ASSEMBLY OF A COMMODITY METER

Abstract: The assembly of a gas meter of the kind having a top casing (13) and an external index casing (14) is made difficult by the necessity of providing a drive passing through the casing wall to the index mechanism. According to the invention the measuring mechanism is first put together with a gear box (12) and drive shaft (11). A magnetic coupling (16, 16′) is mounted on the casing (13) but not yet placed on the meter. The driving part (19) of a clutch mechanism (18) is secured to the shaft (11) and the driven part (27) secured to the magnetic coupling (16, 16′). The driving part comprises a cylinder (19) releasably held retracted by a pin (20) engaging behind a shoulder (21). With the cylinder (19) thus retracted the casing (13) is mounted on the meter. When the meter is first run the rotation of shaft (11) releases the pin (20) so that the clutch (18) engages.

Description: ASSEMBLY OF A COMMODITY METER. This invention relates to the assembly of a commodity meter and to a meter adapted for assembly by the new assembly method. Commodity meters of the kind to which the invention relates comprise top cover and bottom casing members, the bottom casing member having a measuring mechanism, the top casing cover member containing a drive path from the measuring mechanism through the wall of the top casing cover member to an index mounted outside the wall. In such meters there have been found problems of assembly because when the casing cover member is in position on the meter access to the drive path to make the final connections is not possible, but the drive path cannot be completed before the casing cover member is in place because the drive path passes through the casing cover member wall. According to the invention, there is disclosed a method of assembling a commodity meter of the kind comprising a measuring mechanism inside a closed casing, an index mounted on the outside of a casing cover member and a drive path through the casing cover member from the measuring mechanism tq the index, characterized by assembling a clutch mechanism in the drive path through the steps of connecting a driving part of the clutch mechanism to the measuring mechanism, connecting a driven part of the clutch mechanism to a wall of the casing cover member, placing the driving part in a disengaged position, assembling the casing cover mechanism to the meter and operating the meter to cause the clutch mechanism to engage. Thus the final drive connections are made by the first drive motion of the measuring mechanism. The invention also extends to a meter adapted to be assembled by this method. A specific embodiment of the invention is shown in the accompanying drawings, in which: Figure 1 is a side section through a magnetic drive assembly of a gas meter, and Figure 2 is an exterior view of part of the assembLy of Figure 1. A gas meter, part of which only is shown, comprises reciprocating diaphragms, the movements of which are translated into a rotational movement of a shaft (11) through a gear box (12). A meter casing (13) is, in use, full of gas so that the casing must be carefully sealed. However, the rotation of the shaft needs to be carried through the casing wall into an index housing (14) attached to the meter1 without allowing gas to escape. For this purpose a magnetic coupling transfers drive across the wall without the need for a mechanical connection. Magnetic couplings for this purpose are shown also in our U.K. Patent No. 2010596. In the present arrangement, there is a deeply cup-shaped insert (15) secured in the casing wall. The two magnets (16, 16') co-operating to transfer the drive are annular in shape, one encircling thecupshaped insert and the other seated inside the insert. The outer magnet (16) is required to rotate with shaft (11) through a clutch mechanism described hereinafter. - The inner magnet (16') is secured to rotate with an index and counter mechanism (not shown) within the index housing (14). With previous mechanisms of this kind there have been found problems of assembly. The gear box (12) and shaft (11) are mounted as shown in the drawing on interior structure of the meter1 while the magnet (16) of necessity is mounted on the casing (13). Clearly when the casing (13) is being placed in position on the meter1 no direct access is possible to the shaft (11) to connect it to drive the magnet. This problem is met in the presently described embodiment by a clutch mechanism (78) shown engaged in Figure 1 and disengaged in Figure 2. The clutch mechanism comprises a cylinder (19) formed of a plastics material, and having a bore in which is entered a smaller diameter end of shaft (11). Near its free end shaft (1) has a pair of opposed radially-extending pins (20). The bore of the cylinder (19) has for part of its length slots in which the pins slide, the slots ending in shoulders (21) such that the cylinder can be pushed onto the shaft to the position shown in Figure 2, then turned until the pins (20) engage behind the shoulders (21), thus retaining the cylinder in that position. A pair of windows (22) in the cylinder allow the pins to be seen, and also provide a mounting for an end stop (2us), which extends diametrically across the bore and radially out from the windows. A coil spring (24) is located between the end stop (23) and a shoulder (25) formed at the end of cylinder (19). In assembly, when the cylinder is placed into the position of Figure 2, the coil spring (24) is compressed and held compressed by the engagement of the pins (20) on shoulders (21). A finger (31) extending from the cylinder (19) toward the gearbox just clears the surface of the gearbox when the pins (20) are engaged. In this position, as seen in Figure 2, the cylinder (19) is spaced from an engagement spigot (26) forming part of a mounting (27) for the outer magnet (16). The spigot (26), mounting (27) and magnet (16) are assembled together on the casing (13). The shaft (11) and cylinder (19) are assembled on the gearbox (12), with the cylinder (19) in the retracted position shown in Figure 2. There is 'no connection between the two assemblies at this stage. The casing (13) is placed over the gearbox and sealed onto a bottom casing member (30). An index mechanism is then mounted on the casing (13) and covered by index housing (14). The meter is thus fully assembled, but has no connection between the gearbox and the index mechanism. In order to test and calibrate the meter it has to be subjected to flow tests in which gas is passed through the meter. When placed on test the shaft (11) begins to rotate in a clockwise direction as viewed in the direction of arrow A. The cylinder (19) rotates with the shaft (11) until the finger (31) engages a stationary trip (32) on the gearbox casing. The cylinder is then prevented from rotation. Further movement of shaft (11) moves pins (20) off the shoulders (21) thus releasing spring (24) which urges the cylinder (19) rightward as seen in the Figures to engage the spigot (26)as seen in Figure 1. Spigot (26) has two diametrically opposed pins (33), which drivingly engage the interior bore of cylinder (19). The bdre is shaped at the end of the cylinder into a squared section, the pins engaging across the corners of the square. As the cylinder (19) moves rightward the pins (20) engage again in the slots in the bore so forming a driving engagement between the shaft (11) and the cylinder. The cylinder movement also withdraws the path of the finger (31) from the trip (32). Thus the action of placing the meter on test causes the clutch to be engaged and the index mechanism connected without any other step being required. The index mechanism commences operation on connection, indicating that the clutch has been successfully engaged.

Claims: CLAIMS: 1. A method of assembling a commodity meter of the kind comprising a measuring mechanism inside a closed casing (13, 30), an index (14) mounted on the outside of a casing cover member (13) and a drive path through the casing cover member (13) from the measuring mechanism to the index (14), characterized by assembling a clutch mechanism (18) in the drive path through the steps of connecting a driving part (19, 24) of the clutch mechanism (18) to the measuring mechanism, connecting a driven part (26) of the clutch mechanism (18) to a wall of the casing cover member (13), placing the driving part (19,24)¯in a disengaged position, assembling the casing cover member (13) to the meter and operating the meter to cause the clutch mechanism (18) to engage. 2. A method as claimed in claim 1, further characterized by said step of placing the driving.part (19,24) in a disengaged position comprising retracting a cylinder (19) against spring resistance (24) and engaging the cylinder over pin means (20) whereby the cylinder (19) is held in its retracted position. 3. A method as claimed in claim 2, further characterized by said step of operating the meter to cause the clutch mechanism (18) to engage comprising causing relative rotation between the cylinder (19) and the pin means (20) whereby the pin means (20) is disengaged from the cylinder (19). 4. A method as claimed in claim 2 or claim 3, further characterized by said step of causing the clutch mechanism (18) to engage comprising allowing the spring resistance (24) to move the cylinder (19) toward the driven part (26) and to drivingly engage over it. 5. A commodity meter having a measuring mechanism inside a closed casing (13, 30), an index (14) mounted on the outside of a casing cover member (13) and a drive path through the casing cover member (13) from the measuring mechanism to the index (14), characterized by being adapted for assembly by the method of any of claims 1 to 4. 6. A commodity meter as claimed in claim 5, having a magnetic coupling (16, 16') for transferring drive through the casing cover member (13) and further characterized by said clutch mechanism (18) having a driving part (19, 24) mounted on a drive shaft (11) and a driven part (26) forming part of the magnetic coupling (16, 16'). 7. A commodity meter as claimed in claim 5, further characterized by said driving part (l9, 24) comprising a cylinder (19) slidable on said drive shaft (ill) and urged into the engaged position therealong by a spring (24), slots in said cylinder being engaged by pins (20) extending radially from said drive shaft (11), said slots ending in shoulders (21) behind which the pins (20) may engage to hold the cylinder retracted. 8. A commodity meter as claimed in claim 7, further characterized by said cylinder (19) having a finger (31) extending so that when the cylinder (19) is retracted the finger (31) engages stationary structure of the meter on rotation of the cylinder (19) with shaft (ill) whereby the rotation of the cylinder (19) is stopped and continuing rotation of shaft (11) removes pins (20) from shoulders (21).

Inventors: MICHAELIDES, CONSTANTINE, OSMOND, GRAHAM TREVOR, PYE, ALFRED EDWARD
Applicants: SMITH METERS LIMITED
Application year: 1985
Main classification: G01F15
IPC codes: G01F15, G01F3