Although I've already come across these newer Komatsu pumps (like this
one), I could never get enough time to gut one right... Until today,
when I finally got my chance with this little baby from (according to
the owner) a PC 340 excavator.
From my previous experiences I already discovered
that these pumps have simple closed center load sensing controls, with
the only major difference being the fact that Komatsu opted for the use
of an external
upstream LS signal, which on most "classic" LS pumps is connected
internally to the pump's pressure outlet. And this one is no exception,
as you can see from the diagrams - here you have a simple diagram, showing only one pump, and here is something I made to show the complete tandem unit, mainly to demonstrate locations of the test ports.
Like its smaller sisters, it is equipped with two proportional pressure reducing valves,
which provide pilot pressures to override the settings of torque
limiter and LS delta P, which, as modern days dictate, are most surely
controlled by a computer on the actual machine. The small block
under one of the valves is a small spring-loaded accumulator. I would
guess its function it to dampen the pilot pressure spikes.
I said before that these controls are over
engineered, but now, after I've looked into them in detail, I must
admit that this is an elegant solution for a torque limiter, I
even made a small diagram of its function, which is out of proportion and only serves to show the principle of its operation.
This solution is compact and simple, but it requires a lot
of precise low-clearance machining (expensive) and most surely is less
contamination tolerant than "classic" designs. If something goes wrong
with the control, you will have to replace the whole servo-cylinder
assembly, something you won't find anywhere but at the origin... Also,
you can not access this part without partially disassembling the pump.
I, personally, still am an adept of bulkier controls which are
separated form the servo-cylinder, allowing for better serviceability,
but this solution is VERY NEAT. I take my hat off to whoever
designed this control!
The presence of all these plugs and holes in the
servo-piston assembly is, from what I have seen, a weak place in these
pumps. So far I have already seen them plugs come out (causing the
displacement control to malfunction), and, on this particular pump, the
Swiss cheese servo-piston simply split in half (yes, smack in the
middle), which will be soon posted in the kaboom section.
Nevertheless, upon looking further into the pump, I
find a lot of very interesting engineering solutions, like the cartridge valve,
(I do not know if the Komatsu has a name for it, but I baptized it
"cartridge" as it looks like one), which is removable and therefore
allows for some options, like orifice to tank, controlled restriction,
check-valve, etc... This is only my speculation, though, but I still pointed it out in the diagram.
The pump screams high quality and thorough research! I
believe the Komatsu engineers have meticulously designed this pump to
present the best efficiency and self-oscillations free control
performance. As much as I hated old Komatsu designs, I am starting,
well, not to "like", but rather to "find attractive" these newer ones.
The only thing that still is a strong "NO" factor, is the
fact that if something must be replaced, especially is the control
area, there will be no cheap solution.
Despite these drawbacks, these pumps are still on
the top of the "quality pyramid", and like any quality hydraulics, will
not brake "on their own", provided that a reasonable share of "quality
maintenance" is involved.
