JP2511048B2 - Control method of oxygen concentration sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control method of an oxygen concentration sensor which is arranged in an exhaust system of an internal combustion engine and detects an oxygen concentration in exhaust gas.

BACKGROUND ART In order to purify exhaust gas of an internal combustion engine, improve fuel efficiency, etc., the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor,
There is an air-fuel ratio control device that feedback-controls the air-fuel ratio of an air-fuel mixture supplied to an engine to a target air-fuel ratio according to an output signal of an oxygen concentration sensor.

As an oxygen concentration sensor used in such an air-fuel ratio control device, there is one that produces an output proportional to the oxygen concentration in the gas to be measured. For example, an electrode pair is provided on each of the two flat plate-shaped oxygen ion conductive solid electrolyte materials to form an oxygen pump element and a battery element, and a gas retention chamber as a gas diffusion limited area is formed between the oxygen pump element and the battery element. However, there is a sensor having an oxygen concentration detecting element in which the gas retention chamber communicates with the gas to be measured through an introduction hole and the other electrode surface of the battery element faces the atmosphere chamber. It is disclosed in the publication. In such an oxygen concentration sensor, when the voltage generated between the electrodes of the battery element is equal to or higher than the reference voltage, a voltage corresponding to the voltage difference is supplied to the oxygen pump element so that oxygen ions are allowed to pass through the oxygen pump element in the limiting area side electrode. When the voltage generated between the electrodes of the battery element is equal to or lower than the reference voltage, a voltage corresponding to the voltage difference is supplied to the oxygen pump element to move oxygen ions toward the outer electrode in the oxygen pump element. Therefore, at the air-fuel ratios in the lean and rich regions, the current value flowing between the electrodes of the oxygen pump element, that is, the pump current value, is proportional to the oxygen concentration in the gas supplied to the diffusion limited region.

By the way, in such an oxygen concentration sensor, when an excessive pump current is supplied to the oxygen pump element, oxygen is deprived from the solid electrolyte material when the amount of oxygen in the diffusion limited region is smaller than the amount that can be pumped by the pump current. Was found to occur. For example, if the ZrO ₂ (zirconium dioxide) was used as a solid electrolyte material, ZrO by excessive current supply to the oxygen pump element ₂
Oxygen O ₂ is depleted from this and zirconium Zr is deposited.

Further, in such an oxygen concentration proportional type oxygen concentration sensor, in order to obtain an output characteristic proportional to the oxygen concentration, in order to obtain an output characteristic proportional to the oxygen concentration, the oxygen concentration detecting element is set to the exhaust gas during steady operation. It is necessary to make the temperature sufficiently higher than the temperature (for example, 650 ° C. or higher), and a heating element for heating the oxygen concentration detection element is arranged at an appropriate position on the solid electrolyte material.

Therefore, when the engine is started, the oxygen concentration detecting element is usually still in a low temperature state, and it is desired to heat up as quickly as possible. Further, in such a case, the voltage generated between the electrodes of the battery element does not rise sufficiently, and the pump current may become excessive in the configuration in which the pump current is increased or decreased by comparison with the reference voltage.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for controlling an oxygen concentration sensor for an internal combustion engine, which enables an oxygen concentration detection element to be immediately operable immediately after engine startup, while avoiding a blackening phenomenon.

The control method of the oxygen concentration sensor for internal combustion engine according to the present invention starts the heater current supply from the heater current supply means to the heating element when the predetermined engine starting state is detected, and thereafter, the internal resistance of the heating element is within the predetermined range. Is detected, the supply of the pump element from the pump current supply means to the oxygen pump element is started.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 show an electronically controlled fuel injection device equipped with an oxygen concentration sensor to which the control method of the present invention is applied. In this device, the oxygen concentration sensor detection unit 1 is disposed for distillation from the three-way catalytic converter 5 of the exhaust pipe 3 of the engine 2, and the input and output of the oxygen concentration sensor detection unit 1 is ECU (Electro
nic Control Unit) 4.

As shown in FIG. 2, for example, a substantially rectangular parallelepiped oxygen ion conductive solid electrolyte material 12 is provided in the protective case 11 of the oxygen concentration sensor detection unit 1. In the oxygen ion conductive solid electrolyte material 12, a gas retention chamber 13 is provided as a gas diffusion limited area.
Are formed. The gas retention chamber 13 communicates with an introduction hole 14 for introducing the exhaust gas of the gas to be measured from the outside of the solid electrolyte material 12, and the introduction hole 14 allows the exhaust gas to flow into the gas retention chamber 13 in the exhaust pipe 3. Is located. An air reference chamber 15 for introducing the atmosphere is formed in the oxygen ion conductive solid electrolyte material 12 so as to separate the wall from the gas retention chamber 13. Wall between the gas retention chamber 13 and the atmospheric reference chamber 15 and the atmospheric reference chamber 15
Electrode pairs 17a, 17b, 16a, 16b are respectively formed on the wall portion on the side opposite to. The solid electrolyte material 12 and the electrode pairs 16a and 16b act as the oxygen pump element 18, and the solid electrolyte material 12 and the electrode pairs 17a and 17b act as the battery element 19. A heating element 20 for heating the oxygen pump element 18 and the battery element 19 is provided on the outer wall surface of the air reference chamber 15.

ZrO ₂ (zirconium dioxide) is used as the oxygen ion conductive solid electrolyte material 12, and Pt (platinum) is used as the electrodes 16a to 17b.

As shown in FIG. 3, the ECU 4 is provided with an oxygen concentration sensor control unit including a differential amplifier circuit 21, a reference voltage source 22, and a current detection resistor 24. The electrode 16b of the oxygen pump element 18 and the electrode 17b of the battery element 19 are grounded. The differential amplifier circuit 21 is connected to the electrode 17a of the battery element 19, and the differential amplifier circuit 2
1 outputs a voltage corresponding to the difference voltage between the voltage between the electrodes 17a and 17b of the battery element 19 and the output voltage of the reference voltage source 22. The output voltage of the reference voltage source 22 is a voltage equivalent to the theoretical air-fuel ratio (0.4
[V]). The output end of the differential amplifier circuit 21 is connected to the switch 23 having a control end and the electrode 16a of the oxygen pump element 18 via the current detection resistor 24. Current detection resistor 2
Both ends of 4 are output ends of the oxygen concentration sensor and are connected to a control circuit 25 including a microcomputer. A heater current detection resistor 51 is connected in series to the heating element 20, a heater driving circuit 37 is connected to a series circuit of the heating element 20 and the resistor 51, and a switching element connected to a series circuit of the heating element 20 and the resistor 51 (Fig. (Not shown).

The control circuit 25 includes, for example, a potentiometer,
A throttle valve opening sensor 31 that generates an output voltage at a level according to the opening of the throttle valve 26, and an output voltage at a level according to the absolute pressure in the intake pipe 27 provided in the intake pipe 27 downstream of the throttle valve 26. Which generates an absolute pressure contact sensor 32, a water temperature sensor 33 which generates an output voltage at a level corresponding to the cooling water temperature of the engine, and an intake air temperature which is provided near the air intake port 28 and generates an output at a level corresponding to the intake air temperature. A sensor 34 and a crank angle sensor 35 that generates a pulse signal in synchronization with the rotation of a crankshaft (not shown) of the engine are connected. An injector 36 provided in an intake pipe 27 near an intake valve (not shown) of the engine 2 is connected.

In addition to the drive circuit 37 described above, the control circuit 25 has one of the inter-electrode voltage of the oxygen pump element 18, the inter-electrode voltage of the battery element 19, the inter-terminal voltage of the heating element 20 and the both-end voltage of the current detection resistor 51.
One of the multiplexer 38 that selectively outputs one of the two, an A / D converter 39 that converts the signal output from the multiplexer 38 into a digital signal, and a differential input that converts the voltage across the current detection resistor 24 into a digital signal. A / D converter 40, and a level conversion circuit that converts each output level of the throttle valve opening sensor 31, the absolute pressure sensor 32, the water temperature sensor 33, and the intake air temperature sensor 34.
41, a multiplexer 42 that selectively outputs one of the sensor outputs that have passed through the level conversion circuit 41, and an A / A that converts the signal output from this multiplexer 42 into a digital signal.
A D converter 43, a waveform shaping circuit 44 that shapes the output signal of the crank angle sensor 35 and outputs it as a TDC signal, and a generation interval of the TDC signal from the waveform shaping circuit 44 to a clock pulse generation circuit (not shown). A counter 45 that measures the number of clock pulses output from the counter 45, a drive circuit 52 that drives the switch 23, and a drive circuit 46 that drives the injector 36.
And a CPU that performs digital operations according to a program
(Central processing circuit) 47, ROM 48 in which various processing programs and data are written in advance, and RAM 49. A /
D converter 39, 40, 43, multiplexer 38, 42, counter 45,
The drive circuits 37, 46, 52, the CPU 47, the ROM 48 and the RAM 49 are connected to each other by the input / output bus 50. The TDC signal is supplied from the waveform shaping circuit 44 to the CPU 47.

The RAM 49 is an ignition switch (not shown)
Is backed up so that the stored contents are not lost even when the power is off.

In this configuration, the inter-electrode voltage V _P of the oxygen pump element 18 from the A / D converter _39, the inter-electrode voltage V _S of the battery element _19, a heater current flowing between the electrodes voltage V _H and the heating element 20 of the heating element 20 As an alternative to the information of the value I _H, the pump current value I _P flowing from the A / D converter 40 through the oxygen pump element 18 is calculated from the A / D converter 43 to the throttle valve opening θth and the intake pipe absolute pressure P _BA. , The information of the cooling water temperature T _W and the intake air temperature T _{A, and} the information indicating the count value within the generation period of the rotation pulse from the counter 45 to the CPU 47 as the engine speed Ne information via the input / output bus 50. Each is supplied. The CPU 47 reads the above-mentioned information in accordance with the arithmetic program stored in the ROM 48, and in synchronization with the TDC signal based on the information, the injector corresponding to the fuel supply amount to the engine 2 from the predetermined calculation formula in the fuel supply routine. Calculate 36 fuel injection times T _OUT .
Then, the drive circuit 46 drives the injector 36 for the fuel injection time T _OUT to supply fuel to the engine 2.

The fuel injection time T _OUT is calculated, for example, from the following equation.

T _OUT = Ti × Ko ₂ (1) Here, Ti is a reference value for air-fuel ratio control determined by a data map search from ROM 48 according to the engine speed Ne and the intake pipe absolute pressure P _BA. The reference injection time, Ko ₂ is an air-fuel ratio feedback correction coefficient set according to the output level of the oxygen concentration sensor. These Ti and Ko ₂ are respectively set in a subroutine (not shown) of the fuel supply routine. The correction coefficient may be a correction coefficient such as an acceleration amount coefficient or an engine temperature coefficient, but it will not be described in detail here.

Next, the procedure of the control method of the oxygen concentration sensor of the present invention will be described with reference to the operation flow chart of the CPU 47 shown in FIG.

The CPU 47 first reads the engine speed Ne, and the engine speed Ne is the engine complete explosion speed Ne ₁ (for example, 400 rpm
It is determined whether or not m) has been reached (step 61). Ne
When <Ne ₁ , it is determined that the oxygen concentration sensor is inactive, and the heater current supply flag F _H is reset to 0 to prohibit the heater current supply (step 62). Generates a pump current supply stop command (step 63), and makes the air-fuel ratio feedback correction coefficient Ko ₂ equal to 1.0 to stop the air-fuel ratio feedback control (step 64). By setting the heater current supply flag F _H equal to 0, the heater current supply data representing I _H = 0 is supplied to the heater drive circuit 37 in the heater current control subroutine (not shown) executed by the CPU 47 in every predetermined cycle. . Therefore, the heater drive circuit 37 turns off the internal switching element to stop the supply of the heater current to the heating element 20. Further, since the switch drive circuit 52 turns off the switch 23 in response to the pump current supply stop command, the supply of pump current to the oxygen pump element 18 is stopped.

If Ne ≧ Ne ₁ , it is considered that the engine 2 has completed the explosion and the heater current supply flag is set to start supplying the heater current.
Set F _H to 1 (step 65). When the flag F _H is set to 1, the heater current supply data is set for each predetermined cycle so that the internal resistance R _H of the heating element 20 becomes a constant value when the above heater current control subroutine is executed, and the heater drive circuit is set. The switching element is turned on and off in a predetermined cycle at a duty ratio according to the content of the heater current supply data. Heating element 20 when switching element is on
The voltage V _B is applied across the series circuit of the current detection resistor 51 and the current detection resistor 51, and the heater current flows through the heating element 20.
Generates heat. Then, the internal resistance R _H of the heating element 20 is a predetermined value.
It is determined whether R _H1 and R _H2 are within the range (step 6)
6). The internal resistance R _H of the heating element 20 is the voltage V across the heating element 20.
Read _H and heater current value I _H , R _H = (V _H −I _H ) / I _H
It is calculated by the following formula. If R _H <R _H1 or R _H > R _H2 , it is determined that the oxygen concentration sensor is in the inactive state, and the process proceeds to steps 63 and 64. In the case of RH ₁ ≦ R _H ≦ RH ₂ may be, for example, heating of the heating element is held at an appropriate temperature range so that the oxygen concentration sensor is an output characteristic which is proportional to the desired oxygen concentration, the heating element If the internal resistance of the device exceeds RH ₂ , it is possible that the heating element is overheated or that the current in the heating element is almost not flowing due to the destruction of the heating element. The operation is regarded as an inactive state in which no operation is performed. R _H1
If ≦ R _H ≦ R _H2, it is determined that the temperature of the heating element 20 has reached a stable temperature, and a pump current supply command is issued to the switch drive circuit 52 to supply the pump current to the oxygen pump element 18 (step 67). . The switch drive circuit 52 turns on the switch 23 in response to the pump current supply command, so that the pump current is supplied to the oxygen pump element 18. Oxygen pump element 18
Pump current is supplied to. When the supply of the pump current to the oxygen pump element 18 is started, the inter-electrode voltage V _S of the battery element 19 is read and the voltage V _S is within the predetermined voltage V _S1 , V _S2 (provided that V _S1 <V _S2 ). It is determined whether the voltage is within the range (step 68), and the interelectrode voltage of the oxygen pump element 18 is also determined.
V _P is read and its voltage V _P is the predetermined voltage V _P1 , V _P2 (However,
It is determined whether the voltage is within the range of V _P1 <V _P2 ) (step 69). If V _S <V _S1 or V _S > V _S2 , then V
_If Vp <V _P1 or Vp> V _P2 even if _S1 ≦ V _S ≦ V _S2 , the oxygen concentration sensor is determined to be inactive in these cases, and the process proceeds to step 64. V _S1 ≤ V _S ≤ V _S2 and V _P1
If ≦ V p ≦ V _P2 , oxygen pump element 18 and battery element 1
When it is determined that 9 has reached a predetermined temperature and is in the active state, the Ko ₂ calculation subroutine is executed to perform the air-fuel ratio feedback control, and the air-fuel ratio feedback correction coefficient Ko ₂ is calculated (step 70).

In the oxygen concentration sensor, when the supply of the pump current to the oxygen pump element 18 is started, if the air-fuel ratio of the air-fuel mixture supplied to the engine 2 is in the lean region, it is between the electrodes 17a and 17b of the battery element 19. Since the generated voltage V _S becomes lower than the output voltage Vr of the reference voltage source 22, the output level of the differential amplifier circuit 21 becomes a positive level, and this positive level voltage is supplied to the series circuit of the resistor 24 and the oxygen pump element 18. It Oxygen pump element
A pump current flows from the electrode 16a to the electrode 16b in the electrode 18, so that the enzyme in the gas retention chamber 13 is ionized at the electrode 16b and moves in the oxygen pump element 18 to be released as oxygen gas from the electrode 16a. Oxygen in the retention chamber 13 is pumped out.

By pumping out oxygen from the gas retention chamber 13
A difference in oxygen concentration occurs between the exhaust gas in the chamber and the atmosphere in the atmospheric reference chamber 15. The voltage V _S according to this oxygen concentration difference is the battery element
This voltage V _S is generated between the electrodes 17a and 17b of 19 and the output voltage of the differential amplifier circuit 21 is the voltage V _S and the output voltage of the reference voltage source 22.
Since the voltage is proportional to the voltage difference with Vr, the pump current value Ip
Is output as the voltage across the resistor 24.

When the air-fuel ratio is in the rich region, the voltage V _S is the reference voltage source.
22 Output voltage Vr is exceeded. Therefore, the output level of the differential amplifier circuit 21 is inverted from the positive level to the negative level. Due to this negative level, the pump current flowing between the electrodes 16a and 16b of the oxygen pump element 18 decreases, and the current direction is reversed. That is,
Since the pump current flows from the electrode 16b in the direction of the electrode 16a, external oxygen is ionized at the electrode 16a and moves inside the oxygen pump element 18 and is released from the electrode 18b as oxygen gas into the gas retention chamber 13, whereby oxygen is gas. It is pumped into the retention chamber 13. Therefore, oxygen is pumped in or read out by supplying a pump current so that the oxygen concentration in the gas retention chamber 13 is always constant, so the pump current value Ip is the oxygen in the exhaust gas in the lean and rich regions. Each is proportional to the concentration. Feedback correction coefficient Ko ₂ described above in accordance with the pump current Ip is set in the subroutine of Ko ₂ calculation.

As described above, in the oxygen concentration sensor control method of the present invention, when the engine is completely detonated, the heater current supply to the heating element is started, and the heat generation of the heating element causes the oxygen concentration of the pump element and the battery element. The detection element is quickly heated, and then, when it is detected that the internal resistance of the heating element has risen to a value within a predetermined range due to the temperature rise of the heating element, the supply of the pump current to the oxygen pump element is started. Therefore, since the supply of the pump current to the oxygen pump element is started after the temperature of the heating element, that is, the temperature of the oxygen concentration detection element, becomes sufficiently high, the excessive pump current is prevented from flowing and the blackening phenomenon is avoided. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing an electronically controlled fuel injection device to which a sensor control method for oxygen concentration of the present invention is applied, FIG. 2 is a diagram showing the inside of an oxygen concentration sensor detection unit, and FIG. 3 is a block showing a circuit in an ECU. 4 and 5 are flow charts showing the operation of the CPU. Explanation of symbols of main parts 1 …… Oxygen concentration sensor detection unit 3 …… Exhaust pipe 4 …… ECU 12 …… Oxygen ion conductive solid electrolyte material 13 …… Gas retention chamber 14 …… Introduction hole 15 …… Atmosphere reference chamber 18 …… Oxygen pump element 19 …… Battery element 25 …… Control circuit 27 …… Intake pipe 36 …… Injector

Claims (1)

(57) [Claims] 1. An oxygen concentration detecting element having an oxygen pump element and a battery element, which are arranged in an exhaust system of an internal combustion engine and each of which comprises an oxygen ion conductive solid electrolyte material and electrodes sandwiching the solid electrolyte material to form a gas diffusion limited area. A pump current supply means for supplying a pump current between the electrodes of the oxygen pump element,
A method for controlling an oxygen concentration sensor, comprising: a heating element that heats the oxygen concentration detection element in accordance with the supplied current; and a heater current supply means that supplies a heater current to the heating element. When it detects, it starts the heater current supply from the heater current supply means to the heating element, and then when it detects that the internal resistance of the heating element reaches a value within a predetermined range, the pump current supply means A method for controlling an oxygen concentration sensor, characterized in that supply of pump current to the oxygen pump element is started.