Balance shaft
Encyclopedia
Eccentric (mechanism)
In mechanical engineering, an eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle ....
weighted shaft which offsets vibration
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
s in engine designs that are not inherently balanced (for example, most four-cylinder engines). They were first invented and patented by British engineer Frederick Lanchester
Frederick Lanchester
Frederick William Lanchester, Hon FRAeS was an English polymath and engineer who made important contributions to automotive engineering, aerodynamics and co-invented the field of operations research....
in 1904.
Overview
Balance shafts are most common in inline four-cylinderStraight-4
The inline-four engine or straight-four engine is an internal combustion engine with all four cylinders mounted in a straight line, or plane along the crankcase. The single bank of cylinders may be oriented in either a vertical or an inclined plane with all the pistons driving a common crankshaft....
engines which, due to the asymmetry of their design, have an inherent second order vibration
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
(vibrating at twice the engine RPM) which cannot be eliminated no matter how well the internal components are balanced. Four-cylinder flat engine
Flat engine
A flat engine is an internal combustion engine with multiple pistons that move in a horizontal plane. Typically, the layout has cylinders arranged in two banks on either side of a single crankshaft and is sometimes known as the boxer, or horizontally opposed engine. The concept was patented in 1896...
s in the boxer configuration have their piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
s horizontally opposed, so they are naturally balanced and do not incur the extra complexity, cost or power loss associated with balance shafts (though the slight offset of the pistons introduces a rocking couple). This vibration is generated because the movement of the connecting rod
Connecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....
s in an even-firing four-cylinder inline engine
Straight engine
Usually found in four- and six-cylinder configurations, the straight engine, or inline engine is an internal-combustion engine with all cylinders aligned in one row, with no offset...
is not symmetrical throughout the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
rotation; thus during a given period of crankshaft rotation, the descending and ascending pistons are not always completely opposed in their acceleration, giving rise to a net vertical inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
l force twice in each revolution whose intensity increases quadratically
Quadratic growth
In mathematics, a function or sequence is said to exhibit quadratic growth when its values are proportional to the square of the function argument or sequence position, in the limit as the argument or sequence position goes to infinity...
with RPM, no matter how closely the components are matched for weight.
The problem increases with larger engine displacements, since one way to achieve a larger displacement is with a longer piston stroke, increasing the difference in acceleration or by utilizing a larger bore thereby increasing the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
of the pistons. One can utilize both techniques in order to maximize possible engine displacement. In all cases, the magnitude
Magnitude (mathematics)
The magnitude of an object in mathematics is its size: a property by which it can be compared as larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs....
of the inertial vibration increases. For many years, two litres was viewed as the 'unofficial' displacement limit for a production inline four-cylinder engine with acceptable noise, vibration, and harshness
Noise, Vibration, and Harshness
Noise, vibration, and harshness , also known as noise and vibration , is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks...
(NVH) characteristics.
The basic concept has a pair of balance shafts rotating in opposite directions at twice the engine speed. Equally sized eccentric weights on these shafts are sized and phased so that the inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
l reaction to their counter-rotation cancels out in the horizontal plane
Horizontal plane
In geometry, physics, astronomy, geography, and related sciences, a plane is said to be horizontal at a given point if it is perpendicular to the gradient of the gravity field at that point— in other words, if apparent gravity makes a plumb bob hang perpendicular to the plane at that point.In...
, but adds in the vertical plane, giving a net force
Net force
In physics, net force is the total force acting on an object. It is calculated by vector addition of all forces that are actually acting on that object. Net force has the same effect on the translational motion of the object as all actual forces taken together...
equal to but 180 degrees out-of-phase with the undesired second-order vibration of the basic engine, thereby canceling it. The actual implementation of the concept, however, is concrete enough to be patented. The basic problem presented by the concept is adequately supporting and lubricating a part rotating at twice engine speed where the second order vibration becomes unacceptable.
There is some debate as to how much power the twin balance shafts cost the engine. The basic figure given is usually around 15 hp
Horsepower
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...
(11 kW), but this may be excessive for pure friction loss
Friction loss
Friction loss refers to that portion of pressure lost by fluids while moving through a pipe, hose, or other limited space. In mechanical systems such as internal combustion engines, it refers to the power lost overcoming the friction between two moving surfaces.- Causes :Friction loss has several...
es. It is possible that this is a miscalculation derived from the common use of an inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
l dynamometer
Dynamometer
A dynamometer or "dyno" for short, is a device for measuring force, moment of force , or power. For example, the power produced by an engine, motor or other rotating prime mover can be calculated by simultaneously measuring torque and rotational speed .A dynamometer can also be used to determine...
, which calculates power from angular acceleration
Angular acceleration
Angular acceleration is the rate of change of angular velocity over time. In SI units, it is measured in radians per second squared , and is usually denoted by the Greek letter alpha .- Mathematical definition :...
rather than actual measurement of steady state torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
. The 15 hp (11 kW), then, includes both the actual frictional loss as well as the increase in angular inertia of the rapidly rotating shafts, which would not be a factor at steady speed. Nevertheless, some owners modify their engines by removing the balance shafts, both to reclaim some of this power and to reduce complexity and potential areas of breakage for high-performance and racing use, as it is commonly (but falsely) believed that the smoothness provided by the balance shafts can be attained after their removal by careful balancing of the reciprocating components of the engine.
Four-cylinder applications
Mitsubishi MotorsMitsubishi Motors
is a multinational automaker headquartered in Minato, Tokyo. In 2009 it was the fifth-largest Japan-based automaker and the 17th-largest in the world measured by production...
pioneered the design in the modern era with its "Silent Shaft" Astron engines
Mitsubishi Astron engine
The Mitsubishi Astron or 4G5 engine, is a series of straight-4 internal combustion engines first built by Mitsubishi Motors in 1972. Engine displacement ranged from 1.8 to 2.6 litres, making it one of the largest four-cylinder engines of its time....
in 1975, with balance shafts located low on the side of the engine block and driven by chains from the oil pump
Oil pump
Oil pump may refer to:*A hydraulic pump, which pressurizes hydraulic fluid in a hydraulic system*An oil pump , a part of the lubrication system that pressurizes motor oil for distribution around the engine...
, and they subsequently licensed the patent to Fiat
Fiat
FIAT, an acronym for Fabbrica Italiana Automobili Torino , is an Italian automobile manufacturer, engine manufacturer, financial, and industrial group based in Turin in the Italian region of Piedmont. Fiat was founded in 1899 by a group of investors including Giovanni Agnelli...
, Saab and Porsche
Porsche
Porsche Automobil Holding SE, usually shortened to Porsche SE a Societas Europaea or European Public Company, is a German based holding company with investments in the automotive industry....
.
Saab has further refined the balance shaft principle to overcome second harmonic sideways vibrations (due to the same basic asymmetry in engine design, but much smaller in magnitude) by locating the balance shafts with lateral symmetry but at different heights above the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
, thereby introducing a torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
which counteracts the sideways vibrations at double engine RPM, resulting in the exceptionally smooth B234 engine.
Six-cylinder applications
Another balance shaft design is found in many V6 engines. While an inherently balanced V6 engine would have either 60 or 120 degrees angle between the two banks of cylinders, many current V6 engines are derived from older V8 engines, which have a 90-degree angle between the two banks of cylinders. While this provides for an evenly spaced firing orderFiring order
The firing order is the sequence of power delivery of each cylinder in a multi-cylinder reciprocating engine.This is achieved by sparking of the spark plugs in a gasoline engine in the correct order, or by the sequence of fuel injection in a Diesel engine...
in an 8-cylinder engine, in a six-cylinder engine this results in a loping rhythm, where during each rotation of the crankshaft three cylinders fire at 90-degree intervals, followed by a gap of 90 degrees with no power stroke form any cylinder, followed by 3 more cylinders firing at 90-degree intervals. This can be eliminated by using a more complex, and expensive, crankshaft which alters the relationship between the cylinders in the two banks to give an effective 60-degree difference, but recently many manufacturers have found it more economical to adapt the balance shaft concept, using a single shaft with counterweights spaced so as to provide a vibration which cancels out the shake inherent in the 90-degree V6.
Production implementations
- Alfa RomeoAlfa RomeoAlfa Romeo Automobiles S.p.A. is an Italian manufacturer of cars. Founded as A.L.F.A. on June 24, 1910, in Milan, the company has been involved in car racing since 1911, and has a reputation for building expensive sports cars...
2.0L four-cylinder, as fitted to the Alfa Romeo 156Alfa Romeo 156The Alfa Romeo 156 is a compact executive car introduced by Italian automaker Alfa Romeo at the 1997 Frankfurt Motor Show as the replacement for the Alfa Romeo 155... - BMW K75BMW K75The BMW K75 was a standard motorcycle produced by BMW Motorrad from 1985 to 1995. At the time of its introduction, the K75 was BMW's cheapest motorcycle...
motorcycle - Chrysler K engineChrysler K engineThe 2.2 and 2.5 are a family of inline-4 engines developed by Chrysler Corporation originally for the Chrysler K- and L-platforms cars and subsequently used in many other Chrysler vehicles...
- Chrysler 2.4 L and 2.5 L Neon engine
- Ford Modular engineFord Modular engineThe Ford Modular engine is Ford Motor Company's overhead camshaft V8 and V10 engine family, which has been produced in 4.6L, 5.0L , 5.4L, and 6.8L variations. Contrary to popular belief, the Modular engine did not get its name from its design or sharing of certain parts among the engine family...
V10V10 engineA V10 engine is a V engine with 10 cylinders in two banks of five with a distinct exhaust note.- Mechanics :The V10 is essentially the result of mating two even-firing straight-5 engines together. The straight-5 engine shows first and second order rocking motion... - Ford Taunus V4 engineFord Taunus V4 engineThe Taunus V4 was a V4 piston engine with one balance shaft, introduced by Ford Motor Company in Germany in 1962. The German V4 was built in the Cologne plant and powered the Ford Taunus and German versions of the Granada, Capri and Transit...
- Buick 3800 V6
- General Motors Corporation Quad 4GM Quad-4 engineThe engine family known as the Quad 4 was debuted to the public in the spring of 1987. The Quad 4 was a DOHC inline 4-cylinder produced by General Motors' Oldsmobile division...
and EcotecEcotecEcotec is a General Motors trademark that refers to a series of emissions technologies that were implemented throughout a range of GM engines... - GM Atlas engineGM Atlas engineAtlas is a name for a family of modern inline piston engines for trucks from General Motors. The series debuted in 2002 with the Oldsmobile Bravada, and is also used in the Chevrolet TrailBlazer and Colorado and their GMC twins, the Envoy and Canyon...
four- and five-cylinder engines (two balance shafts) - GM Quad-4 engineGM Quad-4 engineThe engine family known as the Quad 4 was debuted to the public in the spring of 1987. The Quad 4 was a DOHC inline 4-cylinder produced by General Motors' Oldsmobile division...
, as used in the 1995 Pontiac SunfirePontiac SunfireThe Pontiac Sunfire was introduced for the 1995 model year as the compact car to replace the Sunbird. Not only was the name changed, but dramatic styling changes were included as well. The new styling was shared with the redesigned Chevrolet Cavalier...
. - GM Vortec engineGM Vortec engineVortec is a trademarked name for a line of piston engines for General Motors trucks. The name first appeared in 1988 on a 4.3 L V6 that used "vortex technology" to create a vortex inside the combustion chamber, creating a better air/fuel mix. Now its used on a wide range of different engines...
V-6 (single balance shaft) - HondaHondais a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...
2.2 L (F22) four-cylinder engine - HondaHondais a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...
Honda CBR1100XXHonda CBR1100XXThe CBR1100XX Super Blackbird is a Honda motorcycle made from 1996 to 2007. The bike was developed to challenge the Kawasaki Ninja ZX-11 as the world's fastest production motorcycle, and Honda succeeded with a top speed of . Two years later the title passed to the Suzuki Hayabusa, which reached...
motorcycle (1997) - Kawasaki Kawasaki Z440LTD
- Kawasaki Kawasaki ZX-14 & Kawasaki 1400GTRKawasaki 1400GTRThe Kawasaki 1400GTR, also known as the Concours 14 or ZG1400 in some markets, is a motorcycle produced by Kawasaki. The 1400GTR was introduced in September 2007 and is based on the ZX-14 platform....
(aka Concours 14) motorcycles (same powerplant) - MazdaMazdais a Japanese automotive manufacturer based in Fuchū, Aki District, Hiroshima Prefecture, Japan.In 2007, Mazda produced almost 1.3 million vehicles for global sales...
's 2.3L MZR engine (two balance shafts) - Mercedes-BenzMercedes-BenzMercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG...
M112Mercedes-Benz M112 engineThe Mercedes-Benz M112 engine is a V6 automobile piston engine family used in the 2000s. Introduced in 1998, it was the first V6 engine ever built by Mercedes...
and M272Mercedes-Benz M272 engineThe Mercedes-Benz M272 engine is a V6 automobile piston engine family used in the 2000s. Introduced in 2004, it is based on the M112 V6 introduced in 1998....
V-6 enginesV6 engineA V6 engine is a V engine with six cylinders mounted on the crankcase in two banks of three cylinders, usually set at either a right angle or an acute angle to each other, with all six pistons driving a common crankshaft... - MitsubishiMitsubishi Motorsis a multinational automaker headquartered in Minato, Tokyo. In 2009 it was the fifth-largest Japan-based automaker and the 17th-largest in the world measured by production...
'Astron' engineMitsubishi Astron engineThe Mitsubishi Astron or 4G5 engine, is a series of straight-4 internal combustion engines first built by Mitsubishi Motors in 1972. Engine displacement ranged from 1.8 to 2.6 litres, making it one of the largest four-cylinder engines of its time.... - Nissan 2.5L (QR25DE) four-cylinder engine
- PorschePorschePorsche Automobil Holding SE, usually shortened to Porsche SE a Societas Europaea or European Public Company, is a German based holding company with investments in the automotive industry....
2.5L, 2.7L and 3.0L inline four-cylinder engines - Subaru EF engineSubaru EF engineThe EF is an automotive engine made by Subaru, introduced in 1984 for the Subaru Justy.It is a water-cooled straight-3 four-stroke engine with a belt-driven single overhead camshaft, and a chain-driven balance shaft...
- Tata NanoTata NanoThe Tata Nano is an inexpensive, rear-engined, four-passenger city car built by the Indian company Tata Motors and is aimed primarily at the Indian domestic market....
- Toyota 2.4L (2AZ-FE), 2.5L (2AR-FE), 2.7L (1AR-FE)
- Saab H engine
- VolvoVolvoAB Volvo is a Swedish builder of commercial vehicles, including trucks, buses and construction equipment. Volvo also supplies marine and industrial drive systems, aerospace components and financial services...
B234F, B204GT and B204FT (four-cylinder, two balance shafts, 16V-head, used in 700 and 900 series) - VW AGVolkswagen GroupVolkswagen Group is a German multinational automobile manufacturing group. , Volkswagen was ranked as the world’s third largest motor vehicle manufacturer and Europe's largest....
BHW 2.0L turbodiesel (Volkswagen, Audi, Skoda) (4-cyl, two balance shafts, chain or gear drives)
Numerous motorcycle engines, particularly parallel twins and larger single-cylinder engines have employed balance shaft systems as well. Other systems used in place of balance shafts include a "dummy connecting rod" in Ducati Supermono
Ducati Supermono
The Ducati Supermono is a lightweight, single-cylinder racing motorcycle made by Ducati. It is named for the Supermono racing class. The Supermono is arguably one of the most collectable Ducatis in any era...
engines and hinged counterweights on the crank as used in BMW F800
BMW GS parallel-twin
The BMW F800GS and F650GS are members of the GS family of dual-sport motorcycles manufactured in Berlin, Germany by BMW Motorrad. Both bikes were launched in 2008, and use the same 798 cc parallel-twin engine with chain drive, but with different power outputs and equipment levels...
motorcycles.
External links
- "Weighing the Benefits of Engine Balancing", Larry Carley, Technical Editor, Babcox.com