Joints and connections – Interfitted members – Clamped members
Reexamination Certificate
1999-08-23
2001-10-30
Browne, Lynne H. (Department: 3629)
Joints and connections
Interfitted members
Clamped members
C403S335000
Reexamination Certificate
active
06309136
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for locking a mechanical member onto a shaft in a removable way and, in particular, a device which allows a mechanical member provided with a conical bore to be locked onto a cylindrical shaft.
BACKGROUND OF THE INVENTION
Devices have long been known which allow the removable locking of mechanical members onto shafts and which provide a split bush having a conical external surface and a cylindrical internal surface. At least a pair of hollows suitably located on the external surface of the bush, in positions corresponding to tapped hollows on the bore of the mechanical member, allows the same bush to be fixed to the hub of the mechanical member by means of bolts or grub-screws. On the external surface of the bush it is further provided a tapped hollow, in a position corresponding to a smooth hollow on the bore of the mechanical member, in order to allow the removal of the bush from the mechanical member by means of one of the two previously removed grub-screws.
A keyway is provided on the internal surface of the bush and on the external surface of the shaft to allow the same bush to be fixed to the shaft. An example of such a known device is commercially available under the trade name SER-SIT®.
The key is not very suitable in the cases in which the mechanical member must be locked in position distant from the ends of the shaft because of the difficulties of working keyways in such positions. Furthermore, the fixed position of the keyway constitutes a limitation of the angular positioning of the mechanical member on the shaft.
The presence of a keyway on the shaft, beyond requiring suitable working, weakens the structure of the some shaft. Therefore, for parity of transmitted torque, it is necessary to provide shafts with wider total section to give the necessary effective section.
Then it is also known that coupling by means of keys causes the formation of fretting corrosion due to the clearance (which increases with the time) between the shaft and the bush fixed on with the key. The clearances generated between bush and shaft causes a loss of precision in the angular positioning of the mechanical member with respect to the shaft and can also cause the break-up of the same key.
Furthermore, the need of providing a tapped hollow on the external surface of the bush requires a long and fine working and a considerable waste of material. Indeed, in order to obtain such a bush, it is necessary to drill and thread a piece having a greater diameter with respect to that of the final bush and then to turn the external surface of the piece until the tapped hollow on the conical external surface is obtained. It is evident that this involves considerable costs of production.
Friction-based locking bushes are also known, which are used for locking mechanical members having a cylindrical bore, comprising at least a pair of taper split bushes.
For allowing the transmission of the torque by friction, the locking bushes of this type develop notable radial pressures which bears on the hub of the mechanical member. Therefore, these locking bushes require mechanical members with very wide hubs compared to the section of the shaft (diameter up to four times the diameter of the shaft for hubs made from cast iron type G-20) and dependent in any case on the yield point of the material of the hub.
Locking bushes of this type can also have dismantling problems owing to the locking of the two split bushes onto the respective coupling surfaces. Until today, although these disadvantages have been known for some time, no suitable product to overcome the cited drawbacks has been proposed to the knowledge of the Applicant.
The above disclosed disadvantages of the known devices cause notable problems, both technical and of cost, and therefore there is a long time need for a technical solution which allows such drawbacks to be overcome.
DISCLOSURE OF THE INVENTION
The object of the present invention is to produce a device for the removable locking of mechanical members onto a shaft which permits a high facility in assembly and dismantling.
Another object of the present invention is to produce a device for the removable locking of mechanical members which could be suited to use with shafts of reduced diameter, as well as with hubs of reduced diameter, and in any case with shafts and hubs having very similar diameters.
Still another object of the present invention is to produce a device which allows a mechanical member to be locked onto a shaft in a removable way with high degree of precision both angular and axial. A further object of the present invention is to produce a device for the removable locking of mechanical members onto a shaft which avoids the formation of fretting corrosion between the mutually joined elements, i.e. between shaft, device and hub.
There arises between the bushes, the shaft and the mechanical member a friction coupling able to transmit particularly high-value torques without the use of a key. Therefore, clearance between the device and the shaft is avoided preventing the formation of fretting corrosion of the surface in contact with the shaft. Moreover, the total absence of clearance assures a more precise and reliable locking over time since it is no longer subjected to a key wearing out or possibly breaking up.
Greater freedom, as well as better precision, of axial and angular positioning of the mechanical member on the shaft is obtained.
For parity of transmitted torque, the device according to the invention uses smaller-section shafts, there not being the necessity of a keyway on the same shaft any longer.
Furthermore, the operations of assembly and/or dismantling of the mechanical member from the shaft are notably simplified, irrespective of the position in which the mechanical member is locked onto the shaft. In fact, the device according to the invention allows different possibilities for the removal of the mechanical member from the shaft. For instance, by acting on the means for fixing the first bush to the mechanical member, it is possible to remove only the mechanical member leaving the locking device fixed to the shaft. Alternatively, acting on the means for varying the relative axial position of the bushes, it is possible to disengage the mutual coupling of the conical bushes while maintaining the joint between the first bush and the mechanical member.
A further advantage is due to the notable economic saving from the reduction in the number and type of mechanical members which must be held in stock by users. The device according to the invention is in fact suitable also for the locking of mechanical members having hubs of reduced dimensions, and also for shafts having reduced diameter, compared to that required for the known type of lockings.
Moreover, the device according to the invention could be used advantageously—without requiring any modification—with mechanical members having a taper bore and which were pre-set for the known type of locking bushes.
According to a preferred embodiment of the invention, only smooth hollows are provided on the external surface of the first bush, thus avoiding the need of a considerable working of the external surface of the bush.
According to a possible embodiment, the first bush consists of a solid bush and the second bush has at least a split portion. Alternatively, also the first bush is of the split type.
The second bush has an annular flange at one of its end and comprises at least one longitudinal cut on at least the portion having the conical external surface.
According to the preferred embodiment, there are provided two diametrically opposite cuts only in the portion having the conical external surface, i.e. without any cut being provided on the annular flange. This ensures a better distribution of the mechanical stress with respect to a completely splitted bush, as well as a better concentricity of the device when it is mounted. Furthermore, a non-cut annular flange is less weakened and does not buckle under the pressure of the screws during the mounting.
In e
Kellenberger Peter
Scaglia Riccardo
Browne Lynne H.
Cobrin & Gittes
Cottingham John R.
Sit S.P.A.
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