JP2006152952A - New opposed piston type two stroke cycle engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reciprocating engine of good fuel economy by reducing cooling loss in a small size two stroke cycle engine for a passenger vehicle or the like. <P>SOLUTION: In this opposed piston type two stroke cycle engine, bent shape cylinders 2 are provided, horizontal surfaces 11 are formed on head surfaces of both pistons 1A, 1B opposing to bent part inner angle side 2A, and the two horizontal surfaces 11 mutually butt at top dead center position to squeeze volume of a combustion chamber 3 provided in a bent part outer angle side. Since TDC combustion chamber wall area is reduced by half as compared to a four stroke engine by adopting this structure, cooling loss can be reduced by 35-45%. A problem that fuel economy of a reciprocating engine at low speed light load operation is bad due to increase of ratio of cooling loss at low speed light load operation can be eliminated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a two-stroke cycle engine. In particular, the present invention relates to a small two-stroke cycle engine for passenger cars.

The problem with passenger car engines is poor fuel economy at low speeds and low loads.
The fuel economy of the latest passenger car diesel engine is excellent.
Its thermal efficiency is as high as about 34 to 39% at high speed and high load.
On the other hand, at low speed and low load, which is typified when traveling in the city, the thermal efficiency is reduced to 20 to 25%.
The main cause is cooling loss of the piston head surface and the cylinder head.
This is because the cooling heat transfer area does not change even at a low speed and a low load, and therefore the cooling loss does not decrease even when the engine output decreases.
At high speed and high load, the cooling loss is as low as 12 to 15% of the fuel heating value, but rapidly increases to 17 to 22% during low and medium speed operation.
In passenger car engines, the frequency of low and medium speed operation is high.
Therefore, in particular, measures for improving fuel consumption should be taken into consideration at the time of low and medium loads.
The mechanism of this cooling loss will be described next.
Between the crank angle of 5 degrees before the TDC (top dead center) and the crank angle after the TDC of 35 degrees, the temperature and pressure are the highest.
The cooling loss here occupies the majority of the whole and greatly affects the decrease in thermal efficiency.
The S / V ratio is defined as the cooling surface area S of the combustion chamber with respect to the TDC combustion chamber volume V. By minimizing the S / V ratio, the cooling loss is reduced and the thermal efficiency is improved.
FIG. 3 is a schematic explanatory diagram showing the shape of the TDC combustion chamber 3 of the latest four-stroke cycle diesel engine.
As a four-stroke cycle diesel engine, the combustion chamber 3 has the best shape, but a method of providing a deep dish recess 12 on the piston head surface has been implemented.
The gap 14 between the piston head surface other than the deep dish recess 12 and the cylinder head 2H is narrowed to reduce the S / V ratio.
However, the complicated cylinder head 2H shape with the intake valve 19 and the exhaust valve 20 is an obstacle, and the shape of the combustion chamber must be flat.
FIG. 4 shows the shape of the combustion chamber 3 in TDC of a conventional opposed piston type two-stroke cycle engine.
The opposed-piston scavenging method has higher scavenging performance and charging efficiency than the Schneille scavenging method that is common in 2-stroke cycle engines.
Therefore, the output performance is high and it has a track record as a high-speed diesel engine for aviation.
The opposed piston type two-stroke cycle engine does not have a cylinder head, has no cooling loss from the cylinder head surface, and is expected to reduce the cooling loss.
However, in this type, the fuel injection valve 10 must be provided on the cylinder side peripheral surface 2, the shape of the TDC combustion chamber 3 becomes flat, and the S / V ratio is not improved.
Therefore, the thermal efficiency is equivalent to other diesel engines.
The biggest drawback is that the piston heat load becomes excessive because most of the severe combustion heat load near TDC is received by the entire head surface of the piston.

An object of the present invention is to provide a reciprocating engine having a small cooling loss and excellent fuel efficiency.

  Hold the refracting cylinder 2 with the horizontal surface 11 on the head surface of both pistons 1A and 1B facing the internal angle side 2A of the refracting part, and butt the two horizontal surfaces 11 at the top dead center position. An opposed piston type two-stroke cycle engine characterized by narrowing the combustion chamber 3 to the external angle side 2B is adopted.

Next, effects of the present invention obtained by adopting the above structure are listed below.
1) The opposed piston type scavenging method with high scavenging performance can be adopted by the two opposed pistons 1A, 1B having the horizontal surface 11 at the head and the refraction cylinder 2.
2) The wall area of the TDC combustion chamber 3 can be minimized. Compared to a 4-stroke engine, the TDC combustion chamber wall area is halved and the cooling heat loss can be reduced by 35 to 45%.
3) The combustion heat load in the vicinity of TDC can be shared to the cylinder 2 side to reduce the heat load on the piston 1 side. This reduces the heat load to the same level as a 4-stroke engine.
4) There is no valve operation required in a 4-stroke cycle engine, and mechanical loss due to valve drive is eliminated.
5) With the rhombus arrangement, multiple cylinders can be arranged compactly, and a high output ratio can be obtained. High speed rotation

1 and 2 show an embodiment of the present invention applied to a two-stroke cycle diesel engine for a small passenger car.
Diamond-shaped cylinders with V-shaped cylinders arranged at the top and bottom are arranged to form two opposed piston type two-stroke cycle engines on the left and right.
Crank rotation shafts 4A and 4B are provided at the upper and lower rhombus corners to form a 4-piston rhombus arrangement.
The combustion chamber 3 is provided on the outer corner side 2B of the left and right rhombus corners.
The opposed piston engine on the right side (back side) is in the process of starting the expansion process at the TDC (top dead center) position.
The counter piston type engine on the left side (front side) is in the scavenging process at the BDC (bottom dead center) position.
That is, the state of the crank angle of 180 degrees is shown on the left and right.
The piston diameter is 54 mm, the stroke is 55 mm, and a four-piston rhombus arrangement is taken as an example, and this is a small engine with a displacement of 504 cc.
The opposed piston type scavenging method of this configuration is shown on the left side of FIG. 1 and is basically the same as the conventional opposed piston type scavenging method.
Exhaust can be pushed straight out by scavenging. It also has the advantages of high scavenging performance and no complicated valves.
As in the conventional opposed piston system, a method of increasing the charging efficiency by advancing the exhaust side piston crank angle by 8 ° from the scavenging side piston crank angle can be used.
The main scavenging port 5 is opened in parallel to the piston horizontal surface 11, and a good single flow is formed.
Although not shown in the drawing, a turbocharger using a crank chamber type scavenging pump and an exhaust turbine is provided on the scavenging side piston 1A side as in the conventional two-stroke cycle engine.
The opening area of the auxiliary scavenging port 5A is relatively small and scavenges the piston recess 12 side.
The distance between the scavenging port 5 and the exhaust port 6 is shortened to about 85 to 90% as compared with the conventional opposed piston type having the straight cylinder 2C, and can be applied to higher rotational speed operation.
The cylinder 2 side combustion chamber shape 3A makes the scavenging flow smooth without becoming a dead zone.
The TDC combustion chamber 3 is formed on the outer corner side 2B of the left and right rhombus corners.
The shape of the combustion chamber can be a shape having the best S / V ratio, that is, a shape approximating a sphere.
FIG. 2 shows the head shape of the piston 1.
A horizontal surface 11 in which the piston head is cut in a horizontal plane, a vertical surface 13 in which the piston is cut in a vertical plane, and a side surface 16 in which the side is cut are formed into a mountain shape.
A spherical wedge-shaped recess 12 is installed at the top of the mountain to constitute a part of the space in the combustion chamber 3.
The combustion chamber outer corner side wall 2 </ b> B belongs to the cylinder 2.
Narrow gaps 14 and 15 called squish areas are formed at the TDC position at the horizontal plane 11 and the vertical plane 13.
Although not shown, a part of the squish area is also formed on the side surface 16.
Since these squish areas do not have a valve, smooth surfaces can be matched. Therefore, the minimum gap can be achieved.
The wall surface area of the TDC combustion chamber space 3 is also applied to the central side wall 3A of the cylinder 2 and the piston-side depressions 12, and the area ratio distribution is 50:50.
The wall area of the piston-side depression 12 is as small as about 30% of the flat piston head area.
On the piston side, only the piston-side depression 12 receives a combustion heat load in the vicinity of TDC, so that the heat load of the entire piston is reduced.
The high-pressure fuel injection valve 10 is installed, and stable combustion control is performed in the spherical combustion chamber.
As described above, it is a feature of the new opposed piston type two-stroke cycle engine that the design around the combustion chamber having a degree of freedom is possible.
By adopting a refractive shape, a large space can be taken on the outer angle side.
Since no valve is required, the optimal combustion chamber design can always be made using the space.

The above embodiment is shown for a diesel engine, but the present invention can be completely applied to any engine that can apply a two-stroke cycle.
The present invention is also applied to the fields of gasoline engines and gas engines.
In particular, since the cooling loss is small, it is most suitable as an internal combustion engine for distributed electric power and heat production.

FIG. 1 is an overall sectional view showing an embodiment in which a rhombus opposed piston type two-stroke cycle engine of the present invention is applied to a gasoline engine. The rhombus opposed two-stroke cycle engine of the present invention is shown symmetrically. The left half shows the stroke state at the bottom dead center position, and the right half shows the stroke state at the top dead center position. FIG. 2 is a perspective view of the piston head, similarly showing the essential points of the present invention. FIG. 3 is a cross-sectional view showing the combustion chamber shape of the latest 4-stroke cycle diesel engine. FIG. 4 is a cross-sectional view showing a combustion chamber shape of a conventional opposed piston type two-stroke cycle diesel engine.

Explanation of symbols

1 Piston 1A Scavenging side piston 1B Exhaust side piston 2 Refraction cylinder 2A Refraction cylinder inside angle side 2B Refraction cylinder outside angle side 2C Straight cylinder 2H Cylinder head 3 Combustion chamber 3A Refraction cylinder outside angle side combustion chamber wall 4A Lower crankshaft center 4B Upper crankshaft center 5 Main scavenging port 5A Sub scavenging port 6 Exhaust port 10 High pressure fuel injection valve 11 Piston head horizontal surface 12 Piston-side depression 13 Piston head vertical surface 14 Squish area 15 generated in piston head horizontal surface 11 Piston head vertical surface 13 Generated squish area 16 Piston head side surface 19 Suction valve 20 Exhaust valve

Claims (1)

Hold the refracting cylinder 2 and have the horizontal surface 11 on the head surface of both pistons 1A and 1B facing the internal angle side 2A of the refracting part, and put the two horizontal surfaces 11 together at the top dead center position. An opposed piston type two-stroke cycle engine characterized in that the volume of the combustion chamber 3 is narrowed to the outer angle side 2B of the refracting portion.

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