Somehow it has happened that
I have had an abiding interest in making
hydraulic systems quieter through nearly all of my working life. The
biggest challenge is to make a high pressure variable displacement pump
silent over all of its operating range; not yet achieved, but still
working on it. The goal is to find the hydraulic equivalent of a
helical gear over a spur gear.
There are many aspects to
quiet operation, from basic rigidity of
components, geometry and so on, but the most important issue in piston
pumps is the timing at the port face.
My first involvement
was in the development laboratory of
R.J. Ifield and Sons Pty Ltd at Dural, NSW, 1968, meticulously
modifying, testing, modifying, testing, modifying, testing port face
notches of a piston pump. An exercise in frustration with too many
variables and the difficulties of sound level measurement and
assessment. We found an answer. We certainly proved that having timing
notches was better than none. But the answer was only quieter - not
The next step was working as
designer under Dick Ifield at his home
office at Beecroft, 1970, on a fixed displacement pump called the Point
Nine because its piston diameter was 0.9 inches. While I was doing the
design iterations of the mechanics, the master was carrying out
incredibly tedius calculations of the timing notches, doing a series of
simulation runs taking fluid compressibility, pump volume change and
instantaneous notch area into account - using a slide-rule! I was
mightily impressed, and forever changed, by this willingness to take
infinite pains to achieve a result – it took weeks to finalise the
The end result was
pretty good. The unit was independently tested at
the University of Eindhoven, Netherlands, and found to be a “most
interesting unit with the highest efficiencies yet to be measured in
pumps of this kind” and “remarkably quiet in operation”. But again it
was quieter, not silent.
Then back to Dural, where my first real try at the
pains” was to optimise the timing for the 3.5T transmission being
designed and built as an automotive development transmission under a
USA DOE contract. This design also incorporated the Reed Valve, US
Patent 4,540,345, which provides increased flexibility in the use of
precompression to reduce timing noise.
By this time
we had acquired an HP85 computer, an early
all-in-one BASIC machine that was luggable for those with strong arms
and not enough sense. This did not make the job any quicker, partly
from the need to develop a simulation program from scratch, but mainly
because it allowed for better optimisation by making more trial and
error simulation runs.
|I would take it home each
night and set it up for a run, to be woken up by the built-in printer
firing up in the early hours of the morning.
The end result was
pleasing, with a measured 8 to10 db reduction in
noise compared with a Sundstrand 20 transmission of the same size. It
sounded almost pleasant, like a large sewing machine, but still some
way from silent.
simulation approach was used for many
development units, some using 5/95 fire resistant fluids. A software
package called Extend replaced the
home-grown code used on the HP85 and imported into bigger computers as
they came along. I still use Extend nearly 20 years later.
simulation work concentrated on providing a smooth transition
of pressure in the pump cylinders as they crossed from the high
pressure port to the low pressure port and then back to the high
pressure port again. Using precompression and decompression it was
possible to make a quiet pump for a single point of speed, pressure and
displacement; the trick being to chose the quiet point so that the
noise was acceptable over the full operating range.
Looking at the timing
notch designs of modern hydraulic pumps, it is obvious
that all manufacturers now use a similar approach, no doubt each with
their proprietary enhancements. Pumps are quieter than they used to be,
but still far from silent.
The reed valve made it
possible to make quiet over a small range of
conditions, pretty good with a fixed displacement unit, but not
effective at small displacements and high pressures.
A second factor was
introduced into the simulation optimisation called
“Jet Impact”. This worked on the concept that the pump noise was a
hammer and bell situation, where an event produces a hammer action
which is then picked up and amplified by the fluid volumes and
mechanical bits that make up the pump. A hammer effect is created by a
sudden change in jet force, as defined by the opening area of the notch
and the pressure drop across it. This analysis technique provided a
small but significant improvement.
During the late 1980’s,
a concept for an inshore mine hunter was
developed in Australia for the Royal Australian Navy using small
catamaran vessels. Two ships were built, HMAS Rushcutter and HMAS
Shoalwater. They were not very successful operationally and have been
original drive system was provided by Dowty UK consisting of a
fixed displacement drive motor with low magnetic signature and a
variable displacement pump. The pump proved to be expensive with
reliability problems, so a decision was made to try a commercial
Denison pump; it proved to be too noisy and I was asked to suggest
means to make it quieter.
The approach I recommended was to redesign the timing to minimise the
noise at source, then look at accumulators and such to further reduce
the noise levels if required.
Ford HPA Vehicle
2002013128 “Hydraulic Power Assist – a Demonstration of Hydraulic
Hybrid Vehicle Regenerative Braking in a Road Vehicle Application” by
R. P. Kepner of the Ford Motor Company describes the application of an
Ifield pump and valve system in a SUV, with useful improvement in fuel
This pump is
essentially of my design,
including the timing. The noise level was knocking on the door of
acceptability – “With further development the noise level and quality
can be acceptable for commercial markets.” Again, not silent.
Australian Navy has six Huon Class minehunters based on the Italian
Gaita, but manufactured by ADI in Newcastle, NSW. They have a dual
propulsion system; a conventional diesel drive with variable pitch
propellor for normal travel; and three fuly azimuthing hydraulic
propulsion units from Cazoni S.p.A of Bologna, used when mine hunting.
HMAS Norman - Huon Class Minehunter
|At least in part due to my good result
with the Estuary Minehunter, I was asked to assist with a problem of
noise from the propulsion motors interfering with the very sensitive
sonar system. The investigation and solving of this problem took a fair
bit of time, money and many trips to Bologna, but was ultimately very
successful, with the complete removal of the interference.
The figures show the
before and after noise traces, measured by a hydrophone mounted in the
case of the hydraulic motor.
|From my point of view this was a
watershed result because, for the first time, we had a silent hydraulic
motor. I will always remember standing at the test rig in Bologna,
stethoscope and all, and listening to a silent piston motor for the
first time in my life.
displacement motor driving a propellor with a unique speed/pressure
curve is relatively easy to work with, so the challenge is to take that
new understanding and extend it to cover a full range variable
So far success eludes,
quieter but still not quiet – but the journey is not yet over. I have a
small development laboratory
where I am researching many possibilities, in my own time, with my own
money, real backyard shed engineering. Wish me luck.