U.S. patent application number 13/170269 was filed with the patent office on 2011-12-29 for particulate matter detection sensor and control device of controlling the same.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Hideaki Itoh, Satoshi NAKAMURA, Takashi Sawada, Hirofumi Takeuchi, Shinya Teranishi.
Application Number | 20110314796 13/170269 |
Document ID | / |
Family ID | 45115927 |
Filed Date | 2011-12-29 |
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United States Patent
Application |
20110314796 |
Kind Code |
A1 |
NAKAMURA; Satoshi ; et
al. |
December 29, 2011 |
PARTICULATE MATTER DETECTION SENSOR AND CONTROL DEVICE OF
CONTROLLING THE SAME
Abstract
A particulate matter (PM) detection sensor is placed in an
exhaust gas pipe of a diesel engine. The PM sensor element has a
detection part composed of a pair of detection electrodes and a
heater part. The detection electrodes and the heater part are
stacked in the PM sensor element. A control circuit instructs a
heater power supply to supply electric power to the heater part
when the diesel engine is started to operate. The heater part heats
the detection part at a predetermined temperature T1 within a range
of 600.degree. C. to 900.degree. C. for a predetermined period S1
of time, for example, 650.degree. C. for 20 seconds, in order to
burn and completely eliminate particulate matter accumulated in the
detection part. This control process avoids incorrect detection of
the PM detection sensor. After this process, the control circuit
executes usual control of the PM detection sensor.
Inventors: |
NAKAMURA; Satoshi;
(Okazaki-shi, JP) ; Teranishi; Shinya; (Chita-gun,
JP) ; Takeuchi; Hirofumi; (Okazaki-shi, JP) ;
Sawada; Takashi; (Chiryu-shi, JP) ; Itoh;
Hideaki; (Kuwana-shi, JP) |
Assignee: |
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
45115927 |
Appl. No.: |
13/170269 |
Filed: |
June 28, 2011 |
Current U.S.
Class: |
60/276 |
Current CPC
Class: |
Y02T 10/40 20130101;
F02D 41/1466 20130101; G01N 15/0656 20130101; Y02T 10/47 20130101;
F01N 9/002 20130101 |
Class at
Publication: |
60/276 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2010 |
JP |
2010-147862 |
Claims
1. A control device of controlling a particulate matter detection
sensor placed in an exhaust gas pipe of an internal combustion
engine through which exhaust gas emitted from the internal
combustion engine flows and discharged to the outside, the
particulate matter detection sensor having a particulate matter
sensor element comprised of an insulation substrate, a detection
part composed of a pair of detection electrodes formed on a surface
of the insulation substrate, and a heater part of generating heat
energy when receiving electric power in order to heat the detection
part at a predetermined temperature, the control device comprising
a control part which detects an electrical resistance value between
the pair of the detection electrodes in the detection part, the
electrical resistance value between the pair of the detection
electrodes in the detection part changing in accordance with a
change of quantity of particulate matter accumulated in the
detection part, and the control part adjusting electric power
supply to the heater part, the control part comprising: combustion
control means which executes combustion control when the internal
combustion engine is started to operate, and in the combustion
control, the combustion control means supplies electric power to
the heater part in order to maintain the detection part of the
particulate matter detection sensor at a predetermined temperature
T1 for a predetermined period S1 of time in order to burn the
accumulated particulate matter in order to eliminate the
accumulated particulate matter from the detection part of the
particulate matter detection sensor; and usual control means which
executes usual control after completion of the combustion control
which is executed when the internal combustion engine is started to
operate, wherein in the usual control, the usual control means
supplies electric power to the heater part in order to maintain the
detection part of the particulate matter sensor element at a
temperature T2 which is less than the predetermined temperature T1
in order to detect particulate matter accumulated in the detection
part.
2. The control device according to claim 1, wherein the control
part further comprises electric power supply timing means which
determines a time to supply electric power to the heater part,
counted from a time when the internal combustion engine is started
to a time when the electric power is supplied to the heater part on
the basis of the operation state of the internal combustion
engine.
3. The control device according to claim 2, wherein the electric
power supply timing means calculates an amount of condensed water
remained in the exhaust gas pipe adhering to the detection part in
the particulate matter detection sensor, and delays the timing to
supply the electric power to the heater part on the basis of the
calculated amount of condensed water.
4. The control device according to claim 1, wherein the combustion
control means supplies the electric power to the heater part in
order to maintain the detection part of the particulate matter
detection sensor at the predetermined temperature T1 within a range
of not less than 600.degree. C. to not more than 900.degree. C.
5. The control device according to claim 4, wherein the combustion
control means supplies the electric power to the heater part in
order to maintain the detection part of the particulate matter
detection sensor at the predetermined temperature T1 of not less
than 650.degree. C. for the predetermined period S1 of time of not
less than 20 seconds.
6. The control device according to claim 1, wherein the usual
control means supplies the electric power to the heater part in
order to maintain the detection part of the particulate matter
detection sensor at a predetermined temperature within a range of
not less than 50.degree. C. to not more than 600.degree. C.
7. The control device according to claim 1, wherein the detection
part is comprised of the pair of the detection electrodes having a
comb shape and detection lead parts formed on a front surface of
the insulation substrate, and the heater part is comprised of
heater electrodes and heater lead parts formed at the front end in
a back surface of the insulation substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is related to and claims priority from
Japanese Patent Application No. 2010-147862 filed on Jun. 29, 2010,
the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the invention
[0003] The present invention relates to particulate matter
detection sensors and control devices of controlling such a
particulate matter detection sensor, and more particularly,
particulate matter detection sensors of an electric-resistance type
and control devices of detecting a quantity of particulate matter
contained in target detection gas such as exhaust gas emitted from
an internal combustion engine. Such a particulate matter detection
sensor is placed in an exhaust gas pipe of an exhaust gas purifying
system of the internal combustion engine and is applied to
detecting defect of a diesel particulate filter which traps or
traps particulate matters contained in the exhaust gas in order to
purify the exhaust gas.
[0004] 2. Description of the Related Art
[0005] In general, a diesel engine exhaust gas system of a diesel
engine is equipped with a diesel particulate filter (DPF). The DPF
is placed in an exhaust gas pipe of the diesel engine exhaust gas
system. The DPF can trap and eliminate conductive particulate
matter PM from exhaust gas emitted from the diesel engine. The
particulate matter PM contains environmental harmful matter, in
particulate, soot and soluble organic fraction (SOF), etc. The DPF
is made of porous ceramics with a high heat resistance. When
exhaust gas passes in the exhaust gas pipe, cell walls having pores
in the DPF trap particulate matter contained in the exhaust gas in
order to purify the exhaust gas.
[0006] When a quantity of particulate matter PM trapped in the DPF
exceeds a predetermined allowable quantity, clogged cell walls
occur in the DPF, and a pressure loss of the DPF is thereby
increased. The clogged cell walls in the DPF allow the particulate
matter contained in the exhaust gas to pass through the DPF without
trapping the particulate matter. This prevents the exhaust gas from
being purified. In order to avoid this, it is required to execute
the regeneration of the DPF every predetermined period of time in
order to recover the trapping function of the DPF.
[0007] For example, it is possible to detect the time to execute
the regeneration of the DPF by using a differential sensor, because
the pressure difference of the differential sensor is increased
when the quantity of trapped particulate matter in the DPF is
increased. In the regeneration of the DPF, combustion exhaust gas
at a high temperature is forcedly introduced into the inside of the
DPF by using a heater or executing post-injection in order to burn
and eliminate the trapped particulate matter from the DPF.
[0008] On the other hand, there has been proposed a particulate
matter detection sensor capable of directly detecting particulate
matter contained in exhaust gas emitted from an internal combustion
engine. Such a particulate matter detection sensor is placed at a
downstream side of the DPF in order to detect the quantity of
particulate matter contained in exhaust gas after passing through
the DPF. For example, an on-board diagnosis device (OBD) monitors
the operation condition of the DPF can use the detection result of
a particulate matter detection sensor in order to detect defect and
damage to the DPF.
[0009] When such a particulate matter detection sensor is placed at
the upstream side of the DPF, it is possible to detect the quantity
of particulate matter contained in the exhaust gas which is
introduced into the DPF and to detect the optimum time to execute
the regeneration of the DPF, instead of using the differential
sensor.
[0010] For example, Japanese patent publication No. JP H02-44386
discloses a soot concentration sensor of an electric resistance
type. In the soot concentration sensor, a pair of conductive
detection electrodes is formed on a front surface of an insulation
substrate, and a heater is formed on the back surface or in the
inside of the insulation substrate. This soot sensor uses
conductive characteristics of soot. The soot sensor detects an
electric resistance which is changed in accordance with the change
of the quantity of soot particles accumulated between the detection
electrodes. The detection electrodes form a detection part in the
soot sensor. A heater part generates heat energy when receiving
electric power in order to heat the detection part at a temperature
within the range of 400.degree. C. to 600.degree. C., and detect
the resistance between the detection electrodes. After detecting
the resistance, the accumulated particulate matter is burned in
order to eliminate the particulate matter from the soot sensor and
regenerate it.
[0011] In addition, Japanese patent laid open publication No.
2009-144577 discloses a device equipped with a particulate matter
trap sensor in which a plurality of electrodes, which face to each
other at a predetermined gap, is formed on an insulation material.
The device calculates an index corresponding to the electric
resistance value between the detection electrodes, and judges
occurrence of faulty in a particulate filter when the detected
index becomes smaller than a predetermined reference value.
Further, the device resets the PM trap sensor every regular
condition (every predetermined driving time, predetermined driving
distance, and quantity of used fuel).
[0012] There are other conventional techniques for detecting
particulate matter contained in exhaust gas on the basis of
detecting heat energy generated by oxidizing particulate matter by
using catalyst and a thermocouple, monitoring temperature and
chemical seeds contained in exhaust gas by using wavelength
variable diode sensor. In particular, particulate matter detection
sensors of an electric resistance type have a simple configuration
and can output a relatively stable output signal.
[0013] By the way, there is a possibility of being particulate
matter emitted from a previous combustion of an internal combustion
engine and trapped and remained in a detection part of a
particulate matter detection sensor when the engine is
restarted.
[0014] The former conventional technique (Japanese patent
publication No. JP H02-44386) previously described burns off
remained particulate matter which is trapped and accumulated on the
particulate matter detection sensor by continuing heating after
completion of the detection process. However, when the detection
process is executed, the temperature of the particulate matter
detection sensor is within a range of 400.degree. C. to 600.degree.
C., and this temperature is not always an adequate high temperature
capable of completely eliminating remained particulate matter from
the particulate matter detection sensor. Still further, it is
difficult to regenerate the particulate matter detection sensor
unless an adequate period of time is elapsed.
[0015] Still further, the sensor disclosed in the latter
conventional technique Japanese patent laid open publication No.
2009-144577 is burned every predetermined period of time for a
predetermined time in order to reset the sensor. However, there is
a possibility of generating the engine stop without resetting the
sensor completely.
[0016] This often causes incorrect output of the sensor after the
engine restart because the characteristics of particulate matter
trapped and remained in the detection part of the particulate
matter detection sensor is changed by the environment during the
engine stop or when the engine restart. For example, the sensor
often outputs an incorrect detection signal during the engine stop
and when the engine is restarted by adhering water and oil
components remained in the exhaust gas pipe to the particulate
matter detection sensor and by evaporating soot organic fraction
(SOF) contained in particulate matter remained in the exhaust gas
pipe.
SUMMARY OF THE INVENTION
[0017] It is an object of the present invention to provide a
particulate matter detection sensor of an electric resistance type
and a control device of preventing particulate matter accumulated
in a detection part of the particulate matter detection sensor from
being remained, and further preventing the detection accuracy of
the particulate matter detection sensor from being deteriorated and
decreased. The particulate matter detection sensor according to the
present invention outputs a stable and correct detection signal
with high accuracy.
[0018] To achieve the above purposes, the present invention
provides a control device which controls the operation of a
particulate matter detection sensor. The particulate matter
detection sensor is placed in an exhaust gas pipe of an internal
combustion engine through which exhaust gas emitted from the
internal combustion engine flows and is discharged to the outside.
The particulate matter detection sensor is equipped with a
particulate matter sensor element. The particulate matter sensor
element is comprised of an insulation substrate, a detection part
and a heater part. The detection part in the particulate matter
sensor element is comprised of a pair of detection electrodes
formed on a surface of the insulation substrate. The heater part
generates heat energy when receiving electric power in order to
heat the detection part at a predetermined temperature for a
predetermined period of time.
[0019] The control device has a control part. The control part
receives a detection signal transferred from the particulate matter
detection sensor and detects an electrical resistance value between
the pair of the detection electrodes in the detection part on the
basis of the received detection signal, etc. In general, the
electrical resistance value between the pair of the detection
electrodes is changed in accordance with a quantity of particulate
matter accumulated in the detection part. The control part supplies
electric power to the heater part. For example, the control part
instructs a heater power supply to supply electric power to the
heater part.
[0020] In particular, the control part is comprised of a combustion
control means and a usual control means. The combustion control
means executes combustion control when the internal combustion
engine starts to operate. The combustion control is executed when
the engine is started or restarted. In the combustion control, the
combustion control means supplies electric power to the heater part
in order to maintain the detection part of the particulate matter
detection sensor at a predetermined temperature T1 for a
predetermined period S1 of time in order to burn the accumulated
particulate matter and eliminate the accumulated particulate matter
from the detection part of the particulate matter detection sensor.
On the other hand, the usual control means executes usual control
after completion of the combustion control previously described
which is executed when the internal combustion engine is started to
operate. In the usual control, the usual control means supplies
electric power to the heater part in order to maintain the
detection part of the particulate matter sensor element in the
particulate matter detection sensor at a temperature T2 which is
less than the predetermined temperature T1 in order to detect
particulate matter adhered to and accumulated in the detection
part.
[0021] The combustion control means in the control circuit
according to the present invention executes the combustion control
every time when the internal combustion engine is started (or
restarted) to operate. In the combustion control, the combustion
control means supplies electric power to the heater part in order
to execute the combustion of particulate matter accumulated in the
detection part of the particulate matter sensor element. This
eliminates the accumulated particulate matter from the detection
part of the particulate matter sensor element. This can prevent
incorrect detection of the particulate matter detection sensor
caused by the particulate matter remained in the detection part,
and prevent the output of the particulate matter detection sensor
from being separated from a correct output value. According to the
present invention, it is possible for the particulate matter
detection sensor to output a stable and correct detection signal
with high accuracy regardless of operation conditions and
environmental condition of the internal combustion engine even if
it is before or after the start or stop of the internal combustion
engine.
[0022] In the control device as another aspect of the present
invention, the control part further comprises an electric power
supply timing means which determines a timing to supply electric
power to the heater part, counted from a time when the internal
combustion engine is started to a time when the electric power is
supplied to the heater part on the basis of the operation state of
the internal combustion engine.
[0023] In general, when the internal combustion engine is
restarted, there is a possibility of adhering water contained in
the inside of the exhaust gas pipe to the particulate matter sensor
element of the particulate matter detection sensor and causing
incorrect detection of the particulate matter detection sensor.
Further, there is a possibility for the particulate matter
detection sensor to be broken by adhering water to the particulate
matter detection sensor. In order to avoid this problem, the
electric power supply timing means in the control device according
to the present invention delays the time to supply electric power
to the heater part of the particulate matter sensor element. It is
therefore possible to prevent the breaking of the particulate
matter detection sensor by adhering water. The control device
according to the present invention allows the particulate matter
detection sensor to output a correct detection signal with high
accuracy.
0014
[0024] In the control device as another aspect of the present
invention, the electric power supply timing means calculates an
amount (or degree of risk) of condensed water remained in the
exhaust gas pipe adhering to the detection part in the particulate
matter detection sensor, and delays the timing to supply the
electric power to the heater part on the basis of the calculated
amount of condensed water.
[0025] According to the present invention, the electric power
supply timing means in the control device calculates the timing
when the electric power is supplied to the heater part on the basis
of the calculated amount (or the degree of risk) of condensed water
adhering to the detection part in the particulate matter detection
sensor. This control makes it possible to avoid the problem caused
by adhering water contained in the exhaust gas pipe to the
particulate matter detection sensor.
[0026] In the control device as another aspect of the present
invention, the combustion control means supplies the electric power
to the heater part in order to maintain the detection part of the
particulate matter detection sensor at the predetermined
temperature T1 within a range of not less than 600.degree. C. to
not more than 900.degree. C.
[0027] The combustion control means in the control device according
to the present invention executes the combustion control executed
when the internal combustion engine is started so that the
detection part in the particulate matter sensor element is
maintained at the temperature T1 which is within the range of not
less than 600.degree. C. to not more than 900.degree. C. This
combustion control makes it possible to maintain the durability of
the particulate matter sensor element and completely eliminate
accumulated particulate matter from the particulate matter sensor
element in the particulate matter detection sensor. Further, this
combustion control can suppress energy cost.
[0028] In the control device as another aspect of the present
invention, the combustion control means supplies the electric power
to the heater part in order to maintain the detection part of the
particulate matter detection sensor at the predetermined
temperature T1 of not less than 650.degree. C. for the
predetermined period S1 of time of not less than 20 seconds.
[0029] The combustion control means in the control device according
to the present invention executes the combustion control executed
when the internal combustion engine is started so that the
detection part in the particulate matter sensor element is
maintained at the temperature T1 of not less than 650.degree. C.
for the period S1 of time of not less than 20 seconds. This
combustion control makes it possible to completely eliminate
accumulated particulate matter from the particulate matter sensor
element with high efficiency.
[0030] In the control device as another aspect of the present
invention, the usual control means supplies the electric power to
the heater part in order to maintain the detection part of the
particulate matter detection sensor at a predetermined temperature
within a range of not less than 50.degree. C. to not more than
600.degree. C.
[0031] The usual control means in the control device according to
the present invention executes the usual control in order to
maintain the detection part at a temperature within a range of not
less than 50.degree. C. to not more than 600.degree. C. The usual
control makes it possible to allow a stable output, namely, a
correct detection signal output from the particulate matter
detection sensor.
[0032] In the control device as another aspect of the present
invention, the detection part is comprised of the pair of the
detection electrodes having a comb shape and detection lead parts
formed on a front surface of the insulation substrate. The heater
part is comprised of heater electrodes and heater lead parts formed
at the front end in a back surface of the insulation substrate.
[0033] According to the present invention, it is possible to easily
produce the particulate matter sensor element in the particulate
matter detection sensor because the detection part is comprised of
the pair of the detection electrodes and detection lead parts
formed on a front surface of the insulation substrate. On the other
hand, the heater part is comprised of heater electrodes and heater
lead parts formed at the front end in the back surface of the
insulation substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] A preferred, non-limiting embodiment of the present
invention will be described by way of example with reference to the
accompanying drawings, in which:
[0035] FIG. 1A is a perspective view showing a schematic structure
of a particulate matter (PM) sensor element in a PM detection
sensor and a control circuit according to an embodiment of the
present invention;
[0036] FIG. 1B is a schematic view showing an entire configuration
of an exhaust gas purifying system of a diesel engine for an motor
vehicle to which the PM detection sensor and the control circuit
according to the embodiment of the present invention are
applied;
[0037] FIG. 2 is an enlarged view showing a cross section of a part
of the PM detection sensor according to the embodiment of the
present invention which is mounted to an exhaust gas pipe in the
exhaust gas purifying system shown in FIG. 1B;
[0038] FIG. 3 is a flow chart showing the process for the control
circuit to supply electric power to a heater part in the PM sensor
element in the PM detection sensor according to the embodiment of
the present invention;
[0039] FIG. 4 is a flow chart showing a detailed process of a
combustion control executed when an internal combustion engine is
started;
[0040] FIG. 5 is a view showing an experimental result of a
relationship between the temperature T1 (C) of the PM sensor
element and the period S1 (seconds) of time to maintain the
temperature of the PM sensor element in the PM detection sensor
according to the embodiment of the present invention;
[0041] FIG. 6A is a timing chart showing the output change of the
PM detection sensor when the usual control is continuously
executed;
[0042] FIG. 6B is a timing chart showing the output change of the
PM detection sensor when the diesel engine is restarted after the
engine stop without executing the PM detection sensor regeneration
control after the detection process is executed by the PM detection
sensor during the usual control; and
[0043] FIG. 6C is a timing chart showing the output change of the
PM detection sensor when the combustion control is executed at the
engine start, but a PM detection sensor regeneration control is not
executed before the engine stop.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Hereinafter, various embodiments of the present invention
will be described with reference to the accompanying drawings. In
the following description of the various embodiments, like
reference characters or numerals designate like or equivalent
component parts throughout the several diagrams.
Embodiment
[0045] A description will be given of a particulate matter
detection sensor 1 and a control circuit 2 as a control device
according to an embodiment of the present invention with reference
to FIG. 1 to FIG. 6A, FIG. 6B and FIG. 6C.
[0046] The embodiment applies the particulate matter detection
sensor 1 (hereinafter, referred to the "PM detection sensor 1") to
an exhaust gas purifying system of an internal combustion
engine.
[0047] FIG. 1A is a perspective view showing a schematic structure
of a particulate matter sensor element 10 (hereinafter, referred to
the "PM sensor element 10") in the PM detection sensor 1 and the
control device 2 according to the embodiment of the present
invention. FIG. 1B is a schematic view showing an entire
configuration of the exhaust gas purifying system of an on-vehicle
diesel engine of an motor vehicle to which the PM detection sensor
1 and the control device 2 according to the embodiment of the
present invention are applied. FIG. 2 is an enlarged view showing a
cross section of a part of the PM detection sensor 1 according to
the embodiment of the present invention. In particular, the PM
detection sensor 1 is mounted to an exhaust gas pipe EX in the
exhaust gas purifying system of an on-vehicle diesel engine as an
internal combustion engine shown in FIG. 1B.
[0048] The diesel engine E/G shown in FIG. 1B is equipped with a
common rail fuel injection system. The common rail fuel injection
system increases the pressure of fuel by a high-pressure pump PMP.
The common rail R stores the fuel at a constant high pressure and
supplies the high pressure fuel to each of the cylinders by an
injector INJ.
[0049] The PM detection sensor 1 is placed at the downstream side
of the diesel particulate filter DPF in the exhaust gas pipe EX of
the diesel engine E/G. The control circuit 2 as the control device
and each of parts of the diesel engine E/G control the operation of
the PM detection sensor 1. The control circuit 2 and the control
method will be explained in detail later.
[0050] A description will now be given of the structure of the
exhaust gas purifying system of the on-vehicle diesel engine of an
motor vehicle with reference to FIG. 1B.
[0051] As shown in FIG. 1B, a turbine TRB is mounted to an exhaust
gas manifold of the diesel engine E/G. When a turbo charger
TRB.sub.CGR in accordance with the rotation of the turbine TRB,
compressed air is supplied to the intake manifold MH.sub.IN through
an intercooler CLR.sub.INT.
[0052] A part of the exhaust gas discharged from an outlet manifold
MH.sub.EX is re-circulated to the intake manifold MH.sub.IN through
an EGR valve V.sub.EGR and an EGR cooler CLR.sub.EGR. Forced
induction increases the quantity of intake air in order to increase
combustion efficiency and EGR (Exhaust Gas Recirculation)
suppresses the combustion of the diesel engine in order to suppress
nitrogen oxide (NOx) from being discharged to the ambient
atmosphere of the motor vehicle.
[0053] A unit having diesel oxidation catalyst DOC and a diesel
particulate filter DPF are mounted to the exhaust gas pipe EX
connected to the outlet manifold MH.sub.EX in order to purify the
exhaust gas emitted from the diesel engine. That is, un-burned
components such as hydro carbon HC, carbon monoxide and nitric
oxide NO are oxidized when the exhaust gas passes through the
exhaust gas pipe EX after emitted from the diesel engine, and the
diesel particulate filter DPF traps soot (Soot), soluble organic
fraction (SOF) and particulate matter (PM) composed of inorganic
components contained in the exhaust gas. The diesel particulate
filter DPF is placed at the downstream side of the unit having the
diesel oxidation catalyst (DOC), as shown in FIG. 1B.
[0054] In general, such a diesel oxidation catalyst DOC is
supported on a surface of a known monolith support, for example, a
ceramic honeycomb structure body made of cordierite. When the
diesel particulate filter DPF is forcedly regenerated, fuel is
supplied and burned in oxidation. This increases the temperature of
the exhaust gas and the diesel oxidation catalyst DOC oxides and
eliminates soot of fraction (SOF) components contains in
particulate matter PM. Nitrogen dioxide NO.sub.2 generated by
oxidizing nitric oxide NO is used as oxidizing agent of particulate
matter PM accumulated in the DPF which is placed at the downstream
side of the unit having the diesel oxidation catalyst DOC. This
makes it possible to execute continuous oxidizing.
[0055] The diesel particulate filter DPF has a filter structure of
a wall flow type which is well known. For example, a porous ceramic
honeycomb structure body is extruded and molded. The porous ceramic
honeycomb structure body is made of heat resistance ceramics such
as cordierite. On the inlet surface of the diesel particulate
filter DPF, cells are alternately plugged by plug members so that
the surface of the inlet surface has a checkered pattern in which
one of adjacent cells is plugged and the other cell is open, and
the outlet surface has the checkered pattern in which one of
adjacent cells is plugged and the other cell is open. That is, the
diesel particulate filter DPF is composed of a plurality of cells
formed by cell walls. One end part of each of the cells is open and
the other end part thereof is plugged so that the plugged parts are
alternately formed on each of the inlet surface and the outlet
surface of the diesel particulate filter DPF.
[0056] Each of the cells is formed in parallel along the
longitudinal direction of the diesel particulate filter DPF. In
particular, the cell walls in the adjacent cells have porous
structure through which the exhaust gas passes. The porous
structure of the cell walls (porous cell walls) traps particulate
matter PM contained in the exhaust gas when the exhaust gas passes
through the porous cell walls.
[0057] It is possible to form a continuous type diesel particulate
filter composed of the diesel oxidation catalyst DOC and the diesel
particulate filter DPF.
[0058] A differential pressure sensor SP is placed in the exhaust
gas pipe EX in order to monitor the quantity of particulate matter
PM accumulated in the diesel particulate filter DPF.
[0059] The differential pressure sensor SP is connected to the
exhaust gas pipe EX at the upstream side and the downstream side of
the diesel particulate filter DPF through pressure introduction
pipes. The differential pressure sensor SP detects the pressure of
the exhaust gas at the upstream side and the downstream side of the
diesel particulate filter DPF, respectively, and outputs a
detection signal corresponding to the pressure difference detected
at the upstream side and the downstream side of the diesel
particulate filter DPF.
[0060] Further, temperature sensors S1, S2 and S3 are placed at the
upstream side of the unit having the diesel oxidation catalyst DOC,
the upstream side and the downstream side of the diesel particulate
filter DPF in order to detect the temperature of the exhaust
gas.
[0061] The control circuit 2 receives the detection signals
transferred from these sensors and monitors the activation state of
the diesel oxidation catalyst DOC and the quantity of particulate
matter PM accumulated in the diesel particulate filter DPF on the
basis of the detection signals. When the quantity of particulate
matter PM accumulated in the diesel particulate filter DPF exceeds
a predetermined allowable value, the control circuit 2 forcedly
executes the process of burning the particulate matter PM
accumulated in the diesel particulate filter DPF in order to
regenerate the diesel particulate filter DPF and eliminate the
particulate matter PM from the diesel particulate filter DPF.
[0062] Further, the particulate matter detection sensor (PM
detection sensor) 1 detects particulate matter PM which passes
through the diesel particulate filter DPF and travels to the
downstream side of the diesel particulate filter DPF.
[0063] As shown in FIG. 1A, the PM detection sensor 1 is composed
of a particulate matter sensor element (PM sensor element) 10. The
PM sensor element 10 is composed of an insulation substrate 13, a
pair of detection electrodes 11 and 12, a pair of electrode leads
111 and 121, and a heater part 300. The insulation substrate 13 is
made of electrical insulation material. The pair of the detection
electrodes 11 and 12 and the pair of the electrode leads 111 and
121 are formed on one surface of the insulation substrate 13. The
detection electrodes 11 and 12 make the detection part 100. The
heater part 300 is formed or laminated on the other surface of the
insulation substrate 13. The heater part 300 generates heat energy
in order to heat the detection part 100 when receiving electric
power.
[0064] The detection part 100 is connected to the control circuit 2
through the electrode leads 111 and 121. The detection part 100
detects a resistance value between the detection electrodes 11 and
12 and outputs a detection signal corresponding to the detected
resistance value. The heater part 300 is composed of a heater
electrode 31 and heater leads 311 and 321. The heater electrode 31
and the heater leads 311 and 321 are formed on the surface of the
insulation substrate 32. The heater part 300 is connected to the
heater power source 21 through the heater leads 311 and 321. The
control circuit 2 instructs the heater power source 21 to supply
electric power to the heater part 300.
[0065] The detection part 100 is produced by the following method.
For example, ceramic material having alumina of a superior electric
insulation and a superior heat resistance is formed on the
insulation substrate 13 of a plate shape by using doctor blade, and
press mold method. The detection electrodes 11 and 12 are formed at
the front end of the insulation substrate 13 so that the detection
electrodes 11 and 12 have a comb structure in which the detection
electrodes 11 and 12 alternately face to each other at a
predetermined gap. The detection electrodes 11 and 12 are formed by
printing conductive paste containing noble metal such as platinum
Pt in a predetermined pattern on a surface (or a front surface) of
the insulation substrate 13. The detection electrodes 11 and 12 are
connected to one end terminal of each of the electrode leads 111
and 121 formed on the surface of the insulation substrate 13.
[0066] On the other hand, the heater part 300 is produced by
printing the heater electrodes 30 and the heater leads 311 and 312
in a predetermined pattern on the surface (the detection part 100
side) of the insulation substrate 32 by using the same method. The
heater electrodes 31 of the heater part 300 are formed directly
below the detection electrodes 11 and 12 in order to heat the
detection part 100 at a predetermined temperature with good
efficiency. In other words, the detection electrodes 11 and 12 are
formed on the front surface of the entire insulation substrate
composed of the insulation substrate 12 and the insulation
substrate 32. The insulation substrate 12 and the insulation
substrate 32 are stacked. The heater part 300 is formed on the back
surface of the entire insulation substrate composed of the
insulation substrate 12 and the insulation substrate 32.
[0067] As shown in FIG. 2, the PM detection sensor 1 has a
cylindrical housing case 50 which is screwed into the wall of the
exhaust gas pipe EX. The PM detection sensor 1 accommodates the
upper half of the PM sensor element 10 which is inserted into and
fixed to a cylindrical insulator 60. The bottom half of the PM
sensor element 10 is fixed to the base part of the cylindrical
housing case 50 and placed in a hollow cover body 40. The hollow
cover body 40 with the bottom half of the PM sensor element 10
projects in the inside of the exhaust gas pipe EX. inlet holes 410
and 411 are formed in the base part and the side part of the hollow
cover body 40 in order to introduce the exhaust gas in the exhaust
gas pipe EX. The exhaust gas flows from the diesel particulate
filter DPF and contains particulate matter PM.
[0068] In order to trap particulate matter PM contained in the
exhaust gas, as shown in FIG. 2, it is preferable to place the PM
detection sensor 1 in the exhaust gas pipe EX so that the detection
part 100 in the PM sensor element 10 faces the upstream side of the
exhaust gas pipe EX. Further, it is possible to avoid incorrect
detection caused by accumulating particulate matter PM between the
electrode leads 111 and 121 when the PM sensor element 10 has a
structure in which an insulation protection layer 14 is formed on
the surface of the insulation substrate 13 excepting the detection
part 100 so that the electrode leads 111 and 121 are covered with
the insulation protection layer 14.
[0069] Next, a description will now be given of the basic operation
of the PM detection sensor 1 according to the present
invention.
[0070] As shown in FIG. 2, the exhaust gas of the diesel engine E/G
is introduced into the inside of the PM detection sensor 1 through
the intake hole 411 which is formed in the cover body 40 of the PM
detection sensor 1. The intake hole 411 faces to the upper stream
side of the exhaust gas in the exhaust gas pipe EX. After being in
contact with the PM sensor element 10, the exhaust gas is
discharged into the exhaust gas pipe EX as the outside of the PM
detection sensor 1 through the hole 410 formed in the base surface
or the hole 411 faced to the downstream side of the exhaust
gas.
[0071] As shown in FIG. 1A, the detection electrodes 11 and 12
having a comb structure at a predetermined gap formed on the
surface of the detection part 100. When the PM detection sensor 1
is in its initial condition, no current flows between the detection
electrodes 11 and 12 because no particulate matter PM is
accumulated between the detection electrodes 11 and 12. When the
exhaust gas is introduced into the PM detection sensor 1,
particulate matter PM of conductive characteristics is gradually
accumulated between the detection electrodes 11 and 12. When the
quantity of particulate matter PM accumulated between the detection
electrodes 11 and 12 exceeds a predetermined value, a current flows
between the detection electrodes 11 and 12. The more the quantity
of particulate matter PM is increased, the more the resistance
value between the detection electrodes 11 and 12 is decreased. It
is therefore possible to detect the resistance value between the
detection electrodes 11 and 12 on the basis of this phenomenon.
That is, it is possible to execute the diagnosis of detecting
defect or failure of the diesel particulate filter DPF on the above
relationship.
[0072] For example, when a defect such as cell-wall defect occurs
in the diesel particulate filter DPF, the diesel particulate filter
DPF cannot execute a correct operation of trapping particulate
matter PM contained in the exhaust gas. This increases the quantity
of particulate matter PM contained in the exhaust gas discharged
from the diesel particulate filter DPF.
[0073] The control circuit 2 monitors the quantity of particulate
matter PM passing through the diesel particulate filter DPF during
a predetermined period of time by using the PM detection sensor 1.
When the monitored quantity of particulate matter PM is clearly
larger than usual quantity, the control circuit 2 judges an
occurrence of failure in the diesel particulate filter DPF. Even if
the diesel particulate filter DPF is in the usual condition, when
the quantity of particulate matter PM accumulated between the
detection electrodes 11 and 12 in the PM sensor element 10 exceeds
the predetermined value, the change rate of the resistance value
between the detection electrodes 11 and 12 becomes low, that is,
the detection accuracy of the PM detection sensor 1 is decreased.
In order to avoid this drawback, it is preferable to execute the
regeneration of the PM detection sensor 1 at a predetermined period
of time.
[0074] By the way, if the diesel engine E/G is stopped and
restarted without executing the regeneration of the PM detection
sensor 1, particulate matter PM previously adhered to the detection
electrodes 11 and 12 in the PM detection sensor 1 is remained. In
this case, the characteristics of particulate matter PM are changed
according to the environmental condition when the diesel engine E/G
is stopped and restarted. This influences the output of the PM
detection sensor 1. For example, when the diesel engine E/G is
stopped under the high temperature of the exhaust gas pipe EX,
there is a possibility of evaporating soluble organic fraction
(SOF) only contained in the particulate matter PM between the
detection electrodes. This changes the conductivity of particulate
matter PM, the output of the PM detection sensor 1 is also changed
when the diesel engine E/G is restarted. Further, when the diesel
engine E/G is started in cold environment, there is a possibility
of adhering water or dew condensation onto the detection part of
the detection electrodes 11 and 12. This changes the conductivity
of particulate matter PM, the output of the PM detection sensor 1
is also changed when the diesel engine E/G is restarted. This
causes incorrect output of the PM detection sensor 1 because the
accumulation of particulate matter PM between the detection
electrodes 11 and 12 is changed or the water is evaporated. The
above conditions when the diesel engine E/G is started are
different every time. Because soluble organic fraction (SOF) is not
evaporated, but hardened or burnt according to the change of the
temperature and conditions (for example, concentration of oxygen)
of the exhaust gas, it is difficult to predict the magnitude of
incorrect output of the PM detection sensor 1.
[0075] In order to solve the above problems causing incorrect
output of the PM detection sensor 1, the control circuit 2 adjusts
the supply of electric power to the heater part 300 at the engine
start and the execution of the usual control. That is, the control
circuit 2 firstly executes the process of burning and eliminating
particulate matter PM accumulated (or remained) in the PM detection
sensor 1 when the diesel engine E/G is started. The control circuit
2 then executes the usual control process which detects the
presence and quantity of particulate matter contained in the
exhaust gas. Thereby, the control circuit 2 suppresses the
fluctuation of the output of the PM detection sensor 1 and avoids
causing incorrect detection of the PM detection sensor 1 by burning
the accumulated particulate matter PM and eliminating the
accumulated particulate matter PM from the PM detection sensor 1
when the diesel engine E/G is started.
[0076] Specifically, the control circuit 2 instructs the heater
power source 21 to supply electric power to the heater part 300
when the diesel engine E/G is started. The detection part 100 of
the PM detection sensor 1 is thereby heated at the temperature T1
during the period S1 of time. The temperature T1 allows the
detection part 100 to burn and eliminate the accumulated
particulate matter PM. That is, the control circuit 2 executes the
combustion control at the engine start. In the combustion control
executed at the engine start particulate matter PM accumulated on
the surface of the detection part 100 is burned and eliminated
completely. This combustion control at the engine start corresponds
to the function executed by the combustion control means used in
the claims.
[0077] After the combustion control at the engine start, the
control circuit 2 adjusts the electric power supply to the
detection part 100 in order to maintain the detection part 300 at a
temperature T2 which is within a temperature range of less than the
temperature T1. This control allows the PM detection sensor 1 to
detect particulate matter PM adhered on the detection electrodes 11
and 12 (as the usual control means used in the claims).
[0078] In the combustion control at the engine start, when the
diesel engine start and the electric power supply to the heater
part 300 are simultaneously executed, condensed water is scattered
in the exhaust gas pipe EX, and the scattered water is adhered to
the detection part 100 in the PM detection sensor 1 of a high
temperature. When the scattered water is adhered to the PM
detection sensor 1 of a high temperature, the PM detection sensor 1
is broken. In order to avoid this, it is necessary to delay the
time to start the electric power supply to the PM sensor element 10
until the condensed water in the exhaust gas pipe EX is dried or no
condensed water is adhered to the PM sensor element 10.
[0079] In order to ensure the above problem, it is necessary for
the control circuit 2 to calculates an amount (or degree of risk)
of condensed water remained in the exhaust gas pipe adhering to the
detection part 100 in the particulate matter detection sensor 1 on
the basis of the operation condition of the diesel engine E/G, and
to delay the execution of the electric power supply to the heater
part 300 on the basis of the calculated amount (or degree of risk)
of condensed water. That is, it is preferable for the control
circuit 2 to delay the execution of the electric power supply to
the heater part 300 until the amount (or degree of risk) of
condensed water adhering to the detection part 100 in the PM
detection sensor 1 is entered into its allowable range. It is also
possible to use the relationship between the timing when the
electric power supply to the detection part 100 and a coefficient
corresponding to the calculated amount (or degree of risk) of
condensed water adhering to the detection part 100 which is
calculated on the basis of the operation condition of the diesel
engine E/G. In the latter case, the control circuit 2 starts the
electric power supply to the detection part 100 in the PM sensor
element 10 at the timing which is determined on the basis of the
coefficient corresponding to the amount (or degree of risk) of
condensed water adhering to the detection part 100. This control
makes it possible to detect the quantity of particulate matter PM
adhered to the PM detection sensor 1 with high accuracy while
suppressing the detection part 100 from being broken by adhering
condensed water to the detection part 100.
[0080] A description will be given of the control operation of the
control circuit 2 with reference to FIG. 3 and FIG. 4.
[0081] FIG. 3 is a flow chart showing the process for the control
circuit 2 to supply electric power to the heater part 100 in the PM
detection sensor 1 according to the embodiment of the present
invention.
[0082] As shown in FIG. 3, when the diesel engine E/G is started,
the control circuit 2 receives detection signals transferred from
various sensors (step S100). At this time, in order to detect the
operation condition of the diesel engine E/G and the temperature
condition in the exhaust gas pipe EX, the control circuit 2
receives detection signals transferred from a water temperature
sensor (not shown) and an oil temperature sensor (not shown). The
water temperature sensor detects the temperature of engine cooling
water. The oil temperature sensor detects the temperature of
lubricating oil.
[0083] The control circuit 2 further receives a detection signal
transferred from an intake air temperature sensor. The intake air
temperature sensor is embedded in an air flow meter AFM capable of
detecting the temperature of ambient air. Still further, the
control circuit 2 receives a detection signal transferred from a
temperature sensor S3 which is placed at the downstream side of the
diesel particulate filter DPF in order to detect the temperature of
the exhaust gas around the PM detection sensor 1. Still further,
the control circuit 2 receives the detection signal transferred
from the rotation sensor capable of detecting the rotation of the
diesel engine E/G, the detection signal transferred from a sensor
capable of detecting the quantity of fuel injection, and the
detection signal transferred from a sensor capable of detecting the
operation time length of the diesel engine E/G.
[0084] In step S101, the control circuit 2 calculates an amount (or
degree of risk) of condensed water adhering to the detection part
100 in the PM sensor element 10 in the PM detection sensor 1 on the
basis of the information obtained from the received detection
signals transferred from the various sensors. Specifically, the
control circuit 2 predicts the quantity of condensed water which is
generated and stayed in the inside of the exhaust gas pipe EX at
the upstream of the PM detection sensor 1 on the basis of the
elapsed period of time, the operation condition and temperature
condition of the diesel engine E/G after the engine start, where,
the elapsed period of time is the time length counted form the time
when the diesel engine E/G is previously started to the current
time.
[0085] The control circuit 2 then calculates the amount (or degree
of risk) of condensed water adhering to the detection part 100 in
the PM detection sensor 1 by using the relationship obtained in
advance on the basis of the shape of the exhaust gas pipe EX. For
example, the ambient temperature is low, water is condensed in the
exhaust gas pipe EX when the temperature of the exhaust gas pipe EX
is decreased after the engine stop or when exhaust gas is
introduced into the inside of the exhaust gas pipe EX at a low
temperature immediately after the engine start. Further, when the
temperature of the exhaust gas pipe EX is relatively high in a
short elapsed period of time after the engine stop, the quantity of
condensed water is low, and the condensed water can be evaporated
within a short period of time. Still further, even if having the
same quantity of condensed water, it is possible to easily generate
condensed water in the exhaust gas pipe EX when the exhaust gas
pipe EX has a curved shape. It is often difficult to scatter the
condensed water in the exhaust gas pipe EX having such a curved
shape. Accordingly, it is necessary to make an additional map in
advance on the basis of experimental results obtained by
considering the above conditions. It is also possible to calculate
the amount (or degree of risk) of condensed water adhering to the
detection part 100 in the PM detection sensor 1 by using the
equation which considers the above conditions.
[0086] In step S102, the control circuit 2 detects whether or not
the calculated amount (or degree of risk) of condensed water, which
indicates a probability that condensed water is sc adhered to the
PM detection sensor 1, is less than a predetermined value. The
predetermined value is the minimum value of causing the PM sensor
element 10 in the PM detection sensor 1 breaking when the electric
power is supplied to the PM detection sensor 1. When the detection
result in step S102 indicates affirmative ("YES" in step S102),
there is no possibility of breaking the PM detection sensor 1. The
operation flow goes to step S103. In step S103, the control circuit
2 executes the combustion control in order to start the operation
of the diesel engine E/G.
[0087] On the other hand, when the detection result in step S102
indicates negative ("NO" in step S102), there is a possibility of
breaking the PM detection sensor 1. The operation flow is returned
to step S100. The control circuit 2 continues the routine of steps
S100, S101 and S102 until there is no more possibility of breaking
the PM sensor 1 in order to delay the start of supplying electric
power to the heater part 300.
[0088] In step S103, the control circuit 2 executes the combustion
control at the engine start. Specifically, the control circuit 2
instructs the heater power source 21 to supply electric power to
the heater part 300 in the PM detection sensor 1 in order to burn
and eliminate particulate matter PM accumulated in the detection
part 100.
[0089] A description will now be given of the combustion control
which is executed when the diesel engine E/G is started or
restarted with reference to FIG. 4.
[0090] FIG. 4 is a flow chart showing a detailed process of the
combustion control at the engine start.
[0091] In step S200, the control circuit 2 receives various data
items in order to obtain the information regarding the quantity of
particulate matter PM accumulated in the detection part 100 in the
PM sensor element 10 in the PM detection sensor 1. The information
is:
[0092] (a1) Period of time counted from the time when the PM
combustion was executed in the previous usual control to the time
when the diesel engine E/G was stopped;
[0093] (a2) Period of time counted from the time when diesel engine
E/G was last stopped to the current time; and
[0094] (a3) Period of time counted from the time at the current
engine start to the time when the combustion control at the engine
start is started.
[0095] The control circuit 2 receives the operation state of the
diesel engine E/G and the temperature and time conditions of the
operation of the diesel engine E/G, for example, receives the
following data items in order to detect the quantity of particulate
matter PM adhered to and accumulated in the detection part 100 in
the PM sensor element 10 of the PM detection sensor 1 and the
change of the quantity of particulate matter PM in each of the
periods (a1), (a2) and (a3):
[0096] (b1) Temperature of cooling water of the diesel engine
E/G;
[0097] (b2) Temperature of lubricating oil;
[0098] (b3) Temperature of ambient atmosphere;
[0099] (b4) Temperature of exhaust gas;
[0100] (b5) Rotation number or speed of the diesel engine E/G;
and
[0101] (b6) Quantity Q of injection fuel.
[0102] In step S201, the control circuit 2 detects and calculates
following values:
[0103] (c1) Quantity of particulate matter PM accumulated in the
detection part 100 in the PM sensor element 10 of the PM detection
sensor 1 at the previous engine stop;
[0104] (c2) Quantity of water and hydro carbon (HC) which are
adhered to the PM detection sensor 1 or evaporated in the exhaust
gas pipe EX during the engine stop; and
[0105] (c3) Quantity of particulate matter PM to be adhered and
accumulated in the detection part 100 in the PM sensor element 10
of the PM detection sensor 1 during the period of time counted from
the current engine start to the time when the combustion control at
the engine start is started.
[0106] Because the change of each of the quantity of accumulated
particulate matter PM during the operation of the diesel engine
E/G, the quantity of water and hydro carbon (HC) during the engine
stop is fluctuated by the operation state of the diesel engine E/G
and the environment of the inside of the exhaust gas pipe EX.
Accordingly, the control circuit 2 calculates these changes by
using the experimental map which is obtained in advance or a
theoretical arithmetic equation.
[0107] The operation flow goes to step S202. In step S202, the
control circuit 2 calculates the combustion condition (Temperature
and Period of time) of burning particulate matter PM accumulated in
the detection part 100 in the PM sensor element 10 of the PM
detection sensor 1 on the basis of the adhesion condition (quantity
and composition of particulate matter PM) of particulate matter PM
calculated in step S201.
[0108] In general, it is preferable to burn accumulated particulate
matter PM at the temperature T1 during the combustion control at
the engine start. This temperature T1 is not less than the
allowable temperature at which particulate matter PM can be
completely burned. In the view of heat resistance of the heater
part 300 in the PM sensor element 10, it is preferable for the
temperature T1 to be not more than 900.degree. C.
[0109] Because the period S1 of time depends on the temperature T1,
the more the temperature T1 is increased, the more the period S1 of
time is decreased. It is preferable for the period S1 of time to be
not more than 5 minutes.
[0110] FIG. 5 is a view showing an experimental result of a
relationship between the temperature of the PM sensor element 10
and the period of time to maintain the temperature of the PM sensor
element 10 in the PM detection sensor 1 according to the embodiment
of the present invention.
[0111] The experimental condition with which the experimental
result shown in FIG. 5 is obtained is as follows.
[0112] As shown in FIG. 1B and previously described, the PM
detection sensor 1 is mounted to the exhaust gas pipe EX. The
control circuit 2 instructed the heater power source 21 to supply
electric power to the heater part 300 in the Pm sensor element 10
of the PM detection sensor 1 after the engine start in order to
maintain the PM sensor 1 at the predetermined temperature T1 for
the predetermined period S1 of time. The quantity of particulate
matter PM accumulated in the PM sensor element 10 of the PM
detection sensor 1 was detected. During this detection, the PM
sensor element 10 was maintained at the temperature within a range
of 550.degree. C. to 750.degree. C., and the period S1 of time was
changed.
[0113] As shown in FIG. 5, it is possible to eliminate the
particulate matter PM from the detection part 100 of the PM sensor
element 10 of the PM detection sensor 1 when the predetermined
temperature T1 was 600.degree. C. and the period S2 of time was not
less than 20 minutes, and when the predetermined temperature T1 was
700.degree. C. and the period S2 of time was not less than 10
minutes.
[0114] However, it is difficult to completely eliminate the
accumulated particulate matter PM from the detection part 100 of
the PM sensor element 10 when the predetermined temperature T1 was
not more than 550.degree. C. and the period S2 of time was 80
minutes. The above experimental results shown in FIG. 5 indicates
that it is necessary to maintain the PM detection sensor 1 at the
temperature T1 of not less than 600.degree. C., preferably, at the
temperature T1 of not less than 650.degree. C. for the period S1 of
time of not less than 20 seconds.
[0115] In step S203, the control circuit 2 executes the combustion
control at the engine start in order to burn the accumulated
particulate matter PM and eliminate them from the PM sensor element
10. That is, in step S203, the control circuit 2 instructs the
heater power source 21 to supply electric power to the heater part
300 of the PM sensor element 10 in the PM detection sensor 1 under
the conditions (temperature T1 and period S1 of time) which are
determined in step S202. This control makes it possible to heat the
detection part 10 at the temperature T1 for the period S2 of time.
The operation flow goes to step S2104. In step S204, the control
circuit 2 completes the combustion control at the engine start.
[0116] Return to the flow chart shown in FIG. 3, the operation flow
progresses to step S104. In step S104, the control circuit 2
executes the usual control. In the usual control in step S104, the
electric power is supplied to the heater part 300 of the PM sensor
element 10 of the PM sensor 1 in order to maintain the detection
part 100 at the temperature T2 which is lower than the temperature
T1. The execution of the usual control makes it possible to detect
the quantity of particulate matter PM accumulated in the detection
part 100 of the PM sensor element 10. As previously described, the
temperature T1 is used during the combustion control executed when
the engine is started (or restarted). Specifically, during the
usual control after completion of the combustion control executed
during the engine start, the control circuit 2 maintains the
detection part 100 in the PM sensor element 10 at the temperature
T2 within a range of 50.degree. C. to 600.degree. C. This control
makes it possible for the PM detection sensor 1 to output a stable
detection signal.
[0117] FIG. 6A is a timing chart showing the output change of the
PM detection sensor 1 when the usual control is continuously
executed. FIG. 6A shows the characteristics of the output of the PM
detection sensor. The output of the PM detection sensor is
increased when the pair of the detection electrodes in the
detection part is conducted after a period of time counted from the
PM sensor detection is executed, and the output of the PM detection
sensor is rapidly increased according to the elapsed of time and
saturated.
[0118] This means that the resistance value between the detection
electrodes is decreased according to increasing the quantity of
particulate matter PM accumulated in the detection part of the PM
sensor element. When the quantity of particulate matter PM
accumulated in the detection part exceeds a predetermined value,
the resistance value between them is not changed. Accordingly, it
is necessary to execute the sensor regeneration control
periodically in order to eliminate the particulate matter PM from
the detection part of the PM sensor element of the PM detection
sensor. The sensor regeneration control in this case can be
executed in parallel to the execution of the combustion control at
the engine start. That is, it is sufficient to maintain the PM
sensor at the predetermined temperature for the predetermined
period of time which allows the accumulated particulate matter from
being burned. For example, it is preferable to maintain the PM
sensor at a temperature within a range of 600.degree. C. to
900.degree. C. for not less than 20 seconds, in more preferable, at
a temperature within a range of 650.degree. C. for not less than 20
seconds, or maintain it at the temperature of 700.degree. C. for 10
seconds. After this, the same steps are continuously executed, as
previously described.
[0119] FIG. 6B is a timing chart showing the output change of the
PM detection sensor when the diesel engine is restarted (without
executing the combustion control at the engine start according to
the embodiment of the present invention) after the engine stop
without executing the PM detection sensor regeneration control
after the detection process is executed by the PM detection sensor
during the usual control.
[0120] The left side in FIG. 6B shows the case when the diesel
engine E/G is stopped after the detection electrodes and in the
pair in the detection part of the PM sensor element are
electrically conducted and the PM detection sensor starts to output
the detection signal. In this case, the combustion control at the
engine start is not executed when the diesel engine E/G is started
(or restarted). At this time, the sensitivity of the PM detection
sensor is changed when compared with the normal output curve
(designated by dotted line in FIG. 6B), and this has a high
possibility of executing incorrect detection of detecting the
quantity of particulate matter PM accumulated in the detection part
because the characteristics of accumulated particulate matter PM is
changed and water is adhered to the detection part when the diesel
engine E/G is stopped (at engine stop soaking).
[0121] The right side in FIG. 6B shows the case in which the diesel
engine E/G is stopped during no output of the PM detection sensor
after the detection electrodes in the pair in the detection part of
the PM sensor element are electrically conducted and the PM
detection sensor starts to output the detection signal. In this
case shown in the right side in FIG. 6B, there is a high
possibility of executing incorrect detection of the quantity of
particulate matter PM accumulated in the detection part because
particulate matter PM is accumulated between the detection
electrodes after the PM detection sensor regeneration control is
still remained in the detection part of the PM sensor element. It
is difficult to detect the quantity of particulate matter
accumulated in the detection part of the PM sensor element of the
PM detection sensor with high accuracy.
[0122] FIG. 6C is a timing chart showing the output change of the
PM detection sensor 1 when the control circuit 2 executes the
combustion control at the engine start. That is, the combustion
control is executed when the diesel engine E/G is started (or
restarted). In the case shown in FIG. 6C, the control circuit 2
does not execute the control of regenerating the PM detection
sensor 1 before the diesel engine E/G is stopped.
[0123] FIG. 6C shows the case in which the control circuit 2
executes the combustion control when the diesel engine E/G is
started without executing the regeneration control of regenerating
the PM detection sensor before the engine stop. As shown in FIG.
6C, it is possible for the present invention to execute the correct
detection of detecting the quantity of particulate matter PM
accumulated in the detection part 100 between the detection
electrodes 11 and 12 with high accuracy without causing the
fluctuation of the detection sensitivity of the PM detection sensor
and the change of the period of time in which the PM detection
sensor outputs no detection signal.
INDUSTRIAL APPLICABILITY
[0124] It is possible to place the PM detection sensor 1 according
to the present invention at the downstream side of the diesel
particulate filter DPF and detect the failure of the diesel
particulate filter DPF under the control of the control circuit 2
according to the present invention. It is also possible to place
the PM detection sensor 1 according to the present invention at the
upstream side of the diesel particulate filter DPF and directly
detect particulate matter PM which is introduced into the diesel
particulate filter DPF under the control of the control circuit 2
according to the present invention.
[0125] While specific embodiments of the present invention have
been described in detail, it will be appreciated by those skilled
in the art that various modifications and alternatives to those
details could be developed in light of the overall teachings of the
disclosure. Accordingly, the particular arrangements disclosed are
meant to be illustrative only and not limited to the scope of the
present invention which is to be given the full breadth of the
following claims and all equivalents thereof.
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