cylinder
A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base.
A cylinder may also be defined as an infin ...
is positioned with its exact center (the bore axis) slightly offset from the center line of the crankshaft. "Désaxé", in French, means "unbalanced". Desaxe engines are usually automotive, but the term can also apply to steam engines.
If the offset is in the direction of rotation, it has the effect of increasing the
lever
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or '' fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is d ...
age applied to the crankshaft during the "power" stroke, and reducing thrust wasted against the cylinder wall.
In a conventional
four-stroke engine
A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directi ...
, each of the strokes (intake, compression, power, exhaust) involves a nominal rotation of 180°, totaling 720° for the complete 4-stroke combustion cycle. A desaxe engine adds to the duration of the two downward strokes (intake and power), and subtracts the same amount from the two upward strokes (compression and exhaust), with the total remaining 720°. A typical desaxe engine will have strokes of 185° - 175° - 185° - 175°, etc., with the differential roughly (but not directly) proportional to the percentage of offset distance to stroke length.
The relative proportion of offset distance versus stroke length ranges from very small to almost 20%; viz. an engine with an 80 mm stroke may have a cylinder offset of 20 mm.
Early adopters of the Desaxe Principle included
Henry Ford
Henry Ford (July 30, 1863 – April 7, 1947) was an American industrialist, business magnate, founder of the Ford Motor Company, and chief developer of the assembly line technique of mass production. By creating the first automobile that ...
who would fully implement the Desaxe offset into the Ford Flathead V8 engine throughout the 1930s while adopting greater offsets into the 1940s.
Use of desaxe engines is now becoming more common.. The Volkswagen VR6 & VR5 engines have desaxe cylinders, with an offset of 12.5 mm. The front bank cylinders are offset forward of the crank while the rear are offset rearward. The
Toyota Prius
The is a car built by Toyota which has a hybrid drivetrain, combining an internal combustion engine with an electric motor. Initially offered as a four-door sedan, it has been produced only as a five-door liftback since 2003.
In 2007, ...
has desaxe cylinder bores offset by 13 mm. The new MT-09 motorcycle is the first Yamaha with desaxe pistons. Ford has a new series of engines called dragon series that have an offset crank shaft.
All single crank split-single engines such as those used by DKW and
Puch
Puch () is a manufacturing company located in Graz, Austria. The company was founded in 1899 by the industrialist Johann Puch and produced automobiles, bicycles, mopeds, and motorcycles. It was a subsidiary of the large Steyr-Daimler-Puch cong ...
had, by necessity, highly desaxe cylinders.
The
Scuderi engine
The Scuderi engine, formally called the Scuderi Split Cycle Engine, is a split cycle, internal combustion engine invented by Carmelo J. Scuderi (April 13, 1925 – October 16, 2002). Scuderi Group, an engineering and licensing company based ...
, as shown in the animated illustration, has highly desaxe cylinders. The compressor (blue) is offset a greater amount than the power cylinder (yellow). Its benefit is to give a better
line of thrust
The line of thrust is the locus of the points, through which forces pass in a retaining wall or an arch. It is the line, along which internal forces flowEngines