Patent Grant
7096843
1. Field of the Invention
The present invention generally relates to a multicylinder four-cycle combustion engine for use primarily in motorcycles and, more particularly, to the multicylinder four-cycle combustion engine of a kind in which the piston pumping loss can be reduced.
2. Description of the Prior Art
In order to reduce the number of component parts of the multicylinder four-cycle combustion engine and, also, to reduce the number of manufacturing steps, it is well known that some of multicylinder four-cycle combustion engines currently used in motorcycles are of a structure in which a cylinder block and a generally upper half of a crankcase are formed integrally with each other. In the case of such multicylinder four-cycle combustion engine, crank chambers one for each cylinder are separated from each other by means of partition walls. Therefore, in order to alleviate the piston pumping loss which would result from as a result of compression of an air within each of the crank chambers that takes place as the corresponding piston moves, the design has been employed, in which the crank chambers for the neighboring cylinders are communicated with each other by means of a communication hole open at one end with an upper or lower portion of one crank chamber and at the other end with an upper or lower portion of the other crank chamber. Each of those communication holes has a round section and is formed by the use of a drilling technique, in which a generally elongated drill is inserted from a position laterally of an engine casing in a direction parallel to the longitudinal axis of the crankshaft, so as to extend transversely between the neighboring crank chambers. See, for example, the Japanese Laid-open Patent Publication No. 11-182325.
In the known multicylinder four-cycle combustion engines of the structure discussed above, since each communication hole is formed by the use of a drilling technique, it has been found that burrs tend to be formed around the leading end of the respective communication hole with respect to the direction of advance of the drill, through which the tip of the drill emerges outwardly. In order to prevent the piston ring from interfering with the burrs so formed and appearing in the inner peripheral wall of the corresponding cylinder bore, the position of each of the communication holes has necessarily and carefully be chosen so that the uppermost edge of the respective communication hole with respect to the direction of movement of the associated piston be located 3 mm or more spaced downwardly from the lowermost end of the piston ring when the piston is held in the bottom dead center position.
Thus, the position of the uppermost edge of the respective communication hole is necessarily limited to a location distant from the lowermost end of the associated piston ring when the piston is held in the bottom dead center position and, on the other hand, the lowermost edge of the respective communication hole must be positioned at a location sufficient to avoid interference with a crank shaft bearing. Those design requirements impose limitations on the size of the leading open end of the respective communication hole, particularly the size of the leading open end as measured in a direction conforming to the direction of reciprocating movement of the piston or a vertical direction.
Since each of the communication holes has a round section as discussed above, the size of the open end in the vertical direction for a given cross-sectional surface area (passage area) of the respective communication hole tends to be large, and accordingly, it is difficult to secure a sufficient passage area for the communication hole under the limitations on such vertical size. Moreover, the presence of the burrs around the open end of the communication hole tends to impose a relatively large resistance to the flow of gases through the communication hole.
Partly because of the insufficient passage area for each communication hole and partly because of the relatively large resistance to the gas flow caused by the burrs, the gases would not flow smoothly therethrough, resulting in increase of the pumping loss. Also, openings through which the drill has been inserted to form the respective communication holes, are left in the lateral portions of the engine casing and, therefore, those openings must be closed by separately prepared plugs, resulting in increase of the number of component parts used and, also, the member of assembling steps.
In view of the foregoing, the present invention is intended to provide a multicylinder four-cycle combustion engine of a type, in which communication holes effective to allow gases to smoothly flow from one cylinder bore to another can be formed easily and in which the piston pumping loss can advantageously be reduced.
In order to accomplish the foregoing object, the present invention provides a multicylinder four-cycle combustion engine, which includes an engine casing having defined therein a plurality of cylinders, each having a cylinder bore, and a crank chamber below the respective cylinder bore. The cylinders are juxtaposed in a direction parallel to a longitudinal axis of a crankshaft, the neighboring cylinder bores and crank chambers being separated from each other by means of a partition wall. The partition wall has a communication hole formed therein so as to extend completely across the partition wall. A major portion of an open edge portion of an uppermost edge of the communication hole at a circumferentially intermediate portion, which open edge portion opens towards the cylinder bore, extends in a direction substantially perpendicular to a longitudinal axis of the cylinder.
According to the present invention, since the major portion of the open edge portion of the uppermost edge of the communication hole, which opens into the cylinder bore, extends in a direction substantially perpendicular to the cylinder longitudinal axis, for example, horizontally, the passage area of the communication hole relative to the size thereof as measured in a direction conforming to the longitudinal axis of the cylinder can advantageously be increased as compared with the round sectioned communication hole. As a result thereof, the passage area, i.e., the cross-sectional surface area of the communication hole can be increased so that gases beneath the reciprocating piston at the end of descent of the reciprocating piston can advantageously be directed smoothly through the communication hole into the adjoining crank chamber. In view of this, the pumping loss within the cylinder can be reduced with the engine output and efficient consequently increased advantageously.
The communication hole may be formed by the use of a milling technique. In this case, unlike the communication hole formed by the use of a drilling technique, formation of the burrs can advantageously be suppressed and hence, a relatively large size of the communication hole as measured in a direction conforming to the longitudinal axis of the cylinder can be secured with the uppermost edge of the communication positioned as close to the piston ring as possible.
In a preferred embodiment of the present invention, the major portion of the open edge portion of the uppermost edge of the communication hole at the circumferentially intermediate portion may be substantially straight. This straight major portion may preferably have a width which is equal to ½ or more of the total width of the open edge portion.
In another preferred embodiment of the present invention, the uppermost edge of the communication hole may be made up of opposite inclined surface areas, which are flared outwardly, and a horizontal surface area continued between the inclined surface areas, when viewed in a cross-section taken along a plane containing respective longitudinal axes of the neighboring cylinders. According to this design feature, the gases within one of the neighboring cylinder bores can flow into the other of the neighboring cylinder bores smoothly through the communication hole past the inclined surface areas thereof.
In a further preferred embodiment of the present invention, the open edge portion of the lowermost edge of the communication hole, which opens towards the cylinder bore has a circumferentially intermediate major portion that may extend in a direction substantially perpendicular to the longitudinal axis of the cylinder.
According to the foregoing design feature, since the open edge portion of the lowermost edge of the communication hole can extend substantially horizontally as well, the passage area thereof can advantageously be increased enough to further reduce the pumping loss. The circumferentially intermediate major portion referred to above is preferably substantially straight.
In a still further preferred embodiment of the present invention, the communication hole may be formed by milling with a milling tool inserted into the cylinder bore in a direction inclined relative to the longitudinal axis of the cylinder bore.
Formation of the communication hole by milling with a milling tool inserted in the manner described above is effective in that not only can the need to form a special opening other than the cylinder bore for removable insertion of the milling tool during the milling process be dispensed with, but also no extra plug member is needed to close such special opening. Because of this, the process of milling to form the communication hole can advantageously be simplified and can efficiently be executed at a minimized cost.
Where the milling tool is employed in the form of, for example, an end mill cutter, the intended milling operation can easily be achieved by inserting into the cylinder bore the end milling cutter from above or below in a direction inclined relative to the longitudinal axis of the cylinder bore to provide a chamfered surface. Moreover, formation of the communication hole by milling the partition wall from left and right is effective to substantially completely eliminate an undesirable formation of burrs.
The uppermost edge of the communication hole may be formed by means of the end mill cutter mentioned above and the lowermost edge thereof may be formed by means of a ball end mill cutter.
In any event, the present invention will become more clearly understood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims. In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views, and:
Hereinafter, the present invention will be described in detail in connection with a preferred embodiment thereof with reference to the accompanying drawings.
Referring first to
A cylinder head 11 is fixedly mounted atop the cylinder block CY, and a cylinder head cover 12, with a valve chamber defined therein, is in turn mounted fixedly on a top surface of the cylinder head 11. An oil reservoir or oil pan 13 is secured to an undersurface of the lower casing component C2. As indicated above, the engine casing EC, the cylinder head 11, the cylinder head cover 12 and the oil pan 13 altogether constitute the engine body 1. It is to be noted that the cylinder head 11 has a plurality of, for example, four exhaust ports 10 defined therein, which are in turn communicated with respective exhaust pipes 15.
Referring to
The engine casing EC has one end portion formed with a chain tunnel 7 defined therein for accommodating a substantially endless chain forming a part of a valve drive mechanism (not shown) housed within the valve chamber. Each of the reciprocating pistons 3A to 3D has piston rings 34 mounted thereon. Each of the partition walls 21 dividing the crank chamber 30A to 30D and the cylinder bores 20A to 20D has a lower portion formed integrally with a boss portion 21a for housing a crankshaft bearing 35.
The neighboring cylinders 2A and 2B, 2C and 2D are communicated with each other by means of respective communication holes 4 each formed in the associated partition wall 21 by the use of a machining technique. Specifically, each of the communication holes 4 is positioned in a lower region of the corresponding partition wall 21 and is so formed as to extend through a lower portion of the corresponding cylinder block CY and an upper portion of the crankcase CR in a direction parallel to the longitudinal axis 60 of the crankshaft 5.
As best shown in
As best shown in
Similarly, an open edge portion 4ba of the lowermost edge 4b of each communication hole 4, which opens towards the cylinder bore 20A has an intermediate primary portion along the circumferential direction of the cylinder bore 20A, which extends in a direction perpendicular to the cylinder longitudinal axis CH, and represents a substantially straight portion extending a distance that is ½ or more, preferably ⅔ or more of the total width W of the respective communication hole 4. In view of the shape of a machining tool as will be described later with reference to
As described above, each communication hole 4 has the open edge portions 4aa and 4ba, major portions of which lie substantially straight, and has an open end of a configuration delimited by all open edge portions 4aa, 4ba and 4ca. This open end of the communication hole 4 represents a generally rectangular shape having a width greater than the height thereof. Accordingly, it is possible to secure a relatively large passage area, even though the size of the open end of each communication hole as measured in a direction conforming to the longitudinal axis CH of the cylinder 2A is limited by the lowermost piston ring 34 and the boss portion 21a housing the crankshaft bearing 35 therein, both shown in
The longitudinal sectional representation of each communication hole 4 (
The flow of the gases G in each communication hole 4 is considerably affected by the size of the open edge portions 4aa, 4ba and 4ca which define respective portions of the inflow port for the gases G. This will now be discussed with reference only to the first cylinder 2A for the sake of brevity.
The gases G within the cylinder 2A, which is urged downwardly as a result of a descending motion of the associated reciprocating piston 3A shown in
It is to be noted that the circle 70 shown in
Hereinafter, the manner in which each of the communication holes 4 is formed will be described in detail with reference to
With the end mill cutter 8 driven, the lower region of the partition wall 21 is machined until a center 80 of the milling tip 8a (free end of the end mill) reaches a position shown by the double-dotted line in
At this time, as shown in
Subsequently, as shown in
Procedures similar to those described above are equally applied to the partition wall 21 between the third and fourth cylinders 2C and 2D in
Thereafter, an elongated ball end mill cutter 9 having a ball (rounded) milling tip 9a is inserted from above into the first and third cylinder bores 20A and 20C of the first and third cylinders 2A and 2C, with the ball milling tip 8a oriented in a direction rightwardly diagonally downwardly towards the lower region of the partition wall 21, to thereby form one end portion (left end portion in
In a manner similar to that described above, the opposite end portion (right end portion of
It is to be noted that
Each of the communication holes 4 so formed as hereinabove described has the open edge portion 4aa of the uppermost edge 4a thereof positioned in the vicinity of the lower edge of the lowermost piston ring 34 when the corresponding piston is held in the bottom dead center position. Depending on the shape of the combustion engine E, however, each communication hole 4 may be formed by milling with the end mill cutter 8 or the ball end mill cutter 9 inserted from below (specifically from a joint surface 50 between the upper casing component C1 and the lower casing component C2) shown in
As hereinbefore fully described, in the multicylinder four-cycle combustion engine according to the preferred embodiment, the communication holes 4 extending across the partition walls 21 between the first and second cylinders 2A and 2B and between the third and fourth cylinders 2C and 2D, respectively, by the use of the milling technique and, therefore, unlike those obtained by the use of a drilling technique, formation of the burrs around the open edge portions 4aa, 4ab and 4ca, shown in
Also, the open edge portions 4aa of the uppermost edge 4a shown in
In addition, since not only the open edge portions 4aa of the uppermost edge 4a of each communication hole 4, but also the open edge portion 4ba of the lowermost edge 4b of each communication hole 4 lies substantially horizontally, each communication hole 4 can have an increased passage area as compared with the round sectioned communication hole having the same size as measured in a direction conforming to the longitudinal axis of the cylinder and, accordingly, a substantial amount of gases G can be allowed to smoothly flow in a short time. As a result, the pumping loss can advantageously be reduced and the output and the efficiency of the combustion engine can be increased as well.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings which are used only for the purpose of illustration, those skilled in the art will readily conceive numerous changes and modifications within the framework of obviousness upon the reading of the specification herein presented of the present invention. By way of example, although in the foregoing embodiment the present invention has been applied to the multicylinder four-cycle combustion engine for use in the motorcycles, the present invention can be equally applied to the multicylinder four-cycle combustion engine used in vehicles other than motorcycles, small marine vessels and power machinery for driving machines.
Accordingly, such changes and modifications are, unless they depart from the scope of the present invention as delivered from the claims annexed hereto, to be construed as included therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-302862 | Aug 2003 | JP | national |
| Number | Date | Country |
|---|---|---|
| 11-182325 | Jun 1999 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20050045121 A1 | Mar 2005 | US |
