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Polish inventors - what have they ever given to the world? [101]
"The Most important invention of the first decade of XXI century" (although it was invented 13 years ago hehe)
In the mind of Polish media perhaps. Otherwise this is a big exaggeration. Please, take your time and read what follows. This is not a propaganda, but engineering facts.
Lucjan £ągiewka's bumper prototype has nothing in common with Malcolm C. Smith's inerter - besides using similar mechanical components: a flywheel and a rack and pinion device. He may fight all he wants with Cambridge, but his chances of revoking the Smith's patent are zero, for many reasons. And since this little war is publicly funded by the Polish state it is also a waste of public money.
He cannot patent the components, because they have been around for many centuries and have been used precisely for the exactly same or similar reasons, as used by both men in their devices. Flywheels have been used as energy storage devices in gyrobuses (1955), Watt's steam locomotives (19 century), toys and recently in KERS (Kinetic Energy Recovery Systems), NASA space docking stations, etc. New technologies and materials, such as carbon components and magnetic bearings have made flywheels the attractive alternatives to chemical batteries.
Rack and pinion device - along with four-bar-linkages, threaded rods, sliders and hydraulic elements - are typical converters of linear/reciprocating motion to a rotational one. The primary applications can be easily found in automotive industry but there are many other applications, such as hydrodynamic screw for power generation - the Archimedes screw pump in reverse.
So, no - these components cannot be patented. However, their functional application could be contested in theory. Unfortunately for Mr. £ągiewka his prototype has no functional similarity to that of the Smith's one. The former is an untuned device for shock reduction, the latter is a tuned device for attenuation of vibrations. Tuned vs. untuned, one-time shock vs. continuous vibrations. See the difference? There is also a huge difference regarding size, mass, and configuration of those devices: the £ągiewska's one is bulky, heavy and placed in front of the vehicle as a bumper - the Smith's one is compact, small and made a part of a car suspension system.
To make it even worse for £ągiewka - in recent years, driven by the demands from the racing cars industry, several new concrete engineering solutions of the original idea of Smith's inerter have been developed and patented, such as the Lotus Renault GP: Fluid Inerter. They still use a flywheel, but no more rack and pinion converter. Instead hydraulic fluid is used to drive the flywheel.
So let me shortly review what it is all about.
1. Classical vibration isolation, a.k.a. vibration suspension, or vibration absorber. Its role is to either reduce the forces transmitted from the environment, such as a bumpy road, into a machine (a vehicle), or to reduce vibrations of rotational/reciprocating machines transmitted to the environment, such as to a plant floor. The solution is generally known as vibration isolation.
All one needs is to suspend the machine (the car) on a soft system of springs, alongside some dashpots to disperse the vibrational energy. The softer the springs the better attenuation efficiency, and the better the driving comfort in case of cars, but the worse operational (driving) control. So there is always some compromise to be made. For example, a machine operating at 1800 RPM (30 Hz) would be very well isolated by a set of rubber springs tuned to 7 Hz, say. In most cases there is no need to go below this number, but there are some special applications, where much softer coil springs (3 Hz), or even air springs (1.5 Hz) would be required.
It is quite easy to isolate reciprocating machines, which operate at a constant frequency, as in the example above. All we need is to stay away from the resonance (7Hz << 30 Hz). However, vibration isolation of racing cars, driving in various road conditions, on various tires is not that easy because they encounter the entire spectrum of excitation frequencies - including the one dangerous resonant frequency, provided by the suspension system. In this case - rather then helping the driver - the engineer, who had designed the absorber, has made the matter much worse for the driver. Vibration isolation does not work in resonance!
As another class of examples, where the resonance becomes troublesome, consider tall structures (chimneys, towers) subjected to various wind conditions. Such a structure can be modelled as a beam, or a mass supported by a spring. It has its own so-called natural frequency - often quite low, 4 Hz say. And sooner or later, among the wind spectrum frequencies, a resonant frequency (4 Hz, say) would appear - causing serious structural damages or even a catastrophic collapse of the structure.
2. Passive tuned mass dampersThis is where one of the oldest technologies (19 century, I guess) comes to rescue. Support a small auxiliary mass (about 1/10 of the primary mass) on a system of springs tuned to the vicinity of the natural frequency of the main structure, add some dashpots to dissipate vibrational energy, and attach some cooling system to remove excessive heat generated in dashpots. This is known as Passive Tuned Mass Damper. Passive - because there is no electronics involved here. Tuned - because the damper has been tuned to one particular frequency. Mass - because its main component is a mass-spring device.
The model: Ground==>Main Spring + Dashpot in parallel ==> Principal Mass ==>Damper's Spring + Dashpot ==> Damper's Mass
I used to design such systems for chimneys of Hydro-Quebec power stations. But the joy and pride of the company I was employed for six years, long before I joined it, were tuned mass dampers designed for CN Tower in Toronto in 1976.
The 102-m steel antenna mast on top of the Canadian National Tower in Toronto (553 m high including the antenna) required two lead dampers to prevent the antenna from deflecting excessively when subjected to wind excitation. The damper system consists of two doughnut-shaped steel rings, 35 cm wide, 30 cm deep, and 2.4 m and 3 m in diameter, located at elevations 488 m and 503 m. Each ring holds about 9 metric tons of lead and is supported by three steel beams attached to the sides of the antenna mast. (...)
Tuned mass dampers were also recently applied to Formula 1 racing cars to reduce vibrations induced by road bumps. Introduced in 2006, banned in 2009, for various reasons, they have been allowed back in 2011. Such dampers differ from conventional suspension system by presence of a secondary mass, attached to the car's body via spring, or spring and damper, system. This auxiliary subsystem is tuned to the first natural frequency of the suspension.
3. InertersInerters, as originally designed by Malcom S Smith from Cambridge, are more sophisticated cousins of Tuned Mass Dampers. In rough approximation - rather than using an auxiliary mass supported by a spring, an inertia of a spinning flywheel is used to to store excessive energy and then dissipate it slowly via dashpots.
There are many descriptions of the interters, but the following one seems to be easy enough to understand:
scarbsf1.wordpress.com/2011/11/29/lotus-renault-gp-fluid-inerter
Besides, it describes the technology far removed from rack and pinion of that of £ągiewka and Smith to further prove the point that inverters and bumpers have nothing in common but the flywheel.
