Abstract:
A method for braking a traction sheave elevator stops the elevator in the event of an emergency by the braking of the elevator using a braking device not comprised in the drive machine. A traction sheave elevator is provided with a braking device not comprised in the drive machine and designed to improve the efficiency of emergency stopping. The maximum force decelerating the elevator and generated by the braking device equals about half the weight of the nominal load of the elevator.

Description:
This application is a Continuation of copending PCT International Application No. PCT/FI00/00783 filed on Sep. 15, 2000, which was published in English and which designated the United States and on which priority is claimed under 35 U.S.C. §120, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method for braking a traction sheave elevator, to a traction sheave elevator and to the use of an emergency power supply. 
     DESCRIPTION OF THE BACKGROUND ART 
     The machine of a traction sheave elevator consists of a traction sheave with the elevator hoisting ropes fitted to its grooves and an electric motor driving the traction sheave either directly or via a gear. The machine is provided with a brake, which applies a braking force to the traction sheave either directly or e.g. via the shaft. The operating brake of the elevator works under positive control such that the brake is always braking when it is not specifically caused by the control system not to brake. In a typical operating brake construction, the brake is closed by the force of a spring or an equivalent element, and a controllable actuator counteracting the closing element releases the brake and keeps it released. When braking is applied to the traction sheave, the braking effect is transmitted further to the elevator ropes by the action of the frictional grip and other gripping forces applied by the traction sheave to the ropes. In an emergency braking situation where the elevator is stopped as quickly as possible, a greater gripping force is likely to be needed than when the elevator is being accelerated and decelerated during normal operation. 
     To improve the grip between the ropes and the traction sheave, the grooves on the traction sheave of especially fast elevators and elevators with a large hoisting height are sometimes heavily undercut. The grip can also be improved by increasing the rope angle. Solutions increasing the rope angle are e.g. ESW (extended single wrap) and double-wrap suspension arrangements, in which crosswise roping or a secondary rope pulley is used to achieve a contact angle larger than 180 degrees between the ropes and the traction sheave. In conventional single-wrap suspension (CSW), the contact angle between the ropes and the traction sheave is 180° or somewhat less if the distance between the ropes is increased using a diverting pulley. Thus, both undercut rope grooves and increasing the undercut as well as increasing the contact angle improve the grip. 
     For normal operation, in most elevators, including high-rise and fast elevators, conventional single-wrap suspension with the hoisting ropes only passing over the traction sheave and a very moderate undercut in the grooves of the traction sheave would be sufficient to guarantee a non-slip grip between the traction sheave and the ropes with all elevator load alternatives. However, to provide for emergency braking, the system has to be designed so as to ensure a better grip. Improving the grip, however, leads to drawbacks that increase the costs of the elevator, especially the costs arising during operation. An undercut promotes wear of the rope and the rope groove; the larger the undercut, the faster the wear. Similarly, in ESW and double-wrap suspension, rope bends following each other at short distances increase rope wear. In ESW and double-wrap suspension, rope skew is another factor increasing rope wear. Double-wrap suspension produces a particularly hard strain on the bearings of the traction sheave and the secondary rope pulley. 
     On the other hand, a point to remember is that emergency braking must not be too effective. If the braking is too effective, the rapid deceleration of the elevator car may involve a danger to the passengers. A deceleration rate exceeding gravitational acceleration during upward travel of the elevator is sufficient for the passengers to loose contact with the floor of the elevator car. Depending on the initial deceleration rate, this will cause the passengers to be hurled against the ceiling of the elevator car or at least to tumble. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to remedy the above-mentioned defects and at the same time to extend the use of conventional elevator suspension based on an advantageous fundamental solution to elevators designed for higher speeds or a greater hoisting height. Another object of the invention is to disclose an easy method for utilizing a brake not comprised in the drive machinery in a situation where passengers are to be freed from an elevator that has stopped due to a power failure. 
     The invention makes it possible to extend the safe field of application of CSW-type elevators to elevators designed for higher speeds or a greater hoisting height without having to compromise on the useful life of the ropes or the traction sheave as a consequence of a significantly improved grip between the ropes and the traction sheave. Using a simple arrangement, the invention also leads to an improvement in the operating characteristics of fast and high-rise elevators. Safe extension of the field of application is achieved by increasing the braking force applied during emergency braking and at the same time taking care that the deceleration of the elevator car is not increased excessively. In high-rise elevators, which are among the fastest elevators, the mass of the car typically equals two to two-and-a-half times the nominal load while the mass of the counterweight typically equals the mass of the car plus half the nominal load. Additional masses to be accelerated in the elevator include e.g. the mass of the ropes. When, according to the basic idea of the invention, the decelerating force generated by a braking device not comprised in the drive machine is kept at a clearly lower level than the weight of the nominal load of the elevator, harmful deceleration rates during emergency braking of the elevator are avoided. 
     As the braking device not comprised in the drive machine but placed at a large distance from the elevator machine room has to be released using an emergency power supply from the machine room or the release of the brake has to be effected in some other way from a distance, the emergency power supply or other emergency device used can be a device with moderate ratings, because the braking device is of a moderate size regarding its braking force and the energy required for its release and therefore also its efficiency. 
     Using the solution of the invention, a longer useful life of the ropes and traction sheave are achieved. The drive machine can be implemented using a solution involving no large internal stresses, thus reducing e.g. the load on the bearings. The service life of the ropes, traction sheave and bearings may even be increased to several times their usual durability. On the whole, simpler solutions regarding the machine and rope suspension can be achieved. As CSW suspension does not require any voluminous diverting pulley arrangements in the machine room, even a very large elevator will only need a moderate machine room floor area. No heavy supporting structures for diverting pulley arrangements are needed. The moderate size and weight of the machine achieved by the invention allow easier machine room lay-out and installation work. High-performance machines are often part of an elevator group of several elevators, and in this situation the advantage regarding space utilization provided by easy placeability is accentuated. The brake not comprised in the drive machine as provided by the invention can be used safely and without any major special measures in a situation where passengers are to be freed from an elevator that has stopped due to a power failure. 
     Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention will be described by the aid of an example of its embodiments, without limiting the range of application of the invention as such, with reference to the attached drawings, wherein 
     FIG. 1 illustrates the placement of a drive machine according to the invention, 
     FIG. 2 presents a brake engaging a guide rail, and 
     FIG. 3 illustrates the principle of an arrangement for the release of brakes not comprised in the drive machine. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates the placement of an elevator drive machine  1  in a machine room  45  above an elevator hoistway  39 . The drive machine is placed on a mounting base  46  constructed from steel beams. The distance between the portions of the hoisting ropes  48  going to the counterweight  3  and to the elevator car  4  has been increased by placing a diverting pulley  47  so that the distance is somewhat larger than the distance corresponding to the diameter of the traction sheave  2 . The brake  6  of the drive machine functions primarily as a hold brake when the elevator is standing still. A preferred method of braking an elevator is electric braking. Generally, in electric braking, even in case of power failure and emergency stop, the motor brakes regeneratively. The operating brake  6  is engaged, increasing the braking power. Thus, the traction sheave is heavily braked while the ropes, counterweight, elevator car and other masses suspended on them tend to continue their movement. If the grip between the traction sheave and the ropes is insufficient, then the rope will start slipping, and braking the traction sheave will not stop the elevator. In an elevator like that in FIG. 1, the risk of rope slip is present when the speed is relatively high or when there is a very great imbalance between the car-side and the counterweight-side parts of the system. In high-rise and fast elevators, however, the car and the counterweight are so heavy that even a 25% overload as such will not cause rope slip. At lower speeds, if the elevator is conventionally designed, the rope does not start slipping when the brakes are suddenly applied as in the case of an emergency stop. At higher speeds, when the speed is several meters per second, it is very likely that the rope will slip, especially if the undercut of the traction sheave rope grooves has been designed to produce only slight rope wear. 
     In practice, the invention is implemented e.g. by providing the drive machine with a brake, the drive machine comprising a traction sheave driving the hoisting ropes and, via the hoisting ropes, moving the elevator car and counterweight suspended on the ropes. In the case of an emergency stop, the brake falls down on the traction sheave to decelerate its motion. Emergency stop is activated in a manner known in itself. Emergency stop is complemented by using a braking device  10  not comprised in the drive machine. There are several alternatives as to the point of application of the braking action of the braking device not comprised in the drive machine, because it is intended to decelerate the motion of the elevator car independently of the friction between the elevator ropes and the traction sheave. The action of the braking device may be applied e.g. to the elevator ropes, to a guide rail or to an equalizing gear. A preferable solution is e.g. a forceps-like device applying a braking action to a rope, a guide rail or an equalizing gear. The braking device not comprised in the drive machine can be caused to start its braking action before the main brake of the elevator is engaged. This may result in avoiding rope slip altogether and accomplishing braking using the brakes only. On the other hand, it is possible to utilize rope slip during braking. This will distribute the heat produced by the braking action to several points. Utilizing the rope slip reduces the required braking force of the braking device not comprised in the drive machine. However, in practice the brake in the drive machine brakes first, or the brake in the drive machine and the braking device not comprised in the drive machine start braking at about the same time. Thus, the auxiliary brake complements the braking by receiving any residual force that the brake of the drive machine may not be able to absorb. 
     As for elevator control, the control of the brakes not comprised in the drive machine is preferably implemented by monitoring the elevator speed as well as the operational state of the brake in the elevator machine. If the brake in the elevator machine starts braking and at the same time the elevator speed is higher than a set speed, e.g. higher than 1 m/s or 1.6 m/s, then the brakes not comprised in the drive machine are applied. In this way, it is possible to avoid tripping the braking device not comprised in the drive machine. 
     If the braking device not comprised in the drive machine is implemented as an eddy current brake, e.g. using permanent magnets by causing the magnets to interact with the elevator guide rails, then the contribution of such a device to the deceleration is dependent on the speed. It is possible to implement a mechanical braking device gripping a guide rail or rope that will only brake when the speed exceeds a set speed. Thus, the braking device will not be tripped e.g. during servicing operation when the elevator is operated at a relatively low speed, even if the safety circuit of the elevator should be open, and the device therefore does not require separate shunting of the safety circuit. On the other hand, the braking power of an eddy current brake is insignificant at a low speed, so such a brake will not hamper servicing operation. 
     FIG. 2 presents a brake  110  applying a braking action to a guide rail. Such a brake may alone constitute a braking device ( 10 ) not comprised in the drive machine according to the invention. However, a preferable braking device solution is one in which two brakes  110  releasable by electromagnetic means and closeable by spring force work together as a brake pair in which each brake applies its braking force to a different guide rail. In the brake  110 , the iron core  113  of the releasing winding (not shown in the figure) of the brake consists of two disk packs  111  which have extensions forming the jaws  112  of the forceps-like brake and are separated by an air gap  116  that changes as the brake is operated. The jaws  112  are provided with brake pads  115 , which are pressed against the guide rail  114 . The integrated iron core brake jaw combination, i.e. the disk packs ill are pivoted on pivot pins  118  located between the jaws  112  and the iron core  113  and fastened to a frame  120  supporting the brake. The braking force of the brake  110  is generated by springs  117  compressing the jaws  112 , presented in the figure as disk springs. Other types of spring, e.g. spiral springs may also be used. The springs are placed around a bar  119  going through the springs  117 . At least one end of the bar is provided with a thread fillet. By means of nuts  121 , the springs are kept compressed between the ends of the bar  119 , applying a pressure to the jaws  112 . Using the nuts  121 , the braking force can be adjusted within the limits imposed by the structure and the components. 
     FIG. 3 presents an arrangement for releasing the brakes  110  not comprised in the drive machine. Normally, the electrical and control equipment  151  of the elevator provide a supply of electricity to and operational control of modules  152  operating the brakes not comprised in the drive machine, which are mounted on the elevator car. These modules  152 , which in their simplest form may be controlled switches, supply a relatively large current to the brakes  110  when the brakes are being released, and subsequently a smaller holding current. The electricity to the brakes is supplied via conductors  153  in the car cable, or by a corresponding method. To allow the brakes mounted on the elevator car to be released via control from the machine room, it is necessary to provide an electricity supply needed for releasing the brakes. In the event of a power failure, the brakes are closed to brake by gripping the guide rail while the main operating brake of the elevator brakes the rotation of the traction sheave. To enable the passengers to leave the car, these brakes need to be released and the elevator car has to be moved to the level of a nearby hoistway door. By using an emergency power supply  154  and a control unit  155  provided in conjunction with the emergency power supply or a separate control unit or control functions comprises in the electrical and control equipment  151  of the elevator, the brakes  110  engaging the guide rails  114  are caused to release their grip. The required releasing and holding current is obtained from the emergency power supply. The emergency power supply also supplies the electric power needed by the control unit used. If the elevator&#39;s own control panel  151  is used, then the normal operating functions and the supply of electricity to the elevator machine are disabled either by control functions or otherwise. Similarly, other activities consuming significant amounts of power are disabled to make sure that the limited power supply capacity of the component, e.g. battery, of the emergency power is supply used to generate or store electric power is not exceeded. After these brakes  110  not comprised in the drive machine have been released, the brake in the drive machine can be released and the elevator car can be moved to a suitable floor to free the passengers. As the brakes not comprised in the drive machine have been designed to provide a relatively low braking power, releasing the brakes does not require a very high operating power. By releasing the brakes  110  chronologically in succession, the maximum current drawn from the emergency power supply will be quite small. 
     It is obvious to the person skilled in the art that the embodiments of the invention are not restricted to the example described above, but that they can be varied within the scope of the following claims.