U.S. patent application number 12/039926 was filed with the patent office on 2009-09-03 for unequal length alternating hydraulic cylinder drive system for continuous material output flow with equal material output pressure.
This patent application is currently assigned to PUTZMEISTER AMERICA, INC.. Invention is credited to Andrew J. Krivsky, Brian G. Sweet.
Application Number | 20090220358 12/039926 |
Document ID | / |
Family ID | 41013315 |
Filed Date | 2009-09-03 |
United States Patent
Application |
20090220358 |
Kind Code |
A1 |
Krivsky; Andrew J. ; et
al. |
September 3, 2009 |
UNEQUAL LENGTH ALTERNATING HYDRAULIC CYLINDER DRIVE SYSTEM FOR
CONTINUOUS MATERIAL OUTPUT FLOW WITH EQUAL MATERIAL OUTPUT
PRESSURE
Abstract
A hydraulic pumping system is provided for delivering a
compressible fluid material from a hopper to an outlet. A primary
hydraulically driven pumping unit has a first interior volume for
receiving the fluid material from the hopper. A secondary
hydraulically driven pumping unit is interconnected with the
primary hydraulically driven pumping unit and has a second interior
volume less than the first interior volume for receiving fluid
material from the primary hydraulically driven pumping unit. The
primary and secondary hydraulically driven pumping units have
hydraulically driven reciprocating piston units with unequal stroke
lengths. The piston units are alternately reciprocated to fill the
first interior volume of fluid material from the hopper, pump a
portion of the first interior volume of fluid material into the
second interior volume and the remainder of the first interior
volume to the outlet, and pump the second interior volume of fluid
material to the outlet while fluid material is being pulled into
the first interior volume in a sequential and simultaneous manner
which will produce substantially continuous delivery of fluid
material to the outlet.
Inventors: |
Krivsky; Andrew J.;
(Franksville, WI) ; Sweet; Brian G.; (West Allis,
WI) |
Correspondence
Address: |
ANDRUS, SCEALES, STARKE & SAWALL, LLP
100 EAST WISCONSIN AVENUE, SUITE 1100
MILWAUKEE
WI
53202
US
|
Assignee: |
PUTZMEISTER AMERICA, INC.
Sturtevant
WI
|
Family ID: |
41013315 |
Appl. No.: |
12/039926 |
Filed: |
February 29, 2008 |
Current U.S.
Class: |
417/254 ;
417/375 |
Current CPC
Class: |
F04B 15/023 20130101;
F04B 11/0075 20130101; F04B 9/1095 20130101 |
Class at
Publication: |
417/254 ;
417/375 |
International
Class: |
F04B 25/02 20060101
F04B025/02; F04B 35/02 20060101 F04B035/02 |
Claims
1. A hydraulically driven pumping system for delivering a
compressible fluid material from a hopper to an outlet, the system
comprising: a primary hydraulically driven pumping unit having a
first interior volume for receiving the fluid material from the
hopper; and a secondary hydraulically driven pumping unit
interconnected with the primary hydraulically driven pumping unit
and having a second interior volume less than the first interior
volume for receiving fluid material from the primary hydraulically
driven pumping unit, the primary and secondary hydraulically driven
pumping units having hydraulically driven reciprocating piston
units with unequal stroke lengths, the piston units being
alternately reciprocated to fill the first interior volume with
fluid material from the hopper, pump a portion of the first
interior volume of fluid material into the second interior volume
and the remainder of the first interior volume to the outlet, and
pump the second interior volume of fluid material to the outlet
while fluid material is being pulled into the first interior volume
in a simultaneous and sequential manner which will produce
substantially continuous delivery of fluid material to the
outlet.
2. The pumping system of claim 1, wherein the piston units are
reciprocated in primary and secondary hydraulic cylinders having
equal bores, unequal lengths, and pistons with equal diameters.
3. The pumping system of claim 1, wherein the piston units are
reciprocated in primary and secondary material cylinders having
equal bores, unequal lengths that have substantially equal output
pressures, and pistons with equal diameters.
4. The pumping system of claim 1, wherein a single check valve is
positioned between the hopper and the primary pumping unit.
5. The pumping system of claim 4, wherein a single check valve is
positioned between the primary pumping unit and the secondary
pumping unit.
6. A hydraulically driven pumping system for delivering a
compressible fluid material from a hopper to an outlet, the system
comprising: a primary hydraulically driven pumping unit having a
primary material cylinder having a piston, a bore and a first
interior volume for receiving the fluid material from the hopper, a
primary hydraulic cylinder provided with a piston, and a bore and
fed by a source of hydraulic fluid and a primary piston unit
movable back and forth over a stroke length within the primary
material cylinder and the primary hydraulic cylinder; a secondary
hydraulically driven pumping unit having a secondary material
cylinder having a piston, a bore and a second interior volume less
than the first interior volume for receiving the fluid material
from the primary material cylinder, a secondary hydraulic cylinder
provided with a piston and a bore and sized smaller than the
primary hydraulic cylinder and fed by the source of hydraulic
fluid, and a secondary piston unit movable back and forth over a
stroke length within the secondary material cylinder and the
secondary hydraulic cylinder, a stroke length of the secondary
piston unit being less than the stroke length of the primary piston
unit; a first check valve located between the hopper and the
primary material cylinder; and a second check valve located between
the primary material cylinder and the secondary material cylinder,
wherein the primary and secondary piston units are hydraulically
controlled and alternately reciprocated over their respective
unequal stroke lengths to fill the first interior volume with fluid
material from the hopper, pump a portion of the first material
volume of first interior volume of fluid material into the second
interior volume and the remainder to the outlet, and pump the
second interior volume of fluid material to the outlet while the
fluid material is being pulled into the first interior volume in a
sequential and simultaneous manner which will produce substantially
continuous delivery of fluid material to the outlet.
7. The pumping system of claim 6, wherein the primary and second
material cylinders have equal bore and piston diameters and unequal
lengths.
8. The pumping system of claim 6, wherein the primary and secondary
hydraulic cylinders have equal bore and piston diameters and
unequal lengths.
9. The pumping system of claim 6, wherein each of the primary and
secondary piston units include material piston adapters and
hydraulic cylinder rods.
10. The pumping system of claim 9, wherein the hydraulic cylinder
rods of the primary and secondary piston units have unequal
diameters and lengths.
11. The pumping system of claim 9, wherein the hydraulic cylinder
rod of the primary piston unit has a diameter that is greater than
a diameter of the hydraulic cylinder rod of the secondary piston
unit.
12. The pumping system of claim 6, wherein the primary and
secondary material cylinders have outlet pressures that are
equalized by appropriately sizing the primary and secondary
material cylinders with equal bore and piston diameters, sizing the
primary and secondary hydraulic cylinders with equal bore and
piston diameters, and driving the primary and secondary piston
units alternately by the same hydraulic pump.
13. The pumping system of claim 6, wherein proximity sensors are
included within the primary and secondary pumping units for
detecting a fully extended position of the primary and secondary
piston units.
14. The pumping system of claim 6, wherein the primary and
secondary hydraulic cylinders are hydraulically connected to each
other and to a source of secondary hydraulic pump pressure.
15. The pumping system of claim 6, wherein the material output rate
is infinitely variable by controlling the hydraulic fluid supplied
to the primary and secondary hydraulic cylinders.
16. The pumping system of claim 6, wherein the primary and
secondary piston units have equal extension speed.
17. The pumping system of claim 6, wherein the primary and
secondary piston units have unequal retraction speed.
18. The pumping system of claim 6, wherein the volume of the
primary material cylinder is substantially twice the volume of the
secondary material cylinder.
19. A method of delivering a substantially constant flow of fluid
material from a hopper to an outlet using a hydraulically driven
pumping system, the method comprising the steps of: a) providing a
primary hydraulically driven pumping unit having a first interior
volume for receiving the fluid material from the hopper; b)
providing a secondary hydraulically driven pumping unit
interconnected with the primary hydraulically driven pumping unit
and having a second interior volume less than the first interior
volume for receiving fluid material from the primary hydraulically
driven pumping unit; c) providing the primary and secondary
hydraulically driven pumping units with hydraulically driven
reciprocating piston units with unequal stroke lengths; and d)
alternately reciprocating the piston units to fill the first
interior volume with fluid material from the hopper, pump a portion
of the first interior volume of fluid material into the second
interior volume and the remainder of the first interior volume to
the outlet, and pump the second interior volume of fluid material
to the outlet while the fluid material is being pulled into the
first interior volume in a sequential and simultaneous manner which
will produce substantially continuous delivery of fluid material to
the outlet.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
pumps, and more particularly, pertains to a positive displacement
pump arrangement designed to produce substantially continuous
delivery of a compressible fluid material.
BACKGROUND OF THE INVENTION
[0002] Constant delivery fluid pumps find useful application in
many fields. One field in which the pumps of this character are
presently employed to advantage is the construction industry
wherein it is relatively common practice to apply cement and
plaster to building surfaces by means of spray nozzles. If a
relatively uniform layer of plaster or cement material is to be
applied to a building surface, the rate of flow of material from
the spray nozzle of the spray unit must be relatively constant.
This, in turn, requires a constant delivery pump capable of
producing substantially a constant rate of material flow to the
spray nozzle.
[0003] Prior art pumps are, of course, known in the art, and are
generally comprised of a pair of pumping units actuated in such a
manner that the pumping discharges from the pumping units overlap
in a manner to produce a substantially constant flow delivery at an
outlet. Valve members are typically provided so that one pumping
unit serves as a primary unit to initially discharge pumped
material concurrently into a delivery line and into a cylinder of
the other pumping unit which then operates as a secondary pumping
unit to discharge its previously received material into the
delivery line.
[0004] One such prior art arrangement is embodied in a pair of
equal stroke length material cylinders alternately driven by equal
stroke length hydraulic cylinders. This arrangement requires either
four separate ball and seat valves or the switching of a tube,
commonly referred to as an S-tube, that changes between the
material cylinders.
[0005] Another prior art arrangement is formed by a pair of unequal
stroke length material cylinders driven by a mechanical pumping
assembly, in which the pumping action of the primary and secondary
pumping units is effected mechanically by the interaction of a
crank arm and a cam with follower. The mechanical pumping assembly
can be variously driven by an engine or electric motor via a
clutch, belts or chains, pulleys or sprockets, and a gearbox, all
of which is undesirably complex. This design requires an external
mechanical pressure limiting device. In addition, the pumping
output rate is sometimes limited to preset pulley or sprocket
ratios. The mechanical pumping assembly can also be variously
driven by an engine or electric motor via a hydraulic pump and
motor combination, but this retains the complexity and the high
number of wearing components inherent to the mechanical pumping
assembly.
[0006] Accordingly, the present invention is concerned more
particularly with a new and improved design of pumping apparatus in
which the inherent draw backs of the prior art have been overcome.
There is a need for a hydraulic equivalent to the prior art
mechanical system wherein the unequal stroke length of the two
material cylinders reduces the number of and simplifies components
required for the pumping system, while allowing the material
pressure to be equalized by controlling the pressure of the
hydraulic fluid and the appropriate size combination of hydraulic
cylinders.
SUMMARY OF THE INVENTION
[0007] It is a general object of the present invention to provide a
positive displacement pump in which operatively associated pumping
units are interconnected hydraulically for alternating operation
such that a substantially constant flow of material will be
produced at an outlet.
[0008] It is also an object of the present invention to provide a
constant delivery hydraulically driven pump having primary and
secondary piston/cylinder units with unequal stroke lengths, and a
pair of valve members for controlling the supply of material into
the pumping units and into a delivery outlet.
[0009] It is another object of the present invention to provide a
hydraulically driven pumping system having unequal stroke length
material cylinders with equal material output pressure.
[0010] It is a further object of the present invention to provide a
pump apparatus which is especially suited to the pumping of cement,
plastic and other abrasive materials.
[0011] It is an additional object of the present invention to
provide a hydraulically driven pumping arrangement for abrasive
materials which offers improved performance, reliability and cost
in installation and service.
[0012] The present invention relates to a hydraulically driven
pumping system for delivering a compressible fluid material from a
hopper to an outlet. The system includes a primary hydraulically
driven pumping unit having a first interior volume for receiving
the fluid material from the hopper. A secondary hydraulically
driven pumping unit is interconnected with the primary pumping unit
and has a second interior volume less than the first interior
volume for receiving fluid material from the primary hydraulically
driven pumping unit. The primary and secondary hydraulically driven
pumping units have hydraulically driven reciprocating piston units
with unequal stroke lengths. The piston units are alternately
reciprocated to fill the first interior volume with fluid material
from the hopper, pump a portion of the first interior volume of
fluid material into the second interior volume and the remainder of
the first interior volume to the outlet, and pump the second
interior volume of fluid material to the outlet while fluid
material is being pulled into the first interior volume in a
simultaneous and sequential manner which will produce substantially
continuous delivery of fluid material to the outlet.
[0013] In the preferred embodiment, the piston units are
reciprocated in primary and secondary hydraulic cylinders of
unequal lengths. The piston units are reciprocated in primary and
secondary material cylinders of unequal lengths that have
substantially equal output pressures. A single ball and seat
combination, functioning as a check valve is positioned between the
hopper and the primary hydraulically driven pumping unit. An
additional single ball and seat combination functioning as a check
valve is positioned between the primary hydraulically driven
pumping unit and the secondary hydraulically driven pumping
unit.
[0014] In another aspect of the invention, a hydraulically driven
pumping system for delivering a compressible fluid material from a
hopper to an outlet includes a primary pumping unit having a
primary material cylinder with a first interior volume for
receiving the fluid material from the hopper, a primary hydraulic
cylinder fed by a source of hydraulic fluid, and a primary piston
unit movable back and forth over a stroke length within the primary
material cylinder and the primary hydraulic cylinder. A secondary
pumping unit has a secondary material cylinder having a second
interior volume less than the first interior volume for receiving
the fluid material from the primary material cylinder, a secondary
hydraulic cylinder sized smaller than the primary hydraulic
cylinder and fed by the source of hydraulic fluid, and a secondary
piston unit movable back and forth over a stroke length within the
secondary material cylinder and the secondary hydraulic cylinder.
The stroke length of the secondary piston unit is less than the
stroke length of the primary piston unit. A first ball and seat
combination functioning as a check valve is located between the
hopper and the primary material cylinder. A second ball and seat
combination functioning as a check valve is located between the
primary material cylinder and the secondary material cylinder. The
primary and secondary piston units are hydraulically controlled and
alternately reciprocated over their respective unequal stroke
lengths to fill the first interior volume with fluid material from
the hopper, pump a portion of the first interior volume of fluid
material into the second interior volume and the remainder to the
outlet, and pump the second interior volume of fluid material to
the outlet while the fluid material is being pulled into the first
interior volume in a simultaneous and sequential manner which will
produce substantially continuous delivery of fluid material to the
outlet.
[0015] The lengths of the primary and secondary material cylinders
are unequal, and the lengths of the primary and secondary hydraulic
cylinders are unequal. Each of the primary and secondary piston
units include a material piston adapter and a hydraulic cylinder
rod having pistons on opposite ends thereof. The primary and
secondary piston units have unequal hydraulic cylinder rod
diameters. The hydraulic cylinder rod of the primary piston unit
has a diameter that is greater than the diameter of the hydraulic
cylinder rod of the secondary piston unit. The primary and
secondary material cylinders have outlet pressures that are
equalized by appropriately sizing the primary and second material
cylinders with equal bore diameters, sizing the primary and second
hydraulic cylinders with equal piston diameters and driving the
primary and secondary piston units alternately by the same
hydraulic pump. Sensors are included within the primary and
secondary pumping units for detecting the position of the primary
and secondary piston units. The primary and secondary hydraulic
cylinders are hydraulically connected to each other and to a source
of secondary hydraulic pump pressure. A material output rate is
infinitely variable by controlling the hydraulic fluid supply to
the primary and secondary hydraulic cylinders. The primary and
secondary piston units have equal extension speed, but have unequal
retraction speed. The volume of the primary material cylinder is
substantially twice the volume of the secondary material
cylinder.
[0016] The invention also contemplates a method of delivering a
substantially constant flow of fluid material from a hopper to an
outlet using a hydraulic pumping system. The method comprises the
step of
[0017] (a) providing a primary hydraulically driven pumping unit
having a first interior volume for receiving the fluid material
from the hopper;
[0018] (b) providing a secondary hydraulically driven pumping unit
interconnected with the primary hydraulically driven pumping unit
and having a second interior volume less than the first interior
volume for receiving fluid material from the primary hydraulically
driven pumping unit;
[0019] (c) providing the primary and secondary hydraulically driven
pumping units with hydraulically driven reciprocating piston units
with unequal stroke lengths; and
[0020] (d) alternately reciprocating the piston units to fill the
first interior volume with fluid material from the hopper, pump a
portion of the first interior volume of fluid material into the
second interior volume and the remainder of the first interior
volume to the outlet, and pump the second interior volume of fluid
material to the outlet while fluid material is being pulled into
the first interior volume in a sequential and simultaneous manner
which will produce a substantially continuous delivery of fluid
material to the outlet.
[0021] Various other features, objects and advantages of the
invention will be made apparent from the following description
taken together with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The drawings illustrate the best mode presently contemplated
for carrying out the invention.
[0023] In the drawings:
[0024] FIGS. 1 and 2 are schematic illustrations of an unequal
length hydraulic cylinder drive system embodying the present
invention and showing alternating phases of operation.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Referring to the drawings, a hydraulic cylinder drive system
10 forms a constant delivery pump used to provide a pressurized
supply of abrasive, compressible fluid material, typically cement,
plaster, mortar or the like, from a reservoir or hopper 12 to an
outlet 14. Material delivered to the outlet 14 is normally directed
to a spray nozzle for distribution to a desired surface, such as a
building wall.
[0026] The system 10 includes a primary hydraulically driven
pumping unit defined by a primary material cylinder 16 have a feed
line 18 in communication within hopper 12 and an interior volume A
at a head of the cylinder 16. A first one-way check valve 20 is
positioned in feed line 18 between hopper 12 and primary material
cylinder 16. The check valve 20 is a conventional mechanical design
having a ball 22 movable between a stop 24 and a seat 26. The check
valve 20 allows flow of material from hopper 12 into material
cylinder 16 through the line 18, but blocks flow in the reverse
direction.
[0027] A primary piston unit 28 has a material piston adapter 30
with a material piston 32 movable within the interior of primary
material cylinder 16, and a hydraulic cylinder rod 34 with a second
piston 36 opposite material piston 32 that is movable within an
interior of primary hydraulic cylinder 38. As will be appreciated,
piston adapter 30, hydraulic cylinder rod 34, and pistons 32, 36
move back and forth in sealed relationship within primary material
cylinder 16 and primary hydraulic cylinder 38. Primary piston unit
28 has a particular stroke length as determined by the lengths of
primary material cylinder 16 and primary hydraulic cylinder 38. One
end of primary hydraulic cylinder 38 is provided with a hydraulic
line 40 connected to a primary hydraulic pump for supplying and
returning hydraulic fluid relative to a source. Flow of hydraulic
fluid through feed line 40 is separately controlled.
[0028] The system 10 further includes a secondary hydraulically
driven pumping unit defined by a secondary material cylinder 42
having a feed line 44 in communication with an interior volume B at
a head of cylinder 42. The feed line 44 is further in communication
with the line 18 extending from the primary material cylinder 16. A
second one-way check valve 46 is positioned in line 44 between
primary material cylinder 16 and the secondary material cylinder
42. The check valve 46 is a conventional design like check valve 20
having a ball 48 movable between a stop 50 and a seat 52. The check
valve 46 allows flow from line 18 into line 44, the secondary
material cylinder 42 and outlet 14, but prevents flow back into
line 18.
[0029] It is important to note that secondary material cylinder 42
has a length that is shorter than the length of primary material
cylinder 16, and that interior volume B of secondary material
cylinder 42 is less than interior volume A of primary material
cylinder 16. Interior diameters of the material cylinders 16 and 42
are substantially equal.
[0030] A secondary piston unit 54 has a material piston adapter 56
with a material piston 58 movable within the interior of secondary
material cylinder 42, and a hydraulic cylinder rod 60 with a
hydraulic cylinder piston 62 opposite material piston 58 that is
movable within an interior of a secondary hydraulic cylinder 64.
Piston adapter 56, hydraulic cylinder rod 60 and pistons 58, 62
move back and forth in sealed relationship within secondary
material cylinder 42 and secondary hydraulic cylinder 64. Secondary
piston unit 54 has a particular stroke length as determined by the
length of secondary hydraulic cylinder 64. It is a key feature of
the invention that the stroke length of secondary piston unit 54 is
less than the stroke length of primary piston unit 28.
[0031] Secondary hydraulic cylinder 64 has a length which is
shorter than the length of primary hydraulic cylinder 38, and an
interior volume which is less than the interior volume of primary
hydraulic cylinder 38. Diameters of the hydraulic cylinder pistons
36, 62 are substantially equal.
[0032] One end of secondary hydraulic cylinder 64 is provided with
a hydraulic line 66 connected to a primary hydraulic pump for
supplying and returning hydraulic fluid relative to the source. A
rod side of secondary hydraulic cylinder 64 is hydraulically
connected with a rod side end of primary hydraulic cylinder 38 by
means of a common line 68. A further hydraulic line 70 is connected
to line 68 and to a secondary hydraulic pump for supplying and
returning hydraulic fluid relative to the rod side of hydraulic
cylinders 38, 64. Proximity sensors 72a, 74a are positioned
adjacent the material cylinders 16, 42 to detect the fully extended
position of piston units 28, 54 therein and signal a change in
direction for both piston units. Alternatively, proximity sensors
72b, 74b are positioned adjacent the hydraulic cylinders 38, 64 to
detect the fully extended position of piston units 28,54 therein
and signal a change in direction for both piston units. Detection
of piston location and signaling direction change may be done by a
means other than a proximity sensor, whether electrical, mechanical
or hydraulic in nature.
[0033] It is another key feature of the present invention that the
diameter of the hydraulic cylinder rod 34 in primary hydraulic
cylinder 38 is greater than the diameter of the hydraulic cylinder
rod 60 of the secondary hydraulic cylinder 64 as will be fully
appreciated below.
[0034] Operation of the system 10 as described above is as follows
referring first to FIG. 1. Material to be pumped is placed in the
hopper 12. A primary hydraulic pump is connected to the piston side
of hydraulic cylinder 64 via line 66 causing secondary piston unit
54 to extend. The hydraulic connection 68 from the rod side of
hydraulic cylinder 64 to the rod side of hydraulic cylinder 38
causes primary piston unit 28 to retract. The retraction of piston
unit 28 causes material to be drawn into primary material cylinder
16 from the hopper 12 past ball 22 and seat 26 and through line 18.
At the full extension of piston unit 54, the proximity sensor 74a
or 74b signals a change in direction for stroking the piston units
28, 54.
[0035] Referring now to FIG. 2, the primary hydraulic pump flow
changes from being directed to the piston side of hydraulic
cylinder 64 to the piston side of hydraulic cylinder 38. Piston
unit 28 extends causing approximately half the material within
material cylinder 16 to be pumped out of the outlet 14, while the
other half is pumped into material cylinder 42 as piston unit 54 is
retracted. Retraction is caused due to the common line 68 from the
rod side of hydraulic cylinder 38 to the rod side of hydraulic
cylinder 64. Retraction is further assisted by the action of
pumping material from material cylinder 16 to material cylinder 42.
The retraction of piston unit 54 causes material to be drawn into
material cylinder 42 from material cylinder 16 past the ball 48 and
seat 52 and through line 44. At the full extension of piston unit
28, the proximity sensor 72a or 72b signals the change in direction
for the piston units 28, 54. The primary hydraulic pump flow
changes from being directed to the piston side of hydraulic
cylinder 38 to the piston side of hydraulic cylinder 64. Piston
unit 54 extends causing its full volume of material in material
cylinder 42 to be pumped out the outlet 14. Material is prevented
from back flowing into line 18 by check valve 46. The piston unit
28 is simultaneously retracted. The above steps are repeated to
provide a substantially continuous flow of material to the outlet
14.
[0036] During operation, piston units 28, 54 fully extend and
retract on each alternating stroke with piston unit 28 having a
longer stroke length than the piston unit 54. The common line 68
establishes a master-slave relationship and allows for transfer of
fluid between the hydraulic cylinders 38, 64 upon reciprocation of
piston units 28, 54. When pumping from material cylinder 16,
approximately one-half the volume is pumped into material cylinder
42 and the other half is pumped out to outlet 14. When pumping from
material cylinder 42, its full volume is pumped out the outlet
14.
[0037] Piston units 28, 54 have an equal extension speed. Hydraulic
cylinders 38, 64 have equal diameter pistons 36, 62. The piston
units 28, 54 are alternately driven by the same primary hydraulic
pump. However, piston units 28, 54 have an unequal retraction
speed. Each piston unit 28 or 54 must reach the fully retracted
position at approximately the same time or before the other piston
unit 28 or 54 is fully extended. The longer stroke piston unit 28
retracts at a faster speed than the piston unit 54 extends. Piston
unit 54 retracts at a slower speed than piston unit 28 extends.
This is accomplished by the rods 34, 60 having unequal rod
diameters such that that the diameter of rod 34 is greater than the
diameter of rod 60. This is further accomplished by making the
hydraulic cylinders 38, 64 with equal rod-side volumes. Retraction
speed of the secondary piston unit 54 may be increased with the
addition of material pressure being pumped from the primary piston
unit 28.
[0038] The piston units 28, 54 fully extend and fully retract on
each alternate stroke due to the proximity sensors 72a, 72b, 74a,
74b which signal the change of direction of the stroking for piston
units 28, 54 upon their full extension. The secondary hydraulic
pump supplies additional hydraulic oil between hydraulic cylinders
38, 64 via lines 68, 70 to ensure full retraction of piston units
28, 54 occurs before the change of signal is actuated.
[0039] Material output rate is infinitely variable by controlling
the primary pump flow delivered to hydraulic cylinders 38, 64.
Material is pumped at equal material pressure from both material
cylinders 16, 42 due to the fact that material cylinders 16, 42
have equal bore diameters, hydraulic cylinders 38, 64 have equal
diameter pistons 36, 62 and the hydraulic cylinders 38, 64 are
driven at the piston side by the same primary hydraulic pump.
Maximum material pressure is accurately limited by a corresponding
maximum hydraulic pressure setting at the primary hydraulic
pump.
[0040] The present invention thus provides a positive displacement
hydraulic cylinder drive system wherein a partial volume A and
volume B of material are pumped on each alternating, unequal length
stroke of coordinating piston units 28, 54 to continuously pump
material to the outlet 14. In contrast with the prior art, the
system 10 reduces the number of components required (minimizing the
number of check valves), eliminates the need for complex drive
systems and separate mechanical pressure limiting devices as
encountered in mechanical systems, and allows a greater control of
the maximum pressure of the material cylinders.
[0041] It should be understood that the hydraulic system 10 can be
either an open loop or a closed loop system. For the purpose of
detecting and signaling change of direction of the piston units,
the type, the amount and/or location of the proximity sensor may
vary. Also, the change in direction could be detected alternately
using hydraulic pressure signals and correspondingly piloted
valves.
[0042] Various alternatives and embodiments are contemplated as
being within the scope of the following claims particularly
pointing out and distinctly claiming the subject matter regarded as
the invention.
* * * * *