4 ms·
>Accellerating, decellerating, and managing mass costs joules Ideally, aside from parasitic losses, shouldn't decelerating pay joules?
by joncrane 6y ago
>Accellerating, decellerating, and managing mass costs joules
Ideally, aside from parasitic losses, shouldn't decelerating pay joules?
- dredmorbius 6y agoNet it's a loss compared to constant velocity. A few years ago an electric bus hypermiled to get some ludicrous range. Turns out the trial stripped all spare mass from the rig (seats, other interior), pumped tyres to munition-rated pressures, hugely oversized the battery, and held a constant speed of about 24 kph (15 mph). https://www.latimes.com/business/autos/la-fi-hy-proterra-range-record-20170919-story.html https://www.latimes.com/business/autos/la-fi-hy-proterra-ran... (The article, as with most, reveals no test conditions though does at least note "a Proterra spokeswoman said they won’t reveal the test bus speed".) In production, range claims seem to be about 1/3 this. Typical city busses stop every block or two, accelerating to about 40 kph, then braking, every 60 seconds or so. Both mileage and wear and tear suffer immensely.
- joncrane 6y agoI'm not sure this is true. I've been told that, for example, the "city" MPG of hybrid cars with regenerative braking is higher than the "highway" MPG. This is because it simply costs energy to maintain speed in the face of hills, wind resistance, and parasitic/rolling losses. However in "city" driving much of the energy is reclaimed through braking. A big part of this is wind resistance; as you know wind resistance increases with the square of the speed, so going 60MPH is going to cost quadruple what it costs to go 30MPH, and presumably "city" driving doesn't go much higher than 30 MPH.