JPH0530211B2 - - 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 end.

[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 the 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, which is called feedback control.

As one of the oxygen concentration sensors used in this type of control device, a ziconium-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. With the development of an oxygen concentration sensor, 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. 58-112958, electricity is cut off to the heater when the internal combustion engine is at high output or when the exhaust temperature is high, to prevent the heater and detection element from becoming too hot. A heater control device has been proposed to prevent the heater from breaking or the detection element from being destroyed due to a rise in exhaust temperature, but the exhaust temperature may drop when the internal combustion engine enters fuel cut operation. No measures have been taken to deal with the drop in element temperature accompanying this, and there is a problem in that good detection results cannot be obtained.
This is because feedback control is not normally executed when the internal combustion engine is in fuel cut operation, so this 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 still decreases. As a result, the problem arises that air-fuel ratio control cannot be performed satisfactorily.

[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 built into 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 for controlling the internal combustion engine, comprising: a detection means for detecting fuel cut operation of the internal combustion engine; a measurement means for measuring the state of progress since the internal combustion engine started the fuel cut operation; and a control device for detecting the internal combustion engine by the detection means. A heater for an oxygen concentration sensor, comprising: a control means for controlling power supplied to the heater according to a state of progress measured by the measuring means while a fuel cut operation of the heater is being detected. The main point is the control device.

[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 2. 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.], and the energization from the heater power source 39 to the heater 15b is controlled according to the duty ratio according to the operating state of the engine 1.

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 1 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 this embodiment, based on the idle switch signal Id and engine speed Ne read in step 101, the idle switch signal Id is "ON",
When the fuel cut condition that the engine rotation speed Ne is equal to or higher than the predetermined rotation speed is satisfied, it is determined that the engine 1 is in a fuel cut operation.

Next, in step 105, which is executed when the engine 1 is not in a fuel cut operation, the value of a counter B used when the engine 1 is in a fuel cut operation, which will be described later, is set to "0", and the process moves to the following step 106. .

Then, in step 106, the above step 101 is executed.
Engine speed Ne and intake pipe pressure determined by
From a map M1 or an arithmetic expression, for example, as shown in FIG. 5, with Pm as a parameter, the heater 15b
The target power amount C is determined, and the process moves to the following step 107. Here, in map M1, as is clear from Fig. 5, engine speed Ne and intake pipe pressure
The target power amount C is set in advance using Pm as a parameter, but this is based on the intake pipe pressure Pm
is large, or when the engine speed Ne is large, the amount of fuel injected into the engine 1 naturally increases, the exhaust temperature rises, and the detection element 15a can be heated by the exhaust gas, so the heater 15b
While reducing the power supplied to the engine, the engine speed
When Ne is small or when the intake pipe pressure Pm is small, the exhaust gas temperature decreases and the detection element is no longer heated, so the power supplied to the heater 15b is set to be large.

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 heater energization control is executed to control the power supplied to the heater 15b.

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 map M1 from the engine speed Ne and intake pipe pressure Pm is 25 [W・100msec.], then the duty ratio D is 50[%]. , energization control circuit 3
The pulse signal sent to 8 is as shown by the solid line in FIG.

On the other hand, if it is determined in step 103 that the engine 1 is in fuel cut operation, the process moves to step 104 as described above, where the value of counter B is incremented. Processing is done.

Then, the process moves to the next step 109, where a process for determining the target power amount C is executed based on the map M2 which uses the incremented value of the counter B as a parameter, and the process moves to step 107.

Here, since this control process is executed at predetermined time intervals, the value of the counter B is determined by the value of the engine 1.
The target power amount C can be set to a value representing the elapsed time since the start of the fuel cut operation, and in step 109, the target power amount C is set in accordance with the elapsed time of the fuel cut operation. In other words, during fuel cut operation, there is no fuel combustion and the exhaust temperature decreases, so the detection element temperature of the oxygen concentration sensor 15 decreases.
For example, as shown in Figure 7, it has been reported that Ts decreases with the elapsed time of the fuel cut operation, making it impossible to obtain good detection results, so this decrease in the detection element temperature In order to compensate for this, the target power amount C is increased according to the elapsed time of the fuel cut operation as shown in FIG. 8, and the detection element temperature Ts is controlled to be maintained at a constant temperature as shown in FIG. 9, for example. That's what I'm doing. In FIGS. 7 to 9, _t1 indicates the time when the engine 1 enters the fuel cut operation, and represents the time when the value of the counter B becomes "1". Also
_T2 is the point in time when the detection element temperature becomes constant when the fuel cut operation of the engine 1 continues, that is, the target power amount C determined in step 106, for example.
It shows the point in time when the heating of the detection element 15a by the heater 15b at the target power amount C and the cooling of the detection element 15a by the exhaust air are balanced. Furthermore, Fig. 8 shows the increase in the target power amount C according to the elapsed time of the fuel cut operation, and the shaded area in the figure is shown in the above-mentioned map M2, and the target power amount C after time _t2 is shown in the diagram. The electric power amount C is set in advance. In the figure, the target power amount C changes from 25 [W・100msec.] to 45 [W・100msec.] between time t ₁ and time t ₂ .
It is set to increase by 20 [W・100msec.] so that
Correction may be made using Ne.

In this way, when the target power amount C of the engine 1 under fuel cut operation is determined in step 109, the process moves to step 107, where the duty ratio D corresponding to this target power amount C is calculated, and the process proceeds to the next step. At 108, energization control of the heater 15b is executed.

As described in detail above, in the oxygen concentration sensor heater control device of this embodiment, when the engine 1 is not in fuel cut operation, the engine rotational speed is
The target power amount C is determined based on Ne and the intake pipe pressure Pm, and when the engine 1 enters fuel cut operation, the target power amount C is increased according to the elapsed time. As shown in FIG. 9, even when the engine 1 is in fuel cut operation, the detection element temperature can be maintained at a predetermined temperature, and the oxygen concentration sensor 15 can be activated at all times. Therefore, according to this control device, even when the engine 1 returns from fuel cut operation and enters feedback control, the oxygen concentration in the exhaust gas can be detected satisfactorily, and the oxygen concentration can be precisely detected according to the operating state. Air-fuel ratio control can now be executed.

In this embodiment, the above-mentioned detection means corresponds to a rotation speed sensor 20 for detecting the engine rotation speed Ne and the idle signal Id, respectively, which are used in determining the fuel cut operation in step 103. and a throttle position sensor 15, and a counter B as an example of the measuring means. Also, the control means includes a series of processes of step 104, step 109, step 107, and step 108 of the above control program, and the energization control circuit 32.
Examples include.

Here, in the above embodiments, some numerical values are expressed in the maps and the like used when executing the above control program, but the present invention is not limited to these numerical values in any way.

Further, in the above embodiments, the power supply control to the heater is performed by controlling the power based on the duty ratio, but it is also possible to control, for example, the voltage applied to the power source for the heater.

Furthermore, in the above embodiment, a counter B that counts every predetermined time (in this case, 100 [msec.]) is used as a measuring means, and the target power is determined according to the elapsed time after the engine 1 enters the fuel cut operation. In addition to this, for example, the engine speed and ignition signal after engine 1 enters fuel cut operation are accumulated using a counter, etc., and the accumulated amount of engine 1 is set. The target power amount C may be set according to the amount of rotation. Further, when measuring the elapsed time as in the above embodiment, for example, a timer or the like may be used in addition to the counter B, and any device that can measure the elapsed time may be used.

Further, in the above embodiment, during fuel cut operation of the engine 1, the target power amount C is determined from a map using the engine speed Ne and the intake pipe pressure Pm as parameters. In addition to the intake pipe pressure Pm and the intake pipe pressure Pm, the intake air amount and the intake air temperature may also be taken into consideration.

[Effects of the Invention] As detailed above, in the control device for the heater for an oxygen concentration sensor of the present invention, the power supplied to the heater is controlled according to the progress state during fuel cut operation of the internal combustion engine. It is composed of Therefore, even when the internal combustion engine enters fuel cut operation and the oxygen concentration sensor is cooled without combustion of fuel, the element temperature can be maintained so that the detection ability of the oxygen concentration sensor does not deteriorate. , feedback control at the time of return to fuel cut operation can be performed satisfactorily. Also, the power supplied to the heater during fuel cut operation does not simply increase;
Because it gradually increases depending on its progress,
There is no possibility of disconnection of the heater or destruction of the detection element due to abnormal heating of the heater, and no wasted power is consumed.

[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. A flowchart showing the heater control process of the oxygen concentration sensor executed in the circuit 25, FIG. 5 is a graph showing the map M1, FIG. 6 is a time chart showing the control signal output to the energization control circuit 38, and FIG. The figure is a graph showing the change in the detection element temperature Ts during conventional fuel cut operation, Fig. 8 is a graph showing the target electric energy C during fuel cut operation, and Fig. 9 is a graph during fuel cut operation under the control of this embodiment. 3 is a graph showing the detection element temperature Ts of FIG. 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 fuel cut operation of the internal combustion engine. a detecting means; a measuring means for measuring a state of progress since the internal combustion engine enters a fuel cut operation; 1. 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 state of progress of the oxygen concentration sensor. 2. The oxygen concentration sensor heater control device according to claim 1, wherein the elapsed state is an elapsed time, and the measuring means is configured to measure the elapsed time since the internal combustion engine started the fuel cut operation. . 3. The oxygen concentration sensor according to claim 1, wherein the elapsed state is the rotation amount of the internal combustion engine, and the measuring means is configured to measure the rotation amount after the internal combustion engine enters fuel cut operation. Heater control device.