Stirling Cycle-type Thermal Device Servo Pump

Abstract

A servo pump assisting a pulsating primary pump. A Stirling cycle engine drives an expansible chamber pump in series with the primary pump. Pulses are transmitted from the primary pump to drive the displacer piston of the engine to drive the pump in phase with the primary pump.

Parent Case Text

This application is a continuation-in-part application of my copending application Ser. No. 812,530, filed 5 Mar. 1969, now U.S. Pat. No. 3,552,120.

Description

This invention relates to an improved Stirling cycle-type thermal device, of the type disclosed in the above application which is suitable for use as a servo pump to assist primary cyclical pumps and particularly a servo pump which is suitable for assisting the heart in pumping blood.

The principles of the Stirling cycle thermal device are well known in the art and a relatively comprehensive review of past and recent developments in Stirling thermal engines and the comparison of such engines with the Otto, Brayton, Carnot and Ericsson cycle engines is found in Volume 68 SAE Transactions 1960, pps. 665-684.

The thermal device as disclosed in the above application generally comprises a displacer cylinder zone; a displacer piston mounted for reciprocation in the zone; a power cylinder; a power piston mounted in the cylinder normally mechanically independent of the reciprocation of the displacer piston; a working fluid in the displacer cylinder zone; means creating a pressure differential between the opposite faces of the displacer piston; the last-named means including means for adding heat to or removing heat from each end of the displacer cylinder zone; means providing a power coupling between the displacer piston and the power piston consisting of fluid communication conductors between one end of the power cylinder and one end of the displacer cylinder zone.

It is an object of the present invention to provide means to incorporate the above-described thermal device into a servo pump for assisting a primary cyclical pump. This is accomplished by utilizing the power piston of the device as a pump drive in the fluid circuit of the primary pump and then initiating the cycle of the displacer piston of the device by a pulse from the pressure stroke of the primary pump.

Although the thermal device servo pump of this invention can be used for general application, the invention is described hereinafter as specifically adapted for use as a heart assist pump for pumping blood. Such a device is intended for use as a portion of the circulatory system of a human being to assist a damaged heart by providing means to reduce resistance to the pumping action of the heart.

In this invention a blood pump is placed in series with the heart and is driven by a Stirling cycle engine, the motion of which is triggered by heart action so that the heart and the pump operate in synchronization.

The invention will be more particularly described in reference to the accompanying drawings wherein:

FIG. 1 is a sectional view of a heart assist servo pump and associated circuit in accordance with the invention; and

FIG. 2 is a fragmentary view similar to FIG. 1 showing a variation in accordance with the invention.

Referring now to FIG. 1 of the drawings, 10 generally designates a Stirling cycle-type servo pump in accordance with the invention connected to the left ventrical of a heart, schematically shown at 12.

The servo pump 10 includes a housing 14 which defines a cylinder in which a displacer piston 18 is mounted for reciprocation.

A power piston 20 is reciprocally mounted in the housing 14 beneath the displacer piston 18 and drives a pump 22. The pump is provided with an inlet 24 controlled by an inwardly opening flapper valve 26 and an outlet 28 controlled by an outwardly opening flapper valve 30.

The pump 22 comprises a housing 32 having a pump piston 34 reciprocally mounted therein to divide the housing into an upper chamber 36, communicative with the outlet 28 and a lower chamber 38 communicative with the inlet 24. Communication between the chambers is provided by check valves, shown schematically at 40, through the piston 34. The power piston 20 drives the pump piston 34 through a hollow drive shaft 42 which traverses communicating openings in adjacent portions of the housing 14 and pump housing 32. A bellows seal 44 is disposed between the shaft 42 and the openings in the housings to provide a seal between housings.

The heart, the left ventricle of which is schematically shown at 12, communicates through a valved return, with the left auricle at 46 and through the aorta 48 is connected to the pump inlet 24. A branch duct 50 also connects the heart to a diaphragm chamber 52 disposed beneath the pump 22. The chamber 52 is provided with a diaphragm 54 which divides that chamber into upper and lower sections 56 and 58, respectively. A flexible bag 60 communicates with the upper section 56 for purposes to be described in greater detail below.

The diaphragm 54 is connected to the displacer piston 18 by means of a drive rod 62 which traverses the pump 22 coaxially through the hollow drive shaft 42 and power piston 20. A bellows seal 64 between the lower end of the shaft 62 and the diaphragm chamber segregates the upper section 56 of that chamber from the lower chamber 38 of the pump 22. A bellows seal 66, around the rod 62 between the lower wall of the pump 22 and the piston 34, segregates the lower chamber 38 from the interior of the hollow drive shaft 42.

The displacer rod 62 runs through a close sliding seal 63 serving to separate the space 76 and its varying pressure from the bounce space 75 which is relatively large and has approximately constant pressure, of, for example, 2,000 p.s.i.

The remainder of the hollow drive rod space including the space within the bellows seals 44, 66, 64, is held at bounce space pressure by means of a hole 77 in the drive rod between the bounce space and the interior of the drive rod. Thus the varying pressures of the gas in space 76 act only on the small area of the displacer drive rod 62, and do not serve to drive the displacer appreciably. The displacer is then free to be driven by the blood pressure acting on diaphragm 54.

The upper end of the housing is provided with heaters, regenerators and coolers, schematically shown at 68, 70 and 72, respectively, in the bypass path around the displacer piston 18. The construction, function and operation of this portion of the thermal device is more fully set forth in the above-referred-to application, particularly in the description of FIG. 6 thereof. For the purposes of this disclosure, it suffices to say that the devices 68, 70 and 72 function, when connected to suitable sources of energy, to cool gas being circulated downwardly therethrough by upward movement of the displacer piston 18 and to heat gas being circulated upwardly therethrough by downward movement of the displacer piston thereby providing a hot zone 74 in the housing above the piston 18 and a cold zone 76 below the piston.

The housing is charged with a gas at high pressure, such, for example, as with helium or hydrogen gas at 2,000 p.s.i. For this reason the housing 14 is fabricated to withstand high internal pressures.

In order to provide a substantially neutral system, e.g., one in which there are no large biasing force acting on the pistons, spring effects are built into one or more of the bellows seals 44, 64 and 66 to balance the charge gas pressures on the moving parts so that they may move readily under the influence of fluid pressure changes.

The upper section 56 of the diaphragm chamber 52 is charged with air or inert gas at ambient pressure. The bag 60 serves to equalize the pressure within the upper section with barometric changes of pressure in the ambient zone.

With the device charged as above, the inlet 24 is connected to the aorta 48, the outlet 28 to the inlet to the arterial system and the pump chambers 36 and 38 and connecting lines are flooded with blood. The branch duct 50 is connected to the heart 12 and the lower section 58 of the diaphragm chamber is filled with blood so that pressure pulses from the heart can be transmitted to the diaphragm 54. The heater 68 and cooler 72 are then energized and the servo pump 10 operates as follows:

a. The heart muscle contracts and develops a positive pressure in the left ventricle 12.

b. The positive pressure is communicated through the duct 50 to displace the diaphragm 54 upwardly.

c. Upward movement of the diaphragm 54, caused by the pressure difference between section 58 and the ambient section 56, drives the rod 62 and displacer piston 18 upwardly.

d. The working gas in the hot zone 74 of the thermal device is displaced through the regenerator 70 and cooler 72 by upward movement of the piston 18 and is cooled thereby.

e. The reduced pressure in working gas in the cold zone 76 caused by the cooling process causes the drive piston 20 to be driven upwardly by the resulting pressure differential between the gas in the space below the piston 20 and the gas in the cold zone.

f. The piston 34 of the pump 22 is drawn upwardly, closing the check valves 40 and pumping blood from the upper chamber 36 through the outlet 28 to the arterial system. Blood is simultaneously drawn into the lower chamber 38 through the inlet 24.

g. The heart muscle relaxes at the completion of its pump stroke lowering the pressure in the left ventricle 12 and therefore in the diaphragm chamber 52.

h. With the lowering of pressure in the chamber 52, the diaphragm 54, rod 62 and displacer piston 18 move downwardly driving gas from the cold zone 76 through the regenerator 70 and heater 68 heating the gas as it enters the hot zone 14.

i. With the increase in pressure caused by the heating of the working gas, the drive piston 20 is driven downwardly.

j. Downward movement of the piston 20 drives the pump piston 34 downwardly through the shaft 42 opening the valves 40 and transferring blood from the lower chamber 38 to the upper chamber 36. The valves 30 and 26 are, of course, shut during this cycle thereby isolating the pump from the system to preclude overpressured return of blood to the heart or return to the pump from the arterial system.

The above cycle is then repeated on the next beat of the heart.

The device may be altered, if so desired such that the pump discharges on the downward stroke by reversing the connections of the upper section 56 and the lower section 58 of the diaphragm chamber 52 so that the ventricle pressure drives the displacer downward. The arterial and aorta connections also must be interchanged so that the blood enters through 28 and leaves through 24. The direction of operation of the valves 26, 30 and 40 must also be reversed for such operation.

In FIG. 2, a variation of the diaphragm chamber 52 of FIG. 1 is illustrated. In this embodiment, components thereof corresponding to like components of the preceding Figure are indicated by the like numerals only of the next higher order. In this embodiment, the chamber 152 is provided with inlet and outlet connections 178 and 180 respectively. The connections communicate, through flapper check valves 182 and 184 respectively, with a lower section 158 of the chamber 152 below a diaphragm 154. The operation of the diaphragm and connected drive rod 162 is identical to that of the embodiment of FIG. 1.

The connections 178 and 180 are connected to the left ventricle 112 of a heart through transmitting and return lines 150 and 151 respectively.

The advantage provided by the above-described variation is that a net blood circulation takes place in the lower section 158 thereby avoiding stagnation at that point. Obviously, other methods of transmitting the pressure pulse to the diaphragm 154, such for example as, a column of inert fluid communicative with a transducer actuated by the heart beat, could function for the purposes of this invention.

What has been set forth above is intended as exemplary to enable those skilled in the art in the practice of the invention. Obviously, the device has general application as a servo in any system in which a small triggering force is required to cause a large effect in phase with the force.

Claims

What is new and therefore desired to be protected by Letters Patent of the United States is:

1. A servo pump for assisting a pulsating primary pump comprising:

a Stirling cycle engine having displacer and power piston means;

an expansible chamber pump driven by said power piston, means connecting said expansible chamber pump in series with said primary pump; and

means for transmitting pulses from said primary pump to initiate drive of said displacer piston to thereby actuate said engine to drive said expansible chamber pump in phase with said primary pump.

2. A servo pump for assisting a pulsating primary pump comprising:

a Stirling cycle engine having displacer and power piston means;

an expansible chamber pump driven by said power piston, means connecting said expansible chamber pump in series with said primary pump; and

means for transmitting pulses from said primary pump to initiate drive of said displacer piston to thereby actuate said engine to drive said expansible chamber pump in phase with said primary pump, wherein said means for transmitting pulses comprises a fluid column interconnecting said primary pump and said engine, and means for translating fluid pressure pulses transmitted through said column to mechanical movement to actuate said displacer piston.

3. A pump in accordance with claim 2 wherein said means for translating includes a diaphragm bisecting a chamber with one side thereof communicating with said fluid column and the other with ambient pressure.

4. A pump in accordance with claim 3 wherein said means for translating further includes a drive rod interconnecting said diaphragm and said displacer piston.

5. A pump in accordance with claim 3 wherein said means for transmitting pulses further comprises a return fluid column and valve means provide flow from said primary pump, through said one side of said chamber and back to said primary pump through said return column.

6. A pump in accordance with claim 1 wherein said expansible chamber pump comprises a pump housing, a pump piston reciprocable in said pump housing, means connecting said pump piston to said drive piston and inlet and outlet means communicative with said pump housing.

7. A pump in accordance with claim 6 wherein said pump piston divides said pump housing into inlet and outlet chambers, said inlet and outlet means comprising check valve controlled conduits communicating with said inlet and outlet chambers, respectively, and check valve means disposed through said pump piston to provide transfer of fluid from said inlet to said outlet chambers.