Seat occupancy sensor

1. A seat occupancy sensor provided in a vehicle seat, comprising a pair of switch modules disposed in an occupant seating area of a seat cushion so as to be laterally spaced from each other, wherein:

each of the switch modules includes a first pressure-sensitive switch and a second pressure-sensitive switch that are disposed on a front part so as to be laterally spaced from each other and a third pressure-sensitive switch disposed on a rear part;

each of the switch modules is configured to be turned on when at least one of the first pressure-sensitive switch and the second pressure-sensitive switch is on and the third pressure-sensitive switch is on; and

the seat occupancy sensor is configured to be turned on when the switch modules are both on.

2. The seat occupancy sensor according to claim 1 , wherein:

each of the first pressure-sensitive switch, the second pressure-sensitive switch, and the third pressure-sensitive switch is a switch configured to be conductive and turned on when a predetermined pressure is applied;

in each of the switch modules, the first pressure-sensitive switch and the second pressure-sensitive switch are electrically connected in parallel and the third pressure-sensitive switch is connected in series with the first pressure-sensitive switch and the second pressure that are connected in parallel; and

the switch modules are electrically connected in series with each other.

3. The seat occupancy sensor according to claim 1 , wherein:

the switch modules include two pairs of left and right switch modules arranged such that one pair is located behind the other;

the rear pair of switch modules includes a first switch module disposed on a right side and a second switch module disposed on a left side;

the front pair of switch modules includes a third switch module disposed on a right side and a fourth switch module disposed on a left side;

the third switch module is located in front of the first switch module;

the fourth switch module is located in front of the second switch module; and

the seat occupancy sensor is configured to be turned on when both the first switch module and the second switch module are on or when both the third switch module and the fourth switch module are on.

4. The seat occupancy sensor according to claim 3 , wherein:

the first switch module and the second switch module are electrically connected in series;

the third switch module and the fourth switch module are electrically connected in series; and

the first switch module and the second switch module that are connected in series are electrically connected in parallel to the third switch module and the fourth switch module that are connected in series.

5. The seat occupancy sensor according to claim 3 , wherein the seat occupancy sensor is configured to be also turned on when the first switch module and the fourth switch module are on or when the second switch module and the third switch module are on.

6. The seat occupancy sensor according to claim 5 , wherein:

the first switch module and the third switch module are electrically connected in parallel;

the second switch module and the fourth switch module are electrically connected in parallel; and

the first switch module and the third switch module that are connected in parallel are electrically connected in series the second switch module and the fourth switch module that are connected in parallel.

7. The seat occupancy sensor according to claim 3 , wherein the third pressure-sensitive switch of each of the first switch module and the second switch module is disposed below a hip point set in the vehicle seat in side view.

8. The seat occupancy sensor according to claim 7 , wherein the third pressure-sensitive switch of the first switch module and the third pressure-sensitive switch of the second switch module are spaced from each other so as to be symmetrically arranged with respect to the hip point in top view.

9. The seat occupancy sensor according to claim 8 , further comprising a first additional pressure-sensitive switch provided to the right of the third switch module and a second additional pressure-sensitive switch provided to the left of the fourth switch module,

wherein the seat occupancy sensor is configured to be turned on regardless of a state of the third switch module and the fourth switch module.

10. The seat occupancy sensor according to claim 1 , wherein in each of the switch modules, the third pressure-sensitive switch is disposed at a center between the corresponding first pressure-sensitive switch and second pressure-sensitive switch with respect to a lateral direction.

11. The seat occupancy sensor according to claim 1 , wherein the vehicle seat constitutes a rear seat of a wheeled vehicle.