JPH10274072A - In-cylinder injection engine with turbocharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an air-fuel ratio from exceeding a misfire limit in an extremely low load region while appropriately corresponding to a fuel demand in a high load region when a supercharger is driven. SOLUTION: Fuel is directly injected near an ignition plug 36 by arranging an injector 35 on a nearly circumferential rim part of a combustion chamber 29. Fuel is injected during a latter period of compression stroke in a low load range, and stratified charge combustion is carried out. Or fuel is injected during intake stroke in a high load range, and uniform burning is carried out. In an operating range for carrying out stratified charge combustion, especially in the operating range of an extremely low load at the time of an idling operation and the like, the closing period of an intake valve 32 is delayed largely so as to set an effective compression ratio smaller than an effective expansion ratio to suppress filling of intake.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection engine having an injector for directly injecting fuel into a combustion chamber, and more particularly to a direct injection engine having a supercharger.

[0002]

2. Description of the Related Art Conventionally, an injector for directly injecting fuel into a combustion chamber is provided, and when the load is low, fuel is injected from the injector at a later stage of the compression stroke, thereby causing a stratified combustion in which a mixture is unevenly distributed around a spark plug. In this way, the air-fuel ratio is made lean to improve combustion while ensuring combustion stability, and at high load, the fuel is diffused by injecting fuel in the intake stroke to perform uniform combustion, thereby achieving the air-fuel ratio. In-cylinder injection type engines that generate high engine output by making the engine rich are generally known.
In addition, a turbocharger is mounted on this type of engine to increase the torque of the engine by supercharging the intake air.

In this type of engine, fuel is pressurized to a constant pressure by a fuel system, and an injector is operated in response to a valve opening time signal (pulse signal) from an ECU as shown in FIG. The fuel is injected from the injector by lifting the needle for a time corresponding to the pulse width. The pressure (fuel pressure) of the fuel is set to a pressure higher than the pressure in the combustion chamber at the latter stage of the compression stroke, so that the fuel can be injected into the combustion chamber at the latter stage of the compression stroke.

[0004]

In the above-mentioned engine, particularly in an engine provided with a supercharger to increase the torque, a large amount of fuel can be supplied in a short time in a high load region in a supercharger driving state. Therefore, the injector is configured to be able to inject a required amount of fuel within a predetermined period under a high fuel pressure, for example, by setting a large nozzle diameter.

[0005] However, in such an engine, although fuel injection is performed well in a high load range, in an extremely low load operation range in which a very small amount of fuel needs to be injected, such as during idling operation, the injector is not used. The operation time becomes extremely short, and for example, in an operation range in which a very small amount of fuel equal to or less than the specific amount Q as shown by a broken line in FIG. 8 is injected, a variation in the injection amount due to an operation error of the injector tends to increase. At this time, when the injection amount is larger than the required injection amount, there is no particular problem. On the contrary, when the injection amount is small, the air-fuel ratio is large and leans to the lean side to possibly exceed the misfire limit. Therefore, it is desired to solve this.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and in a cylinder injection type engine having a supercharger, it is possible to appropriately cope with a fuel demand in a high load region driven by the supercharger. However, it is an object of the present invention to provide a supercharged in-cylinder injection engine that can effectively prevent the air-fuel ratio from exceeding a misfire limit in an extremely low load range.

[0007]

In order to solve the above-mentioned problems, a direct injection type engine with a supercharger according to the present invention includes a supercharger and an injector for directly injecting fuel into a combustion chamber. At the time of load, the fuel is injected from the injector in the compression process in a state where the air-fuel ratio is larger than the stoichiometric air-fuel ratio to perform stratified combustion, and in a supercharged state at full load and the air-fuel ratio is equal to or less than the stoichiometric air-fuel ratio. In a cylinder-injection type engine with a supercharger in which uniform combustion is performed at a time, variable valve operating means for varying the intake timing and intake timing control means for controlling the same are provided to perform stratified combustion. In the operation range on the extremely low load side in the range, the closing timing of the intake valve is set to early closing or late closing in which the effective compression ratio becomes smaller than the effective expansion ratio so that the charging of the intake air is suppressed as compared with the stratified combustion state. To Those were (claim 1).

According to this engine, even when the injection amount varies in an extremely low load region where the injection fuel is extremely small and the injection amount does not reach the required injection amount, the filling of the intake air is suppressed. The air-fuel ratio is large and does not lean to the lean side. In addition, since the intake valve is closed early or late, charging of intake air is suppressed without pumping loss.

In such an engine, a mechanical supercharger is used as the supercharger, and in the operating range of full load driven by the supercharger, the overlap between the intake and exhaust before the piston reaches the top dead center is obtained. It is preferable to control the intake timing so as to be larger than the overlap after reaching the top dead center (claim 2).

In this manner, the scavenging performance can be improved, knocking can be effectively prevented over the entire load range, and the fresh air charging efficiency can be improved.

Further, if the closing timing of the intake valve is controlled so that the effective compression ratio approaches the effective expansion ratio at least in the operating range of the turbocharger drive (claim 3), the load on the turbocharger is reduced. It is possible to reduce fuel consumption and improve fuel efficiency.

Further, if the pressure of the fuel supplied to the injector is kept constant, that is, if the fuel is injected at a high pressure capable of injecting the fuel in the compression stroke regardless of the operating range (claim 4), the injected fuel The vaporization and atomization of the gas are promoted, and the combustibility is enhanced.

[0013]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic view showing an example of a direct injection type engine with a supercharger according to the present invention, and FIG. 2 is a schematic view showing a main part of the engine. In this figure, the engine is
The engine body 10 includes an intake passage 12 and an exhaust passage 13 connected to the engine body 10.

In the intake passage 12, an air cleaner 14, an air flow meter 15, a throttle valve 16, a supercharger 17, an intercooler 18, a surge tank 19 and the like are arranged in this order from the upstream side.

The supercharger 17 is a mechanical supercharger that is mechanically driven by an engine output shaft (not shown) to supercharge the intake air. For example, a supercharger of a Resholm type having a pair of rotors Each of the rotors is rotated in accordance with the transmission of the torque of the engine by the belt transmission mechanism to compress and discharge the intake air. Further, the supercharger 17 is provided with an electromagnetic clutch 20 for interrupting the above-mentioned rotational force. When the electromagnetic clutch 20 is turned on, the rotational force is transmitted and the supercharger 17 is driven. When the electromagnetic clutch 20 is turned off, the transmission of the rotational force is interrupted, and the supercharger 17 is stopped.

The supercharger 17 is further provided in the intake passage 12.
Is provided, and a control valve 22 is provided in the supercharging bypass passage 21 so that intake air is bypassed in accordance with opening and closing of the control valve 22 according to an operation state. I have.

In the exhaust passage 13, O
_Two sensors 23, a catalyst device 24, a silencer 25 and the like are provided. The catalyst device 24 includes, for example, a three-way catalyst, and is configured to absorb HC (hydrocarbon), NOx (nitrogen oxide) and the like in the exhaust gas and purify the exhaust gas.

The engine body 10 comprises a cylinder block and a cylinder head installed on the cylinder block. A piston 28 is provided in the cylinder 27 of the cylinder block, and a combustion chamber 29 is formed between the upper surface of the piston 28 and the lower surface of the cylinder head.

The engine body 10 includes a combustion chamber 29.
An intake port and an exhaust port that are open to each other are formed. For example, two intake ports 30 and two exhaust ports 31 are formed for each cylinder. And, each intake port 30
The intake manifolds forming the intake passages 12 are connected to the respective exhaust ports 31, while the exhaust manifolds forming the exhaust passages 13 are connected to the respective exhaust ports 31.

Each intake port 30 has an intake valve 32
And each exhaust port 31 has an exhaust valve 33
The valves 32, 33 are driven by a cam (not shown) of a cam shaft for each valve 32, 33. In particular, a camshaft that drives the intake valve 32 incorporates a variable valve operating device 34 (shown in FIG. 1) that changes the phase of the cam while operating the intake valve 34 with the cam. The intake timing is variable.

The engine body 10 is further provided with an injector 35 for directly injecting fuel into the combustion chamber 29 and a spark plug 36, as shown in FIG. It is arranged on the substantially peripheral part,
The tip of the spark plug 36 is arranged substantially at the center of the ceiling of the combustion chamber 29.

The injector 35 includes a needle which is urged in a valve closing direction by a return spring, and an electromagnetic coil for lifting the needle. The fuel pressurized by the above is configured to be injected from the nozzle at the tip.

The injector 35 is disposed below the portion where the intake port 30 is disposed on one side of the combustion chamber 29, as shown in the figure, and near the periphery of the combustion chamber facing the portion where the injector is disposed. It is attached to the engine main body 10 in an inclined state so as to inject fuel downward diagonally toward. Thus, the injector 3
By disposing the ignition plug 5 and the ignition plug 36, fuel is injected near the front end of the ignition plug 36 during operation, as indicated by reference numeral F in FIG.

FIG. 3 shows an example of the configuration of the fuel system of the engine. In this figure, reference numeral 40 denotes a fuel tank, and a fuel supply passage 41 and a fuel return passage 42 are connected between the fuel tank 40 and the injector 35.

The fuel supply passage 41 is provided with a low-pressure fuel pump 43, a filter 44, and an engine-driven high-pressure fuel pump 45 in this order from the fuel tank 40 side, and the fuel return passage 42 has a high-pressure regulator 46 and a downstream side thereof. Is provided. Further, a passage 48 that bypasses the high-pressure fuel pump 45 is provided, a check valve 48 a is provided in the passage 48, and a passage 49 that bypasses the high-pressure regulator 46 is provided.
9a is provided.

Normally, the solenoid valve 4
When the high-pressure fuel pump 45 is operated and the high-pressure regulator 46 functions with the 9a closed, the supply fuel pressure (referred to as fuel pressure) acting on the injector 35 becomes high enough to enable the injection described later in the compression stroke. It is adjusted to. Also, when the engine is started when the high-pressure fuel pump 45 is not sufficiently operated, the low-pressure fuel pump 43 is driven and the low-pressure regulator 47 functions by opening the solenoid valve 49a and bypassing the high-pressure regulator 46. As a result, the fuel pressure acting on the injector 35 is adjusted to a low pressure capable of performing the intake stroke injection.

In FIG. 1, reference numeral 50 denotes an E for engine control.
The ECU 50 is a control unit (CU).
There are an accelerator sensor 37 for detecting an accelerator opening (depression amount of an accelerator pedal), an air flow meter 38 for detecting an intake air amount, a water temperature sensor 39 for detecting a temperature of engine cooling water, the O ₂ sensor 23 and From a crank angle sensor or the like.

The ECU 50 includes supercharger control means 51 for controlling the electromagnetic clutch 20 in accordance with the operation state, intake timing control means 52 for varying the intake timing by controlling the variable valve drive 34, And a fuel injection control means 53 for controlling the fuel injection timing and injection amount via an injector drive circuit 55.

The control of the electromagnetic clutch 20 according to the operating state by the supercharger control means 51 of the ECU 50 will be described with reference to FIG.

FIG. 3 shows a supercharger stop area A, which is an operation area in which the supercharger 17 is stopped in the operation state of the engine.
And a supercharger drive region B, which is an operation region in which the supercharger 17 is driven. In the supercharger stop region A, the electromagnetic clutch 20 is turned off, and in the supercharger drive region B, the electromagnetic clutch 20 is turned off. 20 is turned on. Line I in FIG.
The torque at the time when the intake pressure downstream of the supercharger becomes the atmospheric pressure, that is, the torque corresponding to the total torque at the time of no supercharging, and the line II indicates a case where the supercharger 17 supercharges the intake air. Is equivalent to the full opening torque of.

As shown in FIG. 3, on the low-speed side of the predetermined engine speed N1, the turbocharger 17 is stopped on the low-load side and the high-load side after a line slightly exceeding the line I. The state is switched to the driving state. The set rotation speed N1 is set to a rotation speed near the peak of the line II, that is, the rotation speed of the engine at which the maximum torque is obtained when the supercharger 17 supercharges the intake air. On the other hand, on the higher speed side than the set rotation speed N1, the supercharger 17 is driven from the low load side to the high load side. That is, the turbocharger stop region A is a low-load region on a lower speed side than the set rotation speed N1, and the turbocharger drive region B is the set rotation speed N1.
The range is a high load side region lower than 1 and a low load side high load side region higher than the set rotation speed N1.

The fuel injection control means 53 of the ECU 50
The control of the fuel injection timing and the fuel injection amount is performed as shown in FIG.

That is, the injector 35 is controlled to inject fuel in the latter stage of the compression stroke in the supercharger drive region B and to inject fuel during the intake stroke in the supercharger stop region A. However, in the turbocharger stop region A, in a region on a lower rotation side than the specific rotation speed N2 and on a lower load side than a line almost intermediate between the line I and the line II, a part of the total fuel injection amount is The injector 35 is controlled to inject at the latter stage of the compression stroke, that is, to perform split injection of fuel.
The set rotation speed N2 is set to a rotation speed near the rotation speed of the engine that has the highest torque when the intake air is supercharged by the supercharger 17 at a higher rotation speed than the set rotation speed N1.

The fuel injection amount is determined by the injector drive circuit 55
Is controlled by exciting the electromagnetic coil of the injector 35 in accordance with the pulse width of the valve opening time signal (pulse signal) output from the controller. Then, the required injection amount is calculated according to the operating state, and a pulse width is obtained based on the required injection amount and the fuel pressure. A pulse signal of this pulse width is output to the injector 35 to thereby determine the required amount. Fuel is to be injected.

Further, the intake timing control means 5 of the ECU 50
The control of the intake timing by 2 is performed as follows.

Basically, as shown in FIG. 6 (a), the intake valve 32 is opened from a position sufficiently early before the piston reaches the top dead center (TDC) to a position slightly later than the bottom dead center (BDC). The intake valve 32 is closed so that the effective compression ratio approaches the effective expansion ratio, the overlap between the intake and exhaust gas is increased, and the overlap before the top dead center (TDC) is changed after the top dead center (TDC). The intake timing is set to be larger than the overlap (normal timing). By changing the phase of the cam according to the number of revolutions of the engine while maintaining the overlap state, for example, on the lower side than the specific number of revolutions N1, FIG.
While intake is performed at the timing shown in FIG.
On the higher rotation side, as shown in FIG. 6 (b), the intake timing is varied in a direction in which the closing timing of the intake valve 32 is slightly delayed, so that intake is performed so as to obtain an optimal intake charging efficiency according to the engine speed. The timing is controlled.

However, in the supercharger stop region A, in a very low load specific operation region α in which a small amount of fuel is injected, such as during idling operation, the piston has a top dead center as shown in FIG. (TDC), the intake valve 32 is opened from a slightly earlier position, and the intake valve 32 is closed at a position sufficiently later than the bottom dead center (BDC). That is, the effective compression ratio is effectively expanded by closing the intake valve 32 late. The intake timing is controlled so as to be smaller than the ratio (suppress the intake charge) (late closing timing). At this time, the overlap between the intake and exhaust is extremely small.

The operation and effect of the above-described in-cylinder injection type engine with a supercharger according to this embodiment will be described below.

According to the above-described engine, a required amount of fuel according to the operating state is injected by controlling the operation time of the injector 35, that is, the excitation time of the electromagnetic coil. Then, in the supercharger stop region A, the fuel is injected late in the compression stroke, so that the air-fuel mixture is unevenly distributed around the ignition plug 36 and stratified combustion is performed, whereby the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. Combustion is performed in a stable state to save fuel efficiency, and the supercharger drive region B
In most of the operating ranges, the fuel is injected during the intake stroke, whereby the diffusion of the fuel is promoted, the uniform combustion is performed, and the engine output is increased. In the transitional region from the supercharger stop region A to the supercharger drive region B, the fuel split injection is performed as described above.
The combustion state can be switched smoothly.

Further, in the specific operating range α of the supercharger stop region A where the load is extremely low, since the intake timing is the late closing timing, the injection amount tends to vary. Stable combustion is ensured.

That is, in this engine, as described above, the intake timing is set to the late closing timing to suppress the charging of the intake air, so that the intake charging amount in the specific operation range α is smaller than that in the stratified combustion state. ing. For this reason, even when the injected fuel does not reach the required injection amount, the air-fuel ratio does not greatly increase toward the lean side and does not exceed the misfire limit. Therefore, misfires caused by variations in the injected fuel in an extremely low load region, which are likely to occur in this type of engine having a supercharger, are effectively avoided, and thereby stable combustion characteristics are appropriately secured. You.

In the above-described engine, in the operating range other than the specific operating range α, the intake timing is set so that the overlap before the top dead center (TDC) is larger than the overlap after the top dead center (TDC). Is set, the scavenging performance in the full load operation range by the supercharger drive can be sufficiently improved. Therefore, by discharging high-temperature residual gas in this operation range, it is possible to suppress the rise in combustion temperature and effectively suppress the occurrence of knocking, and it is possible to increase the new charging efficiency by the residual gas discharge amount. There is also an advantage.

As described above, according to the engine of the present embodiment, when compared with a conventional in-cylinder injection type engine of this type having a supercharger, the supercharger is driven from an extremely low load region such as during idling operation. Stable combustion can be ensured over the entire load range.

The above-described engine is an example of the in-cylinder injection type engine with a supercharger according to the present invention, and the specific configuration thereof can be appropriately changed without departing from the gist of the present invention.

For example, in the above-mentioned engine, the specific operating range α
, The intake valve is suppressed by closing the intake valve 32 late, so that the air-fuel ratio in the specific operating range α does not exceed the misfire limit.
Before reaching C), the intake valve 32 may be closed, thereby suppressing the filling of intake air. Also in this case, it is possible to prevent misfire in the specific operation range α with the engine. As a method of suppressing the filling of the intake air, besides controlling the intake timing by the intake valve 32, for example, it is conceivable to adjust the opening degree of the throttle valve. In this case, however, the pumping loss is reduced. Therefore, it is more advantageous to control the intake timing.

Further, in the engine of the above-described embodiment, a device that switches the intake timing by changing the phase of the cam while operating the intake valve with a single cam is used as the variable valve operating device 34. For example, a variable valve operating device including two types of cams and a switching mechanism that switches the intake valve to operate with one of these cams may be used.

Since the amount of intake air is largely affected by the closing timing of the intake valves, for example, the closing timings of the intake valves at the two intake ports are made different in advance.
The closing timing of the intake valve may be made variable by selectively blocking the intake passage to one port or selectively stopping the intake valve 32 at one port. In this case, intake is started from a position slightly earlier than the top dead center (TDC) without providing a large overlap unlike the engine of the present embodiment, and the intake valve is opened at the timing shown in FIG. The closing timing of the intake valve may be changed so as to close. That is, the closing timing of the intake valve may be delayed in an extremely low load region where the combustion injection amount is extremely small and in a full load region driven by the supercharger to suppress the charging of intake air. In this way, in the extremely low load range, leaning of the air-fuel ratio can be suppressed to prevent misfiring, and in the full load range driven by the turbocharger, the effective compression ratio is reduced to lower the combustion temperature. Thus, the exhaust gas temperature can be reduced and the occurrence of knocking can be prevented.

[0049]

As described above, the direct injection engine with a supercharger according to the present invention has an injector for directly injecting fuel into the combustion chamber. A variable valve operating means for making the valve variable and an intake timing control means for controlling the variable valve operating means are provided, and the effective compression ratio is used to set the closing timing of the intake valve in an operation range on the extremely low load side in an operation range in which stratified combustion is performed. Since the intake charge is suppressed as compared with the stratified combustion state by making the early closing or the late closing that is smaller than the expansion ratio, the injection amount varies in the extremely low load region where the injected fuel is extremely small, and the injection amount varies. Even when the amount is less than the required injection amount, it is possible to effectively prevent the air-fuel ratio from being large and leaning toward the lean side and exceeding the misfire limit. Therefore, it is possible to appropriately inject the fuel required in the full load operation range by the supercharger drive, and to avoid the occurrence of misfire in the extremely low load range to appropriately secure the stable fuel property. . In addition, because the intake valve is suppressed by filling the intake valve early or late, there is an advantage that occurrence of misfire can be avoided without pumping loss.

In particular, in this engine, a mechanical supercharger is used as the supercharger, and in the operating range of full load driven by the supercharger, the intake / exhaust gas before the piston reaches the top dead center is exceeded. By controlling the intake timing so that the lap is larger than the overlap after reaching the top dead center,
The scavenging performance can be improved, which can effectively prevent knocking in the entire load range,
The fresh air filling efficiency can be improved.

Further, if the closing timing of the intake valve is controlled so that the effective compression ratio approaches the effective expansion ratio at least in the supercharger drive operation range, the supercharger in the supercharger drive range is controlled. The load can be reduced and fuel efficiency can be improved.

Further, if the fuel pressure supplied to the injector is kept constant, that is, if the fuel is injected at a high pressure capable of injecting the fuel during the compression stroke regardless of the operating range,
Vaporization and atomization of the injected fuel can be promoted to enhance the combustibility.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a direct injection type engine with a supercharger according to the present invention.

FIG. 2 is a schematic plan view showing a combustion chamber of the engine body and its vicinity.

FIG. 3 is a configuration diagram showing a fuel system of the engine.

FIG. 4 is a diagram illustrating a drive region of a supercharger.

FIG. 5 is a diagram illustrating fuel injection timing.

FIGS. 6A to 6C are diagrams for explaining intake timing;
(A) and (b) are diagrams showing normal timing, and (c) is a diagram showing late closing timing.

FIG. 7 is a diagram showing an example of control of the intake timing when only the intake stop timing is varied.

FIG. 8 is a graph showing a relationship between a fuel injection amount and an injection time (pulse width) in a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Engine main body 12 Intake passage 13 Exhaust passage 17 Supercharger 35 Injector 40 Fuel tank 41 Fuel supply passage 42 Fuel return passage 43 Low pressure fuel pump 45 High pressure fuel pump 50 ECU 51 Supercharger control means 52 Intake timing control means 53 Fuel injection Control means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02B 29/08 F02B 29/08 A 37/00 302 37/00 302A F02D 13/02 F02D 13/02 B J 23/00 23 / 00 K 23/02 23/02 A 41/04 305 41/04 305B 320 320

Claims (4)

[Claims] 1. A fuel supply system comprising a supercharger and an injector for directly injecting fuel into a combustion chamber, wherein fuel is injected from the injector in a compression process in a state where an air-fuel ratio is larger than a stoichiometric air-fuel ratio at a low load and stratified combustion. And
Valve-operating variable means for varying the intake timing in a supercharged in-cylinder injection type engine that performs uniform combustion in a supercharged state at full load and an air-fuel ratio equal to or less than the stoichiometric air-fuel ratio. And an intake timing control means for controlling the same, and in the operation range on the extremely low load side in the operation range in which the stratified combustion is performed, the closing timing of the intake valve is set so that the effective compression ratio becomes smaller than the effective expansion ratio. An in-cylinder injection type engine with a supercharger, characterized in that charging by intake is suppressed as compared with a stratified combustion state by closing or late closing. 2. A mechanical supercharger is used as the supercharger,
Control the intake timing so that the overlap between the intake and exhaust before the piston reaches the top dead center is greater than the overlap after the piston reaches the top dead center in the full load operation range by the turbocharger drive. The in-cylinder injection type engine with a supercharger according to claim 1, wherein: 3. The supercharger according to claim 1, wherein the closing timing of the intake valve is controlled so that the effective compression ratio approaches the effective expansion ratio at least in an operating range of the supercharger drive. In-cylinder injection engine. 4. The in-cylinder injection type engine with a supercharger according to claim 1, wherein the pressure of fuel supplied to the injector is kept constant.