Patent Description:
In a rotary screw compressor, intake and compression can be accomplished by two tightly-meshing, rotating, helically lobed rotors that alternately draw gas into the threads and compress the gas to a higher pressure. The screw compressor is a positive displacement device with intake and compression cycles similar to a piston/reciprocating compressor. The rotors of the screw compressor can be housed within tightly fitting bores that have built in geometric features that define the inlet and discharge volumes of the compressor to provide for a built in volume ratio of the compressor. The volume ratio of the compressor should be matched to the volume ratio of the system in which the compressor is incorporated, thereby avoiding over or under compression, and the resulting lost work. In a closed loop refrigeration system, the volume ratio of the system is established in the hot and cold side heat exchangers.

Fixed volume ratio compressors can be used to avoid the cost and complication of variable volume ratio machines. A screw compressor having fixed inlet and discharge ports built into the housings can be optimized for a specific set of suction and discharge conditions/pressures. However, the system in which the compressor is connected rarely operates at exactly the same conditions hour to hour, especially in an air conditioning application. Nighttime, daytime, and seasonal temperatures can affect the volume ratio of the system and the efficiency with which the compressor operates. In a system where the load varies, the amount of heat being rejected in the condenser fluctuates causing the high side pressure to rise or fall, resulting in a volume ratio for the compressor that deviates from the compressor's optimum volume ratio.

For example, a refrigeration system can include a compressor, condenser, expansion device, and evaporator. The efficiency of the compressor is related to the saturated conditions within the evaporator and condenser. The pressure in the condenser and evaporator can be used to establish the pressure ratio of the system external to the compressor. In the current example, the pressure ratio/compression ratio can be <NUM>. The volume ratio or Vi is linked to the compression ratio by the relation Vi raised to the power of <NUM>/k; k being the ratio of specific heat of the gas or refrigerant being compressed. Using the previous relation, the volume ratio to be built into the compressor geometry for the current example is <NUM> for optimum performance at full load conditions. However, during part load, low ambient conditions, or nighttime, the saturated condition of the condenser in the refrigeration system decreases while evaporator conditions remain relatively constant. To maintain optimum performance of the compressor at part load or low ambient conditions, the Vi for the compressor should be lowered to <NUM>.

Prior art document <CIT> discloses a compressor comprising a compression mechanism being configured and positioned to receive vapor from an intake passage and provide compressed vapor to a discharge passage. In the compression mechanism, the compressor comprises a port to bypass a portion of the vapor in the compression mechanism to the discharge passage. A valve is configured and positioned to control vapor flow through the port, the valve having a first position to permit vapor flow from the compression mechanism to the discharge passage and a second position to prevent such vapor flow. The compressor has a first volume ratio in response to the valve being in the second position and a second volume ratio, being smaller than the first volume ratio, in response to the valve being in the first position. The valve is positionablc using the pressure vapor entering the intake passage and the pressure of vapor discharged from the discharge passage to operate the compressor at the first volume ratio or the second volume ratio.

Prior art document <CIT> describes a screw compressor comprising an unloader piston disposed in a bore remote from a working chamber of the compressor. The bore is in flow communication with an intake port of the compressor. Flow communication between the bore and the working chamber is provided by a series of unloader ports which can be controlled by the unloader piston in order to vary compressor capacity.

Therefore, what is needed is a system to vary the volume ratio of the compressor at part load or low ambient conditions without using costly and complicated devices such as slide valves.

The present invention is defined by the independent claim.

One advantage of the present application is an improved energy efficiency rating (EER) over a fixed volume ratio compressor due to better part-load performance resulting from the use of a lower volume ratio.

<FIG> shows an exemplary environment for a heating, ventilation and air conditioning (HVAC) system <NUM> in a building <NUM> for a typical commercial setting. System <NUM> can include a vapor compression system <NUM> that can supply a chilled liquid which may be used to cool building <NUM>. System <NUM> can include a boiler <NUM> to supply heated liquid that may be used to heat building <NUM>, and an air distribution system which circulates air through building <NUM>. The air distribution system can also include an air return duct <NUM>, an air supply duct <NUM> and an air handler <NUM>. Air handler <NUM> can include a heat exchanger that is connected to boiler <NUM> and vapor compression system <NUM> by conduits <NUM>. The heat exchanger in air handler <NUM> may receive either heated liquid from boiler <NUM> or chilled liquid from vapor compression system <NUM>, depending on the mode of operation of system <NUM>. System <NUM> is shown with a separate air handler on each floor of building <NUM>, but it is appreciated that the components may be shared between or among floors.

<FIG> and <FIG> show an exemplary vapor compression system <NUM> that can be used in HVAC system <NUM>. Vapor compression system <NUM> can circulate a refrigerant through a circuit starting with compressor <NUM> and including a condenser <NUM>, expansion valve(s) or device(s) <NUM>, and an evaporator or liquid chiller <NUM>. Vapor compression system <NUM> can also include a control panel <NUM> that can include an analog to digital (A/D) converter <NUM>, a microprocessor <NUM>, a non-volatile memory <NUM>, and an interface board <NUM>. Some examples of fluids that may be used as refrigerants in vapor compression system <NUM> are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-<NUM>, R-134a, hydrofluoro olefin (HFO), "natural" refrigerants like ammonia (NH<NUM>), R-<NUM>, carbon dioxide (CO<NUM>), R-<NUM>, or hydrocarbon based refrigerants, water vapor or any other suitable type of refrigerant. In an exemplary embodiment, vapor compression system <NUM> may use one or more of each of variable speed drives (VSDs) <NUM>, motors <NUM>, compressors <NUM>, condensers <NUM>, expansion valves <NUM> and/or evaporators <NUM>.

Motor <NUM> used with compressor <NUM> can be powered by a variable speed drive (VSD) <NUM> or can be powered directly from an alternating current (AC) or direct current (DC) power source. VSD <NUM>, if used, receives AC power having a particular fixed line voltage and fixed line frequency from the AC power source and provides power having a variable voltage and frequency to motor <NUM>. Motor <NUM> can include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source. Motor <NUM> can be any other suitable motor type, for example, a switched reluctance motor, an induction motor, or an electronically commutated permanent magnet motor. In an alternate exemplary embodiment, other drive mechanisms such as steam or gas turbines or engines and associated components can be used to drive compressor <NUM>.

Compressor <NUM> compresses a refrigerant vapor and delivers the vapor to condenser <NUM> through a discharge passage. Compressor <NUM> can be a screw compressor in one exemplary embodiment. The refrigerant vapor delivered by compressor <NUM> to condenser <NUM> transfers heat to a fluid, for example, water or air. The refrigerant vapor condenses to a refrigerant liquid in condenser <NUM> as a result of the heat transfer with the fluid. The liquid refrigerant from condenser <NUM> flows through expansion device <NUM> to evaporator <NUM>. In the exemplary embodiment shown in <FIG>, condenser <NUM> is water cooled and includes a tube bundle <NUM> connected to a cooling tower <NUM>.

The liquid refrigerant delivered to evaporator <NUM> absorbs heat from another fluid, which may or may not be the same type of fluid used for condenser <NUM>, and undergoes a phase change to a refrigerant vapor. In the exemplary embodiment shown in <FIG>, evaporator <NUM> includes a tube bundle having a supply line <NUM> and a return line 60R connected to a cooling load <NUM>. A process fluid, for example, water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable liquid, enters evaporator <NUM> via return line 60R and exits evaporator <NUM> via supply line <NUM>. Evaporator <NUM> chills the temperature of the process fluid in the tubes. The tube bundle in evaporator <NUM> can include a plurality of tubes and a plurality of tube bundles. The vapor refrigerant exits evaporator <NUM> and returns to compressor <NUM> by a suction line to complete the cycle.

<FIG>, which is similar to <FIG>, shows the vapor compression system <NUM> with an intermediate circuit <NUM> incorporated between condenser <NUM> and expansion device <NUM>. Intermediate circuit <NUM> has an inlet line <NUM> that can be either connected directly to or can be in fluid communication with condenser <NUM>. As shown, inlet line <NUM> includes an expansion device <NUM> positioned upstream of an intermediate vessel <NUM>. Intermediate vessel <NUM> can be a flash tank, also referred to as a flash intercooler, in an exemplary embodiment. In an alternate exemplary embodiment, intermediate vessel <NUM> can be configured as a heat exchanger or a "surface economizer. " In the configuration shown in <FIG>, i.e., the intermediate vessel <NUM> is used as a flash tank, a first expansion device <NUM> operates to lower the pressure of the liquid received from condenser <NUM>. During the expansion process, a portion of the liquid vaporizes. Intermediate vessel <NUM> may be used to separate the vapor from the liquid received from first expansion device <NUM> and may also permit further expansion of the liquid. The vapor may be drawn by compressor <NUM> from intermediate vessel <NUM> through a line <NUM> to the suction inlet, a port at a pressure intermediate between suction and discharge or an intermediate stage of compression. The liquid that collects in the intermediate vessel <NUM> is at a lower enthalpy from the expansion process. The liquid from intermediate vessel <NUM> flows in line <NUM> through a second expansion device <NUM> to evaporator <NUM>.

In an exemplary embodiment, compressor <NUM> can include a compressor housing that contains the working parts of compressor <NUM>. Vapor from evaporator <NUM> can be directed to an intake passage of compressor <NUM>. Compressor <NUM> compresses the vapor with a compression mechanism and delivers the compressed vapor to condenser <NUM> through a discharge passage. Motor <NUM> may be connected to the compression mechanism of compressor <NUM> by a drive shaft.

Vapor flows from the intake passage of compressor <NUM> and enters a compression pocket of the compression mechanism. The compression pocket is reduced in size by the operation of the compression mechanism to compress the vapor. The compressed vapor can be discharged into the discharge passage. For example, for a screw compressor, the compression pocket is defined between the surfaces of the rotors of the compressor. As the rotors of the compressor engage one another, the compression pockets between the rotors of the compressor, also referred to as lobes, are reduced in size and are axially displaced to a discharge side of the compressor.

As the vapor travels in the compression pocket, a port can be positioned in the compression mechanism prior to the discharge end. The port can provide a flow path for the vapor in the compression pocket from an intermediate point in the compression mechanism to the discharge passage. A valve can be used to open (completely or partially) and close the flow path provided by the port. In an exemplary embodiment, the valve can be used to control the volume ratio of compressor <NUM> by enabling or disabling the flow of vapor from the port to the discharge passage. The valve can provide two (or more) predetermined volume ratios for compressor <NUM> depending on the position of the valve.

The volume ratio for compressor <NUM> can be calculated by dividing the volume of vapor entering the intake passage (or the volume of vapor in the compression pocket before compression of the vapor begins) by the volume of vapor discharged from the discharge passage (or the volume of vapor obtained from the compression pocket after the compression of the vapor). Since the port is positioned prior to or upstream from the discharge end of the compression mechanism, vapor flow from the port to the discharge passage can increase the volume of vapor at the discharge passage because partially compressed vapor having a greater volume from the port is being mixed with completely or fully compressed vapor from the discharge end of the compression mechanism having a smaller volume. The volume of vapor from the port is greater than the volume of vapor from the discharge end of the compression mechanism because pressure and volume are inversely related, thus lower pressure vapor would have a correspondingly larger volume than higher pressure vapor. Thus, the volume ratio for compressor <NUM> can be adjusted based on whether or not vapor is permitted to flow from the port. When the valve is in the closed position, i.e., the valve prevents vapor flow from the port, compressor <NUM> operates at a full-load volume ratio. When the valve is in an open position, i.e., the valve permits vapor flow from the port, the compressor operates at a part-load volume ratio that is less than the full-load volume ratio. In an exemplary embodiment, there are several factors that can determine the difference between full-load volume ratio and part-load volume ratio, for example, the number and location of the ports and the amount of vapor flow permitted through the ports by the valve can all be used to adjust the part-load volume ratio for compressor <NUM>. In an another exemplary embodiment, the configuration or shape of the ports <NUM> can be used to adjust the part-load volume ratio of compressor <NUM>.

<FIG> show an exemplary embodiment of a compressor not falling in the scope of the claimed invention. Compressor <NUM> includes a compressor housing <NUM> that contains the working parts of compressor <NUM>. Compressor housing <NUM> includes an intake housing <NUM> and a rotor housing <NUM>. Vapor from evaporator <NUM> can be directed to an intake passage <NUM> of compressor <NUM>. Compressor <NUM> compresses the vapor and delivers the compressed vapor to condenser <NUM> through a discharge passage <NUM>. Motor <NUM> may be connected to rotors of compressor <NUM> by a drive shaft. The rotors of compressor <NUM> can matingly engage with each other via intermeshing lands and grooves. Each of the rotors of compressor <NUM> can revolve in an accurately machined cylinder <NUM> within rotor housing <NUM>.

In the exemplary embodiment not falling in the scope of the claimed invention shown in <FIG>, a port <NUM> can be positioned in cylinder <NUM> prior to the discharge end of the rotors. Port <NUM> can provide a flow path for the vapor in the compression pocket from an intermediate point in the rotors to discharge passage <NUM>. A valve <NUM> can be used to open (completely or partially) and close the flow path provided by port <NUM>. Valve <NUM> can be positioned below the rotors and extend across compressor <NUM> substantially perpendicular to the flow of vapor. In an exemplary embodiment, valve <NUM> can automatically control the volume ratio of compressor <NUM> by enabling or disabling the flow of vapor from port <NUM> to discharge passage <NUM>. Valve <NUM> can provide two (or more) predetermined volume ratios for compressor <NUM> depending on the position of valve <NUM>. Port(s) <NUM> can extend through cylinder <NUM> in the portions of cylinder <NUM> associated with the male rotor and/or the female rotor. In an exemplary embodiment, the size of port(s) <NUM> associated the male rotor may differ from the size of port(s) <NUM> associated with the female rotor. Discharge passage <NUM> may partially extend below valve <NUM> and ports <NUM> may include channels fluidly connected to discharge passage <NUM>.

<FIG> show valve <NUM> in an open position and a closed position, respectively, to either permit or prevent vapor flow from port <NUM> to discharge passage <NUM>. In <FIG>, valve <NUM> is positioned in a closed position, thereby preventing or blocking the vapor flow from port <NUM> to discharge passage <NUM>. With valve <NUM> in the closed position, compression of vapor by the rotors in compressor <NUM> can occur through reduction of the volume by the rotors as the vapor travels axially to discharge passage <NUM> which results in the full-load volume ratio for compressor <NUM>.

In <FIG>, valve <NUM> is positioned in an open position, thereby permitting the vapor flow from port <NUM> to discharge passage <NUM>. With valve <NUM> in the open position, compression of vapor by the rotors in compressor <NUM> can occur through reduction of the volume by the rotors as the vapor travels axially toward the discharge passage <NUM>. However, some of the vapor can flow into port <NUM> and then to discharge passage <NUM>. Stated another way, a portion of the vapor in the compression pocket can bypass a portion of the rotors by traveling through port <NUM> to discharge passage <NUM> when valve <NUM> is in an open position. The vapor in discharge passage <NUM> from the discharge end of the rotors and the vapor from port <NUM> results in a greater volume of vapor at discharge and the part-load compression ratio for compressor <NUM>.

Valve <NUM> can include a valve body or shuttle <NUM> snugly positioned in a bore <NUM> to avoid unnecessary leakage. Valve body <NUM> can also include one or more gaskets or seals to prevent the leakage of fluids. Valve body <NUM> can have a varying diameters including a larger diameter portion <NUM> and a smaller diameter portion <NUM>. In one exemplary embodiment as shown in <FIG>, valve body <NUM> can have a large diameter portion <NUM> corresponding to each port <NUM> in cylinder <NUM>. In one exemplary embodiment, the ends of bore <NUM> can be sealed and portions or volumes of bore <NUM> can be pressurized or vented with a fluid to move valve body <NUM> back and forth in bore <NUM>. When the valve body <NUM> is positioned in the closed position (see <FIG> and <FIG>), larger diameter portion(s) <NUM> of valve body <NUM> block or close off ports <NUM>. When the valve body <NUM> is positioned in the open position (see <FIG>), smaller diameter portion <NUM> of valve body <NUM> is positioned near port <NUM> to permit flow of vapor from port <NUM> around smaller diameter portion <NUM> to discharge passage <NUM>.

In an exemplary embodiment, valve <NUM> can be opened or closed automatically in response to suction pressure, e.g., the pressure of vapor entering intake passage <NUM>, and discharge pressure, e.g., the pressure of vapor discharged from discharge passage <NUM>. For example, suction pressure may be applied to larger diameter portion <NUM> located at one end of valve body <NUM> and discharge pressure may be applied to smaller diameter portion <NUM> located at the other end of valve body <NUM>. Fluid at suction pressure can be provided to bore <NUM> and larger diameter portion <NUM> through internal or external piping to create a first force on valve body <NUM>. The first force applied to valve body <NUM> can be equal to the fluid pressure (suction pressure) multiplied by the area of larger diameter portion <NUM>. Similarly, fluid at discharge pressure can be provided to bore <NUM> and smaller diameter portion <NUM> through internal or external piping to create a second force on valve body <NUM> opposing the first force on valve body <NUM>. The second force applied to valve body <NUM> can be equal to the fluid pressure (discharge pressure) multiplied by the area of smaller diameter portion <NUM>.

When the first force equals the second force, valve body <NUM> can remain in a substantially stationary position. When the first force exceeds the second force, valve body <NUM> can be urged or moved in bore <NUM> to position valve <NUM> in either the open position or the closed position. In the exemplary embodiment shown in <FIG>, the first force would move valve body <NUM> toward the closed position. In contrast, when the second force is greater than the first force, valve body <NUM> can be urged or moved in bore <NUM> to position valve <NUM> in the opposite position from the positioned obtained when the first force is larger. In the exemplary embodiment shown in <FIG>, the second force would move valve body <NUM> toward the open position. <FIG> is a chart showing force differentials between the first force and the second force on valve body <NUM> (and corresponding valve positions) for selected saturated discharge temperatures in an exemplary embodiment and gives an example of a specific switch point for valve body <NUM>. The switch point can be moved by adjusting the pressures or spring force acting on valve body <NUM>.

In an exemplary embodiment, the sizing of larger diameter portion <NUM> and smaller diameter portion <NUM> may permit automatic movement of valve body <NUM> when the suction and discharge pressures reach a predetermined point. For example, the predetermined point may correlate with a preselected compression ratio or a preselected volume ratio. In another exemplary embodiment, valve <NUM> can include a mechanical stop, for example a shoulder positioned in bore <NUM>, to limit the movement of valve body <NUM> to two positions (for example, closed and open). In another exemplary embodiment, valve body <NUM> can be moved to an intermediate position between the open and closed position that permits partial flow of vapor from port <NUM> to obtain another volume ratio for compressor <NUM>. In a further exemplary embodiment, valve body <NUM> can have several portions of varying diameters to obtain different volume ratios for compressor <NUM> based on the amount of vapor flow from port <NUM> each varying diameter permits.

In another exemplary embodiment, a spring can be positioned in bore <NUM> near larger diameter portion <NUM> to supplement the first force. The use of the spring can smooth the transition between the closed position and the open position and can avoid frequent switching between positions if the force differential remains near the switching point. In another exemplary embodiment, a spring can also be positioned in bore <NUM> near smaller diameter portion <NUM> to supplement the second force.

In still another exemplary embodiment, the position of valve body <NUM> can be controlled with one or more solenoid valves to vary the pressures at each end of valve body <NUM>. The solenoid valve can be controlled by sensing suction and discharge pressures outside or exterior of compressor <NUM> and then adjusting the pressures on each end of the valve body <NUM>.

In the exemplary embodiment comprising the features of the claimed invention shown in <FIG>, ports <NUM> can be positioned in cylinder <NUM> prior to the discharge end of the rotors. Ports <NUM> can provide a flow path for the vapor in the compression pocket from an intermediate point in the rotors to discharge passage <NUM>. Valves <NUM> can be used to open (completely or partially) and close the flow path provided by ports <NUM>. Valves <NUM> can be positioned below the rotors and extend substantially parallel to the flow of vapor in compressor <NUM>. In an exemplary embodiment, valves <NUM> can control the volume ratio of compressor <NUM> by enabling or disabling the flow of vapor from ports <NUM> to discharge passage <NUM> in response to system conditions. Valves <NUM> can provide two (or more) predetermined volume ratios for compressor <NUM> depending on the position of valves <NUM>. Ports <NUM> can extend through cylinder <NUM> in the portions of cylinder <NUM> associated with the male rotor and/or the female rotor. In an exemplary embodiment, the size of ports <NUM> associated the male rotor may differ from the size of ports <NUM> associated with the female rotor. Discharge passage <NUM> may partially extend below valves <NUM> and ports <NUM> may include channels fluidly connected to discharge passage <NUM>.

<FIG> shows valve 290A positioned in a closed position, thereby preventing or blocking the vapor flow from port <NUM> to discharge passage <NUM> and shows valve 290B positioned in an open position thereby permitting the vapor flow from port <NUM> to discharge passage <NUM>. With valve 290A in the closed position and valve 290B in the open position, compression of vapor by the rotors in compressor <NUM> can occur through reduction of the volume by the rotors as the vapor travels axially toward the discharge passage <NUM> for both valves 290A and 290B. However, some of the vapor can flow into ports <NUM> associated with valve 290B and then to discharge passage <NUM>. The vapor in discharge passage <NUM> from the discharge end of the rotors and the vapor from ports <NUM> associated with valve 290B results in a greater volume of vapor at discharge and a first part-load compression ratio for compressor <NUM>.

When both valves 290A and 290B are in the closed position, compression of vapor by the rotors in compressor <NUM> can occur through reduction of the volume by the rotors as the vapor travels axially to discharge passage <NUM> which results in the full-load volume ratio for compressor <NUM>. When both valves 290A and 290B are in the open position, compression of vapor by the rotors in compressor <NUM> can occur through reduction of the volume by the rotors as the vapor travels axially toward the discharge passage <NUM>. However, some of the vapor can flow into ports <NUM> and then to discharge passage <NUM>. Stated another way, a portion of the vapor in the compression pocket can bypass a portion of the rotors by traveling through ports <NUM> to discharge passage <NUM> when valves 290A and 290B are in an open position. The vapor in discharge passage <NUM> from the discharge end of the rotors and the vapor from ports <NUM> results in a greater volume of vapor at discharge and a second part-load compression ratio for compressor <NUM> that is lower than the first part-load compression ratio.

Valves <NUM> can include a valve body <NUM> snugly positioned in a bore <NUM> to avoid unnecessary leakage. Valve body <NUM> can also include one or more gaskets or seals to prevent the leakage of fluids. Valve body <NUM> can have a substantially uniform diameter. In one exemplary embodiment, one end of bore <NUM> can be sealed and a fluid connection <NUM> can be provided near the sealed end of bore <NUM>. The other end of bore <NUM> can be exposed to fluid at discharge pressure. Fluid connection <NUM> can be used to adjust the magnitude of the fluid pressure in the sealed end of bore <NUM>, i.e., pressurize or vent the sealed end of bore <NUM>, to move valve body <NUM> back and forth in bore <NUM>. Fluid connection <NUM> can be connected to a valve <NUM> (see <FIG>), for example a proportional valve or <NUM>-way valve, that is used to supply fluids of different pressures to the sealed end of bore <NUM> through fluid connection <NUM>. Valve <NUM> can permit fluid at discharge pressure (PD), fluid at a reference pressure less than discharge pressure (PREF), or a mixture of fluid at the discharge pressure and the reference pressure to flow into fluid connection <NUM>. In one exemplary embodiment, the reference pressure can be equal to or greater than the suction pressure. In another exemplary embodiment, valve <NUM> can be operated with oil from the lubrication system. In still another exemplary embodiment, more than one valve can be used to supply fluid to fluid connection <NUM>. Valve <NUM> can be controlled by a control system based on measured system parameters, such as discharge pressure, suction pressure, evaporating temperature, condensing temperature or other suitable parameters. When the valve body <NUM> is positioned in the closed position, valve body <NUM> blocks or closes off ports <NUM>. When the valve body <NUM> is positioned in the open position, valve body <NUM> is at least partially moved away from the ports <NUM> to permit flow of vapor from ports <NUM> to discharge passage <NUM>. The vapor can flow from ports <NUM> to discharge passage <NUM> because the pressure in the compression pocket is at a higher pressure than the discharge pressure. Once the vapor enters ports <NUM> there can be a pressure drop in the vapor because of the expansion of the vapor into bore <NUM>.

In an exemplary embodiment, valves <NUM> can be opened or closed in response to the supply or withdrawal of fluid from the sealed end of bore <NUM>. To move valve body <NUM> into the closed position, fluid at discharge pressure is provided to fluid connection <NUM> by valve <NUM>. The fluid at discharge pressure moves valve body <NUM> away from the sealed end of bore <NUM> to close or seal ports <NUM> by overcoming the force applied to the opposite side of valve body <NUM>. In contrast, to move valve body <NUM> into the open position, fluid at reference pressure is provided to fluid connection <NUM> by valve <NUM>. The fluid at reference pressure enables valve body <NUM> to move towards the sealed end of bore <NUM> to open or uncover ports <NUM> since the force applied to the opposite side of valve body <NUM> is greater than the force applied to valve body <NUM> at the sealed end of bore <NUM>. The use of valve <NUM> to adjust the magnitude of the fluid pressure in the sealed end of bore <NUM> permits valves <NUM> to be opened and closed in response to specific system conditions.

In another exemplary embodiment, a spring can be positioned in the sealed end of bore <NUM> to supplement the force of the fluid used to close the valve. The use of the spring can smooth the transition between the closed position and the open position and can avoid frequent switching between positions if the force differential remains near the switching point.

In a further exemplary embodiment, the valves <NUM> can be independently controlled to permit one valve <NUM> to be opened, while closing the other valve <NUM>. When the valves <NUM> are independently controlled, each valve <NUM> can have a corresponding valve <NUM> that is independently controlled to supply fluid to valve <NUM> as determined by system conditions. In another exemplary embodiment, the valves <NUM> can be jointly controlled to have both valves opened or closed at the same time. When the valves are jointly controlled a single valve <NUM> can be used to supply fluid to the valves <NUM>. However, each valve <NUM> may have a corresponding valve <NUM> that receives common or joint control signals to open or close the valves <NUM>.

In still another exemplary embodiment comprising the features of the claimed invention shown in <FIG>, the bores <NUM> may be connected to discharge passage <NUM> by channels <NUM>. Channels <NUM> may be used when the size of bore <NUM> does not permit a direct fluid connection between bore <NUM> and discharge passage <NUM>. Channels <NUM> can have any suitable size or shape to permit fluid flow from bore <NUM> to discharge passage <NUM>.

In the exemplary embodiment shown in <FIG>, ports <NUM> can be positioned in cylinder <NUM> prior to the discharge end of the rotors. Ports <NUM> can provide a flow path for the vapor in the compression pocket from an intermediate point in the rotors to discharge passage <NUM>. Valve <NUM> can be used to open (completely or partially) and close the flow path provided by ports <NUM>. Valve <NUM> can be positioned below the rotors at a position substantially centered between the rotors and extend substantially parallel to the flow of vapor in compressor <NUM>. In an exemplary embodiment, valve <NUM> can control the volume ratio of compressor <NUM> by enabling or disabling the flow of vapor from ports <NUM> to discharge passage <NUM> in response to system conditions. Valve <NUM> can provide two (or more) predetermined volume ratios for compressor <NUM> depending on the position of valve <NUM>. Ports <NUM> can extend through cylinder <NUM> in the portions of cylinder <NUM> associated with the male rotor and/or the female rotor. In an exemplary embodiment, the size of ports <NUM> associated the male rotor may differ from the size of ports <NUM> associated with the female rotor.

<FIG> shows valve <NUM> positioned in a closed position, thereby preventing or blocking the vapor flow from ports <NUM> to discharge passage <NUM>. When valve <NUM> is in the closed position, compression of vapor by the rotors in compressor <NUM> can occur through reduction of the volume by the rotors as the vapor travels axially to discharge passage <NUM> which results in the full-load volume ratio for compressor <NUM>. <FIG> shows valve <NUM> positioned in an open position thereby permitting the vapor flow from ports <NUM> to discharge passage <NUM>. When valve <NUM> is in the open position, compression of vapor by the rotors in compressor <NUM> can occur through reduction of the volume by the rotors as the vapor travels axially toward the discharge passage <NUM>. However, some of the vapor can flow into ports <NUM> and then to discharge passage <NUM>. Stated another way, a portion of the vapor in the compression pocket can bypass a portion of the rotors by traveling through ports <NUM> to discharge passage <NUM> when valve <NUM> is in an open position. The vapor in discharge passage <NUM> from the discharge end of the rotors and the vapor from ports <NUM> results in a greater volume of vapor at discharge and a part-load compression ratio for compressor <NUM> that is lower than the full-load compression ratio.

Valve <NUM> can include a valve body <NUM> snugly positioned in a bore <NUM> to avoid unnecessary leakage. Valve body <NUM> can also include one or more gaskets or seals to prevent the leakage of fluids. Valve body <NUM> can have a substantially uniform diameter. In one exemplary embodiment, one end of bore <NUM> can be sealed and a fluid connection <NUM> can be provided near the sealed end of bore <NUM>. The other end of the bore can be exposed to fluid at discharge pressure. Fluid connection <NUM> can be used to adjust the magnitude of the fluid pressure in the sealed end of bore <NUM>, i.e., pressurize or vent the sealed end of bore <NUM>, to move valve body <NUM> back and forth in bore <NUM>. Fluid connection <NUM> can be connected to a valve, for example a proportional valve or <NUM>-way valve, that is used to supply fluids of different pressures to the sealed end of bore <NUM> through fluid connection <NUM>. Fluid at discharge pressure (PD), fluid at a reference pressure less than the discharge pressure (PREF), or a mixture of fluid at discharge pressure and reference pressure can flow into fluid connection <NUM>. In another exemplary embodiment, more than one valve can be used to supply fluid to fluid connection <NUM>. The valve supplying fluid connection <NUM> can be controlled by a control system based on measured system parameters, such as discharge pressure, suction pressure, evaporating temperature, condensing temperature or other suitable parameters. When the valve body <NUM> is positioned in the closed position, valve body <NUM> blocks or closes off ports <NUM>. When the valve body <NUM> is positioned in the open position, valve body <NUM> is moved from the ports <NUM> to permit flow of vapor from ports <NUM> to discharge passage <NUM>.

In an exemplary embodiment, valve <NUM> can be opened or closed in response to the supply or withdrawal of fluid from the sealed end of bore <NUM>. To move valve body <NUM> into the closed position, fluid at discharge pressure is provided to fluid connection <NUM>. The fluid at discharge pressure moves valve body <NUM> away from the sealed end of bore <NUM> to close or seal ports <NUM> by overcoming the force on the opposite side of valve body <NUM>. In contrast, to move valve body <NUM> into the open position, fluid at reference pressure is provided to fluid connection <NUM>. The fluid at reference pressure enables valve body <NUM> to move towards the sealed end of bore <NUM> to open or uncover ports <NUM> since the force applied to the opposite side of valve body <NUM> is greater than the force applied to valve body <NUM> at the sealed end of bore <NUM>. The pressurizing or venting of the sealed end of bore <NUM>, permits valve <NUM> to be opened and closed in response to specific conditions.

In another exemplary embodiment, a spring can be positioned in the sealed end of bore <NUM> to supplement the force of the fluid used to close the valve. The use of the spring can smooth the transition between the closed position and the open position.

In exemplary embodiments, the ports and/or the valves of the volume ratio control system can be used to adjust the volume ratio of the compressor by adjusting the size of the ports and/or the valves, and/or the positioning of the ports and/or the valves with respect to the rotors and/or the discharge path. By increasing the size of the ports, a larger volume of the vapor can pass through ports. Similarly, by decreasing the size of the ports, a smaller volume of the vapor can pass through the ports. Additionally or alternatively, including multiple ports with respect to one valve can increase the volume of the vapor. By positioning the ports and valves closer to the discharge end of the rotors, the difference in volume of the vapor traveling through the ports can be lower. Similarly, by positioning the ports and valves farther from the discharge end of the rotors, the difference in volume of the vapor traveling through the ports can be higher.

In other exemplary embodiments, the bores and the valve bodies used in the valves can have standard shapes that are easily manufactured. For example, the bores can have a cylindrical shape, including a right circular cylindrical shape, and the valve bodies can have a corresponding cylindrical or piston shape, including a right circular cylindrical shape. However, the bores and valve bodies can have any suitable shape that can open and close the ports in the cylinder as required.

In another exemplary embodiment, a slide valve and corresponding controls can be used with the volume ratio control system. The use of a slide valve with the volume ratio control system can provide a smoother Vi vs. capacity curve.

Claim 1:
A compressor (<NUM>), comprising:
- a compression mechanism being configured and positioned to receive vapor from an intake passage (<NUM>) and provide compressed vapor to a discharge passage (<NUM>);
- a port (<NUM>) configured to enable a portion of the vapor to at least partially bypass compression by the compression mechanism, and to direct the portion of the vapor to the discharge passage (<NUM>);
- a valve (<NUM>) configured and positioned to control vapor flow through the port (<NUM>), the valve (<NUM>) having a first position configured to permit the portion of the vapor to pass through the port (<NUM>) to the discharge passage (<NUM>), and the valve (<NUM>) having a second position configured to block the portion of the vapor from passing through the port (<NUM>), wherein the valve (<NUM>) extends across the compressor (<NUM>) substantially parallel to a flow of vapor through the compression mechanism;
- the compressor (<NUM>) having a first volume ratio in response to the valve (<NUM>) being in the second position and a second volume ratio in response to the valve (<NUM>) being in the first position, the first volume ratio being greater than the second volume ratio; and
- the valve being controllable in response to predetermined conditions to operate the compressor at the first volume ratio or the second volume ratio.