Balance shaft: Difference between revisions
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{{Short description|Weights used to balance otherwise unbalanced engine movement}} |
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[[Image:Balanceshaft.jpg|thumb|right|250px|Balance shaft in [[Ford Taunus V4 engine]].]] |
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[[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--> |
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In [[piston engine]] engineering, a '''balance shaft''' is an [[Eccentric (mechanism)|eccentric]] weighted shaft which offsets the vibrations of unbalanced engines. |
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'''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. |
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| ⚫ | Balance shafts are |
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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 | |
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The problem increases with larger [[engine displacement]], since the only ways to achieve larger displacement are with a longer [[piston stroke]], increasing the difference in acceleration, or by a larger [[bore]], increasing the [[mass]] of the pistons; either way, 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 [[NVH]] characteristics. The development of the [[General Motors Corporation|General Motors]] 2.3 [[litre]] [[GM Quad-4 engine|Quad 4]] engine in [[1987]], described as "rough as a cob" by one automotive reviewer, and its subsequent development into the much more positively received 2.4 L version with balance shafts confirms the wisdom of this assessment. |
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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. |
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==Overview== |
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The basic concept behind balance shafts has existed for nearly a century and is no longer [[patent]]able. Two balance shafts rotate in opposite directions at twice engine speed. Equally sized eccentric weights on these shafts are sized and phased so that the inertial 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 canceling it. (Some [[motorcycle]] enthusiasts believe that Honda's original application of this technology to their [[V-twin]] motorcycle engine overly damped out the vibration, giving an excessively 'dead' feel, so that they later reduced the size of the balance shafts in order to furnish the rider with some feedback as to engine speed). |
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[[File:Lanchester patent harmonic balancer (Modern Motors, I) 031.jpg|thumb|Lanchester's vertical force balancer. The eccentric masses are labelled "C" and "D".]] |
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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. |
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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> |
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The actual implementation of the concept, however, is concrete enough to be patented. The basic problem presented by the concept is adequately supporting and [[lubrication|lubricating]] a part rotating at twice engine speed, at the higher RPMs where the second order vibration becomes unacceptable. [[Mitsubishi Motors]] pioneered the design in the modern era with its "Silent Shaft" [[Mitsubishi Astron engine|Astron engines]] in [[1975]], with balance shafts located low on the side of the engine block, driven by chains from the [[Petroleum|oil]] [[pump]], |
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and subsequently licensed the patent to [[Porsche]], then to other manufacturers. Since then, other manufacturers have adapted the same basic layout to their needs. |
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==Applications== |
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[[Saab automobile|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, thereby introducing a torque which counteracts the sideways vibrations at double engine RPM, resulting in an exceptionally smooth four cylinder engine. |
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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. |
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There is some debate as to how much power the twin balance shafts cost the engine. The basic figure given is usually around 15 [[horsepower]] (11 kW), but this seems excessive for pure [[friction]] losses. It is likely 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 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, many owners modify their engines by removing the balance shafts, both to reclaim some of this power, but also to reduce complexity and potential areas of breakage for high performance and racing use. As mentioned above, it is commonly 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, but that stems from a basic misunderstanding of their operation. |
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| ⚫ | 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> |
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Another balance shaft design is found in many [[V6]] engines. While an optimally designed V6 engine would have a 60 degree 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 order]] 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 pulse. 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. |
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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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==Production implementations== |
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| ⚫ | [[Image:FordtaunusV4front.jpg|thumb|right |
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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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Other manufacturers producing engines with one or two balance shafts include(d): |
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* [[Alfa Romeo]] 2.0L four-cylinder, as fitted to the [[Alfa Romeo 156]] |
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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. |
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* [[BMW]] 1200GS motorcycle |
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* [[Chrysler Corporation|Chrysler]] 2.4 L and 2.5 L [[Chrysler Neon engine#2.4|''Neon'' engine]] |
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=== Five-cylinder engines === |
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* [[Ford Modular engine]] [[V10 engine|V10]] |
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Balance shafts are also used in [[straight-five engine]]s such as GM [[General Motors Atlas engine#LLR (Vortec 3700)|Vortec 3700]]. |
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* [[Ford Taunus V4 engine]] |
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* [[General Motors Corporation]] [[GM Quad-4 engine|Quad 4]] and [[Ecotec]] |
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=== Six-cylinder engines === |
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In a [[straight-six engine]] and [[flat-six engine]], the rocking forces are naturally balanced out, therefore balance shafts are not required. |
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* [[GM Vortec engine]] V-6 (single balance shaft) |
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* [[Honda]] 2.2 L four cylinder engine |
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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. |
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* [[Mitsubishi Motors|Mitsubishi]] [[Mitsubishi Astron engine|'Astron' engine]] |
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* Nissan 2.5L (QR25DE) four-cylinder engine |
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=== Eight-cylinder engines === |
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* [[Porsche]] 2.5L and 3.0L |
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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> |
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* [[Saab Automobile|Saab]] [[Saab H engine#B234|H engine]] |
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as well as numerous motorcycle engines, particularly [[vertical twin]]s, and even some small single cylinder engines. |
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==See also== |
==See also== |
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* [[ |
* [[Balancing machine]] |
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* [[Engine balance]] |
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== |
==References== |
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{{reflist}} |
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*[http://www.babcox.com/editorial/ar/eb10330.htm Engine balancing] |
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*[http://www.dinamoto.it/DINAMOTO/on-line%20papers/twin%20motors/twin.html Animated representations of the vibrations characteristic of various two cylinder engine and crankshaft configurations]. |
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{{Automotive engine}} |
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[[Category:Motorcycle technology]] |
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[[cs:Vyvažovací hřídel]] |
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Latest revision as of 10:05, 23 September 2023
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]_031.jpg)
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]
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]- ^ "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.
- ^ Frederick William Lanchester (1912-10-31). "US1163832A - Balancing means for reciprocating engines". Google Patents. Retrieved 2021-04-03.
- ^ "Engine Balance and the Balance Shafts". www.zzperformance.com. Retrieved 20 August 2019.
- ^ "Weighing the Benefits of Engine Balancing". www.babcox.com. Archived from the original on 24 February 2009. Retrieved 12 December 2004.
- ^ "Shaking forces of twin engines" Archived 2010-07-15 at the Wayback Machine, Vittore Cossalter, Dinamoto.it
- ^ Carney, Dan (2014-06-10). "Before they were carmakers". UK: BBC. Retrieved 2018-11-01.
- ^ Nadel, Brian (June 1989). "Balancing Act". Popular Science. p. 52.
- ^ "The Physics of: Engine Cylinder-Bank Angles". www.caranddriver.com. 14 January 2011. Retrieved 22 August 2019.
- ^ "Volvo B8444S/Yamaha 4.4 V8 Engine". australiancar.reviews. Retrieved 2022-12-29.