U.S. patent application number 13/698161 was filed with the patent office on 2013-03-07 for selective catalytic reduction system.
This patent application is currently assigned to Isuzu Motors Limited. The applicant listed for this patent is Tomoyuki Kamijyou, Masanobu Minezawa, Koji Sakumoto. Invention is credited to Tomoyuki Kamijyou, Masanobu Minezawa, Koji Sakumoto.
Application Number | 20130055700 13/698161 |
Document ID | / |
Family ID | 44991675 |
Filed Date | 2013-03-07 |
United States Patent
Application |
20130055700 |
Kind Code |
A1 |
Minezawa; Masanobu ; et
al. |
March 7, 2013 |
SELECTIVE CATALYTIC REDUCTION SYSTEM
Abstract
A selective catalytic reduction system includes a urea aqueous
solution tank to retain a urea aqueous solution to be injected into
an exhaust pipe of an engine, a level sensor to detect a solution
level height in the tank, a lowpass filter having a signal response
characteristic in which a time constant is small when an engine rpm
is low and the time constant is larger when the engine rpm is high,
with respect to an output signal of the sensor, a remaining amount
indicator to indicate a remaining amount of the solution based on
an output signal of the sensor processed by the lowpass filter, and
a unit to prohibit the engine from being started when the remaining
amount of the solution is less than a lower limit value.
Inventors: |
Minezawa; Masanobu;
(Fujisawa-shi, JP) ; Sakumoto; Koji;
(Fujisawa-shi, JP) ; Kamijyou; Tomoyuki;
(Fujisawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Minezawa; Masanobu
Sakumoto; Koji
Kamijyou; Tomoyuki |
Fujisawa-shi
Fujisawa-shi
Fujisawa-shi |
|
JP
JP
JP |
|
|
Assignee: |
Isuzu Motors Limited
Tokyo
JP
|
Family ID: |
44991675 |
Appl. No.: |
13/698161 |
Filed: |
May 16, 2011 |
PCT Filed: |
May 16, 2011 |
PCT NO: |
PCT/JP2011/061222 |
371 Date: |
November 15, 2012 |
Current U.S.
Class: |
60/277 |
Current CPC
Class: |
Y02T 10/24 20130101;
F02N 11/101 20130101; F02D 2041/1432 20130101; F02N 2200/022
20130101; F01N 2610/02 20130101; Y02T 10/12 20130101; F01N 3/208
20130101; F02D 2200/101 20130101; Y02T 10/47 20130101; F01N
2900/0404 20130101; F01N 2900/1818 20130101; F01N 11/00 20130101;
F01N 2900/1814 20130101; Y02T 10/40 20130101; G01F 23/0069
20130101; F01N 2900/08 20130101 |
Class at
Publication: |
60/277 |
International
Class: |
F01N 9/00 20060101
F01N009/00; F01N 3/20 20060101 F01N003/20; F01N 11/00 20060101
F01N011/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 17, 2010 |
JP |
2010-113746 |
Claims
1. An SCR system, comprising: a urea aqueous solution tank
configured to retain a urea aqueous solution to be injected into an
exhaust pipe of an engine; a level sensor configured to detect a
solution level height in the urea aqueous solution tank; a lowpass
filter having a signal response characteristic in which a time
constant is small when an engine rpm is low and the time constant
is larger when the engine rpm is high, with respect to an output
signal of the level sensor; a remaining amount indicator configured
to indicate a remaining amount of the urea aqueous solution based
on an output signal of the level sensor processed by the lowpass
filter; and a start prohibiting unit in deficiency of the urea
aqueous solution configured to prohibit the engine from being
started when the remaining amount of the urea aqueous solution is
less than a lowerlimit value.
2. The SCR system according to claim 1, wherein the time constant
of the lowpass filter is 0 in the range of the engine rpm of 0 to a
cranking rpm and increases with the increase in the engine rpm over
the cranking rpm.
Description
TECHNICAL FIELD
[0001] The present invention relates to an SCR system that purifies
exhaust gas by injecting a urea aqueous solution to the exhaust gas
of a diesel vehicle, and more particularly, to an SCR system that
can rapidly cancel engine start prohibition after filling the urea
aqueous solution as well as preventing improper indication of
deficiency of the urea aqueous solution by variation in solution
level in a urea aqueous solution tank and unwanted engine start
prohibition.
BACKGROUND ART
[0002] As an exhaust gas purifying system for purifying NOx in the
exhaust gas of a diesel engine, an SCR system using a SCR
(selective catalytic reduction) apparatus has been developed.
[0003] The SCR system supplies the urea aqueous solution to
upstream of the exhaust gas of the SCR apparatus, generates ammonia
by heat of the exhaust gas, and reduces and purifies NOx on an SCR
catalyst by the ammonia (see, for example, Patent Document 1).
PRIOR ART DOCUMENTS
Patent Documents
[0004] Patent Document 1: Japanese Patent Application Publication
No. 2000-303826
DISCLOSURE OF THE INVENTION
Problems To Be Solved By The Invention
[0005] A sufficient amount of urea aqueous solution needs to be
retained in order for a vehicle to travel while continuously
purifying the exhaust gas, and as a result, the urea aqueous
solution tank is provided. A level sensor that detects a remaining
amount of the urea aqueous solution is provided in the urea aqueous
solution tank, and the remaining amount is indicated by meters.
When the remaining amount is less than a lowerlimit value, the
deficiency of the urea aqueous solution is indicated to warn a
driver and prohibit the engine from being started, thereby
preventing travelling in a state where the exhaust gas cannot be
purified.
[0006] However, the level sensor is a sensor that detects the
position of a float that floats on the solution level of the urea
aqueous solution as a solution level height. Therefore, when
vibration is generated in the vehicle, the solution level vibrates,
and as a result, the detected remaining amount varies. A warning is
given due to the variation in the solution level caused by the
vibration of the vehicle or the engine cannot be started.
[0007] In order to solve the problems, for example, it is
considered that an output signal of the level sensor is input
through a lowpass filter. However, in order to remove a vibration
component of the solution level from the output signal of the level
sensor, a time constant of the lowpass filter may be several
seconds. Therefore, the indication of the remaining amount on an
actual solution level is followed with delay. As a result, for
example, when the driver who verifies that the indication of the
remaining amount indicates the deficiency of the urea aqueous
solution fills the urea aqueous solution tank with the urea aqueous
solution and thereafter, attempts starting the engine without
delay, the indication of the remaining amount has yet indicated the
deficiency of the urea aqueous solution, and as a result, there is
a case in which the engine is not started. Although the urea
aqueous solution is filled up, when the deficiency of the urea
aqueous solution is indicated or the engine is not started, the
driver feels a sense of strangeness. Further, when the urea aqueous
solution is being filled up, if the indication of the remaining
amount is not increased together, it may be misunderstood that the
level sensor breaks down.
[0008] There is a case in which the remaining amount is also
estimated in parallel by adding up an injection amount of the urea
aqueous solution in addition to detecting an actual remaining
amount of the urea aqueous solution tank by the level sensor. In
this case, when the indication of the remaining amount by the level
sensor rises, adding-up is initialized by misjudgment that the urea
aqueous solution is filled up. Further, since the estimated
remaining amount based on the adding-up of the injection amount of
the urea aqueous solution is unilaterally reduced while the
remaining amount detected by the level sensor varies, a difference
between both parts occurs and management of the remaining amount
becomes uncertain.
[0009] Accordingly, an object of the present invention is to solve
the problems, and provide an SCR system that can rapidly cancel
engine start prohibition after filling the urea aqueous solution as
well as preventing improper indication of deficiency of the urea
aqueous solution by variation in a solution level in a urea aqueous
solution tank and unwanted engine start prohibition.
Means for Solving the Problems
[0010] To achieve the object described above, an SCR system
according to the present invention includes: a urea aqueous
solution tank configured to retain a urea aqueous solution to be
injected into an exhaust pipe of an engine; a level sensor
configured to detect a solution level height in the urea aqueous
solution tank; a lowpass filter having a signal response
characteristic in which a time constant is small when an engine rpm
is low and the time constant is larger when the engine rpm is high,
with respect to an output signal of the level sensor; a remaining
amount indicator configured to indicate a remaining amount of the
urea aqueous solution based on an output signal of the level sensor
processed by the lowpass filter; and a start prohibiting unit in
deficiency of the urea aqueous solution configured to prohibit the
engine from being started when the remaining amount of the urea
aqueous solution is less than a lowerlimit value.
[0011] The time constant of the lowpass filter is 0 in the range of
the engine rpm of 0 to a cranking rpm and may increase with the
increase in the engine rpm over the cranking rpm.
Effects of the Invention
[0012] The present invention provides excellent effects as
follows.
[0013] (1) Improper indication of deficiency of the urea aqueous
solution by variation in a solution level in a urea aqueous
solution tank and unwanted engine start prohibition are
prevented.
[0014] (2) Engine start prohibition can be rapidly cancelled after
filling the urea aqueous solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a configuration diagram of principal components of
an SCR system according to an embodiment of the present
invention.
[0016] FIG. 2 is a configuration diagram, in detail, illustrating
the SCR system according to the embodiment of the present
invention.
[0017] FIG. 3 is an input/output configuration diagram of the SCR
system of FIG. 1
[0018] FIG. 4 is a flowchart illustrating a sequence of filter
processing according to the present invention.
[0019] FIG. 5 is a filter characteristic diagram of a lowpass
filter used in the present invention.
BEST MODES FOR CARRYING OUT THE INVENTION
[0020] Hereinafter, a preferred embodiment of the present invention
will be described with reference to the accompanying drawings.
[0021] As illustrated in FIGS. 1 and 2, an SCR system 100 according
to the present invention includes a urea aqueous solution tank 105
configured to retain a urea aqueous solution to be injected into an
exhaust pipe 102 of an engine E, a level sensor 120 configured to
detect a solution level height in the urea aqueous solution tank
105, a lowpass filter 1 having a signal response characteristic in
which a time constant is small when an engine rpm is low and the
time constant is larger when the engine rpm is high with respect to
an output signal of the level sensor 120, a remaining amount
indicator 2 configured to indicate a remaining amount of the urea
aqueous solution based on an output signal of the level sensor 120
processed by the lowpass filter 1, and a start prohibiting unit 3
in deficiency of the urea aqueous solution configured to prohibit
the engine from being started when the remaining amount of the urea
aqueous solution is less than a lowerlimit value.
[0022] The remaining amount indicator 2 is configured by a liquid
crystal or light emitting diode, and is installed in a cabin of a
vehicle, for example, a console panel. An indication content of the
remaining amount indicator 2 is edited by a remaining amount
indication control unit 4. The remaining amount indication control
unit 4 outputs a remaining amount by a pointer, a bar graph, and
the like, and a warning of the deficiency of the urea aqueous
solution to the remaining amount indicator 2.
[0023] The lowpass filter 1 is configured by a digital filter. The
time constant of the lowpass filter 1 is set to 0 in the range of
the engine rpm of 0 to a cranking rpm and is set to increase with
the increase in the engine rpm over the cranking rpm. In detail, a
filter coefficient to give the time constant for each engine rpm is
set in a time constant map 5 referred to as the engine rpm. The
filter coefficient is provided in the digital filter, and as a
result, a signal response characteristic of the lowpass filter 1 is
determined.
[0024] The level sensor 120 includes a scale 6 that stands in the
urea aqueous solution tank 105, a plurality of approximate sensors
(not illustrated) arranged in parallel vertically in the scale 6,
and a float 7 that floats on a solution level S of the urea aqueous
solution and is movable with the scale 6, and is configured to
detect the position of the approximate sensor that detects the
float 7 as the height of the solution level S.
[0025] In detail, as illustrated in FIG. 2, the SCR system 100
primarily includes an SCR apparatus 103 provided in the exhaust
pipe 102 of the engine E, a dosing valve (a urea aqueous solution
injecting device, a dosing module) 104 configured to inject the
urea aqueous solution upstream of the SCR apparatus 103 (the
exhaust gas), a urea aqueous solution tank 105 configured to retain
the urea aqueous solution, a supply module 106 configured to supply
the urea aqueous solution retained in the urea aqueous solution
tank 105 to the dosing valve 104, and a DCU (dosing control unit)
126 configured to control the dosing valve 104 or the supply module
106.
[0026] The lowpass filter 1, the start prohibiting unit 3 in
deficiency of the urea aqueous solution, the remaining amount
indication control unit 4, and the time constant map 5 may be
provided in the DCU 126.
[0027] In the exhaust pipe 102 of the engine E, a DOC (diesel
oxidation catalyst) 107, a DPF (diesel particulate filter) 108, and
the SCR apparatus 103 are sequentially arranged from upstream to
downstream of the exhaust gas. The DOC 107 oxidizes NO in the
exhaust gas exhausted from the engine E to form NO.sub.2 and is
used to improve denitration efficiency in the SCR apparatus 103 by
controlling a ratio of NO and NO.sub.2 in the exhaust gas. Further,
the DPF 108 is used to collect PM (particulate matter) in the
exhaust gas.
[0028] The dosing valve 104 is provided in the exhaust pipe 102
upstream of the SCR apparatus 103. The dosing valve 104 has a
structure in which an injection hole is provided in a cylinder
filled with high-pressure urea aqueous solutions and a valve body
clogging the injection hole is attached to a plunger, and is
configured to inject the urea aqueous solution by making the valve
body be spaced apart from the injection hole by raising the plunger
through electrical conduction to a coil. When the electrical
conduction to the coil stops, the plunger is dropped by internal
elastic force, and as a result, the valve body clogs the injection
hole, thereby stopping the injection of the urea aqueous
solution.
[0029] An exhaust temperature sensor 109 configured to measure the
temperature of the exhaust gas at an inlet of the SCR apparatus 103
(the temperature of an inlet of the SCR) is provided in the exhaust
pipe 102 upstream of the dosing valve 104. Further, an upstream NOx
sensor 110 configured to detect a NOx concentration upstream of the
SCR apparatus 103 is provided upstream of the SCR apparatus 103
(herein, upstream of the exhaust temperature sensor 109), and a
downstream NOx sensor 111 configured to detect the NOx
concentration downstream of the SCR apparatus 103 is provided
downstream of the SCR apparatus 103.
[0030] The supply module 106 includes an SM pump 112 configured to
pump the urea aqueous solution, an SM temperature sensor 113
configured to measure the temperature of the supply module 106 (the
temperature of the urea aqueous solution that flows in the supply
module 106), a urea aqueous solution pressure sensor 114 configured
to measure the pressure of the urea aqueous solution in the supply
module 106 (the pressure at a discharge side of the SM pump 112),
and a reverting valve 115 configured to switch supplying the urea
aqueous solution from the urea aqueous solution tank 105 to the
dosing valve 104 or reverting the urea aqueous solution in the
dosing valve 104 to the urea aqueous solution tank 105 by switching
a path of the urea aqueous solution. Herein, when the reverting
valve 115 is in an off state, the urea aqueous solution from the
urea aqueous solution tank 105 is configured to be supplied to the
dosing valve 104 and when the reverting valve 115 is in an on
state, the urea aqueous solution in the dosing valve 104 is
configured to be reverted to the urea aqueous solution tank
105.
[0031] When the reverting valve 115 is switched to supply the urea
aqueous solution to the dosing valve 104, the supply module 106 is
configured to feed the urea aqueous solution in the urea aqueous
solution tank 105 and suction the fed urea aqueous solution through
a solution sending line (suction line) 116, in the SM pump 112,
supply the suctioned urea aqueous solution to the dosing valve 104
through a pumping line (pressure line) 117, and revert a remnant
urea aqueous solution to the urea aqueous solution tank 105 through
a recovery line (back line) 118.
[0032] An SCR sensor 119 is provided in the urea aqueous solution
tank 105. The SCR sensor 119 includes a level sensor 120 configured
to measure the height (level) of the solution level of the urea
aqueous solution in the urea aqueous solution tank 105, a
temperature sensor 121 configured to measure the temperature of the
urea aqueous solution in the urea aqueous solution tank 105, and a
quality sensor 122 configured to measure the quality of the urea
aqueous solution in the urea aqueous solution tank 105. The quality
sensor 122 detects the concentration of the urea aqueous solution
or whether a heterogeneous mixture is mixed in the urea aqueous
solution, from, for example, a propagation velocity of ultrasonic
waves or electrical conductivity, and detects the quality of the
urea aqueous solution in the urea aqueous solution tank 105.
[0033] A cooling line 123 configured to circulate cooling water for
cooling the engine E is connected to the urea aqueous solution tank
105 and the supply module 106. The cooling line 123 passes through
the urea aqueous solution tank 105 to exchange heat between the
cooling water that flows in the cooling line 123 and the urea
aqueous solution in the urea aqueous solution tank 105. Similarly,
the cooling line 123 passes through the supply module 106 to
exchange heat between the cooling water that flows in the cooling
line 123 and the urea aqueous solution in the supply module
106.
[0034] A tank heater valve (coolant valve) 124 configured to switch
the supply of the cooling water to the urea aqueous solution tank
105 and the supply module 106 is provided in the cooling line 123.
Further, the cooling line 123 is connected to even the dosing valve
104, but the cooling water is configured to be supplied to the
dosing valve 104 regardless of opening/closing of the tank heater
valve 124. Although not illustrated due to simplification of the
drawing in FIG. 2, the cooling line 123 is installed along the
solution sending line 116, the pumping line 117, and the recovery
line 118 through which the urea aqueous solution passes.
[0035] FIG. 3 illustrates an input/output configuration diagram of
the DCU 126.
[0036] As illustrated in FIG. 3, input signal lines from the
upstream NOx sensor 110, the downstream NOx sensor 111, the SCR
sensor 119 (the level sensor 120, the temperature sensor 121, and
the quality sensor 122), the exhaust temperature sensor 109, the SM
temperature sensor 113 and the urea aqueous solution pressure
sensor 114 of the supply module 106, and an ECM (engine control
module) 125 configured to control the engine E are connected to the
DCU 126. Signals of an outdoor temperature and engine parameters
(engine rpm, and the like) are input from the ECM 125.
[0037] An instruction of the engine start prohibition determined by
the start prohibiting unit 3 in deficiency of the urea aqueous
solution, the remaining amount, and the warning are output from the
DCU 126 to the ECM 125. Information on the remaining amount and the
warning is sent from the ECM 125 to the remaining amount indicator
2.
[0038] Output signal lines to the tank heater valve 124, the SM
pump 112 and the reverting valve 115 of the supply module 106, the
dosing valve 104, a heater of the upstream NOx sensor 110, and a
heater of the downstream NOx sensor 111 are connected to the DCU
126. An input/output of signals between the DCU 126 and each member
may be an input/output through individual signal lines or an
input/output through a CAN (controller area network).
[0039] The DCU 126 is configured to determine the amount of the
urea aqueous solution injected from the dosing valve 104 based on
the estimated amount of NOx in the exhaust gas as well as
estimating the amount of NOx in the exhaust gas based on signals of
the engine parameters from the ECM 125 and the temperature of the
exhaust gas from the exhaust temperature sensor 109, and further,
control the dosing valve 104 based on a detection value of the
upstream NOx sensor 110 and adjust the amount of the urea aqueous
solution injected from the dosing valve 104 when the urea aqueous
solution is injected at the amount of the urea aqueous solution
determined in the dosing valve 104.
[0040] Hereinafter, an operation of the SCR system 100 according to
the present invention will be described.
[0041] As illustrated in FIG. 4, in step S41, the lowpass filter 1
refers to the time constant map 5 as the engine rpm and sets the
filter coefficient. Subsequently, in step S42, the lowpass filter 1
filters the output signal of the level sensor 120 to obtain the
remaining amount of the urea aqueous solution.
[0042] Subsequently, in step S43, the start prohibiting unit 3 in
deficiency of the urea aqueous solution determines whether the
remaining amount of the urea aqueous solution is less than the
lowerlimit value. In the case of YES, the process proceeds to step
S44. In the case of NO, the process proceeds to step S45. In step
S44, the start prohibiting unit 3 in deficiency of the urea aqueous
solution prohibits the engine E from being started because the
remaining amount of the urea aqueous solution is less than the
lowerlimit value. Meanwhile, in step S45, the start prohibiting
unit 3 in deficiency of the urea aqueous solution permits the start
of the engine because the remaining amount of the urea aqueous
solution is more than the lowerlimit value.
[0043] According to the above sequence, the output signal of the
level sensor 120 is filtered to become the remaining amount of the
urea aqueous solution and when the remaining amount of the urea
aqueous solution is less than the lowerlimit value, the engine E is
prohibited from being started. Further, although not illustrated in
the sequence, the remaining amount of the urea aqueous solution is
indicated by the remaining amount indicator 2 and when the
remaining amount of the urea aqueous solution is less than the
lowerlimit value, a warning regarding the deficiency of the urea
aqueous solution is indicated in the remaining amount indicator
2.
[0044] Herein, a filter characteristic of the lowpass filter 1
given by the time constant map 5 and an effect accompanied thereby
will be described with reference to FIG. 5.
[0045] The time constant of the lowpass filter 1 is 0 in the range
of the engine rpm of 0 to the cranking rpm. This is equivalent to a
case in which no filter is present and the output signal of the
level sensor 120 becomes the remaining amount of the urea aqueous
solution as it is. Therefore, the indication of the remaining
amount on an actual solution level is followed with delay.
Accordingly, when the urea aqueous solution is being filled up, the
remaining amount indication is increased together, and as a result,
it is not misunderstood that the level sensor 120 breaks down.
Further, when the remaining amount indication indicates the
deficiency of the urea aqueous solution, the urea aqueous solution
is filled in the urea aqueous solution tank 105 to solve the
deficiency of the urea aqueous solution without delay, and as a
result, the engine start is enabled.
[0046] The time constant is increased with the increase in the
engine rpm in the range of the cranking rpm to an idle rpm. For
example, the time constant in the idle rpm is several seconds. The
time constant is gently increased in the idle rpm or more as
compared with the range of the cranking rpm to the idle rpm. When
the time constant is small around the cranking rpm, so called the
filter coefficient is light and an interruption frequency is high.
When the time constant is increased, so called the filter
coefficient is heavy and the interruption frequency is lowered. As
such, since a high-frequency interruption effect by the lowpass
filter 1 is shown in the cranking rpm or more, or a situation in
which the warning is given or the engine is disabled to be started
is prevented, due to the variation in the solution level caused by
the vibration of the vehicle. Therefore, for example, when the
vehicle stops traveling to be in an idle operation, an influence by
the vibration of the engine is removed. Further, while the vehicle
travels, an influence of vibration of a vehicle body by the
travelling is also removed.
[0047] As described above, according to the SCR system 100 of the
present invention, since the output signal of the level sensor 120
is processed to be the remaining amount of the urea aqueous
solution by using the lowpass filter 1 having the signal response
characteristic in which the time constant is small when the engine
rpm is low and the time constant is large when the engine rpm is
high, improper indication of deficiency of the urea aqueous
solution by variation in a solution level in the urea aqueous
solution tank 105 and unwanted engine start prohibition can be
prevented, and further, engine start prohibition after filling the
urea aqueous solution can be rapidly cancelled. When the urea
aqueous solution is being filled up, the remaining amount
indication is increased together, and as a result, it is not
misunderstood that the level sensor 120 breaks down.
EXPLANATION OF REFERENCE NUMERALS
[0048] 1 lowpass filter
[0049] 2 remaining amount indicator
[0050] 3 start prohibiting unit in deficiency of urea aqueous
solution
[0051] 4 remaining amount indication control unit
[0052] 5 time constant map
[0053] 6 scale
[0054] 7 float
[0055] 100 SCR system
* * * * *