METHOD FOR MONITORING GROUND CLEARANCE

Description

[0001] The present invention relates to the use of ultrasonic measuring technology in motor vehicles and in particular to a method for monitoring ground clearance under a motor vehicle, a computer program product, a device and a motor vehicle.

[0002] Motor vehicles are equipped with ultrasonic transceivers that transmit ultrasonic signals into the surroundings of the motor vehicle and receive ultrasonic echo signals from the surroundings of the motor vehicle in order to thereby acquire information about the surroundings of a motor vehicle and transmit this information to a parking assistance system, a driver assistance system or the like.

[0003] DE 10 2018 221517 A1 describes a system in which the surroundings of a motor vehicle are monitored using ultrasonic transceivers arranged in the underbody of a motor vehicle.

[0004] DE 10 2018 130914 A1 describes a system designed to detect objects in the underbody area of ​​a parked vehicle. Ultrasonic measurements are taken in the underbody area at two different times, and the two measurements are compared. The first measurement is taken immediately after the vehicle is parked, and the second measurement is taken at a time when the system is to check whether an object is underneath the vehicle.

[0005] From DE 102014221990 A1 a method for preventing damage to a vehicle is known in which a geometry of a collision-relevant structure of a road surface in the environment is measured and compared with a current configuration of the vehicle.

[0006] From DE 10 2011 012 409 A1 an industrial truck is known which has a distance sensor 12 in the front area as a ground profile determination device.

[0007] From JP S57182544 A a method for detecting insurmountable underground structures is known which uses two downward-directed ultrasonic sensors.

[0008] Especially for off-road vehicles, there is a need for solutions to determine ground clearance under a moving vehicle.

[0009] Against this background, the object of the present invention is to provide an improved method for determining a ground clearance under a motor vehicle.

[0010] According to a first aspect, a method is therefore proposed for monitoring ground clearance under a motor vehicle, on the underbody of which a plurality of spaced-apart ultrasonic transceivers are arranged.The method comprises: a) selecting a first ultrasonic transceiver from among the plurality of ultrasonic transceivers and controlling the first ultrasonic transceiver to transmit a transmission signal; b) selecting a second ultrasonic transceiver from among the plurality of ultrasonic transceivers and controlling the second ultrasonic transceiver to receive a reception signal which is a reflection of the transmission signal transmitted in step a); c) repeating steps a) and b), wherein different pairs of a first and a second ultrasonic transceiver are selected to receive a respective echo signal; d) determining a profile of a ground beneath the motor vehicle based on the received echo signals; and e) determining a minimum ground clearance beneath the motor vehicle by comparing the determined profile of the ground with an underbody profile of the motor vehicle.

[0011] The proposed method has the advantageous effect that, thanks to knowledge of the minimum ground clearance under the vehicle, damage to the underbody of the vehicle can be avoided.

[0012] The proposed method can be carried out particularly advantageously without calibration, ie without comparing two measurements at different times, and is therefore also advantageously suitable for use in a moving motor vehicle.

[0013] With the proposed method, a large number of measuring points can be obtained and a large area beneath the subfloor can be monitored advantageously by permuting the pairs of a first, transmitting and a second, receiving ultrasonic transceiver, even with a small number of ultrasonic transceivers.

[0014] In particular, by the proposed permuting of the pairs, a number of obtainable measurement points scales advantageously quadratically, in particular with N*(N-1), where N is the number of ultrasonic transceivers.

[0015] Ground clearance is understood to mean, in particular, a clear width in the vertical direction, relative to the motor vehicle, between a point on a surface on which the motor vehicle is standing or driving (a point of the specific ground profile) and a point on the underbody of the motor vehicle.

[0016] A transmitted signal and a received signal are each understood to mean, in particular, an ultrasonic signal that can be described by an ultrasonic oscillation with one or more fundamental frequencies and an envelope. The transmitted signal and the received signal can preferably each be a time-limited ultrasonic pulse.

[0017] In particular, the control for receiving the received signal in step b) takes place simultaneously with or after the control for transmitting the transmitted signal in step a).

[0018] The first and second ultrasonic transceivers may be arbitrarily selected from among the ultrasonic transceivers, but in each individual run of step a), the first ultrasonic transceiver is different from the second ultrasonic transceiver.

[0019] Each control can be carried out, for example, by transmitting signals to and receiving signals from an application-specific control circuit (ASIC) mounted on a circuit board of the ultrasonic transceiver, which controls the transmission and reception of ultrasonic signals by the ultrasonic transceiver.

[0020] An echo signal corresponding to a reflection of the transmission signal transmitted in step a) is preferably understood to mean, for example: an echo signal with a frequency corresponding to the frequency of the transmission signal; an echo signal with an amplitude, in particular an envelope amplitude, that exceeds a predetermined threshold value selected taking into account the amplitude of the transmission signal; an echo signal with a signal shape or envelope that corresponds to the signal shape of the transmission signal, and the like. "Corresponding" is understood here to mean an identity relationship or a similarity relationship. A similarity relationship preferably takes into account physical conditions, such as changes in the signal shape, amplitude, and the like, of the transmission signal on its path from the first to the second ultrasonic transceiver.

[0021] A respective one of the ultrasonic transceivers can in particular be configured to transmit a transmission signal in a direction diagonally downwards in the direction of a floor beneath the motor vehicle and to receive an echo signal from one or more directions diagonally from below in the direction of a floor beneath the motor vehicle.

[0022] The multiple spaced-apart ultrasonic transceivers are arranged in particular such that they face one another. "Facing one another" here means, in particular, that, especially assuming a flat floor beneath the motor vehicle, a transmission signal beam emitted by an ultrasonic transceiver is directed toward the floor and reflected by it in such a way that the reflected signal beam reaches at least one, preferably several, and particularly preferably all of the other ultrasonic transceivers arranged at a distance from one another on the underbody. A signal beam is understood here, in particular, to be a signal that is emitted with a certain aperture angle.

[0023] Performing steps a) and b) once can be considered performing a measurement in which a received signal is measured. The result of the measurement (a measurement point) can, for example, be a propagation time difference between the transmission of the transmitted signal and the reception of the received signal.

[0024] "Repeating" means, in particular, performing steps a) and b) several times simultaneously and / or in chronological sequence.

[0025] For the interpretation of the "different pairs" feature in step c), a first pair of two ultrasonic transceivers and a second pair of ultrasonic transceivers are considered different if one of the pairs contains at least one ultrasonic transceiver that is not included in the other pair. In contrast, for the interpretation of the "different pairs" feature in step c), two pairs in which only the first and second ultrasonic transceivers are interchanged are not considered different. Nevertheless, it is conceivable that two measurements are performed with two such pairs that are not considered "different" but only have the ultrasonic transceivers interchanged in order to further increase the number of measurements. However, at least in step c), after all repetitions have been completed, several echo signals from several pairs considered different have been received.

[0026] In the present application, "determining" is to be understood in particular as computational determination by means of a computerized device.

[0027] The "profile of a ground" can, for example, be understood as a set of points that have been determined as points on the ground and form a profile line or a profile surface. For example, the profile can be a data set in which each coordinate indicating a position on a horizontal line or plane beneath the motor vehicle is assigned ground elevation information. The "profile of a ground" can also be a vector representation or any other suitable computer-processable representation of a profile line (line or two-dimensional representation of a profile) or a profile surface (not necessarily a flat surface or three-dimensional representation of a profile).Thus, for example, in a two-dimensional case, a profile can be a data representation of a line indicating a course of a ground height along a longitudinal direction (direction of travel) under the motor vehicle, and in a three-dimensional case, a data representation of a surface indicating a course of the ground height over an imaginary horizontal surface under the underbody of the motor vehicle.

[0028] The profile of the ground can be determined based on the received echo signals, in particular based on the signal propagation times of the received echo signals and on the installation locations of the respective ultrasonic transceivers with which the respective echo signals were received and the respective associated transmission signal was transmitted.

[0029] The "underbody profile of the motor vehicle" can, for example, be a set of points on the underbody of the motor vehicle. The "underbody profile" can also be a vector representation or any other suitable computer-processable representation of a profile line or profile surface of the underbody of the motor vehicle. The underbody profile of the motor vehicle can be known in advance and can, for example, be stored in a control device of the motor vehicle.

[0030] Minimum ground clearance is understood to mean, in particular, the smallest ground clearance along the entire underbody profile.

[0031] According to one embodiment, in step c) at least three different pairs are selected, wherein at least one ultrasonic transceiver of the at least three different pairs is not arranged along a straight line with all other of the plurality of ultrasonic transceivers of the at least three different pairs on the underbody of the motor vehicle.

[0032] Accordingly, it is advantageously possible to determine not only a profile line, but also a profile surface of the soil.

[0033] According to a further embodiment, in step d), for each echo signal, an ellipse or an ellipsoid with possible reflection points at which the transmission signal may have been reflected is determined based on a signal propagation time between the transmission of the associated transmission signal and the reception of the echo signal, as well as on the installation positions of the first and second ultrasonic transceivers with which the transmission signal was transmitted and the echo signal was received; and the profile of the ground is determined by fitting a surface to the determined ellipses or ellipsoids.

[0034] Accordingly, a particularly good approximation of the soil profile to the actual course of the soil can advantageously be achieved.

[0035] In this context, an "ellipse" or "ellipsoid" is understood to mean, in particular, a number of parameters that uniquely describe the ellipse or ellipsoid. Examples of such parameters are coordinates of the, in particular, previously known, installation position of the first ultrasonic transceiver, coordinates of the, in particular previously known, installation position of the second ultrasonic transceiver, and a distance traveled by the signal, with the distance being determined based on the signal propagation time and the speed of sound.

[0036] The ellipse or ellipsoid with possible reflection points at which the transmission signal may have been reflected is in particular an ellipse or ellipsoid whose focal points are the installation positions of the first and second ultrasonic transceivers, wherein for each point of the ellipsoid, a sum of a distance of the point to the first focal point and a distance of the point to the second focal point is equal to the above-mentioned distance traveled by the signal.

[0037] The surface that is adapted to the specific ellipses or ellipsoids can, in particular, be a tangential surface to the specific ellipses or ellipsoids. In particular, the tangential surface can be adapted to the specific ellipses or ellipsoids from below—relative to the motor vehicle.

[0038] Alternatively, the surface can also be a surface that contains all the lowest points of all intersection lines at which two of the specified ellipses or ellipsoids intersect.

[0039] A suitable analytical or numerical method can be used as the fitting method.

[0040] According to a further embodiment, in step d) a temporal and / or spatial averaging of the determined ellipses or ellipsoids is further carried out.

[0041] Accordingly, effects caused by wind or airflow under the underbody can be advantageously averaged out.

[0042] For example, temporal averaging means that measurements are repeated with the same pair of first and second ultrasonic transceivers at short intervals in time and an average value is calculated from the measured signal propagation times or distances, on the basis of which an ellipse or an ellipsoid with possible reflection points is determined.

[0043] Spatial averaging means, for example, that mean foci and a mean path length are determined from spatially adjacent ellipses or ellipsoids and in this way an averaged ellipse or an averaged ellipsoid is determined.

[0044] According to a further embodiment, the method further comprises step f): triggering a process relating to the operation of the motor vehicle as a function of the determined minimum ground clearance.

[0045] Accordingly, the operation of the motor vehicle can be advantageously influenced in order to effectively prevent damage to the motor vehicle due to insufficient ground clearance.

[0046] According to a further embodiment, step f) comprises one or more of the following steps: issuing a warning to a driver of the motor vehicle if the minimum ground clearance falls below a threshold value, and / or displaying the determined minimum ground clearance by means of a display device, and / or displaying a graphic representation of the determined profile of the ground surface under the motor vehicle by means of a display device, and / or initiating automatic braking and / or stopping of the motor vehicle if the minimum ground clearance (9) falls below a threshold value, and / or raising the vehicle by means of a height-adjustable chassis if the minimum ground clearance falls below a threshold value.

[0047] Accordingly, the driver or an automatic device can brake and / or stop the motor vehicle when the ground height approaches the underbody of the motor vehicle by more than the threshold value. Accordingly, damage to the motor vehicle, particularly during off-road driving, can be advantageously prevented.

[0048] According to a further embodiment, the threshold value is selected as a function of a driving speed of the motor vehicle.

[0049] Accordingly, a higher threshold value can advantageously be selected when the motor vehicle is traveling at high speed, since faster driving is likely to result in a faster change in ground level and a longer braking distance, and when the motor vehicle is traveling at low speed, a lower threshold value can be selected in order to also allow for an approach to difficult ground situations when traveling at a sufficiently low speed.

[0050] The driving speed of the motor vehicle can be obtained from a speedometer device or the like.

[0051] According to a further embodiment, the method is carried out while the motor vehicle is driving.

[0052] The proposed ground clearance monitoring can advantageously also be carried out while the motor vehicle is moving, since the proposed method advantageously does not require calibration, comparison with reference measurements, and the like.

[0053] According to a further embodiment, in step d) the determined profile of the ground is extrapolated in a direction of travel of the motor vehicle, and in step e) the extrapolated profile is compared with an underbody profile of the motor vehicle extrapolated in the direction of travel of the motor vehicle in order to determine an extrapolated minimum ground clearance as the minimum ground clearance.

[0054] Accordingly, excessively low ground clearance can be more advantageously anticipated before the motor vehicle has reached the road section with the excessively low ground clearance, and damage to the motor vehicle can be avoided even more reliably.

[0055] Extrapolation can be done, for example, by determining an average gradient in the direction of travel and extending the relevant profile according to the determined gradient.

[0056] The direction of travel can be determined, for example, by a longitudinal direction or front-to-rear direction of the motor vehicle. Preferably, a steering position or the position of the motor vehicle's steerable wheels and / or a driving speed can also be taken into account when determining the direction of travel.

[0057] According to a further embodiment, the repetition in step c) is carried out in such a way that in step a) a first ultrasonic transceiver is selected and step b) is carried out simultaneously with several different second ultrasonic transceivers.

[0058] In this way, measurements can advantageously be carried out simultaneously with several pairs of ultrasonic transceivers, namely all those pairs that contain the selected first ultrasonic transceiver, and thus advantageously more measurements can be carried out in a shorter time.

[0059] According to a further embodiment, the repetition in step c) is carried out in such a way that several steps a) are carried out simultaneously with several different first ultrasonic transceivers, which are controlled in such a way that each of the first ultrasonic transceivers transmits a transmission signal with a different transmission signature, and in step b) a reception signal curve of the second ultrasonic transceiver is demodulated in order to obtain a respective reception signal for each pair of one of the first ultrasonic transceivers and the second ultrasonic transceiver.

[0060] In this way, measurements can advantageously be carried out simultaneously with several pairs of ultrasonic transceivers, namely all those pairs containing the selected second ultrasonic transceiver, and thus advantageously more measurements can be carried out in a shorter time.

[0061] A "transmit signature" is a characteristic of a transmitted signal that allows one to distinguish between different transmitted signals. For example, different transmit signatures can be achieved through different transmission frequencies, frequency modulation, or amplitude modulation.

[0062] A "received signal curve" is understood in particular to mean the entire received signal curve during a time window, beginning with the activation of the respective second ultrasonic transceiver for reception until the termination of the activation for reception. The time window can have a length that is selected accordingly, taking into account the distance between the first and second ultrasonic transceivers and an expected range of ground clearances.

[0063] Such a received signal waveform can be demodulated into several individual received signal waveforms, one for each of the transmitted frequencies. The position (time of arrival) of an echo signal can then be identified in each of the individual received signal waveforms.

[0064] It should be noted that the present and the aforementioned embodiments can be particularly advantageously combined, allowing simultaneous transmission and reception by all ultrasonic transceivers. Specifically, in this case, a respective ultrasonic transceiver that was selected as the first ultrasonic transceiver and has transmitted a transmission signal can be switched to a reception mode immediately after transmitting the transmission signal and selected as the second ultrasonic transceiver, which receives the transmission signals transmitted by the remaining ultrasonic transceivers as reflected reception signals. Accordingly, a maximum number of measurements can advantageously be performed in the shortest possible time.

[0065] According to a further embodiment, in step b), in a received signal curve of the second ultrasonic transceiver, an echo signal which is received first in time after a time of transmission of the transmission signal is identified as the received echo signal which corresponds to the transmission signal transmitted in step a).

[0066] Accordingly, echo signals resulting from multiple reflections that would distort the measurement result can advantageously be ignored, and echo signals resulting from a single reflection can be taken into account.

[0067] This means that the respective received signal path can, in particular, comprise multiple echo signals. In particular, it is conceivable that the transmitted signal is reflected along more than one path with different signal propagation times to the second ultrasonic transceiver, and accordingly, the received signal path comprises more than one echo signal at different times. The different signal propagation times can arise, in particular, from multiple reflections. A multiple reflection occurs, for example, when a transmitted signal is first reflected on the ground, then on the underbody of the motor vehicle, and then again on the ground before reaching the second ultrasonic transceiver as an echo signal.

[0068] According to a further aspect, a computer program product is proposed, comprising instructions which, when executed by a computer device communicatively connected to the plurality of ultrasonic transceivers, cause the computer device to carry out the method as proposed above.

[0069] The computer device can, for example, be an electronic control unit (ECU) of the motor vehicle.

[0070] According to a further aspect, a device for monitoring ground clearance beneath a motor vehicle is proposed. Several spaced-apart ultrasonic transceivers are arranged on the underbody of the motor vehicle. The device is communicatively connected to the plurality of ultrasonic transceivers and configured to implement the proposed method.

[0071] "Communicatively connected" means any type of connection that enables the transmission of drive signals and response signals in response to the drive signals, such as a wired connection, a wireless connection, and the like.

[0072] Furthermore, a motor vehicle is proposed on the underbody of which a plurality of ultrasonic transceivers are arranged at a distance from one another, and which has a device as proposed above.

[0073] The features, advantages and embodiments described for the proposed method also apply accordingly to the proposed motor vehicle, the proposed device and the proposed computer program product.

[0074] Further possible implementations of the invention also include combinations of features or embodiments described above or below with respect to the exemplary embodiments that are not explicitly mentioned. In this case, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0075] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention is explained in more detail below using preferred exemplary embodiments with reference to the accompanying figures. Fig. 1 shows a schematic representation of a motor vehicle according to an embodiment; Fig. 2 shows a flow chart illustrating a method according to an embodiment; Fig. 3 shows a schematic representation to illustrate the method according to an embodiment with a level floor beneath the motor vehicle; Fig. 4 shows a schematic representation to illustrate the method according to an embodiment with an uneven floor beneath the motor vehicle; and Fig. 5 shows a schematic view of an underbody of a motor vehicle according to an embodiment.

[0076] In the figures, identical or functionally equivalent elements have been given the same reference numerals unless otherwise stated.

[0077] Fig. 1shows a schematic representation of a motor vehicle 1 according to an embodiment in a side view. In the embodiments described below, the motor vehicle 1 is an all-terrain vehicle or off-road vehicle. However, there is no restriction in this regard. It should also be noted that in a case where the proposed method is carried out while the all-terrain vehicle 1 is traveling, a direction of travel F of the all-terrain vehicle 1 in the Fig. 1 to Fig. 4 a direction to the right in the respective figure.

[0078] The off-road vehicle 1 has a plurality of ultrasonic transceivers 101, 102, 103 arranged at a distance from one another on an underbody 2. The ultrasonic transceivers are preferably arranged and aligned such that each of the ultrasonic transceivers 101, 102, 103 can emit a signal beam which, when it is applied to a ground (in Fig. 1not shown) is reflected under the off-road vehicle 1, a portion of the signal lobe is reflected in the direction of one or more, and particularly preferably all, of the other ultrasonic transceivers 101, 102, 103.

[0079] Preferably, the ultrasonic transceivers 101, 102, 103 can face each other. This means that a signal beam emitted by the ultrasonic transceiver 101 can be directed diagonally downwards to the right (relative to Fig. 1, i.e., diagonally in the direction of travel and downwards). A signal beam emitted by the ultrasonic transceiver 102 can have a portion that runs diagonally downwards to the left and another portion that runs diagonally downwards to the right. A signal beam emitted by the ultrasonic transceiver 103 can run diagonally downwards to the left. However, all emitted signal beams can also have a portion that runs diagonally downwards to the right and a portion that runs diagonally downwards to the left.

[0080] The off-road vehicle 1 also has a control device (ECU) 3, which is communicatively connected to the plurality of ultrasonic transceivers 101, 102, 103, preferably via line connections 4 of a wiring harness of the off-road vehicle 1.

[0081] The control device 3 is configured to carry out the proposed method for monitoring ground clearance described below by communicating with the plurality of ultrasonic transceivers 101, 102, 103 and controlling them to transmit and receive ultrasonic signals. For this purpose, the control device 3 may comprise a hard-wired circuit, or it may be programmable and execute a computer program product with instructions that cause the control device 3 to carry out the proposed method. The computer program product may be stored in an erasable and rewritable read-only memory (EEPROM) of the control device, or the computer program product may be loaded by the control device upon starting the off-road vehicle 1 or the like via an in-vehicle network from a permanent storage device of the off-road vehicle 1 and / or from a wide-area network such as the Internet.

[0082] The off-road vehicle 1 further comprises a display device 5, such as an instrument or a display in a dashboard or the like. The display device 5 is also communicatively connected to the control device 3.

[0083] In the following, the Fig. 1 to 4 describe a method for monitoring ground clearance under a motor vehicle according to a first embodiment. Fig. 2 a flowchart illustrating the method according to the embodiment; Fig. 3 shows a schematic representation of a lower section of a body of the off-road vehicle 1 to illustrate the method with a flat floor 6 under the off-road vehicle 1, and Fig. 4 shows a schematic representation to illustrate the method according to an embodiment with an uneven ground 6 under the off-road vehicle 1.

[0084] It should be noted that a distance between the underbody 2 of the body of the off-road vehicle 1 and the ground 6 under the off-road vehicle 1 in Fig. 3 and Fig. 4 In order to better illustrate the proposed procedure, it is not shown to scale but exaggerated.

[0085] In step S1, the ultrasonic transceiver 101 is selected as a first ultrasonic transceiver and controlled such that the ultrasonic transceiver 101 transmits a transmission signal generally downwards with respect to the motor vehicle 1. The transmission signal preferably has a wide beam, at least a portion of which is directed diagonally downwards to the right in Fig. 3 runs. In Fig. 3 dashed lines only show the propagation path 71 of that portion of the lobe of the transmission signal of the first ultrasonic transceiver 101 which reaches the ultrasonic transceiver 102.

[0086] In step S2, which is preferably carried out simultaneously with step S2, alternatively in good time before the transmission signal transmitted in step S1 can reach the ultrasonic transceiver 102, the ultrasonic transceiver 102 is selected as a second ultrasonic transceiver and controlled such that the ultrasonic transceiver 102 receives the transmission signal that (the portion of the lobe of the transmission signal that) has propagated along the propagation path 71 and has been reflected on the ground 6 beneath the off-road vehicle 1, as a reception signal.

[0087] From the start of the receiving triggering until the end of the receiving triggering, the ultrasonic transceiver 102 delivers a received signal waveform that can be evaluated by the control device 3. Such an evaluation can be performed immediately at the time step S2 is performed, or the received signal waveform can be recorded and later evaluated in step S4. The received signal waveform can be, for example, a waveform of a voltage signal delivered by a piezo element or the like of the ultrasonic transceiver 102 attached to an ultrasonic membrane, or the received signal waveform can be a waveform of a digital signal delivered by an electronic component of the ultrasonic transceiver 102 and indicative of the voltage signal of the piezo element.

[0088] During the evaluation, a section of the received signal waveform can preferably be identified that is indicative of the received signal (received ultrasonic signal), for example, a peak within the received signal waveform. The section of the received signal waveform identified in this way, which indicates the received ultrasonic signal, can also be referred to herein as "the received signal" for the sake of simplicity.

[0089] If the received signal curve contains multiple peaks, according to an advantageous development, the first peak in time can be identified as the received signal. Preferably, a criterion for the shape and / or height of the peak can also be applied, and the first peak in time can be identified as the received signal that satisfies the specified criterion. In this way, peaks resulting from multiple reflections (floor 6 - subfloor 2 - floor 6) can advantageously be disregarded, thus preventing multiple reflections from distorting the measurement result.

[0090] Instead of recording the entire receive signal curve, the receive signal curve can also be evaluated instantaneously or live / online, and a parameter can be recorded that describes the receive signal, for example a time at which the peak in the receive signal curve occurs, which indicates the reception of the receive signal.

[0091] The described one-time execution of step S1 and step S2 with a pair of ultrasonic transceivers 101, 102 can also be understood as a measurement which is carried out with the pair of ultrasonic transceivers 101, 102 and in which a measurement point (in this case the received signal or an indication of the received signal, such as the time of occurrence of the peak) is obtained.

[0092] Then, in step S3, steps S1 and S2 are carried out with one or more or preferably all possible different permutations of pairs of the ultrasonic transceivers 101, 102, 103 and in this way further measurement points are obtained.

[0093] In step S4, a profile of the ground 6 is determined from the measurement points, ie, based on the received echo signals. A preferred method for implementing step S4 will now be described.

[0094] A first measurement point comprises, in particular, data about a time of arrival of the transmission signal emitted by the ultrasonic transceiver 101, which travels along the propagation path 71, is reflected on the ground 6, and is received by the ultrasonic transceiver 102. Based on a signal propagation time between the transmission of the transmission signal and the reception of the echo signal, a path length is calculated by multiplying this time by the speed of sound in air. This path length is used to determine an ellipse 81 that contains all possible reflection points at which the transmission signal could, in principle, have been reflected in order to propagate along a path of the calculated path length from the ultrasonic transceiver 101 to the ultrasonic transceiver 102.The ellipse 81 is in particular an ellipse in whose focal points the installation locations of the first ultrasonic transceiver 101 and the second ultrasonic transceiver 102 are located, and which describes the set of all points for which the sum of a distance to the first focal point and a distance to the second focal point is equal to the path length along the propagation path 71 determined as described above.

[0095] In the same way, based on the path length of a second propagation path 72 of a transmission signal emitted by the ultrasonic transceiver 102, the reflection of which reaches the ultrasonic transceiver 103, and the path length of a third propagation path 73 of a transmission signal emitted by the ultrasonic transceiver 101, the reflection of which also reaches the ultrasonic transceiver 103, further ellipses 82 and 83 are determined, on which the respective possible reflection points lie.

[0096] It should be emphasized again that the actual propagation paths 71, 72, 73 of the transmission signals of the control unit (3 in Fig. 1 ) that performs the procedure are unknown at this time. Only ellipses 81, 82, and 83 are known at this time.

[0097] In Fig. 3 It can be seen that with a flat bottom 6, the flat bottom 6 forms a tangent line from below to the ellipses 81, 82, 83.

[0098] In Fig. 4 In comparison, a case is shown in which the floor 6 represents a flat section 61 and an inclined section 62. The propagation path 71 and the associated specific ellipse 81 in the area of ​​the flat floor section 61 are the same as in Fig. 3 . In contrast, the propagation paths 72 and 73 or the ellipses 82, 83 determined from the corresponding transmission signals have changed in the area of ​​the inclined ground section 62.

[0099] Also in the Fig. 4In the case shown, the floor with the flat section 61 and the inclined section 62 forms a tangent line from below to the ellipses 81, 82 and 83.

[0100] Accordingly, in step S4, a profile of the ground 6 (a course of the ground 6 reconstructed from the measurements) is determined based on the ellipses 81, 82, and 83. Preferably, a tangential line can be fitted from below to the ellipses 81, 82, and 83. Alternatively, it is also possible to lay (fit) a profile line through the lower intersection points of the ellipses 81, 82, and 83 (lying lower than the underbody 2 of the off-road vehicle 1). The latter method is less precise, but is also useful for determining ground clearance and can be performed algorithmically, possibly with less computational effort. The respective profile line can be fitted using a suitable analytical or numerical method.

[0101] In step S5, a minimum ground clearance 9 under the motor vehicle 1 is then determined by comparing the profile of the ground 6 determined in step S4 with the previously known underbody profile of the underbody 2 of the off-road vehicle 1. The minimum ground clearance 9 is the smallest distance between the profile of the underbody 2 and the profile of the ground 6 along the course of the underbody 2 of the off-road vehicle 1.

[0102] In this way, the minimum ground clearance 9 can advantageously be determined even when the motor vehicle 1 is moving, since no calibration or comparison with a previous reference measurement is required for the measurement. Based on the known minimum ground clearance 9, damage to the off-road vehicle 1 can be avoided in difficult terrain.

[0103] It should be noted that in the present embodiment, Fig. 3 and 4For ease of understanding, a two-dimensional case is described in which the possible reflection points lie on ellipses 81-83, all of which are arranged in a sectional plane of the off-road vehicle 1. The ultrasonic transceivers 101-103 are also all arranged in the same sectional plane of the off-road vehicle 1. For example, the sectional plane with the ultrasonic transceivers 101-103 can be arranged, in a transverse direction perpendicular to the direction of travel, preferably centrally or substantially centrally between the wheels 11 of the off-road vehicle 1. Thus, a profile line of the ground 6 beneath the off-road vehicle 1 can be detected at a position centrally between the wheels, and a minimum ground clearance can be determined there, where the probability that obstacles on the ground 6 extend up to the vicinity of the underbody 2 of the motor vehicle 1 is greatest.

[0104] According to a further development, in step S6, the control unit 3 can initiate a process relating to the operation of the off-road vehicle 1 depending on the minimum ground clearance 9. In particular, if the minimum ground clearance 9 falls below a threshold value selected with regard to safety, the control unit 3 can issue a warning to the driver of the off-road vehicle 1 via the display device 5 or a loudspeaker (not shown) or the like and / or initiate automatic braking and / or stopping of the off-road vehicle 1. Accordingly, damage to the off-road vehicle 1 can be averted when continuing to drive. The threshold value can be fixed or can be selected depending on a driving speed of the off-road vehicle 1, which the control unit 3 can obtain, for example, from a speedometer device (not shown), in particular higher at higher driving speeds than at low driving speeds.Alternatively or additionally, the specific profile of the ground 6 can be graphically visualized on the display device 5, for example, depending on or independently of the threshold being undershot, thus assisting the driver at all times when driving on difficult terrain. If a height-adjustable chassis is present, the vehicle can be raised using the height-adjustable chassis if the minimum ground clearance (9) falls below a threshold.

[0105] According to a preferred development, the specific profile of the floor 6 in the direction of travel (right in Fig. 3 and 4), for example, based on a gradient in a front section of the profile of the ground 6 in the direction of travel. The profile of the underbody 2 can also be extrapolated in the direction of travel. The minimum ground clearance can then be determined as the smallest distance between the extrapolated profile of the ground 6 and the extrapolated profile of the underbody 2. Thus, obstacles on the ground 6 located ahead in the direction of travel F can also advantageously be anticipated.

[0106] Fig. 5 shows a schematic view of an underbody 2 of an off-road vehicle 1 according to a second embodiment. Fig. 1 , Fig. 2 and Fig. 5 Reference is made.

[0107] According to the second embodiment, nine ultrasonic transceivers 101-109 are arranged on the underbody 2 in a two-dimensional grid that essentially covers the entire underbody 2 of the off-road vehicle 1. In other words, in the Fig. 5 shown arrangement form at least three different pairs of a first, transmitting and a second, receiving ultrasonic transceiver 101-109 such that at least one ultrasonic transceiver 101-109 of the at least three different pairs is not arranged along a straight line with all other of the plurality of ultrasonic transceivers 101-109 of the at least three different pairs.

[0108] The method for determining the ground clearance under the off-road vehicle 1 can be carried out using the Fig. 5The measurement of the two-dimensional arrangement of ultrasonic transceivers 101-109 shown can be carried out in a similar manner to the method for determining the ground clearance beneath the off-road vehicle 1 described for the first exemplary embodiment. In particular, in steps S1 to S3, all possible permutations of different pairs of a first and a second ultrasonic transceiver 101-109 are preferably formed, and a measurement is performed for each of these pairs. It should be noted that, since nine ultrasonic transceivers 101-109 are arranged in the second exemplary embodiment, the number of these pairs is seventy-two, thus seventy-two different measurement points are available.

[0109] In contrast to the first embodiment, however, in step S4 instead of the ellipses (71-73 in Fig. 3 and Fig. 4), on which possible reflection points of the transmission signals are arranged, respective three-dimensional ellipsoids with possible reflection points are determined in the second embodiment. The profile of the floor 6 is determined in step S5 by fitting a tangential surface from below to the determined ellipsoids or by fitting a section surface through the lowest intersection points of the ellipsoids.

[0110] In this way, according to the second embodiment, it is advantageously possible to obtain a profile of the ground 6 under the off-road vehicle 1 not only as a profile line in a two-dimensional sectional plane through the off-road vehicle 1, but as a profile surface, which can preferably cover the entire area between the wheels 11 of the motor vehicle 1 or the entire area under the off-road vehicle 1.

[0111] The remaining advantages and features of the first embodiment also apply accordingly to the second embodiment.

[0112] According to a third embodiment, the same ultrasonic transceiver arrangement is used as in the second embodiment, which in Fig. 5is shown. However, measurements are only taken using pairs arranged along the horizontal lines 101-102-103, 104-105-106 and 107-108-109, along the vertical lines 101-104-107, 102-105-108 and 103-106-109 and along the diagonal lines 101-105-109 and 103-105-107. Along each of the lines, measurements are initially taken in steps S1 to S3 in the same way as shown in the first embodiment. For example, along the line 101-102-103, the ultrasonic transceivers 101 and 102, 101 and 103 and 102 and 103 are selected as pairs for a respective measurement, one after the other or simultaneously. Along the line 103-105-107, the ultrasonic transceivers 103 and 105, 105 and 107, and 103 and 107 are selected as pairs. Along the remaining lines, corresponding pair selections are made. In step S4, ellipses with possible reflection points are then determined.The determined ellipses thus lie in vertical sectional planes through the off-road vehicle 1 along the horizontal lines 101-102-103, and 104-105-106 and 107-108-109, along the vertical lines 101-104-107, 102-105-108 and 103-106-109, and along the diagonal lines 101-105-109 and 103-105-107. Three ellipses are determined along each line in step S4, resulting in a total of 24 ellipses. Then, in step S4, a profile surface is fitted from below to the determined ellipses to determine the profile of the ground 6.

[0113] According to the third embodiment, the amount of data to be processed is smaller and the calculation steps can be simplified, thus requiring less computing power. Nevertheless, a satisfactory accuracy in determining the minimum ground clearance can be achieved.

[0114] The remaining advantages and features of the first and second embodiments also apply accordingly to the third embodiment.

[0115] Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

[0116] In particular, it should be noted that the described extrapolation of the determined profile of the ground 6 in the direction of travel of the off-road vehicle 1 is not necessary even when the off-road vehicle 1 is moving in order to achieve the advantages of the proposed solution. If, for example, a part protruding downwards from the underbody 2, such as an oil pan or the like, is arranged in a rear section of the off-road vehicle 1 in the direction of travel F, it is sufficient if, when the off-road vehicle 1 is moving, a drop below the minimum permissible ground clearance is detected in a front section of the off-road vehicle 1 and the driver is warned or the off-road vehicle is braked or stopped in order to prevent the oil pan in the rear section of the off-road vehicle 1 from being damaged by the ground elevation detected by the drop below the minimum permissible ground clearance in the front section of the off-road vehicle 1 as the off-road vehicle 1 continues to travel.In this case, a threshold value for triggering the process relating to the operation of the motor vehicle 1 can be defined taking into account the dimensions of the oil pan or the like.

[0117] The ellipses 81-83 or ellipsoids determined according to the embodiments can be averaged temporally and / or spatially before the tangential line or the tangential profile is adapted to the averaged ellipses or ellipsoids in order to smooth out measurement deviations due to wind and the like.

[0118] For ease of understanding, it was described that steps S1 to S3 are carried out sequentially for the various pairs of ultrasonic transceivers 101-109. However, it is conceivable that in step S1, one ultrasonic transceiver 101-109 is selected as the first ultrasonic transceiver 101-109 and transmits a transmission signal, and that several, and preferably all, of the remaining ultrasonic transceivers 101-109 are selected as a respective second ultrasonic transceiver 101-109, and steps S2 are carried out in parallel or simultaneously for each of the second ultrasonic transceivers 101-109. Furthermore, it is conceivable that several, and preferably all, of the ultrasonic transceivers 101-109 are selected as the first ultrasonic transceivers 101-109, and each of the first ultrasonic transceivers 101-109 transmits a transmission signal with a different transmission signature.In this case, in step 2, the received signal waveform can be demodulated for the or each of the selected second ultrasonic transceivers 101-109 in order to determine a plurality of received signals, one for each of the first ultrasonic transceivers 101-109. In this way, all measurement points can advantageously be determined simultaneously within a very short time. The method is thus particularly well suited for use with a moving off-road vehicle 1.

[0119] The method has been described by way of example for an off-road vehicle 1, but is also suitable for any other vehicles, such as passenger cars, military vehicles, amphibious vehicles and the like, and offers corresponding advantages in this case. LIST OF REFERENCE SYMBOLS

[0120] 1Motor vehicle, off-road vehicle 2Underbody 3Control device 4Cable connections 5Display device 6Ground 9Minimal ground clearance 11Wheel 61Flat section of the ground 62Sloped section of the ground 71-73Propagation paths 81-83Ellipses (ellipsoids) with possible reflection points 101-109Ultrasonic transceiver (ultrasonic transceiver)

Claims

1. Method for monitoring a ground clearance beneath a motor vehicle (1), on the underbody (2) of which are arranged a plurality of ultrasonic transceivers (101-109) spaced apart from one another, comprising: a) selecting (S1) a first ultrasonic transceiver (101-109) from among the plurality of ultrasonic transceivers (101-109) and activating the first ultrasonic transceiver to send a transmission signal; b) selecting (S2) a second ultrasonic transceiver (101-109) from among the plurality of ultrasonic transceivers (101-109) and activating the second ultrasonic transceiver (101-109) to receive a reception signal which is a reflection of the transmission signal sent in step a); and c) repeating (S3) steps a) and b), wherein different pairs consisting of a first and a second ultrasonic transceiver (101-109) are selected to receive a respective echo signal; characterized by d) determining (S4) a profile of a ground beneath the motor vehicle (1) on the basis of the received echo signals; and e) determining (S5) a minimum ground clearance (9) beneath the motor vehicle (1) by comparing the determined profile of the ground (6) with an underbody profile of the motor vehicle (1).

2. Method according to Claim 1, wherein in step c) (S3) at least three different pairs are selected, wherein at least one ultrasonic transceiver (101-109) of the at least three different pairs is not arranged along a straight line with all the other of the plurality of ultrasonic transceivers (101-109) of the at least three different pairs on the underbody (2) of the motor vehicle (1).

3. Method according to Claim 2, wherein in step d) (S4), for each echo signal, on the basis of a signal time of flight between the sending of the associated transmission signal and the reception of the echo signal, and on the basis of installation positions of the first and second ultrasonic transceivers (101-109) with which the transmission signal was sent and the echo signal was received, an ellipse (81-83) or an ellipsoid is determined with possible reflection points at which the transmission signal may have been reflected; and the profile of the ground (6) is determined by fitting a profile surface to the determined ellipses (81-83) or ellipsoids.

4. Method according to Claim 3, wherein in step d) (S4) a temporal and / or spatial averaging of the determined ellipses (81-83) or ellipsoids is also carried out.

5. Method according to any of the preceding claims, further comprising: f) triggering (S6) a procedure affecting the operation of the motor vehicle (1) in accordance with the determined minimum ground clearance (9).

6. Method according to Claim 5, wherein step f) (S6) comprises: issuing a warning to a driver of the motor vehicle (1) if the minimum ground clearance (9) falls below a threshold value, and / or displaying the determined minimum ground clearance (9) by means of a display device (5), and / or displaying a graphical representation of the determined profile of the ground surface (6) beneath the motor vehicle (1) by means of a display device (5) and / or initiating an automatic braking and / or stopping of the motor vehicle (1) if the minimum ground clearance (9) falls below a threshold value, and / or raising the vehicle using a height-adjustable chassis if the minimum ground clearance (9) falls below a threshold value.

7. Method for monitoring a ground clearance according to Claim 6, wherein the threshold value is chosen depending on a driving speed of the motor vehicle (1).

8. Method for monitoring a ground clearance according to any of the preceding claims, wherein the method is carried out while the motor vehicle (1) is driving.

9. Method according to Claim 8, wherein in step d) (S4) the determined profile of the ground (6) is extrapolated in a direction of travel of the motor vehicle (1) and in step e) the extrapolated profile is compared with an underbody profile of the motor vehicle (1) extrapolated in the driving direction of the motor vehicle (1), to determine an extrapolated minimum ground clearance as the minimum ground clearance (9).

10. Method for monitoring a ground clearance according to any of the preceding claims, wherein the repetition in step c) (S3) is carried out in such a way that in step a) a first ultrasonic transceiver (101-109) is selected and step b) (S2) is carried out simultaneously with a plurality of different second ultrasonic transceivers (101-109).

11. Method according to any of the preceding claims, wherein the repetition in step c) (S3) is carried out in such a way that multiple steps a) are carried out simultaneously with a plurality of different first ultrasonic transceivers (101-109), which are activated in such a way that each of the first ultrasonic transceivers (101-109) sends a transmission signal with a different transmission signature, and in step b) a reception signal waveform of the second ultrasonic transceiver (101-109) is demodulated to obtain a respective reception signal for each pair consisting of one of the first ultrasonic transceivers (101-109) and the second ultrasonic transceiver (101-109).

12. Method according to any of the preceding claims, wherein in step b), in a reception signal waveform of the second ultrasonic transceiver (101-109), an echo signal which is the first to be received after the time of sending the transmission signal, is identified as the received echo signal which corresponds to the transmission signal sent in step a).

13. Computer program product comprising commands which, during their execution by a computer device (3) communicatively connected to the plurality of ultrasonic transceivers (101-109), cause said computer device to carry out the method according to any of the preceding claims.

14. Device (3) for monitoring a ground clearance beneath a motor vehicle (1), on the underbody (2) of which are arranged a plurality of ultrasonic transceivers (101-109) spaced apart from one another, wherein the device (3) is communicatively connected to the plurality of ultrasonic transceivers (101-109) and is configured to carry out a method according to any of Claims 1 to 13.

15. Motor vehicle (1), on the underbody (2) of which are arranged a plurality of ultrasonic transceivers (101-109) spaced apart from one another, having a device (3) according to Claim 14.