What Causes Primary Forces In A Piston?
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- Опубликовано: 21 ноя 2017
- There are complicated ways of dealing with primary shaking force, but in multi-cylinder engines it’s easier to let it cancel itself.
With each revolution of the crankshaft, the piston goes up and down once, creating a primary shaking force. We can put counterweights on the crankshaft, leaving the side opposite to the crankpin heavier.
When the piston is at top dead center, it has been decelerating, pulling on the connecting rod, and the counterweight is exerting a force in the opposite direction. But what happens when the piston is at half-stroke?
Now, we have the counterweight exerting a shaking force at a right angle to the piston. The piston is not exerting any shaking force because, in mid-stroke, it’s moving at a constant speed, neither accelerating nor decelerating.
This is the problem of trying to balance an engine with rotating counterweights. Every time we add counterweight, we’re trading one form of imbalance for another. There is no way that a rotating counterweight can cancel a straight-line shaking force.
Primary shaking forces are not the only force. There is another variable in piston height: rod angularity. When the piston is at half-stroke, the connecting rod is at an angle, which has the effect of lowering the piston.
There are four changes in connecting-rod angularity per revolution. That angularity is called a secondary shaking force. For example, in an inline-four with a flat, 180-degree-firing-order crankshaft there are just as many pistons going up as there are going down.
Primary shaking force, therefore, is self-canceling. But the secondary force in an inline-four remains. When manufacturers began to make bigger and bigger inline-fours, they got to a point where the secondary buzz was so annoying that they began to include a secondary balancer.
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Развлечения
Been reading Kevin's articles for like 50 years or so because I'm old enough to remember Joe Parkhurst, Gordon Jennings, Bob Braverman, Cycle Guide, Cycle World, Cycle etc. Kinda neat to see him and hear him. Way before the internet and videos there were magazines. Reading those articles was one of the better influences on me as I was a bit of a motorcycle delinquent in high school - but I WAS reading. In Mr. Cameron's case, I was reading articles written by a Harvard grad with a physics background. No way that could be bad.
50 years...I'm 70, but hadn't discovered Kevin Cameron until 15 or so years ago.....what a world of stuff I've missed...! But I've had bikes since high school also....
Kevin Cameron - Yessir! Nothing beats hands on. Fortunately for me, my first bikes were Japanese - spoiled! Maintenance was a rude awakening with my first Triumph.
Even if you already know what he's explaining, it's still great to watch him do it!
I have known about primary vibration for years but thanks for the explanation of secondary.
Been read Kevin since the mid 80's. Now I have a motorcycle magazine collection going back to the late 60's. Lot's of Cameron and Jennings.
That music, I feel like I'm in Hogwarts learning about muggle's technology.
Beautifully explained
You don't need to turn-down the entire stud (unless you are obsessing about weight reduction). Just make a smooth fillet where the stud necks down to the threads.
Kevin's videos are very informative. The background music is terrible!
Good video but CUT THE MUSIC FFS !
i wouldn't have made the point so strongly myself but i agree, the tinkling music is distracting and unwelcome.
I'd love to go for a drink with Kevin