ES2923866T3 - Reciprocating refrigeration compressor and method of mounting a reciprocating refrigeration compressor - Google Patents

Abstract

The compressor comprises: a crankcase (B) carrying a cylinder (11) and a bearing hub (50) housing a crankshaft (60); a valve plate (40) closing one end of the cylinder (11); a piston (20) reciprocating in the cylinder (11) and driven by the rotation of the crankshaft (60); an electric motor (M) having a stator (70) fixed to the casing (B) and provided with winding grooves (71) and teeth (72), each tooth carrying a respective shoe (72a) and a rotor (80) fixed to the crankshaft (60) and carry magnetic segments (81). 0 stator (70), rotor (80) and crankshaft (60) are mounted in an indexed manner, to present, with respect to each other, a relative positioning that produces, when the electric motor (M) stops and when the crankshaft (60 ) and the rotor (80) in the top dead center condition of the piston (20), a toothing torque capable of moving the piston away from the top dead center. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Reciprocating refrigeration compressor and method of mounting a reciprocating refrigeration compressor

field of invention

The present invention refers to a compressor of the type provided with a piston that is actuated, in an alternative linear movement inside a cylinder, by a connecting rod coupled to the eccentric of a crankshaft fixed to the rotor of an electric motor, being constructed and assembled the electromechanical assembly of the compressor, including the crankshaft, electric motor, connecting rod and piston, to prevent the piston from stopping at or near top dead center when the electric motor is turned off to stop the compressor.

Background of the invention

In refrigeration compressors that have a reciprocating piston, the compression chamber is defined inside the cylinder, between the top of the piston and a valve plate, which contains the suction and discharge valves and is fixed to the crankcase. compressor, closing one end of the cylinder.

In the type of compressor considered here, stopping the piston at or near top dead center reduces the sealing ability of the discharge valve(s), significantly increasing fluid return. refrigerant, from the refrigeration system condenser to the compressor region maintained at low pressure.

The graph depicted in Figure 1 of the accompanying drawings shows the pressure reduction in the discharge region of the compressor, as a function of the position of the crankshaft eccentric, after the engine is turned off to stop the compressor. The 180° position represents the top dead center of the piston, while the 0° and 360° positions represent the bottom dead center.

It can be seen that the rate of pressure drop, representing the leakage through the discharge valve(s), is at least five times greater in those situations where the compressor stops with the piston at the point top dead (180°) or close to it.

The reduction in the sealing capacity of the discharge valve(s), due to the stop of the piston at or near top dead center, is explained by the pressure conditions at that moment in the region of compressor discharge, as schematically represented in Figure 2 of the accompanying drawings. In the situation where the piston 20 stops at or near top dead center, the pressure difference between the inside of the compression chamber C and the downstream side of the discharge valve(s) 40a, inside the cover 41 of the cylinder 11, is small, which reduces the force resulting from the pressure differential required with the function of closing the discharge valve(s) 40a, pressing it(s) against the respective discharge seat defined on the valve plate 40. If there is no minimum pressure differential between the two sides of the discharge valve(s) 40a, the force to close the discharge valve(s) discharge 40a will not be sufficient to guarantee a more efficient closure to prevent the passage of gas through the respective seat in the valve plate 40.

After leaking through the not fully closed discharge valve(s) (40a), the refrigerant fluid flows through the radial gap between cylinder 11 and piston 20 to the region of the compressor and the system. refrigeration, which are at low pressure.

Excessive leakage through the discharge valve(s) 40a after the compressor stops is undesirable, since, after flowing from the condenser to the evaporator of the refrigeration system, passing through the compressor, the fluid The refrigerant contained in the low pressure side of the refrigeration system will absorb the thermal energy contained in the compressor body, transferring said thermal energy to the interior of the refrigerating equipment in which the system's evaporator is installed. This procedure increases the thermal load on the evaporator, which impairs the energy efficiency of the refrigeration system.

In addition, leaks through the discharge valve(s) 40a, after the compressor stops, reduce the energy savings obtained by using check valves installed between the condenser and the expansion device and whose function is avoid a new compression of the refrigerant fluid already stored, at high pressure, in the refrigeration system condenser.

Due to the losses caused by the energy efficiency of a refrigeration system, after the stop of the compressor with the piston 20 at top dead center, it is desirable to provide a technical solution that can avoid such an operating condition.

Additionally, prior art document WO2012091339 discloses the features in the preamble of attached claim 1, which is an alternative refrigeration compressor, comprising: a crankcase that supports a cylinder and a bearing hub that houses a crankshaft provided with an eccentric; a valve plate closing one end of the cylinder; a reciprocating piston inside the cylinder and driven by a connecting rod coupled to the crankshaft eccentric; and an electric motor 200 having a stator fixed to the crankcase and provided with a plurality of winding slots interspersed with teeth, each tooth supporting a respective shoe, and a rotor fixed to the crankshaft and supporting magnetic segments.

Summary of the invention

Taking into consideration the facts mentioned above and related to the state of the art, the present invention has the objective of providing an alternative refrigeration compressor, which is constructed in order to avoid that, after stopping the electric motor of the compressor, the piston remain at or near top dead center where the pressure differential between the downstream and upstream side of the discharge valve(s) is not sufficient to ensure tight shutoff of said valve(s).

A further object of the invention is to provide a new method of assembling the type of reciprocating compressor contemplated herein.

These and other objects of the invention are achieved by a reciprocating refrigeration compressor according to the content of claim 1 and by a method of assembling such a compressor according to the content of claim 2.

According to one aspect of the invention, the reciprocating cooling system, in the top dead center state of the piston, at least one magnetic segment of the rotor has its radial axis of symmetry that coincides with the radial axis of symmetry of a corresponding winding slot , said radial axes of symmetry being positioned between the two stator teeth adjacent to said winding slot, the stator, the rotor and the crankshaft present, with respect to each other, a positioning that produces, after stopping the electric motor and with the set defined due to the position of the crankshaft and the rotor at top dead center of the piston, a holding torque capable of moving the piston away from top dead center, which guarantees the sealing of the discharge valves. The holding torque is defined as the torque resulting from the variation of the reluctance to the passage of the useful magnetic flux, generated by the magnet, between at least one magnetic segment of the rotor and a facing stator tooth.

The invention further provides a method for assembling the aforementioned compressor, according to which the rotor is fixed to the crankshaft, which is already housed in the bearing hub and is held with its eccentric in a position corresponding to the neutral position. upper piston and in which a holding torque is generated capable of moving the piston away from the top dead center, in which the rotor is fixed to the crankshaft with the radial axis of symmetry of at least one magnetic segment coinciding with the radial axis of symmetry of a corresponding winding slot, said radial axes of symmetry being positioned between the two teeth adjacent to said winding slot.

The present proposed construction does not require any relevant constructive alteration to be made to the compressor. However, according to the constructive solution proposed herein, if the electric motor of the compressor stops in a position of the rotor-crankshaft assembly in the top dead center state of the piston, at least one of the magnetic segments of the rotor will produce, with a stator tooth facing each other, a holding torque capable of moving the piston away from the top dead center and its surroundings, after stopping the motor, which creates an unstable equilibrium position, which allows the magnetic fluxes that circulate through the air gap force the rotor and crankshaft to rotate together to a position of least reluctance to the passage of magnetic flux, which stabilizes the rotor-crankshaft assembly in a position in which the piston moves away from its top dead center , a distance capable of producing a pressure differential between the interior of the cylinder compression chamber and the downstream side of the valve(s) of d discharge, sufficient to guarantee the closure of the discharge valve(s).

The solution proposed by the invention transforms the usual stopping system for the compressor's electric motor, in which the piston has random positions inside the cylinder, into a controlled system whereby, after stopping the motor with the piston in top dead center position or close to top dead center position, the rotor-crankshaft assembly will be rotated magnetically to the stable equilibrium position, moving the piston away from top dead center.

Brief description of the drawings

The invention will now be described with reference to the accompanying drawings, by way of example and in which:

Figure 1 represents a graph illustrating the pressure reduction in the discharge region of the compressor, as a function of the piston stop angle after the stop of the electric motor of the compressor;

Figure 2 schematically illustrates the state of excessive gas leakage through the discharge valve after the electric motor of the compressor stops with the piston at the top dead center position;

Figure 3 represents a schematic plan view of the assembly formed by the stator, rotor, crankshaft, connecting rod and piston in the top dead center position, in which the rotor has a pair of magnetic segments that define, with the teeth and shoes respective parts of the stator, a state in which the holding torque is capable of moving the piston away from and near top dead center;

Figure 4 is a view similar to Figure 3, but illustrating the piston moving away from its top dead center position, the crankshaft being rotated further clockwise from the piston top dead center position , defining the magnetic segments of the rotor, with the respective teeth and shoes of the stator, a stable state, that is, of minimum reluctance to the passage of the useful magnetic flux formed between said magnetic segments and the respective teeth and shoes of the stator; Y

Figure 5 is a view similar to that of Figure 4, but illustrating the piston moving away from its top dead center position, the crankshaft being rotated further counterclockwise from the top dead center position of the piston; piston, defining the magnetic segments of the rotor, with the respective teeth and shoes of the stator, a stable state, that is, of minimum reluctance to the passage of the useful magnetic flux formed between said magnetic segments and the respective teeth and shoes of the stator.

Detailed description of the invention

According to the illustrations and as already mentioned above, the present invention applies to a refrigeration compressor, more specifically to an alternative compressor, hermetic or not, of the type described above and which has, inside a casing (not illustrated ), a casing B, generally formed from cast iron and having a generally flat outer face F.

The casing B supports at least one piston hub 10 defining a cylinder 11, which has an open end on the outer face F of the casing and inside which a piston 20 is housed and moves, in reciprocating linear movement. The cylinder 11 it presents said end closed by a valve plate 40 and by a cylinder cover 41, which are seated and fixed, normally by means of screws (not illustrated), against the outer face F of the casing B, as illustrated in figure 2. The valve plate 40 supports at least one discharge valve 40a and one suction valve, not illustrated, said valves being of the vane type and presenting any suitable construction in relation to operation by pressure differential between their upstream and downstream sides. downstream, in order to establish selective fluid communication between a compression chamber C, defined inside cylinder 11 between piston 20 and valve plate 40 and the suction and compressor discharge.

The casing B also supports a bearing hub 50 that houses a crankshaft 60 provided with an eccentric 61 in which one end of a connecting rod 62 is coupled, the opposite end of which is coupled to the piston 20, in order to move the latter by a reciprocating motion inside cylinder 11, between top dead center and bottom dead center positions, by applying rotation to crankshaft 40.

The compressor is driven by an electric motor M having a stator 70 fixed to the casing B and provided with a plurality of winding slots 71 interspersed with teeth 72 each supporting a respective shoe 72a, and a rotor 80 fixed to the crankshaft. 60 and supporting magnetic segments 81, which are arranged in substantially peripheral circumferential alignment.

According to the invention, one of the ways to mount the electromechanical assembly of the compressor is achieved by fixing the stator 70, in a determined design position, in the crankcase B of the compressor. After defining the position of the stator 70 in relation to the crankcase B and, consequently, with the cylinder 11 being defined in the piston hub 10, the crankshaft 60 is mounted in the bearing hub 50 of the crankcase B and is positioned rotatably at top dead center of piston 20.

Once the crankshaft 60 is mounted and angularly positioned on the bearing hub 50, the rotor 80 of the electric motor M can be fixed to a corresponding extension of the crankshaft 60, in a relative angular position, which allows, when the eccentric 61 of the crankshaft 60 is in the top dead center position of the piston 20, generating a holding torque capable of moving the piston away from and in the vicinity of top dead center.

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

According to the invention, the indexing for the fixing of the crankshaft 60 on the rotor 80 and the fixing of the stator 70 on the crankcase B, with the indexing of at least one stator slot 71, relative to the rotational position of the crankshaft assembly 60 and rotor 80, corresponding to the top dead center position of piston 20, allows that, in this position of piston 20, the magnetic forces (not shown), which are present in the rotor-stator assembly, are used to prevent the piston from remaining, in a stationary state, in the top dead center position, if said position of the piston occurs after a stoppage of the electric motor of the compressor.

In the top dead center position of the piston 20, the magnetic forces acting on the rotor 80 create a highly unstable state for the latter, forcing its further rotation, in one direction or the other, through an angle corresponding to 1/ p is the angular distance between each two consecutive unsteady state positions of the rotor 80, where p is the number of rotor poles.

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

In the present solution, whenever the rotor 80 stops in a state of unstable magnetic equilibrium relative to a pair of diametrically opposed magnetic segments 81, it will be magnetically forced to rotate in one direction or the other, towards a state of equilibrium. stable magnetic field generated by the magnetic field (not illustrated), an angle that will depend on the number of poles of the rotor 80 and stator slots 71. In the illustrated example, the angle will be at least 7.5 degrees in either direction. senses. In a six-pole rotor, operating with a nine-slot stator, such an additional magnetic offset angle will be at least 5 degrees.

Claims (3)

1. Reciprocating refrigeration compressor, comprising: - a casing (B) supporting a cylinder (11) and a bearing hub (50) housing a crankshaft (60) provided with an eccentric (61); - a valve plate (40) closing one end of the cylinder (11); - a piston (20) with reciprocating movement inside the cylinder (11) and driven by a connecting rod (62) coupled to the eccentric (61) of the crankshaft (60); - an electric motor (M) having a stator (70) fixed to the casing (B) and provided with a plurality of winding grooves (71) interspersed with teeth (72), each tooth supporting a respective shoe (72a), and a rotor (80) fixed to the crankshaft (60) and supporting magnetic segments (81), the reciprocating refrigeration compressor being characterized in that, in the top dead center state of the piston (20), at least one magnetic segment (81) of the rotor (80) has its radial axis of symmetry coinciding with the radial axis of symmetry of a corresponding winding slot (71), said radial axes of symmetry being positioned between the two stator teeth (72) adjacent to said winding slot (71), presenting the stator (70), the rotor (80) and the crankshaft (60), in relation to each other, a relative positioning that produces, after the electric motor (M) stops and the crankshaft (60) and rotor (80) assembly being in the top dead center state of the piston (20) , a holding torque capable of moving the piston away from top dead center. 2. Method for assembling a reciprocating refrigeration compressor of the type comprising: - a casing (B) supporting a piston hub (10), a cylinder (11) and a bearing hub (50) housing a crankshaft (60) provided with an eccentric (61); - a valve plate (40) and a cover (41) closing one end of the cylinder (11); - a piston (20) with reciprocating movement inside the cylinder (11) and driven by a connecting rod (62) coupled to the eccentric (61) of the crankshaft (60); - an electric motor (M) having a stator (70) fixed to the casing (B) and provided with a plurality of winding grooves (71) interspersed with teeth (72), each tooth supporting a respective shoe (72a), and a rotor (80) fixed to the crankshaft (60) and supporting magnetic segments (81), said method comprising the following steps: - fix the stator (70) to the casing (B); - mounting the crankshaft (60) on the bearing hub (50) of the crankcase (B), rotatingly locking the crankshaft (60) with its eccentric (61) in the top dead center position of the piston (20); the method being characterized in that it comprises the following steps: - fixing the rotor (80) on the crankshaft (60) in a relative angular position, in order to produce a holding torque capable of moving the piston away from the top dead center position; in which the rotor (80) is fixed to the crankshaft (60) with the radial axis of symmetry of at least one magnetic segment (81) coinciding with the radial axis of symmetry of a corresponding winding slot (71), said radial axes of symmetry positioned between the two teeth (72) adjacent to said winding slot (71). 3. Method, according to claim 2, characterized in that the rotor (80) is fixed to the crankshaft (60) with the ^{diametral direction of the crankshaft (60), passing through the geometric center of the eccentric (} 61 ^{), coinciding with the axes} symmetry ^radials of a magnetic segment (81) and of the corresponding winding slot (71).