LunarMist said:
jtr1962 said:
For a 10-second burst of acceleration every now and then you don't need a big engine, you need a way of storing energy, and you also need a more efficient way of delivering it to the wheels.... For a normal vehicle(not an SUV), this might be on the order of 30 HP(mayber 35 HP for AC and other accessories. So now suddenly you can replace 200 HP engines with 35 HP ones and most drivers will notice no change whatsoever in how their vehicle performs.
What about hills? Can this SHEMP system store enough energy to propel a typical 1500 kg auto up a 6% grade for 10-12 minutes at highway speeds?
It doesn't need to. A 35HP engine has enough reserve power to do that on it's own provided the car is designed with a low drag coefficient(~0.2) and fairly low rolling resistance tires. I'm doing the example with a 4% gradient as 6% gradients simply don't exist on any Interstate highways:
Approximate vehicle drag @ 60 mph(level) = 0.007*3300 + 0.0024CAV² = 23.1 + 54.4 = 77.5 lbs
Propulsive HP needed(level) = 77.5*60/375 = 12.4 HP
Additional Gradient Force = 0.06 * 3300 = 132 lbs
Total Propulsive Force(@60 mph, 4% gradient) = 209.5 lbs
Propulsive HP needed(60 mph, 4% gradient) = 209.5*60/375 = 33.5 HP
Note that the Interstate Highway system was designed with 3% gradients maximum so that buses and trucks could maintain speed uphill, so even my reduction of the gradient to 4% represents a greater than worst case scenario. On a 3% gradient a 35 HP, 1500kg car would be able to maintain about 64 mph allowing 5 HP for transmission losses. In all examples I'm assuming a frontal area of 31.5 ft² and a drag coefficient of 0.2. I know 35 HP won't work with an SUV, but such abominably inefficient vehicles have no business being made in large numbers. If the typical SUV owner really believes height and weight make them safer, they should stick to buses and trains instead of these obnoxious gas guzzlers.
A couple of other factors work in my favor, anyway. First of all, 1500kg is
way too heavy for a car. There is zero reason why any 4 to 6 passenger vehicle should weigh that much. Liberal use of composites, styrofoam crash protection, use of plastic windows, the elimination of heavy drivetrain components by using SHEMP in the first place,
and the fact that a 35 HP engine weighs hundreds of pounds less than a 200 HP one should bring the empty weight of such a vehicle under 700 kg or less. Second, frontal area and drag coefficient can certainly be reduced well below my numbers without any sacrifice in either comfort or driveability. Third, the car can pick up speed before reaching the hill so that this stored kinetic energy can be used to maintain a higher average speed up the hill than the car's power plant alone is capable of(trucks and buses do this all the time). Counting all these factors, my hypothetical car would be able to maintain 80+ mph even up your 6% gradient with 35 HP.
I'm really surprised Ford is actively pursuing the SHEP system since this type of system is really only useful on fossil-fuel engined cars. Within a decade or less I'm guessing such cars will be the minority, with the rest being either battery, solar, or fuel cell powered(or some combination of all three). Therefore, it makes more sense to develop a platform similar to what I described which can be used now with fossil-fuel engines(and deliver a huge fuel savings), and converted later on to fuel cell or battery with minimal modification since the input is pure electricity. Perhaps even putting electric pickups on highways similar to amusement car rides might not be a bad idea to consider. The point here is that fossil fuel is a dying, obsolete technology not worth putting any investment into unless that investment can be carried over to non-fossil fuel vehicles. This possibility does not exist for SHEP as far as I can see. The current fad with variable displacement engines seems equally doomed. Best to just make the engine large enough to supply the
average power needed and then run it continuously at one speed.
