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E-Traction's key innovation, Heinen says, is in the design of its wheel motor. Typically, electric motors are designed to spin much faster than the rate of the wheels in order to generate the desired power. But such motors require gears to step down the revolutions per minute, which adds complexity and decreases efficiency. The company has eliminated the need for these gears by designing a large-diameter motor that can deliver the needed torque at low RPMs.
In-wheel motors have met with limited success in the past. In part, that's because it's been difficult to coordinate motors that have no mechanical connection to each other, a problem that the company says it's solved by developing a proprietary electronic control system. But there could be remaining issues. Putting the motors in the wheels places larger demands on the suspension (it has to be stronger to hold on to the much heavier wheels) and can make the motor and electronics more vulnerable to damage, both of which can reduce reliability. "There's little between the wheel and potholes," says Bill Van Amburg, senior vice president at Calstart. Dan Pederson, a researcher at the National Renewable Energy Laboratory, says that the large in-wheel motor is likely very expensive, which could make the system hard to justify without government subsidies.
Heinen says that four years of testing of a prototype system have convinced the company that the reliability issues have been addressed, and that costs for the motor may come down with larger-scale production. In addition to hybrid buses, e-Traction is working on hybrid garbage trucks and is retrofitting a Mercedes G SUV in an effort to move into the passenger-car market.
A U.S.-Chinese venture is out to prove the benefits of quick-charge buses.
An MIT group hopes that its foldable electric vehicles will cut pollution, and ease congestion.
Design effort could make fuel cells practical while pushing the state of the art in hybrid propulsion for all kinds of vehicles.
Wheel motors are an interesting concept, but surely there are power and fiscal benefits from having larger single motors and a drive train. Moreso when you consider the additional protextion need against water, salt, minor knocks, re-balancing, vibrations and shocks from the road. Solution might be to move the motor inboard and use a long shaft to drive the wheel?
Good question. I doubt that the reduction in parts of two U-Joints per drive wheel will make much cost difference between a wheel motor and an inboard more conventional electric motor in a better protected location. Additionally, when applied to lighter vehicles such as passenger cars, wheel motors increase the sprung weight making for a harsh ride. Inboard motors would decrease the sprung weight and make for a better ride. (Kind of like the reason to use light-weight alloy wheels instead of heavy steel wheels.) I am in favor of using 4-wheel electric drive and eliminating the steering system by using control of revolution speed and direction at each wheel under direction of the on-board computer.
Wheel Motors to Drive Dutch Buses
The motor in the wheel is is great for this application , no argument , less parts and more efficient .
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I am just wondering if you use Ultra capacitors to capture the power generated by regenerative breaking which will capture all that generated power as it is made by the motors , whereas the battery pack will only capture some of it because of the nature of the batteries physical limitations to fast charging large amounts of electrons in a short time ( seconds of slowing down ) Check out Maxwell BoostCaps ultra capacitors they are ideal for this application .
Why in wheel? Because an electric motor that has to provide enough torque to drive a vehicle without gears has a large diameter. Building it inside the vehicle will take allot of space and is negative for your building flexibility.
Shocks en water ingress? We are already driving for 4 years with our city bus with the electronics fitted inside of the wheel. Shocks and water have till thus far never been a problem.
Boostcaps? At this stage we have an lithium-ion pack of 30 12,8volt 130Ah valence batteries onboard. These batteries can absorb all the energy that is coming from the wheels in normal breaking situations. For emergency braking we use mechanical brakes(demanded by law).
We also need the longer power of the battery to drive zero emission, which the boostcaps can not provide.
Steering by controlling the speed of the motor? We already have a software differential that helps to steer the bus actively thru a corner. But regulations keep us for steering the complete bus with software instead of mechanically.
Arend Heinen
Thank-You Arend Heinen ,
Yes , with that many cells even though the cells take the power slower than ultra capacitors a little power in each one will work just fine .
Looks like you have a winner here . I would do the same thing , if I was working on the project .
I would still want to take a bus and put some capacitors in it with the batteries just to know for sure that it didn't make any difference . That is the Engineer thinking in me .
They will also make the batteries last a lot longer .
Mr Heinen, could you provide more detailed explanation and maybe some basic calculations to substantiate the fact that the batteries used in your bus can "absorb all the energy that is coming from the wheels in normal breaking situations."
The matter is five days ago I created a topic at one Russian forum for discussing the news on your leading-edge technology, and the discussion is still goin on. Today I was nonplussed by a forum member's critical post as rendered by me in English:
The bus is normally braking by recuperating energy, say from 72 km/hr to zero, i.e. its initial speed is some 20 m/s. Its total weight (including the bus itself and its passengers) is at least 20 metric tons, maybe more.
Hence we can calculate the energy to be absorbed (and later on to be spent on acceleration) as follows:
1/2 * 20,000 * (20 * 20) = 4,000,000 J = 4 MJ
Let's assume that the braking takes about 8 seconds (emergency braking should take some 2.5 seconds, but that surely involves some mechanical braking system). Hence the power the batteries being absorbed for 8 seconds amounts to some 500 kW (the more the better; a little less is admissible too, but only a little: we should always keep in mind that lower power absorbtion rates means longer braking).
What does this 500 kW mean for 30 batteries? It means 17 kW per battery. If we divide that amount by the rated voltage we get the charging current: some 1300 A. You can beleive me, that's a heck of a current!
If we can halve the deceleration (acceleration) rate, the charging (discharging) current will amount to 650 A. Believe me, even for the best batteries with storage capacity of 130 Ah the current of 650 A is just too much. It's possible to meet even such harsh requirements but only at the cost of much lower efficiency, below 50%.
Sure if acceleration and deceleration is done very very smoothly, even 100 kW might be enough, meaning some 250 ... 260 A per battery, which is roughly sufficient to fully charge the battery in 30 minutes. Such batteries do exist but their efficiency is rather low. I tell you again, nowadays' technology can provide high efficiency (up to some 70 percent) only if the charging (discharging) current is below the current necessary to fully charge the battery in 30 minutes.
Your reply will be appreciated.
Check out this wheel-motor electric race car:
http://en.wikipedia.org/wiki/Eliica
One inherent problem with wheel motors is that they increase unsprung weight thus adversely affecting handling and comfort. Also, the fast up and down motion of the wheels puts added stress on the motor.
Unsprung weight worries? This is a bus, not a sports car. I don't think you would notice any changes in handling ability or increased braking distances. The limiting factor is the original design; a rather large, heavy, high center of gravity vehicle.
People always come up with bull$#!% objections and kneeJERK reactions to new ideas. "Unsprung weight" is an engineering problem far less challenging then the wheel motor it self. It's just retarded to raise that as an objection, especially since it's already been solved.
http://www.spectrum.ieee.org/print/2059
"Traditionally, the drawback to wheel motors is what designers call "unsprung weight," or the relatively high mass of the motor components in addition to that of the wheels, whose movements the suspension must accommodate. The more mass in the wheels, the beefier the suspension must be—increasing weight and complexity. Michelin's Varenne, however, notes with pride that the mass of each wheel and its motor unit is just 30 kg, roughly comparable to that of a wheel in a standard vehicle. "
I am thinking about the business side,
Unlike buses which are mostly owned by cities, and towns; garbage trucks in many cases are maintained by private entities that have a strong business interest to hedge their bets against future increases in the prices of fuel.
Private entities that collect garbage are much more likely to adopted hybrid garbage trucks because:
1) The garbage trucks burn up more gas due to frequent stopping,
2) Many times they are larger and increases in fuel cost dramatically affect their bottom line profits (like airlines),
3) These garage companies are actively looking for ways to cut costs and make their fleet more efficient, unlike cities which are notorious for wasting money
Brian Glassman
Innovation Management
Commercialization of technology
The article states that "The battery stores enough power to propel the bus for an hour without the generator running to recharge it." If so, it would be productive to pre-charge the battery from the grid between shifts, saving even more fuel by displacing up to 1/8 of an 8-hour shift's fuel with oil-independent, usually-lower-carbon, and possibly renewable electricity -- more yet with a larger battery pack.
Described at http://www.e-traction.com/batteries.htm, the battery consists of 28 13V, 100 Ah Valence U24 LiFePO4 modules -- 36 kWh, and 364V if all are in series. The accompanying graph shows that Valence modules have about 4C (4 times the Ah rating) discharge capabilities, about 144 kW and 400A for the whole pack, which probably stores about 25 useful kWh at 70%. The bus is rated at 14.8 mpg (http://www.e-traction.com/buses.htm). An efficient (33%) Diesel engine/generator can provide maybe 13.5 kWh per gallon, so the bus probably consumes 900 Wh/mi for an EV range of 28 miles.
Another point: validator is right that 500 kW of regenerative braking would, at 14C, would overtax this battery pack. But 500 kW is not excessive acceleration or deceleration for a large EV -- the tiny Tesla Roadster is capable of accelerating at 215 kW. These hub motors (http://www.e-traction.com/TheWheel.htm) are rated at a peak input power of 384 kW apiece, and a slightly larger battery pack designed to charge at 10C (at optimum temperatures) or a supplementary supercapacitor pack could easily enable most braking to be purely regenerative.
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
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SimonHoer
5 Comments
More substance, please
Very interesting subject, but the article could do with a bit more substance.
For example, what's the innovation that allowed e-Traction's design to succeed? Just building a larger diameter engine can't be all.
Then how about economic viability, how long until (fuel-) savings justify the extra cost of retrofitting? I haven't got a clue how much diesel a bus is using to start with.
Which company is buying the new technology and in which city will they operate?
What happens if one of the engines fails, can the other still get the bus to the next bus stop bay without veering of the road?
Buses are big contributors to particulate matter in cities. If you want to be perceived as environmental friendly you'll have to use diesel particulate filters. Where is the diesel engine coming from and how clean is it? I guess it runs at optimal revs that should make it easy to deal with the exhaust fumes.
Can anyone provide some more facts, please?
Cheers.
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Kevin Bullis
178 Comments
Re: More substance, please
The innovation is the combination of the wheel motor and control system, but the company doesn't want to give away details.
I'll check about the particulate filter / engine--I'm assuming the bus will be equipped to meet European standards, so may need some changes for the U.S. That's a good point about the revs. The GPS system for turning off the engine completely in congested areas should also help.
The motors are in the rear wheels, so it should be able to limp home if one fails. I imagine you could just correct by steering. But I'll check on that, too.
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Kevin Bullis
178 Comments
Re: More substance, please
Response from Arend Heinen:
I do not know what the U.S. emission stands are, but we can fit any type of energy supplier in the back of our vehicle. From biodiesel engine to hydrogen stack.
If we build a bus for the U.S. market it will meet U.S. standards. At this moment we build them according to European standards.
Anyway, we have 50% of the emissions of a standard diesel bus and save at least 70 tons of co2 per year in standard operation.
We can use the same particle filter as normal engines have. We have the extra benefit that the engine will run at a specific rev number to ensure the most efficient burning of the diesel.
Yes we can drive on with one motor easily. The top speed can be reached but the acceleration is less.
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danahyattg
1 Comment
Re: More substance, please
If one follows the news he can read about Hybrid Bus Technology. Therefore predict the next production inovation. Example: A Hybrid Bus Company in San Diego who retrofits used buses and recycles them into city transit buses.
danahyatt.mail@gmail.com
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