Abstract:
The compressor includes a sealed housing defining a suction volume and a compression volume respectively provided on either side of a body contained in the housing, an oil injection circuit supplied with oil from an oil contained in a casing and adapted for injecting oil into the compression volume, the oil injection circuit comprising an electrovalve including a body attached to the wall of the sealed housing and a core movable under the action of a magnetic fluid between a closing position for injecting oil into the compression volume and an opening position preventing or limiting the injection of oil into the compression volume. The compressor includes a control system for moving the core of the electrovalve between the opening and closing positions based on the compressor speed and/or on the cooling gas discharge temperature.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a variable-speed scroll-type refrigeration compressor. 
     DESCRIPTION OF THE PRIOR ART 
     Document FR 2 885 966 describes a scroll compressor, also known as a scroll pump, comprising a sealed enclosure defined by a barrel defining a suction volume and a compression volume, one on either side of a body contained within the enclosure. The barrel defining the sealed enclosure comprises a refrigerant gas inlet. 
     An electric motor is located inside the sealed enclosure, with a stator on the outside, fixed relative to the barrel, and a rotor in a central position connected to a crankshaft-like drive shaft which has a first end driving an oil pump supplying oil from a sump in the bottom of the enclosure to a lubrication way in the center of the shaft. The lubrication way comprises lubrication ports for each guide bearing of the drive shaft. 
     The compression volume contains a compression stage comprising a fixed volute fitted with a scroll engaged in a scroll on a moving volute, the two scrolls defining at least one compression chamber of variable volume. The second end of the drive shaft is fitted with an eccentric which drives the moving volute in an orbital movement to compress the aspirated refrigerant gas. 
     From a practical point of view, the refrigerant gas arrives from the outside and enters the sealed enclosure. Some of the gas is drawn directly into the compression volume, while the rest of the gas passes through the motor before being drawn into the compression stage. All of the gas reaching the compression stage, either directly or first passing through the motor, is drawn by the compression stage into at least one compression chamber defined by the two scrolls, entering at the edge of the compression stage, and as the gas is carried towards the center of the scrolls it is compressed by the diminishing volume of the compression chambers due to the movement of the moving volute relative to the fixed volute. The compressed gas passes out from the center part into the compressed-gas receiving chamber. 
     Depending on the internal flow configuration of this type of compressor, the refrigerant gas entering the compressor can entrain oil, the oil coming from, for example, leaks from bearings or from the gas licking up the surface of the oil in the sump. 
     It should be observed that the proportion of oil in the refrigerant gas varies depending on the speed of rotation of the rotor of the electric motor. 
     Thus, when the rotor is turning slowly, the amount of oil circulating with the refrigerant gas is low, which can lower the performance of the compressor and reduces the lubrication of its various parts. 
     On the other hand, when the rotor is turning fast, the proportion of oil in the refrigerant gas leaving the compressor can become excessive. The direct consequence of this excessive proportion of oil in the gas is less efficient heat exchange by the exchangers situated downstream of the compressor. This is because the oil droplets contained in the gas tend to become deposited on the heat exchangers and form a layer of oil on them. 
     In addition, an excessive proportion of oil in the gas can also drain the oil sump. This could lead to destruction of the compressor. 
     Document U.S. Pat. No. 6,322,339 describes a way of improving the low-speed performance of a variable-speed compressor without harming its efficiency at high speed. The approach is to increase the amount of oil introduced into the gas stream at low speeds only. 
     Document U.S. Pat. No. 6,322,339 thus describes a variable-speed scroll-type refrigeration compressor comprising an oil injection line supplied with oil from oil contained in a sump in the bottom of the enclosure, the injection line being designed to inject oil into the compression volume. 
     The oil injection line comprises a valve housed in the sealed enclosure and movable between an open position allowing oil to be injected into the compression volume, and a closed position preventing the injection of oil into the compression volume, the valve being subjected to the action of a compression spring that tends to keep it in its open position. 
     The compression spring is designed to keep the valve in its open position as long as the pressure difference between the two sides of the valve is less than or equal to the spring&#39;s elasticity. As soon as this pressure difference becomes greater than the elasticity of the spring, the valve is moved to its closed position, preventing oil being injected into the compression volume. 
     It should be observed that the elasticity of the spring requires calibration to allow the valve to be moved to its open position as soon as the speed of rotation of the drive shaft falls below a predetermined value, and to its closed position as soon as the speed of rotation of the drive shaft rises above a predetermined value. 
     This sort of oil injection line has disadvantages as outlined below. 
     This calibration of the elasticity of the compression spring acting on the valve is complex and cannot be performed accurately. As a result, the means employed in document U.S. Pat. No. 6,322,339 are complex and cannot be used to accurately control the injection of oil into the compression volume. 
     Furthermore, the elasticity of the compression spring can vary over time. The means used in document U.S. Pat. No. 6,322,339 do not therefore keep the performance of the compressor constant. 
     Another disadvantage with this type of oil injection line is the fact that particles can insinuate themselves between the walls of the housing in which the valve slides, and the valve itself. These particles can interfere with the operation of the valve and therefore with that of the oil injection line. 
     In addition, locating the valve inside the barrel means that the valve is difficult to maintain. In particular, it is difficult to replace the compression spring or clean out the housing in which the valve slides. 
     Document JP 06 185479 describes a more accurate means of controlling the injection of oil into the compression volume. 
     Document JP 06 185479 describes a variable-speed scroll-type refrigeration compressor comprising an oil injection line supplied with oil from oil contained in a sump in the bottom of the enclosure and designed to inject oil into the compression volume, the oil injection line comprising a solenoid valve having a core that can be made to move by, a magnetic field, between a first position allowing oil to be injected into the compression volume and a second position preventing or limiting the injection of oil into the compression volume. The solenoid valve is on the outside of the sealed jacket of the compressor and comprises an oil inlet port supplied with oil by a supply pipe extending partly out of the sealed enclosure and connected to an outlet port of an oil pump located inside the oil sump, and an oil outlet port connected to an injection pipe extending partly outside of the sealed enclosure and leading into the compression volume. 
     The refrigeration compressor also comprises control means designed to move the solenoid valve core between its first and second positions. 
     The presence of the solenoid valve in the oil injection line gives more precise control over the injection of oil into the compression volume, because the calibration to a given value of the magnetic field which is intended to move the solenoid valve core can be performed accurately via control means. 
     However, the arrangement of the supply and injection pipes, which are at least partly outside of the sealed jacket, can lead to rupturing of the pipes as a result of unforeseen impacts or stresses during maintenance of the compressor. 
     This arrangement of the supply and injection pipes also necessitates creating openings in the sealed jacket of the compressor for the pipes to pass through. Creating such openings can allow leaks of refrigerant fluids into the atmosphere and therefore increase greenhouse gas emissions. 
     The purpose of the present invention is to solve these problems by providing a variable-speed scroll-type refrigeration compressor that is structurally simple and allows easy maintenance of the oil injection line, while allowing precise control over the injection of oil into the compression volume, reducing greenhouse gas emissions, and enhancing the protection of the compressor against external impacts and stresses. 
     SUMMARY OF THE INVENTION 
     To this end, the present invention relates to a variable-speed scroll-type refrigeration compressor comprising:
         a sealed enclosure defining a suction volume and a compression volume, one on either side of a body contained within the enclosure, the enclosure comprising a refrigerant gas inlet,   an oil injection line supplied with oil from oil contained in a sump in the bottom of the enclosure and designed to inject oil into the compression volume, the oil injection line comprising a solenoid valve having a core that can be made to move by a magnetic field, between a first position allowing oil to be injected into the compression volume and a second position preventing or limiting the injection of oil into the compression volume, and   control means for moving the solenoid valve core between its first and second positions,
 
said compressor being characterized in that the solenoid valve has a body attached to the wall of the sealed enclosure and containing the core,
 
and in that the control means are designed to move the solenoid valve core between its first and second positions, in response to the compressor speed and/or the refrigerant gas delivery temperature.
       

     The attachment of the solenoid valve to the wall of the sealed enclosure allows easy maintenance of the solenoid valve because the latter is easily accessible from the outside of the compressor. 
     Moreover, this attachment of the solenoid valve to the wall of the sealed enclosure avoids the creation of openings in the sealed jacket for the passage of the supply and injection pipes, and avoids having at least some of these pipes on the outside of the sealed jacket. This enhances the protection of the injection pipe and hence of the compressor against external impacts and stresses and reduces greenhouse gas emissions. 
     Advantageously, the body of the solenoid valve comprises a first body portion attached to the wall of the enclosure and a second body portion attached removably to the first body portion, outside of the sealed enclosure, the second body portion containing the solenoid valve core. This structure of the solenoid valve body further facilitates the maintenance of this solenoid valve. 
     The control means are preferably designed to move the solenoid valve core to its first position when the compressor speed is below a predetermined value or when the refrigerant gas delivery temperature is above a predetermined value. 
     In another embodiment of the invention, the control means are designed to move the solenoid valve core to its first position when the refrigerant gas delivery temperature is above a predetermined value and the compressor speed is below a predetermined value. 
     In accordance with another feature of the invention, the control means are designed to move the solenoid valve core to its second position when the compressor speed is above a predetermined value. 
     In accordance with yet another feature of the invention, the compressor comprises an electric motor having a stator and, integral with a crankshaft-like drive shaft, a rotor, a first end of which drives an oil pump supplying oil from the sump in the bottom of the enclosure to a way formed in the central part of the shaft, said compressor being characterized in that the oil injection line is supplied with oil by the oil pump which is driven by the first end of the drive shaft. 
     The solenoid valve advantageously comprises at least one oil inlet port supplied with oil by a supply pipe located inside the sealed enclosure and connected to an outlet port of the oil pump which is driven by the first end of the drive shaft, a first oil outlet port opening inside the sealed enclosure, and a second oil outlet port connected to at least one injection pipe located inside the sealed enclosure and opening into the compression volume. The pipes are advantageously subjected to small pressure differentials (that is, less than 3 bar) compared with the pressure in the low-pressure enclosure of the compressor (around 5 to 20 bar). This means that low-pressure pipe can be used. 
     The solenoid valve core is preferably movable, by a magnetic field, between a closed position of the first oil outlet port in which all the oil entering the solenoid valve through the oil inlet port is directed to the second oil outlet port, and an open position of the first oil outlet port in which all or nearly all the oil entering the solenoid valve through the oil inlet port is directed to the first oil outlet port. 
     Thus, whatever position the solenoid valve core is in, all of the oil arriving from the oil pump and entering the solenoid valve is redirected into the sealed enclosure and/or into the compression volume. With these arrangements the invention avoids increasing the delivery pressure of the oil pump, which would use more energy. 
     In another embodiment of the invention, the solenoid valve comprises an annular chamber connecting together the inlet and outlet ports of the solenoid valve. 
     The head losses in the second oil outlet port and in the injection pipe are advantageously much greater than those in the first oil outlet port. 
     In yet another embodiment of the invention, the solenoid valve comprises a pipe connecting the second oil outlet port to a connection port formed in the solenoid valve and leading into a bore formed in the solenoid valve and containing the core of the latter, the bore being connected to a chamber which in turn is connected to the oil inlet port and the first oil outlet port, and in that the core is designed to close the connection port when it is in its open position. 
     The injection pipe preferably comprises an injection nozzle at that end of the pipe which opens into the compression volume. 
     In accordance with another feature of the invention, the end of the injection pipe that opens into the compression volume is inserted into a through-bore formed inside the body separating the compression and suction volumes. 
     A pin is advantageously inserted in the end of the injection pipe that leads into the compression volume in such a way as to compress the injection pipe against the walls of the bore formed inside the body, the pin comprising an injection passage allowing oil to be injected into the compression volume. The pin is preferably a roll pin or a coiled pin. 
     In accordance with another feature of the invention, the compression volume comprises a fixed volute fitted with a scroll engaged in a scroll of a moving volute driven with an orbital movement, the moving volute bearing against the body separating the compression and suction volumes. 
     That end of the bore formed in the body which is directed towards the moving volute preferably comes to an open end outside of the area swept by the moving volute during its orbital movement. 
     Alternatively, that end of the bore formed in the body which is directed towards the moving volute comes to an open end within the area swept by the moving volute during its orbital movement. 
     Advantageously, the moving volute comprises at least one through-port designed to connect, during at least part of the movement of the moving volute, the end of the injection pipe that opens into the compression volume to a volume defined at least partly by the fixed and moving volutes. 
     However, the invention will be understood clearly with the help of the following description, referring to the labeled schematic drawing showing, as non-restrictive examples, a number of embodiments of this scroll compressor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal section through a first compressor. 
         FIGS. 2 and 3  are enlarged sections through a solenoid valve in a first embodiment of the invention in which the valve is shown in its closed and open positions, respectively. 
         FIGS. 4 and 5  are enlarged sections through a solenoid valve in a second embodiment of the invention, showing the valve in its closed and open positions, respectively. 
         FIG. 6  is a longitudinal section through a second compressor. 
         FIG. 7  is a partial longitudinal section through a third compressor. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, the same parts are given the same reference signs in the different embodiments. 
       FIG. 1  shows a variable-speed scroll-type sealed refrigeration compressor occupying a vertical position. However, the compressor according to the invention could occupy an inclined position, or a horizontal position, without significant modification to its structure. 
     The compressor shown in  FIG. 1  comprises a sealed enclosure defined by a barrel  2  whose top and bottom ends are closed by a cap  3  and a base  4  respectively. Weld seams may for example be used to assemble this enclosure. 
     The intermediate part of the compressor is occupied by a body  5  that defines two volumes, a suction volume situated beneath the body  5 , and a compression volume located above the latter. The barrel  2  comprises a refrigerant gas inlet leading into the suction volume to bring the gas to the compressor. 
     The body  5  serves as a mounting for the refrigerant gas compression stage  6 . This compression stage  6  comprises a fixed volute  7  fitted with a fixed scroll  8  which faces downwards, and a moving volute  9  bearing against the body  5  and fitted with a scroll  10  which faces upwards. The two scrolls  8  and  10  of the two volutes fit one inside the other to create compression chambers of variable volume. Gas is admitted into the compression stage from the outside, the compression chambers  11  having a variable volume which decreases from the outside towards the interior, when the moving volute  9  moves relative to the fixed volute  7 . The compressed gas escapes from the centre of the volutes through an opening  12  in the fixed volute  7  leading to a high-pressure chamber  13 , from which it is discharged by a connector  14 . 
     The compressor comprises an electric motor situated inside the suction volume. The speed of the electric motor can be varied by means of a variable-frequency electric generator. 
     The electric motor comprises a stator  15  with a rotor  16  in its center. The motor is attached to the barrel  2  by a collar  17  passing around the stator  15  and connected by tabs  18  to the barrel  2 . 
     The rotor  16  is connected to a drive shaft  19  with its top end off-center in the manner of a crankshaft. This top end is engaged in a sleeve part  20  of the moving volute  9 . When turned by the motor, the drive shaft  19  drives the moving volute  9  in an orbital movement. 
     The bottom end of the drive shaft  19  drives an oil pump  21  which supplies oil from a sump  22  defined by the base  4  to a lubrication way  23  formed inside the central part of the drive shaft. 
     The scroll compressor also comprises an oil injection line supplied with oil by the oil pump  21  driven by the bottom end of the drive shaft  19 . The oil injection line is designed to inject oil into the compression volume, and more particularly between the fixed  7  and moving  9  volutes. 
     The oil injection line comprises a solenoid valve  25  comprising a body  26  attached to the wall of the barrel  2  near the base  4 . 
     As shown more particularly in  FIGS. 2 and 3 , the body of the solenoid valve  25  comprises a first body portion  26   a  attached to the wall of the barrel  2  and a second body portion  26   b  attached removably to the first body portion  26   a  outside of the barrel  2 . 
     The solenoid valve  25  comprises an oil inlet port  27  supplied with oil by a supply pipe  28  arranged inside the barrel and connected to an outlet port of the oil pump  21 . The solenoid valve also comprises a first oil outlet port  29  opening into the barrel  2  and a second oil outlet port  30  connected to first and second injection pipes  31 ,  32  located inside the barrel and each leading into the compression volume. The oil inlet and outlet ports are formed in the first body portion  26   a  and lead into an annular chamber  33  formed in the first body portion  26   a . This annular chamber  33  allows the oil inlet and outlet ports of the solenoid valve to be connected to each other. 
     The solenoid valve comprises a metal core  34  housed in a bore  35  formed in the second body portion  26   b  and movable by a magnetic field, generated by a coil (not shown in the figures) surrounding the core  34 , between a closed position allowing oil to be injected into the compression volume, and an open position which prevents or limits the injection of oil into the compression volume. 
     More specifically, the core  34  of the solenoid valve is movable between a closed position of the first oil outlet port  29  shown in  FIG. 2 , in which all the oil entering the solenoid valve via the oil inlet port  27  is directed to the second oil outlet orifice  30  via the annular chamber  33 , and an open position of the first oil outlet port  29  shown in  FIG. 3  in which all or nearly all the oil entering the solenoid valve through the oil inlet port  27  is directed to the first oil outlet port  29 . 
     When the core is in its open position, all or nearly all the oil entering the solenoid valve is directed to the first oil outlet port  29  because the head losses in the second oil outlet port  30  and in the first and second injection pipes  31 ,  32  are much greater than those in the first oil outlet port  29 . 
     It should be pointed out that the core  34  of the solenoid valve  25  is also subjected to the action of a compression spring  45  housed between the bottom of the bore  35  and the core  34 . This compression spring helps to move the core  34  to its closed position. 
     It should be observed that the ends of the first and second injection pipes  31 ,  32  leading into the compression volume are inserted into through-bores  36 ,  37 , respectively, formed in the body  5  separating the compression and suction volumes. The bores  36 ,  37  are approximately parallel to the compressor axis. 
     As shown in  FIG. 1 , the open ends of the bores  36 ,  37  directed towards the moving volute  9  are outside of the surface swept by the latter in its orbital movement. In another embodiment, either or both of the open ends of the bores  36 ,  37  directed towards the moving volute may be within the surface swept by the latter. 
     The first and second injection pipes  31 ,  32  each comprise an injection nozzle at their end directed into the compression volume. 
     Each injection nozzle takes the form of a pin  38  inserted in the end of the corresponding injection pipe  31 ,  32  directed towards the body  5 . This arrangement of the pins  38  allows the first and second injection pipes  31 ,  32  to be compressed against the walls of the corresponding bores  36 ,  37 , respectively. The result is that the first and second injection pipes  31 ,  32  are held firmly in the body  5 . 
     Each pin  38  comprises an injection passage allowing oil to be injected into the compression volume. The pins  38  are advantageously roll pins or coiled pins. 
     The compressor comprises control means for moving the core  34  of the solenoid valve  25  to its closed position when the speed of the compressor is less than a predetermined threshold value and moving the core of the solenoid valve to its open position when the speed of the compressor is above this predetermined value. 
     The control means are more particularly constructed to modify the magnetic field generated by the coil of the solenoid valve in response to the speed of the electric motor of the compressor in such a way as to allow the core  34  to move between its open and closed positions as the speed of the motor either exceeds or falls below, the predetermined value. 
     The operation of the scroll compressor will now be described. 
     When the scroll compressor according to the invention is started, the rotor  16  turns the drive shaft  19  and the oil pump  21  pumps oil from the sump  22  into the supply pipe  28 . The oil then enters the oil inlet port  27  of the solenoid valve  25 . As long as the speed of the compressor is below the predetermined threshold value, the core  34  of the solenoid valve is in its closed position, and oil that has entered the solenoid valve is therefore directed to the second oil outlet port  30  via the annular chamber  33 , and thence into the first and second injection pipes  31 ,  32 . The oil is finally injected into the compression volume through the injection nozzles. 
     It should be observed that the end of the bore  37  directed towards the moving volute  9  can be closed by the latter for at least part of the orbital movement of the moving volute. This closing off of the end of the bore  37  directed towards the moving volute  9  not only lubricates the interface between the body  5  and the moving volute, but also regulates the amount of oil injected into the compression volume. 
     When the speed of the compressor exceeds the predetermined value, the control means move the core  34  of the solenoid valve to its open position. As a result, all or nearly all the oil entering the solenoid valve through the oil inlet port  27  is directed to the first oil outlet port  29 , because head losses in the second oil outlet orifice  30  and in the first and second injection pipes  31 ,  32  are much greater than those in the first oil outlet port  29 . As a result, all or nearly all the oil that has entered the solenoid valve falls by gravity into the oil sump  22 . 
     The compressor according to the invention allows the amount of oil present in the compression volume, and therefore the proportion of oil in the refrigerant gas to be increased only when the speed of the compressor is low and below the predetermined threshold value. The present invention improves the low-speed performance of the variable-speed compressor without reducing its efficiency at high speed. 
     In another embodiment of the invention, shown in  FIGS. 4 and 5 , the solenoid valve  25  has a pipe  40  connecting the second outlet port  30  to a connection port  41  formed in the second body portion  26   b . The connection port  41  leads into the bottom of the bore  35  containing the core  34  of the solenoid valve. 
     The connection port  41  leads to an annular chamber  42  formed inside the first body portion  26   a  via a passage running between the bore  35  and the core  34 . The oil inlet port  27  and the first oil outlet port  29  connect with the annular chamber  42 . 
     In this embodiment of the invention, the core  34  is movable between a first closed position in which the first oil outlet port  29  is closed and the connection port  41  is open, as shown in  FIG. 4 , and a second position in which the first oil outlet port  29  is open and the connection port  41  is closed, as shown in  FIG. 5 . 
     In the first position of the core  34  shown in  FIG. 4 , all the oil entering the solenoid valve through the oil inlet port  27  is directed towards the second oil outlet port  30  via the annular chamber  42 , the connection port  41  and the pipe  40 . 
     In the second position of the core  34  shown in  FIG. 5 , all of the oil entering the solenoid valve through the oil inlet port  27  is directed towards the first oil outlet port  29  and falls by gravity into the oil sump  22 . 
     As in the embodiment described previously, the control means are designed to move the core  34  of the solenoid valve  25  to its first position when the speed of the compressor is below a predetermined threshold value, and move the core of the solenoid valve to its second position when the speed of the compressor is above this predetermined value. 
       FIG. 6  shows a second scroll compressor. The only difference between this and that shown in  FIG. 1  is that the control means MC are designed to move the solenoid valve core  34  to its closed position when not only the delivery temperature of the refrigerant gas is above a predetermined value but also compressor speed is below a predetermined value, and to move the solenoid valve core to its open position when compressor speed is above a predetermined value. For this purpose the control means have a temperature sensor to measure the refrigerant gas delivery temperature at the connector  14 . 
     In another embodiment, the control means MC are designed to move the solenoid valve core  34  to its closed position when the refrigerant gas delivery temperature is above a predetermined value, and to move the solenoid valve core to its open position when the refrigerant gas delivery temperature is below a predetermined value. 
       FIG. 7  depicts a third scroll compressor. This differs from that shown in  FIG. 1  in that the ends of the two bores  36 ,  37  directed at the moving volute  9  open within the area swept by the latter during its orbital movement, in that these two bores are not oriented parallel to the compressor axis but obliquely inwards relative to this axis, and in that the moving volute  9  comprises first and second through-ports  43 ,  44   
     The first and second through-ports  43 ,  44  are designed to connect together, during at least part of the movement of the moving volute, the ends of the first and second injection pipes  31 ,  32  directed towards the compression volume with a volume defined at least partly by the fixed  7  and moving  9  volutes. 
     It goes without saying that the invention is not limited to the embodiments described above by way of example of this scroll compressor. On the contrary, it encompasses all variants thereof. For instance, the bores  36 ,  37  could be oriented obliquely outward away from the compressor axis, or the number of injection pipes could be other than two.