1. Technical Field of the Invention
This invention relates generally to internal combustion engines, and more specifically to poppet valves for such.
2. Background Art
Internal combustion engines use a variety of types of valves to control the intake and exhaust of gases as the engines operate. Most internal combustion engines are of the four-stroke variety, and most four-stroke engines use poppet valves. Such an engine includes a head which forms the upper surface of the combustion chamber. The intake and exhaust valves open and close to permit or restrict gas flow through their respective intake and exhaust openings in the head. It is generally recognized as highly desirable to provide an engine with large valves, to improve the engine's ability to “breathe”. An engine is essentially a gas pump which pumps in air-fuel mixture and pumps out waste gas or exhaust. Because the exhaust gas is typically under significantly greater pressure than the air-fuel mixture, most engine designs use intake valves which are larger than their exhaust valves.
FIG. 1 illustrates a poppet valve 10 according to the prior art. The valve includes an elongated, cylindrical stem 12 coupled to (and typically integrally formed with) a poppet 14. The poppet is sometimes referred to as the disc of the valve. The poppet is typically adapted with a seating face 16 which is angled to mate with a corresponding surface in the head (not shown) known as the valve seat. The widest part 18 of the poppet limits the size of the valve and the lift, as the valve must not be permitted to strike or interfere with any other engine component.
Modern four-stroke engines use overhead camshafts to open their valves, and valve springs to return the valves to their closed position. In most instances, the valves and their actuating hardware such as shims, buckets, cam followers, and so forth, are designed to permit—and in many cases encourage—the valves to gradually rotate within their valve seats. This improves the evenness of valve wear, and helps prevent loss of compression due to localized carbon buildup and the like. Therefore, valves are constructed as an axisymmetric revolve, meaning that they are symmetrical about the axis of their shaft. This symmetry also improves manufacturability and lowers manufacturing cost.
FIG. 2 illustrates a head 20 according to the prior art. In the interest of clarity and ease of illustration, a variety of well-known features have been omitted from the head, such as water jackets, and the head has been shown as having a flat-roofed combustion chamber. Those of ordinary skill in the art will readily appreciate how these conventional features would exist.
The head includes a block surface 22 which mates to the lower engine components (not shown) such as the cylinder block. The head is indented with a combustion chamber roof 24. A squish band 26 forms an angled transition between the roof and the block surface. A spark plug hole 28 extends through the head and is typically located near the center of the roof so as to provide substantially equal distances that the flame must travel from the spark plug to the outer perimeter 30 of the roof. This outer perimeter defines the “size” of the combustion chamber and is the primary factor limiting the size of the valves.
Within the roof perimeter, the head includes one or more intake valve openings 32 and one or more exhaust valve openings 34. The intake valve openings connect to intake tracts 36, and the exhaust valve openings connect to exhaust ports 38. Each intake valve opening includes an intake valve seat 40, and each exhaust valve opening includes an exhaust valve seat 42.
The intake valve openings have a circumference CIN and the exhaust valve openings have a circumference CEX. The head must not have any interference between the circumferences of the valves, the spark plug hole, and the perimeter of the combustion chamber roof.
Finally, the head is provided with a valve stem guide hole 44 in the center of each valve position.
FIG. 3 illustrates the head as viewed from the camshaft or upper side. The spark plug hole 28 extends through the head, and a spark plug access opening 46 extends into the head to within a short distance (approximately the thread length of the spark plug). One or more sets of camshaft bearing supports 48 are positioned to hold the camshaft(s) (not shown).
FIG. 4 illustrates a head assembly 50 including the head 20, two conventional intake valves 52, and two conventional exhaust valves 54. For convenience, the valves are all shown in their fully opened position to illustrate the “intake curtain area” 56 and the “exhaust curtain area” 58 through which the gases must flow into and out of the combustion chamber.
FIG. 5 illustrates the head assembly 50 in cross-section view, showing the head 20, intake valves 52, and intake curtain areas 56.