Diesel-Electric hybrid vrs Gasolene-Hydraulic hybrid?

Noise, unfamiliarity, maybe efficiency, noise, noise, cost, long payback, noise, noise.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

I'd like to slightly contradict Greg.

It is possible to make a silent hydraulic system, but then you have to substitute six 'cost' and one 'weight' for five 'noise'.

Plus you have to add 'range', which you can improve with better 'efficiency', which adds 'cost'.

Hydraulic hybrids seem a natural for garbage trucks, and for urban deliveries with very short inter-stop distances. Not so much for suburban routes.

Additionally, every part of this statement from the HowStuff site is just flat false:
"Another payoff is the efficiency of the hydraulic components themselves. Because the components are lightweight and use simple mechanics, they're easy to build, maintain and repair. "



Mike Halloran
Pembroke Pines, FL, USA

"Additionally, every part of this statement from the HowStuff site is just flat false:"

I wouldn't say they are false, depends on your point of view. - easy to build, maintain and repair:Yes for a maintenance shop that is already used to rebuilding hydraulic components, such as those used on garbage trucks.
- components are lightweight and use simple mechanics: Yes considering the power hydraulics can transmit in a relatively small package, and the basic designs have been around for many years. And don't even try to compare this fairly simple system vs. a generator/battery large enough for a large refuse truck!
- efficiency of the hydraulic components: if you consider the total system efficiency of a generator/battery pack/electric motor the efficiencies are probably similar to the hydraulic system over time.

A regenerative hydraulic system makes sense on large vehicles that make frequent stops. The added weight penalty gets relatively smaller as the system power goes up.

ISZ

So we agree that maintenance and repair of hydraulics is a specialized operation.

Production of the hydraulic components and repair parts is even more specialized, and much more capital- intensive, partly because of the difficulty of producing the nominally simple internal geometries to extreme levels of precision.



Mike Halloran
Pembroke Pines, FL, USA

I wanna Thank those responding to my query. I have known for years, many people instantly jump on the “smear tactic wagon” on any thought of different applications to historic methods.

IceStationZebra made absolute sense, but the last paragraph was deceiving.

“A regenerative hydraulic system makes sense on large vehicles that make frequent stops. The added weight penalty gets relatively smaller as the system power goes up.”

Click to expand...

1. The weight of 4 hydraulic motors will probably weigh less than one single electric motor of the Torque of one of the hydraulic motors.

2. The weight of a battery may be, in the future, less than a simple 5 gallon Accumulator hydraulic system with Reservoir, cooling system, valves, lines, etc.

3. A hydraulic system would not require a large +200 internal combustion engine.

Large horsepower automotive engines installed in modern cars are never needed for more than a few seconds at a time. Automotive engines are not designed to deliver such power on a continuous basis and an absolute over design for urban stop and go traffic. (Somewhere, a US Dept. of Trans. web site, which I cannot readily find again, showed almost 3 miles driven in urban areas for every mile driven on a US highway.)

My old ‘95 Ford Windstar weighing 4400 lbs., with handicap additions, including elec. wheelchair, and two passengers, calculates a need of slightly less than 27 HP** to maintain a speed of 70 mph on a level highway.(**Provided I did not screw up the decelerations calculation based on loss of 10 mph in 10 seconds as an average of several measured timings.)

The HowStuff article, shows UPS testing is evidently using available shelf hydraulic items. It does not elaborate on essentials such as the internal combustion engine being controlled by a Hydraulic Governor and regulated by the Accumulators’ pressure differential.

Info is not given about the size of the Accumulator, Hydraulic Motors, or of the internal combustion engine. Under normal operation, the engine driven pump would be in by-pass mode when the Accumulator was at max psi, or would add to a low pressured Accumulator while waiting for a green light.

The HowStuff article totally blew it about the electrical workings. Almost any Hydraulic Hybrid will still need a 12 volt system to operate the thingys necessary for comfort plus actuating certain hydraulic/pneumatic devices.

Also, let state outright that I believe there is a gap in existing shelf item hydraulic motors between small units suitable for lawn mowers and larger units for Caterpillar Tractors. None existing that I have found are precisely suited for adaptation to family sized automobile.

Thank Ya'll for allowing the rant about one a favorite subject.



At 74th year working on IR-One2 PhD from UHK - - -

" None existing that I have found are precisely suited for adaptation to family sized automobile"

Exactly.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

Existing hydraulic motors limit the top speed to about 83 mph. This makes auto sales almost impossible.

One solution is to adapt existing hydraulic motors, built structurally for high torque, fitted a transmission/differential arrangement, which stages increasing rpm delivery to the drive axle. These already exist on construction equipment.

My belief is, a pump/transmission manufacturer like Eaton, could easily mold and machine a smaller version for family size automobiles. (These little modern thingys a MAN has to fall into, and equipped with hand gripes to use for arms to enable climbing out, are not family size automobiles.)

Pump/transmission manufacturers, like Eaton, are not in the business of automobile assembly, typical of the so called big three, GM, Ford, and Chrysler. But, someone, as an independent, assemble a usable configuration. It may be adapted to cause an embarrassment to Nitro Dragsters when the 15-hp Briggs and Straton 2 cycle competes in their 1/4 mile elapse time.

At 74th year working on IR-One2 PhD from UHK - - -

Has B&S ever made a 2 cycle?



Mike Halloran
Pembroke Pines, FL, USA

At 74th year working on IR-One2 PhD from UHK - - -

Hydraulic systems can be made both quiet and durable. Most every automobile has a low pressure hydraulic system in both its power steering and automatic transmission. Newer diesel engines have a very high pressure (>20ksi) hydraulic system with a piston pump, in their common rail fuel systems. Automotive hydraulic systems would benefit with regards to reliability if they employed the design practices currently used in aircraft hydraulic systems (ie. sealed fluid circuits, parts designed for on-condition service life, use of HUMS, integrated system designs with a minimum of joints).

The big upside to hydraulic hybrids versus battery-electric, is their lower production cost and ability to recapture a much greater amount of braking energy. The drawback is the limited amount of stored energy potential for a given installation weight.

Until electric battery technology makes some huge improvements, hydraulic hybrids still make more sense overall though.

Regards,
Terry

At 74th year working on IR-One2 PhD from UHK - - -

Well that's a pretty picture which pretty much defines why it won't happen.

Pump motor is in a package critical part of the car, you'll need a new trans tunnel/bulkhead stamping and a crash program. It is alongside the first cat and so will need protection from 700 deg C heat.

The two accumulators displace room from the exhaust system and the fuel tanks.

The rear drive assy is volume feasible, it looks like it'll add a 40-50 kg mass penalty in order to provide good NVH, and will necessitate a rear crash program.

All these problems are solvable, given a new platform and time.


Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

What new is needed for [p] "protection from 700 deg C heat"[/p]different than that presently used in most of the present mass produced automobiles using a hydraulic motor, (torque converter), to rotate the modern day automatic transmission?

Will agree, the accumulator location is in proximity of a 2 to 3 inch diameter tail pipe routing of an exhaust system. But, blocking the entire path? Dah!

:GregLocock said:

All these problems are solvable, given a new platform and time.

Click to expand...

These problems have been functionally solved and time is now being used to physicaly operate practical working models.

At 74th year working on IR-One2 PhD from UHK - - -

Good question and good comments. When the EPA/UPS truck first came out I remember reading an article containing component info but I can’t find it now. Relying on my less than perfect memory I think the main engine driven pump has a capacity of 130cc/rev and the three pump/motors on the differential are 85cc/rev each. The third unit was added to the differential because UPS has a fairly steep hill climb requirement. The system is rated for a maximum working pressure of 5000psi. The pump/motors are rated for 7000psi operation. The pumps were developed and designed for use in this drive, but I don’t know at what point in the process the pump/motors were sized in relation to the selection of the UPS package delivery truck as the demonstration vehicle. The UPS truck has two high pressure and two low pressure accumulators (i.e. reservoirs), each with a 22gallon capacity. Also, someone in the EPA did claim the design is adaptable to a sedan. They claim that the drive would add about $600 to the cost of a sedan if produced in mass quantities. I’m not sure if they meant the cost of production or sticker cost but I assume sticker cost since they used the number in discussing how long it would take for the consumer to recover the cost.

So why don’t we have hydraulic drive sedans? The criticism I hear most about hydraulic drives is that they are too bulky. They are not referring to the pump/motors as being bulky but to the energy storage units. The four large accumulators on the truck provide enough capacity, with moderate efficiencies, to brake the truck from less than 40mph to 0mph or about from 65 to 53mph. That’s less energy than is contained in a single 12Volt Pb-acid deep discharge battery with a 100minute reserve capacity rating. A sedan is much lighter than a Class 6 truck but it is also much harder to create space in a sedan design. I think the lack of energy storage capacity causes hydraulics to be seen as having a limited ability to moderate engine load. So in general, conventional hydraulic drives do not provide enough advantages to balance their shortcomings. But hydraulics can get energy in and out of storage rapidly and efficiently so it’s useful when the primary load profile is frequent power surges or includes a lot of low-speed and high-torque operation. I think the EPA spent a lot of time and money bringing nothing new forward. Their main claim to doing something innovative seems to be their pump/motor design, but I agree it looks like an off-the-shelf design. The patent seems to be more or less design options rather than something new and/or unique and the design doesn’t do anything to overcome the shortcomings of conventional hydraulic drives. Look up companies like Hybra-Drive, Innas, and Artemis for what I think is more interesting work in hydraulic drives. I think the EPA and Eaton do more to inhibit technology than to innovate. I enjoy indulging in a rant every now and then myself.

Using hydraulics like the EPA, Eaton and other axial piston systems for vehicle drive is a simple evolution of hydraulics. Hydraulic component manufactures spend very little on new design R&D so don’t expect any great technology from them.

I do believe hydraulic could become the drive of the future for all types of vehicles if properly implemented. Capturing and reusing 80%+ of the available braking energy can be done with hydraulics cost effectively compared to electric drives.

Just because the car companies have chosen electric drives as their method of choice should be a warning based on current conditions.

Ed Danzer

Here's my idea, except it uses Torque converters at the wheels, instead of hydraulic motors.

Nice find on the Tucker “Flowing power” advertisement, I enjoyed it. It also makes a good point. The torque converter was applied to autos as early as 1947 but did not come into wide use until it was “properly implemented”, i.e. placed between the engine and transmission and a stator mounted on an over-running clutch was added to tighten the coupling. Probably back in the 60s or 70s, then for decades nearly every car on US roads had a torque converter.

So I’d like to turn the question around and ask: How do hydraulic drives need to evolve to become useful in autos?

Hydraulic drives of the torque-converter variety will always have high losses when they are doing the torque-converting (modern automatics have improved their efficiency by locking up i.e. bypassing the torque converter except when starting off from a standstill or momentarily during gear changes).

Honda has an interesting CVT in the new DN-01 motorcycle. It has a swash-plate hydraulic pump and motor in a single housing. Interestingly, it's arranged in a way that as the road speed increases and the required drive ratio thus decreases, more of the drive goes through a direct mechanical path (the hydraulics effectively "lock up") to improve efficiency. But this doesn't lend itself to regenerative braking, etc.

To become useful in an auto, the efficiency and operating speed of positive-displacement hydraulic pumps and motors needs to improve - by a lot. Commercial hydraulic pumps and motors for industrial applications have a rather lousy efficiency compared to what's needed in an automotive transmission.

To make hydraulic drives suitable for vehicle drive train the pump/motor needs to have the same thermal efficiency regardless of load or speed demand. Current swash plate designs have low efficiencies at low speeds and are do not great efficiencies at high speed low load.

Ed Danzer