JP2001323838A - Element temperature measuring device for air-fuel ratio sensor and heater control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize influence on air-fuel ratio detecting performance and measure the element temperature of an air-fuel ratio sensor in the case of detecting air fuel ratio by reading in the output of the air-fuel ratio sensor in the specified crank angle cycle (or the specified time cycle). SOLUTION: The sensor output Vs is read in for detecting the air-fuel ratio in the specified crank angle cycle (REF), and just after the read in, the specified voltage for measuring the internal resistance is applied to a sensor element. During applying the voltage, the sensor output Vs is read in to measure the internal resistance, and the internal resistance of the sensor element relating to the element temperature of the air-fuel ratio sensor is measured on the basis of the read in data. The current supply amount to a heater for heating the sensor element mounted on the air-fuel sensor is feedback controlled so that the element temperature becomes the target temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element temperature measuring apparatus for measuring an element temperature of an air-fuel ratio sensor (including an oxygen sensor) mounted on an exhaust system of an internal combustion engine and used for air-fuel ratio control. The present invention relates to a heater control device that controls a heater for heating a sensor element provided in an air-fuel ratio sensor based on the element temperature.

[0002]

2. Description of the Related Art As an air-fuel ratio control device for an internal combustion engine, an air-fuel ratio sensor detects an actual air-fuel ratio based on the oxygen concentration in exhaust gas and the like, and supplies a fuel to the engine such that the actual air-fuel ratio becomes a target air-fuel ratio. Is known that performs feedback control on the control.

In order to perform the above-described air-fuel ratio feedback control, a precondition is that the air-fuel ratio sensor is activated. The air-fuel ratio sensor is activated when its element temperature reaches a predetermined activation temperature. Therefore, the air-fuel ratio sensor is equipped with a heater for heating the sensor element,
The element temperature is controlled to the target temperature by controlling the energization of the heater (for example, see Japanese Patent Application Laid-Open No. 8-278279).

[0004] Specifically, the internal resistance of the sensor element is measured, and the amount of current supplied to the heater is feedback-controlled based on the element temperature estimated from the sensor element so that the element temperature becomes the target temperature.

[0005]

By the way, in order to measure the internal resistance of the sensor element related to the element temperature of the air-fuel ratio sensor, a predetermined voltage for measuring the internal resistance is applied to the sensor element, and the sensor at that time is applied. When measuring the internal resistance based on the output, the sensor output cannot be used for air-fuel ratio control while the internal resistance is being measured (while the internal resistance measurement voltage is being applied).
It is necessary not to reflect the sensor output on the air-fuel ratio control.

However, the cycle of detecting the air-fuel ratio based on the sensor output is independent of the cycle of measuring the internal resistance.
For example, when the air-fuel ratio detection is performed at a predetermined crank angle cycle and the internal resistance measurement is performed at a predetermined time cycle, particularly on the high rotation side, for example, immediately before the air-fuel ratio detection timing, the internal resistance measurement is performed. However, at a plurality of air-fuel ratio detection timings, the air-fuel ratio cannot be detected, and the number of times the air-fuel ratio cannot be detected increases, and the air-fuel ratio control performance deteriorates.

The present invention has been made in consideration of the above-described conventional problems, and has been made in view of the above-mentioned problems. Accordingly, the present invention has been made in view of the above circumstances. It is an object of the present invention to provide a heater control device for controlling a heater for heating a sensor element by using the device.

[0008]

According to the first aspect of the present invention, as shown in FIG. 1, there is provided an air-fuel ratio detecting means for reading a sensor output at a predetermined cycle and detecting an air-fuel ratio. Immediately after reading the sensor output for detecting the air-fuel ratio, a voltage applying means for measuring the internal resistance to apply a predetermined voltage for measuring the internal resistance to the sensor element, and reading the sensor output during the application of the voltage, And an internal resistance measuring means for measuring the internal resistance of the sensor element related to the element temperature of the air-fuel ratio sensor based on the above.

According to a second aspect of the present invention, the air-fuel ratio detecting means detects an air-fuel ratio by reading a sensor output at a predetermined crank angle cycle. The invention according to claim 3 is characterized in that the air-fuel ratio detection means detects an air-fuel ratio by reading a sensor output at a predetermined time period.

In the invention according to claim 4, while the device temperature measuring device for the air-fuel ratio sensor is provided, the heater for heating the sensor device provided in the air-fuel ratio sensor is set so that the device temperature becomes the target temperature. A heater control device for an air-fuel ratio sensor is provided by providing a heater power control unit for feedback-controlling the power supplied to the heater (see FIG. 1).

[0011]

According to the first aspect of the invention, immediately after reading the sensor output for detecting the air-fuel ratio at the air-fuel ratio detection timing, a predetermined voltage for measuring the internal resistance is applied to the sensor element. Since the internal resistance is measured from the sensor output in the state, the number of times the air-fuel ratio cannot be detected because the internal resistance is being measured at the air-fuel ratio detection timing can be minimized, and the effect on the air-fuel ratio control performance can be minimized. it can.

According to the second aspect of the present invention, when the air-fuel ratio is detected by reading the sensor output at a predetermined crank angle cycle, the air-fuel ratio cannot be detected because the internal resistance is being measured at the air-fuel ratio detection timing. The number of times can be minimized, and the influence on the air-fuel ratio control performance can be minimized.

According to the third aspect of the present invention, when the air-fuel ratio is detected by reading the sensor output at a predetermined time period,
Since the internal resistance is being measured at the air-fuel ratio detection timing, the number of times the air-fuel ratio cannot be detected can be minimized, and the influence on the air-fuel ratio control performance can be minimized.

According to the fourth aspect of the invention, the element temperature of the air-fuel ratio sensor is made to converge to the target temperature by the heater control while minimizing the influence on the air-fuel ratio control performance as described above. The desired active state can be maintained.

[0015]

Embodiments of the present invention will be described below. FIG. 2 shows a system configuration of an air-fuel ratio feedback control device for an internal combustion engine according to an embodiment of the present invention.

An internal combustion engine (hereinafter referred to as an engine) 1 includes:
A fuel injection valve 3 is provided for each cylinder so as to face the intake passage 2 or the combustion chamber. The fuel injection of each fuel injection valve 3 is controlled by the control unit 4.

The control unit 4 calculates a stoichiometric value based on, for example, an intake air amount Qa detected based on a signal from the air flow meter 5 and an engine speed Ne detected based on a signal from the crank angle sensor 6. λ =
1) Calculate a corresponding basic fuel injection amount Tp = K × Qa / Ne (K is a constant), and calculate the air-fuel ratio based on a signal from an air-fuel ratio sensor 8 disposed in the exhaust passage 7 in addition to the target air-fuel ratio tλ. A final fuel injection amount Ti = Tp × (1 / tλ) × α is calculated by correcting with a feedback correction coefficient α, and a fuel injection pulse having a pulse width corresponding to this Ti is synchronized with the engine rotation. Output to each fuel injection valve 3.

Here, the air-fuel ratio sensor 8 is disposed in the exhaust passage 7 and outputs a signal corresponding to the oxygen concentration in the exhaust gas. The control unit 4 operates based on the signal from the air-fuel ratio sensor 8. The air-fuel ratio λ is detected by detecting the air-fuel ratio λ of the air-fuel mixture supplied to the engine 1 and increasing or decreasing the air-fuel ratio feedback correction coefficient α by proportional integral control or the like so that the air-fuel ratio λ becomes the target air-fuel ratio tλ. Feedback control is performed to the target air-fuel ratio tλ.

The air-fuel ratio sensor 8 is a so-called wide-range air-fuel ratio sensor capable of linearly detecting the air-fuel ratio by continuously changing the output voltage according to the air-fuel ratio.
As shown in FIG. 3, a sensor device having a heater 12 for heating the sensor element 11 is used.

FIG. 3 shows a control circuit for the sensor element 11 of the air-fuel ratio sensor 8 and the heater 12 for heating the sensor element. The output voltage Vs of the sensor element 11 of the air-fuel ratio sensor 8 continuously changes according to the air-fuel ratio, and the output Vs
Is input to the control unit 4.

Further, a predetermined voltage Vcc (for example, 5 V) for measuring the internal resistance is applied to the sensor element 11 via the switching element 13 and the reference resistance R0. Therefore, when measuring the internal resistance, the switching element 1
When 3 is turned on, the voltage for internal resistance measurement is superimposed on the output Vs of the sensor element 11.

The heater 12 is applied with a battery voltage VB, and is provided with a switching element 14 in an energizing circuit. The CPU 15 in the control unit 4 turns ON / O the switching element 13 for applying the voltage for measuring the internal resistance.
The sensor element 1 is controlled at a predetermined timing while controlling the FF.
1 is applied to a filter (smoothing circuit) 16 and an A / D
The data is read via the converter 17.

Further, the CPU 15 turns ON / OFF the switching element 14 for controlling the heater through the D / A converter 18.
By controlling the OFF duty, the amount of current supplied to the heater 12 is controlled.

Next, the control contents of the CPU 15 will be described with reference to a flowchart. FIG. 4 is a flowchart of the air-fuel ratio detection routine, and at a predetermined crank angle cycle, specifically,
The process is executed in synchronization with the generation of the reference crank angle signal REF output from the crank angle sensor 6 at every predetermined crank angle in synchronization with the engine rotation.

In step 1 (referred to as S1 in the figure, the same applies hereinafter), it is determined whether or not the internal resistance measurement flag F = 1 or not, and F = 1 (internal resistance measurement = application of internal resistance measurement voltage). In the case of ()), this routine ends. This is because the air-fuel ratio cannot be detected during the application of the internal resistance measurement voltage.

If F = 0, the flow proceeds to step 2 because the air-fuel ratio can be detected. In step 2, the sensor output Vs is read to detect the air-fuel ratio, and the air-fuel ratio λ is detected based on the sensor output Vs. This part corresponds to the air-fuel ratio detecting means.

In step 3, the switching element 13 is turned on, and the voltage V
Start applying cc. That is, immediately after the reading of the sensor output for detecting the air-fuel ratio, the application of the internal resistance measuring voltage Vcc is started. This portion corresponds to an internal resistance measuring voltage applying unit.

In step 4, the timer TM is reset to 0 and started to measure the elapsed time from the start of the application of the internal resistance measuring voltage. In step 5, the flag F = 1 is set to indicate that the internal resistance is being measured, and the routine ends.

FIG. 5 is a flowchart of an internal resistance measurement routine, which is executed at predetermined time intervals. In step 11, the value of the timer TM is read. Then, in step 12, the timer TM reaches the first predetermined time T1 (TM = T
1) is determined, and in step 16, it is determined whether the timer TM has reached a second predetermined time T2 (TM = T2). T1 <T2.

If TM = T1, the process proceeds from step 12 to step 13, where the sensor output Vs is read in order to measure the internal resistance of the sensor element 11. That is, the sensor output Vs during the application of the internal resistance measuring voltage is read.

Note that the sensor output Vs read here includes:
Since an error due to the difference in the generated voltage corresponding to the air-fuel ratio is included, the sensor output read at the air-fuel ratio detection timing immediately before the application of the internal resistance measurement voltage is corrected to V
Assuming that s ′, for example, the correction may be performed as Vs = Vs−Vs ′.

In step 14, the internal resistance Rs of the sensor element 11 is calculated based on the read or corrected sensor output Vs. Specifically, assuming that the current flowing through the sensor element 11 is i, Vs = i.times.Rs Vcc-Vs = i.times.R0. Therefore, from both equations, Rs = Vs / [(Vcc-Vs) / R0]. , The internal resistance Rs is calculated.

Here, the steps 13 and 14 correspond to the internal resistance measuring means. Then, in step 15,
The element temperature Ts is calculated from the internal resistance Rs of the sensor element 11 by referring to a table or the like. This is because the higher the element temperature Ts, the lower the internal resistance Rs, so that the element temperature Ts can be calculated from the internal resistance Rs.

In the case of TM = T2, the process proceeds from step 16 to step 17 where the switching element 13 is turned off so that the internal resistance measuring voltage V
Stop (end) the application of cc. Then, in step 18, the internal resistance measurement in progress flag F is reset to 0 to indicate the end of the internal resistance measurement.

By such control, the processing as shown in FIG. 6 is realized. The air-fuel ratio λ is detected by reading the sensor output Vs in synchronization with the generation of the reference crank angle signal REF. Immediately after the detection of the air-fuel ratio, the application of the internal resistance measurement voltage is started, and after a first predetermined time T1, the sensor output Vs during the voltage application is read, and the internal resistance Rs is measured based on the output. . Then, the second predetermined time T2
The application of the voltage for measuring the internal resistance is terminated later, and the detection of the air-fuel ratio λ based on the sensor output Vs becomes possible.

In this case, in the high rotation region, as shown in FIG. 6, when the next REF signal is generated after the detection of the air-fuel ratio, the air-fuel ratio is not detected because the internal resistance is being measured.
It is sufficient because the air-fuel ratio is detected once every two EF signals.

If the internal resistance measurement is started immediately before the air-fuel ratio detection timing, the air-fuel ratio cannot be detected continuously when two subsequent REF signals are generated, but immediately after the air-fuel ratio detection. By starting the internal resistance measurement, the air-fuel ratio can be detected at least once every two REF signals.

FIG. 7 is a flowchart of the heater control routine, which is executed at predetermined time intervals. This routine corresponds to the heater power control unit. In step 21, FIG.
The latest element temperature Ts calculated by the routine is read.

In step 22, according to the well-known PID control, according to the deviation between the actual element temperature Ts and the target temperature,
The heater duty HDUTY (%) is calculated so that the element temperature Ts approaches the target temperature.

More specifically, when the actual element temperature Ts is lower than the target temperature, the heater duty HDUTY is set so as to increase the amount of power supply (percentage of power supply) to the heater 12.
On the contrary, when the actual element temperature Ts is higher than the target temperature, the heater duty HDUTY is decreased so as to decrease the amount of current (current time ratio) to the heater 12.

In step 23, the calculated heater duty HDUTY is output, whereby the amount of power to the heater 12 is controlled by turning on / off the switching element 14 so that the element temperature Ts converges to the target temperature.

In the above embodiment, the detection of the air-fuel ratio is performed at a predetermined crank angle cycle, that is, in synchronization with the generation of the REF signal. The present invention is also applicable to a case where the routine of FIG. 4 is performed in time synchronization.

In the above embodiment, the sensor element 11
Of the element temperature Ts based on the measured internal resistance Rs.
Is calculated in the feedback control so that the element temperature Ts becomes the target temperature in the heater control. However, since the element temperature Ts is determined by the internal resistance Rs, the element temperature Ts is calculated without calculating the element temperature Ts. ,
Feedback control may be performed so that the internal resistance Rs becomes the target internal resistance.

In this case, the actual internal resistance R
When s is greater than the target internal resistance, the element temperature is low. Therefore, the heater duty HDUTY is increased so as to increase the amount of current supplied to the heater 12, and conversely, when the actual internal resistance Rs is smaller than the target internal resistance. Next, since the element temperature is high, the heater duty HDUTY is reduced so as to reduce the amount of current supplied to the heater 12.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration of the present invention.

FIG. 2 is a system diagram of an air-fuel ratio feedback control device for an engine showing an embodiment of the present invention.

FIG. 3 is a control circuit diagram for a sensor element and a heater of the air-fuel ratio sensor.

FIG. 4 is a flowchart of an air-fuel ratio detection routine.

FIG. 5 is a flowchart of an internal resistance measurement routine.

FIG. 6 is a time chart of air-fuel ratio detection and internal resistance measurement.

FIG. 7 is a flowchart of a heater control routine.

[Explanation of symbols]

 Reference Signs List 1 engine 3 fuel injection valve 4 control unit 6 crank angle sensor 7 exhaust passage 8 air-fuel ratio sensor 11 sensor element 12 heater 13 switching element 14 switching element 15 CPU

Claims (4)

[Claims] 1. An element temperature measuring device for an air-fuel ratio sensor mounted on an exhaust system of an internal combustion engine, comprising an air-fuel ratio detecting means for reading a sensor output at a predetermined cycle and detecting an air-fuel ratio. Immediately after reading the sensor output for air-fuel ratio detection, an internal resistance measurement voltage applying means for applying a predetermined voltage for internal resistance measurement to the sensor element, and reading the sensor output during application of the voltage, And an internal resistance measuring means for measuring an internal resistance of the sensor element related to an element temperature of the air-fuel ratio sensor based on the element temperature measurement apparatus. 2. The device temperature measuring device for an air-fuel ratio sensor according to claim 1, wherein said air-fuel ratio detecting means detects an air-fuel ratio by reading a sensor output at a predetermined crank angle cycle. 3. The device temperature measuring device for an air-fuel ratio sensor according to claim 1, wherein said air-fuel ratio detecting means detects an air-fuel ratio by reading a sensor output at a predetermined time period. 4. An element temperature measuring device for an air-fuel ratio sensor according to any one of claims 1 to 3, wherein an element temperature is lower than a heater for heating a sensor element provided in the air-fuel ratio sensor. A heater control device for an air-fuel ratio sensor, further comprising a heater power control unit that feedback-controls a power supply to a heater so as to reach a target temperature.