Method for detecting presence of human hand in grip region of steering wheel

Abstract

The invention relates to a method for detecting the presence of a hand (1) in a gripping region of a steering wheel (2) by means of a capacitive sensor system, the presence of the human hand (1) in the detection region of the sensor arrangement comprising at least one sensor electrode (4) connected to the first input / output (3.1) of the sensor electronics (3) results in a change in the capacitive coupling (CHand) of the sensor electrode (4) to a reference potential, and wherein the metal core (5) of the steering wheel is connected to the ground potential (GND), characterized in that the sensor arrangement (1) comprises at least one sensor electrode (4) connected to the first input / output (3.1) of the sensor electronics (3). A diagnosis of the connection of the steering wheel core (5) to the ground potential (GND) is carried out during operation in that at least one first contact point (5.1) of the steering wheel core (5) is connected to a second input (3.2) of the sensor electronics (3), which second input carries out a continuous monitoring of the applied potential.

Description

Technical Field

[0001] The invention relates to a method for detecting the presence of a human hand in the gripping area of ​​a steering wheel by means of a capacitive sensor system, wherein the presence of a human hand in a detection area of ​​a sensor structure comprising at least one sensor electrode connected to a first input / output terminal of a sensor electronics component leads to a change in the capacitive coupling of the sensor electrode to a reference potential relative to a reference state in which the hand is not present, and wherein the metallic core of the steering wheel is connected to ground potential. Background Art

[0002] The sensor electrodes used here are single-layer or multi-layer structures of electrically conductive sensor mats in the steering wheel rim. These sensor systems are also referred to as "HOD sensors" (Hands On Wheel Detection). The presence of a hand can be detected here via a capacitive measurement. The fact that there is a capacitive coupling between the hand and the sensor electrode, whose capacitance value C Hand The task of the associated sensor electronics or the measuring method using the sensor electronics is to detect the capacitance C Hand The particular difficulty here is that the capacitor C Hand In particular, the change to be detected is very small compared to other internal capacitances of the steering wheel. For this reason, the so-called integration method is used to measure it, in which a small charge quantity is transferred from the sensor element, whose capacitance value is relatively small and variable, to an integration capacitor with a known fixed and significantly larger capacitance value in a plurality of consecutive cycles. After a predetermined number of such integration cycles, the voltage at the integration capacitor is then measured with the aid of an A / D converter and processed into a sensor amplitude, which in turn is a value for the capacitance C Hand Other factors that may also influence the measured capacitance must therefore be kept as constant as possible. For this purpose, in particular the steering wheel core is placed at a fixed potential.

[0003] Sensor systems for steering wheels of motor vehicles for detecting hands with a capacitive sensor structure are known in principle from the prior art. Thus, for example, DE 203 09 603 U1 discloses a steering wheel with sensor electrodes arranged in a sector shape, which make it possible to detect the approach and / or departure of a human hand and associate it with a specific area of ​​the steering wheel.

[0004] WO 2016 / 087279 A1 discloses a steering wheel for a motor vehicle, which has a capacitive sensor system, and the sensor structure of the sensor system can at least sometimes also be operated as a heating structure. In addition, the steering wheel has a metallic steering wheel core, which is operated as an active shielding element and can be charged with a defined potential in order to reduce interfering capacitive coupling of the sensor structure to the steering wheel core.

[0005] Due to the capacitance C between the hand and the corresponding sensor electrode Hand Significantly larger capacitance C between the steering wheel core and the sensor electrode Core , potential changes in the steering wheel core have a disturbing effect on the HOD measurement. The connection of the steering wheel core to a fixed potential is implemented in the sensor electronics to avoid this problem. This potential connection, which is usually implemented at ground potential GND, typically has C GND Capacitance component >100nF.

[0006] The sensor electrodes and the steering wheel core are usually connected via plug connectors to a cable harness which leads to the HOD electronics and is likewise connected to the HOD electronics via plug connectors.

[0007] This actual situation and the relevant physical quantities are schematically illustrated in FIG. 3 according to the prior art.

[0008] Imperfect contact or cable breakage in the potential connection of the steering wheel core may cause impedance Z GND , especially its capacitive component C GND This can lead to erroneous measurement results. Summary of the invention

[0009] Compared to the prior art described previously, the method according to the invention has the advantage of avoiding such errors.

[0010] This is achieved according to the invention in that a diagnosis of the connection of the steering wheel core to ground potential is carried out during operation in that at least one contact point of the steering wheel core is connected to a second input of sensor electronics which continuously monitors the applied potential.

[0011] Further preferred embodiments of the method according to the invention are apparent from the further dependent claims and from the following description of possible exemplary embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention is described below with reference to the accompanying drawings, wherein:

[0013] Figure 1: shows a schematic illustration of a HOD sensor system for implementing the method according to the invention in a first variant;

[0014] Figure 2 : shows a schematic illustration of a HOD sensor system for implementing the method according to the invention in a first variant;

[0015] FIG. 3 : shows a schematic illustration of a HOD sensor system according to the prior art and the relevant physical quantities. DETAILED DESCRIPTION

[0016] As can be seen in FIG. 3 , which shows the prior art, in a conventional HOD sensor system at least one sensor electrode 4 of a sensor structure of a steering wheel 2 is connected to a first input / output 3 . 1 of sensor electronics 3 .

[0017] The capacitive coupling C of the sensor electrode 4 to the hand 1 due to the presence of the human hand 1 in the detection area of ​​the sensor electrode 4 is detected via this input / output 3 . 1 of the sensor electronics 3 . Hand In contrast, the capacitance C between the sensor electrode 4 and the steering wheel core 5 Core The steering wheel core 5 itself is connected to a fixed potential, usually ground GND, via one or more conductors 6. This connection has an impedance Z GND , whose capacitive component is usually C GND >100 nF. Single and multiple contact connections of the steering wheel core 5 are known, wherein multiple contact connections increase the robustness of the connection. However, targeted diagnosis of the connection (especially for the purpose of identifying interruptions of the connection) is not yet known in the art. Figure 1 A first embodiment of a HOD sensor system for carrying out the method according to the invention in a first variant is shown in . The basic structure of the sensor system and the method for detecting the presence of a hand in the gripping area of ​​a steering wheel are identical to those described above with reference to FIG.

[0018] In addition, however, there is also a connection here of one of the lines 6 connecting the steering wheel core 5 to the ground potential GND to the other, second input 3.2 of the sensor electronics 3. With the aid of the second input 3.2 of the sensor electronics 3, a capacitive voltage measurement is performed, in which the capacitance C between the contact point 5.1 of the steering wheel core 5 and the sensor electrode 4 is used. Core Capacitive coupling. A driving signal is applied to the sensor electrode, and due to the capacitive coupling C Core The voltage U applied to the steering wheel core 5 CoreWhen the connection to the steering wheel core 5 is interrupted at the node 6.1 or 6.2 of the conductor 6, the ratio of the voltage divider and thus the measured voltage U Core The range diagnosis can detect the loss of the connection between the steering wheel and ground potential GND.

[0019] However, the voltage divider is Z GND or C GND Leading (C GND >100nF, C Core ~1 nF). In order to reliably detect an interruption at the node 6.2, the connection to the fixed potential GND must be interrupted during the diagnostic measurement, which is achieved by means of an additional switch 8. Otherwise, the measured voltage change would be too small and therefore not robust with respect to other influences on the measurement.

[0020] exist Figure 2 Another embodiment of a HOD sensor system for implementing the method according to the invention is shown in FIG. Figure 1 , in which, in addition to the connection of the first contact point 5.1 of the steering wheel core 5 to the second input 3.2 of the sensor electronics 3, there is also an additional connection of the second contact point 5.2 of the steering wheel core 5 to a further, third input 3.3 of the sensor electronics 3. However, unlike the conductor 6 connected to the second input 3.2 (in which the node 6.2 is located), the conductor 6' of this additional connection, in which the node 6.1 is located, is not directly connected to the ground potential GND. An interruption of the connection at the node 6.1 or 6.2 can be detected by the short-circuit diagnosis.

Claims

1. A method for detecting the presence of a human hand (1) in a gripping area of ​​a steering wheel (2) by means of a capacitive sensor system, wherein: Relative to a reference state in which the hand (1) is not present, the presence of the human hand (1) in a detection area of ​​a sensor structure comprising at least one sensor electrode (4) connected to a first input / output terminal (3.1) of a sensor electronics (3) results in a capacitive coupling C of the sensor electrode (4) to a reference potential. Hand changes, and wherein a metallic core (5) of the steering wheel is connected to a ground potential (GND), characterised in that a diagnosis of the connection (6) of the steering wheel core (5) to the ground potential (GND) is performed during operation in that at least one first contact point (5.1) of the steering wheel core (5) is connected to a second input (3.2) of the sensor electronics (3), which performs a continuous monitoring of the applied potential.

2. The method according to claim 1, characterized in that A capacitive voltage measurement is performed with the aid of the second input (3.2) of the sensor electronics (3), in which the capacitance C between the steering wheel core (5) and the sensor electrode (4) is used. Core Capacitive coupling.

3. The method according to claim 2, characterized in that The sensor electrode (4) is loaded with a driving signal based on the capacitive coupling C Core The voltage U applied to the steering wheel core (5) Core Also follows the drive signal.

4. The method according to claim 2 or 3, characterized in that: During the diagnostic measurement, the connection (6) of the steering wheel core (5) to the ground potential (GND) is interrupted by an additional switch (8).

5. The method according to claim 1, characterized in that A second contact point (5.2) of the steering wheel core (5) is connected to a third input (3.3) of the sensor electronics (3), and an interruption of the connection (6) of the steering wheel core (5) to the ground potential (GND) or an interruption of the connection (6') of the steering wheel core (5) to the third input (3.3) of the sensor electronics (3) is detected by a short-circuit diagnosis.

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