JPWO2018207307A1 - Engine control method and engine system - Google Patents

Abstract

In the gas mode of the marine dual fuel engine (1), a mixture of fuel gas and air is burned in a combustion chamber. When the output of the output shaft (2) of the engine (1) increases, the timing at which the intake valve (8) of the engine closes is advanced, and the fuel gas supply valve (15) responds to the change in the advance. A control unit (22) for advancing the opening timing of the intake valve, and a variable intake valve timing mechanism (A) for advancing the closing timing of the intake valve (8) according to the closing timing of the intake valve (8) set by the control unit. 30) and a fuel gas supply valve timing mechanism (45) for advancing the valve opening timing of the fuel gas supply valve (15) in response to a change in the advance of the intake valve (8) set by the control unit. Equipped. As the output of the output shaft of the engine (1) increases, the variable intake valve timing mechanism (30) performs control to further reduce the compression ratio of the gas-air mixture in the engine.

Description

  The present invention relates to an engine control method and an engine system using a gas fuel such as natural gas, and more particularly, to an engine control method and an engine using a gas fuel provided with a variable intake valve timing (VIVT) mechanism. It is about the system.

Examples of specific configurations of the variable valve timing mechanism are described in Patent Documents 1 to 3 below.
As shown in FIGS. 20 and 21, the drive mechanism of the variable valve timing mechanism 100 described in Patent Document 1 includes a link mechanism 101 and an actuator 102. In the link mechanism 101, the exhaust valve swing arm 103 connected to the push rod of the exhaust valve of the engine is supported on the link shaft 104, and the intake valve swing arm 105 connected to the push rod of the intake valve is eccentric from the link shaft 104. The eccentric shaft is supported by a tappet shaft 106.
The exhaust valve swing arm 103 and the intake valve swing arm 105 can move forward and backward by eccentric cams 108a of a cam shaft 108, respectively. The link shaft 104 is connected to a piston rod 109 provided on the actuator 102.
Assuming that the position shown in FIG. 21 is before the pop-out operation of the piston rod 109, all the connected swing arms 105 and 103 rotate to one by the pop-out operation of the piston rod 109 by the actuator 102. Therefore, the rotation angles of all the swing arms 105 and 103 can be controlled by the actuator 102 via the link mechanism 101.

Further, as another example, a variable valve timing mechanism described in Patent Documents 2 and 3 is described in FIGS. These parts will be described using the same reference numerals for the same parts as those of the variable valve timing mechanism 100 shown in FIGS.
In the variable valve timing mechanism shown in FIG. 22, the rotation range of the link shaft 104 is restricted within the range of the teeth of the sector gear 120 connected to the actuator 102, and the eccentric disk 123 (eccentric to the tappet shaft) is eccentrically fixed to the link shaft 104. (Equivalent) is held at the base of the exhaust valve swing arm 103 and the intake valve swing arm 105.
Therefore, the position of the eccentric cam 108a of the cam shaft 108 abutting against the exhaust valve swing arm 103 or the intake valve swing arm 105 and pushing up changes with respect to the deviation of the rotational angle position of each eccentric disk 123 from the rotational position of the link shaft 104. I do.

In the example shown in FIG. 23, the exhaust valve swing arm 103 and the intake valve swing arm 105 connected to the rocker arm 127 via the push rod 128 are attached to the tappet shaft 106 of the crank-shaped link shaft 104 (the fulcrum position of the swing arm). It is connected. When the phase of the crank-shaped link shaft 104 is changed (rotated) by the actuator 102, the fulcrum positions of the intake valve swing arm 105 and the exhaust valve swing arm 103 are changed, and as a result, the contact position to the cam shaft 108 is changed. .
Thus, the timing at which the eccentric cam 108a of the camshaft 108 presses the exhaust valve swing arm 103 or the intake valve swing arm 105 with the camshaft 108 to advance and retreat is made variable.

Patent Document 4 discloses a fuel injection device that is provided in an intake port and that injects fuel toward each of a first intake valve and a second intake valve provided in a first intake valve and a second intake valve provided in each combustion chamber. There is disclosed a control device applied to an internal combustion engine including: a variable valve mechanism capable of changing a valve timing of a first intake valve and a valve timing of a second intake valve to different valve timings. . This internal combustion engine controls a variable valve operating mechanism to set the opening timing of the first intake valve before the top dead center, and to set the opening timing of the second intake valve after the top dead center. And a valve timing setting means for setting the closing timing of the second intake valve and the closing timing of the second intake valve after the bottom dead center. Injection timing setting means for setting the injection start timing to a timing later than the top dead center as the amount of gas blown back to the intake port via the first intake valve increases.

Patent Document 4 is for realizing stratified combustion in the internal EGR of a vehicle engine, and the fuel injected toward the first intake valve by the fuel injection device relates to a liquid fuel that can instantaneously terminate the injection. It is.

Patent Document 5 discloses that a negative change rate of a target EGR rate is compared with a predetermined threshold value, and when the negative change rate is equal to or more than the threshold value, the closing operation of the EGR valve is performed during the EGR valve opening period. When the response delay of the EGR gas is detected, the closing timing of the intake valve is corrected so as to increase the actual compression ratio. It is disclosed that the fuel injection timing is corrected so as to approach.

Patent Literature 5 is for dealing with a response delay of EGR gas in an external EGR of a diesel engine. The fuel injected into each cylinder via the injector is a liquid fuel that can be instantaneously charged into the combustion chamber.

Patent Literature 6 relates to a homogeneous charge compression ignition engine of a self-ignition combustion type, in which a set output of the engine is detected, and as the set output increases, an equivalence ratio of the premixed gas (set by a fuel supply amount) is determined. It is said that the actual compression ratio is decreased while increasing. The set output of the engine, in other words, the required output of the engine, is set manually or by detecting the load applied to the crankshaft of the engine. Since the "load applied to the crankshaft" is "set output, in other words, the required output of the engine", it is not the output of the output shaft that the engine actually outputs, but the setting and request for the engine. Output.

Patent Literature 7 describes that in a sub-chamber gas engine, the output of a gas fuel engine is defined by the number of revolutions and torque.

International Publication No. 2015/060117 European Patent Publication No. 2136054 JP-A-62-99606 Patent No.5502033 Patent No. 5338977 JP-A-2002-21608 JP 2013-185515 A

In the conventional gas fuel engine, even if the supply amount of the gas fuel is increased at a high rate in order to rapidly increase the output, the supercharger cannot follow and the required amount of air cannot be supplied. This is because the supercharger is driven by the exhaust gas, so that the output of the gas fuel engine increases and the exhaust gas does not work effectively unless the exhaust gas is sufficiently supplied to the supercharger. If the air amount is insufficient, the air-fuel ratio becomes gas-rich and knocking occurs, leading to engine failure. If the output is increased at a speed that the turbocharger can follow to suppress the knocking, it takes about 10 minutes to increase the output (increase the load). In this specification, the term "output" is used for the power actually output by the engine in principle, and the term "load" is used for the power set and required for the engine. In many cases, “output” = “load”, and the word “load” may be conventionally used instead of “output” (or vice versa).

On the other hand, harmful exhaust gas emission regulations are becoming stricter every year even for marine engines, and there is a need to introduce a dual fuel engine that can meet the emission regulations with low emission of harmful exhaust gas derived from fuel. ing. However, in order to introduce such a dual fuel engine, it was necessary to reduce the load raising time to about 20 seconds in order to satisfy the operation mode of the marine engine.

The present invention has been made in view of the above-described problems, and it is possible to suppress the knocking that occurs when increasing the output of a gas-fueled engine, shorten the load raising time, and to reduce the unburned gas fuel during valve overlap. It is an object of the present invention to provide an engine control method and an engine system that do not deteriorate fuel efficiency due to blow-by of a vehicle.

That is, the present inventors change the valve opening (supply start) timing of the fuel gas supply valve at each VIVT angle, determine the optimum value from the THC concentration and the combustion state, and change the fuel gas supply valve according to the VIVT angle. By setting the valve opening timing, knocking that occurs when increasing the output of the gas fuel engine can be suppressed to reduce the load raising time, and furthermore, the fuel gas supply valve can be used in the torque rich region and the torque poor region. It has been found that the combustion fluctuation and the rotational speed hunting caused by the valve opening timing can be improved, and the present invention has been achieved.

The control method of the engine according to the present invention is a control method of an engine using gas as a fuel. In accordance with an increase in the output of the engine, the timing of closing the intake valve is adjusted by adjusting the advance angle from the intake bottom dead center. It is characterized in that control for lowering the compression ratio of the air-fuel mixture in the room is performed, and the valve opening timing of the fuel gas supply valve is advanced in accordance with a change in the advance angle.

As an engine knocking suppression technique, the effective compression ratio can be reduced by using a variable intake valve timing (VIVT) mechanism. Regarding this point, a knocking suppression technique will be described with reference to FIGS. 19A and 19B. FIG. 19A shows a normal four-stroke cycle process, and FIG. 19B shows a mirror cycle process.
For example, in a gas fuel engine, the intake valve usually closes at the bottom dead center of the piston (see FIG. 19A). On the other hand, if the closing timing is earlier than the bottom dead center as shown in FIG. 19B, the air-fuel mixture continues to expand even after the intake valve is closed, so that the in-cylinder temperature Ts falls from that in FIG. 19A (Ts ^* <Ts). . Since the maximum compression temperature at the top dead center is reduced by that amount (Tc ^* <Tc), self-ignition can be prevented and knocking can be suppressed.
As a drawback of the Miller cycle, the compression temperature decreases and the ignitability in the low load region deteriorates. Therefore, at the time of startup or at a low load, the normal intake valve opening timing shown in FIG. 19A is returned. It is necessary to make the valve opening timing earlier.

According to the engine control method of the present invention, in a gas fuel engine in which the output is increased by increasing the supply amount of the gas fuel, the timing of closing the intake valve is advanced (advanced) from the intake bottom dead center, so that the inside of the combustion chamber of the engine is increased. Control for lowering the compression ratio of the air-fuel mixture is performed. By lowering the compression ratio, the temperature in the combustion chamber at the time of compression becomes lower, so that knocking can be suppressed.
If the compression ratio of the air-fuel mixture is reduced in the combustion chamber, ignitability deteriorates at the time of start-up or low output, and the combustion efficiency departs from an advantageous condition in terms of combustion efficiency. Therefore, in the present invention, in the operating region where the output in which knocking is more likely to occur is higher, the timing at which the intake valve closes is changed to a greater extent to control the compression ratio to decrease at a higher rate. As a result, knocking can be suppressed in accordance with the change in output, and the load raising time can be reduced while preventing deterioration of fuel efficiency. Moreover, by advancing the valve opening timing of the fuel gas supply valve in accordance with the change in the advance angle of the intake valve, it is possible to reduce blow-through of unburned fuel gas when the intake valve and the exhaust valve overlap. .

Further, it is preferable that as the advance of the timing at which the intake valve closes advances, the degree of advance of the valve opening timing of the fuel gas supply valve increases.
This makes it possible to further reduce blow-through of unburned fuel gas in the combustion chamber when the intake valve and the exhaust valve overlap.

In addition, the closing timing of the fuel gas supply valve is calculated based on a deviation between the target rotation speed and the actual rotation speed, and the opening period is set with the opening timing of the fuel gas supply valve as a starting point. It is preferable to determine
The opening period of the fuel gas supply valve is calculated by feedback control such as PID control based on the difference between the target engine speed and the actual engine speed. By setting the valve opening period starting from the valve opening timing of the fuel gas supply valve, the valve closing timing of the fuel gas supply valve can be determined.

Further, it is preferable to increase the supply pressure of the fuel gas with the advance of the timing at which the intake valve closes.
By increasing the supply pressure of the fuel gas in accordance with the advance angle of the closing timing of the intake valve, an appropriate amount of gas fuel for maintaining the output can be supplied within the valve opening period.

Further, it is preferable that the ignition timing of the engine is advanced with the advance of the timing at which the intake valve closes.
The thermal efficiency can be increased by advancing the ignition timing within a range where NOx falls within a predetermined value according to the advance of the closing timing of the intake valve.

Further, the advance angle of the ignition timing has a peak at a cubic characteristic line for a ship, which is a boundary between a torque rich region and a torque poor region in which the output and rotation speed of the engine measured in advance are set as parameters. The advance angle may be reduced from the cubed characteristic line.
Even in this case, since the ignition timing is advanced in the region before the torque rich region and the torque poor region with the peak of the cubic characteristic curve for the boat advanced before the timing of closing the intake valve is advanced, NOx is entirely within the regulation range. And the thermal efficiency is increased. Note that the "marine cubic characteristic" is a characteristic of a marine main engine whose output is proportional to the cube of the rotational speed, but is not always exactly proportional to the cube of an actual ship, and a certain degree of deviation occurs.

In addition, the output of the engine is calculated based on a torque measurement value obtained by measuring the torque of the output shaft of the engine with the torque sensor and a rotation speed measurement value obtained by measuring the rotation speed of the output shaft of the engine with the rotation speed sensor. Preferably, it is an output value.
In the engine according to the present invention, since the gas serving as the fuel is an elastic body, it is relatively difficult to obtain an accurate fuel supply amount as compared with the liquid fuel. Therefore, it is preferable to calculate the output in relation to the rotation speed by actually measuring the torque with a torque sensor. Moreover, the output (load) of the output shaft of the engine can be obtained in real time by multiplying the measured value of the rotational speed of the output shaft obtained by providing the rotational speed sensor and the measured torque value of the torque sensor. Therefore, since the advance angle of the closing timing of the intake valve of the engine and the advance angle of the opening timing of the fuel gas supply valve can be accurately set, the combustion efficiency can be improved and the gas You can drive.

Further, it is preferable that the advance angle of the timing at which the intake valve closes is set from the advance value set using the output values of the plurality of output shafts and the data of the rotational speed measured in advance as parameters.
The preferred value of the advance angle of the closing timing of the intake valve becomes larger when the output is large, but also depends on the rotational speed. Therefore, a map including at least these two parameters is created in advance, and knocking can be further suppressed by controlling the advance of the closing timing of the intake valve according to the change in the output and the rotation speed of the engine.

The engine system according to the present invention is an engine system including a four-stroke engine using gas as a fuel, and when the output of the output shaft of the engine increases, the timing of closing the intake valve of the engine is advanced, and A control unit for advancing the opening timing of the fuel gas supply valve in response to a change in the advancing angle; and a variable intake for changing the timing of closing the intake valve according to the closing timing of the intake valve set by the control unit. A valve timing mechanism, and a fuel gas supply valve timing mechanism for advancing the valve opening timing of the fuel gas supply valve in accordance with a change in the advance angle of the intake valve set by the control unit. With the increase in the engine speed, the variable intake valve timing mechanism performs control to further reduce the compression ratio of the mixture of gas and air in the engine.
In the control method of the engine system according to the present invention, when the supply amount of the gas fuel is increased and the output of the output shaft of the engine is increased, the timing at which the intake valve closes is advanced from the intake bottom dead center, whereby the combustion of the engine is started. Control is performed to reduce the compression ratio of the air-fuel mixture in the room. By lowering the compression ratio, the temperature in the combustion chamber at the time of compression becomes lower, so that knocking can be suppressed.
In addition, in the present invention, control is performed such that the timing of closing the intake valve is changed to a greater extent in an operating region where the output in which knocking is more likely to occur is higher, and the compression ratio is reduced at a larger rate. As a result, knocking can be suppressed in accordance with the change in output, and the load raising time can be reduced while preventing deterioration of fuel efficiency. In addition, by advancing the valve opening timing of the fuel gas supply valve in accordance with the change in the advance angle of the intake valve, the unburned fuel when the intake valve and the exhaust valve overlap with respect to the crank angle of the intake valve is closed. Gas blow-through can be reduced.

A torque sensor for measuring the torque of the output shaft of the engine; and a rotation speed sensor for measuring the rotation speed of the output shaft of the engine. The output shaft is determined from the torque measurement value by the torque sensor and the rotation speed measurement value by the rotation speed sensor. It is preferable to set the change of the closing timing of the intake valve in the control unit in order to obtain the output of the control unit.
In the gaseous fuel engine according to the present invention, it is relatively difficult to obtain an accurate fuel supply amount as compared with liquid fuel because the gas serving as the fuel is an elastic body. Therefore, it is preferable to calculate the output in relation to the rotation speed by actually measuring the torque with a torque sensor. Moreover, the output of the output shaft of the engine can be obtained in real time by taking the product of the measured value of the rotational speed of the output shaft obtained by providing the rotational speed sensor and the measured value of the torque by the torque sensor.

According to the engine control method and the engine system of the present invention, when the output of the output shaft of the engine increases, the compression ratio of the air-fuel mixture in the engine can be reduced. Raising time can be reduced.
Moreover, since the opening timing of the fuel gas supply valve is advanced in accordance with the adjustment of the advance angle of the intake valve, combustion fluctuations and rotational speed hunting caused by the opening timing of the fuel gas supply valve are improved, The operation of the gas fuel engine can be appropriately performed.

FIG. 1 is a block diagram showing a main configuration of a marine dual fuel engine according to an embodiment of the present invention. FIG. 2 is a diagram showing a diesel mode and a gas mode in the dual fuel engine shown in FIG. 1. 4 is a three-dimensional map showing a relationship between an output, a rotation speed, and a VIVT command value. 4 is a three-dimensional map showing a relationship between an output, a rotation speed, and a closing timing of an intake valve. 9 is a graph showing a relationship between an output and an optimum VIVT command value when the rotation speed of the output shaft is constant or changes. 4 is a graph showing the relationship between the valve opening timing of a fuel gas supply valve and the THC concentration when the VIVT command values are different. 7 is a graph showing the relationship between the output and the opening timing of the fuel gas supply valve when the rotation speed of the output shaft is constant and when it changes. It is a graph which shows the fuel gas supply start time corresponding to a VIVT command value. It is a figure showing composition of a control device which performs PID control of a marine dual fuel engine. It is a figure which shows the process of performing PID control so that an actual rotation speed may become a target rotation speed. 5 is a timing chart of an opening / closing operation of an intake valve and a fuel gas supply valve at a normal time and at an advance angle. FIG. 4 is a diagram illustrating a relationship between an output, a valve opening period of a fuel gas supply valve, and a pressure ΔP of fuel gas. 4 is a three-dimensional map showing a relationship among output, rotation speed, and pressure ΔP of fuel gas. 5 is a graph showing a change in NOx corresponding to an air-fuel ratio and a usable range. 3 is a three-dimensional map showing a relationship between a rotation speed, an output, and an air supply pressure. 4 is a graph showing the relationship between the output and the supply pressure when the intake valve closing timing is constant and when the intake valve is advanced. 3 is a three-dimensional map showing a relationship between a rotation speed, an output, and an ignition timing. 5 is a graph showing the relationship between NOx and thermal efficiency when changing the ignition timing. FIG. 4 is a process diagram of a normal cycle of an engine combustion cycle. FIG. 4 is a process diagram of a mirror cycle of an engine combustion cycle. FIG. 9 is a perspective view showing an example of a conventional variable intake valve timing mechanism. It is a front view showing an example of the conventional variable intake valve timing mechanism. FIG. 11 is a perspective view showing another example of the conventional variable intake valve timing mechanism. FIG. 9 is a view showing still another example of the conventional variable intake valve timing mechanism. FIG. 23 is a diagram showing a relationship between an actuator and a link shaft in the conventional variable intake valve timing mechanism shown in FIG. 22.

Hereinafter, as an engine according to an embodiment of the present invention, for example, a four-stroke dual fuel engine 1 used as a marine engine will be described with reference to the accompanying drawings.
The marine dual-fuel engine 1 (hereinafter, sometimes simply referred to as the engine 1) shown in FIGS. 1 and 2 includes engines of a diesel mode D and a gas mode G. The diesel mode D and the gas mode G are operated during operation. It is an organization that can be switched to The dual fuel engine 1 shown in FIG. 1 includes a mechanism of a crankshaft 2 as an output shaft connected to a propeller or the like. The crankshaft 2 is connected to a piston 4 installed in a cylinder block 3. A combustion chamber 6 is formed by the piston 4 and the engine head 5 provided in the cylinder block 3.

The combustion chamber 6 is sealed by an intake valve 8 and an exhaust valve 9 mounted on the engine head 5 and a fuel injection valve 10 used in the diesel mode D. The engine head 5 is provided with a micro pilot oil injection valve 11 used in the gas mode. An intake pipe 13 is connected to an intake port of the engine head 5 where the intake valve 8 is installed, and an exhaust pipe 14 is installed at an exhaust port where the exhaust valve 9 is installed. A fuel gas supply valve 15 composed of an electromagnetic valve for controlling gas injection is installed in the intake pipe 13, and an air cooler 16 and a supercharger 17 communicating with the exhaust pipe 14 are installed upstream of the fuel gas supply valve 15.

Here, the dual fuel engine 1 according to the present embodiment can be operated by switching between the diesel mode D and the gas mode G as shown in FIG. In the diesel mode D, for example, fuel oil A or the like can be mechanically injected as fuel oil from the fuel injection valve 10 into the compressed air in the combustion chamber 6 to ignite and burn. In the gas mode G, a fuel gas such as natural gas is supplied to an intake pipe 13 by a fuel gas supply valve 15 and premixed with an air flow to supply an air-fuel mixture into the combustion chamber 6. Pilot fuel is injected from the pilot oil injection valve 11 to ignite and burn. The micro pilot oil injection valve 11 is, for example, electronically controlled and injects a small amount of pilot fuel as a strong ignition source. The fuel gas supply valve 15 is an electromagnetic valve that forms a large opening with a small stroke and allows a large amount of gas to flow in a short time.

The engine 1 starts in a diesel mode D in which liquid fuel is injected from the fuel injection valve 10 into the combustion chamber 6. After it is confirmed that the gas pressure equal to or higher than the reference value is supplied to the engine 1, gas fuel is supplied to the intake pipe 13 by the fuel gas supply valve 15, mixed with air, and then flows into the combustion chamber 6. The operation is performed in gas mode G for burning gas fuel.
At the time of the stop, the mode is changed to the diesel mode D again, and then the stop is performed. The diesel mode D and the gas mode G can be changed except at the time of starting and stopping.

The dual fuel engine 1 according to the present embodiment includes a gas engine system that performs output control when the load increases in the gas mode G. The structure of the gas engine system will be further described.
In FIG. 1, a rotation speed sensor 20 and a torque sensor 21 are attached to the crankshaft 2. The rotation speed sensor 20 measures the rotation speed (number of rotations) of the crankshaft 2, and the torque sensor 21 detects the engine torque. measure. As the torque sensor 21, for example, a sensor that detects a torque applied to a shaft by distortion can be used. The measurement data measured by the rotation speed sensor 20 and the torque sensor 21 are output as signals to a control unit 22 that controls the engine 1.
The control unit 22 detects the operating state of the engine 1 based on signals from the rotation speed sensor 20, the torque sensor 21, and the like. That is, assuming that the rotation speed (the number of rotations) of the crankshaft 2 measured by the rotation speed sensor 20 is n and the torque measured by the torque sensor 21 is T, the output of the engine 1 is expressed by the following equations (1) and (2). (Load) A is calculated. Here, Lt is the rated output of the engine 1.
Output Lo = 2πTn / 60 (1)
Output (load) A = Lo / Lt × 100 (2)

As a method for obtaining the output (load) of the engine 1, a method for estimating the output amount of the fuel and other information regarding the operating state of the engine 1 and a method for providing a torque sensor 21 in a power transmission system of an output shaft of the engine 1 are provided. There is a method of actually measuring the torque and obtaining the output. In a gas fuel engine, it is relatively difficult to obtain an accurate fuel supply amount as compared with a liquid fuel because a gas serving as a fuel is an elastic body. Therefore, it is preferable to calculate the output by actually measuring the torque with the torque sensor 21.
When the rotational speed n is constant, the output A and the measured torque value T are directly proportional. Under the condition that the rotation speed n is constant, it is desirable to set the advance angle of the closing timing of the intake valve 8 at a larger rate as the output A is larger, that is, as the torque data T is larger.

The control unit 22 stores a first map 24 for determining a first electric signal of the intake valve opening / closing timing created in advance and a second map 25 for determining an opening / closing timing corresponding to the first electric signal. The control unit 22 calculates the engine speed of the engine 1 based on the rotation speed data n and the torque data T corresponding to the output A of the engine 1 measured by the rotation speed sensor 20 and the torque sensor 21 according to the above equations (1) and (2). The output A is calculated. Then, a first electric signal corresponding to the opening / closing timing of the intake valve 8 is selected on the first map 24 based on the rotation speed n and the output A. Based on this first electric signal, the opening / closing timing of the intake valve 8 corresponding to the first electric signal is determined in the second map 25. The method of creating the first map 24 and the second map 25 will be described later.
The second electric signal of the opening / closing timing set by the control unit 22 is transmitted to the electropneumatic converter 27, and the signal of the opening / closing timing is converted into the air pressure by the electropneumatic converter 27. This air pressure is sent to the actuator 28 to control the driving of the variable intake valve timing mechanism 30. The actuator 28 is supplied with air pressures P1 and P2 for driving and control from the first pressure reducing regulator 34 and the electropneumatic converter 27.

The air pressure supplied to the actuator 28 is compressed by an air compressor 32 and stored in an air tank 33. The air pressure in the air tank 33 is reduced to a required pressure by the first pressure reducing regulator 34. The pressure at this time is adjusted by changing the valve opening of the first pressure reducing regulator 34, and is supplied to the actuator 28 as a driving air pressure P1. If the pressure P1 measured by the pressure gauge 36 is equal to or less than a specified value, the engine 1 cannot be started.
The air pressure for driving the electropneumatic converter 27 is further reduced from the first pressure reducing regulator 34 by the second pressure reducing regulator 37 and supplied. The electropneumatic converter 27 supplies the actuator 28 with an air pressure corresponding to the input second electrical signal of the opening / closing timing as an air pressure P2 for adjusting the operation of the actuator 28. The variable intake valve timing mechanism 30 is operated by operating the rod 28a of the actuator 28 based on these air pressures P1 and P2.

The actuator 28 is, for example, a known P cylinder (a cylinder with a position), and controls the advance / retreat of the rod 28a based on the pressures P1 and P2 input from the first pressure reducing regulator 34 and the electropneumatic converter 27. By changing the moving length of the rod 28a of the actuator 28, the drive of the variable intake valve timing mechanism 30 is controlled to advance (advance) or delay (advance) the closing timing of the intake valve 8 from the intake bottom dead center. Angle), the compression ratio is reduced to perform control.
Since the time between the valve opening timing and the valve closing timing of the intake valve 8 does not change, if the valve opening timing advances from the suction bottom dead center, the valve closing timing also advances from the suction top dead center by the same time. Moreover, in the present invention, the timing of opening and closing the valve is changed in accordance with the output of the engine 1 to suppress knocking and reduce the load raising time. The opening and closing timing of the intake valve 8 is set based on the first map 24 and the second map 25 in the control unit 22 based on the output A and the rotation speed n of the engine 1, and the intake valve 8 is controlled by the actuator 28 and the variable intake valve timing mechanism 30. The timing of opening and closing the valve is adjusted to suppress knocking.

The configuration of the variable intake valve timing mechanism 30 is conventionally known, and has a structure similar to that shown in FIGS. That is, in the variable intake valve timing mechanism 30, for example, a link shaft whose rotation angle range is set via a sector gear according to the moving length of the rod 28a of the actuator 28 and a cam shaft having an eccentric cam are arranged in parallel. I have. An exhaust swing arm is connected to the link shaft, and an intake swing arm is connected to a tappet shaft provided at an eccentric position of the link shaft. The intake swing arm is connected to an intake valve 8 via a push rod and a rocker arm, and the exhaust swing arm is connected to an exhaust valve 9 via a push rod and a rocker arm.

The distance between the cam shaft and the intake swing arm changes depending on the rotation angle of the tappet shaft according to the rotation of the link shaft, and the timing at which the eccentric cam of the cam shaft starts to hit changes. Thereby, the valve closing timing can be changed to an advanced angle (or a retarded angle). As the distance from the tappet shaft to the center of the cam shaft increases, the closing timing of the intake valve 8 becomes earlier. The rotation angle of the tappet shaft is changed by the moving length of the rod 28a of the actuator 28. The moving length of the rod 28a is arbitrarily changed according to the pressures P1 and P2 of the control air supplied to the actuator 28.
The magnitude of the advance angle, which is the timing of closing and opening the intake valve 8, is determined by the timing at which the eccentric cam of the cam shaft starts to contact the intake swing arm connected to the tappet shaft of the link shaft.

The rotary device of the tappet shaft in the variable intake valve timing mechanism 30 may use a servo motor (not shown) instead of the actuator 28. In this case, the opening / closing timing signal transmitted from the second map 25 of the control unit 22 is input to the servomotor. The servo motor rotates the link shaft by an amount corresponding to the received signal to rotate the tappet shaft so as to approach or separate from the cam shaft, thereby changing the opening / closing timing of the intake valve 8. When a servo motor is used, the configuration of the actuator 28 and the air compressor 32 to the pressure gauge 38 is unnecessary. Further, instead of the electropneumatic converter 27, a servomotor is driven by a controller.

A mechanism for supplying gas fuel to the fuel gas supply valve 15 that controls gas injection into the intake pipe 13 will be described. In FIG. 1, gas fuel is supplied to a gas vaporizer 41 from an LNG gas tank 40 in which gas fuel such as natural gas is stored, and the gas pressure is further reduced to a required gas pressure by a gas regulator 42.
The gas pressure at this time is displayed on the fuel gas pressure gauge 43, is adjusted by changing the valve opening of the gas regulator 42, and is supplied from the fuel gas supply valve 15 into the intake pipe 13 as gas fuel for combustion. . In the intake pipe 13, gas fuel and supercharged air cooled by the air cooler 16 are mixed and supplied to the combustion chamber 6. When the load is increased, the supply amount of the gas fuel is increased by the operation of the fuel gas supply valve 15.

Moreover, the second electric signal of the opening / closing timing set by the control unit 22 is transmitted to the fuel gas supply valve 15 via the fuel gas supply timing means 44 separately from the electropneumatic converter 27. The fuel gas supply timing means 44 controls the valve opening timing of opening the fuel gas supply valve 15 and supplying gaseous fuel into the intake pipe 13 so as to advance the valve opening timing in accordance with the advance of the closing timing of the intake valve 8. I do. The gas regulator 42 for adjusting the gas pressure and the fuel gas supply timing means 44 for advancing the opening timing of the fuel gas supply valve 15 are included in the fuel gas supply valve timing mechanism 45.
Note that the fuel gas supply timing means 44 may be provided outside the control unit 22. If the fuel gas supply valve timing mechanism 45 can receive the second electric signal from the second map 25 and can advance the valve opening timing of the fuel gas supply valve 15 in accordance with the advance of the closing timing of the intake valve 8 Good.

Next, a method of creating the first map 24 and the second map 25 stored in the control unit 22 will be described. FIG. 3 shows a crank angle of the intake valve 8 when the intake valve 8 is closed, which is a VIVT command value (intake valve closed crank timing, IVC), based on the rotation speed of the crankshaft 2 and the output (load factor) of the engine 1. It is a three-dimensional map showing details of the first map 24 to be determined.
In FIG. 3, a region B operated in a usual (practical) manner is indicated by a broken line. On the other hand, the change (advance angle) of the VIVT command value with respect to the change of the output when the rotation speed performed by the power generation is kept constant is indicated by an arrow line C, and the rotation speed and the output (load factor) performed by the ship are The change (advance angle) of the VIVT command value when it changes simultaneously is indicated by an arrow line D. The arrow line D indicates the cubic characteristic for ships. The marine cubic characteristic indicates a typical characteristic of a marine main engine whose output is proportional to the cube of the rotational speed, and is a characteristic curve of the rotational speed and the output determined by the rated rotational speed of the engine and the rated output. A region where the output (load factor) is higher than the cubic characteristic line D for ships in the normal operation region B indicates a torque rich region, and a region where the output (load factor) is low indicates a torque poor region.

The first map 24 was created based on the steps of the following experimental procedures (1) to (18).
In the experiment, a dual fuel engine 1 of the same model actually used was used.
(1) Start the engine 1 and set the rotation speed (rotation speed) n to 400 min ^-1 , the output (load) A to 10%, and the closing timing of the intake valve 8 to 545 deg (slowest closing timing in terms of structure). Set.
(2) Then, abnormal combustion called knocking that occurs when the engine 1 is driven and the exhaust gas temperature at that time are measured.
Knocking is detected by a knock sensor (not shown) attached to each engine head 5. When the knocking phenomenon occurs, the waveform becomes a waveform in which the high-frequency pressure fluctuation overlaps the normal combustion waveform.

Further, the exhaust gas temperature at the time of knocking measurement is measured by a temperature sensor attached to the exhaust pipe 14.
(3) After completion of the measurement of the exhaust gas temperature at the time of the knocking measurement, the closing timing of the intake valve 8 is reduced by 5 deg, and the measurement of (2) is performed again. The measurement is performed by changing the valve closing timing to 500 deg (the earliest valve closing timing in terms of structure).
(4) When the measurement of (3) is completed, the output A is increased stepwise by 10% until it reaches 110%, and the measurements of (2) and (3) are repeated.

(5) According to the measurements (1) to (4), when the knocking strength is equal to or lower than the reference value and the exhaust temperature is equal to or lower than 500 ° C., knocking is suppressed and the engine 1 can safely operate. Judge.
(6) From the measurement result of the above (5), in the three-dimensional graph of FIG. 4 in which the X-axis is set to the output A, the Y-axis is set to the rotation speed n, and the Z-axis is set to the opening / closing timing, ● (black circles), plot x at unsafe measurement points. Thereby, the knocking suppression range in the relationship between the output A, the rotation speed n, and the valve closing timing can be selected.
(7) a measuring step of the above (1) to (6), the rotational speed n rises to 900 min ^-1 by 100 min ^-1, measured safely driving can range for each rotation speed n.

(8) FIG. 4 is a graph showing the measurement result of the above (7) on three axes of the rotation speed n, the output A, and the valve closing timing. In FIG. 4, a range surrounded by a straight line is a range in which knocking is suppressed and the engine 1 can safely operate.
(9) Next, nitrogen oxides (hereinafter, referred to as NOx) are measured within the three-dimensional area surrounded by a straight line for safely operating the engine shown in FIG. 4 measured by the experiments (1) to (8). Further experiments are performed to find a setting that is below the reference value and has the highest thermal efficiency.
The engine speed n is set to 400 min ^-1 , the output A is set to 10%, and the closing timing of the intake valve 8 is set to 545 deg.

(10) Next, NOx and thermal efficiency are measured. NOx is measured by an exhaust gas analyzer attached to the exhaust pipe 14. The thermal efficiency is calculated by the following equation (3) based on the fuel flow rate L measured from the fuel flow meter attached to the fuel pipe and the output A calculated from the measurement result of the torque sensor 21.
Thermal efficiency η = 360Lo / H / L (3)
Where H is the lower heating value of the fuel gas (J / Nm ³ )
Lo: Current output L: Fuel flow rate

(11) After the completion of the measurement in (10), the valve closing timing of the intake valve 8 is decreased by 5 deg, and the measurement in (10) is performed again. Measurement is performed with the valve closing timing changed to 505 deg (see FIG. 9).
(12) When the measurement of (10) and (11) is completed, the output is increased stepwise by 10% to 110%, and the measurement of (10) and (11) is repeated again. The valve closing timing is changed within a safe driving range shown in FIG.

(13) the measurement of the (9) to (12), the rotational speed n rises stepwise to 900 min ^-1 by 100 min ^-1, to determine a good measurement point most performance for each rotational speed.
(14) Then, the valve closing timing of the intake valve 8 where NOx is equal to or less than the predetermined value and which has the highest thermal efficiency is set for each rotation speed n and output A. Based on this result, a draft of the first map shown in FIG. 3 is created.

(15) Further, the knocking is detected by increasing the rotation speed n and the output A in an arbitrary load increasing pattern. The load raising pattern is a change state of the output A (load factor) and the rotation speed n per time, and changes depending on the propeller specifications (shape, rotation speed) of the marine propulsion device.
(16) The valve closing timing of the measurement point at which the knocking intensity detected in (15) is equal to or larger than the reference value is reduced by 3 deg.
(17) Next, the steps (15) and (16) are repeated until the knocking strength becomes equal to or less than the reference value, and the valve closing timing at which knocking is suppressed is determined. If the valve closing timing is reduced, the thermal efficiency will deteriorate. The setting of the valve closing timing at which the result of NOx and knocking strength being equal to or less than the reference value and having the highest thermal efficiency is set as the set values of the rotation speed n and the output A.
(18) The valve closing timing in which knocking was suppressed from the above (17) was measured at each rotation speed n and output A, and the final first map 24 shown in FIG. 3 was created based on the results.

FIG. 3 is a graph of a three-dimensional plane showing the VIVT command value according to the rotation speed and the output. The upper side in the figure is the direction in which the valve closing timing is advanced. On the three-dimensional plane, a region indicated by a broken line is a practical operation region used in actual operation of the ship propulsion device, and an example of a good load increasing pattern is indicated by a cubic characteristic line D for a ship. In increasing the load in a practical operation range, control is performed to increase the advance angle of the valve closing timing as the output of the engine increases.
In one example of a good load increasing pattern shown by the marine cubic characteristic line D, the advance angle is minimized at the lower right position in the figure where the rotation speed and the output are small, and the advance angle increases as the rotation speed and the output increase. I do. Although the ratio of increasing the advance angle is not constant, the advance angle is increased as the output increases as a whole. Since the output (load ratio) is obtained by the product of the torque and the rotation speed, it can be expressed that the advance angle increases as the torque of the output shaft increases.

Next, the second map 25 was created by the following experiment.
When the rotation of the variable intake valve timing mechanism 30 is controlled by the actuator 28, the second map 25 is created in the following procedure.
(1) The valve closing timing is changed by the actuator 28, and the pressure when changing to each valve closing timing is measured.
(2) A second electric signal required to supply the pressure of (1) above is examined based on the specifications of the electropneumatic converter 27.
(3) Based on the results of (1) and (2), the horizontal axis represents the first electric signal selected in the first map 24, and the vertical axis represents the second map 25 indicating the valve closing timing (second electric signal). create.

The above description is of the case where the actuator 28 is used. When the rotation of the variable intake valve timing mechanism 30 is controlled by a servomotor instead of the actuator 28, the following is performed.
(1) The valve closing timing is changed based on the servomotor, and a second electric signal at the time of changing each valve closing timing is measured.
(2) On the basis of the result of the above (1), a second map 25 showing the first electric signal on the horizontal axis and the valve closing timing (second electric signal) on the vertical axis is created.
The second map 25 is a map representing the relationship between the valve closing timing (second electric signal) and the first electric signal.

In the three-dimensional map shown in FIG. 3, the optimum VIVT command value differs depending on the output between the power generation characteristic line indicated by the solid line C and the marine cubed characteristic line D. That is, as shown in FIG. 5 as an example, even when the output is the same, when the rotation speed is different, the intake valve closing crank angle of the optimum VIVT command value is different.
In this embodiment, in response to a change in the VIVT command value, that is, with respect to various intake valve closing crank angles, the unburned fuel gas flows to the exhaust pipe 14 when the intake valve 8 and the exhaust valve 9 overlap. The opening timing of the fuel gas supply valve 15 that supplies the fuel gas to the intake pipe 13 is set so that the blow-through of the fuel gas is reduced. For that purpose, first, a VIVT command value according to the rotation speed and the output is set. Strictly speaking, it is preferable to set the air-fuel ratio and the ignition timing to optimal values based on the thermal efficiency and NOx, but here, these conditions are not set assuming that the engine 1 can be operated stably. .

As an example of setting the valve opening timing of the fuel gas supply valve 15, the valve opening timing of the fuel gas supply valve 15 by the fuel gas supply timing means 44 under engine operating conditions in accordance with the optimum VIVT command value on the cubic characteristic line D for ships How to determine is described below.
First, the fuel gas is supplied from the fuel gas supply valve 15 using the timing of opening the intake valve 8 as a guide under the respective operating conditions where the output (load factor) of the engine is 25%, 50%, 75%, and 100%. Since the fuel gas is supplied into the intake pipe 13, the fuel gas does not reach the intake valve 8 instantaneously. Therefore, the crank angle position of the valve opening timing of the fuel gas supply valve 15 in consideration of the distance from the fuel gas supply valve 15 to the intake valve 8 is assumed. Then, the crank angle position at the valve opening timing of the fuel gas supply valve 15 is changed every 5 deg before and after that, and the total hydrocarbon concentration (the unburned gas in the exhaust gas at the gas turbine outlet of the supercharger 17 at that time) ( (THC concentration) is measured. The measurement of the THC concentration is repeatedly performed under each operating condition. The THC concentration is preferably measured by a flame ionization method (JIS B 7956).

The valve opening timing of the fuel gas supply valve 15 is changed in accordance with each condition, and each VIVT command value (intake valve closing crank angle) is set to, for example, 40%, 65%, 85%, and 100%. FIG. 6 shows the relationship between the fuel gas valve opening timing and the measured THC concentration at the command value.
As shown in FIG. 6, the valve opening timing of the fuel gas supply valve 15 is based on the crank angle at which the unburned fuel gas blows through at the time of valve overlap is small and the THC concentration is minimized. On the other hand, a sudden change in the valve opening timing of the fuel gas supply valve 15 due to a change in output leads to the above-described combustion fluctuation and rotation speed fluctuation. Therefore, the amount of change in the valve opening timing of the fuel gas supply valve 15 in accordance with the output has a gradient as small as possible, that is, ± 5 deg. C. A crank angle corresponding to the optimal fuel gas opening timing of the fuel gas supply valve 15 is selected within the range of A, and a crank angle corresponding to the optimal opening timing of the fuel gas supply valve 15 is determined under each condition.

The relationship between the crank angle of the optimal valve opening timing of the fuel gas supply valve 15 and the output (load factor) at the optimal VIVT command value of the cubic characteristic line D for ships determined in this way is shown in FIG. Change "is indicated by a polygonal line.
Similarly, the relationship between the crank angle of the optimal valve opening timing of the fuel gas supply valve 15 and the output (load factor) at the optimal VIVT command value at the output at a constant rotational speed performed on the power generation characteristic line C in FIG. Is shown by a polygonal line of "constant rotation speed" in FIG.
As shown in FIG. 7, the optimal valve opening timing of the fuel gas supply valve 15 has different results under the condition that the rotation speed changes and the condition that the rotation speed is constant even if the output is the same.

However, the optimum crank angle of the valve opening timing of the fuel gas supply valve 15 at the optimum VIVT command value of the marine cube characteristic line D and the optimum fuel gas at the optimum VIVT command value of the power generation characteristic line C (constant rotation speed). As shown in FIG. 8, the crank angle of the valve opening timing of the supply valve 15 exhibits one consistent diagram characteristic when the VIVT command value is arranged on the horizontal axis instead of the output. That is, it can be seen that the valve opening timing of the optimum fuel gas supply valve 15 does not depend on the output, but depends on the specified VIVT value (the intake valve closing crank angle).

As is clear from FIG. 8, when the closing timing of the intake valve 8 is changed by the variable intake valve timing mechanism 30, as the advance timing of the closing timing of the intake valve 8 advances, the supply start timing of the fuel gas supply valve 15 advances. The degree of corners is greater.
Therefore, by setting the crank angle of the optimal valve opening timing of the fuel gas supply valve 15 determined under each condition by the fuel gas supply timing means 44 based on the VIVT command value, the fuel gas supply valve 15 according to the VIVT command value is set. Of the valve opening timing can be optimized. In FIG. 8, the unmeasured VIVT command value, fuel gas supply start time, and the like may be determined by an approximate line connecting data before and after the measurement point.

Next, timing control of fuel gas supply end by the fuel gas supply valve 15 will be described with reference to FIGS.
FIG. 9 shows a main configuration of the engine 1 shown in FIG. In FIG. 9, a target rotation speed command unit 50 is provided outside the control unit 22, and a preset target rotation speed is input to the control unit 22. The gas supply time calculation unit 51 of the control unit 22 directly performs PID control of the valve opening period of the fuel gas supply valve 15 based on the deviation between the actual rotation speed and the target rotation speed calculated from the measured value of the rotation speed sensor 20. I do.
A gas supply valve control unit 52 connected to the gas supply time calculation unit 51 calculates a time to be opened from the opening timing of the fuel gas supply valve 15 and outputs the calculated time to the fuel gas supply valve 15 to open the valve. Feedback control is performed so that the fuel gas supply valve 15 is opened only for the time to be performed.

The closing timing control of the fuel gas supply valve 15 is performed as follows. That is, as shown in FIG. 10, the control unit 22 directly determines the valve opening period of the fuel gas supply valve 15 based on the deviation between the target rotation speed set by the target rotation speed command unit 50 and the actual rotation speed by the PID. Control. Specifically, based on the deviation between the target rotation speed and the actual rotation speed, the time during which each fuel gas supply valve 15 is open is controlled by feedback control so that the actual rotation speed follows the target rotation speed.
The gas supply valve control unit 52 controls the closing timing of each fuel gas supply valve 15 based on the valve opening period calculated from the opening timing of the fuel gas supply valve 15 as a starting point. The control unit 22 directly performs PID control on the valve opening period of the fuel gas supply valve 15 so that the actual rotation speed matches the target rotation speed without previously calculating the amount of fuel gas to be supplied.

The supply pressure control of the fuel gas, which will be described later, is performed by adding the supply pressure detected by the supply pressure gauge 54 provided in the intake pipe 13 to the pressure ΔP value set using the output and rotation speed data of the engine 1 as parameters. The fuel gas pressure regulator 55 is feedback-controlled so that the deviation between the value and the value of the fuel gas pressure gauge 43 is eliminated.

FIG. 11 shows the relationship between the advance angle of the variable intake valve timing mechanism 30 displaying the above-described results and the timing of starting and ending the supply of the fuel gas supply valve 15 by the fuel gas supply timing means 44.
FIG. 11 shows the relationship between the crank angle of the engine 1 and the valve lifts of the intake valve 8 and the exhaust valve 9. In the curve showing the opening / closing operation of the intake valve 8, the solid line shows the case where the VIVT (variable intake valve timing) command value is 0%, and the one-dot chain line shows the case of the advance angle (the VIVT command value is 100%). 3 shows an opening and closing operation image in the case of. Then, the valve opening period of the fuel gas supply valve 15 at the time of the advance (the VIVT command value is 100%) is longer than the valve opening period of the fuel gas supply valve 15 when the VIVT command value is 0%.

Further, it is preferable to increase the fuel gas supply pressure by increasing the fuel gas supply pressure as the valve closing timing of the intake valve 8 advances. Therefore, in FIG. 9, the supply pressure of the fuel gas into the intake pipe 13 is set to a value obtained by adding the pressure ΔP value to the supply pressure detected by the supply pressure gauge 54 provided in the intake pipe 13. As described below, the pressure ΔP is set with parameters of the outputs and the rotational speeds of the plurality of engines 1 measured in advance as parameters. As a result, the supply pressure of the fuel gas supplied from the fuel gas supply valve 15 increases with the advance of the timing at which the intake valve 8 closes.

How to set the pressure ΔP of the fuel gas will be described.
FIG. 12 is a diagram showing the relationship between the output, the valve opening period of the fuel gas supply valve 15, and the pressure ΔP. The operating condition of the engine 1 is changed using the output (load factor) and the rotation speed as parameters, and the pressure ΔP is changed under each condition, and the pressure ΔP at each output and the valve open period of the fuel gas supply valve 15 are obtained. If the pressure ΔP is set low based on the output and the rotation speed, the valve-opening period of the fuel gas supply valve 15 becomes long, and if the valve-opening period is too long, it becomes impossible to supply appropriate gas fuel while the intake valve 8 is open. . Conversely, if the pressure ΔP is set high, the opening period of the fuel gas supply valve 15 is shortened, and controllability of the supply amount is deteriorated. Therefore, the pressure ΔP is set to a pressure ΔP that does not adversely affect the operation state of the engine 1.

When the rotation speed is parameterized, the same procedure is repeated to determine the pressure ΔP. 12, regarding the fuel gas supply valve 15, the lower limit of the valve opening time is set by setting the upper limit of the pressure ΔP, and the upper limit of the valve opening period is set by setting the lower limit of the pressure ΔP. The set value of the pressure ΔP is appropriately set as a changeable range within the range between the upper limit value and the lower limit value of the valve opening period, and preferably, the center value between the upper limit value and the lower limit value is set as the set value.
Since the distribution of the air-fuel mixture changes depending on the supply pressure of the fuel gas, it is necessary to pay attention to the combustion state. In FIG. 12, the condition not measured may be determined by an approximate line connecting data before and after the measurement point.

FIG. 13 is a plot of the set ΔP using the output (load factor) and the rotation speed as parameters. In the three-dimensional map in which the output, the rotation speed, and the pressure ΔP shown in FIG. 13 are used as parameters, a range shown by a broken line is a normal (practical) operation region, and a solid line shows a cubic characteristic for ships.
Since the fuel gas supply pressure is determined by the pressure ΔP, when the supply pressure changes, the supply pressure of the fuel gas also changes. In other words, this indicates that the differential pressure upstream and downstream of the fuel gas supply valve 15 is set, and the amount of fuel gas is determined by the differential pressure before and after the fuel gas supply valve 15 and the valve opening period. Even if it changes, there is no significant effect on the relationship between the fuel gas supply pressure determined here and the valve opening period of the fuel gas supply valve 15.
As is clear from FIG. 13, as the output (load factor) of the engine 1 increases, that is, as the timing of closing the intake valve 8 advances, the supply pressure of the fuel gas including the pressure ΔP also increases.

Next, how to determine the supply pressure (air-fuel ratio) in the engine 1 will be described.
In response to the change in the VIVT command value (intake valve closing crank angle) according to the above-described embodiment, the supply pressure supplied to the intake valve 8 from the intake pipe 13 is determined by the output and the rotational speed of the engine 1 measured in advance. According to the target supply pressure set as a parameter, a flow regulating valve provided with a bypass line on each of the compressor side and the turbine side of the supercharger 17 shown in FIG. 9 is controlled to control the supply pressure ( For example, see the one disclosed in Japanese Patent Application No. 2006-027359). The control of the supply pressure is not limited to this control method. A conventionally known supply pressure control method may be used.

A method of determining the above-described supply pressure (air-fuel ratio) will be described below.
The amount of fuel serving as the base of the air-fuel ratio is determined by the relationship between the supply pressure of the fuel gas and the opening period of the fuel gas supply valve 15 shown in FIGS. The suitable amount of fuel is determined by the output (load factor) and the rotation speed of the fuel cell. The air-fuel ratio is determined by the ratio between the amount of air and the amount of fuel gas. Therefore, the amount of air supplied to the combustion chamber 6 is changed by changing the supply pressure. That is, the air-fuel ratio is adjusted by the supply pressure.
The air-fuel ratio is set by changing the operating conditions of the engine 1 using the output (load factor) and the rotation speed as parameters, and setting the output (load factor) to, for example, 25%, 50%, 75%, 100%, and the like. Then, thermal efficiency and NOx data at various air-fuel ratios (supply pressure) are measured and obtained. FIG. 14 shows an example of NOx data when the air-fuel ratio is changed at an arbitrary output and rotational speed.

In FIG. 14, the measured value of the NOx data corresponding to the change in the air-fuel ratio is indicated by a curve as “measured data”. From the measurement data, it can be recognized that NOx increases by adjusting the air-fuel ratio to a small value (lower supply pressure).
Here, the reference value of the NOx value differs depending on the application. For example, the upper limit value and the lower limit value of the reference value are regulated based on the IMO NOx regulation based on the revised MARPOL Annex VI Regulation 13 for marine use, and the NOx emission indicated by the Air Pollution Control Law and the like for land use.
The lower limit of the air-fuel ratio is limited by the upper limit based on the above-mentioned laws and regulations on NOx emissions. However, if abnormal combustion such as knocking occurs before the NOx data reaches the upper limit value, the air-fuel ratio immediately before the abnormal combustion occurs is set to the lower limit.
On the other hand, as the air-fuel ratio increases, NOx decreases, but the engine 1 cannot be operated stably due to misfire or the like. Therefore, the upper limit of the air-fuel ratio at which stable operation can be continued is set to the upper limit. These determine the range of the air-fuel ratio that can be set.

Here, the range of the air-fuel ratio that can be set is determined, and the air-fuel ratio in the middle of the settable range is set as a suitable value, and the supply pressure at that time is set. The same measurement is repeated at an arbitrary output and a rotation speed within a range that is normally used. In other words, the air supply pressure (air-fuel ratio) is changed to obtain a suitable air supply pressure (air-fuel ratio) that satisfies the target performance under the operating conditions of each output and rotation speed.
FIG. 15 is a three-dimensional map in which the intake pressure set in accordance with the output and the rotation speed is plotted. In the figure, a region indicated by a broken line is an image of a normal (practical) operation region, and a cubic characteristic for a ship indicated by a solid line is set within the range. Note that the condition not measured may be determined by an approximate line connecting data before and after the measurement point.
As is clear from FIG. 15, as the output of the engine 1 increases, that is, with the advance of the timing at which the intake valve 8 closes, the required supply pressure also increases.
As described above, the air-fuel ratio control is performed by controlling the timing of starting and ending the supply of the fuel gas supply valve 15, controlling the supply pressure of the fuel gas, and controlling the supply pressure.

When the timing of closing the intake valve 8 is advanced, the air-fuel ratio decreases at the same supply pressure. For this reason, in the relationship between the output and the intake pressure shown in FIG. 16, as compared with the case where the closing timing of the intake valve 8 is constant, the optimal timing associated with the increase in the output increases with the advance of the timing at which the intake valve 8 closes. The rate of increase (gradient of increase) of the supply pressure increases.

Next, it is necessary to change the ignition timing of the fuel in accordance with the change in the designated value of the VIVT (the crank angle of the intake valve closing timing). The ignition timing of the engine 1 is, for example, fuel oil injection timing for ignition by the micro pilot oil injection valve 11, and the ignition timing is set in FIG. 17 in which data of the output value and the rotation speed of the engine 1 measured in advance are set as parameters. Is set from the value of the ignition timing shown in FIG.

A method for determining the ignition timing will be described.
By changing the operating conditions of the engine 1 using the output (load ratio) and the rotation speed as parameters, the thermal efficiency and NOx data of various ignition timings such as, for example, 25%, 50%, 75%, and 100% of the load ratio are obtained. FIG. 18 shows a data example of the thermal efficiency and NOx when the ignition timing is changed at an arbitrary output and a rotation speed. As shown by the solid line in FIG. 18, as the ignition timing is advanced, NOx increases, and the thermal efficiency improves. Therefore, there is a trade-off relationship between thermal efficiency and NOx.
As described above, since NOx has a predetermined reference value, the ignition timing advanced so that the thermal efficiency becomes highest is set as a suitable timing within a set range that satisfies the same reference NOx as the supply pressure. .

However, if abnormal combustion such as knocking starts before the NOx data reaches a predetermined reference value, the ignition timing before the abnormal combustion starts is set to a suitable ignition timing. The measurement of the ignition timing of the micro pilot oil injection valve 11 is repeated at an arbitrary output and a rotational speed within a range that is normally used. In other words, the ignition timing is changed under each operating condition of "output (load factor) and rotation speed" to obtain an ignition timing that satisfies the target performance. The ignition timing was determined by repeating the same adjustment at an arbitrary rotational speed and output within a range that is normally used. Note that the condition not measured may be determined by an approximate line connecting data before and after the measurement point.

As is evident from FIG. 17, a region where the output is lower than the solid line showing the image of the marine cubic characteristic within the range of the normal operation region shown by the broken line indicates the torque poor region. In the torque poor region, as the output of the engine 1 increases, that is, as the timing of closing the intake valve 8 advances, the ignition timing of the micro pilot oil injection valve 11 of the engine 1 also advances.

On the other hand, a region where the output is higher than the marine cubic characteristic line shown by the solid line indicates a torque-rich region. In the torque rich region, the ignition timing has a peak on the broken line in the normal operation region, and the advance angle can be reduced within a range of 30 to 50% of the ignition timing with respect to the peak value. However, within the torque poor region and the torque rich region, the ignition timing can be maintained at an advanced state at the same rotational speed as compared with the case where the VIVT command value is not advanced. That is, with the advance of the intake valve closing crank angle of the VIVT command value, the ignition timing is also advanced with the peak on the solid line indicating the cubic characteristic for ships. Although the degree of advance is reduced in the torque rich region, the fuel injection timing (ignition timing) of the micropilot oil injection valve 11 of the engine 1 is generally smaller than when the VIVT command value is not advanced. Also advances.

As described above, according to the control method of the engine 1 and the engine 1 according to the embodiment of the present invention, the unburned gas fuel to be discharged can be reduced in the normal operation range, so that the thermal efficiency is improved and the greenhouse gas is reduced. Advantages can also be gained for the environment, such as reducing emissions.
Also, as the output of the engine 1 becomes higher, the operable range with respect to the air-fuel ratio becomes narrower. Therefore, maintaining a stable operating state is particularly effective for expanding the operating range in a torque-rich region where the output is higher than the cubic characteristic for ships. Can be obtained.
Further, when the output of the output shaft of the engine 1 increases, the compression ratio of the air-fuel mixture in the engine 1 can be reduced, so that knocking during load increase can be suppressed and the load increase time can be shortened.

Note that the engine according to the present invention is not limited to the dual fuel engine 1 according to the above-described embodiment, and can be appropriately changed or replaced without departing from the gist of the present invention. Hereinafter, modified examples and the like of the present invention will be described, and the same or similar parts as those described in the above-described embodiment will be denoted by the same reference numerals and description thereof will be omitted.

The engine according to the present invention is not limited to the dual fuel engine 1 capable of switching between the diesel mode D using liquid fuel as the main fuel and the gas mode G using gas as the main fuel, and uses gas as fuel. Also applicable to gas fueled engines.
In addition, the present invention is not limited to the load raising pattern of a marine engine, and can be applied to a load raising pattern that can be used in a vehicle or an emergency generator.

In the above-described embodiment, the variable intake valve timing mechanism 30 changes both the valve opening timing and the valve closing timing and does not change the time during which the intake valve 8 is open. The change control may be performed by selecting one or both of and the valve opening timing.

The present invention provides an engine control method and an engine system capable of suppressing knocking at the time of increasing the load by using a pre-mixed gas of gaseous fuel and air and shortening the time of increasing the load.

DESCRIPTION OF SYMBOLS 1 Dual fuel engine 2 Crankshaft 8 Intake valve 9 Exhaust valve 13 Intake pipe 14 Exhaust pipe 15 Fuel gas supply valve 17 Supercharger 20 Rotation speed sensor 21 Torque sensor 22 Control unit 24 First map 25 Second map 27 Electro-pneumatic conversion Device 28 actuator 30 variable intake valve timing mechanism 42 gas regulator 44 fuel gas supply timing means 45 fuel gas supply valve timing mechanism

[0005]
In order to satisfy the operation mode of the engine, it was necessary to reduce the load raising time to about 20 seconds.
[0014]
The present invention has been made in view of the above-described problems, and it is possible to suppress the knocking that occurs when increasing the output of a gas-fueled engine, shorten the load raising time, and to reduce the unburned gas fuel during valve overlap. It is an object of the present invention to provide an engine control method and an engine system that do not deteriorate fuel efficiency due to blow-by of a vehicle.
Means for Solving the Problems [0015]
That is, the present inventors change the valve opening (supply start) timing of the fuel gas supply valve at each VIVT angle, determine the optimum value from the THC concentration and the combustion state, and change the fuel gas supply valve according to the VIVT angle. By setting the valve opening timing, knocking that occurs when increasing the output of the gas fuel engine can be suppressed to reduce the load raising time, and furthermore, the fuel gas supply valve can be used in the torque rich region and the torque poor region. It has been found that the combustion fluctuation and the rotational speed hunting caused by the valve opening timing can be improved, and the present invention has been achieved.
[0016]
The control method of the engine according to the present invention is a control method of an engine using gas as a fuel. In accordance with an increase in the output of the engine, the timing of closing the intake valve is adjusted by adjusting the advance angle from the intake bottom dead center. While performing control to lower the compression ratio of the air-fuel mixture in the room, the valve opening timing of the fuel gas supply valve is advanced in response to a change in the advance angle, and the more the advance angle of the timing at which the intake valve closes, the more the fuel The degree of advance of the valve opening timing of the gas supply valve becomes larger, and the valve closing timing of the fuel gas supply valve is determined by setting the valve opening period starting from the valve opening timing of the fuel gas supply valve. It is characterized by being performed.
[0017]
As an engine knocking suppression technique, the effective compression ratio can be reduced by using a variable intake valve timing (VIVT) mechanism. Regarding this point, a knocking suppression technique will be described with reference to FIGS. 19A and 19B. FIG. 19A shows a normal four-stroke cycle process, and FIG. 19B shows a mirror cycle process.
For example, in a gas fuel engine, the intake valve usually closes at the bottom dead center of the piston (see FIG. 19A). On the other hand, if the closing timing is earlier than the bottom dead center as shown in FIG. 19B, the air-fuel mixture continues to expand even after the intake valve is closed.

[0006]
Ts is lower than in the case of FIG. 19A (Ts * <Ts). By lowering the maximum compression temperature at the top dead center by that amount (Tc * <Tc), self-ignition can be prevented and knocking can be suppressed.
As a drawback of the Miller cycle, the compression temperature decreases and the ignitability in the low load region deteriorates. Therefore, at the time of startup or at a low load, the normal intake valve opening timing shown in FIG. 19A is returned. It is necessary to make the valve opening timing earlier.
[0018]
According to the engine control method of the present invention, in a gas fuel engine in which the output is increased by increasing the supply amount of the gas fuel, the timing of closing the intake valve is advanced (advanced) from the intake bottom dead center, so that the inside of the combustion chamber of the engine is increased. Control for lowering the compression ratio of the air-fuel mixture is performed. By lowering the compression ratio, the temperature in the combustion chamber at the time of compression becomes lower, so that knocking can be suppressed.
If the compression ratio of the air-fuel mixture is reduced in the combustion chamber, ignitability deteriorates at the time of start-up or low output, and the combustion efficiency departs from an advantageous condition in terms of combustion efficiency. Therefore, in the present invention, in the operating region where the output in which knocking is more likely to occur is higher, the timing at which the intake valve closes is changed to a greater extent to control the compression ratio to decrease at a higher rate. As a result, knocking can be suppressed in accordance with the change in output, and the load raising time can be reduced while preventing deterioration of fuel efficiency. Moreover, by advancing the valve opening timing of the fuel gas supply valve in accordance with the change in the advance angle of the intake valve, it is possible to reduce blow-through of unburned fuel gas when the intake valve and the exhaust valve overlap. .
[0019]
[0020]
Further, it is preferable that the valve opening period of the fuel gas supply valve is calculated based on a deviation between a target rotation speed and an actual rotation speed.
For example, PID control based on the difference between the target engine speed and the actual engine speed

[0008]
Preferably, the output is calculated in relation to the rotational speed by actually measuring the torque with a sensor. Moreover, the output (load) of the output shaft of the engine can be obtained in real time by multiplying the measured value of the rotational speed of the output shaft obtained by providing the rotational speed sensor and the measured torque value of the torque sensor. Therefore, since the advance angle of the closing timing of the intake valve of the engine and the advance angle of the opening timing of the fuel gas supply valve can be accurately set, the combustion efficiency can be improved and the gas You can drive.
[0025]
Further, it is preferable that the advance angle of the timing at which the intake valve closes is set from the advance value set using the output values of the plurality of output shafts and the data of the rotational speed measured in advance as parameters.
The preferred value of the advance angle of the closing timing of the intake valve becomes larger when the output is large, but also depends on the rotational speed. Therefore, a map including at least these two parameters is created in advance, and knocking can be further suppressed by controlling the advance of the closing timing of the intake valve according to the change in the output and the rotation speed of the engine.
[0026]
The engine system according to the present invention is an engine system including a four-stroke engine using gas as a fuel, and when the output of the output shaft of the engine increases, the timing of closing the intake valve of the engine is advanced, and A control unit for advancing the opening timing of the fuel gas supply valve in response to a change in the advancing angle; and a variable intake for changing the timing of closing the intake valve according to the closing timing of the intake valve set by the control unit. A valve timing mechanism, and a fuel gas supply valve timing mechanism for advancing the valve opening timing of the fuel gas supply valve in accordance with a change in the advance angle of the intake valve set by the control unit. With the increase of the fuel gas supply valve, the variable intake valve timing mechanism controls the compression ratio of the mixture of gas and air in the engine to be further reduced. The valve closing timing includes a gas supply time calculation unit that calculates a valve opening period of the fuel gas supply valve, and a fuel supply by the fuel gas supply valve based on the valve opening period starting from the valve opening timing of the fuel gas supply valve. And a gas supply valve control unit for instructing a valve closing timing of the gas.
In the control method of the engine system according to the present invention, when the supply amount of the gas fuel is increased and the output of the output shaft of the engine is increased, the timing at which the intake valve closes is advanced from the intake bottom dead center, whereby the combustion of the engine is started. Compression of air-fuel mixture in a room

Claims (14)

A method for controlling a gas-fueled engine, comprising:
With the increase in the output of the engine, while controlling the timing at which the intake valve closes by adjusting the advance angle from the bottom dead center of the intake, the compression ratio of the air-fuel mixture in the combustion chamber is reduced, and
An engine control method, wherein the valve opening timing of a fuel gas supply valve is advanced in accordance with the change in the advance angle.   2. The control method according to claim 1, wherein the advance of the timing of opening the fuel gas supply valve increases as the advance of the timing at which the intake valve closes increases.   The valve closing timing of the fuel gas supply valve is calculated based on a deviation between a target rotation speed and an actual rotation speed, and the valve opening period is set with the valve opening timing of the fuel gas supply valve as a starting point. The method for controlling an engine according to claim 1, wherein the control method is determined by:   The method according to any one of claims 1 to 3, wherein the supply pressure of the fuel gas is increased with an advance of the timing at which the intake valve is closed.   The method according to any one of claims 1 to 4, wherein the ignition timing of the engine is advanced with the advance of the timing at which the intake valve closes. The advance angle of the ignition timing has a peak at a cubic characteristic line for a ship, which is a boundary between a torque rich region and a torque poor region in which the output and the rotational speed of the engine measured in advance are set as parameters.
The engine control method according to claim 5, wherein in the torque rich region, the advance angle is reduced from the cubic characteristic line for ships.   The output of the engine is an output shaft obtained from a torque measurement value obtained by measuring the torque of the output shaft of the engine with a torque sensor, and a rotation speed measurement value obtained by measuring the rotation speed of the output shaft of the engine with a rotation speed sensor. The engine control method according to any one of claims 1 to 6, wherein the output value is an output value.   2. The advance angle of the timing at which the intake valve closes is set from an advance angle value set as a parameter using data of outputs and rotational speeds of a plurality of output shafts measured in advance. 8. The method for controlling an engine according to any one of claims 1 to 7. An engine system having a four-stroke engine using gas as fuel,
A control unit for advancing the timing of closing the intake valve of the engine when the output of the output shaft of the engine increases, and for advancing the valve opening timing of the fuel gas supply valve in response to a change in the advance angle; When,
A variable intake valve timing mechanism that changes the timing at which the intake valve closes according to the timing at which the intake valve closes set at the control unit;
A fuel gas supply valve timing mechanism for advancing the valve opening timing of the fuel gas supply valve in response to a change in the advance angle of the intake valve set by the control unit,
An engine system according to claim 1, wherein the variable intake valve timing mechanism controls the compression ratio of a gas-air mixture in the engine to be further reduced as the output of the output shaft of the engine increases. The engine system according to claim 9, wherein:
A torque sensor for measuring the torque of the output shaft of the engine,
A rotation speed sensor that measures the rotation speed of the output shaft of the engine,
An engine system wherein an output of the output shaft is obtained from a torque measurement value obtained by the torque sensor and a rotation speed measurement value obtained by the rotation speed sensor, and a change in the closing timing of the intake valve in the control unit is set. The engine system according to claim 9, wherein:
The closing timing of the fuel gas supply valve,
A gas supply time calculation unit that calculates a valve opening period based on a deviation between the target rotation speed and the actual rotation speed,
An engine system set by a gas supply valve control unit for instructing a timing of closing the fuel gas by the fuel gas supply valve based on the valve opening period. An engine system according to any one of claims 9 to 11, wherein:
An engine system configured to increase the supply pressure of the fuel gas in accordance with the advance of the timing at which the intake valve closes. The engine system according to any one of claims 9 to 12, wherein
An engine system for advancing the ignition timing of the engine with the advance of the timing at which the intake valve closes. An engine system according to any one of claims 9 to 13, wherein
The advance of the ignition timing of the engine accompanying the advance of the timing at which the intake valve closes is a boundary between the torque rich region and the torque poor region in which the output value and the rotation speed of the engine measured in advance are set as parameters. An engine system having a peak of a cubic characteristic line and reducing an advance angle in the torque rich region.

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