs a commanded speed signal
to the fuel injector 17 which sets the speed of the engine 8 in
accordance with the accelerator operation amount. The controller 16
also outputs a command signal on the basis of the position of the
forward-reverse switching lever 65 to change the state (F, R, N) of
the forward-reverse travel switching valve 24. For instance, when
the forward-reverse switching lever 65 is moved to the
forward-travel position, the controller 16 outputs a command signal
that changes the state of the forward-reverse travel switching
valve 24 to the forward-travel state F.
[0072] Whereas, when determining that the exhaust treatment devices
51, 55 need regeneration, even when the accelerator operation
amount is small, the controller 16 outputs a commanded speed signal
to the fuel injector 17 that adjusts the speed of the engine 8 to a
predetermined speed or greater. Moreover, when the accelerator
operation amount, vehicle speed, and the like satisfy a
predetermined condition during regeneration of the exhaust
treatment devices 51, 55, the controller 16 outputs a command
signal that sets the forward-reverse travel switching valve 24 to
the neutral state N, regardless of the position of the
forward-reverse switching lever 65. In other words the controller
16 switches the discharge direction of the travel hydraulic pump 9
to a neutral state. The details regarding the control performed by
the controller 16 are described below.
[0073] Regenerating the Exhaust Treatment Device
[0074] FIG. 5 is a flowchart illustrating operations in the work
vehicle 1 when regenerating the first exhaust treatment device 51
(DOC) according to the exemplary embodiment. First, the work
vehicle 1 operates normally in step 1. More specifically, the
controller 16 causes the engine 8 to drive the travel hydraulic
pump 9, and causes the hydraulic oil discharged from the travel
hydraulic pump 9 to drive the travel hydraulic motor 12.
[0075] In step 2 the controller 16 determines, on the basis of DOC
temperature detected by the first temperature detector 52, whether
or not a predetermined time t1 or greater has elapsed since the DOC
temperature becomes no greater than a predetermined temperature Td
during the operation of the engine 8. The control returns to step 1
when less than the predetermined time t1 has elapsed since the DOC
temperature becomes the predetermined temperature Td (NO at step
1).
[0076] When the predetermined time t1 or greater has elapsed since
the DOC temperature becomes the predetermined temperature Td (YES
at step 2), in step 3, the controller 16 outputs an alert on the
display unit or the like mounted inside the cab 5 prompting for the
regeneration the first exhaust treatment device 51. Subsequently,
the controller 16 waits until the parking brake 44 is operated (NO
at step S4). The controller 16 operates the parking brake 44 when
the operator operates the parking brake operation member 68 (YES at
step 4).
[0077] When the parking brake is operated (YES at step 4), in step
5 the controller 16 effects a switch of the discharge direction of
the travel hydraulic pump 9 to the neutral state. More
specifically, the controller 16 causes the forward-reverse travel
switching valve 24 to switch to the neutral state N.
[0078] In step 6, the controller 16 causes the engine speed to
increase to or above a predetermined speed N1 regardless of the
magnitude of the accelerator operation amount. The speed N1 is
greater than the speed N0 in FIG. 4. Given that the low idle engine
speed during normal operations is smaller than N0, this signifies
that the controller 16 is increasing the low idle engine speed in
step 6.
[0079] Increasing the engine speed to N1 or greater in step 6
raises the temperature of the exhaust from the engine 8. The
hydrocarbons filling the first exhaust treatment device 51 are
thereby oxidized and exhausted from the first exhaust treatment
device 51. In this manner, the controller 16 effects regeneration
of the first exhaust treatment device 51 in step 7.
[0080] In step 8, the controller 16 measures an amount of time
elapsed since the regeneration of the first exhaust treatment
device 51 and determines whether or not the amount of time elapsed
becomes a predetermined time t2 or greater. The control returns to
step 5 when the amount of time elapsed is less than the
predetermined time t2 (NO at step 8). When the amount of time
elapsed becomes the predetermined time t2 or greater (YES at step
8), the controller 16 causes the regeneration of the first exhaust
treatment device 51 to be finished.
[0081] FIG. 6 is a flowchart illustrating operations during
regeneration of the second exhaust treatment device 55 (SCR)
according to the exemplary embodiment. First, in step 11 the
controller 16 sets a variable RFlag to false on startup of the work
vehicle 1. RFlag is a flag indicating whether or not the conditions
for regenerating the SCR (later described) are met. In this case
RFlag indicates that the conditions for regenerating the SCR are
not met.
[0082] The work vehicle 1 operates normally in step 12. More
specifically, the controller 16 causes the engine 8 to drive the
travel hydraulic pump 9, and causes the hydraulic oil discharged
from the travel hydraulic pump 9 to drive the travel hydraulic
motor 12.
[0083] In the step 13, the controller 16 determines whether the
removal efficiency of an object to be removed (NOx) from the second
exhaust treatment device 55 (SCR) becomes less than a predetermined
value Rth, or whether or not a predetermined time tpth or greater
has elapsed since the latest regeneration of the second exhaust
treatment device 55.
[0084] The controller 16 acquires the concentration DI of NOx
within the exhaust discharged from the engine 8 as detected by a
first concentration measurement unit 56, and a concentration D2 of
NOx within the exhaust discharged from the second exhaust treatment
device 55 as detected by a second concentration measurement unit
58. The controller 16 uses an expression (1-D2/D1) to compute the
NOx removal efficiency.
[0085] In step 13, the control returns to step 12 when the NOx
removal efficiency is at a predetermined value Rth or greater, and
less than a predetermined time tpth has elapsed since the latest
regeneration (NO at step 13). Otherwise, the controller 16 sets the
RFlag to true when that is not the case (YES at step 13). In this
case RFlag indicates that the conditions for regenerating the SCR
are met.
[0086] In step 15, the controller 16 causes the engine speed to
increase to or above a predetermined speed N2 regardless of the
magnitude of the accelerator operation amount. The speed N2 is
greater than the speed N0 in FIG. 4. Given that the low idle engine
speed during normal operation is smaller than N1, this signifies
that in step 15 the controller 16 is increasing the low idle engine
speed. Note that here, the speed N2 may be the same as the speed N1
in step 6 of FIG. 5.
[0087] Increasing the engine speed to N2 or greater in step 15
raises the temperature of the exhaust from the engine 8. Hereby,
the increased temperature of the exhaust thermally decomposes the
fixed deposits (deposit) in the second connecting pipe 53 and the
reductant injector 54 created due to the chemical transformation of
the reductant solution. In this manner, the controller 16 effects
regeneration of the second exhaust treatment device 55 in step
16.
[0088] In step 17 the controller 16 determines whether or not a
predetermined time t4 or greater has elapsed since the SCR
temperature detected by the second temperature detector 57 becomes
a predetermined temperature Ts or greater. The control returns to
step 15 when less than the predetermined time t4 has elapsed since
the SCR temperature becomes the predetermined temperature Ts or
greater (NO at step 17).
[0089] In step 18 the controller 16 finishes the control in step 15
when the predetermined time t4 or more has elapsed since the SCR
temperature becomes the predetermined temperature Ts or greater
(YES at step 17). That is, the controller 16 causes the speed of
the engine 8 to be established in accordance with the accelerator
operation amount. In this manner, the controller 16 finishes the
control of the regeneration of the second exhaust treatment device
55. The control returns to the processing in step 11 after the
completion of step 18.
[0090] FIG. 7 is a flowchart illustrating operations in the
hydraulic driving mechanism 7 when regenerating the second exhaust
treatment device 55 (SCR) according to the exemplary embodiment. In
step 21 the controller 16 determines whether or not control to set
the discharge direction of the hydraulic oil from the travel
hydraulic motor 12 to the neutral state (step 24, later described)
is being carried out. Prior to the SCR regeneration process in step
16 (FIG. 6), there is no processing carried out to set the
discharge direction of the hydraulic oil to the neutral state (NO
at step 21). In this case, the control proceeds to step 22.
[0091] In step 22 the controller 16 determines whether or not the
RFlag is true, the accelerator operation amount detected by the
accelerator operation amount detector 62 is less than a
predetermined operation amount A1, and the vehicle speed obtained
from the rotation speed of the drive shaft 15 detected by the
output speed detector 34 is less than a predetermined speed
Vth.
[0092] When the RFlag is true, the accelerator operation amount
detected by the accelerator operation amount detector 62 is less
than a predetermined operation amount A1, and the vehicle speed is
less than a predetermined speed Vth (YES at step 22), the
controller 16 controls the switching of the discharge direction of
the travel hydraulic pump 9 to the neutral state. More
specifically, the controller 16 causes the forward-reverse travel
switching valve 24 to switch to the neutral state N regardless of
the position of the forward-reverse switching lever 65.
[0093] When the RFlag is false, the accelerator operation amount is
the predetermined operation amount or greater A1, or the vehicle
speed is the predetermined speed Vth or greater (NO at step 22),
the controller 16 does not perform the control in step 24. Namely,
in step 23, the controller 16 outputs a command signal on the basis
of the position of the forward-reverse switching lever 65 to set
the discharge direction of the travel hydraulic pump 9 and to
change the state (F, R, N) of the forward-reverse travel switching
valve 24.
[0094] Once step 23 or step 24 is carried out, the controller 16
performs the processing in step 21 again. When the control in step
24 has already been carried out (YES at step 21), the controller 16
determines whether or not the accelerator operation amount detected
by the accelerator operation amount detector 62 is a predetermined
operation amount A1 or greater in step 25.
[0095] When the accelerator operation amount is an operation amount
Al or greater (YES at step 25), in step 26 the controller 16 ends
the control performed in step 24 for switching the forward-reverse
travel switching valve 24 to the neutral state N. Namely, the
controller 16 outputs a command signal on the basis of the position
of the forward-reverse switching lever 65 to set the discharge
direction of the travel hydraulic pump 9 and to change the state
(F, R, N) of the forward-reverse travel switching valve 24. The
control returns to the processing in step 21 after the completion
of step 26.
[0096] When the accelerator operation amount is less than the
operation amount A1 (NO at step 25), the controller 16 determines
whether or not the RFlag is false, and whether the engine speed
detected by the engine-speed detector 25 is less than a
predetermined speed N3 which is smaller than the above described N2
in step 27. The speed N3 is smaller than the speed NO in FIG. 4.
Consequently, hereafter even if the forward-reverse travel
switching valve 24 is switched to the forward-travel state F, or
the reverse-travel state R, the travel hydraulic pump 9 does not
discharge hydraulic oil into either of the forward travel circuit
20, or the reverse travel circuit 21 and the travel hydraulic motor
12 does not generate any driving power for travel.
[0097] When it is determined that the RFlag is false in step 27,
this signifies that the processing in step 24 is carried out before
the aforementioned determination; i.e., that the RFlag is true.
Consequently, when it is determined that the RFlag is false in step
27, this signifies that the SCR regeneration process is
completed.
[0098] The controller 16 carries out the processing in the
above-described step 26 when the RFlag is false, and the engine
speed is less than the speed N3 (YES at step 27). The controller 16
carries out the processing in the above-described step 24 when
either the RFlag is true, or the engine speed is the speed N3 or
greater (NO at step 27). The control returns to the processing in
step 21 after the completion of step 24 or 26.
[0099] Operation Effects
[0100] Next, the operational effects of the exemplary embodiment
are described.
[0101] The controller 16 according to the exemplary embodiment
increases the speed of the engine 8 to a predetermined speed N1, N2
or greater (step 6 in FIG. 5, step 15 in FIG. 6) during
regeneration of the exhaust treatment devices 51, 55 (step 7 in
FIG. 5, step 16 in FIG. 6), and switches the forward-reverse travel
switching valve 24 to the neutral state N (step 5 in FIG. 5, step
24 in FIG. 7) to switch the discharge direction of the hydraulic
oil flowing from the travel hydraulic pump 9 to the neutral state.
Thus, when the accelerator operation amount is small during low
speeds (step 22 in FIG. 7), this prevents increases in the vehicle
speed even when the engine speed is increased to regenerate the
exhaust treatment devices 51, 55. This also prevents the generation
of creep, which causes the work vehicle 1 to move even when the
accelerator pedal 61 has not been pressed. Consequently, the
vehicle may travel at the speed intended by the operator.
[0102] The speeds N1, N2 are greater than the engine speed N0 in
FIG. 4. With the greater speeds N1, N2, when the forward-reverse
travel switching valve 24 is switched completely to either the
forward-travel state F or the reverse-travel state R, the movement
of the piston 22 in the pump capacity control cylinder 23 causes
the travel hydraulic pump 9 to discharge hydraulic fluid. The range
of variable capacities for the travel hydraulic motor 12 is greater
than zero; therefore, the travel hydraulic motor 12 will cause the
drive shaft 15 to rotate and thereby causes the vehicle to move
when the travel hydraulic pump 9 discharges hydraulic fluid.
Accordingly, setting the forward-reverse travel switching valve 24
to the neutral state N is effective.
[0103] The controller 16 increases the low idle speed to no less
than N1 or N2 during regeneration of the exhaust treatment devices
51, 55. Consequently, the temperature of the exhaust from the
engine 8 can be raised even when the accelerator operation amount
is zero, allowing more reliable regeneration of the exhaust
treatment devices 51, 55.
[0104] The regeneration of the first exhaust treatment device 51
(DOC) can be started when a predetermined time t1 or greater has
elapsed since the temperature of the exhaust from the first exhaust
treatment device 51 (DOC temperature) during the operation of the
engine 8 becomes no greater than a predetermined temperature Td.
The first exhaust treatment device 51 is filled with hydrocarbons
when the DOC temperature is low. Therefore, this allows effective
detection of when an abundance of hydrocarbons are in the first
exhaust treatment device 51, allowing for effective regeneration of
the first exhaust treatment device 51.
[0105] The regeneration of the first exhaust treatment device 51 is
finished when the amount of time elapsed since the regeneration of
the first exhaust treatment device 51 is started becomes a
predetermined time t2 or greater. This enables to finish the
regeneration of the first exhaust treatment device 51 while the
hydrocarbons filling the first exhaust treatment device 51 have
been sufficiently removed therefrom.
[0106] The regeneration of the second exhaust treatment device 55
(SCR) can be started when the removal efficiency in the second
exhaust treatment device 55 for a removal object to be removed
(NOx) becomes less than a predetermined value Rth (step 13 in FIG.
6). Accordingly, the regeneration of the second exhaust treatment
device 55 can be started when the removal performance of the second
exhaust treatment device 55 deteriorates. Moreover, the
regeneration of the second exhaust treatment device 55 can be
started when a predetermined time tpth or greater has elapsed since
the latest regeneration. This hereby allows for periodic
maintenance of the second exhaust treatment device 55.
[0107] The regeneration of the second exhaust treatment device 55
(SCR) is finished when a predetermined time t4 or greater has
elapsed since the temperature of the exhaust from the second
exhaust treatment device 55 (SCR temperature) becomes no greater
than a predetermined temperature Ts. The deposits filling inside
the second connecting pipe 53 and the reductant injector 54 may be
thermally decomposed effectively when the SCR temperature becomes
Ts or greater. This enables to finish the regeneration of the
second exhaust treatment device 55 while the hydrocarbons filling
the second connecting pipe 53 and the reductant injector 54 have
been sufficiently removed therefrom.
[0108] The controller 16 switches the forward-reverse travel
switching valve 24 to the neutral state N (step 24 in FIG. 7) when
the accelerator operation amount is less than a predetermined
operation amount A1, and the vehicle speed is less than a
predetermined speed Vth (step 22 in FIG. 7). Hereby, the controller
16 can switch the discharge direction of the travel hydraulic pump
9 to a neutral state when the operator desires low-speed,
decelerating travel. Accordingly, the work vehicle 1 may function
without obstructing the operator's intent.
[0109] The controller 16 ends the control switching the
forward-reverse travel switching valve 24 to the neutral state N
(step 26 in FIG. 7) when the accelerator operation amount is an
operation amount A1 or greater (step 25 in FIG. 7). Hereby, the
controller 16 can end the control switching the discharge direction
of the travel hydraulic pump 9 to a neutral state when the operator
desires accelerating travel. This improves the operational feel
perceived by the operator.
[0110] The controller 16 finishes the control switching the
forward-reverse travel switching valve 24 to the neutral state N
(step 26 in FIG. 7) when the regeneration of the second exhaust
treatment device 55 (SCR) finishes, and the engine speed becomes
less than a speed N3 which is less than the above-described speed
N2 (step 27 in FIG. 7). The speed N3 is smaller than the speed N0
in FIG. 4. Consequently, hereafter even if the forward-reverse
travel switching valve 24 is switched to the forward-travel state
F, or the reverse-travel state R, the travel hydraulic pump 9 does
not discharge hydraulic oil into either of the forward travel
circuit 20, or the reverse travel circuit 21 and the travel
hydraulic motor 12 does not generate any driving power for travel.
Accordingly, the controller 16 can return the work vehicle 1 to
normal operation without the operator perceiving an interruption,
even if the regeneration of the second exhaust treatment device 55
is finished while the work vehicle 1 is stopped.
[0111] Here ends the description of one exemplary embodiment of the
present invention; the present invention is not limited to these
descriptions but may be modified in various ways insofar as the
modifications do not deviate from the spirit of the present
invention.
[0112] Modification Examples
[0113] Although a wheel loader is provided as an example of the
work vehicle 1 in the above exemplary embodiment, the work vehicle
1 may be any other work vehicle such as a bulldozer.
[0114] The above exemplary embodiment provides a DOC as an example
of the first exhaust treatment device 51, and an SCR as an example
of the second exhaust treatment device 55.
[0115] However, instead of a DOC, a diesel particulate collection
filter (DPF) device may be used as the first exhaust treatment
device 51. In this case, the techniques for regenerating the first
exhaust treatment device 51 are not limited to the techniques
illustrated in FIG. 5.
[0116] For instance, step 3 illustrated in FIG. 5 may be omitted.
Furthermore, while FIG. 7 provides examples of using the same
threshold A 1 as the threshold for the accelerator operation amount
in step 22 and step 25, different thresholds may be used.
[0117] For instance, step 4 illustrated in FIG. 5 may be omitted.
In other words, the forward-reverse travel switching valve 24 may
be switched to the neutral state N without determining whether or
not the parking brake 44 is operated.
[0118] It is not absolutely required for the first concentration
measurement unit 56 is placed in the first connecting pipe 50. The
first concentration measurement unit 56 may be arranged at any
desired location, so long as that location is further upstream than
the inlet to the second connecting pipe 53.
[0119] Herein is provided a work vehicle capable of traveling at
the speed intended by an operator when regenerating an exhaust
treatment device.
* * * * *