JPS58105056A - Controlling method for energization of electric heater for oxygen sensor - Google Patents

Abstract

PURPOSE:To eliminate disconnection of an electric heater, cracking of an oxygen sensor or the like by varying the voltage to be applied to the electric heater in an air-fuel ratio feedback control of the engine employing the oxygen sensor with the electric heater. CONSTITUTION:When the revolutions of the engine detected with a crank angle sensor 29 are below a specified low revolutions, a revolution judging section 44 feeds a logic signal ''0'' to one input side of an exclusive NOR circuit 42 from one output side thereof while feeding a signal ''0'' to one input side of an AND circuit 43 from the other output side thereof. The signal ''0'' is fed to the other input side of the AND circuit 43 when air intake is small. When the revolutions of the engine are below the specified low revolutions, the exclusive NOR circuit 42 moves to a logic value ''1'' on the output side thereof to conduct a transistor 41, causing a Zener diode 33 to be short-circuited. Only a Zener voltage of a Zener diode 32 is applied to the electric heater 3 of an oxygen sensor 1 as lower constant voltage than the specified voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling energization of an electric heating element for an oxygen sensor.

An oxygen sensor detects the oxygen concentration or changes in oxygen concentration in the exhaust gas of an engine that burns a complete mixture of air and fuel, and by feeding back the detection results, it optimizes the mixing ratio of air and soybean. Fuel ratio feedback control technology has advanced in recent years.

FIG. 1 schematically shows a cross section of an oxygen sensor that can be used in this type of technology. on top, first
The pole 4, oxygen ion conductive solid lightning, solute 5, second electrode 6
are laminated and have a structure in which the entire surface is covered with a porous protective layer 7, and the electromotive force corresponding to the difference in oxygen partial pressure on both the surfaces of the solid city and the solute 5 is generated at a value according to the Nernst equation. do. Other oxygen sensors include those using a tubular solid electrolyte and those using an oxide semiconductor whose resistance value changes depending on changes in oxygen partial pressure.

In such an oxygen sensor, the optimum operating temperature of the solid electrolyte 5 and the oxide semiconductor is considerably higher than room temperature;
If only heating by exhaust gas is used, stable operating characteristics cannot be obtained at all times. Therefore, as shown in FIG. 1, stabilization can be achieved by providing an electric heating element 6 for heating. It will be done.

However, in the conventional case, since a predetermined voltage for heating was suddenly applied to the electric heating element 6, the electric heating element 6, which was still cold, was initially subjected to a large amount of heat because its resistance value had a positive temperature characteristic f. If there is a small cross-sectional area or porous part of the electric heating element 3, there is a problem that abnormal heat generation may occur in that area and breakage may occur. This also poses a problem in that large thermal stress may be applied to the oxygen sensor, leading to early deterioration such as cracking.

This invention has been made in view of the above-mentioned conventional problems, and when performing air-fuel ratio feedback control of an engine using an oxygen sensor equipped with an electric heating element for heating, it is difficult to apply an electric current to the electric heating element. By changing the voltage, the purpose is to eliminate problems such as disconnection of the electric heating element and cracking of the oxygen sensor.

The method for controlling energization of an electric heating element for an oxygen sensor according to the present invention includes:
Immediately after the key switch of the vehicle is operated, a voltage lower than the predetermined voltage for heating is applied to the electric heating element, and after a predetermined period of time or when the engine is in a predetermined state, the predetermined heating voltage 1 is applied to the electric heating element. The main feature is that pressure is applied.

Next, the fruit of this invention 7Il! ! The i-mode will be explained.

An example of a control circuit for carrying out the method of controlling current flow of an electric heating element for an oxygen sensor according to the present invention is shown as a block diagram. As shown in FIG. 2, an oxygen sensor section 11, a series-controlled transistor constant voltage circuit 12, It is mainly composed of a DC power supply section 16 and a constant voltage control section 14.

This specific example will be explained with reference to the intake and exhaust system diagram of the engine shown in FIG. In Fig. 3, 15 is an air cleaner;
6 is an intake pipe, 17 is an air cleaner 1', 18 is a throttle valve, 19 is a fuel injection valve, 20 is an engine cylinder, 21 is a piston, 22 is a spark plug, 26 is an exhaust pipe, and 24 is illustrated in FIG. 25 is a contact H converter, 26 is a muffler, 27 is a crankshaft, 28 is a crank pulley, and 29 is a crank angle sensor. . The oxygen sensor section 11 described above has an oxygen sensor 1 with a built-in electric heating element 6, which is shown overlappingly with imaginary lines in FIG. 3 for ease of understanding.

The constant voltage circuit 12U, an NPN transistor 31, and series-connected Zener diodes 62 and 36 are constructed, and the transistor 31 has its emitter connected to the oxygen sensor 1.
Its collector is connected to the DC power source 16, and its base is connected to the cathode of the Zener diode 62 connected in series.

Further, a bias resistor 35'f is connected between the pace and collector of the transistor 610. The anode of the series-connected Zener diode 66 is connected to the electric heating element 6 of the oxygen sensor.
Connected to the other end via ground. Therefore, the electric heating element 6 and the transistor 61 are connected in series. The DC power supply unit 16 includes a DC power supply, for example, a battery 36 and a vehicle key switch 67.
7 is connected to the collector of the transistor 61, and the battery 6 is connected to the collector of the transistor 61.
The cathode of 6 is connected to the anode of a Zener diode 66 and the other end of the electric heating element via ground. Furthermore, the constant voltage control section 14 includes an NPN switching transistor 41, an exclusive NOR circuit 42, an AND circuit 43, and an engine speed determination section 44 into which the output of the crank angle sensor 29 is input.

That is, the emitter and collector of the switching transistor 41 are connected to both ends of the Zener diode 66, respectively, so that the Zener diode 66 can be shunted by the transistor 41, and the pace of the transistor 41 is connected to the output side of the exclusive NOR circuit 42. are doing. Further, one input side of the exclusive NOR circuit 42 is connected to the output side of the AND circuit 46, and the other input side is connected to one output of the engine rotation speed determining section 44, that is, the output side of the low rotation signal S□. ing. Furthermore, one input side of the AND circuit 43 is connected to the detection circuit for k+IS load signal S2, that is, the air flow meter 17, and the other input side is connected to the other output of the engine speed determination section 44, that is, the high rotation signal S.
Connected to the output side of 3.

Furthermore, the input side of the engine speed determination section 44 is connected to the crank angle sensor 29.

To explain the operation of the constant voltage circuit 120 among the circuits configured in this way, the driver operates the key switch 37 to turn it on.
When the battery 66 is in the 1! current flows, causing transistor 61 to conduct, thereby causing series connected Zener diode 32.
The constant voltage determined by the Zener voltage of 63 is the oxygen sensor 1.
is applied to the electric heating element 6.

Now, if the output voltage, that is, the voltage applied to the electric heating element 6 increases, the base voltage of the transistor 610 is constant due to the Zener diodes 32 and 33, so
The emitter voltage becomes -1- negative and the base current decreases,
The collector current decreases further and the collector-emitter resistance of transistor 61 increases, so that the output voltage is held constant. in this way,
By using the constant voltage circuit 12, a constant voltage can be applied to the electric heating element 6.

At this time, if the energization is controlled only by the constant voltage circuit 12, a predetermined heating voltage corresponding to the value required for the desired heating temperature will be applied to the electric heating element 3 at the same time as the key switch 67 is operated. As mentioned above, there is a risk that a large amount of thermal stress will occur in the oxygen sensor 1 due to the rapid temperature rise that occurs in the electric heating element 3, causing cracks, and at the same time, the resistance value will have a positive temperature characteristic. Due to the low temperature, a large amount of current flows rapidly through the electric heating element 6 itself at the beginning of the temperature rise, and as a result, there is a risk that the electric heating element 6 may be disconnected.

Therefore, in the energization control method according to the present invention, immediately after the key switch 67 is operated, a voltage lower than the predetermined heating voltage necessary for heating the electric heating element 6 to a predetermined temperature is applied to the electric heating element 6, and the positive temperature of the resistance value is applied to the electric heating element 6. It prevents a large amount of current from rapidly flowing into the electric heating element 6 having the characteristic metal at the initial stage of temperature rise, and at the same time prevents a sudden temperature rise of the electric heating element 6, thereby preventing disconnection of the electric heating element 6 and oxygen cell 1. Trying to prevent damage from occurring.

Furthermore, if the oxygen sensor 11 is attached to the part of the exhaust pipe 23 close to the engine, the temperature of the exhaust gas will be higher than the optimum heating temperature of the oxygen sensor 1 when the engine is running at high speeds and under high load. As a result, the electric heating element 6 is heated, and the electric heating element 6 itself is heated by electricity and overheated, which may cause a disconnection sound in the electric heating element 3. Therefore, in such a case, it is desirable that the voltage applied to the electric heating element 3 be lower than the predetermined heating voltage necessary for heating to a predetermined temperature.

Therefore, as shown in FIG. 3, in addition to the constant voltage circuit 12, a constant voltage control section 14 is provided. That is, the Zener diode 66 is connected to the switching transistor 4.
When the engine is not started immediately after the key switch 67 is operated, or when cranking at low rotation speed (for example, 30
0 rpm) or when the engine is under high load, the switching transistor 41f becomes conductive and the Zener diode 36 is completely short-circuited, thereby changing the voltage applied to the electric heating element 6 to a predetermined heating value. The value is set to be lower than the voltage.

This will be explained in more detail below.

If the engine speed detected by the crank angle sensor 29 shown in FIG. A logic signal "O# (low rotation signal)" is supplied to one input side of the exclusive NOR circuit 42, and when the rotation speed exceeds a predetermined low rotation speed, a logic signal "'1" is also supplied. .

On the other hand, when the engine speed is below the predetermined high speed v, the AND circuit 46
When the rotation speed exceeds a predetermined high rotation speed, the logic signal ``1'' is supplied to one input side of the
(high rotation signal) is supplied. Further, to the other input side of the AND circuit 43, a high load signal S2, for example, a signal representing the amount of intake air detected by the air flow meter 17 is input. Then, when the amount of intake air is small (for example, when driving downhill), a logic signal "0" is supplied, and when there is a lot of noise (for example, when the engine is running at high speed and under high load), a logic signal "1" is supplied. Full supply.

Therefore, when the engine speed is below a predetermined low speed, both input sides of the exclusive NOR circuit 420 have a logic value of ``0'', and the output side has a logic value of ``1''. The switching transistor 41 becomes conductive as its pace becomes high potential and short-circuits the Zener diode 66. Therefore, in the electric heating element 6 of the oxygen sensor 1, only the Zener voltage and voltage of the Zener diode 62 are higher than the predetermined heating voltage. A low constant voltage is applied.Therefore, since no large current flows through the electric heating element 3, the temperature rises slowly.

Next, when the engine rotation speed exceeds a predetermined low rotation speed and is below a predetermined high rotation speed, one input side of the exclusive NOR circuit 42 becomes a logical value l, and the other input side becomes a logic value l. Since it remains at the logic value "'θ", its output side becomes the logic value "0", which causes the switching transistor 41 to have its pace at a low potential and therefore become non-conductive, as a result of which the heating element 6 has a zener. diode 62
and 63 Zener voltages are applied as the predetermined heating voltage. In this way, even if a high voltage is applied to the electric heating element 6 when the engine speed exceeds a predetermined low rotational speed, the electric heating element 6 has already increased its conductivity at this point and has become a resistor with positive temperature characteristics. Since the value has increased greatly, no large current flows through the electric heating element 6,
Therefore, there is no fear of wire breakage.

Next, when the engine rotational speed exceeds a predetermined high rotational speed and the intake air amount reaches a high speed and high load condition, A
Since both input sides of the ND circuit 43 have a logic value of "1", both input sides of the exclusive NOR circuit 42 also have a logic value of "1".
'', and as a result, the output side becomes the logical value ``l'',
As a result, the switching transistor 41 becomes conductive again as its pace becomes high potential, and the Zener diode 66
short circuit again. Therefore, only the Zener voltage of the Zener diode 62 is applied to the electric heating element 6 as a constant voltage lower than the predetermined voltage for heating, and when the exhaust gas temperature becomes high in a high rotation and high load state, the electric heating element Since heating by B is reduced, damage to the mature body 3 due to overheating can be prevented.

In the control circuit shown in FIG. 3, to give a concrete numerical example, the voltage of the battery 66 is set to t12V, the Zener voltage of both Zener diodes 32 and 33 is set to 5V, and the rotation speed determination section 44 is set to a predetermined low rotation speed. is the idling speed of the engine or a lower speed 3
00 rpm, and the predetermined high rotation speed sound is 4000 rpm. In this setting, when the engine has not started immediately after operating the key switch 67, and even when the engine is started, the rotation speed is 30O
When the rpm is below, the rotation speed of the KFi engine is 40
When the rotation speed exceeds 00 rpm and the intake air amount exceeds a predetermined value, as described above, both inputs of the exclusive NOR circuit 42 become the same, the switching transistor 41 becomes conductive, and the Zener diode 66 is short-circuited, so that the electric heating element Only a voltage of 5V corresponding to the Zener voltage of the Zener diode 62 is applied to the Zener diode 6. On the other hand, if the engine speed is 300
When the speed exceeds 4000 rpm and is below 4000 rpm, the switching transistor 41 becomes non-conductive,
As a result, a voltage equal to the sum of the Zener voltages of 5V from the Zener diodes 62 and 66, that is, a voltage of 10V, is applied to the electric heating element 3, whereby the oxygen sensor 1 is properly heated, and stable air-fuel ratio feedback control is possible. becomes.

-F In the embodiment described above, the engine speed is used to control the conduction and non-conduction of the switching transistor 41, but the present invention is not limited thereto. That is, for example, the switching transistor 41 is always in one state, a timer or a delay circuit is provided in the control circuit for the signal supplied to its base, and these timers or delay circuits are started or operated in conjunction with the key switch 67 to keep the switching transistor 41 in one state for a predetermined period of time. After the switching transistor 4
1 can also be made non-conductive. In addition, for example, a normally closed contact of a relay may be used instead of the switching transistor 41, and the normally closed contact of the relay may be opened after a predetermined time has elapsed due to the operation of a timer or delay circuit, or by the output of the exclusive NOR circuit 42. You can also do it.

Generally, to fully start the engine, first turn on the key switch and then turn on the engine start switch. Therefore, it usually takes about one second for the engine to reach a predetermined state after the key switch is turned on. In addition, the engine is cold immediately after starting, and if the air-fuel ratio is returned to tflllωV in this state, the engine will stop +L.
Therefore, if control is performed to keep the air-fuel ratio i constant for several seconds until the rotation stabilizes, for example, the output of the oxygen sensor will not be used for air-fuel ratio control. Taking these points into consideration, it is preferable that the predetermined time be as short as 1 to several seconds. In particular, if the oxygen sensor is small, such as 4 m x 4 m and 1 piece thick, it is necessary to use 5 mm as an electric heating element.
Use one with W rank. At this time, if a voltage of 5V is applied to the electric heating element and 2 seconds have elapsed, the electric heating element will reach a temperature of about 300℃.
When the voltage is changed from 0°C to 10V, the normal temperature, for example 650°C, is reached in about 2 seconds. Of course, the entire oxygen sensor is 6
It takes about 1 minute to reach 50℃. Therefore, if the voltage is set to a low voltage for one to several seconds, the electric heating element is sufficiently heated, and even if the voltage is changed to 10V thereafter, a large current will not flow.

As explained above, according to the present invention, a voltage lower than the predetermined heating voltage is applied to the electric heating element immediately after the key switch of the vehicle is operated, and after a predetermined time has elapsed or when the engine is in a predetermined state. Since the predetermined voltage for heating is applied to the electric heating element, it is possible to prevent a large current from flowing immediately after the electric heating element is energized, and to prevent disconnection of the electric heating element due to large current and It is possible to prevent damage to the oxygen sensor due to a sudden temperature rise, and after a predetermined period of time or when the engine is operating in a predetermined state, the operation of the oxygen sensor is stabilized and feedback control of the air-fuel ratio is performed effectively. It has excellent effects such as making it possible to

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a structural example of an oxygen sensor applicable to the present invention, and FIG. 2 is a schematic block diagram of an energization control circuit for an electric heating element for an oxygen sensor according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram showing the configuration of the energization control circuit shown in FIG. 2 together with an engine intake/exhaust system diagram. DESCRIPTION OF SYMBOLS 1... Oxygen sensor, 6... Electric heating element, 11... Oxygen sensor part, 12... Constant voltage circuit, 16... DC power supply part, 14... Constant voltage control part, 31.41 ...Transistor, 32.33...Zena diode, 35...
・Bias resistance, 36...Battery, 37...Key switch, 42...Exclusive NOR circuit, 46...A
ND circuit, 44...Engine speed determination section. Patent applicant Nissan Motor Co., Ltd.

Claims (3)

[Claims] (1) When performing air-fuel ratio feedback control of an engine mounted on a vehicle using an oxygen sensor equipped with an electric heating element for heating, immediately after the key switch of the vehicle is operated, the voltage applied to the electric heating element is lower than the predetermined voltage for heating. A method for controlling energization of an electric heating element for an oxygen sensor, characterized in that the predetermined voltage for heating is applied to the electric heating element after a predetermined time has elapsed or when the engine is in a predetermined operating state. (2) Claim No. 1 in which the engine rotational speed is used as a detection element for determining whether or not the engine is operating in a predetermined state.
) A method for controlling energization of an electric heating element for an oxygen sensor according to item 2. (3) The detection factors for whether or not the engine operation is in a predetermined state are the engine rotation speed and the engine intake air amount, and the engine operation is outside the predetermined state when the engine is running at high speed and under high load. A method for controlling energization of an electric heating element for an oxygen sensor according to claim (1).