FIELD OF INVENTION
The Invention relates to an electronic horn provided in automotive vehicles. More particularly, the present invention relates to an electronic circuit which is responsive to variations in the horn supply voltage for maintaining a constant input power to the horn.

BACKGROUND
A typical electric horn comprises of housing with a diaphragm peripherally clamped to it, thus forming a closed casing. A magnetic plunger located at about center of the diaphragm extends into the closed chamber towards a pole piece present on the housing. An electromagnetic coil is mounted within the casing and axially around the pole piece. The electromagnetic coil is periodically energized and provides a reciprocating motion to the magnetic plunger. Thus the diaphragm attached to the plunger exhibits a resilient suspension relative to the periodic energization of the coil. The spring characteristic of the diaphragm and the mass carried by it has a resonant frequency of mechanical vibration. The electromagnetic coil is energized from a voltage source through a mechanically actuated switch which is alternately opened and closed by movement of the plunger with the diaphragm.

Although vehicle horns of the type just described have been eminently successful in the automotive industry for many years, there have been certain problems which, for a long time, have seemingly defied solution. One such problem is that of manufacturing the horn with sufficiently exacting mechanical and electrical relationships so as to obtain a high degree of operating efficiency. Particularly, such horns have not been readily adjustable to obtain operation at the maximum achievable sound pressure level for a given input voltage. Also, another problem that is present in such horns is that the frequency of periodic energization of the coil changes with change in ambient temperature prevalent.

Other problem which conventional horns face while in operation is that the contacts present in a contact break assembly are subject to sparking. The contact sparking may create high voltage spikes caused by switching of inductive load which may damage other electronic circuits present in the vehicle. The contacts may also get burnt due to arcing or oxidation resulting into their deterioration over a period of time.

OBJECT OF THE INVENTION
The object of the present invention is to provide an electronic horn which exhibits optimum sound pressure level for a given input power thus addressing at least some of the problems described in the prior art.

SUMMARY OF THE INVENTION
Accordingly, the present invention relates to an electronic horn provided in an automotive vehicle and being connectable to a voltage source provided therein, said electronic horn comprising a diaphragm; a ferromagnetic plunger locatable at about a central part of the said diaphragm; an electromagnetic coil connected to said voltage source via an electrical path; a switching circuit located in the electrical path and being operable to allow flow of electric current through the electromagnetic coil for a time period TON and for disallowing flow of current through the electromagnetic coil for a time period TOFF, so as to cause excitation of the electromagnetic coil and thereby causing the ferromagnetic plunger to exhibit reciprocating motion; characterized by a voltage sensing arm being connected to the voltage source such that the same is parallel to the electrical path; a temperature sensor; and a microcontroller storing a user inputted initial value of (TON + TOFF), said microcontroller being connected to the voltage sensing arm and the temperature sensor for sensing a value of the input voltage and a value of temperature prevalent respectively and for producing a control signal for modifying the values of TON and TOFF, such that, a ratio between TON and TOFF is varied based on the value of the input voltage thus sensed by the voltage sensing arm; and the value of (TON + TOFF) after modification is equal to the user inputted initial value of (TON + TOFF) despite any change in the value of temperature prevalent.

According to another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the user inputted initial value of (TON + TOFF) is equal to resonance frequency of the diaphragm.

According to yet another aspect of the present invention the electronic horn for an automotive vehicle is described, wherein the initial value of (TON + TOFF) is inputted to the microcontroller by a user via a tuning circuit.

According to still another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the tuning circuit is operatively couple to the microcontroller temporarily and is detached thereafter.

According to an aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the switching circuit is operatively coupled to the microcontroller via a totem pole circuit for enabling switching operation, said totem pole circuit comprising totem pole transistors.

According to another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the totem pole transistors are connected in a push pull configuration.

According to yet another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the totem pole circuit is operatively coupled to a preliminary regulator, the said preliminary regulator comprising a totem pole circuit driving means for providing driving voltage to the totem pole circuit.

According to still another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the preliminary regulator further comprises of overload protection means, the said overload protection means configured to protect the microcontroller and the totem pole circuit from high voltage transients.

According to another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the microcontroller is operatively coupled to a regulated voltage generation means for providing regulated input voltage.

According to yet another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the switching circuit comprises of a switching element, the said switching element being a power MOSFET.

According to still another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein a snubber circuit is connected across drain and source terminals of the power MOSFET to ward off any unnecessary occurrence of electromagnetic interference (EMI).

According to another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the switching circuit, the voltage sensing arm, the microcontroller, the totem pole circuit, the totem pole circuit driving means and the regulated voltage generation means are placed upon a circuit board.

According to yet another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the electromagnetic coil is wound around a cylindrical portion of a bobbin structure.

According to still another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the circuit board and the bobbin structure are housed within an open casing and said opening is covered by the diaphragm.

According to another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the bobbin structure is mounted securely on an inner surface of the casing.

According to yet another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the circuit board is mounted securely on the bobbin.

According to still another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein a damper is provided between the circuit board and the inner surface of the casing, said damper dampens the effect of any vibration produced in the casing on said circuit board.

According to one more aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the output voltage of the voltage source lies in the range of 8V to 40V.

According to another aspect of the present invention, the electronic horn for an automotive vehicle is described, wherein the voltage source is either of 12V or 24V.

BREIF DESCRIPTION OF THE DRAWINGS
Further aspects and advantages of the present invention will be readily understood from the following detailed description with reference to the accompanying drawings. Reference numerals have been used to refer to identical or similar functionally similar elements. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention wherein:

Figure 1a, illustrates a top view of the diaphragm assembly in accordance with an embodiment of the present invention.

Figure 1b, illustrates a bottom view of the diaphragm assembly in accordance with an embodiment of the present invention.

Figure 1c, illustrates a side view of the diaphragm assembly in accordance with an embodiment of the present invention.

Figure 2, illustrates a perspective view of circuit board provided inside the casing in accordance with an embodiment of the present invention.

Figure 3a, illustrates a perspective view of the bobbin structure in accordance with an embodiment of the present invention.

Figure 3b, illustrates a side view of a damper in accordance with an embodiment of the present invention.

Figure 3c, illustrates a perspective view of connector assembly in accordance with an embodiment of the present invention.

Figure 4, illustrates a block diagram of an electronic horn in accordance with an embodiment of the present invention.

Figure 5, illustrates a schematic diagram of an electronic horn in accordance with an embodiment of the present invention.

Skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings, there is shown an illustrative embodiment of the invention electronic horn. It should be understood that the invention is susceptible to various modifications and alternative forms; specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It will be appreciated as the description proceeds that the invention may be used in other types of horns and may be realized in different embodiments.

Before describing in detail embodiments it may be observed that the novelty and inventive step that are in accordance with the present invention reside in the construction of the electronic horn, accordingly, the drawings are showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such setup or device. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus. The following paragraphs explain various aspect of the present invention with reference to figures.

Figure 1a, 1b and 1c show top, bottom and side view of a diaphragm assembly (100) respectively in accordance with the subject invention. The figures illustrate the diaphragm (101) wherein a ferromagnetic plunger (102) is located at about a central location. A bolt (103) protrudes through the center of the diaphragm and a resonator plate (104) and tightly secures the said ferromagnetic plunger (102) to the diaphragm (101) with a nut (105) and a steel washer (106).

In horn, the combined mass of the diaphragm (101), the plunger (102) and the resonator plate (104) along with the spring rate of the diaphragm determine the resonant frequency of the diaphragm assembly. As discussed above, this type of horn operates in such a manner that the ferromagnetic plunger (102) physically strikes a pole piece (201) once, and once only, during each cycle of the vibration of the diaphragm (101). The force of striking action is transmitted through the plunger (102) to the center of the resonator plate (104) and causes it to vibrate at or near its resonant frequency. The sound output from the horn is that generated by the vibration of the resonator plate (104), the sound waves being coupled directly from the resonator plate (104) to the surrounding atmosphere.

Figure 2 shows an open metal casing (200) of the horn. The opening is covered by the diaphragm (101) which is peripherally clamped or crimped to it, thus forming a closed casing. An aperture in an end wall of the casing holds the pole piece (201) towards which the plunger (102) extends when the diaphragm is affixed to the casing. The casing comprises a bobbin structure (202) which is placed axially around the pole piece (201). An electromagnetic coil is wound around a cylindrical portion of the bobbin structure (202) and surrounds adjacent ends of the plunger (102) and the pole piece (201). The bobbin structure (202) is provided with at least three pillars (203) over which a circuit board (204) is securely mounted. The extra height of pillars (203) is diffused by heat spinning operation, thus providing firmness to circuit board (204). Any unnecessary vibration caused during operation of horn is warded off by provision of atleast one damper (205) which is placed between inner surface of the casing (200) and the circuit board (204). A connector assembly (206) placed on the bobbin structure (202) and between a cut-out on the circuit board (204) acts as an intermediary between electrical and electronic components of the horn. In another embodiment of the present invention, the circuit board (204) may be placed outside the metal casing (200).

Figure 3a illustrates an individual perspective view of the bobbin structure (202). A cylindrical portion can be seen around which the electromagnetic coil is wound.

Similarly, Figure 3b and Figure 3c illustrate individual view of damper (205) and connector assembly (206) respectively. The damper (205) is made up of silicon rubber and has a high capability of sustaining any large vibration produced within the horn while in operation. The base (2051) of the damper (205) is affixed to the inner surface of the casing (200) with the circuit board (204) placed around its neck (2052). A plurality of dampers can be placed to provide an effective result. As it can be seen in figure 3, the head (2053) of the damper (205) protrudes out of the circuit board (204). Referring now to the connector assembly (206) in figure 3c is placed on the bobbin structure (202) and between a cut out present on the circuit board (204). The connector assembly (206) connects circuit present on the circuit board (204) with the electromagnetic coil and the voltage source of the automotive vehicle. More particularly, the connector assembly (206) acts as an intermediary between input and output electrical signals.

Now referring to Fig. 4 and Fig. 5 illustrate a block diagram and a schematic diagram of electronic horn respectively. The electronic circuit mainly comprises of a microcontroller (406) and a switching circuit (403) with rest of the components operatively coupled to them. The horn has its electromagnetic coil (402) connected to positive terminal of the DC voltage source via an electrical path. The negative terminal of the DC voltage source is grounded. A diode D7 is connected between electromagnetic coil and the positive terminal of the voltage source to stop any back spikes coming in from the electromagnetic coil (402), thus saving other electric circuits present in the automotive vehicle. A switching circuit (403) preferably comprising a power MOSFET M2 as a switching element is located on the electrical path between a ground terminal and the electromagnetic coil (402). More specifically the power MOSFET M2 has its source connected to ground terminal and its drain connected to electromagnetic coil (402) and further to the voltage source. A snubber circuit comprising capacitors C18 and C28 (411) is connected across drain and source terminals of the power MOSFET M2 to ward off any unnecessary occurrence of electromagnetic interference (EMI). The gate of the power MOSFET M2 is connected to output pin of the microcontroller (406) via a totem pole circuit (404). The microcontroller (406) is adapted to generate a control signal for controlling the switching of power MOSFET M2. The control signal is a pulse width modulated signal whose frequency (TON + TOFF) depends upon the resonant frequency of the coil and pulse width (TON) depends upon the value of instantaneous voltage of the voltage source. The microcontroller (406) is connected to voltage source through a voltage sensing arm (408) which is parallel to the electrical path. The voltage sensing arm (408) comprises of a voltage divider circuit comprising resistors R29 and R30, thus, providing necessary voltage to the microcontroller (406). The microcontroller (406) receives a regulated voltage supply VCC at its input pin through a regulated voltage generation means (407). A zener diode D9, NPN transistor Q10 and resistor R27 act as voltage regulator to provide a regulated voltage VCC at its input pin. The regulated voltage generation means (407) is connected to the voltage source via a preliminary regulator (405). The said preliminary regulator (405) comprises of totem pole circuit driving means and overload protection means. The totem pole circuit driving means provides driving voltage to the totem pole circuit (404) and the overload protection means protects components such as microcontroller (406) and totem pole circuit from high voltage transients (404).

Referring now, specifically to the totem pole circuit (404) connected between power MOSFET M2 and the microcontroller (406). The totem pole circuit (404) comprises of a level shifter which is connected at output pin of the microcontroller (406). The level shifter comprises of resistors R36 and R38 and an NPN transistor Q8 and shifts level of control signal outputted from the microcontroller (406) to a desired level. This shift in level of control signal is fed to totem pole transistors Q6 and Q7 through a resistor R13. R13 is used to prevent overloading of totem pole bases. Totem pole transistors Q6 and Q7 are connected in complimentary mode. More particularly, totem pole transistors are connected in a push pull configuration. A resistor R15 and a zener diode D6 connected between totem pole transistors and power MOSFET M2 help in clamping gate voltage. The totem pole circuit (404) receives its drive voltage from the totem pole circuit driving means which forms part of the preliminary regulator (405). The preliminary regulator (405) as mentioned earlier is connected between voltage source and the regulated voltage generation means (407).

In preliminary regulator (405) the totem pole circuit driving means is formed by resistor R22, zener diode D3 and Darlington pair Q9. Resistors R23 and R24 along with an integrated circuit U5 comprise an overload protection means. More specifically, resistors R23 and R24 and IC U5 provide over voltage shut down to preliminary regulator circuit components, thus protecting overall circuit and more specifically the microcontroller (406) and the totem pole circuit (404) from overload. A diode D10 provided prior to preliminary regulator (405) protects totem pole circuit driving means element Q9 from reverse polarity. Another element capacitor C29 is provided between positive and negative terminals of the voltage source and prevents the electronic circuit from electrostatic discharge. Also, elements C17, C20, C19 and C32 present in preliminary regulator (405) and regulated voltage generation means (407) provide noise and harmonic protection to the circuit.

Now specifically, referring to procedure of initial frequency (TON + TOFF) tuning of the control signal outputted from the microcontroller (406). The initial tuning is done with the help of a tuning circuit (410). This may be done by a user during functional tests of the horn. The tuning circuit (410) is operatively coupled to the microcontroller (406). The user tunes the frequency (TON + TOFF) of the control signal to resonant frequency of the diaphragm. Once, the resonant frequency is achieved the value is inputted and stored within the microcontroller (406). During operation of the horn, the frequency (TON + TOFF) of the control signal is equal to value initially tuned and inputted by the user in the microcontroller (406). The tuning circuit (410) is detached from the circuit board (204), once the initial tuning has been done.

The horn further has a provision of frequency (TON + TOFF) adjustment of control signal which may change with change in ambient temperature prevalent inside the horn during operation of the horn. For this provision of frequency (TON + TOFF) adjustment, a temperature sensor (409) is provided inside the horn to sense the ambient temperature of the horn. The temperature sensor (409) feeds its sensed value of temperature to the microcontroller (406) which adjusts any change in frequency (TON + TOFF) of the control signal equal to resonance frequency of the diaphragm. In another embodiment, the temperature sensor (409) may be located near the electromagnetic coil to sense any change in temperature of the coil.

In addition, to frequency (TON + TOFF) tuning of the horn on the basis of temperature, the microcontroller (406) of the present invention is capable of modifying or modulating pulse width (ratio between TON and TOFF) of the control signal on the basis of instantaneous value of input voltage sensed by the voltage sensing arm (408) thus, maintaining sound consistency at various voltage levels. Here, TON is the time period for allowing flow of electric current through the electromagnetic coil (402) and TOFF is the time period for disallowing the flow of electric current through the electromagnetic coil (402). In other words, TON is the time period the electromagnetic coil (402) takes for charging and TOFF is the time period the electromagnetic coil (402) takes for discharging. In simpler words, TON or ratio between TON and TOFF may be construed as to be the duty cycle of the horn and more specifically of the electromagnetic coil (402).

The electronic circuit as described above is a standard design and is capable of working for a voltage source of 12V and as well as 24V. The electronic circuit is a dual tone horn wherein a dual tone circuit (412) is connected to the microcontroller (406). More particularly, the horn is capable of working for a voltage supply which may vary from 8V to 40V.
In addition of being used as an electronic horn, the above invention can be used as a siren or a burglar alarm in automotive vehicles, thus eliminating the need of having an independent circuit for siren and the siren.

While the particular preferred embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the teachings of the invention. It is therefore contemplated that the present invention covers any and all modifications, variations or equivalents that fall within the scope of the basic underlying principles disclosed above and claimed therein.

ADVANTAGES OF PRESENT INVENTION
1. The horn of the present invention is capable of maintaining sound consistency at various voltage levels.
2. The electronic circuit is a standard design for voltage supply of 12V and 24V.
3. The effect of temperature variation inside the horn is nullified.
4. The electronic circuit is capable of operating within wide voltage range.
5. The horn has a provision for providing protection to the electronic circuit in case of overload.
6. The horn is EMI/EMC protection qualified.
7. The horn provides reverse battery protection.
8. The effect of vibration on circuit board during operation of horn is nullified.
9. The life span of present horn is enhanced by 5 times over those of conventional horns.

We Claim:

1. An electronic horn provided in an automotive vehicle and being connectable to a voltage source provided therein, said electronic horn comprising:
a diaphragm;
a ferromagnetic plunger locatable at about a central part of the said diaphragm;
an electromagnetic coil connected to said voltage source via an electrical path;
a switching circuit located in the electrical path and being operable to allow flow of electric current through the electromagnetic coil for a time period TON and for disallowing flow of current through the electromagnetic coil for a time period TOFF, so as to cause excitation of the electromagnetic coil and thereby causing the ferromagnetic plunger to exhibit reciprocating motion;
characterized by:
a voltage sensing arm being connected to the voltage source such that the same is parallel to the electrical path;
a temperature sensor; and
a microcontroller storing a user inputted initial value of (TON + TOFF), said microcontroller being connected to the voltage sensing arm and the temperature sensor for sensing a value of the input voltage and a value of temperature prevalent respectively and for producing a control signal for modifying the values of TON and TOFF, such that:
a ratio between TON and TOFF is varied based on the value of the input voltage thus sensed by the voltage sensing arm; and
the value of (TON + TOFF) after modification is equal to the user inputted initial value of (TON + TOFF) despite any change in the value of temperature prevalent.

2. The electronic horn for an automotive vehicle as claimed in claim 1, wherein the user inputted initial value of (TON + TOFF) is equal to resonance frequency of the diaphragm.

3. The electronic horn for an automotive vehicle as claimed in claims 1 and 2, wherein the initial value of (TON + TOFF) is inputted to the microcontroller by a user via a tuning circuit.

4. The electronic horn for an automotive vehicle as claimed in claim 3, wherein the tuning circuit is operatively couple to the microcontroller temporarily and is detached thereafter.

5. The electronic horn for an automotive vehicle as claimed in claim 1, wherein the switching circuit is operatively coupled to the microcontroller via a totem pole circuit for enabling switching operation, said totem pole circuit comprising totem pole transistors.

6. The electronic horn for an automotive vehicle as claimed in claim 5, wherein the totem pole transistors are connected in a push pull configuration.

7. The electronic horn for an automotive vehicle as claimed in claim 5, wherein the totem pole circuit is operatively coupled to a preliminary regulator, the said preliminary regulator comprising a totem pole circuit driving means for providing driving voltage to the totem pole circuit.

8. The electronic horn for an automotive vehicle as claimed in claim 7, wherein the preliminary regulator further comprises of overload protection means, the said overload protection means configured to protect the microcontroller and the totem pole circuit from high voltage transients.

9. The electronic horn for an automotive vehicle as claimed in claim 1, wherein the microcontroller is operatively coupled to a regulated voltage generation means for providing regulated input voltage.

10. The electronic horn for an automotive vehicle as claimed in claim 1, wherein the switching circuit comprises of a switching element, the said switching element being a power MOSFET.

11. The electronic horn for an automotive vehicle as claimed in any of the preceding claims, wherein a snubber circuit is connected across drain and source terminals of the power MOSFET to ward off any unnecessary occurrence of electromagnetic interference (EMI).

12. The electronic horn for an automotive vehicle as claimed in any of the preceding claims, wherein the switching circuit, the voltage sensing arm, the microcontroller, the totem pole circuit, the preliminary regulator and the regulated voltage generation means are placed upon a circuit board.

13. The electronic horn for an automotive vehicle as claimed in any of the preceding claims, wherein the electromagnetic coil is wound around a cylindrical portion of a bobbin structure.

14. The electronic horn for an automotive vehicle as claimed in any of the preceding claims, wherein the circuit board and the bobbin structure are housed within an open casing and said opening is covered by the diaphragm.

15. The electronic horn for an automotive vehicle as claimed in any of the preceding claims, wherein the bobbin structure is mounted securely on an inner surface of the casing and is integrated with a connector assembly, said connector provides input and output contacts.

16. The electronic horn for an automotive vehicle as claimed in any of the preceding claims, wherein the circuit board is mounted securely on the bobbin.

17. The electronic horn for an automotive vehicle as claimed in any of the preceding claims, wherein atleast one damper is provided between the circuit board and the inner surface of the casing, said damper dampens the effect of any vibration produced in the casing on said circuit board.

18. The electronic horn for an automotive vehicle as claimed in claim 1, wherein the output voltage of the voltage source lies in the range of 8V to 40V.

19. The electronic horn for an automotive vehicle as claimed in claim 18, wherein the voltage source is either of 12V or 24V.

20. An electronic horn substantially as herein described with reference to the foregoing description and accompanying drawings.