Patent ID: 12248106

In the Figures, identical or functionally equivalent elements are indicated by identical reference marks.

FIG.1shows a motor vehicle1according to one embodiment of the present invention. The motor vehicle1in the present exemplary embodiment is designed as a passenger car. The motor vehicle1comprises a driver assistance system2. With the driver assistance system2, for example, an object3located in the surrounding area4of the motor vehicle1can be detected. In particular, by means of the driver assistance system2a distance between the motor vehicle1and the object3can be determined.

The driver assistance system2comprises at least one ultrasonic sensor device5. The ultrasonic sensor device5, in turn, has at least one ultrasonic sensor5a. The ultrasonic sensor5acomprises a transmitting device6, by means of which at least one ultrasonic signal8, in particular a plurality of ultrasonic signals, can be emitted. The ultrasonic sensor device5in this case is arranged on a front region of the motor vehicle1. The ultrasonic sensor device5can also be arranged on other areas, such as a rear section or a side region of the motor vehicle1. The following example is thus not to be regarded as exhaustive, but only for illustrative purposes.

With the transmitting device6, the ultrasonic signals8can be emitted within a predetermined coverage range E or a predetermined angular range, by means of a diaphragm.

In addition, the ultrasonic sensor device5comprises a receiving device7, by means of which reflected ultrasound signals can be received as echo signals9which have been reflected by the object3, in particular via the diaphragm. With the receiving device7, ultrasonic signals9reflected from the object3can therefore be received as a reception signal. The ultrasonic sensor device5can also have a control device S that can be formed, for example, by a microcontroller and/or a digital signal processor. The driver assistance system2additionally comprises a control device10, which can be formed for example by an electronic control unit (ECU) of the motor vehicle1. The control device10is connected to the ultrasonic sensor device5for data transfer. For example, the data can be transferred via the data bus of the motor vehicle1.

FIG.2shows a schematic frequency-signal amplitude curve for determining a transfer function13of one embodiment of an ultrasonic sensor (5a). On the abscissa A of the graph inFIG.1, in particular, a frequency is plotted in [kHz]. An ordinate O of the graph indicates a signal amplitude in [dB]. The signal amplitude depends on the electrical characteristic parameters K (FIG.4), such as voltage and current. In particular,FIG.1shows that the transfer function13of the ultrasonic sensor5ahas a peak12, which is located in particular at a resonance frequency R of the ultrasonic sensor5a. In the example shown inFIG.1the resonance frequency R is at about 45 kHz. The ultrasonic sensor5ais preferably operated in the resonance mode at the resonance frequency R.

By means of the transfer function13fromFIG.2, in particular the acoustic-electric behaviour of the ultrasonic sensor5acan be represented. In particular, depending upon the design each ultrasonic sensor5ahas a specific transfer function13. In particular, for example, the specific resonance frequency R of the ultrasonic sensor5acan be in a frequency band which is represented inFIG.1using the example of −Δf and +Δf. For example, the frequency band can range between 40 kHz and 50 kHz. In particular, the resonance frequency R of the specific ultrasonic sensor5ain this frequency band can then be checked and determined.

Due to external influences, such as environmental effects, ageing or sensor-related effects, it may be the case that the ultrasonic sensor5awill have a different transfer function13compared to a reference transfer function11of a reference ultrasonic sensor. In particular, the transfer function13is different to the reference transfer function11. By comparing the transfer function13against the reference transfer function11, in particular a functional status of the ultrasonic sensor5acan then be determined. For example, it is possible to determine whether the ultrasonic sensor5ais dirty or affected by ice. The transfer function13is determined as a function of an electrical test signal P (FIG.4), wherein the ultrasonic sensor5ais excited with the electrical test signal P. The electrical characteristic parameter K, which can be in particular a voltage and/or a current in the ultrasonic sensor5a, can then be evaluated and the transfer function13of the ultrasonic sensor5acan be determined as a function thereof. In particular, the transfer function13is then compared with the reference transfer function11, and the functional status of the ultrasonic sensor5acan then be determined depending on the comparison. In particular, it can be provided that the test signal P is generated as a harmonic signal or as a step signal or as a pulse signal by a control device, in particular the control device (S) of the ultrasonic sensor5a.

It can also be provided that the determination of the functional status of the ultrasonic sensor5acan be carried out in a multiplicity of modes of operation of the motor vehicle1, in particular during a driven operation of the motor vehicle1. Thus, the functional status of the ultrasonic sensor5acan be determined at the current time.

FIG.3shows an example schematic frequency-signal amplitude curve for determining an impedance frequency response14of the ultrasonic sensor5a. In particular, the frequency is indicated in [kHz] on the abscissa A and a phase angle α in [°] is plotted on the ordinate O. The impedance frequency response14has a turning point at the resonance frequency R of the ultrasonic sensor5a. In particular, at the resonant frequency R the impedance has a phase angle α of 0.

In particular, it is provided that the transfer function13is determined by means of the impedance frequency response14, wherein the impedance frequency response14describes the electrical characteristic parameter K, in particular as the current and/or voltage as a function of the phase angle α between the two. For example, the impedance frequency response14can then be determined as a function of an injected current as the electrical test signal P, of a measured voltage dependent thereon as an electrical characteristic parameter K, and of a phase angle α of the injected current relative to the measured voltage, which is implemented as an electrical characteristic parameter K. It is also possible for the impedance frequency response14to be determined as a function of an injected voltage as an electrical test signal P, of a measured current dependent thereon as an electrical characteristic parameter K, and of the phase angle α of the injected voltage relative to the measured current, which is implemented as the electrical characteristic parameter K.

FIG.4shows a schematic equivalent circuit diagram of one embodiment of the ultrasonic sensor5aas an electrical model15of the ultrasonic sensor5a. In particular, the electrical model15describes the mechanical ultrasonic transducer5ain electrical terms. In particular, the electrical model15comprises a plurality of components16.

In particular, the electrical model15has a first capacitor17, a second capacitor18, an inductor19and an ohmic resistor20. In particular, parameter values of the components16are chosen such that they can be characterized by the transfer function13. In particular, it is provided that in the electrical model15the second capacitor18, the inductance19and the ohmic resistance20are connected in series and the first capacitor17is connected in parallel with this series circuit.

In particular, the first capacitor17describes a physical capacitance of the ultrasonic sensor5a, for example the ceramic of a piezo-ultrasonic sensor. The second capacitor18can describe, for example, a mechanical compliance, corresponding to the reciprocal of the stiffness, of a membrane of the ultrasonic sensor5a. By means of the inductance19, in particular a moving mass of the membrane can be modelled. The ohmic resistance20can describe, in particular, a damping of the ultrasonic signal8. In particular, by means of the physical capacitance, the mechanical compliance, the moving mass and the damping, the at least one functional status of the ultrasonic sensor5acan be determined.

For example, if a ceramic is defective, the capacitance of the first capacitor17can be reduced, so that a decrease in the first capacitance can be used to deduce a failure of the ceramic. If, for example, ice is present on the diaphragm of the ultrasonic sensor5a, then for example the mechanical compliance and the moving mass may be altered, so that in the electrical model15a change in the second capacitor16or a change in the capacitance of the second capacitor16and a change in the inductance19would be detected. On the basis of the parameter value changes a conclusion can then be drawn as to the functional status of the ultrasonic sensor5a.

In particular, it is provided that the parameter values of the components16are determined by means of a parameter value adjustment, in particular by means of a numerical optimisation, in such a way that with these adjusted parameter values the transfer function13is obtained in the form of a model.

In particular, the reference transfer function11and/or parameter values of a reference ultrasonic sensor that produces the reference transfer function11can then be stored on a storage medium of the ultrasonic sensor device5for a multiplicity of potential functional states. Thus, the individual parameter values of the components16can be compared with the parameter values of the components of the reference ultrasonic sensor and then, from the information stored in the memory, used to draw conclusions about the environmental conditions, the sensor conditions and/or the ageing of the ultrasonic sensor5a.

In particular, it can be provided that information from at least one other sensor, such as a temperature sensor and/or an air humidity sensor and/or other sensor types, can also be taken into account in determining the functional status. The at least one other sensor can be part of the ultrasonic sensor5aand/or the ultrasonic sensor device5and/or the motor vehicle1.

In particular, it is provided that the transfer function13of the ultrasonic sensor5ais therefore measured directly and hence internal to the sensor—without sending ultrasonic signals and evaluating received echo signals—and the functional status of the ultrasonic sensor5ais determined on the basis of the transfer function13. For this purpose, the ultrasonic sensor5ais excited by means of the electrical test signal P. By means of the electrical test signal P the electrical characteristic parameter K of the ultrasonic sensor5ais then manipulated and evaluated by the ultrasonic sensor5a. As a function of the electrical characteristic parameter K, which can be detected in particular in the impedance frequency response14, the transfer function13is determined. The electrical model15provided, with its components16, is matched to the specific transfer function13by parameter value fitting, so that the components16characterize the transfer function13. The matched parameter values are then compared with reference parameter values of a reference ultrasonic sensor and on the basis of the comparison are then used to draw conclusions as to the functional status of the ultrasonic sensor5a.