JPS641641Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an engine rotation speed detection device. Utility Model Registration Application No. 163514 (Utility Model Publication No. 163514) of 1982 (Utility Model Publication No. 163514) detects the height of the set rotation speed with high precision, drives loads such as relay lamps, heaters, or valves, and also detects the detection point. We have revealed a simple and inexpensive rotation speed detection device that is equipped with a hysteresis function to prevent malfunctions of the load due to chattering, etc. In one embodiment of this rotation speed detection device, there was a risk of malfunction if DC power was turned on when the engine was stopped. The present application provides a detection device that eliminates the above-mentioned drawbacks when turning on DC power via a power switch or the like. This will be explained in detail below using the drawings. 1 and 2 are circuit diagrams and operation waveform diagrams of each part of the circuit diagram showing an embodiment of the present invention. In the figures, 1 is a DC power source such as a battery, SW is an on/off switch for the power source 1, and 2 is a DC power source 1. The capacitor A is charged via the resistor r1 and the rotational speed setting resistor r2, and A is an input signal terminal synchronized with the engine rotational speed, which is derived from, for example, a connection point between a contact point and an ignition coil (not shown), etc. . 3 is a waveform shaping circuit for the input signal A, which includes a current limiting resistor r3, a waveform shaping capacitor C1, a resistor r4, a constant voltage diode ZD1, inverters I ₁ and I ₂ forming a logic circuit (for example, a C-MOS buffer circuit), and a differential circuit. It is composed of a capacitor C2, a resistor r5, etc., which form a capacitor C2 and a resistor r5. 4 is a semiconductor switching element (hereinafter referred to as a transistor) connected in parallel with the capacitor 2, and the waveform shaping circuit 3 is connected to its base terminal b.
When the output of
6 forms a discharge circuit for the capacitor 2.
5 is a logic circuit, for example a C-MOS buffer circuit,
A predetermined input level (threshold level) such as an inverter circuit, differential amplification circuit, or TTL, etc.
It has a function of sending out an output when the input signal (voltage) exceeds this. Reference numeral 6 denotes a semiconductor switching element (hereinafter referred to as a transistor) that repeatedly turns on and off in accordance with the output signal of the logic circuit 5, and 7 represents a capacitor that is charged via resistors r1 and r1', and a charging time constant between the resistors r1 and r1'. is set larger than the time constant of the capacitor 2 and the resistor r2. Further, the capacitor constitutes a discharge circuit via the resistor r7 when the transistor 6 is turned on. 8 sends a drive signal to a load drive circuit 9, which will be described later, when the charging voltage of the capacitor 7 reaches a predetermined value.
The logic circuit that sends out the DS (inverter circuit in the figure)
An example of configuring a so-called buffer circuit in which I ₃ and I ₄ are connected in series is shown. ) 9 is a load drive circuit that receives the drive signal.
It consists of a transistor Q that turns on and off in response to the arrival of DS, a rotation speed detection load RL, etc. 10
is a hysteresis circuit consisting of a resistor r8 and the like provided between the input terminal of the logic circuit 5 and one terminal of the logic circuit 8;
ZD2 and C ₀ are power supply stabilization circuit 11 of DC power supply 1
Constant voltage diode and capacitor, r
9 is an operation stabilizing resistor r10, r of transistor 4
11 is a base resistance. The proposed circuit is configured as described above. Next, the operation will be explained with reference to the operation waveform diagram of each part shown in FIG. First, in FIG. 1, the operation of the waveform shaping circuit 3 is omitted and synchronized with the engine speed. The pulse is waveform shaped and transferred to transistor 4.
An example in which the voltage is applied to the base will be explained.

<When the number of revolutions is lower than the set number> First, when the power switch SW is turned on, the capacitor 2 is charged by the DC power supply 1 via the resistors r1 and r2 at a predetermined charging time constant, and its charging voltage increases. (Fig. 2e) The charge in the capacitor 2 is transferred to the base-emitter terminal b- of the transistor 4.
As shown in FIG. 2d during interval e, a discharge occurs through resistor r6 and transistor 4 every time a pulse proportional to (synchronized with) the engine speed arrives. Repeat this operation below. However, when the engine speed is low, the base emitter terminal b of transistor 4
-The pulse interval arriving at e is long. Therefore, it takes a long time to form the discharge circuit of the capacitor 2, and during this time the charging voltage of the capacitor 2 gradually increases. When the charging voltage of the capacitor 2 reaches the threshold level (SL) n of the C-MOS inverter circuit 5 at time tn after a predetermined cycle, the inverter circuit 5 goes high (H) as shown in FIG. Send output. Therefore, transistor 6
is in ON state and capacitor 7 becomes transistor 6
→It is instantly discharged through the path of resistor r7. Therefore, the charging time constant formed by the resistors r1 and r1' of the capacitor 7 is set larger than that of the capacitor _C2 as described above, so that the charging voltage is
It is set in advance so that the threshold level of the logic circuit 8 is not reached until the output signal outputs a high (H) output again (during time f from tn to tn1 in FIG. 2). Therefore,
During this time, the drive output DS of the inverter circuit _I3 is low.
(L) and the transistor Q is inactive, so the load RL
It is detected that the engine speed is less than the set number of sheets.

<When the number of revolutions is higher than the set number> When the number of revolutions of the engine is higher than the set number, the interval between pulses arriving at the base terminal b of transistor 4 is short;
The ON/OFF repetition period becomes shorter. Therefore, since the discharge circuit of the capacitor 2 is frequently formed, the charging period (time) of the capacitor 2 is short, and its charging voltage does not reach the (input) threshold level of the logic circuit 5. This causes the output of the logic circuit 5 to go low.
(L) level, and the transistor 6 is turned off with no base current flowing. Therefore, the discharge circuit of the capacitor 7 is opened, and during this time the capacitor 7 continues to be charged via the resistors r1 and r1', and when the charging voltage reaches the threshold level of the logic circuit 8, the logic circuit 8 becomes high ( H) Sends the output drive signal DS to the load drive circuit 9 and operates the load RL via the transistor Q, thereby detecting that the engine rotation speed has reached the set number.

<Operation of the hysteresis circuit 10> In the above embodiment, the charging voltage of the capacitor 2, which is charged at a preset time constant by the resistor r2 and the capacitance of the capacitor 2, is changed to a discharge formed in proportion to the engine speed. It varies depending on the circuit,
We have explained an example in which the required charging voltage is compared with the input threshold level of the logic circuit 5 to drive the load (detection of rotation speed). The number setting is constant; in other words, load drive is performed when the engine speed reaches the set number. However, by connecting the input terminal of the logic circuit 5 and one terminal of the logic circuit 8 with the resistor r8, when the rotation speed is low, the charging voltage of the capacitor 2 increases and reaches the threshold level of the logic circuit 5. Since the output of the inverter circuit _I4 is at a high level (approximately the voltage across the constant voltage diode _ZD2 ), the capacitor 2 is connected to the resistor r2.
In addition to the charging path passing through the inverter circuit I ₄ → resistor r
8→Capacitor 2, the charging voltage further increases. Then, when the rotational speed increases and reaches the set rotational speed, the charging voltage of the capacitor 2 decreases below the threshold level of the logic circuit 5 at the set rotational speed and operates (detects) to drive the load. Nevertheless, the capacitor 2 is connected to the hysteresis circuit 1 via the resistor r8.
Since the charging voltage of 0 is superimposed, the rotational speed further increases beyond the set number, and unless the discharge circuit is frequently formed by the transistor 4, the rotational speed will not fall below the threshold level. In other words, the resistance r2
When the engine speed reaches a preset engine speed according to the time constant of the capacitor 2, the charging voltage of the capacitor 2 becomes lower than the threshold level of the logic circuit 5, and the load is driven by the drive signal DS of the logic circuit 8, the inverter circuit Since the output of I ₄ is low (L), the capacitor 2 is formed with a discharge circuit passing through the resistor r8 in addition to the discharge circuit passing through the transistor 4, so that its charging potential further decreases. Therefore, unless the rotational speed reaches a rotational speed lower than the preset rotational speed, the drive of the load will not be stopped. By providing the hysteresis circuit in this manner, the operating point and non-operating point of the load drive can have a required width, so that malfunctions due to load chattering or the like near the set rotation speed can be reliably prevented. Note that the above-mentioned required width (hysteresis setting) can be arbitrarily adjusted by selecting the resistance value of the resistor r8.

<Waveform shaping circuit> The pulse signal A synchronized with the rotation of the engine is affected by the voltage waveform (pulse voltage value) contact point of the ignition coil or the discharge gap, and when the battery voltage changes, the base of transistor 4・Emitter voltage waveform (Fig. 2 d)
Since the ON time _of the transistor 4 (Fig _. 2e) changes due to the change in Since the power for the inverter circuits I ₁ and I ₂ is supplied from the power supply stabilization circuit 11 (not shown), the output voltage thereof is constant. Therefore, the time constant of capacitor C2 and resistor r5 that form the differential circuit is constant, so even if the waveform of pulse signal A and battery voltage change, the ON width of transistor 4 is always constant, and the set rotation speed changes with input voltage. It is possible to set highly accurate settings because it is not affected by Note that FIGS. 2a, b, and c show the voltage waveform of the pulse signal A, the voltage waveform across the capacitor C1, and the input voltage waveform of the inverter circuit _I1, respectively.

<Switch closing operation when the engine is stopped> The operation of each part when the engine is running has been explained above, and next, the operation when the engine is stopped will be explained. When the engine is stopped, no pulse is derived from the signal terminal A, so the transistor 4 is in an OFF state. Therefore, when the input switch SW is closed in this state, the capacitor 2 is charged via the resistors r1 and r2, and the capacitor 7 is charged via the resistors r1 and r1'. However, since the charging time constant of capacitor 7 is set larger than that of capacitor 2, the time to reach the threshold level SL of logic circuit 8 is delayed (Fig. 2g). As a result, the transistor 6 becomes conductive via the logic circuit 5. Therefore, the capacitor 7 is discharged and its potential is lowered, and as a result, the logic circuit 8 becomes a low (L) output, the transistor Q is kept OFF, and no load is driven. Therefore, there is an advantage that erroneous operation of rotation speed detection when the engine is stopped can be prevented.

As is clear from the above description, according to the present invention, it is possible to detect the rotational speed with high accuracy even though the configuration is simple and inexpensive, and furthermore, it is possible to prevent malfunction of the load when the engine is stopped, so it has a great practical effect.

[Brief explanation of the drawing]

FIGS. 1 and 2 are a circuit diagram and operation waveform diagrams of each part of the circuit diagram showing an embodiment of the present invention. In the figure 1
is a DC power supply (battery), SW is a switch, 2,
7 is a capacitor, 3 is a waveform shaping circuit, 4 and 6 are semiconductor switching elements (transistors), 5 and 8
9 is a logic circuit, 9 is a load drive circuit, A is a pulse signal (terminal), and DS is a drive signal.

Claims (1)

[Claims for Utility Model Registration] (1) A first battery charged from a DC power supply 1 via a resistor.
a waveform shaping circuit 3 that shapes a (pulse) signal synchronized with the capacitor 2 and the engine rotation speed;
a semiconductor switching element 4 connected in parallel with the capacitor 2 and turned on and off by the output of the waveform shaping circuit 3; and a first semiconductor switching element 4 that outputs an output signal when the charging voltage of the capacitor 2 reaches a predetermined value. A logic circuit 5, a second semiconductor switching element 6 that is turned on and off by the output signal, and a second semiconductor switching element 6 that is charged by the DC power supply 1 through a resistor.
a second capacitor 7 through which a discharge circuit is formed; and a second logic circuit 8 that sends a signal to the load drive circuit 9 when the charging voltage of the capacitor 7 reaches a predetermined value; 7
An engine rotation speed detection device characterized in that a charging time constant at which the charging voltage of the first capacitor 2 reaches a predetermined value is set larger than a charging time constant of the first capacitor 2. (2) Engine rotation speed detection according to claim 1, characterized in that a hysteresis circuit 10 is connected between the input terminal of the first logic circuit 5 and one terminal of the second logic circuit 8. Device.