Infinitly Variable Transmission

As far as i know, in past times some hydraulic trasmissions have been attempted in car too. The presence of idraulic converter in some automatic gear boxes is a witness of that. In past there were, or still there are, trucks that used widely the hydraulic transmission, recently the Truck Transmission division of Eaton corporation had an important recognition for such a kind of application. Many caterpillar and earth moving machines use the hydraulic tramissions and torque multipliers.

For cars the constant difficulty is that generically hydraulic transmissions have a lower efficiency than the corresponding mechanical types; even if compared to an hydraulic one a mechanical transmission is a mess of belts, wheels and selectors (plus an expensive control).
Meaning that in a mechanical transmission if the energy gettin in is 100, the energy coming out is 80. In an hydraulic transmission losses were hygher, resulting in worse fuel consumption.

It is a good bet that the first company realizing a good, cost effective, hydraulic or electric transmission with total efficiency higher than 85% could have a competitive product compared to the mechanical types. If efficiency will reach more than 90%, they will hold the market of trasmissions as far as they want (may be these data have to be updated +/- 2 or 3 %).

Not easy but a good challendge to become great engineers.

I'm not sure I understand your statement: "A constant pressure wobble pump would provide maximum torque at any engine speed, and engine speed would be a function of torque demand" as it would relate to the hydraulic motor over a range of required torques and desired speeds at the wheels. There are a number of "wobble pump" variations and you don't say by what means the constant pressure output is achieved ... is it by variable displacement? Is there a bypass regulator? Are you also using a variable displacement motor?

Could you explain in more detail?

If you mean a single hydraulic motor to drive the wheels, you have described a hydrostatic transmission. These are used to good effect on many pieces of heavy equipment, and also even on some garden tractors. They excel at transmitting power and multiplying torque smoothly at relatively low speeds. Additionally, many pieces of construction equipment are powered at their wheels by hydraulic motors. This makes good sense when a hydraulic pump is needed for other purposes and there is only a low speed requirement for the vehicle. There were several models of diesel-hydraulic (as opposed to diesel-electric) locomotives but they were discontinued as far as I know.

There have been a number of attempts to utilize hydraulic pump and motor arrangements to drive a vehicle but so far, none have succeeded except for special applications. Chrysler combined a hydraulic torque converter with a clutch and manual transmission around the late 1940s / early 50s, which eliminated the problem of "popping the clutch" or lurches when starting off or shifting gears. They called it "Fluid Drive". You could start off smoothly in second gear, and with care even in third, (if you didn't mind abysmal pickup) although it was definitely not recommended. General Motors made two attemps that I know of that were hydraulic automatic transmissions, in particular the Buick Dynaflo and closely related Chevrolet Turboglide transmissions in the 1950s. These were essentially enhanced torque converters that could multiply torque enough that they didn't shift gears in operation. However, there was at least one optional lower gear ratio besides the "normal" one. I know that the Turboglide had a low gear they called "Grade", and I believe the Dynaflo called theirs "Lo". Meanwhile most automatic transmissions make extensive use of hydraulics to operate clutches, shift gears, and their torque converter is in essence a pump and motor arrangement, typically in an axial pump/turbine configuration.

Bottom line, in general, a pure hydraulic drive for an automobile, that has to operate over a very wide range of torques and speeds, without the benefit of different gear ratios would be more costly, heavier, and less efficient than present transmissions when all components were considered. Many, if not most of the the current crop of infinitely variable transmissions are popular with the car makers because they are cheap, and if reasonably well engineered are popular with car buyers because they are "smooth". Also, most current auto transmissions of all types "lock-up" the torque converter section at highway speeds to maximize efficiency.

Finally, some hybrid cars are a step in the conceptual direction of an electric analog to the hydraulic pump/motor. While they still have a "conventional" transmission of some kind, the gas engine generally operates only in its most efficient speed and load ranges, which improves overall economy and minimizes pollution.

Perhaps the following will give you some answer as to the latest innovation in tranmission of power along your description:

http://www.torvec.com/products_ivt.html

In response to VentureBC: Interesting! Thanks for the link.

It is always exciting to see the hitherto highly improbable made plausible. That is one of the things that makes the engineering field so interesting.

The Torvec design certainly seems to be a potential solution, although it must be kept in mind that Torvec is primarily a developmental company only, and hopes to market their technology and patents. Their IVT (infinitely variable transmission) is not only not in production, it is not far beyond the proof of principle stage at this point. They say it can be used "with no cost penalty over existing transmissions" but give no indication on whether that is based strictly on unit cost or includes projected fuel savings factored in, which may be the case. For instance when you factor in the higher initial cost of many hybrids, their subsidies, and future battery replacement costs, applying the time value of money, even though they get better mileage, they don't really save much if anything at present fuel costs.) An additional interesting twist is Torvec's investigating the possibility of using hydraulic accumulators to store energy such as from regenerative braking, which with their IVT would mean a kind of gas/hydraulic hybrid.

They apparently have two basic models for different vehicle applications: a hydromechanical one and a pure hydraulic one. See: http://www.investorshub.com/boards/board.asp?board_id=2255

For one "unbiased" view you can check here:

http://www.autoblog.com/2006/08/07/torvec-targets-medium-duty-market-with-new-infinitely-variable-t/

Definitely something to keep our eyes on along with other "infinitely" (continuously) variable transmission developments both in hydraulic and in competing technologies.

http://www.torotrak.com/

History also tells us not to count out the ongoing improvements in existing drivetrain technologies or combination thereof.

Don't forget the heat. Hydraulic transmision generate a lot of heat. The high temperature of oil must be reduced. This cost more energy from the engine. Field sprayers with 4x4 hydraulic transmision uses an hydraulic 10 HP motor to drive the wing of oil-air chiller.

Car/truck transmissions use Spur gears -- whose transmission efficiency is close to 99%

Hydraulic Pump+Piping+valves+wobble-plate- motor will have an end-to -end transmission efficiency close to 80%

At the kind of wheel RPM's needed by vehicles on the road there simply is no hydraulic motor

And typically the mass (weight) of Hydraulic motors will be 5 times heavier than axle/propeller/differential gear combination.

Hydraulic motors excel at Very- slow + High-Torque drives.

Try to think such a device:

1) divide the speed and get high torque

2) put an hydraulic transmission

3) multiply back the speed

it is expensive, it is heavy but it works . . .

so please, open your mind and stop stating your own truth: we are not integrallystic engineers.

If some people reach the moon and other stay always on earth there is a reason:

Nothing is impossible

excuse for being rude.

Keeping an open mind is a worthy goal and not always easy to achieve.

On the other hand, an open mind derived from ignorance of physical "laws" isn't necessarily a good thing at all.

Your post sounds very much like you are saying you can multiply torque by trading off speed, then get the speed back with no loss in torque ... and that is IMPOSSIBLE! In simple terms they are linked inversely: half the speed will yield twice the torque, minus losses, and twice the speed will yield half the torque, again, minus losses. Except for the magnitude of the losses, it doesn't matter how you achieve this tradeoff, but it will happen.

While life is full of surprises, and current "laws" which are scientifically speaking theories that have not up until now been found wanting are constantly being tested at their extremes. The key word here is "extremes". In anything even remotely pertaining to transmissions here, there are inviolate physical laws that apply.

BTW, did you notice that this is an ENGINEERING forum. Just because it is in no way limited to professionals doesn't mean one can feel free to disrespect the underlying physics.

That "some people reached the moon" was a testament to sound engineering principles and the application of physics ... NOT because they were too ignorant to know they "couldn't go there".

We who strive to apply sound scientific principles can (speaking for myself) make enough mistakes without the introduction of ignorance masquerading as a creative open mind.

Saying "Nothing is impossible" is a bit of a stretch, don't you think?

Respectable sir,

I take as good your observations.
Just desire to explain that my comments were due to the absolutistic intonation of the previous sentence about application of knowledge on hydraulic transmissions and gears: a car transmission is never a single couple of gears and the net efficiency is lower than 99 % !

Knowledge is not to fix limits to ourselves and to the others, but it is to direct the proper ways towards possible goals.
This was the meaning of the comment, it was enclosed in the final excuses but the comment was an irritated one.

Probably we are meaning the very similar things with different words.

Well put.

I suspect that Greg jumped to the conclusion that you were claiming that you could multiply speed while retaining the same torque. I think it is clear that this was not what you were saying, particularly since you started with the suggestion of reducing speed to gain torque (indicating that you were aware that the corollary would also apply).

Your proposal (in post 6) makes sense. It happens that virtually all existing hydrostatic transmissions are for low speed use, so for experimentation especially, first reducing speed to suit the transmission and then multiplying it to achieve a desired road speed would enable you to experiment with a hydrostatic transmission in a road vehicle. As you said, heavy and expensive, but useful for making the possibilities tangible. (In fact, for a prototype, I considered using exactly that strategy, with an available hydrostatic transmission.)

Personally, I am sceptical of the claims for the Hydristor re efficiency, but the inventor claims 97% transmission efficiency, if I recall correctly. On the other hand, he makes several other claims (such as having more than doubled the fuel efficiency of his old Camaro by simply changing gearing to what are now pretty standard ratios) that can only be seen as outlandish. Other claims (such as that 50% of the energy used during acceleration is used only to accelerate the engine's rotating mass, leaving 50% to accelerate the car itself) are absurd. But perhaps the Hydristor itself operates with high efficiency, despite claims that seem to erode rather than buttress support for the invention.

If a hydrostatic transmission were truly hydrostatic (not hydrodynamic) then its efficiency could be as high as other mechanical methods for "gearing" (in the broad sense, to include pulleys, etc.). However, hydrostatic transmissions have to deal with hydrodynamic effects: turbulence, viscosity effects, fluid friction, fluid inertia, etc, all of which reduce efficiency.

I am a "fan" of hydrostatics, and have considered their use in a vehicle I am prototyping. However, the more purely mechanical means for providing CVT or IVT seem to be more efficient, right now. Until the inventors of things like the Hydristor can put their transmissions into controlled studies (such as running identical cars, with standard transmissions vs the invention, on identical courses, repeatedly), then there will always be many skeptics.

Interestingly enough, even heavy equipment now uses electrical drives rather than hydrostatics for tractive force. Some of us think of heavy equipment as being rather low tech, but, in fact, the drive systems are more sophisticated than virtually all cars, other than the Prius, Insight, etc.

Ken, The 72 Camaro was still a simple layout, no smog pumps, air injection reactor, EGR, etc, just a simple car! A 1990 Caprice 350 with 700R4 lockup and a much larger frontal area will ideally reach 25 Mpg at 70 Mph and the engine turns at 2,250. The Camaro did get into the 35 Mpg range just in time for the first gas crises in 1972. I used to fill up the 14 gallon tank, drive 202 miles to an engineering job at Dupont in Wilmington, Delaware from Binghamton, New york, drive around town all week and then drive home Friday night and refill the tank on Monday at 2 AM for the trip back to Dupont.

With the Hydristor system, I will be able to routinely disconnect the engine from the hydraulics, even shutting it off until more energy is needed and run off hydraulic accumulator tanks. The Hydristor can efficiently recycle the energy of forward motion and keep the engine at idle or completely off. There will be blazing performance for all vehicles since an AWD vehicle like the Expedition can deliver '1 g' starts and stops for gas or diesel power. This is a true hybrid and is completely retrofittable to everything. Regarding the 50% mention, what happens to the horsepower developed by the engine in neutral when you floor the gas and the tach zooms up to redline? What happens to your acceleration on the drag strip when you put too high of a numerical rear gear in and find that you are taking longer to traverse the quarter? Ask any professional old school racer. The 300 Hp Corvette was making 300 Hp as the tach hit 6,000+ when the transmission was in neutral and ALL of that horsepower was going into accelerating the total engine inertial flywheel effect with NONE going to accelerate the car. I call that 100/nothing. If you tried to start in top gear, you would be severely limited in 'developed power' because the engine would be seriously lugged down and therefore not be making much power (with a burning clutch). The law of physics is called 'Maximum Power Transfer' and it is usually applied to electronics where drive and load 'impedances' are matched as in amplifiers and speakers. The mathematical anologies convert directly to rotating flywheel inertias and developed horsepower. By the way, the required 'horsepower' (not torque) from a standstill (at the instant of zero speed but starting to accelerate) is the same for a bicycle as for a locomotive; ZERO. That is because horsepower is the instantenous mathematical product of force and speed; and the initial speed is zero (another name for no load) so the initial horsepower load is zero. To recap, the engine is 'lugged down' at startup thus creating minimal power at lower Rpms; half or more of the developed horsepower (ideal ratio) is sucked up by the engine's rotating mass (flywheel inertia) and the initial load is zero. Does that sound like a well engineered drive system? That is why CVTs and IVTs are becoming more popular because they somewhat address the problem I outlined. The Hydristor is really in a class by itself in that it is economically feasable as a retrofit, lowers vehicle weight, and can efficiently do a number of hydrostatically but fluidically common jobs while substantially raising fuel economy and lowering CO2 emissions. You can call me at 607-2068960 to discuss. My e-mail is tkasmer(at)yahoo.com Tom Kasmer

If you have had the experience of revving an engine to near redline, then you will realize that 1. It takes little throttle to do so -- in the old pre rev-limiter days, you could scatter an engine by holding the throttle open for more than a second or so. 2. It takes very little time, because so little energy is expended.

If an engine is held just short of redline with the small throttle opening required to do so, it is producing no useful hp beyond that required to run the accessories. You can prove that to yourself by putting a car on a dyno, and backing the load all the way off. You'll find that the hp produced is very little. Only as you apply load does the torque and therefore hp start to increase. Once you have the engine at full throttle and held with load to the desired RPM do you then know the hp produced at that RPM.

For the purposes of the discussion of energy used to accelerate the flywheel and crank vs that required to accelerate the car as a whole, the ratio is essentially the same as the ratio of the masses: 3500# or car, 35# of flywheel and crank. Of course you are accelerating the rotating parts in two ways, rotationally, and down the road, but the ratio between mass of the car vs mass of the rotating parts is so high that it makes little difference.

You can do the math yourself to verify that spinning up a flywheel takes very little energy:

http://en.wikipedia.org/wiki/Flywheel_energy_storage

The formula there will give you the kinetic energy of the flywheel and crank (35 lb) (You could use r=6", rpm = 2200). Compare that to the kinetic energy of the entire 3500 lb car at 60 mph (where the rpm is also roughly 2200 rpm).

Whether you get to 60 by using 1,2,3 or more gear ratios along the way, the energy consumption will be roughly the same. The only reason it is not exactly the same has to do with the various transmissions' abilities to keep the engine running at a load and rpm where its bsfc is best (and of course internal transmission losses). But for the large engines you been writing about, these curves are surprisingly flat in the range in which the engine will be running in ordinary usage: it won't be too far, one way or another from its torque peak bsfc, no doubt in the range .55 to .65.

Elsewhere on this site we discussed the EPA's hydraulic hybrid design for the UPS trucks. If you search for that, you'll see that the entire group of accumulators (1000# plus) has about 1/3 the energy storage capacity of a Prius's 88# battery. To accumulate a lot of energy hydraulically requires extremely high pressures, or huge volumes.

But I think your transmission is pretty neat, even if I question your numbers. Good luck with it.

Ken, Regarding my 'hypothetical' point of revving the Corvette engine in neutral; it was meant to hypothetically show that ALL the engine's developed horsepower under a 'theoretical floored pedel' would flow into the engine's total flywheel moment and NONE would go to accelerate the car. I was not suggesting actually doing this and blowing the engine. A very very high numerical overall ratio like 1,000:1 would result in a very small fraction of the 'developed' horsepower' accelerating the car with the engine virtually untaxed. A lesser ratio like 100:1 would harvest more of the engine power during acceleration with a slightly increased load on the engine. When you get down to 10:1, you are nearing the point of maximum power transfer. If you drop to 3:1 (rear ratio) and start in direct high gear, the engine is very overloaded and virtually all of it's developed power goes to accelerate. However, the engine is seriously lugged down and doesn't make much power so the 0-60 time gets very large. Thus, there is an ideal overall gear ratio which results in the quickest 0-60 time and I call that maximum power transfer ratio (50% of the developed engine power). That occurs when the reflected vehicle mass-to-inertia load is equal to the engine total flywheel effect.

The total engine flywheel moment consists of the combined total of all the individual rotating component flywheel moments including things like pushrods and rocker arms sinusoidally converted to component inertia, etc, etc. For a Chevy V-8 engine, that total number is ONE slug-feet squared in the English system of units. A 3,216 pound car mas a mass number of 100 slug-feet2. A typical drive tire rolling radius is 12 inches or 1 foot. The mass of the car can be thought of as being located at the point of the tire patch relative to the rotating drive axle. The 'flywheel inertia' of the car is therefore I = MR2 or (100) (1 squared) or 100 slug-feet2. (sorry about the creative formulas, my keyboard is not scientific notation). Inertias reflect through a gear ratio by N-squared (NxN). Assume a 3.1622:1 rear end ratio. Thus, NxN is (3.1622) times (3.1622) or 10. Thus, the drive shaft reduced the vehicle reflected inertia from 100 at the drive axle to 10 at the drive shaft because of the 3.1622 rear end ratio. When the transmission gearbox ratios are included in the equation, say in first gear, (assume first gear is also 3.1622 so that N1xN1 (N1 squared) = 10), there is another gear number squared reduction of the reflected vehicle mass and the engine driving the transmission now sees a reflected flywheel inertia of '1 slug-ft2' of the vehicle reflected inertial load or exactly equal to the engine. So, when the engine accelerates with double it's unloaded total flywheel inertia, half of the developed power goes to accelerate the engine and the other half goes to the car for gear translation into linear acceleration. If you raise the rear end ratio to 4.70, the reflected flywheel inertia presented to the engine is smaller and the lesser loaded engine revs quicker but the higher numerical rear end lowers the resulting linear acceleration. Ask any professional drag racer from the early days of drag cars. If you try to start the 3.1622 rear car in 2nd gear, more of the engine's power goes to accelerate the car BUT the higher load (than 50-50) on the engine limits it's ability to develop horsepower resulting again in a slower acceleration to 60 than the ideal 50-50 case. I have proven this concept many times in engineering of various servo systems, both military and commercial. It is not a well known relationship in engineering. You can find the 'Law of Maximum Power Transfer' in the annuls of physics but it is formulated in electrical impedance terms. The math is totally anologous. For example, electrical impedances reflect through a transformer 'ratio' by the turns ratio squared. An example would be a 100 watt amplifier designed for 8 ohm speakers. At 100 watts output into the 8 ohm speaker, an identical 100 watts is lost in the internal amplifier impedance, hence maximum power transfer or 50-50. If you connect a 4 ohm speaker, the amplifier is overloaded and more than 100 watts is lost in the internal amplifier impedance with less than 100 watts out in the 4 ohm speaker. That is anologous to accelerating the car in high gear where the engine is severely overloaded. If you had used a 16 ohm speaker, the amplifier would not reach 100 watts out and the amplifier would only be partially loaded. Hence, maximum power transfer occurs when the load impedance is equal to the drive impedance. In inertias, maximum power transfer occurs when the load inertia is equal to the drive inertia in the same way with minimum 0-60 time resulting from 'maximum horsepower transfer.

Any transmission having discrete numerical ratios will suffer from this limitation. They just weigh more, cost more to buy and fix and take up space in the car while doing a less than ideal job of efficient propulsion. An IVT like the Hydristor is ideal because it directly drives the output as a torque converter including reverse and infinitely changes ratio like a variable sheave snowmobile and is unlimited in ratio range unlike the snowmobile. 95+ % of the engine's developed power is available for acceleration and the Hydristor can develop full hydraulic braking and energy storage where the energy can be re-used to drive the vehicle. The engine can even be cycled on and off with the Hydristor efficiently restarting the engine when needed. This is a full hydraulic hybrid with full braking capacity from high speed. The electric hybrids cannot do this. A large vehicle like the 7,000 pound Expedition at 70 Mph will develop a braking road horsepower of 1,120 at the first instant of application of the brakes to reach 1g of braking deceleration (for the first ? millisecond) decaying to zero linearly at 1g. That is 825 .73 kilowatts of instantenous dissipation, nearly a megawatt. That is 3,440 amps at a battery supply voltage of 240 volts. Who wants to sit in a car with kind of magnetic field roasting your body parts? What kind of battery will take that? The electric hybrid is not the answer by itself but a combination of Hydristor and electrics could be the final solution. The Hydristor handles the huge road horsepower loads and the electrics handle light, 'average power' loads. That is what I am working on. Regards Tom 607-2068960

Tom,

Sorry, but I'll have to leave this discussion. Much of what you say makes little sense to me. Your post reads, to me, like those of people promoting 300 MPG carburetors. Perhaps you are a nice guy, simply lacking exposure to the most basic physics and math – but you claim to be an engineer? Puzzling. Nevertheless, you took the time to write, so I'll respond.

Your theory that the flywheel effect of the engine and its internal components somehow sucks up large amounts of power is simply wrong. You say: "half or more of the developed horsepower (ideal ratio) is sucked up by the engine's rotating mass (flywheel inertia)" You seem fond of bringing old drag racers into the discussion. Here's what one says:

• "Said Johnson, "Today's Pro Stockers develop 800 foot-pounds of torque, and when multiplied by the 3.1:1 transmission ratio, it amounts to about 2,480 foot-pounds of torque. Add to that the rotational inertia of the flywheel and driveshaft, and you're well over 2,500 foot-pounds. I developed a new rear-end housing for our applications in 1997 that is basically just bigger and stronger to deal with these issues. It's pretty much the same as what the alcohol cars use."

Clearly, flywheel affect is a very small part of the total (20 parts in 2500, <1 percent). But don't take my word for it… or his. Do the math. It takes a large amount of energy to accelerate a 3200 lb car, and a small amount of energy to accelerate the rotating components of an engine. Only in lawn tractors (operating at extremely high gearing ratios) and in cars in which the drive wheels are furiously spinning (but the car is accelerating slowly), can you get close to half the energy lost to accelerating internal engine components (or, for that matter, all the rotating pieces in the entire drivetrain).

Once you get further into the math and quasi-physics of your post, you lose me entirely. For example, "moment," to me, means torque, just as it does to physicists and engineers around the world. The common English system unit for torque is Lb-Ft: a force times a distance. You say:

• "The total engine flywheel moment consists of the combined total of all the individual rotating component flywheel moments including things like pushrods and rocker arms sinusoidally converted to component inertia, etc, etc. For a Chevy V-8 engine, that total number is ONE slug-feet squared in the English system of units."

Thus, you are saying that torque is a mass times a distance times a distance. That's non-sensical, at least for me. You might try some of your calculations in Google, which keeps track of units (even mixed units from different systems) very well. You will find that Google will not output a torque as mass x distance x distance.

Perhaps you were using "moment" to mean "moment of inertia." But then, the discussion becomes even more nonsensical: are we comparing the energy required to spin the car on it axis, vs spinning the engine bits on their axes? If so, the ratios are still anything but 50-50, but the calculation has no utility in a discussion of transmission efficiency.

You go on to say:

• "A 3,216 pound car mas a mass number of 100 slug-feet2."

Again, the units are astounding. A 3216 pound has a mass of 100 slugs, not 100 slug-feet2 (which from context, I can only assume means 32 slug feet squared). You continue to do this sort of thing throughout, making the whole post incomprehensible, other than when read naively and uncritically. But as if the ludicrous math were not enough, you throw in theories from electronics to further confound what should be a simple issue. (Certainly, all Newtonian physics stem from some simple common principals, but applying a relatively complex law from electronics as an analogy for a simple task in mechanics can only be seen as deliberate obfuscation. It's like explaining a lever in terms Bernoulli's principal.) It is as if you deliberately want to leave people so thoroughly confused, so that they will accept your unrealistic claims.

Every day, automotive engineers calculate accelerations of cars and trucks using tractive force versus mass. Tractive force can be easily calculated from engine torque, overall gear ratio and tire radius. Whether the ratios involved are discrete or continuous does not change the fundamental calculations, which are simple and don't rely on exotic analogies or hearsay from old drag racers. If you want to look at ten ratios (out of an infinite number) or twenty, you quickly come to the conclusion that beyond five or six, it really makes no difference: engines have sufficiently broad torque curves that the small differences in ratio don't make a large differences in any aspect of performance. If you want to ignore the math, and look at practical examples, then there is the Audi, available with a very efficient CVT, a manual, and a conventional automatic. The CVT matches the manual almost perfectly in every aspect of performance, meaning that its infinite number of ratios makes little difference. In fact, Audi even includes a six speed mode, (in which discrete ratios are selected), because performance is not measurably different, but people find it more familiar feeling.

You claim to be able to accumulate hydraulic energy (presumably in some useful, practical way). The huge accumulators in the UPS trucks indicate that such accumulation is not practical for any vehicle in which reasonable weight is a virtue. Again, the math is simple, and if you do it, you find that the 1000 lb accumulators on the UPS trucks store a fraction of the energy of the 88 lb battery in the Prius. It is a laughably small amount of energy stored very inefficiently. Sure, energy can be stored in many forms. But there are realistic, proven methods (as in the Prius) and some that are not-so-realistic. If we simply want to dream… why not carry around a 500 foot water tower on the back of your Prius? I presume you are hoping that people will know little about hydraulics, and simply accept at face value that energy storage via hydraulics is simple, practical, and economical. But don't take my word for it: do the math. What pressure and volume are required to even match the tiny storage capability of a Prius battery, let alone the massive requirements for an Expedition. (Of course, a 1 G stop is not fully recovered by electrics without very large capacitors, but designing a regenerative system for 1 G panic stops [especially in an Expedition, which can only manage a .9 G stop in full panic mode] is silly: panic stops occur infrequently.)

If I were to be convinced that your project is legit, then the math would need to be legit. In my view it is not. But that is only my view. Perhaps you can convince others.

In any case, good luck with your project: my hope is that it is a great idea, and that you are not really trying to be confusing.

Ken, I had second thoughts about trying to draft a respectful and insightful response to your previous post. My concerns were about the difficulty in trying to explain concepts that are not in the mainstream. I learned something from your present response. I too am out of this discussion and will spend more time completing my work and less time worrying about naysayers.

wouldn't the fluid-friction losses incurred from moving hydraulic fluid at the high-rates needed for highway speeds be tremendous? Not to mention the inertia of all the fluid pumping through the system wouldn't that effect quick speed changes? Just thinking out loud..

I always assumed this is why it works well for slower moving vehicles like the diesel lawn tractor I used to operate (hydrostatic).

Use bigger, lighter, aerodynamic wheels and put that torque to work.

Maybe on Mars

The wobble pump I had in mind was typical of those used by jet aircraft. It puts out 3000psi regardless of engine speed and is about the size of a soccer ball cut in half and uses about 150HP of engine power at full output. It would be coupled to a single positive displacement hydraulic motor integrated with the pump and a simple speed control valve. No plumbing would be required except for external cooling. It would output to a standard drive shaft/differential.

A shaft lock would be employed at cruise speed to drive direct from the engine so there would not be any heat generation during cruise.

The system would also employ a 3000psi accumulator so the engine would not have to be running when the vehicle is stopped. It would not even require a starter motor as the pump would be used as a starter motor with power provided by the charge in the accumulator. Vehicle breaking energy would also be recovered to further charge the accumulator and pressure would be retained for days/weeks/months. If the pressure was ever released for whatever reason, it could be recharged with a small hand pump enough to start the engine.

Basicly, the engine only needs to run to keep the accumulator charged and to provide direct drive at the desired cruise speed. During acceleration at cruise speed the accumulator would provide extra boost power beyond the engine power. Theoretically a 150 HP engine could provide 300 HP (minus losses) at the wheels during brief acceleration. Maybe more if you go with a more powerful hydraulic motor and larger accumulator.(or higher operating pressure)

Theoretically, pigs could fly if they had wings. You are describing ideal system characteristics then employing erroneous ways to achieve them. The system operates at 3000 constant psi, and performs the role of a continuously variable transmission. How will a 3000 psi acumulator make any contribution when the pump constantly maintains that pressure? The moment you start to draw from the accumulator the pressure drops below 3000 psi then what? You have a positive displacement motor with only a simple "speed control valve", yet you are making all sorts of capability claims and none of it represents the use of anything at all new, rather only the misuse.

It sounds great but the execution fails .... What you are describing is certainly possible but not by the way you say to do it. And just being possible is not the same as practical in the big scheme of things.

While I am not familiar with hydraulic pumps used on jet engines, the constant pressure "regardless" of rpm means it is in fact or equivalence a variable displacement pump. There will of course be a threshold rpm for achieving that pressure at high flowrates ... that would be a factor of the maximum pump displacement. For the arrangement you describe, you want a variable displacement motor, NOT a positive displacement one. Since the pressure will presumably be constant, you want to vary the mechanical advantage over different flowrates (torque versus hydraulic motor rpm) since you are not changing gears.

A positive displacement motor tends (system losses increase with flowrate) to have the same torque at the same at the same pressure regardless of speed. You need high torque, low rpms, with high flows to accelerate in order to get the power from the engine to the wheels. At cruising speeds you want less torque and maximum hydraulic motor rpm with minimum flow.

Yes Greg, you are right. It would require a variable displacement pump That is what aircraft hydraulic pumps are. They are a wobble pump, but instead of using a fixed pitch wobble plate, they employ a "swash" plate, much like the swash plate that controls the rotor pitch angle on a helicopter.The pitch angle is proportional to the flow demand. Of course a threshold engine speed is required to maintain 3000psi under full load. Values are chosen to achieve that threshold at the optimal torque range of the engine.

And Greg, your last point could be addressed by using a wobble pump as the motor to give you max rpm/min flow. The "throttle' would be the pitch control of the driven motor. Maybe another type of variable displacement motor could be used instead I;m not sure wobble pumps make good motors when used in reverse application.

TYCHE, I respect the additional effort you have made to refine your idea in the face of my (blunt) critiques on specifics. That is one of the ways we learn.

You also showed tenacity in holding on to the belief in your idea which is admirable, provided the idea doesn't require breaking any "laws" of physics, and your overall idea does not break any.

Good luck, do your homework, and who knows?

Thank you Greg. I appreciate your blunt critique. No offense taken. It's just an idea that has been kicking around in my head since I've been reading about newer small cars employing belt driven IVTs. They seem on the face of it, a sloppy way to go. I like the idea, but I would never buy one.

As a retired flight test engineer, I think there is a more elegant solution.

Previous (GUEST) was TYCHE

Tom Kasmer, the inventor of the Hydristor, has visited this website, and he has developed one such transmission.

The generic transmission you describe has been in use for many years in lawn tractors and other equipment, and goes by the name hydrostatic transmission. They are reasonably efficient (less efficient than simple multiple speed gearboxes) and do offer the advantage of allowing the engine to run near its torque peak (where it is most efficient) most of the time. In a lawn tractor application, the engine speed is generally left constant, and speed control is entirely through the transmission -- from 0 to full speed. Speed control as very low speeds is excellent, and available wheel torque at those speed is very high. At higher speeds, the control over speed can be rather abrupt, and I think the Hydristor may improve on this.

In the Hydristor, the inventor suggests using a hydraulic accumulator for regenerative braking. However, in my view, the size of tank required for meaningful energy storage is too large to be practical.

In general, hydrostatic transmissions require more precise machining than do other transmissions, and as you say, fluid friction generates some inefficiency. If you take apart the hydrostatic transmission from a tractor and compare it to the CVT transmission of a motor scooter, you will find far fewer and cheaper parts in the latter.

I see your point on the regenerative braking aspect. He's probably correct. An accumulator might just prevent abrupt surges. The idea of always running the engine at high speeds is probably just for simplification in lawn tractor use. But I'll look into them. Thanx

You are right, re lawn tractor use -- such tractors are equipped with throttles, but they are generally set (by the user) at some convenient speed, and the hydrostatic speed (ratio) control is used to change the tractor speed. If you are interested in experimenting you can buy a new surplus lawn tractor hydrostatic transmission for a couple hundred dollars.

In another thread here, this idea came up. (If you search for Kasmer, you'll find the thread.) There, I mentioned having a friend who made a VW-powered dragster with hydraulic motors in each wheel. It was powered by a 40 hp VW engine (driving a pump), but would smoke all four tires. The accumulator was huge. If you do the calculations for something a little more reasonable (such as being able to store enough going down a half mile hill to push you most of the way back up the other side) you find that the accumulator size must be very large. In standard units, PSI x GPM / 1714 = HP. So, for 15 hp, you'd need 8.57 GPM at 3000 psi. If you wanted to be able to supply 15 hp for 5 minutes (as a current Prius hybrid can) you'd need a 43 gallon accumulator, which is many times larger and heavier than its 80 lb battery pack. (The fluid alone would be about 300 lbs.) (Of course, to be realistic, your accumulator would need to be twice this size, to allow for the pressure drop as fluid is used.)

Continuously variable transmissions alone (Audi makes both standard and CVT models for comparison) make small improvements in fuel mileage and acceleration rates. To make large improvements, some form of hybridizing is necessary, and then about a 30 - 40% improvement in fuel economy can be achieved in stop and go driving. Although hydraulics seem to be a good alternative, they suffer from low storage efficiency (at ordinary pressures) and low operating efficiency due to fluid friction. Electric hybrids are both more efficient and cheaper to produce.

Another option that has been considered, and which has its proponents, is pneumatic hybrids. For that, imagine the size of the accumulator for anything close to ordinary pneumatic pressures! If you want to gauge the efficiency of compressing air, put your hand on the cylinder head of a compressor when it's working.

An accumulator would serve other useful purposes though. It would prevent "hammering" in the system. It would also allow the engine to be stopped when the vehicle is not moving and restarted from stored energy when you step on the gas, and provide a short boost in acceleration at cruise speed. And it would probably just keep things working smoother.

Does anyone have a suggestion for what kind of variable displacement hydraulic motors are available.

I had the opportunity to speak with several people at EPA who worked on the hydraulic hybrid vehicle (HHV) projects. There were several points that they made:

* Variable displacement pump/motor is required with flow rates up to 80 cc/revolution [in the range of 1.2 liters/second at 60 mph]

* Accumulator sufficient for 10 gallons at 7,500 psia (pressurized against dry nitrogen) for a typical car

* They have demonstrated 2,000 hp*seconds of storage

* Estimated hydraulic hybridization incremental cost is expected to be in the range $600 in production quantities

* Achieving very high mpg with this technology is not straight forward from a design/implimentation prospective (numerious subltes)

In 2004 EPA demonstrated a modified 7,500 pound SUV that averaged approximately 30 mpg combined average. An earlier demonstration was a 3,900 pound vehicle 0-60 mph in about 8 seconds and averaged 80+mpg.

The real question is how quickly can this level of fuel economy be delivered to the market place cost effectively and what will it take!

s houston

Dear s houston:

I admire your optimism, but your own facts (and those of the EPA and Eaton) re the UPS experiment show how little can be realistically stored in hydraulic accumulators. As you are probably aware, energy can be stored in hundreds of different ways, but the equivalencies can be easily calculated. For example Google will tell you that 1 hp is equivalent to .745 watts. So, in designing a hybrid vehicle, is makes sense to look at all the various possibilities for storage: batteries, tanks of highly compressed air, hydraulic fluid in accumulator tanks, large springs, suspended weights, water in a water tank. In most of these, you can get back out of the storage means very nearly what you put into it. Some, however, intuitively make no sense at all: To get a useful amount out of a water tower strapped to the back of your car, the tower would have to very large and very tall. Others seem promising, at first glance. Hydraulics have been tried many times in the past in hybrid prototypes for that reason. None has gone into production. Why not?

Your own post supplies much of the answer: 2000hp*seconds capacity. What your post does not say is that this capacity was demonstrated in a large UPS truck, and that four 22 gallon accumulators were required. 88 gallons of hydraulic fluid alone weighs 704 lbs. With the accumulators (which must be very heavily built for 5000 psi pressure) the weight goes over 1000 pounds. But 2000hp*seconds sounds like a lot of storage, you might say – and the EPA, having spent lots of our money, would like you to believe that. But here is what Eaton's own spokesperson says about the project:

The U.P.S. van has four "accumulator tanks" of 22 gallons each which can be pressurized as high as 5,000 pounds. When fully charged, the system holds 2,000 horsepower-seconds of energy, according to Benjamin M. Hoxie, engineering manager for hydraulic hybrids at Eaton, an automotive supplier that built the prototype, using technology developed by the E.P.A..

Stated differently, it could deliver 100 horsepower for about 20 seconds. In electrical terms, that is less than half a kilowatt hour — but no electric battery could absorb and deliver energy so quickly.

(That last line is simply false: a very large battery can deliver that amount of energy.) But ignoring that last sentence, the rest is essentially accurate. The actual value of 2000hp-seconds in watts hours is 414 watt-hours. That is substantially less than 1/3 the 1500 watt-hour capacity of the 88 pound battery in a Prius. If the UPS system were to match the Prius's capacity it would have to weigh 3000 lbs: more than the entire weight of the Prius.

As a young engineer, almost fresh out of college back in the early 70's I might have done the calculations on a napkin indicating just what I've suggested above. I worked for a company that lived on hydraulics, and outscored all 52 or 53 engineers on a principals of hydraulics test we all took. I am a hydraulic enthusiast, and have had fun with hydraulics. So I am not a hydraulics naysayer. But to think that 3000# of hydraulics is a reasonable alternative to 88 pounds of battery would have struck me as ludicrous way back then, just as it does now. Further, hydraulics have hardly changed at all since then, but electrics have changed dramatically. (See the recent thread on the EEstor capacitor.)

A friend made a hydraulically-powered drag car in the late sixties as an engineering school stunt. The entire car was an accumulator, with a VW motor hung on the back, driving a pump. Open the valve to the four hydraulic motors, and all four tires would smoke, propelling the thing through a quarter mile in a fraction of the time of any other "VW". Fun. A good Stunt. But the basis for a real vehicle? Hardly.

Ordinarily, I am a supporter of the EPA, and in fact think they should have far more influence than they do in setting realistic reductions in CO2 and other pollutants. But this project has been a phenomenal waste of taxpayer money in my view.

3000# to equal the storage capacity of a 88 lb battery! (To say nothing of the heavy hydraulic pumps, motors, piping, and control valves.)

Why would they use hp-seconds as unit, when Watt-hour is the conventional unit for storage of this magnitude? To mislead. 2000hp-seconds sounds like a lot. (.555 hp hours sound like a tiny amount – but it is the same thing.) They spent millions of our money and want to justify their expense. Same goes for the nebulous " Achieving very high mpg with this technology is not straight forward from a design/implimentation prospective (numerious subltes)" Now they can say, "Gosh golly, we tried but there were numerous subtleties (such as the difference between 3000# and 88 lbs.)

I hate to sound like a grumbling curmudgeon, but I hate to see claims either completely unsupported by real math (and in Kasmer's posts) or claims stated in deliberately misleading ways (as in the EPA numbers). In either case, there is an implied disrespect for real engineering.

BTW: the 80 mpg claim re the 3900 lb vehicle (which was actually a Ford F150) is simply a hoax that has circulated the internet. Consider that the Ford ordinarily gets 18 mph. The best possibly hybrid technology (let alone anything so crude and heavy as hydraulics) could not come close to even doubling this figure.

Toyota and Honda engineers are anything but nitwits. If you want to know when this fuel-saving technology will be available, you have the answer: right now. Buy a Hybrid civic, or a Prius.

More than 20 years ago, I read an article in an auto magazine about an LTD Ford that had been fitted with a spherical oil reservoir,hydraulic pump/motors, and a chip that controlled the engine starting and stopping, via hydraulic power.This was a v8 engine, and it gave particularly good performance in city driving.The braking energy was stored in the reservoir, and was replenished by the engine when nescessary.

When the set-point was reached, the engine cut off, and the car ran on hydraulic power.At the time of the article, the weight was less than an automatic transmission, and the parts were off-the-shelf components.The cost was less than an automatic transmission.The highway milage however, was not as good as an automatic transmission.That was 20 years or more ago.Perhaps hydraulics have made great improvements since then.

Even so, it sounds ideal for city buses and the like, that have a lot of stop and go.

Some 50 years back a colleague described to me how they run flywheel energy-storing/using city buses in Switzerland and ups/downs in terrain did not particularly bother the Swiss engineers.

Could we revisit that concept and merge parts onto the present blog?

I've followed the flywheel idea for about 40 years, and there are buses in Denmark as well as Switzerland. But the situation right now is somewhat similar to that with hydraulics -- it is simply difficult and costly to get it to work in a vehicle, when compared with electrics which are easy and cheap. With hydraulics, weight is the killer: 3000# of accumulators and fluid to match the Prius's 88 pound battery, just for storage, (let alone the heavy pumps, motors, valving, and piping). With flywheels, it is the cost, because of the exotic materials required, and the difficulty of banging the things around in a moving vehicle, given the very high gyroscopic forces, and the difficulty of transmitting 75,000 - 100,000 flywheel speeds to wheels moving 100 - 1000 rpm, maintaining vacuum around the flywheel, etc. The people who make the best of these for UPS (stationary use) don't expect to see many of them used in vehicles.

With hydraulics, if you increase pressure enough, then you can store more in a given space -- but the cost of all the components increases and the weight of the tanks goes up. If it were not so (comparatively) easy to do this stuff with electrics, then some of the other technologies might develop. But with a 30:1 weight disadvantage, hydraulics is hard to manage. Even in the best possible application, a garbage truck, where you are starting and stopping every few feet, it's a tough sell.

So hydraulics and flywheels are unlikely to see widespread use, because with the current state of the art they are both well behind electrics, and the rate of progress with electrics (in battery and supercapacitor tech) is extremely fast.

My post here is loaded with opinion, so if anyone has data that supports using flywheels or hydraulics in production cars, I'd love to hear it. A new thread would make sense.

<My post here is loaded with opinion>

We adore your Opinion--this is Wisdom.

how do i make my vst trany have tighter shifts

Dear Tyche, an engine running to create output power wastes a hell of a lot of energy just to run. By cycling the engine on and off at the sweet spot and employing a pressure storage tank to store the energy of the engine running, AND diverting the mechanical energy of vehicular forward motion to the same tank, a much more efficient use of the fuel energy ensues. My invention, the Hydristor is a totally variable hydraulic transmission/motor/pump which easily accomplishes this at very high efficiency numbers. Many people think the ultimate mileage is attained by a manual transmission of near 100% efficiency but the engine running wastes much energy and there is no recapture of driving energy. The Hydristor system accomplishes all this and is retrofittable into all existing IC engine vehicles. There are a billion vehicles worldwide on the roads and we need to cut back their emissions to stop global warming and reverse it. We can't wait for everything to be scrapped and overload the Earth's resources. We can save the existing fleet by this retrofit and start the rollback of CO2 pollution. regards Tom Kasmer