JPS6098822A - Overheat detector of electromagnetic mechanism - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an overheat detector for an electromagnetic mechanism such as an electromagnetic clutch or an electromagnetic brake.

[Prior art]

In general, the electromagnetic clutch, 'ljl; magnetic brake, magnetic brake magnet', can be controlled intermittently by controlling the power supply of the I7 excitation coil. However, its input shaft rotation speed and output The rotation difference between the shaft rotation speed and the transmitted torque causes excessive friction loss and redundant heat.

For this reason, in the past, in order to prevent burnout, a temperature detector was used to detect electrical heat and various countermeasures were taken.

For example, if magnetic powder is placed in the air gap of a magnetic circuit, the ratio of the exciting coil current to approximately 1'/! There are powder brakes, powder clutches, etc. When a powder clutch is used as an automobile clutch, in order to reduce the above-mentioned difference in rotational speed, the transmission torque is increased to reduce friction loss, and clutch overheat protection is performed.

Thermocouple heat-sensitive elements and the like are known as temperature detectors that can be applied to this type of application, but they are not commonly used due to the increased number of signal lines and the complexity of the mounting structure.

By the way, since the coil resistance is quite close to a portion where friction loss occurs, it changes as the temperature of the electromagnetic mechanism increases due to friction loss. And this coil resistance increases with temperature (
It is known that it changes at about 0.4%/'C with respect to ΔT).

Therefore, in the case of an electromagnetic mechanism that performs current control, a temperature rise can be easily detected from an increase in voltage across the coil resistance.

-Also, in recent years, switching regulator type current control circuits have become quite popular because they are advantageous in terms of power loss.

However, in the case of this switching regulator system, since the excitation coil voltage waveform is a square waveform, it is not possible to make the excitation coil voltage a voltage drop corresponding to the coil resistance. Therefore, there is a problem in that overheating cannot be easily detected from the voltage drop due to the resistance of the exciting coil.

[Summary of the invention]

This invention has been made in view of the above problems, and by calculating the average voltage of the exciting coil to account for changes in coil resistance due to temperature rise, and detecting overheating of the exciting coil using a predetermined judgment curve, It is an object of the present invention to provide an overheat detector using an electromagnetic mechanism that eliminates the need for a temperature detector and can detect overheating even in a switching regulator type current control device.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, l is a comparator, 2 is a smoothing filter, and this smoothing filter 2 is connected to the positive input terminal of the comparator. 100 is a general switching type electromagnetic mechanism/4 current control device, 1 is a power supply, 102 is a main transistor for on/off control, and this transistor 102
The emitter of is connected to the power supply 101 and the resistor 2
1 to the base. 103 ); is a free-wheeling diode, 104 is an excitation coil of an electromagnetic mechanism, 105
is a coil current detection resistor connected in series with this exciting coil 104, and these exciting coil 104 and resistor 105
and the diode 103 are connected in parallel. 10
The negative input terminal of the comparator 106 is connected to the connection point between the excitation coil 104 and the resistor 105, and the positive input terminal is connected to the input of the current command signal Is via the resistor 61 and the resistor 62. is connected to the output terminal via. Further, this output terminal is connected to the base of a signal conversion transistor +07 via a resistor 71't-, and the collector of the transistor 107 is connected to the base of the transistor 102 via a resistor 72. Note that 11.63 is a setting resistor for the comparator 1 and the comparator 106, respectively.

In the overheat detector configured in this way, the maximum deviation in current control is determined by comparator hysteresis, and as the current deviation decreases, the coil resistance voltage becomes approximately the coil average voltage.

The smoothing filter 2 can obtain the virtual coil resistance voltage from the pulse width modulated coil voltage, and in order to equalize the virtual coil resistance voltage IN value, the smoothing filter 2 is driven by a circuit similar to the 1n coil 104. Of course, the time constant allows tracking even during transient times. Note that, instead of the main transistor 102, other semiconductor switching elements such as a silice, a gate-main-off silice, a field effect transistor, etc. may be used.

Fig. 2 is a time chart of the above-mentioned overheating limiter, and Fig. 2(a) shows the '11L flow at each part.
is the current command signal, Is' is the comparator reference voltage, and IC
is the instantaneous coil current waveform. Further, FIG. 2(b) shows the voltages at various parts, where VC is the coil voltage and vR is the coil resistance voltage, and the difference between these causes a smearing pull of 1E voltage due to the coil inductance. Note that Vdc is the power supply voltage, and TON is the main transistor 102.
The on-time of Tc is the switching period. Furthermore, FIG. 2(e) shows the virtual coil resistance voltage detected by the smoothing filter 2. FIG. 3 shows the general temperature Ta.
An example of the characteristic curve of the coil resistance Rt for
The figure shows a curve showing the characteristics of the comparator, and %VAVE is the coil average voltage.

In FIG. 4, the determination line A is tentatively set when the coil resistance is 180°C at the current value Isx. Then, this judgment line A becomes a curve that increases and decreases with the current command Is, and the upper side of the judgment line A indicates overheating, and the lower side indicates normality.

Therefore, by comparing the virtual coil resistance voltage in response to instantaneous current changes, overheating detection that responds instantaneously becomes possible.

FIG. 5 shows an example of a smoothing filter circuit using an operational amplifier. In the figure, 3 is an excitation coil, 24 is an operational amplifier, 201 to 204 are setting resistors, and 205 to 20
6 is a setting capacitor.

In the case of an electromagnetic clutch, etc., it is integrally constructed with either rotating part of the input shaft or output shaft, and an excitation coil may be attached to the rotating part. In this case, a slip ring and a brush are added to the supply of the excitation coil 1'u flow. At this time, a virtual coil voltage including a brush voltage drop is obtained.

FIG. 6 shows another embodiment in which there is a voltage drop across the transistor 109, a voltage drop across the free-wheeling diode 103, and a voltage drop across the brushes 41 and 42. Since the configuration other than the constant voltage diode 23 is the same as that shown in FIG. 1, corresponding parts are given the same reference numerals and explanations thereof will be omitted.

The voltage drop across the brushes 41 and 42 remains at a substantially constant value regardless of temperature or current value, and the transistor 109 and the freewheeling diode 103 are directly affected by the forward drop. Therefore, for the forward drop of the diode 23, the voltage drop of the brush 41, 42 and the voltage drop of the transistor 10 are constant.
The voltage drop of 9 is canceled out, and the voltage drop of freewheeling diode 103 is canceled out for the reverse drop of constant voltage diode 23.

Therefore, the voltage drop of the brush L11, 42, the transistor 109, and the freewheeling diode 103, which is an error with respect to the desired coil resistance average voltage, can be canceled out, thereby improving the detection accuracy of the virtual coil average voltage.

〔Effect of the invention〕

As described above, according to the present invention, the overheat detector includes the current control device that controls on/off the excitation coil current of the electromagnetic mechanism, the filter that detects the excitation coil average voltage, and the virtual coil resistance voltage and current command signal. It is equipped with a comparator that compares the coil resistance as the excitation coil temperature increases, and obtains the excitation coil average voltage as well as the excitation coil average voltage at the upper temperature rise limit value. Since it is configured to detect overheating of the coil, overheating can be detected without using a temperature detector.
In particular, it is possible to easily detect overheating even when power is supplied from a switching type current control device, and it also has the advantage of being able to constantly detect overheating by following an ever-changing current command signal.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of an overheat detector of an electromagnetic FA structure according to an embodiment of the present invention, FIG. 2 is a time chart diagram for explaining the operation of the A heat detector of the electromagnetic machine 11η of FIG. Figure 3 is a temperature characteristic curve diagram of exciting coil resistance, Figure 4 is a comparator setting curve diagram, Figure 5 is a circuit diagram explaining a smoothing filter circuit example, and Figure 6 is a circuit configuration diagram showing another embodiment. It is. DESCRIPTION OF SYMBOLS 1... Comparator, 2... Filter, 23... Constant voltage diode, 100... Current control device of electromagnetic mechanism, 1
01... Power supply, 102... Main transistor, 103
...freewheeling diode, 104...excitation coil, IO
2... Coil current detection resistor, 106... Comparator, 107... Signal conversion transistor, Is...
Current command signal. In addition, the - symbol +;- in the figure indicates the same or equivalent part.

Claims (1)

[Scope of Claims] (]) A current control device It that controls on/off the excitation coil current of an electromagnetic mechanism using a semiconductor switching element, a filter that detects the average voltage of the excitation coil, and a virtual coil obtained by this filter. A comparator that compares the resistance voltage and the current command signal is provided, and the coil resistance change accompanying the temperature rise of the excitation coil is obtained as the excitation coil average voltage, and the coil current and the excitation coil average voltage at the upper limit of temperature rise are obtained. 1. An overheating detector for an electromagnetic mechanism, characterized in that overheating of an excitation coil is detected based on a determination curve predetermined from . (2) A constant voltage diode that provides a constant voltage bias is connected to the filter to offset the brush voltage drop of the electromagnetic mechanism and the transistor voltage drop included in the virtual coil voltage. An overheat detector for an electromagnetic machine 14 according to claim 1.