Pumps – Processes
Reexamination Certificate
2000-03-21
2002-05-21
Tyler, Cheryl J. (Department: 3746)
Pumps
Processes
C417S222200
Reexamination Certificate
active
06390782
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to control valves, and in particular, to a control valve for a variable displacement gas compressor for use in an air conditioning or refrigeration system
2. Description of the Related Art
A gas compressor will change a state of a gas from a low-pressure state to a high-pressure state. Such a compressor is often used in air-conditioning (A/C) systems where expansion of a refrigerant gas compressed by the compressor causes air passing over evaporator gas tubes to cool. After the gas has expanded, it is recycled through the compressor so to be compressed again.
The refrigerant gas is discharged by the compressor at a high pressure known as the discharge pressure. It moves to a condenser, where the high pressure, high temperature gas condenses into a high pressure, high temperature liquid, the energy required for the state change being transferred to air passing over the condenser fins in the form of heat. From the condenser, the liquid travels through an expansion device, where it expands, to an evaporator where it evaporates. The air passing over the evaporator coils gives off its heat to the refrigerant, providing energy needed for the state change. The cooled air passes out into the compartment to be cooled. The degree to which the air is cooled is proportional to the amount of expansion of the refrigerant gas, and the amount of expansion of the gas is directly proportional to how much gas is compressed within the compressor. The pressure of the gas is controlled within the compressor by the amount of displacement of the piston within the compression chamber.
A key concern in designing a cooling system utilizing refrigerant gas is too ensure that the liquid from the condenser does not flow in a quantity and temperature to push the evaporator below the freezing point of water. If there is too much heat absorption by the gas within the evaporator, the water found on the fins and tubes through condensation of water from air passing over the evaporator will freeze up, choking off air flow over the evaporator, thereby cutting off the flow of cool air to the passenger compartment. For this reason, most conventional control valves are calibrated to change the stroke (displacement) of the compressor based on the pressure of the gas returning to the compressor at a set pressure of the gas. The gas returns to the suction area of the compressor. The pressure in this area of the compressor is known as the suction pressure. The desired suction pressure, around which the stroke of the compressor is changed, is known within the art as the set-point suction pressure.
In 1984, a variable displacement refrigerant compressor was introduced which adjusted the flow of the refrigerant gas through the system by varying the stroke of the piston in the pumping mechanism of the compressor in the manner just described. This system was designed for use in an automobile, deriving power to drive the compressor using a drive belt coupled to the vehicle's engine. In operation, when the A/C system load is low, the piston stroke of the compressor is shortened so that the compressor pumps less refrigerant per revolution of the engine drive belt. This allows just enough refrigerant to satisfy the cooling demands of the automobile's occupants. When the A/C system load is high, the piston stroke is lengthened and pumps more refrigerant per revolution of the engine drive belt.
A description of this prior art variable displacement compressor and a conventional pneumatic control valve (CV) is found in U.S. Pat. No. 4,428,718 by Skinner (Skinner '718) which is assigned to the General Motors Corporation of Detroit, Mich. The Skinner '718 description and explanation of the variable displacement compressor, general function, and interaction of the CV with the compressor is hereby incorporated by reference.
FIG. 9
shows a variable displacement refrigerant compressor as described by Skinner '718. There is shown a variable displacement refrigerant compressor
210
of the variable angle wobble plate type connected in an automotive air conditioning system having the normal condenser
212
, orifice tube
214
, evaporator
216
and accumulator
218
arranged in that order between the compressor's discharge and suction sides. The compressor
210
comprises a cylinder block
220
having a head
222
and a crankcase
224
sealingly clamped to opposite ends thereof. A drive shaft
226
is supported centrally in the compressor at the cylinder block
220
and crankcase
224
by bearings. The drive shaft
226
extends through the crankcase
224
for connection to an automotive engine (not shown) by an electromagnetic clutch
236
which is mounted on the crankcase
224
and is driven from the engine by a belt
238
engaging a pulley
240
on the clutch
236
.
The cylinder block
220
has five axial cylinders
242
through it (only one being shown), which are equally spaced about and away from the axis of drive shaft
226
. The cylinders
242
extend parallel to the drive shaft
226
and a piston
244
is mounted for reciprocal sliding movement in each of the cylinders
242
. A separate piston rod
248
connects the backside of each piston
244
to a non-rotary, ring-shaped, wobble plate
250
.
The non-rotary wobble plate
250
is mounted at its inner diameter
264
on a journal
266
of a rotary drive plate
268
. The drive plate
268
is pivotally connected at its journal
266
by a pair of pivot pins (not shown) to a sleeve
276
which is slidably mounted on the drive shaft
226
, to permit angulation of the drive plate
268
and wobble plate
250
relative to the drive shaft
226
. The drive shaft
226
is drivingly connected to the drive plate
268
. The wobble plate
250
while being angularable with the rotary drive plate
268
is prevented firm rotating therewith by a guide pin
270
.
The angle of the wobble plate
250
is varied with respect to the axis of the drive shaft
226
between the solid line large angle position shown in
FIG. 9
, which is full-stroke, to the zero angle phantom-line position shown, which is zero stroke, to thereby infinitely vary the stroke of the pistons and thus the displacement or capacity of the compressor between these extremes. There is provided a split ring return spring
272
which is mounted in a groove on the drive shaft
226
and has one end that is engaged by the sleeve
276
during movement to the zero wobble angle position and is thereby conditioned to initiate return movement.
The working ends of the cylinders
242
are covered by a valve plate assembly
280
, which is comprised of a suction valve disk and a discharge valve disk, clamped to the cylinder block
220
between the latter and the head
222
. The head
222
is provided with a suction area
282
which is connected through an external port
284
to receive gaseous refrigerant from the accumulator
218
downstream of the evaporator
216
. The suction area
282
is open to an intake port
286
in the valve plate assembly
280
at the working end of each of the cylinders
242
where the refrigerant is admitted to the respective cylinders on their suction stroke each through a reed valve formed integral with the suction valve disk at these locations. Then on the compression stroke, a discharge port
288
open to the working end of each cylinder
242
allows the compressed refrigerant to be discharged into a discharge area
290
in the head
222
by a discharge reed valve which is formed integral with the discharge valve disk. The compressor's discharge area
290
is connected to deliver the compressed gaseous refrigerant to the condenser
212
from whence it is delivered through the orifice tube
214
back to the evaporator
216
to complete the refrigerant circuit as shown in FIG.
9
.
The wobble plate angle and thus compressor displacement can be controlled by controlling the refrigerant gas pressure in the sealed interior
278
of the crankcase behind the pistons
244
relative to the suction pressure. In this
Ballard Jay Arthur
Ballard Mark Paul
Booth Steven Brent
Alumina Micro LLC
Tyler Cheryl J.
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