US3193251A - High-speed silent air turbine - Google Patents

Description

July 6, 1965 A. L. 1.. BRUNEL ETAL 3,193,251

HIGH-SPEED SILENT AIR TURBINE Filed July 19, 1962 United States Patent 3,193,251 HEGH-SJEED SILENT AlR TURBINE Andre Lucien Laurent Erunel, 182 Rue de Rivoli, and Robert Maurice lviercier, 172 Blvd. du Montparnasse, both of Paris, France Filed July 19, 1962, Ser. No. 211,046 Claims priority, application France, July 22, 1961, 568,875 Patent 1,303,056 1 Claim. (Cl. 253-56) Turbines which operate more particularly with compressed air as a driving fluid form very high speed engincs, the bulk and Weight of which are very reduced, while they are particularly suitable for incorporation with hand tools and are used very frequently by dentists and for the execution of highly accurate mechanisms.

Generally speaking, such turbines include a one stage rotor subjected to the direct impulse of a jet of compressed air.

Now, in such apparatus, the imperfect expansion of the air and the very simple shape of the blades produce disturbing noises during operation, which are extremely objectionable for the user, while he is executing a lengthy work and chiefly when such a work requires modifications in the speed of the turbine.

We have found after a series of experiments made on the air turbines used for dental surgery that turbines of which the normal speed is equal to 320,000 rpm. require about litres of air per minute, which leads to the production of supersonic waves of which the fundamental frequency is equal to 40,000 cycles, while the supersonic level is equal to 75 to 90 decibels at a distance of centimeters. In addition thereto, there is produced an audible spectrum characterized by a fundamental frequency of 5,000 cycles with an acoustic level of 80 to 95 decibels at a distance of 40 centimeters.

The unvarying ratio between the fundamental acoustic frequency and the fundamental supersonic frequency throughout the range of rotary speeds of the turbine, has led us to suppose that the acoustic vibrations produced were constituted, in the case considered, by lower harmonics of the supersonsic vibrations.

On the other hand, the comparison of the supersonic frequencies with the values of the rotary speeds of the turbine and the number of blades of the turbine rotor has shown that the turbine behaved as an actual hooter generating an acoustic vibration at the passage of each blade in front of the nozzle projecting the jet of compressed air.

Our invention cuts out the disturbance to which the user is subjected and which is ascribable to the vibrations produced, by the production of vibrations of the same amplitude and same frequency but shifted by one halfperiod.

According to our invention as applied to the case of a turbine provided with a driving nozzle, the production of vibrations in phase opposition with the objectionable vibrations, is obtained by means of a second nozzle which is exactly of the same type and size as the first nozzle, but operates the rotor at a point shifted peripherally by about one half blade pitch.

Our invention will be readily understood from the reading of the following description, reference being made to the accompanying drawings illustrating by way of example and by no means in a limiting sense various embodiments of an apparatus incorporating our invention. In said drawings:

FIG. 1 is a front elevational view of a rotor fed by two nozzles which are shown in section together with the diagram of the acoustic waves produce-d.

FIG. 2 shows a rotor having an odd number of blades and fed by two nozzles.

FIG. 3 is a front elevational view of a turbine including two rotors separated by a partition disc and fed by a single common nozzle which is shown in section.

FIG. 3a is a sectional view taken along the line 3a3a on FIG. 3.

FIG. 4 illustrates a turbine subjected to the action of two nozzles and the rotor of which is enclosed inside a stationary stator.

Turning to FIG. 1, it is apparent that the rotor 1 in cluding eight blades and revolving with the spindle 2, is subjected to the act-ion of two jets of compressed air 3 and 3 fed by two identical nozzles 4 and 4' assuming the same slope, the same cross-section and fed by the same supply. The rotation of the rotor across the openings of said nozzles produces upon passage of the blades in front of said openings, a shutting off action which generates acoustic vibrations as would be the case for a hooter. it will be remarked that the chief point of our invention resides in the shifting, by one half-pitch of a blade of the angular positions of the nozzles 4 and i with reference to the corresponding blades of the rotor. This results in that the sinusoids illustrating the acoustic vibrations pro duced by the air passing out of the nozzles 4 and 4', assume the shape of the curves A and A which, by reason of the unvarying relative position between the blades with reference to the nozzles, are constantly in phase opposition so that the sum of their ordinates is constantly equal to zero, which corresponds to the desired silence to be obtained.

.FIG. 2 illustrates a rotor 5 including an odd number of blades subjected to the action of two nozzles 6 and 6. This novel arrangement leads to a more easy execution since the angular shifting between the two jets formed by the nozzles by an odd number of half blade pitches is obtained with two nozzles 6 and 6' extending in accurate parallelism, which allows executing them through the simple boring of two parallel channels in the body of the machine.

FIGS. 3 and 3a illustrate a rotor including two elementary rotors 7 and of equal diameters, carrying a same number of blades and separated by a partition 7' constituted by a disc, while the blades of the two rotors are angularly shifted with reference to each other by one-half blade pitch. The feed with compressed air is ensured by a single fiat nozzle 9 feeding simultaneously equal outputs of compressed air onto the blades of the two wheels '7 and 8. The shifting by one-half blade pitch between the two bladings produces a shitting by one-half period between the vibrations produced by each of the associated rotors 7 and S and ensures the desired silence.

FIG. 4 illustrates the application of our invention to a rotor of a known type, which is supplied together with a metal casing forming the stator. The rotor it is thus contained inside a cylindrical casing 11 including two covers.

According to our invention, this rotor is fed by two nozzles 12 and 13, the angular spacing of which is equal to an odd number of half blade pitches. The air, after transferring its energy to the rotor, escapes through the ports 14 and 15 formed in the casing 11. By reason of the periodical shutting oil of the ports 14 and 15 by the blades, the exhaust of air produces a hooter ellect similar to that produced by the nozzles blowing the driving compressed .air onto the rotor. To this end, also, our invention provides for an angular spacing between the ports 14 and 15 equal to an odd number of half blade pitches in the manner disclosed for the nozzles so that acoustic and supersonic vibrations produced in the two ports may be in phase opposition.

In the different embodiments disclosed hereinabove by way of examples, the number of nozzles has been limited to two but, obviously, the same results may be obtained with any number of identical nozzles having the same output and the same obliquity with reference to the rotor axis, provided their angular positions with reference to the rotor blades are :such that the sum of the ordinates of the curves illustrating the acoustic vibrations produced by each nozzle may be constantly equal to zero.

Lastly, it is a known fact that in certain generators of supersonic waves forming hooters, a rotor assuming a sufiiciently high speed and provided with a suitable number of ports or with a suitable number of blades, generates tor the desired purposes .sounds at predetermined frequencies but, when rising up to normal speed conditions, produces during a more .or less protracted period, audible sounds of a power and sonority which are highly objectionable for the neighborhood and which have prevented the practical use of such generators.

Now, it is possible to produce in such supersonic sound generators in accordance with our invention, vibrations the phase of which is opposed to that for the production of which these generators are designed and this is obtained through the incorporation of arrangements of the type described hereinabove, such as auxiliary ports, nozzles or nose-pieces, the output, obliquity and size of which are identical with those of the corresponding parts of the prior generators while their angular position is shifted by an odd number of half blade pitches with reference to said parts.

The operation of said auxiliary parts may be cut out when desired by an outer control system and it is possible for the operator to resort to their operation only during the periods during which the rotor has not yet reached its operative speed and is liable to produce .audible sounds disturbing the neighborhood. The cut-ting out of the action of the auxiliary parts restores the entire efliciency of the generator as concerns the production of the supersonic vibrations which it is desired to produce.

Obviously, our invention is not strictly limited to the embodiments which have thus been described and illushated and it covers all the modifications thereof falling within the scope of the accompanying claim.

What we claim is:

In a small hand held turbine powered by compressed air and chiefly intended for dental surgery purposes, the combination of .at least one series of blades adapted to revolve at several hundred thousand-s r.p.m., two independent jet means operative to throw onto the blades jets of compressed air under identical conditions at predetermined points along the path of travel of the outer edges of the blades, said points being angularly displaced along said path by an odd number of half-blade pitches to thereby oppose the production of acoustic and supersonic vibrations, and a stator surrounding the rotor and having two exactly identical exhaust ports for the air passing off the blades, said ports being also 'angularly displaced around the rotor axis by an odd number of half-blade pitches.

References Cited by the Examiner UNITED STATES PATENTS 547,667 10/95 Kales 253.-14O X 781,370 1/05 Scott 253-140 803,595 11/05 Hofmann 253-140 981,758 1/11 Goehler 253-440 1,189,376 7/16 Miller 253.-56 X FOREIGN PATENTS 319,746 7/02 France.

328,988 11/20 Germany.

300,002 11/28 Great Britain,

KARL J. ALBRECHT, Primary Examiner.

WALTER BERLOWITZ, JOSEPH H. BRANSON, 1a.,

Examiners.

Images