US 3704080 A
A fluid engine for the transfer of energy between a rotating shaft and a fluid flowing at a constant velocity relative to the angular velocity of the shaft, consisting of a plurality of energy-transfer modules connected hydraulically in series, each module effecting in turn an energy transfer between the fluid and a piston during an active period, the terminal portions of the active periods of adjacently ordered modules being arranged to overlap at a constant velocity.
Claims available in
Description (OCR text may contain errors)
United States Patent Cross FLUID ENGINE  Inventor Grosvenor M. Cross, West Concord,
' Mass. 01742  Filed: July 22, 1970  Appl. No.: 57,165
 U.S. Cl. .417/486, 417/488, 417/518, 417/531  Int. Cl.....F04b 19/00, F04]: 37/00, F0413 21/02, F04b 39/15  Field of Search...417/266, 215, 488 X, 900, 265
 References Cited UNITED STATES PATENTS Riesner ..417/266 X Anderson .417/488 III - NOV. 28, 1972 Stallman ..417/266 X Longenecker ..4 1 7/900 X Primary ExaminerCarlton R. Croyle Assistant xaminerRichard E. Gluck Attorney-Kenway, .lenney and Hildreth  ABSTRACT A fluid engine for the transfer of energy between a rotating shaft and a fluid flowing at a constant velocity relative to the angular velocity of the shaft, consisting of a plurality of energy-transfer modules connected hydraulically in series, each module effecting in turn an energy transfer between the fluid and a piston during an active period, the terminal portions of the active periods of adjacently ordered modules being arranged to overlap at a constant velocity.
8 Claim, 8 Drawing Figures PATENTEDNHV 2 m2 3. 704,080
SHEET 1 [IF 7 INVENTOR GROSVENOR M. CROSS ATTORNEYS PATENTEDNB 91 3.704.080
SHEET 2 BF 7 FIG. 2
-uNIFORM RIsE IaO OvERI AP TOP SLIDER s UNIFORM RIsE 40 IeO 4O OvERI AP BOTTOM SLIDER s TOP OPEN OPEN VALVE l7 CLOSED CLOSED OPEN OPEN BOTTOM VALVE l5 CLOSED CLOSED A B D E F G INVENTOR GROSVENOR M. CROSS ATTOR NEYS PATENTEDnnvzsmz 3,704 080 SHEET 3 OF 7 PATENTEnnuvze I972 3,704,080
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INVENTOR GROSVENOR M. CROSS ATTORNEYS PATENTEDnuvzs I972 SHEET 8 BF 7 FIG. 6
INVENTOR GROSVENOR M. CROSS QZ/AZM ATTORNEYS PATENTEDNUVZBIWZ 3.704 080 sum 7 [IF 7 FIG. 8
INVENTOR GROSVENOR M. CROSS ATTORNEYS FLUID ENGINE The need for pulse-free, positive-displacement pumps and motors is common knowledge. The high destructive stresses and noisy operation of pumps and hydraulic motors with varying input or output is deleterious in all hydraulic installations, and in many chemical and process industries the resulting lack of accuracy constitutes a serious problem. Efforts are commonly made to alleviate these effects by multiplepiston devices and high-speed operation, but the problem cannot thus be eliminated, and such highspeed devices usually entail inertia effects harmful in other ways. No continuous-torque, pulse-free, hydraulic motor composed of low-speed elements, for example, is at present available. The requirements for valving in all present efforts to produce pulse-free pumps are, in addition, so exacting that they can be met in practice only with difficulty.
One object of the present invention is to supply a fluid engine adaptable to use as a fluid pump capable of producing a substantially pulse-free continuous and positive flow of fluid in correspondence to a continuous and positive motion of a mechanical driving means.
Another object is to provide a fluid mechanism capable of producing a continuous and positive motion of a mechanical output in response to a continuous, positive and pulse-free fluid input.
A further object is to supply a pump of elements simple and economical in construction, which is adapted to reverse operation as a motor.
Another object is to produce a fluid mechanism of the class described wherein the valve operation is not critical, there being a definite period of predetermined extent in which valve changes may take place, and thus attain certainty of operation.
An object is also to provide a pumping mechanism capable of rendering an accurate and pulseless flow of fluids at very low velocities and at very low speeds of mechanical actuation.
A still further object is to provide a positive displacement motor of simple construction, capable of supplying a continuous torque at velocities down practically to zero, with all parts operating so slowly as to minimize poor response from inertia effects.
I have discovered that the foregoing objects may be attained and other advantages realized by so relating and interconnecting the valves and pistons that the shift in operating pressure or effort from one piston to another is timed to take place during a predetermined period of the cycle while the pistons are moving in series and when such effort or pressure of the pistons overlaps.
These and other features of the invention will be best understood and appreciated from the following description of a preferred embodiment thereof selected for purposes of illustration and shown in the accompanying drawings in which:
FIG. 1 is a schematic, vertical section of an engine arranged as a pump showing in a simple form the basic principles of my invention.
FIG. 2 is comprised of graphs showing in typical arrangement the operation of the elements of the pump of FIG. 1.
FIG. 3 is a vertical section through a high-precision pump constructed according to the principles of my invention, adapted to the dispensing of corrosive fluid, as well as other purposes.
FIG. 4 is a detailed vertical section through the flow chambers and valving mechanisms of the pump of FIG. 3.
FIG. 5 is a vertical section through an engine usable both as fluid pump and fluid motor.
FIG. 6 is a horizontal section through the machine of FIG. 5.
FIG. 7 is a plan view of the valve-and-piston casing of the device of FIGS. 5 and 6, showing the interconnecting passages of the same.
FIG. 8 is an expanded view of the mechanism and fluid passages of the machine of FIG. 5.
Referring to FIG. I, a vertically disposed valve and piston casing is shown at I. Casing l is shown as bored vertically throughout, but the bore is tranversely interrupted by two openings which extend from one face of the casing inward to a point somewhat beyond the extent of the bore. The above construction divides the casing into three chambers, each formed from the bore described; the upper chamber is chamber 2,.the intermediate chamber 3, the lower chamber 4. A slider 5 is situated between chambers 2 and 3, bearing at its upper end a piston 6, close fitting to the-bore of chamber 2, and at its lower end a piston 7 close fitting to the bore of chamber 3. A similar slider'8 lies between chambers 3 and 4, bearing at its upper end piston 10 close fitting in chamber 3 and at its lower end piston 11 close fitting in chamber 4. .A suitable inlet port 12 communicates with the lower chamber 4, and an outlet port 13 with the chamber 2. Interconnecting passage 14 leads from the lower chamber 4 to a valve 15, shown as a ball check opening upwardly.
From valve IS a passage 16 leads upwardly to a similar valve l7,'and beyond valve 17 a passage 20 continues into chamber 2. Between valves 15 and 17 a passage 21 joins passage 16 to chamber 3. This construction permits flow from chamber 4 into chamber 3, but prevents flow in the opposite direction. Similarly, flow from chamber 3 is permitted into chamber 2 but not from chamber 2 to chamber 3.
A pin 22 is shown as mounted in slider 5, and above it in the casing is located pin 23. An extension spring 24 is illustrated as joining pins 22 and 23, thus yieldingly urging slider 5 and its associated pistons upwardly. A similar construction consisting of pins 25 and 26, with connecting spring 27, urges slider 3 and its associated pistons downwardly.
Centrally in the length of slider 5 a slot 28 is shown, and a similar slot 23 in slider 3. Against the bottom flat surface 31 of slot 28 bears the cylindrical end of an arm 33 which acts in opposition to the raising effect of spring 24. A similar cylindrical end of arm 34 is shown as bearing on the flat upper surface 32 of slot 29 and as restraining slider 8 against the lowering effect of spring 27. Arms 33 and 34 are shown as pivoted at 35 and 36 to some fixed part of the casing 1. Beyond pivot 35, lever 37 extends as a continuation of arm 33 and carries on its outer end a cam roller 41 rotatively mounted. Roller a1 is shown as running on a cam M, which in turn is mounted on driving shaft %3, considered as bushed in some member fixed with respect to pivots 35 and 36 and casing I.
By means of the above illustrative construction, spring 24 maintains slider 5 in contact with arm 33, and cam roller 41 in contact with cam 44, whereby slider 5 and the pistons 6 and 7 are compelled to follow accurately a motion predetermined by the contour of cam 44 and the rotation of shaft 43.
A similar arrangement of lever 40, cam roller 42 and cam 45 compels slider 8 to follow a motion relative to the rotation of shaft 43, predetermined by the contour of cam 45.
Cam 44 is shaped to impart to slider 5 a definite sequence of motion and velocity relative to the successive angular positions of shaft 43; hence when a constant rotative velocity is given shaft 43, pistons 6 and v7 will follow a definite pattern of rise and fall relative to chambers 2 and 3, in time, repetitive for each revolution of the cam. Similarly, by the structure shown, pistons 10 and 11 will follow a predetermined temporal sequence of motion into and out of chambers 3 and 4, such motion resulting from the contour of cam 45.
The detailed operation 'of the device is as follows.
The graphs of FIG. 2 illustrate the displacements of sliders 5 and 8 relative to the angular displacement of the shaft 43. The abscissae represent shaft displacement, the distance A to E representing one revolution. The ordinates, without scale, represent upwardly in the graph, motion of the sliders upwardly in FIG. 1; since the pistons are of equal area the graphs of slider 5 and slider 8 also represent those changes in the volumes of chambers 2 and 3 respectively which are due to the motions of pistons 6 and 10 respectively.
From A to C slider 5 isshown to rise at a constant rate over 180 of cam motion. At the same rate of rise it continues for a further period (called the overlap), of arbitrary extent and labeled illustratively as 40. The steady rise is shown as terminating at the vertical line D. The slider then starts decelerating, comes momentarily to rest, and then returns downward, passing, between D and E, into an accelerative period which once more brings it momentarily to res at the bottom of the stroke and then causes it to rise again until, at IE, it has the same upward velocity as it had at A when beginning its rise.
The motion of slider 8, shown by the second line of the graph, is in general the duplicate of that of slider 5, but takes place over a period 180 behind (or ahead of) the respective motions of slider 5. The graph clearly shows that during the overlap period from C to D both sliders are rising at the same velocity, with slider 5 nearing the top of its stroke and slider 8 rising from near its bottom position. Similarly, at a point 180 later, there occurs a second overlap period, slider 5 now rising from near its bottom position while slider 8 is approaching the termination of its upward rise.
Starting at the point A of FIG. 2, it is seen that valve 15 will remain closed, since it was closed during the previous period. Sliders 5 and 8 and thus pistons 7 and 10 are rising at the same velocity. The diameters of the bores of chamber 3 are shown as equal, so that the volume of chamber 3 remains constant and no fluid passes through valve 17, which is thus allowed time to settle into its seat during the overlap period from A to B. Such closing of valve l7 may be accelerated, of course, by spring-loading the ball or other closing member.
During the period A to B (overlap) the output is determined by the rate of rise of piston 6, or piston 10, since both are rising at the same velocity in bores of the same diameters. Input rate is determined by the rate of rise of piston 11 in the bore of chamber 4, and since rate of rise is identical with the rise of piston 6 in chamber 2, it is clear that input and output of the pump are identical.
When the cam motion reaches the point indicated by line B of FIG. 2, slider 8 and hence piston 10 start to decelerate and the volume of chamber 3 to increase. Valve 17 has by now had ample time to close, so that reverse flow from chamber 2 is prevented, and output continues at the same rate, as determined by the continued steady rise of piston 6. Valve 15 opens as a result of the demand from expanding chamber 3 and fluid flows into that chamber. This condition continues as deceleration reverses the direction of motion of slider 8 and piston 10. During this phase, piston 7 is drawing in fluid past valve 15 at the output rate. Additional fluid passes valve 15 due to the downward motion of piston 10, but the net inflow through input passage 12 is still at the output rate, since the additional flow due to the dropping of piston 10 is exactly compensated by an equal contraction of chamber 4 due to the dropping of piston 1 l in a bore shown as of the same diameter.
At a time between those represented by lines B and C, the deceleration of slider 8 and its pistons changes to acceleration; the pistons slow their downward (negative) velocity until at a point somewhat before the line C their direction reverses, and when the line C is reached, piston 10 is traveling upward at the same output rate as piston 6. I
As piston it) approaches the velocity of pistons 6 and 7 just before the line C, the rate of expansion of chamber 3 diminishes to zero, the flow through valve 15 is correspondingly reduced, and the valve very nearly comes to rest in closed position. In all such valves there is, however, a lag varyingin amount with such factors as valve inertia, fluid viscosity, flow passage area, etc., so that the valve may not close completely until after C is reached. Between C and D, however, when the two pistons 7 and lid are rising at the same velocity, it is immaterial when valve 15 closes, since the load of the output is taken by piston 6, with valve 37 remaining closed. Between C and D ample time is allowed, and valve 15 closes firmly.
At the point D, slider 5 begins its decelerative phase, and its upward motion slows down, thus reducing by the downward motion of piston 6 the volume of chamber 3 and causing valve 7 to open. The conditions from D to E are now an exact repetition of those from B to C, except that the pistons 6 and it) have exchanged functions. The output flow now caused by the steady rise of slider d and hence of piston 10 passes through valve ll7, quite unaffected by the downward motion of slider 5 and its associated pistons or by any upward motion of that slider which is less than that of slider b and its pistons, since such motions expand the volume of chamber 2 by an amount equal to the contraction of the volume of chamber 3, the bores being of equal diameter, and thus cause an increased flow through valve l7, but do not contribute to the total output flow. Input into chamber 4 through inlet passage 12 during this phase continues at the output rate as before, since it is determined by the rate of rise of piston ll.
At E (as also at A), when once more sliders 5 and 8 and their associated pistons begin their periods of simultaneous rise, valve l7 undergoes the same closing process as that which valve 15 underwent at point C; it has been closing during the period of decreasing flow just before E, but may have a lag which extends into the period E to F. Here again ample closing time is allowed during an overlap period, so that valve 17 will have reached its closed position by the time the cycle has reached point F.
Beyond F the cycle repeats that described at the point B, 360 previously.
During the overlap periods (A-B or C-D) it is immaterial which of the two valves 15 or 17 is closed, since pistons 6 and are rising at the same velocity through bores of the same diameter, as long as one or the other, or both, is closed. The overlap period thus contributes a great freedom and certainty-of valve action. This certainty is also important when automatically actuated valves are substituted for the check valves, as will be illustrated later. All that is required, in the period from C to D, is that valve IS-should close at some point before the opening of valve 17; both valves may be closed at the same time before valve 17 opens, as long as valve 17 is open at or before the time the point D is reached. This sequence of valve operation has great latitude between the points C and D, which constitutes one of the valuable features of this invention.
The condition between E and F is similar to that between C and D, except that here it is valve 17 which must close at some time before valve opens. The same latitude of valve action obtains between the points A and B.
The construction shown in FIG. 1 constitutes'a particular, illustrative form of the invention wherein chambers 2, 3 and 4 comprise cylinders of identical bores in which pistons of identical diameters operate. Other means for modifying the volumes of the chambers and in other lineal or nonlineal relationships may be used equivalently, as long as the volumetric changes and relationships remain as described.
Piston 1 1 in chamber 4 has the function of equalizing the input rate into the pump. If chamber 4 were omitted and the input were direct into passage 14, the output of the pump would still be at a uniform rate, although the input would vary widely. The basic minimum purpose of the invention is therefore served by valves 15 and 17, chambers 2 and 3, and the motions of pistons 6, 7 and 10; although the input compensating effect of chamber 4 and the motion of piston 11 are conducive to smooth performance without cavitation at the input, and thus constitute an important adjunct to the invention as applied practically.
When check valves are employed at 15 and 17, as shown, and the device is used as a pump, it is clear that any motions applied to the pistons 6 and 7, and piston 10, will result in a rate of outflow through port 13 exactly corresponding to the maximum rate of volume reduction caused either in chamber 2 by piston 6 or in chamber 3 by the piston 10. It is therefore only necessary that pistons 6 and 10 produce similar volumetric displacements during periods equal to or exceeding the whole cycle of operation (usually one revolution of a cam, when such is used), to assure a continuous output; and since the output at any moment is only equal to the maximum output caused by the motion of either cam, periods in which the outputs overlap will continue at the same output rate and are advantageously utilized I for allowing full latitude in the shifting of valve positions.
Positively actuated valves may be used in place of the check valves 15 and 17 in all embodiments of the invention shown, as will be illustrated later.
A fluid engine arranged as a pumping mechanism and shown in FIGS. 3 and 4 is comprised generally of a driving unit and a pumping unit. The pumping unit is shown as contained in a case 101, bolted to case 114, which contains the driving unit. Cases 101 and 114 are separated by spacing blocks 112. A drive shaft 143 is shown as rotatably mounted at the top and bottom of case 114 by journals 113 and 116. The assembly is preferably used with the driving end of shaft 143 up, and its axis vertical. Within case 114, cams 144 and 145 are affixed to shaft 143, and rotate therewith. Beyond the peripheries of cams 144 and 145, case 114 is widened into a block portion 146 in which are slidably mounted follower rods 147 and 148. The inner end of rod 147 is in operative contact with the contoured periphery of cam 144, and. the inner end of rod 148 is similarly in contact with the cam 145.
Follower rod 147 is maintained in angular alignment by key 149 fixed thereto and sliding in a suitable keyway in the bushing 150, which is pressed into case 114 and forms the sliding support for follower rod 147. Opposite the key 149 a short'rack 153 is cut into the periphery of rod 147.
Intermediate follower rods 147 and 148, a parallel rod 154 is slidably mounted in bushings pressed into case 114. Bushing-155 contains an interior keyway in which key 156 slides, key 156 being fixed to rod 154, thereby maintaining the latter in fixed angular relationship within case 114. A short rack 157 is cut into rod 154 along the side opposite to key 155. The arrangement is such that rack 153 in rod 147 and rack 157 in rod 154 face each other. Between racks 147 and 153 the spur gear 158 is shown as mounted on stud 159 screwed into case 114; the teeth of gear 158 engage rack 153 and rack 157. The above construction gives to rod 154 an exactly opposite and complementary motion to that of rod 147.
Below follower rod 148, parallel rod 163 is slidably mounted in case 114 in a manner similar to the mounting of rod 154 relative to rod 147, and is given a motion exactly opposite and complementary to that of follower rod 148 by means similar to those already described, in general not shown but including the gear 164.
Case 1 14 may be filled with oil in operation, and may therefore be closed by a cover 165, partially shown.
Rods 147, 154, 148 and 163 project through suitable seals into the space between the driver unit and the pump unit, also between the two spacer blocks 1 12.
The pumping unit is shown partly in FIG. 3 and partly in FIG. 4. The case 101 may be fabricated or made from a single block, as shown. Open chamber 166 passes through the case from side to side, as do the two smaller chambers 167 and 168 beyond the valve mechanism shown in FIG. 4. Similar covers are fixed to the front and back of the case 1111, the back cover not shown, the front cover at 1711. The covers are attached to case 191 tightly around their edges, but are hollowed out inside, thus connecting chambers 166, 167 and 168 into a continuous water jacket around the working parts of the pump. Bosses at 171 and 172, in which are shown tapped holes, are supplied as inlets and outlets for water or other temperature-controlling fluids.
Slidable piston rods 106, 107, 110 and 111 pass through chamber 166, their ends entering the valve chamber later to be described and their other ends, after passing through suitable hydraulic seals, passing slidably through the wall of case 101 into the space between 101 and case 1 14 of the driving unit, and there abutting against the outer ends of rods 147, 154, 148 and 163 respectively, with whose axes their axes are aligned.
Springs urge the piston rods of the pumping unit against the rods of the driving unit; shown in FIG. 3 is a triple-nested springs 173 in compression between a suitable recess in 101 and stepped disk 174, which is retained axially on piston rod 106 by a snap ring 175; and as double-nested springs 176 similarly mounted between case 101 and rod 107. An arrangement of springs similar to that on rod 106 urges piston rod 110 against rod 148, and an arrangement similar to that on rod 107 is mounted at piston rod 111. Permanent contact is thus maintained-between the driving rods of the driving unit and the respective piston rods of the pumping unit, and all clearances are taken up in the gearset joining rods 147 and 154, and in that joining rods 148 and 163.
Springs 173 always exert a stronger force than springs 176 so that the net force holding rod 147 against cam 144 always preponderates, with the result that the motion of piston rod 106 in the pumping unit is wholly determined by the contour of cam 144 for every position of the latter, the simultaneous motion of piston rod 107 being equal and opposite to that of rod 106.
Similarly, piston rod 110 has a motion determined by the contour of cam 145, and rod 111 moves in a sense equal and opposite to rod 154.
It is clear that the particular gear-and-rack device shown for reversing the motion of piston rod 107 with respect to that of 106, and that of 111 with respect to 110, is purely illustrative. Many other devices may be employed, such as a center-pivoted rock shaft with ends bearing on rods 147 and 146 or on appropriate elements moving with rods 106 and 107; or simply two more cams with contours complementary to those of cams 144 and 145 and mounted on shaft 113, and against whose peripheries rods 15% and 163 are forced. Obviously, also, since piston rods 107 and 110 open into the common chamber 103, they may be replaced by a common piston rod which, having an appropriate area and actuated by such means as a cam on shaft 143, will give a volumetric effect equivalent to that of the pistons shown.
In FIG. 4 are shown the ends of rods 106, 107, 110 and 111 as they appear in their respective cylindrical openings into the vertical chambers in case 101 which carry the material to be pumped. These chambers are shown in sequence and coaxially; chamber 102 being separated from chamber 103 by upward opening valve member 117, and chamber 103 from chamber 104 by upward opening valve member 115. The cylinder containing piston rod 106 opens into chamber 102, that containing rod 107 and that containing rod 110 open into chamber 103, and that containing rod 111 opens into chamber 101.
The upper valve mechanism, that between chambers 102 and 103 and containing element 117, is assembled generally in a removable valve tube 180. In the bottom of tube streamlining outlet ring 181 lies against a shoulder of the tube. Streamlining inlet ring 182 lies below ring 181, and is held in position by swaging into a recess therein the bottom annular end of tube 180. Between rings 181 and 182 is held annular valve seat 183, against the upper side of the inner aperture of which valve element 117 is held, thus forming the actual closure of the valve. The bottom or outer end of ring 182 is smooth and pressed firmly against a mating shoulder 184 at the upper end of chamber 103, thus sealing the valve mechanism to that chamber. The opening in the top of case 101 containing valve tube 180 is. threaded internally and nut 185 is screwed downwardly, its bottom surface pressing against shoulder 186 formed on the periphery of tube 180, thus supplying the force for the sealing of ring 182 to shoulder 184. The central portion of tube 180 is a press fit in the case 101, and contains a lateral opening at 187 aligned with the horizontal cylindrical opening containing the piston 106.
A narrowed section of valve element 117 extends upwardly past lateral opening 187 and then is shown as widening out into the three wings 188, which fit lightly the inner surface of tube/180 and serve to assist in aligning the valve. Cap 189 terminates the upper end of tube 180. An annular portion of cap 189 is shown as penetrating into tube 180 nearly to the top of the wings 188, thus serving as a stop to the upward motion of valve 117. Valve 117 is yieldingly forced downward by spring 190, interposed between the wings 188 and the ends of three vertical rods 191 pressed into cap 189. The upper end of tube 180 is externally threaded to receive retaining cap 192, which serves to hold cap 189 in place and to act as required as output connector.
The bottom (inlet) valve mechanism, interposed hydraulically between chamber 104, into which the cylinder containing piston 111 opens, and chamber 103, is generally similar to the upper valve mechanism described, except for slight modifications in the form of valve element 115 and the parts corresponding to 181, 132, 183, 184 of the upper valve, in order to accommodate the different direction of fluid flow. The lower end of valve element 115 is shown as passing loosely through the guide 193, held in place by pins 1194 extending inwardly from the wall of tube 195, which corresponds to tube 180 of the upper valve.
An annular terminal cap 196 is fitted to the bottom of tube 195; through cap 196 passes the pin 197 across the central aperture, which constitutes the inlet opening of the pump. Tension spring 198 connects pin 197 to the lower end of valve element 115, thus yieldingly maintaining the latter in its seat. As in the case of the upper valve assembly, tube 105 is pressed tightly into case 101, opening 1% being formed in its side to align with the cylinder containing piston 11 1.
The operation of the device of FIG. 3 and P16. 4, when operating as a constant velocity pump, is now evident. The contour of cam 14 3 is so formed that, with a steady angular motion applied to shaft 143,-rod 147 and piston 106 are given displacements corresponding to those of slider 5 as illustrated in F16. 2. These same displacements are given to rod 148 and to piston 110,
but lagging (or leading) by 180 of cam motion, and thus corresponding to the displacements of slider 8 as shown in FIG. 2. Since all pistons in this case are assumed as of the same diameter, piston 106 causes a volumetric change in chamber 102 exactly corresponding to that produced by the piston 6 of slider in chamber 2; while piston 110 affects the volume of chamber 103 exactly as piston afiects that of chamber 3.
Piston 107 enters chamber 103 with a motion the exact opposite of that with which piston 106 enters chamber 102; that is, the effect is precisely the same as it would be if piston 107 were the lower end of a common connector of which piston 106 was the top end, the whole being directly interposed between chambers 102 and 103. It is thus evident that pistons 106 and 107, valve 117, and chambers 102 and 103 are functional duplicates of pistons 6 and 7, valve 17, and chambers 2 and 3 of FIG. 1.
ln precisely the same way, piston 110 and its complement 111 duplicate the action of pistons 10 and 11 of FIG. 2; valve 115 functionally duplicates valve 15; while chambers 103 and 104 perform precisely like 3 and 4.
It is thus clear that the pump illustrated in FIGS. 3 and 4 is designed functionally exactly as is the illustrative pump of FIGS. 1 and 2, and that its input-output performance will be similar.
Particular advantages of the pump of FIGS. 3 and 4 reside in the water jacketing for the maintenance of a desired temperature in the medium being pumped; the pistons without seals passing between the water in the jacket and the pumping chambers, thus facilitating the transfer of waste matter when the fluid being pumped has a tendency to pelletize or solidify; a sequence of pumping chambers containing no recesses in which sediment may deposit or cavities in which bubbles of air or gas may lodge; and a straight-line construction from the cams to the pistons in the chambers, whereby slack due to clearances is eliminated and mechanical deflections are reduced to a minimum.
FIGS. 5, 6, 7 and 8 illustrate a pump of different construction, which may also be used as a motor. It is comprised generally of a driving unit and a pumping unit when employed as a pump and will be so described, although use as a motor reverses these functions, the pumping unit becoming a hydraulic driving unit, and the driving unit becoming a conversion unit to mechanical energy. The pumping unit is contained in case 201 and the driving unit in a case 214. Cases 201 and 214 are shown as attached by bolts 220. Transversely through case 214 passes drive shaft 243, preferably in a generally horizontal position and rotatably mounted at the sides of case 214 in anti-friction bearings 221. Case 214 is shown as comprised of two halves joined together in a plane through the axes of shaft 243 and bearings 221, by the bolts 246. Cams 244 and 245 are fixed to shaft 243 as by the keys 242. Between cams 244 and 245 eccentric 250 is similarly fixed to shaft 243.
Shaft 247 passes through the case 214 parallel to, below and toward the pumping unit from shaft 243. Shaft 247 is shown as supported at its ends, and at its center by a center riser 248, cast with case 214. Riser 248 continues upwardly and is expanded into a hollow cylinder 298 which is located horizontally and radially from shaft 243. A rod 290 is slidably contained in cylinder 298, its inner end bearing against eccentric 250. At each side of riser 248, follower arms 251 and 252 are pivotedto shaft 247, by anti-friction bearings 253. At the upper end of follower arm 251 is rotatably mounted roller 254, which bears on cam 245, and at the upper end of arm 252 roller 255 is mounted, adapted to bear on cam 244. Between shaft 247 and roller 254, roller 256 is rotatably assembled to follower 251, and similarly roller 257 is mounted to follower arm 252. The vertical section is made in a plane through cam 245, so that the elements associated with arm 252 lie directly behind those associated with arm 251.
The pump case 201 is shown as containing three parallel horizontal bores lying in the general plane of the axis of shaft 243. The first of these lies in radial line with cam 245 and contains slider 208, which divides the bore into chambers 203 and 204. Slider 208 is integral and concentric with rod 260 which extends slidably through bushing 261 in case 201 into the driving unit where it bears against roller 256, and with rod 262 which extends oppositely through bushing 263 beyond the end of case 201. At the latter end of rod 262, it receives the spring plate 264, against which bears compression spring 265. The other end of spring 265 bears on the inside of spring case 266, which is attached by bolts 267 to pump case 201. Spring 265 thus yieldingly urges rod 261 slider 208 and rod 260 against roller 256, which in turn maintains roller 256 in contact with cam 245.
' Slider 208 constitutes a closure in the bore consisting of 203 and 204; its two faces perform different functions on the fluid in these bores, and are thus considered as two interconnected pistons 210 and 211 respectively.
A second bore in the opposite side of case 201 contains elements which are a duplicate of those in the first bore. The bore itself is divided into two chambers 202 and 203!) by slider 205; piston rod 270 extends through bushing 271 and abuts roller 257; piston rod 260 passes through bushing 272 and terminates at spring plate 273; spring 274 is interposed between plate 273 and a suitable recess in the inside of spring case 266; so that plate 273, rod 269, slider 205, rod 270 are yieldingly urged against roller 257, which thus maintains roller 255 in position against the periphery of cam 244.
As in the case of slider 208, the two faces of slider 205 are considered as two conjoined pistons; piston 206 operating on the fluid in chamber 202, and piston 207 on that in chamber 20311.
The third and central bore in pumpcase 201 contains the valve assembly comprised of valve tube 275 and valve slider 277. Tube 275 is held in place in case 201 by nut 276. The valve assembly is an adaptation of a conventional hydraulic slide valve. Tube 275 is bored to an inside diameter in which valve slider 277 may move axially. Tube 275 has an enlarged annular central chamber 2030; access to chamber 203:: is gained preferably by a milled slot in the wall of tube 275. Similar slots are milled into tube 275 for access to the chambers at each side of chamber 203e, denominated in the drawing 2021) and 204k.
Slider 277 comprises three coaxial closures sliding in the bore of tube 275 and joined by the rods of reduced diameter 278 and 279. Closure 281 closes the chamber 203:: when in central position, since its ends somewhat overlap those of chamber 203s. Chamber 20412 is bounded at its inner end by closure 281 and at its outer end by closure 280, which is separated from closure 281 by rod 279 lying within chamber 294b. Beyond closure 280, slider 277 extends into the driving unit where it abuts rod 299. Chamber 202b lies at the opposite side of closure 281, and is bounded beyond by closure 282; the closures being joined by rod 278 lying within the chamber. Slider 277 extends beyond case 201 into spring case 266, where it is terminated by stepped spring disk 283. Compression spring 284 lies between disk 283 and an appropriate locating cavity in the inside of spring case 266, thus maintaining the slider and rod 299 against the eccentric 250.
When closure 281 lies toward shaft 243, chamber 202b is opened to chamber 203e, by the clearance between closure 281 and the end of chamber 203C; thus the end of closure 281 constitutes in effect the active part of a valve 217, which may connect or separate these chambers. Similarly, the opposite end of closure 281 constitutes functionally another valve, numbered 215, which operates between chambers 2030 and 204k. Valves 215 and 217 thus constitute a pair of valves operated conjointly.
The top surface of the portion of case 201 which contains the pistons and valves described may be ground flat to receive the cover plate 285, firmly attached to 201 by bolts 286. Cover plate 285 closes the top side of connecting channels which are milled in the top surface of case 201 above the valve and pistons.
FIG. 7 illustrates connecting holes and channels, with cover plate 285 removed. The holes penetrate as follows: 287 into chamber 202, 288 into chamber 202b, 289 into chamber 204, 290 intochamber 204b, 2291 into chamber 203b, 292 into chamber 203e, 293 into chamber 203. Channel 202a communicates drill holes 287 and 288; channel 204e, drills holes 289 and 290; channel 203d, holes 2911 and 222; channel 203e, holes 292 and 293. Tapped hole 294 in cover plate 285 gives access to channel 2020; and tapped hole 295 to channel 204a The arrangement described may be summarized as follows. Access hole 294, channel 202e, chamber 2021), and chamber 202 comprise functionally a single chamber which may be denominated generalized chamber 202, lying at one side of slider 205, against piston 206. Chambers 203, 203b, 2030 and passages 203d and 2032 functionally comprise a single generalized chamber 203 lying at the other side of slider 205 against piston 207 and at a first side of slider against piston 210. Chambers 204 and 204b, and passage 204a again may be considered a generalized chamber 204 lying at the second side of slider 208 against piston 211 and adapted to outside hydraulic connection by tapped hole 295.
When slider 277 lies far enough toward the driving unit so that valve 2l7 opens by clearing the edge of chamber 203e, generalized chamber 202 will be connected to generalized chamber 203. When slider 277 lies far enough away from the driving unit so that valve 215 opens by clearing the other edge of chamber 203e,
generalized chamber 203 will be connected to generalized chamber 204. When slider 277 lies centrally, the above connections will not be made.
The operation of the device is made more clear in conjunction with FIG. 8, which is a schematic drawing showing the parts in exploded view. in FIG. 8 the generalized chambers 202, 203 and 204 are indicated.
Cam 244 isso contoured that with a steady angular rotation in a counterclockwise sense (as drawn in FIGS. 5 and 8), slider 205 will follow the motion illustrated by the graph for slider 5, in FIG. 2, through the intermediacy of roller 255, follower arm 252, and roller 257. Similarly, the shape of cam 245 is such that the same motion will be given to slider 208, but lagging that of slider 205 by and thus represented by the curve for slider 8 in FIG. 2.
Eccentric 250 is so mounted relative to cams 244 and 245 that slider 277 is moved to its maximum position away from the driving unit when slider 205 is at the center of its uniform rise away from the driving unit. Valve 215 is thus clear of the edge of chamber 203e, which is thus connected to generalized chamber 204 while 203 is closed to 202. At a position 180 later it is clear that the closure 281 will be at the opposite end of its travel; generalized chamber 202 being then connected to generalized chamber 203 by the passage permitted by the position of valve 215 clear of the end of chamber 203e, there being new no connection between generalized chambers 203 and 204. These two positions clearly correspond to the conditions which are illustrated by points midway between B and C, and midway between D and E of the graph of FIG. 2.
At a point in the rotation of cam shaft 243 some halfway between the points described, the sliders and associated pistons will lie in the overlap relationship shown in FIG. 2, and valve slider 281 will completely close both ends of chamber 2030, while passing from one side to the other of center. Although serving the same purpose as the check valves in the preceding embodiments, the detailed action of valve slider 281 is slightly different. in FIG. 2 bottom valve 15 is shown as opening just after B, as it must since it may only be opened by actual fluid flow, which begins at this point. The same is true of valve 17 opening at the point D. The positively opened valve 231, however, must open before the flow begins. The margin by which the length of slider 28R exceeds the length of chamber 203c is selected so that the whole sequence including the closing at one end, the period during which both ends are closed, and then the opening at the other end, takes place well within the limits of the overlap period.
it is clear that the construction described is functionally a duplicate of that illustrated schematically in FIG. ll. Chamber 2 is now represented by the generalized chamber 202; chamber 3 by the generalized chamber 203; chamber 4 by the generalized chamber 204; with slider 205 replacing slider 5 lying between chambers 2 and 3, and slider 208 replacing slider 3 lying between chambers 3 and 4, each slider with associated pistons being driven by its respective cam 244 or 205. Valve 215 is also the equivalent of valve 15, and valve 2E7 of valve 17. The conditions stated above that at all times either one valve or the other, or both, must be closed, and that valves 17 (and 15) must open within the overlap period, are also met.
Hence, when operating as a pump, the mechanism of FIGS. 5, 6 and 7 will function precisely as described in the case of the illustrative device of FIG. 1. lnlet will be through tapped hole 295 opening into generalized chamber 4, and outlet by tapped hole 294 which is connected to generalized chamber 2, as in the case of FIG. 1. Operation of the engine as a motor is as follows.
FIG. 8 shows the motor at approximately the midpoint of the power stroke delivered to cam 245, which is shown as moving with diminishing cam radius. Valve 217 is at its maximum opening and valve 215 is closed, since eccentric 250 is at its maximum retracted position. Fluid under pressure enters through port 294. Since valve 217 is open pistons 206 and 207 may move without restriction and without affecting the flow of the fluid entering through port 294; the fluid then impinges on piston 210, thus communicating driving energy to rocker 251, roller 254, and so to the cam 245. During this phase slider 205 with its pistons is retracted by cam 244 without opposition, since the fluid displaced simply circulates freely.
As the above motions continue, cam 244 reverses the direction of motion of slider 205 and the overlap period is entered, during which sliders 205 and 208 both move toward the cams. Eccentric 250 now moves to a midposition, closing valves 215 and 217. Fluid pressure now forces piston 202 toward the now retreating cam 244 and delivers energy thereto. Energy is still delivered by piston 210 to cam 245. The exact amount of work done by these two pistons is indeterminate, depending on many factors such as relative rates of leakage past pistons 206 and 210, but is of little consequence since the net force is always the same, that lost from one piston being transferred to the other.
Before the end of the overlap period, eccentric 250 has forced valve slider 277 outwardly, maintaining valve 217 closed and opening valve 215. Piston 206 takes the full load, while piston 210 is free to be returned by cam 245 without opposition, since valve 215 opens to pass the displaced fluid to the outlet.
The above motions continue, eccentric 250 opening valve 217 fully and then returning it toward its closed position as cams 244 and 245 approach the next overlap period, during which the direction of motion of piston 210 will have been reversed so that once again both pistons will be doing work on the cams in the same direction. The valve 215 will now close and 217 open, and the first phase described will be repeated.
The inclusion in the machine of piston 211 in chamber 204 produces a steady output flow through hole 295.
It is thus seen that the mechanisms disclosed will give a truly continuous and pulse-free output in response to an input of continuous velocity, when operating either as a pump or as a motor, within those limitations set by fluid compressibility, mechanical deflections, leakages and structural precision common to all mechanisms of this class.
The following terms are used herein in the particular meanings defined below.
A piston is a mechanical element some part of which is movable and which acts usefully as a single interface for the transmission of force or motion between a mechanism and a fluid; such as, for example, one face only of a cylinder sliding in a chamber, or one side of a diaphragm, etc. A piston does not necessarily imply proportionality between mechanical and fluid motions. The invariable corrolary of piston motion is volumetric displacement of fluid, which is considered herein as occurring in a positive sense when the volume of the fluid chamber is reduced and in a negative sense when the volume is increased. 7
A piston doublet (or simply a doublet) is'a mechanical element or combination of elements terminating in two pistons whose simultaneous volumetric displacements are arithmetically equal but algebraically opposite within an operating range. in H6. 4 pistons 106 and 107 constitute a doublet which includes the pistons and the mechanism which causes their respective motions to be as described. In FIG. 1 slider 5 is a singleelement doublet, its two pistons being 6 and 7. A doublet comprised of several elements may be considered as an equivalent single-element doublet and its motion so described.
Any device for the transfer of energy between a moving mechanical element and a moving stream of fluid has at least two ports for the passage of fluid. At a constant mass rate of flow energy transfer is accompanied by difference of pressure between the ports. The principal port carrying the major power stream at the higher pressure and thus with the higher energy content is called herein the high-energy port and the chamber into which it opens the high-energy chamber; the other port is called the low-energy port, and the chamber into which it opens the low-energy chamber. Energy transfer from the mechanical element to the fluid (a pump) obviously accompanies outward flow through the high-energy port; energy transfer from the fluid to the element (a motor) corresponds to an inward flow through the high-energy port. In normal embodiments of the present invention, the high-energy and the lowenergy ports remain the same, independently of the direction of the transfer of energy.
The design flow ratio is the ratio of the rate of volumetric flow through the engine to the rate of rotation of the shaft, in consistent units, when the engine is operatmg.
The net successive volume changes in chamber 3 may be understood by reference to PEG. 2. From A to B pistons 10 and 7 are both rising at the same rate, one decreasing and the other increasing the volume, which thus undergoes no change. From B to C the volume of chamber 3 increases, due firstly to the rise of piston 7 at a rate determined by the design flow ratio and the rate of shaft rotation; secondarily it increases at successive rates of volume change due to the withdrawal of piston 10, the latter changes being identical to the rates of volume decrease in chamber 4 due to piston 11, when present. Hence, from B to C the volume of chamber 3 increases at successive rates relative to the angular motion of the shaft which are equal to the design flow ratio plus the simultaneous rates of volume decrease of the low-energy chamber (or of the volume increase due to the withdrawal of piston 30) relative to the rate of angular motion of the shaft. it should be noted that terminal portions of the displacements due to pistons 10 and 11 occur in opposite senses from the main or central portion; the rates of such portions are of course added negatively, which smooths the rates of volume change to the zero rate at the points B and C. From C to D pistons 7 and 10 are at maximum separation, rather than at minimum as from A to B, but again it is obvious that chamber 3 undergoes no change of volume. From D to E the volume of chamber 3 decreases, due firstly to the rise of piston 10 at a rate determined by the design flow ratio and the rate of shaft rotation; secondarily it decreases at successive rates of volume change due to the motion into the chamber of piston '7, the latter changes being identical to the concurrent rates of volume increase in chamber 2. Hence from D to E the volume of chamber 3 decreases at successive rates relative to the rate of angular motion of the shaft which are equal to the design flow ratio plus the simultaneous rates of volume increase of chamber 2 (the high-energy chamber) relative to the rate of angular motion of the shaft. Negative portions of the latter rates of increase are again added negatively, resulting in smooth changes to the zero rate of volume change from E TO F, identical to the period from A to B and thus beginning the repetition of the cycle.
It is apparent that further units comprised of doublets such as slider 5, valves such as valve 17 and means connecting the doublets to the shaft may be added in hydraulic series with those shown illustratively, the loads being then shared in a rotative series by the different units, with successive overlap periods intervening, each active period then being shorter and the return longer than those of the device as illustrated; such structures lying within the scope of my invention.
Having thus disclosed my invention and described preferred embodiments thereof, 1 claim as new and desire to secure by Letters Patent:
1. A fluid engine for the transfer of energy between a rotating shaft and a fluid in motion, comprising in combination a chambered casing, a fluid passage comprised of a high-energy chamber, a first valve chamber, a middle chamber, a second valve chamber, and a low-energy chamber, the chambers arranged in hydraulic series in the order given, high-energy and low-energy ports opening respectively into the high-energy and the lowenergy chambers, a fluid flow between the ports, a first and a second valve in the first and second valve chamber respectively, a rotatable shaft, movable piston means in piston chambers whose positions therein are adapted to determine the volumes of the high-energy, the middle and the low-energy chambers, and connecting means between the shaft and the piston means adapted to correlate specific angular positions of the shaft with specific positions of the piston means and thus with specific volumes of the high-energy, the middle and the low-energy chambers; the piston and connecting means being so constructed and arranged that a continuous rotation of the shaft at a given angular velocity is correlated (a) with a repeating cycle of alternating periods of decreasing and increasing volumes of the high-energy chamber, each period of decreasing volume including acceleration and deceleration periods, and a period, hereinafter called the active period, during which the rate of decrease of volume relative to the rate of angular rotation of the shaft is equal to the design flow ratio, (b) with a repeating cycle of alternating periods of increasing and decreasing volumes of the middle chamber, the portion of the period of decreasing volume of the middle chamber occurs generally between successive active periods of the high-energy chamber and occurs at a rate equal to the design flow ratio plus the simultaneous rates of volume increase of the high-energy chamber relative to the rate of angular motion of the shaft, and (c) with a repeating cycle of generally alternating periods of decreasing and increasing volume of the low-energy chamber, each period of increasing volume including acceleration and deceleration periods and a period, hereinafter called the low active period, during which the rate of increase of volume relative to the rate of rotation of the shaft is equal to the design flow ratio, the low active period occurring generally in alternation with the active period of the volume change cycle of the high-energy chamber; the portion of the volume changes of each period of increasing volume of the middle chamber which occurs between successive low active periods of the volume changes of the low-energy chamber occuring at successive rates relative to the rate of angular motion of the shaft which are equal to the design flow ratio plus the simultaneous rates of volume decrease of the low-energy chamber relative to the rate of angular motion of the shaft. 1
2. A fluid engine for the transfer of energy between a rotating shaft and a fluid in motion, comprising in combination a chambered casing, a fluid passage comprised of a high-energy chamber, a first valve chamber, a middle chamber, a second valve chamber and a low-energy chamber, the chambers arranged in hydraulic series in the order given, high-energy and low-energy ports opening respectively into the high-energy and the lowenergy chambers, a fluid flow between the ports, a first and a second valve in the first and second valve chamber respectively, a rotatable shaft, movable piston means in piston chambers whose positions therein are adapted to determine the volumes of the high-energy and the middle chambers, and connecting means between the shaft and the piston means adapted to correlate specific angular positions of the shaft with specific positions of the piston means and thus with specific volumes of the high-energy and the middle chambers; the piston and connecting means being so constructed and arranged that a continuous rotation of the shaft at a given angular velocity is correlated with a repeating cycle of alternating periods of decreasing and increasing volumes of the high-energy chamber, each period of decreasing volume including acceleration and deceleration periods and a period, hereinafter called the active period, during which the rate of decrease of volume relative to the rate of angular motion of the shaft is equal to the design flow ratio, and with a simultaneous repeating cycle of alternating periods of increasing and decreasing volumes of the middle chamber separated by periods during which the volume is constant, hereinafter called overlap periods, which occur simultaneously with delimiting portions of the active periods of the cycles of the high-energy chamber, the volume changes of each period of decreasing volume of the middle chamber occurring at successive rates relative to the rate of angular motion of the shaft which are equal to the design flow ratio plus the simultaneous rates of volume increase of the highenergy chamber relative to the rate of angular motion of the shaft.
3. A fluid engine as described in claim 2, together with additional chambered piston means whose positions are adapted to determine the volumes of the lowenergy chamber, and additional connecting means between the shaft and the additional piston means adapted to correlate specific angular positions of the shaft with specific positions of the additional piston means and thus with specific volumes of the low-energy chamber; the additional piston and connecting means being so constructed and arranged that a continuous rotation of the shaft in the direction and at the velocity correlated with the cycles of volume changes described in claim 12 is also correlated with a repeating cycle of generally alternating periods of decreasing and increasing volume of the low-energy chamber, each period of increasing volume including acceleration and deceleration periods and a period, hereinafter called the low-active period during which the rate of increase of volume relative to the rate of rotation of the shaft is equal to the design flow ratio; the low active period occurring generally in alternation with the active period of the volume change cycle of the high-energy chamber, and delimiting portions of the low active period coinciding with overlap periods of the volume change cycle of the middle chamber; the volume changes of each period of increasing volume of the middle chamber taking place at successive rates relative to the rate of angular motion of the shaft which are equal to the design flow ratio plus the simultaneous rates of volume decrease of the lowenergy chamber relative to the rate of angular motion of the shaft.
4. A fluid engine for the transfer of energy between a rotating shaft and a moving fluid, comprising in combination a rotatable shaft, a chambered casing, a highenergy port and a low-energy port, fluid flow between the ports, a piston doublet and a piston in their respective chambers, hydraulic passages between the highenergy port and one of the pistons (hereinafter called the primary piston) of the doublet, between the other piston of the doublet and the piston, and between the piston and the low-energy port; a fluid passage communicating the two pistons of the piston doublet, a valve in that passage, a valve in the hydraulic passage between the piston and the low-energy port, cams mounted on the shaft, contoured surfaces on the cams, cam followers in contact with the contoured surfaces, connections between the followers and the piston and the piston doublet; the followers, the connections and the contoured surfaces of the cams being so constructed and arranged that the volumetric displacement of the piston and that of the primary piston of the piston doublet occur in generally similar cycles, each cycle including one period in which the displacement is in a positive sense and one period in which it is in a negative sense; the two cycles occurring in a generally alternating arrangement whereby the volumetric displacements of the piston and of the primary piston of the doublet occur in generally different senses, except that terminal portions of the period in which the displacement is in a positive sense in one cycle overlap terminal portions of the same period of the other cycle in overlap periods during which the rate of volumetric displacement of the piston and of the primary piston of the doublet remains cons nd e al.
5. rfid en i ne for the transfer of energy between a rotating shaft and a moving fluid, comprising in combination a rotatable shaft, a chambered casing, a highenergy port and a low-energy port, fluid flow between the ports, a plurality of piston doublets connected in hydraulic series between the ports, fluid bypass passages interconnecting the pistons of each doublet, a valve in each bypass passage, cams on the shaft, contoured surfaces on the cams, cam followers in contact with the contoured surfaces and connections between the cam followers and the doublets; the contoured surfaces of the cams, the followers and connections being so constructed and arranged that a continuous rotation of the shaft at a fixed angular velocity is correlated with generally reciprocating motions of the doublets, the volumetric displacements of the doublets occurring in generally similar cycles, each cycle including periods of positive and of negative displacements relative to the hydraulic direction from the low to the high-energy ports; the cycles occurring in a sequential arrangement, terminal portions of the periods in which the displacements occur in a positive sense in adjacent cycles overlapping each other in overlap periods during which the rates of volumetric displacement of the respective doublets remain constant and equal.
6. The fluid engine described in claim 5, one of the valves being a check valve allowing fluid flow through its respective bypass passage in the direction from the low-energy port to the high-energy port, but preventing it in the opposite direction.
7. A fluid engine as described in claim 5, together with connecting means between the shaft and a valve in its respective bypass passage between the pistons of a doublet so constructed and arranged that the valve is maintained generally closed during that portion of the period of the positive displacement of the doublet which lies between the overlap periods and generally open during the balance of the cycle, the changes between open and closed conditions of the valve occurring generally in the overlap periods.
8. A fluid engine as described in claim 5, the contoured surfaces of the cams, the followers and connections being so constructed and arranged that the rate of volumetric displacement during the period of the cycle in which the displacements occur in a positive sense is equal to the design flow ratio in all portions of the period which lie between and include the terminal overlap periods.