Floating rod seal for a stirling cycle machine

An external combustion engine containing a working fluid comprising:

• an airlock space, the airlock space separating a working space from a crankcase, wherein the working space is filled with working fluid at an oscillating working fluid pressure and the crankcase is filled with crankcase fluid at a crankcase pressure;
• an airlock pressure regulator for maintaining a pressure differential between the crankcase fluid and the working fluid;
• and
• a piston rod seal unit comprising:
• a housing located between the working space and the airlock space, wherein a pressure difference between the working space and the airlock space varies with time;
• a cylinder gland;
• and
• at least one floating rod seal assembly mounted in the cylinder gland, the floating rod seal assembly comprising:
• a first stationary bushing mounted to the floating rod seal assembly, the first stationary bushing having a first contacting surface;
• a second stationary bushing mounted to the floating rod seal assembly, the second stationary bushing having a second contacting surface;
• a floating bushing, the floating bushing being located between the first and second stationary bushings, the floating bushing comprising a third contacting surface and a fourth contacting surface, the floating bushing having an axial dimension smaller than the first axial distance, one of the third contacting surface and fourth contacting surface alternatingly forming a metal to metal seal first with the first contacting surface and second with the second contacting surface;
• and
• at least one rod seal mounted onto the floating bushing.

A method to axially seal a reciprocating rod passing through a housing, the housing separating a first volume at a first varying pressure from a second volume at a second varying pressure, the method comprising:

• mounting a cylinder gland to the housing;
• mounting a first stationary bushing in the cylinder gland;
• placing a floating bushing in the cylinder gland substantially axially aligned with the first stationary bushing;
• mounting a second stationary bushing in the cylinder gland at a first axial distance from the first stationary bushing and substantially aligned with the first stationary bushing;
• creating an axial seal between the reciprocating rod and the floating bushing with a rod seal mounted to the floating bushing;
• creating an axial seal between the floating bushing and the first stationary bushing when the first varying pressure is less than the second varying pressure;
• allowing the floating bushing to move radially when the first varying pressure is substantially equal to the second varying pressure;
• and
• reforming an axial seal between the floating bushing and the second stationary bushing when the first varying pressure is greater than the second varying pressure.

A piston rod seal unit comprising:

• a housing located between a first volume and a second volume, wherein a pressure difference between the first volume and the second volume varies with time;
• a cylinder gland;
• and
• at least one floating rod seal assembly mounted in the cylinder gland, the floating rod seal assembly comprising:
• a first stationary bushing rigidly mounted to the floating rod seal assembly, the first stationary bushing haying a first contacting surface;
• a second stationary bushing rigidly mounted to the floating rod seal assembly, the second stationary bushing having a second contacting surface, the second stationary bushing defining an axial gap relative to the first stationary bushing, the axial gap having a first axial distance;
• a floating bushing, the floating bushing having a circumferential rib, the circumferential rib being located between the first and second stationary bushings, the circumferential rib having a thickness less than the first axial distance, the circumferential rib comprising a third contacting surface and a fourth contacting surface, only one of the third contacting surface and fourth contacting surface forming a metal to metal seal with one of the first contacting surface and second contacting surface;
• and
• at least one rod seal mounted onto the floating bushing.

A piston rod seal unit comprising:

• a housing located between a first volume and a second volume, wherein a pressure difference between the first volume and the second volume varies with time;
• a cylinder gland mounted to the housing and located within the first volume;
• a scraper ring mounted in the cylinder gland, the scraper ring exposed to the first volume;
• a port in the cylinder gland, the port fluidically connecting the first volume to an interior volume inside the cylinder gland, the interior volume in fluid communication with the scraper ring;
• a filter on the port;
• and
• at least one floating rod seal assembly mounted in the cylinder gland, the floating rod seal assembly comprising:
• a first stationary bushing rigidly mounted to the floating rod seal assembly, the first stationary bushing having a first contacting surface
• a second stationary bushing rigidly mounted to the floating rod seal assembly, the second stationary bushing having a second contacting surface, wherein the second stationary bushing is located a first axial distance from the first stationary bushing;
• a floating bushing, the floating bushing being located between the first and second stationary bushings, the floating bushing comprising a third contacting surface and a fourth contacting surface, the floating bushing having an axial dimension smaller than the first axial distance, only one of the third contacting surface and fourth contacting surface forming a metal to metal seal with one of the first contacting surface and second contacting surface;
• and
• at least one rod seal mounted onto the floating bushing.