CA1065823A - Low friction, controlled leakage rotary engine - Google Patents

Abstract

Abstract of the Disclosure A rotary engine for use as a fluid motor or pump which employs a rotor carrying pistons that are adapted to rotate within a circular chamber. A working fluid is introduced into and exhausted from the chamber through inlet and outlet ports provided on opposite sides of the rotary blocking valve. The blocking valve is formed with a concaval recess and is driven to turn con-jointly with the pistons so that the latter are success-ively enveloped within and move across the blocking valve.
The inlet port and blocking valve are arranged to provide an?effective pressure stroke of greater than 120° for a three piston engine to prevent stalling and deadspots in the engine's operation. The engine is dynamically bal-anced for high speed operation in the manner of a turbine.
Close-spaced, clearance between the piston and chamber walls is provided. Fluid leaks at a con-trolled rate around the pistons to form a backpressure in the trapped volume ahead of the pressurized volume. Fluid leakage around the rotor is controlled due to back pressure developed in the pressure sealed housing en-closing the elements.

Description

1~658;~3 ~his invention relates in general to rotary en-gines and in particular xelates to rotary engines which operate as either a motor powared fxom a source of pressurized 1uidj such as a gas, or as a pump for devel-~pin~ fluid pressure, Vaxious types of rotary engines have been sug-gested or designed and built for operation as either fluid moto~s or pumps. Positive displacement rotary engines employ the use o~ pistons, vanes or other elements which `~ move in fluid-tight sealing relationship with a housing or chamber wall for confining the working fluid. Engines of this type possess inherent limitations in their speed and efficiency of operation, complexity and cost of ~on-struction and maintenance, high starting friction, and wear on the moving parts, particularly the seal elements.
Many of these engines also cannot be dynamically balanc;ed and this further increases the problems of design, engine life, maintenance and opexating power requirements. Pre-vious air motors have an effective power limit because large rotors cannot run at the higher speeds.
It is recognized that turbine engines solve many of the foregoing problems in that the tuxbine engine i9 d~namically balanced, ~an xun at very high speeds, and has a ~elatively long life and low maintenance requir~ments.
~Iowever, turbine engines posse5s certain limitations, in-aludin~ greater design and construction costs, such as for fabricating the turbine blades. In addition, turbine en-gines are inherently "leaky fluid" engines and therefore must be operated at relatively high speeds to attain acceptable efficiencies. The simple turbine engine a~so

-2- ~

.. . .

.

~ ;S~23 is not readily reversible in operation.
It is a general object of the invention to provide a low-friction, -controlled leakage rotary engine which is a hybrid form of positive displace-ment and turbine engine designs.
The invention provides a rotary engine comprising the combination of a housing formed with an annular chamber concentric with a first longitu- ~
dinal axis, means forming inlet and outlet ports in the housing for directing -a working fluid into and from the chamber, a piston support member mounted within the housing for rotation about the first axis and with one end of the -~, chamber being exposed to the support member, three circumferentially spaced-apart pistons carried by the support member, each piston projecting longitu-dinally from the support member into the chamber and being spaced from the chamber walls with a minimal clearance which is sufficient to direct controlled leakage of fluid therethrough to the volume ahead of a pressure-active piston which is exposed to the inlet port whereby the pressure differential across such piston is insubstantial so as to minimize further fluid leakage past said clearance, a blocking valve positioned across the chamber between said inlet and outlet ports, said valve being mounted for rotation about a second axis parallel with said first axis, said valve being formed with a recess of a size sufficient to substantially envelope the pistons, and means for rotating the valve about the second axis in timed relationship with rotation of the support membcr whereby the pistons carried thereby move through the recess in the valv~ while the latter blocks substantial communication of fluid therethrough between the inlet and outlet ports.
The engine does not employ sliding surfaces between the piston, roto~ and housing so that friction, heat generation, and wear are reduced whereas lubrication of these parts is not required. Lubrication however is ~not undesirable and in some cases can improve the efficiency o~ the controlled ;
leakage. The engine preferably achieves an overlap in the effective pres-sure strokes of the pistons as a result of the size and interrelationship of the blocking valve and inlet port. The pistons are adapted to rotate ~036S8Z3 through the annular chamber by positive displacement of the working fluid and with dynamically balancing of the moving elements. Fluid leakage between the pistons and chamber is controlled to the extent that fluid-tight seals are not required for sealing the chamber, but at the same time operat-ing efficiency is maintained over a relatively wide speed range. Tha effect-iveness of the gas or fluid seals between the pistons and chamber increases with increased rotor speed.
The rotary engine may be of relatively simple design employing a relatively small number of parts for which close tolerance, and fluid-tight seals, are not required so that costs are reduced. The engine has self-cleaning characteristics to prevent jamming in that any small particles entrained in the working fluid can easily pass through the operating piston and valve passageways.
Ihe engine can be operated over a wide range of speeds but yet maintalns efficiency at low speed operation, can be rapidly reversed in its direction of rotation, has a low starting friction, and can start at any rotor angle. The engine can be constructed in a wide range of overall sizes, in which high operating efficiency is achieved with greater engine size, and in which a relatively high horsepower-to-weight ratio is obtainable.
From another aspect, the invention provides a rotary engine for use as a gas engine comprising the combination of a housing formed with a circular chamber having chamber walls, a rotor mounted for rotation within the housing, a plurality Oe at least three Oe circumforentially spaced-apart pistons mounted on the rotor for movement about a circular path within the chamber, each of said pistons having radially spaced inner and outer ;
surfaces with curvatures conEorming generally to the chamber walls and being spaced therefrom a clearance distance which permits controlled leakage ;
of gas therebetween, each piston further being formed with a flat end face which is spaced from the bottom wall of the chamber another clearance distance which permits controlled leakage of gas therebetween, means forming inlet and outlet ports in the housing for directing a gas into and from the chamber, ". , : . . . . , . ~ . ~ . . . . . . .

blocking valve means positioned in the chamber between the inlet and outlet .
ports for blocking gas flow therebetween across the valve while permitting `;
movement of the pistons across the position of the valve, means for rotating ..
the valve in timed relationship with rotation of the rotor and pistons responsive to gas under pressure being directed into the inlet port, with . .
said pressurized gas imparting at torque force on successive pressure-active ~ ~:
pistons which are exposed to the inlet port within the chamber simultaneous with leakage of gas through said clearances to create a pressure in the volume of the chamber on the opposite side of said pressure-active piston :
whereby the pressure differential across the pressure-active piston is insubstantial so that further leakage past such piston is minimized.
Features of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in con-junction with the accompanying drawings.
Brief Description of the Drawings Figure 1 is an axial section view of a rotary engine incorporating the invention;
Figure 2 is a cross-sectional view taken along the line 2-2 of Figure 1 illustrating the elements in one operative position;
Figure 3 is another cross-sectional view similar to Figure 2 illustrating the elements in another operative position;
Figure ~ is another cross-secitonal view similar to Figure 2 illustrating the elements in a further operative position;
Figure S is a partial end velw to a gr~atly r ~ ;
~ ~ 5 . . ~ ..

1065~3Z3 enlarged scale illustrating the configuration of one of the pistons shown in Figures 2-4; and ~igure 6 is a partial cross-sectional view of ' another embodiment of the invention which incorporates an enlarged exhaust port.
ln the drawings Figure 1 illustrates generally at 10 a rotary engine constructed in accordance with the invention and which i5 espacially adapted for use as a motor driven by pressurized gas. When used as a motor the engine's drive shaft 11 is coupled through a suitable drive train arrangement, not shown, with the particular mechanism which is to be operated. Fo,r example, rotary engine 10 can be coupled wl~h a flow control valve in a ''!'' gas transmission pipeline, with pressurized gas being bled from the pipeline and supplied to the engine as the work-ing fluid. As will become apparent from the disclosure herein, the invention will also find application as a motor with other working media or fluids, and also as a ; pump in which shaft 11 is powered for pumping a fluid under pressure.
Rotary engine 10 includes a three-element hous-ing assembly which comprises a central cylinder block 1~, a bell cover 13 at one end o~ the block and a mounting co~er 14 at the other end. The three housing elements are secured together to ~orm a pressuxe sealed chamber by means of a plurality of circumferentially spaced elongate bolts 16 which extend through holes drilled about the peripheries of the two covers, with threaded nuts 17 being mounted on the bolt ends.
The outer end face 18 of cylinder block 12 is 1. ~

.

~L~65~;~3 machined to form a circular recess or chamber 19 concen-tric with the longitudinal axis 21 of the block. The chamber i9 defined by radially spaced side walls 22, 23 and a bottom wall 24.
Drive shaft 11 is mounted for rotation about axis 21 by means of sui~able bearings 26, 27 which are secured within a bore formed through the cylinder block.
When used as a motor the drive shaft is coupled through a suitable drive train to the desired end use application, and when used as a pump the drive shaft i5 powered by a ~, suitable prime mover such as an electric motor. The hous-- ing is pressure sealed around the drive shaft by means ofa ~onical member 25, the inner diameter of which is grooved to seat O-ring seals 15. A plurality of springs 25a are seated in the rim of member 25 to hold the latter in close contact with a stationary bushing 30 which is secured within a circular recess formed in cover 14. The outer flat end of member 25 thus sealably rotates against the inner shoulder of the bushing 30. A rotor 28 which provides a circular piston support member or plate is mounted on one end of the drive shaft. This rotor also serves a~ a flywheel for absorbin~ force impulses on the xotating elements. The inner face 29 of the rotor extends radially outwardly beyond the outer wall 23 of chamber 19. The clearance between the inner face of the rotor and the end face 18 oE the block is maintained at an opti-mum dimension so that movement is frictionless but at the same time leakage of fluid from the chamber around the rotor is controlled. The required clearance depends upon the particular desi~n specifications such as surface 5~1z3 character and/or .inish..and type of fluid medium employed, and where engine 10 is utilized as a motor operating from pressurized gas this clearance preferably, but not neces-sarily, would be in the range of 0.002" to 0.005".
The spacing between bell cover 18 and rotor 28 - ............. ..defines a chamber 31. The fluid which leaks through the clearance between the xotor and cylinder block escapes into this ch~nber so that the contained pressure within the housing builds up to the point that it approaches the ~ input pressure to the engine. This serves to reduce the v l~eakage which would otherwi~e occur so-.that enyine effi-ciency is maintained, and at the same time the clearance between the block and engine permits relative mover.~cnt .
without frictional contact and without the requ.irement for sealing members.
Three pistons 32, 33 and 34 are mounted on the rotor at equally spaced-apart circumferential positions with each of the pistons projecting into circular chamber . 19. The circular bases 20 of the piston are seated tight ly within recesses that are formed about the rotor, and each piston is secured in position by means o.f a bolt 21 mounted in an open.ing extending through the opposit~ :Eac~
o.f the rotor.
Figure 5 S}10WS the configuration for piston 34 which is typical in construction for the three pistons.
The piston is formed with a generally cylindrical cross . section of a dic~neter somewhat greatex than the radial distance between the inner and outer side walls 22, 23 of chambex 19. The inner and outer surfaces 36, 37 of each piston are machined with a curvature conforming generally . -8-1~J!65~;~3 to the inner and outer chamber walls. The clearances be-tween the piston surfaces and chamber walls are preferably maintained within the range ~f 0.002" to 0.005", and this same clearance is provided between the flat end face 38 of each piston and the 1at bottom wall 24 of the chamber.
The clearance between the piston surfaces and the chamber walls permits frictionless relative movement, and also controls leakage of fluid around the pistons in a manner presently to be described. The inner flank sides of each piston are also machin~ed with flat, outwardly diverging surfdces 39, 41.
An inlet port 42 is formed through one side of tlle housing to direct inlet fluid into communication with chamber 19, and an outlet port ~3 is formed on the oppo-site side of the housing to exhaust outlet fluid from the . chamber. The inlet port is sized and positioned in rela-- tion to the size and phasing o~ blocking valve 44 so thatpressurized fluid communicates into recess 50 as each piston sweeps across the inlet, as shown in Figure 4.
This permits pressure to build up behind such piston ba-fore pressure drops o~ on the leading piston, with the result that the e~fective pressure stroke, ~or a three-piston engine, is approximately 130, i.e., 10 ~reater than the 120 spacing between pistons. In other words there is substantially at least a-10 overlap of the pres-sure strokes or the pistons. This precludes engine stal-li.ng and eliminates deadspots in the engine's operation so that it can be started at any rotational angle. The inlet and outlet ports are positioned syl~metrically on either side of the blocking valve and are designed with the same _9_ 1ai6S~23 flow areas so that the operating characteristics of the engine are idçntical in either direction of rotation.
Figure 6 shows an embodiment of the invention for use in unidirectional rotation applications in which an elongate outlet port 45a and tapped opening 45b are formed through cylinder block 12'. Outlet port 45a ex-tends along an arc which is substantially longer in rela-tion to the diameter of the outlet port of the preceding embodiment~ Preferably this outlet port extends along an ~ arc of at least one-half, or 6~, of the exhaust stroke, which,is equal to the 120 arc between adjacent pistons.
This permits outlet gas to exhaust earlier in the exhaust stroke of each piston whereby backpressure is redu~qd for improved operating efficiency.
A blocking valve 44 is mounted between the two ports to block direct fluid communication between the ports so the fluid is directed in a circular path around the length of chamber 19. The blocking valve comprises a semi cylinder 46 having a diameter greater than the radial width of the chamber. The base of the cylinder is carried on a shaft 47 which is mounted OII suitable bearings ~8 for rotation about an axi,s 49 which is parallel with the axis 21 of the drive shaft~ The base of cylinder 46 adjacent the shaft is circular and is rotatably carried within a circular seat formed about the housing opening through which shaft ~7 projects. The opposite end of the cylinder is machined flat for close-spaced relative movement with respect to the inner face 29 of the rotor. A concaval recess 50 is formed in cylinder 46 with a boundary wall siæed in width sufficiently larger than the outer diameter . --10--, .. . . . .
.. . , . , . . ~ , .... .. .

of the pistons so as to su~stantially envelope the pistons as the latter move across the valve location. The portion of the cylinder on the opposite side of the recess is formed with a hollow cavity of a sufficient size to dyna-mically balance the valve for high speed operation.
~ Means is provided to drive blocking valve 44 at a 3:1 speed ratio, and in counter rotation, with respect to rotor 28. Preferably this means includes a large dia-meter gear 52 secured by suitable means such as keying to drive shaft 11, together with a small diameter gear 53 having one third the number o~ teeth of gear 52 and secured by suitable means such as keying to shaft 47. The two gears are in meshing e,.gagement so that the blocking valve undergoes three revolutions for each revolution of the rotor. The gearing is arranged such that rotation of the blocking valve is in precise timed relationship with movement of successive pistons 32-34 to permit the latter to move across the valve location without contacting the blocking va~ve and without losing any appreciable inlet pressure across the valve.
As portrayed in the step-wise positional illus-trations of Figures 2-4 it is the cooperation o~ the con-figuration of valve r~cess ~9 with the con~iguration of the pistons which permits the pistons to be enveloped by the valve without contact while at the same time permit-tiny only a minimum of fluid transfer between the inlet and outlet ports. Thus, as shown in Figure 3, assuming that rotor 28 is turning clockwise, the piston has just entered khe cross-sectional area of rotation of the block-ing valve with recess 50 turned to accept entry o~ the .. ~ --11--~L~6S132~

piston. At the same time leading edge 56 of the recess has moved close to but out of contact with the leading surface of the piston.
Continued movement of the rotor carries piston 34 into the twelve o'clock position of Figure 2 at which ' the valve-has rotated with its recess~facing downwardly.
At this position the circular outer surface of the piston is moving in close-spaced but non-contacting relationship with the inner circular portlon of the recess. In addi-~ tion it will be seen that the two recess edges 56, 57 in this' position are below the,inner wall 22 of chamber 19 for precluding fluid communication between the inle~ and outlet ports.
Further movement of the rotor carries piston 34 to the exit position of Figure 4. In this position the inner surface 36 of the piston has cleared the valve loca-tion and trailing edge 57 of the valve recess is free to move upwardly in close-spaced but non-contacting relation-ship with the trailing surface of the piston. Continued rotation through a complete cycle carries the next two succeéding pistons'33, 32 through the blocking valve in a similar manner. It will also be realiz~d that the en-gine is reversible in operation and that the blocking valve will envelope the pistons in a similar manner with counter~clockwise rotor rotation and cl~ockwise valve ro-tation.
' In operation of the invention, it will be - assumed that rotary engine lO is to be used as a motor ' ' driven from a source of pressurized gas. Inlet port 42 is connec~ed through suitable conduit means and flow control ~65~323 . .
valve means, hot shown, with the source of gas. Assuming that rotor 28 is initially in the position shown in Fig-ure 3 the gas is directed under pressure through the inlet port and into the upper righthand portion of chamber 19 where it reacts against piston 32. The force of the gas acting on this piston imparts a torque to the rotor for clockwise rotation, and this drives the blocking valve counter-clockwise by means of the gears 52, 53. The rotor and pistons have no sliding surfaces and are free to move frictionlessly within chamber 19. The result is that ~tar_ing friction is very low, lubrication is not required for these elements, heat generation and wear are low, and a.l overspeed condition will not char the surfaces as could occur with existing air motors. At the same time the close-spaced clearance between the piston and chamber wall~ controls leakage around piston 32 into the volume 58 behind second piston 33. This trapped volume serves as a gas seal by forming a backpressure against the pressurized voiume behind piston 32. The effectiveness of this air seal increases with increased rotor speeds because there is less time for gas to leak from the chambers on each stroke. The close-spaced clearance between the outer periphery o~ the rotor and ~he housing also controls the leakage of gas into chamber 31, and the housing, and the pressure in the chambér and housing builds up to a value appro~ching the inlet pressure for effectively precluding further leakage from around the rotor. In addition end thrust on the bearings is reduced, and therefore bearing life is increased, as a result of the equalization of pressure forces in the housing which act on the rotor.

~-13-~, , .~

Continued rotation of the rotor carries the elements to the serial positions illustxated in Figures 2 and 4 where the blocking valve 44 envelopes the piston 34 in non-contacting relationship Eor permitting it to pass through the valve location while maintaining fluid isolation between the inlet and outlet ports. As trailing piston 34 sweeps by the inlet port pressure builds up to act on its trailing side while pressure continues to act against next leading piston 32. This condition exists for approximately 10 of rotation until trailing piston 34 move~,across the leading edge of the port to the position of Figure 4, thereby providing an effective pressure stroke of 130. The press~re of the gases isolated in the volume 58 between the pistons 32 and 33 serves as a back pressure to control and limit the degree of fluid leakage around piston 32. This condition is substantially main-.. . .
tained until piston 33 registers with outlet port 43 for exhausting the trapped gas volume 58.
It will be realized that rotary engine 10 per-20 mits high rotational speeds because the elements, includ-ing the rotor and blocking valve, are dynamically balanced and, in addition, the pistons move without Eric~.i.onal COIl-tact with the walls o~ the circular chamber and blocking valve. The Erictionless feature results in the engine having a very low starting torque, in comparison to Eric-tion contact type engine where starting torques are great~
er than running torques. The engine can also be quickly reversed in directional rotation, even whi.le operating at high speed,, by directing the inlet gas into port 43 with port 42 acting as the exhaust. This reversibility feature l~GSS Z3 is important in applications of the invention which in-volve differential response, e.g., for differential valve closing. The operating characteristics of the engine are identical in either direction of rotation.
While being capable of running at high speed in the manner of a turbine, engine 10 may also be operated throughout a full speed range while maintaining operating efficiency. Thus, good efficiency is obtained at low speeds in the manner of a positive displacement engine as a result of controlling the leakage from around the pis-tons. At hlgher rotational speeds efficiency increases as a result of the`reduced le~kage factor. Operating effi-ciency is also increased where the engine is scaled up-wardly in size while main~aining substantially the same clearance dimensions because the ratio of the piston dimensions to leakage gap becomes greater. In addition the larger size engines of the inventio~ can run at high speeds because of the low friction, dynamically balanced features so that a much higher power can be achieved. For ~0 example, doubling the scale of the motor increases the power by a factor of eight.
Rotary engine 10 may be relatively inexpensively con~txucted as a result o`f eliminatin~ the requirement for maintaining close ~olerances between the piston, chamber and valve elements. Because sliding surfaces are not employed, the ~urface finish is not limited to any par-ticular finish. In addition, the engine elements may be fabricated from materials selected for their compatibility with the working medium. For example, stainless steel could be used where the working medium is a noxious gas, , .

~ ;S8~3 or a ceramic material could be used for high temperature gases. The inventlon ~acilitates the use of materials, which would otherwise be infeas~ble in conventional rotary engines, such as refactory materialsp as a result of the finite clearance between the moving elements as well as gas sealing due to the backpressure effect. These fea-tures also result in permitting the engine to be scaled much larger than friction contact type engines and conven-tional turbine engines.
The provision of maintaining a controlled clear-ance between the piston, valve and chamber walls prevents the binding or jamming which could otherwise occur with c:!ose tolerances, especially where small foreign particles may become between the elements, or where the elements may change dimension due to wear or temperature variations.
The engine has a self-cleaning effect due to the relative-ly open operating passages because small foreign particles which could otherwise lodge between the elements are ca/rried throuyh by the mainstream fluid flow. ~urther-more, no lubrication i.s required between the pistons, valve and chamber walls because o~ the elimination of close tolerances and sliding sur~accs~
The ro~ary engine oE the invention will find application as a motor design over a wide power size range from fractional horsepower up to large power station size with substantially the same design configuration. Be-cause of the relatively few number of small parts the engine achieves a relatively low horsepower-to-weight ratio.
In the engine of the present invention driving ~.

~, , ' ' . . ~' '. ' ' ': ' ~

lOGSB%3 torque is applied to the pistons without any substantial gas expansion effect of the type that would occur in ex-panding chamber type engines. This means that the engine operates with substantially continuous full force on the pistons without pressure surges.
The volumetric fuel consumption of this engine is largely a function of speed and inlet pressure and is relatively independent of power. This is in comparison to conventional air motors in which pressure is lost in work-ing against the on-coming vanes moving through the cham-b~r~.
The invention also can be advantageously adapted a~ a compound engine wherein the exhaust from one con-~rolled leakage rotary engine is directed into the inlet of a second similar engine for increasing the overall , efficiency. In addition, operating borque variations can be reduced by coupling two or more of the rotary engines for out-of--phase operation on a common drive shaft.
While the foregoing embodiments are at present considered to be preferred it is understood that numerous variations and modifications may be made therein b~ those skilled in the a~t and it is intended to cover in the append~d claims all such variations and modi~ications as ~all within the true spirit and scope of the invention.

-17 !, ,

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A rotary engine comprising the combination of a housing formed with an annular chamber concentric with a first longitudinal axis, means forming inlet and outlet ports in the housing for directing a working fluid into and from the chamber, a piston support member mounted within the housing for rotation about the first axis and with one end of the chamber being exposed to the support member, three circumferentially spaced-apart pistons carried by the support member, each piston projecting longitudinally from the support member into the chamber and being spaced from the chamber walls with a mini-mal clearance which is sufficient to direct controlled leakage of fluid therethrough to the volume ahead of a pressure-active piston which is exposed to the inlet port whereby the pressure differential across such piston is insubstantial so as to minimize further fluid leakage past said clearance, a blocking valve positioned across the chamber between said inlet and outlet ports, said valve being mounted for rotation about a second axis parallel with said first axis, said valve being formed with a recess of a size sufficient to substantially envelope the pistons, and means for rotating the valve about the second axis in timed relationship with rotation of the support member whereby the pistons carried thereby move through the recess in the valve while the latter blocks substantial communication of fluid therethrough between the inlet and outlet ports.

2. A rotary engine as in claim 1 in which said working fluid is a gas, and the pressure which is maintained in said volume forms a gas seal to control said leakage, said gas seal having an efficiency which increases with increased rotary speed of the support member.

3. A rotary engine as in claim 1 in which said working fluid is a gas, and in which said clearance is in the range of substantially 0.002 to 0.005 inches.

4. A rotary engine as in claim 1, 2 or 3 in which the housing includes a cylinder block, the outer circular portion of said piston support member is spaced from the cylinder block with a second clearance, and said housing forms a closed volume about said rotor to receive fluid leaking through said second clearance and to confine and maintain such fluid under pressure to limit further leakage through said second clearance.

5. A rotary engine as in claim 1, 2 or 3 in which said annular chamber includes radially spaced-apart inner and outer cylindrical walls, and said pistons are formed with radially spaced-apart inner and outer surface portions each having a radius commensurate generally with the respective radii of the inner and outer chamber walls, said surface portions of the pistons being spaced from the respective inner and outer chamber walls by said clearance which controls the leakage of fluid therebetween.

6. A rotary engine as in claim 1, 2 or 3 in which said piston support member comprises a circular rotor having a substantial moment of inertia to function as a flywheel for absorbing force pulses acting on the rotor.

7. A rotary engine as in claim 1, 2 or 3 for use as a fluid pump in which said inlet port is connected to a source of fluid, and drive means is provided to rotate the support member about the first axis whereby fluid is inducted through the inlet port and exhausted under pressure through the outlet port.

8. A rotary engine as in claim 1 in which said inlet port is positioned for communication with the recess of the blocking valve as each successive piston passes the inlet port whereby inlet pressure begins to act against the trailing side of such piston while pressure continues to act against the next leading piston to achieve an overlap of the pressure stroke for each piston.

9. A rotary engine as in claim 8 in which movement of each successive piston past the inlet port builds up pressure on the trailing piston at a rate comparable to the reduction in pressure on the next leading piston.

10. A rotary engine as in claim 9 in which said trailing piston moves through an are of substantially at least 10° across the inlet port while said build up of pressure is occurring whereby a force overlap of substan-tially at least 10° is created in the pressure stroke of each piston.

11. A rotary engine as in claim 1 for use in unidirectional engine rotation application in which said outlet port is elongate in the direction of piston movement for exhausting fluid and reducing backpressure in the exhaust stroke of each piston.

12. A rotary engine as in claim 11 in which said outlet port extends along an are of substantially at least one-half of the exhaust stroke.

13. A rotary engine comprising the combination of a housing formed with an annular chamber concentric with a first longitudinal axis, said chamber having radially spaced inner and outer walls, means forming a cy-lindrical blocking valve positioned across the chamber and being mounted for rotation about a second axis parallel with said first axis, means forming inlet and outlet ports in the housing on opposite sides of the blocking valve for directing a working fluid into and from the chamber, a rotor mounted within the housing for rotation about the first axis with one side of the chamber being exposed to the rotor, three circumferentially spaced-apart pistons carried by the rotor and which project into the chamber, said pistons being formed with radially spaced-apart inner and outer sur-face portions each having a radius commensurate generally with the respec-tive radii of the inner and outer walls of the chamber, said surface por-tions of the pistons being spaced from the respective inner and outer cham-ber walls with a minimal clearance which directs leakage of fluid there-between into the chamber defined between adjacent pistons whereby the pres-sure differential across a pressure-active piston is insubstantial for minimizing further fluid leakage past said clearance, said blocking valve being formed with a recess having a concave boundary wall which opens outwardly through one side of the valve to substantially envelope the pistons, and drive train means for turning the blocking valve in a 3:1 speed ratio with respect to rotation of the rotor whereby the pistons car-ried thereby move through the recess in the valve while the latter sub-stantially blocks direct communication of fluid between the inlet and out-let ports.

14. A rotary engine for use as a gas engine comprising the combination of a housing formed with a circular chamber having chamber walls, a rotor mounted for rotation within the housing, a plurality of at least three of circumferentially spaced-apart pistons mounted on the rotor for movement about a circular path within the chamber, each of said pistons having radially spaced inner and outer surfaces with curvatures conforming generally to the chamber walls and being spaced therefrom a clearance distance which permits controlled leakage of gas therebetween, each piston further being formed with a flat end face which is spaced from the bottom wall of the chamber another clearance distance which permits controlled leakage of gas therebetween, means forming inlet and outlet ports in the housing for directing a gas into and from the chamber, blocking valve means positioned in the chamber between the inlet and outlet ports for blocking gas flow therebetween across the valve while permitting movement of the pistons across the position of the valve, means for rotating the valve in timed relationship with rotation of the rotor and pistons responsive to gas under pressure being directed into the inlet port, with said pressurized gas imparting a torque force on successive pressure-active pistons which are exposed to the inlet port within the chamber simultaneous with leakage of gas through said clearances to create a pressure in the volume of the chamber on the opposite side of said pressure-active piston whereby the pressure differential across the pressure-active piston is insubstantial so that further leakage past such piston is minimized.