Abstract:
To test whether a trailer is coupled to a tractor when the tractor ignition switch is off, a test switch in the trailer connects a high-impedance power source in a trailer to a line carrying energy from the tractor ignition switch to the trailer&#39;s electrical load, and measures the voltage at the line. A high voltage indicates a connection only to the electrical load in the trailer and thus a decouple. A low voltage indicates a measurement of the electrical loads in both trailer and tractor and hence a coupling.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Application Ser. No. 60/896,491 filed 22 Mar. 2007, U.S. Application Ser. No. 60/908,467 filed 28 Mar. 2007, and U.S. Application Ser. No. 60/908,588 filed 28 Mar. 2007. This application is a continuation of U.S. application Ser. No. 12/054,380 filed 24 Mar. 2008, now U.S. Pat. No. 7,911,330 issued 22 Mar. 2011. The contents of these applications are hereby incorporated herein as if fully recited herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to trailer-mounted telematics system, and particularly to telematics system for accurately detecting when a trailer is or is not coupled to a tractor. 
     BACKGROUND OF THE INVENTION 
     In present systems, when a tractor connects to a trailer, the operator completes an electrical connection through a cable between the two units to provide electrical power to the trailer for operation of the lights and the anti-lock braking system. Various devices serve to indicate when the connection is broken. However, when the tractor&#39;s ignition is switched off while still connected to a trailer, such as during a stop en route for the driver to sleep or eat the trailer has no way of determining whether the tractor has in fact been decoupled or if the tractor has merely been shut off. 
     An object of this invention is to overcome this and other problems in the system. 
     SUMMARY OF EMBODIMENTS OF THE INVENTION 
     According to an embodiment of the invention, when the tractor ignition switch is off, a test switch in the trailer connects a high-impedance power source in a trailer to a line carrying energy from the tractor ignition switch to the trailer&#39;s electrical load, and a meter measures the voltage at the line, so that one voltage denotes only the electrical load in the trailer and thus a decouple, and another voltage denotes the electrical loads in both trailer and tractor and hence a coupling. 
     The various features of novelty characterizing the invention are pointed out in the claims. Other objects and advantages of the invention will become evident from the following detailed description when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an embodiment of the invention. 
         FIG. 2  is a schematic diagram illustrating another embodiment of the invention incorporating the embodiment of  FIG. 1 . 
         FIG. 3  is a flow chart illustrating the operation embodying an aspect of the invention. 
         FIG. 4  is a flow chart illustrating the operation embodying another aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the embodiment of  FIG. 1 , a tractor TC 1  and a trailer TL 1  are electrically connected by means of a multi-pin “J560” connector  5  through an auxiliary/ABS (antilock brake system) line  9  and a ground line  10 . Other circuits within this multi-pin connector  5  carry other signals, for example to control trailer lights. When an ignition switch  6  within the tractor TC 1  is closed, battery voltage from a battery  7  appears at ignition switch loads  8  and other electrical loads within the tractor TC 1 . The closed ignition switch  6  and a pin within the multi-pin connector  5  also place the voltage at the battery  7  onto the trailer&#39;s electrical loads  12  (primarily an antilock brake module). A voltage-measuring device  3  in the trailer TL 1  senses the voltage present at the line  9  relative to ground  10 . 
     When the tractor TC 1  is running and is connected to the trailer TL 1 , ignition switch  6  is closed and voltage on the battery  7  appears at the signal line  9 . Circuitry in  3  detects the voltage on battery  7  and informs a controller  11  mounted within the trailer TL 1  that it has been connected to the tractor TC 1 . Should the tractor TC 1  become disconnected from the trailer TL 1 , the voltage on  9  will vanish, and the trailer sensing system will correctly infer that it is no longer connected to a tractor. 
     At installation time, the trailer system is calibrated to the electrical loads present. The trailer TL 1  is left unconnected to any tractor, and a switch  4  is closed. This allows current to pass through resistor  2  to the trailer loads  12  on the Auxiliary/ABS line  9 . The voltage on the line is read by means of meter  3 , which may alternatively be an analog-to-digital converter. Controller  11  stores the value obtained. Resistor  2  is selected to give a small voltage drop during this calibration phase. 
     When the tractor&#39;s ignition switch  6  is opened while the tractor TC 1  is still connected to the trailer TL 1 , voltage is no longer present at line  9 . The controller  11  detects the absence of the voltage at line  9  by sensing the voltage from the meter  3 , and now determines if this loss of voltage is due to a disconnect between tractor TC 1  and trailer TL 1 , or to the ignition switch  6  in the tractor TC 1  being switched off. To do this, the controller  11  responds to the absence of signal at meter  3  and closes the switch  4 , thereby causing a test current to flow through resistor  2  to the line  9  and to the meter  3 . The meter  3  again measures the voltage on the line  9 . Should this voltage be a value stored during the calibration phase, the controller  11  correctly infers that there has been a true disconnect of the trailer TL 1  from the tractor TC 1 . 
     Should the tractor TC 1  still be connected to the trailer TL 1 , then the other electrical loads  8  within the tractor TC 1  will draw current at a level higher than was measured during calibration. The voltage measured at meter  3  will fall to a value below the calibration value. The controller  11  will correctly interpret this as an ignition switch turn-off rather than a tractor disconnect. The controller  11  operates a transmitter TR 1  that transmits the information concerning connect or disconnect. According to one embodiment of the invention, the transmitter TR 1  is part of the controller  11 . According to another embodiment the transmitter TR 1  is external to the controller. According to another embodiment the transmitter TR 1 , while external to the controller  11 , still remains part of the controller 
       FIG. 2  illustrates a trailer fleet of a number of tractor/trailer combinations, wherein each tractor is designated TC 1  and each trailer TR 1 , and wherein each tractor and each trailer includes the respective circuitry shown in  FIG. 1 . In  FIG. 1 , the controller  11  includes the transmitter, shown in  FIG. 2  as TR 1 , that transmits the connect or disconnect information from each tractor/trailer combination to a wireless link WL 1  that transfers the data to a Network Operations Center NOC. An internet link conveys the data to Fleet Managers FM 1  that use the facts to help manage the fleet. 
       FIG. 3  is a flow chart illustrating the operation of the controller  11  during calibration. Here, the calibration starts with step  110  by unhooking the trailer TL 1  from the tractor TC 1 . Step  120  follows by closing switch  4  and reading the voltage with meter  3  in step  130 . In step  140  a memory in the controller  11  stores the voltage of meter  3 , and in step  150  the switch  4  is opened to end the calibration as shown at  160 . 
       FIG. 4  is a flow chart illustrating the operation of the controller  11  during normal operation. At the outset the controller  11  stores the hooked or unhooked (i.e. coupled or uncoupled) state that was previously determined. In the absence of an initial current coupling state stored in the controller  11 , the latter signals a default state of “unhooked”, i.e. uncoupled. In step  210  a clock in the controller  11  initiates a test signal periodically, such as every minute to actuate a determination of the current (i.e. existing) state. The controller then compares the current state with the stored state as it pre-existed just prior to each periodic signal. As indicated, the stored coupling state may be the default state of “unhooked” or uncoupled. 
     If controller  11  has stored an indication that the trailer was previously hooked, step  230  checks the voltage at meter  3 . If the voltage at step  230  is approximately 12 volts this indicates in step  240  that the trailer TL 1  is still hooked. The controller  11  then stores the hooked condition or state and transmits a signal to continue with periodic testing at step  210 . If the voltage at meter  3  in step  230  is approximately 0 volts, the controller  11  executes step  250  and closes switch  4 . The controller  11 , at step  260 , checks the voltage at meter  3 . At step  270  if the voltage is equal to the calibration voltage, the controller has detected an unhook indicating that the state is unhooked at step  280 . At step  290  the transmitter in the controller  11  sends an unhooked message to the fleet managers via the wireless link WL 1  and the center NOC. In step  300  the controller  11  opens the switch  4  and signals to continue with step  210 . The controller  11  stores this unhook condition. 
     In step  260  if the voltage at meter  3  is less than the calibration voltage, step  310  indicates that the ignition switch  6  is off but the trailer is hooked. The controller  11  opens the switch  4  in step  320  and returns to step  210 . The controller  11  stores the hooked state. 
     In step  210  a clock in the controller  11  continues to actuate a determination of the current state in step  220 . If the controller shows a state wherein the trailer is unhooked, step  330  checks the voltage at meter  3 . If the voltage is approximately 0 volts this indicates in step  340  that the trailer TL 1  is still unhooked. The controller  11  then transmits a signal to continue with testing at step  210 . The controller stores this new unhooked state. If the voltage at meter  3  in step  330  is approximately 12 volts, the controller at step  350  recognizes that the status in hooked. At step  360  the transmitter in the controller  11  sends a hooked message to the fleet managers via the wireless link WL 1  and the center NOC and signals the controller to continue at step  210 . The controller  11  the stores the newly hooked state. 
     The controller  11  thus sends a state message only when the current state changes despite the periodic state tests. This limits the bandwidth and transmission time used by the system in reporting changes. 
     The controller  11  is biased into the unhooked condition because typically the controller starts its operation as the trailer TL 1  is coupled to the tractor TC 1 . Thus, the coupling of trailer TL 1  to tractor TC 1  results in a change at step  330  to approximately 12 volts that initiates step  350  and causes the controller  11  to signal that the trailer has become coupled to the tractor. 
     The embodiments of the invention allow a trailer-mounted telematics system to accurately detect when it is or is not coupled to a tractor. Upon change of coupling state, the system can wirelessly send a message to its fleet manager, who can take appropriate action. When a tractor connects to a trailer, the operator completes the electrical connection between the two units by means of a 7-signal cable specified by SAE J560. This allows the tractor to provide electrical power to the trailer for operation of the lights and the anti-lock braking system. One way a trailer-mounted device can detect that it is coupled to a tractor is to monitor the electrical status of the Auxiliary and ABS line (pin  7 ). This line is typically connected to the load side of the tractor&#39;s ignition switch, and therefore is at ˜12 v when the tractor is running. If the trailer-mounted device senses voltage at this pin, it serves as an indication that it has been connected to a tractor; absence of voltage implies that the connection has been broken. 
     The embodiments of the invention overcome an anomaly that may exist when the tractor&#39;s ignition is switched off while still connected to a trailer. This may occur due to any number of reasons, among them stopping en route for the driver to sleep or eat. The embodiments of the invention overcome the difficulty of merely monitoring the voltage of the Auxiliary and ABS signal when the trailer has no way of determining whether the tractor has in fact been decoupled or if the tractor has merely been shut off. 
     The embodiments of the invention surmount this problem by adding the additional circuit in the trailer-mounted device. A nominal 12-volt supply  1  from the trailer TL 1  is temporarily connected to the Auxiliary and ABS line  9  through the current limiting resistor  2 . This resistor  2  is sized to allow a small voltage drop when driving just trailer-mounted loads, but a larger voltage drop when attempting to drive the tractor loads on the switched circuit of the tractor&#39;s ignition switch  7 . During installation, the voltage drop due to the trailer alone is measured and recorded. Thus, if there is a tractor connected, the voltage at the Auxiliary and ABS line  9  will fall to a level below that obtained during calibration; if a tractor is not connected, the voltage will be at the calibration level. Because of the limited current available, none of the tractor loads are energized, and the action of the tractor&#39;s ignition switch is not compromised. The embodiments of the invention limit the bandwidth and transmission time used. 
     The embodiments of the invention prevent a remote monitoring system using telematics from transmitting false disconnect/reconnect sequences and confusing a fleet operator. 
     While embodiments of the invention have been described, it will be evident that the invention may be embodied otherwise.