Planar flexible carrier for use in steering wheel heating and/or sensing
A planar carrier for mounting on a rim of a steering wheel without wrinkles, the planar carrier including a portion of planar flexible foil of roughly rectangular shape having two longitudinal sides and two lateral sides, wherein the length B of the lateral sides is 0.96 to 1.00 times the perimeter of the rim, and wherein N cut-outs per unit length are provided on each of the longitudinal sides. The cut-outs of one side are located in a staggered fashion relative to opposing cut-out portions on the opposite side. The optimum shape and size of the cut-outs may be determined as described. The planar carrier may be implemented as a heat carrier, a heating device and/or a sensing device.
1. A planar carrier for mounting on a rim of a steering wheel without wrinkles, the planar carrier comprising a portion of planar flexible foil having two longitudinal sides and two lateral sides, wherein a length B of the lateral sides is 0.96 to 1.00 times a perimeter of the rim, wherein N cut-outs per unit length are provided on each of the longitudinal sides, and wherein the N cut-outs on one of the two longitudinal sides are arranged in a staggered fashion relative to opposing N cut-outs on the opposite longitudinal side and wherein a width of each of the N cut-outs on the longitudinal sides as a function of an arc length l of the rim, w(l), is
w
(
l
)
=
ɛ
(
l
)
N
wherein ε(l) is a material surplus of the planar flexible foil as a function of the arc length l of the rim, and the arc length l of the rim is measured from a middle (B/2) of the planar flexible foil in perpendicular direction to the longitudinal sides,
N being chosen between 10 and 50 m −1 ,
wherein arc length l of the rim as a function of a radial coordinate r is
l
(
r
)
=
∫
r
r
1
+
r
2
r
(
df
(
r
)
dr
)
2
+
1
dr
wherein r 1 is a radius of the steering wheel, r 2r is a radius of the rim collinear with r 1 , f(r) is a function describing a cross-sectional shape of the rim, and
wherein the material surplus of the planar flexible foil in the planar carrier as a function of the radial coordinate r is
ɛ
(
r
)
=
Δ
l
(
r
)
l
=
-
1
+
r
r
1
+
r
2
r
and wherein, when the rim of the steering wheel has a circular cross-section, the width of each of the N cut-outs on the longitudinal sides as a function of the arc length l of the rim, w(l), is
w
(
l
)
=
(
-
1
+
r
1
+
r
2
r
cos
[
l
r
2
r
]
r
1
+
r
2
r
)
·
N
-
1
.
2. The planar carrier as claimed in claim 1 , wherein, when the rim of the steering wheel includes finger portions, the width of the N cut-outs on one of the longitudinal sides are enlarged relative to w(l).
3. The planar carrier as claimed in claim 1 , wherein the planar flexible foil is stretchable when the rim of the steering wheel includes finger portions.
4. The planar carrier as claimed in claim 1 , wherein the planar carrier is stretchable and a length of the planar carrier is chosen to be up to 5% shorter than an outer perimeter of the rim.
5. The planar carrier as claimed in claim 1 , wherein the planar carrier comprises one or more layers of polymer film, elastomer foils, textile, or any combination thereof.
6. A heat carrier comprising a planar carrier according to claim 1 , wherein the planar carrier is configured to distribute heat from an external source through a cross-section of the planar carrier.
7. A heating device for a steering wheel, comprising a planar carrier according to claim 1 , and at least one heating element arranged on at least one side of the planar carrier, wherein the at least one heating element comprises at least one electrical heating circuit.
8. The heating device as claimed in claim 7 , wherein the at least one electrical heating circuit is a serial or parallel electrical heating circuit.
9. The heating device as claimed in claim 7 , wherein the at least one electrical heating circuit comprises conductive materials selected from at least one of printed polymer thick film (PTF) silver, printed nanosilver and galvanic copper.
10. The heating device as claimed in claim 7 , further comprising at least one dielectric layer between the planar carrier and the at least one heating element.
11. A method for producing a planar carrier for a steering wheel according to claim 1 , the method comprising the steps of:
(a) determining an outer diameter and the cross-sectional shape of the rim to be equipped with the planar carrier,
(b) determining N, the number of cut-outs per unit length,
(c) determining a size of the planar flexible foil based at least in part on the outer diameter of the rim,
(d) preparing the planar carrier for mounting on the rim of the steering wheel, and
(e) providing said portion of planar flexible foil owith the N cut-outs.
12. A method for producing a heating device, a sensing device, or both, for a steering wheel as claimed in claim 7 , comprising the steps of:
(a) determining an outer diameter and the cross-sectional shape of the rim to be equipped with the planar carrier,
(b) determining N, the number of cut-outs per unit length,
(c) determining a size of the planar flexible foil based at least in part on the outer diameter of the rim,
(d) preparing the planar carrier for mounting on the rim of the steering wheel,
(e) providing said portion of planar flexible foil with the N cut-outs, and
(f) arranging at least one heating element on at least one side of the planar carrier.
13. A method of using a planar carrier as claimed in claim 1 , comprising the step of applying the planar carrier to the rim of the steering wheel, wherein the coverage of the rim is at least 86% of the surface of the rim without wrinkles for steering wheels with finger portions and at least 96% of the surface of the rim without wrinkles for steering wheels without finger portions.
14. A method of using a planar carrier as claimed in claim 1 , comprising the step of applying the planar carrier to the rim of the steering wheel for capacitive sensing of the presence of a driver's hand(s) on the steering wheel.
15. The planar carrier as claimed in claim 1 , wherein Nis between 20 and 40 m −1 .
16. A sensing device for a steering wheel, comprising a planar carrier according to claim 1 , and at least one sensing element arranged on at least one side of the planar carrier, wherein the at least one sensing element comprises at least one sensing circuit.
17. The sensing device as claimed in claim 16 , wherein the at least one sensing circuit is a serial or parallel electrical sensing circuit.
18. The sensing device as claimed in claim 16 , wherein the at least one sensing circuit comprises conductive materials selected from at least one of printed polymer thick film (PTF) silver, printed nanosilver and galvanic copper.
19. The sensing device as claimed in claim 16 , further comprising at least one dielectric layer between the planar carrier and the at least one sensing element.