Abstract:
A poppet valve for use in an internal combustion engine. The poppet has a partially-inverted perimeter shape which nevertheless substantially maintains the curtain area of the valve. These improved valves pack more efficiently into the combustion chamber roof area than would conventional, circular-perimeter poppet valves. For the same size combustion chamber, significantly greater total curtain area is achieved, improving engine performance. Valve weight is greatly reduced, enabling the use of lighter return springs, camshafts, desmodromic actuators, and so forth.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field of the Invention  
         [0002]     This invention relates generally to internal combustion engines, and more specifically to poppet valves for such.  
         [0003]     2. Background Art  
         [0004]     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&#39;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.  
         [0005]      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.  
         [0006]     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.  
         [0007]      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.  
         [0008]     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.  
         [0009]     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 .  
         [0010]     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.  
         [0011]     Finally, the head is provided with a valve stem guide hole  44  in the center of each valve position.  
         [0012]      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).  
         [0013]      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.  
         [0014]      FIG. 5  illustrates the head assembly  50  in cross-section view, showing the head  20 , intake valves  52 , and intake curtain areas  56 . 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  shows a conventional poppet valve.  
         [0016]      FIG. 2  shows a conventional head for use in a four-stroke internal combustion engine, as seen from the combustion chamber or bottom side.  
         [0017]      FIG. 3  shows the head of  FIG. 2 , as seen from the camshaft or top side.  
         [0018]      FIG. 4  shows the head of  FIGS. 2 and 3  adapted with two conventional intake valves and two conventional exhaust valves such as shown in  FIG. 1 .  
         [0019]      FIG. 5  shows the head assembly of  FIG. 4  in cutaway view, particularly illustrating the valve curtains.  
         [0020]      FIG. 6  shows the circumference of the conventional valve.  
         [0021]      FIG. 7  shows a geometric relationship between certain figures including overlapping circles.  
         [0022]      FIGS. 8-19  shows, in corresponding pairs of perspective view and top view, a variety of valves according to various embodiments of this invention.  
         [0023]      FIG. 20  shows a head assembly, with two intake valves and two exhaust valves as shown in  FIG. 8 .  
         [0024]      FIG. 21  shows another head assembly, with three intake valves and two exhaust valves as shown in  FIG. 8 .  
         [0025]      FIG. 22  shows a geometric relationship between the circumferences of the two intake valves, two smaller exhaust valves, and combustion chamber area of a conventional (and greatly simplified) head, making maximum usage of the combustion chamber with the largest valves possible.  
         [0026]      FIG. 23  shows a geometric relationship between the circumferences of the three intake valves, two same-sized exhaust valves, and combustion chamber area of another conventional head, making maximum usage of the combustion chamber with the largest valves possible.  
         [0027]      FIG. 24  shows a geometric relationship obtained from a five-valve head according to one embodiment of this invention.  
         [0028]      FIG. 25  shows another head assembly, using different size valves.  
         [0029]      FIG. 26  shows another embodiment of a valve using multiple stem flats for alignment.  
         [0030]      FIG. 27  shows a highly asymmetrical valve having three different sub-circular segments.  
         [0031]      FIG. 28  shows a valve having a truncated finger between inverted arc segments. 
     
    
     DETAILED DESCRIPTION  
       [0032]     The invention will be understood more fully from the detailed description given below and from the accompanying drawings of embodiments of the invention which, however, should not be taken to limit the invention to the specific embodiments described, but are for explanation and understanding only.  
         [0033]      FIG. 6  illustrates the outer perimeter C 1  of a 50 mm valve having, of course, a 25 mm radius poppet. The circumference C of the poppet is, to a first order, a good approximation of the circumference of the curtain area, and is equal to 2πr=157.08 mm.  
         [0034]      FIG. 7  illustrates a geometric relationship between overlapping circles. A center circle C 1  is intersected by three other circles C 2 -C 4 , each having its center equidistant from the center of the center circle. The three circles are disposed at 120° intervals around the center circle. All four circles are of equal radius. Regardless of the relative lengths of the radius and the on-center distance, each pair of overlapping circles will define a pair of arcs S 1  and S 2  (shown in heavier lines) which are of equal arc length. The center circle has three non-overlapped arcs V, each having a length equal to (2πr−3S)/3.  
         [0035]     The reader should take special notice of the fact that the shaded area Z has the same total circumference as does the center circle, 2πr, although its area is significantly smaller than that of the center circle. The shaded shape is essentially a circle which has three inverted arcs at its perimeter.  
         [0036]     If the three circles have a different radius than does the center circle, the perimeter of the shaded area Z will change, but it will change less than the area has changed between the center circle and the shaded area.  
         [0037]     These relationships hold true with numbers of outer circles other than three. And they hold true, albeit to a lesser degree, with outer shapes that are not circular; meaning that arcs of the center circle&#39;s perimeter can be inverted (turned inward or concave), even if they are then changed into somewhat different shapes, and the perimeter will in most simple cases change significantly less than the area changes.  
         [0038]      FIGS. 8-19  illustrate six embodiments of poppet valves according to various embodiments of this invention. Each consecutively-numbered (and vertically aligned) pair of drawings represent the same valve in perspective view and top view, respectively.  
         [0039]      FIGS. 8-9  illustrate a valve  70  which has had its outer perimeter  72  simplistically “folded in” as shown in  FIG. 7 .  
         [0040]      FIGS. 10-11  illustrate a similar valve  74  which has been modified with rounded “ends”  76 . Thus, the perimeter will not exactly match that of the corresponding circle.  
         [0041]      FIGS. 12-13  illustrate a valve  80  which has had a slightly more sophisticated shape applied to it, including the forming of a valve seat mating face  82 . Further, the valve stem has been adapted with a flat  84  for clocking the valve into a fixed rotational position to correctly align it with the head&#39;s valve seat. And a retention groove  86  has been added, to facilitate e.g. desmodromic valve actuation.  
         [0042]      FIGS. 14-15  illustrate a valve  90  which includes two inverted arc perimeter segments  92 ,  94  as well as a portion  96  which retains the original perimeter shape. The valve is, thus, not necessarily strictly symmetric. Because it is not inherently balanced, the designer will need to take appropriate measures to strengthen it adequately.  
         [0043]      FIGS. 16-17  illustrate a valve  100  with a triangular shape with substantially straight edges. The valve is not necessarily based on a starting shape with a circular perimeter.  
         [0044]      FIGS. 18-19  illustrate a valve  110  with a square perimeter shape which has been modified with inwardly folded circular arc segments.  
         [0045]     The valves of  FIGS. 8-19 , and others based upon the principles of this invention, may all be referred to as “inverted poppet valves”.  
         [0046]      FIG. 20  illustrates a head assembly  120  including a head  122  adapted for use with one or more inverted poppet intake valves  124  and one or more inverted poppet exhaust valves  126 . The head includes a roof  128 , squish band  130 , intake tracts  132 , exhaust ports  134 , and spark plug hole  136 . The intake valves may share a common intake tract, or, as shown, each intake valve may be provided with its own, dedicated intake tract. The same is true of the exhaust valves.  
         [0047]      FIG. 21  illustrates a head assembly  140  having three inverted poppet intake valves  124  and two inverted poppet exhaust valves  126 . The head  142  include a common intake tract  144  for all three intake valves, and a common exhaust port  146  for both exhaust valves.  
         [0048]      FIG. 22  illustrates a geometric relationship between the valve perimeters, spark plug hole perimeter, and combustion roof perimeter of a conventional four-valve head. The roof has a perimeter C, within which must fit—without interference or overlap—the perimeters IN 1  and IN 2  of two intake valves, the perimeters EX 1  and EX 2  of two exhaust valves, and the perimeter SP of the spark plug hole. To increase engine performance, the intake valves may be made larger, by reducing the size of the exhaust valves.  
         [0049]      FIG. 23  illustrates a geometric relationship between the valve perimeters, spark plug hole perimeter, and combustion roof perimeter of a conventional five-valve head. The roof has the same perimeter C, within which must fit the perimeters IN 1 , IN 2 , and IN 3  of the three intake valves, the perimeters EX 1  and EX 2  of the two exhaust valves, and the perimeter SP of the spark plug hole. As can be seen by comparison to  FIG. 22 , the five-valve head offers somewhat improved overall valve area.  
         [0050]      FIG. 24  illustrates a geometric relationship between the valve perimeters, spark plug hole perimeter, and combustion roof perimeter of a five-valve head according to one embodiment of this invention, with the geometry overlayed on the head of  FIG. 21 . As can readily be seen, if the valves were “un-inverted”, or converted back to their correspondingly-sized conventional circular perimeter counterpart valves, the perimeters C 1 -C 5  would significantly overlap. This pointedly illustrates the advantage gained from this invention—valve curtain area significantly larger than could be fit within the same-sized combustion chamber using conventional circular poppet valves. Note that each valve includes a portion  150  which intrudes into the perimeter circle of a neighboring valve. However, because that neighboring valve uses an inverted poppet, there is no interference, as the two valves are clocked into a beneficial angular relationship.  
         [0051]     In addition to the significant advantage of increased curtain area, the inverted perimeter valve of the present invention also offers the further advantage of significantly lower valve mass. The poppet contains much less metal. This, in turn, allows the use of a thinner valve stem, further reducing the mass. The reduced valve mass permits improvements in the mass and/or effectiveness of the valve return spring, camshaft, desmodromic actuators, and so forth.  
         [0052]     With the same diameter and length stem, the same diameter poppet, and so forth, the valve of  FIG. 1  has a mass of 55.95 grams, and the valve of  FIG. 8  has a mass of 29.42 grams, for a savings of 26.53 grams or 47.4%. Similarly configured, the valve of  FIG. 12  has a mass of only 24.65 grams; if its stem diameter is reduced from 6 mm to 5 mm, it has a mass of only 20.95 grams, a 62.6% reduction from the original.  
         [0053]     Furthermore, the “inverted” valve has a significantly higher ratio of (1) surface area in contact with the head, to (2) mass, than does a conventional valve of the same “perimeter dimension” or of the same curtain area. This means that the inverted valve will exhibit significantly better heat transfer (from the valve to the head) than a conventional valve exhibits. The inverted valve will not be as susceptible to overheating as the conventional valve.  
         [0054]      FIG. 25  illustrates a head assembly  160  according to another embodiment of this invention, using two or more different sizes of valves. In the embodiment shown, the intake valves  162  are larger than the exhaust valves  164 .  
         [0055]      FIG. 26  illustrates an inverted poppet valve  170  in which the stem is adapted with the same number of flats  172  as the poppet has inverted segments  174 . If the inverted segments of the poppet are the same dimensions and are symmetrically arranged around the poppet, and the flats are the same dimensions and are symmetrically arranged around the stem, the angular orientation of the valve in the head (not shown) will not be as critical as if there is only a single flat. In other words, if there are three flats, there are three possible orientations into which the valve can be placed in the head. This will ease the assembly of the engine, and may further offer an opportunity for the mechanic to rotate the valves (e.g. by 120°) when rebuilding the engine, such that each inverted segment of the valve can then be put into contact with a newly corresponding segment of the head&#39;s valve seat, potentially extending the serviceable life of the valve.  
         [0056]      FIG. 27  illustrates a valve  180  in top view, and is primarily intended simply to illustrate the meaning of the term “sub-circular”, which refers to a poppet perimeter segment which does not extend as far radially outward as if the poppet were a conventional, circular poppet. For example, a concave segment is sub-circular, a flat segment is sub-circular, and a segment having a different radius of curvature may be sub-circular. The valve is shown with reference to a perimeter bounding circle  182  having a given radius (say “R”). A first sub-circular segment  184  has a slightly concave shape whose radius is larger than R. A second sub-circular segment  186  has a highly concave shape whose radius is significantly smaller than R. A third sub-circular segment  188  has a convex shape whose radius is larger than R. These and a variety of other sub-circular segment shapes will allow a head to place larger valves closer together (meaning with overlapping bounding circles) than would be possible using conventional circular poppet valves.  
         [0057]      FIG. 28  illustrates a valve  190  in which the portions between the inverted segments are of different lengths. Two such portions  192  extend to the bounding circle (not shown) of the valve, but a third such portion  194  is truncated short of the bounding circle. This enables the valve to be placed in the head (not shown) in positions and rotational orientations different than with other valves. For example, the truncated “finger”  194  can be oriented toward e.g. the squish band perimeter, or the spark plug hole, or another valve, with the valve being centered closer to that component than would be possible if one of the full-length fingers  192  were pointed in that direction. Shortening a finger gives up some curtain area versus keeping it full length, but this may actually permit e.g. larger valves or a greater number of valves to be used, for a net increase in curtain area. Another way of looking at this is that the other fingers  194  are made longer than they would otherwise be.  
       CONCLUSION  
       [0058]     When components are said to be “coupled” to one another, this is not intended to preclude their being of unitary or monolithic construction, nor to suggest that there are no intervening structures or components between them.  
         [0059]     The various features illustrated in the figures may be combined in many ways, and should not be interpreted as though limited to the specific embodiments in which they were explained and shown.  
         [0060]     Those skilled in the art having the benefit of this disclosure will appreciate that many other variations from the foregoing description and drawings may be made within the scope of the present invention, and that various details of the engine (e.g. camshafts, valve guides, spark plugs, and the like) have been omitted for ease of illustration but are nevertheless well within the ability and familiarity of those skilled in engines. Indeed, the invention is not limited to the details described above. Rather, it is the following claims including any amendments thereto that define the scope of the invention.