Insane Hydraulics

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Principle of Operation of the Axial-Piston Hydraulic Transformer

I want to talk about the technology that will most likely be shaping the distant future of mobile hydraulics - the hydraulic transformer, developed by the INNAS team.

Before I say anything else - if you haven't heard about INNAS - you must check them out! Their innovative ideas, like the floating cup principle (already implemented in the Bucher AX series), or the groove-less valve plate rotary group idea, in which tiny shuttles inside the cylinder block render the pressure-relieving valve plate grooves obsolete, are definitely worth looking into. Just think about it for a second - a valve plate without them pressure relieving grooves?!! Who would have thought about that?! Even though I believe the tiny shuttles will destroy the seats no matter how light they may be (like all shuttles eventually do) - the idea is still pure genius! And when was the last time you saw real innovation in hydraulics anyway? Made you think, didn't I? Do check these guys out - it's gold!

But let's get back to the hydraulic transformer now. I say that this technology will be shaping the distant future of mobile hydraulics and I mean it. The key word is distant. Probably very distant. Because of the enormous inertia of the modern industrial hydraulics. Nobody wants to change stuff that already works and makes money. The changes will only start to appear when they are mandated by the "money part" - i.e. when the efficiency of how hydraulic equipment transforms energy into mechanical motion becomes the main profit-defining factor. Right now it's secondary at best. Productivity is the main profit-determining factor for the 99 percent of hydraulic equipment out there. Equipment owners want tangible sell-able results no matter how much fuel (or electricity) they need to throw at their equipment to get them!

This will change, inevitably. I often refer to this as "industrial smoking". Everybody knows that wasting energy is bad, yet everybody still does it. And everybody knows that eventually, this will have to be addressed. And this is where the hydraulic transformer comes into play as a technology that allows you to strongly reduce energy losses, so common and so under-estimated for traditional hydraulic systems, without compromising productivity!

This is why I believe that knowing the principle of the rotary hydraulic transformer operation is so important. If you don't know it yet - you should wrap your head around it ASAP! Who knows, maybe you will even come up with a revolutionary design of your own after grasping the idea.

So - what is a hydraulic transformer? A hydraulic transformer is a volumetric mechanical device, that can convert pressure with minimal (theoretically zero) loss. An explanation is needed here. I'll do my best.

Throttling-based pressure conversion is bound to have an energy loss. For example - if you are using a reducing valve to get 100 bar from a 200 bar pressure source, there will be a pressure-drop-related loss whenever a flow is present. Now imagine, that instead of using a reducing valve, you used a 2:1 differential area hydraulic cylinder, in which you connected the 200 bar source to the rod end and used the 100 bar from the other side:

No pressure drop losses for the cylinder! So, if you could create such a system, that had a "variable differential area ratio", you would be able to covert pressures without pressure-drop-related losses! And this is exactly what a hydraulic transformer does.

If I were to design such a machine, the first thing that would come to my mind would be a hydraulic motor coupled to a hydraulic pump. Maybe only the pump variable. Maybe both. A very cumbersome, expensive, and impractical arrangement, that will never have something even remotely resembling a dynamic response. But I am a bad designer and an even worse inventor. Luckily - there's a much better solution, exactly the one used by the good folks at INNAS, and I confess that I would never in a million years have thought of something like that! So, the following is my best attempt to explain its genius principle of operation.

Let me set the stage first.

Imagine a normal fixed-displacement swashplate-type hydraulic motor. You have the classic angled surface of the swashplate, the pistons sliding over it on their shiny bronze shoes, the rotating barrel carrying however many pistons, and the classic double kidney port valve plate crowning the assembly. Now place this assembly so that you are looking at the tail end of the shaft through the valve plate, with the top dead center (the place where the pistons are all the way in the barrel) on top. You would be looking at something like this:

A classic axial-piston arrangement, with the TDC on top. Pressurize the kidney on the right, and the barrel will turn clockwise from our point of view. Now the "stage is set", and I hope you have no doubts about what you are looking at.

Now imagine that you threw away the boring classic two-kidney valve plate, and put a three-kidney port plate on top of our classic rotary group:

Insane, right? Can you imagine what is happening inside the kidneys when the rotary group rotates?

The top one is, obviously, going nowhere, because during half of the "kidney-exposed" travel the pistons will be going in the barrel, and the other half - out, essentially canceling their combined pumping action out (and the back-and-forth travel will be tiny as well anyway since we are so close to the TDC). The right bottom kidney will, obviously do some pumping (or motoring), and so will the left one.

Now, imagine that you can turn the valve plate about the shaft axis for a certain amount of degrees, and try imagining what happens inside the kidneys as the timing angle changes.

As you increase the angle, you will see that the three kidney ports become essentially locked volumetric devices with variable displacement!

The genius idea here is, of course, the idea of the valve plate angular offset serving as a variable displacement control! When a kidney is projecting over a dead center - you have no pumping/motoring action, but turn it 90 degrees - and you have all the action you can get! Pretty cool, right? Now, all you have to do to turn this into a hydraulic transformer is distribute the roles to the ports in a clever way, like so - one port as a pressure source, one port as a pressure outlet, and one low-pressure port to provide the necessary oil when needed (or absorb the return flow):

And there you have it - a hydraulic transformer in all its glory! Connect a pressure source to the top port (red), and you can regulate the pressure in the outlet port (yellow) by changing the timing angle of the valve plate, and thus altering the relation between the displacements of the pressure kidney and the outlet kidney. And note that all this happens without throttling losses! Also note that the rotation of the valve plate can be performed fast, which means that such a system can actually have a decent response time!

That's the principle in a nutshell - and you can build so much on it! If it gets inside your head - I bet you won't be able to sleep tonight!

Obviously, a lot of very clever technical solutions need to be invented to turn this principle into a working hydraulic machine - and that is exactly what INNAS has been doing for the last 10+ years! I strongly suggest that after you grasp the principle of operation, you check out their website and the video about their latest hydraulic transformer model, and how it can be used in a simple pressure source (common rail) hydraulic system as a direct (and more efficient) replacement of all these sophisticated DCVs.

I could talk about this system for hours - but that goes beyond the scope of this post, which is already too long. I just wanted to talk about the coolest principle of operation of a hydraulic transformer - a variable-timing-angle three-port valve plate that turns a classic axial-piston rotary group into this crazy pump+motor variable displacement combination, and a great company that has been developing it and innovating on a lot of other hydraulic stuff.

INNAS, I salute you! Keep at it and never stop!