Heater control device and method for exhaust gas sensor

(54) Title: HEATER CONTROL DEVICE AND METHOD FOR EXHAUST GAS SENSOR (30) Unionist Priority: 06/27/2007JP 2007-169284 (73) Holder (s): Toyota Jidosha Kabushiki Kaisha (72) Inventor (es) ): Keiichiro Aoki, Yoshihiro Ide (74) Attorney (s): Dannemann, Siemsen, Bigler & Ipanema Moreira (86) International request: pct iB200800i655de25 / 06/2008 (87) International Publication: wo 2009/001201 of 12/31 / 2008 (57) Summary: heater control device and METHOD FOR EXHAUST GAS SENSOR. The present invention relates to an oxygen concentration sensor (28) which is arranged in an engine exhaust passage. The concentration of alcohol in the fuel used in the internal combustion engine is detected. A target impedance is defined based on the detected alcohol concentration. The actual impedance of a sensor element of the oxygen concentration sensor (28) is detected. The heater output of the exhaust gas sensor is controlled so that the actual impedance becomes equal to the target impedance, whereby the temperature of the sensor element represented by the impedance becomes equal to a target temperature represented by the target impedance.

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ΡΙ0806096-7

Invention Patent Descriptive Report for HEATER CONTROL DEVICE AND METHOD FOR EXHAUST GAS SENSOR.

Field of the Invention

The present invention relates to a heater control device and a heater control method for an exhaust gas sensor.

Background of the Invention

There is a known internal combustion engine in which an exhaust gas sensor that produces an output according to the amount or concentration of a specific component in the exhaust gas, for example, an oxygen concentration sensor that produces an output according to with the oxygen concentration in the exhaust gas, it is arranged in an engine exhaust passage, and the air-fuel ratio is controlled based on the output voltage of the oxygen concentration sensor. However, the exhaust gas sensor output indicated above changes according to the temperature of the sensor element.

To overcome this, the oxygen concentration sensor is provided with an electric heater, which is used to heat the sensor element so that the temperature of the sensor element is maintained at a predetermined target temperature, in a known internal combustion engine ( see Japanese Patent Application Publication No. 2005-2974 (JP-A-2005-2974)). In this technology, the temperature of the sensor element is represented by the impedance of the sensor element. Therefore, a target impedance that represents the target temperature is defined in advance, and the actual impedance of the sensor element is detected, and the output of the electric heater is controlled so that the actual impedance becomes equal to the target impedance.

However, the impedance of the sensor element changes according to the property of the fuel used in the engine. Specifically, in the case where the fuel used in the engine is, for example, gasoline containing alcohol, the impedance of the sensor element changes according to the concentration of alcohol in the fuel. This is because the exhaust gas components vary according to the concentration of alcohol in the fuel and, for example, the electrical resistance of an electrolyte formed from zirconia changes according to the components contained in the exhaust gas. Therefore, even if the actual impedance is maintained at the target impedance, there is a possibility that the actual temperature of the sensor element may not be maintained at the target temperature depending on the property of the fuel used in the engine. This means that the exhaust gas sensor output is not necessarily accurate.

Description of the Invention

A first aspect of the present invention relates to a heater control device for an exhaust gas sensor equipped with a heater arranged in an exhaust passage of an internal combustion engine. This heater control device includes: detection device to detect a property of a fuel used in the internal combustion engine; defining device to define a target impedance based on the detected property of the fuel; and control device for controlling an exhaust gas sensor heater output such that an impedance of an exhaust gas sensor element becomes equal to the defined target impedance. This heater control device is controlled in such a way that a temperature of the sensor element represented by the impedance becomes equal to the target temperature which is represented by the target impedance.

A second aspect of the invention relates to a heater control method for an exhaust gas sensor equipped with a heater arranged in an exhaust passage of an internal combustion engine. This control method includes the step of detecting a property of a fuel used in the internal combustion engine, the step of defining a target impedance of a sensor element of the exhaust gas sensor based on the detected fuel property, and the step of control a heater output from the exhaust gas sensor so that an impedance of the sensor element of the exhaust gas sensor becomes equal to the defined target impedance.

Regardless of the property of the fuel used in the engine, the temperature of the sensor element can be maintained at the target temperature and therefore the accuracy of the exhaust gas sensor output can be maintained.

Brief Description of Drawings

The foregoing and other objectives, resources and additional advantages of the invention will become apparent from the following description of exemplary modalities with reference to the accompanying drawings, in which equal numbers are used to represent equal elements and in which:

Figure 1 is an overview of an internal combustion engine;

Figure 2 is a graph showing the output voltage of an oxygen concentration sensor;

Figure 3 is a diagram showing conceptually the construction of the oxygen concentration sensor;

Figure 4 is a graph showing the Z impedance of a sensor element;

Figure 5 is a diagram showing a graph of the target impedance ZT; and

Figure 6 is a flow chart for performing a sensor temperature control routine.

Detailed Description of Modalities

Figure 1 shows an engine body 1, a cylinder block 2, a cylinder head 3, a piston 4, a combustion chamber 5, an intake valve 6, an intake port 7, an exhaust valve 8, an exhaust port 9 and a spark plug 10. The intake port 7 of each cylinder is connected to a compensation tank 12 by means of a corresponding tube from the intake section tubes 11.0 compensation tank 12 is connected to a filter of air 14 by means of an intake duct 13. An air flow meter 15 and a regulating valve 17 driven by a stepper motor 16 are arranged inside the inlet duct 13. In addition, a fuel injection valve 18 is attached to each inlet port 7. The inlet valves fuel injection 18 are connected to a common rail 19. Common rail 19 is connected to a fuel tank 21 by means of a fuel pump 20 which allows control of the amount of fuel ejection. A fuel pressure sensor 22 is attached to the common rail 19. The amount of ejection by the fuel pump 20 is controlled so that the fuel pressure on the common rail 19 detected by the fuel pressure sensor 22 becomes equal to one target pressure. In addition, a fuel property sensor 23 for detecting a fuel property within the fuel tank 20 is attached to the fuel tank 20.

In one embodiment of the invention, gasoline containing alcohol obtained by mixing gasoline with alcohol is used. In this case, the alcohol concentration in the fuel can vary, for example, from 0% to 100%. Therefore, in this embodiment, a fuel property sensor 23 is formed by an alcohol concentration sensor that produces an output according to the alcohol concentration in the fuel.

On the other hand, the exhaust ports 9 of the cylinders are connected to a catalyst 26 by means of the corresponding section tubes of an exhaust manifold 24 and also by means of a discharge pipe 25. The catalyst 26 is connected to a pipe discharge 27. An exhaust gas sensor 28 is attached to the discharge pipe 25.

The exhaust gas sensor 28 produces an output according to the amount or concentration of a specific component of the exhaust gas. In the embodiment of the invention, the exhaust gas sensor 28 is formed by an oxygen concentration sensor that produces an output voltage according to the oxygen concentration in the exhaust gas. The output voltage V of the oxygen concentration sensor 28 becomes substantially zero (volt) when the oxygen concentration in the exhaust gas is low, and reaches substantially 1.0 (volt) when the oxygen concentration is high, such as shown in figure 2. Incidentally, in figure 2, the output voltage V produced when the air-fuel ratio is a stoichiometric air-fuel ratio is shown as VR. It can be understood in this document that the oxygen concentration in the exhaust gas represents the air-fuel ratio, and that when the output voltage V is substantially zero (volt), the air-fuel ratio is rich, and that when the output V is 1.0 (volt), the air-fuel ratio is poor. In addition, the output voltage V changes sharply as the air-fuel ratio changes through the stoichiometric air-fuel ratio.

Figure 3 shows conceptually the construction of the oxygen concentration sensor 28. As shown in figure 3, the oxygen concentration sensor 28 includes a sensor element 28a and an electric heater 28b. The sensor element 28a produces the output voltage V mentioned above. On the other hand, the electric heater 28b is provided to adjust the temperature of the sensor element 28a. When the output of the electric heater 28b is increased, the temperature of the sensor element 28a increases. When the output of the electric heater 28b is reduced, the temperature of the sensor element 28a decreases.

Referring again to figure 1, an electronic control unit 30 is made up of a digital computer that includes a ROM (read-only memory) 32, a RAM (random access memory)

33, a CPU (central processing unit, or a microprocessor)

34, an input port 35 and an output port 36. They are connected to each other via a bidirectional bus 31. An accelerator pedal 39 is connected to a load sensor 40 that produces an output voltage that is proportional to the amount of accelerator pedal depression 39. The output voltages of the air flow meter 15, the fuel pressure sensor 22, the alcohol concentration sensor 23, the sensor element 28a of the oxygen concentration sensor 28 and the load sensor 40 are supplied to the door input 35 via the corresponding AD 38 converters. In addition, a crank angle sensor 41 produces an output pulse at each rotation of, for example, 30 °, from the crankshaft, and the output pulse is supplied to the input port 35. The CPU calculates engine rotation speed Ne based on the output pulse of crank angle sensor 41. On the other hand, output port 36 is connected to spark plug 10, stepper motor 16, fuel injection 17 and fuel pump 20 by means of the corresponding drive circuits 38.

If the temperature of the sensor element 28a of the oxygen concentration sensor 28 is lower than its activation temperature, there is a possibility that the output voltage of the oxygen concentration sensor 28 may become unstable, that is, the output voltage of the oxygen concentration sensor 28 may fail to accurately represent the oxygen concentration in the exhaust gas. Therefore, according to the embodiment of the invention, the temperature of the sensor element 28a is controlled in order to be maintained at a target temperature that is equal to or greater than the activation temperature.

In this case, the temperature of the sensor element 28a can be represented by the impedance of the sensor element 28a. In the embodiment of the invention, a target impedance that represents the target temperature is defined, and the actual impedance that represents the real temperature of the sensor element 28a is detected, and the output of the electric heater 28b is, for example, controlled by realization, in a manner that the actual impedance becomes equal to the target impedance.

However, the impedance of the sensor element 28a changes according to the alcohol concentration in the fuel. Specifically, as shown in figure 4, since the temperature T of the sensor element 28a is fixed, higher concentrations of AC alcohol in the fuel cause higher Z impedances of the sensor element 28a, and lower concentrations of AC alcohol cause lower Z impedances.

In the embodiment according to the invention, the target impedance Z is changed according to the concentration of CA alcohol in the fuel.

Concretely, as shown in figure 5, the target impedance ZT is defined in order to become higher as the concentration of CA alcohol increases. Consequently, regardless of the concentration of alcohol

AC, the actual temperature of the sensor element 28a can be maintained at the target temperature and therefore the accuracy of the oxygen concentration sensor 28 output can be maintained. The target impedance ZT is pre-stored in ROM 32, in the form of a graph shown in figure 5.

From the previous description, it can be generalized that the property of the fuel used in the internal combustion engine is detected, and a target impedance is defined based on the detected fuel property, and the heater output of the exhaust gas sensor is controlled. so that the impedance of the sensor element of the exhaust gas sensor becomes equal to the target impedance and therefore the temperature of the sensor element represented by the impedance becomes equal to the target temperature which is represented by the target impedance.

Figure 6 shows a sensor temperature control routine of this modality. This routine is executed by an interruption each time it is determined in advance.

Referring to figure 6, first in step 100, the concentration of CA alcohol in the fuel is detected by the alcohol concentration sensor 23. Subsequently, in step 101, a target impedance ZT is derived from the graph shown in figure 5. Subsequently, in step 102, the actual impedance ZA is calculated. Specifically, the voltage and current of the sensor element 28a are detected, and the actual impedance ZA is calculated from the current and voltage. Subsequently, in step 103, the output of the electric heater 28b is controlled so that the actual impedance ZA becomes equal to the target impedance ZT.

In the previous mode, the fuel property is detected by the fuel property sensor. However, several other methods for detecting fuel ownership are also conceivable. For example, the fuel property can be detected based on the deviation from the oscillation center of the air-fuel ratio that occurs when an air-fuel ratio feedback correction is performed. In addition, it is also permissible to detect fuel ownership only once immediately after refueling is performed, and to omit detection of fuel ownership until the next refueling is performed.

In the illustrated mode, the controllers are implemented with general purpose processors. It will be appreciated by those skilled in the art that controllers can be implemented using a single special-purpose integrated circuit (eg ASIC) having a main or central processor section for full system level control, and separate dedicated sections for performing various computations , functions and other different specific processes under the control of the cen10 processor section betrays. Controllers can be a plurality of circuits or other dedicated or integrated programmable electronic devices (for example, physically connected electronic or logic circuits such as circuits of different elements, or programmable logic devices such as PLDs, PLAs, PALs or the like). Controllers can be properly programmed for use with a general purpose computer, for example, a microprocessor, microcontroller or other processing device (CPU or MPU), alone or in conjunction with one or more peripheral data and signal processing devices (for example, integrated circuit). In general, any device or device assembly in which a finite state machine capable of implementing the procedures described in this document can be used as the controllers. A distributed processing architecture can be used for maximum data / signal processing capacity and speed.