JP2007255257A - Egr device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR device capable of effectively performing air bleeding of a coolant in a water-cooled EGR cooler over a short period and preventing a degeneration of engine warm-up performance caused by the air bleeding of the coolant in the EGR cooler after starting an engine. <P>SOLUTION: When the water-cooled EGR cooler 62 is arranged in a location above a radiator 2, air bleeding performance of the coolant in the EGR cooler 62 is degenerated. When air in the coolant in the EGR cooler 62 is sucked out through an air bleeding pipe 7 by making use of negative pressure at a just-before suction location 421 of a water pump 3 where water pressure keeps lowest in a circulating passage 4 of the coolant, the air bleeding of the EGR cooler 62 is effectively performed over a short period. The coolant sucked out from the EGR cooler 62 to the air bleeding pipe 7 as well as air is led to a suction side 31 of the water pump 3 without passing through the radiator 2. Therefore, the air bleeding of the coolant in the EGR cooler 62 is not related to a degeneration of the engine warm-up performance after starting the engine, so that an extension of the engine warm-up period can be prevented. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an EGR apparatus provided with a water-cooled EGR cooler, and more particularly, to an EGR apparatus improved in removing air from cooling water in the EGR cooler.

  For example, as shown in FIG. 3, an EGR device equipped with a water-cooled EGR cooler has a cooling water circulation path 4 that circulates between the engine 1 and the radiator 2 by a water pump 3. The bypass pipe 5 is connected so as to connect the downstream part to the downstream side, a water-cooled EGR cooler 6 is provided in the bypass pipe 5, and the EGR cooler 6 is cooled using the water pressure difference of the cooling water in the circulation path 4. Water is allowed to pass through.

  In the illustrated example, the inlet and outlet portions of the bypass pipe 5 are connected to the upstream portion and the downstream portion of the cooling water upper pipe 41 that connects the engine 1 and the radiator 2. It is also known that the inlet portion of the pipe 5 is connected to a portion on the downstream side of the water pump 3 of the cooling water lower pipe 42 that connects the radiator 2 and the engine 1. In the figure, T / st is a thermostat for circulating the cooling water without passing through the radiator 2 when the temperature of the cooling water is below a predetermined value.

  Cooling water is poured into the engine 1 and the EGR cooler 6 from the upper tank 21 of the radiator 2. In general, since the EGR cooler 6 is disposed at a lower position than the upper tank 21 as shown in the figure, when the cooling water is injected from the lower part of the engine 1, the air inside the EGR cooler 6 naturally becomes the upper tank. It is released toward the air 21 and released to the atmosphere by the gas-liquid separation function of the radiator cap 26. Therefore, no air vent structure is provided.

  By the way, in the field of diesel engines, in order to comply with recent and future exhaust gas regulations, Cooled EGR (Cooled EGR) using an EGR cooler that can cool EGR gas and perform a large amount of EGR is available. It is an essential technology. That is, in order to comply with future exhaust gas regulations, a larger amount of EGR is required, and the EGR cooler 6 is required to further increase the cooling capacity (capacity increase).

  However, when considering mounting on a vehicle, it is difficult to mount one large EGR cooler 6 in terms of space. A method of cooling EGR gas by arranging a plurality of small EGR coolers 6 in series is adopted. It has been. When a plurality of small EGR coolers 6 are mounted, due to space restrictions when mounted on the vehicle, some EGR coolers 6 must be placed above the engine 1, that is, higher than the upper tank 21 of the radiator 2. It may become.

  In this case, when water is poured into the EGR cooler 6, air removal from the EGR cooler 6 at the uppermost position may be insufficient, and fine water bubbles (air) remaining in the cooling water passage in the engine 1 after water injection. May accumulate in the uppermost EGR cooler 6 during operation of the engine 1. If the air inside the EGR cooler 6 through which the high-temperature exhaust gas (EGR gas) passes is insufficient, the amount of cooling water in the EGR cooler 6 becomes insufficient as the load on the engine 1 increases, and the EGR gas is removed. Insufficient cooling may result in an increase in NOx, generation of soot, and a situation in which the gas passage of the EGR cooler 6 becomes overheated and the inside is burnt out.

  Patent Document 1 discloses an EGR device in which a water-cooled EGR cooler 6 is disposed at a position higher than the radiator 2, and an air vent pipe (not shown) between the water jacket of the EGR cooler 6 and the radiator 2. And the air in the cooling water inside the EGR cooler 6 is drawn out to the radiator 2 through the air vent pipe. This is based on the difference between the water pressure (high pressure) in the EGR cooler 6 located on the upstream side of the cooling water circulation path 4 and the water pressure (low pressure) in the radiator 2 located on the downstream side. The air in 6 is discharged to the radiator 2.

Japanese Patent Laying-Open No. 2005-330863

  However, this does not mean that the air in the EGR cooler 6 is exhausted from the EGR cooler 6 by fully utilizing the water pressure difference in the circulation path 4 generated by the water pump 3. There is room for improvement. That is, the water pressure in the radiator 2 located on the downstream side of the circulation path 4 is certainly lower than the water pressure in the EGR cooler 6 located on the upstream side, but the water pressure in the circulation path 4 is further reduced (water pump 3 Therefore, if the air in the EGR cooler 6 is sucked out using the water pressure (negative pressure) in this portion, the air in the EGR cooler 6 can be efficiently vented in a short time.

  Moreover, since the air in the EGR cooler 6 is vented by discharging the cooling water and air in the EGR cooler 6 to the radiator 2 through the air vent pipe, EGR is performed along with the air vent in the EGR cooler 6. It is inevitable that the cooling water in the cooler 6 is also guided to the radiator 2. For this reason, when such air venting is performed after the engine is started, the cooling water of the engine 1 flows into the radiator 2 through the EGR cooler 6 and the air vent pipe, and the warm-up property of the engine 1 is deteriorated. The effectiveness of the heater is deteriorated. That is, if the cooling water in the EGR cooler 6 is vented after the engine is started, the warm-up property is inevitably deteriorated and the warm-up time is prolonged.

  Reference 1 also describes that the air vent pipe is provided with a throttle so that the flow rate A of the cooling water flowing from the EGR cooler 6 to the radiator 2 is suppressed, but in order to vent the air in the EGR cooler 6 Therefore, the flow rate A must be set to a certain level, and this is not an essential solution to the deterioration of warm-up performance.

  Accordingly, an object of the present invention is to efficiently vent the cooling water in the water-cooled EGR cooler in a short time, and to warm up the cooling water in the EGR cooler after starting the engine. It is in providing the EGR apparatus which does not lead to deterioration of the.

  In order to achieve the above object, according to a first aspect of the present invention, a water-cooled EGR cooler is disposed at a position higher than an upper tank of a radiator, and a cooler cooling water outlet pipe is connected to a cooling water outlet of the EGR cooler. Is connected upstream of a thermostat provided in the upper pipe in a cooling water upper pipe interposed between the cooling water outlet of the engine and the cooling water inlet of the radiator. An air vent pipe for taking out the air in the cooling water is connected to the uppermost part, and the tip of the air vent pipe is connected between the cooling water outlet of the radiator and the cooling water inlet of the engine. Connected to a portion of the lower pipe between the water pump provided in the lower pipe, the thermostat, and the connection position of the cooling water short-circuit pipe connecting the lower pipe, Off valve provided to the tube, the valve to the on-off valve which are connected to control means for opening and closing the operating state of the engine.

  Preferably, the control means opens the on-off valve until the coolant temperature reaches a predetermined value after starting the engine, and closes the on-off valve after the water temperature reaches a predetermined value or more. .

  Preferably, the control means opens the on-off valve for a predetermined time every predetermined period after the on-off valve is closed.

  The second aspect of the invention is a cooling water circulation path that circulates between the engine and the radiator by a water pump, one end connected to a portion of the circulation path, and the other end downstream of the cooling water from that portion. The EGR apparatus is provided with a bypass pipe connected to the pipe portion, and a water-cooled EGR cooler is provided on the pipe. The EGR cooler is disposed at a position higher than the radiator, and the EGR cooler itself or the bypass pipe The suction port of the suction pipe in which the air vent pipe for taking out the air in the cooling water is connected to the downstream side of the EGR cooler, and the tip of the air vent pipe is connected to the suction port of the water pump The air vent pipe is provided with an opening / closing valve, and the opening / closing valve is connected to a control means for opening / closing the valve according to the operating state of the engine.

  The EGR device according to the present invention can exhibit the following effects.

  (1) The cooling water in the water-cooled EGR cooler is sucked out of the EGR cooler using the negative pressure immediately before the suction of the water pump where the pressure is the lowest in the cooling water circulation path. Therefore, the air removal of the EGR cooler can be performed efficiently and in a short time.

  (2) During such air venting, the cooling water sucked out together with the air from the EGR cooler is guided to the suction side of the water pump without passing through the radiator. Therefore, venting of the cooling water in the EGR cooler does not deteriorate the warm-up property after starting the engine and can prevent the warm-up time from being prolonged.

  Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, a circulation path 4 through which cooling water pressurized by a water pump 3 circulates is provided between the engine 1 and the radiator 2. The circulation path 4 includes a cooling water upper pipe 41 interposed between the cooling water outlet 11 of the engine 1 and the cooling water inlet 22 of the upper tank 21 of the radiator 2, and a cooling water outlet 24 of the lower tank 23 of the radiator 2. A cooling water lower pipe 42 interposed between the cooling water inlet 12 of the engine 1 is provided. A water jacket (not shown) through which cooling water flows is provided inside the engine 1, and a water pump 3 is provided in the cooling water lower pipe 42. The water pump 3 is driven by the rotation of the crankshaft of the engine 1.

  A cooling water short-circuit pipe 43 is interposed between the upper pipe 41 and the lower pipe 42, and a thermostat T / st is provided at a connection portion between the short-circuit pipe 43 and the upper pipe 41. When the water temperature passing through the thermostat T / st is below a predetermined operating temperature (for example, 80 degrees Celsius), the cooling water flows not to the radiator 2 side but to the cooling water short-circuit tube 43 side, and the water temperature exceeds the above operating temperature. If it has, it has the function to flow cooling water to the radiator 2 side instead of the cooling water short circuit tube 43 side.

  A cooling water injection port 25 is formed in the upper tank 21, and a radiator cap 26 is detachably attached to the water injection port 25. The radiator cap 26 has a built-in pressure valve, suppresses boiling by pressurizing the cooling water to suppress overheating and cavitation of the cooling water, and supplies air in the cooling water circulating in the circulation path 4 to the sub tank. Demonstrates the gas-liquid separation function. The sub tank 27 has a function of absorbing a part of the cooling water heated by the engine 1 and thermally expanded, and the air drawn from the radiator cap 26 to the sub tank 27 is released from the pipe 28 to the atmosphere.

  One end of the circulation path 4 is connected to a part (cooling water outlet 13) inside the engine 1 of the path 4, and the other end is a cooling water upper pipe 41 that is a part downstream of the cooling water from that part. A bypass pipe 5 connected to is provided. The bypass pipe 5 is provided with a water-cooled EGR cooler 6 that cools the EGR gas with cooling water. The EGR cooler 6 includes a first EGR cooler 61 and a second EGR cooler 62 connected in series, and the second EGR cooler 62 is an engine located higher than the upper tank 21 due to space problems when mounted on a vehicle. 1 is arranged above 1.

  The bypass pipe 5 is interposed between the cooling water outlet 13 of the engine 1 and the first EGR cooler 61 and is pressurized by the water pump 3 to introduce a part of the cooling water that has passed through the inside of the engine 1. Thermostat T / st of the inlet pipe 51, the cooling water intermediate pipe 52 interposed between the first EGR cooler 61 and the second EGR cooler 62, the cooling water outlet 63 of the second EGR cooler 62, and the cooling water upper pipe 41 It is comprised from the cooling water exit pipe | tube 53 interposed between the upstream parts. The cooling water outlet 63 of the second EGR cooler 62 is preferably provided at the uppermost position of the water jacket of the cooler 62 in order to efficiently take out the air in the cooling water in the cooler 62.

  The cooling water outlet pipe 53, which is the downstream side of the EGR cooler 6 (second EGR cooler 62) of the bypass pipe 5, has an air vent pipe 7 for taking out the air in the cooling water. Connected to the top. The air vent pipe 7 may be directly connected to the second EGR cooler 63 itself (the water jacket of the cooler 63), in particular, to the uppermost position of the water jacket of the cooler 63. The air vent pipe 7 is intended to allow air rather than cooling water to pass therethrough. Therefore, the air vent pipe 7 is set to be thinner than the piping (the upper pipe 41, the lower pipe 42, etc.) of the circulation path 4 and the bypass pipe 5. In the form, the inner diameter is set to about 1 to 2 mm.

  The tip of the air vent pipe 7 is connected to a portion between the water pump 3 of the cooling water lower pipe 42 and the connection position 431 of the cooling water short-circuit pipe 43. That is, the tip of the air vent pipe 7 is connected to a suction pipe 421 (which constitutes a part of the cooling water lower pipe 42) connected to the suction port 31 of the water pump 3. Specifically, the tip of the pipe 7 is connected to a position (preferably the position just before) of the suction pipe 421 close to the suction port 31.

  The air vent pipe 7 is provided with an electromagnetic valve 8 as an on-off valve, and a control means (electronic control unit) 9 for opening and closing the valve 8 depending on the operating state of the engine 1 is connected to the electromagnetic valve 8. ing. The control means 9 opens and closes the electromagnetic valve 8 based on the flow shown in FIG. 2 according to the rotational speed (rpm) of the engine 1 and the temperature of the cooling water (water temperature).

  The engine 1 is provided with an engine rotation sensor 91 that detects the rotational speed of the crankshaft, and the cooling water upper pipe 41 is provided with a water temperature sensor 92 that detects the water temperature at the cooling water outlet 11 of the engine 1. The outputs of these sensors 91 and 92 are input to the control means 9. The control means 9 opens and closes the electromagnetic valve 8 as described below based on the output values of the sensors 91 and 92 and a timer described later.

  As shown in FIG. 2, when the driver turns the ignition key at the start of the engine 1, first, the key switch is turned on in step S1, all parameters are initialized in step S2, and the electromagnetic valve 8 is initialized in step S3. Is opened. Thereby, the preparation for air bleeding of the second EGR cooler 62 is completed.

  Next, in step S4, it is determined whether the engine speed N exceeds zero, that is, whether or not the crankshaft is rotating. Until the crankshaft rotates, the opening of the solenoid valve 8 is held for the time being. If the crankshaft has rotated, it is determined in step S5 whether or not the coolant water temperature Tw has exceeded a predetermined value (predetermined temperature To: for example, 60 degrees Celsius). Opening is maintained.

  In steps S4 and S5, since the water pump 3 is driven as the crankshaft rotates, the cooling water pressurized by the water pump 3 is sequentially supplied to the engine 1, the first EGR cooler 61, and the second EGR cooler 62. Injected. Then, each part of the cooling water channel in the engine 1 and the air in the first EGR cooler 61 are guided to the second EGR cooler 62 above, and the air in the second EGR cooler 62 is pushed out to the outlet pipe 53 together with the cooling water. The air pump 3 is sucked into the water pump 3.

  Here, the position immediately before the suction port 31 of the water pump 3 to which the tip of the air vent pipe 7 is connected (portion of the suction pipe 421) has the lowest water pressure in the cooling water circulation path 4 (negative pressure). State), the air in the second EGR cooler 62 is sucked out of the cooler 62 with a strong suction force. Therefore, the air removal from the second EGR cooler 62 is achieved efficiently in a short time. Specifically, since the cooling water outlet pipe 53 of the second EGR cooler 62 to which the root of the air vent pipe 7 is connected is located upstream of the cooling water from the radiator 2, it is at least in a higher pressure state than the radiator. Since the air in the cooling water in the outlet pipe 53 which is in a certain high pressure state is sucked out by the negative pressure immediately before the suction port 31 of the water pump 3 where the pressure is the lowest, the second EGR cooler 62 is vented. However, it is achieved efficiently and in a short time.

  The air sucked into the water pump 3 is introduced into the engine 1 from the inlet 12 and dispersed in the cooling water passage (water jacket or the like) in the engine 1 to become minute bubbles or the like and stored in the cooling water passage in the engine 1. Therefore, it is unlikely that all of them are immediately discharged from the outlet 13 and returned to the second EGR cooler 62. Even if a part of the air returns from the engine 1 to the second EGR cooler 62 through the outlet 13, the air stored in the engine 1 (microbubbles) as the air venting through the air vent pipe 7 is continued. ) Increases, the air removal of the second EGR cooler 62 is achieved. At this time, since the water temperature is equal to or lower than the operating temperature of the thermostat T / st, the cooling water does not flow to the upper tank 21 side of the radiator 2.

  In addition, the cooling water inevitably sucked together with the air from the cooling water outlet pipe 53 of the second EGR cooler 62 to the air vent pipe 7 during the air venting does not pass through the radiator 2, that is, by the radiator 2. It is led to the suction side of the water pump 3 without being cooled. Therefore, venting of the cooling water in the second EGR cooler 62 does not deteriorate the warm-up property after the engine is started, and the warm-up time can be prevented from being prolonged.

  If the coolant temperature Tw exceeds the predetermined temperature To in step S5, the timer is reset in step S6, the timer time count is started in step S7, and the solenoid valve 8 is closed in step S8. The When the solenoid valve 8 is closed, the air in the cooling water outlet pipe 53 of the second EGR cooler 62 is not sucked into the water pump 3 through the air vent pipe 7, so that the air venting immediately after the engine is started is finished. That is, after the engine is started, it takes a predetermined time for the water temperature Tw to reach the predetermined temperature To. However, until the predetermined time elapses after the engine is started, the second EGR cooler 62 is vented as described above. If the time has elapsed, that is, if the water temperature Tw has exceeded the predetermined temperature To, this air venting is once terminated. The predetermined temperature To (60 degrees in the present embodiment) is a time during which the predetermined time can sufficiently release the air in the water jacket of the second EGR cooler 62 when water is injected into the second EGR cooler 62 by the water pump 3 after the engine is started. Of course, it is set so as to be.

  In step S9, it is determined whether or not a time Time counted after the timer has started exceeds a first predetermined time Time1 (for example, 5 seconds), and an elapsed time Time after the timer starts counting is a first predetermined time. If it is within Time1, the valve 8 is kept closed. If the first predetermined time Time1 is exceeded, the solenoid valve 8 is opened in Step S10. Next, in step S11, it is determined whether or not the elapsed time Time exceeds a second predetermined time Time2 (for example, 15 seconds). If the elapsed time Time is within the second predetermined time Time2, the solenoid valve 8 is opened. Is maintained, and if the second predetermined time Time2 is exceeded, the electromagnetic valve 8 is closed in step S12. Thus, the electromagnetic valve 8 is opened until the second predetermined time Time2 expires after the first predetermined time Time1 has elapsed (15 seconds−5 seconds = 10 seconds), and the second EGR cooler is operated as described above. 62 is vented.

  Next, in step S13, it is determined whether or not the elapsed time Time exceeds a third predetermined time Time3 (for example, 60 minutes). If the elapsed time Time is within the third predetermined time Time3, the solenoid valve 8 is closed. Is held and the third predetermined time Time3 is exceeded, the timer is reset in step S6, the timer is restarted in step S7, and the same routine is repeated. The third predetermined time Time3 is the time when minute bubbles (air) remaining in the water jacket and each cooling water pipe inside the engine 1 are accumulated in the second EGR cooler 62 at the uppermost position while the engine 1 is operating. In order to prevent the air from accumulating more than a predetermined amount, it is a time period for periodically removing air.

  In steps S6 to S13, the second EGR cooler 62 is vented for 10 seconds every 60 minutes (Time 3) after the engine 1 is started and the coolant temperature Tw has stabilized over To (60 degrees). Time2-Time1) is performed. As a result, the air accumulated in the water jacket of the second EGR cooler 62 disposed at the uppermost position of the cooling water circulation path 4 during engine operation is kept at a predetermined time (Time2-) for every predetermined period (Time 3: 60 minutes). (Time 1 = 10 seconds) Since the air is vented, it is possible to prevent the air from being accumulated and retained in the second EGR cooler 62 so as to cause a problem.

  As a result, it is possible to avoid an increase in NOx and generation of soot due to insufficient cooling of the second EGR cooler 62, and it is possible to avoid a situation in which the gas passage of the second EGR cooler 62 is overheated and the inside is burned out. Maintenance and reliability can be improved. Further, even when the cooling water boils locally in a part of the gas piping in the second EGR cooler 62 and evaporates during the high load operation of the engine 1, the evaporated bubbles remain in the second EGR cooler for a long period of time. Accumulation in 62 is prevented.

  When the engine 1 is started and the temperature of the cooling water Tw exceeds To (60 degrees) and stabilizes the air flow for air release, the air sucked into the water pump 3 is introduced from the inlet 12 into the engine. After being guided into the engine 1, it is dispersed in a cooling water passage (water jacket or the like) in the engine 1 and is stored in the cooling water passage in the engine 1 as fine bubbles or the like. The air that has passed through the cooling water passage is discharged from the outlet 11 to the cooling water upper pipe 41 that is the main circulation path of the cooling water when the temperature of the cooling water becomes equal to or higher than the operating temperature of the thermostat T / st. It is guided to the upper tank 21 of the radiator 2 and is released from the pipe 28 to the atmosphere by the gas-liquid separation function of the radiator cap 26.

  Further, when the operating temperature of the cooling water is equal to or lower than the operating temperature of the thermostat T / st, it is assumed that a part of the fine bubbles (air) stored in the cooling water passage in the engine 1 returns to the second EGR cooler through the outlet 13. However, the air is repeatedly circulated through the outlet pipe 53 and the air vent pipe 7 to be sucked into the water pump 3 again. Thereafter, when the temperature of the cooling water becomes equal to or higher than the operating temperature of the thermostat T / st, the air in the engine 1 is led from the outlet 11 to the upper tank 21 through the upper pipe 41 and is brought into the atmosphere by the radiator cap 26. It will be released.

  In this way, air bleeding after the engine 1 is started and the cooling water temperature Tw exceeds To (60 degrees) and stabilized is achieved.

  The present invention is not limited to the above embodiment. For example, in FIG. 1, the first EGR cooler 61 may be omitted, and the second EGR cooler 62 may be enlarged correspondingly, and one large EGR cooler 62 may be disposed at a position higher than the upper tank 21 of the radiator 2. In FIG. 2, To (60 degrees), Time1 (5 seconds), Time2 (15 seconds), Time3 (60 minutes), and the operating temperature (80 degrees) of the thermostat T / st are exemplifications, etc. It goes without saying that this value may be used.

It is a schematic diagram of the circulation path of the cooling water of the diesel engine provided with the EGR device concerning the suitable embodiment of the present invention. It is a flowchart which shows the control content of a control means. It is a schematic diagram of the circulation path of the cooling water of the diesel engine provided with the EGR device concerning a conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 11 Cooling water outlet 12 Cooling water inlet 2 Radiator 21 Upper tank 22 Cooling water inlet 24 Cooling water outlet 3 Water pump 31 Suction port 4 Circulation path 41 Cooling water upper pipe 42 Cooling water lower pipe 421 Portion (suction pipe)
43 Cooling water short-circuit pipe 431 Connection position 5 Bypass pipe 53 Cooler cooling water outlet pipe 62 EGR cooler (second EGR cooler)
63 Cooling water outlet 7 Air vent pipe 8 On-off valve 9 Control means Tw Water temperature To Predetermined value Time3 Predetermined period Time2-Time1 Predetermined time T / st Thermostat

Claims (4)

A water-cooled EGR cooler is placed above the upper tank of the radiator,
A cooling water outlet pipe is connected to a cooling water outlet of the EGR cooler, and the outlet pipe is connected to the cooling water upper pipe interposed between the cooling water outlet of the engine and the cooling water inlet of the radiator. Connect to the upstream side of the thermostat provided in the pipe,
An air vent pipe for taking out air in the cooling water is connected to the top of the cooler cooling water outlet pipe, and the tip of the air vent pipe is connected between the cooling water outlet of the radiator and the cooling water inlet of the engine. In the cooling water lower pipe interposed in, connected to the portion between the water pump provided in the lower pipe and the connection position of the thermostat and the cooling water short circuit pipe connecting the lower pipe,
An EGR device, wherein an opening / closing valve is provided in the air vent pipe, and a control means for opening / closing the valve according to an operating state of the engine is connected to the opening / closing valve.   2. The control means opens the on-off valve until the coolant temperature reaches a predetermined value after starting the engine, and closes the on-off valve after the water temperature reaches a predetermined value or more. The EGR device described in 1.   The EGR device according to claim 2, wherein the control means opens the on-off valve for a predetermined time every predetermined period after the on-off valve is closed. Bypass piping with one end connected to a part of the circulating path and the other end connected to a part downstream of the cooling water from that part in the circulating path of the cooling water circulating between the engine and the radiator by a water pump An EGR apparatus in which a water-cooled EGR cooler is provided in the pipe,
The EGR cooler is arranged at a position higher than the radiator, and an air vent pipe for taking out air in the cooling water is connected to the EGR cooler itself or a portion of the bypass pipe on the downstream side of the EGR cooler, Connect the tip of the air vent pipe to a position near the suction port of the suction pipe connected to the suction port of the water pump,
An EGR device, wherein an opening / closing valve is provided in the air vent pipe, and a control means for opening / closing the valve according to an operating state of the engine is connected to the opening / closing valve.

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