Title of Invention

A SCREW-TYPE VACUUM PUMP HAVING IMPROVED COOLING SYSTEM

Abstract

This invention relates to a screw-type vacuum pump (1) having Improved cooling system, comprising; an inner pump housing (2,6); a pair of rotors (3,4) rotatably mounted in the inner pump housing (2,6); a drive motor (9) mounted in the inner pump housing (2,6); an outer housing (22) displaced from the Inner pump housing (2,6) to define a passage (23,24) for cooling air therebetween, such that cooling air flowing between the inner and outer housings (2,6,22) removes heat from the rotors (3,4) and drive motor (9); a liquid cooling system (8,10,11,12,26) for circulating a cooling liquid for cooling the drive motor (9) and the rotors (3,4); a heat exchanger (25) mounted to pre-heat the cooling air upstream of the inner housing (2,6), the heat exchanger being connected with the liquid cooling system to move heat from the cooling liquid to the cooling air.

Full Text

FIELD OF INVENTION The invention relates to a screw-type vacuum pump comprising a pump housing with rotors arranged therein, a liquid cooling system for the rotors and a drive motor. More particularly, the invention relates to a screw-type vacuum pump having improved cooling system. BACKGROUND OF INVENTION From DE - A-198 20 523 a screw -type vacuum pump with these characteristics Is know. Said document discloses, moreover, the multiple problems Involved in cooling screw-type vacuum pumps when these shall be built for, and operated at high performance densities - compact and operating at high rotational speeds. BE 1008367 discloses a screw compressor with two cooling systems. The first cooling system is using oil, which is Injected into the pumping gap and cooled by heat exchanger 6,7. The second system uses an air stream, produced by a fan. The invention refers to a screw vacuum pump (not compressor). The heat exchanger according to the Invention Is located adjacent the Inlet 24 of outer housing 22, while the prior art heat exchanger Is located at the outlet 11 of the outer housing 9. The prior art solution cannot have the effect to pre-warm the cooling air. Therefore claim 1 is novel and Inventive, as the citation does not disclose any hint to the Idea of the Inventors, allowing the pump to 'breathe'. The effect as discloses in new claim 3 Is that, what the inventors call 'breathing of the screw vacuum pump'. DE 2 217 022 describes a liquid ring pump. The construction and the field of use of such pumps are completely different from construction and use of screw vacuum pumps. OBJECT OF INVENTION It Is the task of the present Invention to improve the cooling system for a screw- type vacuum pump having the aforementioned characteristics. This task is solved through the features of the present invention. SUMMARY OF INVENTION The additional cooling system in accordance with the present invention for cooling the pump housing from the outside, specifically by way of an Impelled air flow produced by a fan linked to the motor, for example, considerably relieves the liquid cooling system for the rotors accommodated within the pump of stress. In addition, it is possible with the aid of the impelled air flow to also cool a heat exchanger through which the cooling liquid of the rotor cooling system flows. the present invention allows the implementation of a cooling for a screw-type vacuum pump in which the entire machine is air cooled although in addition a liquid cooling system for the rotors is present. The produced heat is in fact dissipated by two different heat carriers (liquid for the inner rotor cooling system, outer cooling system, outer cooling air flow) finally the heat, however, is in total dissipated by the cooling air flow. This also applies to the dissipation of secondary heat flows produced by motor losses, gear and bearing losses etc. Further advantages and details of the present invention shall be explained with reference to an embodiment depicted schematically in the accompanying drawing. BRIEF DESCRIPTION OF THE ACCOMPANYING DRWAING Fig. 1 - Is a longitudinal transverse view of a vacuum pump in accordance with the present invention. DETAIL DESCRIPTION OF THE INVENTION In the drawing figure, the screw -type vacuum pump which is to be cooled is designated as 1, Its pump chamber housing with 2, its rotors with 3,4, its inlet with 5 and the gear/motor chamber housing with 6, the latter being adjacent with respect to the pump chamber housing 2 with the rotors 3,4. An outlet on the delivery side is not depicted. Accommodated in the housing 6 is the gear chamber 7, the motor chamber 8 with eth drive motor 9 and a further chamber 10, being a component of the liquid cooling circuit for the rotors 3,4. The rotors 3,4 are equipped with shafts 11,12 which penetrate the gear chamber 7 and the motor chamber 8. Through bearings in the separating wails between pump chamber and gear chamber 7 (separating wall 13) as well as motor chamber 8 and cooling liquid chamber 10 (separating wall 14), the rotor 3,4 are suspended in a cantilevered manner. The separating wall between gear chamber 7 and motor chamber 8 is designed as 15. Accommodated in the gear chamber 7 is a pair of toothed wheels 16, 17 effecting the synchronous rotation of the rotors 3, 4. The rotor shaft 11 is simultaneously the drive shaft of the motor 9. The motor 9 may even be equipped with a drive shaft differing from the shafts 11, 12. In the instance of such a solution its drive shaft terminates in gear chamber 7 and is equipped there with a toothed wheel which intermeshes with one of the synchronising toothed wheels 16, 17 (or a further toothed wheel, not depicted, of the shaft 12). Shaft 11 penetrates the chamber 10, is run out of the housing 6 of the pump 1 and carriers at its unoccupied end the wheel 20 of a ventilator or 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 face sides. In the sense of the present invention, the fan 21 is operated such that the aperture 24 on the fan/motor side forms the air inlet aperture. Assigned to this aperture is a heat exchanger 25 through which the cooling liquid of the internal rotor cooling system flows. Expediently, the heat exchanger 25 is located upstream of fan 21 so that it simultaneously forms a means of touch protection for the blade wheel 20. The advantage of this arrangement is, 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, 4 attaining during operation of pump 1 relatively high temperatures, do not come into contact with the housing 2. Preferably, the housing 2 and the rotors 3, 4 are made of aluminium for the purpose of improving heat conductance. Moreover, the housing 2 may exhibit fins for improving the thermal contact. Through the size of the heat exchanger 25 and also through the degree by which the pump chamber housing 2 is equipped with fins, the gap between the rotors 3, 4 and the housing 2 is adjusted. The cooling liquid circuit for cooling the rotors 3, 41) is depicted only schematically. In the German patent applications 197 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 conveying the coolant (oil, for example) to and from the rotors 3, 4. In the example of the depicted embodiment, the coolant exiting the rotors 3, 4 collects in the motor chamber 8. From there the coolant is supplied through the line 26 to the heat exchanger 25. The air flow produced by fan 21 dissipates the heat which was dissipated by the cooling liquid in the rotors 3, 4. The liquid exiting the heat exchanger 25 is supplied through the line 26 to the chamber 10. In a manner not depicted in detail it passes from there through bores in the shafts 11, 12 to the rotors 3, 4, flows there through cooling ducts and passes through the shafts 11, 12 back into the motor chamber 8. It has been found to be expedient to adjust the cooling system such that approximately half of the heat generated by the pump is first dissipated by the cooting liquid and thereafter removed through the heat exchanger 25, and such that the other half is dissipated directly by the cooling air flow. Translator's note: The German text states "4, 5" here whereas "3.4" would be more in line with the drawing figures and the remainder of the text. Therefore "3, 4" has been assumed for the translation. In all, the characteristics in accordance with the present invention allow a further increase in the performance density of a screw-type pump. The pump may be designed to be smaller and may be operated at higher surface temperatures. The housing 22 serving the purpose of guiding the outer air flow has, in addition, the function of providing a means of touch protection. 1. A screw-type vacuum pump (1) having improved cooling system, comprising: an inner pump housing (2,6); a pair of rotors (3,4) rotatably mounted in the inner pump housing (2,6); a drive motor (9) mounted in the inner pump housing (2,6); an outer housing (22) displaced from the inner pump housing (2,6) to define a passage (23,24) for cooling air therebetween, such that cooling air flowing between the inner and outer housings (2,6,22) removes heat from the rotors (3,4) and drive motor (9); a liquid cooling system (8,10,11,12,26) for circulating a cooling liquid for cooling the drive motor (9) and the rotors (3,4); a heat exchanger (25) mounted to pre-heat the cooling air upstream of the inner housing (2,6), the heat exchanger being connected with the liquid cooling system to move heat from the cooling liquid to the cooling air. 2. The pump as claimed in claim 1 comprising a fan mounted in the outer housing (22) for propelling air through the heat exchanger (25) and the air cooling passage (23,24) between the inner and outer housings (2,6, 22). 3. The pump as claimed in claim 1 wherein the heat exchanger (25) and the cooling air passage (23,24) are sized such that as the rotors heat and undergo thermal expansion, the inner pump housing (2,6) thermally expands to such an extend that the rotors (3,4) do not come into contact with the inner pump housing (2,6). 4. The screw-type vacuum pump as claimed in claims 1 to 3, wherein in the heat exchanger (25), the fan (21), the motor chamber housing (8) which defines the second chamber to house (25) the drive motor (9) and the pump chamber housing (2) which defines the first chamber (2) that houses the rotors (3,4) are arranged sequentially in a direction of the flow of air. 5. The screw type vacuum pump as claimed in claim 1, wherein the fan (21) is linked to the drive motor (9). 6. The screw type vacuum pump as claimed in claim 5, wherein the fan (21), the drive motor (9) and the rotor housing (2) are arranged sequentially in a direction of the flow. 7. The screw type vacuum pump as claimed in claim 1, wherein at least the rotor housing (2) is equipped with outer fins. 8. The screw type vacuum pump as claimed in claim 1, wherein the rotor housing (2) and the rotors (3,4) are constructed of aluminum. 9. The screw type vacuum pump as claimed in claim 1, wherein the fan (21) is located adjacent the inlet aperture (24). lO.The screw type vacuum pump as claimed in claim 1, wherein the liquid cooling system is designed such that quantities of heat dissipated directly by the first cooling system and the second cooling system, are approximately equal. Dated this 18th day of May, 2004 This invention relates to a screw-type vacuum pump (1) having Improved cooling system, comprising; an inner pump housing (2,6); a pair of rotors (3,4) rotatably mounted In the inner pump housing (2,6); a drive motor (9) mounted in the inner pump housing (2,6); an outer housing (22) displaced from the Inner pump housing (2,6) to define a passage (23,24) for cooling air therebetween, such that cooling air flowing between the inner and outer housings (2,6,22) removes heat from the rotors (3,4) and drive motor (9); a liquid cooling system (8,10,11,12,26) for circulating a cooling liquid for cooling the drive motor (9) and the rotors (3,4); a heat exchanger (25) mounted to pre-heat the cooling air upstream of the inner housing (2,6), the heat exchanger being connected with the liquid cooling system to move heat from the cooling liquid to the cooling air.

Documents:

644-KOLNP-2004-CORRESPONDENCE 1.1.pdf

644-KOLNP-2004-FORM 27 1.1.pdf

644-KOLNP-2004-FORM 27.pdf

644-KOLNP-2004-FORM 3.1.1.pdf

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

644-KOLNP-2004-FORM-27.pdf

644-kolnp-2004-granted-abstract.pdf

644-kolnp-2004-granted-claims.pdf

644-kolnp-2004-granted-correspondence.pdf

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

644-kolnp-2004-granted-drawings.pdf

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

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

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

644-kolnp-2004-granted-form 2.pdf

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

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

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

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

644-kolnp-2004-granted-specification.pdf

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