Steering wheel

A steering wheel includes an annular rim portion, a boss section, one or more spokes interconnecting the rim portion and boss section, and a core member interconnecting these portions, the core member including a wheel portion disposed in the rim portion. The steering wheel further includes a cladding layer disposed around the wheel portion, a skin layer disposed on a front surface of the rim portion, and a sensor layer disposed between the cladding layer and the skin layer for detecting the driver's grip. The sensor layer includes a sheet-shaped substrate having stretch properties, a sensor composed of a conductive ink having stretch properties and applied to a front surface of the substrate, and an insulation sheet covering the sensor and having stretch properties. The sensor layer is generally formed into an annular band and mounted on an outer circumferential portion of the cladding layer by being stretched and expanded.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent Application No. 2020-056566 of Hotta et al., filed on Mar. 26, 2020, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a steering wheel that includes a sensor for detecting the driver's grip in the rim portion.

2. Description of Related Art

JP 2019-137096 A discloses a known steering wheel that includes a rim portion having a generally annular shape, a boss section disposed at the center of the rim portion, a plurality of spokes that interconnect the rim portion and boss section, and a core member that forms a skeleton of the rim portion, boss section and spokes. The steering wheel further includes a cladding layer that is disposed around a wheel portion of the core member disposed in the rim portion, a skin layer that is disposed on the front surface of the rim portion, and a sensor layer that is composed of conductive material and disposed between the cladding layer and skin layer for detecting whether the driver is gripping the rim portion. The sensor layer is composed of a synthetic resin sheet member having approximately 10 to 15% stretch properties, and a sensor composed of a wire that has a round sectional shape and is arranged in a serpentine configuration on the sheet member. The wire forming the sensor concurrently acts as a heating wire. The sheet member has a rectangular shape sized to the length of an inner circumferential portion of the rim portion. When the sensor layer is attached to the cladding layer as has been mounted around the wheel portion of the core member, a first edge in the width direction of the sheet member is firstly disposed in the inner circumferential portion of the rim portion, then the sheet member is attached to and wound around the rim portion toward the outer circumferential portion while being stretched so that a second edge in the width direction of the sheet member is brought close to the first edge. This way the sensor layer is mounted around the cladding layer in the rim portion while preventing wrinkles and slacks from forming.

In the above steering wheel, however, although the sheet member of the sensor layer has stretch properties, the wire forming the sensor impairs the stretch properties when attached to the sheet member because the sensor is composed of a wire which concurrently acts as a heating wire. This is likely to complicate the production process because it is presumed that a special attention would be required for the sensor layer to be arranged around the cladding layer without forming wrinkles and slacks. It would be desirable to provide a steering wheel including a grip sensor layer that has improved assembly easiness.

SUMMARY

An exemplary embodiment of the invention relates to a steering wheel including: an annular rim portion for gripping for steering; a boss section that is disposed at a center of the rim portion; one or more spokes that interconnect the rim portion and the boss section; a core member that interconnect the rim portion, the boss section and the spokes, the core member including a wheel portion that is disposed in the rim portion; a cladding layer that is disposed around the wheel portion of the core member; a skin layer that is disposed on a front surface of the rim portion; and a sensor layer for detecting whether a driver is gripping the rim portion, the sensor layer being disposed between the cladding layer and the skin layer. The sensor layer includes: a sheet-shaped substrate that is disposed toward the cladding layer and has stretch properties; a sensor for detecting whether the driver is gripping the rim portion, the sensor being composed of a conductive ink having stretch properties that is applied to a grip area by the driver on a front surface of the substrate; and an insulation sheet that covers the sensor and is disposed toward the skin layer, the insulation sheet having stretch properties. The sensor layer is generally formed into an annular band and mounted on an outer circumferential portion of the cladding layer in the rim portion by being stretched and expanded.

DETAILED DESCRIPTION

Exemplary embodiments of the invention are described below with reference to the accompanying drawings. However, the invention is not limited to the embodiments disclosed herein. All modifications within the appended claims and equivalents relative thereto are intended to be encompassed in the scope of the claims.

As shown inFIG. 1, a steering wheel W in accordance with an exemplary embodiment includes a rim portion R for gripping for steering, a boss section B that is disposed at the center of the rim portion R, and a plurality of spokes S (SL, SR, SB) that interconnect the boss section B and the rim portion R. The rim portion R has a generally annular shape. The spokes S includes spokes SL, SR that extend respectively toward the left and right from the boss section B, and a spoke SB that extends rearward from the boss section B. The steering wheel W includes an airbag device70that is mounted on top of the boss section B and depicted with dashed-and-double-dotted lines inFIG. 1, a steering-wheel body1, and a lower cover7(not shown) covering an underside of the boss section B.

The steering-wheel body1includes a core member3that interconnects the rim portion R, boss section B and spokes S. The core member3is made from such metal as aluminum alloy. The core member3includes a wheel portion4disposed in the rim portion R, a boss portion5disposed in the boss section B, and spoke portions6(6L,6R) and7that are respectively disposed in the spokes SL, SR, SB and interconnect the wheel portion4and boss portion5. The boss portion5of the core member3includes a boss5aof steel to be connected to the steering shaft of a vehicle. The spoke portions6includes left and right spoke portions6L,6R disposed in the left and right spokes SL, SR, and two spoke portions7that are disposed in the rear spoke SB. The spoke portions7are integral in a side toward the wheel portion4and bifurcate towards the left and right at a vicinity of the boss portion5.

As shown inFIG. 2, in the rim portion R, a cladding layer10is disposed around the wheel portion4of the core member3, and a skin layer20, which is composed of leather21, is disposed on the front surface of the rim portion R. Further, there is disposed, between the cladding layer10and skin layer20, a sensor layer30for detecting whether the driver is gripping the rim portion R. The sensor layer30is disposed in a grip area Ga, which is to be gripped by the driver, in the rim portion R. The sensor layer30includes a sensor50composed of conductive material, as will be described later.

The cladding layer10is disposed around the wheel portion4of the core member3and around portions of the spoke portions6(6L,6R) and7adjoining the wheel portion4. The cladding layer10is fabricated from synthetic resin material such as urethane, and formed around the wheel portion4and spoke portions6,7of the core member3by injection molding or the like. As shown inFIG. 3, the cladding layer10includes, in a leftward portion and in a rightward portion of each of front and rear portions, an annular gutter14(14L,14R),15(15L,15R) extending along a circumference of section of the wheel portion4. As shown inFIG. 8, terminal edges22c,22d,23c,23d,24c,24d,25c,25dof leather members22,23,24,25for forming the skin layer20are respectively tucked into the gutters14L,14R,15L,15R.

The skin layer20of this embodiment is composed of leather21. As shown inFIGS. 1 and 8, the leather21is composed of four leather members22,23,24,25. The leather member22is disposed in the front portion of the rim portion R, the leather member23is disposed in the rear portion of the rim portion R, the leather member24is disposed in a left portion of the rim portion R, and the leather member25is disposed in a right portion of the rim portion R. The leather member22is disposed in the front portion of the rim portion R with the opposite side edges22a,22bin width direction sewn together, with the terminal22ctucked into the gutter14L, and with the terminal22dtucked into the gutter14R. The leather member23is disposed in the rear portion of the rim portion R with the opposite side edges23a,23bin width direction sewn together, with the terminal23ctucked into the gutter15L, and with the terminal23dtucked into the gutter15R. The leather member24is disposed in the left portion of the rim portion R to an adjoining region in the spoke SL with the opposite side edges24a,24bin width direction sewn together, with the terminal24ctucked into the gutter14L, and with the terminal24dtucked into the gutter15L. The leather member25is disposed in the right portion of the rim portion R to an adjoining region in the spoke SR with the opposite side edges25a,25bin width direction sewn together, with the terminal25ctucked into the gutter14R, and with the terminal25dtucked into the gutter15R.

Referring toFIGS. 2 to 4, the sensor layer30includes a sheet-shaped substrate40that is disposed toward the cladding layer10and has stretch properties, a sensor50that is disposed in the grip area Ga of the rim portion R on a front surface40aof the substrate40, and an insulation sheet45that covers the sensor50and is disposed toward the skin layer20. As shown inFIGS. 5 and 6, the sensor layer30of this embodiment is prepared as an assembly31that is formed into a generally annular band which is shaped along a circumferential direction of the rim portion R (more particularly, of the cladding layer10as mounted around the wheel portion4of the core member3), by coupling ends33aof a pair of bilaterally symmetrical split band-shaped members33(33L,33R) together.

The sensor layer30includes a plurality of cut-out portions37formed corresponding to the gutters14,15of the cladding layer10, to allow the terminals22c,22d,23c,23d,24c,24d,25c,25dof the leather members22,23,24,25to be tucked into the gutters14,15. Each of the cut-out portions37is not formed to correspond to an entirely of the gutter14or15. Since the sensor50includes two narrow-width portions50a(FIG. 4) for allowing the sensor50to be arranged continuously, each of the cut-out portions37extends only to a vicinity of the narrow-width portion50a.

The substrate40of the sensor layer30is fabricated of polyurethane or the like having stretch properties and formed into a sheet. The insulation sheet45is composed of a sheet material of polyurethane or the like having stretch properties. In this embodiment, the substrate40and insulation sheet45is of the same material. A thickness t1 of the substrate40is approximately 100 μm (0.1 mm). Accordingly, a thickness t2 of the insulation sheet45is approximately 100 μm (0.1 mm).

The substrate40and insulation sheet45would be difficult to mount on the rim portion R if they were not sufficiently stretchy or too stretchy. More specifically, if the substrate40and insulation sheet45were not sufficiently stretchy, it would be difficult to arrange them on an outer circumferential portion11(FIG. 6) of the cladding layer10. If they were too stretchy, edges31aof the assembly31might lap over one another overly in an inner circumferential edge12portion of the cladding layer10. Accordingly, the substrate40and insulation sheet45in one or more embodiments may have a stretch rate in a range from 10 to 100%. In one or more embodiments, the substrate40and insulation sheet45have a stretch rate in a range from 50 to 80%. The substrate40and insulation sheet45should also have no fear of tear.

The sensor50is composed of conductive ink52that is applied to a region in the front surface40aof the substrate40corresponding to the grip area Ga of the rim portion R. The conductive ink52, as applied to the substrate40, has stretch properties equal to or more than that of the substrate40and insulation sheet45. The conductive ink52contains silicone resin, conductive filler such as silver powder, and solvent or the like, by way of example (the content of the conductive filler is approximately 60 to 70 mass percent).

The conductive ink52forming the sensor50is applied to the front surface40aof the substrate40by screen printing or the like. In this specific embodiment, the conductive ink52is arranged in a lattice pattern54in which a first set of straight band-shaped lines55and a second set of straight band-shaped lines56intersect one another generally perpendicularly, as shown inFIG. 4. The lattice pattern54includes, in the circumference, a frame59in which terminals of the band-shaped lines55and those of the band-shaped lines56intersect one another. In this embodiment, moreover, the lattice pattern54is formed such that its bias direction BD extends along a circumferential direction of the sensor layer30formed into a ring, as shown inFIGS. 4 and 5.

A thickness ts (FIG. 4) of the conductive ink52is approximately 10 μm. Since the lattice pattern54is formed by printing, a thickness of the conductive ink52in intersections57and intersections59(in the frame59) of the band-shaped lines55and56is not thicker than and equal to the thickness ts.

In this embodiment, moreover, a width Wb of each of the band-shaped lines55,56and frame59is approximately 0.5 mm. A margin62in an outer edge31aof the sensor layer30where the conductive ink52is not applied has a width Wx of approximately 10 mm.

Further, a dimension Ws of a gap between the band-shaped lines55and between band-shaped lines56is 3 mm that is in a range from 1 to 9 mm.

To explain an occupancy of the conductive ink52in the front surface40aof the substrate40with respect to the width Wb of each of the band-shaped lines55,56and gap dimension Ws in the lattice pattern54, a 100% occupancy will nullify the significance of forming the lattice pattern54, while a too little occupancy means that the width Wb is small and likely to have a lot of interruptions. Accordingly, the occupancy of the conductive ink52in the front surface40aof the substrate40is 20 to 80% in one or more embodiments. In one or more embodiments, the occupancy is 20 to 50%. In this specific embodiment, the occupancy of the conductive ink52in the front surface40aof the substrate40is approximately 30%.

The sensor layer30of this embodiment includes the substrate40, the sensor50that is composed of the conductive ink52applied to the front surface40aof the substrate40, and the insulation sheet45that is adhered to the front surface40aof the substrate40with not-shown double-faced tapes or the like by the back surface45bin order to cover the sensor50. That is, the substrate40and insulation sheet45sandwich the sensor50.

A thickness t0 of the sensor layer30of this embodiment in which the substrate40and insulation sheet45are adhered together while sandwiching the sensor50is approximately 230 μm (i.e. 0.23 mm).

In this embodiment, moreover, the sensor30is mounted on a front surface10aof the cladding layer10in the form of the generally band-shaped annular assembly31that is formed by coupling ends33aof a pair of the band-shaped members33(33L,33R) together by sewing or adhesive seams35.

Each of the band-shaped members33(33L,33R) includes, in the substrate40and insulation sheet45as coupled together, a protruding portion61that protrudes toward the spoke SL/SB. A connecting wire65, which is to be connected to a not-shown detection circuit for detecting the driver's grip by detecting an electrostatic capacitance, is disposed in an area of the protruding portion61extending from the frame59of the conductive ink52. Since the sensor layer30of this embodiment is composed of the band-shaped members33(L, R) each of which has one sensor50, one each connecting wire65is disposed in each of the band-shaped members33(L, R).

In this exemplary embodiment, as shown inFIG. 5, the assembly31constituting the sensor layer30is formed by coupling the ends33aof the split pair of band-shaped members33(33L,33R) together. Thus, the assembly31has a cylindrical shape except the protruding portions61. A portion of the assembly31(i.e. the sensor layer30) except the protruding portions61will hereinafter be called a general portion60.

In this embodiment, a length in the circumferential direction of the assembly31(a length that is twice a length L1 (FIG. 4) of each of the band-shaped members33of the sensor layer30), namely, a circumferential length CL1 (FIG. 6) of the assembly31is equal to a length of the inner circumferential edge12of the cladding layer10in the rim portion R of the steering wheel W, i.e. equal to a circumferential length CL0 of the inner circumferential edge12of the cladding layer10in the rim portion R of the steering wheel W.

Here in this embodiment, the cladding layer10as mounted on the core member3of the steering-wheel body1has an outer diameter DO (FIG. 6) of approximately φ370, an outer circumferential length CLD of approximately 1160 mm, an inner diameter d0 of approximately φ290, and the inner circumferential length CL0 of approximately φ20 mm. Therefore, the circumferential length CL1 of the sensor layer30as formed into the assembly31is approximately φ20 mm, which is generally equal to the inner circumferential length CL0 of the cladding layer10.

When the assembly31(i.e. the sensor layer30) is arranged on the cladding layer10as has been mounted on the wheel portion4of the core member3, it is wound around the cladding layer10in a circumferential direction of a section of the cladding layer10so that the edges31ain width direction of the assembly31are brought close to each other. Since the skin layer20is further mounted on the front surface30aof the sensor layer30, as shown in (B) ofFIG. 7, the edges31aof the assembly31may slightly overlap except the applied area of the conductive ink52or may be slightly distant from each other when arranged on the cladding layer10. Accordingly, a width WB (FIGS. 4, 5) of the general portion60of the assembly31(i.e. the sensor layer30) except the protruding portions61is generally equal to a circumferential length RL (FIG. 7) of the section of the cladding layer10as mounted on the wheel portion4. The “generally equal” range here connotes a range from approximately 60 to 110% of the circumferential length RL. In the illustrated embodiment, the width WB of the assembly31(i.e. the sensor layer30) is approximately φ0 mm, and the circumferential length RL of the section of the cladding layer10is approximately 100 m.

Assembling of the steering wheel W is now described. Firstly, the cladding layer10is formed on the wheel portion4and portions of the spoke portions6and7adjoining the wheel portion4in the core member3of the steering-wheel body1. Then the sensor layer30is mounted on the front surface10aof the cladding layer10. As shown inFIG. 6, mounting of the sensor layer30is easily conducted by putting the annular sensor layer30on the outer circumferential portion11of the cladding layer10while stretching and expanding the sensor layer30.

Thereafter, as can be seen inFIG. 7, the leather21for forming the skin layer20is used to press both of the edges31aof the sensor layer30toward the inner circumferential edge12of the cladding layer10in the rim portion R and to bring the sensor layer30into close contact with the front surface10aof the cladding layer10. The sensor layer30may be adhered to the front surface10aof the cladding layer10with adhesive.

To describe mounting of the leather21more specifically, the leather member22is placed on the front surface30aof the sensor layer30between the gutters14L and14R in the cladding layer10so that a vicinity of the center in the width direction is positioned in a vicinity of the outer circumferential portion11of the cladding layer10, then the leather member22is wound around the sensor layer30so that the side edges22aand22bare brought close to the inner circumferential edge12of the cladding layer10, then the side edges22aand22bare sewn together as shown in (B) ofFIG. 7. Then the terminal22cof the leather member22is tucked into the gutter14L while the terminal22dis tucked into the gutter14R. Thus, the leather member22is mounted on the front portion of the rim portion R. The leather member23is placed on the front surface30aof the sensor layer30between the gutters15L and15R in the cladding layer10so that a vicinity of the center in the width direction is positioned in a vicinity of the outer circumferential portion11of the cladding layer10, then the leather member23is wound around the sensor layer30so that the side edges23aand23bare brought close to the inner circumferential edge12of the cladding layer10, then the side edges23aand23bare sewn together. Then the terminal23cof the leather member23is tucked into the gutter15L while the terminal23dis tucked into the gutter15R. Thus, the leather member23is mounted on the rear portion of the rim portion R. The leather member24is placed on the front surface30aof the sensor layer30between the gutters14L and15L in the cladding layer10so that a vicinity of the center in the width direction is positioned in a vicinity of the outer circumferential portion11of the cladding layer10, then the leather member24is wound around the sensor layer30so that the side edges24aand24bare brought close to the inner circumferential edge12of the cladding layer10, then the side edges24aand24bare sewn together. Then the terminal24cof the leather member24is tucked into the gutter14L while the terminal24dis tucked into the gutter15L. Thus, the leather member24is mounted on the left portion of the rim portion R. The leather member25is placed on the front surface30aof the sensor layer30between the gutters14R and15R in the cladding layer10so that a vicinity of the center in the width direction is positioned in a vicinity of the outer circumferential portion11of the cladding layer10, then the leather member25is wound around the sensor layer30so that the side edges25aand25bare brought close to the inner circumferential edge12of the cladding layer10, then the side edges25aand25bare sewn together. Then the terminal25cof the leather member25is tucked into the gutter14R while the terminal25dis tucked into the gutter15R. Thus, the leather member25is mounted on the right portion of the rim portion R. Thus, the skin layer20is mounted on the front surface30aof the sensor layer30as well as the sensor layer30is positioned against and brought into close contact with the cladding layer10. The sensor layer30may be provided with an adhesive on the front surface30aso that the leather members22,23,24and25are wound there around.

Thereafter, a not-shown lower cover is mounted on the lower portion of the boss section B of the steering-wheel body1of the steering wheel W as provided with the skin layer20. The boss5aof the boss section B is then fastened to the steering shaft of the vehicle, and the airbag device70is mounted on the boss section B. Thus, the steering wheel W is completed and mounted on the vehicle. When the airbag device70is mounted on the steering wheel W, the connecting wires65of the sensors50are connected to the lead wires extending from the not-shown detection circuit for detecting the driver's grip.

When fingers F (F1, F2, seeFIG. 2) of a hand H of the driver come close to the sensor layer30in the rim portion R of the steering wheel W for holding the rim portion R, the detection circuit detects elevation of electrostatic capacitance, thus detects the driver's grip.

With the steering wheel W in accordance with the exemplary embodiment, when the annular sensor layer30is mounted on the front surface10aof the cladding layer10in the rim portion R, the mounting is easily conducted by putting the sensor layer30on the outer circumferential portion11of the cladding layer10while stretching and expanding the sensor layer30, as can be seen inFIG. 6. If then the sensor layer30is adhered toward the inner circumferential edge12of the cladding layer10, or pressed onto the cladding layer10with the use of the skin layer20, the sensor layer30is quickly disposed over the front surface10aof the cladding layer10(over an entirety of the circumference of the section of the cladding layer10) including the inner circumferential edge12of the cladding layer10, as can be seen inFIG. 7. Since the sensor layer30is composed of the substrate40, the sensor50composed of the conductive ink52and the insulation sheet45all of which have stretch properties, if the circumferential length CL1 of the sensor layer30is so configured as not to cause wrinkles and slacks, the sensor layer30is easily mounted on the front surface10aof the cladding layer10in the rim portion R without an unwrinkling work in the inner circumferential edge12portion of the cladding layer10. Moreover, since the conductive ink52forming the sensor50has stretch properties, it will follow the elongation and contraction of the sensor layer30(i.e. the substrate40and insulation sheet45), thus, there will no fear of disconnection of the sensor50during the mounting work of the sensor layer30. Furthermore, the configuration that the sensor50is composed of the conductive ink52is able to make the sensor layer30thinner when compared with an instance where the sensor is composed of a wire having a round sectional shape, and also reduce uncomfortable feeling caused by the presence of the sensor50, thus improving the touch of the rim portion R.

Therefore, the steering wheel W in accordance with the exemplary embodiment has improved assembly easiness of the sensor layer30for detecting driver's grip with no fear of disconnection of the sensor50. Moreover, it is able to make the sensor layer30thin, and has little uncomfortable feeling caused by the presence of the sensor50, thus having good touch in the rim portion R.

In the steering wheel W in accordance with the exemplary embodiment, in an area between the substrate40and the insulation sheet45where the sensor50is disposed, the conductive ink52is arranged in a lattice pattern54in which a plurality of straight band-shaped lines55,56intersect one another generally perpendicularly.

Even if the band-shaped lines55,56break partially, the configuration that the sensor50is formed by applying the conductive ink52to the substrate40in the lattice pattern54in which the straight band-shaped lines55,56intersect one another generally perpendicularly will keep the sensor50in a conducting state via other intersections57in the lattice pattern54in an entirety of the area where the sensor50is disposed. Accordingly, the steering wheel W with the above configuration has a good durability of the sensor50, thus is able to provide steady grip-detecting performance. Further, the lattice pattern54by the conductive ink52means that the conductive ink52is not applied to the entirety of the area where the sensor50is disposed. The lattice pattern54provides an unapplied area58(FIG. 4) between the band-shaped lines55,56. This will save an amount of the conductive ink52to be applied to the substrate40, and reduce a production cost of the sensor layer30.

In the steering wheel W in accordance with the exemplary embodiment, moreover, the lattice pattern54of the conductive ink52is formed such that the bias direction BD of the lattice pattern54(i.e. a direction of a middle angle of an intersection angle of the band-shaped lines55,56) extends along a circumferential direction of the sensor layer30formed into an annular or ring shape.

With this configuration, when the sensor layer30is stretched for mounting on the cladding layer10, the plurality of the band-shaped lines55,56of the lattice pattern54stretch in the same direction and by the same length as one another, so that the sensor50(the conductive ink52) will have a uniform density in the circumferential direction of the rim portion R. Therefore, this configuration will provide uniform sensitivity in grip-detection and steady grip-detecting performance in the area where the sensor50is disposed.

In the steering wheel W in accordance with the exemplary embodiment, a natural circumferential length CL1 of the sensor layer30(i.e. of the assembly31) formed into an annular shape is substantially equal to the length (i.e. circumferential length) CL0 of the inner circumferential edge12of the cladding layer10in the rim portion R.

With this configuration, when the annular sensor layer30(i.e. the assembly31) is stretched and put on the outer circumferential portion11of the cladding layer10in the rim portion R, as can be seen inFIGS. 6 and 7, both of the edges31ain width direction of the band-shaped sensor layer30(assembly31) are disposed in the inner circumferential edge12portion of the cladding layer10while a vicinity of a center31ain the width direction of the sensor layer30is disposed in the outer circumferential portion11of the cladding layer10in the most elongated state. Influenced by this elongation, the both edges31ain width direction of the band-shaped sensor layer30come close to one another in a shrinking fashion but without forming wrinkles or slacks, toward a top12a((A) inFIG. 7) of the inner circumferential edge12portion of the cladding layer10. Accordingly, the above configuration will help fit vicinities of the both edges31ain width direction of the sensor layer30on the inner circumferential edge12portion of the cladding layer10without causing wrinkles or the like, thus improving assembly easiness of the sensor layer30with respect to the front surface10aof the cladding layer10.

Although the sensor layer30in the foregoing embodiment is composed of the assembly31that was formed by coupling two split band-shaped members33L,33R together, the sensor layer may alternatively be configured like a sensor layer30A depicted inFIG. 9. The sensor layer30A is composed of an assembly31A that is formed into a ring by coupling opposite ends34aof a single band-shaped member34.

The illustrated embodiments have shown the steering wheel W with the rim portion R having a generally round annular shape for the illustrative purpose. However, the shape of the rim portion R should not be limited thereby. As long as it can be covered with a sensor layer having a generally annular shape, the rim portion R may be formed into various shapes such as a square annular shape and an oval annular shape.

The steering wheel in accordance with the exemplary embodiment includes: an annular rim portion for gripping for steering; a boss section that is disposed at a center of the rim portion; one or more spokes that interconnect the rim portion and the boss section; a core member that interconnect the rim portion, the boss section and the spokes, the core member including a wheel portion that is disposed in the rim portion; a cladding layer that is disposed around the wheel portion of the core member; a skin layer that is disposed on a front surface of the rim portion; and a sensor layer for detecting whether a driver is gripping the rim portion, the sensor layer being disposed between the cladding layer and the skin layer. The sensor layer includes: a sheet-shaped substrate that is disposed toward the cladding layer and has stretch properties; a sensor for detecting whether the driver is gripping the rim portion, the sensor being composed of a conductive ink having stretch properties that is applied to a grip area by the driver on a front surface of the substrate; and an insulation sheet that covers the sensor and is disposed toward the skin layer, the insulation sheet having stretch properties. The sensor layer is generally formed into an annular band and mounted on an outer circumferential portion of the cladding layer in the rim portion by being stretched and expanded.

With the steering wheel in accordance with the exemplary embodiment, when the annular sensor layer is mounted on the front surface of the cladding layer in the rim portion, the mounting is easily conducted by putting the sensor layer on the outer circumferential portion of the cladding layer while stretching and expanding the sensor layer. If then the sensor layer is adhered towards an inner circumferential portion of the cladding layer, or pressed onto the cladding layer with the use of the skin layer, the sensor layer is quickly disposed over the front surface of the cladding layer (over an entirety of the circumference of a section of the cladding layer) including the inner circumferential portion of the cladding layer. Since the sensor layer is composed of the substrate, the sensor composed of the conductive ink and the insulation sheet all of which have stretch properties, if a circumferential length of the sensor layer is so configured as not to cause wrinkles and slacks, the sensor layer is easily mounted on the front surface of the cladding layer in the rim portion without an unwrinkling work in the inner circumferential portion of the cladding layer. Moreover, since the conductive ink forming the sensor has stretch properties, it will follow the elongation and contraction of the sensor layer (i.e. the substrate and insulation sheet), thus, there will no fear of disconnection of the sensor during the mounting work of the sensor layer. Furthermore, the configuration that the sensor is composed of the conductive ink is able to make the sensor layer thinner when compared with an instance where the sensor is composed of a wire having a round sectional shape, and also reduce uncomfortable feeling caused by the presence of the sensor, thus improving the touch of the rim portion.

Therefore, the steering wheel in accordance with the exemplary embodiment has improved assembly easiness of the sensor layer for detecting the driver's grip with no fear of disconnection of the sensor. Moreover, it is able to make the sensor layer thin, and has little uncomfortable feeling caused by the presence of the sensor, thus has a good touch in the rim portion.

In one or more embodiments, the conductive ink may be arranged in a lattice pattern in which a plurality of straight band-shaped lines intersect one another generally perpendicularly in an area between the substrate and the insulation sheet where the sensor is disposed.

Even if the band-shaped lines break partially, the configuration that the sensor is formed by applying the conductive ink to the substrate in the lattice pattern in which the straight band-shaped lines intersect one another generally perpendicularly will keep the sensor in a conducting (energized) state via other intersections in the lattice pattern in an entirety of the area where the sensor is disposed. Accordingly, the steering wheel with the above configuration has a good durability of the sensor, thus is able to provide steady grip-detecting performance. Further, the lattice pattern by the conductive ink means that the conductive ink is not applied to the entirety of the area where the sensor is disposed. The lattice pattern provides an unapplied area between the band-shaped lines. This will save an amount of the conductive ink to be applied to the substrate, and reduce a production cost of the sensor layer.

In one or more embodiments, the lattice pattern of the conductive ink may be formed such that a bias direction thereof (i.e. a direction of a middle angle of an intersection angle of the band-shaped lines) extends along a circumferential direction of the sensor layer.

With this configuration, when the sensor layer is stretched for mounting on the cladding layer, the plurality of the band-shaped lines of the lattice pattern stretch in the same direction and by the same length as one another, so that the sensor (the conductive ink) will have a uniform density in the circumferential direction of the rim portion. Therefore, this configuration will provide uniform sensitivity in grip-detection and steady grip-detecting performance in the area where the sensor is disposed.

In one or more embodiments, a natural length of the sensor layer may be substantially equal to a length of an inner circumferential edge of the cladding layer in the rim portion.

With this configuration, when the annular sensor layer is stretched and put on the outer circumferential portion of the cladding layer in the rim portion, both of the edges in width direction of the band-shaped sensor layer will be disposed in the inner circumferential portion of the cladding layer while a vicinity of a center in the width direction of the sensor layer is disposed in the outer circumferential portion of the cladding layer, in the most elongated state. Influenced by this elongation, the both edges in width direction of the band-shaped sensor layer come close to one another in a shrinking fashion but without forming wrinkles or slacks, towards a top of the inner circumferential portion of the cladding layer. Accordingly, the above configuration will help fit vicinities of the both edges in width direction of the sensor layer on the inner circumferential portion of the cladding layer without causing wrinkles or the like, thus improving assembly easiness of the sensor layer with respect to the front surface of the cladding layer.