[ad#post_ad]The Chevrolet Volt’s technical details are now being laid bare for all the world to see. Motor Trend magazine was the first to get a full debriefing on how the Volt’s powertrain functions and according to GM engineers I have just spoken with, have done an excellent job explaining this.
As you are reading this article I am spending a full day driving the Volt more than 100 miles throughout Detroit in both EV and extended range mode and attending technical briefings on the inner working of the car. More on this soon.
Frank Markus of Motor Trend took the car for an extended test drive and found it lived up well to GM’s promises. He also explains the inner workings of the Volt’s transmission for the first time. The previously reported patent application found by our own reader Cab Driver was confirmed as accurate.
Here’s how it works.
The drivetrain has a bit in common with the Prius and Ford hybrids. It consist of a single planetary gearset, two electric motors, and one gas engine. Motor Trend thinks the design is superior and more efficient than Toyota’s, and according to GM engineers with whom I spoke, is on the verge of patented.
There is a large central sun gear turned by the 149 horsepower electric motor at all times. Around it is a planetary carrier which turns the wheels. When the car is in charge depleting mode, an outer ring is locked to the case. The engine and generator are disengaged.
When the car reaches 70 mph the main motor spins too fast to be maximally efficient, and a clutch disengages the ring from the case. This allows the second electric motor to participate and both motors act in parallel to reach speeds of 101 mph with adequate power.
In charge sustaining mode, the gas engine goes on and clutches to the generator causing it to produce electricity to continue powering the main motor.
However of particular interest, when going above 70 mph in charge sustaining mode, and the generator gets coupled to the drivetrain, the gas engine participates in the motive force. GM says the engine never drives the wheels all by itself, but will participate in this particular situation in the name of efficiency, which is improved by 10 to 15 percent.
Markus liked driving the car and he noted he was surprised about the direct mechnical connection.
Motor Trend found 0 to 60 in 8.8 seconds in EV mode and 8.7 seconds in extended range mode. This difference was verified to me by engineers. Noting it to be “no sports car” the Volt still blows the Prius away (9.8 seconds 0 to 60).
Though not specifically tesing it, Markus said drivers should expect fuel effieicny when running on gas from high 30s to low 40s.
He also noted the Volt will flash a dash message “low propulsion power” when going up steep grades in extended range mode and will drop to 40 MPH. This will not happen if mountain mode is engaged ahead of time, which will leave extra energy in the battery, causing the engine to go on sooner.
They found it quiet as well as quick and nippy in traffic.
The brakes were noted to be suprtior to the Prius, and do an excellent job mating and feathering initial regenerative motor braking and eventual disc caliper braking.
Motor Trends bottom line: If the gas/electric and plug-in sport sedans (Fisker, Tesla) and supercars (Jag, Lotus, Porsche, Ferrari) are as well-engineered as this subcompact, enthusiasts need not fear the 60-mpg future.
This entry was posted on Monday, October 11th, 2010 at 12:18 am and is filed under Engineering, Voltec. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.