JPH08326548A - Lag closing mirror cycle engine - Google Patents

Abstract

PURPOSE: To improve the efficiency of a lag closing mirror cycle engine by a method wherein the closing period of an intake valve is set to a value in a specified range after a bottom dead center and an expansion ratio is set to a value in a specified range. CONSTITUTION: In an engine 1, a cylinder 11 having an inner wall over which a piston 13 coupled through a connecting rod 14 is slid is provided. A cylinder head 12 positioned at the upper part of the cylinder 11 and having an intake port 17 and an exhaust port 18 is provided. Further, an intake valve 15 and an exhaust valve 16 to open and close the opening parts of the intake port 17 and the exhaust port 18 are provided. The control system of the engine 1 is sets a control target value so that an air ratio is adjusted to 1.0. In addition to the above, the closing period of the intake valve 15 is set to a value within a range of 70-150 deg. after a bottom dead center. Further, an expansion ratio is set to a value in a range of 12-20. This constitution increases the expansion ratio and improve efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston, a cylinder on which the piston slides on an inner wall, a cylinder head located above the cylinder and having an intake port and an exhaust port, and the intake port and the exhaust port. The present invention relates to a late-closing Miller cycle engine in which an intake valve and an exhaust valve for opening and closing the respective openings are provided, and the intake valve closes the intake port after the crank rotates by a predetermined angle after the bottom dead center has passed.

[0002]

2. Description of the Related Art As a method for improving the thermal efficiency of an internal combustion engine, a Miller cycle engine is known in which the energy of combustion gas is sufficiently expanded and taken out. The Miller cycle engine has an intake early closing system and an intake late closing system.

In the intake early closing system, as shown by the line b in FIG. 5 (valve lift characteristic diagram), the maximum value of the valve lift is the same as the valve lift characteristic of the normal intake valve shown by the line a. However, the characteristics are such that the intake valve closes directly and quickly. However, as a result of such characteristics, the seating speed and acceleration of the intake valve become large, and problems occur in the strength of the valve body and the strength of the valve seat. Here, in order to equalize the seating speed and acceleration of the intake valve, it is sufficient to reduce the valve lift as indicated by line c in the figure, but if the valve lift is reduced, intake efficiency will decrease.

In order to avoid this, as shown in FIG. 6, an opening / closing means, for example, a rotary valve 6 which opens and closes in synchronization with the engine rotation in the middle of the intake pipe 2 reaching the intake port 17 (the valve lift characteristic of the rotary valve is (Indicated by d line in FIG. 5)
Alternatively, a method of interposing a lead or the like (not shown) may be used.

However, as is apparent from FIG. 6, the dead volume (D / D) between the intake valve 15 and the rotary valve 6 is increased.
Due to the presence of V), there is a problem that the air-fuel mixture of “dead volume” (D / V) is sucked in even after the rotary valve is closed. Further, since a complicated mechanism is required for the intake timing, the intake pipe shape, etc., there are concerns such as an increase in cost and durability.

Here, in the intake early closing system, as shown in FIG.
As shown by the line AB in the Shiatsu line diagram, the intake stroke is stopped midway,
Returning to FIG. 6, when the piston 13 further descends from there, the gas inside the cylinder 11 expands, which has the merit of including a so-called internal cooling cycle in which a temperature drop occurs. For,
Requires higher intake pressure.

On the other hand, the valve lift characteristic when the late intake closing system is adopted is shown by the characteristic curve e in FIG. Then, in the case of the late intake closing method, even if the piston moves upward from the bottom dead center, the intake valve remains open, and the intake air once flowing into the cylinder is pushed back to the intake port side (blowback). After that, if the intake valve is closed at the proper piston position, the actual compression stroke starts from that point.

Here, the late closing Miller cycle engine can be realized only by replacing the intake cam, and it is not necessary to provide a rotary valve or the like as in the above-described early closing system. Therefore, it is low in cost and excellent in durability and reliability. Further, since the valve flow area is increased by the area of the hatched region in FIG. 8, the intake efficiency is improved and the intake pressure can be lowered. Then, it is possible to prevent the efficiency of the engine from being lowered due to the fact that the intake pressure is not increased.

In the conventional late-closing Miller cycle engine, the time when the intake valve is closed is in the range of 40 ° to 70 ° after bottom dead center.

[0010]

As described above, the late-closing Miller cycle engine can eliminate the drawbacks when the intake early closing system is adopted. However, there is a demand to further improve the efficiency of late closing Miller cycle engines. The present invention has been proposed in view of such a demand.

[0011]

As a result of various researches and studies, the inventor need not limit the timing of closing the intake valve in the late-closing Miller cycle engine to a range of 40 ° to 70 ° after bottom dead center. I found out.

The Miller cycle engine of the present invention proposed on the basis of such knowledge has a piston, a cylinder on which the piston slides on the inner wall, and an intake port and an exhaust port located above the cylinder. A cylinder head and an intake valve and an exhaust valve for opening and closing the openings of the intake port and the exhaust port, respectively, are provided, and the intake valve opens the intake port after the crank rotates by a predetermined angle after the bottom dead center has passed. The late-closing Miller cycle engine which is closed is characterized in that the intake valve closing timing is in the range of 70 ° to 150 ° after bottom dead center and the expansion ratio is in the range of 12 to 20.

Here, the present invention provides a gas engine (including both a gas engine that burns at a stoichiometric air-fuel ratio and a lean-burn type gas engine), a diesel engine, a gasoline engine, or any other engine that can perform a Miller cycle. All are applicable.

In the present invention, when the engine is a gas engine, the intake valve closing timing is 70 ° to 1 after bottom dead center.
It is preferably in the range of 40 ° and the expansion ratio is in the range of 12 to 16. Here, the gas engine may be a gas engine that burns at a stoichiometric air-fuel ratio or a lean burn type gas engine.

Similarly, when the engine is a gas engine (including both a gas engine that burns at a stoichiometric air-fuel ratio and a lean burn type gas engine), the intake valve closing timing is 100 ° to 150 after bottom dead center. Preferably, the expansion ratio is in the range of 14 to 18 and the expansion ratio is in the range of 14 to 18.

Further, when the engine is a gas engine (including both a gas engine that burns at a stoichiometric air-fuel ratio and a lean burn type gas engine), the intake valve closing timing is 110 ° to 150 ° after bottom dead center. It is also preferred that the expansion ratio is within the range of 16 to 20.

In the practice of the present invention, the blow-back intake air is cooled at the joint between the intake manifold of the late-closing Miller cycle engine and each intake port of the cylinder head in order to cool the air-fuel mixture blown back from inside the cylinder of the engine. It is preferable to provide cooling means.

[0018]

According to the Miller cycle engine of the present invention having the above-described structure, the intake valve closing timing is 70 after the bottom dead center.
In the range of ° to 150 °, the delay angle is extremely large compared to the case where the intake valve closing timing is 40 ° to 70 ° after bottom dead center when the conventional late closing system is adopted. Along with this, the expansion ratio is set within the range of 12 to 20, and this expansion ratio is also a higher value than in the case of the conventional slow-closing method.

Here, in the present invention, since the delay angle is extremely large as described above, the compression ratio does not become so high even if the expansion ratio becomes large. Therefore, it is possible to increase the expansion ratio and improve the efficiency while suppressing the compression ratio to a range that does not cause knocking.

As a result of various experiments and simulations, the conventional slow-closing method (delay angle is 40 ° -70 °)
According to the present invention (delay angle 70 ° -150
The expansion ratio is 12-20, preferably the delay angle is 70.
Expansion ratio of 12-16 and delay angle of 100 at -140 °
Expansion ratio of 14-18 and delay angle of 110 at -150 °
It has been found that the efficiency is improved when the expansion ratio is 16-20) at -150 °.

In order to cool the air-fuel mixture blown back from the cylinder of the gas engine, if a blow-back intake air cooling means is provided, the blow-back intake air is cooled, and the cool intake air with high filling efficiency is provided in the next intake stroke. As a result, the operating efficiency is further improved.

Here, the reason why the delay angle of the intake valve is set to 70 ° or more is that if it is less than 70 °, knocking may occur, and the difference from the conventional slow closing system is eliminated. On the other hand, the reason why the delay angle is 150 ° or less is that it has been confirmed by simulation that the heat loss sharply increases above 150 °, and that if this angle becomes too large (for example, 180 ° or more), It becomes impossible to operate.

[0023]

Embodiments of the present invention will be described below with reference to FIGS. In the illustrated embodiment, a gas engine that burns at a stoichiometric air-fuel ratio will be described. FIG.
In the engine 1, the cylinder 11 on which the piston 13 connected to the inner wall by the connecting rod 14 slides, and the intake port 1 located above the cylinder 11.
7, a cylinder head 12 having an exhaust port 18 and an intake valve 15 and an exhaust valve 16 for opening and closing the openings of the intake port 17 and the exhaust port 18 are provided. An intake pipe 2 is provided in the intake system from an air intake port (not shown) to the intake port 17 of the cylinder head, and the intake pipe 2 is provided with a turbocharger 4 and an intercooler 3. In addition, as shown by reference numeral 5 in FIG. 1, it is preferable to interpose a cooler 5 for blow-back intake cooling, which is a blow-back intake cooling means. However, in the embodiment shown in FIG. 2 and the subsequent drawings, the blow-back intake air cooling cooler 5 is not provided.

Although not clearly shown in FIG. 1, an exhaust system (not shown) of the engine 1 is provided with a three-way catalyst (not shown). The engine is operated by a control system (not shown) so that the air ratio in the air-fuel mixture supplied to the engine 1 becomes around 1.0. In other words, the control target value of the control system of the engine 1 is set so that the air ratio becomes 1.0. In addition to this, the closing timing of the intake valve 15 is
It is set in the range of 70 ° to 150 ° after bottom dead center, and the expansion ratio is in the range of 12 to 20 (for example, if the delay angle is 70 ° -140 ° and the expansion ratio is 12-16, the delay angle is The expansion ratio is 14-18 at 100 ° -150 °, or the expansion ratio is 16-2 at a delay angle of 110 ° -150 °.
It is set to 0). However, the relationship between the closing timing (delay angle) of the intake valve 15 and the expansion ratio differs for each engine. The delay angle and the expansion ratio in the illustrated embodiment are a combination appropriately selected from the above range.

FIG. 2 shows the relationship between the delay angle and the efficiency in the embodiment of FIG. 1, and is a characteristic diagram derived from the results of simulations and experiments. In addition, in FIG.
The filled plots show experimental results. As is clear from FIG. 2, the maximum value (maximum value) of efficiency could be obtained in the range of 100 ° -150 °.

In this case, a very high efficiency can be obtained with the expansion ratio 18 (characteristic curve of a square plot) which has not been considered in the past. As is clear from comparison with the characteristic curve of the expansion ratio 16 (triangle plot) and the characteristic curve of the expansion ratio 14 (circular plot), the higher the expansion ratio, the higher the efficiency.

A straight line N shown by a dotted line in FIG. 3 is a critical line for knocking occurrence, and knocking occurs if the engine characteristic is set on the side where the delay angle is smaller than the straight line (left side in FIG. 3). . And the delay angle is 12
In the range of 0 ° to 150 °, none of the three characteristic curves in FIG. 3 exists in the region where knocking may occur. However, the combination of the delay angle and the expansion ratio determines whether or not there is a region where knocking may occur, so even if the delay angle is 70 ° -120 °, knocking may occur depending on the expansion ratio. Do not wake up.

Next, the relationship between the delay angle and the expansion ratio and compression ratio in the embodiment of FIG. 1 will be described with reference to FIG. In Fig. 3, reference numeral 1-2 indicates an intake stroke, reference numeral 2-
Between 2'is a stroke corresponding to the stroke in which the intake valve is open after bottom dead center, that is, the delay angle, and the intake valve is open in the stroke between 2-2 ', so that the air-fuel mixture in the cylinder is intaken. It will be pushed out by the system. At this time, in the illustrated example, the blowback intake air cooling cooler 5 cools the extruded mixture (blowback intake air).

Reference numeral 2'-3 is a compression stroke, reference numeral 3-4 is a combustion stroke, reference numeral 4-5 is an expansion stroke, and reference numeral 5-7 is an exhaust stroke. Here, in the embodiment of FIG. 1, since the delay angle is extremely large compared to the conventional one, the stroke of reference numeral 2-2 'becomes long and the compression stroke of reference numeral 2'-3 becomes correspondingly short. On the other hand, the expansion stroke of reference numeral 4-5 is the same as that in the case of the conventional slow-closing method. As a result, in the embodiment of FIG.
The expansion stroke indicated by reference numeral 4-5 (FIG. 3) is sufficiently longer than the compression stroke indicated by reference numeral 2'-3, and the expansion ratio can be improved while suppressing the compression ratio within a range where knocking does not occur.

Such an effect is obtained by setting the delay angle to 40 °-
It cannot be obtained with an engine that adopts the conventional late closing method that was limited to 70 °. This is because the stroke of reference numeral 2-2 'in FIG. 3 is relatively short and the compression stroke of reference numeral 2'-3 is relatively long.

FIG. 4 shows the relationship between the delay angle and the heat loss, which is created by simulation. Here, the relationship between the plot of the characteristic curve and the expansion ratio is the same as in FIG. As is clear from FIG. 4, the delay angle is 100
It was possible to obtain the minimum value (minimum value) of heat loss in the range of ° -150 °.

In the illustrated embodiment, a gas engine that burns at a stoichiometric air-fuel ratio is described, but the present invention is not limited to this and can be applied to a lean burn type gas engine. In addition to the gas engine,
It should also be noted that any diesel engine, gasoline engine, or any other engine that can perform a Miller cycle can be applied.

[0033]

As described above, according to the Miller cycle gas engine of the present invention, when the intake valve closing timing is 70 ° to 150 ° after the bottom dead center and the expansion ratio is 12-20 (preferably the delay angle). Is 70 ° -140 ° and the expansion ratio is 12-16
Or, the delay angle is 100 ° -150 ° and the expansion ratio is 14-1.
8 or a delay angle of 110 ° -150 ° and an expansion ratio of 16-20), the optimum delay angle is selected regardless of the limitation of the intake valve closing timing in the conventional slow closing system. It has become possible.

Further, in the present invention, since the delay angle is extremely large, the compression ratio does not become such a high value even if the expansion ratio becomes large, and the expansion ratio is increased while suppressing the compression ratio to the range where knocking does not occur. It is possible to improve efficiency.

Further, if the blow-back intake air cooling means is provided in the present invention, the volumetric efficiency is improved and the thermal efficiency is further improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram of a delay angle and efficiency showing an operation of the embodiment of FIG.

FIG. 3 is a PV diagram showing the combustion cycle of the embodiment of FIG.

FIG. 4 is a characteristic diagram of a delay angle and heat loss showing the operation of the embodiment of FIG.

FIG. 5 is a valve lift characteristic diagram of an early closing Miller cycle.

FIG. 6 is a block diagram showing a conventional early closing Miller cycle engine using a rotary valve.

FIG. 7 is a PV diagram of an early closing Miller cycle.

FIG. 8 is a valve lift characteristic diagram of a late closing mirror cycle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Intake pipe 3 ... Intercooler 4 ... Turbocharger 5, 5A, 5B ... Cooler for blowback intake cooling 6 ... Rotary valve 11 ... Cylinder 12 ... Cylinder head 13 ... Piston 15 ... Intake valve 17 ... Intake port 20 ... Intake manifold 32 ... Cylinder 34 ... Cylinder block

Claims (4)

[Claims] 1. A piston, a cylinder on which the piston slides on an inner wall, a cylinder head located above the cylinder and having an intake port and an exhaust port, and opening and closing openings of the intake port and the exhaust port, respectively. An intake valve and an exhaust valve are provided, and the intake valve closes at the time of bottom dead in a late-closing Miller cycle engine in which the intake valve is closed after the crank has rotated a predetermined angle after the bottom dead center has passed. A late-closing Miller cycle engine characterized by an expansion ratio in the range of 20 to 150 ° and an expansion ratio in the range of 12 to 20. 2. The engine is a gas engine, and the intake valve closing timing is within a range of 70 ° to 140 ° after bottom dead center,
The late-closing Miller cycle engine of claim 1, wherein the expansion ratio is in the range of 12 to 16. 3. The delayed closing mirror according to claim 1, wherein the engine is a gas engine, the intake valve closing timing is within a range of 100 ° to 150 ° after bottom dead center, and the expansion ratio is within a range of 14 to 18. Cycle engine. 4. The late-closing mirror according to claim 1, wherein the engine is a gas engine, the intake valve closing timing is in the range of 110 ° to 150 ° after bottom dead center, and the expansion ratio is in the range of 16 to 20. Cycle engine.