Reciprocating Refrigeration Compressor and Method for Mounting a Reciprocating Refrigeration Compressor

Abstract

The compressor includes: a crankcase carrying a cylinder and a bearing hub which lodges a crankshaft; a valve plate closing one end of the cylinder; a piston reciprocating in the cylinder and driven by the rotation of the crankshaft; an electric motor having a stator affixed to the crankcase and provided with winding grooves and teeth, each tooth carrying a respective shoe, and a rotor affixed to the crankshaft and carrying magnet segments, stator, the rotor and the crankshaft are mounted in an indexed way, in order to present, in relation to one another, a relative positioning which produces, upon the stop of the electric motor and with the crankshaft and rotor being in the upper dead point condition of the piston, a cogging torque capable of taking the piston away from the upper dead point.

Claims

1. A reciprocating refrigeration compressor, comprising: a crankcase carrying a cylinder and a bearing hub which lodges a crankshaft provided with an eccentric; a valve plate closing one end of the cylinder; a piston reciprocating in the interior of the cylinder and driven by a connecting rod coupled to the eccentric of the crankshaft; an electric motor having a stator affixed to the crankcase and provided with a plurality of winding grooves intercalated with teeth, each tooth carrying a respective shoe, and a rotor affixed to the crankshaft and carrying magnet segments; the reciprocating refrigeration compressor characterized in that, in the condition of upper dead point of the piston, at least one magnet segment of the rotor has its symmetry radial axis coinciding with the symmetry radial axis of a corresponding winding groove, said symmetry radial axes being positioned between the two stator teeth adjacent to said winding groove.

2. The compressor, according to claim 1, characterized in that the stator, the rotor and the crankshaft present, in relation to one another, a relative positioning which produces, upon the stop of the electric motor and with the crankshaft and rotor assembly being in the upper dead point condition of the piston, a cogging torque capable of taking the piston away from the upper dead point.

3. A method for mounting the reciprocating refrigeration compressor according to claim 1, the method being characterized in that it comprises the steps of: affixing the stator to the crankcase; mounting the crankshaft in the bearing hub of the crankcase, rotatively locking the crankshaft with its eccentric in the upper dead point position of the piston; affixing the rotor in the crankshaft in a relative angular positioning, in order to produce a cogging torque capable of taking the piston away from the upper dead point position.

4. The method, according to claim 3, characterized in that the rotor is affixed to the crankshaft, with the symmetry radial axis of at least one magnet segment coinciding with the symmetry radial axis of a corresponding winding groove, said symmetry radial axes being positioned between the two teeth adjacent to said winding groove.

5. The method, according to claim 3, characterized in that the rotor is affixed to the crankshaft with the diametral direction of the crankshaft, passing through the geometric center of the eccentric, coinciding with the symmetry radial axes of a magnet segment and of the corresponding winding groove.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention will be described below, by making reference to the appended drawings, by way of example and in which:

[0019] FIG. 1 represents a chart illustrating the pressure reduction in the discharge region of the compressor, as a function of the piston stop angle upon the stop of the electric motor of the compressor;

[0020] FIG. 2 illustrates, schematically, the excessive gas leak condition through the discharge valve upon the stop of the electric motor of the compressor with the piston in the upper dead point position;

[0021] FIG. 3 represents a schematic plan view of the assembly formed by the stator, rotor, crankshaft, connecting-rod and piston in the upper dead point position, in which the rotor has a pair of magnet segments defining, with the respective teeth and shoes of the stator, a condition in which the cogging torque is capable of taking the piston away from the upper dead point and vicinities thereof;

[0022] FIG. 4 represents a view similar to that of FIG. 3, but illustrating the piston away from its upper dead point position, with the crankshaft being additionally turned clockwise from the upper dead point position of the piston, with the magnet segments of the rotor defining, with the respective teeth and shoes of the stator, a stable condition, that is, of minimum reluctance to the passage of the useful magnetic flow formed between said magnet segments and the respective teeth and shoes of the stator; and

[0023] FIG. 5 represents a view similar to that of FIG. 4, but illustrating the piston away from its upper dead point position with the crankshaft being additionally turned anti-clockwise from the upper dead point position of the piston, with the magnet segments of the rotor defining, with the respective teeth and shoes of the stator, a stable condition, that is, of minimum reluctance to the passage of the useful magnetic flow formed between said magnet segments and the respective teeth and shoes of the stator.

DETAILED DESCRIPTION OF THE INVENTION

[0024] According to the illustrations and as already mentioned, the present invention is applied to a refrigeration compressor, more specifically a reciprocating compressor, hermetic or not, of the type described above and which presents, in the interior of a shell (not illustrated), a crankcase B, usually formed in cast iron and presenting a usually flat outer face F.

[0025] The crankcase B carries at least one piston hub 10 which defines a cylinder 11, having one end open to the outer face F of the crankcase and in whose interior is housed and displaced, in a reciprocating linear movement, a piston 20. The cylinder 11 has said end closed by a valve plate 40 and by a cylinder cover 41, which are seated and affixed, usually by screws (not illustrated), against the outer face F of the crankcase B, as illustrated in FIG. 2. The valve plate 40 carries at least one discharge valve 40a and one suction valve, not illustrated, said valves being of the blade type and presenting any construction adequate to the operation by pressure differential between its upstream and downstream sides, in order to establish a selective fluid communication between a compression chamber C, defined in the interior of the cylinder 11 between the piston 20 and the valve plate 40 and the suction and discharge sides of the compressor.

[0026] The crankcase B further carries a bearing hub 50 which houses a crankshaft 60 provided with an eccentric 61 in which is coupled one end of a connecting rod 62 whose opposite end is coupled to the piston 20, in order to displace the latter in a reciprocating movement in the interior of the cylinder 11, between upper dead point and lower dead point positions, by applying rotation to the crankshaft 40.

[0027] The compressor is driven by an electric motor M having a stator 70 affixed to the crankcase B and provided with a plurality of winding grooves 71 intercalated with teeth 72 which carry, each one, respective shoe 72a, and a rotor 80, affixed to the crankshaft 60 and carrying magnet segments 81, which are disposed substantially in a peripheral circumferential alignment.

[0028] According to the invention, one of the ways for mounting the electro-mechanical assembly of the compressor is accomplished by affixing the stator 70, in a determined designed position, in the crankcase B of the compressor. After the position of the stator 70 is defined in relation to the crankcase B and, consequently, to the cylinder 11 which is defined in the piston hub 10, the crankshaft 60 is mounted in the bearing hub 50 of the crankcase B and rotatively positioned in the upper dead point of the piston 20.

[0029] Once the crankshaft 60 is mounted and angularly positioned in the bearing hub 50, the rotor 80 of the electric motor M may be affixed to a corresponding extension of the crankshaft 60, in a relative angular positioning, which allows, when the eccentric 61 of the crankshaft 60 is in the upper dead point position of the piston 20, generating a cogging torque capable of taking the piston away from the upper dead point and from vicinities thereof.

[0030] More specifically, the proposed solution provides the fixation of the rotor 80 to the crankshaft 60 in a relative position in which the symmetry radial axis of at least one magnet segment 81 coincides with the symmetry radial axis of a corresponding winding groove 71, with said symmetry radial axes being positioned between the two teeth 72 adjacent to said winding groove 71.

[0031] According to the invention, the indexation for fixation of the crankshaft 60 in the rotor 80 and the fixation of the stator 70 in the crankcase B, with the indexation of at least one stator groove 71, in relation to the rotational position of the assembly of crankshaft 60 and rotor 80, corresponding to the upper dead point position of the piston 20, allows that, in this position of the piston 20, the magnetic forces (not illustrated), which are present in the rotor-stator assembly, are used to prevent the piston from remaining, in a stationary condition, in the upper dead point position, if said position of the piston occurs upon a stop of the electric motor of the compressor.

[0032] In the upper dead point position of the piston 20, the magnetic forces acting over the rotor 80 create a condition of great instability for the latter, forcing its additional rotation, in one or in the other sense, by an angle which corresponds to 1/p the angular distance between each two consecutive positions of instability condition of the rotor 80, in which p is the number of poles of the rotor.

[0033] Considering that the rotor 80 has an even number of magnet segments 81, the angular distance between each two consecutive positions of magnetic instability of the rotor 80 will correspond to the ratio of 360 for half the product of the number of magnet segments 81 by the number of stator grooves 71. In the example illustrated in FIGS. 3, 4 and 5, the rotor has four magnet segments 81 (four poles) and the stator 70 has six stator grooves 71. In this case, the motor M presents 12 magnetic instability positions (unstable nature) and 12 magnetic stability positions (stable nature) of the rotor 80, which positions are intercalated between one in relation to the other, each two consecutive positions, of the same nature, being angularly spaced from each other by an angle of 30 and also spaced from the adjacent or consecutive positions of other nature, by an angle of 15.

[0034] In the present solution, whenever the rotor 80 stops in a condition of unstable magnetic balance in relation to a diametrically opposite pair of magnet segments 81, it will be magnetically forced to rotate in one or in the other sense, towards a stable magnetic balance condition generated by the magnetic field (not illustrated), by an angle which will depend on the number of poles of the rotor 80 and of the stator grooves 71. In the illustrated example, the angle will be of at least 7.5 degrees in any of the senses. In a rotor of six poles, operating with a stator of nine grooves, said angle of additional magnetic displacement will be of at least 5 degrees.