JP2006220062A - Control device for hydrogenated internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an increase in the amount of NOx generated due to a shortage of air during a lean burn operation due to the addition of hydrogen.
SOLUTION: The intake air amount is controlled by an air amount control means 36 so that the target excess air ratio at the time of lean burn operation is obtained, and the air amount necessary for realizing the target excess air ratio is actually determined by a judging means 70. Determine the shortage of air that can be supplied. When it is determined that the supplyable air amount is insufficient with respect to the required air amount, the EGR control unit 92 (or 44) increases the EGR amount.
[Selection] Figure 1

Description

  The present invention relates to a control device for a hydrogenated internal combustion engine capable of performing lean burn operation by adding hydrogen to liquid fuel, and more particularly to a technique for preventing an increase in the amount of NOx generated due to a decrease in excess air ratio.

Conventionally, as disclosed in, for example, Patent Document 1, a technique of using hydrogen as a fuel for an internal combustion engine together with gasoline is known. By adding hydrogen to gasoline, the lean burn range of the internal combustion engine can be expanded, and remarkable effects such as reduction of NOx generation amount and improvement of thermal efficiency can be obtained.
JP 2004-116398 A

  However, the super lean burn operation (hydrogen addition lean burn operation) by adding hydrogen is difficult to realize in a high load range. This is because there is a limit to the amount of air that can be sucked by opening the throttle valve, so that the amount of intake air is insufficient in a high load range, and an output corresponding to the load cannot be obtained. Insufficient intake air amount increases the combustion temperature in the cylinder and increases the amount of NOx produced.

  As a method of compensating for the shortage of air amount in a high load range, it is conceivable to supercharge intake air by a turbocharger. However, the exhaust energy for driving the turbocharger is insufficient in the low rotation high load region where the exhaust temperature is low and the amount of exhaust gas is small. For this reason, in this operating region, the turbocharger supercharging pressure does not rise sufficiently, and the target excess air ratio may not be reached due to a lack of air volume. That is, even when a turbocharger is used, there remains an operation region in which the target excess air ratio cannot be achieved, and the amount of NOx generated cannot be sufficiently reduced in the operation region.

  As a means for compensating for the shortage of the air amount in the low rotation and high load range, it is conceivable to use a motor-assisted turbocharger that assists the rotation of the compressor by a motor. However, when a motor-assist type turbocharger is employed, not only the cost is significantly increased compared to a normal turbocharger, but also control is complicated. Therefore, it is desired to suppress an increase in the amount of NOx generated due to a shortage of air by a technique applicable to an internal combustion engine equipped with a normal turbocharger.

  The present invention has been made to solve the above-described problems, and controls a hydrogen-added internal combustion engine that can suppress an increase in the amount of NOx generated due to a shortage of air during lean burn operation due to the addition of hydrogen. An object is to provide an apparatus.

In order to achieve the above object, according to a first aspect of the present invention, there is provided a control device for a hydrogenated internal combustion engine capable of performing a lean burn operation by adding hydrogen to a liquid fuel.
An air amount control means for controlling the amount of air supplied to the internal combustion engine so as to achieve a target excess air ratio during lean burn operation;
A determination means for determining a shortage of the air amount that can actually be supplied with respect to the air amount necessary for realizing the target excess air ratio;
EGR control means for increasing the EGR amount of the internal combustion engine when it is determined that the supplyable air amount is insufficient with respect to the required air amount;
It is characterized by having.

  A second invention is characterized in that, in the first invention, the determination means determines the shortage of the supplyable air amount relative to the required air amount based on the rotational speed of the internal combustion engine and the required load.

  According to a third invention, in the first or second invention, the internal combustion engine is a supercharged internal combustion engine comprising a supercharger driven by exhaust energy or output torque of the internal combustion engine. It is said.

  According to the first aspect, since the EGR amount is increased when the supplyable air amount is insufficient with respect to the required air amount, the decrease in the heat capacity due to the shortage of the air amount is compensated by the increase in specific heat due to the introduction of EGR gas. be able to. That is, it is possible to suppress an increase in the combustion temperature and the amount of NOx generated due to a shortage of air.

  Further, according to the second invention, by determining whether the air amount is insufficient based on the rotational speed and the required load, the EGR amount can be increased without delaying the actual air amount, and the amount of NOx generated Can be reliably suppressed.

  Further, according to the third aspect of the invention, it is possible to suppress an increase in the NOx generation amount in a low rotation high load region where the supercharging pressure is insufficient.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4.
FIG. 1 is a diagram showing a schematic configuration of a hydrogenated internal combustion engine to which a control device according to Embodiment 1 of the present invention is applied. The internal combustion engine 2 includes a cylinder block 6 in which a piston 8 is disposed, and a cylinder head 4 assembled to the cylinder block 6. A space from the upper surface of the piston 8 to the cylinder head 4 forms a combustion chamber 10, and an intake port 18 and an exhaust port 20 are formed in the cylinder head 4 so as to communicate with the combustion chamber 10. An intake valve 12 for controlling the communication state between the intake port 18 and the combustion chamber 10 is provided at a connection portion between the intake port 18 and the combustion chamber 10, and an exhaust gas is provided at a connection portion between the exhaust port 20 and the combustion chamber 10. An exhaust valve 14 for controlling the communication state between the port 20 and the combustion chamber 10 is provided. The intake valve 12 is provided with a variable valve timing mechanism (hereinafter referred to as VVT) 92 that variably controls the valve timing. By controlling the valve timing of the intake valve 12 and changing the valve overlap period between the intake valve 12 and the exhaust valve 14, the amount of exhaust gas remaining in the combustion chamber 10 (internal EGR amount) can be adjusted. it can. A spark plug 16 is attached to the cylinder head 4 so as to protrude from the top of the combustion chamber 10 into the combustion chamber 10.

  An intake passage 30 for introducing fresh air into the combustion chamber 10 is connected to the intake port 18 of the cylinder head 4. An air cleaner 32 is provided at the upstream end of the intake passage 30, and fresh air is taken into the intake passage 30 via the air cleaner 32. An air flow meter 76 for measuring the amount of intake air is attached downstream of the air cleaner 32 in the intake passage 30. A downstream portion of the intake passage 30 is branched for each cylinder (for each intake port 18), and a surge tank 34 is provided at the branched portion. An electronically controlled throttle valve 36 is disposed upstream of the surge tank 34 in the intake passage 30.

  Two injectors 50 and 60 for injecting fuel are provided for each cylinder downstream of the surge tank 34 in the intake passage 30. One injector 60 is a gasoline injector and is connected to a gasoline tank 62 through a gasoline passage 64. A gasoline pump 66 is disposed in the gasoline passage 64, and the gasoline in the gasoline tank 62 is compressed by the gasoline pump 66 and supplied to the gasoline injector 60. A gasoline flow meter 86 for measuring the flow rate of gasoline supplied to the gasoline injector 60 is attached downstream of the gasoline pump 66 in the gasoline passage 64.

  The other injector 50 is a hydrogen injector and is connected to a hydrogen tank 52 through a hydrogen passage 54. A hydrogen pump 56 is disposed in the hydrogen passage 54, and hydrogen in the hydrogen tank 52 is compressed by the hydrogen pump 56 and supplied to the hydrogen injector 50. A hydrogen flow meter 82 for measuring the flow rate of hydrogen supplied to the hydrogen injector 50 and a hydrogen pressure sensor 84 for measuring the hydrogen pressure are attached downstream of the hydrogen pump 56 in the hydrogen passage 54.

An exhaust passage 20 for exhausting the exhaust gas in the combustion chamber 10 to the atmosphere is connected to the exhaust port 20 of the cylinder head 4. A catalyst 42 is disposed in the exhaust passage 40, and the exhaust gas is purified when passing through the catalyst 42 and then discharged into the atmosphere. An O ₂ sensor 74 for measuring the oxygen concentration in the exhaust gas is attached upstream of the catalyst 42 in the exhaust passage 40. Further, an EGR flow path 46 for diverting the exhaust gas from the exhaust passage 40 is connected to the exhaust passage 40. The other end of the EGR flow path 46 is connected upstream of the surge tank 34 in the intake passage 30. An EGR valve 44 that controls a communication state between the EGR flow path 46 and the intake passage 30 is provided at a connection portion between the EGR flow path 46 and the intake passage 30. A part of the exhaust gas is supplied into the intake passage 30 through the EGR flow path 46 and recirculated to the combustion chamber 10. The amount of exhaust gas recirculated (external EGR amount) is adjusted by the opening degree of the EGR valve 44.

  The internal combustion engine 2 is configured as a supercharged internal combustion engine to which a turbocharger 90 as a supercharger is attached. The turbocharger 90 includes a compressor and a turbine that rotate integrally, and the compressor is disposed in the intake passage 30 and the turbine is disposed in the exhaust passage 40. When the turbine is driven by the energy of the exhaust gas, the compressor in the intake passage 30 rotates, and the intake air is supercharged.

Further, the internal combustion engine 2 is provided with an ECU (Electronic Control Unit) 70 as its control device. Various devices such as the gasoline injector 60, the hydrogen injector 50, the throttle valve 36, the EGR valve 44, the VVT 92, and the spark plug 16 are connected to the output side of the ECU 70. On the input side of the ECU 70, in addition to the air flow meter 76, the gasoline flow meter 86, the hydrogen flow meter 82, the hydrogen pressure sensor 84, the O ₂ sensor 74, various sensors such as an accelerator opening sensor 78 and a rotational speed sensor 80 are provided. Is connected. The accelerator opening sensor 78 is a sensor that outputs a signal corresponding to the opening of the accelerator pedal, and the rotational speed sensor 80 is a sensor that outputs a signal corresponding to the rotational speed of the crank angle (engine rotational speed). The ECU 70 drives each device according to a predetermined control program based on the output of each sensor.

  As one of the controls of the internal combustion engine 2 performed by the ECU 70, there is fuel supply control for controlling the gasoline supply amount from the gasoline injector 60 and the hydrogen supply amount from the hydrogen injector 50. In the fuel supply control by the ECU 70, an operation mode corresponding to the load condition of the internal combustion engine 2 is selected, and the gasoline supply amount and the hydrogen supply amount are controlled according to the selected operation mode. In the present embodiment, as the operation mode of the internal combustion engine 2, at least hydrogen addition lean burn operation in which operation is performed at an air-fuel ratio that is significantly leaner than stoichiometric by adding hydrogen to gasoline can be selected.

  In the hydrogen addition lean burn operation, the load factor (target load factor) and the hydrogen addition rate of the internal combustion engine 2 corresponding to the accelerator opening and the engine speed are calculated using a map prepared in advance. The load factor is a numerical value representing the load state of the internal combustion engine 2, and is 0% when there is no load and 100% when there is a full load. The ECU 70 calculates the gasoline injection amount and the hydrogen injection amount from the load factor and the hydrogen addition ratio, respectively, and drives the gasoline injector 60 and the hydrogen injector 50 based on each injection amount.

  In the hydrogen addition lean burn operation, a target excess air ratio is set, and a target intake air amount is calculated based on the target excess air ratio and the injection amount of each fuel. The target excess air ratio is set to a value (for example, 2 or more) that is extremely larger than 1 (stoichiometric) in order to realize super lean burn operation. The ECU 70 controls the opening degree of the throttle valve 36 so that the intake air amount measured by the air flow meter 76 becomes the target intake air amount.

By the way, the internal combustion engine 2 with the turbocharger 90 as in this embodiment has a sufficient amount of air by supercharging the turbocharger 90 even in a high-rotation and high-load region where the amount of air is insufficient with a naturally aspirated internal combustion engine. Obtainable. However, the supercharging pressure of the turbocharger 90 does not rise sufficiently due to a lack of exhaust energy in a low rotation high load region where the exhaust temperature is low and the amount of exhaust gas is small. For this reason, even if the opening degree of the throttle valve 36 is set to fully open, it is not possible to obtain an air amount sufficient to achieve the target excess air ratio, and the actual excess air ratio is smaller than the target excess air ratio. turn into. Here, FIG. 4 is a graph showing the relationship between the excess air ratio λ, the thermal efficiency, and the NOx generation amount. As shown in the figure, the thermal efficiency at the time of the excess air ratio lambda is the target excess air ratio lambda _O (e.g. 2) becomes approximately maximum, NOx generation amount can be suppressed to a very low value. However, as shown by points A ′ and A in the figure, if the excess air ratio λ is lower than the target excess air ratio λ _O , the thermal efficiency is slightly reduced and the NOx generation amount is greatly increased. .

  In the present embodiment, the following control is performed by the ECU 70 in order to prevent an increase in the NOx generation amount in the low rotation high load region. The flowchart of FIG. 2 shows a routine executed by the ECU 70 when the hydrogen addition lean burn operation is executed. This routine is a routine for controlling the amount of EGR gas during the hydrogen addition lean burn operation.

  In the first step 100 of this routine, the current engine speed is obtained from the signal from the speed sensor 80, and the current accelerator opening is obtained from the signal from the accelerator opening sensor 78. In the next step 102, the load factor of the internal combustion engine 2 is calculated from the engine speed and the accelerator opening.

  In step 104, it is determined from the engine speed acquired in step 100 and the load factor calculated in step 102 whether or not the current operating state is in a predetermined low rotation and high load range. The map shown in FIG. 3 is a map for determining the operation mode of the internal combustion engine 2 from the engine speed and the load factor. As shown in this map, the EGR increase region is set on the low rotation side and the high load side in the region where the hydrogen addition lean burn operation is executed. In step 104, it is determined whether or not the current operating state of the internal combustion engine 2 is within this EGR increase region.

  As a result of the determination in step 104, if it is determined that the operating state of the internal combustion engine 2 is outside the EGR increase region, that is, outside the low rotation high load region, the process of step 106 is executed. In step 106, means for controlling the EGR amount, that is, the respective operation amounts of the VVT 92 and the EGR valve 44 are adjusted so that the EGR amount becomes a normal amount during the hydrogen addition lean burn operation. The EGR amount includes an internal EGR amount determined by the valve timing of the intake valve 12 and an external EGR amount determined by the opening degree of the EGR valve 44. At normal times, the valve overlap between the intake valve 12 and the exhaust valve 14 is set small so that the EGR amount is minimized, and the EGR valve 44 is closed.

  As a result of the determination in step 104, when it is determined that the operating state of the internal combustion engine 2 is in the EGR increase region, that is, in the low rotation and high load region, the processing in step 108 is executed. In step 108, the EGR amount of the internal combustion engine 2 is increased. The EGR gas to be increased may be either an internal EGR gas or an external EGR gas. Alternatively, both the internal EGR gas and the external EGR gas may be increased. When increasing the internal EGR gas, the valve timing of the intake valve 12 is changed by the VVT 92 so that the valve overlap between the intake valve 12 and the exhaust valve 14 is expanded. When increasing the amount of external EGR gas, the opening degree of the EGR valve 44 is made larger than normal.

  According to the above routine, in the low rotation and high load region where the air amount is insufficient, the decrease in the heat capacity of the in-cylinder gas due to the insufficient air amount can be compensated by the increase in the EGR gas having a high specific heat, and the combustion in the cylinder An increase in temperature can be suppressed. In particular, in the hydrogenated internal combustion engine as in the present embodiment, the EGR gas contains a large amount of water vapor due to the combustion of hydrogen. However, since the specific heat of the water vapor is particularly large, the effect of suppressing the combustion temperature by increasing the EGR amount Is extremely expensive. In lean burn operation using only gasoline as fuel, misfiring may occur if the combustion temperature decreases, but in hydrogen-added lean burn operation, misfire is prevented by the addition of hydrogen with excellent combustibility. The As a result, as the EGR amount is increased, the thermal efficiency is slightly reduced as compared with the case of the normal EGR amount (A ′ point and A point), as indicated by points B ′ and B in FIG. However, an increase in the amount of NOx generated can be effectively suppressed. Note that the EGR amount to be increased may be determined in consideration of the NOx production reduction effect due to the increase in the EGR amount and the reduction in thermal efficiency that is a side effect thereof.

  In the above embodiment, the “air amount control means” of the first invention is realized by the ECU 70 controlling the throttle valve 36 so as to achieve the target excess air ratio during the hydrogen addition lean burn operation. Further, the ECU 70 executes the processing of steps 100 to 104 of the above routine, thereby realizing the “determination means” of the first invention. Further, the ECU 70 controls the VVT 92 or the EGR valve 44 according to the processing of step 108 of the above routine, thereby realizing the “EGR control means” of the first invention.

  While the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the following modifications may be made.

  In the configuration of FIG. 1, the hydrogen injector 50 is arranged in the intake passage 30, but the arrangement is not limited to this. That is, the hydrogen injector 50 may be incorporated in the cylinder head 4 so that hydrogen can be injected directly into the combustion chamber 10. The same applies to the gasoline injector 60, and the gasoline injector 60 may be incorporated in the cylinder head 4 so that gasoline can be injected directly into the combustion chamber 10.

  In the configuration of FIG. 1, the VVT 92 is provided in the intake valve 12, but the exhaust valve 14 may be provided with VVT. By variably controlling the valve timing of the exhaust valve 14, the valve overlap period can be changed to adjust the internal EGR amount. In the present invention, both the EGR device and the VVT are not necessarily required, and any one of them may be provided. That is, it is only necessary to be able to adjust either the external EGR amount or the internal EGR amount.

  In the above-described embodiment, the EGR amount is increased in the low rotation high load region because it is assumed that the air amount is insufficient in the low rotation high load region due to the rotation characteristics of the turbocharger. However, depending on the rotation characteristics of the turbocharger, the amount of air may be insufficient even in a high rotation and high load range. In such a case, it is desirable to increase the EGR amount not only in the low rotation high load region but also in the high rotation high load region.

  Further, in the above embodiment, the lack of air amount is determined from the engine speed and the load factor, but it can also be determined by other methods. For example, the shortage of air amount may be determined based on the difference between the intake air amount measured by the air flow meter 76 and the intake air amount necessary to achieve the target excess air ratio. Alternatively, the supercharging pressure of the turbocharger 90 may be measured and the lack of air amount determined from the supercharging pressure.

  In the above-described embodiment, the present invention is applied to an internal combustion engine with a turbocharger. However, other than a supercharger that is driven by exhaust energy or output torque of the internal combustion engine, such as a mechanical supercharger. The present invention can also be applied to an internal combustion engine with a supercharger. The present invention can also be applied to a naturally aspirated internal combustion engine that does not include a supercharger. In any type of internal combustion engine, by increasing the EGR amount in the operating region where the air amount is insufficient, it is possible to suppress an increase in the NOx generation amount due to the insufficient air amount.

1 is a diagram showing a schematic configuration of a hydrogenated internal combustion engine to which a control device as an embodiment of the present invention is applied. It is a flowchart shown about the EGR amount control routine performed in embodiment of this invention. It is a map used for selection of an operation mode in an embodiment of the invention. It is a figure for demonstrating the effect by the routine shown in FIG. 2 using the relationship between an excess air ratio, thermal efficiency, and NOx production amount.

Explanation of symbols

2 Internal combustion engine 10 Combustion chamber 12 Intake valve 14 Exhaust valve 30 Intake passage 36 Throttle valve 40 Exhaust passage 42 Catalyst 44 EGR valve 46 EGR passage 50 Hydrogen injector 60 Gasoline injector 70 ECU (Electronic Control Unit)
76 Airflow meter 78 Accelerator opening sensor 80 Rotation speed sensor 90 Turbocharger 92 Variable valve timing mechanism (VVT)

Claims (3)

In a control device for a hydrogenated internal combustion engine capable of lean burn operation by adding hydrogen to liquid fuel,
An air amount control means for controlling the amount of air supplied to the internal combustion engine so as to achieve a target excess air ratio during lean burn operation;
A determination means for determining a shortage of the air amount that can actually be supplied with respect to the air amount necessary for realizing the target excess air ratio;
EGR control means for increasing the EGR amount of the internal combustion engine when it is determined that the supplyable air amount is insufficient with respect to the required air amount;
A control apparatus for a hydrogenated internal combustion engine, comprising:   2. The control device for a hydrogenated internal combustion engine according to claim 1, wherein the determination unit determines whether the supplyable air amount is insufficient with respect to the required air amount based on a rotational speed of the internal combustion engine and a required load.   3. The control of a hydrogenated internal combustion engine according to claim 1, wherein the internal combustion engine is a supercharged internal combustion engine including a supercharger that is driven by exhaust energy or output torque of the internal combustion engine. apparatus.

Images