JP2000235015A - Heater control device of air/fuel ratio sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To start the reloading to a heater at appropriate timing after an engine is started without causing deterioration of engine starting properties or an unstable state of idling operation, in the case of a heater control device having the function of preheating air/fuel ratio sensors. SOLUTION: When a sensor temperature T is below an activating temperature Te (step 154), the execution of air/fuel ratio feedback control is prohibited (step 158). A reference value NO is found based on the sensor temperature T (step 162), and if an engine speed NE is in excess of the reference value NO, the repowering of a heater 68 of air/fuel ratio sensors 58, 60 is permitted, and if the engine speed NE is less than the reference value NO, the repowering of the heater 68 is prohibited (steps 164, 160, 166).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heater control device for an air-fuel ratio sensor, and more particularly to a heater control device for an air-fuel ratio sensor having a function of preheating the air-fuel ratio sensor before starting the engine.

[0002]

2. Description of the Related Art In an internal combustion engine, air-fuel ratio feedback control for controlling the air-fuel ratio toward a stoichiometric air-fuel ratio is performed by correcting the fuel injection amount based on the air-fuel ratio of an exhaust passage. According to the air-fuel ratio feedback control, it is possible to obtain an effect that the purification performance of the exhaust gas by the catalytic converter is maintained at a high level, and the deterioration of the fuel efficiency is prevented. In order to realize such air-fuel ratio feedback control, an air-fuel ratio sensor for detecting the air-fuel ratio is provided in the exhaust passage. Generally, the air-fuel ratio sensor has a characteristic of outputting a signal corresponding to the oxygen concentration in an activated state heated to an activation temperature of several hundred degrees or more. For this reason, the air-fuel ratio sensor has a built-in heater for heating the sensor element to the activation temperature. After energization of the heater of the air-fuel ratio sensor is started, until the sensor temperature reaches the activation temperature,
It takes some time before the air-fuel ratio feedback control based on the output signal of the air-fuel ratio sensor becomes possible. Therefore, conventionally, preheating for starting energization of the heater before the start of the engine has been performed so that the air-fuel ratio feedback control can be started immediately after the start of the internal combustion engine.

For example, in the air-fuel ratio control device disclosed in Japanese Patent Laid-Open No. 5-202785, when the opening of the vehicle door is detected, the start of the internal combustion engine is predicted, and the preheating of the heater of the air-fuel ratio sensor is started. I do. In this air-fuel ratio control device, the lower the temperature of the internal combustion engine, the higher the target temperature in preheating is set. According to this method, even at the time of low-temperature start, the sensor temperature can be raised to the activation temperature immediately after the start.

[0004]

Generally, when cranking of the internal combustion engine is started, energization of the heater of the air-fuel ratio sensor is stopped in order to secure sufficient power supply to the starter motor. Since the air-fuel ratio sensor is cooled when the power supply to the heater is stopped, after the engine is started,
From the viewpoint of starting the air-fuel ratio feedback control early, it is desirable to immediately start re-energizing the heater. However, if the power supply to the heater is restarted before the cranking is completed, the power supplied to the starter motor becomes insufficient, and the engine startability deteriorates. Further, even after the cranking start is completed, if the power supply to the heater is started before the engine operation state is stabilized, the load on the alternator increases due to an increase in the discharge power of the battery, and the idle operation state is reduced. It becomes unstable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made to re-energize the heater of the air-fuel ratio sensor while smoothly starting the internal combustion engine and realizing a stable operation state after the engine is started. It is an object of the present invention to provide a heater control device for an air-fuel ratio sensor that can be started.

[0006]

The above object is achieved by the present invention.
A heater control device for controlling energization of a heater included in an air-fuel ratio sensor provided in an internal combustion engine, wherein the preheating means energizes the heater before starting the engine; Energization stopping means for stopping energization by the means, operating state detecting means for detecting an engine operating state, and energizing timing setting means for setting energizing start timing to the heater after engine start based on the engine operating state. This is achieved by a heater control device for an air-fuel ratio sensor comprising:

In the first aspect of the present invention, the power supply stopping means stops power supply to the heater by the preheating means when the engine is started. When the heater is re-energized after the engine is started, the discharged power of the battery increases. For this reason, when the power supplied to the starter motor is insufficient, the startability of the internal combustion engine is deteriorated, or the load on the alternator is increased, so that the operation state of the internal combustion engine is changed to an unstable state. On the other hand, the power supply timing setting means sets the power supply start timing to the heater after the engine is started based on the engine operation state. Therefore, according to the present invention, it is possible to prevent the engine startability from deteriorating due to the start of energization of the heater, or to prevent the operation state after the engine is started from becoming unstable.

According to a second aspect of the present invention, there is provided a heater control apparatus for an air-fuel ratio sensor according to the first aspect, further comprising a sensor temperature detecting means for detecting a temperature of the air-fuel ratio sensor, The timing setting means is
The present invention is also achieved by a heater control device for an air-fuel ratio sensor that sets the energization start timing based on the engine operating state and the temperature of the air-fuel ratio sensor.

According to the second aspect of the present invention, the power supply stopping means stops the power supply to the heater by the preheating means when the engine is started. Therefore, after the engine is started, the temperature of the air-fuel ratio sensor is maintained until the power supply to the heater is started. Sensor temperature) temporarily decreases. In this case, the higher the sensor temperature at the start of energization, the lower the power consumption of the heater. In other words, the higher the sensor temperature after the engine is started, the smaller the effect of the start of energization on the heater on the engine startability and operation stability becomes. Therefore, energization of the heater can be started earlier. Therefore, according to the present invention, the energization timing setting means sets the energization start timing based on the engine operation state and the sensor temperature, so that deterioration of the engine startability and instability of the operation state are not caused. By energizing the heater at an early stage, the activity of the air-fuel ratio sensor can be quickly restored.

In this case, an engine speed may be used as the engine operating state. Further, the impedance of the air-fuel ratio sensor changes according to the sensor temperature. Therefore, as described in claim 4, the sensor temperature detecting means may detect the temperature of the air-fuel ratio sensor based on the impedance of the air-fuel ratio sensor.

[0011]

FIG. 1 is a system configuration diagram of an internal combustion engine to which a heater control device for an air-fuel ratio sensor according to an embodiment of the present invention is applied. The internal combustion engine of the present embodiment is controlled by an electronic control unit (hereinafter, referred to as ECU) 10. As shown in FIG. 1, the internal combustion engine includes a cylinder block 1
2 is provided. Inside the cylinder block 12, a cylinder 14 and a water jacket 16 are formed. The water jacket 16 is provided with a water temperature sensor 18. The water temperature sensor 18 outputs a signal corresponding to the temperature of the cooling water flowing inside the water jacket 16 (hereinafter, referred to as water temperature THW) to the ECU 10. E
The CU 10 determines the water temperature T based on the output signal of the water temperature sensor 18.
HW is detected.

A piston 20 is provided inside the cylinder 14. The piston 20 can slide inside the cylinder 14 in the vertical direction in FIG. A cylinder head 22 is fixed to an upper portion of the cylinder block 12. An intake port 24 and an exhaust port 26 are formed in the cylinder head 22. The bottom surface of the cylinder head 22, the top surface of the piston 20, and the side wall of the cylinder 14 define a combustion chamber. The above-described intake port 24 and exhaust port 26 are both
8 is open. The tip of the ignition plug 30 is exposed in the combustion chamber 28. The ignition plug 30 ignites fuel in the combustion chamber 28 by receiving an ignition signal from the ECU 10.

The internal combustion engine also has an intake valve 34 and an exhaust valve 36. Intake port 24 and exhaust port 26
A valve seat for the intake valve 34 and the exhaust valve 36 is formed at the opening to the combustion chamber 28, respectively. Intake valve 3
4 and the exhaust valve 36 are separated from and seated on each valve seat,
The intake port 24 and the exhaust port 26 are opened and closed, respectively.

The intake port 24 has an intake manifold 3
8 are in communication. A fuel injection valve 40 is provided in the intake manifold 38. The fuel injection valve 40 is ECU1
Fuel is injected into the intake manifold 38 according to a command signal given from zero. A surge tank 42 communicates with the upstream side of the intake manifold 38. An intake pipe 44 communicates further upstream of the surge tank 42. The intake pipe 44 is provided with a throttle valve 46. In the vicinity of the throttle valve 46, a throttle opening sensor 48 is provided.

An air flow meter 50 communicates upstream of the intake pipe 44. The air flow meter 50 is connected to the intake pipe 4.
A signal corresponding to the flow rate of the air passing through 4 is output to ECU 10. The ECU 10 detects the intake air amount of the internal combustion engine based on the output signal of the air flow meter 50.
Further upstream of the air flow meter 50 is an air cleaner 5.
Two are communicating. The outside air filtered by the air cleaner 52 flows into the intake pipe 44.

On the other hand, an exhaust passage 54 communicates with the exhaust port 26 of the internal combustion engine. A catalytic converter 56 is provided in the exhaust passage 54. Catalytic converter 56
Purifies the exhaust gas by reacting hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the exhaust gas. Air-fuel ratio sensors 58 and 60 are disposed upstream and downstream of the catalytic converter 56, respectively. The air-fuel ratio sensors 58 and 60 have the same configuration, and these configurations will be described later. In this embodiment, the air-fuel ratio sensors 58 and 60 are the same, but may be different.

The internal combustion engine also has a rotation speed sensor 62. The rotation speed sensor 62 outputs a pulse signal to the ECU 10 every time the internal combustion engine rotates by a predetermined crank angle. The ECU 10 detects a rotation speed of the internal combustion engine (hereinafter, referred to as an engine rotation speed NE) based on an output signal of the rotation speed sensor 62. The ECU 10 includes a door switch 64
Is connected. The door switch 64 is a switch that is turned on only when the vehicle door is opened. The ECU 10 detects the opening of the vehicle door based on the ON / OFF state of the door switch 64.

FIG. 2 shows an internal configuration of the air-fuel ratio sensors 58 and 60 together with a connection circuit with the ECU 10. As shown in FIG. 2, the air-fuel ratio sensors 58 and 60 have a sensor element 66 therein made of a material such as zirconia.
And a heater 68 for heating the sensor element 66. One terminal of the sensor element 66 is connected to the constant voltage source 70, and the other terminal is connected to the ECU 10 and grounded via the resistor 71. When the constant voltage is applied to the sensor element 66 in this manner, a current flowing through the sensor element 66 (hereinafter, referred to as a sensor current I)
Indicates that the temperature of the sensor element 66 (hereinafter referred to as the sensor temperature T) is a predetermined activation temperature Te (for example, from 650 ° C. to 7
When the temperature is equal to or greater than (00 ° C.), the pressure varies according to the oxygen concentration in the exhaust passage 54. A voltage corresponding to the sensor current I is input to the ECU 10.

The sensor element 66 is connected to the ECU 10 via an impedance detection circuit 72. The impedance detection circuit 72 applies an AC voltage having a predetermined frequency to the sensor element 66 in response to a control signal supplied from the ECU 10, and sends a signal corresponding to the magnitude of the AC current flowing through the sensor element 66 to the ECU 10. Output. The ECU 10 detects the impedance of the sensor element 66 based on the output signal of the impedance detection circuit 72. The sensor element 66 has a characteristic that the impedance decreases as the sensor temperature T increases.
Therefore, the ECU 10 detects the sensor temperature T based on the impedance of the sensor element 66.

On the other hand, the heater 68 is connected to the ECU 10 via a power supply control circuit 74. Energization control circuit 74
Performs duty control of a current supplied to the heater 68 using the vehicle-mounted battery 75 as a power supply in accordance with a control signal supplied from the ECU 10. A heater voltage detection circuit 76 and a heater current detection circuit 78 are connected to the heater 68. The heater voltage detection circuit 76 outputs a signal corresponding to the voltage applied to the heater 68 to the ECU 10. The heater current detection circuit 78 outputs a signal corresponding to the current flowing through the heater 68 to the ECU 10.
The ECU 10 detects a voltage applied to the heater 68 and a current supplied to the heater 68 based on these signals.

During the operation of the internal combustion engine, the ECU 10 controls the amount of power supplied to the heater 68 so that the temperature of the sensor temperature T is equal to or higher than the activation temperature Te and at a level that does not damage the sensor element 66. Control. As described above, when the sensor temperature T is maintained at the activation temperature Te or higher, the current flowing through the sensor element 66 changes according to the oxygen concentration. Therefore, the ECU 10 can detect the oxygen concentration in the exhaust passage 54, that is, the air-fuel ratio, based on the sensor current I by controlling the amount of current supplied to the heater 68 as described above. Then, the ECU 10 executes air-fuel ratio feedback control for performing feedback control of the fuel injection amount based on the air-fuel ratio.

In the air-fuel ratio feedback control, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the fuel injection amount is reduced, and when the air-fuel ratio is leaner, the fuel injection amount is increased. Is maintained within a predetermined range near the stoichiometric air-fuel ratio. The above-described catalytic converter 56 exhibits high purification performance when the air-fuel ratio is near the stoichiometric air-fuel ratio. Therefore, according to the air-fuel ratio feedback control, HC, CO, and NOx in the exhaust gas are
Can be more effectively removed. Further, according to the air-fuel ratio feedback control, the air-fuel ratio does not become excessively rich or lean, so that it is possible to prevent both deterioration of the fuel efficiency and instability of the combustion state.

During a cold start of the internal combustion engine, the sensor temperature T
Since the temperature has almost dropped to the outside temperature, it takes some time before the sensor temperature T is heated to the activation temperature Te. Therefore, in the present embodiment, in order to start the execution of the air-fuel ratio feedback immediately after the start of the internal combustion engine, if the engine start is predicted (for example, if the opening of the vehicle door is detected), , The power supply to the heater 68 of the air-fuel ratio sensors 58 and 60 is started. Hereinafter, energization of the heater 68 performed before the engine is started is referred to as preheating of the air-fuel ratio sensors 58 and 60.

The air-fuel ratio sensors 58 and 60 have different structures. For example, only the air-fuel ratio sensor 58 has a heater 68.
Is provided, the preheat is performed by the air-fuel ratio sensor 58.
Will be performed only for During the execution of the preheating, the power of the vehicle battery 75 is consumed. Therefore,
In this embodiment, when the cranking start is started,
In order to secure sufficient power supply to the starter motor, preheating will be stopped. In this case, after starting the engine,
From the viewpoint of immediately starting the air-fuel ratio feedback control, it is desirable to start the re-energization of the heater 68 as early as possible. On the other hand, if the re-energization to the heater 68 is started before the cranking start is completed, the power supply to the starter motor becomes insufficient, and the engine startability is reduced. Further, even after the cranking start is completed, if re-energization to the heater 68 is started before the idling operation state is stabilized, the load on the alternator increases due to an increase in the discharge power of the vehicle-mounted battery 75. As a result, the idle operation state becomes more unstable.

On the other hand, the system according to the present embodiment sets the restart timing of energization to the heater 68 based on the engine speed NE and the sensor temperature T at the time of starting the engine.
It is characterized in that the air-fuel ratio feedback control can be started early while ensuring good engine startability and stability in the idling operation state. FIG. 3 shows a map representing the relationship between the sensor temperature T and the reference value N0 of the engine speed NE for resuming the energization of the heater 68. In the present embodiment, a reference value N0 is determined from the sensor temperature T with reference to the map shown in FIG. 3, and when the engine speed NE exceeds the reference value N0, re-energization to the heater 68 is started. You. As the sensor temperature T increases, the power consumption of the heater 68 when the power supply to the heater 68 is restarted (that is, the power consumption required to raise the sensor temperature T to the activation temperature Te or higher).
Is small. Therefore, in the present embodiment, as shown in FIG. 3, as the sensor temperature T is higher, the reference value N0 is set to a smaller value, so that re-energization is started at a point in time when the engine speed NE is lower.

FIG. 4 shows (A) a time change of the sensor temperature T after the preheating of the air-fuel ratio sensors 58 and 60 is started,
(B) A time change of the ON / OFF state of energization to the heater 68 and (C) a time change of the engine speed NE are illustrated. In FIG. 4C, the engine speed NE when the power supply to the heater 68 is started before the engine speed NE reaches the reference value N0 is indicated by a dashed line.

As shown in FIGS. 4 (A) and 4 (B), the air-fuel ratio sensor 5
By performing preheating of 8, 60, the sensor temperature T
Rises toward the target temperature Tc. When the cranking is started at time t1, the power supply to the heater 68 is stopped, and thereafter, the sensor temperature T gradually decreases and falls below the activation temperature Te. On the other hand, as shown by the solid line in FIG. 4C, the engine speed NE rises with the start of cranking at time t1, and after the cranking ends at time t2, the engine starts to operate even after the combustion of the internal combustion engine starts. The rotation speed NE keeps increasing. Then, at time t3, when the engine speed NE exceeds the reference value N0, re-energization to the heater 68 is started as shown in FIG. 4B, and the sensor temperature Tc is reduced as shown in FIG. Turn to ascent.

As described above, when re-energization of the heater 68 is started, the discharge power of the vehicle battery 75 increases. Therefore, as shown by the dashed line in FIG. 4C, when re-energization is started in a state where the engine speed NE has not reached the reference value N0, the load on the alternator increases,
The engine speed NE does not rise sufficiently.
Further, when the timing at which the re-energization is started is during cranking, as described above, the power supply to the starter motor is insufficient, so that the smooth start of the internal combustion engine cannot be realized.

On the other hand, in the present embodiment, as described above, the re-energization is started when it is determined that the engine speed NE exceeds the reference value N0 and a stable operation state is secured. Therefore, according to the present embodiment, re-energization to the heater 68 can be started while ensuring good engine startability and a stable idle operation state. Also, the heater temperature T
Is higher (that is, the power consumption associated with the start of re-energization of the heater 68 is smaller), the reference value N0 is set to a smaller value, so that the startability and operating stability of the internal combustion engine are not affected. Within the range, the energization can be started at a timing as quick as possible. That is, according to the present embodiment, it is possible to start the air-fuel ratio feedback control early, while ensuring good startability and a stable idle operation state of the internal combustion engine.

The details of the specific processing executed by the ECU 10 in this embodiment will be described below. FIG. 5 shows the ECU 1 that performs preheating of the air-fuel ratio sensors 58 and 60.
0 is a flowchart of a routine executed. Also,
FIG. 6 shows that the ECU 10 starts re-energizing the heater 68.
5 is a flowchart of a routine executed by the user. The routine shown in FIGS. 5 and 6 is a periodic interruption routine started at a predetermined time interval. First, the routine shown in FIG. 5 will be described. When the routine shown in FIG. 5 is started, the process of step 100 is executed.

In step 100, it is determined whether or not execution of preheating is permitted. Specifically, in step 100, after the opening of the vehicle door is detected,
If the internal combustion engine is not started, that is, if the internal combustion engine is expected to be started, it is determined that the execution of the preheat is permitted. If it is determined in step 100 that the execution of the preheat is not permitted, the process of step 102 is executed next. Step 1
At 00, if execution of the preheat is permitted, the process of step 104 is executed next.

In step 102, the air-fuel ratio sensor 58,
Duty ratio H in energization control of heater 60
Tduty is set to “0”. Therefore, step 100
According to the processes of and 102, the energization of the heater 68 is stopped when the internal combustion engine is started after the start of the preheating. When the processing of step 102 ends,
This routine is ended.

In step 104, the sensor temperature T is detected based on the impedance of the sensor element 66. In step 106 following step 104, the sensor temperature T
Is higher than the target temperature Tc. As a result, if T> Tc is satisfied, then step 10
At 8, the amount of power to the heater 68 is reduced by reducing the duty ratio HTduty by the predetermined value α. On the other hand, if T> Tc is not satisfied in step 106, then in step 110, the duty ratio THduty is increased by a predetermined value α, so that the amount of power to the heater 68 is increased. Step 106, 10
According to the processes of 8 and 110, the sensor temperature T is controlled toward the target temperature Tc. Step 108 or 110
Is completed, the current routine ends.

The change width α of the duty ratio HTduty may be variable based on the magnitude of the difference between the sensor temperature T and the target temperature Tc. Next, the routine shown in FIG. 6 will be described. When the routine shown in FIG. 6 is started, the processing of step 150 is executed. In step 150, it is determined whether or not the engine speed NE is "0". As a result, when NE = 0 is established, it is determined that the engine is not yet started, and the current routine is terminated. On the other hand, if NE = 0 is not satisfied in step 150, the process of step 152 is executed next.

In step 152, the sensor temperature T is detected based on the impedance of the sensor element 66. In step 154 following step 152, the sensor temperature T
Is higher than or equal to the activation temperature Te. As a result, if T ≧ Te holds, the air-fuel ratio sensor 58,
60 is determined to be active, then step 156
Is performed. On the other hand, in step 154,
If T ≧ Te is not satisfied, the process of step 158 is executed next.

In step 156, the F / B permission flag F
1 is set to "1". The ECU 10 permits the execution of the air-fuel ratio feedback control when the F / B permission flag F1 is set to “1”. Step 156
When the process is completed, the process proceeds to step 160. In step 160, the re-energization permission flag F2 is set to "1". When the re-energization permission flag F2 is set to “1”, the ECU 10 permits re-energization to the heater 68 and controls energization to the heater 68 to maintain the sensor temperature T at or above the activation temperature Te. Execute. Therefore, step 1
The process of 60 guarantees that the air-fuel ratio feedback control is properly executed based on the output signals of the air-fuel ratio sensors 58 and 60. When the process of step 160 ends, the current routine ends.

On the other hand, in step 158, the execution of the air-fuel ratio feedback control is prohibited by resetting the feedback permission flag F1 to "0". When the processing in step 158 ends, the flow advances to step 162. In step 162, a reference value N0 is obtained from the sensor temperature T by referring to the map shown in FIG.

In step 164 following step 162, it is determined whether or not the engine speed NE exceeds the reference value N0. As a result, if NE> N0 is not satisfied, then in step 166, the re-energization permission flag F
This routine is terminated after re-energizing the heater 68 is prohibited by resetting 2 to “0”.
On the other hand, if NE> α is satisfied in step 164, then, in step 160, the re-energization permission flag F2 is set to “1”, so that the heater 68
After the re-energization of the power supply is permitted, the current routine ends.

As described above, according to the present embodiment, when the engine speed NE exceeds the reference value N0, re-energization of the heater 68 is permitted, so that the discharge power of the vehicle battery 75 can be increased. Accordingly, it is possible to prevent the deterioration of the startability or the instability of the idling operation state. The reference value N
In accordance with the map shown in FIG. 3, 0 is set to N0 so that the higher the sensor temperature T, the smaller the reference value N0 becomes. Can be started again, whereby the air-fuel ratio feedback control can be started early.

In the above embodiment, the rotation speed sensor 62 corresponds to the operating state detecting means described in the claims. The ECU 10 executes the routine shown in FIG. 5, and the preheating means described in the claims executes the processing of steps 100 and 102 in the routine shown in FIG. The stopping means executes step 152 of the routine shown in FIG. 6 so that the sensor temperature detecting means executes steps 162, 164, 160,
And 166, the energization timing setting means described in the claims is realized.

In the above-described embodiment, the sensor temperature T is detected based on the impedance of the sensor element 66. However, the method for obtaining the sensor temperature T is not limited to this, and the method for obtaining the sensor temperature T is based on the heater resistance R. The sensor temperature T may be detected. That is, since the heater resistance R increases as the temperature of the heater 68 increases, the heater temperature may be obtained from the heater resistance R, and the heater temperature may be used as the sensor temperature T.

In the above-described embodiment, the air-fuel ratio is detected by the air-fuel ratio sensors 58 and 60 having a characteristic that the sensor current I continuously changes according to the oxygen concentration.
The present invention is not limited to this. Instead of one or both of the air-fuel ratio sensors 58 and 60, the rich / lean 2
An O ₂ sensor that outputs a step signal may be used. Further, in the above embodiment, the duty amount of the power supply to the heater 68 is controlled. However, the present invention is not limited to this, and the power supply amount may be controlled by changing the current value linearly. In this case, in steps 108 and 110 of the routine shown in FIG. 5, the energizing current may be decreased and increased, respectively.

Furthermore, in the above embodiment, the start timing of re-energizing the heater 68 is set based on the engine speed NE. However, the present invention is not limited to this. For example, a negative pressure sensor for detecting an intake pipe negative pressure is used. And the start timing of re-energization may be set based on the intake pipe negative pressure.

[0044]

As described above, according to the first aspect of the present invention, it is possible to ensure good engine startability and a stable operation state after the engine is started, and to supply the heater of the air-fuel ratio sensor after the engine is started. The energization can be resumed. According to the second aspect of the present invention, it is possible to quickly start energizing the heater within a range in which a good engine startability and a stable operation state after the engine start can be ensured. Thus, the activity of the air-fuel ratio sensor can be recovered at an early stage.

According to the third aspect of the invention, the engine speed can be used as the engine operating state. Furthermore, according to the invention described in claim 4, the sensor temperature can be detected based on the impedance of the air-fuel ratio sensor.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an internal configuration of an air-fuel ratio sensor included in the system of the present embodiment, together with a connection circuit with an ECU.

FIG. 3 is a map showing a relationship between a heater temperature T and a reference value N0.

FIG. 4 (A) is a diagram showing a sensor temperature T from the start of preheating of an air-fuel ratio sensor to the start of an internal combustion engine.
FIG. 6 is a diagram illustrating a time change of the scalar. FIG. 4B is a diagram exemplifying a temporal change in an on / off state of energization to the heater of the air-fuel ratio sensor. FIG. 4C is a diagram illustrating a change over time of the engine speed.

FIG. 5 is a flowchart of a routine executed by an ECU to start preheating of an air-fuel ratio sensor in the embodiment.

FIG. 6 is a flowchart of a routine executed by the ECU to start re-energizing the air-fuel ratio sensor in the embodiment.

[Explanation of symbols]

 Reference Signs List 10 ECU 58, 60 Air-fuel ratio sensor 62 Rotation speed sensor 68 Heater 72 Impedance detection circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Koji Ide 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 2G004 BJ01 BK04 BK10 BL08 BL20 3G301 KA01 KA07 LC10 NA08 NC02 ND13 ND15 ND41 PA01Z PA07Z PA11Z PD05B PD05Z PD13Z PE01Z PF16Z PG01Z PG02Z

Claims (4)

[Claims] 1. A heater control device for controlling energization of a heater provided in an air-fuel ratio sensor provided in an internal combustion engine, comprising: preheating means for energizing the heater before starting the engine; Energization stopping means for stopping energization by the means, operating state detecting means for detecting an engine operating state, and energizing timing setting means for setting energizing start timing to the heater after starting the engine based on the engine operating state. And a heater control device for an air-fuel ratio sensor. 2. The heater control device for an air-fuel ratio sensor according to claim 1, further comprising: a sensor temperature detecting unit that detects a temperature of the air-fuel ratio sensor, wherein the energization timing setting unit includes the engine operating state and the air-fuel ratio. A heater control device for an air-fuel ratio sensor, wherein the energization start timing is set based on a temperature of a sensor. 3. The heater control device for an air-fuel ratio sensor according to claim 1, wherein the engine operation state is an engine speed. 4. The heater control device for an air-fuel ratio sensor according to claim 2, wherein the sensor temperature detecting means detects the temperature of the air-fuel ratio sensor based on the impedance of the air-fuel ratio sensor.