Abstract: The reciprocatable power piston of a free-piston Stirling machine is drivingly linked to a reciprocatable component body of an associated apparatus by at least one spring with no rigid connection linking the piston to the component body. The spring drive linkage allows the power piston and the reciprocatable component body of the associated apparatus to reciprocate at different amplitudes of oscillation. Therefore, the Stirling machine and the associated apparatus can be optimized at different amplitudes of piston and the component body oscillation thereby improving the optimization of two very different dynamic systems that are drivingly connected together.

Abstract: A feedback control method and circuit for inclusion in a control system of an electrical power generating source that comprises a free piston Stirling engine driving a linear alternator. An instantaneous value of a variable, Vinternal, is continuously derived from other sensed and computed parameters and used in a negative feedback control loop of the control system to control engine piston stroke in order to maintain the power produced by the engine equal to the power transferred from the engine to the alternator. Vinternal is the sum of the voltage induced on the alternator winding and the voltage across the equivalent circuit lumped resistance of the alternator winding. A switching mode rectifier connects the alternator winding to an energy storage capacitor or battery. A negative feedback, alternator current control loop has an output connected to the pulse width modulator of the switching mode rectifier and has a feedback circuit comprising a current sensor for sensing instantaneous alternator current.

Abstract: The concentricity and coaxiality of a central bore through a piston for a free piston Stirling machine is improved with a piston that has a sleeve with a core constructed from at least two, separate, axially-engaging core components sealed within the sleeve. During fabrication, a central bore is machined through each of the core components. The piston is assembled by heating the sleeve and cooling the core components, inserting the core components into the sleeve and then allowing the sleeve to cool and the core components to warm. This drives the core components into sealed engagement with each other and with the sleeve and aligns the central bore coaxially with the outer cylindrical surface of the sleeve.

Abstract: An electrical power source including a free-piston Stirling engine driving an alternator to supply power through a bus to a user load and controlled by an engine/alternator controller. A bidirectional DC/DC converter is connected between a battery and the bus. The stroke of the engine piston is modulated between a maximum and a minimum stroke to maintain the bus voltage at a design nominal bus voltage (V1), and charge the battery if it is not charged, when and so long as the bus voltage does not fall below a design nominal bus voltage (V1). The Stirling engine is operated at its maximum piston stroke, and the battery is charged if it is not charged, when the bus voltage is in the range between the design nominal bus voltage (V1) and a design minimum battery charging bus voltage (V2).

Abstract: A feedback control circuit and method for a control system used to control an electrical power generating source that comprises a free piston Stirling engine driving a linear alternator. A switching mode rectifier connects the alternator winding to an output circuit that includes an electrical energy storage means and is controlled by a pulse width modulator that controls the rectifier switching duty cycle and phase. The control system controls the pulse width modulator. The improvement computes a voltage across a virtual tuning capacitor and uses the computed voltage to control the switching mode rectifier so that the switching mode rectifier is switched in a manner that makes the alternator circuit operate as if a tuning capacitor were actually present and so that the control system controls the piston of the Stirling engine to maintain balance of the mechanical power generated by the Stirling engine and the electrical power absorbed from the engine by the alternator.

Abstract: A feedback control method and circuit for inclusion in a control system of an electrical power generating source that comprises a free piston Stirling engine driving a linear alternator. An instantaneous value of a variable, Vinternal, is continuously derived from other sensed and computed parameters and used in a negative feedback control loop of the control system to control engine piston stroke in order to maintain the power produced by the engine equal to the power transferred from the engine to the alternator. Vinternal is the sum of the voltage induced on the alternator winding and the voltage across the equivalent circuit lumped resistance of the alternator winding. A switching mode rectifier connects the alternator winding to an energy storage capacitor or battery. A negative feedback, alternator current control loop has an output connected to the pulse width modulator of the switching mode rectifier and has a feedback circuit comprising a current sensor for sensing instantaneous alternator current.

Abstract: A feedback control circuit and method for a control system used to control an electrical power generating source that comprises a free piston Stirling engine driving a linear alternator. A switching mode rectifier connects the alternator winding to an output circuit that includes an electrical energy storage means and is controlled by a pulse width modulator that controls the rectifier switching duty cycle and phase. The control system controls the pulse width modulator. The improvement computes a voltage across a virtual tuning capacitor and uses the computed voltage to control the switching mode rectifier so that the switching mode rectifier is switched in a manner that makes the alternator circuit operate as if a tuning capacitor were actually present and so that the control system controls the piston of the Stirling engine to maintain balance of the mechanical power generated by the Stirling engine and the electrical power absorbed from the engine by the alternator.

Abstract: A system for precisely centering a workpiece within a cylindrical bore such that the center of the workpiece is coaxial with the central axis of the bore. An arbor is used within the cylindrical bore to sense and calculate the location of the central axis. The position of the workpiece is also sensed so that it can be aligned with the central axis. A computer system is used to perform the calculations and provide an indication of alignment of the workpiece and the central axis. The position of the central axis and the workpiece are found via a location determining system that may incorporate electromechanical and optical position sensing systems. For instance, a plurality of light transmitters and light receivers may be used to generate and transmit beams of light used in determining positions. The apparatus has particular application to free piston machines, and particularly free piston coolers.

Abstract: A feedback control method and circuit for inclusion in a control system of an electrical power generating source that comprises a free piston Stirling engine driving a linear alternator. An instantaneous value of a variable, Vinternal, is continuously derived from other sensed and computed parameters and used in a negative feedback control loop of the control system to control engine piston stroke in order to maintain the power produced by the engine equal to the power transferred from the engine to the alternator. Vinternal is the sum of the voltage induced on the alternator winding and the voltage across the equivalent circuit lumped resistance of the alternator winding and a switching mode rectifier connects the alternator winding to an energy storage capacitor or battery.

Abstract: The cool down time for a multi-stage, pulse tube cryocooler is reduced by configuring at least a portion of the acoustic impedance of a selected stage, higher than the first stage, so that it surrounds the cold head of the selected stage. The surrounding acoustic impedance of the selected stage is mounted in thermally conductive connection to the warm region of the selected stage for cooling the acoustic impedance and is fabricated of a high thermal diffusivity, low thermal radiation emissivity material, preferably aluminum.

Abstract: An improved pulse tube cooler having a resonator tube connected in place of a compliance volume or reservoir. The resonator tube has a length substantially equal to an integer multiple of ¼ wavelength of an acoustic wave in the working gas within the resonator tube at its operating frequency, temperature and pressure. Preferably, the resonator tube is formed integrally with the inertance tube as a single, integral tube with a length approximately ½ of that wavelength. Also preferably, the integral tube is spaced outwardly from and coiled around the connection of the regenerator to the pulse tube at a cold region of the cooler and the turns of the coil are thermally bonded together to improve heat conduction through the coil.

Abstract: A clamping apparatus for allowing pre-close-out access to the head of a Stirling machine and facilitating subsequent close-out welding of the head. The head is axially separable into removable and fixed portions, each portion having an end that engages the other. Each portion has an annular flange extending radially outwardly at its engaging end, and each flange has an annular groove. O-rings are seated in the grooves. A temporary sealing ring surrounds and engages the O-rings. Clamping rings, having axially facing end surfaces along their interfacing axial edges, seat against axially opposite sides of the abutting annular flanges. The clamping rings have a plurality of holes spaced annularly around the rings and the holes of one ring are axially aligned with the holes in the other. Fasteners pass through each pair of holes and draw the rings together when tightened, thereby drawing the fixed and removable portions of the head together and securing them against relative axial movement.

Abstract: An apparatus and method for compressing gas refrigerant using two different compressors operated alternatively in a series or parallel mode for obtaining two different compression ratios and thereby provide efficient operation for both a relatively lower suction pressure and a relatively higher suction pressure. This system avoids an unbalanced mass flow rate when the compressors are operated in series by unloading a downstream one of the compressors. When operated in the series mode, refrigerant is bypassed back to a suction inlet of the downstream compressor during a portion of a compression stroke of the downstream compressor for equalizing the mass flow rate through the two compressors.

Abstract: A piston position sensing circuit for sensing the instantaneous position of a piston of a free piston Stirling machine or a compressor mechanically connected to a reciprocating member of a linear electric motor or alternator. A source of a high frequency, alternating, electrical signal applies a high frequency signal to the winding circuit of the linear alternator or motor. A filter circuit is connected to the winding circuit and passes electrical signals at the frequency of the high frequency source and blocks signals at the operating frequency of reciprocation. A peak detector circuit is connected to the filter circuit and detects the peak of the filter circuit output signal to provide an instantaneous peak magnitude that is proportional to the instantaneous piston position.

Abstract: A cryocooler having two operating modes so that its operating range is broadened, its gas bearing system is maintained in an operable state and it can utilize piston stroke modulation for energy efficiency. A piston stroke modulator modulates the piston stroke when the commanded piston stroke exceeds the minimum stroke and maintains the minimum stroke when the commanded stroke is less than the minimum stroke. A heater applies heater power to the thermal load when the commanded piston stroke is less than the minimum piston stroke. A closed loop feedback control system is used which has two branches of its dynamic leg. One branch controls the modulation of the cryocooler and the second, parallel branch controls the modulation of the heater.

Abstract: Apparatus and method for separating oxygen directly from air, operating at substantially atmospheric pressure and recuperating energy used for cooling incoming air. An ambient air input leads from the atmosphere to a vessel for confining gases. A cryocooler has a cooled surface in the vessel for directly condensing oxygen from the air at substantially atmospheric pressure. The cryocooler cools the cold surface to a temperature greater than the boiling point temperature of nitrogen and not greater than the boiling point temperature of oxygen for condensing oxygen. A liquid/gas separator separates the liquid oxygen from residual gases which both flow out through separate outputs. Air is propelled through the system at substantially atmospheric pressure by an air impeller. A heat exchanger recovers cooling energy and dehumidifies incoming air by transferring heat from the incoming air to outgoing gases.

Abstract: A method and system for precisely centering a workpiece within a cylindrical bore such that the center of the workpiece is coaxial with the central axis of the bore. An arbor is used within the cylindrical bore to sense and calculate the location of the central axis. The position of the workpiece is also sensed so that it can be aligned with the central axis. A computer system is used to perform the calculations and provide an indication of alignment of the workpiece and the central axis. The position of the central axis and the workpiece are found via a location determining system that may incorporate electromechanical and optical position sensing systems. For instance, a plurality of light transmitters and light receivers may be used to generate and transmit beams of light used in determining positions. The method has particular application to free piston machines, and particularly free piston coolers.

Abstract: A Stirling cycle machine heat exchanger and a method for making the heat exchanger including, forming an annular ring of a solid heat conductive mass, the annular ring having a central axis and having axially opposite faces. A plurality of passages are drilled through the annular ring and through the opposite faces to provide passages for the flow of a fluid through the passages and transfer of heat energy between the mass and the fluid. The passages are preferably parallel to the axis and have a circular cross section and are arranged in a plurality of circumferentially spaced sets of passages, each set having a plurality of radially spaced passages.

Abstract: A heat transfer member having an external heat transfer member including an insertion hole having an adaptor ring inserted thereinto, and at least one of a base blocking protrusion and a grove blocking protrusion formed on a predetermined portion of the surface of the base confronting the inserted adaptor ring inside the insertion groove, for increasing the coupling strength of the external radiating member and the adaptor ring and the transition member.

Abstract: A regenerator having a plurality of involute foils disposed in an annular gap between an inner cylindrical tube and an outer cylindrical tube. The involute shape of the foils provides uniform spacing throughout the entire regenerator and substantial surface area for fluid contact.

Abstract: An alkali metal thermoelectric conversion device formed from a porous tube or plate coated with a thin film of beta-alumina, the porous tube or plate is sintered metal or metal alloy having a coefficient of thermal expansion which approaches that of the beta-alumina to form a mechanically stable device with high electrical output.