Hybrid Car – More Fun with Less Gas

70 mpg - Page 15

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Posted by Josepi on January 17, 2010, 4:11 pm

The Camry claim (non-hybrid) was about 80kph tuning for optimum economy.

news:eb5d529d-090b-46a6-b263-> steady 70 mph with The Prius' optimum fuel
efficiency is achieved when running
constantly at about 40-50 mph on a flat surface.  The Prius
fuel efficiency should be the same at a fixed speed when
its payload is within its designed load (825 lbs). When the
payload is significantly over the designed limit ( Payload
is > 1000 lbs) - the added weight to the drive train and
the additional rolling friction  resistance will most likely
cause some decrease in fuel efficiency even if it only
appears as a fractional increase in energy cost.

Posted by Neo on January 18, 2010, 5:16 pm

80 kph would be about 50mph

Posted by Bruce Richmond on January 17, 2010, 7:40 pm

Look up "pulse and glide" sometime.

The reason for my post about hauling coal in my Prius wasn't to
advocate getting them for that purpose, it was to counter someone's
claim that the reason for US cars getting poor fuel milage was that
they were to heavy.  The difference in weight doesn't come close to
accounting for the poorer fuel mileage.  We constantly hear fuel
saving tips telling us not to haul anything extra around as if an
extra 50 lbs will make a significat difference in your mileage.  If
hauling 800 lbs of coal had for all practical purposes no effect on
mileage then how much effect do you think 50 lbs has?

I tend to think the cause is more due to the minimum power many
consider acceptable, whether they actually ever use that power or
not.  If the engine size of the Prius had been increased so that it
was able to accelerate at the same rate that it did without the coal
then it would use more fuel.  So weight is a factor but it is not the
primary cause.

Last time I filled the tank I decided to see what I could get for
mileage on the 38 mile ride to home.  The first 5 miles were slightly
down hill, dropping at most 200 feet over the five miles, and it
averaged 70 mpg.  The next 5 miles climbed to about the same level as
the starting point and the overall average dropped to 60 mpg.  For the
remaining 28 miles the mileage went up and down with the changes in
elevation, ending with it at 60 mpg.  It was about 10 F degrees at the
time.  Since the engine was up to temp and the battery charged when I
filled the tank I don't think the cold was much of a factor.  I was
wearing winter clothing so riding with the heater turned off wasn't a
problem.  When I went back to normal driving the next day the mileage
dropped into the 50's.

Posted by Neo on January 18, 2010, 6:07 pm

If one uses  hypermiler techniques like pulse and glide
or stealth warp  - one can achieve high FE in other
driving conditions but they require special skills.

The vehicle weight is a  factor in fuel efficiency.
But as stated by another, in a conventional ICE
vehicle, it is really the gross-weight-to-power-ratio
which contributes to a vehicle's overall FE (as well
the power-transmission-to-drivetrain efficiency).
This is because a lighter vehicle will allows
a more energy efficient ICE which could
requires less energy to accelerate to its
optimum speed for FE,

Hybrid FE is based on the fact that an
electric motor is more energy efficient than an
equivalent ICE motor. So while a Prius
is much heavier than a Corolla, it has the
ability to use an electric motor which has
the higher  FE.  However, the energy density
for the fuel for an ICE is over  10x higher
than the energy density for the electric
storage unit/battery needed to run the
electric motor. Thus the electric mode can
only be use for a short time   In addition,
the gross weight of a hybrid is a signficant
factor  in its FE  -  the gross weigh being the
sum of the curb weight plus the total
payload (passenger+cargo/payload).
Heavier hybrids like the Camry and Highlander
are less energy efficient than the Prius.  As
with most motor vehicles, the payload is
only a fraction of the gross weight so I agree
that most adding  an 50lb extra is not
going to effectively change the gas mileage.

However, this makes me wonder what would
happen if a driver had put 800 lbs of coal
in a 2008 Smart Fortwo  mini car?

Maybe I should get her
a scangauge II for her birthday? (9_9)

Posted by harry on January 18, 2010, 6:27 pm

m> wrote:

The mass of the car is a major factor in fuel efficiency.  If the car
has a ICE then the kinetic energy is wasted when the brakes are
With electric cars, this energy can be retrieved with "regenerative
ie, the first pressure on the brake pedal enables the motor to
generate,eg when descending hills.   A lot of energy is wasted in the
ICE when the engine is in overrun ie descending hills. In days of yore
some cars were fitted with a "freewheel device"  to economise in
fuel.  You never see them now.   Dangerous in town I should think.
Saab and Rover spring to mind.
The most efficient European cars are built like paper bags. high
tensile steel is the minimum plus lots od plastic eg doors boot, &
bonnet lids.   Some are mainly aluminium (glued together) & carbon

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