JPH08121260A - Exhaust gas recirculation diagnosis device of engine - Google Patents

Abstract

PURPOSE: To enable exhaust gas recirculation diagnosis with high precision at low cost by introducing air into an exhaust pipe by means of a secondary air introduction means during the exhaust gas recirculation operation by means of an exhaust gas recirculation amount adjusting means and diagnosing an exhaust gas recirculation condition during the introduction of air. CONSTITUTION: An exhaust gas recirculation diagnosis device of an engine is provided with a thermal air flow meter 202, an intake pipe throttle valve opening degree sensor 203, a crank angle sensor 207, and an oxygen concentration sensor 208, and signals of these sensors are inputted into an engine controller 201. Actuators such as an exhaust gas recirculation valve 211 which opens and closes an exhaust gas recirculation pipe 210 in accordance with the judged engine operation condition and a fuel injection valve 204 are driven and controlled. In this case, a secondary air introduction pump 208 is driven during the exhaust gas recirculation to introduce secondary air into an exhaust system. Fluctuations of output of the oxygen concentration sensor 208 at that time or fluctuations of air-fuel ratio compensation coefficient in the air-fuel ratio feedback control are monitored to diagnose normal/abnormal condition of the exhaust gas recirculation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for diagnosing whether exhaust gas recirculation to an engine is normally performed.

[0002]

2. Description of the Related Art In order to reduce the concentration of nitrogen oxides in exhaust gas discharged from a vehicle engine, a part of the exhaust gas is recirculated into an intake pipe of the engine. This exhaust gas recirculation is performed when the engine is in a predetermined operating range. However, if the valve provided in the exhaust gas recirculation passage malfunctions, the pipe is blocked, or the pipe is damaged due to corrosion or the like, the exhaust gas recirculation device will not operate normally.

It is known to use a change in intake pipe pressure when the recirculation passage is opened and when the recirculation passage is closed to diagnose whether the exhaust gas recirculation device is operating normally. For example, in JP-A-4-347354, the intake pipe pressure when the return passage is opened is stored, the return passage is closed, and the deviation between the intake pipe pressure at that time and the stored intake pipe pressure is a predetermined time. It is described that the reflux controller is judged to be normal when the judgment value is exceeded.

[0004]

When trying to diagnose the exhaust gas recirculation system by the deviation of the intake pipe pressure, it is relatively easy to detect the intake pipe pressure fluctuation when the exhaust gas recirculation rate is relatively large. When the exhaust gas recirculation rate is small, the pressure fluctuation is small and a highly accurate intake pipe pressure sensor is required. Therefore, the cost of the diagnostic system increases.
Further, there are many disturbance factors with respect to the intake pipe pressure such as intake pulsation, intake temperature, blow-by gas, etc. The control block becomes complicated to remove these disturbances, and the load on the microcomputer also increases. An object of the present invention is to provide a low cost and highly accurate exhaust gas recirculation diagnostic device.

[0005]

In order to achieve the above object, an exhaust gas recirculation diagnostic apparatus according to the present invention uses an intake air amount detecting means provided in an intake pipe of an engine and an output of the intake air detecting means. The exhaust gas recirculation passage that connects the intake pipe and the exhaust pipe of the engine downstream from the installation position of the intake air amount detection means, and the means for calculating the amount of fuel supplied to the engine, and the exhaust gas recirculation passage were installed in the middle. The exhaust gas recirculation amount adjusting means, the secondary air introducing means for introducing air into the exhaust pipe, and the exhaust pipe installed upstream of the air introducing position by the secondary air introducing means for detecting the oxygen concentration in the exhaust gas. The oxygen concentration detecting means, the fuel amount correcting means for correcting the amount of fuel supplied to the engine based on the output from the oxygen concentration detecting means, and the secondary air during the exhaust gas recirculation operation by the exhaust gas recirculation amount adjusting means. Means for introducing air into the exhaust pipe by guide means, characterized in that a diagnostic means for diagnosing the exhaust gas reflux into the air introduction.

The oxygen concentration detector provided in the exhaust pipe, the secondary air introduction position, and the opening of the exhaust gas recirculation passage are preferably provided in this order from the upstream side to the downstream side along the gas flow. , Can also be provided in a horizontal row. The diagnosis means diagnoses whether the exhaust gas recirculation is normally performed based on the output of the oxygen concentration detection means or the correction amount of the fuel amount correction means. The oxygen concentration detecting means may be an oxygen concentration sensor that generates two output values with a constant value of the oxygen concentration as a threshold value, or an oxygen concentration sensor that continuously outputs depending on the oxygen concentration.

[0007]

The oxygen concentration at the inlet side of the engine is measured by the intake air amount detecting means, and the oxygen concentration entering from the secondary air introducing means for introducing the atmosphere into the exhaust pipe through the exhaust gas recirculation passage is It is measured by an oxygen concentration sensor installed in the exhaust pipe. The correction index that requests the fuel system to correct this oxygen concentration is the exhaust gas recirculation amount.

The oxygen concentration sensor can calculate the recirculation amount even if the exhaust gas recirculation rate is small, as long as the oxygen concentration sensor has two output values with a predetermined concentration of oxygen concentration as a threshold value. Further, in the case of the oxygen concentration sensor having a linear output value with respect to the oxygen concentration, the dynamic range is wide and the reflux amount can be easily calculated. According to the present invention, the device required for diagnosis can be simplified or a conventional product can be used, and the exhaust gas recirculation amount can be detected with a simple control block.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a control block diagram of an embodiment of an engine exhaust gas recirculation diagnostic device according to the present invention. The output of an oxygen concentration sensor that detects the oxygen concentration of the exhaust gas of the internal combustion engine and the engine speed detected from the crank angle of the internal combustion engine are input to this control block. Block 101
Is means for detecting the amount of air passing through the throttle valve of the internal combustion engine. A block 102 is a means for performing a weighted average (filtering process) on the throttle valve passing air amount detected in the above block 101. Block 103 is means for calculating the basic fuel amount required by the engine from the above-mentioned weighted averaged air amount and the above-mentioned engine speed. A block 104 is means for calculating the actual injected fuel amount by correcting the basic fuel amount with respect to the water temperature and the like after the engine is started. The block 105 is a means for performing a feedback control correction from the exhaust gas oxygen concentration to the above-mentioned injected fuel amount. Block 106 is a means for supplying fuel to the engine based on the signal of the injected fuel amount calculated in the blocks 101, 102, 103, 104 and 105 described above. A block 107 is a means for performing feedback control so that the air-fuel ratio becomes the stoichiometric air-fuel ratio and calculating a correction coefficient based on the output of the exhaust gas oxygen concentration sensor of the engine.

A block 108 is a means for judging whether or not it is a region where the exhaust gas is recirculated to the intake side of the engine, based on the engine speed and the basic fuel amount calculated in the above-mentioned block 103. A block 109 is a unit that actually recirculates the exhaust gas to the engine based on the determination of the above block 108. A block 110 is a means for determining whether or not the exhaust gas recirculation means is in a region to be diagnosed, and the basic fuel amount of the block 103, the recirculation region diagnosis signal of the block 108, and the engine speed are inputted.

A block 112 is a means for diagnosing the exhaust gas recirculation means, to which the diagnosis area determination signal of the block 110 and the output of the air-fuel ratio feedback control means of the block 107 are input. The block 111 is the block 1 described above.
It is a means for introducing secondary air to the exhaust side of the engine based on the diagnostic region determination signal of 10. Block 113 is
It is means for displaying an abnormality of the recirculation means based on the exhaust gas recirculation means diagnostic signal of the block 112.

FIG. 2 is a diagram showing an example of the overall configuration of the system of the present invention. The engine 200 includes a thermal air flow meter (hereinafter abbreviated as H / W sensor) 202 for measuring a mass flow rate of intake air, an intake pipe throttle valve opening sensor 203 for detecting a throttle valve opening of an intake pipe, A fuel injection valve 204 for supplying fuel to the engine, a spark plug 206 for igniting an air-fuel mixture flowing into an engine cylinder, a crank angle sensor 207 for detecting a crank angle of the engine, an oxygen concentration sensor 208 for detecting an oxygen concentration of exhaust gas, A secondary air introduction pump 209 that introduces secondary air into the exhaust pipe of the engine, an exhaust gas recirculation pipe 210 that connects the intake pipe and the exhaust pipe of the engine and recirculates exhaust gas, and an exhaust gas recirculation that opens and closes the exhaust gas recirculation pipe. Signals from the valve 211, the three-way catalyst 212 that purifies the exhaust gas by the redox reaction, and the signals from the various sensors described above are calculated based on a prestored procedure. Based on the calculation results consisting of an engine control unit 201 for generating a signal for controlling driving of the actuator such as the aforementioned fuel injection valve.

FIG. 3 shows internal circuit blocks of the engine control unit 201. The engine control device inputs signals of various sensors shown in FIG. 2 and can perform a digital arithmetic process on an analog signal of the driver circuit 201-1 which converts a low level signal (transistor TTL level) into a high level signal for driving an actuator. Interface circuit 201-2 that performs signal processing as described above, an arithmetic circuit 201-3 that has a microcomputer that performs digital arithmetic processing or an arithmetic circuit that is equivalent thereto, an arithmetic circuit 201-
A memory for storing constants, variables and programs used in the arithmetic processing of No. 3 is provided. A nonvolatile ROM 20 is used as the memory.
1-4 and volatile RAM 201-5. In addition, a backup power supply 201-6 for supplying a voltage for holding the contents of the volatile RAM 201-5 is provided.

In this embodiment, the digital arithmetic unit is used, but it goes without saying that an analog arithmetic unit can also be used. In this embodiment, the thermal air flow meter,
Signals from the throttle open sensor (throttle valve opening sensor), crank angle sensor, oxygen concentration sensor are input, fuel injection valve signal, spark plug signal, electric air pump (secondary air introduction pump) drive signal, exhaust gas recirculation valve The drive signal is being output.

FIG. 4 shows an example of a concrete method of the air amount detecting means 101 passing through the intake pipe throttle valve of the engine of FIG. H / installed upstream of the engine intake pipe
The voltage signal of the W sensor 202 removes electrical noise with a hard filter including a resistor 202-1 and a capacitor 202-2. The voltage signal from which the noise has been removed is subjected to voltage-flow rate conversion in a block 202-3 of the engine control device 201 to obtain a throttle passing air amount.

FIG. 5 shows another specific example of the throttle passing air amount detecting means of FIG. The electric signal of the throttle valve opening sensor 203 installed in the throttle valve of the intake pipe of the engine is
Noise is removed by a filter composed of a resistor 203-1 and a capacitor 203-2, and a block 203-3 performs a map search for the engine speed and the throttle passing air amount to detect the intake air amount.

The intake air amount filtering process in block 102 of FIG.
When the current intake air amount detected in 1 is Qa, the previous intake air amount is Qaold, and the weighted average weight is WEIGHT, it is performed based on the following equation. Qanew = WEIGHT / Qa + (1-WEIGHT)
Qaold The weighted average weight is changed according to the engine speed by setting WEIGHT = f (N), where N is the engine speed. This change is done by table lookup.

The basic fuel calculation means 103 divides the weighted average intake air amount Qa by the engine speed N and multiplies it by the fuel injection valve coefficient K to calculate the basic fuel amount Tp by the following equation. Tp = K · Qa / N The injected fuel calculation means 104 calculates the basic fuel amount Tp by
Engine speed N, basic fuel amount Tp, engine water temperature Tw
The injection valve invalid time Ts is added by multiplying the correction coefficient Coef calculated based on Ti = Coef · Tp + Ts Coef = g (N, Tp, Tw)

The air-fuel ratio correction means 105 has the following equation:
The actual injected fuel amount Tiout is calculated by multiplying the above-mentioned injected fuel amount Ti by the correction coefficient α calculated by feedback control with the oxygen concentration sensor output O ₂ . Tiout = αTi α = h (O ₂ )

FIG. 6 shows that the engine control device of this embodiment is
The behavior of the output of the oxygen concentration sensor 208 and the output of the air-fuel ratio feedback control means 107 when the secondary air introduction pump 209 is operated to introduce the secondary air during the exhaust gas recirculation is shown. When secondary air is introduced into the exhaust pipe of the engine during normal exhaust gas recirculation, the air flow rate (non-measured air flow rate) that cannot be measured by the thermal air flow meter 202 in the exhaust gas increases, and oxygen The concentration sensor output is on the fuel lean side. Along with this, the air-fuel ratio correction coefficient α
Indicates that becomes larger. On the other hand, when the exhaust gas recirculation is not normally performed, for example, when the exhaust gas recirculation passage is blocked or the opening operation of the exhaust gas recirculation valve 211 is defective, the secondary air is introduced. However, the flow rate of air flowing through the exhaust gas recirculation passage does not change much. Therefore, no particular change appears in the oxygen concentration sensor output, and the air-fuel ratio correction coefficient α in the air-fuel ratio feedback control does not change before or after the introduction of the secondary air, or the change width is small.

In this way, by introducing the secondary air into the exhaust gas recirculation and monitoring the output of the oxygen concentration sensor or the fluctuation of the air-fuel ratio correction coefficient α in the air-fuel ratio feedback control at that time, the exhaust gas recirculation is normally performed. It can be diagnosed whether it is done. It is also possible to find the difference between the set exhaust gas recirculation amount and the actual exhaust gas recirculation amount, that is, the non-recirculation amount. When a hole is formed in the exhaust gas recirculation passage, the output of the oxygen concentration sensor is always on the fuel lean side, and the air-fuel ratio correction coefficient α is always biased to a large value.
Diagnosis can be made by monitoring the oxygen concentration sensor output or the air-fuel ratio correction coefficient α.

In this embodiment, a binary sensor is used as the oxygen concentration sensor, but an oxygen concentration sensor that produces an output proportional to the oxygen concentration may be used. FIG. 7 shows an example of a control block of the exhaust gas recirculation region determination means of the block 108 of FIG. 1 of the present embodiment. Determine the recirculation region with the basic fuel amount, or the intake air amount and the engine speed,
Produce an output signal. In the example of this figure, the exhaust gas recirculation valve is
This is the case of an ON / OFF type valve. FIG. 8 shows another example of the control block of the exhaust gas recirculation region determination means in the block 108 of FIG. 1 of the present embodiment. Based on the basic fuel amount or the intake air amount and the engine speed, the duty signal of the valve that linearly opens or the step number of the step motor that drives the valve is output.

FIG. 9 is a block 110 of FIG. 1 according to this embodiment.
3 is a control block diagram of the exhaust gas recirculation means diagnostic area determination means of FIG. AND gate G110-5, comparator G110-3,
In G110-4, the basic fuel amount is threshold values G110-1, G110.
It is determined whether the value is an intermediate value between 110-2. AND gate G110-10, comparators G110-8, G110-9
Indicates that the engine speed is a threshold value G110-6, G110-7.
It is judged whether it is an intermediate value of. Time delay device G11
0-11, subtractor G110-13, comparator G110-1
5 determines whether the throttle valve opening n times before the calculation cycle and the current throttle valve opening are equal to or less than the threshold value G110-14.
In the present embodiment, the calculation cycle n is searched in the table from the engine speed. The logical product G110-16 is
When the above conditions are satisfied and the exhaust gas recirculation region is in effect, a signal indicating that the exhaust gas recirculation device diagnostic region is in effect is output. Further, the secondary air introduction means 111 in FIG. 1 starts the secondary air introduction based on this signal.

FIG. 10 is a block 11 of FIG. 1 according to this embodiment.
2 is a control block of exhaust gas recirculation means diagnostic means 2;
Constants G112-2, G110-5, time delay device G112
-4, the multipliers G112-3, G112-6, and the adder G112-7 perform a weighted average of the air-fuel ratio feedback control signal (air-fuel ratio correction coefficient) outside the diagnostic region. Constant G112-8,
G110-11, time delay unit G112-10, multiplier G
112-9, G112-12, and adder G112-1
3 performs a weighted average of the air-fuel ratio feedback control signal in the diagnostic area. The adder G112-14 calculates the difference between the air-fuel ratio feedback control signals inside and outside the diagnostic region. The weighted average calculation switching of the air-fuel ratio feedback control signal inside and outside the diagnostic region is performed by the switch G112-1 based on the diagnostic region determination signal. Also,
The weight of the weighted average is searched in the table from the engine speed in block G112-15. The comparator G112-19 is
It is determined whether or not the difference value of the air-fuel ratio feedback control signal is larger than the engine speed and the threshold value obtained by the map search using the basic fuel amount signal. If it is larger, switch G112
-21 is switched and the difference value between the difference value of the air-fuel ratio feedback control signal and the threshold value for which the map is searched is multiplied by the engine speed and the flow rate conversion coefficient for which the map is searched for the basic fuel amount signal, and the product is integrated. Start. It should be noted that this integration is reset every fixed time or every fixed crank angle of the engine. The value before reset is output as the exhaust gas non-recirculation amount.

FIG. 11 is a general flow chart for calculating the amount of injected fuel in the engine control system of this embodiment. In step S101, the intake air amount of the engine is detected. In step S102, the intake air amount is filtered. In step S103, the basic fuel amount is calculated based on the intake air amount and the engine speed described above. In step S104, the amount of injected fuel is calculated by making a correction according to the engine state.
The air-fuel ratio feedback control signal is read in step S107, and the air-fuel ratio is corrected in step S105. Step S106
The fuel amount calculated in step 3 is transmitted to the fuel injection means, and fuel is injected.

FIG. 12 is a flow chart of the air-fuel ratio feedback control of this embodiment. In step S107-1, the oxygen concentration sensor is read, and in step S107-2, it is determined whether the output of the oxygen concentration sensor is inverted. In the case of reversal, the differential value is added to or subtracted from the air-fuel ratio feedback control signal according to the reversal of lean to rich and rich to lean (step S10).
7-3, S107-4, S107-5). If it is determined in step S107-2 that the air-fuel ratio has not been reversed, the integrated value is added to or subtracted from the air-fuel ratio feedback control signal due to the enrichment or leaning of the air-fuel ratio (S107-6, S107-7, S107-8).

FIG. 13 shows a flow chart of the exhaust gas recirculation means diagnostic area determination means of this embodiment. Step S1
At 10-1, it is judged whether or not there is an exhaust gas recirculation signal. If yes, steps S110-2, S110-3, S11
At 0-4, the basic fuel amount is read, and it is determined whether the basic fuel amount is within the upper and lower thresholds. If it is, the engine speed is read in steps S110-5, S110-6, and S110-7, and it is determined whether the engine speed is within the upper limit and the threshold values. If yes, step S110-
8, S110-9, S110-10, S110-11
Then, the output of the throttle opening sensor is read, and it is determined whether the amount of change in the throttle opening is within the threshold value. A table is searched for the calculation interval of the change in the throttle opening based on the engine speed. If it is within the threshold value, a diagnostic region determination signal is output in step S110-12. If the basic fuel amount, the engine speed, and the throttle opening change amount are outside the threshold values, the diagnosis area determination signal output is stopped in step S110-13.

FIG. 14 shows a flow chart of the exhaust gas recirculation means diagnostic means of this embodiment. Step S112-
1, the engine speed is read in S112-2, and the weighted average weight is searched in the table. Step S112-3, S
At 112-4, S112-5, and S112-6, the weighted average of the air-fuel ratio feedback control correction coefficients inside and outside the diagnostic region is calculated, and the difference between the two is calculated. In steps S112-7 and S112-8, the basic fuel amount is read, and a threshold value map search is performed based on the basic fuel amount and the engine speed. Steps S112-9 and S112
-10 and steps S112-16, S112-17,
In S112-15, the input value to the integrator is determined by whether or not the difference value of the air-fuel ratio feedback control correction coefficient described above exceeds the threshold value searched for in the map described above. If the threshold is exceeded, steps S112-12 and S112-1
3, the difference value between the threshold value searched for in the map and the difference value of the air-fuel ratio correction coefficient weighted average value in S112-14 is multiplied by the basic fuel amount and the flow rate conversion coefficient searched by the map from the engine speed to be integrated. Input into the vessel. If it does not exceed the threshold value, 0 is input to the integrator (no integration is performed).

[0029]

According to the present invention, it is possible to comprehensively diagnose a failure of each mechanical system of the exhaust gas recirculation device (from the exhaust pipe to the exhaust gas recirculation valve and from the exhaust gas recirculation valve to the intake pipe). Further, since the deviation of the air-fuel ratio correction coefficient is multiplied by the flow rate conversion coefficient, the recirculation amount can be calculated.

Further, the atmosphere is mixed with the exhaust gas and is recirculated to the intake side, so that the combustion speed is reduced, and the exhaust gas recirculation device can be diagnosed without increasing the nitrogen peroxide due to the dilution of the air-fuel ratio. it can. At the same time, since the atmospheric air is also mixed in the exhaust gas toward the catalyst, it is possible to burn the hydrocarbon due to the misfire during exhaust gas recirculation with the catalyst during the diagnosis.

[Brief description of drawings]

FIG. 1 is a control block diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration around an engine of the present invention.

FIG. 3 is an internal block diagram of an engine control device according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of an example of an engine intake air amount detection means of the present invention.

FIG. 5 is an explanatory view of another example of the intake air amount detecting means of the engine of the present invention.

FIG. 6 is a diagram showing an example of behavior of exhaust gas oxygen concentration and output of air-fuel ratio engine control means in an embodiment of the present invention.

FIG. 7 is a diagram showing an example of a control block of exhaust gas recirculation region determination means according to the embodiment of the present invention.

FIG. 8 is a diagram showing another example of the control block of the exhaust gas recirculation region determination means according to the embodiment of the present invention.

FIG. 9 is a diagram showing an example of a control block of an exhaust gas recirculation means diagnostic area determination means of an embodiment of the present invention.

FIG. 10 is a diagram showing an example of a control block of an exhaust gas recirculation means diagnostic means of an embodiment of the present invention.

FIG. 11 is a diagram showing an example of a flowchart of fuel control of the engine control device of the present invention.

FIG. 12 is a diagram showing an example of a flowchart of air-fuel ratio engine control of the engine control system of the invention.

FIG. 13 is a diagram showing an example of a flow chart of exhaust gas recirculation means diagnostic area determination means of the present invention.

FIG. 14 is a view showing an example of a flowchart of exhaust gas recirculation means of the present invention.

[Explanation of symbols]

Reference numeral 101 ... Intake air amount detection means, 107 ... Air-fuel ratio engine control means, 108 ... Exhaust gas recirculation area determination means, 110 ... Exhaust gas recirculation means diagnostic area determination means, 111 ... Secondary air introduction means, 112 ... Exhaust gas recirculation means Diagnostic means, 200 ...
Engine, 201 ... Engine control device, 202 ... Thermal air flow meter, 208 ... Oxygen concentration sensor, 209 ... Secondary air introduction pump, 211 ... Exhaust gas recirculation valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location F02D 41/14 310 C

Claims (10)

[Claims] 1. An intake air amount detecting means provided in an intake pipe of an engine, a means for calculating an amount of fuel supplied to an engine using an output of the intake air detecting means, and an installation of the intake air amount detecting means. An exhaust gas recirculation path that joins the intake pipe and an engine exhaust pipe downstream of the position, an exhaust gas recirculation amount adjusting means installed in the middle of the exhaust gas recirculation path, and a secondary that introduces air into the exhaust pipe. An air introducing means, an oxygen concentration detecting means installed in the exhaust pipe upstream of an air introducing position by the secondary air introducing means for detecting an oxygen concentration in the exhaust gas, and an oxygen concentration detecting means Fuel amount correcting means for correcting the amount of fuel supplied to the engine based on the output, and means for introducing air into the exhaust pipe by the secondary air introducing means during the exhaust gas recirculation operation by the exhaust gas recirculation amount adjusting means. And an exhaust gas recirculation diagnostic device for an engine, comprising: and a diagnostic means for diagnosing an exhaust gas recirculation state during the introduction of air. 2. The exhaust gas recirculation diagnosing device for an engine according to claim 1, wherein the diagnosing means makes a diagnosis based on an output of the oxygen concentration detecting means. 3. The exhaust gas recirculation diagnosing device for an engine according to claim 1, wherein the diagnosing means diagnoses based on a correction amount of the fuel amount correcting means. 4. The exhaust gas recirculation diagnostic device for an engine according to claim 1, wherein the exhaust gas recirculation amount adjusting means includes means for opening and closing the exhaust gas recirculation path. 5. The exhaust gas recirculation diagnostic device for an engine according to claim 1, wherein the exhaust gas recirculation amount adjusting means includes means for controlling a cross-sectional area of the exhaust gas recirculation path. . 6. The exhaust gas recirculation diagnostic device for an engine according to claim 5, wherein the means for controlling the cross-sectional area of the passage uses an electromagnetic valve. 7. The exhaust gas recirculation diagnostic device for an engine according to claim 5, wherein the means for controlling the cross-sectional area of the passage uses a step motor. 8. The engine according to claim 1, wherein the oxygen concentration detecting means generates two output values by using a constant value of the oxygen concentration as a threshold value. Exhaust gas recirculation diagnostic device. 9. The exhaust gas recirculation diagnosis system for an engine according to claim 1, wherein the oxygen concentration detection means generates a continuous output according to the oxygen concentration. apparatus. 10. A vehicle comprising the exhaust gas recirculation diagnostic device according to any one of claims 1 to 9.