Patent Description:
<CIT> discloses a Stirling refrigerator. Conventional reciprocating compressors have a piston housed inside a cylinder and a rod mechanically connected to the piston in order to drive it. The cylinder has an opening wherein the rod can slide in order to allow reciprocating motion of the rod. This opening needs to be sealed around the piston rod in order to reduce gas leakage from the cylinder.

According to known solutions, sealing of the opening of the cylinder around the piston rod is accomplished by a packing arrangement comprising a series of rings made of semi-crystalline thermoplastic, such as polyether ether ketone commonly known as "PEEK", arranged around the piston rod and housed in so-called "cups". The PEEK rings are basically split in design and are embraced by spring elements which compress the split rings circumferentially so that they protrude against the piston rod, positively sealing the clearance between the rings and the piston rod.

Disadvantageously, the PEEK rings pressed against the piston rod do not provide a perfect sealing and, some gas may escape from the cylinder through the cups during the reciprocating motion of the piston rod. Also, the PEEK rings pressed against the piston rod determine friction during the reciprocating motion of the piston which leads to energy consumption and to wear of the piston rod.

A reciprocating compressors with a cylinder having an improved sealing of the gap around the piston rod would be desirable.

According to a first aspect, the subject-matter disclosed herein relates to a reciprocating compressor; the reciprocating compressor includes a cylinder and a piston sliding inside the compression chamber of the cylinder; a piston rod is mechanically connected to said piston and passes through a hole of the cylinder so that there is an annular gap between the piston rod and the hole; in order to avoid (or at least limit) leakage of gas from the gap, a jacket is arranged around the piston rod; the jacket is attached to the piston on one side and to the cylinder of the other side.

According to a second aspect, the subject-matter disclosed herein relates to a method of avoiding or limiting leakage from a compression chamber of a reciprocating compressor; in particular, leakage occurs through a gap around a rod of a piston of the reciprocating compressor; leakage is avoided (or at least limited) by isolating the piston rod from the gas in the compression chamber; advantageously, isolation is accomplished by arranging a jacket around the piston rod.

A more complete appreciation of the disclosed embodiments and of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:.

In prior-art reciprocating compressor, i.e. compressors in which a piston moves back and forth inside a compression chamber, gas may exit the compression chamber from a gap between a rod of the piston and a hole in a wall of the compression chamber while the piston rod moves back and forth through the hole. In order to avoid the exit of the gas, in the inventive reciprocating compressors, the piston rod has a sealing jacket so that gas surrounding the piston rod cannot get in contact with the piston rod and flow through the gap around the piston rod.

Reference now will be made in detail to embodiments of the disclosure, an example of which is illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope of the disclosure.

<FIG>, <FIG> and <FIG> show a reciprocating compressor <NUM>. These figures, in particular <FIG> and <FIG>, show one cylinder <NUM> and one piston <NUM> of reciprocating compressor <NUM>. However, alternative reciprocating compressors according to the subject-matter disclosed herein may have any number of cylinders and pistons; in particular, according to some embodiments, one piston may be mechanically connected to two piston rods on opposite sides the piston.

A piston rod <NUM> is mechanically connected to piston <NUM> and protrudes from a first side of piston <NUM>. Piston rod <NUM> may be integral with piston <NUM> or rigidly connected to it.

Cylinder <NUM> has a compression chamber <NUM>; in <FIG>, reference number <NUM> is placed both above and below piston rod <NUM> to make it clear that the compression chamber surrounds laterally the piston rod and may be cylinder-shaped. Alternative reciprocating compressors according to the subject-matter disclosed herein may have another compression chamber on the opposite side of the piston which side is not shown in <FIG>.

Piston <NUM> is slidably arranged in compression chamber <NUM> in order to be movable in a reciprocating translational motion along an axis of translation "T" to compress the gas inside compression chamber <NUM>; piston rod <NUM> has a corresponding reciprocating translational motion. In particular, piston <NUM> is movable between a head-side position, corresponding to the position of the piston in <FIG>, and a crank-side position, corresponding to the position of the piston in <FIG>; in the head-side position a big portion of piston rod <NUM> is located inside compression chamber <NUM> while in the crank-side position a small portion of piston rod <NUM> is located inside compression chamber <NUM>.

According to the embodiment of the figures, cylinder <NUM> comprises a lateral wall <NUM>, a crank-side wall <NUM> and a head-side wall, not shown in the annexed figures; the lateral wall may be cylindrical; the crank-side wall and head-side wall may be circular. Lateral cylindrical wall <NUM> has one or more flow passages <NUM> fluidly coupled to valves (not shown in the annexed figures) which control the inlet gas flow and outlet gas flow to and from compression chamber <NUM>. The head-side wall and the crank-side wall are arranged perpendicularly to the axis of translation "T". Crank side wall <NUM> has an opening <NUM> for piston rod <NUM>, in particular located at the axis of translation "T", an internal surface <NUM> facing compression chamber <NUM> and an external surface <NUM> opposite to internal surface <NUM>. Piston rod <NUM> is arranged to pass through opening <NUM>.

According to alternative embodiments, both the crank-side wall and the head-side wall may have an opening, in particular both located around the axis of translation "T", for two piston rods; in this case, the reciprocating compressor has two compression chambers.

According to the embodiment of the figures, a so-called "packing body" <NUM> is sealingly connected to crank-side wall <NUM> at opening <NUM>. Packing body <NUM> has a hole <NUM> for piston rod <NUM>, preferably located along the axis of translation "T". Piston rod <NUM> is slidably inserted through hole <NUM>, and has a head-side end mechanically connected to piston <NUM> and is located inside compression chamber <NUM> at any operating time of the alternating compressor, and a crank-side end mechanically connected to a crank mechanism (not shown in the annexed figures) and is located outside of compression chamber <NUM> at any operating time of the alternating compressor. The crank mechanism is arranged to drive piston <NUM> in its reciprocating motion. Packing body <NUM> may be arranged to provide a degree of sealing to hole <NUM> when piston rod <NUM> moves inside it with reciprocating motion.

Advantageously, packing body <NUM> is or includes a flanged bushing <NUM> defining hole <NUM> and having a flange <NUM> arranged to be fastened to crank-side wall <NUM>, as it is shown in <FIG>.

In particular, flange <NUM> of bushing <NUM> has an annular surface <NUM> arranged to be pressed against crank-side wall <NUM>. Preferably, a sealing element is interposed between annular surface <NUM> of the packing body <NUM> and crank-side wall <NUM>. Tie rods <NUM> may be used to press packing body <NUM> against crank-side wall <NUM> in order to sealingly couple them. In the configuration shown in the figures (see in particular <FIG>), packing body <NUM> may be installed on and removed from crank-side wall <NUM> from the outside of compression chamber <NUM>.

Bushing <NUM> is completely inserted into opening <NUM> when packing body <NUM> is mounted to crank-side wall <NUM>; alternatively, the bushing is inserted only partially into the opening. Advantageously, bushing <NUM> has another annular surface <NUM> arranged to face compression chamber <NUM> when packing body <NUM> is mounted to crank-side wall <NUM>, that may be used for attaching a jacket of the piston rod that will be described in the following; in particular, the radial position of annular surface <NUM> is inner with respect to the radial position of annular surface <NUM>.

Advantageously, cylinder <NUM>, in particular crank-side wall <NUM>. has a recess <NUM> for housing at least partially a jacket that will be described in the following. In the embodiment of the figures (see in particular <FIG>), recess <NUM> is part of opening <NUM> and partially defined by annular surface <NUM> of the packing body <NUM> internal surface <NUM> of the crank-side wall <NUM> (see dashed line in <FIG>).

Reciprocating compressor <NUM> further includes a jacket <NUM> arranged around piston rod <NUM>, and located inside compression chamber <NUM>, in order to seal compression chamber <NUM> with respect to hole <NUM>. Jacket <NUM> extends from a piston-side end <NUM> to a cylinder-side end <NUM>. Thanks to the sealing effect provided by the jacket, the packing body may be designed so to provide no sealing or only limited sealing to the hole where the piston is inserted.

The piston-side end <NUM> of the jacket <NUM> is sealingly attached to piston <NUM>, in particular to a piston flange <NUM> fixed to piston <NUM> in order to sealingly couple piston-side end <NUM> to piston <NUM>. Preferably, jacket <NUM> and the piston flange <NUM> are bounded through pressing process and/or by using a bonding agent. Advantageously, piston flange <NUM> is arranged around piston rod <NUM> and has an inner e.g. cylindrical surface <NUM> which faces piston rod <NUM> and match with the shape of an outer surface e.g. cylindrical of piston rod <NUM>.

Cylinder-side end <NUM> of jacket <NUM> is sealingly attached to cylinder <NUM>, in particular to the packing body <NUM> that is fixed to crank-side wall <NUM> of cylinder <NUM>. Advantageously, cylinder <NUM> comprises a cylinder flange <NUM> fastened to inner annular surface <NUM> of packing body <NUM>, in order to sealingly connect cylinder-side end <NUM> of jacket <NUM> to packing body <NUM>. Preferably, jacket <NUM> and cylinder flange <NUM> are bounded through pressing process and/or by using a bonding agent. Advantageously, cylinder flange <NUM> is arranged around piston rod <NUM> and has an inner e.g. cylindrical surface <NUM> which faces piston rod <NUM> and match with the shape of an outer surface e.g. cylindrical of piston rod <NUM>.

Jacket <NUM> is arranged to adapt to different positions of piston <NUM> between the head-side position (see <FIG>) and the crank-side position (see <FIG>). In particular, jacket <NUM> is extendable along the axis of translation "T"; in the head-side position of piston <NUM> corresponding to the maximum distance of piston <NUM> from packing body <NUM>, jacket <NUM> is in its extended configuration or maximum extension; in the crank-side position of piston <NUM> corresponding to the minimum distance of piston <NUM> from packing body <NUM>, jacket <NUM> is in its retracted configuration or minimum extension. It is to be noted that, according to the embodiment of the figures, jacket <NUM> is always partially housed in recess <NUM>; however, in the retracted configuration a bigger part of the jacket is housed in the recess up to the whole jacket.

<FIG> differs from <FIG> in that piston <NUM> is closer to crank-side wall <NUM> of cylinder <NUM> and packing body <NUM>; consequently, piston flange <NUM> is closer to cylinder flange <NUM>; jacket <NUM> is retracted; the volume of compression chamber <NUM> is smaller.

Preferably, jacket <NUM> is made of a gas-poof, flexible and durable material such as a synthetic rubber material or a flexible composite material.

According to the embodiment of the figures, jacket <NUM> is bellow-shaped and foldable in order to adapt to the different positions of piston <NUM> between the head-side position and the crank-side position. Advantageously, jacket <NUM> may be not only bellow-shaped but also elastically extendable.

According to other embodiments not illustrated in the annexed figures, the piston may have a recess located around the piston rod in order to house at least partially the jacket especially when the jacket is in its retracted configuration and the piston is in its crank-side position.

According to still other embodiments not illustrated in the annexed figures, both the cylinder and the piston may have recesses in order to house at least partially the jacket especially when the jacket is in its retracted configuration and the piston is in its crank-side position.

According to another aspect, the subject matter described herein related to a method of avoiding (or at least limiting) leakage from a compression chamber of a reciprocating compressor through a gap around a rod of a piston sliding inside a cylinder of the reciprocating compressor. The method is implemented for example by the embodiment of reciprocating compressor described above and shown in the annexed figures; the following description of the method will make reference to this embodiment without any limiting intention.

The method comprises a step of sealingly isolating the piston rod from the gas in the compression chamber. For example, according to the above mentioned embodiment, piston rod <NUM> is isolated from the gas in the compression chamber <NUM> at any operating time of the alternating compressor.

Advantageously, for example in the embodiment of the annexed figures, the step of isolating comprises arranging a jacket, labeled <NUM> in the annexed figures, around the piston rod, labeled <NUM> in the annexed figures.

Claim 1:
A reciprocating compressor (<NUM>), comprising:
- a piston (<NUM>);
- a piston rod (<NUM>) mechanically connected to said piston (<NUM>);
- a cylinder (<NUM>) comprising a compression chamber (<NUM>) slidingly housing said piston (<NUM>), said cylinder (<NUM>) comprising a crank-side wall (<NUM>) with an opening (<NUM>), and a packing body (<NUM>) sealingly mounted to said crank-side wall (<NUM>) at said opening (<NUM>), wherein said packing body (<NUM>) is annular and defines a hole (<NUM>) wherein said rod (<NUM>) is arranged to slide; and
- a jacket (<NUM>) arranged around said piston rod (<NUM>), said jacket (<NUM>) comprising a piston-side end (<NUM>) sealingly attached to said piston (<NUM>) and a cylinder-side end (<NUM>) sealingly attached to said cylinder (<NUM>) in order to seal said compression chamber (<NUM>); and
wherein said cylinder-side end (<NUM>) of said jacket (<NUM>) is sealingly attached to said packing body (<NUM>).