V-TYPE MULTIPLE CYLINDER TWO-CYCLE ENGINE

Abstract: A crank case (3) of a V-type multiple cylinder two-cycle engine is provided with a plurality of crank chambers (4,5) and housings for mounting lead valves (9) for the respective crank chambers. The crank case (3) is constructed by upper and lower case halves usually casted and the split surface of the case halves (3a,3b), when combined, passes the axis of the crank case and one of the lead valve mounting housings (9) which is desirably disposed on the side of a carburettor.

Description: Background of the Invention This invention relates to a two-stroke engine provided with V-type multiple cylinders each having a crank case onto which lead valves are mounted. With a multiple cylinder engine, particularly, a V-type multiple cylinder engine, the cylinders and engine components are generally supported by a crank case through which a crank shaft extends. The crank case is splittable into two parts along a split surface passing the axis of the crank shaft. Figures 3 to 8 are illustrations of conventional crank cases for V-type multiple cylinder engines of the type described above. Referring to Figure 3, a front cylinder 100 and a rear cylinder 101 of the V-type multiple cylinder arrangement are coupled to mating portions 103 and 104 of a crank case 102 respectively. The crank case 103 is constructed to be splittable into two portions along a split surface 105 which passes through and along the axis of a crank shaft 106 but does not cross the mating portions 103 and 104 of the crank case 102. A transmission case 107 integrally connected to the crank case 102 is also constructed to be splittable into two portions so as to support by a counter shaft 108 and a drive shaft 109. Referring to Figure 4, the front and rear cylinders 100 and 101 of the V-type multiple cylinder arrangement are positioned largely forwardly, i.e. leftwardly as viewed, and inclined in comparison with the example shown in Figure 3, and the crank case 102 and the transmission case 107 are constructed to be splittable into two portions along the split surface 110. The mating portion 103 of this example is also splittable along the axis of the front cylinder 100 into two portions which clamps a base portion of the front cylinder 100 when combined. Figures 5 and 6 are illustrations of V-type multiple cylinder two stroke engines each having a lead valve which is mounted on the crank case 102. Figures 5 and 6 have cylinder arrangements similar to those shown in Figures 3 and 4, respectively, but the mating portions 104 for the rear cylinders 101 are provided with housings 112 for mounting lead valves 111. However, in the conventional structure of the crank case of the splittable type, the lead valve mounting housing 112 is constructed so as not to include the split surface and hence not to be splittable therealong, so that the lower portion of the lead valve mounting housing 112 is restricted by the split surface 105 or 110 of the crank case 102 and the transmission case 107. This arrangement of the lead valve mounting housing causes a problem in the connection to the rear cylinder such that the flow of intake or scavenge fuel gas is not made smooth and the volume of the lead valve 111 is undesirably limited, and accordingly, when it is required to ensure a large volume for the lead valve, the mating portion 113 of the lead valve mounting housing 112 largely projects beyond the mating portion 104, thus degrading the workability of the crank case. Figures 7 and 8 show the other examples in which the crank cases 102 are largely shifted so as to receive the front and rear cylinders 100 and 101 in a largely inclined manner to thereby avoid the interference of the transmission case 107 with the lead valve mounting housing 112. With these examples, however, the problems described above still remain because the split surface 105 or 110 is also inclined as shown. As described above with reference to Figures 3 to 8, with the conventional V-type multiple cylinder engine provided with a crank case equipped with a lead valve, it is difficult to define sufficient space for locating the lead valve mounting housing to enable a smooth connection to cylinders for the smooth flowing of the intake or scavenge fuel gas to be made. With other crank cases which are provided with crank chambers for the respective cylinders of a V-type multiple cylinder two-stroke engine, the lead valve mounting housings are provided for the corresponding cylinders, and for example, with a two-cylinder two-stroke engine, the lead valve mounting housing is provided for the front and rear cylinders. However, with the conventional engines of these types, the crank cases and the transmission cases are constructed to be splittable into two portions, respectively, through the split surfaces by substantially the same manners as described above with reference to Figures 3 to 8, though not shown specifically, and substantially the same problems as those described above have been provided. It is known from US patent 4178888 to provide a single cylinder two-stroke engine in which the crank case is split along a split surface which is perpendicular to the crank shaft axis and which passes through a lead valve housing for a carburettor. Summary of the Invention An object of this invention is to substantially eliminate the defects or drawbacks of the conventional technique described above and to provide a V-type multiple cylinder two-stroke engine capable of effectively disposing a lead valve mounting housing having a large volume to thereby improve the fuel gas intake efficiency. Another object of this invention is to provide a V-type multiple cylinder two-stroke engine including a crank case splittable into two portions along a split surface passing through and along the axis of the crank shaft and the lead valve mounting housing so as to effectively dispose the lead valve mounting housing without being influenced with the split surface to thereby improve the operative connection of the cylinders and other members such as a carburettor. According to the present invention there is provided a V-type multiple cylinder two-stroke engine comprising a plurality of cylinders arranged in V-shape, a crank case housing a crank shaft and being provided with a plurality of crank chambers each communicating with a corresponding cylinder and provided with a plurality of housings for mounting lead valves for the respective crank chambers and a transmission case integrally connected to the crank case, characterized in that said crank case comprises upper and lower case halves divided by a split surface X-X passing through and along the crank shaft axis and through one of the lead valve mounting housings mounted on the crank case on the same side as the carburettor. According to the embodiment of this invention, the crank case provided with a lead valve mounting housing is constructed, i.e. casted, by upper and lower case halves by a split surface passing the axis of the crank shaft and the lead valve mounting housing. Accordingly, in a combined state, the crank case can be located freely without being influenced with the split surface in consideration of the connection of the cylinders and other members such as carburettor thereby to improve the fluidity of the intake and scavenge fuel gas with reduced resistance. The free location of the lead valve mounting housing can improve the inner volume of the valve housing and the performance of the engine. The lead valve mounting housing is reduced in height beyond the crank case, thus improving the effective space in the engine system. The preferred embodiments of this invention will be described further in detail hereunder with reference to the accompanying drawings, in which Figure 1 is a side view of an elevational section of a crank case of a V-type two-cylinder two-stroke engine according to this invention; Figure 2 is an end view of a lower case half of the crank case shown in Figure 1 with reference to a split surface X-X; and Figures 3 through 8 are illustrated side views of crank cases provided with split surfaces of conventional type. Referring to Figure 1, a front cylinder 1 and a rear cylinder 2 are arranged in V-shape in parallel to a crank case 3 in the axial direction thereof. The crank case 3 is provided with independent crank chambers 4 and 5 which are continuous with the front and rear cylinder blocks 1 and 2, as shown in Figure 2, through cylinder connection bosses 6 and 7. Housings 8 and 9 for mounting lead valves are also provided for the respective crank chambers 4 and 5 and project outwardly therefrom. A transmission case 13 is integrally connected to the crank case 3, and in the illustration of Figure 1, reference numerals 10, 11 and 12 denote journal bores for receiving a crank shaft, a counter shaft and a drive shaft, respectively. Structure or construction as a two-stroke engine will be described hereunder with reference to the rear cylinder 2. The rear cylinder 2 is provided with a cylinder bore 14 with which an exhaust port 16 and a scavenge port 17 are communicated to be opened or closed by the displacement of a piston member 15, and an intake passage member 19 is operatively connected to the housing 9 through a lead valve 18 mounted therein. When the piston member 15 is upwardly displaced as viewed in Figure 1, fuel gas is taken in the crank chamber 5 through the intake passage 19 and the taken-in fuel gas is primarily compressed when the piston 15 is downwardly displaced. The downward displacement of piston 15 is carried out by the combustion of the fuel gas, and the exhaust port 16 is opened by way of the downward displacement of the piston 15 towards the bottom dead center to exhaust the combustion gas, and the scavenge port 17 is then opened to be filled with the primarily compressed fuel gas. When the piston 15 is again upwardly displaced, the filled fuel gas is compressed and the fuel gas is subsequently taken into the crank chamber 5. These processes are performed every one revolution of the crank shaft and the engine is driven by repeating these intake-compression-combustion-exhaust cycles. On the other hand, with respect to the front cylinder 1, substantially the same structure or construction is provided for, and substantially the same operation is performed, so that the fuel gas is, in each revolution of the crank shaft, taken in the crank chamber 4, compressed, and fills in the cylinder bore 14 disposed at the upper portion of the piston 15 through the scavenge passage. In order to improve the fuel gas filling efficiency, the size and locating position of the lead valve has significant meanings. The crank case 3 is usually constructed by an upper case half 3a and a lower case half 3b, because of workability generally in a casting operation, which are combined in use by mating the split surfaces thereof. According to this invention, the crank case is casted so that the common split surface X-X extends from a position directly downward of the connection boss 6 for the front cylinder 1 towards the lead valve mounting housing 9 for the rear cylinder block 2 through and along axis 0 of the crank shaft and to split the lead valve mounting housing 9 for the rear cylinder 2. In other words, the upper case half 3a and the lower case half 3b include portions of the lead valve mounting housing 9 respectively which are combined into the complete lead valve mounting housing 9 when they are mated along the split surface X-X. The setting of the split surface X-X in the manner described above so as to split the lead valve mounting housing 9 into two portions effectively ensures the location of the lead valve mounting housing 9 without being restricted by the setting position of the split surface, so that the size, dimensions and position of the lead valve mounting housing can be freely designed. According to this constructional feature, the lead valve mounting housing 9 which is located between the rear cylinder 2 and the crank case 3 can be maximumly downwardly located at a portion substantially contacting to the upper surface of the crank case 3, so that the lead valve mounting housing 9 can be constructed with a reduced projecting amount from the mating surface 7a of the connection boss 7 connecting the rear cylinder 2, thus improving the workability of the lead valve mounting housing 9 and hence the crank case 3. Moreover, this construction makes it possible to design the fuel gas intake passage and scavenge passage at angles so as to have reduced flow resistance, and in addition, to make large the inner volume of the lead valve mounting housing 9 in connection with other members or elements such as carburettor, thus improving the fuel gas intake efficiency and hence the performance of the engine. In the foregoings, although there is described a lead valve mounting housing disposed in connection with a rear cylinder, this invention is not limited to the illustrated embodiment and a lead valve mounting housing disposed in connection with a front cylinder may be constructed to be splittable into two portions. In this case, substantially the identical effects to those described in connection with the rear cylinder may be expected. However, it will be easily understood by those skilled in the art that the splittable structure of the rear cylinder block 2 is superior or ideal in comparison with the splittable structure of the front cylinder block 1 in view of the location of other elements such as carburettor and the flow of the fuel gas. Moreover, although the illustrated embodiment is related to a V-type two-cylinder two-stoke engine, this invention is of course applicable to a V-type multiple cylinder two-stroke engine.

Claims: 1. A V-type multiple cylinder two-stroke engine comprising a plurality of cylinders (1, 2) arranged in V-shape, a crank case (3) housing a crank shaft and being provided with a plurality of crank chambers (4, 5) each communicating with a corresponding cylinder and provided with a plurality of housings (8, 9) for mounting lead valves for the respective crank chambers and a transmission case (13) integrally connected to the crank case, wherein said crank case (3) comprises upper and lower case halves (3a, 3b) divided by a split surface X-X passing through and along the crank shaft axis (0) and through one of the lead valve mounting housings (9) mounted on the crank case on the same side as the carburettor. 2. An engine according to Claim 1, wherein a forwardly located cylinder (1) and a rearwardly located cylinder (2) is provided, the split surface X-X being arranged to pass from a position directly downward of a connection boss (6) for the forwardly located cylinder (1), through and along the crank shaft axis (0) and through a lead valve housing (9) located between the rearwardly located cylinder (2) and the crank case (3). 3. An engine according to Claim 1 or 2, wherein two cylinders (1, 2) are provided.

Inventors: OKABE, YUTAKA
Applicants: SUZUKI JIDOSHA KOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: F02B75
IPC codes: F02F7, F02B75, F02F1, F02B61