Canberra-Sydney Loop – Better economy

The latest run from Canberra to Sydney and back produced a very good result.  Temperature range was 10°c to 22°c on the way up and 20°c to 13°c on the way back.

I filled up at Sutton Forest, halfway to Sydney.  After 796.5 km, of which about 20% was city driving, I put in 34.49 litres for an average of 4.3l/100km Cost was $1.49.9 for Shell 91 RON.  (The HSI displayed 4.1l/100km.)

L/100km MPG(UK) MPG(US) km/L
4.3 (tank) 65.7 55.0 23.3

From fill-up to Newtown and then the City ended as 132.9km for 3.4l/100km at an average of 86km/h.  Adding 5.8% to the HSI display gives 3.6l/100km.  (Corrected figures shown in italics.)  That’s my best ever run into Sydney, though it doesn’t include the hills between Canberra and Sutton Forest.

L/100km Corrected MPG(UK) MPG(US) km/L
3.4 (HSI) 3.6 78.5 65.7 27.8

Return trip was quite cool.  Sydney didn’t get very warm on Saturday and the temperature dropped steadily as we travelled South.  I used 2/3 lower grill block on the way up, in case I encountered temperatures much above 18°c on the way up.  After a brief stop on the way back, I restored the full grill block.  Upon return, the tank trip was 418.8km, 4.0l/100km (4.2 corrected) at 79km/h.

The Canberra to Sydney loop was 564.0km, 4.1l/100km at 80km/h.

L/100km Corrected MPG(UK) MPG(US) km/L
4.0 (HSI) 4.2 66.8 55.8 23.6
4.1 (HSI) 4.3 65.1 54.5 23.1

Why the improvement from previous loops?

I’d put it down to never using the cruise control.

The beauty of the Prius’ cruise control is that it can regulate speed very well.  If you are coming down a steep hill, it can use regenerative braking to hold your speed.  (If the HV battery is already charged, the engine will be forced to run to “burn off” some of the excess charge.  This is also the only time that you would use the B (Brake) position; to prevent overcharging.)

Steep hills can be easily scaled by changing to the PWR Mode so that the speed doesn’t decrease as much before the acceleration takes over.  Leave it in ECO Mode and the speed will drop so far that all resources will be called upon to leap back to the set speed; a far less economical way to drive.

Radar cruise control in the iTech is even spiffier.  Except that every press of the accelerate or decelerate lever changes speed by 1 km/h and every long press by 10 km/h.  While this is very logical (Mercedes-Benz use this method) and is more accurate than holding until the desired speed is reached, it did catch out Steve “Woz” Wozniak, allegedly.

Freeway Driving without Cruise Control

How can I even suggest such a thing?  Surely CC makes a journey bearable.  Well… the Canberra to Sydney run is not very flat and once you reach the flat sections, the traffic increases.  Neither are ideal conditions for cruise control. And the Prius will allow me to take over from the CC, however results can be mixed.  If I am pushing the accelerator, say to speed up before a steep hill, but the car dips below the set speed, CC will not try to maintain the set speed.  Take my foot off the accelerator, the CC springs back into life.  I expect my foot to complement CC, not override it.

ECO Mode makes the accelerator less sensitive, which in turn makes it easier for the right leg to control speed.  Using Pulse and Glide techniques, long downhills can be used to charge the HV battery, or increase speed.  In short, you can control what the CC can’t see.

Having throttle control allows me to find the Super Highway Mode for very low consumption driving at high speed.  I was able to maintain 2.0 – 3.0 l/100 km at 110km/h for flat and slightly downhill sections by keeping the Ignition Timing (IGN) in the range +12-+16.  In fact, I was merely reading the instantaneous FC figure from the Scangauge-e rather than resorting to maths.

Because the accelerator pedal is quite light in ECO Mode, driving is not a chore.  And since I don’t have radar CC, I find myself cancelling CC when approaching slower traffic anyway.

I’ll use the CC selectively in future.

 

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First 1000km tank

I’ve spent 9 months learning about the Prius and how to get the best out of it.  Finally! After many attempts, much frustration and a little learning I have broken into the 600 mile and the 1000km club.

First 1000km tank. The “CONS: 3.9l/100km” is optimistic by about 5.8% as the true figure was just over 4.1l/100km.  And I was still nowhere near empty.

1002.8km (622 miles) at 4.125l/100km (68.5 mpg(Imp) 57.3 mpg(US) 24.2km/l) at an average speed of 44km/h (27mph). (The HSI displays 3.9l/100km as it is optimistic by about 5.8%.)

I used 41.37l from a 45l tank of 94RON E10 from Shell. While Toyota Australia recommends 95 RON, I follow advice from PriusChat that recommends that anything over 91 RON is not worth the extra.

Sadly, the joy of reaching 1000km coincided with a 12¢ jump in petrol prices to $1.57.9 per litre.  At current exchange rates that’s AUD6.00/ USD6.21 per US gallon.  It cost me $65.32 (USD67.63) to fill up.

Recent mods include fill 100% lower grill blocking and 45psi in the tyres. The weather over the last 3 weeks has been about 5-10°c warmer than during my last tank (4.6l/100km), which is probably a key factor.

As previously posted the Distance to Empty calculation is very conservative.  DTE=0km was reached at about 865km, so I beat my previous beyond zero record of 35km by over 100km.
Not to sound unkind, but my wife, who thinks that P&G is a company that makes toiletries, tends to drive as if the accelerator and brake were on/off switches. She drove about 200km of that tank at about 5.0l/100km, so my achievement is even better than I expected.

Read more: http://priuschat.com/threads/600-mile-club.112285/page-7#ixzz29prGdcGf

Canberra to Sydney – Economy Run and Return

With my father convalescing at my sister’s house in Sydney, Chikako and I have visited him the last two weeks.  So I’ve had a few more opportunities to see the effect of various hypermiling techniques and tweaks on fuel consumption (FC).

On 8/07/2012 I did drove the normal run using cruise control set to 114km/h (true 110km/h, officer) some A/C use and a single stop in both directions.  “To” trip was, Federal Highway, Hume Highway, M5, Southern Cross Drive, park near Hyde Park, some shopping in the city and then up the Pacific Highway.  Return was from Fox Valley Way, Pennant Hills Road, M2, M7, Hume, Federal, home.  The numbers were 613.7km at 4.6l/100km (corrected to 4.9l/100km based on 6.5% HSI error) at an average speed of 86km/h.

Since then I replaced the slowly-leaking and basically bald OEM Bridgestone B250 tyre (77,000km ain’t bad, but a nail ain’t good) and one of the Ovation ecovision VI-682 black round things with 2 Bridgestone ecopia PZ-X tyres.  I also started using 91 RON fuel.

TOP TIP: Extensive testing by Prius owners has confirmed that anything above 91 RON (or 87 AKI in USA) is a waste of money and often brings higher FC.

Then on Friday 20 July I had an 80,000km service, which is the major service interval for the Prius.  I immediately saw an astonishing difference in FC. See below for details

Driving to Sydney and back brings a different set of challengers for hypermiling.  For a start, Pulse and Glide techniques don’t seem to be applicable when you need to maintain 110km/h for a few hours.  To recap, in May 2012 I stuck with Cruise Control at 114km/h indicated, but then tried a few new ideas.  If I changed to PWR mode before steep hills, my speed didn’t drop so much on the way up.  This avoided the sudden acceleration that happens in ECO mode as the speed drops way below the set value and the Prius delivers an almighty application of everything in its arsenal. PWR mode seemed to reduce FC on very steep hills by maintaining momentum and gradually increasing the throttle.  for example, the very steep climb from the Towrang intersection maxed at 15.5l/100km in PWR mode compared to 17l/100km in ECO mode.

On Saturday 21/7 we were in no hurry to reach Northern Sydney, so the first thing was to not use the cruise control to try a little experiment.  (I set it at 114km/h but cancelled it so that I could resume as a fall-back position.)  The second thing was to forget any notion of maintaining a steady speed up a hill but instead maintain a steady pedal pressure without touching the PWR zone on the HSI.  This takes some forethought: If a car was approaching at speed I flashed my right indicator to invite them to pass and I had to be careful not to squeeze cars entering the highway.  There’s not many slow vehicle lanes on the highway except on the steepest hills.  On the climb out of Towrang intersection I only reached 9.5l/100km, compared to cruise controlled 15.5l/100km in PWR mode and 17l/100km in ECO mode.

It was a -4°c start.  I’ve recently confirmed that the coldest part of the garage, which is near the back of the car where the HV battery lives, bottoms out at 5°c even on long, cold nights.  Unfortunately, I haven’t fitted my engine heater, so it was chilly to start.  When I entered the Federal Highway the coolant was only at 60°c.

The route was Federal Highway, Hume Highway, M7, M2 to the turn-off at Pacific Highway Chatswood and then to Chatswood shops.  There was a few kilometres of road work on the Hume and the M2 was almost entirely under renovation.  While 60km/h zones can help FC, that’s more than offset by the rough road surface, twists and turns and lack of momentum in hills that are normally taken at 90km/h.

To my astonishment the FC figures were very good for the whole journey.  Canberra to the Mobil at Pheasants Nest returned 195.7km 4.1l/100km (4.36l/100km corrected, 64.8 mpg(Imp) 54.2 mpg(US) 22.94km/l) at 95km/h.  Pheasants Nest is about 290m ASL, so there’s still some descending to do.

Even more surprising was completing the trip to Chatswood: 304.2km, 3.9l/100km (4.1l/100km corrected, 68.9 mpg(Imp), 57.6 mpg(US) 24.39km/l) at an average of 90km/h.  (See the new blog header) The 107.4km leg from Pheasants Nest to Chatswood used 4.09l at 3.8l/100km (72.4 mpg(Imp), 60.6mpg(US), 25.6km/l) according to the Garmin ecoroute HD.

Eventually I rolled into Turramurra 318.1, 3.9l/100km (4.1 corrected) at an average speed of 77km/h (the traffic from Chatswood was fierce.)

Return was a similarly relaxed affair.  Remember, Canberra is 600m ASL and there’s several 750m peaks in the Southern Highlands.  This is where the passive hill-climbing technique became interesting.  On a particularly long, steep hill I dropped from 110km/h to almost 70km/h.  Fortunately there was a slow vehicles lane to retreat to so the other cars had two lanes to overtake.

Turramurra to Marulan was 186.8km 4.8l/100km at 88km/h.  ecoroute HD read 185km at 5.0l/100km with 9.3l of petrol used.

After 815km I put 38.02l of BP 91 RON for a tank average of 4.66l/100km.  Considering the amount of climbing to get to Marulan at 640m ASL, that’s starting to look pretty good.  The leg from Marulan to Home was 114.1km, 4.5l/100km at 95km/h (ecoroute HD 113.1km, 4.7l/100km, 5.31l used).

So, the round trip on Saturday 21/7/2012 was 619km at a corrected 4.56l/100km (62 mpg(Imp) 51.8 mpg(US) 21.93km/l).  That compared well against Sunday 8/7/2012, which was 613.7km at a corrected 4.9l/100km (57.6mpg(Imp) 48.2mpg(US) 20.4km/l).

Unfortunately I introduced too many variables (new tyres, major service, 91 RON, new driving techniques) to pinpoint which had the greatest effect on FC.  The only one I’m uncertain of is the 91 RON petrol, but since it is 10-20¢ per litre cheaper than 95 RON I could afford to increase FC by almost 10% and still be in front.

My next trick will be to run well beyond the zero on the very conservative “Distance to Empty” reading to see if I can join the 600 mile club (965.4km) on one tank.  Considering that the tank is 45l but the most I’ve squeezed in is 38.02l, that should be easy with another 7 untapped litres!  But I’ll take 5 litres spare just in case.

Latest fuel consumption improvements: Is it my pulsing or my gliding?

On Sunday I had about the worst type of journey I could have for fuel consumption (FC) a short trip with a very steep climb, fast speeds, a dirt road and cold temperatures necessitating both A/C and rear and mirror defogging.  I returned a 5.0l/100km (5.3l corrected) for that trip.  Today’s work round trip has returned to the very good numbers of late last week.

Date Trip Distance Cons +6.5% Ave km/h
12/06/2012 Home to AIS 12.2 4.0 4.3 42
12/06/2012 Round 33.3 4.2 4.5 38

How am I doing this? Any reasonable person would think that the most efficient way to drive is to maintain a constant speed.  It is certainly more efficient than treating the accelerator and brake as an on/off switch.  Hard acceleration and braking can increase FC by 30% or more without much thought. But there’s a benefit to being smooth but inconsistent.

The key term is Brake Specific Fuel Consumption (BSFC)

Engines are funny things. It seems obvious that revving the ring out will use more fuel, but an engine under load generally uses fuel more efficiently.  There is a balance.  Here’s a very good explanation with lots of pretty pictures, though the author is referring to the original NVW11 Prius when he shows the BSFC curve.  It is a fairly complicated concept and does seem counter-intuitive, but then so is Quantum Mechanics.
Understand one thing; the Prius is pre-destined to run its engine in the area of maximum BSFC and therefore get the most out of each drop of fuel.  The clever computer keeps the engine revs within the 220g/kWh zone as much as possible. A typical reading from the gauges on my Garmin ecoroute HD might be engine load 90% at 1900 RPM.   Driving in this zone will produce gentle acceleration as the revs are low, but you can always put the foot down and lose a little bit of BSFC to gain torque and power if conditions require it.

As a rough guide, keeping the Hybrid System Indicator between 75-100% (that is, from halfway along the “ICE” section to the edge of PWR) will keep the engine speed in an ideal range to take advantage of the lowest BSFC.  This zone will maximise the recharging of the HV battery, which is important for the next point.

BSFC graph for 2ZR-FXE 1.8L Prius compared to the 1NZ-FXE 1.5L. The larger “sweet spot” of the 1.8 is obvious.

I think that I have finally cracked the secret of “Pulse and Glide

P&G is a hypermiling technique that is particularly well suited to the Prius Hybrid but can be done in most cars.  In short, you Pulse to gain speed or climb a hill and then Glide by getting the car to coast until the speed drops.  If the pulse is reasonably gentle, the engine will be in its sweet spot and the HV battery will get a charge as well.  What’s makes the glide easy with the Prius is that you don’t need to shift to neutral or switch off the engine; the car can do that for you.  You just have to learn how to press the accelerator ever so slightly to avoid its kinetic energy being used to charge the HV battery.  Here’s a video that explains everything:

So it looks like I have somehow cracked the P&G code such that despite cold starts, high speeds and stop-start traffic, I am getting close to the fantasy FC figures that ADR81/02 under fairly poor conditions.  I think that I’ll still buy that engine heater (that’s another post for another time.)

Suddenly, my fuel consumption is much, much better…

…and I don’t know why!?!

Hypothesis

  1. If a Prius is not used for several months, it may become less fuel efficient.
  2. Using the Prius regularly prevents degradation of HV battery.
  3. After a period of inactivity, regular use can restore normal service and fuel consumption.

Background

I’ve been following the great advice on the PriusChat forum to improve my fuel consumption (FC)/mileage. The ADR81/02 fuel consumption figure for the NVW30 Prius is 3.9l/100km (72.4 mpg(UK) 60.6 mpg(US) 25.6km/l).  I have been getting nowhere near that!  Measuring FC tank by tank since I got the car has averaged 4.87l/100km (58/48.5/20.5). I seemed to be getting good results recently as my last 2 tanks averaged 4.7l/100km (60/50/21.3).

But then, suddenly, I seemed to step into the rarefied world of the hypermiler.

The other background bit before I get to the point

I just started a new job and I’m driving everyday instead of taking the bus. For the first time since I bought it the car is being used everyday instead of every weekend.  I used the Hybrid System Indicator (HSI) to measure the distance, FC and average speed each morning.  I then returned home and checked the total for the day.  Note: The HSI is 6.5% optimistic.  You’ll notice that the trips aren’t identical but the conditions are comparable.  Here’s what I measured:

Date Trip Distance Cons +6.5% Ave km/h
5/06/2012 Home to AIS 24.9 4.9 5.2 41
5/06/2012 Round 38.4 4.8 5.1 30
6/06/2012 Home to AIS 12.2 4.7 5.0 36
6/06/2012 Round 24.3 4.7 5.0 39
7/06/2012 Home to AIS 12.2 4.6 4.9 37
7/06/2012 Round 28.4 4.9 5.2 35
8/06/2012 Home to AIS 12.2 4.9 5.2 41

These numbers are in line with my previous efforts.  The trips are short, the mornings are very cold so the engine runs much longer to warm up and doesn’t drive the wheels until abut 1 minute after starting, there’s stop-start traffic followed by a 90km/h zone I have to use the A/C and defogger a little… all of which are bad for FC.
But then suddenly on Friday afternoon and then again Saturday I was scoring 4.0l/100km with little effort and no change of technique or conditions!

Date Trip Distance Cons +6.5% Ave km/h
8/06/2012 Home to AIS 12.2 4.9 5.2 41
8/06/2012 Round 60.7 4.2 4.5 39
9/06/2012 Everywhere 115.2 4.0 4.3 42

I repeated the line for Friday to show that I travelled 12.2km @ 4.9 to get the work, but then only @ 4.0 for the next trip of 48.5km, despite extra stops, hills and more stuff in the car to get a final score of 4.2l/100km.
And today after a very cold start I drove all over and up and down Canberra, made about 10 stops, short trips, several high speed moments and a few hill climbs and only used 4.0l/100km (4.3 corrected). Overall, not ideal hypermiling conditions but still returning much better fuel consumption than when I tried really hard to be good.

Car

  • Built May 2009, Gen III NVW30 RHD Australia-delivered, Base model (like USA Prius Two but with fog lamps as standard.)
  • From July 2009 to June 2011 it travelled 68027km (42200 miles)
  • From June 2011 until I bought it in January 2012, it travelled just 314km (195 miles), sitting at the dealer in Canberra.
  • Now that I look at the service record (!)… the previous fleet owner seems to have missed the 30000km and 50000km services.
  • I use RON 95. I don’t think that there are any winter additives.

Environment

  • Canberra is 600m (c. 2000ft) above sea level and it is not flat.
  • Winter (now) averages below 0°c at night and 10-15°c dry with generally sunny days. May averaged -0.2°c at night and reached -5° a few times with 15.6°c days. So far June is averaging 1.0°c (but the last 3 nights were -4 – -5°c) and 12.5°c days.
  • Lots of 70km/h (43mph) and 80km/h (50mph) connecting roads and 50km/h (31mph) or 60km/h (37mph) suburban roads.
  • Once a month I drive to Sydney, 300km away and 600m below, with 200km of mountains in between at 110km/h (68mph)

What I did to help, which didn’t seem to make a lot of difference at the time

  • Pulse and Glide
  • Dead 12 volt battery replaced a few months ago
  • Tyre pressure was in the low 30’s. 42/40 psi for the past few months.
  • Replaced some lights with LED.
  • Minimal A/C and defogger use. Heater off when warming the engine, then on Auto 21°c.
  • Headlights off when waiting at traffic lights. (Trick I learnt driving in Japan; doesn’t dazzle other drivers, saves a bit of fuel.)
  • On cold mornings, I let the car idle for 50s before I move.
  • Garmin 2460LT with ecoroute HD shows coolant temperate, RPM etc. and instantaneous fuel consumption. (It is more accurate than the HSI.)
  • Will be buying a DEFA engine heater. Possibly.

What is working against me

  • Ovation ecovision tyres’ rolling resistance is an unknown quantity, except to say that if their poor grip is a anything to go by…
  • Garage stays above 5°c. Coolant temperature is 10-15°c on start in the mornings.
  • I live at the bottom of a short but steep hill, great for returning in EV mode, bad for starting on a cold morning.
  • High average road speeds in Canberra make P&G tricky and EV less useful.

What is my problem?

  • The US EPA standard is 51/48/50 mpg(US) or about 4.6-4.9l/100km, which is what I was getting before. The ADR81/02 figure of 3.7/3.9/3.9 litres/100km is obviously unrealistic. But the UK claims 72.4mpg(UK) & 3.9l/100km.
  • That’s 2 trips. Show me 2 tanks and then you’ll have some evidence.