Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates generally to load
handling devices and more particularly concerns an improved
swing drive and parking brake assembly for large loa~ handling
_ cranes and the like.
It is known in the art that the lifting capacity of
a load handling device, such as a crane, can be increased by
providing the device with a large diameter roller path for
supporting on rollers an opposed boom and a counterweight
assembly. One example of such a device is shown in U.S.
patent No. 3,485,383. A similar device is disclosed in U.S.
patent No. 4,013,174, which also discloses a swing drive assembly
with automatic shut-down control which permits free swinging
of the crane upper works due to wind induced rotational forces
when the engine is shut down.
It is the primary aim of the present invention to
provide an improved swing drive assembly of the type disclosed
in U.S. patent No. 4,013,174, including parking brake means
to prevent rotation of the swing drive assembly when the crane
engine is temporarily shut off. The present invention also
includes hydraulic accumulator means for maintaining pressure
in the hydraulic act:uators which bias the swing drive pinions
into engagement with the ring gear even when the crane engine
~s shut off. A mechanical swing lock may also be provided
to lock the crane upper works against rotation for longer
periods of down time.
According to the present invention therefore there
is provided a swing drive assembly for a load handling device
having upper works rotatably supported on a large ring roller
path with a frame element mounted on said upper works and
3Q extending outwardly therefrom to adjacent said roller path,
means defining a ring gear secured to one peripheral edge of
said roller path, mounting means on said frame element for
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journalling a pinion gear for normal engagement with said ring
gear and for moving said pinion gear toward and away from said
ring gear, a guide flange mo~mted on said roller path concentric
with said ring gear, a guide roller supported by said frame
element and jouranalled for engagement with said flange, means
including a reversible hydraulic motor for driving said pinion
against said ring gear so as to swing said upper works on said
roller path, a hydraulic actuator~for urging said pinion toward
said ring gear and said roller into engagement with said flange
so as to maintain substantially constant backlash between said
pinion and ring gear regardless of eccentricities in said roller
path, hydraulic pump means for selectively pressurizing said
motor and for constantly pressurizing said hydraluic actuator
during normal swing drive operation, hydraulic accumulator rneans
for maintaining hydraulic fluid in said actuator means under
pressure for urging said pinion toward said ring gear and said
roller into engagement with said.flange when said pump means
is shut down and brake means connected to said pinion for re-
straining rotation thereof and means for selectively operating
said brake means.
The present invention will be further illustrated
by way of the accompanying drawings in which:
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riglll^e I is a rr~glllelltary plan view of a portion of the
upper works of a crane with whi.ch the i.mproved swing drive assembly
of the present inventi.on Is associated;
Figure 2 is an enlarged vertical section substantially as
seen along line 2-2 in Figure l; and
Figure 3 is a schematic diagram of the hydraulic circuit
for the improved swing drive assembly of the present invention.
Turning now to the drawings, there is shown in Figure 1 a
portion of the upper works, in the fo.rm of a boom carrier, indi-
cated generally at 10, of a large load handling device such as, forexample, a heavy duty lift crane. Such a lift crane is disclosed
in U.S. patent No. 4,013,174 and reference may be made to that
patent for further details of the upper works of a crane of the
type with which the present invention is associated. As also dis-
closed in the aforementioned patent, the exemplary crane is provided
with lower works which includes a large diameter ring 12 and roller
path 14 for supporting the boom carrier 10 on rollers (not shown).
The forward end of the boom carrier 10 is formed of a
generally box-shaped beam with laterally extending wings 16, which,
with intermediate framing 18, support a carrier plate 20 on which
the crane boom and mast (neither shown) are pivotally mounted in
suitable connecting plates such as 22 and 24, respectively.
For rotating the boom carrier 10 relative to the ring 12,
one or more swing drive assemblies 30 are provided. In the illustra-
ted embodiment shown in Figs. 1 and 2, and internally
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toothed ring gear 32 is rigidly secured on the inner periphery
of the roller path 14 and the boom carrier 10, which acts as a
frame element, carries a pivotal link 33 (for each drive
assembly 30) which supports a drive pinion 34 journalled for
engagement with the ring gear 32. Concentric with the ring
gear 32, a guide flange 36 is mounted on the inner periphery
of the roller path 14 and a guide roller 38 is mounted
concentric with the pinion 34.
Hydraulic actuator means 40 are provided for urging the
pinion 34 into engagement with the ring gear 32 and the guide
roller 38 into engagement with the guide flange 36 during
normal swing operation. By properly dimensioning the diameter
of the guide roller 38 relative to the depth of the teeth on
the pinion 34 and ring gear 32, the extent of engagement of
the respective teeth can be regulated so as to maintain the
backlash on the pinion 34 substantially constant regardless of
eccentricities or other irregularities in the formation of the
ring gear 32. Accordingly, the roller path 14 and the ring
gear 32 may be formed of a plurality of arcuate segments
bolted or otherwise rigidly secured together at the ~ob site.
The guide flange 36 may also be formed in arcuate segments
but, preferably, it is rigidly and accurately secured to its
companion ring gear segment such as by welding.
It will also be understood that since the guide roller 38
maintains the engagement of the teeth on the pinion 34 and
ring gear 32 substantially constant, precision machining of
the ring gear teeth to close tolerances is not essential.
Rather, the ring gear teeth may be cut with reasonable
accuracy even by current flame-torch cutting techniques.
Moreover, while the ring gear 32 and guide flange 36 are shown
in the illustrated embodiment secured to the inner periphery
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of the roller path 14, it should be appreciated that they
could be secured to the outer periphery. In that case, of
course, the pinion 34 and guide roller 38 would likewise be
urged inwardly into respective engagement with the ring gear
32 and guide flange 36.
SWING DRIVE
For driving each of the pinions 34, a reversible hydraulic
motor 42 is supported by the links 33 and a pinion drive shaft
44 is splined to the output shaft 46 of the motor 42. The
shaft 44 is journalled in bearings mounted in a housing 48 at
the free end of the link 33 (see Fig. 2).
Referring now to Fig. 3, there is shown a schematic
diagram of the power source and hydraulic circuit for driving
the swing drive motors 42. The power source preferably includes
an internal combustion engine 50 which drives a pair of
variable displacement, reversible output pumps 52 through a
transmission case 54. Hydraulic fluid is drawn by the pumps
52 from a tank 56 through supply lines 58 each having a filter
60 therein. Each of -the pumps 52 has a control 62 Eor
regulating the pump displacement and the direction of
discharge through reversible supply/return lines 64, 66
coupled to each of the motors 42. The casing of each of the
pumps 52 also drains to a sump line 68 connected to the tank
56 and has a heat exchanger 69 therein. A return line 70 is
also provided to drain oil leakage from the casings of the
motors 42.
To supply fluid to the actuators 40, the engine 50 also
drives a fixed displacement pump 72 from an output shaft 74 on
the transmission case 54. The pump 72 draws fluid from the
tank 56 through one of the supply lines 58 and delivers fluid
to the actuators 40 through a delivery line 76. A pressure
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relief valve 78 is connected to the delivery line 76 so that
the pressure delivered to the actuators 40 is maintained
constant when the swing drive assembly is in operation.
Excess pressure from the relief valve 78 discharges into the
sump line 68.
Returning to the embodiment shown in Fig. 1, each of the
links 33 is pinned at 82 on a bracket 84 secured to one of the
wings 16. Referring also to Fig. 1, the actuator 40 is pinned
at one end to a lug 88 on the housing 48. Preferably the link
33 is disposed substantially tangentially to the pitch line of
the pinion 34 and ring gear 32 so that the driving force is
imparted essentially through the axis of the pin 82 in the
bracket 84. While two swing drive assemblies 30 are shown in
the illustrated embodiment supported by links 33 pivoted to
brackets 84 on the boom carrier 10, it will be appreciated
that additional swing drives 30 may be mounted on other frame
elements (such as a counterweight carrier, not shown) extending
outwardly from the upper works of the crane to adjacent the
roller path 14.
REE SWINGING
~ s pointed out in the aforementioned U.S. patent No.
4,013,174, the upper works of the crane, particularly the boom
and mast, present a considerable area against which the wind
impinges. When the wind direction changes, especially during
gusty periods, it creates a substantial force on the upper
works, including the boom carrier 10, tending to rotate it
about the ring 12 somewhat like a huge weather vane. This
wind induced rotational force is opposed by the torque generated
in the motors 42 as the pinions 34 are rotated around the ring
gear 32. Under these conditions, of course, it will be
understood that the motors 42 actually operate as pumps and
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the opposing torque is dependent on the pressure generated
internally in the motors 42 and in the reversible lines 64,
66. If flow through these lines is effectively blocked, for
example, by the pumps 52 which are coupled through the
transmission case 54 to the engine 50, tremendous back
pressure builds up in the lines 64, 66 and the rotation
opposing torque exerted by the pinions 34 on the ring gear 32
is very high. This, in turn, creates large separating forces
between the teeth of the pinions 34 and ring gear 32 and,
unless relieved, can cause tooth breakage and/or uneven and
rapid wear due to partial tooth separation at high loads.
In the illustrated embodiment, means are provided for
reducing the back pressure in lines 64, 66 and thus the wind
induced torque applied to the pinions 34 when the engine 50
and pumps 52 are shut down. For this purpose, by-pass valves
92 are connected to lines 64 and 66, respectively, to shunt
the flow of hydraulic fluid around the pumps 52 when the
valves 92 are open. This greatly reduces the back pressure in
the lines 64 and 66 to a level dependent only upon their
internal flow restrictions. Consequently, the opposing torque
of the pinions 34 and forces tending to separate them from the
ring gear 32 are also significantly reduced.
When the engine 50 is shut down, the valves 92 are
automatically biased to the open position. As shown in Fig.
3, a spring biased actuator 98 is provided having its piston
rod end connected to the valves 92 so as to normally move them
to the open position. The cylinder end of the actuator is
connected by a line 100 to receive charge pressure from one of
the pumps 52 when it is operated by the motor 50. Pressure in
the cylinder end of the actuator 98 compresses the spring and
moves the by-pass valves 92 to the closed position. This
places the pumps 52 in direct communication with the motors 42
for normal swing drive operation as previously described.
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During free swinging, means are also provided for
maintaining the pinions 34 in constant mesh with the ring gear
32 when the engine 50 and pumps 52 are shut down. ~o this
end, a spring 102 is interposed between the boom carrier 10
and the housing 48 of the swing drive assembly 30 (see Fig.
2). The spring 102 serves to bias the pinion 34 toward the
ring gear 32 and the guide roller 38 into engagement with
guide flange 36. Preferably, the spring 102 is mounted above
and parallel to the actuator 40 by means of lugs 104 and 106
on the boom carrier 10 and the housing 48, respectively. It
should be understood, however, that this mounting arrangement
could be modified or even reversed to suit the space available
on a particular machine. It will also be appreciated that
because the valves 92 are opened, when the engine 50 is shut
down, the torque and the separating forces on the pinions 34
are reduced and therefore the counteracting force required by
the springs 102 is only a fraction of the force imposed by the
hydraulic actuators 40 during normal swing drive operation.
SWING LOCK
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If free swing:ing of the crane upper works is not desired,
the boom carrier 10 may be mechanically locked to the ring 12.
For this purpose, a swing lock actuator 110 is provided for
advancing and retracting a toothed gear segment 112 into and
out of engagement with the teeth of the ring gear 32. In the
preferred embodiment, the swing lock actuator 110 includes a
reversible rotary hydraulic motor 114 which turns an axial
screw mechanism 116 to move the gear segment 112 into and out
of engagement with the ring gear 32. It will be appreciated
that when the teeth of the gear segment 112 and ring gear 32
are engaged, the upper works of the crane is locked against
rotation on the ring 12. While one or more swing lock
actuators 110 could be located most anyplace on the crane
upper works adjacent the ring 12, a single actuator 110 has
been illustrated here as being mounted on the boom carrier 10
(see Fig. 1~.
To power the swing lock actuator 110, hydraulic fluid is
delivered through a line 118 from a port in the adjustable
relief valve 78 to the intake side of a spring centered two-
way shuttle valve 120. When the shuttle valve 120 is in its
centered or neutral position, flow through line 118 is
blocked. When the shuttle valve 120 is moved in one direction
(such as to the right in Fig. 3) by a suitable operator, for
example an air cylinder 122) hydraulic fluid flows from line
118 through the valve into line 124 to one side of the screw
motor 114 to advance the screw mechanism 116 and cause the
gear segment 112 to mesh with the ring gear 32. Hydraulic
fluid returns from the other side of the motor 114 through a
line 126 to the shuttle valve 120 and out through a return
line 128 connected to sump line 68. Conversely, when it is
desired to un]ock the gear segment 113 from the ring gear 32,
the shuttle valve 120 is moved in the opposite direction by
another ai.r cylinder 130 which reverses the flow of hydraulic
fluid through lines 124, 126 and causes the screw mechanism
116 to retract the gear segment~ll2~from engagement with the
ring gear 32. It will be appreciated, of course, that once
the gear segment has been fully advanced or retracted, the
shuttle valve 120 would be normally returned by its internal
springs to its neutral position blocking line 118. Utilization
of the swing lock actuator 110 may be desired, for example,
when wind induced loads are low and/or the crane is used to
hold or apply a load for an extended period of time.
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PARKING BRAKE
Pursuant to the present invention, means are also provided
for temporarily preventing rotation of the crane upper works
when the ensine is shut off without energizing the swing lock
actuator 110, as discussed above. Such temporary restraint
may be desired when it is required to perform some fabrication
or adjustment work on a suspended load or on the structure to
which the load is to be secured.
As shown in Fig~ 2, each of the swing drive units 30
includes a brake drum 13Q mounted on the pinion drive shaft 44
within a protective housing 132. Surrounding the brake drum
130 is a brake band 134, one end of which is fixed to the
housing 132 and the other end connected to an operating lever
136 for tightening the brake band 134 against the brake drum.
The operating lever 136 is preferably connected through a
suitable mechanical linkage (not shown) to the piston end of a
pneumatic cylinder 138 which may be selectively pressurized by
the crane operator to apply the temporary parking brake. The
cylinder 138 preferably includes an internal spring mechanism
for expanding the brake band when the air cylinder is
depressurized.
It is another feature of the invention that means are
provided for maintaining pressure in the hydraulic actuators
40 during temporary shut down of the engine 50. As noted
previously hydraulic fluid is supplied to the actuators by
pump 72 through delivery line 76 and pressure relief valve 78.
Also connected between the relief valve 78 and each of the
actuators 40 is a check valve 140 and a hydraulic accumulator
142. The check valves 140 prevent reverse flow of hydraulic
fluid even when the pump 72 is shut off and the accumulators
142 maintain hydraulic pressure in the actuators 40. The
accumulators 142 preferably include a pre-charged bladder
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filled with an inert gas, such as nitrogen, to cushion and
maintain pressure within the accumulators. A separate
pressure gauge 144 is also provided for each accumulator to
register the pressure therein. Also the check valves 140 may
be provided with a manual bypass to bleed pressure from the
accumulators as may be required to permit safe service and
repair of the system.
From the foregoing, it will be seen that the present
invention provides an improved swing drive arrangement for
heavy duty crane assemblies rotatably supported on large
diameter roller paths. During normal swing drive a hydraulic
actuator 40 urges a guide roller 38 into engagement with a
guide flange 36 to provide substantially constant backlash of
the pinion gear regardless of irregularities in the large ring
gear 32. When the engine 50 is temporarily shut down,
pressure is maintained in the actuators 40 by hydraulic
accumulators 142 and check valves 140. Each of the swing
drive assemblies 30 also includes a parking brake which may be
applied to prevent rotation of the drive pinions 34 when the
pumps 52 are shut down. For longer periods of non-use a
mechanical swing lock actuator 110 is provided for engaging a
toothed gear segment 112 with the teeth of the ring gear 32.
Alternatively, if it is desired to permit the crane upperworks
to free swing in the wind (or "weather vane") automatic bypass
valves 92 open to shunt hydraulic fluid around the pumps 52
and thereby prevent excessive pressure from developing in the
hydraulic supply/return lines 64, 66 as the pinions 34 rotate.
A large compression spring 102 serves to hold each drive
pinion 34 in engagement with the ring gear 32 even if the
hydraulic system is shut down for a prolonged period of time.
