Seat occupancy sensor having an array of sensors shifted from a center of a seat of a vehicle

A seat occupancy sensor includes: a first sensor group having a plurality of first sensor cells that are arrayed in a front-rear direction of a seat and become conductive as a load is applied thereto; a second sensor group having a plurality of second sensor cells that are arrayed in the front-rear direction, farther on a front side of the seat and closer to an end of the seat in a width direction than the first sensor group, and that become conductive as a load is applied thereto; and an electronic control unit. The electronic control unit determines that someone is sitting on the seat when both of at least one of the first sensor cells and at least one of the second sensor cells become conductive.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2017-043816 filed on Mar. 8, 2017 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a seat occupancy sensor.

2. Description of Related Art

Examples of hitherto known seat occupancy sensors include the one described in Japanese Patent No. 4629124. This seat occupancy sensor is formed by a so-called membrane switch, and is disposed in a seat surface of a vehicle seat to determine (detect) whether someone is sitting on the seat.

SUMMARY

Japanese Patent No. 4629124 states that a plurality of detection units (sensor cells) of the seat occupancy sensor are disposed according to a load pressure region that reflects the shapes of the buttocks and the femoral region of a seated person. However, these detection units are collectively disposed closer to the rear side of a seat, and thus are substantially subjected to the load of the buttocks of a seated person. Therefore, for example, when baggage is placed at a position corresponding to the buttocks of a seated person, the detection units subjected to the load of this baggage may become conductive, leading the seat occupancy sensor to erroneously determine that someone is sitting on the seat.

The present disclosure provides a seat occupancy sensor that can determine, with higher accuracy, whether someone is sitting on a vehicle seat.

A seat occupancy sensor according to an aspect of the present disclosure includes: a first sensor group having first detection units as a plurality of detection units that are arrayed in a front-rear direction of a seat of a vehicle and that become conductive as a load is applied thereto; a second sensor group having second detection units as a plurality of detection units that are arrayed in the front-rear direction, farther on the front side of the seat and closer to an end of the seat in a width direction than the first sensor group, and that become conductive as a load is applied thereto; and an electronic control unit configured to determine that someone is sitting on the seat when both of at least one of the first detection units and at least one of the second detection units become conductive.

According to this configuration, one of the first detection units of the first sensor group that is located farther on the rear side of the seat and farther away from the end of the seat in the width direction than the second sensor group, is highly likely to become conductive as a load is applied thereto from the buttocks of a seated person. On the other hand, one of the second detection units of the second sensor group that is located farther on the front side of the seat and closer to the end of the seat in the width direction than the first sensor group, is highly likely to become conductive as a load is applied thereto from the femoral region of a seated person. Therefore, when both of at least one of the first detection units and at least one of the second detection units become conductive, it is highly likely that the load is applied from the buttocks and the femoral region of the seated person at the same time, i.e., someone is sitting on the seat. This electronic control unit determines that someone is sitting on the seat when both of at least one of the first detection units and at least one of the second detection units become conductive, and thus can determine, with higher accuracy, whether someone is sitting on the seat.

In the above seat occupancy sensor, the detection sensitivity of the first detection units may be lower than the detection sensitivity of the second detection units. Since the load applied from the buttocks of a seated person is usually larger than the load applied from the femoral region of the seated person, the first detection units are highly likely to become conductive even when the detection sensitivity thereof is lower than the detection sensitivity of the second detection units. According to this configuration, the detection sensitivity of the first detection units is lower than the detection sensitivity of the second detection units, so that it is less likely that one of the first detection units becomes conductive, for example, due to baggage placed on the seat. Therefore, the likelihood of the seat occupancy sensor erroneously determining that someone is sitting on the seat can be reduced.

In the above seat occupancy sensor, the first detection units may have an electrode area smaller than the electrode area of the second detection units so as to have the detection sensitivity lower than the detection sensitivity of the second detection units.

According to this configuration, it is possible to set the detection sensitivity of the first detection units to be lower than the detection sensitivity of the second detection units by using a very simple structure based on the size relationship between the electrode areas. The above electronic control unit may be configured to determine that someone is sitting on the seat when both of one of the plurality of first detection units and one of the plurality of second detection units that is separated from that one first detection unit by a predetermined distance become conductive.

According to this configuration, when the first detection unit and the second detection unit that become conductive are separated from each other by the predetermined distance, it is more highly likely that the load is applied from the buttocks and the femoral region of the seated person at the same time, i.e., someone is sitting on the seat. Thus, this electronic control unit can determine, with even higher accuracy, whether someone is sitting on the seat.

The above electronic control unit may be configured to determine that someone is sitting on the seat when both of one of the first detection units and one of the second detection units that is located farther toward the front side of the seat from that one first detection unit with two of the detection units therebetween, become conductive.

In the above seat occupancy sensor, the seat may be a center seat section that is disposed at the center of a plurality of seat sections provided side by side in a width direction of the vehicle in a rear seat that is disposed on the rear side of the vehicle. According to this configuration, the first sensor group and the second sensor group are disposed in the center seat section. The center seat section is often subjected to a load, for example, as a person sitting on the adjacent seat section rests his or her hand on the center seat section. However, the characteristics of such a load are naturally different from those of a load that is applied from the buttocks and the femoral region of a seated person at the same time. Thus, the likelihood of the seat occupancy sensor erroneously determining that someone is sitting on the seat can be reduced.

The above aspect offers an advantage that whether someone is sitting on a vehicle seat can be determined with higher accuracy.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of a seat occupancy sensor will be described below. In this embodiment, a front-rear direction of a vehicle coincides with a front-rear direction of a seat, and both directions will be hereinafter referred to as the “front-rear direction.” As shown inFIG. 1, a rear seat10installed on a rear seat side of a sedan, for example, is provided with three seat sections11R,11C,11L side by side in a vehicle width direction. The seat section11C that is a center seat section and disposed at the center of the plurality of seat sections11R,11C,11L has a dimension in the vehicle width direction that is set to be smaller than (e.g., to about half) the dimension of each of the seat sections11R,11L in the vehicle width direction. A seat occupancy sensor20is installed in a seat surface12of the seat section11C.

The seat occupancy sensor20integrally has: a first detection strip21that extends in the front-rear direction on a rear side of the seat surface12; a second detection strip22that extends in the front-rear direction, farther on the front side (the front side of the seat section11C) than the first detection strip21; and a connection portion23of which both ends are respectively connected to a front end of the first detection strip21and a rear end of the second detection strip22. The first detection strip21is disposed somewhat closer to an end (on the right side inFIG. 1) in the vehicle width direction relative to a centerline L of the seat surface12extending in the front-rear direction, while the second detection strip22is disposed even more closer to the end (on the right side inFIG. 1) in the vehicle width direction than the first detection strip21. The connection portion23is inclined so as to be directed toward the end in the vehicle width direction while extending toward the front side according to the positions of the first and second detection strips21,22.

The seat occupancy sensor20is formed by a membrane switch, in which a pair of electrode sheets (contact sheets) that are insulating films (e.g., polyester films) with an electrically conductive ink (e.g., a silver paste or a carbon paste) printed thereon are laminated with an insulating spacer (e.g., a polyester film) therebetween.

As shown inFIG. 2, the first detection strip21is provided with a first sensor group25that has a plurality of (three) substantially circular first sensor cells26F,26C,26R as detection units24or first detection units arrayed in a longitudinal direction of the first detection strip21(front-rear direction). The first sensor cells26F,26C,26R are each composed of a pair of electrodes that are respectively printed on a pair of electrode sheets and face each other, and become conductive as a first predetermined load F1is applied thereto. Similarly, the second detection strip22is provided with a second sensor group27that has a plurality of (three) substantially circular second sensor cells28F,28C,28R as detection units24or second detection units arrayed in a longitudinal direction of the second detection strip22(front-rear direction). In the front-rear direction, the first and second sensor cells26F,28F, the first and second sensor cells26C,28C, and the first and second sensor cells26R,28R are separated from each other by predetermined distances AF, AC, AR, respectively, that are equal to or longer than a fixed distance A (e.g., 100 mm). The fixed distance A is set based on a distance at which, when a person sitting on the seat section11R or11L puts his or her hand on the seat surface12of the adjacent seat section11C, a load that is equal to or larger than both the first and second predetermined loads F1, F2cannot be applied from that hand. The first and second sensor groups25,27are separated from each other by a predetermined distance B (e.g., 20 to 50 mm) in the width direction. The predetermined distance B is set, for example, based on a distance by which the buttocks and the femoral region of a person sitting on the seat section11C are separated from each other in the width direction. It should be understood that the second sensor group27is located farther on the front side and closer to the end in the width direction than the first sensor group25.

The second sensor cells28F,28C,28R are each composed of a pair of electrodes that are respectively printed on a pair of electrode sheets and face each other, and become conductive as the second predetermined load F2smaller than the first predetermined load F1is applied thereto. This means that the detection sensitivity of the first sensor cells26F,26C,26R is set to be lower than the detection sensitivity of the second sensor cells28F,28C,28R. Specifically, the first sensor cells26F,26C,26R have a diameter set to be smaller than the diameter of the second sensor cells28F,28C,28R so as to have the detection sensitivity set to be lower than the detection sensitivity of the second sensor cells28F,28C,28R. In other words, the first sensor cells26F,26C,26R have an electrode area set to be smaller than the electrode area of the second sensor cells28F,28C,28R so as to have the detection sensitivity set to be lower than the detection sensitivity of the second sensor cells28F,28C,28R. A cable31for external connection is provided at a rear end of the seat occupancy sensor20(first detection strip21).

As shown in the equivalent circuit diagram ofFIG. 3, in the seat occupancy sensor20, the series-connected first and second sensor cells26F,28F, the series-connected first and second sensor cells26C,28C, and the series-connected first and second sensor cells26R,28R are connected in parallel to one another. Thus, the seat occupancy sensor20becomes conductive when both of one of the plurality of first sensor cells26F,26C,26R and one of the second sensor cells28F,28C,28R that is connected in series to that one conductive first sensor cell become conductive. The second sensor cell28F is located farther toward the front side than the first sensor cell26F, with two detection units24therebetween. The first and second sensor cells26C,28C and the first and second sensor cells26R,28R are disposed in the same manner.

The cable31is electrically connected to both terminals29a,29bof an electric circuit (switch circuit) composed of the first and second sensor groups25,27. The seat occupancy sensor20is provided with an electronic control unit (ECU)30that is electrically connected to both terminals29a,29bthrough the cable31. The seat occupancy sensor20outputs a detection signal S according to a conductive state or a non-conductive state of the seat occupancy sensor20to the ECU30through the cable31. The ECU30determines whether someone is sitting on the seat section11C based on the detection signal S output from the seat occupancy sensor20. Specifically, when the seat occupancy sensor20becomes conductive, the ECU30determines that someone is sitting on the seat section11C. Then, the ECU30outputs a control signal according to this determination result to an appropriate device. Specifically, for example, when the ECU30determines that someone is on the seat section11C, the ECU30outputs a control signal for activating a notification member (warning lamp etc.) that prompts the person to wear a seatbelt.

FIG. 4is an illustration of a load pressure distribution map formed by a person sitting on the seat surface12of the seat section11C. This load pressure distribution map shows a load pressure value measured at each of small seat surface regions into which the seat surface12is divided in a lattice pattern. Regions with larger load pressure values are indicated by darker shading. As shown inFIG. 4, each load pressure region with equivalent load pressure values assumes a substantially concave shape that is (bilaterally) symmetrical with respect to the centerline L. The load pressure value is larger as the load pressure region is located farther on the inside, and it is conversely smaller as the load pressure region is located farther on the outside. Medium load pressure regions with relatively small load pressure values each extend frontward to a larger extent at both sides in the width direction. This is because the load pressure on the inside is higher according to the position of the buttocks of the seated person. Moreover, this is because the load pressure on the outside is lower and the distribution of the load pressure extends toward the front side according to the position of the femoral region of the seated person.

It can be seen that at least one of the plurality of first sensor cells26F,26C,26R is disposed in the inner load pressure regions with larger load pressure values. Thus, at least one of the first sensor cells26F,26C,26R is highly likely to become conductive as a relatively high load pressure (load) is applied thereto. On the other hand, it can be seen that at least one of the second sensor cells28F,28C,28R is disposed in the outer load pressure regions with smaller load pressure values. Thus, a relatively low load pressure (load) is applied to at least one of the plurality of second sensor cells28F,28C,28R. However, as the detection sensitivity of the second sensor cells28F,28C,28R is set to be relatively high, this one second sensor cell is highly likely to become conductive.

In other words, when both of at least one of the plurality of first sensor cells26F,26C,26R and at least one of the plurality of second sensor cells28F,28C,28R become conductive, it is highly likely that the load is applied from the buttocks and the femoral region of the seated person at the same time, i.e., someone is sitting on the seat section11C. In this case, a seat occupancy sensor200may have an equivalent circuit as shown inFIG. 6.

FIG. 5is an illustration of a load pressure distribution map formed by baggage placed on the seat surface12of the seat section11C, more particularly, by a seatback (not shown) that is reclined so as to be folded over the seat surface12and baggage placed on this seatback. As shown inFIG. 5, each load pressure region with equivalent load pressure values is substantially (bilaterally) symmetrical with respect to the centerline L. However, basically the load pressure value is larger as the load pressure region is located farther on the front side, and it is conversely smaller as the load pressure region is located farther on the rear side. This is because a load is more likely to be exerted on the front side of the seat surface12when the seatback is reclined.

It can be seen that at least one of the plurality of second sensor cells28F,28C,28R is disposed in the front load pressure regions with larger load pressure values. Thus, at least one of the second sensor cells28F,28C,28R is highly likely to become conductive, also because the detection sensitivity thereof is set to be relatively high. On the other hand, it can be seen that at least one of the first sensor cells26F,26C,26R is disposed in the rear load pressure regions with smaller load pressure values. However, as the detection sensitivity of the plurality of first sensor cells26F,26C,26R is set to be relatively low, this one first sensor cell is hardly likely to become conductive.

Thus, baggage placed on the seat surface12of the seat section11C causes none of the plurality of first sensor cells26F,26C,26R to become conductive; therefore, it is hardly likely that the seat occupancy sensor20erroneously determines that someone is sitting on the seat section11C.

Next, effects of this embodiment will be described along with advantages thereof. (1) In this embodiment, one of the first sensor cells26F,26C,26R of the first sensor group25that is located farther on the rear side of the seat section11C and farther away from the end of the seat section11C (closer to the centerline L) in the width direction than the second sensor group27, is highly likely to become conductive as a load is applied thereto from the buttocks of a seated person. On the other hand, one of the second sensor cells28F,28C,28R of the second sensor group27that is located farther on the front side of the seat section11C and closer to the end of the seat section11C in the width direction than the first sensor group25, is highly likely to become conductive as a load is applied thereto from the femoral region of a seated person. Therefore, when both of at least one of the plurality of first sensor cells26F,26C,26R and at least one of the plurality of second sensor cells28F,28C,28R become conductive, it is highly likely that the load is applied from the buttocks and the femoral region of the seated person at the same time, i.e., someone is sitting on the seat section11C. The seat occupancy sensor20determines that someone is sitting on the seat section11C when both of at least one of the plurality of first sensor cells26F,26C,26R and at least one of the plurality of second sensor cells28F,28C,28R become conductive, and thus can determine, with higher accuracy, whether someone is sitting on the seat.

It is possible to reduce the likelihood of the seat occupancy sensor20erroneously determining that someone is sitting on the seat section11C, for example, due to baggage placed on the seat section11C. (2) Since the load applied from the buttocks of a seated person is usually larger than the load applied from the femoral region of the seated person, the first sensor cells26F,26C,26R are highly likely to become conductive even when the detection sensitivity thereof is lower than the detection sensitivity of the second sensor cells28F,28C,28R. In this embodiment, the detection sensitivity of the first sensor cells26F,26C,26R is set to be lower than the detection sensitivity of the second sensor cells28F,28C,28R, which makes it less likely that one of the first sensor cells26F,26C,26R may become conductive, for example, due to baggage placed at a position corresponding to the buttocks of a seated person. Thus, the likelihood of the seat occupancy sensor20erroneously determining that someone is sitting on the seat section11C can be further reduced.

While the load applied from the femoral region of a seated person is generally smaller than the load applied from the buttocks of the seated person, setting the detection sensitivity of the second sensor cells28F,28C,28R to be relatively high allows the seat occupancy sensor20to more reliably detect that someone is sitting on the seat section11C.

(3) In this embodiment, the seat occupancy sensor20determines that someone is sitting on the seat section11C when both of one of the plurality of first sensor cells26F,26C,26R and one of the plurality of second sensor cells28F,28C,28R that is separated from that one of the first sensor cells26F,26C,26R by the predetermined distance AF, AC, or AR become conductive. In other words, the seat occupancy sensor20determines that someone is sitting on the seat section11C when both of one of the plurality of first sensor cells26F,26C,26R and one of the plurality of second sensor cells28F,28C,28R that is located farther toward the front of that one conductive first sensor cell with two detection units24therebetween become conductive. When one of the first sensor cells26F,26C,26R and one of the second sensor cells28F,28C,28R that become conductive are separated from each other by the predetermined distance AF, AC, or AR, it is more highly likely that the load is applied from the buttocks and the femoral region of the seated person at the same time, i.e., someone is sitting on the seat section11C. Thus, the seat occupancy sensor20can determine, with even higher accuracy, whether someone is sitting on the seat.

For example, even when a person sitting on the seat section11R or11L rests his or her hand on the adjacent seat section11C and thereby applies a load, it is little likely that this load is applied at two points separated from each other by the predetermined distance AF, AC, or AR. Accordingly, it is little likely that the seat occupancy sensor20erroneously determines that someone is sitting on the seat section11C due to this load.

(4) In this embodiment, the first and second sensor groups25,27are disposed in the seat section11C that is disposed at the center of the plurality of seat sections11R,11C,11L provided side by side in the vehicle width direction in the rear seat10that is disposed on the rear side of the vehicle. The seat section11C is often subjected to a load, for example, as a person sitting on the adjacent seat section11R or11L rests his or her hand on the seat section11C. However, the characteristics of such a load are naturally different from those of a load that is applied from the buttocks and the femoral region of a seated person at the same time. Thus, the likelihood of the seat occupancy sensor20erroneously determining that someone is sitting on the seat section11C due to such a load can be reduced.

(5) In this embodiment, the seat occupancy sensor20is basically disposed in such a direction that the seat occupancy sensor20is long in the front-rear direction. Thus, the seat occupancy sensor20can be more suitably installed in the seat section11C that is long in the front-rear direction (vertically long).

(6) In this embodiment, the actual distances by which the first sensor cells26F,26C,26R and the second sensor cells28F,28C,28R are respectively separated from each other can be increased by an offset (predetermined distance B) in the width direction between the first and second sensor groups25,27. This can further reduce the likelihood that the seat occupancy sensor20may erroneously determine that someone is sitting on the seat section11C, for example, when a person sitting on the seat section11R or11L rests his or her hand on the adjacent seat section11C. In other words, it is possible to further reduce the likelihood that the seat occupancy sensor20may erroneously determine that someone is sitting on the seat section11C, regardless of how a person rests (puts) his or her hand on the seat section11C.

(7) In this embodiment, it is possible to set the detection sensitivity of the first sensor cells26F,26C,26R to be lower than the detection sensitivity of the second sensor cells28F,28C,28R by using a very simple structure based on the size relationship between the electrode areas.

The above embodiment may be changed as follows. In the above embodiment, the first detection strip21(first sensor group25) may extend on the centerline L in the front-rear direction.

In the above embodiment, the number of the first sensor cells in the first sensor group25may be any plural number. Similarly, the number of the second sensor cells in the second sensor group27may be any plural number. For example, the number of the first sensor cells and the number of the second sensor cells may be different from each other.

In the above embodiment, the seat occupancy sensor20may be provided in at least one of the seat sections11R,11L, instead of the seat section11C or in addition to the seat section11C. Alternatively, the seat occupancy sensor20may be provided in a driver's seat or a front passenger seat.

In the above embodiment, the predetermined distances AF, AC, AR may be the same or different from one another. In the above embodiment, the number of the detection units24between one of the first sensor cells26F,26C,26R and one of the second sensor cells28F,28C,28R that become conductive at the same time when the seat occupancy sensor20determines that someone is sitting on the seat section11C may be any number, provided that these two sensor cells are separated from each other by the fixed distance A or longer. In particular, when changing the number of the first sensor cells or the number of the second sensor cells, it is preferable to change the number of the detection units24located between two sensor cells according to the change.

In the above embodiment, it is not absolutely necessary that one of the first sensor cells26F,26C,26R and one of the second sensor cells28F,28C,28R that become conductive at the same time when the seat occupancy sensor20determines that someone is sitting on the seat section11C are separated from each other by the fixed distance A or longer.

In the above embodiment, for example, the thickness of the insulating spacer in the first detection strip21may be set to be larger than the thickness of the insulating spacer in the second detection strip22so that the detection sensitivity of the first sensor cells26F,26C,26R is set to be lower than the detection sensitivity of the second sensor cells28F,28C,28R.

In the above embodiment, the detection sensitivity of the first sensor cells26F,26C,26R and the detection sensitivity of the second sensor cells28F,28C,28R may be equivalent to each other. In the above embodiment, the seat occupancy sensor20may determine that someone is sitting on the seat section11C when both of at least one of the plurality of first sensor cells26F,26C,26R and at least one of the plurality of second sensor cells28F,28C,28R become conductive.

It is not absolutely necessary that the front-rear direction of the seat section11C (seat) coincides with the front-rear direction of the vehicle.