Undercompression and overcompression free helical screw rotary compressor

SWEDEN [B] (19) SE (11) PUBLISHING LETTERS

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PATENT AND

REGISTRATION AUTHORITY (51) International class² (44) Application submitted and publication document published (41) Application publicly available (22) Patent application received (30) Priority information

78-07-31 Publication number

76-01-27

75-07-01

7507554-9 F 04 C 17/12

403 171 (32) Date (33) Country (31) Nr

74-07-26 US 492,084

The numbers in brackets indicate international identification code. INID code. Letters in cherries indicate international document code (71) Applicant: DUNHAM-BUSH, INC., WEST HARTFORD, CONN. US (72) Inventor: DN Shaw, Unionville, Conn.

(74) 0mbud: Wennborg &lt;54) Name: Screw compressor

The present invention relates to screw compressors and more particularly to the use of slide valves for controlling the compressor capacity and the outlet pressure.

Screw compressors operate with forced displacement of the working fluid, which is trapped in the closed threads of screw rotors with interlocking thread chambers and grooves. The screw rotors are rotatably mounted in intersecting boreholes, which have shafts located in a common plane and form the cylinder portion of the compressor housing. In order to allow control of the compressor capacity and the pressure of the working fluid at the compressor outlet, the compressor has been provided with valve slides arranged in axially extending recesses in the cylinder part, which are in open communication with said bores on the respective sides of the screws which engage one another. As an example of the use of such slide valves in screw compressors, reference can be made to US Patent 3,088,659

In order to improve the lubrication and cooling of the parts of the compressor that form its working chamber, attempts have been made to inject liquid coolant, water, oil and gas at relatively low levels.

Temperature in the closed thread of the compressor by means of a port arranged in the valve slide, which opens into the compressor's working chamber on the upstream side of the outlet port of the compressor and is movable together with the valve slide to allow an automatic displacement thereof in the displacement of the valve slide. , which regulates the machine's capacity by redirecting a portion of the compressed working fluid to the suction port. Such injection of liquid coolant is described in US Patent 3,795,117 ·

The present invention relates to a screw compressor of the type in which the compressor housing comprises a cylinder part which is provided with intersecting bores with axes lying in a common plane, which bores are located between axially spaced apart gable parts. wherein low-pressure and high-pressure ports communicate with the bores at opposite ends thereof and screw rotors with mutually threaded cam and groove are rotatably arranged in the bores. An axially extending recess is provided in the cylinder portion of the compressor housing in open communication with said bores, and a valve slide is disposed axially displaceable in the recess, the inner surface of the valve slide being complementary to the circumference of the portion of the bore, the recess being opposite. provided in sealing abutment against the screw rotors. The outlet port has at least a portion of the same located in the cylinder portion of the compressor housing, the valve slide being movable between the extreme positions in which the outlet port is open and open, respectively. closed. The valve slide is of sufficient length to cover the entire remaining length of the center of the rotor device within the entire range of the valve slide mobility between its extremity positions. According to the invention there are means for sensing the pressure of the working fluid in a closed thread adjacent the end of the valve slide which can close communication between the outlet port and the closed thread, and means for sensing the pressure of the working fluid in the outlet port and for comparing these two pressures. Further, motor or drive means for automatic movement of the valve slide in the axial direction are provided to provide a smoothing between said pressure and prevent under-compression or over-compression of the working fluid in the closed thread prior to the discharge of the fluid therefrom.

The valve slide may conveniently be provided with a sensing port which communicates with the closed thread, wherein connecting passages in the slide valve can connect said port to the means located outside the compressor housing for comparing the discharge pressure of the compressor with the outlet port of the compressor. The valve slide can be moved axially by a drive piston which is slidably received in an associated cylinder and connected to the valve slide by a piston rod. A control valve actuated by the pressure difference regulates the flow of drive fluid to oeh from either side of said piston to adjust the valve slide so that the two gas pressures are equal. The control valve, which regulates the drive fluid supply to the respective valve. from the piston, may suitably comprise a valve piston which has at its opposite ends portions which are directly exposed to the pressure in the closed thread and, respectively. the pressure at the outlet port of the compressor to be affected by said pressure.

In a second embodiment of the invention there are a pair of valve slides on mutually opposite sides of the interlocking screw rotors. These valve slides, which are identical, are located at opposite sides of the cylinder part of the compressor housing and are movable between external positions, in which an associated gate is fully open and open, respectively. is substantially closed, the length of each valve slide being sufficient to cover the remaining length of the center of the rotor assembly and the two valve slides being mutually oriented. The screw compressor can be optionally operated in either direction, the ports acting either as suction ports or outlet ports for the compressor depending on the direction of rotation. The valve slides provide either a control of the compressor capacity or an adjustment of the pressure in the closed thread to the pressure in the compressor outlet line. The possibility of reversing the direction of rotation of the compressor eliminates the need for a reversing valve when the compressor is to be used as a heat pump for defrosting a cooling system.

The invention is further described below with reference to the accompanying drawings, in which Fig. 1 shows a longitudinal section through a screw compressor according to a first embodiment of the invention, which is provided with a valve for adjusting the pressure in the closed thread at the output side of the machine to the pressure in the outlet line at the outlet port, fig. 2 a longitudinal section through a reversible screw compressor according to a second embodiment of the invention, which is intended for heat pump use and is provided with a plurality of sliding valves, Fig. 3 shows a pressure diagram for the compression cycle of a screw compressor included in a heat pump system in Fig. 2 compared to a compressor with a single conventional slide valve for capacity control,

Fig. 4 is a pressure diagram of the screw compressor of Fig. 2 during a heating cycle compared to a similar conventional screw compressor with a single conventional capacity valve control valve, and Fig. 5 is an electrical wiring diagram of one as the drive motor of the compressor of Fig. 2. used electric motor with associated reversing switch.

The screw compressor 10 shown in Fig. 1 comprises a compressor housing with a central cylinder part 12, which is located between two gable parts 14 and 16 and contains a working chamber formed by two intersecting bores, of which only one, denoted by 18, has shown. In these bores, two screw rotors 20 and 21 with parallel shafts are rotatably mounted in engagement with each other. The screw compressor is with respect to the design of the rotors and their storage of conventional design. Thus, the two rotors have helically extending cams and intermediate grooves by which they engage each other, and are rotatably stored in respective bores by suitable bearings. Thus, for example, the rotor 20 is mounted on a shaft 22 which is stored at one end of it in the end portion 14, while on the other side of the screw 20 it is mounted in ball bearings 26 supported by the end portion 16 which are mounted inside a end cap 28 by means of of a sleeve 30 ·

The shaft 22 protrudes outside the housing 28 and is provided at its end with a wedge groove 32, intended to facilitate a secure connection with an electric motor or other external drive for the compressor.

In the embodiment of Fig. 1, the compressor is intended to rotate only in one direction, namely in such a way that gas or other working fluid will pass through an inlet duct 34 in the end portion 14 and an inlet port 36 into the working chamber formed by the one another. engaging screw threads. No capability control device is shown in Fig. 1. The characteristic of the invention instead consists in the fact that the compressor is provided with a slide valve element 38 which serves to adjust the pressure in the closed thread at the outlet side of the compressor, ie. adjacent to the end portion 16, to the gas pressure prevailing in the outlet channel of the compressor at the outlet port 40. At the end of the slide valve member 38. A characteristic feature of the screw rotors is that the flanks of the so-called the thread chambers of the screw or male screw rotor are convexly arched and that the intermediate grooves are located substantially inside the dividing or rolling circle of the so-called slider or female screw rotor. A further distinguishing feature of such rotors is that it

7507554-9 effective enclosure angle of the thread chambers is less than 360 °. The compressor housing is therefore provided with a high pressure outlet port 40, the main part of which is located on one side of a plane through the rotor shafts, the outlet port being arranged in the end portion 16 located at the high pressure side of the compressor. The outlet port 40 communicates with an outlet channel 28 in the end wall 42. As previously mentioned, the gable portion 14 of the compressor housing located on the low pressure side is provided with an inlet duct 34 which is connected via an inlet port 36 to the corresponding end of the respective bore 18 on the opposite side of the plane passing through the rotor shafts in relation to the outlet port 40.

The cylinder part 12 is further provided with a centrally located, axially extending cylindrical recess 44, which at one end is connected to the outlet port 40 and at its other end extends axially past the low wall side 26. The recess 44 is open to the the boreholes formed the working chamber. In this recess 44, the slide valve element 38 is arranged longitudinally displaceable. The axial position of the valve slide 38 within the recess 44 can be changed by means of a piston rod 46 which mechanically connects the valve slide 38 with a piston 48 of a servo motor 51. The piston 48 is sealed and slidably mounted in a cylinder $ 0 mounted at the end portion 14 , which is provided with a sealed opening through which the piston rod 46 passes. A cover 52 is provided at the outer end of the cylinder 5θ to seal tightly the chamber cf. within the cylinder in which the piston 48 is slidably disposed. The inner surface facing the screw rotors% of the valve slide 38 is so designed as to replace the cut parts of the bore holes for the screw rotors. A portion of the valve slide 38 engages slidably and sealingly with a recessed portion 60 of the end portion 14 so that the valve slide, regardless of its position, has sufficient length to cover the entire remaining length of the rotor device facing the same within the entire range of mobility between its extremity positions, which are determined of the recessed portion 60 and the valve surface as the contact surface with the end surface 62 serving the high pressure side 16 located.

In compression, an elastic fluid, which may consist of a gaseous coolant, for example Freon, will be sucked in through the low pressure or inlet port 36 and fill the rotor grooves. As the rotors rotate, interacting pairs of thread chambers of the rotors which engage with each other at the high pressure side of the compressor will form fish bone-like working chambers. During the continued rotation of the rotors, these working chambers, which form compression chambers or closed threads, will

7507554-9 decrease in volume as the point of engagement between any pair of thread chambers forming the top of a given compression chamber or thread moves axially to the high pressure side wall 64 while decreasing the volume of the compression chamber until it becomes equal to zero. reaches the plane of the end wall 64. The compression chamber is closed by the interface% of the valve slide 38 which faces and seals against the tops of the thread chambers, which restrict the compression chambers and the chambers respectively. the closed threads. Outflow of compressed fluid occurs when the peaks of the rotor chambers forming the leading edge of the compression chambers pass the control edge 66 of the valve slide 38, which is substantially the right edge of the valve slide 38, establishing a connection between the closed thread or compression chamber and the outlet port 40. Moving the valve slide 38 in the left direction causes a shortening of the compression time, while a movement of the valve slide to the right causes an increase in the compression time and an increase in the pressure ratio between the compressor inlet and outlet. Thus, assuming that the initial volume of the closed thread before it reaches the edge of the valve slide 66 is constant, the valve slide can provide a variation of the compressor's compression ratio. In reality, this means a possibility of controlling the pressure of the gas which is discharged from the closed thread to the outlet port 40.

If the pressure in the outlet port 40 is lower than in the closed thread when it reaches the edge 66, over-compression occurs, with the pressure ethos of the gas volume immediately reduced to conform with the pressure in the outlet port of the compressor so that the over-compression effect is lost. This can result in considerable power losses. Similarly, if the pressure of the working fluid in the closed thread, before it reaches the edge 66., is lower than the pressure in the outlet port, the output gas will be compressed to the pressure prevailing in that port when the connection is opened between the outlet port and the closed port. thread. Significant power losses. can thus occur as a result of either under-compression or over-compression. These losses have been graphically illustrated in Figures 3 and 4.

The invention is intended to enable an automatic adjustment of the valve slide 38 to adjust the fluid pressure in the closed thread or the working chamber at the discharge point determined by the valve slide edge 66 to the working pressure of the working fluid at the outlet port 40. The slide valve can for this purpose be provided with an inclined direction.

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70, which at the inwardly facing surface% of the valve body forms a sensing port 72 which opens at the closed thread and allows a sensing of the pressure of the compressed working fluid therein at a stage of the compression cycle immediately prior to the dispensing time. In addition, the valve slide is drilled at a location designated by 74 and provided with a widened recess 76 through which a diameter-reduced portion 46a of the piston rod 46 passes. A portion 46b of the larger diameter piston rod forms a shoulder 78 which cooperates with a head 81 at the end of the piston rod to lock the valve slide 38 at the piston rod. The piston rod 46 has a central bore 80 which extends along practically its entire length but is closed by the diameter enlarged head 81. A plurality of radial holes 82 are provided in the piston rod 46 to connect the central bore 80 to the annular cavity formed by the recess 76 in the valve slide 38, which is connected to the port 72 via the channel 70. The piston rod 46 carries a telescopic-like manner at its opposite end. with the cover 52 rigidly and sealingly connected tube 84, which is slidably received in the bore 80. A fluid passage 86 in the lid 52 is connected by a conduit 88 to the valve housing 90 of a control valve 92. The control valve 92 has inside the valve housing a longitudinal cylindrical bore 94 in which a valve piston 96 is slidably received. The valve piston 96 has four piston chambers 98, 100, 102 and 104, the diameter of which is slightly smaller than the diameter of the bore 94 in the valve housing 90. The various piston chambers are connected to each other by means of intermediate diameter reducing parts 106. The valve housing 90 has an axially directed port 108 at each end, respectively. 110. Furthermore, in the casing wall of the valve body there is an inlet port 112 which is connected via a conduit 114 to a supply source for supplying a feeder fluid in the direction indicated by arrow 116. In addition, the valve housing has two ports 118 and 120 connected to a common outlet line 122 through which the fluid in question can be discharged from the control valve 92 in the direction indicated by arrow 124. On the opposite side of the valve housing 90 are two ports 126 and 128, which via 130 and 130 respectively. 132 designated lines are connected to mutually opposite sides of piston 48 located within chamber 54 located within cylinder 50. This chamber 54 is closely spaced from bore 80 of piston rod 46. Control valve 90 and piston 48 together form a conventional circuit. Optionally, a driving fluid represented by arrow 116 is supplied to the space on the left or right side of the piston 48 while fluid is discharged from the opposite side of the piston through the control valve 92 through the port 118 and 21, respectively. 120 and to the outlet conduit 122, from which said fluid is fed back to a sump or reservoir for the driving fluid.

An important relation of the device is that the conduit 88 connects the sensing port 72 of the closed thread with the left end surface of the control valve piston cam 98. The port 110 located at the opposite end of the control valve is connected to the outlet duct 4-2 by a conduit 136, whereby the pressure in this duct , i.e. the pressure in the outlet pipe of the compressor will act on the outer end surface of the control valve piston cam 104-. The two aforementioned end surfaces of the piston chambers 98 and 104- are mutually similar in size, which means that the valve piston 96 will shift to the right or left depending on whether the pressure in the compressor outlet duct 4-2 is lower or higher than the pressure sensed at the port 72 in the closed thread. When the piston 96 of the steering valve is in the position shown in FIG. 1 in the position shown, the drive fluid 116 will be directed to the space to the left of the piston 4-8 and endeavor to shift this piston in the right direction to cause the compressor to discharge gas under higher pressure to the outlet port 4-0. This, of course, results in an increase in the pressure sensed at the port 72, which is transmitted via the channel 70, the recess 76, the radial channels '82, the bore 80 in the piston rod 4-6, the channel 86 in the lid 52, the conduit 88 and the port 108. the end surface of the piston cam 98. When this pressure exceeds the pressure acting simultaneously on the opposite side of the valve piston 96, i.e. on the outer end surface of the piston cam 104-, and if the pressure prevailing in the outlet duct 4-2, the control valve piston 96 will be moved to the right from its shown position. Hereby, the drive fluid will instead be measured to the space located to the right of the piston 4-8, whereby it seeks to move the valve slide 38 to the left to provide a reduction in the pressure of the closed thread at its outlet end by opening the connection between the closed thread and the gate 4-0 at an earlier stage during the compression cycle.

Fig. 2 shows a second embodiment of the invention, wherein the screw compressor is arranged to operate optionally in either of the two possible directions. The inlet or low pressure side of the compressor can hereby change to become its high pressure or outlet side and vice versa. Elements included in the device according to Fig. 2, which are correspondingly in the device according to Fig. 1, are provided with the reference numerals used in the latter figure. In the embodiment of FIG. 2 shown in the embodiment there is a second slide valve element 38 * which is slidably stored in the compressor housing

7507554-9 on the opposite side of the interlocking screw rotors with respect to the valve slide 38. This second valve slide 38 is forcibly controlled between its outer positions by means of a servo-controlled actuating piston, which is in principle arranged in the same way as the actuating piston for the valve slide 38 and is provided. with an associated control valve. The two valve slides 3θ and 38 'are mutually opposite in orientation and arranged at the outlet and the machine respectively. inlet side, which, however, changes when the direction of rotation of the compressor is reversed. The screw compressor 10 'shown in Fig. 2 has a housing or housing with a central cylinder part 12^z, which is located between two gable parts 1V and 16 'and contains a working chamber formed by two intersecting bores. In these bores, two screw rotors 20 and 21 with helically extending cams and intermediate grooves are arranged in engagement with each other and with their shafts in a common plane. The rotor 20 is mounted on a shaft 22 in substantially the same manner as in the first embodiment. Many of the former with reference to FIG. 1 The details described herein will be omitted for the purpose of brevity and refer to the earlier description of the embodiment of Fig. 1. In order to illustrate the similarity of function between the two embodiments, it can be mentioned that the working fluid, for example a gaseous coolant, can flow into the inlet duct 34 and pass to the inlet port 36 at the suction side of the machine and to the working chamber formed by the two mutually engaging the rotors and those for recording these serving bores. In the device of FIG. 2 however, the capacity of the machine is controlled by the valve slide 38, which, relative to the valve slide 38, is located on the opposite side of the plane in which the two rotary shafts of the cooperating screws 20 and 21 are located. The shaft 22 passes through a gable cover 28 ^ and is stored in the manner previously described with reference to Fig. 1. The shaft 22 is further provided with a wedge groove 32 for connecting the same with a reversible electric drive motor M of FIG. 5 schematically shown embodiment. Contrary to the embodiment of Fig. 1, the compressor of Fig. 2 can be caused to rotate in the inverted direction, the outlet duct 4-2 forming the suction duct, while the suction duct 34 forming the duct duct. The compressor housing is provided with a port 4-0, which in this case acts as a high-pressure outlet port and is located on one side of a plane passing through the two rotor shafts adjacent one end of the machine 16. The gate 4-0 is connected to the outlet duct 4-2.

In the second embodiment, the cylinder part 12 of the compressor housing is provided with two opposed, centrally located and axially extending cylindrical recesses 44 and 44 'which face the working chamber formed by the bores of the screw rotors and facing each other. The valve slide 38 is stored longitudinally slidable in the recess 44, while the oppositely oriented valve slide 38 'is slidably stored in the recess 44'. The axial position of the valve slide 38 can be controlled in the same way as in the first embodiment by means of a piston rod 46 which mechanically connects the valve slide 38 with the drive or actuating piston 48 of a servomotor 51. The piston is sealed and slidably stored in a cylinder 5θ. whereby the valve slide 38 can be moved axially between the end positions determined by the end wall 64 of the compressor housing part 16 'and a recess 60 in the part 14'. 92 denotes a control valve which regulates the supply and discharge of pressurized drive fluid to the cylindrical chamber 54 in which the actuating piston 48 is stored. By means of the control valve 92, the driving fluid can be directed to the space located on one or the other side of the piston 48, at the same time as the driving fluid is diverted from the space on the opposite side of this piston to an outlet line 124 and a sump connected to it. The control valve 92 is the front dog with the cylinder 5θ by two lines 130 and 132. The valve piston 96 belonging to the control valve 92 is designed and arranged to operate in substantially the same way as in the embodiment of Fig. 1. The inner surface 56 of the valve slide 38 facing the adjacent rotor is designed to replace the cut-off portions of the rotor bore wall of the compressor housing, a portion of the valve slide 38 constantly engaging displaceable and sealing with a recessed portion of the end portion 14 and the valve slide 38, regardless of its instantaneous position, is of sufficient length to cover the remaining portion of the rotor assembly within the entire range of movement of the valve slide between its end positions; which are determined by a recessed portion 60 and the surface 64 of the end portion 16 '.

Correspondingly, the inner surface 56 'of the valve slide 38' facing the rotors is arranged to provide a replacement for the cut-away portion of the bore serving to receive said rotor and a portion of the valve slide 38 'engages slidably and seals with a recessed portion 60 'at the end portion 16, wherein the valve slide is of sufficient length to cover the remaining length of the rotor assembly facing the same within the entire range of movement of the valve slide between its extremity positions, which is determined by the portion 60 * and the end surface 64 *. Except that the valve slide 38 'is opposite in relation to the valve slide 38, the two relays are mutually similar and arranged to operate in a similar manner except that they perform various functions during machine operation, which are automatically shifted depending on the direction of rotation of the compressor. The valve slide 38 * is connected by a piston rod 48 * to a piston 48 * associated with a servo motor 51 *, which is slidably stored within a cylinder JO *. A pipe 84 * which is fixedly mounted in a lid 52^z slides into the piston rod 46 *, which is provided with a longitudinal central channel 80 * which connects via the tube 84 * the line designated 88 * to the pressure sensing port 72 'of the valve slide 38 *. This connection is completed by an obliquely directed channel 70 ° and a recess 76 * in the valve slide 38 * and radial holes 82 * in the piston rod 46 *. The valve slide 38 * is fixed to the piston rod 46 *, which is also rigidly connected to the piston 48 *. The valve slide 38 * will thereby move together with the piston 48 *, the position of which inside the chamber 5 ^ "is changed depending on on which side of the piston said chamber receives driving fluid under pressure via the line 130 'and respectively. 132 * from the control valve 92 *. The control valve 92 * is in principle a copy of the valve 92 and the servo system for the valve slide 38 * corresponds to that of the valve slide 38. Pressure fluid is fed to the control valve 92 'via a conduit 114 * for forwarding to the portion of the chamber 54 * located on one or other side of the piston 48 *, depending on the position of the control valve piston 96 *. At the same time, fluid is fed back to the pump through the conduit 122 * from the space on the opposite side of the piston relative to that at which the fluid supply occurs. The gas pressure in the closed thread at port 72 * is transmitted via conduit 88 * to control valve 92 *, so that said pressure will act on the outer end surface of control valve piston cam 98 *. At the opposite side of the control valve, the end surface of the piston cam 104 * is simultaneously exposed to the fluid pressure in a conduit 136 *, which is connected to the duct 34 in the end portion 14 * of the compressor housing.

Contrary to the case of the first embodiment, the lines 88 and 110 respectively connected to ports 108 and 110 of the control valve 92 are respectively. 136 and corresponding lines 88 'and 136 *, which are connected to the ports 108 * and 110 * of the control valve 92 * provided with shut-off valves which allow a selective control of the functions of the slide valves depending on whether the compressor is operated in one or the other direction. The conduit 88 is thus provided with a valve 150 connected thereto, while the conduit 136 contains a valve 152 and the conduit

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Ι36 'is equipped with a valve 152' and finally the conduit 88 'contains a valve 150'. These valves can be automatic or manual! controlled oeh serves to close or open said lines.

Further, a conduit 154 containing a further shut-off valve 158 is connected to the conduit 88 between the valve 150 and the port 108. of the control valve 92. On the opposite side of the control valve 92, a conduit 156 containing a shut-off valve l60 is connected to conduit 136 between shut-off valve 152 and control valve port 110. Similarly, a conduit 154 'containing a shut-off valve 158 * is connected to the conduit 88' between the valve 150 'and the port 108', while a conduit 156 'containing a shut-off valve 160' is connected to the conduit 136 'between the port 110 'and valve 152'.

The lines 154, 154 ', 156 and 156' can be selectively applied to fluid pressure signals which allow the control valves to be adjusted to actuate associated valve valves in a manner corresponding to the desired function of the compressor. This allows one of the two valve slides 38 and 38 'to provide a capacity control, while the other simultaneously serves to automatically adjust the pressure in the closed thread in the compressor's working chamber to the pressure in the compressor outlet line at the outlet port.

Assuming that duct 34 constitutes an inlet duct and duct 42 forms the outlet duct of the compressor, as indicated by the arrows, valve slide 38 will serve to adapt the pressure in the closed thread to the pressure in the outlet conduit at outlet port 40, while the valve slide 38 'provides a capacity of the valve. In this case, for the servo system which controls the valve slide 38, the valves 158 and 160 in the lines 154 and 16 respectively apply. 156 are closed, while valves 150 and 152 in conduits 88, respectively. 136 are open. Instead, in the servo system for valve slide 38 ', valves 152' and 150 'in conduits 136' and 2 'respectively. 88 'closed, while the valves l60' and 158 'in the conduits 156' respectively. 154 'are open. This means that the valve piston 96 of the control valve 92, by means of its outer piston chambers 98 and 104, can make a comparison between the pressure in the closed thread at the port 72 and the conduction pressure at the outlet side of the compressor, ie. the pressure in the outlet duct 42. The valve slide 38 will hereby automatically move to the right or left to balance these two pressures. Thus, in this setting of the device, valve slide 38 will perform identically the same function as in the embodiment of Fig. 1.

7507554-9 • When valves 152 * and 150 * are closed, valve slide 38 'will perform a capacity control. As indicated by arrow CP on the upstream side of valve 160 'in conduit 156', a control signal represented by the hoist, said arrow, when applied to the end surface of control valve 92 piston cam 104 *, moves valve piston 96 'to the right so that drive fluid can be fed. to chamber 54 'through conduit 130 * to act on the right end surface of piston 48 *. This results in a tendency for movement of valve slide 38 * in the left direction, causing a decrease in the area of ​​port 36 as a result of the edge 66 * of valve valve 38 * being shifted to the left. The screw compressor is designed to have minimal capacity when the valve slide 38 * with its end surface 62 * abuts against the end surface 64 * of the end portion 14 *. As the valve slide 38 * moves in the left-to-right direction, an increase in compressor capacity is obtained, as an increasing portion of the screw rotors and the bores of these defined working chambers are exposed to the inlet port. The flowing gas from the inlet duct 34 is subjected to adiabatic expansion and re-compression without consuming any energy by the machine until the pressure of the enclosed volume in the closed thread reaches the inlet pressure while reducing said volume. Since the interlocking screws are open to the suction side of the machine via the edge 66 * of the valve slide 38 *, a given volume of aspirated gas will be trapped in a closed thread and this volume expand as the volume of the closed thread increases momentarily before recompression. during this period of the cycle as the adiabatic expansion and recompression occurs. However, this occurs without absorption of energy from the compressor until the inlet pressure is reached during subsequent reduction of the trapped volume.

Fig. 3 shows a pressure-volume diagram of a cooling cycle for the compressor of Fig. 2, whereby the adiabatic expansion and recompression at ideal relief is effected by the valve slide 38 *. Expansion can occur at the compressor according to Fig. 2 between points A and B and recompression between points B and C. For a compressor with a conventional slide valve, the corresponding process takes place along the curve from point A to point B * and thence to point C *.

In the known case, the slide valve allows an initial compression of the enclosed volume, some of which is then returned to the suction side of the machine, the partial compression of the enclosed volume constituting a loss work.

If it is necessary to increase the capacity of the machine, a control signal is applied to the line 154 * while the valves l60 *, 152 *

7507554-9 lL and 150 'are closed. The valve 158 'is open to allow the control signal to be fed to the outer end surface of the piston cam 98' and cause a displacement of the valve body 96 'to the left so that high pressure fluid can be supplied to the space located to the left of the piston 4-8'. cause a displacement of the valve slide 38 'serving as a capacity control or relief mechanism to increase the compressor load.

While valve slide 38 'serves to regulate the machine's capacity according to prevailing needs, slide valve 38 is automatically adjusted to adapt the pressure sensed at port 72 in the closed thread to the pressure in compressor outlet duct 4-2 immediately downstream of outlet port 4-0. In this case, the valves 150 and 152 are open, while the valves 158 and 160 are closed. This function is illustrated in Fig. 3.

Assuming that the gas in the closed thread is compressed to a higher pressure than that prevailing in the outlet conduit 4-2, said gas pressure immediately after the closed thread has reached the point where it is exposed to the outlet port 4-0 from the edge 66 of the slide valve 38 to be changed to conform to the pressure prevailing in the outlet duct. The pressure drop due to over-compression and the corresponding loss of energy can be observed by comparing the curve between points B and E and the actual work on the surface located within points D, E and F. Thus, the variable shut-off of the output makes it possible to achieve an ideal compression process and the ideal output point are constantly maintained regardless of the changes in operating conditions to which the compressor is subjected.

As shown in Figure 5? the motor M is provided with three windings A, B and C, intended to be supplied from a three-phase voltage source with phases 1, 2 and 3 · By 170, the contacts included in a supply switch are denoted by which the motor connection lines 172, 174 and 176 can be disconnected from the supply line. Two of the connection lines can be reversed or switched by means of an electromagnetically controlled switch 178 with an operating winding 180. The switch 178 then switches on the connection between the supply line and the connection lines 174- and 176, which are normally connected to the phases 2 and 3 of the supply lines, so that the motor winding A is instead connected to the phase 3 of the supply line, while the winding C is connected to the phase of the supply line 17

2nd The motor should be switched off from the supply voltage before the switch 178 is actuated to adjust its contacts.

The above described connection of the motor makes it possible to drive the compressor 10 'optionally in either direction, making the compressor particularly suitable for heat pump use or allowing the compressor. can be driven in the reverse direction to supply hot coolant to the condenser coil for cyclic defrosting without the need for special reversing valves or the like, as is the case with conventional plants. In FIG. 4 shows a pressure-volume diagram which relates to the heating cycle when using the compressor 10 as a heating point and illustrates how the slide valves according to the invention eliminate energy losses of the kind that occur due to the adiabatic expansion and recompression of a compressor with a conventional slide valve . Duct 34- is assumed in the case shown to act as an outlet duct, while duct 4-2 acts as an inlet duct. In addition to the loss of known devices eliminated by the invention and represented in the diagram by the area within points A, B and C *, the energy loss occurring by known compressors represented by the area defined by points E, D and D is also eliminated. . Namely, if there is no possibility of sensing the pressure in the closed thread, a sub-compression occurs and when the closed thread is opened at the outlet side of the compressor, the pressure in the closed thread rises immediately to the pressure in the outlet port, whereby excess energy is absorbed for the discharge of the compressed gas. flowing back into the closed thread.

Although not shown in the drawing, the compressor and the drive motor when the compressor is used in a heat pump system can be designed as a fully enclosed device, where the gas is allowed to pass directly along the windings of the motor. Hereby, the engine is cooled directly either by the inflow or outflow gas, the engine being cooled at the outflow from the compressor during one cycle, for example during the cooling cycle, while it is cooled by the inlet gas during the second cycle.

From the above description it can be seen that the invention results in an absolutely minimal power consumption irrespective of the operating cycle, condensing temperature, percent load on the compressor, etc. The compressor seeks by sensing parameters associated with it itself to balance the pressure in the closed thread to conform to the pressure in the outlet line. fully automatic way and without the need for complicated external control means.

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