GB2199685A - Improvements in electric horns - Google Patents

Abstract

An electric horn comprises a diaphragm 11 secured at its periphery to a housing 13. An electromagnet with a coil 15 is secured in the housing 13. A movable armature 18 is secured to the middle of the diaphragm 11. A pair of contacts 21 are connected in circuit with the electromagnet. When the horn is energised the armature 18 is drawn towards the coil 15. As the armature moves, an abutment flange 26 carried by the armature 18 engages an abutment surface 25 on a spring 24 which carries the movable contact 23 of the pair of contacts 21, to open the contacts 21. The current to the coil 15 is thus interrupted and the coil 14 is deenergised. As the armature 18 returns under the spring action of the diaphragm 11, the contacts 21 close and the cycle is repeated as current is restored to the coil 15. The diaphragm 11 is thus caused to vibrate. The fixed contact 22 of the pair of contacts 21 is carried by an adjustable support 40 which can pivot about its middle axis 41. The contact 22 is on one side of the axis and an adjusting screw 45 engages the support 40 on the other side of the axis 41. The adjusting screw 45 may be self-tapping so that a convoluted spiral passage is formed around the screw threads, via which the space within the housing 13 can breathe. <IMAGE>

Description

IMPROVEMENTS IN ELECTRIC HORNS The present invention relates to improvements in electric horns.

A conventional motor vehicle horn consists of a diaphragm secured at its periphery to a housing and connected at its middle to an armature of an electromagnet. The diaphragm is caused to vibrate by rapidly energising and de-energising the electromagnet which causes the armature to move back and forth, thus vibrating the diaphragm. To cause the rapid energising and de-energising of the electromagnet, current is supplied to the electromagnet through a pair of normally-closed contacts adjacent the armature. As the armature is moving towards the electromagnet under the action of its magnetic field, an abutment carried by the armature engages a movable contact of the contact pair so as to open the contact thereby causing the electromagnet to be de-energised and the armature to move away from the electromagnet.As the armature moves away the contacts are closed and the electromagnet is once again reenergised.

It is important for satisfactory operation of such horns that the contacts open at the correct time as the armature moves towards the electromagnet. In order to correct for variations in the positioning arising out of variations, for example, in paint thickness due to manufacturing tolerances, it is desirable to be able to adjust the position of the fixed contact. In the known vehicle horn adjustment is provided by mounting the fixed contact on a lever arm which is pivoted at one side of the housing, the lever extending around the armature to the other side of the housing where its position is adjustable in a direction parallel to the movement of the armature by means of a screw.The fixed contact is mounted at a position intermediate the ends of the lever so that by adjusting the screw the position of the fixed contact is moved thereby altering the position at which the contacts open.

A disadvantage of this arrangement is that the relatively long lever arm tends to flex causing a reduction in contact pressure. A contact pressure of approximately 1,200 gms is desirable in vehicle horns. It is also liable to cause contact bounce.

According to the present invention an electric horn comprises a diaphragm secured at its periphery to a housing, an electromagnet having a coil secured to the housing and a movable armature secured to the middle of the diaphragm, a pair of contacts in the housing connected in circuit with the electromagnet, the contacts including a movable contact and a fixed contact, the movable contact being operable by an abutment carried by the armature to open the contacts as the armature moves towards the electromagnet, the fixed contact being carried by an adjustable support which pivots about an axis intermediate its ends, the fixed contact being carried by the support on one side of the pivot axis and an adjusting screw engaging the support on the other side of the pivot axis.With such an arrangement, the adjustment screw and the contact can be arranged on the same side of the armature and therefore the lever arm is much shorter than in the known arrangement, thereby reducing the problems of flexing of the lever arm. Preferably the pivot is provided by a torsion spring arrangement so that the torsion of the spring maintains the support in contact with the end of the adjustment screw. Conveniently, the adjustable support and the torsion spring can be cut from a single piece of metal, the torsion spring being formed by sections of the of reduced width. This makes the adjustable contact support cheaper to manufacture. By locating the contact, the adjusting screw and the pivot points close together the problems of reduced contact pressure arising from flexing of the support are reduced.

In electric horns of the known type it is necessary to make provision for air to escape from the diaphragm chamber in order to avoid a pumping action. Elaborate systems have been devised which allow the chamber to breathe and yet prevent moisture entering the chamber. One known arrangement is to provide a breather membrane which allows air to pass through it and yet is repellant to moisture on the outside.

We have found that a simple and satisfactory arrangement for allowing the chamber to breathe whilst preventing the ingress of moisture is to use a self-tapping screw for the adjusting screw.

Where the self-tapping screw passes through the wall of the housing it forms a convoluted passage between the interior of the housing and the exterior which is sufficient for the required breathing and yet does not admit moisture into the housing.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings of which: FIG. 1 shows a cross-section through a horn in accordance with the invention; FIG. 2 shows a plan view of an internal sub-assembly of the horn of FIG. 1; FIG. 3 shows a section on the line Ill-Ill of FIG. 1; FIG. 4 shows a cross-section of the contact support on the line IV-IV of FIG. 2; FIG. 5 shows a side view of the movable contact support of FIG.

1; FIG. 6 shows a section on the line VI-VI of FIG. 5; and FIG. -7 shows a section on the line VII-VII of FIG. 5.

Referring to the drawings, these show an electric vehicle horn in accordance with the present invention. The horn comprises a circular steel diaphragm 11 secured at its periphery to a peripheral flange 12 on the open side of a cup-shaped housing 13. A channelshaped ring 14 is clamped around the edges of the diaphragm 11 and flange 12 to hold them together.

A coil 15 of an electromagnet is wound on a cylindrical core 73 formed integrally with a mounting plate 16 of electrically insulating moulded plastics material. The plate 16 is fixed by rivets 17, 48 and 49 to the housing so that the coil fits into a recess 64 at the bottom of the housing. An armature 18 is fixed by a rivet 19 to the centre of the diaphragm 11. The armature 18 extends partially into the space 20 inside the core of the coil 15.

A pair of contacts 21 are connected in circuit with the coil 15. The contacts comprise a fixed contact 22 and a movable contact 23. The movable contact 23 is carried on one limb 70 of a U-shaped phosphor bronze spring 24. The other limb 71 of the spring is located on an annular projection 75 on the upper surface of the mounting plate 16. At the free end of the limb 70 that carries the contact 23 is an abutment surface 25. The surface 25 projects into the path of a peripheral flange 26 carried by the armature. As the armature moves down towards the coil of the electromagnet 15 an abutment surface 27 on the flange engages the abutment surface 25.

When the horn is not energised, the resilience of the spring steel diaphragm 11 holds the armature in a position as shown in FIG. 1 in which the abutment allows the contacts 21 to be closed. When the horn is connected to a source of electricity and switched on, current passes through the contacts 21 to energise the coil 15, thereby drawing the armature 18 downwardly into the coil. As the armature moves down, the abutment surface 27 on the flange 26 of the armature engages the abutment surface 25 on the contact spring 24 causing the contact spring to move down and the contacts 21 to open.

Opening of the contacts 21 interrupts the supply of current to the coil 15 and the electromagnet is de-energised. The armature moves up under the spring action of the diaphragm 11 and the movement of the abutment surface 27 allows the contacts 21 to close again. The current supply to the coil 15 is restored and the cycle is repeated at a frequency of approximately 400 cycles per second.

An adjustable end stop 30 is screw-threaded in a re-entrant portion 32 at the bottom of the housing and locked in position with a locking nut 33. When the armature is at the lower end of its travel it strikes the end stop 30. A circular disc 34 is secured in front of the diaphragm 11 and has its outer edge free. When the armature strikes the end stop 30 the shock wave transmitted through the armature causes the plate 34 to vibrate at frequencies in the audible range. Thus, the plate 34 generates the noise from the horn.

The position at which the contacts 21 open is critical to the optimum working of the horn. Variations in dimensions of components within manufacturing tolerances make it desirable to be able to adjust the position at which the contacts open. In accordance with the invention, the contacts are adjustable by mounting the fixed contact 22 on an adjustable support 40.

The support 40 is stamped from spring steel sheet and comprises a central plate portion 41 which can pivot on a middle axis 42. On one side of the axis 42 the plate portion carries the fixed contact 22. On the underside of the plate portion on the other side of the axis 42 is a small depression 44 for receiving the end of an adjustment screw 45. The adjusting screw 45 is a self-tapping screw which passes through a bore 46 in an integral tubular extension 66 on the mounting plate 16.

The ends of the adjustable support are bent to form mounting brackets 47 which are separated from the plate portion 41 by portions of reduced width 46. The reduced width portions serve as torsion spring pivots allowing the plate portion 41 to pivot relative to the remainder of the support but exerting a torsion force which maintains the depression 44 in contact with the adjustment screw 45. The adjustable support 40 is secured to the mounting plate and housing by rivets 48 and 49 which pass through the mounting brackets 47 and also serves to conduct electricity into the housing.

When it is desired to adjust the setting of the fixed contact 22, the self-tapping screw 45 is turned in its bore 46 so as to move axially up or down. The movement of the screw tilts the plate portion 41 of the adjustable support about the axis 42. Because of the close spacing of the contact, the screw 45 and the pivot points formed by the regions of reduced width 46, the support 40 is not prone to flexing and therefore it is possible to maintain a high contact pressure and a resistance to contact bounce.

The adjustable support described with reference to the drawings is an inexpensive and convenient way of constructing a support in accordance with the invention. Other forms of support may be used.

For example, the plate portion 41 may be formed as a separate plate mounted on a pivot. The pivot may be a flat torsion spring and may be keyed to the plate.

The self-tapping screw 45 provides means for allowing the space 50 within the housing to breathe. As the self-tapping screw cuts its thread in the bore 46 a convoluted spiral passage is formed around the screw-threads through which air can pass. However because of the narrow dimensions of the air passage and its convoluted nature, moisture cannot enter the housing through the passage.

Referring, particularly to FIG. 3, this shows the way in which the current is supplied to the horn. Connectors 60 and 61 for connection to the vehicle battery and horn switch are secured beneath the rivets 48 and 49 on the outside of the housing. The connectors 60 and 61 are electrically insulated from the housing by a plastic moulded spacer 80. The connector 60 is electrically connected by the rivet 48 to the adjustable support 40 and thus to the fixed contact 22. The connector 61 is electrically connected by the rivet 49 to a connector plate 62 on the inside of the housing secured under the top of the rivet 49 and electrically insulated from the support 40 by an insulating washer 63. The connector 62 is connected by a wire 64 to a connector 65 secured to the rivet 17 which forms one terminal of the coil 15. The other terminal of the coil 15 (not shown) is connected by a wire 66 to a terminal tab 67 formed on the U-shaped spring 24. Thus, when the contacts 21 are closed and the horn is operated current passes through the connector 60, the rivet 48, the adjustable support 40, the fixed contact 22, the moving contact 23, the U-shaped support 24, the wire 66, the coil 15, the connector 65, the wire 64, the connector 62, the rivet 49 and the connector 61.

It will be appreciated that the horn described above is relatively inexpensive to manufacture and yet provides for the adjustment necessary satisfactory operation of the horn.

Claims (7)

CLAIMS:

1. An electric horn comprising a diaphragm secured at its periphery to a housing, an electromagnet having a coil secured to the housing and a movable armature secured to the middle of the diaphragm, a pair of contacts in the housing being connected in circuit with the electromagnet, the contacts including a movable contact and a fixed contact, the movable contact being operable by an abutment carried by the armature to open the contacts as the armature moves towards the electromagnet, the fixed contact being carried by an adjustable support which pivots about an axis intermediate its ends, the fixed contact being carried by the support on one side of the pivot axis and an adjusting screw engaging the support on the other side of the pivot axis.

2. A horn according to claim 1 in which the adjustment screw and the contact are arranged on the same side of the armature.

3. A horn according to claim 2 in which the pivot is provided by a torsion spring arrangement so that the torsion of the spring maintains the support in contact with the end of the adjustment screw.

4. A horn according to claim 3 in which the adjustable support and the torsion spring are cut from a single piece of metal, the torsion spring being formed by sections of the of reduced width.

5. A horn according to any of the preceding claims in which the adjusting screw is a self-tapping screw.

6. A horn according to any of the preceding claims in which the movable contact is carried by a spring with an abutment which projects into the path of the abutment carried by the armature.

7. A horn substantially as hereinbefore described with reference to the accompanying drawings.