United States Patent [19], [11] Patent Number: 4,736,717 Fujikawa Et Al

United States Patent [19], [11] Patent Number: 4,736,717 Fujikawa Et Al

United States Patent [19], [11] Patent Number: 4,736,717 Fujikawa et al. [45] Date of Patent: Apr. 12, 1988 [54] VALVE GEAR FOR FOUR-CYCLE ENGINE [56] References Cited " _ _ U.S. PATENT DOCUMENTS [75] Inventors: 351:: 1319;??? Egi’iii?uyukl 386,213 7/1888 Nash ......... .. 123/901 3 ’ 1 ’ "n ’ 779,328 1/1905 Svebilios 123/901 Kalmgwa, all Of Japan 1,248,597 12/1917 Baker ........... .. 123/901 1,409,710 3/1922 Haltenberger ................... .. 123/902 [73] Ass1gnee: JKasgilllsakl Jukogyo Kabushlkl Kaisha, Primary Examiner_lra s_ Lazarus [57] ABSTRACT [21] Appl. No.: 848,206 A valve gear for a four-cycle engine having an over hung crankshaft connecting with an output shaft, [22] Filed; AP“ 4, 1936 wherein a guide portion having such a shape folding the output shaft as to return back to a starting point in two . turns, is formed on the output shaft, and an interlocking [30] Forelgn Apphcatlon Pmmty Data mechanism guided by the guide portion is provided to APR 4, 1935 [JP] Japan - 60-71716 open the valves for the four-cycle engine. It is prefera F?‘b. 17, 1986 Japan ................................ .. 61-32539 ble that the guide pol-fig“ is formed as cam face displac ing the interlocking mechanism. The guide portion can [51] Int, (11,4 _ _ _ . _ _ _ , _ _ _ _ _ _ _ , , _ _ _ _ ,, F01L 1/04 be formed on a block other than the output shaft for [52] US. Cl. .......................... .. 123/90.2; l23/90.6 easy machining and also for adjustable valve timing. [58] Field of Search ............... .. 123/902, 90.21, 90.22, ‘ 123/ 90.23, 90.6 1 Claim, 5 Drawing Sheets US. Patent Apr. 12, 1988 Sheet 1 of5 4,736,717 4a 34 37a 3 , 36 / 1O 32 12 16”‘\/ “ “ ‘ Ky? 18 38 \ 37 24c 28 {V . 2272a A-\ 2 1e / ‘7' 21¢ 27b \IOa 25b 21a 26a 27a 24a 14 20 21b 24b US. Patent Apr. 12, 1988 Sheet 2 of5 4,736,717 26a US. Patent Apr. 12,1988 Sheet 3 of5 4,736,717 US. Patent Apr. 12,1988 Sheet 5 of5 4,736,717 4,736,717 1 2 FIG. 1 is a vertical sectional view of a ?rst embodi VALVE GEAR FOR FOUR-CYCLE ENGINE ment for a four-cycle engine according to the invention. FIG. 2 is a vertical sectional view of a sliding piece in FIELD OF THE INVENTION AND RELATED FIG. 1. ART STATEMENT FIG. 3 is a sectional view taken along line III—III in This invention relates to a valve gear adapted for the FIG. 2. general-purpose four-cycle engine of small size and FIG. 4 is a segmentary side view of the guide portion. simple construction having an overhung crankshaft to FIG. 5 is a vertical sectional view of another embodi which an output shaft is connected. ment for the four-cycle engine according to the inven Generally, the small general-purpose four-cycle en 10 tion. FIG. 6 is a partly sectional fragmentary illustration gine requires low cost, light weight and compactness. taken along line VI-—VI in FIG. 5. To meet aforesaid requirements, the prior art with FIG. 7 is a vertical sectional view of a third embodi relation to the overhung crankshaft has‘been known, ment for the engine. wherein the cam shaft for driving the valves is disposed FIG. 8 is a vertical sectional view of the major parts at right angles to the crankshaft to transmit the power of an engine according to a fourth embodiment. from the crankshaft to the cam shaft through screw FIG. 9 is a sectional view taken along line IX—IX in gearing. FIG. 8. This construction, however, requires not only the FIG. 10 is a schematic illustration showing the con cam shaft but also the bearings for the cam shaft, which struction of the centrifugal governor operating at high makes the engine large in size owing to a space for speed. containing both of them. Furthermore, the con?guration results in high cost DETAILED DESCRIPTION OF THE caused by the cam shaft and screw gearing, reduced PREFERRED EMBODIMENT reliability due to the wear of the screw gearing, and 25 FIG. 1 shows a small and versatile overhead valve more complicated construction. type four-cycle engine according to the invention. In FIG. 1, Numeral 10 designates an engine block. A cylin OBJECT AND SUMMARY OF THE INVENTION der 12, a crankcase 14 and side cover 16 etc. are inte It can be said that the purpose and object of this grated into the engine block 10. The engine block 10 is invention is to provide a valve gear adapted for the 30 opened cut obliquely at the right lower end portion four-cycle engine low in cost, light in weight, compact thereof in the ?gure and enclosed by means of an oil pan and simple in construction, and high in reliability, elimi 10a. nating aforesaid problems associated with the conven A piston 18 slidably ?ts into the cylinder 12, and a tional valve gear using the screw gearing. overhung crankshaft 20 is rotatably supported by the To achieve aforesaid object, a valve gear according 35 crankcase 14. And the piston 18 is connected to the to the invention adapted for the four-cycle engine hav overhung crankshaft 20 through a connecting rod 22. ing the overhung crankshaft connected to the output The overhung crankshaft 20 is a one-piece forging shaft, comprises a guide portion formed around the consisting of an output shaft 210, a crank web 21b and a output shaft into such a shape as to return back to the crankpin 210. A side plate 21d is mounted on the crank starting point in turns, and an interlocking mechanism pin 210 by means of a bolt 21e. The output shaft 21a is guided by the guide portion to open and close the valve supported to the crankcase 14 by two bearings 24a and system of the four-cycle engine. 24b spaced by a fixed gap. The reason why the bearing It is advisable that aforesaid guide portion be formed 24b is larger in diameter than the other bearing 24a is to into a cam face which displaces the interlocking mecha bear the combustion force acting on the overhung nism as to open and close the valves. 45 crankshaft 20, to readily load the bearings 24a and 24b, Forming aforesaid guide portion between bearings and to easily force-?t the output shaft 210. Numeral 24c designates an oil seal. disposed at two separate locations on the output shaft, prevents the rotation axis of the guide portion from On the output shaft 21a between the bearings 24a and being ?uctuating due to the combustion force in the 24b. a guide groove 26a (guide portion) for the intake engine acting on the crankshaft. 50 valve is formed adjacent to a guide groove 26b (guide portion) for the exhaust valve. Furthermore, aforesaid small guide portion is prefera The guide grooves 26a and 26b have such a shape as bly prefabricated from a block other than the output “?gure-eight” when developed (See FIG. 4), folding shaft for accurate machining. around the output shaft 21a portion of the overhung And, if aforesaid guide portion is prefabricated sepa 55 crankshaft 20 while returning back to the starting point rately from the crankshaft and assembled thereon rotat in two turns. The roots of the guide grooves 260 and ably, and also a timing control mechanism to adjust the 26b are formed as cam faces, and higher portions 27a circumferential angle position of the guide portion on and 27b (FIG. 1) are respectively formed at one loca the crankshaft is provided for variable timing control, tion as to extend outwards in the radial direction of the the timing control mechanism enables the valve timing 60 output shaft 21a, and are circumferentially disposed so to be matched for engine performance. as to coincide with the crank angle respectively corre BRIEF DESCRIPTION OF THE DRAWING sponding to each valve opening timing of the intake and exhaust valves. In the accompanying drawings, there are shown illus A sliding piece 28 (an interlocking mechanism) for trative embodiments of the invention from which these 65 the intake valve is engaged with the guide groove 26a, and other of its objectives, novel features and advan and at the upper end thereof is provided with a sliding tages will be readily apparent. I shaft portion 29a formed into vertical slender rod shape In the drawings: as shown in FIG. 2. The sliding shaft 290 is rotatably 4,736,717 3 4 and vertically slidably supported by a supporting wall 36 and the exhaust valve caused by the sliding piece 28 15a forming a part of the crankcase 14 in the engine and 31 through the push rods 32 and 38. block 10. At the lower end of the sliding piece 28, an Furthermore, a space, normally dead space in the arm 29b sideways extends essentially over the highest prior art, surrounded with the side cover 16 over the longitudinal line on the outer surface of the output shaft crankcase 14, can be effectively utilized by disposing portion 21a, and can swing about the vertical axis of the the push rods 32 and 38 therein, which results in making sliding piece 28 as one-piece with the sliding piece 28. the engine compact as a whole. A ball 30 is rotatably pivoted on the tip end of the The following is the description of a second embodi arm 29b extending sideways to engage with the guide ment according to the invention, referring to FIG.

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