Hydraulic Hybrid

[NeilBlanchard]

Here's something that may be of interest:


(click on image for link)

The T&C will use a 2.4-liter, inline four-cylinder gasoline engine that will share motivation duties with a 117 cc engine pump, a 45 cc drive electric motor and a two-speed automatic transmission. The hydraulic fluid will be stored in a 14.4-gallon high pressure accumulator that can get up to 5,000 psi. If there's enough energy in the accumulator, the motor will shut down until it's needed again. If it all works as advertised, then overall fuel economy will be improved around 30-35 percent, while city miles per gallon will be improved by up to 60 percent.

Here's some additional articles:

http://gas2.org/2011/01/19/chrysler-...aulic-hybrids/

http://www.greencarcongress.com/2011...les-.html#more

[Frank Lee]

Huh. First link says hydraulic is quiet... second one says that's what they need to work on. I've been under the impression that hydraulic systems to date were objectionably noisy. Ever run a hydrostatic tractor? Hope they figure out how to quiet it down... I like the idea of hydraulic energy storage more than that of batteries, flywheels, etc..

[mort]

The problem for a car is that the self discharge rate for hydraulic storage is screwy.
But I like the idea and hope they can get these thing on the market.
-mort

[mnmarcus]

Originally Posted by mort

The problem for a car is that the self discharge rate for hydraulic storage is screwy.
But I like the idea and hope they can get these thing on the market.
-mort

What? You must be talking about the motors efficiency or losses in the plumbing of hydraulic systems...? If I close the valve on a hydraulic accumulator I could come back a year later and the psi(energy) would be nearly the same. Battery pack?... Not even close.

On top of that the reported brake regen for the EPA’s hydraulic hybrids typically capture at least 70 percent of the braking energy otherwise lost to heat. Estimates for electric hybrids capture more like 20 to 25 percent, because their batteries have comparatively poor power density.

high-pressure hydraulic accumulators usually charged in excess of 3,000 psi. The best of these accumulators have power densities of roughly 500 kW/kg, according to Jim O’Brien, founder and chief technology officer for Hybra Drive Systems, a start-up focusing on the development of hydraulic power trains.

I do not understand the 500 kW/kg -vs- 300W/kg... Hydraulics can't have almost 2000x the energy density of a typical Li-on battery pack... ?

See Lithium-ion battery - Wikipedia, the free encyclopedia

~250-~340 W/kg, Charge/discharge efficiency 80-90%, and Self-discharge rate of 8% at 21 °C -to- 31% at 60 °C. Cycle durability 400-1200 cycles.

[user removed]

500 KW seconds versus 300 W hours.
3600 seconds per hour.

Batteries can only accept energy at a fractional rate of what they can discharge energy.

How much do you need and how long do you need to store, energy wise.

Hydraulics can recover energy at the limit of the tires adhesion, and reapply the energy at the same rate.

Lets assume you have an 80% efficient hydraulic recovery system. The last I heard was 78% (2006). That's wheel to wheel in regenerative braking. Now lets think about the drive as being in the 80-82 % efficiency range. Not what a manual transmission would be efficiency wise, but with capabilities no manual can duplicate.

An accumulator allows you to limit engine operation to only best bsfc, no matter what the acceleration or regenerative state of the vehicle.

Every technique the hypermiler utilizes can be incorporated into the vehicle itself. No matter how fast you stop or start off from a light, the energy used for acceleration is basically the same.

The hydraulic system would allow acceleration to be accomplished with no fuel consumed. The engine and engine driven pump are either on, charging the accumulator or off when accumulator storage is at designed maximum.

Vastly more fuel is used in initial acceleration, and vast amounts of fuel are wasted in braking. This is exactly where the hydraulic system would allow no fuel to be used.
We hypermilers understand that and try to avoid both situations with significant results.

A purposely designed hydraulic hybrid does it itself, a self hypermiling car.

This is what most people do not understand. The hydraulic hybrid is capable of pulse and glide, while maintaining a constant speed. The new Hundai Sonata Hybrid does this same thing cycling between engine and battery power at cruising speeds. It accomplishes this by using the higher load of an engine driving the vehicle and charging the lithium battery. Then the engine shuts off and speed is maintained by the electric motor and battery for about 40 seconds at 60 MPH.

That is exactly what the hydraulic hybrid can do, and it has been proven in the Artemis design as well as the INNAS design. Automatic constant speed engine off P&G, without the speed variations necessary with a typical manual transmission vehicle. While the hydraulic drives may not be quite as efficient as a manual transmission, the difference could be so close that the constant speed versus the high peak speed in the pulse phase is a wash since total aero drag is lower at average speeds versus variable speeds when using pulse and glide, to say nothing about the effect of speed variations on other drivers around you.

In wheel drives eliminate the rest of the typical power train components, which would easily cover the weight of the accumulator. The mileage increase in both the INNAS and Artemis systems is 100 % combined cycle.

You can argue that the increase is not that great at higher speeds, but that holds true for any hybrid system. Sustained high speeds allow high bsfc levels with proper gearing in conventional vehicles with the Civic VX as an excellent example.

Better aero, rolling resistance, and light weight all contribute to better mileage. In the future hydraulic hybrid those improvements automatically mean better mileage.

regards
Mech

[user removed]

Originally Posted by Frank Lee

Huh. First link says hydraulic is quiet... second one says that's what they need to work on. I've been under the impression that hydraulic systems to date were objectionably noisy. Ever run a hydrostatic tractor? Hope they figure out how to quiet it down... I like the idea of hydraulic energy storage more than that of batteries, flywheels, etc..

Frank, I think you will find that most of the hydraulic noise issues are due to pressure fluctuations in piston driven pumps, which require dampners to absorb the fluctuations. It's one of the reasons I have always been an advocate of in wheel drives where tire noise is the major factor.

I am thrilled that Chrysler has decided to take the hydraulic route. Maybe, if I can get lucky I might get the chance to show them my design.

regards
Mech

[mnmarcus]

500 KW seconds versus 300 W hours.
3600 seconds per hour.

500 kW seconds -vs- 1,080,000 W seconds (which would be 1,080 kW seconds) would mean the avg. Li-on pack would dis/charge 2x as fast as the best hydraulics? Someone has made a mistake there.

But dropping the /kg units changes what we are talking about completely. Or is it 500 kW*sec/kg ? That might make more sense to me. That would mean you'd need twice (by weight) the accumulator to equal a Li-on pack...

So 2 identical engineless vehicles except ones has a 200 kg Li-on with an extra 200 kg "equalizer" weight added and the other has a 400 kg hydraulic accumulator. Say also each's motors are magically the same. They are fully charged and take off at max acceleration in a straight line until their respective packs are empty. IF discharge rates are the same they would run the same distance neck and neck till there packs were empty, right? Then the BOTH switch to recharge mode and start filling at max. The hydraulic recharges to only 80% because of inefficiencies until stopped while the electric charges to only about 25% in the same amount of time (but has not stopped?) The main advantage being that you can charge the accumulator more fully in the same amount of time than the Li-on?

[mort]

Originally Posted by mnmarcus

If I close the valve on a hydraulic accumulator I could come back a year later and the psi(energy) would be nearly the same.

You are forgetting heat. When the hydraulic system is fully charged it will have converted some energy to heat due to compressing the fluid. If you throw that heat away it is lost efficiency. If you store the heat and use the pressurized fluid soon, (like regenerative braking and then accelerating from a stop) you won't waste the heat. If you brake down a grade and park you may lose it all. For mineral oil like fluids the heat of compression is about .01 K per psi. At full charge the tank will be at 5000psi and about 345K. But when it cools to room temperature the pressure drops to about 4200psi. The residual 85% is there forever. A storage battery has more like a logarithmic self discharge, like a couple percent or remaining capacity per day.

Originally Posted by mnmarcus

Estimates for electric hybrids capture more like 20 to 25 percent, because their batteries have comparatively poor power density.

Ford claims nearly 94%

-mort

[mnmarcus]

An accumulator allows you to limit engine operation to only best bsfc, no matter what the acceleration or regenerative state of the vehicle.

Except that for every hp second you put into the accumulator at 80% efficiency you can only put .64 hp to the ground because you are doubling your losses. Meaning the best FE may not be to run at best BSFC but to throttle back on ICE and run through a more efficient drive train. A 36% drop in efficiency is significant so the "island of better FE through engine throttle" would be large.

[user removed]

Guys the 80% is wheel to wheel. Not wheel to accumulator, make that 90+%. Heat losses from the compressed gas in the accululator would be a factor over time but that assumes a completely discharged accumulator and no insulation factor over the pressurized gas portion of the accumulator.

The accumulator can discharge completely in seconds, try that with a battery.

One 0-60 stop is the amount of energy needed to maintain 60 MPH for .7 mile.

Comparing batteries to accumulators is false logic. An accumulator is more like a capacitor, and remember a properly designed HH would weigh the same or less than a conventional car. There are even HH bicycles.

Long term storage is the batterie's forte, as far as energy density, while an accumulator has a practically unlimited durability and when the bladder wears out it is easily rebuildable.

If you want a limited range use a battery for your consumable energy storage, no law is written that limits a HH to an IC engine. In fact you could have exchangeable power modules of both types, or if you want increased vehicle weight both modules could be in the vehicle all the time.

Accumulators could also be designed differently to incorporate them into the vehicle's structure. You won't see that with batteries in our lifetimes.

regards
Mech