Patent Publication Number: US-6218934-B1

Title: Mini-trip computer for use in a rearview mirror assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a rearview mirror assembly for use in a motor vehicle and, more particularly, to a mini-trip computer embedded in a center-mounted rearview mirror assembly. 
     2. Discussion 
     Rearview mirrors, both center-mounted inside a vehicle passenger compartment and side-mounted outside the passenger compartment, are used to enable a driver of the vehicle to observe objects that are behind the vehicle while the driver&#39;s gaze remains directed generally forward. Such mirrors are ubiquitous means for providing actual visual images of objects that are behind the vehicles. 
     A significant amount of data is also presented to a driver of the vehicle in analog form (e.g., by gages) and/or in digital form (e.g., by digital display instrumentation). As recognized by the present invention, it can be advantageous to combine data sources not only to realize manufacturing cost savings, but also to promote safety and effectiveness in data presentation. In the context of a rearview mirror, the present invention recognizes that most drivers readily accept and use mirrors to know what objects are behind their vehicles, thereby improving driving safety. The present invention further recognizes that the use of mirrors can be promoted even further by presenting additional data on the mirrors to stimulate relatively more frequent use of the mirrors. Moreover, the effectiveness of the presentation of the data is improved by presenting data on a mirror that otherwise would be presented at a perhaps less convenient location in the vehicle. In other words, the present invention recognizes that it is possible that data presented on a mirror is more accessible than data presented in other locations that would not otherwise attract the driver&#39;s attention. 
     Nevertheless, problems exist with locating display devices on rearview mirror assemblies which may otherwise be exposed to considerable ambient light, such as in a convertible top vehicle. Therefore, it is also desirable to provide a display device for use in a mirror assembly, such as a liquid crystal display device, which does not exhibit diminished contrast when exposed to considerable ambient light. 
     It is further known to incorporate electronic components into the housing of a vehicle mirror assembly. For instance, it is known to mount courtesy lights and associated switches in the casing of an interior mirror assembly. In addition, electrochromatic rearview mirrors typically incorporate light sensors in order to detect light levels in the vicinity of the vehicle. In each of these cases, the electronic components are stand alone components which operate independent from the remainder of the vehicle data communication system. 
     On the contrary, a trip computer needs additional information from extraneous vehicle control modules in order to determine vehicle trip information. Most trip computers are located in the overhead console or in the instrument panel of the vehicle, and thus can be easily interfaced to the vehicle data communication system. However, in some convertible top vehicles there is no room to package a trip computer in the instrument panel of the vehicle. 
     Therefore, it is desirable to provide a rearview mirror assembly which incorporates a trip computer. In order to receive extraneous vehicle trip information, additional wires would have to be run from the trip computer in the mirror assembly to the instrument panel or other electronic components. As a result, the manufacturer would likely incur substantial additional costs for incorporating a trip computer into the mirror assembly. Thus, it is also desirable to interconnect the trip computer embedded in the mirror assembly via a single wire bus network to the other vehicle control modules in the vehicle. In this way, the trip computer no longer needs to be hardwired to receive an ignition on signal which is used to power up the mirror assembly. Moreover, the trip computer has access to any additional information needed for determining and displaying vehicle trip information. Lastly, it is desirable to provide a wake-up circuit which upon detection of bus activity over the bus network is able to power up the trip computer. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a trip computer is incorporated into a rearview mirror assembly for displaying trip information to the driver of a motor vehicle. The mirror assembly includes a reflective element, a housing for the reflective element, a trip computer for determining vehicle trip information, and a display device for displaying the vehicle trip information, where the display device is electrically connected to the trip computer and embedded within the reflective element. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of the interior of a motor vehicle; 
     FIG. 2 is a front perspective view of a rearview mirror assembly in accordance with the present invention; 
     FIG. 3 is a rear perspective view of the rearview mirror assembly of the present invention; 
     FIG. 4 is a cross-sectional view, taken along A—A of FIG. 2, through the center of the rearview mirror assembly of the present invention; 
     FIG. 5 is a cross-sectional view, taken along B—B of FIG. 2, through the display device of the rearview mirror assembly of the present invention; 
     FIG. 6 is a cross-sectional view, taken along B—B of FIG. 2, of an alternative embodiment of the rearview mirror assembly of the present invention; 
     FIG. 7 is a block diagram showing the components of a vehicle data communication system in accordance with the present invention; and 
     FIG. 8 is a schematic of a wake-up circuit for use in the trip computer of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a schematic view illustrating various rearview mirror assemblies which are adapted in a conventional manner to be installed in a motor vehicle. For instance, an interior center-mounted rearview mirror assembly  10  couples to the front windshield via a support  11  which extends from the mirror assembly  10 . As will be apparent to those skilled in the art, the rearview mirror assembly  10  faces the rear of the vehicle and can be viewed by the driver of the vehicle. While the following description is provided with reference to an interior center-mounted rearview mirror assembly, it is readily understood that the explanation is applicable to other interior and/or external mirror assemblies which are for use in a motor vehicle. 
     Referring to FIG. 2, the rearview mirror assembly  10  includes a mirror member  12 , a housing  14 , and a plurality of switches  18 , and a display device  20  embedded into the mirror member  12 . The switches  18  are used to operate one or more electronic components associated with the mirror assembly  10 , such as map courtesy lights (not shown) mounted on the underside of the mirror assembly  10 . 
     In a first preferred embodiment, an electrochromic mirror is used as the mirror member  12  for the rearview mirror assembly  10 . In general, an electrochromic mirror automatically dims to eliminate unwanted headlight glare from following vehicles. To do so, the electrochromic mirror is comprised of a relatively thin electrochromic medium sandwiched and sealed between two glass elements. More specifically, the electrochromic medium is disposed in a sealed chamber defined by a transparent front glass element, a peripheral edge seal and a rear glass element. Conductive layers are provided on the inside of the front and rear glass elements. The conductive layers are connected to electronic circuitry which is operable to electrically energize the electrochromic medium. The rear glass element also includes a reflective layer which provides the reflective characteristic of the mirror. In this case, the mirror assembly further includes a drive voltage supply for the electrochromic medium, an ambient light sensor, a glare light sensor, as well as their associated electronic circuitry. 
     In operation, a forward-facing ambient light sensor recognizes low ambient light levels and signals to the electrochromic mirror to begin detecting unwanted glare. A rearward-facing glare sensor then detects glare from vehicles traveling behind the vehicle and sends a voltage to the electrochromic medium in proportion to the amount of glare detected. As a result, the mirror dims in proportion to the glare. When the glare is no longer detected, the glare sensor ceases to provide a voltage to the mirror. Although the present invention is not limited to an electrochromic mirror, an exemplary electrochromic mirror is manufactured by the Gentex Corporation of Zeeland, Mich. 
     There are a variety of known housings for rearview mirror assemblies, but a preferred housing  14  is shown in FIGS. 2-5. In this case, the housing  14  is a single-piece casing molded from a thermoplastic material. A bezel  16  is used to conceal the peripheral edge portions of the mirror member  12  as well as to couple the mirror member  12  to the housing  14 . Thus, the bezel  16  extends around the entire periphery of an opening in the housing  14  and attaches to an interior surface of the housing  14 . There are a variety of known bezel designs which may be used to couple the mirror member  12  to the housing  14 . 
     The housing  14  is further adapted to support a circuit board  22 . The circuit board  22  is preferably a conventional circuit board, such that it includes a series of metal traces deposited on a substrate. In this way, various electronic components and circuitry can be incorporated into the rearview mirror assembly  10 . In accordance with the present invention, a trip computer  30  for determining vehicle trip information is coupled to the circuit board  22 . A trip computer generally provides the driver with vehicle trip information, including but not limited to outside ambient temperature, compass reading, average fuel economy, instantaneous fuel economy, a trip odometer reading and elapsed ignition on time. One skilled in the art will readily recognize that extraneous vehicle information is needed for determining the above-described vehicle trip information at the trip computer  30 . As will be more fully explained below, the trip computer  30  is therefore electrically connected via a bus network to the vehicle data communication system. An exemplary mini-trip module for use in a mirror assembly is available from DaimlerChrysler of Auburn Hills, Mich. 
     A display device  20  is used for displaying the vehicle trip information to the driver. Thus, the display device  20  is electrically connected to the trip computer  30 . As shown in FIG. 5, the display device  20  is positioned behind the mirror member  12 , such that a section of its reflective material is partially removed to exposed the display device  22  to the driver. The display device  20  is coupled to a second display circuit board  24 , where the housing  14  is adapted to support the second circuit board  24 . Although a vacuum fluorescent display is presently preferred, this is not intended as a limitation on the broader aspects of the present invention. On the contrary, other types of display devices may be suitable, including liquid crystal displays, field emission displays and light emitting diode displays. 
     An alternate embodiment of the rearview mirror assembly  40  is shown in FIG.  6 . To improve high ambient daylight visibility and reduce electromagnetic interference inherent with the drive power supply associated with VF display devices, a liquid crystal display (LCD) device  42  is incorporated into the rearview mirror assembly  40 . Although different types of LCD devices may be incorporated into the present invention, an exemplary LCD device is manufactured by Optrex America, Inc. of Detroit, Mich. 
     Again, the rearview mirror assembly  40  includes a mirror member  44  and a housing  46 , where the reflective member  44  couples to an interior surface of the housing  46 . As shown, the LCD device  42  is positioned behind the mirror member  44 , such that a section of its reflective material is partially removed to exposed the LCD device  22  to the driver. In this case, the LCD device  42  is coupled via two or more soldering pins  47  to a circuit board  48 . The circuit board  48  is in turn coupled to the interior surface of the housing  46 . 
     Two or more sub-miniature light emitting diodes (LEDs)  52  serve as the light source for the LCD device  42 . The LEDs  52  are also coupled to the circuit board  48 . As shown, a light shield  54  for enclosing the LEDs  52  is positioned between the reflective member  44  and the circuit board  48 . In this way, the light shield  54  is used to eliminate any ambient light which may diminish the contrast of the LCD device  42 . An anti-rattle pad  56  for reducing vibrations may be positioned between the light shield  54  and the mirror member  44 . It is also noteworthy that an incandescent lamp may be used in place of the LEDs. In this case, a parabola surface may be used to focus and direct the light towards the LCD device  42 . 
     In accordance with the present invention, a vehicle data communication system  70  is depicted in FIG.  7 . In order to receive extraneous vehicle trip information, the trip computer  30  is interconnected to other vehicle control modules within the vehicle. For instance, a body control module  72 , an engine control module  74 , a transmission control module  76  and other vehicle control modules  78  may communicate with the trip computer  30  using a bus network architecture. The various control modules communicate with each other via messages whose structure and characteristics are defined by a known communication protocol (e.g., the SAE J1850 standard). A single wire serial data communication network or bus network  80  is used to carry the messages between the vehicle control modules. As will be apparent to one skilled in the art, a two wire bus network might also be used to interconnect the modules. Each vehicle control module usually includes a microprocessor or microcontroller and its associated bus interface circuitry as is well known in the industry. 
     In accordance with the present invention, the trip computer  30  receives vehicle speed, odometer information and outside air temperature information from the engine control module  74 . This information is then used to calculate at least some of the vehicle trip information. In addition, the trip computer  30  receives an ignition on message from the body control module  72 . The ignition on message may be used by the trip computer  30  to power up its display device and/or the electrochromic mirror. 
     Furthermore, by interfacing with other vehicle control modules, the trip computer  30  is able to incorporate other enhanced functionality into the mirror assembly  10 . For instance, the trip computer  30  may receive gear selection information from the transmission control module  76 . Upon detecting that the vehicle is in reverse, the trip computer  30  may terminate the anti-glare feature of an electrochromic mirror. The trip computer  30  may also transmit information to other vehicle control modules. For example, when a courtesy map light is turned on, a message is sent by the trip computer  30  to the body control module  72 . In the event the ignition is turned off and the light is inadvertently left on by the driver, the light can be turned off as part of a typical time-out function provided by the body control module  72 . By interfacing the trip computer with other vehicle control modules, it is envisioned that other functions may be incorporated into the mirror. 
     In order to power up the trip computer, the present invention utilizes a wake-up circuit which is responsive to any bus activity occurring in the vehicle data communication system  70 . A preferred embodiment of a wake-up circuit  90  is shown in FIG.  8 . The wake-up circuit  90  includes a signal input stage  92 , a bus detection stage  94 , a noise isolation stage  96 , and a signal output stage  98 . Upon detecting bus activity on the bus network  80 , the bus detection stage  94  switches on the input stage  92 . As a result, the input stage  92  provides voltage to the output stage  98  which in turn applies power to the trip computer  30 . Once powered up, the trip computer  30  then waits for the body control module  72  to send an ignition on signal over the bus network  80 . When the ignition on signal is received by the trip computer  30 , it will in turn power up the display device  20 . In this way, the trip computer  30  does not need to be directly hardwired to receive an ignition on signal from the vehicle data communication system  70 . 
     More specifically, the bus detection stage  94  is comprised of transistor Q 9  which electrically connects through a resistor R 44  to the bus network  80 . A bias voltage on the base of transistor Q 9  indicates that messages are being sent (i.e., bus activity) over the bus network  80 . The bias voltage received by the bus detection stage  94  turns on transistor Q 9 . In addition, the emitter of transistor Q 9  is coupled to ground and the collector of transistor Q 9  is connected via resistor R 41  to the input stage  92 . 
     The input stage  92  provides a switching function for an input voltage source  102 . The input stage  92  is further defined as a MOSFET device O 8 , such that the drain of MOSFET device O 8  receives an input voltage V i  from the input voltage source  102 . When transistor Q 9  is turned on, the MOSFET device O 8  is switched on. To do so, the collector of transistor Q 9  is coupled through resistor R 41  to the gate of MOSFET device O 8 . When switched on, MOSFET device O 8  provides the input voltage V i  to the remainder of the wake-up circuit. In this case, the input voltage source  102  is supplied by the 12-volt battery of the motor vehicle. As will be apparent to one skilled in the art, the input stage  92  further includes known circuitry positioned between the input voltage source  102  and the source of MOSFET device O 8  for preventing voltage spikes in the circuit. 
     Next, a noise isolation stage  96  is positioned between the input stage  92  and the output stage  98 . The noise isolation stage  96  includes a series pass transistor Q 6 , where the collector of the second transistor is coupled to the source of MOSFET device O 8  from input stage  92 . The emitter of the second transistor is then coupled to the output stage  98 . In addition, the source of MOSFET device O 8  may be coupled through switches to other electronic components associated with the mirror assembly (e.g., courtesy lights). In this way, these components receive a 12-volt power supply. Again, the noise isolation stage  96  further includes known circuitry for preventing voltage spikes in the circuit as shown in FIG.  8 . 
     Lastly, the output stage  98  provides power to the logic circuitry associated with the trip computer  30 . In particular, the series pass transistor Q 6  drives a 5-volt voltage regulator U 2  on, thereby applying an output voltage V o  to the trip computer  30 . Thus, the series pass transistor Q 6  of the noise isolation stage  96  isolates the voltage regulator U 2  from any noise occurring in the earlier stages of the circuit. 
     While the above description constitutes the preferred embodiment of the invention, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope or fair meaning of the accompanying claims.