Tech Briefs Magazine - February 2022 - MD-7

State Valve 1 State
1
OFF
ON
2
3
4
5
6
7
OFF
ON
OFF
ON
OFF
ON
Table 1: Three-valve DPV states.
same over-all flow coefficient and thus is
inherently hysteresis-free. The tradeoff
for this is the stepped approximation
to smooth proportional control. As we
will see, however, this tradeoff has other
benefits.
The DPV concept in its simplest form
does require steady-state power; however,
by incorporating a latching solenoid
design into the valve actuator,
the steady-state power requirement can
be eliminated. In a latching design,
permanent magnets are used to hold
the solenoid in the " latched " condition
without power, and a reverse-polarity
pulse is used to release the valve. The
result is a valve that maintains the set
flow condition with zero power input.
Components that eliminate steady-state
power draw are critical to achieving the
highest efficiencies from EV designs.
A true zero-flow state is a native attribute
of a DPV valve system (all valves off).
Other implementations of proportional
control can also provide effectively zero
flow; however, tight mechanical tolerances
can be required, which raise the
risk level with regard to debris sensitivity
and wear. Tight mating tolerances also
increase cost. The DPV concept achieves
a zero-flow state without requiring this
trade-off. The debris tolerance of a DPV
design can tailored to the application
since it is a simple combination of on-off
valves. The actuator can be isolated from
the main fluid flow via a diaphragm to
limit ingress of debris to the actuator.
DPV Control
The control system to drive a DPV
valve system can be implemented in
essentially two ways:
Motion Design, February 2022
MD Fluid Power Feature 0222_1.indd 7
1. Control system embedded in the valve
system; analog or digital input used to
command the system.
2. Electrical connection only to the DPV
system, control centralized remotely.
The first schema requires some intelligence
be built into the valve system as
well as power electronics to control each
valve. This DPV Control Board would require
a minimum of only three incoming
wires: power, ground, and signal. The
Control Board would translate the desired
state, communicated on the signal
line, into commands to the valves. The
Control Board would also provide for the
failsafe state if it detects a loss of power.
The second schema requires two wires
for each valve in the DPV system. The
control electronics can then be centralized,
which may provide advantages in
environmental protection but increases
the amount of wiring required. In an
actual vehicle application, some of the
benefits of both options may be realized
by co-locating multiple DPV systems on
a manifold and locating the control electronics
close by. Such a configuration
would also be desirable from a fluidics
perspective.
The control electronics for a DPV system
is inherently simple. Since hysteresis
need not be accounted for, complicated
PID control algorithms are not required.
A simple mapping of desired flow to
DPV state is all that is needed. The single
complicating factor for DPV control
is a result of the zero steady-state power.
Opening a valve requires a forward
current pulse, while closing the same
valve requires a reverse current pulse.
The requirement for both polarities
eliminates the possibility of a common
Valve 2 State
OFF
OFF
ON
ON
OFF
OFF
ON
ON
Valve 3 State
OFF
OFF
OFF
OFF
ON
ON
ON
ON
Total Flow
1
2
3
4
5
6
7
ground and requires two independent
connections to each valve. Even with
remote electronics, however, the wiring
requirements for a three-valve system
are not onerous.
The DPV concept addresses reliability
with a two-pronged approach. The primary
driver for high reliability is the employment
of simple, well-characterized
solenoid valve technology.
The second is the elimination of the
need for continuous duty electromagnetics,
which dramatically reduces heat
build-up. The DPV design also has two
additional built-in fault-tolerant features:
1. The control system can be designed
such that on loss of power, the valve
fails in a specific condition. Since
only a momentary current pulse is
required to set valve position, a capacitive
charge can be used to provide
the pulse on power loss, either setting
the valve open or closing it.
2. The DPV system does not have a single
point of failure that can disable
the entire system. The multiple-valve
design of the system, and the independent
wiring of each valve imply
that a failure of one valve would leave
the others functional, and still able
to control flow to a degree. While a
failed valve is still highly undesirable,
a failure-tolerant system is a highly
desirable attribute.
Conclusions
The DPV concept provides advantages
that match the unique needs of electric
vehicle cooling and energy management
systems. The advantages are directly related
to the simplicity and design flexibility
of the approach. While the DPV
concept does not provide for smooth
control of output, but rather stepped
control, it alleviates the need for deadbands
and eliminates hysteresis completely,
simplifying control algorithms. It
is also a power-efficient solution in line
with the demands of next-generation
EVs. Not only is the DPV concept power-efficient,
but it also has the potential
to enable further efficiency gains by
aiding in re-use of heat that otherwise
would be rejected to the environment.
This article was written by Fritz Byle,
Senior Project Manager, engineering,
and Chris Kujawski, Design Engineer, at
TLX Technologies (Pewaukee, WI). For
more information, visit http://info.hotims.
com/82318-280.
7
Cov
ToC
1/18/22 9:11 AM
http://info.hotims.com/82318-280 http://info.hotims.com/82318-800
Tech Briefs Magazine - February 2022

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