JP4168766B2 - Engine capable of compression ignition operation - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an engine capable of compression self-ignition operation.
[0002]
[Prior art]
Gasoline engines usually use spark plugs to perform spark ignition operation, but in recent years, a combustion system that causes the gasoline engine to self-ignite an air-fuel mixture (also called a “premixed self-ignition combustion system”) Is being considered. In this self-ignition combustion method, for example, gasoline is premixed with intake air, and self-ignition is performed by compression. The use of such self-ignition combustion has the advantage that the fuel efficiency is improved and the amount of air pollutants (especially NOx) can be greatly reduced.
[0003]
As an engine starting method capable of such compression self-ignition operation, the one described in Patent Document 1 is known. In the method of Patent Document 1, the ignition plug is ignited for several cycles at the start of the engine, and after confirming that the ignition has been ignited, the compression self-ignition operation is started. In the present specification, “starting the engine” means starting up and down movement of the piston.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-303957
[Problems to be solved by the invention]
However, the method of Patent Document 1 has a problem that unburned fuel may be discharged from the exhaust pipe to the outside during several cycles until ignition.
[0006]
The present invention has been made to solve the above-described conventional problems, and can prevent unburned fuel from being discharged from the exhaust pipe to the outside when starting an engine capable of performing compression ignition operation. The purpose is to provide technology.
[0007]
[Means for solving the problems and their functions and effects]
In order to achieve at least a part of the above object, an engine of the present invention is an engine capable of compression ignition operation,
A combustion chamber composed of a cylinder and a piston;
A fuel injection valve for directly injecting fuel into the combustion chamber;
A spark plug provided in the combustion chamber;
An intake valve and an exhaust valve provided in the combustion chamber;
First and second valve drive mechanisms capable of switching whether to open and close the intake valve and the exhaust valve;
A sensor for detecting whether combustion is occurring in the combustion chamber;
A control unit for controlling the fuel injection valve, the spark plug, and the first and second valve drive mechanisms;
With
The control unit keeps the intake valve and the exhaust valve in a closed state after fuel is injected into the combustion chamber at least once at the start of the engine, and ignites the spark plug in each cycle, There is a start mode in which opening and closing operations of the intake valve and the exhaust valve are started after combustion is detected by the sensor.
[0008]
In this engine, after the fuel is injected at the time of starting, the intake valve and the exhaust valve are kept closed until ignition occurs. It is possible to prevent the fuel from being discharged to the outside.
[0009]
The controller opens the intake valve immediately after starting the engine and opens the intake valve to introduce fresh air into the combustion chamber, and then closes the intake valve and the exhaust valve. You may make it keep.
[0010]
According to this configuration, since fresh air can be introduced into the combustion chamber at the time of starting, the starting can be facilitated.
[0011]
The control unit may open the exhaust valve immediately before starting the engine and before the opening timing of the intake valve.
[0012]
According to this configuration, the gas remaining in the combustion chamber during the stop can be discharged, so that fresh air can be sufficiently introduced into the combustion chamber, and the starting can be facilitated.
[0013]
The controller may inject fuel from the fuel injection valve in each cycle before combustion is detected by the sensor.
[0014]
According to this configuration, since a relatively small amount of fuel is injected in each cycle, it is easy to vaporize and mix the fuel in the combustion chamber.
[0015]
Note that the amount of fuel injected into the combustion chamber in each cycle before the combustion is detected by the sensor is preferably set to an amount that allows the engine to perform a compression auto-ignition operation.
[0016]
According to this configuration, it is possible to smoothly shift to the compression self-ignition operation after ignition at start-up.
[0017]
In the first fuel injection after the engine is started, the control unit causes the fuel injection valve to inject two or more fuels to be injected in each cycle after combustion is detected by the sensor, After the first fuel injection, fuel injection by the fuel injection valve may not be performed until combustion is detected by the sensor.
[0018]
According to this configuration, after a relatively large amount of fuel is injected first, the fuel in the combustion chamber is vaporized and mixed to achieve a concentration capable of propagating flame as the cycle progresses, so it is easier to start by spark ignition. become.
[0019]
As the sensor, either a sensor for detecting the pressure in the combustion chamber or a sensor for detecting the rotational speed of the engine can be employed.
[0020]
According to this configuration, it is possible to determine whether or not combustion has occurred in the combustion chamber according to a change in pressure in the combustion chamber or a change in rotational speed.
[0021]
The present invention can be realized in various modes. For example, an engine, an engine control method or device, a computer program for realizing the function of the method or device, and the computer program are recorded. It can be realized in the form of a recording medium or the like.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
A. First embodiment:
Next, embodiments of the present invention will be described based on examples. FIG. 1 is an explanatory view conceptually showing the structure of a gasoline engine 100 as a first embodiment of the present invention. FIG. 1 shows the structure of the combustion chamber when a cross section is taken at the center of the combustion chamber of the gasoline engine 100.
[0023]
The combustion chamber of the gasoline engine 100 includes a hollow cylindrical cylinder 142 provided in the cylinder block 140, a piston 144 that slides up and down in the cylinder 142, and a cylinder head 130 provided on the cylinder block 140. Is formed by. A cylindrical body constituted by both the cylinder block 140 and the cylinder head 130 is called a “cylinder” in a broad sense. Each combustion chamber is provided with an in-cylinder pressure sensor 36 (also referred to as “combustion pressure sensor”) for measuring the internal pressure (also referred to as “in-cylinder pressure”) of the combustion chamber.
[0024]
The cylinder head 130 includes an intake valve 132 that opens and closes an opening of an intake port through which intake air flows, an exhaust valve 134 that opens and closes an opening of an exhaust port through which exhaust gas flows out, a spark plug 136, and a combustion chamber. A fuel injection valve 14 for injecting fuel spray is provided. The intake valve 132 and the exhaust valve 134 are driven by electric actuators 162 and 164, respectively. The electric actuators 162 and 164 can open and close the respective intake valves 132 and exhaust valves 134 at an arbitrary timing. Note that the intake valve 132 and the exhaust valve 134 may be driven by a hydraulic actuator or a cam mechanism instead of the electric actuator. However, as a drive mechanism for these valves 132 and 134, a mechanism having a function of switching whether or not to perform the valve opening / closing operation is used.
[0025]
An intake passage 12 that guides intake air is connected to the intake port, and an exhaust passage 16 through which exhaust gas passes is connected to the exhaust port. A catalyst 26 for purifying air pollutants contained in the exhaust gas and a turbine 52 of the supercharger 50 are provided downstream of the exhaust passage 16. Exhaust gas passing through the exhaust passage 16 is released into the atmosphere after rotating the turbine 52. The intake passage 12 is provided with a compressor 54 for the supercharger 50. The compressor 54 is connected to the turbine 52 via a shaft 56, and the compressor 54 also rotates when the turbine 52 rotates by the exhaust gas. As a result, the compressor 54 pressurizes the air sucked from the air cleaner 20 and then pumps it toward the intake port.
[0026]
Since air temperature rises when pressurized by the compressor 54, an intercooler 62 is provided downstream of the compressor 54 in order to cool the intake air. A surge tank 60 and a throttle valve 22 are also provided in the intake passage 12. The surge tank 60 has a function of relaxing pressure waves generated when the combustion chamber sucks air, and the throttle valve 22 is set to an appropriate opening degree by the electric actuator 24 to adjust the intake air amount. It has a function to do.
[0027]
The piston 144 is connected to a crankshaft 148 via a connecting rod 146, and a crank angle sensor 32 that detects a crank angle is attached to the crankshaft 148.
[0028]
The operation of the gasoline engine 100 is controlled by an engine control unit (hereinafter referred to as ECU) 30. The ECU 30 detects the engine rotational speed Ne and the accelerator opening degree θac, and executes control of the opening degree of the throttle valve 22, ignition timing control of the spark plug 136, and control of the fuel injection valve 14 based on these. The engine speed Ne is detected by the crank angle sensor 32, and the accelerator opening degree θac is detected by an accelerator opening sensor 34 built in the accelerator pedal.
[0029]
The ECU 30 has a function of determining whether combustion is occurring in each combustion chamber from a change in the internal pressure of each combustion chamber measured by the in-cylinder pressure sensor 36. The engine 100 can be switched between two-cycle operation and four-cycle operation by adjusting valve timing, fuel injection timing, and the like.
[0030]
FIG. 2 is an explanatory diagram showing a method of starting the engine in the first embodiment. Here, regarding the six cycles after the driver operates the ignition key to start engine 100, the amount of air and burned gas in the cylinder, the amount of fuel in the cylinder, the intake valve 132 and the exhaust valve The presence / absence of the opening / closing operation 134 and the presence / absence of ignition of the spark plug 136 are shown. In this example, four-cycle operation is performed, and one cycle is configured with a crank angle of 720 °. Note that the amounts of air, burned gas, and fuel are not accurate and are simplified for convenience of explanation.
[0031]
In the first cycle immediately after the engine 100 is started, the intake valve 132 is opened, new air is supplied into the cylinder, and fuel is injected from the fuel injection valve 14. However, the exhaust valve 134 remains closed. The amount of fuel injected in one cycle is preferably set to an amount that allows the compression ignition operation. In the first cycle, the spark plug 136 is ignited, but the air-fuel mixture in the cylinder is not ignited. This is because the temperature of the cylinder is low at the start, and the fuel in the cylinder is not sufficiently mixed with air.
[0032]
In the second cycle, the intake valve 132 and the exhaust valve 134 are kept closed, and fuel is injected from the fuel injection valve 14. In this embodiment, the amount of fuel injected in each cycle is assumed to be the same, but instead, the fuel injection amount in the first cycle may be set slightly higher than the injection amount in the second and subsequent cycles. Good.
[0033]
In the cylinder of the second cycle, air supplied in the first cycle and fuel for two cycles are accommodated. In this example, the air-fuel mixture is not ignited even when the ignition plug 136 is ignited in the second cycle. Similarly, in the third cycle and the fourth cycle, the intake valve 132 and the exhaust valve 134 are kept closed, and additional fuel is injected from the fuel injection valve 14. Therefore, the fuel in the cylinder gradually increases as the cycle proceeds. Further, since the air-fuel mixture in the cylinder is compressed and expanded in each cycle, the fuel premixing and the temperature rise tend to gradually become easier to burn. In the example of FIG. 2, in the fourth cycle, the air-fuel mixture is ignited according to the ignition of the spark plug 136.
[0034]
The ECU 30 detects that combustion has occurred in the cylinder according to the output signal of the in-cylinder pressure sensor 36, and starts the operation of the exhaust valve 134 and the intake valve 132 in response to this detection. Therefore, after the exhaust operation in the fourth cycle in which ignition has occurred, the intake valve 132 and the exhaust valve 134 each perform an opening / closing operation. The valve timing at this time is preferably set so that the valve opening periods of the intake valve 132 and the exhaust valve 134 do not overlap (that is, have a so-called “negative overlap”). By doing so, a considerable amount of burned gas (internal EGR gas) can be left in the cylinder. The burned gas increases the average temperature of the air-fuel mixture in the cylinder, and thus has the effect of easily generating self-ignition combustion. In the fifth cycle of FIG. 2, newly supplied air, burned gas, and newly supplied fuel are accommodated in the cylinder.
[0035]
In cycles after ignition, valve timing and fuel injection suitable for self-ignition operation are performed for each cycle, and self-ignition operation is executed. In the present embodiment, since the fuel injection amount of each cycle before ignition is set to an amount suitable for the self-ignition operation, it is possible to smoothly shift to the self-ignition operation after ignition.
[0036]
In the cycle after the self-ignition operation has started, the ignition plug 136 may be ignited to prevent misfire more reliably. However, since the ignition timing in this case is for ignition when self-ignition does not occur, it is retarded from the ignition timing of normal spark ignition operation (about 10 ° advance side from the top dead center). It is preferable to set the timing on the side.
[0037]
As described above, in the example of FIG. 2, after the intake valve 132 is opened in the first cycle after the start, both the intake valve 132 and the exhaust valve 134 are kept closed. However, it is possible to prevent unburned fuel from being discharged out of the combustion chamber.
[0038]
FIG. 3 is an explanatory diagram showing a method of starting the engine in two-cycle operation. The main difference from FIG. 2 is the opening timing of the intake valve 132 and the exhaust valve 134. As is well known, in the two-cycle operation, the intake valve 132 and the exhaust valve 134 are both opened in the middle of one cycle, and so-called scavenging is performed.
[0039]
Also in the example of FIG. 3, the intake valve 132 is opened at the opening timing of the first intake valve 132 after the start, and new intake air is supplied into the cylinder. In each cycle, fuel injection and ignition by the spark plug 136 are performed, but the intake valve 132 and the exhaust valve 134 remain closed. Further, the amount of fuel injected in one cycle is set to an amount that allows the engine 100 to perform the compression ignition operation. When the air-fuel mixture is ignited, the self-ignition operation is executed in the subsequent cycles.
[0040]
As described above, when the two-cycle operation is performed, the intake valve 132 and the exhaust valve 134 are both closed after the intake valve 132 is opened in the first cycle after the start, as in the case of the four-cycle operation. By keeping, unburned fuel can be prevented from being discharged out of the combustion chamber when ignition is not performed at the time of starting.
[0041]
B. Second embodiment:
FIG. 4 is an explanatory view showing an engine starting method (two-cycle operation) in the second embodiment. The only difference from FIG. 3 is that the exhaust valve 134 is opened in the first cycle after starting, and the other points are the same as FIG.
[0042]
In this way, if the exhaust valve 134 is opened in the first cycle, the gas remaining in the cylinder during the stop can be discharged, and a larger amount of new air can be introduced into the cylinder. As a result, there is an effect that starting can be performed more easily. In addition, also when performing 4 cycle operation at the time of starting, it is preferable to open the exhaust valve 134 before the valve opening timing of the intake valve 132 similarly to the case of 2 cycle operation.
[0043]
C. Third embodiment:
FIG. 5 is an explanatory diagram showing an engine starting method (two-cycle operation) in the third embodiment. The only difference from FIG. 3 is that the fuel for four cycles is injected in the first cycle after the start, and the fuel injection is not performed after the second cycle until ignition occurs. Are the same.
[0044]
Injecting multiple cycles of fuel in the first cycle does not ignite because the fuel is not sufficiently vaporized / mixed at the beginning. Therefore, ignition is performed in response to ignition of the spark plug 136. In general, injecting fuel for two cycles or more in the first cycle is preferable in that the subsequent vaporization and mixing of the fuel may be accelerated.
[0045]
However, depending on the injection characteristics of the fuel injection valve 14, if an excessively large amount of fuel is injected in one cycle, the fuel is not injected in a sufficiently sprayed state, so that the fuel vaporization / mixing may be delayed. When such a fuel injection valve 14 is used, it is preferable to inject fuel in each cycle as in the example of FIG.
[0046]
Similarly, in the 4-cycle operation, fuel for two cycles or more may be injected in the first cycle. In the third embodiment, the exhaust valve 134 may be opened at a timing before the intake valve 132 is opened in the first cycle, as in the second embodiment of FIG.
[0047]
D. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.
[0048]
D1. Modification 1:
As a sensor for detecting whether or not combustion is occurring in the combustion chamber, other types of sensors other than the in-cylinder pressure sensor may be used. For example, when combustion occurs, the engine speed increases. Therefore, it is also possible to detect whether combustion is occurring in the combustion chamber according to whether the engine speed has increased by using a rotation speed sensor that detects the engine speed.
[0049]
D2. Modification 2:
In the above embodiment, the engine capable of switching between 2-cycle operation and 4-cycle operation has been described. However, the present invention can also be applied to an engine that performs only 2-cycle operation or an engine that performs only 4-cycle operation. is there.
[0050]
D3. Modification 3:
In the above embodiment, the same start method is adopted for each cylinder of the multi-cylinder engine. However, the start method of the above embodiment is adopted only for some cylinders of the multi-cylinder engine, and for other cylinders. The intake valve and the exhaust valve may be opened and closed before ignition. However, if the starting method of the above embodiment is applied to all the cylinders, there is an advantage that the amount of unburned fuel discharged from each combustion chamber to the outside can be further reduced.
[0051]
D4. Modification 4:
As can be understood from the first to third embodiments described above, in the present invention, after the fuel is injected into the combustion chamber at least once at the start of the engine, the intake valve and the exhaust valve are kept closed, and It is preferable to have a start mode in which the ignition plug is ignited in the cycle and the opening and closing operations of the intake valve and the exhaust valve are started after combustion is detected by the sensor. By adopting such a start mode, it is possible to prevent unburned fuel from being discharged from the exhaust pipe to the outside when the engine is started.
[0052]
However, the ECU (control unit) of the engine may have other start modes. For example, when the cylinder temperature is sufficiently high, the opening / closing operation of the intake valve 132 and the exhaust valve 134 may be started from the first cycle. In addition, since compression auto-ignition is particularly difficult at low temperature start, the effect of preventing discharge of unburned fuel is remarkable by adopting the start method as in the above-described embodiment.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram conceptually showing the structure of a gasoline engine 100 as a first embodiment of the present invention.
FIG. 2 is an explanatory diagram showing an engine starting method (four-cycle operation) in the first embodiment.
FIG. 3 is an explanatory view showing an engine starting method (two-cycle operation) in the first embodiment.
FIG. 4 is an explanatory diagram showing an engine starting method (two-cycle operation) in a second embodiment.
FIG. 5 is an explanatory diagram showing an engine starting method (two-cycle operation) in a third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 12 ... Intake passage 14 ... Fuel injection valve 16 ... Exhaust passage 20 ... Air cleaner 22 ... Throttle valve 24 ... Electric actuator 26 ... Catalyst 30 ... ECU
32 ... Crank angle sensor 34 ... Accelerator opening sensor 36 ... In-cylinder pressure sensor 50 ... Supercharger 52 ... Turbine 54 ... Compressor 56 ... Shaft 60 ... Surge tank 62 ... Intercooler 100 ... Gasoline engine 130 ... Cylinder head 132 ... Intake valve 134 ... Exhaust valve 136 ... Spark plug 140 ... Cylinder block 142 ... Cylinder 144 ... Piston 146 ... Connecting rod 148 ... Crankshaft 162, 164 ... Electric actuator

Claims (7)

An engine capable of compression ignition operation,
A combustion chamber composed of a cylinder and a piston;
A fuel injection valve for directly injecting fuel into the combustion chamber;
A spark plug provided in the combustion chamber;
An intake valve and an exhaust valve provided in the combustion chamber;
First and second valve drive mechanisms capable of switching whether to open and close the intake valve and the exhaust valve;
A sensor for detecting whether combustion is occurring in the combustion chamber;
A control unit for controlling the fuel injection valve, the spark plug, and the first and second valve drive mechanisms;
With
The control unit keeps the intake valve and the exhaust valve closed and ignites the spark plug in each cycle after fuel is injected into the combustion chamber at least once at the start of the engine, An engine having a start mode in which opening and closing operations of the intake valve and the exhaust valve are started after combustion is detected by a sensor. The engine according to claim 1,
The control unit opens the intake valve at a timing to open the intake valve immediately after starting the engine and introduces fresh air into the combustion chamber, and then keeps the intake valve and the exhaust valve closed. engine. The engine according to claim 2,
The engine, wherein the control unit opens the exhaust valve immediately before starting the engine and before the opening timing of the intake valve. The engine according to any one of claims 1 to 3,
The said control part is an engine which injects a fuel from the said fuel injection valve in each cycle before combustion is detected by the said sensor. The engine according to claim 4,
An engine in which the amount of fuel injected into the combustion chamber in each cycle before combustion is detected by the sensor is set to an amount that allows the engine to perform compression auto-ignition operation. The engine according to any one of claims 1 to 3,
In the first fuel injection after the engine is started, the control unit causes the fuel injection valve to inject two or more fuels to be injected in each cycle after combustion is detected by the sensor, An engine that does not perform fuel injection by the fuel injection valve after the first fuel injection until combustion is detected by the sensor. The engine according to any one of claims 1 to 6,
The engine is one of a sensor that detects a pressure in the combustion chamber and a sensor that detects a rotational speed of the engine.

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