EP0300884B1 - Hermetic or semi-hermetic refrigeration motor compressor unit - Google Patents

Abstract

1. A refrigeration motor-compressor unit comprising a positive displacement rotary compressor (2, 8) driven by a motor (5, 6), means (11) for supplying refrigerating fluid in the innerspace of the motor for cooling the motor, said innerspace being connected by a piping (10) to an economiser hole (9) of said compressor, characterized by closure means (12, 112) disposed in said piping, said closure means being connected to an intake pressure of said compressor and being adapted to clear said piping (10) against biasing means (14) when the pressure at said economiser hole (9) exceeds by a predetermined differential amount said intake pressure, and to partially obturate said piping (10) in the contrary case.

Description

The present invention relates to a refrigerated, hermetic or semi-hermetic motor-compressor fitted with an economizer.

According to generally accepted terminology, hermetic motor-compressors are those in which sealing is obtained by welded assemblies, while semi-hermetic motor-compressors are those in which sealing is obtained by removable connections and seals.

Hermetic or semi-hermetic motor-compressors are known in which the engine is cooled by gas or liquid, or a mixture of gas and liquid coming from the condenser of the refrigeration circuit. The gas including the volume of gas created by the vaporization necessary to cool the engine is sent from the engine to an economizer hole of the compressor, this economizer hole being at an intermediate pressure between the intake pressure and the pressure of compressor exhaust.

US-A-4,553,399 and 4,573,324 give examples of such motor-compressors.

It is more advantageous to send the gas resulting from the cooling flow through the engine to the economizer hole than to send this gas to the compressor inlet, as this allows the compressor to fully utilize its capacity. inlet to suck gas from the evaporator. In other words, the use of partial flow to cool the engine does not result in a reduction of the refrigerating capacity of the machine.

When a compressor such as a screw compressor operates under partial load, the closing of each compression chamber with respect to the intake of the compressor is delayed until the volume of this chamber has significantly decreased. This reduces the effective capacity of each chamber, and therefore the capacity of the compressor. Under these conditions, each room is only closed when it will soon communicate or already communicates with the economizer hole. Thus, the pressure in the economizer hole is very close to the intake pressure and the engine is therefore no longer at an intermediate pressure between the intake and the discharge.

This leads to a series of problems since, for example, it becomes difficult to drain the liquid from the engine to the evaporator, in particular if the evaporator is in an elevated position relative to the engine.

The object of the invention is to overcome these problems.

According to the invention, the refrigerating motor compressor comprising a rotary positive displacement compressor driven by an engine, means for introducing refrigerating fluid inside the engine to cool the engine, said interior being connected by a pipe to a hole of economizer of the compressor, is characterized in that in said pipe are arranged closing means connected to an inlet pressure of the compressor and designed to release said pipe, against the action of a return means, in the case where the pressure at the economizer hole exceeds the inlet pressure by a predetermined differential pressure, and for partially closing said pipe if not.

When the compressor is operating at partial speed, the pressure at the economizer hole drops to, or near, the intake pressure. In this case, the closure means reduces the flow rate, and this establishes, upstream of the closure means, a pressure which is determined by the action of the return means on the closure means. It is thus possible to maintain in the engine a minimum pressure useful for removing from the engine the liquid separated from the gas. But when the compressor is operating at full speed, this constriction of the flow would adversely affect the efficiency since it would create a pressure drop between the engine and the economiser hole, and would lead to supplying the economiser hole with gas whose pressure would be reduced by the means of closure.

This drawback is avoided because the flow is only throttled when the pressure difference between the economizer hole and the compressor intake is less than a predetermined threshold. Above this threshold, the closure means allows substantially free communication between the interior of the engine and the economizer hole.

Certainly from US-A 3 898 862, a device is known which is mounted on a duct connecting an economizer chamber situated upstream of the evaporator, to an economizer gas inlet on a two-stage centrifugal compressor . The aforementioned device closes the duct when, when the compressor starts, the pressure in the economizer chamber applied to one side of a shutter piston is less than the suction pressure of the compressor, applied to the other side of the piston . But this piston never ensures a partial obturation and one does not see what would be the utility of such a partial obturation. This prior art has no relation to compressor motors cooled by refrigerant.

To minimize the volumes occupied by the pipe of the invention, the closing means can comprise a piston mounted in an extension of the pipe between the interior space of the engine and the economiser hole, and when said difference - or differential pressure - exceeds the threshold, the piston retracts beyond the economiser hole, so that the pipe between the economiser hole and the interior of the engine is completely free from any piston when the compressor is at full speed. This is achieved by testing the spring so that its force is significantly less than the force created on the piston by the differential pressure when it is equal to the threshold.

• - la figure 1 montre partiellement en coupe un moto-compresseur selon l'invention, et schématiquement le circuit frigorifique associé; et
• - les figures 2 et 3 sont des vues partielles en coupe d'un second et d'un troisième mode de réalisation du compresseur.

The present invention will be better understood on reading the description which follows, relating to nonlimiting examples, with reference to the appended drawings, in which:

• - Figure 1 shows partially in section a motor-compressor according to the invention, and schematically the associated refrigeration circuit; and
• - Figures 2 and 3 are partial sectional views of a second and a third embodiment of the compressor.

A shaft 1 (Figure 1) carries a screw 2 cooperating with pinions (not shown) as is well known for example from US-A-3 180 565. This shaft is supported by bearings 3 and 4 and driven in rotation by an electric motor consisting of a rotor 5 attached to the shaft 1 beyond the bearing 4 and rotating inside a stator 6 which is fixed in an envelope 7 secured to the casing 8 of the compressor.

With the exception of connections to pipes for fluids which will be described later, the casing 7 is sealed and the interior space of the casing 7 is sealed from the inlet 20 of the compressor by means of a bearing support flange 4a, carrying a bearing 4. The bearing support flange 4a is provided with a sealing device 22 cooperating with the shaft 1.

The discharge port 31 of the compressor is connected to an intake port 32 of the compressor through a refrigeration circuit comprising in series in the following order: a condenser 33, a tank 34, an expansion valve 36 and an evaporator 37.

The casing 8 is provided with an economizer hole 9 as described in numerous patents, for example US-A-4,261,691, this hole being connected to the inside of the casing 7 of the engine by a pipe 10 .

The engine is cooled by liquid and / or gas reaching the interior of the casing 7 of the engine by a pipe 11 which is shown in the axis of the engine but which could be located elsewhere, for example at the top of the engine.

This liquid and / or gas passes through the engine cooling it. The gas having cooled the engine is sucked by the compressor through the economizer hole 9. The liquid and / or gas arriving in the casing 7 through the pipe 11 may be, as shown, liquid arriving directly from the condenser 33 to through a conduit and partially vaporizing in the engine as described in US-A-4,573,324. This may also be liquid with or without gas coming from a centrifugal economizer which would be mounted at the end of the shaft 1 beyond the rotor 5. Such a centrifugal economizer is described in US - A - 4,509,341. It could also, quite simply, be gas originating from a conventional economizer.

Whatever the case, the motor casing is generally used to separate the liquid intended to be discharged to another point. For example, as shown, and as described in US-A-4,573,324, the liquid is collected in the bottom of the casing 7 and sent to the evaporator 37 by a conduit 38, by exploiting the prevailing pressure in the casing 7, pressure which is higher than downstream of the valve 36.

When using compressors without oil injection, as taught in US-A-4,553,399, it is advantageous to use the engine casing to collect the oil separated from the vaporized liquid and by the heat of the engine and send it to the landings.

In all cases, when the compressor is operating at full speed, the pressure in the engine is significantly higher than the intake pressure of the compressor. When operating with "R22" type refrigerant, the differential pressure in a conventional air conditioning system can range between 200 to 300 and 800 to 900 kPa.

This differential pressure is useful for moving the liquid refrigerant towards the evaporator, particularly when the evaporator is installed at a level higher than that of the compressor, or to move the oil.

However, when the compressor operates at partial speed and the pressure at the economizer hole 9 approaches or reaches the intake pressure, the aforementioned differential pressure tends to disappear and, without the invention, it would become difficult or impossible to discharge the liquid to the evaporator or the oil respectively to the bearings. According to the invention, a piston 12 is mounted in a sliding and sealed manner in an extension 13 of the pipe 10. This extension extends between the economizer hole and a space 19 subjected to the intake pressure, provided at- beyond bearing 3 away from the engine.

The space 19 is connected to the intake region 20 through the bearing 3 and through a passage 21 passing through the screw 2.

The piston 12 thus has a front face 12a subjected to the economizer pressure and a rear face 12b, of the same area, subjected to the intake pressure. The piston 12 is biased by a spring 14 so that, in the absence of differential pressure, the piston 12 moves to its position 15 shown in dotted lines, close to a shoulder 16 of the pipe 10, and forms therewith. ci a choke 17.

Thus, when the pressure at the economizer hole 9 falls to the intake pressure, the piston moves and a pressure drop is created through the throttle 17 so as to maintain in the casing 7 of the engine, a pressure exceeding the intake pressure enough to discharge the liquid refrigerant to the evaporator 37 or the oil to the bearings 3 and 4.

However, when the compressor is operating at full speed, the front face 12a of the piston 12 is at economiser pressure while the rear face 12b is subjected to the intake pressure.

The spring 14 is designed so that in the position shown in solid lines, in which the economizer hole 9 is completely released by the piston 12, the elastic force is balanced by a differential pressure equal to a threshold value of approximately 250 kPa, i.e. corresponding to a pressure at the economiser hole exceeding 250 kPa the intake pressure.

In this position, the piston 12 does not show any pressure drop between the engine and the economizer hole 9. As is obvious and well known, such a pressure drop would be very detrimental to the efficiency of the compressor.

In the embodiment shown in FIG. 2, which will only be described with regard to its differences from that of FIG. 1, the extension 13 is no longer provided, and the piston 12 is housed in a bore 39 which is arranged in the casing 8 transversely to the axis of the motor-compressor, so as to connect the pipe 10 and the intake region 20. The bore 39 has a shoulder 16 designed to cooperate with the face 12a of piston 12.

An upstream part 1 Oa of the pipe 10, extending between the motor casing 7 and the bore 39, meets the bore 39 beyond the shoulder 16, while a downstream part 10b of the pipe 10 , extending between the bore 39 and the economizer hole 9, is connected to the bore 39 so as to communicate with the part 10a through the shoulder 16 provided that the piston 12 does not rest against the shoulder 16. The spring 14 is a tension spring extending through the shoulder 16.

When the pressure at the economizer hole 9 exceeds the intake pressure by at least 250 kPa, the piston 12 is pushed back against the action of the spring 14, and there is free communication between the parts 10a and 10b of the pipe 10.

Otherwise, the spring 14 brings the piston 12 back towards the shoulder 16 and the piston 12 forms therewith a pressure regulating throttle, maintaining in the part 10a, and consequently in the motor casing 7, a pressure significantly exceeding 250 kPa the intake pressure.

In the embodiment of Figure 3, the closure means is a butterfly 112 which is pivotally mounted in the pipe 10 between the portions 10a and 10b thereof, about a pivot axis 41 which is offset laterally with respect to the axis 42 of the pipe 10. Thus, if the pressure upstream of the butterfly 112 (part 10a of the pipe) exceeds the pressure downstream of the butterfly 112 (10b of the pipe), the butterfly 112 is stressed at the opening.

A lever 43 rigidly connected to the downstream face of the butterfly 112 is pivotally and slidingly connected to a rod 44 of a piston 46 mounted in a sliding and sealed manner in a bore 47 extending between the part 10b of the pipe 10 and the admission region 20.

The piston 46 thus has a front face 46a subjected to the pressure at the economizer hole, and a rear face 46b subjected to the intake pressure. The pressure at the economizer hole acts on the piston 46 to open the butterfly 112. The intake pressure and the return spring 14 act together on the piston 46 in the direction of closing the butterfly 112.

If the pressure at the economiser hole exceeds at least 250 kPa the intake pressure, the piston 46 opens the butterfly 112.

Otherwise, the piston 46-spring 14 combination tends to close the butterfly 112. However, this creates in the part 10a of the pipe an overpressure which acts on the butterfly 112 to slightly open it.

This regulates the overpressure in part 10a of the pipe connected to the motor housing 7 (not shown in this figure).

The present invention has been described in the case of a single screw compressor but could, without change, apply to any type of compressor which can be equipped with an economizer hole, in particular a stationary economizer, for example twin screw compressors, mobile vane compressors, fixed vane compressors.

In a less efficient embodiment of the invention, the closing member, instead of regulating the pressure in the engine casing when the differential pressure at the economiser hole is low, could simply create a fixed calibrated passage for the gas from the engine casing.

The shutter could be of different types from the examples which have been described.

Claims (8)

1. A refrigeration motor-compressor unit comprising a positive displacement rotary compressor (2, 8) driven by a motor (5, 6), means (11) for supplying refrigerating fluid in the innerspace of the motor for cooling the motor, said innerspace being connected by a piping (10) to an economiser hole (9) of said compressor, characterized by closure means (12, 112) disposed in said piping, said closure means being connected to an intake pressure of said compressor and being adapted to clear said piping (10) against biasing means (14) when the pressure at said economiser hole (9) exceeds by a predetermined differential amount said intake pressure, and to partially obturate said piping (10) in the contrary case.

2. A refrigeration motor-compressor unit as claimed in claim 1, characaterized in that the closure means comprises a closure member (12, 112) which, when the pressure at the economiser hole does not exceed the intake pressure by said differential amount, is positioned by the equilibrium of forces created by the intake pressure, the pressure in the innerspace of the otor, and the biasing means (14), so as to regulate the pressure in the motor innerspace by variably restricting flow from motor innerspace towards the economiser hole.

3. A refrigeration motor-compressor unit as claimed in claim 1 or claim 2, characterized in that said closure means comprises a slidable piston (12) having a first face (12b) subjected to said intake pressure of the compressor, and a second face (12a) subjected to the pressure in the innerspace of the motor, said biasing means biasing the piston towards a position in which said piston provides a restriction to flow from said motor innerspace to said economiser hole (9) and increases pressure in the motor innerspace with respect to the pressure at the economiser hole (9), the stroke of said piston (12) and the strength of the biasing means (14) being so selected that said piston establishes a substantially unrestricted communication between said motor innerspace and said economiser hole (9) when the pressure difference between the economiser hole (9) and said intake pressure overrides said predetermined differential amount.

4. A refrigeration motor-compressor unit as claimed in claim 3, characterized in that a path of fluid from said motor innerspace to said economiser hole (9) extends through a shoulder (16) with which said piston (12) cooperates for providing said flow restriction.

5. A refrigeration motor-compressor unit as claimed in claim 3, characterized in that said piston (12) is mounted in an extension (13) of said piping (10) connecting the motor innerspace to the economiser hole (9), said extension (13) extending between the economiser hole (9) and a low pressure space (19) provided at an end of the compressor remote from the motor.

6. A refrigeration motor-compressor unit as claimed in claim 5, characterized in that said compressor is a screw compressor having an intake region (20) adjacent the motor, and in that said low pressure space (19) is connected to the intake region (20) through a bearing (3) of the compressor and through a longitudinal duct (21) provided through a screw-rotor of said screw compressor.

7. A refrigeration motor-compressor unit as claimed in claim 3, characterized in that the piston (12) is mounted in a bore (39) arranged transversely of said piping (10) connecting the motor innerspace to the economiser hole (9), said bore (39) extending between said piping (10) and an intake region (20) of the compressor.

8. A refrigeration motor-compressor unit as claimed in claim 7, characterized in that said piping (10) comprises two piping portions (10a, 10b) communicating with each other through a shoulder (16) of said bore (39), said shoulder (16) being adapted to cooperate with the piston (12) for providing said flow restriction.

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