Coupling apparatus

The invention relates to a coupling apparatus connecting two rotatable shafts of a turbocompressor.

A bearing apparatus for a turbocompressor is known from the specification DE 26 58 687 A1. This bearing apparatus is suitable in particular for turbo machines which are designed to be very long and which have a plurality of compressor wheels which are arranged adjacently on a common shaft. The rotor shaft of this known bearing apparatus is completely electromagnetically journalled by means of electromagnetic radial bearings as well as an electromagnetic axial bearing. It is disadvantageous in this known bearing apparatus that the axial bearings have a low carrying force. In particular when a plurality of compressor wheels are arranged on the bearing shaft, relatively large force variations can arise in the axial direction, through which the known bearing apparatus could be overloaded or damaged. Further disadvantageous in the known bearing apparatus is that the axial bearing can have an unfavorable effect on the rotor-dynamic behavior of the shaft.

The object of the present invention is to create an apparatus for a turbocompressor which enables a more advantageous operation.

According to the invention, a coupling apparatus for connecting two rotatable shafts of a turbocompressor includes a first and a second coupling part which are designed for firm connection to one end section of the shafts each, as well as comprising a third coupling part which is designed in disc-shape and which is to be arranged between the first and the second coupling part. The first, second and third coupling part are firmly connectable to one another. The third coupling part has a section which projects beyond the first or second coupling part in the radial direction and which is designed as a bearing disc of an axial bearing.

The coupling apparatus in accordance with the invention has the further advantage that the bearing disc can be designed to be relatively large radially in order to produce a large force in the axial direction with the electromagnetic axial bearing. Due to the high speed of rotation of a turbocompressor, large radial forces or large centrifugal forces respectively arise at a heavy bearing disc or at a bearing disc with relative large diameter respectively. The coupling apparatus in accordance with the invention permits the bearing disc to be designed in such a manner that it is suitable for high speeds of rotation, for example for a peripheral speed of 400 m/s. In a preferred embodiment the bearing disc is designed as a through-going bearing disc, without a bore in its center. In addition the bearing disc is preferably forged. A bearing disc which is designed in this manner has the required material properties in order also to be operated safely at high speeds of rotation. In a further, advantageous embodiment the bearing disc is designed to become thinner outwardly in order to reduce its mass and thereby to achieve a constructional shape which is optimized in regard to stress.

The shaft of a turbocompressor has large radial deflections in particular in the region of the first, second, third or fourth critical resonance frequency, with the shaft developing oscillation bulges and oscillation nodes in its direction of extent. An advantage of the coupling apparatus in accordance with the invention is that through the shortening of the constructional length which results from the integration of the axial bearing disc into the coupling, a better possibility of influencing the rotor dynamics can be achieved.

The invention will be explained in the following with reference to a plurality of exemplary embodiments, with identical reference symbols relating to identical objects.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

In the drawings:

FIG. 1 is a longitudinal sectional view of a turbocompressor with an electric motor, a radial turbocompressor and a coupling apparatus;

FIG. 2 is a longitudinal sectional view through a coupling apparatus;

FIG. 3 is a longitudinal sectional view through a further coupling apparatus;

FIG. 4 is a longitudinal sectional view through the bearing disc of an axial bearing;

FIG. 5 is a side view of the bearing disc in accordance with FIG. 4 .

Referring to the drawings in particular, FIG. 1 shows schematically a turbocompressor which comprises a radial turbocompressor 3 with a shaft 3 a and a driving electric motor 2 with a shaft 2 a. The two shafts 2 a, 3 a are connected to one another via a coupling 4 comprising three coupling parts 4 a, 4 b, 4 c, so that the electric motor 2 drives the shaft 3 a of the radial turbocompressor 3 via the shaft 2 a and the coupling 4 . The two shafts 2 a, 3 a are journalled through three electromagnetic radial bearings 5 . The coupling 4 comprises a first coupling part 4 a, a second coupling part 4 b as well as a third coupling part 4 c which is arranged between them and which at the same time forms the bearing disc of the axial bearing 7 , for which reason electromagnets 7 c comprising electromagnetic coils 7 a are arranged directly adjacently to the coupling part 4 c in order thus to form an electromagnetic axial bearing 7 .

The turbocompressor 1 which is illustrated in FIG. 1 comprises a hermetically sealed pressure housing 6 within which the electric motor 2 and the radial turbocompressor 3 are arranged. An inlet line 6 c and an outlet line 6 d which pass through the pressure housing 6 connect the radial turbocompressor 3 in a fluid conducting manner to an apparatus which is located outside the pressure housing 6 or to a process which is running outside the pressure housing. The electric motor 2 comprises the rotor 2 b and the stator 2 c, with the rotor 2 b forming part of the motor shaft 2 a. The motor shaft 2 a is journalled in the radial direction at both sides in the electromagnetic radial bearing 5 , comprising a support apparatus 5 a and an electromagnetic coil 5 b each. The motor shaft 2 a is connected at its one end section via a coupling 4 to the end section of the rotor 3 a of the radial turbocompressor 3 . In addition to the coupling 4 the electromagnetic axial bearing 7 is also arranged at the connection location between the motor shaft 2 a and the compressor shaft 3 a. The motor shaft 2 a and the rotor 3 a form a common shaft. Two compressor wheels 3 b, which form a first compressor stage 3 c and a second compressor stage 3 d, are arranged in the direction of extent of the rotor 3 a. Not illustrated are the guide blades or the diffusor respectively of the radial turbocompressor 3 . The main mass flow 8 of the fluid to be compressed, preferably in the form of a gas, enters via the inlet opening 6 a and the inlet line 6 c into the first compressor stage 3 c, is then conducted to the second compressor stage 3 d and is then conducted via the outlet line 6 d to the outlet opening 6 b.

The turbocompressor 1 could also have a plurality of compressor wheels 3 b which are arranged with spacing in the direction of extent of the rotor 3 a, thus for example a total of three, four, five, six, seven, eight, nine or ten compressor wheels 3 b. The compression pressure which is to be achieved is largely open upwardly, with a compression pressure of for example 600 bar being achievable through a corresponding number of compressor wheels 3 b which are connected in series. The turbocompressor 1 could also comprise one or more further radial turbocompressors 3 and/or electric motors 2 which are arranged in the direction of extent of the rotor 3 a; 2 a, with all rotors 3 a; 2 a forming a common shaft. This common shaft could be journalled through radial bearings, in particular magnetic radial bearings 5 , with a single radial bearing 5 preferably being arranged between each radial turbocompressor 3 . All radial turbocompressors 3 are preferably arranged together with the electric motor 2 or the electric motors 2 in a common, single pressure housing 6 .

The electromagnetic radial bearings 5 and the sections of the shafts 2 a and 3 a which are associated with the radial bearings 5 have further components, which are obvious for the expert and therefore are not illustrated, in order to form an electromagnetic radial bearing 5 , such as electrical coils, ferromagnetic parts etc. The same holds for the electric motor 2 , which is likewise only schematically illustrated.

Relatively large forces can arise at the common shaft 2 a, 3 a during the operation of the turbocompressor 1 which is illustrated in FIG. 1 . The coupling apparatus 4 in accordance with the invention enables the formation of an electromagnetic axial bearing 7 with a relatively large bearing disc 4 c, which allows large axial bearing forces to be produced.

The longitudinal section through the coupling apparatus 4 which is illustrated in FIG. 2 shows the motor shaft 2 a with conically extending end section 3 d as well as the shaft 3 a of the radial turbocompressor 3 with conically extending end section 3 f, which are rotationally fixedly connected to one another with the coupling apparatus 4 . The first coupling part 4 a is shrunk on onto the end section 2 d of the motor shaft 2 a and is firmly connected to the latter in this manner. The second coupling part 4 b is shrunk on onto the end section 3 f of the shaft 3 a and is firmly connected to the latter in this manner. The third coupling part 4 c, which is formed as a full disc, is clamped in between the first and the second coupling part 4 a, 4 b. The coupling part 4 c has, as can be seen in the side view in accordance with FIG. 5, a plurality of bores 4 k which are arranged with spacing in the peripheral direction; and the first and the second coupling part 4 a, 4 b has bores which are arranged to be correspondingly matched so that, as illustrated in FIG. 2, the three coupling parts 4 a, 4 b, 4 c, are held together in each case by a common screw 4 h with nut 4 i. Preferably 6 , 8 or 12 screws 4 h with nuts 4 i of this kind are regularly arranged with spacing in the peripheral direction of the coupling apparatus 4 in order to hold the three coupling parts 4 a, 4 b, 4 c together and to transfer the required torque. The third coupling part 4 c forms at the same time the bearing disc of the axial bearing 7 . Along the section 41 of the bearing disc 4 c which projects beyond the first or second coupling part 4 a, 4 b in the radial direction, electromagnets 7 c comprising a laminated soft iron 7 b and electromagnetic coils 7 a are arranged on both sides in order to cause a force acting in the axial direction A on the bearing disc 4 c.

FIG. 3 shows in a longitudinal section a further exemplary embodiment of a coupling apparatus 4 , with the ends of the motor shaft 2 a and the shaft 3 a being formed as coupling flanges 4 a, 4 b which are rotationally fixedly connected together with the third coupling part 4 c by means of screws 4 h, 4 i. The details of the axial bearing 7 , such as electromagnets 7 c and coils 7 a, are not illustrated, but can be designed as illustrated in FIG. 2 .

FIG. 4 shows in a longitudinal section a further exemplary embodiment of a third coupling part 4 c or of a bearing disc 4 c respectively. The bearing disc 4 c comprises an inner disc part 4 m which is clamped in between the first and second coupling part 4 a, 4 b and an outer disc part 41 along which the electromagnets 7 c are arranged. Radially to the axial direction A a the outer disc part 41 is designed to become thinner outwardly in order thereby to save on mass. Arranged at the inner disc part 4 m is a rounding out 4 o which extends in the peripheral direction and which, as seen in FIG. 2, permits a centering of the first and the second coupling part 4 a, 4 b with respect to the third coupling part 4 c. The rounding out 4 o also has a rounding out in order to avoid notch stresses. For the same reason a recess 4 n which extends in the peripheral direction is arranged in the inner disc part 4 m.

The third coupling part 4 c is not manufactured by a chip forming method but rather through a reshaping processing, preferably through forging. The term reshaping process is understood to mean a shaping through the application of force and without chip forming machining. After the reshaping process the surface of the worked article can still be machined, for example through grinding or turning. The third coupling part 4 c could also have an aperture or bore which is arranged at the center of rotation. Thus the coupling part 4 c which is illustrated in FIG. 4 could have an aperture which extends starting from the point represented by 4 n up to the center of rotation A. In order to withstand the large centrifugal forces, the third coupling part 4 c is however preferably designed as a through-going bearing disc, as is illustrated in FIG. 4 . In addition it is preferably observed that the third coupling part 4 c has no bore at the center of rotation A, and that at the periphery only few bores are arranged and in addition preferably with bore cross-sections which are as small as possible in order not to or only slightly to reduce the stress resistance of the third coupling part 4 c.

The maximum diameter of the coupling part 4 c or of the bearing disc respectively is determined by the maximum possible peripheral speed. The bearing disc 4 c can for example have a maximum diameter of 50 cm.

The coupling 4 in accordance with the invention has two functions, namely the coupling and the axial journalling of the two shafts 2 a, 3 a. Since the coupling 4 in accordance with the invention performs both functions the entire shaft, comprising the shafts 2 a, 3 a and the coupling 4 , has a short constructional length. An advantageous oscillation behavior of the entire shaft is achieved through this short constructional length. The short constructional length also has the advantage that the length of the total shaft can be increased in the event for example that this is advantageous for oscillation-technical reasons.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.