WO2015071397A1

WO2015071397A1 - Piston-cylinder assembly for a reciprocating compressor

Info

Publication number: WO2015071397A1
Application number: PCT/EP2014/074570
Authority: WO
Inventors: Riccardo Bagagli; Francesco Chiesi; Massimo Benvenuti; Leonardo Tognarelli
Original assignee: Nuovo Pignone Srl
Priority date: 2013-11-15
Filing date: 2014-11-14
Publication date: 2015-05-21
Also published as: ITCO20130059A1

Abstract

A piston-cylinder assembly (1) for a reciprocating compressor comprises a cylinder (2); a piston (4) inside the cylinder (2), the piston (4) defining a first (6) and a second working chamber (7) for compressing a working fluid; the working chambers (6, 7) having each an intake opening (6a, 7a) and a discharge opening (6b, 7b) for the working fluid; a flow regulator (9) acting on the working chambers (6, 7) for controlling an outgoing flow of working fluid through said discharge openings (6b, 7b), the flow regulator (9) comprising a bypass duct (10) in fluid connection with the first (6) and with the second working chamber (7), at least a regulating valve (16) located along the bypass duct (10) for opening and/or closing the bypass duct (10) so that the fluid can flow between the first (6) and the second working chamber (7), wherein said bypass duct (10) is placed inside the piston (4).

Description

PISTON-CYLINDER ASSEMBLY FOR A RECIPROCATING COMPRESSOR DESCRIPTION

The subject matter of the present disclosure relates to a piston-cylinder assembly, in particular for a reciprocating compressor. Specifically, the disclosure relates to a double acting piston-cylinder assembly.

A piston-cylinder assembly is known from the state of the art. Such piston- cyl inder assembly comprises a cylinder and a piston assembly. The piston assembly itself comprises a piston inside said cylinder. The piston assembly also comprises a rod attached to the piston, which is able to move the piston back and forth inside the cylinder.

Specifically, the piston defines a first and a second working chamber inside the cyl inder. Indeed, these working chambers are located at opposite ends of the cyl inder with respect to the piston . Consequently, these working chambers have an internal volume that varies with the motion of the piston . With additional detail, the working chambers have each an intake opening and a discharge opening for the fluid . Each of the intake opening is provided with a respective intake valve, while each discharge opening has a discharge valve. In other words, each working chamber receives the working fluid through its intake valve and releases it through its discharge valve.

During the functioning of the above described piston-cyl inder assembly, the reciprocating motion of the piston alternatively compresses and expands each working chamber. When the volume of each working chamber expands, the working fluid fills the working chamber. Conversely, when the volume of the working chamber decreases the fluid inside the working chamber is compressed and, afterwards, is expelled from the working chamber through the discharge opening .

The above described piston-cylinder assembly is designed for achieving a preset output flow rate. It is sometimes necessary to change such output flow rate during the functioning of the reciprocating compressor. To perform this, the prior art device is provided with a flow regulator acting on one or both of the working chambers. The flow regulator leaves the intake valve open after the chamber has expanded to the maximum volume and has been filled with working fluid . As the piston begins compressing the working chamber, the working fluid flows back out of the intake opening . When the working chamber has shrunk up to a desired volume, the intake valve is closed, and the working fluid is compressed normally.

SUMMARY

A disadvantage of the known piston-cyl inder assembly is that precise control of the intake valve is required . Thus the intake valve cannot be a passive valve, but has to be actuated, adding to the complexity of a reciprocating compressor incorporating such known piston-cylinder assembly.

A first embodiment according to the invention is a piston-cylinder assembly for a reciprocating compressor, comprising a cylinder and a piston assembly having a piston inside the cyl inder, the piston defining a first and a second working chamber for compressing a fluid . Each of the working chambers has an intake opening and a discharge opening for the working fluid . The piston-cylinder assembly also comprises a flow regulator acting on the working chambers for controlling an outgoing flow of the working fluid through the discharge openings. The flow regulator comprises a bypass duct in fluid connection with the first and with the second working chamber, a regulating valve located along the bypass duct for opening and/or closing the bypass duct so that the working fluid can flow between the first and the second working chamber.

An advantage of such piston-cylinder assembly is that active control of the intake valves is no longer necessary.

A second embodiment of the present invention relates to a reciprocating compressor comprising a piston-cylinder assembly according to the first embodiment. Another aspect of the invention is related to a method for retrofitting a piston-cylinder assembly of the type comprising a cylinder, a piston inside the cylinder, the piston defining a first and a second working chamber for compressing a working fluid having each an intake opening and a discharge opening for the working fluid . The method comprises the steps of providing a flow regulator comprising a bypass duct and a regulating valve located along the bypass duct; linking the bypass duct to the working chambers so that the bypass duct is in fluid connection with the first and with the second working chamber.

An advantage of such method is that it can be used to upgrade a known piston-cylinder assembly, thus minimizing the production costs.

Another embodiment of the invention relates to a method for regulating the output mass flow of a piston-cylinder assembly. Such method comprises the step of performing a forward stroke of the piston, thereby performing a compression phase inside the first working chamber and a suction phase inside the second working chamber.

The method also comprises a step of performing a backward stroke of the piston, thereby performing a suction phase inside the first working chamber and a compression phase inside the second working chamber.

The regulating valve is opened at the beginning of the forward stroke to increase the clearance of the first working chamber and at the beginning of the backward stroke to increase the clearance of the second working chamber. The flow of working fluid can be regulated by increasing clearance volume, thereby increasing the time that the regulating valve is open at the beginning of each stroke, as this decreases the gas volume compressed .

Advantageously, by using such method it is possible to adapt the capacity of the piston-cylinder assembly without wasting any energy. Indeed, the energy spent is proportional to the amount of gas handled .

In other words, the possibility to short cut one effect of the piston-cylinder to the other through the piston valve, allows having at disposal an additional clearance volume with a capacity equal to the displacement itself. In practice, compared to the actual additional clearance volume devices, this is the maximum clearance volume that can be reached . Therefore, in this way the minimum possible energy is spent for recycling .

Alternatively or additionally, the regulating valve can be opened at the end of the forward stroke to allow the working fluid to move from the first to the second working chamber. The regulating valve can also be opened at the end of the backward stroke to allow the working fluid to move from the second to the first working chamber.

In addition to the higher clearance volume, this system allows the flowing of the gas from head end effect to the crank end effect and vice versa. Thanks to the double way valve, it is also possible to perform 0% of loads, recycling totally the gas between the two effects.

Further details and specific embodiments will refer to the attached drawings, in which :

- Figure 1 is a schematic side sectional view of a piston-cyl inder assembly according to a first embodiment of the present invention;

- Figure 2 is a schematic side sectional view of a piston-cyl inder assembly according to a second embodiment of the present invention; and - Figure 3 is a schematic representation of the functioning of a part of an embodiment of the present invention.

DETAILED DESCRIPTION The following description of exemplary embodiments refer to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

With reference to the attached drawings, with the number 1 is indicated a piston-cylinder assembly for a reciprocating compressor. The piston-cylinder assembly 1 comprises a cylinder 2. The cylinder has a central axis "A". A lateral wall 15 revolves around the central axis "A", and develops along the central axis "A" itself. With further detail, the cylinder has and an end wall 8 joined to the lateral wall 15. The end wall 8 closes the head end of the cylinder 2, and is therefore transversal to the central axis "A". Similarly, the cylinder 2 has a back wall 11, also placed transversally with respect to the central axis "A" and attached to the lateral wall 15. In other words, the back wall 11 closes the crank end side of the cylinder 2, which is opposite end of the cylinder 2 with respect to the end wal l 8.

The piston-cyl inder assembly 1 also comprises a piston assembly 3. The piston assembly 3 comprises a rod 5 and a piston 4 attached to the rod 5. With add itional detail , the piston 4 has a front surface 4a facing the end wal l 8 of the cyl inder 2. The piston 4 has also a back surface 4b, on an opposite side with respect to the front surface 4a . The above mentioned rod 5 is also attached to the piston 4 on the back surface 4b.

The piston 4 is placed inside the cyl inder 2. Indeed , the piston 4 defines a first 6 and a second working chamber 7 for compressing a working flu id . In detail , the first working chamber 6 is defined between the front surface 4a of the piston 4 and the end wall 8 of the cyl inder 2. The second working chamber 7 is defined between the back surface 4b of the piston 4. The rod 5 is inside the second working chamber 7. It is to be noted that the rod 5 is partially outside the cyl inder 2, and crosses the back wall 1 1 through a hole 1 2. An appropriate seal 22 is provided on the hole 1 2 between the rod 5 and the back wal l 1 1 of the cyl inder 2. Such seal 22 can be of any known type, and will therefore not be described in further detail .

It is further to be noted that the working chambers 6, 7 have a variable internal volume. In other words, each working chamber 6, 7 has a volume wh ich is variable between a fully expanded configuration ad a fully compressed configuration .

With add itional detail , a forward stroke of the piston assembly 3 (namely, a movement of the piston 4 toward the end wal l 8 of the cyl inder) decreases the volume of the first working chamber 6. Also, the forward stroke increases the volume of the second working chamber 7.

On the contrary, a back stroke of the piston assembly 3 (a movement of the piston 4 toward the back wall 1 1 ) decreases the volume of the second working chamber 7. Th is also increases the volume of the first working chamber 5.

Indeed, the sum of the volumes of the working chambers 6, 7 minus the volume occupied by the rod 5 is constant.

With additional details, the working chambers 6, 7 have each an intake opening 6a, 7a. The working chambers 6, 7 have each a discharge opening 6b, 7b. Preferably, the intake 6a and the discharge opening 6b of the first working chamber are positioned on the lateral wall 15 next to the end wall 8. Similarly, the intake 7a and the discharge opening 7b of the second working chamber 7 are positioned on the lateral wall 15 next to the back wall 11. In alternative embodiments, the intake 6a and the discharge opening 6b of the first working chamber can be positioned on the end wall 8. Similarly, the intake 7a and the discharge opening 7b of the second working chamber 7 can be positioned on the back wall 11.

The working fluid enters inside the working chambers 6, 7 through the respective intake openings 6a, 7a and exits through the respective discharge openings 6b, 7b. Indeed, the flow of the working fluid inside the working chambers 6, 7 is determined by their expansion/contraction as a consequence of the motion of the piston 4 of the piston assembly 3 inside of the cylinder 2. Each intake opening 6a, 7a is provided with a respective intake valve 13a, 14a. Each discharge opening 6b, 7b is provided with a respective discharge valve 13b, 14b. These valves 13a, 13b, 14a, 14b can be any kind of valve known to the person skilled in the art. Preferably, the valves 13a, 13b, 14a, 14b are check valves, arranged to allow the flow only according to the expected direction. In other words, the valves 13a, 13b, 14a, 14b are preferably unidirectional. Even more preferably, these valves 13a, 13b, 14a, 14b are of the pressure-actuated type. In other words, the valves 13a, 13b, 14a, 14b are passive valves, which do not need an active control system. Advantageously, this greatly simplifies the construction and maintenance of the assembly 1.

According to the embodiments shown, the assembly 1 comprises a flow regulator 9 acting on the working chambers 6, 7 in order to control an outgoing flow of working fluid, in particular through the discharge openings 6a, 6b.

In detail, the flow regulator 9 comprises a bypass duct 10 in fluid connection with the first working chamber 6. The bypass duct 10 is also in fluid connection with the second working chamber 7. In other words, the bypass duct 10 allows the working fluid 10 to move from the first 6 to the second working chamber 7 and vice-versa.

It is to be noted that the bypass duct 10 can be of any type, as long as it allows the working fluid to travel between the working chambers 6, 7. Specifically, the bypass duct 10 can be placed outside the cylinder 2. Therefore, it is possible to upgrade a known piston-cylinder assembly by attaching the bypass duct 10, the regulating valve 16 and the other above described components to the cylinder, eventually replacing the valves 13a, 13b, 14a, 14b if necessary.

Alternatively, the bypass duct 10 can be placed inside the piston 4 of the piston assembly 3. In other words, in this case the bypass duct 10 is a bypass hole 17. If this embodiment is selected, the regulating valve 16 is also placed inside the piston 4. Advantageously this is a more compact arrangement that provides all the above discussed enhancements.

Please note that the bypass duct 10 is connected to the working chambers 6, 7 at separate bypass openings 6c, 7c, as shown for example in figure 1 and 2.

The flow regulator 9 also comprises at least a regulating valve 16. This regulating valve 16 is located along the bypass duct 10 so it can open and/or close the bypass duct 10. Indeed, the regulating valve 16 is placed between the first 6 and the second working chamber 7. Therefore, the fluid can flow between the first 6 and the second working chamber 7 when the regulating valve 16 is open, and is prevented to do so when the regulating valve 16 is shut. The function of the regulating valve 16 is to allow a reduction of the flow rate processed by the assembly 1. Indeed, the regulating valve 16 can be opened while the first working chamber 6 is in the fully expanded configuration. Therefore, when the volume of the first working chamber is reduces during the forward stroke of the piston assembly 3, the working fluid can flow to the second working chamber 7 through the bypass duct 10 without being compressed. When the regulating valve 16 is shut the working fluid remaining in the first chamber 6 is compressed normally. This also works during the return stroke of the piston assembly 3, by reversing the roles of the first 6 and the second working chamber 7. The regulating valve 16 can advantageously be electrically actuated. Therefore, the regulating valve 16 can be actuated by a control system such as the one that will be described in the following part of the disclosure.

The assembly 1 can also comprise an inductive generator 21 placed on the piston assembly 3. This generator is configured to generate electricity from a reciprocating motion of the piston assembly 3. Advantageously, the inductive generator 21 can be linked to the regulating valve 16 in order to provide electric power to the regulating valve 16.

The flow regulator 9 comprises a control unit 17 acting on the regulating valve 16. The control unit 17 can be configured to open the regulating valve 16 when the pressure inside either the first 6 or the second working chamber 7 has reached a predefined threshold P1.

In the following part of the disclosure the control unit 17 will be described as comprising a plurality of modules. These modules are to be understood as a way of describing the functionality of the control unit 1 7 without any particular restriction on the actual implementation . Indeed, these modules can be implemented entirely or partially in software or in hardware. These modules can either be implemented by a single local electronic device or can be distributed over a network.

The control unit 1 7 comprises at least a sensor module 1 8. This module is configured to acquire an input P, which can be for example a crank angle value, which is related to the angular position of the crankshaft attached to the piston 4. Such crank angle value can then be used to extrapolate a pressure value. In an alternative embodiment, a can be measured directly from one or more sensors. The sensor module 1 8 is also configured to emit a signal S1 . This signal can for example represent a value of pressure previously measured or extrapolated . The control unit 1 7 also comprises an evaluation module 1 9. This module is configured to compare the input signal S1 with the predefined threshold P1 , and to emit an activation signal A1 as a result of the comparison . The control unit 1 7 comprises also an actuation module 20, associated with the evaluation module 1 9 and to the regulating valve 1 6. The actuation module 20 is configured to open/close the regulating valve 1 6 in response to the activation signal A1 from the evaluation module 1 9.

The sensor module 1 8 can also acquire an input V, which can be for example a value of volume of the working chamber 6, 7. In a preferred embodiment, the value of V can also be extrapolated from the crank angle measurement, as described above. The sensor module 1 8 then emits a signal S2, which can for example represent a volume of either the first 6 or the second working chamber 7. The evaluation module 1 9 also acquires S2. Then the evaluation module 1 9 checks S2 is equal or less than a predefined threshold volume V1 . If this is true, the evaluation module 1 9 emits an activation signal A2 to the actuation module 20. In response to the activation signal A2, the actuation module 20 closes the regulating valve 16, so that the working fluid can be compressed normally.

The above described operations can be performed by the control unit 17 either in the first 6 or the second working chamber 7 or, preferably, in both.

An embodiment of the present invention also refers to a method for retrofitting a piston-cylinder assembly of the known type. Optionally, if the regulating valve 16 is placed inside the piston 3, the piston 3 itself is extracted from the cylinder 2.

This method comprises the steps of providing at least a flow regulator 9 comprising a bypass duct 10 and a regulating valve 16 along the bypass duct 10. The step of providing the flow regulator 9 can comprise the sub- step of drilling a bypass hole 17 inside the piston 4.

The bypass duct 10 is then linked to the working chambers 6, 7 so that the bypass duct 10 is in fluid connection with the first 6 and with the second working chamber 7. The step of linking the bypass duct 10 to the working chambers 6, 7 can be performed by placing the piston 4 back inside the cylinder 2, if it was previously extracted.

An embodiment of the present invention also relates to a method for regulating the output mass flow of a piston-cylinder assembly 1 as described above. Such method comprises the steps of performing a forward stroke of the piston 3, thereby performing a compression phase inside the first working chamber 6 and a suction phase inside the second working chamber 7.

Also, when a backward stroke of the piston 3 is performed, there is a suction phase inside the first working chamber 6 and a compression phase inside the second working chamber 7. The regulating valve 16 is opened at the beginning of the forward stroke in order to increase the clearance of the first working chamber 6. The regulating valve 16 is also opened at the beginning of the backward stroke to increase the clearance of the second working chamber 7.

Optionally, alternatively or additionally, the regulating valve 1 6 can be opened at the end of the forward stroke to allow the working fluid to move from the first 6 to the second working chamber 7. The regulating valve 1 6 can also be opened at the end of the backward stroke to allow the working fluid to move from the second 7 to the first working chamber 6.

Claims

1 . Piston-cyl inder assembly (1 ) for a reciprocating compressor comprising a cyl inder (2); a piston (4) inside said cylinder (2), said piston (4) defining a first (6) and a second working chamber (7) for compressing a working fluid ; said working chambers (6, 7) having each an intake opening (6a, 7a) and a discharge opening (6b, 7b) for said working fluid; a flow regulator (9) acting on said working chambers (6, 7) for controlling an outgoing flow of working fluid through said discharge openings (6b, 7b), said flow regulator (9) comprising a bypass duct (1 0) in fluid connection with said first (6) and with said second working chamber (7), at least a regulating valve (1 6) located along said bypass duct (10) for opening and/or closing said bypass duct (1 0) so that said fluid can flow between said first (6) and said second working chamber (7); wherein said bypass duct (10) is placed inside the piston (4).

2. Piston-cylinder assembly (1 ) according to claim 1 , wherein said regulating valve (1 6) is placed between said first (6) and said second working chamber (7).

3. Piston-cylinder assembly (1 ) according to any preceding claim, wherein said regulating valve (1 6) is electrically actuated .

4. Piston-cylinder assembly (1 ) according to any preceding claim, wherein said flow regulator (9) comprises a control unit (17) acting on said regulating valve (16) and configured to open said regulating valve (16) when the pressure inside the first (6) or the second working chamber (7) has reached a predefined threshold (P1 ) for allowing a flow of working fluid between said first (6) and said second working chamber (7).

5. Piston-cylinder assembly (1 ) according to claim 4, wherein said control unit (17) comprises a sensor module (18) configured to acquire an input signal (S1 ) representing a value of pressure; an evaluation module (19) configured to compare said input signal (S1 ) with said predefined threshold (P1 ) of pressure and to emit an activation signal (A1 ) as a result of the comparison; an actuation module (20) associated to said evaluation module (1 9) and to said regulating valve (1 6), said actuation module (20) being configured to open/close said regulating valve (1 6) in response to said activation signal (A1 ) from said evaluation module (1 9).

6. Piston-cylinder assembly (1 ) according to any preceding claim, also comprising an inductive generator (21 ) placed on said piston assembly (3) and configured to generate electricity from a reciprocating motion of said piston (4), said inductive generator (21 ) being linked to said regulating valve (1 6) in order to provide electric power to said regulating valve (1 6).

7. Piston-cylinder assembly (1 ) according to any preceding claim, wherein said intake opening (6a, 7a) is provided with an intake valve (1 3a, 14a), said intake valve (1 3a, 14a) being unidirectional .

8. Piston-cylinder assembly (1 ) according to any preceding claim, wherein said intake valve (1 3a, 14a) is of the pressure-actuated type.

9. Reciprocating compressor comprising a piston-cylinder assembly (1 ) according to any one of the preceding claims.

10. Method for retrofitting a piston-cyl inder assembly of the type comprising a cylinder (2), a piston (4) inside said cylinder (2), said piston (4) defining a first (6) and a second working chamber (7) for compressing a working fluid , said working chambers (6, 7) having each an intake opening (6a, 7a) and a discharge opening (6b, 7b) for said working fluid; the method comprising the steps of providing a flow regulator (9) comprising a bypass duct (10) and a regulating valve (1 6) located along said bypass duct (1 0); l inking the bypass duct (1 0) to the working chambers (6, 7) so that said bypass duct (1 0) is in fluid connection with said first (6) and with said second working chamber (7).

1 1 . Method according to the previous claim, wherein the step of providing a flow regulator (9) comprising a bypass duct (10) comprises the sub-step of drilling a bypass hole (17) inside said piston (4).

12. Method according to claim 10 or 1 1 , also comprising the step of extracting the piston (3) from the cylinder (2).

13. Method according to claim 12 and 1 1 , wherein the step of linking the bypass duct (10) to the working chambers (6, 7) is performed by placing the piston (4) back inside the cylinder (2).

14. Method for regulating the output mass flow of a piston-cylinder assembly (1 ) according to any claim from 1 to 8, comprising the steps of performing a forward stroke of the piston (3), thereby performing a compression phase inside the first working chamber (6) and a suction phase inside the second working chamber (7); performing a backward stroke of the piston (3), thereby performing a suction phase inside the first working chamber (6) and a compression phase inside the second working chamber (7); wherein the regulating valve (16) is opened at the beginning of the forward stroke to increase the clearance of the first working chamber (6) and at the beginning of the backward stroke to increase the clearance of the second working chamber (7).

15. Method according to the previous claim, also comprising the steps of opening the regulating valve (16) at the end of the forward stroke to allow the working fluid to move from the first (6) to the second working chamber (7); opening the regulating valve (16) at the end of the backward stroke to allow the working fluid to move from the second (7) to the first working chamber (6).