Traditionally, the operation of the emergency brake or safety gear of an elevator is based on the utilization of a centrifugal force, in other words, when the speed of rotation of a certain wheel in- creases beyond a given limit value, the centrifugal force will push a certain braking or gripping element to an operating position. This movement of the braking or gripping element caused by the centrifugal force is generally opposed by a mechanically operated spring device, which is used to determine the operating lim- its and sensitivity of the device.

Prior-art devices are in themselves simple in construction and reliable in operation, but they are difficult to adjust and the stability of adjustments made is insecure. This is because the devices are op- erated very seldom, if ever, and therefore the proper- ties of mechanical springs and equivalent may change in the course of time.

The object of the present invention is to overcome the above-described drawbacks. A specific ob- ject of the invention is to disclose a new type of overspeed governor which is more reliable in opera- tion, more versatile in regard of adjustability and more accurately adjustable and better able to preserve the accuracy than prior-art devices.

As for the features of the invention, refer- ence is made to the claims.

The overspeed governor of the invention, which is designed for use in conjunction with the rope wheel of a triggering rope connected to the emergency brake or safety gear of an elevator, comprises a frame, an auxiliary frame secured to the frame and ro-

tatable in relation to it and a brake element secured to the auxiliary frame for braking the rotation of the rope wheel. In addition, the auxiliary frame is pro- vided with magnetizing means for creating a magnetic field and in conjunction with the rope wheel a pro- jecting part made of electrically conductive material and arranged to extend into the magnetic field and ro- tate with the rope wheel. Further according to the in- vention, the overspeed governor comprises a holdback extending into the magnetic field for determining the position of the auxiliary frame relative to the frame.

Thus, the overspeed governor of the invention is based on a projecting part of electrically conductive mate- rial moving in a magnetic field, wherein the eddy cur- rents generated in the projecting part produce a force acting on the magnetizing means and via these on the auxiliary frame and the braking element, said force triggering the overspeed governor into operation.

In an embodiment of the invention, the mag- netizing means consist of a pair of permanent magnets forming a gap in which the projecting part has been arranged to be movable. Although other types of mag- netizing means are in themselves applicable, a perma- nent magnet is the best and most reliable device be- cause its operation and stability are independent of external factors and remain unchanged even in the long run.

In an embodiment of the invention, the pro- jecting part consists of a disc-like plate or flange, e. g. a round and relatively thin aluminum plate, which is rigidly connected to the rope wheel so that it al- ways rotates at the same speed with the rope wheel.

Thus, the disc-like plate may be secured directly to the rope wheel or it may be mounted on the same shaft with the rope wheel so that it will rotate simultane- ously with it.

The holdback used in the overspeed governor is arranged to resist the motion of the magnetizing means caused by the forces produced by the eddy cur- rents. The holdback is preferably secured to the frame of the overspeed governor. The material, position and shape of the holdback can be used as means of adjust- ing and controlling the operation of the overspeed governor.

In an embodiment of the invention, the hold- back consists of a plate or strip of ferromagnetic ma- terial extending into the gap formed by the magnetiz- ing means. The holdback may also be so designed that it comprises at least two hold stations for holding the auxiliary frame in different rotational positions relative to the frame, depending on the magnitude of the force generated by the eddy currents.

In an embodiment of the invention, efficient braking is accomplished when the braking element com- prises a brake pad implemented as a wedge-shaped body which, when the braking device is actuated, is thrust into a rope groove functioning as a braking surface.

The overspeed governor of the invention pref- erably comprises adjusting elements for adjustment of the air gap between the magnetizing means and the pro- jecting part, i. e. of the eddy currents produced.

Likewise, the overspeed governor preferably comprises an adjusting device for adjustment of the air gap be- tween the magnetizing means and the holdback. Thus, the force acting between the magnetizing means and the holdback can be adjusted by means of the distance be- tween them, the shape of the holdback and/or the posi- tion of the holdback.

As compared with prior art, the overspeed governor of the invention has significant advantages.

The overspeed governor is very reliable in operation and independent of external influences and distur- bances. It can be easily adapted for use in different

applications by only making mechanical adjustments, i. e. by using different air gap sizes. The adjustments remain unchanged and stable even over long periods of time.

In the following, the invention will be de- scribed in detail with reference to the attached draw- ing, wherein Fig. 1 presents a diagrammatic partially sec- tioned view of an overspeed governor according to the invention, and Fig. 2 presents a diagrammatic side view of the overspeed governor in Fig. 1.

An overspeed governor according to the inven- tion as presented in the drawing comprises a fixed frame 3 in conjunction with the rope wheel 2 of a triggering rope 1 connected to the emergency brake or safety gear of an elevator, the rope wheel 2 being ro- tatably mounted in relation to said fixed frame. Se- cured to the frame 3 is an auxiliary frame 4, which is turnable in relation to it. The free turning movement of the auxiliary frame 4 relative to the frame 3 can be controlled or limited e. g. by means of a suitable spring or by gravity. Secured to the auxiliary frame 4 is a braking element 5 for braking the rotation of the rope wheel 2. The braking element 5 is provided with a wedge-shaped brake pad 11, which has been fitted to brake the rope wheel by the wedge-shaped rope groove 10 of the wheel.

In addition, the overspeed governor comprises magnetizing means 6 secured to the auxiliary frame 4 and consisting of a pair of permanent magnets, which form a gap 9 between them. Mounted on the same shaft with the rope wheel 2 is a projecting part 7, i. e. a round aluminum plate extending into the gap 9 formed by the pair of permanent magnets between them, so that it rotates simultaneously with the rope wheel. Ar-

ranged to extend into the same gap is also a holdback 8, i. e. a thin band-like steel strip.

The overspeed governor of the invention pre- sented in the drawing works as follows. At normal op- erating speeds, the aluminum plate 7 rotates in the gap 9 so that the eddy currents produced are insig- nificant and do not generate any forces that would cause operation of the device. On the other hand, in exceptional conditions when the rope wheel for some reason rotates at an excessive speed, the aluminum plate is rotating at a corresponding speed, in other words, moving at this speed in the gap 9. In this situation, due to the strong eddy currents set up in the aluminum disc, a sufficiently strong force is gen- erated between the aluminum disc and the permanent magnet, causing the auxiliary frame 4 and together with it the braking element 5 to turn. Thus the brake pad 11 gets wedged into the rope groove 10 of the rope wheel 2 and stops the rope wheel and therefore the triggering rope 1, which again leads to the final ac- tion, such as operation of the safety gear.

In the foregoing, the invention has been de- scribed by way of example with reference to the at- tached drawing while different embodiments of the in- vention are possible within the scope of the inventive concept defined in the claims.