Two stage reciprocating compressors and associated HVAC systems and methods

A variable capacity gas compressor having a block with a plurality of cylinders formed therethrough, said cylinders having open discharge ends, a piston reciprocally mounted in each said cylinder, a valve plate mounted on said block over the open ends of said cylinders and defining a plurality of compression chambers, said plate having a plurality of discharge valves adapted to place said compression chambers in communication with the high side of said compressor, a plurality of suction valves on said compressor adapted to place said compression chambers in communication with the low side of said compressor, a crankshaft rotatably mounted on said block and having a rotational axis and a plurality of crankpins formed thereon, a connecting rod for each said piston and mounted on a crankpin, at least one of said crankpins being complex and having an eccentric cam rotatably mounted on an inner shaft of said crankpin and serving as a journal for said bearing means, at least one stop element on said crankshaft at one or more predesigned angular positions, at lest one dog element on said cam at one or more predesigned angular positions, said stop and dog elements defining end points of rotatability of said cam on said crankpin shaft, a reversible motor on said compressor for driving said crankshaft selectively in either rotational direction in accordance with operational signals transmitted thereto, said cam being rotatable to one said end point upon rotation of said crankshaft in one direction and to the other end point upon rotation of said crankshaft in the reverse direction, said stop and dog elements forming a junction at each said end point, and a stabilizing structure for at least one of said junctions and comprising at least one structure selected from the group consisting of:

• (A) a positive lock structure selected from the group consisting of
• (a) a latching device having cooperating elements on said crankshaft and cam, said elements being engageable and disengageable at least at one of said end points by the application of or the release of, respectively, centrifugal force applied to one of said elements, or
• (b) a pressure differential operable device having cooperating elements on said crankshaft and cam, said elements being engageable and disengageable by sudden and opposite angular motion respectively between said crankpin shaft and cam at least at one of said end points;
• (B) a friction drag device having cooperating elements on said cam and said crankpin shaft and being engageable to resist destabilizing forces tending to rotate said cam on said crankpin shaft and separate the junction at least at one of said end points;
• and
• (C) a pressure regulating device which functions to minimize any differential in pressure between the low side of the compressor and the compression chamber of a cylinder which has been placed in a passive mode.

A two stage reciprocating compressor comprising:

• a block having at least one cylinder and an associated compression chamber and piston;
• a crankshaft including an eccentric crankpin;
• a reversible motor for rotating that crankshaft in a forward and a reverse direction;
• an eccentric, two position cam rotatably mounted over the crankpin, said cam rotating to and operating at a first position relative to said crankpin when the motor is running in the forward direction and rotating to and operating at a second position relative to said crankpin when the motor is running in the reverse direction,
• the eccentricities of said crankpin and said cam combining to cause the piston to have a first stroke when the motor operates in the forward direction and a second stroke when the motor operates in the reverse direction, said second stroke being less than the first stroke;
• and
• a control for selectively operating said motor either in the forward direction at a first preselected fixed power load or in the reverse direction at a second preselected fixed power load, said second power load being less than said first power load.

A two stage reciprocating compressor comprising:

• a block having at least two cylinders in the block, the first cylinder having an associated first compression chamber and a piston and the second cylinder having an associated second compression chamber and piston;
• a reversible motor for rotating in a forward and a reverse direction,
• a mechanical system between the motor and the pistons that causes both pistons to reciprocate within the cylinders at their respective full strokes when the motor is rotated in the forward direction and that causes the first piston to reciprocate at full stroke and the second piston to have a substantially zero stroke, when the motor is rotated in the reverse direction;
• a control for selectively operating said motor in the forward direction at a first preselected fixed power load or in the reverse direction at a second preselected fixed power load, said second power load being less than said first power load;
• and
• a pressure relief system associated with the compression chamber of the second piston for relieving any pressure differential between the low side of the compressor and the compression chamber of the second piston when the motor rotates in the reverse direction.

A crankshaft for a variable load compressor having at least one cylinder and an associated piston driven by the combination of a crankpin and an eccentric cam on the crankpin, the crankshaft comprising:

• a shaft with a proximal end and a distal end with at least one eccentric crankpin formed between the proximal and distal ends;
• one or more stops formed on or adjacent the crankpin at a pair of angularly separate points;
• an eccentric cam for riding on said crankpin, said cam having a diameter equal to or larger than the diameter of the crankshaft at its distal end, said cam including a pair of dogs for selective engagement with said stops;
• and
• a mechanical system for holding the cam in its axial position on the crankpin.

A method of assembling a crankshaft with a eccentric cam comprising the steps of:

• providing a crankshaft with proximal and distal ends, a sump journal on the distal end of the crankshaft and axially aligned with the crankshaft, an idler segment adjacent the sump journal and out of alignment with the axis of the crankshaft, and a crankpin between the idler segment and the proximal end of the crankshaft, said crankpin including a radial hole formed in it and extending to its outer surface;
• providing an eccentric cam having an internal bore equal to or larger than the diameter of the sump journal and the idler segment and an axial length less than the axial length of the idler segment;
• sliding the cam over the sump journal and idler segment and onto the crankpin;
• connecting the cam to the crankpin by inserting a pin through the radial hole of the crankpin until the pin is fixed to the crankpin.

A two stage reciprocating compressor comprising:

• a block;
• at least one cylinder having an associated compressor chamber and associated piston;
• a crankshaft including a crankpin;
• a reversible motor for rotating the crankshaft;
• a connecting rod attached at one end to said piston and having a circular bearing surface at the other end;
• an eccentric, two position cam rotatably mounted over the crankpin and rotatably held within the circular bearing surface of said connecting rod, said cam operating in the first position when the motor rotates in a forward direction and a second position when the motor rotates in a reverse direction;
• the eccentricities of said crankpin and said cam combining to cause the piston to have a first stroke when the motor rotates in the forward direction and a second stroke when the motor rotates in the reverse direction, said second stroke being less than the first stroke;
• and
• a lubricating system for applying lubricant to the engaging surfaces of the crankshaft and the cam and between the cam and the bearing surface of the connecting rod.

A system for cooling a space comprising:

• a two stage compressor that operates either at a first fixed maximum load or at a reduced second fixed load;
• an evaporator, a condenser, and an expansion device in a refrigeration loop with said compressor;
• a two stage evaporator blower that operates either at a first fixed maximum load or at a second reduced fixed load;
• and
• a control system interconnected with the compressor and blower and designed to operate the compressor and blower at the respective first stages when the cooling requirement exceeds a preselected value and at the respective second stages when the cooling requirements fall below that preselected value.

A method of cooling a space comprising the steps of:

• providing an air conditioning system including a two stage compressor having a first fixed load and a second fixed load, an evaporator, a two stage evaporator blower, an expansion device, and a condenser;
• sensing the condition of the space to be cooled;
• and
• controlling the compressor and blower motor to operate at their respective first stages when cooling load exceeds a predetermined level and to operate at their respective second stages when the cooling load falls below the predetermined level.

A heat pump system comprising:

• a two-stage compressor;
• condenser;
• an expansion device;
• an evaporator;
• means for operating the compressor, condenser, expansion device, and evaporator as a heat pump that can selectively provide air conditioning and heating, as required;
• and
• a control system for operating the system in a heating mode with the compressor running at the first stage or the second stage, based upon the heating requirements, and for operating the system in an air conditioning mode with the compressor running only at the first stage.

A method of cooling and heating a space with a heat pump in a cold climate environment, said method including the steps of:

• providing a heat pump system including a two stage compressor having a fixed first load and a fixed second load, a condenser, an evaporator, and a single expansion device;
• sensing the outside temperature;
• operating the compressor only at the first stage when the system is operating in the cooling mode;
• running the compressor at the first stage in the heating mode whenever the outside temperature is above the preselected limit;
• and
• operating the compressor at the second stage in the heating mode whenever the temperature outside falls below a preselected limit.