System and method for monitoring a car trailer

State of the art

0001The invention is based on a system and method for monitoring motor vehicle trailers while driving, with particular attention being paid to the relative orientation of the rear end of the tractor and the front of the trailer in passenger car combinations.

0002Vehicle combination of towing vehicle and trailer are particularly accident-prone. The trailer can rock while driving and then be difficult to bring under control. In particular, passenger cars with trailers such as caravans tend to above certain critical speeds to unstable driving behavior. Here, the trailer can perform periodic, aufschaukelnde pendulum movements to the trailer hitch of the towing vehicle, or suddenly break out of the track. These dangers are increasingly on gradients, because here the speed increase often not noticed by the driver, or deliberately caused. Gusts of wind from passing vehicles or on bridges can let the team out of control. This can usually lead to inexperienced drivers that they lose control of the team, which, for example, can lead to uncontrollable skidding and "buckling" of the trailer. By timely braking in such a situation, the team could be stabilized again.

0003Various systems are known for monitoring a team in driving. In the Trailer Stability Program (TSP), which was published by Opel on the Internet at opel.automagazin24.de/astra/astra2003/index.htm on 12.09.03, a team is stabilized via the ESP of the towing vehicle. Upon detection of a critical driving situation, the TSP system automatically initiates certain stabilization measures. However, the TSP system only measures vehicle dynamics data in the towing vehicle itself, so that the system does not always have the latest trailer orientation. The only indirect measurement of the instability of the trailer from the vehicle dynamics data of the towing vehicle is complex in their calculation and disadvantageously relatively inaccurate.

0004In the German patent application DE 19901953 a system for monitoring a team in driving is disclosed, which observes the trailer directly. On the basis of at least two ultrasonic sensors while the distance to certain points of the trailer and derived therefrom the frequency and amplitude of the yaw angle of the trailer is monitored and concluded from the values ​​thus determined on an unstable behavior of the team. However, the yaw angle is calculated only indirectly from two distance values ​​determined by means of ultrasonic sensors. This indirect determination of the yaw angle has the disadvantage that due to inhomogeneities of the front wall of the trailer, such as by a flanged spare wheel, the distance-over-yaw angle is no longer continuous and no longer monotonous. Thus, completely false yaw angles can be erroneously calculated, especially if the relief structure data of the trailer front wall are not known to the system. Furthermore, the method in DE 19901953 offers no solution against a single break as well as against instabilities due to pitching and / or tilting movements of the trailer.

0005Japanese Utility Model Publication JP 2003-148938 discloses a method of directly measuring the yaw angle with a video camera for a semi-trailer. For this purpose, a contrast plate is mounted horizontally in front of the coupling on the tractor so that it is partially covered by the semi-trailer of the trailer. The contrast plate carries a pattern easily detectable by a suitable image processing algorithm. The front contour of the semi-trailer is detected as a boundary line of the visible pattern of the contrast plate. This edge line changes depending on the yaw angle between towing vehicle and trailer.

0006A disadvantage of the method in JP 2003-148938 is that a contrast plate attached to the towing vehicle is required for angle determination. In passenger vehicles is located under the drawbar relatively far away from the tractor trailer front edge only the road. A contrast plate would therefore have to be mounted far projecting under the trailer hitch, resulting in additional effort and lack of acceptance by the driver would result. Furthermore, the system is provided in JP 2001-350349 according to the invention only for shunting and not for monitoring the trailer at higher speeds.

Advantages of the invention

0007With the measures of the independent claims, a cost-effective improved system and method for monitoring motor vehicle trailers is provided that determines reliable information about the current orientation angle for any trailer while driving, and provides a statement about the stability of the current driving condition of the team for driving operation-relevant further processing. The claims will be referred to below.

0008In its most general aspect, the present invention discloses a system for monitoring motor vehicle trailers while driving, with a<ol id="ol0001" ol-style=""><li>a) camera device for the visual detection of the relative orientation of the rear end of the tractor and the front of the trailer, which may for example be a reversing camera already present on the vehicle,</li><li>b) an evaluation subsystem for the collected data</li><li>c) and interfaces to the driving-relevant further processing of the evaluated data,</li></ol>characterized in that that in the evaluation subsystem one or more, each defining a specific relative orientation defining templates can be stored, which serve the reference subsystem as reference data for associated alignment angles of the vehicle combination, and the evaluation subsystem is set up by programming to perform correlations between images of the currently detected, relative orientation and template (s), to determine information about the instantaneous orientation angle between the longitudinal and / or transverse axes and / or vertical axes of towing vehicle and trailer, and about orientation angle, that indicate a critical driving situation, to detect and to transmit appropriate signals to the interfaces for driving operation-relevant further processing.

0009According to the invention, the rear end of the towing vehicle and its trailer coupling area belong to the rear end of the towing vehicle. The trailer front area includes the drawbar and the front wall of the trailer.

0010The orientation angle may include information about the yaw, pitch and / or roll angle between the longitudinal and / or transverse axes of towing vehicle and trailer. It can also be limited to a subset of these angles. The longitudinal axes are the centrally extending in the longitudinal direction of the respective vehicle, hitting the trailer hitch axles. The yaw angle defines the angle between the longitudinal axes of towing vehicle and trailer. The transverse axis is perpendicular to the respective longitudinal axis parallel to the lower edge of the respective vehicle body. The roll angle defines the angle between the transverse axes of towing vehicle and trailer. The vertical axis is perpendicular to the longitudinal and vertical axis and therefore, for example, parallel to the A-pillar (towing vehicle) or vertical outer edge of the trailer. The pitch angle defines the angle between the vertical axes of towing vehicle and trailer.

0011Templates stored in an evaluation subsystem according to the invention contain complete images or images reduced only to significant lines and points, to which certain, predefined, relative orientations of the rear end of the tractor and the front of the trailer are assigned. By means of correlations according to the invention between images of the currently detected, relative orientation and the template (s) (template matching), information about the instantaneous orientation angle can be determined in a straightforward manner without any vehicle-mounted aids for any trailer. By means of this template matching according to the invention, the system is suitable without any problems for any shapes of the trailer front area and the rear end of the towing vehicle.

0012According to the invention, the system recognizes alignment angles which indicate a critical driving situation and transmits corresponding signals to interfaces for further operation relevant to driving operation. Such processing includes, for example, predetermined measures to prevent accidents, such as automatic braking or issuing warnings to the driver, such as "Braking lightly to stabilize your vehicle".

0013In the dependent claims advantageous refinements developments and improvements of the respective subject of the invention are given.

0014According to an advantageous embodiment of the present invention, a multiplicity of different orientation defining templates for an "IF adjustment" are stored in the correlation with the current camera image. Only a large number of templates are stored once in the course of the referencing process in order to obtain a sufficient number of templates for different orientation angles. This saves computing time during the determination of the current orientation angle, because the current camera image or the template do not need to be rotated.

0015An advantageous development of the present invention provides a device for detecting the instantaneous steering angle. If the current steering angle is known, the correct yaw angle between towing vehicle and trailer in dependence on the steering angle can be determined in particular for stable cornering. This relationship allows for improved vehicle stability for a currently measured orientation angle.

0016According to a further advantageous embodiment of the present invention, the determined angle information, in particular for detecting spin movements, contains information about the instantaneous yaw angle between the longitudinal axes of towing vehicle and trailer. The yaw angle can be determined particularly well by the image capture of the trailer hitch area of ​​the rear end of the tractor and a portion of the drawbar of the trailer front area, because the instant yaw angle can be determined directly without the need for distance information using template matching.

0017A further advantageous embodiment of the present invention provides the detection of angle information that contains information about the current rolling and / or pitch angle between the transverse and / or vertical axes of towing vehicle and trailer. By measuring the roll angle, lateral tilting movements and pitching movements of the trailer leading to instability of driving can be detected.

0018This angle information can be determined particularly well by means of template correlation evaluation of significant points and / or lines and / or significant image patterns of a section captured by the camera device of the opposite wall of a vehicle of the team, in particular the wall opposite the towing vehicle. Thus, a pitch angle for known distance information can be determined simply by a vertical displacement of the line of the front trailer lower edge. The roll angle is determined in a similarly simple manner by measuring the rotation of the trailer lower edge line, for example, because of the geometric dependence of the position of the trailer lower edge in the camera image of both the roll angle and the yaw angle always the yaw angle must be known. This is relevant when the yaw angle is not equal to zero due to a cornering, and at the same time the roll angle due to a possibly tire on the trailer is also not equal to zero. If the drawbar in the camera image is in a straight-ahead position (yaw angle = zero) and the trailer lower edge is inclined (flat tire), the trailer is in straight-ahead driving, with roll angle not equal to zero. However, if both the drawbar oblique and the trailer end wall, then there is a non-zero yaw angle, and it is not just the roll angle that makes the face appear obliquely. For exact calculation of the roll angle, the yaw angle must be known in this case.

0019According to a further advantageous development of the present invention, the system includes a light-section projector which spans a light line for active illumination (measuring principle: active laser triangulation), and whose line-like images are evaluated in the trailer front area in the evaluation subsystem. Thus, on the one hand, highly visible lines can be used as markings and, on the other hand, the angle calculations can be supported by means of active triangulation. The light section method can be used advantageously in the dark, since it works largely independently of the daylight. Furthermore, the line-like information can be easily extracted from the camera image and evaluated with little computational effort, and there is a high detection security. It is also advantageous that the roll angle measurement is decoupled from the yaw angle measurement. The roll angle can thus be measured directly without the yaw angle or other parameters such as the drawbar length must be known.

0020The light section method can be used alternatively or in addition to the dike template matching. An additional advantage in the test according to the invention as to whether the yaw angle in relation to the steering angle is within predetermined limits for stable cornering provides the determination of the drawbar length for this angular relationship using the measured yaw and steering angles during a previous stable cornering. The drawbar length is the distance of the hitch receiving point to the trailer wheel axle. A direct measurement of the drawbar length is therefore unnecessary. It can thus be determined automatically during the course of a calibration run or a reference run to record the templates. Referencing is eg Travel at low speed and quasi-stationary angle, so that stable conditions can be assumed. After referencing, the system is available.

drawings

0021With reference to the drawings, embodiments of the invention will be explained.

Show it

0022<dl id="dl0001"><dt>Fig. 1</dt><dd>a block diagram of an embodiment of the system according to the invention for monitoring a motor vehicle trailer;</dd><dt>Fig. 2</dt><dd>a flowchart of an embodiment of the inventive method for monitoring a motor vehicle trailer;</dd><dt>Fig. 3</dt><dd>a schematic sketch of a partial view of the trailer with trailer drawbar from the bird's eye view to illustrate an example of the detection of the yaw angle according to the invention;</dd><dt>Fig. 4</dt><dd>a schematic sketch of a trailer front wall to illustrate an example of the detection of the pitch angle according to the invention, and</dd><dt>Fig. 5</dt><dd>a schematic sketch of a trailer front wall to illustrate an example of the detection of the roll angle according to the invention.</dd></dl>

Description of exemplary embodiments

0023In the figures, the same reference numerals designate the same or functionally identical components.

0024In <b>Fig. 1</b> an embodiment of the inventive system 3 for monitoring a motor vehicle trailer is shown as a schematic block diagram. The monitoring system 3 comprises a video camera 5 mounted in the rear (schematically) of the towing vehicle 1 for monitoring a trailer. The current, digital image data arrive from the camera device 5 to an evaluation sub-unit 7. There, according to the invention, they are checked for correlations in a computing device 11 with templates stored in a data memory 9, ie with images stored in reference driving situations, or templates of the camera image area reduced to striking points or lines of the drawbar area (tamplate matching) Alignment angle of the trailer to the towing vehicle 1 to determine. The computing device 11 is, for example, a conventional, suitably programmed computer chip, or a special ASIC or FPGA device.

0025The computing device 11 transmits the orientation angle determined in this way to an evaluation unit 13 assigned to the evaluation subsystem 7. This receives data on the current curve angle of the towing vehicle. 1 This is ideally sourced directly from the ESP, as the current curve angle of the towing vehicle is available there in both stable and unstable driving. The ESP model-based calculates the current curve angle from the steering angle sensor (driver's request) and the yaw rate sensor (actual curve movement). According to the invention, the evaluation unit 13 checks, from a predetermined angular relationship between the curve angle and the orientation angle, whether the angles currently measured indicate a critical driving situation. Such a critical driving situation would be given, for example, if the yaw angle of the trailer deviates over 10% from the value for stable cornering at the momentarily measured steering angle.

0026If a critical driving situation is detected, the evaluation unit 13 transmits corresponding signals to interfaces 17 to which the output and / or actuator units 19 are connected. These units 19 are for example a display, a loudspeaker of the audio system which is present anyway in the motor vehicle, an automatic brake control or an automatic acceleration control in the towing vehicle 1. Thus, upon receiving the signals for a critical driving situation, predetermined measures to prevent accidents are initiated. Such measures are, for example, a warning sign on the display, an audible warning (s. above), automatic deceleration, countersteer, or deceleration.

0027In <b>Fig. 2</b> a flow chart of an embodiment of the method according to the invention is shown. The first four steps are used to initialize the system. In step 100, the zero position of the yaw angle between towing vehicle and trailer during a calibration drive is determined. The team drives for a long time at low speed straight ahead. During this time, the camera device 5 picks up an image of the trailer coupling area with the drawbar in step 110, which is stored in step 120 as a template with the defined orientation of the yaw angle zero in the evaluation subsystem 7. Further templates are calculated or recorded at different fixed curve radii, which saves computing time.

0028Thereupon, in step 130, a calibration run is performed to determine the drawbar length. The drawbar length is necessary to calculate trailer motion instabilities, because it is included in the angular relationship between trailer yaw angle and towing vehicle steering angle. From this angular relationship can be inventively detect whether the current yaw angle fits the current steering angle, ie whether the trailer is in a stable lane, or has already begun to "unstable" around the trailer hitch. The drawbar length is determined in a stable cornering at low speed as the last indeterminate size of the following angular relationship from the following formula, where yaw and steering angles and calculable therefrom the curve radius, are known.<maths id="math0001" num=""><math display="block"><msub><mi>α</mi><mi>D</mi></msub><mo>=</mo><mi>arcsin</mi><mfrac><msub><mi>L</mi><mi>D</mi></msub><mrow><msqrt><msup><mfenced><mfrac><msub><mi>L</mi><mi>R</mi></msub><mrow><msub><mrow><mi>tan</mi><mtable /><mi mathvariant="normal">α</mi></mrow><mi mathvariant="italic">L</mi></msub><mtable /></mrow></mfrac></mfenced><mn>2</mn></msup></msqrt><mo>+</mo><msub><mi>L</mi><msup><mi>K</mi><mn>2</mn></msup></msub></mrow></mfrac><mo>+</mo><mi>arctan</mi><mfrac><mrow><msub><mi>L</mi><mi>K</mi></msub><mo>⋅</mo><msub><mrow><mi>tan</mi><mtable /><mi mathvariant="normal">α</mi></mrow><mi>L</mi></msub><mtable /></mrow><msub><mi>L</mi><mi>R</mi></msub></mfrac></math><img file="EP1593552B1_D0001.tif" /></maths> in which<dl id="dl0002" compact="compact"><dt>αD:</dt><dd>Trailer yaw</dd><dt><i>L</i>D:</dt><dd>drawbar length</dd><dt><i>L</i>R:</dt><dd>Wheelbase of towing vehicle (known)</dd><dt>αL:</dt><dd>Curve angle of towing vehicle</dd><dt><i>L</i>K:</dt><dd>Distance trailer hitch from the rear axle of the towing vehicle (known)</dd></dl>

0029The initialization can be carried out for any type of trailer without having to manually enter the data of the trailer into the system. This increases the user comfort and the acceptance of the system by the consumer, who often wants to know as few technical details as possible and should be protected from the risk of incorrect manual entries.

0030After completing this initialization phase, the system is ready for use. In step 140, the camera device figuratively detects the instantaneous alignment of the drawbar with the towing hitch area of ​​the towing vehicle in a permanent mode of operation. On the basis of these digital images, in accordance with the invention a correlation is carried out in step 150 with the tiller tyres stored in the system and defining the yaw angle zero. For this purpose, either the drawbar template is rotated over the desired angle range and a correlation measure is calculated in each case or the current camera image in the drawbar environment is transformed by the respective angle. The maximum of the correlation measure reflects the current yaw angle in camera coordinates. In this case, a plausibility check takes place, for example via a threshold value method. If it turns out that the calculated correlation measure is not large enough, the system is currently considered "not available". Otherwise, in step 160, the system determines the current yaw angle from the result of the correlation. It transforms the camera coordinates (in pixels) into Cartesian "world coordinates" (in mm) by means of the camera parameters, the coordinates of the trailer coupling and the camera installation position and orientation, which are described by the longitudinal, transverse and vertical axis.

0031In step 170, a steering angle sensor 15 determines the steering angle and transmits the data to the evaluation unit 13, which checks in step 180 according to the invention, whether the determined yaw angle in relation to the steering angle within predetermined for a stable cornering or straight ahead, allowed limits. It is assumed that the above-mentioned angular relationship for a stable cornering. The permissible limits are, for example, a deviation of the measured yaw angle of less than 10% from the yaw angle calculated according to the above formula for the instantaneous steering angle.

0032If an exceeding of these limits is detected at a current yaw angle, see the NO branch from decision 180, In step 190, the system initiates measures to avoid accidents, for example by issuing a dedicated control signal to a higher-level vehicle dynamics monitoring system. such as audible warnings, or triggering a monitoring loop known in the art, which corrects the target / actual deviation of the yaw angle. Regardless - see the two-way feedback arrows from step 180 back to step 140 - the system continually monitors the trailer yaw angle while driving. At the next iteration, step 140 begins the next-time evaluation step, in which a camera image recorded later is processed analogously to the above description. Depending on the computing power of the evaluation subsystem and the frame rate of the reversing camera, the evaluation frequency can be set. A reasonable value is about 25 evaluations per second, advantageously taking advantage of the full frame rate.

0033In <b>Fig. 3</b> is a partial view of the trailer with a trailer drawbar 24 from a bird's eye view schematically illustrating an example of the detection of the yaw angle 28 according to the invention sketched.

0034A trailer 20, for example a caravan, is coupled with its V-shaped drawbar 24 to the trailer coupling 22. A built in the rear of the towing vehicle 1 camera device 5 of the system according to the invention captures an area 26 in which the trailer hitch 22 and the drawbar are located. If the camera is mounted relatively high up, it looks down obliquely.

0035Device of the trailer 20 during the drive of the towing vehicle 1 to spin or breaks, the camera detects 5 the corresponding position of the drawbar 24 relative to the towing vehicle 1. In dashed lines, for example, a deflection of the trailer 20 is drawn with a yaw angle 28 of about thirty degrees , This yaw angle 28 is determined according to the invention by means of template matching.

0036In <b>Fig. 4</b> is the front wall 30 of a coupled trailer 20 schematically illustrating an example of the detection of the pitch angle 32 according to the invention.

0037The camera image captured by the tractor from a section 26 of the front wall 30 of a coupled trailer 20th The calculation of the pitch angle 32 is based on the parallel displacement of the lower edge of the structure of the trailer 20. With the distance from the trailer hitch to the trailer front wall 30, the pitch angle 32 can thus be determined relative to the towing vehicle. For example, in each case a height offset of lower edge or Top of the trailer by a pitching movement of the trailer 20 up and down while driving shown in dashed lines. A warning is given if, by means of the template matching according to the invention, an excessive oscillation of the pitch angle 32 is detected, as may occur with relatively light trailers, high speeds, uneven road surfaces, or slipping loads in the trailer - a single change. The determination of the pitch angle can generally only take place if the yaw angle is known beforehand.

0038In <b>Fig. 5</b> is schematically sketched a trailer front wall 30 for illustrating an example of the detection of the roll angle 34 according to the invention.

0039The skew of the superstructures of the trailer 20 relative to the towing vehicle is determined via a built-in rear camera device by evaluating the position of the lower edge of the trailer 20 or other significant points of the trailer front wall 30 according to the invention using Tamplate Matching. With the distance from the trailer hitch to the trailer front wall 30 and the yaw angle required due to geometrical dependence, the roll angle 34 can thus be determined relative to the towing vehicle. For example, an oblique position to the right and to the left by tilting movements of the trailer 20 while driving in dashed lines is shown. A warning occurs when a value of the roll angle 34 that is too large for a stable position is detected, for example from an angle of 10 degrees or more.

0040With further relation to <b>4 and FIG. 5</b> In the following, a variant for pure gray value image processing by matching with draw frame templates is given as a further exemplary embodiment. In this case, a system with active lighting is used and a so-called light-section method is performed. Basic information is available in the following sources:<ul id="ul0001" list-style="none" compact="compact"><li>Schmalz, G .: Technical Surface Science, Berlin: Springer-Verlag, 1936, p. 75, or</li><li>Haug, K .: laser light section sensor for the automation of metal inert gas welding processes, dissertation University Stuttgart, Jost Jetter publishing house, Heimsheim, 2002, or</li><li>Heckel, W .: Optical 3D contour detection and on-line bending angle measurement with the light-section method. Diss. University of Erlangen-Nuremberg, Carl Hanser Verlag, 1995.</li></ul>

0041At least one line projector is used for active lighting. This can be realized for example from a laser diode with upstream line optics in the form of a cylindrical lens. The light section sensor is then made up of a line projector and reversing camera. The line projector can advantageously be integrated in tail lights / reversing lights, in other sensors, such as in ultrasonic parking pilots sensors or in other existing functional groups.

0042To measure the yaw angle, the lighting level of the line projector is ideally chosen horizontally or contains a horizontal component. To measure the pitch angle, a second line projector is selected whose measurement plane is vertical. In principle, the reversing camera must not be in the measuring plane in both cases. It is advantageous in both cases, a large base distance between rear view camera and line projector, so that this example is designed integrated into the bumper, while the rear view camera is running above the license plate integrated into the tailgate. The light line projectors for pitch and roll angles can be combined, eg by using a cross projector. The camera looks in the described embodiment, for example at 45 ° to the horizontal down. The field of view is symmetrical to the longitudinal axis.

0043The projected laser line becomes visible to the camera on the front wall of the trailer as a light cut line. The laser line can be selected both in the visible and in the infrared (advantage: not visible to humans, but also more dangerous), with the spectral sensitivity of the reversing camera must support the selected wavelength. Due to the known relative position between reversing camera and line projector, the line position of camera coordinates can be transformed into world coordinates.

0044Depending on the orientation of the light cut line, its image is evaluable for the purposes of the present invention, as was the drawbar image in the previous example. In Fig. 4 is a horizontal line 40 for yaw angle measurement and in FIG. 5 a vertical laser light section line 42 for pitch angle measurement drawn. A roll angle measurement is not possible based on the trailer front wall projected lines, since the plane of the trailer front wall does not change depending on the roll angle. However, a roll angle measurement on a light intersection basis is possible if horizontal surfaces on the trailer can be illuminated by the towing vehicle with a line projector.

0045Changes in <b>Fig. 4</b> The yaw angle of zero, for example, to a value of about 20 degrees, so there is a visible rotation of the laser light section line 40 by an angle that depends in addition to the yaw angle of the relative position and orientation between rear view camera and projector.

0046This new, dashed drawn line image can now be evaluated by means of line matching to determine the yaw angle, comparable to the description given above of the current drawbar image (drawbar mating). It is also evaluable after a transformation in world coordinates to determine the pitch and the roll angle.

0047In FIG. 5, the vertically drawn light-section line 42 is evaluated to determine the pitch angle, provided that the camera and the projector are not arranged vertically one above the other. The variation in the pitch angle results in the dashed line for the evaluation and further processing according to the invention as described above.

0048If the evaluation of a light intersection already provides a clearly interpretable result in the determination of an angle (yaw, pitch or roll), no further evaluation is required. Is not it unambiguous, perhaps because the in Fig. 4 drawn course of the line image can occur even when driving straight and roll angle not equal to zero, so an additional evaluation should be made - for example by including the steering angle, the yaw rate, matching the drawbar templates, etc., until the statement about the desired angle is unique. The light section method can be used advantageously in the dark, as it works regardless of the daylight level. Furthermore, the line-like information can be easily extracted from the camera image and evaluated with little computational effort, and there is a high detection security. It can be used alternatively or in addition to the Deichseltemplate Matching.

0049It is also advantageous that the measurements of yaw and pitch angle are decoupled. The pitch angle is advantageously not linked to the visibility of the trailer lower edge and to a length of the drawbar to be determined, but can be determined directly. Although the present invention has been described above with reference to preferred embodiments, it is not limited thereto but modifiable in a variety of ways.

0050For example, the camera device may be set up as a normal reversing camera when driving without a trailer. Advantageously, only one software is ever loaded into the control unit of the camera: If the conventional reversing camera is active (activated via reverse), then the conventional reversing camera software is loaded from the non-volatile memory into RAM. If trailer monitoring is active (activated via recognized trailer as described in German Patent Application DE 1 99 01 953), the trailer monitoring software is loaded. The charging time of a few 100 ms does not bother. This results in the advantage that not two software functions need to be kept in memory at the same time, which saves storage space and computing resources.

0051It is also possible to support the system according to the invention with other sensors, for example ultrasound sensors or tilt sensors. Thus, additional information can be obtained for plausibility. Furthermore, by temporal differentiation from the determined angle values, the angular accelerations can be derived, which can also be used for warning strategies.

0052The match process can also be varied by either rotating the camera image and comparing it to one or more fixed templates, or by rotating a fixed template or template with the least angular deviation and comparing it with the camera image, or a combination thereof Action is taken.

0053Of course, the inventive method can also be supported by a camera 5, which is mounted on the trailer front area and looks at the drawbar and the rear of the towing vehicle.

0054Finally, the features of the subclaims can be combined substantially freely with one another and not by the order given in the claims, provided that they are independent of each other.