EP2342709A2

EP2342709A2 - An electronic horn for a vehicle

Info

Publication number: EP2342709A2
Application number: EP09745102A
Authority: EP
Inventors: Hari Prakash; Ashok Kumar; Sudhir Dahiya
Original assignee: Gerres Stephan
Current assignee: Gerres Stephan
Priority date: 2008-09-26
Filing date: 2009-09-25
Publication date: 2011-07-13
Also published as: WO2010035123A2; WO2010035123A3

Abstract

The present invention discloses an electronic horn for a vehicle having a housing sub-assembly; a diaphragm sub-assembly; wherein a chip on board circuit is riveted to a terminal block outside the housing and the chip on board circuit has clipping means for eliminating surge voltages.

Description

AN ELECTRONIC HORN FOR A VEHICLE Field of invention:

This invention relates to an electronic horn for a vehicle. In particular this invention relates to an electronic horn having a chip on board (COB) circuit for contactless switching protected against surges and high vibration environment.

Background of the invention:

Conventional horns used in automotive vehicles have a vibrating diaphragm driven by an electromagnetic device. The said electromagnetic device is a coil driven by current pulses. Current pulses are developed by a mechanical switch such as a circuit breaker wherein such switch would energize a magnetic coil to cause the diaphragm movement. Diaphragm movement during its travel would open the switch, allowing the diaphragm to return in the reverse direction due to the elastic energy accumulated in the diaphragm thus closing the switch again. Switching and corresponding movement of the diaphragm causes the cycle to repeat at a particular frequency equal to the fundamental frequency which can be adjusted by a screw.

The life of such horns is limited by the life of the mechanical switch due to the limitations associated with the mechanical switch. In such mechanical switches there will be fall out in the maximum sound output with time. Further, there will be considerable wear and tear of the switch contacts due to sparking, which lead to variations in the time of operation. Also sparking causes the Ozone generation which corrodes the internal parts of Horn faster. Λ^' Also, such systems provide eccentric loading on to the diaphragm increasing the stress on the vibrating diaphragm thus reducing the life of the diaphragm./ In conventional horns with mechanical switches, there is an increased | occurrence of warranty failure and customer line return especially considering the excess use of horns. Consequently, there is a growing demand for horns with increased reliability and improved life. To meet this demand, different methods were designed to replace the mechanical switch in conventional horns with electronic switches. Various electronic horns providing alternatives to the , mechanical switch have been designed, wherein mechanical switch was replaced by systems incorporating solid state circuits. However, requirement of . high power, high frequency variation to the order of ±20 Hz, immunity to high voltage spikes caused by switching an inductive load and mechanical ruggedness place severe limits on the existing technology that may be successfully used.

Conventional electronic horns are implemented with a simple series connection between a coil, an electronic circuit connected to a battery and an energizing coil within the horn itself. The electronic circuit forms an electro-mechanical system together with the coil connected in series therewith. Current pulses developed by an electronic switch energize a magnetic coil secured in the housing to cause diaphragm movement towards the coil against its spring bias and when the switch opens due to switching in the electronic circuit, diaphragm returns to its original position. These kinds of systems normally; use solid state energizing circuits for switching and generating sound in the horn, however these methods have certain drawbacks as the chip on board circuit is placed inside the housing. Initially, placement of the chip inside the housing was considered to be beneficial as it reduced the cost of preparing a separate housing for the electronic circuit. It was also believed that this arrangement reduced the extent of vibration thus reducing the circuit failure, however with time it was noticed that the major reason for horn failure was due to damage to the electronic circuit with vibrations. Further, it was observed that temperature inside the housing increases with the operation of the horn and this variation in temperature causes changes in the characteristics of the solid state circuits. It was observed that the electronic circuits function normally up to 80° C, beyond this temperature electronics circuits start malfunctioning thus affecting the sound output. It was noted that when the electronic circuits are placed inside the housing it is necessary to maintain the temperature at a constant level but due to excessive production of heat it is not possible to maintain the temperature below the specified level. Temperature rise causes the change of fundamental frequency of driver circuit which is not matched with the resonant frequency and hence causes loss of sound output. In order to obviate these drawbacks, horns having chip on board circuits click fitted outside on the housing were designed. In case of click fit PCB, solid state energizing circuit in the form of a single chip integrated circuit is placed inside an arc shaped circuit casing on the housing. This obviates the drawbacks associated with circuits placed inside the housing, wherein circuits start malfunctioning due to increase in temperature with horn operation. However, the click fit PCB is quite prone to displacements and breakages due to disturbances during high vibrations. Components of click fit PCBs are further susceptible to wear and tear during high vibrations as they are loosely fitted to the housing. Thus, their application to horns entails severe risk and disadvantages.

In electronic horns of the prior art having solid state energizing circuits, surge voltages are generated while switching an inductive load. Surge voltages are generally associated with high frequency inductive coil circuits and generation of surge voltages can damage the electronic components associated with the circuit leading to failure of the horn. Therefore, there is a need to design and develop an electronic horn with surge protected contactless switching system and reducing failure due to vibration such that life cycle of the vehicles horn is improved.

Objects of the invention: It is an object of the invention to provide an electronic horn with surge protected contactless switching system such that the life cycle of the horn is increased and its operation is simplified.

It is also an object of the invention to provide a chip on board circuit for generating continuous pulses at a particular frequency to a driver circuit electro-magnetically coupled to the diaphragm so as to cause the diaphragm to oscillate at the frequency of the continuous pulses of the said electronic chip on board.

It is yet another object of the invention to provide an electronic horn, which is stable in conditions of high vibrations due to secured grip through riveting.

It is one more object of the invention to provide an electronic horn which eliminate mechanical contacts so as to eliminate contact oxidation, wear and tear of the parts and reduce extra stress put on the diaphragm.

It is one more object of the invention to provide an electronic horn having a contactless switching system independent from the movement of the diaphragm.

It is one more object of the invention to provide an electronic horn, which eliminates frequency variations caused by mechanical parts. It is yet another object of the invention to provide an electronic horn, which obviates the requirement of adjusting screw.

It is one more object of the invention to provide an electronic horn, which is simpler in construction, operation and compact in size.

Summary of the Invention:

In accordance with this invention there is provided an electronic horn for a vehicle comprising a housing sub-assembly; a diaphragm sub-assembly and a chip on board circuit riveted to a terminal block outside the housing. The said chip on board circuit having clipping means for eliminating surge voltages.

Brief description of the invention with accompanying drawings:

The invention may be better understood and further advantages and uses thereof more readily apparent, when considered in view of the following detailed description of exemplary embodiments, taken with the accompanying drawings in which:

Figure 1 illustrates a schematic circuit diagram of a solid state energizing circuit on a printed circuit board of the prior art. Figure 2 illustrates a cross sectional view of the housing sub assembly for an electronic horn according to the present invention.

Figure 3 illustrates a cross sectional view of electronic block sub assembly according to the present invention.

Figure 4 illustrates a cross sectional view of the diaphragm sub assembly for disc type electronic horn according to one embodiment of the present invention.

Figure 5 illustrates a cross sectional view of the diaphragm sub assembly for trumpet type electronic horn according to one embodiment of the present invention.

Figure 6 illustrates a block diagram of the chip on board circuit of the electronic horn according to the present invention.

Detailed description of the drawings:

The present invention provides an electronic horn. The electronic horn according to the present invention is now described in detail with reference to the accompanying drawings, wherein reference numerals used in the accompanying drawings correspond to the like elements throughout the description.

Figure 1 illustrates a schematic circuit diagram of a solid state energizing circuit on a printed circuit board of the prior art. In such circuit, a power supply is provided through a battery to a voltage regulator. Output from the said voltage regulator is further coupled to a timer through a limiting resistor for generating a pulse wave having frequency similar to the resonance frequency. The timer is connected to an adjustable resistor for varying the timer output frequency as well as the duty cycle. Output of the timer is further connected to a switching device, which is a MOSFET having its source connected to the ground and its drain is coupled to the coil. Positive terminal of the power supply is further connected to the other end of the coil. When current is passed through the coil, said coil is energized and consequently generates sound in the horn. In such circuits of the prior art, due to inductive loading involved, voltage surges are generated, which are harmful to the electronic components of the solid state circuits as these sudden high voltages can damage the electronic components. Also the prior art does not disclose a method to eliminate such surge voltages. Further, said electronic circuit of the prior art is placed inside a metal casing and is click fitted to the housing on the planar annular portion of the housing. It has been observed that during conditions of high vibrations associated with automotive vehicles, the click fitted printed circuit board is displaced and hence causes failure of the electronic horn due to the damage to the printed circuit board.

Figure 2 illustrates a cross sectional view of the housing sub assembly (101) for an electronic horn according to the present invention. The housing sub- assembly (101) comprises a cup shaped housing (102) and a coil body assembly (116). The cup shaped housing (102) is made of metal or plastic casing to protect inner components which are safely secured inside the housing (102) from being damaged. The housing (102) is stepped to define a small closed end portion (106) comprising an end wall (108) and a larger open end portion (110) terminating in a radial flange (112). The small end portion (106) and the larger end portion (110) are connected by means of an intermediate section, such as a planar annular portion (114). The coil body assembly (116) is provided for mounting an energizing coil (129) which generates a magnetic field inside the housing (102). The coil body assembly (116) is engaged with the housing (102) by rivets (122) through the apertures (not shown) provided in the annular portion (114) and the coil body assembly (116). The rivets (122) through the coil body assembly (116) and the housing (102) are also connected to an electronic block sub-assembly (not shown) having a chip on board circuit (not shown) placed inside a terminal block (130). The chip on board circuit (not shown) is placed inside a metal casing (not shown) to protect the chip from being damaged. The chip on board circuit (not shown) may be in any form, however an arc shaped chip on board fits easily above the annular portion, (114) of the said housing (102). The casing (not shown) and said terminal block (130) are also provided with a similar shape as that of the chip on board, so that said chip on board is placed properly inside the terminal block (130). The casing (not shown) may be plastic or metal casing made of non heat dissipating material so that the heat generated in the housing due to reciprocating movement of the diaphragm is not transmitted to the chip on board circuit (not shown) inside the metal casing (not shown) .

The rivets (122) are basically mechanical fasteners having a factory head and a buck tail. Different types of rivets may be used for the fastening purpose such as solid rivets, blind rivets, multi grip rivets, grooved rivets, peel type blind rivets, self pierce rivets, plastic rivets, tubular rivets and the like. The rivets (122) provide better fastening between the housing and the chip on board circuit (not shown) placed inside a metal casing (not shown) compared to click fitted PCB used in the prior art where the click fitted PCB used to fail during conditions of high vibrations associated with the vehicles. The terminal block (130) has shape similar to that of the chip on board circuit (not shown) and provides covering to the chip on board circuit (not shown). The terminal block (130) receives the rivets (122) through the chip on board circuit (not shown) and has terminals (142) to connect an external power supply (not shown) through a battery, to the chip on board circuit (not shown) inside the metal casing (not shown) . An aperture (not shown) in the end wall (108) of the housing holds an anchor bolt (126) which extends towards the coil body assembly (116). One end of the anchor bolt (126) receives the coil body assembly (116) and the opposite end of the anchor bolt (126) is threaded to receive a mounting bracket (128). The mounting bracket (128) is further secured with a securing nut (134) so as to connect the said housing to the vehicle body. The anchor bolt securely connects the said mounting bracket with the vehicle so that vibrations associated with the vehicles do not affect the secured connection between the housing (102) and the mounting bracket (128).

As mentioned earlier, the coil body assembly (116) of the housing sub assembly (101) has an energizing coil (129) , which is secured inside the cup-shaped housing (102) by means of said rivets (122) connected through the apertures (not shown) inside the coil body assembly (116) and the cup- shaped housing (102). The energizing coil (129) is made up of a conductor such as a solid copper wire or the like and wound around a core to form an inductor or electromagnet. The coil (129) is further coated with varnish or wrapped with an insulating tape to provide insulation and to secure the wire in place. Said coil (129) acts as an electromagnetic driver when current is passed through it and is connected to the output of the chip on board circuit (not shown). When current is passed through the energizing coil (129) a magnetic field is produced inside the housing (102) which attracts the diaphragm (not shown) towards the coil body assembly (116) and the anchor bolt (126). Figure 3 illustrates a cross sectional view of the electronic block sub assembly (140) according to the present invention. The electronic block sub assembly (140) comprises of a terminal block (130) placed above the COB (132) and covering the said chip on board (132) placed inside a metal casing (133), so as , to protect the COB (132) from getting damaged. The chip on board circuit is (132) placed inside the metal casing (133) and upon the planar annular portion (114) which interconnects the smaller end portion (108) and the larger portion (110) of the housing (102). The chip on board circuit (132) comprises of a printed circuit board ( PCB) (180) having an embedded chip (182) like a layer of chip wafer. The chip on board also comprises of, linear elements like resistors and non-linear elements like junction diodes mounted on it. The PCB (180) along with other elements mounted on it are further placed inside a metal or plastic casing (133) which does not dissipate heat and thus does not allow the characteristics of electronic components to vary with changes in the temperature. The terminal block (130) and the chip on board circuit (132) are connected to each other and the housing by means of rivets (122) through apertures (138) in the terminal block (130) and chip on board circuit (132). The chip on board circuit (132) comprises of a solid state switching circuit which is provided inside an electronic circuit casing (133) and is located outside the cup-shaped housing (102). The electronic circuit casing (133) may be of any form, nevertheless, in general the casing (133) has the shape of an arc which : easily fits on the planar annular portion (114) of the housing inside the

^' . 12 _. ^• . ^{■ ■'' •}. ^{• '} . ^".... ^;:. ^'' .^'; \: terminal block (130). The terminal block (130) is made of plastic or metallic material which does not allow the heat produced inside the housing to dissipate to the chip on board circuit (132) and prevents heating of the riveted, casing (133) from the heat generated inside the housing (102) thus preventing damage and malfunction of said electronic circuit. The terminal block (130) comprises of terminals (142) connecting an external power supply (not shown) to provide desired electric current to the chip on board circuit (132) which is further connected to said energizing coil (129).

The chip on board circuit (132) provides an electrical output to the energizing coil (129) mounted on the coil body assembly (116) thereby magnetizing the energizing coil (129). Riveting of the said chip on board circuit (132) inside the metal casing (133) with the housing (102) increases the life of horn by reducing failure from dislocation of the chip on board and loosening of connections between different components of the chip on board during jerks and vibrations in the vehicle.

Figure 4 illustrates a cross sectional view of the diaphragm sub assembly for disc type electronic horn according to one embodiment of the present invention. A diaphragm sub-assembly (151) comprises a diaphragm (150) made of a resilient metal with good elastic properties and an armature (152). The diaphragm (150) is made of a material such that when the coil (129) is energized by passing current through it, a magnetic field is generated around the coil (129) which pulls the diaphragm (150) and the armature (152) towards the energizing coil (129). The armature (152) is riveted to the diaphragm (150) along with a resonator plate or an oscillator (154). The diaphragm (150) is clamped to the periphery of the radial flange (112) in the cup shaped housing (102). The resonator plate or the oscillator (154) is further secured to the second sub assembly by a nut (156) with a cap cover (158). Said oscillator (154) is responsible for producing metallic sound inside the disc horn and this metallic beep sound distinguishes disc horns from other horns. The housing sub-assembly (101) is then assembled together with the diaphragm assembly (151) by a sealing ring (168).

When power supply is provided to the terminals (142) of the terminal block (130), a magnetic force is generated in the energizing coil (129) and the anchor bolt (126) due to current supplied by the chip on board (132). The energizing coil (129) and the anchor bolt (126) get subsequently magnetized resulting in pulling of the diaphragm (150) at the centre towards the anchor bolt (126). The chip on board subsequently withdraws supply of current to the energizing coil (129) and the diaphragm returns to its original position due to demagnetization of the energizing coil (129). The electromagnet is excited again by the chip on board circuit (132) in the same manner leading the diaphragm (150) to commence a new oscillation cycle at the same frequency as that of resonance frequency of the electronic chip on board circuit (132). The switching action in the system is completed by chip on board circuit (132) which results in reciprocating movement of diaphragm (150) along with the oscillator (154) resulting in sound generation by the horn.

Figure 5 shows a cross sectional view of the diaphragm sub assembly for trumpet type electronic horn according to another embodiment of the present invention. Diaphragm sub-assembly (151¹) comprises a metal diaphragm (150⁵) and an armature (152*). The armature (152*) is connected to the diaphragm (150*) by riveting it to the diaphragm (150% Metal diaphragm is clamped to the periphery of the radial flange (112) in the housing (102). A disc plate (16O¹) and a trumpet (162^s), which is provided by welding the said trumpet (162*) to the disc plate (160*) using ultrasonic welding. A packing disc (170*) is provided for better packing between the disc plate (160*) and the diaphragm (150") so that the air pressure generated inside the diaphragm assembly (151") is not released and is fully transferred through the disc plate (160") to projectors (172¹J for obtaining maximum sound output. The disc plate (16O¹) has an aperture (not shown) in the centre to transmit the pressure produced inside the diaphragm assembly (151^s) due to reciprocating movement of the diaphragm (150*) to the projectors (172⁵). Depending on the type of sound that is required, dimensions of the projectors (172") are varied accordingly. Said air pressure built up inside the diaphragm assembly (151") when passed through the projectors (172f produce a honk sound. The honk sound distinguishes the trumpet from other horns. Both the sub-assemblies are then assembled together by a sealing ring (168¹). When power supply is provided to the terminals (142) on the terminal block (130) the magnetic force is generated around the coil (129) and the anchor bolt (126). Coil and anchor bolt get subsequently magnetized resulting in pulling of the diaphragm (150*) assembly at the centre towards the anchor bolt (126) as described previously. This reciprocating movement of the diaphragm (150^s) generates an air pressure inside the diaphragm sub-assembly which is passed through an aperture (not shown) in the disc plate (160") and through the projector (170*) in the trumpet to produce honk sound and this production of honk sound distinguishes the trumpet horns from other horns

Figure 6 is a block diagram of the chip on board circuit of the electronic horn according to one embodiment of the present invention. The chip on board circuit (132) may be used in different types of horns available and need not be limited to electronic horn comprising a switching circuit (602) coupled to a battery (600) for providing switching action. Switching circuit (602) provides a pulse train having frequency similar to the resonance frequency of the diaphragm assembly to a driver circuit (604). Switching circuit (602) has a clipping circuit (606) having a clipping means for completely clipping surge voltages which are generated in high frequency inductive coil circuits. Either a series or shunt clipper can be used as a clipping circuit. Normally a resistor in combination with a diode is used but such circuit does not provide proper protection to the entire electronic circuit components from the surge voltages

• generated due to inductive loading. According to one embodiment of the , present invention clipping means is a transil diode connected in the clipping; circuit (606) to provide better clipping. The clipping circuit (606) has the transal : diode which totally eliminates surge voltage generated due to inductive loading : v and provides better protection to the electronic circuit components from damage and malfunction. The clipping circuit (606) is further connected to a _; timer in the switching circuit (602) for outputting pulse train having frequency > similar to the resonance frequency of the diaphragm assembly. According to . one embodiment of the present invention timer circuit is normally an IC 55S or IC556 or an operational amplifier. Output from the timer is coupled to a switching means to provide switching at a frequency similar to the resonance frequency of the electromechanical system. According to one embodiment of the , present invention switching means may be a Metal Oxide-Semiconductor Field Effect Transistor (MOSFET) connected to the driving circuit. Output of the switching circuit (602) is provided to the driver circuit (604), wherein the driver ! ^■ circuit (604) comprises of an energizing coil mounted on the coil body assembly , of the horn and an electromagnetic means for energizing the coil (129).,^' According to another embodiment of the present invention, the energizing cαϋ (129) mounted on the coil body assembly is energized by electromagnetic means by passing current through the coil (129). The current thereby produces a magnetic field around the coil which pulls the diaphragm towards the coil ^! (129). The coil body assembly (116) and the anchor bolt (126) get magnetized simultaneously upon being energized by electric current and thereby puffing

17 ' .. ^{■ ■} - ^{• ' ■} :. ^{■ •} _ .

SUBSTITUTE SHEET (RUL.E 26) ; V' K_; V the diaphragm assembly at the centre towards the anchor bolt (126). Thereafter the supply of electric current is stopped by the switching circuit, resulting in return of the diaphragm in the reverse direction due to the elastic energy associated with diaphragm. The same cycle repeats whenever switching circuit starts the cycle enabling oscillatory motion to the diaphragm at the resonance frequency of the electromechanical system, hence generating sound in the horn.

In view of the present disclosure which describes the current best mode for providing a horn switching arrangement, many modifications and variations would present themselves to those skilled in the art without departing from the scope and spirit of this invention. All changes, modifications and variations coming within the meaning and range of equivalency are considered within the scope. Although the invention has been with respect to disc and trumpet type horns, the same may be useful with respect to various horn models.

Claims

We claim:

1. An electronic horn for a vehicle comprising: a housing sub-assembly; a diaphragm sub-assembly; wherein a chip on board circuit is riveted to a terminal block outside the housing and said chip on board circuit has clipping means for eliminating surge voltages.

2. An electronic horn as claimed in claim 1, wherein said clipping means is a transil diode.

3. An electronic horn as claimed in claim 1 is a disc horn.

4. An electronic horn as claimed in claim 1 is a trumpet horn.

5. An electronic horn as claimed in claim 1, having said switching circuit coupled to a battery.

6. An electronic horn as claimed in claim 1, wherein said chip is IC 555, IC 556 timer or an operational amplifier.