ELECTRIC MOTOR

Abstract: An electric motor (4, 30) enclosed in a flameproof housing (1, 2, 44) which also encloses a cavity (8) in which is a contactor (9) for the switching the motor, wiring (18) to the contactor is lead from a terminal block (11) in a separate enclosed cavity (10) through a flameproofed aperture or apertures (17) in the housing on the contactor. Cavities (8) and (10) are preferably formed in a part (2) of the housing which also provides a bracket for the rotor shaft (7). The cavities are preferably accessed from the exterior through cover plates (12, 13) the sealing planes (52, 54) of which are offset to provide additional safety. The motor provides a very safe power unit for a forecourt petrol pump.

Description: This invention relates to an electric motor for use in a potentially explosive atmosphere. When using electrical machinery in an explosive atmosphere, such as is common in or near petrol pumps, it is essential to confine any terminations, contacts or parts subject to breakdown within a flameproof housing to prevent sparks or flames reaching the surrounding potentially explosive atmosphere. Furthermore the housing must be strong enough to withstand the pressure developed by an explosion within the housing. When using such motors for petrol pumps the capacitor start induction run flameproof petrol pump motor has firmly established itself by virtue of its cheapness of construction utilising as it does a squirrel cage rotor and minimum maintenance. Single phase motors are used mainly in the U.K., U.S.A., and their export territories. Three phase motors are common in Europe. To facilitate ease of control and in order to prevent such a motor being a hazard in a petrol pump two approaches have been used. The British and U.S. approach for electronically controlled petrol pumps has been to provide a single phase motor switched by a separate solid state relay nearby in the pump casing with a signal line running to the: kiosk from the control unit of the pump. The motor is fully flameproofed to British Standards BS 5501 parts 1 and 5 (European Standards EN 50 014 and 50 018 respectively) and is normally referred to as an Ex'd' motor. The installation is very safe but the solid state relay is subject to overloads which can cause the relay to break down and the motor control to fail. The continental approach has been to provide a three phase motor protected to a lesser standard see British Standards BS 5501 part 6 (European Standard EN 50 019) and is normally referred to as an Ex'e' motor. This type of motor is substantially cheaper than the Ex1d' motor but to prevent a dangerous overheating of the Exte' motor it is necessary to provide a carefully matched and therefore expensive contactor to break the current supply in the event of overheating. Furthermore to ensure safety it is necessary to locate the contactor well away from the pump which in a typical forecourt installation means the kiosk. To control this contactor it is necessary to run the contactor controls from a solid state pump relay in the pump casing back to the remote contactor and then run the cables for the power supplies from the remote contactor back to the pump and to the motor. This is expensive in cabling and when a typical forecourt with several pumps is considered expense is clearly multiplied by the number of pumps. Furthermore the motor itself is inherently less safe than a conventional Vex'do motor. According to the present invention a motor is enclosed with a flameproof housing and one or more sealed flameproof apertures in the housing to provide for entry of wiring into the housing for connecting the motor to an exterior power supply, the housing comprising a body shell having a first end member in which one end of the rotor is journalled and a second end member in which the other end of the rotor is journalled characterised in that the housing also encloses a first cavity in which a remotely operable contactor is mounted, the contactor being wired operatively to the motor, wherein the housing defines a second cavity or wherein a wall means is mounted on the housing defining a second cavity, the second cavity containing a terminal block, wiring from the block to the contactor operative to control the contactor and wiring from the block to the contactor for supplying power to the motor, the wiring from the block being passed from the second cavity through the flameproof aperture or apertures to the contactor. By locating the contactor adjacent the motor stator and rotor within the flameproof housing several important advantages ensue. Firstly the contactor control cables can be provided as a short run from a solid state relay within the pump casing thereby saving a long control cable run to a remote contactor. Secondly the power cables need only be run once from the kiosk to the pump and then on to the next pump thereby considerably shortening the power cable runs. Thirdly the risk of overloading the relay is eliminated by considerably reducing the maximum current to the relay to typically less than 0.1 amps at 230 volts, and this reduces pump failure and consequential maintenance. Fourthly the motor is rendered inherently much safer. Fifthly matched contactors are not required which reduces costs. Preferably the enclosure means forms a part of the second end member so that the second end member at least partly encloses the second cavity. In this way a simple casting may be provided which is economically advantageous. Further economies result if both cavities are provided at least partially in the second end member. Preferably access covers for each cavity are provided to give easy access to the contactor and terminal block. In order to ensure that the contactor cavity is fully flameproofed the contactor cavity access plate is carefully dimensioned with a planar flanged and bolted sealing joint of a width at least 9 mm from the interior to the bolt holes and preferably with a total width across the face of the joint not less than 12.5 mm and preferably 22 and 30 mm, In order to prevent a pressure blow out causing a flash between the two cavity covers the covers are preferably arranged so that the sealing plane of each cover are in separate planes. One cover plate may be facing away radially with respect to the motor axis to the other cover plate but it is most convenient for installation and mai-ntenance to have both cover plate facing in a single direction at one end of the motor. In order to provide planar separation of the sealing surfaces it is preferable to set one plate back from the other to obtain a planar separation of at least 4 mm and for the sake of safety this separation should be preferably between 15 and 25 mm. The invention further extends to a forecourt petrol pump having a casing, a hose, a gun type lever operable nozzle on the hose, a pump control means in the casing operable by the gun type lever, the control means including a relay to operate a pump motor contactor and thence an electric pump motor enclosed in a flameproof housing and one or more sealed flameproof apertures in the housing to provide entry of wiring into the housing for the connecting the motor to an exterior power supply, the housing comprising a body shell surrounding the motor stator and rotor and a first end member in which one end of the rotor is journalled and a second end member in which the other end of the rotor is journalled, characterised in that the housing also encloses a first cavity in which the contactor is mounted, wherein mounted to the housing in an enclosure means defining a second cavity containing a terminal block, wiring from the block to the contactor and wiring from the block to the contactor for supplying power to the motor, the wiring from the block being passed from the second cavity through the flameproof aperture or apertures to the contactor. Preferably the enclosure is an integral part of the second end member and provides a second cavity for the terminal block sealed by a separate cover plate. In order that the invention may be fully understood, preferred embodiments thereof will now be described with reference to the accompanying drawings in which: Figure 1 is a longitudinal cross-sectional view of a flameproof housing in accordance with this invention and enclosing a squirrel cage motor; Figure 2 is a transverse cross-sectional view of the housing shown in Figure 1; Figure 3 is a cross-section through that part of the housing through which leads connecting a terminal block to a contactor pass and which incorporates a flameproof barrier; Figures 4 and 5 shows a modification of the way in which the leads are held in a flameproof barrier shown in Figure 3; ; Figure 6 shows diagrammatically a typical forecourt petrol pump having the motor of Figure 1 and Figure 7 shows in partial cross-section a manual resetting thermal cut-out fitted as an optional feature to the housing of the motor of Figure 1. The flameproof housing shown in Figures 1 and 2 comprises a formed steel sheel body 1 manufactured from carbon steel sheet, a first end member 44 (not shown in Figure 1) and a second end member 2, a rotor shaft 3 for the rotor 30 of a three phase squirrel cage induction motor being rotatably supported in the first and second end members with the motors' stator 4 located within the shell body 1. The second end member 2 comprises a casting having a wall 5 housing centrally thereof a bearing 6 for end 7 of the rotor shaft 3, a first cavity 8 formed in the casting housing a conventional 3 phase contactor 9 and a second cavity 10 housing a terminal block 11. A cover plate 12 seals the first cavity 8 and a cover plate 13 seals the second cavity 10. The flatness and width of the flange faces 14 of the first cavity 8 and the mating surfaces 15 of the cover plate 12 must be such as to provide a flameproof barrier between the inside of the cavity 8 and the atmosphere surrounding the casting, meeting the requirements set out in the aforementioned BSI standard 5501 Part 5 (EN 50 018). The seal between the cover plate 13 and the second cavity 10 is not so critical and need not necessarily be flameproof as a flameproof barrier 16 is provided between the cavity 10 and the interior of the shell body 1. The barrier 16 may be formed from a twopart epoxy quick setting putty inserted in an aperture 17 in the wall 5 through which passes leads 18 from the terminal block 11 mounted on a bracket 20 in the cavity 10, the leads then passing through another aperture 21 in the wall 5 to the contactor 9. The leads pass through a red fibre separator 22 in the aperture 17 and either have cable clips fitted to the leads, as shown in Figure 3, or the leads are knotted as shown in Figure 4 to provide a firm anchorage in the epoxy quick setting putty. In a further embodiment shown in Figure 5 the aperture 17' is threaded and a gland or bushing 24 with hexagonal head 25 is screwed into the aperture. The cables 18 are set into the gland with a resin 26 and the gland is given an outer coating of a suitable retainer such as Loctite (Trade Mark) to prevent vibration from loosening the gland. Thus the enclosure formed by the body shell 1 and the cavity 8 is rendered flameproof, communication between the shell and cavity 8 being provided by the aperture 21. The leads from the motor are connected to the contactor 9 via the aperture 21 and leads from the contactor are passed through the flameproofed aperture 17 to the cavity 10. It is not necessary for the enclosure for the terminal block 11 formed by cavity 10 to be part of the casting, it could be a separate box but making the enclosure an integral part of the end member saves costs and allows for short runs of lead between the terminal block 11 and the contactor 9. One or more cable entries 23 are provided at the top of the casting leading into the cavity 10 to accommodate power cables 32 and leads 34 for a contactor coil energizing signal from a solid state relay 36 in the computing head 38 of a petrol pump 40 (see Fig. 6). The housing described herein is adapted for a motor having a shaft extending from the bearing 6 out of the first end member 44 to a pump 42 - but a double ended shaft may be used. The first end member has a shaft to housin-g bearing (not shown) with a flame restricting path which forms a flameproof joint of the kind for instance as shown in BS 5501 Part 5 (EN 50 018) Flameproof enclosure 'd' at Figure 15 or Figure 17. The enclosure formed by the end member 44, shell 1 and cavity 8 sealed by cover plate 12 is constructed to withstand a predetermined internal pressure so that it will contain an explosion or rapid pressure increase within the housing. The sealing of the cover plate 12 onto the casting forming wall 5 as previously indicated is carefully formed to standard BS 5501 Part 5 (EN 50 018) and the flange faces 14 and the metal to metal mating surfaces 15 have a surface finish of 6.3 The width of the sealing joint from the interior to bolt hole 50 is a minimum of 8 mm according to the above standard but preferably at least 9 mm. The total width of the flanged joint 52 across the bolt holes is between 22 and 30 mm and with a minimum requirement of 12.5 mm and preferably 26 mm. It will be seen in Figure 1 that cover plate 13 with its planar sealing joint 54 is set back from joint 52, the planes of the joints being parallel and separated from each other by at least 4 mm and preferably between 15 and 25 mm. The reason for this is to prevent pressure piling jumping across the gap between the plates and is an important feature of the housing design. Whilst similar protection would be given by placing the covers on diametrically opposite sides of the housing so they faced away from each other, it is more convenient for installation and maintenance to have both covers facing the same way and preferably facing axially outwards. In Figure 7 a thermal cut-out 60 is shown which may be fitted as an optional item to the inside of cover plate 12. The cut-out is connected by leads 62 in the operating coil circuit of the contactor 9. A manual reset button 64 projects through a small close fitting aperture 66 in the cover plate such as will not destroy the flameproof integrity of the cover plate. The cut-out 60 is provided to give additional safety for the motor so that when a predetermined excess temperature is reached in the enclosure formed in shell 1 and cavity 8, the contactor operating circuit is broken and the motor is switched off. A typical layout of a forecourt pump 40 is shown in Figure 6 in which the described flameproofed motor is fitted. It will be seen that the only high power cables running to the forecourt pump are those at 32 carrying a normal full load of about 2.2 amps for a 230 volt 0.5 HP (o.37 kW) motor Leads 68 for very low power signal currents run from the computer head 38 to the kiosk where the pump monitor is located. Low power ancillary leads may of course be provided for example pump illumination. Whilst the embodiment described above utilises a three phase motor, a single phase motor may be used instead with an appropriate contactor mounted in the first cavity 8 along with the capacitor and centrifugal switch required for a capacitor start induction motor. By providing a flameproof housing as described above which contains both the motor and the contactor, substantial cable runs are avoided which reduces the costs of a petrol pump forecourt installation. Whilst the flameproof housing disclosed herein has been described with reference to its use in a petrol pump, it will be appreciated that such a housing and motor may be used to drive other forms of machinery, such as fans, in a hazardous environment.

Claims: CLAIMS: 1. An electric motor enclosed in a flameproofed housing and one or more sealed flameproof apertures in the housing to provide for entry of wiring into the housing for connecting the motor to an exterior power supply, the housing comprising a body shell having a first end member in which one end of the rotor is journalled and a second end member in which the other end of the rotor is journalled, characterised in that the housing (1, 5) also encloses a first cavity (8) in which a remotely operable contactor (9) is mounted, the contactor being wired operatively to the motor, wherein the housing defines a second cavity (10) or wherein a wall means is mounted on the housing defining a second cavity, the second cavity containing a terminal block (11), wiring (18) from the block to the contactor operative to control the contactor and wiring (18) from the block to the contactor for supplying power to the motor, the wiring from the block being passed from the second cavity through the flameproof aperture or apertures to the contactor. 2. An electric motor as claimed in Claim 1 further characterised in that the second cavity (10) is defined by a part (5) of the second end member (2), so that the second end member at least partly encloses the second cavity (10). 3. An electric motor as claimed in Claim 1 or 2 further characterised in that the first cavity (8) is formed within at least a part (5) of the second end member (2) so that the second end member at least partly encloses the first cavity (8). 4. An electric motor as claimed in any one of Claims 1 to 3 wherein one or other of the cavities (8, 10) are provided with a cover plate (12, 13) which can be removed to give access to the one or other of the cavities from the exterior of the housing. 5. An electric motor as claimed in any one of Claims 1 to 3 wherein both cavities (8, 10) are provided with a cover plate (12, 13) which can be removed to give access to the cavities from the exterior of the housing. 6. An electric motor as claimed in Claim 5 wherein both cover plates are arranged to seal around paths (52, 54) in planes separated from each other. 7 An electric motor as claimed in Claim 6 wherein the sealing planes (52, 54) are substantially parallel and separated from each other by at least 4 mm and preferably between 15 and 25 mm. 8. An electric motor as claimed in Claims 1 to 7 wherein the cavity (8) for the contactor (9) is covered by a cover plate (12) having a planar flanged and bolted sealing joint (52) of a width across the joint at least 9 mm from the interior to bolt holes (50) for bolts securing the plate and preferably with a total width across the bolt holes of between 22 and 30 mm. 9. An electric motor as claimed in any one of Claims 1 to 8 wherein the motor is a three phase AC motor of the squirrel cage induction type. 10. A forecourt petrol pump having a casing a hose, a gun type lever operable nozzle on the hose, pump control means in the casing operable by the gun type lever, the control means including a relay to operate a pump motor contactor and thence an electric pump motor enclosed in a flameproof housing and one or more sealed flameproof apertures in the housing to provide entry of wiring into the housing for the connecting the motor to an exterior power supply, the housing comprising a body shell surrounding the motor stator and rotor and a first end member in which one end of the rotor is journalled and a second end member in which the other end of the rotor is journalled characterised in that the housing also encloses a first cavity in which the contactor is mounted, wherein mounted to the housing is an enclosure means defining a second cavity (10) containing a terminal block (11), wiring (18) from the block to the contactor operative to control the contactor and wiring (18) from the block to the contactor for supplying power to the motor, the wiring from the block being passed from the second cavity through the flameproof aperture or apertures to the contactor. 11. A forecourt petrol pump as claimed in Claim 10 and any one of Claims 2 to 8.

Inventors: WILLIAMS, NORMAN ERNEST
Applicants: TUSCAN ENGINEERING COMPANY LIMITED
Application year: 1983
Main classification: H02K5
IPC codes: H02K5, H02K17