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The ordinary shock absorber is a straight tube. Inside are usually another straight tube, a spring and some interacting friction material between the two tubes, kind of like brake pads. When a mechanical shock is applied to the device in the correct direction, the friction material converts most of
it into heat thereby reducing the magnitude of the shock, and the spring gently restores the device to its original configuration, ready for the next mechanical shock.
Normally shock absorbers are oriented to absorb the direct straight-line thrust of a shock, and so this is why they are simple straight tubes. But in some cases, it may be better if the shock absorber had a curved shape. Here is an example:
Consider the modern bicycle, with all the bells and whistles. It tends to have two straight shock absorbers for the front whell fork, and that is fine, since the front wheel generally experiences straight-thrust shocks. The rear wheel, however, on the fanciest bicycles, is also mounted in a way that includes a shock absorber, and that one is usually rather small and specialized. Part of the reason for that involves the bicycle drive chain; too much allowed motion can lead to the drive chain coming off the sprockets.
The preceding leads us to the reason why curved shock absorbers would be useful. Let us re-design that back wheel shock-mount, as follows:
Start with your basic ordinary bicycle frame where the back wheel is fixed, there is no shock absorption at all, except by your butt on the seat. There is a Triangle of framework, from the seat down toward the pedals, from the seat down toward the rear wheel axle, and from the pedals toward the rear wheel axle.
Suppose we snipped out that second item, the frame from the seat down to the rear wheel axle. Now we add a pivot at the pedal-axle, so the frame between them and the rear wheel axle can go up and down (meaning that shock absorbers can take the place of the snipped-out frame).
Study the MOTION OF THE REAR WHEEL AXLE, when that pivot is in play. Viewed from the side of the bicycle, the pivot at the pedal axle is the same as the center of a circle, and the rear-wheel axle is a point moving along the curve of that circle. You CAN'T effeciently use straight shock absorbers in this design, when the rear wheel hits a bump!
But two nicely curved shocks, exactly matching the curve of that circle, and replacing the snipped-out frame, would work perfectly.
Finally, note also that the ENTIRE drive chain assembly, from pedal-sprockets to rear-axle-sprockets, remains tensioned exactly the same, no matter how far the rear-wheel-axle moves along the curve of the circle, because the entire drive chain assembly is just as associated with the pedal-axle pivot as the rear wheel axle.
In closing, it seems to me that curved shocks might be useful in other places. For example, in an ordinary automobile, the wheels are often (not always) mounted in such a way that when they experience a shock, their motion follows a curve more so than a straight line. It seems to me that auto shocks wear out faster than they need to, due to the shocks being straight while the motion they are damping is curved. That is, if the shock absorbers were themselves appropriately curved, they might last longer.
patent EP0669247
http://v3.espacenet...C&IDX=EP0669247&F=0
[xaviergisz, Aug 21 2007]
Top of the line machine
http://www.cannonda...large/7VCG1_bbq.jpg
note geometry of the frame, resulting in a 220mm travel at the rear wheel for a 3 to 1 or 4 to 1 ratio at the shock. [jhomrighaus, Aug 21 2007]
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Didn't quite make it through the entire idea, but it sounds good to me [+]. |
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The rear shock on a bike allows the hub of the rear wheel to move in a curve. There is a hinge at the bottom, near the crank and the shock absorber at the top. |
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I don't know whether there are any cars that use this method but there are certainly radio-controlled cars that do. The entire rear axle and motor assembly has a hinge attachment at the front and a spring at the back. |
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I like the idea of keeping a fixed distance between drive and wheel sprockets, but I don't think you need the complexity of a curved (coaxial) shock absorber. For example, the patent in the link has a *bending* curved shock absorber which seems more practical. |
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On compresssion a curved shock absorber would generate force in a direction perpendicular to wheel movement, requiring a massive increase in the strength and weight of the shock absorber. [-] |
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[xaviergisz] The bike suspension I described does that. |
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Shock absorbers, vibration and mass are all concerned with this problem of isolating the irregularity of the road surface, which generates vibration, very much like a phonograph disc's irregular groove transmits sound vibrations to the pick-up needle. |
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Considering the light weight of the bicycle frame and wheels, and the mass of the rider, the entire rider-bicycle system should be thought of as one unit. It would seem the right objective of the shock absorbing system is to insulate the rider as much as possbile. The frame of the bicycle should be thought of as the ridgid portion of the unit, particularly considering the complexity associated with rigid leverage moments required between the drive parts of the power transmission system and the friction required between the roadway and the revolving wheels. It thus follows, it would be most essential to allow the frame, power transmission and wheel system to vibrate and to insulate the rider as much as possible. I belive the scissor frame system to be the best for this design. This allows the greatest movememnt between the seat and the frame, thus allowing longer shock absorbers and greater absorbtion of momentum induced by vibration of the road surface. Shorter shock absorbers can only isolate higher frequincy vibrations, exposing the rider to the many longer frequenchy vibrations. Longer shocks also allow greater time for the movement of the system to absorb the longer vibrations. This is a design criteria the motor cycle engineers have solved with great success. In short, design your bicylce like a motor cycle and your problem is solved....Of course, then, greater shock systems mean greater weight...and more power required of the rider. Solution, eliminate the bicycle shocks entirely, and just slightly bend your knees, taking advantage of your naturallly given shock absorbers...your legs! Hold the bike gently, but firmly, letting it follow the gyrations fo the road under you....watch professional bicyle riders...do what they do. You don't see shocks on their bikes. |
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Most modern bike frames privide a pivot at almost exactly the position that you describe and many if not most rely on a leverage concept to provide high wheel travel for a small shock travel which limits any side loading effects on the shock. A curved shock would need to as mentioned be much heavier and would be subject to much greater wear due to side loading on the OD of the tube and shaft. Straight shocks are not subject to this type of wear at all(Though struts are sometimes) |
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A properly designed suspension system will isolate the forces on the shock to a direct linear motion while the side loads are carried by the suspension members themselves. |
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this is kindof long if you read the last two paragraphs you'll see at least one reson why this won't work... |
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correct me if I'm wrong but i think your way off on what a shock absorber is and it's use. a shock absorber, also called a dampener, is the two tubes that you are referring to but are much more complicated. the dampeners are oil filled and dampen the movement of the spring via 2 small holes that the fluid travels though in the middle of the dampener. the springs and the dampeners make up the only part of the suspension. the whole suspension system includes the wheels, and tiers along with the linkages that attach the wheels to the body of the car or bike. it can also include may more things such as a sway brace depending on the setup. |
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All these systems work together to grip the road as much as possible and provide the rider comfort. (though comfort and grip usually contradict each other) |
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there is a problem with the whole idea that a wheel will bounce in a curved manner. if you toss a wheel down a bumpy road there's a oscillating motion as the wheel travels and skips over bumps. now when you travel with it the wheel on a bike you complete the forward motion and the up and down motion is completed by the springs. In other words, in order to accommodate the oscillating motion of the wheel you need some way to provide a up and down motion without the whole bike moving. springs and dampeners help dissipate this up and down motion. (sometimes there an axis that makes is easier to have dampers and springs in a different location than up and down on the wheel but you still have only a one liner motion to begin with) |
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the second and major flaw with this idea is that any adjustment to curve the dampener would force the spring to move to a different area instead of around the dampener because this would curve the spring so that the spring would wear out too fast for this to be practical. You would then have to have something to allow the spring to travel only in a singular liner fashion that would neglect any type of dampening effect of your idea if it did actually work. |
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more info on what I'm trying to say? carbible.com/wikipedia Suspension/ or just google Suspension. |
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Put simply, you're making a simple system complex. <well done, by the way, very 1/2 B of you> |
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If you simply have pivot bushes at either end of the shock strut (as in all shockies I have ever seen), the shock strut does not need to be curved. Wheel travel can be as curved as you like. In fact, much design effort goes into modern high performance bikes to obtain linear wheel travel, or in some cases, exotic whell travel arcs, designed to better perform under conditions such as large jumps, pedal bob, etc. |
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Oh, and as [FROG] says, the internals of a shock absorber are more complex than you think. |
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lastly, what you are calling a shock absorber is actually a strut, being a combination of a spring and dampner. On bikes these are often combined in the same tube, especially in rear shocks, which are often spring-over-shock design. Some bike forks have the spring in one fork, and the shock in the other. |
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Anyway, this seems to be a convoluted solution to a nonexistent problem. |
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Building a curved shock absorber is going to be complicated. Unless there is some hint of how to make one, this "idea" is really a wish for one. |
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But there's no need for curved shock absorbers. (I'll try to keep this shorter than the idea.) |
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If you look at the back of a common suspension bike as a triangle, you see that the chain stay and the seat tube make two sides, thus: < , with a pivot where they meet, on most suspensions. The third side of the triangle is made of the shock absorber: <| . |
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As we all learned in geometry and trigonometry, when one side of a triangle (the shock) changes length, the angles must change. Well, as [Custardguts] points out, there are two bushings at the ends of the shock absorber to allow the angles to change and the shock to stay straight. It's cheap and simple. |
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Plus, the compression load on a straight shock absorber is always a line through it. If you build a curved shock absorber, <) , it's always going to be at risk of jamming, bending, breaking and firing out through the back of the bike. |
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Two bushings and their little mountings are cheap. They also serve as attach points for the shock absorber, allowing easy removal and replacement. If you build a curved shock absorber, it's going to have to be mounted very securely to the bike--it could even be built in--and changing it is going to be a pain. |
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Shock absorbers don't contain springs, nor do they work by friction of one solid surface against another. They use a piston in a cylinder, pushing a fluid through a restricted opening. The spring is a separate component. |
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Occasionally the spring and shock absorber are integrated into a single unit - a suspension strut - but only in light service applications, because in heavy use (such as motor vehicles) the shock absorbers tend to need replacing much more frequently than the springs - they overheat if you go too fast over rough surfaces for too long without giving them a chance to cool down. |
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There have been curved shock absorbers, with a curved piston (part of a toroid) running in a curved cylinder. The only reason for these is to enable them to be put into awkward spaces where there wasn't room for a straight one. They're much more expensive to make, and suffer much worse wear - you still need bushings at the ends, because otherwise you can't get the piston and cylinder aligned properly; and there are large buckling forces on the sliding surfaces that are negligible on straight shock absorbers. |
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