Attachment structure of a load sensor for a vehicle seat

An attachment structure for installing a load sensor to a vehicle seat includes the load sensor having a plate-shaped strain unit and a strain gauge for detecting a strain of the plate-shaped strain unit. The load sensor is structured that one end of the plate-shaped strain unit is fixed to a seating portion of the vehicle seat and the other end of the strain unit is fixed to a vehicle body. Also, a strain portion is defined between each fixed end of the plate-shaped strain unit, and the strain portion is deformable in a vertical direction relative to the vehicle seat. In addition, a load input point from the seating portion is defined approximately at a central portion of the strain portion of the plate-shaped strain unit.

CROSS REFERENCE OF RELATED APPLICATION

This application is based on and claims priority under 35 U.S.C. §119 with respect to Japanese Application No. 2001-278516 filed on Sep. 13, 2001, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to an attachment structure of a load sensor for a vehicle seat. More particularly, the present invention pertains to an attachment structure of a load sensor which detects a load on a seating portion of a seat when a passenger sits on the vehicle seat.

BACKGROUND OF THE INVENTION

In recent years, there is a tendency toward enforcing a safety of a passenger of a vehicle. In order to improve the safety of the passenger who sits on a seat, a restraint function of a seat belt and an operating function of an air bag in accordance with a weight of the passenger have been developed. When these devices are adopted, an accurate detection of a weight of the passenger is needed. As for one such means, a known device is disclosed in Japanese Patent Laid-Open Publication No.2001-12998. The known device applies a means for attaching a weight sensor (ie., an attachment structure of a load sensor) to a seat mounted in a vehicle (ie., a vehicle seat).

Normally, as for a weight sensor to detect a weight of the passenger who sits on a seat cushion of the vehicle seat, a sensor with a strain gauge disposed in a plate-shaped strain unit is used for detecting a vertical strain of the strain unit. Therefore, in order to detect the weight of the passenger on the seat accurately, a precise input of the weight from the seating portion to a strain portion of the strain unit is needed. Thus, an attachment structure of a load sensor for a vehicle seat is particularly important.

However, in the known device, such importance of the attachment structure of the load sensor to the vehicle has not been recognized, and is designed merely not to exceed a height of the seating portion in a normal sitting condition when the weight sensor is attached.

SUMMARY OF THE INVENTION

Accordingly, an object of this invention is to provide an attachment structure of a load sensor for a vehicle seat which can precisely detect a weight of a passenger on a seat.

According to the first aspect of the invention, the attachment structure for installing the load sensor to the vehicle seat includes the load sensor having a plate-shaped strain unit and a strain gauge for detecting a strain of the plate-shaped strain unit. The load sensor is structured that one end of the plateshaped strain unit is fixed to a seating portion of the vehicle seat and the other end of the strain unit is fixed to a vehicle body. Also, a strain portion is defined between each fixed end of the plate-shaped strain unit, and the strain portion is deformable in a vertical direction relative to the vehicle seat. In addition, a load input point from the seating portion is defined approximately at a central portion of the strain portion of the plate-shaped strain unit.

According to the second aspect of the invention, the attachment includes a strain restriction means for restricting the strain of the plate-shaped strain unit in the vertical direction to a predetermined value.

According to the third aspect of the invention, the attachment structure has a first attachment bracket for holding the one fixed end of the plate-shaped strain unit and attached to the vehicle seat through a connecting pin located at a portion upward or downward relative to and opposed to the central portion of the strain portion of the plate-shaped strain unit. The attachment structure also has a second attachment bracket for holding the other fixed end of the strain unit and attached to the vehicle body. Furthermore, the strain restriction means for restricting the strain of the plate-shaped strain unit in the vertical direction to the predetermined value is formed by inserting the connecting pin into a stopper hole provided in the second attachment bracket with a predetermined clearance in the vertical, direction relative to the vehicle seat.

According to the fourth aspect of the invention, an attachment structure is characterized in that the connecting pin is rotatably attached to either one of the first attachment bracket and the seating portion of the vehicle seat through a bush relative to the seating portion of the vehicle seat.

As the first aspect of the invention, the strain portion is defined between each fixed end of the plate-shaped strain unit, and it is deformable in a vertical direction relative to the vehicle seat. Furthermore, a load input point from the seating portion is defined approximately at a central portion of the strain portion of the plate-shaped strain unit. Consequently, the maximum stress can be reduced by improving a stress balance of the stress generated by a load input (shown inFIG. 6(c) in comparison withFIG. 7(C)). Therefore, downsizing and weight reduction of the strain plate can be achieved.

Since the load input point from the seating portion is defined approximately at the central portion of the strain portion of the strain unit, when the load is inputted into the attachment structure unit, stress is distributed that both ends of the strain portion receive the maximum stress and the central portion of the strain portion receives the minimum stress, being deformed in the vertical direction relative to the vehicle seat, (shown inFIG. 6(c)). Because the maximum stress is reduced and the stress balance is improved, secular change is also reduced. Thus, the load sensor can maintain a precise detection of the load from the seating portion, in other words, a weight of a passenger. In this case, it is desirable to install a strain restriction means for restricting a strain of the strain unit in a vertical direction in the attachment structure which is mounted with the load sensor.

Also, according to the second aspect of the invention, the strain restriction means is formed by inserting the connecting pin in the second attachment bracket. In other words, the strain restriction means can be disposed inside the attachment structure unit without increasing a number of parts, and an accuracy of the positions of the component members which form the attachment structure unit is secured. As a result, the manufacturing accuracy can be improved as well.

Furthermore, the connecting pin is located at the portion upward or downward relative to and opposed to the central portion of the strain portion of the plate-shaped strain unit. In other words, because the connecting pin is positioned on an axial line of the load input, the strain can be restricted precisely.

In addition, the connecting pin is rotatably attached to the first bracket or the seating portion of the vehicle seat through a bush. Thus, a stress generated by friction between the connecting pin and the first attachment bracket or between the connecting pin and the seating portion of the vehicle seat can be prevented. As a result, effects related to the stress on the strain portion of the strain unit are prevented. Therefore, a stabilization of a performance of the load sensor can be achieved.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of this invention will be explained with reference to the attached drawings.FIG. 1shows a vehicle seat with a load sensor by applying an attachment structure according to one example of this invention. The vehicle seat10is comprised of a seat cushion10a, a seat back10b, a reclining mechanism10c, a slide mechanism10d, and an attachment structure unit20bwith a load sensor20ainstalled between the seat cushion10a, and the slide mechanism10d.

In the vehicle seat10, a lower end of the seat back10bis installed in a rear end of the seat cushion10athrough the reclining mechanism10c. The seat back10bis held in a standing position by a function of the seat reclining mechanism10c, and a reclining position of the seat back10bin a longitudinal direction relative to the seat cushion10acan be adjusted by operating the reclining mechanism10c.

In the vehicle seat10, a seat body is disposed on a floor of a vehicle body through the slide mechanism10dhaving an upper rail12and a lower rail13. A cushion frame11of the seat cushion10aforming the vehicle seat10is supported through each of the attachment structure units20bapplied to attach four load sensors20ain the upper rail12forming the slide mechanism10d.The seat body is fixed to a required position by a function of the slide mechanism10d, and by operating the slide mechanism10d, a longitudinal position of a seat body relative to the vehicle seat10can be adjusted.

In the vehicle seat10, the seat cushion10acorresponds to a seating portion of a seat of the present invention, and the slide mechanism10dcorresponds to a vehicle body of the present invention. The four load sensors20aare arranged between the cushion frame11of the seat cushion10and the upper rail12of the slide mechanism10d. More specifically, two of the load sensors20aare placed in right and left portions in a front side relative to the seat cushion10a, and the other two load sensors20aare arranged at right and left portions in a back side of the vehicle seat10relative to the seat cushion10a.

In the vehicle seat10shown inFIG. 1, structures of both attachment structure units20bmounted with load sensors20arespectively are identical except that the load sensors20ain the front and back are placed in reverse in longitudinal direction relative to the vehicle seat10. Therefore, with respect to a description of the attachment structure of the load sensor20a, the attachment structure of the load sensor20alocated in back and left sides of the seat cushion10arelative to the vehicle seat10and its attachment structure unit20bwill be described in detail. On the other hand, the load sensors20aarranged at the other parts of the vehicle seat10and their attachment structure units20bwill be described only when necessary.

As shown inFIG. 3andFIG. 4, the load sensor20aincludes a strain plate21(ie., a strain unit) and a strain gauge22. The strain gauge22is adhered to a middle portion of a lower surface of the strain plate21in the longitudinal direction relative to the strain plate21, and the load sensor20ais assembled within the attachment structure unit20b.

As shown inFIG. 3andFIG. 4, the load sensor20aincludes an upper bracket23, a lower bracket24, and a base bracket25as primary components, and cross sectional surfaces of the upper bracket23and the lower bracket24are close to “L” shape. A shape of the base bracket25is a slightly bent flat plate. The lower bracket24is fixed on an upper end of the base bracket25by welding. The base bracket25functions to fix the lower bracket24in an arm12a(ie., a longitudinal wall relative to the vehicle seat10) of the upper rail12located in the slide mechanism10d.

In the attachment structure unit20b, the upper bracket23corresponds to a first attachment bracket of the present invention, and one end of the strain plate21forming the load sensor20ais fixed by being retained between an upper spacer26aand a lower spacer26bthrough a rivet26c. Furthermore, as shown inFIG. 5, the upper bracket23is installed in a side panel11aof the cushion frame11, and the upper bracket23is connected to the base25through the load sensor20a. In addition, a positioning portion26b1is formed in a lower spacer26bto engage each notch disposed in the strain plate21, the upper bracket23, and the upper spacer26ato fix them together by detent. By this structure, a position of a strain portion21cis determined accurately (ie., a determination of the value of the strain portion).

Also, in the attachment structure unit20b, the lower bracket24is integral with the base bracket25, forming a second attachment bracket of the present invention. On an upper surface of an upper wall of the lower bracket24, the other end of the strain plate21forming the load sensor20ais fixed through a pair of rivets26e, being retained between the lower bracket24and a spacer26d. As shown inFIG. 4andFIG. 5, the base bracket25is fixed by securing its lower side surface portion in the arm12aof the upper rail12through a bolt14, a nut15, a bolt28a, and a connecting rod28. Furthermore, the base bracket25is connected to the upper bracket23through the lower bracket24and the load sensor20a.

A pierce nut27a, a bush27b, and a bolt27care used for connecting the side panel11a of the cushion frame11to the upper bracket23, and as shown inFIG. 5, the bush27bis fitted in an installation hole23aof the upper bracket23by staking. A bearing metal with low frictional resistance is used for the bush27b. The pierce nut27ais inserted into a stopper hole25aof the base bracket25with a predetermined clearance6in the vertical direction relative to the vehicle seat10. Under this condition, an end portion of the pierce nut27ais fitted within an inner hole of the bush27bso that the pierce nut27acan be rotated relatively with the bush27b.

The bolt27cis screwed into the pierce nut27awhich is fitted as shown inFIG. 5by being inserted from outside the side panel11aof the cushion frame11. The pierce nut27aand the bolt27bare integral with one another, forming a connecting pin of the present invention. Also, the pierce nut27aand the stopper hole25aof the base bracket25forms a strain restriction means for restricting a strain (ie., an elastic deformation) of the strain plate21in the vertical direction relative to the vehicle seat10to a predetermined value, functioning as a limiter (ie., protecting the sensor from a breakdown by not reaching a bottom when an excessive load is put on the sensor) against a great load (ie., 1000–1500N) from the seat cushion10a.

In the attachment structure in which the load sensor20ais attached, as shown inFIG. 3, the strain portion21cwhich is deformable in the vertical direction relative to the vehicle seat10is located between retained portions21aand21b, and the strain gauge22is located in a central portion of a lower side of the strain portion21c. Furthermore, a connecting portion of the side panel11aof the cushion frame11and the upper bracket23(the pierce nut27aand the bolt27b) is located in a lower surface of a central portion of the strain portion21c.

In both attachment structure units20barranged at right and left sides of the seat cushion10arelative to the vehicle seat10, both base brackets25which form the attachment structure units20bare connected to each other through the connecting rod28shown inFIG. 2andFIG. 4. The connecting rod28is installed by fitting its both ends in the base bracket25and the upper rail12respectively through the bolt28a.

By the above structure, as shown schematically inFIG. 2, the connecting rod28maintains a predetermined width between the base brackets25of right and left of the seat cushion10arelative to the seating portion by connecting the base brackets25of the right and left of the seat cushion10arelative to the seating portion. In other words, the connecting rod28maintains the predetermined width of the attachment structure units20bwhich are integral with the base brackets25. Moreover, with respect to a connection of the attachment structure units20bof the right and left of the seat cushion10arelative to the vehicle seat10, the upper brackets23disposed in the attachment structure units20bof the right and left of the seat cushion10arelative to the vehicle seat10can be connected each other through the connecting rod28. By this structure, the width between the attachment structures20bof the right and left of the seat cushion10arelative to the vehicle seat10can also be maintained consistently.

In the attachment structure (ie., the attachment structure unit20b) described above, one end of the strain plate21forming the load sensor20ais fixed to the cushion frame11of the seat cushion10alocated in the seating portion by way of one or more connecting members such as those described above. At the same time, the other end of the strain plate21is fixed to the upper rail12of the slide mechanism10dlocated in the vehicle body by way of one or more connecting members such as those described above. A strain portion21cis defined between the fixed ends of the strain plate21, and a load input position from the seat cushion10a(le., a load F shown with the arrow inFIG. 3) is defined at an approximately center of the strain portion21cof the strain plate21.

Therefore, when the load F is inputted into the attachment structure unit20bas shown inFIG. 6(a), the strain portion21cof the strain plate21is deformed in the vertical direction relative to the vehicle seat10as shown inFIG. 6(b), and a stress (ie., a strain) is distributed that the both ends of the strain plate21receive the maximum positive and negative stresses respectively, and the central portion of the strain plate21receives the minimum stress as shown inFIG. 6(c). However, if the load input point from the seat cushion10ais defined in one side of the strain portion21c, when the load is inputted into the attachment structure unit20b, the stress (ie., the strain) is distributed that, as shown inFIG. 7(c), the other end of the strain plate21receives the maximum stress (ie., a greater value than the maximum value shown inFIG. 6), and the one end of the strain plate21receives the minimum stress. Therefore, the stress distribution of a structure shown inFIG. 7not only causes an uneven stress distribution, it also increases the maximum stress. If an excessive stress is put on the strain plate21, a residual strain in the strain portion21can be occurred. Consequently, the stress distribution shown inFIG. 7can damage the strain plate21, and an accurate detection of the load from the seating portion becomes impossible.

Therefore, according to the attachment structure unit20b, by minimizing the maximum stress and improving the balance of the stress generated by the load input toward the strain portion21cof the strain plate211(ie.,FIG. 6(c) compared withFIG. 7(c)), the structure in which the stress is inputted into the attachment structure unit20bprevents the strain plate21from damages caused by the excessive stress and uneven stress distribution. Also, by the above structure, downsizing and weight reduction of the strain plate21can be achieved. At the same time, by designing the strain portion within the value of predetermined stress (or strain), an extraction of a strain signal from the strain gauge22on a large scale becomes possible. Thus, from a viewpoint of levels of the signals (S/N ratio) toward noise, the attachment structure unit20bis improved, maintaining high accuracy of the detection. Furthermore, because the maximum stress is reduced and the stress balance is improved, a secular change is also reduced. Thus, the load sensor20acan maintain a precise detection of the load from the seating portion, in other words, a weight of a passenger.

Moreover, according to the attachment structure, the attachment structure unit20bhas the upper bracket23installing one end of the strain plate21to the seat cushion10aof the vehicle seat by retaining one end of the strain plate. The attachment structure unit20balso has the lower bracket24integral with the base bracket25which is installed in the upper rail12located in the vehicle body by retaining the other end of the strain plate21.

In addition, in the attachment structure unit20b, the bolt27cof the upper bracket23side is screwed and connected to the pierce nut27cwhich is inserted into the stopper hole25ain a portion downward relative to and opposed to the central portion of the strain portion21c. By this structure, the strain restriction means is formed by forming, the circularly-ranged clearance (ie., the clearance6in the vertical direction relative to the vehicle seat10) between a circular outer periphery of the pierce nut27aand a circular inner periphery of the stopper hole25aof the base bracket. The strain restriction means restricts the strain of the strain plate21in the vertical direction relative to the vehicle seat10to the predetermined value. Also, the pierce nut27ais installed by being screwed into a connecting hole23athrough the bush27bwith low frictional resistance (ie., a low coefficient of friction).

According to the attachment structure unit20b, the strain restriction means can be achieved without increasing the number of parts within the attachment structure unit20b. Furthermore, upon an assembly process of the attachment structure unit20b, the upper bracket23and the lower bracket24are assembled in both ends of the strain plate21at first. Under this condition, the installation hole23is aligned coaxially with the stopper hole25aof the base bracket25as the lower bracket24and the base bracket25are welded. By this assembly process, an accuracy of the position of each component member comprising the attachment structure unit20bis assured. Consequently, a manufacturing accuracy can be heightened. Also, as shown inFIG. 3, the pierce nut27aand the stopper hole25a, in other words, the strain restriction means, are arranged on the input line of the load F. Therefore, the strain of the strain plate21in the vertical direction relative to the vehicle seat10can be restricted precisely to the predetermined value. Moreover, by the above structure, the stress generated by the friction in the installation hole23aof the upper bracket23of the pierce nut27acomprising the connecting pin is prevented. As a result, effects related to the stress on the strain portion21cof the strain plate21are prevented. Therefore, a stabilization of a performance of the load sensor20acan be achieved.

On the other hand, in the vehicle seat10, four load sensors20aare placed in the side portions of the front and back of the seat cushion10arelative to the vehicle seat10respectively, and the base brackets25of the attachment structures20bon the right and left of the seat cushion10arelative to the vehicle seat10are connected to each other by the connecting rod28. By this structure, attachment errors relative to each load sensor20aon the right and left of the seat cushion relative to the seating portion and an unnecessary stress affecting the load sensor20acaused by the pitch discrepancy between the rails can be prevented. Moreover, an unnecessary stress caused by the distortion and deflection of the seat cushion10awhen the passenger sits on the seat cushion10acan be prevented as well (In order to acquire this function effectively, it is desirable to apply the structure that the upper brackets23of the attachment structure units20bof the right and left are connected each other by the connecting rod28).

In the embodiment of this invention, the strain restriction means for restricting the strain of the strain plate21in the vertical direction relative to the vehicle seat10in the predetermined value is installed in the portion located downward relative to and opposed to the central portion of the strain portion21cof the strain plate21. However, it is possible to install the strain restriction means in a portion located upward relative to and opposed to the central portion of the strain portion21cof the strain plate21. Furthermore, although the strain plate21and the spacers26a,26b, and26dare formed separately, it is possible to integrate them together (manufacturing by forging or cutting) to stabilize the performance and reduce the number of parts.

Also, in the embodiment of this invention, as shown inFIG. 1, the load sensor20aof the front and back relative to the seat cushion are placed opposing each other. However, as shown inFIG. 8, it is possible to place them in the same direction. Moreover, it is possible to place the load sensors20ashown inFIG. 1in back to front, or place the load sensors20ashown inFIG. 8in back to front.