JPS60202350A - Control apparatus of heater for oxygen sensor - Google Patents

Abstract

PURPOSE:To hold a proper temp. by avoiding the overheating of a heater, by changing the supply of power to a heater to a steady value after the change in an operative state after a delay time set by using the high rotary speed or the magnitude or succeeding time of an engine before the change in the operative state as a function. CONSTITUTION:An oxygen sensor 10 for detecting the concn. of oxygen in the exhaust gas of an engine is provided and the output thereof is supplied to an electronic control fuel injection computer 50 for controlling a fuel injection valve 94. The sensor 10 is heated by a heater 28. The computer 50 receives the supply of outputs of an air flow meter 44, a rotary speed sensor 46 and a throttle sensor 48 and changes the supply of power to the heater 28 to a steady value after the change in an operative state after a delay time, which is set by using the high rotary speed or the magnitude or succeeding time of the high load of the engine before the change in the operative state as a function, when the engine changes from a high rotary speed or high load to a low rotary speed or low load, and the supply of a current to the heater 28 is controlled by the signal of an output port 54. By this mechanism, the overheating of the heater is avoided and a proper temp. can be held.

Description

TECHNICAL FIELD The present invention relates to a heater control device that heats an oxygen sensor provided in an exhaust system for controlling the air-fuel ratio of an air-fuel mixture supplied to an engine.

Background Art The oxygen concentration and air-fuel ratio of the exhaust gas of an internal combustion engine have a good correlation in the air-fuel ratio that is larger than the stoichiometric air-fuel ratio, that is, in the region of lean mixture, so by measuring the oxygen concentration of the exhaust gas in this region, , the exhaust gas air-fuel ratio can be detected accurately. As an oxygen sensor for measuring the exhaust gas oxygen concentration in such a region, an air permeability measuring electrode provided on the side of the exhaust gas to be measured, a known oxygen
A sensor is used which includes a bottomed cylindrical sensor element consisting of a gas permeable counter electrode placed on the side of a reference gas containing agricultural products, such as the atmosphere, and a solid electrolyte, such as stabilized zirconia, located between the two electrodes. In such an oxygen sensor, when a current is passed between the two electrodes, oxygen can be moved in one direction through the electrolyte, but the micropores allow less oxygen to be delivered than the oxygen delivery capacity of the constant voltage electrode on the ventilated side. By covering this permeability measuring electrode with a diffused resistance layer, its current can be maintained at approximately a certain value over a certain applied voltage range.

This current value is called a limiting current value, and since it changes linearly almost in proportion to the oxygen concentration, the oxygen concentration can be continuously detected from changes in this current value. On the other hand, in order for this oxygen sensor to output a current value proportional to the amount of oxygen in the exhaust gas with a constant applied voltage, it is necessary to heat the sensor element to approximately 650°C or higher and maintain it in an active state. There is.

For this reason, a heater is provided in the center hole of the oxygen sensor to maintain the oxygen sensor at an active temperature, but if the oxygen sensor temperature is 850°C or higher, that is, the heater temperature
If the temperature exceeds 1008C, there is a problem that the heater heating element may be thermally deteriorated or fused.

Therefore, the power supplied to the heater depends on the engine speed, load,
The power supplied to the heater is controlled in relation to vehicle operating parameters such as engine speed and vehicle speed, but when the engine shifts from a high rotational speed or high load state to an idle state in a short period of time, the power supplied to the heater is If the temperature rises to a value above 1100° C., heater 'tii+'+8 may reach a temperature of 1100°C or higher. Furthermore, if the engine is at high rotational speed or high load (fm) and the heater is energized as soon as the idle switch that detects the idling opening of the throttle valve is turned on, the oxygen sensor temperature will decrease as the exhaust gas temperature decreases. 6
It becomes difficult to accurately detect oxygen concentration immediately after the temperature drops to 50° C. or lower and the transition from high rotational speed or high load to low rotational speed or low load occurs.

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a control device for an oxygen sensor heater that can maintain an oxygen sensor within an appropriate temperature range even during transient conditions while avoiding overheating of the heater.

In order to achieve this object, according to the present invention, an oxygen sensor that detects the oxygen concentration in the exhaust gas of the engine is provided in the exhaust system, and the power supplied to the heater that heats the oxygen sensor is adjusted to the operating parameters of the engine. In the related control device for the oxygen sensor heater, when the operating state of the engine changes from high rotational speed or high load to low rotational speed or low load, a predetermined delay time Td is set from the time of this change.
Afterwards, the power supplied to the heater is switched to the steady value after the change in the operating state, and the delay time Td is made a function of the rotational speed of the engine or the magnitude of the load before the change in the operating state.

Further, according to the present invention, an oxygen sensor for detecting the oxygen concentration in the exhaust gas of the engine is provided in the exhaust system, and the oxygen sensor for controlling the power supplied to the heater that heats the oxygen sensor in relation to the operating parameters of the engine. In the sensor heater control device, when the operating state of the idler changes from high rotational speed or high load to low rotational speed or low load, the power supply to the heater is stopped after a predetermined delay time Td from the time of this change. Switching to steady value after change in operating status, delay time Td
is a function of the duration of high engine speed or high load before the change in operating conditions.

The higher the engine rotational speed or load before the change in operating conditions, and the longer the high rotational speed or high load continues, the more the oxygen sensor is sufficiently heated by the exhaust gas, The time at which the power supply is switched to the steady value in wet conditions where the heater is subject to problems such as thermal deterioration due to an increase in the power supply after the change is delayed by a predetermined delay time Td from the time when the operating state changes. and this delay time Td corresponds to the change in operating condition 1) tI
This is a function of the engine rotational speed or the magnitude of the load, or the duration of high engine rotational speed or high load, so the heater generates less heat while residual heat remains at high rotational speed or high load. The increase in the amount of heat generated is suspended, and the power supplied to the heater is increased only after an increase in the amount of heat generated is required. In this way, the heater can be maintained at the activation temperature while preventing the heater from reaching a critical temperature or higher.

Since the engine rotation speed or load has a nearly functional relationship with the intake air flow rate, the engine rotation speed and load size,
Alternatively, high rotational speeds and high loads can be detected from the intake air flow rate.

It is advantageous to control the power supplied to the heater by the duty ratio of the drive pulse to the heater.

Example The present invention will be described with reference to the embodiments shown in the drawings.

FIG. 1 shows an oxygen sensor 10 used in the present invention, in which a bottomed cylindrical oxygen ion ring-transversing solid electrolyte 12 made of zirconia has an air-permeable platinum thin film electrode 14 as an anode and an air-permeable platinum thin film electrode 14 as a cathode on its inner and outer surfaces. These electrodes 14 and 16 are each coated with a breathable platinum thin film electrode 16 of
A DC voltage is applied between the lead wires 18 and 20 connected to the lead wires 18 and 20. A porous ceramic layer 22 is provided on the outer surface of the cathode 16 as a diffusion resistance layer.

In order to heat the sensor element 24 thus formed, a tubular ceramic heater 28 with an air hole 26 in the center leading to the atmosphere projects through the insulating bushing 30 into the sensor element 24 and is supplied with electrical power via leads 32,34. be done. The sensor element 24 is housed in a casing 38 having a number of holes 36 and projects through the wall 40 of the exhaust passageway, for example the exhaust pipe, and into the exhaust pipe.

FIG. 2 is a block diagram of an electronically controlled fuel injection device that also serves as a heater control device. The air flow meter 44 is provided in the intake passage to detect the intake air flow rate, and the rotation speed sensor 4
6 detects the rotational speed of the engine, and a throttle sensor 48 detects the throttle opening. In the electronically controlled fuel injection computer 50, the input port 52, the output port 54, and the R
OM 56 , RAM 58 , and MPU 60 are connected to each other via an address data bus 62 . The analog output of the air flow meter 44 is sent to the buffer 64.
and A/D (Analog/Digital Converter) 66 to input port 52, and the output pulses of rotational speed sensor 46 and throttle sensor 48 are sent to input port 52 via buffers 68 and 70, respectively. The output voltage vb of the battery 72 is sent to the input port 52 via the A/D 74, and the output current of the oxygen sensor 19 is I/V.
(current/voltage converter) 76, amplification n78, and A/D
80 to input port 52. battery 72
is a heater 28, a power transistor 82, and a resistor 84.
connected to ground via. power transistor 8
2 receives an on/off control signal from the output boat 54;
Terminal voltage Vr of resistor 84 is sent to input port 52 via A/D 86. Down counter 88 is output port 5
When the count number decreases to 0, the SR flip-flop 90 is reset. S.R.
The Q terminal of flip-flop 90 is sent via amplifier 92 to fuel injector 94 of the intake boat. CLOCK96
The clock pulse of MPU 60, down counter 88,
and is sent to the S terminal of the SR flip-flop 9o.

Data corresponding to the fuel injection amount is set in the down counter 88, and the fuel injection valve 94 is connected to the SR flip-flop 90.
It remains open only for the period that is set.

Figure 3 shows the intake air flow rate Ga and the basic power PO of the heater 28.
It shows the relationship between As the rotational speed or load of the engine increases, the intake air flow: mGa also increases, so
The rotational speed or load of the engine is a function of the intake air flow rate Ga. Therefore, as the rotational speed or load of the engine increases, that is, as the intake air flow rate Ga increases, the exhaust gas temperature increases, so the basic power PO decreases as the intake air flow rate Ga increases.

FIG. 4 shows the relationship between the intake air flow rate Ga and the basic duty ratio DO of the drive pulse of the heater 28. Heater 2
The power supplied to the power transistor 8 is controlled by turning on and off the power transistor 82 shown in FIG. 2, that is, by the duty ratio of the drive pulse. Although the voltage vh applied to the heater 28 also changes as the voltage of the battery 72 changes, the duty ratio for supplying the basic power PO to the heater 28 when Vh is at the reference voltage is defined as the basic duty ratio DO.

The actual power P supplied to the heater 28 in FIG. 2 is calculated from the following equation.

P: Vh -1h = (Vb-Vt-Vr)・Vr/Rr However, ■h: Applied voltage of heater 28 lh: Applied current of heater 28 ■b: Voltage of battery 72 Note that Vt t Rr is constant, and Vb+ Vr is detected by A/D 74.86 respectively.

Due to fluctuations in the voltage vb of the battery 82, the power P supplied to the heater 28 changes even if the duty ratios are the same. Therefore, the power supply correction coefficient α=P.

/P and correcting the duty ratio to D·α, the power P supplied to the heater 28 can be made accurate.

FIG. 5 shows the relationship between the intake air flow QGa and the delay time Td. When the engine is at high rotational speed or high load, the magnitude and duration of the rotational speed or load is measured. In Figure 5, Ga > 20 g/s
The range of ec is defined as a high rotational speed or high load range, and this range is divided into Ga1+ at regular intervals starting from the lowest Ga value.
Divide into Ga2+... regions. In the period until the throttle valve reaches the idle link opening, that is, until the idle switch of the throttle sensor 48 is turned on, the total time of each region Gal+Ga2+ (count number Tal+Ta2+ of the time calculator) is measured. In this way, when the idle switch is turned on, that is, when the operating state of the engine changes from high rotation speed or high load to low rotation speed or low load, Ta1. T
a2. ...The maximum value Tax and its maximum value Tax
The delay time Td is calculated from this Gax and Tax.

Note that when the region of Ca I + Ga2+... is defined as a very narrow region, the characteristic line of the delay time Td is expressed as an almost continuous line as shown in Fig. 5; Since the region has a predetermined range, if the delay time Td is defined for each region, the actual characteristic line will be expressed in a step-like manner.

The delay time Td increases as Gax is in a larger region of Ga.
Also, the larger Tax is, the larger the value is set, and the heater 2
The time at which the power supplied to the engine 8 is switched to a steady value after a change to a low rotational speed or a low load of the engine is set to be a delay time Td after the change time.

The oxygen sensor 10 is sufficiently heated by the exhaust gas when Gax and Tax are large, and the amount of heat generated by the heater 28 is increased to recover from thermal deterioration of the heater 28 when the idle switch changes from off to on. needs to be kept small. As shown in Figure 5, the delay time Td is
By defining it as a function of x and Tax, it is possible to appropriately delay the increase in the amount of heat generated by the heater 28 and prevent thermal deterioration and melting of the heater 28.

Further, even after the idle switch is turned on from off, the predetermined heat generation of the heater 28 is ensured, thereby preventing the oxygen sensor lO from becoming inactive due to a drop in exhaust gas temperature.

FIG. 6 illustrates the waveform of the drive pulse for the heater 28. (a) is a steady period when Ga is a dog, (b) is an idling period during steady state, and (c) is a waveform in a transient bright period with a delay time Td from the time when the idle switch is turned on. (a).

In the steady period (b), the duty ratio is defined as shown in Fig. 4, but in the steady period (C), the delay time Td
The value within is deferred from reaching the steady value after the change.

FIG. 7 is a flowchart of the heater control routine.

This routine is executed as a 4m5ec time interrupt routine. Drive pulse period T (for example, 48m5e
During the count Tci corresponding to c), the heater 28 is energized by the count Dx corresponding to the duty ratio. The duty ratio is calculated for each period of the drive pulse,
If the idle switch is off (step +28)
, and the time change ΔGa of the intake air flow rate Ga is small (step 132), the duty ratio is defined according to FIG. 4, and the count number T( The duty ratio in IX is set to a value corresponding to Gax in FIG.

Each step in FIG. 7 will be explained in detail. Note that Tc+Dx- is the value of the period counter and the energization counter.

and Tal+Ta2+ are set to initial values Tc i + Dx i and 0, respectively, by an initial setting routine executed immediately after the engine switch is turned on. In step 100, the intake air flow rate Ga is set to RA
Get familiar with M58. In step +02, Ga and the predetermined value G
ac (in Fig. 5, Gac corresponds to 20 g/sec), and if Ga≧Gac, that is, if the engine is in a high rotation speed or high load state, step +
Proceed to step 04, and if Ga < Gac, that is, if the engine is in a low rotational speed or low load state, proceed to step 1.
Proceed to 06. In step 104, the region G of Ga at that time
The counter value Tan corresponding to an is increased by l.

In step 106, it is determined whether or not the conditions for executing heater control are satisfied, and if the determination is positive, the process proceeds to step 108, and if not, the process proceeds to step 118.

For example, the cooling water temperature is 60° as an execution condition for heater control.
C": In other words, the warm-up operation has already been completed. In step 4108, the value Tc of the period counter is decreased by 1. Step month O
Then, compare Tc and 0, and if Tc≦0, that is, if the period has elapsed, proceed to step 120, and Tc>O
If so, that is, if the period has not yet elapsed, the process advances to step 112. In step 112, the value 1)x of the energization counter is decreased by 1. Dx at step +14
and O, and if DX≦0, that is, heater 2
If the energization time of 8 has passed, O is substituted for Dx in step 116, and then the heater is turned off in step 118.
Further, if Dx>0, that is, if the heater 28 is within the energization time, the process advances to step 152 and the heater 28 is turned on. In step 120, the voltage vb of the battery 72
and the current rh of the heater 28 is written into the RAM 58.

Note that Ih is calculated from Vr/Rr. Step +22
Then, the actual power P supplied to the heater 28 is P-(Vb-Vt
-Vr)・rh. In step +24, the digital correction coefficient α is calculated from α=Po/P.

In step +26, the duty ratio is calculated from Do·α, and the corresponding value of D is set as Dx. In step +28, it is determined whether the idle switch is on or off, and if it is on,
That is, if the engine is at low rotation speed or low load, the process proceeds to step 130, and if the engine is off, the process proceeds to step +50. At step +30, the value of the setting flag F for the delay time Td is determined. If F=1, that is, Td has already been set, the process proceeds to step 140, and if F:Ol, that is, Td is still set. If it has not been set, the process advances to step 132. In step +32, the absolute value 1ΔGa of the amount of change ΔGa in the intake air flow uCa per predetermined time
Compare l with a predetermined value C, and if 1ΔGa1≧C,
That is, if it is a transition period, the process advances to step 134, and IΔ
If Cal<C, the process advances to step 150. Step 1
34, the maximum value Tax among Tal, Ta2+...
and the area Gax where the maximum value Tax was. In step 136, the delay time Ta is calculated based on Tax and Cax according to the graph of FIG. 5, and the corresponding value of Td is substituted for Tdx of 4 as the count number. Step 1
In step 38, the Td setting flag F is set, and Ta 1
Assign O to +1' a 2 , +... In step 140, Tdx is decreased by one. Step 14
In step 2, Tdx is compared with 0, and if Tdx≦0, that is, if the delay time Td has already passed, step 1 is executed.
If 'l'dx > Q, that is, if the delay time '1'd has not yet elapsed, the process proceeds to step 44.
Proceed to step 6. At step +44, the Td setting flag F is reset, and the process proceeds to step 150. In step 146, the basic power PO corresponding to Gax obtained in step 134 is determined according to FIG. 3, and a correction coefficient αX is calculated from the ratio Po/P of Po and the actual power supply P of the heater 28. In step 148, the basic duty ratio D corresponding to Gax is
The product DO·αX of O and αX is substituted into D, and the corresponding value of D is substituted into Dx. In step 150, Tc and Tci
Substitute. In step 152, heater 28 is turned on.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an oxygen sensor with a heater, Figure 2 is a block diagram of an electronically controlled fuel injection device that also serves as a heater control device, Figure 3 is a graph showing the relationship between intake air flow rate and basic power of the heater, Figure 4 is a graph showing the relationship between the intake air flow rate and the basic duty ratio of the heater drive pulse, Figure 5 is a graph showing the relationship between the intake air flow rate and delay time, and Figure 6 is the graph showing the relationship between the heater IJIl and the driving pulse. Diagram showing example waveforms, No. 7
The figure is a flowchart of the heater control routine. 10...Oxygen sensor, 28...Heater, 44...
Air flow meter, 48... Throttle sensor, 72
...Battery, 82...Power transistor, 84.
...Repayment of mortgage. Patent applicant Toyota Motor Corporation lr. Agent Patent Attorney Haruka Nakahira □ Intake air flow rate G. Do O204060 [915e. ] □ Intake air flow rate G. Figure 5 Figure 6 □ Time

Claims (1)

[Scope of Claims] l An oxygen sensor that detects the oxygen concentration in exhaust gas of the engine is provided in the exhaust system, and an oxygen sensor that controls the power supplied to the heater that heats the oxygen sensor in relation to the operating parameters of the engine. In the sensor heater control device, when the eight operating states of the engine change from high rotational speed or high load to low rotational speed or low load, the heater is turned on after a predetermined delay time Td from the time of this change. Control of an oxygen sensor heater, characterized in that the supplied power is switched to a steady value after a change in the operating state, and the delay time Td is a function of the rotational speed of the engine or the magnitude of the load before the change in the operating state. Device. 2. Intake air flow 1 based on engine rotational speed and load size
2. The control device according to claim 1, wherein the control device detects from i. 3. The control device according to claim 2, wherein the power supplied to the heater is controlled by a duty ratio of a driving pulse of the heater. 4. An oxygen sensor heater control device that is provided in the exhaust system with an oxygen sensor that detects the oxygen concentration in the exhaust gas of the engine, and that controls the power supplied to the heater that heats the oxygen sensor in relation to the operating parameters of the engine. In, the engine M
When the iE state changes from high rotational speed or high load to low rotational speed or low load, the power supplied to the heater is switched to the steady value after the change in operating condition after a predetermined delay time Td from the time of this change. A control device for an oxygen sensor heater, characterized in that the delay time Td is a function of the duration of high rotational speed or high load of the engine before a change in operating conditions. 5#+! 5. The control device according to claim 4, wherein the high rotational speed and high load of the engine are detected from the intake air flow rate. 6. The control device according to claim 5, wherein the power supplied to the heater is controlled by a duty ratio of a drive pulse for the heater.