Digital electrochromic mirror system

Abstract

An electrochromic rearview mirror system for a vehicle includes an electrochromic reflective element having an electrochromic cell, wherein the reflective element colors to a partial reflectance level in response to a drive signal applied to the cell. The rearview mirror assembly additionally includes a drive circuit which applies a pulsed drive signal to the electrochromic cell in order to establish the partial reflectance level of the reflective element. The drive circuit controls the partial reflectance level as a function of the duty cycle of the pulsed drive signal, which has a pulse repetition rate of at least approximately 10 cycles per second and preferably at least approximately 20 cycles per second. The drive circuit additionally adjusts the amplitude of the pulses as a function of the voltage developed across the electrochromic cell.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
     
         1 . An electrochromic rearview mirror assembly for a vehicle comprising: 
 an electrochromic reflective element having an electrochromic cell wherein said reflective element colors to a partial reflectance level in response to a drive signal applied to said electrochromic cell; and    a drive circuit which applies a pulsed drive signal to said electrochromic cell in order to establish said partial reflectance level of said reflective element said drive circuit controlling said partial reflectance level at least as a function of the duty cycle of said pulsed drive signal.    
     
     
         2 . The electrochromic rearview mirror assembly in  claim 1  wherein said drive circuit applies a direct current signal to said electrochromic cell during one portion of each duty cycle and sinks a direct current signal from said electrochromic cell during another portion of each duty cycle.  
     
     
         3 . The electrochromic rearview mirror assembly in  claim 2  wherein said drive circuit controls the amplitude of said pulsed drive signal.  
     
     
         4 . The electrochromic rearview mirror assembly in  claim 3  wherein said drive circuit monitors the voltage across said electrochromic cell and adjusts at least one of the direct current signal applied during subsequent pulses and the duty cycle of the pulsed drive signal as a function of the voltage across the electrochromic cell.  
     
     
         5 . The electrochromic rearview mirror assembly in  claim 4  wherein said drive circuit monitors the voltage across said electrochromic cell sampling the voltage near the end of said one portion.  
     
     
         6 . The electrochromic rearview mirror assembly in  claim 2  wherein said drive circuit monitors the voltage across said electrochromic cell between said portions of each duty cycle when said drive circuit is neither applying a direct current signal to said cell nor sinking a direct current signal from said cell in order to control at least one of the amplitude and the duty cycle of said pulsed drive signal.  
     
     
         7 . The electrochromic rearview mirror assembly in  claim 1  wherein said drive circuit monitors the voltage across said electrochromic cell and adjusts at least one of the amplitude of said drive signal during subsequent pulses and the duty cycle of the pulsed drive signal as a function of the voltage across the electrochromic cell.  
     
     
         8 . The electrochromic rearview mirror assembly in  claim 1  wherein said pulsed drive signal has a repetition rate of at least approximately 10 cycles per second.  
     
     
         9 . The electrochromic rearview mirror assembly in  claim 8  wherein said pulsed drive signal has a repetition rate of at least approximately 20 cycles per second.  
     
     
         10 . The electrochromic rearview mirror assembly in  claim 1  wherein said drive circuit comprises a microcomputer.  
     
     
         11 . The electrochromic rearview mirror assembly in  claim 10  further including a display and at least one of a compass and an outdoor temperature sensor, wherein said display displays vehicle heading, outdoor temperature, or both vehicle heading and outdoor temperature.  
     
     
         12 . The electrochromic rearview mirror assembly in  claim 11  wherein said microcomputer controls the intensity of said display.  
     
     
         13 . The electrochromic rearview mirror assembly in  claim 12  including a light sensor which senses light level around the vehicle, wherein said microcomputer adjusts the intensity of said display in response to said light sensor as a function of the light level around the vehicle.  
     
     
         14 . The electrochromic rearview mirror assembly in  claim 13  wherein said display is positioned behind said electrochromic cell, wherein said display is viewed through said electrochromic cell and wherein said microcomputer adjusts the intensity of said display as a function of the reflectance level of said reflective element.  
     
     
         15 . The electrochromic rearview mirror system of  claim 14  wherein said drive circuit monitors the voltage across said electrochromic cell when said cell is open-circuited in order to determine the reflectance level of said reflective element.  
     
     
         16 . The electrochromic rearview mirror assembly in  claim 13  further including at least one indicator, wherein said microcomputer adjusts the intensity of said at least one indicator in response to said light sensor as a function of the light level around the vehicle.  
     
     
         17 . The electrochromic rearview mirror assembly in  claim 12  wherein said display is positioned behind said electrochromic cell, wherein said display is viewed through said electrochromic cell and wherein said microcomputer adjusts the intensity of said display as a function of the reflectance level of said reflective element.  
     
     
         18 . The electrochromic rearview mirror assembly in  claim 17  wherein said drive circuit monitors the voltage across said electrochromic cell when said cell is open-circuited in order to determine the reflectance level of said reflective element.  
     
     
         19 . An electrochromic rearview mirror assembly for a vehicle, comprising: 
 an electrochromic reflective element having an electrochromic cell, wherein said reflective element colors to a partial reflectance level in response to a drive signal applied to said electrochromic cell; and    a drive circuit which applies a drive signal to said electrochromic cell in order to establish the partial reflectance level of said reflective element, said drive circuit including a source, a digital controller, a switching device responsive to an output of said controller for applying said source to said electrochromic cell and an input of said controller responsive to the voltage developed across said electrochromic cell by said source, wherein said digital controller monitors the voltage developed across said electrochromic cell, adjusts said source, and closes and opens said switching device according to a particular duty cycle in order to control said partial reflectance level.    
     
     
         20 . The electrochromic rearview mirror assembly in  claim 19  wherein said controller adjusts said source in order to cause said voltage developed across said electrochromic cell to extend beyond said predetermined range during transitions between substantially different reflectance levels of said reflective element.  
     
     
         21 . The electrochromic rearview mirror assembly in  claim 19  wherein said source is a voltage divider and wherein said controller adjusts said source by connecting at least one resistor in said voltage divider.  
     
     
         22 . The electrochromic rearview mirror assembly in  claim 21  wherein said at least one resistor includes at least two resistors of substantially different values and wherein said controller adjusts said source by connecting one or the other or both of said at least two resistors in said voltage divider.  
     
     
         23 . The electrochromic rearview mirror assembly in  claim 22  wherein said controller includes outputs operable between at least three different states, wherein said controller additionally adjusts said source by selecting a particular state for connecting one or the other or both of said at least two resistors in said voltage divider.  
     
     
         24 . The electrochromic rearview mirror assembly in  claim 19  including another switching device responsive to an output of said controller for draining charge from said electrochromic cell, wherein said controller alternatingly closes said switching devices according to said particular duty cycle.  
     
     
         25 . The electrochromic rearview mirror assembly in  claim 24  wherein said controller keeps both said switching devices open during a portion of said duty cycle in order to sample residual voltage across said electrochromic cell and thereby determine the reflectance level of said reflective element.  
     
     
         26 . The electrochromic rearview mirror assembly in  claim 19  wherein said controller samples said input when said binary switching device is closed in order to monitor the voltage developed across said electrochromic cell by said source.  
     
     
         27 . The electrochromic rearview mirror assembly in  claim 26  wherein said controller samples said input immediately prior to opening said switching device.  
     
     
         28 . The electrochromic rearview mirror assembly in  claim 19  wherein said digital controller closes and opens said switching device at a repetition rate of at least approximately 10 cycles per second.  
     
     
         29 . The electrochromic rearview mirror assembly in  claim 28  wherein said digital controller closes and opens said switching device a repetition rate of at least approximately 20 cycles per second.  
     
     
         30 . The electrochromic rearview mirror assembly in  claim 19  wherein said digital controller comprises a microcomputer.  
     
     
         31 . The electrochromic rearview mirror assembly in  claim 30  further including a display and at least one of a compass and an outdoor temperature sensor, wherein said display displays vehicle heading, outdoor temperature, or both vehicle heading and outdoor temperature.  
     
     
         32 . The electrochromic rearview mirror assembly in  claim 31  wherein said microcomputer controls the intensity of said display.  
     
     
         33 . The electrochromic rearview mirror assembly in  claim 32  including a light sensor which senses light level around the vehicle wherein said microcomputer adjusts the intensity of said display in response to said light sensor as a function of light level around the vehicle.  
     
     
         34 . The electrochromic rearview mirror assembly in  claim 33  wherein said display is positioned behind said electrochromic cell, wherein said display is viewed through said electrochromic cell and wherein said microcomputer adjusts the intensity of said display as a function the reflectance level of said reflective element.  
     
     
         35 . The electrochromic rearview mirror assembly in  claim 34  wherein said drive circuit monitors the voltage across said electrochromic cell when said cell is open-circuited in order to determine the reflectance level of said reflective element.  
     
     
         36 . The electrochromic rearview mirror assembly in  claim 33  further including at least one indicator, wherein said microcomputer adjusts the intensity of said at least one indicator in response to said light sensor as a function of light level around the vehicle.  
     
     
         37 . The electrochromic rearview mirror assembly in  claim 32  wherein said display is positioned behind said electrochromic cell, wherein said display is viewed through said electrochromic cell and wherein said microcomputer adjusts the intensity of said display as a function the reflectance level of said reflective element.  
     
     
         38 . The electrochromic rearview mirror assembly in  claim 37  wherein said drive circuit monitors the voltage across said electrochromic cell when said cell is open-circuited in order to determine the reflectance level of said reflective element.  
     
     
         39 . An electrochromic rearview mirror assembly for a vehicle, comprising: 
 an electrochromic reflective element having an electrochromic cell, wherein said reflective element colors to a partial reflectance level in response to a drive signal applied to said electrochromic cell; and    a drive circuit which applies a drive signal to said electrochromic cell in order to establish the partial reflectance level of said reflective element, said drive circuit including a digital controller, a first switching device responsive to an output of said controller for applying a source to said electrochromic cell and a second switching device responsive to an output of said controller for draining charge from said electrochromic cell, wherein said controller alternatingly closes said switching devices according to a particular duty cycle in order to control said partial reflectance level at least as a function of said duty cycle, wherein said digital controller closes and opens said switching devices at a repetition rate of at least approximately 10 cycles per second.    
     
     
         40 . The electrochromic rearview mirror assembly in  claim 39  wherein said digital controller closes and opens said switching devices at a repetition rate of at least approximately 20 cycles per second.  
     
     
         41 . The electrochromic rearview mirror assembly in  claim 39  wherein said digital controller comprises a microcomputer.  
     
     
         42 . The electrochromic rearview mirror assembly in  claim 41  further including a display and at least one of a compass and an outdoor temperature sensor, wherein said display displays vehicle heading, outdoor temperature, or both vehicle heading and outdoor temperature.  
     
     
         43 . The electrochromic rearview mirror assembly in  claim 42  wherein said microcomputer controls the intensity of said display.  
     
     
         44 . The electrochromic rearview mirror assembly in  claim 43  including a light sensor which senses light level around the vehicle wherein said microcomputer adjusts the intensity of said display in response to said light sensor as a function of light level around the vehicle.  
     
     
         45 . The electrochromic rearview mirror assembly in  claim 44  wherein said display is positioned behind said electrochromic cell, wherein said display is viewed through said electrochromic cell and wherein said microcomputer adjusts the intensity of said display as a function the reflectance level of said reflective element.  
     
     
         46 . The electrochromic rearview mirror assembly in  claim 45  wherein said drive circuit monitors the voltage across said electrochromic cell when said cell is open-circuited in order to determine the reflectance level of said reflective element.  
     
     
         47 . The electrochromic rearview mirror assembly in  claim 44  further including at least one indicator, wherein said microcomputer adjusts the intensity of said at least one indicator in response to said light sensor as a function of light level around the vehicle.  
     
     
         48 . The electrochromic rearview mirror assembly in  claim 43  wherein said display is positioned behind said electrochromic cell, wherein said display is viewed through said electrochromic cell and wherein said microcomputer adjusts the intensity of said display as a function the reflectance level of said reflective element.  
     
     
         49 . The electrochromic rearview mirror assembly in  claim 48  wherein said drive circuit monitors the voltage across said electrochromic cell when said cell is open-circuited in order to determine the reflectance level of said reflective element.