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car horn

2021-02-10 408
Working principle
The car electric horn produces sound by the vibration of the metal diaphragm. Automobile electric horn is composed of iron core, magnetic coil, contact, armature, diaphragm and so on. When the driver presses the horn switch, the current passes through the coil through the contact, and the coil generates magnetic force to attract the armature, forcing the diaphragm to move. The armature moves to disconnect the contact, the current is interrupted, and the magnetic force of the coil disappears. The diaphragm is elastic and spring sheet. Under the action, it returns to the original position together with the armature, the contact closure circuit is connected again, and the current flows through the contact through the coil to generate magnetic force, and the above action is repeated. In this way, the diaphragm keeps vibrating and generates sound. The sounding board and the diaphragm are rigidly connected, which can make the vibration smooth and make the sound more pleasing (ie the principle of electromagnet).
Classification and principle
According to the sound power, car horns are divided into two types: air horn and electric horn; according to their appearance, they are divided into three types: cylindrical, spiral and basin; according to the sound frequency, they are divided into two types: tweeter and woofer.

car horn

Air horn
The working principle of the air horn is to use the airflow of compressed air to make the metal diaphragm vibrate and produce sound, so it must be able to be used above the car with an air compressor. Generally, air horns are installed on buses and heavy trucks, especially when long-distance transport vehicles are driving in mountainous areas or curved roads, they use air horns to sound, which can effectively remind pedestrians and the other drivers to pay attention. Because the air horn has a large volume, a good residual sound, the sound is pleasing and spreads far. Air horns are generally cylindrical, and use two horns, high pitch and low pitch, to work together.
Electric horn
The working principle of the electric horn is to use electromagnetic attraction to vibrate the metal diaphragm to produce sound. It is a kind of horn widely used in automobiles. According to the structure, it is divided into three types: cylindrical, spiral and basin. Generally, it is made into spiral or basin.
The commonly used electric horns can be divided into two types: mechanical and electronic according to their working mode. Among them, electronic horns are divided into contact type and non-contact type. The contact-type electric horn uses the closing and opening of the contacts to control the on and off of the excitation current in the electromagnetic coil, so that the core (or armature) can move up and down at a certain frequency. And the vibrating metal diaphragm produces sound. The non-contact electric horn uses electronic circuits to control the on-off of the excitation current in the electromagnetic coil, so that the core moves at a certain frequency and drives the metal diaphragm to vibrate to produce sound.
The electric horn has the advantages of convenient energy, simple structure, small size, small quality, low noise, easy maintenance, loud sound and pleasant sound quality.
The non-contact electric horn overcomes the shortcomings of the contact type electric horn that the contact is ablated and oxidized, which causes the horn to change its sound, and is more durable. And its tone and volume are easier to adjust than the contact type, so it is the development direction of car horns.

1. Spiral electric horn
The diaphragm continuously vibrates to emit a certain tone of sound wave, and the sound is strengthened through the soundboard and speaker tube and then transmitted. The sound board is rigidly connected with the diaphragm, and it produces accompanying sound when it vibrates, enhancing the volume and improving the timbre, making the sound pleasant to the ears. A capacitor is connected in parallel between the contacts. It plays the role of extinguishing the arc, protecting the contacts, and improving the tone.

2. Pot-shaped electric horn
The working principle is the same as that of the spiral electric horn, and the structure is basically the same, except that there is no speaker tube, and the sound is resonated by the sound board. In addition, the magnetic circuit uses a solenoid type electromagnet instead of an E-type iron core. The solenoid type has a smaller volume and a stronger electromagnetic attraction than the E-type electromagnet.

Horn relay
When a single electric horn is installed on a car, it is generally directly controlled by the horn button. However, in order to obtain a more pleasing sound effect, most cars often install high and low speakers, or even high, medium, and low tones. When two or one electric speakers work at the same time, the current It can reach 15A or above 20A. If the horn button is used for direct control, the high current will quickly burn out the horn button, so a horn relay is used.

The button controls the on and off of the current in the relay coil, and then controls the horn through the relay contact. Horn relays used on 12V electric vehicles generally require closing voltage not greater than 6V and release voltage not less than 3V; the relay coil is usually 1000 turns, and the resistance at 20°C is 26Ω; the rated current of the relay is generally more than 20A. The rated current of the basin-shaped electric horn is usually 3A~4A. Although the current is not large, in order to improve the service life of the button, many cars are still equipped with a horn relay.
The working principle of the horn relay is shown in Figure 4.

Press the horn button 3, the relay coil 2 is energized, and the contact arm 1 is engaged with the contact 5 to connect the power circuit of the horn. Loosen the horn button 3, the relay coil 2 loses power, the contact 5 is separated from the contact arm 1, and the horn does not work.
When adjusting, note that the gap between the iron core and the armature must be uniform, flat, and not skewed, otherwise it is easy to collide with each other during work, causing the horn to produce harsh noise.
The volume of the electric horn is related to the current passing through the horn coil. The larger the current, the louder the volume, and vice versa. Adjusting the contact pressure can change the volume. The adjustment of speaker volume and sound quality are interrelated, so it needs to be adjusted repeatedly to get the best sound.
(1) Always keep the appearance of the speaker clean, and the wiring must be firm.
(2) Frequently check and tighten the fixing screws of the horn and bracket to ensure reliable grounding.
(3) The fixing method of the horn has a great influence on its pronunciation. In order to make the sound of the horn normal, the horn cannot be installed rigidly, so it is fixed on the buffer bracket, that is, a leaf spring or rubber pad should be installed between the horn and the fixed bracket.
(4) Check the generator output voltage frequently. Too high voltage will burn out the horn contacts, and too low voltage (lower than the rated voltage of the horn) the horn will make abnormal sounds.
(5) When washing the car, do not directly flush the horn with water, so as to prevent water from entering the horn and making the horn silent.
(6) When overhauling the horn, pay attention to the positions of the metal pads and insulating pads, and do not install them wrong.
(7) The continuous sound of the speaker should not exceed 10s to avoid damage to the speaker.
(8) Do not put all kinds of foreign objects into the speaker to avoid abnormal sound.
Performance indicators and parameters
1. Rated power (W)
The rated power of the speaker refers to the output power that the speaker can work for a long time, also known as the undistorted power, which is generally marked on the nameplate at the back of the speaker. When the speaker is working at the rated power, the voice coil will not produce overheating or mechanical vibration overload, etc., and the sound emitted does not show distortion. Rated power is an average power, but in fact the speaker works in a variable power state, which varies with the strength of the input audio signal. In weak music and sound signals, the peak pulse signal will exceed the rated power many times, due to the longer duration. Short without damaging the speakers, but distortion may occur. Therefore, in order to ensure good sound quality when the peak pulse occurs, the speaker needs to leave enough power headroom. The maximum power that a general speaker can follow is 2-4 times the rated power.
2. Frequency characteristics (Hz)
The frequency characteristic is an index to measure the width of the audio band of the speaker. The high-fidelity playback system requires that the speaker system should be able to reproduce the human audible range of 20Hz-20000Hz. Since it is not easy to achieve this sound range with a single speaker, the current high-fidelity speaker system uses three speakers of high, medium and low to achieve full-band playback coverage. In addition, the frequency characteristics of high-fidelity speakers should be as flat as possible, otherwise it will introduce frequency distortion in the playback. The high-fidelity playback system requires that the frequency characteristic unevenness of the speaker in the playback frequency range is less than 10dB.
3. Rated impedance (Ω)
Impedance refers to the ratio of the voltage to the current of the input signal of the car speaker, and its unit is ohm (Ω). In layman's terms, impedance is the resistance presented by the car speaker to the current. Impedance is not equal to resistance, but includes resistance and reactance, that is, three parts including resistance and inductance, and inductance and capacitive reactance generated by capacitance. The sum of the three on the vector.
Under the same voltage, the higher the impedance, the smaller the current, and the lower the impedance, the greater the current. When the power amplifier is the same as the output power, a low-impedance car speaker can obtain a larger output power, but if the impedance is too low, it will cause underdamping and bass degradation. Generally, the lower the impedance of a car speaker, the more difficult it is to push. The impedance is not a constant value, but constantly changes and fluctuates with the frequency of the music being played. It may be as high as ten or twenty ohms at a certain frequency, or as low as one ohm or below at a certain frequency. The lowest impedance value between the resonance peaks at the resonance frequency is used as its nominal value. Currently, the impedance of most car speakers is 2-8 ohms. The preferred values of speaker impedance specified by my country's national standards are 4Ω, 8Ω, and 16Ω (the international standard recommended value is 8Ω).
4. Harmonic distortion (TMD%)
There are many kinds of speaker distortion, common harmonic distortion (mostly caused by the uneven magnetic field of the speaker and distortion of the vibration system, often generated at low frequencies), intermodulation distortion (because two signals of different frequencies are added to the speaker at the same time, Deterioration of sound quality caused by mutual modulation) and transient distortion (because the inertia of the vibration system cannot follow the change of the signal, causing signal distortion) and so on. Harmonic distortion refers to the addition of harmonic components that are not in the original signal during playback. The harmonic distortion of the speaker comes from the non-uniform magnetic field of the magnet, the characteristics of the diaphragm, and the displacement of the voice coil. At present, the harmonic distortion index of better speakers is not more than 5%.
5. Output sensitivity (dB/W)
Most hosts have a set of RCA outputs, which can output low-voltage signals, so that they can be directly transmitted from the host to the external power amplifier. The host usually has 1-3 pairs of RCA outputs. Of course, the more the better, the frequency The division will be more detailed. The output sensitivity is actually the output voltage of RCA: generally between 0.2V-4V. Choose a host with high voltage output, such as 6V, which will greatly help the output power of the audio system.
6. Directivity

The sound pressure frequency characteristics of the loudspeaker for radiation in different directions are different. This characteristic is called the directivity of the loudspeaker. It is related to the caliber of the loudspeaker. The directivity is sharp when the caliber is large, and the directivity is wide when the caliber is small. Directivity is also related to frequency. Generally speaking, there is no obvious directivity for low-frequency signals below 250 Hz. It has obvious directivity to high frequency signals below 1.5kHz.

7. Physical parameters
The parameters of the loudspeaker refer to the specific various performance parameter values of the loudspeaker tested by a dedicated loudspeaker test system.
The parameters mainly include: Z, Fo, η0, SPL, Qts, Qms, Qes, Vas, Mms, Cms, Sd, BL, Xmax, Gap gauss. The following are the physical meanings of these parameters.
Z: refers to the resistance value of the speaker, including: rated impedance and DC impedance. (unit: ohm/ohm), usually refers to the rated impedance. The rated impedance of the speaker Z: is the minimum after the first maximum value of the impedance curve Impedance modulus, it is the basis for calculating the electrical power of the speaker. DC impedance DCR: refers to the impedance value measured by a DC signal when the voice coil coil is stationary. What we usually call 4 ohms or 8 ohms is Refers to the rated impedance.
Fo (lowest resonance frequency) refers to the frequency corresponding to the first maximum value of the speaker impedance curve. Unit: Hertz (Hz). The impedance curve of the speaker is measured by the constant current method or constant voltage method under normal working conditions. Obtain the curve of speaker impedance modulus with frequency.
η0 (the efficiency of the speaker): refers to the ratio of the output sound power of the speaker to the input electric power.
SPL (Sound Pressure Level): refers to the sound pressure generated by the speaker at a point 1m away from the speaker on the reference axis when a voltage with a rated impedance of 1W is applied to the speaker. Unit: decibel (dB).
Qts: The total quality factor value of the speaker.
Qms: The mechanical quality factor value of the speaker.
Qes: The electrical quality factor value of the speaker.
Vas (effective volume of the horn): refers to the volume when the sound compliance of the air enclosed in a rigid container is equal to the sound compliance of the speaker unit. Unit: liter (L).
Mms (vibration mass): refers to the total mass of the components that participate in the vibration of the speaker during the movement, including the drum paper part, the voice coil, the elastic wave, and the air quality involved in the vibration. Unit: grams (gram).
Cms (Li Shun): Refers to the compliance of the supporting parts of the speaker vibration system. The larger the value, the softer the entire vibration system of the speaker. Unit: mm/Newton (mm/N).
Sd (vibration area): refers to the effective vibration area of the drum paper/diaphragm during the vibration of the speaker. Unit: square meter (m2).
BL (Magnetic Force): The product of the gap magnetic induction intensity and the effective voice coil line length. Unit: (T*M).
Xmax: The linear stroke of the voice coil during vibration. Unit: millimeter (mm).
Gap Gauss: Gap magnetic induction intensity value. Unit: Tesla (Tesla).
The main reasons why the horn does not sound or the sound is hoarse are insufficient battery storage, damage to the horn relay and buttons, and damage to the horn. details as follows:
1. Check the sound of the horn. If you feel that the sound is not clear, crisp, deep and weak, it is mostly caused by poor contact.
2. Press the switch of the horn repeatedly. If the horn sometimes sounds and sometimes does not sound, the contacts inside the switch are mostly not in contact.
3. Rotate the steering wheel left and right. If there is a loud "hissing" friction sound, you can spray some grease into the relevant joints.
4. If the horn does not sound at all, first check the fuse to see if it is blown, then unplug the horn and use a multimeter to measure whether there is electricity when pressing the horn switch. If there is no electricity, check the horn harness and horn relay; if there is electricity, it is the problem of the horn itself. At this time, you can also try to adjust the adjustment nut on the horn to see if it can sound. If it still does not sound, you need to replace the horn.
5. If the sound of the horn is dull, it is likely that the horn itself is faulty. At this time, just knock on the horn, and most of it can be improved. All the connectors are not in good contact, especially the wires around the steering wheel, which are prone to wear due to frequent use.
6. Lax sealing is easy to be damp. Although the inside of the horn is airtight, if the sealing is not tight, go to the car wash. It is easy to get into the mist or there is water vapor in the air in the internal space. Water vapor will easily cause the contacts to become damp and not work properly. .
7. The working condition of the horn is related to the working condition of the battery when the car is at low speed. If the energy of the battery is reduced, the sound of the horn will also be reduced. Check whether the storage battery is normal.
In addition, when you press the horn button, you can use a multimeter or inspection light to check to see if there is electricity flowing to the terminal of the horn. If there is current to the terminal but the horn does not sound, use the inside of the horn. Adjust the nut to adjust:
1. Loosen the fixing nut of the adjusting screw of the horn, and then turn the adjusting nut. The direction of rotation will vary depending on the function of the horn, so it is difficult to say which side to turn, but you must first turn a little bit, then try to honk the horn, and then turn it further.
2. Fix the adjusting nut where the horn sound is best.
3. Fix the fixing nut of the screw.
4. If the volume is insufficient, measure the voltage at the terminal connected to the speaker and compare it with the voltage of the battery. If the voltage is low, check the connection points and lines of the wiring.

After the above tests, the situation of no sound of the horn can basically be solved. Usually, attention should be paid to the problems of contact ablation and poor contact of the joints. Qiqiwang reminds us that if the horn is faulty, try to seek professional maintenance technicians.

Help, don't change the horn blindly, and pay attention to the choice of the horn.
Use attention
1. When washing the car, remember to prevent the horn from getting wet. If the horn is in water, blow it dry as soon as possible.
2. Try not to always press the horn for a long time, which may cause premature ablation of the horn contacts.
3. If the speaker fails, try to seek the help of a professional maintenance technician. Do not change the speaker blindly, which may cause unnecessary waste.
Related Laws
In the traffic laws, the use of car horns has been stipulated as follows:
1. When a motor vehicle is approaching sharp bends, the top of a ramp and other road sections that affect the safe visual range, and when overtaking or in an emergency, it should slow down and honked.
2. When a motor vehicle encounters a vehicle in front of it parked in a queue or is driving slowly, it shall stop and wait or drive in sequence, and shall not enter non-motorized vehicle lanes or sidewalks, and shall not honk to urge vehicles or pedestrians.
In other words, the role of car horns is to warn in advance on special roads, and to warn in certain emergency situations to ensure traffic safety.
Common malfunctions
1. Poorly sealed and easy to be damp: Although the inside of the horn is airtight, if it enters the mist or water vapor in the internal space when washing the car, the water vapor will easily cause the contacts to be damp and not work properly.
2. Poor contact of the solenoid coil terminals: Some horns internal solenoid coil enameled wire terminal joints are crimped by aluminum metal rivets, which are not firmly welded. If the insulating paint on the enameled wire on the end is not clean or the rivet crimping is not firm, it is easy to produce The false connection failure causes the speaker to work badly. This kind of failure is due to the quality of the speaker, which cannot be repaired and can only be replaced with a new one.
3. Contact ablation: If you press the horn for a long time, it is easy to cause the horn contact to ablate and generate impedance. The current flowing through the electromagnetic coil will be weakened, and the electromagnetic attraction will not attract the armature to drive the diaphragm to vibrate normally, resulting in hoarse or even no sound. . But when the horn is kept on, if the instantaneous strong current passes through the impedance, it can still work normally, so it will be good and bad.
There are several situations where the car horn does not sound. One is that it does not sound sometimes, the other is that it sounds awkward, and the other is that the car horn does not sound at all.
1. Sometimes it does not sound. Press the horn switch. If the horn sometimes sounds and sometimes does not sound, it is mostly because the contacts inside the horn switch are not in good contact, and some are also problems with the horn itself.
2. Hoarse voice. It is mostly due to poor contact of the plug, especially the contacts around the steering wheel. Due to frequent use, the contacts are likely to wear out.
3. No sound at all. First check the fuse to see if it is blown, then unplug the horn, use a multimeter to measure whether there is electricity when pressing the horn switch. If there is no electricity, check the horn harness and horn relay; if there is electricity, it is the problem of the horn itself. At this time, you can also try to adjust the adjustment nut on the horn to see if it can sound. If it still does not sound, you need to replace the horn.
Auto repair experts say that in the failure of car horns, the problem is often the failure of the horn itself. When the horn does not sound, the common faults are nothing more than 3 points, namely the horn itself, the horn switch contact and the horn wiring harness. When the car horn fails, it can be resolved according to the above classification. It can't be solved, it is recommended to go to the auto repair shop.

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