JP5104195B2 - Spark ignition internal combustion engine - Google Patents

Description

  The present invention relates to control of fuel injection timing in a direct injection engine.

  In-cylinder spark ignition internal combustion engines that can inject fuel directly into the combustion chamber have been developed. In a cylinder injection spark ignition internal combustion engine, fuel can be supplied directly into the combustion chamber, so that the fuel injection timing can be adjusted (see Patent Document 1).

Further, since the fuel is injected into the combustion chamber separately from the intake air, various effects can be generated according to the fuel injection direction. The fuel injection direction is designed to produce a desired effect. Depending on the desired effect to be exerted, the injection direction may be determined so that the fuel is injected toward the bore inner wall.
JP-A-7-286520

  By the way, the injected fuel is required to be sufficiently vaporized before being ignited. However, in a situation where the fuel is difficult to vaporize, such as when cold, there is a possibility that a part of the fuel injected to the inner wall of the cylinder cannot be vaporized and adheres to the inner wall of the cylinder.

  The cylinder inner wall is covered with lubricating oil, and the fuel that could not be vaporized is adsorbed by the lubricating oil. The adsorbed fuel is also vaporized, but may not be completely vaporized before ignition. Therefore, the amount of fuel combusted for each cycle varies, and torque variation may occur. Further, the adsorbed fuel continued to be vaporized during the exhaust stroke after the explosion stroke, and there was a risk of increasing the unburned gas in the exhaust gas.

  An object of the present invention is to suppress torque fluctuation and increase in unburned gas even in a situation where fuel cannot be sufficiently vaporized in a combustion chamber in a spark ignition internal combustion engine capable of directly injecting fuel into a cylinder.

The spark ignition internal combustion engine according to the present invention includes injection means, detection means, and control means. The injection means injects fuel toward an injection point that is a predetermined position between the top dead center and the bottom dead center on the inner wall of the cylinder. The detection means detects a factor that affects the vaporization of the fuel injected by the injection means in the combustion chamber. The control means allows the piston that moves from the top dead center to the bottom dead center during the intake stroke to pass through the injection point when a factor detected from a predetermined range in which vaporization of fuel in the combustion chamber is promoted deviates from the threshold value. Control is performed so that the fuel is injected into the injection means earlier than the timing.

According to the present invention, when the fuel cannot be sufficiently vaporized in the combustion chamber, the fuel injection timing is advanced earlier than the timing when the piston in the intake stroke passes the injection point. Therefore, since fuel is injected not to the inner wall of the cylinder but to the piston, it is possible to promote fuel vaporization.

In the spark ignition internal combustion engine according to the present invention, in addition to the configuration of the first invention, the factor detected by the detecting means is a factor that affects the vaporization in the bore inner wall on the injection point side. The control means controls the fuel injection timing by the injection means based on the factor.

According to the present invention, fuel vaporization can be promoted more accurately by paying attention to the fuel vaporization in the bore inner wall that has the greatest influence on the fluctuation of the vaporization amount for each cycle.

In the spark ignition internal combustion engine according to the present invention, in addition to the second configuration, the factor affecting the vaporization is the bore inner wall temperature on the injection point side.

According to the present invention, fuel vaporization can be effectively promoted by controlling the injection timing using the bore inner wall temperature on the injection point side as a factor having the greatest influence on the vaporization in the bore inner wall. Become.

The spark ignition internal combustion engine according to the present invention includes an intake port in addition to the first configuration. The intake port performs intake into the combustion chamber so as to generate a tumble flow in the combustion chamber. The injection point is determined so that the tumble flow is strengthened by the injection means injecting fuel toward the injection point.

According to the present invention, it is possible to prevent a problem that occurs when a jet of fuel injection is used for strengthening tumble, that is, fuel vaporization becomes insufficient.

In the spark ignition internal combustion engine according to the present invention, in addition to the fourth configuration, the intake port generates a forward tumble flow in the combustion chamber, and the injection point is determined on the inner wall of the exhaust side bore.

According to the present invention, in an engine that generates a general forward tumble flow, it is possible to prevent insufficient fuel vaporization as described above.

In the spark ignition internal combustion engine according to the present invention, in addition to the configuration of the first invention, the control means injects the fuel into the injection means earlier as the factor changes in the direction of promoting fuel vaporization outside the predetermined range. To control.

According to the present invention, it is possible to prevent the injection timing from being advanced more than necessary, and to suppress the increase in smoke that increases the generation amount as the advance is advanced.

  According to the present invention, it is possible to suppress fluctuations in torque and increase in unburned gas under a situation where fuel is not sufficiently vaporized in the combustion chamber.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an engine (spark ignition internal combustion engine) to which an embodiment of the present invention is applied.

  The engine 10 is connected to a fuel tank 11, an intake passage 12, and an exhaust passage 13. Fuel is supplied to the engine 10 from a fuel tank 11. In addition, air is drawn into the engine 10 through the intake passage 12. The fuel supplied by the sucked air is burned. Exhaust gas generated by combustion in the engine 10 is discharged to the outside through the exhaust passage 13.

  The engine 10 includes a cylinder block (not shown), a cylinder head 14, a piston 15, an intake valve 16, an exhaust valve 17, an injector 18, a spark plug 19, and the like.

  The cylinder block is provided with a plurality of cylinders 20. Each cylinder 20 is provided with a piston 15. The piston 15 is slidable in the cylinder height direction of the cylinder 20. A space surrounded by the cylinder 20, the cylinder head 14, and the piston 15 is formed as a combustion chamber 21.

  The combustion chamber 21 communicates with the intake passage 12 and the exhaust passage 13. An intake valve 16 and an exhaust valve 17 are disposed in the intake passage 12 and the exhaust passage 13, respectively. By opening the intake valve 16 at a predetermined time, air is sucked into the combustion chamber 21 through the intake passage 12. By opening the exhaust valve 17 at a predetermined time, exhaust gas is discharged from the combustion chamber 21 through the exhaust passage 13.

  Note that air sucked from the intake passage 12 is forward tumble flow in the combustion chamber 21 (see T in FIG. 1), that is, the sucked air descends on the exhaust valve 17 side in the combustion chamber 21 and enters the combustion chamber 21. The intake port 12a is formed in a shape that generates a tumble flow that rises on the intake valve 16 side.

  The injector 18 is provided in the cylinder head 14 so as to inject fuel directly into the combustion chamber 21. Fuel is supplied from the fuel tank 11 to the injector 18. The injector 18 injects a predetermined amount of fuel into the combustion chamber 21 at a predetermined time.

  The fuel injection direction of the injector 18 is determined in a direction in which the forward tumble flow T generated by the air sucked from the intake port 12a is strengthened by the penetration force of the injected fuel. That is, in the direction in contact with the forward tumble flow, the same direction as the forward tumble flow is determined as the injection direction. For example, the direction toward the predetermined injection point P between the top dead center and the bottom dead center of the piston 15 on the inner wall on the exhaust valve 17 side is determined as the fuel injection direction.

  The injector 18 has a slit-like nozzle and injects fuel in a substantially fan shape having a relatively small thickness. The injector 18 is mounted so that the fuel spray thickness center plane coincides with the longitudinal plane passing through the cylinder center axis parallel to the forward tumble flow T.

  The spark plug 19 is provided in the combustion chamber 21. The air-fuel mixture sucked into the combustion chamber 21 is ignited at a predetermined timing by the spark plug 19. The ignited air-fuel mixture burns to generate exhaust gas, which is exhausted through the exhaust passage 13.

  A fuel temperature sensor 22 is provided in the fuel tank 11. The fuel temperature of the fuel stored in the fuel tank 11 is detected by the fuel temperature sensor 22. The detected fuel temperature is transmitted to the ECU 23 as a signal.

  An intake air temperature sensor 24 is provided in the intake passage 12. An intake air temperature of air to be taken into the combustion chamber 21 is detected by the intake air temperature sensor 24. The detected intake air temperature is transmitted to the ECU 23 as a signal.

  The engine 10 is provided with a water temperature sensor 25 and a rotation sensor 26. The coolant temperature of the engine 10 and the rotation speed of the engine 10 are detected by the water temperature sensor 25 and the rotation sensor 26, respectively. The detected coolant temperature and rotation speed are transmitted to the ECU 23 as signals.

  The ECU 23 controls the operation to be performed by each part of the engine 10 based on the acquired data. For example, as will be described later, the fuel injection timing from the injector 18 is controlled. Further, the ECU 23 also controls the ignition timing of the spark plug 19 and the amount of fuel injected from the injector 18.

  In order to determine the fuel injection timing, the ECU 23 determines whether the fuel injected during the intake stroke in the combustion chamber 21 is sufficiently vaporized before the start of the explosion stroke. In order to make the determination, the cylinder bore inner wall temperature when the torque fluctuation for each cycle is not substantially generated for a certain fuel injection amount is determined in advance as the inner wall temperature threshold TV1.

  The higher the cylinder bore inner wall temperature, the higher the fuel vaporization speed. Therefore, it can be determined that the higher the cylinder bore inner wall temperature, the more fuel vaporization is promoted in one cycle. Since the cylinder bore inner wall temperature is correlated with the water temperature, the cylinder bore inner wall temperature is calculated based on the water temperature.

  When it is determined that the cylinder bore inner wall temperature exceeds the inner wall temperature threshold TV1 and the fuel is sufficiently vaporized, the vicinity of the BDC in the intake stroke is determined as the fuel injection timing. As described above, the forward tumble flow T is generated in the combustion chamber by the air sucked from the intake port 12a in the intake stroke. The generated forward tumble flow T attenuates during the period from the intake stroke to the compression stroke TDC, but the forward tumble flow T is strengthened by injecting fuel in the vicinity of the intake stroke BDC. By strengthening the forward tumble flow T, the forward tumble flow T is reliably maintained even in the compression stroke, and turbulence is generated in the cylinder in the vicinity of the TDC in the compression stroke. This turbulence in the cylinder improves the ignitability of the air-fuel mixture.

  When the cylinder bore inner wall temperature falls below the inner wall temperature threshold TV1 and it is determined that the fuel cannot be sufficiently vaporized based on other factors as will be described later, the top surface of the piston 15 passes the injection point P during the intake stroke. The timing to perform is determined as the reference injection timing for fuel injection. Incidentally, at a temperature equal to or lower than the inner wall temperature threshold TV1, a correspondence map of the advance angle correction value with respect to the cylinder bore inner wall temperature is predetermined (see FIG. 2), and the advance angle is corrected from the reference injection timing. Therefore, the ECU 23 advances the fuel injection timing as the cylinder bore inner wall temperature increases in a situation where the cylinder bore inner wall temperature is lower than the inner wall temperature threshold TV1.

  In addition, in order to determine the fuel injection timing in the ECU 23, the fuel temperature, the intake air temperature, and the engine speed when the torque fluctuation for each cycle is not substantially generated with respect to a constant fuel injection amount are the fuel temperature threshold value. It is predetermined as TV2, intake air temperature threshold TV3, and rotation speed threshold TV4.

  The higher the fuel temperature and the intake air temperature, the higher the fuel vaporization speed. Therefore, it can be determined that the higher the fuel temperature and the intake air temperature, the more fuel vaporization is promoted in one cycle. Further, when the engine speed increases, the time of the intake stroke and the compression stroke in one cycle is shortened, so that the amount of fuel vaporized decreases. Accordingly, it can be determined that the fuel cannot be sufficiently vaporized in one cycle as the engine speed increases.

  Similar to the cylinder bore inner wall temperature, it is determined that the fuel is sufficiently vaporized when the fuel temperature exceeds the fuel temperature threshold TV2, the intake air temperature exceeds the intake air temperature threshold TV3, or the engine speed falls below the rotation speed threshold TV4. . As described above, when it is determined that the fuel is sufficiently vaporized due to any factor, the vicinity of the BDC in the intake stroke is determined as the fuel injection timing.

  Similar to the cylinder bore inner wall temperature, when the fuel temperature is below the fuel temperature threshold TV2, the intake air temperature is below the intake air temperature threshold TV3, and the engine speed is above the engine speed threshold TV4, the top surface of the piston 15 is in the intake stroke. The timing for passing the injection point P is determined as the reference injection timing.

  Incidentally, at a temperature equal to or lower than the fuel temperature threshold TV2, a correspondence map of the advance angle correction value with respect to the fuel temperature is predetermined (see FIG. 3), and the advance angle is corrected from the reference injection timing. Therefore, the ECU 23 advances the fuel injection timing as the fuel temperature increases in a situation where the fuel temperature is lower than the fuel temperature threshold TV2.

  Incidentally, at a temperature equal to or lower than the intake air temperature threshold TV3, a correspondence map of the advance angle correction value with respect to the intake air temperature is determined in advance (see FIG. 4), and the advance angle is corrected from the reference injection timing. Therefore, the ECU 23 advances the fuel injection timing as the intake air temperature increases in a situation where the intake air temperature is lower than the intake air temperature threshold TV3.

  It should be noted that at a rotation speed equal to or higher than the rotation speed threshold TV4, a correspondence map of the advance correction value with respect to the engine rotation speed is determined in advance and the advance angle is corrected from the reference injection timing. Therefore, the ECU 23 advances the fuel injection timing as the engine speed decreases in a situation where the engine speed exceeds the rotation speed threshold TV4.

  Next, the control for determining the fuel injection timing that the ECU 23 causes each part of the engine 10 to execute according to the cylinder bore inner wall temperature and the like according to the present embodiment will be described using the flowchart of FIG. 6. In the control of determining the fuel injection timing, various operations are executed at a time determined for each step until the engine 10 is warmed up.

  In step S100, the ECU 23 acquires water temperature data of the engine 10. In the next step S101, the ECU 23 calculates the cylinder bore inner wall temperature on the exhaust valve 17 side based on the acquired water temperature data.

  In the next step S102, it is determined whether or not the calculated cylinder bore inner wall temperature is lower than the inner wall temperature threshold TV1. When the cylinder bore inner wall temperature exceeds the inner wall temperature threshold TV1, the process proceeds to step S112. When the cylinder bore inner wall temperature is lower than the inner wall temperature threshold TV1, the process proceeds to step S103.

  In step S103, the ECU 23 acquires fuel temperature data. In the next step S104, it is determined whether or not the fuel temperature is below the fuel temperature threshold TV2. When the fuel temperature exceeds the fuel temperature threshold TV2, the process proceeds to step S112. If the fuel temperature falls below the fuel temperature threshold TV2, the process proceeds to step S105.

  In step S105, the ECU 23 acquires intake air temperature data. In the next step S106, it is determined whether or not the intake air temperature is lower than the intake air temperature threshold TV3. When the intake air temperature exceeds the intake air temperature threshold TV3, the process proceeds to step S112. When the intake air temperature is lower than the intake air temperature threshold TV3, the process proceeds to step S107.

  In step S107, the ECU 23 acquires engine speed data. In the next step S108, it is determined whether or not the engine speed exceeds a speed threshold TV4. If the engine speed is below the speed threshold TV4, the process proceeds to step S112. If the engine speed is below the speed threshold TV4, the process proceeds to step S109.

  In step S109, the timing at which the top surface of the piston 15 passes the injection point P in the intake stroke is determined as the reference injection timing T1. In step S110, an advance correction value corresponding to the cylinder bore inner wall temperature calculated in step S101 is acquired. Further, the advance correction value corresponding to the fuel temperature acquired in step S103 is read. Further, the advance correction value corresponding to the intake air temperature acquired in step S105 is read. Further, the advance correction value corresponding to the engine speed acquired in step S107 is read. In step S111, the fuel injection timing is determined by correcting the reference injection timing T1 determined in step S109 with each advance angle correction value acquired in step S110.

  As described above, when the cylinder bore inner wall temperature exceeds the inner wall temperature threshold TV1 at step S102, when the fuel temperature exceeds the fuel temperature threshold TV2 at step S104, when the intake air temperature exceeds the intake temperature threshold TV3 at step S106, or step When the engine speed is lower than the rotation speed threshold TV4 in S108, the process proceeds to step S112, and the fuel injection timing is set near the intake stroke BDC.

  According to the spark ignition internal combustion engine having the above-described configuration, it is possible to suppress torque fluctuation and an increase in unburned gas in the exhaust gas in a situation where fuel cannot be sufficiently vaporized in the combustion chamber. Below, the effect of this embodiment is demonstrated in detail.

  Generally, in order to increase the combustion speed during homogeneous combustion, generation of tumble and enhancement of tumble are required in the combustion chamber 21. In order to reinforce the tumble generated by the intake air from the intake port 12a, it is desirable to inject fuel near the BDC.

  On the other hand, in the injection in the vicinity of the BDC toward the injection direction designed to strengthen the tumble, fuel is injected to the inner wall of the cylinder bore. During normal operation, such as when the engine 10 is warmed up or when the fuel temperature is high, the fuel is sufficiently vaporized before reaching the cylinder bore inner wall, or liquid fuel that has reached the cylinder bore inner wall is also present. It is fully vaporized until the explosion process. However, when the fuel temperature and the intake air temperature are low, or when the engine speed is high, the fuel cannot be sufficiently vaporized before reaching the cylinder bore inner wall, and liquid fuel may adhere to the cylinder bore inner wall. Further, when the cylinder bore inner wall temperature is low, the attached fuel cannot be sufficiently vaporized by the explosion stroke on the cylinder bore inner wall.

  Therefore, in the present embodiment, when the fuel cannot be sufficiently vaporized by the time of ignition as described above, the fuel is advanced to the piston 15 by advancing the fuel injection timing from the vicinity of the BDC in the intake stroke to a time earlier than the injection point P. (See FIG. 7).

  The cylinder bore inner wall is covered with lubricating oil, and the injected fuel is absorbed by the lubricating oil. On the other hand, the top surface of the piston 15 is not covered with lubricating oil. Generally, the vaporization rate of the fuel adhering to the top surface of the piston 15 is faster than the vaporization rate of the fuel absorbed in the lubricating oil. Therefore, the fuel adhering to the top surface of the piston 15 is sufficiently vaporized until ignition, and as described above, fluctuations in the amount of fuel vaporized for each cycle can be suppressed, and fluctuations in torque and unburned fuel can be suppressed. It becomes possible to suppress an increase in gas.

  In the state where the top surface of the piston 15 is advanced from the time when it passes through the injection point P, the fuel injection position to the top surface of the piston 15 increases from the inner wall surface of the cylinder bore on the exhaust valve 17 side as the advance amount increases. Move away (see FIG. 8). Therefore, the amount of fuel that reaches the cylinder inner wall surface decreases as the advance amount increases.

  On the other hand, as the advance amount increases, the amount of fuel attached to the piston 15 increases. The amount of smoke generated increases as the amount of fuel adhering to the top surface of the piston 15 in a state where the cylinder bore inner wall temperature is low. With respect to this problem, in the present embodiment, the injection timing is greatly advanced as the cylinder bore inner wall temperature increases in the range below the wall temperature threshold TV1.

  The higher the cylinder bore inner wall temperature, the faster the vaporization speed of the fuel adhering to the piston, so the amount of smoke generated is small. That is, if the cylinder bore inner wall temperature is high, it is possible to keep the amount of smoke generated low even if the cylinder bore is advanced greatly. Therefore, when the cylinder bore inner wall temperature is high, it is possible to suppress the occurrence of smoke while making a large advance to reduce the amount of fuel reaching the cylinder inner wall.

  On the other hand, the lower the cylinder bore inner wall temperature, the slower the vaporization speed of the fuel adhering to the piston, and the more smoke is generated. Therefore, when the cylinder bore inner wall temperature is low, it is possible to suppress the occurrence of smoke by reducing the amount of advancement from the injection point P and reducing the amount of fuel adhering to the piston 15. By reducing the advance amount, the amount of fuel reaching the cylinder inner wall surface increases. However, when the cylinder bore inner wall temperature is low, the amount of fuel vapor absorbed in the lubricating oil itself is greatly reduced. It is possible to suppress fluctuations in torque and increase in unburned gas.

  Note that, when the fuel injection timing is controlled according to the fuel temperature, the intake air temperature, and the engine speed as in the present embodiment, the same effect as the control according to the cylinder bore inner wall temperature can be obtained.

  In the present embodiment, as described above, the advance amount is adjusted according to the cylinder bore inner wall temperature, fuel temperature, intake air temperature, or engine speed, but the cylinder bore inner wall temperature, fuel temperature, or intake air is adjusted. A configuration may be adopted in which the injection timing is advanced by a predetermined advance amount without adjusting the advance amount when the temperature falls below the respective threshold value or when the engine speed exceeds the revolution number threshold TV4. If fuel is injected before the top surface of the piston 15 passes through the injection point P, fuel is not directly injected into the inner wall of the cylinder 20, so that the amount of fuel absorbed by the lubricating oil on the inner wall of the cylinder can be greatly reduced. Therefore, it is possible to sufficiently suppress the variation in the amount of vaporization for each cycle as compared with the case of injection near the BDC.

  In the present embodiment, the fuel injection timing is advanced from the intake stroke BDC according to the cylinder bore inner wall temperature, fuel temperature, intake air temperature, and engine speed. The injection timing may be advanced according to any factor given.

  In the case where the advance timing of the injection timing is adjusted based on other factors, the fuel injection timing is determined in the vicinity of the BDC in the intake stroke when the factors are within a range where it is determined that fuel vaporization is promoted. Is done. On the other hand, when the factor is out of the range, the fuel injection timing is determined earlier than when the top surface of the piston 15 passes the injection point P in the intake stroke.

  In this embodiment, the fuel injection timing is determined based on the cylinder bore inner wall temperature, the fuel temperature, the intake air temperature, and the engine speed, but the injection timing is determined based on at least one factor. Also good. In particular, the cylinder bore inner wall temperature has a greater effect on fuel vaporization than other factors, and therefore it is possible to simplify the process by determining the injection timing using only the cylinder bore inner wall temperature.

  Further, in the present embodiment, it is assumed that the fuel injection timing is performed once during the intake stroke, but the present invention is also applicable to a case where fuel injection is performed a plurality of times during a single cycle, for example. For example, when fuel injection is normally performed in the vicinity of the intake stroke BDC in at least one fuel injection among a plurality of injections, the injection timing is advanced as in the present embodiment when the fuel cannot be sufficiently vaporized. Horned.

  Further, in the present embodiment, the injection direction of the injector 18 is determined in the direction of the inner wall of the cylinder 20 in order to strengthen the tumble. However, not only for the purpose of strengthening the tumble but also for any other purpose. If the injection direction is the direction facing the inner wall surface of the cylinder 20 between the top dead center and the bottom dead center of the piston 15, the present embodiment is applicable.

  In this embodiment, the fuel temperature of the fuel and the temperature of the intake air are directly detected by the temperature sensor, but the fuel temperature and the like are indirectly set so that the cylinder bore inner wall temperature is detected by detecting the water temperature. It may be detected.

1 is a block diagram schematically showing a schematic configuration of an engine to which an embodiment of the present invention is applied. It is a graph which shows the advance correction value with respect to cylinder bore inner wall temperature. It is a graph which shows the advance correction value with respect to fuel temperature. It is a graph which shows the advance correction value with respect to intake air temperature. It is a graph which shows the advance correction value with respect to an engine speed. It is a flowchart which shows the program structure of the fuel injection timing determination control which ECU performs. It is a figure which shows the injection state when a fuel is injected before a piston passes an injection point. It is a figure explaining the effect produced by the magnitude | size of the advance amount of injection timing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 12a Intake port 15 Piston 18 Injector 20 Cylinder 21 Combustion chamber 22 Fuel temperature sensor 23 ECU
24 Intake air temperature sensor 25 Water temperature sensor 26 Rotation sensor

Claims (2)

An intake port for intake air into the combustion chamber so as to generate a tumble flow in the combustion chamber;
Fuel toward a predetermined What position der, injection point that is determined to enhance the tumble flow by injecting fuel into its position between the top dead center and the bottom dead center in the bore Injection means for injecting
Detecting means for detecting the bore inner wall temperature on the injection point side, which is a factor affecting vaporization of the fuel injected by the injection means in a combustion chamber;
A piston that moves from a top dead center to a bottom dead center during the intake stroke when the temperature of the bore inner wall detected by the detection means deviates from a predetermined range in which the fuel vaporization in the combustion chamber is promoted is injected. In order to inject the fuel into the injection means earlier than the timing of passing the point, the fuel is injected into the injection means as the bore inner wall temperature changes in a direction that promotes vaporization of the fuel outside the predetermined range. A spark ignition internal combustion engine comprising: control means for controlling an injection timing of the fuel by the injection means so as to inject quickly . 2. The spark ignition internal combustion engine according to claim 1 , wherein the intake port generates a forward tumble flow in the combustion chamber, and the injection point is defined on an inner wall of the exhaust side bore.

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