Abstract:
A steering wheel movement detection device has a magnetic flux source and a magnetic sensor. The magnetic sensor is mounted on the steering column and the magnetic flux source is attached to the steering shaft or steering wheel and moves in accordance therewith. The magnetic flux source has lines or bands of varying magnetic flux. The magnetic sensing device is mounted adjacent and opposing the magnetic flux source so that when the steering wheel moves varying magnetic flux impinges upon the magnetic sensing device. The magnetic sensing device forms the inductive component of a resonant LC tank circuit and the frequency of that circuit varies in accordance with the flux impinging on the sensing device. A microcontroller integrates or averages the varying frequency signal over brief periods of time and when the average frequency does not have sufficient deviations an alarm signal is produced. A speaker is driven by the alarm signal to signal the driver to a state of alertness. A cruise control deactivation signal is also produced by the apparatus to disengage cruise control mode when driver alertness is in question.

Description:
This invention claims the benefit of provisional application No. 60/078,455, filed Mar. 18, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention is in the field of vehicle steering and speed sensitive devices to detect a lack of driver alertness and emit a warning thereupon. 
     BACKGROUND OF THE INVENTION 
     Numerous systems are known that sense vehicle steering corrections during a given time period as an indication of driver alertness. One such system is disclosed in U.S. Pat. No. 4,278,969 to Richard Woods, entitled “Driver Warning System”. The &#39;969 Woods device incorporates a light source and photocell mounted on the steering column that directs a light beam towards a strip having alternate bands of reflective and non-reflective material. During normal driving patterns, the steering wheel is corrected a given number of times during any predetermined time period. When steering corrections fall below the predetermined number, the driver is usually inattentive due to any of a number of reasons. An audible driver warning system during such conditions has been shown to be effective to arouse the driver to a state of alertness to prevent a vehicle accident. For example, the Woods system is coupled with vehicle speed sensing devices which make it inoperative below a certain vehicle speed so that when the vehicle is parked or moving at a relatively slow speed, the audible alarm will not be sounded even though the necessary steering corrections are not made within the given time period. One significant shortcoming of the Woods device is its reliance on optics for motion detection. 
     Optical devices used in a motor vehicle environment are subject to significant amounts of dirt, grime, grease and other likely contaminants. Such contaminants will likely interfere with and prevent the Woods device from functioning properly. A steering wheel movement detection device that is unaffected by such contaminants is needed. 
     SUMMARY OF THE INVENTION 
     A steering wheel movement sensing apparatus for use with a vehicle having a steering shaft, according to one aspect of the present invention, comprises magnetic sensing means for detecting variations in magnetic flux, the magnetic sensing means attached at a fixed location within the vehicle in close proximity to the steering shaft, the magnetic sensing means producing a magnetic signal in accordance with the magnetic flux impinging thereon, a magnetic strip having varying magnetic flux lines, the magnetic strip attached to the steering shaft and in close proximity to the magnetic sensing means so that magnetic flux emanating from the magnetic strip impinge upon the magnetic sensing means, and wherein the magnetic strip moves with respect to the magnetic sensing means when the steering shaft is rotated, circuit means responsive to the magnetic signal for producing an alarm signal in accordance with a lack of deviation in the magnetic signal, and alarm means responsive to the alarm signal for producing an audible sound in accordance with the alarm signal. 
     One object of the present invention is to provide an improved steering wheel movement detection device. 
     Another object of the present invention is to provide steering wheel movement detection device that is unaffected by contaminants normally encountered in a motor vehicle environment. 
     Yet another object of the present invention is to provide a more reliable and more economical steering wheel movement detection device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a steering wheel movement sensing device according to one aspect of the present invention. 
     FIG. 2 is a block diagram of another embodiment of a steering wheel movement sensing device according to another aspect of the present invention. 
     FIG. 3 is an electrical circuit schematic for the embodiments shown in FIGS. 1 and 2. 
     FIG. 4 is a flowchart for the program executed by microcontroller  24  of FIGS. 1 and 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Referring now to FIG. 1, a block diagram of a magnetic steering wheel movement sensing device  10  according to the present invention is shown. Device  10  includes a magnetic strip  12 , a magnetic sensor  14 , a sensor circuit  16 , a mode switch  18 , a mode indicator or lamp  20 , a power indicator or lamp  22 , a microcontroller  24 , a speaker  26 , a power supply regulator  28  and a power switch  30 . Magnetic strip  12  includes a plurality of magnetized areas  13  that produce a plurality of magnetic lines of flux emanating from strip  12 . Magnetic sensor  14  includes a bobbin  15  about which a coil  17  is wound. Additionally, a magnet  19  is mechanically attached to bobbin  15  as shown. Bobbin  15  is made of ferrite or other known magnetic materials. Conductors  17 a are the two leads from coil  17 . Conductors  17 a are connected to sensor circuit  16 . Circuit  16  is shown in more detail in FIG.  3 . Circuit  16  includes an oscillator circuit wherein the coil  17  provides the inductive component of the LC oscillator circuit. As magnetic strip  12  is moved with respect to sensor  14 , the inductance of coil  17  is altered accordingly. Thus, the oscillator circuit of sensor circuit  16  will vary in frequency correspondingly with the magnetic flux lines from magnetic strip  12  that impinge upon sensor  14 . 
     Sensor circuit  16  supplies an oscillator signal microcontroller  24 . Microcontroller  24  monitors the frequency signal from circuit  16  and produces an alarm signal supplied to speaker  26  when the deviation in frequency in the signal from circuit  16  fails to exceed a predetermined deviation over a predetermined time period. Mode switch  18  provides an input signal to microcontroller  24  so that microcontroller  24  is signaled or instructed to enter into an alternative mode of operation. Alternative modes of operation are useful during the installation process of device  10  into a motor vehicle. Mode light  20  receives an activation signal from microcontroller  24  to indicate the current mode of operation of the microcontroller. Switch  30  provides a mechanism to switch on and off the power supplied by an external DC power source (not shown). Power supply regulator  28  produces a regulated DC output signal used by microcontroller  24  and sensor circuit  16 . Power lamp  22  receives a power signal from regulator  28 . Power lamp  22  provides a visual indication that power is supplied to device  10 . 
     Operationally speaking, magnetic strip  12  is attached to the steering shaft or steering wheel of a motor vehicle. Magnetic sens or  14  is mounted in a fixed position adjacent and in close proximity to magnetic strip  12 . As the steering wheel or steering shaft is rotated, strip  12  is moved with respect to sensor  14  thereby causing a variation in the inductance of coil  17 . Sensor circuit  16 , which include an LC oscillator circuit (FIG. 3) or tank circuit produces an oscillator signal that is supplied to microcontroller  24 . As magnetic strip  12  moves versus the stationary sensor  14 , the frequency of t he signal produced by the circuit  16  varies in accordance with the flux impinging on the sensor from strip  12 . Under normal driving conditions, microcontroller  24  monitors the oscillator signal from circuit  16  in a continuous fashion. Preferably, the period of the oscillator signal is averaged over a fixed period of time to determine a current frequency. Then, the period of the oscillator signal is averaged again over a second interval of time (for example 25-200 milliseconds), and compared with the previous average to ascertain whether sufficient deviation is detected. If the frequency deviation fails to exceed a predetermined deviation quantity over a three to five second period, then microcontroller  24  will produce an alarm signal supplied to speaker  26 . Finally, a cruise control disable signal  32  is produced by microcontroller  24  when the alarm signal supplied to speaker  26  is produced. Signal  32  is connected to a cruise control device (not shown) to deactivate the cruise control device from “cruise” mode and begin deceleration of the vehicle when the lack of steering wheel movement indicates the driver may not be alert. 
     Referring now to FIG. 2, another embodiment of a steering wheel movement sensing device  40  according to the present invention is shown. All of the components shown in FIG. 2 are identical with those shown in FIG. 1 with the exception of the toothed wheel  32 . Wheel  32  takes the place of magnetic strip  12  in device  40 . All components of FIG. 2 that are like numbered in FIG. 1 have the same characteristics and functionality as those device described with respect to device  10  of FIG.  1 . The toothed wheel  32  provides an inductive interaction with sensor  14  so that small variations in the inductance of coil  17  are present on the leads  17   a  from coil  17 . Leads  17   a  are connected into an LC tank circuit in sensor circuit  16 . Toothed wheel  32  is mounted on or attached to the steering wheel or steering shaft of a motor vehicle and rotates in accordance with the steering shaft. In all other aspects of operation, device  40  is identical in functionality and components with device  10 . 
     Referring now to FIG. 3, a schematic diagram of an electrical circuit used with the steering wheel movement sensing devices  10  and  40  is shown. Inductor L 1  corresponds to coil  17  of FIGS. 1 and 2. Sensor circuit  16  is indicated by a broken line and includes an oscillator circuit  50  and a common emitter amplifier circuit  52 . The oscillator circuit  50  is a traditional Colpitts oscillator well known in the art of electronics, and further discussion thereof is not necessary herein. Capacitor C 1  and C 2  and inductor L 1  provide the LC components of the oscillator circuit  50 . Resistors R 1 , R 2  and R 3  provide DC bias voltages to transistor Q 1 . The oscillator signal from circuit  50  passes through decoupling capacitor C 3  and into the common emitter amplifier circuit  52  comprised of resistors R 4 , R 5 , R 6  and R 7  and transistor Q 2 . Resistors R 4 -R 7  provide the DC bias voltages for amplifier transistor Q 2 . Amplifier circuit  52  is a high gain amplifier and transforms the oscillator signal delivered to the base of Q 2  into a square wave signal. 
     The output of sensor circuit  16  is an approximately seven kilohertz frequency signal that is supplied to an input of microcontroller  24  indicated in FIG. 3 as U 1 . Microcontroller U 1  received an input signal from switch S 1  that corresponds with the mode switch  18  in FIGS. 1 and 2. LED D 1  corresponds to the mode light  20  in FIGS. 1 and 2. LED D 1  is illuminated or activated when microcontroller U 1  detects insufficient frequency deviation in the oscillator signal from sensor circuit  16  in the aforementioned three-five second time period. Speaker  26  corresponds to the device labeled “beeper 1 ” in FIG.  3 . Microcontroller  24  provides two different output signals to jumper block JP 1 , and depending on the brand of speaker or beeper used, a short is installed between pins  1  and  2  of JP 1  or between pins  2  and  3  of JP 1 . Crystal Y 1  and capacitors C 6  and C 7  provide an oscillator signal to microcontroller U 1 . U 2  is a 5 volt regulator device well known in the electronics art for reducing a higher DC voltage such as that produced by a motor vehicle (+12 VDC) to the five volts DC required by microcontroller U 1 . 
     Referring now to FIG. 4, a flowchart of the computer program executed by microcontroller  24  is shown. The flowchart begins at step  60 . Next, at step  62 , the input and output ports of the microcontroller are initialized to a predetermined desired state. At step  64 , internal timers of the microcontroller are loaded with values so that a 50 millisecond and a 250 millisecond timer signal are produced. Next, at step  66 , several registers or program variables are initialized. These include measured frequency registers, FREQ_COUNT variable, FREQ_TOTAL variable, FREQ_TOTAL variable, and a FREQ_TOTAL_NEW variable. Timer and frequency inputs interrupts are intialized next at step  68 . At steps  70  and  72  program operational features are activated in accordance with the ground/floating state of the signals labeled TIME 1 , TIME 2 , TIME 3 , TIME 4 , CADE and SENS shown in the schematic of FIG.  3 . For example, the TIME 1 , TIME 2  and TIME 3  inputs provide a 3-bit binary input to microcontroller  24  to establish 1 of 8 possible alarm duration periods (such as 1-8 seconds) that the alarm signal will be produced when the frequency deviation of the signal from sensor circuit  16  is less than a predetermined deviation limit (as determined by microcontroller  24 ). The CADE signal instructs the microcontroller  24  to produce either a continuous alarm signal or an intermittent alarm signal based upon the ground/floating state thereof. Finally, the sensitivity of sensor circuit  16  may vary from installation to installation (the minimum and maximum frequency produced by circuit  16 ) and the SENS signal instructs microcontroller  24  to establish a smaller or larger frequency deviation limit when testing the frequency of the signal from circuit  16 . 
     The microcontroller program control loop begins at step  74 . At step  76 , the frequency signal from circuit  16  is detected and averaged over a 50 millisecond time period. Then, at step  78 , the current frequency average is compared with the previously computed frequency average, and if the difference is greater than a predetermined value, program execution continues at step  80  and the alarm timer is reset. After step  80 , program execution continues at step  74 . If the comparison at step  78  results in a deviation in frequency that is less than the limit, then program execution will continue to step  82 . 
     At step  82 , the alarm timer is tested to ascertain whether it has expired. If so, then the program continues at step  84  where the state of the “armed flag” is checked. If the armed flag is active, then program execution continues at step  86 . At step  86  the alarm is activated. Next, at step  88 , the microcontroller pauses for one second. Then, at step  90 , the microcontroller activates the external alarm output signal causing an alarm signal supplied to speaker  26 . Program execution continues at step  74  following step  90 . 
     If at step  82  the alarm timer has not expired, then program execution will continue with step  92 . At step  92 , microcontroller  24  detects whether switch S 1  is pressed. Recall that switch S 1  in the FIG. 3 schematic corresponds to the mode switch  18  in FIGS. 1 and 2. If at step  92  the switch is detected as pressed, then step  94  is executed and the toggle armed flag step is performed. Program execution continues at step  74  following step  94 . 
     If the button is not pressed at step  92 , then program execution continues at step  98 . If at step  98  it is determined that the button has been pressed for more than three seconds, then step  96  is executed and the test mode operation of device  10  is toggled on or off, or activated/deactivated. Test mode causes microcontroller  24  to produce a feedback alarm signal useful in establishing the appropriate distance when installing the magnetic strip  12  and magnetic sensor  14  into a motor vehicle. Test mode provides continuous feedback in the form of audible short beeps from speaker  26  indicating to the installer that frequency deviations in the signal from sensor circuit  16  are being sensed by microcontroller  24 . Following step  96  program execution returns to step  74 . 
     If at step  98  the button has not been impressed for more than three seconds then step  100  is executed and the alarm time is set to the value on jumpers TIME 1 , TIME 2  and TIME 3 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description of the preferred embodiment, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.