AUTO TECH: In automotive math, less is more

Hey there, time traveller!
This article was published 27/07/2012 (4914 days ago), so information in it may no longer be current.

Just like the new math taught in our school systems, there is new math used when selecting a vehicle. It goes like this: four equals six and six equals eight. Fortunately this automotive math makes more sense than school math.

There are two things pushing this new automotive math — driver demand for performance and the U.S. Corporate Average Fuel Economy (CAFE) standards. Current U.S. standards are 27.5 miles per gallon for passenger cars and 23.5 miles per gallon for trucks, but these will be raised progressively from 2012 to 2016 until they reach a combined 37.5 miles per gallon.

Projections for 2025 are for standards to be set between 51 and 56 mpg. Canada’s Company Average Fuel Consumption (CAFC) standard follows the U.S. CAFE standards but are voluntary. Vehicles sold in Canada will likely be the same as the U.S. when it comes to fuel economy standards.

While there are many techniques auto manufacturers are using so vehicles can meet these standards such as lowering vehicle size and weight, reducing friction and aerodynamic drag and using low-rolling resistance tires, one of the major methods is to use smaller displacement engines. Instead of V-8, a V-6 is used or in place of a V-6, a four-cylinder is used. Not only do the smaller engines use less fuel, they also have less parts so they weigh less. All this helps fuel economy.

Countering this is consumer demand for performance, safety, comfort and convenience features. Every feature added to a vehicle increases weight and requires more fuel. Performance isn’t just about power, but also includes handling, throttle response and fuel economy. We want to have our cake and eat it too. Fortunately research, engineering and new technologies are enabling auto manufacturers to give us both fuel economy improvements and meet our driving desires.

So how do they do this? There’s not just one magic technology that lets this happen — the quest for performance and fuel economy is won in many small steps, but there are some technologies that do stand out. One of these is variable camshaft/valve timing. To produce power, the engine needs air and fuel. Injecting fuel is easy. Getting air into the engine would be relatively easy if the engine always operated at the same r.p.m., but engine speeds vary greatly during a drive cycle. Designs that allow good airflow at low r.p.m. tend to limit it at higher r.p.m. Likewise, designs that let air in at high r.p.m. make the engine operate very poorly at low r.p.m. By varying the timing of the valve opening throughout the r.p.m. range, airflow can be improved all the time.

Turbocharging also improves airflow. In simple terms, a turbocharger is an air compressor that is driven by exhaust gases. By using a turbocharger to pump additional air into the engine, the engine produces more power when needed. The rest of the time the turbocharger is almost freewheeling. Turbocharging is another technology that lets a small engine have the power of a bigger one.

A third improvement has been the introduction of direct fuel-injection to gasoline engines. Direct injection sprays the fuel directly into the cylinders under high pressure. Liquid fuel must be converted into a vapour before it can be burned, and the fine fuel mist produced by direct injection atomizes almost instantly. Port fuel injection sprays fuel into the intake ports, so some of the fuel doesn’t get atomized and goes out the exhaust as harmful emissions. Direct fuel injection improves on this.

Another advantage of direct fuel injection is that it can spray the fuel in short pulses instead of one longer pulse. This feature keeps cylinder pressures higher as the piston travels down on the power stroke, so more power is obtained from the same amount of fuel.

These three technologies combined with others allow a four-cylinder engine to produce power like a bigger V-6 and V-6 engines to have equal or more power than most V-8s.

In the hot-rod culture there is a saying: There is no substitute for cubic inches. That may be true if you only want to go racing, but in the real world we need a combination of performance and economy. Technology is enabling that. When it comes to engines that use this technology, four is equal to (or even better than) six, and six is better than eight. New math does make sense.

 

Jim Kerr is an experienced mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists’ Association of Canada.

kerr.jim@sasktel.net