Apparatus and method for adjusting the angular position of the optical axis of a motor vehicle headlight

Abstract

A method for adjusting the angular position of the optical axis (18) of a front headlight (10) of a motor vehicle is proposed, in which the pitch angle is determined from the signal of at least one MEMS acceleration sensor (22). The device is characterized in that the MEMS acceleration sensor (22) is a component of a control device (28) for the front headlight (10), and the front headlight has a pitch angle adjustment motor (30) set up to adjust the angular position of the optical axis. The device is set up to determine the longitudinal acceleration of the motor vehicle by means of the MEMS acceleration sensor (22) and use this to control the pitch angle adjustment motor by means of a computational model. One independent claim is directed to a corresponding method.

Description

[Technical Field]

[0001] The present invention relates to a device for adjusting the angular position of the optical axis of a front headlight of a motor vehicle as set forth in the preamble of claim 1. The angular position depends on the static pitch angle of the motor vehicle when the motor vehicle is stationary on a road surface or when the motor vehicle is moving linearly on a road surface at a constant speed. The static pitch angle is determined from the signal of at least one MEMS acceleration sensor and depends on the load distribution and the road surface gradient.

[0002] Further to the above, the present invention relates to a method for adjusting the angular position of the optical axis of a motor vehicle headlight, the angular position being dependent on a static pitch angle occurring when the motor vehicle is stationary on a road surface or moving in a straight line at a constant speed on a road surface, the static pitch angle being determined from the signal of at least one MEMS acceleration sensor. [Background technology]

[0003] Such an apparatus and such a method are known from U.S. Pat. No. 8,838,343 B2. The pitch, roll, and yaw angles are quantities that describe the attitude of a motor vehicle in space. These quantities are defined in DIN ISO 8855:2013-11, Road Vehicles, Vehicle Dynamics, and Driving Behavior, Concepts (ISO 8855; 2011), Berlin: Voigt Verlag, 2013. The pitch angle describes the rotational deflection of the vehicle's longitudinal axis about the vehicle's lateral axis. The roll angle describes the rotational deflection of the vehicle's lateral axis about the vehicle's longitudinal axis. The yaw angle describes the rotational deflection of the vehicle's longitudinal axis about the vehicle's vertical axis.

[0004] Since 1998, regulatory authorities have required compensation for the effects of load changes on the position of the optical axis of a motor vehicle's front headlights. This aims to avoid dazzling oncoming traffic while simultaneously achieving the longest possible low-beam reach. Devices that fulfill this role are also called Vertical Aiming Control (VAC) devices. Manual VAC devices are known, in which the driver manually adjusts the position of the optical axis from the dashboard. Automatically reactive devices (AVAC) are also known, which compensate for changes in the static position of the optical axis that occur as a result of changing load conditions. The aforementioned U.S. Pat. No. 8,838,343 B2 utilizes MEMS acceleration sensors, but is limited to compensation for static position changes only.

[0005] Furthermore, dynamic AVAC systems are also known that compensate for changes in the position of the optical axis that occur dynamically while the vehicle is moving. These systems utilize deflection sensors to detect the position of the optical axis. This solution is already disadvantaged by the cost associated with wiring the four deflection sensors, which are usually required. Summary of the Invention

[0006] Against this background, the object of the present invention is to provide a device of the type mentioned at the beginning that allows for the correction of dynamic changes in the position of the optical axis without sacrificing the wiring costs associated with the use of deflection sensors.

[0007] This problem is solved by the features of the independent claims. The device according to the invention differs from the prior art mentioned at the outset in that the MEMS acceleration sensor is a component of a control device for a front headlight of a motor vehicle, the front headlight having at least one light module with an optical axis of the motor vehicle headlight and a pitch angle adjustment motor set up to adjust the angular position of the optical axis, the control device being set up to determine the longitudinal acceleration of the motor vehicle from the acceleration of the motor vehicle detected by the MEMS acceleration sensor, combine this by multiplication with a preset coefficient to form a product, combine this product by addition to form a static pitch angle and a total pitch angle, and adjust the angular position by controlling the pitch angle adjustment motor depending on the total pitch angle. In principle, the invention is suitable for any type of headlight for which a vertical adjustment device is provided. In such headlights, the radiation direction of the light module is usually adjusted.

[0008] The method according to the present invention is characterized in that the longitudinal acceleration of the vehicle is detected by a MEMS acceleration sensor and combined by multiplication with a preset coefficient to form a product, and this product is combined by addition to form a static pitch angle and a total pitch angle, and the angular position is adjusted depending on the total pitch angle.

[0009] From the viewpoint of the device aspect, a pitch adjustment motor is preferably mechanically linked to the light module and set up to adjust the pitch angle position of the optical axis.

[0010] It is also preferred that the angular position is dependent on a static roll angle that occurs when the vehicle is stationary on a road surface or moving linearly on a road surface at a constant speed, the static roll angle being determined from signals from at least one MEMS acceleration sensor, the front headlight having a roll angle adjustment motor set up to adjust the optical axis of the light module, the control device being set up to determine a lateral acceleration of the vehicle from the acceleration of the vehicle detected by the MEMS acceleration sensor, the lateral acceleration of the vehicle being combined by multiplication with a preset coefficient to form a product, and this product being combined by addition to form a static roll angle and a total roll angle, and the angular position is adjusted depending on the total roll angle.

[0011] A roll angle adjustment motor is also preferably mechanically linked to the light module and set up to adjust the roll angle position of the optical axis.

[0012] Preferably, the device further has a bus connection to another front headlight, the MEMS acceleration sensor being connected to a control device of the other front headlight via the bus connection, the control device of the other front headlight being set up to combine the longitudinal acceleration of the vehicle detected by the MEMS acceleration sensor by multiplying it with a preset coefficient to form a product, combine this product by adding it to form a static pitch angle and a total pitch angle, and adjust the angular position by controlling another pitch angle adjustment motor depending on the total pitch angle, and further be set up to combine the lateral acceleration of the vehicle detected by the MEMS acceleration sensor by multiplying it with a preset coefficient to form a product, combine this product by adding it to form a static roll angle and a total roll angle, and adjust the angular position by controlling another roll angle adjustment motor depending on the total roll angle.

[0013] Another preferred embodiment provides that the acceleration sensor is an acceleration sensor that detects acceleration about two mutually perpendicular axes.

[0014] Preferably, the control device is also set up to convert accelerations detected by the acceleration sensor about two mutually perpendicular spatial directions into longitudinal accelerations and lateral accelerations.

[0015] Furthermore, the acceleration sensor is preferably an acceleration sensor that detects acceleration in three spatial directions that are perpendicular to one another.

[0016] In terms of an embodiment of the method, it is preferred that the angular position additionally depends on a static roll angle that occurs when the vehicle is stationary on a road surface or moving linearly on a road surface at a constant speed, the static roll angle being determined from the signal of at least one MEMS acceleration sensor, the lateral acceleration of the vehicle being detected by the MEMS acceleration sensor and combined to form a product by multiplication with a preset coefficient, this product being combined to form the static roll angle and a total roll angle by addition, and the angular position being adjusted depending on the total roll angle.

[0017] Further advantages will become apparent from the following description, the drawings and the dependent claims. Naturally, the features listed above and those further described below can be applied not only in the respective combinations described, but also in other combinations or alone, without departing from the framework of the invention. Exemplary embodiments of the invention are shown in the drawings and explained in more detail in the following description. Here, respectively in schematic form, are shown: [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing a front headlight of an automobile. [Figure 2] FIG. 2 shows the relationship between longitudinal acceleration and low-pass filtered pitch angle for a fixed load distribution. [Figure 3] FIG. 3 shows an embodiment of a front headlight having a roll angle adjustment motor for adjusting the angular position of the optical axis of the front headlight. [Figure 4]FIG. 4 shows an embodiment of the device having a bus connection with another front headlight. [Figure 5] FIG. 5 is a flow chart of an embodiment of a method according to the invention for adjusting the pitch angle position of the optical axis of a motor vehicle headlight. [Figure 6] FIG. 6 is a flow chart of an embodiment of a method according to the invention for adjusting the roll angle position of the optical axis of a motor vehicle headlight. DETAILED DESCRIPTION OF THE INVENTION

[0019] 1 shows a front headlight 10 for a vehicle having a housing 12 whose light exit opening is covered by a transparent cover glass 14. The x-direction corresponds to the longitudinal direction of the vehicle, whereas the y-direction corresponds to the lateral direction and the z-direction corresponds to the vertical direction of the vehicle. This conventional example applies to all embodiments.

[0020] The front headlight 10 has a light module 16, the optical axis 18 of which is the optical axis of the front headlight 10. The light module 16, and thus the optical axis 18, can be pivoted about the lateral direction y. Such a pivoting movement can, for example, change the height of the light-dark boundary of the low-beam distribution generated by the light module 16. This height changes, for example, as the pitch angle Phi of the vehicle changes. The pitch angle Phi changes (statically) when the load on the vehicle changes, for example, when the rear drops and the front rises. A static pitch angle Phi_0 of the vehicle occurs when the vehicle is stationary on a road surface or when it is moving in a straight line on a road surface at a constant speed.

[0021] Dynamic changes in the pitch angle Phi occur in the longitudinal direction due to dynamic changes in the axle load when braking or accelerating while traveling.

[0022] The resulting change in angular position of the optical axis 18 can be compensated for by pivoting the light module 16 in the opposite direction about the lateral direction y.

[0023] The front headlight 10 comprises a device 20 for adjusting the angular position of the optical axis 18. This device 20 includes a MEMS acceleration sensor 22, known per se, which is arranged in a control device 28 of the front headlight 10 together with a processor 24 and a final stage 26. The control device 28 controls, in particular, a pitch adjustment motor 30, which is linked to the light module 16 via tie rods and a joint in such a way that an adjustment movement of the pitch adjustment motor 30 causes the light module 16 to pivot about the y direction. The pitch adjustment motor 30 is another component of the device 20, which is mechanically linked to the light module 16 and is set up to adjust the pitch angle position of the optical axis 18.

[0024] The control device 28 is set up to determine the static pitch angle Phi_0 from the signal of at least one MEMS acceleration sensor 22. The MEMS acceleration sensor comprises, for example, an elastically suspended inertial mass with one or more electrodes. Depending on the deflection of the mass, the spacing of one or more electrodes relative to one or more corresponding electrodes changes, which can be measured capacitively. This allows the static change in the angular position of the optical axis 18 to be measured. Such measurements are not considered part of the present invention.

[0025] According to the invention, the control device 28 is set up to determine the longitudinal acceleration ax of the vehicle from the acceleration of the vehicle detected by the MEMS acceleration sensor 22, combine this with a preset coefficient Phi_1 by multiplication to form a product, combine this product with the static pitch angle Phi_0 by addition to form a total pitch angle Phi, and adjust the angular position of the optical axis 18 by means of the pitch angle adjustment motor 30 depending on the total pitch angle Phi.

[0026] While it is theoretically sufficient for the present invention if the MEMS accelerometer 22 is an accelerometer that detects acceleration about two mutually perpendicular axes, in practice it is preferable to use a MEMS accelerometer 22 that detects acceleration in three mutually perpendicular spatial directions. Such a MEMS accelerometer 22 can be mounted on the control device 28 in any orientation, allowing the detected forward-backward acceleration, and optionally also the left-right acceleration, to be calculated from the measurements using a 3D rotation matrix.

[0027] Figure 2 shows the relationship between low-pass filtered pitch angle, plotted on the vertical axis, and longitudinal acceleration, plotted on the horizontal axis. This relationship was recorded during a test drive. It is clear that this relationship can be modeled with a low-order polygon, and a linear relationship is shown here. Performing a test drive with alternating lateral acceleration yields a similar relationship between lateral acceleration and the resulting roll angle.

[0028] From these observations, a calculation model for the pitch and roll angles can be formulated as simultaneous linear equations. Pitch angle: Phi=Phi_0+Phi_1 * ax Roll angle: Theta = Theta_0 + Theta_1 * ay

[0029] The inventors have found that the accuracy of such a simple calculation model is sufficient for the purposes of dynamic lighting distance control (vertical, pitch angle Phi) and possibly supplementary horizontal adjustment (roll angle Theta), and can be directly used to feed into existing adjustment algorithms for controlling the angular position of the optical axis 18 of the front headlight 10.

[0030] This calculation model is Roll angle Theta_0 and Theta_1 for Theta, and Pitch angleThe coefficients Phi_0 and Theta_0 represent the static pitch angle and static roll angle.

[0031] The coefficients Phi_1 and Theta_1 represent the pitch and roll angle changes that occur when driving as a result of the longitudinal acceleration ax and the lateral acceleration ay. These accelerations can be generated by gravity in relation to changes in the longitudinal and / or lateral inclination of the road surface or by the influence of the vehicle's driving.

[0032] These coefficients depend on the design of the automobile chassis and can be defined as parameters that are characteristic of a particular chassis (particular vehicle suspension). Both of these parameters can also be determined from information detected during driving and updated repeatedly throughout the vehicle's service life, allowing for monitoring of the aging state and for timely maintenance or repair of the suspension system.

[0033] Naturally, the accuracy of the computational model can be improved by considering higher dimensions that reflect square and cube contributions.

[0034] Yet another option for improving accuracy is to utilize a six-axis sensor with a three-axis gyroscope and a three-axis accelerometer. The gyroscope measures angular velocity. The accelerometer measures linear acceleration along one or more axes. For example, data fusion with the gyroscope output can improve the determination of the total pitch and roll angles. The data fusion process is preferably performed by complementary filters, where the accurate high-frequency information provided by the gyroscope is combined with the accurate lower-frequency components of the total pitch and roll angles provided by the accelerometer, as already explained above.

[0035] The integration of the gyroscope output allows the determination of changes in the sensor's orientation. However, due to sensor bias errors, the orientation determined in this way contains an error that grows infinitely over time. It is true that the accelerometer only allows the determination of the sensor's orientation with strong noise. This is especially true in dynamic driving situations. However, the orientation error in this case is finite and does not grow infinitely over time. The basic idea of ​​a complementary filter is to combine the slowly changing accelerometer signal with the rapidly changing gyroscope signal.

[0036] The acceleration sensor allows for orientation determination under static conditions. The gyroscope allows for orientation determination under dynamic conditions. Preferably, the acceleration sensor signal is low-pass filtered and the gyroscope signal is high-pass filtered. The filtered signals are then combined. The frequency responses of the high-pass and low-pass filters add up to unity at any frequency, so that the combined signal is either high-pass or low-pass filtered at any time. In one preferred embodiment, complementary filters are used to combine information obtained from the suspension model, thereby enabling an even more improved angle determination.

[0037] FIG. 3 shows an embodiment of a front headlight as shown in FIG. 1 with an additional roll angle adjustment motor to compensate for changes in the roll angle of the optical axis of the front headlight 10.

[0038] As explained above, the angular position of the optical axis 18 depends on the static roll angle Theta_0 that occurs when the vehicle is stationary on a road surface or moving linearly on a road surface at a constant speed. The static roll angle Theta_0 is determined from the signal of at least one MEMS acceleration sensor 22. The front headlight 10 has a roll angle adjustment motor 32 that is set up to adjust the optical axis 18 of the light module 16. The control device 28 is set up to determine the lateral acceleration ay of the vehicle from the acceleration of the vehicle detected by the MEMS acceleration sensor 22. The lateral acceleration ay of the vehicle is combined by multiplication with a preset coefficient Theta_1 to form a product. This product is combined by addition to form the static roll angle Theta_0 and the total roll angle Theta. The angular position of the optical axis 18 is adjusted depending on the total roll angle Theta thus formed.

[0039] The roll angle adjustment motor 32 is mechanically linked to the light module 16 and is set up to adjust the roll angle position of the optical axis 18. To that end, the roll angle adjustment motor 32 is set up in particular to rotate the light module 16 about the optical axis 18 of the light module 16.

[0040] FIG. 4 shows an embodiment of the device 20 having a bus connection 34 to another front headlight 36, in which the MEMS acceleration sensor 22 is connected via the bus connection 34 to another control device 38 that is a component of the other front headlight 36.

[0041] Another control device 38 of the other front headlight 36 is set up to process the longitudinal acceleration ax of the vehicle detected by the MEMS acceleration sensor 22 as if it were detected by its own MEMS acceleration sensor located in the other front headlight 36. In other words, the other control device 38 is set up to combine the detected longitudinal acceleration ax with a coefficient by multiplication to form a product, combine this product with a static pitch angle and a total pitch angle by addition, and adjust the angular position depending on the total pitch angle by controlling another pitch angle adjustment motor 40. Furthermore, with regard to the roll angle, the other control device 38 is set up to combine the lateral acceleration ay of the vehicle detected by the MEMS acceleration sensor 22 with a preset coefficient Theta_1 by multiplication to form a product, combine this product with a static roll angle Theta_0 and a total roll angle Theta by addition, and adjust the angular position of the optical axis 18 depending on the total roll angle by controlling another roll angle adjustment motor 42, which is a component of the other front headlight 36.

[0042] In one preferred alternative, the total pitch and roll angles are calculated by the controller 28 and passed to the separate controller 38. This is technically preferable to passing raw data to the controller because this preferred approach requires less information to be passed and the separate controller 38 has to perform fewer complex calculations.

[0043] 5 shows an embodiment of a method for adjusting the angular position of the optical axis of a vehicle headlight, where the angular position depends on the static pitch angle. In a first step 100, the static pitch angle is determined from the signal of at least one MEMS acceleration sensor 22. In a second step 102, the longitudinal acceleration ax of the vehicle is detected by the MEMS acceleration sensor 22 and combined with a predetermined coefficient Phi_1, which is characteristic of the chassis, to form a product by multiplication in a third step 104. In a fourth step 106, this product is combined with the static pitch angle Phi_0 to form a total pitch angle by addition. In a fifth step 108, the angular position of the optical axis 18 is adjusted depending on the total pitch angle Phi by controlling the pitch angle adjustment motor 30 to make the appropriate correction.

[0044] 6 shows a flow chart of an embodiment of a method according to the present invention for additionally correcting the dependence of the angular position of the optical axis on the roll angle. In a first step 200, a static roll angle Theta_0 is determined from the signal of at least one MEMS acceleration sensor 22. In a second step 202, the lateral acceleration ay of the vehicle is detected by the MEMS acceleration sensor 22. In a third step 204, the detected lateral acceleration ay is multiplied by a preset coefficient Theta_1 to form a product. In a fourth step 206, this product is added together with the static roll angle Theta_0 to form a total roll angle Theta. In a fifth step 208, the angular position of the optical axis 18 is adjusted as a function of the total roll angle Theta by correspondingly controlling the roll angle adjustment motor 32.

Claims

1. An apparatus (20) for adjusting the angular position of an optical axis (18) of a front headlight (10) of a motor vehicle, the angular position being dependent on the static pitch angle of the motor vehicle when the motor vehicle is stationary on a road surface or moving linearly on a road surface at a constant speed, the static pitch angle being determined from the signal of at least one MEMS acceleration sensor (22), the MEMS acceleration sensor (22) being a component of a control device (28) of the front headlight (10), the front headlight (10) having the optical axis (18) of the front headlight (10). the control device (28) is set up to determine a longitudinal acceleration of the vehicle from the acceleration of the vehicle detected by the MEMS acceleration sensor (22), combine it with a preset coefficient by multiplication to form a product, combine this product with a static pitch angle by addition to form a total pitch angle, and adjust the angular position of the optical axis (18) by controlling the pitch motor (30), depending on the total pitch angle; the angular position is dependent on a static roll angle that occurs when the vehicle is stationary on a road surface or moving linearly on a road surface at a constant speed, the static roll angle being determined from a signal of at least one MEMS acceleration sensor (22); the front headlight (10) has a roll angle adjustment motor (32) set up to adjust the optical axis (18) of the light module (16); the control device (28) is set up to determine a lateral acceleration of the vehicle from the acceleration of the vehicle detected by the MEMS acceleration sensor (22), the lateral acceleration of the vehicle being combined by multiplication with a preset coefficient to form a product, and the product being combined by addition to form a static roll angle and a total roll angle, and the angular position of the optical axis (18) is adjusted depending on the total roll angle; the device (20) has a bus connection (34) to another front headlight (36), the MEMS acceleration sensor (22) is connected to a control device (38) of the other front headlight (36) via the bus connection (34), the control device (38) of the other front headlight (36) being set up to combine the longitudinal acceleration of the vehicle detected by the MEMS acceleration sensor (22) by multiplication with a preset coefficient to form a product, combine the products by addition to form a static pitch angle and a total pitch angle, and adjust the angular position by controlling a further pitch angle adjustment motor (40) in dependence on the total pitch angle, and further set up to combine the lateral acceleration of the vehicle detected by the MEMS acceleration sensor (22) by multiplication with a preset coefficient to form a product, combine the products by addition to form a static roll angle and a total roll angle, and adjust the angular position of the optical axis (18) by controlling a further roll angle adjustment motor (42) in dependence on the total roll angle.

2. 2. The device (20) of claim 1, wherein the pitch adjustment motor (30) is mechanically linked to the light module (16) and is set up to adjust the pitch angle position of the optical axis (18).

3. The device (20) described in claim 1, characterized in that the roll angle adjustment motor (32) is mechanically linked to the light module (16) and is set up to adjust the roll angle position of the optical axis (18).

4. An apparatus (20) described in any one of claims 1 to 3, characterized in that the MEMS acceleration sensor (22) is an acceleration sensor that detects acceleration around two axes that are perpendicular to each other.

5. The device (20) described in claim 4, characterized in that the control device is set up to convert the acceleration detected by the acceleration sensor centered around two spatial directions perpendicular to each other into left-right acceleration and forward-backward acceleration of the vehicle.

6. An apparatus (20) described in any one of claims 1 to 3, characterized in that the MEMS acceleration sensor (22) is an acceleration sensor that detects acceleration in three spatial directions perpendicular to each other.

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