JPS6123804Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a speed detection circuit for automobiles.

In conventional speed detection circuits for automobiles, the vehicle speed detection sensor includes a rotating body made of magnets and a reed switch, generates pulses with a period proportional to the vehicle speed, and introduces these pulses into the detection circuit.

When the detection circuit is composed of an analog circuit, a so-called ripple phenomenon occurs. In order to prevent malfunctions due to this ripple phenomenon, a capacitor element is placed in the detection circuit,
It formed an integral waveform.

Since this conventional speed detection circuit for automobiles includes a capacitor element, its operation is delayed and it is difficult to detect an appropriate vehicle speed.

The present invention was devised to eliminate the above-mentioned drawbacks, and its purpose is to provide a speed detection circuit for an automobile that is completely unaffected by the ripple phenomenon and operates stably.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an automobile speed detection circuit according to the present invention will be described below with reference to the drawings.

Reference numeral 1 denotes a vehicle speed sensor, which is composed, for example, of a magnet 1a having a rotation function and a reed switch 1b arranged corresponding to the magnet 1a, and rotates the magnet 1a in proportion to the vehicle speed, turning the reed switch 1b ON and OFF to generate a pulse.

2 is a resistor and 3 is a capacitor, respectively.
It is connected to the output section 23 of the vehicle speed sensor 1.
The output side of the capacitor 3 is a resistor 4 and a diode 5.
and 6 are connected, and 24 is the connection point. A capacitor 7, discharge resistors 8 and 9, and a diode 10 are connected to the cathode side of the diode 6.
is its connection point. Therefore, capacitors 7 and 2
The connection configuration of the two resistors 8 and 9 constitutes an integrating circuit that outputs a voltage signal corresponding to the output signal of the vehicle speed sensor 1 through charging and discharging action.

12 is a second transistor of NPN type, the base of which is connected to the connection point between resistor 8 and resistor 9;
Emitsuta is grounded. Thus, the predetermined first reference voltage for operating the second transistor 12 is set by the two resistors 8 and 9. The collector of the second transistor 12 is connected in series to the connection branch of the two voltage dividing resistors 21 and 13, and connected to the positive terminal of the power supply 16 via the key switch 15, thereby forming a series circuit. Reference numeral 11 denotes a first transistor of NPN type, the base of which is connected to the cathode of the diode 10, and the emitter connected to the connection point between the resistor 21 and the resistor 13. Thus, the predetermined second reference voltage for operating the first transistor 11 is:
By operating the second transistor 12,
This will be set to a higher level than the first reference voltage.

Reference numeral 14 denotes a PNP type third transistor, the emitter of which is connected to the positive side of a power source 16 via a key switch 15.

The base of the third transistor 14 is connected to the collector of the first transistor 11 via a resistor 17. Reference numeral 18 is a load, such as an automobile audio generator. The load 18 is connected to the collector of the third transistor 14. A so-called feedback circuit is constituted by a series circuit of a resistor 19 and a diode 20, one of which is connected to the connection point between the collector of the third transistor 14 and the load 18, and the other is connected to the connection point between the base of the first transistor 11 and the diode 10. connected to the connection point.

Resistor 22 is connected to the base of third transistor 14 .

Next, the operation will be explained.

When the key switch 15 is turned on and the car starts running, the magnet 1a rotates and the reed switch 1b repeats ON and OFF operations. Vehicle speed sensor 1
An output pulse as shown in FIG. 2a is generated at the output section 23 of the device.

This output pulse is a voltage waveform and is differentiated by the capacitor 3. This differential waveform is the connection point 24
The waveform appears as shown in FIG. 2b.

The output pulse is then charged by the capacitor 7 via the diode 6. Since the resistance value of resistor 2 is small, charging is completed quickly. Also, the charged capacitor 7 performs a discharging action via resistors 8 and 9. Since the resistance value of the resistor 8 is relatively large, the discharge period is long. The voltage waveform at the connection point 25 is as shown in FIG.
When the number of pulses is increasing, a high value voltage waveform will be generated. In the waveform of FIG. 2c, L indicates a ripple value, and it is clear that a change in the waveform occurs due to a ripple phenomenon.

In this manner, when the voltage value at the connection point 25 increases and reaches the first reference voltage, the second transistor 12 is turned on.

In this case, the second transistor 12 may be affected by the ripple phenomenon at the initial point in time, but as the voltage value at the connection point 25 further increases, it is completely turned on without being affected by the ripple phenomenon. do.
Then, the emitter voltage value of the first transistor 11 is set by the voltage dividing resistors 21 and 13, that is, the second reference voltage at which the first transistor 11 can operate is set. At this point, the second transistor 12 is in stable ON operation, and the second reference voltage is also set at a stable value.

Thereafter, when the voltage value at the connection point 25 further increases and reaches the second reference voltage, the first transistor 11
is activated. At the same time, the third transistor 14 is also turned on.

Therefore, a current flows through the branch of the third transistor 14, the resistor 19, the diode 20, and the first transistor 11, and the third transistor 14 and the first
Both transistors 11 can always maintain conduction even when a ripple phenomenon occurs.

Thus, power is supplied to the load 18 via the power supply 16, key switch 15, and third transistor 14, and the load 18 can be operated. For example, the vehicle speed
When the load 18 is used as an audio alarm at a speed of 10 km/hour, it can emit a sound saying, for example, "Let's lock the door!"

Next, when the vehicle speed becomes low, such as when the vehicle stops, the voltage value at the connection point 25 also decreases, and when it becomes lower than the first reference voltage, the second transistor 12 is immediately turned off. Then,
The first transistor 11 is turned off at the same time when the voltage value of its emitter becomes the power supply voltage. Therefore, the third transistor 14 is also turned off at the same time.

Therefore, the load 18 will stop operating.

Since the speed detection circuit for an automobile according to the present invention has the above-described structure and operation, it has the following advantages.

There is no malfunction at all even if a ripple phenomenon occurs.

Furthermore, there is no need to provide a capacitor to absorb ripple phenomena, and there is no problem of delay in operation.
Furthermore, since the operating hysteresis between the first transistor and the second transistor can be set to the minimum in response to fluctuations in the ripple phenomenon, responsiveness to changes in vehicle speed is good, and the output signal of the vehicle speed sensor is The integrating circuit as a corresponding waveform output means is 1
Only one circuit is required, which simplifies the circuit configuration.

For example, if the load is used in an audio alarm or the like, a multi-channel audio warning device system can be provided, and the scope of its application is wide.

It has various effects such as a simple circuit configuration and easy integration into an IC.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram showing an embodiment of an automobile speed detection circuit according to the present invention. Figure 2 a, b
and c are time charts showing the operating status of Fig. 1, and Fig. 2 a shows the output section of the vehicle speed sensor;
FIG. 2B shows the pulse waveform of the connection point B, and FIG. 2C shows the pulse waveform of the connection point C. 1...Vehicle speed sensor, 7...Capacitor, 11
...first transistor, 12...second transistor, 14...third transistor, 18...load,
19...Resistor, 20...Diode.

Claims (1)

[Scope of utility model registration request] A vehicle speed sensor, an integrating circuit which is composed of a capacitor and two discharge resistors and outputs a voltage signal based on the signal from the vehicle speed sensor, and a base is connected between the two discharge resistors so that the output of the integral circuit is set to a predetermined value. It consists of a second transistor that is activated when it reaches a first reference voltage, and a series connection of two voltage dividing resistors and the second transistor. a series circuit for setting a second reference voltage; a first transistor with an emitter connected between the two voltage dividing resistors and activated when the output of the integrating circuit reaches the second reference voltage; and the first transistor. a third transistor that responds to the operation of the transistor; and a feedback circuit that is interposed between the first and third transistors and is a connection circuit of a resistor and a diode for maintaining conduction of the third transistor and the first transistor. , and a load connected to the third transistor.