JPH07102982A - Engine having supercharger - Google Patents

Abstract

PURPOSE:To improve emission and fuel consumption performance, and further improve an engine torque by increasing a supercharging pressure while sufficiently delaying a closing timing of an intake valve to avoid knocking, and providing a proper skish area corresponding to the delayed closing of the intake valve. CONSTITUTION:In an engine provided with a supercharger and an intercooler, a closing timing of an intake valve is set after the bottom dead center by at least 65 degrees in a high load area. A skish area 33 is formed at a portion composing a combustion chamber 4. The area of the skish area 33 has a ratio ranging between 15% and 25% in respect to a sectional area of a cylinder bore per a cylinder. Proper skish flow is thus provided correspondingly to the delay of the closing timing of the intake valve, for improving a combustion condition in the engine of this kind.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine with a supercharger having an intake passage provided with a supercharger and an intercooler located downstream thereof.

[0002]

2. Description of the Related Art Conventionally, an engine with a supercharger has been generally used in which the intake air is supercharged by a mechanical or exhaust turbocharger to increase the intake charge and to increase the engine torque. Are known.

Further, a method (so-called Miller cycle) in which the effective compression ratio is made smaller than the expansion ratio to reduce the compression work by delaying the closing timing of the intake valve largely from the bottom dead center (so-called Miller cycle) is a conventional method. However, recently, there has been proposed an engine equipped with a supercharger and an intercooler, which utilizes such a method to increase the torque while suppressing knocking. For example, in the engine disclosed in Japanese Patent Laid-Open No. 63-239312, a supercharger and an intercooler are provided in the intake passage, while the geometric compression ratio of the engine is set to a high compression ratio of 8.5 or more, Further, the intake valve closing timing is set to a late closing such that it is 50 ° or more after bottom dead center when defined with a 1 mm lift (70 ° or more after bottom dead center when defined with a 0 mm lift). According to this engine, while the expansion ratio is increased, the effective compression ratio is reduced compared to this, so that the compression top dead center temperature is lowered and knocking and exhaust temperature rise are suppressed.
In this state, the charging amount is increased by supercharging and the torque is effectively increased.

[0004]

In this type of engine with a supercharger, delaying the intake valve closing timing affects the combustion speed and may also affect the HC emission amount.
There is room for improvement in terms of improving flammability. It is possible to bend the intake port in the cylinder circumferential direction to generate swirl in order to improve the combustibility, but in order to reduce the intake resistance during high supercharging, the intake port should be placed in the approximate cylinder axis direction. It is preferable to use a tangential port that is open, and in this case, the combustion promoting action by swirl cannot be expected.

By the way, as another technique for promoting combustion, a squish area which becomes a minute gap at the top dead center is formed in the inner wall of the cylinder head and the top wall of the piston which constitute the combustion chamber, and near the compression top dead center. It is known in the prior art to generate a squish flow in (for example, Japanese Patent Publication No. 57-50924).

However, in the above engine with a supercharger, no particular consideration has been given to the squish area, and even if a squish area is provided, the intake valve closing timing is delayed as described above. On the other hand, it has not been known in the past how the proportion of the squish area is related.

In view of the above circumstances, the present invention is designed to increase the supercharging pressure while avoiding knocking, etc. by sufficiently delaying the intake valve closing timing in an engine with a supercharger.
It is an object of the present invention to provide an engine with a supercharger capable of improving emission and fuel consumption and further increasing engine torque by a proper squish area corresponding to this.

[0008]

In order to achieve the above object, the present invention provides an engine with a supercharger having a supercharger in an intake passage and an intercooler located downstream thereof.
At least in the high load region, the intake valve closing timing is set to be late at 65 ° or more after the bottom dead center in the crank angle, and the cylinder head inner wall and the piston top wall forming the combustion chamber face each other in parallel and at the time of top dead center. By forming a squish area which is a minute gap, the ratio of the area of the squish area to the cylinder bore cross-sectional area per cylinder is set to 15% to 25%.

In the present invention, it is preferable that a plurality of intake ports be formed for each cylinder, and that each intake port be a tangential port that opens substantially in the cylinder axis direction.

A mechanical supercharger is provided as the supercharger,
The geometric compression ratio of the engine is preferably 8.5 or more.

[0011]

According to the present invention, by closing the intake valve late, the compression top dead center temperature is lowered and knocking and exhaust gas temperature rise are suppressed, while the charging amount is increased by supercharging and the squish area is also increased. Combustibility is enhanced by the squish flow. In particular, while the intake valve closing timing is delayed to 65 ° or more after bottom dead center, the combustion speed is properly adjusted by setting the proportion of the area of the squish area to 15% to 25%. It is possible to obtain effects such as suppressing the discharge amount and increasing the maximum torque.

Further, if a plurality of intake ports are formed for each cylinder and tangential ports are used, intake resistance during high supercharging can be reduced. In this case, the combustion promoting action by the intake swirl cannot be expected, but in this case as well, the tendency of the decrease in the combustion speed is corrected by the squish flow.

Further, a mechanical supercharger is provided as the supercharger,
When the geometrical compression ratio of the engine is 8.5 or more, high supercharging is performed while maintaining an appropriate effective compression ratio because of the late closing of the intake valve.

[0014]

Embodiments of the present invention will be described with reference to the drawings.
1 and 2 schematically show an engine with a supercharger according to an embodiment of the present invention. In these drawings, reference numeral 1 denotes an engine main body, which includes a plurality of cylinders 2. The geometric compression ratio of the engine is a high compression ratio of 8.5 or more.

In each of the cylinders 2, a combustion chamber 4 is formed above the piston 3 inserted in the cylinder bore. A plurality of intake ports are opened in the combustion chamber 4, for example, two intake ports 5 are opened and two exhaust ports 6 are further opened. The intake port 5 and the exhaust port 6 are opened and closed by an intake valve 7 and an exhaust valve 8, respectively, and the intake valve 7 and the exhaust valve 8 are provided on a pair of camshafts 9 and 10 for the intake valve and the exhaust valve. It is driven by the cam. An ignition plug 11 is arranged in the center of the combustion chamber 4.

Reference numeral 12 is an intake passage for supplying intake air to the engine body 1, and a common intake passage 13 on the upstream side.
And the intake manifold 14 on the downstream side.
The intake manifold 14 includes the independent intake passage 1 for each cylinder.
5, the downstream side of each independent intake passage 15 is divided into two passages by a partition wall and communicates with each of the intake ports 5.

The common intake passage 13 is provided with an air cleaner 16, an air flow meter 17 for detecting the amount of intake air, and a throttle valve 18 which operates in response to depression of an accelerator pedal (not shown), and is provided downstream of the throttle valve 18. A supercharger 20 is provided. Illustrated supercharger 20
Is a Rishorum type mechanical supercharger, and is driven by an engine output shaft via a transmission mechanism 21 such as a belt. Further, an intercooler 22 is provided downstream of the supercharger 20.

An injector 23 for injecting and supplying fuel is arranged in each of the independent intake passages 15. If necessary, an opening / closing valve 24 that closes in a low load region or the like may be provided in a passage communicating with one of the intake ports 5 on the downstream side of each independent intake passage 15. Further, the exhaust port 6 is communicated with the exhaust passage 26 for each cylinder of the exhaust manifold 25.

3 and 4 show the structure of the combustion chamber portion. As shown in these figures, a squish area 33 is formed in a part of the part that constitutes the combustion chamber 4 (the part shaded in FIG. 3). That is, the inner wall 31 of the cylinder head 30 that constitutes the ceiling portion of the combustion chamber 4 is basically in a pent roof shape as shown in FIG. Is provided with a substantially horizontal wall surface 32 that faces in parallel with, and the wall surface 32 and a part of the top wall of the piston 3 corresponding to the wall surface 32 form a squish area 33 that becomes a constant minute gap at the top dead center. There is.

Further, both intake ports 5 are opened in the inclined surface portion on one half side of the inner wall 31 of the cylinder head 30 which constitutes the ceiling portion of the combustion chamber, and both exhaust ports are formed in the inclined surface portion on the other half side. 6 is open, and a squish area 33 is formed outside these port openings.

Both of the intake ports 5 are tangential ports having a small intake resistance, that is, when viewed from the side, as shown in FIG. It is formed so as to open in a substantially cylinder axis direction, and extends substantially straight in a plan view (see FIG. 3).

By the way, the closing timing of the intake valves 7 provided in both intake ports 5 and the ratio of the area of the squish area 33 to the cylinder bore cross-sectional area per cylinder are set as follows.

FIG. 5 shows the valve lift characteristic I of the intake valve 7.
C schematically shows, and as shown in the figure, the intake valve 7 opens near the top dead center TDC and closes after the bottom dead center BDC. The engine is significantly delayed as compared with the engine of No. 1, and is set in the range of ABDC 65 ° CA or more, preferably up to ABDC 100 ° CA. Note that ABDC means after bottom dead center, and CA means crank angle.

The intake valve closing timing IC referred to here is a timing at which the intake valve is considered to be substantially closed, for example, a timing at which a minute lift amount corresponding to the height of the ramp portion in the valve lift characteristic IC is closed. , 0.4 in this embodiment
The intake valve closing timing is set at the time of mm lift (see Fig. 6).

The intake valve closing timing IC is set to ABDC 65 ° C.
The reason why it is set to be slower than A is to fully exhibit the effect of knocking suppression by lowering the compression top dead center temperature, which will be described later, and the reason why it is set to ABDC 100 ° CA is that the closing timing is delayed from this. This is because there is a concern that the compression top dead center temperature will fall below the start limit and start will be difficult.

The ratio (100 × Sq / Sb) of the area (Sq) of the squish area to the cylinder bore cross-sectional area (Sb) per cylinder is set to 15% to 25%.

According to the engine of this embodiment as described above,
By delaying the intake valve closing timing to ABDC 65 ° CA or more and providing the supercharger 20 and the intercooler 22, knocking and the like can be suppressed and the engine torque can be increased. That is, the supercharged air from the supercharger 20 is cooled by the intercooler 22 and supplied to the combustion chamber, and the effective compression ratio becomes smaller than the expansion ratio due to the delay of the intake valve closing timing. Dead center temperature is lowered. As a result, knocking and an increase in exhaust temperature are suppressed, and the supercharging pressure by the supercharger 20 is increased, so that the engine torque is increased.

In this case, if a plurality of intake ports 5 are formed and are tangential ports, the intake resistance at the time of high supercharging is reduced, which is advantageous for increasing torque due to high supercharging. .

If the mechanical compression ratio of the engine is 8.5 or higher, which is higher than the geometrical compression ratio (7.5 to 8.5) of a general supercharged engine, thermal efficiency is increased and expansion is achieved. The cost is earned, and thus the intake valve closing timing I
By delaying C to ABDC 65 ° CA or more, the effective compression ratio is appropriately lowered. Further, the engine torque is effectively increased by performing high supercharging by the mechanical supercharger 30 such as the Rishorum type.

By the way, when the intake valve closing timing is delayed in this way, the combustion speed tends to decrease accordingly,
Further, if the intake port 5 is a tangential port, the above tendency becomes remarkable because the combustion promoting action due to the turbulence of the intake air such as swirl cannot be sufficiently obtained. However, this tendency is set so that the squish area is appropriately large. It is compensated by doing. That is, when the squish area is appropriately increased, the combustion is accelerated by the squish flow generated near the compression top dead center to increase the combustion speed, and the decrease in the combustion speed due to the delay of the intake valve closing timing is compensated. This reduces harmful components such as HC in the exhaust gas, and
Combustion is efficiently performed and unburned components are reduced, so that fuel efficiency is also improved.

Moreover, the engine torque can be further increased by the synergistic effect of delaying the intake valve closing timing to perform high supercharging as described above and promoting combustion by the squish flow.

Next, the intake valve closing timing is set to ABDC 65 ° CA.
The range of the squish area which is effective in the case of setting the delay later will be described with reference to FIGS. 7 and 8.

FIG. 7 shows the normal operating range (engine speed 15
000 rpm) and the squish area ratio (ratio of the area of the squish area to the cylinder bore cross-sectional area per cylinder). This HC emission amount serves as a barometer showing the combustion state, and the smaller the amount, the higher the combustion efficiency and the better the fuel consumption as well as the emission. Also, FIG.
Shows the relationship between the maximum torque and the squish area ratio, which are obtained at high rotation with a full open load. It should be noted that each of these figures shows data when the intake valve closing timing is variously changed, and in addition to the case where the intake valve closing timing is set to ABDC 65 ° CA and later than this, as a comparative example, an ABDC50.
The case of ° CA is also shown.

According to FIG. 7, when the intake valve closing timing is changed, the smaller the intake valve late closing, the smaller the HC discharge amount due to the rise in the combustion temperature, and the HC exhaust amount as the intake valve closing timing becomes late. Will increase. On the other hand, when the squish area ratio is changed, as the squish area ratio increases to a certain extent, the HC emission amount decreases as the combustibility is increased by the squish flow, and the HC emission amount increases when the squish area ratio is about 18%. Is the smallest. By increasing the squish area ratio to this extent, the HC emission amount is sufficiently reduced even when the intake valve closing timing is delayed.

If the squish area ratio is made larger than this level, the amount of HC emission tends to increase due to an increase in the unburned air of the air-fuel mixture in the squish area. However, when the squish area ratio becomes large, the influence of the combustion temperature becomes relatively small because the squish flow greatly affects the combustion, and therefore the degree of increase in the HC emission amount by delaying the intake valve closing timing becomes small. . Then, up to a squish area ratio of about 25%, the amount of HC emission can be suppressed to an allowable level.

Further, according to FIG. 8, when the intake valve closing timing is changed, as the intake valve closing timing becomes late, the maximum torque becomes high due to the above-mentioned action. Further, when the proportion of the squish area is changed, the maximum torque is increased to some extent by the combustion promoting action of the squish flow. That is, the maximum torque is significantly increased by delaying the intake valve closing timing and increasing the squish area ratio to some extent. Then, the intake valve closing timing is set to ABDC65.
When the temperature is above CA, the squish area ratio is 15
If it is at least about%, the maximum torque can be sufficiently increased.

From the data shown in FIGS. 7 and 8,
When the intake valve closing timing is ABDC 65 ° CA or more,
By setting the squish area ratio within the range of 15% to 25%, both the effect of sufficiently increasing the maximum torque and the effect of suppressing the HC emission amount to a relatively low level are achieved.

Further, the intake valve closing timing is ABDC 65 ° CA.
When the squish area ratio is in the range of 15% to 25% in the state of being retarded as described above, the combustion speed does not increase more than necessary, and the increase of NOx can be prevented.

Although the opening / closing timing of the intake valve is fixed in the above embodiment, the opening / closing timing of the intake valve may be changed according to the operating condition by a variable valve timing mechanism (not shown). The valve closing timing may be delayed closing at least ABDC 65 ° CA at least in the high load range.

The supercharger is not limited to the mechanical supercharger as in the above embodiment, but may be a turbocharger.

[0041]

As described above, according to the present invention, in the engine equipped with the supercharger and the intercooler, the intake valve closing timing is set to be 65 ° or more after the bottom dead center at least in the high load range, and the squish area is set. Is formed and the ratio of the area of the squish area to the cylinder bore cross-sectional area per cylinder is set to 15% to 25% (Claim 1). By supercharging, the engine torque can be increased, and the squish flow due to the squish area can improve the combustibility. In particular, by setting an appropriate squish area ratio corresponding to the slow closing of the intake valve as described above, the synergistic effect of these increases the engine torque further, and the complementary effect of these improves the emission and fuel consumption. You can

In the present invention, the intake port is set to 1
If a plurality of cylinders are formed and each intake port is a tangential port that opens substantially in the cylinder axis direction (claim 2), intake resistance at the time of high supercharging can be reduced and the effect of improving torque can be enhanced. . Further, a mechanical supercharger is provided as a supercharger, and the geometric compression ratio of the engine is set to 8.5.
With the above configuration (claim 3), it is possible to effectively increase the torque by sufficiently increasing the supercharging pressure while closing the intake valve late.

[Brief description of drawings]

FIG. 1 is an overall schematic plan view of an engine with a supercharger according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of the engine.

FIG. 3 is a schematic plan view of a combustion chamber constituent portion of the engine.

FIG. 4 is a sectional view of a constituent part of a combustion chamber.

FIG. 5 is an explanatory diagram showing opening / closing timing of an intake valve.

FIG. 6 is an explanatory diagram regarding definition of intake valve closing timing.

FIG. 7 is a graph showing the relationship between the squish area ratio and the amount of discharged HC for various intake valve closing timings.

FIG. 8 is a graph showing the relationship between the squish area ratio and the maximum torque for various intake valve closing timings.

[Explanation of symbols]

 1 Engine Main Body 2 Cylinder 3 Piston 4 Combustion Chamber 5 Intake Port 7 Intake Valve 12 Intake Passage 20 Supercharger 22 Intercooler 33 Squish Area

Claims (3)

[Claims] 1. A supercharged engine having a supercharger and an intercooler located downstream thereof in an intake passage,
At least in the high load region, the intake valve closing timing is set to be late at 65 ° or more after the bottom dead center in the crank angle, and the cylinder head inner wall and the piston top wall forming the combustion chamber face each other in parallel and at the time of top dead center. An engine with a supercharger, characterized in that a squish area having a minute gap is formed, and a ratio of an area of the squish area to a cylinder bore cross-sectional area per cylinder is set to 15% to 25%. 2. A plurality of intake ports are formed per cylinder,
Moreover, each intake port is a tangential port that opens substantially in the cylinder axis direction.
Engine with supercharger as described. 3. The supercharged engine according to claim 2, wherein a mechanical supercharger is provided as the supercharger, and the geometric compression ratio of the engine is set to 8.5 or more.