Transient temperature control system and method for preventing destructive collisions in free piston machines

• US 6,782,700 B1
• Filed: 02/24/2004
• Issued: 08/31/2004
• Est. Priority Date: 02/24/2004
• Status: Active Grant

• Current Assignee: Sunpower Corporation (Totalenergies Se)
• Original Assignee: Sunpower Corporation (Totalenergies Se)
• Inventors: Holliday, Ezekiel S., Unger, Reuven Z-M
• Primary Examiner(s): NGUYEN, HOANG M
• Application Number:
  US10/785,319
• Time in Patent Office: 189 Days
• Field of Search: 605/17, 605/18, 605/23, 605/24
• US Class Current: 60/517
• CPC Class Codes: F25B 2309/001 with a linear configuration or a linear motor
• CPC Class Codes: F25B 2309/1428 Control of a Stirling refrigeration machine
• CPC Class Codes: F25B 2500/26 characterised by the startup of the refrigeration cycle
• CPC Class Codes: F25B 9/14 characterised by the cycle used, e.g. Stirling cycle

Abstract

The free piston cooler transient temperature control system of the present invention eliminates collisions during the transient cool-down period in a free piston cooler upon start-up. The transient temperature control system incorporates a free piston cooler, having a cold head and a warm end, a cold head temperature sensor, a relational interface, and a temperature controller. The cold head temperature sensor senses the temperature of the cold head and generates a temperature signal. The relational interface is in communication with the temperature signal and contains a predetermined relationship between the cold head temperature and a maximum piston stroke during the transient cool-down temperature range. The relational interface generates a transient range maximum allowable stroke signal from the temperature signal and the predetermined relationship. The temperature controller is in communication with the relational interface and limits the piston stroke during the transient cool-down temperature range to prevent collisions.

Claims

1. A transient temperature control system for preventing collisions during a transient cool-down temperature range of a free piston cooler from a first operating temperature of a cold head to a set point operating temperature, the cooler having a piston reciprocating in linear oscillation within a cylinder at a variable stroke, the system comprising:

(a) a cold head temperature sensor for sensing the temperature of the cold head and generating a temperature signal;

(b) a relational interface in communication with the temperature signal and containing a predetermined relationship between the cold head temperature and a maximum piston stroke during the transient cool-down temperature range, the relational interface generating a transient range maximum allowable stroke signal from the temperature signal and the predetermined relationship; and

(c) a temperature controller in communication with the relational interface, capable of receiving the transient range maximum allowable stroke signal and limiting the stroke to prevent collisions within the cooler during the transient cool-down temperature range, and capable of controlling the stroke of the piston while the cold head operates at approximately a steady state cold head temperature.

2. The control system in accordance with claim 1, wherein the predetermined relationship between the cold head temperature and the stroke comprises a plurality of stored data experimentally determined by operating the cooler during the transient cool-down temperature range, and recording the stroke resulting in collision at a plurality of cold head temperatures and generating a transient controlled stroke by applying a stroke reduction factor to the collision stroke.

3. The control system in accordance with claim 2, wherein the plurality of stored data are resident in a table form for reference by the relational interface in generating the transient range maximum allowable stroke signal.

4. The control system in accordance with claim 2, wherein the plurality of stored data are resident as a stored algorithm for reference by the relational interface in generating the transient range maximum allowable stroke signal.

5. A method for preventing collisions during a transient cool-down temperature range of a free piston cooler from a first operating temperature of a cold head to a set point operating temperature, the cooler having a piston reciprocating in linear oscillation within a cylinder at a variable stroke, the method comprising:

(a) sensing the temperature of the cold head and generating a temperature signal;

(b) generating a transient range maximum allowable stroke signal in response to the temperature signal and a predetermined relationship between the cold head temperature and a maximum piston stroke during the transient cool-down temperature range; and

(c) limiting the stroke of the piston during the transient cool-down temperature range, to prevent collisions within the cooler, in response to the transient range maximum allowable stroke signal.

6. The method in accordance with claim 5, further including the step of experimentally developing the predetermined relationship between the cold head temperature and the stroke by operating the cooler during the transient cool-down temperature range, and recording the stroke resulting in collision at a plurality of cold head temperatures and generating a transient controlled stroke by applying a stroke reduction factor to collision stroke.

7. The method in accordance with claim 6, further including the step of referencing an electronic database, having the predetermined relationship between the cold head temperature and the stroke, when generating the transient range maximum allowable stroke signal.

8. The method in accordance with claim 6, further including the step of referencing an algorithm, having the predetermined relationship between the cold head temperature and the stroke, when generating the transient range maximum allowable stroke signal.

9. An apparatus for preventing collisions during a transient cool-down temperature range of a free piston cooler from a first operating temperature of a cold head to a set point operating temperature, the cooler having a piston reciprocating in linear oscillation within a cylinder at a variable stroke, the apparatus comprising:

(a) a means for sensing the temperature of the cold head and generating a temperature signal;

(b) a means for generating a transient range maximum allowable stroke signal from the temperature signal and a predetermined relationship between the cold head temperature and a maximum piston stroke during the transient cool-down temperature range; and

(c) a means for controlling the stroke of the piston during the transient cool-down temperature range, to prevent collisions within the cooler, from the transient range maximum allowable stroke signal, and controlling the stroke of the piston during approximately steady state cold head temperature conditions to prevent collisions within the cooler.

10. The apparatus in accordance with claim 9, wherein the predetermined relationship between the cold head temperature and the stroke comprises a plurality of stored data experimentally determined by operating the cooler during the transient cool-down temperature range, and recording the stroke resulting in collision at a plurality of cold head temperatures and generating a transient controlled stroke by applying a stroke reduction factor to the collision stroke.

11. The apparatus in accordance with claim 10, wherein the plurality of stored data are resident in a table form for reference by the generating means in generating the transient range maximum allowable stroke signal.

12. The control system in accordance with claim 10, wherein the plurality of stored data are resident as a stored algorithm for reference by the generating means in generating the transient range maximum allowable stroke signal.