Electric alarm siren with arc-like runner legs

An electric alarm siren of low power has a relatively high sound intensity and a good timbre due to a runner with arch-shaped blades. The electric alarm siren includes a central part which is divided by a partition wall into a driving part with a built-in motor being enclosed in a compact whole by a cover, and into an acoustical part comprising the runner and a front part.

The technical problem that the invention should solve is the construction 
of a siren having a good timbre and relatively high sound intensity and 
the siren and electromotor being relatively small sized, compact and 
reliable. 
An electrical alarm siren of low power is disclosed in the Yogoslav Pat. 
Appln. No. P 816/80, which corresponds to U.S. Pat. No. 4,393,374. The 
siren consists of a supporting part onto which a driving electromotor is 
fixed with a cover over the motor. The front sound generating part is made 
in the form of a funnel-shaped horn with air outlet orifices along the 
circumference. A runner is fastened to the motor shaft and is placed in 
the front part at the height of the orifices and has radial blades 
provided with air cutters at their ends. The siren has a good sound 
timbre, but does not reach a maximum efficiency, i.e. maximum loudness. 
Another siren of this type is disclosed in the Patent FR 2 371 034. The 
siren has no housing, the runner is provided with a ring along the outer 
edge of the air cutters and rotates in the front part with orifices along 
the circumference. The runner has radial blades, the front part is not 
formed as a funnel-shaped horn. The sound efficiency is still lower than 
the siren according to the Yogoslav Pat. Appln. P 816/80, which 
corresponds to U.S. Pat. No. 4,393,374. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is the aim of the invention to provide an electric siren of low power 
with relatively high intensity and good timbre of sound. The low power 
electric alarm siren in accordance with the invention is made of aluminium 
casting in such a way that the runner has arch-shaped blades, which 
substantially affects the intensity and colour of the sound. The runner 
rotates in the supporting central part.

DETAILED DESCRIPTION 
The electric alarm siren in accordance with the invention includes the 
following parts: a runner 1 with arch-shaped blades 1c, a front part 2 
having a funnel-shaped nozzle, a central part 3 with fixing accessories 
for an electromotor 5, a front part 2 axially extending outboard from the 
central part, and a cover 4 with slots 3c, a cover 4 and an electromotor 
5. As shown in FIG. 7, front part 2 extends axially outboard from central 
part 3 which means that part 3 is closer to the longitudinal centerline 
(as viewed in FIG. 7 along the axial extent of the siren) as compared with 
part 2. Therefore, "outboard" refers to items farther from the 
longitudinal centerline or center plane as compared to another referenced 
item. Contrariwise, "inboard" means the item is closer to the center plane 
as compared to another reference item. Central part 3 includes a first 
portion which has circumferential slots 3c. Axially outboard from the 
first portion is front part 2. As shown in FIG. 7, front part 2 has a 
funnel-shaped nozzle open to the axial front end of the siren. 
The runner 1 includes a circular plate 1a whose axially inboard back is 
flat, whereas in the centre of the front, at the radially innermost 
portion of the axially outboard front thereof, there is a convexity 1d 
with a bore for the shaft 5a of the electromotor 5. As can be seen by 
comparing FIGS. 1 and 7, the axially inboard face of runner 1 (the face on 
the right-hand side of the runner in FIG. 7) is flat. In contrast, the 
axial outboard face of runner 1 is not flat but has varying dimensions, 
i.e., compare in FIG. 1, rib 1b, convexity 1d and blades 1c. The convexity 
1d extends as a continuity radially into several low ribs 1b that continue 
into higher blades 1c. Both the ribs 1b and blades 1c are arch-shaped away 
from the radius in such a way that the blades 1c tangentially approach the 
circumference of the runner 1, where they are formed as air cutters 1g. 
The outer arc 1e of the blade 1 c is shorter than the inner arc 1f, the 
outer arc 1e being approximately as long as the air cutter 1g. There are 
spaces between the air cutters 1g being as long as the air cutters 1g 
themselves. 
The runner 1 according to FIG. 2 is suitable only for a clockwise rotation. 
The inwardly bent front part 2 of the siren forms a funnel-shaped nozzle 
and has a circular opening 2a in the middle. The inner circumference of 
the front part is intended to be fixed to the central part 3, viz. to the 
ring 3j. 
The central part 3 is cylindrically shaped member having at its first half 
air slots 3c in the shape of rectangles being uniformly distributed in 
pairs arranged along the circumference. 
The number of pairs of slots 3c equals the number of the air cutters of the 
runner 1. The first half ends with an axially outboard ring 3j onto which 
the front part 2 is fixed. In the second half of the central part 3, two 
legs 3a are fixed to the siren. The second half also ends with a narrow 
ring 3b of somewhat smaller diameter than the central part 3 itself; there 
are three right-angled appendages 3d with screw holes on it. At one leg 3a 
there is an opening 3f for a connecting cable. 
In the middle of the central part 3 there is a partition wall 3e with a 
bearing part 3g intended to receive the shaft 5a of the electromotor 5; 
the wall is smooth and separates the acoustical portion of the siren from 
the driving portion. There are two bores 3h in the partition wall 3e for 
screw fastening of the motor 5. On the partition wall 3e at the bores 3h, 
four brackets 3k support the core of the electromotor 5. 
The cover 4 encloses the electromotor 5 thereby providing a protection and 
compactness of the siren. Under the cover 4 there is beside the 
electromotor 5 a space provided for a relay. There are also three screw 
holes 4a on the cover 4. 
The siren is assembled by sticking the shaft 5a of the electromotor into 
the bearing part 3g and by fixing the electromotor 5 with screws through 
the bores 3h in the partition wall 3e of the central part 3. 
The cover 4 is fastened to the central part 3 by means of screws through 
the screw holes 4a and appendages 3d. A power supply cable extends through 
opening 3f. 
The runner 1 is stuck on the shaft 5a, thereupon the front part 2 is firmly 
pressed upon the border of 3b.