U.S. patent number 3,827,587 [Application Number 04/846,569] was granted by the patent office on 1974-08-06 for automatic self-leveling forks.
This patent grant is currently assigned to Carrier Corporation. Invention is credited to Samuel E. Harvey, Harvey W. Liberman, Steven C. Voorhees.
United States Patent |
3,827,587 |
Liberman , et al. |
August 6, 1974 |
AUTOMATIC SELF-LEVELING FORKS
Abstract
Apparatus for automatically leveling the forks of vertically
moveable hoist arms. In a typical embodiment, the arms are used on
refuse collection vehicles for lifting and dumping detachable
containers into the body of the vehicle. The arms are pivotally
mounted at one end on the vehicle and the opposite ends of the arms
has fork devices for engaging brackets on opposite end walls of the
detachable containers. Swinging movement of the arms and of the
forks is accomplished by means of hydraulic cylinders or rams. A
hydraulic pump supplies fluid under pressure to the arm cylinders
for raising the arms. A portion of the fluid is conducted to the
fork cylinder by means of a gear or vane type flow divider, so that
the rate of extension of the piston in each fork cylinder is at a
predetermined ratio of the displacement of the arm piston. This
causes the forks to swing downwardly at a predetermined rate while
the arms are being raised toward a dumping position, thereby
maintaining the container approximately horizontal until it is in a
position to be inverted for dumping.
Inventors: |
Liberman; Harvey W. (Knoxville,
TN), Harvey; Samuel E. (Knoxville, TN), Voorhees; Steven
C. (Knoxville, TN) |
Assignee: |
Carrier Corporation (Syracuse,
NY)
|
Family
ID: |
25298308 |
Appl.
No.: |
04/846,569 |
Filed: |
July 31, 1969 |
Current U.S.
Class: |
414/420; 414/699;
414/810; 414/408 |
Current CPC
Class: |
B65F
3/04 (20130101); B65F 2003/0279 (20130101) |
Current International
Class: |
B65F
3/02 (20060101); B65f 003/02 () |
Field of
Search: |
;214/301,302,303,315,771,763 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Makay; Albert J.
Assistant Examiner: Mannix; John
Attorney, Agent or Firm: Burns, Doane, Swecker &
Mathis
Claims
What is claimed is:
1. A method of maintaining a detachable container substantially
horizontal during upward swinging movement of a lifting arm, said
container being attached to said arm by a fork pivotally mounted on
said arm, said swinging movement being effected by a hydraulic ram
with a reciprocating piston therein and swinging movement of said
fork relative to said arm being effected by a second ram with a
moveable piston therein connected between said fork and said arm,
said method comprising:
conducting fluid under pressure from a source to one end of said
arm cylinder, thereby urging said arm piston in the direction of
upward swinging movement of said arm;
conducting fluid under pressure from a source to one end of said
fork cylinder, thereby urging said fork piston in the direction of
downwardly swinging movement of said fork;
restricting the discharge of fluid from said arm cylinder and said
fork cylinder, and
regulating the rate of flow of fluid to said fork cylinder in
proportion to the rate of flow of fluid to said arm cylinder, said
regulating step including causing fluid discharged from said fork
cylinder to flow through a first control zone, and including
causing fluid from said source to flow through a second control
zone, fluid from said control zones flowing to said arm cylinder,
said first and second control zones restricting the volume rate of
flow through said first zone at a rate of flow that is at a
predetermined proportion of the rate of flow through said second
zone,
whereby the fork swings downwardly at a predetermined rate during
the upward swinging movement of the arm.
2. The method according to claim 1 including trapping said fluid on
opposite sides of said arm cylinder and said fork cylinder when
flow from said sources stops, whereby said fork and said arm are
held stationary.
3. The method according to claim 1 wherein said regulating step
includes dividing flow of fluid from the opposite end of said arm
cylinder and supplying a predetermined portion of said divided
fluid to said one end of said fork cylinder.
4. The method according to claim 3 wherein said restricting step
includes interrupting flow of fluid from said arm cylinder to a
zone of low pressure in response to a reduction in pressure of
fluid from said source to said arm cylinder.
5. The method according to claim 1 wherein said restricting step
includes conducting fluid discharged from said opposite end of said
fork cylinder to said one end of said fork cylinder, and said
regulating step includes controlling the rate of discharge of fluid
from said fork cylinder opposite end in proportion to the rate of
flow of fluid to said arm cylinder.
6. The method according to claim 5 including said fluid from a
common source through independent paths to said fork cylinder and
said arm cylinder.
7. The method according to claim 1 wherein said regulating step
includes conducting fluid from said source independently to said
arm cylinder and said fork cylinder and controlling the rate of
flow of fluid in one path in direct proportion to the rate of flow
of fluid in the other path.
8. The method according to claim 7 including combining fluid from
said separate paths and supplying said combined fluid to said arm
cylinder after the piston of said fork cylinder has reached its
maximum extent of travel.
9. A method of maintaining a detachable container substantially
horizontal during upward swinging movement of a lifting arm, said
container being attached to said arm by a fork pivotally mounted on
said arm, said swinging movement being effected by a hydraulic ram
with a reciprocating piston therein and swinging movement of said
fork relative to said arm being effected by a second ram with a
moveable piston therein connected between said fork and said arm,
said method comprising:
conducting fluid under pressure from a source to one end of said
arm cylinder, thereby urging said arm piston in the direction of
upward swinging movement of said arm;
conducting fluid under pressure from a source to one end of said
fork cylinder, thereby urging said fork piston in the direction of
downwardly swinging movement of said fork;
restricting the discharge of fluid from said arm cylinder and said
fork cylinder, and
regulating the rate of flow of fluid to said fork cylinder in
proportion to the rate of flow of fluid to said arm cylinder, said
regulating step including causing fluid discharged from said fork
cylinder to flow through a first control zone, and including
causing fluid from said source to flow through a second control
zone, fluid from said control zones flowing to said arm cylinder,
said first and second control zones restricting the volume rate of
flow through said first zone at a rate of flow that is at a
predetermined proportion of the rate of flow through said second
zone,
whereby the fork swings downwardly at a predetermined rate during
the upward swinging movement of the arm,
transferring energy from fluid discharging from said fork cylinder
to fluid flowing from said source to said arm cylinder whereby the
force exerted by said arm cylinder is increased,
said regulating step includes passing fluid through a rotary
positive displacement device in each of said separate paths and
connecting together the rotors of said devices.
10. Apparatus for coordinating swinging movement of a lifting arm
and a fork hingedly mounted on said arm, said movement being
effected by a hydraulic ram having a moveable piston connected with
said arm and a hydraulic ram having a moveable piston and being
connected between said arm and said fork, said apparatus comprising
means for conducting fluid under pressure along a first path and
along a second path, means for connecting said first path with said
arm cylinder at one side of said piston, means for connecting the
second path with said fork cylinder at one side of said piston, and
means in said paths for regulating the flow of fluid along said
first and second paths in a predetermined proportion to each other
independently of the relative sizes of said cylinders, whereby
displacement of the pistons in said arm cylinder and said fork
cylinder occurs simultaneously and at predetermined rates relative
to each other.
11. The apparatus according to claim 10 wherein said other path
communicates between said arm cylinder at the opposite side of said
piston and said fork cylinder at said one side of said piston, said
regulating means including a flow regulating device in said second
path directing a predetermined portion of fluid from said arm
cylinder opposite end to said fork cylinder and, whereby
displacement of the fork piston occurs at a proportionate rate to
the displacement of the piston in the arm cylinder.
12. Apparatus for coordinating swinging movement of a lifting arm
and a fork, hingedly mounted on said arm, said movement being
effected by a hydraulic ram having a moveable piston connected with
said arm and a hydraulic ram having a moveable piston and being
connected between said arm and said fork, said apparatus comprising
means for conducting fluid under pressure along a first path and
along a second path, means for connecting said first path with said
arm cylinder at one side of said piston, means for connecting the
second path with said fork cylinder at one side of said piston, and
means in said paths for regulating the flow of fluid along said
first and second paths in a predetermined proportion to each other
independently of the relative sizes of said cylinders, whereby
displacement of the pistons in said arm cylinder and said fork
cylinder occurs simultaneously and at predetermined rates relative
to each other, said regulating means includes a flow regulating
device capable of operating alternatively as a pump and as a motor,
and conduit means connecting said fork cylinder at the opposite
side of said piston with said regulating device.
13. Apparatus according to claim 12 including means for combining
flow from said separate paths and conducting said combined flow to
said arm cylinder at said one side of said piston.
14. The apparatus according to claim 12 including means for
conducting fluid from said second path regulating device to a zone
of lower pressure.
15. The apparatus according to claim 14 wherein said zone of lower
pressure is the interior of said fork cylinder at one side of said
piston.
16. In a container hoist of the type having a swinging arm for
lifting a container attached to the arm by a fork, said fork being
pivotally mounted on said arm for swinging relative to the arm,
said arm and fork each having a fluid operated double acting ram,
control means for said rams comprising;
a source of fluid under pressure, first means for selectively
conducting said fluid to said arm ram on one side of the ram
piston,
second means for conducting said fluid from the opposite side of
said arm ram piston to said fork ram on one side of the fork ram
piston, said second conducting means including means for diverting
a predetermined portion of said fluid from said second conducting
means, whereby said fork ram piston is displaced in response to
displacement of said arm ram piston at a predetermined rate to
maintain said fork level during lifting of said arm.
17. The apparatus according to claim 16 including means for
controlling flow of fluid to opposite sides of said fork piston
independently of said first conducting means.
18. The apparatus according to claim 16 including a reservoir, and
wherein said first means includes a control valve means
communicating with said source of fluid and said reservoir and said
arm ram, and includes fluid transfer means operatively connected to
said control valve means and said fork ram to accommodate fluid
flow therebetween, said control valve means having a first control
element shiftable to a transfer position directing pressure fluid
to the arm ram, said means for diverting including flow divider
means for directing a predetermined portion of said fluid from said
arm ram to said fork ram.
19. The apparatus according to claim 18 further comprising check
valve means located in said fluid transfer means intermediate said
flow divider means and the second motor adapted to prevent reverse
flow through said transfer means from the second motor to said
control valve means.
20. The apparatus according to claim 18 further comprising second
control valve means communicating with said source of fluid and
said reservoir and said fork ram, said second valve means having an
associated second control element shiftable to direct fluid from
said source of fluid to said fork ram to actuate the same and to
override actuation of the fork ram by said predetermined portion of
fluid from said flow divider means.
21. The apparatus according to claim 18 wherein said flow divider
means communicates with the reservoir through a discharge conduit,
and directs said predetermined portion to said fork ram the
remainder portion of said fluid to said reservoir through said
discharge conduit.
22. In a container hoist of a type having a swinging arm for
lifting a container attached to the arm by a fork, said fork being
pivotally mounted on said arm for swinging relative to the arm,
said arm and said fork each having a fluid operated double acting
ram, control means for said rams comprising;
valve means for controlling movement of the arm ram, valve means
for controlling movement of the fork ram, first means for
conducting fluid from said arm valve to said arm ram on one side of
the piston, second conduit means for conducting fluid from the arm
valve to fork ram at one side of the piston, third conduit means
conducting fluid from the fork ram at the opposite side of the
piston to said arm ram at said one side of the piston, and flow
regulating means in said first and third conduit means for
regulating the rate of flow through said first and third conduit
means in a predetermined proportion, whereby downward swinging
movement of the fork is coordinated with upward swinging movement
of the arm.
23. In a container hoist of a type having a swinging arm for
lifting a container attached to the arm by a fork, said fork being
pivotally mounted on said arm for swinging relative to the arm,
said arm and said fork each having a fluid operated double acting
ram, control means for said rams comprising:
valve means for controlling movement of the arm ram, valve means
for controlling movement of the fork ram, first means for,
conducting fluid from said arm valve to said arm ram on one side of
the piston, second conduit means for conducting fluid from the arm
valve to fork ram at one side of the piston, third conduit means
conducting fluid from the fork ram at the opposite side of the
piston to said arm ram at said one side of the piston, and flow
regulating means in said first and third conduit means in a
predetermined proportion, whereby downward swinging movement of the
fork is coordinated with upward swinging movement of the arm, said
regulating means includes a rotary positive displacement device in
said first conducting means and a second positive displacement
rotary device in said third conducting means, each of said devices
having a rotor, and shaft means joining together said rotors for
rotation at the same speed, whereby energy may be transferred from
one rotor to the other.
Description
BACKGROUND OF THE INVENTION
This invention relates to materials handling equipment, and more
particularly to apparatus for lifting and dumping detachable
containers.
It has become a common practice to provide a number of detachable
containers at various locations for receiving refuse. These
containers are emptied periodically into the body of a truck, in
which the refuse is compacted and then transported to a disposal
area. The collection vehicle typically has an enclosed body with an
opening at the top for receiving the material from the container. A
pair of hoist arms are mounted for vertical swinging movement about
a horizontal axis located behind the cab of the vehicle on the
truck frame. The hoist arms each have a fork which is adapted to
fit into sleeves on opposite sides of the container. The container
has hinged cover doors at the top and when the hoist arms are
raised, the container is picked up and transported over the cab and
then inverted, causing the contents to fall from the container
through the opening in the top of the body. The container is then
returned to the ground by swinging the arms downwardly.
Usually, the forks are pivotally mounted on the hoist arms and the
angular displacement of the forks relative to the hoist arms is
controlled by hydraulic cylinders connected at one end with the
hoist arms and at the opposite end with the forks. The fork
cylinders are used primarily to tilt the container relative to the
hoist arms as it is being raised to a dumping position. Examples of
container dumping vehicles of this type are described in U.S. Pat.
Nos. 2,951,600 and 3,078,000.
Conventional container hoist apparatus is controlled by manual
hydraulic valves. One valve lever controls the raising and lowering
of the hoist arms, another valve lever controls the angle of tilt
between the forks and the hoist arms and a third valve lever
controls movement of a packer head in the body for compacting the
refuse after it has been dumped out of the containers. When the
operator of the vehicle dumps a container into the body of the
truck, it is necessary first to swing the arms downwardly until the
forks are aligned with the sleeves on the container which is
located directly in front of the vehicle. The vehicle is then moved
forward to allow the forks to enter the sleeves in the container.
At this time, the forks are approximately horizontal. The hoist
arms are then raised toward the opening in the top of the body. As
the arms swing vertically, the forks must be lowered gradually in
order to maintain the container approximately horizontal, and
thereby to avoid spilling the contents of the container. Typically
this is done by opening the manual fork valve and using the weight
of the container to swing the forks downwardly as the hoist arms
are being raised. This requires careful coordination by the
operator between movement of the arm valve lever and the fork valve
lever. An inexperienced operator often has difficulty in
coordinating these movements and will usually resort to a step-wise
operation in which the arms are raised a few degrees and stopped,
and then the forks are lowered a few degrees to compensate for the
movement of the arms. These steps are then repeated until the
container is over the hopper and ready for dumping. The lack of
coordination between the movement of the forks and the arms does
not allow the lifting portion of the operation to be performed at
its optimum efficiency. Also, there is a danger that the fork valve
lever will be moved in the wrong direction inadvertently, thereby
spilling the contents of the container. Another problem with
individual manual controls for the hoist arms and the forks is that
additional time is required to train new operators to coordinate
movement of these controls.
Various attempts have been made to provide automatic leveling of
the forks while raising the hoist arms. It has been proposed, for
example, to use limit switches and various cam devices for
operating the fork cylinders in response to predetermined positions
of the hoist arms. Another suggestion has been the use of a
parallelogram linkage between the hoist arms and the forks. Neither
of these proposals is satisfactory. The use of limit switches or
other mechanical devices on the body of the truck requires
accurately positioning the devices on the vehicle, but the vehicle
is usually subjected to severe shock, leading to inaccuracies in
the operation. Also, these systems require extensive wiring and are
difficult to install on existing equipment. The parallelogram type
loader has several moveable interconnecting links and the joints
connecting these links are subject to wear and are a source of
possible failure.
SUMMARY OF THE INVENTION
In view of the deficiencies noted above, it is an object of this
invention to provide an improved container hoist.
It is a further object of this invention to provide a vehicle
mounted hoist in which the fork arms are automatically maintained
approximately horizontal during raising of the hoist arms.
Another object of this invention is to provide a container hoist
which automatically maintains the forks approximately horizontal
while lifting a container, but is capable of manual swinging
movement of the forks relative to the hoist arm at any position of
the hoist arm.
A still further object of this invention is to provide an improved
container hoist in which the forks are automatically leveled during
raising of the arms and in which the hydraulic system minimizes
power and fluid requirements.
These objects are accomplished in accordance with a preferred
embodiment of the invention by proportioning the flow of fluid to
the fork cylinders and the arm cylinders at a fixed ratio to cause
the forks to swing downwardly as the arms swing upwardly. The
proportion of hydraulic fluid discharging from the fork cylinders
is selected to maintain the forks approximately horizontal as the
hoist arms are being raised. The rate of flow of fluid to the arm
cylinders and the fork cylinders is controlled by means of a gear
or vane type flow divider and fluid is trapped on opposite sides of
the arm and fork pistons so that the arms and the forks are
maintained at any position when the flow of fluid in the system is
stopped. Various alternate preferred embodiments include two
nonregenerative systems.
DESCRIPTION OF THE DRAWINGS
These preferred embodiments are illustrated in the accompanying
drawings in which:
FIG. 1 is a side elevational view of the fork and arm assembly
mounted on a refuse collection vehicle;
FIG. 2 is a cross sectional view of a vehicle; along the line 2--2
in FIG. 1;
FIG. 3 is a side elevational view, partially schematic, showing the
movement of the arms and forks;
FIG. 4 is a schematic diagram of the first embodiment of the
hydraulic circuit for operating the arms and forks;
FIG. 5 is a schematic diagram of the second embodiment of the
hydraulic circuit for operating the arms and forks;
FIG. 6 is a schematic diagram of the third embodiment of the
hydraulic circuit;
FIG. 7 is a schematic diagram of a modification of the third
embodiment of the hydraulic circuit; and
FIG. 8 is a schematic diagram of the fourth embodiment of the
hydraulic circuit.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIG. 1, a truck chassis 2 includes a cab 4 which
houses the operator and the controls for the vehicle. A refuse body
6 is supported on the chassis 2 and has an opening 8 at the top
through which refuse may be dumped into the interior of the body 6.
Typically, the body 6 includes a movable packer head 10 for
compacting the refuse toward the rear of the body.
The vehicle also includes a pair of arms 12 which are positioned on
opposite sides of the cab 4, with one end of each arm being secured
on a torque tube or shaft 14 which extends transversely of the
chassis 2, as shown in FIG. 2. The arms are fixed on the tube 14,
so that they cannot swing relative to each other, but are free to
swing vertically relative to the truck chassis. A hydraulic ram 16
is positioned at each side of the body 6 for swinging the arms 12
vertically. The head end of each arm cylinder 16 is pivotally
connected to the body 6 by a bracket 18 on the cylinder and a pin
on the body. The piston rod 20 of each hydraulic cylinder 16 is
pivotally connected with the arm 12 by means of a pin 22 spaced
from the torque tube 14. The arms 12 are spaced apart from each
other a distance greater than the width of the cab 4 and of the
body 6, so that the arms are free to swing from the position shown
in full lines in FIG. 1 to the fully raised position indicated at
A.
Each arm 12 has a fork 24 mounted on a shaft 26 for swinging
movement relative to the arm 12. A lever 28 is also secured on the
shaft 26, so that the lever swings with the fork 24. A bracket 30
on the arm 12 pivotally supports the head end of a hydraulic
cylinder 32. The piston rod 34 of the cylinder 32 is connected with
the lever 28 by a pin 36. When the piston rod 34 is drawn inwardly
of the cylinder 32, the lever 28 swings upwardly, as viewed in FIG.
1, causing the fork 24 also to swing upwardly.
A detachable container 36 is positioned in front of the truck
chassis 2. The container 36 has sides which are spaced apart a
distance slightly less than the distance between the arms 12 and
the opposite sides are provided with sleeves 38 for receiving the
forks 24 of each arm 12. The general arrangement of the arms 12,
the forks 24, and the container 36 is illustrated and described in
U.S. Pat. Nos. 2,951,600 and 3,078,000.
The controls for operating each lifting arm cylinder 16 and each
fork cylinder 32, as well as the packer 10 are shown schematically
in FIG. 4. A control valve 40 for the forks 24 includes a three
position valve spool which is biased toward the center position by
opposed springs 42 and is movable by means of a manual lever. A
second manual spool valve 44 is provided for controlling the
lifting arms 12. A three position spool valve 48 is also provided
for the packer 10. Each of the valves 40, 44 and 48 have three
positions and are biased toward a neutral position by opposed
springs 42, 46 and 50, respectively. Hydraulic fluid is supplied
under pressure from a reservoir 52 by a pump 54 which draws fluid
through a filter 56.
The arm cylinders 16 and the fork cylinders 32 are indicated
schematically in FIG. 4. The piston rods 20 are connected with the
pistons in the cylinders 16 and the piston rods 34 are shown
schematically as being connected with the pistons in the fork
cylinders 32. When the valve spools are in the positions shown in
FIG. 4, fluid passes through the center position of each valve and
returns to the reservoir 52. Fluid is trapped in each arm cylinder
16 and in each fork cylinder 32, so that the arms and forks are
held stationary.
The hydraulic circuit of FIG. 4 also includes a pair of positive
displacement reversible rotary flow regulating devices 58 and 59.
Preferably, these devices preferably include a housing and gear
type or vane type rotors which limits the volume rate of flow of
fluid passing through the housing for a particular speed of
rotation. The devices 58 and 59 can operate as motors or pumps
depending on whether energy is being supplied or removed from the
motor shaft. The rotor shaft of the device 58 is joined with the
rotor of the device 59 by a shaft 60, as indicated schematically in
FIG. 4. This causes the rotors to turn together, thereby
transmitting torque from one device to the other. These devices 58
and 59 are connected together so that one of the devices acts as a
motor driven by the flow of fluid through the device and torque is
transmitted from the motor to the other device for pumping fluid
from a zone at lower pressure to a zone at higher pressure. Also,
since the devices have a constant displacement, the ratio of flow
rates through the devices remains constant, regardless of the
pressure differential across the respective devices.
Referring to FIG. 3, when the lifting arms 12 are being raised by
operation of the arm cylinders 16, it is desirable for the forks 24
to remain nearly horizontal to avoid spilling the contents of the
container. Since the arms 12 swing rearwardly, it is necessary to
extend the piston in the fork cylinder 32 at a rate that
corresponds to the displacement of the piston in the cylinder 16.
When the spool of the arm valve 44 is manually displaced toward the
right as viewed in FIG. 4 fluid is conducted from the pump 54 under
pressure through check valves 62, 64 and 66 to the reversible
rotary device 58. Fluid under pressure is also conducted through
the conduit 65 to the head end of the fork cylinders 32, urging the
piston rods 34 outwardly. A spring biased relief valve 68 is set at
a higher pressure than that delivered by the pump 54 and opens only
in the event of overload to conduct fluid back to the tank or
reservoir 52. Since the rod end of the fork cylinders 32 is filled
with fluid, movement of the pistons toward the left as viewed in
FIG. 4 forces fluid from the rod end of the cylinders 32 through
the conduit 69 to the device 59. Since the movement of the piston
in the fork cylinders 32 is limited by the rate of discharge of
fluid from the rod end of the fork cylinder, the downward swinging
movement of the forks 24 is positively controlled.
The volume rate of flow through the device 58 is at a predetermined
ratio to the flow through the device 59 because the rotors of the
devices are connected together. Due to the area differential on
opposite sides of the fork piston, fluid is conducted to the device
59 at a higher pressure than the pressure supplied by the pump 54.
Consequently, the device 59 acts as a motor transmitting torque
through the shaft 60 to the device 58 which acts as a pump. The
discharge pressure downstream from the pump 58 and motor 59 is
between the pressure supplied by the pump 54 and pressure at the
rod end of the fork cylinders 32. The combined flow from the pump
58 and motor 59 is conducted to the rod end of the arm cylinders 16
through the conduit 71 for displacing the pistons toward the right
as viewed in FIG. 4. Fluid is discharged from the head end of the
arm cylinders through the conduit 75 and through the valve 44 to
the tank 52.
When the fork piston has reached the outermost extent of travel,
flow from the rod end of the cylinders 32 stops thereby cutting off
the supply of fluid energy for driving the device 59. In this
condition, the device 59 acts as a pump driven by the device 58 and
the discharge pressure of the devices 58 and 59 is less than the
pressure supplied by the pump 54. The check valve 70 permits fluid
to be drawn from the reservoir 52 into the conduit 65 by the rotary
device 59 to avoid cavitation. The supply of fluid to the rod end
of the cylinders 16 continues, without interruption, and the arms
continue to move upwardly, although at a faster rate.
In order to lower the lift arms 12 it is necessary to reverse the
position of the spool in the valve 44, so that the right-hand
position is aligned with the conduit from the pump 54 and to the
reservoir 52. Fluid under pressure is then conducted from the pump
54 through the conduit 75 directly to the head end of the arm
cylinders 16. Fluid is discharged from the rod end of the cylinders
16 and conducted through a conduit 77 and through an overcenter
valve 72 to the reservoir 52. The overcenter valve is used to
control the speed of the piston when the load tends to move the
piston faster than fluid is being supplied by the pump. Overcenter
valves are well known in the art and are available commercially
from Fluid Controls, Inc. Mentor, Ohio.
The valve 72 includes a relief valve 74 which is set to open at a
pressure greater than the pressure due to the fluid acting on the
head end of the arm pistons and a pilot valve 76 urges the relief
valve 74 to open as long as fluid is being supplied to the head end
of the cylinder at about pump pressure. Thus, any tendency for the
load to displace the piston at a greater rate than fluid can be
supplied to the head end of the cylinder results in a reduction of
pilot pressure at the valve 76 and the relief valve 74 closes until
sufficient fluid is supplied to the head end of the cylinder 16 to
build up the pressure at the pilot valve. As a practical matter,
very little displacement of the piston is required to operate the
overcenter valve 72 and the lifting arms 12 can be lowered at a
predetermined rate without the danger of the load causing the arms
to drop too rapidly.
Although the flow rate of fluid to the fork cylinders and arm
cylinders is proportioned in such a way that the forks remain
approximately horizontal, the manual valve 40 controlling the
position of the forks can be operated at any time to swing the
forks relative to the lifting arms 12. Displacement of the valve 40
toward the right as viewed in FIG. 4 directs fluid under pressure
from the pump 54 through the check valve 73' and through the
conduit 69 directly to the rod end of the fork cylinders 32. The
valve 40 also connects the head end of the cylinders 32 through the
conduit 65 with the reservoir 52. This causes the piston rods 34 to
move inwardly and the forks 24 to swing upwardly. Conversely,
shifting the spool of the valve 40 toward the left as viewed in
FIG. 4, causes fluid to flow through the conduit 65 to the head end
of the fork cylinders and causes fluid to flow from the rod end of
the fork cylinders through the conduit 69 to the reservoir 52. A
change in position of the forks by means of the manual valve 40
does not affect the proportioning that occurs at the devices 58 and
59.
The operation of the arms and forks in accordance with the
hydraulic circuit of FIG. 4 is shown schematically in FIG. 3. The
arms 12 are initially lowered to the position shown in solid lines
in FIG. 3 with the forks positioned approximately horizontal for
engagement with the sleeves 38 on the container 36. The valves 40,
44 and 48 are initially in the position shown in FIG. 4, so that
the arms 12, the forks 24 and the packer head 10 are held
stationary. To lift the container 36, the spool of the valve 44
controlling the arms is then displaced toward the right as viewed
in FIG. 4 and fluid from the pump 54 is conducted through the
device 58 and through the conduit 71 to the rod end of the arm
cylinder 16. A portion of the fluid is also directed from the pump
54 through the conduit 65 to the head end of the fork cylinders 32.
As the piston rods 20 are drawn into the cylinders 16, the arms 12
swing upwardly. Concurrently with the movement of the arms 12, the
forks 24 swing downwardly as the arms move toward the position
indicated by the letter B in FIGS. 1 and 3. Intermediate positions
of the forks are shown in dotted lines. When the arms 12 are at
position B, the piston in the fork cylinders has reached its
outermost extent of travel. As shown in FIG. 3, the included angle
between the lower end of the arm 12 and the fork 24 progressively
increases as the lifting arms are raised.
From the position of the lifting arm 12 marked B to the position
marked A, swinging movement of the arms 12 is at a slightly greater
rate, since all of the fluid from the pump 54 is conducted directly
to the rod end of the arm cylinder 16. There is flow of fluid
through the device 59, the fluid being drawn from the reservoir 52
through the check valve 70 to avoid cavitation in the device 59.
Fluid discharged from the head end of the arm cylinder 16 is
conducted directly to the reservoir 52 through the valve 44. When
the lifting arms 12 have reached the position marked A in FIGS. 1
and 3, the spool of the valve 44 is manually returned to the
central position to hold the arms stationary, while the spool of
the fork valve 40 is displaced toward the right as viewed in FIG. 4
to direct fluid under pressure to the rod end of the fork cylinders
32 thereby swinging the forks toward the opening 8 in the top of
the body 6 and inverting the container 36, so that the contents of
the container fall through the open top of the container into the
interior of the body 6.
After emptying the container, the fork valve 40 is returned to the
center position and the arm valve 44 is displaced toward the left
as viewed in FIG. 4 to conduct fluid through the conduit 75 to the
head end of the arm cylinders 66. Fluid flowing out of the rod end
of the arm cylinders flows through the conduit 77 and through the
overcenter valve 72 before reaching the reservoir 52. The outward
movement of the pistons in the arm cylinders causes the arms to
swing downwardly to the position shown in full lines in FIG. 3 with
the container resting on the ground. It is usually necessary to
operate the fork valve 40 to return the container to a level
position before depositing it on the ground and disconnecting the
forks 24 from the container sleeves 38. The packer valve 48 may
then be operated to displace the packer head 10 (FIG. 1) toward the
rear of the body 6 for compressing the refuse against the rear wall
of the body. Reversing the valve 48 returns the packer head to its
initial position.
An important advantage of the hydraulic circuit shown in FIG. 4 is
that the rate of downward movement of the forks is directly
proportioned to the upward movement of the lifting arms so that the
container is automatically leveled. Also, fluid discharged from the
fork cylinders 32 is supplied to the arm cylinders, as the arms 12
are being raised, thereby increasing the lifting capacity of the
arms, without requiring increased power from the main pump 54. This
hydraulic circuit not only provides automatic coordination of the
forks and lifting arms, but also provides for independent swinging
movement of the forks at any time.
The second preferred embodiment of the invention is shown
schematically in FIG. 5. In this circuit, the fluid discharged from
the fork cylinders during lifting of the arms does not supplement
the fluid supplied by the main pump to the arm cylinders and
therefore this circuit is not regenerative, as is the circuit shown
in FIG. 4. Those components of this circuit which are substantially
the same as the components described in the circuit of FIG. 4 are
designated by the same numerals with the suffix a. As previously
described with respect to the circuit of FIG. 4, manual control
valves 40a, 44a and 48a are provided for the forks, arms and
packer, respectfully. Displacement of the spool of the arm valve
44a toward the right as viewed in FIG. 5 causes fluid to be
conducted through an overcenter valve 78 by means of the by-pass
valve 80 to the rod end of the arm cylinders 16a.
Fluid discharged from the head end of the arm cylinders 16a is
conducted to a pilot operated check valve 82. The valve 82 is
maintained in an open condition in response to pressure at or
slightly below the discharge pressure of the pump 54a being present
in the conduit 84 connecting the valve 82 with the discharge
conduit from the overcenter valve 78. Thus, as fluid is being
conducted to the rod end of the arm cylinders, the check valve 82
remains open and fluid is conducted to a pair of pumps 58a and 59a
which have their rotors rigidly connected together by a shaft 60a.
These devices 58a and 59a function as a flow divider, since the
rate of flow through the respective devices is a constant ratio. A
portion of the flow from the head end of the arm cylinders 16a is
conducted through the device 59a and through a check valve 86 to
the head end of the fork cylinders 32a. This causes the pistons of
the fork cylinders to be displaced toward the left as viewed in
FIG. 5, thereby lowering the forks.
Fluid discharged from the rod end of the fork cylinders passes
through an overcenter valve 88, which is opened in response to
pilot pressure conducted through a tap 90 communicating with the
head end of the fork cylinders. By this arrangement, the load on
the forks 24 cannot displace the piston in the fork cylinders
unless fluid is being supplied to the head end of the fork
cylinders at a sufficiently high pressure to maintain the valve 88
open. When the pistons of the fork cylinders reach their outermost
position, fluid pressure builds up in the head end of the arm
cylinders until the spring biased relief valve 92 opens to
discharge fluid through the arm valve 44a to the reservoir 52a. The
relative capacities of the devices 58a and 59a are selected to
provide the appropriate rate of swinging movement of the forks and
the lifting arms, so that the forks remain substantially horizontal
as the arms are raised toward a dumping position.
In order to lower the arms, the spool of the arm valve 44a is
displaced toward the left as viewed in FIG. 5, so that fluid from
the main pump 54a is supplied through the check valve 94 to the
head end of the arm cylinders 16a, thereby displacing the pistons
toward the left as viewed in FIG. 5. Fluid discharged from the rod
end of the arm cylinders 16a is conducted through the overcenter
valve 78 as long as fluid pressure in the tap 96 is slightly below
the discharge pressure of the pump 54a. Thus, the arms are under
positive control at all times during lowering of the arms. The
pilot pressure in the conduit 84 is selected such that the valve 82
remains closed while fluid is flowing outwardly through the
overcenter valve 78 toward the reservoir 52a.
In operation, the controls 40a, 44a and 48a are initially in the
central position, as shown in FIG. 5. When the spool of the valve
44a is displaced toward the right, as viewed in FIG. 5, the arms
are raised by fluid flowing to the rod end of the arm cylinders. As
the arms move from the position shown in full lines in FIG. 3 to
position B, the forks swing progressively downwardly to maintain
the forks substantially level. After the fork pistons are fully
extended, the arms continue to swing from position B to position A.
The arms are returned to a lowered position by displacing the spool
of the valve toward the left as viewed in FIG. 5. As in the circuit
of FIG. 4, the forks can be raised and lowered manually by the
valve 40a at any time.
The circuit illustrated in FIG. 5 provides automatic leveling of
the forks during raising of the lifting arms, and yet has
approximately the same lifting capacity as conventional systems in
which the arm cylinders are controlled independently of the fork
cylinders by means of the manual valves.
A third embodiment of the invention is illustrated in FIG. 6. In
the schematic diagram, the components which are the same as those
described and shown in FIG. 4 are designated by the same number
with the suffix b.
When the valve 44b is displaced toward the right as viewed in FIG.
6 fluid under pressure is conducted from the pump 54b, through the
check valves 64b and 66b to the device 58b. Fluid from the main
pump 54b is also conducted to the head end of the fork cylinders
32b. Fluid discharged from the rod end of the fork cylinders is
conducted to the device 59b. From the device 59b, fluid passes
through a pilot operated check valve 98 in which pressure from the
head end of the fork cylinders is applied through a tap 100 to
maintain the valve 98 open as long as fluid at a pressure slightly
less than the discharge pressure of the main pump 54b is being
supplied to the head end of the fork cylinders.
Due to the differential area across the piston in each fork
cylinder, the pressure of fluid discharged from the rod end is
greater than that at the head end of fork cylinders. Fluid from the
valve 98 supplements fluid from the main pump 54b to cause
displacement of the fork pistons at a faster rate than can be
provided by the pump 54b. Also, as fluid passes through the device
59b, the fluid pressure differential provides energy for turning
the rotor and produces torque which is transmitted by the shaft 60b
to drive the rotor of the device 58b. In this way, the pressure of
the fluid flowing to the arm cylinders downstream from the device
58b is increased. In comparison with the circuit of FIG. 4, the
circuit of FIG. 6 produces a faster angular displacement of the
forks relative to upward swinging movement of the arms because
fluid from the rod end of the fork cylinders is supplied to the
head end of the fork cylinders. The increase in pressure produced
by the motor action of the device 59b on the device 58b is greater
than in the circuit of FIG. 4 because the pressure downstream from
the device 59b is less in the FIG. 6 circuit than it is in the FIG.
4 circuit.
The arms 12 are raised by moving the spool of the valve 44b toward
the right, as viewed in FIG. 6, causing concurrent upward swinging
movement of the forks 24 and the arms 12, and after the forks 24
are fully lowered, the arms continue to move toward the dumping
position. Lowering of the arms is accomplished by displacing the
valve 44b toward the left, as viewed in FIG. 6, thereby directing
fluid under pressure to the head end of the arm cylinder 16b and
discharging fluid from the rod end of the arm cylinders through the
overcenter valve 72b in the same manner as described with respect
to the diagram of FIG. 4.
A modified form of the embodiment of FIG. 6 is shown in FIG. 7. The
pilot operated check valve 98 of FIG. 6 is replaced by a pilot
operated check valve 98c in which the pilot pressure is supplied
through a tap 100c connected with the head end of the fork
cylinders. The discharge side of the check valve 98c is connected
directly with the reservoir 52c. In comparison with the circuit of
FIG. 6, the modified circuit of FIG. 7 produces a larger pressure
differential across the device 59b, thereby providing greater
torque for driving the device 58b. Consequently, the modified form
of FIG. 7 produces a greater boost or regenerative effect than the
circuit of FIG. 6.
A fourth embodiment of the invention is shown schematically in FIG.
8 and includes components that are the same as those of FIG. 4.
These components are designated by the same reference numeral as in
FIG. 4, but with a suffix letter d. When the valve 44d is displaced
toward the right as viewed in FIG. 8, fluid from the pump 54d is
directed to the rod end of the arm cylinders 16d through the device
58d. Fluid is also conducted through the device 59d and through the
check valve 102 to the head end of the fork cylinders 32d. The
positive connection between the devices 58d and 59d by the shaft
60d proportions the rate of flow of fluid to the arm cylinders and
fork cylinders to cause the forks to remain approximately
horizontal while the arms are being raised.
As fluid flows to the head end of the fork cylinders, sufficient
pressure is applied to an overcenter valve 104 to allow fluid to
flow from the rod end of the fork cylinders through the valve 104
to the reservoir 52d. While the pistons in the arm cylinders are
moving toward the right, as viewed in FIG. 8, the fluid discharged
from the head end of the cylinders is conducted through the valve
44d to the reservoir 52d. After the fork cylinder pistons have been
displaced to the maximum extent, the flow from the device 59d
passes through a crossover check valve 106 and combines with fluid
from the device 58d which is being supplied to the arm cylinders
16d. As long as the fork cylinders are not fully extended, the
pressure required to operate the overcenter valve 104 is
considerably less than the pressure at the rod end of the arm
cylinders. Therefore, the flow to the head end of the fork
cylinders transfers most of its energy to the device 58d in passing
through the device 59d. At the same time, the fluid pressure at the
rod end of the arm cylinders is greater than the pressure at the
head end of the fork cylinders and this pressure differential
maintains the check valve 106 closed until the fork cylinders have
been fully extended. A relief valve 108 is connected upstream from
the devices 58d and 59d to direct fluid to the reservoir 52d, to
prevent pressure from becoming excessively high due to overload on
the arms.
The arm cylinders may be lowered by displacing the valve 44d toward
the left as viewed in FIG. 8, thereby directing fluid under
pressure to the head end of the arm cylinders 16d. Fluid discharged
from the rod end of the arm cylinders is conducted through the
overcenter valve 72d to the reservoir 52d. A check valve 110
prevents flow from the rod end of the arm cylinders toward the pump
58d.
Valve 40d may be operated at any time during the lifting or
lowering of the arms to swing the forks independently of the arms.
The check valve 102 prevents fluid from flowing from the valve 40d
to the arm cylinders 16d.
In each of the embodiments of this invention, the fluid which
acuates the arm cylinders is also directed to the fork cylinders in
a predetermined proportion to extend the piston rods of the fork
cylinders at a predetermined rate relative to the rate of lifting
movement of the arms. The various components of the system of this
invention may be readily substituted in existing hoist units
without changing the manual control valves or the arm and fork
cylinders in order to convert the existing systems from manual
operation to automatic operation. Furthermore, this invention
permits manual override by means of the control valves at any
position of the arms or the forks. Thus, the operator is in full
control of the equipment at all times.
While this invention has been illustrated and described in several
embodiments, it is recognized that variations and changes may be
made therein without departing from the invention as set forth in
the claims.
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