JP2000234548A - Heater control device for air-fuel ratio sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep an activated state of an air-fuel ratio sensor even when the sensor is cooled by exhaust gas after starting an engine, in a heater control device having function for preheating the air-fuel ratio sensor. SOLUTION: Execution of preheating is allowed by opening door, etc., (step 100). Afterward, temperatures T of air-fuel ratio sensors 62, 63 are sensed (step 104). An idling engine speed in first idling is estimated based on water temperature THW (step 106). A target temperature Tc is determined based on the idling engine speed (step 108). In this case, the higher the idling engine speed is, the higher the target temperature TC is set. The sensor temperature T is controlled for the target value TC by duty-controlling current carrying to a heater 68 (steps 110, 112, 114).

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 to the activation temperature. After energization of the heater of the air-fuel ratio sensor is started, a certain period of time is required until the sensor temperature reaches the activation temperature, that is, until the air-fuel ratio feedback control based on the output signal of the air-fuel ratio sensor becomes possible. Needed. Therefore,
2. Description of the Related Art Conventionally, preheating for starting energization of a heater before starting an engine has been performed so that air-fuel ratio feedback control can be started immediately after starting 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 such a method, even at the time of low-temperature start, the sensor temperature can be immediately increased to the activation temperature immediately after the start.

[0004]

At the time of first idling immediately after the start of the internal combustion engine, a higher idling speed is realized by increasing the intake air amount as the engine temperature is lower. When the idle speed increases, the flow rate of the exhaust gas increases, so that the air-fuel ratio sensor is easily cooled by the exhaust gas. Therefore, in order to maintain the active state of the air-fuel ratio sensor even at the time of the first idling, it is necessary to determine the target temperature of the preheating in consideration of the cooling effect of the air-fuel ratio sensor by the exhaust gas. However, in the above-described conventional air-fuel ratio control device, the target temperature for preheating is determined without any consideration regarding cooling by exhaust gas during first idling. For this reason, at the time of low temperature start with a high first idle speed,
It may happen that the air-fuel ratio sensor is excessively cooled by the exhaust gas and the active state of the air-fuel ratio sensor cannot be maintained.

The present invention has been made in view of the above points, and has a heater control device for an air-fuel ratio sensor capable of maintaining the air-fuel ratio sensor at a required temperature regardless of the idle speed after the engine is started. The purpose is to provide.

[0006]

The above object is achieved by the present invention.
A heater control device for controlling energization to a heater provided in an air-fuel ratio sensor provided in an exhaust passage of an internal combustion engine, wherein a preheating means for starting energization to the heater before starting the engine; An exhaust gas amount estimating unit for estimating an exhaust gas amount at the time of starting, and an energizing amount setting unit for setting an energizing amount to the heater by the preheating unit based on the estimated exhaust gas amount. Heater control device for the air-fuel ratio sensor.

According to the first aspect of the present invention, the preheating means starts energizing the heater before starting the engine,
The air-fuel ratio sensor is heated prior to starting the engine. The exhaust gas amount prediction means predicts an exhaust gas amount at the time of starting the engine.
After the engine is started, the preheated air-fuel ratio sensor is cooled to a degree corresponding to the amount of exhaust gas. On the other hand, the power supply amount setting means determines the power supply amount to the heater by the preheating means based on the predicted exhaust gas amount. For this reason, the air-fuel ratio sensor is heated to a temperature according to the degree of cooling by the exhaust gas before the engine is started. Therefore, according to the present invention, the activity of the air-fuel ratio sensor can be maintained after the engine is started, regardless of the degree of cooling of the air-fuel ratio sensor by the exhaust gas.

In this case, the internal combustion engine includes idle control means for controlling an idle speed according to the engine temperature, and the exhaust gas amount predicting means includes an idle control means for controlling the engine speed according to the engine temperature. The exhaust gas amount may be predicted based on the idle speed. In the second aspect of the invention, the idle control means controls the idle speed according to the engine temperature. When the idle speed changes, the amount of exhaust gas also changes accordingly. Therefore, the exhaust gas amount prediction means can predict the exhaust gas amount based on the idle speed according to the engine temperature.

[0009]

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.

The internal combustion engine has a bypass passage 50 that bypasses the throttle valve 46. In the bypass passage 50, an idle speed control valve (hereinafter, referred to as ISCV) 52 is provided. ISCV
52 changes the opening degree according to the drive signal supplied from the ECU 10. When the internal combustion engine is idling, that is, when the throttle valve 46
Is fully closed, the opening of the ISCV 52 (hereinafter referred to as ISC opening) is controlled so that an appropriate amount of air flows through the bypass passage 50.

An air flow meter 54 communicates upstream of the intake pipe 44. The air flow meter 54 outputs a signal corresponding to the flow rate of the air passing through the intake pipe 44 to the 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 54. An air cleaner 5 is provided upstream of the air flow meter 54.
6 are in communication. The outside air filtered by the air cleaner 56 flows into the intake pipe 44.

On the other hand, an exhaust passage 58 communicates with the exhaust port 26 of the internal combustion engine. The exhaust passage 58 is provided with a catalytic converter 60. Catalytic converter 60
Purifies the exhaust gas by reacting hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the exhaust gas. Air-fuel ratio sensors 62 and 63 are disposed upstream and downstream of the catalytic converter 60, respectively. In the present embodiment, the air-fuel ratio sensors 62, 6
Although the configuration of 3 is the same, it may be different.

The internal combustion engine also has a rotation speed sensor 64. The rotation speed sensor 65 outputs a pulse signal to the ECU 10 every time the internal combustion engine rotates by a predetermined crank angle. The ECU 10 detects the rotation speed of the internal combustion engine based on the output signal of the rotation speed sensor 64. The door switch 65 is connected to the ECU 10. The door switch 65 is a switch that is turned on only when the vehicle door is opened. The ECU 10 controls the door switch 6
The door open is detected based on the on / off state of No. 5.

FIG. 2 shows an internal configuration of the air-fuel ratio sensors 62 and 63 together with a connection circuit with the ECU 10. As shown in FIG. 2, the air-fuel ratio sensors 62 and 63 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 72. In this state, the current flowing through the sensor element 66 (hereinafter, referred to as sensor current I) is the temperature of the sensor element 66 (hereinafter, sensor temperature T).
Is higher than a predetermined activation temperature Te (for example, from 650 ° C. to 700 ° C.), it changes according to the oxygen concentration in the exhaust passage 58. A voltage corresponding to the sensor current I is input to the ECU 10, and the oxygen concentration in the exhaust gas, that is, the air-fuel ratio is detected based on the input voltage.

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 resistance value of the heater 68 (hereinafter, referred to as a heater resistance R) based on these signals.

During operation of the internal combustion engine, the ECU 10 controls the amount of electricity 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 temperature that does not damage the sensor element 66. Control. Note that the heater resistance R changes according to the temperature of the heater 68. Therefore, ECU1
0 calculates the temperature of the heater 68 based on the heater resistance R,
This heater temperature is used as the sensor temperature T.

As described above, the sensor temperature T becomes the activation temperature T
In a state where the value is maintained at e or more, the sensor current I changes according to the air-fuel ratio. Therefore, the ECU 10 controls the sensor current I by controlling the amount of current supplied to the heater 68 as described above.
The air-fuel ratio can be detected based on And E
The CU 10 executes an air-fuel ratio feedback control that performs a feedback control of the fuel injection amount based on the air-fuel ratio. In this air-fuel ratio feedback control, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the fuel injection amount is reduced,
In the case of the lean side, the air-fuel ratio is maintained within a predetermined range near the stoichiometric air-fuel ratio by increasing the fuel injection amount. The above-described catalytic converter 60 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 can be effectively removed by the catalytic converter 60. 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 enable the execution of the air-fuel ratio feedback immediately after the start of the internal combustion engine,
When the engine start is expected (for example, when the opening of the vehicle door is detected), the power supply to the heater 68 of the air-fuel ratio sensors 62 and 63 is started before the engine start. Hereinafter, energization of the heater 68 performed before the engine is started is referred to as preheating.

By the way, at the time of cold start of the internal combustion engine, first idle is realized in order to quickly warm up. FIG. 3 is a map illustrating the relationship between the water temperature THW and the idling speed in the first idling. FIG.
As shown in (1), at the time of first idling, as the water temperature THW is lower, the ISC opening is increased and the amount of intake air is increased, so that the idle speed becomes higher.

When the idling speed during the first idling is increased, the flow rate of the exhaust gas flowing through the exhaust passage 58 is increased.
2, 63 are easily cooled by the exhaust gas. The system of this embodiment is characterized in that the preheating target temperature Tc of the air-fuel ratio sensors 62 and 63 is set in consideration of the cooling by the exhaust gas at the first idle.

When the air-fuel ratio sensors 62 and 63 have different configurations and only the air-fuel ratio sensor 62 has a heater 68, preheating is performed only on the air-fuel ratio sensor 62. Become. FIG. 4 shows (A)
For example, the time change of the sensor temperature T after the start of the internal combustion engine is predicted due to the detection of the opening of the vehicle door or the like, and (B) the time change of the on / off state of the preheat of the air-fuel ratio sensors 62 and 63 Is exemplified. FIG.
(A) shows the sensor temperature T for three cases where the idle speed is different (that is, the water temperature THW is different). FIG. 5 shows an example of a map that is referred to when determining the target temperature Tc in preheating based on the predicted idle speed.

As shown in FIG. 4, after the start of the internal combustion engine due to the opening of the door at time t0, the preheating is started, and the sensor temperature T rises toward the target temperature Tc. In this case, as shown in FIG. 5, the target temperature Tc is set higher as the predicted idle speed is higher (ie, as the water temperature THW is lower). It should be noted that the map shown in FIG. 5 shows the idling speed and the air-fuel ratio sensors 62 and 6 corresponding to the exhaust gas amount corresponding to each idling speed.
The relationship with the degree of cooling of No. 3 was obtained, for example, by experimentally obtaining the relationship.

When the cranking start of the internal combustion engine is started at time t1 shown in FIG. 4, the execution of the preheating is ended to prevent the consumption of the vehicle battery 75. As described above, as the idle speed in the first idle is higher, the air-fuel ratio sensor 62,
63 is cooled to a large degree, so that the sensor temperature T
Drops quickly. On the other hand, as described above, the target temperature Tc in the preheat is set higher as the idle speed in the first idle is higher. As a result, even at time t2 when the first idle ends, the sensor temperature T
Is surely maintained at the activation temperature Te or higher.

FIG. 6 shows the ECU 1 for realizing the above functions.
0 is a flowchart of a routine executed. When the routine shown in FIG. 6 is started, first, the process of step 100 is executed. In step 100, it is determined whether the execution of the preheat is permitted. In particular,
In step 100, when the opening of the vehicle door is detected and before the start of the internal combustion engine, that is, when the start of the internal combustion engine is predicted, 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,
Next, the process of step 102 is performed. On the other hand, if the execution of the preheat is permitted in step 100, the process of step 104 is executed next.

In step 102, the air-fuel ratio sensor 62,
Duty ratio H in energization control to heater 68 at 63
When Tduty is set to “0”, energization of the heater 68 is stopped. When the processing of step 102 ends,
This routine is ended. In step 104, the current sensor temperature T is detected.

In step 106, the idle speed at the first idle is predicted based on the water temperature THW by referring to the map shown in FIG. 3, and in step 108, the map shown in FIG. 5 is referred to. The target temperature Tc in preheating is determined based on the predicted idle speed. 3 and 5
May be integrated to create a map indicating the relationship between the water temperature THW and the target temperature Tc, and the target temperature Tc may be directly obtained from the water temperature THW by referring to this map. When the process of step 108 ends, the process proceeds to step 110.

In step 110, it is determined whether or not the sensor temperature T is higher than the target temperature Tc. As a result, when T> Tc is satisfied, the duty ratio HTduty is reduced by a predetermined value α in step 112, so that the amount of power to the heater 68 is reduced.
This routine is ended. On the other hand, if T> Tc is not satisfied in step 110, then in step 11
In 4, the duty ratio THduty is increased by a predetermined value α, so that the amount of power to the heater 68 is increased, and then the current routine is terminated.

As described above, according to the present embodiment, the target temperature Tc in the preheating is set higher as the idling speed in the first idling is higher, that is, as the degree of cooling of the air-fuel ratio sensors 62 and 63 by the exhaust gas is larger. Accordingly, the sensor temperature T after the engine is started is maintained at the activation temperature Te or higher. Therefore, according to the present embodiment, after the engine is started, the active state of the air-fuel ratio sensors 62 and 63 can be maintained regardless of the level of the first idling speed, whereby the air-fuel ratio feedback control is performed immediately after the engine is started. Can be started reliably.

Further, as described above, the target temperature Tc is set in consideration of the cooling in the first idle, so that the air-fuel ratio sensors 62 and 63 are heated to the minimum necessary range in the preheating, and thereby the vehicle-mounted battery is heated. Unnecessary consumption of power of 70 is prevented. Therefore, according to the present embodiment, good engine startability can be ensured by supplying sufficient power to the starter motor, and
The capacity of the vehicle-mounted battery 70 can be reduced and the life thereof can be improved. In addition, since the load on the alternator that charges the vehicle-mounted battery 70 is reduced by realizing power saving, it is possible to improve the stability of idling operation and improve fuel efficiency.

In the above embodiment, the ECU 10
By executing the routine shown in FIG. 6, the preheating means described in the claims executes the processing in step 106 of the routine shown in FIG. 6, and the exhaust gas amount estimating means described in the claims becomes effective. 6 implements the energization amount setting means by executing the processing of step 108 of the routine shown in FIG. 6, and the ECU 10 sets the idle speed based on the water temperature THW so that the relationship shown in FIG. 3 is realized. By performing the control, the idle control means described in the claims is realized. Further, in the above embodiment, the water temperature THW corresponds to the engine temperature described in the claims.

In the above embodiment, the heater resistance R
The temperature of the heater 68 is obtained based on the above, and this temperature is used as the sensor temperature T. However, the method of obtaining the sensor temperature T is not limited to this. For example, the sensor element 66 has a characteristic that the impedance decreases as the sensor temperature T increases. Therefore, an AC voltage having a predetermined frequency may be applied to the sensor element 66 and the sensor temperature T may be obtained by measuring the impedance of the sensor element 66 from the relationship between the applied voltage and the current.

While the engine is stopped, the oxygen concentration in the exhaust passage 58 is kept constant (a value equal to the oxygen concentration at atmospheric pressure). On the other hand, the sensor current I under the condition where the oxygen concentration is kept constant increases as the sensor temperature T increases until the sensor temperature T reaches the activation temperature. Therefore, based on the sensor current I before the engine starts, the sensor temperature T
Can also be requested.

Further, in the above embodiment, the air-fuel ratio sensors 62 and 63 in which the sensor current I continuously changes according to the air-fuel ratio.
Although the present invention is not limited to this, the present invention is not limited to this, and instead of one or both of the air-fuel ratio sensors 62 and 63, a two-stage signal of rich / lean is output according to the air-fuel ratio. _Two sensors 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 may be controlled by changing the current value linearly. In this case, in steps 110 and 112 of the routine shown in FIG. 5, the energized current may be decreased and increased, respectively.

Further, in the above embodiment, the target temperature Tc in the preheating is determined based on the idle speed, but the present invention is not limited to this.
Heater 6 in preheating based on idle speed
6 may be determined. The change width α of the duty ratio HTduty may be variable based on the difference between the sensor temperature T and the target temperature Tc.

[0038]

As described above, according to the first aspect of the present invention, by setting the amount of energization in preheating based on the amount of exhaust gas at the time of starting the engine, cooling of the air-fuel ratio sensor by the exhaust gas is considered. Thus, the air-fuel ratio sensor can be preheated. Therefore, according to the present invention, the active state of the air-fuel ratio sensor can be maintained after the engine is started, regardless of the idle speed.

According to the second aspect of the present invention, since the idle speed is controlled in accordance with the engine temperature, the amount of exhaust gas can be estimated based on the idle speed in accordance with the engine temperature.

[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 diagram showing an example of a map representing a relationship between a water temperature THW and an idle speed realized in first idle in the present embodiment.

FIG. 4A is a diagram illustrating a time change of the temperature T of the air-fuel ratio sensor after an engine start is predicted for three cases where water temperatures are different. FIG. 4B is a diagram exemplifying an execution state of preheating after an engine start is predicted.

FIG. 5 is a diagram showing an example of a map referred to for determining a target temperature Tc in preheating based on an idle speed in the present embodiment.

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

[Explanation of symbols]

 10 ECU 62, 63 Air-fuel ratio sensor 68 Heater

Continued on the front page (72) Inventor Koji Ide 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 2G004 BJ01 BK04 BL08 BL20 3G084 BA00 CA01 CA02 DA10 FA07 FA10 FA30 FA33 FA38 3G301 HA01 JA13 JA20 KA01 KA05 KA07 MA11 ND41 NE18 PA01Z PA11Z PD04A PD04Z PD05A PD05Z PD09A PD09Z PD13A PD13Z PE01Z PE03Z PE08Z PG02A

Claims (2)

[Claims] 1. A heater control device for controlling energization of a heater included in an air-fuel ratio sensor provided in an exhaust passage of an internal combustion engine, comprising: preheating means for energizing the heater before starting the engine; Exhaust gas amount estimating means for estimating the amount of exhaust gas at the time, and energizing amount setting means for setting an energizing amount to the heater by the preheating means based on the estimated exhaust gas amount. Control device for the air-fuel ratio sensor. 2. The engine according to claim 1, wherein said internal combustion engine includes idle control means for setting an idle speed in accordance with an engine temperature, and said exhaust gas amount estimating means includes means for controlling said exhaust gas based on said idle speed in accordance with said engine temperature. 2. The heater control device for an air-fuel ratio sensor according to claim 1, wherein a gas amount is predicted.