Red marquis: /* Steam engines */

2008-10-30T10:39:27Z

Steam engines

← Older revision		Revision as of 10:39, 30 October 2008
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	===Steam engines===		===Steam engines===
	The question of mechanical balance was addressed on [[steam engine]]s long before the invention of the [[internal combustion engine]]. [[Steam ~~locomotive]]s~~ commonly have balancing weights on the driving wheels to control [[Hammer blow\|wheel hammer]] caused by the up and down motion of the [[tie rod]]s and to some degree the [[connecting rod]]s. Again, the balance is a compromise.		The question of mechanical balance was addressed on [[steam engine]]s long before the invention of the [[internal combustion engine]]. Steam locomotives commonly have balancing weights on the driving wheels to control [[Hammer blow\|wheel hammer]] caused by the up and down motion of the [[tie rod]]s and to some degree the [[connecting rod]]s. Again, the balance is a compromise.

	==Component balancing==		==Component balancing==

Red marquis: /* Single cylinder engines */

2008-10-30T10:38:52Z

Single cylinder engines

← Older revision		Revision as of 10:38, 30 October 2008
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	A [[single cylinder]] engine produces three main vibrations. In describing them we will assume that the cylinder is vertical.		A [[single cylinder]] engine produces three main vibrations. In describing them we will assume that the cylinder is vertical.

	Firstly, in an engine with no balancing counterweights, there would be an enormous vibration produced by the change in [[momentum]] of the [[piston]], [[connecting rod]] and [[crankshaft]] once every revolution. Nearly all single-cylinder crankshafts incorporate balancing weights to reduce this.		Firstly, in an engine with no balancing counterweights, there would be an enormous vibration produced by the change in momentum of the [[piston]], [[connecting rod]] and [[crankshaft]] once every revolution. Nearly all single-cylinder crankshafts incorporate balancing weights to reduce this.

	While these weights can balance the crankshaft completely, they cannot completely balance the motion of the piston, for two reasons. The first reason is that the balancing weights have horizontal motion as well as vertical motion, so balancing the purely vertical motion of the piston by a crankshaft weight adds a horizontal vibration. The second reason is that, considering now the vertical motion only, the smaller piston end of the connecting rod is closer to the larger crankshaft end of the connecting rod in mid-stroke than it is at the top or bottom of the stroke, because of the connecting rod's angle. So during the 180° rotation from mid-stroke through top-dead-center and back to mid-stroke the minor contribution to the piston's up/down movement from the connecting rod's change of angle has the same direction as the major contribution to the piston's up/down movement from the up/down movement of the crank pin. By contrast, during the 180° rotation from mid-stroke through bottom-dead-center and back to mid-stroke the minor contribution to the piston's up/down movement from the connecting rod's change of angle has the opposite direction of the major contribution to the piston's up/down movement from the up/down movement of the crank pin. The piston therefore travels faster in the top half of the cylinder than it does in the bottom half, while the motion of the crankshaft weights is sinusoidal. The vertical motion of the piston is therefore not quite the same as that of the balancing weight, so they can't be made to cancel out completely.		While these weights can balance the crankshaft completely, they cannot completely balance the motion of the piston, for two reasons. The first reason is that the balancing weights have horizontal motion as well as vertical motion, so balancing the purely vertical motion of the piston by a crankshaft weight adds a horizontal vibration. The second reason is that, considering now the vertical motion only, the smaller piston end of the connecting rod is closer to the larger crankshaft end of the connecting rod in mid-stroke than it is at the top or bottom of the stroke, because of the connecting rod's angle. So during the 180° rotation from mid-stroke through top-dead-center and back to mid-stroke the minor contribution to the piston's up/down movement from the connecting rod's change of angle has the same direction as the major contribution to the piston's up/down movement from the up/down movement of the crank pin. By contrast, during the 180° rotation from mid-stroke through bottom-dead-center and back to mid-stroke the minor contribution to the piston's up/down movement from the connecting rod's change of angle has the opposite direction of the major contribution to the piston's up/down movement from the up/down movement of the crank pin. The piston therefore travels faster in the top half of the cylinder than it does in the bottom half, while the motion of the crankshaft weights is sinusoidal. The vertical motion of the piston is therefore not quite the same as that of the balancing weight, so they can't be made to cancel out completely.

Red marquis at 10:38, 30 October 2008

2008-10-30T10:38:20Z

Show changes

74.77.175.16: ecmxdpeLniYnGM

2008-10-30T10:28:58Z

ecmxdpeLniYnGM

← Older revision		Revision as of 10:28, 30 October 2008
Line 1:		Line 1:
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76.78.149.55: xTUZOMMPiWntnPrRrau

2008-10-30T10:20:49Z

xTUZOMMPiWntnPrRrau

New page

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Engine balance - Revision history

Red marquis: /* Steam engines */

Red marquis: /* Single cylinder engines */

Red marquis at 10:38, 30 October 2008

74.77.175.16: ecmxdpeLniYnGM

76.78.149.55: xTUZOMMPiWntnPrRrau