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Drive shaft and axle engine

Pipe engine rather than pancake engine
  (+4, -3)
(+4, -3)
  [vote for,

Drive shafts are being made thinner using new composite materials. Replacing that thickness with an electric motor wrapping the drive shaft could be extremely useful:

For a 340 HP =~ 250 kwh truck motor, you typically have drive shafts 3 meters long (And another 2 meters of axle). So lets say only on the shaft, we would need the equivalent of 1000 bicycle motors 3 mm thin with output of 250 wh (watt hour). Doesn't seem impossible...

You then turn any truck into an EV, without the need to do any changes to the motor. After battery prices go down, the truck will run on batteries alone. Till then, the truck will run on a generator and a small battery storage.

You get regenerative braking power, motive power free of transmission losses, most of the time, no need for idling, with air conditioning still working during your stops, and when the low cost battery stations come out, all existing trucks and vans are instantly ready for the party. Till then you could always continue using your old 1.5 km per liter diesel engine, or if you really don't like the system, just replace the new drive shaft with your old one.

pashute, May 06 2010


       [-] A motor using the driveshaft as a rotor has no redeeming features whatsoever: no traction control (which wheelmotors have) and added unsprung weight (unlike a short motor *between* the transmission and the driveshaft which would have the same driving paramters). And what are you going to anchor the ends (and middles) of a 9' electric motor to ?   

       [edit: [+], got some neat points to it]
FlyingToaster, May 06 2010

       how are you getting power to a rotating driveshaft?
MisterQED, May 06 2010

       Could I suggest a cup of tea?
MaxwellBuchanan, May 06 2010

       1) Check your units. kWh and Wh are units of energy, such as the capacity of batteries. KW and W are units of power, such as the maximum output of motors.   

       2) Check the rotating mass of 1000 bicycle motors. A 3 metre propshaft with that mass would be very difficult to keep under control. Conventional propshafts are made from thin walled tube so that they are stiff in bending and don't thrash around and destroy themselves when rotating at several thousand RPM.   

       3) Pancake motors are so designed because the shape gives the motor a useful torque output. A long thin motor will produce relatively little torque.   

       The easy way to add an electric motor to a truck transmission is by driving the gearbox output. An add-on similar to an overdrive box would allow switching between internal combustion and electric drive.
Twizz, May 07 2010

       Sorry, I didn't get what was meant by a cup of tea.   

       Answering all the other annotations in one:   

       I am proposing to put an electric motor (like the motor of an electric drill) around the drive shaft. I'll be making a thinner driveshaft than the ones you see today on trucks, and then the motor will be the width ("thickness") of existing driveshafts. (I thought this was clear from the title and description).   

       A long cylinder motor may have the benefits and achieve features similar to the pancake motor, since you have many more "control points" on the single power output, than in a single circle fixed length motor (such as the usual electric motors found in car starters, or electric drills). This design (where power is not aligned in straight lines) can give the motor both a useful torque, and the possibility of efficient high rotational speed. So a cylinder motor, because of the way it is built, can give the equivalent of an efficient transmission system, without the need for any transmission system. I had applied for a patent some time ago on a device like this, and a professional paid patent search found several relevant patents and companies manufacturing this type of motor.   

       While correct that kW/hour is a unit of energy (and hence work - or power consumption), I must use that term, since a motor must also be built to withstand ongoing usage of its output, whereas maximum output may depict a feature of the motor which is only momentarily useful. But I'm willing to drop the argument and use the standard power units, if it makes the idea more clear.   

       The weight of the motor on the shaft:
a. There are ever evolving lighter BLDC motors being developed for the aviation industry, so (reminder: this is halfbakery) it should be possible to find lightweight materials. b. Early driveshafts (still most of the ones used in the industry) where quite heavy even with the "thin wall tubes". Modern composite materials make it possible to use a fraction of the mass. I would only be "putting" the mass back on.

       As to anchoring the motor to the underbody of the trucks - that is easily duable and not an issue at all. Try to imagine that I put a static pipe in place of the current driveshaft, and anchor that to the body in several places. The new driveshaft will be turning INSIDE the anchored pipe. This is standard practice in the industry, nothing new here. At most, an extra lightweight but strong frame could be added.
pashute, May 12 2010

       //Sorry, I didn't get what was meant by a cup of tea.//   

       A shell, open on the upper surface, made from vitrified or otherwise heat treated clay or ceramic, containing a liquid above ambient temperature, consisting of water in which are dissolved plant extracts from the leaves of Camellia Sinensis.
pocmloc, May 12 2010

       //anchor that to the body in several places// Unless you plan on using IRS (Independent Rear Suspension) where the differential is bolted to the body (found on cars and some SUV's but not truck trucks), that's very much going to not work. Interesting spreading out the poles though... pending [ ]
FlyingToaster, May 12 2010

       The parasitic magnetic and wiring losses would be huge. This is the exact opposite of how you would want to design an efficient motor.   

       // Till then, the truck will run on a generator and a small battery storage. //   

       Define 'small.' The amount of energy contained in your gastank roughly equates to a large trailer load of batteries.
RayfordSteele, May 12 2010

       "Trailer full"... Not true anymore. See wikipedia for energy density of Li-ion for instance. Its only the cost that's prohibitive now. Not the weight, nor the size. And never ending advances.   

       I define small, by the amount that would typically be used by the truck for a lag (ie between traffic light stops, driver rests etc). This probably wouldn't be great for a long distance truck, but there are so many short distance trucks on the road , especially when reaching the destination area.
pashute, May 28 2010

       Having just posted an idea that included full length axle motors I gotta change my vote to [+] for the general idea, but I still don't think it'd work well: a driveshaft isn't that heavy until you put an extra hundred pounds of electric motor onto one. And you cant make the driveshaft any thinner unless you're planning on lessening the amount of power going through it.
FlyingToaster, Jul 31 2012

       [pashute] what do they call a long thin electric motor ? (ie: the opposite of a pancake motor). I really like the idea of a many pole motor for fine control: useful for off-road where you might want to move 1 cm, not 10. ("spindle motor" seems to be closest but their ratio of diameter to length seems to be 2:1'ish whereas your driveshaft motor wants 25:1 (and my half-shaft axles 8:1))
FlyingToaster, Aug 03 2012


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