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  #11  
Old 04-20-2017, 09:32 PM
brian_ brian_ is offline
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Default Re: Switched Reluctance pancake EV drive-train

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 GMs 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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  #12  
Old 04-20-2017, 10:12 PM
brian_ brian_ is offline
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Default Re: Switched Reluctance pancake EV drive-train

Quote:
Originally Posted by henrykeultjes View Post
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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  #13  
Old 04-20-2017, 11:21 PM
Karter2 Karter2 is offline
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Default Re: Switched Reluctance pancake EV drive-train

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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  #14  
Old Yesterday, 03:27 PM
brian_ brian_ is offline
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Default Re: Switched Reluctance pancake EV drive-train

Quote:
Originally Posted by Karter2 View Post
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.

Quote:
Originally Posted by Karter2 View Post
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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  #15  
Old Today, 09:36 PM
aeroscott aeroscott is offline
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Default Re: Switched Reluctance pancake EV drive-train

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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