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{{Short description|Weights used to balance otherwise unbalanced engine movement}}
[[Image:Balanceshaft.jpg|thumb|right|250px|Balance shaft in [[Ford Taunus V4 engine]].]]<!--Please note - Taunus is not a typo: the Taunus is a Ford for the Europe market, not to be confused with the Taurus, a U.S. domestic brand-->
[[Image:Balanceshaft.jpg|thumb|right|Balance shaft in [[Ford Taunus V4 engine]].]]<!--Please note - Taunus is not a typo: the Taunus is a Ford for the Europe market, not to be confused with the Taurus, a U.S. domestic brand-->


'''Balance shafts''' are used in [[piston engine]]s to reduce [[vibration]] by cancelling out unbalanced dynamic forces. The counter balance shafts have [[eccentric (mechanism)|eccentric]] weights and rotate in opposite direction to each other, which generates a net vertical force.
In [[piston engine]] engineering, a '''balance shaft''' is an [[Eccentric (mechanism)|eccentric]] weighted shaft that offsets [[vibration]]s in engine designs that are not [[Engine balance|inherently balanced]]. The balance shaft was invented and patented by British engineer [[Frederick W. Lanchester]] in 1904.<ref name="autozine">[http://www.autozine.org/technical_school/engine/smooth2.htm "Engine Smoothness"], Mark Wan, ''AutoZine Technical School'', 1998–2000</ref>

The balance shaft was invented and patented by British engineer [[Frederick W. Lanchester]] in 1907.<ref name="The Royal Society 1948 p. 761">{{cite journal | title=Frederick William Lanchester, 1868-1946 | journal=Obituary Notices of Fellows of the Royal Society | url=https://royalsocietypublishing.org/doi/pdf/10.1098/rsbm.1948.0010 | publisher=The Royal Society | volume=5 | issue=16 | year=1948 | issn=1479-571X | doi=10.1098/rsbm.1948.0010 | page=761| doi-access=free }}</ref><ref name="Google Patents 1912">{{cite web | author=Frederick William Lanchester |
title=US1163832A - Balancing means for reciprocating engines. | website=Google Patents | date=1912-10-31 | url=https://patents.google.com/patent/US1163832A/en | access-date=2021-04-03}}</ref> It is most commonly used in [[inline-four]] and [[V6 engines]] used in automobiles and motorcycles.


==Overview==
==Overview==
[[File:Lanchester patent harmonic balancer (Modern Motors, I) 031.jpg|thumb|Lanchester's vertical force balancer. The eccentric masses are labelled "C" and "D".]]
⚫
Balance shafts are most common in [[straight-4|inline four-cylinder]] engines, which, due to their design asymmetry, have an inherent second order [[vibration]] (vibrating at twice the engine [[revolutions per minute|RPM]]) that cannot be eliminated no matter how well the internal components are balanced. This vibration is generated because the movement of the [[connecting rod]]s in an even-firing four-cylinder [[straight engine|inline engine]] is not symmetrical throughout the [[crankshaft]] 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]]l force twice in each revolution whose intensity [[quadratic growth|increases quadratically]] with RPM, no matter how closely the components are matched for weight.<ref>[http://www.dinamoto.it/dinamoto/8_on-line_papers/twin%20motors/twin.html "Shaking forces of twin engines"], Vittore Cossalter, Dinamoto.it</ref>
The operating principle of a balance shaft system is that two shafts carrying identical eccentric weights rotate in opposite directions at twice the engine speed. The phasing of the shafts is such that the [[centrifugal forces]] produced by the weights cancel the vertical second-order forces (at twice the engine [[RPM]]) produced by the engine.<ref>{{cite web |title=Engine Balance and the Balance Shafts |url=https://zzperformance.com/blogs/import1/engine-balance-and-the-balance-shafts |website=www.zzperformance.com |access-date=20 August 2019 |language=en}}</ref> The horizontal forces produced by the balance shafts are equal and opposite, and so cancel each other.


The balance shafts do not reduce the vibrations experienced by the [[crankshaft]].<ref>{{cite web |title=Weighing the Benefits of Engine Balancing |url=http://www.babcox.com/editorial/ar/eb10330.htm |website=www.babcox.com |url-status=dead |archive-url=https://web.archive.org/web/20090224032857/http://www.babcox.com/editorial/ar/eb10330.htm |archive-date=24 February 2009 |access-date=12 December 2004 }}</ref>
Four-cylinder [[flat engine]]s in the boxer configuration have their [[piston]]s horizontally opposed, so they are naturally balanced and do not incur the extra complexity, cost or frictional losses associated with balance shafts (though the slight offset of the pistons introduces a rocking couple).


==Applications==
The problem increases with larger [[engine displacement]]s, since larger displacement is achieved with a longer [[piston stroke]], which increases the difference in acceleration—or by a larger bore, which increases the [[mass]] of the pistons. One can use both techniques to maximize engine displacement. In all cases, the [[Magnitude (mathematics)|magnitude]] 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]] (NVH) characteristics.
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=== Two-cylinder engines ===
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Numerous motorcycle engines— particularly [[parallel-twin engine]]s— have employed balance shaft systems, for example the [[Yamaha TRX850]] and [[Yamaha TDM850]] engines have a 270° crankshaft with a balance shaft. An alternative approach, as used by the [[BMW GS parallel-twin]], is to use a 'dummy' connecting rod which moves a hinged counterweight.


⚫
=== Four-cylinder engines ===
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]]l reaction to their counter-rotation cancels out in the [[horizontal plane]], but adds in the vertical plane, giving a [[net force]] equal to but 180 degrees out-of-phase with the undesired second-order vibration of the basic engine, thereby cancelling 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.
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[[Image:FordtaunusV4front.jpg|thumb|right|Valve timing gears on a [[Ford Taunus V4 engine]]. The balance shaft runs off the small gear on the left (the large gear is for the [[camshaft]], causing it to rotate at half the speed of the crankshaft).]]


⚫
Balance shafts are often used in [[inline-four engine]]s, to reduce the [[engine balance#Secondary vibration|second-order vibration]] (a vertical force oscillating at twice the engine [[revolutions per minute|RPM]]) that is inherent in the design of a typical inline-four engine. This vibration is generated because the movement of the [[connecting rod]]s in an even-firing inline-four engine is not symmetrical throughout the crankshaft 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 force twice in each revolution (which increases [[quadratic growth|quadratically]] with RPM).<ref >[http://www.dinamoto.it/dinamoto/8_on-line_papers/twin%20motors/twin.html "Shaking forces of twin engines"] {{Webarchive|url=https://web.archive.org/web/20100715064543/http://dinamoto.it/DINAMOTO/8_on-line_papers/twin%20motors/twin.html |date=2010-07-15 }}, Vittore Cossalter, Dinamoto.it</ref>
There is some debate as to how much power the twin balance shafts cost the engine. The basic figure given is usually around 15&nbsp;[[horsepower|hp]] (11&nbsp;kW), but this may be excessive for pure [[friction loss]]es. It is possible that this is a miscalculation derived from the common use of an [[inertia]]l [[dynamometer]], which calculates power from [[angular acceleration]] rather than actual measurement of steady state [[torque]]. The 15&nbsp;hp (11&nbsp;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.{{Citation needed|date=October 2007}}


The amount of vibration also increases with engine displacement, resulting in balance shafts often being used in inline-four engines with displacements of {{convert|2.2|L|cuin|0|abbr=on}} or more. Both an increased [[stroke (engine)|stroke]] or [[bore (engine)|bore]] cause an increased secondary vibration; a larger stroke increases the difference in acceleration and a larger bore increases the mass of the pistons.
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==Twin-cylinder applications==
⚫
Numerous motorcycle engines, particularly [[Straight-twin engine|parallel twins]], have employed balance shaft systems. The [[Yamaha TRX850]] and [[Yamaha TDM850|TDM]] twins both have a 270° crankshaft with a balance shaft. Some twins use other systems rather than balance shafts, such as a "dummy connecting rod" in [[Ducati Supermono]] engines and hinged counterweights on the crank as used in [[BMW GS parallel-twin|BMW F800]] motorcycles. Some larger single-cylinder engines have also used balance shaft systems.


The Lanchester design of balance shaft systems was refined with the [[Mitsubishi Astron engine#Design|Mitsubishi Astron 80]], an inline-four car engine introduced in 1975. This engine was the first to locate one balance shaft higher than the other, to counteract the second order rolling couple (i.e. about the crankshaft axis) due to the torque exerted by the inertia caused by increases and decreases in engine speed.<ref name="bbc1">{{cite web |url=http://www.bbc.com/autos/story/20140609-before-they-were-carmakers |title=Before they were carmakers |last=Carney |first=Dan |publisher=BBC |location=UK |date=2014-06-10 |access-date=2018-11-01}}</ref><ref name="PS-Jun89">{{cite magazine |last=Nadel |first=Brian |date=June 1989 |title=Balancing Act |magazine=Popular Science |page =52 }}</ref>
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==Four-cylinder applications==
[[Mitsubishi Motors]] developed the design in the modern era with its [[:ja:サイレントシャフト|"Silent Shaft"]] [[Mitsubishi Astron engine|Astron engines]] in 1975, with balance shafts located low on the side of the engine block and driven by chains from the [[oil pump (internal combustion engine)|oil pump]], and they subsequently licensed the patent to [[Fiat]], [[Saab (automobile)|Saab]] and [[Porsche]].<ref name="autozine"/>


In a [[flat-four engine]], the forces are cancelled out by the pistons moving in opposite directions. Therefore balance shafts are not needed in flat-four engines.
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]]. This introduces a [[torque]] that counteracts the sideways vibrations at double engine RPM, resulting in the exceptionally smooth [[Saab H engine#B204 & B234|B234 engine]].


=== Five-cylinder engines ===
Toyota also began to use balance shafts in their 3RZ-FE engines in the mid 90s. These engines started as a 2RZ-FE, but creating greater torque and horsepower required a longer stroke. That longer stroke required balance shafts to counterbalance the added vibration. The longer stroke transformed the displacement in the 2RZ-FE from 2.4L to the 2.7L for the 3RZ-FE.
Balance shafts are also used in [[straight-five engine]]s such as GM [[General Motors Atlas engine#LLR (Vortec 3700)|Vortec 3700]].


==Six-cylinder applications==
=== Six-cylinder engines ===
In a [[straight-six engine]] and [[flat-six engine]], the rocking forces are naturally balanced out, therefore balance shafts are not required.
Due to the odd number of cylinders in each bank, V6 designs are inherently unbalanced, regardless of their V-angle. All straight engines with an odd number of cylinders suffer from primary dynamic imbalance, which causes an end-to-end rocking motion. Each cylinder bank in a V6 has an odd number of cylinders, so the V6 also suffers from the same problem unless steps are taken to mitigate it. In the horizontally opposed flat-6 layout, the rocking motions of the two straight cylinder banks offset each other, while in the inline-6 layout, the two ends of engine are mirror images of each other and compensate every rocking motion. Concentrating on the first order rocking motion, the V6 can be assumed to consist of two separate straight-3 where counterweights on the crankshaft and a counter rotating balance shaft compensate the first order rocking motion.


V6 engines are inherently unbalanced, regardless of the V-angle. Any inline engine with an odd number of cylinders has a [[engine balance#Primary balance|primary imbalance]], which causes an end-to-end rocking motion. As each cylinder bank in a V6 has three cylinders, each cylinder bank experiences this motion.<ref>{{cite web |title=The Physics of: Engine Cylinder-Bank Angles |url=https://www.caranddriver.com/features/a15126436/the-physics-of-engine-cylinder-bank-angles-feature/ |website=www.caranddriver.com |access-date=22 August 2019 |date=14 January 2011}}</ref> Balance shaft(s) are used on various V6 engines to reduce this rocking motion.
==Production implementations==
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[[Image:FordtaunusV4front.jpg|thumb|right|250px|[[Poppet valve|Valve]] timing [[gear]]s on a [[Ford Taunus V4 engine]] — the small gear is on the [[crankshaft]], the larger gear is on the [[camshaft]]. Since the camshaft gear is twice the circumference of the crankshaft gear, it runs at half the crankshaft RPM. See [[gear ratio]]. The small gear left is on the balance shaft.]]
Other manufacturers having produced engines with one or two balance shafts include:


=== Eight-cylinder engines ===
* [[BMW K75]] motorcycle
Examples are the [[Mercedes-Benz OM629]] and [[Volvo B8444S engine|Volvo B8444S]] engine.<ref>{{cite web|author= |url=http://www.australiancar.reviews/Volvo_B8444S_Engine.php |title=Volvo B8444S/Yamaha 4.4 V8 Engine |work=australiancar.reviews |date= |access-date=2022-12-29}}</ref>
* [[Fiat Chrysler Automobiles]]
** [[Alfa Romeo Twin Spark engine]]
** [[Alfa Romeo]] [[JTS engine]]
** [[Chrysler Corporation|Chrysler]] [[Chrysler 2.2 & 2.5 engine|K Engine]] (2.5 litre)
** Chrysler [[Chrysler PowerTech engine|PowerTech Engine]] (3.7 litre)
** [[Lancia]] (Delta's twin counter rotating balance shafts)
* [[Ford Motor Company]]
** [[Ford Essex V6 engine]]{{dn|date=November 2016}}
** [[Ford Modular engine]] (V10)
** [[Ford Taunus V4 engine]]
* [[General Motors]]
** [[Buick V6 engine#3800 V6|Buick 3800 V6]] (> 1988)
** [[GM Atlas engine]] four- and five-cylinder engines (two balance shafts)
** [[Iron Duke engine]], or Tech-4 engine, four cylinder OHV (single balance shaft introduced 1988)
** [[GM Quad-4 engine]], as used in the 1995 [[Pontiac Sunfire]]
** [[Family II engine|Family II]]
** [[GM Ecotec engine|Ecotec]]
** [[Chevrolet 90-degree V6 engine]] V-6 (single balance shaft)
** [[GM Medium Gasoline Engine|Medium Gasoline Engine]]
* [[Honda]]
** [[Honda F engine#F22A|2.2&nbsp;L (F22)]] four-cylinder engine
** [[Honda H engine#H22|2.2&nbsp;L (H22)]] four-cylinder engine
** [[Honda K engine#K20Z3|2.0&nbsp;L (K20)]] four-cylinder engine
** [[Honda K engine#K24A4|2.4&nbsp;L (K24)]] four-cylinder engine
** [[Honda 500 twins]]
** [[Honda CBR1100XX]] motorcycle (1997)
** [[Honda CRF450]] motorcycle
** [[Honda ST1300]] motorcycle
* [[Jaguar Land Rover]]
** [[Jaguar_AJ-V8_engine#AJ126|Jaguar AJ126]]
** JLR ''Ingenium''
* [[Kawasaki Heavy Industries Motorcycle & Engine|Kawasaki]]
** [[Kawasaki Z440LTD]]
** [[Kawasaki ZX-12R]]
** [[Kawasaki ZX-14]] & [[Kawasaki 1400GTR]] (aka Concours 14) motorcycles (same powerplant)
* [[Mazda]]'s [[Mazda MZR engine#2.3|2.3L MZR engine]] (two balance shafts)
* [[Mercedes-Benz]] [[Mercedes-Benz M112 engine|M112]] and [[Mercedes-Benz M272 engine|M272]] [[V6 engine|V-6 engines]]
* [[Mitsubishi Motors|Mitsubishi]] [[Mitsubishi Astron engine|'Astron' engine]]
* [[Nissan]] 2.5L (QR25DE) four-cylinder engine
* [[Groupe PSA]] (all feature twin balance shafts driven through a [[gear#helical|helical gear]] off the crankshaft)
** [[PSA EW/DW engine#DW12|DW12 diesel engines]] (except DW12 UTED)
** [[PSA EW/DW engine#DW10|DW10 FC diesel engine]]
* [[Porsche]] [[List of Porsche engines#Porsche 944 engines|2.5L, 2.7L and 3.0L]] inline four-cylinder engines
* [[Saab Automobile|Saab]] [[Saab H engine#B204 & B234|H engine]]
* [[Subaru EF engine]]
* [[Tata Nano]]
* [[Toyota]] 2.4L (2AZ-FE), 2.5L (2AR-FE), 2.7L (1AR-FE)
* [[Volvo]] B234F, B204GT and B204FT (four-cylinder, two balance shafts, 16V-head, used in 700 and 900 series)
* [[Volkswagen Group|VW AG]] BHW 2.0L turbodiesel (Volkswagen, Audi, Skoda) (4-cyl, [[W8 engine]], two balance shafts, chain or gear drives)


==See also==
==See also==
* [[Balancing machine]]
* [[Balancing machine]]
* [[Engine balance]]


==References==
==References==
{{reflist}}
{{reflist}}


⚫
{{Automotive engine}}
==External links==
*[http://www.babcox.com/editorial/ar/eb10330.htm "Weighing the Benefits of Engine Balancing"], Larry Carley, Technical Editor, Babcox.com.

⚫
{{Automotive engine |collapsed}}


[[Category:Engine technology]]
[[Category:Engine technology]]

Latest revision as of 10:05, 23 September 2023

Balance shaft in Ford Taunus V4 engine.

Balance shafts are used in piston engines to reduce vibration by cancelling out unbalanced dynamic forces. The counter balance shafts have eccentric weights and rotate in opposite direction to each other, which generates a net vertical force.

The balance shaft was invented and patented by British engineer Frederick W. Lanchester in 1907.[1][2] It is most commonly used in inline-four and V6 engines used in automobiles and motorcycles.

Overview

[edit]
Lanchester's vertical force balancer. The eccentric masses are labelled "C" and "D".

The operating principle of a balance shaft system is that two shafts carrying identical eccentric weights rotate in opposite directions at twice the engine speed. The phasing of the shafts is such that the centrifugal forces produced by the weights cancel the vertical second-order forces (at twice the engine RPM) produced by the engine.[3] The horizontal forces produced by the balance shafts are equal and opposite, and so cancel each other.

The balance shafts do not reduce the vibrations experienced by the crankshaft.[4]

Applications

[edit]

Two-cylinder engines

[edit]

Numerous motorcycle engines— particularly parallel-twin engines— have employed balance shaft systems, for example the Yamaha TRX850 and Yamaha TDM850 engines have a 270° crankshaft with a balance shaft. An alternative approach, as used by the BMW GS parallel-twin, is to use a 'dummy' connecting rod which moves a hinged counterweight.

Four-cylinder engines

[edit]
Valve timing gears on a Ford Taunus V4 engine. The balance shaft runs off the small gear on the left (the large gear is for the camshaft, causing it to rotate at half the speed of the crankshaft).

Balance shafts are often used in inline-four engines, to reduce the second-order vibration (a vertical force oscillating at twice the engine RPM) that is inherent in the design of a typical inline-four engine. This vibration is generated because the movement of the connecting rods in an even-firing inline-four engine is not symmetrical throughout the crankshaft 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 force twice in each revolution (which increases quadratically with RPM).[5]

The amount of vibration also increases with engine displacement, resulting in balance shafts often being used in inline-four engines with displacements of 2.2 L (134 cu in) or more. Both an increased stroke or bore cause an increased secondary vibration; a larger stroke increases the difference in acceleration and a larger bore increases the mass of the pistons.

The Lanchester design of balance shaft systems was refined with the Mitsubishi Astron 80, an inline-four car engine introduced in 1975. This engine was the first to locate one balance shaft higher than the other, to counteract the second order rolling couple (i.e. about the crankshaft axis) due to the torque exerted by the inertia caused by increases and decreases in engine speed.[6][7]

In a flat-four engine, the forces are cancelled out by the pistons moving in opposite directions. Therefore balance shafts are not needed in flat-four engines.

Five-cylinder engines

[edit]

Balance shafts are also used in straight-five engines such as GM Vortec 3700.

Six-cylinder engines

[edit]

In a straight-six engine and flat-six engine, the rocking forces are naturally balanced out, therefore balance shafts are not required.

V6 engines are inherently unbalanced, regardless of the V-angle. Any inline engine with an odd number of cylinders has a primary imbalance, which causes an end-to-end rocking motion. As each cylinder bank in a V6 has three cylinders, each cylinder bank experiences this motion.[8] Balance shaft(s) are used on various V6 engines to reduce this rocking motion.

Eight-cylinder engines

[edit]

Examples are the Mercedes-Benz OM629 and Volvo B8444S engine.[9]

See also

[edit]

References

[edit]
  1. ^ "Frederick William Lanchester, 1868-1946". Obituary Notices of Fellows of the Royal Society. 5 (16). The Royal Society: 761. 1948. doi:10.1098/rsbm.1948.0010. ISSN 1479-571X.
  2. ^ Frederick William Lanchester (1912-10-31). "US1163832A - Balancing means for reciprocating engines". Google Patents. Retrieved 2021-04-03.
  3. ^ "Engine Balance and the Balance Shafts". www.zzperformance.com. Retrieved 20 August 2019.
  4. ^ "Weighing the Benefits of Engine Balancing". www.babcox.com. Archived from the original on 24 February 2009. Retrieved 12 December 2004.
  5. ^ "Shaking forces of twin engines" Archived 2010-07-15 at the Wayback Machine, Vittore Cossalter, Dinamoto.it
  6. ^ Carney, Dan (2014-06-10). "Before they were carmakers". UK: BBC. Retrieved 2018-11-01.
  7. ^ Nadel, Brian (June 1989). "Balancing Act". Popular Science. p. 52.
  8. ^ "The Physics of: Engine Cylinder-Bank Angles". www.caranddriver.com. 14 January 2011. Retrieved 22 August 2019.
  9. ^ "Volvo B8444S/Yamaha 4.4 V8 Engine". australiancar.reviews. Retrieved 2022-12-29.
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