Abstract:
A vehicle deceleration display system includes a serial data bus operable for communicating a plurality of sequentially-measured vehicle speed datums in a respective sequential manner. A control unit is operatively connected to the serial data bus and is operable for receiving and processing the vehicle speed data therefrom. The control unit is programmed to sequentially calculate vehicle deceleration values respectively corresponding with the sequential speed data to provide a variable output signal. The variable output signal corresponds with and varies in accordance with the sequential vehicle deceleration values. A variable display is connected to the control unit and varies in response to the deceleration values. A method of calculating and displaying vehicle deceleration values is also provided.

Description:
TECHNICAL FIELD 
     This invention relates to vehicle deceleration display systems and calculation methods. 
     BACKGROUND OF THE INVENTION 
     Vehicles typically employ conventional on/off brake lights that are triggered by application of a brake pedal to indicate that the vehicle&#39;s brakes are applied. Some vehicles are equipped with sequentially illuminating lamps visible to a trailing driver. The sequentially illuminating lamps may be illuminated upon decreasing vehicle velocity that is measured from a wheel speed sensor. Others of such systems may base deceleration on vehicle speed determined from a sensor attached to a brake pedal. Still other vehicles equipped with sequentially illuminating lamps may base vehicle deceleration upon measurements from a decelerometer. 
     SUMMARY OF THE INVENTION 
     The present invention includes a vehicle deceleration display system for a leading vehicle that provides an indication to trailing drivers of vehicle deceleration and optionally, implementation of an antilock brake system, a traction control system, occurrence of an under steer event or a rollover event. A variable display on the leading vehicle is varied based upon information provided from the vehicle&#39;s serial data bus. The information is received and processed by a control unit on the vehicle. 
     A vehicle deceleration display system includes a serial data bus operable for communicating a plurality of sequentially measured vehicle speed datums in a respective sequential manner. A control unit is operatively connected to the serial data bus and operable for receiving and processing the vehicle speed data therefrom. The control unit is programmed to sequentially calculate vehicle deceleration values respectively corresponding with the sequential vehicle speed data to provide a variable output signal. The variable output signal corresponds with and varies in accordance with the sequential vehicle deceleration values. The variable display is operatively connected to the control unit. The variable display varies in response to the output signal. 
     In one aspect of the invention, each datum is a measurement of the speed of an output shaft of a transmission on the vehicle. The control unit is further programmed for controlling the transmission using the sequential vehicle speed data. As many modern vehicles already include a serial data bus that relays transmission output shaft speed to a control unit, the invention permits existing components (i.e., the serial data bus and the control unit) to be utilized, thus maximizing cost efficiency. 
     In another aspect of the invention, each of the vehicle deceleration values (Dec INST ) is defined by the equation Dec INST =(V C −V P )/T. V C  and V P  are consecutively-received vehicle speed data. V C  is received subsequently to V P . T is the elapsed time between reception of the respective data. 
     In another aspect of the invention, each of the vehicle&#39;s deceleration values represents an average of a number of sequentially calculated deceleration values: 
               Dec   AVG     =       ∑     n   =   1     N     ⁢       (       (       V     n   +   1       -     V   n       )     /     (       T     n   +   1       -     T     n   ⁢                 )       )     /   N             
V n  and V n+1  are consecutively-received vehicle speed data. V n+1  is received subsequently to V n . T n+1  is the time of reception of V n+1 . T n  is the time of reception of V n . N is the number of sequential speed data over which the vehicle deceleration value Dec AVG  is calculated.
 
     In yet another aspect of the invention, the control unit is programmed to calculate the difference between a first calculated vehicle deceleration value and a second calculated vehicle deceleration value. The second deceleration value is calculated based on later sequential speed data than the first deceleration value is based upon. The control unit provides the output signal varying in correspondence with the second deceleration value after a first amount of time T 1  when the second deceleration value is greater than the first deceleration value by a first amount. The control unit provides the output signal varying in correspondence with the second deceleration value after a second amount of time K 2  when the second deceleration value is less than the first deceleration by a second amount. K 1  is different than K 2 . Accordingly, the output signal varies to correspond with the second deceleration value at a different rate when vehicle deceleration is increasing than when vehicle deceleration is decreasing. 
     In another aspect of the invention, the control unit is further programmed to compare the vehicle deceleration value with the minimum threshold value. The control unit does not provide the output signal when the vehicle deceleration value is less than the minimum threshold value. Accordingly, the variable display does not vary in response to deceleration values less than the minimum threshold value. 
     In yet another aspect of the invention, the serial data bus is further operable for communicating to the control unit vehicle stability data. Vehicle stability data includes at least one of implementation of an anti-lock brake system, implementation of a traction control system, occurrence of an under steer event, and occurrence of a rollover event. The control unit provides the output signal at a preset level when the vehicle stability data is communicated. Different preset levels may be provided for each of the above-listed stability data. 
     In yet another aspect of the invention, the variable display comprises a plurality of light-emitting diodes (LEDs) arranged in an array (preferably a horizontal array) and mounted on the rear of the vehicle. The LEDs are illuminated in sequential pairs outward from a center of the array. The number of sequential pairs illuminated is in increasing non-linear proportion to the magnitude of the output signal. “Increasing nonlinear proportion” means that the number of sequential pairs illuminated increases at a rate greater than linearly as the magnitude of the output signal increases. 
     In yet another aspect of the invention, at least some of the LEDs are illuminated in response to application of a vehicle brake pedal. The LEDs illuminated in response to application of the brake pedal are centrally-located in the array. 
     A method includes calculating vehicle deceleration values from sequentially-measured vehicle speed data received via a serial data bus. The method further includes providing an output signal that varies in accordance with the calculated vehicle deceleration values. 
     In one aspect of the invention, the method further includes varying a variable display in response to the output signal. 
     In yet another aspect of the invention, the variable display comprises a plurality of light emitting diodes (LEDs) arranged in an array and mounted on the rear of the vehicle. Varying the variable display includes illuminating the LEDs in sequential pairs outward from a center of the array. The number of sequential pairs illuminated is in increasing nonlinear proportion to the magnitude of the output signal. 
     In yet another aspect of the invention, the vehicle speed data comprises a plurality of sequentially-measured speeds of an output shaft of a transmission. The method includes controlling the transmission via the control unit using the sequential vehicle speed data. 
     In another aspect of the invention, the output signal varies increasingly nonlinearly with increasing vehicle deceleration values. 
     In yet another aspect of the invention, calculating includes subtracting a received vehicle speed datum (V p ) from a consecutive, subsequently-received vehicle speed datum (V c ) and dividing the result (V c −V p ) by the elapsed time between receipt of the respective data. 
     In another aspect of the invention, the method includes averaging a number of sequentially-calculated vehicle deceleration values to calculate an average deceleration value defined by the formula: 
               Dec   AVG     =       ∑     n   =   1     N     ⁢       (       (       V     n   +   1       -     V   n       )     /     (       T     n   +   1       -     T     n   ⁢                 )       )     /     N   .               
V n  and V n+1  are consecutively-received vehicle speed data. V n+1  is received subsequent to V n . T n+1  is the time of reception of V n+1 . T n  is the time of reception of V n . N is the number of sequential speed data over which the vehicle deceleration value Dec AVG  is calculated.
 
     In yet another aspect of the invention, the method includes calculating the difference between a first calculated vehicle deceleration value and a second calculated vehicle deceleration value. The second deceleration value is calculated based on later sequential speed data than the first deceleration value is based on. The method further includes varying the output signal to correspond with the second deceleration value after a first amount of time K 1  when the second deceleration value is greater than the first deceleration value by a first amount, and after a second amount K 2  when the second deceleration value is less than the first deceleration by a second amount K 1 . K 1  is different than K 2 ; accordingly, the output signal varies to correspond with the second deceleration value at a different rate when vehicle deceleration is increasing than when vehicle deceleration is decreasing. 
     In yet another aspect of the invention, the method includes comparing each of the vehicle deceleration values with a minimum threshold value. The method further includes setting the output signal to zero when the vehicle deceleration is less than the minimum threshold value. 
     In yet another aspect of the invention, the method includes recognizing when a vehicle stability event has occurred. A vehicle stability event includes at least one of implementation of an anti-lock brake system, implementation of a traction control system, occurrence of an under steer event and occurrence of a rollover event. The method includes setting the output signal to a preset level when occurrence of a vehicle stability event is recognized. 
     The above features and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a vehicle deceleration display system; 
         FIG. 2  is a plan view of an array of LEDs within the vehicle deceleration display system of  FIG. 1 ; 
         FIG. 3  is a schematic illustration of an indicator circuit used to drive the array of LEDs in the vehicle deceleration display system of  FIG. 1 ; and 
         FIG. 4  is a flow diagram illustrating a vehicle deceleration calculation method. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like components, a vehicle  10  having a vehicle deceleration display system  12  is shown in  FIG. 1 . The vehicle includes a transmission  14  having a transmission output shaft  16 . A speed measuring device  18  is connected to the transmission output shaft  16 . The speed measuring device  18  relays speed data (V) to a serial data bus  22 . Preferably, the serial data bus  22  also relays other vehicle information. For instance, a vehicle stability information relaying device  24  relays vehicle stability data  26  to the serial data bus  22 . The vehicle stability information relaying device may be an anti-lock brake system, a traction control system, or a sensor mounted to the vehicle which senses the occurrence of an under steer event or a rollover event. Accordingly, vehicle stability data may include implementation of the anti-lock brake system, implementation of the traction control system, the occurrence of an under steer event and/or the occurrence of a rollover event. 
     The serial data bus  22  is operatively connected to a control unit  30 . The control unit  30  receives the vehicle speed data V as well as the vehicle stability data  26  from the serial data bus  22 . The serial data, including the output shaft speed V and the vehicle stability data  26 , may be transmitted on the bus  22  in either a periodic or non-periodic manner, depending on the particular bus protocol in use. In either case, the shaft speed V is transmitted via the bus  22  to the control unit  30  that controls the transmission; typically a power control module (PCM), an engine control module (ECM), or a separate transmission control module (TCM). The speed transmitted via the serial data bus  22 , which may be referred to as a serial data message, is stored into a last speed buffer  32 . The speed stored into the last speed buffer may be referred to as V p , the previous speed. A subsequently received speed data message V c  (i.e., a currently received speed) is then received by the control unit  30 . V p  and V c  are consecutively received speed data. The control unit  30  calculates a deceleration value  34 . The deceleration value  34  may be referred to as Dec INST . Dec INST  is defined by the following deceleration value function:
 
 Dec   INST =( V   C   −V   P )/ T.  
 
T is the elapsed time between reception of V c  and V p . The value of T may or may not be constant, depending upon whether the speed data are transmitted onto the serial data bus  22  in a periodic or non-periodic manner, respectively.
 
     Because the vehicle transmission speed versus time may not form a particularly smooth curve, particularly in rough road environments, and because the formula of Dec INST  is essentially a time-derivative, calculating deceleration in this manner will have the affect of exaggerating any unevenness in the curve. Therefore, some form of smoothing or filtering of the deceleration value is preferable. Accordingly, the control unit  30  includes a deceleration buffer  38 . Deceleration buffer  38  includes a plurality of buffer locations zero (0) to N. The buffer  38  operates in a first in first out (FIFO) manner. Data stored in the buffer is processed by the control unit  30  to calculate a filtered or averaged deceleration value Dec AVG    42 . Dec AVG  is defined by the following deceleration value averaging (i.e., filtering) function: 
               Dec   AVG     =       ∑     n   =   1     N     ⁢       (       (       V     n   +   1       -     V   n       )     /     (       T     n   +   1       -     T     n   ⁢                 )       )     /     N   .               
V n  and V n+1  are consecutively-received vehicle speed data. V n+1  is received subsequent to V n  and is stored in a subsequent buffer location. T n+1  is a time of reception of V +n+1  and T n  is the time of reception of V n . N is the number of sequential speed data over which the vehicle deceleration value Dec AVG    42  is calculated. N corresponds with the number of buffer locations in the deceleration buffer  38 . After the function  42  (as well as functions  44  and  48  discussed below) is performed by the control unit  30 , the control unit  30  provides an output signal S OUT  to illuminate a variable display  60  (which, in this embodiment is an LED array) via an indicator circuit  56  (which includes an LED driver  64 ). The output signal S OUT  is preferably in the form of a level of voltage but may be presented by the control unit  30  in other forms within the scope of the invention.
 
     In addition to the deceleration filtering function  42 , the control unit  30  provides a threshold truncation or clipping function  44 . The threshold truncation function  44  operates to limit varying of the display  60  to those deceleration conditions meriting such a display. Thus, changes in deceleration determined to be insignificant with respect to warning the trailing driver will not cause a variation in the display  60 . The value of the low-end threshold will vary based on vehicle weight, aerodynamics, engine inertia, drive train loss and other physical vehicle phenomena. The low-end threshold should be calibrated on a per-vehicle basis. 
     In addition to the deceleration filtering function  42  and the threshold truncation function  44 , an additional attack-decay clamp function  48  is implemented by the control unit  30 . The attack-decay clamp function  48  operates to limit the ramp-up and decay rates of the illuminated LEDs (i.e., the rate of increase and rate of decrease, respectively, in the number of illuminated LEDs) to calibratable thresholds. For example, if a rough road condition causes the vehicle speed, as measured at the output shaft of the transmission  14 , to drop and then suddenly increase, the attack-decay clamp function would prevent the number of illuminated LEDs from dropping quickly, forcing them instead to switch off at a slower rate. Specifically, the control unit  30  compares a first calculated vehicle deceleration value with a second calculated vehicle deceleration value that is calculated based on later sequential speed data than the first deceleration value. For instance, if the attack-decay clamp function  48  receives deceleration values that have been calculated subject to the deceleration filtering function  42 , the second calculated vehicle deceleration value is based on filtered values received from the buffers  38  after a first deceleration value received from earlier information in the deceleration buffers  38 . The attack-decay function  48  operates by applying a different time constant affecting the variation of the output signal S OUT  when the vehicle deceleration is increasing than when the vehicle deceleration is decreasing. Accordingly, the control unit  30  provides an output signal S OUT  that varies in correspondence with the second deceleration value after a first amount of time K 1  when a second deceleration value is greater than the first deceleration value by a first amount             Dec 1  (i.e., when the vehicle deceleration is increasing), and after a second amount of time K 2  when the second deceleration value is less than the first deceleration value by a second amount           Dec 2  (i.e., when the vehicle deceleration is decreasing). K 1  is different than K 2 . Accordingly, the output signal varies to correspond with the second deceleration value at a different rate when the vehicle deceleration is increasing than when the vehicle deceleration is decreasing. Thus, the ramp up rate (i.e., the rate of increasing illumination of LEDs when vehicle deceleration is increasing) and the decay rate (i.e., the rate of de-illumination or turning off of LEDs when the vehicle deceleration is decreasing) may be varied. Additionally, the logic may implement the ramp up and decay controls in K 1  and K 2  at different thresholds Δ Dec 1  and Δ Dec 2 , providing further sophistication of output signal S OUT  variance.
     After passing through the deceleration filtering function  42 , the threshold truncation function  44  and the attack-decay clamp function  48 , a modified deceleration value (Dec MOD ) is passed to an output logic function  50  of the control unit  30 . The output logic function  50  produces the hardware output signal, S OUT . The output logic function  50  operates such that S OUT  varies nonlinearly with the input Dec MOD . The exact nonlinear relationship will vary on a vehicle to vehicle basis, dependent upon factors such as the size and location of the indicator LEDs, and the desired level of LED display determined to be most easily interpreted by trailing drivers. Preferably, the existing output logic already in use on the control unit  30  for various other applications throughout the vehicle is reused and adapted to the present invention. By re-using the existing output logic, separate, stand-alone implementation of output logic specifically for the deceleration display system  12  is not needed. The graph of Dec MOD  versus S OUT  shown on the output logic function  50  shows a nonlinear correlation. S OUT  remains low at low values of Dec MOD . This is a result of the threshold truncation function  44  discussed above. Notably, within the scope of the invention, any one or any two of the functions  42 ,  44  or  48  may be performed by the control unit  30  (in lieu of performing all three of the functions  42 ,  44  and  48 , as described herein). 
     In addition to being correlated with transmission output shaft speed, as modified through the various functions described in the control unit  30 , S OUT  is also correlated with and responsive to the vehicle stability data  26  provided on the serial data bus  22  from the vehicle stability information relaying device  24 . For instance, when an automatic braking system/traction control system activation signal (i.e., one of the possible vehicle stability data) is relayed to the control unit  30 , the output logic function  50  operates to provide an output signal S OUT  at a preset (i.e., latched) level upon detecting the ABS/traction activation control. Communicated vehicle speed V from the transmission  14  may appear erratic upon implementation of an anti-lock brake system, a traction control system, the occurrence of an under steer event or the occurrence of a rollover event. The occurrence of such events are easily detected with the present invention as, on many current vehicles, their occurrence is typically accompanied by the controlling ECU alerting all other ECUs on the serial data bus  22 . Thus, these events are easily detected and communicated via the serial data bus  22 , and no additional hardware is required in order to detect and communicate these events to the control unit  30 . By latching the algorithm output S OUT  to a preset level upon detection of any of these events, the variable display (to be discussed with respect to  FIGS. 3 and 4 ) will illuminate at a constant level during one of these events rather than at a potentially erratically-changing level that would result if based upon transmission output shaft speed V. 
     The output signal S OUT  is relayed to the indicator circuit  56  (including the LED driver  64 ) which is operatively connected to and illuminates a variable display  60 . In this embodiment, the variable display  60  is an LED array. 
     Referring to  FIG. 2 , one embodiment of the variable display is an array  60  of LEDs numbered L 1 –L 20  mounted on the rear  62  of the vehicle  10  and arranged in a horizontal manner. (Alternatively, within the scope of the invention, the array may arranged other than horizontally.) The LEDs illuminate in pairs sequentially outward from a center C of the array  60 . For instance, L 1  and L 2  illuminate simultaneously, as a pair, as do L 3  and L 4 , and so on. More illuminated LEDs indicates a greater deceleration. Accordingly, a “growing” brake light is visible to trailing drivers. 
     Many production vehicles include a center high-mounted stop lamp (CHMSL). CHMSLs are illuminated by application of a vehicle brake pedal. The array  60  may incorporate the CHMSL by dedicating the center-most LEDs to the existing CHMSL circuit. Accordingly, the existing CHMSL circuit could be altered to serve the purposes of the present invention, thus minimizing the cost of implementation and utilizing existing parts. Even if the center most LEDs are not actuated by the brake pedal, the existing CHMSL circuit may be used and altered to enable the array  60 . In the embodiment shown in  FIG. 2 , the LEDs L 1 –L 4  may be actuated by application of the brake pedal. By contrast, the LEDs L 5 –L 20  are illuminated in proportion to S OUT . The LEDs L 5 –L 20  are illuminated in pairs; LED&#39;s L 5  and L 6  are illuminated first while LEDs L 19  and L 20  are illuminated last, with the number of LED pairs between L 5  and L 6  and L 19  and L 20  illuminated being in proportion to the magnitude of the output signal S OUT . 
     Referring to  FIG. 3 , the indicator circuit  56  used in conjunction with the ECU  30  (and the logic functions performed therein) includes a simple LED driver  64 . One model of an LED driver  64  that may be employed is National Semiconductor part number LM3914. The indicator circuit  56  requires three inputs; a high or supply rail  66 , a ground  68  and a control line  70 . The high rail  66  is connected to a battery on the vehicle (not shown) which typically has a voltage of 9.0 to 14.0 volts. If the vehicle has a CHMSL, the ground  68  may be the existing ground of the CHMSL. Accordingly, additional wiring would not be required to provide a ground to the circuit  56 . The control line  70  is connected to the ECU  30  and carries the output S OUT  of the ECU  30  (see  FIG. 1 ), as discussed above. Only the single control line  70  must be routed to the ECU  30 . 
     The indicator circuit  56  includes resistors R 1  an R 2  which control the amount of current through each of the LEDs (i LED ) in accordance with the range of input voltage (V INP ) (i.e., the range of values of S OUT  provided by the control unit  30 ). R 1  and R 2  can be customized to the needs of the particular application using the following formulae: 
                 i   LED     =     12.5   R1       ;       and   ⁢           ⁢     V   INP       =     1.25   ⁢       (     1   +     R2   R1       )     .               
(The above formulae assume a battery voltage of 12.5 volts.) For example, to deliver an LED current of 25 mA, in using a control voltage range of 0 to 5 volts (i.e., when V INP  varies between 0 and 5 volts) the values of R 1  and R 2  should be 500 ohms and 1,500 ohms, respectively. This allows control of the exact amount of current through each pair of LEDs, as well as the input range for the indicator circuit  56 . Accordingly, use of the resistors R 1  and R 2  insures that a variety of output logic  50  (see  FIG. 1 ) in the ECU  30  (i.e., logic having a range of 0–3 volts, 0–5 volt, 0–12 volt, etc.) may be used to provide a desired i LED  and V INP  for maximum cost effectiveness. Thus, output logic systems already in use on typical modern vehicles may be adapted to provide the desired i LED  and V INP  by use of the correct combination of resistors R 1  and R 2 . Note that the LED array  60  of  FIG. 3  is shown schematically; it may be arranged in a horizontal manner as shown in  FIG. 2 .
 
     Referring to  FIG. 4 , a vehicle deceleration calculation and display method  200  is illustrated. The method  200  includes calculating vehicle deceleration values  202  from sequentially-measured vehicle speed data received via a serial data bus. Preferably, the vehicle speed data are measured from an output shaft of a transmission. Calculating vehicle deceleration values  202  may include subtracting a received vehicle speed datum (V p ) from a consecutive, subsequently-received vehicle speed datum (V c ) and dividing the result (V c −V p ) by the elapsed time between receipt of the respective data. The method  200  further includes providing a variable output signal  204  that corresponds with the calculated deceleration values. The output signal may vary increasingly nonlinearly with increasing vehicle deceleration values. The method  200  further includes varying a variable display  206  in response to the output signal. The variable display may include a plurality of light-emitting diodes (LEDs) arranged in a horizontal array and mounted on the rear of a vehicle. Varying the variable display  206  may include illuminating LEDs in sequential pairs outward from a center of the array, the number of sequential pairs illuminated being in increasing nonlinear proportion to the magnitude of the output signal. 
     Consistent with the deceleration filtering function  42  discussed with respect to  FIG. 1 , the method  200  may include averaging a number of sequentially calculated vehicle deceleration values  208  to calculate and average deceleration value: 
               Dec   AVG     =       ∑     n   =   1     N     ⁢       (       (       V     n   +   1       -     V   n       )     /     (       T     n   +   1       -     T     n   ⁢                 )       )     /     N   .               
V n  and V n+1  are consecutively-received vehicle speed data. V n+1  is received subsequently to V n . T n+1  is the time of reception of V n+1  . T n  is the time of reception of V n  . N is the number of sequential speed data over which the vehicle deceleration value Dec AVG  is calculated.
 
     Consistent with the threshold truncation function  44  discussed with respect to  FIG. 1 , the method  200  may include comparing each deceleration value with a minimum threshold value  210 . The method  200  may further include setting the output signal to zero  212  when the vehicle deceleration value is less than the minimum threshold value. 
     Consistent with the attack-decay clamp function  48  discussed with respect to  FIG. 1 , the method  200  may include calculating the difference between first and second vehicle deceleration values  214 . The second deceleration value is calculated based on later sequential speed data than the first deceleration value. The method  200  may further include varying the output signal  216  to correspond with the second deceleration value after a first amount of time K 1  when the second deceleration value is greater than the first deceleration value by a first amount, and after a second amount of time when the second deceleration value is less than the first deceleration value by a second amount K2. K1 is different than K2. Thus, the output signal varies to correspond with the second deceleration value at a different rate when the vehicle deceleration is increasing than when the vehicle deceleration is decreasing. 
     The method  200  may further include recognizing the occurrence of a vehicle&#39;s stability event  218 . A potential vehicle stability event includes those discussed with respect to  FIG. 1 . The method  200  may further include setting the output signal to a preset level when the occurrence of a vehicle stability event is recognized  220 . 
     The method  200  may further include controlling the transmission  222  via the control unit using the sequential speed data. Thus, the same control unit used to control the transmission may be utilized to calculate an output signal to vary the variable display. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.