Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUN_ OF T~IE INVENTION
eld_of the Invention:
The in~ention relates in general to elevator
system~, and more specifically to elevator systems
having increased traction efficiency.
Descri~tion of the Prior Art:
In an elevator system of the traction type,
the rating of the traction machine connected to rotate
the drive or traction shea~e is determined by its
traction efficiency. The higher its traction efficiency,
the smaller the machine rating required. Traction
efficiency may be defined as being responsive to the
ratio of the rope and/or sheave life to the required
tractive effort~
Adequately lubricating the ~raction sheave
and wire ropes would increase their life, but tractive
ef~ort suf~ers with increased lubrication, lowering
the traction efficiency. Thus, the rvpes and shea~es
are sparingly lubricated.
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Further, în order to increase tractive effort,
it has been necessary to design the cable grooves of the
drive sheave with relatively wide undercuts, such as
about 3/~ inch for 1/2 inch rope, in order to pinch the
rope and/or an additional ~ap around the drive sheave
is required. About the same .75 ratio of undercut width
to cable diameter would be maintained for larger diameter
cables~ A wide undercut in the cable groove severely
pinches the rope, adversely af~ectinG its useful opera-
ting life, and the double wrap doubles the load on the
shafts and bearings of the drive sheave, in addition to
adversely af~ecting the operating life of the rope due
to the additional bends therein. These structures also
limit the operating pressure in the cable grooves, which
usually requires that the diameter of the drive sheave
be increa~ed and/or a larger number of ropes, resulting
in uneconomical low speed machines.
SUMMARY OF THE INVENTION
Briefly, the present invention is a new and
improved elevator system in which the ropes and drive
sheaves are deliberately lubrîcated, including for
example lubrication by suitable dispensing means, with
a sy~hetic traction lubricant which increases the
coefficient of friction between the ropes and cable
grooYes of the sheave to at least about .145, and
preferably to at least about .17 and when using lubri-
~ant in the fonm o~ a grease, to as high as about .2.
~his results in hi~her tractive effort for a given
pressure.
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The deliberate lubrication of the ropes and
sheave increases rope life and reduces sheave wear, and
enables the t~dth of the undercut in the cable grooves,
the sheave diameter, and machine rating, to be reduced.
For example~ in the prior art the ratio of undercut
width to rope diameter required to obtain the desired
traction is about .75. m e present in~ention enables
this ratio to be reduced to about .375.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be better understood and
further advantages and uses thereof more readily apparent,
when considered in view o~ the following detailed des-
cription of the exemplary embodiments, taken with the
accompan~ing drawings, in which:
Figure 1 is a perspective view of an elevator
system of the traction type roped 1 to 1, which may use
the teachings of the invention;
Figure 2 is an enlarged cross-sectional view o~
elevator rope ~hich may be lubricated in accordance with
the teachings of the invention and functionally illus-
trating automatic lubricating means for adequately
maintaining proper lubrication of the rope during opera-
ting service;
~'igures 3A and 3B are fragmentary cross-sectional
views of the drive sheave shown in Figure 1, taken along
a line between arrows III-III illustrating undercut cable
grooves constructed according to the prior art, and
according to the teachings of the lnvention, respectively;
Figures 4A and 4B compare sheave diameters and
machine ratings of the prior art with those which are con-
3tructed according to the teachings of the invention;
Figure 5A is a fragmentary croæs-sectional view
Or a drive sheave illustrating meanæ con~tructed accordin~
to the teachings of the invention for automatlcally lubri-
cating ~he drive sheave and rope;
Figure 5B is a fragmentary cross-sectional vlew
of the drive heave constructed according to the teachings
of the invention, illustrating a continuous automatlc
lubricating arrangement;
Figure 6A is a perspective view of a prlor art
double wrap drive arrangement;
Figure 6B is a fragmentary cross-sectional view :
of the drive sheave shown in FIgure 6A, taken along a line
between arrows VI-VI;
Figure 7A is a perspective view of a single wrap
drive arrangement which may be used instead of the double
wrap arrangement shown in Figure 6A, when following the
teachings of the invention;
Figure 7B is a fragmentary cross-sectlonal view
of the drive sheave shown in Figure 7A, taken along a
line between arrows VII-VII;
Figure 8 is a dlagrammatic representation of
an elevator system roped 2 to 1, which may use the teachlngs
of the invention; and
Flgures 9A and 9B are fragmentary cross-sectional
vlews of the drive sheave shown in Figure 8, taken along
a line between arrows IX-IX, illustrating cable grooves
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constructed according to the prior art and accordlng to
the teachings of the lnvention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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Referring now to the drawings 3 and Figure 1 in
particular, there is shown a perspective view of an elevator
system 10 of the traction type, which may utili,ze the
teachings of the invention. The elevator system 10 inaludes
a traction machine 12, which in this embodiment is a geared
machine. The traction machine 12 is generally mounted ln
the penthouse of a structure having a plurality of floors
to be served by the elevator system, over a holstway 13
shown in phantom. Traction machine 12 lnclud s a grooved
traction or drive sheave 14, a geared drive 16, such as a
worm and main gear reduction drive, an electric drive motor
18, and a brake assembly '(not shown). Geared machines -'
are used in relatively low speed appllcations, up to
about 400 ft./min.
An elevator car 20 is mounted for movement in
the hoistway 13 to serve the floors or landings of the
associated bullding or structure. The elevator car 20 is
connected to a cou~kerweight 22 by a plurality of ropes
or wire cables 24 which pass around the tractlon sheave
14. A deflection or ~econdary sheave may be used when
necessary to properly space the car and counterweight.
The ropes 24 are thus held in frictional engagement with
; the cable grooves disposed in the periphery of the drive
sheave 14 by'the weight of the car 20 and counterw,ei~ht 22.
~ he elevator system 10 shown in Figure 1 is
roped 1 to 1, i.e., the car moves at the peripheral speed
of the traction sheave 14, and the ropes or cables make a
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half-wrap around the sheave 14, which is also commonly
called "single wrap".
Flgure 2 i5 an enlarged cross- ectional vlew of
one of the ropes 24, lllustrating a typical construction
thereo~ which include~ a plurallty of outer strands 26,
such as the six strands illustrated in the figure, or
eight strands~ with these outer s~rands being closed around
a center portion 28. The center portlon 28 may be formed of
fiber, as illustrated, or of steel. Each strand includes
a center wire, six inner wires, six filler wires, and
twelve outer wires. Typlcal diameters for hoist ropes are
1.2 lnch, 9/16 inch, 5/8 lnch and 3/4 inch.
The wires and core of the rope 24 are lubricated,
according to the prior art, wlth a petroleum type lubricant
while the wire is being fabricated, as some lubrication
of the rope is essential to achievin~ satisfactory operating
life. Ropes with fiber centers have an advantage over ropes
wlth a steel center in that they retain the lubrlcant over a
longer perlod of time. Extreme care, however, must be
taken by the rope manufacturer to lubricate sparingly.
Otherwise, tractive effort between the cable and the cable
grooves of the drive sheave will be less than that required
for adequate traction effort, due to a reduction in the
coefficient of friction between the cables and the cable
grooves. Therefore, in the prior art, the sheave and
cable wear is greater than that which could be achieved
with full lubrication, but lubrication is compromised to
achieve an adequate tractlve effort.
Even with carefully controlled lubrlcation of
3~ the ropes and associated sheaves, it has been necessary to
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severely pinch the ropes and the cable grooves by providing
substantially V-shaped grooves with relatively wide under-
cuts at the bottom thereof. Figure 3A is a cross-sectional
view of sheave 14 taken alon~ a line between arrows III-III
in Figure 1, illustrating a typical prior art cable groove
30 in which a rope 24 is disposed. The rope 24 contacts
the relatively flat sides of the substantially V-shaped
groove 30, and is wedged or forced downwardly to partially
enter undercut 32, which is typically about 3/8 inch wide
for 1/2 lnch rope. This .75 ratio of undercut width to
rope diameter is maintained for larger diameter ropes. As
an aid ln referring to this ratio, the width of the undercut
is referred to as W, and the diameter of the rope 1~ re-
ferred to as D. The wedging and pinching action of the
groove 30 and undercut 32 on the cable 34 increases the
tractive effort, but it has a dlsadvantage of hastenin~
cable and sheave wear. It has the further disadvantage of
limiting the operating pressure in the groove, which thus
requires a larger diameter sheave and/or a larger number
of rope Increasing the traction sheave diameter increases
the torque arm and thus a traction machine with a larger
ratlng ls required to drlve the trac~ion sheave.
The present invention utllizes a synthetic lu-
brlcant which substantially increases the coefficient of
friction between the rope and grooves of the drive sheave,
compared with petroleum lubrlcants~ The coefficient of
friction achieved with the ~ynthetic lubricant ~hould be
at lea~t about .145, and i5 preferably hl~her, such as in
the range of about .145 to about o2~
While the invention is not limited to any
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specific synthetlc lubricant, it has been found that a
synthetic hydrocarbon lubricant which includes isopropyl- -
cyclohexane will provlde the specifled range of coefficient
of friction. Appropriate additives may be used with the
isopropylcyclohexane, such as an ester. The lower part of
the range, about .145 to about .17 ls achieved by utlllzing
the synthetic lubricant in liquld form, having a viscosity
which enables it to be poured below a temperature of 0F,
and the upper part of the range, from about .17 to about .2
is achieved by adding a thickening agent to the llquld
synthetic lubricant, such as one of the 90ap8 commonly
added to petroleum lubricants, to provide a grease
Suitable synthetic lubricants are available
commercially ln dlfferent viscosities from Monsanto Chemlcal
Company which lubricants are sold under the trade mark
SANTOTRACo ShNTOTRAC synthe~ic lubricants have been sold
for the purpose of increasing the coefflcient of traction
between two rolling members in rolling contact type drives,
i.e., to increase the power transmitted through a rolling
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contact drive, and also for the purpose of lubricating
rolling contact bearings where skidding or slidlng contact
is a problem. These applications, however, are fundamen-
tally different than the application of lubricating wire
hoist rope and the drive sheave of an elevator system,
and do not suggest the unexpected advantages obtained by
the new and improved combination dlsclosed in thls appli-
cation.
The hoist ropes 24, according to the invention,
are fully lubricated when fabricated with a synthetlc
lubricant which will provide a coefficient of friction
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between the ropes and drive sheave of at least ~145 when
held in frictional engagement with the grooves of the drlve
sheave by the weight of the elevator car and the counter-
weight means, which in itself wlll lncrea~e the useful
operating life of the ropes and sheave compared with the
sparingly lubricated ropes and sheaves of the prior art.
Thus, without further changing the structure of the drive
sheave, this arrangement will provide substantial savings ~-
by reduclng maintenance costs of the ropes and sheaves.
The combination wlth the synthetic lubricant
further permits new and improved structural changes to be
- made in elevator systems, which changes cooperate to
further reduce rope and sheave wear, as well as reducing
sheave dlameter, and the rating of the traction drive
machine This new and improved combination allows for the
first time an automatlc lubrication sy~tem t-o adequately
lubricate the ropes and sheaves in service. It allows
double wrap drive arrangements to be replaced by slngle
wrap arrangements. It allows the cable grooves to be
restructured to reduce cable and sheave wear.
More specifically, referring to the geared
arrangement ~hown ln Figure l,~ the ~able groove 30 and
undercut 32 may be changed to the structure shown in Flgure
3B The undercut 32 shown in Figure 3A may be changed
to an undercut 32' shown in Figure 3B, which has a width
dimension of only about 3/16 inch for 1/2 inch rope,
compared with the wide 3/8 inch used in the prior art for
1/2 inch rope. Thi new ratio of .375 of undercut width
W to rope diameter D would be used for larger diameter
rope. Further, the relatively straight sides of the V-
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shaped groove 30 of the prior art may be more rounded
or U-shaped, as illustrated at 30' in Figure 3B. The
groove and undercut construction shown in Figure 3B
thus reduces the severity of the pinching of the cables
increasing the useful operating life of both the cables
and the sheave.
The new groove and undercut arrangement of Figure
3B lifts the restriction on groove pressure, necessary in
the prior art arrangement shown in Figure 3A, enabling the
sheave diameter to be reduced substantially. ~or example,
the sheave dlameter may be reduced by at least 25% when
selecting the synthetic lubricant to provide at least a
25% increase in the coefflcient of friction over the prior
art petroleum lubricant used to lubricate elevator rope
and shea~e arrangements. A 25% reduction in the diameter
of the drive sheave results in at least a 25% reduction
in the torque ratlng of the associated elevator drive
mach~ne. These relationships are illustrated in Figures
4A and ~B, with Figure 4A diagrammatically illustrating an-
elevator machine 40 having a drive 42 rated T and a drlvesheave having a diameter D. Figure 4B illustrates an
elevator machine 40' which has the ropes and sheave lubri-
cated according to the teachings of the invention, with
a synthetic lubricant selected to provide at least a
25% increaæe in the coefficien~ of friction between the
; ropes and sheave, compared with a petroleum lubricant,
which would normally provide a coefflcient of friction of
about .133 to .137 when sparingly lubricated, and less
when lubricated more fully. Thus, to achieve the 25%
reduction in sheave diameter and torque rating of the
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drive machine, would require a synthetic lubricant which
would provide a coefficient of friction of about .17,
which the synthetic grease of the type hereinbefore
mentioned would easily achieve~
As hereinbefore mentioned, the ropes, including
all the strands thereof, may for the first time be ade-
quately lubricated during manufacture of the rope. Further,
the adequate lubrication may be automatically maintained
during operating service without regard to losing tractive
effort due to this adequate lubrication. Figure 2 func-
tionally illustrates automatic lubrication dispensing means
50, associated with rope 2~, which, for example, may be
of the spray, drip or ~pe type with the latter being
illustrated by the wick 51. The automatic mechanism may
take into account the RPM of the sheave, as well as the
weight of the car and sheave, to dispense the synthetic
lubricant.
Figures 5A and 5B illustrate two additional
arrangements for automatically lubricating the ropes and
drive sheave during operation. Figure 5A is a fragmentary,
cross-sectional view of a portion of a drive sheave 52.
The drive sheave 52 defines one or more chambers or
cavities ~4, which chambers are in communication with the
cable grooves 569 such as through openings disposed to
intercept the narrow undercut 5~, when an undercut is
utilized. A grease fitting 60 may be used to charge the
chamber 54 with the synthetic lubricant during ~cheduled
maintenance of the elevator system. A grease disposed
in the chamber 5~ may be prevented from being forced out
through the openings which communicate with the cable
grooves too rapidly, by properly selecting the diameter
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of the openings; by disposing screens over the openings
with the mesh being selected to properly meter the
tran~fer of lubricant; by a spring-loaded closure member
(not shown) which is operated to the open posltlon
against the spring bias by the ropes 62 when they contact
the cable grooves; or, by any other suitable arrangement.
Figure 5B i~ a fragmentary, cross-sectional
view of a drive sheave 70, in which at least the metal
which surrounds the cable grooves is formed of a sintered
metal impregnated with the synthetic lubricant, which will
automatically lubricate the rope 72 as the rope 72 presses
against the sides of the cable groove. The sintered metal
may be in the form of removable insertsj which are replaced
when necessary to maintain adequate lubrlcation of the
~ystem and/or due to wear.
The elevator applications specifically mentioned
to this point have been of the geared machine type, but
; the synthetic lubrlcant and its advanta~es are equally
applicable to the higher speed elevator systems which use
a gearless drlve, i.e., a DC motor, and a source of ad~ust-
able direct current voltage. For example, in the gearless
systems it ls common to utilize a double or full wrap of
the hoist ropes in order to obtain the tractive effort
required. Figure 6A is a perspective view of a double wrap
gearless system 80, including a grooved traction or drive
sheave 82, a grooved secondary sheave 84, and a rope 86
which passes around the drive sheave 82 twice. Figure 6B
; is a fragmentary perspectlve view of the drive sheave 82
shown in Figure 6A, taken generally along a line which
extends between arrows Vl-VI Wlth the double wrap
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arrangement illustrated, it will be noted that the
groove 88 is contoured to flt the rope 86, and an undercut
ls usually not necessary, as the double wrap arrangement
provides the required tractive effort. The double wrap
arrangement, however, deleteriously affects rope life,
due to the additional bends required in the rope. Further,
the double wrap increases the loading on the drive machine 3
c~ompared with the single wrap, and a larger sheave diameter
i9 u~ually necessary in order to increase the radius of
curvature in the rope as it wraps around the sheave.
Figure 7A is a perspective view of a gearless
elevator system 80' constructed with a synthetic lubricant
for'the ropes and'sheave which increases the coefficient
of friction therebetween to at least .145. The rope
86' pasges over the drive sheave 82' and secondary sheave
84', when the secondary sheave is necessary in order to
properly space the counterweight and car, with a single
wrap. As illustrated in Figure 7B, which is a fragmentary
cross-sectiona] view of drive sheave 82' taken ~enerally
along a line between arrows VII-VII, a small undercut of
3/16 inch for 1~2 inch rope, and large~ according to the
; same ratio for larger diameter rope, along wlth the synthe~ic
lubricant, provides sufficient tractlve effort for a gear-
less systemy eliminating the necessity for the double
wrap shown in Figure 6A. Thus, the number of bends in the
rope 86' are reduced by one-half, the loading on the drive
machine is reduced by one-half, and the diameter of the
sheave 82l may be reduced, compared with the diameter of
the sheave 82 shown in Flgure 6A.
Gearless machines of the prior art which utilize
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a single wrap and a relatively wide undercut in the cable
groove, whether roped 1 to 1 or 2 to 1, may be improved
by using the synthetic lubricant to increase the coeffi-
clent of friction between the ropes and sheave. For example,
Figure 8 is a diagrammatlc representation of a gearless
system 90 roped 2 to 1, having a car 92, a counterweight
94, a drive sheave 96, and a gearless machine 98. In
addit1on to the drlve or traction sheave 96, sheaves 98
and 100 are provided on the car 92 and counterweight 94,
respectively. The hoi~t rope 102 is dead-ended in the
overhead beam~ at 104, passed under sheave 98 on the car
92, over the traction sheave 96, under the sheave 100 on the
counterweight, and back to the overhead beams where it is
dead-ended at 106. -~
Figure gA ls a fragmentary, cross-sectional view
of the drlve sheave 96 shown in Figure 8, with a groove
108 and undercut 110 constructed according to the teachings
of the prior art, having a ratio W/D of about .75. The
groove 108 is V-shaped with slightly curved sides which
wedge the rope downwardly and pinch the rope in the rela-
tively wide undercut. The synthetic lubricant with a
coe~ficient of friction in;the range of .145 to ,2 enables
: the groove 108 and undercut 110 to be con~tructed as
shown in Figure 9B, which utilizes a groove 108~ having
a contour which more nearly matches that of the rope 102',
The undercut 110' i8 reduced in width such that the ratio
W/D is about .375. The diameter of the drive ~hé-ave 96
and rating of the drive 98 may also be reduced, with the
reduction, compared wi~h a gearless system of the prior art,
depending upon the coefficient of friction of the synthetic
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lubricant which is selected, with a 25~ reduction being
easily achievable, as hereinbefore described relative to
geared systems.
The ropes and sheaves in the gearless embodiments
of the invention may be automatically lubricated, as herein-
before described relative to the geared embodiments of
the invention.
The upper limit of about .2 of the coefflcient
of friction is selected because it enables the advantages
of the invention to be utillzed wlthout adversely affecting
the safety advantage of the traction type elevator system.
In other words, a coefficient of frlction of about .2
will not cauæe exce~slve llfting of the counterweight
when the car is drlven into lts buffer, and the car will -
not be pulled lnto the overhead when the counterweight
; ls drlven lnto its buffer.
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; The isopropylcyclohexane material herelnbefore
mentioned has a characteristlc whlch is deslrable in an
elevator applicatlon, in that tractlve effort is reduced
when the pressure between the rope and sheave is reduced,
such as when the car or counterweight hits its buffer.
Further, this material has the characteristic of lncreasing
its viscosity with pre3sure, whlch is also deslrable in
an elevator applicatlon.
; In summary, the use of new and lmproved lubri-
cated wire rope in an elevator system, without changing ~-
the remainder of the elevator system, would enable large
savings to be reallzed in maintenance of the ropes and
sheaves. Th~ new and improved groove and undercut construc-
t~ons disclosed hereln which permit increased groove
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pressures without deleterlously arfecting rope and
sheave li~e, enable large savings to be realized by using
smaller, more efflcient machlnes for a given application.
The deliberate lubrication of the rope and sheave, to the
extent necessary to provide adequate lubricatlon, not
practical in the prior art, increases rope and ~heave life
even when the sheave groove and undercut arrangement i~
changed to utilize higher groove pressures. The disclosed
arrangements will also facilitate the move to the more
economical higher tensile ropes, whose use has heretofore
been limited due to excessive sheave wear.
While the disclosed arrangements permit the ratio
W/D to be reduced from about .75 to about .375, lt is to
be understood that the ratio W/D may be varled somewhat
from .375 without departing from the teachings of the
invention.
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