EP0161130B1 - Volumetric screw compressor - Google Patents

Description

The present invention relates to screw compressors, and more particularly to volumetric compressors or blowers intended for supercharging or scanning thermal engines of motor vehicles.

The present invention relates more specifically to front inlet screw compressors, of the type comprising a cooperating male rotor and a female rotor, respectively disposed in a pair of interconnected parallel cylindrical chambers formed in a housing, an inlet passage communicating with one end. of the pair of chambers by an entry opening delimited, at this end of the pair of chambers, by a wall partially obscuring adjacent portions of each chamber, and an outlet passage communicating with the other end of this pair of chambers .

A compressor of this type is described in document FR-A-1216086. In this document, where the rotors are cantilevered in one end of the housing and the female rotor is driven by contact with the male rotor, the inlet opening is formed by the other open front end of the housing and is partially obscured by a small cover plate obscuring the interpenetration zone of two veins each belonging to one of the rotors to avoid direct communication between the inlet opening and the outlet opening, which covers axially more half the length of the rotors and partially radially the end portions of the rotors opposite the inlet opening.

The present invention relates to improvements to this type of compressor and to propose a new arrangement of openings for the production of a compact positive displacement compressor, with low inertia, fast rotation and high efficiency, by limiting the number of threads. rotors sweeping at a given instant the associated inlet opening so as to permanently provide, in each rotor, between the inlet and outlet openings, a buffer vein along which there prevails an intermediate pressure evolving between the pressure atmospheric intake and discharge overpressure at the exhaust, while allowing a correct supply of this vein.

To do this, according to a characteristic of the invention, the inlet opening consists, for each chamber, of an annular sector with an opening angle less than 200 ° and greater than about 165 °, the two sectors annulars being arranged substantially symmetrically with respect to the plane of intersection of the chambers and separated from each other by a central portion of the wall, the adjacent radial ends of the annular inlet sectors forming an angle of less than 90 between them °.

According to another characteristic of the invention, the outlet passage communicates with the chambers by an outlet opening formed in a peripheral wall of the housing, this outlet opening having a general V shape substantially centered on the plane of intersection of the rooms. and whose edges converging towards each other are, in projection, substantially parallel to the threads of the respective rotors.

• la figure 1 est une vue frontale d'un compresseur selon l'invention, montrant l'agencement relatif des sections annulaires constituant l'ouverture d'entrée d'air ;
• la figure 2 est une vue schématique du dessus du compresseur de la figure 1 montrant la disposition de l'ouverture de sortie ; et
• la figure 3 est une vue schématique en perspective du compresseur des figures 1 et 2.

Other characteristics and advantages of the present invention will emerge from the following description of an embodiment, given by way of illustration and in no way limiting, made in relation to the appended drawings, in which:

• Figure 1 is a front view of a compressor according to the invention, showing the relative arrangement of the annular sections constituting the air inlet opening;
• Figure 2 is a schematic top view of the compressor of Figure 1 showing the arrangement of the outlet opening; and
• FIG. 3 is a schematic perspective view of the compressor of FIGS. 1 and 2.

As can be seen in the figures, the screw compressor according to the invention comprises a male rotor (1) and a female rotor (2) each comprising helical threads arranged, so that the threads of each rotor cooperate with those of the 'other rotor in slight mutual contact, in a pair of parallel cylindrical chambers (3) and (4), respectively, intercommunicating longitudinally along a plane of intersection parallel to the axes Z and Z' common to the male rotor (1) and to the chamber (3), on the one hand, and to the female rotor (2) and to the chamber (4) on the other. The rotors (1) and (2) are coupled at one of their ends, in the example shown, to a pair of gears (6) and (7) cooperating mutually without play to synchronously drive the rotors (1) and (2). The gears (6) and (7) are arranged in an interior cavity of the housing (5) separated in a sealed manner from the chambers (3) and (4) by a front partition in which the rotors (1) are supported in turn. and (2), the latter comprising at their ends opposite the gears (6) and (7), bearings supported on an end end wall (8) attached to the housing (5). Preferably, the axis (9) of the gear (7) and the female rotor (2) is coupled to a compressor drive device, the gear (7) of the female rotor (2) therefore being the drive gear of the gear (6) of the male rotor (1), according to a general arrangement which is the subject of document EP-A-0101345.

According to one aspect of the invention, in the front end wall (8) are formed two through cutouts in the form of annular sectors (11) and (12) constituting the inlet opening of the compressor. Each annular sector (11) or (12) has an external profile centered on the corresponding axis Z or Z 'and of radius corresponding to that of the associated chamber (3) or (4), and an internal profile in the form of arc of a circle, also centered on the corresponding axis Z or Z ' and of radius corresponding to the radius of the corresponding rotor hub (1) or (2). Advantageously, the male rotor comprises 4 lobes or threads and the female rotor comprises 6 threads, the threads being of symmetrical or slightly asymmetrical profile. As can be seen in FIG. 1, the two sectors (11) and (12) are substantially symmetrical with respect to the plane of intersection of the chambers (3) and (4) and are separated, at the level of their closest zones. one from the other, by a central portion (13) of the wall (8). The adjacent edges (14) and (15) of the sectors (11) and (12) extend radially towards the respective axes Z and Z ', forming between them an angle less than 90 °, typically about 80 °. The annular sector (11) of the male screw has an opening angle a less than 180 °, typically about 165 °. On the other hand, the annular sector (12) of the female screw (2) has an opening angle j3 greater than 180 ° but less than 200 °, typically around 190 °.

As seen in Figures 2 and 3, in a side wall of the housing (5) opposite, relative to the plane of the axes Z and Z ', to the central separation portion (13) of the wall (8), is formed a V-shaped outlet opening (16) of generally triangular profile with a base perpendicular to the axes Z and Z ', at a slight distance from the end of the rotors (1) and (2) opposite the wall (8), and converging edges (17) and (18) extending, in projection in a plane parallel to the plane of the axes Z and Z ', substantially parallel to the threads of the respective rotors (1) and (2), as can be seen in FIG. 2. Preferably, the top of the triangle is truncated, the outlet opening (16) consequently having a small transverse edge (19) opposite the base and parallel to the latter. Correspondingly, the base has a central projecting portion (20) of transverse extension corresponding substantially to that of the short side (19). As seen in Figure 2, the outlet opening (16) is substantially centered on the plane of intersection of the chambers (3) and (4) but has a slight asymmetry to take account of the number of different threads on the male (1) and female (2) rotors. According to one aspect of the invention, the maximum axial height of the opening (16) (between its large base and the short side (19)) is less than twice the axial distance between two adjacent rotor threads, typically of about 1.25 times the axial distance between adjacent rotor threads. In the example shown in FIG. 3, it will be noted that the overall length of the rotors corresponds substantially to half the pitch of the threads of each rotor.

With the arrangement thus described, and with reference to the configuration shown in the drawings, it is noted, taking into account the directions of rotation shown by the arrows, that the vein B of the male screw (1) and the vein B 'of the female screw (2) enter into communication or interpenetration with one another being isolated, on the side of their intake end, from the inlet openings (11) and (12). It is the same for the veins C and C 'which will cease to be confused to enter on the other hand in communication with the corresponding inlet openings (11) and (12). Furthermore the vein A, also concealed by the wall (8) is in communication with the vein D 'of the female screw (2) which it communicates with the inlet opening (12). On the other hand, the vein A ′, in the configuration shown, is it completely closed. It will therefore be understood that the veins B and B 'remain closed for a half-rotation of each rotor, these veins thus playing the role of buffer veins between the intake (11, 12) and the exhaust (16), the pressure of the air in these veins B and B 'increasing by a value equal to atmospheric pressure up to a nominal compression pressure, of the order of 1.6 bar absolute, at the limit of the exhaust. In this way, in a particularly compact and large pitch arrangement, a perfect insulation is achieved between the intake and the exhaust thanks to the buffer veins where the pressure gradually increases as the rotation proceeds, up to the nominal pressure. compression, at the limit of the exhaust, thus providing a substantially constant discharge pressure and having greatly attenuated beats.

Claims (10)

1. Screw compressor, incorporating a male rotor (1) and a female rotor (2) which cooperate and are situated in a pair of intercommunicating cylindrical chambers (3, 4) formed in a casing (5), an inlet passage (11, 12) communicating with one end of the pair of chambers (3, 4) through an inlet opening (11, 12) defined, at this end of the pair of chambers, by a wall (8) partially obstructing the adjacent portions of each chamber (3, 4), and an outlet passage communicating with the other end of this pair of chambers, characterized in that the inlet opening consists, for each chamber (3, 4), of an annular sector (11, 12) with an opening angle (a, p) of less than 200° and greater than approximately 165°, the two annular sectors being arranged essentially symmetrically relative to the plane of intersection of the chambers (3, 4) and separated from one another by a central portion (13) of the wall (8), the adjacent radial ends (14, 15) of the annular inlet sectors (11, 12) forming between them an angle of less than 90°.

2. Compressor according to Claim 1, characterized in that the outlet passage communicates with the chambers (3, 4) through an outlet opening (16) formed in a peripheral wall of the casing (5), this outlet opening (16) having a general V-shape whose centre lies essentially in the plane of intersection of the chambers (3, 4) and whose convergent edges (17, 18) are parallel, in projection, to the threads of the respective rotors (1, 2).

3. Compressor according to Claim 2, characterized in that the axial height of the V of the outlet opening (16) is less than twice the axial distance between two adjacent rotor threads.

4. Compressor according to Claim 3, characterized in that the axial height of the V of the outlet opening (16) is essentially equal to 1.25 times the axial distance between two adjacent rotor threads.

5. Compressor according to one of the preceding claims characterized in that it incorporates one pair of gearwheels (6, 7) for driving the rotors (1, 2) in synchronism supported in the casing (5) in the region of the said other end of the pair of chambers (3, 4).

6. Compressor according to Claim 5, characterized in that the said wall (8) defining the inlet opening is a wall which is attached to the opposite end of the casing (5) from the gear wheels (6, 7) and which supports bearings for the rotors (1, 2).

7. Compressor according to one of the preceding claims, characterized in that the male rotor (1) incorporates four threads and the female rotor (2) six threads.

8. Compressor according to Claim 7, characterised in that the annular inlet sector (11) for the male rotor (1) has an opening angle (a) of less than 180°.

9. Compressor according to Claim 7 or Claim 8, characterised in that the annular inlet sector (12) for the female rotor (2) has an opening angle (β) greater than 180°.

10. Compressor according to one of the preceding claims characterized in that the adjacent radial ends (14, 15) of the annular inlet sectors (11, 12) form between them an angle which is in the region of 80°.

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