Postby Chemical » October 2nd, 2007, 10:57 am
Engine technology has improved so much over the past couple of decades that it is seldom we encounter any serious problems with them. Keep the oil changed and the level up, don't over rev them and change the air filter when dirty. Even spark plugs and wires last much longer, sometimes longer than you own your vehicle! This durability can be accredited to three major factors - better materials, improved construction design and computer control technology.
Better materials include more precise manufacturing control of alloys, composite materials and resins. While it was possible to provide this quality of materials before, consistency during mass production was always a challenge. Now, computerized monitoring of every aspect of the material production has enabled that quality consistency, so engines last longer.
Design is another area where there have been major changes. Today, computers and computer-aided design programs are used not only to draw the components but to test them for durability as well. After the part is drawn on the computer screen, the program is then instructed to bend, twist, cycle and vibrate the part as required. Stresses in the part show up as different colours on the part and the engineers can then add material or change component shapes to reduce or distribute the stresses. It also allows the engineers to remove material where there is minimal or no stress, lightening the part. The engine is the heaviest component in a vehicle and every gram of weight removed improves handling, acceleration, braking and fuel economy.
Control technology has improved as well. Electronic fuel injection started commonly appearing in the mid 1980's. The computers used on these systems are now antiques just as the home computer you bought 15 years ago is an antique. Today's computers are many times more powerful, calculate much faster and are able to handle many more functions. Besides improved fuel control, one of the most important control features on many vehicles is camshaft position control.
Changing the position of the camshaft in relation to the crankshaft is the same as saying you are changing the opening of the engine valves in relation to the piston position. An idling engine has ample time for the air and fuel to flow past the intake valve into the combustion chamber. There is also lots of time for exhaust gases to flow out. Speed that same engine up a few thousand rpm and the time for the air to flow becomes much shorter.
Engine camshaft design has always been a compromise. If the valves are held open too long at low engine rpm, then the engine will idle rough. If they are not held open long enough, then there won't be enough time for air to enter at high rpm and performance suffers. Current computer controls have changed this.
The computer can change the position of the camshaft in relation to the crank by switching oil pressure on and off to a device that changes the camshaft position. Moving the camshaft back (retarding it) allows less time for air to enter but provides a smooth idle. Moving it forward (advancing it) allows more time for air to enter for high rpm performance. Many manufacturers advertise variable camshaft timing as a feature on some of their engines, and this is one of the ways we are able to achieve both fuel economy and performance.
With DOHC (double overhead camshaft) engines, the computer is able to control each camshaft separately for optimum performance (if equipped with variable cam timing). Single camshaft engines, with either the cam in the cylinder head or in the block, can advance or retard the complete camshaft. This improves performance significantly but not as much as the DOHC system. However, single camshaft designs are much cheaper to produce, reducing the price of the vehicle. The Dodge Viper has a special setup that uses two camshafts concentric with each other. One shaft has the exhaust cam lobes. The other shaft has the intake cam lobes. One shaft is placed inside the other hollow shaft and the lobes are pressed in place. This allows them to control the position of intake and exhaust cams separately just like a DOHC system but with the compactness of a single camshaft design.
Looking back, it is really computer controls and programs that have improved all aspects of our automobiles. The designers and engineers have always had good ideas but the computers have enabled them to bring ideas to production that were not feasible before.
