BRPI0715186A2 - Screw compressor and Method to operate compressor - Google Patents

Abstract

SCREW COMPRESSOR AND METHOD FOR OPERATING COMPRESSOR. A screw compressor has a housing (22; 302) having first (53; 330) and second (58; 340) ports along a flow path. A first rotor (26; 306) has a lobulated body. A second rotor (28; 308, 310) has a lobed body entangled with the body of the first rotor. The rotors and the housing cooperate to define a compression path between the suction (60; 332) and discharge (62; 342) position along the flow path. Means (100, 110, 120; 200, 210, 220, 370, 380, 390) provide relative longitudinal movement between a locking portion (57; 352) of the housing and at least one of the first rotor and second rotor in the middle: a first condition where a pocket of the first and second rotors is closed by the blocking part; and a second condition where the blocking part does not close the pocket. To provide capacity control, a control system (110; 390) is configured to provide control of the mandatory movement cycle.

Description

SCREW COMPRESSOR AND METHOD FOR OPERATING COMPRESSOR

BACKGROUND

The present invention relates to compressors. More particularly, the present invention relates to screw type refrigerant compressors.

Screw compressors are generally used in air conditioning and refrigeration applications. In such a compressor, the geared male and female lobed bolts or rotors are rotated about their axes to pump operating (refrigerant) liquid from a low pressure inlet end to a high pressure outlet end. During rotation, the sequential male rotor lobes serve as pistons that carry the downstream refrigerant and compress it into the space between an adjacent pair of female rotor lobes and the housing. Similarly, the female rotor sequential lobes produce refrigerant compression within a space between an adjacent pair of male rotor lobes and the housing. The spaces between the male and female rotor lobes in which compression occurs form compression pockets (described alternatively as the male and female portions of a common compression pocket joined in a mesh zone). In one embodiment, the male rotor is coaxial with an electric drive motor and is supported by bearings on the inlet and outlet sides of its lobed operating part. There may be several female rotors coupled to a male rotor referred to or vice versa.

When one of the spaces between lobes is exposed to an inlet port, the refrigerant enters the space essentially at suction pressure. As the rotors continue to rotate, at some point during rotation the space is no longer in communication with the inlet port and the refrigerant flow into the space is cut off. After the inlet door is closed, the refrigerant is compressed while the rotors continue to rotate. At some point during rotation, each space crosses the associated output port and the closed compression process ends. The inlet port and the outlet port can each be radial, axial, or a hybrid combination of an axial port and a radial port.

It is often desirable to temporarily reduce the mass of refrigerant flowing through the compressor by delaying the inlet port closing (with or without a reduction in the compressor volume index) when full capacity operation is not required. Such discharge is often provided by a slide valve having a one or several part valve element whose positions (as the valve is translated) control the respective suction side closure and discharge discharge side opening of the compression pockets. The primary effect of a slide valve discharge displacement is to reduce the volume of initial trapped suction (and hence the capacity of the compressor); A reduction in volume index is a typical side effect. Exemplary slide valves are described in US Patent Application Publication 20040109782 A1 and US Patent 4,249,866 and 6,302,668.

SUMMARY

One aspect of the present invention involves a screw compressor having a housing having first and second ports along a flow path. A first rotor has a lobed body and shaft and is mounted on the housing for shaft rotation. A second rotor has a lobed body entangled with the body of the first rotor. The second rotor has a shaft and is mounted in the housing for rotation about that shaft. The rotors and casing cooperate to define a compression path between the suction and discharge positions along the flow path. The means provides relative longitudinal movement between a housing locking portion and at least one of the first rotor and the second rotor between a first condition and a second condition. In the first condition, a pocket of the first and second rotor is closed by the locking part. In the second condition, the blocking part does not close the pocket. To provide capacity control (to achieve a desired loading condition), a control system is configured to provide control of the required movement cycle.

In several embodiments, at least one movable rotor of the first and second rotors may be mounted for translation between the first and second position along their axis. An actuator may be coupled to at least the movable rotor to move the movable rotor. Alternatively, the means may provide longitudinal movement of the locking portion relative to a remainder of the housing between a first position associated with the first condition and a second position associated with the second condition.

Details of one or more embodiments are set forth in the accompanying drawings and description below. Other features, objects and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view of a base compressor.

FIG. 2 is a partial, partially schematic view of a re-designed compressor in a loaded condition.

FIG. 3 is a view of the compressor of FIG. 2 in a discharged condition.

FIG. 4 is a partial, partially schematic view of a second re-planned compressor in a loaded condition.

FIG. 5 is a view of the compressor of FIG. 4 in a discharged condition.

FIG. 6 is a longitudinal sectional view of a second re-designed compressor in a loaded condition.

FIG. 7 is a cross-sectional view of the compressor of FIG. 6 taken along line 7.7.

FIG. 8 is a longitudinal sectional view of the compressor of FIG. 6 taken along line 8.8.

FIG. 9 is a longitudinal sectional view of the compressor of FIG. 6 in a discharged condition.

Reference numbers and designations in the various drawings indicate the same elements.

DETAILED DESCRIPTION

FIG. 1 shows a base compressor 20 having a housing assembly 22 containing a motor 24 driving rotors 26 and 28 having respective central longitudinal axes 500 and 502. For purposes of illustration, the basic structure of the compressor is taken from an existing compressor. However, other configurations of the existing or still developed compressor are possible.

In the exemplary embodiment, the rotor 26 has a male lobed body or an operating part 30 extending between a first end 31 and a second end 32. The operating part 30 is entangled with a female lobed body or an operating part 34 of the female rotor 28. The operating part 34 has a first end 35 and a second end 36. Each rotor includes shaft parts (e.g., tips 39, 40, 41, and 42 formed unitarily with the associated operating part) extending from the first and second ends of the associated operating part. Each of these shaft ends is mounted to the housing by one or more bearing assemblies 44 for rotation about the associated rotor shaft.

In the exemplary embodiment, the motor is an electric motor having a rotor 45 and a stator 46. One of the shaft ends of one of the rotors 26 and 28 may be coupled to the motor rotor to allow the motor to drive that rotor about its axis. . When thus driven in a first operating direction on the shaft, the rotor drives the other rotor in a second opposite direction. Exemplary housing assembly 22 includes a rotor housing 48 having an upstream / inlet end face 49 approximately midway along the motor length and an essentially coplanar downstream / discharge end face 50 with the ends of the rotor body 32 and 36. Many other configurations are possible.

Exemplary housing assembly 22 further comprises a motor housing / inlet 52 having a compressor inlet / suction port 53 at an upstream end and having a downstream face 54 mounted to the downstream face of the rotor housing (e.g. , through the screws through both parts of the housing). The assembly 22 further includes an outlet / discharge housing 56 having an upstream face 57 mounted to the downstream face of the rotor housing and having an outlet / discharge port 58. The rotor housing, motor / inlet housing, and the exemplary outlet housing 56 may each be formed as castings subject to additional machine finishing.

The surfaces of the housing assembly 22 combine with the entangled rotor bodies 30 and 34 to define inlet and outlet ports for the compression pockets that compress and conduct a refrigerant flow 504 from a suction plenum 60 to one. discharge plenum (outlet) 62. A series of pairs of male compression pockets 66 and female compression pockets 68 are formed by housing assembly 22, male rotor body 30 and female rotor body 34. Each compression pocket is limited by outer surfaces of the entangled rotors, portions of cylindrical surfaces of the male and female rotor hole surfaces in the rotor housing, and face portions 57. The pockets sequentially form, close, compress, and open then to a discharge port on face 57 along a network of associated rotor pairs.

In the prior art, various mechanisms are used for unloading the screw compressor. Trigger and slide valves are used for mechanical unloading as variable speed actuators are used for unloading through shaft speed modulation. Slide valves offer improved part loading efficiency over trigger valves by providing continuous modulation (against step changes in capacity). Variable speed drives further provide an improvement over slide valves by extending the scale of continuous modulation. The cost of these unloading systems increases along with improved performance (lower cost triggers, then slide valves, then variable speed drives being higher cost). The exemplary base compressor has a slide valve system 70 having a slide valve element 72 activated by a fluid actuator 74 (e.g., refrigerant).

FIGS. 2 and 3 show an actuator 100 coupled to the second rotor 28 to provide relative longitudinal movement between the second rotor and a housing blocking portion (e.g. upstream face 57). Exemplary relative motion comprises displacing the second rotor between the first and second positions. In the first position / condition (FIG. 2), normal sealing spacing is provided between the end of the body / face 36 and the upstream face of the discharge housing 57 so that the face locks / closes the compression pockets. In the second position / condition (FIG. 3), the second rotor 28 is moved relatively far away from the discharge housing to open a hole of thickness T-seal between the body / face end 36 and upstream face of the discharge housing. discharge 57. These discharges open the compression pockets so that the compressor (for example, fully discharges).

Intermediate capacities can be achieved by bistatic modulation between the two positions (for example, by changing the required cycle under a pulse width modulation type control). Exemplary controller 110 is a microcontroller or computer configured by one or both hardware and software to provide the cycle control required to achieve a target capability. The controller could be specific to the compressor or a larger system. The controller can determine the target / desired capacity (eg as a fraction of total capacity) responsive to the detected parameters (eg temperatures at various positions in a cooling / cooling system) and / or programmed or the user sets parameters ( for example thermostat adjustments).

A basic example is a fixed frequency system where the mandatory cycle is controlled. With an exemplary frequency of 0.05Hz, the cycle period / (time) is twenty seconds. The mandatory cycle can be determined as the fraction of the cycle period that the rotor body end is in the second coupled position (or alternatively in the first uncoupled position).

More complex modulations can be provided. For example, the modulation frequency can be dynamically controlled ("instantaneously") for various performance results. For example, a low frequency may be advantageous to minimize wear and power consumption of actuator 100. However, a higher frequency may provide a more homogeneous overall coolant flow and may reduce variations in motor loading and associated wear. of the engine. To control engine wear, an engine temperature can be directly or indirectly measured through a discharge temperature. In such a situation, the control system may be configured to operate at an initial frequency and thereafter to increase the frequency if the motor temperature or other motor loading indication exceeds a desired value. For example, the frequency may be incrementally increased to a maximum value. For example, starting at an initial value of 0.05Hz, the frequency could be incrementally increased to an upper limit (for example, a value of 0.4Hz). Return control can reduce loop frequency or anyway to the low starting value.

Also, the frequency could be similarly increased if detected temperature variations (for example, in the conditioned environment such as a refrigerated room or climate controlled room) exceed a desired threshold (ΔΤ). As with motor load, feedback may decrease the frequency responsive to subsequent decreases in temperature fluctuations.

Thus, the controller can be configured to modulate the

rotor position to provide target capacity (subject to acceptable deviation) when low modulating frequency balancing attributes (eg, actuator wear and power consumption) against higher frequency attributes (eg motor and energy consumption and tolerance to fluctuations).

In various embodiments, a spring 120 may tilt the second rotor 28 from the discharged condition to the loaded condition. Alternatively, the polarization (and the associated normal / standard position) may be reversed. Exemplary spring 120 is a metal tension coil spring positioned at the end / side of the discharge.

Similarly, FIGS. 4 and 5 show the first and second positions / conditions of a compressor where an actuator 200 and metal compression coil spring 220 are positioned at the suction end / side. The exemplary spring 220 tilts the rotor 28 toward the first loaded position (FIG. 4) of the second discharged position (FIG. 5). Actuator 200 may extend against spring bias to shift from first position / condition to second position / condition. Modulated operation may be similar to that of actuator 100 discussed above. However, reciprocating push / pull actuators may eliminate spring bias or supplement the force of spring bias in the corresponding direction.

In various embodiments, the actuator may be fluid (eg operating using fluid pressure such as the compressor lubrication oil recovery system or the refrigerant gas from the low and high pressure (suction and discharge) sides of the refrigeration system ). Alternative actuators can be electromechanical or electromagnetic. The actuator and spring can cooperate with the rotor through one or more bearing systems that support the rotor.

In alternative embodiments, the actuator may be positioned to move both rotors (for example, from a two-rotor compressor). In a three rotor compressor, the actuator can be positioned to move the center rotor, the other two rotors, or all three. Depending on the performance, the actuator may be positioned at either end of the associated rotors. FIGS. 6 through 9 show a redesigned compressor

300. The re-designed compressor 300 of a base compressor slightly different from the compressor of FIG. 1. Instead of a displacement of a rotor while the casing remains stationary, the exemplary compressor 300 displaces a locking part of the casing while the axial / longitudinal positions of the rotors remain unchanged.

Compressor 300 has a housing assembly 302 containing a motor 304 which drives a male lobed rotor 306 and female lobed rotors 308 and 310 (FIG. 8) having respective central longitudinal axes 510, 512, and 514. The operating part of the The male rotor has a first (upstream / suction) end 320 and a second (downstream / discharge) end 322. Each of the operating parts of the female rotor has a first end 324 and a second end 326. Other details may be similar. exemplary housing assembly 302 has an inlet port 330 to a suction plenum 332. The housing assembly includes an outlet port 340 of a discharge plenum 342. A check valve 344 may be close to exit door.

In the exemplary compressor 300, modification of a base condition differs from modification of FIG. 2 - 5 of compressor 20. Whereas the modification of the compressor of FIG. 2-5 adds means for longitudinally displacing one or more rotors, the compressor 300 reflects a redesign where the discharge housing is modified to include a displaceable plate 350. The plate 350 seals with the downstream end of the rotor operation to define the associated compression pockets. The plate 350 has an upstream face 352 and a downstream face 354. A periphery 356 joins the upstream face 352 and the downstream face 354. The plate 350 and its upstream face 352 serves as the carcass of the normally blocking blocking portion. / closes the compression pockets. The plate has a plurality of direct openings. FIG. 7 shows plate 350 having through openings 358, 359, and 360 accommodating the tips of the downstream / downstream end spindles of the rotors. FIG. 7 further shows the plate as having apertures defining a first discharge port 362 and a second discharge port 364. The first discharge port is positioned to discharge from the compression pocket between male rotor 306 and first female rotor 308. The door outlet 364 is positioned to discharge refrigerant from the compression pocket of male rotor 306 and second female rotor 310.

The plate 350 may be detached from the sealing of the compression pockets by a longitudinal translation away from the rotors (e.g., to a second (unloading) condition of FIG. 9). A spring 370 within the discharge housing may tilt plate 350 to the first / sealed / loaded condition from the second / unsealed / discharged condition. Movement beyond the second condition may be restricted as by a shoulder 372 of the carcass. In re-planning for compressor configuration 300, the discharge housing may be extended along with the discharge end shaft ends.

Capacity may be controlled by a modulated displacement of plate 350 (e.g., between the first (FIG. 6) and second (FIG. 9) conditions (positions)). An exemplary modulation is fluid controlled. FIG. 6 shows a fluid actuated travel mechanism 380 for valve travel. The mechanism can be activated by a

usually controller parts 390 (for example, similar to controller 110). FIG. 6 further shows a motor temperature sensor 392 and a discharge temperature sensor 394 that can be used by controller 390 to provide the feedback control over the modulation frequency discussed above. Displacement mechanism 380 includes a three-way valve 382. The three-way valve is coupled by a first line (pipe) 384 to a suction condition / position (e.g., to a port 385 in suction plenum 332). A second line 386 is coupled to a high pressure position (e.g., ports 387) positioned to cross the compression pockets well in front of the normally open compression pockets for discharge plenum 342. A third line 388 communicates with the discharge plenum 342 (for example, through a port 389 downstream of the downstream face 354 of the plate).

To discharge the compressor, valve 382 may be actuated to bring lines 384 and 388 into communication with each other. This communication drops the pressure along the downstream face 354 to the suction pressure. Meanwhile, the upstream face 352 is exposed to even higher pressure of the compressed refrigerant in the compression pockets. The pressure differential across plate 350 will shift plate 350 from the first condition (FIG. 6) to the second (FIG. 9) condition (for example, and compresses spring 370).

To recharge the compressor, valve 382 is actuated to establish communication between lines 386 and 388. These more closely balance the pressure forces across plate 350. This force balance, combined with the diagonal force of spring 370, will displace the plate 50 back to the first condition by sealing plate 350 to the rotors and maintaining the integrity of the compression pocket. Spring 370 may also preload plate 350 and prevent vibration of plate 350 from partial discharge of the compressor when a fully charged condition is desired. In addition, additional damping means may be provided (for example, a viscous or hydraulic damper (shown now)).

Multiple executions can have one or several of the many advantages. For example, there may be an advantageous cost and performance balance. Continuous control similar to relatively expensive systems (e.g., slide valve or variable speed systems) could be provided at similar cost to relatively inexpensive systems (eg, trigger thread valve systems). For example, in a re-planning situation, the re-planned compressor configuration could be less expensive to manufacture than the base compressor. Such re-planning may involve the elimination of a discharge valve (for example, a slide valve) and its associated actuation hardware. Such re-planning can eliminate variable speed motor control (for example, by eliminating variable frequency drive (VFD) also known as variable speed drive (VSD)). However, although some systems may thus lack a discharge valve and / or lack variable speed motor control, current characteristics may also be performed on compressors that have one or both variable speed discharge and motor control valves.

One or more embodiments have been described. However, it will be understood that various modifications may be made. For example, in a re-planning or remanufacturing situation, details of the existing compressor configuration may particularly influence or dictate execution details. Accordingly, other embodiments are within the scope of the following claims.

Claims (30)

A screw compressor comprising: a housing (22; 302) having first (53; 330) and second (58; 340) ports along a flow path; a first rotor (26; 306) having a lobed body (30) and an axis (500) and mounted to the housing for rotation about the first rotor axis; and a second rotor (28; 308, 310) having: a lobed body (34) entangled with the first rotor body (30); and an axis (502), the second rotor mounted to the housing for rotation about the second rotor axis and cooperating with the first rotor (26; 306) and housing (22; 302) to define a compression path between the positions of (60; 332) and discharge (62; 342) along the flow path, characterized in that: means (100, 110, 120; 200, 210, 220; 370, 380, 390) for providing the relative longitudinal movement between a locking portion (57; 352) of the housing and at least one of the first rotor and second rotor between: a first condition where a pocket of the first and second rotors is closed by the locking part; and a second condition where the locking part does not close the pocket; and a control system (110; 390) configured by one or both hardware and software to provide control of the required motion cycle. Compressor according to claim 1, characterized in that: the means (380, 390) provide longitudinal movement of the locking part (352) relative to a remainder of the housing between a first position associated with the first condition and a second position associated with the second condition. Compressor according to Claim 2, characterized in that the means comprise: a spring (370) inclining the locking part of the second position towards the first position. Compressor according to claim 1, characterized in that: the control system is configured by one or both hardware and software to provide mandatory cycle control as a bistatic pulse width modulation. Compressor according to Claim 1, characterized in that: the means (100, 110, 120; 200, 210, 220) provide longitudinal movement of a single of the first rotor and the second rotor relative to the locking part. (57) Compressor according to Claim 1, characterized in that: the means provide longitudinal movement of at least one movable rotor (28) of the first and second rotors between the first and second positions; and the means comprises an actuator (100; 200) coupled at least to the movable rotor of the first and second rotors to move the movable rotor. Compressor according to Claim 6, characterized in that: a spring (120; 220) tilts the movable rotor from the second position towards the first position. Compressor according to Claim 1, characterized in that: the compressor does not have a discharge valve. Compressor according to Claim 1, characterized in that: the compressor does not have variable speed motor control. Compressor according to claim 1, characterized in that: the control system is configured to vary a mandatory cycle control frequency responsive to a condition of a compressor motor. Compressor according to claim 1, characterized in that: the control system is configured to vary a compulsory cycle control frequency responsive to a condition of a compressor motor and a fluctuation in a temperature detected at a conditioned environment. Method for operating a compressor according to claim 1, characterized in that it comprises: determining a desired loading state; and binding cycle modulation of the means to provide the desired loading state. A method according to claim 12 further comprising: altering a compulsory cycle modulation frequency responsive to a loading condition of a compressor motor. The method of claim 12 further comprising: altering a frequency of the obligatory cycle modulation responsive to a detected temperature fluctuation of a conditioned environment. A method according to claim 12 further comprising: varying a frequency of compulsory cycle modulation responsive to a detected temperature of a compressor motor. Method according to claim 12, characterized in that: the compulsory cycle modulation comprises a bistatic pulse width modulation. A screw compressor comprising: a housing (302) having first (330) and second (340) ports along a flow path; a first rotor (306) having a lobed body and shaft (510) and mounted to the housing for rotation about the first rotor shaft; and a second rotor (308; 310) having: a lobed body entangled with the body of the first rotor; and an axis (512; 514), the second rotor mounted to the housing for rotation about the second rotor axis and cooperating with the first rotor (306) and housing (302) to define a compression path between the suction position ( 332) and discharge (342) along the flow path, characterized in that: a blocking part (352) of the housing is mounted for longitudinal movement of the blocking part (352) relative to a remainder of the housing between a first position that engages the lobed bodies to define at least one compression pocket and a second retracted position from the first position. Compressor according to claim 17, characterized in that it further comprises: an actuator (380) coupled to the locking portion to move the locking portion between the first and second positions. Compressor according to Claim 17, characterized in that it further comprises: means (380, 390) for moving the locking part between the first and second positions. Compressor according to Claim 17, characterized in that: a spring (370) inclines the locking portion of the second position towards the first position. Compressor according to Claim 17, characterized in that: the first position is relatively towards one end of the housing section; and a spring (370) tilts the movable rotor from the second position to the first position. Compressor according to Claim 17, characterized in that: the actuator is fluid operated. Compressor according to Claim 22, characterized in that: the liquid is refrigerant. Compressor according to claim 17, further comprising: a controller (390) coupled to the actuator and configured to provide control of the compressor capacity by modulating the locking portion between the first and second positions. Compressor according to Claim 17, characterized in that: the compressor does not have a discharge valve. Compressor according to Claim 17, characterized in that: the compressor does not have variable speed control. Compressor method according to claim 17, characterized in that it comprises: determining a desired loading state; and binding cycle by modulating an actuator (380) of movement between first and second positions to provide the desired loading state. Method according to claim 27, characterized in that: the compulsory cycle modulation is performed while operating a compressor motor at an essentially fixed speed. A method according to claim 27, characterized in that: the compulsory cycle modulation is performed via a controller and the actuator operates fluidly to provide the desired loading state. Method according to claim 27, characterized in that: the actuator modulation (380) operates against a bias spring (370).