Fluid level alarm device

A fluid level alarm device which is capable of warning a person of a shortage in level of an operating fluid stored in a fluid tank and in which the critical fluid level at which an alarm signal is produced is determined with a maximized accuracy by positioning a magnetically operable reed switch, electrically connected to an alarm, within the tank at a predetermined vertical location in a manner so that, when the fluid stored in the tank is lowered below a specified level, said reed switch is magnetically closed to operate the alarm.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to a fluid level alarm device for use with 
automotive vehicles and more specifically to such an alarm device of the 
kind which is capable of informing the operator of a vehicle of a 
reduction below a certain level of an operating fluid stored in a fluid 
tank associated with a master cylinder to serve the purpose of preventing 
any resulting failure in operation of the master cylinder. 
In the past, fluid level alarm devices of the kind described have been 
known which generally include a float member arranged afloat over the 
operating fluid or hydraulic oil stored in a fluid tank and provided with 
a permanent magnet, and a switch cylinder arranged in the tank and 
mounting therein a magnetically operable reed switch at a prescribed 
definite position in a manner so that as the fluid in the tank is reduced 
below a certain level, the float member moves downwardly and the magnet 
attached thereto comes into the proximity of the reed switch to 
magnetically close it, thereby operating an appropriate alarm means 
electrically associated therewith to produce an alarm signal. In such 
conventional devices, however, it is very difficult to set the reed switch 
within the tank at a predetermined definite position and hence there are 
great differences in the critical fluid levels among the devices at which 
an alarm signal is produced mainly because the positioning of the reed 
switch within the tank is usually affected by the length of the lead lines 
connected thereto and therefore errors are unavoidably introduced in the 
fabrication of the devices. 
Therefore, the present invention is intended to provide a novel and 
improved fluid level alarm device of the kind described which can 
eliminate the afore-mentioned deficiency involved in similar prior art 
similar devices. 
The above and other objects, advantages and features of the present 
invention will be apparent from the following description, when taken in 
conjunction with the accompanying drawing which illustrates one preferred 
embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing, reference numeral 1 represents a fluid tank 
adapted to store an operating fluid such as hydraulic oil and having an 
outlet port formed at the bottom thereof, the outlet port being in 
communication with a fluid chamber of a conventional type of brake master 
cylinder (not shown) for an automotive vehicle. The fluid tank 1 has its 
open top end threadedly fitted with a cap member 4 having a packing or 
wave shield plate 3 interposed therebetween. The wave shield plate 3 and 
the cap member 4 are provided with respective vent holes 5, 6 in offset 
retation with each other. 
Integrally connected with the cap member 4 at the central portion of the 
under side thereof is a switch cylinder 7 which extends therefrom 
downwardly through the wave shield plate 3 into the operating fluid F in 
the tank 1. 
A float member 8 is fitted over the outer periphery of the switch cylinder 
7 for vertical sliding movement therealong in a floating state on the 
surface of the operating fluid F, the float member having an annular 
permanent magnet 10 embedded therein on the radially inner side thereof. A 
stopper element 9 is fixedly mounted on the lower end of the switch 
cylinder 7 so as to define the lower limit of the downward movement of the 
float member 8. 
Disposed within the switch cylinder 7 is a switch base plate 13 on which 
are mounted a magnetically responsive type of reed switch 11 and a 
resistor 12 in a manner as will be detailed later. It is to be noted that 
the positioning of the switch base plate 13 within the switch cylinder 7 
is effected by abutting engagement of the lower end thereof with the 
bottom inner surface of the switch cylinder. 
The switch base plate 13 is formed of phenol resin or other similar 
non-conductive materials and have two pairs of lower and upper through 
holes 16, 16' and 17, 17' formed therethrough at respective definite 
positions, as clearly shown in FIG. 2. On one side of the switch base 
plate 13, there are printed corresponding two pairs of lower and upper 
connector terminals 18, 18' and 19, 19' respectively in surrounding 
relation with the respective through holes 16, 16', 17 and 17', a first 
current path 20 extending from the lowermost connector terminal 18 to a 
point near the uppermost connector terminal 19' and a second current path 
21 connecting the intermediate connector terminals 18', 19. 
The reed switch 11 has a pair of end terminals 14, 14' extended therefrom, 
which are first passed through the through holes 18, 18' formed in the 
switch base plate 13 in a direction from the front to the back side 
thereof, then bent inwardly toward each other at the back side as 
indicated by the broken lines in FIG. 2 and soldered to the lower 
connector terminals 18, 18'. Thus, the reed switch is firmly secured to 
the switch base plate 13 at a fixed location. Also, the resistor 12 has a 
pair of end terminals 15, 15' soldered to the upper connector terminals 
19, 19' in a manner similar to the reed switch 11. A pair of lead lines 
22, 22' are soldered at one end to the uppermost connector terminal 19' 
and the upper end of the first current path 20, respectively. In this 
manner, the reed switch 11 is positioned in the fluid tank 1 so that it is 
magnetically closed by the permanent magnet 10 attached to the float 
member 8 when the float member 8 is moved downwardly under gravity along 
the switch cylinder 7 into abutting engagement with the stopper element 9. 
Sealingly fitted in the switch cylinder 7 at the open top end thereof is a 
grommet 25 through which the lead lines 22, 22' extend in air-tight 
retation therewith, one of the lead lines, 22, being soldered at the other 
end to the positive pole of a battery 24 by way of an alarm means 23 such 
as an alarm lamp, which may be installed on the instrument panel of an 
automobile, while the other lead line 22' is connected at the other end to 
the battery 24 by way of a main switch 27. A dust shield boot 26 is 
provided to enclose the upper end of the grommet 25, serving the purpose 
of sealing the interior of the switch cylinder 7 from the atmosphere. 
Description is now made of the operation of the embodiment described above. 
When the fluid tank 1 is filled with an operating fluid or hydraulic oil F 
above a predetermined definte level, the float member 8 floating over the 
fluid surface assumes an upper position remote from the reed switch 11, 
wherein the reed switch is free from the influence of the magnetic force 
exerted by the permanent magent 10 embedded in the float member and thus 
held in its open condition. Consequently, in this state, even if the main 
switch 27 is closed to operate the associated automotive vehicle, the 
alarm means 23 will remain inoperative. 
On the other hand, however, in cases where the fluid level in the fluid 
tank 1 is reduced below the predetermined definite level due to fluid 
leakages or some other failures at the output side of the associated 
master cylinder, float member 8 lowers along the switch cylinder 7 to abut 
against the stopper element 9 so that the reed switch 11 is brought into 
the proximity of the magnet 10 to be magnetically closed under the action 
of the magnet 10 to operate the alarm means 23 for warning purposes. In 
this manner, the operator of the vehicle is informed of such unusual 
shortage of the fluid in the fluid tank 1 and such warning continues until 
the tank is replenished to raise the float member 8 above a certain level. 
In brief, according to the present invention, the first and second current 
paths 20, 21, electrically connected to the alarm means 23, are printed on 
the switch base plate 13 on one side thereof, which is arranged inside the 
hollow switch cylinder 7, and the reed switch 11 is firmly secured to the 
switch base plate 13 with its end terminals 14, 14' fixedly soldered to 
the connector terminals 18, 18' respectively formed on the first and 
second current paths 20, 21. With this arrangement, it is possible to set 
the reed switch 11 in the fluid tank 1 at a predetermined fixed position 
relative to the connector terminals 18, 18' printed on the switch base 
plate 13 with a maximum of accuracy, while introducing little or no 
practical errors in the manufacture of the device. For this reason, any 
perilous shortage of the operating fluid stored in the fluid tank 1 can be 
detected correctly so that the operator of a vehicle equipped with the 
present inventive device can be warned of such fluid reduction without 
fail, thereby preventing any possible resulting failure in operation of 
the master cylinder of the vehicle associated with the tank. 
Although one preferred embodiment of the invention 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 of 
the invention or from the scope of the appended claim.