JPH0139596B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sound generator or contactless buzzer, particularly for use in a motor vehicle to provide an audible and visual alarm indication upon the occurrence of one or more predetermined conditions. The present invention relates to a sound generator particularly suitable for

Under current federal regulations, if you attempt to operate a motor vehicle without wearing your seat belt properly, you will receive a penalty of 4 to 8.
It is necessary to equip all motor vehicles with a device that gives a second audible warning. Typically such devices take the form of a buzzer unit controlled by a bimetallic timer circuit adjusted to expire within an appropriate amount of time. Although the warning light must be activated at the same time as the buzzer, federal regulations require that the audible alarm be activated regardless of the absence or failure of the warning light. The same buzzer may be used to provide a "headlight left on" alarm and a "key left in ignition" alarm.

It is important that this type of automotive acoustic generator can be easily produced at low cost, and above all,
It is important to be able to produce a uniform sound and maintain the same sound under all conditions of use. In particular, the sound generated must be of uniform magnitude and must be constant in pitch over a wide range of ambient temperature and pressure conditions.

That is, automobiles are generally operated in areas where the temperature can vary from -40 to 50 degrees Celsius to +120 degrees Celsius, and where the altitude can vary from below sea level to the top of a high mountain. Atmospheric pressure changes greatly at these different altitudes, sometimes rapidly. Even when a vehicle is operated under conditions that vary over a wide range of conditions, the sound generator installed in the vehicle must generate sound that has a constant volume and a constant pitch. is necessary.

None of the conventional sound generators could satisfy the above-mentioned requirements.

An object of the present invention is to provide a sound generator that can meet the requirements as described above.

According to the invention, there is provided an acoustic generator of the type having a case containing a diaphragm, electromagnetic means for causing said diaphragm to vibrate and circuit means for energizing said electromagnetic means, said diaphragm and said mounting means for mounting the diaphragm within the case such that a closed acoustic cavity is formed by a portion of the case; the portion includes a retaining means for retaining in a sandwiched manner between a rigid, inflexible first retaining member and an elastically compressed second retaining member, said second retaining member , the relatively rapid pressure changes normally encountered in the use of acoustic generators, the compressed state exerts sufficient pressure to seal the acoustic cavity against the diaphragm, but the ambient within the acoustic cavity on one side of the diaphragm, being flexible and allowing gradual leakage of air into or out of the acoustic cavity when temperature and pressure change relatively slowly; An acoustic generator, wherein the pressure can be substantially equal to the ambient pressure on the other side of the diaphragm, thereby preventing undesirable changes in the tone generated by the acoustic generator. provided.

Further objects and advantages of the invention will become apparent from the following detailed description of preferred embodiments of the invention, taken in conjunction with the accompanying drawings.

Referring to FIG. 1, a cross-sectional view of an assembled acoustic generator 10 according to the present invention is shown. The acoustic generator 10 described herein has very small dimensions, approximately 6.25 cm (2.5 inches) square by 2.5 cm.
(1 inch) high and very inexpensive to manufacture, yet particularly suitable for mass production.
The sound generator 10 according to the invention is therefore suitable for use in motor vehicles as a warning device to indicate the existence of various predetermined conditions. In particular, the present invention protects drivers when the headlights remain on after the ignition is turned off, when the key remains in the ignition position, and when an attempt is made to operate the vehicle without properly fastening the seat belt. It can sometimes be used to give a warning. As stated above, current federal regulations require that an audible warning signal be provided for 4 to 8 seconds when the seat belt is not buckled when the vehicle is started. The control circuit of generator 10 in accordance with the present invention may also be used to automatically time the seat belt warning signal to specified times over a wide ambient temperature range.

The sound generator 10 is basically a diaphragm 24
, and this diaphragm 24 is caused to vibrate by an electromagnetic coil 30 and thus generate sound. The electromagnetic coil 30 is electrically driven by an oscillation circuit (FIG. 4). The diaphragm 24 is located in the recess 18 of the cover 12 of the unit.
and an elastic foam gasket 2
6 and a plastic retaining ring 28. This retaining ring 28 is simply punched into the overhang 25 of the cover 12 as shown. Therefore, a closed acoustic cavity 18 is formed within the recess of the cover 12.

It is important to note that although cavity 18 is closed, it is not hermetically sealed. In particular, the diameter of the diaphragm 24 is
Please note that the inner diameter of the overhanging portion 25 of No. 2 is slightly smaller than the inner diameter of the overhang portion 25 of No. 2. Therefore, since a porous foam gasket 26 exists around the diaphragm 24, air can slowly leak out from around the diaphragm 24 even if a pressure difference is maintained on both sides of the diaphragm. . Therefore,
This closed acoustic cavity 18 due to changes in ambient temperature
The diaphragm 24 will not bend or bulge even if the air inside it is heated or cooled. Furthermore, this slow air leakage allowed around the diaphragm 24 is
The difference in expansion coefficients between cover 12 and diaphragm 24 also prevents tension or pressure forces from being imposed on diaphragm 24 over a wide ambient temperature range. At the same time, however, the seal formed around the diaphragm 24 by this intumescent gasket 26 prevents the relatively fast movement of air caused by the oscillation of the diaphragm 24 when excited by the electromagnetic coil 30 into the closed acoustic chamber 18. It is in a sealed state that could be considered a cavity. Generally speaking,
The seal formed by the diaphragm 24, intumescent gasket 26, and retaining ring 28 prevents air leakage from occurring to balance the pressure differential across the diaphragm even when sustained pressure differentials occur due to changes in ambient temperature. If the diaphragm 24 vibrates at the frequency at which the device produces sound, resulting in rapid air movement, then the closed cavity 18 would be considered sealed. It is something.

The magnitude and quality of the radiated sound produced by the acoustic generator of the present invention is determined by the diaphragm 24 having a mass M, a compliance Cr provided by the foam gasket 26, and a compliance Cc provided by the air in the closed cavity 18. It is mainly determined by the characteristics of the resonant acoustic system. This physical configuration can be shown to be equivalent to an electrical series resonant circuit, where M is equivalent to inductance L and C is equivalent to capacitance C. Therefore, the resonant frequency F of this system is given by the following equation.

In the sound generator of the invention, this frequency is selected to be the same as the operating frequency of the oscillator circuit (FIG. 4).

As mentioned above, the diaphragm 24 is caused to vibrate by the "pull and push forces" applied to the diaphragm by the pole pieces 32 of the electromagnetic coil 30. As is well known to those skilled in the art, in order for diaphragm 24 to vibrate properly, pole piece 3 must
It is important that a proper air gap exist between 2 and diaphragm 24. Known devices often require separate manual adjustments to set the proper air gap. However, in the sound generator according to the present invention, the air gap between the pole piece 32 and the diaphragm 24 is automatically set to an appropriate distance when the unit is assembled. In particular, the printed circuit board 1 to which the electromagnetic coil 30 is firmly fixed
6 is a pair of support posts 5 integral with the cover 12;
The support posts 54 are spaced a predetermined distance from the diaphragm 24 by 4 and are mated with a pair of support posts 56 integral to the case 14 of the unit. Each of the support posts 54 has a protrusion 55 projecting from its end that extends through a hole in the circuit board 16 and fits into a hole in the top of an opposing support post 56 that projects from the case 14. In this manner, when the cover 12 is heated and laminated to the case 14, the printed circuit board 16 is mounted on the diaphragm 24 such that the pole piece of the coil 30 mounted thereon is automatically spaced the appropriate distance from the diaphragm 24. 24. Therefore, once the unit is assembled, the proper air gap 52 will be set.

Referring now to FIG. 2, the case 14 of the acoustic generator 10 according to the present invention is shown in detail. As previously discussed, a closed acoustic cavity 18 is formed within the recess of the cover 12 and above the diaphragm. Furthermore,
An acoustic cavity 22 is also formed within the case 14 and below the diaphragm 24 . The closed cavity 18 above the diaphragm 24 constitutes the primary acoustic cavity of the unit, while the ported cavity 22 below the diaphragm 24 constitutes the secondary acoustic cavity of the unit. The secondary acoustic cavity 22 is ported by a series of holes 20 formed in the case 14 of the unit 10.
The secondary acoustic cavity 22 is ported to tune it to the main frequency of the oscillator circuit. In particular, the size and number of acoustic ports 20 are selected such that the effective port size of the open acoustic cavity 22 resonates at the main frequency of the diaphragm 24. In other words, by varying the number and/or size of the acoustic ports 20, the volume of the sound generated by the acoustic generator 10 is varied.

5a and 5b, the manner in which electromagnetic coil 30 is mounted to printed circuit board 16 is shown in detail. Electromagnetic coil 30 consists of multiple turns of magnetic wire 36 wound around a plastic bobbin 34. The bobbin 34 has three mounting legs 38-40 integral therewith which connect the coil 30 to the printed circuit board 16.
Used for fixing to. Specifically, mounting legs 39 and 40 are first inserted through a pair of holes 46 and 47, respectively, in printed circuit board 16, coil 30 is then swung down, and locking tab 42 at the end of remaining mounting leg 38 is inserted. leg 38 until it engages the underside of printed circuit board 16.
is inserted into the third hole 48 of the printed circuit board 16. It is therefore clear that the coil 30 is easily secured to the printed circuit board 16 without the need for special clips or mounting screws.

5b, one end 44 of coil wire 36 is wrapped around and terminated to mounting leg 40, and the other end 43 is wrapped to and terminated to mounting leg 39. Please note that. The steps of wrapping and terminating the wire 36 around the mounting legs 39 and 40 of the bobbin 34 are performed when the wire 36 is initially machine wrapped around the bobbin 34 and requires no additional manual intervention. Accordingly, as will be readily apparent from the accompanying drawings, when coil 30 is mounted on a printed circuit board as described above, ends 43 and 44 of coil wire 36 are secured to a suitable copper plate on the underside of printed circuit board 16. Padded 50 and 5
1 each automatically. Thus, the connection of coil wire 36 to printed circuit board 16 can be flow brazed with other electrical components on printed circuit board 16 in a conventional manner. This eliminates labor-intensive additional operations.

Referring now to FIG. 4, a circuit diagram of a timing control circuit for sound generator 10 in accordance with the present invention is shown. The illustrated control circuit provides a 4 to 8 second audible warning when it receives a signal indicating that the seat belt is not properly fastened, and the headlights remain on even after the ignition is turned off. It is used to issue a continuous audible alarm when a signal is received indicating that an alarm is occurring. Additionally, appropriate panel lamps are activated to provide a visual alarm signal consistent with the audible alarm thus issued. Although not included in the circuit shown, with slight circuit modifications the circuit can be easily adapted to provide additional alarms such as "key left in ignition", "door ajar", etc. can.

Generally, this control circuit includes timing circuits, logic circuits that determine the existence of some predetermined condition, oscillator circuits,
It also includes a drive circuit that drives the electromagnetic coil assembly. The timer circuit essentially consists of Figures 6a and 6.
It consists of a triple PTC element of the type shown in Figure b.
As is apparent from Figures 6a and 6b, three separate PTC resistors are created in one disk 80 by simply cutting a pair of cavities 82 and 84 in the metallization of the surface of the element. Separate leads 86-88 are attached to each of the three metallized surface areas, and one lead 90 is attached to the rear surface of disk 80. Thus, lead 90
A separate PTC resistor is created between and each of the three front leads 86-88.

PTC resistors are characterized by their rapid change in resistance at a given temperature and their temperature coefficient of resistance. The temperature at which the temperature coefficient of PTC increases rapidly is called the "transition temperature." PTC
The characteristic transfer temperature of the resistor is determined by the specific barium titanate-based porcelain composition of the PTC resistor. Characteristically, the temperature coefficient of the PTC resistance is typically low and constant below its transfer temperature. Thus, for example, the resistance of a PTC resistor varies from 5 ohms below its transition temperature to 5 kilohms above its transition temperature.

Referring now to FIG. 7, there is shown a simplified circuit diagram illustrating the particular manner in which a triple PTC element is utilized in the present invention. Basically, three
The PTC resistors are used for three separate purposes: one PTC resistor (R _ad ) is used as the main heating element for PTC element 60, and another PTC resistor (R _ac ) is used to operate the seat belt warning lamp. is used as a switch element to control the third
The PTC resistor (R _ab ) is used as a logic switch element to provide the logic signal that controls the operation of the electromagnetic coil. As is readily apparent to those skilled in the art, the seventh
The basic triple PTC timing circuit shown in the figure can be easily applied to a wide variety of uses beyond the timing control circuit of an automobile seat belt warning unit. In practice, in virtually any case where a bimetallic element is used to provide a timing signal, the bimetallic element may be used as shown in FIG.
The above effects of the PTC circuit can be obtained by replacing it with a heavy PTC circuit. Additionally, PTC timing circuits can be used in many applications where the use of high metal components is either impossible or impractical.

When power is first applied to this circuit, there are three
All PTC resistors have a nominal resistance value. A high level signal is therefore present on logic line 74 and lamp 73 is activated. However, the heating element
Since a substantial current is derived through _Rad , 3
Just because two resistors are placed on the same PTC element, the entire PTC element 60 begins to heat up.
Furthermore, although the PTC resistors R _ab and R _ac heat to some extent by their own current conduction, this effect is transferred from the heating element R _ad due to the added resistance in their current path. It is not as severe as the fever that occurs. When the transition temperatures of the two switch elements R _ab and R _ac are reached, the resistance of these two PTC resistors increases significantly, thereby causing the lamp 7
3 and bring the signal on the theoretical line 74 to level 2. It is important to note that the operation of logic PTC resistor R _ab is not affected in any way if lamp 73 is removed from the circuit or if lamp 73 burns out. However, if logic line 74 were simply coupled to the midpoint of PTC resistor R _ac and alarm amplifier 73 (shown in phantom), logic line would never go low in the event of a lamp failure. I mean,
This is because the pull-down resistance of the lamp is lost. Additionally, if an additional resistor were connected in parallel with lamp 73 to eliminate this condition (also shown in phantom), the increased voltage drop across this resistor would prevent the lamp from igniting properly. . Therefore, in order for theoretical line 74 to operate regardless of lamp circuit failure, the triple PTC configuration described herein is required.
Of course, when power is finally removed from the main heating element R _ad , the temperature of the triple PTC element 60 will rapidly return to its ambient temperature condition, and the effective resistances of the two switch elements R _ab and R _ac will likewise rise. Return to their initial minimum value. Therefore, as shown in FIGS. 6a and 6b, the lamp PTC resistance R _ac
must be large enough so that the resistance below the transition temperature of PTC element 60 is low enough to light the lamp brightly. Similarly,
The heated PTC resistor R _ad generates enough heat to cause the logic PTC resistor R _ab to exceed the transition temperature of the PTC element 60 within a specified 4 to 8 second time period even if the lamp burns out. must be large enough to Additionally, as shown, a lamp PTC resistor R _ac is preferably disposed between a heating PTC resistor R _ad and a logic PTC resistor R _ab so that the lamp PTC resistor is relatively It heats up evenly and prevents the lamp from gradually dimming.

Now, referring to FIG. 4, the triple PTC element 60
is clearly connected to the control arrangement as shown in FIG. In particular, the heating element
PTC resistor R _ad is connected between the terminal of the ignition device and ground, PTC element R _ac is connected between the terminal of the ignition device and the terminal connected to the seat belt warning lamp, and is a logic switch element PTC resistance
_Rad is connected between the igniter terminal and logic line 74. A pull-down resistor R9 connected between logic line 74 and ground together with PTC resistor _Rad forms a voltage divider network that determines the switching time of the signal on logic line 74. especially,
The value of resistor R9 is selected such that the signal on theoretical line 74 switches from a high level state to a low level state within a specified time period of 4 seconds to 8 seconds.

If the seat belt is not fastened when the ignition system is turned on, resistor R1 is connected to the ignition system terminal.
Although a high level signal is sent through the node 72, the node 72 is pulled to ground potential. When the signal at node 72 is low, the oscillator circuit 75, and in particular the NOR gate 68 therein, is enabled. Conversely, if the seat belt is properly fastened when the ignition is turned on, the signal at node 72 will be high, thereby disabling oscillator circuit 75.

The oscillation circuit 75 is activated by the low level signal at the coupling point 72.
In the enabled state, the oscillation circuit 75 starts oscillating when the logic enable signal is received from the output of the NOR gate 64. As previously discussed, upon initiation of ignition, the signal on logic line 74 will be high for a predetermined 4 to 8 seconds, causing the output signal of NOR gate 64 to be low for a corresponding 4 to 8 seconds. If the output signal of the NOR gate 64 is at a low level and the signal at the coupling point 72 is at a low level,
Oscillator circuit 75 oscillates and provides a square wave drive signal to the base of transistor Q1 via resistor R5. Thereby, a substantially triangular current waveform is induced in coil L1, which in turn causes the diaphragm to vibrate at the frequency of the current waveform and generates an audible alarm signal. When the signal on logic line 74 goes low after the specified 4 to 8 seconds, the output from NOR gate 64 goes high, disabling oscillator circuit 75.

Additionally, the control circuit shown herein may also be used to provide a persistent alarm signal when the headlight remains on after the ignition is turned off. This is accomplished by connecting the panel lamp terminal indicating the status of the headlight to the other input of NOR gate 64 through resistor R7. Since the state of the headlight is only relevant when the ignition system is turned off, the terminal of the ignition system is connected to the Noah gate 64 via resistor R2, inverter 62, and diode D2.
is connected to the other input of the above. Thus, when the ignition is turned on, the signal at this input of NOR gate 64 is pulled low, disabling the headlight input signal. However, when the igniter is turned off, the high level signal from the panel lamp terminal causes the output of NOR gate 64 to go low, thereby enabling oscillator circuit 75. I mean,
This is because the signal at node 72 is also low since the igniter is off. Therefore, an audible alarm is generated that lasts until the headlight is turned off.

As mentioned above, oscillator circuit 75 also drives transistor Q1 with a square wave output signal. However, the square wave signal has many harmonics and therefore does not provide a good drive signal for the coil L1. Of course, rather than a pure sine wave oscillator (which requires very expensive circuitry and does not generate harmonics) a square wave oscillator circuit 75 is used. However,
The current actually induced through the coil L1 is converted from a square wave signal into an "approximate" sine wave by the inductance of the coil L1 and the resistance of a resistor R6 carried in parallel with the coil L1. Therefore, the current signal flowing through coil L1 is further triangulated, which closely approximates a sinusoidal signal and causes the diaphragm to produce a purer acoustic than if driven by a direct square wave signal. Oscillate in only one mode. In particular, if this triangular drive signal is combined with the characteristics of the resonant acoustic system described above,
A sound generator according to the invention produces a substantially pure sinusoidal sound output.

Thus, a low cost sound generator capable of producing relatively pleasant yet clear audible sound of uniform quality over a wide range of ambient temperature and pressure conditions, and which is easily mass-produced, is in the works. It should be clear that what is provided by the invention. As noted above, the present invention is particularly suited for use as an automobile alarm system, but may also find use in a wide variety of other applications where an inexpensive, reliable, yet low cost sound generator is desired. Easy to apply.

Although a preferred embodiment of this invention has been described, it will be apparent to those skilled in the art that changes and modifications can be made without departing from the scope of this invention.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the assembled sound generator according to the present invention, FIG. 2 is a view showing the case of the sound generator shown in FIG. 1, and FIG. A diagram showing the cover of the sound generator, FIG. 4 is a circuit diagram of the control circuit of the sound generator shown in FIG. 1,
Figures 5a and 5b show details of how the electromagnetic coil is mounted on a printed circuit board; Figures 6a and 6b show a triple PTC element of the type used in the acoustic generator of Figure 1; Figure 7 showing
The figure is a simplified circuit diagram of a PTC timing circuit forming part of the control circuit of FIG. 4. DESCRIPTION OF SYMBOLS 10... Acoustic generator, 12... Cover, 14... Case, 16... Printed circuit board, 18... Recess (acoustic cavity), 20... Hole (port), 22... Acoustic cavity, 24
...diaphragm, 26...foam gasket, 28
...Plastic retaining ring, 30...Electromagnetic coil,
32... Electrode piece, 34... Plastic bobbin, 36
...Magnetic wire, 52...Air gap, 54, 56
…Support post.

Claims (1)

[Claims] 1. A sound generator of the type having a case containing a diaphragm, electromagnetic means for causing said diaphragm to vibrate, and circuit means for energizing said electromagnetic means, said diaphragm and a part of said case mounting means for mounting the diaphragm within the case so that a closed acoustic cavity is formed;
The mounting means is configured such that the diaphragm is held in a state in which a peripheral portion of the diaphragm is held between a rigid and inflexible first holding member and an elastically compressed second holding member. and retaining means for retaining the second retaining member at a position where the second retaining member, by virtue of its compressed state, under the relatively rapid pressure changes normally encountered in use of the acoustic generator. Applying sufficient pressure to the diaphragm to seal the acoustic cavity, but being flexible when ambient temperature and pressure changes relatively slowly, The pressure within the acoustic cavity on one side of the diaphragm can be substantially equal to the ambient pressure on the other side of the diaphragm, allowing gradual leakage of air from the acoustic generator generated by the acoustic generator. 1. A sound generator characterized in that undesirable changes caused by the noise are prevented.