Method for detecting a touch of a steering wheel, and vehicle steering wheel system

Abstract

A method for detecting a touch of a steering wheel (12) by means of an electrical sensor conductor (34) arranged in the steering wheel (12) comprises the following steps: a) the sensor conductor (34) is operated alternately in a temperature measurement mode, in which the temperature of the sensor conductor (34) is determined, and a touch measurement mode, in which the impedance or the capacitance of the sensor conductor (34) is determined, and b) a touch of the steering wheel (12) is determined on the basis of the determined temperature and the determined impedance or capacitance of the sensor conductor (34). Furthermore, a vehicle steering wheel system (10) having a control unit (14) for carrying out such a method is provided.

Description

[0001] Method for detecting a touch of a steering wheel and vehicle steering system

[0002] The invention relates to a method for detecting a touch on a steering wheel. Furthermore, the invention relates to a vehicle steering wheel system comprising a steering wheel and a control unit configured to perform such a method.

[0003] Methods for detecting a touch of a steering wheel, also known as hand touch detection, and vehicle steering wheel systems that perform such a method are known.

[0004] To detect a touch on the steering wheel, the change in capacitance, induced, for example, by a hand gripping the steering wheel, is usually detected by means of an electronic sensor in the steering wheel.

[0005] Such sensors have a complex structure, especially when the steering wheel is heated. Steering wheel systems with internal heating and external electrical control typically have a three-layer design. One conductive layer forms the heating element, while the other two layers are required for hand touch detection. One layer forms the sensor, and the other layer is positioned between the sensor and the heating element to shield the sensor from temperature fluctuations. The shielding layer must consist of a dense mesh to ensure consistent hand touch detection across a wide temperature range.

[0006] The object of the invention is to provide a method for detecting a touch on a steering wheel that requires a less complex design of the vehicle steering system. A further object of the invention is to provide such a vehicle steering system that is configured to carry out this method.

[0007] The problem is solved by a method for detecting a touch of a steering wheel by means of an electrical sensor conductor arranged in the steering wheel, comprising the following steps: a) the sensor conductor is operated alternately in a temperature measurement mode, in which the temperature of the sensor conductor is determined, and a touch measurement mode, in which the impedance or the capacitance of the sensor conductor is determined, and

[0008] b) Touching the steering wheel is determined based on the measured temperature and the measured impedance or capacitance of the sensor conductor.

[0009] In step b), the contact measurement is temperature-compensated using the determined temperature.

[0010] It was discovered according to the invention that, in this way, reliable detection of steering wheel touches can be achieved using only the sensor conductor as a sensor. By operating the sensor conductor alternately in temperature measurement mode and touch measurement mode, all information required for the method is obtained via the sensor conductor, so that no information from additional sensors is needed. Thus, the method can also be used with heated steering wheels, and can be carried out independently of any heating control system.

[0011] According to one approach, the temperature of the sensor conductor is determined based on its electrical resistance. This allows for a quick and easy determination of the sensor conductor's temperature.

[0012] It may be provided that the dependence of the electrical resistance on the temperature of the sensor conductor is known in order to determine the temperature particularly accurately.

[0013] Additionally or alternatively, the time intervals of the temperature measurement mode and the touch measurement mode can each have period durations of less than one tenth of a second, so that a touch of the steering wheel can be reliably detected several times per second.

[0014] In one embodiment, the sensor conductor is not a heating wire intended for heating the steering wheel. In other words, the sensor conductor is specifically designed to detect touches to the steering wheel and does not include or implement a heating function. If the steering wheel has a heating function with a heating wire, the heating wire is separate from the sensor conductor.

[0015] According to the invention, to solve the above-mentioned problem, a vehicle steering wheel system is also provided with a steering wheel that has an electrical sensor conductor and a control unit that is designed to carry out the inventive method with the aforementioned advantages.

[0016] In this case, the sensor conductor can be arranged in a foam covering of the steering wheel rim, thus saving space in the steering wheel.

[0017] In one embodiment, in addition to the sensor conductor, a heating wire is arranged in the steering wheel, which is intended for heating the steering wheel. In this way, the steering wheel can be heated by means of the heating wire, while touches on the steering wheel can be detected separately via the sensor conductor.

[0018] In another embodiment, the sensor conductor is arranged radially between the heating wire and a grip surface of the steering wheel. The grip surface is the outer surface intended for contact, for example, for holding or gripping the steering wheel. This positions the sensor conductor close to the grip surface, making hand touch detection particularly reliable.

[0019] Additionally or alternatively, the heating wire can be arranged in a foam covering of the steering wheel rim, thus saving space within the steering wheel.

[0020] Furthermore, the vehicle steering wheel system may have a heating control unit to control the heating wire in order to control or regulate the temperature of the steering wheel, thereby increasing comfort.

[0021] Furthermore, it is optionally provided that the control unit can perform the procedure independently of the heating control unit by preventing the heating control unit from transmitting any information to the control unit. This allows the control unit to be designed separately from the heating control unit, increasing the design freedom of the vehicle steering system. Further advantages and features are described below and illustrated in the accompanying drawings. These show:

[0022] - Figure 1 shows a schematic representation of a vehicle steering wheel system according to the invention,

[0023] - Figure 2 shows a perspective view of a steering wheel of the vehicle steering wheel system according to the invention from Figure 1, and

[0024] - Figure 3 shows a sectional view of the cross-section of a steering wheel rim of the steering wheel from Figure 2.

[0025] The detailed description below, in conjunction with the accompanying drawings, in which identical numbers refer to identical elements, is intended to describe various embodiments of the disclosed subject matter and is not meant to represent the only embodiments. Each embodiment described in this disclosure serves only as an example or illustration and should not be construed as preferable or advantageous over other embodiments.

[0026] All features disclosed below with reference to the exemplary embodiments and / or the accompanying figures can be combined alone or in any subcombination with features of the aspects of the present disclosure, including features of preferred embodiments, provided that the resulting combination of features is meaningful to a person skilled in the art.

[0027] Figure 1 shows a vehicle steering wheel system 10 for a vehicle, comprising a steering wheel 12, a control unit 14 and a heating control unit 16.

[0028] The steering wheel 12 is designed for steering the vehicle and has a steering wheel hub 18 (see Figure 2), a steering wheel rim 20 and several spokes 22 that connect the steering wheel hub 18 and the steering wheel rim 20.

[0029] Furthermore, the steering wheel 12 has a steering wheel frame 24 (see Figure 3) and a foam covering 26 that surrounds the steering wheel frame 24 on the outside, at least in the area of ​​the steering wheel rim 20, for example completely in the circumferential direction. The foam covering 26 is surrounded on the outside by a sheathing 28, which forms a gripping surface 30 in the form of an outer surface of the steering wheel rim 20.

[0030] The covering 28 is made, for example, of leather or imitation leather. The steering wheel frame 24 forms a core 32 of the steering wheel rim 20 and is made of a solid material, for example, a light metal alloy. The foam covering 26 is made, for example, of polyurethane foam (PUR). Several electrical sensor conductors 34 are provided in the foam covering 26, which are connected to the control unit 14 for signal transmission, for example, via an electrical connection (not shown) on one of the spokes 22.

[0031] The electrical sensor conductors 34 are made of a material whose electrical resistance is known to depend on the temperature of the material, for example, a PTC thermistor such as copper or a copper alloy. These materials have a temperature coefficient greater than 0.003 1 / K, so that even small temperature changes result in a comparatively large change in electrical resistance.

[0032] In principle, the vehicle steering wheel system 10 or the steering wheel 12 can only have one sensor conductor 34, which extends, for example, several times around the steering wheel rim 20 in the direction of rotation of the steering wheel 12.

[0033] Furthermore, several heating wires 36 are provided in the foam covering 26, which are electrically connected to the heating control unit 16, for example via an electrical connection (not shown) on one of the spokes 22.

[0034] Naturally, the vehicle steering wheel system 10 or the steering wheel 12 can only have one heating wire 36, which extends, for example, several times around the steering wheel rim 20 in the direction of rotation of the steering wheel 12.

[0035] In the illustrated embodiment, the sensor conductors 34 and heating wires 36 are arranged in incisions 38 in the foam covering 26, which extend substantially radially inwards from the outside. The incisions 38 extend circularly around the steering wheel hub 18 along the steering wheel rim 20. Several circular incisions 38 may be present, running substantially parallel to each other, or one or more of these incisions 38 may also be guided along the steering wheel rim 20 in several revolutions around the steering wheel hub 18 with a slight distance between them, so that a substantially spiral incision 38 is produced.

[0036] The heating wires 36 are each arranged at a radial depth ti relative to the handle surface 30, while the sensor conductors 34 are each arranged at a radial depth t2 relative to the handle surface 30.

[0037] The depth t2 is smaller than the depth ti, i.e. the sensor conductors 34 are located closer to the handle surface 30 than the heating wires 36, while the heating wires 36 are located closer to the core 32 than the sensor conductors 34.

[0038] Furthermore, in the present embodiment, each sensor conductor 34 is arranged in a radial direction between the handle surface 30 and an associated heating wire 36.

[0039] The distance between the sensor conductor 34 and the associated heating wire 36 can be constant, for example in each notch 38.

[0040] For example, the depth ti is a maximum of 4 mm, preferably a maximum of 2.5 mm, while the depth t2 is between 0 and 1.5 mm.

[0041] The distance (ti - t2) between the sensor conductor 34 and the associated heating wire 36 can be between 0 and about 3 mm, preferably 0.8 to 1.5 mm.

[0042] The heating wires 36 are designed to heat the steering wheel 12 by applying an electric current to the heating wires 36 via the heating control unit 16 (see Figure 1), which heats them due to their electrical resistance.

[0043] The heat emitted to the steering wheel 12 via the heating wires 36, and thus the temperature of the grip surface 30, can be controlled and / or regulated via the heating control unit 16. The sensor conductors 34 form a touch sensor by means of which the control unit 14 can detect contact with the steering wheel 12, more precisely with the grip surface 30, using the procedure described below.

[0044] The control unit 14 has for this purpose an impedance measuring unit 40 (see Figure 1), a temperature measuring unit 42 and a multiplexer 44, via which the impedance measuring unit 40 and the temperature measuring unit 42 can each be connected to or disconnected from the sensor conductors 34 for signal transmission.

[0045] The temperature measuring unit 42 is designed to determine the temperature of the sensor conductors 34 based on the electrical resistance and the temperature coefficient of the sensor conductors 34.

[0046] The impedance measuring unit 40 is designed to determine the impedance of the sensor conductor 34.

[0047] In an alternative embodiment, the control unit 14 can have a capacitance measuring unit instead of the impedance measuring unit 40, which is configured to determine the electrical capacitance of the sensor conductors 34.

[0048] In this context, the control unit 14 is designed separately from the heating control unit 16, and the procedure for detecting a touch of the steering wheel 12 is carried out by the control unit 14 independently of the heating control unit 16.

[0049] The method for detecting a touch of the steering wheel 12 is described below using the vehicle steering wheel system 10 with an impedance measuring unit 40 shown in Figure 1 as an example. For a vehicle steering wheel system 10 with a capacitance measuring unit, the method is analogous, except that instead of the impedance of the sensor conductors 34, the capacitance of the sensor conductors 34 is determined by the capacitance measuring unit.

[0050] In a first step, the control unit 14 is operated alternately in a temperature measurement mode and a touch measurement mode. In temperature measurement mode, the temperature measuring unit 42 is connected to the sensor conductors 34 via the multiplexer 44 for signal transmission, while the impedance measuring unit 40 is disconnected from the sensor conductors 34.

[0051] In contact measurement mode, the impedance measurement unit 40 is connected to the sensor conductors 34 via the multiplexer 44 for signal transmission, while the temperature measurement unit 42 is disconnected from the sensor conductors 34.

[0052] For example, the time intervals of the temperature measurement mode and the contact measurement mode each have periods of less than one tenth of a second.

[0053] In temperature measurement mode, the temperature of the sensor conductor 34 is determined in a manner known per se based on the electrical resistance and the temperature coefficient of the sensor conductor 34.

[0054] For example, the current flowing through the sensor conductors 34 and the electrical voltage applied to them are first measured, and the electrical resistance of the sensor conductors 34 is calculated from these measurements. Finally, the temperature of the sensor conductors 34 is determined using the temperature coefficient of the sensor conductors 34, which is stored in the control unit 14, and the electrical resistance of the sensor conductors 34.

[0055] The determined temperature of the sensor conductor 34 is further dependent on the temperature inside the steering wheel 12, which can be derived from the determined temperature of the sensor conductor 34.

[0056] In contact measurement mode, the impedance of the sensor conductor 34 is determined with the impedance measuring unit 40 in a manner known per se.

[0057] Whether or not the steering wheel 12 has been touched is determined in a subsequent step based on the determined temperature and the determined impedance of the sensor conductor 34, since touching the steering wheel 12 leads to a significant change in the impedance of the sensor conductor 34.

[0058] Consequently, it is determined whether the measured impedance at the measured temperature exceeds a threshold value that indicates a touch of the steering wheel 12. In other words, a touch of the steering wheel 12 is detected if the measured impedance is greater than or equal to the threshold value. If the measured impedance is less than the threshold value, no touch of the steering wheel 12 is detected.

[0059] In an alternative embodiment, the temperature of the sensor conductor 34 can be determined in any way, for example by means of an NTC thermistor.

[0060] In all embodiments, a method for detecting a touch of a steering wheel 12 and a vehicle steering wheel system 10 for carrying out such a method are provided in this way, by means of which touches of the steering wheel 12 are reliably detected.

[0061] In contrast to conventional vehicle steering wheel systems, where a virtually calculated temperature of a sensor layer is used for temperature compensation, the temperature for temperature compensation in the method according to the invention is determined directly via the sensor conductors 34. Thus, temperature compensation can be carried out without knowledge of the heating intensity or current and voltage information of the heating control unit 16.

[0062] The vehicle steering wheel system 10 is designed to be compact and has very few components.

[0063] Because the sensor conductors 34 run in close proximity to and in the same manner as the heating wires 36, temperature changes of the steering wheel 12 are detected particularly accurately.

[0064] Furthermore, the heating wires 36 are arranged close to the handle surface 30, which makes the heating performance particularly favorable.

Claims

Patent claims 1. Method for detecting a touch of a steering wheel (12) by means of an electrical sensor conductor (34) arranged in the steering wheel (12), comprising the following steps: a) the sensor conductor (34) is operated alternately in a temperature measurement mode, in which the temperature of the sensor conductor (34) is determined, and a touch measurement mode, in which the impedance or the capacitance of the sensor conductor (34) is determined, and b) a touch of the steering wheel (12) is determined on the basis of the determined temperature and the determined impedance or capacitance of the sensor conductor (34).

2. Method according to claim 1, wherein the temperature of the sensor conductor (34) is determined based on the electrical resistance of the sensor conductor (34).

3. Method according to claim 1 or 2, wherein the time intervals of the temperature measurement mode and the touch measurement mode each have period durations of less than one tenth of a second.

4. Method according to one of the preceding claims, wherein the sensor conductor (34) is not a heating wire (36) provided for heating the steering wheel (12).

5. Vehicle steering wheel system (10) comprising a steering wheel (12) having an electrical sensor conductor (34) and a control unit (14) configured to perform the method according to one of the preceding claims.

6. Vehicle steering wheel system (10) according to claim 5, wherein the sensor conductor (34) is arranged in a foam covering (26) of a steering wheel rim (20) of the steering wheel (12).

7. Vehicle steering wheel system (10) according to claim 5 or 6, wherein, in addition to the sensor conductor (34), a heating wire (36) is arranged in the steering wheel (12) for heating the steering wheel (12).

8. Vehicle steering wheel system (10) according to claim 7, wherein the sensor conductor (34) is arranged radially between the heating wire (36) and a grip surface (30) of the steering wheel (12).

9. Vehicle steering wheel system (10) according to claim 7 or 8, wherein the heating wire (36) is arranged in a foam covering (26) of a steering wheel rim (20) of the steering wheel (12).

10. Vehicle steering wheel system (10) according to one of claims 7 to 9, wherein the vehicle steering wheel system (10) has a heating control unit (16) for controlling the heating wire (36).

11. Vehicle steering wheel system (10) according to claim 10, wherein the control unit (14) performs the method independently of the heating control unit (16).

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