Interesting from a production point of view.  If they have a need for low 
quantities (relative) of motors with different HP then it might make sense to 
tools once and then be able to vary the characteristics during assembly.  I was 
thinking it might be more interesting if they put the rotor on a lead screw and 
allowed the positioning of the magnets w.r.t. the coils to be adjusted.  Would 
provide something like field weakening on a permanent magnet motor.

Lawrence Harris

> On Jan 4, 2018, at 15:09, ROBERT via EV <> wrote:
> I do not see the advantage except having the capability to use one motor core 
> for multiply HP motors.  Does anyone think GM is going to use different 
> magnet lengths in the same motor?  Does this have some efficiency 
> improvement?  Do you think they are going modify the controller to allow 
> different magnet lengths in the same motor?  Anyone have any thoughts on this 
> subject?
> ________________________________
> From: EV <> on behalf of brucedp5 via EV 
> <>
> Sent: Thursday, January 4, 2018 2:43 PM
> To:
> Cc: brucedp5
> Subject: [EVDL] EVLN: GM's Multiple-Magnet-Length Electric-Motor Patent
> Anyone who thinks General Motors isn’t serious about electric vehicle
> leadership doesn’t have a clue.
> Despite Silicon Valley’s derogatory ideology regarding conventional car
> companies like General Motors, the dinosaur from Detroit has been at the
> forefront of electrifying personal mobility. GM’s flirtation with electric
> vehicles began in earnest back the early ’60s. It started with the
> Electro-Vair and Electro-Maro programs in the ’60s, then came a
> battery-powered Chevette in 1977, followed by production of the EV1 in the
> late ’90s, before culminating with the Chevrolet Bolt, the industry’s first
> long-range-yet-affordable-mainstream-electric-car.
> But the company isn’t resting on its laurels, as Tesla Model 3 reviews begin
> to hit the internet, GM is busy working on a new family of electric cars due
> in 2021. While advancements in battery technology have long been heralded as
> the key to consumer adoption, GM engineers haven’t forgotten that a motor is
> still what propels a vehicle forward, electric or not.
> Published on December 19, 2017, by the USPTO, GM has filed a patent for an
> electric motor with multiple magnet lengths which could totally change how
> the company thinks about manufacturing electric propulsion systems.
> For example, the Chevrolet Bolt uses a permanent magnet brushless motor,
> where a magnetic field is produced by the spinning magnet and rotor assembly
> which then transfers to the stator core and interacts with flowing current
> to create torque. Differing magnet lengths will change the torque output,
> smaller magnets decrease torque, while longer ones increase torque,
> proportionally.
> What the company is proposing is a new “modular” lamination sheet which
> would be capable of accepting multiple magnet lengths. Instead of being
> forced to re-engineer the lamination stack each time a change in magnet
> length is required, GM proposes a series of tabs within the apertures of the
> lamination sheets which, when layered, can be assembled to delineate the
> magnet slots.
> Effectively, the tabs will allow the stacks to accept either short or long
> magnets–the tab will support the shorter magnet halfway down the aperture or
> get pushed out of the way upon inserting a longer magnet. GM claims there
> will be at least a 25-percent difference in magnet lengths.
> It’s helpful to think about GM’s work with modular lamination stacks almost
> like powertrain sharing–take GM’s naturally-aspirated 6.2-liter small-block
> V8, which is offered in LT1 and L86 guise. As the high-performance version,
> the LT1 is equipped with a shorter intake runner for better high-rpm
> breathing, different exhaust manifolds, and unique cam timing; while the
> trucks make use of longer intake runners in order to fatten up the mid-range
> torque curve.
> What will be of interest moving forward is how GM plans to implement the
> respective magnet lengths, will the smaller magnets be used for efficiency,
> while the bigger ones left for high-performance or hauling? Possibly, but
> there are also drawbacks to simply increasing magnet size; larger magnets
> may create more torque, but they also force the coil to fight through more
> resistance as the higher torque values lead to an increase in eddy and
> hysteresis.
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