JP2016113918A - Control device of fuel injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of a fuel injection system which can raise common rail pressure without making it exceed a usable upper limit.SOLUTION: A control device (50) is used in a fuel injection system (10) which is mounted with an internal combustion engine which automatically stops on the basis of the establishment of a prescribed stop condition. The fuel injection system comprises: a pressurization pump (16) which is driven by the power of the internal combustion engine, and pressure-sends fuel; a common rail (20) which stores the fuel pressurized by the pressurization pump; common rail pressure detection means (22) which detects fuel pressure in the common rail; and discharge amount control means (18) which adjusts a discharge amount of the pressurization pump to the common rail. The control device controls the discharge amount control means so that the fuel pressure which is detected by the common rail pressure detection means becomes lower than usable upper limit rail pressure as a usable upper limit value of the pressurization pump, and also the discharge amount of the pressurization pump is increased.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a control technology for a fuel injection system at the time of idling stop of a vehicle including a common rail internal combustion engine.

  A common rail fuel injection system that stores fuel pressurized to a high pressure by a pressurizing pump (hereinafter referred to as a fuel supply pump) in a common rail and injects fuel into a cylinder at a predetermined time from a fuel injection valve connected to the common rail. There is an engine provided.

  Here, in recent years, there are vehicles that perform engine stop / restart control (hereinafter referred to as idling stop control) that stops the engine during idling for the purpose of improving fuel consumption and reducing exhaust gas.

  Such a vehicle generally has a characteristic that the starter motor cannot be driven unless the rotation of the engine is completely stopped. Therefore, when performing idling stop control, it is desired to shorten the engine stop time.

  Therefore, in an internal combustion engine equipped with a common rail type fuel injection system, a technique is disclosed in which the load on the fuel supply pump is maximized at the time of idling stop, thereby shortening the engine stop time and increasing the common rail pressure (patent) Reference 1).

JP2008-163796

  By the way, in the technique disclosed in Patent Document 1, the common rail pressure is increased when idling is stopped. At this time, due to the decrease in the rotational speed of the fuel supply pump, the upper limit rail pressure that indicates the upper limit value of the common rail pressure that becomes the limit of use of the fuel supply pump decreases. Therefore, the increased common rail pressure may exceed the upper limit rail pressure, and the fuel supply pump may be damaged.

  The present invention has been made to solve the above-described problems, and a main object of the present invention is to provide a control device for a fuel injection system capable of increasing the common rail pressure without exceeding the upper limit rail pressure for use. It is in.

  The present invention is a control device applied to a fuel injection system mounted on an internal combustion engine that is automatically stopped when a predetermined stop condition is satisfied, and the fuel injection system is driven by the power of the internal combustion engine. A pressure pump that is driven by the power of the internal combustion engine to pump fuel, a common rail that stores fuel pressurized by the pressure pump, and a fuel pressure in the common rail is detected. Common rail pressure detecting means, a fuel injection valve for injecting fuel stored in the common rail into a cylinder of the internal combustion engine, and a discharge amount control means for adjusting a discharge amount of the pressurizing pump to the common rail. And the control device is configured such that the fuel pressure detected by the common rail pressure detecting means corresponds to a driving state of the pressurizing pump before the internal combustion engine is stopped. And to be lower than the upper limit rail pressure as the upper limit value, it increases the discharge amount of the pressure pump and controls the discharge amount control means so welcome a maximum peak.

  According to the above configuration, the internal combustion engine is automatically stopped when a predetermined stop condition is satisfied. A fuel injection system mounted on the internal combustion engine includes a pressurizing pump, a common rail, and a fuel injection valve. For this common rail, the common rail pressure detecting means detects the fuel pressure in the common rail. For the pressurizing pump, the discharge amount control means adjusts the discharge amount to the common rail.

  The control device that controls the fuel injection system adjusts the discharge amount of the pressurizing pump to increase before the internal combustion engine stops. At this time, the discharge amount control means is controlled so that the fuel pressure detected by the common rail pressure detection means does not become higher than the use upper limit rail pressure as the use upper limit value of the pressurizing pump according to the driving state. Since the pressurizing pump includes a lubrication mechanism that is driven by the power of the internal combustion engine, the supply of the lubricant decreases as the rotational speed of the internal combustion engine decreases, and there is a possibility that seizure occurs on the sliding portion. For this reason, the use upper limit rail pressure is set, for example, as an upper limit rail pressure that can be used safely without causing seizure of the sliding portion. Therefore, by increasing the discharge amount so as not to exceed the use limit of the pressurizing pump, the stop time of the internal combustion engine can be shortened without causing damage to the pressurizing pump.

It is a schematic structure figure of a fuel injection system concerning this embodiment. It is a control flowchart performed by ECU concerning this embodiment. It is a time chart of control operation performed by ECU concerning a comparative example. It is a time chart of control operation performed by ECU concerning this embodiment. It is a graph used for calculating the use upper limit rail pressure of a fuel supply pump.

  Hereinafter, the present embodiment will be described with reference to the drawings. FIG. 1 shows a fuel injection system 10 of the present embodiment.

  The accumulator fuel injection system 10 includes a fuel supply pump 16, a common rail 20, a pressure sensor 22, a pressure reducing valve 30, a fuel injection valve 40, an electronic control unit (ECU) 50, an electronic driving unit (EDU). ) And the like, and injects fuel into each cylinder of a four-cylinder diesel engine (hereinafter also simply referred to as an engine) (not shown) as an internal combustion engine. In FIG. 1, only the control signal line from the EDU 52 to one fuel injection valve 40 and the injection pipe 202 from the common rail 20 to one fuel injection valve 40 are shown in order to avoid the complexity of the figure. Yes.

  The fuel filter 14 removes foreign matters in the fuel sucked by the fuel supply pump 16 from the fuel tank 12. The fuel supply pump 16 has a built-in feed pump that sucks fuel from the fuel tank 12, pressurizes the sucked fuel, and discharges it to the common rail 20 through the supply pipe 200.

  A fuel supply pump (corresponding to a pressurizing pump) 16 is a known pump that pressurizes fuel sucked into a pressurizing chamber by reciprocating a plunger as the cam of the camshaft rotates. The ECU 50 controls the metering valve (corresponding to the discharge amount control means) 18 of the fuel supply pump 16 to meter the amount of fuel sucked in by the fuel supply pump 16 in the suction stroke. Then, the amount of fuel discharged from the fuel supply pump 16 is adjusted by adjusting the intake amount. It should be noted that a metering valve for metering the fuel discharge amount may be installed on the discharge side of the fuel supply pump 16 to meter the discharge amount.

  The common rail 20 accumulates the fuel discharged from the fuel supply pump 16 to maintain the fuel pressure at a predetermined high pressure corresponding to the engine operating state, and supplies the fuel to the fuel injection valve 40 through the injection pipe 202. The pressure sensor (corresponding to the common rail pressure detecting means) 22 outputs a signal corresponding to the fuel pressure (actual rail pressure) inside the common rail 20.

  The pressure reducing valve 30 is an electromagnetic valve that opens by energization control and discharges the fuel inside the common rail 20 to the return pipe 204 on the low pressure side.

  The fuel injection valve 40 is mounted in each cylinder of a four-cylinder diesel engine, and injects fuel accumulated in the common rail 20 into the cylinder. The fuel injection valve 40 performs multi-stage injection including pilot injection and post injection before and after the main injection in one combustion cycle based on the operating state of the engine. The fuel injection valve 40 is a known electromagnetically driven injection valve that controls the fuel injection amount by controlling the pressure in the back pressure chamber that applies fuel pressure to the nozzle needle in the valve closing direction. The electromagnetic drive unit of the fuel injection valve 40 is constituted by a piezo actuator or an electromagnetic coil.

  The back pressure control valve 42 opens when the pressure in the back pressure chamber of the fuel injection valve 40 exceeds a predetermined pressure, and discharges the fuel in the back pressure chamber to the return pipe 204. This prevents the pressure in the back pressure chamber of the fuel injection valve 40 from exceeding a predetermined pressure.

  The ECU 50 is mainly composed of a microcomputer (microcomputer) mainly including a rewritable nonvolatile memory such as a CPU, a ROM, a RAM, and a flash memory, an input / output interface, and the like.

  The ECU 50 includes a pressure sensor 22, a brake sensor 60 that detects an operation amount Ab of the brake pedal, a speed sensor 62 that detects a traveling speed ve of the vehicle, an accelerator sensor 64 that detects an accelerator opening Acc that is an operation amount of the accelerator pedal, and the like. The engine operating state is acquired from the output signals of the various sensors. Then, the ECU 50 takes in output signals from various sensors and controls the engine operating state.

  The ECU 50 executes various controls of the fuel injection system 10 by executing a control program stored in the ROM or flash memory. For example, the ECU 50 controls the discharge amount of the fuel supply pump 16 and the opening / closing of the pressure reducing valve 30 to detect the actual rail pressure detected from the output signal of the pressure sensor 22 and the target rail pressure set based on the engine operating state. Based on the differential pressure, feedback (F / B) control for causing the actual rail pressure to follow the target rail pressure is executed.

  The EDU 52 is a drive device for supplying drive current or drive voltage to the pressure reducing valve 30 and the fuel injection valve 40 based on a control signal output from the ECU 50.

  Hereinafter, the control content regarding the fuel injection system 10 which ECU50 performs is demonstrated. The control related to the fuel injection system 10 shown in FIG. 2 is repeatedly executed by the ECU 50 at a predetermined cycle during the power-on period of the ECU 50.

  When this control is activated, it is first determined in step 100 whether or not an idling stop permission condition (corresponding to the stop permission condition) is satisfied. The idling stop permission condition (idling stop permission flag) is a driving operation status of the vehicle in which the engine is to be temporarily stopped, and the condition is exemplified below. (I) The key position is turned ON (the switch for operating the engine is turned ON), (ii) the brake is ON (Ab> Ab0 (predetermined amount)), and (iii) the traveling speed is predetermined. Below the speed (ve <ve0 (predetermined speed)), (iv) The battery charge rate SOC is greater than or equal to the predetermined remaining capacity (SOC> SOC0 (predetermined remaining capacity)), and (v) (i) to (iv) automatic stop After satisfying all the achievement conditions, a predetermined time α (corresponding to a second predetermined time) that is set shorter than a predetermined time γ described later and enables an operation before the idling stop is executed. Specifically, in the present embodiment, the ECU 50 regards that the idling stop permission condition is satisfied (idling stop permission flag on) when the condition (v) is satisfied.

  If the idling stop permission condition is not satisfied (S100: NO), the process proceeds to step 108, the target rail pressure during normal traveling is calculated, and this control is terminated.

When the idling stop permission condition is satisfied (S101: YES), the process proceeds to step 101. Since the engine rotation speed and the rotation speed (pump rotation speed) Np of the fuel supply pump 16 are in a proportional relationship, the pump rotation speed Np can be calculated from the engine rotation speed. In step 101, the upper limit rail pressure for use is set from FIG. 5 which shows the use range of the fuel supply pump 16 based on the pump rotation speed Np converted as described above, and the process proceeds to step 102.
Note that the upper limit rail pressure in the low rotation speed range (rotation speed of 1000 rpm or less in a large lift) is smaller than the low speed side limit rail pressure provided as a threshold that may cause seizure of the tappet constituting the fuel supply pump 16. Is set to Here, the large lift and the small lift indicate the magnitude of the lift amount of the plunger. There is a difference in pump rotation speed Np corresponding to the common rail pressure between the large lift and the small lift. This is because as the lift amount increases, the lift slip amount in the fuel supply pump 16 increases. That is, the large lift can discharge more fuel to the common rail 20 than the small lift, and the actual rail pressure can be increased at a low pump rotation speed Np.

  The fuel supply pump 16 rotates in conjunction with the rotation of the engine. At this time, the limit rail pressure of the fuel supply pump 16 decreases as the pump rotational speed Np decreases in the low rotational speed range (depending on the driving state). This is because the fuel supply pump 16 includes a lubrication mechanism that is driven by the power of the internal combustion engine, so that the fuel for lubrication sent from the fuel tank 12 is reduced due to the lower pump rotation speed Np. ing. If the actual rail pressure becomes higher than the limit rail pressure, the tappet that constitutes the fuel supply pump 16 may be seized, resulting in damage to the fuel supply pump 16. The use upper limit rail pressure is determined as an upper limit value at which the fuel supply pump 16 can be used safely by setting it lower than the limit rail pressure.

  In step 102, a value obtained by subtracting the predetermined value β from the use upper limit rail pressure determined as described above is set as the target rail pressure for early stop, and the process proceeds to step 103. Since the actual rail pressure is made to follow the target rail pressure by executing F / B control, even if the target rail pressure is increased and then decreased, the actual rail pressure cannot immediately respond to the change and is over May shoot. The predetermined value β is set as a value that does not exceed the use upper limit rail pressure even if the actual rail pressure overshoots.

  In step 103, it is determined whether an idling stop execution condition (corresponding to the stop execution condition) is satisfied. The idling stop execution condition is a predetermined time γ (first time) set as a determination time whether or not the engine idling stop is actually executed when the conditions satisfying (i) to (iv) in the idling stop permission condition are satisfied. This refers to the case of continuing for longer than the predetermined time.

  If the idling stop execution condition is not satisfied (S103: NO), the routine proceeds to step 105. If the idling stop execution condition is satisfied (S104: YES), the fuel injection by the fuel injection valve 40 is stopped and the routine proceeds to step 105.

  In step 105, it is determined whether or not the actual rail pressure is smaller than the target rail pressure for early stop. When the actual rail pressure is not smaller than the target rail pressure for early stop (S105: NO), the process proceeds to step 107, the discharge amount from the fuel supply pump 16 is decreased by F / B control, and this control is finished. . When the actual rail pressure is smaller than the target rail pressure for early stop (S105: YES), the process proceeds to step 106, the discharge amount from the fuel supply pump 16 is increased by F / B control, and this control is terminated.

  Next, problems that may occur when this control system is not adopted will be described with reference to FIG.

  In the control system of the fuel injection system 10 in FIG. 3, since the idling stop permission condition is not set, this control is executed when the idling stop execution condition is satisfied.

  When the idling stop execution condition is satisfied, the fuel injection by the fuel injection valve 40 is stopped, and at the same time, the discharge amount instruction value of the fuel supply pump 16 is controlled to the maximum (see time t1). Then, the fuel is discharged from the fuel supply pump 16 with a slight delay, and the actual rail pressure in the common rail 20 increases accordingly (see time t2).

  When the engine rotation speed becomes zero, the pump rotation speed is also zero, so that the fuel discharge from the fuel supply pump 16 stops. At this time, the use upper limit rail pressure may decrease as the engine speed decreases, and may become higher than the use upper limit rail pressure at which the actual rail pressure has decreased (see time t3). In this case, the tappet constituting the fuel supply pump 16 may be burned out.

  A control operation of the fuel injection system 10 executed by the ECU 50 devised to avoid such a situation will be described with reference to FIG. This control operation describes the control content of FIG. 2 along the time series.

  When the idling stop permission condition is satisfied, the target rail pressure for early stop is set (see time t0). Based on the differential pressure between the target rail pressure for early stop and the actual rail pressure in the common rail 20 detected by the pressure sensor 22 by F / B control such as PID control, the discharge amount instruction value of the fuel supply pump 16 is set. Set.

  Then, when the idling stop execution condition is satisfied, the fuel injection by the fuel injection valve 40 is stopped. At this time, fuel discharge from the fuel supply pump 16 to the common rail 20 is started slightly after the setting of the discharge amount instruction value (see time t1).

  As the fuel is discharged, the actual rail pressure in the common rail 20 increases, and the engine rotation speed starts decreasing at a certain point (see time t2). At this time, when the engine rotation speed starts to decrease, the use upper limit rail pressure also decreases. Therefore, based on the method for calculating the target rail pressure for early stop, the target rail pressure for early stop is also decreased by the amount corresponding to the decrease in engine speed. The discharge amount instruction value of the fuel supply pump 16 is set to no discharge because the actual rail pressure has to be reduced as the target rail pressure for early stop decreases.

  Then, fuel discharge by the fuel supply pump 16 is stopped according to the discharge amount instruction value. At this time, due to the response delay due to the F / B control, the actual rail pressure may overshoot (see time t3) when fuel discharge by the fuel supply pump 16 continues even for a short time. . However, since the target rail pressure for early stop is set as a value in consideration of overshoot, it is possible to suppress the maximum peak of the actual rail pressure from exceeding the upper limit rail pressure.

  Thereafter, the target rail pressure is set to 0 (see time t4) when the engine speed decreases and stops completely.

  The embodiment described above has the following effects.

  -ECU50 adjusts so that the discharge amount of the fuel supply pump 16 may be increased, before an engine stops. At this time, the metering valve 18 is controlled so that the actual rail pressure detected by the pressure sensor 22 does not become higher than the use upper limit rail pressure as the use upper limit value corresponding to the driving state of the fuel supply pump 16. Since the fuel supply pump 16 includes a lubrication mechanism that is driven by the power of the engine, the supply of the lubricant decreases as the engine speed decreases, and the tappet may be seized. For this reason, the upper limit rail pressure is set as the upper limit rail pressure that can be used safely without seizing the tappet. Therefore, by increasing the discharge amount so as not to exceed the use limit of the fuel supply pump 16, the engine stop time can be shortened without causing damage to the fuel supply pump 16.

  The ECU 50 controls the metering valve 18 so as to increase the discharge amount of the fuel supply pump 16 when the idling stop permission condition is satisfied. For this reason, considering the response delay of the fuel supply pump 16, the discharge capacity of the fuel supply pump 16 is increased without waiting for the fuel injection to stop, so that the pump load increases when the fuel injection stops. It becomes possible.

  The ECU 50 determines the discharge amount so that the fuel pressure in the common rail 20 detected by the pressure sensor 22 approaches the target rail pressure set lower than the upper limit rail pressure that may cause the fuel supply pump 16 to be damaged. Adjust. For this reason, it can suppress that the fuel pressure in the common rail 20 exceeds a use upper limit rail pressure, and it becomes possible to suppress damage to the fuel supply pump 16.

  The target rail pressure is set as a value obtained by subtracting a predetermined value β from the upper limit rail pressure for use. For this reason, it becomes possible to suppress that overshoot occurs and the actual rail pressure becomes higher than the use upper limit rail pressure.

  In the present embodiment, the stop permission condition is satisfied before the stop execution condition is satisfied. In order to set the target rail pressure when the stop permission condition is satisfied, the metering valve 18 may be controlled to increase the discharge amount of the fuel supply pump 16 before the fuel injection into the cylinder is stopped. It becomes possible. As a result, the actual rail pressure can be increased when the fuel injection is stopped.

  ・ The upper limit rail pressure is determined based on the engine speed. Since the pump rotational speed Np can be calculated from the engine rotational speed, it is possible to determine the upper limit range of use of the common rail 20 that changes depending on the pump rotational speed.

  When the pump rotation speed Np is in the low rotation speed range, the use upper limit rail pressure decreases as the pump rotation speed Np decreases. For this reason, it becomes possible to set appropriately the use upper limit rail pressure when the pump rotation speed Np is in the low rotation speed range.

  In addition, the said embodiment can also be changed and implemented as follows.

  -The use upper limit rail pressure was determined based on the pump rotational speed Np. In this regard, the use upper limit rail pressure may be set in any manner as long as the use upper limit rail pressure is equal to or lower than the limit rail pressure shown in FIG. Specifically, the low speed side limit rail pressure shown in FIG. 5 may be provided as the use upper limit rail pressure. In this case, a larger pump load can be generated, and the engine stop time can be further shortened.

  The ECU 50 sets the target rail pressure so as to increase the discharge amount of the fuel supply pump 16 when the idling stop permission condition is satisfied. For this, it is not always necessary to provide the idling stop permission condition. Specifically, when a condition capable of performing idling stop is satisfied, the target rail pressure is set so as to increase the discharge amount of the fuel supply pump 16 at the earliest possible timing, and then fuel injection by the fuel injection valve 40 is performed. May be stopped.

  -Regarding the idling stop permission condition and idling stop execution condition, the automatic stop achievement conditions (i) to (iv) must be satisfied in common. Regarding this, further conditions may be added or deleted. Specifically, the condition (v) accelerator OFF (Acc <Acc0 (predetermined value)) may be added, or the condition (i) may be deleted.

  -When setting the target rail pressure for early stop, the value obtained by subtracting the predetermined value β from the upper limit rail pressure for use was set as the target rail pressure for early stop. In this regard, the quotient obtained by dividing the use upper limit rail pressure by the predetermined value ω (ω> 1) may be set as the target rail pressure for early stop. Further, the predetermined value β and the predetermined value ω may be variable according to the engine operating state and the like.

  -The target rail pressure for early stop was set when the idling stop permission condition was satisfied. In this regard, it is not always necessary to provide the target rail pressure for early stop if the actual rail pressure can be contained within the upper limit rail pressure. Specifically, the discharge amount instruction value of the fuel supply pump 16 is set to a fixed value based on data obtained in advance through experiments or the like, and the discharge amount instruction value of the fuel supply pump 16 is set to 0 after a predetermined time. Control. At this time, the fixed value is set as a value that is unlikely to increase the actual rail pressure exceeding the upper limit rail pressure even if overshoot occurs.

  -Although the said embodiment is a control apparatus devised for the object of a normal diesel vehicle, it is applicable also to a diesel hybrid vehicle.

DESCRIPTION OF SYMBOLS 10 ... Fuel injection system, 16 ... Fuel supply pump, 18 ... Metering valve, 20 ... Common rail, 22 ... Pressure sensor, 40 ... Fuel injection valve, 50 ... ECU.

Claims (8)

A control device (50) applied to a fuel injection system (10) mounted on an internal combustion engine that is automatically stopped based on establishment of a predetermined stop condition,
The fuel injection system includes:
A pressure pump (16) that includes a lubrication mechanism that is driven by the power of the internal combustion engine, and that is driven by the power of the internal combustion engine to pump fuel.
A common rail (20) for storing fuel pressurized by the pressure pump;
Common rail pressure detection means (22) for detecting fuel pressure in the common rail;
A fuel injection valve (40) for injecting fuel stored in the common rail into a cylinder of the internal combustion engine;
A discharge amount control means (18) for adjusting the discharge amount of the pressure pump to the common rail;
With
The control device is configured such that the fuel pressure detected by the common rail pressure detecting means is lower than a use upper limit rail pressure as a use upper limit value corresponding to a driving state of the pressurizing pump before the internal combustion engine is stopped. The control device for the fuel injection system controls the discharge amount control means so as to increase the discharge amount of the pressurizing pump.   The control device controls the discharge amount control means to increase the discharge amount of the pressurizing pump before the fuel injection into the cylinder is stopped when the predetermined stop condition is satisfied. The control device for the fuel injection system according to claim 1.   3. The fuel injection system according to claim 1, wherein the control device adjusts the discharge amount so as to approach a target rail pressure set to be lower than the upper limit rail pressure for use. Control device.   The control apparatus for a fuel injection system according to claim 3, wherein the target rail pressure is set to be lower than the upper limit rail pressure by a predetermined pressure. The predetermined stop condition is composed of a stop permission condition and a stop execution condition,
Satisfaction of the stop execution condition means that the switch for operating the internal combustion engine is turned on, the brake pedal is stepped on more than a predetermined amount, the vehicle speed is slower than the predetermined speed, and the remaining capacity of the battery is equal to the predetermined remaining capacity. More than the remaining, these four stop attainment conditions indicate a case of continuing longer than the first predetermined time provided as a determination time whether or not to stop the internal combustion engine,
The establishment of the stop permission condition indicates a case where the four stop achievement conditions continue longer than a second predetermined time set shorter than the first predetermined time,
5. The fuel injection according to claim 1, wherein when the stop permission condition is satisfied, the discharge amount control unit is controlled to increase a discharge amount of the pressurizing pump. System control unit.   The fuel injection system control device according to any one of claims 1 to 5, wherein the upper limit rail pressure is determined based on a rotational speed of the internal combustion engine.   The fuel according to any one of claims 1 to 6, wherein when the rotation speed of the internal combustion engine is in a low rotation speed range, the use upper limit rail pressure decreases as the rotation speed decreases. Control device for injection system. A control device for a fuel injection system according to any one of claims 1 to 7,
A pressurizing pump that includes a lubrication mechanism that is driven by the power of the internal combustion engine and that is driven by the power of the internal combustion engine to pump fuel;
A common rail for storing fuel pressurized by the pressure pump;
Common rail pressure detecting means for detecting fuel pressure in the common rail;
A fuel injection valve for injecting fuel stored in the common rail into a cylinder of the internal combustion engine;
A discharge amount control means for adjusting a discharge amount to the common rail of the pressure pump;
A fuel injection system comprising:

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