GAS CONCENTRATION DETECTING APPARATUS

A sensor control apparatus of a gas concentration detecting apparatus is provided with a sensor detecting unit, a temperature detecting unit, a heater control unit, a change rate calculation unit and a calibration outputting unit. The change rate calculation unit calculates a change rate of a heater current flowing through a heater when a heater control unit maintains the temperature of a sensor cell detected by a temperature detecting unit to be at a target temperature. The calibration outputting unit utilizes a change rate of a heater current to calibrate the sensor output as a sensor current detected by the sensor detecting unit and calculates a sensor calibration output of a gas sensor.

BACKGROUND

Technical Field

The present disclosure relates to a gas concentration detecting apparatus.

Description of the Related Art

The gas concentration detecting apparatus is configured using a gas sensor disposed at an exhaust pipe of a vehicle and a sensor control apparatus that controls an operation of the gas sensor. The gas sensor includes a sensor cell of which the pair of electrodes are disposed in the solid electrolyte and a heater generating heat when being energized to heat the sensor cell. Usually, the heater is energized with PWM (pulse width modulation) control to accomplish high responsivity to a load variation.

SUMMARY

A first aspect of the present disclosure is a gas concentration detecting apparatus including: a gas sensor having one or more sensor cells each provided with a pair of electrodes on a solid electrolyte, and a heater generating heat when being energized to heat the sensor cell; and a sensor control apparatus that controls an operation of the sensor cell and the heater.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The gas concentration detecting apparatus is configured using a gas sensor disposed at an exhaust pipe of a vehicle and a sensor control apparatus that controls an operation of the gas sensor. The gas sensor includes a sensor cell of which the pair of electrodes are disposed in the solid electrolyte and a heater generating heat when being energized to heat the sensor cell. Usually, the heater is energized with PWM (pulse width modulation) control to accomplish high responsivity to a load variation.

When performing the PWM control of the heater, pulse-wave voltage is applied to the heater such that a duty ratio indicating an ON-OFF ratio in each period of the pulse-shaped voltage is appropriately changed, thereby controlling the temperature of the sensor cell to be a target temperature. As a gas concentration detecting apparatus that performs PWM control for the heater, for example, JP-A-2004-093386 discloses one example.

According to the gas concentration detecting apparatus, a noise component superposed on the output signal of the sensor cell is eliminated from the output signal by an averaging process. More specifically, when the heater is turned ON, positive noise occurs on the output signal and when the heater is turned OFF, negative noise occurs on the output signal. According to the gas concentration detecting apparatus of the above patent literature, an averaging process is applied such that the positive noise and the negative noise appears in the opposite side so as to cancel the noise.

However, the inventor has found by research that other noise components are present in the noise components superposed on the output signal of the sensor cell other than a short-period of noise component due to ON-OFF switching of the energization of the heater (i.e. switching noise component). Specifically, in the case where the temperature of the sensor cell is maintained at the target temperature under the PWM control of the heater, it is identified that noise components having longer period (temperature control noise component) than that of the switching noise component is superposed on the sensor cell. The temperature control noise component is understood as a periodical shift in a temperature change or an effective value of the temperature change, and it is discovered that the temperature control noise component has a change speed different from that of the switching noise component.

Therefore, further improvement is required when eliminating the noise component contained in the output signal of the sensor cell to enhance the detection accuracy of the gas concentration detecting apparatus.

With reference to the drawings, preferred embodiments of the above-described gas concentration detecting apparatus will be described.

First Embodiment

As shown inFIGS.1to4, a gas concentration detecting apparatus1according to the present embodiment is provided with a gas sensor10and a sensor control apparatus5. The gas sensor10includes one or more sensor cells21in which a pair of electrodes311and312are provided in the solid electrolyte31, and a heater34that produces heat when being energized, thereby heating the sensor cells21. The sensor control apparatus5is configured to control the operation of the sensor cells21and the heater34.

As shown inFIG.5, the sensor control apparatus5includes a sensor detecting unit51, a temperature detecting unit52, a heater control unit53, a change rate calculation unit54and a calibration outputting unit55. The sensor detecting unit51detects sensor current Is generated in the sensor cell21. The temperature detecting unit52detects a temperature of the sensor cell21. The heater control unit53adjusts an application voltage Vth to the heater34.

The change rate calculation unit54calculates a change rate ΔS of the heater current Ih flowing through the heater34when the heater control unit53maintains the temperature of the sensor cell21detected by the temperature detecting unit52to be at the target temperature. The calibration outputting unit55utilizes change rate ΔS of the heater current Ih calculated by the change rate calculation unit54to calibrate the sensor output which is the sensor current Is detected by the sensor detecting unit51, thereby calculating a sensor calibration output Os of the gas sensor10.

Hereinafter, a gas concentration detecting apparatus1according to the present embodiment will be described in detail.

As shown inFIG.1, the gas sensor10is disposed at a mount hole71of an exhaust pipe7of an internal combustion engine (engine) of a vehicle. The gas sensor10is used for detecting an oxygen concentration, a specific gas concentration in a detection object gas which is an exhaust gas G flowing through the exhaust pipe7. The gas sensor10can be used as an air-fuel ratio sensor (i.e. A/F sensor) that obtains the air-fuel ratio in the internal combustion engine based on the oxygen concentration and unburnt gas concentration in the exhaust gas10. The air-fuel ratio sensor is configured to detect the air-fuel ratio continuously and quantitively from a fuel rich state where a ratio of fuel to air is larger than the theoretical air-fuel ratio to a fuel lean state where a ratio of fuel to air is smaller than the theoretical air-fuel ratio.

A catalyst is provided in the exhaust pipe7to purify toxic substances in the exhaust gas G and the gas sensor10may be disposed at either in an upper stream side or down stream side of the catalyst in the flow direction of the exhaust gas G in the exhaust pipe7. Further, the gas sensor10may be disposed in an inlet side pipe of a supercharger that enhances a density of an intake air of the internal combustion engine using the exhaust gas G. Moreover, a pipe to which the gas sensor10is disposed may be a pipe of an exhaust gas recirculation mechanism allowing a part of the exhaust gas G exhausted to the exhaust pipe7from the internal combustion engine to recirculate into the inlet pipe of the internal combustion engine.

As shown inFIGS.2to4, the sensor cell21and the heater34of the gas sensor10is formed of the sensor element2. The sensor cell21is configured of a solid electrolyte31, an exhaust electrode311and an atmosphere electrode312provided in the solid electrolyte31. For the solid electrolyte31, an insulator33A and33B are laminated, and the heater34is configured of a heating element embedded to the insulator33A and33B.

For the sensor cell21according to the present embodiment, one sensor cell21is formed in the gas sensor10to configure the air-fuel ratio sensor. Other than this, a plurality of sensor cells21may be formed in the gas sensor10so as to configure a NOx (nitrogen oxide) sensor. The sensor cell21in this case may be configured as a pump cell that lowers the oxygen concentration of the exhaust gas G, a monitor cell that detects residual oxygen concentration of the exhaust gas G and a detection cell that detects the NOx concentration of the exhaust gas G.

The gas sensor10may be provided with a plurality of sensor cells21for detecting the air-fuel ratio, the NOx concentration and the like. For the sensor cell21that calibrates the sensor output with the change rate calculation unit54and the calibration outputting unit55, a plurality of sensor cells21may be provided.

As shown inFIGS.2to4, the sensor element2of the present disclosure is formed in a long rectangular shape and provided with a solid electrolyte31, an exhaust electrode311, an atmosphere electrode312, a first insulator33A, a second insulator33B, a gas chamber35, an atmospheric air duct36and a heater34. The sensor element2is configured as a laminate type element in which respective insulators33A and33B, and the heater34are laminated.

According to the present embodiment, the longitudinal direction L of the sensor element2refers to a direction with which the sensor element2rectangularly extends. Further, a direction orthogonal to the longitudinal direction L, along which the solid electrolyte31and respective insulators33A and33B are laminated, is referred to a laminate direction D. Further, a direction orthogonal to both the longitudinal direction L and the laminate direction is referred to as a width direction W. Further, a tip end side L1 with respect to the longitudinal direction L of the sensor element2is defined as a portion exposed to the exhaust gas G, and the opposite side of the tip end side L1 is defined as a base end side L2. Also, in the gas sensor10, a direction the same as the longitudinal direction L of the sensor element2is defined as the longitudinal direction L.

As shown inFIGS.2to4, the solid electrolyte31has a conductivity for oxygen ion (O2−) at a predetermined activation temperature. The exhaust electrode311exposed to the exhaust gas G is provided on a first surface301of the solid electrolyte31, and the atmosphere electrode312exposed to atmospheric air A is provided on a second surface302of the solid electrolyte31. The exhaust gas electrode311and the atmosphere electrode312are arranged at a portion mutually overlapping in the laminate direction D via the solid electrolyte31in a tip end side L1 exposed to the exhaust gas G in the longitudinal direction L of the sensor element. In a tip end side L1 in the longitudinal direction L of the sensor element2, the sensor cell21is formed by the exhaust electrode311and the atmosphere electrode312, and a portion of the solid electrolyte31between these electrodes311and312. The first insulator33A is formed on the first surface301of the solid electrolyte31, and the second insulator33B is formed on the second surface302.

The solid electrolyte31is composed of zirconia-based oxide containing zirconia as a main component (containing 50% mass % or more), such as a stabilized zirconia or a partial stabilized zirconia where a part of zirconia is substituted with a metallic element of the rare earth group or an alkaline-earth metal. A part of zirconia that constitutes the solid electrolyte31is substituted by yttria, scandia or calcia.

The exhaust electrode311and the atmosphere electrode312contain platinum as a noble metal indicating catalytic activity to oxygen and a zirconia-based oxide as a co-material of the solid electrolyte31. As shown inFIG.1, an electrode lead part313is connected to the exhaust electrode11and the atmosphere electrode312for electrically connecting them to outside part of the gas sensor10. The electrode lead part313is drawn out to a portion in the base end side L2 in the longitudinal direction L of the sensor element2. A terminal connection part22is formed in an end portion in the base end side L2 in the longitudinal direction L of the electrode lead part313.

As shown inFIGS.2and3, the gas chamber35surrounded by the first insulator33A and the solid electrolyte31is adjacently formed on the first surface301of the solid electrolyte31. The gas chamber35is formed at a portion accommodating the exhaust electrode311in a tip end side L1 in the longitudinal direction L of the first insulator33A. The gas chamber35is formed as a space part closed by the first insulator33A and a diffusion resistance part32and the solid electrolyte31. The exhaust gas G flowing through the exhaust pipe7is introduced to the gas chamber35passing through the diffusion resistance part32.

As shown inFIG.3, the diffusion resistance part (gas introduction part)32according to the present embodiment is provided at both sides of the gas chamber35in the width direction W. The diffusion resistance part32is formed by providing a porous body of metal oxide such as aluminum oxide in an introduction hole formed at the first insulator33A. The diffusion speed (flow rate) of the exhaust gas G introduced in the gas chamber35is determined by limiting the speed of the exhaust gas G passing through pores in the porous body in the diffusion resistance part32. Note that the diffusion resistance part32may be provided at a portion in the tip end side L1 of the gas chamber35in the longitudinal direction L.

As shown inFIGS.2to4, the atmospheric air duct36surrounded by the second insulator33B and the solid electrolyte31is adjacently formed on the second surface302of the solid electrolyte31. The atmospheric air duct36is formed from a portion on the second insulator33B accommodating the atmosphere electrode312in the longitudinal direction L to a base end portion of the sensor element2in the longitudinal direction L.

As shown inFIGS.2to4, the first insulator33A forms the gas chamber35, and the second insulator33B forms the atmospheric air duct36includes the heater34embedded thereto. The first insulator33A and the second insulator33B are formed of metal oxide such as alumina (aluminum oxide). The respective insulators33A and33B are formed of a dense body through which the exhaust gas G or the atmospheric air cannot transmit.

As shown inFIGS.3and4, the heater34is configured as a heating element and embedded to the second insulator33B that forms the atmospheric air duct36. The heater34includes a heating part341that generates heat when being energized and a heating lead part342connected to a portion in a base end side L2 of the heating part341in the longitudinal direction L. The heating part341is disposed in a portion where a part of the heating part341is overlapping with the exhaust electrode311and the atmosphere electrode312in a laminate direction D of the solid electrolyte31and respective insulators33A and33B. The heater34is configured of a metal material having conductivity. The terminal connection part22is formed at an end portion in the base end side L2 of the heating lead342in the longitudinal direction L.

As shown inFIG.1, a surface protection layer37that covers the sensor cell21is formed at a portion in the tip end side L1 of the sensor element2in the longitudinal direction L. The surface protection layer37is configured of a plurality of mutually coupled ceramic particles as a ceramic material having pores that allow the exhaust gas G to pass through.

(Configuration of Other Sensor Element2)

Although illustration is omitted, the sensor element2is not limited to the one having a single solid electrolyte31, but the sensor element2may be one having two or more solid electrolyte31. The electrodes311and312provided in the electrolyte31are not limited to a pair of the exhaust electrode311and the atmosphere electrode312but may be a plurality of pairs of electrodes. In the case where a plurality of pairs of electrodes are provided on one or more electrolyte31, the heating part341of the heater34can be provided at a portion facing the plurality of pairs of electrodes in the lamination direction D.

(Configurations Other than Gas Sensor10)

As shown inFIG.1, in order to dispose the sensor element2on the exhaust pipe7to be connected to the sensor control apparatus5, the gas sensor10is provided with a housing31, an element support42, a terminal support43, a contact member431, a contact terminal44, a tip end side cover45, a base end side cover46, a bush47, a lead wire48and the like.

The housing41is used for fastening the gas sensor10to the mount hole71of the exhaust pipe7. The housing41supports the sensor element2via the element support42. The sensor element2is supported by the element support42via the glass powder421. The element support42is supported by the housing41via a caulking material422,423and424. The terminal support43that supports the contact terminal44is coupled to a portion in a base end side L2 of the element support42in the longitudinal direction L. The terminal support43is supported by the base end side cover46with the contact member431.

The contact terminal44contacts with the base end portion of the electrode lead part313as the terminal connection part22and contacts with the base end portion of the heating lead part342as the terminal connection part22in the sensor element2, so as to electrically connect the electrode lead part313and the heating lead part342to the lead wire48. The contact terminal44is connected to the lead wire48via a connection fitting441in a state of being disposed in the terminal support43.

As shown inFIG.1, the tip end side cover45is provided in a tip end side L1 of the housing41in the longitudinal direction L, covering the sensor cell21of the sensor element2. For the tip end side cover45, a gas communicating hole451is formed to allow the exhaust gas G touching the sensor element2to pass therethrough. The sensor cell21of the sensor element2and the tip end side cover45are provided in the exhaust pipe7of the internal combustion engine. A part of the exhaust gas G flowing in the exhaust pipe7flows inside the tip end side cover45from the gas communicating hole451of the tip end side cover45. Then, the exhaust gas G inside the tip end side cover45passes the surface protection layer37of the sensor element2and the diffusion resistance part32and is guided to the exhaust electrode311.

The base end side cover46is provided in the base end side L2 of the housing41in the longitudinal direction L, covering a wiring part positioned in the base end side L2 of the gas sensor10in the longitudinal direction L so as to prevent the wiring part from being exposed to atmospheric moisture in the atmospheric air A. The wiring part is configured of, as a portion electrically connected to the sensor element2, the contact terminal44, a connecting part (i.e. connection fitting441) between the contact terminal33and the lead wire48, and the like.

The bush47is supported at an inner periphery side of a portion in the base end side L2 of the base end side cover46in the longitudinal direction L. An atmospheric air introduction hole461is formed at the base end side cover46for introducing the atmospheric air A from outside the gas sensor10. The atmospheric air introduction hole461is covered by a water repellent filter462. The base end position of the atmospheric air duct36in the sensor element2is opened to a space inside the base end side cover46, and the atmospheric air A is guided to the atmosphere electrode312in the atmospheric air duct36.

As shown inFIG.1, the lead wire48in the gas sensor10is electrically connected to the sensor control apparatus5that controls a gas detection of the gas sensor10. The sensor control apparatus5performs an electrical control of the gas sensor10together with an engine control apparatus5that controls a combustion operation of the engine. The sensor control apparatus5is configured of various control circuits, a computer and the like. The sensor control apparatus5may be configured within the engine control apparatus6.

FIG.5schematically shows an electrical configuration of the sensor control apparatus5. The sensor detecting unit51, the temperature detecting unit52, the heater control unit53and a heater current detecting unit56are mainly configured of a control circuit. The change rate calculation unit54and the calibration outputting unit55are mainly configured of a computer50. In the sensor control apparatus5, the temperature of the sensor cell21detected by the temperature detecting unit52is feed-backed and the heater control unit53performs a feedback control of the temperature of the sensor cell21. Also, in the sensor control apparatus5, a heater current Ih detected by the heater current detecting unit56is utilized to calculate the change rate ΔS of the heater current Ih by the change rate calculation unit54. Then, the calibration outputting unit55calibrates the sensor current Is detected by the sensor detecting unit51based on the change rate ΔS and calculates the sensor calibration output Os.

As shown inFIG.2, the sensor detecting unit51is provided with a voltage application circuit511that applies DC voltage between the exhaust electrode311and the atmosphere electrode312and a current detecting circuit512that measures current flowing between the exhaust electrode311and the atmosphere electrode312. The voltage application circuit511applies DC voltage between the electrodes311and312, where an amount of the DC voltage is determined to be a value causing limit current characteristics on the sensor cell21due to the diffusion resistance of the diffusion resistance part32when the exhaust gas G flows into the gas chamber35. The voltage application circuit511applies the DC voltage between the electrodes311and312such that the positive side electrode is the atmosphere electrode312to discharge oxygen in the gas chamber35.

In the sensor detecting unit51, when the exhaust gas G after being combusted in the internal combustion engine at a fuel lean state reaches the exhaust electrode311, the sensor current Is at the positive side is mainly detected, and when the exhaust gas G after being combusted in the internal combustion engine at a fuel rich state reaches the exhaust electrode311, the sensor current Is at the negative side is mainly detected.

As shown inFIG.2, the temperature detecting unit52includes a detecting circuit521that detects a resistance or an impedance of the sensor cell21. The temperature detecting unit52is configured to utilize the resistance or the impedance detected by the detecting circuit521to detect the temperature of the sensor cell21. In the case where the composition of the exhaust gas G is close to a stoichiometric region (i.e. theoretical air fuel ratio), the sensor current Is detected by the sensor detecting unit51is almost zero. With the state where variation of the composition of the exhaust gas G is small in the stochiometric region, the current value when the voltage is applied between the electrodes311and312of the sensor cell21is detected, whereby the resistance value or the impedance value thereof can be detected. Then, the temperature detecting unit52detects the temperature of the sensor cell21based on the resistance value or the impedance value using a correlation between the resistance value or the impedance value and the temperature of the sensor cell21.

The temperature detecting unit52may be configured to estimate the temperature of the sensor cell21by detecting the resistance value or the impedance value of the heater34. Also, in this case, the temperature detecting unit52may be configured to be similar to the case of detecting the resistance value or the impedance value of the sensor cell21.

As shown inFIG.3, the heater control unit53is configured to apply an application voltage Vh as a pulse-wave AC voltage to the heating lead part342as a heating element that constitutes the heater34. The heater control unit53is configured using an energization control circuit531that energizes the heater34. The heater control unit53is configured to perform a pulse-width modulation control (PWM control) in which the duty ratio of the pulse-wave application voltage Vh is changed to adjust the application voltage Vh of the heater34.

As shown in (a) ofFIG.6, when applying the pulse-wave application voltage Vh to the heater34, an effective voltage Ve, which is a product of multiplication of ON voltage of the pulse-wave application voltage Vh and the duty ratio, is substantially applied to the heater34. The duty ratio is expressed by ON voltage/one period, that is, a ratio of a duration of ON voltage to the one period of AC voltage. The target temperature to heat the sensor cell21by the heater control unit53is set to be, for example, a predetermined temperature from 600° C. to 900° C. as an activation temperature of the sensor cell21.

As shown inFIG.3, the sensor control apparatus5includes the heater current detecting unit56that detects a heater current Ih flowing through the heater34. The heater current detecting unit56is configured using the current detecting circuit561that detects the heater current Ih. The heater current detecting unit56is configured to detect an effective current depending on the effective voltage Ve when the heater control unit53applies the pulse-wave application voltage Vh to the heater34. The heater current detecting unit56is configured to measure the voltage across a shunt resistor disposed in the energization control circuit531so as to detect the heater current Ih.

The heater current detecting unit56according to the present embodiment detects the heater current Ih flowing through the heater34near the stoichiometric region where the air fuel ratio of the internal combustion engine is controlled. In the exhaust pipe7in which the gas sensor10is disposed, in the case where an external disturbance is present causing a temperature variation of the sensor cell21, the heater current Ih varies when the heater control unit53attempts to maintain the temperature of the sensor cell21to be the target temperature. As an external disturbance, variations in a temperature and an amount of flow of the exhaust gas G flowing through the exhaust pipe7are present.

As shown inFIG.6(b)andFIG.7, the sampling period t1 during which the heater current detecting unit56detects the heater current Ih is shorter than the period t2 of the pulse-wave application voltage Vh controlled by the heater control unit53. With this configuration, a change in the heater current Ih can be appropriately detected. Further, according to the present embodiment, the heater current detecting unit56sets the sampling period t1 during which the heater current detecting unit56detects the heater current Ih to be shorter than 1/10 of the period t2 of the pulse-wave application voltage Vh controlled by the heater control unit53. An interval of the period during which the sensor detecting unit51detects the sensor current Is and an interval of the period during which the temperature detecting unit52detects the resistance value of the impedance value of the sensor cell21may be set to be smaller than the sampling period t1 during which the heater current detecting unit56detects the heater current Ih. Note thatFIG.7shows a part ofFIG.6(c).

As shown inFIG.3,FIG.6(b), (c)andFIG.7, the change rate calculation unit54is configured to calculate the change rate ΔS of the heater current Ih detected by the heater current detecting unit56. When the heater control unit53maintains the temperature of the sensor cell21detected by the temperature detecting unit52at the target temperature, the temperature of the sensor cell21may vary increasingly ort decreasingly with respect to the target temperature. Further, when the heater control unit53maintains the temperature of the sensor cell21to be at the target temperature, and the temperature of the sensor cell21increases or decreases, it is assumed that the temperature of the sensor cell21barely varies. In these cases, the heater current Ih varies depending on an energization amount of the heater control unit53, and the heater current Ih has a change rate depending on the variation of the heater current Ih.

According to the present embodiment, as shown inFIG.6(c), the change rate calculation unit54calculates the change rate ΔS of the heater current Ih to be a change rate ΔS of the effective current of the heater34depending on the effective voltage Ve which is a product of multiplication of ON voltage of the pulse-wave application voltage Vh and the duty ratio. The change rate ΔS of the effective current does not reflect small-period noise component (i.e. switching noise component) accompanied with ON-OFF switching operation of the heater34by the heater control unit53. The change rate ΔS of the effective current reflects a change in noise component having a larger period than the switching noise component when the temperature of the sensor cell21is maintained at the target temperature.

As shown inFIG.6(b), in the change rate calculation unit54, the heater current Ih detected by the heater current detecting unit56is calculated as an average value a of the heater current Ih during a predetermined period which is longer than the period t2 of the pulse-wave application voltage Vh controlled by the heater control unit53. Then, the change rate ΔS of the heater current Ih is calculated based on an amount of change in the heat current Ih (difference value) during a predetermined period longer than the predetermined period with which the average value a of the heater current Ih is calculated or based on the differential value thereof. The change rate ΔS is expressed by an inclination of the waveform of the heater current Ih shown inFIG.6(b). The average value a of the heater current Ih may be calculated using a period which is an integer multiple of the period t2 of the pulse-wave application voltage Vh controlled by the heater control unit53.

In the case where the heater control unit53continuously applies the pulse-wave application voltage Vh having the same duty ratio to the heater34, the average value a of the heater current Ih is constant and the change rate ΔS of the heater current Ih is zero. In the case where the heater control unit53applies the pulse-wave application voltage Vh having different duty ratios to the heater34, the average value a of the heater current Ih is not constant and the change rate ΔS of the heater current Ih has a predetermined value.

As shown inFIGS.6(b) and (d), the change rate ΔS of the heater current Ih indicates an amount (change amount) of change of the heater current Ih per unit time. It is found that the change amount of the heater current Ih per unit time generates a change amount of temperature control noise component on the sensor current Is of the sensor cell21detected by the sensor detecting unit51. In other words, it is found that the sensor current Is of the sensor cell21detected by the sensor detecting unit51varies accompanied with a phase delay ta depending on a change in the heater current Ih.

As shown inFIGS.2,3and6(d), the calibration outputting unit55reduces an influence on the sensor output which is the sensor current Is detected by the sensor detecting unit51, caused by the change amount of the heater current Ih per unit time, and outputs the calibration output Os of the gas sensor10. In particular, the calibration outputting unit55eliminates the temperature control noise component contained in the sensor output and calculates the sensor calibration output Os. The calibration outputting unit55outputs the sensor calibration output Os reflecting an amplitude and a period of a change in the heater current Ih and a phase delay ta produced when a change in the heater current Ih appears as a change in the sensor current Is. With this configuration, the accuracy of the sensor calibration output Os is improved.

The calibration outputting unit55utilizes the change rate ΔS of the effective current of the sensor current Is to calibrate the sensor output so as to cancel an induced current generated in the sensor cell21, thereby calculating the sensor calibration output Os. When an amplitude of the change in the heater current Ih becomes larger, an amplitude of the temperature control noise component superposed to the sensor current Is tends to become larger. Also, when a period of the change in the heater current Ih becomes shorter (i.e. frequency becomes higher), an amplitude of the temperature control noise component superposed to the sensor current Is tends to become larger. An amplitude and a period of a change in the heater current Ih are reflected to the change rate ΔS of the heater current Ih. Hence, the calibration outputting unit55sets an amount of calibration for cancelling the temperature control noise component in the sensor current Is such that the larger the change rate ΔS of the effective current of the heater current Ih, the larger the amount of calibration is set. With this configuration, the temperature control noise component contained in the sensor current Is (sensor output) can be effectively eliminated.

Further, as shown inFIGS.6(b) and (d), the phase delay ta produced when a change in the heater current Ih appears as a change in the sensor current Is has an own value depending on magnetic permeability and permittivity of the insulators33A and33B, and the atmospheric air duct36disposed between the heater34and respective electrodes311,312and respective electrode lead parts313. Here, the magnetic permeability refers to a degree of likelihood of magnetic flux permeating to the respective electrodes311and312and respective electrode lead parts313from the heater34. The magnetic flux readily permeates as the magnetic permeability becomes higher.

Further, the permittivity is correlated to an electrostatic capacitance of a pseudo capacitor formed between the heater34and respective electrodes311and312, and respective electrode lead parts313. The electrostatic capacitance becomes larger proportionally to the permittivity. The higher the electrostatic capacitance, the slower the permeability rate of magnetic flux.

The phase delay ta of the temperature control noise component may be acquired by an evaluation test after producing a prototype of the gas sensor10. Then, the calibration outputting unit55calibrates the sensor current Is using the phase delay ta. Specifically, the calibration outputting unit55shifts the time by a value corresponding to the phase delay ta and calibrates the sensor current Is, thereby calculating the sensor calibration output Os.

The sensor current Is generated in the sensor cell21contains an induction current as a temperature control noise component produced, depending on the effective current in the heater34, on respective electrode lead parts313connected to the exhaust electrode311and the atmosphere electrode312in the sensor cell. When the heater control unit53performs a pulse width modulation control of the heater34, a current changes in the heater34accompanied with ON-OFF switching of the pulse-wave application voltage Vh, and a magnetic flux is produced depending on the current change around an axis line of the heater34in the lead-wire direction. Then, the magnetic flux causes an induction current on the respective electrode lead parts312connected to the exhaust electrode311and the atmosphere electrode312in the sensor cell21, and the induction current is superposed to the sensor current Is. Also, the induction current is superposed to the sensor current Is accompanied with the phase delay ta.

FIG.8is a graph showing a relationship between the change rate ΔS [A/sec] of the heater current Ih and an amount of change [uA] of the sensor current Is. The relationship is obtained in the following manner. When the heater control unit53appropriately changes the application voltage Vh to the heater34, the heater current detecting unit56detects the heater current Ih and the sensor detecting unit51detects the heater current Ih, thereby obtaining the relationship between the change rate ΔS [A/sec] of the heater current Ih and an amount of change [uA] of the sensor current Is. Note that the larger the change rate ΔS of the heater current Ih, the larger the change rate of the sensor current Is. InFIG.8, the amount of change (change amount) of the sensor current Is relative to the change rate ΔS of the heater current Ih is plotted.

As shown inFIG.9, the sensor control apparatus5has a correlation map M that shows a correlation between the change rate ΔS of the heater current Ih and an amount of calibration of the sensor current (sensor output) calculated by the calibration outputting unit55. Since the amount of change of sensor current Is is considered as a temperature control noise component, the calibration amount of the sensor current Is is defined as a value where a negative sign is added to the change amount of the sensor current Is.

In the correlation map M, the change rate ΔS of the heater current Ih includes a positive side change rate ΔS which is an increasing side of the heater current Ih and a negative side change rate ΔS which is a decreasing side of the heater current Ih. In the correlation map M, when the change rate ΔS of the heater current Ih is on the positive side, a correlation is present in which the higher the change rate ΔS of the heater current Ih on the positive side, the higher the calibration amount of the sensor current Is is set in the negative direction. Further, in the correlation map M, when the change rate ΔS of the heater current Ih is in the negative side, a correlation is present in which the higher the change rate ΔS of the heater current Ih in the negative side, the higher the calibration amount of the sensor current Is is set in the positive direction.

The calibration outputting unit55calibrates the change rate ΔS based on the calibration amount of the sensor current Is determined by comparing with the correlation map M and output the sensor calibration output Os. Also, the calibration outputting unit55utilizes, when calculating the sensor calibration output Os, the calibration amount of the sensor output at a time earlier than the current time by the phase delay ta of the temperature control noise component. The correlation map M is utilized, whereby the calibration of the sensor output Is by the calibration outputting unit55can readily be performed.

(Operation of Gas Concentration Detecting Apparatus1)

FIG.6(a)shows a change in the pulse-wave application voltage Vh applied to the heater34by the heater control unit53. InFIG.6(a), an effective value of the application voltage Vh applied to the heater34is also shown.FIG.6(b)shows the heater current Ih flowing through the heater34which is detected by the heater current detecting unit56. The heater current Ih has a similar waveform to the effective value of the application voltage Vh applied to the heater34.

FIG.6(c)shows a time-varying wave of the change rate ΔS of the heater current Ih. The time-varying wave of the change rate ΔS of the heater current Ih refers to an amount of change of the heater current Ih per unit time which is calculated by the change rate calculation unit54. The change rate ΔS of the heater current Ih is calculated by a difference value or the like of the heater current Ih in an integer multiple of a period of the pulse-wave application voltage Vh.

FIG.6(d)shows a time-varying wave of the sensor current Is detected by the sensor detecting unit51. The sensor current Is is detected as a waveform having a phase delay ta with respect to a time change value of the heater current Ih. Then, a time change value of the sensor current Is accompanied by a time change of the heater current Ih, as a temperature control noise component, is calibrated with the change rate ΔS of the heater current Ih considering the phase delay ta. Thus, the sensor calibration output Os after calibration is not influenced by the temperature control noise component.

(Detection Method of Gas Concentration)

Hereinafter, with reference to a flowchart ofFIG.10, an example of detection method of gas concentration using the gas concentration detection apparatus1will be described. The gas sensor10and the sensor control apparatus5are activated in response to an activation of the internal combustion engine of the vehicle and the engine control apparatus6thereof. In the sensor control apparatus5, the heater control unit53performs pulse width modulation control for the heater34and the heater34heats the sensor cell21(step S101). Subsequently, the temperature detecting unit52detects the temperature of the sensor cell21(step S102), and continuously heats the sensor cell21till the temperature of the sensor cell21reaches the activation temperature (step S103). The activation temperature of the sensor cell21is the target temperature with which the heater control unit53heats the sensor cell21.

Next, when the temperature of the sensor cell21is detected by the temperature detecting unit52, the sensor detecting unit51detects the sensor current Is at a predetermined sampling interval (step S104) and the heater current detecting unit56detects the heater current Ih (step S105). Next, the sensor current Is and the heater current Ih are detected a plurality of times and when determined that one or more predetermined intervals where an average value of the heater current Ih is acquired has passed (step S106), the change rate calculation unit54calculates the change rate ΔS of the heater current Ih flowing through the heater34(step S107).

At this moment, the change rate ΔS of the heater current Ih is acquired by dividing a difference value between the average value a of the heater current Ih at the current time and the average value a of the heater current Ih at a past time by a time difference between the current time and the past time.

Next, the calibration outputting unit55compares the change rate ΔS of the heater current Ih with the correlation map M, thereby determining the calibration amount of the sensor current Is (step S108). Then, the calibration outputting unit55calculates the sensor calibration output Os by using the calibration amount of the sensor current Is at a time earlier than the current time by a phase delay ta of the temperature control noise component and the average value a of the heater current Ih at the current time (step S109).

When the calibration value of the sensor current Is is in a negative side, the calibration value of the sensor current Is is subtracted from the average value a of the sensor current Is at the current time, and when the calibration value of the sensor current Is is on the positive side, the calibration value of the sensor current Is is added to the average value a of the sensor current Is at the current time. Thereafter, processes at steps S104to S110are repeatedly executed until the control of the sensor control apparatus5is stopped (step S110).

Effects and Advantages

According to the sensor control apparatus5of the gas concentration detecting apparatus1of the present embodiment, the change rate calculation unit54calculates the change rate ΔS of the heater current Ih flowing through the heater34when the heater control unit53maintains the temperature of the sensor cell21detected by the temperature detecting unit52to be the target temperature. The change rate ΔS is indicated as a rate of change calculated when the application voltage Vh of the heater34is adjusted so as to avoid temperature change in the temperature cell21from the target temperature in the case where the temperature of the sensor cell21is influenced by an external disturbance.

When the temperature of the sensor cell21is influenced by an external disturbance and the sensor cell detecting unit51detects the sensor current Is generated in the sensor cell21to be a sensor output, the sensor output is highly likely to contain a temperature control noise component superposed thereon which is accompanied by a change in the application voltage Vh as an effective value to the heater34. Here, the calibration outputting unit55calibrates the sensor output using the change rate ΔS of the heater current Ih calculated by the change rate calculation unit54and outputs the sensor calibration output Is of the gas sensor10.

With this configuration, according to the gas concentration detecting apparatus1of the present embodiment, an influence of the temperature control noise component to the sensor output is eliminated and the detection accuracy of the sensor output of the gas sensor10is enhanced. Further, the change rate ΔS of the heater current Ih is used, thereby effectively enhancing the detection accuracy of the sensor output of the gas sensor10.

Second Embodiment

As shown inFIG.12(a), (b), (c) and (d), according to the gas concentration detecting apparatus1of the present embodiment, the calibration outputting unit55of the sensor control apparatus5calibrates the sensor output as the sensor current Is using a temperature detected by the temperature detecting unit52other than the change rate ΔS of the heater current Ih. The calibration outputting unit55of the present embodiment calibrates the sensor current Ih considering a fact that a temperature of the sensor cell21influences an amount of the sensor current Is and the phase delay ta of the sensor current Is, and calculates the calibration output Os.

FIG.11schematically shows an electrical configuration of the sensor control apparatus5according to the present embodiment. In the sensor control apparatus5, the heater current Ih detected by the heater current detecting unit56is utilized and the change rate calculation unit54calculates the change rate ΔS of the heater current Ih. Then, the calibration outputting unit55calibrates the sensor current Is detected by the sensor detecting unit51based on the change rate ΔS and a temperature change ΔT of the sensor cell21by the heater control unit53, and outputs the sensor calibration output Os.

The temperature of the sensor cell21detected by the temperature detecting unit52influences an amount of the temperature control noise component generated on the sensor current Is and the phase delay ta. The magnetic permeability of the insulators33A and33B and the atmospheric air duct36disposed between the heater34and respective electrodes311,312and respective electrode lead parts313becomes higher as the temperature increases. In other words, the higher the temperature of the sensor element2, the larger a variation of the sensor current Is accompanied with a change in the heater current Ih is. This is an inverse relationship of a case where the higher the temperature, the higher the resistance value of the heater34is, and the heater current Ih is difficult to flow.

Further, the permittivity and the electrostatic capacitance of the insulators33A and33B and the atmospheric air duct36disposed between the heater34and respective electrodes311,312and respective electrode lead parts313becomes lower as the temperature increases. For an induction current generated at the respective electrodes311and312and the respective lead parts313of the sensor cell21, the smaller the electrostatic capacitance, the shorter the phase delay ta till superposing on the sensor current Is, depending on a change in the heater current Ih. That is, the higher the temperature of the sensor element2, the shorter the phase delay ta of a change in the sensor current Is with respect to a change in the heater current Ih is.

Similar to the first embodiment,FIG.12(a), (b)show time-varying waveforms of the pulse-wave application voltage Vh and the heater current Ih.FIG.12(c)shows a temperature change ΔT of the sensor cell21when the heater current Ih changes. The temperature change ΔT of the sensor cell21has a predetermined phase delay tb with respect to a change in the heater current Ih similar to the sensor current Is shown inFIG.12(d). The phase delay ta of the sensor current Is and the phase delay tb of the temperature change ΔT with respect to a change in the heater current Ih are considered to be similar values.

The sensor control apparatus5according to the present embodiment is provided with a first correlation map M1 showing a correlation between the change rate ΔS of the heater current Ih and the calibration amount of the sensor current Is calculated by the calibration outputting unit55, and a second correlation map M2 showing a correlation between the temperature of the sensor cell21and the calibration amount of the sensor current Is outputted by the calibration outputting unit55. The first correlation map M1 is similar to the correlation map M of the first embodiment shown inFIG.9.

FIG.13is a graph showing a relationship between a temperature change ΔT [° C.] indicating an amount of increase in the temperature of the sensor cell21and an amount of change [μA] of the sensor current Is, where the heater current detecting unit56detects the heater current Ih and the sensor detecting unit51detects the sensor current Is when the heater control unit53changes the application voltage Vh to the heater34, thereby acquiring the relationship using the change rate ΔS [μA/sec] of the heater current Ih as a parameter. The temperature change ΔT refers to a temperature change from the target temperature. The higher the temperature change ΔT, the larger the change amount of the sensor current Is is. Further, the higher the change rate ΔS of the heater current Ih, the larger a step of the change amount of the sensor current Is with respect to the temperature change ΔT is.

InFIG.13, the change rate ΔS of the heater current Ih is shown at 0.1 Hz, 0.2 Hz and 0.3 Hz. InFIG.13, values of the change amount of the sensor current Is with respect to the temperature change ΔT are plotted with a parameter of the change rate ΔS of the heater current Ih.

As shown inFIG.14, Since the change amount of the sensor current Is is considered as a temperature control noise component, the calibration amount of the sensor current Is is defined as a value where a negative sign is added to the change amount of the sensor current Is. The calibration amount of the sensor current (sensor output) Is has a relationship in which the larger the change rate ΔS of the heater current Ih, the larger the calibration amount of the sensor current IS is, and the higher the temperature change ΔT, the larger the calibration amount of the sensor current IS is.

As shown inFIG.14, in the second correlation map M2, the temperature change ΔT includes a positive side change rate in which the temperature change ΔT changes increasingly and a negative side change rate in which the temperature change ΔT changes decreasingly. In the second correlation map M2, when the temperature change ΔT is on the positive side, a correlation is present such that the larger the change rate ΔT in the positive side, the larger the calibration amount of the sensor current Is is on the negative side. Further, in the second correlation map M2, when the temperature change ΔT is in the negative side, a correlation is present such that the larger the change rate ΔT in the negative side, the larger the calibration amount of the sensor current Is is on the positive side.

The calibration outputting unit55calculates the sensor calibration output Os based on a first calibration amount of the sensor current Is determined by comparing the change rate ΔS of the heater current Ih with the first correlation map M1, and a second calibration amount of the sensor current Is determined by comparing the change rate ΔS of the heater current Ih and the temperature change ΔT with the second correlation map M2. Also, the calibration outputting unit55utilizes, when calculating the sensor calibration output Os, the first calibration amount of the sensor current Is at a time earlier than the current time by the phase delay ta and the second calibration amount of the sensor current Is at a time earlier than the current time by the phase delay tb.

In other words, the calibration outputting unit55of the present embodiment sums the first calibration amount of the sensor current Is at a time earlier than the current time by the phase delay ta and the second calibration amount of the sensor current Is at a time earlier than the current time by the phase delay tb to outputs the sensor calibration output Os. The first correlation map M1 and the second correlation map M2 are used, whereby calibration accuracy of the sensor current Is by the calibration outputting unit44can be further enhanced.

(Operation of Gas Concentration Detecting Apparatus1)

FIGS.15(a), (b) and (c)illustrate, for a conventional gas concentration detecting apparatus (comparative example) having no change rate calculation unit54and calibration outputting unit55, a change in the sensor current (sensor output) Is when an external disturbance causes variations in the heater current Ih and the temperature of the sensor cell21in the case where the heater control unit53controls the temperature of the sensor cell21to be the target temperature. InFIGS.15(a), (b) and (c), a case will be described in which change in the temperature of the exhaust gas G supplied to the gas sensor10is simulated by a sinusoidal wave.

FIG.15(a)illustrates a change in the heater current Ih,FIG.15(b)illustrates a change in the temperature of the sensor cell21andFIG.15(c)illustrates a change in the sensor current (sensor output) Is. As shown inFIGS.15(a), (b) and (c), it is realized that the sensor current Is varies due to a predetermined phase delay ta when the heater current Ih and the temperature of the sensor cell21vary.

FIGS.16(a), (b) and (c)illustrate a change in the sensor current Is when the step of a change amount of the temperature21becomes small for a comparative example. It can be seen that a change in the sensor current Is is small when the step of a change amount of the temperature21becomes small. Although illustration is omitted, when the period of the heater current Ih becomes shorter (frequency of vibration becomes larger), an amplitude of the sensor current Is becomes larger.

FIGS.17(a), (b) and (c)illustrate, for the gas concentration detecting apparatus1(embodied example) of the second embodiment 2 provided with the change rate calculation unit54and the calibration outputting unit55, a change in the sensor current (sensor output) Is when an external disturbance causes variations in the heater current Ih and the temperature of the sensor cell21in the case where the heater control unit53controls the temperature of the sensor cell21to be the target temperature. Also inFIGS.17(a), (b) and (c), a case will be described in which change in the temperature of the exhaust gas G supplied to the gas sensor10is simulated by a sinusoidal wave.

As shown inFIG.17(c), for the embodied product, it is realized that a change in the sensor current Is is minimized by the calibration of the sensor current Is performed by the change rate calculation unit54and the calibration outputting unit55.

Other configurations, effects and advantages and the like in the gas concentration detecting apparatus1of the present embodiment is similar to those in the first embodiment. Also in the present embodiment, constituents indicated by the same reference symbols as those in the first embodiment are the same as the constituents in the first embodiment.

Other Embodiments

The sensor detecting unit51may be configured to convert the sensor current Is to the sensor voltage for the detecting. In this case, the calibration outputting unit55calibrates the sensor voltage and outputs the sensor calibration voltage Os.

Moreover, the change rate calculation unit54may calculate the change rate of the application voltage Vh applied to the heater34instead of calculating the change rate ΔS of the heater current Ih. The application voltage Vh applied to the heater34appropriately changes depending on a change in the temperature of the sensor cell21. The change rate of the application voltage Vh applied to the heater34is determined as a rate of change of the effective value of the application voltage Vh. Also in this case, the calibration outputting unit55may preferably calibrate the sensor current Is using a change in the temperature of the sensor cell21described in the second embodiment. Further, the change rate calculation unit54may utilize both the change rate ΔS of the heater current Ih and the change rate of the application voltage Vh applied to the heater34.

The heater control unit53may utilize the pulse frequency modulation (PFM) instead of utilizing the pulse-width modulation (PWM) to apply the application voltage Vh to the heater34. In the PFM control, the interval of the pulse application voltage Vh having the same width applied to the heater34is appropriately changed.

The present disclosure is not limited to the respective embodiments, but may constitute different embodiments without departing from the spirit of the present disclosure. The present disclosure includes various modification examples and modification examples within an equivalent thereof. Further, various combinations of constituents and embodiments anticipated from the present disclosure are included in the technical scope of the present disclosure.

CONCLUSION

The present disclosure provides a gas concentration detecting apparatus capable of enhancing the detection accuracy of the sensor output of the gas sensor, in which noise components produced when a change in a voltage is applied to the heater as an effective value are prevented from affecting the sensor output.

A first aspect of the present disclosure is a gas concentration detecting apparatus including: a gas sensor having one or more sensor cells each provided with a pair of electrodes on a solid electrolyte, and a heater generating heat when being energized to heat the sensor cell; and a sensor control apparatus that controls an operation of the sensor cell and the heater.

The sensor control apparatus includes: a sensor detecting unit that detects a sensor current or a sensor voltage produced in the sensor cell; a temperature detecting unit that detects a temperature of the sensor cell; a heater control unit that adjusts an application voltage applied to the heater; a change rate calculation unit that calculates at least either a change rate of an application voltage applied to the heater or a change rate of a heater current flowing through the heater when the heater control unit maintains the temperature detected by the temperature detecting unit to be at a target temperature; and a calibration outputting unit that utilizes the change rate calculated by the change rate calculation unit to calibrate a sensor output which is the sensor current or the sensor voltage detected by the sensor detecting unit, thereby calculating a sensor calibration output of the gas sensor.

According to the sensor control apparatus of a gas concentration detecting apparatus of the above first aspect, at least either the change rate of the application voltage applied to the heater or the change rate of the heater current flowing through the heater is calculated by the change rate calculation unit when the heater control unit maintains the temperature of the sensor cell detected by the temperature detecting unit to be at the target temperature. These change rates are each expressed as a rate of change calculated when adjusting the application voltage of the heater such the temperature of the sensor cell is not shifted from the target temperature in the case where the temperature of the sensor cell is influenced by an external disturbance.

In the case where the temperature of the sensor cell is influenced by an external disturbance, when the sensor detecting unit detects the sensor current or the sensor voltage generated in the sensor cell as the sensor output, a noise component accompanied by a change in the application voltage as an effective voltage applied to the heater is most likely to become superposed on the sensor output. For this reason, the calibration outputting unit calibrates the sensor output using the change rate calculated by the change rate calculation unit, and calculates the sensor calibration output of the gas sensor.

With this configuration, according to the gas concentration detecting apparatus of the first aspect, the sensor output is prevented from being influenced by the noise component accompanied by a change in the application voltage as the effective value applied to the heater, and the detection accuracy of the sensor output of the gas sensor.

The detection of the temperature of the sensor cell by the temperature detecting unit includes a case of estimating the temperature based on various information.