JP2008274872A - Exhaust gas recirculation control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently secure NOx reduction effect by recirculation of exhaust gas under an operation condition where oxygen concentration in EGR gas is high. <P>SOLUTION: This exhaust gas recirculation device for an internal combustion engine includes an exhaust gas recirculation means such as an EGR passage, and re-circulates exhaust gas after passing through an oxidation catalyst to an intake passage. The exhaust gas recirculation means can be a so-called high pressure loop EGR device and/or a low pressure loop EGR device. The oxidation catalyst can be provided in the EGR passage or in the exhaust passage. Oxygen concentration in exhaust gas is acquired, and fuel is supplied into exhaust gas by a fuel supply means when the acquired oxygen concentration is higher than predetermined value. Since the fuel reacts in the oxidation catalyst and consumes oxygen, oxygen concentration in exhaust gas is reduced. Since exhaust gas in which oxygen concentration is dropped is returned to an intake side, sufficient NOx reduction effect is provided even under the operation condition where oxygen concentration in exhaust gas is high. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to control of an internal combustion engine including an exhaust gas recirculation passage that recirculates exhaust gas from an exhaust passage to an intake passage.

  Conventionally, in an internal combustion engine such as a diesel engine, exhaust gas recirculation that suppresses the generation of nitrogen oxides (NOx) by returning a part of the exhaust gas from the exhaust passage to the intake passage and lowering the combustion temperature in the engine. (EGR: Exhaust Gas Recirculation) devices are known. An example of a diesel engine equipped with an EGR device is described in Patent Document 1.

  In addition, a diesel engine equipped with a turbocharger is provided with an EGR path for returning exhaust gas upstream from the turbocharger to the intake side and an EGR path for returning exhaust gas downstream from the turbocharger to the intake side. Documents 2 and 3 describe.

JP 2004-150319 A JP 2005-264821 A Japanese Patent Laid-Open No. 2004-162675

  In an internal combustion engine equipped with an EGR device, the oxygen concentration in the EGR gas greatly affects the NOx reduction effect, and the NOx reduction effect increases as the oxygen concentration decreases. The oxygen concentration in the exhaust gas can be basically reduced by lowering the air-fuel ratio during combustion, but there is a limit from the viewpoint of combustion stability. Therefore, for example, after the fuel cut is performed at the time of deceleration of the vehicle, the NOx reduction effect by EGR is reduced in an operating state in which the oxygen concentration in the EGR gas is high.

  The present invention has been made in view of the above points, and it is an object of the present invention to sufficiently ensure the NOx reduction effect due to exhaust gas recirculation even in an operating state in which the oxygen concentration in the EGR gas is high.

  In one aspect of the present invention, an exhaust gas recirculation device for an internal combustion engine includes an oxidation catalyst, exhaust gas recirculation means for recirculating exhaust gas that has passed through the oxidation catalyst to an intake passage, and oxygen that acquires an oxygen concentration in the exhaust gas A concentration acquisition means; a fuel supply means for supplying fuel into the exhaust gas flowing through the oxidation catalyst; and an oxygen concentration reduction request amount in the exhaust gas by the fuel supply means when the oxygen concentration is greater than a predetermined value. Oxygen concentration control means for supplying the fuel.

  The exhaust gas recirculation device for the internal combustion engine has exhaust gas recirculation means such as an EGR passage, and recirculates the exhaust gas that has passed through the oxidation catalyst to the intake air passage. The exhaust gas recirculation means may be a so-called high pressure loop EGR device and / or a low pressure loop EGR device. The oxidation catalyst may be provided on the EGR passage or may be provided on the exhaust passage. When the oxygen concentration in the exhaust gas is acquired and greater than a predetermined value, fuel is supplied into the exhaust gas by the fuel supply means. As the fuel supply means, a fuel injection valve that performs post injection may be used, or a fuel addition valve that is provided separately from the fuel injection valve may be used. Since the fuel supplied into the exhaust gas reacts with the oxidation catalyst and consumes oxygen, the oxygen concentration in the exhaust gas can be lowered. Since the exhaust gas with the reduced oxygen concentration is returned to the intake side, the NOx reduction effect can be sufficiently obtained even under operating conditions where the oxygen concentration in the exhaust gas is high.

  In one aspect of the above exhaust gas recirculation apparatus, the oxygen concentration control means determines the oxygen concentration reduction request amount based on the oxygen concentration. Thereby, an amount of fuel necessary for lowering the oxygen concentration at that time to a predetermined level can be supplied to the exhaust gas.

  In another aspect of the exhaust gas recirculation device, an exhaust purification device that purifies the exhaust gas, and a regeneration request in the exhaust gas by the fuel supply means to recover the exhaust purification performance of the exhaust purification device. A regeneration control means for supplying an amount of fuel, and the oxygen concentration control means stops the supply of the oxygen concentration reduction required amount when the regeneration required amount of fuel is supplied by the regeneration control means. At the same time, the exhaust gas recirculation amount by the exhaust gas recirculation means is controlled based on the regeneration requirement amount and the oxygen concentration reduction requirement amount.

  In this aspect, when the request for reducing the oxygen concentration in the exhaust gas and the regeneration request for the exhaust purification device are generated at the same timing, the regeneration request for the exhaust purification device is given priority and the necessary amount of fuel is supplied to the exhaust gas. To do. At the same time, the exhaust gas recirculation amount is adjusted in order to meet the demand for oxygen concentration reduction. In a preferred embodiment, the oxygen concentration control means decreases the recirculation amount when the regeneration requirement amount is larger than the oxygen concentration reduction requirement amount. If the regeneration requirement is greater than the oxygen concentration reduction requirement, the oxygen consumption at the oxidation catalyst will increase, and the oxygen concentration in the intake air will decrease more than necessary, and combustion may become unstable. By adjusting the flow rate, the NOx reduction effect is obtained while stabilizing the combustion.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a schematic configuration of an internal combustion engine 100 according to the first embodiment of the present invention. In FIG. 1, solid arrows indicate the flow of intake and exhaust, and broken arrows indicate control signals.

  In FIG. 1, an internal combustion engine 100 includes an in-line four-cylinder diesel engine 10. Each cylinder of the engine 10 is connected to an intake manifold 11 and an exhaust manifold 12. The engine 10 includes a fuel injection valve 15 provided in each cylinder, and a common rail 14 that supplies high-pressure fuel to each fuel injection valve 15. The common rail is in a high-pressure state by a fuel pump (not shown). Supplied.

  In the intake passage 20 connected to the intake manifold 11, there are an air flow meter 21 that measures the amount of air flowing into the engine 10, a throttle 22 valve, a compressor 23 a of the turbocharger 23, and an intercooler 24 that cools the intake air. Is provided. On the other hand, the turbine 23 of the turbocharger 23 is connected to the exhaust passage 25 connected to the exhaust manifold 12.

  Furthermore, the upstream position of the turbine 23 a in the exhaust passage 25 and the downstream position of the intake passage 20 from the intercooler 24 are connected by an EGR passage 31. The EGR passage 31 is provided with an oxidation catalyst 32 and an EGR valve 33 for controlling the EGR amount. The EGR device having the EGR path upstream of the turbocharger is hereinafter referred to as a “high pressure loop EGR device”.

  Each element of the internal combustion engine 10 is controlled by the ECU 7. Specifically, the ECU 7 receives the signal S1 indicating the intake flow rate from the air flow meter 21, and sends a control signal S2 to the throttle valve 22 to control the opening degree of the throttle valve 22. Further, the ECU 7 sends a control signal S3 to the EGR valve 33 to control its opening, and sends a control signal S4 to the fuel injection valve 15 to control the fuel injection amount. The ECU 7 also controls other components of the internal combustion engine 100, but description of portions that are not particularly related to the present embodiment is omitted.

Next, the oxygen concentration reduction control of the EGR gas according to the present invention will be described. As described above, the EGR device lowers the combustion temperature by recirculating a part of the exhaust gas to the intake side and reduces the generation of NOx, but the oxygen concentration in the EGR gas recirculated to the intake side is high. As the result, the NOx reduction effect decreases. Therefore, for example, in an operating state in which the oxygen concentration in the EGR gas is high, such as after a fuel cut is performed during deceleration of the vehicle, it is necessary to reduce the oxygen concentration to ensure the NOx reduction effect. Therefore, in the present invention, the oxygen (O ₂ ) concentration in the exhaust gas is monitored, and when the concentration is higher than a predetermined concentration, unburned fuel is supplied into the exhaust gas. Thereby, oxygen is consumed when the fuel supplied into the exhaust gas reacts with the oxidation catalyst, so that the oxygen concentration in the EGR gas recirculated to the intake side can be reduced. In this case, the reaction that occurs in the oxidation catalyst is to generate water (H ₂ O) and carbon dioxide (CO ₂ ) from hydrocarbon (HC) and oxygen (O ₂ ) in the fuel.

  In the above configuration, the EGR passage 31 functions as exhaust gas recirculation means, the fuel injection valve 15 functions as fuel supply means, and the ECU 7 functions as oxygen concentration acquisition means and oxygen concentration control means.

  In the first embodiment, post injection by the fuel injection valve 15 is used as a method of supplying fuel into the exhaust gas. Note that “post-injection” generally refers to injecting fuel at a timing that does not affect combustion using the fuel injection valve 15 that injects fuel for combustion in an internal combustion engine.

  FIG. 2 is a flowchart of the oxygen concentration reduction control of the EGR gas according to the first embodiment. This control is mainly executed by the ECU 7.

  First, the ECU 7 calculates the oxygen concentration in the exhaust gas based on the fresh air amount calculated from the operating state and the fuel injection valve injection amount (step S101). This process can be performed as follows, for example. Specifically, the ECU 7 obtains a new air amount (referred to as “X”) introduced into the intake passage based on the signal S <b> 1 from the air flow meter 21. Further, the ECU 7 determines the oxygen consumption amount corresponding to the current fuel injection amount based on the fuel injection amount actually injected from the fuel injection valve 15 in the current operation state and the theoretical air-fuel ratio (A / F). That is, the amount of oxygen actually consumed by combustion in the engine 10 (referred to as “Y”) is calculated. Then, since the difference between the fresh air amount X and the actual oxygen consumption amount Y is the oxygen amount contained in the exhaust gas, the oxygen concentration in the exhaust gas is calculated from the oxygen amount and the entire exhaust gas amount.

  When the oxygen concentration in the exhaust gas thus obtained is higher than a predetermined concentration, the ECU 7 calculates a post injection amount for the exhaust gas (step S102). Specifically, since the amount of oxygen in the exhaust gas is known from the calculation in step S101, the ECU 7 calculates the amount of fuel necessary to consume the oxygen by the reaction in the catalyst, and the fuel injection valve The post injection amount from 15. Then, the ECU 7 sends a control signal S4 to the fuel injection valve 15 to instruct to perform post injection with the calculated post injection amount (step S103).

  Thus, in the first embodiment, by performing post injection, oxygen in the exhaust gas can be consumed by the catalyst, so that the oxygen concentration in the EGR gas can be reduced, and the NOx reduction effect by EGR can be reduced. Can be maintained to the maximum. In particular, even when re-acceleration is performed after fuel cut during deceleration as described above, a sufficient NOx reduction effect by EGR can be ensured.

[Second Embodiment]
The second embodiment is the same as the first embodiment in that the oxygen concentration of the EGR gas is lowered by supplying a necessary amount of fuel into the exhaust gas. However, in the first embodiment, fuel is supplied into the exhaust gas by post-injection using a fuel injection valve, whereas in the second embodiment, a fuel addition valve provided separately from the fuel injection valve is used. .

  FIG. 3 is a block diagram showing a schematic configuration of the internal combustion engine 100a according to the second embodiment. The same constituent elements as those of the internal combustion engine 100 shown in FIG. As understood from comparison with FIG. 1, in the internal combustion engine 100a of the second embodiment, a fuel addition valve 17 for injecting fuel is provided in the exhaust manifold 12 in addition to the fuel injection valve 15 provided for each cylinder. ing. The amount of fuel added from the fuel addition valve 17 is controlled by a control signal S5 supplied from the ECU 7. Other points are the same as in the first embodiment. The fuel addition valve 17 can also be used as a fuel addition valve for adding fuel for catalyst regeneration generally provided in the exhaust passage.

  In the above configuration, the EGR passage 31 functions as exhaust gas recirculation means, the fuel addition valve 17 functions as fuel supply means, and the ECU 7 functions as oxygen concentration acquisition means and oxygen concentration control means.

  FIG. 4 is a flowchart of the oxygen concentration reduction control of the EGR gas according to the second embodiment. As understood from comparison with FIG. 2, the control of the second embodiment is basically the same as the control of the first embodiment except that the fuel addition valve 17 is used. That is, the ECU 7 first calculates the oxygen concentration in the exhaust gas (step S201), and calculates the amount of fuel to be supplied from the fuel addition valve 17 to the exhaust gas when it is higher than the predetermined concentration (step S202). . This fuel addition amount can be calculated by the same method as in step S102 in the first embodiment. The ECU 7 then injects fuel from the fuel addition valve 17 with the calculated fuel injection amount (step S203). Thus, the oxygen concentration of the EGR gas can be reduced and the NOx reduction effect can be maintained.

  In addition, when performing post injection like 1st Embodiment, since the fuel injection valve 15 which performs fuel injection for normal fuel is utilized, there is a possibility that post injection may affect the fuel to some extent, The amount of fuel that can be supplied is limited to some extent because of the risk of diluting the oil. In this regard, there is no problem as described above if a fuel addition valve 17 separate from the fuel injection valve 15 is used as in the second embodiment.

[Third Embodiment]
In the third embodiment, the present invention is applied to an internal combustion engine equipped with an EGR device (hereinafter referred to as “low pressure loop EGR device”) that takes out EGR gas from the downstream side of the turbocharger. FIG. 5 shows a schematic configuration of an internal combustion engine 100c according to the third embodiment. As can be seen from comparison with the internal combustion engine 100b of the second embodiment shown in FIG. 3, in the internal combustion engine 100c of the third embodiment, there is no EGR passage 31 upstream of the turbocharger 23 and downstream of the turbine 23b of the exhaust passage 25. An EGR passage 35 is provided to connect the position on the side and the position upstream of the compressor 23 a of the intake passage 20. The EGR passage 35 is configured to take out EGR gas from a position downstream of the oxidation catalyst 36 provided in the exhaust passage 35. The EGR passage 35 is provided with an EGR valve 37 for controlling the amount of EGR gas, and the opening degree of the EGR valve 37 is controlled by a control signal S6 from the ECU 7.

  The internal combustion engine 100c according to the third embodiment is the same as the internal combustion engine 100b according to the second embodiment except that a low-pressure loop EGR device is employed instead of the high-pressure loop EGR device. Therefore, the oxygen concentration reduction control of the EGR gas is performed in the same manner as in the second embodiment shown in FIG. FIG. 5 shows a configuration in which fuel is supplied into the exhaust gas using the fuel addition valve 17 as in the second embodiment, but instead, a fuel injection valve as in the first embodiment. The fuel may be supplied to the exhaust gas by post-injection using the No. 15.

  In the above configuration, the EGR passage 35 functions as exhaust gas recirculation means, the fuel addition valve 17 functions as fuel supply means, and the ECU 7 functions as oxygen concentration acquisition means and oxygen concentration control means.

  When the present invention is applied to an internal combustion engine having a high-pressure loop EGR device as in the first and second embodiments, the post-injection position by the fuel injection valve 15 or the fuel addition position by the fuel addition valve 17 and the EGR passage 31 Since the distance from the provided oxidation catalyst 32 is short, the diffusion and evaporation of the fuel supplied in the exhaust gas becomes insufficient, and there is a possibility that the fuel is clogged in the EGR passage. In this regard, when the present invention is applied to an internal combustion engine having a low-pressure loop EGR device as in the third embodiment, the distance between the fuel supply position and the oxidation catalyst 36 is long, so that sufficient fuel evaporation time is secured. can do. Further, the exhaust gas after the fuel supply is agitated when passing through the turbine 23b of the turbocharger 23. Therefore, unlike the case of the high-pressure loop EGR device, it is possible to reduce the possibility that a problem such as fuel clogging occurs. Further, when the low-pressure loop EGR device is used as in the present embodiment, the large-sized oxidation catalyst 36 originally provided for processing the exhaust gas can be used, so that the oxygen consumption in the oxidation catalyst 36 is reduced. There is also an advantage that it can be performed more effectively and the effect of reducing NOx by reducing the oxygen concentration can be more sufficiently secured.

[Fourth Embodiment]
In the fourth embodiment, the present invention is applied to an internal combustion engine including both a high-pressure loop EGR device and a low-pressure loop EGR device. FIG. 6 shows a schematic configuration of an internal combustion engine 100d according to the fourth embodiment. As illustrated, the internal combustion engine 100d includes an EGR passage 31 that constitutes a high-pressure loop EGR device, and an EGR passage 35 that constitutes a low-pressure loop EGR device. That is, the internal combustion engine 100d is configured by combining the internal combustion engine 100b of the second embodiment shown in FIG. 3 and the internal combustion engine 100c of the third embodiment shown in FIG.

  In the above configuration, the EGR passages 31 and 35 function as exhaust gas recirculation means, the fuel addition valve 17 functions as fuel supply means, and the ECU 7 functions as oxygen concentration acquisition means and oxygen concentration control means.

  The EGR gas oxygen concentration reduction control executed by the internal combustion engine 100d of the fourth embodiment is the same as that of the first to third embodiments. 6 shows a configuration in which fuel is supplied into the exhaust gas using the fuel addition valve 17 as in the second embodiment, but instead, a fuel injection valve is used as in the first embodiment. The fuel may be supplied to the exhaust gas by post-injection using the No. 15.

[Fifth Embodiment]
The fifth embodiment relates to a process in the case where fuel supply for catalyst regeneration is requested at the same timing as the oxygen concentration reduction control of the EGR gas in the internal combustion engines 100 to 100d of the first to fourth embodiments. Here, the “catalyst” refers to an exhaust purification device such as a DPF (Diesel Particulate Filter) that processes particulate matter and a NOx occlusion reduction type catalyst that processes NOx. This catalyst is provided at a downstream position of the turbine 23b in FIGS. 1 and 3, and at a downstream position of the oxidation catalyst 36 in FIGS. “Catalyst regeneration” refers to PM (Particulate Matter) regeneration in the case of DPF, so-called rich spike control for reducing and treating the stored NOx in the case of a NOx occlusion reduction type catalyst. It is performed by adding.

  As described above, the present invention supplies fuel into the exhaust gas in order to reduce the oxygen concentration in the EGR gas. This process is called “fuel supply by oxygen concentration reduction request”, and the fuel supply amount at that time is called “oxygen concentration reduction request amount”. Separately from this, the fuel is supplied into the exhaust gas for the regeneration treatment of the catalyst provided in the exhaust passage as described above. This process is called "fuel supply by catalyst regeneration request", and the fuel supply amount at that time is called "catalyst regeneration request amount". When these two fuel supplies are requested at different timings, the fuel supply may be performed independently at the required fuel supply amounts. However, when two fuel supplies are requested at the same timing, it is necessary to adjust the fuel supply amount.

  Therefore, in the present embodiment, when two fuel supplies are requested at the same timing, priority is given to the fuel supply by the catalyst regeneration request, and the fuel is supplied into the exhaust gas at the catalyst regeneration request amount. However, in this case, if the required amount of catalyst regeneration is larger than the required amount of oxygen concentration reduction, the oxygen consumption in the oxidation catalyst becomes large, and the engine combustion becomes unstable as a result of the intake air becoming lower than necessary. There is a fear. Therefore, the ECU 7 supplies the fuel with the catalyst regeneration request amount and corrects the opening degree of the EGR valve as necessary based on the catalyst regeneration request amount and the oxygen concentration reduction request amount, thereby obtaining the oxygen concentration of the intake air. Is maintained in an appropriate state.

  The above catalyst functions as an exhaust purification device in the present invention, the ECU 7 functions as a regeneration control device for the exhaust purification device, and the catalyst regeneration request amount corresponds to the regeneration request amount in the present invention.

  FIG. 7 is a flowchart of oxygen concentration reduction control according to the fifth embodiment. Steps S301 and S302 are the same as steps S101 and S102 of the first embodiment. That is, the ECU 7 first calculates the oxygen concentration in the exhaust gas (step S301), and when it is higher than the predetermined concentration, calculates the oxygen concentration reduction request amount (step S302).

  Next, the ECU 7 determines whether or not a catalyst regeneration request has been made (step S303). When the catalyst regeneration request is not made (step S303; No), the ECU 7 supplies the fuel by the oxygen concentration reduction process similarly to the first to fourth embodiments, and ends the process.

  On the other hand, when the catalyst regeneration request is made (step S303; Yes), the ECU 7 first calculates the catalyst target temperature (step S304), and the fuel supply amount necessary for raising the catalyst to the catalyst target temperature, that is, the catalyst. A reproduction request amount is calculated (step S305). Then, the ECU 7 supplies the calculated catalyst regeneration required amount of fuel to the exhaust gas (step S306) and adjusts the opening degree of the EGR valve 33 and / or 37 (step S307). Specifically, if the catalyst regeneration requirement amount is larger than the oxygen concentration reduction requirement amount, the consumption of oxygen in the oxidation catalyst is excessive, and the oxygen concentration in the intake air may be lowered and the fuel may become unstable. The opening degree of the EGR valve is reduced so that the amount of EGR gas returned to the intake side decreases. On the other hand, when the catalyst regeneration requirement amount is smaller than the oxygen concentration reduction requirement amount, the opening degree of the EGR valve is increased so that the EGR gas amount increases. This prevents a problem that the effect of reducing the oxygen concentration of the EGR gas cannot be obtained when priority is given to fuel supply in response to a catalyst regeneration request. Note that when the EGR opening degree is controlled in step S307, the opening degree of the throttle 22 is actually controlled as necessary.

  The control according to the fifth embodiment can be applied to any configuration of the first to fourth embodiments.

[Modification]
In each of the above embodiments, the oxygen concentration in the exhaust gas is calculated from the fresh air amount, the fuel injection amount, etc., but instead, it is obtained using a sensor output such as an oxygen sensor provided in the exhaust passage. It is good.

1 is a schematic block diagram of an internal combustion engine according to a first embodiment. It is a flowchart of oxygen concentration reduction control by 1st Embodiment. It is a schematic block diagram of the internal combustion engine which concerns on 2nd Embodiment. It is a flowchart of oxygen concentration reduction control by 2nd Embodiment. It is a schematic block diagram of the internal combustion engine which concerns on 3rd Embodiment. It is a schematic block diagram of the internal combustion engine which concerns on 4th Embodiment. It is a flowchart of oxygen concentration reduction control by 5th Embodiment.

Explanation of symbols

7 ECU
DESCRIPTION OF SYMBOLS 10 Engine 15 Fuel injection valve 17 Fuel addition valve 20 Intake passage 23 Turbocharger 25 Exhaust passage 31, 35 EGR passage 32, 36 Oxidation catalyst 33, 37 EGR valve

Claims (4)

An oxidation catalyst,
Exhaust gas recirculation means for recirculating exhaust gas that has passed through the oxidation catalyst to the intake passage;
Oxygen concentration acquisition means for acquiring oxygen concentration in the exhaust gas;
Fuel supply means for supplying fuel into the exhaust gas flowing through the oxidation catalyst;
An exhaust gas recirculation for an internal combustion engine, comprising: oxygen concentration control means for supplying, by the fuel supply means, an amount of oxygen concentration reduction required fuel into the exhaust gas when the oxygen concentration is greater than a predetermined value. apparatus.   2. The exhaust gas recirculation apparatus for an internal combustion engine according to claim 1, wherein the oxygen concentration control means determines the required oxygen concentration reduction amount based on the oxygen concentration. An exhaust purification device for purifying the exhaust gas;
In order to recover the exhaust purification performance of the exhaust purification device, the fuel supply means includes a regeneration control means for supplying the regeneration requested amount of fuel into the exhaust gas,
The oxygen concentration control means stops the supply of the oxygen concentration reduction request amount and supplies the regeneration request quantity and the oxygen concentration reduction request when the regeneration request quantity of fuel is supplied by the regeneration control means. The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2, wherein the exhaust gas recirculation amount by the exhaust gas recirculation means is controlled based on the amount.   The exhaust gas recirculation apparatus for an internal combustion engine according to claim 3, wherein the oxygen concentration control means reduces the recirculation amount when the regeneration requirement amount is larger than the oxygen concentration reduction requirement amount.

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