Hydraulic pump overhauling is a delicate procedure which resembles
hospital visits. Sometimes you have planned routine check-ups,
sometimes - emergency 911 calls. This particular overhaul could pretty
much be described as an urgent reanimation with elements of miraculous
resurrection.
Very unknown and very protected, this mysterious
Komatsu was brought to my shop by a man claiming that after two odd
weeks of extensive diagnostics the OEMechanics came to the conclusion
that the machines problem was pump-related and kindly suggested him an
option of buying a new pump. No need to say that the price made his
hair move, so an alternative solution had to be found urgently as this
was a crucial piece of equipment for the hole construction site.
Every time I get a Komatsu (or Caterpillar, or
any other protected brand), I get a warm feeling inside. First, because
any so called protected brand pump represents a nice back-engineering
puzzle, and second, it's always a chance to kick them in their
over-protected nuts.
Don't get me wrong, I don't think that Komatsus are
bad. Quite the opposite, actually, very efficient, fuel saving,
comfortable, innovative, computerized, you name it. It's that I happen
to judge machinery from the point of serviceability, simplicity and
availability of spare parts for the machine's hydraulics, that's all.
Please note that there is no protected
information disclosure here, only my own thoughts of how the stuff
works, (which, by the way may be wrong)
.
I have absolutely no information about the
model reference, only some casting numbers seen on the pics, which I am
not sure identify anything at all. I do know it came from a PC 240
excavator, so chances are this one is a proud part of a Hidraumind
super patented system presented so well in Komatsu's brochures. Yet
another reason to gut it up from head to toes.
Here is what I came up with after an hour of spraying and marking:
It is an open circuit double pump with closed
center load sensing and torque limiting control (sum of both pumps),
equipped with two proportional solenoid valves (pressure reducers)
which allow to override torque limiter setting and load sensing delta P
setting. That's it. A good example of how a scary unknown protected
pump turns out to be quite simple after all. For the proportional
valves to work you must supply them with a pressure feed, I used 35 bar
during testing, worked just fine. The valves will need around 500 ma to
fully open. The more the current, the lower is the torque setting, or
the delta P. The second pump is a classic closed center LS control,
where the delta P is measured between the pumps outlet and the LS
signal port. The first pump uses the same spool assembly (pic.7),
but the "outlet side" of the spool, instead of being connected to the
pump's pressure port, has an external connection, which means that
delta P higher reading can be taken at a remote point. Why? No idea
without seeing the actual machine, which I haven't. Maybe to exclude
the influence of the long hose connection between the pump and the
distributor on the delta P due to the hose losses. I have some ideas
but none making too much sense so far. At least I know what the pump's
control is supposed to do and was able to prove it during testing.
I found the design of the control very interesting,
with the whole torque limiting assembly "hidden" inside the servo
piston. A neat idea, though completely over-engineered from my point of
view. Japanese engineers have their ways to make simple things
complicated, but hey, their right, right? I liked oversized o'rings
compared to earlier models, which probably solved at least partially
leaks problem, typical to Japanese 1000o'rings designs, so prone to oil
leaks after several thousand hot hours. Rotary group almost perfect,
with Linde-like piston shoe design, compact and efficient, (yet more
expensive to produce).
If I was to design a Komatsu pump, I would probably
maintain the rotary group but would have at least tried to simplify the
control part. I must admit here that this particular model turned out
to be very compact for a double, hundred odd cc pump (test showed
around 130 cc max displacement), so at least here Komatsu engineers
drastically improved earlier designs. These pumps (as well as machines)
have Japanese quality on their side and protected designs against them.
You should be well aware that most of the times you will have to "turn
to the source" when in trouble if you use Komatsu. I personally
wouldn't buy a Komatsu, BUT, I DO admire many new and innovative
technical solutions they find, and absolutely sure at least half of
their claimed patens are, actually, something new AND useful.
