GB2199896A

GB2199896A - Oval cylinder i.c. engine valve gear

Info

Publication number: GB2199896A
Application number: GB08805393A
Authority: GB
Inventors: Takao Tomita; Masaaki Matsuura; Makoto Hirano; Masao Handa; Tomoo Shiozaki
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1985-01-29
Filing date: 1986-01-29
Publication date: 1988-07-20
Also published as: GB2199922A; GB2199896B; GB2199922B; GB8805393D0; GB8805392D0

Description

"Internal Combustion Engine" This invention relates to internal combustion engines having cylinders of non-circular crosssection.

Engines have been developed which employ cylinders of non-circular cross-section. Such engines which have an oblong cross-section can increase the inlet and outlet port areas relative to the cross-sectional area of the cylinder over that which is possible with cylinders of circular cross-section. Valve arrangements have been devised for such engines to increase aspiration efficiency.

One such engine is illustrated in U. S. Patent No.

4,256,068.

Such existing internal combustion engines whose cylinders are not circular in cross-section have been devised in accordance wit the shapes illustrated in Figures 1,2 and 3 of the accompanying drawings. In Figure 1, the cylinder H is shown to be two semi-circular sections connected by two straight segments. The semi-circular sections have the radius r and the straight sections extend between points P1. Figure 2 illustrates another embodiment of a cylinder H having circular segments si of short radius ri and circular segments S2 of long radius r2. The segments are connected at points P2. Engine cylinders as illustrated in Figures 1 and 2, constructed of distinct differently curved segments, require points of curvature discontinuity such as found at P1 and P2. With such discontinuities, a cutter employed in the forming of the surfaces of such cylinders is unable to smoothly traverse these points. As a result, high accuracy cannot be obtained, excessive time is required for the processing of the cylinder, and the cutter experiences early wear. Thus, mass production becomes difficult, although engines conforming to the cylinder designs of Figures 1 and 2 can improve gas flow efficiency and can be made using limited production techniques.

A further cylinder H which has been previously contemplated for cylinders of non-circular crosssection is illustrated in Figure 3. This has a true eliptical form and is more amenable to mass production techniques. As there is no curvature discontinuity, high accuracy, reduced processing time, and longer cutter life may be realized.

However, such a true elipse creates areas D at each end of the cylinder which are narrowed considerably compared to the midsection of the cylinder.

Dead spaces occur in these areas as there is insufficient room for valve placement. Furthermore, the end portions of the cylinder are so tightly curved that it becomes difficult to prepare and assemble a ring on a conforming piston in these areas.

Piston rings for such cylinders having noncircular cross-section have been devised. One such type of ring is the"expansion type"which is pressed outwardly against the wall of the cylinder by a device fitted between the piston and the piston ring. One such device is illustrated in U. S. Patent No. 4,362,135. Another type of piston ring which has been devised for such cylinders is the self tension type which is pressed against the wall of the cylinder by means of its own tensile strength, with the relaxed condition of the ring being larger than the cylinder within which it is compressed.

One such ring for a non-circular cylinder is disclosed in U. S. Patent No. 4,198,065. The self tensioning type of piston ring has tended to be more widely used as it has more avantages in terms of better sealing quality and cost.

As mentioned above, certain problems may accompany the fabrication and installation of piston rings on pistons designed to conform to non-circular cylinders. With each of the cross-sectional shapes of cylinders illustrated in Figures 1 and 2, the abrupt or discontinuous change in curvature at points P1 and P2 which is also required of the piston ring, can result in stress concentrations in use. Fabrication of rings with such curves may also be more difficult, and where straight sections are employed these preferably have inwardly curved configurations in the relaxed state, to overcome bending loads when positioned in the cylinder.

Maintaining accuracy in the fabrication of such complex curves becomes difficult.

Consequently, the fabrication and assembly of components for engines havig non-circular cylinders as illustrated in Figures 1 and 2 can be difficult.

The configuration of Figure 3 overcomes certain of the fabrication problems encountered with the configurations of Figures 1 and 2, but ring assembly may then be difficult, and dead spaces can occur at the narrowed ends of the elliptical cylinder.

Viewed from one aspect the present invention provides an internal combustion engine comprising: a cylinder having a continuously curving symmetrical oval cross-section with a major axis of symmetry and a minor axis of symmetry ; an oval piston in said cylinder ; and a cylinder head covering one end of said cylinder and including a plurality of valved ports in said head which are symmetrically arranged relative to said minor axis with some of said plurality of ports being at a different distance from said minor axis than others of said plurality of ports, said ports closest to said minor axis having a larger port area than said ports furthest from said minor axis.

Viewed from another aspect the invention provides an internal combustion engine including a cylinder having a continuously curving symmetrical oval cross-section with a first axis of symmetry and a second axis of symmetry perpendicular to said first axis of symmetry, said oval cross-section being generated at a preselected constant outwardly normal distance from a closed curve, said closed curve including two spaced points on said first axis and two curved portions extending between said points and curving outwardly from said first axis, said closed curve being configured to have a curvature without discontinuity.

Viewed from a further aspect the invention provides n internal combustion engine comprising: a cylinder having a continuously curving symmetrical oval cross section with a major axis of symmetry and a minor axis of symmetry; an oval piston in said cylinder ; a cylinder head covering one end of said cylinder and including a plurality of intake and exhaust ports in said head which are symmetrically arranged relative to said minor axis with some of said ports being at a different distance from said minor axis than others of said plurality of ports, said ports closest to said minor axis being at a different distance from said major axis than said ports furthest from said minor axis. intake valves in said intake ports; exhaust valves in said exhaust ports; a first camshaft coupled with said intake valves ; and a second camshaft coupled with said exhaust valves.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is an illustration of a first noncircular cylinder configuration of the prior art; Figure 2 is a schematic illustration of a second non-circular cylinder configuration of the prior art ; Figure 3 is a schematic illustration of a third known non-circular cylinder configuration ; Figure 4 is a schematic plan view of a first embodiment of the present invention, illustrating a cylinder of non-circular cross-section ; Figure 5 is a cross-sectional elevation taken along line V-V of Figure 4; Figure 6 is a cross-sectional elevation taken along line VI-VI of Figure 4; Figure 7 is a schematic plan view of a second embodiment of the present invention; Figure 8 is a cross-sectional elevation taken along line VIII-VIII of Figure 7; Figure 9 is a cross-sectional elevation taken along IX-IX of Figure 7; Figure 10 is a schematic plan view of a third embodiment of the present invention; Figure 11 is a cross-sectional elevation taken along line XI-XI of figure 10 ; Figure 12 is a plan view of a piston ring illustrated in full in a compressed state and in phantom in a relaxed state, which may be employed in the embodiments of Figures 4,7 and 10; Figure 13 illustrates the construction of a cylinder in accordance with the present invention, and a corresponding graph of radius of curvature versus axial position along the major axis of the cylinder cross-section; Figure 14 ilustrates a fourth embodiment of a cylinder of non-circular cross-section according to the invention and its attendant profile of radius of curvature versus axial position along the major axis of the cylinder cross-section; Figure 15 is a curve illustrating the relationships of the axes as labelle ; and Figure 16 is a curve illustrating the relationship of these axes as labelled.

Turning in detail to the drawings, Figures 4,5 and 6 illustrate a first embodiment of the present invention. The engine is shown to include a cylinder head 1 and cylinder body 2. The cylinder body 2 has a cylinder 3 therein. The cylinder 3 is illustrated in Figure 4 to have a continuously curving symmetrical oval cross-section having a major axis of symmetry along line L1 and a minor axis of symmetry along line L2. The cylinder head 1 closes one end of the cylinder and is secured to the cylinder body 2. The cylinder head 1 has a ceiling 4 defining one portion of the combustion chamber. Two intake passages 5 direct incoming mixture to the combustion chamber while two exhaust passages 6 direct exhaust away from the combustion chamber on the other side theeof. Each of the intake passages 5 and each of the exhaust passages 6 is shown to be branched so as to extend to separate ports. Larger intake ports 7 are arranged near the minor axis of symmetry L2 on one side of the major axis of symmetry L1. Smaller intake ports 8 are located more distant from the minor axis of symmetry L2 and closer to the major axis of symmetry L1 than the larger intake ports 7. Similarly, exhaust ports 9 and 10 are provided. The exhaust ports 9 are larger than the exhaust ports 10 and are closer to the minor axis of symmetry L2 and further from the major axis of symmetry Lu. Two spark plug ports 11 are spaced from one another along the major axis of symmetry L1* The piston 12 conforms to the continuously curving symmetrical cross-section of the cylinder 3. Piston rings and oil rings 13 provide a seal between the piston 12 and the surrounding cylinder wall 3. The piston is constrained to reciprocate within the cylinder 3, being attached by means of a wrist pin 14 to dual connection rods 15.

The flow through intake passages 5 from carburetors 16 is controlled at the intake ports 7 and 8 by means of intake valves 17 and 18. In this first embodiment, the intake valves 17 and 18 are shown to be mutually askew in order to better conform to the curved ceiling 4 of the cylinder head 1.

Similarly, exhaust valves 19 and 20 control the exhaust ports 9 and 10 respectively, to exhaust gases through the exhaust passages 6 to an exhaust system, not shown.

The arrangement of the ports 7 to 10 provides an advantageous use of the cylinder configuration.

The smaller ports 8 and 10 may be placed closer together and, therefore, nearer the narrowed ends of the cylinder cross-section. Their placement closer to the major axis of symmetry Ll of the cylinder cross-section also enables their placement at the more extreme positions. Under certain conditions, it may be advantageous to only employ the center ports 7 and 9. Mechanisms have been devised for disabling valves under certain operating conditions.

The location of the spark plugs 11 reduces the length of the flame path upon ignition and avoids interfering with the valves and valve port area.

The foregoing arrangement illustrates a noncircular cylinder having four intake valves on one side of the major axis of symmetry of the cylinder cross-section and four exhaust valves on the other side of such axis. The valves are shown to be symmetrically arranged relative to the minor axis of symmetry of the cylinder cross-section. However, different numbers or arrangements of intake valves may be employed when desired. For example, an additional intake valve may be located on the minor axis of symmetry to further enhance intake operation.

Other configurations might include a third spark plug located centrally in the cross-section.

A second embodiment of the present invention is illustrated in Figures 7 to 9. Similar reference numerals have been given to the elements of this second embodiment where they are identical or equivalent. A principal change compared with the first embodiment is in the size and orientation of the intake ports 21 and exhaust ports 22. Both sets of ports are arranged in this embodiment along straight lines parallel to the major axis of symmetry Llof the cylinder cross-section. The ports 21 are all of the same size, as are the ports 22.

In accordance with the size and orientation of the ports 21 and 22, the intake valves 23 are all aligned in parallel with one another, as are the exhaust valves 24.

A third embodiment is illustrated in Figures 10 and 11. Again, similar references numerals have been assigned to identical or equivalent elements.

In Figure 11 the orientation of the valves is illustrated, with each intake valve 25 and each exhaust valve 26 pointing toward a respective intake camshaft 27 and exhaust camshaft 28. In this way, the valves 25 and 26 may be driven directly by these cams.

As can be seen in Figure 10, the valves 25 and 26 at the outer ends of the cylinder are placed closer to the major axis of symmetry of the cylinder than are the inner valves.

A piston ring is illustrated in Figure 12 which may be employed with the cylinders and pistons of Figures 4 to 11. The piston ring 23 is shown as having a break at one end. In the free configura tion of the piston ring, illustrated in phantom, it can be seen that the ring continuously curves without reversing its curvature at any point.

Consequently, the outwardly normal lines 29 do not intersect one another. The ring 13 is shown in its compressed state in full lines.

The construction of the cylinder having a continuously curving symmetrical oval cross-section is best understood with reference to Figure 13.

The curve defining the cylinder wall is generated at a preselected constant outwardly normal distance from a closed curve. The closed curve is identified as X in Figure 13 and the curved cylinder is generated by the normal thereto. This normal may be best understood as the locus of outermost points defined by a circle of a given radius r as the center of that circle moves about the closed curve X. The curve X extends symmetrically about the major axis of symmetry of the cylinder cross-section between two spaced points C1 and. The curve X is curved outwardly from the major axis between these points on each side of the major axis. As can be seen from the curve assocated with Figure 13 illustrating the relationship between the radius of curvature and the location along the major axis, the curvature is continuous about the entire cylinder cross-section. The selection of the curve X is designed to accomplish this result.

If the closed curve X is selected to be a formal elipse, such a continuously varying curvature without discontinuities therein will result. The nature of the closed curve X employed for generating the curve of the cylinder determines the path which a cutter is required to follow having a radius r to cut the appropriate cylinder wall. If the closed curve X is a formal elipse, for example, the cutter will not be required to undertake any discontinuous movements. This facilitates processing, reduces machining time, increases the life of the cutter, and increases accuracy. The resulting curvature of the cylinder, the associated piston, and the associated piston rings, also avoids high stress points and thermal stress concentrations at discontinuities. The employment of this technique in the generation of the cylinder configuration creates broadened end portions which are not realized with a cylinder of an eliptical shape. Consequently the intake and exhaust ports may be positioned deep in the narrowed portions of the cylinder, to avoid dead spaces.

A variety of curves may be selected to define the cylindrical wall. Figure 14 illustrates yet another cylinder arrangement generated by the same means. In spite of the steep slopes evident in these curves, they remain continuous. These slopes reflect the very tight curves near the points C and C2 on curve X where they transition to the much straighter sections. Naturally, the more steep the curves, the more difficulty the cutter has in following curve X to cut the cylinder.

A formal ellipse which also may be employed for curve X typically is reflected in more gradual slopes on such curves resulting in less abrupt cutter action in forming the associated cylinder.

Looking now to Figures 15 and 16, the special characteristics of cylinders according to the foregoing embodiments are illustrated, with the assumptions that the diameters of the intake and exhaust outlets h, as representated in Figure 13, are 18 millimeters, the radius r of the generating circle is 20 millimeters, and the cross-sectional area of the cylinder is fixed. Figure 15 represents the relationship between the ratio of the long diameter A to the short diameter B of the cylinder curve and the distance between the centers of the most distant of either the intake or exhaust ports h, when the intake and exhaust ports are arranged as in Figure 7. Assuming four intake ports and four exhaust ports with a diameter of 18 millimeters,. the distance L, as seen in Figure 13, between the centers of the ports must be at least 54 millimeters. In this case, A/B becomes more than 1.6 in accordance with Figure 15. Referring to Figure 16, the relationship of the foregoing ratio A/B and the ratio of the long diameter a of the closed curve X to the short diameter b of the closed curve X is illustrated. As can be seen from Figure 16, for any value of a/b, A/B never exceeds 2.3. Consequently, from Figures 15 and 16 it can be seen that under the foregoing assumptions, with ports in the foregoing relationship, the ratio A/B is greater than or equal to 1.6 and is less than or equal to 2.3. As a result, preferred relationships of components preferably satisfy the foregoing limitations.

Thus, cylinders having non-circular crosssections are disclosed which may be fabricated under mass production conditions, avoid dead spaces in the combustion chamber adjacent the ends of oblong cylinders, and provide improved valve configurations and improved piston ring configurations.

It is to be clearly understood that there are no particular features of the foregoing specification, or of any claims appende hereto, which are at present regarded as being essential to the performance of the present invention, and that any one or more of such features or combinations thereof may therefore be included in, added to, omitted from or deleted from any of such claims if and when amended during the prosecution of this application or in the filing or prosecution of any divisional application based thereon.

Claims

Claims 1. An internal combustion engine comprising: a cylinder having a continuously curving symmetrical oval cross section with a major axis of symmetry and a minor axis of symmetry; an oval piston in said cylinder; a cylinder head covering one end of said cylinder and including a plurality of intake and exhaust ports in said head which are symmetrically arranged relative to said minor axis with some of said ports being at a different distance from said minor axis than others of said plurality of ports, said ports closest to said minor axis being at a different distance from said major axis than said ports furthest from said minor axis; intake valves in said intake ports; exhaust valves in said exhaust ports; a first camshaft coupled with said intake valves; and a second camshaft coupled with said exhaust valves.
2. An internal combustion engine as claimed in claim 1, wherein said intake valves are on one side of said major axis and point at the centerline of said first camshaft and said exhaust valves are on the other side of said major axis and point at the centerline of said second camshaft.
3. An internal combustion engine comprising: a cylinder having a continuously curving symmetrical oval cross-section with a major axis of symmetry and a minor axis of symmetry; an oval piston in said cylinder ; and a cylinder head covering one end of said cylinder and including a plurality of valved ports in said head which are symmetrically arranged relative to said minor axis with some of said plurality of ports being at a different distance from said minor axis than others of said plurality of ports, said ports closest to said minor axis having a larger port area than said ports furthest from said minor axis.
4. An internal combustion engine as claimed in claim 3, further comprising a piston ring about said piston and extending to said cylinder.
5. An internal combustion engine as claimed in claim 3 or 4, wherein said plurality of ports includes intake ports on one side of said maior axis and exhaust ports on the other side of said major axis.
6. An internal combustion engine as claimed in claim 5, wherein there are four said intake ports.
7. An internal combustion engine as claimed in claim 5 or 6, wherein there are four said exhaust ports.
8. An internal combustion engine as claimed in claim 5, wherein there are an equal number of intake and exhaust ports.
9. An internal combustion engine as claimed in any of claims 5 to 8, wherein all of said ports are symmetrically arranged relative to said minor axis.
10. An internal combustion engine as claimed in any of claims 3 to 9, wherein said ports furthest from said minor axis are closer to said maior axis than said ports closest to said minor axis.
11. An internal combustion engine as claimed in any of claims 3 to 10, further comprising two spark plugs symmetrically disposed on the respective sides of said minor axis and on said major axis.
12. An internal combustion engine including a cylinder having a continuously curving symmetrical oval cross-section with a first axis of symmetry and a second axis of symmetry perpendicular to said first axis of symmetry, said oval cross-section being generated at a preselected constant outwardly normal distance from a closed curve, said closed curve including two spaced points on said first axis and two curved portions extending between said points and curving outwardly from said first axis, said closed curve being configured to have a curvature without discontinuity.
13. An internal combustion engine as claimed in claim 12, further comprising: an oval piston in said cylinder; and a piston ring about said piston and extending to said cylinder to seal between said piston and said cylinder, said piston ring being curved in free configuration such that lines facing outwardly normal to said ring do not mutually intersect.
14. An internal combustion engine as claimed in claim 12 or 13, wherein said first axis is the major axis of symmetry of said symmetrical oval cross-section.
15. An internal combustion engine as claimed in any of claims 12 to 14, wherein said closed curve is an elipse.