The V6 design had been considered earlier by others in the industry, but was typically rejected as unworkable. Its most notable mention had been by Dr. Ing. Hans Schrön, a leading professor of automotive engineering based in Munich, Germany. He had studied alternative engine configurations beginning in the 1920s, and in 1939 he published an extensive article about different engine layouts. In this analysis he included a V6, but the work was limited, focusing more on torsional vibration; proper balancing of the V6 was a problem yet to be solved. In the spring of 1943, De Virgilio was asked to review a 39-degree V6 that had been part of the work conceived by Lancia engineers in Turin in the fall of 1942. After his initial review of the motor, he prepared his first balancing sketches in April, followed by several more complete studies in August. The first was drawn up in detail as the 60-degree V6 balancing diagram, solved in August 1943. This design was his most important work and would become the layout for the Aurelia production motor introduced seven years later. De Virgilio’s research on the V6 was a combination of both inspiration and a deductive process; His April inspiration was a reflection of his freedom at Lancia to explore and start with a clean sheet of paper. This ability to “think anew” was not widely common in the industry, as engine designers more typically relied on proven answers, building their engines as multiples of previously known configurations. Their base engines were singles, twins, or perhaps even three-cylinder motors; larger engines were seen as combinations of these smaller base units.
3D model made of a Lancia V6 crankshaft; notice the webs are in groups of three, with the intermediate web thicker. A difficult crank to machine.
Seen in this light, De Virgilio’s work on the V6 is remarkably clear. It was a design previously rejected as unworkable, but De Virgilio combined several things to make it work: His analysis included pistons and conrods as reciprocating elements, which contributed to a dynamically balanced solution (not common at the time). The arrangement of the crankpins was such that the addition of two couples (one primary, one secondary) were zero; the unresolved primary couple was addressed with counterweights on the crankshaft; and the unresolved secondary couple was of the second order and minor, and the resulting small vibration was eliminated through use of soft motor mounts. The solution was a combination of theoretical ideals and practicality to make the design work. The 60-degree configuration had other benefits, as well: with less stress on the block than a comparable straight six and with minimal bending forces on the crankshaft, use of a lightweight aluminum block and crankcase was feasible. The V6 crankshaft was organized with a sequential arrangement of the connecting rod journals (when seen from one end, it was 1-2-3-4-5-6), a response to his analysis; however, this was not conducive to forging or casting, and it was difficult to machine from a single billet. The answer was developed using a combination of manufacturing techniques: first forged, and then, while still hot, its end sections were rotated 60 degrees, to reduce the amount of required machining.
B20 V6 crank seen from the end
B20 V6 crank from the side, where the spiraling of the journals can be seen
site design and content copyright G. Goldberg, images as noted Proudly powered by Weebly