WOBBLE PLATE COMPRESSOR
A wobble plate compressor (101) comprises at least one wobble plate (017) assigned at least two piston-cylinder assemblies. The wobble plate compressor (101) forms a multistage compressor in which the piston-cylinder assemblies are connected in series in the flow and the cubic capacity of the piston-cylinder assemblies is progressively reduced in series.
The present invention relates in general to compressors and, for example, to a wobble plate compressor as well as to use of a wobble plate compressor for compressing natural gas.
BACKGROUND OF THE INVENTIONWobble plate machines are essentially piston machines in which the piston(s) is/are not driven by a crank but by a swash or wobble plate, i.e. a plate skew seated on an axis which “wobbles” on rotation of the axis, but not like a radial plate in which the points rotate in the vicinity of the edge, instead in a rotary plane inclined to the axis. Arranged opposite this wobble plate for each piston is a stationary con rod substantial parallel to the drive shaft and the con rod(s) are advanced or retracted by the wobbling plate.
In practice such wobble plate machines are mainly employed as pumps (i.e. for pumping incompressible fluids, in other words liquids). Basic use of the wobble plate design in pumps is known, for example, from the German “Dubbel” mechanical engineering text book, 17th Edition, published by Springer-Verlag, 1990, pages H4-H8.
In addition, wobble plate machines also find use as compressors (i.e. compressors for compressible fluids, i.e. gases), particularly in refrigerators. Thus wobble plate type refrigerant compressors are known, for example, from U.S. Pat. No. 4,008,005 as well as from EP 0 530 730 A1. In these wobble plate machines the actual wobble plate is non-rotatable but is controlled by a rotatable wobble member to produce the wobble motion. To compensate, at least in part, one disadvantage of non-compensated forces and moments general to wobble plate machines (substantially resulting from gas forces during compression and sudden relaxation when the outlet valve is opened and the mass forces stemming from the reciprocating pistons) it is proposed in the cited documents to arrange a plurality of (in this case, five or six) piston-cylinder assemblies regularly distributed circumferentially. The plurality of cylinders is connected in parallel as regards the delivery of the gas flow to be compressed. It is generally the case that these known wobble plate pumps have a relatively low compression ratio since a refrigerant is compressed generally to not more than 2 bar.
A further wobble plate type refrigerant compressor is known from EP 0 599 642 A1 in which it is proposed to equip the piston-cylinder assemblies with piston rings of polytetrafluoroethylene (PTFE).
Known in conclusion are special types of wobble plate compressors in which the piston-cylinder assemblies extend not just to one side of the wobble plate but to both sides as it reads from U.S. Pat. No. 5,611,675 (with a swash plate), DE patent 530 071 and FR patent 918.307 (with two wobble plates seated on a common shaft, inclined to each other).
SUMMARY DESCRIPTION OF THE INVENTIONThe invention relates to a wobble plate compressor comprising at least one wobble plate associated with at least two piston-cylinder assemblies. The wobble plate compressor forms a multistage compressor in which the piston-cylinder assemblies are connected in series in the flow and the cubic capacity of the piston-cylinder assemblies is progressively reduced in series.
A further aspect relates to a method in which one such wobble plate compressor is used for compressing natural gas to a pressure of at least 200 bar.
Another aspect relates to a wobble plate compressor comprising at least one pair of wobble plates, each of which is associated with at least one piston-cylinder assembly. Each of the two wobble plates is powered by a drive shaft stub, the two drive shaft stubs being arranged coaxially counter-rotating.
Further features read implicitly from the disclosed devices or are evident to the person skilled in the art from the following detained description of embodiments and the attached drawing.
BRIEF DESCRIPTION OF THE DRAWINGEmbodiments of the invention will now be described by way of example with reference to the attached drawing in which:
In some of the embodiments as described in the following a wobble plate type compressor is provided suitable for achieving a high overall compression ratio. For this purpose the wobble plate compressor in some embodiments is configured as a multistage compressor in which a plurality of piston-cylinder assemblies is connected in series in the flow and the cubic capacity of the piston-cylinder assemblies is progressively reduced in series. Multistage compressors are known (e.g. as it reads from the German “Dubbel” mechanical engineering text book, 17th Edition, published by Springer-Verlag, 1990, pages P23-P33); these known multistage compressors are all crankshaft type piston compressors, however.
In some of the embodiments the piston-cylinder assemblies connected in series are interconnected in series by conduit and valve assemblies.
The multistage configuration achieves substantial final pressures: based on atmospheric pressure and ignoring the effects of the gas being heated and cooled and its friction loses, some embodiments are capable of achieving, for example, with a compression ratio of roughly 1:4 per cylinder, an increase in pressure of 16 bar and 256 bar in a two and four cylinder series assembly respectively. However, the true pressures attained are usually less, because of the effects ignored in the above achievements. In some embodiments forced cooling of the cylinders and/or of their interconnecting conduits is needed to achieve an effective intermediate cooling, e.g. by forced ventilation with ambient air or cooling by cooling water, etc. In other embodiments merely convection cooling of the pistons and/or the conduits by ambient air is provided for.
In some embodiments e.g. four piston-cylinder assemblies are assigned per wobble plate, whereas in other embodiments just two piston-cylinder assemblies are provided per wobble plate which, as such, is less favorable as regards force and moment compensation. But in a few of these embodiments—as detained further on below—a second wobble plate is provided in a casing, powered counter-rotatively to the first wobble plate and arranged together therewith in a common casing. The casing can thus absorb the forces and moments of the two wobble plate assemblies in partly compensating them counterwise, since due to the counter rotative arrangement they are employed opposite in sign at least in part.
When again assuming the gas is not heated in compression, it neither being cooled nor any friction loses existing, then—because of maintaining the mass flow of the compressed gas—the series piston-cylinder assemblies are to be dimensioned so that (for the same number of strokes per unit of time for the individual stages) the inlet cylinder volume of a stage in consideration substantially equals the outlet cylinder volume of the previous stage. Accordingly, in some of the embodiments the cubic capacity of the piston-cylinder assemblies in series is progressively reduced. In reality the above assumption—because of the aforementioned effects—does not apply precisely but only approximately (see German “Dubbel” mechanical engineering text book, 17th Edition, published by Springer-Verlag, 1990, pages P30-P31), that the cubic capacity is progressively reduced from stage to stage basically holds, however.
In some of these embodiments progressively reducing the cubic capacity is achieved by the piston-cylinder assemblies—having the same stroke because of their assignment to one and the same wobble plate—assigned to a wobble plate comprising a progressively reduced diameter.
Other embodiments incorporate two wobble plates in which, for example, first the piston-cylinder assemblies of the first wobble plate and then the piston-cylinder assemblies of the second wobble plate are connected in series with a progressively reduced cubic capacity. In some of these embodiments progressively reducing the cubic capacity extends over the wobble plates by reducing the cylinder diameter; i.e. the piston-cylinder assembly of the second wobble plate first in flow has a smaller diameter that the piston-cylinder assembly of the first wobble plate last in flow.
Since in a wobble plate compressor the cylinder stroke is defined relative to the axis of rotation due to the inclination of the wobble plate, a smaller cubic capacity is achievable also by a lesser slant of the wobble plate. In some of these embodiments the second wobble plate is arranged less slanted than the first wobble plate to achieve the reduction in cubic capacity.
In some of these embodiments both means of reducing the cubic capacity are also combined with each other, i.e. the second wobble plate is arranged less slanting than the first wobble plate to reduce the stroke, and in addition the first piston-cylinder assembly of the second wobble plate features a smaller diameter than that of the last piston-cylinder assembly of the first wobble plate.
In some of the multistage embodiments the compressor stages are dimensioned for the multistage increase in pressure so that—e.g. starting with atmospheric pressure (1 bar)—an increase in pressure to at least 200 bar, in other embodiments to even at least 400 bar, is achieved. The compressor is thus particularly useful for compressing gases which at room temperature practically defy liquifying, such as hydrogen, nitrogen, oxygen, air, rare gases and especially natural gas (mainly methane).
In a compressor a sudden drop in gas pressure in the cylinder occurs due to the typically sudden opening of the outlet valve when maximum compression is attained in a cylinder, resulting in a shock moment about the drive axis (i.e. the longitudinal centerline) of the compressor where a wobble plate compressor is concerned. As already mentioned above, in some embodiments two wobble plates are provided, each of which is powered by a drive shaft stub counter rotatively, whereby the two drive shaft stubs are arranged coaxial, for instance. In some of these embodiments the two counter rotating wobble plates are intercoupled in such an angular relationship that outlet timing of cylinders forming such cylinder pairs coincide in each case. For example, the outlet timing of the first and third stage and that of the second and fourth stage coincide. Because of this synchronism and the counter rotation of the two drive shaft stubs the shock moments occur substantial simultaneously and are opposite in sign, so that in this arrangement the cited shock moments are compensated at least in part.
The assembly mentioned above of two counter rotatively powered wobble plates has the effect of reducing the shock also in wobble plate compressors other than the multistage type, e.g. in compressors in which the plurality of piston-cylinder assemblies belonging to a stage is connected in parallel, or in which a plurality of independent gas flows from the individual cylinder is compensated in a single-stage, for example, for application in air-conditioning compressors or the like. The cylinder diameters and strokes of the individual piston-cylinder assemblies are more or less the same in such single-stage embodiments. Although the instant claim 1 is directed at a multistage compressor, the present application docs thus disclose also in general a wobble plate compressor with counter rotatively powered wobble plates irrespective of the compressor configured multistage or single-stage. The applicant thus reserves the right to direct an independent claim at an assembly with two counter rotatively powered wobble plates which does not require that the wobble plate compressor is a multistage compressor. Such an independent claim would read e.g. a wobble plate compressor comprising two wobble plates each assigned at least two piston-cylinder assemblies, each of the two wobble plates being powered by a drive shaft stub, the two drive shaft stubs being arranged coaxial and counter rotatively. The features of the current claim 1, of the remaining claims and of the description/drawing can as dependent claims relating back to this independent claim.
In some of the embodiments having counter rotatively powered wobble plates a bevelled drive gear is mounted at each inner end of the drive shaft stub, between which a bevel pinion is arranged for powering both wobble plates simultaneously counter rotatively.
In some of the embodiments the wobble plates themselves are non-rotatable, they being controlled by a rotatable wobble member similar to the assembly as it reads from the aforementioned U.S. Pat. No. 4,008,005, for instance. In such an assembly the con rods of the cylinder are exposed to no bearing or friction forces produced by the actual rotation, but merely to bearing or friction forces due to the wobble motion.
In some embodiments the con rod does not directly engage the piston (as is usual in prior art). Instead, in these embodiments a piston guide rod is disposed between con rod and piston, suitable guided e.g. in a locating hole machined in an inside cover. The piston guide rod prevents transverse forces being transmitted from the con rod to the piston which when the wobble plate is stationary are in any case only slight.
In some embodiments some or all of the bearings between relatively rotatable parts are angular contact roller bearings which due to their angular location are suitable for absorbing axial forces. For example one or more of the following bearings is/are configured as angular contact roller bearings: (i) bearing of a non-rotatable wobble plate relative to a rotatable wobble plate (in embodiments with a non-rotatable wobble plate); (ii) bearing of a rotatable wobble plate (in embodiments with a rotatable wobble plate) or a rotatable wobble member (in embodiments with a rotatable wobble member) relative to a casing; and (iii) bearing of a drive shaft stub relative to a casing (in embodiments with drive shaft stubs). In some embodiments the angular contact roller bearings are relative to needle bearings at an angle to the axis of rotation, in others the bearings involved have angled rollers so that even without angular location of the roller axes they are capable of absorbing axial forces, such as bevelled roller bearings and barrelled bearings (also combinations thereof in which e.g. some bearings are angular needle bearings, other and bevelled roller bearings exist). In some embodiments the bearings supporting the drive shaft or each drive shaft stub are two angular contact roller bearings facing away from each other. In some embodiments both the wobble member or the wobble plate and the drive shaft stub run in angular contact roller bearings in the casing, and the wobble member or wobble plate and the drive shaft stub are axial shiftingly (but non-rotatable) connected to each other so that wobble member or wobble plate and drive shaft stub are decoupled from each other as regards the axial forces. The angular contact roller bearings mounting the wobble plate in the wobble member and those of the wobble plate member in the casing are specially suitable to absorb the axial and radial components of the forces occuring on actuation of the pistons.
One problem as known with compressors is that lubricants can evaporate from the cylinder walls into the gas being compressed. In addition to this, at high compressor temperatures the lubricant may be decomposed. This is why in some embodiments the pistons and/or the walls of the cylinders are lined at least in part with anti-friction plastics, such as e.g. polytetrafluroethylene (PTFE). For the pistons PTFE piston rings may be involved, for example, and as regards the cylinder wall cylinder shells. Such anti-friction linings permit doing away altogether with lubrication of the pistons in the cylinder by liquid lubricants (e.g. oil) in some embodiments, or at least to reduce the amount of lubricant needed.
Some embodiments relate to methods in which a wobble plate compressor of the kind as described presently is used to compress gases which at room temperature practically defy liquifying, such as hydrogen, nitrogen, oxygen, air, rare gases and/or natural gas to a pressure of at least 200 bar, preferably to at least 400 bar. One particularly suitable use involves the compression of natural gas (mainly methane) for fuelling vehicles operated on compressed natural gas (CNG).
Referring now to
The two wobble plate assemblies 102, 103 are accommodated facing each other at the drive end in a substantially tubular casing identified as a whole by 006 and assembled from a plurality of parts.
Running through the casing 006 central and at right angles to its longitudinal centerline mounting two drive shaft stubs 009 is a main drive shaft. Of the two drive shaft stubs 009 only one is shown identified as such, the same as the many parts of the two wobble plate assemblies 102, 103 which are identified just for one or other wobble plate assembly, since the parts for both are provided similar or identical, albeit mirror-inverse to each other. Mounted at the outer end (relative to the casing 006) of the main drive shaft is a drive flange for connecting a drive means by means of a nut 005 and a splined joint. Inserted in the wall of the casing 006, configured flat in this case, is a bearing mount 002 mounting two angular contact roller bearings 003, 004. Seated at the inner end of the main drive shaft is a bevel pinion 001.
The bevel pinion 001 engages two bevel gears 007. These are seated on a flange 008 bolted in each case to the drive shaft stubs 009. The drive shaft stubs 009 each run in two angular contact roller bearings 011, 012 secured in a cylindrical bearing support 010 bolted to a cross plate penetrating the casing 006.
Seated at the other side of this cross plate is a bearing base 013 supporting a rotating wobble member 015 via an angular contact roller bearing 014. In this arrangement the middle of the bearing base 013 is recessed to permit the end of the drive shaft stubs 009 facing away from the bevel gears 007 to pass through without contact, to which the wobble member 015 is splined and secured in place by a fastener nut.
Mounted on the free outboard flange of the wobble member 015 oriented slanting to the longitudinal centerline of the drive shaft stub 009 is a further angular contact roller bearing 016 supported by a non-rotatable wobble plate 017 which in turn is supported by a bevel toothing 018 and a middle ball 019 on a fixed part 020. The fixed part 020 is secured between two walls 021 which in turn are bolted to a crosswall.
The bevel toothing 018 permits the wobble plate 017 to follow the wobble motion of the wobble member 015 without being included in its rotation, since one part of the bevel toothing 018 is stationary and is thus non-rotatable, resulting in the wobble plate 017 also being unable to rotate because of the mesh, whilst the ball 019 permits the pivoting motion.
At the side of the wobble plate 017 facing away from the wobble member 015 two spherical recesses are sited radially opposed and equally spaced away from the center point of the ball 019, the recesses being covered by a cover 022. The cover 022 comprises a hole in the middle, i.e. is configured just as a rim and is likewise spherically hollowed around this hole.
Inserted in the recesses is the spherical end of a con rod 023 which is held by the cover 022. The con rod 023 ends also at the other side in a ball. This other ball is located in a similar spherical recess covered by a cover 024 and which is configured in the end of a piston rod 025 in each case which in turn is guided in a locating hole 036 oriented parallel to the drive shaft stub 009. The locating holes 036 are configured in the aforementioned crosswall and coated with polytetrafluoroethylene (PTFE) or the like to obtain a totally linear motion of the piston rods 025 without resulting in any substantial friction being produced thereon.
Rotation of the bevel pinion 001 results in rotation of the two wobble members 015 at the same speed, but counter rotatively, producing reciprocation of the piston rods 025: the two in-line piston rods 025 shown at the top in the drawing move towards each other in the same sense, but in opposite sense to the likewise in-line piston rods 025 moving towards each other in the same sense as shown at the bottom in the drawing.
The spherical ends of the con rods 023 and/or the recesses seating them are coated to reduce friction, for instance with PTFE and run, like the piston rods, dry in operation. The ball 019 and/or the sections of the bevel toothing 018 seating it are also coated to reduce friction, for instance with PTFE as is the case in some embodiments also with the bevel toothing 018 and with the bevel drive 001/007. The angular contact roller bearings require no lubrication, they being sealed for life so that the dual wobble plate compressor 101 runs dry in operation. In other embodiments, however, at least the middle part of the casing with the bevel drive 001/007 and the angular contact roller bearings 011, 012 are provided with grease lubrication or with an oil sump which lubricates through the bearing 014 also the remainder of the wobble plate compressor as described hitherto. On the far side of the locating hole 036 the following parts in the embodiment as shown run dry.
The piston-cylinder assemblies 026, 031; 027, 032; 039, 033; 038, 034 form in this sequence of the reference numerals the first, second, third and fourth compression stage, they for this purpose being connected in series in the gas flow and comprise from stage to stage a progressively reduced cubic capacity. This reduction in cubic capacity is achieved in the embodiment as shown by a reduction in the cylinder diameter from stage to stage and in addition by a reduced stroke in the third and fourth stage as compared to that of the first and second stage.
The pistons 026, 027, 038, 039 are powered by the piston rods 025 to which they are fastened by means of a nut 035, 045, 046. The pistons 026, 027, 038, 039 feature piston rings of PTFE or the like. In some embodiments—in addition thereto or as an alternative—the inner surfaces of the cylinders 031, 032, 033, 034 are coated with PTFE or the like.
The cylinders 031, 032, 033, 034 are each formed by two tubular sections located in a crosswall (comprising the locating holes 036). The crosswall stands crosswise on a base plate 042. The two each tubular sections are interconnected or connected to the crosswall by connecting flanges 029, 030, 041, 042 to form a full-length cylinder 031, 032, 033, 034 and to secure the cylinder to the crosswall. At the outer end the cylinders 031, 032 of the first and second stage (i.e. the right-hand cylinders) and the cylinders 033, 034 of the third and fourth stage (i.e. the left-hand cylinders) are closed off from the outside by each cover 028, 040 seating valves having a free valve cross-section which is progressively reduced from stage to stage. Provided furthermore fronting the cover 028, 040 in each case is a cylinder end flange 047, 048 receiving in common the ends of the two right-hand cylinders 031, 032 and left-hand cylinders 033, 034 respectively. In the embodiment as shown the valves are gas-controlled valves, e.g. combined pressure opening/check valves opening in the inlet direction so that on the inwards stroke gas flows in each of the cylinders and which in the outlet direction do not open until a certain pressure (progressively increasing from stage to stage) is attained typically just before the outer dead center. In other embodiments separate inlet and outlet valves are provided. In some embodiments the valves are not controlled by the gas flow but mechanically by a valve control mechanism which derives its motion from the rotation of the wobble plate drive.
Porting into each cover 028, 040 are two pipes 049, 050 and 051, 052 respectively. In an external pipe connecting system these pipes are interconnected as well as to a low-pressure gas input and a high-pressure gas outlet so that the gas flows from the low-pressure gas input to the first stage, from there to the second stage and so on in finally flowing from the fourth stage to the high-pressure gas outlet. In embodiments having valves and pipe sections used in common for the inlet and outlet, directional control valves (e.g. gas controlled directional control valves of the check valve type) ensure that the gas flow takes a different path depending on the direction concerned (for instance, when inlet in the second stage, the path from the first stage to the second stage, whereas when outlet from the second stage, the path from the second stage to the third stage). In embodiments with separate valves and pipes for the inlet and outlet, no such directional control valves are provided; instead, the pipe from the input through the individual stages to the output is guided as a single loop. In some embodiments the pipes between the stages and leading to the output are cooled for a better intercooling of the gas to be compressed.
In the position as shown in
As evident from
This compressor with its two wobble plates as shown is mounted as a whole in a casing which due to the crosswalls and covers is particularly torsionally rigid, despite its length. Although the substantial part of the compressors runs dry, there is no corrosion of the PTFE coated surfaces even when temperatures are attained at which lube oil would already be decomposed.
With this simple, small multistage compressor (low friction when PTFE coated) gases can be compressed to pressures in the range 200 to 400 bar. Referring now to
The embodiments described thus provide an improved high pressure compressor which e.g. is suitable for equipping CNG filling stations.
All publications and existing systems cited in this description are incorporated therein by referencing.
Although certain products and methods built in agreement with the teaching of the invention have been described, the scope of protection afforded by this patent is not restricted thereto. On the contrary, the patent covers all embodiments of the teaching of the invention reading literally or by the equivalence doctrine from the scope of protection as claimed.
Claims
1. A wobble plate compressor comprising at least one wobble plate associated with at least two piston-cylinder assemblies, wherein the wobble plate compressor forms a multistage compressor in which the piston-cylinder assemblies are connected in series in the flow and the cubic capacity of the piston-cylinder assemblies is progressively reduced in series.
2. The wobble plate compressor as set forth in claim 1 wherein the piston-cylinder assemblies associated with a wobble plate comprise a progressively reduced diameter to achieve a progressively reduced cubic capacity.
3. The wobble plate compressor as set forth in claim 1 comprising at least two wobble plates each associated with piston-cylinder assemblies wherein to progressively reduce the cubic capacity, the piston-cylinder assembly first in the flow of the wobble plate comprises a smaller diameter than the piston-cylinder assembly last in flow of the first wobble plate.
4. The wobble plate compressor as set forth in claim 1 comprising at least two wobble plates each associated with piston-cylinder assemblies wherein to progressively reduce the cubic capacity the second wobble plate is arranged less skew than the first wobble plate.
5. The wobble plate compressor as set forth in claim 1 wherein the individual compressor stages are dimensioned for a multistage increase in pressure of the gas to be compressed to at least 200 bar.
6. The wobble plate compressor as set forth in any of the claim 1 comprising two wobble plates each powered by a drive shaft stub, the drive shaft stubs being arranged coaxial and counter rotatively.
7. The wobble plate compressor as set forth in claim 6 wherein the inner end of the drive shaft stubs seats in each case a bevel gear between which a bevel pinion is disposed for simultaneously, counter rotatively drive of both wobble plates.
8. The wobble plate compressor as set forth in claim 1 wherein the wobble plates are non-rotatable and are controlled by a rotatable wobble member.
9. The wobble plate compressor as set forth in claim 1 comprising bearings disposed between relatively rotatable parts, at least one of the following bearings being configured as an angular contact roller bearing: (i) bearing of a non-rotatable wobble plate relative to a rotatable wobble member; (ii) bearing of a rotatable wobble member relative to a casing; and
- (iii) bearing of a drive shaft stub relative to a casing.
10. The wobble plate compressor as set forth in claim 1 wherein the pistons and/or the walls of the cylinders are lined at least in part with anti-friction plastics.
11. A wobble plate compressor comprising at least one pair of wobble plates, each wobble plate associated with at least one piston-cylinder assembly, each wobble plate of the pair powered by a drive shaft stub, the drive shaft stub being arranged coaxial and counter rotatively.
12. A method in which a wobble plate compressor as set forth in claim 1 is used for compressing natural gas to a pressure of at least 200 bar.
Type: Application
Filed: Feb 16, 2007
Publication Date: Aug 23, 2007
Applicant: Factor 4 S.A. (Cordoba Capital)
Inventor: Ernesto Almaraz (Cordoba Capital CP)
Application Number: 11/675,669
International Classification: F04B 3/00 (20060101);
