actuators
Article
Design, Implementation and Evaluation of a
Pump-Controlled Circuit for Single Rod Actuators
Ahmed Imam, Moosa Rafiq, Ehsan Jalayeri and Nariman Sepehri *
Fluid Power & Telerobotics Research Laboratory, Department of Mechanical Engineering,
University of Manitoba, Winnipeg, MB R3T5V6, Canada; [email protected] (A.I.);
[email protected] (M.R.); [email protected] (E.J.)
* Correspondence: [email protected]; Tel.: +1-204-223-7856
Academic Editor: Delbert Tesar
Received: 20 November 2016; Accepted: 14 February 2017; Published: 20 February 2017
Abstract: Pump-controlled hydraulic circuits are more efficient than valve-controlled circuits, as they
eliminate the energy losses due to flow throttling in valves and require less cooling effort. Presently
existing pump-controlled solutions for single rod cylinders encounter an undesirable performance
during certain operating conditions. This paper investigates the performance issues in common
pump-controlled circuits for the single rod actuators. Detailed analysis is conducted that identifies
these regions in a load-velocity plane and the factors affecting them. The findings are validated by
experimental results. A new design is then proposed that employs a limited throttling valve alongside
two pilot operated check valves for differential flow compensation to improve the performance.
The valve is of the flow control type and is chosen to have a throttling effect over critical regions;
it has the least throttling over other operating regions, thus maintaining efficiency. Experimental
work demonstrates improved performance in a full operating range of the actuator as compared to a
circuit that uses only the pilot-operated check valves. This circuit is energy efficient and capable of
recuperating energy.
Keywords: pump-controlled actuation; single rod actuator; counterbalance valve; efficiency
1. Introduction
It has been seen that pump-controlled hydraulic circuits have better efficiency compared to
valve-controlled circuits. Cleasby and Plummer [1] reported that their pump-controlled circuit
consumed only 11% of energy required by a valve-controlled circuit to perform the same task. On the
other hand, valve-controlled circuits, to date, exhibit better dynamic performance [2]. However,
machine efficiency is becoming a real concern from economic and environmental points of view,
especially in mobile hydraulic industry. Throttling losses in valves represent one of the main energy
losses in hydraulic circuits presently used in these machines. To reduce throttling losses, load-sensing
technologies have been extensively used in the mobile industry [3,4]. However throttling losses still
represent 35% of the energy received by a hydraulic system equipped with load-sensing technology
in a typical excavating machine [5]. Large energy saving can be obtained by eliminating/reducing
metering losses. The purpose of this paper is to further contribute to the development of efficient,
yet high-performance, pump-controlled actuation.
Pump-controlled circuits have been well-developed for double-rod cylinders [6–8]. For example,
the new Airbus A380 airliner aircraft, is equipped with this technology [9]. However, single-rod
cylinders are used in at least 80% of the electro-hydraulic applications [8]. Many initiatives to develop
pump-controlled circuits for single-rod cylinders have also been done [1,6,10–16]. Rahmfeld and
Ivantysynova [11] introduced a circuit that comprises a variable displacement piston pump and two
pilot-operated check valves (POCVs) to compensate for the differential flow in single-rod cylinders.
Actuators 2017, 6, 10; doi:10.3390/act6010010
www.mdpi.com/journal/actuators
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Williamson et al. [17] studied the performance of a skid-steer loader equipped with this circuit. They
reported boom velocity oscillations and a pump mode of operation switching during lowering light
loads at high speeds. Williamson et al. [17] and Wang et al. [12] showed that the circuit with two POCVs
is unstable at low loading operations. To deal with this problem, Williamson and Ivantysynova [18]
designed and implemented a feedforward controller. Their solution was tested on custom-build pumps
with fast rise time of 80 ms [19]. Commonly-used pumps on the market [20] possess a rise time of about
500 ms, like the one used in this research. Wang et al. [12] replaced the POCVs with a closed-center
three-way, three-position shuttle valve for flow compensation. They added two electrically-activated
regulating valves to dampen the undesirable oscillations through leakage control. This approach,
however, requires additional control effort and extra sensors that increases system cost and complexity.
Calishan et al. [13] simplified the previous design [12] by utilizing an open-center shuttle valve to
incorporate the leakage control together with flow compensation. The design required less control
effort and showed stable performance. However, they reported that their solution works best under
certain actuator velocities. Additionally, their experimental work is limited to low loading conditions
and lacks the effect of mass inertia. Jalayeri et al. [6,21] and Altare and Vacca [15] introduced the
idea of regulating the load motion with the help of counterbalance valves, which belong to throttling
elements. To compensate for the differential flow Jalayeri et al. [21] used an on/off solenoid valve
and a check valve, while Altare and Vacca [15] utilized a special form of shuttle valve, which they
called a dual-pressure valve. Both designs are more energy efficient as compared to conventional
valve-controlled alternatives and accurate enough for many industrial applications. Nevertheless,
these designs cannot regenerate energy [21]. From the above discussion it is seen that in spite of the
large amount of studies on the topic, throttle-less actuation technology for single rod cylinders has not
been fully explored, compared to valve-controlled actuation, in terms of dynamic performance [22].
In this paper, we first re-examine the undesirable performance of pump-controlled single rod
actuation systems in detail. The effects of the cylinder area ratio, charge pump pressure, transmission
lines losses, friction, and pilot-operated check valve characteristics on the performance of the actuator
are investigated. Next, we introduce a new design that improves performance using limited flow
restriction in the problematic regions. We show how specially-utilized counterbalance valves can be
incorporated in a novel manner in the circuit to enhance the performance and, at the same time, allow
energy regeneration. The trade-off between energy efficiency and performance is also investigated.
2. Circuit Utilizing Two Pilot Operated Check Valves
Figure 1 shows the commonly used circuit that utilizes two pilot operated check valves (POCVs)
for motion control of a single-rod hydraulic actuator. Piloted lines to both POCVs are pressurized
through the cross-pressure line of the circuit. The accumulator in the charging circuit is meant to boost
the charge pump supplement flow to the circuit when needed. Pressure difference across the pump is
defined as P = p a − pb , where p a and pb are pressures at the pump ports. Q is the flow rate through
the pump, which is positive when the hydraulic oil flows from port b to port a. The circuit works
in pumping mode if P and Q possess the same sign. Otherwise, it works in motoring mode. From
the actuator perspective, when the cylinder velocity, v a , and external force, FL , have the same sign
(for example, the cylinder extends against the load) the actuator works in resistive mode. Otherwise it
works in assistive mode.
Consider extending the actuator against the resistive external load, as shown in Figure 1, the pump
delivers flow Q in a clockwise direction to the cap side of the cylinder through transmission line A.
As the pressure in line A (p a , p1 and p A ) builds up, it opens the cross pilot-operated check valve,
POCVB , which allows flow, Q2 , to compensate for the cylinder differential flow. In this case, the main
pump works in pumping mode. Clearly, motion will not begin unless the POCVs are in the proper
working positions to compensate for the differential flow of the cylinder. Otherwise, poor responses
would be experienced in certain regions of operation, which will be discussed next.
Actuators 2017, 6, 10
The dynamics
Actuators
2017, 6, 10
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of the actuator can be described as follows:
3 of 15
.
mv a = (=p(A A A −−p B A B )) −
− FL
− Ff −
(1)
(1)
.
K
p A = = oil ( Q
(A−
− A A v a))
VA
(2) (2)
.
K
p B = = oil (−
(−Q B +
+ A B v a))
VB
(3) (3)
where
m represents
the the
equivalent
moving
mass.
Pressures
atat
actuator
where
represents
equivalent
moving
mass.
Pressures
actuatorports
portsare
aredenoted
denotedby
byp A and
andp B .
Q A and
Q
are
the
flow
rates
to
and
from
the
actuator
ports.
Piston
effective
areas
are
represented
.
and
are the flow rates to and from the actuator ports. Piston effective areas are representedby
B
A Aby
and Aand
modulus.
The oil volumes
at each side
of theside
cylinder
represented
. the oil
is bulk
the oil
bulk modulus.
The oil volumes
at each
of theare
cylinder
are
B . Koil is
by represented
VA and VB . by
and .
Figure1.1.Circuit
Circuitutilizing
utilizing pilot-operated
pilot-operated check
Figure
checkvalves.
valves.
Frictionforce,
force,F , is
, isassumed
assumedtoto be
be the
the sum
sum of
of the
the Stribeck,
Stribeck, Coulomb,
Friction
Coulomb,and
andviscus
viscusfriction
friction
f
components [23]:
components
[23]:
(4) (4)
| cv| |v a | sgn
Ff== F(1
1 (+ (K−b 1)
− 1) e −
va ) + f v va
( )(+
)
C +
FC== FPr
+ +(f c ( P
+A +) PB )
(5) (5)
represents
Coulombfriction;
friction; Kb and
andcv denote
denotebreakaway
breakaway friction
and
where
where
FC represents
thethe
Coulomb
frictionforce
forceincrease
increase
and
velocity
transition
coefficients,
respectively;
and
are
the
viscous
and
Coulomb
friction
velocity transition coefficients, respectively; f v and f c are the viscous and Coulomb friction coefficients,
coefficients,Frespectively.
represents the preload force generated due to seal deformation inside
respectively.
Pr represents the preload force generated due to seal deformation inside the cylinder
the cylinder
during
installation.
In Equation
(5), F
Coulomb
friction
is assumed to be the
during
installation.
In Equation
(5), Coulomb
friction
C is assumed to be the summation of the seals
summation
of
the
seals
deformation
due
to,
initially,
preloading
force,
and
the squeezing
force related
to to
thethe
deformation due to, initially, preloading force, and the force related to the seal
due
seal
squeezing
due
to
the
operational
pressure
effect.
It
is
clear
from
Equation
(5)
that
the
Coulomb
operational pressure effect. It is clear from Equation (5) that the Coulomb friction increases as the load
friction increases as the load and corresponding actuator pressures increase.
and
corresponding actuator pressures increase.
Amongst various types of POCVs, the commonly-used one uses the pilot line pressure
Amongst various types of POCVs, the commonly-used one uses the pilot line pressure referenced
referenced to charge pressure
[12]. This type is preferred in the pump-controlled circuits because
to charge pressure pc [12]. This type is preferred in the pump-controlled circuits because it provides
it provides less interference margin during operation of both valves in the circuit, which supports the
less interference margin during operation of both valves in the circuit, which supports the system
system stability [12]. The dynamics of a POCV have low impact on the overall system dynamics.
stability [12]. The dynamics of a POCV have low impact on the overall system dynamics. Hence,
Hence, it is simply considered as a switching element in this paper. POCVs are normally closed and
it iscan
simply
considered
a switching
element
in this
paper. the
POCVs
and can
be opened
in twoasways.
They can
be opened
through
pilot are
linenormally
pressure closed
as presented
inbe
opened
in two
Theythe
cancharge
be opened
throughdescribed
the pilot by
lineEquation
pressure(7)
as[19,24].
presented
Equation
Equation
(6),ways.
or through
line pressure
The in
two
cracking(6),
conditions are represented, for POCVB, by the following equations:
Actuators 2017, 6, 10
4 of 15
or through the charge line pressure described by Equation (7) [19,24]. The two cracking conditions are
represented, for POCVB , by the following equations:
Actuators 2017, 6, 10
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K p ( p1 − pc ) − ( p2 − pc ) ≥ pcr
(
−
)−(
−
pc − p2 ≥ pcr
−
)≥
(6)
(6)
≥p
(7)
+
(8)
(7)
where K p and pcr are the POCV pilot ratio and cracking pressure, respectively. In this circuit,
where
and
are
POCV
pilot ratio
pressure,
Inactuator
this circuit,
the is
the operation
of
POCVs
is the
mainly
controlled
byand
thecracking
pilot pressures
p1 respectively.
and p2 , while
motion
operation
of
POCVs
is
mainly
controlled
by
the
pilot
pressures
and
,
while
actuator
motion
monitored by pressures p A and p B . The differences between p1 and p A and p2 and p B are due toisthe
monitored by pressures
and . The differences between
and
and
and
are due to
losses in the transmission lines. This pressure drop is calculated using the lumped resistance model as
the losses in the transmission lines. This pressure drop is calculated using the lumped resistance
follows [21]:
model as follows [21]:
∆p = Cdt q + Cdl q2
(8)
∆ =
where q is the flow in a transmission line, and Cdt and Cdl represent the combined viscous friction in
where is the flow in a transmission line, and
and
represent the combined viscous friction
transmission
line and local drag coefficients, respectively.
In normal
operation only one of the POCVs
in transmission line and local drag coefficients, respectively. In normal operation only one of the
is expected to be opened while the other is closed. However, interference in operation is expected
POCVs is expected to be opened while the other is closed. However, interference in operation is
when the two activating pressures p1 and p2 are close to each other [12]. This undesirable interference
expected when the two activating pressures
and
are close to each other [12]. This undesirable
shows
up in three ways: either both valves are closed or both are open or they alternatively open
interference shows up in three ways: either both valves are closed or both are open or they
and alternatively
close.
open and close.
Williamson
andand
Ivantysynova
[17][17]
observed
thatthat
when
lowering
lightlight
loads
at high
speeds
during
Williamson
Ivantysynova
observed
when
lowering
loads
at high
speeds
assistive
retraction
mode
the
above
circuit
encounters
low
performance.
They
reported
that
when
during assistive retraction mode the above circuit encounters low performance. They reported that
the pump
changes
modes during
movement,
the cylinder
encounters
a sudden
when the
pumpoperating
changes operating
modes actuator
during actuator
movement,
the cylinder
encounters
a
change
in velocity.
et Wang
al. [12]etidentified
these conditions
as operating
thethe
circuit
sudden
change inWang
velocity.
al. [12] identified
these conditions
as operating
circuitaround
aroundthe
the load,
critical
. load
Critical
was identified
as the actuating
force
when at
pressure
at both of
critical
Fcrload,
. Critical
wasload
identified
as the actuating
force when
pressure
both chambers
A
B
(1 −
) where
= .
= α=
chambersequals
of thetoactuator
equals
to the i.e.,
charge
i.e.,
the actuator
the charge
pressure,
Fcr =pressure,
A A Pc (1 −
α) where
A A . Calishan et al. [13]
further
specified
two
load
limits
(F
and
F
)
for
this
zone
in
a
load-velocity
(F
–v
)
plane,
as
shown
and
) for this zone Lin aaload-velocity ( – in
Calishan et al. [13] further specified
limits (
L2
L1 two load
Figure) 2.
FL1 and
FL2 areinthe
loads
the shuttle
valve
reaches
open from
center
position
plane,
as shown
Figure
2. when
and
are the
loads
when fully
the shuttle
valvethe
reaches
fully
open in
from
the center
position The
in either
direction
of limits
motion.
The values
of these
limits
depend
on the shuttle
either
direction
of motion.
values
of these
depend
on the
shuttle
valve
operational
pressures
operational
pressures
and the actuator effective areas.
and valve
the actuator
effective
areas.
Figure 2. Critical zone shown by hashed lines in circuits utilizing shuttle valve according to [13].
Figure 2. Critical zone shown by hashed lines in circuits utilizing shuttle valve according to [13].
Here we further illustrate how transition lines losses, POCVs characteristics, and frictional force
Here we to
further
illustrate
transition
lines losses,
POCVs
characteristics,
frictional
contribute
the location
andhow
shape
of the undesirable
regions
(critical
zones). To and
include
the
forcetransmission
contribute lines
to thelosses
location
and
shape
of
the
undesirable
regions
(critical
zones).
To
include
effect, the critical force,
, is defined as the actuating force at the cylinderthe
)|force.at
when bothlines
pressures
the POCVs
pilot ports
i.e., as=the (actuating
−
During
this
transmission
lossesateffect,
the critical
force,are
Fcrequal,
, is defined
the cylinder
condition,
the pressure
the cylinder
chambers
and POCVs
are
different
due
tothis
when
both pressures
at theat
POCVs
pilot ports
are equal,
i.e., Fcr piloting
= A A ( pports
−
αp
.
During
)|
B p1 = p2
A
pressure
in transmission
lines,chambers
describedand
by aPOCVs
quadratic
relation
in Equation
(8), which
condition,
thelosses
pressure
at the cylinder
piloting
ports
are different
due toaffects
pressure
the critical zone shape. Initially at zero velocity, critical force can be represented as
= |
=
Actuators 2017, 6, 10
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losses in transmission lines, described by a quadratic relation in Equation (8), which affects the critical
zone shape. Initially at zero velocity, critical force can be represented as Fcr0 = Fcr |va =0 = A A pc (1 − α).
Actuators line
2017, 6,losses
10
15 critical
Transmission
depend on the flow rates and direction of motion. Accordingly,5 of
the
force regions
are represented by a quadratic curve as shown in Figure 3.
(1 − ). Transmission line losses depend on the flow rates and direction of motion. Accordingly,
Thethewidth
theregions
criticalare
zone
in circuits
the POCVs
between
FL10 and FL20 and
criticalofforce
represented
by awith
quadratic
curve as (difference
shown in Figure
3.
FL30 and FL40
inwidth
Figure
3) depends
oninthe
cracking
pressures
of the POCVs
and actuator
piston
The
of the
critical zone
circuits
with the
POCVs (difference
between
and
and areas.
in Figureas
3) depends
on the cracking
pressures
of the
POCVs
and actuator
areas.pressure
Let the forceand
FCV be defined
the corresponding
force
created
at the
cylinder
due topiston
the extra
Lettothe
force
be defined
the corresponding
corresponding force
created
the cylinder
due totothe
extraPOCV ,
required
open
the POCV.
Noteasthat
force
to theatpressure
needed
open
A
pressure required to open the POCV. Note that corresponding force to the pressure needed to open
FCVA = pcr A A , is higher than that is needed to open POCVB , FCVB = pcr A B . In pumping mode, the
POCVA,
=
, is higher than that is needed to open POCVB,
=
. In pumping mode,
pump generates
required
crackingcracking
pressure
pcr to guarantee
proper
configurations
the pump the
generates
the required
pressure
to guarantee
proper
configurationsofofPOCVs.
However,
in the
motoring
mode,
the external
works
create
this cracking
pressure.
POCVs.
However,
in the
motoring
mode, theload
external
loadto
works
to create
this cracking
pressure.
Figure 3. Construction of critical zones (5 and 6) considering the effect of transmission line losses,
Figure 3.
Construction of critical zones (5 and 6) considering the effect of transmission line losses,
Coulomb and viscous frictions, and POCVs cracking pressures.
Coulomb and viscous frictions, and POCVs cracking pressures.
To study the effect of the friction force components on the shape of the critical zones, we
actuator
equation
of force
motion
(ignoring theon
inertial
and Stribeck
terms) to
To rearrange
study thethe
effect
of the
friction
components
the shape
of thefrictional
critical zones,
wefind
rearrange
out the external load, , at critical condition:
the actuator equation of motion (ignoring the inertial and Stribeck frictional terms) to find out the
(9)
( )−
−
external load, FL , at critical condition: =
Since friction force acts against the actuator velocity, the above equation shows that friction force
FL = Fincrthe
−F
− f vsections
va
(9)
(v a )lower
affects the critical zone shape differently
upper
of the –
plane. As seen
C sgnand
in Figure 3, during positive velocity, Coulomb friction component shifts the critical zone to the left
while
viscousforce
friction
bends
it to the
with an velocity,
angle related
the viscous
friction
coefficient.
These force
Since
friction
acts
against
theleft
actuator
thetoabove
equation
shows
that friction
effects
are
reversed
for
negative
velocities.
affects the critical zone shape differently in the upper and lower sections of the FL –v a plane. As seen in
Built upon the above analysis, Figure 3 shows the different limits describing the undesirable
Figure 3, during
positive velocity, Coulomb friction component shifts the critical zone to the left while
performance regions. Regions 1, 2, 3, and 4 in Figure 3 represent the good performance areas, while
viscous the
friction
bends it to the left with an angle related to the viscous friction coefficient. These effects
performance deterioration occurs in regions 5 and 6. Mathematical representation of the different
are reversed
for
velocities.
limit lines negative
can be shown
as follows:
Built upon the above analysis, Figure 3 shows the different limits describing the (10)
undesirable
=
−
performance regions. Regions 1, 2, 3, and 4 in Figure 3 represent the good performance areas, while
=
− −
the performance deterioration occurs in
regions
5 and 6. Mathematical representation of (11)
the different
(12)
limit lines can be shown as follows: = +
(13)
=
+
FL1 +
= Fcr − Ff
(10)
where at zero velocity we have, F = =
F − − ,F − =
− −
,
=
+ , and
FCVA
cr
L2
f
=
+ +
. With reference to Figure 3, region 5 represents the pump mode of operation
switching (motoring to pumping) during actuator
FL3 = Fextension.
cr + Ff Pressures at both sides of the circuit are
almost equal and less than the charge pressure which keeps both POCVs open. In this case charge
FL4 with
= Fcr
+ Ff + flow
FCVBand the actuator velocity is not fully
pump supplies both sides of the circuit
hydraulic
controllable. While region 6 represents the pump mode of operation switching (motoring to
(11)
(12)
(13)
where at zero velocity we have, FL10 = Fcr0 − FC , FL20 = Fcr0 − FC − FCVA , FL30 = Fcr0 + FC , and
FL40 = Fcr0 + FC + FCVB . With reference to Figure 3, region 5 represents the pump mode of operation
switching (motoring to pumping) during actuator extension. Pressures at both sides of the circuit are
Actuators 2017, 6, 10
6 of 15
almost equal and less than the charge pressure which keeps both POCVs open. In this case charge
pump supplies both sides of the circuit with hydraulic flow and the actuator velocity is not fully
controllable. While region 6 represents the pump mode of operation switching (motoring to pumping)
Actuators 2017, 6, 10
6 of 15
during actuator retraction. Pressures at both sides of the circuit are almost equal and higher than the
charge pumping)
pressureduring
and both
valves,
initially,
are critically
closed.
Opening
POCV
motoring
B supports
actuator
retraction.
Pressures
at both sides
of the circuit
are almost
equal
and higher
mode while
motion
due
to valves,
less assistive
On the closed.
other hand
opening
than the
chargedecelerates
pressure and
both
initially,load.
are critically
Opening
POCVBPOCV
supports
A supports
motoring
while motion
deceleratesConsequently,
due to less assistive
load. On
the other
hand opening
pumping
modemode
and motion
acceleration.
the pump
mode
of operation
and POCVs
POCVA keeps
supports
pumpingand
mode
and motion
acceleration.
Consequently, the pump mode of
configuration
switching
pressure
and velocity
oscillates.
operation and POCVs configuration keeps switching and pressure and velocity oscillates.
3. Experimental Verification of Poor Performance Regions
3. Experimental Verification of Poor Performance Regions
FigureFigure
4 shows
the test
rigrig
constructed
thisstudy
studyand
and
schematic
drawing.
test
4 shows
the test
constructedfor
for this
its its
schematic
drawing.
The testThe
rig is
a rig is a
John Deere
attachment
(JD-48) (JD-48)
equipped
with anwith
electrically-controlled
variable
displacement
John backhoe
Deere backhoe
attachment
equipped
an electrically-controlled
variable
displacement
unit, aunit
charge
unit and instrumentations.
It is
facilitate
the
pump unit,
a chargepump
pressure
andpressure
instrumentations.
It is designed
todesigned
facilitatetothe
implementation
implementation
different hydraulic
Figure
shows
theof
fullthe
setup
the where
test rig motion
of different
hydraulicofactuation
circuits.actuation
Figure circuits.
4a shows
the4a
full
setup
testofrig
where motion of the mass at the end of the stick link generates the four quadrants of operation at the
of the mass
at the end of the stick link generates the four quadrants of operation at the actuator.
actuator. Furthermore, the external force at the actuator varies proportionally to the actuator
Furthermore,
the external force at the actuator varies proportionally to the actuator displacement.
displacement. Figures 4c,d shows the reconfigured setup where load is considered to be constant,
Figure which
4c,d shows
the reconfigured
setup
where load
is considered
to be
constant,
assists extension
and retraction,
respectively.
Specifications
of the main
components
arewhich
given assists
extension
and 1.
retraction, respectively. Specifications of the main components are given in Table 1.
in Table
(a)
(c)
(b)
(d)
Figure 4. Experimental test rig: (a) main components: (1) JD-48 backhoe attachment, (2) main pump
Figure unit,
4. Experimental
test rig: (a) main components: (1) JD-48 backhoe attachment, (2) main pump
(3) charge pump unit, (PS) pressure sensors, and (DS) displacement sensor; (b) full setup
unit, (3)schematic;
charge pump
unit, (PS) setup
pressure
sensors,
andand
(DS)
displacement
sensor;
(b) full setup
schematic;
(c) reconfigured
to test
the second
third
quadrants; and
(d) reconfigured
setup
(c) reconfigured
setup
test quadrants.
the second and third quadrants; and (d) reconfigured setup to test the
to test the first
andto
fourth
first and fourth quadrants.
Actuators
Actuators2017,
2017,6,6,1010
77ofof15
15
Table 1. Experimental test rig specifications.
Table 1. Experimental test rig specifications.
Main Components
Main
Components
JD-48 backhoe
attachment
stick
JD-48
backhoe
attachment
actuator
cap-side
area,
area
1
stick actuator
cap-side area,
ratio
and stroke
1
area ratio and stroke
2
2
3
3
PS
DS
PS
DS
Main pump unit
Main pump unit
Charge pump unit
Charge pump unit
Pressure transducer
Pressure transducer
Displacement sensor
Displacement sensor
Specification
Specification
31.67 cm , 0.75, 55 cm
31.67 cm2 , 0.75, 55 cm
28 cm ⁄rev electrically-controlled variable swash plate
28 cm3pump
/rev electrically-controlled
variablecoupled
swash plate
piston
(Sauer-Danfoss 42 series)
with 50
piston pump (Sauer-Danfoss 42 series) coupled with
hp, 1775 rpm induction motor (Toshiba 320 TC)
50 hp, 1775 rpm induction motor (Toshiba 320 TC)
1.25–1.96 MPa adjustable pressure van pump
1.25–1.96 MPa adjustable pressure van pump
(NorthmanVPVC-F40-A1)
VPVC-F40-A1)
(Northman
Ashcroft K1, accuracy 0.5% at 3000 psi
Ashcroft K1, accuracy 0.5% at 3000 psi
Bourns, accuracy 5 μm
Bourns, accuracy 5 µm
Different loading conditions (mass of 0, 41, 82, 123, 164, 204, and 245 kg) were applied to the
Different
conditions
(mass
of 0, 41, at
82,different
123, 164, velocities
204, and 245
applied
the stick
stick actuatorloading
and responses
were
obtained
in kg)
eachwere
of the
four to
quadrants.
actuator
and responses
were
obtained at
velocities in
eachof
of the
the test
fourrig
quadrants.
Experimental
Experimental
work was
performed
ondifferent
the reconfigured
setup
shown in
Figure 4c,d.
work
was performed
the reconfigured
setup of
the test
rig runs
shown
in in
Figure
Experimental
Experimental
results on
showed
good performance
when
pump
only
single4c,d.
mode
of operation
results
showed
performance
runs 3.
only
in singleperformance
mode of operation
away from
the
away from
thegood
switching
regions when
shownpump
in Figure
However,
deteriorates
at certain
switching
regions. regions shown in Figure 3. However, performance deteriorates at certain regions.
Figure
Figure55shows
showsthe
theresults
resultscategorized
categorizedbased
basedon
onquality
qualityofofperformance
performanceand
andplotted
plottedononthe
theFL –v a−
plane.
Each
vertical
set set
of points
in in
thethe
figure
represents
different
actuator
plane.
Each
vertical
of points
figure
represents
different
actuatorvelocities
velocitiesfor
forone
oneload
load
value.
value.Areas
Areashatched
hatchedwith
withdashed
dashedlines
linesare
areregions
regionswhere
wherethe
thepump
pumpswitches
switchesthe
themode
modeofofoperation
operation
during
extension
and retraction.
Operation
in these regions
exhibits
deteriorated
duringactuator
actuator
extension
and retraction.
Operation
in these
regions
exhibits performance.
deteriorated
Figure
6 showsFigure
a typical
circuit
performance
twocovering
regions. two
The regions.
experiment
done for
a
performance.
6 shows
a typical
circuit covering
performance
The was
experiment
was
245
kgfor
mass
during
extension
Ascm/s).
can beAsseen,
second
done
a 245
kg mass
during(vextension
( and
= 5 retraction
cm/s) and (v
retraction
( = −9
can the
be seen,
the
a = 5 cm/s)
a = −9 cm/s).
portion
the circuit
performance
at oscillatory
retraction.
secondillustrates
portion illustrates
the
circuit performance
at oscillatory
retraction.
Figure5.5.Experimental
Experimentalidentification
identificationof
ofcritical
criticalzone
zone(shown
(shownby
byhashed
hashedlines)
lines)for
forcircuits
circuitsutilizing
utilizing
Figure
POCVs
(Figure
1).
POCVs (Figure 1).
It is clearly seen that experimental results validate the discussion presented earlier. In the next
It is clearly seen that experimental results validate the discussion presented earlier. In the next
section we present a circuit that improves the performance while maintaining efficiency.
section we present a circuit that improves the performance while maintaining efficiency.
Actuators 2017, 6, 10
Actuators 2017, 6, 10
8 of 15
8 of 15
Figure 6. Performance of circuit with POCVs only in extension and retraction of a 245 kg attached
Figure 6. Performance of circuit with POCVs only in extension and retraction of a 245 kg attached mass:
mass:
(a) control
signal;
(b) actuator
velocity;
(c) pressures
at pump
(solid
line)
and port
(a) control
signal; (b)
actuator
velocity; (c)
pressures
at pump port
a (solidport
line)a and
port
b (dotted
line);b
(dotted
line);
and
(d)
pressures
at
actuator
port
a
(solid
line)
and
port
b
(dotted
line).
and (d) pressures at actuator port a (solid line) and port b (dotted line).
4. Proposed Circuit
4. Proposed Circuit
The main idea behind the new circuit is to utilize flow throttling to control the actuator motion,
The main idea behind the new circuit is to utilize flow throttling to control the actuator motion,
exclusively, in the regions where responses are not satisfactory. In other regions, motion is controlled
exclusively, in the regions where responses are not satisfactory. In other regions, motion is controlled
in a throttle-less manner. Throttling of hydraulic fluid creates a pressure drop across the valve orifices
in a throttle-less manner. Throttling of hydraulic fluid creates a pressure drop across the valve orifices
maintaining increased pressure in cylinder chambers compared to pump ports, which contribute
maintaining increased pressure in cylinder chambers compared to pump ports, which contribute
towards a stiffer actuator [21,25]. The proposed circuit possesses a comparable energy efficiency and
towards a stiffer actuator [21,25]. The proposed circuit possesses a comparable energy efficiency and
energy regeneration ability to the circuit with POCVs at high loading conditions and the stability of
energy regeneration ability to the circuit with POCVs at high loading conditions and the stability of the
the circuits with throttling valves at low loading conditions. Furthermore, the new design does not
circuits with throttling valves at low loading conditions. Furthermore, the new design does not require
require additional electronic control which is desirable in industrial settings. In order to achieve such
additional electronic control which is desirable in industrial settings. In order to achieve such a goal,
a goal, a special valve is needed to be fitted in either transmission lines A or B. The special valve
a special valve is needed to be fitted in either transmission lines A or B. The special valve should be
should be pilot-operated through the same pilot lines to the POCVs in order to dampen the
pilot-operated through the same pilot lines to the POCVs in order to dampen the undesirable responses
undesirable responses in the regions of interest. Additionally, it should also throttle the flow in the
in the regions of interest. Additionally, it should also throttle the flow in the transmission line when the
transmission line when the two pilot pressures are close to each other. Finally, it should allow free
two pilot pressures are close to each other. Finally, it should allow free flow in and out of the actuator
flow in and out of the actuator when the two pilot pressures are not close to each other and throttling
when the two pilot pressures are not close to each other and throttling is unnecessary. Figure 7 shows
is unnecessary. Figure 7 shows the proposed circuit incorporating the special valve installed in line
the proposed circuit incorporating the special valve installed in line A of the circuit. For illustration
A of the circuit. For illustration simplicity, the charging system is represented only by accumulator.
simplicity, the charging system is represented only by accumulator.
Locating the valve in line A is preferred since initial experiments showed that oscillatory
Locating the valve in line A is preferred since initial experiments showed that oscillatory motions
motions occur during actuator retraction of assistive load (see also Figure 5). The valve is activated
occur during actuator retraction of assistive load (see also Figure 5). The valve is activated by pressures
by pressures from the two POCVs pilot inputs. The valve should be designed with a special flow area
from the two POCVs pilot inputs. The valve should be designed with a special flow area as function of
as function of the piloting pressure differential. A spool-sleeve throttling configuration and balance
the piloting pressure differential. A spool-sleeve throttling configuration and balance springs should
springs should be used such that the valve possesses the area profile shown in the inset of Figure 7.
be used such that the valve possesses the area profile shown in the inset of Figure 7. Presently such
Presently such a valve is not commercially available in the market. Thus, in order to implement this
a valve is not commercially available in the market. Thus, in order to implement this circuit, we use
circuit, we use two counterbalance valves (CBVs). Generally, CBVs are throttling valves used for
two counterbalance valves (CBVs). Generally, CBVs are throttling valves used for safety requirements
safety requirements through the whole working range actuator operation. They have been used in
through the whole working range actuator operation. They have been used in some pump-controlled
some pump-controlled applications [6,15,21,26], but with no ability to regenerate energy [21]. Here,
applications [6,15,21,26], but with no ability to regenerate energy [21]. Here, the CBVs are utilized to
the CBVs are utilized to only restrict flow at low loading conditions to enhance the performance while
allowing free flow at high loading conditions to allow energy regeneration. Figure 8 shows the
proposed circuit implementation utilizing CBVs.
Actuators 2017, 6, 10
9 of 15
only restrict flow at low loading conditions to enhance the performance while allowing free flow at high
loading conditions to allow energy regeneration. Figure 8 shows the proposed circuit implementation
utilizing
CBVs.
Actuators 2017, 6, 10
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Actuators 2017, 6, 10
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Figure 7. Proposed circuit incorporating a special valve.
Figure 7. Proposed circuit incorporating a special valve.
Figure 7. Proposed circuit incorporating a special valve.
Figure 8. Proposed circuit implementation utilizing two CBVs.
Figure
8.isProposed
circuit
implementation
utilizing
CBVs.
Figure
8. Proposed
implementation
utilizing
two
CBVs.
The need for two
CBVs
due tocircuit
the
fact
that CBVs restrict
thetwo
flow
in only one direction of
motion. Note that each CBV is activated by two pressures; the first one is the pump cross-pilot
The need for two CBVs is due to the fact that CBVs restrict the flow in only one direction of
pressure and the other one is the load-induced pressure (see Figure 8). Both activation lines indicate
motion. Note that each CBV is activated by two pressures; the first one is the pump cross-pilot
the loading condition of the circuit which allows adjusting the CBVs to work in the required range of
pressure and the other one is the load-induced pressure (see Figure 8). Both activation lines indicate
the loading condition of the circuit which allows adjusting the CBVs to work in the required range of
Actuators 2017, 6, 10
10 of 15
The need for two CBVs is due to the fact that CBVs restrict the flow in only one direction of
motion. Note that each CBV is activated by two pressures; the first one is the pump cross-pilot
Actuators 2017,
10 other one is the load-induced pressure (see Figure 8). Both activation lines indicate
10 of 15
pressure
and 6,the
the loading condition of the circuit which allows adjusting the CBVs to work in the required range of
interest.Careful
Carefulselections
selections of
ofCBVs
CBVsflow
flowratings,
ratings,pilot
pilotratios
ratiosand
andcracking
crackingpressures
pressuresare
areneeded
neededfor
for
interest.
high
performance.
Given
our
circuit
specifications,
the
low
loading
conditions
is
considered
when
high performance. Given our circuit specifications, the low loading conditions is considered when
thecircuit
circuit pressure
pressure values
values are
are less
in
the
less than
than 15%
15% of
ofthe
themaximum
maximumoperating
operatingpressure
pressure(given
(givennumber)
number)
the
circuit.
At
this
loading
condition,
the
CBVs
act
as
a
throttling
valve
while
at
higher
loading
in the circuit. At this loading condition, the CBVs act as a throttling valve while at higher loading
conditionsthey
theyare
arefully
fullyopen
openwith
withminimum
minimumpressure
pressuredrop.
drop.Using
Usingan
anoversized
oversizedCBVs
CBVsprovides
providesaa
conditions
kindof
ofparabolic
parabolicrelation
relationbetween
betweenthe
thethrottling
throttlingarea
areaand
andactivating
activatingpressures
pressureswhich
whichsatisfies
satisfiesthe
the
kind
above
requirement.
above requirement.
ExperimentalEvaluation
Evaluationof
ofProposed
ProposedCircuit
Circuit
5.5.Experimental
Thefirst
firstexperiment
experimentwas
wasdesigned
designedtotodemonstrate
demonstrateperformance
performanceimprovements
improvementsatatlow
lowloading
loading
The
conditions. The second
second set
set of
of tests
tests were
were performed
performed to
to show
show the
the circuit
circuitperformance
performance and
and energy
energy
conditions.
consumption during
during operation
operation that
thatcover
coverall
allfour
fourquadrants.
quadrants. The
The first
first experiment
experiment isisdesigned
designedtoto
consumption
provethe
theoscillation-free
oscillation-free response of the
done
on on
the
prove
the proposed
proposed circuit
circuitin
inthe
thecritical
criticalregion
region6.6.It was
It was
done
reconfigured
setup
of of
thethe
test
system oscillation
oscillationisis
the
reconfigured
setup
testrig
rigininFigure
Figure4c.
4c.As
Aswas
was explained
explained earlier, the system
expectedduring
duringactuator
actuator
retraction
when
pressures
at both
ofcircuit
the circuit
are to
close
expected
retraction
when
thethe
twotwo
pressures
at both
sidessides
of the
are close
eachto
each
other.
Figure
9
shows
the
performance
in
a
typical
retraction—extension
of
actuator
with
other. Figure 9 shows the performance in a typical retraction—extension of actuator with constant load
constant
load This
(245 figure
kg mass).
This
figure
shows
that actuator
velocity
and are
pressure
graphs are
(245
kg mass).
shows
that
actuator
velocity
and pressure
graphs
non-oscillatory
innonthe
oscillatoryportion
in the retraction
portionsignal)
(negative
control
signal)
where at
thethe
two
pressures
at are
the close
actuator
retraction
(negative control
where
the two
pressures
actuator
ports
to
portsother.
are close to each other.
each
(a)
(b)
(c)
(d)
Figure9.9.Performance
Performanceof
ofthe
theproposed
proposedcircuit
circuitin
inretraction
retractionand
andextension
extensionof
ofaa245
245kg
kgattached
attachedmass:
mass:
Figure
(a)control
controlsignal;
signal;(b)
(b)actuator
actuatorvelocity;
velocity;(c)
(c)pressures
pressuresatatpump
pumpports
portsaa(solid
(solidline)
line)and
andbb(dashed
(dashedline);
line);
(a)
and
(d)
pressures
at
actuator
ports
a
(solid
line)
and
b
(dashed
line).
and (d) pressures at actuator ports a (solid line) and b (dashed line).
In the second set of experiments, two masses (41 kg and 368 kg) were applied to the full setup
In the second set of experiments, two masses (41 kg and 368 kg) were applied to the full setup
shown in Figure 4a. The experiments were repeated for both the circuit that utilizes the POCVs and
shown in Figure 4a. The experiments were repeated for both the circuit that utilizes the POCVs and
the proposed circuit (see Figures 1 and 9). First, a wave square control signal input (Figure 10) was
the proposed circuit (see Figures 1 and 9). First, a wave square control signal input (Figure 10) was
applied to the pump to move the stick link carrying a 41 kg mass.
applied to the pump to move the stick link carrying a 41 kg mass.
Results for both circuits are shown in Figures 11–13. It is clear that the circuit with the POCVs
only exhibits oscillation during switching from assistive to resistive loading modes in actuator
retraction. The oscillatory response is shown clearly in velocity, pump pressures, and actuator
pressures. Results also show that performance of the proposed circuit is smooth without any
significant oscillation during switching modes.
Actuators 2017, 6, 10
11 of 15
Results for both circuits are shown in Figures 11–13. It is clear that the circuit with the POCVs only
exhibits oscillation during switching from assistive to resistive loading modes in actuator retraction.
The oscillatory response is shown clearly in velocity, pump pressures, and actuator pressures. Results
also show that performance of the proposed circuit is smooth without any significant oscillation during
Actuators
2017,
6, 10
11 of 15
switching
modes.
Figure 10.
10. Control
Control signal
signal (electrical
(electrical voltage)
voltage) applied
applied to
to the
the pump
pump swash
swash plate
plate for
for experimental
experimental
Figure
evaluation
of
the
circuit
with
POCVs
and
the
proposed
circuit.
evaluation of the circuit with POCVs and the proposed circuit.
The
The proposed
proposed circuit,
circuit, however,
however, consumes
consumes more
more energy
energy than
than the
the circuit
circuit with
with only
only POCVs
POCVs as
as
shown
shown in
in Figure 13. The
The delivered/received
delivered/receivedhydraulic
hydraulicenergy
energy from/to
from/tothe
thepump
pumpto
to the
the circuit
circuit is
is
calculated
the multiplication
multiplicationofofthe
themeasured
measured
pressure
differential
across
pump
by flow
the flow
calculated as the
pressure
differential
across
thethe
pump
by the
rate,
rate,
. calculated
was calculated
by multiplying
the actuator
measured
velocity
and
the
Wpmh = ( p a=−( pb )−Q. Q) was
by multiplying
the actuator
measured
velocity
and the
piston
piston
effective
area. Results
bothconsume
circuits consume
energy
load isand
resistive
and
effective
area. Results
showedshowed
that boththat
circuits
energy when
loadwhen
is resistive
recuperate
recuperate
energy
when
the load is
assistive.
For this experiment,
the average
delivered
hydraulic
energy when
the load
is assistive.
For
this experiment,
the average delivered
hydraulic
energy
from
energy
from
the circuit
pump was
to the
circuit
17.1that
W for
circuit
that
utilizes
and
36 W
the pump
to the
17.1
W forwas
circuit
utilizes
only
POCVs
andonly
wasPOCVs
36 W for
thewas
proposed
for
the proposed
circuit.
The average
received
(recuperated)
from
circuit
circuit.
The average
received
(recuperated)
hydraulic
energyhydraulic
from the energy
circuit to
thethe
pump
are to
7.2the
W
pump
and 2.9
for circuit
utilizes
POCVs and
the proposed
circuit,
and 2.9are
W7.2
forW
circuit
thatWutilizes
onlythat
POCVs
andonly
the proposed
circuit,
respectively.
Therespectively.
extra energy
The
extra energy
by the was
proposed
circuit
was used
to overcome
the hydraulic
resistance
consumed
by theconsumed
proposed circuit
used to
overcome
the hydraulic
resistance
generated
by the
generated
by the the
CBVs
to stabilize
the the
system.
thatenergy
the extra
neededasenergy
decreases
asThis
the
CBVs to stabilize
system.
Note that
extraNote
needed
decreases
the load
increases.
load
increases.
canexperiment
be observedwith
for 368
the experiment
with 368
kgstick
masslink.
attached
to theobservation
stick link.
can be
observedThis
for the
kg mass attached
to the
One more
One
more
observation
is that
the aoriginal
a slightly
higher
strokemore
and mechanical
performed
is that
the original
circuit
reached
slightlycircuit
higherreached
stroke and
performed
slightly
slightly
more
work than
the
proposed
circuit in This
the same
time duration.
This is attributed
work than
themechanical
proposed circuit
in the
same
time duration.
is attributed
to the response
delay in
to
the
response
delay
in
the
proposed
circuit
due
to
the
extra
resistance
of
the
CBVs.
the proposed circuit due to the extra resistance of the CBVs.
Figure
showsthe
theactuator
actuatorvelocity
velocity
four
quadrants
of operation
forkg
368
kg for
mass
the
Figure 14 shows
at at
four
quadrants
of operation
for 368
mass
thefor
circuit
circuit
with
the and
POCVs
and the circuit.
proposed
circuit.
Results
show that performances
were
with only
theonly
POCVs
the proposed
Results
show
that performances
were acceptable
for
acceptable
forAcceptable
both circuits.
Acceptable
referthat
to responses
that do
not exhibit oscillations.
both circuits.
results
refer toresults
responses
do not exhibit
oscillations.
The
The main
main pump
pump delivered/received
delivered/receivedhydraulic
hydraulicenergies
energiesare
areshown
shownin
inFigure
Figure15.
15. ItIt is
is clear
clear from
from
the
the graph
graph that
that the
the energy
energy consumptions
consumptions for
for both
both circuits
circuits are
are almost
almost the
the same.
same. The
The average
average delivered
delivered
hydraulic
hydraulic energies
energies from
from the
the pump
pump to
to the
the circuit
circuit are
are 145.1
145.1 W
W and
and 148.9
148.9 W
W for
for circuit
circuit that
that utilizes
utilizes only
only
POCVs
POCVs and
and the
theproposed
proposed circuit,
circuit,respectively.
respectively. The
The average
average received
received (recuperated)
(recuperated) hydraulic
hydraulic energies
energies
from
from the
the circuit
circuit to
to pump
pump are
are 108.7
108.7 W
W and
and 102.2
102.2 W
W for
for the
the circuit that
that utilizes
utilizes only
only POCVs
POCVs and
and the
the
proposed
circuit,respectively.
respectively.
to mention
that
the pump
chargeinpump
in both
circuits
proposed circuit,
WeWe
alsoalso
needneed
to mention
that the
charge
both circuits
consumed
consumed
W. The
average
total delivered/received
hydraulic
energy
forwith
the POCVs
circuit with
about 49.5 about
W. The49.5
average
total
delivered/received
hydraulic energy
for the
circuit
only
POCVs
and the
proposed
circuit,
the consumption,
charge pump are
consumption,
W and 96.2
and the only
proposed
circuit,
including
the including
charge pump
85.9 W andare
96.285.9
W, respectively,
W,
the proposed
consumed
more energy
comparedused
to a pump-controlled
commonly used
i.e.,respectively,
the proposedi.e.,
circuit
consumedcircuit
12% more
energy12%
compared
to a commonly
pump-controlled
circuit
thatatuses
only POCVs
at thecondition
maximum
loading
condition
our test
circuit that uses only
POCVs
the maximum
loading
in our
test rig
(which isinalmost
halfrig
of
(which
is almost
half of the actuator capacity).
the actuator
capacity).
Actuators 2017, 6, 10
Actuators 2017,
2017, 6,
6, 10
10
Actuators
12 of 15
12 of
of 15
15
12
Figure 11.
11. Performance
Performance of
of
the
circuit
utilizing only
only
POCVs for
for control
control signal
signal in
in Figure
Figure 10
10 at
at four
four
Figure
Performance
of the
the circuit
circuit utilizing
utilizing
only POCVs
POCVs
for
control
signal
(a)
actuator
velocity,
;
(b)
actuator
displacement;
(c)
quadrants
of
operation
and
41
kg
mass:
(a) actuator
velocity,
; (b) actuator
displacement;
(c)
quadrants ofofoperation
operation
and
41 mass:
kg mass:
quadrants
and
41 kg
(a) actuator
velocity,
v a ; (b) actuator
displacement;
(c) pressures
pressures
at pump
pump
portsb,a,
a,pb ; and
and
b,pressures
and at
(d)actuator
pressures
at actuator
actuator
ports
and b,
b, are..
pressures
at
and
;; and
(d)
pressures
at
and
at
pump ports
a, p a ports
and
(d)b,
ports
a,
p A andports
b, p Ba,
.a,Oscillations
Oscillations are
are
experienced
ats–7
time
periods
s–7
and
24 s–25
s–25
and
circled
in the
the velocity
velocity graph.
graph.
Oscillations
experienced
time
periods
66 s–7
ss and
24
ss and
circled
in
experienced
at time
periods 6at
s and
24 s–25
s and
circled
in the
velocity
graph.
(a)
(a)
(b)
(b)
(c)
(c)
(d)
(d)
Figure 12.
12. Performance of
of the proposed
proposed circuit for
for control signal
signal in Figure
Figure 10 at
at four
four quadrants
quadrants of
of
Figure
Figure
12. Performance
Performance of the
the proposed circuit
circuit for control
control signal in
in Figure 10
10 at four
quadrants of
(a)
actuator
velocity,
;
(b)
actuator
displacement;
(c)
pressures
at
pump
operation
and
41
kg
mass:
(b)actuator
actuator displacement;
displacement; (c)
(c) pressures
pressures at
at pump
pump
operation and
operation
and 41
41 kg
kg mass:
mass: (a)
(a) actuator
actuatorvelocity,
velocity, v a ;;(b)
and
b,
;
and
(d)
pressures
at
actuator
ports
a,
and
b,
.
ports
a,
and
b,
;
and
(d)
pressures
at
actuator
ports
a,
and
b,
.
ports
a,
ports a, p a and b, pb ; and (d) pressures at actuator ports a, p A and b, p B .
Actuators 2017, 6, 10
Actuators 2017, 6, 10
13 of 15
13 of 15
Actuators 2017, 6, 10
13 of 15
Actuators 2017, 6, 10
13 of 15
Figure
Figure 13.
13. Hydraulic
Hydraulic power
power delivered/received
delivered/received by
by main
main pump
pump in
in circuit
circuit utilizes
utilizes only
only POCVs
POCVs and
and the
the
proposed
circuit
for
control
signal
in
Figure
10
at
four
quadrants
of
operation
and
41
kg
mass.
Figure 13. Hydraulic power delivered/received
main
pump inofcircuit
utilizes
POCVs
Figure 10 atby
four
quadrants
operation
andonly
41 kg
mass. and the
proposed
circuit for control
signal in Figure 10 by
at four
of operation
41POCVs
kg mass.
Figure
13. Hydraulic
power delivered/received
mainquadrants
pump in circuit
utilizesand
only
and the
proposed circuit for control signal in Figure 10 at four quadrants of operation and 41 kg mass.
(a)
(a)
(b)
(b)
Figure 14. Actuator velocity response to the control signal in Figure 10 at four quadrants of operation
(a) with
(b)quadrants of operation
for
368 14.
kg
(a) circuit
only POCVs;
(b) proposed
circuit.
Figure
14.mass:
Actuator
velocity
response
tothe
thecontrol
control
signalin
inFigure
Figure10
10atatfour
four
Figure
Actuator
velocity
response
to
signal
quadrants of operation
for368
36814.
kgmass:
mass:(a)
(a)circuit
circuitwith
with
onlyPOCVs;
POCVs;
(b)proposed
proposed
circuit.
for
kg
only
(b)
circuit.
Figure
Actuator
velocity
response
to the control
signal in
Figure 10 at four quadrants of operation
for 368 kg mass: (a) circuit with only POCVs; (b) proposed circuit.
Figure 15. Hydraulic power delivered/received by the main pump in the circuit utilizing only POCVs
and
the 15.
proposed
circuit
for experiment
in Figure
at main
four quadrants
of circuit
operation
and 368
kgPOCVs
mass.
Figure
Hydraulic
power
delivered/received
by10the
pump in the
utilizing
only
and the15.
proposed
circuit
fordelivered/received
experiment in Figure
10 at
fourpump
quadrants
operation
and only
368 kg
mass.
Figure
Hydraulic
power
by the
main
in theofcircuit
utilizing
POCVs
Figure 15. Hydraulic power delivered/received by the main pump in the circuit utilizing only POCVs
6. Conclusions
and the
the proposed
proposed circuit
circuit for
for experiment
experiment in
in Figure
Figure 10
10 at
at four
four quadrants
quadrants of
of operation
operation and
and 368
368 kg
kg mass.
mass.
and
6. Conclusions
In this paper, performance of the pump-controlled hydraulic circuit that utilizes two pilot6. Conclusions
operated
check
valves
was analyzed
and
the regions in the
load-velocity
planeutilizes
that show
In this
paper,
performance
of the
pump-controlled
hydraulic
circuit that
two poor
pilot6. Conclusions
performance
were
identified
and
experimentally
validated.
It
was
shown
that
how
cylinder
area
ratio,
operated
check
valves
was
analyzed
and
the
regions
in
the
load-velocity
plane
that
show
poor
In this paper, performance of the pump-controlled hydraulic circuit that utilizes two pilotIn this
paper,
performance
of the
pump-controlled
hydraulic
circuit
that
utilizes
two
pilot-operated
charge
pump
pressure,
transmission
lines
losses,
friction
forces,
and
pilot-operated
check
valve
performance
were
identified
and
experimentally
validated.
It
was
shown
that
how
cylinder
area
ratio,
operated check valves was analyzed and the regions in the load-velocity plane that show poor
check
valves
was
analyzed
and
the
regions
in
the
load-velocity
plane
that
show
poor
performance
characteristics
influence
the
performance
at critical
regions.
circuit
that
enhances
the response
in
charge pumpwere
pressure,
transmission
lines
losses,
frictionItA
forces,
and
pilot-operated
check
performance
identified
and experimentally
validated.
was
shown
that
how cylinder
area valve
ratio,
were
identified
and
experimentally
validated.
It demonstrated
was
shownAthat
how
cylinder
areathe
ratio,
charge
these
regions
was
proposed.
Experimental
results
oscillation-free
performance
for
the
characteristics
influence
the
performance
at
critical
regions.
circuit
that
enhances
response
in
charge pump pressure, transmission lines losses, friction forces, and pilot-operated check valve
pump
pressure,
transmission
lines
losses,
friction
forces,
and pilot-operated
check valve
characteristics
proposed
circuit.
Energy
studies
showed
that
the
proposed
circuit
consumed
12%
more
energy
these
regions
was
proposed.
Experimental
results
demonstrated
oscillation-free
performance
for
the
characteristics influence the performance at critical regions. A circuit that enhances the response in
influence
the
atstudies
critical
regions. that
A circuit
that
enhances
thepilot-operated
response
in 12%
these
regions
was
compared
to
aperformance
commonly
pump-controlled
that
usescircuit
only
check
valves
at
proposed
circuit.
Energyused
showed
the
proposed
consumed
more
energy
these
regions
was
proposed.
Experimental
resultscircuit
demonstrated
oscillation-free
performance
for
the
proposed.
Experimental
results
demonstrated
oscillation-free
performance
for
the
proposed
circuit.
max
loading
condition
in
our
test
rig
(which
almost
half
of
the
actuator
capacity).
This
extra
energy
compared
to
a
commonly
used
pump-controlled
circuit
that
uses
only
pilot-operated
check
valves
at
proposed circuit. Energy studies showed that the proposed circuit consumed 12% more energy
Energy
studies
showed
that
the
proposed
circuit
consumed
12%
more
energy
compared
to
a
commonly
was
used
to
stabilize
oscillations
in
circuit
pressures
and
actuator
velocity,
and
it
is
inversely
max loading
in used
our test
rig (which almost
half
of the
capacity). This
extra
energy
compared
to acondition
commonly
pump-controlled
circuit
that
usesactuator
only pilot-operated
check
valves
at
used
pump-controlled
circuit
thatproposed
uses
only circuit
pilot-operated
check
valves
atrecuperate
max and
loading
condition
proportional
to
load
value.
The
has
the
capability
to
energy.
This
was
used
to
stabilize
oscillations
in
circuit
pressures
and
actuator
velocity,
it
is
inversely
max loading condition in our test rig (which almost half of the actuator capacity). This extra energy
in
our testisrig
(which
half
the with
actuator
capacity).
extrabyenergy
was
used to stabilize
capability
toalmost
the
ability
deal
the
regenerated
energy
either
transferring,
reusing,
proportional
to
load
value.
Thetoofproposed
circuit
has and
theThis
capability
to recuperate
This
was
used tolimited
stabilize
oscillations
in circuit
pressures
actuator
velocity,
and it energy.
is inversely
oscillations
in
circuit
pressures
and
actuator
velocity,
and
it
is
inversely
proportional
to
load
value.
or
storing it.is limited
capability
the ability
deal withcircuit
the regenerated
energy byto
either
transferring,
reusing,
proportional
to loadtovalue.
The to
proposed
has the capability
recuperate
energy.
This
or
storing
it.
capability is limited to the ability to deal with the regenerated energy by either transferring, reusing,
or storing it.
Actuators 2017, 6, 10
14 of 15
The proposed circuit has the capability to recuperate energy. This capability is limited to the ability to
deal with the regenerated energy by either transferring, reusing, or storing it.
Acknowledgments: The authors would like to thank the Natural Sciences and Engineering Research Council
(NSERC) of Canada for providing financial support for this research. The first author would also like to
acknowledge the Egyptian Armament Authorities for awarding the allowance and scholarship to Canada.
Author Contributions: A.I. designed the hydraulic circuit and the test rig, provided theoretical analysis,
conducted data gathering, data analysis and wrote the draft of the paper. M.R. and E.J. contributed to the
design and construction of the test rig, gathering of data and writing the paper. N.S. initiated, coordinated and
supervised the research work that resulted in publication of this paper, contributed to the analysis of data and
writing the paper.
Conflicts of Interest: The authors declare no conflict of interest. The founding sponsors had no role in the design
of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the
decision to publish the results.
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