Device for controlling the brightness of an instrumentation light of an automobile

[0002] The present invention relates to a device for controlling the brightness of dashboard lights in a motor vehicle, in which an electro-optical transducer aligned in the direction of travel changes the light intensity of the dashboard lights, using the output signal, as a finction of the ambient brightness in front of the vehicle, and the output signal of the electro-optical transducer, which is weighted by an evaluation unit using predefined algorithms, being supplied to a control unit for influencing the brightness of the dashboard lights.

[0003] A device for controlling the brightness of dashboard lights is described in German Published Patent Application No. 32 45 299. In this case, a photodetector is used as an electro-optical transducer, which is joined to the windshield of the motor vehicle by a fiber-optic guide. In this manner, the photodetector detects the brightness of the ambient range in front of the motor vehicle. The output signal of the photodetector, which is weighted by a microprocessor using predefined algorithms, is supplied to a control unit for changing the brightness of the dashboard lights. The brightness of the ambient range in front of the motor vehicle is only approximately monitored by this device, meaning that the change in brightness of the dashboard lights is inadequate, especially when there are objects driving ahead or objects located in the ambient range.

[0004] A similar device having a phototransistor as an electro-optical transducer is described in German Published Patent Application No. 44 09 777. The analog output signal of the phototransistor is converted into a digital signal, and the characteristic curve of the phototransistor is compensated for by a processing device in such a manner, that a signal proportional to the ambient brightness is acquired for changing the brightness of the dashboard lights.

[0005] Japanese Laid-Open Patent No. 60 24 0545 describes a device for automatically switching the headlights of a vehicle on and off, when it drives into and out of a tunnel. In this case, the change in the brightness in front of the vehicle is monitored using an image-processing sensor, e.g. a CCD camera, and the change is used by an evaluation and control unit for switching the headlights.

[0006] A CCD camera for controlling the brightness of the dashboard lights is not suitable as an electro-optical transducer, since the CCD camera has a small dynamic range and does not allow an absolute determination of brightness. An absolute determination of brightness would only be attainable by aperture and illumination-time regulation, which, however, can never be exactly determined.

[0007] An object of the present invention is to provide a device in which the absolute ambient brightness in front of the motor vehicle is detected and used for optimally adjusting the brightness of the dashboard lights.

[0008] This object is achieved by the present invention, in that a logarithmic CMOS image-processing sensor used as an electro-optical sensor and having a non-linear conversion characteristic, decreases with increasing incident light.

[0009] An extreme dynamic range is achieved by this new image-processing sensor having a non-linear conversion characteristic, which will allow a large brightness range to be imaged in a technically limited voltage or current range.

[0010] In this context, the output signal of the image-processing sensor can also be weighted using suitable object-detection algorithms. For example, this can prevent a truck painted in a dark color from causing the ambient-brightness signal to be too small. Additional sensors (Lidar Radar) can also acquire information about an object, which is supplied to the evaluating unit and used in the above-described manner for controlling the brightness of the dashboard lights.

[0011] FIG. 1 shows a section along the longitudinal axis of the motor vehicle with the positioning of the image sensor.

[0012] FIG. 2 shows the nonlinear conversion characteristic of the image sensor.

[0013] FIG. 3 shows a block diagram of the device for controlling the brightness of the dashboard lights

[0014] An image sensor 2 (camera) is arranged in the interior of a motor vehicle 1 in the upper area behind the windshield. The space behind the rearview mirror (not shown) which is mounted in this area is preferably used for this purpose. Image sensor 2 points in the direction of vehicle travel and detects the conical traffic zone in front of motor vehicle 1 as indicated. Image sensor 2 is composed of multiple individual sensors for measuring the absolute brightness of the detected traffic zone in a location-selective manner.

[0015] As FIG. 2 shows, image sensor 2 has a nonlinear conversion characteristic. With an increase in light signal L, there is also an increase in voltage U or current I delivered, but slope ΔU/ΔL or ΔI/ΔL decreases. This leads to implementation of a highly dynamic image sensor 2. With a technically limited voltage or current range, a large brightness range can be imaged. It is especially advantageous to use an image sensor with a logarithmic conversion characteristic, because then the contrast resolution is constant over a brightness range of multiple decades.

[0016] Image sensor 2 supplies an electric “surface” image signal to an analyzer unit 3 which analyzes the image signal with the goal of measuring the ambient brightness. The ambient brightness signal or a dashboard brightness signal derived from it is relayed over a bus line 8 to a control unit 4 which controls dashboard lights 5. Analyzer unit 3 can weight the image signal of image sensor 2 according to preselected algorithms of object detection and use it for a suitably adjusted control of dashboard lights 5. Additional sensors 6 optionally provided for object detection or for other functions send additional information for adjusting the control signals for control unit 4 of dashboard lights 5 over a bus line 8 of analyzer unit 3. Sensors 6 may be used for object detection and for detection of the condition of the vehicle lighting.