A Vehicle Trailer Coupling Sensor
Field
This invention relates to a device for determining between coupled and uncoupled conditions as between a vehicle and a trailer and which utilises an electrical connection sensor which senses the electrical interconnection of a vehicle tractor unit to a trailer unit.
Background of the Invention
Commercial tractor/trailer units are coupled together by both mechanical and electrical couplings. The electrical coupling between truck tractor units and trailers provides for such services as lights, brake lights, indicators and is a standardised 7 pin ISO 1185 (24N) connector and other auxiliary equipment may be connected through a 7 pin ISO 3731 (24S) connector. Most trailers are equipped with both types of connector and additionally some trailers may be equipped with an ISO 7638 connector for the ABS system on trailer if fitted. As an alternative to the latter connector the ABS system can be activated through a stop light pins of the ISO 1185 connector. Recently a new ISO 12098 15 pin connector has been introduced to combine all the features of the other three connectors.
With the variety in Make, type and age of trailers, the only standard connector which all trailers have is the ISO 1185 connector and even when some trailers have other additional connectors some drivers only make the minimum electrical connections between the tractor unit and trailer to operate the lights and indicator, i.e. using the ISO 1185 connector, and therefore the trailer is provided with only intermittent electrical power when the brakes, lights, or indicators are operated through the ISO 1185 connector.
It is becoming desirable to install trailer tracking and/or data logging systems in vehicle trailers to report on the trailer locations and/or status e.g. coupled or uncoupled to the motor vehicle. An intermittent power supply to a trailer makes it impossible to automatically detect whether the trailer is coupled or uncoupled to a tractor unit by sensing the power supply to
the trailer. One means over overcoming this problem is disclosed in the applicants published application W0-A-02/ 12004 in which a pin of the ISO 1185 connector is used to operate an electrical switch on connection and disconnection of the electrical connector. GB-A- 2176957 discloses an electrical device for detecting the coupled/uncoupled status of a trailer and trailer.
Object of the Invention
The present invention provides a device that can determine the coupled/uncoupled status between a vehicle and a trailer and which can be retrospectively incorporated into the existing light circuits of either a vehicle tractor unit or the trailer.
Statements of Invention
According to the present invention there is provided a detection device for determining between a coupled and uncoupled conditions of a tractor unit and a trailer, the device sensing the status of an electrical connector interconnecting electrical circuits on the tractor unit and a trailer and including a signal generator which generates a test signal and a monitor which monitor the impedance to said signal in said electrical circuits on both the tractor and trailer, the monitor detecting a change in impedance between electrically connected and disconnected conditions characterised in that the device includes a non linear element and the monitor detects a change in impedance by measuring the voltage across the non linear element when the detection device in use is located in series with said electrical circuits, and produces a further signal indicative of connection or disconnection.
The term "tractor unit" means any vehicle which is specifically adapted for towing a trailer, including articulated trailers, and draw bar trailers.
The non linear element has high resistance to DC at low voltages and a low resistance to DC above a predetermined voltage. The non linear element may be made from a bridge rectifier with its output shorted and is preferably formed from a pair of Schottky rectifier diodes connected anode -to- cathode in parallel.
A micro controller acts as both the signal generator and monitor and pulses a small electrical current ( for example 0.5mA) to the lighting circuit and measures voltage in the circuit, preferably across a non linear element. The voltage ( which is a function of the resistance ) is passed through an amplifier and then to the micro controller. From the voltage amplitude the microcontroller determines if the connector is coupled . When the resistance is above a predetermined value ( for example 200 Ohms) the tractor and trailer circuits are disconnected , and when the resistance is below the predetermined value the circuits are connected. The processor then sends a signal indicative of the condition of the connector. The resistance of light bulbs is small when cold , and the predetermined value is set such that it is immaterial how many bulbs in the circuits conduct the test pulse when either hot or cold.
Also according to the invention there is provided a tractor trailer combination having an electrical connector operable to interconnect a tractor lighting circuit with a trailer lighting circuit wherein a detection device according to the present invention is located in a lighting circuit in one of the tractor or trailer.
The lighting circuits may include the normal vehicle lighting circuits or alternatively may include a special dedicated electrical circuit installed specially for the operation of the detection device.
The device is conveniently placed in the trailer wiring system, preferably in series with the common ground line for the lighting systems.
If one of the tractor or trailer has a tracking and monitoring system thereon , then the detection device is installed on said one of the tractor or trailer.
Also according to the present invention there is provided a method of detection between coupled and uncoupled conditions between a tractor unit and trailer, in said method an electrical connector links the electrical lighting circuits on a tractor unit with electrical lighting circuits on a trailer and by a change of impedance in said lighting circuit when passing between trailer connected and trailer disconnected conditions is detected by measurement of the voltage across a non linear element when a small current is passed through the existing vehicle wiring circuit..
The change in impedance is measured in the common ground line for the tractor and trailer. The integrity of the lighting circuit is maintained by use of the non-linear element.
Description of the drawings The invention will be described by way of example and with reference to the accompanying drawings in which:
Fig 1 shows a front elevation of the trailer half of a known tractor/trailer electrical connector showing the connector pin array, Fig. 2 is a schematic drawing of tractor trailer circuits including the detection device according to the present invention, and
Fig.3 is a circuit diagram of the detection device.
Detailed Description of the Invention
The invention seeks to determine when a tractor unit and trailer unit are in a coupled or uncoupled state by sensing when the tractor and trailer are electrically interconnected . With reference to Fig.1 there is shown half of a 7 pin standard trailer lighting connector 10 (ISO 1185). ISO stands for International Standards Organisation which aims for world wide interchangeability as is agreed by committees of experts. The seven pins 11-17 have various functions, pin 11 is common ground line , pins 12 and 16 are power inputs for the tail lights, pins 13 and 15 are power inputs for the direction indicators, pin 14 is a power inputs for the stop lights and pin 17 in the UK is typically a blank pin, but may be used in other countries for selected auxiliary functions.
With reference now to Fig. 2, there is illustrated the lighting circuits L 1 for the tractor which are represented through by a single bulb 21 and circuit to the left of the dotted line L and the lighting circuits L2 for the trailer are represented by a single bulb 22 and circuit to the right of the line L. The tractor and trailer lights 21 22 are operated by switch 24. The two circuits are shown in the interconnected condition through a ISO connector 10. In this example the trailer is provided with a tracking & monitoring unit 23 however it will be appreciated that such systems may be installed in the tractor unit if desired. A detection unit 30 according to the present invention is installed in series in the common ground line Gl in the trailer which leads to the pin 11 on the connector 10. The pin 11 connects into the common ground line G2 in the tractor unit. The common ground line G2 is connected to all the lighting circuits on the tractor unit. The respective light bulb filiaments in each circuit are connected to their respective trailer circuits through the
respective power pins 12-16. Any output signal S from the detector 30 will therefore pass through the connector pin 11, ground line G2, through the bulbs 21 in the tractor, back through the respective power lines and connector pins 12, 13, 14, 15, and 16, trailer bulbs 22, through the ground line Gl and back to the detector unit 30.
The detector unit 30 senses a change in impedance in the combined tractor and trailer lighting circuits between the connected and disconnected condition when impedance is effectively infinite i.e. there is a open circuit.
With reference to Fig. 3 there is shown the circuit for the detection unit or device 30 which uses a microcontroller 33 to sense the change in resistance in the lighting circuit between a connected condition and a disconnected condition.
The detection device receives a 12 v power supply via terminal 1 of junction block 36 which is passed through a voltage regulator 34 in the form of a low drop out exact 5 V smooth power supply which provides a constant 5V supply to pin 1 in the microcontroller 33 and to an amplifier 32.
The software in the microcontroller applies the sensing pulse, measures the resulting voltage pulse, and compares it to the pulse amplitude in the uncoupled state to determine if the trailer is electrically connected or disconnected. The microcontroller 33 produces a pulsed signal (0.5mA) which is output from pin 3. The microcontroller software provides timing and control of the pulse drive signal, so that the sensing is carried out effectively constantly, but is pulsed to conserve battery power. The microcontroller 33 outputs the 0.5mA test pulse of lmS duration 5 times a second.
The pulsed signal passes through the lighting circuits via junction block 37 and the ground lines Gl & G2 and the resulting voltage in the circuit is measured by the microcontroller 33, in this case across a non linear element 31 placed across the test pulse out and return lines. Because the resistance of the non linear element is very high at very low voltages, a low current test signal of 0.5mA (5 x 10Λ-4 Amperes) can be used to produce a measurable Voltage across the non-linear element.
The voltage signal from the lighting circuit is passed through an amplifier 32 and the amplified signal passes to pin 7 of the microcontroller 33. In the described embodiment, the amplifier 32 amplifies the signal to about 2 Volts DC. The micro controller software carries out Analogue to Digital conversions to sample the pulse voltage at a number of times relative to the start and end of the test current pulse, in order to determine the rise time and fall time of the voltage pulse. These time constants depend upon the AC impedance of the ground pin of the connector 10 , allowing detection of changes in capacitance and inductance and well as resistance.
Output pin 2 of the microcontroller is driven high to +5V to signal when the trailer is coupled, and low to 0V to signal when uncoupled. This signal is used to drive the tracking unit 23 or other electronic security systems, or can drive a LED indicator. The pin 2 is connected to terminal 2 of the junction block 36 to facilitate connection to the tracking unit.
The software further provides gating and timing of the returned voltage pulse, to determine reliably in the presence of noise or electrical leakage, if the trailer is coupled or not.
The low amplitude current test signal results in a small Voltage signal of about 0.150 Volt DC, when the connector 10 is not coupled . When the connector 10 is coupled, the parallel resistance of the lighting circuits in the vehicle will produce loading and consequent reduction in amplitude of this test signal, according to Ohm's law, which can be detected. When the connector 10 is disconnected the resistance approaches infinite.
The non linear element 31 will have a very high resistance to DC current at very low voltages (less than 0.2 Volts) but will have a very low resistance to DC current at any voltage higher than threshold voltage , in this case 0.2V. The non linear element above 0.2 volts is forward biased and conducts so that the detection device is sensitive to small changes in impedance, while also introducing a negligibly small voltage loss into the lighting circuit. When the 24V vehicle lighting circuit is operated by switch 24 the non linear element prevents a high voltage signal from entering the detection device circuit. The non-linear element 31 is made using two inverse parallel connected Schottky rectifier diodes. This will conduct current in either direction because the two individual rectifiers are connected anode-to-cathode in parallel. Because the resistance of the non linear element is very low at the DC voltages at which the vehicle electrics normally operate (24V DC for a commercial vehicle) it will have no adverse effect on the vehicle electrical system .
A conventional Silicon rectifier 35 is connected in parallel with the non linear element 31 so that the electrical circuit has continuity in the event of an open circuit failure in one of the Schottky diodes.