They aren't going away (hydraulic hybrids)

[NeilBlanchard]

We'll see what the real world benefits are if/when this car comes out, I guess. It's all well and good that it has better efficiency for regenerative braking; but if it is limited in the energy storage, or if it weighs more (including protective structures), or if it costs more than the equivalent electric system, then it may or may not be useful.

The 1.4kWh Prius battery is not big enough in my opinion; so even given that it is less efficient at regathering energy, it's efficiency is limited by the storage capacity. So, if you are going to have a larger battery (as the Plugin Prius has), then it would be a huge benefit to be able to pre-charge it.

So, what is the energy storage capacity of this PSA Peugeot Citroën and Bosch system? Is it greater or less than the standard Prius?

[user removed]

Neil, the information in the articles I have read seems to be somewhat limited and probably contains some inaccuracies, either intentionally or in the information provided to the writer of the article itself. In particular the "air" hybrid statement, since there are definitely issues with using the atmosphere as a compressed gas source, with humidity and the potential of combustion when it could create danger. It may be that the same charateristic of spontaneous combustion of highly compressed atmosphere and any combustioble liquid or gas actually could become useful instead of undesirable and potentially dangerous. Injecting any combustible liquid or vapor into a atmoshere compressed to 3000 PSI could be potentially dangerous, but it could also be potentially beneficial, if done properly.

In my opinion and based on considerable research and investigation of my own, I believe the hydraulic system can be inbcorporated into a vehicle without any weight penalty, when you consider the considerable amount of conventional components that could be eliminated, basically the whole powertrain, if the drives replace the conventional braking system as they are in the configuration I envisage.

Driving the wheelsls directly whether inboard or in the wheels themselves replaces all of the mechanical connections between the power source and the wheels. It also eliminates the cumulative energy losses inherent in those same components. A third benefit is that hydraulic motors are most efficient at wheel speeds compared to engine or propshaft speeds. Direct drives with better designed motors offer efficiencies comparable to manual transmissions with low viscosity lubricants (IE ATF versus gear lube).

I believe eventually the battery electric will replace the IC engine in vehicles, as you do. The only question is how long will that transition take and at what cost? The development of a direct drive HH powertrain platform will enhance all other developments in materials and aerodynamics, a system that takes advantage of every improvement outside the powertrain itself.

My experience is unfortunately, it requires a dedicated commitment, with a fairly huge capital commitment, to the purpose of powertrain improvement. In the end, driving technique will have a much lower effect on overall vehicle mileage, but that may take decades to evolve.

To see Bosch and Peugeot make that commitment is a huge step in the right direction, and if my beliefs are correct, others will follow. At some pont in the future our beliefs and subsequent designs will merge into a transportation mode that is better than the sum of the parts and our design priorities. As Patrick Henry stated, we all need to hang together or we will be hung separately. Hopefully the end result will be a vehicle that adresses the legitimate concers about the effect on planetary climate before we actually reach a point of no return.

regards
Mech

[jamesqf]

Originally Posted by Old Mechanic

James seems to lack a lot of knowledge about hydraulic accumualtors and their application in a hybrid vehicles. Try studying the UPS hydraulic hybrid trucks which have been on the road for years.

I have. They're trucks, which means large & heavy, which means the weight of the hydraulic accumulator is not much of an issue. They're also DELIVERY trucks, which means that they have a largely stop & go drive cycle, which is perfectly suited to the limited but efficient hydraulic energy storage.

When you have acquired some knowledge and understanding the size of the UPS accumulators, in relation to the gross weight of the trucks (26,000 lbs), you will be better informed to make judgements about the amount of weight and space necessary, especially in a car weighing less than 10% of that amount. The weight penalty issue is non existant.

On the contrary. The UPS & similar HH trucks have very limited energy storage, just enough for a few starts (because in stop & go operation, the energy for each start is mostly replaced by the next braking). Very few cars spend much time being driven in stop & go cycles. (I suppose some applications, like urban taxis, might be.) You aren't going to store enough energy for 10-40 miles of driving in any sort of portable hydraulic accumulator.

Plenty of accumulators available today, with operating pressures of 3000 PSI which is what is used in many commercial applications right now...

Sure, and if they store significant amounts of energy, they are large & heavy. It's just physics - which determines how much energy is stored in compressed gas - and strength of materials.

The catastrophic failure issue has been resolved long ago.

Sure, by making the accumulators sufficiently strong, which means heavy.

As far as size and weight, to quote one of the EPA heads of the research in 2006, Charles Gray, "I can hold a 500 HP hydraulic motor in my hand."

Now who's dodging issues? The weight of the motor isn't the issue: the weight of the accumulator is.

When you get down to the basic physics involved, hydraulic energy storage is really nothing but a spring. You just can't store the same amount of energy (per mass) mechanically as you can chemically. It's why we use gunpowder instead of catapults.

[IamIan]

Originally Posted by Old Mechanic

What is the all electric range of a first generation Insight?

3.7 km on my 2000 started from stop and slight up hill , when I tested it back in 2006.
It just isn't as efficient as others due to ICE air pumping losses.
I personally never bought the interest others have in a EV mode on a non-Plug HEV... but that's just me... and a different topic.

Originally Posted by Old Mechanic

Hydraulic accumulators can reach 99% efficiency, while you loose 15% just charging the battery on a Nissan Leaf. Just filling the "tank".

Best wheel to wheel efficiency of regeneration.
Hydraulic-close to 80% (in 2006).
Electric- close to 33% (also in 2006).

Remembering wheel to wheel, the hydraulic option allows for P&G while maintaining constant speed while gas electric hybrids can not exploit the highest levels of efficiency of an IC engine without giving away that same efficiency in conversion losses.

While I agree that both electric and hydraulic options would loose the cycle efficiency when used as a constant vehicle speed variation of P&G ... but , the best wheel to wheel Electric is much better than 33%... ie the gap is smaller than that 33% vs 80%.

The IMA motor and inverter have a combine top energy efficiency of 92%.
(Added: up to 90% as low as 1,000 RPMs , nearly ICE idle speed )

I've tested my A123 Pouch cells at over 94% cycle energy efficient.
That would be a combine electric cycle of about ~79% mechanical back out of what you put in.

The IMA motor is not the best efficiency motor ... it tops out at 95% ... while other motor designs are up to 98% efficient ... and A123 cells might not be the very best cycle efficient battery as well ... so the upper end max using best technology would be higher than even the ~79%.

Of course some given specific HEV design could be lower ... maybe down to 1% cycle or something ... but that isn't a function of the HEV platform itself , as much as it is that specific HEV design , or application context... just like some specific hydraulic design could be lower than 80% cycle .. would also not be a function of the Hydraulic platform itself as much as that one specific design application.

- - - - -

Still ... I encourage all progress ... let the best tech win ... whatever that ends up being ... not just in raw capabilities ... but of course $ also matters... right now , HEV is on top ... if that changes because something else got better performance per $ ... great ... I look forward to seeing it commercialized more than HEVs have been.

[California98Civic]

Very interesting read. Thanks Mech for bringing it to the forum. When you think of all the interesting efficiency technologies that have come into service in the last 10-15 years and compare that to the previous decades, it is amazing. When we they let me have the Jetsons flying cars I wanted? I guess there are still another 49 years until 2062.

[Air-Hybrid]

Originally Posted by Old Mechanic

I believe the hydraulic system can be incorporated into a vehicle without any weight penalty, when you consider the considerable amount of conventional components that could be eliminated, basically the whole powertrain, if the drives replace the conventional braking system as they are in the configuration I envisage."

What's to stop a number of accumulators forming structural elements of the vehicle's chassis?


I would have thought the worst issue when using ambient air for compressing (rather than a separate heavy tank of dry N2) is not the oxygen component but the water, as it is likely to freeze when re-expanded.
Could some chemical process 'trap' the humidity on it's way into the system, and then use waste engine heat to 'free' the H20 again, as available? - this extra source of humidity could actually improve engine efficiency in some cases, could it not?

[user removed]

In the article they show a high and low pressure accumulator, which is a good indication of a closed system, which typically operates with an inert gas. Using air brings on the potential for an explosion, combining air with any trace of a combustible liquid or gas such as any lubricant could create the same process as a diesel engine, especially when you consider 3k PSI pressures which are many times greater than the general 400 PSI compression pressures of a diesel engine before the mixture is ignited. An inert gas eliminates that possibility.

The issue with accumulators being used as structural components would be the fact that there are dimensional differences between an accumulator at a low state of charge and a high state of charge, which requires the accumulator to be insulated from structural components. Basically the answer is yes for low pressure accumulators and no for high pressure accumulators. Tubular frame components might be used for fluid transfer, but the same expansion issues would exist in that application.

Since you are building a vehicle that is subject to catastrophic collisions then potential catastrophic leakage must be considered.

This is why they positioned the high pressure accumulator in the "transmission" tunnel, which is one of the safest places for survival in accidents. Safety must come first in a vehicle design.

When Va Tech looked at my design they calculated the power of each wheel drive at 35HP and 385 pounds feet of torque at 0 speed, which when you consider 4 separate drives means 140 HP and 1540 pounds feet of torque which would provide more than adequate performance in a Dodge (Mercedes) Sprinter size vehicle. Abs and traction control functions would be incorporated into the designs by variable stroke position control at each wheel individually.

regards
Mech

[jamesqf]

Originally Posted by Old Mechanic

Using air brings on the potential for an explosion, combining air with any trace of a combustible liquid or gas such as any lubricant could create the same process as a diesel engine, especially when you consider 3k PSI pressures which are many times greater than the general 400 PSI compression pressures of a diesel engine before the mixture is ignited. An inert gas eliminates that possibility.

There's another potential problem for automotive use. Compressing a gas creates heat (and uncompressing it absorbs heat), which is why scuba tanks are generally filled in a water bath. What happens to that heat in a car? Especially when you're doing something like descending a mountain?

[user removed]

Adressing the issue of the amount of power from a fully charged accumulator. You have a choice for range or weight. Balancing the two means you can increase range but you also increase system weight. Electric cars face this same issue with the additional consideration of battery cost as a factor.

In my opinion you want enough capacity for a single 0-70 acceleration event, as well as the capacity to recover the same energy in a single panic stop. This is your worst case scenario. Higher accumulator operating pressures mean greater storage capacity. Some here try to compare battery capacity to accumulator capacity, but you must understand the purpose of the two systems is not the same. One is the primary energy source, the other is a demand "shock absorber" with a high percentage of recovery capability.

Ian made a good point about the efficiency of electric regeneration. My counterpoint is a worst case scenario where you are forced to make a panic stop. In 20 revolutions of the wheels you have to recover your several hundreds of horsepower-seconds of energy in a vehicle weighing over 1 ton. That basically means every revolution of each wheel needs to be able to recover about 10 horsepower seconds of energy in a total time of a few seconds. In this scenario I am not aware of any electric powered vehicle with this capability. Maybe the KERS system in the new Formula 1 designs, but at what cost?

Primary propulsion is the "fuel tank", be it a battery or a tank of liquid fuel. A capacitive energy recovery system has a different purpose which is to smooth out the extreme variations in energy demand in a vehicle. Considering that coasting in neutral is 0 energy demand (engine off), the graph of energy demand goes from positive to negative, with positive being when you require primary fuel to provide power and negative when you have regenerative opportunities. Capacitive energy storage covers the extemes of the two demands, with negative being recovered for positive applications.

The resultant graph of energy demands goes from vasty changing points to a very flat graph with periods of replenishment when primary fuel sources provide for accumulator recharging. In either IC or electric vehicles the graph remains the same and in an electric vehicle you no longer need to modulate the amount of current to control vehicle speed. You only need an on or off switch to operate either the electric motor or the iC engine. No power modulation is necessary since the HH system performs that function irrelevant of engine-motor power production.

regards
Mech

[user removed]

Originally Posted by jamesqf

There's another potential problem for automotive use. Compressing a gas creates heat (and uncompressing it absorbs heat), which is why scuba tanks are generally filled in a water bath. What happens to that heat in a car? Especially when you're doing something like descending a mountain?

A good point james, compressing the gas in an accumulator means compressing the heat energy in the gas, most of the time measured in kelvin degrees. Decompressing the gas means it cools rapidly as it heats rapidly when compressed. The concentrated heat energy also contributes to the pressure of the compressed gas. I would think you would want to insulate the accumulator to conserve the heat energy for better overall efficiency.

In situations where you are faced with prolonged downhill grades where your capacity is not suffecient for recovery of all of the available energy you have two choices. In crease the size of the accumulator or bypass the accumulator with fluid passing through a variable restrictor to provide braking energy, but also loosing the potential energy you might recover otherwise.

This would require consideration of the driving environment and sizing the accumulator accordingly. In an electric vehicle, excess energy could be returned to the battery.

This scenario is also where all electric vehicles would also suffer dramatic range reductions. Consider the range of a Nissan Leaf if you drove it up Pikes Peak at maximum speed. It might not make it the 12 mile distance of the course.

regards
Mech