JPH0473099B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a control device for a heater included in an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas of an internal combustion engine, and particularly relates to a control device for a heater provided in an oxygen concentration sensor that detects the oxygen concentration in exhaust gas of an internal combustion engine. The present invention relates to a control device that compensates for sensor temperature.

[Prior art] Conventionally, a three-way catalytic converter has been used as an air-fuel ratio control device for vehicle internal combustion engines to reduce CO,
In order to efficiently purify the three components of HC and NOx,
It is known that an exhaust system is equipped with an oxygen concentration sensor to detect the oxygen concentration in the exhaust gas, and the air-fuel ratio of the internal combustion engine is controlled to be the stoichiometric air-fuel ratio, thereby performing so-called feedback control.

As one of the oxygen concentration sensors used in this type of control device, a zirconia-based limiting current type sensor with a built-in heater for heating the detection element has recently been proposed in Japanese Patent Application Laid-Open No. 57-48648. An oxygen concentration sensor has been developed, and it has become possible to obtain a detection current corresponding to the oxygen concentration.

By the way, since this type of oxygen concentration sensor can obtain a detection current corresponding to the oxygen concentration, it can be used to control the air-fuel ratio to the lean side during low-load engine operation, for example, to improve fuel efficiency. This makes it possible to execute more precise air-fuel ratio control such as lean burn control, but on the other hand, in order to execute such precise air-fuel ratio control, it is necessary to always obtain good detection results using an oxygen concentration sensor. In order to obtain this, it is necessary to heat and activate the detection element using a heater. Furthermore, in order to activate the detection element, it is sufficient to heat the element to a predetermined temperature or higher, but if the element is heated too much, problems such as the heater may break or the detection element may be destroyed may occur. Therefore, it is necessary to control the power supplied to the heater so that the element temperature can be maintained within a predetermined temperature range, for example, 650°C to 750°C.

Therefore, in recent years, as shown in Japanese Utility Model Application Publication No. 112958/1983, electricity is cut off to the heater when the internal combustion engine is at high output or when the exhaust temperature is high, so that the heater and detection element do not become too hot. A heater control device has been proposed that controls the temperature of the exhaust gas to prevent heater disconnection and detection element damage due to a rise in exhaust temperature. No countermeasures have been taken against the drop in element temperature accompanying the drop, and there is a problem in that good detection results cannot be obtained. This means that when the internal combustion engine is running with fuel cut,
Normally, feedback control is not executed and does not pose a problem, but even when the internal combustion engine returns from fuel cut operation and feedback control is restarted, the element temperature has decreased, so air-fuel ratio control cannot be performed properly. Without it, the problem will occur.

[Object of the Invention] Therefore, the present invention provides a control device for a heater for an oxygen temperature sensor that can maintain the temperature of a detection element within a predetermined temperature range at all times even when an internal combustion engine enters fuel cut operation. By the way,
The purpose is to enable more precise air-fuel ratio control of internal combustion engines.

[Configuration of the Invention] As shown in FIG. 1, the configuration of the present invention to achieve the above object is to control a heater provided in an oxygen concentration sensor installed in the exhaust system of an internal combustion engine to detect the oxygen concentration in the exhaust gas. A control device comprising: an output signal detection means for detecting an output signal of the oxygen concentration sensor; an operation state detection means for detecting fuel cut operation of the internal combustion engine; and an operation state detection means for detecting a fuel cut operation of the internal combustion engine. A control means for controlling power supplied to the heater according to an output signal of the oxygen concentration sensor detected by the output signal detection means while fuel cut operation is detected. The gist of this paper is a control device for a heater for an oxygen concentration sensor.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 2 is a schematic system diagram showing a vehicle internal combustion engine (hereinafter abbreviated as engine) in which the oxygen concentration sensor heater control device of this embodiment is mounted and its peripheral devices.

In the figure, 1 is an engine, 2 is a piston, 3 is a cylinder, and 4 is a cylinder head.The exhaust port 5 of each cylinder in the cylinder head 4 has an exhaust manifold 6, and the intake port 7 of each cylinder in the cylinder head 4 has an exhaust manifold 6. Intake manifolds 8 are connected to each other. The intake manifold 8 is also provided with a surge tank 9 to prevent pulsation of intake air.
The surge tank 9 is equipped with an intake pressure sensor 10 that detects the pressure inside the intake manifold 8, that is, the intake pipe pressure Pm.

Next, 11 is a throttle valve that controls the amount of intake air sent to each cylinder via the surge tank 9;
12 is an intake air bypass path that bypasses the throttle valve 11; 13 is an intake air temperature sensor that detects the intake air temperature;
Throttle position sensor 14 includes a throttle valve opening sensor that outputs a signal corresponding to the opening of the throttle valve 11 and an idle switch that is turned on when the engine 1 is idling.
are directly connected. Further, 15 is an oxygen concentration sensor attached to the exhaust manifold 6 and includes a detection element for detecting the oxygen concentration in the exhaust gas and a heater for heating, 16 is a water temperature sensor for detecting the cooling water temperature of the engine 1, and 17 is a water temperature sensor for detecting the engine 1. A distributor 20 applies a high voltage output from an igniter 19 to the spark plug 18 of the engine 1 at a predetermined timing; each represents.

Various detection signals from the intake pressure sensor 10, intake temperature sensor 13, throttle position sensor 14, oxygen concentration sensor 15, water temperature sensor 16, and rotational speed sensor 20 are output to the control circuit 25. Based on the detection signal, fuel injection valve 2
Various control processes such as fuel injection amount control of 6, ignition timing control of the spark plug 18, or heater control of the oxygen concentration sensor 15 are executed.

Next, FIG. 3 shows a block diagram showing the configuration of the above-mentioned control circuit 25. In the figure, 31 is an application power source for applying a predetermined voltage to the detection element 15a of the oxygen concentration sensor 15, 32 is a resistor for detecting the current flowing through the detection element 15a, and 33 is a resistor 32.
34 is an output signal from the amplifier circuit 33, that is, an analog signal corresponding to the oxygen concentration in the exhaust gas;
This is an A/D converter that receives analog signals detected by the intake pressure sensor 10, intake temperature sensor 13, throttle position sensor 14, water temperature sensor 16, etc., and converts them into digital signals. Further, 35 represents a drive circuit which is controlled by the control signal calculated and outputted by the microcomputer 37, and which is driven by the fuel injection valve 26 and injects the desired amount of fuel calculated by the microcomputer 37. This circuit outputs a drive signal to be supplied to the engine 1. Igniter 19 is also microcomputer 3
At 7, the high voltage is controlled to be output to the distributor 17 at a predetermined timing.

Next, 38 is the heater 15b of the oxygen concentration sensor 15.
This is an energization control circuit for controlling the power supplied to the heater, and controls energization from the heater power source 39 in accordance with a control signal from the microcomputer 37. Further, 40 is a heater voltage detection circuit that detects the heater voltage when the heater 15b is energized, and 41 is a heater current detection circuit that similarly detects the heater current.

In the control circuit of this embodiment configured in this way, various controls such as fuel injection amount control, ignition timing control, oxygen concentration sensor heater control, etc. are executed as described above. Next, the heater control of the oxygen concentration sensor, which is the main control process related to the present invention, will be explained in detail according to the control program shown in FIG.

The heater control of the oxygen concentration sensor shown in Fig. 4 is as follows:
It is executed at predetermined time intervals, for example, every 100 [msec.],
The heater 15b is energized from the heater power source 39 by duty control of the heater energization according to the operating state of the engine 1 and the detection result of the oxygen concentration sensor 15.

When the process starts, first, in step 101, the engine rotation speed Ne, intake pipe pressure Pm, detection current Is of the oxygen concentration sensor 15, and idling state of the engine 1 are shown based on signals from the above-mentioned sensors and detection circuits. Idle switch signal Id, heater voltage
Various parameters such as Vh and heater current Ih are read, and the process proceeds to step 102.

In step 102, from the heater voltage Vh and heater current Ih read in step 101, the amount of power when the heater 15b is energized for a predetermined period of time, for example, 100 [msec.], that is, the duty ratio is 100%. The process of calculating the electric power amount A is executed, and the process moves to step 103. In the following, all values of electric energy are expressed as electric energy per 100 [msec.].

In step 103, it is determined whether the engine 1 is currently in fuel cut operation. If the fuel cut operation is in progress, the process moves to step 104, whereas if the fuel cut operation is not in progress, the process moves to step 105. Here, the determination as to whether or not the engine 11 is in fuel cut operation may be performed by checking the fuel injection amount in fuel injection amount control that is processed in a separate routine (not shown); In the example, the idle switch signal Id and engine speed read in step 101 above
Based on Ne, the idle switch signal Id is "ON"
, and the fuel cut condition that the engine rotation speed Ne is equal to or higher than the predetermined rotation speed is satisfied,
It is assumed that it is determined that the engine 1 is in fuel cut operation.

Next, in step 105, which is executed when the engine 1 is not in fuel cut operation, the target power amount B of the heater 15b during fuel cut operation is set to a predetermined value, for example, 35 [w・100 msec.], and the following step is performed. Move to 106.

In step 106, the target power amount C of the heater 15b is determined from a map M or an arithmetic expression as shown in FIG. 5, using the engine speed Ne and intake pipe pressure Pm determined in step 101 as parameters, and The process moves to the next step 107. Here, in the map M, as is clear from Fig. 5, the target power amount C is set in advance using the engine speed Ne and the intake pipe pressure Pm as parameters, but this is because the intake pipe pressure Pm is large. case,
Or if the engine speed Ne is large,
Naturally, the amount of fuel injected into the engine 1 increases, the exhaust temperature rises, and the detection element 15a is heated by the exhaust gas, so the power supplied to the heater 15b is reduced, and on the other hand, when the engine speed Ne is small Alternatively, when the intake pipe pressure Pm is small, the exhaust gas temperature decreases and the detection element cannot be heated, so the power supplied to the heater 15b is set to be increased.

When the target power amount C is determined in step 106,
Next, in step 107, this target power amount C,
Duty ratio 100 found in step 102 above
% electric energy A as a parameter, the duty ratio D for supplying the target electric energy C to the heater 15b is calculated using the following formula D=(C/A)×100.

Then, in step 108, a pulse signal of the duty ratio D determined above is sent to the energization control circuit 38, and a process of controlling the power supplied to the heater 15b is executed.

Here, for example, the amount of electricity A at a duty ratio of 100% is
50 [w・100msec.], and the target power amount determined by the map M from the engine speed Ne and intake pipe pressure Pm is 25 [w・100msec.], then the duty ratio D is 50[%]. , energization control circuit 38
The pulse signal sent out is as shown by the solid line in FIG.

Next, in step 104, which is executed when it is determined in step 103 that the engine 1 is in fuel cut operation, the detected current Is of the oxygen concentration sensor 15 read in step 101 is 25
A determination is made as to whether or not it is equal to or greater than [mA].
And if Is≧25 [mA], the following step 109
Then, the target electric energy B during the fuel cut operation is lowered by 1 [w・100 msec.], and if Is<25 [mA], the target electric energy B is lowered by 1 in the subsequent step 110.
[w・100msec.] Can be raised.

At step 109, the target power amount B is 1 [w・100m
sec.], in the subsequent step 111 it is determined whether the target power amount B is 25 [w・100msec.] or more, and if B≧25 [w・100msec.], the process continues to step 112. , while B < 25 [w・
100msec.], set the target power amount B to 25 [w・100msec.] in step 113, and then step 112.
to move to.

Further, in step 110, the target power amount B is set to 1 [w・
100 msec.], step 114 is executed, and it is determined whether the target power amount B is larger than 45 [w·100 msec.]. and B > 45
[w・100msec.], the process moves to step 115, where the target electric energy B is set to 45 [w・100msec.], and the process moves to step 112;
sec.], the process directly proceeds to step 112.

Then, in step 112, the step 107 is
Similarly, the target power amount B set in the series of steps 109, 111, and 103, or the series of steps 110, 114, and 115, and the target power amount B determined in step 102 above. The duty ratio D for supplying the target power amount B to the heater 15b is calculated from the following equation D=(B/A)×100 using the power amount A at a duty ratio of 100% as a parameter, and the process moves to step 108.

Here, the processing in step 104 is performed by the engine 1.
By determining whether the detected current of the oxygen concentration sensor 15 has become less than the set value (25 [mA] in this case) during the fuel cut operation, the oxygen concentration can be determined as the exhaust temperature decreases during the fuel cut operation. This detects a decrease in the element temperature of the detection element 15a of the sensor 15, that is, a decrease in the detection ability. In addition, as the setting value used for this determination, since the intake air is exhausted as is during fuel cut operation, the current value that flows when the oxygen concentration sensor 15 detects an oxygen concentration of 20% in the air can be used. good. Furthermore, even if the oxygen concentration sensor is of the same type, the detection current may vary within the range of 30 [mA] to 35 [mA] as shown in Figure 7 due to variations in the detection element. In this case, if you set it to the minimum detected current value or a smaller value, for example, the detected current will be 30 [mA] at an oxygen concentration of 20%.
The detection element can be activated to a certain extent without performing unreasonable control such as heating a heater so that a detection current of 35 [mA] flows through the sensor.

Also, if the detected current is higher than the set value, the step will start.
109, step 111, and step 113 are executed, but this series of processing is controlled so that the power supplied to the heater 15b is small and the detected current is above the set value, and the consumption is This suppresses power consumption and prevents disconnection of the heater and destruction of the detection element due to abnormal heating.

Furthermore, the series of processes of step 110, step 114, and step 115, which are executed when the detected current is below the set value, increases the power supplied to the heater to control the detected current to be above the set value, and also When the power amount B is 45 [w・100msec.] or more, it is kept at 45 [w・100msec.] to suppress power consumption and prevent heater disconnection and detection element destruction due to abnormal heating. It is.

As described in detail above, according to the oxygen concentration sensor heater control device of this embodiment, when the engine 1 is not in fuel cut operation, the engine rotational speed Ne
Since the amount of electric power to be supplied to the heater 15b is determined based on the intake pipe pressure Pm and the intake pipe pressure Pm, and the energization control of the heater 15b is executed, the temperature of the detection element 15a can be kept constant. Furthermore, even if the engine 1 enters fuel cut operation, the oxygen concentration sensor 1
Since the detection current Is is controlled to obtain a good detection current Is within a range of low power consumption according to the detection current Is of No. 5, the detection element can be kept activated at all times. Therefore, even when the engine 1 returns from fuel cut operation and enters feedback control, the detection result of the oxygen concentration sensor 15 remains a highly reliable value.
Feedback control can be performed well.

In this embodiment, the above-mentioned step 103 corresponds to the above-mentioned driving state detection means.
The engine speed sensor 20 and the throttle position sensor 15, which respectively detect the engine speed Ne and the idle switch signal Id, which are used when determining fuel cut operation in Examples include the resistor 32 and the amplifier circuit 33 in the control circuit 25. Examples of the control means include the processing of step 104 and steps 109 to 115 which are processed during the fuel cut operation in the control program shown in FIG. 4, and the energization control circuit 38.

Here, in the above embodiment, the target power amount B and the detected current Is used when executing the control program are
Although the currents are expressed as numerical values, the present invention is not limited to these numerical values in any way.

Further, in the embodiment described above, power is controlled by the duty ratio as the energization control of the heater 15b, but in addition to this, for example, the voltage applied to the heater power source may be controlled.

Furthermore, in the above embodiment, when the engine 1 is not in fuel cut operation, the target power amount C of the heater 15b is determined in step 106 from a map using the engine speed Ne and the intake pipe pressure Pm as parameters. However, these engine speeds
In addition to Ne and intake pipe pressure Pm, intake air temperature, intake air amount, etc. may be determined as parameters.

[Effects of the Invention] As described in detail above, in the oxygen concentration sensor heater control device of the present invention, the power supplied to the heater is controlled according to the output signal of the oxygen concentration sensor during fuel cut operation of the internal combustion engine. is configured to do so. Therefore, even when the internal combustion engine enters fuel cut operation and there is no combustion of fuel and the oxygen concentration sensor is cooled, the element temperature can be maintained so that the detection result of the oxygen concentration sensor does not drop.
Feedback control when returning to fuel cut operation can be performed satisfactorily. In addition, the power supplied to the heater during fuel cut operation is not simply increased, but is controlled according to the output signal of the oxygen concentration sensor, which makes it possible to suppress wasteful power consumption. There will be no wire breakage or damage to the detection element.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of the present invention, Figure 2 is a block diagram showing the configuration of the present invention.
The figure is a schematic system diagram showing the engine and its peripheral equipment equipped with the oxygen concentration sensor heater control device according to the embodiment of the present invention, FIG. 3 is a block diagram showing the configuration of the control circuit 25, and FIG. 4 is the control circuit. FIG. 5 is a flow chart showing the heater control process of the oxygen concentration sensor executed in the circuit 25. FIG. 5 is a graph showing the map M. FIG. 6 is a time chart showing the control signal output to the energization control circuit 38. The figure is a graph illustrating variations in detected current due to variations in oxygen concentration sensors. 1...Engine, 6...Exhaust manifold, 1
4... Throttle position sensor, 15... Oxygen concentration sensor, 20... Rotation speed sensor, 25...
Control circuit, 37...Microcomputer, 38
...Electrification control circuit.

Claims (1)

[Scope of Claims] 1. A control device for controlling a heater included in an oxygen concentration sensor installed in an exhaust system of an internal combustion engine to detect oxygen concentration in exhaust gas, the control device detecting an output signal of the oxygen concentration sensor. an output signal detection means; an operation state detection means for detecting a fuel cut operation of the internal combustion engine; and an operation state detection means for detecting a fuel cut operation of the internal combustion engine; A control device for a heater for an oxygen concentration sensor, comprising: a control means for controlling power supplied to the heater according to a detected output signal of the oxygen concentration sensor.