FILTER DEVICE FOR FILTERING A SUPPLY VOLTAGE OF AN ULTRASONIC SENSOR OF A MOTOR VEHICLE, ULTRASONIC SENSOR DEVICE AND MOTOR VEHICLE

Abstract

The invention relates to a filter device (9) for filtering a supply voltage (Ub) of an ultrasonic sensor (10) of a motor vehicle (1), wherein the filter device (9) is electrically connectable on the input side to a voltage source (8), which provides the supply voltage (Ub), and on the output side to the ultrasonic sensor (10) and wherein the filter device (9) comprises a low-pass filter with a resistor (R1) and a capacitor (C1), wherein the filter device (9) comprises a diode (D2), which is connected in parallel with the resistor (R1).

Claims

1. A filter device for filtering a supply voltage (Ub) of an ultrasonic sensor of a motor vehicle, wherein: the filter device is electrically connectable on an input side to a voltage source, which provides the supply voltage (Ub), and on an output side to the ultrasonic sensor, the filter device comprising a low-pass filter with a resistor (R1) and a capacitor (C1), wherein the filter device comprises a diode (D2) connected in parallel with the resistor (R1).

2. The filter device according to claim 1, wherein the diode (D2) and/or the resistor (R1) are dimensioned in such a way that the diode (D2) conducts when a specified transmission current (Is) flows through the filter device during a transmit phase of the ultrasonic sensor.

3. The filter device according to claim 1, wherein the diode (D2) and/or the resistor (R1) are dimensioned in such a way that the diode (D2) does not conduct when a specified evaluation current (Ia) flows through the filter device during an evaluation phase of the ultrasonic sensor.

4. The filter device according to claim 3, wherein the diode (D2) and/or the resistor (R1) are dimensioned in such a way that a resistance value of the resistor (R1) is less than a quotient of a forward voltage (Ud) of the diode (D2) and the evaluation current (Ia).

5. The filter device according to claim 1, wherein the filter device comprises an additional diode (D1), which is connected in series with the resistor (R1) of the low-pass filter.

6. The filter device according to claim 1, wherein the filter device has at least one additional capacitor, which is connected in parallel with the capacitor of the low-pass filter.

7. An ultrasonic sensor device for a motor vehicle comprising an ultrasonic sensor; and a filter device according to claim 1.

8. A motor vehicle having at least one ultrasonic sensor device according to claim 7.

Description

[0021] These show:

[0022] FIG. 1 a motor vehicle in accordance with one embodiment of the present invention, which has a plurality of ultrasonic sensor devices;

[0023] FIG. 2 a schematic representation of an ultrasonic sensor device that is connected to a voltage source of the motor vehicle;

[0024] FIG. 3 a circuit of a filter device of the ultrasonic sensor device in accordance with the prior art; and

[0025] FIG. 4 a circuit of a filter device in accordance with an embodiment of the present invention.

[0026] In the Figures, identical and functionally equivalent elements are indicated by identical reference marks.

[0027] FIG. 1 shows a motor vehicle 1 according to one embodiment of the present invention in a plan view. The motor vehicle 1 in the present case is designed as a passenger car. The motor vehicle 1 comprises a driver assistance system 2, which in turn comprises a control device 3. The driver assistance system 2 additionally comprises at least one ultrasonic sensor device 4. In the present case, the driver assistance system 2 comprises eight ultrasonic sensor devices 4, wherein four ultrasonic sensor devices 4 are arranged in a front section 5 of the motor vehicle 1 and four ultrasonic sensor devices 4 in a rear section 6 of the motor vehicle 1. As explained in more detail below, each of the ultrasonic sensor devices 4 comprises one ultrasonic sensor 10, with which objects in a surrounding area 7 of the motor vehicle can be detected. In this regard, the ultrasonic sensors 10 can be arranged on the bumpers of the motor vehicle 1. The respective ultrasonic sensor devices 4 can be controlled by means of the control device 3.

[0028] The motor vehicle 1 also comprises a voltage source 8, which is provided for example by an electrical energy store of the motor vehicle 1. Such an electrical energy store of the motor vehicle 1 can be, for example, a battery or an on-board power supply of the motor vehicle 1. The respective ultrasonic sensor devices 4 are electrically connected to the voltage source 8. The ultrasonic sensor devices 4, or the ultrasonic sensors 10, are supplied with electrical energy by the voltage source 8 when in operation.

[0029] FIG. 2 shows a schematic representation of an ultrasonic sensor device 4, which is electrically connected to the voltage source 8. The voltage source 8 provides a supply voltage Ub. The ultrasonic sensor device 4 comprises a filter device 9, which is used to filter this supply voltage Ub. The filter device 9 is connected on the input side to the voltage source 8. On the output side the filter device 9 is connected to the ultrasonic sensor 10. At the output of the filter device 9 the filtered supply voltage Uf is present. This filtered supply voltage Uf is used to supply the ultrasonic sensor 10.

[0030] The ultrasonic sensor 10 is used, on the one hand, to emit an ultrasonic signal during a transmit phase. In a subsequent evaluation phase the ultrasonic signal reflected from the object is received again by means of the ultrasonic sensor 10. The ultrasonic sensor 10 comprises a diaphragm, which is stimulated into mechanical vibration with the aid of a corresponding transducer element. In order to operate the transducer element, during the transmit phase a transmission current is provided, which can be, for example, 1 A. In the subsequent evaluation phase, the transducer element is not operated. Here, with the voltage source 8 an evaluation current Ia is provided, with which the ultrasonic sensor 10 and, in particular, a processing unit or microprocessor of the ultrasonic sensor 10 is operated. During the evaluation phase, by means of the transducer element the reflected ultrasound signal, which strikes the membrane and excites it into vibration, is detected. In particular during the evaluation phase of the ultrasonic sensor 10, it is necessary that interference is filtered out of the supply voltage Ub to be able to detect the reflected ultrasound signals reliably.

[0031] FIG. 3 shows a circuit of a filter device 9 according to the prior art. The circuit has the input terminals at which the supply voltage Ub of the voltage source 8 is applied. In addition, the filter device 9 comprises a low-pass filter or RC element. This low-pass filter comprises a resistor R1 and a capacitor C1. The capacitor C1 is connected in parallel with the input terminals and in parallel with the resistor R1. Depending on the resistance value of the resistor R1 and the capacitance of the capacitor C1, a specific time constant =R1*C1 is obtained. The cutoff frequency fc of the low-pass filter is given by: fc=**.

[0032] The capacitance of the capacitor C1 cannot be selected to be arbitrarily large, due to space limitations. For example, the capacitance of the capacitor C1 can be 100 nF. If the resistor R1 has a resistance of 100 Ohm, a time constant of 6.8 ms and a cutoff frequency of 24 Hz are obtained. If a transmission current Is of 1 A flows through the resistor during the transmit phase, this results in a voltage drop on the resistor R1 of 100 V.

[0033] In order to prevent such a significant voltage drop across the resistor R1, the resistance value of the resistor R1 could be chosen to be very small. For example, if the resistance value of the resistor R1 were to be 0.5 Ohm, this results in a time constant of 10 s and a cutoff frequency of 16 kHz. For a transmission current Is of 1 A this would result in a voltage drop of 0.5 V. In this case a small voltage drop is obtained across the resistor R1. However, this means in turn that the cutoff frequency fc of the low-pass filter increases very rapidly for a constant capacitance of the capacitor C1, so that the effect of the filter significantly decreases. The filter device 9 also comprises a diode D1, which is connected in series with the resistor R1. This diode D1 is used for reverse polarity protection. In addition, the filter device comprises the additional capacitors C2 and C3. The capacitances of the capacitors C2 and C3 can each be 10 F. These capacitors C2 and C3 are used as energy stores for the processor device, or microprocessor of the ultrasonic sensor 10.

[0034] FIG. 4 shows a circuit of a filter device 9 according to one embodiment of the invention. In comparison to the circuit according to FIG. 3, the filter device 9 additionally comprises a diode D2, which is connected in parallel with the resistor R1. By connecting the diode D2 in parallel with the resistor R1, when the high transmission current Is is applied the voltage drop is limited to the forward voltage Ud or the diode clamping voltage. The forward voltage Ud of the diode D2 can be, for example, 0.5 V. If the transmission current is provided during the transmit phase, the low-pass filter has almost no effect, but this is not required during the transmit phase of the ultrasonic sensor 10. During the evaluation phase, in which the evaluation current Ia flows through the low-pass filter, the diode D2 has a high resistance, so that the filter time constant is now defined by the resistor R1. This considerably higher value results in a much better filter effect.

[0035] The resistor R1 must be dimensioned in such a way that at the evaluation current Ia, or the operating current, the diode D2 has a high resistance. The following must apply: R1*Ia<Ud. If the resistor R1 has a resistance of 100 Ohm, for a capacitance of the capacitor C1 of 100 nF this results in a cutoff frequency of 24 Hz. If a transmission current is provided which is equal to 1 A, this results in a voltage drop on the diode D2 equal to the forward voltage Ud, which can be, for example, 0.5 V. For the evaluation phase the evaluation current is subject to the constraint Ia<Ud/R1. Even if a forward voltage Ud of 0.4 V is assumed, a permissible current of 4 mA is obtained for the evaluation current Ia or operating current. At such a current, the full effect of the low-pass filter or the RC element can be realized. At the same time, during the transmit phase the transmission current Is is provided without an excessive voltage drop. It can also be provided that a pulsed current Is is supplied during the transmit phase. With this circuit or this filter device, high pulse currents are thus possible for the transmit phase while in the subsequent evaluation phase with the low evaluation current Ia the advantageous filter effect of the low-pass filter can still be achieved. Therefore, the filter device 9 can be used overall to provide a dynamic supply voltage filter.