Abstract:
A method of monitoring faults in a vehicle bulb circuit including bulb and a fuse. The method includes detecting acceleration of the vehicle and comparing the acceleration of the vehicle to a limit. Based on the relationship of the acceleration to the limit, it is determined whether a fault exists in the bulb circuit. An indicator is activated in response to detecting a fault in the bulb circuit. A system for implementing the method is also disclosed.

Description:
TECHNICAL FIELD 
     This invention relates to a method and system for indicating bulb circuit failure. 
     BACKGROUND OF THE INVENTION 
     Vehicles such as automobiles and motorcycles employ a number of bulbs to signal driver actions to other drivers, pedestrians, etc. Such bulbs include brake lamps, turn signal lamps and reverse lamps. Such bulbs are part of a bulb circuit which typically includes a fuse for protecting the bulb circuit wiring in the event of a short circuit. Operators of vehicles are not always aware of a failure in the bulb circuit and thus do not know to obtain service for the bulb circuit. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is a method of monitoring faults in a vehicle bulb circuit including a bulb and a fuse. The method includes detecting acceleration of the vehicle and comparing the acceleration of the vehicle to a limit. Based on the relationship of the acceleration to the limit, it is determined whether a fault exists in the bulb circuit. An indicator is activated in response to detecting a fault in the bulb circuit. A system for implementing the method is also disclosed. 
    
    
     The above described and other features are exemplified by the following figures and detailed description. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the Figures wherein like elements are numbered alike. 
     FIG. 1 is a schematic diagram of an exemplary system for indicating bulb circuit failure. 
     FIG. 2 is a flowchart of an exemplary main control loop. 
     FIG. 3 is a flowchart of an exemplary process for setting a check done flag. 
     FIG. 4 is a flowchart of an exemplary process for monitoring faults in a bulb circuit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a schematic diagram of an exemplary system  10  for indicating bulb circuit failure. The bulb circuit includes a fuse  12  connected to a bulb  14 . When switch  16  is closed, current flows from source  13 , through fuse  12  to illuminate bulb  14 . In an exemplary embodiment, bulb  14  is a brake indicator bulb in a vehicle (e.g., automobile, motorcycle) and switch  16  is closed when the brake pedal is depressed. 
     A control system  18  has an input terminal  20  connected to one terminal of bulb  14  through a diode  22 . At least one sensor input terminal  23  receives vehicle parameters such as a speed signal from a speed sensor. The control system  18  may correspond to one or more existing vehicle control systems such as a cruise control system, anti-lock brake system, traction control system, drive train control system, chassis control system, etc. The control system includes an indicator  24  that may be illuminated when the control system detects a failure in the bulb circuit. In an exemplary embodiment, the control system  18  is a microprocessor-based control system executing steps described herein in response to a computer program in a storage medium. 
     Input terminal  20  is coupled to a voltage (e.g., 12 volts) through a resistance  26 . In normal operation, when switch  16  is open, a current flows through resistor  26 , through diode  22  and bulb  14 . The current is small and thus bulb  14  does not light. The control system  18  receives a low voltage at input terminal  20 . When switch  16  is closed, current flows from a voltage source  13 , through fuse  12  to bulb  14  and has a magnitude sufficient to illuminate bulb  14 . In this mode, the diode  22  is non-conductive. Thus, the voltage at input terminal  20  is a relatively high voltage. 
     Detection of failure of the bulb circuit is performed by the control system  18  by monitoring voltage at input terminal  20  along with other vehicle parameters. Operation of the control system  18  is described with reference to FIGS. 2-4. FIG. 2 is a flowchart of a main control loop  100  executed by the control system  18 . The main control loop  100  may be executed periodically (e.g., once per millisecond). The process begins at step  102  where it is determined whether the control system  18  is active with the indicator  24  actuated. In this mode, the control system  18  is performing its primary function (e.g., cruise control) and thus does not monitor for faults in the bulb circuit. The control system may execute multiple processes simultaneously, but in the embodiment shown in FIG. 2, if the primary function is active, then the bulb circuit monitoring is not performed. In this scenario, the main loop ends at step  112 . 
     If the primary function is not enabled at step  102 , flow proceeds to step  104  where control system  18  determines if a fuse fault count has exceeded a fuse fault limit. As described in further detail herein, a fuse fault count is incremented or cleared depending on operating parameters of the vehicle (e.g., acceleration) and a signal indicative of whether the bulb  14  is illuminated. If the fuse fault count exceeds the fuse fault limit, flow proceeds to step  106  where the control system  18  is disabled. At step  108 , the indicator  24  is actuated to indicate a fault. In the embodiment in FIG. 2, the indicator  24  is flashed with a period (e.g., 250 ms) to indicate a fault in the bulb circuit. Alternatively, the indicator could appear in a different color or an audible tone could be generated. The indicator  24  may also be actuated in a first manner to indicate a fuse fault and a second manner to indicate a bulb fault. For example, indicator  24  may be flashed in yellow to indicate a bulb fault and flashed in red to indicate a fuse fault. 
     If the fuse fault count has not exceeded the fuse fault limit at step  104 , flow proceeds to step  110  where a bulb fault count is compared to a bulb fault limit. As described in further detail herein, a bulb fault count is incremented or cleared depending on operating parameters of the vehicle (e.g., acceleration) and a signal indicative of whether the bulb  14  is illuminated. If the bulb fault count exceeds the bulb fault limit, flow proceeds to step  108  where the indicator  24  is activated to indicate a fault in the bulb circuit. If the bulb fault count does not exceed the bulb fault limit, the main loop  100  terminates at step  112 . The main loop may be executed periodically (once per second) to continuously monitor bulb circuit faults. 
     FIG. 3 depicts an exemplary process  200  for setting the status of a check done flag. The process is periodically implemented by control system  18  (e.g., every 125 ms). The check done flag indicates that the monitoring of bulb circuit faults has been performed. The process begins at step  202  where the acceleration of the vehicle is determined. The acceleration may be obtained from a sensor (e.g., accelerometer) or computed from another value (e.g., derivative of speed signal). At step  204 , the acceleration is compared to a steady state range. If the acceleration is within a range of moderate deceleration (e.g., −1 mph/sec) and moderate acceleration (e.g., 0.996 mph/sec), then the vehicle is traveling at a substantially uniform speed and the check done flag is cleared at step  206  and the process terminates at step  208 . If the vehicle is not traveling at a substantially uniform speed as indicated by the acceleration, then the process ends at step  208  without clearing the check done flag. The effect of process  200  is that a period of uniform acceleration clears the check done flag. As discussed further with respect to FIG. 4, this allows the control system to monitor bulb circuit failure the next time the vehicle experiences significant positive or negative acceleration. 
     FIG. 4 depicts an exemplary bulb circuit monitoring process  300  implemented by control system  18 . The process is implemented periodically (e.g., every 16 ms). The process begins at step  302  where it is determined whether bulb circuit fault monitoring is enabled. Whether the bulb circuit monitoring function is enabled may be a customer-specified option. If the bulb circuit monitoring function is not enabled, then flow proceeds to step  304  where the bulb fault count and the fuse fault count are cleared and the process terminates at step  306 . 
     If the bulb circuit monitoring process is enabled, flow proceeds to step  308  where it is determined if there have been recent changes in any switch inputs to control system  18 . Switch inputs include, but are not limited to, inputs such as switch  16 . For example, if control system  18  is a cruise control unit, then switch inputs include brake switch  16  along with other cruise control inputs such as set, resume, etc. If recent changes are detected (e.g. change of state within the past 16 ms) at step  308 , the process terminates at step  306 . This allows the control system  18  to respond to user inputs before executing the bulb circuit monitoring process. 
     If no recent switch changes are detected, flow proceeds to step  310  where the vehicle acceleration is compared to a deceleration limit. If the acceleration is less than the deceleration limit, this indicates that the vehicle is experiencing a significant deceleration. If so, at step  312  it is determined whether bulb  14  has been illuminated. This is determined by monitoring the voltage at input terminal  20 . When significant negative acceleration is detected, this indicates that switch  16  is closed (i.e., brakes are applied). If fuse  12  is operational, diode  22  will be placed in a non-conductive state and a high voltage will be at input terminal  20 . In FIG. 4, a high voltage at input terminal  20  indicates that the bulb  14  has been illuminated. In this situation, flow proceeds to step  314  where fuse fault counter is reset to zero and the process ends at step  306 . 
     If at step  312  it is determined that bulb  14  has not been illuminated, flow proceeds to step  316  where the status of the check done flag is detected. If the check done flag indicates that the bulb circuit has already been monitored during this period of deceleration, the process terminates at step  306 . Thus, the check done flag prevents the fuse fault count from being incremented more than once during any period of deceleration. 
     If the check done flag is not set at step  316 , flow proceeds to step  318  where the fuse fault count is incremented and the check done flag is set. Since the check done flag is set, the fuse fault count will not be incremented further during the same period of deceleration. 
     If at step  310  significant deceleration is not detected, flow proceeds to step  320  where it is determined if the acceleration exceeds an acceleration threshold. If the acceleration is greater than the acceleration limit, this indicates that the vehicle is experiencing a significant acceleration indicating that the bulb  14  should not be illuminated. If so, at step  322  it is determined whether bulb  14  has been illuminated. This is determined by monitoring the voltage at input terminal  20 . When significant positive acceleration is detected, this indicates that switch  16  is open (e.g., brakes are not applied). If bulb  14  is operational, diode  22  will be placed in a conductive state and a low voltage will be at input terminal  20 . In this situation, the low voltage at input terminal  20  causes step  322  to be answered in the negative and flow proceeds to step  324  where the bulb fault count is reset to zero and the process ends at step  306 . 
     If the bulb  14  is burnt out, there is no current path through diode  22  and a high voltage will be present at input terminal  20 . In this situation, flow proceeds to step  326  where the status of the check done flag is detected. If the check done flag indicates that the bulb circuit has already been monitored during this period of acceleration, the process terminates at step  306 . Thus, the check done flag prevents the bulb fault count from being incremented more than once during any period of acceleration. 
     If the check done flag is not set at step  326 , flow proceeds to step  328  where the bulb fault count is incremented and the check done flag set. Since the check done flag is set, the bulb fault count will not be incremented further during the same period of acceleration. 
     As discussed with reference to FIG. 2, the bulb fault count and the fuse fault count are used in the main control loop  100 . If either the bulb fault count or the fuse fault count exceeds respective limits, the indicator  24  is actuated to notify the operator of a fault in the bulb circuit. 
     While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.