Ask Joe Mechanic: Supercharging

Before I start this week’s article, I want to publicly thank Stephanie, who collaborated with me on the Meet Joe Mechanic article, for stepping in at a late time last week when for medical reasons I could not put my column together and found a suitable and timely replacement for me. I am now on the mend and am resuming my duties on a slightly limited basis.

            Supercharging in theory is very similar in what it does to turbocharging. In fact, turbocharging was originally called turbo-supercharging. The main difference between the two is where the power is created that forces the intake charge into the engine. In turbocharging, we already saw that that force was the use of the exhaust escaping the engine, which forced the intake charge into the engine. In supercharging, it is by external mechanical means, usually a belt, a chain or direct drive from the crankshaft of the engine.

            Ironically, the first effective use of supercharging had nothing at all to do with an engine. In 1860, Brothers Francis and Philander Roots of Connersville, Indiana, were exploring the means to get more air into blast furnaces for making steel and other industrial applications. Their company, Roots Blower Company, developed the first operating supercharger, which forced air into those blast furnaces.  It was that design which became the most commonly used supercharger design for many years.

           

The first use of a supercharger on a functioning engine was by Dugald Clerk in 1878 on a two-stroke engine. Gottlieb Daimler, a name well known in early automotive history, received a German patent for a supercharger on an internal combustion engine in 1885. Louis Renault, another well-known name of the Renault automotive family, received a French patent for a centrifugal supercharger in 1902.

            Ironically, the first known application of a supercharger took place in Pottstown, Pennsylvania by Lee Chadwick in 1908 and his car achieved an almost unheard of speed for that time of 100 miles per hour. The Chadwick factory still stands in Pottstown, in recent years in was home to the Bill Pollack, of Pollack Steel Company, automobile collection. That collection included a couple very rare Chadwick automobiles. The Chadwick will be a subject of a future Automotive History article, as I knew the late Bill Pollack personally and have been to his museum a number of times.

            The first production road cars with superchargers were built in 1921 by whom else, but Mercedes. The models were the 6/25/40HP and the 10/40/65HP and had Roots superchargers. They were designated “Kompressor,”, a designation that Mercedes uses to this day on all supercharged cars they build.

            Another design for a supercharger received a patent in 1878 by Heimrick Krigar of Germany. This was for a screw type supercharger, which is actually a much more efficient design, but its parts are very difficult to machine. The design utilizes two opposing screws with a 180 degree twist along their length which combines to create a full 360 degree turn. The design was so advanced for its time that it took until 1935 to be able to create the first working model by Alf Lysholm of Sweden working for Ljungstroms Angturbin AB, which became the Svenska Aeroplaten Company, which eventually became Saab. Who ironically became the first mass-produced successful turbocharged automobile and at the time the only company which produced an all turbocharged model line.

            There are two main types of superchargers, which are designated by the method of air transfer. The two types are positive displacement and dynamic compressors. Positive displacement blowers deliver an almost constant pressure increase at all engine speeds. Dynamic compressors do not build pressure at idle or low speeds; above a certain threshold speed pressure increases with engine speed. Positive displacement pumps deliver a nearly fixed volume of air per engine revolution at all speeds, minus leakage, which means its importance decreases at higher speeds.

            Positive displacement pumps are further subdivided into two groups, internal and external compression. Roots superchargers are of the external type, although the high-helix roots blowers try to have the same effectiveness as the Lysholm screw. All other superchargers have some degree of internal compression. Internal compression means that the compression of the air charge takes place inside the body of the supercharger. This is more effective and efficient than the backflow compression of the Roots type and means a smoother transition to boost than the other type. Internal compression superchargers usually have a fixed boost pressure which equals the compression pressure of the supercharger, thus back flow is zero. If the boost pressure is higher, back flow will occur, but if properly matched, they achieve a very high factor of efficiency.

Some information for this article was sourced from www.wikipedia.org.