Wednesday, March 25, 2009

2010 Prius Preview: A Hypermiler's perspective.

March 25th, 2009
by Dan Bryant, ECO LLC.
Tucson Press Preview

Clamoring around the small fleet of pre-production Priora (Prius'es) were a gaggle of reporters all interested, in their own way, as to what Toyota had up their sleeve with the new 2010 Prius.  Each had their own expectation and set of questions as the day began.  I, in many regards, was likely the odd man out.  The black sheep ringer pulled in from the Houston Hybrid Club to really see just what this car was capable of.  I was ready to get to work. 

The design for the new Prius began 3 years ago in the Toyota think tank.  Prius had not yet begun it's iconic ascent into the eco flagship it is today.  The engineers goals were still lofty.  Typical of many marketing scope documents, the objectives seemed mutually exclusive.
  1. Increase fuel economy.
  2. Answer demands for more aggressive styling and design.
  3. Advanced tech to make the Prius the "must have" gadget of 2010.
  4. Increased performance to make the Prius quicker, more agile, and more responsive.
As the Hypermiler Ringer in the crowd, my attention zeroed in on objective #1.  I remained both curious and skeptical as to how the rest of the goals would fall into place without sacrificing fuel economy.

Pooring over the technical documents (not in short supply) and listening to the presentations, fuel economy did, in fact seem better.  Amazingly, the Prius underwent a 90% redesign with dozens of refinements tweaking the performance and style of the vehicle.

The first, and most obvious tweak to improve FE was the air-foil.  The new design achieves an astonishing drag coefficient of 0.25 Cd, which is one of the lowest drag coefficient of any mass-produced car (the original Honda Insight ties it).  To achieve such low drag, they've moved high point of the car (top of the hump) back about 4 inches.  Harder edging down the body and around the bumper to better channel air-flow.  The Big Surprise, however, us under the car.  At long last they have added under-body panels to reduce the chaotic air flow underneath the vehicle as it travels at speed.  Other changes include a larger lower grill and a smaller upper grill intake, as well as a slightly longer spoiler; similar to the 2009 Touring Prius.

Motor Generators, 1 and 2,  were other major components of the 2010 Prius to go on a Fuel Diet.  Both of the MGs are smaller and more efficient.  MG2 now operates at a much higher peak RPM of 13,500.  Additionally, the inverter/converter is now more tightly integrated into the cooling loop allowing the design to shrink in size and weight without suffering thermally.  Efficiencies were added to the new gas engine as well.  Coolant is now circulated through the exhaust system at start-up, reducing warm-up by upwards of 3 minutes.  This improvement allows the coolant thermos to be discarded saving a marginal amount of weight.  The new engine also has a confirmed EGR system designed to better equalize pressure across the engine further reducing losses.

Now, while many components of the engine were getting smaller, others were getting larger.  The coolant pump, previously belt driven, is now its own electric pump.  Although this may add a marginal amount of weight, there are big savings by reducing the vampire load that the pump previously had on the drive-train.  Another change which initially appears counter-intuitive to improved fuel-efficiency, is the added 300ccs of displacement.  The new Prius will be sporting a new 1.8 liter engine compared to the smaller 1.5 liter engine in the current 2009 models.  Although this bloat can add some unwanted heft, their logic becomes clear when the highway fuel efficiency numbers are examined.  By adding a larger engine the 2008 EPA test cycle scores the 2010 Prius an improved highway rating of 48 mpg.  The technical documentation tended to spin the heftier engine as purely targeting increased fuel efficiency, but I couldn't help but notice that the zero-to-sixty time dropped below 10 seconds.

Now, beyond obvious improvements to the body and engine/generator designs, there appeared to be an almost complete overhaul of the control software.  As much as I would have loved to get a peak of some of the new code, that was not something I was privy too.  Reasons for re-authoring these software components are obvious, but for the Hypermiling Community there is a cost.  Much of the 2004 design was reverse-engineered to the point that a properly programmed ScanGauge could decode the various communication bouncing from one control system to another.  This was wonderful if you happened to be interested in some of the finer minutia of vehicle operation, as are many Hypermilers.  Although there are probably significant improvements in the new software, veteran Pilots in the 2010 Prius will be stripped of all the extra Prius-hacking data that they have grown to love.  But, on the flip side, an entire new mystery of control logic exists for those new Prius-hacking Pioneers to unwind.

Well, with all the groundwork in place, I was ready to take my little beauty for a test drive which brings me back to the gaggle of reporters huddled around the Priora (Prius'es).  While the master of ceremonies released us with "drivers start your (electric) engines", I was busily wiggling myself under the nearest Prius to marvel at those wonderful under-body panels.  It wasn't until that particular Prius was claimed that I realized the Prius stable was rapidly emptying.  After a quick conference with the organizers, I ascertained that there were two base models.  One was driving off,  but a bit of running landed me in the second one before the guy behind me got to it.  As interesting as the gadgetry is in the "fully loaded" models, the base models can offer slightly better fuel efficiency with the 15" tires and lighter body.  The larger 17" rims and added options yield lower fuel efficiency, marginally I grant you, but every little pip counts.

In the pilots seat, the very first thing I noticed, was the presence of the ever familiar EV button.  Previously only reserved for Prius Hackers on the 2009 model, the 2010 comes with an EV button stock.  Beside the EV button are two other drive mode buttons, ECO mode and PWR mode.  All in all, the new Prius allows 4 new drive modes:
  1. Normal - This is the mode the EPA rates the Prius fuel efficiency under.
  2. ECO Mode - This mode improves fuel efficiency by smoothing out throttle requests.
  3. PWR Mode - This mode improves performance by boosting throttle requests.
  4. EV Mode - This mode allows the vehicle to be driven on batteries only, if conditions permit.
Behind the wheel, the first thing I had to become familiar with was the new instrument panel.  One interesting redesign is that all of the driving info is up by the speedometer in the HUD display.  The good news is that drivers aren't looking down onto the NAV unit's LCD to get feedback, the bad news is the information is compressed and a bit harder to digest, and if you ever get refused EV mode, the error message covers the display for about 2 seconds.  

The base system displays on the new 2010 model have four toggleable screens, in the same way the 2009 toggles between "Energy Display" and "Consumption":
  1. Energy Display - This is exactly like the 2009 display and should be familiar.
  2. Past Record - This shows your MPG on all your previous trips / tanks (since reset).
  3. Consumption Display - Similar to the 2009 Consumption screen, but can show consumption in either 1 minute or 5 minute increments.
  4. Hybrid System Indicator - A totally new screen that shows how much battery or engine power is being utilized.
As I drove off on the first route, the new design did feel a bit larger.  The weight reduction in some systems is offset by the larger engine and body, and the final product is over 200 pounds heavier.  Since I had a passenger, the initial driving impression was somewhere between a 2009 Prius and a 2009 Camry Hybrid.  Trying to Hypermile the 2010 exactly like the 2009 Prius does not work.  These are essentially deferment beasts.  The premise is the same, but the feel is definitely different.  I began to try to feel these differences out.

First among these differences was determining at what throttle I would find optimal acceleration.  The 1.8L engine coupled with the Eco-Mode setting put (what felt like) optimal acceleration at a much heavier throttle than I was accustomed to.  The next major difference was the EV button.  The 2010 Prius seems much more finicky about when and where you can toggle the EV button.  An ev-button-hacked 2009 Prius, fully warmed up (160 °F), with sufficient charge (5 bars) will enter EV so long as your driving below 30 mph.  For the 2010 Prius, this seemed to be a bit more elusive.  At lower speeds (below 20 mph) toggling EV was permitted, but at the higher speeds (25 - 30 mph) all attempts to toggle EV seemed to be refused.  Secondary sources put the toggle point at 25 mph max.

When I finished my first run with the new Prius, I felt a little disappointed.  My first run on the River Route yielded only moderate results:

2010 Prius on River Route
Distance: 21.5 mi
Average Speed: 24 mph
Fuel Efficiency: 82.5 mpg

For second spin around Tucson, I yielded my seat to another reporter as we went through the Mountain Route.  After going through a hypermiling preview with me, he was ready to see what kind of power the new Prius could deliver.  Switching to Power Mode, we were off and running.

The new Power Mode does deliver what it advertises.  In power mode, the throttle is adjusted to provide more power when RPMs are optimal.  On the steep mountain grades this provided ample acceleration to meet most anyone's expectations of a 4 cylinder engine.  Off the line acceleration in Power Mode is definitely surprising.  Initial acceleration with pack assist has always been good, but there is an extra kick that the larger engine provides to fill in the gaps.  The net result is a constant and consistent acceleration from low to high speed for those who require it.

After we got back, I hooked up my gauges, ate lunch and prepared for our final run.  I was ready to lay it on the line for the MPG competition.  I was anxious to see what I could get out of this new contender in fuel efficient autos.  The competition route was 38 miles, with dozens of lights, traffic, four miles of highway, and significant hills to navigate; certainly not an optimal Hypermiler's course.

Impressed with some of the readings I saw on the Mountain Route, I switched my display to Hybrid System Indicator.  This display was basically a throttle indicator broken into 4 main segments.  On the far left, a "CHG" area indicating that when throttle is light, regen will be used to charge the batteries.  On the far right is a PWR area indicating that you are out near peak power (red-line).  As you apply throttle the Indicator will fill from left to right.  When your throttle reaches the middle of the display, the engine will turn on.  This simple interface provides a simple way for you to maintain throttle and predict when your about to light the engine.  Everything a hypermiler needs.

With a ScanGauge and the Hybrid System Indicator up, I started on the route working on a Pulse and Glide regiment.  The basic idea is to accelerate at peak throttle ("pulse") till you reach around 30-40 mph, then let off the throttle just enough to let the engine cut off, then "glide" down to a lower speed of 20-30 mph.  Reading RPM on my ScanGauge for my first pulse, I realized why my previous drive yielded such low numbers.  I was pulsing with far too little throttle.  After about two or three attempts, I found the 1600-1700 RPM range I was seeking.  Once I found the sweet spot in the throttle it was easy to repeat by watching the Hybrid System Indicator.  Filling the "fat" bar up about 3/4 of the way seemed to be perfect and consistent.

Once I had the "pulse" down, the next step was to figure out the best way to "glide".  In the 2009 and previous Prius, I would have to come almost completely off the throttle to coax the engine of.  Much to my surprise, the 2010 Prius is far less particular.  Once warmed up, the engine will consistently cut of (reverting to electric propulsion) whenever the Hybrid System Indicator is on the left of the middle divider.  Unlike previous models, you don't have to come off the throttle, simply ease up on it a bit, and the engine will cut out just as you would expect.

Although there was only a short amount of highway driving on the route, its presence proved useful in checking highway modes of driving.  In the current (2009 and previous) Toyota hybrids, there is a definite "efficient mode" that can be found on the highway.  At very light throttle, Motor Generator 1 seems to back off of charging the pack and direct all available power from the engine to the drive train.  In Hypermiler circles, this is called "Super Highway Mode".  Once I got up to speed on the highway, I backed off the throttle till the RPMs dropped below 1300 RPMs and the Hybrid System Indicator was just past center.  Sure enough a few seconds later I could feel MG1 release and see MPG jump to the 70-80 MPG range.  Just what I had hoped, "Super Highway Mode" works in the new Prius just as it did in the older ones.

Since the start and end of the MPG route were at the highest elevation, most of the run was over 100 MPG, reading 99.9 for CONS on the display.  Unfortunately the last 3 miles of the course required the steep climb back to the finish line, and physics set in.  The final numbers yielded:

2010 Prius on MPG Route
Distance: 38.7 mi
Average Speed: 22 mph
Fuel Efficiency: 90.6 mpg

These were results I could live with, but I was still a bit curious.  Could I have done better in my 2007 Prius?  The answer was staring me in the face... literally.  As I turned in the keys to the Master of Ceremonies and received my Prize of Undisclosed Value for winning the MPG run, I saw that some of the organizers were working around a 2009 Prius they had out on rental.  With very little coaxing I was offered up the 2009 Prius to run through the same course for a head-to-head comparison.  Since the event was winding down I took the 2009 Prius out for a solo run.  The absence of a navigator meant it was lighter.  I was also able to hook up both of my ScanGauges to get the full detailed system information that was not available in the 2010.  And finally with over 30,000 miles of experience hypermiling the older model, I was expecting this to be a close race.

Since my second run was later in the afternoon, the 2009 Prius had a bit more traffic to contend with.  The temps were about the same on both runs, and I diligent to ensure that the starting charge on both cars was the same, at approximately 5 bars on the battery display.  The numbers from turn to turn, and segment to segment were almost identical.  The two didn't really separate until the last three miles on the assent back to the finish line.  The final numbers for the 2009 Prius were:

2009 Prius on MPG Route
Distance: 38.8 mi
Average Speed: 21 mph
Fuel Efficiency: 89.6 mpg

This was something that did surprise me.  The new 2010 redesigned Prius proved better on the MPG run than the 2009 model that I am familiar with.  The new 2010 also provided a larger engine and an increase in net system horsepower of over 20%.  The new model has noticeably more aggressive styling (less frumpy, more sporty).  And finally, the new model comes with a laundry list of new features optional (to name a few):
  • Heated Seats.
  • Lumbar Support.
  • Solar Cell supplemented AC controls.
  • LED head-lights and tail-lights.
  • iPhone bluetooth MP3 steaming.
  • Four selectable driving modes.
  • EV button.
  • More trip computers (Trip A mpg and Trip B mpg).
  • Sunroof.
  • Pre-collision system.
  • Lane Keep Assist.
  • Dynamic Radar Cruise Control.
  • Intelligent Parking Assist.
  • Knee Airbags.
The new design of the Prius will still give Hypermilers the big numbers they strive for, but the real improvement will likely be seen by the everyday driver.  With "ECO-Mode" enabled, most "normal" driving will likely meet or beat EPA ratings on the vehicle.  The new warm up cycle, with the engine coolant getting heated by exhaust, will also be a hit for those with short commutes frustrated at poor fuel efficiency.  In all, it looks like Toyota did deliver on its objectives; better fuel economy, more performance, better styling, and enough gadgetry to make the most discerning technophile grin.

Dan Bryant.  <dan [at] 106mpg [dot] com>
Efficencies Consulting and Operations LLC. <>
Impressions of the March 2009 Press Preview of the 2010 Prius in Tucson Arizona.


  1. Great review Dan! Impeccable detail as expected. Now I am really anxious to get ours.

  2. Wonderful article, Dan. Thanks for writing! Looking forward to the next hyprmiler meet in Cypress ..

  3. I doubt there will be anymore hybrid meets, there hasnt been one in ages... :(

  4. Anon: I hear your critique. I've added an event for this weekend for anyone who is available.

    -Dan <11011011>