JP2824311B2 - Oxygen sensor heater control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heater control device for an oxygen sensor having a heater for heating a gas-sensitive element.

[Prior art] Conventionally, as an oxygen sensor for detecting the oxygen concentration in exhaust gas of an internal combustion engine or the like, a gas such as an oxide of a transition metal element such as TiO ₂ , CoO, NiO or SnO is used. Some gas-sensitive metal oxides (gas-sensitive elements) whose electrical resistance changes when they come into contact with them. Usually, such gas-sensitive elements include a catalyst such as platinum to promote the reaction. It is carried.

In this type of oxygen sensor, in order to accurately and stably detect the oxygen concentration, the heater is energized to heat and activate the gas-sensitive element, and the voltage applied to the heater is adjusted. Temperature of gas-sensitive element (hereinafter referred to as element temperature)
Is controlled to keep the temperature in a temperature range suitable for activation.

For this reason, a heater energization control device that measures the internal resistance of the heater and controls the heater applied voltage so that the magnitude of the resistance is constant to thereby keep the element temperature within a predetermined temperature range has been considered. Have been.

Alternatively, a heater power value corresponding to the intake pressure and the rotation speed of the internal combustion engine is set in advance, and the heater applied voltage is set according to the operation state of the internal combustion engine so as to have a set power value corresponding to the operation state. A heater energization control device that controls the element temperature within a predetermined temperature range by controlling the temperature is also considered.

[Problems to be Solved by the Invention] However, in the former device, since there is a large individual difference between the oxygen sensors in the correlation characteristic between the heater resistance and the element temperature, an appropriate heater according to the characteristics of each oxygen sensor is used. It was difficult to control the applied voltage.

On the other hand, in the latter device, in addition to the problem that a great deal of labor is required for actually measuring the heater power value, there is a problem that the set heater power value must be corrected for each type of the internal combustion engine.

Further, when the catalytic activity of the oxygen sensor changes due to poisoning or the like, there is a problem that the conventional heater control cannot detect the oxygen concentration appropriately.

Accordingly, an object of the present invention is to provide a heater energization control device for an oxygen sensor that can appropriately control a heater applied voltage according to the characteristics of each oxygen sensor.

[Means for Solving the Problems] A heater control device for an oxygen sensor according to claim 1, which has been made to solve the above problems, is provided in an exhaust system of an internal combustion engine, as exemplified in FIG. What is claimed is: 1. A heater control device for an oxygen sensor S, comprising: a gas-sensitive element whose electric resistance changes when gas comes in contact therewith; and a heater H for heating said gas-sensitive element, wherein said heater is capable of adjusting a voltage applied to said heater H An energizing means M1, a median calculating means M2 for obtaining a median between the lean output signal and the rich output signal based on the lean output signal and the rich output signal output from the oxygen sensor S, and a median calculating means M2 An output determining means M3 for comparing the calculated median value with a predetermined set value as an output reference value of the oxygen sensor S to determine the magnitude of the median value and the set value; M3 Therefore, when it is determined that the median value exceeds the set value, the heater application voltage reducing means M4 for reducing the heater applied voltage by the heater energizing means M1 and the output determining means M3 set the median value to the set value. If it is determined that the temperature is below the value, the heater energizing means M1
And a heater application voltage increasing means M5 for increasing the heater application voltage according to (1).

[Operation] According to the heater control device for an oxygen sensor according to claim 1 configured as described above, the heater energizing means M1 energizes the heater of the oxygen sensor S, and the gas is contacted by the heat generated by the heater H. When the gas sensing element whose electric resistance changes is activated, the oxygen sensor S outputs a lean output signal when the air-fuel ratio of the fuel mixture is lean, and outputs a rich output signal when the air-fuel ratio is rich.

Here, the median value calculating means M2 calculates a median value between the lean output signal and the rich output signal based on the lean output signal and the rich output signal. Next, the output determination means M3 compares the median value with a set value predetermined as an output reference value of the oxygen sensor S, and determines the magnitude of the median value and the set value.

If it is determined that the median value is greater than the set value, the heater applied voltage is reduced by driving the heater energizing means M1 by the heater applied voltage reducing means M4, so that the temperature of the heater is decreased.

On the other hand, when it is determined that the median value is lower than the set value, the heater applied voltage is increased by driving the heater energizing means M1 by the heater applied voltage increasing means M5, so that the temperature of the heater increases.

That is, in the present invention, the operation is such that when the median value exceeds the set value, the temperature of the heater is decreased, and when the median value is less than the set value, the temperature of the heater is increased.

 Hereinafter, the reason for such a configuration will be described.

In an oxygen sensor having a gas-sensitive element whose electric resistance changes when gas comes in contact, when the temperature of the gas-sensitive element heated by the heater is within an appropriate range, both the rich output signal and the lean output signal are constant. Level stable. However, when the element temperature exceeds the appropriate range, the rich output signal is stabilized at a constant level, but the lean output signal tends to increase as the temperature rises, and when the element temperature falls below the appropriate range, the lean output signal increases. The output signal is stable at a constant level, but the rich output signal tends to decrease as the temperature decreases.

If it falls down, an example is shown in FIG. FIG. 5 shows an oxygen sensor attached to an internal combustion engine. For example, in an atmosphere with an excess air ratio λ = 0.9 at the time of lean and an excess air ratio λ = 1.1 at the time of rich, the oxygen sensor is changed by changing the heater applied voltage. 3 is a plot of the lean output signal and the rich output signal of FIG.

As can be seen from the figure, when the element temperature is in the range of about 650 ° C., the median between the rich output signal and the lean output signal is substantially constant. Therefore, if the median value is set as a set value, for example, when the element temperature exceeds 700 ° C., in that region, the lean output signal increases as the temperature rises, so that the median value also increases and exceeds the set value. Therefore, at this time, if the heater temperature is lowered, that is, the heater applied voltage is lowered to lower the element temperature to an appropriate range, the lean output signal becomes stable.

On the other hand, when the element temperature falls below 600 ° C., in that region, the rich output signal falls as the temperature falls, so that the median value also falls below the set value. Therefore, at this time, if the heater temperature is raised, that is, the heater applied voltage is raised, and the element temperature is raised within an appropriate range, the rich output signal becomes stable.

As described above, the preset value set as the output reference value of the oxygen sensor is compared with the median value of the lean output signal and the rich output signal, and when the median value exceeds the set value, the heater applied voltage is reduced, and When the median value is lower than the set value, the output signal of the oxygen sensor can always be stabilized by increasing the heater applied voltage.

[Example] Hereinafter, an example to which the present invention is applied will be described with reference to the drawings. FIG. 2 is a system configuration diagram of a heater control device of the oxygen sensor according to the embodiment.

As shown in FIG.
Is provided with an electronic control unit (hereinafter simply referred to as ECU) 3 for detecting various states of the engine 2 and performing various controls such as an air-fuel ratio.

The engine 2 includes a combustion chamber 7 including a cylinder 4, a piston 5, and a cylinder head 6, and an ignition plug 8 is disposed in the combustion chamber 7.

The intake system of the engine 2 has an intake valve 9, an intake port 1
0, intake pipe 11, surge tank 1 to absorb pulsation of intake air
2. It is composed of a throttle valve 14 for adjusting the amount of intake air and an air cleaner 15. The exhaust system of the engine 2 includes an exhaust valve 16, an exhaust port 17, an exhaust manifold 1
8, catalytic converter 19 and exhaust pipe 20 filled with three-way catalyst
It is composed of

The ignition system of the engine 2 includes an igniter 21 that outputs a high voltage required for ignition and a distributor 22 that distributes and supplies the high voltage generated by the igniter 21 to the ignition plug 8 in conjunction with a crankshaft (not shown).

The fuel system of the engine 2 includes an electromagnetic fuel injection valve 25 that injects fuel from a fuel tank (not shown) to the vicinity of the intake port 10.

Further, as sensors for detecting the operating state of the engine 2, an intake pressure sensor 31 for detecting the pressure of the intake air, an intake temperature sensor 32 for detecting the temperature of the intake air, a throttle valve
A throttle position sensor 33 for detecting the opening of 14, a water temperature sensor 35 for detecting the temperature of the cooling water, an oxygen sensor 36 as an oxygen sensor for detecting the oxygen concentration in the exhaust gas before flowing into the catalytic converter 19, and a cam for the distributor 22 Cylinder discrimination sensor that outputs a reference signal for each rotation of the shaft
38, a rotation speed sensor 39 for outputting a rotation angle signal every 1/24 rotation of the camshaft of the distributor 22 is provided.

The detection signal of each sensor is input to the ECU 3, and the control of the engine speed, the air-fuel ratio, and the like is performed based on the signal. The ECU 3 is configured as a logical operation circuit centered on a known CPU 3a, ROM 3b, RAM 3c, backup RAM 3d, and timer 3e, and is connected to an input / output port 3g via a common bus 3f to perform input / output with the outside.

Further, the ECU 3 inputs detection signals of the intake pressure sensor 31, the intake temperature sensor 32, the throttle position sensor 33, the water temperature sensor 35, and the oxygen sensor 36 via the A / D converter 3h and the input / output port 3g. Further, detection signals from the cylinder discrimination sensor 38 and the rotation speed sensor 39 are input via the waveform shaping circuit 3i and the input / output port 3g.

The CPU 3a, via the input / output port 3g and the drive circuit 3j,
The drive of the igniter 21 and the fuel injection valve 25 is controlled.
Further, the heater control voltage of the oxygen sensor 36 is controlled via the input / output port 3g and the well-known programmable power supply 3k capable of adjusting the output voltage (described later in detail).

The electrical resistance of the oxygen sensor 36 changes when the surrounding gas comes into contact. For example, a gas-sensitive metal oxide such as TiO ₂ (gas-sensitive element) and a heater (not shown) for heating the gas-sensitive element are configured as main parts, and according to the oxygen concentration in the exhaust gas of the engine 2. That is, an electric signal is output according to the air-fuel ratio.

The backup RAM 3d of the ECU 3 is supplied with power from a path that does not pass through an ignition switch (not shown), and data VHD of a heater application voltage VH described later is held regardless of the state of the ignition switch. Is configured.

Next, based on the flowchart of FIG.
The process of the heater energization control of the oxygen sensor 36 executed by the above will be sequentially described. This process is performed when performing feedback control of the air-fuel ratio using the output of the oxygen sensor 36.

First, a process of setting the standard voltage VSTD to the applied voltage VH of the heater and energizing the heater is executed to activate the gas-sensitive element (step 100).

Then, the air-fuel ratio is made rich (for example, the excess air ratio λ = 0.
9) is set (step 105), and it is determined whether or not the gas-sensitive element is activated in that state (step 110). That is,
In the state where the element temperature is not activated at 500 ° C. or less, the output signal of the oxygen sensor 36 is 500 mV or less even in a rich atmosphere.For example, if the output signal exceeds 500 mV, the element is determined to be active. is there.

Here, when it is determined that the element is not activated, the heater application voltage VH is increased by ΔV to perform heating more strongly (step 115), and the activation of the element is determined again in step 110.

On the other hand, when it is determined that the element has been activated, the fuel injection valve 25 and the like are drive-controlled based on the output of the oxygen sensor 36 to perform the air-fuel ratio feedback control (step 12).
0).

With this feedback control, the oxygen sensor
The maximum value and the minimum value of the output signal level of 36 are detected. That is, the output signal level (hereinafter, referred to as a lean output signal) VL of the oxygen sensor 36 at the time of lean operation (for example, λ = 1.02) is detected (step 130), and the oxygen sensor 36 at the time of rich operation (for example, λ = 0.98) is detected. (Hereinafter referred to as a rich output signal) VR (step 140).

Next, from the lean output signal VL and the rich output signal VR detected in steps 130 and 140, a median value (slice level) VSL is calculated (VSL ← (VL + V
R) / 2, step 150). Subsequently, the median value VSL and a predetermined set value VST as an output reference value of the oxygen sensor 36 are determined.
It is determined whether or not D is equal (step 160).

Then, in step 160, the median value VSL and the set value VS
When it is determined that TD is not equal, it is determined whether the median value VSL is lower than the set value VSTD (step 1).
70) Here, when the median value VSL is lower than the set value VSTD, a voltage (VH + ΔV) obtained by increasing the heater applied voltage VH by ΔV is set as the heater applied voltage VH, and the heater is energized (step 180). Then, the process returns to step 130.

On the other hand, when the median value VSL is higher than the set value VSTD, the voltage (VH−
ΔV) is set as the heater applied voltage VH, the heater is energized (step 190), and the process returns to step 130.

On the other hand, if it is determined in step 160 that the median value VSL is equal to the set value VSTD, it is determined whether the lean signal output VL is equal to or greater than a predetermined lean set value VL0 (step 200).

If a positive determination is made in step 200, the rich signal output VR
Is determined to be equal to or less than a predetermined set value VR0 (step 210).

If a positive determination is made in step 210, that is, if the lean signal output VL and the rich signal output VR are VL ≧ VL0 and VR ≦ VR0, the heater applied voltage VH is increased by ΔV (step 220). Return to step 130. Note that even if a negative determination is made in steps 200 and 210, step 1
Return to 30.

As a result of the above processing, the heater applied voltage VH is controlled to increase or decrease so that the median value VSL and the set value VSTD become equal. Therefore, as described above, the temperature of the gas-sensitive element heated by the heater falls within an appropriate range, and both the rich output signal VR and the lean output signal VL are stabilized at a constant level.

Further, when the amplitude of the output signal of the oxygen sensor 36 is small, a large voltage is applied to the heater to increase the element temperature, so that the catalyst is sufficiently activated and the air-fuel ratio can be suitably detected.

Next, an experimental example in which the effect is confirmed using the heater control device 1 of the oxygen sensor 36 of the present embodiment will be described.

(Example) In this experimental example, the oxygen sensor 36 is set to 6 cylinders, 2.0 [l].
The following shows an example of an experiment conducted by attaching to an engine.

FIG. 4 shows that the adjustment range of the heater applied voltage VH is set to 5 to 20 [V] under the conditions that the rotation speed is 2000 [rpm], Rc = 50 kΩ, and the excess air ratio λ = 1.0, and the element temperature is increased. Is a plot of the control air-fuel ratio when the
FIG. 4A shows this embodiment, and FIG. 4B shows a conventional comparative example.

As can be seen from FIG. 4 (A), the oxygen sensor of the present embodiment
When the heater control device 36 is used, the target control air-fuel ratio can be kept almost constant over a wide range of the element temperature. On the other hand, as shown in FIG. 4 (B), in the comparative example, when the element temperature rises beyond the appropriate range or falls below the appropriate range, the control air-fuel ratio shifts.

As described above, in the present embodiment, the temperature of the gas sensing element is maintained in an appropriate range by controlling the increase / decrease of the heater applied voltage VH so that the median value VSL and the set value VSTD become equal. Output signal level is stabilized, whereby the air-fuel ratio of the fuel mixture can be accurately detected.

[Effects of the Invention] As described in detail above, the invention of claim 1 is a heater control device for an oxygen sensor having a gas-sensitive element whose electric resistance changes when gas comes into contact with the gas, the reference value of the oxygen sensor The preset value is compared with the median value of the lean output signal and the rich output signal. When the median value exceeds the set value, the heater applied voltage is decreased. When the median value is less than the set value, the heater applied voltage is decreased. Is increased, the output signal level of the oxygen sensor can be stabilized, and the oxygen concentration can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a view showing an example of a basic configuration of the invention according to claim 1, FIG. 2 is a system configuration diagram of a heater control device according to an embodiment, FIG.
FIG. 4 is a flowchart showing a heater energization control process executed by the electronic control unit. FIG. 4 is a graph showing a correlation between a control air-fuel ratio and an element temperature in an experiment using the heater control unit. 5 is a graph showing a correlation between an output signal level of a sensor and an element temperature. M1 ... heater energizing means M2 ... median value calculating means M3 ... output determining means M4 ... heater applied voltage reducing means M5 ... heater applied voltage increasing means 1 ... heater control device 2 ... engine 3 ... electronic control Equipment (ECU) 36 ... Oxygen sensor

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Toshitaka Matsuura 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Special Ceramics Co., Ltd. (56) References JP-A-62-157255 (JP, A) JP-A-57-13246 (JP, A) JP-A-57-122134 (JP, A) JP-A-58-8246 (JP, A) JP-A-63-106343 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) F02D 41/14 F02D 45/00

Claims (1)

(57) [Claims] 1. An oxygen sensor heater control device provided in an exhaust system of an internal combustion engine, comprising: a gas-sensitive element whose electric resistance changes when gas comes into contact; and a heater for heating the gas-sensitive element. A heater energizing unit that can adjust a voltage applied to the heater; a median value calculating unit that calculates a median value between the lean output signal and the rich output signal based on the lean output signal and the rich output signal output by the oxygen sensor. Output determination means for comparing the median value calculated by the median value calculation means with a set value predetermined as an output reference value of the oxygen sensor, and determining the magnitude of the median value and the set value; A heater applied voltage reducing unit configured to reduce a heater applied voltage by the heater energizing unit when the output determining unit determines that the median value exceeds the set value; When the output determining means determines that the median value is lower than the set value, the heater applying voltage increasing means for increasing the heater applied voltage by the heater energizing means; and Heater control device.