WO2015096869A1

WO2015096869A1 - Piston head for use in a reciprocating compressor and method of producing the same

Info

Publication number: WO2015096869A1
Application number: PCT/EP2013/078009
Authority: WO
Inventors: Nazim Arda EYYUBOGLU; Tolga Yaroglu
Original assignee: Arcelik Anonim Sirketi
Priority date: 2013-12-26
Filing date: 2013-12-26
Publication date: 2015-07-02
Also published as: EP3090176A1; CN106062362A; BR112016015104A2

Abstract

The present invention relates to a method of producing a piston head (1) for use in a reciprocating compressor (2). The method comprises a step of forming from a raw material a cylindrical body which includes: an upper base section (3); a cylindrical lateral section (4); and a lower base section (5), wherein the upper base section (3) is leveled but has a projection portion (6) for releasably fitting into a discharge port. In the method according to the present invention, particularly in the forming step an annular rim flange (7) is formed on the lower base section (5). An upper surface of the annular rim flange (7) is also leveled. The annular rim flange (7) has a height h which is equal to or higher than height h' of the projection portion (6). The projection portion (6) is formed directly above a region of the lower base section (5), which is enclosed by an inner side of the annular rim flange (7).

Description

PISTON HEAD FOR USE IN A RECIPROCATING COMPRESSOR AND METHOD OF PRODUCING THE SAME

The present invention relates to a piston head for use in a reciprocating compressor and a method of producing a piston head.

A domestic refrigerator is typically provided with a reciprocating compressor for circulating a refrigerant of a refrigeration circuit. The conventional reciprocating compressor conveys the refrigerant from an evaporator side to a condenser side. The conventional reciprocating compressor comprises a cylinder block which has a chamber in which the refrigerant is cyclically compressed; a piston mechanism for compressing the refrigerant in the chamber; and an electrical motor for driving the piston mechanism. In the conventional reciprocating compressor, the cylinder block further includes an intake chamber and a discharge chamber. The intake chamber is on a downstream side of the evaporator. The discharge chamber is on an upstream side of the condenser. The intake chamber and the discharge chamber are usually formed within the cylinder head. A valve plate is interposed between the cylinder block and the cylinder head. By virtue of the valve plate, the compression chamber is selectively brought into fluid communication with the intake chamber and the discharge chamber. The valve plate generally comprises an intake port and a discharge port. The intake port fluidly connects the intake chamber with the compression chamber upon suction of the piston mechanism. The discharge port fluidly connects the compression chamber with the discharge chamber upon compression of the piston mechanism. In the conventional reciprocating compressor, the piston mechanism includes a piston head arranged to reciprocate within the chamber, a piston rod pivotably coupled to the piston head and a crank shaft pivotably coupled to the piston rod. The crankshaft has a counterweight for smoothing the operation of the piston mechanism. The crankshaft is rotatably supported by the cylinder block. In the conventional reciprocating compressor, the electrical motor includes: a stator and a rotor which are typically configured as an asynchronous motor or a brushless direct current motor. The rotor is fixed to the crank shaft of the piston mechanism.

A problem with the conventional reciprocating compressor is that as the crankshaft maximally pushes the piston head into the chamber, a small fraction of the refrigerant in the vicinity of the discharge port remains undischarged due to a groove shape of the discharge port. To improve an efficiency and capacity of the compressor, the piston head is usually provided with a projection portion which loosely fits into the groove as the crankshaft is moved to its dead point.

JP 57-056133 (A) discloses a method for manufacturing a cylindrical piston head with a projection portion. This piston head has a cylindrical body which includes: an upper base section, a cylindrical lateral section and a lower base section. According to this method, the piston head is produced through cold forging without any after-treatment such as grinding or the like.

In general, the grinding process is indispensable for obtaining fine finishes and accurate dimensions. Several grinding techniques are known. An efficient way of grinding the piston head is to use a centerless grinding technique since a plurality of the piston heads can be stacked upon each other and commonly grinded. Thereby, a capacity of the grinding machine can be fully utilized the manufacturing cost can be reduced.

A drawback of the above prior art piston head is that it cannot be stacked upon another one unless e.g., a suitable dummy is arranged in between two neighboring piston heads. However, the use of dummies reduces the grinding capacity and increases the costs. A further drawback of the aforementioned piston head is that it easily interferes with the counterweight of the crankshaft due to a shape of its skirt unless it is arranged sufficiently away from the counterweight. However such an arrangement reduces the compression capacity of the chamber.

An objective of the present invention is to provide a method of producing a piston head which overcomes the aforementioned problems of the prior art and which enables a highly accurate and a cost effective production of a piston head.

This objective has been achieved by the method of producing a piston head according to the present invention as defined in claim 1, and the piston head according to the present invention as defined in claim 8. Further achievements have been attained by the subject-matters respectively defined in the dependent claims.

In the method of producing the piston head according to the present invention, an annular rim flange is formed on the lower base section of the cylindrical body. The annular rim flange has a height which is equal to or higher than a height of the projection portion. In addition, the projection portion is formed on the upper base section directly above a region of the lower base section, which is enclosed by an inner side of the annular rim flange. The upper surface of the annular rim flange and the surface of the upper base section except for the projection portion are both leveled.

In an embodiment, in the forming step also one or more than one cut out is formed in the annular rim flange. The cut outs prevent an interference between the counterweight of the crankshaft and the annular rim flange.

In another embodiment, the piston head is integrally formed through a die forging process. In an alternative embodiment, the piston head is integrally formed through a cast molding process.

In another alternative embodiment the cut outs are formed through a machining process which is performed subsequent to said die forging process or said cast molding process.

In an alternative embodiment the annular rim flange and the cut outs are both formed through a machining process subsequent to said die forging process or said cast molding process.

In another embodiment, the method further comprises a step of centerless grinding in which a plurality of cylindrical bodies are stacked on top of each other and their cylindrical lateral sections are commonly grinded. In this embodiment, no dummies are placed in-between the plurality of piston heads.

By virtue of the annular rim flange, the piston heads can be directly stacked on top of each other to obtain a stack of a plurality of piston heads. In the stacked configuration, each projection portion is stowed away in the gap enclosed by the annular rim flange of an adjacent piston head and each upper surface of the annular rim flange uniformly abuts against the surface of the upper base section of the other adjacent piston head. Thereby, the stacked piston heads can be stably subjected to a centerless grinding process. The presence of the cut outs does not hamper the centerless grinding process even when this process is carried out without dummies.

Additional advantages of the piston head according to the present will become apparent with the detailed description of the embodiments with reference to the accompanying drawings in which:

Figure 1a – is a schematic perspective rear view of a piston head according to an embodiment of the present invention, prior to forming of a cut out in a rim flange thereof through a machining process;
Figure 1b – is a schematic perspective front view of the piston head shown in Fig. 1a;

Figure 2a – is a schematic perspective rear view of the piston head according to an embodiment of the present invention with a pair of cut outs formed in the rim flange;

Figure 2b – is a schematic perspective front view of the piston head shown in Fig. 2a;

Figure 3a – is a schematic perspective rear view of the piston head according to another embodiment of the present invention with a single cut out formed in the rim flange;

Figure 3b – is a schematic perspective front view of the piston head shown in Fig. 3a;

Figure 4a – is a schematic side view of a stack of a plurality of piston heads shown in Figs. 2a and 2b, prior to subjecting their cylindrical lateral sections to a centerless grinding process without using any dummies;

Figure 4b – is a schematic cross sectional side view of the stack of the plurality of piston heads shown in Fig. 4a, taken along the line A-A;

Figure 5 – is a schematic partial side view of a reciprocating compressor which includes the piston head shown in Figs. 2a and 2b.

The reference signs appearing on the drawings relate to the following technical features.

Piston head
Reciprocating compressor
Upper base section
Lateral section
Lower base section
Projection portion
Rim flange
Cavity
Cut out
Counterweight
Crankshaft
Piston rod

The piston head (1) is suitable for use in a reciprocating compressor (2) (Fig. 5). The piston head (1) comprises a cylindrical body which includes: an upper base section (3), a cylindrical lateral section (4) and a lower base section (5) (Figs. 1 to 3). The upper base section (3) is leveled but has a projection portion (6) for releasably fitting into a discharge port (not shown) (Fig. 5).

In the piston head (1) according to the present invention, the lower base section (5) has an annular rim flange (7) (Figs. 1 to 3). The upper surface of the annular rim flange (7) is also leveled (Fig. 4). The annular rim flange (7) has a height h which is at least equal to a height h´ of the projection portion (6) (Fig. 4). Herein, the height h and the height h´ are both defined in a direction parallel to a rotational axis of the cylindrical lateral section (4). The projection portion (6) of the upper base section (3) is located directly above a region of the lower base section (5), which is enclosed by an inner side of the annular rim flange (7) (Fig. 4).

In an embodiment, the annular rim flange (7) extends in a direction parallel to a rotational axis of the cylindrical lateral section (4) (Fig. 4). An outer surface of the annular rim flange (7) is flush with an outer surface of the cylindrical lateral section (4) (Fig. 4). The upper surface of the annular rim flange (7) is leveled parallel to a surface of the upper base section (3) and also vertical to the rotational axis of the cylindrical lateral section (4) (Fig. 4). Thereby, a piston heads (1) can be stably stacked on top of another piston head (1) for the purpose of centerless grinding, polishing or the like (Fig. 4).

In another embodiment, the annular rim flange (7) includes one or more than one cut out (9) which defines a passage for a counterweight (10) of a crankshaft (11) (Fig. 5). In a version of this embodiment, the piston head has two equally shaped cut outs (Fig. 2). These two cut outs define a passage for the counterweight (10) as it swings nearby the piston head (1) (Fig. 5). A portion of the annular rim flange (7) separates the two cut-outs (9) (Fig. 2). When the piston head (1) is mounted to the compressor (2), the two cut outs (9) are symmetrically located with respect to a vertical diametric line bisecting the piston head (1) (Fig. 5). In another version of this embodiment, the piston head (1) has a single cut out (Fig. 3). The single cut out (9) similarly defines a passage for the counterweight (10) as it swings nearby the piston head (1). This passage is bound by the annular rim flange (7) only from below. Therefore, the single cut out (9) can accommodate a more massive counterweight (10) which e.g., extends upwards. When the piston head (1) is mounted to the compressor (2), the single cut out (9) is symmetrically located with respect to a vertical diametric line bisecting the piston head (1).

In another embodiment, the lower base section (5) includes a cavity (8) (Figs. 1 to 4). Thereby, a weight of the piston head and, thus, a load on the electrical motor (not shown) are reduced. In addition, the piston rod (12) is pivotably coupled to the piston head (1) through a pin (not shown) which is arranged within the cavity (8). In another alternative embodiment, a ball pivot (not shown) is used instead of the pin.

In another embodiment, the piston head (1) is made of metal. In another alternative embodiment, the piston head (1) is made of ceramic or composite material

The reciprocating compressor (2) of the present invention is suitable for use in a refrigeration appliance, in particular a domestic refrigerator (not shown) (Fig. 5). The reciprocating compressor (2) comprises: a cylinder block (not shown) which has a chamber (not shown) for compressing a refrigerant and a piston mechanism for compressing the refrigerant in the chamber (Fig. 5). The piston mechanism includes: a piston head (1) of the present invention; a piston rod (12) which is pivotably coupled to the piston head (1) and a crank shaft (11) which has a counterweight (10) and an electrical motor (not shown) for driving the crankshaft (11). The piston head (1) is arranged to reciprocate in the chamber. The crankshaft (11) is pivotably coupled to the piston rod (12) (Fig. 5).

The refrigeration appliance (not shown) of the present invention comprises: one or more than one refrigeration compartment for refrigerating item and a refrigeration circuit which includes a reciprocating compressor (2) of the present invention, a condenser, an expansion valve or the like, and one or more than one evaporator which are serially connected to circulate a refrigerant.

In an embodiment, the refrigeration appliance is a domestic refrigerator (not shown) which has a freezer compartment and a cooling compartment.

In the subsequent description, a method of producing the piston head (1) of the present invention will be explained.

The method comprises: a step of forming from a raw material a cylindrical body which includes: an upper base section (3), a cylindrical lateral section (4) and a lower base section (5), wherein the upper base section (3) is leveled but has a projection portion (6) for releasably fitting into an discharge port (Figs. 1 to 3; Fig. 5).

In the method according to the present invention, particularly in the forming step an annular rim flange (7) is formed on the lower base section (5) (Figs. 1 to 3). An upper surface of the annular rim flange (7) is leveled. The annular rim flange (7) has a height h which is equal to or higher than a height h´ of the projection portion (6) (Fig. 4). The projection portion (6) of the upper base section (3) is formed directly above a region of the lower base section (5), which is enclosed by an inner side of the annular rim flange (7) (Figs. 1 to 4).

In an embodiment, in the forming step also one or more than one cut out (9) is formed in the annular rim flange (7). The cut outs (9) define a passage for a counterweight (10) of a crankshaft (11) (Figs. 2 to 3; Fig. 5). The size, shape and location of the cut outs (9) in the rim flange (7) are determined in accordance with the size, shape, and location of the counterweight (10) of the crankshaft (11) (Fig. 5).

In another embodiment, in the forming step also a cavity (8) is formed into the lower base section (5).

In another embodiment, the cylindrical body including the projection portion (6), the annular rim flange (7), and the cavity (8) is integrally formed through a die forging process. In an alternative embodiment, the cylindrical body including the projection portion (6), the annular rim flange (7), and the cavity (8) is integrally formed through a cast molding process.

In another embodiment each cut out (9) is also formed through said die forging process or said cast molding process.

In another alternative embodiment each cut out (9) is formed through a machining process subsequent to said die forging process or said cast molding process.

In another alternative embodiment, the annular rim flange (7) and the cut outs (9) are formed through the machining process subsequent to the die forging process or the cast molding process.

In another embodiment, the method further comprises a step of centerless grinding of the cylindrical lateral sections (4) of a plurality of cylindrical bodies which are stacked on top of each other. In this embodiment, no dummies are placed in-between the plurality of piston heads (1) (Fig. 4). The presence of the cut outs (9) does not hamper the centerless grinding process to be carried out without dummies since in the stacked configuration, the upper surface of the annular rim flange uniformly abuts against the surface of the upper base section (3). Therefore, the piston heads (1) can stably roll during the grinding process. In addition, in the stacked configuration the projection portion (6) of the upper base section (3) is stowed away into the space enclosed by the annular rim flange (7) of the adjacent piston head (1). Therefore, the need of using dummies is completely obviated.

By the present invention, the piston head (1) can be manufactured with the requisite shape and number of cut outs so as to allow a proper counterweight (10) to be mounted to the crankshaft (11). By the method of the present invention, the piston heads (1) can be stackwise grinded by a centerless grinding process without using any dummies despite of the projection portion and the cut outs.

Claims

A method of producing a piston head (1) for use in a reciprocating compressor (2), the method comprising:

a step of forming from a raw material a cylindrical body which includes an upper base section (3), a cylindrical lateral section (4) and a lower base section (5), wherein the upper base section (3) is leveled but has a projection portion (6) for releasably fitting into a discharge port,

characterized in that

in the forming step an annular rim flange (7) is formed on the lower base section (5),

wherein an upper surface of the annular rim flange (7) is also leveled,

wherein the annular rim flange (7) has a height h which is equal to or higher than height h´ of the projection portion (6), and

wherein the projection portion (6) is formed directly above a region of the lower base section (5), which is enclosed by an inner side of the annular rim flange (7).
The method according to claim 1, characterized in that in the forming step

one or more than one cut out (9) is formed in the annular rim flange (7), wherein said one or more than one cut out (9) defines a passage for a counterweight (10) of a crankshaft (11).
The method according to claim 1 or 2, characterized in that in the forming step a cavity (8) is formed into the lower base section (5).
The method according to claim 3, characterized in that in the forming step the cylindrical body including the projection portion (6), the annular rim flange (7), and the cavity (8) are together formed through a die forging process or a cast molding process.
The method according to claim 4, characterized in that in the forming step, said one or more than one cut out (9) is also formed through said die forging process or said cast molding process.
The method according to claim 4, where dependent on claim 2, characterized in that in the forming step said one or more than one cut (9) is formed through a machining process subsequent to said die forging process or said cast molding process.
The method according to any one of claims 1 to 6, further comprising a step of centerless grinding of the cylindrical lateral sections (4) of a plurality of cylindrical bodies which are stacked upon each other without placing dummies in-between the cylindrical bodies.
A piston head (1) for use in a reciprocating compressor (2), the piston head (1) comprising

a cylindrical body which includes an upper base section (3), a cylindrical lateral section (4) and a lower base section (5), wherein the upper base section (3) is leveled but has a projection portion (6) for releasably fitting into a discharge port,

characterized in that

the lower base section (5) has an annular rim flange (7),

wherein the upper surface of the annular rim flange (7) is leveled,

wherein the annular rim flange (7) has a height h which is at least equal to height h´ of the projection portion (7), and

wherein the projection portion (6) is located directly above a region of the lower base section (5) which is enclosed by an inner side of the annular rim flange (7).
The piston head (1) according to claim 8, characterized in that the annular rim flange (7) includes one or more than one cut out (9) which defines a passage for a counterweight (10) of a crankshaft (11).
The piston head (1) according to claim 8 or 9, characterized in that the lower base section includes a cavity (8).
The piston head according to any one of claims 9 to 10, characterized in that said raw material is metal.
A reciprocating compressor (2) for use in a refrigeration appliance, in particular a domestic refrigerator, the compressor (2) comprising

a cylinder block which has a chamber for compressing a refrigerant,

a piston mechanism for compressing the refrigerant in the chamber, wherein the piston mechanism includes a piston head (1) according to any one of claims 8 to 11, the piston head being arranged to reciprocate in the chamber; a piston rod (12) pivotably coupled to the piston head (1) and a crank shaft (11) which has a counter weight (10), the crankshaft (11) being pivotably coupled to the piston rod (12) and

an electrical motor for driving the crankshaft (11).
A refrigeration appliance, in particular a domestic refrigerator comprising

a refrigeration compartment for refrigerating items and

a refrigeration circuit including: a reciprocating compressor (2) according to claim 12, a condenser, an expansion valve or the like and an evaporator serially connected to circulate a refrigerant.