Since the earliest days of mobile police, fire, and emergency medical services, mechanical sirens have helped to clear the way producing a particular whoo—whoo sound distinctly different from the bells, horns, and whistles of the other vehicles.
The present invention makes the unique sound by rapidly momentarily turning on-off-on-off the air flow of its centrifugal air pump. These sirens were originally hand cranked, later driven by friction wheels against other rotating machinery, and still later by their own electric motor. In his 1925 U.S. Pat. No. 1,566,761 Miles disclosed an open rotor with straight pumping vanes radiating from the center with small right angle end flanges for closing the stator ports. In a subsequent U.S. Pat. No. 1,739,727 Miles demonstrates curved vanes and confirms that “as the air is forced outwardly and the ports are intermittently opened and closed by the rotor flanges a loud noise will be produced.”
Refinement of the siren during the 30's and 40's brought better rotor shapes for improved air flow, enclosed rotors for less resistance, and rotor clutches for coasting. The motor driven electromechanical sirens of the 60's were producing 120+decibels of square wave form sound from 10 inch diameter 37 pound machines drawing over 300 starting amps and 175 running amps of 12 volt power.
By the 70's increasing demand for electrical power in emergency equipment brought on by more warning lights, communication radios, and computers prompted the industry wide switch to electronic sirens requiring only 15 to 20 amps of power. These sirens mimic the whoo—whoo sound electronically with transistors and then project it from speakers. This sound is in a sine wave form, much like the ripples on the lake from where a rock was tossed.
During the last 30 years improvements in automobile insulation and soundproofing are rendering the electronic siren ineffective. It is not uncommon for the Fire Chief to have to climb down out of his fire truck and walk ahead to a stopped motorist so he can tap on their window in order to get their attention and ask them to pull their vehicle to the right.
However, the motor driven mechanical siren of this application with its square form sound wave penetrates through a closed modern vehicle, even with the air conditioning and the radio on, to alert the driver of an approaching emergency vehicle.
Therefore, there is a strong desire for a new mechanical siren which is only 5 inches in diameter and yet able to deliver an appropriate 123 decibels of sound while drawing only 28 amps of power.
The present invention is directed to mechanical sirens and primarily to the rotor and stator which pump and redirect air. This rotor pumps air from the siren central intake bore and accelerates it to the rotor velocity of 10,700 feet per minute where half of it passes out to the outside, through slots in the siren stator. This function is like breathing, but this is not the source of the loud sound.
As the rotor revolves, every 15 degrees (for a 6 port), the stator blanks off the air pumping channels of the rotor completely. At this moment the accelerated air yet in the channels compresses, changes direction, and then bounces back out the throat. This is the source of the loud sound. In testing a siren in the open spaces, at 100 feet the rebound air sound wave is 6 dB louder than the exhaust air sound from the side slots, measured at a line 90 degrees to the intake and axis of rotation. On the logarithmic sound pressure scale, a 6 dB increase, nose to side, is a doubling of the sound.
A sirens effective performance efficiency may be measured as a function of auditable sound as measured in dB from inside of a closed modern insulated automobile, verses the input siren electrical power. To maximize this rebounding sound, several factors apply:
A significant benefit of this siren to the community is the lessening of emergency vehicle noise pollution. By virtue of the spiraling square form wave, as generated by the mechanical siren, much of the sound has a short life, being dissipated as it strikes the ground and vegetation. However the broadly expanding horizontal sine wave pattern of the electronic siren is heard for long distances.
It is yet a further object of this present invention to provide a siren which produces sound waves with sufficient velocity to exceed the vehicle's speed, and thus improving the imminent safety of the emergency response crew.
These and other objects, features, aspects, and advantages of the present invention will become better understood with reference to the following description and accompanying drawings.
Referring to the drawings,
Now turning to
In order to maximize this rebounding sound wave 21, a firm crisp square wave must be generated. Factors effecting this wave are: 1) the diametrial clearance 23 between the outside of the rotor 3 and the inside the stator 9, and 2) the lower axial overlap 24 which is equal to the upper axial overlap 25, seen in
Now, these air dams around the rotor pumping channels 12 establish the firm footing for the rebounding sound wave 21 to press against, allowing the rotor/stator clearance 23 to be the maximum (large) gap for mobile equipment operation and yet provide the desired warning sound.
Although a preferred embodiment has been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the spirit and scope of the present invention.
U.S. Pat. No. 1,566,761 December 1925 Miles Early RotorU.S. Pat. No. 1,586,101 May 1926 Miles Driven by Engine Fan BeltU.S. Pat. No. 1,739,727 December 1929 Miles Coaster, Teach pumping outU.S. Pat. No. 1,792,858 February 1931 Miles Poor RotorU.S. Pat. No. 2,068,427 January 1937 Meussdofor Direct Dricve, pull BrushesU.S. Pat. No. 4,393,374 July 1983 Bandelj Cheap Siren, Poor rotorU.S. Pat. No. 4,558,656 December 1985 Powell Comp Air Driven, tight fit rotor/stator
Number | Name | Date | Kind |
---|---|---|---|
539711 | Smith | May 1895 | A |
1019571 | West | Mar 1912 | A |
1428684 | Erick | Sep 1922 | A |
1618210 | McClure | Feb 1927 | A |
1772614 | Miles | Aug 1930 | A |
2471028 | Fletcher | May 1949 | A |
3089458 | Jacques | May 1963 | A |
4138673 | Faust | Feb 1979 | A |
4691194 | Kavcic | Sep 1987 | A |
4847590 | Gosswiller | Jul 1989 | A |
5146434 | Bromley | Sep 1992 | A |
Number | Date | Country |
---|---|---|
3803388 | Aug 1989 | DE |
358055828 | Apr 1983 | JP |
Number | Date | Country | |
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20040200401 A1 | Oct 2004 | US |