JPH07122627B2 - Heater controller for oxygen concentration sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control device for controlling electric power supplied to a heater provided in an oxygen concentration sensor for detecting oxygen concentration.

[Conventional technology]

The heater control device provided in the conventional oxygen concentration sensor detects the resistance value of the heater provided in the oxygen concentration sensor, and is determined according to the state of the internal combustion engine when the resistance value is equal to or more than a predetermined value. Japanese Patent Application Laid-Open No. 60-202348 discloses that the electric power supplied to the heater is reduced and corrected.
Such a configuration utilizes the fact that the relationship between the temperature of the heater and the resistance value of the heater (heater resistance-temperature characteristic) is substantially linear.

[Problems to be solved by the invention]

However, the relationship (characteristics) between the resistance value of the heater and the temperature of the heater varies depending on each product. Even if the resistance value is the same due to the variation in the characteristics as shown in FIG.
The temperature will be different even at 300 ℃.

By the way, in order to continuously detect the oxygen concentration in the exhaust gas, the detection element of the limiting current type oxygen concentration sensor must be kept at a high temperature of 650 ° C. or higher and kept in an active state. In addition, the heater must be controlled at 1120 ° C or lower to prevent deterioration of the heater element.

And because the exhaust temperature is low depending on the engine operating conditions,
There is a region where the heater temperature is 1100 ° C and the oxygen concentration sensor reaches 650 ° C, and there is a region where the exhaust temperature is 650 ° C even when the heater is not energized because the exhaust temperature is sufficiently high.

Therefore, when it is necessary to raise the temperature of the heater to the limit of 1120 ° C., the resistance of the heater exceeds 1120 ° C. even though the temperature of the heater exceeds 1120 ° C. due to the variation of the resistance-temperature characteristic of the heater in the configuration of the above publication. Because the value is low, the calculated power is supplied to the heater without correction,
It causes deterioration of the heater element, or the resistance value exceeds the specified value even though the heater temperature has not reached 1100 ° C, the calculated power is corrected and the heater temperature becomes low. However, there is a problem in that the temperature of the detection element of the oxygen concentration sensor may fall below 650 ° C. and accurate detection may not be possible.

Therefore, the object of the present invention is to compensate for the variations in the heater temperature due to the variations in the resistance-temperature characteristics of the heater described above,
It is an object of the present invention to provide a heater control device for an oxygen concentration sensor that can control the temperature of the heater with high accuracy.

[Means for solving problems]

In order to solve the above problems, in the present invention,
As shown in FIG. 11, a heater provided in an oxygen concentration sensor installed in the exhaust system of the internal combustion engine to detect the oxygen concentration in the exhaust, an operating state detecting means for detecting the operating state of the internal combustion engine, and the operating state detection A basic electric power setting means for setting a basic electric power supplied to the heater in accordance with the operating state detected by the means; a heater resistance value detecting means for detecting the resistance value of the heater; A storage unit for storing the resistance value of the heater detected by the heater resistance value detection unit when the operation state is a predetermined operation state; and a resistance value detected by the heater resistance value detection unit. Target power determination means for correcting the basic power set by the basic power setting means based on the resistance value stored in the storage means and determining the target power to be supplied to the heater. , And the control unit of the oxygen concentration sensor heater, characterized in that and a control unit for controlling electric power supplied to the heater in accordance with the target power determined by said target power determining means.

[Action]

According to the above configuration, the basic electric power of the heater provided in the oxygen concentration sensor is set based on the operating state of the engine, and the resistance value of the heater in which the set basic electric power is stored and the resistance value of the heater at that time are set. And the target power is determined, the power supplied to the heater is controlled according to the target power, and the temperature of the heater is adjusted to a temperature according to the supplied power.

〔Example〕

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

First, FIG. 1 is a schematic system diagram showing a vehicle internal combustion engine (hereinafter abbreviated as engine) equipped with a controller for a heater for an oxygen concentration sensor of the present embodiment and its peripheral devices.

In the figure, 1 is an engine, 2 is a piston, 3 is a cylinder, 4 is a cylinder head, and an exhaust manifold 6 is provided in an exhaust port 5 of each cylinder of the cylinder head 4, and an intake port 7 of each cylinder of the cylinder head 4 is provided. The intake manifolds 8 are connected to each other. Further, the intake manifold 8 is connected to a surge tank 9 for preventing pulsation of intake air, and the surge tank 9 is provided with an intake pressure sensor 10 for detecting the pressure in 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 through the surge tank 9, 12 is a bypass path for intake air that bypasses the throttle valve 11, and 13 is an intake air temperature sensor that detects the intake air temperature. Yes, throttle valve
A throttle position sensor 14 having 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 is directly connected to the throttle valve 11. Also
Reference numeral 15 is an oxygen concentration sensor attached to the exhaust manifold 6 and provided with a detection element for detecting the oxygen concentration in the exhaust gas and a platinum 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. A distributor for applying the high voltage output from the igniter 19 to the ignition plug 18 of the engine 1 at a predetermined timing, 20 is a distributor 17
2, a rotation speed sensor for generating a pulse signal corresponding to the rotation speed of the engine 1, and a vehicle speed sensor 21 for detecting a vehicle speed.

Various detection signals of the intake pressure sensor 10, the intake air temperature sensor 13, the throttle position sensor 14, the oxygen concentration sensor 15, the water temperature sensor 16, the rotation speed sensor 20 and the vehicle speed sensor 21 are input to the control circuit 25, which is then controlled by the control circuit 25. Based on the above detection signals, various control processes such as fuel injection amount control of the fuel injection valve 26, ignition timing control of the spark plug 18, and heater control of the oxygen concentration sensor 15 are executed.

Next, FIG. 2 is a block diagram showing the configuration of the control circuit 25 described above. In the figure, 31 is the detection element 15 of the oxygen concentration sensor 15.
Applied power source for applying a predetermined voltage to a, 32 is a resistor for detecting the current flowing in the detection element 15a, 33 is a resistor 32
An amplifier circuit for amplifying the voltage drop in
34 is an output signal from the amplification circuit 33, that is, an analog signal corresponding to the oxygen concentration in the exhaust gas, an opening pressure sensor of the intake pressure sensor 10, an intake air temperature sensor 13, and a throttle position sensor 14.
An A / D converter that receives an analog signal detected by the water temperature sensor 16, the vehicle speed sensor 21, and the like, and converts it into a digital signal. Further, 35 is based on the signal input through the A / D converter in the microcomputer 37 including the CPU, ROM, RAM and backup RAM and the signal from the rotation speed sensor 20 and the idle switch 14b of the throttle position sensor 14. This is a circuit that represents a drive circuit that is controlled by the control signal that is calculated and output, and that is a circuit that outputs a drive signal for supplying a desired amount of fuel calculated by the microcomputer 37 to the engine 1 to the fuel injection valve 26. . The igniter 19 is also controlled by the microcomputer 37 to output a high voltage to the distributor 17 at a predetermined timing.

Next, 38 is an energization control circuit for controlling the power supplied to the heater 15b of the oxygen concentration sensor 15, which controls energization from the heater power supply 39 according to a control signal of 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 also detects the heater current.

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

The heater control of the oxygen concentration sensor shown in FIG. 3 is executed at predetermined time intervals, for example, every 100 [m sec.], And the power supply 39 for the heater is energized to the heater 15b. This is performed by controlling the duty of the heater energization according to the detection result of.

When the process is started, first in step 301, various parameters such as engine speed Ne, intake pipe pressure Pm, heater voltage Vh, heater current Ih, etc. are read based on signals from the above-mentioned sensors and detection circuits, and then in step 302 Move to.

In step 302, the heater resistance value RH is obtained from the heater voltage Vh and the heater current Ih read in step 301. When platinum is used as the element of the heater 15b as described above, the relationship between the resistance value and the temperature of the heater has a substantially linear relationship as shown in FIG.

Next, in step 303, in step 303, it is checked whether or not the learning value BRH regarding the heater resistance value currently stored in the backup RAM is in a normal state. If it is determined that the state is not normal, step 304
Then, the learning value BRH is set to a predetermined value (4Ω) and then the process proceeds to step 305. When it is determined that the normal state is achieved, the process directly proceeds to step 305. Note that the learning value BRH is checked in step 303, and when the learning value BRH is rewritten previously, the inverted value 1 / BRH of the rewritten learning value BRH is also stored in the backup RAM and this step 303 The normality of the learning value BRH is judged on the basis of both values.

Next, in step 305, the learning value BRH related to the heater resistance value
It is determined whether the learning condition of is satisfied. Here, the establishment of this learning condition means that feedback control is executed based on the output of the detection element 15a of the oxygen concentration sensor 15, the intake pipe pressure Pm is a predetermined value or less, and the rotation speed Ne is a predetermined value. The following conditions have been maintained for 1 minute or longer, and the power supplied to the heater has satisfied all three conditions above the specified value, that is, the heater temperature has been controlled to 1100 ° C. Stable The learning condition is satisfied when the vehicle is in the operating state. It should be noted that the feedback control based on the output of the detection element 15a of the oxygen concentration sensor 15 described above is not started, and it is determined that the warm-up is completed by the engine cooling water temperature (water temperature 70 ° C or higher). , The amount of fuel after startup has been increased, the amount of warm-up has been increased, the amount of fuel has been increased, or the amount of fuel has been accelerated, such as acceleration has not been executed, the fuel cut has not been executed, and the oxygen concentration sensor It is executed when all the conditions that 15 is judged to be active are satisfied.

When it is determined in step 305 that the learning condition is satisfied, the learning value BRH is rewritten to the heater resistance value RH obtained in step 302 in step 306, and the rewritten learning value BRH is stored in the buffer RAM. After letting step
Proceed to 307. By storing in the backup RAM in this way, even if the control circuit 25 is de-energized due to engine stop, the learned value BRH is not erased and can be reflected until the next engine operation. .

If it is determined in step 305 that the learning condition is not satisfied, the process proceeds to step 307 without performing the rewriting process.

In step 307, it is determined whether or not the cold correction condition for the oxygen concentration sensor 15 is satisfied. Here, the cold correction condition is determined by whether it is within 10 minutes from the start of the engine 1, and is determined by another program not shown, and in this step 307, only the determination result is used. To be

When it is determined that the cold correction condition is satisfied, the routine proceeds to 308, where the learning value BRH stored in the backup RAM and the current heater resistance value RH obtained in step 302 are calculated.
The cold power correction amount Pcold is obtained from the map stored in the ROM on the basis of the difference between and. The difference between the heater resistance value RH and the learning correction value BRH stored in this map (BRH
The relationship between −RH) and the cold power correction amount Pcold is set as shown in the characteristic diagram of FIG.

If it is determined that the cold correction condition is not satisfied, the process proceeds to step 309, and the cold power correction amount Pcold is set to zero.

Then, the basic electric energy P _B described later is increased and corrected by this correction amount Pcold in the processing described later to detect the detection element 15 of the oxygen concentration sensor 15 in the cold state immediately after the engine is started.
The a is rapidly heated, and the activation of the detection element 15a is accelerated.
In addition, the difference between the learned value BRH and the current heater resistance value RH (BRH-
Since the correction amount Pcold is set to increase as RH) increases, the power supplied to the heater 15b increases as the heater resistance value RH decreases, that is, the heater temperature decreases, and the detection element 15a rapidly increases. Heated, and the difference (BRH-
When RH) is small, the correction amount Pcold is set to a small value or 0, so it is possible to sufficiently prevent excessive power from being supplied to the heater 15b.

When the processing of step 308 or step 309 is completed, the routine proceeds to step 310, where it is judged whether or not the starting element cooling correction condition is satisfied. Here, the start element cooling correction condition is determined by whether or not it is within 3 minutes from the time when the vehicle speed changes from 0 km / h to a state where the vehicle speed is not 0 km / h, and this judgment is also not shown. It is judged by another program, and only the judgment result is used in this step 310.

Then, when it is determined that the start element cooling condition is satisfied, the process proceeds to step 311, and the learning value BRH stored in the backup RAM and the current heater resistance value RH obtained in step 302 are set. The starting power correction amount Prh is obtained from the map stored in the ROM based on the difference between Note that the relationship between the difference (BRH-RH) between the learning value BRH and the heater resistance value RH stored in this map and the starting power correction amount Prh is as shown in the characteristic diagram of FIG. It is set.

If it is determined that the start element cold correction condition is not satisfied, the process proceeds to step 312, and the start power correction amount P
Set rh to 0.

By the way, the starting power correction amount Prh is set for a predetermined time after the vehicle is started in this way, immediately after the vehicle starts from the idle operation state, the exhaust manifold 6 to which the oxygen concentration sensor 15 is attached and the engine. Even though the temperature of the exhaust gas from the heater is not sufficiently warm, the heater 15 increases as the rotation speed Ne and the intake pipe pressure Pm rise.
In order to prevent the detection element 15a from cooling because the basic power amount P _B described later with respect to b decreases, in the process described later for the basic power amount P _B described later,
The correction amount Prh is used for increasing correction to prevent the element 15a from being cooled.

The determination result of the starting element cooling correction condition used in step 310 was determined based on the vehicle speed, but after the rotation speed Ne exceeds a predetermined value or the idle switch 14b is turned off. Whether or not the correction condition is satisfied may be determined based on whether or not the correction condition is within 3 minutes.

When step 311 or step 312 is completed, step
In step 313, it is determined whether or not the OT correction condition is satisfied. Whether or not the OT correction condition is satisfied is determined by another program routine shown in FIG. 7, and only the determination result is used in step 313.

The program routine shown in FIG. 7 is executed by an interrupt signal every 1 second, and it is determined in step 701 whether the engine is currently being started. If it is being started, the counter COTP is set to 0 in step 702. After clearing, this routine ends.

If it is determined in step 701 that the engine is not being started, it is determined in step 703 whether the current rotation speed Ne is Ne ≧ 3000 rpm. If Ne ≧ 3000 rpm, the counter CO is counted in step 704.
TP is incremented by 1, and if Ne <3000 rpm, the counter COTP is decremented by 1 in step 705.

After the processing of step 704 or 705, it is determined in step 706 whether the counter COTP is COTP ≧ 0. If COTP <0, the COTP is set to 0 in step 707, and then the process proceeds to step 708.
If COTP ≧ 0, the process directly proceeds to step 708. Step 7
In 08, it is judged whether the counter COTP is COTP ≧ 180, and the COT
If P ≧ 180, the COTP is set to 180 in step 709, and then the process proceeds to step 710. If COTP <180, the process proceeds to step 710.

At step 710, it is determined whether the rotation speed Ne is Ne <3000 rpm. If Ne <3000 rpm, the routine proceeds to step 711, where it is determined whether the counter COTP is COTP ≧ 10. And COTP ≧
If 10, proceed to step 712. In step 710, Ne
≧ 3000 rpm or COTP <in step 711
If it is determined to be 10, the process proceeds to step 713. Then, in step 712, the flag in the RAM indicating that the correction condition is satisfied is set and then this routine is terminated. In step 713, the OT correction condition is not satisfied, so the flag in the RAM is set. Reset and finish this routine.

That is, the OT correction condition is satisfied from the time when the rotation speed Ne is lower than 3000 rpm until the counter COTP determined according to the period when the rotation speed Ne is higher than 3000 rpm is less than 10.

In the third time again, if it is determined in step 313 that the OT correction condition is satisfied, the process proceeds to step 314, and the learning value BRH stored in the backup RAM and the current heater obtained in step 302. The OT power correction amount Potp is obtained from the map stored in the ROM based on the difference from the resistance value RH. The relationship between the difference (RH-BRH) between the learning value BRH and the heater resistance value RH and the OT power correction amount Potp stored in this map is set as shown in the characteristic diagram of FIG. ing.

If it is determined that the OT correction condition is not satisfied, the process proceeds to step 315, and the OT power correction amount Potp is set to 0.

By the way, the OT power correction amount Potp is set for a predetermined time after the vehicle has been traveling at high speed in this way because the temperature of the exhaust gas is high immediately after traveling at high speed, and the basic power amount P _B, which will be described later, is supplied to the heater 15b as it is. In order to prevent the heater temperature from rising too much, the basic electric energy P _B described later is reduced and corrected by the correction amount Potp in the processing described later to raise the temperature of the heater 15b and the detection element 15a. Prevent overdoing.

When the process of step 314 or 315 is completed, the process proceeds to step 316, and in step 316, from the heater voltage Vh and the heater current Ih read in step 301, a predetermined time, for example, 100 (m sec), _A process for calculating the amount of electric power when the heater 15b is energized, that is, the amount of electric power P _A with a duty ratio of 100% is executed, and the routine proceeds to step 317. In the following, all electric power is the electric power per 100 [m sec].

Next, at step 317, the heater 15b is calculated from the map or arithmetic expression stored in the ROM as shown in FIG. 8 using the engine speed Ne and the intake pipe pressure Pm obtained at step 301 as parameters. Basic electric power P _B
And shifts to the subsequent step 318. Here, in this map, as is clear from FIG.
When Pm is large, or when the engine speed Ne is large, the amount of fuel injected into the engine 1 naturally increases and the exhaust gas temperature rises so that the detection element 15a can be heated by the exhaust gas, so the power supplied to the heater 15b is increased. On the other hand, while the engine speed Ne is small, or the intake pipe pressure Pm
When is small, the exhaust temperature is lowered and the detection element cannot be heated. Therefore, the power supplied to the heater 15b is set to be large.

Next, in step 318, the above steps 308, 311, 314
Each power correction amount pCold obtained by, Prh, the basic power amount P _B is corrected using the following equation _{P C = P B + Pcold +} Prh-Potp by POTP, actually the target amount of power P _C supplied to the heater 15b calculate.

When the target power amount P _C is obtained in this way, in the following step 319 this target power amount P _C and the power amount P _A with the duty ratio of 100% obtained in step 316 above are used as parameters The duty ratio D for supplying the target power amount P _C to the heater 15b is calculated by using D = (P _C / P _A ) × 100.

Then, in the following step 320, the pulse signal of the duty ratio D obtained above is sent to the energization control circuit 38, and the heater
The process of controlling the power supplied to 15b is executed, and this control process ends.

Here, for example, the electric energy P _A with a duty ratio of 100% is 50 [w · 1
00m sec.], And the target power amount P _C is 25 [w · 100m sec.], The duty ratio D becomes 50 [%], and the pulse signal sent to the energization control circuit 38 is as shown in FIG. It will be as shown by the solid line.

As described above, according to the configuration of this embodiment, the heater
The heater resistance value RH in a stable engine state in which the temperature of 15b is controlled to a temperature of approximately 1100 ° C is stored as a learning value BRH, and this learning value BRH and the heater resistance value R at that time are stored.
Rotation speed Ne and intake pipe pressure Pm corrected by the difference from H
Since the basic electric energy P _B determined based on and is corrected,
It becomes possible to supply the necessary electric power to the heater 15b without excess or deficiency. Therefore, there is a sufficient problem that the heater 15b excessively heats up or the detection element 15a falls to a temperature that deviates from the active state. Can be resolved.

In the above embodiment, when the basic electric energy P _B is calculated,
Although the engine speed Ne and the intake pipe pressure Pm are used, the intake air amount and the throttle valve 11 are also used.
May be used, or only one of the engine speed Ne and the intake pipe pressure Pm may be used.

Further, in the above embodiment, the energization control of the heater 15b is 100%.
The duty is controlled by the energization time per [m sec.], But other than this, for example, the power supplied to the heater 15b may be obtained and the voltage applied to the heater 15b may be controlled.

〔The invention's effect〕

As described above, according to the present invention, the heater resistance value in a predetermined operating state of the engine is stored, and the stored resistance value and the current heater resistance value detected by the heater resistance value detection means are stored. Based on the above, the target power is determined by correcting the basic power to the heater that is determined according to the operating state, so that the power supplied to the heater can be determined while compensating for the characteristic variations of the heater elements. Therefore, it is possible to prevent excessive supply of electric power to the heater and insufficient supply of electric power to the heater, and thus it is possible to obtain a good detection result from the oxygen concentration sensor at all times. .

[Brief description of drawings]

FIG. 1 is a schematic system diagram showing an engine equipped with a controller for a heater for an oxygen concentration sensor according to an embodiment of the present invention and its peripheral devices, and FIG. 2 is a block diagram showing a configuration of a control circuit 25, FIG. Is a flow chart showing heater control processing of the oxygen concentration sensor executed by the control circuit 25, FIG. 4, FIG.
6 and 6 show the difference between the learning value BRH and the resistance value RH and the correction amount P.
FIG. 7 is a characteristic diagram showing the relationship between cold, Rrh, and Potp, FIG. 7 is a flowchart showing the process for determining the success or failure of the OT correction condition executed by the control circuit 25, and FIG. 8 is the basic electric energy P _B. Fig. 9 is a graph showing the contents of the map for obtaining, Fig. 9 is a time chart showing the control signal output to the energization control circuit 38, Fig. 10 is a characteristic diagram showing the relationship between heater temperature and heater resistance value, Fig. 11 FIG. 1 is a block diagram showing a schematic configuration of the present invention. 1 ... Engine, 6 ... Exhaust manifold, 10 ... Intake pressure sensor, 15 ... Oxygen concentration sensor, 15a ... Detection element, 15b ...
… Heater, 20 …… Revolution sensor, 21 …… Vehicle speed sensor, 25…
… Control circuit, 37 …… Microcomputer, 38 …… Energization control circuit, 40 …… Heater voltage detection circuit, 41 …… Heater current detection circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keisuke Tsukamoto 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP 61-207960 (JP, A) JP 60-202350 (JP, A) JP-A-60-214251 (JP, A)

Claims (1)

[Claims] 1. A heater provided in an oxygen concentration sensor installed in an exhaust system of an internal combustion engine for detecting an oxygen concentration in exhaust gas, an operating state detecting means for detecting an operating state of the internal combustion engine, and the operating state detecting means. In accordance with the operating state detected by, the basic power setting means for setting the basic power to be supplied to the heater, the heater resistance value detecting means for detecting the resistance value of the heater, and the operating state detecting means. A storage unit that stores the resistance value of the heater detected by the heater resistance value detection unit when the operation state is a predetermined operation state; and a resistance value that is detected by the heater resistance value detection unit. A target power determining unit that corrects the basic power set by the basic power setting unit based on the resistance value stored in the storage unit and determines a target power to be supplied to the heater; Control device for a heater for an oxygen concentration sensor, characterized in that a control unit for controlling electric power supplied to the heater in accordance with the target power determined by the target power determining means.