JP7413025B2 - Compressor, piston, and connecting rod - Google Patents

Description

The present invention relates to a compressor, a piston, and a connecting rod.

As an example of a multi-stage compressor that can also handle high pressure, Patent Document 1 describes a multi-stage compressor in which a low-pressure compressor and a high-pressure compressor are connected, in which an oscillator is installed in the cylinder of the low-pressure compressor. The locking piston is arranged to be movable and slidable, and the locking piston is swingably and slidably arranged in the cylinder of the high-pressure compressor. It is stated that the angle is smaller than the rocking angle of the locking piston of the low pressure compressor.

Japanese Patent Application Publication No. 2015-132267

Conventionally, in reciprocating compressors that compress fluid, there are two types: a normal piston type, in which a bearing is provided at the end of the connecting rod on the compression chamber side, and a piston is swingably supported by the bearing; There is a swinging piston type that does not have a bearing on the chamber side and has a seal ring that elastically deforms and seals compressed fluid on the piston that is integrated with the connecting rod.

The latter oscillating piston method has a simpler structure than the normal piston method because it does not have a bearing or piston pin, there is no design restriction due to bearing temperature, and the reciprocating mass can be reduced. It has many advantages such as.

In such a swinging piston, as described in Patent Document 1, a structure in which the piston is screwed to a connecting rod from the seat side may be adopted.

However, in this screw-fastening structure, since the metal parts are exposed on the upper surface of the piston, which serves as the seating surface, there is a problem in that compression heat is transmitted to the connecting rod side via the metal parts. If the compression heat is transferred to the connecting rod side, there is a concern that the lubrication state of the big end bearing will deteriorate, so different countermeasures are required.

On the other hand, as a result of intensive studies by the present inventors, we found that in the swing piston system, the piston is made of a resin with excellent wear resistance, and the outer peripheral surface of the piston is made into a spherical surface with a diameter smaller than the diameter of the cylinder. I came up with the idea.

With this structure, even in reciprocating compressors with long piston strokes and large connecting rod inclination angles (oscillation angles), the gap between the piston outer circumferential surface and the cylinder inner wall surface is maintained at a minute level, resulting in a smooth It has become clear that the effect of being able to slide freely can be obtained.

However, even in such a structure, the resin that forms the seating surface is directly subjected to the axial force associated with fastening the screws, so there is room to improve the loosening of the screws due to creep deformation of the piston made of resin. The present inventors' studies have revealed that there is a problem.

In particular, during compressor operation, the upper surface of the piston is exposed to high temperatures due to the heat of compression, so creep deformation progresses rapidly. Once the screws become loose, the piston may wobble due to the reciprocating inertia force and the frictional force with the cylinder, which may lead to a chain reaction of breakage of the screws and damage to the piston.

This failure mode may ultimately cause problems with compressor operation, such as breaking of the connecting rod and destruction of the crankcase, so countermeasures are essential.

As part of measures against such resin creep, one idea is to select a resin material with excellent creep resistance. However, such resins are generally expensive. In the above structure, the piston, which is a sliding part, requires periodic replacement due to wear, and the increased cost directly leads to an increased burden on the user. Therefore, it is desirable to take simpler and cheaper measures.

The present invention provides a compressor, a piston, and a connecting rod that are capable of suppressing loosening of the screws due to creep deformation of the resin in a structure in which a swinging piston made of resin is fixed with screws.

The present invention includes a plurality of means for solving the above problems, and to give one example, a piston that reciprocates within a cylinder, a valve plate that closes an end of the cylinder, and a valve plate that supports the piston. The piston includes a connecting rod, a crankshaft that applies rotational force to an end of the connecting rod, and a crankcase that rotatably supports the crankshaft, and the piston swings within the cylinder as the crankshaft rotates. The piston is of a rocking type that reciprocates while moving, and the piston is made of a wear-resistant resin at least on a surface that contacts the inner peripheral side of the cylinder and a surface on the valve plate side , and the piston is made of a resin having wear resistance. The member constituting the side surface has an insert, and the outer circumferential surface of the piston is a spherical surface with a diameter smaller than the diameter of the cylinder , and the insert is inserted into the connecting rod from the crankcase side. It is characterized by being fixed with a fixing member .

According to the present invention, in a structure in which a resin-made swing piston is fixed with a screw, loosening of the screw due to creep deformation of the resin can be suppressed. Problems, configurations, and effects other than those described above will be made clear by the description of the following examples.

1 is a diagram showing an example of the overall configuration of a compressor in Example 1 of the present invention. FIG. 3 is a diagram showing an example of the configuration of a compressor main body in Example 1. FIG. 3 is a diagram showing an example of the configuration of a piston in Example 1. FIG. 3 is a diagram showing an example of the cross-sectional configuration of a piston in Example 1. FIG. FIG. 3 is a diagram showing another cross-sectional configuration example of the piston in Example 1. It is a figure which shows the example of the cross-sectional structure of the piston in Example 2 of this invention.

Examples of the compressor, piston, and connecting rod of the present invention will be described below with reference to the drawings.

First, the compressor of the present invention can be applied to various compressors that can adopt a swinging piston type among compressors that compress various fluids such as air and refrigerant, and the type, model, and application are particularly limited. Not done.

<Example 1>
Embodiment 1 A compressor, a piston, and a connecting rod according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4.

First, the overall configuration of the compressor of this embodiment will be explained using FIGS. 1 and 2. FIG. 1 is a schematic diagram of a compressor in Example 1. Moreover, FIG. 2 is a diagram showing the internal structure of the compressor main body 1 in FIG. 1.

A compressor 10 shown in FIG. 1 includes a compressor main body 1, an electric motor 2 that drives the compressor main body 1, and a tank 3 for storing fluid discharged by the compressor main body 1.

The compressor main body 1 compresses fluid, and its internal structure, as shown in FIG. It has a valve plate 26 that closes the (upper end), a cylinder head 23, and a crankcase 21 that rotatably supports a crankshaft 24 at the center.

In the compressor main body 1, the crankshaft 24 in the crankcase 21 rotates to apply rotational force to one end of the connecting rod 32, and the piston 33 installed in the cylinder 22 reciprocates in the vertical direction. As a result, fluid is sucked from outside the cylinder 22, compressed, and discharged into the tank 3.

In order to simplify the explanation, the compressor shape in Figures 1 and 2 is a one-cylinder, one-stage compressor with only one pair of pistons and cylinders. - It may be a compressor having a cylinder.

In the compressor main body 1, a crankshaft 24 is arranged and fixed on the tank 3 in a state parallel to the rotation axis of the electric motor 2. Further, a compressor pulley 4 is fixed to the crankshaft 24, and a motor pulley 5 is fixed to the rotating shaft of the electric motor 2. The compressor pulley 4 attached to the compressor body 1 has blades, and generates cooling air toward the compressor body 1 as it rotates, thereby promoting heat dissipation from the compressor body 1.

A transmission belt 6 for transmitting 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. As a result, as the electric motor 2 rotates, the crankshaft 24 of the compressor body 1 is rotationally driven via the electric motor pulley 5, the transmission belt 6, and the compressor pulley 4, and the compressor body 1 compresses the fluid.

In FIG. 1, to simplify the explanation, the compressor main body 1 is connected to the electric motor 2 via the transmission belt 6, but the crankshaft 24 of the compressor main body 1 and the rotating shaft of the electric motor 2 are connected by a cup. The two may be integrated by directly joining them using a joining means such as a ring.

Next, the peripheral structure of the piston will be explained using FIG. 2. The piston 33 shown in FIG. 2 is of a swing piston type in which the piston 33 and the connecting rod 32 are integrated. In this system, as the crankshaft 24 rotates, the piston 33 reciprocates within the cylinder 22 while swinging.

Next, the detailed structure of the piston 33 and connecting rod 32 will be explained using FIGS. 3A to 4. FIG. 3A is a diagram showing an example of the configuration of a piston, FIG. 3B is a diagram showing an example of the cross-sectional configuration of the piston, and FIG. 4 is a diagram showing another example of the cross-sectional configuration of the piston.

The piston 33 shown in FIGS. 3A and 3B is a separate part from the connecting rod 32 that supports the piston 33, and at least the outer peripheral surface 33a that contacts the inner peripheral side of the cylinder 22 and the upper surface 33c on the valve plate 26 side are Constructed from abrasion-resistant resin. In this embodiment, the piston 33 is made of resin that has excellent wear resistance, except for a piston insert 41 that will be described later.

Examples of resin materials with excellent wear resistance include those using polytetrafluoroethylene (PTFE) as the main body of the piston 33. Further, in consideration of the coefficient of thermal expansion, examples of the resin material for the piston 33 include polyether sulfone (PES).

Further, the outer peripheral surface 33a of the piston 33 is a spherical surface having a diameter slightly smaller than the diameter of the inner peripheral side of the cylinder 22.

A convex portion 33e is formed on the outer peripheral portion of the surface of the piston 33 on the connecting rod 32 side, and has a structure in which it fits into the convex portion 32d of the connecting rod 32.

Further, the piston 33 is molded with a piston insert 41 made of metal such as an aluminum alloy embedded therein. This piston insert 41 has a shape in which an edge 41a bites into the circumferential direction of the piston 33 so that the piston 33 does not slip out even when the piston 33 receives a lifting load toward the cylinder head 23 due to reciprocating inertia force or frictional force. It has become.

The piston insert 41 is formed with one or more female threaded holes 41c (two in this embodiment) which are opened on the crankcase 21 side, which is the end side fixed to the connecting rod 32 side. It is fastened (fixed) from the crankcase 21 side with a screw 35 in a direction perpendicular to the crankshaft 24.

In order to correspond to this, in this embodiment, in the connecting rod 32 shown in FIGS. 3A and 3B, a hole 32c for the screw 35 is formed in the seat surface that supports the piston 33 at a location that coincides with the female threaded hole 41c. have.

As shown in FIG. 3B, the piston insert 41 of this embodiment has a dish shape with the cylinder head 23 side at the bottom, and the seating surface of the connecting rod 32 is also fitted into the recess in the center of the dish shape of the piston insert 41. A recess 32b is formed at a corresponding position. With this structure, a hollow portion 41b is formed between the lower surface of the piston insert 41 and the upper surface of the connecting rod 32. The surface of the hollow portion 41b on the valve plate 26 side is covered with the piston insert 41.

The piston 33 uses a piston ring 34 as a seal ring for sealing compressed gas, and the piston ring 34 fits into a ring (annular) groove 33b provided on the outer peripheral surface 33a of the piston 33 with a certain gap. ing. Note that it may be configured without using the piston ring 34 and the ring groove 33b.

In this embodiment, a case is described in which the female threaded holes 41c of the piston insert 41 are provided at two locations in a direction perpendicular to the crankshaft 24, but the present invention is not limited to this arrangement. For example, a plurality of them can be provided in a row in the direction of the crankshaft 24, and at least one or more can be provided in an oblique direction with respect to the crankshaft 24.

However, when the piston 33 descends, considering the direction of the moment that tries to peel off the piston 33 due to the frictional force between its outer circumferential surface 33a and the cylinder inner wall surface 22a, the female threaded hole 41c is arranged in a direction perpendicular to the crankshaft 24. By providing two or more locations, the pulling force applied to the screw 35 can be reduced.

In addition, in this embodiment, the shape of the piston insert 41 is described as a dish-shaped one with the bottom facing the cylinder head 23 side. However, as in the piston 33A shown in FIG. It is sufficient to just set it to 42. This insert nut 42 also has two or more female screw holes 42c arranged in a direction perpendicular to the crankshaft 24, and is fixed to the connecting rod 32A from the crankcase 21 side with screws 35.

In this case, it becomes possible to use a commercially available insert nut, which provides a cost advantage, and it is also possible to simplify the manufacturing process by driving the insert nut after resin molding.

In the case of the form shown in FIG. 4, when forming a hollow portion 41b as shown in FIG. 3B in order to reduce the reciprocating mass, the resin itself that makes up the piston 33 must bear the gas load during the reciprocating movement. Therefore, it is desirable to take some measures to ensure strength.

Also in the form shown in FIG. 4, the piston 33A, except for the insert nut 42, is made of a resin having wear resistance.

Further, as shown in FIGS. 3B and 4, the female threaded hole 41c of the piston insert 41 and the female threaded hole 42c of the insert nut 42 are provided parallel to the axial direction of the cylinder 22, but the present invention is limited to this arrangement. isn't it. For example, the female threaded hole can be arranged at an angle with respect to the central axis of the cylinder 22.

Next, the effects of this embodiment will be explained.

The pistons 33 and 33A of the first embodiment of the present invention described above are of a swinging type that reciprocate while swinging within the cylinder 22 as the crankshaft 24 rotates, and at least the inner peripheral side of the cylinder 22. The outer circumferential surface 33a in contact with the valve plate 26 side and the upper surface 33c on the valve plate 26 side are made of a wear-resistant resin, and the end side fixed to the connecting rod 32 side has a female screw hole 41c open to the crankcase 21 side. 42c, and the outer peripheral surface 33a is a spherical surface with a diameter smaller than the diameter of the cylinder 22.

As a result, the axial force of the screw 35 that fixes the piston 33 to the connecting rod 32 is received by the bearing surface 32a of the connecting rod 32, so that problems such as loosening due to creep deformation of the resin when fastening and fixing with the screw 35 are less likely to occur. can do. Therefore, in the swinging piston system, the gap between the outer circumferential surface of the pistons 33, 33A and the inner wall surface of the cylinder 22 is kept small, so that smooth sliding is possible, and the creep of the resin can be easily prevented. Moreover, it can be done at low cost. These effects allow the compressor to operate stably over a long period of time.

Furthermore, the pistons 33 and 33A have a piston insert 41 or an insert nut 42 having female screw holes 41c and 42c inside, and the piston insert 41 or the insert nut 42 is screwed into the connecting rod 32 from the crankcase 21 side. 35, the resin pistons 33, 33A can be firmly fixed to the connecting rod 32 by the piston insert 41 or the insert nut 42, and therefore more stable operation can be performed.

Furthermore, the piston insert 41 or the insert nut 42 is made of metal, and the pistons 33, 33A are made of resin, except for the piston insert 41 or the insert nut 42, so that the pistons 33, 33A are not connected to the connecting rod 32. This allows for more secure fixation and smoother sliding movement.

In addition, since two or more female threaded holes 41c and 42c are arranged in a direction perpendicular to the crankshaft 24, the pistons 33 and 33A, which are formed on spherical surfaces, are stably fixed to the connecting rod 32 in the circumferential direction. Since the connecting rod 32 can be more firmly fixed to the connecting rod 32, more stable operation can be performed.

Furthermore, since the female screw holes 41c and 42c are arranged at an angle with respect to the central axis of the cylinder 22, a large space can be secured for a tool to be inserted in the work of tightening the screw 35, so that ease of assembly can be improved. .

In addition, by forming the hollow portion 41b between the piston 33 and the connecting rod 32, the mass of the reciprocating parts including the piston 33 can be reduced, so vibrations of the compressor main body due to reciprocating inertia force can be reduced. can be improved.

Furthermore, since the surface of the hollow part 41b on the valve plate 26 side is covered with the piston insert 41, the piston 33 can be held from the inside by the piston insert 41, and when the hollow part 41b is formed, Also, it is possible to reduce the amount of deformation such as contraction of the piston 33 during molding and expansion due to compression heat during operation.

Furthermore, since the piston insert 41 has the edge 41a extending in the circumferential direction of the piston 33, the piston insert 41 can be maintained even when a lifting load is applied to the cylinder head 23 side due to reciprocating inertia force or frictional force. Since the piston 33 can be prevented from slipping out from the piston 33, the piston 33 can be more stably fixed to the connecting rod 32.

<Example 2>
A compressor, a piston, and a connecting rod according to a second embodiment of the present invention will be described using FIG. 5. Components that are the same as those in the first embodiment are denoted by the same reference numerals, and explanations thereof will be omitted. The same applies to the following examples. FIG. 5 is a diagram showing an example of the cross-sectional configuration of a piston in the second embodiment.

The present embodiment has a structure in which the material cost of the piston is further reduced compared to the first embodiment. This will be explained below using FIG. 6.

In the first embodiment, as shown in FIG. 3B, the entire periphery of the piston insert 41 or the insert nut 42 is made of resin having excellent wear resistance. However, resin materials, such as PTFE, that have excellent abrasion resistance and are used in particular for sliding and sealing parts of compressors are generally expensive, and considering the burden on the user as regularly replaced parts as mentioned above, it is necessary to It is desirable to reduce its volume.

When considering the function of each part of the piston, sliding performance is required only on the outer circumferential surface that slides on the cylinder inner wall surface 22a, and for other parts, especially the upper surface 33c, insulation properties are required. Bye.

Therefore, in this embodiment, as shown in FIG. 5, the piston 33B has a piston cover 43 that constitutes the surface on the valve plate 26 side, and this piston cover 43 is a separate part, and the outer circumferential surface of the piston 33B 45a.

The piston cover 43 is different from the outer circumferential surface 45a which is made of a resin having wear resistance, and is made of an inexpensive resin with excellent heat resistance such as phenol resin. It is desirable to use the same material as the resin forming the piston 33 of the first embodiment described above as the resin forming the outer circumferential surface 45a.

Of the piston 33B, a piston insert 44 made of metal with a female screw hole 43c provided on the surface facing the crankcase 21 is cast inside the piston cover 43. These surfaces are screwed to the connecting rod 32 so as to sandwich the convex portion 33e on the inner circumferential surface of the piston 33B.

In this embodiment as well, the piston insert 44 has a dish shape with the cylinder head 23 side as the bottom, and the seating surface of the connecting rod 32 also has a recess 32b at a position corresponding to the center recess of the dish shape of the piston insert 44. is formed, and a hollow portion 43b is formed.

A surface of the hollow portion 43b on the valve plate 26 side is covered with a piston insert 44.

Note that the axial force of the screw 35 acts to tighten the center 33d of the piston 33, but with this structure, a much wider pressure receiving area can be secured than simply fixing with the screw 35, so creep deformation is significantly reduced. It is possible to prevent the screws 35 from loosening.

The other configurations and operations are substantially the same as those of the compressor, piston, and connecting rod of the first embodiment described above, and the details will be omitted.

In the compressor equipped with the piston 33B having the piston cover 43 constituting the surface on the valve plate 26 side of the second embodiment of the present invention and the outer circumferential portion 45 constituting the outer circumferential surface 45a, the above-described implementation is also possible. Almost the same effect as the compressor of Example 1 can be obtained.

Further, the inside of the piston cover 43 has a piston insert 44 having a female threaded hole 43c, and the piston insert 44 is fixed to the connecting rod 32 from the crankcase 21 side with a screw 35. Since the resin piston 33B can be firmly fixed to the connecting rod 32 by the insert 44, more stable operation can be performed.

Furthermore, the piston insert 44 is made of metal, the piston cover 43 is made of heat-resistant resin, and the outer peripheral part 45 is made of abrasion-resistant resin. This embodiment has the advantage that the volume of the excellent resin can be reduced and the cost of the entire piston 33B can be suppressed compared to the first embodiment.

<Others>
Note that the present invention is not limited to the above-described embodiments, and includes various modifications. The above-mentioned embodiments have been described in detail to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to having all the configurations described.

Further, it is also possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is also possible to add, delete, or replace some of the configurations of each embodiment with other configurations.

1... Compressor body 2... Electric motor 3... Tank 4... Compressor pulley 5... Electric motor pulley 6... Transmission belt 10... Compressor 21... Crank case 22... Cylinder 22a... Cylinder inner wall surface 23... Cylinder head 24... Crankshaft 26... Valve plates 32, 32A...Connecting rod 32a...Seat surface 32b...Concave portion 32c...Bore 32d...Protrusion 33, 33A, 33B...Piston 33a...Outer circumferential surface 33b...Ring groove 33c...Top surface 33d...Center 33e...Protrusion 34...Piston ring 35... Screw 41... Piston insert 41a... Edge 41b... Hollow part 41c... Female threaded hole 42... Insert nut 42c... Female threaded hole 43... Piston cover 43b... Hollow part 43c... Female threaded hole 44... Piston insert 45... Outer periphery 45a... Outer periphery surface

Claims (13)

A piston that reciprocates within the cylinder,
a valve plate closing an end of the cylinder;
a connecting rod that supports the piston;
a crankshaft that applies rotational force to the end of the connecting rod;
a crankcase rotatably supporting the crankshaft;
The piston is of a rocking type that reciprocates while rocking within the cylinder as the crankshaft rotates,
The piston is
At least a surface in contact with the inner peripheral side of the cylinder and a surface on the valve plate side are made of a resin having wear resistance ,
The member constituting the surface on the valve plate side has an insert,
The outer peripheral surface of the piston is a spherical surface with a diameter smaller than the diameter of the cylinder ,
A compressor , wherein the insert is fixed to the connecting rod from the crankcase side by a fixing member . A piston that reciprocates within the cylinder,
a valve plate closing an end of the cylinder;
a connecting rod that supports the piston;
a crankshaft that applies rotational force to the end of the connecting rod;
a crankcase rotatably supporting the crankshaft;
The piston is of a rocking type that reciprocates while rocking within the cylinder as the crankshaft rotates,
The piston is
At least a surface in contact with the inner peripheral side of the cylinder and a surface on the valve plate side are made of a wear-resistant resin, and
The end portion fixed to the connecting rod side has a female threaded hole opened to the crankcase side,
The outer peripheral surface of the piston is a spherical surface with a diameter smaller than the diameter of the cylinder,
The inside of the piston has an insert having the female threaded hole,
A compressor, wherein the insert is fixed to the connecting rod from the crankcase side with a screw. The compressor according to claim 2,
the insert is made of metal;
A compressor, wherein the piston is made of the resin except for the insert. A piston that reciprocates within the cylinder,
a valve plate closing an end of the cylinder;
a connecting rod that supports the piston;
a crankshaft that applies rotational force to the end of the connecting rod;
a crankcase rotatably supporting the crankshaft;
The piston is of a rocking type that reciprocates while rocking within the cylinder as the crankshaft rotates,
The piston has a piston cover that constitutes a surface on the valve plate side, and an outer peripheral part that constitutes an outer peripheral surface,
At least a surface in contact with the inner peripheral side of the cylinder and a surface on the valve plate side are made of a wear-resistant resin, and
The end portion fixed to the connecting rod side has a female threaded hole opened to the crankcase side,
The outer peripheral surface of the piston is a spherical surface with a diameter smaller than the diameter of the cylinder,
The inside of the piston cover has an insert having the female screw hole,
A compressor, wherein the insert is fixed to the connecting rod from the crankcase side with a screw. The compressor according to claim 4 ,
the insert is made of metal;
The piston cover is made of heat-resistant resin,
The compressor, wherein the outer peripheral portion is made of the abrasion-resistant resin. The compressor according to claim 2 or 3 ,
A compressor, wherein two or more of the female screw holes are arranged in a direction perpendicular to the crankshaft. The compressor according to claim 2 or 3 ,
A compressor, wherein the female threaded hole is arranged obliquely with respect to the central axis of the cylinder. The compressor according to claim 2 or 4 ,
A compressor, characterized in that a hollow portion is formed between the piston and the connecting rod. The compressor according to claim 8 ,
The compressor, wherein a surface of the hollow portion on the valve plate side is covered with the insert. The compressor according to claim 2,
A compressor, wherein the insert has an edge extending in a circumferential direction of the piston. A rocking piston that reciprocates while rocking within a cylinder as the crankshaft rotates,
At least a surface in contact with the inner peripheral side of the cylinder and a surface on the valve plate side are made of a wear-resistant resin,
The end side that is fixed to the connecting rod side has a female screw hole that opens to the crankcase side.
The outer peripheral surface is a spherical surface with a diameter smaller than the diameter of the cylinder ,
The inside of the piston has an insert having the female threaded hole,
The piston , wherein the insert is fixed to the connecting rod from the crankcase side with a screw . A rocking piston that reciprocates while rocking within a cylinder as the crankshaft rotates,
At least a surface in contact with the inner peripheral side of the cylinder and a surface on the valve plate side are made of a wear-resistant resin,
It has a piston cover constituting a surface on the valve plate side, and an outer circumferential part constituting an outer circumferential surface,
The end side that is fixed to the connecting rod side has a female screw hole that opens to the crankcase side.
The outer peripheral surface is a spherical surface with a diameter smaller than the diameter of the cylinder,
The inside of the piston cover has an insert having the female screw hole,
A piston , wherein the insert is fixed to the connecting rod from the crankcase side with a screw . A connecting rod comprising: a seating surface for supporting the piston according to claim 11 or 12; and a connecting rod having a screw hole at a location on the seating surface that matches the female threaded hole.

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