AU599768B2 - A stationary reciprocating compressor for compressing natural gas - Google Patents

Description

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F 21 768 Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COM/PLETE SPECIFICATION

(ORIGINAL)

Class Application Number: Lodged: ~Complete Specification Lodged: I t. Class Priority: Accepted: Published: Th1 8 document COUtain, the and is e"Orw tOr pritrIag Related Art: It

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ft ii N~dme of Applicant: SULZER BROTHERS LIMITED Address of Applicant Actual Inventor: Address for Service: CH-8401 Winterthur, Switzerland HEINZ BAUMANN EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention entitled: A STATIONARY RECIPROCATING COMPRESSOR FOR COMPRESSING NATURAL GAS The following statement is a full description of this invention, including the best method of performing it known to :,u Parnkroph 2 oholll be cninpItted by Iho, in' de- 0nWutiofl of !lt. e.w..

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of the nld I None of Inoent, r, W DECLARED at Winterthur...... Switzerland 17th.E a a M arch.... this 1 day of M ar ch 19 88 Suilzer Bothes Limited A stationary reciprocating compressor for compressing natural gas re0o 0 e 0 o 0 i 20 The invention relates to a stationary reciprocating compressor driven by an electric motor, for compressing natural gas used as fuel in the engine of motor vehicles and stored in the compressed state in the vehicle to be driven, with four cylinders which are arranged in series on the gas side and which guide respective pistons.

Piston compressors of this type are therefore used to refuel motor vehicles with compressed natural gas.

They are intended to be placed in or in the vicinity of a private garage or near a parking space belonging to the vehicle owner, provided that there is a connection to a natural gas supply network. Known refuelling plants of this type have used three- or four-stage reciprocating compressors, as is customary for breathing-air compressors for filling compressed-air, bottles. The pistons of these compressors are driven by way of a crankshaft and connecting rods. Such r.

,i compressors run unevenly, due to uncompensated inertia forces, leading to disturbing noise. Also, these compressors are oil-lubricated. Since the compressors used in the refuelling plant must operate in a temperature range of +500 C to -4 0 0 C, there is the problem of the lubricating oil becoming viscous at low temperatures. The oil may be so viscous that when the electric motor is switched on, the compressor does not start or else requires excessive starting current. The compressor therefore demands a relatively large to O "Ooa electrical power supply, which is not normally available 00 o for domestic use.

00 00 An object of the invention is to improve a reciprocating compressor of the type initially described by further reducing the noise it generates, and by 'a reducing its driving torque on starting so that the .o o electric motor can be connected to the normal supply.

To this end, according to the invention, two pistons at a time, lying opposite one another on a common axis, are interconnected with their piston rods by way of a yoke to form a pair, the axes of the two pairs of pistons so formed intersect one another, and each pair of pistons is disposed in a substantially horizontal plane, a common crank pin, as driving .eans, engages in the two yokes of the piston pairs by way of a slider, the gas to be compressed is supplied on the piston side remote from the compression chamber of the first compression stage by way of at least one suction 3.

valve situated in the piston, and the drive motor for the compressor is situated below the horizontal planes of the two piston pairs.

Because, in accordance with the invention, the four pistons are arranged in two intersecting pairs of pistons and the drive is by way of a slider movable in the yokes, the free inertia forces are substantially compensated and the compressor therefore runs more evenly. Because the gas to be compressed is supplied on the underside of the piston in the first compression stage and the suction valve is provided in the piston for this stage, it is possible to keep the diameter of this cylinder relatively small; the suction valve is therefore no longer placed in the cylinder wall or end wall defining the compression chamber. This also keeps dead space to a minimum. The compressor is operated without lubricating oil, so eliminating the problem of high driving torque due to excessively viscous lubricating oil at low temperatures. The arrangement 2 of the drive motor below the compressor has the effect that because of the vertical ventilation of the motor any mixture of air and natural gas forming outside the compressor does not reach the vicinity of the motor.

Further advantageous features of the invention are listed in the sub-claims.

Two embodiments of the invention will now be described in more detail by way of example with reference to the drawings, in which: I 0 Figure 1 represents a section on two horizontal planes through a reciprocating compressor in accordance with the invention; Figure 2 shows a vertical section through the central portion of the compressor shown in Figure 1; Figure 3 shows the compressor with the electric motor below it; Figure 4 is a perspective view of a drive, modified relative to Figure 1, for the compressor; and Figure 5 illustrates diagrammatically the arrangement of slots in the yokes relative to the direction of movement of the pairs of pistons in Figure 4.

As Figure 1 shows, the compressor has four cylinders 1, 2, 3 and 4, of which cylinders 1 and 2 have a common axis 5 lying in the plane of Figure 1, whereas cylinders 3 and 4 have a common axis 6 set slightly back relative to the plane of Figure 1. In cylinder 1 a piston 7 is mounted, which is connected by a piston rod 8 to a yoke 9 which transmits the driving force from a crank pin 10 by way of a cam 11 to the piston 7. Also connected to the yoke 9, by way of a piston rod 13, is a piston 12 movably mounted in a cylinder insert 14 in the cylinder 2. The compression chamber 15 of the cylinder 1 which forms the first compression stage, and which is smallest when the piston 7 is in the position shown in Figure 1, is defined by a plate 16 inserted in the cylinder 1 and carrying a pressure regulating valve 17 C I r* r+ 4i

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in the vicinity of an aperture. Opposite the pressure regulating valve in the piston 7 there is a suction valve 18, which, during the suction stroke of the piston 7, connects the compression chamber 15 to that side of the piston remote from the chamber. The cylinder 1 is provided with a cylinder cover 19, releasably attached to it and connected to a duct 20 (indicated by a chain line), which carries the gas compressed to, for example, bar in the compression chamber 15 to the next compression stage in the cylinder 2.

The piston 12 for the second compression stage is t at its bottom dead centre position when as shown in Figure i, so that the compression chamber 21 is at its largest. The chamber 21 is defined at one end by a plate 22 containing two apertures associated with a suction valve 23 and a pressure regulating valve 24.

The cylinder insert 14 and plate 22 are held by a cylinder cover 25 releasably attached to the cylinder 2. From the cylinder cover 25 a duct 26 indicated by a chain line carries the gas compressed to, for example, 19 bar in the compression chamber 21 to the third compression stage in the cylinder 3. This cylinder is also provided with a cylinder insert 27, in which a piston 28 is slidably mounted, its piston rod 29 being attached to a second yoke 30. The yoke 30 also has a bore in which there slides a cam 31 (Figure which forms one piece with the cam 11 in the yoke 9 and is also rotatably mounted on the crank pin 10. The two 1 I cams 11, 31 are offset relative to one another by 1800. Attached to the yoke 30 opposite the piston 28 there is a piston 32, mounted in a cylinder insert 33 in the cylinder 4. The insert 33 here also forms the cylinder cover, containing a compression chamber 34, a suction valve (not shown) and a pressure regulating valve The cylinder insert 27 in the cylinder 3, like the insert 14 in the second compression stage, cooperates with a plate 36 to define a compression chamber 37, and is held in the cylinder 3 together with the plate 36 by a releasable cylinder cover 38. The plate 36 contains two apertures associated with a suction valve 39 and a pressure regulating valve 40. From the cylinder cover 38 a duct 41 shown by chain lines carries the gas compressed to, for example, 60 bar in the third compression stage to the fourth compression stage in the cylinder 4. The gas compressed here to the final pressure of, for example, 180 bar leaves the compressor by a duct 42 connected to the cylinder insert 33.

As Figure 2 shows, two counterweights 43 are mounted on the czank pin 10 and rotate with it. The four cylinders 1 to 4 form with the housing 44 enclosing the yokes 9 and 30, the cams II and 31 and the counterweights 43 a structural unit. The crank pin turns at the lower end in Figure 2 into a shaft stub connected by a coupling member 46 (Figure 3) to an electric motor 47. The shaft stub 45 is mounted in a

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i B Ii i1 ~11 i:2 r -r I 7 i ~a~ bearing cover 48 releasably fixed to the housing 44.

The free end of the crank pin 10 is supported by way of a sleeve 50, which bears the upper counterweight 43 in Figure 2, in a bearing cover 49 which, like the bearing cover 48, is mounted in the housing 44.

On the housing 44 between the cylinders 2 and 3 is a connection bore 65, through which the gas to be compressed is drawn from a source (not shown) at a pressure of, for example, 1 bar. This gas flows through. the housing 44 and cylinder 1, to which end a connecting duct (not shown) is provided in a piston guide member 8a for the piston 7. From the side of the piston remote from the compression chamber 15 the gas then passes through the suction valve 18 during the suction stroke of the piston 7 into the compression chamber 15. Alternatively, the connection bore 65 may be connected directly to the cylinder 1, more specifically to the underside of the piston 7 near the end of the latter's suction stroke.

As Figure 3 shows, the electric drive motor 47 is situated below the compressor, whose cylinders 1 to 4 are situated in two substantially horizontal planes.

The compressor, with the electric motor 47, is attached to a support framework 51, which surrounds the electric motor on three sides and is fixed to the ground by four rubber bearings 52. Also attached to the framework 51 is an electrically operated fan 53 which draws in ambient air and sends it down along a duct in the 8.

framework 51 to a chamber 54 beneath the motor 47. The connecting ducts 20, 26 and 41 are run into this chamber 54, in order to cool the gas to be carried in them from one compression stage to the next. Between the fan 53 and chamber 54 is an electrical switch box 55, which however is outside the air duct. The apparatus so far described is enclosed in a hood 56, divided into an upper and a lower portion. Halfway up the two portions overlap to some extent. Within the overlap an air filter 57 is provided between the two portions for the a.0 t ambient air drawn in by the fan 53. At its upper end 3 the hood 56 forms a central collar 58, which is capped by a cover 59, an air filter 60 being provided between r the collar and cover. The cooling air flowing through the chamber 54 escapes through this air filter 60, after rising beside the electric motor 47 and flowing round and thereby cooling the compressor. A pin 61 attached to the top of the compressor and carrying the cover 59 may receive an eye 62 for a lifting hook.

In the embodiment shown in Figure 4, the yokes 9 and 30 are driven not by a slider with two cams, but by a slider 63 in the form of a square. The square member 63 has two parallel sides, horizontal in Figure 4, sliding in a horizontal slot 64 in the yoke 9. The slot 64 therefore runs transversely relative to the direction of motion of the pistons 7 and 12. Similarly, the two parallel sides of the square member 63 which are vertical in Figure 4 are movable in a vertical slot in 9.

the yoke 30, that is, again transversely relative to the motion of the pistons 28 and 32. Between the sliding Isurfaces of the square member 63 and the slots there may be rolling members, for example in needle form. Such members may also be provided between the crank pin extending through the square member and the surrounding bore in the square member 63.

As a modification of the example described with Sreference to Figure 3, the fan 53 and its drive motor may be omitted, and instead a ventilating fan may be mounted on the shaft of the electric motor 47, either on the coupling 46 or on a shaft stub projecting from the lower end of the electric motor. Also, it may suffice for the connecting ducts 20, 26 and 41 to run only inside the two planes in which the cylinders extend, so that there is no need to guide these ducts up and down between the compressor and the chamber 54. Another possibility is to make the hood 56- double-walled and to fill the space between its two walls with lightweight concrete or water. Such an embodiment could be advantageous where extremely good sound absorption is required.

Figure 3 shows a high-pressure header 66 for the compressed natural gas, while a pressure switch 67 is provided to switch the electric motor 47 on and off.

Claims (2)

1. 3. A compressor as claimed in claim 2, char-7terised in that between each cam and the surrounding bore in the associated yoke there is a
2. 11. rolling bearing, preferably a needle bearing. 4. A compressor as claimed in claim 1, characterised in that the slider comprises a square member mounted on the crank pin and mounted by two mutually parallel sides at a time in a slot in the yokes, the slot being transverse relative to the direction of motion of the associated piston pair. A compressor as claimed in claim 2 or 4, [j characterised in that a rolling bearing, preferably a needle li bearing, is provided in the slider between the crank pin and a bore surrounding the latter. 6. A compressor as claimed in any one of claims 1 Sto 5, characterised in that the cylinders and the housing surrounding the yoke are in one piece,.and each cylinder is i 1accessible through a releasable cylinder cover. j| 7. A compressor as claimed in any of claims 1 to 6, characterised in that the compressor includes cooling tubes, a high-pressure header, a pressure switch, an electric motor, a cooling fan, cooling air ducting, a filter for the cooling air and the filter for heated air are housed in a sound-absorbing, weather-resistant housing, which together with components contained in it forms a testable unit. DATED this ist day of May, 1990 SULZER BROTHERS LIMITED WATERMARK Patent Trademark Attorneys, "The Atrium", 290 Burwood Road, Hawthorn, Victoria, 3122, AUSTRALIA. L IAS/LPS:EK(12:27) I b