Centering system for free piston machine

Abstract

A centering apparatus for a free piston Stirling engine including a pressure regulator valve which connects a passageway between the work space and the back space when both (a) the average pressure in the back space exceeds the average pressure in the work space as a result of the piston deflecting a spring, and simultaneously (b) the instantaneous pressure in the back space exceeds the instantaneous pressure in the work space. A diaphragm spans across an actuator housing cavity, dividing the cavity into an upper chamber and a lower chamber. A connector valve is linked to the diaphragm for opening and closing the valve upon displacement of the diaphragm. When the average back space pressure exceeds the average work space pressure, the diaphragm is displaced to open the valve, connecting the work space and the back space in fluid communication. A check valve permits the flow of gas in only one direction: from the back space to the work space. A similar arrangement can be included to also cause flow from the work space to the back space when the average work space pressure exceeds the average back space pressure, so as to center the piston against leaks in either direction.

I claim:  
     
       1. An improved piston centering apparatus for a free piston machine having a housing, including a cylinder and a piston sealingly reciprocatable in the cylinder, and a spring connected between the piston and the housing, said spring being relaxed and exerting substantially no force on the piston when the piston is in a centered position, said housing enclosing a first machine space bounded by a first end of the piston and also enclosing a second machine space bounded by the opposite, second end of the piston, the second machine space having a working fluid with an average fluid pressure and the first machine space having a working fluid with a fluid pressure varying periodically in opposite directions from said average pressure, said pressure variation causing a net leakage flow of working fluid from the first machine space to the second machine space, wherein the improvement comprises: 
       (a) a connector valve through which the first and second machine spaces are connected;  
       (b) a valve actuator linked to the connector valve, the actuator having a first actuator chamber and a second actuator chamber for opening the connector valve in response to the pressure of the second actuator chamber exceeding the pressure of the first actuator chamber, the first actuator chamber connected in communication with the first machine space through a restriction for maintaining a pressure in the first actuator chamber substantially equal to the average pressure in the first machine space, and the second actuator chamber connected in communication with the second machine space; and  
       (c) a check valve directed to permit a flow of working fluid from the first  second machine space to the second  first machine space when the connector valve is open.  
     
     
       2. An apparatus in accordance with  claim 1 , wherein the free piston machine is a free piston Stirling cycle machine, the first machine space is a work space and the second machine space is a back space. 
     
     
       3. An apparatus in accordance with  claim 2 , wherein the first chamber of the actuator is connected in fluid communication with the work space of the machine, and the second chamber of the actuator is connected in fluid communication with the back space of the machine. 
     
     
       4. An apparatus in accordance with  claim 1 , wherein the actuator includes a housing having a cavity formed within the actuator housing, and a diaphragm divides the cavity into the first and second actuator chambers. 
     
     
       5. An apparatus in accordance with  claim 4 , wherein the connector valve comprises a needle drivingly linked to the diaphragm and movably mounted in an aperture formed in the actuator housing, for being displaced in response to displacement of the diaphragm, thereby opening and closing the connector valve. 
     
     
       6. An apparatus in accordance with  claim 1 , wherein the restriction is an orifice of predetermined size. 
     
     
       7. An apparatus in accordance with  claim 1 , wherein the restriction is a capillary tube of predetermined size. 
     
     
       8. An apparatus in accordance with  claim 1 , wherein the free piston machine is a free piston Stirling cycle machine, the first machine space is a back space and the second machine space is a work space. 
     
     
       9. An apparatus in accordance with  claim 1 , wherein the invention further comprises a second connector valve through which the first and second machine spaces are connected, a second check valve directed to permit a flow of working fluid from the second machine space to the first machine space when the second connector valve is open, and wherein the valve actuator is linked to the second connector valve for opening the second connector valve in response to the pressure of the first actuator chamber exceeding the pressure of the second actuator chamber.