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green_is_now
The switches need to be able to handle both high current in one scenario and ...
green_is_now
The problem is in all the IR and reactive losses of the matrix wiring and ...
Electric hub motor improves EV range: Part 1—Technology basics
Roland Marbot, EZ Consulting
4/28/2011 3:52 PM EDT
Part 2 of this feature covers applications at higher, more practical speeds and manufacturability.
Most of the electric cars currently available are using brushless permanent magnet (PM) motors. These motors have very good characteristics, but their control circuitry consumes a lot of power, that may require liquid cooling. This wasted energy is taken from the energy stored in the battery, reducing the range of the car.
For hybrid vehicles using series power train technology (the combustion engine drives an electrical generator charging the battery), this waste of energy translates into a reduction of the miles covered per gallon of gas.
This series describes the concept of a brushless DC motor with an "electronic gearbox," requiring an almost lossless control circuitry. This translates into improved range, which is also increased by a nearly 100% regenerative braking energy recovery, as well as reduced manufacturing cost and better reliability.
The motor described here is designed to fit into the wheels of a 4WD car. The same concept can be used for implementations of a centralized electrical motor with mechanical transmission. Other implementations of the concept can be considered.
Motor and gearbox basics
The axle of the motor is fixed, with no transmission of any mechanical energy from the vehicle to the wheels (which allows for simplified shock absorbers and improvement of the energy transmission yield). The stator of the motor, "tied" to the axle, is made of printed circuits with copper electric wires. The rotor of the motor is made of magnets and is joined to the rim of the wheel, turning around the axle.
The described motor is made up of a dozen “stacks.” Each stack is 5-mm thick, and is made of a disk of magnets, 3-mm thick, and a printed-circuit disk, 1.8-mm thick, with a 0.2-mm gap between the stator and rotor.
Below is a front view (top) and side view of the motor.
The magnet disks consist of 24 magnets, oriented as radial segments with a magnetization in the direction of the thickness of the disk. These segments occupy 50% of the area of the disk (non-adjacents) and are polarity alternated (N-S magnet, S-N magnet, N-S, S-N, etc). External diameter of the disk is 40 cm; internal diameter is 10 cm. Each magnet segment is 15 cm long.
A 1 Tesla (T) magnetic field can be generated in the air gap of this configuration (2-mm gap for 3 mm magnet thickness) using neodymium rare-earth materials.
Next: Motor calculations
Most of the electric cars currently available are using brushless permanent magnet (PM) motors. These motors have very good characteristics, but their control circuitry consumes a lot of power, that may require liquid cooling. This wasted energy is taken from the energy stored in the battery, reducing the range of the car.
For hybrid vehicles using series power train technology (the combustion engine drives an electrical generator charging the battery), this waste of energy translates into a reduction of the miles covered per gallon of gas.
This series describes the concept of a brushless DC motor with an "electronic gearbox," requiring an almost lossless control circuitry. This translates into improved range, which is also increased by a nearly 100% regenerative braking energy recovery, as well as reduced manufacturing cost and better reliability.
The motor described here is designed to fit into the wheels of a 4WD car. The same concept can be used for implementations of a centralized electrical motor with mechanical transmission. Other implementations of the concept can be considered.
Motor and gearbox basics
The axle of the motor is fixed, with no transmission of any mechanical energy from the vehicle to the wheels (which allows for simplified shock absorbers and improvement of the energy transmission yield). The stator of the motor, "tied" to the axle, is made of printed circuits with copper electric wires. The rotor of the motor is made of magnets and is joined to the rim of the wheel, turning around the axle.
The described motor is made up of a dozen “stacks.” Each stack is 5-mm thick, and is made of a disk of magnets, 3-mm thick, and a printed-circuit disk, 1.8-mm thick, with a 0.2-mm gap between the stator and rotor.
Below is a front view (top) and side view of the motor.
The magnet disks consist of 24 magnets, oriented as radial segments with a magnetization in the direction of the thickness of the disk. These segments occupy 50% of the area of the disk (non-adjacents) and are polarity alternated (N-S magnet, S-N magnet, N-S, S-N, etc). External diameter of the disk is 40 cm; internal diameter is 10 cm. Each magnet segment is 15 cm long.
A 1 Tesla (T) magnetic field can be generated in the air gap of this configuration (2-mm gap for 3 mm magnet thickness) using neodymium rare-earth materials.
Next: Motor calculations
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Bob Lacovara
4/29/2011 10:16 AM EDT
It's a nifty motor, and might find application in non-automotive applications. To read that some of the control circuitry now in use needs liquid cooling is rather discouraging: that's a lot of wasted energy. One other point: recovering braking energy isn't merely a matter of being able to lay hands on it at the motor. You have to do something with it, typically put it into your battery. Trouble is, batteries don't recharge in seconds, and some fraction of that energy is lost. Some type of supercap might be indicated.
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Efried
5/4/2011 3:30 AM EDT
batteries might be designed for 2C-5C charging, supercaps failed so far to define their business model in transport - too bulky, too expensive
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prabhakar_deosthali
4/29/2011 10:19 AM EDT
A very informative article on hub motors for EVs. I would have liked this article to contain some graphics - Torque speed waveforms and schematics showing how commutation is achieved. Some comparative charts showing the efficiency and range improvement over other similar motors will also add value to this article.
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agk
4/30/2011 6:40 AM EDT
By reading this article my thoughts go back to the VCR 's head drum direct drive and capstan direct drive motors. The same design in a small size and lower power it was working there. But here this motor has to meet many more things as shock proof, water proof,dust proof,heat proof and carry atleast two times more than the specified weight.
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elPresidente
5/2/2011 5:15 AM EDT
This seems awfully naive(full blame is on EET editors for accepting the piece), almost like it was written by a high school kid, and there's nothing novel or "nifty" about it for all you guys caught agasp in the comments section - do the math on the cost of a printed circuit motor with enough layers to be both mechanically and electromagnetically sound, appropriate layup Tg, and copper thickness and you very quickly have a $8000 weak torque motor per axle.
The Maker community have been building axial flux alternators and generators (which is what this is) for well over a decade for wind power and have figured out how to bury windings ECONOMICALLY without the excessive cost of prepregs and laminating presses. Read Hugh Pigot's book if you want reality and cost-effectiveness versus fantasyland equation based nonsense.
The issue of flux saturation and reluctance in the air/epoxy gap also is not addressed in this math exercise, which will seriously limit the mag field contribution of the 1 Tesla magnets that are being assumed in force calculations.
To suggest fixing the axle to the frame of the vehicle to "simplify shock absorbers", is extremely naive as well as is the notion that much less than 10cm is a large enough axle stub to support a 1.5 tonne vehicle hitting a pothole...LOL this has the same shaft diameter as a 1/2HP furnace blower motor. Clearly, the author's never designed autmotive drivelines; apparently just a dreamer with a glass of wine and a fireplace and enough engineering knowledge to be reckless.
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roldan
5/7/2011 8:37 AM EDT
I would very much like to be a naive high school kid. Unfortunately, I am a retired electronics engineer, with 40 years of background in the industry, acting now as an independent consultant. Almost twenty patents filed. Six presentations at international conferences. One invited paper at ISSCC. My career is behind me.
To be fully honnest, when I tried to patent this concept, I found that this was already done almost twenty years ago. There are at least two naive high school kids dreaming in the world. But, apparently, the other one failed in promoting the concept.
I think, but you can disagree, that it can be very beneficial for the whole industry, and not only the automotive one. For an independent consultant, the automotive industry is too big. I'm more interested in other applications, looking for attractive small niches. But, if I can convince the automotive industry to go in this direction, this should help for developing smaller businesses.
I would enjoy replying to technical questions. In your comment, I can't see any requesting an answer. Please, consider the concept, and not the implementation details.
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davealle007
5/11/2011 10:42 AM EDT
Thats kinda scarey, just anyone that knows enough to be dangerous can post all this with the editor of EE times to go ahead and let it happen. I guess thats the downside of this kind of forum. The good side is that someone like roldan speaks up to reprove it, but is he right?
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WarlockofOz
6/5/2011 11:27 PM EDT
I think you are getting confused between cm and mm. A 10cm(100mm) axil will, depending on what it is made from will easily hand up to 5 x 1.5 tons. I've lifted components up to 30 tons on pins that thick.
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elPresidente
5/2/2011 5:16 AM EDT
And, as any HIGH SCHOOL kid can tell you, it's 1/2 m*v*v for energy, which is VERY significant energy as anyone who's hit a wall at 50km/h can tell you....you don't dump it into a resistor, especially for a vehicle carrying limited stored energy on board to start with...streetcars used to do that one 75 years ago to heat the cabin. We are supposed to be cooling the planet, not heating it with printed circuit motor braking systems or failing to recycle it for later use in moving the vehicle.
Has anyone done the math for the commutation "switches" in this wundermotor? For a 20A "starting torque" you are dissipating 400*5.6 or 2.25kW PER MOTOR, or 10kW of power in the switches for 4WD. Now add in your winding resistance. It gets a lot worse when you are using the 'sports car' 30A example that was calculated in a prior page - almost DOUBLE. The Chevy Volt only carries 16kW of batteries....
Thanks for the laughs - can't wait to see part deux. A new low, EET; a new low.
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Efried
5/4/2011 3:36 AM EDT
Please add some outlook to your criticism:
What about SRM?
Why is the mass per weight so bad with current electric motors?
Please allow for some innovation - even in early stage- My guess is that electric mobility will fail with current low RPM motor designs.
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Efried
5/4/2011 3:36 AM EDT
mass per power of course kg/kW
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astrayelmgod
5/3/2011 9:33 PM EDT
0.5mm looks like about 14 oz copper. My VERY limited experience with making coils out of PC boards was with 4 oz copper, and even that was a lot more expensive than making it the usual way. So, what is the attracttion for using PC stock?
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BOY Dela Pena
5/5/2011 9:23 AM EDT
The design looks very good and will have some other usage, The main thing is how much it will cost and how you can have more detailed information.
Thank you,
Godofredo Dela Pena
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DrQuine
5/9/2011 6:37 PM EDT
Two years ago "EE Times" reported that "Daimler bus combines hub motors, fuel cells" (http://www.eetimes.com/electronics-news/4197774/Daimler-bus-combines-hub-motors-fuel-cells) so it would appear that the deployment problems for hub motors are not insurmountable. It sounds like one challenge will relate to car handling characteristics having additional mass that will be moving with the wheels (rather than the vehicle body). This is probably less of an issue for a bus. Another design issue will be to ensure that the hub mounted motors are designed to tolerate exposure to the elements near the wheels rather than being protected in the engine compartment.
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graduatesoftware
6/25/2011 9:13 PM EDT
Readers are directed to two sites:
http://www.technologyreview.com/energy/21666/
http://www.launchpnt.com/portfolio/aerospace/uav-electric-propulsion/
It doesn't look like Exro weathered the recession very well since I haven't seen anything from them lately, but my original analysis of their approach/patent (switched coils to change torque characteristics) led me to believe that the engineering was sound. Likewise for LaunchPoint.
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HoosierDaddy0
7/5/2011 1:33 PM EDT
Has anyone heard of BionX, www.bionx.ca? They make hub motors used in boost systems for bicycles and velomobiles. Their systems go up to 500 watts and are priced around $2,000 with a control system using regenerative braking, http://www.youtube.com/watch?v=eSFE151tRdM. Is the system described here better or cheaper than the BionX system?
I want to mass produce velomobiles with boost systems controlled by I-pads, and could use the help of some smart guys like you.
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green_is_now
1/4/2013 11:02 PM EST
The problem is in all the IR and reactive losses of the matrix wiring and switches, and there cost
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green_is_now
1/4/2013 11:07 PM EST
The switches need to be able to handle both high current in one scenario and high voltage in the other extreem.
So the semiconductors size and cost go throught the roof, add the IR loss gain for needed worst case voltage needed, making this not feasible quickly.
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