What PSRU Can we Really Trust???

Originally Posted by Starman

If you want a variable reduction then how about an automatic transmission? I don't know how the weight compares to a PSRU, probably not too badly, and an automatic also automatically eliminates torsional vibration. Well proven too.

automatics only get rid of the reversals because they have a torque converter, which is a fluid coupling, the fluid acts as a non friction point that stops it in its tracks.

Perhaps some of the old 2 speed torque converters as fitted to Buicks, Caddys etc back in the early 60's could do with a revisit, that is or was an epicyclic gear train within the converter/fluid coupling. Only problem I can 'see' other than the possible oil heating issue ( And I am not totally convinced of that either... tractors/loaders/forklifts/dozers operate 24/7 with a fluid coupling that works very hard in terms of never reaching anything like lockup with nothing more than a few cooling fins on the coupling case & a fixed non circulated oil amount--- unlike a torque converter in an auto trans which has a relatively small continous oil flow thru it at all times ) is that it would have to be closely matched to the torque characteristics of the engine its fitted to in order to function in as suitable manner during climb/cruise conditions.
This means we are still at the ...No one size fits all scenario.

The smaller the torque converter the more slippage there is and the more energy you lose as heat so if you use one you want the largest and heaviest one you can get You still lose at least 3% I think but that may well be at low power settings, it depends on the torque/size match and at high (normal) power you may lose more efficiency.

the size and ability of the torque converter is relative. For example...

The 99-01 dodge ram's fitted witht he CTD had alot of transmission problem, but the transmissions were fine it was a under powered torque converter that caused all the rucus. The use of a single disk torque converter allowed for the most slippage and thus heat generated.

SO the solution for may dodge owners as to go buy a heft triple disk torque converter, why because the stock one only provides 37 inches of coverage, while the triple disk tops of at 105. This added coverage allows you to have better gripping power and of course this means less heat produced.

SO with that out of the question i would think a triple disk would be more then suitable for a smaller motor, and that the tq coupled to a dual clutch transmission would just shine.

Just remember to have the TQ LOCK UP when in high gear, this whay you will have NO slippage.

Just curious... doesn't less slippage and lock-up mean more torsional pulses transmitted instead of being absorbed?

Sorry- duplicated.

Originally Posted by Starman

If you want a variable reduction then how about an automatic transmission? I don't know how the weight compares to a PSRU, probably not too badly, and an automatic also automatically eliminates torsional vibration. Well proven too.

But the automatic transmission works opposite to what we need. It increases output RPM for cruise while reducing input RPM. For the large-diameter controllable prop, we want to increase the pitch on that prop and reduce its RPM while keeping engine RPM up where it's producing useful horsepower.

A large prop works well for takeoff and climb but its tip speeds limit the cruise speed. Take the square root of the sum of the tip speed squared plus the forward speed squared, and see that the tip speed increases as cruise speed increases, for a given prop RPM. All high-speed prop-driven aircraft have controllable or constant-speed props to increase pitch for improved cruise, but they also have to reduce prop RPM to limit tip speed unless the prop is very small, whereupon they lose the takeoff and climb performance. And for most of them, reducing RPM means reducing horsepower output, since HP is a function of torque times RPM.

Automatic transmissions have been tried in boats; they burn out quickly because they are designed for automobile use, where cruise power is typically 25-30%. Full power is rarely used, and then only for a few seconds. Boat transmissions are typically single-speed affairs that have massive gears and they weigh a lot. I have a Borg-Warner Velvet drive in my inboard; it weighed more than 100 lbs and was rated at about 200 hp. And all it had was forward-neutral-reverse, with one planetary set and two clutch packs. No torque converter. Boat transmissions don't have to deal with the massive rotational inertia and the resulting vibration and torque pulse hassles that aircraft props introduce, and they're still massive.

The Toyota Prius, I would think, won't have a variable-ratio drive. It's just an electric motor driven by batteries and an engine-driven generator, similar to the locomotive or diesel-electric mine truck. Maybe someone who knows the workings of that car can correct me.

Dan

The Prius "Hybrid Synergy Drive" turns the wheels with both the electric motor and the gasoline motor. A "Power split device" channels power from the gasoline motor either into the transmission or into the generator for the batteries, or some combination of both. Under "braking", the device takes wheel torque and feeds it back to the generator, which pumps a little juice back into the batteries "for free." Description and diagrams here.

Turns out the Prius does not have a Continuously Variable Transmission (CVT), but cars from several other manufacturers do. Here's a description of the device and links to some cars that have them.

I have no illusions that one could simply borrow a CVT from any automobile and use it in an airplane PSRU. I can't imagine that it would work, given the vastly different operational uses. But the technology might be adaptable, for the type of variable output speeds we're talking about in the last few posts.

Originally Posted by Topaz

Turns out the Prius does not have a Continuously Variable Transmission (CVT), but cars from several other manufacturers do. Here's a description of the device and links to some cars that have them.

I have no illusions that one could simply borrow a CVT from any automobile and use it in an airplane PSRU. I can't imagine that it would work, given the vastly different operational uses. But the technology might be adaptable, for the type of variable output speeds we're talking about in the last few posts.

That article says that Nissan has a CVT that handles 290 hp, but I wonder how it would hold up over the long term at those high power levels. As with auto transmissions, it might be OK for the occasional burst, but fail soon if expected to maintain that level.

Fiat fooled with CVTs years ago, too, using belts to drive the rear wheels. Short belt life and slippage were problems.

Dan

Like I said, I don't think any of the auto-manufacturer CVTs are suitable for drop-in use in an airplane PSRU. The auto manufacturers claim that they've got the service-life issues beaten. I can't vouch for that one way or the other. I've read auto-magazine reviews of cars that have them, and supposedly the slippage problem is a thing of the past as well.

But some people were talking about wanting a variable-reduction PSRU, for a variety of good-sounding reasons. The technology used in automotive CVTs might be a way forward in that quest, but very significant R&D would have to be done to develop one for airplane use.

you just need to run it backwards, then an automatic would work, like ive said a dual twin clutch would work great. REMEMBER the output shaft can be constant, as long as the input shaft changes.

And no the Torque reversals don't follow through the TC

Guys, where do you think I got all my vibration experience? 18 Years in Automatic Transmission Engineering at Ford Motor Company. Management grade engineer. I will cover a few topics now...

All automatic transmissions are HEAVY. All torque converters have significant energy losses (roughly equal to the fraction they are slipping, usually somewhere around 10% if you are carrying much power) when operating on the hydrodynamic drive, and have the potential issues we have been describing with vibrations when the clutch is applied. And the heat issues... well, they are real and serious and cooling turnover of the internal oil is necessary unless they are on really mild duty cycles. Yes.

As far as oil flows through torque converters go, they are not small. Itty bitty automatics turn over 2-4 l/min when the engine is making serious power, the C-6/E4OD/4R100/5R110 uses more like 10-12 l/min, and that is really about half of what it ought to be if you want oil out temps from the converter to stay below the magic 300 F mark over any reasonable duty cycle.

You can calibrate a box to carry the rpms and torque anywhere you want, but you will need to find somebody who can do all of that programming.

Friction drive CVT's with the Van Doorne push belt or LuK chain were in the a number of products including some Fords. They don't like high power settings and pump losses to maintain grip on the belt/chain are significant. Other friction drive CVT's exist with toroidal variators, and they have similar pump losses. Ultimately, step ratio boxes with six and even more speed is where the world has gone to because wider speed ratios are available, mechanical efficiency is higher, and weight is lower. Oh, and they cost less.

Prius (and Escape Hybrid and Focus Hybrid and Camry Hybrid) all use the same gadget, and it is best described as an electric CVT. Mechanical path and electric path in parallel with a differential between them to give you ratio based upon what you decided to do with the motors. The electric motor path loses a few percent of every bit of energy that passes through it. You can store electricity or draw from it, but when you do that you lose over 10% of the energy moved into the battery, and then you lose that much again when you draw it back out. In the high continuous power application of airplanes, it is way more weight and complexity and inefficiency than you want to carry around. No torque converter in this gadget, but lots of vibration management...

More later.

Billski

Other torque converter benchmarks. The ZF 6HP26 and the 6R60/75/80 that are based upon it flow 15 l/min (4 gal/min) at stall, and that will only hold the oil out temperature rise to about 100F for 5 seconds. They run the V-6 and V-8 gas engines in trucks with that.
And on high torque ratio tests (low SR), all of the test labs use direct external water cooling to keep the gadget from getting above 300 F.

Physics of the torque converter - efficiency is speed ratio times torque ratio. Above the coupling point, torque ratio is about 0.99, so the energy wasted is equal to the energy input (torque*speed) times the 1 - the efficiency (0.99*(1-SR)). You are not going to get much above the coupling point if your torques are up, like they would be in cruise or climb because the torque carrying capacity of the device drops off rapidly once you are above the coupling point. Next math is an equation from high school chemistry we used for calorimitry - h = m*deltaT*Cp, which for flows becomes hdot = mdot*deltaT*Cp, solve for deltaT=hdot/(mdot*Cp) make sure that your units are all consistent and your Cp is in the ballpark, and you can calculate the efficiency and the steady state oil temperature rise of a system with oil pumped through the converter.

I can not fathom a torque converter used in any start-stop-start application without pumped turnover of the internal oil. The early Ford (Borg-Warner) torque converters had a finned cast aluminum housing that served as a fan and included ducting to the bell housing. This was much more expensive and bulky than a steel housing and a cooler. They did have significant oil flow through the converter even then...

More later.

Billski

Originally Posted by wsimpso1

Prius (and Escape Hybrid and Focus Hybrid and Camry Hybrid) all use the same gadget, and it is best described as an electric CVT. Mechanical path and electric path in parallel with a differential between them to give you ratio based upon what you decided to do with the motors. The electric motor path loses a few percent of every bit of energy that passes through it. You can store electricity or draw from it, but when you do that you lose over 10% of the energy moved into the battery, and then you lose that much again when you draw it back out. In the high continuous power application of airplanes, it is way more weight and complexity and inefficiency than you want to carry around. No torque converter in this gadget, but lots of vibration management...

More later.

Billski

The world seems to be moving toward hybrid, a company in Germany has an aviation hybrid in process. I was thinking maybe the electric motor could also be used to absorb some torsional vibration. The electric motor could pulse at just the right time to counter the combustion pulse. Like a Bose noise canceling headset. Just need a computer to do the work.

Originally Posted by BBerson

The world seems to be moving toward hybrid, a company in Germany has an aviation hybrid in process. I was thinking maybe the electric motor could also be used to absorb some torsional vibration. The electric motor could pulse at just the right time to counter the combustion pulse. Like a Bose noise canceling headset. Just need a computer to do the work.

If there is a direct link from the prop to the engine, then maybe (though I'm not sure how that would work). I would guess that putting in a force to oppose another would simply increase the stresses on all parts involved.

If the prop is powered entirely by the electric motor and the engine only turns a generator, then there is no need.

Bruce