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.
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
Two-cylinder engines
Numerous motorcycle engines— particularly straight-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
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.
V6 engines are inherently unbalanced, regardless of the V-angle.[citation needed] 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. Unlike 90° V6 engines, 60° V6 engines do not require a balance shaft.[citation needed]
^"Frederick William Lanchester, 1868-1946". Obituary Notices of Fellows of the Royal Society. The Royal Society. 5 (16): 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.
^. www.babcox.com. Archived from the original on 24 February 2009. Retrieved 12 December 2004.
^"Shaking forces of twin engines", 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.
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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 Balance shaft in Ford Taunus V4 engine 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 Contents 1 Overview 2 Applications 2 1 Two cylinder engines 2 2 Four cylinder engines 2 3 Five cylinder engines 2 4 Six cylinder engines 2 5 Eight cylinder engines 3 See also 4 ReferencesOverview 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 EditTwo cylinder engines Edit Numerous motorcycle engines particularly straight 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 citation needed 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 Unlike 90 V6 engines 60 V6 engines do not require a balance shaft citation needed Eight cylinder engines Edit Examples are the Mercedes Benz OM629 and Volvo B8444S engine 9 See also EditBalancing machine Engine balanceReferences Edit Frederick William Lanchester 1868 1946 Obituary Notices of Fellows of the Royal Society The Royal Society 5 16 761 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 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 Retrieved from https en wikipedia org w index php title Balance shaft amp oldid 1130291323, wikipedia, wiki, book, books, library,
