Originally Posted by Old Mechanic
Instead of hijacking another thread I would suggest looking at the tactical portion of the high mileage vehicle.
Consider the 5 states of operation
1. Idling
This accounts for about 13% of all energy consumption in motor vehicles.
Idling in the conventional sense should be eliminated altogether. This can be done with smart charging systems and slightly higher capacity batteries.
Also needed is a start stop engine system that provides rapid restarts.
2. Acceleration
While this is the most fuel consuming portion of operation, it is also the point of best efficiency of the engine, when acceleration is done properly. An infinitely variable transmission allows for acceleration to occur at best bsfc point, unless the rate of acceleration is greater than what we would consider normal traffic acceleration.
3. Deceleration
Deceleration by my definition is when the drag of the engine is slowing down the vehicle. This is actually the second worse state of operation, only exceeded by friction braking. Fuel shut off in EFI engines allows fuel consumption to be eliminated in most vehicles, but the friction, reciprocation, and pumping losses contribute to significant losses even without fuel consumption. Even without fuel consumption deceleration is energy negative, meaning you are throwing away the inertia previously bought with fuel during acceleration.
4. Coasting
This is where significant improvements in overall mileage can be achieved. If done with engine off coasting results in infinite mileage. Even with engine on coasting can produce mileage in excess of 200 MPG, depending on vehicle speed and idle fuel consumption.
5. Braking
The absolute worst of the five states is when you take the previously fuel consuming acceleration event and waste it generating heat in brake drums and rotors.
Now lets look at the same five states with the ideal vehicle.
1. Idling
Does not exist
2. Acceleration
Accomplished with capacitive energy storage by several means, but needs to be primarily derived from recovery of any type of deceleration or braking event. In other words, whenever you must slow down you would be storing the lost inertia as a reserve for highly efficient reapplication to assist in restoring the prior inertial state before deceleration was necessary.
3. Deceleration
Should not exist. The engine does not need to be revolving during deceleration. Instead the inertia lost to deceleration should be stored to be reapplied in future acceleration events.
4. Coasting
Since coasting is one of the most efficient states possible, the only improvement would be to minimise every source of friction in the power train that would affect the coasting distance.
5. Braking
Although hyper milers avoid braking like the plague, in almost every driving scenario it is inevitable that you will have to apply the brakes. Braking is the hyper milers worst nightmare, when all of your carefully bought inertia is wasted to heat the atmosphere.
The solution to this is to be capable of storing that energy very rapidly for reapplication. In a panic stop a car can stop from 60 MPH in less than 25 revolutions of the wheels. That is a lot of energy to recover and very little time in which to recover that energy.
To understand the basics of vehicle operation is probably well know by most people here. The car of th future will be capable of very high rates of energy recovery during deceleration and braking. It will never waste fuel idling. It will use recovered and stored energy to provide almost all of the acceleration necessary.
Engine operation will be limited to only the best portion of the bsfc map. The engine will not necessarily be small displacement. It will necessarily be designed for limited high speed operation, with a practical RPM limit of less than 3500 RPM. Some form of supercharging, or turbocharging will be utilized a very small percentage of the total operational cycle for merging into high speed traffic, and climbing sustained grades at high speeds.
This applies equally to electric motors and batteries, if they are the energy source of choice, of course without any need for forced induction.
While for many this may seem like I am "preaching to the choir", the five states are fairly simple and straightforward. Understanding each individual state and the necessary improvements to really approach the point of perfection in vehicle efficiency is something that needs to be better understood by everyone, especially those who give it little consideration.
I understand the benefits of aerodynamic and rolling resistance improvements. In the end they will allow less fuel consumption per mile of vehicle operation, and in a system that automatically compensates for lower aero drag and rolling resistance the better it gets, the significantly higher the mileage.
regards
Mech
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