JP2010059816A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit formation of sludge and deterioration of oil. <P>SOLUTION: An internal combustion engine 1 is provided with an oil drop passage 18 providing communication between a crank chamber 9 and a valve chamber 8 on a cylinder head 5, and is provided with a check valve 19 opened by weight of oil stored inside in the oil drop passage 18. Invasion of blow-by gas to the valve chamber 8 in which water is easily formed due to condensation, and formation of sludge and deterioration of oil are inhibited. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an internal combustion engine, and more particularly to an internal combustion engine suitable for sludge generation and suppression of oil deterioration.

  2. Description of the Related Art An internal combustion engine for automobiles or the like is known that has a blow-by gas processing device that circulates blow-by gas leaking into a crank chamber into an intake passage and re-combusts it. Here, blow-by gas refers to gas that leaks into the crank chamber from the gap between the piston ring and the cylinder bore of the cylinder block. For example, in Patent Document 1, in an internal combustion engine in which an intake valve lift is continuously variable and intake amount control is possible, a negative pressure control valve is provided in an intake passage and a negative pressure on the downstream side thereof is controlled so that oil is discharged from the crankcase. A device that circulates blow-by gas to an intake passage through a drop passage and a head cover is disclosed.

JP 2006-132360 A

  By the way, it is known that sludge is generated due to deterioration of the oil which is the lubricating oil, and this has various adverse effects on each part of the engine. Sludge is mainly composed of olefins contained in oil, NOx and SOx contained in blow-by gas, and water. These main components react by the power of heat and acid, and precursors such as sludge precursor and sludge binder are added. It is generated after. The sludge is visually a mud or sludge-like substance, and for example, when it accumulates in a passage inside the internal combustion engine, it causes a problem that the passage is blocked.

  In particular, an acidic substance produced by a reaction between water generated by condensation in the head cover or the like and NOx or SOx contained in the blow-by gas serves as a catalyst for generating sludge. The mixing of such acidic substances into the oil accelerates the generation of sludge, accelerates the deterioration of the oil, and lowers the functions of the lubricating oil.

  Therefore, the present invention has been made in view of the above-described problems, and an object thereof is to provide an internal combustion engine that can suppress generation of sludge and deterioration of oil.

  According to one aspect of the present invention, a check valve is provided which has an oil drop passage communicating with a valve operating chamber on a cylinder head and a crank chamber, and opens in the oil drop passage by the weight of oil stored therein. An internal combustion engine is provided.

  When an oil dropping passage that connects the valve operating chamber on the cylinder head and the crank chamber is provided, the blow-by gas in the crank chamber normally moves upward in the oil dropping passage and enters the valve operating chamber. However, the valve chamber is a portion where water is likely to be generated due to condensation or the like, and when blow-by gas enters, acidic substances are generated due to the reaction between NOx and the like contained therein and water, and sludge is likely to be generated. In one aspect of the present invention, a check valve that opens according to the weight of the oil stored in the oil dropping passage is provided in the oil dropping passage, so that only the fall of the oil in the oil dropping passage is allowed and the blow-by gas is increased. Can be prevented. As a result, it is possible to prevent the blow-by gas from entering the valve operating chamber and suppress sludge generation and oil deterioration.

  Preferably, a head cover is provided on an upper portion of the cylinder head, the valve head chamber is defined by the cylinder head and the head cover, and a chain case is connected to the cylinder head and the head cover. Are not connected.

  When the chain case and the valve chamber are not in communication as described above, it is possible to prevent the blow-by gas from entering the valve chamber from the inside of the chain case.

  Preferably, the oil dropping passage is defined by a hole penetrating the cylinder head and a cylinder block provided below the cylinder head.

  Alternatively, a chain case is provided on the side of the cylinder head, and the oil drop passage is defined by the chain case. This eliminates the need for through holes in the cylinder head and cylinder block.

  According to another aspect of the present invention, there is provided an oil drop passage that communicates the valve chamber on the cylinder head and the crank chamber, and the lower end of the oil drop passage is provided at the oil level of the oil stored in the bottom of the crank chamber. An internal combustion engine characterized by being positioned at a lower position is provided.

  If it carries out like this, since the lower end of an oil dropping channel | path will be immersed in oil, the penetration | invasion of the crank chamber blow-by gas from the lower end into an oil dropping channel | path can be prevented. As a result, it is possible to prevent the blow-by gas from entering the valve operating chamber and suppress sludge generation and oil deterioration.

Preferably, the internal combustion engine is
A blow-by gas passage connecting the crank chamber and an intake passage downstream of the throttle valve;
A crank chamber-side fresh air passage connecting the crank chamber and the intake passage upstream of the throttle valve;
A valve chamber-side fresh air passage that connects the valve chamber and the intake passage on the upstream side of the connection portion of the crank chamber-side fresh air passage;
Is provided.

  According to the present invention, an excellent effect that production of sludge and deterioration of oil can be suppressed is exhibited.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 schematically shows a front sectional view of an internal combustion engine according to the present embodiment. As shown, the engine 1 includes a cylinder block 2, a piston 3, a crankcase 4 provided at the lower part of the cylinder block 2, a cylinder head 5 provided at the upper part of the cylinder block 2, A head cover 6 provided at the upper portion and covering the above from above, and an oil pan 7 provided at the lower portion of the crankcase 4 and covering it from below are provided. In the present embodiment, the cylinder block 2 and the crankcase 4 are integrally formed, but may be formed separately.

  A valve operating chamber 8 is defined on the cylinder head 5, and the valve operating chamber 8 is specifically defined by the cylinder head 5 and the head cover 6 and includes a space surrounded by both. The valve operating chamber 8 includes an intake valve Vi and an exhaust valve Ve that open and close the intake port Pi and the exhaust port Pe, respectively, and a valve spring (not shown) that urges the intake valve Vi and the exhaust valve Ve in a closing direction, respectively. An intake camshaft Ci and an exhaust camshaft Ce are provided for driving the intake valve Vi and the exhaust valve Ve in the opening direction, respectively. The valve train chamber 8 is supplied with oil for valve train lubrication from an oil supply port (not shown).

  On the other hand, a crank chamber 9 is defined by the crankcase 4 and the oil pan 7, and a crankshaft (see Cr in FIG. 2) is provided in the crank chamber 9, and oil (not shown) is stored at the bottom thereof. .

  A throttle valve 11 and an air filter 12 are provided in the intake passage 10. A surge tank 13 is provided on the downstream side of the throttle valve 11 and distributes intake air from the surge tank 13 to the intake port Pi of each cylinder of the engine 1 which is a multi-cylinder internal combustion engine. An exhaust passage (not shown) is connected to the exhaust port Pe of each cylinder.

  The engine of the present embodiment is a vehicle spark ignition internal combustion engine, and includes an injector In that injects fuel into an intake port and an ignition plug (not shown) attached to the cylinder head 5. There is no particular limitation on the number, use, and the like.

  The crank chamber 9 and the surge tank 13 are connected and communicated by a blow-by gas passage 14. The blow-by gas passage 14 is a passage for sending blow-by gas in the crank chamber 9 to the intake passage 10, particularly to the surge tank 13. A PCV valve 15 whose opening degree is changed according to the magnitude of the intake negative pressure is provided in the blow-by gas passage 14, particularly the inlet portion thereof. PCV is an abbreviation for Positive Crankcase Ventilation.

  On the other hand, the crank chamber 9 and the intake passage 10 upstream of the throttle valve are connected and communicated by a crank chamber fresh air passage 16. Further, the valve operating chamber 8 and the intake passage 10 upstream of the connecting portion of the crank chamber-side fresh air passage 16 are connected and communicated by a valve operating chamber-side fresh air passage 17. The connection portion of the valve chamber side fresh air passage 17 with respect to the intake passage 10 is preferably as far as possible from the connection portion of the crank chamber side fresh air passage 16. In the present embodiment, the former connection portion is directly downstream of the air filter 12. Located on the side.

  The cylinder block 2 and the cylinder head 5 are provided with holes 2A and 5A penetrating up and down, and an oil dropping passage 18 for communicating the valve operating chamber 8 and the crank chamber 9 is formed by the holes 2A and 5A. The A plurality of oil drop passages 18 are preferably provided as in this embodiment. The oil dropping passage 18 is a passage for dropping oil accumulated on the cylinder head 5 after the lubrication of the valve system toward the crank chamber 9 and the oil pan 7.

  The oil dropping passage 18 is provided with a check valve 19 that opens according to the weight of oil stored therein. As will be described in detail later, the check valve 19 allows the oil to flow from the valve chamber 8 side to the crank chamber 9 side, that is, allows the oil to flow, but does not allow blowby gas to flow from the crank chamber 9 side to the valve chamber 8 side. The flow or rise is discouraged. The check valve 19 is preferably disposed at the lower end of the oil dropping passage 18 as in the present embodiment, and is provided in all of the plurality of oil dropping passages 18. As a result, the valve operating chamber 8 is isolated from the crank chamber 9 at least through the oil drop passage 18.

  FIG. 2 schematically shows a partial sectional side view of the internal combustion engine. As shown in the figure, the intake camshaft Ci (not shown in the figure), the exhaust camshaft Ce, and the crankshaft Cr project forward (right side in the figure) from the cylinder head 5 and the crankcase 4, respectively, and the sprocket They are connected by Si (not shown), Se, Sr, and the drive chain 20. And the chain case 21 which covers these is provided. The chain case 21 is connected to the front end surfaces of the cylinder head 5, the cylinder block 2, and the crankcase 4, connected to the lower end surface of the head cover 6, and connected to the upper end surface of the oil pan 7. In the chain case 21, oil for lubricating the chain drive unit is supplied from an oil supply port (not shown).

  In particular, the chain case 21 is not in communication with or isolated from the valve operating chamber 8, but is in communication with the crank chamber 9, particularly the oil pan 7, through the communication port 22. Therefore, the lubricating oil supplied into the chain case 21 is returned into the oil pan 7 through the communication port 22. On the other hand, even if blow-by gas enters the chain case 21, it does not enter the valve operating chamber 8.

  3 and 4 show a preferred example of the check valve 19. First, the check valve 19A shown in FIG. 3 will be described. The check valve 19A includes an umbrella valve type valve element 31 that can be moved up and down in the oil drop passage 18, and an oil discharge port that is opened and closed by the valve element 31. 32, a valve seat member 33, a spring member (specifically a coil spring) 34 that urges or pushes the valve body 31 in the closing direction, and a support member 35 that supports the lower end of the spring member 34. . The valve seat member 33 and the support member 35 are fixed to the inner wall of the oil dropping passage 18 by press fitting or the like. A plurality of holes 36 are provided in the support member 35 so that oil that has dropped from the oil discharge port 32 can be dropped into the crank chamber 9 through the holes 36.

  When a predetermined amount of oil is stored in the oil drop passage 18 above the closed check valve 19A, the valve body 31 is pushed down against the spring member 34 by the weight of the oil, and the oil discharge port 32 is opened and opened. In the valve state, the stored oil is dropped through the oil discharge port 32 and the hole 36. As a result, the weight of the stored oil is reduced and the check valve 19 is closed, and at the same time, the upward movement of blow-by gas from the crank chamber 9 to the valve operating chamber 8 through the oil dropping passage 18 is prevented.

  Next, the check valve 19B shown in FIG. 4 will be described. The check valve 19B includes a leaf spring type valve body member 41 fixed in the oil dropping passage 18 by press fitting or the like. The valve body member 41 is provided with two cuts 42 and 42 parallel to each other. One end of each of the cuts 42 and 42 is completely cut and the other end is left without being cut. As shown by the phantom line in FIG. 4B, the portion (opening / closing portion) 43 between these cuts 42 and 42 can be elastically deformed downward with respect to the remaining portion with the connected base end portion as a fulcrum. Allows oil to pass through. On the other hand, the fixing portions 44 on both sides of the opening / closing portion 43 are provided with stoppers 45 for preventing the opening / closing portion 43 from being deformed upward and maintaining the valve closed state.

  The operation of the check valve 19B is substantially the same as that of the check valve 19A. When a predetermined amount of oil is stored in the oil drop passage 18 above the closed check valve 19B, the opening / closing portion 43 is elastically deformed downward by the weight of the oil, and between the opening / closing portion 43 and the inner wall of the oil drop passage. A gap is formed, the valve is opened, and the stored oil is dropped through the gap. As a result, the weight of the stored oil is reduced, the opening / closing part 43 returns to the original position, the check valve 19B is closed, and at the same time, the blow-by gas through the oil dropping passage 18 from the crank chamber 9 to the valve operating chamber 8 is closed. Is prevented from moving up.

  Next, the flow of blow-by gas and fresh air in this internal combustion engine will be described. As shown in FIG. 5, when the engine is lightly loaded, the PCV valve 15 is opened, and the blow-by gas in the crank chamber 9 is returned to the intake passage 10, particularly the surge tank 13 through the blow-by gas passage 14 by the intake negative pressure, and then the cylinder It is burned in the combustion chamber in block 2. On the other hand, at this time, as the blow-by gas is discharged from the crank chamber 9, the crank chamber 9 is replenished with fresh air from the intake passage 10 upstream of the throttle valve through the crank chamber-side fresh air passage 16.

  On the other hand, as shown in FIG. 6, the PCV valve 15 is closed and the return of the blow-by gas through the blow-by gas passage 14 is prohibited when the engine is heavily loaded, such as when the throttle valve is fully open (WOT). Further, blow-by gas in the crank chamber 9 may be returned to the intake passage 10 upstream of the throttle valve through the crank chamber-side fresh air passage 16 (backflow). However, since the pressure at the connection portion of the crank chamber-side fresh air passage 16 to the intake passage 10 is almost atmospheric pressure, the blow-by gas ring flow rate is small.

  On the other hand, regardless of the engine load state, the check valve 19 is normally closed, so that blow-by gas in the crank chamber 9 does not reach the valve operating chamber 8 through the oil dropping passage 18. The oil that has finished lubrication of the valve train in the valve train chamber 8 flows into the oil drop passage 18 from the bottom surface of the valve train chamber 8 and gradually accumulates in the oil drop passage 18. When a predetermined amount of oil is accumulated in the upper part of the check valve 19, the check valve 19 is opened and the stored oil is dropped and discharged into the crank chamber 9. At this time, only the oil passes through the check valve 19 and falls, and the fresh air for the discharged oil is replenished to the valve operating chamber 8 through the valve operating chamber-side fresh air passage 17. The blow-by gas inside does not pass through the check valve 19 and ascends (backflows) in the oil drop passage 18 and does not reach the valve operating chamber 8. When the load is high, blow-by gas in the crank chamber 9 is returned to the intake passage 10 through the crank chamber-side fresh air passage 16 as shown in FIG. Is located upstream of the connecting portion of the crank chamber side fresh air passage 16, the blow-by gas returned to the intake passage 10 is prevented from entering the valve chamber 8 through the valve chamber fresh air passage 17. From this point of view, it is preferable that the connecting portion of the valve chamber side fresh air passage 17 is located on the upstream side as far as possible from the connecting portion of the crank chamber side fresh air passage 16. In this embodiment, the connecting portion of the air filter 12 is directly downstream. Located in.

  As a result, the intrusion of blow-by gas into the valve operating chamber 8 is always prevented, whereby the generation of sludge can be suppressed for the following reasons, and the deterioration of the oil can be suppressed.

  The blow-by gas includes HC (hydrocarbon) as a fuel component, NOx and SOx contained in the already burned gas, moisture, and oil mist as a gas generated by stirring and evaporation of the oil in the crank chamber 9. Yes. In addition, water tends to be present on the inner surface of the head cover 6 and the valve operating chamber 8 because condensed water due to condensation or the like tends to be generated on the inner surface of the head cover 6 that comes into contact with the outside air particularly at low temperatures. On the other hand, an acidic substance (nitric acid water or the like) produced by a reaction between NOx and SOx contained in blow-by gas and water generated by condensation or the like serves as a catalyst for generating sludge and further oxidizes oil. Therefore, in an environment where blow-by gas and water are present, sludge generation is induced and oil deterioration is promoted.

  However, in this embodiment, although condensed water is generated in the valve operating chamber 8, since there is no blow-by gas, it is possible to prevent the generation of acidic substances, and as a result, sludge in all the oil in the valve operating chamber 8 can be prevented. Generation and oil deterioration can be suppressed. In particular, sludge generation and adhesion on the inner surface of the head cover 6 can be effectively prevented. In this regard, since the sludge adhering to the inner surface of the head cover 6 cannot be expected to be washed away by the oil in the valve operating chamber 8, the configuration of this embodiment is very advantageous.

  Another advantage is that the valve chamber side fresh air passage 17 can be prevented from being blocked by sludge in the valve chamber 8.

  Next, a modification of the above embodiment will be described. The same elements as those in the above embodiment are denoted by the same reference numerals in the drawing, detailed description thereof will be omitted, and differences will be mainly described below. As shown in FIG. 7, this modification mainly differs in that the chain case 21 defines an oil dropping passage 50 and the space in the chain case 21 is used as the oil dropping passage 50. Accordingly, the oil drop passage 50 is communicated with the valve operating chamber 8 so that oil from the valve operating chamber 8 can be introduced. A check valve 51 is provided at the communication port 22 that connects the oil drop passage 50 and the crank chamber 9. The check valve 51 has the same configuration as the check valve 19 of the above embodiment, and is preferably provided at the lower end of the oil dropping passage 50 as in this embodiment.

  Specifically, the crankcase 4 has no communication portion with the oil dropping passage 50, and the oil pan 7 communicates with the oil dropping passage 50 only at the communication port 22. A check valve 51 is provided at the communication port 22, and the communication port 22 is normally closed. There may be a plurality of communication ports 22, and in this case, check valves 51 are provided in all the communication ports 22. Along with the oil drop passage 50 in the chain case 21, the oil drop passage 18 and the check valve 19 provided in the oil drop passage 18 in the above embodiment are omitted. The blow-by gas passage 14, the crank chamber-side fresh air passage 16, and the valve chamber-side fresh air passage 17 are provided in the same manner as in the above embodiment.

  Also by this modification, the same effect as the said embodiment is acquired. In other words, since the check valve 51 is normally closed, the blow-by gas in the crank chamber 9 is prevented from entering the valve operating chamber 8 through the oil drop passage 50. Further, when a predetermined amount of oil is accumulated on the upper part of the check valve 51, the check valve 51 is opened and the stored oil is dropped and discharged into the oil pan 7. At this time, the blow-by gas in the crank chamber 9 is also checked valve. 51 is prevented from flowing back into the oil dropping passage 18. Intrusion of blow-by gas into the valve operating chamber 8 is reliably prevented, and sludge generation and oil deterioration can be suppressed.

  Moreover, according to this modification, the penetration of blow-by gas into the chain case 21 that defines the oil dropping passage 18 is also prevented. The chain case 21 is in contact with the outside air particularly at low temperatures, and condensate due to condensation is likely to be generated on the inner surface of the chain case 21, and this tendency is strong in the vicinity of the upper end portion in contact with the head cover 6. Therefore, when blow-by gas enters, acidic substances are generated and sludge adheres to the inner surface of the chain case 21 or sludge is likely to be generated in the oil, but this modification prevents it.

  Next, another embodiment will be described. The same elements as those in the above embodiment are denoted by the same reference numerals in the drawing, detailed description thereof will be omitted, and differences will be mainly described below. As shown in FIG. 8, this other embodiment has an oil drop passage 18 extended from the above embodiment shown in FIGS. 1 to 6, and the lower end of the oil stored in the bottom of the crank chamber 9. The point located in the position lower than the oil level H is greatly different. Here, in the illustrated example, the oil level H is inclined rather than horizontal, because the illustrated engine 1 is inclined in the mounted state. The height position of the oil level H here refers to the height position of the oil level when oil lubrication is performed in the engine operating state and the oil level is lowered.

  Specifically, an extension pipe 61 is attached to the bottom of the cylinder block 2 so as to extend the holes 5A and 2A provided in the cylinder head 5 and the cylinder block 2, and oil is dropped by the passages in the holes 5A and 2A and the extension pipe 61. A passage 18 is defined. The lower end of the extension pipe 61 is brought as close as possible to the bottom surface of the oil pan 7, and the lower end of the extension pipe 61 is always immersed in the oil. The check valve 19 provided in the above embodiment is omitted. When there are a plurality of oil drop passages 18 as in the present embodiment, the same configuration is made for all the oil drop passages 18. The extension pipe 61 is arranged at a position so as not to interfere with a crankshaft (not shown). The extension pipe 61 in the illustrated example is a straight pipe, but may be a bent pipe. Similarly, the holes 5A and 2A may also be bent holes (the same applies to the above embodiment).

  According to the other embodiments, the same effects as those of the above embodiment can be obtained. That is, since the lower end of the oil drop passage 18 is immersed in the oil, blow-by gas in the crank chamber 9 above the oil is prevented from entering the oil drop passage 18. Therefore, the penetration of blow-by gas into the valve operating chamber 8 through the oil dropping passage 18 is prevented. The oil from the valve operating chamber 8 is directly dropped into the crank chamber 9 (oil pan 7) through the oil dropping passage 18 and discharged. At this time, naturally, blow-by gas does not enter the oil dropping passage 18 from the crank chamber 9. In this way, intrusion of blow-by gas into the valve operating chamber 8 is reliably prevented, and sludge generation and oil deterioration can be suppressed.

  In addition, since the check valve can be omitted, there is an advantage that the configuration can be simplified.

  As mentioned above, although preferred embodiment of this invention was described, this invention can also take other embodiment other than the above. For example, an oil separator for separating oil from blow-by gas may be provided in the blow-by gas passage 14. Further, the oil dropping passage may be defined by piping provided outside the cylinder head and the cylinder block.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 is a schematic front sectional view of an internal combustion engine according to an embodiment of the present invention. FIG. 2 is a schematic partial cross-sectional side view of the internal combustion engine of FIG. 1. It is a front sectional view showing an example of a check valve. The other example of a non-return valve is shown, (A) is a top view, (B) is front sectional drawing. FIG. 2 is a schematic front sectional view showing the flow of blow-by gas and fresh air when the internal combustion engine of FIG. 1 is lightly loaded. FIG. 2 is a schematic front sectional view showing the flow of blow-by gas and fresh air when the internal combustion engine of FIG. 1 is under a high load. It is a general | schematic fragmentary sectional side view which shows the modification of embodiment of FIG. It is a schematic front sectional view of an internal combustion engine according to another embodiment of the present invention.

Explanation of symbols

1 Engine 2A, 5A Hole 4 Crankcase 5 Cylinder head 6 Head cover 7 Oil pan 8 Valve chamber 9 Crank chamber 10 Intake passage 11 Throttle valve 14 Blow-by gas passage 16 Crank chamber side fresh air passage 17 Valve chamber side fresh air passage 18 , 50 Oil drop passage 19, 19A, 19B, 51 Check valve 21 Chain case H Oil level

Claims (6)

  An internal combustion engine characterized in that an oil dropping passage communicating with a valve operating chamber on a cylinder head and a crank chamber is provided, and a check valve that opens according to the weight of oil stored in the oil dropping passage is provided in the oil dropping passage. organ.   A head cover is provided at an upper portion of the cylinder head, the valve operating chamber is defined by the cylinder head and the head cover, a chain case is connected to the cylinder head and the head cover, and the inside of the chain case is not connected to the valve operating chamber. The internal combustion engine according to claim 1, wherein the internal combustion engine is in communication.   3. The internal combustion engine according to claim 1, wherein the oil dropping passage is defined by a hole penetrating the cylinder head and a cylinder block provided at a lower portion thereof.   2. The internal combustion engine according to claim 1, wherein a chain case is provided on a side portion of the cylinder head, and the oil dropping passage is defined by the chain case.   An oil dropping passage that communicates the valve chamber on the cylinder head and the crank chamber is provided, and the lower end of the oil dropping passage is positioned lower than the oil level of the oil stored in the bottom of the crank chamber. An internal combustion engine. A blow-by gas passage connecting the crank chamber and an intake passage downstream of the throttle valve;
A crank chamber-side fresh air passage connecting the crank chamber and the intake passage upstream of the throttle valve;
A valve chamber-side fresh air passage that connects the valve chamber and the intake passage on the upstream side of the connection portion of the crank chamber-side fresh air passage;
The internal combustion engine according to any one of claims 1 to 5, further comprising:

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