JPH0568653B2 - - Google Patents

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 the oxygen concentration of the exhaust gas in this region is measured. This makes it possible to accurately detect the exhaust gas air-fuel ratio. An oxygen sensor for measuring exhaust gas oxygen concentration in such a region includes a gas permeability measurement electrode provided on the side of the exhaust gas to be measured, a gas permeability counter electrode provided on the side of a reference gas having a known oxygen concentration, for example, the atmosphere, and a gas permeability measurement electrode provided on the side of the exhaust gas to be measured. A sensor is used that includes a bottomed cylindrical sensor element made of a solid electrolyte, such as stabilized zirconia, between electrodes. When a current is passed between the electrodes in such an oxygen sensor, oxygen can move in one direction through the electrolyte, but the microporous diffusion resistance layer transports less oxygen than the oxygen delivery capacity of the air permeability measuring electrode. By coating this permeability measuring electrode with , it is possible to maintain its current at approximately a specific value over a certain applied voltage range. This current value is called the limiting current value, and since it changes linearly almost in proportion to the oxygen concentration,
Oxygen concentration can be continuously detected from changes in this current value. On the other hand, in this oxygen sensor,
In order to output a current value proportional to the oxygen concentration of 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.

For this reason, a heater is installed in the center hole of the oxygen sensor to maintain the oxygen sensor at an active temperature. However, when the oxygen sensor temperature exceeds 850℃, that is, the heater temperature exceeds 1100℃, the heater heating element turns off. There are problems such as thermal deterioration and melting.

Therefore, the power supplied to the heater is controlled in relation to operating parameters such as engine speed, load, and vehicle speed. When the power supplied to the heater increases to a value corresponding to a state where the amount of intake air is small,
The heater temperature may exceed 1100℃. Also, during the period when the engine is in a state where the amount of intake air is large,
If the heater is de-energized as soon as the idle switch that detects the idling opening of the throttle valve is turned on, the oxygen sensor temperature will drop below 650°C as the exhaust gas temperature decreases, and the intake air will start from a state where the intake air amount is large. Immediately after transition to a state where the amount of air is small, it becomes difficult to accurately detect oxygen concentration.

DISCLOSURE OF THE INVENTION It is an object of the present invention to avoid overheating of the heater while
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 a transient period.

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 engine intake air flow rate changes from a large state to a small state, the heater is The power supply is switched to the steady value after the change, and the delay time Td is made a function of the air intake flow rate to the engine before the change.

Further, according to the present invention, an oxygen sensor for detecting the oxygen concentration in exhaust gas of the engine is provided in the exhaust system,
In the oxygen sensor heater control device that controls the power supplied to the heater that heats the oxygen sensor in relation to engine operating parameters, when the intake air flow rate changes from a large state to a small state in the engine, A predetermined delay time is set from the time this change occurs.
After Td, the power supplied to the heater is switched to the steady value after the change, and the delay time Td is a function of the duration of the state in which the intake air flow rate of the engine is large before the change.

The higher the engine intake air flow rate before the change in operating conditions, the more the oxygen sensor is sufficiently heated by the exhaust gas, and the heater may be thermally degraded due to the increase in power supply after the change in operating conditions. There is a high risk that the temperature will rise above the point at which such problems (critical temperature) occur. In the present invention, the time at which the power supplied to the heater is switched to a steady value at a low intake air flow rate is a predetermined delay time from the time when the operating state changes.
Since the delay time Td is made a function of the engine intake air flow rate before the change in operating conditions or the duration of the engine intake air flow rate, residual heat from when the intake air flow rate is large still remains. During this period, the increase in the amount of heat generated by the heater is suspended, and the power supplied to the heater is increased only when 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.

Advantageously, the power supplied to the heater is controlled by the duty ratio of the heater drive pulse.

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 conductive 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. A DC voltage is applied between lead wires 18 and 20, which are each covered with a gas-permeable platinum thin film electrode 16 and connected to these electrodes 14 and 16. 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 having an air hole 26 in the center communicating with the atmosphere penetrates the insulating bushing 30 and protrudes into the sensor element 24, and is supplied with power via lead wires 32, 34. be done. The sensor element 24 is housed in a casing 38 having a number of holes 36 and projects into the exhaust pipe through a wall 40 of the exhaust passage, for example the exhaust pipe.

FIG. 2 is a block diagram of an electronically controlled fuel injection device that also serves as a heater control device. An air flow meter 44 is provided in the intake passage to detect the intake air flow rate, a rotational speed sensor 46 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 ROM 5
6, RAM 58, and MUP 60 are connected to each other via address data bus 62. The analog output of the air flow meter 44 is buffer 6.
4 and A/D (analog/digital converter) 6
6 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. Output voltage of battery 72
Vb is sent to the input port 52 via the A/D 74, and the output current of the oxygen sensor 10 is I/V (current/
voltage converter) 76, amplifier 78, and A/D8
0 to input port 52. Battery 72 is connected to ground via heater 28, power transistor 82, and resistor 84. The power transistor 82 receives an on/off control signal from the output port 54, and receives a terminal voltage of the resistor 84.
Vr is sent to input port 52 via A/D 86. Down counter 88 is set with data from output port 54 and resets SR flip-flop 90 when the count decreases to zero.
The Q terminal of the SR flip-flop 90 is connected to the amplifier 92.
is sent to the fuel injection valve 94 of the intake port. The clock pulse of CLOCK96 is MPU60,
It is sent to the down counter 88 and the S terminal of the SR flip-flop 90. down counter 88
Data corresponding to the fuel injection amount is set in , and the fuel injection valve 94 is held open only while the SR flip-flop 90 is set.

FIG. 3 shows the relationship between the intake air flow rate Ga and the basic power Po of the heater 28. 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. The power supplied to the heater 28 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. The voltage Vh applied to the heater 28 also changes as the voltage of the battery 72 changes, but the duty ratio D 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・Ih=(Vb−Vt−Vr)・Vr/Rr Where, Vh: Applied voltage of heater 28 Ih: Applied current of heater 28 Vb: Voltage of battery 72 Vt: Voltage across transistor 82 Vr: Resistor 84 Rr: the resistance value of the resistor 84. Note that Vt and Rr are constant, and Vb and Vr are detected by A/Ds 74 and 86, respectively.

Due to fluctuations in the voltage Vb of the battery 82, even if the duty ratio D is the same, the power supplied to the heater 28 P
changes. Therefore, power supply correction coefficient α=Po/
By correcting the duty ratio D 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 rate Ga and the delay time Td. If the engine has a high intake air flow rate, the intake air flow rate and duration are measured.
In FIG. 5, the range of Ga20g/sec is defined as the range in which the intake air flow rate is large, and this range is divided into regions of Ga1, Ga2, . . . at regular intervals in ascending order of Ga. In each region during the period until the throttle valve reaches the idling opening, that is, until the idle switch of the throttle sensor 48 is turned on.
Measure the total time of Ga1, Ga2, ... (time counter counts Ta1, Ta2, ...).In this way, when the idle switch is turned on, that is, when the engine intake air flow rate changes from high to low. When changing to a certain operating state, Ta1, Ta2,...
The maximum value Tax and the area Gax where the maximum value Tax is located are determined, and the delay time Td is determined from this Gax and Tax. Note that if the region of one Ga, Ga2, ... is defined as a very narrow region, the characteristic line of the delay time Td will be expressed as an almost continuous line as shown in Fig. 5, but for Ga1, Ga2, ... 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 is set to a larger value as Gax is in a larger region of Ga and as Tax is larger, and the delay time Td is set to a larger value as Gax is in a larger region of Ga and as Tax is larger, and the delay time Td is set to a larger value. The time at which the switch is made is set to be a delay time Td after the change time. The oxygen sensor 10 is sufficiently heated by the exhaust gas as Gas and Tax are larger, and the amount of heat generated by the heater 28 is reduced to avoid thermal deterioration of the heater 28 when the idle switch changes from off to on. Need to keep it small. As shown in Figure 5, the delay time Td is set to Gax and
By defining it as a function of Tax, heater 2
It is possible to appropriately delay the increase in the amount of heat generated by heater 8 and prevent thermal deterioration and melting of heater 28. Further, even after the idle switch is turned on from off, the predetermined heat generation of the heater 28 is ensured, so that the oxygen sensor 10 is prevented 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 waveform during a steady period when Ga is large, (b) is an idling period during steady state, and (c) is a waveform during a transient period with a delay time Td from the time when the idle switch is turned on. In the steady periods of (a) and (b), the duty ratio D is defined as shown in Figure 4.
In the case of (c), the steady state value after the change is suspended within the delay time Td.

FIG. 7 is a flowchart of the heater control routine. This routine is executed as a 4msec time interrupt routine. The heater 28 is energized by the count number Dx corresponding to the duty ratio D during the count number Tci corresponding to the period T of the drive pulse (for example, 48 msec). The duty ratio D is calculated for each period of the drive pulse, and if the idle switch is off (step 128), and the intake air flow rate is
If the time change ΔGa of Ga is small (step 132),
The duty ratio D is defined according to FIG.
is set to a value corresponding to Gax in FIG.

Each step in FIG. 7 will be explained in detail. In addition, Tc, Dx as values of the period counter and energization counter,
and Ta1, Ta2, . . . are set to initial values Tci, Dxi 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 RAM5.
Write in 8. In step 102, Ga and the predetermined value Gac are
(In Fig. 5, Gac corresponds to 20 g/sec.) If GaGac, that is, if the period is in a state where the intake air flow rate is large, proceed to step 104, and if Ga<Gac, proceed to step 104. , that is, if the intake air flow rate of the engine is small, the process advances to step 106. In step 104, the counter value Tan corresponding to the Ga area Gan at that time is increased by one. In step 106, it is determined whether the execution conditions for heater control are satisfied, and if the determination is positive, the step is executed.
Proceed to step 108, and if not, proceed to step 118. For example, the cooling water temperature is 60℃ as an execution condition for heater control.
This means that the warm-up operation has already been completed. In step 108, the value Tc of the period counter is decremented by one. In step 110, Tc is compared with 0, and if Tc is 0,
That is, if the period has elapsed, the process proceeds to step 120, and if Tc>0, that is, if the period has not yet elapsed, the process proceeds to step 112. step 112
Then, the value Dx of the energization counter is decreased by 1.
In step 114, Dx is compared with 0, and if Dx is 0, that is, if the energization time of the heater 28 has passed, 0 is assigned to Dx in step 116, and then the heater is turned off in step 118. If >0, that is, if the heater 28 is within the energization time, the process advances to step 150 and the heater 28 is turned on. In step 120, the voltage Vb of the battery 72 and the current Ih of the heater 28 are written into the RAM 58.
Note that Ih is calculated from Vr/Rr. In step 122, the actual power P supplied to the heater 28 is calculated as P=(Vb-
Calculated from Vt−Vr)・Ih. In step 124, a power supply correction coefficient α is calculated from α=Po/P. In step 126, the duty ratio D is calculated from Do·α, and the corresponding value of D is set as Dx. In step 128, it is determined whether the idle switch is on or off. If it is on, that is, if the engine has a small intake air flow rate, the process proceeds to step 130, and if it is off, the process proceeds to step 152.
Proceed to. In step 130, the value of the setting flag F for the delay time Td is determined, and if F=1, that is,
If Td has already been set, the process proceeds to step 140, and if F=0, that is, if Td has not yet been set, the process proceeds to step 132. In step 132, the absolute value of the amount of change ΔGa in the intake air flow rate Ga per predetermined time is compared with a predetermined value C. If |ΔGa|C, that is, it is a transient period, the process proceeds to step 134, and | If ΔGa|<C, proceed to step 150. In step 134, Ta1,
The maximum value Tax of Ta2, ... and its maximum value
Find the area where Tax is hot, Gax. step 136
Now, based on Tax and Gax, calculate the delay time Ta according to the graph in Figure 5, and calculate the delay time Ta as a count number.
Assign the corresponding value of Td to Tdx. In step 138
Set the setting flag F of Td, and set Ta1, Ta2,
Assign 0 to .... In step 140, Tdx is 1
decrease only. In step 142, Tdx is compared with 0, and if Tdx is 0, that is, the delay time is
If Td has already passed, proceed to step 144,
If Tdx>0, that is, if the delay time Td has not yet elapsed, the process advances to step 146. At step 144, the Td setting flag F is reset, and the process proceeds to step 150. In step 146, step 134
The basic power Po corresponding to the Gax obtained in step 1 is obtained according to FIG. 3, and the correction coefficient αx is obtained from Po, the actual power supply P of the heater 28, and the ratio Po/P.
In step 148, the product Do・αx of the basic duty ratio Do and αx corresponding to Gax is assigned to D, and this D
Assign the corresponding value of to Dx. Tc at step 150
Substitute Tci for . In step 152, the heater 28
Turn on.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of an oxygen sensor with a heater, Figure 2
The figure shows a block diagram of an electronically controlled fuel injection system that also serves as a heater control device. Figure 3 is a graph showing the relationship between the intake air flow rate and the basic power of the heater. Figure 4 shows the basic duty of the intake air flow rate and the heater drive pulse. Figure 5 is a graph showing the relationship between intake air flow rate and delay time, Figure 6 is a diagram showing an example waveform of the heater drive pulse, and Figure 7 is a flowchart of the heater control routine. It is. 10...Oxygen sensor, 28...Heater, 44...
...Air flow meter, 48...Throttle sensor, 72...Battery, 82...Power transistor, 84...Resistor.

Claims (1)

[Claims] 1. An oxygen sensor that detects the oxygen concentration in the 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 intake air flow rate of the engine changes from a large state to a small state, the power supplied to the heater is changed to the steady state after the change after a predetermined delay time Td from the time of the change. A control device for an oxygen sensor heater, characterized in that the delay time Td is a function of the intake air flow rate of the engine before the change. 2. An oxygen sensor heater control device that includes an oxygen sensor that detects the oxygen concentration in engine exhaust gas and that controls the power supplied to the heater that heats the oxygen sensor in relation to engine operating parameters. When the intake air flow rate of the engine changes from a large state to a small state, the power supplied to the heater is switched to the steady value after the change after a predetermined delay time Td from the time of this change, and the delay is Time Td
is characterized in that it is a function of the duration of the state in which the intake air flow rate of the engine is large before the change,
Control device for oxygen sensor heater.