Electricity: magnetically operated switches – magnets – and electr – Permanent magnet-actuated switches
Reexamination Certificate
2000-07-13
2002-11-05
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Permanent magnet-actuated switches
C335S151000, C340S618000
Reexamination Certificate
active
06476699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a reed switch unit used for detecting a liquid level of a reservoir tank of a master cylinder.
2. Description of the Related Art
A brake device, used in a vehicle, has such a construction that a brake liquid is circulated in a hydraulic circuit provided between a master cylinder, connected to a brake pedal or the like, and a wheel cylinder connected to a wheel brake. A reservoir tank, which holds the brake liquid so as to supply it, is mounted on the master cylinder.
In order to always ensure a proper operation of such a brake device, it is necessary that the brake liquid should always be stored in an amount, not smaller than a predetermined amount, in the reservoir tank. Therefore, a liquid level detection sensor for detecting the position of the liquid level of the brake liquid stored in the reservoir tank, is provided at the reservoir tank so that an alarm can be given to the driver or the like when the brake liquid in the reservoir tank decreases to an amount smaller than the predetermined amount.
The liquid level detection sensor comprises a float installed with a magnet, which can move upward and downward in accordance with the upward and downward movement of the liquid level, and a reed switch unit including a reed switch for detecting the upward and downward movement of the float.
The reed switch is an electrical part in which a contact is closed when the magnet in the float approaches this reed switch.
A conventional reed switch unit is shown in
FIGS. 10 and 11
.
The reed switch unit
10
comprises a reed switch
11
, and a unit main body
12
of a synthetic resin on which the reed switch
11
is mounted.
In the reed switch
11
, a contact portion
14
is formed such as to be sealed in a glass tube
16
, and a contact of this contact portion
14
is closed when a magnet approaches the reed switch. Inert gas (e.g. nitrogen gas) is sealed in the glass tube
16
to prevent oxidation and dew condensation from developing on the contact portion
14
.
Reed portions
18
are provided respectively at opposite ends of the glass tube
16
so as to extend in an axial direction. The reed portions
18
are connected to the contact portion
14
.
A right portion (in the drawings) of the unit main body
12
, made of a synthetic resin, is formed into a connector portion
12
a
connectable to other electrical circuit, whereas a left portion thereof is formed into a mounting portion
12
b
on which the reed switch
11
is mounted.
Two metal terminals
20
and
20
are provided at the mounting portion
12
b
, and the two reed portions
18
and
18
of the reed switch
11
are connected to these metal terminals
20
and
20
, respectively.
Each of the terminals
20
comprises a plate-like body which extends upwardly from the mounting portion
12
b
, and has a slit
22
in which the reed portion
18
is fitted. The terminals
20
are connected respectively to connection terminals
23
indicated in broken lines at the connector portion
12
a
.
The two reed portions
18
and
18
of the reed switch
11
are fitted respectively in the slits
22
and
22
, formed respectively in the terminals
20
and
20
, and then are soldered to the terminals
20
and
20
, respectively, thus fixing the reed switch
11
to the unit main body
12
. Since the reed portions
18
are fixed respectively to the terminals
20
by soldering, the physical fixing and electrical connection of the reed portions
18
are both effected positively.
A rib
24
is formed integrally with the unit main body
12
, and projects upwardly from that portion of the mounting portion
12
b
, on which the glass tube
16
is to be disposed, in such a manner as to surround side surfaces of the glass tube
16
. The rib
24
serves to position the glass tube
16
when fixing the reed switch
11
to the terminals
20
.
With the rib
24
thus provided, when mounting the reed switch
11
, the glass tube
16
is first received within the rib
24
, and then the reed portions
18
are fitted respectively in the slits
22
of the terminals
20
, and then are secured thereto by soldering, so that the reed switch
11
is positively fixed at the predetermined mounting position (see, for example, Japanese Patent Unexamined Publication No. Hei. 7-220817).
In the fixing method as described the above, the glass tube
16
may contact the rib
24
surrounding it. Therefore, when the reed switch unit
10
is mounted on a vehicle, there arises a problem that stresses due to vibrations and thermal expansion and thermal contraction develop in the glass tube
16
, so that the glass tube
16
can be damaged or deformed.
Besides, the glass tube
16
of the reed switch
11
to be mounted on the unit main body
12
has a dimensional irregularity, and it is inaccurate to perform the positioning of the contact portion
14
by using the glass tube
16
as a reference, to thereby invite a problem that variations occurs in the detection of the liquid level.
SUMMARY OF THE INVENTION
Therefore, this invention has been made in order to solve the above problems, and an object of the invention is to provide a reed switch unit in which damage of a glass tube due to stresses is prevented, and also when fixing a reed switch to a unit main body, the positioning of the reed switch is not performed using the glass tube as a reference.
The above object has been achieved by the following constructions of the invention.
According to the invention, there is provided a reed switch unit for detecting a liquid level of a reservoir tank of a master cylinder, including: a reed switch including a contact portion sealed in a glass tube, and reed portions extending respectively from opposite ends of the glass tube in a direction of an axis thereof; and a unit main body including terminals which support the reed portions, respectively, in electrically-connected relation thereto to fix the reed switch, wherein the reed switch is fixed to the unit main body in such a manner that the glass tube is disposed in non-contact relation to the unit main body.
With this construction, the glass tube does not contact any portion of the unit main body, and thermal stresses, which are produced by heat when mounting the reed switch on the unit main body, and stresses due to vibrations, developing after mounting the reed switch unit on a vehicle, will not be applied to the glass tube, and therefore the glass tube can be prevented from damage.
According to another aspect of the invention, there is provided a reed switch unit for detecting a liquid level of a reservoir tank of a master cylinder, comprising: a reed switch including a contact portion sealed in a glass tube, and reed portions extending respectively from opposite ends of the glass tube in a direction of an axis thereof; and a unit main body including terminals which support the reed portions, respectively, in electrically-connected relation thereto to fix the reed switch, wherein the position of mounting of the reed switch on the unit main body is set by determining the positions of the reed portions.
With this construction, the positioning of the reed switch in its mounting position is effected not by using the glass tube, but by using the reed portion. Therefore, damage, deformation and so on of the glass tube can be prevented, and besides the inaccurate positioning by the use of the glass tube, subjected to dimensional variations, is thus eliminated, and therefore variations in the detection of the liquid level in the reservoir tank can be suppressed.
In the reed switch unit, a stopper wall is formed on the unit main body, and the position of mounting of the reed switch in the axial direction is determined by abutting one end of the reed portion against the stopper wall, and the terminal has a fitting portion which receives the reed portion in such a manner as to determine the position of mounting of the reed switch in a radial direction.
With this construction, when mounting the reed switch on the unit main body, the positioning of the reed switch in the axial dir
Amano Tsutomu
Ota Kazuhiro
Donovan Lincoln
McGuireWoods LLP
Nissin Kogyo Co. Ltd.
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