JP3617252B2 - Compression ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a compression ignition engine.
[0002]
[Prior art]
In a normal compression ignition type engine typified by a diesel engine or the like, fuel is injected and combusted in the vicinity of the compression top dead center of a piston where the inside of the cylinder becomes high temperature and high pressure. The injected fuel then splits from the liquid column state into droplets, evaporates from the surface of the droplets to become a mixture, and the mixture is ignited to form a flame. By being supplied, combustion is continued.
[0003]
In such a normal diesel engine, immediately after fuel injection, a flame is formed in a state where the fuel (air mixture) is still unevenly distributed in the cylinder inner space. For example, in the case of a five-hole nozzle, flames are formed in five fuel injection regions, respectively. For this reason, local combustion temperature becomes high and NOx is generated. Further, since the subsequent injected fuel supplied into the flame is burned in a state where air is insufficient, smoke (soot) is generated.
[0004]
On the other hand, as shown in FIG. 6, fuel is injected at a relatively low pressure during the intake stroke or compression stroke of the engine from the single injection nozzle c provided with an umbrella-shaped fuel collision portion b at the tip of the needle valve a. There is known a compression ignition type engine in which fuel droplets d which are injected and formed at the time of injection are ignited and burned all at once at the compression top dead center of a piston (Japanese Patent Laid-Open No. Hei 7- No. 317588).
[0005]
According to this compression ignition type engine, since combustion can be performed in the entire area of the cylinder, the local combustion temperature can be lowered, generation of NOx is suppressed, and fuel is widely dispersed in the cylinder. And no new fuel is supplied during the flame, combustion in an air-deficient state can be avoided, and the occurrence of smoke can be suppressed.
[0006]
[Problems to be solved by the invention]
However, the compression ignition type engine keeps fuel droplets d having a relatively large particle diameter, which are injected during the intake stroke or during the compression stroke, up to the vicinity of the compression top dead center, and then boil / evaporate (ignition / combustion) there. As a result, the following problems arise.
[0007]
That is, the fuel droplets d gradually evaporate from the surface, but since the particle size is large, all of the fuel droplets d cannot evaporate by the start of combustion, and the fuel at the center of the droplet d is enveloped in the flame, and the air Smoke is generated due to insufficient combustion.
[0008]
Further, around the fuel droplet d, an air-fuel mixture is formed that is rich in the vicinity of the droplet d and becomes lean as it moves away from the droplet d. An air-fuel mixture having a high air excess ratio of about 1.1 to 1.2 is also formed, and the local combustion temperature cannot be lowered as expected, and NOx is generated.
[0009]
Further, the fuel droplets d having a large particle diameter easily fall in the cylinder due to their own weight and adhere to the top surface of the piston. When the droplet adheres to the top surface of the piston and forms a liquid film, the NOx and smoke Not only will the generation increase, it will also lead to the generation of unburned HC.
[0010]
An object of the present invention created in view of the above circumstances is to provide a compression ignition type engine capable of preventing the generation of smoke, NOx, and HC.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a compression ignition engine in which fuel and intake air injected from a fuel injection nozzle into a cylinder are compressed by a piston and ignited, and a plurality of small injection nozzles having a diameter of 0.1 mm or less. A fuel injection nozzle having a hole and a plurality of large injection holes having a diameter larger than the hole, and a control means for controlling fuel injection by the fuel injection nozzle, the control means is configured to perform the above-described operation during low load operation of the engine. A nozzle selection means that opens only the small nozzle hole and opens the large nozzle hole at high load operation , and a uniform air-fuel mixture in the cylinder until the piston reaches top dead center at low load operation. and forming the mixture so as to compression ignition in the compression top dead center near the injection timing also during the intake stroke of the engine is in the compression stroke, the injection timing for the compression top dead center near the engine at the time of high load operation When jetting And it has a changing means.
[0012]
According to the present invention, fuel injected from a plurality of small injection holes having a diameter of 0.1 mm or less during the intake stroke or compression stroke of the engine has a small particle size of fuel droplets formed at the time of injection. The steam is substantially vaporized immediately after the injection, and a lean and uniform air-fuel mixture is formed in the cylinder until the piston reaches the top dead center. Thereafter, when the piston reaches the vicinity of the top dead center, the inside of the cylinder becomes high temperature and high pressure, and therefore, the entire air-fuel mixture is ignited and burned (lean and uniform premixed combustion) almost simultaneously in almost the entire space in the cylinder.
[0013]
Such lean uniform premixed combustion lowers the local combustion temperature and suppresses the generation of NOx, and also prevents the generation of smoke because combustion in an air-deficient state is avoided. In addition, since the fuel injected from the small injection holes having a diameter of 0.1 mm or less is substantially vaporized immediately after the injection, fuel droplets having a relatively large particle diameter are evaporated near the compression top dead center as in the prior art. The problem of NOx and smoke due to the generation of the fuel, and the problem of unburned HC due to the fuel droplets falling inside the cylinder and adhering to the piston top surface do not occur.
[0014]
By the way, in an engine that compresses and ignites such a lean uniform premix, the air-fuel mixture ignites during the compression stroke before the piston reaches top dead center during medium to high load operation when the temperature in the cylinder becomes high. can not control the ignition timing, it may become impossible efficient operation. Therefore, in the present invention, normal compression ignition combustion (diesel combustion) in which fuel is injected in the vicinity of the top dead center is performed during medium to high load operation, and the aforementioned lean uniform premixed combustion is performed during low load operation . .
[0015]
In order to perform such switching of combustion, the present invention forms a plurality of small injection holes having a diameter of 0.1 mm or less and a plurality of large injection holes having a diameter larger than that in the fuel injection nozzle. when the load operation is opened only the small injection hole opened to the large injection hole at the time of high load operation, the injection timing at the time of low load operation or during the intake stroke of the engine is in the compression stroke by the injection timing changing means high load During operation, the injection timing is set near the compression top dead center of the engine.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0017]
As shown in FIG. 1, a fuel injection nozzle 3 for injecting fuel into the cylinder 2 is attached to the cylinder head 1. A piston 6 connected to the crankshaft 4 via a connecting rod 5 is accommodated in the cylinder 2. A cavity 7 is recessed at the top of the piston 6.
[0018]
As shown in FIG. 3, a first needle valve accommodation hole 9 is formed in the nozzle body 8 of the fuel injection nozzle 3 in the axial direction. The lower tip of the first needle valve accommodation hole 9 is covered with a valve seat 10 formed in a conical shape. A hemispherical hole 11 is formed at the most distal portion of the valve seat 10.
[0019]
A first needle valve 11 formed in a cylindrical shape is accommodated inside the first needle valve accommodation hole 9 so as to be slidable in the axial direction. The first needle valve 11 has a large diameter portion 11a slightly smaller in diameter than the first needle valve accommodation hole 9, a small diameter portion 11b that forms a predetermined gap between the first needle valve accommodation hole 9, and a small diameter portion 11b. It has the pressure receiving part 11c which connects the large diameter part 11a to a taper shape. The pressure receiving portion 11c receives the pressure of the fuel supplied through the fuel passage 12 formed in the nozzle body 8 and between the first needle valve accommodating hole 9 and the small diameter portion 11b, and lifts the first needle valve 11. A tapered first seat surface 11 d seated on the valve seat 10 is formed at the distal end portion of the first needle valve 11.
[0020]
A second needle valve accommodation hole 12 is formed in the first needle valve 11 along the axial direction. The second needle valve accommodation hole 12 accommodates a second needle valve 13 formed in a columnar shape so as to be slidable in the axial direction. The second needle valve 13 includes a large diameter portion 13a slightly smaller in diameter than the second needle valve accommodation hole 12, a small diameter portion 13b that forms a predetermined gap between the second needle valve accommodation hole 12, and a small diameter portion 13b. It has the pressure receiving part 13c which connects the large diameter part 13a to a taper shape. The pressure receiving portion 13c lifts the second needle valve 13 in response to the fuel pressure after the first needle valve 11 is lifted. A tapered second seat surface 13 d that is seated on the valve seat is formed at the tip of the second needle valve 13.
[0021]
The valve seat 10 is formed with a plurality of small injection holes 14 having a diameter of 0.1 mm or less facing the first seat surface 11d at intervals in the circumferential direction, and facing the second seat surface 13d with a diameter of 0. A plurality of large nozzle holes 15 having a diameter of 2 mm or more are formed at intervals in the circumferential direction. Specifically, the diameter of the small injection hole 14 is preferably about 0.08 to 0.05 mm in consideration of atomization of fuel injected therefrom and workability of the injection hole. In addition, the diameter of the large injection hole 15 is set to 0.24 mm in consideration of injection characteristics therefrom (injecting fuel in the form of a liquid column as in a normal direct injection engine).
[0022]
The first needle valve 11 is urged in the valve closing direction by a first return spring 16. One end of the first return spring 16 is in contact with the top portion 17 of the first needle valve 11, and the other end is in contact with a first spring holder 18 formed in the nozzle body 8. Similarly, the second needle valve 13 is urged in the valve closing direction by the second return spring 19. One end of the second return spring 19 is in contact with the top 20 of the second needle valve 13, and the other end is in contact with a second spring holder 21 formed in the nozzle body 8.
[0023]
According to the above configuration, when the lift force due to the fuel acting on the pressure receiving portion 11c of the first needle valve 11 through the fuel passage 12 exceeds the set force of the first return spring 16, the first needle valve 11 is lifted. Thus, the small nozzle hole 14 is opened. Then, when the lift force by the fuel acting on the pressure receiving portion 13c of the second needle valve 13 exceeds the setting force of the second return spring 19, the second needle valve 13 is lifted and the large injection hole 15 is opened. The Therefore, the said 1st needle valve 11 and the 2nd needle valve 13 are equivalent to the nozzle hole selection means of Claim 2 of a claim.
[0024]
Inside the first and second spring holders 18 and 21, a push rod 22 is slidably penetrated in the axial direction. One end of the push rod 22 abuts on the top 20 of the second needle valve 13, and a command piston 23 is provided at the other end. The command piston 23 is accommodated in a cylinder 24 formed on the upper part of the nozzle body 8. A holding spring 25 that urges the command piston 23 downward with a very weak force is accommodated in the cylinder 24. The holding spring 25 holds the command piston 23 so as not to float.
[0025]
An oil passage 26 is connected to the cylinder 24. The oil passage 26 is connected to an oil gallery 28 and an oil pan 29 via a switching valve 27. The switching valve 27 selects whether the oil gallery 28 and the oil passage 26 are communicated or the oil pan 29 and the oil passage 26 are communicated according to a command from the controller 30. The controller 30 receives the engine load and the rotational speed. The controller 30 issues a command for communicating the oil gallery 28 and the oil passage 26 at low load (region A in FIG. 2), and the oil pan 29 and oil passage at high load (region B in FIG. 2). A command for communicating with the control valve 26 is issued to the switching valve 27.
[0026]
When the oil gallery 28 and the oil passage 26 are communicated with each other by the switching valve 27 at low load, the command piston 23 is lowered by the oil pressure from the oil gallery 28, and the urging force in the valve closing direction is applied to the second needle valve 13. work. Therefore, at this time, even if the lift force due to the fuel acting on the pressure receiving portion 13c of the second needle valve 13 exceeds the setting force of the second return spring 19 after the lift of the first needle valve 11, the second needle valve 13 The lift is not performed unless the total force in the valve closing direction including the oil pressure acting on the command piston 23 is exceeded. Therefore, fuel is injected only from the small nozzle holes 14 at low load.
[0027]
On the other hand, when the oil pan 29 and the oil passage 26 are communicated by the switching valve 27 at the time of high load, the oil pressure applied to the command piston 23 is relieved to the oil pan 29. Therefore, at this time, the second needle valve 13 causes the lift force by the fuel that acts on the pressure receiving portion 13c of the second needle valve 13 after the first needle valve 11 is lifted to set the second return spring 19 to the set force (more precisely, to this). In addition, it lifts when it exceeds the setting force of the holding spring 25). Therefore, fuel is injected from the large nozzle hole 15 in addition to the small nozzle hole 14 at the time of high load.
[0028]
A fuel injection pump 31 shown in FIG. 4 is connected to the fuel passage 12 of the fuel injection nozzle 3. The fuel injection pump 31 is supplied with fuel from a fuel tank through an inlet 32. The fuel supplied from the introduction port 32 is pressurized by a feed pump 34 provided on a drive shaft 33 that is rotated by the crankshaft of the engine, and is controlled to a predetermined pressure or less by a pressure regulating valve 35, and from the discharge port 36 to the pump chamber. 37 is discharged.
[0029]
A cam disk 38 is attached to the drive shaft 33 via a cross coupling 39 so as to be movable in the axial direction. The cam disk 38 is pressed against the roller 41 by the plunger spring 40. The roller 41 is attached to a roller holder 42 separated from the drive shaft 33. According to this structure, when the drive 33 shaft rotates, the cam disk 38 rotates and is pushed on the roller 41 by the spring 40 and reciprocates, and in synchronization with this, the plunger 43 attached to the cam disk 38 rotates. While reciprocating.
[0030]
The plunger 43 has a suction groove 44, a fuel passage 45, a discharge passage 46, and a leak passage 47. The plunger barrel 48 has a suction port 49 that meets the suction groove 44 and a discharge port 50 that meets the discharge passage 46. Is formed. According to this configuration, when the suction groove 44 of the plunger 43 encounters the suction port 49 of the barrel 48, the fuel in the pump chamber 37 is guided into the compression chamber 52 through the introduction passage 51, and the discharge passage of the plunger 43. When 46 comes in contact with the outlet 50 of the barrel 48, the fuel in the compression chamber 52, which has been made high by the plunger 43, opens the delivery valve 53 and travels toward the fuel passage 12 of the fuel injection nozzle 3 shown in FIG.
[0031]
A control sleeve 54 is slidably fitted to the plunger 43 so as to cover the leak passage 47. The control sleeve 54 is moved in the axial direction of the plunger 43 (left-right direction in FIG. 7) by a control rod 55 connected to an electronic governor actuator (not shown). When the control sleeve 54 is moved to the left (leak side), the effective stroke of the plunger 43 is reduced and the injection amount is reduced. When the control sleeve 54 is moved to the right (anti-leak side), the effective stroke of the plunger 43 is reduced. Increases and the injection amount increases.
[0032]
Now, a roller holder pin 57 for driving the timer 56 is attached to the roller holder 42. The timer 56 includes a timer piston 58 into which the roller holder pin 57 is inserted, and a cylinder 59 that slidably accommodates the timer piston 58. Inside the cylinder 59, the timer piston 58 causes the fuel in the pump chamber 37 to be guided through the high pressure introduction path 60, and the fuel before being pressurized by the feed pump 34 via the low pressure introduction path 62. It is partitioned into a low pressure chamber 63 to be guided. The low pressure chamber 63 accommodates a timer spring 64 that biases the piston 58 toward the high pressure chamber 61.
[0033]
The high pressure chamber 61 and the low pressure chamber 63 are connected by a bypass passage 65. A timing control valve 66 is provided in the bypass passage 65. When the timing control valve 66 is closed, the fuel pressure in the high pressure chamber 61 overcomes the urging force of the spring 64 in the low pressure chamber 63, and the piston 58 moves to the left in FIG. 4 via the roller holder pin 57. Thus, the roller holder 42 rotates in the direction opposite to the rotation direction of the drive shaft 33, and the injection timing is advanced. When the timing control valve 66 is opened, the fuel in the high pressure chamber 61 leaks to the low pressure chamber 63 side through the bypass passage 65, so that the piston 58 moves to the right in FIG. Thus, the roller holder 42 rotates in the same direction as the rotation direction of the drive shaft 33, and the injection timing is retarded.
[0034]
The timing control valve 66 is opened and closed by a command from the controller 67 to which the engine load and the rotational speed are input. Specifically, the timing control valve 66 is controlled to open and close in a short cycle, and can be controlled continuously from a fully closed state to a fully open state. That is, assuming that the opening time of the timing control valve 66 is the ON time and the closing time is the OFF time, the OFF time / (ON time + OFF time) is called the duty ratio, and by changing the duty ratio from 0% to 100%, The opening degree of the timing control valve 66 is continuously controlled in a pseudo manner from the fully open state (retarded angle) to the fully closed state (advanced angle).
[0035]
An alternate long and short dash line 68 shown in FIG. 5 indicates the timer characteristics of a normal direct injection diesel engine. As shown in the figure, the maximum advance angle when the duty ratio is 100% is 20 degrees before the top dead center. That is, the injection timing of a normal direct-injection diesel engine is adjusted between 20 degrees before top dead center and top dead center according to the operating state (load / rotation speed) of the engine. On the other hand, the timer characteristic of the engine of this embodiment has a maximum advance angle of 80 degrees before the top dead center when the duty ratio is 100%, as indicated by a solid line 69 in FIG. The injection timing can be adjusted between 80 degrees and top dead center.
[0036]
This timer characteristic is obtained by greatly changing the stroke of the timer piston 58 and changing the control duty ratio of the timing control valve 66. Specifically, the axial length of the piston 58 is shortened, the axial length of the cylinder 59 is increased, or both, and the control duty ratio of the timing control valve 66 is set in the pump chamber 37. Depending on the fuel pressure and the urging force of the timer spring 64, it is as shown by the solid line in FIG.
[0037]
When the engine is in a low load operation (region A in FIG. 2), the controller 67 sets the duty ratio to 75% to 100% and optimally controls the injection timing between 80 degrees and 60 degrees before top dead center according to the operating state. When the engine is in a high load operation (region B in FIG. 2), the duty ratio is set to 0% to 25%, and the injection timing is optimally controlled according to the operating state between 20 degrees before top dead center and top dead center. Therefore, the timer 56 corresponds to the injection timing changing means of claim 2 of the claims.
[0038]
As a result, in the area A of FIG. 2, the fuel is injected only from the small injection holes 14 of the fuel injection nozzle 3 of FIG. 3, and the injection timing is from 80 degrees to 60 degrees before the top dead center as shown by A of FIG. Thus, the injection is as shown in FIG. Further, in the region B of FIG. 2, fuel is injected from the small injection hole 14 and the large injection hole 15 of the fuel injection nozzle 3 of FIG. 3, and the injection timing is the same as that of a normal engine as shown by B of FIG. The top dead center starts at 20 degrees before the top dead center, and the injection is as shown in FIG. Therefore, the timer 56, the first needle valve 11 and the second needle valve 13 correspond to the control means of claim 1 of the claims.
[0039]
The operation of the present embodiment having the above configuration will be described.
[0040]
During low load operation of the engine shown in region A of FIG. 2, as shown in FIG. 1A, the fuel is compressed from the plurality of small injection holes 14 of the fuel injection nozzle 3 to 80 degrees to 60 degrees before the top dead center. It is injected according to the driving state during the stroke. Note that the injection timing may be further advanced to inject during the intake stroke.
[0041]
Then, since the fuel F injected from the small injection hole 14 has a small injection hole diameter, the particle size of the fuel droplet formed at the time of injection becomes small, and is substantially vaporized immediately after the injection, and the piston 6 is top dead. In the course of reaching the point, a lean and uniform air-fuel mixture is formed in the cylinder 2. Thereafter, when the piston 6 reaches the vicinity of the top dead center, the inside of the cylinder 2 is compressed to a high temperature and a high pressure, and therefore, the entire air-fuel mixture is ignited and burned substantially simultaneously in substantially the entire space in the cylinder 2.
[0042]
Such lean uniform premixed combustion prevents local combustion, thereby lowering the local combustion temperature and suppressing generation of NOx, and avoiding combustion in an air-deficient state, and also generating smoke. It is suppressed. In addition, since the fuel F injected from the small injection hole 14 having a diameter of 0.1 mm or less is substantially vaporized immediately after the injection, the fuel droplets are evaporated near the compression top dead center as in the prior art. The problem of NOx and smoke, and the problem of unburned HC caused by fuel droplets falling in the cylinder 2 and adhering to the top surface of the piston 6 do not occur.
[0043]
2, even if the engine speed increases and the fuel supply pressure to the fuel injection nozzle 3 shown in FIG. 3 increases, the lift of the second needle valve 13 is forcibly pressed by the command piston 23, The large injection hole 15 does not open, and fuel is injected only from the small injection hole 14, and the above-described lean uniform premixed combustion can be performed. In other words, if the lift of the second needle valve 13 is not forcibly pressed by the command piston 23, the fuel supply pressure of the fuel injection pump 31 increases at high engine speeds depending on the fuel supply pressure to the fuel injection nozzle 3. Although the second needle valve 13 is lifted and fuel is injected from the large injection hole 15, there is a possibility that the lean uniform premixed combustion cannot be realized, but this embodiment avoids this.
[0044]
Also, as shown in region B of FIG. 2, when the engine is operating at a high load, as shown in FIG. 1B, the fuel F is added to the small nozzle holes 14 and a plurality of large nozzle holes having a diameter of 0.2 mm or more. 15 is also injected in the form of a liquid column according to the operating state in the vicinity of the compression top dead center at 20 degrees before the top dead center. Thereby, normal compression ignition combustion (diesel combustion) is performed. That is, lean uniform premixed combustion is performed at the time of low load operation of the engine shown in region A of FIG. 2, but is switched to normal compression ignition combustion (diesel combustion) at the time of high load operation of the engine shown in region B of FIG. .
[0045]
The reason for switching the combustion in this way is as follows. That is, when the lean uniform premixed gas is compressed and ignited, the mixed gas is ignited during the compression stroke before the piston 6 reaches the top dead center during the medium to high load operation when the temperature in the cylinder 2 becomes high. It is difficult to control the ignition timing, and efficient operation may not be possible. For this reason, at the time of high load operation, it is switched to normal compression ignition combustion (diesel combustion) in which the ignition timing can be easily controlled.
[0046]
In addition, instead of the fuel injection nozzle 3 in FIG. 3 and the fuel injection pump 31 in FIG. 4, a well-known common rail type fuel injection system is used, and the injection hole of an injector having a small injection hole and a large injection hole connected to the common rail is used. You may make it implement | achieve this invention by controlling opening and closing by electricity supply etc. to a solenoid valve.
[0047]
【The invention's effect】
As described above, according to the compression ignition type engine according to the present invention, the lean uniform premixed combustion can be performed, so that the generation of smoke, NOx, and HC can be prevented.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing a state of fuel injection of a compression ignition type engine showing an embodiment of the present invention, where (a) is a low load operation (lean uniform premixed combustion), and (b) is a high Indicates load operation (compression ignition combustion).
FIG. 2 is a diagram showing a map for switching between lean homogeneous premixed combustion in FIG. 1 (a) and normal compression ignition combustion in FIG. 1 (b) depending on the rotational speed and load.
FIG. 3 is a side sectional view of a fuel injection nozzle.
FIG. 4 is a side sectional view of a fuel injection pump.
FIG. 5 is a diagram showing injection timing characteristics.
FIG. 6 is a side sectional view of a tip portion of a fuel injection nozzle showing a conventional example.
[Explanation of symbols]
2 Cylinder 3 Fuel injection nozzle 6 Piston 11 First needle valve (injection hole selection means, control means)
13 Second needle valve (injection hole selection means, control means)
14 Small injection hole 15 Large injection hole 56 Timer (injection timing changing means, control means)

Claims (2)

A compression ignition engine in which fuel and intake air injected from a fuel injection nozzle into a cylinder are compressed by a piston and ignited, and a plurality of small injection holes having a diameter of 0.1 mm or less and a plurality of larger injection holes A fuel injection nozzle having a large injection hole, and a control means for controlling fuel injection by the fuel injection nozzle. The control means opens only the small injection hole during low load operation of the engine, A nozzle selection means for opening the large nozzle hole during load operation and a uniform air-fuel mixture in the cylinder until the piston reaches top dead center during low load operation, and near the compression top dead center. the mixture so as to compression ignition, the injection timing is also during the intake stroke of the engine is in the compression stroke, characterized in that during high load operation and an injection timing changing means for the compression top dead center near the injection timing engine Compression ignition engine. The compression ignition type engine according to claim 1, wherein the diameter of the large nozzle hole is 0.2 mm or more .

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