Recent years have seen a considerable upsurge in the focus of attention upon positive displacement rotary mechanisms to be utilized as engines, compressors, expanders or the like. The interest is in a large part due to the considerable reduction in the number of moving parts required in a rotary mechanism versus a reciprocating mechanism of similar displacement. This considerable advantage has, at the same time, been offset to some degree by disadvantages associated with rotary mechanisms. For example, in rotary mechanisms utilized as engines, there frequently is a high surface to volume ratio of the working volumes which reduces efficiency of the combustion process thereby reducing the amount of work obtained from a given unit of fuel and which will frequently result in an increase in hydrocarbon emissions over that generated by a reciprocating mechanism of similar displacement.
More particularly, when extended areas of opposed moving parts defining a working volume are in extremely close proximity to each other, the volume of working fluid between such parts in such an area does not participate in the combustion process, generally because the surfaces of the mechanical parts are cool and the spacing of the parts with respect to each other is so small that temperatures sufficient to maintain combustion cannot be obtained. In other words, as soon as the flame of combustion attempts to enter the space, it is immediately quenched by the cool surfaces. Consequently, fuel in the volume between the two closely adjacent surfaces does not burn and exits the mechanism as a hydrocarbon emission.
A volume of this type forming part of a working volume of an engine is known as "parasitic volume" because it does not assist in producing energy and in fact may actually absorb energy through the heat rejection process. In many cases, it may limit the maximum attainable compression ratio to some value less than the optimum value; and in most cases, the higher the compression ratio, the more efficient the engine will operate. And in cases where, due to engine geometry, the maximum compression ratio is less than that determined to be optimum to permit the engine to operate on a particular cycle as, for example, a diesel cycle, the problem of maximizing engine efficiency is made more acute.
Trochoidal mechanisms are typical of those wherein engine geometry limits the maximum attainable compression ratio. For reasons that not need be elucidated here, as one alters the geometry of a trochoidal engine to increase its compression ratio, the engine becomes bulky for the same power. Excessive bulk occurs at some point which is less than desirable. Therefore, it has been necessary to provide such engines with multiple stages, generally two, the first for initial compression of air and final expansion of combustion gases and the second for final compression of air, combustion and initial expansion of combustion gases. This, of course, complicates the engine and increases the number of moving parts thereby making a rotary mechanism less attractive when compared to a reciprocating one.
Engine geometry difficulties as far as obtaining high compression ratios are nowhere near as prevalent in slant axis rotary piston mechanisms and while the given slant axis rotary piston mechanism has a maximum compression ratio determined by its geometry, it will be sufficiently high that optimal diesel cycle compression ratios can be obtained without multiple staging. Nonetheless, other practical difficulties are present.
For example, in U.S. Pat. No. 3,485,218 issued Dec. 23, 1969 to Clarke, there is disclosed a slant axis rotary piston mechanism which may be used as an engine, compressor, expander or the like. In the several embodiments therein illustrated, a number of seals for sealing the various working volumes are carried by housing components but in each case, the various apexes on the rotor flanges must be sealed by seals carried by the rotor. It has been determined that, as a practical matter, interfacing the rotor seals with those carried by the housing to prevent substantial leakgage is extraordinarily difficult. Consequently, while the sealing configuration illustrated in the above identified Clarke patent minimizes parasitic volume, there is sufficient leakage so as to more than overcome the advantage obtained by minimizing parasitic volume.
As a consequence, resort has been made to seal configurations wherein all seals are carried by the rotor so that the various seals may be satisfactorily interfaced with each other to cut leakage to an absolute minimum. This has resulted in seal grid configurations along the lines of that illustrated in U.S. Pat. No. 4,026,662 issued May 31, 1977 to Goloff. A consideration of the operation of a slant axis rotary mechanism and the disposition of the so-called hub seals therein employed when in a grid configuration such as illustrated in the Goloff patent will show that there is a considerable area of the hub between the hub seal and the rotor flange at maximum compression which is closely adjacent the inner spherical wall of the mechanism resulting in considerable parasitic volume at maximum compression and at points in the cycle close to maximum compression. In fact, this parasitic volume becomes non-existent substantially only at full expansion. Thus, while high rates of seal leakage are eliminated by configurations such as shown by Goloff, some undesirable parasitic volume, and the disadvantages accompanying the same, comes into existence.
The present invention is directed to overcoming one or more of the above problems.