Choke system for a small four stroke engine

Abstract: A four stroke engine has a base plate (21) provided on a side of the engine and having an opening communicated with a carburettor (10). A choke plate (31) is pivotally mounted on the base plate (21), and a choke lever (32) is pivotally mounted on the base plate (21). A transmitting means is provided for transmitting the opposite rotation of the choke lever (32) to the choke plate (31) so as to rotate the choke plate (31).

Description: The present invention relates to a choke system for a small four stroke engine. The choke system for a small engine has a choke plate and a choke lever for rotating the choke plate. When starting an engine, especially a cold engine, the choke lever is operated to restrict or choke off the airflow to produce a richer air-fuel mixture. For a portable engine used in; a bush cutter, hedge trimmer or blower, the two stroke engine is employed, because, the two stroke engine is small and lightweight and has a large power compared with the same sized four stroke engine. In the two stroke engine, the carburettor is provided on a side of the cylinder block as described in Japanese Utility Model Laid Open Publication 7-22054. The carburettor is disposed at a position lower than the cylinder head (7), and hence the choke system attached to the carburettor can also be located at a lower position. Therefore, the two stroke engine can be designed to be small in size. However, in recent years, demand for the four stroke engine is rising because of the emission control. But, in the four stroke engine of the over head valve type, the carburettor is disposed on a side portion of the cylinder head (7), so that the choke system is provided at the same level as the cylinder head (7) or higher. As a result, the engine cannot be reduced in size. The choke lever is disposed on a side portion of the engine. When the choke lever is rotated up, the choke plate is closed, and when rotated down, the choke plate is opened. This manner of operation operating has become customary and must therefore be kept. An object of the present invention is to provide a choke system for a four stroke engine which may be reduced in size, keeping the conventional manner operation of the choke lever. According to the present invention, there is provided a choke system for a four stroke engine having a cylinder head (7) and a carburettor provided on the cylinder head (7), the system comprising a base plate to be provided on a side of the engine and having an opening for communication with the carburettor, a choke plate pivotally mounted on the base plate, and provided to close the opening, a choke lever pivotally mounted on the base plate, and outwardly projected from the base plate, transmitting means for transmitting opposite rotation of the choke lever to the choke plate so as to rotate the choke plate. Preferably, the transmitting means comprises a toothed flange formed on a periphery of each of the choke plate and choke lever, and the transmitting means is provided so that the choke plate closes the opening when the choke lever is rotated up. Preferably, the choke lever comprises a shaft portion and an arm, the arm has a size so as to be inserted in a hole of the pivot of the choke lever, the shaft portion is rotatably inserted in a hole formed in the base plate. Preferably, a fixing plate is attached to the base plate together with the choke plate and the choke lever, and an end portion of the fixing plate is abutted on an end of the shaft portion of the choke lever so as to rotatably hold the shaft portion in the hole. These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. Fig. 1 is a sectional front view of a four stroke engine provided with a choke system of the present invention; Fig. 2 is a side view of the engine, removing a cover for showing the choke system; Fig. 3 is a plan view of the choke system; and Figs. 4a to 4j show an assembling method of a choke lever. Referring to Fig. 1, a portable four stroke engine 1 to which the present invention is applied is a single cylinder four stroke engine of the over head valve type. The engine 1 has a cylinder block 3 in which a cylinder 2a and a piston 2 are provided, a combustion chamber 4 formed in the cylinder block 3, and a cylinder head 7 having an intake port 5, and an exhaust port 6. The intake port 5 is opened at a side wall of the cylinder head 7, and communicated with an intake manifold On the end of the intake manifold 8, a carburettor 10 is provided. The carburettor 10 has an air passage 11 coaxial with an intake passage 9 of the intake manifold 8. The air passage 11 extends horizontally, namely in the direction perpendicular to the axis of the cylinder 2a. At an opening 12 of the air passage 11, an air cleaner box 20 is provided. The air cleaner box 20 comprises a base plate 21 and a cover 22. A guide plate 22a is fixed on the cover 22. In the base plate 21, an opening 23 is formed, communicated with the opening 12 of the air passage 11. The opening 23 is surrounded by an annular projected peripheral wall 23a. On a horizontal line 23b passing the centre of the opening 23, a pair of guide pipes 25 and 26 are formed at opposite sides of the opening 23, and the guide pipes 25 and 26 are fixed in the base plate 21. Adjacent to the opening 23, a choke system 30 is provided. The choke system 30 comprises a choke plate 31 and a choke lever 32. The choke plate 31 comprises a large diameter plate 31a and a small diameter plate 31b integral with the large diameter plate 31a. The choke plate 31 is pivotally secured to the base plate 21 by a guide pipe 25, and screw 24 screwed in the carburettor 10, interposing a fixing plate 33 at the small diameter plate 31b. Another end portion of the fixing plate 33 is secured to the base plate 21 by a screw 24a screwed in the carburettor 10. The large diameter plate 31a has a small opening 31f and is adapted to be slid on the peripheral wall 23a so as to close the opening 23. The choke lever 32 comprises an arm 32a, a manipulating portion 32b outwardly projected from the cover 22, and a shaft portion 32c pivotally engaged with a hole 27 formed in the base plate 21 at a position near the horizontal line 23b so as to be aligned with the guide pipes 25, 26. The shaft portion 32c has a spherical shoulder 32d. The shaft portion 32c has a toothed flange 32e projected from the periphery thereof. The teeth of the toothed flange 32e is engaged with teeth of a toothed flange 31g formed on the small diameter plate 31b. Thus, by rotating the arm 32a of the choke lever 32, the choke plate 31 is rotated about the guide pipe 25. Figs. 4a to 4j show method for attaching the choke lever 32 to the base plate 21 of the air cleaner box 20. The choke lever 32 is inserted in the hole 27 at the manipulating portion 32b as shown in Fig. 4a until the shaft portion 32c abuts the base plate 21. Then the arm 32a in rotated in the clockwise direction about the contact point of the shaft portion 32c with the base plate 21. The spherical shoulder 32d enters the hole 27, rotating. Finally, the choke lever 32 is attached to the base plate 21 as shown in Fig. 4j. At the position, an end portion 33c of the fixing plate 33 is abutted on the end of the shaft portion 32c of the choke lever 32 50 that the choke lever is rotatably held in the hole 27. Thus, the toothed flange 32e is resiliently contacted with the base plate 21. In operation, when the choke lever 32 is downwardly rotated as shown in Fig. 2, the choke plate 31 is rotated in the counter clockwise direction and downwardly. Thus, the opening 23 is opened as shown in Fig. 2. When the choke lever 32 is upwardly rotated shown by the broken line in Fig. 2, the choke plate 31 closes the opening 23. This manipulation is the same as the conventional manner. Since the opening 23 is communicated with the air passage 11 of the carburettor 10, the pivot of the choke plate 31 and the pivot of the choke lever 32 are arranged approximately in the horizontal direction, the height of the engine 1 can be reduced. In addition the manipulating portion 32b of the choke lever 32 when upwardly rotated can be located at lower position, thereby preventing the choke lever from catching foreign things. Furthermore, since the pivot of the choke lever is positioned near the outside wall of the air cleaner box, the length of the choke lever can be reduced. While the invention has been described in conjunction with preferred specific embodiment thereof, it will be understood that this description is intended to illustrate and not limit the scope of the invention, which is defined by the following claims.

Claims: A choke system for a four stroke engine having a cylinder head (7) and a carburettor (10) provided on the cylinder head (7), comprising: a base plate (21) to be provided on a side of the engine and having an opening (12) for communication with the carburettor (10); a choke plate (31) pivotally mounted on the base plate (21), and provided to close the opening (12); a choke lever (32) pivotally mounted on the base plate (21), and projecting out from the base plate (21); transmitting means for transmitting opposite rotation of the choke lever (32) to the choke plate (31) so as to rotate the choke plate (31). The system according the claim 1 wherein the transmitting means comprises a toothed flange (32e) formed on a periphery of each of the choke plate (31) and choke lever (32). The system according to claim 1 or claim 2 wherein the transmitting means is provided so that the choke plate (31) closes the opening when the choke lever (32) is rotated up. The system according to any one of claims 1 to 3 wherein the choke lever (32) comprises a shaft portion (32c) and an arm (32a), the arm (32a) has a size so as to be inserted in a hole of the pivot of the choke lever (32), the shaft portion (32c) is rotatably inserted in a hole formed in the base plate (21). The system according to claim 4 comprising a fixing plate (33) attached to the base plate (21) together with the choke plate (31) and the choke lever (32), and an end portion of the fixing plate (33) abutts an end of the shaft portion (32c) of the choke lever (32) so as to rotatably hold the shaft portion (32c) in the hole.

Inventors: IMAFUKU KENJI, KOGUCHI TAKANOBU, WATANABE MITSUNORI, IMAFUKU, KENJI, KOGUCHI, TAKANOBU, WATANABE, MITSUNORI, Imafuku, Kenji, Tokyo Gijutsu Kenkyusho, Koguchi, Takanobu, Fuji Jukogyo Kabushiki Kaisha, Watanabe, Mitsunori, Fuji Robin Kabushiki Kaisha
Applicants: FUJI ROBIN KK, SHIN DAIWA KOGYO CO LTD, FUJI ROBIN KABUSHIKI KAISHA, SHIN-DAIWA KOGYO CO. LTD
Application year: 1998
Main classification: F02M1
IPC codes: F02B63, F02D11, F02B75, F02M1