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Old 03-27-2015, 10:31 AM   #1 (permalink)
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Hydraulics is b-a-c-k! (correction)

For Old Mechanic: CR4 - Blog Entry: Hydraulic Efficiency Looms Larger and Larger


Last edited by gone-ot; 03-27-2015 at 01:58 PM.. Reason: corrected Pneumatics to Hydraulics
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Old 03-27-2015, 01:17 PM   #2 (permalink)
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I did not realize that pneumatics had left, but much prefer hydraulics to avoid compressibility issues. I like my compressibility limited to the bladder (inert gas) in the accumulator.

To boil it down a little consider the hydraulic launch assist, an independent system that works on the (otherwise undriven) rear axle of a fwd vehicle.

Basically it converts inertia to pressure, in two steps. wheel to accumulator-accumulator to wheel. Efficiency about 95% overall, regen to apply. On flat ground you can basically turn it into a hill, "climbing" while using better bsfc to add pressure over maintaining velocity in your vehicle, once the accumulator charge reaches capacity (always with a reserve), you reverse stroke on the launch assist rear axle, which drives the car, allowing the engine to shut down, for a distance approaching 1.5 mile, before the cycle is renewed.

Purchased as an option or retrofitted, a launch assist rear axle makes any car a hybrid or better yet EVERY car a hybrid, capable of automated pulse and glide without any variation is vehicle speed, which has been shown to double efficiency overall.

Capacity? One acceleration event from 0-75 mph, or onepulse inevery 1.5 miles on perfectly flat ground, very close to the range of a 1gen Insight on battery alone.

Don't worry, the patent expires in another 12.5 years.

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Old 03-27-2015, 02:00 PM   #3 (permalink)
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OOPS! I read one thing (Hydraulics) but typed another (Pneumatics)...duh!
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Old 03-27-2015, 02:03 PM   #4 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post
Efficiency about 95% overall, regen to apply.
Not sure how you came to that conclusion? The eaton system only says it captures %70 of the braking energy (which implies it could lose another %30 when accelerating, i.e. only 49% efficient). Any sources for that figure?
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Old 03-27-2015, 02:20 PM   #5 (permalink)
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Check it out: Try a Hydraulic Drive Train: This Car of the Future Gets 75 MPG - Green Transportation - MOTHER EARTH NEWS

And: Can an Inertial Storage Transmission Double Your Car's Mileage? - Green Transportation - MOTHER EARTH NEWS

I read these back in the 80s (I used to collect MEN, I have since become a bit less wide-eyed) and I thought we'd finally see it getting some traction when I read Ford was exploring the concept a few years ago: Ford F-150 Used to Develop 40 MPG Hydraulic Hybrid Powertrain - PickupTrucks.com News

But nothing has come of it yet. Now buyers have cut their teeth on one kind of hybrid and the automakers have seen that we are willing to make a small extra investment if it means paring some out of our eventual fuel purchase. I like the hydro option in particular because it is, in my opinion, more sustainable than potentially toxic batteries. You would need to get your pressure vessels hydrotested periodically, however.

I also had high hopes for flywheel load leveling schemes, but I think I'm more afraid of those than I am of the pressure vessels. A disk burst in a flywheel energy storage device could release a catastrophic amount of energy, the space and weight it takes to build a containment vessel for it might negate the advantages of a flywheel.
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Old 03-27-2015, 02:57 PM   #6 (permalink)
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In practice hydraulic systems leak. Even ones not designed to stop a truck.

But there are systems in production, usually only cost effective in large vehicles.
claims up to %25 improvement in garbage trucks. http://www.boschrexroth-us.com/count...80_2012-10.pdf

%25 isn't small potatoes on a truck, but an electric hybrid has no problem improving mpg by %25 or more in a car sized vehicle (all this assuming a "dumb" driver).
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Old 03-27-2015, 05:23 PM   #7 (permalink)
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You think nuke subs leak p-hack.

Your 70% quote is off by a mile and a few decades. Do you have to refill your hyradulic brake system daily and throw oildry under your parked car, LMAO.

Here is 10 year old documentation from the EPA, Eaton. Ford, and the University of Michigan, and your BEV loses 15% just charging the battery.

Specify, with concrete evidence, how you propose to recover 80% of the energy (wheel to wheel) of a 60-0 mph stop, in 20 revolutions of the wheels.
Say 600 horsepower seconds of energy in 130 feet.

In a device that can reach 99% efficiency, like a bladder accumulator, made of carbon fiber.

It's a shame that something so important will be diluted with opinions with no basis infact.

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mech
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Old 03-27-2015, 06:30 PM   #8 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post
In a device that can reach 99% efficiency, like a bladder accumulator, made of carbon fiber.
I asked you for a source. Hydraulic fluid has viscocity, pumps have drag, switches aren't %100 efficient, drivelines aren't 100% efficient.

You stated 95% efficient regen from decel to accel, and don't have a source for that I guess.

I agree hydraulic is power dense, and electric is energy dense. Not saying there is no application for hydraulic, there already is, just calling BS on %95 efficient claims.
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Old 03-28-2015, 01:21 PM   #9 (permalink)
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Post 7 first attached illustration, accumulator is listed at 97% pump at 91-92%. In the same documents it was recognized that the pump, which was running at prop shaft speed, was the weakest part of the design, a bent axis type (variable displacement) that dated back 70 years. My design is in wheel turning at 30% of the prop shaft, where efficiencies approach the accumulators posted 97%, with much lower flow rates and pump-motor shaft speeds.

On the highway at higher rpms above 3k, the bent axis pump-motor efficiency declines rapidly, down to 75%, an issue that does not exist in in wheel drives where 1000 rpm exceeds 80 mph.

In the real world, with todays technology 95% maybe slightly high, especially under conditions like stop and go congestion where fliud reversion and velocity are practically non issues. Even then you are talking about the level of efficiency of a manual transmission and a parts count about 30% lower for the powertrain as a whole (hundreds fewer parts), and the alternative has no regeneration capability whatsoever.

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Old 03-28-2015, 04:00 PM   #10 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post
.Even then you are talking about the level of efficiency of a manual transmission and a parts count about 30% lower for the powertrain as a whole (hundreds fewer parts), and the alternative has no regeneration capability whatsoever.
Unless you have been living in a cave the past 15 years, you might have noticed that there are millions upon millions of the alternative on the roads.

And given this is fossil fuel free, any modern EV gets regen for free (talk about low parts count).

But regen is a really hard thing to quantify, as you know. If you have to build it like a nuclear sub, then it is gonna be expensive and heavy, and have a definite effect on rolling resistance and etc. So you kind of have to iteratively look at it.

if you start looking at components and not at their effect on the system, or dropping various losses, then you can come up with all kinds of figures, i.e. %95 efficient regen for a ford focus electric? (top it off, drive up a hill, take a picture, coast down the hill). Actually it looks like 72%, which is going to be hard to beat, especially on a cost/weight/complexity basis, especially on an EV.
Ford Focus Electric gets a 95% braking regen efficiency | PluginCars.com

I expect a hydraulic system would be in major bleed-off after the the first 100 wheel revolutions too coming back down the hill.


Last edited by P-hack; 03-28-2015 at 04:17 PM..
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