Nice explaination Tom.
Al
----- Original Message -----
From: "tomw via EV" <[email protected]>
To: <[email protected]>
Sent: Saturday, November 08, 2014 10:36 AM
Subject: Re: [EVDL] Range vs Speed
I looked at the effect of acceleration and deceleration rates on energy
used
per acceleration-deceleration cycle a while back. To simplify the
calculation I assumed the same rate for acceleration and deceleration.
You
do get more energy into the pack stopping faster with regen. For example,
at a faster deceleration rate, 6 mph/sec, 7.7% of the vehicle K.E. is lost
to work against drag and rolling resistance forces, and at a slower
deceleration rate, 2 mph/sec, 23.1% is lost. If you assume a combined
motor/controller loss of 20% and drive train loss of 10%, then for the
faster deceleration rate 100 – (20 + 10 + 7.7) = 62% of vehicle kinetic
energy goes into the battery pack, and at the slower deceleration rate
100 –
(20 + 10 + 23.1) = 47% goes into the battery pack.
However, you don't get a lot of difference in energy into the pack as a
percentage of total energy used when considering a trip with travel at
constant speed and a number of acceleration-deceleration cycles. For
Example:
(1) My car accelerates at 6 mph/sec to 60 mph, drives 10 miles, then
decelerates at the same rate to a stop, estimated percent of total energy
used that is regained with regen is: 2.7%
(2) Acceleration at 6 mph/sec to 35 mph and deceleration at same rate 10
times in 10 miles: 12.7%
(3) Acceleration at 6 mph/sec to 35 mph and deceleration at same rate 20
times in 10 miles: 20.7%
At 3 mph/sec, or 1.34 m/s (0 to 60 mph in 20 sec). Then the same three
scenarios give 2.4%, 12%, and 20%, so a factor of 2 slower rate doesn’t
change the result that much. At 2 mph/sec acceleration/deceleration rate
the
three scenarios give 2.2%, 11%, and 19%.
Increasing total miles traveled, d, to 30 in scenario (1) gives 0.9%.
Increasing stops in this scenario to 3, with 30 miles total, gives 2.7%.
Increasing vehicle mass increases the percentage of energy recovered, but
it’s a small effect for larger number of stop/starts. For example the
first
scenario goes from 2.7% to 3.8%, second goes from 12.7% to 14.7%, third
goes
from 20.7% to 23.2% if vehicle mass is doubled.
Decreasing losses in the motor/controller and drive train of course
increases the energy recovered. For example, decreasing motor/controller
loss to 15% in scenario (2) increases the energy gained from 12.7% to
16.5%.
--
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