A DEVICE FOR ASSEMBLING AN IMPELLER ON A DRIVING SHAFT

Abstract: In a device for assembling an impeller (1) on a driving shaft (36) the impeller is supported on the driving shaft by a radial bearing (3) having a small radial clearance. This bearing admits a relative rotary motion between impeller and shaft. An elastic or resilient element (9) is mounted between the shaft and the impeller to transmit the torque from the shaft to the impeller.

Description: A device for assembling an impeller on a driving shaft. The present invention relates to a device for assembling an impeller on a driving shaft. The torque delivered by drive motors is hardly ever constant but varies more and less. The variation or pulsation of the torque is accentuated if speed control is incorporated in the driving system for the impeller. Such driving systems can include e.g. electric motors with frequency converters or electronic variators, or diesel motors. Such pulsating torques often give rise to resonance vibrations in parts of the machine e.g. the impeller blades, which results in fatigue failor of such parts of the machine- So far this problem has been solved by introducing an adapted elastic or resilient coupling between the driving shaft of the motor and the impeller shaft. This prior art solution is shown in Fig. 1 applied to a fan, where an elastic coupling is showV) at 20 between the driving shaft 21 of the motor 22 and the fan shaft 24 which supports the fan inpeller 26. The fan shaft 24 is carried in separate bearings 28, 30. This solution for protecting the fan from pulsating torques from the motor is, however, expensive and takes up a large space and is therefore impossible to use for certain application. The purpose of the present invention is to provide a new solution of the problems caused by pulsating torques in which the mentioned disadvantages of the prior art construction are remedied. This purpose is obtained by a device according to claim 1. With a device according to the invention the problem with pulsating torques are eliminated also for constructions where the impeller is directly supported by the driving shaft of the πptor. Thus, the need for an elastic or resilient coupling between separated driving and impeller shafts is eliminated which simplifies the construction and makes it less expensive and especially provide a compact construction with a considerable reduction of the space required which is of utmost importance for certain fan applications. According to an advantageous embodiment of the invention the device is disposed inside the hub of the impeller. An embodiment exemplifying the invention will now be described more in detail with reference to Figures 2 and 3 of the drawings. On the drawing Fig. 1 shows a prior art device for protecting a fan against pulsating torques, Fig. 2 illustrates a compact assembly of drive motor and fan where the device according to the invention can be used, Fig. 3 is a cross section of a fan impeller hub with an embodiment of the device according to the invention and Fig. 4 illustrates another example of providing an elastic or resilient coupling useful in a device according to the invention. In Fig. 2 a compact assembly is shown where the fan impeller 32 is directly supported by the driving shaft from the motor 34. A comparison of Figures 1 and 2 directly shows the different needs for space of the two assemblies with the fan shaft separated from the driving shaft and mounted in separate bearings as shown in Fig. 1 and the assembly according to Fig. 2, respectively. In Fig. 3 an embodiment of the device according to the invention is shown installed in an assembly of the type shown in Fig. 2 for protecting the fan from pulsating torques from the drive motor by damping and filtering the pulsations such that resonance frequencies are not excited in e.g. impeller or shaft. Thus, Fig. 3 shows a fan impeller 1 attached to an annular plate 2 by a bolted joint 15, 16, 17. To this plate a cover 4 is attached at 6 and by this cover 4 a ball bearing 3 is fixed in axial direction on the driving shaft 36. Inside the cover 4 a distance ring is positioned between the bearing 3 and a shoulder 38 on the driving shaft 36. An elastic annular element 9 is also secured to the plate 2. This element 9 is clamped towards a centering ring 8 by screws 11 and a clamp ring 10. This ring 8 is fixed in radial direction between the clamp ring 10 and a shoulder 40 on the plate 2. With this arrangement the torque is transmitted from elastic ring 9 to the plate 2 through the contact surfaces of the centering ring 8 towards the elastic ring 9 and the plate 2. The elastic ring 9 is also secured to the hub part 7 by a second clamp ring 12 and screws 13. The hub part 7 in its turn is keyed on the driving shaft 36 and screwed axially at 14, 18. Also this connection is designed such that the torque is transmitted from the driving shaft 36 to the elastic ring 9, substantially through the contact surfaces between the elastic ringf 9, on one hand, and the hub part 7 and the clamp ring 12, on the other. As indicated above a key (not shown) is used for the torque transmission between the shaft 36 and the hub 7. The hub part 7-is * * screwed axially on the driving shaft 36 by the bolt 18 and the washer 14. Thus, with the bolt 18 the whole hub construction with the device according to the invention is tightened on the drivϊpg shaft 36 towards the shoulder 38. The torque from the driving shaft 36 is thus transmitted to the impeller 1 through the elastic ring 9. Pulsations or variations in the torque from the driving shaft 36 are damped or filtered due to the function of the elastic ring 9 which absorbs these pulsa- tions and variations by admitting a certain rotary motion -bejv f een impeller 1 and driving shaft 36 by the bearing 3 which is centering the impeller 1 on the driving shaft 36 in'radial direction with a small clearance. The elastic ring which forms one example of realizing ^ the elastic coupling is preferably made of rubber, and the bearing can be of any suitable type, such as a ball bearing, a roller bearing, a plain bearing, or a bearing comprising a bushing in which Jthe driving shaft can rotate. f ' In figure 4 a second embodiment of the invention is shown. In this embodiment the elastic or resilient coupling between the driving shaft and the impeller comprises a toth wheel 42 disposed inside a surrounding cylinder 44 having inwardly directed teeth or projections 46. In the spaces between adjacent teeth 46 of the cylinder 44 and those 48 of the wheel 42 pads 50 of an elastic material, such as rubber, are provided. By attaching the driving shaft 36 to the tooth wheel 42 and the impeller 1 to the cylinder 44 an elastic coupling is realized which will damp or filter pulsa¬ tions and variations in the torque from the driving shaft 36. It is also possible to provide an elastic or resilient coup- ling between the driving shaft and the impeller by means of springs. The device according to the invention is applicable to fans up to a certain size. For very large fans the impeller can normally no longer be supported by the driving shaft from the motor because of its large size and weight. For such large impellers an arrangement of the type shown in Fig. 1 must be used. Tests have been performed with the device according to the invention installed on an axial fan with the fan impeller directly fitted on the end of the motor driving shaft. A drive system of 75 kW with a variable speed was used. With a rigid assembly on the motor driving shaft the first natural mode of vibration of the blades was excited at a high level by the pulsating torque. With an assembly comprising the device according to the invention the amplitude of the vibrations at the resonance speed was reduced by a factor of about 40. Another advantage achieved with the device according to the invention is that a softer start of the fan can be obtained which is of importance for certain applications. The device according to the invention is useful for fans of axial as well as centrifugal types and can also be used on other kinds of turbomachineries.

Claims: Claims 1. A device for assembling an impeller on a driving shaft, characterized in that said impeller is supported on the driving shaft by a radial bearing having a small radial clearance and admitting a relative rotary motion between impeller and shaft and in that at least one elastic or resilient element fs mounted between said shaft and said impeller to transmit the torque from said shaft to said impeller. 2. The device according to claim 1, characterized in that said elastic or resilient element is formed of an elastic ring secured to said shaft and to said impeller. 3. The device according to claims 1 or 2, characterized in that said elastic or resilient element is formed of rubber. 4. The device according to anyone of the claims 1 - 3, characterized in that said radial bearing comprises a ball bearing, or a roller bearing, or a plain bearing or a movable bushing. 5. The device according to anyone of the claims 1 - 4, characterized in that said radial bearing and elastic or resilient element are disposed inside the hub of said impeller. 6. The device according to claim 1, characterized in that outwardly directed, radial projections integral with or connected to the driving shaft are extending into the spaces between inwardly directed, radial projections on the inner surface of a cylinder to which the impeller is attached, elastic pads being disposed between adjacent outwardly and inwardly directed projections respectively.

Inventors: GODICHON ALAIN, GODICHON, ALAIN
Applicants: FLAEKT AB
Application year: 1989
Main classification: F04B29
IPC codes: F04D29, F16D3