U.S. patent number 3,815,478 [Application Number 05/084,978] was granted by the patent office on 1974-06-11 for pipelayer hydraulic drawworks with free-fall.
This patent grant is currently assigned to Caterpillar Tractor Co.. Invention is credited to Evald Gustav Axelsson, David Collier.
United States Patent |
3,815,478 |
Axelsson , et al. |
June 11, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
PIPELAYER HYDRAULIC DRAWWORKS WITH FREE-FALL
Abstract
In cable winding gear driven by a hydraulic motor of the kind
having radial pistons driving a surrounding cam ring, a control is
provided for applying differential pressure to the motor pistons so
that they are disengaged from the cam ring which can then rotate
freely. This provision enables the cable to be run out freely, so
that, for example, in a crane free fall of the load can be allowed
while avoiding damage to the motor. Pipe-laying equipment including
the free-fall provision is described.
Inventors: |
Axelsson; Evald Gustav
(Stafford, EN), Collier; David (Brewood,
EN) |
Assignee: |
Caterpillar Tractor Co.
(Peoria, IL)
|
Family
ID: |
10317622 |
Appl.
No.: |
05/084,978 |
Filed: |
October 29, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Jun 26, 1970 [GB] |
|
|
31078/70 |
|
Current U.S.
Class: |
91/497 |
Current CPC
Class: |
B66D
1/08 (20130101); F15B 11/04 (20130101); F16H
61/40 (20130101); F03C 1/0425 (20130101); F16H
61/4157 (20130101); B66C 23/44 (20130101); F15B
2211/30525 (20130101); F15B 2211/50536 (20130101); F15B
2211/7053 (20130101); F15B 2211/611 (20130101); F15B
2211/324 (20130101); F15B 2211/715 (20130101); F15B
2211/20538 (20130101); B66D 2700/0133 (20130101); F15B
2211/865 (20130101); F15B 2211/615 (20130101); F15B
2211/20584 (20130101); F15B 2211/7058 (20130101); F15B
2211/30505 (20130101); F15B 2211/8755 (20130101); F15B
2211/5151 (20130101); F15B 2211/7128 (20130101) |
Current International
Class: |
F15B
11/00 (20060101); F03C 1/04 (20060101); B66D
1/08 (20060101); B66D 1/02 (20060101); F15B
11/04 (20060101); F03C 1/00 (20060101); F16H
61/40 (20060101); F01b 013/06 () |
Field of
Search: |
;91/472,491 ;417/214
;254/186 ;60/52 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Freeh; William L.
Attorney, Agent or Firm: Phillips, Moore, Weissenberger,
Lempio & Strabala
Claims
We claim:
1. In a system for operating and controlling a winding gear driven
by a rotary hydraulic motor of the kind including a first member
having a plurality of radial bores, a motor element displaceable in
each of the bores and each having an associated driving means, a
cam ring having cam faces engaged by the driving means and means
for selectively supplying hydraulic fluid to the bores to displace
the motor elements radially in a predetermined sequence and by
pressure engagement of the driving means with the cam faces to
produce relative rotation between the cam ring and said first
member, the system including pump means for supplying hydraulic
fluid to the hydraulic motor, normally applied brake means for said
winding gear, fluid pressure means including fluid communication
means for releasing said brake means, the improvement comprising;
free-run means including fluid communication means for applying to
the motor elements of the hydraulic motor a hydraulic pressure
differential to displace the motor elements radially inwardly and
withdraw the associated driving means from contact with the cam
faces of the cam ring whereby the cam ring can rotate freely, said
free-run means including means for preventing said fluid pressure
means from releasing said brake means until said pressure
differential has been developed to condition said motor elements
and associated driving means to move radially inwardly away from
contact with said cam faces of said cam ring, the hydraulic
pressure for the free-run means being derived from a source
separate from the pump means supplying the motor.
2. The invention of claim 1 including a casing for said hydraulic
motor and means for applying, on actuation of the free-run means, a
hydraulic pressure in the interior of said casing of the motor
higher than that obtaining in said bores.
3. The invention of claim 1 including means for reducing, on
actuation of the free-run means, standing hydraulic pressure in
said bores.
4. The invention of claim 2 further including valve means for
actuating the free-run means.
5. The invention of claim 4 including a casing for said hydraulic
motor and wherein said valve means are adapted, on actuation, to
connect a source of hydraulic pressure to the interior of said
casing.
6. The invention of claim 5 further including means for maintaining
a standing pressure in the bores when the motor is idle and wherein
said valve means, on actuation, operate means for releasing said
standing pressure from the bores of the motor.
7. In a system for operating and controlling a winding gear driven
by a rotary hydraulic motor of the kind including a first member
having a plurality of radial bores, a motor element displaceable in
each of the bores and each having an associated driving means, a
cam ring having cam faces engaged by the driving means and means
for selectively supplying hydraulic fluid to the bores to displace
the motor elements radially in a predetermined sequence and by
pressure engagement of the driving means with the cam faces to
produce relative rotation between the cam ring and said first
member, the system including pump means for supplying hydraulic
fluid to the hydraulic motor, normally applied brake means for said
winding gear, fluid pressure means including fluid communication
means for releasing said brake means, the improvement comprising;
free-run means including fluid communication means for applying to
the motor elements of the hydraulic motor a hydraulic pressure
differential to displace the motor elements radially inwardly and
withdraw the associated driving means from contact with the cam
faces of the cam ring whereby the cam ring can rotate freely, said
free-run means including means for preventing said fluid pressure
means from releasing said brake means until said pressure
differential has been developed to condition said motor elements
and associated driving means to move radially inwardly away from
contact with said cam faces of said cam ring, valve means for
actuating the free-run means, a casing for hydraulic motor and
wherein said valve means are adapted, on actuating, to connect a
source of hydraulic pressure to the interior of said casing, means
for maintaining a standing pressure in the bores when the motor is
idle and wherein said valve means, on actuation, operate means for
releasing said standing pressure from the bores of the motor, said
valve means, on restoration to its normal position after actuation,
acting to connect a source of hydraulic pressure to the bores of
the motor to restore the standing pressure.
8. The invention of claim 7 wherein said valve means, on
restoration of its normal position after actuation, connect a
source of hydraulic pressure to the bores of the motor to restore
the standing pressure, said means for preventing brake means
release being also provided for ensuring that the brake means is
applied before the standing pressure is restored.
9. In a system for operating and controlling a winding gear driven
by a reversible rotary hydraulic motor, driving means for
selectively supplying hydraulic fluid to said rotary hydraulic
motor to rotate said hydraulic motor and said winding gear, said
driving means including first supply means for supplying hydraulic
pressure fluid to said hydraulic motor, normally applied brake
means for said winding gear, fluid pressure means including fluid
communication means for releasing said brake means, free-run means
including fluid communication means for applying to a portion of
the hydraulic motor a hydraulic pressure to allow said hydraulic
motor to rotate freely without load, said free-run means including
second supply means for supplying said hydraulic motor portion,
said second supply means including a source of hydraulic fluid
separate from the source of hydraulic fluid for said drive means,
said free-run means including means for preventing said fluid
pressure means from releasing said brake means until said hydraulic
pressure has been supplied to said portion of said motor to
condition said motor to rotate freely without load, said driving
means for said reversible rotary hydraulic motor further including
a motor control valve for controlling flow of hydraulic fluid to
said hydraulic motor for driving rotation thereof, said control
valve having a first portion for supplying fluid to cause said
motor to rotate in a first direction, a second position for
supplying fluid to cause said motor to rotate in the reverse
direction, and a neutral position in which fluid flow to and from
said hydraulic motor is blocked and a hydraulic fluid lock is
created which retards rotation of said hydraulic motor in either of
said first or reverse directions, said free-run means further
including a secondary valve means separate from said motor control
valve for controlling the supply of hydraulic fluid pressure to
said motor portion.
10. In a system for operating and controlling a winding gear driven
by a rotary hydraulic motor, driving means for selectively
supplying hydraulic fluid to said rotary hydraulic motor to rotate
said hydraulic motor and said winding gear, said driving means
including first supply means for supplying hydraulic pressure fluid
to said hydraulic motor, normally applied brake means for said
winding gear, fluid pressure means including fluid communication
means for releasing said brake means, free-run means including
fluid communication means for applying to a portion of the
hydraulic motor a hydraulic pressure to allow said hydraulic motor
to rotate freely without load, said free-run means including second
supply means for supplying said hydraulic motor portion, said
second supply means including a source of hydraulic fluid separate
from the source of hydraulic fluid for said drive means, said
free-run means including means for preventing said fluid pressure
means from releasing said brake means until said hydraulic pressure
has been supplied to said portion of said motor to condition said
motor to rotate freely without load, said free-run means further
including tertiary valve means for preventing said rotary hydraulic
motor from returning from the freely rotating condition to the
driving condition prior to the re-application of said brake
means.
11. In a system for operating and controlling a winding gear driven
by a rotary hydraulic motor of the kind including a first member
having a plurality of radial bores, a motor element displaceable in
each of the bores and each having an associated driving means, a
cam ring having cam faces engaged by the driving means and means
for selectively supplying hydraulic fluid to the bores to displace
the motor elements radially in a predetermined sequence and by
pressure engagement of the driving means with the cam faces to
produce relative rotation between the cam ring and said first
member, the system including pump means for supplying hydraulic
fluid to the hydraulic motor, normally applied brake means for said
winding gear, fluid pressure means including fluid communication
means for releasing said brake means, the improvement comprising;
free-run means including fluid communication means for applying to
the motor elements of the hydraulic motor a hydraulic pressure
differential to displace the motor elements radially inwardly and
withdraw the associated driving means from contact with the cam
faces of the cam ring whereby the cam ring can rotate freely, said
free-run means including means for preventing said fluid pressure
means from releasing said brake means until said pressure
differential has been developed to condition said motor elements
and associated driving means to move radially inwardly away from
contact with said cam faces of said cam ring, an operator's control
for the motor wherein the free-run means includes means coupled to
the operator's motor control for ensuring that the free-run means
can only be actuated when the motor control is in the off
position.
12. In a system for operating and controlling a winding gear driven
by a rotary hydraulic motor, driving means for selectively
supplying hydraulic fluid to said rotary hydraulic motor to rotate
said hydraulic motor and said winding gear, said driving means
including first supply means for supplying hydraulic pressure fluid
to said hydraulic motor, normally applied brake means for said
winding gear, fluid pressure means including fluid communication
means for releasing said brake means, free-run means including
fluid communication means for applying to a portion of the
hydraulic motor a hydraulic pressure to allow said hydraulic motor
to rotate freely without load, said free-run means including second
supply means for supplying said hydraulic motor portion, said
second supply means including a source of hydraulic fluid separate
from the source of hydraulic fluid for said drive means, said
free-run means including means for preventing said fluid pressure
means from releasing said brake means until said hydraulic pressure
has been supplied to said portion of said motor to condition said
motor to rotate freely without load.
13. The invention of claim 12 wherein said rotary hydraulic motor
is reversible and said hydraulic motor drive means further includes
a motor control valve for controlling flow of hydraulic fluid to
said hydraulic motor for driving rotation thereof, said control
valve having a first position for supplying fluid to cause said
motor to rotate in a first direction, a second position for
supplying fluid to cause said motor to rotate in the reverse
direction, and a neutral position in which fluid flow to and from
said hydraulic motor is blocked and a hydraulic fluid lock is
created which retards rotation of said hydraulic motor in either of
said first or reverse directions.
Description
This invention is concerned with improvements in or relating to
systems for operating and controlling winches, hoists, windlasses
or the like which are driven by hydraulic motors.
In particular, this invention is concerned with systems embodying a
hydraulic motor of the kind including a stationary cylinder having
a number of radial bores in each of which a piston is displaceable,
and a cam ring which is rotatably driven by the pistons. The cam
faces of the cam ring are engaged by driving means, such as rollers
mounted on the radially outward ends of the pistons, or the outer
end faces of the pistons, and hydraulic fluid is selectively
supplied to the bores to radially displace the pistons in a
predetermined sequence whereby the pressure engagement of the
driving means with the cam faces rotates the cam ring from which
the drive is obtained in any suitable manner. Such hydraulic motors
as above described are herein referred to as of the kind
specified.
Hydraulic motors of the kind specified are already well known and
they are used for driving winches, hoists, windlasses or the like.
Although in such applications hydraulic motors of the kind
specified are very satisfactory, it is most desirable to be able to
operate the winch or the like in the conventional manner in which
the drive can be disengaged so as to allow the winch drum or the
like to rotate freely or over-run the drive. For example, it is
desirable to provide an operating condition such that the load
supported by the winch can fall freely under gravity, or such that
the cable or drag line can run out freely.
In systems having a mechanical drive transmission this drive-free
condition can easily be achieved by a releasible clutch
arrangement. However, with a hydraulic motor of the kind specified
direct drive to the winch or the like is utilised. We have found
that in a hydraulic system where the source of hydraulic fluid for
the motor is derived solely from one or more pumps, and not a
pressure accumulator, free-rotation of the cam ring cannot be
obtained without risk of damaging the hydraulic motor. The reason
for this is that in a hydraulic motor of the kind specified the
flow of hydraulic fluid is arranged so that the pistons are urged
radially outward whereby the driving means are maintained in
engagement with the cam faces. Even if the supply of hydraulic
fluid to the bores is interrupted or reduced, then at least some of
the pistons will fall radially outwardly of their bores due to
gravity so that at least some of the driving means engage with the
cam faces. Accordingly, when the cam ring is not being driven by
the driving means, but is rotated by the torque applied by the load
on the winch cable or the like, the uncontrolled engagement of the
driving means with the cam faces of the rotating cam ring causes
excessive damage to the motor; in certain instances the cam faces
are damaged, or the motor bearing may crack or break up.
It is an object of this invention to provide in a system for
operating and controlling a winch hoist or the like driven by a
hydraulic motor of the kind specified, an improvement whereby such
free fall of the load, or free-running out of the load cable can be
achieved without the aforementioned risk of damage to the hydraulic
motor.
Further objects of this invention are to provide an improved
hydraulic system for operating and controlling a winch, hoist or
the like driven by a hydraulic motor of the kind specified, and to
provide a winch, hoist or the like operated and controlled by such
improved hydraulic system.
Other objectives will be apparent from the description of preferred
embodiment of this invention given later herein.
According to the broadest aspect of this invention, we provide in a
system for operating and controlling winding gear, such as a winch,
hoist, windlass or the like, driven by a hydraulic motor of the
kind specified and to which hydraulic fluid is supplied by pump
means, the improvement of valve means for controlling the flow of
hydraulic fluid and which valve means on actuation is arranged to
produce in the hydraulic motor a hydraulic pressure differential
acting on the pistons to displace them radially inwards to an
extent such that the driving means are maintained out of contact
with the cam faces of the cam ring which can then rotate
freely.
In theory there are probably many ways in which such hydraulic
pressure differential may be developed by controlling the flow of
hydraulic fluid through valve means. However, practical
considerations are of paramount importance because of problems that
may arise such as, the adaptability of the hydraulic motor, the
overheating of the hydraulic fluid, the maximum flow capacity of
the pump means, and the overall complexity and cost of providing a
special valve arrangement. We believe that we have devised a most
practical system which avoids the kinds of problems
aforementioned.
One of the preferred ways of obtaining the hydraulic pressure
differential in the hydraulic motor is to arrange for the valve
means to reduce hydraulic pressure in the cylinder bores and to
maintain a low hydraulic pressure in the motor casing so as to
develop a pressure differential sufficient to displace the pistons
radially inwards. In this manner a relativey low hydraulic pressure
in the motor casing can be utilised to displace the pistons, and
when the drive is to be restored, hydraulic fluid can be supplied
to the cylinder to re-engage the driving means with the cam ring,
and then hydraulic fluid for driving the motor may be supplied at
the required flow rate.
Although it is envisaged within the scope of this invention to
arrange for the valve means merely to control the flow of hydraulic
fluid into the motor casing so as to develop therein a hydraulic
pressure acting on the radially outer parts of the pistons greater
than the hydraulic pressure in the cylinder bores as applied to the
radially inner parts of the pistons, this has the disadvantage that
the motor casing, including the cam ring will have to be designed
to withstand very high bursting loads due to the high hydraulic
pressures involved. Additionally, the flow capacity of the pump
means and overheating of the hydraulic fluid may lead to further
problems. Usually a hydraulic motor of the kind specified is
designed to operate with no or very low hydraulic pressure in the
motor casing, and thus where it is desired merely to apply our
invention to existing hydraulic motors of the kind specified the
aforementioned preferred way of developing the hydraulic pressure
differential can most conveniently be adopted.
Of course the valve means has to be arranged to act, on actuation,
in concert with the other essential operational controls of the
winch or the like which must be maintained either inoperative or
functional, for instance when the load is released the winch brake
must be held off. However, these considerata will be fully
understood from an embodiment of the invention which is described
later herein.
This invention is also deemed to include a winch, hoist, windlass
or the like operated and controlled by a hydraulic system,
embodying our improvement as well as the hydraulic system per
se.
One application of this invention is in a hydraulic system for
operating and controlling pipe-laying apparatus adapted for
attachment to, or incorporation in a tractor, preferably of the
tracked type.
By way of example an embodiment of this application of this
invention will now be described with reference to the accompanying
drawings in which:
FIG. 1 is a front-elevation of pipe-laying apparatus according to
the invention mounted on a tractor;
FIG. 2 is a diagrammatic view of a hydraulic motor of the kind
specified;
FIG. 3 is a diagram of the hydraulic operation and control system
for the boom of the pipe-laying apparatus of FIG. 1 and;
FIG. 4 is a diagram of the hydraulic operation and control system
for counterweights and a hoist of the pipe-laying apparatus.
The principal components of the pipe-laying apparatus which are
mounted on the tractor comprise a saddle 1 on one side of which are
carried a set of hydraulically controlled counterweights 2 and two
winches 3 each adapted to be driven by a hydraulic motor of the
kind specified and of which further details will be given later. On
the other side of the saddle is mounted the boom 4 which is raised
and lowered by one of the winches 3, and the other end of the boom
carries the hoist 5 which is raised and lowered by the other winch
3. The hoist 5 and boom 4 can be operated independently or
simultaneously.
The hydraulic motors driving the winches 3 are each of the kind
shown in FIG. 2 and including a stationary cylinder block 6 having
a number of radial bores in each of which a piston 7 is
displaceable, and a cam ring 8 which is rotatably driven by the
pistons. The cam faces of the cam ring 8 are engaged by driving
means, such as rollers 9 mounted on the radially outward ends of
the pistons, or the outer end faces of the pistons, and hydraulic
fluid is selectively supplied to the bores to displace the pistons
7 radially in a predetermined sequence whereby the pressure
engagement of the driving means with the cam faces rotates the cam
ring from which the drive is obtained in any suitable manner.
The hydraulic system depicted in FIGS. 3 and 4 is for operating and
controlling the foregoing apparatus and its ancillary parts. The
power is derived from the tractor engine independently of drive
transmission, and it is arranged to drive the fixed displacement
hydraulic pumps which supply hydraulic fluid to the three parts of
the hydraulic system for actuating:
i. the boom 4;
ii. the counterweights 2; and
iii. the hoist 5.
Each of these three parts of the system will now be described with
reference to FIGS. 3 and 4 which are in the form of circuit
diagrams with all the control valves shown in the neutral
position.
i. The Boom System
A fixed displacement hydraulic pump 10 driven from the engine draws
hydraulic fluid through a suction filter 12 from an open or low
pressure reservoir 11. Hydraulic fluid supply from the output line
13 of the pump 10 is controlled by a three position open-centre
valve 14 which is shown in the neutral position. By means of the
valve 14 hydraulic fluid may be supplied to a reversible hydraulic
motor 15 of the kind specified which is connected directly to the
winch drum, and the hydraulic fluid may be returned to the
reservoir 11.
For raising the boom 4, the valve 14 is displaced to a second
position, which corresponds to moving it to the extreme right in
the accompanying drawing. In this second position the motor 15 is
rotated in one sense by hydraulic fluid supplied through line 16 to
the motor 15 and discharged through the line 17 through the valve
14, to line 18 returning to the reservoir 11. Hydraulic fluid is
also drained from the motor casing through line 19 back to the
reservoir 11.
Associated with line 16 is a valve 20 which is normally closed, but
which on actuation serves to connect the line 16 with line 21
leading to the reservoir 11. The valve 20 is actuated by the
engagement of a spring loaded abutment 22 which is arranged to be
engaged by the boom if it is raised to an over-centre position, or
other predetermined attitude of elevation in relation to the
tractor. As will be appreciated, on such actuation of the valve 20,
the supply of hydraulic fluid through line 16 to the motor 15 is
prevented as the line 16 is connected through valve 20 to the
reservoir return line 21, and further elevation of the boom is
prevented.
For lowering the boom, the motor 15 is rotated in the opposite
sense by changing the direction of flow of the hydraulic fluid
supplied to the motor 15. This is achieved by displacing the valve
14 to a third position, corresponding to the extreme left in the
accompanying drawing. In this third position, hydraulic fluid is
supplied to the motor 15 from the pump output line 13 through line
17 and discharged through line 16, through valves 14 to line 18
which is connected to the reservoir 11.
In order to maintain the boom at a particular attitude, the motor
15 is provided with a counterbalance valve arrangement as depicted
in the rectangular outline referenced 23. This counterbalance valve
arrangement is adapted only to open when a predetermined high
pressure is exceeded so that the motor can operate with full back
pressure.
The boom winch is provided with a conventional spring operated band
brake that is arranged to be held in the "off" position by a
hydraulic brake cylinder 25 which is connected to the valve 14 by a
line 26. Hydraulic pressure is maintained in the brake cylinder 25
whilst the motor 15 is driven in either sense. When no hydraulic
fluid is supplied to the motor 15, namely when valve 14 is in the
neutral position as depicted, the brake line 26 is open to the
reservoir return line 18 and the hydraulic cylinder 25 is released
so that the brake is applied. Additionally, if there should be a
loss of hydraulic fluid with consequent reduction in pressure in
any of the supply lines aforementioned the brake is automatically
applied.
By way of further explanation of the boom system of FIG. 3, the
control valve 14, when in the neutral position shown, blocks lines
16 and 17 from lines 13 and 18 and communicates flow from pump 10
to tank 11 via conduits 13 and 18. In this condition, the brake 25
is in communication with the tank via the conduit 26 which is a
branch of conduit 13. Brake 25, which is normally applied by spring
force, is allowed to be applied to restrict movement of the boom.
Release of the brake is accomplished by pressurization of the brake
cylinder to overcome the spring bias when desired.
In order to lower the boom, the selector control valve 14 is
shifted to position 92 in which it allows pump flow to be
communicated to motor 15 via the conduit 17 and to the
counter-balance valve 93 via the conduit 94.
The orifice choke 96 modulates pilot flow to the counter-balance
valve 93 and prevents over sensitive operation thereof. When the
pilot pressure reaches the range of 300-500 psi, the valve 93 will
shift to an open position in which is allowed communication between
the motor ports 102 and the tank 11 via conduits the 97,98,99,16
and 18. The counter-balance valve 93 maintains a minimum back
pressure range of 300-500 psi in the motor which pressure assures
the release of the brake 25 prior to the lowering of the boom and
prevents cavitation in the motor 15.
The two-way relief valve 100 protects the motor circuitry by
directing flow back to the motor inlet via the conduits 101 and 17
at such times that the load is excessive and back pressure in the
motor reaches the 3,000 psi level. This provision also reduces
cavitation in the motor by supplying make-up fluid to the inlet
ports when the load becomes excessive.
Shifting of the selector control valve 14 to position 90 places the
circuit in a boom raise mode. In this condition, flow from pump 10
is communicated through conduits 13 and 16 to motor 15. Conduit 26
also communicates the pressurized pump flow to the brake 25 for the
release thereof. The two-way relief valve 100 establishes maximum
motor pressure at 3,000 psi and relieves the system by
communicating relief flow to the tank 11 via the conduits 101 and
17. Relief valve 106 protects the pump 10 from excessive pressure
by communicating conduit 13 with conduit 18 and with tank 11.
Check valves 104 and 105 are provided to block flow in the
direction indicated and to maintain fluid in the respective
associated conduits and also to block flow to the motor 15 until
after the brake spring force is overcome by pressurized fluid and
the brake is released.
The Counterweight System
The lateral position of the counterweights (not shown) relative to
the tractor is hydraulically controlled by a three position valve
27 similar to valve 14. Two hydraulic cylinders 28, 29 are arranged
to move the counterweights transversely of the tractor centre-line
by means of hydraulic fluid supplied through line 30 from the small
section of a double hydraulic pump 31 of the fixed displacement
type drawing hydraulic fluid through a suction filter 83 from the
reservoir 11.
When the valve 27 is in the central neutral position as depicted,
the supply of hydraulic fluid is straight through is straight
through the open-centre of valve 27 into line 36 connected to the
hoist system which is described later. If the valve 27 is displaced
into either a second or third position, then hydraulic fluid is
supplied to one end of the hydraulic cylinders 28, 29 through one
of lines 32, 33 and displaced hydraulic fluid flows out of the
other end of the hydraulic cylinders 28, 29 through the other one
of lines 32, 33. A counterbalance valve arrangement 34 is provided
in line 33. A pressure relief valve 35 is associated with valve 27
and is connected to line 36.
The Hoist System
The supply of hydraulic fluid to the hoist system is derived from
the large section of the double hydraulic pump 31. Hydraulic fluid
in output line 37 is directed through line 39 to a three-position
valve 38, through line 40 to a two-position valve 41 with the
output line 37 including a by-pass filter 42.
The valve 38 is for controlling a two speed hydraulic motor 43 of
the kind specified. Valve 38 is substantially the same as the other
three position valves 27 and 14, except that it includes a
restrictor 44 which serves to throttle flow to the reservoir 11
through line 45 when the valve 38 is in its second or third
position.
The valve 41 is provided for operating the valve 46 of the
hydraulic motor 43 that controls, in known manner, the speed of the
motor. The valve 41 is connected to a line 47 leading to the
reservoir 11, and in either operative position provides a through
passage for hydraulic fluid to the brake cylinder 48 of the
spring-operated band type winch brake (not shown) that is held off
by the brake cylinder 48.
With reference to the operation of the brake cylinder 48, when the
valve 38 is in the neutral position depicted in the drawing there
is no hydraulic fluid supplied to the brake cylinder 48 and the
brake is in the applied position. The hydraulic fluid in line 39
flows through the open centre of valve 38 to the reservoir 11 via
return line 45. The brake cylinder line 52 is also open to the
reservoir 11 through shuttle valve 51, line 54 through shuttle
valve 50, and the line 49, valve 41 to line 40 and thence to the
reservoir 11 through open-centred valve 38.
When the valve 38 is in either its second or third positions, that
is when the hydraulic motor 43 is being driven, hydraulic fluid is
supplied to the brake cylinder 48 to hold the winch brake in the
"off" position. When the motor speed control valve 41 is in the
position depicted, hydraulic fluid flows through line 40 through
port p to port a of valve 41. Flow is then through line 49, through
shuttle valve 50 into line 54 to actuate shuttle valve 51 and into
the brake line 52. The actuation of the shuttle valve 51 prevents
the return flow of hydraulic fluid to the reservoir 11 through line
57. When the motor speed control valve 41 is in its other position,
the hydraulic fluid flows through line 40, through port p to port b
of valve 41, through line 53 to actuate shuttle valve 50 to close
line 60. The flow is then to the brake line 52 through line 54 and
shuttle valve 51 which is actuated in the same way as just
described.
As will be appreciated, when there is a reduction in hydraulic
pressure in the brake line 52, the winch brake will be applied.
Such reduction in hydraulic pressure will occur when valve 38 is
moved to the neutral position, or if a supply line fails, or under
other circumstances which will be explained later in connection
with the system for operating the hoist winch with free fall of the
load.
The speed of the hydraulic 43 is controlled in known manner by the
actuation of spool valve 46 to which hydraulic fluid is supplied
through line 60 when the control valve 41 is in the position
depicted and valve 38 is in its second or third position with
hydraulic fluid being supplied through line 40.
The supply of hydraulic fluid for driving the motor 43 is either
through line 58, or through line 59 depending on the position of
valve 38. The return flow of hydraulic fluid from the motor 43 is
through either line 59 or 58. There is also provided an arrangement
of valves to maintain a predetermined pressure acting on the motor
pistons. This arrangement includes a non-return pressure limiting
circuit 78 and a counter-balance valve 79. From this arrangement of
valves the hydraulic fluid returns through the valve 38, restrictor
44 to the line 45 leading to the reservoir 11.
The crux of this invention is that the hydraulic motor 43 can be
operated so that free fall of the hoist load can be obtained, and
controlled without risk of damage to the motor 43. This operation
and control will now be explained having regard to the foregoing
description and explanation.
The free-fall hydraulic system associated with control valve 56 is
arranged so that it can only be effective when the hoist control
valve 38 is in the neutral central position, that is when the
hydraulic motor is not being driven, such as when a load is
suspended on the hoist in mid-air. This is done by providing a
drain valve 64 which is mechanically coupled by a suitable linkage
to the operating linkage of valve 38. When valve 38 is in either
its second or third position, the line 66 leading to valve 64 is
open to the reservoir 11 through drain line 65 and thus pressure
cannot be developed in line 67 which is in the free fall system.
Accordingly, free fall of the load can only be obtained when the
hoist valve 38 and drain valve 64 are in the operative positions
depicted in the accompanying drawing.
The free fall of the hoist load is controlled by the control valve
56 to which hydraulic fluid flows from the control valve 27 of the
counterweight system, through line 36 including by-pass filter 61.
The free fall control valve 56 is depicted in the inoperative
position whereby the brake line 52 is open to the reservoir 11,
flow being through line 55, line 62 including restrictor 63,
through port B to port T of the valve 56 to the reservoir return
line 57. The hydraulic fluid flows through port P to port A of
valve 56, through line 68 to a non-return valve 69 in line 70, to a
line 71 and thus to an open reservoir 72 to which flow is
controlled by a non-return valve 73 having a predetermined opening
pressure. The line 71 also includes a pressure relief valve 74 for
relieving the pressure in line 36, but under normal conditions as
now being described, this relief valve 74 merely acts as a
non-return valve in line 71.
The open reservoir 72 which may be integral with reservoir 11, is
also connected to the motor casing by line 75 so that a minimum
pressure is maintained in the motor casing by the restricted
opening pressure of the non return valve 73. The pressure is
selected in accordance with the necessary hydraulic pressure
differential which has to be developed before free rotation of the
cam ring of the hydraulic motor 43 is allowed.
When the free fall control valve 56 is actuated hydraulic fluid
flows through port P to port B into line 62 and through restrictor
63 into line 55, through shuttle valve 51 into brake line 52 so as
to actuate the brake cylinder 48. Hydraulic fluid also flows from
the line 62 to line 67 connected to a pair of spool valves 76, 77,
which are thus actuated. The lower hydraulic pressure which is
present in the idle hydraulic motor 43 and which is determined by
the valves 78, 79 is vented to an open reservoir through the valves
76, 77 on their actuation, and thus the pressure maintained in the
motor casing by the valve 73 is greater than that in the motor
cylinder bores and the pistons are displaced radially inwards by
the hydraulic pressure in the motor casing so that the driving
means as aforedescribed is moved out of engagement with the cam
ring.
Accordingly, as the spool valves 76, 77 are merely operated by a
relatively low pilot pressure, and the brake cylinder 48 has a much
higher actuation pressure, the brake is released slightly after the
motor pistons have been displaced.
In practice, we have found that if the motor cylinder bore pressure
can be reduced to a very low figure, then a motor casing pressure
of from 22 p.s.i. to 36 p.s.i. is sufficient in a hydraulic motor
of the kind specified developing a maximum torque of 545 ft. lbs,
per 100 p.s.i.
To stop the free fall of the load, the free fall control valve 56
is returned into the position as depicted in the drawing. However,
now there is no hydraulic pressure in the motor supply and
discharge lines 59, 58. A positive pressure, greater than the motor
casing pressure has to be developed quickly to render the motor 43
operative again for operating the hoist winch. This development of
operative hydraulic pressure in the motor 43 to displace the
pistons radially outwards to re-engage the driving means with the
cam ring is achieved when the free fall control valve 56 is
returned to position depicted in the drawing. When valve 56 is in
this position hydraulic fluid from line 36 flowing now through line
68 can overcome the two non-return valves 80, 81 in line 82
connected to motor lines 58, 59. The operating opening pressures of
these valves 80, 81 are set lower than the non-return valve 69,
thus the minimum operating pressure determined by the arrangement
of valves 78 and 79 is quickly restored. Hydraulic fluid also flows
to the reservoir 11 from the brake line 52, through shuttle valve
51 through line 55, through the restrictor 63 in line 62, and
through valve 56 to line 57. This exhausts the brake cylinder 48
which is released and the brake is applied. The spool valves 76 and
77 are also released again by the pressure drop in line 67, but a
throttle non-return valve 84 in line 67 the restrictor 63 provides
a restriction which delays the release of the spool valves 76, 77
for a short time to ensure that the brake is applied slightly
before the motor pistons are displaced outwards to re-engage the
driving means. The hoist winch is then ready for operation under
the control of valve 38.
It will be appreciated that the opening and limiting pressures are
calculated in relation to a specific application with a particular
motor and pump capacity, and without detracting from the scope of
this invention, a modified form of hydraulic circuit as just
described could be employed to achieve the same result. However, in
this embodiment of the invention simple operation and control is
achieved, and other advantages are obtained.
It should be noted that the three-position valves 14, 27 and 38 are
of the open-centre kind so that when any of these valves are
maintained in the neutral position, such as when the tractor is
idling, the hydraulic fluid is returned directly to the reservoir
111 without passing through the associated hydraulic circuits. This
arrangement is most advantageous because excessive heating of the
hydraulic fluid is prevented and the provision of additional oil
coolers can be avoided.
The actuation of the hoist winch brake is synchronised with the
readiness of the hydraulic motor, and this provides a fail-safe
feature. Additionally, the coupling of the drain valve 164 to the
hoist winch motor control valve 138 provides another fail-safe
feature. Each of the manually operable control valves are of the
"dead-man" type biased to return to the neutral position.
Additionally, if there should be a failure in the hydraulic fluid
supply to the hoist winch motor 143 it is still possible to operate
the free fall to release, for instance a suspended load. This is
because the hydraulic fluid supply to actuate the free fall
sub-system is taken from the counterweight system.
With this invented system a luffing crane can be controlled and
operated completely by a hydraulic system embodying hydraulic
motors of the kind specified. This reduces the overall complexity
and weight of hydraulic/mechanical arrangements.
Although the preferred embodiment of this invention as just
described is directed to operating and controlling the winches and
counterweights of pipe-laying apparatus adapted for attachment to a
tractor, it will be appreciated by those familiar with hydraulic
engineering that this invention may be embodied in the original
equipment of the tractor or embodied in other apparatus such as
simple lifting hoists, jib cranes, and winches for trawling or
dredging by appropriately modifying the hydraulic systems.
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