WO2001063128A1

WO2001063128A1 - Scroll compressor equipped with an inlet deflector

Info

Publication number: WO2001063128A1
Application number: PCT/IB2001/000218
Authority: WO
Inventors: Jean De Bernardi; Laure Georjon; Alexandre Montchamp
Original assignee: Danfoss Maneurop S.A.
Priority date: 2000-02-22
Filing date: 2001-02-19
Publication date: 2001-08-30
Also published as: FR2805314B1; AU2001233999A1; FR2805314A1

Abstract

In this compressor the deflector (18) has a wall (19) arranged inside the casing (2) some distance therefrom, facing the gas suction port (4), which wall is connected to the interior face of the casing by at least two returns, top and bottom (22, 23), and which stretches circumferentially to the casing (2) over part of the periphery thereof, thus delimiting a corridor in which the gases are guided circumferentially between the port (4) formed in the casing (2), and the suction chamber (3).

Description

SCROLL COMPRESSOR EQUIPPED ITH AN INLET DEFLECTOR

The subject of the present invention is a scroll compressor equipped with a deflector facing the suction port formed m its casing.

A scroll compressor comprises a hermetic casing, inside which there is formed a suction chamber equipped with an inlet port for the gas and a discharge chamber or pressure chamber. The suction and discharge chambers are separated by a separating wall. A pump, designed to raise the pressure of the suction gas, consists of two scrolls: a stationary scroll secured to the separating wall, and a mobile scroll driven by the shaft of an electrical motor mounted m the suction chamber, this mobile scroll being eccentric with respect to the shaft so that it describes an orbital movement and delimits, with the stationary scroll, pockets of varying and increasingly small volumes as the shaft rotates. The gas is therefore compressed in these pockets before escaping into the discharge chamber .

It is known practice, particularly from documents US 5,114,322 and US 5,055,010, for a scroll compressor to be equipped with a deflector arranged inside the suction chamber facing the port through which the gases enter it. A deflector of this kind is intended to spread more gas inside the suction chamber, towards the two inlets to the compression stage, thereby ensuring good performance of the compressor in terms of energy consumption by allowing some of the gases to pass directly towards the compression stage while at the same time allowing the motor to be cooled by virtue of the proportion of gases which is deflected downwards . However, during occasional operation of the refrigeration plant, during defrost cycles or hot/cold cycle inversions, which correspond to use m heat-pump mode, the fluid let into the compression chamber may be not gas, but liquid. This is what is known as 'slugging". In this case, a significant amount of liquid may be sucked in and directed directly towards the compression stage of the compressor. As the volume of the pockets decreases, as a result of the orbital movement of the mobile scroll, an attempt at compressing the liquid occurs and causes breakage of the rotating parts, if nothing is provided for remedying this.

It is known practice for a mechanical system which allows the wheels to move apart axially and radially when liquid is sucked in to be integrated into the rotating device. It is thus possible to avoid destroying the compressor. However, although this system is theoretically satisfactory, it can happen that the Oldham coupling which is the part which allows the relative orbital movement of the wheels, suffers fatigue failure. Although the time before destruction is longer than in the previous case, this latter device suffers a lack of reliability because the compressor may experience breakage.

The object of the invention is to supply a scroll compressor equipped with a deflector, which is able to safeguard the compression device against breakage resulting from it possibly sucking in liquid, without the need to resort to a mechanical system that allows the wheels to move apart in the presence of liquid.

To this end, in the compressor to which it relates, the deflector has a wall arranged inside the casing some distance therefrom, facing the gas suction port, which wall is connected to the interior face of the casing by at least two returns, top and bottom, and which stretches circumferentially to the casing over part of the periphery thereof, thus delimiting a corridor in which the gases are guided circumferentially between the port formed in the casing, and the suction chamber. Advantageously, the wall of the deflector is also connected to the interior face of the casing by an end return.

This deflector prevents any liquid from reaching the compression stage by employing two physical effects.

The deflector forces the sucked-m gases or any liquid to begin to rotate along the low-pressure casing of the compressor, which corresponds to a centrifugmg effect. In consequence, if liquid reaches the suction port, it is centrifuged and has to follow a long path before reaching the wheels of the compression stage. The liquid therefore has time to be evaporated by heat exchange with the walls and, if it is not, the loss in kinetic energy combined with the lengthening of the path means that gravity takes over and the fluid drops at the end of its path towards the bottom of the machine. The second physical phenomenon is that of liquid pressure drops. The deflector creates a pressure drop which m standard operation, that is to say when gas is being sucked in, is negligible but which becomes predominant when liquid is flowing.

When the refrigerant is sucked m m the liquid state, it is always close to its saturation curve. It therefore tends to evaporate as soon as it encounters a pressure drop, that is to say is subjected to a strong enough depression. The deflector according to the invention provides a tailored pressure drop which allows the liquid to evaporate. During this evaporation, a plug of vapour occurs and acts as a brake on the incoming liquid. In consequence, the liquid can no longer reach the wheels of the compression stage.

The passage cross-sectional area delimited by the deflector and the length thereof need to be defined to suit the general characteristics of the compressor so as to allow the formation of a plug of gas if liquid is sucked in that acts as a brake and allows the incoming liquid to evaporate. According to another feature of the invention, the end of the wall which has a vertical end return is located close to the suction port formed in the casing. According to a first embodiment of this compressor, the wall of the deflector is curved and parallel to the casing.

According to another embodiment of this compressor, the wall of the deflector is approximately flat. In order to increase the pressure drop and encourage the formation of a plug of gas, the wall of the deflector has a boss facing towards the casing and locally reducing the cross-sectional area for the passage of gases through the corridor delimited by the deflector.

As a preference, in this case, the boss is directed parallel to the axis of the compressor.

According to one possibility, the axis of the deflector makes an angle with the horizontal, that is to say with a plane perpendicular to the axis of the compressor. This angle may, for example, be 20°, and the axis of the deflector may be orientated in such a way that the outlet is higher up or lower down than the suction port. This arrangement prevents the gas from flowing along a line lying in a plane perpendicular to the axis of the compressor and being thus able to be directed so as to avoid, for example, the gas being thrown into the bath of oil located at the base of the body, if the suction port is formed in the bottom part of the compressor.

According to another feature, the bottom return has at least one port intended to return oil to the sump delimited by the casing of the compressor. As the gas let in through the suction port is laden with oil, these ports guarantee that the oil is returned to the confines of the compressor, preventing it from stagnating in the corridor delimited by the deflector.

In any event, the invention will be clearly understood with the aid of the description which follows, with reference to the appended diagrammatic drawing which, by way of non-limiting examples, depicts a number of embodiments of a deflector which can be fitted to a scroll compressor. Figure 1 is a view in longitudinal section of a scroll compressor equipped with this device.

Figure 2 is a view in cross section on the line II-II of Figure 1.

Figure 3 is a view in perspective of the deflector equipping the compressor of Figures 1 and 2.

Figures 4 and 5 are two views in section on a horizontal plane of two other deflectors.

The compressor depicted in Figure 1 comprises a hermetic casing 2, inside which there are formed a suction chamber 3 equipped with an inlet 4 for the gas and a discharge chamber or pressure chamber 5 equipped with an outlet 6 for the gas. The suction chamber 3 and discharge chamber 5 are separated by a separating wall 7. Mounted inside the suction chamber 3 is an electric motor, the stator 8 and rotor 9 of which are depicted diagrammatically in the drawing. The rotor 9 is associated with a shaft 10 passing through a body 11 of the compressor and guided in rotation in a lower bearing 12 and at least one upper bearing. The pump for raising the pressure of the suction gas consists of two scrolls, a stationary scroll 14 secured to the separating wall 7 and a mobile scroll 15 driven by the motor shaft 10 and eccentric with respect to this shaft so that it describes an orbital movement and delimits, with the stationary scroll, as the shaft rotates, pockets of variable and increasingly small volume in which the gas is compressed before escaping through a port 16 towards the discharge chamber 5. A valve system, denoted by the general reference 17, is mounted on the outlet 16, so as to allow gas to pass to the pressure chamber 5 and prevent gas from passing from this same chamber 5 to the suction chamber 3 when the compressor is not running. The suction chamber 3 is equipped with a deflector 18 opposite the suction port 4. In the embodiment depicted m Figure 2, the deflector 18 comprises a wall 19 arranged inside the casing and some distance therefrom, this wall being curved and parallel to the casing 2. This wall is bounded at one of its ends by a vertical return 20 and along its entire length by two returns 22 and 23, top and bottom respectively. The end vertical return 20 is located near the suction port 4. The other end of the wall 19 is free, which means that the deflector 18 delimits a corridor m which the gases are guided circumferentially between the port 4 formed in the casing and the actual suction chamber proper. The cross-sectional area and the length of this corridor are determined according to the characteristics of the compressor so as to create pressure drops which are strong enough to allow any liquid sucked m through the port 4 to evaporate, according to the two physical phenomena mentioned earlier.

Figure 4 depicts, viewed m section, a deflector 18a comprising a wall 19a which is not curved, but flat, and has, near the open end of the deflector, a boss 24 facing the casing 2 and directed parallel to the axis of the compressor. This boss 24 reduces the cross-sectional area for the passage of gases and creates a depression phenomenon which encourages the liquid to evaporate.

Figure 5 depicts another embodiment of a deflector 18b in which the wall 19b is flat. It may be noted that, when the wall is flat, the cross-sectional area for the passage of gases decreases between the central part of the deflector and the outlet end thereof, thus encouraging the liquid to evaporate. As is clear from the foregoing, the invention provides a great improvement to the current state of the art by providing a scroll compressor equipped with a deflector which makes it possible to avoid the presence of a device for protecting the compression stage from destruction due to the intake of liquid. This is because the deflector, through its structure, and although being simple, causes the evaporation or the centrifuging of any liquid which may have been sucked in through the suction port.

As goes without saying, the invention is not restricted merely to the embodiments of this deflector which have been described by way of examples; on the contrary, it encompasses all alternative forms thereof. Thus, in particular, the deflector could be made in several parts, or alternatively, the suction port arranged facing the deflector could be formed in the bottom part of the casing, that is to say below the motor, without in any way departing from the scope of the invention.

Claims

1. Scroll compressor equipped with a deflector facing the suction port formed m its casing, and opening into the suction chamber of the compressor, characterized in that the deflector (18) has a wall (19) arranged inside the casing (2) some distance therefrom, facing the gas suction port (4), which wall is connected to the interior face of the casing by at least two returns, top and bottom (22, 23) , and which stretches circumferentially to the casing (2) over part of the periphery thereof, thus delimiting a corridor in which the gases are guided circumferentially between the port (4) formed m the casing (2), and the suction chamber ( 3) .

2. Compressor according to Claim 1, characterized in that the wall (19) of the deflector is also connected to the interior face of the casing by an end return (20) .

3. Compressor according to Claim 2, characterized in that the end of the wall (19) which has a vertical end return (20) is located close to the suction port (4) formed m the casing (2) .

4. Compressor according to one of Claims 1 to 3, characterized in that the wall (19) of the deflector is curved and parallel to the casing (2) .

5. Compressor according to one of Claims 1 to 3, characterized in that the wall (19a, 19b) of the deflector (18a, 18b) is approximately flat.

6. Compressor according to one of Claims 1 to 5, characterized in that the wall (19a) of the deflector

(18a) has a boss (24) facing towards the casing (2) and locally reducing the cross-sectional area for the passage of gases through the corridor delimited by the deflector .

7. Compressor according to Claim 6, characterized in that the boss (24) is directed parallel to the axis of the compressor.

8. Compressor according to one of Claims 1 to 7, characterized m that the axis of the deflector makes an angle with the horizontal, that is to say with a plane perpendicular to the axis of the compressor.

9. Compressor according to one of Claims 1 to 8, characterized in that the bottom return (23) has at least one port intended to return oil to the sump delimited by the casing (2) of the compressor.