[0001] The invention relates to elevators and, in particular, to elevators wherein the elevator
cage is mounted on one or more ropes or belts by means of a pulley arrangement.
[0002] Pulley arrangements are commonly used in the elevator industry to mount and drive
an elevator cage along ropes arranged within a hoistway in a building. In such an
arrangement a pulley box containing two pulleys is mounted on the cage so that as
the rope is driven, whether by hydraulic ram or traction sheave, it travels down along
one side of the hoistway, engages with one of the pulleys deflecting it through 90°,
traverses across the car, engages with the other pulley which deflects it back into
the vertical plane, and travels upwards along the opposite side of the hoistway. The
pulley box can be mounted to the cage at a point above the passenger car or it can
be mounted below the passenger car in which case it is called an underslung arrangement.
Such an arrangement is illustrated and described in EP-A2-0983957.
[0003] According to European Standard EN 81-1:1998 and United States ASME Code A17.1-2000,
the ratio of the diameter of the pulleys to the nominal diameter of the suspension
ropes should be at least 40. Hence, the diameter of each pulley is significantly larger
than its width and consequently the height of the pulley box is greater that its width.
[0004] In the prior art as exemplified in Fig. 1, an upper surface 18 of the pulley box
8 is mounted to the cage either directly to a base of the passenger car or, if the
car is contained within a frame, to a lower yoke of the car frame. However, in use,
the majority of the vertical forces F are transferred through the lowermost portions
A of the pulleys 9. Accordingly, if the pulley box 8 tilts by an angle α, a relatively
large bending moment is exerted about the mounting point of the pulley box. The magnitude
of the bending moment is defined by the equation M = Fx, where F is the vertical force
and x is the horizontal distance between the mounting point on the upper surface 18
of the pulley box 8 and the point of application of the vertical force F. Furthermore,
the value x can be expressed as x = L cos α where L is the distance between the mounting
point on the upper surface 18 and the lowermost portions A of the pulleys 9. Accordingly,
for a given vertical force F and a given tilt angle α, the bending moment M is directly
proportional to the value L. However, since the dimension L is principally dependent
on the diameter of the pulley 9 which in turn is determined by regulatory bodies as
discussed in the preceding paragraph, there is very little scope for reducing the
bending moment M.
[0005] Hence, both the pulley box 8 itself and the conventional means for mounting the pulley
box 8 to the cage must be capable of withstanding substantial bending moments, otherwise
as the cage and the pulley box tilt, the unrestrained bending moment and the tilt
angle of the pulley box would progressively increase until eventually the pulley box
is permanently deformed or torn from its mounting.
[0006] This phenomenon is further exaggerated when the suspension rope is replaced by a
belt as any torsion in the belt may be transferred to the pulley box to establish
a bending moment about the mounting point even without any tipping of the pulley box.
[0007] Accordingly, the objective of the present invention is to reduce the bending moments
about the point at which the pulley box is mounted to the cage. This objective is
achieved by providing an elevator cage comprising a car, a support member connected
to the car, and a pulley box housing a pair of pulleys mounted to the pulley box by
pulley axles, CHARACTERISED IN THAT the pulley box is mounted to the support member
through one or more points located below a first line bisecting the pulley axles and
above a second line defining a lowest common tangent between the pulleys. In comparison
to the prior art, the mounting points of the invention are located closer to the lowermost
portions of the pulleys through which the majority of the vertical forces are transferred
and hence the bending moments about the mounting points are significantly reduced.
[0008] Preferably, the pulley box is mounted on one or more mounting axles extending from
the support member. This arrangement greatly simplifies the assembly of the elevator
cage on site and makes horizontal adjustment of the pulley box much easier since the
mounting axles are relatively accessible after installation in comparison to the bolts
used in the prior art to mount an upper surface of the pulley box to a car floor or
to the yoke. Furthermore, the transmission for any vibration from the pulley box to
the car can be significantly reduced by providing resilient material between the pulley
box and each mounting axle.
[0009] The invention permits an arrangement wherein the support member is a yoke which is
fixed directly to a floor of the car. If this configuration is used, it is beneficial
to provide a closing plate which is secured to the floor of the car and engages with
each mounting axle at an end remote from the yoke such that the pulley box is disposed
between the closing plate and the yoke. Accordingly, vertical forces are transmitted
not only through the yoke but also through the closing plate. As the force transmitted
through the yoke is reduced, it can have a light weight structure in comparison to
the prior art. Preferably, the yoke and the closing plate are both formed from sheet
metal.
[0010] Alternatively, the support member may form a part of a frame in which the car is
suspended. Preferably, the car is resiliently suspended within the frame so that vibrations
from the frame are dampened before they reach the car.
[0011] The present invention is herein described by way of specific examples with reference
to the accompanying drawings of which:
Figure 1 is a simplified diagram illustrating the forces exerted on a prior art pulley
box;
Figure 2 is a general schematic front view of an elevator incorporating an elevator
cage according to the present invention;
Figure 3 is a partial side view of the underslung pulley arrangement of Fig. 2;
Figure 4 is a partial side view of an underslung pulley arrangement according to a
second embodiment of the present invention; and
Figure 5 is a general schematic front view of an elevator incorporating an elevator
cage according to a further embodiment of the present invention.
[0012] Throughout the following, features that are common to more than one of the embodiments
have the given the same reference numerals so as to avoid unnecessary repetition thereof
in the description of the invention.
[0013] Fig. 2 shows an elevator cage 1 supported by a pulley box 8 on ropes 11 within an
elevator hoistway (not shown). The cage 1 comprises a conventional car 2 having a
plurality of side walls 3, a roof 4 and a floor 5 defining a transport space for passengers
and/or goods. A support yoke 6 is mounted directly beneath the floor 5 of the car
2. The yoke 6 has two parallel mounting axles 7 extending horizontally outwards into
corresponding holes 22 in the pulley box 8. A diverting pulley 9 is mounted on a pulley
axle 10 at either end of pulley box 8 to engage with the suspension ropes 11.
[0014] The mounting axles 7 and the corresponding holes 22 are located between a first line
P bisecting the pulley axles 10 and a second line Q defining a lowest common tangent
between the pulleys 9. In the present embodiment, the lowest common tangent Q corresponds
to a line between the lowermost sections A of the pulleys 9.
[0015] As the ropes 11 are driven, they travel down along one side of the car 2, engage
with one of the pulleys 9 deflecting them through 90°, traverse underneath the car
2, engage with the other pulley 9 which deflects them back into the vertical plane,
and travel upwards along the opposite side of the car 2.
[0016] Fig. 3 is a partial side view of arrangement of Fig. 2 which further illustrates
the yoke 6 and pulley box 8. As shown, the yoke 6 is a solid I-beam with upper flanges
12 that are firmly secured to the bottom of the car floor 5 by a series of bolts or
rivets 13. Each mounting axle 7 is inserted into a through-hole 14 in the I-beam 6
and secured in position at weld points 15. Further elevator components (not shown)
such as guide shoes or safety gear can be mounted to a bottom surface 16 of the yoke
6.
[0017] The pulley box 8 is of an inverted U-shape construction having opposing side sections
17 interconnected by an intermediate section 18. Preferably the pulley box 8 is fabricated
from sheet metal. Bolts 19 are used to fasten the free edges of the opposing side
sections 17 together and thereby improve the overall structural rigidity of the pulley
box 8. Each diverting pulley 9 is rotatably mounted on a pulley axle 10 via a bearing
20. The pulley axles 10 are secured to the opposing side sections 17 of the pulley
box 8 in any conventional manner. Outer circumferential grooves 21 are provided on
the diverting pulley 9 to engage and retain the suspension ropes 11.
[0018] The mounting axles 7 are inserted through the mounting holes 22 in the opposing side
sections 17 of the pulley box 8. In use, as the pulleys 9 rotate due to their interaction
with the ropes 11, vibrations can be generated in the pulley box 8. A resilient ring
insert 23 is provided between each of the mounting holes 22 and the respective mounting
axles 7 to absorb this vibration.
[0019] Fig. 4 shows an alternative embodiment of the invention wherein the relatively heavy
I-beam used as the support yoke 6 in the previous embodiment is replaced by a light
weight structure. The yoke 6 in this instance comprises a pair of vertically aligned
sheet metal plates 24 interconnected by rigid web members 25. As in the previous embodiment,
upper flanges 26 on the sheet metal plates 24 are firmly secured to the bottom of
the car floor 5 by a series of bolts or rivets 13 and the mounting axles 7 are secured
in position at weld points 15. Furthermore, a closing plate 27 is provided at opposing
ends of the mounting axles 7 such that the pulley box 8 is positioned intermediate
the yoke 6 and the closing plate 27. The closing plate 27 is formed from a sheet metal
plate which is bent over to give a double wall structure. An upper flange 29 of the
closing plate 27 is secured to the car floor 5 by a series of bolts or rivets 13 and
holes 28 are punched through the closing plate 27 to accommodate the mounting axles
7. The closing plate 27 is not fixed to the mounting axles 7 and therefore it cannot
transmit any horizontal forces between the pulley box 8 and the car 2. However, any
vertical forces between the pulley box 8 and the car 2 are shared between the closing
plate 27 and the support yoke 6.
[0020] An alternative to the previously described underslung arrangements is shown in Fig.
5. In this embodiment the car 2 is supported through anti-vibrational pads 33 to a
frame 30. The frame 30 comprises an upper crosshead 31, a lower yoke 6 and a pair
of uprights 32. The pulley box 8 in this instance is supported on mounting axles 7
extending from the crosshead 31.
[0021] It will be appreciated by a person skilled in the art, that the pulley box 8 and
the pulleys 9 can easily be modified to engage with a belt or belts instead of the
ropes 11 previously described.
1. An elevator cage (1) comprising a car (2), a support member (6;31) connected to the
car (2), and a pulley box (8) housing a pair of pulleys (9) mounted to the pulley
box (8) by pulley axles (10), CHARACTERISED IN THAT the pulley box (8) is mounted to the support member (6;31) through one or more points
located below a first line (P) bisecting the pulley axles (10) and above a second
line (Q) defining a lowest common tangent between the pulleys (9).
2. An elevator cage (1) according to claim 1, wherein the pulley box (8) is mounted on
at least one mounting axle (7) extending from the support member (6;31).
3. An elevator cage (1) according to claim 2 further comprising resilient material (23)
between the pulley box (8) and each mounting axle (7).
4. An elevator cage (1) according to claim 2 or claim 3, wherein the support member is
a yoke (6) secured to a floor (5) of the car (2).
5. An elevator cage (1) according to claim 4 further comprising a closing plate (27)
secured to the floor (5) of the car (2) and engaging with each mounting axle (7) at
an end remote from the yoke (6).
6. An elevator cage (1) according to claim 5, wherein at least one of the yoke (6) and
the closing plate (27) are formed from sheet metal.
7. An elevator cage (1) according to any of claims 1 to 3, wherein the support member
(6;31) forms a part of a frame (30) in which the car (2) is suspended.
8. An elevator cage (1) according to claim 7, wherein the support member is a lower yoke
(6) of the frame (30).
9. An elevator cage (1) according to claim 7, wherein the support member is an upper
crosshead (31) of the frame (30).