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Diamond-Core Mechanical Linkages

For higher working speeds
  [vote for,

A mechanical linkage can be represented by a rod of metal. If a mechanical force is applied to one end of the rod, that force will cause the rod to move, but only AS a wave-form of mechanical energy conducts through the rod at the speed of sound to the other end. The far end of the rod absolutely cannot begin to move until that mechanical waveform of force reaches it.

Well, when using mechanical linkages in high-speed systems, this can pose a problem. A reasonably well-known example was the "valve rods" in old-fashioned auto engines. At high-enough RPMs, the rods could not conduct mechanical forces to the valves fast enough to open them at the right timing-points in the combustion cycle. This problem was solved by replacing the rods with a cam system (shortening the distance that the mechanical forces needed to move, which thereby decreased the time needed for those mechanical forces to traverse the linkages and do their jobs).

Keep in mind that while the valve-rod problem was reasonably well known, the general problem involving the transmission of mechanical forces at high speeds remains a limiting factor in all mechanical systems.

Okay, a general solution to the problem is what I'm getting at here. See, different materials have different speed-of-sound in those materials. Thus an alternate solution to the valve-rod problem could have been to pick a "faster" material for the rods. This leads to something of a conundrum, in that "faster" materials are also generally harder AND MORE BRITTLE materials. The best/worst of the lot is diamond.

Thus this Idea. Companies are now beginning to manufacture large nearly-flawless chunks of diamond (genuine crystalline carbon, MORE flawless than found in Nature) for industrial purposes. See link. So imagine a "connecting rod" which has a diamond core, and an outer metal covering. We would want the coefficient of thermal expansion of the two substances to match, of course. When a mechanical force is applied to one end of this rod, the "metal softens the blow" and protects the diamond core from shattering. In turn the diamond core, having the highest speed-of-sound of all ordinary materials, conducts the mechanical force throughout the rod at a tremendous rate, allowing the force to reach the next part of the mechanical system in minimum time.

Vernon, Feb 15 2006

(?) A manufacturer of nearly-flawless synthetic diamond http://www.apollodiamond.com/about.html
As mentioned in the main text [Vernon, Feb 15 2006]

Speed of sound in diamond http://hyperphysics.../tables/soundv.html
[spidermother, Feb 15 2006]

Stuff on poppet valves http://en.wikipedia.org/wiki/Poppet_valve
The real problem was wear [ldischler, Feb 15 2006]


       I don't see how the metal would protect the diamond - wouldn't the much higher resistance to compression of the diamond lead to its behaving as if the metal jacket were not there?   

       Out of interest, what is the speed of sound in diamond?   

       This would be neat for Babbage engines. They would then be not quite so many billions of times slower than semiconductor computers.
spidermother, Feb 15 2006

       The speed of sound in steel is 13,000 mph. You sure that was the reason?
ldischler, Feb 15 2006

       //Out of interest, what is the speed of sound in diamond?// About twice that of steel.
ldischler, Feb 15 2006

       I have a value of 12 000metres/sec for diamond, 43 200 km/h or 27 000 mph.
The 13 000mph (5790 metres/sec)figure is for stainless, and structural steel is about 10 000mph (4512 metres/sec)
coprocephalous, Feb 15 2006

       Yep, me too (link). Also, if the metal turned out to be unnecessary, think of all the shiny things we'd have.
spidermother, Feb 15 2006

       I think the problem was that pushrod engines had more inertia in the valve system, compared to overhead cam systems.
Ling, Feb 15 2006

       I don't think the problem was the speed of sound in the material. I think it was that the greater the acceleration, the more force you need to apply per unit mass. Hence the tensile stresses rise, and eventually a speed is reached at which the tensile stress through the cross-section equals the UTS and it breaks.   

       If you double the length of the pushrod, then the mass of the rod _per unit cross-sectional area_ will also double. Thus the force that needs to go through the cross-section will also double, and so the maximum permissible acceleration will halve. Thus overhead cams are much better; the revolving camshaft is not constantly accelerating and decelerating and is thus not subject to the same restrictions as a pushrod, while the much shorter valve stems can cope with very high acceleration.
david_scothern, Feb 15 2006

       Forumla 1 cars use a pneumatic system running on manifold pressure to close the valves, because steel springs can not close the valves fast enough.   

       At 19,000 rpm, 316.7 revolutions and 1,583.3 ignitions take place each second in the BMW F1 engine. 9,500 engine speed measurements are made, the pistons cover a distance of 25 metres, and 550 litres of air are drawn in. In the P84, maximum piston acceleration was 10,000g. Peak piston speed was 40 metres per second.
Giblet, Feb 16 2006

       That's very interesting, [Giblet]. But please note that the air drawn in will not equal the total displacement, if you consider standard conditions for the gas. The pressure of the gas in the cylinder at the end of the induction stroke will not be atmospheric pressure.
Ling, Feb 16 2006

       Actually it can be with the right port flows, cam timing, and intake/exhaust tuning. In the 80's in Australia the 5.3L Jaguar V12's had (in racing trim) achieved 110% volmetric efficiency at peak torque, and ~94 onwards Ford Falcons also achieved 100% (in completely standard road trim) at peak torque. You can be damn sure F1 engines are doing this as well. But that's off topic.   

       Closer to topic - bent pushrods are caused by the weight of the valves, retainers, rockers, and top part of the valve spring being shut (and due to conservation of motion wanting to stay that way), plus the valve spring tension holding it shut. The cam is trying to push all of this open, and does this quite violently. The pushrod is just the easiest thing to bend in the equation (being long, skinny, and most of the time hollow steel).
BLSTIC, Sep 08 2009

       There is one area where the compression wave harmonic does come into play and that is in the action of the coil wound spring itself. The speed of sound in the material of the coil spring and the length of it's winding causes it to have distinct periods of harmonic action does cause a decrease in tension.   

       This invention is completely wrong. If we are building a high performance engine then the materials are going to be light and fatigue resistant, Aluminum and aluminum alloys. And all surfaces where tensile strength is a question will be equipped with narrow steel bearings or shafts (pistons pins, cranks). Vernon strays too far from the theoretical exposing himself to the dangerously tested and examined conditions in the real world.
WcW, Sep 08 2009


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