EP0750326A1

EP0750326A1 - An electric switch with a self-cleaning mobile contact

Info

Publication number: EP0750326A1
Application number: EP96108312A
Authority: EP
Inventors: Paolo Barile
Original assignee: Bitron SpA
Current assignee: Bitron SpA
Priority date: 1995-06-23
Filing date: 1996-05-24
Publication date: 1996-12-27
Also published as: ITTO950525A1; IT1276435B1; ITTO950525A0

Abstract

An electric switch comprises a pair of fixed contacts (10, 20) and a mobile contact (32) having a range of motion with a stopping position (32b) in which the fixed contacts (10, 20) are electrically connected. The mobile contact is a bar (32) of circular cross-section secured at one point (31) of its length such to oscillate in said range of motion and rotate about its longitudinal axis (A). The bar (32) rolls along one of the two fixed contacts (10, 20) towards the stopping connection position (32b).

Description

The present invention refers to an electric switch with a self-cleaning mobile contact.
At present, one of the main problems encountered in the field of 12V electric switches for use in motorcar industry is that of cleaning the contacts of oxides and other contaminants such as dirt, which tend to form when the electric current is interrupted. The problem is of primary importance in the automobile field, as the available space and the cost targets that are fixed not always allow installation of self-cleaning sliding contacts. As a consequence, permanent front closing contacts are used. With prolonged use, these contacts are soiled and oxidise such to cause a voltage drop, or in severe cases, not allowing current passage. These contacts have therefore a limited useful lifetime. As apparent, this is unacceptable for actual industrial requirements, particularly of the motor vehicle construction field.
It is an object of the present invention to provide a switching device which can obviate the above discussed drawbacks. Particularly, an object of the invention is to provide a long lasting switch capable of self-cleaning with use. A further object of the invention is to provide a switch of low constructional cost.
These and further objects which will be more apparent hereinafter are attained according to the present invention by an electric switch comprising a pair of fixed contacts and a mobile contact having a range of motion with a stopping position in which said fixed contacts are electrically connected, characterised in that the mobile contact consists of a bar of substantially circular cross-section secured at one point of its length such to oscillate in said range of motion and rotate about its longitudinal axis, rolling on a guiding surface towards said connection position.
For a better understanding of the present invention, reference is made to the following detailed description of various exemplary embodiments considered in combination with the accompanying drawings in which:

FIG. 1: is a schematic front view of a switching device in accordance with the present invention;
FIG. 2: is a top view of the switch of FIG. 1;
FIG. 3: is a top view of another embodiment of the switch of this invention;
FIG. 4: is a vertical cross sectional view taken along the line III-III of FIG. 2;
FIG. 5: is a front view of the switch of FIGS. 3 and 4; and
FIG. 6: is a partial perspective view of the switch.

Referring to the drawings, reference numerals 10 and 20 designate overall two contact laminas fixed in a support plate 30 of electrically non conductive material. The mobile part of the contact consists of a bar 32, preferably of circular cross-section. Bar 32 is secured to support plate 30 at a point 31 substantially equally spaced from laminas 10 and 20. The securing point 31 is such to allow the bar to oscillate both in a vertical plane y perpendicular to the support plate 30 and in a horizontal plane, and also rotate about its own longitudinal axis A.
Bar 32 has an end portion 32a inserted with clearance in a seat in form of an upwardly tapered and open vertical slot 33, the sides of which are determined by laminas 10 and 20. Slot 33 has an upper opening 43 having a width d being the minimum distance between the laminas. The laminas and the bar are suitably shaped and sized such that the diameter D of the bar is greater than the minimum distance d separating the laminas. This determines a unique upper closing position of the contacts, illustrated in phantom in FIG. 1 and designated at 32b.
According to the present invention, the longitudinal axis A of mobile bar 32 is not comprised in the centre plane x of slot 33. Securing point 31 is such that it normally keeps the bar in an open contact condition contacting only one of the two fixed laminas. In the preferred embodiment illustrated in the drawings, the bar is given a certain angle α relative to the centre plane x. In other variant embodiments (not shown) of the present invention, the bar may be differently arranged with respect to the fixed contacts, for example shifting the bar sideways towards one of the two contacts instead of providing an angle.
However, the arrangement should be such in moving towards the closing position 32b, the bar is pushed against a surface 35 rolling thereon and performing self-cleaning action. Preferably, as illustrated in the present embodiment, rolling surface 35 consists of the same lamina against which the bar is pushed.
Repetition of opening and closing cycles cause the contacts point of the bar to change continuously.
With reference to the exemplary embodiment of FIGS. 3, 4 and 5, constraint 31 is a hinge constituted of upper and lower rests 31a, 31b, at the secured end portion of the bar, such to allow the bar to oscillate in passing from condition 32a to the closing position 32b. In a preferred embodiment, the bar is accommodated in a guiding and containing receptacle 41 having side walls 41a, 41b suitably spaced apart to contain bar 32 with a clearance allowing it to perform the required movements. The longitudinal axis k of receptacle 41 can determine an angle α with the axis x to give the bar a preferred position contacting one of the two fixed contacts. In the embodiment depicted in FIGS. 3 to 5 the bar is inclined towards contact 10.
Fixed contacts 10 and 20 are arranged such that the bar 32 reaches a central position only in the position 32b closing on both contacts 10 and 20.
Preferably, the force that drives bar 32 from position 32a to closing position 32b is provided by a helical spring 50 underneath the bar. Spring 50 is compressed and urges the bar directly. Generally, any resilient member different from the preferred helical compression spring 50 and acting on bar 32 may be suitable for the purpose, for example tensile helical springs, flat springs, volute springs, etc.
In the illustrated exemplary embodiment, spring 50 is such that it tends to keep bar 32 in the closing position 32b against the bias of a switch control 60. Those skilled in the art will obviously be able to provide an reversed arrangement in which the spring 50 acts so to normally keep the open position 32a, while the control 60 resists the action of the spring in forcing the bar to the closing position 32b.
It will be appreciated that besides providing an advantageous self-cleaning action, the continuous combined movements of rolling and sliding reduce, if not eliminate, problems concerning wear of the bar.
It is to be understood that the embodiments described above are merely exemplary and that persons skilled in the art may make many modifications without departing from the spirit and scope of the invention. All such modifications and variations are intended to be included within the scope of the invention as defined by the appended claims.

Claims

An electric switch comprising:
- a pair of fixed contacts (10, 20);

- a mobile contact (32) having a range of motion with a stopping position (32b) connecting said fixed contacts (10, 20);
characterised in that the mobile contact consists of a bar (32) of substantially circular cross-section secured at one point (31) of its length such to oscillate in said range of motion and rotate about its longitudinal axis (A), rolling on a guiding surface (35) towards said connection position (32b).
A switch as claimed in claim 1, characterised in that the bar (32) is so secured (31) as to roll and slide on the guiding surface (35).
A switch as claimed in claim 1, characterised in that the guiding surface (35) is provided by one of the two fixed contacts (10, 20).
A switch as claimed in claim 1, characterised in that the fixed contacts (10, 20) consist of a pair of laminas determining therebetween a slot (33) in which an end portion of said bar (32) oscillates, said slot (33) having a tapered end determining an opening (34) the width (d) of which is smaller than the diameter (D) of the bar.
A switch as claimed in claim 1, characterised in that the bar (32) oscillates in a plane (y) not coincident with the centre plane (x) of the slot (33).
A switch as claimed in claim 5, characterised in that the bar (32) is so secured as to form an angle (α) between said planes (x, y).
A switch as claimed in claim 6, characterised in that the constraint (31) is a hinge constituted of upper (31a) and lower (31b) rests at one end of the bar (32), such to allow the bar to oscillate in passing from an open position (32a) to said closing position (32b).
A switch as claimed in claim 7, characterised in that the bar (32) is accommodated in a guiding and containing receptacle (41) having side walls (41a, 41b) suitably spaced as to contain the bar (32) with the necessary clearance to allow the required movements.
A switch as claimed in claim 8, characterised in that the receptacle (41) has a longitudinal axis (k) disposed at an angle (α) relative to said plane (x) for giving the bar (32) a preferred contact position on one of said two fixed contacts (10, 20).
A switch as claimed in claim 1, characterised in that the bar is secured (31) and urged elastically against said surface (35).