Title of Invention	METHOD FOR TEMPERING A SCREWTYPE VACUUM PUMP AND A SCREW TYPE VACUUM PUMP
Abstract	This invention relates to a screw vacuum pump (1) is tempered such that characteristics of the pump are not substantially altered when the pump is subjected to thermal stress. In order to achieve said aim, cooling is adjusted according to an operating state of the screw-type vacuum pump (1), preferably to nraintain a substantially constant pump gap (4).

Full Text

FIELD OF INVENTION The invention relates to a method for tempering a screw-type vacuum pump. The Invention further relates to a screw-type vacuum pump for implementing said method. BACKGROUND OF INVENTION From DE-A-198 20 523 a screw-type vacuum pump of the here affected kind is known. The multitude of heat problems has been disclosed. Cooling of the rotors revolving in a pump chamber Involves special difficulties when the threads of the rotors exhibit a pitch which decreases from the intake side to the delivery side, frequently even also in combination with an increase in the width of the thread ridges. Rotors of this kind are subjected during operation to severe thermal stresses, in particular in the area of their delivery side, since the compression of the pumped gases produces a not insignificant amount of heat. Since the quality of a screw-type vacuum pump depends significantly on the gap between the rotors and the pump chamber housing, the manufacturers strive to keep this gap ver/ small. However, opposed to this aim is the thermal expansion of the thermally highly stressed areas, rotors and housing. The pump chamber housing does not, or only slightly, take part in the thermal expansion of the rotors. A sufficiently large gap must be present. It was previously only in this manner possible to prevent the rotors from making contact with the housing with the attendant risk of standstill seizing. The problem detailed grows to be particularly grave when the rotors and the housing consist of different materials. In the instance of the coefficient of expansion of the housing being smaller than the expansion of coefficient of the rotor material (for example, housing made of cast iron, rotors of aluminium) there exists the risk of the rotors running against the lousing. If the reverse expansion conditions exists, the pump's gap can Increase :;uch that the performance of the pump decreases. OBJECTS OF INVENTION It is the task of the present invention to design and be able to operate a screw- type vacuum pump of the affected kind such that during thermal stresses Its properties will not change substantially. SUMMARY OF THE INVENTION This task is solved by the present invention through the characterizing features as disclosed hereinafter. Through the present invention it is possible to have an Influence on the effect of the cooling, respectively tempering, with the aim of permitting a temperature Increase In the pump chamber housing which does not exceed Inadmissible limits. During an increased thermal stress on the pump, the only slightly cooled pump chamber housing expands jointly with Its rotors. The risk of making contact does no longer exist. The cooling system is controlled expediently such that the size of the gaps in the pump chamber housing remains substantially unchanged during the different operating conditions. For example, the outside temperature of the pump chamber housing may be employed as the controlled variable. If the screw-type vacuum pump is air cooled, then the cooling air flow may be controlled depending on the operating status of the pump, for example by controlling the rotational speed of a fan producing the cooling air flow. This requires that the fan be equipped with a drive being independent of the drive motor of the pump. If the fan is linked to the drive of the pump, control of the cooling air flow can be implemented with the aid of adjustable screens, throttles or alike. If the pump is cooled by liquids, control can be effected by adjusting the quantity (flow rate) or the temperature of the cooling liquid. If the pump is air cooled form the outside and if its rotors are equipped with a liquid cooling system, it is expedient to arrange a heat exchanger in the cooling air flow so as to dissipate the heat dissipated by the liquid (oil, for example). When said heat exchanger is arranged, with respect to the direction of the flowing cooling air, upstream of the pump chamber housing, well-aimed tempering of the pump chamber housing is possible. Again, the outside temperature of the pump chamber housing may serve as the controlled variable; also the temperature of the cooling liquid may be employed as the controlled variable. Arrangements of this kind allow, above all, cooling of the pump to be controlled such that the gap between the rotors and the housings is maintained during operating of said pump at a substantially constant width. Moreover, it is expedite when the pump is equipped with an inner a rotor cooling system (liquid) and a housing cooling system (from the outside with liquid), and where both cooling systems are controlled matched to each other such that during all operating modes of the pump a substantially constant gap is maintained. The desired control with the aim of a constant gap is effected such that the quantities of liquid supplied to the cooling systems for example with the aid of a heat exchanger, are contro9lled depending on cooling demand. In order to be able implement the desired control, the utilization of sensors is required. These may be temperature sensors, the signals of which are supplied to a control centre. The control centre in turn regulates the intensity of the cooling, preferably in such a manner that the pump gap is maintained at a substantially constant width. Instead of one or several temperature sensors, also a distance sensor may be employed which supplies direct information on the size of the gap. BRIEF DESCRIPTION OF THE ACOMPANYING DRAWINGS Further advantages and details of the present invention shall be explained with reference to the examples of embodiments depicted in the accompanying drawing figures 1 to 4. Depicted are in - drawing figure 1, an air cooled screw-type vacuum pump - drawing figures 2 and 3 each an air and liquid cooled screw-type vacuum pump and - drawing figure 4, a screw-type vacuum pump equipped with two cooling systems. DETAIL DESCRIPTION OF INVENTION In the drawing figures, the screw-type vacuum pump to be cooled is designated as 1, its pump chamber housing with 2, its rotors with 3, the gap on the delivery side between the rotors 2 and the pump chamber housing 2 with 4, its inlet with 5 and the gear/motor chamber housing adjacent with respect to the pump chamber housing 2 containing the rotors 3 is designated as 6. It is only schematically outlined that the rotors 3 are equipped with threads, with their pitch and ridge width decreasing from the intake side to the delivery side. An cutlet located on the delivery side is not depicted. Located in housing 6 Is gear chamber 7, the motor chamber 8 with the drive motor 9 and a further chamber 10, being the bearing chamber (drawing figure 1) or part of a cooling liquid circuit for the rotors 3 (drawings figures 2 and 3). The rotors 3 are equipped with shafts 11, 12 which penetrate the gear chamber 7 and the motor chamber 8. By means of bearings in the separating walls between the pump chamber and the gear chamber 7 (separating wall 14) as well as motor chamber 8 and bearing respectively a cooling liquid chamber 10 (separating wall 14), the rotors 3 are suspended in a cantilevered manner. The separating wall between gear chamber 7 and motor chamber 8 is designated as 15. Located in the gear chamber 7 is the [pair of toothed wheels 16,17 effecting the synchronous rotation of the rotors 3. The rotor shaft 11 forms simultaneously the drive shaft of the motor 9. The motor 9 may exhibit a drive shaft different from the shafts 11,12. In the instance of such a solution, the drive shaft of said motor terminates in gear chamber 7 and is there equipped with a toothed wheel. which engages with one of the synchronising toothed wheels 16,17 or a further toothed wheel, not depicted, of the shaft 12), In the embodiments according to the drawings figures 1 to 3, cooling of the housings 2 and 6 of the pump 1 is effected with the aid of a flow being produced by the wheel 20 of a fan 21. A housing 22 encompassing the pump 1 serves the purpose of guiding the air movement produced by blade wheel 20, said housing being open (apertures 23, 24) in the area of both its face sides. Fan 21 is arranged such that the aperture 24 on the fan/motor side of the housing 22 forms the air inlet aperture. In the embodiments according to the drawing figures 1 and 2, the fan 21 ahs a drive motor 25 being independent of the drive mdtor 9 of the pump 1. This solution is advantageous for screw-type vacuum pumps, the motor 9 of which is designed by way of a canned motor, thereby being encapsulated. In the embodiments according to the drawing figures 3 and 4, the shaft 11 penetrates the chamber ID, is run out of the housing 6 of the pump 1 and carries at its unoccupied end the wheel 20 of the ventilator or fan 2l. In all drawing figures a control facility is in each instance schematically represented by way of block 26. It is linked through lines depicted by way of dashed lines to sensors supplying the signals of desired manipulated variables. As examples, two alternatively or simultaneously employable temperatuie sensors 27 and 28 are outlined. Sensor 27 supplies signals corresponding to the temperature of the housing 2. Said sensor is preferably affixed at the housing 2 in the area of the delivery side of the rotors 3. Sensor 28 is located in the motor chamber 8 and supplies signals which correspond to the temperature of the cooling liquid, respectively oil temperature. Through further lines the control facility is linked in each instance to facilities aiding controlled cooling of the pump 1 in the desired manner. In the embodiment according to drawing figure 1, the air flow produced by the fan 21 Is controlled. For this purpose the control facility 26 is connected through the line 29 to the drive motor 25. Corresponding to the signals supplied by one or both sensors 27 or 28, control of the rotational speed of the blade wheel 20 s effected. Since the signals supplied by sensors 27 provide information on the housing temperature and the signals supplied by sensors 28 provide information on the rotor temperature, the utilization of both sensors can be employed to perform a different control with respect to the gap 4. In the instance of an alternative solution, only one sensor 29 may sensor 29 may be provided instead of the two temperature sensors 27,28, said sensor 29 being located, for example, at the location of the temperature sensor 27, i.e. in the area of the delivery side of the pump chamber 2. This sensor 29 is a distance sensor which supplies direct information as to the magnitude of the pump gap 4. Sensor of this kind are basically known. Changes in capacitance or - preferably - changes in an eddy current which occur depending on the size of the gap are employed for producing the sensor signals. Alone depending on one sensor 29 of this kind, tempering of the pump 1 can be controlled. If, for example, during operation of the pump the size of the gap decreases in that the rotors 3 expand, cooling of the housing 2 is reduced by reducing the quantity of cooling air by a reduction in speed of the ventilator 20. Thus the housing expands so that the decrease In gap size can be compensated. If during operation of the pump 1 the gap size increases, this increase may be compensated by increasing the cooling effect (shrinking of housing 2). The embodiment according to drawing figure 2 differs from the embodiment according to drawing figure 1 in that the pump 1 is equipped with a liquid cooling system for the rotors. The cooling liquid circuit for cooling the rotors 3 is only outlines schematically. In the German patent applications 167 45 616, 199 63 171.9 and 199 63 172.7 cooling systems of this kind are described in detail. The shafts 11 and 12 serve the purpose of transporting the coolant (oil, for example) to and from the rotors 3. In the example of an embodiment presented, the coolant exiting the rotors 3 collects in the motor chamber 8. From there it is supplied through the line 31 to a heat exchanger 32. The heat exchanger 32 may be air or water cooled. Especially expedient - as depicted - is an arrangement where the air flow produced by the fan 21 dissipates the heat dissipated by the cooling liquid in the rotor 3. The liquid exiting the heat exchanger 32 is supplied through the line 33 into the chamber 10. In a manner not depicted in detail said cooling liquid passes from there through bores located in the shafts 11,12 to the rotors 3, flows there through cooling ducts and passes through the shafts 11,12 back into the motor chamber 8. In order to control the liquid cooling system, two alternatives for the actuating variable (already described sensors 27, 280 and two alternatives for controlled cooling of the cooling liquid in the heat exchanger 32 are depicted in drawing igure 2. Either, as depicted in drawing figure 1, the rotational speed of a blade (A/heel 20 is controlled depending on one of the manipulated variables. In the instance of the other alternative there is located in the line a control valve 35 which defines the quantity of cooling liquid flowing through the heat exchanger per unit of time. In the instance of the solution according to drawing figure 2 the pump 1 may be tempered in addition by the air flow of the fan 21. In this Instance it is expedient to arrange the heat exchanger 32 and fan 21 in the area of the aperture 24. The advantage of this arrangement is such that the air flow cooling the pump chamber housing 2 of the pump 1 is pre-warmed. In this manner it is achieved that thermal expansions of the pump chamber housing 2 are allowed to such an extent that the rotors 3 which during operation of the pump 1 attain relatively high temperatures, will not make contract with the housing 2. Preferably the housing 2 and the rotors 3 consist of aluminium for the purpose of improving heat conductance. Moreover, the housing 2 may exhibit fins for improving thermal contact. Irrespectively whether the air flow produced by fan 21 cools only the heat exchanger 32 or the heat exchanger 32 and the housing 2, 6 of the pump, it is expedient to locate the heat exchanger 32 upstream of the blade wheel thereby ensuring a means of touch protection. In the instance of the solution according to drawing figure 3, the blade wheel 20 is coupled to the motor shaft 11. Since screw-type vacuum pumps are commonly operated at constant rotational speeds, there no longer exists the possibility of controlling the air flow with the aid of the fan 21. For the purpose of controlling the air flow, a controllable aperture (iris aperture for example) throttle or alike is provided in the instance of the embodiment according to drawing figure 3. Said aperture is located between the blade wheel 20 and the heat exchanger 32, is only depicted schematically and reference number 32 has been assigned to it. Through the line 37 the aperture 36 is connected to the control facility 26. Control of the magnitude of the cooling air flow and/or cooling of the liquid is effected is effected corresponding to the control arrangement detailed for drawing figure 2 by controlling the flow cross-section of the air flow, preferably wi :h respect to a constant gap size. Additionally, the cooling liquid circuit in the instance of the solution according to drawing figure 3 is equipped with a thermostatic valve 38. It is located in the line 31 and is preferably also controlled by the facility 26. During the phase of operational start-up of pump 1 in which the cooling liquid has not yet attained its operating temperature, said thermostatic valve has the task of blocking the line 31 and supplying the cooli8ng liquid through the bypass line 39 directly into line 33 by passing the heat exchanger. When the temperature of the cooling liquid has attained its operating temperature, line 39 is blocked and line 31 is opened (drawn position of the valve 38). The bypass solution reduces the time needed for the start-up phase. In the example of the embodiment according to drawing figure 4, the screw-type vacuum pump is equipped with the already described inside cooling system for the rotors as well as with a housing cooling system 41 operated with a liquid. Said housing cooling system comprises a cooling jacket 42 (filled with liquid, for example) located at the outlet area of the rotor housing 2, where in said cooling there is located a cooling coil 43 through which the actual coolant flows. Alternatively the cooling liquid may flow also through the cooling jacket 42 Itself. In the presented example of an embodiment, the outlet of the housing cooling system is linked to the motor chamber 8 into which also the cooling liquid exiting the internal rotor cooling system flows. Through the line 31 the cooling liquid passes into the heat exchanger 32. Connected downstream thereto is the line 44 with a 3/2 way valve 47 which allows splitting of the quantities of the cooling liquid supply between the lines 45 and 46. Line 45 is linked to the inlet of the internal rotor cooling system, line 46 is linked to the inlet of the outer housing cooling system 41. The valve 47 is a control valve being controlled by the controller 26. In the example of the embodiment according to drawing figure 4 the ventilator 20 and the heat exchanger 32 are located, as in the instance of the embodiment according to drawing figure 2 and 3, in the area of the aperture 24 of the housing 22. Since cooling by an air flow is no longer an absolute necessity (if need be only for cooling the motor and gear housing 6), the heat exchanger 32 and its cooling system (air or liquid) may also be arranged at a different location and independently of the drive motor 9. For cooling circuits also separate heat exchangers may be provided. Finally, the housing 22 need not be present. In the embodiment according to drawing figure 4 tempering of the pump 1 may - as also in the instance of all other examples of embodiments - be effected such that its pumping gap 4 is maintained substantially constant. The sensors 27 and 28 supply signals which are related to the temperature of the housing 2 on the one hand and the rotors 3 on the other hand. Depending on these signals the valve 45, respectively the split of the cooli8ng liquid shares to both cooling systems is controlled. In all, the features according to the present invention permit a further increase in performance density of a screw-type pump. The pump may be designed to be smaller and may be operated at higher surface temperatures. The outer housing 22 serving the purpose of guiding the air also serves the purpose of providing a means of touch protection. It has been found expedient to adjust the cooling, respectively tempering system such that in the instance of two cooling system (inner rotor cooling system and outer housing cooling system) approximately half of the heat produced by the pump is dissipated by each of the two cooling systems. WE CLAIM 1. Method for tempering a screw-type vacuum pump (1), characterized in that cooling of the pump chamber housing (2) and rotors (3) Is controlled to ensure equal thermal expansion or contraction so that said rotors do not run against pump chamber housing during operation. 2. Method as claimed in claim 1, wherein cooling control is implemented such that between the rotors (3) and their housing (2) a substantially constant gap (4) is maintained during operation. 3. Method as claimed in claim 1 or 2, wherein cooling control is effected depending on the outside temperature of the pump chamber housing (2). 4. Method as claimed In claim 1,2 or 3, wherein the pump (1) is cooled from the outside with an impelled air flow. 5. Method as claimed in claim 4, wherein a fan (21) produces the Impelled air flow and wherein the rotational speed of the blade wheel (20) is controlled. 6. Method as claimed in claim 4 or 5, wherein the impelled air flow is produced by a fan (21) and wherein the flow cross-section of the air flow is controlled. 7. Method as claimed in one of the claims 1 to 6, wherein the pump Is cooled from the outside and wherein the rotors are cooled from the inside. 8. Method as claimed in one of the claims 1 to 7, wherein the rotors of the screw - type vacuum pump (1) are cooled with the aid of a liquid cooling system. 9. Method as claimed in claim 8 and one of the claims 4 to 7, wherein an external heat exchanger (32) for the cooling liquid is being cooled by the impelled air flow. 10. Method as claimed in claim 1, 8 or 9, wherein the screw-type vacuum pump (1) is equipped with a liquid cooling system for Its rotors (3) and wherein control of the liquid cooling system is effected depending on the temperature of the cooling agent. 11. Method as claimed in claim 9, wherein besides the inner rotor cooling system a liquid housing cooling system (41) is employed. 12. Method as claimed in one of the claims 7 to 10, wherein an themrial heat exchanger (32) with controller heat exchange for controlling the cooling system is employed, with the cooling liquid flowing through said heat exchanger. 13. Method as claimed in claim 11, wherein the quantity of liquid flowing through the heat exchanger (32) is controlled. 14. Method as claimed in one of the claims 10,11 or 12, wherein the liquid exiting the heat exchanger (32) is supplied to the Inner rotor cooling system and the housing cooling system (41), and wherein the liquid shares are controllable. 15. Method as claimed in claim 14, wherein to each of the cooling circuits a separate heat exchanger is assigned. 16. Method as claimed in one of the claims 7 to 14, wherein the quantity of heat dissipated from the internal rotor cooling system and the quantity of heat dissipated from the housing cooling system are approximately equal. 17. A cooled screw vacuum pump, having a suction side and a pressure side (17,18), comprising a housing (4) and two rotating systems (5,6), each system comprising a screw rotor (5), a shaft (6), mutually spaced bearings (7,8) on each shaft (6) supporting the rotors (5) in a cantilever fashion characterized in that, the bearings (7,8) being disposed on the same side of the rotors (5), and a cavity (31) defined In each rotor (5), open on the bearing side (34), within which cavity (31) there is respectively located a cooling element (36) which cools the rotor (5) internally, the bearing (7,8) closest to the rotor (5) being located outside the cavity (31) in the rotor (5). 18. Pump as claimed in claim 17, wherein for the purpose of producing an Impelled air flow, a fan (21) is provided being equipped with means of speed control or means of air mass flow control. 19. Pump as claimed In claim 18, wherein fan (21), drive motor (9) and pump housing (2) are arranged after each other in the direction of the flow. 20. Pump as claimed in claim 17, 18 or 19 wherein at least the pump housing (2) is equipped with outer fins. 21. Pump as claimed in one of the claims 17 to 20, wherein the housing (2) and the rotors (3) consist of aluminium. 22. Pump as claimed In one of the claims 17 to 21, wherein an outer housing (22) for guiding the cooling air is provided and where the fan (21) is located on the air inlet side (24). 23. Pump as claimed in claim 17, wherein it is equipped with a liquid inner rotor cooling system and with a liquid housing cooling system. 24.Pump as claimed in one of the claims 17 to 23, wherein for the purpose of cooling liquid, one or two heat exchanger/s (32) is/are provided. 25. Pump as claimed in claim 23 or 24, wherein the cooling liquid circuit is equipped with a control valve (35). 26. Pump as claimed in claim 23,24,25, wherein the liquid circuit is equipped with a thermostatic valve (38) which links either the supply line (31) to the inlet of the heat exchanger (32) or links the supply line to a bypass line (39) bypassing the heat exchanger (32). 27. Pump as claimed in one of claims 17 to 26, wherein it is equipped with a liquid cooling system and an air cooling system and an air cooling system and an air cooling system and wherein the fan (21) serving the purpose of air cooling also effects cooling of the heat exchanger (32) of the liquid cooling circuit. 28. Pump as claimed in claim 27, wherein the heat exchanger (32) is located in the cooling air flow upstream of the fan (21). 29. Pump as claimed in one of the claims 23 to 28, wherein the liquid housing cooling system (41) is located in the area of the delivery side of the pump housing. 30. Pump as claimed in claim 22 and claim 27 or 28, wherein the inlets of the inner rotor cooling system and the housing cooling system (41) are connected through a control valve to the outlet of the heat exchanger 31. Pump as claimed in claim 28, 29 or 30, wherein the outlets of the liquid cooling systems open out into the motor chamber (8). Dated this 18th day of May, 2004 This invention relates to a screw vacuum pump (1) is tempered such that characteristics of the pump are not substantially altered when the pump is subjected to thermal stress. In order to achieve said aim, cooling is adjusted according to an operating state of the screw-type vacuum pump (1), preferably to nraintain a substantially constant pump gap (4).

Documents:

645-KOLNP-2004-FORM 27.pdf

645-KOLNP-2004-FORM-27-1.pdf

645-KOLNP-2004-FORM-27.pdf

645-kolnp-2004-granted-abstract.pdf

645-kolnp-2004-granted-claims.pdf

645-kolnp-2004-granted-correspondence.pdf

645-kolnp-2004-granted-description (complete).pdf

645-kolnp-2004-granted-examination report.pdf

645-kolnp-2004-granted-form 1.pdf

645-kolnp-2004-granted-form 18.pdf

645-kolnp-2004-granted-form 26.pdf

645-kolnp-2004-granted-form 3.pdf

645-kolnp-2004-granted-form 5.pdf

645-kolnp-2004-granted-reply to examination report.pdf

645-kolnp-2004-granted-specification.pdf

645-kolnp-2004-granted-translated copy of priority document.pdf