58 replies to this topic

[Charlieman]

A logical reason for the slow development of the V6 engine is the perceived smoothness of the inline 6 at low speed. Inline 6s for road and sports cars were popular in press reviews, and designers understood their limitations and work arounds. The V6 was largely unknown and required unfamiliar design and production. The long crank of an inline 6 was a vulnerability at high rotational speed, so it was not necessarily appropriate for a racing car. Or perhaps only appropriate to a racing car that would be properly maintained.

 

Thanks to Geoffg for bringing this thread to life. Why did De Virgilio concern himself with the V6 design? Was it a personal obsession with the mathematics and dynamics? Or did he realise that engines which were a little bit shorter would become a requirement?

[Allan Lupton]

The straight-six has almost unbeatable dynamic balance characteristics, so is smooth at all speeds. Its weakness is that its crankshaft is prone to torsional vibration, but effective damping was introduced very early in its history so if that's what you mean by a limitation and work around it has not been a problem since the first decade of the 20th century.

By contrast, the V6 is an invention of the devil - see posts above for some of the detail - but is a more suitable package shape for a modern road car.

[geoffg]

Not to tell the book's story in a paragraph or two, but…. 

 

Lancia had a long history in V engines, starting c. 1915 with studies of V12s for airplanes in WWI. Vincenzo Lancia got interested in reducing the exterior size of the engine so it would fit in places. He started by reducing width with narrow Vs. The narrow V was moved into auto production in 1922 with their Lambda, with a sister V8 engine for the Trikappa at the same time, both narrow Vs of around 14º. The V angle was empirically derived, not theoretically determined, chosen as the best combination to make all the bits work for a smaller mono block engine. This became a line-of-thought for the company through many different sized and iterations over the next two decades, used in all their cars - the Dilambda, Astura (both narrow V8s), and  the Artena, Augusta, Aprilia and Ardea (narrow V4s), each engine a unique design, with different angles, valve train, size varying from 903cc to 4 liters. It continued post-war in the Appia and Fulvia (until c. 1973), and was resuscitated by VW's narrow angle engines recently. 

 

If you like this sort of thing, this was a rather inventive group of people working off a central theme (narrow angle V motors) and its a study of variations around form factors. If you prefer to rationalize engine design around performance (such as Alfa DOHC), then this isn't likely to be your cup of tea.

 

One of the difficulties with narrow Vs was carburetor placement: in the beginning they were on the side of the engine, resulting in rather strange internal porting. In the 1930s, the The Astura had the carb on top and in the middle for better routing but with a tall engine profile. They started to consider other possibilities c. 1940, looking into a wider V angle (patented studies on this - all in the book!). De Virgilio was given a crankshaft design  for a 39º V6 to check as he was a young engineer, fresh out of school with new theory.

 

He ran his calcs, and said it wouldn't work. The company was used to unusual thinking so they gave him room to work. He started first doodles in April 1943 and developed a detailed methodology on crankshaft design by August 1943, solving the balancing issues and concluding 60º was optimal. The V6 engine balancing is unlike in-line motors, and is complicated.

 

It took time for this to be implemented. Lancia was initially only interested in a narrow angle V6 to fit their 1500cc Aprilia, and so in 1945 De Virgilio designed a 45º V6. After trying it in the car, Gianni Lancia decided its was a compromise, and he made the decision to go for a new car with a new engine design based around the optimally balanced 60º V6. This was the Aurelia, introduced in 1950. The rest is history. 

 

There was also some personal drama in the story - De Virgilio did his engine work at Lancia under the mentorship of Vittorio Jano (ex-Alfa from 1938) head of Lancia's engineering until 1955, and worked closely with Gianni Lancia, the emerging young head of the company. After the death of Vincenzo in 1937, the company had to reinvent itself after the war, and young Gianni had to grow into the job. And then there is the role of Gianni's first cousin, Rita, the woman in the mix…. 

Edited by geoffg, 17 January 2015 - 17:10.

[Charlieman]

The straight-six has almost unbeatable dynamic balance characteristics, so is smooth at all speeds. Its weakness is that its crankshaft is prone to torsional vibration, but effective damping was introduced very early in its history so if that's what you mean by a limitation and work around it has not been a problem since the first decade of the 20th century.

Effective damping was a significant limitation. It was an expensive servicing cost, best mitigated by not flogging the engine.

[Charlieman]

Not to tell the book's story in a paragraph or two, but…

Thanks. Mr G.

[Allan Lupton]

Effective damping was a significant limitation. It was an expensive servicing cost, best mitigated by not flogging the engine.

I disagree but you may know of more modern engines (say post Jaguar AJ6) than I do, and it may be that lessons have to be relearned.

Most decent straight sixes would be designed not to have the vibration period at a much-used speed, the damper therefore only rarely doing its bit.

As for servicing cost, again you must know of some engine that is expensive, but I can't call one to mind.

[Charlieman]

I disagree but you may know of more modern engines (say post Jaguar AJ6) than I do, and it may be that lessons have to be relearned.

I was fluffing a bit, and I really meant vintage inline 6 when comparing V6. My student notes of analysis of engine vibration are in my loft, so you must appreciate that it may take some time to recomprehend.

 

How expensive? I'm not in the repair business so I only know what I know: too bloody expensive for me to consider.

[Michael Ferner]

And then there is the role of Gianni's first cousin, Rita, the woman in the mix…. 

 

Now, don't you dare stopping just when it gets interesting...! 

[geoffg]

"The woman in the mix" is Rita Lancia, Gianni's first cousin, and daughter of Giovanni Lancia, Vincenzo's brother. De Virgilio was introduced to her in 1941-42.

 

De Virgilio was from the south of Italy and for him to marry into the Lancia family was unusual. He started work at the company in 1939, and by 1941 he was recognized as "a bright boy" in the company's engineering dept, and was introduced. By mid-1942, he's casually picnicking (in a suit) at the family house with the young Gianni, his sisters and first cousin Rita. De Virgilio and Rita were married five years later, in 1947 (pictures from the picnic and wedding are in the book). 

 

After the war, the company had to reinvent itself, having lost the company's founder and leader, Vincenzo Lancia,  in 1937. There was commercial success to carry them thru the 1930s and the war years, with the newly introduced Aprilia, the smaller Ardea of 1939, and the sales of  more than 10,000 heavy trucks to the Italian Army during the war. Lancia was healthy enough, and had about 5,000 employees, but they needed a new car design for after the war. First tried was a radical idea they had patented in the 1930s for a rear-engine three seater. A prototype was built in 1944, using a new rear-mounted 2-liter 90º V8 with a conventional crankshaft. This design was not accepted, and the question of the next new car remained. 

 

By 1948, this was resolved with a full commitment to De Virgilio's 60º V6 engine.This was not done casually: choosing the 60º V6 meant they had to design an entirely new car and chassis, as theirs were unit bodies, and this engine would not fit any existing chassis. It took time for Gianni and Jano to embrace the V6 motor, but they liked the fact it was breaking new ground. This required a deep trust of De Virgilio, as he had never designed a motor before, something he learned from Jano. 

 

Innovation doesn't happen in a vacuum: De Virgilio's embrasure by the family at this time must also have been a factor. Without Rita and their marriage, would there have been the Aurelia? Food for thought. 

Edited by geoffg, 18 January 2015 - 18:09.