GB2163127A - Elevators with improved car levelling - Google Patents

Abstract

An elevator drive sheave 18, from which a car is suspended by cables 16, has a drive shaft 24 rotatably supported by a frame 28a. A main hoist motor 30 is coupled to the drive shaft 24 through gearing 34, and means (32) is operable for absorbing reaction rotational torque of the hoist motor 30. The means (32) includes auxiliary drive means 37 for selectively pivoting the hoist motor 30 and thereby the drive sheave 18 about the axis of the drive shaft 24 while a hoist motor brake is engaged. As a result; the car may be repositioned, by actuating auxiliary drive motor 37 to rotate screw 38 with respect to a nut carried by the housing of the gearing 34, while the car is stopped at a landing and without using the hoist motor. In another arrangement, the auxiliary drive means is operable to pivot the hoist motor and the drive sheave about an axis spaced from the axis of the drive shaft. <IMAGE>

Description

SPECIFICATION Elevators with improved car levelling The present invention is concerned with levelling an elevator car and in particular with re-levelling the car while at a landing with the doors open.

In a conventional traction-type elevator system, the main hoist motor is controlled so as to stop a moving elevator car at a desired floor so as to be level with the landing sill. When positioned, the main hoist motor is stopped, and the elevator brake is engaged to hold the car in position while the elevator doors are open.

Although the elevator control is normally adjusted to stop the car level on its original approach to the landing, variations in levelling accuracy can be caused by for example misadjustment, wear or temperature. Even if the car is stopped level, it is common for the elevator car to move relative to the landing sill while the doors are open, This occurs due to the fact that the elevator cables are resilient and the fact that the weight of the car changes as passengers enter and leave. For such reasons, it is sometimes necessary to re-level the elevator car with the doors open.

It is a common practice to utilize the main hoist motor to correct errors in the level of the elevator car. In the event re-levelling is required and the elevator car is stopped at the landing, the holding brake is released, and the main hoist motor is actuated by bypassing the hoistway door interlocks and the car gate switch, which normally disable the motor. However, it is difficult to carry out this procedure without producing undesired car movement. While the car is stopped, the holding brake supports the net unbalance in the system. The release of the brake must therefore be coordinated precisely with the energisation of the motor so that the motor has developed sufficient torque to support this unbalance as the brake releases. Correspondingly, to avoid a jerking motion, the brake should not remain engaged too long afterthe main hoist motor is actuated.

In addition to the difficulty of synchronising the release of the brake with the actuation of the motor, the controls for effecting simultaneous motor/brakerelease operations are subject to misadjustment or variations overtime. As a result, during the initiation of re-levelling operations, it is possible that the car may be permitted to move further away from the level of the landing sill before actual correction occurs. This is obviously undesirable since, during this time, people may be entering or leaving the car.

Some prior art elevator systems have attempted to pre-torque the hoist motor before releasing the brake by sensing the load in the car. This method is inadequate since the load in the car is only one of the conditions contributing to the unbalance. In an uncompensated system, the weight of the hoist ropes can change the unbalance depending on the vertical position of the car in the hatchway. Travelling cables also contribute to the unbalance, depending on car position.

In addition to the difficulty of transmitting smoothly the weight-holding function from the brake to the motor, another shortcoming of these known systems lies in the fact that the equipment used to accomplish this task is designed to move the car large distances, at high speeds. However, the intent of the levelling action is to move the car only incremental distances, at low speed. This further complicates the re-levelling procedure, and a control malfunction could cause the car to move abruptly.

In place of using the main hoist motor for relevelling, it has been proposed to interpose a linear actuator between the elevator sling and the hitch plate to which the hoist ropes are fastened. A motor, positioned in the top of the elevator car, actuates the linearactuatorto move the sling up ordown relative to the hoist ropes, without using the main hoisting machine.

Such a system has disadvantages. The auxiliary motor must lift both the car and all equipment supported by the car as well as the live load. No part of this load is counter-weighed as far as the auxiliary hoist is concerned and, therefore, a relatively large auxiliary motor needs to be mounted on the car. In addition, powerforthis auxiliary hoist motor must be carried through travelling cables, and it is difficult to make an auxiliary hoist motor on the car that is sufficiently quiet.

Movement of the elevator car away from the landing is detected by levelling transducers, normally mounted on the elevator sling; or the car level may be controlled by a selector mechanism, having a selector cable fastened to the elevator sling. In either case, the indicia of car position used is the position of the sling. However, the cab floor can move with respect to the sling due to compression of rubber or deflection of other parts. Use of the conventionally mounted levelling transducer or the selector to position the sling may result in the cab platform being some distance from the landing sill.

An aim of the present invention has been to provide an elevator having an improved levelling system, whereby the height of the elevator car may be adjusted without releasing the brake or energising the main hoist motor.

In accordance with the present invention, an elevator comprises: a car supported by a cable and vertically displaceable between landings in a hoistway; a frame; a drive sheave supporting said cable and having a drive shaft rotatably supported directly or indirectly by said frame; a main motor means coupled to said drive shaft for transmitting rotational torque to said drive sheave, for moving the car between landings; a brake means selectively engageable for stopping said main motor means and said drive shaft, for holding the car at a selected landing; and means operable between said main motor means and said frame for absorbing reaction torque and including auxiliary drive means for selectively pivoting said main motor means and thereby said drive sheave about a pivot axis while said brake means is engaged, for raising or lowering the position of the car.

In other words, the main traction (drive) sheave in the penthouse and the main driving (hoist) motor are supported so that the drive sheave may be turned about its own axis or about somme other pivot axis in order to move the car and the counterweight while the hoist motor brake is engaged.

Ina preferred embodiment, the drive shaft is mounted in bearings directly on the frame. The main hoist motor is connected through a gear reducer to the drive shaft, and the gear reducer housing is connected to the frame through a screw-type linear actuator. When the actuator is stationary, the connection absorbs the reaction torque of the main motor so that the main motor can turn the drive sheave, when the actuator is actuated, the gear reducer housing is caused to move relative to the frame, such that its pivots about the axis of the drive sheave. This motion rotates the drive sheave and raises or lowers the hoist ropes connecting the car a pre-selected amount. Preferably, a pair of stops are provided to limit the degree of motion permitted of the housing.Also preferably, a pair of switches are provided to sense the centre position of the housing, and a control means is provided to return the housing to the centre position as the car moves between floors.

The invention may be utilised in arrangements both where the cable passes over a single drive sheave, and where an idler sheave is used. In the latter case, it may be preferable to support the linear actuator overhead of the drive and the idler sheaves.

In each case, the linear actuator is arranged to engage the housing at an angle tangent to a circle centred on the pivot axis, which in this case is the axis of rotation of the drive sheave.

In an alternative arrangement, the drive shaft is supported indirectly by the frame on a member pivotable relative to the frame. This pivot axis is spaced from and parallel to the rotational axis of the drive sheave. Both the main hoist motor and the drive shaft are pivotable by a linear actuator arranged between the pivoting member and the frame. An idler sheave is provided such that the drive and idler sheaves are located on opposite sides of the pivot axis in a "seesaw" type of structure.

Preferably, levelling transducers are mounted on the elevator cab, and actuating cams or vanes are positioned at each of the floors. The car is stopped at selected floors by these levelling transducers. These levelling transducers are then utilised to actuate the linear actuators so as to complete the levelling process, if the car is slightly misadjusted, and also to re-level the car during the time the elevator doors are opened. When the elevator car doors are again closed, and the elevator is travelling between floors, the linear actuator is energised to return the main hoist motor housing to its centre position so that upon arriving at the next floor, it can be moved in either direction to raise or lower the car as required.

Preferably, means are also provided to produce an analog signal indicative of the magnitude and direction of the weight unbalance in the system without regard to the cause of the unbalance. This analog signal may be used to pre-torque the hoist motor to cancel the effect of the unbalance before releasing the brake.

The torque arm connection is an ideal place to measure this static unbalance. In one embodiment, a pressure transducer is used with a hydraulic actuator. Alternatively, a strain gauge is used with a mechanical actuator. Based on this transducer output, the motor torque is set-before the brake is released.

The preferred features of the present invention may be expressed in the following terms.

Said pivot axis may be concentric with the axis of said drive shaft in which case, if said main motor means has a housing, said auxiliary drive means may be connected between said housing and said frame. Said main motor means may have an output shaft and a plurality of gears coupling said output shaft and said drive shaft in which case, if said plurality of gears has a housing, said auxiliary drive means may be connected between said housing and said frame. Alternatively said pivot axis may be spaced from the axis of said drive shaft, and said drive sheave and an idler sheave may be disposed on opposite sides of said pivot axis.

Preferably: said auxiliary drive means includes a linear actuator; said linear actuator extends tangentially to a circle centered on said pivot axis; said linear actuator is in the form of a screw-threaded member for rotary movement relative to a nut-like member; said screw-threaded member is pivotally mounted to said frame; and end stops on said frame restrict pivotal movement of said main motor means about said pivot axis.

In some arrangements, position sensor means is mounted on the car, and control means is provided for disabling said main motor means and engaging said brake means when the car is at a landing, said control means being responsive to said position sensor means, when said main motor means is disabled and said brake means is engaged, for selectively actuating said auxiliary drive means.

Means may be provided for detecting a centre position of said auxiliary drive means, said control means being responsive to said centre positiondetecting means when said main motor means is energized for actuating said auxiliary drive means for returning said auxiliary drive means to its centre position, with said position sensor means being positioned at each landing and on the car for sensing misalignment between the car and a selected landing.

In other arrangements, the car includes a cab having a platform and position sensor means is mounted on said cab and isfixed relative to said platform for controlling said auxiliary drive means.

Means may be provided for sensing a centre position of said auxiliary drive means and for responding to travel of the car between landings for returning said auxiliary drive means to its centre position, with said position sensor means being positioned at each landing and on the car for sensing misalignment between the car and a selected landing.

Finally, load sensor means is preferably connected to said means for absorbing reaction torque for generating a signal indicative of elevator unbalance, said signal being usable for controlling restarting of a stopped car.

Several elevators, in accordance with the present invention, will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a front, schematic view of an elevator having an improved levelling system; Figures 2 and 3 are front and side views, respectively, of a first specific embodiment of the invention; Figure 3a is a side view similar to Figure 3 of a second specific embodiment having a belt-driven gear reducer; Figures 4 and 5 are front and side views, respectively, of a third specific embodiment; Figures 6 and 7 are front and side views, respectively of a fourth specific embodiment; Figure 8 is a side view of a fifth specific embodiment; and Figure 9 is a schematic circuit diagram of a control system for any of the elevators shown in Figures 1 to 8.

Referring to Figure 1, an elevator has a car 10 which includes a cab 12 supported within a sling 14.

The car 10 is suspended from cables 16 which are wrapped over a drive sheave 1 and extended around an idler sheave 20 to counterweights 22. The car is vertically displaceable between landings in a hoistway in a conventional manner.

The drive sheave 18 has a drive shaft 24 rotatably supported, by bearings 26, on a frame portion 28 in the penthouse of the elevator. A main hoist motor 30 is coupled, either directly or through intermediate gears, to the drive shaft 24, and a coupler 32, which is indicated only schematically, is connected between the motor 30 and frame 28 for absorbing reaction torque. As discussed below, the coupler 32 includes a linear actuator or other such device.

In Fig. 1, the car 10 is stopped at a landing L so that the platform 1 2a of cab 12 is level with the landing sill S. A positioning indicator 15, e.g. a transducer, is mounted on the platform 12a, and registers with an actuating device 17, e.g. a cam or vane, attached at a fixed position on the hoistwaywall H, for indicating the position of the platform 12a relative to the landing sill S. Leveling transducers and the like for indicating relative position, are well known. Alternatively, the actuating cam or vane may be mounted on the elevator guide rails (not shown).

Figs. 2-3 show a first arrangement in which the drive shaft 24 of the drive sheave 18 is mounted for rotation on the frame 28a in a pair of spaced bearing blocks 27. The drive sheave 18 is connected -to a conventional gear reducer 34, which in turn engages the output shaft of a main hoist motor 30. The gear reducer may be a so-called "hollow output shaft" gear reducer, and is "hung" on an extension of the sheave drive shaft. The motor 30 is flange mounted to the gear box of the reducer 34. A disk brake 36 (Figure 3) on the hoist motor output shaft may be selectively engaged to lock the main hoist motor 30, and thereby the drive shaft 24, from rotating.

Since the main hoist motor and reduction gear box are hung from the shaft 24, the gear box must have e torque arm connection, i.e. coupler 32 as shown diagrammatically in Fig.1, to produce the reaction to its output torque. In Figs. 2-3, this torque arm connection includes a motor-driven linear actuator, which comprises an auxiliary motor 37, pivotally connected at 41 to the frame, driving an output screw 38. The screw 38 is threaded through a nut 39 retained by a yoke shaped torque arm flange 40 of the gear box housing 34, such that rotation of the screw 38 by motor 37 causes the flange 40 to move linearly back and forth along the screw axis. Preferably the nut 39 is pivotable in the yoke 40, as indicated at 43, the pivotable connections of the nut 39 and motor 37 permitting the yoke 40 to move back and forth without binding.

As can be seen, when the flange 40 is displaced by the screw 38, the entire gear box housing and shaft 24, which are locked together as a unit when the brake 36 is engaged, rotate about the axis of shaft 24, thereby rotating the drive sheave 18. As such, the cables 16 and elevator car 10 can be moved a limited amount for re-leveling without releasing the brake or energizing the hoist motor.

A pair of mechanical end stops 42 are provided at either end of the travel of flange 40 to limit the extent by which the motor/gear box unit can pivot and also to engage the gear box in the event of a failure of the screw 38 or nut 39. In addition, as shown, a pair of switches 44,45 and a centering cam 46 may be provided as an indication of the center position of the flange 40.

Fig. 3a is similar to Figs. 2-3, except that the output shaft of motor 30 is coupled to the gear reducer 34 through a pulley/belt arrangement 34a, rather than being connected directly to the input shaft of the reducer 34. The mechanical stops and centering switches have been omitted for clarity. In Fig. 3a, gear reducer 34 is upside down, as compared with Fig. 3, and motor 30 is fixed to the upper portion of the housing for clearance. Also, yoke flange 40 extends from the end of the reducer housing opposite that in Fig. 3, but in operation the leveling mechanisms of Figs. 2-3 and 3a are equivalent.

In the embodiment shown in Figs. 4-5, the drive shaft 24 of the drive sheave 18 is supported in bearing blocks 26b on a pair of spaced channels 48 of the frame. The linear actuator motor 37 is pivotally mounted at pivot 50 to a portion of the frame 28b so as to be overhead of the drive sheave 18. An idler sheave 20b is also mounted in bearing blocks 52 on the channel members 48 so that the ropes 16 pass over the drive sheave 18 and idler sheave to the car 10 and counterweights 22, respectively. The hoist ropes are double-wrapped for added traction.

The gear reducer 34 extends vertically up from the shaft 24 so that the motor 30 and torque arm flange 40 are overhead to engage the screw portion 38 of the linear actuator shaft. As in the Figs. 2-3 embodiment, the screw 38 engages the flange 40 at an angle tangent to the axis of rotation of the gear box housing about shaft 24.

Figs. 6-7 illustrate an embodiment of the invention in which the drive shaft 24 of the sheave 18 is pivotably supported by the frame. A pair of support channels 60 are pivotably supported between frame members 62, and rotatably support the shafts of the drive sheave 18 and idler sheave 20d on opposite sides of the pivot. The output shaft of the main hoist motor 30, through a solidly mounted gear reducer 34, is connected to the drive shaft 24 of the drive sheave 18. A linear actuator 32 is attached between the channels 60 and the fixed portion of the frame 28d, so that the channels, sheaves, and main hoist motor may be pivoted about the pivot axis. A pair of end stops 42a are provided, which limit the angle of pivot of the channels 60 provided by the screw 38/nut 39 combination.Although not shown, centering switches may be provided in a manner similar to the other embodiments. As shown, the ropes are double wrapped around the drive and idler sheaves for greater traction.

Fig.8 illustrates a leveling mechanism used with a gearless elevator drive. A DC motor 30' has an output drive shaft 24' supported in bearings in a pair of spaced pedestals 27', forming part of frame 28'.

Drive sheave 18' is mounted directly on the output shaft 24'.

Atorque-arm connection, in the form of linear actuator 37, 38 engaging a nut 39' pivotably mounted to the motor housing, absorbs rotational torque when the motor 30' is running. The linear actuator is also capable of selectively pivoting the motor 30' and drive sheave 18' about sheave axis 24' when the motor 30' is stopped and disc brake 36' is engaged. End stops 42' may be provided on either side of the motor (one pair is shown), between the motor and frame, to limit rotational movement.

A strain gauge 90 is positioned on linear actuator 37,38, to provide an indication of the instantaneous imbalance in the system. Alternatively, a pressure transducer or the like may be employed. The load signal maybe used as an input to known control systems for starting a stopped car, which pretorques the main hoist motor to compensate for imbalance, priorto releasing the brake.

As discussed above, imbalance results from a number of factors. Unlike the known inputs to such compensating systems, typically weight sensors attached to the car, the sensor 90 provides a true indication of system imbalance acting on the main drive sheave, without regard to the source of that imbalance.

In Fig. 8, the motor shaft 24', which is also the drive shaft for drive sheave 18', extends from either end of the motor housing to be supported in bearing blocks. Alternative support configurations are possible. For example, one end of the shaft may be supported in a bearing in the end bell 31' portion of the motor housing. This bearing may then extend into a bearing into the pedestal block.

In operation, once the car is at the landing, the main hoist motor is stopped and the elevator brake engages. While the car is at the landing, the net load of the car, and the amount of elongation in the hoist ropes, may change as passengers enter and leave. If the elevator cab moves away from the landing sill S by greater than a predetermined distance, the auxiliary motor 37 is actuated to either raise or lower the car.

A loaded elevator, arriving at a lobby of a fairly tall building, might have to re-level several times as the passengers exit the elevator. In the elevator in accordance with the invention, the cab platform may be maintained very close to the level of the landing since corrections as small as 1.6mm can easily be made. It is almost impossible to release the brake and move the main hoist machine such a small distance, or as quickly and as smoothly as the present invention.

If desired, the present invention may be utilized for final positioning of the car at the landing sill when the elevator is arriving. Accordingly, the main hoist motor may be used to move the cab to approximately the position of the sill, and thereafter the auxiliary positioning system may be actuated for final leveling. However, as discussed above, even elevator systems in which the main hoist motor initially positions the cab with sufficient accuracy have the need for the re-leveling feature when the doors are open.

Fig. 9 is a diagram ofan illustrative control circuit for adjusting the position of the car relative to the landing sills. A conventional circuit for actuating the main hoist motor includes a pair of relays 110, 112, which enerize the main hoist motorforthe up and down directions, respectively, and a relay 114which when actuated releases the holding brake. The hoist up relay 110, when actuated, also opens "up" switch 116, and closes "up" switch 118. The down relay 112, when actuated opens "down" switch 120 and closes"down" switch 122. A door interlock switch 128 is also provided, which interrupts the main hoist motor actuating circuit when the doors are open, so that the elevator car cannot be moved by the main hoist motor.

The element 200 is a switch (relay contact) that is opened as the car begins a high speed run, and closes, during slowdown, as the car approaches the target floor. For stopping the moving elevator car, a pair of leveling switches, a "platform level up" switch 130, and a "platform level down" switch 132, are provided. Switches 130,132 are part of positioning indicator 15 (see Fig. 1). When the sling and cab of the moving elevator reach a landing, depending upon the direction of car movement, switch 130 or 132will be closed to actuateasling level up relay 134 our a sling level down relay 136.The relays 134,136 open the sling level up switch 138 and sling level down switch 140, respectively, to open the energizing circuit of the actuated relay 110 or 112, and stop the main hoist motor.

An "up run" switch 124 and "down run" switch 126 are also provided. The switches 124 and 126 are used for re-starting a stopped elevator once the doors are again closed. As shown, the switches 124, 126 by-passshe switches 118, 122, 138 and 140 so that, once tfie doors close (re-closing switch 128), the relay 110 or 112 may be actuated, to re-start the elevator, regardless of the position of the other switches. Switches 124,126 should open about the time that the door zone is energized so that switches 138 and 140 have control of the stopping of the elevator. Finally, a door zone switch 142 (see also Fig. 1) normally connected to be closed when the sling is in position near the sill to actuate a door zone relay 144 to allow power door operation.

The switch 200 prevents the "Level Up", "Level Down", and "Door Zone" relays from operating as the car leaves a landing, or is running past landings at high speed, or during the initial part of the deceleration if the slowdown distance is greater than one floor. It is closed while a car is stopped.

A pair of oppositely acting "run" switches 174, 176 are arranged in series with the switches 150, 152 and switches 44, 45 whose function is described below.

When the car is stationary, switch 174 is closed and switch 176 is open. While the car is moving, switch 174 is open and switch 176 is closed. Accordingly, only one of the parallel circuits, that containing switches 150, 152 or that containing switches 44,45 is active at one time.

As noted above, "platform level up" switch 130 and "platform level down" switch 132 are mounted to be actuated when the elevator car is not level with the sill. These switches, through relays 134, 136, are used to stop the moving car level with the sill.

Relays 134, 136 also actuate switches 150, 152. The circuit containing switches 150 and 152 is inoperative while the car is moving (switch 174 is open), and thus in this embodiment switches 150,152 do not affect the stopping procedure. But, when the main hoist motor is stopped, i.e. when the switch 174 is closed, and the car is stopped at the landing, the circuit containing switches 150, 152 is active. Closing of switch 150 or 152, which occurs when one of the switches 130, 132 is closed (indicating the car is not level), will re-level the car as described below.

In the position of the switches shown, the car is stopped at the landing, and switch 174 is closed. The platform either had been stopped by the main hoist motor below the level of the sill, or has since moved down relative to the sill. As a result, the "platform level up" switch 130 has been closed. Closing of switch 130 energizes relay 134 to close switch 150. A corresponding result occurs if the car is too high, actuating switch 132, to cause switch 152 to close.

The switches 150, 152 selectively actuate a "platform level up relay" 154ora "platform level down relay" 156. Actuation of either of the relays 154, 156 closes an appropriate switch to energize the auxiliary motor 37, to actuate the linear actuator and cause the car to move up or down. The relays 154, 156 are shown schematically as being connected to a triple switch 160, for reversing the direction of rotation of the motor 37; however, any appropriate arrangement may be used.

In view of the direct electrical positioning control effected by this arrangement, a transducer or switches 150, 152, or other such position indicator may be directly mounted on the cab, so that the level of the cab is accurately measured and precisely controlled.

When the elevator car is repositioned, the torque arm 40 or 4a (Figs. 6-7) moves relative to the screw 38, that is, the linear actuator is no longer at its center position, which causes one of the switches 44, 45 to close. As shown the switches 44, 45 are arranged in parallel relative to the corresponding switches 150, 152 and while the car is stopped, switch 176 is open, so that switches 44, 45 do not interfere with the leveling function of switches 150, 152.

As soon as the car moves away from the landing toward the next floor, switch 174 is opened, dis abling the circuit containing switches 150, 152, and switch 176 is closed. At such time, if the linear actuator is out of center position, the actuator centering switches 44,45 energize the appropriate relay 154 or 156 to cause motor 37 to re-center the torque arm.

Switch 176 should be closed responsive to move ment of the car between landings. Closing of switch 176 may be responsive to energization of the main hoist motor. Alternatively, the closing of switch 176 can be velocity responsive. In this case, the closing of switch 176 should be delayed until the car velocity is appreciably greater than that produced by the linear actuator so as to "mask" the velocity change produced by the linear actuator during the centering operation.

The foregoing represent preferred embodiments of the invention. Variations and modifications of the emodiments shown will be apparent to persons skilled in the art without departing from the inventive concepts disclosed herein. For example, the drive arrangement in the Figs. 2-7 embodiments may also be gearless. Also, while a screw-type linear actuator has been shown, such is only illustrative and any suitable adjustment mechanism or device, hydraulic, electrical, or mechanical, which is capable of taking up the counter-torque of the motor and of selectively pivoting the motor and sheave drive shaft may be employed. All such modifications and variations are intended to be within the scope of the present invention as defined in the following claims.

Claims (20)

1. An elevator comprising: a car supported by a cable and vertically displaceable between landings in a hoistway; a frame; a drive sheave supporting said cable and having a drive shaft rotatably supported directly or indirectly by said frame; a main motor means coupled to said drive shaft for transmitting rotational torque to said drive sheave, for moving the car between landings; a brake means selectively engageable for stopping said main motor means and said drive shaft, for holding the car at a selected landing; and means operable between said main motor means and said frame for absorbing reaction torque and including auxiliary drive means for selectively pivoting said main motor means and thereby said drive sheave about a pivot axis while said brake means is engaged, for raising or lowering the position of the car.

2. An elevator as defined in claim 1, wherein said pivot axis is concentric with the axis of said drive shaft.

3. An elevator as defined in claim 2, wherein said main motor means has a housing, and said auxiliary drive means is connected between said housing and said frame.

4. An elevator as defined in claim 2, wherein said main motor means has an output shaft and a plurality of gears coupling said output shaft and said drive shaft.

5. An elevator as defined in claim 4, wherein said plurality of gears has a housing, and said auxiliary drive means is connected between said housing and said frame.

6. An elevator as defined in claim 1, wherein said pivot axis is spaced from the axis of said drive shaft.

7. An elevator as defined in claim 6, wherein said drive sheave and an idler sheave are disposed on opposite sides of said pivot axis.

8. An elevator as defined in any preceding claim, wherein said auxiliary drive means includes a linear actuator.

9. An elevator as defined in claim 8, wherein said linear actuator extends tangentially to a circle centered on said pivot axis.

10. An elevator as defined in claim 8 or claim 9, wherein said linear actuator is in the form of a screw-threaded member for rotary movement relative to a nut-like member.

11. An elevator as defined in claim 10, wherein said screw-threaded member is pivotally mounted to said frame.

12. An elevator as defined in any one of claims 8 to 11, wherein end stops on said frame restrict pivotal movement of said main motor means about said pivot axis.

13. An elevator as defined in any one of claims 1 to 12, wherein position sensor means is mounted on the car, and control means is provided for disabling said main motor means and engaging said brake means when the car is at a landing, said control means being responsive to said position sensor means, when said main motor means is disabled and said brake means is engaged, for selectively actuating said auxiliary drive means.

14. An elevator as defined in claim 13, wherein means is provided for detecting a centre position of said auxiliary drive means, said control means being responsiveto said centre position-detecting means when said main motor means is energized for actuating said auxiliary drive means for returning said auxiliary drive means to its centre position.

15. An elevator as defined in claim 13 or claim 14, wherein said position sensor means is positioned at each landing and on the car for sensing misalignment between the car and a selected landing.

16. -An elevator as defined in any one of claims 1 to 12, wherein the car includes a cab having a platform and position sensor means is mounted on said cab and is fixed relative to said platform for controlling said auxiliary drive means.

17. An elevator as defined in claim 16, wherein means is provided for sensing a centre position of said auxiliary drive means and for responding to travel of the car between landings for returning said auxiliary drive means to its centre position.

18. An elevator as defined in claim 16 or claim 17, wherein said position sensor means is positioned at each landing and on the carfor sensing misalignment between the car and a selected landing.

19. An elevator as defined in any preceding claim, wherein load sensor means is connected to said means for absorbing reaction torque for generating a signal indicative of elevator unbalance, said signal being usabie for controlling restarting of a stopped car.

20. An elevator substantially as hereinbefore described with reference to Figures 2 and 3, Figures 3a, Figures 4 and 5, Figures 6 and 7, or Figure 8, of the accompanying drawings.