Electricity: motive power systems – Plural – diverse or diversely controlled electric motors – Synchronizing or phasing control
Patent
1995-11-21
1998-06-16
Ip, Paul
Electricity: motive power systems
Plural, diverse or diversely controlled electric motors
Synchronizing or phasing control
318 41, 318616, 318625, 318 49, H02P 546, F04C 2900, G05D 1362
Patent
active
057676356
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to a displacement machine for compressible media, in particular a dry-running evacuation pump, having at least two rotors which are configured as profiled bodies and whose profiles engage with one another in the manner of gearwheels during rotation and run without making contact with one another, the rotors being respectively driven by their own electric motors.
(2) Description of the Related Art
These displacement machines are invariably multi-shaft machines. The rotor profiled bodies arranged on these shafts run in a housing and, specifically, with a very narrow clearance both between the flanks of the profiled bodies relative to one another and relative to the housing walls surrounding the profiled bodies at the ends and at the outer periphery. Spaces between the flanks of the individual rotors and the inner wall of the housing are released and contracted again by the rotation of the profiled bodies, it being possible for delivery medium to flow into this space through appropriately arranged control edges/ports during the release of the space and for the compressed medium to emerge again through other appropriate control edges/ports during the contraction of the space.
So that the delivery function can be fulfilled in an optimum manner, i.e so that a high efficiency and a high level of operational reliability can be achieved, the narrow clearances mentioned above, between the profiled body flanks relative to one another and relative to the housing walls, are necessary, on the one hand, because the spaces at different pressures within the pump are sealed against one another by the resulting gaps and loss flows through these gaps directly affect the efficiency of the pump. On the other hand, the rotors must however run together without making contact despite the very narrow clearance, i.e. they must rotate relative to one another at each instant in an accurately defined rotational speed relationship and with an exactly determined angular attitude or angular position.
One possibility for ensuring this synchronization is the use of gearwheels. These have a fixed arrangement on the rotor shafts parallel to the displacement bodies and are accommodated in gearboxes located to the side. This places very high requirements on the accuracy of the gearwheels and on the circumferential backlash between the flanks if the accurate running of the rotors relative to one another, as described above, is to be ensured. The same applies to the fixing of the gearwheels with respect to the setting of rotor profiles, i.e. in order to achieve this synchronization of the various rotors, a very high level of effort has to be applied to the accuracy of manufacturing and assembly. Further disadvantages of this known solution are associated with the relatively high design volume and weight and in the sealing which is necessary between the gearboxes and the pump delivery space. This sealing is necessary because the gearwheels must, of course, run with appropriate oil lubrication and oil or oil mist must not pass into the delivery medium. Particularly in the case of vacuum displacement machines, the extra requirements due to the necessary sealing between the oil-lubricated gearwheel synchronization mechanism and the desirably oil-free delivery space are very substantial because of the low absolute pressures and the simultaneously high pressure ratios. Furthermore, this sealing problem can never be solved completely satisfactorily because the shaft seals either have noticeable leakage or are subjected to very high wear.
Because of the large design volume and the weight of this solution, high costs naturally arise during the procurement and also during the assembly and dismantling--i.e. during the repair--of such a pump.
In order to avoid the disadvantages mentioned, the individual rotors can each be driven by their own electric motors and these can be controlled to run synchronously with respect to angular position and rotational speed by means of electronic
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Volk, Paul, "Automatisierung mechanischer Produktionsprozesse", Sonderdruck aus der Elektrotechnischen Zeitschrift, Ausgabe A, 83. Jahrg., 1962, 26.Heft, pp. 893-900, Siemens-Schuckertwerke AG, pp. 3-11.
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Salmen Andreas
Steffens Ralf
Ip Paul
SIHI GmbH & Co. KG
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