JP7268580B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device for an internal combustion engine. In particular, the present invention relates to a control system for an internal combustion engine with port injectors and direct injectors.

In some cases, retardation correction is performed to retard the ignition timing of the internal combustion engine. For example, when the occurrence of knocking is detected, retardation correction is performed to suppress knocking. However, retarding the ignition timing causes an increase in the exhaust temperature. A rise in the temperature of the exhaust gas causes deterioration of the function of the catalyst provided in the exhaust passage. Therefore, it is known that when the ignition timing is retarded, a "fuel increase process" is performed to increase the fuel injection amount in order to suppress the increase in the exhaust gas temperature.

Patent Literature 1 discloses a fuel injection control device for an internal combustion engine that includes a port injector and a direct injector. Consider a case where the command value (target value) of the total fuel injection amount exceeds the maximum injection amount that can be injected from the direct injector in a situation where fuel is injected only from the direct injector. In this case, the fuel injection control device sets the fuel injection amount from the direct injector to the maximum injection amount and injects the remaining fuel from the port injector.

JP 2014-129738 A

Consider a case where the method described in Patent Document 1 is applied to the above-described fuel amount increase process. In this case, the increase in fuel injection amount requested in the fuel amount increase process is achieved by increasing the fuel injection amount from the direct injector as much as possible. Then, when the fuel injection amount from the direct injector reaches the maximum injection amount, the remaining fuel is injected from the port injector.

However, increasing the amount of fuel injected from a direct injector typically requires a further increase in fuel pressure. In order to increase the fuel pressure, it is necessary to increase the driving torque of the high-pressure pump that supplies high-pressure fuel to the direct injector. An increase in drive torque of the high-pressure pump causes an increase in drive loss of the high-pressure pump. An increase in drive loss causes a decrease in fuel consumption and engine output.

One object of the present invention is to provide a technique capable of suppressing an increase in the fuel pressure of fuel injection from a direct injector when performing a fuel increase process with retardation correction of ignition timing.

SUMMARY OF THE INVENTION In one aspect of the present invention, a control system for an internal combustion engine is provided.
An internal combustion engine includes a port injector that injects fuel into an intake port and a direct injector that directly injects fuel into a combustion chamber.
A controller controls fuel injection from the port injectors and fuel injection from the direct injectors.
Further, the control device performs a fuel increase process for increasing the total fuel injection amount by the first increase amount along with the retardation correction of the ignition timing.
The fuel amount increase processing includes processing for increasing the fuel injection amount from the port injector by a first increase amount.

A control apparatus for an internal combustion engine according to one aspect of the present invention performs a fuel amount increase process for increasing the total fuel injection amount by a first increase amount along with retardation correction of ignition timing. The fuel amount increase processing includes processing for increasing the fuel injection amount from the port injector by a first increase amount. If the amount of fuel injected from the port injector increases by the first increment, the amount of fuel injected from the direct injector does not increase. Therefore, there is no need to increase the fuel pressure for fuel injection from the direct injector. Since there is no need to increase the fuel pressure, there is no need to increase the drive torque of the high-pressure pump that supplies high-pressure fuel to the direct injector. As a result, an increase in driving loss of the high-pressure pump is suppressed, and a decrease in fuel consumption and engine output is also suppressed.

1 is a schematic diagram showing a configuration example of an internal combustion engine according to a first embodiment of the present invention; FIG. FIG. 4 is a conceptual diagram for explaining fuel amount increase processing according to the first embodiment of the present invention; 4 is a flowchart briefly showing processing related to fuel injection control according to the first embodiment of the present invention; FIG. 7 is a conceptual diagram for explaining fuel amount increase processing according to the second embodiment of the present invention; It is a flowchart which shows step S700 in the 2nd Embodiment of this invention. FIG. 11 is a conceptual diagram for explaining fuel amount increase processing according to a third embodiment of the present invention; It is a flowchart which shows step S700 in the 3rd Embodiment of this invention. FIG. 11 is a conceptual diagram for explaining fuel amount increase processing according to a fourth embodiment of the present invention; It is a flow chart which shows Step S700 in a 4th embodiment of the present invention.

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

1. First Embodiment 1-1. Configuration of Internal Combustion Engine FIG. 1 is a schematic diagram showing a configuration example of an internal combustion engine 1 according to a first embodiment. The internal combustion engine 1 is mounted on a vehicle and includes an engine body 10, a sensor group 80, and a control device 100. The engine body 10 includes a combustion chamber 20, an intake port 30, an exhaust port 40, a port injector 50, a direct injector 60, and a spark plug .

A combustion chamber 20 is a space in which fuel combustion takes place and is surrounded by a cylinder 21 , a cylinder head 22 and a piston 23 .

An intake port 30 and an exhaust port 40 are formed within the cylinder head 22 and communicate with the combustion chamber 20 . An intake valve 31 is provided at an opening of the intake port 30 to the combustion chamber 20 . An exhaust valve 41 is provided at the opening of the exhaust port 40 to the combustion chamber 20 .

Port injector 50 is a fuel injector for injecting fuel into intake port 30 . The port injector 50 is connected to a fuel supply system (not shown) via a fuel pipe 51 . The fuel supply system includes a fuel tank and a pump, and supplies fuel to the port injector 50 through a fuel pipe 51 .

Direct injector 60 is a fuel injector for directly injecting fuel into combustion chamber 20 . The direct injector 60 is connected to a fuel supply device 62 via a fuel pipe 61 . A fuel supply device 62 includes a fuel tank and a high-pressure pump, and supplies high-pressure fuel to the direct injector 60 through a fuel pipe 61 .

The spark plug 70 is installed so as to enable spark ignition within the combustion chamber 20 .

The sensor group 80 detects the operating state (engine state) of the internal combustion engine 1 . For example, the sensor group 80 includes a rotational speed sensor, an airflow meter, a temperature sensor, and the like. A rotational speed sensor detects the engine rotational speed. The airflow meter detects the amount of intake air (fresh air flow rate). The temperature sensor detects the intake air temperature and the temperature of various parts.

A control device 100 controls the operation of the internal combustion engine 1 . Typically, controller 100 is a microcomputer with a processor and memory. The control device 100 is also called an ECU (Electronic Control Unit). Various information is stored in the memory. For example, the memory stores engine state information indicating the engine state detected by the sensor group 80 . The processor executes various processes by executing a control program, which is a computer program. In particular, the processor (control device 100) performs various processes based on the engine state information stored in the memory.

For example, the control device 100 controls ignition timing of the spark plugs 70 . More specifically, control device 100 determines ignition timing based on engine speed, engine load, and the like. The engine load is calculated based on the engine rotation speed, the amount of intake air, and the like.

The control device 100 also controls fuel injection from the port injector 50 (hereinafter referred to as "port injection") and fuel injection from the direct injector 60 (hereinafter referred to as "direct injection").

More specifically, the control device 100 calculates target values (command values) for the fuel injection amount and the fuel pressure for each cycle. The fuel injection amount (target value) from the port injector 50 is hereinafter referred to as "port injection amount QP". The fuel injection amount (target value) from the direct injector 60 is hereinafter referred to as "direct injection amount QD". The total fuel injection amount QT is the sum of the port injection amount QP and the direct injection amount QD.

The control device 100 calculates the total fuel injection amount QT for realizing the target air-fuel ratio based on the engine state such as the engine rotation speed and the amount of intake air. Furthermore, the control device 100 calculates the distribution ratio of the total fuel injection amount QT, that is, the port injection amount QP and the direct injection amount QD, based on the engine rotation speed, the engine load, and the like. Typically, port injection is performed in the low speed, low load range, and direct injection is performed in the high speed, high load range.

The control device 100 also calculates the fuel pressure (target value) based on the engine rotation speed, the engine load, and the like. Typically, the higher the engine load, the higher the fuel pressure, and the lower the engine load, the lower the fuel pressure. The control device 100 obtains a desired fuel pressure by controlling the operation of the fuel supply device. For example, controller 100 obtains high fuel pressure for direct injection by controlling the operation of the high pressure pump of fuel supply system 62 .

Then, the control device 100 performs port injection and direct injection according to the port injection amount QP, the direct injection amount QD, and the fuel pressure. More specifically, the control device 100 determines the fuel injection period required to realize the port injection amount QP based on the port injection amount QP, the fuel pressure, etc. Inject. Further, the control device 100 determines the fuel injection period required to realize the direct injection amount QD based on the direct injection amount QD, the fuel pressure, etc., and performs direct injection from the direct injector 60 during the fuel injection period. conduct.

1-2. Fuel increase processing In some cases, retardation correction is performed to retard the ignition timing. For example, when the occurrence of knocking is detected, retardation correction is performed to suppress knocking. However, retarding the ignition timing causes an increase in the exhaust temperature. A rise in the temperature of the exhaust gas causes deterioration of the function of the catalyst provided in the exhaust passage.

Therefore, the control device 100 according to the present embodiment increases the total fuel injection amount QT in order to suppress the rise in the exhaust gas temperature when retarding the ignition timing. Such processing is hereinafter referred to as "fuel increase processing". The amount of increase in the total fuel injection amount QT requested in the fuel amount increase process is hereinafter referred to as "increase amount ΔQ". That is, the control device 100 executes the fuel amount increasing process for increasing the total fuel injection amount QT by the amount of increase ΔQ (first amount of increase) along with retardation correction of the ignition timing.

First, as a comparative example, consider the case of applying the method described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2014-129738) to the fuel amount increase process. In this case, the increase amount ΔQ requested in the fuel amount increase process is achieved by increasing the direct injection amount QD as much as possible. Then, when the direct injection amount QD reaches the maximum injection amount, the remaining fuel is injected from the port injector 50 .

However, in order to increase the direct injection amount QD, it is typically necessary to further increase the high fuel pressure for direct injection (hereinafter referred to as "direct injection fuel pressure PD"). In order to increase the direct injection fuel pressure PD, it is necessary to increase the drive torque of the high pressure pump that supplies high pressure fuel to the direct injector 60 . An increase in drive torque of the high-pressure pump causes an increase in drive loss of the high-pressure pump. An increase in drive loss causes a decrease in fuel consumption and engine output.

Therefore, the present embodiment proposes a technique capable of suppressing an increase in the direct injection fuel pressure PD in the fuel amount increase process accompanying retardation correction of the ignition timing.

FIG. 2 is a conceptual diagram for explaining the fuel amount increase processing according to this embodiment. The horizontal axis represents the amount of increase ΔQ required in the fuel amount increasing process. The vertical axis represents the direct injection amount QD and the port injection amount QP. The direct injection amount QD and the port injection amount QP when retardation correction (that is, fuel amount increase processing) is not required are hereinafter referred to as "reference direct injection amount QD0" and "reference port injection amount QP0" for convenience. In the high-speed, high-load region, typically only direct injection is performed, so the reference port injection amount QP0 is zero (but not limited to this).

According to the present embodiment, the entire increase amount ΔQ is covered by the increase in the port injection amount QP. That is, the control device 100 increases the port injection amount QP from the reference port injection amount QP0 by the increase amount ΔQ in the fuel amount increase process (QP=QP0+ΔQ). On the other hand, the control device 100 maintains the reference direct injection amount QD0 without changing the direct injection amount QD (QD=QD0).

Since the direct injection amount QD does not increase, there is no need to increase the direct injection fuel pressure PD. Therefore, there is no need to increase the drive torque of the high-pressure pump that supplies high-pressure fuel to the direct injector 60 . As a result, an increase in driving loss of the high-pressure pump is suppressed, and a decrease in fuel consumption and engine output is also suppressed.

1-3. Processing Flow FIG. 3 is a flowchart schematically showing processing related to fuel injection control according to the present embodiment.

In step S100, the sensor group 80 detects the engine state. Control device 100 receives engine status information indicating the detected engine status.

In step S200, control device 100 calculates the fuel injection amount and fuel pressure for fuel injection control based on the engine state. The fuel injection amount includes total fuel injection amount QT, direct injection amount QD, and port injection amount QP. The direct injection amount QD and the port injection amount QP calculated here correspond to the reference direct injection amount QD0 and the reference port injection amount QP0 described above.

In step S300, the control device 100 determines whether or not the ignition timing is to be retarded. For example, when the occurrence of knocking is detected, retardation correction is required to suppress knocking. As another example, it may be determined whether retardation correction is necessary based on the intake air temperature or the water temperature. If retardation correction is not performed (step S300; No), the process proceeds to step S800. On the other hand, if retardation correction is to be performed (step S300; Yes), the process proceeds to step S400.

In step S400, the control device 100 determines whether or not fuel increase processing is necessary based on the engine state and the retard correction amount. For example, the control device 100 estimates the temperature of the catalyst provided in the exhaust passage based on the engine state and the retard correction amount. When the estimated catalyst temperature exceeds the predetermined threshold, the control device 100 determines that the fuel amount increasing process is necessary to suppress the increase in the exhaust temperature (step S400; Yes). In that case, the process proceeds to step S500. Otherwise (step S400; No), the process proceeds to step S800.

In step S500, the control device 100 performs fuel increase processing to correct the fuel injection amount. Step S500 includes steps S600 and S700.

In step S600, control device 100 calculates an increase amount ΔQ of total fuel injection amount QT. Specifically, control device 100 sets increase amount ΔQ based on the determination result in step S400 described above. For example, the increase amount ΔQ is set to increase as the difference between the estimated catalyst temperature and the predetermined threshold increases.

In step S700, control device 100 corrects the fuel injection amount. In this embodiment, step S700 includes step S710.

In step S710, the control device 100 increases the port injection amount QP from the reference port injection amount QP0 by an increase amount ΔQ (QP=QP0+ΔQ). On the other hand, the control device 100 maintains the reference direct injection amount QD0 without changing the direct injection amount QD (QD=QD0). The process then proceeds to step S800.

In step S800, the control device 100 performs fuel injection control. That is, the control device 100 performs port injection and direct injection according to the port injection amount QP, the direct injection amount QD, and the fuel pressure.

1-4. Effect As described above, according to the present embodiment, control device 100 performs fuel increase processing for increasing total fuel injection amount QT by increase amount ΔQ as ignition timing is retarded. In the fuel amount increase process, the control device 100 increases the port injection amount QP by the increase amount ΔQ. That is, the entire increase amount ΔQ is covered by the increase in the port injection amount QP. Therefore, the direct injection amount QD does not increase. Since the direct injection amount QD does not increase, there is no need to increase the direct injection fuel pressure PD. Therefore, there is no need to increase the driving torque of the high-pressure pump that supplies high-pressure fuel to the direct injector 60 . As a result, an increase in drive loss of the high-pressure pump is suppressed, and a decrease in fuel consumption and engine output is also suppressed.

In particular, in a high-speed, high-load region, direct injection is mainly performed, and the direct injection fuel pressure PD is also set high. It is preferable that the direct injection fuel pressure PD does not need to be further increased even if retardation correction of the ignition timing is required in such a high-speed, high-load region.

The present embodiment is also suitable when high fuel pressure is required for direct injection fuel atomization, such as during catalyst warm-up operation.

2. 2nd Embodiment FIG. 4 : is a conceptual diagram for demonstrating the fuel amount increase process which concerns on 2nd Embodiment. The format of FIG. 4 is the same as that of FIG. 2 already described. Explanations overlapping with those of the first embodiment will be omitted as appropriate.

The minimum port injection amount QPmin is the minimum value of the port injection amount QP (target value) that can be accurately followed. The minimum port injection period TPmin is the minimum value of the fuel injection period realizable in the port injector 50 . The minimum port injection quantity QPmin is determined from the minimum port injection period TPmin.

FIG. 4 specifically considers the situation in which the reference port injection quantity QP0 is zero (QP0=0). To accurately follow the port injection amount QP (target value) even if the port injection amount QP increases by the increase amount ΔQ when the increase amount ΔQ required in the fuel amount increase process is less than the minimum port injection amount QPmin. can't. Therefore, in that case, instead of the port injection amount QP, the direct injection amount QD is increased by the increase amount ΔQ.

FIG. 5 is a flow chart showing step S700 (correction of fuel injection amount) in the second embodiment. The steps other than step S700 are the same as those of the first embodiment. In this embodiment, step S700 includes steps S720-S722.

In step S720, control device 100 determines whether or not the sum of reference port injection amount QP0 and increase amount ΔQ is less than minimum port injection amount QPmin. If the sum of the reference port injection amount QP0 and the increase amount ΔQ is less than the minimum port injection amount QPmin (step S720; Yes), the process proceeds to step S721. Otherwise (step S720; No), the process proceeds to step S722.

In step S721, the control device 100 increases the direct injection amount QD from the reference direct injection amount QD0 by an increase amount ΔQ (QD=QD0+ΔQ). QD0+QPmin is set to be equal to or less than the maximum fuel injection amount that can be injected from the direct injector 60.

Step S722 is the same as step S710 in the first embodiment. That is, the control device 100 increases the port injection amount QP from the reference port injection amount QP0 by an increase amount ΔQ (QP=QP0+ΔQ).

According to this embodiment, basically the same effects as those of the first embodiment can be obtained. Moreover, even in a special situation where the port injection quantity QP is equal to or less than the minimum port injection quantity QPmin, the desired increase ΔQ can be achieved. That is, the fuel amount increase process can be executed with high accuracy.

3. Third Embodiment FIG. 6 is a conceptual diagram for explaining fuel amount increase processing according to a third embodiment. The format of FIG. 6 is the same as that of FIG. 2 already described. Descriptions overlapping those of the first and second embodiments will be omitted as appropriate.

FIG. 6 specifically considers the situation where the reference port injection quantity QP0 is zero (QP0=0). To accurately follow the port injection amount QP (target value) even if the port injection amount QP increases by the increase amount ΔQ when the increase amount ΔQ required in the fuel amount increase process is equal to or less than the minimum port injection amount QPmin. can't. Therefore, in that case, the port injection amount QP is set to the minimum port injection amount QPmin (QP=QPmin). At the same time, the direct injection amount QD is decreased so that the total fuel injection amount QT does not change.

FIG. 7 is a flow chart showing step S700 (correction of fuel injection amount) in the third embodiment. The steps other than step S700 are the same as those of the first embodiment. In this embodiment, step S700 includes steps S730-S732.

At step S730, the control device 100 determines whether or not the sum of the reference port injection amount QP0 and the increase amount ΔQ is less than the minimum port injection amount QPmin. If the sum of the reference port injection amount QP0 and the increase amount ΔQ is less than the minimum port injection amount QPmin (step S730; Yes), the process proceeds to step S731. Otherwise (step S730; No), the process proceeds to step S732.

In step S731, the control device 100 sets the port injection amount QP to the minimum port injection amount QPmin (QP=QPmin). Further, the control device 100 sets the direct injection amount QD to "QD0-QPmin+ΔQ". Since the increase amount ΔQ is equal to or less than the minimum port injection amount QPmin, the direct injection amount QD becomes equal to or less than the reference direct injection amount QD0.

Step S732 is the same as step S710 in the first embodiment. That is, the control device 100 increases the port injection amount QP from the reference port injection amount QP0 by an increase amount ΔQ (QP=QP0+ΔQ).

According to this embodiment, the same effects as those of the first embodiment can be obtained. In step S731, the direct injection amount QD is decreased without being increased. Therefore, the direct injection fuel pressure PD does not increase. Further, as in the case of the second embodiment, it is possible to realize the desired amount of increase ΔQ even in a special situation, that is, it is possible to accurately execute the fuel amount increase process.

4. Fourth Embodiment FIG. 8 is a conceptual diagram for explaining fuel amount increase processing according to a fourth embodiment. Explanations overlapping with those of the first embodiment will be omitted as appropriate.

In addition to the port injection amount QP and the direct injection amount QD, FIG. 8 also shows the direct injection period TD and the direct injection fuel pressure PD. A direct injection period TD is a period of fuel injection from the direct injector 60 . The maximum direct injection period TDmax is the maximum value of the fuel injection period that can be realized in direct injector 60 .

When the direct injection period TD is shorter than the maximum direct injection period TDmax, the direct injection amount QD can be increased without increasing the direct injection fuel pressure PD by extending the direct injection period TD. In the example shown in FIG. 8, by extending the direct injection period TD to the maximum direct injection period TDmax, the direct injection amount QD can be increased by the allowable increase amount ΔQa without increasing the direct injection fuel pressure PD. Taking this into account, the allowable increase amount ΔQa of the increase amount ΔQ is covered by the increase in the direct injection amount QD. The remaining increase (ΔQ-ΔQa) is covered by the increase in the port injection amount QP.

FIG. 9 is a flowchart showing step S700 (correction of fuel injection amount) in the fourth embodiment. The steps other than step S700 are the same as those of the first embodiment. In this embodiment, step S700 includes steps S740-S744.

In step S740, the control device 100 determines whether or not the direct injection period TD can be extended, that is, whether or not the direct injection period TD is shorter than the maximum direct injection period TDmax. If the direct injection period TD cannot be extended any longer (step S740; No), the process proceeds to step S741. On the other hand, if the direct injection period TD can be extended (step S740; Yes), the process proceeds to step S742.

Step S741 is the same as step S710 in the first embodiment. That is, the control device 100 increases the port injection amount QP from the reference port injection amount QP0 by an increase amount ΔQ (QP=QP0+ΔQ).

In step S742, control device 100 determines whether or not increase amount ΔQ can be achieved only by extending the direct injection period TD. In other words, the control device 100 determines whether or not the amount of increase ΔQ is equal to or less than the allowable amount of increase ΔQa described above. If the increase amount ΔQ is equal to or less than the allowable increase amount ΔQa (step S742; Yes), the process proceeds to step S743. On the other hand, if the increase amount ΔQ exceeds the allowable increase amount ΔQa (step S742; No), the process proceeds to step S744.

In step S743, the control device 100 increases the direct injection amount QD from the reference direct injection amount QD0 by an increase amount ΔQ by extending the direct injection period TD (QD=QD0+ΔQ).

In step S744, control device 100 extends the direct injection period TD to the maximum direct injection period TDmax (TD=TDmax). As a result, the direct injection amount QD increases by the allowable increase amount ΔQa (QD=QD0+ΔQa). Further, the control device 100 increases the port injection amount QP from the reference port injection amount QP0 by the remaining increase amount (ΔQ-ΔQa) (QP=QP0+(ΔQ-ΔQa)).

Also according to the present embodiment, it is possible to execute the fuel amount increasing process without increasing the direct injection fuel pressure PD. Therefore, the same effects as in the first embodiment can be obtained.

1 internal combustion engine 10 engine body 20 combustion chamber 30 intake port 40 exhaust port 50 port injector 60 direct injector 62 fuel supply device 70 spark plug 80 sensor group 100 control device QD direct injection amount QP port injection amount ΔQ increase amount

Claims (2)

A control device for an internal combustion engine,
The internal combustion engine is
a port injector that injects fuel into the intake port;
Equipped with a direct injector that directly injects fuel into the combustion chamber,
The control device controls the fuel injection from the port injector and the fuel injection from the direct injector, and increases the total fuel injection amount by a first increment in accordance with retardation correction of the ignition timing. configured to process
a reference port injection amount is a fuel injection amount from the port injector when the fuel amount increasing process is not performed;
The minimum port injection amount is the minimum value of the fuel injection amount determined from the minimum fuel injection period that can be realized in the port injector,
The fuel amount increasing process includes:
a process of increasing the fuel injection amount from the direct injector by the first increase amount when the sum of the reference port injection amount and the first increase amount is less than the minimum port injection amount;
and a process of increasing the fuel injection amount from the port injector by the first increase amount when the sum of the reference port injection amount and the first increase amount is equal to or greater than the minimum port injection amount. A control device for an internal combustion engine,
The internal combustion engine is
a port injector that injects fuel into the intake port;
Equipped with a direct injector that directly injects fuel into the combustion chamber,
The control device controls the fuel injection from the port injector and the fuel injection from the direct injector, and increases the total fuel injection amount by a first increment in accordance with retardation correction of the ignition timing. configured to process
a direct injection period is a period of fuel injection from the direct injector;
The maximum direct injection period is the maximum value of the fuel injection period that can be realized in the direct injector,
The allowable increase amount is a fuel injection amount that can be increased by extending the direct injection period to the maximum direct injection period without increasing the fuel injection pressure from the direct injector,
The fuel amount increasing process includes:
if the direct injection period cannot be extended to the maximum direct injection period, a process of increasing the fuel injection amount from the port injector by the first increase amount;
a process of increasing the fuel injection amount from the direct injector by the first increase amount by extending the direct injection period when the first increase amount is equal to or less than the allowable increase amount;
When the first increase amount exceeds the allowable increase amount, the direct injection period is extended to the maximum direct injection period, and fuel is injected from the port injector by the difference between the first increase amount and the allowable increase amount. A control device comprising: a process for increasing the volume;

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