Abstract:
An on-board diagnostic (OBD) scan tool device is provided with a current sense disconnect to enable vehicular installation of the device whereby the device automatically senses the connection of another device to an OBD communications bus and prevents communication errors by disconnecting from the bus. The device prevents communication conflicts on an OBD bus that ordinarily occur when two OBD scan tools attempt to communicate on the same bus. The device includes a sense circuit to determine when another device is attached to the bus. When another device is sensed, switching components are used to disconnect transceivers from the OBD bus. Furthermore, virtually seamless integration into existing OBD systems is possible through the use of a Y-cable.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of co-pending U.S. Provisional Patent Application Ser. No. 60/709,788, filed Aug. 19, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to on-board diagnostic (OBD) systems, and more specifically to an on-board scan tool including an automatic communications bus disconnect that enables connection of a plurality of scan tools to a single OBD system.  
         [0003]     On-board diagnostic (OBD) systems are generally known in the field of automotive maintenance, and indeed installation of them is required in many vehicles. OBD systems allow diagnosis and recordation of certain system parameters. It is desirable in some situations, such as fleet management, to have an OBD scan tool installed in a particular system. Fleet managers typically monitor data such as location, speed, fuel usage, mileage, air bag deployment, etc. Logging of this type of data can be accomplished by installing an OBD scan tool in the vehicle, as opposed to simply externally connecting one to a vehicle.  
         [0004]     Currently, there exist many problems associated with vehicle-installed OBD scan tools, such as false error codes, bus collisions leading to corrupt communications, and connection latency.  
         [0005]     The primary problem associated with vehicle-installed OBD scan tools is that communication problems occur when additional scan tools are connected, such as when vehicle diagnostics is run by a service technician. Some on-board scan tools attempt to address the problem. However, the main problem with conventional solutions is that some communications protocols remain operative when a subsequent device, such as an external OBD scan tool, attempts to establish communication on the same communications bus. The continued communication causes the external OBD device to show errors on the OBD bus leading to unnecessary maintenance on a vehicle.  
         [0006]     Also, other potential communications problems are communications bus collisions that are caused by intermittent messages on the protocols that remain active. Bus collisions require an external OBD device to retry corrupted messages, possibly resulting in error codes being generated by the external device.  
         [0007]     In addition to communications problems, connection latency is an extant problem. Present on-board devices wait a specific time period to stop communicating on the bus. Therefore, once an external device is connected, access to the bus by the external device is delayed and can result in significant connection latency.  
       SUMMARY OF THE INVENTION  
       [0008]     In view of the foregoing disadvantages inherent in the known types of on-board devices now present in the art, the present invention provides a new OBD scan tool device construction wherein the device enables vehicular installation of an internal OBD scan tool that automatically disconnects from the bus when another, external scan tool is connected. The device allows an internal OBD scan tool to be installed in a vehicle to acquire data requested by a fleet management application. To prevent communications conflicts on the vehicle&#39;s OBD communications bus, the internal device removes itself from the bus when an external device is sensed.  
         [0009]     The present invention generally comprises an OBD scan tool including a sense circuit to determine when another device, such as an external scan tool, is attached to the bus. Switching components disconnect transceivers from the OBD bus. Blocking diodes prevent the reverse flow of current when the device is un-powered. A bypass diode provides the ability to pass current to an external OBD tool. Further, a Y-cable connects to a vehicle OBD port and passes power through the sense circuit to another OBD connection, which provides a diagnostic access port for an external device.  
         [0010]     There has thus been outlined, rather broadly, certain features of the invention in order that the detailed description thereof may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter.  
         [0011]     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting.  
         [0012]     A primary advantage of the present invention is that it provides an OBD scan tool device that will overcome the shortcomings of the prior art devices.  
         [0013]     An advantage of the present invention is to enable installation of the device on a vehicle, wherein the device automatically disconnects from the OBD communications bus when another OBD device is connected.  
         [0014]     Another advantage is that the tool disconnects from the OBD bus in a timely fashion, thereby preventing communication errors and allowing an external device to connect to the bus without delay and without any errors occurring.  
         [0015]     Still another advantage is that the device reconnects to the OBD bus in a timely fashion when an external OBD device is removed from the OBD bus, thereby allowing an on-board application access to OBD data soon after the external device is removed.  
         [0016]     Yet another advantage is that the device provides only minimal loading to an OBD bus when an external device is attached to the OBD bus. Unnecessary loading of the OBD bus may cause communication failures resulting in errors generated by the external OBD device. This may ultimately result in unnecessary maintenance on the vehicle.  
         [0017]     A further advantage is that the device does not cause bus collisions when an external OBD device is attached. Bus collisions require the external device to retry protocol messages, possibly resulting in an error being generated by the external device.  
         [0018]     Another advantage is that the device does not cause a significant drain on a vehicle battery.  
         [0019]     A still further advantage is that the device preferably detects a current draw of an external scan tool without dropping a significant amount of voltage across the sensing element. If too much voltage is dropped across a sensing element it may cause problems with the external OBD device. Minimizing voltage drop is important if the system voltage is already at a low level.  
         [0020]     Other advantages of the present invention will become obvious to the reader and it is intended that these advantages are within the scope of the present invention.  
         [0021]     To the accomplishment of the above, this invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a partial cut away perspective view of a system incorporating an embodiment of the present invention.  
         [0023]      FIG. 2  is a representative block diagram of an embodiment of the present invention.  
         [0024]      FIG. 3  is a schematic representation of a preferred embodiment of a connectivity sensor used in an embodiment of the present invention.  
         [0025]      FIG. 4  is a schematic representation of a relationship between a first transceiver and switching components.  
         [0026]      FIG. 5  is a schematic representation of a second transceiver and biasing circuitry.  
         [0027]      FIG. 6  is a schematic representation of a relationship between a third transceiver and a switching component. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     Referring to  FIG. 1 , a partial cut away view of a system  10  that incorporates a device embodiment  11  of the present invention is shown. Although shown installed behind the dashboard or driving console  15  of a vehicle  16 , the device  11  could be installed anywhere on the vehicle  16 . The device  11  connects to the vehicle  16  OBD system at one connector  13  and provides a diagnostic access port at a second connector  12  for an external OBD scan tool (not shown). Furthermore, the device  11  provides a data analysis access port  14  for external connectivity to external analysis tools, such as an external computer used to download stored data.  
         [0029]     Now turning to  FIG. 2 , a representative block diagram of an embodiment of the present invention is shown. This embodiment comprises a current sense disconnect OBD scan tool device  100 , which comprises a microcontroller  101 , at least one transceiver  102 , a connectivity sensor  103 , a power supply  104 , and external connection ports  105 . While the power supply  104  could be a stand alone supply, specific to, and included with the device  100 , it is preferable to connect the device  100  to the power supply of a vehicle in which it is installed. The microcontroller  101  facilitates control of the device  100  and logging of desired data. The transceiver  102  provides communications ability on at least one type of diagnostics bus  116 , wherein the communication messages generally originate in the microcontroller  101  and are placed on the bus  116  by the transceiver  102 . The transceiver  102  comprises at least one transceiver, preferably of the configuration of those in  FIGS. 4-6 , and may include multiple transceivers. External connection ports  105  are provided to enable connectivity to a vehicle OBD connector  108 , to an external scan tool  110 , and to an external data analysis tool  109 . The connectivity sensor  103  determines when another device, such as an external scan tool  110 , is coupled with the bus  116 . Upon sensing an external tool  110 , switching components are used to automatically disconnect the transceiver  102  from the OBD bus  116 .  
         [0030]     A Y-cable  111  connects the device  100  to the vehicle&#39;s original OBD connector  108  and passes power through the device  100  and to a second, diagnostic access port  113  that replaces the vehicle&#39;s original OBD connector  108 . The Y-cable  111  comprises preferably three connectors: a DB15 male  114 , an OBD female connector  113 , and an OBD male connector  112 . The OBD female connector  113  on the Y-cable  111  serves as the diagnostic access port for an external OBD device  110 . The cable  111  preferably adheres to the OBD specification as far as wire size, current handling capability, and capacitance. This Y-cable  111  is specifically designed for an OBD device but could easily be converted for a heavy duty vehicle application utilizing Deutsch 9 and Deutsch 6 connectors.  
         [0031]      FIG. 3  depicts a schematic representation of the following preferred implementation of an embodiment of the connectivity sensor  103  used in the present invention. Generally, the circuit  200  comprises preferably a sense resistor R 5  and an op-amp U 2  to generate a signal indicative of subsequent device connection. More specifically, the circuit  200  comprises a sense resistor R 5 , an op-amp U 2 , switches Q 1 - 4 , and a voltage regulator U 1 . The current drawn by an external scan tool  110  passes through the sense resistor R 5 . The sense resistor R 5  is able to handle the power generated by the current drawn through it by the external scan tool  110 . The current drawn by the external scan tool  110  will generate a voltage across the sense resistor R 5 . The op-amp U 2  preferably has a rail-to-rail input since the voltage differential across R 5  will likely be small and the non-inverting input is at the power rail. The op-amp U 2  also preferably has a small input offset voltage due to the small voltage that will be generated across the sense resistor R 5 . When used in a motor vehicle such as a car, the op-amp U 2  preferably operates on a supply voltage in the range of about 8V to about 20V DC. Other voltages will be apparent to those in the art, depending on the specific application. Further, if the device is to remain active while the vehicle is inoperative, the op-amp U 2  preferably has a low quiescent current to minimize drain on the vehicle battery. Different values can be used for the sense resistor R 5  and biasing resistors R 2  and R 10  to change the trip point of the circuit  200 . Larger resistor R 5  values will reduce the output voltage supplied to the externally connected OBD device. Although the op-amp U 2  can have a high quiescent current, such current draw may limit the time the vehicle can sit out of service. Although an op-amp U 2  is preferred, the op-amp U 2  could be replaced by a bipolar transistor. A transistor, however, may require a larger voltage to be dropped across the sense resistor R 5  and therefore less voltage is available at the output for the externally connected OBD device.  
         [0032]     The circuit  200  includes a bypass diode D 3  intended to pass power to an externally connected device  110 . The bypass diode D 3  is preferably a high current Schottky diode. When the voltage across R 5  reaches a certain level current begins to bypass the sense resistor R 5  and flow through the diode D 3 . The bypass diode D 3  is preferably rated for at least  4  amps because that is the minimum required by the OBD specification. Transient voltage suppressors Z 1 ,Z 2  protect against power spikes on the lines. R 2  and R 3  protect the op-amp U 2  from power spikes above and below the power rails. The bypass diode D 3  preferably has a small forward voltage drop so as to not interfere with an externally attached OBD device  110 . Alternatively, a rectifier diode could be used instead of a Schottky diode, but a rectifier diode may drop additional voltage leaving less for the externally attached OBD device  110 .  
         [0033]     The circuit  200  and various transceiver biasing circuitry also includes switching components. The switching components Q are comprised generally of transistors and preferably MOSFETs. Both P type and N type MOSFETs are used. The switching components Q pass current and allow the circuit to operate when voltage is applied to the rest of the device  100 . The MOSFETs Q are used in the circuit to activate the pull up and pull down resistors as well as some termination loads. The MOSFETs Q generally have a low on resistance so as to not affect the circuit  200 . The transistors Q used in the circuit should be chosen with the peak operating voltage in mind. That is, the breakdown voltage of the chosen transistors Q preferably equals or exceeds the peak operating voltage of the system in which the device  100  is installed. While other transistors Q could be used, MOSFETs are preferred because they require only a voltage differential to operate, rather than current.  
         [0034]     Referring also to  FIGS. 4-6 , representative transceiver circuits are shown. The interface transceivers are known in the art and may be of various types, including: SAE J1850 VPW, SAE J1850 PWM, ISO 9141, SAE J2284, and DaimlerChrysler SCI.  FIG. 4  shows an SAE J2284 CAN transceiver U 5  with switching components Q 16 ,Q 17 . Specifically, with reference to  FIGS. 5 and 6 , blocking diodes  117  provide protection from reverse current flow. The blocking diodes  117  preferably comprise Schottky diodes on the power pins of certain OBD interface transceivers.  FIG. 5  shows ISO transceivers U 6 ,U 7  with blocking diodes D 10 ,D 11 ,D 13 .  FIG. 6  shows an SAE J1850 transceiver U 8  with a switching component Q 10  and a blocking diode D 9 . The blocking diodes  117  are preferably Schottky diodes due to their low forward voltage drop. Schottky diodes allow the maximum voltage to be presented to the OBD transceivers when power is applied. The Schottky diodes also preferably have a low reverse leakage current so that minimal loading is detectable on the OBD bus. A rectifier diode could be used instead of a Schottky diode, but a rectifier diode may drop additional voltage leaving less for the OBD transceivers. A rectifier diode would generally be acceptable as long as the transceivers can operate at a lower voltage.  
         [0035]     Referring to  FIG. 2 , the basic connection of the device  100  may be understood. To use the device  100 , the OBD male end  112  of the Y-cable  111  is plugged into the in-vehicle OBD connector  108 . The OBD female connector  113  of the Y-cable  111  mimics the in-vehicle OBD female connector  108 , thereby providing a diagnostic access port for an external device  110 . The DB15 connector  114  on the Y-cable  111  is coupled to the device  100 . As stated above, vehicle power is preferably used to power the device  101 . Power can be taken from the OBD interface  108  on the vehicle. This power is routed from the Y-cable  111  OBD male connector  112  to the DB15 connector  114  and into the device  100 . This power is then routed through the sense resistor R 5  and the bypass diode D 3  and to the diagnostic access port  113 . This is the power that is preferably used for any external OBD device  110 .  
         [0036]     The operation of the device  101  can be better understood with reference to  FIGS. 3-6 . When an external OBD device  110  is plugged into the Y-cable female connector  113 , current is drawn by the external device  110  through the sense resistor R 5 . This current causes a voltage drop across the sense resistor R 5 , which presents a voltage differential at the inputs of the op-amp U 2 . The op-amp U 2  activates a MOSFET Q 2  to draw current through a biasing resistor R 2  causing a voltage drop across the biasing resistor R 2  resulting in the potentials at the non-inverting and inverting inputs of the op-amp U 2  to be equal. The current flowing through the biasing resistor R 2  also flows through R 10  creating a voltage drop across R 10 . A filter circuit R 9 ,C 3  is present to de-bounce noise spikes from ignitions and other interference. The voltage across R 10  then charges the filter capacitor C 3  through the filter resistor R 9 . Once the filter capacitor C 3  is charged enough to meet the threshold voltage of MOSFET Q 4 , the MOSFET Q 4  will turn on. Turning Q 4  on causes MOSFET Q 3  to turn off. Deactivation of Q 3  causes deactivation of Q 1 , which electrically breaks the connection of power to a power regulator U 1 . The disconnect of power from the power regulator U 1  interrupts the power supply to the rest of the device  100 . Alternatively, the connectivity sensor  103  could also be used to control some other types of devices as opposed to the power regulator as is done in this system. For example, a relay or switch could be placed in line with the output of the power supply and controlled by the modified electrical signal generated by the sensor  103 .  
         [0037]     Referring now to  FIGS. 4-6 , to maintain a virtual open impedance state, when the circuit  200  powers down it deactivates switching MOSFETs Q 10 ,Q 16 ,Q 17  which connect the pull up and pull down resistors and termination resistors of the OBD interfaces from the OBD bus. The power generated by the voltage regulator U 1  is coupled to the gates of the N-type switching MOSFETs and causes them to deactivate when power is removed. MOSFET deactivation combined with the blocking diodes  117  where necessary, coupled to the transceivers effectively removes all loading circuits from the network thereby creating a virtual high impedance state on the bus  116  lines relative to the device  100 . This allows an external OBD device  110  to connect to and communicate with the OBD network as if there were no other OBD scan tools connected to the OBD bus  116 .  
         [0038]     After external scanning is complete and the external OBD device  110  is removed, the current flow through the sense resistor R 5  ceases, which allows the voltage at the op-amp U 2  inputs to be equal. This causes the op-amp U 2  to shut off Q 2 , stopping the current flow through R 10 . The capacitor C 3  then discharges through R 9  and R 10  until the voltage at the gate of Q 4  drops below the threshold voltage of Q 4 . At that time, Q 4  turns off, resulting in Q 1  and Q 3  to turn on. Q 1  turning on causes power to be applied to the voltage regulator U 1  which powers up the rest of the device  100 . When this power is activated it turns on the switching MOSFETs connecting the various OBD interfaces to the bus  116 .  
         [0039]     The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.