SEALED COMPRESSOR

TECHNICAL FIELD

The present invention relates to a sealed compressor for use in a refrigeration cycle such as an electric refrigerator, an air conditioner, and a refrigerator-freezer.

BACKGROUND ART

In recent years, energy-saving refrigerators for household use have been developed. Sealed compressors incorporated into the refrigerators for household use have been developed to attain higher efficiency.

Under the circumstances, conventionally, there is a sealed compressor incorporated into the refrigerator for household use, in which to improve efficiency, a piston is provided with a projection to reduce a dead volume of a discharge hole, to reduce a loss which would otherwise be caused by re-expansion of a compressed gas, and to thereby suppress a reduction of a refrigeration ability (see, e.g., Patent Literature 1).

FIG. 7 is a longitudinal sectional view of the conventional sealed compressor disclosed in Patent Literature 1. FIG. 8 is a perspective view of a piston of the conventional sealed compressor. FIG. 9 is a cross-sectional view of major components of the conventional sealed compressor, which is taken along A-A of FIG. 8.

As shown in FIGS. 7 to 9, a conventional sealed compressor 1 includes a compression component 5 and an electric component 7 which are accommodated into a sealed container 3, and its internal space is filled with a refrigerant gas 9.

The compression component 5 has a configuration in which a piston 13 is reciprocatingly inserted into a cylinder 11 of a substantially cylindrical shape, and is connected to an eccentric shaft 19 of a crankshaft 17 via a connecting means 15.

A valve plate 25 having a suction hole 21 and a discharge hole 23 is provided at an end portion of the cylinder 11. The valve plate 25 is provided with a suction valve (not shown) and a discharge valve 27 to open and close the suction hole 21 and the discharge hole 23, respectively.

The cylinder 11, the valve plate 25 and the piston 13 define a compression chamber 29. According to a rotation of the crankshaft 17 for transmitting a rotational power of the electric component 7, the piston 13 reciprocates inside of the cylinder 11, which constitute a compression mechanism for suctioning the refrigerant gas 9 into the compression chamber 29, compressing the refrigerant gas 9 in the compression chamber 29, and discharging the refrigerant gas 9 out of the compression chamber 29.

As shown in detail in FIGS. 8 and 9, the conventional sealed compressor 1 is configured such that the piston 13 is provided with a projection 31 on an end surface (tip end surface) at the valve plate 25 side in a position in which the projection 31 enters (moves into) the discharge hole 23, to reduce a dead volume (region expressed as meshed pattern) of the discharge hole 23.

To reduce a change in the refrigerant gas 9 in a flow direction 39 of the refrigerant gas 9, side surfaces of the projection 31 of the piston 13 are set such that a gradient thereof changes continuously in a circumferential direction, is minimum in a region of a side surface 33 and is maximum in a region of a side surface 35.

An inner peripheral surface 37 of the discharge hole 23 has a gradient (slope) set so that the inner peripheral surface 37 is substantially parallel to the side surface 33 and the side surface 35 of the projection 31 of the piston 13.

Regarding a fluid technique, there is known a book which discloses a technique for reducing a loss of the fluid in a peripheral region of an entrance of a discharge hole through which the fluid is discharged, which loss is caused by a flow of the fluid, by forming a bell mouth having a circular-arc cross-section in the peripheral region of the entrance (see, e.g., Non-patent Literature 1).

CITATION LIST
Patent Literature

U.S. Pat. No. 5,980,223 specification

Non-Patent Literature

Non-patent Literature 1: Basic Engineering Fluid Dynamics Third revision version (Baifukan 1990 p. 184 to 185)

SUMMARY OF INVENTION
Technical Problem

In the structure shown in FIG. 9, the side surface 33 having a gentle slope (small gradient) in the projection 31 can reduce a change in the refrigerant gas 9 in the flow direction 39. However, since the projection 31 has a truncated cone shape, a portion of the refrigerant gas 9 which should flow from the suction hole 21 to the discharge hole 23 flows toward peripheral walls (side surfaces) of the projection 31.

Because of this, on an end surface (tip end surface) of the projection 31, portions of the refrigerant gas 9 flowing from the entire side surfaces interfere with each other, which causes a turbulent (disordered) flow. This results in a situation in which some of the refrigerant gas 9 does not flow out of the compression chamber 29 into the discharge hole 23, but is left in the interior of the compression chamber 29, and the refrigerant gas 9 left (remaining) in the interior of the compression chamber 29 without being discharged re-expands according to a suction operation of the piston 13. As a result, a suction loss or the like is generated. Under the circumstances, the dead volume cannot be reduced effectively, and the flow of the refrigerant gas cannot be improved effectively in the sealed compressor 1.

It is assumed that the configuration disclosed in the above mentioned Non-patent Literature 1 is applied to the discharge hole 23 of the above described conventional sealed compressor 1. However, it is estimated that adequate advantages cannot be expected due to a loss of the refrigerant gas (complicated behavior of the refrigerant gas) in the vicinity of the discharge hole 23, which is associated with the projection 31.

The present invention is directed to solving the above described problem associated with the prior art, and an object of the present invention is to provide a sealed compressor which can attain a high efficiency, in which a dead volume is reduced to reduce a loss caused by re-expansion of a refrigerant gas, and a flow of the refrigerant gas is improved to reduce a loss of a discharged refrigerant gas in an interior of a compression chamber and a discharge hole.

Solution to Problem

To solve the problem associated with the prior art, a sealed compressor of the present invention comprises an electric component; a compression component actuated by the electric component; and a sealed container accommodating the electric component and the compression component; wherein the compression component includes: a cylinder block defining a compression chamber; a piston which reciprocates in an interior of the compression chamber; and a valve plate disposed to close an opening end of the compression chamber and having a suction hole through which a refrigerant gas to be compressed in the interior of the compression chamber flows into the interior of the compression chamber, and a discharge hole through which the refrigerant gas compressed in the interior of the compression chamber is discharged from the interior of the compression chamber; wherein the piston is provided with a projection on a tip end surface which faces the valve plate; and wherein the projection is configured such that side surfaces thereof include at least one flat surface and a gradient α of the flat surface with respect to the tip end surface of the piston is smaller than a gradient β of another side surface of the projection with respect to the tip end surface of the piston.

In this configuration, since the projection provided on the tip end surface of the piston enters (moves into) the discharge hole, a dead volume can be reduced, and re-expansion of the refrigerant gas can be reduced. As a result, efficiency of the compressor can be improved. In addition, in the flow of the refrigerant gas from the suction hole toward the discharge hole, the refrigerant gas collides against the flat surface and is prevented from flowing toward the peripheral walls extending in an axial direction of the projection. The refrigerant gas can be efficiently guided toward the discharge hole along the flat surface. Therefore, the amount of the refrigerant gas left in the interior of the compression chamber without being discharged, at the end of a compression stroke, can be lessened, and a suction loss which would otherwise be caused by re-expansion of the refrigerant gas left in the interior of the compression chamber without being discharged, can be reduced.

Advantageous Effects of Invention

A sealed compressor of the present invention is capable of reducing a loss of a flow of a discharged gas in an interior of a compression chamber and a discharge hole and of reducing a suction loss which would otherwise be caused by re-expansion of the refrigerant gas left in the interior of the compression chamber without being discharged. Therefore, the sealed compressor of the present invention can increase its efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view of a sealed compressor according to Embodiment 1.

FIG. 2 is a perspective view showing major components of a piston of the sealed compressor according to Embodiment 1.

FIG. 3 is a cross-sectional view of the piston of the sealed compressor according to Embodiment 1, which is taken along B-B of FIG. 2.

FIG. 4 is a schematic view showing a tip end surface of the piston of the sealed compressor according to Embodiment 1, when viewed from a direction in which the piston retracts.

FIG. 5 is a view showing a characteristic indicating a relationship between a gradient α of a side surface of a projection, and coefficient of performance COP in the sealed compressor according to Embodiment 1.

FIG. 6 is a perspective view showing major components of a piston according to a modified example of Embodiment 1.

FIG. 7 is a longitudinal sectional view of a sealed compressor disclosed in Patent Literature 1.

FIG. 8 is a perspective view of a piston of the sealed compressor disclosed in Patent Literature 1.

FIG. 9 is a cross-sectional view of the piston of the sealed compressor disclosed in Patent Literature 1, which is taken along A-A of FIG. 8.

DESCRIPTION OF EMBODIMENTS

A sealed compressor of the present invention comprises an electric component; a compression component actuated by the electric component; and a sealed container accommodating the electric component and the compression component; wherein the compression component includes: a cylinder block defining a compression chamber; a piston which reciprocates in an interior of the compression chamber; and a valve plate disposed to close an opening end of the compression chamber and having a suction hole through which a refrigerant gas to be compressed in the interior of the compression chamber flows into the interior of the compression chamber, and a discharge hole through which the refrigerant gas compressed in the interior of the compression chamber is discharged from the interior of the compression chamber; wherein the piston is provided with a projection on a tip end surface which faces the valve plate; and wherein the projection is configured such that side surfaces thereof include at least one flat surface and a gradient α of the flat surface with respect to the tip end surface of the piston is smaller than a gradient β of another side surface of the projection with respect to the tip end surface of the piston.

With this configuration, a dead volume formed in the discharge hole can be reduced, and a suction loss which would otherwise be caused by re-expansion of the refrigerant gas can be reduced. As a result, efficiency of the compressor can be improved. In addition, the refrigerant gas is prevented from flowing toward the side surfaces of the projection by the flat surface having the gradient α. Moreover, since the gradient α of the flat surface is set smaller than the gradient β of another side surface, a passage resistance of the flow of the refrigerant gas along the flat surface can be reduced.

As a result, the refrigerant gas colliding against the flat surface and is prevented from flowing toward the peripheral walls by the flat surface can be efficiently guided toward the discharge hole. Therefore, the amount of the refrigerant gas left (remaining) in the interior of the compression chamber without being discharged, at the end of a compression stroke, can be lessened, and a suction loss which would otherwise be caused by re-expansion of the refrigerant gas left in the interior of the compression chamber without being discharged, can be reduced. Thus, efficiency of the sealed compressor can be improved.

In the sealed compressor of the present invention, the flat surface having the gradient α may be placed to face the suction hole.

In such a configuration, the refrigerant gas flowing into the compression chamber through the suction hole can be more efficiently guided to flow toward the discharge hole along the flat surface. In particular, the amount of the refrigerant gas left (remaining) in the interior of the compression chamber without being discharged, at the end of the compression stroke, can be further reduced. As a result, a suction loss which would otherwise be caused by re-expansion of the refrigerant gas left in the interior of the compression chamber without being discharged, can be reduced. Thus, efficiency of the sealed compressor can be further improved.

In the sealed compressor of the present invention, the discharge hole may have an opening area which increases from the compression chamber side toward an opposite side of the compression chamber.

In this configuration, an area of a flow passage defined by the side surface of the projection and the inner peripheral surface of the discharge hole can be increased. Because of this, it becomes possible to reduce a passage resistance of the refrigerant gas flowing through the discharge hole. As a result, the compressed refrigerant gas can be smoothly discharged from the discharge hole, excessive compression of the refrigerant gas during the compression stroke can be reduced, and the amount of electric power input to the sealed compressor can be reduced.

In the sealed compressor of the present invention, an opening portion of the discharge hole in the valve plate, which opening portion is at the compression chamber side, may have a circular-arc cross-section.

In this configuration, the refrigerant gas can be guided to the discharge hole more smoothly. As a result, the amount of the refrigerant gas left (remaining) in the interior of the compression chamber without being discharged, at the end of the compression stroke, can be reduced. Therefore, a suction loss which would otherwise be caused by re-expansion of the refrigerant gas left in the interior of the compression chamber without being discharged can be reduced, and hence efficiency of the sealed compressor can be further improved.

In the sealed compressor of the present invention, a cross-section of the projection which is taken along a plane which is substantially parallel to the tip end surface of the piston may have a polygonal shape.

In this configuration, the refrigerant gas collides against plural flat surfaces defining the polygonal shape, and is prevented from flowing toward the side surfaces of the projection by the flat surfaces. The portions of the refrigerant gas colliding against the plural flat surfaces flow along the flat surfaces, and therefore can be guided toward the discharge hole. Thus, the amount of the refrigerant gas left (remaining) in the interior of the compression chamber without being discharged, at the end of the compression stroke, can be further reduced. As a result, a suction loss which would otherwise be caused by re-expansion of the refrigerant gas left in the interior of the compression chamber without being discharged can be reduced, and hence efficiency of the sealed compressor can be further improved.

In this configuration, the refrigerant gas flowing toward the discharge hole is guided along the four flat surfaces defining the projection. Therefore, the flow to the side surfaces of the projection can be suppressed, and the refrigerant gas can be smoothly guided toward the discharge hole. Moreover, the amount of the refrigerant gas left (remaining) in the interior of the compression chamber without being discharged, at the end of the compression stroke, can be reduced, and a suction loss which would otherwise be caused by re-expansion of the refrigerant gas left in the interior of the compression chamber without being discharged, can be reduced. As a result, efficiency of the sealed compressor can be further improved.

In the sealed compressor of the present invention, the gradient α may be in a range of 65 degrees≦α≦80 degrees.

In this configuration, the refrigerant gas can be flowed smoothly toward the discharge hole. Especially, the amount of the refrigerant gas left (remaining) in the interior of the compression chamber without being discharged, at the end of the compression stroke, can be reduced, a suction loss which would otherwise be caused by re-expansion of the refrigerant gas left in the interior of the compression chamber without being discharged can be reduced, and efficiency of the sealed compressor can be further improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Throughout the drawings, the same or corresponding components are designated by the same reference symbols, and will not be described in repetition. In addition, throughout the drawings, components required to describe the present invention are depicted and the other components are not illustrated. Moreover, the present invention is not limited to the embodiments described below.

Embodiment 1
Configuration of Sealed Compressor

FIG. 1 is a longitudinal sectional view of a sealed compressor according to Embodiment 1. FIG. 2 is a perspective view showing major components of a piston of the sealed compressor according to Embodiment 1. FIG. 3 is a cross-sectional view of the piston of the sealed compressor according to Embodiment 1, which is taken along B-B of FIG. 2. FIG. 4 is a schematic view showing a tip end surface of the piston of the sealed compressor according to Embodiment 1, when viewed from a direction in which the piston retracts.

As shown in FIG. 1, in a sealed compressor (hereinafter will be referred to as a compressor) 100, a refrigerant gas 103 is filled into a sealed container 101. The sealed container 101 accommodates a compression component 107 and an electric component 105 for actuating the compression component 107. The compression component 107 and the electric component 105 are elastically supported on the sealed container 101 by means of a suspension spring 109.

The compression component 107 mainly includes a crankshaft 111 for converting a rotational motion of the electric component 105 into a reciprocation motion, and a cylinder block 115 including a cylinder 113 defining a compression chamber 135 of a substantially cylindrical shape.

The crankshaft 111 includes a main shaft section 119 to which a rotor 117 of the electric component 105 is fastened and an eccentric section 121 having a center axis which is eccentric with respect to the main shaft section 119. The main shaft section 119 is supported on a main shaft bearing unit 123 of the cylinder block 115.

A piston 125 is reciprocatingly inserted into the cylinder 113. The piston 125 is connected to the eccentric section 121 of the crankshaft 111 via a connecting means 127. That is, one end of the connecting means 127 is rotatably connected to the eccentric section 121 of the crankshaft 111, while the other end thereof is rotatably connected to a piston pin 129 attached to the piston 125. This allows the connecting means 127 to convert a rotational motion of the eccentric section 121 caused by a rotation of the crankshaft 111 into a reciprocation motion and transmit the reciprocation motion to the piston 125.

A valve plate 133 is attached to an end portion 131 of the cylinder 113. The valve plate 133 closes the end portion 131 (compression chamber 135) of the cylinder 113. The valve plate 133 is provided with a suction hole 137 and a discharge hole 139 each of which has a circular opening. A shape of the discharge hole 139 will be described later.

The valve plate 133 is provided with a suction valve (not shown) for opening and closing the suction hole 137 and a discharge valve 145 (see FIG. 3) for opening and closing the discharge hole 139. A configuration (shape) of the suction valve and a configuration (shape) of the discharge valve 145 are well-known, and therefore detailed description thereof will be omitted.

The valve plate 133 is covered with a cylinder head 141. Inside of the cylinder head 141, a discharge chamber 147 communicated with the discharge hole 139 is provided. A discharge pipe 149 is connected to the discharge chamber 147. An exit pipe 151 is connected to the discharge pipe 149 such that the exit pipe 151 extends to outside of the sealed container 101. Furthermore, as shown in FIG. 1, a suction muffler 143 is retained between the cylinder head 141 and the valve plate 133.

As shown in FIG. 3, the discharge hole 139 provided in the valve plate 133 is formed such that its opening area increases in a direction from the compression chamber 135 side toward an opposite side (discharge chamber 147 side) of the compression chamber 135. An opening portion 173 of the discharge hole 139 in the valve plate 133, which opening portion is at the compression chamber 135 side, has a circular-arc cross-section. In more detail, the cross-section of the opening portion 173 which is taken along a direction in which the piston 125 moves has a circular-arc shape which is round. A radius of the circular-arc of the opening portion 173 of the discharge hole 139 may be set as desired. Hereinafter, the opening portion 173 of the circular-arc shape will be referred to as a bell mouth portion 173.

The discharge hole 139 has a size to allow a projection 155 of the piston 125 to easily move thereinto. As shown in FIG. 4, the discharge hole 139 is provided in a position of a center axis 159 which is eccentric outward relative to a center axis 157 of the compression chamber 135.

Therefore, a center axis 161 of the projection 155 is provided in a position so that the projection 155 closes and exposes the discharge hole 139 during the reciprocation motion of the piston 125, and (substantially) conforms to the center axis 159 of the discharge hole 139. That is, the center axis 161 of the projection 155 is in the position which is eccentric outward relative to the center axis 157 of the compression chamber 135 and the center axis 163 of the piston 125 (substantially) conforming to the center axis 157.

As shown in FIG. 4, the projection 155 (discharge hole 139) and the suction hole 137 provided in the valve plate 133 do not overlap with each other when viewed from the direction in which the piston 125 moves. Specifically, the suction hole 137 is positioned within a projection plane (hatched region) from a line X which is an extended line of a side of the projection 155 (bottom of a side wall 165a as will be described later) which is closest to the center axis 163 of the piston 125 to a region which is beyond the center axis 163 of the piston 125.

As shown in FIGS. 2 to 4, a tip end surface 153 of the piston 125 at the valve plate 133 side (surface facing the valve plate 133) is provided with the projection 155 such that the projection 155 overlaps with the discharge hole 139 when viewed from the direction in which the piston 125 moves. The projection 155 is integral with the piston 125, and closes and exposes the discharge hole 139 according to the reciprocation motion of the piston 125.

The projection 155 has a rectangular shape in cross-section which is taken along a plane parallel to the tip end surface 153 of the piston 125, i.e., substantially rectangular-parallelepiped shape (including truncated pyramid shape), and has four flat surfaces (hereinafter will be referred to as side walls) 165a, 165b, 165c, 165d, and a top surface 167. The projection 155 has a shape in which the top surface 167 perpendicular to the center axis 163 of the piston 125 has a substantially rectangular shape.

The projection 155 is configured such that a gradient (slope) formed between the four side walls 165a, 165b, 165c, 165d, and the tip end surface 153 of the piston 125 is less than 90 degrees. In other words, the projection 155 is configured such that the cross-section which is taken along a plane parallel to the tip end surface 153 of the piston 125 has an area which is reduced toward a top portion (top surface 167) which is distant from the tip end surface 153 of the piston 125.

As shown in FIG. 4, the side wall 165a of the projection 155 is oriented such that an angle θ (hereinafter will be referred to as placement angle) formed between the line X and a line Y passing through the center axis (center) 169 of the suction hole 137 and the center axis (center) 163 of the piston 125, is set to about 52 degrees.

The placement angle θ may be defined as a placement relationship in which a line Z which is perpendicular to the side wall 165a and passes through a center of the side wall 165a crosses the line Y passing through the center axis 169 of the suction hole 137 and the center axis 163 of the piston 125 at a predetermined angle.

As shown in FIG. 3, a gradient (slope) a formed between the side wall 165a and the tip end surface 153 of the piston 125 is set to 70 degrees. According to a result of an experiment as described later, the gradient α may be set to a desired value in a range of 65 degrees≦α≦80 degrees, and may be α≦79 degrees. Note that there is a little tolerance in the gradient α because the piston 125 and the projection 155 are molded using a die.

A gradient (slope) β formed between other side walls 165b, 165c, 165d, and the tip end surface 153 of the piston 125 is set to about 85 degrees. The gradient β is an angle except for a draft angle (about 5 degrees) during the above stated die molding, and may be set to a desired value. The gradient α and the gradient β are set such that the gradient α is smaller than the gradient β.

A curved surface 171 having a specified diameter is formed in a portion (base end portion of the projection 155) of the tip end surface 153 of the piston 125 which the side wall 165a of the projection 155 crosses. In other words, the side wall 165a of the projection 155 partially has the curved surface 171.

[Operation and Advantage of Sealed Compressor]

Next, operation and advantages of the sealed compressor 100 configured as described above will be described. In the compressor 100, as should be well-known, a refrigerant circuit connecting a condenser (not shown), a pressure-reducer (not shown), and an evaporator (not shown) is connected between a suction pipe (not shown) and the exit pipe 161, thus constituting a well-known refrigeration cycle. As the refrigerant gas 103 to be compressed, R600a is used.

When the electric component 105 is supplied with an electric current, the rotor 117 rotates and the crankshaft 111 rotates. A rotational motion of the eccentric section 121 of the crankshaft 111 is transmitted to the piston 125 via the connecting means 127. This causes the piston 125 to reciprocate inside of the cylinder 113.

In a suction (intake) stroke in which the piston 125 moves from a top dead center toward a bottom dead center, the volume of the compression chamber 135 increases according to the motion of the piston 125 toward the crankshaft 111. Therefore, the pressure in the interior of the compression chamber 135 decreases. Due to a pressure difference between an interior of the suction muffler 143 and the interior of the compression chamber 135, the suction valve (not shown) opens, so that the compression chamber 135 and the suction muffler 143 are communicated with each other via the suction hole 137. Thereby, the refrigerant gas 109 is guided from the refrigerant circuit to the interior of the sealed container 101, and suctioned into the interior of the compression chamber 135 through the suction muffler 143 and the suction hole 137.

Then, in a compression stroke in which the piston 125 moves from the bottom dead center toward the top dead center, the volume of the compression chamber 135 decreases according to the motion of the piston 125 toward the valve plate 133. Therefore, the pressure in the interior of the compression chamber 135 increases. Due to a pressure difference between the interior of the suction muffler 143 and the interior of the compression chamber 135, the suction valve (not shown) closes. Then, the refrigerant gas 103 in the interior of the compression chamber 135 is compressed, and the pressure in the interior of the compression chamber 135 further increases.

When the pressure in the interior of the compression chamber 135 increases to a value which is equal to or higher than the pressure in the interior of the discharge chamber 147, the discharge valve 145 opens due to a pressure difference between an interior of the discharge chamber 147 and the interior of the compression chamber 135. Until the piston 125 reaches the top dead center, the compressed refrigerant gas 103 is discharged from the discharge hole 139 to the discharge chamber 147 inside of the cylinder head 141.

The refrigerant gas 103 discharged to the discharge chamber 147 flows through the discharge pipe 149 and is sent out from the exit pipe 151 to the refrigerant circuit outside of the sealed container 101, thus forming a refrigeration cycle.

The above described suction, compression and discharge strokes are repeated each time the crankshaft 111 rotates, and the refrigerant gas 103 circulates within the refrigeration cycle.

The flow of the refrigerant gas 103 discharged from the discharge hole 139 in the above described discharge stroke, will be described in detail with reference to FIG. 3. Herein, a description will be given of a case where it is assumed that the discharge stroke is included in the compression stroke based on the motion of the piston 125, for the sake of convenience.

The piston 125 moves in the direction in which the projection 155 moves into the discharge hole 139. In a latter half of the compression stroke, as shown in FIG. 3, the tip end surface 153 of the piston 125 gets closer to the valve plate 133, and the projection 155 gets closer to the discharge hole 139 which faces the projection 155. Then, according to an increase in the pressure in the interior of the compression chamber 135, the discharge valve 145 opens.

Upon the discharge valve 145 opening, the refrigerant gas 103 compressed in the interior of the compression chamber 135 is discharged to the interior of the discharge chamber 147 inside of the cylinder head 141 all at once via the discharge hole 139, as indicated by arrows in FIG. 3.

When the compression stroke progresses, the projection 155 of the piston 125 moves into the discharge hole 139. The compression stroke finishes in a state in which a portion of the compressed refrigerant gas 103 is left within the dead volume (portion expressed as meshed pattern) defined by the projection 155 and the discharge hole 139.

The flow of the refrigerant gas 103 in the interior of the compression chamber 135 in the compression stroke is a three-dimensional flow in which a flow velocity and a flow direction change significantly, and which exhibits a complicated behavior. As described above, in the compressor disclosed in Patent Literature 1, since the projection 31 has the truncated cone shape, the refrigerant gas 9 flows toward the peripheral walls (side walls) of the projection 31, which causes a turbulent (disordered) flow.

However, in Embodiment 1, since the projection 155 provided on the tip end surface 153 of the piston 125 has a substantially rectangular parallelepiped shape having the four side walls 165a, 165b, 165c, 165d, the refrigerant gas 103 is less likely to flow toward the peripheral portions of the projection 155.

In particular, at a time point which is near the end of the compression stroke, a flow passage (portion expressed as meshed pattern in FIG. 3) defined by the discharge hole 139 and the projection 155 is narrower, as the piston 125 moves in the direction in which the projection 155 moves into the discharge hole 139. This makes the flow velocity of the refrigerant gas 103 flowing through the flow passage higher. It is estimated that this causes the refrigerant gas in the interior of the compression chamber 135 to be guided to the discharge hole 139 along the side walls 165a, 165b, 165c, 165d.

Specifically, the refrigerant gas 103 present in the vicinity of the inner wall of the cylinder 113 flows toward the discharge hole 139 along the tip end surface 153 and its flow is blocked by the side walls 165b, 165d of the projection 155 (collides against the side walls 165b, 165d of the projection 155). After colliding against the side walls 165b, 165d, the refrigerant gas 103 flows along the side walls 165b, 165d and is guided to inside of the discharge hole 139. It is estimated that at corner portions formed by the side walls 165b, 165d and the adjacent side walls 165a, 165c, a turbulent flow occurs, but a flow component guided to inside of the discharge hole 139 increases.

It is also estimated that portions of the refrigerant gas 103 flowing from the corner portions toward the side wall 165c of the projection 155 collide against each other, and a portion the refrigerant gas 103 is guided to the discharge hole 139 along the surface of the side wall 165c.

It is estimated that the refrigerant gas 103 flowing toward the discharge hole 139 along the tip end surface 153 collides against the side wall 165a, its flow is blocked by the side wall 165a, and a flow component of refrigerant gas 103 which is guided to the discharge hole 139 along the surface of the side wall 165a increases.

In Embodiment 1, a base portion of the tip end surface 153 of the piston 125 from which the projection 155 projects is the curved surface 171. With this structure, it is expected that the flows of the refrigerant gas 103 along the side walls 165a, 165b, 165c, 165d, can be made smooth.

It is well known that the volume of the dead volume defined by the projection 155 and the discharge hole 139 significantly affects the efficiency of the sealed compressor 100. In addition, in the present invention, through an experiment, it was discovered that the shape of the projection 155 of the piston 125 affects the efficiency of the sealed compressor 100, to a degree equal to or more than that of the volume of the dead volume.

Hereinafter, advantages achieved by the shape of the projection 155 of the piston 125 will be described.

FIG. 5 is a view showing a characteristic indicating a relationship between the gradient α of the side surface of the projection, and coefficient of performance COP in the sealed compressor according to Embodiment 1. In FIG. 5, a horizontal axis indicates the gradient α formed between the side wall 165a of the projection 155 and the tip end surface 153 of the piston 125, while a vertical axis indicates the coefficient of performance COP.

A measurement result of FIG. 5 is of the compressor 100 having a cylinder volume of 6.0 cc and an operating frequency of 50 Hz. As can be seen from FIG. 5, it was confirmed through the experiment that the efficiency was higher when the gradient α of the side wall 165a of the projection 155 was in a range of 65 degrees≦α≦80 degrees.

Next, the experiment result of the gradient α shown in FIG. 5 will be considered, and estimation will be made as follows.

Among the four side walls 165a, 165b, 165c, 165d of the projection 155, the gradient α formed between the side wall 165a facing the suction hole 137 and having a larger area and the tip end surface 153 of the piston 125, is set in a range of 65 degrees≦α≦80 degrees. This causes a passage area of a flow passage defined by the side wall 165a and the inner peripheral surface of the discharge hole 139 to be greater than a passage area of a flow passage defined by each of the side walls 165b, 165c, 165d and the inner peripheral surface of the discharge hole 139. Because of this, it becomes possible to reduce a passage resistance in the flow passage defined by the side wall 165a and the inner peripheral surface of the discharge hole 139, and hence increase the refrigerant gas 103 guided to the discharge hole 139, along the side wall 165a of the projection 155.

Furthermore, the gradient α of the side wall 165a is set smaller than the gradient β of the side walls 165b, 165c, 165d. This reduces a passage resistance of the flow of the refrigerant gas along the side wall 165a, which allows the refrigerant gas 103 of a larger amount to be guided to the discharge hole 139.

That is, the passage resistance of the refrigerant gas 103, which is caused by the structure in which the projection 155 and the inner peripheral surface of the discharge hole 139 are close to each other, is reduced. In association with this, the flow of the refrigerant gas 103 is more effectively faired, the amount of the refrigerant gas 103 left in the interior of the compression chamber 135 without being discharged, is reduced, and a suction loss which would otherwise be caused by re-expansion of the refrigerant gas 103 left in the interior of the compression chamber without being discharged, at a time point just before the suction stroke starts, is reduced. As a result, electric input to the compressor 100 can be effectively reduced (coefficient of performance COP can be improved).

If the gradient β is set smaller than 65 degrees, the refrigerant gas 103 guided toward the discharge hole 139 along the side wall 165a increases in amount. However, the refrigerant gas 103 guided toward the discharge hole 139 along the side wall 165a interferes with the refrigerant gas 103 guided toward the discharge hole 139 along the side wall 165c, causing a turbulent flow. Thereby, all of the refrigerant gas 103 does not flow out of the compression chamber 135 and a portion of the refrigerant gas 103 is left (remains) in the compression chamber 135. The refrigerant gas 103 left in the interior of the compression chamber 135 without being discharged re-expends according to a suction operation of the piston 125, and as a result, a suction loss is generated. In this way, in the sealed compressor 100, the dead volume cannot be effectively reduced, and the flow of the refrigerant gas cannot be effectively improved.

The result of the experiment supports that in addition to the volume of the dead volume, the shape of the discharge hole 139, and the shape of the projection 155 of the piston 125, the gradient α formed between the side wall 165a closest to the center axis 169 of the suction hole 137, among the four side walls 165a, 165b, 165c, 165d of the projection 155, and the tip end surface 153 of the piston 125, affects the efficiency of the compressor 100.

It was also confirmed through the experiment that the projection 155 of Embodiment 1 is able to improve the efficiency of the compressor 100 in operating frequencies which is near the operating frequency of 50 Hz described with reference to FIG. 5, although there is a difference in improvement of efficiency among the operating frequencies.

Therefore, it is expected that the compressor 100 of Embodiment 1 is able to achieve further energy saving in the case of using the setting of the gradient α of the side wall 165a of the projection 155 and inverter actuation control by plural operating frequencies including 50 Hz.

In addition, in Embodiment 1, the refrigerant gas 103 is smoothly guided toward the discharge hole 139 by providing the bell mouth portion 173 in the periphery of the entrance of the discharge hole 139, a loss in the entrance of the discharge hole 139 can be lessened.

The refrigerant gas 103 faired in an axial direction of the discharge hole 139 by the side walls (flat surfaces) 165a, 165b, 165c, 165d of the projection 155 easily flows along the circular-arc contour of the bell mouth portion 173 and smoothly flows through the discharge hole 139.

In other words, the flow of the refrigerant gas 103 is made smooth by a synergetic effect produced by the projection 155 and the bell mouth portion 173. Therefore, the refrigerant gas 103 left in the interior of the compression chamber 135 without being discharged, at the end of the compression stroke, is reduced.

Therefore, in addition to the reduction of the dead volume in the discharge hole 139 because of the projection 155, a loss which would otherwise be caused by re-expansion of the refrigerant gas 103 left in the compression chamber 135 without being discharged, can be reduced, and hence the input to the compressor 100 can be reduced. Although in Embodiment 1, the valve plate 133 is provided with the bell mouth portion 173, the present invention is not limited to this. The valve plate 133 may not be provided with the opening 173.

Furthermore, in Embodiment 1, by forming the discharge hole 139 such that its opening area increases from the compression chamber 135 side toward an opposite side of the compression chamber 135 (discharge chamber 147 side), the area of the flow passage defined by the projection 155 and the inner wall of the discharge hole 139 can be increased, and thus, the passage resistance of the refrigerant gas 103 flowing through the discharge hole 139 can be reduced.

The cross-sectional area of the flow passage defined by the projection 155 and the inner wall of the discharge hole 139, which is taken along the plane parallel to the tip end surface 153, increases toward an exit of the discharge hole 139 (discharge chamber 147). Because of this, the passage resistance is reduced, which allows the refrigerant gas 103 to easily flow into the discharge chamber 147. In this way, the refrigerant gas 103 left in the interior of the compression chamber 135 without being discharged, at the end of the compression stroke, can be reduced, and hence a loss which would otherwise be caused by re-expansion of the refrigerant gas 103 left in the interior of the compression chamber 135 without being discharged, can be reduced. As a result, electric power input to the compressor 100 can be reduced in amount.

Although in Embodiment 1 the discharge hole 139 is formed such that its opening area increases from the compression chamber 135 side toward an opposite side of the compression chamber 135, the present invention is not limited to this. It is expected that even the discharge hole 139 of a cylindrical shape having a uniform opening area can improve the efficiency as compared to the conventional sealed compressor 1, although there is some difference in improvement of the efficiency from that of the structure in which the opening area increases from the compression chamber 135 side toward an opposite side of the compression chamber 135. Therefore, this configuration may be used.

Modified Example 1

Next, a sealed compressor of Modified example 1 of Embodiment 1 will be described.

FIG. 6 is a perspective view showing major components of a piston according to modified example of Embodiment 1.

As shown in FIG. 6, the compressor 100 according to Modified example 1 has basically the same configuration as that of the compressor 100 of Embodiment 1, but is different from the same in shape of the projection 155 of the piston 125. Specifically, in Modified example 1, the projection 155 has substantially a truncated cone shape, and a flat surface 155a is formed on a portion of the truncated cone shape. The flat surface 155a is formed such that a gradient of the flat surface 155a with respect to the tip end surface 153 of the piston 125 is the gradient α.

The compressor 100 according to Modified example 1 so configured can achieve the same advantages as those of the compressor 100 of Embodiment 1.

Numeral modifications and alternative embodiments of the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, the description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and/or function may be varied substantially without departing from the spirit of the invention.

INDUSTRIAL APPLICABILITY

A sealed compressor of the present invention is a sealed compressor which has a high productivity and a high efficiency and is inexpensive, and is applicable to a sealed compressor for use in a refrigeration cycle and incorporated in various refrigeration units. An article storage device incorporating such a sealed compressor is used as various devices such as refrigerators for household uses, dehumidification machines, show cases, and vending machines, and is applicable as various storage devices which can lessen electric power consumption.

REFERENCE SIGNS LIST

- 100 sealed compressor
- 101 sealed container
- 103 refrigerant gas
- 105 electric component
- 107 compression component
- 115 cylinder block
- 125 piston
- 133 valve plate
- 135 compression chamber
- 137 suction hole
- 139 discharge hole
- 153 tip end surface
- 155 projection
- 165
  a side wall (flat surface)
- 165
  b side wall (flat surface)
- 165
  c side wall (flat surface)
- 165
  d side wall (flat surface)
- 173 bell mouth portion
- α gradient
- β gradient

SEALED COMPRESSOR

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