Patent Grant
6868712
The present application is based upon and claims priority of Japanese patent Application Nos. Hei. 9-106103 filed on Apr. 23, 1997 and Hei. 10-89619 filed on Apr. 2, 1998, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a gas concentration sensor and, more particularly, to a method for controlling an oxygen concentration sensor for sensing the oxygen concentration in the exhaust gas of an on-vehicle internal combustion engine when the sensor is active by using the element resistance thereof.
2. Description of the Related Art
There have been demands recently for improved accuracy in air-fuel ratio control of motor vehicle engines. In response to these demands, a linear air-fuel ratio sensor, or oxygen concentration sensor, has been developed. The sensor linearly detects, over a wide range, the air-fuel ratio of an air-fuel mixture sucked into the internal combustion engine corresponding to the concentration of oxygen in the exhaust gas. In order to maintain detection precision in such an air-fuel sensor, maintaining the air-fuel sensor in an active state is important. In general, the air-fuel sensor is maintained in an active state by supplying a current to a heater equipped to the air-fuel sensor and heating an element of the air-fuel sensor.
During excitation of the heater, there is conventionally disclosed a technique for sensing the temperature of the sensor element and thereby performing feedback control of the element temperature so that the element temperature reaches a desired activation temperature (e.g. approximately 700° C.). In this case, in order to sense the instantaneous element temperature, a method of equipping a temperature sensor to the sensor element and drawing out the element temperature from the sensed result is known and is commercially practiced. However, in this method, the cost is increased due to the necessity of adding the temperature sensor. On this account, it has been proposed to detect the resistance of the sensor element based on a prescribed correspondence relationship between the element resistance and the element temperature. Thus, it is thereby possible to draw out the element temperature from the detected element resistance. It is to be noted that the detected result of the element resistance is used, for example, also for determining the degree of deterioration of the air-fuel sensor.
The above-described conventional technique is one which detects element resistance (d.c. impedance) by applying a d.c. voltage to the sensor element. In contrast to this, Japanese Patent Laid-Open Publication No. Hei. 4-24657 discloses a technique of detecting element resistance by applying an a.c. voltage to the sensor element. The a.c. voltage is applied continuously to the air-fuel ratio sensor, and the resulting sensor output is passed through a low pass filter, and high pass filter, for separate air-fuel ratio calculations. Thereafter, the both air-fuel ratios are averaged to thereby determine the a.c. impedance. This procedure of detection is generally known as a method of detection of the element resistance that uses the a.c. characteristic of the air-fuel ratio sensor.
According to the above-described d.c. impedance method, the sensor current Ineg that is output when the negative rectangular wave applied voltage Vneg has been applied sharply fluctuates as illustrated in FIG. 32B. If the oxygen concentration is detected during this time period, it is impossible to detect a true oxygen concentration.
Also, according to the a.c. impedance method discussed above, since the air-fuel ratio is detected by passing the sensor output through the low pass filter, there arises the problem that a phase lag occurs in the air-fuel ratio output. Also, a.c. noises are liable to be superimposed on the air-fuel ratio output. These problems are prominent, particularly when the operational state of the internal combustion engine is in a transition state.
In an air-fuel ratio detection microcomputer, as the number of processings to be executed with the same timing increases, the processing load increases. The simultaneous detection processing of the air-fuel ratio, detection processing of the element resistance, and control processing of the element heater with respect to the oxygen concentration sensor all add to the processing load. As a result, processing time length exceeds the processing period, resulting in deviation of the timing of processing during subsequent period.
Further, because the sensor signal is small, when noises are superimposed thereon at the time of detecting the element resistance of the oxygen concentration sensor, the determined element resistance value differs greatly from a true element resistance value.
Further, when detecting the element resistance of the oxygen concentration sensor and thereby selecting the applied voltage from a relevant map, if noises are superimposed on the sensor signal, the selection made with respect to the map becomes unstable.
The present invention obviates the above-described inconveniences.
More particularly, an air/fuel sensor generates an A/F signal proportional to an oxygen concentration in the exhaust gas from an internal combustion engine upon application of a voltage based on an instruction from a microcomputer. Periodically, an element resistance detection cycle is performed to detect the resistance of a sensor element for sensor temperature control purposes. The element resistance detection cycle, however, causes an inaccurate A/F signal to be output. The present invention prevents the detected A/F value from becoming abnormal during the resistance detection cycle through programmed control routines and specific hardware implementation. As a result, an accurate A/F control can be executed, even during the element resistance detection cycle.
An object of the present invention is to provide a method for controlling the oxygen concentration sensor which, at the time of detecting the element resistance, prevents the detected value of the oxygen concentration from becoming abnormal. Another object of the present invention is to provide a control method for controlling the oxygen concentration sensor which enables the execution of a more precise air-fuel ratio control with the use of the detected element resistance.
The above and other objects, features and advantages of the present invention will become apparent from the following description when the same is read in conjunction with the accompanying drawings in which:
The present invention will now be explained on the basis of embodiments thereof. In the following embodiments, reference will be made to cases where the gas concentration sensor according to the present invention is used as an oxygen concentration sensor for detecting the concentration of oxygen in the exhaust gas of an on-vehicle internal combustion engine.
In
Next, an explanation will be given with reference to a table of
It is seen from
Also, in the voltage-current characteristic of
On the other hand, in
Also, the bias control circuit 40 detects, by its current detection circuit 50, the value of the current that flows out from the A/F sensor 30 upon application of a voltage thereto. An analog signal indicating the current value detected by the current detection circuit 50 is input through an A/D converter 23 to the microcomputer 20. The current value detected by the current detection circuit 50 is then converted to an oxygen concentration signal, and is output as an A/F signal through the sample/hold circuit 70 and LPF 71. A heater 31 equipped to the A/F sensor 30 is operationally controlled by the heater control circuit 60. That is, by this heater control circuit 60, the element temperature of the A/F sensor 30 and the power supplied from a battery power source (not illustrated) to the heater 31 in correspondence with the heater temperature are controlled in terms of the duty ratio. The control of heating of the heater 31 is thereby executed.
Next, the electrical construction of the bias control circuit 40 will be explained with reference to the circuit diagram of FIG. 3.
In
The first voltage supply circuit 45 includes a voltage follower circuit. A voltage Va that is the same as the reference voltage Va of the reference voltage circuit 44 is supplied from the first voltage supply circuit 45 to a first terminal 42 of the A/F sensor 30. More specifically, the first voltage supply circuit 45 includes an operational amplifier 45a whose positive side input terminal is connected to a voltage-dividing point between the voltage-dividing resistors 44a and 44b, and whose negative side input terminal is connected to the first terminal 42 of the A/F sensor 30. The circuit 45 also includes a resistor 45b with a first end connected to an output terminal of the operational amplifier 45a, and a second end being connected to the bases of an NPN transistor 45c and PNP transistor 45d. The collector of the NPN transistor 45c is connected to the constant voltage Vcc. The emitter thereof is connected to the terminal 42 of the A/F sensor 30 through a current detection resistor 50a of the current detection circuit 50. Also, the emitter of the PNP transistor 45d is connected to the emitter of the NPN transistor 45c, and the collector thereof is grounded.
The second voltage supply circuit 47 is also a voltage follower circuit. A voltage Vc that is the same as the output voltage vc of the LPF 22 is supplied from the second voltage supply circuit 47 to the second terminal 41 of the A/F sensor 30. More specifically, the second voltage supply circuit 47 includes an operational amplifier 47a whose positive side input terminal is connected to an output terminal of the LPF 22, and whose negative side input terminal is connected to the second terminal 41 of the A/F sensor 30. A resistor 47b has one end connected to an output terminal of the operational amplifier 47a, and a second end connected to the bases of an NPN transistor 47c and PNP transistor 47d. The collector of the NPN transistor 47c is connected to the constant voltage Vcc. The emitter thereof is connected to the second terminal 41 of the A/F sensor 30 through a resistor 47e. Also, the emitter of the PNP transistor 47d is connected to the emitter of the NPN transistor 47c, and the collector thereof is grounded.
With the above-described construction, to the one terminal 42 of the A/F sensor 30 there is at all times supplied the constant voltage Va. When the voltage Vc, which is lower than the constant voltage Va, is applied to the terminal 41 of the A/F sensor 30 through the LPF 22, the A/F sensor 30 is positively biased. Also, when the voltage Vc is higher than the constant voltage Va and is applied to the terminal 41 through the LPF 22, the A/F sensor 30 is negatively biased.
The microcomputer 20 controls the S/H circuit 70 and the A/F signal detection permission/inhibition signal, thereby stabilizing the A/F signal. That is, the S/H circuit 70 is normally set to the sample state by the microcomputer 20. Therefore the present A/F signal is output from the S/H circuit 70. On the other hand, at the time of detecting the element resistance, the S/H circuit 70 is set to the hold state by the microcomputer 20. Therefore the A/F signal obtained previously, when the S/H circuit 70 was in the preceding sample state, is output from the S/H circuit 70. Also, from the microcomputer 20, the A/F signal detection permission signal is normally output. At the time of detecting the element resistance, the A/F signal detection inhibition signal is output.
Next, the function of the air-fuel ratio detecting apparatus having the above-described construction will be explained.
In
Next, the routine advances to step S300, where it is determined whether a prescribed time period T2 has elapsed from a point in time at which the element resistance was previously detected. Here, the prescribed time period T2 is a time period corresponding to the detection period of the element resistance and is selectively set in correspondence with, for example, the operational state of the internal combustion engine 10. This detection period is set to be, for example, 2 sec at a normally changing time (stationary operation time) when the change in A/F is relatively small. The detection period is set to be, for example, 128 ms at a sharply changing time (transition operation time) when the A/F sharply changes. When the determination condition at step S300 is not satisfied, processing from step S100 to step S300 is repeatedly executed, whereby the A/F is detected each time the prescribed time period T1 elapses.
On the other hand, when the determination condition at step S300 is satisfied and the prescribed time period T2 has elapsed from the previous element resistance detection time, the routine advances to step S400, where the element resistance detection processing is executed. Thereafter, the flow returns to step S100, whereby the same processing is repeatedly executed.
Next, a subroutine for executing the element resistance detection processing in step S400 of
In
After the switch processing of the applied voltage in step S402 or in step S403, the routine proceeds to step S404 where the amount of change in the voltage ΔV and the amount of change in the sensor current ΔI detected by the current detection circuit 50 are read. Next, the routine proceeds to step S405 where the element resistance R is calculated using the ΔV and ΔI (R=ΔV/ΔI). The subroutine subsequently ends.
At this time, since, in the case of “lean”, the applied voltage is changed to the negative side, and, in the case of “rich”, the applied voltage is changed to the positive side to thereby determine the sensor current that corresponds to each change in voltage, there is no possibility that this sensor current will exceed the dynamic range (see
On the other hand, the element resistance R that has been determined in the above manner has a relationship illustrated in
Next, an explanation will be given according to the flow diagram of
In
In this way, the invention is embodied as the control method for controlling the A/F sensor 30 for outputting the sensor current (current signal) corresponding to the A/F ratio (oxygen concentration) in the exhaust gas upon application of a voltage. Namely, at the time of detecting the element resistance R of the A/F sensor 30, according to the amount of change in the current ΔI that follows the amount of change in the voltage ΔV, the change in current in the A/F sensor 30 is interrupted, and the A/F signal that indicates the sensor current corresponding to the A/F ratio that has theretofore prevailed is held.
As the applied voltage, and the sensor current changes, in order to detect the element resistance R of the A/F sensor 30, the A/F signal also inconveniently changes.
Therefore the A/F signal obtained at this time is not a true A/F signal. Accordingly, as the element resistance R is detected by the use of the A/F sensor 30, the change in current in the A/F sensor 30 is interrupted. The A/F signal obtained before the voltage is changed for the purpose of detecting the element resistance is held. As a result, because the A/F signal obtained before the timing with which the element resistance is detected is held, there is no possibility that an erroneous A/F signal may be used when detecting the element resistance.
Next, an explanation will be given according to a flow diagram of
In
The second embodiment is directed to a control method for controlling the A/F sensor 30 to output the sensor current corresponding to the A/F ratio in the exhaust gas upon application of the voltage. Namely, at the time of detecting the element resistance R of the A/F sensor 30 according to the amount of change in the current ΔI that follows the amount of change in the voltage ΔV, a signal is output for inhibiting the use of the A/F signal from the A/F sensor 30. That output signal indicates the sensor current corresponding to the A/F ratio.
That is, while changing the applied voltage and thereby changing the sensor current in order to detect the element resistance R of the A/F sensor 30, the A/F signal also changes. Therefore, the A/F signal obtained at that time is not a true A/F signal. Accordingly, when detecting the element resistance R by the use of the A/F sensor 30, the use of the A/F signal is inhibited. As a result, when detecting the element resistance, because the use of the A/F signal is inhibited, there is no possibility that an erroneous A/F signal may be used.
Next, an explanation will be given according to a flow diagram of
That is, as illustrated in
Further, as illustrated in
Referring to
Thus, this embodiment is directed to method for controlling the A/F sensor 30 to output the sensor current corresponding to the A/F ratio in the exhaust gas upon application of a voltage. Namely, at the time of detecting the element resistance R of the A/F sensor 30 according to the amount of change in the current ΔI which follows the amount of change in the voltage ΔV, the change in current in the A/F sensor 30 is interrupted. The A/F signal is then held to indicate the sensor current corresponding to the A/F that has theretofore prevailed, whereby use of the A/F signal from the A/F sensor 30 that indicates the sensor current corresponding to the A/F ratio is inhibited.
That is, while changing the applied voltage and thereby changing the sensor current in order to detect the element resistance R of the A/F sensor 30, the A/F signal also changes. Therefore the A/F signal obtained at that time is not a true A/F signal. Accordingly, at the time of detecting the resistance R by the use of the A/F sensor 30, the change in current in the A/F sensor 30 is interrupted. The A/F signal obtained before the voltage change is held to detect the element resistance. Thus, the use of the A/F signal is inhibited until the same coincides with the actual A/F signal. As a result, when detecting the element resistance, because the A/F signal obtained before the timing with which the element resistance is detected is held, consideration is given also to the annealed portion of the signal annealed by the LPF or the like, and inhibition is made of the use of the A/F signal during the element resistance detection, there is no possibility that an erroneous A/F signal may be used.
Next, referring to
First, the processing contents and processing loads which correspond to the processing timings of the microcomputer 20 will be explained with reference to FIG. 17.
In
In contrast to this, the load of the microcomputer 20 that is applied when the critical current A/F detection process and element resistance detection process are executed simultaneously, as illustrated as the processing contents “2”, or when the critical current A/F detection process and element heater control process are executed simultaneously, as illustrated as the processing contents “3”, is, of course, higher than the load of the microcomputer 20 that is applied when only the critical current A/F detection process is executed, as illustrated as the processing contents “1”. However, the load can be decreased in the case of the processing contents “0”. In this way, the processing contents are smoothed so that, with the process needed to be executed with the earliest processing timing by the microcomputer 20 as a reference, the other processes can be executed with different processing timings. Therefore, it is possible to suppress the processing load of the microcomputer 20.
Specifically, in
Next, the routine proceeds to step S1400 in which it is determined whether the prescribed time period T32 has elapsed. This prescribed time period T32 is a time period that corresponds to the element resistance detection period. In the initial stage from the start of the control, T32 is set to the same time length as that corresponding to the prescribed time period T31. After the A/F sensor 30 has been activated due to a rise in its temperature, T32 is set to be, for example, 128 ms. When it has been determined at step S1400 that the prescribed time period T32 has elapsed, the routine proceeds to step S1500, where the element resistance detection process illustrated in
The above-described embodiment is directed to a control method for controlling the A/F sensor 30 for outputting the sensor current corresponding to the A/F ratio in the exhaust gas upon application of the voltage. Namely, this embodiment is directed to differentiating the execution timings for executing the process for detecting the element resistance R of the A/F sensor 30 according to the amount of change in the current ΔI that follows the amount of change in the voltage ΔV, and the process for raising the temperature of the A/F sensor 30.
Accordingly, since smoothing is performed so that, with the A/F detection process being used as a reference, the element resistance detection process and element heater control process can be executed with different processing timings. Therefore, it is possible to suppress the processing load of the microcomputer 20.
Next, an explanation will be given according to a flow diagram of
In
In this way, the control method of this embodiment controls the A/F sensor 30 for outputting the sensor current corresponding to the A/F ratio in the exhaust gas upon application of a voltage. Namely, this embodiment is directed to limiting the amount of change with respect to the element resistance R detected by the A/F sensor 30 according to the amount of change in the current ΔI that follows the amount of change in the voltage ΔV.
Accordingly, the change in the element resistance R of the A/F sensor 30 is limited to the amount of change in the permissible range, i.e. as illustrated from
Also, this embodiment is directed to changing the amount-of-change limitation value dR according to prescribed conditions. Accordingly, the element resistance R of the A/F sensor 30 can be rounded by an appropriate permissible range of its amount of change in accordance with the condition of use of the element. For this reason, the limitation values dR0 and dR1 can be changed according to, for example, the operational condition of the internal combustion engine, and not according to the rising operation in temperature of the A/F sensor 30. Therefore, it is possible to execute a stable control with respect to the A/F sensor 30.
And, according to this embodiment, when the temperature of the A/F sensor 30 is rising, the amount-of-change limitation value dR is set to be large. After the rise in the temperature of the A/F sensor 30, dR is set to be small. Namely, by changing the permissible range of the amount of change of the element resistance R during a rise in temperature thereof and after the rise in temperature thereof, it is possible to execute a stable control of the A/F sensor 30 while realizing an early activation demanded of the A/F sensor 30.
Next, an explanation will be given according to a flow chart of
In
Thus, this embodiment is directed to embodying the invention as the control method for controlling the A/F sensor 30 for outputting the sensor current corresponding to the A/F ratio in the exhaust gas upon application of a voltage. Namely, this embodiment is directed to passing the A/F sensor signal through the LPF, with respect to the element resistance R detected by the A/F sensor 30, according to the amount of change in the current ΔI that follows the amount of change in the voltage ΔV.
Accordingly, the change in the element resistance R of the A/F sensor 30 is limited to the amount of change in the permissible range. Therefore, the execution range of control with respect to the A/F sensor 30 can fall within a normal execution range. Namely, at the time of detecting the element resistance of the A/F sensor 30, it is possible to prevent the detected element resistance value from varying greatly from a true value due to the fact that the sensor signal is a very small signal. Therefore, noises are superimposed thereon due to conditions such as the operational condition of the internal combustion engine, and the wired condition of the sensor signal. That is, since the sensor signal is passed through the LPF sufficiently responsive to a change in the element resistance of the A/F sensor 30, it is possible for the change in the element resistance not to fall outside a normal range of control. And, since the detection of the element resistance is not affected by a very small magnitude of change, no effect is had on the control based on a normal change in the element resistance. As a result, a responsiveness that is determined according to the heater control based on such parameters as detected element resistance is obtained.
Also, this embodiment is directed to changing the time constant dL of the LPF according to prescribed conditions. Accordingly, the time constant of the LPF is changed so that the element resistance R of the A/F sensor 30 may be sufficiently responsive to a normal change in the element resistance in accordance with the condition of use of the element. Namely, the time constants dL0 and dL1 of the LPF, through which the sensor signal is passed for detecting the element resistance, are changed according to, for example, the operational condition of the internal combustion engine 10, and not according to the state of rise in temperature of the A/F sensor 30. Thus, it is possible to execute a stable control with respect to the A/F sensor 30.
Also, according to this embodiment, when the temperature of the A/F sensor 30 is rising, the time constant of the LPF is set to be large. After the rise in the temperature of the A/F sensor 30, the time constant is set to be small. Namely, by switching the LPF to be sufficiently responsive to the change in the element resistance during the rise in temperature of the A/F sensor 30, and by switching the LPF to be sufficiently responsive to the change in the element resistance after the rise in temperature of the A/F sensor 30, it is possible to execute a stable control of the A/F sensor 30 while realizing an early activation demanded of the A/F sensor 30.
Next, an explanation will be given according to the flow diagram of
In
In this way, this embodiment is directed to the control method for controlling the A/F sensor 30 for outputting the sensor current corresponding to the A/F ratio in the exhaust gas upon application of the voltage. Namely, this embodiment is directed to limiting the amount of change with respect to the element resistance R detected by the A/F sensor 30 according to the amount of change in the current ΔI that follows the amount of change in the voltage ΔV, and also to passing the sensor signal through the LPF.
Accordingly, the change in the element resistance R of the A/F sensor 30 is limited to the amount of change in the permissible range. In addition, the change in element resistance is LPF processed, with the result that the execution range of control with respect to the A/F sensor 30 can fall within a normal execution range. Namely, at the time of detecting the element resistance of the A/F sensor 30, it is possible to prevent the detected element resistance value from becoming greatly different from a true value, as the sensor signal is a very small signal. Therefore noises are superimposed thereon due to operational conditions such as the condition of the internal combustion engine, or the wired condition of the sensor signal. That is, since the change in the element resistance of the A/F sensor 30 is limited to the amount of change in the prescribed range, and in addition is subjected to LPF processing, as the LPF is sufficiently responsive to the change in the element resistance, it is possible for the change in the element resistance not to fall outside a normal range of control. And, since the detection of the element resistance is not affected by a very small magnitude of change, no effect is had on the control based on a normal change in the element resistance. As a result, a responsiveness is obtained that is determined according to the heater control based on parameters such as the detected element resistance.
Next, an explanation will be given according to a flow chart of
In
In this way, this embodiment is directed to a control method for controlling the A/F sensor 30 for outputting the sensor current corresponding to the A/F ratio in the exhaust gas upon application of a voltage. Namely, this embodiment is directed to averaging a plurality of element resistances detected by the A/F sensor 30 according to the amount of change in the current ΔI that follows the amount of change in the voltage ΔV.
Accordingly, the changes in the element resistance R of the A/F sensor 30 are averaged, whereby the effect of abnormal data is suppressed. As a result, the execution range of control with respect to the A/F sensor 30 can fall within a normal execution range. Namely, at the time of detecting the element resistance of the A/F sensor 30, it is possible to prevent the detected element resistance value from varying greatly from a true value due, as the sensor signal is a very small signal. Therefore noises are superimposed thereon due to conditions such as the operational condition of the internal combustion engine or wired condition of the sensor signal. That is, since the changes in the element resistance of the A/F sensor 30 are averaged, it is possible for the change in the element resistance not to fall outside a normal range of control. Since the detection of the element resistance is not affected by a very small magnitude of change, no effect is had on the control based on a normal change in the element resistance. As a result, a responsiveness is obtained that is determined according to the heater control based on parameters such as the detected element resistance.
Next,
In
In this way, this embodiment is directed to the control method for controlling the A/F sensor 30 for outputting the sensor current corresponding to the A/F ratio in the exhaust gas upon application of the voltage. Namely, this embodiment is directed to limiting the map selection range after the rise in temperature of the A/F sensor 30 when changing the voltage applied to the A/F sensor 30 at the time of detecting the A/F ratio thereof, according to the map preset using the element resistances R of the A/F sensor 30 as parameters.
While the voltage applied to the A/F sensor 30 at the time of detecting the A/F ratio is changed according to the map using the element resistances R as parameters, the execution range of control with respect to the A/F sensor 30 can fall within a normal execution range, as the map is fixed by determining that, after the rise in temperature, the change in the element resistance R is small. Namely, at the time of detecting the element resistance of the A/F sensor 30, it is possible to prevent the voltage applied to the sensor from becoming abnormal. As a result, it is possible to prevent the detected oxygen concentration value from becoming different from a true value due to the fact that the sensor signal is a very small signal. Therefore noises are superimposed thereon due to conditions such as the operational condition of the internal combustion engine, and the wired condition of the sensor signal. Therefore, the detected element resistance value differs from a true value. That is, since large changes in the element resistance of the A/F sensor 30 are ignored after the completion of the rise in temperature, it is possible for the change in the element resistance not to fall outside a normal range of control.
Next, an explanation will be given in view of the flow diagram of
In
The above embodiment is directed to the control method for controlling the A/F sensor 30 for outputting the sensor current corresponding to the A/F ratio in the exhaust gas upon application of a voltage. Namely, this embodiment is directed to providing a hysteresis with respect to determining the map selection when changing the voltage applied to the A/F sensor 30 at the time of detecting the A/F ratio thereof, according to the map preset using the element resistances R of the A/F sensor 30 as parameters.
The voltage applied to the A/F sensor 30 at the time of detecting the A/F ratio thereof is changed according to the map using the element resistances R as parameters. A map selection is made based on the fact that the element resistance of the A/F sensor 30 ordinarily gradually decreases due to a rise in temperature. Therefore, correct map selection can be made according to the direction in which the element resistance changes. As a result, the execution range of control with respect to the A/F sensor 30 can fall within a normal execution range. Namely, at the time of detecting the element resistance of the A/F sensor 30, it is possible to prevent the voltage applied to the sensor from becoming abnormal. As a result, it is possible to prevent the detected oxygen concentration value from varying from a true value due to the fact that the sensor signal is a very small signal, therefore causing noises to be superimposed thereon due to conditions such as the operational condition of the internal combustion engine, and the wired condition of the sensor signal, and therefore causing the detected element resistance value to differ from a true value. That is, since large changes in the element resistance of the A/F sensor 30 are ignored, it is possible for the change in the element resistance not to fall outside a normal range of control.
Next, an explanation will be given according to the flow diagram of
In
After the applied voltage map selection processing of step S522 or S523, the routine proceeds to step S524 and it is determined whether the conditions under which an applied voltage map for calculating the voltage applied when detecting the A/F ratio by the A/F sensor 30 by using the presently detected element resistance as a parameter are fixed. Here, it is determined whether the element resistance decreases, for example, below 50 Ω due to a rise in temperature, with the result that the A/F sensor 30 is almost in an already activated state. When the determination condition in step S524 is satisfied, the routine proceeds to step S525, and the applied voltage map available after the fixing conditions are satisfied is selected (refer to the fixation of the map selection made after the rise in temperature illustrated in FIG. 31). On the other hand, when the determination condition in step S524 is not satisfied, step S525 is skipped. Next, the routine proceeds to step S526 and the voltage applied to the A/F sensor 30 is calculated according to the selected applied voltage map. Next, the routine proceeds to step S527, and the element resistance used for the presently selected applied voltage map is stored for the next applied voltage map selection, after which this routine is ended.
In this way, this embodiment is directed to embodying the invention as the control method for controlling the A/F sensor 30 for outputting the sensor current corresponding to the A/F ratio in the exhaust gas upon application of a voltage. Namely, this embodiment is directed to providing a hysteresis for determining the map selection when changing the voltage applied to the A/F sensor 30 at the time of detecting the A/F ratio thereof according to the map preset, using the element resistances R of the A/F sensor 30 as parameters, and also to limiting the map selection range after the rise in temperature of the A/F sensor 30.
While the voltage applied to the A/F sensor 30 at the time of detecting the A/F thereof is changed according to the map using the element resistances R as parameters, the execution range of control with respect to the A/F sensor 30 can fall within a normal execution range. This is possible because a map selection can be based in part on the fact that the element resistance of the A/F sensor 30 ordinarily gradually decreases due to a rise in temperature. Thus, map selection may be made according to the direction in which the element resistance changes, and, since after the rise in temperature the map is fixed, by determining the change in the element resistance R as being small. Namely, at the time of detecting the element resistance of the A/F sensor 30, it is possible to prevent the voltage applied to the sensor from becoming abnormal and, as a result, prevent the detected oxygen concentration value from becoming different from a true value due to the fact that the sensor signal is a very small signal, and therefore noises are superimposed thereon due to conditions such as the operational condition of the internal combustion engine, and the wired condition of the sensor signal. Therefore the detected element resistance value differs from a true value. That is, since the direction in which the element resistance changes is taken into consideration during the rise in temperature of the A/F sensor 30, and large changes in the element resistance of the A/F sensor 30 are ignored after the rise in temperature, it is possible for the change in the element resistance not to fall outside a normal range of control.
While in the above-described embodiments the invention has been explained by taking as an example the control method for controlling the oxygen concentration sensor for detecting the oxygen concentration as the current signal corresponding to the oxygen concentration signal, this oxygen concentration sensor may be a 1-cell critical current type oxygen concentration sensor or a 2-cell critical current type oxygen concentration sensor.
Also, the present invention can be similarly applied in the same way as in the case of the oxygen concentration sensor as a control method for controlling other sensors which are directed to detecting the concentration of gases such as NOx, HC, CO and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 9-106103 | Apr 1997 | JP | national |
| 10-89619 | Apr 1998 | JP | national |
This application is a division of application No. 09/064,163, filed Apr. 22, 1998 now U.S. Pat. No. 6,347,544, the entire content of which is hereby incorporated by reference in this application.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4385611 | Harper et al. | May 1983 | A |
| 4419190 | Dietz et al. | Dec 1983 | A |
| 4543176 | Harada et al. | Sep 1985 | A |
| 5245979 | Pursifull et al. | Sep 1993 | A |
| 5781878 | Mizoguchi et al. | Jul 1998 | A |
| 6083370 | Kato et al. | Jul 2000 | A |
| 6120677 | Yamada | Sep 2000 | A |
| 6656337 | Kurokawa et al. | Dec 2003 | B2 |
| Number | Date | Country |
|---|---|---|
| A 4-24657 | Apr 1992 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20020056310 A1 | May 2002 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09064163 | Apr 1998 | US |
| Child | 10032582 | US |
