Patent Description:
HVAC&R systems are used in a variety of settings and for many purposes. For example, HVAC&R systems may include a vapor compression refrigeration cycle (e.g., a refrigerant circuit having a condenser, an evaporator, a compressor, and/or an expansion device) configured to condition an environment. The vapor compression refrigeration cycle may include a compressor that is configured to direct refrigerant through various components of the refrigerant circuit. In some cases, a pressure of refrigerant at various positions along the refrigerant circuit may fluctuate during operation of the vapor compression refrigeration cycle. Accordingly, a compression ratio (e.g., a ratio between a low or suction pressure and a high or discharge pressure) of the compressor may be adjusted to maintain operating parameters of the vapor compression refrigeration cycle at target levels. To adjust the compression ratio of the compressor, a speed of one or more rotors of the compressor may be adjusted via a motor or another suitable drive. Additionally, a volume ratio of the compressor may be adjusted based on the compression ratio to maintain a performance of the compressor.

Existing compressors may be configured to adjust the volume ratio in response to a given compression ratio via stepwise control of a piston between one or more positions. Additionally or alternatively, a proportional valve may be utilized to supply a fluid into a piston chamber to adjust the position of the piston.

For example, <CIT> relates to a variable-efficiency screw compressor for use in a closed-looped system configured to perform refrigeration is provided. The known variable-efficiency screw compressor includes an inlet port to draw refrigerant into the variable-efficiency screw compressor, one or more rotating screws in fluid communication with the inlet port to compress the refrigerant, forming a compressed refrigerant, a discharge port in fluid communication with the rotating screws to receive the compressed refrigerant and discharge the refrigerant, wherein the discharge port includes an adjustable piston movable within the discharge port by means of a pressure fed through a proportional valve from a first position in which volume is higher to a second position in which volume is lower, the adjustable piston arranged and disposed to adjust volume of the discharge port in response to a change in demand.

Unfortunately, existing techniques for controlling the volume ratio of the compressor may be limited based on the finite number of positions of the piston and/or may increase costs by including additional components, such as the proportional valve and corresponding control devices.

The invention is solely defined by the subject-matter of the appended claims.

These described embodiments are only examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification.

As discussed above, a vapor compression refrigeration cycle may include a compressor that is configured to circulate a refrigerant through a refrigerant circuit of the vapor compression refrigeration cycle. In some cases, various operating parameters of the refrigerant may fluctuate during operation of the vapor compression refrigeration cycle. A compression ratio of the compressor may be adjusted in order to maintain and/or adjust operating parameters of the refrigerant within the refrigerant circuit toward target levels. The compression ratio of the compressor may be controlled via a motor that supplies torque to one or more rotors of the compressor. Therefore, an operating speed of the motor is adjusted in order to control the compression ratio to be a target value. Further, a volume ratio of the compressor may be adjusted based on the compression ratio in order to maintain a performance (e.g., an efficiency) of the compressor during operation. Indeed, in some cases, an amount of refrigerant drawn into the compressor may exceed an amount that achieves the target compression ratio. Accordingly, the volume ratio may be adjusted by enabling refrigerant to bypass a compression portion of the compressor in order to reduce the volume ratio. Similarly, an amount of refrigerant drawn into the compressor may be less than an amount that achieves the target compression ratio. In such instances, the volume ratio may be adjusted by blocking refrigerant from bypassing the compression portion in order to increase the volume ratio of the compressor.

Existing compressors may control the volume ratio of the compressor using a piston that may be adjusted to a finite number of positions. For example, the piston may be in fluid communication with a high pressure side of the compressor to enable the refrigerant to bypass the compression portion of the compressor based on the position of the piston. Further, some existing compressors may include a proportional valve that directs a working fluid toward a piston chamber to generate movement of the piston, thereby providing control over the position of the piston. However, such existing systems may be limited in controlling the volume ratio and/or may increase costs of the vapor compression refrigeration cycle.

As such, embodiments of the present disclosure are directed to an improved volume ratio control system that may enhance control of the volume ratio of the compressor without including relatively expensive components. For instance, the volume ratio control system of the present disclosure may include a biasing device, such as a spring, to control a position of a piston disposed within a chamber of the compressor. The chamber and/or the piston may be in fluid communication with both a low pressure portion (e.g., suction side) of the compressor and a high pressure portion (e.g., discharge side) of the compressor, such that a pressure differential is generated within the chamber and/or across the piston. Under some operating conditions, the pressure differential within the chamber and/or across the piston may exceed a threshold, thereby causing the piston to move in a first direction to adjust the volume ratio of the compressor (e.g., increase the volume ratio of the compressor in response to an increase in compression ratio). When the pressure differential falls below the threshold, the biasing device may cause the piston to move in a second direction, opposite the first direction, to adjust the volume ratio of the compressor (e.g., decrease the volume ratio of the compressor in response to a reduction in compression ratio). The piston may be configured to move in the second direction to expose openings that enable refrigerant to bypass a compression portion (e.g., at least a portion of a compression chamber) of the compressor, such that the volume ratio is reduced when the piston exposes or does not cover the openings. Similarly, the volume ratio of the compressor may be increased when the piston moves in the first direction to cover and/or block the openings, thereby reducing the amount of refrigerant that bypasses the compression portion. The volume ratio control system of the present disclosure is thus a passive system that utilizes the pressure differential within the chamber and a biasing force applied to the piston by the biasing device in order to adjust the volume ratio of the compressor. Indeed, the volume ratio control system may be infinitely variable, such that the piston may move toward virtually any position within the chamber and is not limited to predetermined or discrete positions.

Turning now to the drawings, <FIG> is a perspective view of an embodiment of an environment for a heating, ventilation, air conditioning, and/or refrigeration (HVAC&R) system <NUM> in a building <NUM> for a typical commercial setting. The HVAC&R system <NUM> may include a vapor compression system <NUM> that supplies a chilled liquid, which may be used to cool the building <NUM>. The HVAC&R system <NUM> may also include a boiler <NUM> to supply warm liquid to heat the building <NUM> and an air distribution system which circulates air through the building <NUM>. The air distribution system can also include an air return duct <NUM>, an air supply duct <NUM>, and/or an air handler <NUM>. In some embodiments, the air handler <NUM> may include a heat exchanger that is connected to the boiler <NUM> and the vapor compression system <NUM> by conduits <NUM>. The heat exchanger in the air handler <NUM> may receive either heated liquid from the boiler <NUM> or chilled liquid from the vapor compression system <NUM>, depending on the mode of operation of the HVAC&R system <NUM>. The HVAC&R system <NUM> is shown with a separate air handler on each floor of building <NUM>, but in other embodiments, the HVAC&R system <NUM> may include air handlers <NUM> and/or other components that may be shared between or among floors.

<FIG> and <FIG> illustrate embodiments of the vapor compression system <NUM> that can be used in the HVAC&R system <NUM>. The vapor compression system <NUM> may circulate a refrigerant through a circuit starting with a compressor <NUM>. The circuit may also include a condenser <NUM>, an expansion valve(s) or device(s) <NUM>, and a liquid chiller or an evaporator <NUM>. The vapor compression system <NUM> may further include a control panel <NUM> (e.g., a controller) that has an analog to digital (A/D) converter <NUM>, a microprocessor <NUM>, a non-volatile memory <NUM>, and/or an interface board <NUM>.

In some embodiments, the vapor compression system <NUM> may use one or more of a variable speed drive (VSDs) <NUM>, a motor <NUM>, the compressor <NUM>, the condenser <NUM>, the expansion valve or device <NUM>, and/or the evaporator <NUM>. The motor <NUM> may drive the compressor <NUM> and may be powered by a variable speed drive (VSD) <NUM>. The VSD <NUM> receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor <NUM>. In other embodiments, the motor <NUM> may be powered directly from an AC or direct current (DC) power source. The motor <NUM> may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor <NUM> compresses a refrigerant vapor and delivers the vapor to the condenser <NUM> through a discharge passage. In some embodiments, the compressor <NUM> may be a screw compressor. The compressor <NUM> includes a fluid (e.g., oil) that lubricates components of the compressor. The refrigerant vapor delivered by the compressor <NUM> to the condenser <NUM> may transfer heat to a cooling fluid (e.g., water or air) in the condenser <NUM>. The refrigerant vapor may condense to a refrigerant liquid in the condenser <NUM> as a result of thermal heat transfer with the cooling fluid. The refrigerant liquid from the condenser <NUM> may flow through the expansion device <NUM> to the evaporator <NUM>. In the illustrated embodiment of <FIG>, the condenser <NUM> is water cooled and includes a tube bundle <NUM> connected to a cooling tower <NUM>, which supplies the cooling fluid to the condenser <NUM>.

The refrigerant liquid delivered to the evaporator <NUM> may absorb heat from another cooling fluid, which may or may not be the same cooling fluid used in the condenser <NUM>. The refrigerant liquid in the evaporator <NUM> may undergo a phase change from the refrigerant liquid to a refrigerant vapor. As shown in the illustrated embodiment of <FIG>, the evaporator <NUM> may include a tube bundle <NUM> having a supply line <NUM> and a return line 60R connected to a cooling load <NUM>. The cooling fluid of the evaporator <NUM> (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator <NUM> via return line 60R and exits the evaporator <NUM> via supply line <NUM>. The evaporator <NUM> may reduce the temperature of the cooling fluid in the tube bundle <NUM> via thermal heat transfer with the refrigerant. The tube bundle <NUM> in the evaporator <NUM> can include a plurality of tubes and/or a plurality of tube bundles. In any case, the refrigerant vapor exits the evaporator <NUM> and returns to the compressor <NUM> by a suction line to complete the cycle.

<FIG> is a schematic diagram of the vapor compression system <NUM> with an intermediate circuit <NUM> incorporated between condenser <NUM> and the expansion device <NUM>. The intermediate circuit <NUM> may have an inlet line <NUM> that is directly fluidly connected to the condenser <NUM>. In other embodiments, the inlet line <NUM> may be indirectly fluidly coupled to the condenser <NUM>. As shown in the illustrated embodiment of <FIG>, the inlet line <NUM> includes a first expansion device <NUM> positioned upstream of an intermediate vessel <NUM>. In some embodiments, the intermediate vessel <NUM> may be a flash tank (e.g., a flash intercooler). In other embodiments, the intermediate vessel <NUM> may be configured as a heat exchanger or a "surface economizer. " In the illustrated embodiment of <FIG>, the intermediate vessel <NUM> is used as a flash tank, and the first expansion device <NUM> is configured to lower the pressure of (e.g., expand) the refrigerant liquid received from the condenser <NUM>. During the expansion process, a portion of the liquid may vaporize, and thus, the intermediate vessel <NUM> may be used to separate the vapor from the liquid received from the first expansion device <NUM>. Additionally, the intermediate vessel <NUM> may provide for further expansion of the refrigerant liquid because of a pressure drop experienced by the refrigerant liquid when entering the intermediate vessel <NUM> (e.g., due to a rapid increase in volume experienced when entering the intermediate vessel <NUM>). The vapor in the intermediate vessel <NUM> may be drawn by the compressor <NUM> through a suction line <NUM> of the compressor <NUM>. In other embodiments, the vapor in the intermediate vessel may be drawn to an intermediate stage of the compressor <NUM> (e.g., not the suction stage). The liquid that collects in the intermediate vessel <NUM> may be at a lower enthalpy than the refrigerant liquid exiting the condenser <NUM> because of the expansion in the expansion device <NUM> and/or the intermediate vessel <NUM>. The liquid from intermediate vessel <NUM> may then flow in line <NUM> through a second expansion device <NUM> to the evaporator <NUM>.

As discussed above, embodiments of the present disclosure are directed to an improved volume ratio control system for a compressor, such as the compressor <NUM>. The volume ratio control system includes a piston and a rod (e.g., a stationary rod) disposed within a chamber of the compressor. The piston is disposed within at least a portion of the chamber that is exposed to a high pressure side of the compressor. For example, the high pressure side may be a discharge side of the compressor, such that an exterior surface of the piston is also exposed to the discharge side of the compressor (e.g., a discharge pressure of the compressor). In some embodiments, the exterior surface of the piston may be additionally or alternatively be exposed to an oil pressure of the compressor. Further, a cavity of the piston is in fluid communication with a low pressure side of the compressor. For example, the low pressure side may be a suction side of the compressor (e.g., a suction pressure of the compressor), thereby exposing an interior surface of the piston to the suction side of the compressor. As such, a pressure differential force may be applied to the piston as opposing pressure forces applied to the exterior surface and the interior surface of the piston vary. The pressure differential force may at least partially control a position of the piston with respect to the chamber and/or the rod. Additionally, a biasing device, such as a spring, may be disposed in the cavity between the piston and the rod. The biasing device directs movement of the piston (e.g., with respect to the rod) when the pressure differential force falls below a threshold value. As used herein, the threshold value of the pressure differential force may be a function of a biasing force of the biasing device and/or a position of the piston within the chamber (and/or with respect to the rod). Indeed, the threshold value of the pressure differential force may change based at least on a current length and/or a current level of extension of the biasing device. For instance, the biasing force exerted by the biasing device may change as the biasing device extends and/or contracts from a natural or unbiased position (e.g., the biasing force increases as the biasing device moves further from the natural or unbiased position).

In any case, the volume ratio control system of the present disclosure is passive in that the volume ratio control system adjusts the volume ratio of the compressor as a result of the pressure differential established between the chamber and the cavity of the piston, which may be indicative of the compression ratio of the compressor. In other words, additional mechanical components, such as valves, motors, and/or other devices, may not be included to adjust the volume ratio of the compressor. Further, the volume ratio control system is generally infinitely variable because a position of the piston within the chamber is not limited to stepwise or predetermined positions. Therefore, the volume ratio control system enables accurate and/or precise volume ratio control of the compressor without including relatively expensive components that add costs to the vapor compression system <NUM>.

For example, <FIG> is a cutaway perspective view of an embodiment of a compressor <NUM>, such as the compressor <NUM>, having a volume ratio control system <NUM>. As shown in the illustrated embodiment of <FIG>, the compressor <NUM> includes two volume ratio control systems <NUM>. In other embodiments, the compressor <NUM> may include a single volume ratio control system <NUM> or more than two volume ratio control systems <NUM> depending on a size and/or capacity of the compressor <NUM>. In any case, the compressor <NUM> may include a low pressure side <NUM> (e.g., suction side, suction portion) that draws refrigerant from a component disposed along a refrigerant circuit of the vapor compression system <NUM> (e.g., from the evaporator <NUM>) and a high pressure side <NUM> (e.g., a discharge side, discharge portion, oil pressure) that directs high-pressure refrigerant toward a component disposed along the refrigerant circuit (e.g., toward the condenser <NUM>). The compressor <NUM> includes rotors <NUM> that are configured to rotate and compress the refrigerant received on the low pressure side <NUM>, thereby increasing the pressure of the refrigerant exiting the compressor <NUM> via a discharge port positioned on the high pressure side <NUM>. For instance, the rotors <NUM> may be driven to rotate via a motor. As the rotors <NUM> rotate, threads of the rotors <NUM> may reduce a volume of the refrigerant within a compression chamber <NUM> of the compressor <NUM>, which in turn, increases the pressure of the refrigerant.

As shown in the illustrated embodiment of <FIG>, the compressor <NUM> includes openings <NUM> within a housing <NUM> of the compressor <NUM> that enable refrigerant to bypass at least a portion <NUM> of the compression chamber <NUM> and direct the refrigerant toward the high pressure side <NUM>. In other words, refrigerant flowing through the openings <NUM> may reduce an amount of refrigerant that is ultimately compressed by the rotors <NUM>, thereby reducing a volume ratio of the compressor <NUM>. In some embodiments, the openings <NUM> may be formed in a portion of the housing <NUM> associated with and/or containing one of the rotors <NUM>. For example, a first set of openings <NUM> may be formed in a portion of the housing <NUM> associated with and/or containing one of the rotors <NUM> (e.g., a male rotor), and a second set of openings <NUM> may be formed in a portion of the housing <NUM> associated with and/or containing another of the rotors <NUM> (e.g., a female rotor). As mentioned above, the illustrated compressor <NUM> includes two volume ratio control systems <NUM>. Each volume ratio control system <NUM> may be associated with one of the sets of openings <NUM> and may operate to occlude and/or expose the respective set of openings <NUM> in the manner described below. However, in other embodiments, the compressor <NUM> may include one volume ratio control system <NUM> associated with both sets of openings <NUM>, such that the single volume ratio control system <NUM> operates to occlude and/or expose the openings <NUM> associated with both rotors <NUM> (e.g., a male rotor and a female rotor).

The volume ratio control system <NUM> is configured to adjust an amount of the refrigerant within the compressor <NUM> that flows through the openings <NUM> and bypasses at least the portion <NUM> of the compression chamber <NUM>. For example, the volume ratio control system <NUM> includes a piston <NUM> (e.g., an annular piston) disposed within a chamber <NUM> formed into the housing <NUM>. The chamber <NUM> may be in fluid communication with the openings <NUM> and may extend into a first portion <NUM> of the housing <NUM> that is proximate to the low pressure side <NUM>. Additionally, the chamber <NUM> may extend into a second portion <NUM> of the housing <NUM> that is proximate to the high pressure side <NUM>. In any case, the piston <NUM> is configured to move within the chamber <NUM> to block and/or expose the openings <NUM> to control the amount of refrigerant bypassing the portion <NUM> of the compression chamber <NUM>.

As is described in further detail herein, movement of the piston <NUM> within the chamber <NUM> may be passively controlled by a biasing device <NUM> (e.g., a spring) and/or a pressure differential between a cavity <NUM> formed within the piston <NUM> (e.g., fluidly coupled to the low pressure side <NUM> of the compressor <NUM>, such as via ports, conduits, etc.) and at least a portion <NUM> of the chamber <NUM> (e.g., fluidly coupled to the high pressure side <NUM> of the compressor <NUM>, such as via a discharge line <NUM>). In some embodiments, the volume ratio control system <NUM> includes a rod <NUM> (e.g., a stationary rod) disposed within the chamber <NUM> and within the cavity <NUM> of the piston <NUM>. As shown in the illustrated embodiment of <FIG>, the biasing device <NUM> may be disposed between the rod <NUM> and the piston <NUM> within the cavity <NUM>. Additionally, the rod <NUM> may include a passage <NUM> that fluidly couples an additional portion <NUM> of the chamber <NUM> (e.g., fluidly coupled to the low pressure side <NUM> of the compressor <NUM>) and the cavity <NUM>. Accordingly, in some embodiments, the pressure within the cavity <NUM> of the piston <NUM> may be substantially equal to (e.g., within <NUM>% of, within <NUM>% of, or within <NUM>% of) a low or suction pressure of the compressor <NUM>.

In any case, the biasing device <NUM> and the pressure differential between the cavity <NUM> and the portion <NUM> of the chamber <NUM> may enable movement of the piston <NUM> within the chamber <NUM> and/or with respect to the rod <NUM>. For instance, the cavity <NUM> may include a relatively low pressure associated with refrigerant entering the compressor <NUM> on the low pressure side <NUM>, whereas the portion <NUM> of the chamber <NUM> may include a relatively high pressure associated with refrigerant exiting the compressor <NUM> on the high pressure side <NUM>. The pressure differential between the cavity <NUM> and the portion <NUM> of the chamber <NUM> may direct movement of the piston <NUM> within the chamber <NUM> upon reaching and/or exceeding a threshold pressure differential (e.g., a variable pressure differential threshold). For example, when the pressure differential is at and/or exceeds the threshold pressure differential, a force is exerted on the piston <NUM> to direct movement of the piston <NUM> in a first direction <NUM> along an axis <NUM> defining a length <NUM> (see, e.g., <FIG>) of the chamber <NUM>. As the piston <NUM> moves in the first direction <NUM>, the piston <NUM> may block and/or cover one or more of the openings <NUM> to the chamber <NUM> (e.g., block refrigerant from bypassing the portion <NUM> of the rotors <NUM> and/or compression chamber <NUM>). Accordingly, as the compression ratio of the compressor <NUM> increases, the volume ratio is increased by the volume ratio control system <NUM> to maintain a performance (e.g., efficiency) of the compressor <NUM>.

Further, the biasing device <NUM> exerts a force on the piston <NUM> that may direct movement of the piston <NUM> in a second direction <NUM>, opposite the first direction <NUM>, along the axis <NUM> when the pressure differential between the cavity <NUM> and the portion <NUM> falls below the pressure differential threshold (e.g., a variable pressure differential threshold). For example, the biasing device <NUM> may include target parameters that apply a target biasing force on the piston <NUM> at various positions within the chamber <NUM> to enable movement of the piston <NUM> in the second direction <NUM> when the pressure differential between the cavity <NUM> and the portion <NUM> falls below the pressure differential threshold for the given position of the piston <NUM> within the chamber <NUM>. Parameters of the biasing device <NUM> that may be selected or modified to achieve a desired biasing force or range of biasing forces may include a material (e.g., metal, polymer) of the biasing device <NUM>, a coil diameter of the biasing device <NUM>, an internal diameter of the biasing device <NUM>, an external diameter of the biasing device <NUM>, a coil pitch of the biasing device <NUM>, a number of coils of the biasing device <NUM>, a spring rate of the biasing device <NUM>, a free length of the biasing device <NUM>, a block length of the biasing device <NUM>, another suitable parameter of the biasing device <NUM>, or any combination thereof. In any case, the pressure differential between the cavity <NUM> and the portion <NUM> and the target biasing force of the biasing device <NUM> may passively direct movement of the piston <NUM> within the chamber <NUM> to adjust the volume ratio of the compressor <NUM>.

<FIG> is a schematic diagram of a cross-section of a portion of the compressor <NUM>, illustrating the chamber <NUM> of the volume ratio control system <NUM>. As shown in the illustrated embodiment of <FIG>, the piston <NUM> is disposed within the portion <NUM> of the chamber <NUM>. Additionally, the rod <NUM> extends between the additional portion <NUM> of the chamber <NUM> and the portion <NUM> of the chamber <NUM> via an opening <NUM> (e.g., an opening formed in the housing <NUM> between the portion <NUM> and the additional portion <NUM> of the chamber <NUM>). The rod <NUM> may be secured within the opening <NUM> via a fastener <NUM> (e.g., a threaded fastener), which may block movement of the rod <NUM> with respect to and/or within the chamber <NUM>. However, in other embodiments, the rod <NUM> may be secured within the opening <NUM> and/or relative to the chamber <NUM> via other mechanisms or features. For example, the rod <NUM> and the opening <NUM> may each include threads configured to engage with one another to secure the rod <NUM> within the opening <NUM>.

Further, the rod <NUM> may form a seal between the additional portion <NUM> of the chamber <NUM> and the portion <NUM> of the chamber <NUM> to maintain a pressure differential that is substantially equal to a pressure differential between the low pressure side <NUM> and the high pressure side <NUM> of the compressor <NUM>. In some embodiments, the rod <NUM> includes the passage <NUM> that enables fluid communication between the additional portion <NUM> of the chamber <NUM> and the cavity <NUM>. Accordingly, a pressure within the cavity <NUM> may be substantially equal to the suction pressure of the compressor <NUM> (e.g., the additional portion <NUM> of the cavity <NUM> is exposed to the low pressure side <NUM> of the compressor <NUM>). Additionally, the portion <NUM> of the chamber <NUM> may be fluidly coupled to the high pressure side <NUM> of the compressor <NUM> via the discharge line <NUM> and/or fluidly coupled to the openings <NUM>.

Thus, a first pressure force (e.g., represented by arrow <NUM>) may be applied to an interior surface <NUM> of the piston <NUM>, where the first pressure force is indicative of the low (e.g., suction) pressure of the compressor <NUM>. A second pressure force (e.g., represented by arrow <NUM>) may be applied to an exterior surface <NUM> of the piston <NUM>, where the second pressure force is indicative of the high (e.g., discharge, oil) pressure of the compressor <NUM>. The first (e.g., low) pressure force is less than the second (e.g., high) pressure force, such that a pressure differential force (e.g., a difference between the first pressure force and the second pressure force) may be applied to the piston <NUM> in the first direction <NUM>. Moreover, a biasing force (e.g., represented by arrow <NUM>) may be applied to the piston <NUM> by the biasing device <NUM> in the second direction <NUM> opposite the first direction <NUM>. Accordingly, when the pressure differential force exceeds the biasing force, the piston <NUM> moves in the first direction <NUM> toward an end <NUM> of the portion <NUM> of the chamber <NUM> that is proximate to the openings <NUM>. The piston <NUM> may cover and/or block one or more of the openings <NUM>, such that the volume ratio of the compressor <NUM> increases. Similarly, when the pressure differential force is less than the biasing force, the biasing device <NUM> enables the piston <NUM> to move in the second direction <NUM> away from the end <NUM> of the portion <NUM> of the chamber <NUM> proximate to the openings <NUM>. Thus, one or more of the openings <NUM> may be exposed or uncovered, such that refrigerant may bypass the portion <NUM> of the compression chamber <NUM> and reduce the volume ratio of the compressor <NUM>.

As shown in the illustrated embodiment, the piston <NUM> includes a first segment <NUM> and a second segment <NUM> that are each configured to move (e.g., jointly) in the first direction <NUM> and the second direction <NUM> within the portion <NUM> of the chamber <NUM>. For example, the first segment <NUM> and the second segment <NUM> may be a single piece that forms the piston <NUM>. The first segment <NUM> may include a first radial thickness <NUM> that is greater than a second radial thickness <NUM> of the second segment <NUM>. In some embodiments, an overall diameter <NUM> of the piston <NUM> corresponds to a diameter <NUM> of the portion <NUM> of the chamber <NUM>. For instance, the overall diameter <NUM> may be slightly less than the diameter <NUM> to enable the piston <NUM> to move along the axis <NUM> within the portion <NUM> of the chamber <NUM>.

As shown in the illustrated embodiment of <FIG>, the exterior surface <NUM> of the first segment <NUM> of the piston <NUM> is exposed to an interior of the portion <NUM> of the chamber <NUM>, and thus, refrigerant within the portion <NUM> of the chamber <NUM>. In some embodiments, the exterior surface <NUM> of the first segment <NUM> of the piston <NUM> may be exposed to an oil pressure of the compressor <NUM>. As set forth above, the refrigerant in the portion <NUM> may include a pressure that is substantially equal to the discharge pressure of refrigerant exiting the compressor <NUM> (and/or an oil pressure of the compressor <NUM>). Additionally, the second segment <NUM> of the piston <NUM> may include a second surface <NUM> that is also exposed to the interior of the portion <NUM> of the chamber <NUM> and, thus, the refrigerant within the portion <NUM> of the chamber <NUM> (and/or an oil pressure of the compressor <NUM>). As such, the exterior surface <NUM> and the second surface <NUM> may be exposed to refrigerant at substantially the same pressure. As is shown in <FIG>, a surface area of the exterior surface <NUM> is greater than a surface area of the second surface <NUM>, such that an increase in discharge (or oil) pressure may cause movement in the first direction <NUM> via a pressure force applied to the exterior surface <NUM>. Further still, the interior surface <NUM> of the first segment <NUM> of the piston <NUM> is exposed to refrigerant that includes a pressure substantially equal to the suction pressure of refrigerant entering the compressor <NUM>. Accordingly, as the pressure differential between the cavity <NUM> and the portion <NUM> of the chamber <NUM> increases, the piston <NUM> is directed in the first direction <NUM> via the pressure differential force.

In some embodiments, the biasing device <NUM> (e.g., a spring) may be disposed within the cavity <NUM> of the piston <NUM> between the rod <NUM> and an internal surface <NUM> of the piston <NUM>. The rod <NUM> may be substantially stationary within the chamber <NUM>, such that the piston <NUM> is configured to move along at least a portion of a length <NUM> of the rod <NUM>. For example, the rod <NUM> may be coupled to the opening <NUM> of the chamber <NUM> separating the portion <NUM> and the additional portion <NUM>. In some embodiments, the rod <NUM> may be coupled to the opening <NUM> via threads, as mentioned above, via bolts or other fasteners, via a weld, or via another suitable coupling technique that enables the rod <NUM> to maintain a position with respect to the chamber <NUM>. Further, the biasing device <NUM> may be coupled to an end <NUM> of the rod <NUM>, such as welded to the end <NUM>, fastened to the end <NUM> via fasteners (e.g., screws, bolts, or other suitable fasteners), or coupled to the end <NUM> via another suitable technique. In any case, the biasing device <NUM> exerts a force on an end <NUM> of the piston <NUM> (e.g., such as the interior surface <NUM>) in the second direction <NUM> or toward a natural position (e.g., unbiased position) of the biasing device <NUM>. As the piston <NUM> is directed in the first direction <NUM>, the biasing device <NUM> may compress against the end <NUM> of the rod <NUM> and exert a greater force on the piston <NUM>. In some embodiments, the rod <NUM> may also act as a guide for the biasing device <NUM> as it compresses and decompresses due to variations in the pressure differential. For example, the biasing device <NUM> may be configured to move along an outer surface <NUM> of the rod <NUM> as the piston <NUM> moves within the portion <NUM> of the chamber <NUM>. In any case, the pressure differential threshold that drives movement of the piston <NUM> may vary based on an amount of compression of the biasing device <NUM> and/or a current length of the biasing device <NUM> compared to a natural or unbiased length of the biasing device <NUM>.

As the pressure differential between the cavity <NUM> and the portion <NUM> of the chamber <NUM> decreases, the biasing device <NUM> may direct the piston <NUM> to move in the second direction <NUM> by applying a force on the piston <NUM> in the second direction <NUM>. For example, <FIG> illustrates the piston <NUM> in a substantially open position (e.g., when a volume ratio of the compressor <NUM> is reduced), and <FIG> illustrates the piston <NUM> in a substantially closed position (e.g., when a volume ratio of the compressor <NUM> is increased). As shown in the illustrated embodiment of <FIG>, the biasing device <NUM> is in a compressed position <NUM> and exerts a force on the piston <NUM> in the second direction <NUM>.

As discussed above, an amount of force exerted on the piston <NUM> by the biasing device <NUM> may be based on a position of the piston <NUM> within the portion <NUM> of the chamber <NUM> relative to the axis <NUM>, an amount of extension and/or compression of the biasing device <NUM>, parameters of the basing device <NUM> itself, other suitable parameters, or any combination thereof. For instance, parameters of the biasing device <NUM> that may contribute to the magnitude of the biasing force applied to the piston <NUM> may include a material (e.g., metal, polymer) of the biasing device <NUM>, a coil diameter of the biasing device <NUM>, an internal diameter of the biasing device <NUM>, an external diameter of the biasing device <NUM>, a coil pitch of the biasing device <NUM>, a number of coils of the biasing device <NUM>, a spring rate of the biasing device <NUM>, a free length of the biasing device <NUM>, a block length of the biasing device <NUM>, another suitable parameter of the biasing device <NUM>, or any combination thereof.

In any case, both the pressure differential within the cavity <NUM> of the piston <NUM> and the portion <NUM> of the chamber <NUM> applying a force on the exterior surface <NUM> of the piston <NUM> in the first direction <NUM> and the biasing force applied to the piston <NUM> by the biasing device <NUM> in the second direction <NUM> control movement and the position of the piston <NUM> within the chamber <NUM>. The pressure differential threshold for directing movement of the piston <NUM> in the first direction <NUM> may vary based on the position of the piston <NUM> and/or the level of extension and/or compression of the biasing device <NUM>. As such, the piston <NUM> may be positioned (e.g., stationary) at virtually any location within the portion <NUM> of the chamber <NUM> relative to the axis <NUM> when the opposing forces applied by the pressure differential and the biasing device <NUM> are substantially equal. Thus, the volume ratio control system <NUM> of the present disclosure may enable infinitely or substantially infinitely variable control of the volume ratio of the compressor <NUM>.

Claim 1:
A compressor (<NUM>, <NUM>) comprising:
- a housing (<NUM>); and
- a volume ratio control system (<NUM>) configured to adjust a volume ratio of the compressor (<NUM>, <NUM>), the volume ratio control system (<NUM>) comprising:
- a chamber (<NUM>) formed within the housing (<NUM>) of the compressor (<NUM>, <NUM>), wherein the chamber (<NUM>) is in fluid communication with a high pressure side (<NUM>) of the compressor (<NUM>, <NUM>);
- a piston (<NUM>) disposed within the chamber (<NUM>), wherein the piston (<NUM>) comprises a cavity (<NUM>) in fluid communication with a low pressure side (<NUM>) of the compressor (<NUM>, <NUM>); and
- a biasing device (<NUM>) disposed within the chamber (<NUM>) and configured to enable movement of the piston (<NUM>) in response to a pressure differential between the low pressure side (<NUM>) of the compressor (<NUM>, <NUM>) and the high pressure side (<NUM>) of the compressor (<NUM>, <NUM>) falling below a threshold value,
wherein the biasing device (<NUM>) is disposed within the cavity (<NUM>) of the piston (<NUM>), wherein the volume ratio control system (<NUM>) further comprises a rod (<NUM>) extending into the chamber (<NUM>) and extending into the cavity (<NUM>), and
wherein the rod (<NUM>) is configured to form a seal between the chamber (<NUM>) and the cavity (<NUM>) of the piston (<NUM>).