GB2505570A

GB2505570A - An ultrasonic distance measuring device with sensor temperature measurement

Info

Publication number: GB2505570A
Application number: GB1315478.6A
Authority: GB
Inventors: Jing Cai; Dirk Schmid
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-08-31
Filing date: 2013-08-29
Publication date: 2014-03-05
Anticipated expiration: 2033-08-29
Also published as: GB201315478D0; DE102012215493A1; FR2995087B1; DE102012215493B4; FR2995087A1; CN103675822B; GB2505570B; CN103675822A

Abstract

An ultrasonic distance measuring device suitable for vehicle based applications, such as parking sensors or parking aids, whereby the temperature of the ultrasonic sensor is calculated. The thermometer may be located in the ultrasonic sensor and may be in the ASIC or transistor in particular. The sensor may be a semiconductor thermometer in the form of a diode (p-n junction). The ultrasonic sensor may be calibrated based on a temperature dependent characteristic and/or frequency. The temperature and/or frequency characteristics may be saved to a storage means housed in the ultrasonic sensor. Additionally the temperature sensor may measure the air temperature or another ambient air temperature sensor may be used. The temperature of the sensor and/or air may be communicated and this may be via a pulse code modulation and/or pulse width modulation. This communication may be via a CAN bus and/or a LIN bus. The current temperature may be transmitted cyclically or when it lies outside of a predetermined temperature difference or limit.

Description

Description Title

Increasing the robustness of ultrasound systems State of the art The present invention relates to ultrasound systems such as have long been known in the state of the art, for example as parking aids.

The function of ultrasonic sensors is frequently based on the echo-sounder principle, i.e. they operate both as transmitters and as receivers. In this connection, a control unit gives the, ultrasonic sensor (ultrasonic transceiver) the command to transmit. Other, non-driven adjacent sensors provided in the integrated unit are switched to receive during this time. The distance measurement is now undertaken in accordance with the reflection principle. The distance traversed by the ultrasonic signal corresponds to twice the spacing between -the respective sensor and an. obstacle which is possibly present, on which the emitted ultrasonic signals have been reflected. In the sensor the amplitude of the analogue signal is cornared with a threshold value (the so-called -comparator threshold) . If *the analogue signal -corresponding to the reflected signal lies below the threshold value, the associated digital signal is equal to the sensor supply voltage (high) If, on the other hand, the associated analogue signal exceeds the comparator threshold, the digital signal switches to sensor earth * (low) . From this change in the voltaqe-level, a received echo is inferred. At the sensors the comparator threshold * (corresponding to the sensitivity of the sensor) can be adjusted as a function of the echo transmission time.. This is necessary, in order to take account of echo-signal amplitudes decreasing by reason of increased transmission distance by virtue of an increased detection sensitivity.

The proqression of sensitivity over time is described as the characteristic, and is held within the system. It can be programmed into the sensors by the controi unit and can be changed as required. As is generally known, the sensitivity of the ultrasonic sensor is greatly dependent on the ambient temperature and also on the air humidity.

Both quantities influence considerably the absorption of sound in the enviroament, and hence the amplitudes of the echo signals. In order to keep the sensitivity as.constant as possible independently of these quantities, nowadays an air-temperature signal is made available to the parking-aid control unit by the vehicle (for example, from the engine management system or from the instrument cluster) via a bus system (e.g. a CAN bus or LIN bus). For the air humidity, no use of sensors ir3 production vehicles is known, with a few exceptions. If a certain temperature range is reported by the air-temperature sensor, an associated characteristic stored in the control unit is selected by the control unit and is programed into the ultrasonic sensors.

Particularly for longer echo transmission times (e.g. for a maximum range at the present time of about 4.5 m), such a tracking of the sensor sensitivity via the air temperature is beneficial to the result of evaluation. However, the centrally ascertained temperature signal which is made available, via the vehicle CAN is normally only a guide 4. . t value for the outside air temperature, which is processed by other control units by filtering and hysteresis. Over and above this, the sensitivity of the ultrasonic sensor is dependent not only on the air temperature but also on the temperature of the ultrasonic sénsqr itself or, to be more exact, of the transducer contained therein, since a temperature dependence is inherent in certain sensor components. In the state of the art, when a suitable characteristic is being selected by the control unit it is assumed that the ultrasonic sensors have roughly the same temperature as the ambient air. However, given constant air temperature and relatively long engine-running time, the sensors integrated close to the engine may be hotter than those which have been arranged on the cooler side of the vehicle, facing away from the engine. A switching of characteristic by reason of known measurements of air tenperature will, in this scenario, be unable to eake account of changing sensor temperature. As a consequence of this, the sensitivity of the hotter sensors may be reduced considerably, without this being compensated by a selection of a more suitable characteristic. In this case, for example, by virtue of a changing sensor temperature with unchanged, sensitivity characteristic the detection range may be reduced from about 1 m to 80 cm for an obstacle in the form of a round post in the case of heating of the. sensor by 40 K. The effects on driving safety are self-evidently considerable. Also, if in winter a vehicle is driven out of a heated garage onto the road, known systems that merely take account of the air temperature of the ambient air may provide disadvantageous result's. After such a drop in air temperature, systems pertaining to the state of the art would load a more sensitive characteristic immediately. However, in the course of exiting the heated garage the sensors cool ddwn only in delayed manner.

Correspondingly, their sensitivity decreases only slowly.

In conjunction with the characteristic loaded by reason of the ambient temperature, many unwanted echoes are the consequence, due to oversensitivity of the sensors.

The object underlying the invention is to circumvent the aforementioned disadvantages.

Disclosure of the invention

In accordance with the invention the aforementioned object is achieved by an ultrasonic sensor for a vehicle-based spacing-measuring system having the features according to Claim 1. By an ultrasonic sensor' within the scope of the present invention a device is understood that is capable of radiating ultrasonic signals into the environment and, at the same time or subsequently, of receiving ultrasonic signals from the environment, and of converting them into electrical signals. Therefore an ultrasonic sensor could, within the scope of the present invention, also be designated as an ultrasonic transceiver. The vehicle-based spacing-measuring system may include one or more such ultrasonic sensors and may have been set up to inform a user of the system, or, to be more exact, a driver of the vehicle, visually and/or acoustically about the spacing of his/her vehicle from ambient objects. An ultrasonic sensor according to the invention can preferably also come into operation in a so-called park-pilot system which has been * set up to evaluate spacing-measuring signals and to initiate and supervise movements of the vehicle unaided (automatically) . In accordance with the invention, the ultrasonic sensor -which, for example, may have been arranged as a component within a bumper of the vehicle -includes a temperature sensor. The temperature sensor in this case has been set up to measure a temperature of the ultrasonic sensor itself and tb make results available that are capable of being evaluated with regard to the temperature of the ultrasonic sensor. The temperature sensor that is provided in accordance with the invention accordingly differs from the devices known in the state of the art, in that it does not measure the temperature of the air surrounding the vehicle but instead measures the temperature of at least one component of the ultrasonic sensor, such as, for example, the electroacoustical transducer and/or further components that have been provided for evaluation and further processing of the ultrasonic signals.

The dependent claims present preferred further developments of the invention.

The temperature sensor may preferably include a p-n junction in the ultrasonic sensor. The p-n junction (for example, in the form of a semiconductor element such as e.g. a diode and/or a transistor) may in this case be supplied with electrical energy by a constant current or a constant voltage, so that the temperature dependence of its conductivity permits an inference as to its temperature by means of electrical variables of state. In further preferred manner, the p-n junction may be present in an ASIC (application-specific integrated circuit) that has been providedfor generating and/or evaluating ultrasonic-sensor signals and/or for implementing the bus communication with the vehicle environthent.

In further preferred manner, a temperature-dependent sensitivity characteristic may have been assigned to the ultrasonic sensor, by means of which threshold values for detecting *an echo in a sensor signal are established.

Depending on the temperature, a respectively assigned total-echo level is consequently established as threshold .0 value, above which the presence of an echo in the transducer signal is inferred. Alternatively or additionally, a family of characteristics may be provided, in which, depending on the frequency and the temperature of the ultrasonic sensor or its components, a plurality of threshold values have been predefined. The sensitivity characteristic or the family of characteristics may have been saved in the memory within the ultrasonic sensor and/or, in the case where a certain temperature value for the ultrasonic sensor is reported by a control unit, may be transmitted to the respective ultrasonic sensor. For this purpose, within the control unit an appropriate storage means has been provided, in which the characteristic or the family of characteristics has been stored. Whereas the first possibility keeps the data traffic on the bus system slight, by virtue of the second possibility the capacities for storage means held within the ultrasonic sensors are capable of being diminished.

In further preferred manner, an ultrasonic sensor according to the invention may include a further temperature sensor that has been set up to ascertain the temperature of the ambient air and to make said temperature available for further processing. Alternatively or additionally, the temperature sensor may also have been configured within the ultrasonic sensor in such a way that it can ascertain both the temperature of the components of the ultrasonic sensor and a measured quantity representing the temperature of the ambient air. For example, such a sensor may exhibit a sensor head facing towards the surface of the ultrasonic sensor, by means of which the temperature of the ambient air is ascertained, and may include a second sensor head or sensor reqion within the ultrasonic sensor, by means of which the temperature of components of the ultrasonic sensor can be ascertained. In this way, numerous possibilities arise to check the plausibility of ascertained temperature values in relation to one another and to predict developments of the ultrasonic-sensor temperature that are to be expected.

In further preferred manner, an ultrasonic sensor according to the invention may include a communications interface that has been set up to make available the temperature of the ultrasonic sensor and/or of the components within the integrated unit of the vehicle. This may be effected in wire-bound or wireless nanner. For example, the communications interface may in this case make use of a pulse-code modulation and/or of a pulseTwidth modulation for information coding. Both communication methods offer a high degree of security in relation to signal perturbations on the respective communication medium.

In this case the ultrasonic sensor may have been set up to dispatch, at predefined temporal intervals (cyclically), a data record representing the current temperature, or to initiate such a communication in response to a change of a temperature by a certain amount. In this way, the data cdrnmunication within the communications channel being used can be event-controlled, and unnecessary data traffic can 5. be avoided in this way: In particular, a controller-area-network (CAN) bus can be used as communications channel, in which case the communications interface includes a so-called CAN controller. Inasmuch as CAN is a communication standard that is widely used at the present time in the automobile industry, a high degree of integration potential and cost saving is on offer in the case where use is made of ultrasonic sensors according to the invention with CAN interfaces.

Likewise widely used in the automobile industry as communication standard is LIN (local interconnect network) This bus interface is likewise very well suited as a cost-effective cothmunications channel between control unit and ultrasonic sensors.

According to a further aspect of the present invention, a spacing-measuring system is made available that includes a control unit for evaluating spacing signals, and also one or more ultrasonic sensors as discussed above in different configurations. The spacing-measuring system according to the invention further includes *a communications channel between the control unit and the ultrasonic sensor, which has been set up to transmit signals relating to the spacing measurement and/or the temperature, in particular the sensor temperature. In other words, the control unit has been set up, oti the one hand, to provide ultrasonic signals to be transmitted, and, on the other hand, to implement the evaluation of received echoes. Alternatively or additionally, the ultrasonic sensors being used may also include an evaluating logic circuit, so that the sensors can transmit already interpreted (digital) signals to the control unit via the communications channel. In accordance with the invention there is now provision, furthermore, that messages or signals relating to the sensor temperature and/or to the temperature of the ambient air can also reach the control unit via the communications channel, and, where appropriate, characteristics saved in the control unit can be transmitted via the communications channel to the ultrasonic sensors according to the invention with a view to calibratioi thereof. A spacing-measuring system configured in.such a manner offers an increased robustness in comparison with temperature-dependent fluctuations in sensitivity of ultrasonic sensors being used.

According to a further aspect, a vehicle is proposed including an ultrasonic sensor discussed above and/or a previously discussed spacing-measuring system. A vehicle that has been set up in such a manner offers an increased degree of driving safety in relation to undesirable collisions with objects and/or persons pertaining to the vehicle environment, in that temperature-dependent fluctuations in sensitivity are taken into account better. 4 -

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Brief description of. the drawings

Exemplary embodiments of the invention will be described in detatl in the following with reference to the accompanying drawings. In the drawings: Figure 1 is a schematic representation of an exemplary embodiment of an ultrasonic sensor according to the invention, illustrating components in the interior of said sensor; Figure 2 is an exemplary embodiment of a spacing-measuring system according tb the invention; and Figure 3 is an electrical circuit diagram for an exemplary embodiment of the present invention for realising a temperature measurement, -. provided in accordance with the invention, 2Q within an ultrasonic sensor.

Embodiments of the invention Figure 1 shows a schematic representation of an ultrasonic sensor 1 in which a temperature sensor 2 according to the invention with a microcontroller 3 has been provided by way of evaluating unit for ultrasonic signals and temperature signals. With the microcontroller 3, furthermore a memory 4 has been provided by way of storage means for holding characteristics and fields of characteristics for a calibration of the ultrasonic sensor to different temperature values. Via connecting leads 6, a -11 -communications interface 7 provided within the ultrasonic sensor 1 can receive ultrasonic signals to be transmitted from a central control unit (not represented in Figure 1) and can relay them to the rnicrocofltroller 3. The microcontroller 3 ma include, for example, a receiving circuit and also a transmitter amplifier, via which transmitted signals can be transmitted to a diaphragm 5 and can be received from the diaphragm 5 and processed. The components of the ultrasonic sensor 1 that have been represented may, for example, have been arranged (e.g. cast) in a plastic housing, by virtue of which the body of the ultrasonic sensor 1 exhibits a thermal inertia in relation to fluctuations in temperature of the ambient air.

Therefore the temperature signals emitted from the temperature sensor 2 may differ distinctly -particularly in the case of changing ambient temperatures -from temperature signals that reproduce the temperature of the ambient air.

Figure 2 shows a spacing-Measuring system 10 in which ultrasonic sensors represented.in detail in Figure 1 have been connected to one another via connecting leads 6 by way of bus system. The master of the spacing-measuring system which has been represented is constituted by a control unit 8. In the control unit 8 the spacing-measuring system nay hold waveforms that can be radiated into the environment via one or more ultrasonic sensors 1. Tn response to echoes ofthe emitted signals arriving at the ultrasonic sensors 1, which reach the control unit 8 via the connecting leads 6, the control unit 8 can determine actions that have been predefined for the case of correspohding spacing-measuring signals. For the purpose -12 -of communication via the connecting leads 6 -which, for example, may have been realised as a CAN bus or LIN bus -the ultrasonic sensors 1 and also the control unit B may each include CAN controllers or LIN controllers, in order S to implement the communication via the cbnnecting leads 6.

Figure 3 shows a circuit diagram for an electrotechnical realisation of a temperature sensor 2 in an ultrasonic sensor 1. In other words, the circuit 100 which has been represented is contained within the temperature sensor 2 known from Figure 1. In the circuit 100 the transistor 11 represents an exemplary embodiment of a p-n junction, by means of which the temperature within the ultrasonic sensor 1 can be measured. For this purpose the transistor 11 is supplied with a constant current 12 via a supply voltage 14 and a current-source 13. The collector and the base of the transistor 11 have been short-circuited with each other.

The transistor 11 itself has been realised as an n-p-n transistor. The flow voltage through the transistor 11 in this case is temperature-dependent, so a voltage measurement can provide a measured value that is equivalent to the temperature of the ultrasonic sensor. For example, for ttis purpose the equation U0 -L7 mV/K * (T-300 K) can be used, in which U0 is a constant voltage value of about 0.7 V, depending on the semiconductor process being used. Given measured flow voltage 0flow, this equation pan be solved for T, in order to obtain a current temperature value of the p-n junction. Via the resistors 15 and 16 and also the operational amplifier17, which is supplied with a --+ r 13 -reference voltage 13, the variable voltage tJ1. can be transformed via the transistor 11 into a range of values that corresponds to the dynamic range of the downstream analogue/digItal (AID) converter 19. The output signal 20 thereof is received by the sequencer (not represented) of an ASIC and is communicated in suitable manner to the control unit 8. represented in Figure 2 via the communications interface 7 represented in Figure 1.

A central idea of the present invention consists in resolving discrepancies between the air temperature of a vehicle environment and the temperature of the components of ultrasonic sensors arranged in the vehicle, in that a temperature sensor is provided that has been set up to ascertain the temperature of the ultrasonic sensor itself and to draw upon said temperature in connection with the selection of characteristics or families of characteristics for the calibration of the ultrasonic sensor.

Even if the aspects according to the invention and the advantageous ernbodimehts have been described in detail on the basis of the exemplary embodiments elucidated in conjunction with the appended Figures of the drawing, modifications and combinations of features of the exemplary embodiments that have been represented are possible for a person. skilled in the art without departing from the bounds of the present invention, the range of protection of which is defined by the appended claims.