US3767325A

US3767325A - Free piston pump

Info

Publication number: US3767325A
Application number: US00264483A
Authority: US
Inventors: M Schuman
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-06-20
Filing date: 1972-06-20
Publication date: 1973-10-23
Anticipated expiration: 1990-10-23

Abstract

A thermally driven pump for pumping fluids or driving a load includes a free piston oscillating in a cylinder. A coasting region for the piston is provided by means of a bypass having displaced ports in the cylinder walls. The bypass includes a thermal regenerator. A fluid to be pumped is introduced into the cylinder through a check valve, biased to be open in response to the pressure in the cylinder being less than the pressure of the source of fluid. Closing of the check valve is delayed until the piston is wholly within the coasting region on its rebound stroke toward the coasting region. Efficiency of the device can be improved when driving an oscillating load, such as a free piston linear alternator, by providing a thermal lag cooler between the pump outlet and the oscillating load. The cooling means and oscillating load can be combined as a bellows. The temperature differential required for operating the pump can be provided by hot gas and cold gas being pumped.

Description

Schuman Oct. 23, 1973 FREE PISTON PUMP [76] Inventor: Mark Schuman, 101 G St., S.W., Wash., DC.

[22] Filed: June 20,1972

Appl. No.: 264,483

Related U.S. Application Data Continuation-in-part of Ser. No. 205,651, Dec. 7,

Primary ExaminerWilliam L. Freeh Assistant Examiner-G. P. LaPointe Attorney-Allan M. Lowe et al.

[5 7] ABSTRACT A thermally driven pump for pumping fluids or driving a load includes a free piston oscillating in a cylinder. A coasting region for the piston is provided by means 1971. of a bypass having displaced ports in the cylinder I walls. The bypass includes a thermal regenerator. A [52] U.S. Cl 417/207, 60/24, 4l7/375 fluid to be pumped is introduced into the cylinder [5i] Int. Cl. F04b 19/24, F03g 7/06 through a check valve, biased to be open in response [58] Field of Search 60/24; 417/207, 375 to the pressure in the cylinder being less than the pressure of the source of fluid. Closing of the check valve [56] References Cited is delayed until the piston is wholly within the coasting UNITED STATES PATENTS region on its rebound stroke toward the coasting re- 3 563 028 2,1971 common at 31 60/24 gion. Efficiency of the device can be improved when 3552120 H1971 Beale 60,24 driving an oscillating load, such as a free piston linear 3:525:25 8/1970 Conrad 60/24 alternator, by Providing a thermal g Cooler between 3,484,616 12/1969 Baomgardner et al. 60/24 the P p Outlet and the Oscillating load-The cooling 3,559,398 2/1971 Meijer et al. 60/24 means and oscillating load can be combined as a bel- 3,583,155 6/1971 Schuman 60/24 lows. The temperature differential required for operat- 3,604,8 2l 9/1971 Martini 60/24 ing the pump can be provided by hot gas and cold gas 3.597.766 8/1971 BUCk..... 60/24 being pumped 3,608,311 9/1971 Roesel 60/24 I 24 Claims, 3 Drawing Figures STORAGE TANK 451 52 1:

THERMAL LAG COOLER LOAD "L 'lOb 'l'il:

l4ll I 1 1 s 1 A BB 655 |5b b 6gb J1 Q PAIENIEDoma am 3.76? 325 rTORAeE 1 ANK 61a Gig l Hal Y VT? 496 v TIQ 'IOa

mew

LAG COOLER LOAD 7 80 g ll 8t LOAD H f 18 COOLER. '1

FREE PISTON PUMP RELATIONSHIP TO COPENDING APPLICATION The present application is an improvement and continuation-in-part of my copending application entitled Free Piston Apparatus, filed Dec. 7, 1971, Ser. No. 205,651.

BACKGROUND OF INVENTION In the copending application, there is disclosed a thermally powered compressible fluid pump wherein a free piston oscillates in a cylinder between ends of the cylinder. A coasting region in the cylinder is provided by a cylinder bypass having a pair of displaced ports in the cylinder between the cylinder ends. The bypass means is provided for obtaining a temperature difference for compressible fluid at opposite ends of the cylinder. The piston shunts the fluid in alternate directions through the bypass and regenerator between the heating and cooling means, or sources of hot and cold fluid, at opposite ends of the cylinder to produce alternating pressure for pumping fluid or driving a load. Compressible fluid to be pumped may be introduced into the cylinder through a check valve biased to be open in response to pressure within the cylinder being approximately equal to or less than the pressure of a source of the compressible fluid. Thereby, the compressible fluid at the inlet generally is admitted into the cylinder while the piston is moving in a direction tending to cool the gas and decrease pressure within the cylinder. A port is provided to exhaust fluid through an outlet check valve in response to the cylinder pressure being higher than the pressure at an outlet of the check valve.

1 While the piston is within the coasting region the pressures at opposite faces of the piston are substantially equal at any given time, because of the bypass around the piston. Thereby, pressure variations during coasting do not tend to stall the piston. However, during rebound of the piston at either end of the cylinder, the bypass is blocked at one end by the piston wall, so that pressure is generally not equal at opposite faces of the piston and may tend to stall the piston if pumping work is attempted during a rebound portion of the cycle. It is thus desirable in general to delay the closing of any inlet check valve which opens during piston rebound, so that compression by the piston of the gas drawn into the cylinder through the inlet does not begin until the piston has reached the, coasting region. If fluid is being pumped during rebound, the piston, at this time, functions to a certain extent as a working piston rather than solely as areversing piston. In piston pumps of the type disclosed in my copending application, it is desirable for the piston, while it is in the rebound region, to function exclusively as a reversing piston, and not as a working piston because of the possibility of the piston being stalled or decreasedin frequency or amplitude of oscillation by the gas it is compressing. Since the piston is preferably driven while in the rebound region by a thermal lag heating chamber which appears to be a relatively low efficiency device, energy cannot be efficiently transferred to a gas being compressed, and the pumping efficiency is low during rebound. However, while the piston is moving through the coastin'g region, it functions in a very efficient manner, as a Stirling type displacer piston to convert thermal energy tolpneumatic energy. Thereby, it is desirable to pump the compressible fluid while the piston is moving through the coasting region but it is generally not desirable to admit and then compress fluid, while the piston is in the rebound region.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, the aforementioned pump of my copending application is modified so that the volume above an upper face of the piston is vented as the piston moves toward an entry location in the cylinder for the fluid. Venting occurs until all of the piston is within the coasting region so that substantially no fluid drawn into the cylinder through the inlet is compressed by the upper face of the piston until the piston enters the coasting region. Thereby, stalling of the piston due to back pressure building up against the piston upper face is precluded. In addition, efficiency of the device is maintained at a relatively high level since the fluid is compressed only while the piston functions as a displacer piston as it moves through the coasting region and not while the piston functions as a reversing piston when it is in the rebound region.

In a preferred embodiment, the coasting region is vented through the simple mechanism of delaying the closing time of a check valve provided in a conduit connecting the fluid entry location into the cylinder with the source of fluid. The delay time is such that the check valve, when is normally open in response to the pressure from the source exceeding the pressure in the cylinder, does not close until the piston is wholly within the coasting region during its movememt back toward the entry location.

A further feature of the invention resides in providing a pair of piston cylinder pumps operated in synchronism so that the two pistons approach a central thermal lag heating chamber atthe same time. The thermal lag heating chamber can function as the sole heating means.

According to an additional feature, efficiency of a regenerative free piston device connected to an oscillating load is enhanced by providing a thermal lag cooler in circuit with the load. If the load is a bellows, the bellows also functions as'the thermal lag cooler. For other types of oscillating loads (e.g., a pressure driven alternator) a twin path, check valves, and a cooling chamber are used between the pump and the load whereby gas flowing from the pump to the load is not cooled but gas returning to the pump from the load is cooled. Thereby, pressure of fluid is reduced by cooling only after it has done its work on the load and is flowing back into the pump for later heating. The thermal lag cooler does this to a lesser extent.

It is, accordingly, an object of the present invention to provide a new and improved pump utilizing compressible fluid.

Another object of the present invention is to provide a new and improved compressible fluid pump employing at least one free piston which has a very low probability of being stalled.

A further object of the present invention is to provide.

a new and improved thermally driven free piston regenerative cycle pump having a relatively An efficiency. An additional object of the invention is to provide a thermally driven free piston pump wherein a cylinder containing the piston is vented in a facile manner as the piston is rebounding toward the coasting region within a cylinder bypass region.

Another object of the invention is to provide a thermally driven piston apparatus wherein an oscillating load also functions as a cooler to enhance efficiency.

An additional object is to provide an efficient thermally driven pump for driving an oscillatory load wherein means are provided for cooling fluid flowing from the load to the pump.

Yet a further object of the present invention is to provide a thermally driven free piston pump wherein fluid drawn into the pump is compressed only while the piston is acting as a displacer piston.

Still another object of the present invention is to provide a thermally powered free piston pump having means for delaying the closing of an inlet check valve to substantially avoid compression work by the piston during rebound.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of several specific embodiments thereof, especially when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of a preferred embodiment of the present invention;

FIG. 2 is a schematic diagram of a segment of the FIG. 1 embodiment in accordance with a modification wherein check valves, twin conduits, and a cooler are employed to cool fluid returning to the pump from an oscillatory load; and

FIG. 3 is a schematic diagram of a segment of the FIG. 1 embodiment, in accordance with a further modification wherein an oscillating bellows comprises the oscillating load and cooling means.

In the drawing, a free piston pump is illustrated as containing a pair of cylinders and a pair of synchronized free pistons. It is to be understood, however, that the principles of the invention are applicable to a pump having any number of piston cylinder combinations, i.e., the pump may include only one piston cylinder combination or it may include more than two piston cylinder combinations interconnected in the same manner as the pair of piston cylinder combinations illustrated.

DETAILED DESCRIPTION OF THE DRAWING Reference is now made to FIG. 1 of the drawing wherein there is illustrated a gas pump including a pair of sealed cylinders 11a and 11b through which free pistons 12a and 12b are respectively oscillated in synchro nism with each other so that both pistons approach and recede from adjacent faces of cylinders 11a and 11b simultaneously. (In the description, corresponding parts associated with the upper and lower cylinders 11a and 11b are provided with the suffix letters a and b, respectively. If no mention is made in the description of the drawing of the suffix letters a and b and the part is included in or associated with the cylinders 11a and 11b, it is to be understood that the elements of both cylinders are being considered.) The opposite faces 13 and 14 of piston 12 form end walls for first and second chambers 15 and 16 of cylinder 11.

The walls of cylinder 11 and piston 12 are so close to each other that the piston provides a reasonably good seal between the opposite faces thereof. Therefore, while piston 12 is near the end walls 17 and 18 of chambers 15 and 16, respectively, there is a substantial difference between gas pressures at opposite faces of the piston. In a central region of cylinder 11, the pressure difference between faces 13 and 14 of piston 12 is virtually zero due to a bypass formed by conduits 21 and 22, between which is connected regenerator 23. Lines or conduits 21 and 22 are connected to the side wall of cylinder 11 at disparate points along the cylinder by ports 24 and 25. The length of piston 12 is determined in such a manner that both conduits 21 and 22 communicate with chambers 15 and 16 while piston 12 is coasting in the central region between the ports. The positions of ports 24 and 25 and the length of piston 12 are such that the piston covers and blocks conduit 21 while the volume in chamber 15 is a minimum, and for a certain time interval on either side of the minimum volume; and the piston blocks conduit 22 while the volume in chamber 16 is a minimum and for a certain time interval on either side of the minimum volume. Chambers 15, 16 and thermal lag heating chamber 31 form gaseous springs at each end of cylinder 11 so that compressible fluid in chambers 15 and 16 when the chamber volumes are minimized result in rebound of piston 12 from end faces 17 and 18 of cylinder 11.

Synchronized oscillation of pistons 12a and 12b is sustained by a thermal device comprising thermal lag heating chamber 31 having a centrally located heating core 32. Surrounding heating core 32 are elongated fluid passageways 33 within a housing 34. Heated passageways 33 are in fluid flow relationship with the end faces 18a and 18b of chambers 16a and 16b by virtue of conduits 35 being connected to a common T element 36 having one leg connected to conduit 37 which provides a fluid flow path from the interior of thermal lag heating chamber 31 to conduits 35. As described in my copending application, Oscillating Piston Apparatus, Ser. No. 227,514, filed Feb. 18, 1972, the thermal lag heating chamber is responsive to a periodic surge of compressible fluid resulting from piston face 14 coming into proximity with cylinder end wall 18. The compressible fluid is forced through conduits 3S and 37 to the interior of thermal lag heating chamber 31. The fluid resides in the thermal lag heating chamber 31, is heated therein, and, while still being heated, expands out of the thermal lag heating chamber as piston 12 is rebounding near end wall 18.

Sources of a cold and a hot fluid, e.g., air, to be pumped by the apparatus of the present invention feed chambers 15 and 16 through conduits 41 and 42 and valves 43 and 44. The cold and hot fluids passing through valves 43 and 44 are introduced into chambers 15 and 16, respectively, via check valves 45 and 46, conduits 47 and 48, and ports 49 and 50. Ports 49 and 50 are respectively aligned with ports 24 and 25 leading to conduits 21 and 22 of the bypass. Thereby, the entire coasting portion of the cycle is available for intake of fluid. Further, there is less leakage around the piston during rebound near end faces 17 and 18 than if ports 49 and 50 were closer to these end faces. Valves 45 and 46 are polarized so that they are normally open in response to the pressure of the gas emerging from valves 43 and 44 exceeding the pressure within chambers 15 and 16; conversely, valves 45 and 46 are normally closed in response to the pressure within chambers 15 and 16 exceeding the pressure of gas at the inlets of check valves 45 and 46.

Valve 45 is provided with delay means to prevent closure thereof as soon as the pressure in chamber exceeds the pressure of the gas at the inlet of valve 45.

The closure of valve 45 is delayed for a time equal to the'travel time of piston 12 from adjacent the end wall 18 of cylinder 11 until the bypass has been completely established as the piston is moving toward inlet port 49. By delaying closure of valve 45 until the bypass region has been established, stalling of piston 12 is virtually precluded because face 13 of piston 12 sees a substantially constant pressure throughout piston rebound near cylinder end wall 18. Since chamber 15 is vented in response to valve 45 being open no substantial net pumping of gas occurs, and there is no substantial positive net intake of gas into chamber 15, while the rebound chamber below face 14 is established. Gas is pumped when piston 12 reaches the coasting region by the displacement of gas from chamber 15 to chamber 16 by piston 12. Piston 12 would not function efficiently as a pump while the bypass is closed, when chambers 15 or 16 are rebound chambers, because of the relatively inefficient nature of thermal lag heating chamber 31.

Two separate types of delay means are illustrated for check valves 45a and 45b to provide an increased number of examples of possible delay means which may be utilized. It is to be understood, however, that in an actual device, the two delay means would be preferably the same. The delay means of check valve 45a comprises a spring 52a having opposite ends connected to wafer 53a and stem 54a of adjustable plug 55a. The amount of delay in the closure of wafer 53a is determined by the position of stem 54a in the housing of valve 45a. The delay for valve 45b is provided by appropriately positioning stop 56b for wafer 53b relative to the wafer seat against wall 60b of the housing of valve 45b.

The selection of whether to employ spring means or a selected back stop-seat distance as the delay device for check valve 45 involves a number of considerations. The spring 52a of valve 45a, may not be as sensitive to orientation of the device in a gravitational field as is free floating wafer 53b, and may then provide a more positive and predictable delay time which can be adjusted at will by controlling the position of stem 54a. The spring, however, has the disadvantage of being more complex than the wafer, back stop valve 45b. A further, and perhaps more important, disadvantage of the spring is that during each cycle of piston operation, two and possibly three fluid pulses flow backward through check valve 45a; generally only a single pulse of fluid flows backward through the check valve if wafer back stop check valve 45b is employed. The extra pulse or pulses occur if the spring is employed because the spring biases wafer 53a to cause the wafer to open in response to the pressure in chamber 15 or conduit 47a not being sufficiently greater than that of the source to overcome spring compression, which generally occurs after piston 12 has entered the coasting region on its travel away from wall 17 and also as the piston is rebounding toward the coasting region.

In operation, the compressible fluid in chambers 15 and 16 is alternately and cyclically cooled and heated as piston 12 coasts away from and towards cylinder end face 17. Fluid in chamber 15 is cooled in response to cold fluid flowing into chamber 15 through port 49; and fluid flowing into chamber 15 through the bypass is cooled by regenerator 23 and optional cooling chamber 58. Fluid in chamber 16 is heated in response to hot fluid flowing through port 50; fluid flowing into chamber 16 through the bypass is heated by regenerator 23 and optional heating chamber 59; and fluid flowing from chamber 16 into thermal lag heating chamber 31 is heated by thermal lag passageways 33. Cold and hot chambers 58 and 59 are respectively located in conduits 21 and 22 such that fluid flowing in conduits 21 and 22 must pass through chambers 58 and 59. Pumping power and performance can be controlled by varying the amount of cooling and heating of fluid by chambers 58 and 59 by providing variable shunt paths 61 and 62 around the cold and hot chambers. The flow of fluid through chambers 58 and 59 is controlled by three-way variable ratio valves 63 and 64 which respectively connect conduit 21 with conduit 61 and conduit 22 with conduit 62. Conduits 61 and 62 shunt fluid around chambers 58 and 59 in conduits 21 and 22 so that, in conjunction with valves 63 and 64, any fraction (from zero to one) of the fluid flowing in conduits 21 and 22 can be diverted around chambers 58 and 59 without increasing the flow impedance of the bypass.

To enable fluid compressed by piston 12 within cylinder 11 to be evacuated from the cylinder, the cylinder includes outlet ports 65 and 66 respectively aligned with inlet ports 49 and 50. Ports 65 and 66 are circumferentially displaced from ports 49 and 50, as well as ports 24 and 25, to emphasize the fact that the location of any port can be independently varied along or around the cylinder axis. Port locations other than those shown in FIG. 1 are feasible.

Ports 65 and 66 are respectively connected to check valves 67 and 68, having outlets connected to storage tanks 69 and 70. Check valves 67 and 68 are arranged so that the wafers 71 and 72 thereof are open only in response to the pressure within chambers 15 and 16 exceeding the pressures within tanks 69 and 70. It is to be understood that, if desirable, tanks 69a and 69b can be a single tank or other load driven in parallel; and that tanks 70a and 70b can also be combined. Such combining of like loads helps balance the multi-piston pump about its axis of symmetry and generally improves piston synchronization. Symmetry of design about the axis of symmetry generally contributes to piston synchronization. Instead of, or in addition to, supplying the gas fed through check valve 68 to storage tank 70 or other load, this gas can be heated by solar radiation and returned to the hot fluid inlet 42, in order to provide heat for operating the pump. 1n such a configuration, the two conduits carrying hot gases from

valves

68a and 68b are preferably combined in a T element, heated and then supplied to the

hot inlets

42a and 42b after passing through a further T element. This external heating loop, which may contain an additional load to be driven by hot gas, can also supply heat to thermal lag heating chamber 31 by passing the loop through a heat exchanger formed on chamber 31. The cold gases fed through check valves 67a and 67b can also be combined in a T element, cooled by an ambient air, water, radiative, or other cooling means, and recirculated back to inlets 41a and 41b after passing through a further T and optional load. Thus solar heating and ambient cooling could provide the sole thermal energy for operating the pump. Solar energy can thus be converted by this device into pneumatic energy and thence into electrical or other form of energy.

To describe the operation of the device, initially assume that piston 12 is oscillating in cylinder 11, with oscillation being started by a pneumatic or other impulse as described in Ser. No. 205,651. Also, assume that piston face 13 is adjacent and has just begun moving away from cylinder end wall 17. At this time, piston 12 blocks bypass port 24, inlet port 49, outlet port 65, and port 76 to substantially eliminate fluid flow between the cylinder and these ports during rebound, and to avoid pumping work by the piston which might tend to slow or stall the piston. Thereby, the pressure in chamber is now in a maximum range while the pressure in chamber 16 is less than in chamber 15.

Next, assume that the cycle has progressed so that piston 12 has moved away from end wall 17 and has just entered the coasting region, whereby ports 24, 49, 65 and 76 are open. Thereby, the bypass is established and hot gas flows into the bypass from chamber 16 and cooled gas flows from the bypass into cold chamber 15. This cooling of gas in the bypass decreases the pressure in chambers 15 and 16. The pressures on the opposite faces 13 and 14 of piston 12 are substantially equalized because of the low impedance path of the bypass. When piston 12 initially moves into the coasting region, valve 45 remains closed or closes after a short delay because the pressure in chamber 15 exceeds that of the source connected to conduit 41. As the piston moves farther through the coasting region, the decreasing pressure within chamber 15 becomes almost equal to the pressure of the source connected to the conduit 41, whereby valve 45a opens by virtue of its spring compression and fluid flows from chamber 15 back to the source of cold fluid. As pressure in chambers 15 and 16 become lower than the cold and hot fluid sources, fluid from the cold and hot sources is drawn into chambers 15 and 16 through valves 45 and 46. Cold fluid continues to flow through valve 45 from the source connected to conduit 41 as piston 12 continues to move away from wall 17 and out of the coasting region into the rebound region near cylinder end wall 18.

When piston 12 is in the rebound chamber, the bypass is cut off due to the sealing action of piston 12 against port 25. When the rebound chamber volume is minimized, and chamber 15 pressure approximately at its minimum, piston 12 begins to move away from cylinder end wall 18, by virtue of a pneumatic spring between face 14 and end wall 18, as well as in response to the pressure supplied to this piston face 14 by thermal lag heating chamber 31. As piston 12 moves upwardly through the rebound region, the pressure in chamber 15 increases, tending to close valve 45. The valve, however, does not close because of its delayed closure action, as described supra. Thereby, a relatively constant and low back pressure acts against piston face 13, to prevent stalling of piston 12. Valve 45 continues to remain open until piston 12 has moved into the coasting region of cylinder 11, at which time the backflow of gas through check valve 45 is sufficient to close valve 45. Because valve 45 is open during this entire rebound portion of the cycle, there is a substantially zero net flow of gas into chamber 15 during this rebound, and substantially zero pumping work by the piston. Alternatively, valve 45 could be solenoid operated by a sensor responsive to piston position so as to be closed or open during the entire time of this rebound; in the former case the valve would not have substantial delay characteristics. As piston 12 moves through the coasting region toward cylinder end wall 17, the pressure in chamber 15 increases as a result of the heating of gas flowing from chamber 15 to chamber 16 via the bypass. The increasing pressure in chamber 15 becomes suffciently great to open valves 67 and/or 68, whereby fluid is fed to loads 69 and/or 70. Valves 67 and 68 remain open while piston 12 is in the coasting region approaching end wall 17.

In response to piston face 13 passing a plane defined by ports 24, 49 and 65 in the travel of the piston toward end wall 17, port 65 becomes blocked, whereby fluid no longer flows to load 69. Cylinder 12, at this time, enters a second rebound chamber formed between piston end face 13 and cylinder end wall 17, while ports 24, 49 and 65 are blocked by the piston side walls. The pressure in the second rebound chamber increases until a pneumatic spring between piston face 13 and end wall 17 is sufficiently great to reverse the motion of the piston, whereby the piston begins to move back towards cylinder end wall 18.

Valve 46, connecting the hot source to chamber 16, generally opens and closes in synchronism with opening and closing of valve 45 while piston 12 is in the coasting region. This is because the pressures in chamber 15 and 16 are substantially the same while piston 12 is in the coasting region. While piston 12 is in the rebound chamber defined by the volume between piston face 14 and cylinder end wall 18, flow through valve 46 is restricted by piston 12 blocking port 50. Valve 46 is generally closed while piston 12 is in the rebound chamber defined between piston face 13 and cylinder end wall 17 because the chamber 16 pressure is generally greater at this time than the pressure of the source of hot fluid. The small drop in chamber 16 pressure during this rebound portion of the cycle is generally insufficient to cause valve 46 to open. If, however, the outlet of valve 67 or valve 68 or conduit 77 is connected to a low impedance load, such as the atmosphere in an extreme case, the pressure in chambers 15 and 16 remains relatively constant as piston 12 is moving through the coasting region toward end wall 17. Thereby, in response to piston 12 entering the rebound region between piston end face 13 and cylinder end wall 17, the pressure in chamber 16 drops to slightly less than that of the hot fluid source connected to conduit 42, whereby there is flow through valve 46 at this time. Intake and compression of gas in chamber 16 during this rebound would tend to slow or stall piston 12, which is supposed to function as a displacer piston and not a working piston. Under these conditions, therefore, it may be desirable to provide a delay for valve 46,

using means similar to those described for valve 45. The delay time can be adjusted in the same manner as the delay time for valve 45, i.e., to equal to the time while piston 12 is rebounding from near cylinder end wall 17 toward the coasting region.

In certain instances, it is desirable to utilize cylinder 11 to drive an oscillatory load 75, such as an alternator of the type disclosed in my copending application Ser. No. 205,651. In such an instance, no check valves need be provided between the cylinder outlet ports and the load and load is connected to be driven by fluid pumped through ports 76a and 76b to

conduits

77a and 77b which are connected to T element 78 that in turn feeds gas through conduit 79 to the load. In response to the oscillatory pressure variations in conduit 79, the load 75 is cyclically driven to perform useful work. An

alternate or second load can be connected to port 66 to be driven by hot, rather than cool, gas.

To increase the efficiency of the device and reduce losses due to heating of conductors and magnetic material of the alternator, optional thermal lag cooler 80 is connected in line 79 to cool gas flowing between load 75 and cylinder chamber 15. Thermal lag cooler 80 is provided with relatively wide fluid passageways, as described in my previously referenced copending applications. Cooling of the passageways can be performed by substituting a cooling element for heating element 32 of chamber 31 and by providing an inlet and outlet on opposite sides of the chamber. Alternatively, cooling fins which are in heat exchange relationship with ambient air can be provided for cooling. Because the thermal lag cooler includes relatively wide passageways, much of the cooling occurs after the gas has done its work on the load at relatively high pressure and is returning from the load to chamber at decreasing pressure for later heating and pressure increase within the pump. The relatively great passageway width also reduces fluid drag of the cooling means.

In FIG. 2 there is illustrated an alternative arrangement for cooling gas returning from the oscillatory load to the cold end of the cylinder, wherein check valve 81, biased to pass fluid from cooling chamber 180, which can be of either'the conventional or thermal lag type, to T element 78 in response to the pressure of fluid in the pump dropping below that of the load 75, is connected between the cooler and T element. A further check valve 82,'polarized to pass fluid from T element 78 to load 75 in response to pump pressure exceeding load pressure, is connected between the T element and load in parallel with 'cooler 180 and check valve 81.

In accordance with a further aspect of the invention the oscillating load is bellows 85, FIG. 3, connected directly to T element 78 via conduit 79. Bellows 85 is inherently a thermal lag cooling device that cools fluid within the bellows folds while supplying the fluid back to cylinder chamber 15 for subsequent heating and pressure increase.

While there has been described and illustrated several specific embodiments of the invention, it will be clear that variations in the details of the embodiments specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims. For example, it is not necessary to feed gas into either end of cylinder 11. Compressible fluid can be introduced into only one end of the cylinder or it can flow to and from the ends of the cylinder solely from the bypass. Also,

the fluid flowing through conduits 41 and 42 need not necessarily be derived from cold and hot sources. However, in order to operate the pump, a means must be provided to obtain a difference in temperature between fluid in opposite ends of the cylinder. Thus there must be at least one means for cooling and at least one means for heating. The cooling can be a source of cool fluid, a cooling chamber in the bypass, or a cooling means between the pump and an oscillatory load as described supra, or any combination of these cooling means. Correspondingly, the means for heating can be a source of hot fluid, a heater in the bypass, a thermal lag heating chamber, a heating means associated with a load or between the pump and a load, or any combination of these heating means.

If there is a fluid inlet to the pump there must, of course, be a fluid outlet. The outlet can be at the cold end of the cylinder, the hot end, or both, irrespective of whether the inlet is at the cold end, the hot end, or at both ends of the cylinder or coasting region. An oscillatory load, such as a bellows, can be driven whether or not inlet and outlet ports and associated check valves are provided, since the net flow to a strictly oscillatory load is zero. However, a long bypass containing a regenerator, for coasting of the piston and modified regenerative thermodynamic cycle output, is generally desirable in any embodiment of this invention illustrated or discussed above in order to obtain relatively high energy conversion efficiency and stall-free operation.

lt should be understood that other types of delayed closing valve, such as a ball type check valve, can be used instead of the wafer check valve. If spring biasing is not utilized, the distance of travel of the ball or wafer from its backstop to its seat, as well as the mass of the wafer, must be great enough for adequate delay.

I claim:

1. A thermally driven pump utilizing compressible fluid, comprising a cylinder, a free piston in the cylinder, means for obtaining a temperature differential between fluid in opposite ends of the cylinder, means for sustaining oscillation of the piston in the cylinder, a fluid bypass having displaced ports between ends of the cylinder, whereby a coasting region for the piston is formed between the ports, a regenerator in the bypass, a rebound chamber near each end of the coasting region, inlet means for feeding fluid from a source of fluid into a portion of the cylinder, said inlet means including valve means for connecting the cylinder in fluid flow relationship with the source of fluid only while the pressure within the portion is less than the pressure of the source of fluid, and means for venting the coasting region fora selected time interval while the piston is in a rebound chamber and moving toward the coasting region.

2. The pump of claim 1 wherein the selected time interval is substantially the entire time while the piston is in the rebound chamber and moving toward the coasting region.

3.'The pump of claim 1 wherein the means for sustaining oscillation includes a thermal lag chamber.

4. The pump of claim 1 wherein the means for venting includes a check valve.

5. The pump of claim 1 wherein the means for venting includes a spring biased check valve.

6. The pump of claim 1 wherein the means for ventingcomprises a check valve including a'wafer and a back stop.

7. The pump of claim 1 wherein the means for ob taining a temperature differential includes means for feeding cool fluid into the cylinder near one end of the cylinder, and means for feeding hot fluid into the cylinder near the other end of the cylinder.

8. The pump of claim 7 wherein the means for sustaining oscillation includes a thermal lag chamber.

9. The pump of claim 1 further including outlet means for feeding fluid to a load.

10. The pump of claim 1 further including means for supplying fluid to a load and means for cooling fluid flowing from the load to the pump.

11. The pump of claim 10 wherein the means for cooling includes a thermal lag cooling chamber.

12. The pump of claim 11 wherein the load and the thermal lag cooling chamber are combined as a bellows.

13. A thermally powered pump utilizing compressible fluid comprising a plurality of cylinders, a free piston in each of the cylinders, means for sustaining synchronized oscillation of the ,pistons in the cylinders, a fluid bypass for each cylinder, each bypass having displaced ports for allowing fluid to bypass a portion of its respective cylinder between ends of the cylinder, whereby a coasting region for each piston is formed between the displaced ports of the respective cylinders, a rebound chamber for each piston near each end of the cylinder, inlet means for normally providing a fluid flow path from a fluid source into a portion of each cylinder only while the pressure within the portion is less than the pressure of the source of fluid, and means for venting the coasting region of each cylinder during a selected time interval of the rebound portion of the oscillation cycle.

14. The pump of claim 13 wherein the means for sustaining includes a thermal lag heating chamber in fluid flow relation with a rebound chamber of each cylinder.

15. The pump of claim 13 further including means for feeding cold fluid into each cylinder near one end of each cylinder and means for feeding hot fluid into each cylinder near the other end of each cylinder.

16. In combination, a cylinder, a piston in the cylinder, means, including heating means, for sustaining oscillation of the piston in the cylinder, a load responsive to fluid compressed by the piston in a chamber adjacent one end of the cylinder, said load including a bellows in fluid flow relation with and driven in response to fluid in said chamber, whereby the cooling of fluid within the bellows as the fluid is returning to the chamber assists in supplying energy to the load.

17. The combination of claim 16 further including means for feeding hot fluid into a cylinder chamber adjacent the opposite end of the cylinder.

18. The combination of claim 17 wherein the piston is a free piston and further including a bypass for the cylinder between the chambers whereby a coasting region is established for the free piston within the bypass region of the cylinder, and a regenerator in said bypass.

19. The combination of claim 16 wherein the means for sustaining oscillation includes a thermal lag heating chamber.

20. An oscillating piston apparatus comprising a cylinder, a free piston in the cylinder dividing the cylinder into first and second variable volumes, means for sustaining oscillation of the piston in the cylinder, a bypass between the first and second volumes such that the piston coasts through a region of the cylinder between ends of the cylinder, a regenerator means in the bypass, means for blocking the bypass during the piston oscillation while at least one volume has a value in a minimum range, means for feeding cool fluid into the second volume, means for feeding hot fluid into the first volume, means for supplying fluid from the cylinder to a load, and means for cooling fluid returning to the cylinder from the load.

21. The apparatus of claim 20 wherein the means for cooling returning fluid includes a thermal lag cooling chamber located in a conduit connecting the cylinder and the load.

22. The apparatus of claim 20 wherein the means for supplying includes an outlet conduit and check valve for passing fluid only from the cylinder to the load, and means, including a return conduit, cooling chamber, and check valve, for passing fluid only from the load through the cooling chamber and check valve to the cylinder.

23. The apparatus of claim 20 wherein the load and the means for cooling returning fluid are combined in a bellows.

24. The apparatus of claim 20 further including valve means for preventing a substantial net flow of fluid into the variable volume containing the coasting region while the piston is in a rebound region beyond the coasting region.

Claims

1. A thermally driven pump utilizing compressible fluid, comprising a cylinder, a free piston in the cylinder, means for obtaining a temperature differential between fluid in opposite ends of the cylinder, means for sustaining oscillation of the piston in the cylinder, a fluid bypass having displaced ports between ends of the cylinder, whereby a coasting region for the piston is formed between the ports, a regenerator in the bypass, a rebound chamber near each end of the coasting region, inlet means for feeding fluid from a source of fluid into a portion of the cylinder, said inlet means including valve means for connecting the cylinder in fluid flow relationship with the source of fluid only while the pressure within the portion is less than the pressure of the source of fluid, and means for venting the coasting region for a selected time interval while the piston is in a rebound chamber and moving toward the coasting region.

3. The pump of claim 1 wherein the means for sustaining oscillation includes a thermal lag chamber.

4. The pump of claim 1 wherein the means for venting includes a check valve.

6. The pump of claim 1 wherein the means for venting comprises a check valve including a wafer and a back stop.

7. The pump of claim 1 wherein the means for obtaining a temperature differential includes means for feeding cool fluid inTo the cylinder near one end of the cylinder, and means for feeding hot fluid into the cylinder near the other end of the cylinder.

13. A thermally powered pump utilizing compressible fluid comprising a plurality of cylinders, a free piston in each of the cylinders, means for sustaining synchronized oscillation of the pistons in the cylinders, a fluid bypass for each cylinder, each bypass having displaced ports for allowing fluid to bypass a portion of its respective cylinder between ends of the cylinder, whereby a coasting region for each piston is formed between the displaced ports of the respective cylinders, a rebound chamber for each piston near each end of the cylinder, inlet means for normally providing a fluid flow path from a fluid source into a portion of each cylinder only while the pressure within the portion is less than the pressure of the source of fluid, and means for venting the coasting region of each cylinder during a selected time interval of the rebound portion of the oscillation cycle.