JP2000180405A - Control device of air/fuel ratio sensor for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To judge fuel properties before an oxygen concn. detecting element reaches an active state. SOLUTION: An oxygen concn. detecting element 2 outputting a current proportional to the concn. of oxygen in a gas to be detected when voltage is applied, a low frequency AC impedance detecting means applying low frequency AC voltage to the oxygen concn. detecting element 2 to detect the impedance of the oxygen concn. detecting element 2 and a fuel property judging means for judging the properties of fuel supplied to an internal combustion engine from the impedance of the oxygen conc. detecting element 2 detected by the low frequency AC impedance detecting means are provided. The low frequency AC impedance detecting means and the fuel property judging means are executed by the processing of the air/fuel ratio control unit 10 of ECU.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an air-fuel ratio sensor of an internal combustion engine, and more particularly to a control device for an air-fuel ratio sensor of an internal combustion engine for determining properties of fuel supplied to the internal combustion engine.

[0002]

2. Description of the Related Art In a cold state after an internal combustion engine (hereinafter simply referred to as an engine) is started, a large amount of injected fuel adheres to a wall surface of an intake pipe. In addition, since the less volatile heavy fuel has a greater amount of wall flow than the more volatile light fuel, the same amount of fuel injection is supplied to the engine until the engine is warmed up. However, the amount of fuel sucked into the combustion chamber of the engine greatly differs depending on the fuel properties. Therefore, at the time of cold start of the engine, the properties of the fuel supplied to the engine are determined,
Until the engine is warmed up, the fuel injection amount supplied to the engine according to the determined fuel properties is increased and corrected when it is determined to be heavy fuel, to ensure drivability and prevent deterioration of exhaust emissions. It is carried out.

Some of the above fuel properties are determined using an oxygen concentration (air-fuel ratio) sensor. In this determination method, since the wall flow increases when the fuel is heavy, the oxygen concentration sensor detects that the exhaust air-fuel ratio temporarily becomes lean until the engine is warmed up after the engine is started. In the case of light fuel, the wall flow is reduced.Thus, until the engine is warmed up, the oxygen concentration sensor temporarily detects that the exhaust air-fuel ratio becomes rich. Is what you do.

[0004] The fuel property discrimination device disclosed in Japanese Patent Application Laid-Open No. 5-106503 has an internal combustion engine provided with secondary air supply means for introducing secondary air into an exhaust system in order to promote purification of a catalyst when the engine is warmed up. In this case, the fuel property cannot be determined from the rich / lean exhaust air-fuel ratio due to the secondary air, so the supply of the secondary air is temporarily stopped when the fuel property is determined.

[0005] In addition, some fuel properties are determined using an engine speed sensor in addition to the oxygen concentration (air-fuel ratio) sensor. In this determination method, the fuel injection timing FIT of the engine is changed, and if the time from fuel injection to ignition becomes longer, the amount of fuel adhering to the intake pipes and cylinders on the wall increases, and the fuel properties change greatly. The fuel property is determined by estimating the above-mentioned wall adhesion amount from the change in the engine speed NE (combustion state) when the engine speed is changed.

[0006] A fuel property detection device for an internal combustion engine disclosed in Japanese Patent Application Laid-Open No. 9-256898 discloses a fuel injection timing FI.
Even if T is changed, the amount of wall adhering to the intake pipe or cylinder does not actually change so much. Therefore, in order to solve the problem that the fuel property cannot be accurately determined, auxiliary equipment such as an air conditioner is forcibly applied. The change in engine load is caused by switching, and the fuel supply amount changes in accordance with the load change, and the amount of change in the amount of adhesion to the wall surface increases. Therefore, the change in the engine speed NE detected by the engine speed sensor at this time. Quantity (ΔN
E) or a change in the exhaust air-fuel ratio detected by the air-fuel ratio sensor (ΔA / F) to determine the fuel property.

[0007]

However, Japanese Patent Application Laid-Open Nos. 5-106503 and 9-2568 disclose the above-mentioned publications.
The device disclosed in Japanese Patent Publication No. 98 requires a secondary air supply means and an auxiliary device to determine the fuel property, respectively.
In an internal combustion engine not provided with these, there is a problem that determination of fuel properties cannot be performed with high accuracy.

[0008] Further, in these devices, during a cold start until the engine is warmed up, the rich / lean determination of the air-fuel ratio is determined until the oxygen concentration sensor (air-fuel ratio sensor) is activated. No fuel properties can be determined. As a result, the fuel injection amount supplied to the engine cannot be corrected according to the fuel properties until the oxygen concentration sensor (air-fuel ratio sensor) reaches the active state, so that drivability cannot be secured and exhaust emission cannot be prevented. There's a problem.

[0009] Therefore, the present invention solves the above-mentioned problem, and before the oxygen concentration sensor (air-fuel ratio sensor) reaches an active state,
An internal combustion engine that can determine fuel properties, can quickly supply a fuel injection amount corresponding to the fuel properties to the engine, and can accurately determine fuel properties even in an internal combustion engine that does not have secondary air supply means or auxiliary equipment. It is an object to provide a control device for a fuel ratio sensor.

[0010]

According to a first aspect of the present invention, there is provided a control device for an air-fuel ratio sensor of an internal combustion engine which outputs a current proportional to the oxygen concentration in a gas to be detected when a voltage is applied. An oxygen concentration detecting element, a low frequency AC impedance detecting means for applying a low frequency AC voltage to the oxygen concentration detecting element to detect the impedance of the oxygen concentration detecting element, and the low frequency AC impedance detecting means. Fuel property determining means for determining the property of the fuel supplied to the internal combustion engine from the impedance of the oxygen concentration detecting element.

With the above configuration, the low-frequency AC impedance of the oxygen concentration detecting element is detected, and the property of the fuel supplied to the internal combustion engine is determined from the detected impedance. In the control device for an air-fuel ratio sensor of an internal combustion engine according to a first aspect of the present invention, a temperature detecting means for detecting a temperature of the oxygen concentration detecting element, and a temperature of the oxygen concentration detecting element detected by the temperature detecting means. Element deactivation determining means for determining whether or not the oxygen concentration detecting element is in an inactive state, wherein the low-frequency AC impedance detecting means is configured such that the oxygen concentration detecting element is deactivated by the element deactivating determining means. When the state is determined, the impedance is detected.

The low-frequency impedance of the oxygen concentration detecting element is detected by the temperature detecting means and the element inactivity determining means when the oxygen concentration detecting element is in an inactive state, and the detected impedance is supplied to the internal combustion engine. Since the property of the fuel is determined, the fuel injection amount can be corrected in accordance with the fuel property at an early stage, and the exhaust emission and drivability during this time are improved.

In a control apparatus for an air-fuel ratio sensor of an internal combustion engine according to a first aspect of the present invention, a high-frequency AC impedance for applying a high-frequency AC voltage to the oxygen concentration detecting element and detecting an impedance of the oxygen concentration detecting element is provided. Detecting means for detecting the temperature of the oxygen concentration detecting element from the impedance of the oxygen concentration detecting element detected by the high frequency AC impedance detecting means;

The temperature of the oxygen concentration detecting element is detected from the high frequency impedance of the oxygen concentration detecting element detected by the high frequency AC impedance detecting means, and the inactive state of the oxygen concentration detecting element is detected from the temperature. Since the properties of the fuel supplied to the internal combustion engine are determined from the low-frequency impedance of the oxygen concentration detecting element, no special measuring device is required to detect the temperature of the oxygen concentration detecting element.

A control device for an air-fuel ratio sensor of an internal combustion engine according to a second aspect of the present invention that solves the above-mentioned problem is provided in an exhaust system of the internal combustion engine, and when a voltage is applied, the control device reduces the oxygen concentration in the exhaust gas of the internal combustion engine. An oxygen concentration detection element that outputs a proportional current, temperature detection means for detecting the temperature of the oxygen concentration detection element, and the oxygen concentration detection element is determined based on the temperature of the oxygen concentration detection element detected by the temperature detection means. Element deactivation determining means for determining whether or not the element is in an active state; air-fuel ratio detection means for detecting an air-fuel ratio of the exhaust gas from an output of the oxygen concentration detecting element; and A fuel property determining a property of fuel supplied to the internal combustion engine from an air-fuel ratio of the exhaust gas detected by the air-fuel ratio detecting means when the determining means determines that the fuel cell is in an inactive state; Characterized by comprising a constant means.

According to the above configuration, the air-fuel ratio when the oxygen concentration detecting element is in the inactive state is detected, and the property of the fuel supplied to the internal combustion engine is determined from the detected air-fuel ratio. The corrected fuel injection amount can be corrected, and the exhaust emission and drivability during this time can be improved. In the control device for an air-fuel ratio sensor of an internal combustion engine according to a second aspect of the present invention, the air-fuel ratio detection means detects an impedance of the oxygen concentration detection element by applying a low frequency AC voltage to the oxygen concentration detection element. Thus, the air-fuel ratio is detected.

The air-fuel ratio detecting means detects a low frequency impedance of the oxygen concentration detecting element when the oxygen concentration detecting element is in an inactive state, and detects an air-fuel ratio from the detected low frequency impedance. In a control device for an air-fuel ratio sensor of an internal combustion engine according to a second aspect of the present invention, a high-frequency AC impedance detecting means for applying a high-frequency AC voltage to the oxygen concentration detecting element and detecting an impedance of the oxygen concentration detecting element is provided. The temperature detecting means detects the temperature of the oxygen concentration detecting element from the impedance of the oxygen concentration detecting element detected by the high frequency AC impedance detecting means.

The temperature of the oxygen concentration detecting element is detected from the high frequency impedance of the oxygen concentration detecting element detected by the high frequency AC impedance detecting means, and the inactive state of the oxygen concentration detecting element is detected from the temperature. Since the properties of the fuel supplied to the internal combustion engine are determined from the low-frequency impedance of the oxygen concentration detecting element, no special measuring device is required to detect the temperature of the oxygen concentration detecting element.

[0019]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of an embodiment of an air-fuel ratio sensor control device for an internal combustion engine according to the present invention. From FIG. 1 onward, the same components are denoted by the same reference numerals. An air-fuel ratio sensor 1 that is disposed in an exhaust passage of an internal combustion engine (not shown) and detects an exhaust air-fuel ratio of the engine includes an air-fuel ratio sensor element (hereinafter, referred to as a sensor element) 2 and a heater 4. A voltage is applied from an air-fuel ratio sensor circuit (hereinafter, referred to as a sensor circuit) 3, and power is supplied to the heater 4 from a battery 5 under the control of a heater control circuit 6. The sensor circuit 3 receives an analog application voltage from an air-fuel ratio control unit (A / FCU) 10 including a microcomputer via a low-pass filter (LPF) 7 and applies the voltage to the sensor element 2.

The air-fuel ratio sensor 1 is disposed in an exhaust passage of an engine together with a catalyst (not shown), and is used for maximally purifying harmful components (HC, CO, NOx, etc.) in exhaust gas by the catalyst. ing. The air-fuel ratio feedback control is
The engine air-fuel ratio detected by the air-fuel ratio sensor 1 is controlled to be a target air-fuel ratio, for example, a stoichiometric air-fuel ratio. As the air-fuel ratio sensor 1, a limiting current type oxygen concentration detecting element that outputs a limiting current in proportion to the oxygen concentration contained in the exhaust gas discharged from the engine is usually used. The limiting current type oxygen concentration detecting element detects the exhaust air-fuel ratio of the engine in a wide range and linearly from the oxygen concentration, and is useful for improving the air-fuel ratio control accuracy and performing lean burn control.

The A / FCU 10 includes an electronic control unit (EC) together with the sensor circuit 3, the heater control circuit 6, and the LPF 7.
U) It forms a part of 100, converts digital data calculated according to the processing described later into a rectangular analog voltage by a D / A converter provided inside, and outputs it to the sensor circuit 3 via the LPF 7. The LPF 7 outputs a smoothing signal from which a high-frequency component of a rectangular analog voltage signal has been removed, thereby preventing a detection error of the output current of the sensor element 2 due to high-frequency noise. With the application of the voltage of the anneal signal to the sensor element 2, the A / FCU 10
That is, the current flowing through the sensor element 2 which changes in proportion to the oxygen concentration in the exhaust gas and the voltage applied to the sensor element 2 at that time are detected. The A / FCU 10 has an internal A / FCU 10 for detecting these currents and voltages.
An analog voltage corresponding to a current flowing from the sensor circuit 3 to the sensor element 2 and a voltage applied to the sensor element 2 are received by the / D converter and converted into digital data, and these digital data are used for processing described later.

The output of the air-fuel ratio sensor 1 cannot be used for air-fuel ratio feedback control unless the sensor element 2 is activated. Therefore, the A / FCU 10 supplies electric power from the battery 5 to the heater 4 incorporated in the sensor element 2 at the time of starting the engine, energizes the heater 4, activates the sensor element 2 early, and the sensor element 2 is activated. After that, power is supplied to the heater 4 so as to maintain the active state.

However, focusing on the fact that the resistance of the sensor element 2 depends on the temperature of the sensor element 2, that is, the resistance of the sensor element 2 decreases with an increase in the temperature of the sensor element 2, the resistance of the sensor element 2 changes the activation state of the sensor element 2. By supplying power to the heater 4 so as to have a resistance value corresponding to the maintained temperature, for example, 30Ω, the temperature of the sensor element 2 is set to a target temperature, for example, 7Ω.
Control for maintaining the temperature at 00 ° C is performed. The air-fuel ratio control unit (A / FCU) 10 has an A
An analog voltage corresponding to the voltage and current of the heater 4 is received from the heater control circuit 6 for heating the sensor element 2 by the / D converter and converted into digital data, and this digital data is used for processing described later. For example, a resistance value of the heater 4 is calculated, power is supplied to the heater 4 according to the operating state of the engine based on the resistance value, and the temperature of the heater 4 is raised (O
The temperature of the heater 4 is controlled so as to prevent T).

Air-fuel ratio control unit (A / FCU) 10
Are, for example, CPU, ROM, RAM, B (battery backup). It comprises a RAM, an input port, an output port, an A / D converter and a D / A converter.
The respective routines such as an impedance calculation routine of the sensor element, fuel property determination and fuel injection amount calculation are performed.

FIGS. 2A and 2B are diagrams showing input / output signals of the air-fuel ratio sensor, FIG. 2A is a diagram showing a waveform of an input voltage applied to the air-fuel ratio sensor, and FIG. 2B is a diagram detected by the air-fuel ratio sensor. FIG. 4 is a diagram illustrating a waveform of an output current. The horizontal axis shows time,
The vertical axis indicates voltage. As shown in FIG. 2A, a direct current voltage of 0.3 V is constantly applied as an input voltage Vm applied to the air-fuel ratio sensor. In order to measure the impedance of the sensor element, the air-fuel ratio sensor was subjected to ± 0.2
A pulse voltage of the first frequency of V is applied while being superimposed on the DC voltage of 0.3 V. On the other hand, as shown in FIG. 2B, while the output current Im detected from the air-fuel ratio sensor is applied with only the DC voltage of 0.3 V to the air-fuel ratio sensor, the output current Im A value corresponding to the concentration is shown.
When the voltage is superimposed on 3 V and applied, the value immediately before the application is changed.
At this time, the change in the voltage applied to the air-fuel ratio sensor and the change in the output current from the air-fuel ratio sensor are detected to calculate the impedance of the sensor element. The impedance characteristics of the air-fuel ratio sensor element are as shown in FIGS.

FIG. 3 is a diagram showing voltage-current characteristics of the air-fuel ratio sensor. The horizontal axis shows the applied voltage V to the air-fuel ratio sensor, and the vertical axis shows the output current I of the air-fuel ratio sensor. As can be seen from FIG. 3, the applied voltage V and the output current I are in a substantially proportional relationship, and the current value changes to the positive side when the air-fuel ratio is lean and to the negative side when the air-fuel ratio is rich (see FIG. 3 shows a characteristic line L1 indicated by a one-dot chain line). That is, the limit current increases as the air-fuel ratio becomes leaner, and decreases as the air-fuel ratio becomes richer. When the output current I is 0 mA, the air-fuel ratio becomes the stoichiometric air-fuel ratio (= 14.5).

Next, a routine for calculating the impedance of the sensor element will be described in detail. FIG. 4 is a first half flowchart of a sensor element impedance calculation routine according to an embodiment of the present invention.
9 shows a flowchart of the latter half of the sensor element impedance calculation routine. More specifically, FIG. 5 is a flowchart of the first (high) frequency superposition processing in the sensor element impedance calculation routine, and FIGS. 6 and 7 are flowcharts of the interrupt processing routine required to perform the first frequency superposition processing. FIG. 8 is a flowchart of the second (low) frequency superposition processing in the sensor element impedance calculation routine, and FIGS. 9 and 10 are flowcharts of an interrupt processing routine necessary for performing the second frequency superposition processing. It is a flowchart. The routine shown in FIGS. 4, 5, and 8 is executed at a predetermined cycle, for example, every 1 msec.

First, at step 401, it is determined whether an ignition switch IGSW (not shown) is on or off. If the IGSW is on, the routine proceeds to step 402, where I
When the GSW is off, this routine ends. In step 402, it is determined whether or not a DC voltage of Vm = 0.3V has already been applied to the air-fuel ratio sensor 1. If the determination result is YES, the process proceeds to step 403. If the determination result is NO, the process proceeds to step 403. Proceed to step 404. Step 40
In step 4, a DC voltage of 0.3 V is applied to the air-fuel ratio sensor.

In step 403, a direct current voltage of 0.3 V is applied to the air-fuel ratio sensor in step 404, followed by 4 msec.
Is determined by, for example, a counter to determine whether or not it is the time when 4 msec has elapsed since the current Ims of the air-fuel ratio sensor was read in the previous processing cycle of this routine,
When one of these determination results is YES, the process proceeds to step 405, and when both of the determination results are NO, the present routine ends. In step 405, the current Ims of the air-fuel ratio sensor is read. As can be seen from these steps, the current Ims is read every 4 msec.

Next, a flow chart of the first frequency superposition process in the sensor element impedance calculation routine will be described with reference to FIGS. An example will be described in which 5 KHz is used as the first frequency. First, step 501
Then, the current processing cycle is k × 64 msec from the start of this routine.
(K is an odd number 1, 3, 5,...) Is used to determine whether or not the time has elapsed, for example, using a counter.
S, that is, the current processing cycle is 64 ms from the start of this routine.
Step 50 for ec, 192 msec, 320 msec, ...
Step 801 if the result of the determination is NO
(See FIG. 8). In step 502, a pulse voltage of -0.2V is superimposed on the applied voltage Vm (= 0.3V) to the air-fuel ratio sensor. Therefore, the voltage Vm1 applied to the air-fuel ratio sensor at this time is 0.1 V. In step 502, the first timer interrupt shown in FIG. 6 is started.

Here, the first timer interrupt processing of FIG. 6 will be described. In step 601, it is determined whether or not 85 μs has elapsed after the activation of the first timer interrupt. If the determination result is YES, the process proceeds to step 602, where the output current Im1 of the air-fuel ratio sensor is read, and the determination result is If no, the process returns to step 601. In step 603, it is determined whether 100 μs has elapsed after the activation of the first timer interrupt. If the determination result is YES, step 604
And apply a voltage of Vm2 = 0.5V to the air-fuel ratio sensor,
When the determination result is NO, the process returns to step 601. In step 604, the second timer interrupt shown in FIG. 7 is started.

Here, the second timer interrupt processing of FIG. 7 will be described. In step 701, it is determined whether 100 μs has elapsed after the activation of the second timer interrupt. If the determination result is YES, the flow advances to step 702 to apply a voltage of Vm = 0.3V to the air-fuel ratio sensor. Then, the process returns to the normal air-fuel ratio detection state. When the determination result is NO, the process returns to step 701.

Referring back to FIG. In step 503,
This processing cycle is (k × 64 + 4) ms from the start of this routine
It is determined whether ec (k is an odd number 1, 3, 5,...) has passed. If the determination result is YES, the process proceeds to step 504. If the determination result is NO, the routine ends. In step 504, the first frequency when the first frequency voltage is applied
(High frequency) impedance Zac1 is calculated from the following equation.

Zac1 = ΔVm / ΔIm = 0.2 / (Im1−Ims) In step 505, guard processing of Zac1, that is, Z
Let ac1 be the lower guard value KREL1 and the upper guard value KREH
Then, a process of setting KREL1 ≦ Zac1 ≦ KREH1 to be within the range of 1 is executed. Specifically, Zac1 is KREL1 ≦
If Zac1 ≤ KREH1, leave as it is, and Zac1 <KREH1.
When REL1, Zac1 = KREL1 = 1 (Ω),
When KREH1 <Zac1, Zac1 = KREH1 = 20
A process for setting the value to 0 (Ω) is executed. Note that the guard processing is usually performed to ignore data due to disturbance, A / D conversion error, and the like.

Next, referring to FIG. 8 to FIG.
A flowchart of the second frequency superimposition process in the sensor element impedance calculation routine will be described. An example in which 500 Hz is used as the second frequency will be described. When it is determined NO in step 501 in the flowchart of FIG. 5, step 801 is executed. In step 801, k × 64 msec (k is an even number 2, 4, 6,
..) Is determined by, for example, a counter, and the determination result is YES, that is, 128 mse
c, step 80 for 256 msec, 384 msec, ...
The routine proceeds to 2, and if the determination result is NO, this routine is ended. In step 802, a pulse voltage of -0.2V is superimposed on the applied voltage Vm (= 0.3V) to the air-fuel ratio sensor. Therefore, the voltage Vm1 applied to the air-fuel ratio sensor at this time is 0.1 V. In step 802, a third timer interrupt is started.

Here, the third timer interrupt processing of FIG. 9 will be described. In step 901, it is determined whether 0.95 msec has elapsed after the activation of the third timer interrupt. If the determination result is YES, the process proceeds to step 902, where the output current Im2 of the air-fuel ratio sensor is read, and the determination is performed. When the result is NO, the process returns to step 901. In step 903, it is determined whether or not 1 msec has elapsed after the activation of the third timer interrupt. If the determination result is YES, the flow advances to step 904 to apply a voltage of Vm2 = 0.5V to the air-fuel ratio sensor. If the determination result is NO, the process returns to step 901. In step 904, the fourth timer interrupt shown in FIG. 10 is started.

Here, the fourth timer interrupt processing of FIG. 10 will be described. In step 1001, it is determined whether 1 msec has elapsed after the activation of the fourth timer interrupt. If the determination result is YES, the flow advances to step 1002 to apply a voltage of Vm = 0.3V to the air-fuel ratio sensor. Then, the process returns to the normal air-fuel ratio detection state. When the determination result is NO, the process returns to step 1001.

Returning to FIG. In step 803,
This processing cycle is (k × 64 + 4) ms from the start of this routine
It is determined whether or not it is the time when ec (k is an even number 2, 4, 6,...) has elapsed. If the determination result is YES, the process proceeds to step 804, and if the determination result is NO, the present routine ends. In step 804, the second frequency when the second frequency voltage is applied
The (low frequency) impedance Zac2 is calculated from the following equation.

Zac2 = ΔVm / ΔIm = 0.2 / (Im2−Ims) In step 805, guard processing of Zac2, that is, Z
ac2 is the lower guard value KREL2 and the upper guard value KREH
2 and KREL2 ≦ Zac2 ≦ KREH2. Specifically, Zac2 is KREL2 ≦
If Zac2 ≤ KREH2, leave as it is, and Zac2 <KREH2.
In the case of REL2, Zac2 = KREL2 = 1 (Ω),
When KREH2 <Zac1, Zac2 = KREH2 = 20
A process for setting the value to 0 (Ω) is executed.

In the embodiment of the present invention described above, the first frequency is 5 kHz and the second frequency is 500 Hz.
Although z was used, the present invention is not limited to this. These frequencies can be appropriately selected in consideration of the materials of the electrolyte and electrodes of the air-fuel ratio sensor, the characteristics of the sensor circuit, the applied voltage, the operating temperature, and the like. Next, the energization control of the heater for maintaining the air-fuel ratio sensor in the active state will be described below.

It is essential that the oxygen concentration detecting element as the air-fuel ratio sensor be maintained in an active state in order to maintain the detection accuracy of the air-fuel ratio, and usually, a heater attached to the oxygen concentration detecting element from the start of the engine. When the power is supplied to the heater, the heater is heated to activate the element at an early stage, and the heater is controlled so as to maintain the active state. FIG. 11 is a diagram showing a correlation between the temperature of the oxygen concentration detecting element and the high frequency impedance. The correlation between the temperature of the oxygen concentration detecting element (hereinafter simply referred to as the element) and the high-frequency impedance as shown in the figure, that is, the relation that the high-frequency impedance of the element attenuates as the element temperature increases. There is. Focusing on this relationship, in the above-described heater energization control, the high-frequency impedance of the element is detected to derive the element temperature, and feedback is performed so that the element temperature becomes a desired activation temperature, for example, 700 ° C. Controlling. For example, as shown in FIG. 11, when the high frequency impedance Zac1 of the element is equal to or higher than 30Ω of the high frequency impedance of the element corresponding to the control element temperature of 700 ° C. (Zac1 ≧ 30), that is, when the element temperature is equal to or lower than 700 ° C. When the heater is energized and Zac1 is smaller than 30Ω (Zac <30), that is, when the element temperature exceeds 700 ° C., the heater is deenergized to control the element temperature to the activation temperature 700. ° C or more, and the active state of the element is maintained. When the heater is energized, the deviation between the high frequency impedance of the element and its target value (Zac-3
The amount of current required to eliminate 0) is obtained, and duty control is performed to supply the amount of current.

FIG. 12 is a flowchart of the heater control routine. This routine has a predetermined period, for example, 128
Executed every msec. In this routine, PID control of the duty ratio of energization to the heater 4 is performed based on the deviation Zacerr (= Zactg-Zac1) between the impedance Zac1 of the air-fuel ratio sensor 1 and the element temperature target value Zactg with respect to the high frequency. First, in step 1201, a proportional term KP is calculated from the following equation.

KP = Zacerr × K1 (K1: constant) In step 1202, an integral term KI is calculated from the following equation. KI = ΣZacerr × K2 (K2: constant) In step 1203, a differential term KD is calculated from the following equation. KD = (ΔZacerr / Δt) × K3 (K3: constant) In step 1204, the PID gain KPID is calculated from the following equation.

KPID = KP + KI + KD In step 1205, the output duty ratio is calculated from the following equation. DUTY (i) = DUTY (i-1) * KPID In step 1206, the output duty ratio DUTY (i)
DUTY (i) is set to the lower limit KDUTY
Between L and upper limit value KDUTYH KDUTY ≦ DUTY
(i) Perform processing to satisfy ≦ KDUTYH. Specifically, when KDUTY ≦ DUTY (i) ≦ KDUTYH, it is left as it is, and when DUTY (i) <KDUTY, DUTY (i) = KDUTYL, and KDUTYH <DU
If it is TY (i), a process of setting DUTY (i) = KDUTYH is executed.

Next, an oxygen concentration detecting element as the air-fuel ratio sensor 1 will be described below. The structure, equivalent circuit, and impedance characteristics of the oxygen concentration detecting element will be described below. 13A and 13B are views showing the structure of the air-fuel ratio sensor element, FIG. 13A is a cross-sectional view, FIG. 13B is a partially enlarged view of the electrolyte part, and FIG. 14 is a view showing an equivalent circuit of the air-fuel ratio sensor element. It is. In FIG. 14, R1 is a bulk resistance of an electrolyte made of, for example, zirconia (grain part in FIG. 13),
R2 is the grain boundary resistance of the electrolyte (see grain boundary in FIG. 13).
), R3 indicates an interface resistance of an electrode made of, for example, platinum, C2 indicates a capacitance component at a grain boundary of the electrolyte, C3 indicates a capacitance component at an electrode interface, and Z (W) indicates a periodic component when polarization by AC is performed. Shows the impedance (Wirble impedance) generated due to the change in the interface concentration.

FIG. 15 is a diagram showing impedance characteristics of the air-fuel ratio sensor element. The horizontal axis shows the real part Z 'of the impedance Z, and the vertical axis shows the imaginary part Z ". The impedance Z of the air-fuel ratio sensor element is represented by Z = Z' + jZ". FIG. 15 shows that the electrode interface resistance R3 converges to 0 as the frequency approaches 1 to 10 KHz. The curve shown by the broken line indicates the impedance that has changed depending on the atmosphere of the air-fuel ratio sensor element. From the portion of the impedance characteristic indicated by the broken line, it is understood that R3 changes depending on the atmosphere of the air-fuel ratio sensor element, particularly, the oxygen concentration.

FIG. 16 is a diagram showing the relationship between the frequency of the AC applied voltage to the air-fuel ratio sensor element and the impedance of the element. FIG. 16 is obtained by converting the horizontal axis into frequency f and the vertical axis into impedance Zac in FIG. From FIG. 15, the impedance Z is shown at a frequency of 1 kHz to 10 MHz.
It can be seen that ac converges to a predetermined value (R1 + R2), and the impedance Zac decreases on the higher frequency side than 10 MHz and converges to R1. Therefore, in order to detect the impedance Zac in a stable state, it is desirable to detect the impedance Zac at a high frequency of about 1 KHz to 10 MHz where the Zac becomes a constant value regardless of the frequency without including the electrode interface resistance R3. I understand. The curve shown by the broken line shows the impedance when an AC voltage of a low frequency (less than 1 KHz) that can be measured including R3 that changes depending on the atmosphere of the air-fuel ratio sensor element, particularly oxygen concentration, is applied.

The fuel property determination routine and the fuel injection quantity correction routine according to the fuel property according to the present invention will now be described. Prior to this, when the air-fuel ratio sensor element is in an inactive state, the sensor element is controlled by the atmosphere of the sensor element. The change of the electrode interface resistance R3 will be described below. FIG. 17 is a diagram showing a result of impedance detection when either the temperature of the air-fuel ratio sensor element or the air-fuel ratio is changed. A, b, and c on the horizontal axis indicate that the sensor element temperature is maintained at 500 ° C., 600 ° C., and 700 ° C., respectively, and A, B, and C on the vertical axis indicate the sensor element temperature. The atmosphere changes from lean to rich, that is, 20% O ₂
(80% N ₂ ), 10% O ₂ (90% N ₂ ), 0% O ₂
(100% N ₂ ). FIG. 17 is a bar graph showing experimental results when detecting low-frequency impedance (Zac2 = R1 + R2 + R3) and high-frequency impedance (Zac1 = R1 + R2) of the sensor element under these conditions. As can be seen from FIG. 17, the high frequency impedance Zac1 hardly changes due to the atmosphere of the sensor element as long as the temperature of the sensor element is kept constant. On the other hand, it can be seen that the low frequency impedance Zac2 changes depending on the atmosphere of the sensor element even when the sensor element temperature is kept constant. Further, it can be seen that the amount of change in the low frequency impedance Zac2 due to the atmosphere of the sensor element increases as the sensor element temperature increases from 500 ° C. to 700 ° C.

FIG. 18 is a diagram showing the relationship between the temperature of the air-fuel ratio sensor element, the air-fuel ratio, and admittance. In FIG. 18, the horizontal axis indicates the sensor element temperature, and the vertical axis indicates the admittance of the sensor element. A line 181 indicates the admittance Yh (1 / Ω) of the sensor element detected when a high-frequency voltage is applied to the sensor element while varying the temperature of the sensor element. A line 182 indicates that the atmosphere of the sensor element is stoichiometric. (Stoichiometric air-fuel ratio), the admittance Yl (1 / Ω) of the sensor element detected when a low-frequency voltage is applied to the sensor element while varying the temperature of the sensor element, and a line 183 represents the sensor element. The admittance Yl when the atmosphere is lean is shown, and the line 184 shows the admittance Yl when the atmosphere of the sensor element is rich.

FIG. 18 shows that the sensor element temperature T1 (# 40
0 ° C) and the fuel property determination temperature T2 (= 550 °)
C), the sensor element temperature target temperature T3 (= 700)
Up to (° C), the admittance Yl of the sensor element detected when the low frequency voltage is applied changes depending on the atmosphere of the sensor element. The admittance Yh of the sensor element detected when a high-frequency voltage is applied slightly changes depending on the atmosphere of the sensor element, but is not remarkable.

FIG. 19 is a diagram showing the relationship between the air-fuel ratio of the air-fuel ratio sensor element and admittance. FIG. 19 shows the relationship between the admittance Yl of the sensor element detected when a low-frequency voltage is applied to the sensor element and the air-fuel ratio of the atmosphere of the sensor element when the temperature of the sensor element is the temperature T2 for judging the fuel property in FIG. Show. When the atmosphere of the sensor element has an air-fuel ratio AF1 richer than stoichiometric, the admittance Yl1 of the sensor element is lower than the stoichiometric air-fuel ratio AF1.
It can be seen that the admittance Yl2 of the sensor element at the time of 2 is smaller than Y2. Here, it should be noted that when the sensor element is in the inactive state, the air-fuel ratio of the atmosphere of the sensor element can be detected from the impedance of the sensor element or the admittance of the reciprocal thereof. Focusing on this point, the present invention detects the air-fuel ratio of the sensor element atmosphere from the impedance or admittance of the sensor element when the sensor element is in an inactive state, and attempts to determine the fuel property from the detected air-fuel ratio. It is.

FIG. 20 is a flowchart of a fuel property determination routine. This routine has a predetermined period, for example, 8 msec.
It is executed every time. First, in step 2001, the engine water temperature THW detected from a water temperature sensor (not shown) for detecting the engine cooling water temperature falls within a predetermined range (THW1 <THW <THW).
2) is determined, and if the result of the determination is YES, it is determined that the water temperature condition for fuel property determination has been satisfied, and the routine proceeds to step 2002. If the determination result is NO, the same water temperature condition is determined. Is determined not to be established, and this routine is terminated. The water temperature condition for determining the fuel property is determined for the following two reasons.

1. When the cylinder inner wall temperature of the engine is low and it is judged that it is difficult to ensure complete combustion of the air-fuel mixture in the cylinder due to the cooling effect of the wall surface, at a water temperature THW1 (= -20 ° C) or lower,
It is not suitable for judging fuel properties by detecting exhaust gas. 2. Water temperature THW2 (= 8) at which it is determined that the engine has been warmed up
0 ° C), that is, at the time of cold start, the time when fuel adheres to the intake pipes and cylinder walls of the engine.
This is a suitable time for fuel property determination.

Next, at step 2002, it is determined whether or not the engine is idling, that is, if the engine
Idle speed after starting beyond 0 RPM, for example 600
It is determined whether or not the engine is operating at the RPM. If the result of the determination is YES, the process proceeds to step 2002, and if the result of the determination is NO, the present routine ends. A signal XIDLE of an idle switch (not shown) for detecting that the throttle valve is fully closed is on (indicating full closure), and the vehicle speed detected by a vehicle speed sensor (not shown) is 2K.
When it is less than m / h, it is determined that the engine is idling. The condition of the fuel property determination that the engine is idle is that when the vehicle speed exceeds the idle speed during cold start, the drivability deteriorates, the air-fuel ratio in the exhaust gas is disturbed, and the fuel property is determined from the exhaust gas. This is because it is unsuitable to do so.

Next, in step 2003, it is determined whether or not the temperature of the air-fuel ratio sensor element is the fuel property determination temperature. If the result of the determination is YES, the process proceeds to step 2004. If the result of the determination is NO, the routine proceeds to step 2004. End the routine. The fuel property determination temperature is the sensor element temperature (T1) at which the sensor element is in an inactive state and the air-fuel ratio changes depending on the atmosphere.
Within a range of <T <T3), the amount of change in the low frequency admittance Yl is set to a predetermined temperature T2 which becomes more significant depending on the atmosphere of the sensor element. Further, at the temperature T2, when a low-frequency voltage is applied to the sensor element, it is detected as shown in FIG.
A map showing the relationship between the admittance of the sensor element and the air-fuel ratio of the atmosphere of the sensor element as shown in FIG. 9 is stored in the ROM in advance. As shown in FIG. 18, the high frequency admittance Yh of the sensor element is substantially proportional to the temperature of the sensor element regardless of the air-fuel ratio of the atmosphere of the sensor element. Therefore, whether the sensor element temperature is T2 or not is determined by determining whether the high frequency admittance of the sensor element is within the allowable error α of Yh2 (Yh2−α ≦ Yh ≦ Yh2).
+ Α).

In step 2004, it is determined whether or not the low frequency admittance Yl of the sensor element is smaller than a predetermined value Yl1. If the result of the determination is YES, it is determined that the fuel is light fuel, and the flow proceeds to step 2005. If NO, the process proceeds to step 2006. In step 2005, the light fuel flag LFLFG is set. In step 2006, the low frequency admittance Yl of the sensor element is set to a predetermined value Y.
l2 is determined, and if the result of the determination is YES, it is determined that the fuel is heavy, and the process proceeds to step 2007.
Proceed to 08. In step 2007, the heavy fuel flag HF
Set FLG. In step 2008, both the light fuel flag LFLFG and the heavy fuel flag HFFLG are reset.

In step 2009, a fuel injection amount correction routine shown in FIG. 21 is executed according to the fuel properties determined by the above-described processing. FIG. 21 is a flowchart of a fuel injection amount correction routine. This routine has a predetermined cycle,
For example, it is executed every 1 msec. First, step 2101
Then, based on a rotational speed NE obtained from a signal from a crank angle sensor (not shown) of the engine and an intake air amount GA detected from an air flow meter (not shown), the exhaust air-fuel ratio is set to a stoichiometric air-fuel ratio. A fuel injection amount TP is obtained, and a warm-up correction coefficient FWL for accelerating the atomization of fuel according to the engine coolant temperature THW is increased for a predetermined period after the start to wet the intake port since the intake port is dry after the start. The fuel injection amount TAU is calculated from the following correction coefficient FASE and other correction coefficients K by the following equation. Note that these correction coefficients FWL, FASE and K are stored in the ROM in advance.

TAU = TP × FWL × FASE × K Next, at step 2102, it is determined whether or not the fuel is heavy fuel.
Heavy fuel flag HF determined by the fuel property determination routine of
Judge by FLG. When HFFLG = 1 in step 2102, it is determined that the fuel is heavy, and the process proceeds to step 2103.
If HFFLG = 0, it is determined that the fuel is not heavy fuel, and the routine ends. In step 2103, the engine coolant temperature THW is read. In step 2104, the post-start elapsed time CSTA is read.

In step 2105, the fuel injection amount TAU
Is calculated according to the following equation according to the fuel property. TAU = TAU (FLF × KFLF) Here, FLF is a temperature correction coefficient, and KFLF is a time correction coefficient. Next, a map of these correction coefficients shown in FIG. 22 will be described.

FIGS. 22A and 22B are diagrams showing a map of a correction coefficient relating to fuel properties. FIG. 22A shows a map of a temperature correction coefficient FLF, and FIG. 22B shows a map of a time correction coefficient KFLF. As shown in FIG. 22A, the temperature correction coefficient FL
F is set to a large value when the cooling water temperature THW is low, and is set so as to increase the fuel injection amount.
It is set so as to gradually decrease as HW increases. This is because the wall surface of the intake pipe and the wall surface of the cylinder are dry immediately after the start, and the fuel is liable to be attached thereto. As shown in FIG. 22B, the time correction coefficient KFLF is set to a large value when the starting time has not passed much,
It is set so as to gradually decrease over time. The post-start elapsed time CATA is a value measured using a counter at the end of the start, that is, the time elapsed after the engine speed NE exceeds 400 RPM.

In the above-described fuel property determination routine,
The sensor element temperature detecting means is based on detecting a high frequency impedance (admittance) of the sensor element. However, the present invention is not limited to this. The sensor element temperature detecting means may be, for example, a sensor element. May be estimated from the water temperature of the engine or from the amount of electric power supplied to the heater of the sensor element.

[0062]

As described above, according to the control device for an air-fuel ratio sensor of an internal combustion engine of the present invention, the fuel property can be determined before the air-fuel ratio sensor (oxygen concentration detecting element) is activated. The fuel injection amount according to the fuel property can be supplied to the engine at an early stage, whereby the exhaust emission and drivability can be favorably maintained.

Further, according to the control device for an air-fuel ratio sensor of an internal combustion engine of the present invention, the air-fuel ratio sensor of the internal combustion engine can accurately determine the fuel property even in an internal combustion engine having no secondary air supply means or auxiliary equipment. Can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an air-fuel ratio sensor control device for an internal combustion engine according to the present invention.

FIG. 2 is a diagram showing input / output signals of an air-fuel ratio sensor;
(A) is a diagram showing a waveform of an input voltage applied to the air-fuel ratio sensor, and (B) is a diagram showing an output current waveform detected from the air-fuel ratio sensor.

FIG. 3 is a diagram showing voltage-current characteristics of an air-fuel ratio sensor.

FIG. 4 is a first half flowchart of a sensor element impedance calculation routine according to an embodiment of the present invention.

FIG. 5 is a flowchart of a first frequency superposition process in a sensor element impedance calculation routine.

FIG. 6 is a flowchart of a first interrupt processing routine necessary for performing the first frequency superposition processing.

FIG. 7 is a flowchart of a second interrupt processing routine necessary for performing the first frequency superposition processing.

FIG. 8 is a flowchart of a second frequency superimposition process in a sensor element impedance calculation routine.

FIG. 9 is a flowchart of a third interrupt processing routine necessary for performing the second frequency superposition processing.

FIG. 10 is a flowchart of a fourth interrupt processing routine necessary for performing the second frequency superposition processing.

FIG. 11 is a diagram showing a correlation between the temperature of the oxygen concentration detecting element and the high frequency impedance.

FIG. 12 is a flowchart of a heater control routine.

FIG. 13 is a view showing the structure of an air-fuel ratio sensor element;
(A) is a sectional view, and (B) is a partially enlarged view of an electrolyte part.

FIG. 14 is a diagram showing an equivalent circuit of the air-fuel ratio sensor element.

FIG. 15 is a diagram illustrating impedance characteristics of an air-fuel ratio sensor element.

FIG. 16 is a diagram showing the relationship between the frequency of an AC applied voltage to the air-fuel ratio sensor element and the element impedance.

FIG. 17 is a diagram showing a detection result of impedance when one of the temperature of the air-fuel ratio sensor element and the air-fuel ratio is changed.

FIG. 18 is a diagram showing the relationship between the temperature of the air-fuel ratio sensor element, the air-fuel ratio, and admittance.

FIG. 19 is a diagram showing the relationship between the air-fuel ratio of the air-fuel ratio sensor element and admittance.

FIG. 20 is a flowchart of a fuel property determination routine.

FIG. 21 is a flowchart of a fuel injection amount correction routine.

FIGS. 22A and 22B are diagrams showing a map of a correction coefficient relating to fuel properties, in which FIG. 22A shows a map of a temperature correction coefficient FLF, and FIG. 22B shows a map of a time correction coefficient KFLF.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 air-fuel ratio sensor 2 sensor element 3 sensor control circuit 4 heater 5 battery 6 heater control circuit 7 low-pass filter (LPF) 10 air-fuel ratio control unit (A / FCU) 11 microcomputer 12 D / A converter 13-16 A / D converter 100 Electronic control unit (ECU)

Continued on the front page (72) Inventor Shinsuke Inagaki 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G084 CA02 DA00 DA04 DA10 DA15 EA01 EA02 EA07 EA11 EB25 EC06 FA00 FA29

Claims (6)

[Claims] An oxygen concentration detecting element for outputting a current proportional to the oxygen concentration in a gas to be detected when a voltage is applied, and a low frequency AC voltage is applied to the oxygen concentration detecting element to apply the voltage to the oxygen concentration detecting element. Low-frequency AC impedance detecting means for detecting impedance; fuel property determining means for determining the property of fuel supplied to the internal combustion engine from the impedance of the oxygen concentration detecting element detected by the low-frequency AC impedance detecting means; A control device for an air-fuel ratio sensor of an internal combustion engine, comprising: 2. A temperature detecting means for detecting a temperature of the oxygen concentration detecting element, and whether or not the oxygen concentration detecting element is in an inactive state based on a temperature of the oxygen concentration detecting element detected by the temperature detecting means. And a low-frequency AC impedance detecting means for detecting the impedance when the oxygen concentration detecting element is determined to be in an inactive state by the element inactivity determining means. The control device for an air-fuel ratio sensor of an internal combustion engine according to claim 1. 3. High-frequency AC impedance detecting means for applying a high-frequency AC voltage to the oxygen concentration detecting element to detect the impedance of the oxygen concentration detecting element, wherein the temperature detecting means comprises the high-frequency AC impedance. 3. The control device for an air-fuel ratio sensor of an internal combustion engine according to claim 1, wherein a temperature of the oxygen concentration detection element is detected from an impedance of the oxygen concentration detection element detected by a detection unit. 4. An oxygen concentration detecting element which is disposed in an exhaust system of an internal combustion engine and outputs a current proportional to an oxygen concentration in exhaust gas of the internal combustion engine when a voltage is applied, and detects a temperature of the oxygen concentration detecting element. Temperature detection means for performing, element deactivation determination means for determining whether or not the oxygen concentration detection element is in an inactive state based on the temperature of the oxygen concentration detection element detected by the temperature detection means; and Air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas from the output of the element, and detection by the air-fuel ratio detection means when the oxygen concentration detection element is determined to be inactive by the element inactivity determination means And a fuel property determining means for determining a property of fuel supplied to the internal combustion engine from the air-fuel ratio of the exhaust gas thus obtained. 5. The air-fuel ratio detecting means according to claim 4, wherein the air-fuel ratio detecting means detects the air-fuel ratio by applying a low frequency AC voltage to the oxygen concentration detecting element and detecting an impedance of the oxygen concentration detecting element. A control device for an air-fuel ratio sensor of an internal combustion engine according to the above. 6. A high-frequency AC impedance detecting means for applying a high-frequency AC voltage to the oxygen concentration detecting element to detect the impedance of the oxygen concentration detecting element, wherein the temperature detecting means comprises the high-frequency AC impedance Detecting the temperature of the oxygen concentration detection element from the impedance of the oxygen concentration detection element detected by the detection means,
A control device for an air-fuel ratio sensor for an internal combustion engine according to claim 4 or 5.