U.S. patent application number 16/170444 was filed with the patent office on 2019-05-09 for sensor system.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Kinji MORIHIRO.
Application Number | 20190136738 16/170444 |
Document ID | / |
Family ID | 66328390 |
Filed Date | 2019-05-09 |
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United States Patent
Application |
20190136738 |
Kind Code |
A1 |
MORIHIRO; Kinji |
May 9, 2019 |
SENSOR SYSTEM
Abstract
A sensor system includes: a controller configured to: predict a
temperature of exhaust gas of an internal combustion engine in a
position in which an exhaust gas sensor having a sensor element is
arranged; and control a heater so as to make a temperature of the
sensor element close to a target temperature included in a
predetermined range, wherein in cases where the predicted
temperature of the exhaust gas is higher than a reference
temperature, the controller is configured to make the target
temperature lower when the predicted temperature is high than when
it is low, within a range lower than the reference temperature,
whereas in cases where the predicted temperature is lower than the
reference temperature, the controller is configured to make the
target temperature lower when the predicted temperature is high
than when it is low, within a range higher than the reference
temperature.
Inventors: |
MORIHIRO; Kinji;
(Susono-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Toyota-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
66328390 |
Appl. No.: |
16/170444 |
Filed: |
October 25, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01N 13/008 20130101;
F01N 2560/20 20130101; F01N 2900/1404 20130101; F01N 2560/06
20130101; F01N 2900/1411 20130101; F01N 2900/1602 20130101; F01N
11/00 20130101; F01N 11/005 20130101 |
International
Class: |
F01N 11/00 20060101
F01N011/00; F01N 13/00 20060101 F01N013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2017 |
JP |
2017-214657 |
Claims
1. A sensor system comprising: an exhaust gas sensor that is
arranged in an exhaust passage of an internal combustion engine,
and is provided with a sensor element and a heater configured to
heat said sensor element; and a controller configured to: predict a
temperature of exhaust gas of said internal combustion engine in a
position in which said exhaust gas sensor is arranged; and control
said heater so as to make a temperature of said sensor element
close to a target temperature included in a predetermined range,
wherein in cases where a prediction temperature, which is the
temperature of the exhaust gas predicted by said controller, is
higher than a reference temperature included in said predetermined
range, said controller is configured to make said target
temperature lower when said prediction temperature is high than
when it is low, within a range lower than said reference
temperature, whereas in cases where said prediction temperature is
lower than said reference temperature, said controller is
configured to make said target temperature lower when said
prediction temperature is high than when it is low, within a range
higher than said reference temperature.
2. The sensor system as set forth in claim 1, wherein said
controller is further configured to: predict, based on an operating
state of said internal combustion engine, a flow rate of the
exhaust gas of said internal combustion engine in a position in
which said exhaust gas sensor is arranged; and make an amount of
deviation of said target temperature from said reference
temperature larger when the flow rate of the exhaust gas predicted
by said controller is large than when it is small.
3. The sensor system as set forth in claim 1, further comprising:
an accelerator opening sensor that detects an accelerator opening
degree; wherein said controller is further configured to predict
said temperature of the exhaust gas based on the accelerator
opening degree detected by said accelerator opening sensor.
4. The sensor system as set forth in claim 2, further comprising:
an accelerator opening sensor that detects an accelerator opening
degree; wherein said controller is further configured to predict
said flow rate of the exhaust gas based on the accelerator opening
degree detected by said accelerator opening sensor.
5. The sensor system as set forth in claim 1, wherein said
controller is further configured to provide an upper limit on a
rate of change at the time of changing said target temperature.
6. A sensor system comprising: an exhaust gas sensor that is
arranged in an exhaust passage of an internal combustion engine,
and is provided with a sensor element and a heater configured to
heat said sensor element; an accelerator opening sensor that
detects an accelerator opening degree; and a controller configured
to control said heater so as to make a temperature of said sensor
element close to a target temperature included in a predetermined
range; wherein in cases where said accelerator opening degree is
such that the temperature of the exhaust gas in the surrounding of
said exhaust gas sensor becomes higher than a reference temperature
included in said predetermined range, said controller is configured
to make said target temperature lower when said accelerator opening
degree is large than when it is small, within a range lower than
said reference temperature, whereas in cases where said accelerator
opening degree is such that the temperature of the exhaust gas in
the surrounding of said exhaust gas sensor becomes lower than said
reference temperature, said controller is configured to make said
target temperature lower when said accelerator opening degree is
large than when it is small, within a range higher than said
reference temperature.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Japanese Patent
Application No. 2017-214657 filed on Nov. 7, 2017 the entire
contents of which are incorporated by reference herein.
TECHNICAL FIELD
[0002] The present disclosure relates to a sensor system.
BACKGROUND ART
[0003] Some of sensors for detecting components contained in
exhaust gas of an internal combustion engine are provided with a
heater for heating a sensor element. For example, in an air fuel
ratio sensor, a detected value of the sensor changes with the
temperature of a sensor element even in the case of the same air
fuel ratio, and hence, detection accuracy of the air fuel ratio is
maintained by controlling the heater in such a manner that the
temperature of the sensor element falls within a predetermined
range. In addition, there has been known a technology in which the
temperature of a sensor element is adjusted within a predetermined
range, in order to change the detection sensitivity of the sensor
element with respect to specific exhaust gas components (e.g., NOx,
HC, CO) (refer to patent literature 1, for example). With the
technology described in patent literature 1, at the time when an
internal combustion engine is operated at a lean air fuel ratio at
which NOx tends to be generated under high load, etc., the
temperature of the sensor element is raised so as to increase its
reactivity with respect to NOx, whereas at the time when the
internal combustion engine is operated at a rich air fuel ratio at
which HC and CO tend to be generated under low load, etc., the
temperature of the sensor element is lowered so as to increase its
reactivity with respect to HC, CO.
CITATION LIST
Patent Literature
[0004] Patent Literature 1: Japanese patent application laid-open
publication No. 2003-314350
SUMMARY
Technical Problem
[0005] Even if the temperature of the sensor element is adjusted by
a heater to fall within the predetermined range in order to
maintain the detection accuracy of the sensor, for example, in
cases where the internal combustion engine is operated at high
load, the temperature of the exhaust gas is high, so the sensor
element receives heat from the exhaust gas, and the temperature of
the sensor element goes up, without being heated by the heater. As
a result, when the sensor element is further heated to raise its
temperature by means of the heater, the temperature of the sensor
element will become excessively high, and may be deviated from the
predetermined range. That is, there is a fear that the detection
accuracy of the sensor will drop.
[0006] The present disclosure has been made in view of the problems
as mentioned above, and the object of the disclosure is to maintain
the temperature of a sensor element in a suitable range.
Solution to Problem
[0007] One aspect of the present disclosure resides in a sensor
system which comprises: an exhaust gas sensor that is arranged in
an exhaust passage of an internal combustion engine, and is
provided with a sensor element and a heater configured to heat said
sensor element; a controller configured to: predict a temperature
of exhaust gas of said internal combustion engine in a position in
which said exhaust gas sensor is arranged; and control said heater
so as to make a temperature of said sensor element close to a
target temperature included in a predetermined range, wherein in
cases where a prediction temperature, which is the temperature of
the exhaust gas predicted by said controller, is higher than a
reference temperature included in said predetermined range, said
controller is configured to make said target temperature lower when
said prediction temperature is high than when it is low, within a
range lower than said reference temperature, whereas in cases where
said prediction temperature is lower than said reference
temperature, said controller is configured to make said target
temperature lower when said prediction temperature is high than
when it is low, within a range higher than said reference
temperature.
[0008] The exhaust gas sensor is a sensor which can adjust the
temperature of the sensor element by controlling electrical supply
to the heater. The temperature of the sensor element can be changed
by the heat which is received by the sensor element from the
exhaust gas or the heat which is deprived by the exhaust gas from
the sensor element, irrespective of the heater. Here, it is
considered that the heater is controlled in a feedback manner so
that the temperature of the sensor element becomes close to the
target temperature, but when the electrical supply to the heater is
controlled after the temperature of the sensor element has actually
changed, the electrical supply control of the heater will be
delayed with respect to the temperature change of the sensor
element, giving rise to a fear that the temperature of the sensor
element may deviate from the predetermined range. Here, note that
the predetermined range is a range of temperature where the
detection accuracy of the exhaust gas sensor falls within an
allowable range, and it is a range based on a range of activation
temperature of the sensor element. Also, note that the
predetermined range may be a range equal to the activation range of
the sensor element, or may be a range narrower than the activation
range in order to provide a margin so that the temperature of the
sensor element does not deviate from the activation range. The
reference temperature for the temperature of the sensor element may
be a temperature at which the detection accuracy of the exhaust gas
sensor becomes the highest, or may also be a central temperature of
a temperature range in which the detection accuracy of the exhaust
gas sensor becomes the highest. In addition, the reference
temperature may also be a central temperature of the predetermined
range.
[0009] The temperature of the exhaust gas in the surrounding of the
exhaust gas sensor can be predicted from an operating state of the
internal combustion engine, a heat capacity in an exhaust system
from the internal combustion engine to the exhaust gas sensor, etc.
That is, the temperature of the exhaust gas flowing out from the
internal combustion engine has a correlation with the operating
state of the internal combustion engine, and so can be predicted,
even before the exhaust gas is actually discharged from the
internal combustion engine. In addition, the exhaust gas discharged
from the internal combustion engine is deprived of heat by the
exhaust system and the temperature of the exhaust gas drops, while
flowing through the exhaust system. This amount of temperature drop
can also be predicted in advance. Accordingly, even before the
exhaust gas of the internal combustion engine reaches an area or
vicinity surrounding the exhaust gas sensor, the temperature of the
exhaust gas at the time when the exhaust gas reaches the area
surrounding the exhaust gas sensor can be predicted. Then, when
changing the temperature of the sensor element in advance based on
a predicted temperature of the exhaust gas, it is possible to
suppress the temperature control of the sensor element from being
delayed with respect to a change in the temperature of the exhaust
gas. That is, in cases where the predicted temperature of the
exhaust gas is higher than the reference temperature, the target
temperature of the sensor element is made lower than the reference
temperature, whereby the temperature of the sensor element can be
made low in advance, even if the temperature of the exhaust gas
becomes high. On the other hand, in cases where the predicted
temperature of the exhaust gas is lower than the reference
temperature, the target temperature of the sensor element is made
higher than the reference temperature, whereby the temperature of
the sensor element can be made high in advance, even if the
temperature of the exhaust gas becomes low. Moreover, the target
temperature of the sensor element is made lower when the predicted
temperature of the exhaust gas is high than when it is low, whereby
the temperature of the sensor element can be made low according to
the temperature of the exhaust gas in advance, even if the
temperature of the exhaust gas becomes high, whereas the
temperature of the sensor element can be made high according to the
temperature of the exhaust gas in advance, even if the temperature
of the exhaust gas becomes low. In addition, by changing the target
temperature within the predetermined range, it is possible to
suppress the target temperature from becoming excessively high or
excessively low. Accordingly, the temperature of the sensor element
can be maintained in a suitable range.
[0010] Further, said controller can predict, based on the operating
state of said internal combustion engine, a flow rate of the
exhaust gas of said internal combustion engine in a position in
which said exhaust gas sensor is arranged, and make an amount of
deviation of said target temperature from said reference
temperature larger when the flow rate of the exhaust gas predicted
by said controller is large than when it is small.
[0011] The flow rate of the exhaust gas in the surrounding of the
exhaust gas sensor has a correlation with the operating state of
the internal combustion engine, etc., similar to the temperature of
the exhaust gas in the surrounding of the exhaust gas sensor, and
so can be predicted from the operating state of the internal
combustion engine, etc. That is, even before the exhaust gas of the
internal combustion engine reaches the exhaust gas sensor, the flow
rate of the exhaust gas at the time when the exhaust gas reaches
the area surrounding the exhaust gas sensor can be predicted. Here,
in cases where the temperature of the exhaust gas is higher than
the temperature of the sensor element, the temperature of the
sensor element rises more quickly as the flow rate of the exhaust
gas is larger. On the other hand, in cases where the temperature of
the exhaust gas is lower than the temperature of the sensor
element, the temperature of the sensor element falls more quickly
as the flow rate of the exhaust gas is larger. That is, the rate of
the temperature change of the sensor element becomes larger than
when the flow rate of the exhaust gas large than when it is small.
Even if the temperature of the exhaust gas is the same and a
temperature finally reached by the sensor element is the same, a
period of time until the sensor element reaches the final
temperature varies with the flow rate of the exhaust gas. In
contrast to this, when the target temperature is made to change
according to the flow rate of the exhaust gas, the target
temperature can be set not only according to the temperature
finally reached, but also according to the rate of the temperature
change of the sensor element. Even in this case, too, by setting
the target temperature within the predetermined range, it is
possible to suppress the target temperature from becoming
excessively high or excessively low. Here, it is shown that in
cases where the amount of deviation of the target temperature from
the reference temperature is made larger, when the target
temperature is lower than the reference temperature, the target
temperature is made further lower, whereas when the target
temperature is higher than the reference temperature, the target
temperature is further higher.
[0012] Moreover, further provision can be made for an accelerator
opening sensor that detects an accelerator opening degree, and said
controller can predict the temperature of said exhaust gas based on
the accelerator opening degree detected by said accelerator opening
sensor.
[0013] Because the operating state of the internal combustion
engine changes according to the accelerator opening degree, the
operating state of the internal combustion engine and the
accelerator opening degree are in correlation with each other.
Accordingly, the accelerator opening degree and the temperature of
the exhaust gas flowing out from the internal combustion engine are
in correlation with each other, so the temperature of the exhaust
gas flowing out from the internal combustion engine can be
predicted based on the accelerator opening degree. Thus, the
temperature of the exhaust gas at the time when this exhaust gas
reaches the area surrounding the exhaust gas sensor can also be
predicted, as described above. Accordingly, the temperature of the
exhaust gas in the surrounding of the exhaust gas sensor can be
easily predicted based on the accelerator opening degree.
[0014] Moreover, further provision can be made for an accelerator
opening sensor that detects an accelerator opening degree, wherein
said controller can predict the flow rate of said exhaust gas based
on the accelerator opening degree detected by said accelerator
opening sensor.
[0015] The flow rate of the exhaust gas in the surrounding of the
exhaust gas sensor also changes with the accelerator opening
degree, so the flow rate of the exhaust gas in the surrounding of
the exhaust gas sensor can be easily predicted based on the
accelerator opening degree.
[0016] Further, said controller can provide an upper limit on a
rate of change at the time of changing said target temperature.
[0017] By providing the upper limit on the rate of change of the
target temperature, the temperature of the exhaust gas sensor can
be suppressed from changing suddenly, thus making it possible to
suppress the breakage of the exhaust gas sensor, and the occurrence
of a deviation of the detected value.
[0018] In addition, another aspect of the present disclosure
resides in a sensor system which comprises: an exhaust gas sensor
that is arranged in an exhaust passage of an internal combustion
engine, and is provided with a sensor element and a heater
configured to heat said sensor element; an accelerator opening
sensor that detects an accelerator opening degree; and a controller
configured to control said heater so as to make a temperature of
said sensor element close to a target temperature included in a
predetermined range; wherein in cases where said accelerator
opening degree is such that the temperature of the exhaust gas in
the surrounding of said exhaust gas sensor becomes higher than a
reference temperature included in said predetermined range, said
controller is configured to make said target temperature lower when
said accelerator opening degree is large than when it is small,
within a range lower than said reference temperature, whereas in
cases where said accelerator opening degree is such that the
temperature of the exhaust gas in the surrounding of said exhaust
gas sensor becomes lower than said reference temperature, said
controller is configured to make said target temperature lower when
said accelerator opening degree is large than when it is small,
within a range higher than said reference temperature.
[0019] As described above, the accelerator opening degree and a
future temperature of the exhaust gas in the surrounding of the
exhaust gas sensor are in correlation with each other, so the
target temperature of the sensor element can also be directly set
based on the accelerator opening degree, without predicting the
future temperature of the exhaust gas in the surrounding of the
exhaust gas sensor.
Advantageous Effects
[0020] According to the present disclosure, the temperature of a
sensor element can be maintained in a suitable range.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a view showing the schematic construction of an
internal combustion engine as well as its intake and exhaust
systems according to an embodiment of the present disclosure.
[0022] FIG. 2 is a cross sectional view of an air fuel ratio
sensor.
[0023] FIG. 3 is a view showing a relation between a temperature of
exhaust gas ET in the surrounding of the air fuel ratio sensor to
be predicted, and an offset amount (a target offset amount) of a
target temperature of a sensor element from a reference
temperature.
[0024] FIG. 4 is a view for correcting the target offset amount
shown in FIG. 3.
[0025] FIG. 5 is a time chart showing the changes over time of a
variety of kinds of values in the case of setting the target
temperature of the sensor element constant at the reference
temperature.
[0026] FIG. 6 is a time chart showing the changes over time of a
variety of kinds of values in cases where sensor element impedance
control according to a first embodiment is carried out.
[0027] FIG. 7 is a flow chart showing a flow for setting a duty
ratio in the sensor element impedance control according to the
first embodiment.
[0028] FIG. 8 is a flow chart showing a flow for setting a duty
ratio in the sensor element impedance control according to the
first embodiment, in cases where a flow rate of exhaust gas is not
taken into consideration.
[0029] FIG. 9 is a flow chart showing a flow for setting a duty
ratio in sensor element impedance control according to a second
embodiment.
DESCRIPTION OF THE EMBODIMENTS
[0030] Hereinafter, embodiments carrying out the present disclosure
will be described in detail by way of example with reference to the
attached drawings. However, the dimensions, materials, shapes,
relative arrangements and so on of component parts described in the
embodiments are not intended to limit the scope of the present
disclosure to these alone in particular as long as there are no
specific statements.
First Embodiment
[0031] FIG. 1 is a view showing the schematic construction of an
internal combustion engine 1 as well as its intake and exhaust
systems according to a first embodiment of the present disclosure.
The internal combustion engine 1 is a gasoline engine mounted on a
vehicle 50. Here, note that this embodiment is also able to be
applied to a diesel engine. An exhaust passage 2 is connected to
the internal combustion engine 1. Although a catalyst 3 is arranged
in the exhaust passage 2, this catalyst 3 is not an indispensable
construction.
[0032] Further, in the exhaust passage 2 at a location upstream of
the catalyst 3, there are arranged an air fuel ratio sensor 11 that
detects an air fuel ratio of exhaust gas flowing into the catalyst
3, and a temperature sensor 12 that detects a temperature of the
exhaust gas flowing into the catalyst 3. This air fuel ratio sensor
11 is, for example, a limiting current type oxygen sensor, and
generates an output which is substantially proportional to the air
fuel ratio over a wide air fuel ratio range. Here, note that the
air fuel ratio sensor 11 is not limited to the limiting current
type oxygen sensor, but may also be an electromotive force type
(concentration cell type) oxygen sensor, for example. Also, note
that in this embodiment, the air fuel ratio sensor 11 corresponds
to an exhaust gas sensor in the present disclosure.
[0033] FIG. 2 is a cross sectional view of the air fuel ratio
sensor 11. The air fuel ratio sensor 11 includes a sensor element
11A which generates an output corresponding to the air fuel ratio
(or this may also be an oxygen concentration) of the exhaust gas,
and a heater 11B which heats this sensor element 11A. The sensor
element 11A includes a solid electrolyte layer 101, an A-chamber
side electrode 102, a B-chamber side electrode 103, and a diffusion
rate controlling layer 104. The solid electrolyte layer 101 serves
to separate an A-chamber leading to the atmosphere and a B-chamber
leading to the interior of the exhaust passage 2 from each other.
The solid electrolyte layer 101 is composed of a porous insulating
material such as zirconia (Zr.sub.2O.sub.3). The A-chamber side
electrode 102, which is composed of platinum, is arranged on an
A-chamber side wall surface of the solid electrolyte layer 101, and
the B-chamber side electrode 103, which is composed of platinum, is
arranged on a B-chamber side wall surface of the solid electrolyte
layer 101. A surface of the B-chamber side electrode 103 is covered
with the diffusion rate controlling layer 104, and a part of
exhaust gas flowing through the exhaust passage 2 passes through
the interior of the diffusion rate controlling layer 104, and comes
into contact with the B-chamber side electrode 103. In addition,
the heater 11B is arranged in the A-chamber side in a state where
it is sandwiched between insulating substrates 105.
[0034] In the air fuel ratio sensor 11 of such a construction, when
a predetermined voltage is applied between the A-chamber side
electrode 102 and the B-chamber side electrode 103, an electric
current of a magnitude corresponding to a concentration of oxygen
in the exhaust gas will flow into the air fuel ratio sensor 11 by
the application of this voltage. Because this electric current has
a correlation with the air fuel ratio, the air fuel ratio sensor 11
detects the air fuel ratio based on this electric current.
[0035] In addition, on each of cylinders of the internal combustion
engine 1, there are mounted a spark plug 5 for generating an
electric spark, and a fuel injection valve 6 for injecting fuel
into a corresponding cylinder. Moreover, an intake passage 7 is
connected to the internal combustion engine 1. In the intake
passage 7, there are arranged an air flow meter 23 and a throttle
valve 8. The air flow meter 23 is a sensor which serves to detect
an amount of intake air sucked into the internal combustion engine
1. The throttle valve 8 serves to adjust the amount of intake air
sucked into the internal combustion engine 1.
[0036] Then, an ECU 10, which is an electronic controller, is
provided as a control device (controller) in combination with the
internal combustion engine 1. A program for controlling the
internal combustion engine 1, an exhaust gas purification
apparatus, etc., is stored in the ECU 10, so that the ECU 10
controls the internal combustion engine 1, the exhaust gas
purification apparatus, etc., according to this program. A crank
position sensor 21, which outputs a signal corresponding to the
rotational speed of the internal combustion engine 1, an
accelerator opening sensor 22, which outputs a signal corresponding
to the degree of opening of an accelerator pedal (an accelerator
opening degree), and a vehicle speed sensor 24, which outputs a
signal corresponding to the travel speed of the vehicle 50, in
addition to the above-mentioned various kinds of sensors, etc., are
electrically connected to the ECU 10, so that the output values (or
signals) of these individual sensors are passed or transmitted to
the ECU 10.
[0037] Accordingly, the ECU 10 can grasp an operating state of the
internal combustion engine 1, such as an engine rotational speed
based on the detection of the crank position sensor 21, an engine
load factor based on the detection of the accelerator opening
sensor 22, etc. On the other hand, the spark plugs 5, the fuel
injection valves 6, the throttle valve 8 and the heater 11B are
connected to the ECU 10 through electrical wiring, so that these
parts are controlled by means of the ECU 10. That is, ignition
timing, a fuel injection amount, fuel injection timing, a throttle
opening degree, and the temperature of the heater 11B are
controlled by the ECU 10.
[0038] The ECU 10 sets a target torque with respect to the internal
combustion engine 1 based on the accelerator opening degree
detected by the accelerator opening sensor 22. Here, note that the
relation between the accelerator opening degree and the target
torque has been obtained in advance by experiments, simulations or
the like, and stored in the ECU 10. Then, the ECU 10 controls the
internal combustion engine 1 so that the target torque is achieved
(i.e., the torque of the internal combustion engine 1 becomes the
target torque). Such control is referred to as torque demand
control. This torque demand control is well-known control, and is
to carry out the opening degree control of the throttle valve 8 and
the ignition timing control of the spark plug 5, etc., in order to
achieve the target torque. In other words, a target throttle
opening degree is calculated based on the target torque, and
ignition timing necessary to achieve the target torque with an
amount of intake air at the target throttle opening degree is
calculated. That is, a torque, which will be obtained if the
ignition timing is set to an optimum ignition timing (MBT (Minimum
Advance for Best Torque)) with the above-mentioned amount of intake
air, is estimated, and an amount of retardation of the ignition
timing (an amount of retardation from the MBT) is calculated
according to the ratio of the target torque with respect to the
torque thus estimated, whereby the opening degree control of the
throttle valve 8 and the ignition timing control of the spark plug
5 are carried out so as to obtain the target throttle opening
degree and the amount of retardation of the ignition timing (target
ignition timing) thus calculated, thereby controlling the torque of
the internal combustion engine 1 so as to become the target torque.
Here, note that in the torque demand control, the ECU 10 calculates
a future engine rotational speed and a future engine load factor
based on the accelerator opening degree.
[0039] Moreover, the ECU 10 controls the amount of fuel injection
or the throttle opening degree in a feedback manner so that the air
fuel ratio (detection air fuel ratio) detected by the air fuel
ratio sensor 11 becomes the target air fuel ratio. This control is
referred to as air fuel ratio feedback control.
[0040] Further, the ECU 10 controls the heater 11B in such a manner
that the temperature of the sensor element 11A falls within a
predetermined range, in order to maintain the detection accuracy of
the air fuel ratio sensor 11. When the temperature of the sensor
element 11A deviates from this predetermined range, the correlation
between the detected value of the air fuel ratio sensor 11 and the
actual air fuel ratio will change, so the detection accuracy of the
air fuel ratio by the air fuel ratio sensor 11 becomes low. This
predetermined range is set to a range of temperature in which the
sensor element 11A is activated (e.g., a range from 650 degrees C.
to 750 degrees C.). In this case, the temperature of the sensor
element 11A can be represented by an impedance of the sensor
element 11A. That is, there is the following relation: as the
temperature of the sensor element 11A becomes higher, the impedance
thereof becomes smaller. In this embodiment, a target impedance
indicating the target temperature is set, and an actual impedance
indicating an actual temperature of the sensor element 11A is
detected, wherein the ECU 10 controls the output of the heater 11B
in a feedback manner so that the actual impedance becomes equal to
the target impedance. This control is referred to as sensor element
impedance control. Here, note that the sensor element impedance
control in this embodiment is an example of the temperature control
of the sensor element 11A, and the temperature control of the
sensor element 11A may be carried out by other control.
[0041] In the sensor element impedance control, the ECU 10 sets the
target temperature (target impedance) so that even if the air fuel
ratio sensor 11 receives heat from the exhaust gas or heat is taken
from the air fuel ratio sensor 11 by the exhaust gas, the
temperature of the sensor element 11A of the air fuel ratio sensor
11 falls within the predetermined range, and the ECU 10 carries out
duty control of the heater 11B so that the temperature of the
sensor element 11A becomes equal to the target temperature.
[0042] The temperature of the sensor element 11A is adjusted by the
sensor element impedance control. However, when the engine load
factor becomes high, the temperature of the exhaust gas becomes
high, so the temperature of the sensor element 11A may be raised by
the heat received from this exhaust gas of high temperature. In
this case, the temperature of the sensor element 11A rises
irrespective of the sensor element impedance control, and hence,
there is a fear that the temperature of the sensor element 11A may
become higher than an upper limit of the predetermined range. On
the other hand, when the engine load factor becomes low, the
temperature of the exhaust gas becomes low, so the temperature of
the sensor element 11A may be lowered by the heat deprived by this
exhaust gas of low temperature. In this case, the temperature of
the sensor element 11A is raised by means of the sensor element
impedance control, but in cases where the amount of heat deprived
by the exhaust gas is large, there is a fear that the temperature
of the sensor element 11A may become lower than a lower limit of
the predetermined range.
[0043] Accordingly, the ECU 10 adjusts the temperature of the
sensor element 11A in advance based on the temperature (prediction
temperature) of the exhaust gas predicted in the surrounding of the
air fuel ratio sensor 11. That is, in cases where the temperature
of the exhaust gas passing in future through the surrounding of the
air fuel ratio sensor 11 is lower than the temperature of the
sensor element 11A so that the temperature of the sensor element
11A may drop, the temperature of the sensor element 11A is raised
in advance before the exhaust gas of low temperature actually
lowers the temperature of the sensor element 11A. At this time, the
target temperature in the sensor element impedance control is made
high. On the other hand, in cases where the temperature of the
exhaust gas passing in future through the surrounding of the air
fuel ratio sensor 11 is higher than the temperature of the sensor
element 11A so that the temperature of the sensor element 11A may
rise, the temperature of the sensor element 11A is lowered in
advance before the exhaust gas of high temperature actually raises
the temperature of the sensor element 11A.
[0044] The prediction of the temperature of the exhaust gas in the
surrounding of the air fuel ratio sensor 11 is carried out by using
the engine rotational speed and the engine load factor which are
calculated in the torque demand control. Because there is a
correlation among the engine rotational speed, the engine load
factor, and the temperature of the exhaust gas discharged from the
internal combustion engine 1, this correlation has been obtained in
advance by experiments, simulations or the like, and has been
mapped and stored in the ECU 10. In addition, the heat possessed by
the exhaust gas is released outside through the wall surface of the
exhaust passage 2 until the exhaust gas having flowed out from the
internal combustion engine 1 reaches the air fuel ratio sensor 11
while flowing through the exhaust passage 2, so the temperature of
the exhaust gas drops. This amount of drop in the temperature of
the exhaust gas is affected by the influence of the heat capacities
of those members with which the exhaust system leading from the
internal combustion engine 1 to the air fuel ratio sensor 11 is
provided, and hence, the temperature of the exhaust gas in the
surrounding of the air fuel ratio sensor 11 is calculated in
consideration of these heat capacities.
[0045] For example, the temperature of the exhaust gas flowing out
from the internal combustion engine 1 is predicted based on the
engine rotational speed and the engine load factor which are
calculated in the torque demand control, and by multiplying a
predetermined coefficient to this predicted temperature, a
temperature of this exhaust gas at the time when this exhaust gas
reaches the surrounding of the air fuel ratio sensor 11 can be
predicted. This predetermined coefficient may be set according to
the flow rate of the exhaust gas flowing out from the internal
combustion engine 1. That is, the smaller the flow rate of the
exhaust gas, the more largely the temperature of the exhaust gas is
affected by the influence of the heat capacity of the exhaust
system, so the larger the amount of drop in the temperature of the
exhaust gas until the exhaust gas reaches the air fuel ratio sensor
11 becomes. The relation between the amount of exhaust gas and the
predetermined coefficient has been obtained and mapped in advance
by experiments, simulations or the like, and stored in the ECU 10.
In addition, the flow rate of exhaust gas has a correlation with
the amount of intake air, so the predetermined coefficient may be
obtained based on the amount of intake air in place of the flow
rate of exhaust gas.
[0046] In addition, for example, assuming that the heat capacity of
the exhaust system is constant, a relation among the engine
rotational speed, the engine load factor, and the temperature of
the exhaust gas in the surrounding of the air fuel ratio sensor 11
may have been obtained and mapped in advance by experiments,
simulations or the like, and stored in the ECU 10. Moreover, an
amount of heat dissipation in the exhaust passage 2 may be obtained
by a physical model taking account of the heat dissipation in the
exhaust passage 2, or by a map or a formula of the amount of heat
dissipation in the exhaust passage 2, etc., and the temperature of
the exhaust gas at the time when the exhaust gas reaches the air
fuel ratio sensor 11 may be predicted based on the amount of heat
dissipation thus obtained and the temperature of the exhaust gas
flowing out from the internal combustion engine 1.
[0047] FIG. 3 is a view showing a relation between a temperature of
exhaust gas ET in the surrounding of the air fuel ratio sensor 11
to be predicted, and an offset amount (a target offset amount) of
the target temperature of the sensor element 11A from a reference
temperature. The temperature of the exhaust gas ET on the axis of
abscissa is the temperature of the exhaust gas in the surrounding
of the air fuel ratio sensor 11 predicted from the operating state
of the internal combustion engine 1, and is calculated based on the
accelerator opening degree used in the torque demand control. The
reference temperature shown in FIG. 3 is the reference temperature
of the sensor element 11A, and is 700 degrees C., for example. This
reference temperature is a temperature which becomes a reference at
the time of controlling the temperature of the sensor element 11A
so as to fall within the predetermined range. Here, note that the
reference temperature may also be set to a temperature at which the
detection accuracy of the air fuel ratio sensor 11 becomes the
highest. Accordingly, the temperature of the exhaust gas ET
indicated by ET3 shows that the predicted temperature of the
exhaust gas in the surrounding of the air fuel ratio sensor 11 is
equal to the reference temperature of the sensor element 11A.
[0048] The target offset amount on the axis of ordinate in FIG. 3
indicates an offset amount from the reference temperature at the
time of setting the target temperature of the sensor element 11A.
"+30" in the target offset amount represents that the target
temperature of the sensor element 11A is made higher by 30 degrees
C. than the reference temperature, and "0" represents that the
target temperature of the sensor element 11A is made equal to the
reference temperature, and "-30" represents that the target
temperature of the sensor element 11A is made lower by 30 degrees
C. than the reference temperature.
[0049] In cases where the temperature of the exhaust gas ET is
lower than ET3, the predicted temperature of the exhaust gas ET in
the surrounding of the air fuel ratio sensor 11 will be lower than
the reference temperature. In this case, when the exhaust gas of
low temperature actually reaches the air fuel ratio sensor 11, the
heating of the air fuel ratio sensor 11 by the heater 11B will be
late or insufficient, so the temperature of the sensor element 11A
may drop. For that reason, in cases where the temperature of the
exhaust gas in the surrounding of the air fuel ratio sensor 11 is
predicted to become lower than the reference temperature (i.e., in
cases where the temperature of the exhaust gas ET is predicted to
become lower than ET3), the temperature of the sensor element 11A
is raised in advance. In this case, the sensor element impedance
control is carried out in a state where the target temperature of
the sensor element 11A in the sensor element impedance control is
made higher than the reference temperature.
[0050] In FIG. 3, in cases where the temperature of the exhaust gas
ET is in a range from ET1 to ET2, the smaller the temperature of
the exhaust gas ET, the larger the target offset amount is made.
That is, by making the target offset amount larger as the predicted
temperature of the exhaust gas ET becomes lower, the temperature of
the sensor element 11A is made high in advance according to the
predicted temperature of the exhaust gas ET. Here, note that in
FIG. 3, the target offset amount is continuously changed according
to the temperature of the exhaust gas ET, but instead of this, the
target offset amount may be changed in a stepwise manner.
[0051] On the other hand, an upper limit of the target offset
amount is set to +30 degrees C. For this reason, in cases where the
temperature of the exhaust gas ET is lower than ET1, the target
offset amount is fixed to +30 degrees C. Here, note that in cases
where the prediction of the temperature of the exhaust gas is
wrong, the temperature of the sensor element 11A may deviate from
the predetermined range, so a certain amount of margin is given to
the upper limit of the target offset amount. That is, the upper
limit of the target offset amount is set so as to change the target
temperature of the sensor element 11A in a range which is narrower
than the predetermined range (e.g., a range from 650 degrees C. to
750 degrees C.). However, the upper limit of the target offset
amount may be increased to an offset amount (e.g., +50 degrees C.)
corresponding to the upper limit (e.g., 750 degrees C.) of the
predetermined range. By doing in this manner, the target
temperature of the sensor element 11A can be adjusted within the
predetermined range, so that when the heater 11B heats the sensor
element 11A, it is possible to suppress the temperature of the
sensor element 11A from becoming excessively high, and hence
deviating from the predetermined range. ET1 is an upper limit value
of the temperature of the exhaust gas at which the temperature of
the sensor element 11A may exceed the upper limit of the
predetermined range, when the target offset amount is made larger
according to the temperature of the exhaust gas.
[0052] Moreover, when the temperature of the exhaust gas ET is in a
range from ET2 to ET3 even if it is lower than ET3, the target
offset amount is set to 0. Here, the predicted temperature of the
exhaust gas ET is close to the reference temperature, and hence,
even in cases where the predicted temperature of the exhaust gas ET
is lower than the reference temperature, the amount of heat taken
from the sensor element 11A is small, as a result of which in this
temperature range, the temperature of the sensor element 11A
becomes a value close to the reference temperature, even if the
target temperature is not made to change. Accordingly, in the range
from ET2 to ET3, the target offset amount may be set to 0, without
being changed. With this, simplification of control can be
attained. However, even if the temperature of the exhaust gas ET is
in the range from ET2 to ET3, the lower the temperature of the
exhaust gas ET, the larger the target offset amount may be made, as
in the case where the temperature of the exhaust gas ET is in the
range from ET1 to ET2. ET2 can be obtained as a lower limit of the
temperature of the exhaust gas ET at which the temperature of the
sensor element 11A can be made to fall within the predetermined
range, even if the target temperature or the target offset amount
is not changed.
[0053] In cases where the temperature of the exhaust gas ET is
higher than ET3, the predicted temperature of the exhaust gas ET in
the surrounding of the air fuel ratio sensor 11 will be higher than
the reference temperature. In this case, when the exhaust gas of
high temperature actually reaches the air fuel ratio sensor 11, the
temperature of the sensor element 11A may rise, even if the amount
of heating by the heater 11B is decreased, which will be late. For
that reason, in cases where the temperature of the exhaust gas in
the surrounding of the air fuel ratio sensor 11 is predicted to
become higher than the reference temperature (i.e., in cases where
the temperature of the exhaust gas ET is predicted to become higher
than ET3), the temperature of the sensor element 11A is lowered in
advance. In this case, the sensor element impedance control is
carried out in a state where the target temperature of the sensor
element 11A in the sensor element impedance control is made lower
than the reference temperature.
[0054] In FIG. 3, in cases where the temperature of the exhaust gas
ET is in a range from ET4 to ET5, the larger the temperature of the
exhaust gas ET, the smaller the target offset amount is made. That
is, by making the target offset amount smaller as the predicted
temperature of the exhaust gas ET becomes higher, the temperature
of the sensor element 11A is made low in advance according to the
predicted temperature of the exhaust gas ET. Here, note that in
FIG. 3, the target offset amount is continuously changed according
to the temperature of the exhaust gas ET, but instead of this, the
target offset amount may be changed in a stepwise manner.
[0055] On the other hand, a lower limit of the target offset amount
is set to -30 degrees C. For this reason, in cases where the
temperature of the exhaust gas ET is higher than ET5, the target
offset amount is fixed to -30 degrees C. Here, note that in cases
where the prediction of the temperature of the exhaust gas is
wrong, the temperature of the sensor element 11A may deviate from
the predetermined range, so a certain amount of margin is given to
the lower limit of the target offset amount. That is, the lower
limit of the target offset amount is set so as to change the target
temperature of the sensor element 11A in a range which is narrower
than the predetermined range. However, the lower limit of the
target offset amount may be decreased to an offset amount (e.g.,
-50 degrees C.) corresponding to the lower limit (e.g., 650 degrees
C.) of the predetermined range. ET5 is a temperature at which the
temperature of the sensor element 11A may be lower than the lower
limit of the predetermined range. By doing in this manner, the
target temperature of the sensor element 11A can be adjusted within
the predetermined range, thus making it possible to suppress the
temperature of the sensor element 11A from becoming excessively
low, and hence deviating from the predetermined range. ET5 is a
lower limit value of the temperature of the exhaust gas at which
the temperature of the sensor element 11A may fall below the lower
limit of the predetermined range, when the target offset amount is
made smaller according to the temperature of the exhaust gas.
[0056] Further, when the temperature of the exhaust gas ET is in a
range from ET3 to ET4 even if it is higher than ET3, the target
offset amount is set to 0. Here, the predicted temperature of the
exhaust gas ET is close to the reference temperature, and hence,
even in cases where the predicted temperature of the exhaust gas ET
is higher than the reference temperature, the amount of heat given
to the sensor element 11A is small, as a result of which in this
temperature range, the temperature of the sensor element 11A
becomes a value close to the reference temperature, even if the
target temperature is not made to change. Accordingly, in the range
from ET3 to ET4, the target offset amount may be set to 0, without
being changed. With this, simplification of control can be
attained. However, even if the temperature of the exhaust gas ET is
in the range from ET3 to ET4, the lower the temperature of the
exhaust gas ET, the smaller the target offset amount may be made,
as in the case where the temperature of the exhaust gas ET is in
the range from ET4 to ET5. ET4 can be obtained as an upper limit of
the temperature of the exhaust gas ET at which the temperature of
the sensor element 11A can be made to fall within the predetermined
range, even if the target temperature or the target offset amount
is not changed. Each of ET1, ET2, ET3, ET4 and ET5 can be obtained
in advance by experiments, simulations, or the like.
[0057] Here, note that the amount of heat taken by the exhaust gas
from the sensor element 11A per unit time changes with the flow
rate of the exhaust gas, too. Accordingly, the target offset amount
may be set in consideration of the flow rate of the exhaust gas, in
addition to the temperature of the exhaust gas ET. For example, in
cases where the temperature of the exhaust gas ET is lower than ET3
in FIG. 3, the larger the flow rate of the exhaust gas, the larger
the rate of temperature drop of the sensor element 11A becomes,
even if the temperature of the exhaust gas ET is the same. On the
other hand, in cases where the temperature of the exhaust gas ET is
higher than ET3 in FIG. 3, the larger the flow rate of the exhaust
gas, the larger the rate of temperature rise of the sensor element
11A becomes, even if the temperature of the exhaust gas ET is the
same. Thus, a difference in the rate of temperature change of the
sensor element 11A occurs according to the flow rate of the exhaust
gas, the temperature of the sensor element 11A may not immediately
change due to a change in the temperature of the exhaust gas ET,
but it may take a certain period of time. Accordingly, when the
target offset amount of the sensor element 11A is made to change
according to the temperature of the exhaust gas ET, the target
offset amount will change excessively with respect to the amount of
increase or decrease of the heat in the sensor element 11A, thus
giving rise to a fear that the temperature of the sensor element
11A may deviate from the predetermined range.
[0058] For that reason, the target offset amount may be corrected
according to the flow rate of the exhaust gas. The prediction of
the flow rate of the exhaust gas flowing through the surrounding of
the air fuel ratio sensor 11 has a correlation with the accelerator
opening degree used in the torque demand control, or the engine
rotational speed and the engine load factor calculated in the
torque demand control, and so is performed based on these values.
Here, note that there is a correlation among the engine rotational
speed, the engine load factor, and the flow rate of the exhaust gas
at the time when the exhaust gas having flowed out from the
internal combustion engine 1 reaches the air fuel ratio sensor 11
in the case where the internal combustion engine 1 is operated at
the engine rotational speed and the engine load factor, and hence,
this relation has been obtained and mapped in advance by
experiments, simulations or the like, and stored in the ECU 10.
[0059] FIG. 4 is a view for correcting the target offset amount
shown in FIG. 3. In FIG. 4, the axis of ordinate represents the
predicted temperature of exhaust gas ET, and the axis of abscissa
represents the predicted flow rate of exhaust gas EQ. The flow rate
of exhaust gas EQ is the flow rate of the exhaust gas in the
surrounding of the air fuel ratio sensor 11 predicted from the
operating state of the internal combustion engine 1, and is
calculated based on the accelerator opening degree used in the
torque demand control. In FIG. 4, "NO CORRECTION" indicates that
the target offset amount shown in FIG. 3 is not corrected; "SMALL"
indicates that the target offset amount shown in FIG. 3 is
corrected to become small (i.e., a negative value becomes large);
and "LARGE" indicates that the target offset amount shown in FIG. 3
is corrected to become large (i.e., a positive value becomes
large).
[0060] As shown in FIG. 4, in cases where the predicted flow rate
of exhaust gas EQ is smaller than a predetermined flow rate, the
correction of the target offset amount based on the flow rate of
exhaust gas EQ is not carried out, irrespective of the predicted
temperature of exhaust gas ET. The predetermined flow rate referred
to herein is an upper limit value of the flow rate of exhaust gas
at which the temperature of the sensor element 11A is able to be
controlled to within the predetermined range, by carrying out the
sensor element impedance control based on the target offset amount
shown in FIG. 3. That is, in cases where the flow rate of exhaust
gas EQ is smaller than the predetermined flow rate, the influence
of the flow rate of exhaust gas EQ on the temperature rise or
temperature drop of the sensor element 11A is small, so the
correction of the target offset amount according to the flow rate
of exhaust gas EQ is not carried out. Accordingly, the target
temperature of the sensor element 11A is set according to the
relation shown in FIG. 3.
[0061] On the other hand, even in cases where the predicted flow
rate of exhaust gas EQ is more than the predetermined flow rate, if
the temperature of the exhaust gas ET is in the vicinity of the
reference temperature, the influence of the flow rate of exhaust
gas EQ on the temperature rise or temperature drop of the sensor
element 11A is small. For that reason, the temperature of the
sensor element 11A is suppressed from deviating from the
predetermined range, so the correction of the target offset amount
according to the flow rate of exhaust gas EQ is not carried out.
Accordingly, the target temperature of the sensor element 11A is
set according to the relation shown in FIG. 3. The lower limit and
the upper limit of the temperature of the exhaust gas ET at this
time may be set to ET2 and ET4 in FIG. 3, respectively, or may also
be values different from these. These values can be obtained in
advance through experiments, simulations or the like.
[0062] In addition, in a range indicated by "SMALL" in FIG. 4, even
if the temperature of the exhaust gas ET is the same, the target
offset amount is corrected so as to be smaller (i.e., the amount of
deviation of the target temperature from the reference temperature
becomes larger) when the predicted flow rate of the exhaust gas is
large than when it is small. In cases where the predicted flow rate
of exhaust gas EQ is more than the predetermined flow rate, and in
cases where the predicted temperature of exhaust gas ET is higher
than an upper limit of a range indicated by "NO CORRECTION" in FIG.
4, the rate of temperature rise of the sensor element 11A due to
the heat received from the exhaust gas becomes larger according to
the flow rate of the exhaust gas. For that reason, the target
offset amount obtained based on FIG. 3 is corrected according to
the flow rate of the exhaust gas. However, the lower limit of the
target offset amount thus corrected is set to the lower limit shown
in FIG. 3 (e.g., -30 degrees C.). With this, the temperature of the
sensor element 11A is suppressed from deviating from the
predetermined range, in cases where the prediction of the
temperature or the flow rate of the exhaust gas is wrong. In this
range, the temperature of the exhaust gas ET is high and the flow
rate of exhaust gas EQ is large, so the temperature of the sensor
element 11A is predicted to further rise. For this reason, the
temperature of the sensor element 11A is made further lower in
advance, whereby the temperature of the sensor element 11A is
suppressed from exceeding the upper limit of the predetermined
range.
[0063] On the other hand, in a range indicated by "LARGE" in FIG.
4, even if the temperature of the exhaust gas ET is the same, the
target offset amount is corrected so as to be larger (i.e., the
amount of deviation of the target temperature from the reference
temperature becomes larger) when the predicted flow rate of the
exhaust gas is large than when it is small. In cases where the
predicted flow rate of exhaust gas EQ is more than the
predetermined flow rate, and in cases where the predicted
temperature of exhaust gas ET is lower than a lower limit of the
range indicated by "NO CORRECTION" in FIG. 4, the rate of
temperature drop of the sensor element 11A due to the heat deprived
from the exhaust gas becomes larger according to the flow rate of
the exhaust gas. For that reason, the target offset amount obtained
based on FIG. 3 is corrected according to the flow rate of the
exhaust gas. However, the upper limit of the target offset amount
thus corrected is set to the upper limit shown in FIG. 3 (e.g., +30
degrees C.). With this, the temperature of the sensor element 11A
is suppressed from deviating from the predetermined range, in cases
where the prediction of the temperature or the flow rate of the
exhaust gas is wrong. In this range, the temperature of the exhaust
gas ET is low and the flow rate of exhaust gas EQ is large, so the
temperature of the sensor element 11A is predicted to further drop.
For this reason, the temperature of the sensor element 11A is made
further higher in advance, whereby the temperature of the sensor
element 11A is suppressed from falling below the lower limit of the
predetermined range.
[0064] Here, note that the range of "NO CORRECTION" is provided in
FIG. 4, but instead of this, without providing the range of "NO
CORRECTION", the target offset amount may be corrected so as to
make the amount of deviation of the target temperature from the
reference temperature larger when the flow rate of exhaust gas EQ
is large than when it is small, as long as the temperature of the
exhaust gas ET is the same.
[0065] Also, note that a new target offset amount may be obtained
by multiplying a correction coefficient obtained by the relation
shown in FIG. 4 to the target offset amount shown in FIG. 3, or a
relation among the temperature of the exhaust gas ET, the flow rate
of exhaust gas EQ and the target offset amount may have been
obtained and mapped in advance by experiments, simulations or the
like, and stored in the ECU 10.
[0066] FIG. 5 is a time chart showing the changes over time of a
variety of kinds of values in the case of setting the target
temperature of the sensor element 11A constant at the reference
temperature. In FIG. 5, there are shown, in order from the top, the
vehicle speed, the accelerator opening degree, the temperature of
the exhaust gas, the flow rate of the exhaust gas, the temperature
of the sensor element 11A, and the duty ratio of the heater 11B
(heater duty). The temperature of the exhaust gas and the flow rate
of the exhaust gas are values in the surrounding or periphery of
the air fuel ratio sensor 11, and it is assumed that they are equal
to the predicted temperature of the exhaust gas and the predicted
flow rate of the exhaust gas as mentioned above. An alternate long
and short dash line in the temperature of the sensor element 11A
shows the target temperature thereof in the sensor element
impedance control, and a solid line shows the actual temperature
thereof. Here, note that in FIG. 5, the target temperature of the
sensor element 11A is constant at the reference temperature. FIG. 5
may also be a time chart in the case of carrying out conventional
sensor element impedance control.
[0067] In FIG. 5, when the accelerator opening degree becomes large
at T1, the vehicle speed goes up. It takes a certain period of time
(i.e., a period of time from T1 to T2) before the gas discharged
from the internal combustion engine 1 at T1 reaches the air fuel
ratio sensor 11. At T2 after this response delay, the temperature
of the exhaust gas and the flow rate of the exhaust gas in the
surrounding or vicinity of the air fuel ratio sensor 11 begin to
increase. In FIG. 5, because the temperature of the exhaust gas in
T2 is lower than the reference temperature, the amount of heat
taken from the sensor element 11A increases with an increase in the
flow rate of the exhaust gas. Accordingly, the temperature of the
sensor element 11A begins to decrease at T3, later than the
increase in the flow rate of the exhaust gas.
[0068] In order to increase the temperature of the sensor element
11A from T3, the heater duty increases, but the temperature rise of
the sensor element 11A is late so the temperature of the sensor
element 11A drops. This temperature drop of the sensor element 11A
continues until the temperature of the exhaust gas reaches the
reference temperature at T4. For this reason, the temperature of
the sensor element 11A will become lower than the lower limit of
the predetermined range in a period of time from T3 to T4. When the
temperature of the exhaust gas exceeds the reference temperature at
T4, the sensor element 11A is heated by the exhaust gas, so the
temperature drop of the sensor element 11A ends. For this reason,
the heater duty does not substantially increase. After that, the
sensor element 11A is heated by the heater 11B and the exhaust gas,
so the temperature of the sensor element 11A goes up.
[0069] At T5, the accelerator opening degree becomes 0, and the
vehicle speed begins to decrease. Thus, when the accelerator
opening degree becomes 0 and the vehicle speed decreases, the flow
rate of the exhaust gas accordingly becomes smaller, so the sensor
element 11A can be heated by the heater 11B, even if the
temperature of the exhaust gas is equal to or less than the
reference temperature. As a result, the temperature of the sensor
element 11A continues to rise. Thereafter, the temperature of the
sensor element 11A reaches the reference temperature.
[0070] In this manner, when the target temperature of the sensor
element 11A is fixed at the reference temperature, the temperature
of the sensor element 11A may become lower than the lower limit of
the predetermined range, in cases where the temperature of the
exhaust gas is low.
[0071] On the other hand, FIG. 6 is a time chart showing the
changes over time of a variety of kinds of values in cases where
sensor element impedance control according to this embodiment is
carried out. In FIG. 6, similar to FIG. 5, there are shown, in
order from the top, the vehicle speed, the accelerator opening
degree, the temperature of the exhaust gas, the flow rate of the
exhaust gas, the temperature of the sensor element 11A, and the
duty ratio of the heater 11B. Here, note that the changes over time
of the vehicle speed, the accelerator opening degree, the
temperature of the exhaust gas and the flow rate of the exhaust gas
in FIG. 6 are the same as in FIG. 5. Also, note that the sensor
element impedance control according to this embodiment is started
from T11.
[0072] When the accelerator opening degree becomes large at T11,
the ECU 10 predicts the temperature of the exhaust gas and the flow
rate of the exhaust gas, whereby the target temperature of the
sensor element 11A is changed. At T12, the temperature of the
exhaust gas and the flow rate of the exhaust gas in the surrounding
of the air fuel ratio sensor 11 change corresponding to an increase
in the accelerator opening degree at T11, but the rise of the
target temperature of the sensor element 11A begins before T12.
That is, because it is predicted that the predicted temperature of
the exhaust gas is lower than the reference temperature and that
the flow rate of the exhaust gas increases, the target temperature
of the sensor element 11A is raised in advance from T11 so that the
temperature of the sensor element 11A does not drop. For that
reason, the heater duty increases from T11. After that, too, the
temperature of the exhaust gas and the flow rate of the exhaust gas
are successively predicted, and the target temperature of the
sensor element 11A is adjusted accordingly.
[0073] The exhaust gas at the temperature and the flow rate
predicted at T11 reaches the surrounding of the air fuel ratio
sensor 11 at T12. At this time, the actual temperature of the
sensor element 11A is higher than the reference temperature, and
hence, even if the flow rate of the exhaust gas at low temperature
increases, the temperature of the sensor element 11A is suppressed
from becoming lower than the lower limit of the predetermined
range.
[0074] Moreover, at T13, the temperature of the exhaust gas has
reached the reference temperature. Accordingly, after T13, the
sensor element 11A is heated by the exhaust gas, so the target
temperature is dropped so as to make the temperature of the sensor
element 11A lower. For that reason, the heater duty is also made
small. Then, at T14, the vehicle speed begins to decrease.
[0075] In this manner, when the target temperature of the sensor
element 11A is changed according to the predicted temperature of
the exhaust gas and the predicted flow rate of the exhaust gas, it
is possible to suppress the temperature of the sensor element 11A
from becoming lower than the lower limit of the predetermined
range, even in cases where the temperature of the exhaust gas is
low and the flow rate of the exhaust gas is large.
[0076] FIG. 7 is a flow chart showing a flow or routine for setting
the duty ratio in the sensor element impedance control according to
this embodiment. The routine in this flow chart is carried out by
means of the ECU 10 at each predetermined time interval. Here, note
that the sensor element impedance control is separately carried out
by the ECU 10.
[0077] In step S101, the temperature of the exhaust gas is
predicted, and in step S102, the flow rate of the exhaust gas is
predicted. The temperature of the exhaust gas and the flow rate of
the exhaust gas referred to herein are those in the surrounding of
the air fuel ratio sensor 11. The future temperature of the exhaust
gas and the future flow rate of the exhaust gas are calculated
based on the engine rotational speed and the engine load factor
which are calculated in the torque demand control. A map is used
for this calculation. This map takes into consideration a drop or
decrease in the temperature of the exhaust gas by the release of
heat at the time when the exhaust gas flows through the exhaust
passage 2.
[0078] In step S103, the target temperature of the sensor element
11A is calculated based on the temperature of the exhaust gas
calculated in step S101 and the flow rate of the exhaust gas
calculated in step S102. A map is used for the calculation of this
target temperature.
[0079] In step S104, the duty ratio in the sensor element impedance
control is calculated. The relation between the target temperature
and the duty ratio has been obtained in advance by experiments,
simulations, or the like. Then, in step S105, the duty ratio
calculated in step S104 is set as the duty ratio in the sensor
element impedance control. Here, note that in this embodiment, the
ECU 10 carries out the processing of steps S101 through S105, and
thus functions as a controller in the present disclosure.
[0080] Here, note that when the temperature of the sensor element
11A changes suddenly, the sensor element 11A may be damaged, or the
characteristic of the sensor element 11A may be changed to shift
the detected value thereof. Accordingly, when the target
temperature of the sensor element 11A is changed, the breakage or
damage of the sensor element 11A and the deviation of the detected
value thereof may be suppressed by providing an upper limit on the
rate of change of the target temperature, etc., so as to change the
target temperature in a gradual manner. The upper limit of the rate
of change of the target temperature has been obtained in advance by
experiments, simulations or the like as a rate of change at which
the breakage or damage of the sensor element 11A can be suppressed,
or as a rate of change at which the deviation of the detected value
of the air fuel ratio sensor 11 falls within an allowable
range.
[0081] In this embodiment, the temperature of the exhaust gas and
the flow rate of the exhaust gas are predicted and the target
temperature of the sensor element 11A is set based on these
predicted values, but instead of this, only the temperature of the
exhaust gas may be predicted, and the target temperature of the
sensor element 11A may be set based on this predicted value. That
is, although the target offset amount is set based on the relation
shown in FIG. 3, the correction based on the relation shown in FIG.
4 may not be made. Here, in cases where the predicted temperature
of the exhaust gas is higher than the reference temperature, the
larger the flow rate of the exhaust gas, the more easily the
temperature of the sensor element 11A rises. On the other hand, in
cases where the predicted temperature of the exhaust gas is lower
than the reference temperature, the larger the flow rate of the
exhaust gas, the more easily the temperature of the sensor element
11A drops. Accordingly, by setting the target temperature of the
sensor element 11A in consideration of the flow rate of the exhaust
gas, it becomes possible to perform the temperature control of the
sensor element 11A with higher precision. However, even in cases
where the flow rate of the exhaust gas is not taken into
consideration, it is possible to set the target temperature of the
sensor element 11A according to the change of the temperature of
the exhaust gas, and hence, the target temperature can also be set
without taking into consideration the flow rate of the exhaust
gas.
[0082] FIG. 8 is a flow chart showing a flow or routine for setting
the duty ratio in the sensor element impedance control according to
this embodiment, in cases where the flow rate of exhaust gas is not
taken into consideration. The routine in this flow chart is carried
out by means of the ECU 10 at each predetermined time interval.
Here, note that the sensor element impedance control is separately
carried out by the ECU 10.
[0083] In step S201, the temperature of the exhaust gas is
predicted. The temperature of the exhaust gas referred to herein
represents the temperature of the exhaust gas in the surrounding of
the air fuel ratio sensor 11. The future temperature of the exhaust
gas is calculated based on the engine rotational speed and the
engine load factor which are calculated in the torque demand
control. A map is used for this calculation. This map takes into
consideration the drop or decrease in the temperature of the
exhaust gas by the release of heat at the time when the exhaust gas
flows through the exhaust passage 2.
[0084] In step S202, the target temperature of the sensor element
11A is calculated based on the temperature of the exhaust gas
calculated in step S201. A map is used for the calculation of this
target temperature.
[0085] In step S203, the duty ratio in the sensor element impedance
control is calculated. The relation between the target temperature
and the duty ratio has been obtained in advance by experiments,
simulations, or the like. Then, in step S204, the duty ratio
calculated in step S203 is set as the duty ratio in the sensor
element impedance control. Here, note that in this embodiment, the
ECU 10 carries out the processing of steps S201 through S204, and
thus functions as the controller in the present disclosure.
[0086] As described above, according to this embodiment, the target
temperature in the sensor element impedance control is set based on
the predicted temperature of exhaust gas and the predicted flow
rate of exhaust gas, and the temperature of the sensor element 11A
has been changed before the temperature of the exhaust gas and the
flow rate of exhaust gas actually change, so it is possible to
suppress the adjustment of the temperature of the sensor element
11A from becoming late. With this, the temperature of the sensor
element 11A can be maintained within the predetermined range, thus
making it possible to suppress a decrease in the detection accuracy
of the air fuel ratio sensor 11.
[0087] Here, it is also considered that even in cases where the
temperature of the sensor element 11A is made to change in advance
based on the predicted temperature of exhaust gas and the predicted
flow rate of exhaust gas, the exhaust gas of the predicted
temperature reaches the air fuel ratio sensor 11 before the change
of the temperature of the sensor element 11A is completed. That is,
the adjustment of the temperature of the sensor element 11A may be
late. However, even in such a case, the adjustment of the
temperature of the sensor element 11A is started before the exhaust
gas actually reaches the sensor element 11A. Accordingly, the
adjustment of the temperature of the sensor element 11A can be
started more early than when the adjustment of the temperature of
the sensor element 11A is started after the temperature of the
sensor element 11A has changed, so a certain amount of effect can
be expected.
[0088] In addition, in this embodiment, an explanation has been
made using the air fuel ratio sensor 11 as an example, the present
disclosure can be applied to other sensors each having a heater.
For example, even in cases where a heater is controlled in a PM
sensor, an NOx sensor, or an HC sensor, too, the present disclosure
can be applied as in this embodiment. Moreover, in this embodiment,
the temperature of the exhaust gas is predicted based on the engine
rotational speed and the engine load factor which are obtained in
the torque demand control, but instead of this, the temperature
sensor 12 may directly detect the temperature of the gas discharged
from the internal combustion engine 1. In this case, it is
preferable to arrange the temperature sensor 12 as close to the
internal combustion engine 1 as possible. Then, the temperature of
the exhaust gas in the surrounding of the air fuel ratio sensor 11
can be predicted by further estimating a temperature drop until the
exhaust gas with its temperature detected by this temperature
sensor 12 flows through the exhaust passage 2 and reaches the air
fuel ratio sensor 11. Further, the temperature of the gas
discharged from the internal combustion engine 1 can be estimated
based not only on the engine rotational speed and the engine load
factor obtained in the torque demand control, but also on the
engine rotational speed detected by the crank position sensor 21
and the engine load factor detected by the accelerator opening
sensor 22, and hence, the temperature of the exhaust gas in the
surrounding of the air fuel ratio sensor 11 may be predicted based
on the temperature of this gas. The relation of the temperature of
the gas discharged from the internal combustion engine 1 or the
temperature of the exhaust gas in the surrounding of the air fuel
ratio sensor 11 with respect to the number of engine revolutions
per unit time and the engine load can be obtained in advance by
experiments, simulations, or the like.
[0089] Furthermore, the degree of opening of the throttle valve 8
and the temperature of the gas discharged from the internal
combustion engine 1 are in correlation with each other, so the
temperature of the gas discharged from the internal combustion
engine 1 may be predicted based on the degree of opening of the
throttle valve 8. The temperature of the exhaust gas in the
surrounding of the air fuel ratio sensor 11 can be predicted by
further estimating the temperature drop until this exhaust gas
flows through the exhaust passage 2 and reaches the air fuel ratio
sensor 11.
Second Embodiment
[0090] In the first embodiment, the temperature of the exhaust gas
and the flow rate of the exhaust gas are predicted based on the
accelerator opening degree, etc., and the target temperature of the
sensor element 11A is set based on the temperature of the exhaust
gas and the flow rate of the exhaust gas thus predicted. On the
other hand, in a second embodiment, the target temperature of the
sensor element 11A is set directly from the accelerator opening
degree. Here, in cases where the accelerator opening degree becomes
larger, the required torque of the internal combustion engine 1
becomes larger, so the amount of intake air and the amount of fuel
injection are increased, and the temperature of the exhaust gas
becomes higher, and the flow rate of the exhaust gas becomes
larger. Similarly, in cases where the accelerator opening degree
becomes smaller, the required torque of the internal combustion
engine 1 becomes smaller, so the temperature of the exhaust gas
becomes lower, and the flow rate of the exhaust gas becomes
smaller. Thus, there is a correlation among the accelerator opening
degree, the temperature of the exhaust gas, and the flow rate of
the exhaust gas. Accordingly, in this second embodiment, in cases
where the accelerator opening degree becomes larger, the
temperature of the sensor element 11A can become higher, so the
temperature of the sensor element 11A is made lower in advance. On
the other hand, in cases where the accelerator opening degree
becomes smaller, the temperature of the sensor element 11A can
become lower, so the temperature of the sensor element 11A is made
higher in advance.
[0091] FIG. 9 is a flow chart showing a flow or routine for setting
a duty ratio in the sensor element impedance control according to
this second embodiment. The routine in this flow chart is carried
out by means of the ECU 10 at each predetermined time interval.
Here, note that the sensor element impedance control is separately
carried out by the ECU 10.
[0092] In step S301, the accelerator opening degree is detected.
The accelerator opening degree is detected by the accelerator
opening sensor 22. In step S302, the target temperature of the
sensor element 11A is calculated based on the accelerator opening
degree detected in step S301. A map is used for the calculation of
this target temperature. This map is set so that the target
temperature of the sensor element 11A becomes lower when the
accelerator opening degree is large than when it is small. The map
showing the relation between the accelerator opening degree and the
target temperature of the sensor element 11A has been obtained in
advance by experiments, simulations or the like, and stored in the
ECU 10. Here, note that this map is made such that in cases where
the accelerator opening degree is such that the temperature of the
exhaust gas in the surrounding of the air fuel ratio sensor 11
becomes higher than the reference temperature of the sensor element
11A, the target temperature of the sensor element 11A is made lower
than the reference temperature, whereas in cases where the
accelerator opening degree is such that the temperature of the
exhaust gas in the surrounding of the air fuel ratio sensor 11
becomes lower than the reference temperature of the sensor element
11A, the target temperature of the sensor element 11A is made
higher than the reference temperature. Further, this map is also
made such that the target temperature falls within the
predetermined range. Here, note that the ECU 10 may have stored a
physical model or a formula in place of the map, and may calculate
the target temperature of the sensor element 11A according to the
physical model or the formula.
[0093] In step S303, the duty ratio in the sensor element impedance
control is calculated. The relation between the target temperature
and the duty ratio has been obtained in advance by experiments,
simulations, or the like. Then, in step S304, the duty ratio
calculated in step S303 is set as the duty ratio in the sensor
element impedance control. Here, note that in this second
embodiment, the ECU 10 carries out the processing of steps S302
through S304, and thus functions as the controller in the present
disclosure.
[0094] In this manner, it becomes possible to control the
temperature of the sensor element 11A in a simplified manner based
on the accelerator opening degree.
* * * * *