BACKGROUND OF THE INVENTION
[0001] The present invention relates to an elevator apparatus and, more particularly, to
an elevator apparatus provided with a hoisting machine required to be small-sized.
[0002] Hitherto, an elevator apparatus provided with a hoisting machine which is required
to be small-sized is constructed as disclosed in JP A 63-277190, JP B2 7-45315, JP
A 9-506237 (Laid-open PCT application), for example.
[0003] Any of the above-mentioned prior arts does not take disassembling and assembling
of the hoisting machine into consideration, and they each have a problem that a lot
of labor and time is needed for disassembling and assembling.
SUMMARY OF THE INVENTION
[0004] An object of the present invention is to provide an elevator apparatus having a hoisting
machine which is easily disassembled and assembled.
[0005] In order to achieve the object, a sheave on which a rope hanging a cage is wound
is detachably mounted on a rotating portion other than a shaft of a motor driving
the sheave.
[0006] With the above-mentioned construction, the motor and the sheave can be assembled
and disassembled as separate parts, so that the operation can be simple and exchange
of the sheave or the like can be effected each part unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007]
Fig. 1 is a partially sectional view of a hoisting machine of an elevator apparatus
of an embodiment of the present invention;
Fig. 2 is a front view of the hoisting machine shown in Fig. 1;
Fig. 3 is a perspective view showing an elevator apparatus according to the present
invention;
Fig. 4 is a partially sectional view of an hoisting machine of an elevator apparatus
of another embodiment of the present invention;
Fig. 5 is a front view showing an arrangement of practical device and apparatus of
the elevator apparatus according to the present invention;
Fig. 6 is an enlarged plan view of Fig. 5; and
Fig. 7 is a partially sectional view of an hoisting machine of an elevator apparatus
of another embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0008] An embodiment of the present invention will be described hereunder, referring to
Figs. 1 to 3.
[0009] A cage 3 is guided to be able to ascend and descend in an up and down direction by
a pair of guide rails 2A, 2B for cage provided to be upright inside an elevator shaft
1 at a distance therebetween. The cage 3 has a cage door 3D for passengers and supports
shafts of a pair of guide pulleys 4A, 4B on both width sides of a bottom of the cage.
A main rope 5 is wound on the guide pulleys 4A, 4B and passes through the bottom of
the cage 3. One end of the main rope 5 is supported, for example, on a beam 6 on the
ceiling side of the elevator shaft 1.
[0010] Further, in the elevator shaft 1, a pair of counterweight guide rails 7A, 7B are
provided uprightly with a distance therebetween in parallel to the cage guide rails
2A, 2B, and a counterweight 8 is guided thereby to be movable in a vertical direction.
A shaft of a guide pulley 9 is supported to an upper portion of the counterweight
8, and the other end of the above-mentioned main rope 5 is wound on the guide pulley
9 and supported on the beam 6 on the ceiling side.
[0011] On the other hand, on an upper portion of the elevator shaft 1, a support rest 10
is mounted and a hoisting machine 11 is supported on the support base 10. The hoisting
machine 11 has a sheave 26, and the sheave 26 winds thereon the main rope 5 led to
the guide pulley 9 of the counterweight 8 through the guide pulleys 4A, 4B at the
bottom of the cage 3.
[0012] Next, a concrete constitution of the hoisting machine 11 is explained. The hoisting
machine 11 is fundamentally constructed on the base 12 fixed to the support rest 10.
That is, a fixed frame 13 having a vertical plane 14 is provided on the base 12, and
a fixed shaft 15 perpendicular to the vertical plane 14 and extending horizontally
is cantilevered by the fixed frame 13. The fixed shaft 15 has a large diameter portion
15a at the side of the vertical plane 14 and a small diameter portion 15b at a free
end side. A rotating frame 16 is rotatably supported on the small diameter portion
15b of the fixed shaft 15 through bearings 18A, 18B.
[0013] The rotating frame 16 is formed in a shape of cylinder with bottom or in a cup-shape
by a disc-shaped bottom portion 17 and a peripheral wall 19 formed at the periphery
thereof, and a bearing retaining portion 18 is formed at the center of the bottom
portion 17. The rotating frame 16 is rotatably supported on the small diameter portion
15b of the fixed shaft 15 through the bearings 18A, 18B, whereby an bottom-having
cylinder shaped opening side peripheral edge, that is, an opening side peripheral
edge of the peripheral wall 19 is placed to be equally close to the vertical plane
14 of the fixed frame 13. It is desirable for stable rotation of the rotating frame
16 to arrange the bearings 18A, 18B at an axial interval therebetween. An outer peripheral
surface 20 of the bearing retaining portion 18 of the rotating frame 16 and inner
and outer peripheral surfaces of the peripheral wall 19 each are formed concentrically
with a shaft center of the fixed shaft 15.
[0014] The rotating frame 16, which is supported to be concentric with the fixed shaft 15
in this manner, supports a rotor 21 on the inner periphery of the peripheral wall
19. The rotor 21 can be formed by adhering a plurality of permanent magnet pieces
on the inner periphery of the peripheral wall 19, or arranging a rotor core having
a plurality of permanent magnetic pieces embedded therein on the inner periphery of
the peripheral wall 19.
[0015] A stator 22 having a radial gas to the rotor 21 is fixed to the fixed frame 13. The
stator 22 is composed of a stator core 23 formed by laminating silicon steel plates
each having a hole at the center through which the above mentioned fixed shaft passes,
and a stator winding 24 wound on the stator core 23. The stator 22 is fixed to the
fixed frame 13 through a bracket 25.
[0016] An outer rotation type motor is composed of the rotor 21, the stator 22, the fixed
frame 13 supporting the stator 22, the rotating frame 16 supporting the rotor 21 and
the fixed shaft 15 supporting the rotating frame 16. Here, an outer diameter portion
of the motor is an outer peripheral surface of the peripheral wall 19 of the rotating
frame 16 supporting the rotor 21.
[0017] Further, the rotating frame has the sheave 26 fixed to an outer side of the bottom-having
cylindrical bottom portion 17, that is, to the rotating frame 16 at an opposite side
to the fixed frame 13. That is, the sheave 26 is fixed by utilizing the outer peripheral
surface 20 of the bearing retaining portion 18 formed at the bottom portion 17 of
the rotating frame 16 so as to be concentric with the fixed shaft 15. In this construction,
since the rotating frame 16 forms a rotating portion of the motor, the sheave 26 is
to be mounted on and fixed to the rotating portion of the motor. In order to make
the motor small in size, the sheave 26 is formed so that rope grooves 26G are smaller
in diameter than the outer diameter of the motor, that is, the outer peripheral surface
of the peripheral wall 19 of the rotating frame 16. The sheave 26 is fixed to the
rotating frame 17 by screwing bolts 27 into the bottom portion 17 of the rotating
frame 16. Further, a mounting hole 28 is formed at a central portion of the sheave
26 so that the center of the mounting hole 28 is the same as the center of rope grooves
26G, and the diameter of the mounting hole 28 is formed in such size that the bearing
retaining portion 18 can be inserted in the hole with a very small gap with the outer
peripheral surface of the bearing retaining portion 18. Therefore, since the outer
peripheral surface of the bearing retaining portion 18 is formed to be concentric
with the shaft center of the fixed shaft 15, the center of the rope grooves 26G coincides
with the shaft center of the fixed shaft 15 only by mounting the sheave 26G on the
outer peripheral surface of the bearing retaining portion 18 of the rotating frame
16.
[0018] Further, the sheave 26 has the rope grooves 26 each formed in V-groove in order to
secure necessary frictional force between the main rope 5 when the main rope 5 is
wound on the sheave 26 and driven to ascend and descend the cage 3 and the counterweight
8. The sheave 26 is made of material which is a different kind from the rotating frame
16 and excellent in wear resistance so that it can be used for long time, irrespective
of friction with the main rope 5.
[0019] Further, as for the sheave 26, if it has a function of winding the main rope 5 and
driving it, its shape is not limited to a specific shape, for example, it can be formed
in a cylindrical shape on the outer peripheral surface of which rope grooves 26G are
cut,
[0020] In addition to the above-mentioned matters, a brake 29 is provided on the periphery
of the peripheral wall 19 of the rotating frame 16. The brake 29 comprises a pair
of brake arms 30A, 30B each one end of which is pivotally supported on the base 12,
brake shoes 31A, 31B supported by shafts on intermediate portions of the brake arms
30A, 30B so as to face the outer peripheral surface of the peripheral wall 19, a pair
of brake shafts 32A, 32B passing through the other ends of the brake arms 30A, 30B
and facing each other , brake springs 33A, 33B provided so as to attract the brake
shafts 32A, 32B and an electromagnet 34 operating so as to distract the brake shafts
32A, 32B against the brake springs 33A, 33B. By utilizing the peripheral wall 19 of
the rotating frame 16 opposite to the brake shoes 31A, 31B as a rotating drum, a drum
type brake is constructed.
[0021] The peripheral wall 19 of the rotating frame 16 also wears away in some degree by
sliding in contact with the brake shoes 31A, 31B, however, since the sliding in contact
with the peripheral wall 19 of the brake shoes 31A, 31B occurs right before the cage
3 sufficiently decreases in speed and stops, the wear amount is very small compared
with that due to contact of the sheave 26 and the main rope 5. Therefore, exchanging
time period of the peripheral wall 19 of the rotating frame 16 which is a rotating
drum of the brake 29 is longer than the rope drum 26 is exchanged once every 5 to
10 years.
[0022] Further, a cylindrical member 35 extending concentrically with the fixed shaft 15
from the bottom portion 17 of the rotating frame 16 is provided in a space surrounded
by the fixed frame 13 and the rotating frame 16. The cylindrical member 35 extends
so as to cross the vertical plane 14 of the fixed frame 13 at right angles, and has
a plurality of slits (not shown) distantly arranged in the circumferential direction
thereof. A sensor 36 is supported on the fixed frame 13 so as to sandwich the slits
of the cylindrical body 35 from both sides and detects speed of the motor.
[0023] Further, since the cylindrical member 35 and the sensor 36 should be free from dusts,
a sealing portion is formed between the vertical plane 14 of the fixed frame 13 and
an end of the peripheral wall 19 to prevent dust entrance. As a concrete structure
of the sealing portion, a structure that prevents dust entrance by providing a seal
body 37 sliding on any one of the vertical plane 14 and the peripheral wall 19 relative
to the other, or a structure that prevents dust entrance by projecting a partition
wall 14R from the side of the vertical plane 14 adjacent to the end of the peripheral
wall 19 so as to oppose the whole periphery of the inner peripheral surface of the
peripheral wall 19 with a small gap therebetween, are considered. However, the sealing
body 37 and the partition wall 14R can be jointly used or only one of the sealing
body 37 and the partition wall 14R can be used for prevention of dust entrance, according
to a place and circumstance in which the elevator apparatus is installed.
[0024] In the above construction, since maintenance inspection of the brake 29 can be viewed
from the outside by person's eyes, it is unnecessary to disassemble for effecting
maintenance inspection. However, since the hoisting machine 11 is made small in size,
maintenance inspection of the motor, sensor 36, etc. can not be effected without disassembling.
However, according to the present embodiment of the present invention, the rotor 21
of the motor, the cylindrical member 35 and the sheave each fixed to the rotating
frame 16 can be simultaneously taken off by extracting the rotating frame 16 from
the fixed shaft 15 toward the opposite side to the fixed frame 13. After the rotating
frame 16 is extracted from the fixed shaft 15, it is possible to effect maintenance
inspection of the stator 22 of the motor and the sensor 36 fixed supported by the
fixed frame 13 as they are, and parts can be exchanged if necessary. On the other
hand, since cup-shaped inside of the extracted rotating frame 16 can be viewed by
eyes, it is possible to effect maintenance inspection of the rotor 21 and the cylindrical
member 35 and exchange of parts.
[0025] After the maintenance inspection, the rotating frame 16 is mounted on the fixed shaft
15 in turn reverse to the disassembling, whereby the operation is completed.
[0026] Further, the sheave 26 may slip in some cases relative to the main rope 5 due to
wear of the rope grooves 26G in its use for a long time, in this case the sheave 26
should be exchanged. However, according to the present embodiment of the invention,
a new sheave 26 is fixed, with the rope grooves 26G being concentric with the fixed
shaft 15 by taking off the bolts 27 to withdraw the sheave 26 from the rotating frame
16, inserting the new sheave 26 using the outer peripheral surface 20 of the bering
retaining portion 18 as a guide, and screwing the bolts 27 into the rotating frame
16.
[0027] In this manner, according to the present embodiment of the invention, it is possible
to easily disassemble and assemble the hoisting machine 11 and alignment after assembling
becomes simple, so that the working time for the disassembling and assembling can
be shortened.
[0028] Fig. 4 shows another embodiment of the present invention. What is different from
the previously described embodiment is a peripheral shape of the rotating frame 16,
and the same reference numbers as in Figs 1 to 3 denote the same parts, so that repeated
explanation thereof is omitted.
[0029] According to the present embodiment, a disc 38 crossing the fixed shaft 15 at right
angles is formed on extension of the bottom portion 17 of the peripheral wall 19 of
the rotating frame 16 and a well-known electromagnetic disc brake (not shown) is arranged
so as to sandwich the disc 38, whereby a hoisting machine 11 with electromagnetic
disc brake can be provided.
[0030] Further, instead of the disc 38, a disc 39 is formed on the opening side of the peripheral
wall 19 of the rotating frame 16 and an electromagnetic disc brake (not shown) is
arranged so as to oppose the disc 39, whereby the disc 39 becomes a reinforcing annular
ring of thick thickness and it is possible to raise the rigidity of the peripheral
wall 19 on the opening side, so that it is possible to make thin the thickness of
the peripheral wall 19.
[0031] Next, Figs. 5 and 6 show an optimum arrangement of device and apparatus inside the
electromagnet. In Figs 5 and 6, the same reference numbers as in Figs. 1 to 3 denote
the same parts and repeated explanation is omitted.
[0032] Inside the electromagnet, a pair of cage guide rails 2A, 2B are vertically arranged
at an interval on the both sides of the cages 3 in the width direction parallel with
the cage door 3D. Further, guide pulleys 4A, 4B are supported by shaft on the bottom
portion of the cage 3 at an interval in the same width direction, and the guide pulleys
4A, 4B are arranged on an opposite side to the cage door 3D with respect to the cage
guide rails 2A, 2B.
[0033] In a space between the guide rail 4A side of the cage 3 and a side wall of the elevator
shaft 1, a pair of counterweight guide rails 7A, 7B are vertically arranged at an
interval along the direction of inlet outlet of the cage 3 and guide to ascend and
descend the counterweight 8. Further, the pair of counterweight guide rails 7A, 7B
are arranged, viewed it on plane, on an opposite side to the cage door 3D with respect
to the cage guide rail 2A.
[0034] On the other hand, viewing it on plane, they are arranged so that a diameter-directional
one end of the sheave 26 of the hoisting machine 11 overlaps or is adjacent to the
end of the guide pulley 4A projecting outside from the side wall of the cage 3. The
side face of the sheave 26 is arranged in parallel with the interval direction of
the pair of counterweight guide rails 7A, 7B, and the other diameter-directional end
is positioned on the side of the counterweight guide rail 7B.
[0035] On the upper portion of the counterweight 8, the guide pulley 9 is supported by shaft.
The guide pulley 9 is arranged to incline against the interval direction of the counterweight
guide rails 7A, 7B so that a diameter-directional end of the guide pulley 9 overlaps
or is adjacent to the other diameter-directional end of the sheave 26.
[0036] In the above-mentioned relation to the cage 3, the counterweight 8, the respective
guide pulleys 4A, 4B, 9 and the sheave 9 are arranged, so that they can be effectively
installed in a narrow inside of the elevator shaft 1, and even if the hoisting machine
is installed inside the elevator shaft 1, it is unnecessary to increase the area of
the elevator shaft 1.
[0037] Each embodiment as described above is of the hoisting machine 11 using the outer
rotation type motor in which the rotor 21 inside the rotating frame 16 is arranged
on the outer diameter side of the stator 22, however, the same effect can be obtained
even if an inner rotation type motor in which the rotor 21 is arranged on the inner
diameter side of the stator 22 is used for the hoisting machine 11, as shown in Fig.
7.
[0038] In the case of the above-mentioned inner rotation type motor, the stator 22 is supported
on the fixed frame 13 through a retaining member 22Y positioned on the outer diameter
side of the stator 22, so that an outer diameter portion as the motor is an outer
peripheral portion of the retaining member 22Y.
[0039] As mentioned above, a sheave of a hoisting machine used for an elevator apparatus
according to the present invention is mounted on a rotating frame, which is one of
rotating portion, supported by the fixed shaft. However, in the case where the motor
of which the rotor is constituted on a rotating shaft is used for a hoisting machine,
it also is considered to mount a sheave on the rotating shaft and fix it thereto,
however, since the rotating shaft is small in diameter, it is troublesome in structure
to detachably mount the sheave there, so that in such a case, it is necessary to detachably
mount the sheave on a rotating portion of the motor other than the rotating shaft.
[0040] As explained above, according to the present invention, it is possible to provide
an elevator apparatus provided with a hoisting machine in which disassembling and
assembling can be easily carried out.
1. An elevator apparatus having a hoisting machine installed inside an elevator shaft
and a cage ascending and descending in said elevator shaft by a rope wound on a sheave
of said hoisting machine, characterized in that
said sheave is detachably mounted on a rotating portion other than a shaft of a motor
driving said sheave.
2. An elevator apparatus in which a rope is wound on a sheave of a hoisting machine installed
inside an elevator shaft and a cage is driven by said rope to ascend and descend,
characterized in that
said sheave of smaller diameter than an outer diameter of a motor driving said sheave
is detachably mounted on a rotating portion other than a shaft of said motor.
3. An elevator apparatus, in which a rope is wound on a sheave of a hoisting machine
installed inside an elevator shaft and a cage is driven by said rope to ascend and
descend, having a hoisting machine in which on a rotating portion other than a shaft
of motor driving said sheave, said sheave of material different from said rotating
portion is detachably mounted.
4. An elevator apparatus provided with a hoisting machine comprising a fixed shaft supported
by a fixed frame, a rotating frame rotatably supported by shaft on said fixed shaft,
a motor constructed between said rotating frame and said fixed frame and a sheave
rotating together with said rotating frame, and constructed so that a rope is wound
on said sheave to ascend and descend a cage, characterized in that
said sheave is detachably mounted on a central portion of said rotating frame.
5. An elevator apparatus provided with a hoisting machine comprising a fixed shaft supported
by a fixed frame, a rotating frame rotatably supported by shaft on said fixed shaft,
a motor constructed between said rotating frame and said fixed frame and a sheave
rotating together with said rotating frame, and constructed so that a rope is wound
on said sheave to ascend and descend a cage, characterized in that
said motor has a rotor and a stator arranged to face each other through a radial air
gap, and said sheave is formed so that the outer diameter is smaller than that of
said sheave and detachably mounted on said rotating frame.
6. An elevator apparatus provided with a hoisting machine comprising a fixed shaft supported
by a fixed frame, a rotating frame rotatably supported by shaft on said fixed shaft,
a motor constructed between said rotating frame and said fixed frame and a sheave
rotating together with said rotating frame, and constructed so that a rope is wound
on said sheave to ascend and descend a cage, characterized in that
said rotating frame is formed in a bottom-having cylindrical shape, the bottom center
of said rotating frame is supported by shaft on said fixed shaft and said sheave is
detachably mounted on the bottom portion of said rotating frame.
7. An elevator apparatus provided with a hoisting machine comprising a fixed shaft supported
by a fixed frame, a rotating frame rotatably supported by shaft on said fixed shaft,
a motor constructed between said rotating frame and said fixed frame, a sheave rotating
together with said rotating frame and a brake braking rotation of said rotating frame,
said motor and said brake being arranged to axially overlap each other, and constructed
so that a rope is wound on said sheave to ascend and descend a cage, characterized
in that
a vertical portion crossing said fixed shaft at right angles is provided on said fixed
frame, said rotating frame is formed in a bottom-having cylindrical shape, an opening
portion of said rotating frame is arranged in an adjacent relation to said vertical
portion of said fixed frame and said sheave is detachably mounted on the bottom portion
of said rotating frame.
8. An elevator apparatus in which a rope is wound on a sheave of a hoisting machine installed
inside an elevator shaft and a cage is driven by said rope to ascend and descend,
characterized in that
said hoisting machine comprises a fixed shaft supported horizontally by a fixed frame,
a bottom-having cylindrical rotating frame rotatably supported by shaft on said fixed
shaft, a motor constructed between said rotating frame and said fixed frame, a sheave
rotating together with said rotating frame and a brake braking rotation of said rotating
frame,
said motor and said brake are arranged to axially overlap each other, and
said sheave is detachably mounted on said rotating frame.
9. An elevator apparatus provided with a hoisting machine comprising a fixed shaft supported
by a fixed frame, a rotating frame rotatably supported by shaft on said fixed shaft,
a motor constructed between said rotating frame and said fixed frame, a sheave rotating
together with said rotating frame and a brake braking rotation of said rotating frame,
said motor and said brake being arranged to axially overlap each other, and constructed
so that a rope is wound on said sheave to ascend and descend a cage, characterized
in that
a vertical portion crossing said fixed shaft at right angles is provided on said fixed
frame, said rotating frame is formed in a bottom-having cylindrical shape,
an opening portion of said rotating frame is arranged in an adjacent relation to said
vertical portion of said fixed frame,
said sheave is formed to be smaller in diameter than said motor, and mounted on the
bottom portion of said rotating frame, and
said sheave is made of metal material of a kind different from said rotating frame.
10. An elevator apparatus provided with a hoisting machine comprising a fixed shaft supported
by a fixed frame, a rotating frame rotatably supported by shaft on said fixed shaft,
a motor constructed between said rotating frame and said fixed frame and a sheave
rotating together with said rotating frame, and constructed so that a rope is wound
on said sheave to ascend and descend a cage, characterized in that
said rotating frame is formed in a bottom-having cylindrical shape to position an
opening end thereof at a side of said fixed frame,
a bottom center of said bottom-having cylindrical rotating frame is supported by shaft
on said fixed shaft,
an outer peripheral surface concentric with said fixed shaft is formed in said bottom-having
cylindrical bottom portion,
a mounting hole concentric with rope grooves of said sheave and fittable with the
outer peripheral surface of said bottom-having cylindrical bottom portion is provided,
and
said sheave is detachably mounted on said rotating frame by fitting the outer peripheral
surface of said bottom-having cylindrical bottom portion in said mounting hole.
11. An elevator apparatus provided with a hoisting machine comprising a fixed shaft supported
by a fixed frame, a rotating frame rotatably supported by shaft on said fixed shaft,
a motor constructed between said rotating frame and said fixed frame and a sheave
rotating together with said rotating frame, and constructed so that a rope is wound
on said sheave to ascend and descend a cage, characterized in that
a vertical portion crossing said fixed shaft at right angles is provided in said fixed
frame,
said rotating frame is formed in a bottom-having cylindrical shape and arranged so
that an opening portion thereof is adjacent to said vertical portion of said fixed
frame,
said sheave is detachably mounted on a bottom portion of said rotating frame, and
a sealing portion is provided between the bottom-having cylindrical opening portion
of said rotating frame and said fixed frame.
12. An elevator apparatus according to claim 4, 5, 6, 7, 8, 9, 10 or 11, characterized
in that said fixed shaft is cantilevered by said fixed frame.
13. An elevator apparatus characterized in that
a cage guided so as to ascend and descend is arranged inside an elevator shaft,
a hoisting machine driving said cage to ascend and descend is installed in a space
between a side wall in a width direction of said cage and a wall of said elevator
shaft when viewed in plane at the top of said shaft,
said hoisting machine has a sheave detachably mounted on a rotating portion other
than a motor shaft,
a counterweight guided so as to ascend and descend is arranged under said hoisting
machine, and
a rope supporting said cage and said counterweight is wound on said sheave.
14. An elevator apparatus according to claim 13, characterized in that
said cage has a pair of guide pulleys supported by shaft on both side of a bottom
portion of said cage in a width direction,
one end, in a diameter direction, of said sheave is arranged adjacently to one end,
in a diameter direction, of one of said pair of guide pulleys, in plane,
said counterweight has a guide pulley supported by shaft to incline so that one end,
in a diameter direction, of said pulley contacts with the other end, in a diameter
direction, of said sheave, and
said rope is wound on said sheave and said respective guide pulleys and both end of
said rope are fixed to an upper portion of said shaft.
15. An elevator apparatus according to any preceding claim, wherein said motor comprises
a rotor having permanent magnet fixed to a rotating portion or rotating frame and
a stator arranged in a fixed portion or fixed frame so as to oppose said rotor with
an air gap therebetween.