Abstract:
A theft prevention device, having a first switch capable of movement between a first position and a second position, the first position electrically connecting an electrical system to a power supply of a vehicle and the device includes a switch bypass circuit being electrically connected to said power supply when the switch is in the second position, the switch bypass circuit allows a current from the power supply to reach the electrical system, this current is less than the current traveling through the switch when the switch is in the first position, the current is sufficiently large enough to maintain volatile memories of electrical components in a vehicle.

Description:
RELATED APPLICATIONS 
     This application is related to U.S. Pat. Nos. 4,958,084, 5,977,654 and 5,965,954, the contents of which are incorporated herein by reference thereto. 
    
    
     TECHNICAL FIELD 
     The present application relates to anti-theft devices for motor vehicles and, more particularly, to an apparatus and method for preventing an unauthorized starting of a vehicle. 
     BACKGROUND OF INVENTION 
     One of the unpleasant aspects of owing a vehicle is dealing with the potential theft of the vehicle itself. In fact, one factor contributing to the overall cost for owning and operating a motor vehicle is the insurance premiums necessary to cover the inconveniences associated with a theft of the vehicle. 
     In an attempt to address these problems, a substantial industry has been developed to manufacture and promote various mechanisms for hindering the ease by which an automobile or other motor vehicle can be stolen. These devices include steering wheel locks, alarm systems, and devices which disable certain essential components of the vehicle when a theft is attempted. 
     SUMMARY OF THE INVENTION 
     A method and apparatus for allowing a limited amount of current to bypass a switch which prevents an amount of current necessary to start the vehicle engine when the anti-theft device is armed. The amount of current allowed to bypass the switch is sufficient to maintained the volatile memories and such vehicle accessories such as clock time, radio presets and the engine control computer. 
     The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of an anti-theft system; 
     FIG. 2 is a schematic illustration of an alternative configuration of the anti-theft system illustrated in FIG. 1; 
     FIG. 3 illustrates remote activation of the anti-theft system; 
     FIG. 4 is a schematic illustration of a latching relay used with the anti-theft system; 
     FIG. 5 is a schematic illustration illustrating an alternative configuration of the latching relay used with the anti-theft system; 
     FIG. 6 illustrates possible AC waveforms generated at the terminals of a battery in a vehicle; 
     FIG. 7 is a schematic illustration of a circuit for measuring the AC waveforms illustrated in FIG. 6; and 
     FIG. 8 is a flowchart illustrating the command sequence of a computer algorithm utilized in the FIG. 7 embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a battery control system  10  is illustrated. Battery control system  10  is anticipated for use with a vehicle starting system. Of course, battery control system  10  may be used in other applications. 
     A power supply  12  is connected to battery control system  10  through a positive connection  14  at one end and a ground  16  at the other. Positive connection  14  is coupled to a switch  18  and a resistive element  20 . Alternatively, the battery control system is connected to the power supply through a negative connection  15  at one end and a ground at the other. 
     In an exemplary embodiment, switch  18  is a latching relay. Of course, other switching methods are contemplated for use with battery control system  10 . For example, switch  18  can be either mechanical or electrical (e.g. MOSFET or BJT) switches. 
     Battery supply  12  provides the necessary power for maintaining the volatile memories of the vehicle functions and also provides the cranking power necessary to start the vehicle engine. After, the engine is running the vehicle electrical systems are generally powered by an alternator. 
     Resistive element  20  is connected to either end of switch  18 . Resistive element  20  is positioned on a path that allows a current to bypass switch  18  when switch  18  is in the open configuration illustrated in FIG.  1 . 
     Switch  18  has a first end  22  and a second end  24  which are bridged by a movable switch  26  of switch  18 . 
     The output of battery control system  10  is received into an electrical system  28  of a vehicle (FIG.  3 ). Electrical system  28  includes but is not limited to the following: vehicle accessories  30 , an alternator  32  and a starter circuit  34 . 
     In an exemplary embodiment, and referring now to FIGS. 3-5, switch  18  is remotely activated by a radio frequency emitted by a hand held transmitter  36  which sends an arm/disarm signal to switch  18 . In an exemplary embodiment, transmitter  36  is a key fob that is capable of being installed on a key chain. 
     Transmitter  36  sends a first signal for positioning switch  18  into an open position (FIG. 4) and a second signal for positioning latching relay into a closed position (FIG.  5 ). As an alternative, transmitter  36  sends a signal for alternating the switch (latching relay) position. 
     Switch  18  has a solenoid  37  with a plunger  38  for moving the mechanical relay. The coil of solenoid  37  is excited to open the switch by applying power in a first direction. Once in this opened position, a magnet  39  will retain the mechanical relay in an open configuration. 
     In order to close the mechanical switch power is applied to the coil an opposite direction creating a magnetic force which will reverse the position of switch into the closed position illustrated in FIG. 5. A spring or urging mechanism  40  provides an urging force to assist in the closing of the latching relay. 
     Of course, other mechanical means for opening and closing be latching relay the via a signal sent by a remote transmission device are contemplated for use with the antitheft system of the present application. 
     Resister  20  allows an amount of current from power supply  12  sufficient enough to maintained the volatile memories of vehicle accessories such as computer control module, radio presets and clocks. 
     In an exemplary embodiment resister  20  has a value between a high-end of 1 ohm and a low-end of 10 milli-ohms. Of course, the value of resister  10  may be greater than or less than the after mentioned range. The preferred value of resister  20  is a value that will prevent the loss of volatile memory when the antitheft system is engaged (i.e. switch  18  open) while preventing a current strong enough to start a vehicle engine to pass through. 
     Referring now to FIG. 2, a preferred schematic of an antitheft mechanism  10  is illustrated. Here a MOSFET  42  is positioned between the input of resister  20  and the power supply  12 . MOSFET  42  provides a protective feature that prevents resister  20  from being burned out due to an excessive load trying to pass through resister  20 . This could be caused by an unauthorized attempt to start the vehicle when the antitheft system has been armed and switch  18  is in an open position. In this situation, MOSFET  42  will open up and completely disconnect the system from power supply  12 . 
     A driver circuit  44  samples the current passing through resister  20 . In addition, driver circuit  44  will instruct MOSFET  42  to open in the event an excessive amount of current is attempting to pass through resister  20 . 
     For example, and in a situation where an unauthorized attempt to start the vehicle occurs (i.e. antitheft mechanism armed and a switch  18  is in an open position) a substantially large amount of current will be detected by the driver circuit  44 . At this point, the driver circuit  44  will immediately instruct the MOSFET to open. At this point the vehicle electrical system will be completely removed from the power supply. This will prevent resistive element  20  from being burned out by the current. 
     The driver circuit will sample the voltage drop across the resister element or alternatively (as illustrated by the dashed lines in FIG. 2) the driver circuit will look at the output of the battery control system. 
     Referring now to FIGS. 1-4 an alternative embodiment of the system also utilizes a means for discriminating the AC waveforms that appear through the battery terminals, as a result of engine ignition. When these waveforms are present, software using a pattern recognition algorithm to detect these conditions will then inhibit the arming of the anti-theft device. This will prevent the system from arming while the vehicle is running. 
     The engine-on detection system only requires electrical connections at the battery terminals. No other electrical connections are required by virtue of the fact that the engine-on signal can be detected through the battery terminals. 
     The engine-on detection sub-system uses the AC component of any signal that appears between the positive and negative battery terminals as an input and amplifies it and then transmits it to the microprocessor, which then samples this waveform in real time. 
     When the engine is running, the waveform has a profile that is unique with respect to frequency range and amplitude to any other components or conditions, which will create a signal between the positive and negative battery terminals. 
     FIG. 6 illustrates the AC waveform created by the electrical system when the engine is on. In addition, FIG. 6 illustrates some other possible waveforms which may be generated at the terminals up the battery. 
     It is unlikely that any other part of the electrical system will generate an AC waveform with the AC amplitude exhibited by the engine on condition. Referring now to FIG. 7, the circuitry of the amplifier that detects the load fluctuation, which prevents anti-theft arming, is comprised of two parts. 
     The first part is an amplifier that amplifies the AC waveform existing across the vehicle electrical load at the junction  50  of the battery control system and the vehicle load. 
     The second part is a comparator that inputs the amplified threshold voltage into a comparator. The comparator is set to create a square wave pulse into an interrupt pin of the microcontroller. 
     Amplifier  52  receives the AC component of the signal present at junction  50  due to the engine ignition activity. An exemplary minimum value would be 50 mV peak-to-peak. Amplifier  52  transmits this signal with a gain to an analog-to-digital microprocessor input  54  of a microprocessor  56 . The frequency and amplitude of this signal is a function of engine rpm, and is discriminated by the microcontroller for use in inhibiting a battery disconnect. 
     Referring now to FIG. 8, a flowchart  60  illustrates portions of a command sequence employed by the control algorithms stored in the microprocessor of the anti-theft system. A first step or decision node  62  depicts a request for arming of the anti-theft mechanism. A second decision node  64  determines whether the vehicle engine is running, an operating condition in which it may be undesirable to arm the anti-theft mechanism. 
     This is determined by utilizing signal processing and pattern recognition software wherein the unique waveform (FIG. 6) produced by the vehicle engine at the battery terminals is compared to profile signals that are stored in the memory of an EEPROM (FIG.  7 ). 
     If decision node  64  determines that the engine is running the vehicle battery cannot be disconnected and the system returns to decision node  64 . In addition, the signal processing and pattern recognition software can be configured to detect other conditions in which a battery disconnect may be undesirable. For example, hazard flashers and wipers-on are situations in which a battery disconnect would be undesirable. 
     In addition, and as yet another alternative, the pattern recognition software can be configured to detect any waveform with a peak to peak the value above a predetermined value. Accordingly, if the pattern recognition software detects any AC signal above a predetermined threshold the arming of the antitheft mechanism would be prevented. Otherwise, and if the presence of such a signal is not detected, the arming of the system would be allowed. 
     The sensing of the engine on is accomplished by discriminating the profile of the electrical activity that is impressed upon the 12V bus due to the ignition system. The circuitry for discriminating ignition activity separates the AC component due to the ignition system from the total DC. The AC signal is then conditioned for input into the microcontroller. The microcontroller determines whether the signal is consistent with the expected engine-on profile, or if the signal is due to some other electrical activity such as the radiator fan motor, the ventilation blower motor, etc. 
     Accordingly, and if it has been determined that the vehicle engine is running, decision node  64  prevents the arming of the anti-theft switch until the engine is off. If on the other hand decision node  64  determines that the engine is not on, a command step arms the anti-theft mechanism. 
     Accordingly, and based upon the profile incorporated into the microcontroller, the battery can be disconnected only if the engine is not on. 
     While the invention has been described with reference to a preferred 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.