JP2004278339A - High compression ratio engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system capable of rationally treating a variable function of a real compression ratio and a variable function of a swirl ratio with the same device to realize premixed combustion which is excellent in exhaust gas characteristics in a high compression ratio engine equipped with a means for controlling a fuel injection timing in order to carry out premixed combustion. <P>SOLUTION: There is provided with a swirl port 26b, an intake valve 25b to open and close it for each cylinder, a straight port 26a and a suction valve 25a to open and close it. There is provided with a variable valve lift mechanism (hydraulic cylinders 30a and 30b and a flow regulating valve) to open and close the intake valves 25a and 25b individually and a means (ECU 15) to control a lift and the opening and closing timing of the suction valves so as to increase the swirl ratio and lower the real compression ratio targeting the variable valve lift mechanism of the intake valves 25a and 25b at the time of premixed combustion. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in a high compression ratio engine represented by a diesel engine.
[0002]
[Prior art]
In a diesel engine, fuel injection is performed in the vicinity of the top dead center (TDC) of the compression stroke, and combustion is started almost simultaneously with fuel injection. In order to reduce the amount of fuel, there is disclosed a device including means for controlling the fuel injection timing for premix combustion and means for controlling the closing timing of the intake valve so as to lower the actual compression ratio (effective compression ratio). (See Patent Documents 1 and 2).
[0003]
[Patent Document 1]
JP 2000-130200 A [Patent Document 2]
JP-A-8-254134
[Problems to be solved by the invention]
In FIG. 9, when the fuel injection timing of the normal combustion (1) (diffusion combustion) is controlled as (2) or (3), the premixing period (ignition delay period) before the end of fuel injection to compression ignition is started. ) Is given, during which fuel and air are mixed. However, in the case of (2), fuel noise (knocking) is likely to occur due to early ignition. In the case of (3), the combustion period is greatly delayed from near the top dead center of the compression stroke, so that the thermal efficiency is reduced. In both (2) and (3), the amount of unburned fuel tends to increase, and fuel efficiency is poor.
[0005]
Therefore, if the in-cylinder temperature is lowered by lowering the compression ratio, the combustion period of (2) can be made close to the top dead center of the compression stroke while securing the premixing period θmix as shown in (4). become. If the compression ratio is set low by changing the piston, etc., the output cannot be ensured.Therefore, in order to perform the Miller cycle operation, a variable valve timing mechanism is provided, and the actual compression ratio is controlled by controlling the closing timing of the intake valve. Lower it. Further, in order to optimize the swirl in order to reduce the amount of unburned fuel, a swirl ratio variable mechanism may be assembled to the intake port or the intake manifold.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide a system capable of rationally processing a variable function of an actual compression ratio and a variable function of a swirl ratio with the same device in order to realize premixed combustion with good exhaust characteristics.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a high compression ratio engine including a means for controlling fuel injection timing for premix combustion, a swirl port for each cylinder and an intake valve for opening and closing the same, and a straight port and an intake valve for opening and closing the same. The variable valve lift mechanism that opens and closes these intake valves individually, and the intake valve lift mechanism that increases the swirl ratio and lowers the actual compression ratio for the variable valve lift mechanism of each intake valve during premix combustion. Means for controlling the amount and the valve closing timing.
[0008]
A second invention provides a high compression ratio engine including an EGR device that recirculates a part of exhaust gas to an intake system and a unit that controls a fuel injection timing to perform premix combustion. In addition to providing an intake valve that opens and closes, a straight port and an intake valve that opens and closes it, a variable valve lift mechanism that opens and closes these intake valves individually, and a variable valve lift mechanism for each intake valve during premix combustion. It is characterized by comprising means for controlling the lift amount and the valve closing timing of the intake valve so as to increase the swirl ratio and decrease the actual compression ratio, and means for controlling so as to increase the EGR rate during premix combustion.
[0009]
According to a third aspect of the present invention, a high-compression system includes a variable nozzle turbocharger that supercharges intake air, an EGR device that recirculates part of exhaust gas to an intake system, and a unit that controls a fuel injection timing to perform premix combustion. In a specific engine, a swirl port for each cylinder and an intake valve for opening and closing the same, and a straight port and an intake valve for opening and closing the same are provided, while a variable valve lift mechanism for individually opening and closing these intake valves, and a premix combustion. Means for controlling the lift amount and closing timing of the intake valve so as to increase the swirl ratio and decrease the actual compression ratio for the variable valve lift mechanism of each intake valve, and a turbine for increasing the EGR amount during premix combustion. Means for controlling the variable nozzle so that the inlet pressure of the compressor is higher than the outlet pressure of the compressor. That.
[0010]
According to a fourth aspect of the present invention, there is provided a high-compression system including a variable nozzle turbocharger for supercharging intake air, an EGR device for recirculating a part of exhaust gas to an intake system, and means for controlling a fuel injection timing for premix combustion. In a specific engine, a swirl port for each cylinder and an intake valve for opening and closing the same, and a straight port and an intake valve for opening and closing the same are provided, while a variable valve lift mechanism for individually opening and closing these intake valves, and a premix combustion. Means for controlling the lift amount and closing timing of the intake valve so as to increase the swirl ratio and decrease the actual compression ratio for the variable valve lift mechanism of each intake valve, an intercooler for cooling the supercharged air, and an EGR gas. Cooler that cools the turbine and the compressor inlet pressure to increase the EGR amount during premix combustion. Means for controlling the variable nozzle so remote higher, characterized in that it comprises a.
[0011]
According to a fifth aspect, in the high compression ratio engine according to any one of the first to fourth aspects, the swirl port is set to a helical type intake port, and the straight port is set to a tangential type intake port. It is characterized by.
[0012]
【The invention's effect】
In the first invention to the fifth invention, when the fuel injection timing is controlled so as to perform the premix combustion, a premix period is given before the end of the fuel injection to the compression ignition, and the fuel and the air are mixed. An air-fuel mixture is generated. While the swirl ratio is increased and the mixing of fuel and air is promoted, the actual compression ratio is reduced and the in-cylinder temperature is reduced. As a result, the combustion period is brought close to the top dead center of the compression stroke while securing the premixing period, so that the amount of unburned fuel and the soot and NOx can be sufficiently reduced.
[0013]
In this case, two controls of the swirl ratio and the actual compression ratio can be rationally processed by the same device (variable valve lift mechanism). That is, it is not necessary to provide a different device for each control, the configuration of the system is simplified, and a reduction in cost can be promoted.
[0014]
In the second aspect of the present invention, by increasing the EGR rate, the combustion temperature can be reduced and NOx can be reduced. In addition, by lowering the actual compression ratio and optimizing the swirl, the pre-combustion before the end of fuel injection to compression ignition can be achieved. The mixing period can be increased, and the reduction of the amount of unburned fuel is promoted.
[0015]
In the third aspect of the present invention, the control of the variable nozzle compensates for an increase in the amount of EGR, so that the premixing period from the end of the fuel injection to the compression ignition can be reliably obtained, realizing the premixed combustion and the exhaust gas. Can be reduced.
[0016]
In the fourth aspect, the intercooler and the EGR cooler ensure that the actual compression ratio decreases, and the increase in the EGR amount can also prevent the in-cylinder temperature from increasing. When the fuel injection timing is controlled to perform premix combustion, the devices are also controlled at the same time, the swirl ratio is increased, the actual compression ratio is reduced, the effects of EGR and supercharging are utilized, and good exhaust characteristics are obtained. Mixed combustion can be realized.
[0017]
In the fifth aspect of the invention, the combination of the helical intake port and the tangential intake port makes it easy to set a layout in which the intake ports are not complicated.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
In FIG. 1, reference numeral 10 denotes an engine, which controls a fuel injection device 11, a system 12 for controlling a swirl ratio and an actual compression ratio, an EGR device 13, a variable nozzle type turbocharger 14, and these devices in accordance with an operation state. And a control unit 15 (ECU) for performing control.
[0019]
In the case of FIG. 2, the fuel injection device 11 employs a common rail system. A fuel injection valve 20 (injector) is arranged for each cylinder. The injector 20 is connected to a common rail 21 (pressure accumulator), and injects high-pressure fuel stored in the common rail 21 to the combustion chamber 10a under the control of the ECU. Reference numeral 22 denotes a high-pressure pump that supplies high-pressure fuel to the common rail 21, and includes a low-pressure pump (feed pump) that supplies fuel from a fuel tank to the high-pressure pump 22 (not shown).
[0020]
In the system 12 for controlling the swirl ratio and the actual compression ratio, two intake valves 25a and 25b are arranged for each cylinder. As shown in FIG. 3, the intake port 26 is divided into two systems. One of the two systems is formed as a tangential straight port 26a, and the other is formed as a helical swirl port 26b. Reference numeral 28 denotes an exhaust port, the upstream side of which is formed at a branch portion to two exhaust valves 29a and 29b (driven by a cam-type valve operating mechanism), which are connected downstream to a junction.
[0021]
Each intake valve 25a, 25b is provided with a variable valve lift mechanism. In the case of FIG. 2, the variable valve lift mechanism is of a hydraulic type. Reference numerals 30a and 30b denote hydraulic cylinders 30a and 30b connected to the intake valves 26a and 26b, each of which is provided with a flow control valve (not shown) for supplying and discharging an operating pressure to each of the hydraulic cylinders 30a and 30b. When the hydraulic cylinders 30a and 30b receive the hydraulic pressure (operating pressure) from the flow control valves, the hydraulic cylinders 30a and 30b open the intake valves 25a and 25b to the lift amount corresponding to the supply amount, and release (discharge) the supply pressure from the flow control valves. ) Is pressed by the urging force of the valve spring to close the intake valves 25a and 25b.
[0022]
FIG. 4 illustrates the relationship between the swirl ratio and the lift of the intake valves 25a and 25b. The swirl increases as the lift of the intake valve 25a decreases and the lift of the intake valve 25b relatively increases. The ratio is controlled to be high and vice versa. Regarding the valve closing timing of the intake valves 25a and 25b, in FIG. 6, the best point of the charging efficiency is "normally closed". Is controlled.
[0023]
The EGR device 13 includes an EGR passage 34 that communicates between an intake system and an exhaust system, an EGR valve 35 that controls an EGR rate, an EGR cooler 36 that cools EGR gas, and an opening degree of the EGR valve 35 according to a command from the ECU 15. (Not shown). The variable nozzle type turbocharger 14 includes a turbine and a compressor, and is provided with an actuator (not shown) for adjusting a variable nozzle of the turbine to an opening degree according to a command from the ECU 15. An intercooler (not shown) for cooling the supercharged air is provided downstream of the variable nozzle type turbocharger 14.
[0024]
The ECU 15 stores a map (see FIG. 7) for setting an operation region for premixed combustion and an operation region for normal combustion, a map for controlling premixed combustion, and a map for controlling normal combustion. In order to detect an operation state, a crank angle sensor 16 for detecting a crank angle (also serving as an engine rotation sensor for detecting an engine rotation speed) and an accelerator opening sensor 17 for detecting an engine load are provided. In the map of FIG. 7, the high-speed high-load region is set to the normal combustion operation region, and the other region is set to the premixed combustion operation region.
[0025]
FIG. 8 is a flowchart for explaining the control contents of the ECU 15. In S1, a detection signal of the crank angle sensor 16 and a detection signal of the accelerator opening sensor 17 are read. In S2, based on these detection signals, it is determined from the map of FIG. 7 whether or not the engine is in the premix combustion operation region. If the determination in S2 is yes, the process proceeds to S3, and control based on a map of premixed combustion is selected. When the determination in S2 is no, the process proceeds to S4, and the control based on the map of the normal combustion is selected.
[0026]
In the case of control based on the premix combustion map, the injector 20 of the fuel injection device 11 is controlled so as to add a predetermined advance angle to the fuel injection timing. The lift amounts of the intake valves 25a and 25b are controlled based on the swirl port 26b side being fully open and the straight port 26a side being half open (see FIG. 5). The closing timing of the intake valves 25a, 25b is controlled based on "early closing" or "late closing" in FIG. 6 in order to lower the actual compression ratio.
[0027]
By the advance of the fuel injection timing, a premixing period θmix (see FIG. 9) is given before the end of the fuel injection to the compression ignition, and an air-fuel mixture of fuel and air is generated. While the swirl ratio is increased and the mixing of fuel and air is promoted, the actual compression ratio is reduced and the in-cylinder temperature is reduced. As a result, the combustion period is brought close to the top dead center of the compression stroke while securing the premixing period, so that the amount of unburned fuel and the soot and NOx can be sufficiently reduced.
[0028]
The EGR valve 35 is controlled to increase the EGR rate, and the variable nozzle of the turbocharger 14 is controlled so that the inlet pressure of the turbine is higher than the outlet pressure of the compressor. The high EGR rate lowers the combustion temperature and reduces NOx. In addition, the premixing period θmix from the end of fuel injection to the start of compression ignition can be obtained, and the control of the variable nozzle compensates for the increase in the EGR amount. Thus, the reduction of the amount of unburned fuel is greatly promoted. The supercooled air is cooled by the intercooler, the EGR gas is cooled by the EGR cooler 36, and an increase in the in-cylinder temperature due to an increase in the EGR amount can be avoided.
[0029]
When the fuel injection timing is controlled to perform the premixing in this manner, the swirl ratio is increased, the actual compression ratio is reduced, the EGR amount is increased, and the intercooler and the EGR cooler 36 make use of the effects of EGR and supercharging. Therefore, in the operation region except the high-speed high-load region, the premixed combustion with good exhaust characteristics can be realized.
[0030]
In the case of the control based on the map of the normal combustion, the fuel injection timing of the injector 20 is controlled near the top dead center of the compression stroke. The lift amounts of the intake valves 25a and 25b are controlled based on the half-open state on the swirl port 26b side and the fully open state on the straight port 26a side (see FIG. 5). The closing timing of the intake valves 25a, 25b is controlled based on "normal closing" in FIG. The EGR valve 35 is controlled to a predetermined low EGR rate, and the EGR amount compensation control using the variable nozzle is not actively performed.
[0031]
When fuel injection is started near the top dead center of the compression stroke, compression ignition occurs before the end of fuel injection, and the combustion mode is mainly diffusion combustion, and the actual compression ratio is not lowered and is maintained at a high compression ratio. Therefore, sufficient fuel efficiency and output can be ensured. This normal combustion is performed in a high-speed, high-load operation range, so that low-temperature startability can be improved.
[0032]
In the system 12, since the variable valve lift mechanisms of the intake valves 25a and 25b are controlled by the ECU 15, the two controls of the swirl ratio and the actual compression ratio can be rationally processed. That is, it is not necessary to provide a different device for each control, the configuration of the system is simplified, and a reduction in cost can be promoted. Variation of the swirl ratio also depends on the lift amount of the intake valves 25a and 25b, and since there is no special variable means inside the intake port or the intake manifold (intake passage), it is possible to control responsively and accurately.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.
FIG. 2 is a partial configuration diagram of the same.
FIG. 3 is a schematic diagram illustrating a configuration of an intake port.
FIG. 4 is a characteristic diagram of a valve lift according to the swirl ratio control.
FIG. 5 is an explanatory diagram relating to control of a swirl ratio.
FIG. 6 is a characteristic diagram of valve timing related to control of the actual compression ratio.
FIG. 7 is a map for explaining setting of a premixed combustion region and a normal combustion region.
FIG. 8 is a flowchart illustrating control contents of a control unit.
FIG. 9 is an explanatory diagram relating to a normal combustion state and a premixed combustion state.
[Explanation of symbols]
Reference Signs List 10 engine 11 fuel injection device 12 variable system of swirl ratio & actual compression ratio 13 EGR device 14 variable nozzle type turbocharger 15 control unit (ECU)
25a, 25b Intake valve 26a Straight port 26b Swirl port 30a, 30b Hydraulic cylinder

Claims (5)

In a high compression ratio engine provided with a means for controlling fuel injection timing for premix combustion, a swirl port and an intake valve for opening and closing the same, and a straight port and an intake valve for opening and closing the same are provided for each cylinder. For the variable valve lift mechanism that opens and closes the intake valves individually, and for the variable valve lift mechanism of each intake valve during premixed combustion, the lift amount and closing timing of the intake valve are increased so that the swirl ratio is increased and the actual compression ratio is reduced. Controlling means for controlling the high compression ratio. In a high compression ratio engine including an EGR device that recirculates a part of exhaust gas to an intake system and a unit that controls fuel injection timing for premix combustion, a swirl port for each cylinder and an intake valve that opens and closes the swirl port, While providing a straight port and an intake valve that opens and closes the straight port, the swirl ratio is increased and increased for the variable valve lift mechanism that individually opens and closes these intake valves and the variable valve lift mechanism of each intake valve during premix combustion. A high compression ratio engine comprising: means for controlling a lift amount and a valve closing timing of an intake valve so as to reduce a compression ratio; and means for controlling so as to increase an EGR rate during premix combustion. In a high compression ratio engine including a variable nozzle turbocharger for supercharging intake air, an EGR device for recirculating a part of exhaust gas to an intake system, and means for controlling fuel injection timing for premix combustion, A swirl port and an intake valve for opening and closing the same, and a straight port and an intake valve for opening and closing the straight port.A variable valve lift mechanism for individually opening and closing these intake valves, and a variable valve mechanism for each intake valve during premix combustion. Means for controlling the lift amount and closing timing of the intake valve so as to increase the swirl ratio and lower the actual compression ratio for the valve lift mechanism, and increase the turbine inlet pressure of the compressor to increase the EGR amount during premix combustion. Means for controlling the variable nozzle so as to be higher than the outlet pressure. Jin. In a high compression ratio engine comprising a variable nozzle turbocharger for supercharging intake air, an EGR device for recirculating a part of exhaust gas to an intake system, and a means for controlling fuel injection timing for premix combustion, A swirl port and an intake valve for opening and closing the same, and a straight port and an intake valve for opening and closing the straight port.A variable valve lift mechanism for individually opening and closing these intake valves, and a variable valve mechanism for each intake valve during premix combustion. Means for controlling the lift amount and closing timing of the intake valve so as to increase the swirl ratio and lower the actual compression ratio for the valve lift mechanism; an intercooler for cooling the supercharged air; and an EGR cooler for cooling the EGR gas. In order to increase the amount of EGR during premixed combustion, the inlet pressure of the turbine becomes higher than the outlet pressure of the compressor High compression ratio engine characterized in that it comprises means for controlling the urchin variable nozzle, the. The high compression ratio engine according to any one of claims 1 to 4, wherein the swirl port is set to a helical type intake port, and the straight port is set to a tangential type intake port.

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