Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Balance Shaft shopping experience:
1. Compare - without doubt the biggest advantage that the Balance Shaft offers shoppers today is the ability to compare thousands of Balance Shaft at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.
2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about
3. Testimonials - don't know anybody that has bought a Balance Shaft? Wrong! If the Balance Shaft is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.
4. Questions - Got a question about Balance Shaft then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
5. Reputation - Never heard of the company selling Balance Shaft? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Balance Shaft and build up a picture of their reputation for sales, returns, customer service, delivery etc.
6. Returns - still worried that even after all of the above your Balance Shaft wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.
7. Feedback - happy with your Balance Shaft then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.
8. Security - check for the yellow padlock on the Balance Shaft site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Balance Shaft, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
10. Payment - ready to pay for your Balance Shaft, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.
.In
piston engine engineering, a
balance shaft is an
Eccentric (mechanism) weighted shaft which offsets vibrations in engine designs that are not inherently balanced (for example, most four-cylinder engines). They were first invented by British engineer
Frederick Lanchester in 1904. "Engine Smoothness", Mark Wan,
AutoZine Technical School, 1998–2000
Overview
Balance shafts are most common in straight-4 engines which, due to the asymmetry of their design, have an inherent second order vibration (vibrating at twice the engine
RPM) which, contrary to popular belief, cannot be eliminated no matter how well the internal components are balanced. This vibration is generated because the movement of the connecting rods in an
straight 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
inertial force twice in each revolution whose intensity
quadratic growth with RPM, no matter how closely the components are matched for weight. "Shaking forces of twin engines", Vittore Cossalter, Dinamoto.it
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) 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 basic concept behind balance shafts has existed for nearly a century and is no longer
patentable. 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. 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 at the higher RPMs 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 horsepower (11 kW), but this may be excessive for pure
friction losses. It is possible that this is a miscalculation derived from the common use of an inertial 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, 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 Motors pioneered the design in the modern era with its "Silent Shaft" Mitsubishi Astron engine in 1975, with balance shafts located low on the side of the engine block and driven by chains from the
oil pump, and they subsequently licensed the patent to
Fiat,
Saab (automobile) and Porsche.
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 Saab H engine#B234.
Six cylinder applications
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.
Production implementations
timing
gears 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 producing engines with one or two balance shafts include(d):
as well as numerous motorcycle engines, particularly
vertical twins, and even some small single cylinder engines.
See also
References
External links
- "Weighing the Benefits of Engine Balancing", Larry Carley, Technical Editor, Babcox.com
.In
piston engine engineering, a
balance shaft is an Eccentric (mechanism) weighted shaft which offsets
vibrations in engine designs that are not inherently balanced (for example, most four-cylinder engines). They were first invented by British engineer
Frederick Lanchester in 1904. "Engine Smoothness", Mark Wan,
AutoZine Technical School, 1998–2000
Overview
Balance shafts are most common in straight-4 engines which, due to the asymmetry of their design, have an inherent second order
vibration (vibrating at twice the engine RPM) which, contrary to popular belief, cannot be eliminated no matter how well the internal components are balanced. This vibration is generated because the movement of the
connecting rods in an
straight 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
inertial force twice in each revolution whose intensity
quadratic growth with RPM, no matter how closely the components are matched for weight. "Shaking forces of twin engines", Vittore Cossalter, Dinamoto.it
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) 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 basic concept behind balance shafts has existed for nearly a century and is no longer
patentable. 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. 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 at the higher RPMs 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 horsepower (11 kW), but this may be excessive for pure friction losses. It is possible that this is a miscalculation derived from the common use of an inertial
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, 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 Motors pioneered the design in the modern era with its "Silent Shaft" Mitsubishi Astron engine in 1975, with balance shafts located low on the side of the engine block and driven by chains from the oil pump, and they subsequently licensed the patent to Fiat, Saab (automobile) and Porsche.
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 Saab H engine#B234.
Six cylinder applications
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.
Production implementations
timing
gears 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 producing engines with one or two balance shafts include(d):
as well as numerous motorcycle engines, particularly
vertical twins, and even some small single cylinder engines.
See also
References
External links
- "Weighing the Benefits of Engine Balancing", Larry Carley, Technical Editor, Babcox.com
