JP4816147B2 - Control device for oxygen sensor heater - Google Patents

Description

  The present invention relates to an oxygen sensor heater control device that controls energization of a heater that activates (heats) an oxygen sensor provided in an exhaust pipe of an internal combustion engine.

  In order to control the air-fuel ratio of an automobile internal combustion engine (engine), the oxygen concentration of exhaust gas discharged from the internal combustion engine is detected by an oxygen sensor, and the air-fuel ratio is feedback-controlled based on the detected oxygen concentration. Has been done.

  The oxygen sensor described above has a sensor main body made of a solid electrolyte or the like, and has an exterior made of ceramics. This oxygen sensor is provided in an exhaust pipe connected to an internal combustion engine, with one end of the sensor facing the inside (exhaust side) of the exhaust pipe and the other end of the sensor facing the outside (atmosphere side) of the exhaust pipe. The electromotive force is generated in accordance with the oxygen concentration difference between the exhaust side and the atmosphere side.

  The sensor voltage output from the oxygen sensor changes suddenly with the theoretical air-fuel ratio as a boundary, and becomes a high voltage on the rich side and a low voltage on the lean side. Therefore, it can be determined from the sensor voltage output from the oxygen sensor whether the air-fuel ratio is larger or smaller than the stoichiometric air-fuel ratio, and thereby the oxygen concentration can be detected. The sensor voltage generated when the air-fuel ratio is the stoichiometric air-fuel ratio is referred to as “stoichiometric voltage” in this specification.

  By the way, the oxygen sensor does not generate a sensor voltage unless the temperature is higher than a certain temperature (activation temperature), and generates a sensor voltage when heated to a temperature higher than the activation temperature by high-temperature exhaust gas or the like.

When an engine having a low engine temperature is started, the temperature of the exhaust gas is low immediately after the start and gradually rises with time. As a result, when the engine is started, a predetermined time is required until the temperature of the oxygen sensor becomes equal to or higher than the activation temperature.
Thus, in a state (period) in which the temperature of the oxygen sensor does not become the activation temperature or higher, the oxygen concentration cannot be detected, and as a result, air-fuel ratio control can be performed in this period (for example, the initial period after the start of startup). Can not.

  Therefore, an oxygen sensor equipped with an electric heater has been developed and put to practical use so that the oxygen sensor temperature can be quickly raised to the activation temperature or higher even when the engine is started so that air-fuel ratio control can be started quickly. Has been. In an oxygen sensor equipped with an electric heater, the oxygen sensor is heated by energizing the electric heater immediately after the engine is started to generate heat, so that the temperature of the oxygen sensor quickly becomes equal to or higher than the activation temperature.

In the oxygen sensor provided with the electric heater, the electric heater is energized even after the temperature of the oxygen sensor becomes equal to or higher than the activation temperature.
The current value supplied to the electric heater is controlled in accordance with, for example, the engine load and the engine speed so that the temperature of the oxygen sensor is maintained at the activation temperature or higher regardless of the operating state of the engine. That is, the current value supplied to the electric heater is increased as the engine load and the engine speed are lower, and the current value supplied to the electric heater is decreased as the engine load and the engine speed are higher.

Here, a conventional example of the oxygen sensor heater control device will be described with reference to FIG.
The oxygen sensor 1 shown in the figure is provided in the exhaust pipe, and generates an internal electromotive force eo corresponding to the air-fuel ratio and has an internal resistance Ri.

As shown in FIG. 6, the internal resistance Ri has a characteristic that it decreases when the temperature of the oxygen sensor 1 is high (for example, 300 ° C. or higher), but increases sharply when the temperature of the oxygen sensor 1 is low. Yes.
The internal electromotive force eo is high on the rich side and low on the lean side.
Since it has such internal resistance characteristics and internal electromotive force characteristics, the sensor voltage Vs output from the oxygen sensor 1 is as shown in FIG.
(1) Below the activation temperature, the internal resistance Ri is extremely large, so it becomes zero.
(2) When the temperature is higher than the activation temperature, the internal resistance Ri decreases, so that a high voltage is obtained in the rich state and a low voltage is obtained in the lean state.

  Therefore, when the temperature of the oxygen sensor 1 is equal to or higher than the activation temperature, the sensor voltage Vs is high in the rich state and low in the lean state, as shown in FIG.

  The oxygen sensor 1 is provided with an electric heater 2. A battery voltage Vb is applied to the electric heater 2, and the ground side of the electric heater 2 is grounded via the switching element 3.

A sensor voltage Vs output from the oxygen sensor 1 is input to an analog input port of an electronic control unit (ECU) 4 via an input resistance r. The sensor voltage Vs input to the analog input port is A / D converted, and the voltage value is taken into the electronic control unit 4 as digital information.
The electronic control unit 4 is also input with information such as engine load, engine speed, and engine coolant temperature.

  The electronic control unit 4 performs duty control of the switching element 3. For this reason, when the energization rate is increased by duty control, the value of the current flowing through the electric heater 2 increases and the amount of heat generated by the electric heater 2 increases. On the other hand, when the energization rate is reduced by duty control, the value of the current flowing through the electric heater 2 is reduced and the amount of heat generated by the electric heater 2 is reduced.

  Conventional duty control of the switching element 3 by the electronic control unit 4 is performed as follows.

  First, the energization rate by the duty control is reduced for a certain time from the start. At the time of start-up, the temperature of the oxygen sensor 1 is generally low. Therefore, it is desired to rapidly raise the temperature of the oxygen sensor 1 by passing a large current through the electric heater 2. The current value flowing through the electric heater 2 is suppressed by decreasing the rate (for example, by setting the energization rate to 30%).

For example, when the engine is started immediately after the engine is temporarily stopped (for example, after 10 seconds), the temperature of the oxygen sensor 1 is high (for example, 400 ° C.). However, once the engine is stopped, water is generated in the exhaust pipe.
In such a state, when a large current is passed through the electric heater 2 and the already high temperature oxygen sensor 1 is further rapidly heated, water in the exhaust pipe adheres to the high temperature oxygen sensor 1. The oxygen sensor 1 which becomes the ceramic exterior will be broken.
Therefore, in order to prevent such a problem, the energization rate by the duty control is deliberately reduced for a certain period from the start to suppress a rapid temperature increase of the oxygen sensor 1.

After a certain period of time has elapsed since the start, the temperature of the oxygen sensor 1 becomes equal to or higher than the activation temperature due to the heating by the electric heater 2 and the heat from the exhaust gas, so that the electronic control unit 4 depends on the engine load and the engine speed. The duty is controlled. That is, the current value supplied to the electric heater 2 is increased by increasing the electric power as the engine load and the engine speed are lower, and the current value supplied to the electric heater 2 by decreasing the current ratio as the engine load and the engine speed are higher. Is controlled to lower.
As a result, the temperature of the oxygen sensor 1 is maintained at the activation temperature or higher regardless of the operating state of the engine.

  The electronic control unit 4 determines whether the exhaust gas is rich or lean based on the sensor voltage Vs, and feedback-controls the air-fuel ratio of the engine.

  In FIG. 9, the horizontal axis indicates the elapsed time after engine start, and the vertical axis indicates the sensor voltage Vs input to the electronic control unit 4. The electronic control unit 4 determines that the rich state is established when the input sensor voltage Vs is equal to or higher than the stoichiometric voltage (0.5 V), and the lean state when the sensor voltage Vs is less than the stoichiometric voltage (0.5 V). It is determined that there is, and the air-fuel ratio of the engine is feedback controlled.

  As shown in FIG. 9, in a certain period I from the engine start, the temperature of the oxygen sensor 1 is lower than the activation temperature, so the sensor voltage Vs is not output. After this period I has elapsed, the temperature of the oxygen sensor 1 becomes equal to or higher than the activation temperature, so that the electronic control unit 4 determines that the sensor is in the rich state when the sensor voltage Vs is greater than the stoichiometric voltage (0.5 V). The engine air-fuel ratio is controlled to the lean side, and when the sensor voltage Vs is smaller than the stoichiometric voltage (0.5 V), it is determined that the engine is lean and the engine air-fuel ratio is controlled to the rich side. The air-fuel ratio is feedback controlled to the stoichiometric air-fuel ratio.

Next, conventional conditions for starting air-fuel ratio control after starting an automobile engine will be described.
The air-fuel ratio control after the engine is started is started when any one of the following conditions (1) to (3) is satisfied.
(1) When the value of the sensor voltage Vs output from the oxygen sensor 1 becomes equal to or higher than the stoichiometric voltage (for example, 0.5 V in the above-described conventional example).
(2) When a predetermined set time has elapsed after the engine is started.
(3) The integrated air amount taken into the engine exceeds a predetermined integrated air amount determined by the engine water temperature at the start.
The air-fuel ratio control once started is continued until the engine key is turned off.

JP 60-235047 A JP-A-5-107299

  By the way, the above-described prior art has the following problems.

[First problem]
When the engine is started when a relatively short time has elapsed after the engine is temporarily stopped (for example, when 10 minutes have elapsed since the engine was stopped), the engine warm-up state is maintained and the engine water temperature is set at 80 Although the temperature is ° C., the oxygen sensor 1 has a small heat capacity, so the element is cooled down to the ambient temperature.

When the engine is warmed up as described above, there is a request to immediately start air-fuel ratio control.
However, as described above, conventionally, since the current value flowing through the electric heater 2 is suppressed for a certain time from the start, the temperature increase of the oxygen sensor 1 is slow, and the temperature of the oxygen sensor 1 is equal to or higher than the activation temperature. It took time to become.
Therefore, the sensor voltage Vs output from the temperature sensor 1 becomes equal to or higher than the stoichiometric voltage, and the air-fuel ratio control is started when the engine is delayed in time.

  In this way, when the engine is restarted while the engine is warmed up, the start timing of the air-fuel ratio control is delayed although it is desired to immediately start the air-fuel ratio control. Moreover, the air-fuel ratio in the engine cylinder varies when the engine is started. As a result, the exhaust gas at the start may be deteriorated.

[Second problem]
Further, when the vehicle travels down a long slope for a long time, engine control for cutting fuel to the engine is performed. When the fuel cut is performed in this way, the temperature of the exhaust gas is lowered. At this time, when the temperature of the outside air is extremely low, the oxygen sensor 1 cools down to below the activation temperature, and the sensor voltage Vs becomes smaller than the stoichiometric voltage (0.5 V).

Since the electronic control unit 4 monitors only the sensor voltage Vs, if the sensor voltage Vs becomes smaller than the stoichiometric voltage (0.5 V), whether the air-fuel ratio has become lean or the oxygen sensor 1 It is not possible to determine whether the temperature of the water has become lower than the activation temperature.
Therefore, even though the air-fuel ratio is actually in a rich state, the oxygen sensor 1 is cooled by the fuel cut and becomes less than the activation temperature, so that the sensor voltage Vs is smaller than the stoichiometric voltage (0.5 V). When this happens, the electronic control unit 4 erroneously determines that the engine is in the lean state and controls the air / fuel ratio of the engine to a richer side, leading to deterioration of exhaust gas.

  As described above, conventionally, when the engine is in a traveling state in which the fuel is cut during a cold time, the air-fuel ratio may not be accurately determined, and as a result, exhaust gas may be deteriorated.

After all, in the prior art, it was impossible to accurately determine whether or not the temperature of the oxygen sensor 1 is higher than the activation temperature. Therefore, in order to prevent the electric heater 2 from cracking at the time of starting, The current value flowing through the electric heater 2 is suppressed for a certain period of time. This has caused the first problem.
In the prior art, since it was not possible to accurately determine whether or not the temperature of the oxygen sensor 1 is equal to or higher than the activation temperature, the second problem has occurred.

  In view of the above prior art, the present invention can accurately determine whether the temperature of the oxygen sensor is equal to or higher than the activation temperature, and the oxygen concentration is rich in a state where the oxygen sensor is equal to or higher than the activation temperature and activated. It is an object of the present invention to provide a control device for an oxygen sensor heater that can accurately determine whether the sensor is lean.

The configuration of the oxygen sensor heater control device of the present invention that solves the above problems is as follows.
An oxygen sensor that is provided in an exhaust pipe connected to the internal combustion engine, and that outputs a voltage according to the oxygen concentration of the exhaust gas when the activation temperature is exceeded,
An electric heater provided in the oxygen sensor, to which a battery voltage is applied and a switching element is connected to the ground side, and a current value flowing by controlling the duty of the switching element is controlled;
An offset voltage application circuit connected to the ground side of the oxygen sensor and applying an offset voltage to the oxygen sensor;
When a sensor voltage that is a voltage output from the oxygen sensor is input with reference to the ground-side potential of the entire circuit, and the input sensor voltage is equal to or higher than the offset voltage, the temperature of the oxygen sensor is equal to or higher than the activation temperature. The current value flowing through the electric heater is adjusted by controlling the duty of the switching element so that the current value flowing through the electric heater is less than the offset voltage. An electronic control unit that controls the duty of the switching element so that a predetermined current value larger than a current value that flows through the electric heater when is equal to or higher than an offset voltage;
It is characterized by having.

The configuration of the oxygen sensor heater control device of the present invention is as follows.
An oxygen sensor that is provided in an exhaust pipe connected to the internal combustion engine, and that outputs a voltage according to the oxygen concentration of the exhaust gas when the activation temperature is exceeded,
An electric heater provided in the oxygen sensor, to which a battery voltage is applied and a switching element is connected to the ground side, and a current value flowing by controlling the duty of the switching element is controlled;
An offset voltage application circuit connected to the ground side of the oxygen sensor and applying an offset voltage to the oxygen sensor;
When a sensor voltage that is a voltage output from the oxygen sensor is input with reference to the ground-side potential of the entire circuit, and the input sensor voltage is equal to or higher than the offset voltage, the temperature of the oxygen sensor is equal to or higher than the activation temperature. The current value flowing through the electric heater is adjusted by controlling the duty of the switching element so that the current value flowing through the electric heater is less than the offset voltage. The duty of the switching element is controlled so that a predetermined current value larger than the current value flowing through the electric heater when the voltage is equal to or higher than the offset voltage, and the input sensor voltage becomes equal to or higher than the offset voltage. Then, feedback control is performed on the air-fuel ratio of the internal combustion engine based on the output of the oxygen sensor. And an electronic control unit,
It is characterized by having.

According to the present invention, the offset voltage is applied to the oxygen sensor by the offset voltage application circuit. For this reason, when the sensor voltage output from the oxygen sensor becomes equal to or higher than the offset voltage, it can be determined that the temperature of the oxygen sensor has become equal to or higher than the activation temperature, and when the sensor voltage is lower than the offset voltage, the temperature of the oxygen sensor becomes the activation temperature. Can be determined to be less than
As a result, since the temperature of the oxygen sensor is lower than the activation temperature, when the sensor voltage is lower than the offset voltage, a large current can be passed through the electric heater to quickly bring the temperature of the oxygen sensor to the activation temperature or higher. . For this reason, the air-fuel ratio control can be started quickly, and the state of the exhaust gas can be well controlled.

  In the present invention, air-fuel ratio control is started when the temperature of the oxygen sensor becomes equal to or higher than the activation temperature and the sensor voltage output from the oxygen sensor becomes equal to or higher than the offset voltage. Therefore, when the sensor voltage becomes equal to or higher than the offset voltage, the detection voltage of the oxygen sensor accurately indicates whether the sensor is in a lean state or a rich state, so that reliable air-fuel ratio feedback control can be performed. it can.

  The best mode for carrying out the present invention will be described below in detail based on examples.

An oxygen sensor heater control apparatus according to Embodiment 1 of the present invention will be described with reference to FIG.
As shown in the figure, the oxygen sensor 11 is provided in an exhaust pipe connected to an engine of an automobile, generates an internal electromotive force eo corresponding to the air-fuel ratio, and has an internal resistance Ri. .

The internal resistance Ri has a characteristic that it decreases when the temperature of the oxygen sensor 11 is high (for example, 300 ° C. or more), but increases sharply when the temperature of the oxygen sensor 11 is low (see FIG. 6).
The internal electromotive force eo is high on the rich side and low on the lean side.

  The output side of the oxygen sensor 11 is connected to the electronic control unit 14 via the input resistor r, and the ground side is connected to the offset voltage application circuit 20.

  The offset voltage application circuit 20 includes voltage dividing resistors R21 and R22 that divide the battery voltage Vb, and a buffer amplifier 23. The offset voltage application circuit 20 applies an offset voltage Voff (for example, 0.5 V) to the ground side of the oxygen sensor 11.

The sensor voltage Vs output from the oxygen sensor 11 is as shown in FIG.
(1) Below the activation temperature, the internal resistance Ri is extremely large, so even if the bias voltage Vb is applied, it becomes zero,
(2) Since the internal resistance Ri is reduced above the activation temperature, a voltage corresponding to the oxygen concentration of the exhaust gas, that is, a high voltage in the rich state, and a low voltage in the lean state.
The voltage values in the rich state and the lean state in FIG. 2 are values obtained by adding the offset voltage Voff (0.5 V) to the voltage values in the conventional rich state and the lean state shown in FIG.

Therefore, when the temperature of the oxygen sensor 1 is equal to or higher than the activation temperature, as shown in FIG. 3, the sensor voltage Vs is a high voltage in the rich state and a low voltage in the lean state.
The voltage values in the rich state and the lean state in FIG. 3 are values obtained by adding the offset voltage Voff (0.5 V) to the voltage values in the conventional rich state and the lean state shown in FIG.

  In FIG. 4, the horizontal axis indicates the elapsed time after engine start, and the vertical axis indicates the sensor voltage Vs input to the electronic control unit 14. The sensor voltage Vs in FIG. 4 has a value obtained by adding an offset voltage Voff (0.5 V) to the conventional sensor voltage Vs shown in FIG.

  The oxygen sensor 11 is provided with an electric heater 12. A battery voltage Vb is applied to the electric heater 12, and the ground side of the electric heater 12 is grounded via the switching element 13.

A sensor voltage Vs output from the oxygen sensor 11 is input to an analog input port of an electronic control unit (ECU) 14 via an input resistance r. The sensor voltage Vs input to the analog input port is A / D converted, and the voltage value is taken into the electronic control unit 14 as digital information.
Information such as engine load, engine speed, engine coolant temperature, and the like is also input to the electronic control unit 14.

When the sensor voltage Vs becomes equal to or higher than the offset voltage Voff (0.5 V), the electronic control unit 14 starts air-fuel ratio feedback control.
The electronic control unit 14 determines that the rich state is present when the input sensor voltage Vs is equal to or higher than the stoichiometric voltage (1.0 V), and the sensor voltage Vs is offset when the sensor voltage Vs is less than the stoichiometric voltage (1.0 V). When the voltage is Voff (0.5 V) or higher, it is determined that the engine is in a lean state, and feedback control of the air-fuel ratio of the engine is executed.

  Furthermore, when the sensor voltage Vs is less than the offset voltage Voff (0.5 V), the electronic control unit 14 determines that the temperature of the oxygen sensor 11 is less than the activation temperature. In this state, air-fuel ratio feedback control is not performed.

  The electronic control unit 14 performs duty control of the switching element 13. For this reason, when the energization rate is increased by duty control, the value of the current flowing through the electric heater 12 increases and the amount of heat generated by the electric heater 12 increases. On the contrary, when the energization rate is reduced by duty control, the value of the current flowing through the electric heater 12 is reduced and the amount of heat generated by the electric heater 12 is reduced.

  The duty control of the switching element 13 in this embodiment by the electronic control unit 14 is performed as follows.

(1) When the voltage value of the sensor voltage Vs is equal to or higher than the offset voltage Voff (0.5 V).
At this time, the electronic control unit 14 sets the current value supplied to the electric heater 12 to, for example, the engine load and the engine speed so that the temperature of the oxygen sensor 11 is maintained at the activation temperature or higher regardless of the operating state of the engine. The duty of the switching element 13 is controlled so as to adjust accordingly.
(2) When the voltage value of the sensor voltage Vs is less than the offset voltage Voff (0.5 V).
At this time, the electronic control unit 14 immediately raises the temperature of the oxygen sensor 11 so that the temperature becomes equal to or higher than the activation temperature. Next, the duty of the switching element 13 is controlled.
This “rapid temperature rise current value” is set to a value larger than the current value that flows through the electric heater 12 when the voltage value of the sensor voltage Vs is equal to or higher than the offset voltage Voff (0.5 V).

[Control action in the first situation]
In this embodiment, when the voltage value of the sensor voltage Vs after starting the engine is less than the offset voltage Voff (0.5 V), the current value supplied to the electric heater 12 is a large sudden temperature increase current determined in advance. Since the duty of the switching element 13 is controlled so as to be a value, the temperature of the oxygen sensor 11 which has been lower than the activation temperature immediately rises to become the activation temperature or higher.

Therefore, when the engine whose engine temperature is low is started, the temperature of the oxygen sensor 11 quickly becomes equal to or higher than the activation temperature. That is, in FIG. 4, the period i from the engine start time to the time when the temperature of the oxygen sensor 11 becomes equal to or higher than the activation temperature is shortened.
Then, after the period i has passed, the sensor voltage Vs becomes equal to or higher than the offset voltage Voff (0.5 V), whereby the air-fuel ratio feedback control can be started.

  Therefore, the period from when the engine in the cold state is started to when the air-fuel ratio feedback control is started (that is, the period i) is shorter than the conventional case. As described above, since the air-fuel ratio feedback control can be started early, when the engine in the cold state is started, the state of the exhaust gas can be controlled well only after a short time has elapsed since the engine was started.

[Control operation in second state]
Further, since the engine is started immediately after the engine is stopped (for example, after 10 seconds), the sensor voltage Vs is set to the offset voltage Voff in a state where the temperature of the oxygen sensor 1 is high (for example, 400 ° C.). (0.5V) or more.
For this reason, since the value of the current flowing through the electric heater 12 is suppressed to a value that allows the temperature of the oxygen sensor 11 to be maintained at the activation temperature or higher, the oxygen sensor 11 is not heated more than necessary. Therefore, even if water generated in the exhaust pipe adheres to the oxygen sensor 11, the oxygen sensor 11 does not break.
Further, since the sensor voltage Vs is equal to or higher than the offset voltage Voff (0.5 V), the air-fuel ratio feedback control is immediately started. As a result, immediately after the engine is restarted, the exhaust gas state can be controlled well. it can.

[Control action in the third state]
In addition, since the engine is started when a relatively short time has elapsed after the engine is temporarily stopped (for example, when 10 minutes have elapsed since the engine was stopped), the engine is kept warm and the engine water temperature is, for example, 80 Although the temperature is ° C., the oxygen sensor 1 has a small heat capacity, so that the sensor voltage is less than the offset voltage Voff (0.5 V) in a state where the element is cooled and is at about the outside air temperature.

  In this way, when the voltage value of the sensor voltage Vs is smaller than the offset voltage Voff (0.5 V), the switching element is set so that the current value supplied to the electric heater 12 becomes a predetermined large sudden temperature increase current value. Since the duty control of 13 is performed, the temperature of the oxygen sensor 11 that has been lower than the activation temperature immediately rises to become the activation temperature or higher. Thus, since the sensor voltage Vs becomes equal to or higher than the offset voltage Voff (0.5 V), the air-fuel ratio feedback control can be started early.

There is a request to immediately start the air-fuel ratio control when the engine warm-up state is maintained, but in this embodiment, such a request can be satisfied, and a short time elapses after the engine is started. Only the state of the exhaust gas can be controlled well.
Therefore, the first problem of the prior art can be solved.

[Control operation in the fourth state]
Further, since the engine is controlled so that the automobile travels down a long hill for a long time and cuts the fuel to the engine, the oxygen sensor 11 is cooled down below the activation temperature. The voltage Vs becomes less than the offset voltage Voff (0.5 V) (state in the period ii in FIG. 4).

Thus, when the voltage value of the sensor voltage Vs becomes less than the offset voltage Voff (0.5 V), switching is performed so that the current value supplied to the electric heater 12 becomes a predetermined large sudden temperature increase current value. Since the duty of the element 13 is controlled, the temperature of the oxygen sensor 11 that has been lower than the activation temperature immediately rises to become the activation temperature or higher. In this way, when the sensor voltage Vs becomes equal to or higher than the offset voltage Voff (0.5 V), the air-fuel ratio feedback control can be restarted early even in a state where engine control for cutting fuel to the engine is performed. it can.
Therefore, the second problem of the prior art can be solved.

[Disconnection detection operation]
The electronic control unit 14 can also detect the disconnection of the electric wire connecting the oxygen sensor 11 and the electronic control unit 14 by monitoring the sensor voltage Vs.
That is, when the temperature of the oxygen sensor 11 is equal to or higher than the activation temperature,
(1) When there is no disconnection, the sensor voltage Vs is always equal to or higher than the offset voltage Voff (0.5 V) regardless of the lean state or the rich state.
(2) When disconnection occurs, the sensor voltage Vs becomes zero.
As described above, when the sensor voltage Vs becomes zero even though the temperature of the oxygen sensor 11 is equal to or higher than the activation temperature, it can be determined that the wire is disconnected.

The block diagram which shows the control apparatus of the heater for oxygen sensors concerning the Example of this invention. The characteristic view which shows the relationship between sensor temperature and sensor voltage of the oxygen sensor in the Example of this invention. The characteristic view which shows the relationship between the air fuel ratio and sensor voltage of the oxygen sensor in the Example of this invention. The characteristic view which shows the relationship between the elapsed time from the engine starting of the oxygen sensor in the Example of this invention, and a sensor voltage. The block diagram which shows the control apparatus of the heater for oxygen sensors concerning a prior art. The characteristic view which shows the relationship between the temperature of an oxygen sensor, and internal resistance. The characteristic view which shows the relationship between sensor temperature and sensor voltage of the oxygen sensor in a prior art. The characteristic view which shows the relationship between the air fuel ratio and sensor voltage of the oxygen sensor in a prior art. The characteristic view which shows the relationship between the elapsed time from the time of engine starting, and sensor voltage of the oxygen sensor in a prior art.

Explanation of symbols

1,11 Oxygen sensor 2,12 Electric heater 3,13 Switching element 4,14 Electronic control unit (ECU)
20 Offset voltage application circuit R21, R22 Voltage dividing resistor 23 Buffer amplifier eo Internal electromotive force Ri Internal resistance Vs Sensor voltage Voff Offset voltage Vb Battery voltage r Input resistance

Claims (2)

An oxygen sensor that is provided in an exhaust pipe connected to the internal combustion engine, and that outputs a voltage according to the oxygen concentration of the exhaust gas when the activation temperature is exceeded,
An electric heater provided in the oxygen sensor, to which a battery voltage is applied and a switching element is connected to the ground side, and a current value flowing by controlling the duty of the switching element is controlled;
An offset voltage application circuit connected to the ground side of the oxygen sensor and applying an offset voltage to the oxygen sensor;
When a sensor voltage that is a voltage output from the oxygen sensor is input with reference to the ground-side potential of the entire circuit, and the input sensor voltage is equal to or higher than the offset voltage, the temperature of the oxygen sensor is equal to or higher than the activation temperature. The current value flowing through the electric heater is adjusted by controlling the duty of the switching element so that the current value flowing through the electric heater is less than the offset voltage. An electronic control unit that controls the duty of the switching element so that a predetermined current value larger than a current value that flows through the electric heater when is equal to or higher than an offset voltage;
An oxygen sensor heater control device comprising: An oxygen sensor that is provided in an exhaust pipe connected to the internal combustion engine, and that outputs a voltage according to the oxygen concentration of the exhaust gas when the activation temperature is exceeded,
An electric heater provided in the oxygen sensor, to which a battery voltage is applied and a switching element is connected to the ground side, and a current value flowing by controlling the duty of the switching element is controlled;
An offset voltage application circuit connected to the ground side of the oxygen sensor and applying an offset voltage to the oxygen sensor;
When a sensor voltage that is a voltage output from the oxygen sensor is input with reference to the ground-side potential of the entire circuit, and the input sensor voltage is equal to or higher than the offset voltage, the temperature of the oxygen sensor is equal to or higher than the activation temperature. The current value flowing through the electric heater is adjusted by controlling the duty of the switching element so that the current value flowing through the electric heater is less than the offset voltage. The duty of the switching element is controlled so that a predetermined current value larger than the current value flowing through the electric heater when the voltage is equal to or higher than the offset voltage, and the input sensor voltage becomes equal to or higher than the offset voltage. Then, feedback control is performed on the air-fuel ratio of the internal combustion engine based on the output of the oxygen sensor. And an electronic control unit,
An oxygen sensor heater control device comprising:

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