The present invention relates to a compressor.
In a reciprocating compressor of the related art which compresses a fluid, for example, as illustrated in Patent Document 1 and Patent Document 2, a technique has been known by which a central axis of a cylinder is disposed to be shifted by a certain offset amount with respect to a rotation center of a crankshaft.
When the cylinder is disposed to be offset by the application of the technique of Patent Document 1 and Patent Document 2, the oscillation angle at a top dead center is not 0, so that the gap volume increases and the volumetric efficiency of the compressor deteriorates, which is a critical problem.
In Patent Document 1, as illustrated in
However, the piston is not at the top dead center in
In addition, FIG. 6 of Patent Document 2 illustrates a case in which the crank angle is 0 degrees to be described later, and in that case, an upper surface of a piston and a crankcase side surface of a valve plate are parallel to each other. In such a configuration, in Patent Document 2, similar to Patent Document 1, when a transition is made to the state of the top dead center, there is a possibility that the upper surface of the piston and the crankcase side surface of the valve plate interfere with each other, and the effect of reducing the gap volume is also not sufficient.
An object of the present invention is to prevent interference between a piston and a valve plate, and suppress an increase in gap volume.
According to one preferred example of the present invention, there is provided a compressor including: a piston that reciprocates inside a cylinder; a valve plate that closes an end portion of the cylinder; a connecting rod that supports the piston; a crankshaft that applies a rotating force to an end portion of the connecting rod; and a crankcase that rotatably supports the crankshaft.
The piston is an oscillating piston that reciprocates while oscillating inside the cylinder according to rotation of the crankshaft.
A central axis of an inner diameter of the cylinder is disposed at a position shifted by an offset amount e with respect to a rotation center axis of the crankshaft.
An upper surface of the piston is substantially parallel to a crankcase side surface of the valve plate in a state where the piston is at a top dead center.
According to the present invention, interference between the piston and the valve plate can be prevented, and an increase in gap volume can be suppressed.
Hereinbelow, embodiments of the present invention will be described in detail with reference to the drawings.
The compressor illustrated in
When the crankshaft 24 inside the crankcase 21 rotates, a rotating force is applied to an end portion of a connecting rod 32 to cause a piston 33, which is installed inside the cylinder 22, to reciprocate in the vertical direction, and as a result, the compressor main body 1 suctions a fluid from outside the cylinder, compresses the fluid, and discharges the compressed fluid.
Incidentally, in
The compressor main body 1 is disposed on and fixed to the tank 3 in a state where the crankshaft 24 is disposed in parallel to a rotating shaft of the electric motor 2. A compressor pulley 4 is fixed to the crankshaft 24, and an electric motor pulley 5 is fixed to an electric motor shaft. The compressor pulley 4 provided in the compressor main body 1 includes blades, and as the blades rotate, cooling air is generated toward the compressor main body 1 to promote heat dissipation of the compressor main body 1.
A power transmission belt 6 which transmits power between the compressor pulley 4 and the electric motor pulley 5 is wound around the compressor pulley 4 and the electric motor pulley 5. Accordingly, as the electric motor 2 rotates, the crankshaft 24 of the compressor main body 1 is rotationally driven via the electric motor pulley 5, the power transmission belt 6, and the compressor pulley 4, so that the compressor main body 1 compresses a fluid.
In this case, a rotation direction of the crankshaft 24 is a counterclockwise direction, and a state where a line segment connecting the rotation center of the crankshaft 24 and the center of a big end portion bearing 31 of the connecting rod 32, namely, a crank arm exactly points toward the top of the figure is defined as 0 degrees. This crank angle also indicates a state where the crank arm and a central axis of a cylinder inner diameter 22a are parallel to each other.
Incidentally, in
The structure around the piston in
In the oscillating piston type, as a main seal ring structure, the piston 33 may include a lip ring 36 in contact with the cylinder inner peripheral surface (cylinder inner diameter) 22a as illustrated in
In each seal ring type, the following problems occur as the oscillation angle increases.
<Lip Ring>
When a lip portion 36a repeatedly comes into contact with the cylinder inner diameter 22a, bending stress increases, and thus fatigue breakage occurs in the vicinity of the root of a rounded portion.
<Piston Ring>
A. Since there is no component such as the lip ring 36 which guides the piston 33, there is a risk that upper and lower end corners of the piston 33 interfere with the cylinder inner diameter (cylinder inner peripheral surface) 22a. When a relief cut is provided at the lower end corner to avoid interference, the area of a lower surface of a ring groove that supports the piston ring 37 which has received a gas load is reduced. Therefore, the cylinder gap 38 in the oscillation direction is increased, thereby causing deformation in which the piston ring falls into the gap.
B. Deformation occurs in which the piston ring falls into the cylinder gap 38 in the oscillation direction.
C. Since the piston ring is thicker and more rigid than the lip ring, the followability with respect to the cylinder inner diameter 22a during oscillation deteriorates, the sealing performance decreases, and the blowby loss increases.
In order to solve the problems of the lip ring or the problems A to C of the piston ring described above, in the present embodiment, the oscillating piston illustrated in
A piston ring 34 is used as a seal ring, and the piston ring 34 is fitted to a ring groove 33b, which is provided in the piston 33, with a certain gap therebetween. Incidentally, instead of using the piston ring and the ring groove, the configuration illustrated in
When the compressor main body 1 is an oil-free type in which an oil is not used for lubrication of sliding parts, the piston 33 is made of a resin material having good wear resistance. Accordingly, the outer peripheral surface 33a of the piston can directly slide against the cylinder inner peripheral surface 22a.
In addition, an extension line of a central axis 22b of the cylinder inner peripheral surface 22a in
In this case, the following relational expression is established for the offset amount e1.
[Equation 1]
βTDC=−βLmin (1)
Here, β represents an oscillation angle. Subscripts TDC and Lmin represent an oscillation angle at a top dead center and a minimum oscillation angle at a compression stroke, respectively. Incidentally, the offset amount e1 is related to the oscillation angles as shown in the following equations.
Here, θ represents a crank angle, and the subscripts TDC and Lmin represent a crank angle at the top dead center and a minimum crank angle at the compression stroke, respectively. r represents a crank radius, and L represents the length of the connecting rod and the length of a line segment connecting the center of the big end portion bearing 31 of the connecting rod and the center of the spherical outer peripheral surface 33a of the piston.
Namely, Equations (1) to (3) represent that the offset amount e1 is determined such that the absolute value of the oscillation angle of the connecting rod at the top dead center and the absolute value of the minimum value (
The crank angle at the bottom dead center is an angle slightly smaller than 180 degrees.
The crank angle at the top dead center is an angle of approximately 355 degrees slightly smaller than 360 degrees.
The oscillation angle refers to an angle between the line segment 27, which connects the center of the big end portion bearing 31 of the connecting rod and the center 33d of the spherical outer peripheral surface 33a of the piston, and the central axis of the cylinder inner diameter.
In addition,
For this reason, the upper surface 33c of the piston is also not parallel to the lower surface of the valve plate 26 in a state where the crank angle is 0 degrees.
The upper surface 33c of the piston 33 and the lower surface of the valve plate 26 are designed to be parallel to each other at the top dead center where a center point of the spherical outer peripheral surface 33a of the piston is farthest from the rotation center 24a of the crankshaft.
The present embodiment has the following merits.
Interference between the piston 33 and the valve plate 26 can be prevented, and an increase in gap volume can be suppressed.
Since the spherical outer peripheral surface 33a of the piston can directly slide against the cylinder inner peripheral surface 22a, the piston 33 can be allowed to interfere with the cylinder 22. In addition, even when the oscillation angle increases, the upper and lower end corners of the piston 33 do not come into contact with the cylinder inner peripheral surface 22a, so that wear or frictional loss caused by angled contact can be prevented.
Further, referring to
However, in view of the ease to assemble and the thermal expansion of the piston 33 or the amount of crush deformation caused by the internal pressure of the compression chamber to be described later, it is desirable that a very small gap is provided between the spherical outer peripheral surface 33a of the piston and the cylinder inner peripheral surface 22a in an initial state at room temperature. In this case, when the piston ring 34 is provided as illustrated in
In this case, in the present embodiment, since the central axis 22b of the cylinder inner peripheral surface is disposed to be offset to the counterload side by the optimum amount e1 with respect to the rotation center 24a of the crankshaft, the inclination of the piston ring 34 at the compression stroke can be suppressed, and a deterioration in sealing performance can be prevented. The effects will be described in detail below.
Since the amount of blowby loss leaking from the piston ring 34 increases as the internal pressure of the cylinder 22 increases, the sealing performance is further affected at the top dead center than at a crank angle of 270 degrees (3/2π) where the oscillation angle is naturally minimized. For this reason, it is necessary that the appropriate value of the offset amount is determined by balance between two oscillation angles described above.
In addition, since the upper surface 33c of the piston and the lower surface of the valve plate 26 are parallel to each other at the top dead center as illustrated in
In the present embodiment, this state can be created by inclining the upper surface 33c of the piston, and naturally, the same state can be created by inclining the lower surface (crankcase side surface) of the valve plate 26 as illustrated in
Further, in the present embodiment, for simplicity of description, the central axis of the cylinder inner peripheral surface 22a is always depicted as being aligned in the vertical direction of the figures; however, for example,
Incidentally, according to
[Equation 5]
e
2
≤e≤e
3 (5)
Meanwhile, e2 represents an offset amount at which the following equations are established.
Here, a subscript BDC represents the bottom dead center. Namely, e2 represents an offset amount at which the absolute values of the oscillation angle at the bottom dead center and the minimum oscillation angle (
When this offset amount is set, while the crankshaft 24 rotates one revolution, the oscillation angle in the middle of the compression stroke can be suppressed. In addition, e3 represents an offset amount at which the following equation is established.
[Equation 10]
e
3
=r (10)
Namely, e3 is equal to the crank radius r (amount of eccentricity of the crankshaft). When this offset amount is set, while the crankshaft 24 rotates one revolution, the connecting rod 32 can be substantially parallel to the central axis of the cylinder inner peripheral surface 22a at the moment when the internal pressure of the cylinder 22 reaches the operating pressure of the compressor, and the oscillation angle in the middle of the compression stroke can be suppressed.
Further, the piston is made of a resin having good wear resistance based on the assumption that the compressor main body 1 is a non-lubricating type in which a lubricant is not used for lubrication of the sliding parts. However, this configuration can also be applied to a lubricating type. In this case, a lubricant film may intervene between the cylinder and the spherical outer peripheral surface 33a of the piston by splash lubrication or the like to lubricate sliding surfaces. In this configuration, for example, the piston 33 can also be made from aluminum and integrally formed with the connecting rod 32, so that the number of components and the assembly man-hours can be reduced.
In a second embodiment, a configuration will be described in which similar effects can be obtained without offsetting the cylinder 22 as illustrated in the first embodiment.
Incidentally,
The configuration illustrated in the first embodiment has restriction in designing the disposition of components or the shape of the compressor main body, and when the offset amount of the cylinder 22 cannot be sufficiently taken, inevitably, the effects also diminish. Such restriction is likely to be generated particularly when the components are common to other products.
In the first embodiment, the piston ring 34 is disposed to be orthogonal to the straight line 27 connecting the center 33d of the piston and the center of the big end portion bearing 31 of the connecting rod.
On the other hand, in the present embodiment, the piston ring 34 is not orthogonal to the straight line 27 but inclined by a certain offset angle φ.
Accordingly, while the crankshaft 24 rotates one revolution, the inclination of the piston ring 34 can be changed by the offset φ. Therefore, when the piston ring 34 is inclined in a direction opposite to the rotation direction (clockwise direction when the compressor main body rotates counterclockwise) of the compressor main body, even if the offset amount of the cylinder 22 is 0, the inclination of the piston ring 34 at the compression stroke can be reduced, so that a deterioration in sealing performance can be prevented.
Incidentally, the offset amount e of the cylinder 22 and the offset angle φ of the piston ring 34 can be set in combination, and a method can be used in which the cylinder 22 is offset in the allowable range of the restriction in design and the piston ring 34 is offset by an insufficient amount.
Meanwhile, a change in inclination of the piston ring 34 is slightly differently affected by the offsets of the types, and there are merits and demerits to be described below.
When the cylinder 22 is offset, at the top dead center at which the reciprocating inertial force of reciprocating components including the piston 33 and a piston side of the connecting rod 32 is maximized, the vector of the inertial force and the vector of the centrifugal force of a balance weight of the crankshaft 24 are shifted from each other. For this reason, the vibration during rotation of the compressor main body becomes worse in principle, which is a problem.
When the piston ring 34 is offset, the above problem does not occur. However, on the other hand, since the piston ring is not orthogonal to the connecting rod 32, a part of a compressed gas load received by the piston ring 34 acts to press the piston 33 against the cylinder inner peripheral surface 22a. Therefore, the frictional loss or the amount of wear of a piston top is caused to increase.
In a third embodiment, a configuration will be described in which the gap volume between the piston 33 and the valve plate 26 at the top dead center can be further reduced than in the first embodiment.
In the configuration illustrated in the first embodiment, the upper surface of the piston 33 is parallel to the valve plate 26 at the top dead center, and it seems that the gap volume is the smallest at a glance. However, in view of movements approximately at the top dead center, when the piston 33 is inclined with respect to the valve plate 26, the highest points of right and left corners of the piston 33 reach a height slightly exceeding the position at the top dead center.
Therefore, in order to avoid interference between the piston 33 and the valve plate 26, it is necessary that a gap equivalent to the difference is provided in the reciprocating direction in advance. The difference increases as the size of the inner diameter of the cylinder 22 increases, thereby causing an increase in gap volume.
Therefore, as illustrated in
Since such a shape is adopted, as illustrated in
Number | Date | Country | Kind |
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2019-181197 | Oct 2019 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2020/010175 | 3/10/2020 | WO | 00 |