Brilliant design built for a long life
Geneva, Mar 05, 2002
The number twelve has always had a rather special significance in
engine manufacturing. Karl Maybach was well aware of this when, in
1929, he presented to the world what a company brochure of the time
modestly described as "the first ever volume-produced twelve-cylinder
engine".
The engine, which made its debut in the Maybach 12, was indeed a pioneering
achievement. It offered the advantages of a twelve-cylinder engine
- powerful, silky smooth operation - combined with a brilliantly simple
design concept, high reliability and a long life.
The "Type 12" engine benefited from Wilhelm and Karl Maybach's
many years of experience in building multi-cylinder engines for the
Zeppelin airships "ZR III" and "Graf Zeppelin".
The V12 engine had a displacement of 6922 cubic centimetres and developed
110 kW/150 hp at 2800 rpm in the Maybach 12 of 1929 and the Maybach
DS 7 Zeppelin of 1930, while a larger 7922 cc version in the Maybach
DS 8 Zeppelin of 1931 developed 147 kW/200 hp at 3200 rpm. These were
truly dazzling statistics for the times.
A company brochure of the period described the basic design principles
of the engine as follows: "The twelve-cylinder engine exhibits
largely the same basic configuration as the Maybach airship engines
used to such brilliant effect in the 'Graf Zeppelin' airship. The
two banks of six cylinders form a 60-degree V and the cylinders in
each bank are offset by the width of a big-end bearing." Maybach
used a single crank arm on the eight-bearing crankshaft to control
each pair of cylinders, one on the right and one on the left - a brilliant
design which meant that effectively the twelve-cylinder engine was
able to operate with just a six-cylinder crank-shaft.
Other brilliant design ideas further simplified the design of the
twelve-cylinder engine compared with competitor products. The keynote
was a high level of parts commonality. For example the two six-cylinder
blocks were completely identical, as were the removable cylinder heads
and the rocker arms and their bearings.
Accent on reliability
One concern very much on the mind of the designers was reliability.
For example the upper section of the engine block was a single-piece
aluminium casting incorporating cylinder liners which were water-cooled
along their entire length. This not only provided reliable cooling,
it also increased the rigidity of the engine. The over-head intake
and exhaust valves were controlled by pushrods and rocker arms actuated
by a seven-bearing camshaft mounted between the cylinder blocks.
For the camshaft drive, a brilliantly simple solution was found:
a helical gear on the crankshaft meshed with a Novotex gear wheel
on the camshaft, making light work of valve adjustment.
Other maintenance tasks were just as easy: "Components like
the water pump, alternator and distributor are situated between the
cylinders, with a clarity of arrangement and accessibility which sets
new standards", a Maybach brochure pro-claimed. Needless to say,
Karl Maybach had provided for other contingencies as well: in case
of poor fuel quality, the engine was equipped for the first time not
only with automatic spark timing but also with a manual spark timing
control on the dashboard.
Two dual carburettors supplied the twelve-cylinder engine with an
average 28 litres of fuel per 100 km. Considering the power of the
engine and the size of the car, this figure was hailed at the time
as outstanding.
Good reasons for using a twelve-cylinder engine
As Karl Maybach himself stated, his motivation for using a twelve-cylinder
engine in a passenger car was to safeguard the technical leadership
which had always been a hallmark of his company. His experience as
a designer had taught him that for the same displacement and at the
same engine rpm, considerably more power could be obtained from a
twelve-cylinder engine than from an eight- or six-cylinder unit. Using
twelve intake and exhaust valves, that much more gas could flow into
and out of the combustion chambers per stroke than with a smaller
number. At the same time there were also benefits for the combustion
process, which meant that there was no significant rise in fuel consumption.
Further advantages were lower engine speeds, resulting in reduced
stress, and considerably smoother engine operation. And if anyone
was still not convinced, Karl Maybach had some statistics to hand:
at 60 km/h, a "Type 12" engine ran at 1425 crankshaft revolutions
per minute with an average piston speed, based on the stroke of 100
millimetres, of 4.7 metres per second.
Six- and eight-cylinder engines of similar power operated at speeds
of up to 1900 rpm, resulting in considerably higher piston speeds
of between 6.6 and 8.1 metres per second. And while the twelve-cylinder
engine fired 8,490 times per minute, the six- and eight-cylinder engines
fired only between 4,275 and 7,640 times.
Maybach explained the advantages in a brochure as follows: "For
every revolution, six power impulses are imparted to the easily balanced
crankshaft compared with three or four impulses for six- or eight-cylinder
engines. With this kind of uniform power output, only minimal balancing
masses are required to maintain the regular-ity of the rotational
momentum".
In January 1930 the magazine "Motor" delivered a glowing
test verdict on the Maybach engine: "The twelve-cylinder engine
operates almost like an explosion turbine."
©DaimlerChrysler
