Patent Publication Number: US-6911905-B2

Title: Device and system for indicating rapid deceleration in vehicles

Description:
RELATED APPLICATIONS 
   This application claims the benefit of and is a divisional of U.S. patent application Ser. No. 09/538,592, filed on Mar. 27, 2000, now U.S. Pat. No. 6,417,767, issued Jul. 9, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field 
   The present invention relates to urgent deceleration indicating devices and systems and, more particularly to devices and systems that augment existing vehicle braking indicating devices and systems. 
   2. Related Art 
   Vehicles have long incorporated brake lights for warning others that the vehicle is decelerating. The brake lights are turned on when the brake pedal is depressed to indicate to the following driver that the vehicle is likely decelerating. However, the brake light merely indicates to the following driver whether the brakes are applied and give no indication as to the urgency of the braking condition or any indication of the magnitude of deceleration of the vehicle. Thus, the following driver must always be alert and realize that any illumination of a vehicle&#39;s brake lights can be a gentle deceleration or a sudden urgent deceleration. 
   Prior devices and systems have been described that detect and indicate the urgency of a braking condition by illumination of a light. Some of these warning devices are self-contained and include some means for detecting deceleration in the primary direction of vehicle motion. For example, these devices use one or more accelerometers to determine vehicle deceleration in the primary direction of vehicle motion. An indication, such as illumination of the light when the deceleration exceeds a threshold, is then provided. 
   Because these devices only detect acceleration and only in one direction, they do not measure acceleration independent of gravitational effects and, thus, are prone to false triggers or trigger failures if the vehicle is not in a horizontal orientation when it urgently decelerates. When the vehicle is tilted, e.g., on a slope, the acceleration due to gravity is sensed by the accelerometer, but is assumed to be driver induced by the control circuit of the device. Thus, because of the sensed acceleration due to gravity, these warning devices will cause a false trigger or will fail to trigger such as when the vehicle is travelling up or down a slope. 
   The prior art also shows that some false triggers or trigger failures may be decreased by warning systems that are responsive to other vehicle operating parameters such as pressure sensed in the hydraulic braking system, wheel velocity or slip sensed by the anti-lock braking system, or distance sensed by a proximity radar system. However, these warning systems are not self-contained, and in addition, require a complex system of multiple sensors with extensive wiring. As a result, these warning systems are difficult and costly to manufacture and install, particularly if retro-fitting existing vehicles. 
   SUMMARY OF THE INVENTION 
   The present invention is therefore directed to a device and system to indicate an urgent deceleration that overcome the above-noted and other disadvantages of prior warning devices and warning systems. The present invention results in a warning device and system that indicate urgent deceleration independent of gravity effects. The device and system are capable of sensing acceleration in at least one direction, for example, the primary direction of vehicle motion and correcting for acceleration forces due to gravity before initiating a warning. In this respect, the Inventors have found that correcting for the acceleration due to gravity, an example of which is described herein, may be employed to render a warning device less prone to false triggering or trigger failures. 
   In one illustrative embodiment of the invention, an urgent deceleration indicating device to selectively activate a warning indicator is disclosed. A sensor system, having a sensor output, is responsive to acceleration in a primary direction of vehicle motion. A controller responds to the sensor system, corrects for gravitational effects, and initiates at least one warning indicator when the acceleration exceeds at least one threshold value. 
   In another illustrative embodiment of the invention, a system for indicating an urgent deceleration condition independently of gravity is provided. The system includes at least one warning indicator suitable for mounting to a vehicle. A sensor system, having a sensor output, is responsive to acceleration in a primary direction of vehicle motion. A controller responds to the sensor system, corrects for gravitational effects, and initiates at least one warning indicator when the acceleration exceeds at least one threshold value. 
   In still another embodiment of the invention, an urgent deceleration indicator is provided. The indicator includes means for indicating a warning and means for detecting acceleration having at least one output. The indicator also includes means responsive to the output of the detecting means. The means for responding also corrects for gravitational effects and initiates the means for indicating when the acceleration exceeds at least one threshold value. 
   In yet another illustrative embodiment of the invention, a device for use in a vehicle to indicate an urgent deceleration condition independently of gravity is provided. The device includes a base constructed and arranged to mount to the vehicle. The base has a first axis which is substantially alignable with a primary direction of vehicle motion. The base also has a second axis which is different from the first axis. The device also includes at least one sensor mounted to the base for sensing acceleration in the first axis. The device includes a controller which communicates with the at least one sensor and corrects for gravitational effects. The controller initiates at least one warning indicator when the acceleration exceeds at least one threshold value. 
   In another illustrative embodiment of the invention, a method for indicating an urgent deceleration condition independently of gravity is disclosed. The method includes the step of detecting acceleration substantially in a primary direction of vehicle motion. The method further includes the steps of correcting for effects due to gravity and comparing the acceleration with at least one threshold value. The method further includes the step of initiating at least one warning indicator when the acceleration exceeds at least one threshold value. 
   In a further embodiment of the invention, a device for use in a vehicle to rearwardly indicate a rapid deceleration of the vehicle is provided. The device includes an elongated array of light emitting diodes extending substantially perpendicular to the longitudinal axis of the vehicle. The device also includes a circuit that has sensor output responsive to acceleration in the direction of the longitudinal axis of the vehicle. The circuit is aligned primarily parallel to and behind the elongated array. 
   Various embodiments of the present invention provide certain advantages and overcome certain drawbacks of prior devices and systems. Embodiments of the invention may not share the same advantages and those that do may not share them under all circumstances. This being said, the present invention provides numerous advantages including the noted advantage of reducing false triggering or trigger failures. 
   Further features and advantages of the present invention as well as the structure and method of making various embodiments of the present invention are described in detail below with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a block diagram of an embodiment of the invention; 
       FIG. 2  is a schematic representation of an embodiment of the coordinate system of one embodiment of the invention; 
       FIG. 3  is a flow chart of an embodiment of the invention; 
       FIG. 4  is a schematic representation of an embodiment of the invention; 
       FIG. 5A  is a front view of an embodiment of the invention; 
       FIG. 5B  is a rear view of an embodiment of the invention; 
       FIG. 6  is a schematic representation of an embodiment of the invention; and 
       FIG. 7  is a block diagram of an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   The present invention is directed to a device and system for indicating rapid deceleration in a vehicle, and more particularly to a device and system that augment existing brake indicating systems to warn the vehicle operator and/or others of an urgent deceleration condition, and method of indicating the same. The disclosed device, system, and method indicate an urgent deceleration independent of gravity effects. The device includes at least one sensor that is responsive to acceleration in the primary direction of vehicle motion. A controller communicates with the sensor and resolves the output from the sensor into an acceleration in the primary direction of vehicle motion and corrects for gravitational effects. The controller initiates a warning when the acceleration exceeds a threshold value and thereby indicates an urgent deceleration condition. It should be noted that the term “acceleration” may be used herein generically to indicate the rate of change of velocity of a moving object. In addition, the term “acceleration” may be used to indicate both an increase in the rate of change of velocity and a decrease in the rate of change of velocity and is used interchangeably with the term “deceleration.” 
   Although the invention for indicating rapid deceleration to which this patent is addressed is discussed below particularly in connection with use in a motor vehicle such as a car, truck, motorcycle, or tractor, it should be appreciated that the present invention is not limited in this respect, and that the aspects of the present invention described below may be used in association with other types of vehicles or machinery. 
     FIG. 1  illustrates one embodiment of an indicating device  10  for indicating rapid deceleration of a vehicle. Indicating device  10  is responsive to acceleration in a first axis that is substantially in the primary direction of vehicle motion X′. As shown in the illustrative embodiment of  FIG. 2 , the primary direction of vehicle motion X′ is along the longitudinal axis of vehicle  24 , i.e., the normal, forward direction of motion of a vehicle  24 . Continuing with  FIG. 1 , device  10  includes an indicator  14  and a sensor system  16 . The sensor system  16  is responsive to acceleration in the primary direction of vehicle motion X′. Controller  20  communicates with sensor system  16 , resolves sensor system  16  output into an acceleration sensed in the primary direction of vehicle motion X′, and corrects for effects due to gravity, using, for example, the pitch angle of the vehicle, as will be further described hereinafter. When travelling up or down a slope, the acceleration due to gravity may be sensed in the X′ direction by sensor system  16 . Thus, the acceleration sensed in the X′ direction is a function of the pitch angle of the vehicle  24 . The Inventors have found that accounting for gravity reduces false initiation of the warning indicator  14  and reduces failures to initiate the warning indicator  14 . It should be noted that the term “indicator failure” is used herein to indicate a false initiation of warning indicator  14  or a failure to initiate warning indicator  14 . 
   If the acceleration exceeds the acceleration threshold value, controller  20  communicates Is with indicator  14  and initiates the warning indicator  14  to indicate the urgent deceleration condition. In one embodiment of the invention, the acceleration threshold is preset and is not adjustable, however, those skilled in the art will recognize the possibility of allowing for adjustment of the acceleration threshold by the vehicle operator or by a certified technician. 
   In one embodiment of the invention, the effects due to gravity sensed in the X′ direction may be calculated using the equation:
 
 X   grav   =M   grav * sin θ  [1]
 
where X grav  is the acceleration due to gravity sensed in the X′ direction, M grav  is the magnitude of acceleration due to gravity, and θ is the pitch angle of the vehicle  24 . In one embodiment of the invention, controller  20  may assume the constant acceleration due to gravity to be equal to 1.0 G. Any variations in the gravity acceleration due to temperature, location, or altitude are substantially negligible. However, the present invention is not limited in this respect and the threshold value may be adjusted based on these or other parameters. If the magnitude of acceleration due to gravity is equal to 1.0 G, then the acceleration due to gravity sensed in the X′ direction is merely the sine of the pitch angle of the vehicle.
 
   In another embodiment of the invention, the controller  20  may use the calculated acceleration due to gravity in the X′ direction to resolve the output of sensor system  16  into an acceleration in the X′ direction independent of gravity effects using the equation:
 
 X   ind   =X −sin θ  [2]
 
where X ind  is the acceleration in the X′ direction independent of gravity effects, X is the component of acceleration sensed substantially along the primary direction of vehicle motion X′, sin θ is the acceleration due to gravity sensed in the X′ direction assuming that the acceleration due to gravity is substantially equal to 1.0 G, and θ is the pitch angle of vehicle  24 . In one illustrative embodiment of the invention, sensor system  16  has a first output indicating the sensed acceleration substantially exclusively in the primary direction of vehicle motion X′. Thus, the X component in the above equation is merely the first output of sensor system  16 . It is to be appreciated that the present invention contemplates systems and devices that are responsive to acceleration in other directions than the primary direction of vehicle motion. However, if sensor  16  does not have an output which substantially exclusively indicates X in the X′ direction, then other parameters, such as the mounting angle of sensor  16 , may be required to separate the output into its corresponding vector components in the X′ direction.
 
   Thus, in one embodiment of the invention, the acceleration in the X′ direction is corrected for effects due to gravity and the threshold may equal the acceleration indicative of an urgent deceleration condition. In one illustrative embodiment of the invention, a deceleration greater than a threshold value of 0.3 G is considered to be an urgent deceleration. In one embodiment of the invention, the controller  20  may initiate warning indicator  14  if the absolute value of the corrected acceleration of the vehicle in the X′ direction exceeds the threshold value indicative of an urgent deceleration condition. In one embodiment of the invention, controller  20  communicates with the vehicle  24  braking system and any detected acceleration, whether acceleration or deceleration, is assumed to be deceleration if it exceeds the acceleration threshold, since vehicles usually decelerate when the brake is applied. In another embodiment of the invention, the controller  20  determines the direction of the detected acceleration forces and only initiates warning indicator  14  when those forces indicate a deceleration. 
   Rather than correcting for the effect of gravity in the acceleration sensed in the X′ direction, controller  20  may correct the threshold on the opposite side of the above equation, for effects due to gravity. Thus in another embodiment of the invention, the acceleration in the X′ direction which includes the acceleration effects due to gravity is compared to a threshold value that equals the acceleration indicative of an urgent deceleration and the acceleration due to gravity in the X′ direction. Thus, the threshold G is dependent on the acceleration indicative of an urgent deceleration condition G urgent  and the pitch angle θ of the vehicle, as in the equation:
 
 G=G   urgent +sin θ  [3]
 
Thus, if the acceleration indicative of an urgent deceleration condition equals 0.3 G, then, in a level situation, the acceleration threshold may equal 0.3 at a pitch angle of 0 degrees. When in a downhill situation, the acceleration threshold may equal −0.04 at a pitch angle of 20 degrees. In another example, the acceleration threshold may equal −0.41 at a pitch angle of 45 degrees. In contrast, when in a uphill situation, the acceleration threshold may equal 0.64 at a pitch angle of 20 degrees and the acceleration threshold may equal 1.01 at a pitch angle of 45 degrees. Controller  20  may determine these dynamic threshold values from the pitch angle and the preferred deceleration indicative of an urgent deceleration condition, however, those skilled in the art will recognize that many methods are capable of determining the proper threshold value, including, but not limited to table look up values.
 
   Those skilled in the art will recognize that many devices are capable of determining the acceleration of the vehicle in the X′ direction, including but not limited to accelerometers, proximity radar systems, vehicle locator devices including the Global Positioning System, and inertia switches. Furthermore, those skilled in the art will recognize that many devices are capable of determining the pitch angle of the vehicle, including but not limited to, pitch indicators, horizon sensors, digital or analog inclinometers, and accelerometers. Although the sensor system below may be discussed below particularly in connection with multiple accelerometers, it should be appreciated that the present invention is not limited in this respect, and that the aspects of the present invention may include other types of single or multiple sensors and/or systems. 
   In one embodiment of the invention shown schematically in  FIG. 7 , sensor system  16  may include at least two accelerometers, a first accelerometer  16   a  and a second accelerometer  16   b . First accelerometer  16   a  is responsive to acceleration in the primary direction of vehicle motion X′. Second accelerometer  16   b  is responsive to acceleration in a direction other than the primary direction of the vehicle Z′. As shown in the illustrative embodiment of  FIG. 2 , the vehicle vertical direction Z′ may be substantially aligned with the local vertical, i.e., the direction of the Earth&#39;s local gravity vector, when the vehicle  24  is level. 
   Although the vehicle vertical direction Z′ is shown and described as being substantially orthogonal to the primary direction of vehicle motion X′, it is to be appreciated that the present invention is not limited in this respect and that other angular relationships between the Z′ direction and the X′ direction may be employed as long as the Z′ direction and X′ direction are not parallel. Thus, it is to be appreciated that the present invention contemplates systems and devices that are responsive to acceleration in both the primary direction of vehicle motion and in directions other than the primary direction of vehicle motion. 
   Continuing with  FIG. 7 , although two accelerometers  16   a ,  16   b  are schematically shown and described, the present invention is not limited in this respect and a single accelerometer, as discussed above, or multiple accelerometers may be employed provided acceleration may be sensed in the primary direction of vehicle motion X′ and their output may be corrected for effects due to gravity. Accelerometers  16   a ,  16   b  are well known in the art and are preferentially micro-mechanical or solid state accelerometers. In addition, accelerometers  16   a ,  16   b  may be capable of being fine tuned to detect deceleration within 0.1 G and may detect acceleration within one millisecond. In one embodiment of the invention, acceleration measurements are made using part numbers AD XL202 or AD XL210 Dual Axis iMEMS Accelerometer with Digital Output, both available from Analog Devices of Norwood, Mass., USA. Additional accelerometers and/or pitch indicators may be employed for redundancy. 
   Calibration of accelerometers  16   a ,  16   b  is well known in the art and may correct or compensate for electronic offset of the accelerometer output, output scaling errors, or pitch offset. Zeroing the output of accelerometers  16   a ,  16   b  may remove any electronic offset inherent in any output of accelerometers  16   a ,  16   b . Additional calibration may be performed to ensure that the measured acceleration is correct, however, normal factory output is typically within 1-2% of the actual sensed acceleration. Preferably, any errors may be removed from the output of accelerometers  16   a ,  16   b  by a scaling factor programmed within controller  20 . In one embodiment, controller  20  may automatically compensate for any pitch offset of accelerometers  16   a ,  16   b  using suitable techniques, such as coordinate transformation. The present invention is not limited in these respects and the outputs of accelerometers  16   a ,  16   b  may be adjusted using these or other parameters or methods. 
   Controller  20  communicates with accelerometers  16   a ,  16   b  and in one embodiment may resolve their output by calculating the acceleration sensed in the X′ direction and calculating the pitch angle of the vehicle  24 . As above, the controller  20  may then determine the corrected acceleration in the X′ direction independent of gravity effects and compare it with an acceleration indicative of an urgent deceleration condition. Alternatively, the controller  20  may determine the uncorrected acceleration sensed in the X′ direction and compare it with the acceleration indicative of an urgent deceleration condition including the effects of gravity. 
   In a further embodiment of this invention, controller  20  may determine the magnitude of acceleration sensed in both the X′ and Z′ directions and compare the magnitude of acceleration to a magnitude acceleration threshold. The magnitude acceleration threshold is dependent on the acceleration indicative of an urgent deceleration situation, the acceleration due to gravity, and the pitch angle of the vehicle  24 . The magnitude acceleration threshold is determined, as is well known, by the equation:
 
 M=√{square root over (X     2     +Z     2     )}   [4]
 
where the X component is the acceleration indicative of an urgent deceleration condition including the effects of gravity due to the pitch angle of the vehicle and the Z component is the acceleration due to the effects of gravity in the Z′ direction. Thus, if the acceleration indicative of an urgent deceleration condition equals 0.3 G, then examples of the magnitude acceleration threshold at various pitch angles are as follows: 1.04 at a pitch angle of 0 degrees; 1.14 at a pitch of 20 degrees; and 1.38 at a pitch angle of 45 degrees.
 
   In calculating the magnitude of the acceleration in the X′ and Z′ directions, controller  20  also uses the above magnitude equation [4] to resolve the output from accelerometers  16   a ,  16   b  into an acceleration magnitude, however the X component in the above equation is the component of acceleration sensed substantially along the primary direction of vehicle motion X′ and the Z component in the above equation [4] is the acceleration sensed substantially in a direction orthogonal to primary direction of vehicle motion, i.e., vehicle vertical direction Z′. 
   In the illustrative embodiment described, first accelerometer  16   a  is responsive to acceleration substantially exclusively in the primary direction of vehicle motion X′ and second accelerometer  16   b  is responsive to acceleration substantially exclusively in the vertical direction Z′. Thus, the X component in the magnitude equation is merely the output of first accelerometer  16   a  and the Z component in the above equation is the output of second accelerometer  16   b.    
   As mentioned above, many different accelerometer sensing orientations may be employed to provide sensing of acceleration in the X′ and Z′ directions. For example, accelerometers  16   a ,  16   b  oriented orthogonal to each other substantially in the X′-Z′ plane but not substantially aligned in the X′ and Z′ directions, may be employed for sensing acceleration in the vehicle vertical direction Z′ and in the primary direction of vehicle motion X′. The magnitude of the acceleration remains the sum of the squares of the outputs of accelerometers  16   a ,  16   b  as described in equation [4]. Thus, if accelerometers  16   a ,  16   b  are oriented substantially orthogonal to one another, the magnitude equation is substantially independent of the mounting angle of accelerometers  16   a ,  16   b.    
   In addition, those skilled in the art will recognize that accelerometers  16   a ,  16   b  need not be oriented substantially orthogonal to each other. However, if accelerometers  16   a ,  16   b  sense acceleration in respective directions that are not substantially orthogonal to each other, as will be readily appreciated by those of skill, then other parameters, such as the angle of their orientation from the X′ axis or Z′ axis, may be required to separate each output into its corresponding X and Z vector components before controller  20  may determine the acceleration magnitude and the magnitude acceleration threshold. 
   If at least one accelerometer  16   b  senses acceleration substantially in the vehicle vertical direction Z′ or if accelerometers  16   a ,  16   b  are oriented orthogonal to each other, the pitch angle of the vehicle  24  may be calculated or if the vehicle  24  is level, the mounting angle of accelerometers  16   a ,  16   b  may be calculated. Knowing that acceleration is substantially equal to 1.0 G due to the effects of gravity, the pitch angle of the vehicle  24  or the mounting angle of accelerometers  16   a ,  16   b  may be calculated as the arc-cosine of the reciprocal of the acceleration substantially in the vehicle vertical direction Z′. As is noted above, the pitch angle of the vehicle  24  may be determined by other methods and/or with other devices known in the art. 
   To decrease the incidence of indicator failures due to bumps, pot holes, etc., in one embodiment of the invention, the pitch angle of the vehicle may be used to further augment the acceleration threshold to initiate warning indicator  14 . Thus, in one embodiment of the invention, warning indicator  14  is initiated only when the acceleration exceeds the acceleration threshold value and when the absolute value of the pitch angle of the vehicle  24  is not greater than an angle threshold value. Thus, if the vehicle  24  is pitched up or down at an angle sufficient to indicate a sudden bump, controller  20  will not initiate warning indicator  14 . Controller  20  will assume that any sensed deceleration is not an urgent deceleration, but rather, a sudden and momentary deceleration. In one embodiment, the angle threshold value is substantially equal to 45 degrees, although other and/or additional angle thresholds may be employed. As with the acceleration threshold, the angle threshold may be adjustable. The invention is not limited in this respect as other suitable methods for compensating for road irregularities may be implemented. 
   In some instances, it may be necessary to correct for the calculated pitch angle. For example when determining the pitch angle of the vehicle using the arc-tangent of Z divided by X, controller  20  may compare the current pitch value with an initial value of pitch determined before the deceleration condition since the X value will indicate acceleration in the primary direction of vehicle motion X′. Thus, in one embodiment, if the current pitch angle of the vehicle is less than the initial pitch angle plus the angle threshold value or is greater than the initial pitch angle minus the angle threshold value, controller  20  may assume that any sensed deceleration is an urgent deceleration condition. 
   Now referring to  FIG. 3 , a flow chart of an embodiment of the invention directed to a method of indicating rapid deceleration independent of gravity is shown. The controller is powered on at step  110 , and in one embodiment, this power is provided through a switch by application of the brake pedal. Of course, other means for powering the controller may be employed. Preferably, the controller may initiate the warning indicator within 2 milliseconds of being powered on. After the controller is powered, the controller initializes its processor at step  120 . At step  130 , at least one sensor measures acceleration in the X′ direction and stores that value in the controller as X 1 . In one embodiment of the invention, the at least one sensor also measures acceleration in the Z′ direction and stores that value in the controller as Z 1 . At step  140 , the controller may then determine the initial pitch angle P i  of the vehicle, which, in one embodiment of the invention, is the arc-cosine of Z 1  or, as noted above, is an output from the at least one sensor. At step  150 , the sensor measures acceleration in the X′ direction and the controller stores that output as X. In one embodiment of the invention at step  150 , then sensor may also measure acceleration in the Z′ direction and the controller may store that output as Z. Also at step  150 , the controller, in one embodiment of the invention, may compensate for any manufacturing or installation offsets in the sensor output. At step  160 , the controller corrects for gravitational effects, as noted above, in the acceleration value stored as X, in threshold value G, or in using a magnitude of acceleration. In one embodiment of the invention, the controller may determine the acceleration in the primary direction of vehicle motion X′ by subtracting the sine of the initial pitch angle P i  from the value stored as X. In another embodiment of the invention, the controller may determine an acceleration threshold which includes the effects of gravity in the X′ direction. In another embodiment of the invention, the controller may determine the magnitude of acceleration in the X′ and Z′ directions and may calculate or look up a magnitude acceleration threshold. At step  170 , the controller compares the acceleration with a threshold value G. If the absolute value of the acceleration does not exceed the threshold value G, then the sensor continues to measure acceleration in the X′ direction as input into the controller by returning to step  150 . If the acceleration exceeds threshold G, then in one embodiment of the invention, at step  180  the controller calculates the current pitch angle P f . At step  190 , the controller compares the calculated pitch value P f  with a pitch threshold angle. If the absolute value of the current pitch angle P f  exceeds the pitch threshold angle, then the sensor continues to measure acceleration in the X′ direction by returning to step  150 . If the absolute value of the current pitch angle P f  does not exceed the pitch threshold angle, then at step  200 , the controller initiates the warning indicator, which in one embodiment is lights. The warning indicator may intermediately actuate, such as blinking or flashing, or may continuously actuate, such as steadily burn. In one illustrative embodiment, the warning indicator remains activated for at least as long as the urgent deceleration condition occurs, and more preferably for an additional period of time, which in one embodiment, is approximately in the range of 5-10 seconds. 
   Controller  20  may be any suitable controller now known or later developed. Controller  20  may be a stand-alone controller, such as an electronically programmable chip, or any other programmable device such as a CPU. The controller  20  may communicate with any vehicle controller, such as the electronic engine controller, the vehicle navigational computer, or the vehicle communications equipment such as analog or digital wireless phones or other communication devices. Alternatively, a separate controller  20  need not be provided at all, rather, the device  10 , without the controller  20 , may be coupled to any of the aforementioned devices. Controller  20 , which in turn may power the accelerometers  16   a ,  16   b  and the warning indicator  14 , may be powered by an independent power source (not shown) well known in the art including batteries or the vehicle power source. The controller  20  may be continuously powered or powered through depression of the brake pedal. 
   To further augment device  10 , controller  20  may also accept input from other systems of the vehicle, including, but not limited to, a pressure sensor in the hydraulic braking system, a wheel velocity or slip sensor in the anti-lock braking system, or a proximity radar sensor sensing distance to other vehicles or objects. These systems may improve performance of the device  10  when the vehicle is in an urgent braking condition but is not substantially decelerating. Such a condition may occur when the vehicle  24  is skidding on ice or some other low friction surface. For example, accelerometers  16   a ,  16   b  may not detect any deceleration if the vehicle  24  is skidding, and controller  20  may not initiate warning indicator  14 . Thus, additional input indicating a vehicle skid may initiate warning indicator  14 . 
   Warning indicator  14  comprises any suitable device known in the art and preferably provides a sufficient warning of an urgent deceleration condition. Those skilled in the art will recognize that many warning indicators, including but not limited to lights and audible alarms, may be employed to indicate an urgent deceleration condition. Lights suitable for use as warning indicator  14  are well known in the art and include, but are not limited to, incandescent bulbs, halogen bulbs, light emitting diodes (LEDs), and fiber optic cables. These lights may be suitable for use as a vehicle brake lamp, a center high mount stop lamp, or a vehicle cargo light. In one embodiment of the invention, warning indicator  14  is a light placed contiguous to an existing vehicle light such as a brake lamp, center high mount stop lamp, or cargo light. For example, as shown in  FIGS. 4 ,  5 A, and  5 B, warning indicator  14  includes a first light or set of lights  14   a  placed to one side of the vehicle light or set of lights  14   b  and a second light or set of lights  14   c  placed to the other side of the vehicle light or set of lights  14   b . When initiated, controller  20  may illuminate the light of warning indicator  14  with a constant illumination, flash the light, or if two or more lights or set of lights  14   a ,  14   c  are used, the lights or set of lights  14   a ,  14   c  may alternately flash when initiated. If flashing is used, the flash rate may be substantially equal to 2 times per second, although other flash rates may be employed. 
     FIGS. 5A and 5B  illustrate one embodiment of an indicating device  10  for indicating rapid deceleration of the vehicle  24 . As discussed above, warning indicator  14  includes a first light or lights  14   a  placed to one side of a vehicle light or lights  14   b , for example, a center high mount stop lamp. Warning indicator  14  also includes a second light or lights  14   c  placed to the other side of the vehicle light or lights  14   b . In the illustrated embodiment, warning indicator lights  14   a ,  14   c  are positioned contiguous to a center high mount stop lamp  14   b.    
   Warning indicators  14   a ,  14   b ,  14   c  may be mounted to base  12 , which provides a sound, stable, and durable platform. Accelerometers  16   a ,  16   b  may also be mounted to base  12 , which provides a sound, stable, and durable platform from which to detect acceleration of the vehicle  24 . In one embodiment, accelerometers  16   a ,  16   b  are mounted to a circuit  28  which may then be shaped and sized to mount to base  12  in a suitable orientation as shown in FIG.  5 B. For example, circuit  28  may be mounted to extend in a plane that is substantially perpendicular to the place of the base  12 . Controller  20  may also be mounted on the circuit  28 . 
   In one illustrative embodiment, the device  10  for indicating rapid deceleration is self-contained within a structural housing unit  22 . Thus, base  12 , warning indicator  14 , sensor system  16 , and controller  20  are all mounted within housing unit  22  which may even comprise base  12 . In a further embodiment of the invention, housing unit  22  is a center high-mount brake light assembly suitable for use in a motor vehicle, such as a car, truck, or motorcycle. 
   Device  10  may also include a manual switch  30  to initiate warning indicator  14  despite no urgent deceleration condition being indicated by controller  20 . The manual switch  30  may be preferably located within the vehicle  24  for easy access by the operator to warn others of an upcoming danger or to augment existing urgent light flashing systems in the vehicle  24 . 
   In one embodiment of the invention as shown in  FIG. 6 , warning indicator  14  may be a set of LEDs which are mounted on one side of circuit  28  facing outward towards the rear of the vehicle. Appropriately oriented sensor system  16  and/or controller  20  may be mounted parallel to and behind circuit  28  and in one embodiment of the invention, may be mounted on the opposite side of circuit  28  containing the LEDs, thus, decreasing the parts and volume of device  10  by combining warning indicator  14 , sensor system  16 , and controller  20 , into one unit, namely, circuit  28 . Many devices are capable for mounting LEDs, sensor systems, and controllers, including, but not limited to, circuits such as circuit boards and integrated chips. 
   As described above, warning indicator  14  may be a single warning indicator or may be multiple warning indicators. Multiple warning indictors may be initiated by controller  20  when output from sensor  16  exceed the threshold value or, each warning indicator might have its own associated threshold value such that one or more warning indicators are initiated as different thresholds are exceeded. For example, if the acceleration exceeds a first threshold, then controller  20  may initiate a subset of warning indicator  14 . If acceleration exceeds a second threshold, controller  20  may initiate another subset of warning indicator  14 . Of course, any suitable combination of one or more subsets of warning indicator  14  may be initiated depending upon which threshold is exceeded. 
   In one illustrative embodiment, warning indicator  14  will remain initiated by controller  20  for as long as the urgent deceleration condition occurs. More preferably, warning indicator  14  will remain initiated for a predetermined period of time after the urgent deceleration condition is complete.