Chevrolet Bolt EV gearbox details

[picasso]

Another great snippet of article from InsideEVs:
http://insideevs.com/chevy-bolt-200-mile-ev-battery-cooling-and-gearbox-details-bower/

Tesla Model S, and BMW i3 however use simple parallel-helical single speed gear reduction gear sets. What do we see in the Bolts Gearbox?

It is still a co-axial gearbox. The drive shafts are on the same axis as the motor.

However, the gear reduction set is now a simple parallel-helical gear set like Tesla and BMW i3.

Simple and lower cost than a planetary reduction set that was used in the Spark.

GM followed the “keep it simple” principal in the Bolt without sacrificing performance. This is essential if we want lower cost EV’s for the masses that are also fun to drive.

 

[laev]

The technical information. It's always helpful for us who are not that inclined to have it laid out nice for us like that

 

[NeilBlanchard]

Simple and elegant - I like it!

 

[Robaroni]

The thing I question is the front wheel drive. I read somewhere they current limit the motors to prevent torque steer. I'll have to see when I drive it. Personally I don't like front wheel drive cars, in an EV you would think it was cheaper to use rear wheel drive and also do away with the stress on CV joints.

Rob

 

[SeanNelson]

The thing I question is the front wheel drive. I read somewhere they current limit the motors to prevent torque steer. I'll have to see when I drive it. Personally I don't like front wheel drive cars, in an EV you would think it was cheaper to use rear wheel drive and also do away with the stress on CV joints.

I've seen a review that stated the Bolt EV has virtually no torque steer despite its very high low-speed torque. Apparently the drivetrain has been carefully engineered to minimize the effect by keeping both driveshafts pretty close to equal lengths.

 

[NeilBlanchard]

Yes, the best thing about the motor / gearbox IS that the half shafts are exactly the same length.

 

[Robaroni]

Yes, the best thing about the motor / gearbox IS that the half shafts are exactly the same length.

Good to hear.

 

[ssspinball]

I've seen a review that stated the Bolt EV has virtually no torque steer despite its very high low-speed torque. Apparently the drivetrain has been carefully engineered to minimize the effect by keeping both driveshafts pretty close to equal lengths.

This claim seems to always appear whenever a new FWD car comes out and in my experience, is never true. I can always feel the torque steer and it is awful when you are used to a RWD daily driver. I noticed the concept VW I.D. is RWD, but that is not due until 2020 (if it even happens then). Hopefully more manufacturers will switch back to RWD now that the cost is not at issue with EVs like it is with gas cars.

 

[Robaroni]

I've seen a review that stated the Bolt EV has virtually no torque steer despite its very high low-speed torque. Apparently the drivetrain has been carefully engineered to minimize the effect by keeping both driveshafts pretty close to equal lengths.

This claim seems to always appear whenever a new FWD car comes out and in my experience, is never true. I can always feel the torque steel and it is awful when you are used to a RWD daily driver. I noticed the concept VW I.D. is RWD, but that is not due until 2020 (if it even happens then). Hopefully more manufacturers will switch back to RWD now that the cost is not at issue with EVs like it is with gas cars.

I'm not sure EVs are any better than ICE cars. Equal length half shafts help but I think as you turn the wheel and hit the 'gas' engine torque can still cause problems. In fact EV's are probably worse as they have a flat torque curve basically and lots of it.

RWD is really much nicer.
Rob

 

[GetOffYourGas]

I've seen a review that stated the Bolt EV has virtually no torque steer despite its very high low-speed torque. Apparently the drivetrain has been carefully engineered to minimize the effect by keeping both driveshafts pretty close to equal lengths.

This claim seems to always appear whenever a new FWD car comes out and in my experience, is never true. I can always feel the torque steer and it is awful when you are used to a RWD daily driver. I noticed the concept VW I.D. is RWD, but that is not due until 2020 (if it even happens then). Hopefully more manufacturers will switch back to RWD now that the cost is not at issue with EVs like it is with gas cars.

Not only do EVs solve the cost issue, but the weight distribution issue too. ICE cars have their weight over the front wheels. BEVs can have their weigh split 50/50. Or moved aft if desired. Plus the near-instant response of EVs can lead to very effective traction control.

I *really* hope that we start to see RWD EVs. Other than Tesla, of course. Naturally, they get it.

 

[Breezy]

The i-MiEV and the i3 are both RWD.

FWD sells better in snowy climates. I'm not going to argue whether it is better, because we aren't going to solve that today.

Suffice it to say I'm happy that the Bolt is FWD.

 

[GetOffYourGas]

True, I wasn't thinking of those. I would rather see RWD become the norm for EVs, though.

As for which is better in a slippery climate? Well, given the points I made above, I would argue that RWD *should* be just as good as FWD (if done right) during slick conditions, and *will* be much better during dry conditions.

As a point of reference, I live in Syracuse, NY. We have cold, snowy winters. My friend's RWD BMW 328i handled the slippery conditions just as well as your typical FWD car. He naturally used good snow tires. But BMW's traction control system was impressive. Put that on a BEV, like the i3, and it should do even better!

 

[NeilBlanchard]

Front wheel drive has much higher potential for regen.

 

[Zoomit]

Front wheel drive has much higher potential for regen.

Not true in practice. Regen maxes at about 0.3g deceleration. Under most all conditions the rear tires have enough traction to create that regen deceleration force. If they don't, I'll suggest you are traveling too fast for conditions. Either way, the traction/stability control would stop the car safely, it just wouldn't save that energy for the battery. This would only happen in a fraction of a fraction of the braking events.

One other point to consider is that the forward weight transfer of a vehicle under braking is a function of it's wheelbase and CG height. As a percentage, a Jeep Wrangler will see much more weight transfer than a Ferrari. An EV with a skateboard battery/chassis generally has a long wheelbase and lower CG as compared to similar cars. It will experience less weight transfer for any given deceleration rate than a similar ICE vehicle and certainly less than a higher clearance SUV.

 

[BoltyMcBoltFace]

Regen maxes at about 0.3g deceleration.

Why? A Tesla can accelerate at over 1 g, so if it can suck that much power out of the battery why can't it push something close to that back in? It seems like an engineering consideration rather than a limitation due to physics. And for a Tesla, it probably is a limitation of how much deceleration you can safely do with just the rear wheels. But I'm just an enthusiast, not an engineer, so I may be missing something.

 

[Robaroni]

Regen maxes at about 0.3g deceleration.

Why? A Tesla can accelerate at over 1 g, so if it can suck that much power out of the battery why can't it push something close to that back in? It seems like an engineering consideration rather than a limitation due to physics. And for a Tesla, it probably is a limitation of how much deceleration you can safely do with just the rear wheels. But I'm just an enthusiast, not an engineer, so I may be missing something.

It seems to me that regen should create a benefit right up to tire slippage. The only limiting factor would be maximum battery current, are you saying that happens at .3 G's?

 

[Zoomit]

Regen maxes at about 0.3g deceleration.

Why? A Tesla can accelerate at over 1 g, so if it can suck that much power out of the battery why can't it push something close to that back in? It seems like an engineering consideration rather than a limitation due to physics. And for a Tesla, it probably is a limitation of how much deceleration you can safely do with just the rear wheels. But I'm just an enthusiast, not an engineer, so I may be missing something.

It seems to me that regen should create a benefit right up to tire slippage. The only limiting factor would be maximum battery current, are you saying that happens at .3 G's?

Let me clarify. The engineers across many car companies have designed the regen systems to max out around 0.3g. I haven't collected data, but recall that that approximate value has been used for GM, BMW, and Tesla. There's no question that the tires could generate higher levels of regen during dry conditions. The motor and larger batteries could support more if there was the design intent. 0.3g is not an inherent engineering limitation.

I speculate that the reason roughly 0.3g is common across EVs is simply due to human factors; specifically, 1) higher levels of regen could create safety issues when drivers inadvertently applied excess regen, by having their foot slip off the accelerator pedal for example and 2) needing to decelerate faster than 0.3g is an anomaly, both from a statistical and driver experience perspective. Braking that much indicates the driver has come across an unexpected situation, has misjudged the situation or is just driving very aggressively. In those circumstances, max braking effectiveness is needed, thus the friction brakes are priority and the efficiency gained from regen in this rare situation is a secondary concern.

 

[Robaroni]

Why? A Tesla can accelerate at over 1 g, so if it can suck that much power out of the battery why can't it push something close to that back in? It seems like an engineering consideration rather than a limitation due to physics. And for a Tesla, it probably is a limitation of how much deceleration you can safely do with just the rear wheels. But I'm just an enthusiast, not an engineer, so I may be missing something.

It seems to me that regen should create a benefit right up to tire slippage. The only limiting factor would be maximum battery current, are you saying that happens at .3 G's?

Let me clarify. The engineers across many car companies have designed the regen systems to max out around 0.3g. I haven't collected data, but recall that that approximate value has been used for GM, BMW, and Tesla. There's no question that the tires could generate higher levels of regen during dry conditions. The motor and larger batteries could support more if there was the design intent. 0.3g is not an inherent engineering limitation.

I speculate that the reason roughly 0.3g is common across EVs is simply due to human factors; specifically, 1) higher levels of regen could create safety issues when drivers inadvertently applied excess regen, by having their foot slip off the accelerator pedal for example and 2) needing to decelerate faster than 0.3g is an anomaly, both from a statistical and driver experience perspective. Braking that much indicates the driver has come across an unexpected situation, has misjudged the situation or is just driving very aggressively. In those circumstances, max braking effectiveness is needed, thus the friction brakes are priority and the efficiency gained from regen in this rare situation is a secondary concern.

I can see that but I also expect variable regenerative braking in the future. The harder you press the brake the more regeneration you get. So now you brake for an animal crossing the road and you get the full benefit of Newton's Second Law (F=MA). The less you use friction braking the greater your range - that approaches the ideal, I want to see cars go 500 plus miles on a charge. Right now I think EVs are over powered, make an EV that takes 10 seconds to get to 60 and tops out at 90. There are millions of ICE cars on the road doing that so cut back on the power required and go longer on the range. Right now EVs have to show their 'stuff', the Bolt gets to 60 in 6.5 to 7 seconds. Personally I don't need a car that goes that fast, I'll opt for mileage given the choice.

 

[BoltyMcBoltFace]

I understand why they'd want to limit to .3g when lifting off the accelerator, but you should get more when you hit the brake pedal. It's my understanding that GM, Nissan and Kia do this, while Tesla and BMW do not. To me that's very lazy engineering on the part of BMW and Tesla, wasting energy that should have gone into the battery.

 

[NeilBlanchard]

The front wheels provide ~70% of the stopping power. That's just physics. So the front wheels have far more potential to provide regen.