# Switched Reluctance pancake EV drive-train



## henrykeultjes (Apr 13, 2017)

Looking at a recent Automobile magazine article about electric cars from the automobilemag site (PM for details) 


and the beginning comments "As it stands today, battery electric vehicles (BEVs) are little more than loss-making goodwill devices" and at the end "Research tells us that in 15 years time, 65% of the car-buying population will consider a BEV. Today that number is below 5 percent." 

Given growth like that, it seems logical that alternatives to the current electric motors will receive strong consideration because, as that article states near the end, "EVA2 models will be no more expensive than comparable gas or diesel models." 

Considering that Switched Reluctance Motor/Generator (SRMG) are powered by DC, generate DC and that batteries can only be charged with DC, the incentives for using SRMGs seem to be enough to invest in the development of SRMG based automotive drive-trains, especially as a means of reducing both weight and cost. 

The design of the Switched Reluctance based drive-train depicted in the attached illustrations are available for use by anyone to use (PM for details) Very much like Open Source in software. My expectation is for others to build on this design and share their additions, including a suitable circuit design, with others, as I am willing to elaborate to the best of my ability on the design details. Tesla, Toyota and others have already made their patent portfolios available to others and this design is offered in a similar vein. 

Electric Vehicles (EVs) have gained their popularity mostly because of their positive environmental impact. However, in a 90 million unit vehicle annual world market, the environment can be helped only when EVs gain a substantial percentage of that market. If that is to happen, they need to be more in the price range of the Chevy Spark and similar vehicles that can be bought for under $15,000 (in Mansfield Ohio for under $11k) or the Ford Ka, my original target for this design. 

This Creative Commons submission is a way of helping anyone, wanting to help that environmental goal, build on this submission. 

Pictured in the attached illustration #1 is the Switched Reluctance Motor/Generator (SRMG) in RED on top of the differential, just for mentally illustrating, the rear of a Ford Escape Four-Wheel Drive or similar, turned vertical, rather than horizontal, as they are normally deployed, and without the viscous clutch. 

1. An SRMG is powered by DC, generates DC in its regenerative charging mode and, of course, batteries can only be charged with DC. 

2. A SRMG does not require an inverter and, because of 48 Volt automotive technology being heavily pursued, DC to DC and intelligent charging could reduce the cost of the overall BEV drive-train. Intelligent charging in this case means that electricity "drips" from the generator to an electronic accumulator of sorts, perhaps a capacitor, that "flips" a "unit" of the accumulated power into the battery at whatever "flip" it is set for. 

3. A pancake configuration is more torqy 

4. You can see in illustration #2 the rotor and stator are modular, typically magnetic steel based, components that are captured in aluminium castings. 

5. This design allows both the motor and the generator to be engaged in phases so that employing one of the, for example, four phases produces minimal torque or braking while deploying all, for example, four phases produces maximums. Those phases need to be balanced, of course. 

6. SRMG's do not use environmentally problematic rare earth materials. 

7. Using aluminium to "stretch" the poles reduces the overall weight. 

8. The aluminium reduces the undesirable reluctance interference to the adjoining poles. 

9. The aluminium castings allow more effective cooling channels than totally steel would, and those channels will become part of the climate control system. 

10. The pancake configuration sits directly on top of the pinion shaft to the ring-gear eliminating the typical EV 90 degree gearing from the motor to the differential. Gearing could be inserted there, if desirable. 

11. Torque vectoring clutches, preferably based on intermittent electro-magnetic slipping, rather than constant electromagnetic activation that takes more current, could be used instead of a differential. 

12. The pancake configuration on top of the differential allows the SRMG to be bolted to the differential through the bottom of the enclosed compartment that holds the SRMG and controller thus physically separated from the rest of the drive-train. 

13. That compartment will be clean and out of the mud capturing additional heat for climate control purposes, rather than wasting that energy to the atmosphere. Cooling can, of course, be done with a, preferably scroll compressor based, heat-pump like made by Copeland Division of Emerson in Sydney Ohio. 

16. Image #3 attached is an illustration of a standard Switched reluctance device where the poles face each other, rather than where the rotor poles run through u-shaped stator poles that have the coils inside the bottom of the U as shown in RED in the animation, image #4 - in email #2 

15. The regenerative braking function of an SRMG driven electric vehicle is, of course, identical to the generator function of the witched Reluctance Generator (SRG) in a wind-turbine. 

Therein lies the rest of the story. How Henry Keultjes pursuing development of a wind-turbine came upon this EV drive-train. 

A write-up about rationale of the EVs and the ability of car companies to exploit the very same manufacturing technologies like stamping, die casting and even electronics can be readied in a day or two. 

Henry Keultjes will be glad to share further details under the same Creative Commons license through DIYElectric Car or <[email protected]> 

Henry Keultjes 
Mansfield Ohio USA 
Direct 419-525-1111


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## Karter2 (Nov 17, 2011)

What happened to the "attached diagrams" ??


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## major (Apr 4, 2008)

henrykeultjes said:


> Looking at a recent Automobile magazine article about electric cars from the automobilemag site (PM for details)
> 
> 
> and the beginning comments "As it stands today, battery electric vehicles (BEVs) are little more than loss-making goodwill devices" and at the end "Research tells us that in 15 years time, 65% of the car-buying population will consider a BEV. Today that number is below 5 percent."
> ...


Hi henry,

That's interesting. Loaded with misinformation followed with bad ideas. But please prove me wrong. For instance, explain or reference a treatise on how aluminum can "stretch" (7) the poles or reduce undesirable reluctance interference to the adjoining poles (8) in switched reluctance machines.

Regards,

major


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## brian_ (Feb 7, 2017)

With no diagrams, there is no useful contribution here. Even with diagrams, it is not obvious that there is any original content, as switched reluctance machines have been around for a very long time.



henrykeultjes said:


> 1. An SRMG is powered by DC, generates DC in its regenerative charging mode and, of course, batteries can only be charged with DC.
> 
> 2. A SRMG does not require an inverter...


A switched reluctance machine is *switched* - that means it does not run on direct current; it runs on the output of multiple phase outputs of the controller... which is effectively the same as an inverter used to run a three-phase AC PM motor, or the controller of a electronically-commutated DC PM motor.



henrykeultjes said:


> ... because of 48 Volt automotive technology being heavily pursued, DC to DC and intelligent charging could reduce the cost of the overall BEV drive-train. Intelligent charging in this case means that electricity "drips" from the generator to an electronic accumulator of sorts, perhaps a capacitor, that "flips" a "unit" of the accumulated power into the battery at whatever "flip" it is set for.


The reference to 48 volts suggests that the author has negligible understanding of electrical power. Huge currents resulting from a low operating voltage are not desireable.

The final "drips and flips" stuff just looks like nonsense.



henrykeultjes said:


> 6. SRMG's do not use environmentally problematic rare earth materials.


This is the only advantage I see in a SRM. The same is true of induction motors, yet all serious production EVs use PM motors.

_Edit note_: as discussed in the following posts, Tesla is the exception. Thanks to Duncan for catching my error.


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## Duncan (Dec 8, 2008)

brian_ said:


> This is the only advantage I see in a SRM. The same is true of induction motors, yet all serious production EVs use PM motors.


 Really? - I was under the impression it was the opposite and that Tesla and all of the others used induction motors

Some of the older hybrids used PM motors


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## ishiwgao (May 5, 2011)

Duncan said:


> Really? - I was under the impression it was the opposite and that Tesla and all of the others used induction motors
> 
> Some of the older hybrids used PM motors


did read somewhere (a long time ago) that inductions were cheaper than PM motors hence used by many manufacturers, though not as powerful or efficient or something of that sort compared to PM.


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## brian_ (Feb 7, 2017)

Duncan said:


> Really? - I was under the impression it was the opposite and that Tesla and all of the others used induction motors
> 
> Some of the older hybrids used PM motors


Ah, good catch. Tesla does apparently still use an induction motor, probably because it's cheaper, especially in large (for cars) sizes, and because their initial motor and controller partner used induction motors.

Toyota hybrids, GM hybrids and the Volt Spark EV and Bolt, current Honda hybrids, and the Mitsubishi i-MiEV use PM motors, for best efficiency; rotor design details and magnet design have changed over the generations of Toyota hardware, but they're still PM as far as I know. The rare-earth magnets are an expensive and problematic part of the design. Honda is working on methods to reduce or eliminate the use of rare-earth elements, but still uses magnets.

The Nissan Leaf motor is usually described as "synchronous", which applies to any PM motor as well as some non-PM AC designs, but non-PM AC synchonous motors are impractical for cars and diagrams (including one in this forum) call out the rare-earth magnets in the rotor. Here's an article from the introduction of the Leaf:
Nissan LEAF EV and What is a Permanent Magnet AC Motor?

Because the stator is the same and even the rotors look externally similar in PM and induction designs, it can be hard to tell which type a motor is, without an explicit statement in the specifications.


To be clear, while I have great reservations about the value of the post which started this thread, I do think that non-PM motor designs (induction and switched reluctance) are valuable in the right circumstances and may be even more valuable with development.


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## henrykeultjes (Apr 13, 2017)

Sorry folks, but I am not good at dealing with all those negatives. I am not a guy that went to Delft but I have ideas and a fairly good understanding of what might be possible and this post was submitted in that vein. My email address is on the post and if someone is truly interested in pursuing this and make it work, email me because I will not be back on this site. Henry


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## dcb (Dec 5, 2009)

henrykeultjes said:


> Sorry folks, but I am not good at dealing with all those negatives.


Look, posting nonsense is negative.
"Considering that Switched Reluctance Motor/Generator (SRMG) are powered by DC, generate DC and that batteries can only be charged with DC"

What da faq does that how make sense bad?!? You *can* make it pulsed DC, but who cares?


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## brian_ (Feb 7, 2017)

henrykeultjes said:


> Sorry folks, but I am not good at dealing with all those negatives.


Although the tone of the responses - including mine - was not very supportive, the real world has lots of negatives. Perhaps it's time to learn to deal with them... with knowledge and understanding.

Certainly posting a pile of text referring to diagrams and not providing the diagrams should be expected to result in some negativity.



henrykeultjes said:


> I am not a guy that went to Delft but I have ideas and a fairly good understanding of what might be possible and this post was submitted in that vein.


Henry, your post does not convey either original ideas or much understanding. Perhaps it's mostly a communication issue?

By the way, I'm not familiar with Delft. Do you mean the university in the Netherlands... then it's not surprising, although I'm sure it's a fine institution. I don't think anyone here cares as much about formal education as relevant ideas, effectively communicated.



henrykeultjes said:


> My email address is on the post and if someone is truly interested in pursuing this and make it work, email me because I will not be back on this site. Henry


Not a problem. If I am interested in SRMs, I'll read the existing texts and contact manufacturers of these products. I genuinely do not understand what idea was supposed to have been conveyed by the original post, and it must not be important if you're not willing to pursue it here.


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## brian_ (Feb 7, 2017)

In a press release about the Spark, GM provided some information about the motors which they use (and they even build some of them):
Chevrolet Showcases Spark EV Electric Motor

While the attached "Electric Motors 101" document only explicitly lists models using permanent magnet motors (Volt and Spark), it does imply that some GM hybrids have used induction motors, particularly in GM’s eAssist mild-hybrid system. It looks like the low-powered eAssist is induction, and the "A" motor in the CT6 PHEV is their first high-power induction motor.

The first advanced GM hybrid - the Two-Mode - used permanent magnet motors (82 kW each).


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## brian_ (Feb 7, 2017)

henrykeultjes said:


> 3. A pancake configuration is more torqy
> ...
> 10. The pancake configuration sits directly on top of the pinion shaft to the ring-gear eliminating the typical EV 90 degree gearing from the motor to the differential. Gearing could be inserted there, if desirable.
> ...
> 12. The pancake configuration on top of the differential allows the SRMG to be bolted to the differential through the bottom of the enclosed compartment that holds the SRMG and controller thus physically separated from the rest of the drive-train.


Yes, a "pancake" or large-diameter (and axially short) motor design is suitable for high-torque low-speed applications. With a motor having these characteristics, the reduction gearing can be a single step, such as the pinion and ring gears of a traditional final drive unit.

There is no connection between the SRM type of motor and a pancake configuration - all types of motor (but especially permanent magnet types) can be built as a pancake.
GM's Spark uses a slow high-torque motor and a single-stage reduction gear system (with a ratio of less than 4:1); this is not a new or unique idea.

Since the ring-and-pinion (in a traditional longitudinal drivetrain) are a right-angle drive (or "90 degree gearing"), this doesn't eliminate the right-angle drive. In a transverse design (like a typical front-wheel-drive car) there is no right-angle drive, but a pancake motor with a single reduction doesn't work because the large diameter of the motor case blocks one side of the output from the differential... although it could work in a two-motor setup (separate left and right motors, no differential).

If I understand the post correctly, the packaging would place a pancake motor with a vertical shaft, driving an existing final drive unit mounted rotated 90 degree about the lateral axis so the input (pinion shaft) is vertical. This would be an interesting idea for a DIY conversion, but lubrication of the gears might be problematic. For a production vehicle, the common and more efficient configuration is a transverse motor with a planetary reduction gear on the motor axis, and output through the hollow shaft of the motor.

The idea of putting the motor in the interior of the vehicle doesn't seem like an advantage to me. Yes, putting the controller inside seems like a way to protect it, but I think in practice all of this hardware belongs outside of the passenger compartment - especially if liquid-cooled - just like it is in production vehicles.

____________________

If anyone chooses a high-torque low-speed motor for a DIY conversion and drives the pinion of a longitudinal final drive directly, I suggest tilting the motor/pinion shaft up just enough to get sufficient ground clearance under the motor... for packaging, and to minimize lubrication issues.


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## Karter2 (Nov 17, 2011)

The hypoid bevel crown and pinion driven differential is probably the least efficient (high friction losses) component in any drive train.
A spurr gear drive is much preferred, even if, like Tesla, you have an intermediate gear between the motor and the differential gear.


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## brian_ (Feb 7, 2017)

Karter2 said:


> The hypoid bevel crown and pinion driven differential is probably the least efficient (high friction losses) component in any drive train.


Agreed. While an efficient right-angle drive can be made with a simple spiral bevel gear (the axes of the pinion and ring gears intersect), I've seen multiple sources quote a typical hypoid ring-and-pinion as only 90% to 93% efficient, versus 98% to 99% for a straight or helical gear set. The problem is that in a hypoid gear set, the teeth slide against each other. Production cars and light trucks with longitudinal drivetrains normally have hypoid final drive gears; I think this is interesting, since AWD systems routinely use non-hypoid bevel gears to make the multiple turns required and efficiency is so important now.



Karter2 said:


> A spurr gear drive is much preferred, even if, like Tesla, you have an intermediate gear between the motor and the differential gear.


The two-stage parallel gear reduction train, with intermediate shaft, serves two purposes: it shifts the final output centreline far enough to clear the motor case in a transverse configuration (without resorting to a chain or an excessively large driven gear), and it provides a higher reduction ratio than practical with a single stage. Losses in two gear sets are the cost of these benefits. Tesla, Nissan Leaf, Mitsubishi i-MiEV, Toyota rear power units in AWD hybrids, and probably lots of others use this design.

GM uses only a single reduction stage for the Spark, but uses a planetary gearset and coaxial outputs (through the hollow motor shaft) which avoid the need for lots of offset to clear the motor case; Honda's latest electric drive units (rear of AWD MDX/Pilot hybrid, front of NSX) are also planetary coaxial designs.


The main reason to consider hooking a motor to a stock bevel (unfortunately usually hypoid) final drive is just to avoid custom gearbox design and construction, although packaging is an issue, too: a transverse setup is unlikely to fit where a longitudinal-input final drive was originally.


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## aeroscott (Jan 5, 2008)

LTI had told me they use srm's because of low pull out heating of the rotter.
The other advantage is no shoot threw inverter and higher eff. {square wave , but higher igbt count. 
LTI Laterno international incorp.


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## brian_ (Feb 7, 2017)

aeroscott said:


> LTI had told me they use srm's because of low pull out heating of the rotter.
> The other advantage is no shoot threw inverter and higher eff. {square wave , but higher igbt count.
> LTI Laterno international incorp.


Interesting. 
Is "LTI" or "Laterno international incorp." actually mining equipment company LeTourneau Technologies Inc, which is now a part of Joy Global?
If so, they put those SR machines (generator and motors) into diesel/electric series hybrid wheel drives for machines such as the P&H L-950 Wheel Loader (their smallest model), which has a 1050 hp engine and an operating weight over 100 tons. I'm not sure how well motor characteristics scale down by a factor of a hundred.

But what is "pull out heating of the rotor"? Heating of the rotor in high-load low-speed conditions, perhaps?
Also, what does "shoot through inverter" mean (assuming that "threw" was supposed to be through)?


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## major (Apr 4, 2008)

With synchronous motors, pull out torque is the maximum torque (sustained for like one minute) before the rotor cogs or loses synch.

Shoot through is the condition in the inverter where top and bottom switches are both on causing a direct short of positive to negative DC bus rails. The topology of of the SRD switching electronics does not allow this as there is always a motor coil in the circuit even in the event of multiple device failures. A safer failure mode so-to-speak.


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## brian_ (Feb 7, 2017)

major said:


> With synchronous motors, pull out torque is the maximum torque (sustained for like one minute) before the rotor cogs or loses synch.
> 
> Shoot through is the condition in the inverter where top and bottom switches are both on causing a direct short of positive to negative DC bus rails. The topology of of the SRD switching electronics does not allow this as there is always a motor coil in the circuit even in the event of multiple device failures. A safer failure mode so-to-speak.


Thanks!
Those characteristics make sense.

Pull-out torque and heating don't seem like big concerns for a car (assuming it is not entered in a tractor pull). Are failures resulting in shoot-through a common concern in inverters for PM or induction AC motors?


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## brian_ (Feb 7, 2017)

Exploring the idea of the switched reluctance motor, we were discussing which vehicles used the somewhat similar induction motor design, instead of permanent magnet motors. In posts #7 and #11, I listed a number of specific vehicles, so to continue to build the list...


The *Fiat 500e* uses a PM AC motor (in a typical transverse double-spur-reduction package, motor ahead of axle, in the front of the car).
The *VW eGolf* appears to use a PM AC motor (in a typical transverse double-spur-reduction package, motor ahead of axle, in the front of the car)... at least in a photo, the rotor has the no-windings appearance of a PM rotor.
The *Ford Focus Electric* also appears to use a PM AC motor judging from a photo (in a transverse double-spur-reduction package, with the output and differential coaxial with the hollow motor shaft, driving the front wheels)

The summary so far is that it seems like only Tesla uses induction motors in pure EV mass-production cars.

As discussed in post #14, transverse motors and parallel (spur) reduction gears are normal practice.


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