Tuesday, August 21, 2012

2012 Chevrolet Volt - Is it a Real Car? Technology

While it is relatively straightforward to grok how a conventional car works (fuel burns, moves pistons, this drives a car forward through gears and drive shafts and axles...the Volt is a touch harder if only because of its different technique.

So, we've talked at a high level about how it works, now lets go a bit deeper.

Where we have been:

For well over 100 years, cars have been powered almost exclusively by burning of fossil fuel.  This centers on capturing the energy of burning fuel into mechanical motion that is transferred through transmissions, drive shafts, axles, to wheels.

Returning to a stop is accomplished by using plates (brake calipers), covered in a friction material (brake pads), that rub against disks or drums to slow the vehicle by turning that motion into heat.

The rub here is that once fuel is burned, it quickly escapes as waste heat (radiated from the engine having done nothing to move the car or exiting through the exhaust system having only helped in the case of a turbo-charged car that reclaims that exhaust energy to boost the engine's power) or becomes motion that ultimately dies an unceremonious death as heat through the brakes or other friction (with the air, with the road through tires, or in countless other places where that energy passes on its way to move the car along).

Where we are going:

You can use the word 'efficiency' to refer to how much work is done (to move the car from point A to point B) by that burned fuel before it becomes heat in one of those many forms and is lost.

So, all of the efforts to achieve 'high efficiency' in cars are exercises in increasing efficiency by doing something to get more motion out of the energy put into the system.

Techniques that can be used include reducing friction.  Aerodynamics reduce the friction with the air.  Low rolling resistance tires reduce friction with the road.  Optimizations in the moving parts of a car can reduce loss of energy through friction, either through improved lubrication or changing the types of connections to ones that might be more expensive, but lose less energy to friction.

Vehicles that carry batteries and electric motors of any kind (hybrids, full electrics, and cars like the Volt) also carry out another trick - they reclaim energy of motion back into the battery through a technique known as regenerative braking.  Electric motors that can propel the car reverse their function and become generators powered by the motion of the car itself.  Turning that motion into electricity slows the car.  The electricity is stored in batteries that then power the motors again to re-propel the car later.

So, that covers some of the techniques generally used today to improve efficiency but how does a Volt work?

A Volt is not exactly as a hybrid like a Toyota Prius nor a pure battery electric vehicle like a Nissan Leaf - rather it can be thought of as an electric car with an on-board generator powered by gasoline.

So, how is that different than a hybrid like the Prius?

A hybrid uses a gasoline engine and electric motor/battery to propel the car.  At low speeds, the electric motor can propel the car by itself, but at moderate to high speeds (or when significant acceleration is needed), the gasoline engine must be engaged to assist.  The efficiency gains of a hybrid occur mainly in stop and go driving when the regenerative braking and low speed electric operation combine to reclaim energy and use it again, reducing the amount of fuel that has to be burned in slow-speed operation (this also points to why hybrids typically have better mileage in city driving than on the highway - the electric propulsion either doesn't come into play on the highway or is insignificant).

Also, there is added complexity that comes from having the gas engine and electric motor operating simultaneously to move the car along - both have to supply power to a common transmission that then combines the inputs and supplies a single output force to the drive wheels.  Obviously this works, but it is complex.

Volt's 1.4l Gas engine (front and center) and the brains of
its electric drive (to the right).  Orange high-capacity power
cables let the energy flow to where it's needed.
A Volt, by contrast, provides drive power to the wheels through a pair of electric motors.  They get their electric power from a battery pack or from the generator driven by the gas engine.  In normal operation, when there is power in the battery pack, all the electricity needed to drive the Volt is coming from its battery and the gas engine does not run.  In my testing, I was often able to go 50+ miles (arguably, my first 8+ miles are down a long mountain grade, so that is why my range is higher than the  EPA rated 35 miles) before the gas engine needed to start.  If my daily drive was less than that 50 miles, I would not burn any gasoline at all.

So, it is like an electric car like a Nissan Leaf?  Not exactly.

In a battery-only electric car like the Leaf, you can only go as far as the energy in the battery can sustain you.  Once you have run out of electricity, you must re-charge.  The downfall of this is the recharge time of a modern battery.  Even with higher voltage 240V (level-2) charging, it will take hours to 'refill' the battery.  Compare this against the sub-10 minute refill time of a gasoline powered car and you see that an electric is often limited to commuter car duty, and why some people have a problem buying into this technology - even if it would actually meet their needs.

In a Volt, once the battery is depleted, a gas engine (1.4 liter 4-cylinder that runs on premium fuel) starts and runs an electrical generator.  Power from this generator now becomes the input to the electric motors that propel the car.  Since the engine/generator pair only put out the equivalent of 74hp, less than half the 150hp combined output of the electric motors, the Volt is actually slower in this mode than when the battery pack is being used.  However, I found that even in this mode, the Volt could sustain 50-55mph up mountain grades and interstate speeds were no problem.

This combination of battery with generator fall-back give the Volt a real-world advantage over both a traditional hybrid and a full-electric car.  Efficiency in normal day-to-day driving is significantly better than a hybrid and for the occasional drive that exceeds your electric-only range, you just continue on as you always have in gasoline-powered cars of old.

However, this dual-power trick the Volt attempts isn't without its own complexities.  First of all, you are carrying both the electric propulsion items (motors, electronics, batteries) as well as all the parts you know from a conventional gasoline powered car (gas tank, engine, radiator).  All of this brings weight and complexity (though not really more than you would get with a hybrid that also has a dual-power system).

Secondly, because of the expected short time the gas engine would be used in day-to-day driving, the Volt carries only a small (9.3 gallons) tank of fuel.  This provides a somewhat shorter range than a conventional gas-powered car.  And, even with this small a tank, there needs to be logic built into the Volt that occasionally runs the engine to burn off fuel before it becomes 'stale' in the tank.  The tank is also lightly pressurized to extend the life of the gasoline even further.

Finally, there is the complexity that comes with carrying batteries.  The Volt does have a fairly large battery pack.  This pack is made of 288 individual lithium-ion cells similar to those found in modern portable electronics.  The battery in a Volt has a total capacity of 16kWh, though you may have noticed that I only saw 10kWh of energy before the car switched to gas engine/range extended mode.  This is because of an interesting little secret of lithium-ion batteries.  Li-Ion really hates to be fully charged or fully discharged.  Putting in as much power as it can hold or pulling all the power completely out reduces its lifespan greatly (which is why the battery in your cell phone dies a couple years after you bought it - portable electronics use the full capacity of the battery.)  In an automotive application, a battery needs to live closer to 10 years.  In order to get there, GM designed the Volt's battery to only use the middle of its capacity - they never fully charge or discharge the pack and, as a result, expect 70-90% of its new capacity to be retained after 10 years.  Time will tell if this actually ends up to be true.

One last piece of the efficiency game, the regenerative braking trick used by hybrids, etc., is also used here.  So, slowing a Volt will put power back into the battery for later use.  The 'gear' selector has settings for Park, Reverse, Neutral, Drive, and Low - Drive and Low are different only in the amount of regenerative braking they provide - Low is useful in steep grades and in stop and go traffic where more pronounced slowing is nice to have.  In fact, during stop-and-go driving, I could often use Low to slow the car all the way down to 3-5 mph before touching the brake pedal.  This technique, which was far from 'hypermiling', maximized the energy I reclaimed.

So, as you can see, the Volt uses a combination of techniques and technologies to provide yet another take on the 'efficient car' game.  It's downfalls are complexity, weight and cost of carrying dual power sources, and - strangely enough - the difficulty in explaining how this is different than a battery powered car or a hybrid.  Call it an electric and that doesn't seem quite right.  Call it a hybrid and that doesn't capture it either.  Call it, like GM does, a Range-Extended Electric Vehicle - and you likely will get blank stares.  But at least you know how it works now.

Next up, we cover a very busy day of driving and get back into how it is to live with in real-world use...

Thursday, August 16, 2012

2012 Chevrolet Volt - Is it a Real Car? Trivia

A little bit of Volt trivia, in light of it's green car mission.  Specifically CO2 Emissions.

For my commute - I'm seeing about 50 miles of driving (actually a bit more, but let's be conservative here) on 10kWh of electricity, approximately 12kWh to recharge, taking into account losses in the charging system.

The numbers I was able to find shows that Colorado's electricity averages 1.93 lb /kWh of CO2 emitted.  This is actually worse than the national average which is about 1.3-ish.

I had to do some digging to get CO2 emissions for gasoline powered cars.  I found you are getting 20lbs of CO2 per gallon, 2 gallons for a 50 mile drive in my 25mpg car, so 40 lbs for the same distance. (data and explanation of how you end up with more than the weight of a gallon of gasoline from http://www.fueleconomy.gov/feg/co2.shtml )

So, figuring 12kWh is getting me about 50 miles - that maps to 23.16 lb of CO2 for that 50 miles (12kWH * 1.93 lb/kWH)

So, for _me_ (my drive, in my state) it appears CO2 emissions would be cut almost in half.

Also note, this does _not_ take into account things like emissions of any other pollutant, mainly from manufacturing the Volt (or any other new car).  I'm just presenting this as a data point, nothing more.

More tomorrow.

Wednesday, August 15, 2012

2012 Chevrolet Volt - Is it a Real Car? Initial Impressions

DAY 1 Driving Impressions:

Well, technically the car was delivered yesterday with most of the battery capacity run out by the delivery drivers getting to Boulder from Denver.  So, this morning marks the first official part of the test (though, as you'll see, I did get some insights from driving it yesterday as well).

Let's give a bit of context to this set of pics below (taken after my first drive to work after charging fully):

I charged fully, overnight, from 120V using the Volt's included power cord (that normally lives under the cargo area floor).  It took 10 hours to go from a complete discharged battery to full.  Doing so resets the stats of the center display's energy usage stats.  Normally this display shows the miles since last recharge divided by electric and gasoline powered miles as well as kWh used (the Volt has a 16kWh batter pack, of which 10.4kWh is usable - more on that in a bit) and gallons used.  Also a measure of overall, lifetime mpg is shown (this is simply total miles divided by total gallons and ignores any sort of electricity to gasoline conversion like the EPA uses to generate their MPGe numbers.

Starting out, the car showed 39 miles of projected electric range.  However, given my 8 mile downhill drive at the beginning of my commute, it used regenerative braking (using the electric motors as generators to turn energy you'd burn off as heat through the brakes back into electricity) to put even more charge into the battery than allowed by having it plugged-in (the car does some strange things with the battery pack to protect its lifespan, essentially leaving a fudge-factor at the charged and discharged end for things like 'a place to put regen energy when the battery shows full' and also 'a place to get reserve passing power when the battery shows empty'  I've experienced both extremes in the course of less than 24 hours.

Tangent #1 - on the prior day's up-hill drive with a stated 'empty' battery, I did experience what felt like a kick-down to passing gear at one point on the hill.  This apparently was the Volt deciding to let me tap into the reserve in the battery.  However, the reserve was not enough to get me home before giving a warning message of  'reduced power' and I ended up losing about 10mph in the last 2 miles of the climb.  This happened over the course of an 8-mile drive with 1500' elevation gain.  Maximum speed ended up in this stress test as 50-55mph.

Tangent #2 - On the downhill side, I put the car into L ('mode') to increase the regenerative braking.  This did successfully keep the downhill speed under control until it filled the reserve capacity of the battery.  So, about 2/3 of the way down the hill, I went from having a feel of 'engine-braking' through the regeneration pulling off speed as electricity into the battery to then feeling like I was coasting (and then need to use the actual brakes to keep speed down).

In both cases, you have to understand what the car is doing with energy management to not be caught off-guard by the behavior.  I wonder if 'average' Volt buyers are going to understand what is going on - at least the first time.

But, I digress, the stated range on electric got as high as 50 miles by the time I got down to the bottom of that same 1500' elevation change and had pulled every bit of extra energy from the drop and stored it into the battery pack's reserve capacity.

I topped off the tank (premium fuel required), to have a good baseline, and it took about 1.5 gallons to have the tank full - we'll see after a week how much gas I really burn.

As you can see in at the end of my drive to work, I had gone 23.5 miles, using 3.7 kWh or electricity (the Volt battery is 16kWh with a stated 10.4kWh usable).  0.00 gallons of gas used.  Range shows 36 miles of electric driving left - which says a lot more about the downhill to-work nature of my specific commute, but it is kind of fun to see 23.5 miles traveled on essentially 3 miles worth of stated electric range. (I reset my trip gauge at the fuel-top-off, which is where the 14.0 miles comes from, if you were wondering).

We'll just ignore the pie-in-the-sky figure of 250+ mpg for the trip for now.

The rest of the day saw a trip across town in Boulder, a drive up and through Longmont, then back to up the hill for the 1500 ft elevation gain to home.

I was able to make all but the last 7.4 miles of today's driving on electric.  As you can see in the attached end of day energy use stats, I managed 52.5 miles of electric driving (not bad for a car that is rated at 35 miles of electric range - even if you figure the first 10 miles were essentially free as they were all down-hill).

I didn't use the Volt's 'mountain mode' to prepare for the climb.  Mountain mode attempts to keep 40% charge in the battery.  It will run the range extender at high-speed to charge the battery to this level if you are below, or do nothing at all if you are already at that charge level.  This is to preserve some capacity for hill-climbing and would have been a good choice.

I ran out of juice only a couple miles right before the climbing beings in earnest and this time did not run into the dreaded 'reduced power' mode.  However, this is largely due to keeping my speeds down to the 55mph that I was limited to in the reduced power mode the night before.  Even so, the gas engine was revving quite high to generate all the power it could to keep things moving along (the generator is capable of 74hp - which is only slightly less than half the 150hp the electric drive motors can consume, which is why hill-climbing in this mode is not slower than if you have a charged battery.

Tomorrow will not have the extra errands thrown in, so I might be able to make the full drive on battery power - we'll see.

That said, you can see that I burned 0.4 gallons of premium gas (@ 3.699/gallon) and used an even 10.0kWh of electricity.

@ 8.7-ish cents per kWh for me, that means a total cost of driving today of $2.35.

Figuring the same drive in my comparably sized sedan @ 25mpg, I would have burned $8.85 of gas.

So, the Volt paid for my lunch today.  ;-)

More tomorrow.

Tuesday, August 14, 2012

2012 Chevrolet Volt - Is it a Real Car? Introduction

2012 Chevrolet Volt
Quick, how many automotive segments can you name?  How do you even define the segments?  Cars, trucks, SUVs, vans?  How about sub-divisions between segments (crossovers anyone?).  What about sizes within a segment?  However you slice it, we are inundated with choices of cars and trucks and everything in between.  In a world with such a wide array of options, imagine introducing a model that is something completely new.  That is the daunting task facing GM with its Chevrolet Volt electric.  They have the multiple tasks of introducing a new model as well as educating consumers about what makes is tick and why they should care.

The Volt is GM's latest foray into the electric car market.  To the most jaded, it could be called a plug-in hybrid because in addition to electric drive it also is equipped with a gasoline engine.  However, to the optimist as well as the marketers at GM, it can be (and likely, should be) viewed as an electric car that doesn't limit you to the range of its battery pack in per-day driving.

So, first, the requisite background.  What has led GM, a company largely known for their trucks and SUVs, to bring to market this unique take on the electric car?  And, what is it that makes this a unique electric and not just another hybrid?

The real beginning of the Volt owes a lot to the hire of Bob Lutz by GM in 2001.  While Mr. Lutz is known for shepherding development of cars such as the Viper and the big-rig inspired Ram truck (while at Chrysler in the 90's), part of what he did while working at GM was see a perception problem towards GM (especially compared to their closest competitor, Toyota).

2007 Chevrolet Volt Concept
Looking for a way to flex GM's engineering muscle and give the corporation a product with a similar green halo as Toyota's Prius...he challenged his team to do better than a mere hybrid.  Faced with the cost and limited range of a car with only a battery pack (and the long time to recharge) - GM decided to pursue a novel solution championed by then VP of Global Vehicle Development, Jon Lauckner - the range extender.

Unlike GM's previous electric, the EV1 (leased in California and Arizona in the late 1990's), the Volt enhanced it's electric power-train with an on-board gasoline powered generator.  The drive wheels are powered by electric motors, but once the battery was exhausted, the 'range extender' would start, running a generator that would then provide the electricity.  In this way, the Volt concept would be able to run on battery power for most day-to-day driving without the danger of leaving an owner stranded and in need of an hours-long re-charge to get back on the road.

This solution acts as a bridge between a future of fast-charge/high-capacity batteries by allowing the Volt to run on pure electricity for the first 40 miles but also allowing trips of practically any distance beyond on gasoline.  Need to drive back and forth to work?  Battery will likely get the job done.  Need to drive to grandma's across a couple states?  The Volt has you covered there as well.

There is a certain engineering brilliance in the concept - provide electric-only driving for 80% of the world's commuters without the electric having to be a 'third car' in the garage.  The other benefit is in allowing a smaller battery pack than any electric that has to provide all-day usability on a single charge (dual benefit due to the high cost of lithium-ion batteries and their long recharge times that only get longer with larger capacity).

Almost 2 years later, in September 2008, Chevrolet debuted the production version of the Volt.  It was obvious from the radical styling change the Chevrolet was caught somewhat flat-footed by the positive response to the original concept.  Changes had to be made to the shape of the car to even approach the promised 40 mile electric range (and even then, the best the engineers could do was 35 miles) through improved aerodynamics.  Another surprising miss of the production car vs the concept was in MSRP.  Where the concept was expected to come in in the upper-20k range (a projection tossed out during the concept's debut by Bob Lutz based on the cost of a comparable compact sedan + $8000 for the advanced battery pack), the production car ended up coming in at $40k, though with a $7500 federal tax credit it is down in the low $30k range.  The cost over-run was another victim of efficiency needed by a car that runs everything off of battery capacity - items as varied as the stereo to the wiper motors had to be designed from scratch with an eye toward energy efficiency.

So, does the Volt, a car that missed by marginal amounts the promises made by GM during the concepts debut, still live up to the promise of this unique take on the electric car?

Subsequent posts here UOWCars.com will show what we found out.  Stay tuned.