Protection device for electricity supply circuit

Patent metadata

Field	Value
Publication number	US-9472940-B2
Application number	US-201414510651-A
Country	US
Kind code	B2
Filing date	Oct 9, 2014
Priority date	Apr 24, 2012
Publication date	Oct 18, 2016
Grant date	Oct 18, 2016

Abstract

When a power switch is turned off, a protection device for an electricity supply circuit starts keeping time using a timer and turns on a disconnection flag. Then the protection device turns off the disconnection flag when the timer has counted a predetermined time. When the power switch is turned off, the disconnection flag does not subsequently turn off until the predetermined time has passed. Therefore, it is possible to prevent an excessive temperature increase in the power switch and prevent damage to the power switch.

First claim

What is claimed is:

1. A protection device for an electricity supply circuit, which is configured to disconnect the electricity supply circuit when an overcurrent flows to the electricity supply circuit connected to a load, thereby to protect the electricity supply circuit, the protection device comprising:
a power switch that switches between conduction and disconnection of the electricity supply circuit; and
a controller configured to output a switching command signal to the power switch in accordance with an operating signal through an input switch,
the controller comprising:
a timer that, when the input switch is turned off, counts an elapsed time since the power switch has been turned off;
a disconnection flag setting unit configured to turn on a disconnection flag when an anomaly in the electricity supply circuit is detected, and turn off the disconnection flag when a disconnection flag release signal is inputted; and
a disconnection release control unit configured to output the disconnection flag release signal to the disconnection flag setting unit when the timer has counted a predetermined time that is set for a time required to lower an estimated temperature of the electricity supply circuit, wherein
during a period that the disconnection flag is turned on, the controller is configured to control the power switch so that the power switch would be maintained in an OFF state even if the input switch is turned on.

2. The protection device of claim 1 , wherein
the timer is configured to reset the elapsed time being counted when the input switch is turned on.

3. The protection device of claim 1 , further comprising
a current detector for detecting current flowing to the electricity supply circuit, wherein
the controller comprises:
a temperature estimation unit that, when the power switch is turned on, estimates an increasing temperature of the electricity supply circuit based on a current value detected by the current detector and an electricity supply time, and when the power switch is turned off, estimates a decreasing temperature of the electricity supply circuit based on the elapsed time, and that estimates a temperature of the electricity supply circuit based on the increasing temperature and the decreasing temperature; and
an anomaly determination unit that judges whether or not the estimated temperature of the electricity supply circuit estimated by the temperature estimation unit exceeds a predetermined temperature, and
the disconnection flag setting unit turns on the disconnection flag when the anomaly determination unit judges that the temperature of the electricity supply circuit has exceeded the predetermined temperature.

4. The protection device of claim 3 , wherein:
the temperature estimation unit estimates the increasing temperature of the electricity supply circuit according to expression (1):
X 1= i 2 ×R on ×Δt   (1);

where, i is the current value, R on is resistance of the electrical supply circuit connected to the load, and Δt, is a sampling time in seconds; and
the estimated temperature of the electricity supply circuit for a present time period is calculated by adding the estimated rising temperature obtained by dividing the quantity of heat X 1 calculated from the expression (1) by a heat capacity of the electricity supply circuit, to an estimated temperature calculated from a previous time period.

5. The protection device of claim 4 , wherein:
the temperature estimation unit estimates the decreasing temperature of the electricity supply circuit according to expression (2):
Y 1= Q /( C th ×R th /Δt )  (2);

where, Q is heat quantity of the of the electrical supply circuit, C th is heat capacity of the electricity supply circuit, R th is thermal resistance of the electricity supply circuit;
the estimated temperature of the electrical supply circuit for the present time period is calculated by subtracting the estimated decreasing temperature obtained by dividing the quantity of heat radiation Y 1 , calculated from the expression (2) by the heat capacity of the electricity supply circuit, from an estimated temperature calculated for the previous time period.

6. The protection device of claim 1 , wherein the controller comprises:
an input determination control unit;
a disconnection release control unit;
a temperature estimation unit;
an anomaly determination unit;
an AND gate;
an inverter;
a disconnection flag setting unit; and
terminals for connection with external equipment.

7. The protection device of claim 6 , wherein:
the input determination control unit is connected to the input switch through one of the terminals; and
the input determination control unit outputs a switch input signal to the AND gate and the disconnection release control unit when the input switch inputs an OFF command or an ON command.

8. The protection device of claim 7 , wherein the temperature estimation unit acquires a current detection signal from the power switch through one of the terminals, calculates, based on a current value associated with the current detection signal, a heat generation quantity and a heat radiation quantity of a power line constituting the electricity supply circuit, and estimates a temperature of the power line constituting the electricity supply circuit, based on one or more of a thermal resistance and a heat capacity of the power line.

9. The protection device of claim 8 , wherein the anomaly determination unit outputs a command to turn on a disconnection flag to the disconnection flag setting unit when the estimated power line temperature reaches a predetermined threshold temperature.

10. The protection device of claim 7 , wherein:
the timer is activated when a switch input signal representing the OFF command is outputted from the input determination control unit to count the elapsed time since the OFF-command signal is inputted;
when the timer has counted the predetermined time, the disconnection release control unit outputs the disconnection flag release signal to the disconnection flag setting unit; and
when a switch input signal representing the ON command is outputted from the input determination control unit to the disconnection release control unit in a condition in which the disconnection flag is on, the disconnection release control unit resets the timer.

11. The protection device of claim 10 , wherein:
the disconnection flag setting unit turns on the disconnection flag when an ON command is outputted from the anomaly detection unit to the disconnection flag setting unit;
the disconnection flag setting unit turns off the disconnection flag when the disconnection flag release signal is outputted from the disconnection release control unit to the disconnection flag setting unit;
the disconnection flag setting unit outputs a logic high (H) signal to the inverter when the disconnection flag is turned on, and outputs a logic low (L) signal to the inverter when the disconnection flag is turned off; and
the inverter inverts and outputs the signal output from the disconnection flag setting unit.

12. The protection device of claim 11 , wherein:
one input terminal of the AND gate is connected to an output terminal of the input determination control unit and the other input terminal of the AND gate is connected to an output terminal of the inverter;
when the output signal of the input determination control unit is a logic high (H) signal and the output signal of the inverter is the H signal, the AND gate outputs a logic high (H) signal through one of the terminals; and
the power switch is turned on so that the load is supplied with electricity.

Assignees

• Yazaki Corp

Inventors

• Nakamura Yoshihide
• Maruyama Akinori
• Ikuta Yoshinori
• Ueta Keisuke

Classifications

• H02H3/06 Primary

  with automatic reconnection · CPC title

• H02H3/0935 Primary

  the timing being determined by numerical means · CPC title

• H02H6/00

  Emergency protective circuit arrangements responsive to undesired changes from normal non-electric working conditions using simulators of the apparatus being protected, e.g. using thermal images · CPC title

• H02H3/085

  making use of a thermal sensor, e.g. thermistor, heated by the excess current (also responsive to the temperature of the protected device H02H5/041, thermal images H02H6/00) · CPC title