JPS6133734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a positive temperature coefficient resistance element for an automobile seat belt monitoring device.

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.

Although such devices are adequate for their intended purpose, there are certain drawbacks inherent in devices using bimetallic elements. A bimetallic element typically operates to open a circuit by causing the element to warp when heated by a heating coil wrapped around the element. However, to produce the desired time delay, the physical orientation of the bimetallic element must be manually adjusted so that the deflection of the bimetallic element interrupts the circuit at the appropriate time. Additionally, the thin wires that are wrapped around the bimetallic elements typically must be spot welded together with the other components of the circuit rather than simply being flow brazed.
It is therefore clear that manufacturing a buzzer unit with bimetallic elements is a very labor-intensive process and therefore adds considerable manufacturing costs to the basic component costs of the unit. Furthermore, in that bimetallic elements are temperature-responsive devices, the time delay provided by bimetallic elements is affected by changes in ambient temperature. Therefore,
The accuracy of the unit will be seriously compromised if it is subjected to significant temperature changes. Additionally, unless adequate heat dissipation is provided, the substantial heat generated by the bimetallic elements can cause problems for other circuit elements.

SUMMARY OF THE INVENTION The main object of the present invention is therefore to provide a positive temperature coefficient resistance element which can be used in place of bimetallic elements in order to overcome the drawbacks inherent in the use of bimetallic elements in acoustic generators of this type. The idea of using a PTC resistor in place of a bimetal element is not new and has already been attempted in the past, but certain problems always arise that make it impossible to simply replace it with a PTC resistor. In particular, since the resistance value of the PTC resistor is temperature sensitive, simply connecting the PTC resistor in series with the lamp and logic line will not result in a circuit that will function satisfactorily over the required temperature range. Furthermore, the lamp
The separate metallized surface of the disk 80 for the PTC resistor Rac must be large enough so that the lamp PTC resistor Rac resistance when below the transition temperature of the PTC element 60 is low enough to light brightly. It won't happen. Similarly, the separate metallized surface of the disk 80 for the heating PTC resistor Rad ensures that the logic PTC resistor Rac remains within the specified 4 to 8 second time period even if the lamp burns out. It must be large enough to generate enough heat to exceed the transition temperature of 60°C.

The present invention uses one PTC resistor as the main heating element, another PTC resistor as the switch element of the lamp, and a third PTC resistor as the logic switch element of the logic signal regulating the sound generator. The unique triple PTC element solves the above problem. The problems caused by the use of PTC resistors described above are thus eliminated. In particular, a separate logic switch element is provided, separate from the switch and heating elements that control lamp operation, so that the circuit continues to function properly and remains within the specified range even in the absence or failure of the lamp. Gives an audible alarm of the hour. Furthermore, because of the use of separate heating elements, the delay time of the unit is maintained within a specific time period of 4 to 8 seconds over a wide range of ambient temperatures. Importantly, PTC elements are inexpensive and can be flow-brazed onto a printed circuit board with other circuit elements without requiring separate manual adjustments to set delay times. Therefore, when manufacturing an acoustic generator using the positive temperature coefficient resistance element according to the present invention, manufacturing costs can be reduced considerably.

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 now to FIG. 1, there is shown a cross-sectional view of an assembled acoustic generator 10 utilizing a positive temperature coefficient resistance element according to the present invention. The acoustic generator 10 described here has very small dimensions, approximately 6.25 mm
It is 2.5 cm (2.5 inches) square by 2.5 cm (1 inch) high and is very inexpensive to manufacture, making it especially suitable for mass production. Accordingly, the sound generator 10 is suitable for use in a motor vehicle as a warning device to indicate the existence of various predetermined conditions. In particular, this sound generator is used when the headlights remain on after the ignition has been turned off, when the key is left in the ignition position, and when an attempt is made to drive 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 is also used to time a seat belt warning signal to the vehicle at a specified time over a wide range of ambient temperatures.

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 is held in place by a foam gasket 26 and a plastic retaining ring 28. This retaining ring 28 is simply snapped onto the bulge 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 does not bend or bulge even when the air inside it is heated or cooled. Furthermore, this loose air leakage allowed around the diaphragm 24 is caused by the difference in expansion coefficients between the cover 12 and the diaphragm 24 over a wide ambient temperature range.
4 is also prevented from being subjected to tension or compression forces.
At the same time, however, the seal formed around the diaphragm 24 by this intumescent gasket 26 is such that the acoustic seal formed around the diaphragm 24 during the relatively rapid movement of air caused by the vibration of the diaphragm 24 when excited by the electromagnetic coil 30 closes the cavity 18. It is in a sealed state that could be considered a cavity. Generally speaking, the seal formed by diaphragm 24, intumescent gasket 26, and retaining ring 28 is such that the seal formed by diaphragm 24, intumescent gasket 26, and retaining ring 28 balances the pressure differential across the diaphragm even when sustained pressure differentials occur due to changes in ambient temperature. This closed cavity 18 is considered sealed if rapid air movement occurs due to the vibration of the diaphragm 24 at a frequency at which air leakage can occur and the device produces sound. It is something that can be done.

The magnitude and sound quality of the radiated sound generated by this acoustic generator are determined by the mass M, the intumescent gasket 26
is primarily determined by the characteristics of the resonant acoustic system consisting of the diaphragm 24 with a compliance Cr given by the air in the closed cavity 18 and a compliance Cr given by the air in the closed cavity 18.
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 this sound generator, 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 provided by the electromagnetic piece 32 of the electromagnetic coil 30. It is caused to vibrate by "tension force and extrusion force". As is well known to those skilled in the art, it is important that a proper air gap exist between the pole piece 32 and the diaphragm 24 in order for the diaphragm 24 to vibrate properly. Known devices often require separate manual adjustments to set the proper air gap. However, in this acoustic generator, 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 16 to which the electromagnetic coil 30 is securely secured is spaced a predetermined distance from the diaphragm 24 by a pair of support posts 54 integral to the cover 12;
The support posts 54 are then fitted with a pair of support posts 56 integral with the case 14 of the unit. Each of the support posts 54 has a protrusion 55 projecting from its end.
, which extends through a hole in circuit board 16 and has an opposing support post 56 projecting from case 14 .
fits into the hole at the top of the In this way, when the cover 12 is heated and laminated to the case 14, the printed circuit board 16 is attached to the coil 3 mounted thereon.
The zero pole piece is positioned relative to the diaphragm 24 so that it is automatically spaced the appropriate distance from the diaphragm 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 is shown in detail. As mentioned above,
A closed cavity 18 is formed within the recess of the cover 12 and above the diaphragm. Additionally, an acoustic cavity 22 is 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 primary acoustic cavity of the unit.
Next, configure the acoustic cavity. The secondary acoustic cavity 22 is a series of holes 20 formed in the case 14 of the unit 10.
Ported by. 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 are used to secure the coil 30 to the printed circuit board 16. 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 tabs at the ends of remaining mounting legs 38 are inserted. This leg 38 is inserted into the third hole 48 of the printed circuit board 16 until the leg 42 engages the underside 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. I would like to draw your attention to this. The steps of winding and terminating the wire 36 around the mounting legs 39 and 40 of the bobbin 34 are performed during the initial mechanical winding of the wire 36 around the bobbin 34 and do not require any additional manual intervention. Thus, as is readily apparent from the accompanying drawings, when the coil 30 is mounted to a printed circuit board as described above, the ends 43 and 44 of the coil wire 36 are attached to a suitable copper plate on the underside of the printed circuit board 16. Padded 50 and 5
1 each automatically. Thus, the connection of the coil wire 36 to the printed circuit board 16 can be flow brazed with other electrical components on the printed circuit board 16 in a conventional manner. This eliminates labor-intensive additional operations.

Referring now to FIG. 4, a circuit diagram of the timing control circuit of sound generator 10 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 minor circuit modifications the circuit can be easily adapted to provide additional alarms such as "key left in ignition" or "door ajar". Shikiru.

Generally, this control circuit includes a timing circuit, a theoretical circuit that determines the existence of a certain predetermined condition, an oscillator circuit,
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 according to the invention of the type shown in figure b. As is clear from FIGS. 6a and 6b, a pair of cavities 8 are formed in the metallized portion of the surface of this element.
By simply ticking 2 and 84, three separate PTC resistors are created in one disk 80. 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 and three front leads 86-88
A separate PTC resistor is made for each of the .

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 transition temperature of the resistor is determined by the specific barium titanate-based porcelain composition of the PTC resistor. Characteristically, the temperature coefficient of PTC resistance is typically low and constant below its transition 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.

Now, referring to FIG. 7, the triple PTC of the present invention
A simplified circuit diagram is shown illustrating a particular manner in which the elements may be utilized. Basically, three
The PTC resistors are used for three separate purposes: one PTC resistor Rad is used as the main heating element for PTC element 60, and the other PTC resistor Rac is used as a switch element to control the operation of the seat belt warning lamp. and the third PTC resistor Rab is used as a logic switch element to provide a logic signal that controls the operation of the electromagnetic coil. As will be readily apparent to those skilled in the art, the basic triple PTC timing circuit shown in FIG. 7 can be readily adapted to a wide variety of uses other than timing control circuits for automobile seat belt warning units. In practice, virtually any time a bimetallic element is used to provide the timing signal,
The above-described effects of the PTC circuit can be obtained by replacing the bimetallic element with the triple PTC circuit shown in FIG. Additionally, PTC timing circuits can be used in many applications where the use of bimetallic elements 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 Rab and Rac heat up to a certain extent by their own current conduction, this effect is offset by the heat transferred from the heating element Rad due to the added resistance in their current path. It's not significant in comparison. When the transition temperatures of Rab and Rac of the two switch elements are reached, these two
The resistance of the PTC resistor increases significantly, thereby extinguishing lamp 73 and bringing the signal on logic line 74 to a low level. It is important to note that the operation of logic PTC resistor Rab 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 is simply
If it were coupled to the midpoint of the PTC resistor Rac and the alarm lamp 73 (shown in phantom), the logic line would never go low if the lamp failed. This is because the lamp's pull-down resistance (through the lamp to ground) 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 logic 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 Rad, the temperature of the triple PTC element 60 will rapidly return to its ambient temperature condition.
The effective resistance values of the two switch elements Rab and Rac similarly return to their minimum values. Therefore,
As shown in FIGS. 6a and 6b, the separate metallized surface of the disk 80 for the lamp PTC resistor Rac is such that the resistance value of the lamp PTC resistor Rac below the transition temperature of the PTC element 60 is the lamp PTC resistor Rac. must be large enough to be low enough to illuminate brightly. Similarly, heating PTC
The separate metallized surface of the disc 80 for resistance Rad provides logic within the specified 4 to 8 second time period even if the lamp burns out.
PTC resistor Rac must be large enough to generate enough heat to exceed the transition temperature of PTC element 60. Additionally, as shown, the lamp
PTC resistor Rac heats up PTC resistor Rad and logic PTC resistor
Rab, so that the lamp PTC resistor is heated relatively evenly and the lamp is prevented from dimming.

Now, referring to FIG. 4, the triple PTC element 60
is clearly connected to the control circuit as shown in FIG. In particular, the heating element
The PTC resistor Rad is connected between the terminal of the ignition device and ground, the PTC element Rac is connected between the terminal of the ignition device and the terminal connected to the seat belt warning lamp, and the PTC resistor is a logic switch element.
Rab is connected between the igniter and logic line 74. A pull-down resistor R9 connected between logic line 74 and ground together with PTC resistor Rab forms a voltage divider network that determines the switching time of the signal on logic line 74. In particular, the resistance R
A value of 9 is selected such that the signal on logic line 74 switches from a high state to a low 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 resistance 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. Upon initiation of ignition, as described above, the signal on logic line 74 goes high for a predetermined 4 to 8 seconds, causing the output signal of NOR gate 64 to go 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 R7. 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 a specified period of 4 to 8 seconds,
The output from NOR gate 64 becomes high level, disabling oscillation 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 has been 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.
Connected to the other input. 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. 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 rectangular parallel signal to an "approximate" sine wave by the inductance of the coil L1 and the resistance value of the resistor R6 connected in parallel with the coil L1. Ru. Therefore,
The current signal flowing through coil L1 is further triangulated, which closely approximates a sinusoidal signal and forces the diaphragm into one mode to produce a purer acoustic than if driven by a direct square wave signal. Make it vibrate with a chisel. In particular, when this triangular drive signal is combined with the characteristics of the resonant acoustic system described above, this acoustic generator generates a substantially pure sinusoidal acoustic output.

Thus, it can be seen that the positive temperature coefficient resistance element of the present invention provides a low cost sound generator that is capable of producing relatively pleasant yet clear audible sounds and that is easily mass-produced. It should be obvious. As noted above, the present invention is particularly suited for use in automotive alarm systems, 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 the drawing]

FIG. 1 is a sectional view showing an assembled acoustic generator using a positive temperature coefficient resistance element according to the present invention, FIG. 2 is a diagram showing the case of the acoustic generator shown in FIG. 1, and FIG. The figures show the cover of the sound generator shown in Fig. 1, Fig. 4 is a circuit diagram of a control circuit using a positive temperature coefficient resistance element according to the present invention, and Fig. 5
Figures a and 5b are views showing details of how to mount the electromagnetic coil on a printed circuit board; figure 6a;
6b are diagrams showing a triple PTC element according to the present invention, and FIG. 7 is a simplified circuit diagram of a PTC timing circuit forming part of the control circuit of FIG. 4. 10... Sound generator, 12... Cover, 14...
... Case, 16 ... Printed circuit board, 18 ... Recess (acoustic cavity), 20 ... Hole (port), 22 ...
Acoustic cavity, 24... diaphragm, 26... intumescent gasket, 28... plastic retaining ring, 30... electromagnetic coil, 32... electrode piece, 34
...Plastic bobbin, 36...Magnetic wire,
52... Air gap, 54, 56... Support post, 60... PTC element, 80... Disk, 8
2, 84... Blank space, 86, 87, 88, 90...
Lead, Rac, Rab, Rad...PTC resistance, 73...
...Warning lamp, 74...Logic line.

Claims (1)

[Claims] 1. A PTC object with a certain transition temperature in a positive temperature coefficient resistance element for an automobile seat belt monitoring device for providing a timed audible signal and an audible signal when driving the automobile without properly fastening the seat belt. The PTC object has conductive surface layers on opposite surfaces, one of the conductive surface layers is adapted to be connected to a power source, and the other conductive surface layer is adapted to be electrically connected to each other. creating first, second and third contact areas separated by each other, each of the first, second and third contact areas providing a respective first, second and third contact area to said one electrically conductive surface layer; second and third PTC resistors are formed;
The first contact area is adapted to be connected to electrical ground, the second contact area is adapted to be connected to a lamp for providing the visual signal, and the third contact area is adapted to be connected to a lamp for providing the visual signal. a contact area is adapted to be connected to provide the audible signal, the second contact area being disposed between the first contact area and the third contact area;
The first, second and third contact areas are connected to the third contact area.
the first contact area for the first PTC resistor is sufficient such that the first PTC resistor generates sufficient heat such that the PTC resistor exceeds the transition temperature within a predetermined period of time; the second contact area for the second PTC resistor is of such a size that the resistance value of the second PTC resistor when below the transition temperature is small enough to light the lamp brightly; A positive temperature coefficient resistance element characterized in that it is distributed so as to have a sufficient size.