U.S. patent number 3,747,351 [Application Number 05/191,912] was granted by the patent office on 1973-07-24 for hydraulic system.
This patent grant is currently assigned to Bertea Corporation. Invention is credited to A. P. Henry, William D. Wilkerson.
United States Patent |
3,747,351 |
Wilkerson , et al. |
July 24, 1973 |
HYDRAULIC SYSTEM
Abstract
A hydraulic system comprising an actuator including a housing
and a piston movable in the housing, a reversible, variable speed
pump, and conduits for connecting the pump to both sides of the
piston so that the pump can pump hydraulic fluid from one side of
the piston to the other. The pump is driven by a reversible,
variable speed drive with the direction of piston movement being a
function of the direction in which the pump is driven. The rate of
piston movement is a function of the speed at which the pump is
driven. The actuator may be an unbalanced actuator, in which event
the unbalance can be compensated for by the pump or by suitable
piping connections.
Inventors: |
Wilkerson; William D. (Santa
Ana, CA), Henry; A. P. (Irvine, CA) |
Assignee: |
Bertea Corporation (Irvine,
CA)
|
Family
ID: |
22707429 |
Appl.
No.: |
05/191,912 |
Filed: |
October 22, 1971 |
Current U.S.
Class: |
60/476;
91/420 |
Current CPC
Class: |
F15B
7/006 (20130101) |
Current International
Class: |
F15B
7/00 (20060101); F15b 015/18 () |
Field of
Search: |
;60/52R,476 ;91/420 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Geoghegan; Edgar W.
Claims
We claim:
1. A hydraulic system comprising:
an actuator including a housing and a fluid-responsive member
movable in said housing, said member and said housing defining
first and second chambers on opposite sides, respectively, of said
member;
a reversible, variable speed pump, the output of said pump being a
function of the speed at which said pump is driven;
conduit means for connecting said pump to both of said chambers
whereby said pump can selectively pump hydraulic fluid from the
first chamber to the second chamber and from the second chamber to
the first chamber to thereby move the fluid-responsive member;
reversible, variable speed drive means for driving said pump;
means for controlling the direction in which and the speed at which
said pump is driven by said drive means whereby the direction which
the pump is driven controls the direction of movement of the
fluid-responsive member and the speed at which the pump is driven
controls the rate of movement of the fluid-responsive member;
said actuator being an unbalanced actuator whereby the change in
volume of the first chamber is greater than the change in volume of
the second chamber for a given displacement of the
pressure-responsive member;
said conduit means including a first conduit leading from the pump
to the first chamber and a second conduit leading from the pump to
the second chamber;
a third conduit leading from the pump to a source of hydraulic
fluid;
said pump including means for supplying make-up from the third
conduit through the first conduit to the first chamber when the
volume of the first chamber is being increased and means for
dumping excess hydraulic fluid from the first chamber through the
first conduit to said source when the volume of the first chamber
is being decreased; and
said pump including a barrel pump and a valve plate, said valve
plate having first, second and third ports therein communicating,
respectively, with said first, second and third conduits.
2. A hydraulic system as defined in claim 1 wherein said drive
means includes a reversible, variable speed electric motor, said
pump including a positive displacement pump.
3. A hydraulic system comprising:
a differential actuator including a housing and a piston movable in
said housing, said piston dividing said housing into first and
second chambers on opposite sides of said piston, respectively,
whereby movement of said piston causes the volumes of said chambers
to change;
said actuator including means for causing the volume of said first
chamber to undergo a greater change than the volume of said second
chamber in response to a predetermined amount of piston
displacement;
a reversible pump having first and second ports;
a first conduit interconnecting the first port and said first
chamber;
a second conduit connecting said second port and said second
chamber whereby the pump can pump hydraulic fluid through said
conduits between said chambers to thereby move the piston;
drive means for driving said pump, said drive means being
reversible to change the direction in which hydraulic fluid is
pumped by said pump to thereby control the direction in which the
piston is moved;
first valve means operatively associated with the first conduit and
responsive to the first conduit being on the discharge side of the
pump to open to permit hydraulic fluid to be supplied to the first
chamber through the first conduit;
second valve means operatively associated with the second conduit
and responsive to the second conduit being on the discharge side of
the pump to open to permit hydraulic fluid to be supplied to the
second chamber through the second conduit;
a first valve actuator responsive to the second conduit being on
the discharge side of the pump for opening said first valve means
to permit hydraulic fluid to be drawn from the first chamber by
said pump;
a third conduit leading from said first conduit for dumping excess
hydraulic fluid when said first chamber is being reduced in volume
by said movement of the piston;
a control valve for closing said third conduit when said first
conduit is on the discharge side of the pump and for opening said
third conduit when said second conduit is on the discharge side of
the pump;
means defining a restriction in said third conduit to provide back
pressure for said pump when said control valve is open; and
means for supplying make-up hydraulic fluid to said first chamber
when the volume of said first chamber is being increased.
4. A hydraulic system as defined in claim 3 wherein said
restriction is downstream of said control valve.
5. A hydraulic system as defined in claim 3 wherein said first
valve actuator also opens said control valve whereby a single valve
actuator operates both said first valve means and said control
valve.
6. A hydraulic system as defined in claim 3 wherein said reversible
drive means is a variable speed reversible drive means, thereby
providing for better control of the movement of said piston.
7. A hydraulic system comprising:
a differential actuator including a housing and a piston movable in
said housing, said piston dividing said housing into first and
second chambers on opposite sides of said piston, respectively,
whereby movement of said piston causes the volumes of said chambers
to change;
said actuator including means for causing the volume of said first
chamber to undergo a greater change than the volume of said second
chamber in response to a predetermined amount of piston
displacement;
a reversible pump having first and second ports;
a first conduit connecting the first port and said first
chamber;
a second conduit connecting said second port and said second
chamber whereby the pump can pump hydraulic fluid through said
conduits and between said chambers to thereby move the piston, the
direction of fluid flow through said conduits being a function of
the direction in which said pump is driven;
reversible drive means for driving said pump to thereby control the
direction in which the piston is moved;
first valve means operatively associated with the first conduit and
responsive to the first conduit being on the discharge side of the
pump to open to permit hydraulic fluid to be supplied through the
first conduit to the first chamber;
a third conduit leading from said first conduit for dumping excess
hydraulic fluid from the first chamber when said first chamber is
being reduced in volume by said movement of the piston;
a control valve for opening and closing said third conduit;
a valve actuator for opening said control valve and said first
valve means in response to said second conduit being on the
discharge side of said pump whereby a single valve actuator opens
said first valve means to allow the pump to draw fluid from the
first chamber and opens the control valve to permit dumping of any
excess hydraulic fluid through the third conduit; and
means for providing make-up fluid to the first chamber when the
volume of the first chamber is being increased.
8. A hydraulic system as defined in claim 7 wherein said reversible
drive means includes a reversible variable speed drive means
whereby fine control of piston movements can be accomplished.
9. A hydraulic system comprising:
an actuator including a housing and a piston movable in said
housing, said actuator being an unbalanced actuator whereby
movement of said piston causes a greater change in said piston
volume on one side of the piston than on the other side of the
piston;
a reversible barrel-type pump, including a valve plate having
first, second and third ports;
a first conduit leading from said first port to said one side of
piston;
a second conduit leading from the second port to said other side of
the piston whereby said pump can pump hydraulic fluid from said one
side of the piston to said other side of the piston and from said
other side of the piston to said one side of the piston with the
direction of fluid flow being a function of the direction in which
the pump is driven;
a third conduit leading from the third port to a source of
hydraulic fluid;
said valve plate having first and second segments, said first port
being at least partially on said first segment and said second and
third ports being at least partially on said second segment;
said first and second segments being on the intake and discharge
sides, respectively, of said pump when said pump is being driven in
one direction and said first and second segments being on the
discharge and intake sides, respectively, of said pump when said
pump is driven in the opposite direction, said third conduit
drawing hydraulic fluid from said source of hydraulic fluid when
said pump is being driven in said opposite direction and supplying
hydraulic fluid to said source when the pump is driven in said one
direction; and
said ports being sized and positioned on said segments to
substantially compensate for the unbalance of said actuator whereby
said pump supplies more hydraulic fluid to said one side of said
piston than it draws from said other side of said piston and
supplies less hydraulic fluid to said other side of said piston
than it draws from said one side of said piston.
10. A hydraulic system as defined in claim 9 wherein a region of
said second port is on said first segment.
11. A hydraulic system as defined in claim 9 including a casing,
said pump and at least a portion of said source being within said
casing.
12. A hydraulic system as defined in claim 9 including a
reversible, variable speed drive means for driving said pump.
13. A hydraulic system comprising:
an actuator including a housing and a piston movable in said
housing, said actuator being an unbalanced actuator whereby
movement of the piston causes a greater change in volume on one
side of the piston than on the other side of the piston;
a pump including first, second and third ports;
a first conduit for providing communication between said first port
and said one side of said piston;
a second conduit leading from the second port to said other side of
the piston;
a third conduit for providing communication between said third port
and a source of hydraulic fluid;
said pump being drivable in one direction to pump hydraulic fluid
from said one side of said piston through said first and second
conduits to said other side of said piston and being drivable in
the opposite direction to pump hydraulic fluid from said other side
of the piston through said second and first conduits to said one
side of said piston; and
said pump including first means for directing fluid from said first
conduit to said second and third conduits when said first conduit
is on the intake side of said pump and second means for directing
fluid from the second and third conduits to the first conduit when
said first conduit is on the discharge side of said pump to thereby
at least partially compensate for the unbalance of the
actuator.
14. A hydraulic system as defined in claim 13 wherein said pump
includes a barrel-type pump and said first and second means include
a valve plate having a plurality of ports therein sized and
positioned to substantially compensate for the unbalance of the
actuator.
Description
BACKGROUND OF THE INVENTION
Hydraulic systems are used to perform many different control
functions. One type of hydraulic system includes an actuator and a
pump. The actuator includes a cylinder and a piston, and the pump
selectively pumps hydraulic fluid from one side of the piston to
the other to thereby control movement of the piston.
One problem with systems of this kind is how to provide fine
control of piston movement. With prior art devices of this type, it
is difficult or impossible to very accurately position the
piston.
The problem of accurate piston positioning is compounded when an
unbalanced actuator is used. In an unbalanced or differential
actuator movement of the piston causes a greater change in volume
on one side of the piston than on the other. It then becomes
necessary to provide means to compensate for the unbalance.
Unbalance is typically caused by the presence of a connecting rod
on one side of the piston which effectively reduces the volume of
the chamber on that side of the piston.
SUMMARY OF THE INVENTION
The present invention relates generally to a hydraulic system in
which a pump moves hydraulic fluid from one side of a
pressure-responsive member such as an actuator piston to another to
thereby control the position of the pressure-responsive member. The
present invention provides several improvements to this kind of
system including solutions to the above described problems.
With the present invention, fine control of piston movement is
obtained by using a variable speed drive for the pump. This can be
used to advantage whether the actuator is balance or
unbalanced.
The rate of piston movement is a function of the speed at which the
pump is driven. Accordingly, for fine control of piston movement,
the pump is driven at a relatively low velocity. This causes pump
delivery rate to be relatively low and consequently the piston
moves slowly.
Although other drive means could be used for the pump, it is
preferred to use a variable speed reversible electric motor. The
direction of piston movement is a function of the direction in
which the pump is driven.
The present invention also provides two novel ways of compensating
for actuator unbalance. According to the first of these, the pump
includes means for compensating for the unbalance. More
particularly, the pump is of the barrel-type and includes a valve
plate having first, second and third ports. The piston divides the
cylinder into first and second chambers with the piston being
movable to displace more fluid in the first chamber than is taken
into the second chamber. First and second conduits provide
communication between the first and second ports and the first and
second chambers, respectively. A third conduit provides
communication between the third port and a source of hydraulic
fluid.
When the pump is driven in a first direction, hydraulic fluid is
withdrawn from the first chamber. Because a greater volume of fluid
is displaced in the first chamber than is taken into the second
chamber in response to piston movement, only the fluid required in
the second chamber is transmitted thereto by the pump. The excess
fluid is transferred through the third port and the third conduit
to the source of hydraulic fluid, thereby compensating for actuator
unbalance.
To move the piston in the opposite direction, the pump withdraws
fluid from the second chamber and supplies it through the first
conduit to the first chamber. However, additional make-up fluid is
required in that for any given piston movement, the volume of the
first chamber increases more than the volume of the second chamber
decreases. This make-up is provided by the pump which draws the
additional make-up fluid from the source of the hydraulic fluid
through the third conduit and supplies it via the first conduit to
the first chamber.
These desirable results are obtained by appropriately sizing and
locating the ports in the valve plate. The valve plate may be
considered as including first and second segments with a portion of
the first port being in the first segment and with portions of the
second and third ports being in the second segment. The direction
of fluid flow through the first segment is opposite the direction
of fluid flow through the second segment. For example, during the
intake stroke of the pump, hydraulic fluid may be drawn in from the
first chamber through the first port. During the discharge portion
of the stroke, the fluid taken in is discharged through the second
and third ports, i.e., to the second chamber and to the source of
hydraulic fluid to thereby compensate for the unbalance. The pump
is preferably housed in a casing filled with hydraulic fluid and
this may form a portion of the third conduit or a portion of the
source of hydraulic fluid.
According to the second method of compensating for actuator
unbalance, the present invention provides first and second conduits
providing communication between the first and second chambers and
the pump. A third conduit connects the first conduit with a source
of hydraulic fluid. The first and second conduits contain first and
second valves, respectively, for controlling the flow of hydraulic
fluid into and out of their associated chambers. A control valve
selectively opens and closes the third conduit.
According to this form of the invention, the first valve means and
the control valve are open when fluid is being withdrawn from the
first chamber by the pump. This permits excess fluid to flow
through the third conduit means to the source of hydraulic
fluid.
One feature of this invention is the provision of a restriction in
the third conduit to provide back pressure for the pump to prevent
starving of the pump. This restriction may be a simple,
inexpensive, relief valve which is set at the desired pump back
pressure.
Another feature of this form of the invention is that a common
valve actuator can be utilized to open both the control valve and
the first valve means when the first and third conduits are on the
intake side of the pump. The common actuator is preferably
responsive to the second conduit being on the discharge side of the
pump for opening the control valve and the first valve means. This
represents a simplification of the structure and a reduction in the
cost of manufacture.
When the piston is moving in a direction to enlarge the first
chamber, make-up hydraulic fluid must be provided. This is
preferably provided by a fourth conduit which interconnects the
second conduit with the source of hydraulic fluid.
Another advantage of the present invention is that the first and
second valve means automatically hold the piston in a fixed
position in the absence of any command for piston movement. Thus,
the pump is not required to hold pressure in a stand-by condition.
Another advantage of this construction is that in the event of a
hydraulic failure resulting in loss of hydraulic fluid outside of
the cylinder, the first and second valve means hold the piston in
position.
The invention can best be understood by reference to the following
description taken in connection with the accompanying illustrative
drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a diagrammatic view of one form of hydraulic system
constructed in accordance with the teachings of this invention.
FIG. 2 is a planned view of one form of valve plate which may be
utilized by the pump which forms a portion of the system showing
FIG. 1.
FIG. 3 is a diagrammatic view of a second form of hydraulic system
constructed in accordance with the teachings of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a hydraulic system 11 constructed in accordance with
the teachings of this invention. Generally the hydraulic system 11
includes a hydraulic actuator 13, a pump 15, a motor 17 for driving
the pump, and a motor controller 19.
The actuator 13 includes a housing or cylinder 21, a piston 23
slidable in the cylinder, and a connecting rod 25 for joining the
piston to a controllable member 26, the position of which is to be
controlled. The piston 23 divides the cylinder 21 into chambers 27
and 29. Because of the presence of the rod 25 in the chamber 29,
movement of the piston 23 causes displacement of more hydraulic
fluid in the chamber 27 than is taken into the chamber 29. Stated
differently, the volume of the chamber 27 changes a greater amount
than the volume of the chamber 29 in response to predetermined
displacement of the piston 23. Actuators of this type are known as
unbalanced actuators.
The chambers 27 and 29 communicate with the exterior of the
cylinder 21 through ports 31 and 33, respectively. The flow of
hydraulic fluid to and from the chambers 27 and 29 is controlled by
identical, pilot-operated check valves 35 and 37. Of course, the
specific form of the valves 35 and 37 can be varied by those having
ordinary skill in the art.
The check valve 35 includes a hollow housing 39 defining a valve
seat 41. A valve element in the form of a ball 43 is urged by a
spring 45 into fluid tight sealing relationship with the valve seat
41.
The valve element 43 can be moved away from the valve seat 41 to
open the valve 35 by an actuator 47 which is slidable in the
housing 39 and which is normally biased by a spring 48 out of
engagement with the valve element 43. The valve 37 is identical to
the valve 35 and parts of the valve 37 corresponding to parts of
the valve 35 are designated by corresponding reference numerals
followed by the letter a.
Conduits 49 and 51 interconnect the pump 15 and the valves 35 and
37, respectively. The conduits 49 and 51 are placed in
communication with a source 53 of hydraulic fluid by conduits 55
and 57, respectively. Check valves 59 and 61 in the conduits 55 and
57 allow for the flow of hydraulic fluid out of the source 53 and
prevent back flow to the source through the conduits 55 and 57. In
the embodiment illustrated, the source 53 is closed and
pressurized.
The conduit 49 is placed in communication with the actuator 47a by
the conduit 55 and another conduit 63. The actuator 47 is placed in
communication with the conduit 51 by a conduit 65.
The pump 15 is a reversible, variable speed barrel-type pump. Pumps
of this type are known and disclosed, for example, in U.S. Pat.
Nos. 2,525,934 and 3,291,067. The pump 15 includes a cylinder
barrel 67 suitably mounted for rotation, a plurality of cylinders
69 in the barrel and pistons 71 mounted for reciprocation in the
cylinders 69, respectively. The cylinders communicate with ports
74, respectively. The pistons 71 are driven by plungers 73 which
rotate with the cylinder 69 and which bear against a fixed cam
plate 75. Accordingly, as the barrel 67 rotates, the pistons 71 are
reciprocated in their respective cylinders 69. Reciprocation of the
pistons 71 causes intake of fluid into the cylinders 69 during one
part of each cycle and discharge of such fluid during another part
of the cycle. This is standard barrel pump operation.
The pump 15 also includes a valve plate 77 which is stationary
during rotation of the barrel 67. As shown in FIG. 2, the valve
plate 77 has three arcuate ports 79, 81 and 83 separated by
commutating lands 84. The valve plate 77 may be considered as being
divided into segments 85 and 87 one of which if for intake and the
other of which is for discharge. In the embodiment illustrated,
this division is made by an imaginary line 89. The top of the line
89 represents top dead center, and the bottom of the line 89
represents bottom dead center. In the embodiment illustrated, the
port 79 and relatively small portions of the ports 81 and 83 are
located in the segment 85. Relatively larger portions of the ports
81 and 83 are located in the segment 87.
The ports 79, 81 and 83 are in communication with the conduits 49
and 51 and with the interior of a casing 90 for the pump 15. A
conduit 91 provides communication between the interior of the
casing 90 and the source 53 of hydraulic fluid under pressure. With
the barrel 67 of the pump 15 rotating in a first direction, the
slot 79 and the portions of the slots 81 and 83 in the segment 85
are in communication with the cylinders 69 during the intake stroke
and the portions of the slots 81 and 83 in the segment 87 are in
communication with the cylinders 69 during the discharge
stroke.
The pump 15 can be driven in either direction and at different
speeds by the motor 17 which is a variable speed, reversible,
electrical motor. The discharge rate of the pump 15 is a function
of the speed at which the pump is driven with the discharge rate
increasing as the rate at which the pump is driven increases.
The motor controller 17 can be any device suitable for varying the
speed and direction of rotation of the motor 17. The controller 19
may be operated automatically or manually. By way of example, the
motor controller 19 may include the control system shown in common
assignee's copending application, Ser. No. 169,345, filed on Aug.
5, 1971, entitled "Acoustic Control System," and naming Curtis E.
Stevens as the inventor. Because motor speed is variable the cam
plate 75 need not be adjustably mounted.
If it is desired to move the piston 23 to the left, the motor
controller 19 causes the motor 17 to rotate in a first direction.
This places the conduits 49 and 51 on the intake and discharge,
respectively, of the pump 15.
The motor 17 drives the barrel 15 in a direction so that the ports
and port portions on the segment 85 of the valve plate 77 are on
the intake side of the pump and the port portions on the segment 87
are on the discharge side of the pump. Assuming that the barrel 67
is rotating in the direction of the arrow A in FIG. 2, each piston
71 will draw fluid into its associated cylinder 69 through the port
83 while that piston confronts the portion of the slot 83 on the
segment 85. Similarly, fluid is drawn into each of the cylinders 69
through the slot 79 and the portion of the slot 81 on the segment
85 while the cylinders confront these slots in the segment 85. The
quantity of fluid drawn into the cylinders from each of the ports
79, 81 and 83 is a function of the lengths and angular orientations
of the respective ports on the segment 85. In the embodiment shown
in FIG. 2, a relatively large quantity of fluid is drawn in from
the conduit 49 through the slot 79 and minor quantities of fluid
are drawn in from the case 90 through the slot 83 and from the
conduit 51 through the slot 81. Minor quantities are drawn in
through the slots 81 and 83 because (1) their lengths on the
segment 85 are relatively short, and (2) they are located near
bottom and top dead center, respectively, where the rate of pump
piston movement is relatively slow. Drawing in fluid through the
slot 81 does not cause a loss of pressure in the conduit 51 because
the pump 15 includes a sufficient number of pistons, e.g., 7 or 9,
so that at any instant more fluid is being discharged into the slot
81 and the conduit 51 than is being withdrawn.
With the pump 15 being driven in the direction of the arrow A in
FIG. 2, each of the pistons 71 discharges fluid through the slots
81 and 83 in volumetric amounts which is a function of the lengths
and angular orientation of these slots. Because fluid is drawn into
the cylinders 69 from the slot 81 and also discharged from the
cylinders 69 into the slot 81, the effectiveness of the slot 81 for
discharge purposes is reduced. Because the slot 79 is longer than
the portion of the slot 81 on the segment 87 and located where pump
piston velocity is greater, the pump draws in more fluid from the
conduit 49 than it discharges into the conduit 51. This amount can
be accurately apportioned so as to precisely compensate for the
unbalance of the actuator 13. The fluid which is not discharged
into the conduit 51 through the port 81 is discharged through the
slot 83, the case 90 and the conduit 91 to the source 53. It should
be understood that the valve plate 77 could be constructed in
different ways so long as more fluid is drawn in from the conduit
49 than is discharged into the conduit 51.
Each of the ports 74 is sufficiently long so that the associated
cylinder 69 is always in communication with at least one of the
slots 79, 81 and 83. In FIG. 2 one of the ports 74 is illustrated
between the slots 79 and 83 and the remaining ports 74 are not
shown. In the position of the port 74 shown in FIG. 2, it
communicates with the slots 79 and 83.
When the conduit 51 is on the discharge side of the pump 15, the
actuator 47 is urged by the fluid under pressure in the conduit 65
upwardly as viewed in FIG. 1 to move the valve element 43 off of
the seat 41 against the biasing force of the spring 45. This
permits the pump to draw fluid from the chamber 27 through the
conduit 49.
The hydraulic fluid at discharge pressure in the conduit 51 acts to
unseat the valve element 43a so that hydraulic fluid is supplied to
the chamber 29 through the valve 37. The pump 15 can also draw
fluid from the source 53 through the check valve 59 and the conduit
55. This may be necessary to develop enough pressure in the conduit
51 to unseat the valve element 43. Drawing of fluid from the source
53 may also be necessary to make-up for leakage.
As the piston 23 moves to the left, it displaces a greater volume
of fluid in the chamber 27 than is taken into the chamber 29.
However, because of the arrangement of the valve plate 77, the pump
can be adapted to compensate precisely for this unbalance.
Specifically, excess hydraulic fluid discharged from the chamber 27
is delivered through the port 83 to the case 90.
The rate at which the piston 23 moves can be controlled by the
speed of the motor 17. Thus, for inching, the motor 17 may be
caused by the motor 19 to turn very slowly so that the piston 23
can be accurately positioned. When the desired position of the
piston 23 has been reached, the motor 17 is de-energized and
thereafter the normally closed check valves 35 and 37 maintain the
piston at the preset position. If a failure causes loss of fluid
pressure outside of the actuator 13, the normally closed check
valves 35 and 37 continue to maintain the piston 23 in the preset
position.
To move the piston 23 to the right as viewed in FIG. 1, the motor
17 is energized by the controller 19 in the opposite to the
direction A in FIG. 2. This causes the pump 15 to be driven in a
direction opposite to the direction in which it was initially
driven. The result is that the segment 87 of the valve plate 77
becomes the intake segment and the segment 85 becomes the discharge
segment. Accordingly, as the barrel 67 rotates, it draws in fluid
through the portions of ports 81 and 83 on the segment 87 and
discharges the fluid through the port 79 and the portions of the
ports 81 and 83 on the segment 85. Because of the relative lengths
and orientations of the slots 79 and 81, the pump discharges more
fluid into the conduit 49 through the slot 79 than it draws in from
the conduit 51 through the slot 81. The additional fluid is
supplied from the source 53 through the conduit 91, the case 90 and
the slot 83.
With the conduit 49 on the discharge side of the pump 15, fluid
under pressure is transmitted through the conduit 63 to cause the
actuator 47a to unseat the valve element 43a. This permits the pump
15 to draw fluid out of the chamber 49 and into the conduit 51.
The hydraulic fluid at discharge pressure in the conduit 49 acts
directly against the valve element 43 to unseat the latter to
thereby permit hydraulic fluid under pressure to be discharged into
the chamber 27 to move the piston 23 to the right as viewed in FIG.
1. If make-up is required for start-up or during operation, it can
be obtained from the source 53 through the check valve 61 and the
conduit 57.
FIG. 3 shows a hydraulic system 111 constructed in accordance with
the teachings of this invention. The hydraulic system 111 is very
similar to the hydraulic system 11 except that it provides
alternate means for compensating the unbalance of the actuator. The
portions of the hydraulic system 111 corresponding to portions of
the hydraulic system 11 are designated by corresponding referenced
characters preceded by the numeral 1.
Generally, the hydraulic system 111 includes an actuator 113, a
pump 115, a motor 117, and a motor controller 119. The actuator
113, the motor 117, and the motor controller 119 are identical to
the corresponding elements described hereinabove with reference to
FIG. 1. The pump 115 is preferably any reversible, variable speed,
positive displacement pump and in the embodiment illustrated is a
gear pump.
Pilot operated check valves 135 and 137 control the flow of
hydraulic fluid into and out of the chambers 127 and 129,
respectively. The check valve 137 is identical to the check valve
37 shown in FIG. 1. The check valve 135 is identical to the check
valve 35 shown in FIG. 1 except that the actuator 147 includes a
pair of lands defining a groove 210 and the body of the valve
includes ports 203 and 205. Thus, the actuator 147 and the body of
the valve 135 cooperate to form a control valve 206 which is
normally biased to the closed position shown in FIG. 3. However, it
can be moved to an open position in which the groove 201 provides
communication between the ports 203 and 205.
The pump 115 has two ports, 207 and 209, which are connected by
conduits 149 and 151, respectively, to the valves 135 and 137. A
conduit 211 provides communication between the conduit 149 and the
source 153 of hydraulic fluid under pressure. A restriction which,
in the embodiment illustrated is in the form of a pressure relief
valve 213, is positioned in the conduit 211 intermediate the
control valve 206 and the source 153.
As in the embodiment of FIG. 1, conduits 165 and 157 provide
communication between the conduit 151 and the actuator 147 and the
source 153, respectively. Similarly, a conduit 155 provides
communication between the conduit 149 and the source 153 and the
conduit 163 provides communication between the conduit 149 and the
actuator 147a.
In the operation of the system 111, the motor controller 119
energizes the motor 117 to cause movement of the piston 123 in the
desired direction, such as to the left as viewed in FIG. 3. Motor
speed 117 is similarly adjusted so that the piston 123 will move at
the desired rate. The pump 115 is driven by the motor 117. In order
to move the piston 123 to the left, the port 207 is the intake port
and the port 209 is the discharge port. With the conduit 151 on the
discharge side of the pump 115, the hydraulic fluid under pressure
in the conduit 165 moves the actuator 147 upwardly to unseat the
valve element 143 and to open the control valve 206 by aligning the
groove 201 with the ports 203 and 205. Thus, the control valve 206
and the valve 135 are opened by a single actuator. The unseating of
the valve element 143 allows the pump 115 to draw hydraulic fluid
from the chamber 127.
The opening of the control valve 206 provides communication between
the intake of the pump 115 and the relief valve 213. The conduit
211, the control valve 206 and the pressure relief valve 213
provide means for dumping excess hydraulic fluid from the chamber
127. This is the excess hydraulic fluid which is not required in
the chamber 129 due to the unbalance of the actuator 113.
The relief valve 213 is set at a preselected pressure which is
preferably relatively low to thereby provide back pressure for the
pump. If the relief valve 213 or some other restriction were not
present, the back pressure on the pump may be insufficient and
cavitation may result.
The hydraulic fluid discharged by the pump 115 unseats the valve
element 143a to permit this hydraulic fluid to be supplied to the
chamber 129. This causes the piston 123 to move to the left at a
rate which is a function of the velocity at which the pump 115 is
being driven. When the desired position of the piston 123 has been
reached, the motor 117 is de-energized by the controller 119 and
thereafter the check valves 135 and 137 maintain the piston 123 in
the preset position. Ordinarily, with the piston 123 being moved to
the left as viewed in FIG. 3, there will be an excess of hydraulic
fluid which is returned to the source 153 via the conduit 211, the
control valve 206, and the pressure relief valve 213. However, if
for any reason make-up hydraulic fluid is required, it can be
supplied from the source 153 through the check valve 161 and the
conduit 155 to the conduit 149.
To move the piston 123 to the right as viewed in FIG. 3, it is only
necessary to reverse the direction of the motor 117, thereby
reversing the direction in which the pump 115 is driven. This
causes the conduit 149 to be on the discharge side of the pump 115
with the result that the actuator 147a is moved upwardly to unseat
the valve element 143a. This allows the hydraulic fluid in the
chamber 129 to escape into the conduit 151 to feed the pump 115. In
addition, the hydraulic fluid under pressure in the conduit 149
unseats the valve element 143 to permit the supply of fluid under
pressure to the chamber 127 and consequent movement of the piston
123 to the right. As the conduit 151 is on the intake side of the
pump 115, the control valve 206 remains in the closed position
shown in FIG. 3.
To move the piston 123 to the right, it is necessary to supply more
hydraulic fluid to the chamber 127 than can be drawn from the
chamber 129. The additional fluid is supplied from the source 153
through the check valve 159 and the conduit 157 to the conduit 151.
Of course, the check valves 159 and 161 prevent reverse flow of
hydraulic fluid to the source 153.
Although exemplary embodiments of the invention have been shown and
described, many changes, modifications and substitutions may be
made by one having ordinary skill in the art without necessarily
departing from the spirit and scope of this invention.
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