DE10323426A1 - Exhaust gas recirculation system for combustion engine detects covering of EGR valve and carries out forced opening of valve only during operation of combustion engine after turning of combustion engine is finished - Google Patents

Abstract

The exhaust gas recirculation (EGR) system includes an electronic control unit (ECU) that has a covering detection unit for detecting if an EGR valve is covered when in a closed valve position during the operation of a combustion engine after the turning of the combustion engine is finished. If a covering of the EGR system is detected, the ECU carries out a forced opening of the EGR valve. An opening degree of the EGR valve is set by a control member only during the operation of the combustion engine after the turning of the combustion engine is finished.

Description

The present invention relates to an exhaust gas recirculation system (EGR system) for recirculating one Part of an exhaust gas from an internal combustion engine, such as one Diesel engine, to an air intake side of the engine.

Because the emissions regulation in the past has become stricter, the EGR system has become increasingly important and must have one Control the degree of an opening of an EGR valve of the EGR system between the minimum value and the maximum value based on the Operating state of the internal combustion engine are carried out.

For example, in a diesel internal combustion engine may be a part of an exhaust gas to an air intake side of the internal combustion engine be recirculated to the amount of exhaust gas or emissions while reduce the idle period of the internal combustion engine. however is the intake vacuum in the idle period of the diesel engine of the diesel engine is relatively low and the exhaust pressure of the diesel internal combustion engine is also relatively low. This is for recirculation the required amount of the exhaust gas to the intake side of the diesel engine relatively high degree of opening EGR valve required. At this point, however, oily particles may appear for example, stick to a valve seat of the EGR valve and can the adherent oily Particles sometimes open up of the EGR valve (which prevents the EGR valve from sticking in the closed state).

In the EGR system, the degree the opening of the EGR valve varies, the actual degree of opening of the EGR valve, for example, based on the amount of valve lift or the amount of intake air received. The EGR valve is feedback-controlled in such a way that the actual degree the opening of the EGR valve essentially with the target degree of opening of the EGR valve matches.

If so according to the state of the art the EGR valve in the closed valve position due to the for example, particles adhering to the valve seat are glued, becomes a value of a valve opening instruction gradually elevated, so that a driving force for opening the EGR valve increases. If the driving force to the required level to open the EGR valve is increased the EGR valve is opened.

Therefore there is a time lag between the time the valve opening instruction was issued to the EGR valve and the time of the actual opening of the EGR valve. If the EGR valve is stuck in the closed Valve position occurs, namely a period of unavailability the EGR (exhaust gas recirculation) disadvantageous extended, while the appropriate amount of EGR is not available.

Furthermore, the valve opening after Solving the Gluing the EGR valve over the The above operation is usually excessive the opening the EGR valve, which is the target degree of opening of the EGR valve. So with the next one Feedback control operation the actual Degree of opening of the EGR valve reduced. This means, that according to the prior art the excessive actual degree of opening of the EGR valve is set so that it essentially matches the Target degree of opening of the EGR valve matches. Thus, the time it takes to achieve the target degree of opening of the EGR valve is required, disadvantageously extended.

To avoid sticking the EGR valve in the closed valve position, a technique has been developed to force energize an actuator (e.g., a linear solenoid) of the EGR valve during a period between when the ignition switch is turned on (or the starter switch is turned on) and when Initiation of normal control operation to control the degree of opening of the EGR valve to release the sticking of the EGR valve is proposed (see, for example, Japanese Unexamined Patent Publication No. 7-293355 ).

In Japanese Unexamined Patent Publication No. 7-293355 is a technique for forcing the EGR valve to open during a period between when the ignition switch is turned on (or when the starter switch is turned on) and when a predetermined period of time has elapsed or, alternatively, the time of detection of the EGR sticking solution. Valve disclosed, which is detected by the use of a sensor.

Thus, the EGR valve is forced to open during cranking of the internal combustion engine and the ratio of the unburned gas in the gas mixture that is drawn into a corresponding combustion chamber during cranking of the internal combustion engine is increased, which results in a reduction in the ratio of the air in the gas mixture. Due to the deterioration of the air / fuel ratio of the gas mixture, the ignitability of the gas mixture is reduced at the time of cranking the internal combustion engine. Thus, the cubic time between the time of initiating cranking of the internal combustion engine (or the time of turning on the ignition switch) and the time of reaching a complete explosion at the internal combustion engine (in particular re of the occurrence of a sequential explosion or combustion over all cylinders of the internal combustion engine) and a relatively large amount of smoke is generated at the time of cranking the internal combustion engine.

Furthermore, to avoid the Deterioration of starting ability of the internal combustion engine only the time for forced opening of the EGR valve a period of time between when the ignition switch is turned on and the timing of initiating cranking of the internal combustion engine limited (in particular the time when the rotation was initiated the internal combustion engine). However, this results in a relatively short period of time for forced opening of the EGR valve. Therefore, even if the EGR valve is stuck, there is reinforced the possibility, that the EGR valve is stuck due to the very short period of time forced Open of the EGR valve is not released or is fixed.

According to the Japanese Unexamined Patent Publication No. 7-293355 The disclosed technique is postponed even after the engine cranking is finished, unless the EGR valve sticking solution is detected, the normal control operation for controlling the EGR valve opening degree is deferred, and the EGR valve is forced to open by forced actuator re-energization of the EGR valve.

However, even with this technique the EGR valve during the cranking of the internal combustion engine before the forced re-excitation of the EGR valve actuator positively opened to deteriorate the air-fuel ratio. Due to the deterioration of the air / fuel ratio becomes the time period for cranking or starting the internal combustion engine extended and will be a relatively large one Amount of smoke at the time the engine is cranking generated.

The present invention is based on addressed the above disadvantage. So it's a job of the present invention to provide an EGR system which in the Is able to release an EGR valve from sticking without any essential Deterioration of engine starting ability is caused.

To achieve the object of the present invention to solve, is an EGR system for one Internal combustion engine provided. The EGR system has an EGR valve and a control device. The EGR valve is in an EGR pipe of the internal combustion engine used between an inlet pipe of the Internal combustion engine and an exhaust pipe of the internal combustion engine connects to a degree of connection in the EGR pipe between the inlet pipe and the outlet pipe respectively adjust the exhaust pipe. The EGR valve has an actuator on that an actual Degree of opening of the EGR valve adjusts to a degree of connection in the EGR pipe adjust. The control device controls the actual one Degree of opening of the EGR valve based on an operating state of an internal combustion engine by driving the actuator so that the actual Degree of opening of the EGR valve normally by the actuator in a normal one Control mode is set so that it essentially with a target degree of opening of the EGR valve matches. The control device has an adhesion detection device for detecting the occurrence of sticking of the EGR valve in a closed valve position while the internal combustion engine is running after completion of cranking the internal combustion engine. If the adhesion detection device detects the occurrence of an adhesion of the EGR valve is detected, leads the control device forcibly opens the EGR valve Providing a necessary driving force to open the EGR valve is required in the closed valve position is glued for that Actuator only during the engine run after cranking is finished of the internal combustion engine.

The invention together with the task of additional Features and their advantages are best understood from the following description, the attached claims as well as the associated Understand drawings.

1 10 is a schematic view of an EGR system according to an embodiment of the present invention;

2 Fig. 4 is a cross-sectional view of an EGR valve of the EGR system;

3 Fig. 14 is a flowchart showing a control operation for releasing the EGR valve from sticking;

4 is a graph showing the EGR valve sticking solution.

An exhaust gas recirculation (EGR) system for an internal combustion engine according to an embodiment of the present invention is described with reference to FIG 1 described. In this embodiment, a diesel engine is used as an internal combustion engine.

As in 2 is shown, the EGR system has an EGR valve 5 and an engine control unit (ECU) 6 corresponding to a control device of the present invention. The EGR valve 5 is in an EGR pipe 4 inserted between an inlet pipe 2 and an outlet pipe 3 in the internal combustion engine 1 connects. The ECU 6 sets the degree of opening (especially a valve position) of the EGR valve 5 on.

As in 2 are shown with the EGR valve 5 two valve seats 8th on a partition wall 7 provided between an inlet side space 4a of the EGR pipe 4 that with the inlet pipe 2 communicates, and an outlet pipe side space 4b of the EGR pipe 4 separates that with the outlet pipe 3 communicates. The valve seats 8th are through two valve elements 9 opened and closed. The valve elements 9 are represented by a linear solenoid 10 driven (for example, an actuator). The linear solenoid 10 is through the ECU 6 Duty cycle-controlled to the degree of opening of each valve element 9 (according to the degree of connection in the EGR pipe 4 between the inlet pipe 2 and the outlet pipe 3 ) between 0% and 100%.

The ECU 6 is for controlling the internal combustion engine 1 (including control of the EGR valve 5 ) on the basis of, for example, the current operating state of a vehicle. The ECU takes to detect the operating state of the vehicle 6 Levies from various sensors.

Examples of these sensors include an air flow sensor 11 , a throttle position sensor 12 , an engine speed sensor 13 , a coolant temperature sensor 14 and a stroke sensor 15 as in 1 is shown. An air flow sensor 11 measures the amount (or flow rate) of intake air through the intake pipe 2 steps through. The throttle position sensor 12 measures a position of an accelerator pedal operated by an operator of the vehicle. The engine speed sensor 13 measures the engine speed (rpm). The coolant temperature sensor 14 measures the temperature of the coolant of the internal combustion engine 1 , The stroke sensor 15 directly measures the degree of opening of the EGR valve 5 ,

The EGR valve 5 is usually through the ECU 6 feedback regulated so that the actual amount of valve lift (corresponding to the actual degree of opening) of the EGR valve 5 essentially with the target amount of valve lift (corresponding to the target degree of opening) of the EGR valve 5 matches. Here is the target amount of valve lift of the EGR valve 5 calculated using a map or an image or a mathematical equation based on the operating state of the vehicle, which is measured with the sensors. The actual amount of valve lift of the EGR valve 5 is with the stroke sensor 15 measured.

That to the inlet pipe 2 through the EGR valve 5 Recirculated exhaust gas passes through the valve seats 8th of 2 , so that particles contained in the exhaust gas, for example on the valve seats 8th and the valve elements 9 can cling to. Especially in the low load condition of the internal combustion engine 1 , for example in the idle state of the internal combustion engine 1 , a relatively large amount of EGR is required and the exhaust gas temperature is relatively low. Thus, the particles contained in the exhaust gas become oily.

Therefore, the oily particles that are on the valve seats 8th and the valve elements 9 adhere, possibly causing the valve elements 9 at the valve seats 8th stick while the valve seats 8th through the valve elements 9 getting closed. This means that the oily particles are sticking the EGR valve 5 can cause while the EGR valve 5 is in the closed valve position.

For this reason, the ECU 6 an adhesion detection device (or a program) for detecting the occurrence of the adhesion of the EGR valve 5 in the closed valve position while the internal combustion engine is running 1 (especially during the speed of the internal combustion engine 1 is above the crank speed of the internal combustion engine) after cranking the internal combustion engine 1 (especially after turning off the starter switch and ending cranking).

If at the ECU 6 the bond detection device the bond of the EGR valve 5 detected in the closed valve position, the normal feedback control of the EGR valve 5 temporarily during the running of the internal combustion engine 1 stopped and the driving force (in this embodiment, this is the duty ratio of 100%), which is used to open the EGR valve 5 is required, the linear solenoid 10 for forced opening of the EGR valve 5 fed. When opening the EGR valve 5 through the stroke sensor 15 normal feedback control is resumed.

• (I) eine Differenz zwischen einem Sollbetrag des Ventilhubs des EGR-Ventils 5, der durch die ECU berechnet ist, und dem tatsächlichen Betrag des Ventilhubs des EGR-Ventils 5, der durch den Hubsensor 15 gemessen wird, ist gleich wie oder größer als ein vorbestimmter Wert (insbesondere der Sollbetrag des Ventilhubs – der tatsächliche Betrag des Ventilhubs ≥ der vorbestimmte Wert);
• (II) der Zielbetrag des Ventilhubs des EGR-Ventils 5, der durch die ECU 6 berechnet ist, ist gleich wie oder größer als ein vorbestimmter Wert (insbesondere der Zielbetrag des Ventilhubs ≥ der vorbestimmte Wert); und
• (III) die Bedingung von (I) und die Bedingung von (II), die vorstehend erwähnt sind, werden durchgehend über zumindest eine vorbestimmte Zeitdauer erfüllt (insbesondere die Zeitdauer von (I) und (II) ≥ die vorbestimmte Zeitdauer).

The adhesion detection device of the present embodiment detects or determines that the EGR valve 5 is glued to the closed valve position if the following first to third conditions (I) - (III) are all fulfilled:

• (I) a difference between a target amount of valve lift of the EGR valve 5 calculated by the ECU and the actual amount of valve lift of the EGR valve 5 by the stroke sensor 15 is measured is equal to or greater than a predetermined value (in particular the target amount of the valve lift - the actual amount of the valve lift ≥ the predetermined value);
• (II) the target amount of valve lift of the EGR valve 5 by the ECU 6 is calculated to be equal to or larger than a predetermined value (in particular, the target amount of valve lift ≥ the predetermined value); and
• (III) the condition of (I) and the condition of (II) mentioned above are continuously satisfied over at least a predetermined period (in particular, the period of (I) and (II) ≥ the predetermined period).

Furthermore, when performing the forced valve opening described above (particularly, when outputting the duty ratio of 100%, which is a "valve full opening instruction") to the linear solenoid 10 ) the forced valve opening and resumes normal feedback control when the following fourth condition (IV) is met, that is, when the actual amount of valve lift is that with the stroke sensor 15 is measured, the predetermined amount of valve lift is reached (in particular the actual amount of valve lift ≥ the predetermined amount of valve lift).

However, even when the EGR valve is sticking together 5 in the closed valve position by the use of the adhesion detection device, the above-described forced valve opening by the ECU 6 not performed if the following fifth and sixth conditions (V), (VI) are both fulfilled:
(V) the speed of the internal combustion engine 1 is equal to or greater than a predetermined speed; and
(VI) the load of the internal combustion engine 1 is equal to or greater than a predetermined load (for example, when the amount of fuel injection is equal to or greater than a predetermined amount of fuel injection). In this way, it is possible to prevent a deterioration in vehicle drivability caused by a rapid change in the amount of EGR at the relatively large torque of the internal combustion engine 1 is induced.

The ECU 6 has a program that stops the forced valve opening described above and outputs an abnormal signal indicating the abnormality of the EGR valve 5 indicates when the EGR valve is opening 5 not within a predetermined period of time since the forced valve opening was initiated when the EGR valve sticking was detected 5 is detected when the valve is closed.

If the abnormal signal from the EGR valve 5 is output, a diagnostic logic that is in the ECU 6 as a program to diagnose the EGR valve 5 implemented. In this way, the abnormality of the EGR valve 5 recognized and issued a warning to the passenger, for example, by a warning lamp, a warning tone or the like.

Next, control operation of the ECU 6 with reference to a flow chart of FIG 3 described.

In this control mode, it is first determined that the internal combustion engine 1 currently after the cranking of the internal combustion engine has ended 1 runs at step S1. More specifically, it is determined whether the speed of the internal combustion engine 1 is greater than a predetermined speed (speed of the internal combustion engine 1 at the time of cranking) while an ignition switch (IG switch) is on. If the answer to the inquiry at step S1 is "NO", control returns to the beginning of the flowchart (in particular, it returns to START in 3 back).

If the answer to the inquiry at step S1 is "YES", step S2 is proceeded to, at which it is determined whether the control operation of the EGR valve 5 is currently underway. If the answer to the inquiry at step S2 is "NO", control returns to the beginning of the flowchart.

If the answer to the request is "YES" at step S2, it proceeds Control proceeds to step S3, in which it is determined whether “a bond state mark” indicates the bond of EGR valve 5 indicates has not been set.

If the answer to the inquiry at step S3 is "YES", control proceeds to step S4, where it is determined whether the first condition (I) and the second condition (II) are both satisfied. If the answer to the Inquiry at step S4 "NO" becomes the normal state of the EGR valve 5 determines or detects at step S5, and control returns to the beginning of the flowchart.

If the answer to the request is "YES" at step S4, the Control proceeds to step S6. At step S6, it is determined whether the first condition (I) and the second condition (II) consistently over the predetermined period of time met have been. If the answer to the inquiry at step S6 is "NO", control returns back to the beginning of the flowchart. If the answer to the request is "YES" at step S6, the Control proceeds to step S7 at which the bond state mark is set. Then control returns to the beginning of the flowchart back.

If the answer to the inquiry at step S3 is "NO", in particular if the bond state flag is set at step S7 in the previous run, control proceeds to step S8. At step S8, it is determined whether the fourth condition (IV If the answer to the request at step S8 is "YES", it is determined that the EGR valve is stuck 5 is resolved or no longer exists, and control proceeds to step S5.

If the answer to the inquiry at step S8 is "NO", control proceeds to step S9. At step S9, it is determined whether the fifth condition (V) and the sixth condition (VI) described above have been met. If the answer if the request at step S9 is "YES", control proceeds to step S10. At step S10, the maximum duty ratio becomes 100% to the EGR valve 5 output. Control then returns to the beginning of the flowchart.

If the answer to the request at step S9 is "NO", control returns to the beginning of the flowchart without performing the forced valve opening described above to deteriorate the vehicle Prevent driveability by changing the amount of EGR at the relatively large torque of the internal combustion engine 1 is induced. In the above operation, steps S4-S7 correspond to the adhesion detection device of the present invention.

Referring to a graphic of 4 becomes the appearance of the EGR valve sticking 5 while the engine is running 1 after cranking the internal combustion engine 1 below along with a change in duty cycle associated with the EGR valve 5 is supplied, and a change in the degree of opening of the EGR valve 5 described.

If the target amount of the valve lift by the ECU 6 based on the operating state of the internal combustion engine 1 is calculated in a way that is indicated by a dotted line A in 4 is shown, the duty cycle that the EGR valve increases 5 is supplied, as indicated by a solid line B.

At the time of EGR valve sticking 5 the actual amount of valve lift does not increase in a manner indicated by a solid line C in 4 is indicated when the target amount of the valve lift increases, as shown by the dotted line A.

• (I) Die Differenz zwischen dem Sollbetrag des Ventilhubs und dem tatsächlichen Betrag des Ventilhubs ist gleich wie oder größer als der vorbestimmte Wert (siehe die eingekreiste Zahl 1 in 4);
• (II) der Sollbetrag des Ventilhubs ist gleich wie oder größer als der vorbestimmte Wert (siehe die eingekreiste Zahl 2 in 4); und
• (III) die Bedingung von (I) und die Bedingung von (II), die vorstehend erwähnt sind, werden durchgängig über zumindest die vorbestimmte Zeitdauer erfüllt (siehe die eingekreiste Zahl 3 in 4).

The ECU 6 detects or determines that the EGR valve 5 is closed and glued if the following conditions (I) - (III) are all met:

• (I) The difference between the target amount of the valve lift and the actual amount of the valve lift is equal to or larger than the predetermined value (see the circled number 1 in 4 );
• (II) The target amount of the valve lift is equal to or larger than the predetermined value (see the circled number 2 in 4 ); and
• (III) the condition of (I) and the condition of (II) mentioned above are met consistently for at least the predetermined period of time (see the circled number 3 in 4 ).

If the ECU 6 detects or determines that the EGR valve 5 is closed and glued, the ECU holds 6 temporarily indicates the normal feedback control and gives the duty cycle ratio of 100 (in particular the valve opening instruction) to the EGR valve 5 from.

If the EGR valve 5 receives the valve full opening instruction, the relatively large valve opening force on the EGR valve 5 generated. If the EGR valve is stuck 5 then released at the closed valve position, the actual amount of valve lift begins to increase, as indicated by the solid line C in 4 is indicated.

When the actual valve lift amount reaches a predetermined valve lift amount (see the circled number 4 in 4 ), the forced valve opening is then stopped and normal feedback control is resumed.

In the EGR system according to the present embodiment, when the EGR valve is stuck 5 in the closed valve position while the internal combustion engine is running 1 after cranking the internal combustion engine 1 is detected or determined, as described above, the driving force (for example, the duty ratio of 100%) that is used to open the EGR valve 5 the EGR valve is required 5 fed. Thus the EGR valve 5 forced open. In this way, the EGR valve can be glued 5 while the engine is running 1 be solved within a relatively short period of time. Even if the EGR valve is stuck 5 occurs in the closed valve position, as described above, the EGR valve may stick 5 are quickly resolved so that the appropriate amount of EGR can be obtained quickly.

According to the prior art, which is disclosed in Japanese Unexamined Patent Publication No. 7-293355 and the forced opening of the EGR valve at the time of cranking the engine (especially before reaching full explosion at the engine), the EGR valve is forced to open during cranking of the engine so that the air / Fuel ratio deteriorates at the time of cranking the engine. Due to the deterioration of the air / fuel ratio, the time period for cranking the internal combustion engine is extended and a relatively large amount of smoke is generated. In contrast, according to the present embodiment, the technique for forced opening of the EGR valve 5 only while the internal combustion engine is running 1 after completion of cranking the internal combustion engine 1 provided when the EGR valve is glued 5 while the engine is running 1 is recorded. Therefore, the air / fuel ratio becomes high during the cranking of the internal combustion engine 1 not deteriorated according to the present embodiment. Thus, the time period for cranking the engine 1 is not prolonged and a relatively large amount of smoke is not generated.

(Modifications)

In the above embodiment, the linear solenoid 10 as an exemplary actuator for adjusting the degree of opening of the EGR valve 5 used. Alternatively, any other suitable actuator, such as a vacuum actuator or an electric motor, can be used instead of the Li nearsolenoids 10 be used.

Furthermore, in the above-mentioned embodiment, the stroke sensor 15 which gives a signal based on the movement of the valve elements 9 as the exemplary sensor for measuring the actual degree of opening of the EGR valve 5 used. Alternatively, the actual degree of opening of the EGR valve 5 for example, based on the amount of intake air measured.

Additional advantages and modifications will be apparent to those skilled in the art. The invention in its broader meaning is therefore not on the specific details, limits the illustrative device and explanatory examples that are described and shown.

In the EGR system, the ECU thus points 6 the adhesion detection device S4-S7 for detecting the occurrence of the adhesion of the EGR valve 5 in the closed valve position while the internal combustion engine is running 1 after completion of cranking the internal combustion engine 1 on. When the adhesion detection device S4-S7 the occurrence of the adhesion of the EGR system 5 detected, the ECU leads 6 forced opening of the EGR valve 5 by providing the driving force required to open the EGR valve 5 is necessary, which is glued in the closed valve position for the actuator 10 , which is the actual degree of opening of the EGR valve 5 sets, only while the internal combustion engine is running 1 after completion of cranking the internal combustion engine 1 out.

Claims (6)

EGR system for an internal combustion engine ( 1 ), the EGR system comprising: an EGR valve ( 5 ) in an EGR pipe ( 4 ) of the internal combustion engine ( 1 ) is used, which is a connection between an inlet pipe ( 2 ) of the internal combustion engine ( 1 ) and an outlet pipe ( 3 ) of the internal combustion engine ( 1 ) for setting a degree of connection in the EGR pipe ( 4 ) between the inlet pipe and the outlet pipe ( 3 ), the EGR valve ( 5 ) an actuator ( 10 ) that has an actual degree of opening of the EGR valve ( 5 ) to adjust the degree of connection in the EGR pipe ( 4 ) sets; and a control device ( 6 ) indicating the actual degree of opening of the EGR valve ( 5 ) based on an operating state of the internal combustion engine ( 1 ) by driving the actuator ( 10 ) controls such that the actual degree of opening of the EGR valve ( 5 ) normal through the actuator ( 10 ) is set during normal control operation so that it essentially corresponds to a target degree of opening of the EGR valve ( 5 ), characterized in that in the EGR system the control device ( 6 ) an adhesion detection device (S4-S7) for detecting the occurrence of an adhesion of the EGR valve ( 5 ) in a closed valve position while the internal combustion engine is running ( 1 ) after the cranking of the internal combustion engine ( 1 ) having; and wherein when the adhesion detection means (S4-S7) the occurrence of the adhesion of the EGR valve ( 5 ) detects the control device ( 6 ) forced opening of the EGR valve ( 5 ) by providing the necessary driving force to open the EGR valve ( 5 ) that is glued in the closed valve position to the actuator ( 10 ) only while the internal combustion engine is running ( 1 ) after the cranking of the internal combustion engine ( 1 ) executes. EGR system according to claim 1, characterized in that the adhesion detection device (S4-S7) detects that the EGR valve ( 5 ) is stuck in the closed valve position if both of the following two conditions are met: (I) a difference between the target degree of opening of the EGR valve ( 5 ) and the actual degree of opening of the EGR valve ( 5 ) is equal to or greater than a predetermined value; and (II) the target degree of opening of the EGR valve ( 5 ) is equal to or larger than a predetermined value. EGR system according to claim 1, characterized in that the adhesion detection device (S4-S7) detects that the EGR valve ( 5 ) is stuck in the closed valve position if all of the following three conditions are met: (I) a difference between the target degree of opening of the EGR valve ( 5 ) and the actual degree of opening of the EGR valve ( 5 ) is equal to or greater than a predetermined value; (II) the target degree of opening of the EGR valve ( 5 ) is equal to or greater than a predetermined value; and (III) condition (I) and condition (II) are met continuously over at least a predetermined period of time. EGR system according to one of claims 1 to 3, characterized in that the control device ( 6 ) the forced opening of the EGR valve ( 5 ) also when detecting the occurrence of the sticking of the EGR valve ( 5 ) via the bond detection device (S4-S7) if both of the following two conditions are met: a rotational speed of the internal combustion engine ( 1 ) is equal to or greater than a predetermined speed; and a load of the internal combustion engine ( 1 ) is equal to or greater than a predetermined load. EGR system according to one of claims 1 to 4, characterized in that when the control device ( 6 ) opening the EGR valve ( 5 ) when executing the forced opening of the EGR valve ( 5 ) after the occurrence of the EGR valve sticking ( 5 ) detected by the bond detection device (S4-S7), the control device ( 6 ) performing the forced opening of the EGR valve ( 5 ) stops and resumes normal control operation at which the actual degree of opening of the EGR valve ( 5 ) by the actuator ( 10 ) is set so that it essentially corresponds to the target degree of opening of the EGR valve ( 5 ) matches. EGR system according to one of claims 1 to 5, characterized in that when the control device ( 6 ) the opening of the EGR valve ( 5 ) over a predetermined period of time when the EGR valve is forced to open ( 5 ) after detecting the occurrence of the EGR valve sticking ( 5 ) not detected by the adhesion detection device (S4-S7), the control device ( 6 ) performing the forced opening of the EGR valve ( 5 ) and an abnormal signal that indicates an abnormality of the EGR valve ( 5 ) displays.