Vehicle equipment control with semiconductor light sensors

Details Vehicle equipment control with semiconductor light sensors Vehicle equipment control with semiconductor light sensors

2002-02-28

2004-06-01

Sikder, Mohammad Yunus (Department: 2872)

Optical: systems and elements

Glare or unwanted light reduction

With mirror

C359S601000, C359S602000, C359S605000, C359S608000

Reexamination Certificate

active

06742904

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to automatically controlled automotive vehicle equipment of the type using light sensors to monitor light levels.
BACKGROUND ART
The continuing reduction in the size and cost of electronic circuits, in particular microprocessors, makes possible the inclusion of an increasing amount of intelligence for the automatic control of automotive vehicle equipment. Examples include: rearview mirrors that adjust their reflectivity in response to the levels of ambient light and glare from other vehicles; moisture on windows sensed and removed by automatic wipers, defrosters, defoggers, and the like; windows that automatically close when rain is detected; headlamps switched in response to ambient light levels; and heating and cooling of the vehicle passenger compartment automatically adjusted in anticipation of changes in external conditions.
Systems that automatically control automotive equipment can advantageously employ one or more sensors for measuring light levels. Automatically dimmable rearview mirrors, and in particular electrochromic mirrors, using light sensors, are described in U.S. Pat. No. 4,902,108 to Byker; U.S. Pat. No. 5,724,187 to Varaprasad et al.; U.S. Pat. No. 5,928,572 to Tonar et al.; and U.S. Pat. No. 6,020,987 to Baumann et al. In the case of mirrors having automatic reflectivity control, such as electrochromic mirrors, it is advantageous to use sensors to detect both forward and rear light levels. Among the dual sensor designs proposed include those described in U.S. Pat. No. 3,601,614 to Platzer; U.S. Pat. No. 3,746,430 to Brean et al.; U.S. Pat. No. 4,580,875 to Bechtel et al.; U.S. Pat. No. 4,793,690 to Gahan et al.; U.S. Pat. No. 4,886,960 to Molyneux et al.; U.S. Pat. No. 4,917,477 to Bechtel et al.; U.S. Pat. No. 5,204,778 to Bechtel; U.S. Pat. No. 5,451,822 to Bechtel et al.; and U.S. Pat. No. 5,715,093 to Schierbeek et al. A vision system is disclosed in U.S. patent application Ser. No. 09/001,855, entitled “VEHICLE VISION SYSTEM,” filed by Jon H. Bechtel et al. on Dec. 31, 1997, the disclosure of which is incorporated herein by reference thereto.
Various moisture detectors are also known that employ a light sensor. Examples of such detectors include those described in U.S. Pat. No. 5,821,863 to Schröder et al.; U.S. Pat. No. 5,796,106 to Noack; U.S. Pat. No. 5,661,303 to Teder; U.S. Pat. No. 5,386,111 to Zimmerman; U.S. Pat. No. 4,973,844 to O'Farrell et al.; U.S. Pat. No. 4,960,996 to Hochstein; U.S. Pat. No. 4,930,742 to Schofield et al.; U.S. Pat. No. 4,871,917 to O'Farrell et al.; U.S. Pat. No. 4,867,561 to Fujii et al.; U.S. Pat. No. 4,798,956 to Hochstein; U.S. Pat. No. 4,652,745 to Zanardelli; and RE No. 35,762 to Zimmerman. A moisture detection system is disclosed in U.S. Pat. No. 5,923,027, entitled “MOISTURE SENSOR AND WINDSHIELD FOG DETECTOR USING AN IMAGE SENSOR,” issued on Jul. 13, 1999, to Joseph S. Stam et al., the disclosure of which is incorporated herein by reference thereto.
A variety of systems for controlling headlamps using a light sensor are also known, including those described in U.S. Pat. No. 4,891,559 to Matsumoto et al.; U.S. Pat. No. 5,036,437 to Macks; U.S. Pat. No. 5,235,178 to Hegyi; U.S. Pat. No. 5,537,003 to Bechtel et al.; U.S. Pat. No. 5,416,318 to Hegyi; U.S. Pat. No. 5,426,294 to Kobayashi et al.; U.S. Pat. No. 5,666,028 to Bechtel et al., and U.S. Pat. No. 5,942,853 to Piscart. Such systems employ a light sensor to detect conditions under which the headlamp light intensity is altered. Other systems are disclosed in U.S. Pat. No 5,837,994, entitled “CONTROL SYSTEM TO AUTOMATICALLY DIM VEHICLE HEAD LAMPS,” issued Nov. 17, 1998, to Joseph S. Stam et al.; U.S. Pat. No. 5,990,469, entitled “CONTROL CIRCUIT FOR IMAGE ARRAY SENSORS,” issued to Jon H. Bechtel et al. on Nov. 23, 1999, and U.S. Pat. No. 5,998,929, entitled “CONTROL SYSTEM FOR AUTOMOTIVE VEHICLE HEADLAMPS AND OTHER VEHICLE EQUIPMENT,” issued on Dec. 7, 1999, to Jon H. Bechtel et al., the disclosures of which are incorporated herein by reference thereto.
Such automatically controlled equipment may employ one or more cadmium sulfide (CdS) cell as a light sensor. CdS cells are photosensitive resistors exhibiting increasing conductance with increasing light levels. CdS cells offer some advantages, such as being relatively low in cost, demonstrating good sensitivity to low light levels, and providing a spectral response somewhat similar to that of the human eye. However, equipment employing such cells can not fully realize these advantages due to other characteristics of CdS cells, such as: a high degree of variance between cells, slow response at low light levels, poor environmental stability, limited dynamic range, and difficulty being assembled in automated electronic manufacturing processes and equipment. Rearview mirrors employing CdS cells for sensing ambient light and glare may incorporate the CdS cell into a full or partial bridge to increase the dynamic range of the cell. However, the bridge output will only represent a fixed relationship between an ambient light level and a glare level, which fixed relationship is often not appropriate throughout the range of ambient light levels monitored.
Vehicle equipment, such as automatic dimming mirrors, has also used one or more discrete photodiodes configured as a light-dependent current source. Relative to equipment using CdS cells, equipment using photodiodes will experience less operational variance due to the light sensor part performance, will demonstrate better environmental stability, and will be more easily adapted to automated manufacturing. However, photodiodes themselves are relatively expensive and produce very low currents at low light levels. These low currents require the inclusion of special amplification techniques to achieve a useful signal for the electronic components, increasing the cost and complexity of the equipment.
Another approach to providing equipment responsive to ambient light is described in U.S. Pat. No. 5,760,962 issued to Schofield et al. wherein an automatically dimmable mirror is disclosed that incorporates a large imaging array to gather light from behind and beside the vehicle. Each light transducer, or pixel, within the array views a separate area within the target spatial distribution of the light sensor. The equipment measures ambient light by examining pixels generally directed sideways. The cost of the imaging array, the required lens, and the complicated signal processing logic make equipment using the imaging array prohibitively expensive for many automotive applications. An additional problem is that light collected from a side view less accurately represents the ambient light experienced by the vehicle operator than does light from a forward view.
One difficulty with providing equipment employing light sensors is the occurrence of operating anomalies when the equipment is subject to high temperatures. Some equipment employs light sensors that are extremely non-linear at high temperatures. Other equipment may suffer a permanent change in operating characteristics after being exposed to high temperatures. Such a permanent change can occur in equipment using a CdS cell exposed to prolonged sun on a hot day, such as prolonged exposure to temperatures in excess of 87° C. Sensors may even provide completely false readings, such as by identifying a bright light condition in low light conditions, due to excessive thermal noise. Traditionally, the only way to deal with this problem has been to incorporate a temperature sensor and additional electronics into the vehicle equipment to compensate for sensor performance changes resulting from temperature variations. Such electronics add cost and complexity to the equipment.
It can thus be seen that a difficulty with implementing automatically controlled equipment is accommodating the light sensor. Inclusion of light sensors typically introduces complex and costly manufacturing processes. However, the equipment needs to be inexpensive to fall within the range deeme

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