Magnetic Gears Reduce Friction

Friction between moving parts in the engine and transmission consumes a considerable percentage of all fuel used by a vehicle. Any technique for reducing this friction gives an increase in fuel economy. Here is a demonstration of two magnetic gears which use magnetic fields to transfer force instead of gear pins in physical contact. Avoiding metal on metal contact leads to much, much less friction in the system. Of course, generating magnetic fields strong enough to support the loads experienced by transmissions in contact with a couple of hundred horsepower engine is more than challenging. But it is always good to keep an eye out for possible future technologies that could help us save on gas.

Fiat Start and Stop System

A great way to waste gas is to sit still with your engine idling. Every second of idle wastes gas to turn the engine over without getting you anywhere. Stop and go city traffic can be a big gas waster because of this. While it is fairly easy to remember to shut off the car while waiting to pick up a friend, for example, it is much harder to manage stopping and starting the engine while you are driving in city traffic. The Fiat 500 Start & Stop System is a technological fix to that problem. The Start and Stop System automatically shuts off the engine when the car comes to a stop and automatically starts it again when the driver presses the accelerator. The driver does not have to think about idling at all. The system takes care of avoiding those fuel sucking idles.

The Start and Stop System is based around a special high performance starter and battery that together are able to quickly start up the engine over and over again. If you tried to replicate that with an ordinary car, you would find the starter would not have to power to instantly fire up the engine. Worse, after a half hour of starting and stopping in stop and go traffic, you would drain the battery and be stopped dead! Of course the Fiat Start and Stop System also depends on computer control to decide exactly when to stop and start the engine.

This is an excellent example of a relatively simple technology being put to work to save on gas. There are many other similar non revolutionary but rather incremental changes that could be combined to produce cars that get double the fuel economy of typical Detroit products. Fortunately for those who want to save on gas, nobody has to wait on Detroit anymore: just buy from the Europeans!

Fuel Efficiency and the Economy

The possible effects of increased fuel efficiency on the economy are wide ranging and complex. Fuel Efficiency and the Economy is a well written and understandable overview. It contains an input-output analysis showing how proposed changes to automotive fuel-efficiency standards would propagate through the national economy. Of particular interest is Figure 3, which shows a range of current and near future technologies giving for each one a band of estimated fuel economy improvements and possible increases in retail cost. Also of interest is Figure 2, which demonstrates how since the 80's Detroit has been putting increases in engine efficiency into achieving shorter and shorter 0 to 60 times for heavier and heavier vehicles instead of using fewer gallons per hundred miles.

Smaller Vehicles Designed for Maximum Utility

We are at the last in our series. The purpose of a car is to move passengers and their cargo. If we can design the smallest, lightest car that does this, we will get better fuel economy. However to meet standards of comfort and provide sufficient cargo capacity it is not possible to just miniaturize everything. The idea is to rearrange the interior space of the car to make the space inside as usable as possible while keeping the overall shape as tightly fit to the interior as possible. Some of the techniques that can be used are illustrated in the Mazda Washu concept.

The Washu has features such as steer by wire, which allows reduction of the steering column. Additionally the steering wheel can stow away to provide even more space when parked. The beltline is widened outwards to give more interior space. The feel of roominess is enhanced by putting windows everywhere possible. The rearmost seats can be efficiently folded down to carry long cargo. The rear cargo door consists of a combination of a hatchback and a tailgate that slides straight down vertically (instead of swiveling on a hinge to be parallel with the ground) to make it as easy as possible to load bulky freight. The cabin roof is arched to open up a little more volume.

Design attention like this can open up more space for passengers and cargo without needing to make the overall vehicle larger. This means that there is less structure per usable functionality, and that in turn means carrying around less metal with you. The result is a savings on gas.

Lighter Construction with Composites and Lighter Metals

Here is number six in our series looking at fuel economy technologies. If a vehicle can lower its weight it will be able to run with less fuel. There are two main reasons for this. One is that the mechanical friction suffered by the vehicle is proportional to the weight. A heavier vehicle has to spend more fuel fighting more friction. Note that this does not apply to the aerodynamic air resistance friction that begins to really bite at higher speeds. The air resistance does not increase with vehicle weight, assuming the shape of the body stays the same. The other is the investment in kinetic energy to speed up the vehicle. The amount of kinetic energy needed to reach a given speed is proportional to the mass. So to speed up a heavier car, you have to burn more fuel. Then when the car slows down or stops, all of this energy is lost, mainly as heat in the brakes. Heavier car equals greater loss in this way.



The video above explains the Rocky Mountain Institute's Hypercar concept. It is a car made of only fourteen panels of carbon fiber composite. The carbon fiber has half the mass of steel. Because there are only 14 pieces the overall strength of the body is greater than if it were made of steel. The result is a much more fuel efficient vehicle.

NuVinci Continuously Variable Planetary Transmission

The transmission is the connection between the speed of the engine and the speed of the vehicle. Conventional transmissions provide a series of gears. Each gear has a fixed ratio between engine speed and vehicle speed. If you wish to go at a given speed and your transmission has for example five gears the engine has to run at one of five speeds. Each engine is most fuel efficient at exactly one specific RPM. If none of the five speeds is at that RPM, your engine will not be able to drive you at your chosen speed as efficiently as possible.

Continuously variable transmissions provide a range of ratios between engine RPM and driveshaft rotation (vehicle speed). This allows the engine to always run at its most fuel efficient RPM. Changing vehicle speed is accomplished by changing the transmission gearing ratio instead of the engine RPM.



There have been many implementations of continuous variable transmissions using a variety of techniques. Good old Wikipedia has a list of automobiles using them. Although automakers have only really been getting serious about their use in the last five years or so. Fallbrook Technologies has recently been developing a new type : the NuVinci. Watch the video above to see how it works. I think it is an ingenious mechanical system. This is a planetary continuously variable transmission. The name comes from Leonardo da Vinci, who first invented continuously variable transmissions 500 years ago. And Detroit has only seen the value about 5 years ago. Oh well, better late then never.

Variable Valve Timing

This is the second in our series of seven fuel economy technologies Detroit could have pursued but did not. Although almost all of the world's automakers have made at least one engine with variable valve timing within the last 10 years, before that time they were rare. Even today the majority of engines have fixed timings.

The video illustrates the idea. Basically, the fuel-air intake valves and the exhaust valves open a certain distance and stay open for a certain time. Also the location in the piston cycle at which they are open is important. At a given RPM, the engine has to open the valves different amounts at different positions for different times to get maximum efficiency. If the valves have fixed timings, the engine will only be at its top efficiency at one narrow RPM band. However, if the valves can modify their timing, the engine can reach high efficiency over a wider band of RPM.

In normal operation, there is a moment near the end of the exhaust stroke when the exhaust valve and the intake valve are both open. Also the exhaust valve stays open a little while into the intake stroke. This time when both valves are open is known as the overlap, and is one of the most important variables to control. At low RPM, the overlap should be low. This is because at low RPM the airflow is fast relative to the engine speed. At high RPM, the engine is moving so fast relative to the air that it is better to open the intake valve early so that the air has a better chance to enter.

The first vehicles with variable valve timing technology were not introduced to the US market by Detroit. Instead Alfa Romeo, Nissan and Honda blazed the trail. One more chance missed by Detroit.

Could we Have Had Better Fuel Economy?

The average fuel economy of the US vehicle fleet is not very good. Sure, this is because until recently oil and gasoline were cheap like water. Now that is starting to change. With countries like China and India beginning to reach high standards of living the demand on global resources is set to soar. And at the same time, some of those resources are going past their peak, like for example oil. The result is that in the future fuel economy will be something to care about.

Look at this abstract and you can see that in the whole history of the automobile in the US, the fuel economy has been poor. I didn't buy the paper, so I am going to quote only the abstract below, but it gets the idea across. Also note that I converted the MPG numbers in the quote to GPHM, so it is not a straight quote.

This article documents and analyzes the changes in fuel efficiency of vehicles on US roads between 1923 and 2006. Information about distances driven and fuel consumed was used to calculate the on-the-road fuel efficiency of the overall fleet and of different classes of vehicles. The overall fleet fuel efficiency decreased from 7.14 GPHM in 1923 to 8.40 GPHM in 1973. Starting in 1974, efficiency increased rapidly to 5.92 GPHM in 1991. Thereafter, improvements have been small, with efficiency reaching 5.81 GPHM in 2006.

So the vehicle fleet considered en masse went from 7.14 gallons per hundred miles in 1923 down to 5.81 gallons per hundred miles in 2006. That is an improvement, but it doesn't seem like much considering that we are talking about 83 years. Of course in that time we added more weight to our vehicles, drove them at higher speeds and added all kinds of powered comforts like air conditioning. In fact, most of the technical advances in cars and trucks are in these other areas because fuel economy was never a concern.

But what if fuel economy had been a concern? Could Detroit have followed a different path and left us today with better fuel economy? I think the answer is yes, and so do other people. Here is a comment giving a list of changes Detroit could supposedly make to improve fuel economy by 40%. The list is copied here:

• Miller cycle
• variable valve timing
• variable displacement
• turbo-compounding
• NuVinci-style CV transmission
• lighter construction with composites and lighter metals
• smaller vehicles, designed for maximum utility

The next 7 posts here on Save on Gas will look at each of these technologies to see what advantages it could provide and speculate on why it has not been widely deployed by Detroit.