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Having some trouble sleeping tonight so I though I would use the time constructively.
The scenario is a long steep grade of lets say 8% for several miles. The elevation change would be 2800 feet vertical.
In my VX you just have to bite the bullet and downshift and run the engine at 4k RPM or somewhat near that to keep your speed at 60 MPH. This is the type of situation where you will see the big rigs struggling to maintain 35 MPH in the truck lane on the right side of the road. There is a grade like this near Blacksburg Va, that I have driven many times on Interstate 81.
This is where you want your vehicle to be as light as possible. Even the battery in a Prius would probably be depleted by the time you reached the top of that several mile 8% grade.
How do you handle it with the proposed hh?
First, you have to have enough engine to sustain the desired speed up the grade. Your energy reserve is depleted quickly (as Robert noted). Coming down the other side of the mountain will require no fuel and you will recharge the accumulator.
Remember the size of the engine determines the average percentage of overall recharge cycles versus engine off cycles, which in the INNAS setup was 11% running and 89% off. In this scenario the duty cycle would be 100% instead of 11%.
Downsizing the engine reduces overall vehicle weight and requires less total energy to maintain your speed up the grade, to the point in downsizing where you can no longer maintain the desired speed.
Too much engine size and power means you are using more energy to climb the grade.
Downsizing the engine can only be done to the point where you can maintain a reasonable speed during the uphill climb. The lighter your car the better.
If your car weighed 2200 pounds (just because it's easy to figure) you need 4 horsepower per second to climb one foot per second, or 32 horsepower at the wheels to climb an 8%grade, above and beyond what you would need to maintain the same speed on level ground.
If you added another 1100 pounds of passengers and cargo that would go up by 50%.
That means assuming you need 15 hp on level ground, 32 hp for the grade, and another 16 for the load you need to sustain an output of 63 HP.
Now you want to do that without having to run the engine too far outside its sweet spot, so you need to size the engine to produce that much power at the highest point of BSFC, which means it would need to be about a 140 HP engine if it was configured as they are in cars today.
Running at less than 3000 RPM at best BSFC, the engine would have to be about 2-2.5 liters to maintain best BSFC while producing that amount of total horsepower. The engine has no throttle control or full load enrichment. It is not designed to go over 3000RPM so you compensate with greater displacement. You could reduce that displacement and use some form of supercharging for this situation which would allow the displacement to be considerably smaller. In either situation you would design the engine for best BSFC almost without exception. Never full load enrichment, never idling, operating in the range of 1500-3000 RPM exclusively.
Going downhill on the other side of the mountain would be the same technique as the hypermiler uses. The accumulator would be rapidly recharged and you would have to use engine braking to keep your speed down to the desired level.
Additional safety could be incorporated into the in wheel drives by allowing them to push fluid through a bypass circuit with a restrictor in the circuit for additional braking if it was needed.
And yes, as the law requires a separate mechanical emergency friction brake on the rear wheels would be there in case the several other systems failed simultaneously. This was discussed at Tech, and there are multiple redundancies in the system as described.
The tactic is the same as a hypermiler would use in a conventional vehicle in the same situation and mileage would suffer compared to flat land cruising much the same it would suffer in any other configuration. Even in a BEV like the Nissan Leaf the energy required to climb that much of a grade would have a significant impact on your range.
Adding any type of storage capacity to try to recover more energy, adds weight to the vehicle and requires more energy in the climb phase.
The best energy source in this example would be liquid fuel, with diesel being the best choice of the liquid fuels due to its energy density which far exceeds any battery or accumulator as has been noted.
Arguing the energy density point will always place the accumulator or battery at a serious disadvantage compared to a gallon of fuel, be it diesel, gas, bio diesel,or alcohol.
Second point:
As far as how you convert your fuel energy into accumulator reserve. Let me see if I can make it clear.
As the various energy conversion systems mature over the next decades, what is now the best method could easily change very quickly, if a breakthrough is made in one technology.
We have no control over that progression. We can only make predictions as to how it will evolve. 20 years from now it may be batteries have the energy density of a tank of fuel. No one really knows for sure.
Right now, if you look at the percentage of vehicles on the road in the US gasoline is the obvious winner, propelling close to 19 out of 20 cars on US highways. Europe has a much higher percentage of diesel cars.
Its not which fuel conversion system I think will be the predominant one now or at some point in the future. The powertrain system I am proposing would be just as effective with any one you want to choose.
Maybe the battery issue will be resolved and we go all electric.
Maybe the IC engine will see efficiency hit 60% on bio fuels.
Maybe my engine design might have a place, even if only for a few years or decades.
Maybe something completely new will appear and render all of the above irrelevant.
I love the idea of capturing energy from the sun, tides, and wind. They are all related to the suns heating and evaporation of water, and the moons gravitational effects on the Earth. I also like geothermal energy, since it is almost limitless. Hydroelectric is another preference as long as its environmental effects can be mitigated.
I do believe fossil fuels will someday become obsolete as our prime energy source, but for the time being my philosophy is to get the most work out of every BTU of energy you use regardless of the source of that energy, and the less environmental risk involved the better as long as it is done rationally with some consideration for cost effectiveness.
regards
Mech
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