Volt vs Prius drivetrains

[evnow]

Check these ...

http://www.motortrend.com/roadtests/alternative/1010_2011_chevrolet_volt_test/index.html

http://www.motortrend.com/features/editorial/1010_unbolting_the_chevy_volt_to_see_how_it_ticks/index.html

http://gm-volt.com/2010/10/11/motor-trend-explains-the-volts-powertrain/

 

[LKK]

I've looked at both the Volt and Prius drivetrains and am struck by how similar they are. Both use planetary gear sets with one ICE and 2 motor/generators. I wonder how they would compare if they were similarly equipped, that is, what if a future Prius was equipped with m/g with similar power to the Volt and a 16 KWH battery. Seems to me both would go around 40 miles on a charge, and be capable of 100 MPH, but because the ICE on the Prius is directly connected to the powertrain, its gasoline consumption would be better. The current Prius gets 50 MPG, adding components similar to the Volt would of course reduce this, but I don't think it would drop to the Volt's 38 MPG.

The difference is the Prius has an Atkinson cycle engine which is supposed to be about 15% more efficient than an ordinary ICE and it doesn't have to suffer dual losses incurred in (1) turning a generator to make electricity (about 6%) and (2) then using that electricity to turn a motor to drive the wheels (another 6% loss).

 

[evnow]

Well, if you add 16kwh of battery, I don't think prius will get 50 mpg.

BTW, this is for Ford.

 

[garygid]

How many clutch-mechanisms does the Volt have?

 

[planet4ever]

How many clutch-mechanisms does the Volt have?

Right. The Volt has two clutches and a brake, all controlling the behavior of the planetary gear and what is linked to it. The Prius has no clutch and no brake as part of that unit. The Prius planetary gear is purely (and simply) a power distribution mechanism to send part of the power to the wheels and the rest to the generator. The Volt planetary gear is the heart of complex system that works in half a dozen different modes to route power in various directions with differing gear ratios.

Both use planetary gear sets with one ICE and 2 motor/generators.

Well, yes, in a literal sense, but extremely misleading. In the Volt, both motors can be used to drive the wheels. In the Prius, one of the motor/generators is almost exclusively a generator. Its only role as a motor is to start the ICE.

 

[LKK]

The Volt has three clutches. One locks or unlocks the ring gear to the case, a second switches the smaller motor/generator in or out, and a third locks the ICE to the motor/generator.

The primary driving force is from the main 149 HP traction motor. The smaller M/G is not used to drive the Volt, it acts as a generator in the range extension. At higher speeds, in battery mode, the ring gear is unlocked from the case and is spun by the M/G, this is done not to increase output power, but to allow the main traction motor to operate at a lower, more efficient RPM. In the battery mode the Volt's power never exceeds the 149 HP produced by the main traction motor.

When the ICE is active in the range extension mode one clutch locks the ring gear to the case, the second unlocks the M/G from the ring gear, and the third locks the ICE to the M/G. In this mode the ICE turns the M/G and produces up to 70 HP worth of electricity. Note that this is considerably less than 149 HP that the main traction motor is capable of. It is however, enough electricity to meet less stressful requirements such as crusing down the highway and city driving, but not enough to climb steep hills or travel at very high speeds. When the demand for power exceeds 70 HP, the Volt draws on the battery to meet the excess demands. There is a small buffer designed into the battery, about 10%, once this is exhausted the Volt is limited to only the electrical power generated by the M/G. I believe this situation remains until regen braking or excess power from the ICE and M/G recharges the buffer.

 

[evnow]

LKK, I don't think the explanation is entirely accurate. For eg., we know ICE can directly drive the wheels, mechanically.

When the ICE is active in the range extension mode one clutch locks the ring gear to the case, the second unlocks the M/G from the ring gear, and the third locks the ICE to the M/G. In this mode the ICE turns the M/G and produces up to 70 HP worth of electricity.

Are you saying the electricity produced then powers the motor to drive the wheels ?

 

[planet4ever]

The Volt has three clutches. One locks or unlocks the ring gear to the case

Sorry if my terminology is wrong. I am not an engineer, automotive or otherwise. To me, a "clutch" with one side fixed, not rotatable, is logically a brake, and that is why I used that term.

At higher speeds, in battery mode, the ring gear is unlocked from the case and is spun by the M/G, this is done not to increase output power, but to allow the main traction motor to operate at a lower, more efficient RPM. In the battery mode the Volt's power never exceeds the 149 HP produced by the main traction motor.

I consider that semantics. It appears to me that both motors are applying force to the planetary system, and the combination of those forces is being used to power the car.

The bottom line, so far as I am concerned, is that the Volt system is far more complex than the Prius system, and not at all comparable.

 

[LKK]

LKK, I don't think the explanation is entirely accurate. For eg., we know ICE can directly drive the wheels, mechanically.

When the ICE is active in the range extension mode one clutch locks the ring gear to the case, the second unlocks the M/G from the ring gear, and the third locks the ICE to the M/G. In this mode the ICE turns the M/G and produces up to 70 HP worth of electricity.

Are you saying the electricity produced then powers the motor to drive the wheels ?

Yup you are correct. I was going to describe that part of the Volt but ran out of space, we are only allowed 6000 characters.

When the ICE is running there are two modes of operation. One is where the ICE is locked to the M/G (operating as a generator) and this electricity is used to power the traction motor. The other is at higher speeds, and this is the case you mention. In this case the ring gear is unlocked while the ICE is connected to the M/G. This results in the M/G generating electricity for the traction motor as in the previous case, and any addition torque generated by the ICE is transferred mechanically to the drive wheels. As before the M/G spins the ring gear to reduce the rotational speed of the traction motor without decreasing torque.

The Volt's drivetrain is complex, but the Prius drivetrain is, in my opinion, just as complex. Take a look at Wikepedia's description of the Prius Hybrid Synergy Drive. I'm amaze at its complexity and how well it works.

 

[Herm]

if you define complexity by the parts count then the Volt is way more complex than a Prius, but the Volt has many benefits of its own, and GM charges you for it. The Leaf is the simplest configuration.