JP2009296826A - Relay control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To protect a relay circuit 12 by cutting off the circuit when the relay circuit 12 is in an overheated state after detecting a temperature rise of the relay circuit on the basis of a change in resistance value of a relay coil 122. <P>SOLUTION: A voltage-dividing resistor R1 is provided in a circuit that connects a battery VB with the relay coil 122 while a series connection circuit of resistors R2, R3 is provided between the battery VB and a ground. A voltage V2 of a connection point P2 between the relay coil 122 and the resistor R1 and a voltage V1 of a connection point P1 between the resistors R2, R3 are compared with each other by a comparator CMP1. It is determined that the relay coil 122, eventually, the relay circuit 12 is in an overheated state when the comparison result is reversed, and then, a MOSFET (Q1) is cut off. Accordingly, it is possible to reliably protect the relay circuit 12 from heat generation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a relay control device having a function of detecting a temperature of a relay coil and shutting off a circuit and protecting the circuit when the temperature reaches a predetermined temperature.

  For example, various loads such as lamps and motors mounted on vehicles are often used to switch between driving and stopping using a relay circuit. The relay circuit includes a relay coil and a relay contact. When an electronic switch provided between the relay coil and the power supply is turned on and a current flows through the relay coil, the relay coil is excited and the relay contact is turned on. To do. As a result, since the power supply voltage is supplied to the load connected to the relay contact, the load can be driven. When the current is interrupted, the relay contact is turned off, and the load connected to the relay contact is stopped.

  In a load circuit using a relay circuit, an overcurrent may flow through the relay coil and damage the relay coil. To avoid such trouble, for example, JP 2007-242314 A (Patent Document 1). ) Is known.

FIG. 8 is a circuit diagram showing a relay control circuit described in Patent Document 1. In this relay control circuit, when the relay circuit 101 is turned on and electric power is supplied to the load 104, the transistor 103 is turned on at a time point before the current flows through the relay coil 101a. Thereafter, the transistor 102 is turned on to energize the relay coil 101a, and the transistor 103 is turned off after the relay contact 101b is turned on. Thereby, it is possible to prevent an inrush current from flowing through the relay contact 101b.
JP 2007-242314 A

  However, in the conventional example disclosed in Patent Document 1 described above, when the relay contact 101b is turned on and then the entire relay circuit 101 generates heat due to an overcurrent flowing through the relay contact 101b, this can be detected. However, the relay coil 101a and the relay contact 101b were overheated, and eventually damaged.

  The present invention has been made in order to solve such a conventional problem. The object of the present invention is to monitor the temperature change of the entire relay circuit based on the resistance value of the relay coil and to generate a large amount of heat. In some cases, it is an object to provide a relay control device capable of protecting a relay circuit by interrupting the circuit.

  In order to achieve the above object, a first aspect of the present invention provides a voltage dividing resistor provided in a circuit connecting a power source and the relay coil in a relay control device for controlling a relay circuit having a relay coil and a relay contact. And a voltage detection means for measuring a voltage generated at both ends of the relay coil when energizing the relay coil to turn on the relay contact, and a voltage generated at both ends of the relay coil by the voltage detection means. Control means for detecting that the relay circuit is in an overheated state when it is detected that the voltage exceeds a predetermined threshold voltage.

  The invention according to claim 2 is generated at a connection point between a threshold voltage generation circuit that is connected to the power source and generates the threshold voltage by dividing an output voltage of the power source, and the voltage dividing resistor and the relay coil. Comparing means for inputting a measurement voltage to one input terminal, inputting the threshold voltage to the other input terminal, and outputting an output signal corresponding to a comparison result of the threshold voltage and the measurement voltage, and The control means detects that the relay circuit is in an overheated state when the output signal of the comparison means changes.

  According to a third aspect of the present invention, the control means calculates a resistance value of the relay coil using a predetermined arithmetic expression based on the measurement voltage, and based on the calculated resistance value of the relay coil, the relay It is characterized by determining whether or not the circuit is in an overheated state.

  According to a fourth aspect of the present invention, an electronic switch is provided in a circuit connecting the power source and the relay coil, and the control means shuts off the electronic switch when detecting that the relay circuit is overheated. It is characterized by doing.

  According to the first aspect of the present invention, the voltage generated at both ends of the relay coil is detected, and when this voltage exceeds a predetermined threshold voltage, it is determined that the relay coil and thus the entire relay circuit is overheated, and the circuit is shut off. Therefore, when the relay circuit is overheated, it can be immediately detected to protect the relay circuit. For this reason, environmental load can be reduced.

  In the invention of claim 2, the measured voltage generated at both ends of the relay coil is compared with the threshold voltage generated by the threshold voltage generating circuit, and the relay circuit is overheated when the measured voltage exceeds the threshold voltage. Therefore, when the relay circuit is overheated, this can be detected quickly.

  In the invention of claim 3, based on the measured voltage generated at both ends of the relay coil, the temperature of the relay coil is calculated using a predetermined arithmetic expression, and when the calculated coil temperature exceeds the threshold temperature, the relay coil and thus the relay Since it is detected that the entire circuit is overheated, it is possible to reliably prevent the relay circuit from being overheated.

  In the invention of claim 4, when the relay coil is overheated, the electronic switch is cut off to stop energization of the relay coil and the relay contact is cut off, so that the circuit can be reliably protected. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a load circuit equipped with a relay control device according to the first embodiment of the present invention. This load circuit is a circuit for supplying and driving a battery voltage to a load such as a lamp or a motor mounted on the vehicle, for example, and as shown in FIG. 1, between the battery VB (power source) and the load 11. Is provided with a relay circuit 12.

  The relay circuit 12 includes a relay contact 121 and a relay coil 122, and the relay contact 121 is connected between the battery VB and the load 11. On the other hand, one end of the relay coil 122 is connected to the battery VB via a resistor R1 (voltage dividing resistor), and the other end is grounded via a MOSFET (Q1; electronic switch).

  The gate of the MOSFET (Q1) is connected to the gate driver 132 of the control unit 13. Therefore, when the drive signal is output from the gate driver 132, the MOSFET (Q1) is turned on, the voltage output from the battery VB is applied to the relay coil 122, and the relay contact 121 is turned on.

  Further, a series connection circuit (threshold voltage generation circuit) of resistors R2 and R3 is provided between the battery VB and the ground, and a connection point P1 (voltage V1) between the resistors R2 and R3 is a comparator CMP1 ( To the inverting side input terminal of the comparison means).

  Furthermore, the connection point P2 (voltage V2) between the resistor R1 and the relay coil 122 is connected to the normal rotation side input terminal of the comparator CMP1. The output terminal of the comparator CMP <b> 1 is connected to a temperature abnormality detection unit 131 provided in the control unit 13.

  Here, when the resistance values of the resistors R1, R2, and R3 are the resistance Ra when the relay coil 122 is normal (when normal current is flowing), the voltage V1 (threshold voltage) at the connection point P1 is the connection point. It is set to be slightly larger than the voltage V2 (measurement voltage) of P2. That is, the resistance values of the resistors R1, R2, and R3 are set so that the following equation (1) is satisfied.

R3 / (R2 + R3)> Ra / (R1 + Ra) (1)
Therefore, when a current flows through the relay coil 122 and the relay contact 121 is turned on, V1> V2 is established, and the output signal of the comparator CMP1 is at the L level.

  The control unit 13 is configured by a microcomputer, for example, and includes a temperature abnormality detection unit 131 and a gate driver 132. The temperature abnormality detection unit 131 determines whether or not the relay coil 122 is in an overheated state according to the output signal of the comparator CMP1.

  When an ON signal for the relay circuit is supplied from the outside, the gate driver 132 outputs a drive signal to the gate of the MOSFET (Q1) to drive the MOSFET (Q1). When the MOSFET (Q1) is turned on, the voltage output from the battery VB is applied to the relay coil 122, so that the relay coil 122 is excited and the relay contact 121 is turned on. Here, the control unit 13 has a function as a control unit, and also has a function as a voltage detection unit that detects a voltage (V2) generated at both ends of the relay coil 122.

  2A and 2B are explanatory views schematically showing the structure of the relay circuit 12. FIG. 2A shows a state where the relay contact 121 is turned off, and FIG. 2B shows that the relay contact 121 is turned on. The state is shown. As shown in FIG. 2A, the relay circuit 12 includes a cylindrical iron core 123, and a relay coil 122 is spirally wound around the iron core 123. Further, a movable iron plate 124 and a movable contact 125 connected to the movable iron plate are provided at the upper end portion of the iron core 123. When no current flows through the relay coil 122 (when the contact is separated), the movable iron plate 124 is provided. Is biased in a direction away from the upper end of the iron core 123. At this time, the movable contact 125 is in contact with the contact 126a, and therefore the load circuit shown in FIG. 1 is cut off. Note that the relay contact 121 shown in FIG. 1 is configured by the movable iron plate 124 and the movable contact 125 shown in FIG. 2.

  When a current flows through the relay coil 122 and the relay coil 122 is excited, the movable iron plate 124 is attracted downward by the magnetic force generated in the iron core 123 as shown in FIG. It contacts the upper end of 123. Along with this, the movable contact 125 fixed to the movable iron plate 124 is urged downward and contacts the contact 126b. As a result, the relay contact 121 of the relay circuit 12 shown in FIG. 1 is turned on, and the voltage of the battery VB is supplied to the load 11 to drive the load 11. That is, in FIGS. 2A and 2B, terminals 127 a and 127 b are two terminals of the relay contact 121 shown in FIG. 1, and terminals 128 a and 128 b are two terminals of the relay coil 122.

  Hereinafter, the operation of the relay control device according to the present embodiment will be described with reference to the flowchart shown in FIG.

  When the load 11 shown in FIG. 1 is driven, a relay-on signal is supplied to the control unit 13. The gate driver 132 outputs a drive signal to the gate of the MOSFET (Q1) when the relay-on signal is supplied. At this time, the drive signal may be a PWM signal having a predetermined duty ratio.

  The MOSFET (Q1) is switched from off to on when a drive signal is input. As a result, a current flows in the path of battery VB → resistor R1 → relay coil 122 → MOSFET (Q1) → ground, and the relay coil 122 is excited by this current, so that the relay contact 121 is turned on. As a result, the voltage of the battery VB is supplied to the load 11 and the load 11 is driven.

  Further, the control unit 13 monitors the voltage V2 generated in the relay coil 122 by detecting the output signal of the comparator CMP1 (step S1 in FIG. 3). As described above, when the current flowing through the relay contact 121 is a normal current, the temperature of the relay coil and the coil voltage are substantially constant and stable, and the voltage V1 at the connection point P1 is the voltage V2 at the connection point P2. Therefore, the output signal of the comparator CMP1 becomes L level.

  Here, when an overcurrent flows through the relay contact 121 due to a short circuit accident or the like, the heat generated at the relay contact 121 is transmitted to the relay coil 122, and the temperature of the relay coil 122 rises. The resistance Ra of the coil 122 increases. That is, as shown in the characteristic curve of FIG. 7, the temperature T of the relay coil 122 and the resistance Ra of the relay coil 122 have a linear function relationship, and the resistance value increases as the temperature rises. Accordingly, when the relay coil 122 exceeds a certain temperature (threshold temperature), the right side of the above-described equation (1) becomes larger than the left side (the inequality is inverted), and V1 <V2 and the output signal of the comparator CMP1 Is inverted from the L level to the H level (YES in step S2).

  Next, when detecting that the output signal of the comparator CMP1 is inverted from the L level to the H level, the temperature abnormality detection unit 131 determines that a temperature abnormality has occurred in the relay coil 122 and outputs a relay abnormality signal to the outside. (Step S3). Thereby, for example, an alarm signal can be issued.

  Furthermore, the temperature abnormality detection unit 131 outputs a relay cutoff signal to the gate driver 132 (step S4).

  When the relay cut-off signal is supplied, the gate driver 132 stops outputting the drive signal to the MOSFET (Q1) and cuts off the MOSFET (Q1) (step S5). As a result, the voltage supply to the relay coil 122 is stopped, and the circuit can be protected.

  Next, the above operation will be described with reference to a timing chart shown in FIG. 4A is a characteristic diagram showing a change in temperature (coil temperature) of the relay coil 122, and FIG. 4B is a characteristic diagram showing a change in voltage (coil voltage) generated in the relay coil 122. 4 (c) is a characteristic diagram showing a change in current (energization current) flowing through the relay contact 121. FIG.

  When the MOSFET (Q1) is turned on at time t1 and a current flows through the relay contact 121, the coil temperature and the coil voltage are stabilized at substantially constant values. At this time, the coil temperature is lower than the threshold temperature, and the coil voltage is lower than the threshold voltage.

  At time t2, when a short circuit accident or the like occurs and an overcurrent flows through the load 11, the energization current of the relay contact 121 increases as shown in FIG. 4 (c), and accordingly, the coil temperature gradually increases. The coil voltage starts to rise and the coil voltage gradually rises. As shown in FIG. 4B, when the coil voltage reaches the threshold voltage at time t3, the output signal of the comparator CMP1 shown in FIG. 1 is inverted from the L level to the H level, and the MOSFET (Q1) is turned off. Thus, the relay circuit 12 is turned off. That is, when the temperature of the relay coil 122 and the entire relay circuit 12 is overheated, the MOSFET (Q1) can be cut off to protect the circuit.

  Thus, in the relay control device according to the first embodiment of the present invention, the voltage generated in the relay coil 122 is monitored, and the voltage (V2) generated in the relay coil 122 exceeds the preset threshold voltage (V1). In this case, it is determined that a temperature abnormality has occurred in the relay coil 122 and thus the entire relay circuit 12, and the energization of the relay coil 122 is stopped. Therefore, when the temperature of the relay circuit 12 rises, this can be detected reliably and the circuit can be shut off, and damage to the relay circuit 12 can be prevented.

  In the relay control device according to the first embodiment, since the resistor R1 is provided between the relay coil 122 and the battery VB, the voltage applied to the relay coil 122 can be reduced, and as a result, the relay coil. The current flowing through 122 can be reduced. As a result, power consumption can be reduced.

  Further, in the first embodiment described above, if the resistors R1, R2, and R3 are made of a material having the same temperature characteristics as the relay coil 122, the circuit can be more reliably operated at a predetermined temperature without being affected by the ambient temperature. Can be blocked.

  Next, a second embodiment of the present invention will be described. FIG. 5 is a circuit diagram showing a configuration of a load circuit equipped with a relay control device according to the second embodiment of the present invention. Similar to the first embodiment described above, this load circuit is a circuit for supplying and driving a battery voltage to a load such as a lamp or a motor mounted on a vehicle, for example, as shown in FIG. A relay circuit 12 is provided between the battery VB and the load 11.

  The relay circuit 12 includes a relay contact 121 and a relay coil 122, and the relay contact 121 is connected between the battery VB and the load 11. On the other hand, one end of the relay coil 122 is connected to the battery VB via a resistor R1, and the other end is grounded via a MOSFET (Q1; electronic switch).

  The gate of the MOSFET (Q1) is connected to the gate driver 143 of the control unit 14. Therefore, when the drive signal is output from the gate driver 143, the MOSFET (Q1) is turned on, the voltage output from the battery VB is applied to the relay coil 122, and the relay contact 121 is turned on.

  The control unit 14 is configured by, for example, a microcomputer, and includes an A / D conversion unit 141, a temperature abnormality detection unit 142, and a gate driver 143. The A / D converter 141 reads the voltage V11 generated at the connection point P11 between the resistor R1 and the relay coil 122, converts this voltage V11 into a digital signal, and calculates the temperature of the relay coil 122. A method for calculating the temperature will be described later.

  The temperature abnormality detection unit 142 determines whether or not the relay circuit 12 is in an overheated state based on the temperature of the relay coil 122 obtained by the A / D conversion unit 141. When the relay circuit 12 is overheated, a relay abnormality signal is output to the outside.

  When the ON signal of the relay circuit is supplied from the outside, the gate driver 143 outputs a drive signal to the gate of the MOSFET (Q1) to drive the MOSFET (Q1). When the MOSFET (Q1) is turned on, the voltage output from the battery VB is applied to the relay coil 122, so that the relay coil 122 is excited and the relay contact 121 is turned on. Further, when a relay cut-off signal is output from the temperature abnormality detection unit 142, the MOSFET (Q1) is cut off and the energization to the relay coil 122 is stopped.

  Next, a procedure for calculating the temperature of the relay coil 122 from the voltage V11 in the A / D conversion unit 141 will be described. FIG. 6 is an explanatory diagram showing an arithmetic expression for obtaining the resistance value of the relay coil 122 based on the voltage V11 generated in the relay coil 122 and the output voltage of the battery VB. As shown in FIG. 6, the voltage V11 generated in the relay coil 122 is expressed by the following equation (2).

V11 = {Ra / (R1 + Ra)} * VB (2)
However, “Ra” is a coil resistance.

  From the above equation (2), the coil resistance Ra is expressed by the following equation (3).

Ra = {V11 / (VB−V11)} R1 (3)
Further, the temperature T of the relay coil 122 and the resistance Ra of the relay coil 122 have a linear function relationship as shown in FIG. That is, using the constants α and β, the coil resistance Ra and the coil temperature T are expressed by the following equation (4).

Ra = αT + β (4)
Therefore, the A / D converter 141 shown in FIG. 5 obtains the coil resistance Ra from the above equation (3) based on the voltage V11 at the connection point P11, and further calculates the coil temperature T from the equation (4). Will be able to.

  The temperature abnormality detection unit 142 outputs a relay abnormality signal when the coil temperature T calculated by the A / D conversion unit 141 exceeds the threshold temperature, and further outputs an output stop signal to the gate driver 143. Then, the MOSFET (Q1) is stopped.

  Thus, in the relay control device according to the second embodiment, the voltage V11 generated in the relay coil 122 is measured, the resistance value of the relay coil 122 is obtained based on the voltage V11, and further, based on the resistance value. The temperature of the relay coil 122 is calculated. Therefore, when the temperature of the relay coil 122 rises and exceeds the threshold temperature, this can be detected immediately and the circuit can be shut off.

  Although the relay control device of the present invention has been described based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each unit is replaced with an arbitrary configuration having the same function. Can do.

  For example, in each of the above-described embodiments, the example in which the MOSFET (Q1) is used as the electronic switch has been described. However, other semiconductor switches such as an IGBT (insulated gate bipolar transistor) may be used.

  When the relay coil generates heat, it is extremely useful for immediately protecting the relay circuit by interrupting the circuit.

It is a circuit diagram which shows the structure of the relay control apparatus which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows typically the structure of the relay circuit used for the relay control apparatus which concerns on 1st Embodiment of this invention, (a) shows the time of contact separation, (b) shows the time of contact holding. It is a flowchart which shows operation | movement of the relay control apparatus which concerns on 1st Embodiment of this invention. It is a characteristic view which shows the change of the electric current which flows into the coil temperature, coil voltage, and relay contact of the relay control apparatus which concerns on 1st Embodiment of this invention. It is a circuit diagram which shows the structure of the relay control apparatus which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows the procedure which concerns on 2nd Embodiment of this invention and calculates coil resistance from a coil voltage. It is a characteristic view which shows the relationship between the temperature of a relay coil, and coil resistance value. It is a circuit diagram which shows the structure of the conventional relay control apparatus.

Explanation of symbols

11 Load 12 Relay Circuit 13 Control Unit (Control Unit)
14 Control unit (control means)
121 relay contact 122 relay coil 123 iron core 124 movable iron plate 125 movable contact 126a, 126b contact 127a, 127b terminal 128a, 128b terminal VB battery Q1 MOSFET (electronic switch)
R1 voltage dividing resistor

Claims (4)

In a relay control device for controlling a relay circuit including a relay coil and a relay contact,
A voltage dividing resistor provided in a circuit connecting the power source and the relay coil;
Voltage detecting means for measuring a voltage generated at both ends of the relay coil when the relay coil is energized to turn on the relay contact;
Control means for detecting that the relay circuit is in an overheated state when the voltage detection means detects that the voltage generated at both ends of the relay coil exceeds a predetermined threshold voltage;
A relay control device comprising: A threshold voltage generation circuit connected to the power source and dividing the output voltage of the power source to generate the threshold voltage;
A measurement voltage generated at a connection point between the voltage dividing resistor and the relay coil is input to one input terminal, the threshold voltage is input to the other input terminal, and the comparison result of the threshold voltage and the measurement voltage is used. A comparison means for outputting an output signal;
The relay control device according to claim 1, wherein the control unit detects that the relay circuit is in an overheated state when an output signal of the comparison unit changes.   The control means calculates a resistance value of the relay coil using a predetermined arithmetic expression based on the measured voltage, and based on the calculated resistance value of the relay coil, whether the relay circuit is in an overheated state or not. The relay control device according to claim 1, wherein: An electronic switch is provided in a circuit connecting the power source and the relay coil,
The relay control device according to any one of claims 1 to 3, wherein the control means shuts off the electronic switch when detecting that the relay circuit is in an overheated state.

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