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Friday
Jul172009

Prius Gen II vs Ford Fusion Hybrid drive test

My daughter has a Gen II Prius (2007).  She's home from school so I took the Prius out on my test loop.  This loop is 14 miles long and I've taken the FFH around it a few times, getting 54-55 mpg.  Its got a mixture of driving conditions - some hills and some relative flats, some over 50 mph stretches, but no highway.  I wanted to see what kind of mileage I could get in the Prius.  While I've driven the Prius before, I've never been able to get more than about 40 mpg in it.  After learning some tricks with my FFH I thought I could do better.

First I did a small drive to warm the Prius up.  I always start my test loop with a warmed up engine so the car is ready to use EV mode.  One of the first things I noticed was the Prius does not have much power in EV mode. Starting from a stop usually turns the engine on. The FFH often has enough power in EV mode to pull away from a stop or go up a small hill.

Prius engine and electric motor driving wheels while battery is chargingThe Prius has an energy flow diagram like the FFH.  The Prius one is easier to read.  The flow lines are color-coded green, orange, red, and dark gray, and clearly indicate flow direction - much easier to interpret than the gradually widening flow lines on the FFH diagram (the FFH energy diagram does indicate intensity of flow by varying the thickness of the flow lines which is nice).

I soon began to miss the gauges in the FFH.  The Energy Monitor screen is the only tool the Gen II Prius has for monitoring what's happening in the drive train. In the Prius it was difficult to predict when the switch from EV mode to "engine on" would From L to R: Battery & engine power, Battery charge indicator, Speedometer, Fuel gauge, Instantaneous MPGoccur because there is no gauge for that, nor is there an indicator for when you are in EV mode. The FFH has a rich set of gauges. Depending on which ones you enable, you can see engine RPM, power draw from the battery and the engine, battery state of charge, instantaneous MPG, when the car is in EV mode, and how much acceleration you can apply in EV mode before the engine turns on.

During my drive I used the "pulse and glide" technique as often as possible.  In the Prius, its easy to move from the "pulse" to the "glide" - there is a sweet spot between taking your foot too far off the throttle and starting to regen and having too much throttle and initiating electric motor assist.  You can easily see when you are gliding using the Energy Monitor because all the flow lines are dark gray.  Getting a good glide going in the FFH is harder - its not as easy to get the exact balance between regen and motor assist. 

The Prius really sings during a glide!  It has less drag than the FFH.  The FFH drag while gliding was explained by Wayne Gerdes as "back EMF build" which I guess means that the electric motors are providing resistance so the FFH is not rolling along completely freely.

The FFH can go faster in EV mode before the engine turns on, 47 mph to the Prius's 42, which means you can pulse up to a higher speed before initiating a glide in EV mode.

The Prius is a great car. I could tell fairly quickly that I would get better mileage, and I did - 70.7 mpg!  I prefer the driving experience of the FFH, but if you're going for MPG the Prius is the one to get.