Device for Measuring the Displacement Travel of a Hydraulic
Displacement Mechanism
The present invention relates to a device for measuring the displacement travel of a hydraulic displacement mechanism for the blades of the impeller of an axial-flow fan having the features of the introductory portion of claim 1.
Modern axial-flow fans are regulatable work machines that convert mechanical energy into kinetic energy. The regulation of the axial-flow fans is effected by the speed or the angle of the blade. If the position of the blade is to be altered during operation, the blade must be secured to a supported shaft via the spindle. The alteration of the blade position is generally effected hydraulically. For this purpose, a hydraulic displacement mechanism is installed on the impeller of the axial-flow fan. Such a displacement mechanism is essentially comprised of a hydraulic displacement cylinder arrangement that rotates with the speed of the fan, and a non-rotating oil transfer element to which the oil supply lines are connected.
The position of the blades of the axial-flow fan correspond to a specific position of the displacement cylinder arrangement. This position is

indicated externally of the fan housing, via a position indicator that is mechanically connected to the displaceable component of the displacement cylinder arrangement, and can also be conveyed to an observation means by means of an attached angle coder. Such a mechanical arrangement for indicating position is relatively imprecise. Furthermore, due to the mechanical connection wear in the connecting parts must be taken into consideration.
The present invention deals with the problem of providing an advantageous device for measuring the displacement travel of the hydraulic displacement mechanism of axial-flow fans. Such a device must be suitable for the measuring inset on the blade adjustment device in the hub space of the axial-flow fan.
It is an object of the present invention to provide a displacement-measuring device for a device of the aforementioned general type that operates with relatively great precision, delivers absolute values, and is free of wear.
The object is realized for a device of the aforementioned type pursuant to the invention by the characterizing features of claim 1.

Advantageous embodiments of the invention are provided in the dependent claims.
The realization of the object is in the use of a magnetostrictive displacement-measuring device for the indicated purpose. Magnetostrictive displacement-measuring devices are known, for example, from US Patent 3,898,555 A. The devices are characterized by a relatively high precision, a low linearity tolerance, and a very high precision of measuring reproducibility. The displacement-measuring devices deliver an absolute value measurement, so that encountering or approaching a reference marked can be dispensed with. Finally, the measuring system operates without contact, so that no wear occurs between the components of the measuring system and of the displacement mechanism that rotate and are displaceable relative to one another. Pursuant to the invention, the magnetostrictive displacement-measuring devices are installed on the blade adjustment device in the hub space of the axial-flow fan, and are advantageously adapted to the special structural conditions that exist there.
Several embodiments of the invention will be described in greater detail n the following and are illustrated in the drawing, in which:

Fig. 1 is a longitudinal cross-sectional view through an
impeller of an axial-flow fan having a displacement mechanism according to the invention, and
Fig. 2 is a longitudinal cross-sectional view through an
impeller of an axial-flow fan having a displacement mechanism pursuant to another embodiment
A rotor or impeller 1 of an axial-flow fan is provided on its periphery with a plurality of vanes or blades 2, one of which is partially shown. The blades 2 are adjustable about their longitudinal axis to adapt the axial-flow fan to the various operating conditions. For this purpose, a spindle 3 that supports the blades 2 is rotatably mounted in a support ring 4 of the impeller 1. Secured to each spindle 3 is an offset displacement lever 5, which is guided in a groove disposed on the periphery of an adjustment disk 22.
Pursuant to Fig. 1, the adjustment disk 22 is connected to a piston rod 8 on which is secured a piston 7. The piston 7 in turn is disposed within a displacement cylinder 6. The piston rod 8, along with the piston 7 and the adjustment disk 22, are disposed so as to be displaceable along the axis of the axial-flow fan, and rotate at the same

speed as do the impeller 1 and the displacement cylinder 6. The displacement cylinder 6 is connected to the impeller 1, and is stationary relative to the piston rod 8 and the piston 7.
For extension purposes, that end of the piston rod 8 that is remote from the impeller 1 is screw-connected to a shaft 23 that rotates within a non-rotating oil transfer element 13. Axially extending control channels 9, 10 are guided through the piston rod 8 and the shaft 23 and respectively open out into a piston chamber 11,12 disposed on the two sides of the piston 7. The oil transfer element 13 serves for supplying the displacement cylinder 6 with oil under pressure, and is provided with a leakage oil outlet 16 and with two supply lines 14, 15 for the two piston chambers 11, 12. The supply lines 14, 15 serve the respective piston chamber not only as a feed but also as a return, depending upon in which direction the piston 7 is to be displaced on the piston rod 8 with the adjustment disk 22.
To measure the displacement stroke or travel that the piston 7 carries out on the piston rod 8 for adjusting the blades 2, a magnetostrictive displacement-measuring device 24 is provided, such as is known, for example, from US Patent 3,898,555 A.

In the illustrated embodiment, the magnetostrictive displacement-measuring device 24 is comprised of various components, and in particular a rod-shaped sensor housing 25 that surrounds a wave guide 26 of ferromagnetic material, a sensor head 27 that is connected to the sensor housing 25 and carries the electronics for signal preparation, and a permanent magnet 28, as a position transmitter or indicator, that is movable relative to the sensor housing 25. The sensor housing 25 can also be embodied as a profiled design or the like.
Pursuant to Fig. 1, the sensor head 27, together with the rod-shaped sensor housing 25 of the magnetostrictive displacement-measuring device 24, is fixedly disposed in an annular flange 29 that is secured to the oil transfer element 13. In this connection, the sensor housing 25 is oriented in the direction of the axis of the axial-flow fan, and hence in the direction of movement of the piston rod 8. Instead of one displacement-measuring device 24, as illustrated, it would also be possible to dispose a plurality of displacement-measuring devices in the annular flange 29 of the oil transfer element 13.
The magnet 28 of the magnetostrictive displacement-measuring device 24 is embodied as an annular magnet having an internal magnetic band. The magnet 28 thus surrounds the sensor housings 25 of all

mounted or installed magnetostrictive displacement-measuring devices 24 in a predetermined zone.
The displacement-measuring device 24 and the oil transfer element 13 are surrounded by a protective tube 30 that is connected to the displacement cylinder 6. The annular magnet 28 is secured to the wall of the protective tube 30. Thus, the protective tube 30 serves as a support for the magnet 28. The protective tube 30, along with the magnet 28, rotates with the speed of the axial-flow fan. The annular flange 29, as well as the sensor housing 25 that is secured to the annular flange, do not rotate.
In order to adjust the blades 2 of the axial-flow fan, the piston rod 8, and hence also the oil transfer element 13, are moved axially. In so doing, when viewed in an axial direction the magnet 28, which is secured to the protective tube 30 that is connected to the displacement cylinder 6, remains in its position. The displacement-measuring device 24, which is comprised of the sensor housing 25 and the sensor head 27, along with the annular flange 29, are moved on the oil transfer element 13, and thus deliver the displacement travel as a displacement signal.

The embodiment of a displacement mechanism for an axial- flow fan illustrated in Fig. 2 corresponds in its manner of operation to the displacement mechanism illustrated in Fig. 1. However, in contrast to Fig. 1 the displacement cylinder 6' of the displacement mechanism of Fig. 2 can be displaced axially, and the piston rod 8' is disposed so as not to be displaceable axially.
The displacement cylinder 6' is fixedly connected with the axially displaceable adjustment disk 22. The piston rod 8\ with the piston 7 secured thereto, is connected to the impeller 1 by means of a conical support 31. That end of the piston rod 8' that is remote from the impeller 1 rotates as a shaft 23 within the non-rotating oil transfer element 13.
With the displacement mechanism illustrated in Fig. 2, the sensor head 27, together with the rod-shaped sensor housing 25 of the magnetostrictive displacement-measuring device 24, are fixedly disposed in a support flange 32. The support flange 32 is secured to the oil transfer element 13, which here is not axially displaceable. In this connection, the sensor housing 25 is oriented in the direction of the axis of the axial-flow fan and hence in the direction of movement of the displacement cylinder 6'. Instead of one displacement-measuring

device 24 as illustrated, it would also be possible to dispose a plurality of displacement-measuring devices in the support flange 32 of the oil transfer element 13.
The magnet 28 of the magnetostrictive displacement-measuring device 24 is embodied as an annular magnet that surrounds the sensor housing. Each magnetostrictive displacement-measuring device 24 that is installed or used has its own magnet 28.
The displacement cylinder 6' is fixedly connected to a return rod 33 that carries out the same axial movement as does the displacement cylinder., The return rod 33 is fixedly connected with a support 34 on which, in turn, are secured the magnet 28 or the magnets 28 of the possible multiple displacement-measuring devices.
To adjust the blades 2 of the axial-flow fan, the displacement cylinder 6', and hence also the displacement disk 22 and the return rod 33, are moved axially. In so doing, the position of the magnet 28 is also moved axially. The displacement-measuring device 24. which is comprised of the sensor housing 25 and the sensor head 27, and the support flange 32 on the oil transfer element 13. do not move axially.

The displacement-measuring device 24 thus delivers the displacement travel as a displacement signal.

Patent Claims
Device for measuring the displacement travel of a hydraulic displacement mechanism (6, 6', 7, 8, 8', 9, 10, 11, 12) for blades (2) of an impeller (1) of an axial-flow fan, whereby the displacement mechanism is essentially comprised of a displacement cylinder (6, 6') and a piston rod (8, 8') having a piston (7), of which one component is axially displaceable and one component is not axially displaceable, whereby the axially displaceable component is connected to a displacement disk (22) to which are secured, via rotatable displacement levers (5), respective spindles (3) of the blades (2), and whereby an extension of the piston rod (8, 8') that extends out of the displacement cylinder (6, 6') is surrounded by an oil transfer element (13) that serves for an oil supply (14, 15) to the displacement cylinder (6, 6'), characterized in that the displacement mechanism is coupled with a magnetostrictive displacement-measuring device (24) comprised of sensor housing (25) having a wave guide (26), sensor head (27) and annular magnet (28), in that the sensor housing (25) and the sensor head (27) of the magnetostrictive displacement-measuring device (24) are connected with the oil transfer element (13), and in that the magnet (28) is connected to that

component of the displacement mechanism that is axially displaceable relative to the oil transfer element (13).
Device according to claim 1, characterized in that the magnetostrictive displacement-messing device (24) is surrounded by a protective tube (30), and in that the magnet (28) of the magnetostrictive displacement-measuring device (24) is secured to the protective tube (30), which is connected with the axially not displaceable displacement cylinder (6).
Device according to claim 2, characterized in that the oil transfer element (13), which surrounds the extension of the axially displaceable piston rod (8), is provided with an annular flange (29), and in that the sensor housing (25) and the sensor head (27) of one or more magnetostrictive displacement-measuring devices (24) are secured in said annular flange (29).
Device according to claim 1, characterized in that the magnet (28) of the magnetostrictive displacement-measuring device (24) is indirectly connected to the axially displaceable displacement disk (22).

Device according to claim 4, characterized in that a return rod (33) is guided through the piston rod (8'), in that one end of the return rod (31) is connected to the displacement disk (22), and in that the magnet (28) is secured to the other end of the return rod (33) via a support (34).
Device according to claim 4 or 5, characterized in that the oil transfer element (13) is provided with an support flange (29), and in that the sensor housing (25) and a sensor head (27) of one or more magnetostrictive displacement-measuring devices (24) are secured in the support flange (29).