Electric power source for motor vehicle

1. An electric power source for a motor vehicle, comprising:

a battery;

a contactor shutting off a voltage outputted from the battery; and

an interlock circuit controlling the contactor, the interlock circuit detecting a disconnected state of an interlock wire and turning off the contactor to shut off a power supplied from the battery,

wherein the interlock circuit comprises:

a current output circuit outputting a detectable current via a diode to the interlock wire;

a first current detection subcircuit, connected via the interlock wire and the diode to the current output circuit, for detecting the detectable current outputted from the current output circuit;

a second current detection subcircuit, connected to a connection point operatively located between the current output circuit and the diode, for detecting the detectable current outputted from the current output circuit; and

a judgment circuit judging a disconnected state of the interlock wire, based on the detectable current detected at the first current detection subcircuit and the second current detection subcircuit, and thus cutting off the contactor, and

wherein when the detectable current is detected at the second current detection subcircuit and when the detectable current is not detected at the first current detection subcircuit, the judgment circuit judges the interlock wire to be in a disconnected state and thus cuts off the contactor.

2. The electric power source for a motor vehicle as recited in claim 1 , wherein the current output circuit comprises a first current output subcircuit and a second current output subcircuit, so that the judgment circuit is adapted to control an output state of the first current output subcircuit and the second current output subcircuit.

3. The electric power source for a motor vehicle as recited in claim 1 , the electric power source comprising an interlock switch connected in series to the battery, wherein a detection switch detecting an on-and-off state of the interlock switch is connected in series to the interlock wire, so that when the interlock switch is turned off, the judgment circuit is adapted to judge the interlock wire to be in a disconnected state and turns off the contactor.

4. The electric power source for a motor vehicle as recited in claim 1 wherein the interlock wire is connected to a vehicle side via an output connector connecting an output terminal of the battery to the vehicle side, so that when the output connector is detached, the interlock wire comes to a disconnected state, so that the contactor is turned off to shut off the power outputted from the battery.

5. The electric power source for a motor vehicle as recited in claim 1 , wherein when both of the first current detection subcircuit and the second current detection subcircuit is operable to detect the detectable current, the judgment circuit controls the current output circuit not to output; then if the detectable current is detected at the first current detection subcircuit and if the detectable current is not detected at the second current detection subcircuit, the judgment circuit judges the interlock wire to be short-circuited to the electric source for either the interlock circuit or the vehicle side.

6. The electric power source for a motor vehicle as recited in claim 1 , wherein when both of the first current detection subcircuit and the second current detection subcircuit is operable to detect the detectable current, the judgment circuit controls the current output circuit not to output; then if the detectable current is detected at the first current detection subcircuit and the second current detection subcircuit, the judgment circuit judges the current output circuit to be in failure.

7. The electric power source for a motor vehicle as recited in claim 2 , wherein the judgment circuit controls the first current output subcircuit to output and the second current output subcircuit not to output, with both of the first current detection subcircuit and the second current detection subcircuit not detecting the detectable current; then if the judgment circuit controls the second current output subcircuit to output and if the detectable current is not detected at the first current detection subcircuit and the second current detection subcircuit, the judgment circuit judges the interlock wire to be short-circuited to ground.

8. The electric power source for a motor vehicle as recited in claim 2 , wherein the judgment circuit controls the first current output subcircuit to output and the second output subcircuit not to output, with both of the first current detection subcircuit and the second current detection subcircuit not detecting the detectable current; then if the judgment circuit controls the second current output subcircuit to output and if the detectable current is detected at either or both of the first current detection subcircuit and the second current detection subcircuit, the judgment circuit judges the first current output subcircuit to be in failure.

9. The electric power source for a motor vehicle as recited in claim 1 , wherein the current output circuit has, on an output side thereof, an output switch controlled by the judgment circuit.

10. The electric power source for a motor vehicle as recited in claim 1 , wherein the interlock circuit comprises a power source.

11. The electric power source for a motor vehicle as recited in claim 1 , wherein the second current detection subcircuit comprises an amplifier having a resister connected on an input side.

12. The electric power source for a motor vehicle as recited in claim 1 , wherein positive-side contactor and negative-side contactor are switched on and off in delay under the control by a delay switch.