U.S. patent application number 13/343219 was filed with the patent office on 2012-07-19 for exhaust gas purification system for working machine.
This patent application is currently assigned to Hitachi Construction Machinery Co., Ltd.. Invention is credited to Yasushi ARAI, Shohei KAMIYA.
Application Number | 20120180459 13/343219 |
Document ID | / |
Family ID | 45440422 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120180459 |
Kind Code |
A1 |
KAMIYA; Shohei ; et
al. |
July 19, 2012 |
Exhaust Gas Purification System for Working Machine
Abstract
Disclosed is an exhaust gas purification system for a working
machine. The system is provided with a filter for capturing
particulate matter contained in exhaust gas from an engine, a
differential pressure sensor for detecting a differential pressure
between an exhaust upstream side and an exhaust downstream side of
the filter, and a controller having a regeneration determination
unit for determining whether or not a time, at which forced
regeneration is needed, has been reached. The controller includes
one that has a variation determination unit for determining whether
or not a state quantity relevant to an operation of the engine, for
example, an engine speed has varied abruptly and that, when the
state quantity is determined to have abruptly varied, performs
processing to invalidate the determination by the regeneration
determination unit during a predetermined time in which an effect
of the state quantity is considered to diminish.
Inventors: |
KAMIYA; Shohei;
(Tsuchiura-shi, JP) ; ARAI; Yasushi;
(Tsuchiura-shi, JP) |
Assignee: |
Hitachi Construction Machinery Co.,
Ltd.
Tokyo
JP
|
Family ID: |
45440422 |
Appl. No.: |
13/343219 |
Filed: |
January 4, 2012 |
Current U.S.
Class: |
60/286 |
Current CPC
Class: |
E02F 9/0866 20130101;
F02D 41/029 20130101; F02D 2200/0812 20130101 |
Class at
Publication: |
60/286 |
International
Class: |
F01N 9/00 20060101
F01N009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 13, 2011 |
JP |
2011-004960 |
Claims
1. An exhaust gas purification system for a working machine
provided with working equipment, a main body with the working
equipment attached thereto, and an engine arranged on the main body
to drive the working equipment, said exhaust gas purification
system being provided with a filter for capturing particulate
matter, which is contained in exhaust gas from the engine, on an
exhaust downstream side, a differential pressure sensor for
detecting a differential pressure between an exhaust upstream side
and the exhaust downstream side of the filter, and a controller
having a regeneration determination unit for determining, by a
comparison between the differential pressure detected at the
differential pressure sensor and a determinative differential
pressure as a threshold level for determination, whether or not a
time, at which forced regeneration is needed to burn the
particulate matter captured on the filter, has been reached,
wherein: the controller comprises one that has a variation
determination unit for determining whether or not a state quantity
relevant to an operation of the engine has varied abruptly and
that, when the state quantity is determined to have abruptly varied
by the variation determination unit, performs processing to
invalidate the determination by the regeneration determination unit
during a predetermined time in which an effect of the state
quantity is considered to diminish to a negligible extent.
2. The exhaust gas purification system according to claim 1,
wherein: the controller has a first computing unit for computing a
flow rate of exhaust gas, and a second computing unit for computing
the determinative differential pressure based on the flow rate of
exhaust gas as computed at the first computing unit and a map
preset in the controller and indicating correlations between flow
rates of exhaust gas and determinative differential pressures.
3. The exhaust gas purification system according to claim 2,
wherein: the exhaust gas purification system is further provided
with: a fuel control unit for controlling an injection quantity of
fuel to be fed to the engine, an intake air volume sensor for
detecting a volume of intake air to be fed to the engine and
outputting a detection signal to the controller, an intake air
temperature sensor for detecting a temperature of intake air and
outputting a detection signal to the controller, and an exhaust gas
temperature sensor for detecting a temperature of exhaust gas from
the engine and outputting a detection signal to the controller; the
controller further comprises: a fuel injection quantity instruction
unit for outputting an instruction signal to instruct the injection
quantity of fuel to the fuel control unit, and an intake air weight
computing unit for computing a weight of intake air based on a
density of intake air, which is determined according to the
temperature of intake air as detected at the intake air temperature
sensor and a map preset in the controller and indicating
correlations between intake air temperatures and intake air
densities, and the volume of intake air as detected at the intake
air volume sensor; an exhaust gas weight computing unit for
computing a weight of exhaust gas based on the weight of intake air
as computed at the intake air weight computing unit and the
injection quantity of fuel as instructed by the fuel injection
quantity instruction unit; and the first computing unit of the
controller performs processing to compute a flow rate of exhaust
gas based on a density of exhaust gas, which is determined
according to the temperature of exhaust gas as detected at the
exhaust gas temperature sensor and a map preset in the controller
and indicating correlations between exhaust gas temperatures and
exhaust gas densities, and the weight of exhaust gas as computed at
the exhaust gas weight computing unit.
4. The exhaust gas purification system according to claim 3,
wherein: the exhaust gas purification system is further provided
with: an engine speed sensor for detecting a revolution speed of
the engine and outputting a detection signal to the controller; and
the state quantity relevant to the operation of the engine is at
least one of the revolution speed of the engine as detected at the
engine speed sensor, the injection quantity of fuel as instructed
by the fuel injection quantity instruction unit, the volume of
intake air as detected at the intake air volume sensor, and the
flow rate of exhaust gas as computed at the first computing unit of
the controller.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority of Japanese Patent
Application 2011-004960 filed Jan. 13, 2011, which is incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust gas purification
system for a working machine such as a hydraulic excavator, which
is provided with a filter for removing particulate matter
(hereinafter abbreviated as "PM") contained in exhaust gas from an
engine.
[0004] 2. Description of the Related Art
[0005] As a conventional technology of this type, there is one
disclosed in JP-A-2005-307878. This conventional technology is
provided with a filter for capturing PM, which is contained in
exhaust gas from an engine, on an exhaust downstream side, an
exhaust gas temperature sensor, and a differential pressure sensor
for detecting a differential pressure between an exhaust upstream
side and the exhaust downstream side of the filter. The
conventional technology is also provided with a computing unit for
computing a flow rate of exhaust gas and a regeneration
determination unit for determining, by a comparison between the
differential pressure detected at the differential pressure sensor
and a determinative differential pressure as a threshold level for
determination, whether or not a time, at which forced regeneration
is needed to burn PM captured on the filter, has been reached.
[0006] According to the conventional technology having such a
constitution as described above, a differential pressure .DELTA.P1
and a determinative differential pressure .DELTA.P2 are compared
with each other at the regeneration determination unit of the
controller and, when .DELTA.P1>.DELTA.P2, forced regeneration is
determined to be needed. The differential pressure .DELTA.P1 is
determined by converting a detected differential pressure .DELTA.P,
which is detected at the differential pressure sensor, to a
corresponding value at a standard temperature of exhaust gas from a
correlation between a temperature of exhaust gas as detected at the
exhaust gas temperature sensor and the standard temperature. The
determinative differential pressure .DELTA.P2, on the other hand,
is a threshold level at the standard temperature, which corresponds
to a flow rate of exhaust gas as computed at the computing unit of
the controller.
[0007] Forced regeneration is to inject fuel into exhaust gas from
an engine such that using an oxidation reaction by an oxidation
catalyst, the temperature of exhaust gas is raised to burn off PM
deposited on a filter. Clogging of the filter can, therefore, be
solved by forced regeneration.
[0008] With the above-described conventional exhaust gas
purification system, an appropriate value can be calculated as the
above-mentioned determinative differential pressure .DELTA.P
insofar as it is applied to a vehicle, such as a truck, that does
not undergo much abrupt variations in the injection quantity of
fuel or abrupt variations in the volume of intake air, because the
flow rate of exhaust gas remains stable during an operation. In a
working machine, such as a hydraulic excavator, for which the
present invention is useful, however, its body undergoes frequent
abrupt variations such as variations in load and variations in
swing torque so that the flow rates of exhaust gas as calculated at
the time of the respective variations also vary significantly. As a
consequence, no appropriate determinative differential pressure
.DELTA.P2 may be calculated in some instances. When the
conventional technology is applied to a working machine and a
determination is made at the regeneration determination unit of the
controller by using such a determinative differential pressure
.DELTA.P2, a problem may hence arise that, even if PM has not
deposited much on the filter actually, .DELTA.P1>.DELTA.P2 is
determined and forced regeneration is performed although it is not
needed. Such unnecessary forced regeneration results in a wasteful
injection of fuel, and leads to a deterioration in fuel
economy.
SUMMARY OF THE INVENTION
[0009] With the foregoing circumstances of the above-described
conventional technology in view, the present invention has as an
object thereof the provision of an exhaust gas purification system
for a working machine, which can realize forced regeneration
without being affected by abrupt variations of a body.
[0010] To achieve the above-described object, the present invention
provides, in one aspect thereof, an exhaust gas purification system
for a working machine provided with working equipment, a main body
with the working equipment attached thereto, and an engine arranged
on the main body to drive the working equipment, said exhaust gas
purification system being provided with a filter for capturing
particulate matter, which is contained in exhaust gas from the
engine, on an exhaust downstream side, a differential pressure
sensor for detecting a differential pressure between an exhaust
upstream side and the exhaust downstream side of the filter, and a
controller having a regeneration determination unit for
determining, by a comparison between the differential pressure
detected at the differential pressure sensor and a determinative
differential pressure as a threshold level for determination,
whether or not a time, at which forced regeneration is needed to
burn the particulate matter captured on the filter, has been
reached, wherein the controller comprises one that has a variation
determination unit for determining whether or not a state quantity
relevant to an operation of the engine has varied abruptly and
that, when the state quantity is determined to have abruptly varied
by the variation determination unit, performs processing to
invalidate the determination by the regeneration determination unit
during a predetermined time in which an effect of the state
quantity is considered to diminish.
[0011] The present invention has been made with an attention
focused on the fact that upon occurrence of an abrupt variation on
a body, a state quantity relevant to an operation of an engine,
such as the engine speed or the injection quantity of fuel, varies
abruptly. According to the present invention, when the state
quantity relevant to the operation of the engine is determined by
the variation determination unit of the controller to have abruptly
varied in response to an abrupt variation of the body, processing
is performed by the controller to invalidate the determination by
the regeneration determination unit that determines whether or not
forced regeneration is to be performed, in other words, to
terminate a determination function of the regeneration
determination unit during a predetermined time in which an effect
of the abrupt variation in the state quantity is considered to
diminish. The above-described predetermined time can be set
experimentally or empirically in view of load variations which may
occur on the associated working machine. As a consequence, the
present invention can realize forced regeneration without being
affected by abrupt variations of the body.
[0012] The controller may preferably have a first computing unit
for computing a flow rate of exhaust gas, and a second computing
unit for computing the determinative differential pressure based on
the flow rate of exhaust gas as computed at the first computing
unit and a map preset in the controller and indicating correlations
between flow rates of exhaust gas and determinative differential
pressures.
[0013] Preferably, the exhaust gas purification system may be
further provided with a fuel control unit for controlling an
injection quantity of fuel to be fed to the engine, an intake air
volume sensor for detecting a volume of intake air to be fed to the
engine and outputting a detection signal to the controller, an
intake air temperature sensor for detecting a temperature of intake
air and outputting a detection signal to the controller, and an
exhaust gas temperature sensor for detecting a temperature of
exhaust gas from the engine and outputting a detection signal to
the controller; the controller may further comprise a fuel
injection quantity instruction unit for outputting an instruction
signal to instruct the injection quantity of fuel to the fuel
control unit, and an intake air weight computing unit for computing
a weight of intake air based on a density of intake air, which is
determined according to the temperature of intake air as detected
at the intake air temperature sensor and a map preset in the
controller and indicating correlations between intake air
temperatures and intake air densities, and the volume of intake air
as detected at the intake air volume sensor; an exhaust gas weight
computing unit for computing a weight of exhaust gas based on the
weight of intake air as computed at the intake air weight computing
unit and the injection quantity of fuel as instructed by the fuel
injection quantity instruction unit; and the first computing unit
of the controller may perform processing to compute a flow rate of
exhaust gas based on a density of exhaust gas, which is determined
according to the temperature of exhaust gas as detected at the
exhaust gas temperature sensor and a map preset in the controller
and indicating correlations between exhaust gas temperatures and
exhaust gas densities, and the weight of exhaust gas as computed at
the exhaust gas weight computing unit.
[0014] The exhaust gas purification system may preferably be
further provided with an engine speed sensor for detecting a
revolution speed of the engine and outputting a detection signal to
the controller; and the state quantity relevant to the operation of
the engine may preferably be at least one of the revolution speed
of the engine as detected at the engine speed sensor, the injection
quantity of fuel as instructed by the fuel injection quantity
instruction unit, the volume of intake air as detected at the
intake air volume sensor, and the flow rate of exhaust gas as
computed at the first computing unit of the controller.
[0015] In the exhaust gas purification system of the present
invention for the working machine equipped with the working
equipment, the controller is constituted to comprise one that has
the variation determination unit for determining whether or not the
state quantity relevant to an operation of the engine has varied
abruptly and that, when the state quantity is determined to have
abruptly varied by the variation determination unit, performs
processing to invalidate the determination by the regeneration
determination unit during the predetermined time in which the
effect of the state quantity is considered to diminish. Owing to
this constitution, it is possible to realize forced regeneration
without being affected by abrupt variations of the body. Described
specifically, it is possible to minimize the performance of
unnecessary forced regeneration that would otherwise tend to be
performed in response to abrupt variations of the body, thereby
making it possible to prevent wasteful injections of fuel and hence
to improve the fuel economy of the working machine equipped with
the exhaust gas purification system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a side view showing a hydraulic excavator
described as an example of a working machine in which an exhaust
gas purification system according to one embodiment of the present
invention can be arranged.
[0017] FIG. 2 is a diagram illustrating the constitution of the
exhaust gas purification system according to the embodiment as
arranged in the hydraulic excavator shown in FIG. 1.
[0018] FIG. 3 is a block diagram depicting an essential
constitution of a controller included in the embodiment.
[0019] FIG. 4 is a diagram illustrating characteristics available
from the embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0020] The exhaust gas purification system according to the one
embodiment of the present invention for the working machine will
hereinafter be described based on the drawings.
[0021] As shown in FIG. 1, the hydraulic excavator which makes up
the working machine is provided with a travel base 1 and an
upperstructure 2 mounted on the travel base 1. These travel base 1
and upperstructure 2 make up a main body. This hydraulic excavator
is also provided with working equipment 3 attached tiltably in
up-and-down directions to the upperstructure 2 and including a
boom, an arm and so on, an operator's cab 4 arranged on the
upperstructure 2, a counterweight 5 for assuring a weight balance,
and an engine compartment 6 arranged between the operator's cab 4
and the counterweight 5.
[0022] This hydraulic excavator is also provided, as illustrated in
FIG. 2, with an engine 10 accommodated in the engine compartment 6,
an air cleaner 11 for removing dust from air to be inducted into
the engine 10, that is, from intake air, an air compressor 12 of a
turbocharger for compressing the intake air cleaned by the air
cleaner 11 and guided through an intake air passage 30, intake air
passages 31,32 for guiding into the engine 10 the intake air
compressed by the compressor 12, and an air cooler 13 arranged
between the intake air passage 31 and the intake air passage 32 for
cooling the intake air to be fed to the engine 10. The hydraulic
excavator is further provided with a turbine 14 of the turbocharger
and an exhaust gas passage 33, both of which guide exhaust gas from
the engine 10, recirculation passages 34,35 for recirculating a
portion of exhaust gas from the engine 10 and feeding it again into
the engine 10, and an EGR (Exhaust Gas Recirculation) cooler 15
arranged between these recirculation passages 34 and 35 for cooling
the exhaust gas to be fed to the engine 10.
[0023] The exhaust gas purification system of this embodiment for
the hydraulic excavator of such a constitution as described above
is provided, as also illustrated in FIG. 2, provided with a filter
20 for capturing PM, which is contained in the exhaust gas from the
engine 10, at an exhaust downstream side and a differential
pressure sensor 21 for detecting a differential pressure between an
exhaust upstream side and the exhaust downstream side of the filter
20. This embodiment is also provided with a controller 22 having a
regeneration determination unit 22a depicted in FIG. 3. By a
comparison between the differential pressure detected at the
differential pressure sensor 21, namely the detected differential
pressure .DELTA.P and a determinative differential .DELTA.Po as a
threshold level for determination, the regeneration determination
unit 22a determines whether or not a time, at which forced
regeneration is needed to burn PM captured on the filter 20, has
been reached. When it is determined at the regeneration
determination unit 22a that the time, at which forced regeneration
is needed, has been reached, a control signal is outputted from the
controller 22 to a fuel injector 28, and by this fuel injector 28,
a predetermined quantity of fuel is injected to mix it into exhaust
gas from the engine 10.
[0024] Referring back to FIG. 2, this embodiment is also provided
with an intake air volume sensor 23, an intake air temperature
sensor 24 and an exhaust gas temperature sensor 27. The intake air
volume sensor 23 detects a quantity of air guided into the intake
air passage 30, that is, a quantity of intake air, and outputs a
detection signal to the controller 22. The intake air temperature
sensor 24 detects a temperature of the intake air, and outputs a
detection signal to the controller 22. The exhaust gas temperature
sensor 27 detects a temperature of exhaust gas guided into the
exhaust gas passage 33, and outputs a detection signal to the
controller 22.
[0025] This embodiment is further provided, as depicted in FIG. 3,
with a fuel control unit 25 and an engine speed sensor 26. The fuel
control unit 25 controls a quantity of fuel, which is to be fed to
the engine 10, response to a control signal outputted from a fuel
injection quantity instruction unit 22e included in the controller
22. The engine speed sensor 26 detects a revolution speed of the
engine 10, and outputs a detection signal to the controller 22.
[0026] In this embodiment, the controller 22 includes, as depicted
in FIG. 3, one that has a variation determination unit 22b for
determining whether or not a state quantity relevant to an
operation of the engine 10, for example, an engine speed detected
at the engine speed sensor 26 has varied abruptly, and that, when
the engine speed is determined to have abruptly varied by the
variation determination unit 22b, performs processing to invalidate
the above-mentioned determination by the regeneration determination
unit 22a during a predetermined time in which an effect of the
abrupt variation in engine speed is considered to diminish.
[0027] A determinative revolution speed variation .DELTA.N1 as a
threshold level for the determination of an abrupt variation in
engine speed is stored in the controller 22. The variation
determination unit 22b compares the determinative revolution speed
variation .DELTA.N1 with an actual revolution speed variation
.DELTA.N computed based on the detection value by the engine speed
sensor 26 and, when .DELTA.N>.DELTA.N1, determines that the
engine speed has varied abruptly.
[0028] The above-mentioned predetermined time can be set
experimentally or empirically in view of variations of the body,
such as variations in load and variations in swing torque, which
can occur on the hydraulic excavator shown in FIG. 1.
[0029] The controller is also provided, as depicted in FIG. 3, with
a first computing unit 22c and a second computing unit 22d. The
first computing unit 22c computes an exhaust gas flow rate Vex. The
second computing unit 22d computes a determinative differential
pressure .DELTA.Po based on the exhaust gas flow rate Vex computed
at the first computing unit 22c and a map preset in the controller
22 and indicating correlations between exhaust gas flow rates and
determinative differential pressures.
[0030] The controller is further provided with an intake air weight
computing unit 22f, which computes an intake air weight
Gin(=f2.times.Vin) based on a intake air density f2, which is
determined according to an intake air temperature Tin detected at
the intake air temperature sensor 24 and a map preset in the
controller 22 and indicating correlations between intake air
temperatures and intake air densities, and an intake air volume Vin
detected at the intake air volume sensor 23.
[0031] The controller 22 is still further provided with an exhaust
gas weight computing unit 22g for computing an exhaust gas weight
Gex(=Gin+q) based on the intake air weight Gin computed at the
intake air weight computing unit 22f and a fuel injection quantity
q instructed by the fuel injection quantity instruction unit
22e.
[0032] The above-mentioned first computing unit 22c of the
controller 22 performs processing to compute an exhaust gas flow
rate Vex(=Gex/f3) based on an exhaust gas density f3 and the
exhaust gas weight Gex computed at the exhaust gas weight computing
unit 22g. The exhaust gas density f3 is determined according to an
exhaust gas temperature Tex detected at the exhaust gas temperature
sensor 27 and a map preset in the controller 22 and indicating
correlations between exhaust gas temperatures and exhaust gas
densities. Based on the determinative differential pressure
.DELTA.Po computed at the second computing unit 22d in accordance
with the exhaust gas flow rate Vex computed at the first computing
unit 22c and the detected differential pressure .DELTA.P detected
at the differential pressure sensor 21, the above-mentioned
regeneration determination unit 22a determines, as mentioned above,
whether or not the time, at which forced regeneration is needed,
has been reached.
[0033] According to this embodiment constituted as described above,
when as indicated by a sensing range S1 in FIG. 4, the load A is
relatively stable and the engine speed N is maintained at a
constant high revolution speed, the actual revolution speed
variation .DELTA.N calculated based on the detection value detected
at the engine speed sensor 26 is not higher than the determinative
revolution speed variation .DELTA.N1, that is,
.DELTA.N.ltoreq..DELTA.N1, so that at the variation determination
unit 22b of the controller 22, the engine speed is determined to
have undergone no abrupt variation. Therefore, the regeneration
determination unit 22a functions normally, and performs a
determination as to whether or not the time, at which forced
regeneration is needed to burn PM captured on the filter 20, has
been reached, specifically a determination that compares the
detected differential pressure .DELTA.P and the determinative
differential pressure .DELTA.Po with each other.
[0034] When .DELTA.P.ltoreq..DELTA.Po is determined at the
regeneration determination unit 22a, it is determined that the
time, at which forced regeneration is needed, has not been reached.
As a consequence, no control signal is outputted to activate the
fuel injector 28. When .DELTA.P>.DELTA.Po is determined at the
regeneration determination unit 22a, on the other hand, it is
determined that the time, at which forced regeneration is needed,
has been reached, and the fuel injector 28 performs an injection to
mix fuel in the exhaust gas from the engine 10 as mentioned above.
As a result, the temperature of the exhaust gas rises under the
action of the oxidation catalyst, the PM captured on the filter 20
burns, and the clogging of the filter 20 is solved.
[0035] When the load A has undergone an abrupt variation and the
engine speed has undergone, for example, an abrupt drop, both at
the variation determination unit 22b of the controller 22, as
indicated by a sensing range S2 in FIG. 4, an actual revolution
speed variation .DELTA.N calculated based on a detection value of
the engine speed sensor 26 becomes greater than the determinative
revolution speed variation .DELTA.N1, that is,
.DELTA.N>.DELTA.N1 is obtained, processing is performed at the
controller 22 to invalidate the determination processing by the
regeneration determination unit 22a during a predetermined time T
in which the effect of the rapid variation in engine speed is
considered to diminish.
[0036] According to this embodiment constituted as described above,
it is possible to perform forced regeneration without being
affected by abrupt variations in the engine speed N, in other
words, without being affected by abrupt variations of the
upperstructure 2 or travel base 1. As a consequence, it is possible
to minimize the practice of unnecessary forced regeneration, which
would otherwise tend to be performed in response to abrupt
variations of the upperstructure 2 or travel base 1 and to prevent
wasteful injections of fuel. Owing to this feature, it is possible
to improve the fuel economy of a hydraulic excavator equipped with
an exhaust gas purification system.
[0037] In the above-described embodiment, the engine speed N is
described as the state quantity relevant to the operation of the
engine 10 to be determined at the variation determination unit 22b
of the controller 22. It is, however, to be noted that this state
quantity can be the fuel injection quantity q instructed by the
fuel injection quantity instruction unit 22e of the controller 22,
the intake air volume Vin detected at the intake air volume sensor
23, the exhaust air flow rate Vex computed at the first computing
unit 22c, or the like. It is also to be noted that the exhaust gas
purification system may be designed to determine plural ones of
these state quantities at the variation determination unit 22b.
* * * * *