Dutch Invention Uses Electric Engines For Wheels 380
Makarand writes "A Dutch invention is
promising to make vehicles atleast 50% more efficient
and also bring down the soot and carbon dioxide emissions. This is made possible by replacing
the conventional wheels by 'in-wheel' electric engines which are normal electric engines turned inside
out. No transmission is necessary as the in-wheel engines are powered by battery-packs installed on
the vehicle. A diesel-powered generator which replaces the original engine on the vehicle
charges the battery-pack continuously. The Dutch company
E-Traction has built a bus using this technology that
will undergo testing for the next six months."
Oh puLEASe (Score:4, Informative)
see this this page [porsche.com]
Popular approach for ships lately (Score:3, Informative)
I got the impression that one significant benefit is the flexibility of electric engines in terms of size and manoeuverability. Being able to have your thrusters turn 360 is critical for ocean going cranes, bow thrusters, and such, and is less complicated using an electric engine than would be required for a direct mechanical linkage.
In the cruise ship example, I kind of got the impression that so much electricity is required for the ship in general, that large generators were a given to start with, so powering the thrust of the ship from the same makes a lot of sense.
Very interesting to see this technology potentially cross over to the consumer. It will be interesting to see if the efficiency makes it feasible.
Re:Not trying to pick nits, but... (Score:3, Informative)
pros/cons (Score:3, Informative)
This will not work so well for cars beause the high unsprung weight will make a car handle very poorly and the friction losses in a u-shaft would be better than extra weight in the wheels.
Re:Just an improvement of standard hybrid technolo (Score:2, Informative)
- the diesel engine runs at it's optimal speed (that gives an easy 50-70% gain - engines usually run on sub-optimal speed)
- losses only occur in the electrical cirquits (the current regulaters and so), can cost like 10% of the energy
- and a significant energy gain is made by reversing the enige to generator when braking! (though I assume also a mechanical break for emergency stops). As it is a city bus, it will spend most time either accellerating or decellerating.
Wouter.
Re:electric engines (Score:5, Informative)
A diesel-powered generator which replaces the original engine on the vehicle charges the battery-pack continuously.
The electro motors are not used as an engine but just as a clever way of transmission. This system has been in diesl-electric trains for ages, since most diesel engines can operate quite efficiently if they always run at the same RPM.
Re:If I know something about batteries... (Score:4, Informative)
Lead-acid batteries are highly recyclable [epa.gov]. (Though, like computers, because of poor regulation such batteries are often just dumped on third-world nations [fish.com].)
Re:A quiet bus in a busy city... (Score:4, Informative)
I'd wondered about using wheel revolutions as a charging source for onboard electric systems myself -- good to see engineers applying it. (IANAE
Re:This isn't anything new. (Score:3, Informative)
I'm not convinced (Score:3, Informative)
Diesel-electric technology has been used to power locomotives for 60 years. D-E locomotives have no mechanical transmission and the motors drive the axles directly. This electric transmission affords good efficiency, a very wide range of torque conversion, and allows the engine to operate within its optimal RPM range. Almost all of the efficiency benefits that this article attributes to the wheel motor can be had by this 60-year-old design.
There's also nothing new about regenerative braking, though it isn't practical for locomotives.
The real novelty here is that the motor turns with the wheel, rather than being stationary and transmitting its torque through a half-shaft. The benefit is the elimination of these half-shafts and a couple of CV joints. The cost is huge size and tremendous unsprung weight of the motors, plus significant engineering challenges of running high-current wires across a sprung connection, and the concern about competition with the brakes for the limited space and heat-dissipation capacity of the wheel area.
Have a look at the rear wheels of the bus in the photo. They're HUGE - the bus has obviously been modified to fit them.
In summary, the only novelty in this design is in transmitting the power the last 2 feet to the wheels. A conventional design would use half-shafts and CV joints while this design uses high-current electrical transmission. It may be that the engineering challenges of the latter can be overcome, but I remain to be convinced that there's any overall advantage. The company's interests would be better served by an article with more restrained hyperbole.
Cost of batteries (Score:3, Informative)
This means that even if increased the gas engine efficiency to 0 cents per kWHr (through smaller engine run at peak efficiency to only charge batteries) but ran all the power flows through the lead acid batteries, you costs would increase from 40 cents to 60 cents per kWHr delivered to the wheels.
Anyway, this argument is for series power flows. The traditional automatic transmission is a series power flow, at best 80 percent efficient. The automotive industry has latched on to parallel power flows as a way to boost efficiency. Modern automatic transmissions use split-torque direct drive and torque converter together with direct-drive clutches to boost this efficiency. The commercial hybrids today are parallel electric and gas engine drive. The Toyota Prius is gear shift free, but instead of the Diesel locomotive series drive of engine-generator-traction motor, the Prius has the gas engine, generator, and traction motor tied to a planetary gear set so there are parallel mechanical and electric torque paths, again to boost the efficiency.
If you have a parallel hybrid, obviously you need to use your 60 cents/kWHr battery electricity under circumstances where the gas engine electricity costs more than 60 cents/kWHr, or perhaps use it to resize the gas engine for greater efficiency while consuming the minimum of expensive 60 cents/kWHr juice. But given that batteries are 1) expensive, and 2) wear out (think laptop or cellphone or iPod battery), the hybrid vehicle is not a slam dunk.
unsprung weight problems completely ignored (Score:3, Informative)
It's actually not technically sound at all. It drastically raises the unsprung weight at each wheel- the thing will ride like crap, and contact with the road will be extremely poor. It might be OK for slow moving busses, but certainly not passenger cars, SUVs, or light trucks.
The difference between a 15lb rim and a 30lb rim(rim= wheel minus tire, ie, the metal part) on your car is extremely noticeable, and racers/performance enthusiasts will go to all lengths to find lighter rims, and even braking systems made up of higher-tech, lighter materials(hence Porsche's ceramic brakes, for example.) Even suspension components themselves are usually made up of carefully designed aluminum components to be lightweight. Less unsprung weight means that it's easier for the suspension to keep the wheel firmly planted to the ground, to grossly simplify the situation.
This thing will eat tires like no tomorrow, too; it'll cause a lot of stress in the tire because the tire will need to flex a lot more than normal. Flexing takes energy, by the way- and that can add up fast. Improperly inflating your tires causes more flexing in the tire than usual, and can have a noticeable effect on your mileage.
Putting an electric motor inside the wheel is about the stupidest thing I've ever heard of- it should, if anything, be in the center of the car, with a traditional half-shaft and CV joints(slight loss)...or instead of using a standard automatic transmission, they should be using a CVT(constantly variable transmission) or something like Audi's DSG(Direct Shift Gearbox).
Two more words: (Score:4, Informative)
Unsprung weight.
Making a wheel that is an electric motor would make such a heavy wheel thtat the vehicle would handle and drive like total crap. The huge weight of the wheels would require shock absorbers with huge dampening ability to keep the wheel planted on the road over uneven surfaces. It would ride like a dump-truck.
Re:Will it stand the test of time? (Score:5, Informative)
Interesting idea, but the real test will be with long term cost of operation.
While any new tech carries risks, this one has a lot going for it.
Diesel-electric is well proven as a technology. All diesel train engines use it. The difference is in the batteries. No battery pack could contribute much to storing the kinetic energy of a train. However, they do brake electrically. The big grid on the top of the engine is a simple resistance heater to dump the energy from the motors operating as generators.
Electric motors are simple things. The only moving part is a bering, a well understood part. Because of that, industrial motors tend to run for a very long time with minimal maintainance. These motors are not THAT different than other motors, so will likely have the same desirable characteristic.
Transmissions and differentials DO have a lot of moving parts subject to wear and tear. The generator/motor combo replaces all of that.
Engines running at constant RPM and load experiance less wear then on that runs at variable speeds and loads. The engine is smaller as well, so cheaper.
Because of th nature of the system, it doesn't need the latest and greatest cutting edge batteries. I don't know what they're using, but it probably isn't finniky expensive LiIon polymer.
A later generation could easily switch to composite flywheel once that's better proven and manufacturing costs come down. Because of the system design, it would likely be a drop-in replacement.
Even without the fuel savings and quiet operation, the new design might be worthwhile due to savings in maintainance and improved reliability.
But bumps "beat the daylights" out of the motor? (Score:3, Informative)
Re:Oh puLEASe (Score:2, Informative)
Re:Oh puLEASe (Score:5, Informative)
As the weight of the wheel goes up so does its inertia. It starts to resist movement more and more. This is a Bad Thing. When you hit the right bump at the right speed the wheel hops off the ground rather than moving the suspension up with the irregularity, upsetting the entire car and losing traction at that corner. The sprung to unsprung mass ratio becomes important because with heavy wheels and a light chassis the mass of the wheel reacts more strongly on the mass of the chassis. The suspension can't move with the bump but the chassis does. A loaded bus chassis is much more massive compared to the wheels than a loaded car is.
The people in the car experience this as ride harshness.
Active suspension systems are ones that use sensors and mechanical actuators to move the suspension ( as opposed to springs). They can "anticipate" the movement needed and partially compensate for the added mass, but only partially.
I can'na change the laws of physics.
A heavier wheel rim also takes more energy to accelerate, more so than the same mass on the chassis does, and increases gyroscopic effects.
This is why the solid spoked wheel gave way to the tensioned wire spoked wheel, than the pressed steel wheel and ultimately the "mag" ( which is really only a mag if it's actually made of magnesium. The aluminum wheels you get in the dress up stores are actually often heavier than the cheaper steel wheels they are purchased to replace). The lighter the wheel the higher the ultimate performance of the vehicle in every catagory (this is why bicyclists are absolutely rabid about wheel weight).
Is this system feasable for a car? Oh, absolutely. But you have to be careful to at least keep the motors as low weight and compact as possible. The GM Sunracer managed to contain them within something that looked very much like a standard bicycle hub, although rather heavier. Copper and magnets aren't light.
KFG
Re:this was done before by porshe (Score:2, Informative)
May not be new but interesting nonetheless (Score:3, Informative)
Nor is there anything new in the way the control system would work. In Europe, most washing machines are front-loaders. The drum has to be able to revolve at a low speed in both directions for washing, and at a high speed for spin drying. Instead of using a gearbox, the motor's windings are split so they can be connected in various series and parallel combinations. Electronically there is no difference {a motor doing 300 watts of work is using 300 watts of electricity and just looks like a resistance dissipating 300 watts of heat} -- mechanically there may be an improvement {the speed-changer need only be a set of relay contacts, not a solenoid-operated or electro-hydraulic gearbox}.
Many trains in Britain {where not all railways are electrified} use a Diesel engine to spin a generator at constant RPM {everyone knows this is the most efficiengt way to run any sort of engine}, which then drives several small electric motors via an electronic control system which actually depends on the waveform of freshly-generated, as opposed to stored, electricity. I think this was invented by our baguette-munching neighbours at the SNCF {Societe/ Nationale de Cattle Freight by my own experience} but not sure so don't quote me on that.
So, all in all it's not much new. But hey, it's an interesting application anyway
Batteries don't have to cost that much (Score:3, Informative)
If you take a look at that graph, you'll see that even a lead-acid battery can last many thousands of cycles as long as they are shallow. The Yellow Tops in question are, I believe, rated at 55 AH (20-hour rate, don't ask me what discharge rate was used for the test) or about 660 WH nominal. The total throughput over 4500 cycles to 25% depth of discharge is over 600 KWH.
Let's make an assumption here. Let's assume that mass-production batteries like the Yellow Tops would cost about the same per AH as a deep-cycle trolling/starting battery does now. I bought a 105 AH unit for about $65 a couple years ago, assume $70 today or $0.66/AH or $55/KWH nominal. 4500 cycles to 25% depth would cost $(55/1125) or 4.9 cents per KWH. Depending where you're buying your juice, this is somewhere between one-third to one times the cost of your off-peak electricity.
Gasoline costs quite a bit more. At 6.67 lb/gallon and 0.4 lb/HP-hr, you'd get 16.7 HP-hr/gallon or 12.7 KWH/gallon; this is about 36.5% of the 119,000 BTU/gallon of energy that gasoline really carries. At $1.50/gallon you're already talking 19 cents per KWH. Hybrid propulsion using reclaimed (regenerated) energy appears to be quite a bit cheaper than making power from scratch, and charging from the grid when opportunity allows would be cheaper than buying fuel even at today's US prices. At typical European prices, it's a no-brainer.
That said, it makes you wonder why the in-wheel-motor hybrid scheme hasn't been done for the last 50 years. I recall seeing one of Ferdinand Porsche's early attempts to power a string of trailers using in-wheel electric motors... for World War One, to move war materiel. There is very little that's truly new under the sun.