JP2926138B2 - Electromagnetic clutch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic clutch having a function of detecting a rotational slip in a state where a rotor and an armature are attracted to each other.

[0002]

2. Description of the Related Art Conventionally, for example, a compressor of a car air conditioner is used as an auxiliary device, and an electromagnetic clutch is used for driving the auxiliary device. This type of electromagnetic clutch has a rotor and an armature having a plurality of arc-shaped slots formed in the circumferential direction, and supplies current to the electromagnetic coil to demagnetize the slots between the outer pole and the inner pole. The rotor and the amateur are adsorbed as a path. In other words, a belt is stretched between a pulley provided integrally with the rotor and a drive source such as an engine, and the rotor is driven to rotate from the drive side. The rotation torque is transmitted to the auxiliary machine side by causing the rotor to attract the rotor according to the above. In such an electromagnetic clutch, when the rotation of the auxiliary machine is locked or when an abnormally high load is generated, the rotor and the armature rotate and slip in the attracted state. If such a slip state is maintained for a long time, belts, bearings, and the like are damaged due to heat generated on the friction surface between the rotor and the amateur. In recent years, power is often transmitted by a single belt to a rotor of an electromagnetic clutch similarly provided for an auxiliary machine such as an alternator, a water pump, an oil pump for power steering, and an air pump.
If the belts, bearings, and the like are damaged, transmission of power to all the auxiliary machines becomes impossible, and the running of the automobile becomes dangerous.

Therefore, conventionally, it has been considered to detect the slip state between the rotor and the armature based on the current flowing through the electromagnetic coil and cut off the current supplied to the electromagnetic coil. For example, in an "electromagnetic friction clutch device" disclosed in JP-A-59-205030, a current induced in an electromagnetic coil due to a change in inductance or magnetic flux in a magnetic circuit is detected, and a slip between a rotor and an amateur is detected. The state is detected and the supply current to the electromagnetic coil is cut off. That is, in an electromagnetic clutch including a yoke accommodating an electromagnetic coil, a rotor having an annular groove into which the yoke is engaged, and an armature magnetically attracted to the rotor, a radial direction is applied to a friction surface of the rotor. A plurality of notches (grooves) extending in the circumferential direction are formed at intervals in the circumferential direction, and the same number of slits (grooves) are formed in the amateur corresponding to the notches, and according to the overlapping situation of the notches and the slits. By detecting the current flowing through the changing electromagnetic coil,
Rotational slip between the rotor and the amateur is detected, and the supply current to the electromagnetic coil is cut off.

An electromagnetic clutch having a function of detecting such a rotational slip is disclosed in US Pat.
No. 9828, and a special shape of a magnetically disconnected portion (slot) for forming a circuit of a magnetic flux that bypasses from the rotor to the armature and returns to the rotor when the electromagnetic coil is excited. In addition, the current induced in the electromagnetic coil is detected by increasing the variation of the inductance and the magnetic flux in the magnetic circuit. Then, as a specific measure, the AC component in the DC current is detected by the filter means and compared with a predetermined threshold value. When the AC component exceeds the threshold value, the supply current to the electromagnetic coil is cut off. Is explained.

[0005]

However, if it is attempted to determine the slip based on the peak value of the magnetic noise, it is difficult to discriminate between the slip noise in a low engine speed range and the rotational noise in a high engine speed range. Also, ON / OFF of various electrical components
Since the disturbance due to OFF or the like is amplified as it is and is erroneously recognized as a slip, the reliability of the rotation slip detection function becomes a problem.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an electromagnetic clutch having a highly reliable rotation slip detecting function.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention comprises a rotor having an interrupting portion for forming a magnetic flux circuit and an armature, and supplies an electric current to an electromagnetic coil. In an electromagnetic clutch that attracts the rotor and the armature, a current detecting unit that detects a current flowing through the electromagnetic coil and outputs a voltage corresponding to the current, an amplifying unit that amplifies a voltage output by the current detecting unit, A bandpass filter for extracting an AC component having a frequency equal to or lower than a predetermined frequency included in the voltage amplified by the amplifying unit, and an instantaneous value of the AC component extracted by the bandpass filter and a threshold value are compared. Means for sending a comparison output while the threshold value exceeds a threshold value, and a threshold value for increasing the threshold value as the rotation speed of the rotor increases. When a predetermined number of comparison outputs are confirmed between a time when a first time of the first output of the comparison means and the comparison means transmitted from the rising means and a predetermined time elapses, the rotation of the rotor and the amateur in the suction state is performed. While judging as slip,
And a slip judging means for repeating a rotation slip judging operation using a next comparative output as a first output when a predetermined number of comparative outputs cannot be confirmed before a predetermined time elapses. is there.

[0008]

Therefore, according to the present invention, when the rotational angular position of the rotor and the armature changes, the inductance changes rapidly and the current supplied to the electromagnetic coil is braked, and the change in the supplied current appears as a change in the amplified voltage. This change is extracted as an AC component. Then, the extracted instantaneous value of the AC component is compared with a threshold value that increases as the rotation speed of the rotor increases, and a comparison output is sent while the instantaneous value of the AC component exceeds the threshold value. You. Then, when a predetermined number of comparison outputs are confirmed before a predetermined time elapses after the first occurrence of the comparison output,
It is determined that the slip is caused by the rotation of the rotor and the armature in the attraction state. If a predetermined number of comparison outputs cannot be confirmed before the predetermined time elapses, the rotation slip determination operation is repeated with the next comparison output as the first output.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electromagnetic clutch according to the present invention will be described in detail. FIG. 2 is a side sectional view of a mechanism section showing one embodiment of the electromagnetic clutch. In FIG. 1, reference numeral 1 denotes a housing of a compressor of a car air conditioner, and an annular yoke 2 is fixedly supported via a support plate 3. The electromagnetic coil 4 is housed in the annular groove 2-1 of the yoke 2.

The nose portion 1a of the housing 1 has a bearing 6
And a rotor 8 having an annular groove 8a for engaging the yoke 2 is provided on the outer ring of the bearing 6 by a projection 8b and a snap ring 9. It is fitted and fixed with its movement in the axial direction restricted.

Reference numeral 10 denotes a V-pulley which is fitted on and integrated with the outer peripheral surface of the rotor 8, and a V-belt is stretched between the V-pulley 10 and a driving source (engine in this embodiment). The rotor 8 is driven to rotate from the driving side.

On the other hand, a rotating shaft 11 which passes through a center hole of the housing 1 and is supported by a bearing (not shown) on the housing 1 side.
An armature hub 12 formed in the shape of a disk with a boss is fixed to a tip end of the armature with a bolt 13 and a washer 14, and is attached to a portion which divides the outer peripheral portion into a plurality of portions in the circumferential direction. An armature 16 formed in an annular shape is fixedly supported at the free end of the leaf spring 15 between the rotor 8 and the armature hub 12. The armature 16 is urged by the leaf spring 15 in a direction away from the rotor 8.

The annularly formed electromagnetic coil 4 having a self-fusing property is inserted into a coil bobbin 17 formed in an annular shape having a U-shaped cross section in a state of being previously hardened, and a half thereof. Are exposed outside the coil bobbin 17. The exposed portion of the electromagnetic coil 4 is covered with a cover 18 formed in an annular shape having a U-shaped cross section.

FIG. 3 is a plan view of the armature 16. The amateur 16 is provided with a plurality of (six) arc-shaped slots 16-1 (16-11 to 16-16) along the circumferential direction as a magnetically disconnected portion, and each slot 16-1 has a circumferential direction. Has a semicircular shape. 16-A (16-A1
16-A6) are minute joints between adjacent slots 16-1 (hereinafter, referred to as bridge portions).

FIG. 4 is a plan view of the rotor 8. Rotor 8
A plurality of (six) arc-shaped slots 8-1 (8-11 to 8-16) are formed along the circumferential direction on the inner circumferential side as a magnetically disconnected portion. On the side, arc-shaped slots 8-2 (8-21 to 8-2) are arranged along the circumferential direction.
6) are opened (six), and each slot 8-1
And 8-2 are semicircular in the circumferential direction.
8-A (8-A1 to 8-A6) and 8-B (8-B1
.. -8-B6) are between adjacent slots 8-1 and 8-
This is a minute joint between the two (hereinafter, referred to as a bridge portion).

The slots 16-11 to 1 of the amateur 16
6-16 are the rotors 8 in the assembled state shown in FIG.
The opening position is determined as opposed to the annular plate surface between the slots 8-11 to 8-16 and 8-21 to 8-26. Also, the bridge part 1 of the amateur 16
6A and the bridge portions 8-A and 8-B of the rotor 8
The circumferential dimension h is the same.

FIG. 1 is a diagram showing a control circuit attached to the mechanism of the electromagnetic clutch. In FIG.
Tr1 is a power transistor (switching transistor: P-channel MOS • FET), and is connected between one end of the electromagnetic coil 4 and a power supply line (DC12V).

Reference numeral 100 denotes a current detection circuit, which is constituted by a minute resistance (about 0.1Ω) R1 for current detection.
The current detecting minute resistor R1 is connected between the other end of the electromagnetic coil 4 and a ground line.

Reference numeral 200 denotes an inverting amplifier, which comprises an operational amplifier IC1, resistors R2 to R6, and capacitors C1 and C2. The operational amplifier IC1 includes resistors R2 to R
By setting 6, a gain of about 20 is set. A series circuit of a capacitor C2 and a resistor R6 is connected in parallel to a feedback resistor R5 connected between the inverting input terminal and the output terminal of the operational amplifier IC1. As the capacitor C2, for example, a capacitor of 1000 PF is used, thereby cutting a component of a carrier wave (high frequency). In this embodiment, since the current detection circuit 100 outputs a waveform of 0.1 V / A, the inverting amplifier 200 outputs about 2 V / A.
Will be output.

Reference numeral 300 denotes a band pass filter (low filter), which includes an operational amplifier IC2, resistors R7 to R11, a variable resistor R12, capacitors C3 to C5, and a diode D1.
And amplifies the AC component of the output waveform of the inverting amplifier circuit 200. In this bandpass filter 300,
A waveform of about 2 V / A is set to about 100 V / A, and only an AC component of 2 kHz or less is extracted.

Reference numeral 400 denotes a comparison circuit, which is a comparator I
C3, resistors R13 to R19, a variable resistor R20, and diodes D2 and D3. Comparator I
The output of the bandpass filter 300 is provided to the inverting input terminal of C3. To the non-inverting input terminal of the comparator IC3,
A reference voltage VP1 from a reference voltage generator 400-1 including resistors R13 to R16 and a variable resistor R20, and a set voltage V from an engine speed detection circuit 1000 to be described later.
The higher voltage of P2 is set as the threshold voltage V1.

Reference numeral 500 denotes a continuous waveform confirmation circuit (slip determination circuit), which includes a slip pulse counter 500-1;
Abnormal signal holding circuit 500-2 and reset timer circuit 5
00-3. The slip pulse counter 500-1 is constituted by a frequency divider IC5, and the abnormal signal holding circuit 500-2 is constituted by a D flip-flop IC6 and a resistor R21. Reset timer circuit 50
0-3 are a frequency divider IC7 and a D flip-flop IC8
, A resistor R22, and an oscillator 500-31. Oscillator 500-31 is connected to inverter IC9, I
It comprises C10, resistors R23 and R24, and capacitor C6, and its oscillation frequency is about 30 Hz.

A delay circuit 600 includes resistors R25 and R25.
26, negative logic output OR gate IC11, inverter IC
12, a frequency divider IC13, and a D flip-flop IC14, and an oscillation output from the oscillator 500-31 is supplied to a clock terminal of the frequency divider IC11.

Reference numeral 700 denotes a power-on reset circuit (differentiating circuit), which comprises a resistor R27, a capacitor C7, and a diode D4.
The power-on reset signal is the potential at the connection point with the node.

Reference numeral 800 denotes a temperature measuring circuit, which comprises a comparator IC15, resistors R28 to R30, a variable resistor R31, and a capacitor C8. The voltage generated at the connection point between the thermistor TH and the variable resistor R31 is calculated by the comparator IC1.
5 inverting input. The thermistor TH is arranged near the electromagnetic coil 4.

An overcurrent protection circuit 900 includes an operational amplifier IC16, a comparator IC17, a flip-flop circuit IC18, resistors R32 to R36, and a capacitor C9. The operational amplifier IC16 detects a minute voltage detected by the current detection circuit 100. It is amplified (about 1 V / A) and compared with a predetermined voltage by the comparator IC17.

Reference numeral 1000 denotes an engine rotation detection circuit.
Operational amplifier ICs 19 to 21, photocoupler FT1, logical operation circuit IC22, resistors R37 to R55, variable resistor R5
6, 57, inverter IC23, capacitors C10 to C
19, a diode D5, an NPN transistor Tr2, and switches SW1 to SW5. By setting internal circuits according to the type of engine such as the number of cylinders, 2 cycles / 4 cycles / rotary, etc., an ignition coil (not shown) from the minus terminal side is used. The frequency of the ignition pulse is divided, and a voltage (1 V / 1000 rpm) proportional to the number of revolutions of the engine is given to the comparison circuit 400 as the set voltage VP2.

In FIG. 1, Tr3 is an NPN transistor, and the gate of the FET Tr1 is connected to the connection line between the collector and the resistor R58. The base of the transistor Tr3 is supplied with the negative logic input of the AND gate IC24 via the resistor R59, and the output of the abnormal signal holding circuit 500-2 in the continuous waveform confirmation circuit 500 and the overcurrent protection circuit 90 are supplied to the AND gate IC24.
0 and the output of the inverter IC 12 in the delay circuit 600 are provided.

In FIG. 1, the IC 25 has a negative logic input OR gate OR3, OR4, a negative logic output OR gate O2.
A logic circuit composed of R5, Tr4 and Tr5 are NPN transistors, PD1 is a light emitting diode, FT2 and FT3
Is a photocoupler, SW6 is a reset switch, SW7 is a clutch switch, DCC is a DC / DC converter for converting DC 12V to DC 5V, and IC4 is an inverter.

Next, the operation of the electromagnetic clutch configured as described above will be described with reference to the change in the current (excitation current) I flowing through the electromagnetic coil 4 shown in FIG. 5 and the signal waveforms of each part shown in FIG. I do. 6A shows the output of IC1 in the inverting amplifier circuit 200, FIG. 6B shows the inverting input to IC3 in the comparison circuit 400, and FIG.
3, (d) is the output from the abnormal signal holding circuit 500-2 in the continuous waveform confirmation circuit 500 (Q output of IC6), (e) is the clutch drive signal CLON, and (f) is the output of IC14 in the delay circuit 700. Q bar output, (g) is the output of AND gate IC24.

In FIG. 2, when the V-pulley 10 is driven and rotated from the drive source (engine) side, the rotor 8 integrated therewith rotates on the nose 1a of the housing 1 via the bearing 6.

In such a situation, in the control circuit shown in FIG. 1, when the switch SW7 is turned on and the clutch drive signal CLON becomes "L" level (point t1 shown in FIG. 6 (e)), the IC 11 The output becomes “H” level and I
The output of C12 becomes "L" level and AND gate I
The output of C24 becomes “H” level (point t1 shown in FIG. 6 (g)), the FET Tr1 is turned on, and the current I starts to be supplied to the electromagnetic coil 4 (point t1 shown in FIG. 5).

When the electromagnetic coil 4 is excited, a magnetic flux circuit is formed from the yoke 2 via the outer pole of the rotor 8, then to the armature 16 and back to the yoke 2 via the inner pole of the rotor 8. The rotor 8 is attracted against the urging force of the leaf spring 15 (point t2 shown in FIG. 5: t1 to t2).
Is amateur suction time). That is, by supplying the current I to the electromagnetic coil 4, the slots 8-1, 8-2,
The armature 16 is attracted to the rotor 8 by using the magnetic field 16-1 as a demagnetizing portion. As a result, the armature 16 rotates integrally with the rotor 8, the rotating shaft 11 integrated with the armature 16 rotates, and the air compressor starts operating.

Thereafter, the supply current I to the electromagnetic coil 4 increases as shown in FIG. 5, and eventually reaches a saturation value (steady current).
Reach On the other hand, when the output of the IC 12 goes to the “L” level, the reset state of the IC 13 is released, the IC 13 starts counting the oscillation output of the oscillator 500-31, and when the count reaches the predetermined count value (0 in this embodiment). .5 sec), the Q output is set to the “H” level. That is, the IC 13 sets its Q output to the “H” level at time t3 after a predetermined time (connection time) T1 has elapsed after the supply current I to the electromagnetic coil 4 has reached the saturation value, and thereby the Q bar of the IC 14 The output becomes “L” level (FIG. 6
(Point t3 shown in (f)). Q bar output of IC14 is "L"
Level, the output of OR5 becomes “H” level,
The output of the reset timer circuit 500-3 (Q bar output of IC8) is supplied to the slip pulse counter 500 via OR4.
-1 is effectively acted on.

Assume that a rotational slip has occurred at time t4 shown in FIG. In this case, the supply current I to the electromagnetic coil 4 is small but gradually decreases due to heat generated on the friction surface between the rotor 8 and the armature 16. On this occasion,
The supply current I to the electromagnetic coil 4 is S1, S2, S3,.
As shown in the figure, the waveform suddenly drops partially, resulting in a characteristic waveform. This characteristic waveform shows that when the rotation angle positions of the bridge portions 8-A and 8-B of the rotor 8 and the bridge portion 16-A of the armature 16 match, the inductance changes rapidly, and the electromagnetic coil 4 This is caused by the braking of the supply current I to the motor.

The supply current I to the electromagnetic coil 4 is detected by the current detection circuit 100, and a voltage corresponding to the current is supplied to the inverting amplification circuit 200. Inverting amplifier circuit 200
Inverts and amplifies the voltage supplied from the current detection circuit 100 (see FIG. 6A), and
Give to. The bandpass filter 300 cuts an AC component of 2 kHz or more as noise, and extracts only an AC component of 2 kHz or less. Thereby, the AC components corresponding to the characteristic waveforms S1, S2, S3,... In FIG. 5 pass through the band-pass filter 300 and are provided to the comparison circuit 400.

In the comparison circuit 400, the instantaneous value of the AC component supplied from the band-pass filter 300 and the threshold value V1
When the instantaneous value of the AC component exceeds the threshold value V1, a comparison output of the "L" level is sent out (FIG. 6).
(See (b) and (c)). Thus, the comparison circuit 400 continuously generates an "L" level comparison output (slip pulse) according to the characteristic waveforms (slip noise) S1, S2, S3,... In FIG.

Here, the threshold value V1 in the comparison circuit 400 is equal to the reference voltage VP from the reference voltage generator 400-1.
1 or the set voltage VP2 from the engine speed detection circuit 1000, whichever is higher. That is, the reference voltage VP1 is set as the threshold value V1 until the rotation speed exceeds a predetermined rotation speed (the rotation speed in an extremely low speed range), and if the rotation speed exceeds the predetermined rotation speed, the set voltage V2 is set as the threshold value V1. . The set voltage V2 increases as the rotational speed of the engine increases, that is, as the rotational speed of the rotor 8 increases. By increasing the threshold value V1 as the number of rotations of the rotor 8 increases, rotation noise is not erroneously detected as slip noise.

That is, when the rotor 8 and the armature 16 rotate in the attracted state, the magnetic resistance of each part on the circumference is different, so that the clutch functions as a generator and a weak rotation noise is added to the exciting current I. The peak value of the rotation noise and slip noise on the excitation current I increases as the rotation speed of the rotor 8 increases. For this reason, when the threshold value V1 is fixed, when the rotation speed of the rotor 8 increases and the peak value of the rotation noise increases, there is a possibility that this is detected as slip noise. On the other hand, in the present embodiment, the threshold value V1 increases as the rotation speed of the rotor 8 increases.
Rise, so even if the peak value of the rotation noise increases,
This is not erroneously detected as slip noise.

The slip pulse sent from the comparison circuit 400 is directly and inverted by the inverter IC4 and applied to the continuous waveform confirmation circuit 500. Continuous waveform check circuit 50
At 0, IC8 is reset by the first slip pulse inverted and applied by inverter IC4. As a result, the output of OR4 is set to "L" level on the assumption that the Q bar output of IC8 is set to "H" level and delay time T1 has elapsed, and IC5 in slip pulse counter 500-1 is set to "L" level. Is released from the reset state. As a result, the IC 5 starts counting the slip pulse from the comparison circuit 400.

On the other hand, when the IC 8 is reset, its Q
The output goes to the “L” level, and the IC 7 outputs the oscillator 500−
The counting of the oscillation output from 31 starts. The IC 7 sets the Q output to the “H” level when the IC 7 reaches the predetermined count, that is, when T2 seconds (approximately 4 seconds in this embodiment) have elapsed since the start of counting the oscillation output. As a result, the Q output of IC8 becomes “H” level and the Q bar output becomes “L” level, and IC7 and IC5 are reset.

Here, a period from when the Q bar output of the IC 8 becomes "H" level to when it returns to "L" level, that is, until T2 seconds elapse after the first slip pulse is generated. During this time, a predetermined number of ICs 5 (1 in this embodiment)
When 28 (28) slip pulses are counted, the Q output thereof becomes the “H” level, and the Q output of the IC 6 becomes the “H” level (see FIG. 6D). As a result, the transistor Tr4 is turned on, and the light emitting diode PD1 is turned on to notify the occurrence of the rotation slip. Also, the transistor Tr5 is turned on, and an ERR signal (abnormal signal) is sent to a control unit (not shown) of the system to notify the occurrence of a rotational slip. Thereby, the control unit of the system executes appropriate abnormality processing.

On the other hand, when the Q output of the IC 6 goes to the "H" level, the output of the AND gate IC 24 goes to the "L" level (see FIG. 6 (g)). The supply current I to the coil 4 is cut off.
When the supply current I to the electromagnetic coil 4 is cut off, the armature 16 is separated from the rotor 8 by the urging force of the leaf spring 15, the transmission of the rotational torque is released, and the rotation of the rotary shaft 11 stops.

On the other hand, when the IC 5 cannot count a predetermined number of slip pulses until T2 seconds elapse after the first slip pulse is generated, I
The Q output of C5 is reset when T2 seconds have elapsed without being at the "H" level. Then, after the IC 5 is reset, the IC 8 is reset again using the slip pulse transmitted next by the comparison circuit 400 as the first pulse, and the above-described rotation slip determination operation is repeated.

That is, according to the electromagnetic clutch of the present embodiment, a characteristic waveform that partially drops sharply from a predetermined time after the supply current I reaches the saturation value is monitored. When a predetermined number of slip pulses are generated during a predetermined time T2 after the generation of the slip pulse, it is determined as a rotational slip, so other spontaneous noise (disturbance noise due to ON / OFF of various electric components and the like). Malfunction can be prevented, and the reliability can be improved.

Further, according to this embodiment, when the rotation angle positions of the bridge portions 8-A and 8-B of the rotor 8 and the bridge portion 16-A of the armature 16 coincide with each other, Since the rotational slip is detected based on the change in the supply current I, it is not necessary to perform any special additional processing on the existing rotor 8 and the armature 16, which is economical.

Further, according to the present embodiment, since the frequency component of 2 kHz or more is cut by the band-pass filter 300, the noise generated by the alternator, which is a peripheral accessory, can be removed, and the slip noise can be reduced. False positives are avoided and reliability is further improved.

It should be noted that I in the continuous waveform confirmation circuit 500
The setting state of C6, that is, the cutoff state of the supply current to the electromagnetic coil 4 can be restored as necessary by giving a reset signal RST. That is, when the switch SW6 is turned on, the reset signal RST of the "L" level is supplied to the OR3, the output of the OR3 becomes the "H" level, the IC6 is reset, and the Q output is returned to the "L" level. .

In this embodiment, when the resistance value of the thermistor TH becomes lower than a specified value due to Joule heat of the electromagnetic coil 4 or rise in the ambient temperature of the electromagnetic clutch, the output of the comparator IC 15 in the temperature measuring circuit 800 becomes “H”.
Level. As a result, the output of the IC 11 becomes “L”.
Level, the output of the IC 12 becomes “H” level, the output of the AND gate IC 24 becomes “L” level, the ON drive of the FET Tr 1 is interrupted, and the supply current I to the electromagnetic coil 4 is cut off. This is often
Used for protection of compressor heating.

When the temperature drops due to the heating protection by the thermistor TH and the output of the comparator IC15 in the temperature measuring circuit 800 returns to the "L" level, the output of the IC11 goes to the "H" level and the output of the IC12 goes to the "L" level. Level, the delay circuit 600 starts the delay operation, the output of the AND gate IC 24 goes to the “H” level, the FET Tr 1 is turned on, and the current I is supplied to the electromagnetic coil 4. Become. Thereby, the self-recovery function after the heating protection by the thermistor TH is secured.

In this embodiment, when an overcurrent flows through the electromagnetic coil 4, the overcurrent protection circuit 900
The output of the DUT 17 is at the “L” level. With this, IC
18 becomes "H" level, and the AND gate IC2
4 becomes "L" level, the ON driving of the FET Tr1 is interrupted, the supply current I to the electromagnetic coil 4 is cut off, and the destruction of the FET Tr1 is prevented.

In this embodiment, when the power is turned on, the operation of the power-on reset circuit 700 causes
C18, IC5 and IC6 are reset, and the control circuit is always initialized.

In the above description, the clutch drive signal CLON is set to the "L" level by turning on the switch SW7.
The clutch drive signal CLON can also be set to the "L" level by giving a signal of the "H" level to the photocoupler FT2 via the. In the above description, the switch SW6 is turned on to supply the “L” level reset signal RST.
By providing an “H” level signal to the photocoupler FT3 via the “L” level reset signal RS
T can also be given.

In the above description, the current detection circuit 10
Although the output voltage of 0 is inverted and amplified, it is also possible to amplify without inverting and to extract an AC component. Further, in this embodiment, the drive source is an engine, but it goes without saying that the drive source is not limited to the engine, and the shape and arrangement of the slots as the demagnetizing portions can be variously changed.

[0055]

As is apparent from the above description, according to the present invention, a change in the supply current is extracted as an AC component, and increases as the instantaneous value of the extracted AC component and the rotation speed of the rotor increase. The threshold value is compared, and the comparison output is sent while the instantaneous value of the AC component exceeds the threshold value. Even if the peak value of the rotation noise becomes high, this is erroneously detected as slip noise. The rotation slip is determined when a predetermined number of comparison outputs are confirmed during a predetermined time after the generation of the first slip pulse. Malfunction due to disturbance noise due to ON / OFF of electrical components and the like can be prevented, and the reliability of the rotation slip detection function can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a control circuit for controlling the driving of an electromagnetic clutch according to an embodiment of the present invention.

FIG. 2 is a side sectional view of a mechanism of the electromagnetic clutch.

FIG. 3 is a plan view of an armature used for the electromagnetic clutch.

FIG. 4 is a plan view of a rotor used in the electromagnetic clutch.

FIG. 5 is a diagram showing a change in a supply current I to an electromagnetic coil.

FIG. 6 is a time chart for explaining the operation of the control circuit shown in FIG. 1;

[Explanation of symbols]

 4 Electromagnetic coil 8 Rotor 8-1, 8-2 Slot (disconnected part) 8-A, 8-B Connecting part (bridge part) 16 Amateur 16-1 Slot (disconnected part) 16-1A Connecting part (bridge part) 100 current detection circuit 200 inverting amplification circuit 300 band-pass filter 400 comparison circuit 500 continuous waveform confirmation circuit 500-1 slip pulse counter 500-2 abnormal signal holding circuit 500-3 reset timer circuit 600 delay circuit 1000 engine speed detection circuit

Claims (1)

(57) [Claims] 1. An electromagnetic clutch, comprising: a rotor having a magnetically disconnected portion for forming a magnetic flux circuit; and an armature, wherein a current is supplied to an electromagnetic coil to attract the rotor and the armature. Current detecting means for detecting a current flowing through the current detecting means, and outputting a voltage corresponding to the current; an amplifying means for amplifying a voltage output from the current detecting means; a predetermined frequency included in the voltage amplified by the amplifying means; Comparing the instantaneous value of the alternating-current component extracted by the band-pass filter with a threshold value, and sending out a comparison output while the instantaneous value of the alternating-current component exceeds the threshold value; Comparison means; threshold value increasing means for increasing the threshold value as the number of rotations of the rotor increases; comparison transmitted by the comparison means; When a predetermined number of comparison outputs are confirmed during a period from the occurrence of the first output to a predetermined time, while it is determined that the rotor is slipping in the suction state between the rotor and the amateur, the predetermined time is determined. If a predetermined number of comparison outputs cannot be confirmed before the time elapses, slip determination means for repeating the rotation slip determination operation using the next comparison output as the first output is provided. And an electromagnetic clutch.