WO2010107139A1

WO2010107139A1 - Method for manufacturing a small gasoline engine with high expansion ratio

Info

Publication number: WO2010107139A1
Application number: PCT/KP2009/000019
Authority: WO
Inventors: Bong Dae Lee; Gwan Chol Sin; Gwang Il Kim; Chang Rim Pak
Original assignee: Bong Dae Lee
Priority date: 2009-03-18
Filing date: 2009-12-23
Publication date: 2010-09-23

Abstract

The present invention relates to the method for manufacturing a small gasoline engine with high expansion ratio. This method includes selecting the reasonable gas distribution phase to have a higher expansion ratio than the compression ratio, then installing a cutoff (10) between the carburetor and the intake valve to baffle the backdraught which results in the change of the gas distribution phase, adjusting the ignition advance angle and the strength of the spring in the governor to prevent the instability at low speed operation and increasing the number of the bleed holes in the carburetor to reduce the density of the fuel.

Description

METHOD FOR MANUFACTURING A SMALL GASOLiNE ENGINE WITH HIGH EXPANSION RATIO

BACKGROUND OF THE INVENTION 1. Field of the invention

The present invention relates to the method for manufacturing the small gasoline engine with high expansion ratio without using any expensive accessory apparatuses such as a supercharger or electronic controls for gas distribution phase.

2. Description of the background

In the situation that the price of petroleum is now raising dramatically in the world but its fields for use are being further expanded, economy in fuel in internal combustion engines is considered as a pressing, problem^ and so the research on this problem is being intensified further. Also, the increase of disaster by global worming day after day makes economy in fuel, more important.

Therefore,, the competition is being held actively on a worldwide level for developing a high performance engine which lias low fuel consumption and little environment pollution.

In the nineteen nineties an asymmetric gasoline engine with high expansion ratio (Miller cycle engine) in which the expansion ratio is higher than the compression ratio has been invented and began to be used. In a research paper it was disclosed that the thermal efficiency was improved up to 12% when the expansion ratio was made 1.5 times higher than the compression ratio, and then the maximum thermal efficiency was maintained in all the load ozones by predetermining the expansion ratio as the optimal one in the aspect of thermal efficiency and the actual compression ratio highly up to the value corresponding to a knocking limit.

In Summa of Scientific Lecture Meeting (Automobile Technology Society) No. 975 1997-10 page 39 and No. 946 1994-10 page 77, a Japanese magazine, some methods for raising an expansion ratio in the engines of automobile and their efficiency was published. According to them the engines with high expansion ratio so far developed require some complicated controls or .have intricate structures due to the electronic control for gas distribution phase and like, so their production costs are very high and after all it lias not been introduced in small engines. That's because it's impossible to ensure economic profit by means of expensive production cost whereas fuel consumption may be decreased if a high expansion ratio is given to small gasoline engines using some additional controls- Therefore, an economic small gasoline engine with high expansion ratio ias not been yet invented.

The practical significance will be very .great if. a small .gasoline engine with high expansion ratio is manufactured without using any expensive accessory apparatuses such as a supercharger or electronic controls for gas distribution phase.

SUMMARY OF THE INVENTION

The object of -the present invention is to provide the method for manufacturing a small gasoline engine with high expansion, ratio without using any complicated controls. The engines with high expansion ratio have two types, that is, early closing type and late closing type of intake valve. ,In the former the dynamic property of gas distribution mechanism gets worse uv a high-speed engine since the cam, grows sharper due to decrease of, its working duration of intake. In the latter this problem does not occur, but the output is decreased since the backdraught to the suction pipe arises. IrLgeneraLthe engines with high expansion jatio Jiave the advantage of high thermal efficiency and low fuel consumption but the maximum output is decreased.

It is most important to select .a reasonable -gas distribution phase in manufacturing a small gasoline engine with. high, expansion ratio. The reasonable gas distribution phase means ihe one in which the maximum output of the engine is maintained and its specific fuel consumption is minimum.

This was selected based on a simulation, on- computer and an, analysis, by the operational experiment method. The reasonable section was decided with changing the intake valve closing, crank, angle and exhaust valve opening crank angle within some ranges in a calculation program for working process, simulation, A.V.L.4.0. As a result it was desirable that the intake valve is closed at 80 to 85 degrees after the lower dead point and the exhaust valve is opened at 61. to 64 degrees before the lower, dead point. Then the volume of the combustion chamber was xeduced so that the expansion ratio was 9.8 to 10.5 and the compression, ratio was 8.0 to 8.5,. so the engine was given.ahigh expansion ratio.

In the late closing- engine with- high, expansion ratio the au>fuel mixture grows considerably denser due to the backdraught by which the mixture is put out to the suction, passage, during- compression stroke since the intake valve is not even closed after the piston has passed the lower dead point during intake stroke. To prevent this backdraught its flow characteristic was analyzed experimentally on computer. This backdraught ϋows .from the cylinder to the suction, pipe through the intake valve,- so the distribution of its flow velocity in the cross section was simulated on computer and confirmed experimentally.

The result of analysis by a computer application, "FLUENT" showed that the flow velocity of the backdraught, which is. fastest in. the center of the suction pipe and grows slower to the wall of the pipe, has a parabolic distribution. Accordingly a cutoff which has one or more annular holes was installed between the carburetor and the intake valve. The part for baffling the backdraught in the cutoff which should have the minimum resistance during intake .stroke was made cone-shaped. And in .all the experiments the signal-to-noise ratio (A/E) that horse power loss, dose not exceed 5% but the specific fuel consumption is minimum was decided using "MATLAB" application and main design characters were confirmed in the engine performance experimentaccording to the quality engineering method.

The instability at low-speed, operation can be removed by adjusting, the ignition advance angle and the strength of the spring in the governor. The ignition, advance angle that keeps the maximum output and is suitable to low-:speed and. highspeed operation in accordance with the change of the consumption condition in the cylinder was confirmed experimentally. As a result it was better to decrease the ignition advance angle slightly. Moreover,, the strength of the spring, in- the governor was enhanced within.5 to 12% limit of rotation variation xate to prevent the fluctuation of the gas valve in the carburetor at low-speed operation. The density of air-fuel mixture which results in the backdraught was restricted by the extension of the air compensation channel in the carburetor. The change of air-to-fuel ratio (AJF) by the backdraught causes significant deflection of air-to-fuel ratio (A/F) between full-load and partial load due to influence of gas valve opening angle.

The air compensation channel of the main nozzle is an element that can adjust the air-to-fuel ratio (A/F) according to the size of gas valve opening angle in the carburetor (i.e. a negative pressure). When the opening angle is small (that is, the negative pressure is small), air is injected through only the upper bleed holes but the lower bleed holes do not work. But at full-load the negative pressure grows bigger, the oil level around the main nozzle gets lower, and so the lower bleed holes are opened.

To reduce the deflection of air-to-fuel ratio (A/F) between full-load and partial load some bleed holes which only work at full-load were further drilled at the lower portion of the main nozzle so that even at full-load the air-to-fuel ratio (A/F) can be kept in the order of 12 to 13.

The present invention has the following economic effectiveness;

First, fuel can be economized up to 12 to 18% by making the expansion ratio higher than the compression ratio in a small gasoline engine and so lowering the minimum specific fuel consumption much more than before.

Second, since the whole structure of the engine according to the present invention has no obvious difference with the previous one the structure is simple and the production cost is nearly the same as before.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is an embodiment of the small gasoline engine with high expansion ratio according to the present invention.

Fig. 2 shows the .gas distribution phase in one embodiment of the small gasoline engine with high expansion ratio according to the present invention. Fig. 3 is the structure of a cutoff for baffling the backdraught in one embodiment of the small gasoline engine with high expansion ratio according to the present invention.

Fig. 4 is the structure of the main nozzle in. the carburetor in one embodiment of the small gasoline engine with high expansion ratio according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is an embodiment of the small gasoline engine with high expansion xatio according to the present invention. In Fig. 1 the engine comprises an intake valve l_τ a valve spring %. a retainer 3 of the valve spring, a rocker arm 4, a push rod 5, a. tappet 6, a cam 7, a piston 8, a combustion chamber 9, a cutoff for baffling the backdraught 10 and an intake channel 1 L As shown here, no the engine has any other controls except for the cutoff for baffling the backdraught installed between the carburetor and the intake valve.

Fig. -2 shows the gas distribution phase in one embodiment of the small gasoline engine with high expansion ratio according, to the present invention. In this embodiment the intake valve closing angle and exhaust valve opening angle at which a predetermined output is maintained and the specific fuel consumption is minimum were decided using the calculation program for working process simulation, AJV.LA0, while the intake valve closing angle was changed from 57 degrees to 93 degrees after the lower dead point and the exhaust valve opening angle from 63 degrees to 36 degrees before the lower dead point.

As a result in case the intake valve closing angle was 84 degrees after the lower dead point and the exhaust valve opening angle was 63 degrees before the lower dead point the output was maximum and the specific fuel consumption, was minimum. And then by decreasing the volume of the consumption chamber about 25% to make the expansion ratio 10.2 and the compression ratio 8.4 the engine was given me high expansion ratio.

Since the backdraught to the suction pipe occurs in late closing engines a cutoff for baffling it was installed between the carburetor and the intake valve. At that time the structure of the cutoff was shaped so that the intake resistance .got minimum. Fig. 3 is the structure of a cutoff for baffling the backdraught Ln one embodiment of the small .gasoline engine with high expansion ratio according to the present invention. In Eig. 1 an intake valve seat L2, a cylinder head 13, . a sleeve 14 of the intake valve and a flange 15 are included. As shown in Fig~ 3 the main components of the cutoff contain the conical portion in the center for baffling the backdraught and an annular hole around LL In the figure the letter P indicates the direction of intake of the air-fuel mixture, L is the length of the fluid channel from the intake valve to the cutoff, D is the diameter of the flow channel of the fluid, d is the diameter of the cone base and αis the cone angle. In this embodiment three factors,. Including the diameter (d) of the cone base, the length (L) of the fluid channel from the intake valve to the cutoff and the cone angle (α) were defined as the design characters of the cutoff and the _ o _

experiment was made based on an orthogonal table which has them as the parameters. As a result d is 18.0mm,Lis 70mm.and α is 97 degrees.

In an embodiment according to the present invention to remove the instability at Jow-speed operation the ignition advance angle was made 22 degrees that is smaller 2 degrees than before and the strength of the spring in the governor was enhanced so that thejotation variation rate was kept about

7%.

Pig. 4 is the structure of the jnain nozzle in the carburetor in one embodiment of the small gasoline engine with high expansion ratio according to the present invention. In Fig. 4, a new bleed hole 16, the main nozzle 17, the body of the carburetor 18_r the float 19_y the float chamber 20

-and the main jet^ J- are included. In this embodiment to reduce the deflection &f ak-to-fuel ratiα between full- load and partial Joad. two Jiew bleed Jioles which work only atϋill-load time were drilled at the lower portion of the main nozzle in the carburetor and thus the.airτto-fuel ratio (A/F).atiull-load time was increased 0.93.

In an embodiment of the present invention, the minimum specific fuel consumption was decreased irom the previous ,230g/(HP:h) to less than 210g/(HP h) and accordingly fuel was economized up to 18%_^

Claims

1. The method for manufacturing a small gasoline engine with high expansion ratio, which includes selecting the reasonable gas distribution phase, installing a cutoff between the carburetor and the intake valve foe baffling the backdraught, adjusting the ignition advance angle and the strength of the spring in the -governor to remove the instability at low-speed operation and extending the air compensation channel of the carburetor to reduce the density of fuel.

2. The method according to claim l_r wherein the intake valve is closed at 82 to 85 degrees after the lower dead point.

3. The method according to claim. 2,. wherein, the volume of the combustion chamber is decreased so that the expansion ratio is 9.8 to 10.5 and the compression ratio is 8.0 to 8.5.

4. The jnethod according to claim J, wherein the backdraught cutoff has one or more annular boles.

_5. The method according to claim 1, wherein to remove instability at low-speed operation the ignition advance angle is decreased within thexange that the .power decrease does .not occur and the strength of the spring in the governor is enhanced within 5 to 12% limit of rotation variation rate.

6. The method according to claim 1, wherein the number of bleed holes in ihe main nozzle of the carburetor is increased to keep the air-to- fuel ratio (A/F) in the order of 12 to 13.