GB2296744A

GB2296744A - Turbomachine pitch adjustment utilising a frequency-controlled motor

Info

Publication number: GB2296744A
Application number: GB9526043A
Authority: GB
Inventors: Horst Schafer; Gunter Schaaf; Martin Ilijevec
Original assignee: KSB AG; Klein Schanzlin and Becker AG
Current assignee: KSB AG; Klein Schanzlin and Becker AG
Priority date: 1994-12-24
Filing date: 1995-12-20
Publication date: 1996-07-10
Also published as: GB9526043D0; FR2728617A1; DE4446621A1

Description

A FREQUENCY-CONTROLLED ADJUSTING MOTOR 2296744 THIS INVENTION RELATES TO

an adjusting device for a turbomachine having a variable-pitch screw carried by a shaft, transmission elements of an adjusting mechanism being disposed in the shaft and being connected to an electrical adjusting motor for the transmission of forces.

In adjusting devices of this kind such as are known from DE-A-43 06 131 and DE-A-43 06 141 the adjusting motor operates only for the duration of the actual adjusting operation. In normal operation of the turbo-machine the rotor of the adjusting motor rotates at the same speed as the shaft which is connected to the variable-pitch screw and in which the transmission elements of the adjusting mechanism are also disposed. Depending upon the mass inertia moments of the rotor of the adjusting motor there is a risk of accidental adjusting movements occurring when the turbo-machine starts and stops. If the frictional resistances in the adjusting mechanism are less than the acceleration forces produced by mass inertia moments of the adjusting motor there is a risk of an accidental adjusting movement occurring. In the worst case, the adjusting mechanism may move into one of its end positions, with the result that mechanical damage may occur should the mechanism run on to limiting stops. This can be countered by the rotating field of the adjusting moment always corotating in synchronism with the rotating parts of the adjusting mechanism by the use of control processes and corresponding positive or negative accelerations to obviate an adjustment caused by excessive mass inertia moments. However, this requires an elaborate sensor and control technology.

2 It is therefore the object of the invention to solve the problem of controlling the adjusting mechanism of the kind concerned by simple means.

According to the invention there is provided an adjusting device for a turbo-machine having a variablepitch screw carried by a shaft, transmission elements of an adjusting mechanism being disposed in the shaft and being connected to an electrical adjusting motor for the transmission of forces.

The means necessary for varying the drive frequency of the motor then needs to be activated only briefly at starting and stopping of the turbomachine and during the actual adjusting operation. To this end, the rotating field of the adjusting motor is adjusted synchronously to the speed of the turbo-machine shaft and is varied for correction purposes and/or for an adjusting operation relatively to the speed of the shaft connected to the screw. Varying the motor drive frequency therefore results in a relative movement between the shaft and the motor rotor either positively or negatively so that the actual adjusting movement can be initiated.

In preferred embodiments the use of a frequencyvarying device with an integrated control unit considerably reduces control complexity. In normal operation of the turbo-machine the frequency-varying device, which may be a frequency converter, does not have to be in operation. The integrated controller unit, which can be an electronic computer unit, a microprocessor or the like, and the associated sensors, make control convenient. A device varying the drive frequency can therefore be adapted in programmable manner to operating conditions by the variation of corresponding parameters. The use of sensors 3 to detect torque enables torque to be controlled with reduced control complexity. The volume of sensors and associated wiring can therefore be reduced considerably. When a blade adjustment is required, the device receives a start instruction, e.g. from a computer. On starting or stopping of the turbo-machine and in an operating state in which there is no slip between the parts to be moved, the adjusting motor operates only in the event of an intended adjustment. Slip-free operation is ensured in the case of unfavourable mass inertia moments by the use of a synchronous element. When an adjustment is required the frequency-varying device is to some extent run up to speed idly until the speed has been synchronised. After speed synchronisation the frequency-varying device energises the servomotor with a torque. This triggers the adjusting operation. The blades can be adjusted in both directions of rotation. After the required blade setting has been reached the frequency-varying device is switched off. A controller module in the device evaluates the signal of a displacement transducer and of a connected set-value input. The device then controls out the variation from the set value automatically.

A set-value transducer and two rotating sensors may be connected to the frequency varying device. These rotating sensors may take the form of incremental transducers. An adjusting device having such sensors is of use in turbo-machines in which frequent and very accurate adjustment is required. The adjusting device, which for this purpose is always in operation, can adjust a turbomachine to a required operating point rapidly and quite accurately. This is useful for turbo-machines in which slip-free operation cannot be ensured in all circumstances.

4 According to another aspect of the invention, there is provided a method of operating an adjusting device of a turbo-machine which has a variablepitch screw. the same being connected to a shaft in which transmission elements for an adjusting mechanism are disposed, the adjusting forces being transmitted by an electric adjusting motor to the adjusting mechanism, characterised in that the adjusting motor is an electric motor whose drive frequency is variable, in that the rotating electric field of the motor is synchronised with the speed of the shaft for an adjusting movement and in that a variation of the drive frequency of the adjusting motor triggers a relative movement of the adjusting device relatively to the shaft speed and triggers the adjusting operation.

By means of the device which varies the drive frequency of the adjusting motor, its rotor rotating at shaft speed always rotates synchronously therewith. For an intended adjustment the synchronous speed of the adjusting motor is varied deliberately in order to trigger an Adjusting operation. This kind of control provides a rapid and smooth adjusting movement. Because of the friction in the adjusting mechanism the rotor of the adjusting motor runs synchronously with the shaft speed.

Exemplified embodiments of the invention are shown in the drawings and will be described hereinafter. In the drawings:

Fig. 1 shows the circuit diagram of an adjusting electric motor of variable drive frequency; and Fig. 2 shows a variant transducers are used as sensors.

in which rotating An adjusting electric motor I of a blade adjustment facility is shown in the block schematic diagram of Fig. 1 and is connected by an electric line 2 to a frequencyvarying device 3. A controller unit 4 is incorporated in device 3, which is usually a frequency converter, and is connected to sensors and set-value transducers. A sensor 5 serves to register the torque recording in an adjusting device (not shown). Another sensor 6 serves to sense the displacements in the adjusting device and provides to device 3 a signal representing the actual blade position (i.e. pitch) of the variable-pitch screw. By means of a set-value transducer 9 the required blade position is entered as a value in the device 3. Depending upon the sensors used, it may be necessary to prepare their signals by evaluators 7, 8 in order that signal processing may be adapted to the frequency-varying device 3.

When it is intended to adjust the blades of a variable-pitch screw, the required blade position is preselected on a set-value transducer 9 and fed into the frequency-varying device 3, 4. The latter so adapts the speed of the motor 1 that there is a relative movement between an adjusting shaft and a drive shaft which triggers an adjusting operation in an adjusting transmission.

Fig. 2 shows a frequency-varying device 10 into which a signal from a main motor 11 is additionally injected as actual value. The motor 11 drives a variablepitch screw and has a rotary sensor 12 which is usually in the form of an incremental transducer. An adjusting motor 1 also has a corresponding rotary sensor 13. The sensors 12, 13 deliver signals of such accuracy that by means of the frequency-varying device 10 - in this case a 11servoconverter" - the servomotor 1 can be controlled dead accurately. The required blade position is preselected by 6 means of a set-value transducer 9. A sensor 14 acting as distance transducer reports the actual blade position back to the device 10, whereafter the integrated control unit 4 therein triggers the corresponding control operations.

It will be appreciated that in the embodiments described above, the adjusting motor I may be an electric motor of the synchronous type and may be arranged to drive an adjusting shaft co-axial with the screw of the turbomachine and which adjusting shaft rotates in synchronism with the screw except during screw-pitch adjustment.

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Claims

C L A I M S

An adjusting device for a turbo-machine having a variable-pitch screw carried by a shaft, transmission elements of an adjusting mechanism being disposed in the shaft and being connected to an electrical adjusting motor for the transmission of forces, characterised in that the drive frequency of the adjusting motor (1) is variable.
2. An adjusting device according to claim 1, characterised in that a device (3, 10) which varies the drive frequency and which has an integrated controller unit (4) acts on the adjusting motor (1).
3. An adjusting device according to claim 1 or 2, characterised in that the frequency-varying device (3, 10) has one or more sensors (5, 6; 12, 13, 14) to detect speeds, torques or travels of the adjusting mechanism.
4. An adjusting device according to claim 3, characterised in that the frequency-varying device (3, 10) is in the form of a frequency converter.
5. An adjusting device according to claim 3 or 4, characterised in that a set-value transducer (9) and one sensor (5, 6) each for torque recording and distance recording are connected to the frequency-varying device (3, 10).
6. An adjusting device according to one or more of claims 1 to 7, characterised in that synchronous elements are disposed between a rotor of the adjusting motor and the adjusting device.

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7. An adjusting device according to claim 3 or 4, characterised in that a set-value transducer (9) and two rotating sensors (12, 13) are connected to the frequencyvarying device (3, 10).
8. An adjusting device according to claim 7, characterised in that the rotating sensors (12, 13) are in the form of incremental transducers.
9. A method of operating an adjusting device of a turbo-machine which has a variable-pitch screw, the same being connected to a shaft in which transmission elements for an adjusting mechanism are disposed, the adjusting forces being transmitted by an electric adjusting motor to the adjusting mechanism, characterised in that the adjusting motor (1) is an electric motor whose drive frequency is variable, in that the rotating electric field of the motor (1) is synchronised with the speed of the shaft for an adjusting movement and in that a variation of the drive frequency of the adjusting motor (1) triggers a relative movement of the adjusting device relatively to the shaft speed and triggers the adjusting operation.
10. An adjusting device for a turbo-machine having a variable-pitch screw, substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawings.
11. An adjusting device for a turbo-machine having a variable-pitch screw, substantially as hereinbefore described with reference to and as shown in Figure 2 of the accompanying drawings.
12. Any novel feature or combination of features disclosed herein.