The invention disclosed herein pertains generally to couplings for turbomachines, and more particularly to rigid couplings for turbogenerators.
Large torque transmitting couplings whose outer diameters must, for practical reasons, be limited in size are usually unable to transfer full nominal torques because of limits on the cross-sectional areas of the members, e.g., friction flanges, used for this purpose. In the event of a short-circuit or an electrical switching process within the power network an additional torque of much greater magnitude will be superimposed on this nominal torque either in the same or in the opposite direction of rotation. The torque component which cannot be transferred by frictional contact can be transferred by shearing bushings. Thus the friction members whose surfaces are used for the purpose of transmitting torques can then be used primarily to produce frictional contact and to absorb axial forces and bending stresses.
Large, interchangeable, torque-transmitting coupling halves, such as large flanges, require relatively large manufacturing tolerances for the placement of the bores which accommodate the shearing bushings; this is necessary in order to properly mate these coupling halves. The resulting loose fit of the shearing bushings will cause the coupling to slide or shift in the radial direction when frictional contact is lost. This will produce relative radial shifts, with respect to one another, of the driving and driven shaft axes of a turbomachine, for example, which will cause undue vibrations and a detrimental stress of shafts, bearings and the structural parts of the turbomachine.
In order to eliminate the undesirable effects mentioned above, various solutions have been proposed, but have been found to be impractical. Thus efforts are still being directed at narrowing the tolerances for the diameters and relative positions of the bores accommodating the shearing bushings in the two coupling flanges, while still making allowances for the problems arising during assembly. The aim of these efforts is the creation of a rigid coupling. Stated alternatively, the aim is the prevention of excessive relative motion between the coupling halves in the event that frictional contact between the adjacent frontal areas of the coupling flanges is lost. Such a loss of frictional contact may arise in the event of an overload.
A rigid coupling for turbomachines according to the present invention comprises coupling flanges for the shafts to be connected, bolts for connecting the coupling flanges, and shearing bushings which encompass these bolts and which engage the frontal areas of the two coupling flanges. A preferred embodiment of a rigid coupling according to the present invention includes shearing bushings which have the following two features: one half of the outer sidewall surface of each shearing bushing is both oversized relative to the respective bore provided for it in one of the coupling flanges and fitted in by shrinking; the second half of the outer sidewall surface of each shearing bushing, and its associated bore in the other coupling flange, has a conical shape. Upon assembly the two coupling flanges form an interference fit.
A primary object of the present invention is to provide a rigid coupling for turbomachinery, i.e., a coupling wherein excessive relative motion between the coupling halves is prevented in the event of an overload.
A further object of this invention is to provide a rigid coupling for turbomachinery which employs friction flanges for transmitting torques, bolts for connecting these flanges, and shearing bushings which encompass these bolts and which prevent relative motion between the flanges in the event of an overload.
Yet another object of this invention is to provide a rigid coupling employing shearing bushings wherein the tolerances for the diameters and relative positions of the bores accommodating the shearing bushings in the two coupling flanges are not as critical as has been the case up until the present time.