Title:
CRANK CHAMBER COMPRESSION-TYPE TWO-CYCLE ENGINE
United States Patent 3687118


Abstract:
A crank chamber compression-type two-cycle engine wherein an intake passage is communicated with the interior of a cylinder through an intake port which is opened and closed by a piston disposed in the cylinder for reciprocal motion therein, and a crank chamber and the combustion chamber in the cylinder are communicated with each other through a scavenging port, opened and closed by the piston, and a scavenging passage.



Inventors:
NOMURA KAZUHIKO
Application Number:
05/053949
Publication Date:
08/29/1972
Filing Date:
07/10/1970
Assignee:
YAMAHA HATSUDAKI KK.
Primary Class:
Other Classes:
123/73A, 123/73B, 123/73CC, 123/73PP
International Classes:
F01L3/20; F02B25/00; F02B25/14; F02B33/04; F02B33/30; F02B75/16; F02M69/04; F02M69/10; F02B75/02; F02B75/12; (IPC1-7): F02B33/04
Field of Search:
123/73PP,73CC,73V,73A,73B,65A,65E,73C,65WV
View Patent Images:
US Patent References:
3530841IDLE AIR INLET VALVE1970-09-29Schultz
3107659Two-cycle internal combustion engine1963-10-22Steinlein et al.
1346001Internal-combustion engine1920-07-06Casey
1239488N/A1917-09-11Hoshel
1149296N/A1915-08-10Scott et al.
0996434N/A1911-06-27
0980134N/A1910-12-27
0890335N/A1908-06-09



Foreign References:
FR615162A
DE504909C
Primary Examiner:
Burns, Wendell E.
Assistant Examiner:
Zupcic A. M.
Claims:
I claim

1. A crank chamber compression-type two-cycle engine comprising a cylinder, a piston disposed in said cylinder for reciprocal motion therein, a crank chamber, a crank shaft rotatably supported in said crank chamber, a connecting rod connecting said piston to said crank shaft, a scavenging passage means communicating said crank chamber with said cylinder through at least one scavenging port which is open in the side wall of the cylinder and opened and closed by the piston, an intake passage means communicating with said crank chamber through an intake port which is opened and closed by said piston, said intake passage means being connected to said cylinder at a point downstream of said check valve means through an auxiliary scavenging passage means which is open into the cylinder through an auxiliary scavenging port opened and closed by the piston, an exhaust passage means communicating with the interior of said cylinder and a check valve means provided in said intake passage means and being operative in such a manner that it passes a gas flowing in a direction toward said crank chamber but blocks a gas flowing in an opposite direction, the opening timing of said intake port being located 140° to 100° before the top dead center whereby the intake air flows into the cylinder continuously.

2. A crank chamber compression-type two-cycle engine as defined in claim 1, wherein a carburetor is provided in said intake passage means and a fuel-air mixture is introduced into said crank chamber.

3. A crank chamber compression-type two-cycle engine as defined in claim 1, wherein said check valve means is a reed valve comprising a V-shape valve seat having at least one opening and at least one reed member connected to said valve seat for closing said opening and adapted to be opened with pressure exerted thereon in one direction through the opening in the valve seat.

4. A crank chamber compression-type two-cycle engine as defined in claim 1, wherein said auxiliary scavenging passage means is provided therein with a check valve being operative in such a manner that it passes a gas flowing in a direction toward the cylinder but blocks a gas flowing in an opposite direction.

5. A crank chamber compression-type two-cycle engine as defined in claim 1, wherein said auxiliary scavenging passage means is provided therein with a fuel injection nozzle and a check valve positioned on the intake passage side with respect to said nozzle and being operative in such a manner that it passes a gas flowing in a direction toward the cylinder but blocks a gas flowing in an opposite direction.

6. A crank chamber compression-type two-cycle engine as defined in claim 1, wherein said auxiliary scavenging passage means consists of a groove formed in the wall of the cylinder.

7. A crank chamber compression-type two-cycle engine as defined in claim 5, wherein said auxiliary scavenging port is opened with a slight delay after the main scavenging port is opened.

8. A crank chamber compression-type two cycle engine comprising a cylinder, a piston disposed in said cylinder for reciprocal motion therein, a crank chamber, a crank shaft rotatably supported in said crank chamber, a connecting rod connecting said piston to said crank shaft, a scavenging passage means communicating said crank chamber with the interior of said cylinder through at least one scavenging port which is open in the side wall of the cylinder and opened and closed by the piston, an intake passage means communicating with said crank chamber through an intake port which is opened and closed by said piston, an exhaust passage means communicating with the interior of said cylinder, a check valve means provided in said intake passage means and being operative in such a manner that it passes a gas flowing in a direction toward said crank chamber but blocks a gas flowing in an opposite direction, and an auxiliary scavenging passage means communicating said intake passage means with said cylinder at a point downstream of said check valve means through a port which is opened and closed by the piston.

Description:
BACKGROUND OF THE INVENTION

This invention relates to a two-cycle internal combustion engine and particularly to a crank chamber compression-type two-cycle engine. More particularly, the invention relates to a crank chamber compression-type two cycle engine of the type wherein an intake passage is communicated with a crank chamber through an intake port which is opened and closed by a piston reciprocating in a cylinder, and the crank chamber is communicated with the combustion chamber in the cylinder through a scavenging port, opened and closed by said piston, and a scavenging passage.

DESCRIPTION OF THE PRIOR ART

In a crank chamber compression-type two-cycle engine, it is well known to provide in the intake passage communicating directly with the crank chamber a reed valve which passes a gas flowing in a direction toward the crank chamber but blocks a gas flowing in an opposite direction. In the ordinary crank chamber compression-type two-cycle engines having an intake port which is opened and closed by a piston reciprocating in a cylinder, the timing at which the piston begins to open the intake port is about 80° , or less than 100° at most, before the top dead center, whereas in the engines incorporating the aforesaid reed valve the timing at which the reed valve begins to be opened is about 160° - 200° before the top dead center as result. It is also known that the two-cycle engines of the type incorporating such reed valve have the advantage that an improved power can be obtained during normal operation, because they have longer intake period.

On the other hand, the two-cycle engines having the reed valve provided in the intake pipe have the disadvantage that starting of the engine is difficult due to the fact that the intake air flow at the engine start speed is relatively low.

SUMMARY OF THE INVENTION

The primary object of the present invention is to eliminate the above-described disadvantage of the crank chamber compression-type two-cycle engine having a reed valve provided in the intake passage.

According to one aspect of the present invention, there is provided a crank chamber compression-type two-cycle engine wherein an intake passage is communicated with a crank chamber through an intake port which is opened and closed by a piston reciprocating in a cylinder, and the crank chamber is communicated with the combustion chamber in the cylinder through a scavenging port, opened and closed by said piston, and a scavenging passage, characterized in that said intake passage is provided therein with a reed valve which passes a gas flowing in a direction toward the crank chamber but blocks a gas flowing in an opposite direction, and the opening timing of said intake port is selected within the range from 140° to 100° before the top dead center.

According to the feature of the invention set forth above, the power increasing effect of the reed valve, provided in the intake passage, can be sufficiently achieved and the intake air flow speed at the engine start becomes sufficiently high, so that starting of the engine becomes relatively easy. It is known that when the intake port opening timing is advanced from about 140° before the top dead center, a sufficiently high intake air flow speed cannot be obtained at the engine start and hence starting of the engine becomes difficult, whereas when the same is retarded from 100° before the top dead center, the power increasing effect of the reed valve cannot be obtained.

According to another aspect of the invention, there is provided a two-cycle engine of the character described above, wherein the intake passage is communicated with the interior of the cylinder through an auxiliary scavenging passage and an auxiliary scavenging port, at a point downstream of the reed valve and said auxiliary scavenging port is opened and closed with substantially the same timing as the main scavenging port. With such arrangement of the invention, the scavenging efficiency in the interior of the cylinder can be drastically enhanced and the burned gas residing in the cylinder can be completely scavenged.

According to still another aspect of the invention, there is provided a two-cycle engine of the character described above, wherein a fuel injection nozzle is provided in the auxiliary scavenging passage and a reed valve which opens only in a direction toward the cylinder is provided at the point where the auxiliary scavenging passage opens in the intake passage. In this case, the auxiliary scavenging port opening time is slightly retarded from the main scavenging port opening time, whereby the cylinder is at first scavenged with air only and then a fuel-air mixture is introduced into the cylinder. Therefore, the rate of fuel consumption can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of the two-cycle engine according to the present invention;

FIG. 2 is a diagram graphically showing the intake air flow speed;

FIG. 3 is a cross-sectional view of another embodiment of the two-cycle engine according to the invention;

FIG. 4 is a transverse cross-sectional view taken along the line A--A of FIG. 3;

FIG. 5 is a cross-sectional view of a modification of the engine shown in FIG. 3; and

FIG. 6 is a cross-sectional view of still another embodiment of the engine of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, the engine generally indicated by numeral 1 has a cylinder 2 and a piston 3 disposed in said cylinder for reciprocal motion therein, and a crank chamber 8 is formed beneath the cylinder 2 which is enclosed by a crank case 11. An intake pipe 6 having a carburetor 5 is communicated with the crank chamber 8 through an intake port 4 which is opened and closed by the vertically reciprocating piston 3. The intake pipe 6 is also provided therein with a reed valve 7 between the intake port 4 and carburetor 5. This reed valve 7 is operative in such a manner that it passes a gas flowing in a direction toward the crank chamber 8 but blocks a gas flowing in an opposite direction. The cylinder 2 is provided with an exhaust port 9. The piston 3 is connected to a crank shaft 13 by a connecting rod 10. Numeral 12 designates a scavenging passage provided in a conventional manner. In the present invention, the timing at which the piston 3 begins to open the intake port 4 is selected within the range from 100° to 140° before the top dead center, and is 100° before the top dead center in the embodiment shown.

The function of the intake device of the invention will be described with reference to FIG. 2. A curve a of FIG. 2 shows the relationship between the crank angle and the intake air flow speed of a conventional engine having a reed valve in the intake passage, and a curve b shows the same of the engine according to the invention now under consideration. As will be clear from the diagram, in the conventional engine the suction starts at a point about 160° before the top dead center, and the intake air flow speed increases gradually and then decreases gradually. In the present invention, as contrasted thereto, the intake air flow speed sharply increases at a point slightly beyond the point 100° before the top dead center and the fuel-air mixture is agitated vigorously. The intake air quantities in both engines, which are represented by the areas defined by the curves a and b are substantially the same.

Thus, it will be understood that according to the instant invention, as compared with the case wherein use is made only of a reed valve, an equally high power can be obtained and in addition, the starting characteristic of the engine can drastically be improved since the intake air flow speed is higher.

FIG. 3 shows another embodiment of the invention in which the corresponding parts are indicated by the same numerals as in FIG. 1. In this embodiment, a reed valve 7 which permits the fuel-air mixture to flow from a carburetor 5 to an intake port 4 but blocks the same flowing in an opposite direction, comprises a valve seat 7a of a V-shape in cross-section having openings 7b, reed members 7c connected to said valve seat 7a so as to open and close said respective openings 7 b and stoppers 7d to restrain the movement of said reed members 7c . Further, in this embodiment an auxiliary scavenging passage 15 is provided which is open at one end into the intake passage 6 at a point between the reed valve, and at the other end 7 and the intake port 4 or downstream of the reed valve, and at the other end into a cylinder 2 through an auxiliary scavenging port 14. The auxiliary scavenging port 14 is located substantially immediately above the intake port 4, and it is most ideal that the auxiliary scavenging port begins to be opened slightly before the intake port 4 is completely closed but such timing is always necessary because the intake air has an inertia and there is an pressure accumulating effect in the intake passage.

In this embodiment, when the intake port 4 is opened by the side wall of the piston 3, the fuel-air mixture from the carburetor 5 flows into the crank chamber 8 through the intake port 4 after forcibly opening the reed members 7c of the valve 7 and passing through the intake passage 6. The fuel-air mixture in the crank chamber 8 is preliminarily compressed by the bottom of the piston 3 and then injected into the cylinder from the crank chamber 8 through a main scavenging passage 12 when the main scavenging port is opened by the side wall of the piston 3. On the other hand, the auxiliary scavenging port 14 is concurrently opened, so that the fuel-air mixture in the crank chamber 8 is led into the intake passage 6 through the intake port 4 and injected into the cylinder 2 via the auxiliary scavenging passage 15. In this case, the fuel-air mixture entering the intake passage 6 is not permitted to flow back into the carburetor since the openings 7b of the valve 7 are closed by the reed members 7c.

The fuel-air mixture thus injected into the cylinder 2 through the main scavenging port and the auxiliary scavenging port 14 scavenges the burned gas in said cylinder into an exhaust passage 9 and the interior of the cylinder has almost entirely been filled with the fresh gas. Another embodiment shown in FIG. 5 is a modification of the engine of FIGS. 3 and 4, in which an elongate recess is formed in the side wall of the cylinder 2 to define an auxiliary scavenging passage 15' by the side wall of the piston 3 and the wall of said elongate recess, so as to facilitate the provision of the auxiliary scavenging passage and the production of the engine only by a modification of the presently available engines. The other construction is the same as that of the engine shown in FIGS. 3 and 4.

The construction of the engine shown in FIG. 6 is essentially similar to that of the engine of FIGS. 3 and 4, but in this embodiment the carburetor is not provided in the intake passage 6 and a fuel injection nozzle 16 is provided in the auxiliary scavenging passage 15 and further a reed valve 17 which is open only toward the cylinder 2 is provided at the point where the auxiliary scavenging passage 15 opens into the intake passage 6. According to this arrangement, any adverse effects on the operation of the reed valve 7 can be eliminated because the pressure fluctuation within the cylinder does not have direct influence on the pressure in the intake pipe 6 and, moreover, the rate of fuel consumption can drastically be enhanced by slightly retarding the opening time of the auxiliary scavenging port from the opening time of the main scavenging port.