JPH0559263B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a limiting current type oxygen concentration sensor that is installed in the exhaust system of an internal combustion engine and detects deterioration of the limiting current type oxygen concentration sensor that detects the oxygen concentration in exhaust gas. The present invention relates to a deterioration detection device.

[Prior Art] Conventionally, in order to operate an internal combustion engine in an optimal state,
There is a method in which a limiting current type oxygen concentration sensor is attached to the exhaust system to detect the amount of residual oxygen contained in the exhaust gas of the internal combustion engine and to feedback control the ignition timing, air-fuel ratio, fuel injection timing, etc. of the internal combustion engine. Widely adopted. These methods make it possible to operate the internal combustion engine under optimal operating conditions, but for this purpose it is an absolute prerequisite that the limiting current type oxygen concentration sensor always operates normally.

However, because the limiting current type oxygen concentration sensor is installed in the exhaust system of an internal combustion engine, the ambient temperature of the limiting current type oxygen concentration sensor changes over a wide range depending on the operating state of the internal combustion engine, and the temperature in the exhaust gas Unburnt substances contained in the fuel and various impurities contained in the fuel cause deterioration of the limiting current type oxygen concentration sensor due to thermal fatigue and contamination of the detection surface. In order to prevent these deteriorations, a heater is installed to suppress temperature changes in the limiting current type oxygen concentration sensor.
A device (Utility Model Application Publication No. 58-112958) has been proposed that controls the energization of the heater according to the operating state of the internal combustion engine, but it causes problems such as deterioration of the heater section and a large amount of power consumption in the heater section. There is a new problem. Various proposals have been made to solve this new problem (Japanese Patent Laid-Open No. 58-83241, Japanese Patent Laid-Open No. 58-83251), but these also do not allow the temperature change of the limiting current type oxygen concentration sensor to become zero. Instead, thermal fatigue does exist, and no countermeasures have been suggested for the causes of deterioration, such as contamination of the detection surface.

When the limiting current type oxygen concentration sensor deteriorates, its detection output decreases compared to when the limiting current type oxygen concentration sensor is normal. Therefore, if the internal combustion engine is feedback-controlled based on the detected output, fuel supply will be restricted more than necessary. This may lead to improper control of the internal combustion engine, such as by using a limiting current type oxygen concentration sensor, and the purpose of installing the limiting current type oxygen concentration sensor may not be fully achieved. Therefore, in order to detect the deterioration state of the limiting current type oxygen concentration sensor, we use the atmosphere whose oxygen concentration is known in advance, and by knowing the output of the limiting current type oxygen concentration sensor when measuring the oxygen concentration in the atmosphere, we can detect the deterioration state. It has been proposed to detect However, the limiting current type oxygen concentration sensor has complicated characteristics, and even in order to detect the same oxygen concentration, the voltage value to be applied must be changed depending on the temperature of the sensor itself, and furthermore, the voltage value to be applied must be changed depending on the temperature of the sensor itself. Even when detecting the temperature state, the applied voltage must be increased approximately in proportion to the detected oxygen concentration. For example, if an unreasonably high voltage is applied at the same temperature, there is a risk of destruction of the device, and conversely, if the voltage is too low, the oxygen concentration cannot be determined accurately. Therefore, when detecting residual oxygen in the exhaust gas of an internal combustion engine, that is, when detecting a low concentration, a low voltage is used.
Then, by applying a voltage that matches the temperature of the exhaust gas, the atmosphere of the limiting current type oxygen concentration sensor becomes the same as the atmosphere, and the concentration is detected. It is necessary to apply a voltage that also matches the temperature of the oxygen concentration sensor, and there is a need for a deterioration detection device for a limiting current type oxygen concentration sensor that can easily and accurately control this voltage.

[Object of the Invention] The present invention has been made in response to the above-mentioned needs, and it is an object of the present invention to provide a deterioration detection device for a limiting current type oxygen concentration sensor that easily and accurately detects the deterioration state of a limiting current type oxygen concentration sensor. It is an object.

[Configuration of the Invention] In order to achieve the above object, the configuration of the present invention, as shown in the basic configuration diagram of FIG. a fuel cutoff means for detecting operating conditions of the engine A and stopping fuel supply to the internal combustion engine A according to the detection result; and a fuel cutoff means for stopping the fuel supply to the internal combustion engine A according to the detection result; Voltage application means for applying a voltage increasing at a predetermined speed to the sensor; Increase amount calculation means for detecting the output of the limiting current type oxygen concentration sensor to which voltage is applied by the voltage application means and calculating the amount of increase. and a comparison means for comparing the output of the limiting current type oxygen concentration sensor with a preset reference value when the increase amount calculated by the increase amount calculation means becomes less than or equal to a predetermined value. The gist of this paper is a deterioration detection device for a limiting current type oxygen concentration sensor.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

First, FIG. 2 is an explanatory diagram showing an internal combustion engine and its peripheral equipment to which a deterioration detection device for a limiting current type oxygen concentration sensor according to an embodiment of the present invention is installed.

1 is an internal combustion engine body, 2 is a piston, 3 is a spark plug, 4 is an exhaust manifold, 5 is a limit current type oxygen concentration sensor provided in the exhaust manifold 4 and detects the residual oxygen concentration in exhaust gas, 6 is an internal combustion engine body 1 is a fuel injection valve that injects fuel into intake air; 7 is an intake manifold; 8 is an internal combustion engine main body 1
9 is a water temperature sensor that detects the temperature of the internal combustion engine cooling water; 10 is a throttle valve; 14 is an air flow meter that measures the intake air amount, and 15 is a surge tank that absorbs the pulsation of the intake air.

16 is an igniter that outputs the high voltage necessary for ignition; 17 is a distributor that is linked to a crankshaft (not shown) and distributes the high voltage generated by the igniter 16 to the spark plugs 3 of each cylinder; 18 is a distributor A rotation angle sensor 19 is installed in the distributor 17 and outputs 24 pulse signals per one revolution of the distributor 17, that is, two revolutions of the crankshaft. 20 is an electronic control circuit, 21 is a key switch, and 22 is a starter motor. 26 represents a vehicle speed sensor that is linked to the axle and transmits a pulse signal according to the vehicle speed.

Next, FIG. 3 shows a block diagram of 20 examples of electronic control circuits and their related parts.

30 is a central processing unit (hereinafter simply referred to as CPU) that inputs and calculates the data output from each sensor according to a control program and performs processing for controlling the operation of various devices; 31 is a control program and an initial processing unit; 32 is a read-only memory (hereinafter simply referred to as ROM) in which data is stored, and a random access memory (hereinafter simply referred to as ROM) in which data input to the electronic control circuit 20 and data required for arithmetic control are temporarily read and written.
33 is a backup random access memory (hereinafter referred to simply as backup RAM) which is a non-volatile memory backed up by a battery so as to retain the data necessary for subsequent operation of the internal combustion engine even when the key switch 21 is turned off. ), 34 to 37 are buffers for the output signals of each sensor, 38 is a multiplexer that selectively outputs the output signal of each sensor to the CPU 30, 39 is an A/D converter that converts the analog signal into a digital signal,
40 is an input/output port that sends each sensor signal to the CPU 30 via a buffer or via the buffer, multiplexer 38 and A/D converter 39, and outputs control signals for the multiplexer 38 and A/D converter 39 from the CPU 30; It represents.

41 is a buffer that temporarily stores the output signal of the limiting current type oxygen concentration sensor 5; 41A is an A/D converter that converts the analog signal from the buffer 41 into a digital signal; and 42 is a drive for the limiting current type oxygen concentration sensor 5. A voltage application circuit 43 generates and applies a voltage, and 43 represents a shaping circuit that shapes the waveforms of the output signals of the rotation angle sensor 18 and the cylinder discrimination sensor 19, and each sensor signal such as the throttle opening sensor 11 is directly or The data is sent to the CPU 30 via the input/output port 46 via the buffer 41 and the like.

Furthermore, 47 and 48 are the fuel injection valves 6 and 48 in response to signals from the CPU 30 via output ports 49 and 50, respectively.
Each of the drive circuits that drive the igniter 16 is shown. Also, 51 is a bus line that serves as a path for signals and data, and 52 is a bus line for the CPU 30 and ROM 3.
1, represents a clock circuit that sends a clock signal serving as a control timing to the RAM 32, etc. at predetermined intervals.

Next, a control program which is a main part of this embodiment will be explained.

FIG. 4 is a flowchart of the first embodiment.
The illustrated control procedure is stored as a program in the ROM 31 in advance to be executed by the electronic control circuit 20.
Processing is performed according to the timing given by . This deterioration detection routine is executed, for example, by interruption at predetermined time intervals or at each predetermined rotation speed of the internal combustion engine 1.

When the processing of the CPU 30 shifts to this routine, step 100 is first executed. In this step, the RAM 32, which will be used by executing this routine from now on, will be
Clears the storage area of , and sets data required for calculation, etc., in preparation for the following processing.

Next, step 110 is executed, and it is determined whether the processing conditions of this routine are satisfied, that is, whether or not the internal combustion engine 1 is under fuel cutoff control.

Fuel cutoff control means that, for example, if the internal combustion engine 1 is in deceleration operation according to the output of the vehicle speed sensor 26, and the output of the throttle opening sensor 11 indicates a fully closed state, the internal combustion engine 1 operates as a so-called engine brake. Therefore, it is determined that there is no need to further supply fuel to the internal combustion engine 1, and the output of the drive signal to the fuel injection valve 6 is stopped. Therefore, if the fuel cutoff control is being executed, no fuel is burned in the combustion chamber of the internal combustion engine 1, and the piston 2 simply acts as a load and moves up and down.

If it is determined in this step that fuel cut-off control is being performed, the next step 120 is executed; otherwise, the process of this routine is no longer performed, and the process of another routine is executed.

In step 120, the voltage VM currently being applied to the limiting current type oxygen concentration sensor 5 is increased by a predetermined minute voltage value ΔV, and the voltage VM is applied to the limiting current type oxygen concentration sensor 5. Then, the output In of the limiting current type oxygen concentration sensor 5 to which the voltage VM is newly applied
is loaded into the RAM 32 via the input/output port 46 by executing the next step 130.

In step 140, the output current value of the limiting current type oxygen concentration sensor 5 taken into this RAM 32 is
The output current value In _-1 of the limiting current type oxygen concentration sensor 5, which was previously taken into the RAM 32 in the same manner as described above, is subtracted from In, and the voltage VM applied to the limiting current type oxygen concentration sensor 5 is changed by ΔV in step 120. It is calculated how much the output of the limiting current type oxygen concentration sensor 5 has increased due to the increase. When the process of this step is executed for the first time, the value of the current value In _-1 indicates that the limiting current type oxygen concentration sensor 5 has detected the residual oxygen concentration in the exhaust gas immediately before the fuel cutoff control of the internal combustion engine 1 is performed. The output current value at the time is RAM32
It is executed during the normal process of detecting the concentration of residual oxygen in exhaust gas.

The next step 150 is to determine how the increased amount ΔI of the output current In of the limiting current type oxygen concentration sensor 5 obtained as described above is compared with the predetermined amount IA stored in the ROM 31. It is determined whether there is. Applied voltage V of limiting current type oxygen concentration sensor 5
A graph of the output current I and the output current I (the temperature of the limiting current type oxygen concentration sensor 5 is constant) is shown in FIG. In the figure, the solid line represents the case when the oxygen concentration in the exhaust gas is extremely low, that is, when there is a large supply of fuel, and the dashed-dotted line represents the case when the internal combustion engine 1 is operating, but the oxygen concentration in the exhaust gas is extremely high. represents the output of the limiting current type oxygen concentration sensor 5. Also,
The two-dot chain line is the output when the limiting current type oxygen concentration sensor 5 detects the atmospheric oxygen concentration. In this way, the output current I of the limiting current type oxygen concentration sensor 5 has a certain current value that is proportional to the oxygen concentration and is a nearly constant value regardless of changes in the applied voltage V. Therefore, the predetermined amount IA used in this step takes a value close to "0". As a result, it is possible to determine whether the current value In currently output from the limiting current type oxygen concentration sensor 5 is in an increasing state as shown by ΔI in FIG.
Alternatively, it is possible to accurately determine whether a constant output proportional to the oxygen concentration being detected is being provided. In addition, since the limiting current type oxygen concentration sensor 5 has such characteristics, the limiting current type oxygen concentration sensor 5 has the following characteristics: The characteristic curve of the concentration sensor 5 gradually moves in the direction of the arrow in the figure. Therefore, if it is determined in this step that ΔI>IA, the process returns to step 110 and the same processing is executed to determine ΔI.
If it is determined that ≦IA, the process moves to the next step 160. Here, considering the processing time when it is determined that ΔI>IA and the process returns to step 110, and the time during which the characteristics of the limiting current type oxygen concentration sensor 5 change in the direction of the arrow shown in FIG. If the time is longer and the processing time is faster, take steps as necessary to prevent the processing from overtaking the characteristic transition.
A delay step or the like may be provided during the return from step 150 to step 110, or techniques may be used such as moving to another routine and returning to the main routine again after a predetermined period of time has elapsed.

In the next step 160, the application of the high voltage VM applied to the limiting current type oxygen concentration sensor 5 in step 120 is terminated, and the voltage is reset to a low voltage value suitable for detecting the oxygen concentration in the exhaust gas again. This is a step to take. At this step, control of the limiting current type oxygen concentration sensor 5 is completed, and the process moves to the next step 170.

In step 170, the output current value In of the limiting current type oxygen concentration sensor 5 at the time of the applied voltage VM finally obtained in the RAM 32 through the processing up to the previous step 160 and the reference current stored in the ROM 31 in advance are calculated. value
In this step, the deterioration state of the limiting current type oxygen concentration sensor 5 is calculated using the IB. Reference current value
IB represents, for example, the output current value at the time of atmospheric oxygen concentration detection, which was measured before deterioration occurred in the limiting current type oxygen concentration sensor 5, and the current measured current value is compared with this reference current value IB. ValueIn
Quantify the deterioration of the limiting current type oxygen concentration sensor 5 by calculating how much it has changed as a percentage, etc.
The value is stored in the backup RAM 33 as a variable K. This variable K is used in subsequent output processing of the limiting current type oxygen concentration sensor, and by integrating the variable K with the actual sensor output, it is possible to easily obtain a correction value for the output.

At this step, all processing of this routine is completed, and the CPU 30 moves on to processing of other routines.

Next, a process in which deterioration of the limiting current type oxygen concentration sensor 5 is detected as described above will be described in the case where there is a temperature change in the limiting current type oxygen concentration sensor 5.

FIG. 6 is a diagram showing the relationship between the applied voltage and the output current of the limiting current type oxygen concentration sensor 5 under the same oxygen concentration but at different temperatures.

As described above, the limiting current type oxygen concentration sensor 5 exhibits a characteristic that the output current value hardly changes with respect to changes in the applied voltage under the same oxygen concentration, and the output current value is constant. Therefore, although the oxygen concentration can be detected stably even when the temperature changes, the voltage V applied for the detection must have a small value almost proportional to the temperature. The limiting current type oxygen concentration sensor 5 is installed in the exhaust manifold 4 of the internal combustion engine 1 as shown in FIG. It changes over time.

However, even in response to such temperature changes, the applied voltage VM is gradually increased by setting the minute increase ΔV of the applied voltage VM used in step 120 of this routine to be inversely proportional to the temperature, and the output current I
This can be easily dealt with by performing the same processing as described above until the value becomes approximately constant.

In addition, considering the temperature characteristics shown in Figure 6, a technology has been proposed in which a heater is attached to the limiting current type oxygen concentration sensor and the power supply is interrupted to maintain the temperature of the limiting current type oxygen concentration sensor at a nearly constant value. However, in order to apply the present invention to such a limiting current type oxygen concentration sensor, the above considerations are not necessary.

In the deterioration detection routine described above, step 120 processes the voltage application means, and step 130
and step 140 is the processing of the increase amount calculation means, step 170
corresponds to the processing of comparison means.

As described above, the deterioration detection device for the limiting current type oxygen concentration sensor of this embodiment applies the signal starting from the stop of the drive signal of the fuel injection valve 6 for stopping the fuel supply to the internal combustion engine 1, which is the fuel cutoff means. The voltage VM is increased by ΔV, and the optimal applied voltage VM is applied to the limiting current type oxygen concentration sensor 5 while monitoring the sensor output while following the gradual displacement of the exhaust manifold 4 by the atmosphere. It is applied. Therefore, it is possible to accurately measure the atmospheric oxygen concentration without causing damage to the limiting current type oxygen concentration sensor 5, and to compare the measurement result In with the current value IB serving as a reference. Therefore, deterioration of the limiting current type oxygen concentration sensor 5 can be easily detected.

Next, a second embodiment of the present invention will be described.

FIG. 7 shows the same figures as those in the first embodiment.
This is a flowchart of this embodiment in which deterioration of a limiting current type oxygen concentration sensor is detected using the internal combustion engine and its peripheral devices shown in the figure. In the figure, steps 200, 210, and 220 to
270 is a flowchart of the first embodiment, steps 100 to 110 and steps 120 to 1 in FIG.
The same processing as step 170 is performed. This example applies the applied voltage shown in the first example.
The applied voltage that was applied to the limiting current type oxygen concentration sensor 5 by increasing VM by a predetermined voltage ΔV
Steps 211 and 212 for changing the increase in VM according to the rotational speed of the internal combustion engine 1 are added. That is, in the first embodiment, the applied voltage VM
The amount of increase ΔV is a constant stored in the ROM 31 in advance, and the rate of increase in the applied voltage VM is fixed. However, in this embodiment, in step 220, the predetermined voltage ΔV(N) is set, and the internal combustion engine It is made variable as a function of the number of rotations N of the engine. Therefore,
When it is determined in step 210 that fuel cutoff control is being performed, the rotational speed N of the internal combustion engine 1 is acquired by the rotation angle sensor 18 in step 211, and then in step 212 the voltage increase amount ΔV determined by this rotational speed N is determined. (N) is obtained from, for example, a map prepared in advance in the ROM 31, and is used in the processing after step 220 below.

Such a deterioration detection device for a limiting current type oxygen concentration sensor sets ΔV(N) to a large value when the rotational speed N of the internal combustion engine 1 is high and the gas in the exhaust manifold 4 is replaced quickly. ΔV(N) can be made small when the gas exchange rate in the exhaust manifold 4 is low. Therefore, when the minimum fuel cutoff control period is carried out, the voltage VM applied to the limiting current type oxygen concentration sensor 5 quickly becomes a value suitable for measuring the oxygen concentration in the atmosphere, and the purpose of deterioration detection is achieved at an early stage. There are effects that can be achieved.

[Effects of the Invention] As described above in detail, the deterioration detection device for a limiting current type oxygen concentration sensor of the present invention detects the deterioration state of the limiting current type oxygen concentration sensor while the internal combustion engine is under fuel cutoff control by the fuel cutoff means. The voltage applied to the sensor is increased at a predetermined speed, the amount of increase in the sensor output current is determined each time, and the output current obtained when the amount of output increase is approximately 0 is compared with the reference value. It is detected by Therefore, depending on the applied voltage value, accurate concentration measurement cannot be performed.
Furthermore, it is possible to always apply an appropriate voltage to the limiting current type oxygen concentration sensor, which can cause destruction, without being affected by changes in characteristics due to temperature, and it is possible to easily detect a deterioration state.

In addition, appropriately detecting deterioration of the limiting current type oxygen concentration sensor means that accurate information is always sent to various feedback processing systems that are executed based on the output of the limiting current type oxygen concentration sensor, which improves the internal combustion engine. The secondary effects are significant, such as energy saving and exhaust gas control, which allows the engine to be operated accurately under desired operating conditions.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram of the present invention, Fig. 2 is a schematic diagram of an internal combustion engine and its peripheral equipment to which the embodiment is applied, Fig. 3 is a block diagram of an electronic control circuit, and Fig. 4 is a diagram of the first embodiment. Flowchart of Example, Figures 5 and 6
The figure shows an output characteristic diagram of the limiting current type oxygen concentration sensor, and FIG. 7 shows a flowchart of the second embodiment. 1... Internal combustion engine, 2... Piston, 5... Limit current type oxygen concentration sensor, 6... Fuel injection pump,
18...Rotation angle sensor, 20...Electronic control circuit.

Claims (1)

[Scope of Claims] 1. A limiting current type oxygen concentration sensor installed in an exhaust system of an internal combustion engine, which detects operating conditions of the internal combustion engine, and stops fuel supply to the internal combustion engine according to the detection result. a fuel cutoff means; a voltage application means for applying a voltage that increases at a predetermined speed to the limiting current type oxygen concentration sensor from the time when the fuel supply is stopped by the fuel cutoff means; and a voltage is applied by the voltage application means. an increase amount calculating means for detecting the output of a limiting current type oxygen concentration sensor and calculating an increase thereof; A deterioration detection device for a limiting current type oxygen concentration sensor, comprising a comparison means for comparing an oxygen concentration sensor output with a preset reference value. 2. The deterioration detection device for a limiting current type oxygen concentration sensor according to claim 1, wherein the predetermined rate of voltage increase in the voltage applying means is set based on the rotation speed of the internal combustion engine.