GB2511095A

GB2511095A - Trailer and bulb failure detection

Info

Publication number: GB2511095A
Application number: GB1303208.1A
Authority: GB
Inventors: Mark Downing
Original assignee: Scorpion Automotive Ltd
Current assignee: Scorpion Automotive Ltd
Priority date: 2013-02-22
Filing date: 2013-02-22
Publication date: 2014-08-27
Also published as: GB201303208D0

Abstract

The invention provides a lighting interface 21 between a vehicle (1, Figure 1A) and a trailer (2, Figure 1A) with a plurality of lighting circuits 22, 23, 24 powered by the vehicle, which preferably comprise at least a stop signal circuit 22 and direction indicator circuits 23, 24. The vehicle preferably detects the presence of the trailer by detecting a path to ground through a bulb or LED of at least one of the lighting circuits 22, 23, 24. Interface 21 preferably comprises circuitry providing a path to ground for each circuit within a predetermined resistance range, irrespective of the condition of the lighting circuit. Preferably a resistor (100, Figure 4B) is provided to simulate the load of a filament bulb if LEDs are provided in a lighting circuit; advantageously, the resistor is bypassed if a filament bulb is used. A MOSFET (63, Figure 6A) may be provided to switch to a high resistance path if a fault, such as a failed bulb or LED or an overload, is detected.

Description

Trailer and bulb failure detection Figures 1A and lB show that a trailer 2 (i.e. a vehicle used for transport of e.g. goods and materials), which may removeably be towed by a tractor 1, includes at least: a brake circuit 23, a left hand directional indicator, L/H Dl, circuit 22, and a right hand directional indicator, R/H Dl, circuit 24.

Usually the circuits 22, 23 and 24 comprise bulbs (i.e. filament lamps), and, in order to control the circuits 22, 23 and 24 of the trailer 2, the tractor I often includes a by-pass relay which draws current from rear bulbs 12 of a lighting harness of the tractor I (including also usually a brake bulb, a L/H Dl bulb and a R/H Dl bulb), in order to power the corresponding bulbs 22, 23 and 24 of the trailer 2. Other systems not using the tractor lighting harness in order to control the bulbs 22, 23 and 24 of the trailer 2 may also be possible.

The tractor 1 also includes trailer detection and bulb-check systems 11, in order to detect the presence of the trailer 2 and to check the status of the bulbs on the trailer 2, in order to be able to trigger specific safety features, such as trailer stability programs (including anti snaking trailer and specific braking programs) or bulb failure reporting.

The systems 11 are often proprietary and thus different from a tractor brand to another tractor brand (for example, some systems use current pulses to detect the trailer, whilst others use charges and discharges in electronic LCR circuits or others uses a low intensity constant current). The trailer detection and monitoring units are thus designed for a specific tractor.

The inventors have however managed to design a unit which may be fitted in a trailer and which may cooperate with all sorts of tractors.

Another issue is that, in some cases (e.g. when the trailer is detected by a current flowing in a bulb of the trailer) failure of the bulbs 22, 23 and 24 may impact the detection of the trailer. However it is understood that the presence of the trailer 2 must be detected in order to trigger the appropriate specific safety features.

The invention provides trailer detection regardless of the status of the bulbs of the trailer, thereby improving safety.

Yet another issue is that the bulbs 22, 23 and 24 are currently more and more replaced by Light Emitting Diode, LED, lamps (or clusters) in trailers. However electrical features of LED lamps (including their low resistor) make it more difficult for the existing systems 11 on the existing tractors Ito detect the presence of the trailer 2 and to check the status of the LED lamps on the trailer 2. However it is understood that the presence of the trailer 2 must be detected in order to trigger the appropriate specific safety features, and the status of the LED lamps must be correctly assessed so that appropriate measures (such as reporting the lamp failure) may be taken.

The invention provides trailer detection regardless of the type of the lamp of the trailer, either filament lamp or LED lamp, thereby improving safety.

Embodiments of the present invention thus aim to ameliorate at least one of the above mentioned issues.

Aspects and preferred examples of the present invention are set out in the appended claims.

In one aspect, there is provided a lighting interface for a vehicle and trailer combination, wherein the trailer has a plurality of lighting circuits including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect the presence of the trailer by detecting a path to ground through a bulb of at least one of the lighting circuits, the interface comprising circuitry for providing a path to ground for at least one circuit within a predetermined resistance range, irrespective of the condition of the lighting circuit.

The circuitry may be arranged for providing a path to ground for each of the stop and two direction indicator circuits. The circuitry may be arranged to provide a current load when a short duration pulse is applied to the interface in order to detect the presence of the trailer, or to provide a current load when a low voltage, insufficient to power the lighting circuits significantly, is applied to the interface in order to detect the presence of the trailer.

The circuitry may comprise a depletion mode transistor in series with a resistor, whereby the transistor may be configured to remain in a conducting state if insufficient power is applied to power logic controlling said transistor. The interface may further be arranged to provide a load to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb.

In another aspect, there is provided a lighting interface for a vehicle and trailer combination, wherein the trailer has a plurality of lighting circuits including at least one of a stop signal and direction indicator signals to be powered by the vehicle, and wherein the interface may further comprise circuitry arranged to provide a load to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb.

The circuitry may be arranged to signal a fault to the vehicle by providing a high resistance path to ground or open circuit on detection of a fault in the trailer lighting circuit.

In another aspect, there is provided a lighting interface for a vehicle and trailer combination, wherein the trailer has a plurality of lighting circuits including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect a path to ground through at least one of the lighting circuits, wherein the interface further comprises circuitry arranged to signal a fault to the vehicle by providing a high resistance path to ground or open circuit on detection of a fault in the trailer lighting circuit.

The interface may comprise circuitry arranged to disconnect a path to ground for a trailer detection signal from the vehicle, optionally wherein the circuitry may comprise a depletion mode transistor in series with a current load, whereby the transistor may be configured to open if a filament bulb is detected. The interlace may be arranged not to connect said fudher load if a filament bulb is detected in the trailer lighting circuit.

In another aspect, there is provided a lighting interface for a vehicle and trailer combination, wherein the trailer has a plurality of lighting circuits including indicator to be flashed by spaced apart power pulses provided by the vehicle, wherein the vehicle is arranged to detect a path to ground through at least one of the lighting circuits, wherein the interlace comprises: energy storage circuitry for storing energy provided by the power pulses, for a time period at least equal to the expected spacing between adjacent power pulses, and latching circuitry arranged, on detection of a fault during a first pulse of power from the vehicle, to signal the detected fault to the vehicle by providing a high resistance path to ground or open circuit at the next pulse of power.

The energy storage circuitry may be arranged for storing energy for a time period sufficient to power the latching circuitry in order to signal the detected fault at the next pulse of power, such as for at least two seconds.

In another aspect, there is provided a lighting interlace for a vehicle and trailer combination, wherein the trailer has a plurality of lighting circuits including at least a stop signal circuit and a tail signal circuit which are interconnected, to detect a path to ground through at least one of the lighting circuits, wherein the interface comprises circuitry arranged to detect a fault condition in the stop circuit, irrespective of whether the tail circuit is powered.

The interlace may comprise circuitry providing a voltage drop between the stop signal circuit and the tail signal circuit, in order to facilitate discrimination of the power voltage of the stop signal circuit and the tail signal circuit for the fault detection.

The fault may comprise an open circuit or failure of an LED light, based on an LED light current threshold, or an open circuit or failure of a filament light, or an overload or short circuit based on an overload current threshold.

The interface may be arranged to disconnect the trailer lighting circuit in an overload condition! and optionally may comprise an enhancement mode transistor arranged to be in series with the lighting circuits, whereby the transistor may be configured not to conduct if an overload condition is detected.

In another aspect, there is provided a lighting interface for a vehicle and trailer combination, wherein the trailer has a plurality of lighting circuits including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect the presence of the trailer by detecting a path to ground through a bulb of at least one of the lighting circuits, the interface comprising circuitry comprising a depletion mode transistor in series with a current load comprising a resistor, whereby the transistor is configured to remain in a conducting state if insufficient power is applied to power logic controlling said transistor; wherein the circuitry is arranged for providing, for at least one circuit: a path to ground through the resistor, when a short duration pulse or a low voltage insufficient to power the lighting circuits significantly is applied to the interface.

irrespective of the condition of the lighting circuit, to enable trailer detection by the vehicle; and a current load through the resistor in order to simulate a filament bulb when the trailer light circuit is powered by the vehicle and comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb.

The transistor may be configured to open if a filament bulb is detected and/or if a fault in the trailer lighting circuit is detected.

In another aspect, there is provided a lighting interface for a vehicle and trailer combination, wherein the trailer has a plurality of lighting circuits including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to provide power supply to the interface and to detect the presence of a path to ground through at least one of the lighting circuits; the interface comprising circuitry comprising a depletion mode transistor in series with a resistor, whereby the transistor is configured to remain in a conducting state if insufficient power is applied to power logic controlling said transistor; wherein the circuitry is arranged for providing a current load through the resistor in order to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb; and wherein the interface is arranged, on detection of a power supply voltage drop below a predetermined threshold, to keep the transistor in series with the resistor for at least a predetermined time period, such as at least two seconds, in order to avoid detection of a fault in the trailer lighting circuit due to short term transient voltage drops.

The power supply may be comprised in a predetermined nominal voltage supply range of [+18V; +32V], and the predetermined threshold is +18V.

In another aspect, there is provided a lighting interface for a vehicle and trailer combination, wherein the trailer has a plurality of lighting circuits including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect a path to ground in at least one of the lighting circuits; wherein the interface further comprises circuitry arranged to provide a load to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb; wherein the interface further comprises circuitry arranged to, on detection of a current draw of the light emitting element below a predetermined LED light current threshold, signal a fault in the light emitting element of the trailer lighting circuit to the vehicle by providing a high resistance path to ground or open circuit, irrespective of the current draw in other elements of the interface.

The interface may be connected to each of the stop and two direction indicator circuits.

In another aspect, there is provided a lighting interface for a vehicle and trailer combination, wherein the trailer has a plurality of lighting circuits including at least a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect the presence of the trailer by detecting a path to ground through a bulb of at least one of the lighting circuits; the interface comprising circuitry for providing a path to ground for the or each circuit within a predetermined resistance range, irrespective of the condition of the lighting circuit, and a load to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb, whilst not providing a further load if a filament bulb is detected in the lighting circuit; wherein the circuitry optionally comprises a depletion mode transistor in series with a resistor, whereby the transistor is configured to remain in a conducting state if insufficient voltage is applied to power logic controlling said transistor and arranged to disconnect a path to ground for a trailer detection signal from the vehicle, and to open if a filament bulb is detected; the interface further comprising circuitry arranged to signal fault to the vehicle by providing a high resistance path to ground or open circuit on detection of a fault in the trailer lighting circuit; wherein the trailer has a plurality of lighting circuits including indicator to be flashed by spaced apart power pulses provided by the vehicle; wherein the interface comprises: energy storage circuitry for storing energy provided by the power pulses, for a time period at least equal to the expected spacing between adjacent power pulses, and latching circuitry arranged, on detection of a fault during a first pulse of power from the vehicle, to signal the detected fault to the vehicle by providing a high resistance path to ground or open circuit at the next pulse of power.

The trailer may have a plurality of lighting circuits including at least a stop signal circuit and a tail signal circuit which are interconnected, wherein the vehicle may be arranged to detect the presence of a bulb in at least one of the lighting circuits, wherein the interface may comprise circuitry arranged to detect a fault condition in the stop circuit, irrespective of whether the tail circuit is powered.

The current load may be equivalent to a cold bulb resistance. The depletion mode transistor may be a MOSFET. The load may be equivalent to a 21W filament lamp powered by nominal 24V, and may preferably comprise a resistor having a resistance of about 30Q ±50%. The LED light current threshold may be comprised between 2mA and 500mA. The overload current threshold may be comprised between 2.SA and 7.SA, preferably 4.2A.

A filament bulb may be detected in the trailer lighting circuit on detection of a current draw superior or equal to a current representative of a filament bulb through the lighting circuits, the current draw being comprised between 0.5A and 2A, preferably 0.8A.

The interface may comprise a logic arranged on a Printed Circuit Board placed in a housing.

The interface may comprise a heat sink, the heat sink, preferably may comprise radiating fins and preferably may be fitted on a housing of the unit using an elastomer 0-ring.

The interface may comprise a housing comprising: an input from the at least one lamp circuit of the trailer; and an output to the controller adapted to be fitted on the vehicle, wherein the housing is filled with potting compound to seal the input and the output.

The interface may comprise a housing adapted to be fitted on the trailer.

The load may have a variable resistance, whereby the load may be arranged to be configurable with a plurality of sets of lighting circuits, the load being configured to a specific set of lighting circuits by setting the resistance of the load. The load may be arranged to be manually configured. The interface may comprise logic adapted to measure a level of a working current of the plurality of lighting circuits of the trailer when powered by the vehicle and to automatically configure the load.

The interface may be built-in with the lighting circuits (22, 23, 24) of the trailer.

As already mentioned, advantages of the invention include that the unit may be fitted in a trailer and may cooperate with all sorts of legacy tractors, regardless of the way the tractors are arranged to detect the trailer or to monitor the status of the lighting circuits.

They also include that the invention enables the presence of the trailer to be detected in all the cases, regardless of the status of the lighting circuits, in order to trigger the appropriate specific safety features of the tractor, thereby improving safety. Furthermore any fault in a circuit is always signalled to the tractor by an open circuit. Bulb simulation is not performed when the lighting circuits comprise at least a bulb, in order to avoid overload.

The invention also enables trailer detection and bulb simulation with a same resistor, which simplifies the layout of the circuit. The invention is also preferably adapted to work even in the event of cranking voltage drops, and for flashing direction indicator lights.

The invention also enables fault detection in a stop circuit even in the case where the tail and stop circuit are combined, and fault detection in a low current draw LED lamp irrespective of the draw current of other elements in the unit.

The invention is usually designed for specific lighting circuits, but embodiments may be configurable to all sorts of circuits, manually or automatically.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1A and 1 B, already discussed, schematically show a trailer and tractor; Figures 2A and 2B schematically show elevation views of a unit according to the invention; Figure 3 schematically shows example steps of a method performed by a unit according to the invention; Figure 4A and 4B schematically show an example electrical diagram in a unit according to the invention; Figures SA, SB and SC respectively schematically show example electrical diagrams of bulb simulators referred to as SA, SB and SC in Figure 4A; -10-Figures 6A, 6B and 6C respectively schematically show example electrical diagrams of simulation controls referred to as 6A, 6B and 6C in Figures 5A, 5B and 50 respectively; and Figures 7A, 7B and 7C respectively schematically show example electrical diagrams of low power controls referred to as 7A, 7B and 7C in Figures 5A, 5B and 50 respeGtively.

With reference to the drawings in general, it will be appreciated that the Figures are not necessarily to scale, and that for example relative dimensions may have been altered in the interest of clarity in the drawings. All the dimensions are shown as examples, and it will be appreciated that other dimensions are possible. Also any functional block diagrams are intended simply to show the functionality that exists within the unit and should not be taken to imply that each block shown in the functional block diagram is necessarily a discrete or separate entity. The functionality provided by a block may be discrete or may be dispersed throughout the unit or throughout a pad of the unit. In addition, the functionality may incorporate, where appropriate, hard-wired elements, software elements or firmware elements or any combination of these.

Overview Figures 1A and lB show that a trailer 2 may removeably be towed by a tractor 1 (such as a vehicle such as a truck) including a trailer detection and bulb-check system 11, and includes at least: a brake lamp circuit 23, a left hand directional indicator, L/H Dl, lamp circuit 22, and a right hand directional indicator, R/H Dl, lamp circuit 24.

Optionally, the trailer 2 may further include: a fog lamp circuit 25; a left hand tail lamp circuit 26; and a right hand tail lamp circuit 27.

The tractor 2 also comprises a unit or lighting interface 21 which is fitted on the trailer 2.

Two elevation views of an example unit 21 according to the invention are shown in Figures 2A and 2B. As explained in more detail below, the unit 21 takes power from its connection with the tractor 1 (e.g. using a connection when the trailer 2 is connected to the tractor 1), which has the advantage that no permanent power supply is required in the unit 21. In embodiments the unit is built-in with the lighting circuits 22, 23 and/or 24 of the trailer 2.

As described in more detail below, the unit 21 preferably comprises three modules 5A, SB or SC, i.e. one for each the lamp circuits 22, 23 and 24, acting as a bulb monitor and a bulb simulator. Each of the modules operate independently.

As can be seen from the Figures, the unit 21 provides an interface between the lamp circuits 22, 23 and 24, and optionally 25, 26 and 27, and the system 11 of the tractor 1.

Electrical Specifications

Table I shows examples of the main electrical features of the unit 21.

Supply Voltage* -i-ISV to -1-32V Ambient Operating Temperature** -40°C to +85°C Operating current, no bulb simulation*** c 2OmA, e.g. Max l5mA LED bulb failure detection Factory set Bulb simulation current Standard 21W filament bulb LED bulb failure trip speed <Sms

Table I

*Freferred supply voltage: 24V ± 0.5 V; **Preferred Operating Temperature Range: 25°C ± 5°C; Operating Voltage: 12 to 45 Vdc; ***Current Consumption for a single channel with bulb monitoring, i.e. Dl or Stop: <2OmA, e.g. Max l5mA; Quiescent current during fault condition for a single channel with bulb monitoring, i.e. Dl or Stop: <3mA; and Overload trip current: 4.2A.

Usually tail and fog channels do not include bulb monitoring, and in that case draw -12-approximately 8OmA each.

Mechanical Specifications

In one embodiment, the unit 21 has a housing 216 with a length of 200mm, a width of 120mm, and height of 70mm. Other dimensions are possible.

As is shown in Figures 2A and 2B, the housing 216 may be fitted on the trailer 2 using holes 2161 cooperating with screws, although it is understood that other means to fit the unit 21 on the trailer 2 are also possible.

As is shown in Figures 2A and 2B, the housing 216 includes a built-in heat sink 213 which allows the unit 21 to meet power dissipation requirements, and the unit 21 has thus the advantage of solving the issue of power dissipation of bulb simulation resistors 100, shown in Figure 4B. In embodiments, the heat sink 213 includes radiating fins 2131 to improve heat dissipation. The heat sink 213 is preferably fitted on a housing 216 of the unit using an elastomer 0-ring 217.

The housing 216 also comprises a cable entry 214 (forming an input from the at least one lamp circuit 22, 23, 24 of the trailer 2) and a cable exit 215 (forming an output 215 to the system 11 fitted on the tractor 1 via a connector, as explained in greater detail below) provided in the housing 216.

The unit 21 is fitted in series with at least each one of the circuits 22, 23, 24, and is preferably also fitted in series with the circuits 25, 26 and 27. Preferably any other circuit cabling (such as reverse lamp or registration plate cablings) passes through the cable entry 214 and the cable exit 215 through the housing 216 without being necessarily wired to a Printed Circuit Board (PCB) of the module 21.

The connection of the circuits 22, 23, 24 and optionally 25, 26 and 27 to the unit 21 is preferably performed via cable mounted, inline connectors, and cable harness connection to the Printed Circuit Board is preferably performed via spade terminal connectors. -13-

The fact that the unit 21 is fitted in series with the circuits 22, 23, 24 and optionally 25, 26 and 27 means that the unit 21 is only active when the cirGuits 22, 23, 24, and optionally 25, 26 and 27, are active.

The housing 216 is preferably filled with potting Gornpound, in order to seal the cable entry 214 and exit 215.

Detailed Electrical Specifications

As shown in Figures 4A and 4B, the unit 21 comprises connections (such as solder pads), referred to as SK in the Figures, adapted to be connected to corresponding plugs of the system 11 of the tractor 1, and thus provides an interface between the system 11 and the lamp circuits 22, 23 and 24, and optionally 25, 26 and 27.

The unit 21 preferably mainly comprises three modules 5A, SB and 5C: the module 5A being a bulb simulation module corresponding to the RIH Dl circuit 24; the module 56 being a bulb simulation module corresponding to the L/H Dl circuit 22; and the module 5C being a bulb simulation module corresponding to the brake (also sometimes referred to stop) circuit 23.

The three modules work independently of each other and require no additional power.

Each one of the modules 5A, 5B and SC has a Field Effect Transistor (FET) current input and an IN current input.

The Field Effect Transistor (FET) current input (RH_DI, LH_DI and STOP respectively) comes from a corresponding simulation resistor 100 provided in a Jumper connector Ji shown in Figure 4B and flows to an electrical ground 66 through a simulation switch 63 as shown in Figures 6A, 6B and 6C. As explained in more detail below, the unit thus comprises circuitry referred to as 100 and 63, comprising the simulation resistor or current load 100, for providing a path to ground for at least one circuit 22, 23 or 24 within a predetermined resistance range, irrespective of the condition of the lighting circuit. In -14-that case the current load 100 is equivalent to a cold bulb resistance. This enables trailer detection. In embodiments the circuitry 100, 63 is also arranged to provide a current load to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb As explained in more detail below, in the embodiments of the Figures the circuitry comprises the switch 63 comprising a depletion mode transistor in series with the resistor 100, whereby the transistor is configured to remain in a conducting state if insufficient power is applied to power logic controlling said transistor.

In order to enable trailer detection, the circuitry is arranged to provide the current load when a shod duration pulse is applied to the interface in order to detect the presence of the trailer, or when a low voltage, insufficient to power the lighting circuits 22, 23, or 24 significantly, is applied to the interface in order to detect the presence of the trailer. Trailer detection is thus enabled for all types of legacy tractors.

The IN current input is derived from a corresponding control current from the respective circuits 24, 22, 23 (RH_DI, LH_DI and STOP respectively), as controlled by the tractor 1 (e.g. when voltage is applied, e.g. the preferred 24V, e.g. from connection 9, 11 or 13 respectively).

As shown in Figure 4B, the bulb simulation resistors 100 are connected in series with the IN current and they are configured to deliver a power corresponding to a standard 21W filament bulb power, dissipated by the heat sink 213. The load is equivalent to a 21W filament lamp powered by nominal 24V, preferably comprising the resistor 100 having a resistance of about 30Q ±50%.

Each of the modules 5A, SB and 5C has an OUT current output (RH_DI, LH_DI and STOP respectively), back to the system 11, via e.g. the connection 10, 12 or 14 respectively. As described in greater detail below, when the circuits 22, 23 or 24 are powered up, the status of the OUT current output enables the system 11 to: detect a bulb current if the corresponding lamp is in normal operation, regardless -15-of the LED or filament type of the lamp; or detect an overloaded or an insufficient current, i.e. in that case there is no OUT current, thus providing a high resistance path to ground or open circuit to the system 11.

S As already explained, when the circuits are not powered up significantly, the invention also provides trailer detection both when the trailer circuit 22, 23 or 24 comprises bulbs or LEDs, and regardless of the status of the lamps, i.e. whether they are faulty or not.

The modules 5A, SB and SC are shown in greater detail in Figures 5A, SB and SC respectively.

As shown in Figures SA, SB and SC, each module 5A, SB and SC comprises a circuit 50 which monitors a current flowing in a resistor R53, R39 or R60 respectively. The current flowing in the resistor R53, R39 or R60 respectively, corresponds to the IN currents RH Dl IN, LH_DI_IN and STOP_IN respectively of Figure 4A. The circuit SO is also adapted to output a measure current I_OVERLOAD representative of the current in the resistor RS3, R39 or R60, and to that effect mainly comprises a comparator 501 whose inputs are connected upstream and downstream of the resistor RS3, R39 or R60 respectively. The comparator also outputs a current ISIM.

Each module SA, SB and SC also comprises a circuit Si which monitors a current flowing in a resistor RSO, Ri? or RS7 respectively. The current flowing in the resistor RSO, Ri? or RS7 respectively corresponds to the IN currents RH_DI_IN. LH_DI_IN and STOP_IN respectively. The circuit Si is also adapted to output a measure current IBULB representative of the current in the resistor RS0, Ri 7 or R57, and thus mainly comprises a comparator 511 whose inputs are connected upstream and downstream of the resistor R50, Ri7 or R57 respectively. The comparator also outputs a current ITRIP.

A switch 52, mainly comprising e.g. an enhancement metal-oxide-semiconductor field-effect transistor (MOSFET) 014, 03 or 019 respectively, is located in the yIN-OUT branch of the module 5A, SB or SC of Figure 4A respectively, between the circuits 50 and Si. -16-

When the circuits 22, 23 or 24 are not powered up significantly (typically when the trailer 2 is connected to the tractor 1 but no lamp control current is sent from the system 11), the switch 52 is open (because the enhancement mode MOSFET 014, 03 or 019 is OFF by default). Any trailer detection current from system 11 thus flows through the bulb simulation resistor 100, and through the closed switch 63, as explained below.

When the circuits 22, 23 or 24 are powered up and operating in the normal operation mode, the switch 52 is closed.

The switch 52 is also controlled by a current FAULT_LATCHED corresponding to the presence in the circuit 22, 23 or 24 of an overload or an insufficient current. The current FAULT_LATCHED is provided by an output from a low power control module 7A, TB or 7C respectively, as described in greater detail below. In other words, when the current FAULT_LATCHED is asserted, the switch 52 is opened by the current FAULT_LATCHED, thereby opening the branch yIN-OUT and preventing a current from flowing in the yIN-OUT branch of the module 5A, SB or SC of Figure 4A respectively.

thereby "switching off' the corresponding module.

In the absence of output from the modules 5A, SB or SC, the system 11 concludes that a fault is present in the circuit 22, 23 or 24 respectively, and thus warns the driver of the tractor 1. The driver can thus take steps according to the appropriate legislation. It is understood that opening the switch 52 also provides output overload protection for the system 11. It is also appreciated that the system 11 is provided with a high resistance to ground or open circuit, irrespective of the nature of the fault, i.e. overload (in embodiment an overload current threshold is comprised between 2.SA and 7.SA, and is preferably equal to 4.2A) or insufficient current (in embodiments the insufficient current is based on a LED light current threshold which is comprised between 2mA and SOOmA (for LED strings or clusters), depending on the circuits 22, 23 and 24).

As explained above, the modules 5A, SB, SC are powered up and active only when the circuits 22, 23 and 24 are controlled to be active.

It is understood that there is a settling or reaction time for the unit to detect a fault, for -17-example in a still working but faulty LED lamp (such as low current). There is also a time to decide to open the circuit. This could be a problem with the direction indicators, because the reaction time might represent a significant proportion of the power up of the Dl circuits. The detection might therefore not be reliable.

In order to solve this problem, the unit 21 comprises energy storage circuitry 53 for storing energy provided by the power pulses, for a time period at least equal to the expected spacing between adjacent power pulses. During and just after the first pulse, the detection of the fault can take place thanks to the energy storage circuitry 53. The unit also comprises latching circuitry 70 arranged, on detection of a fault during a first pulse of power from the vehicle, to signal the detected fault to the vehicle by providing a high resistance path to ground or open circuit at the next pulse of power. The decision can thus more rapidly take place during and just after the second pulse.

Thus preferably each module 5A, 5B and 5C thus also comprises a power storage circuit 53, comprising a capacitor C2, Cl or C70 respectively (lO0pF) which stores power from a power supply from the system 11 derived from the branch yIN. The power storage by the circuit 53 enables the modules 5A, SB and SC to operate for long enough (typically a few seconds) after the power supply is switched off. This solves the problem of the circuits 22, 23 or 24 not being powered on for long enough to allow appropriate operation of the modules 5A, 5B or SC (e.g. a flash of a Dl lamp). A fault status of the circuit is thus latched for a predetermined time at least corresponding to an interval between direction indicator flashes as explained above. Also in embodiments the power storage by the circuit 53 enables the modules 5A, SB and SC to operate for long enough when a power supply voltage drop occurs below a predetermined threshold (typically when a power supply is comprised in a predetermined nominal voltage supply range of [+18V; +32V], the predetermined threshold is +18V), in order to keep a transistor in series with the resistor 100 for at least a predetermined time period, such as at least two seconds, in order to avoid detection of a fault in the trailer lighting circuit due to short term transient voltage drops. The resistor 100 is thus arranged to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb even during short term cranking power supply voltage drops. -18-

Each module 5A, SB and 50 comprises moreover: a simulation control module 6A, 6B or 60 respectively, as shown in greater detail in Figures 6A, 6B or 60; and a low power control block 7A, 7B or 70 respectively, as shown in greater detail in Figures TA, 7B or 7C.

As shown in Figures 6A, 6B and 60, each simulation control module 6A, 6B or 6C comprises, as inputs, currents corresponding to: TAIL_IN; yIN; IBULB; ITRIP; I_OVERLOAD; FAULT_LATCHED; SIM_FET_CONTROL; +5V0; and -5V0.

Each simulation control module 6A, 6B or 60 comprises, as outputs, currents corresponding to: OVERLOAD_N; and ISOLATE_N.

Each simulation control module 6A, 6B or 60 comprises a trailer detection circuit 63 comprising mainly a switch 63 connected in series between the bulb simulation resistor 100, located in the connector Ji of Figure 4B, and the electrical ground 66. The switch 63 comprises e.g. a depletion mode MOSFET 011, 012 or 026 respectively. It will be appreciated that when the circuits 22, 23 or 24 are not powered up, the switch 63 is closed (because the depletion mode MOSFET 011,012 or 026 is ON by default), thus providing a path to the ground 66 for a trailer detection current (typically e.g. 5mA) from the system 11. This has the advantage that the trailer 2 may be detected regardless of -19-the status or type of the circuits 22, 23 or 24. The bulb simulation resistor 100 and the MOSFET 011, 012 or 026 respectively thus provide a resistor equivalent to a cold bulb resistor to the system 11 (low resistance), which thus detects the presence of the trailer 2.

It will be appreciated that the trailer detection is thus not provided by a trailer detection current from the tractor flowing through a LED or a filament lamp of any of the circuits 22, 23 or 24, but rather is provided by a single bulb simulation resistor 100 and a single switch 63, the bulb simulation resistor not being connected to the actual lamps of the circuits 22, 23 or 24. The trailer detection is thus provided regardless of the status or type of the circuits 22,23 or 24.

Each simulation control module 6A, 6B or 6C comprises a determination circuit 60 which determines a measure current representative of the current IBULB, by comparing it to a threshold TI (e.g. I.6V, approximately 0.8A). To that effect, the circuit 60 mainly comprises a comparator 601 whose inputs are connected to IBULB (-input) and a reference (+ input) respectively. The value of T1=0.8A is an example only, and the threshold may be any value representative of a filament lamp, such as comprised between e.g. 0.5A and 2A.

If the current IBULB is higher than the threshold Ti (e.g. 1.6V, corresponding to approximately 0.8A), then the circuit 22, 23 or 24 respectively comprises at least a filament lamp. In that case preferably the simulation resistor 100 is isolated from the ground 66, in order to avoid overload of the circuit and power consumption. To that effect, the output of the comparator 601 controls and opens the switch 63, e.g. comprising the depletion mode MOSFET 63.

It is appreciated however that in that case the switch 52 is closed when the circuit 22, 23 or 24 comprising the filament lamp is powered up (e.g. by a 24V voltage from the tractor 1), such that there is current flowing through the resistors R53 and R50, or R39 and R17, or R60 and R57 respectively, and also the filament lamp of the circuit 22, 23 or 24, such that the output current of the module 5A, SB or 5C to the system 11 is representative of a filament lamp, although the simulation resistor is isolated from the ground 66.

-20 -If the current IBULB is lower than the threshold Ti, then the circuit 22, 23 or 24 respectively comprises LED lamps only. In that case, the resistance of the LED lamps of the circuit 22, 23 or 24 is too low and cannot be representative of a filament lamp. The simulation resistor 100 thus needs to be connected to the ground 66, in order to simulate properly a filament lamp to the system 11. To that effect, the output of the comparator 601 does not control the depletion mode MOSFET 63 which thus remains in the ON status.

Once again, in that case the switch 52 is closed when the circuit 22, 23 or 24 comprising the LED lamps is powered up, such that there is current flowing through the LED lamps of the circuit 22, 23 or 24 respectively, the resistors R53 and R50, or R39 and R17, or R60 and R57 respectively, and also the simulation resistor 100 of the connectorJl, such that the output current of the module 5A, SB or SC to the system 11 is also representative of a filament lamp, with the simulation resistor being connected to the ground 66.

As explained above, the unit 21 is adapted to detect the presence of a LED lamp and simulate a bulb to the tractor. In the case where the circuit comprises filament lamps, the bulb simulator does not operate, to avoid unnecessary overload of the unit 21. In both cases, in normal operation the system of the tractor 1 thus monitors a bulb, and the unit 21 enables the bulb failure monitoring system 11 on the tractor 1 to operate correctly, enabling the required functions to conform to the legislation for bulb failure monitoring.

The system 11 of the tractor 1 thus experiences no difference when connected to a trailer 2 provided with LED lamps or filament lamps.

Furthermore, in normal operation mode, IBULB also ensures that the circuits 7A, 7B and do not latch as explained in greater detail below without a current FAULT_LATCHED being asserted.

The current FAULT_LATCHED, when asserted, controls the circuitry 64 of Figures 6A, 6B and 6C and opens the switch 63 of the modules 5A, SB or SC, by controlling the depletion mode MOSFET 63. The simulation resistor 100 is then isolated from the -21 -ground 66.

As explained below, the current FAULT_LATCHED, when asserted, also controls the switch 52 and opens the branch yIN-OUT of Figure 5A, SB or SC.

Each module 6A, 6B and 60 also comprises an overload detection circuit 61, comprising a comparator U18, US or U22 respectively, which determines if the current I_OVERLOAD (output of circuit 50) is higher than a threshold T2 (e.g. 4.2A corresponding to 4.2V applied at the input + of U18, US or U22 respectively). As indicated by the Figures 6A, 6B or 6C, if the current I_OVERLOAD is higher than the threshold, then there is an output current OVERLOAD_N coming out of the circuit 61.

The value of T2=4.2A is an example only, and the threshold may be any value representative of an overload current, such as comprised between e.g. 2.5A and 7.5A.

Each module 6A, 6B and 6C also comprises a trip detection circuit 62, comprising a comparator U2:A, U1:A or U6:A respectively, which determines if the current I_TRIP (output of circuit 51) is lower than a threshold T3 (e.g. 4OmA corresponding to 0.8V applied at the input -of U2:A, U1:A or U6:A respectively). As indicated by the Figures 6A, 6B or 60, if the current I_TRIP is lower than the threshold, then there is an output current ISOLATE_N coming out of the circuit 62. The value of T3=4OmA is an example only, and the threshold may be any value representative of an insufficient current, such as comprised between e.g. 2mA and 500mA, depending on the circuits 22, 23 or 24.

T3 is indeed specific to the circuits 22, 23 or 24 so that the circuitry, such as trip detection circuit 62 and switch 52, is arranged to, on detection of a current draw of the LED (such as I_TRIP) below a predetermined LED light current threshold, signal a fault to the vehicle by providing a high resistance path to ground or open circuit, irrespective of the current draw in other elements of the interface.

In embodiments having e.g. only one LED, and thus where the LED light current threshold may be as low as 3mA, the switch 52 thus may open up when a draw current in the LED is insufficient, even if the drive circuit of the unit still drives a current up to e.g. 1 OmA even if the circuit is faulty. This has the advantage that the unit does not consider -22 -that this remnant lOmA drive current as a normal LED draw current.

The inputs OVERLOAD_N (from the circuit 61) and ISOLATE_N (from the circuit 62) are wired as a logic OR in the low power control blocks TA, 7B and 70 described in greater detail below, and as soon as a OVERLOAD_N or ISOLATE_N is asserted by the blocks TA, TB and TC, the corresponding module 5A, SB or 50 is switched off', via the opening of the switch 52 as explained above.

As shown in Figures TA, TB and TO, each block TA, TB or TC comprises, as inputs, currents corresponding to: OVERLOAD_N; ISOLATE_N; +5VOSW; and i-5V0.

Each block TA, TB or TC comprises, as an output, a current corresponding to FAULT_LATCHED.

As shown in Figures TA, TB and TC, each block TA, TB and TC also comprises a circuit comprising a latch TO (comprising e.g. an enhancement mode MOSFET 031, 010 or 039, respectively) which latches the current FAULT_LATCHED once a current OVERLOAD_N or ISOLATE_N is asserted and as long as energy is supplied by power storage circuit 53. In other words the fault is remembered by the unit 21, even when the unit 21 is switched off (e.g. between flashes of a Dl lamp or when the power supply to the unit is momentarily insufficient), providing thus the current FAULT_LATCHED, as long as a current OVERLOAD_N or ISOLATE_N is asserted and as long as energy is supplied by power storage circuit 53.

As explained above, trailer detection circuits comprising the switch 63, corresponding to the unit 21, are built into the circuits 22, 23 and 24 respectively, by providing a path to the ground 66 for a current from the tractor 1 (e.g. using 5K7 and SK8), thus ensuring that the system 11 is able to detect the trailer 2 when the trailer is connected to the tractor 1 and when the circuits are not powered up, i.e. when a short duration pulse is applied to -23 -the interface in order to detect the presence of the trailer or when a low voltage, insufficient to power the lighting circuits 22, 23, or 24 significantly, is applied to the interface in order to detect the presence of the trailer. The circuits enable the existing systems 11 of the different brands of tractors 1 to detect the trailer 2, regardless of the operation mode of the tractor The invention thus provides both a bulb simulator and a trailer detector which are combined in an innovative way, and which minimise costs and maximise compatibility with existing tractor systems II.

As shown in Figure 4A, in embodiments, additional trailer detect circuits 45 (comprising e.g. resistors R5, R6, R7), 46 (comprising e.g. resistors RI, R8, R9) and 47 (comprising e.g. resistors RIO, RIl, R12) respectively, are added to the fog circuit 25, the L/H tail circuit 26 and the R/H tail circuit 27 respectively, to further compatibility with existing tractor systems II.

In some embodiments of trailers, the tail lamp is used also by the brake circuit, and the intensity of the tail lamp is higher when the brake is in operation. Extra circuitry is thus preferably included to address the needs of single LED lighting units that combine stop and tail functions. In that case, in embodiments, the unit 21 comprises circuits 46 and 47 creating a voltage drop in the tail circuits 26 and 27 (e.g. for circuit 47 using at least diodes D4, D5, D26 and D27, and e.g. for circuit 46 using at least diodes D6, D7, D12 and D21), to ensure that it is possible to distinguish between the voltage in the stop circuit 23 and in the tail circuits 26 and 27 (this facilitates discrimination of the power voltage of the stop signal circuit 23 and the tail signal circuit 26 or 27 for the fault detection), and that a current may flow in the stop circuit 23 despite the tail circuits 26 and 27, when it is desired. The unit thus comprises circuitry arranged to detect a fault condition in the stop circuit, irrespective of whether the tail circuit is powered.

In that case, each module 6A, 6B and 6C also comprises a differentiating circuit 65, comprising a comparator U2:B, Ul:B or U6:B respectively whose inputs are connected to the tail circuits 26 and 27 (current representative of TAIL_IN in the + input, see also Figure 4A) and the stop circuit 23 (current representative of VIN in the -input). The comparator U2:B, Ul:B or U6:B determines if the current representative of TAIL_IN is higher than the current representative of VIN. As indicated by the Figures 6A, 6B or 6C, if -24 -the current TAIL_IN is higher than yIN, then the output of the comparator U2:B, Ui:B or U6:B respectively controls and closes a switch 67 (comprising e.g. an enhancement mode MOSFET 033, 06 or 034 respectively). The value of T3 is thus lowered, which means that the condition: ITRIP> T3 is more easily verified and the switch 52 is therefore less easily opened.

Operation As can be seen from Figure 3, the unit 21 detects the trailer in S21, using the path to the ground 66 through the respective simulation resistors 100.

In S22, the unit 21 determines if the lamp circuit 22, 23 or 24 includes at least a bulb (i.e. a filament lamp), using the measure of the current IBULB compared to TI.

If the circuit 22, 23 or 24 comprises at least a filament lamp, then the corresponding simulation resistor is isolated from the ground 66 by opening the switch 63. This avoids unnecessary overload of the unit 21.

In S23 the unit 21 determines if there is a failure in the relevant bulb (an overload or an insufficient current), using circuits 61 and 62 and the corresponding currents OVERLOAD_N or ISOLATE_N.

If no failure is determined, then in S24 the normal operation of the bulb is reported to the system 11, since the system 11 measures current coming from the relevant bulb through branch yIN-OUT.

If a failure is determined, then in S25 the switches 63 and 52 are opened and the system 11 detects an open circuit and thus a failure status of the bulb, and appropriate steps according to legislation are taken. This also provides overload protection for STOP, L/H and RIH circuits.

If in S22 it is determined that the circuit 22, 23 or 24 only comprises Light Emitting Diode, LED, lamps, then the corresponding simulation resistor is kept connected to the ground -25 - 66 via the closed switch 63. This simulates a bulb to the system 11 with the same resistors 100 as for trailer detection.

In 326 the unit 21 determines if there is a failure in the relevant LED (an overload or an insufficient current), using circuits 61 and 62 and the corresponding currents OVERLOAD_N or ISOLATE_N.

If no failure is determined, then in S27 normal operation of a bulb is reported to the system 11, since the system 11 measures current coming from the LED lamp through branch VIN-OUT, but mainly current in the corresponding simulation resistor 100 to the ground 66 via the switch 63.

If a failure is determined, then in S28 the switches 63 and 52 are opened and the system 11 detects an open circuit and thus a failure status of the lamp, and appropriate steps according to legislation are taken. This again provides overload protection for STOP, L/H and RIH circuits.

The invention thus provides a unit 21 which enables bulb failure monitoring of different types of lamps fitted to the trailer 2. The unit 21 is configured to distinguish between filament lamps and LED lamps.

The invention thus overcomes the issues of the different bulb failure monitoring and trailer detection for different types of tractors.

Modifications and Variations Various features described above may have advantages with or without other features described above.

The above embodiments are to be understood as illustrative examples of the invention.

Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other -26 -of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

For example, a unit dedicated to specific circuits has been described. In other embodiments, the load has a variable resistance and is arranged to be configurable with a plurality of sets of lighting circuits. The load may be configured to a specific set of lighting circuits by setting the resistance of the load once in place. In that case, the load may be arranged to be manually configured, e.g. using a knob connected to a rheostat or potentiometer. Alternatively or additionally, the unit may comprise logic adapted to measure a level of a working current of the plurality of lighting circuits of the trailer when powered by the vehicle, thus automatically detecting whether or not the circuits comprise LEDs or bulbs, and adapted to automatically configure the load to the circuits.

The invention may be applied to any type of trailer, such as recreational vehicles or travel trailers.

Claims

-27 -CLAIMS1. A lighting interface (21) for a vehicle (1) and trailer (2) combination, wherein the trailer has a plurality of lighting circuits (22, 23, 24) including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect the presence of the trailer by detecting a path to ground through a bulb of at least one of the lighting circuits, the interface comprising circuitry (100, 63) for providing a path to ground for at least one circuit within a predetermined resistance range, irrespective of the condition of the lighting circuit.
2. The interface of claim 1, wherein the circuitry (100, 63) is arranged for providing a path to ground for each of the stop and two direction indicator circuits.
3. The interface of any one of claims I or 2, wherein the circuitry is arranged to provide a current load (100) when a short duration pulse is applied to the interface in order to detect the presence of the trailer.
4. The interface of any one of claims 1 to 3, wherein the circuitry is arranged to provide a current load (100) when a low voltage, insufficient to power the lighting circuits (22, 23, 24) significantly, is applied to the interface in order to detect the presence of the trailer.
5. The interface of any one of claims 1 to 4, wherein the circuitry comprises a depletion mode transistor (63) in series with a resistor (100), whereby the transistor is configured to remain in a conducting state if insufficient power is applied to power logic controlling said transistor.
6. The interface of any one of claims 1 to 5, wherein the interface is further arranged to provide a load (100) to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb.
7. A lighting interface (21) for a vehicle (1) and trailer (2) combination, -28 -wherein the trailer has a plurality of lighting circuits (22, 23, 24) including at least one of a stop signal and direction indicator signals to be powered by the vehicle, and wherein the interface further comprises circuitry (100, 63) arranged to provide a load (100) to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb.
8. The interface of any preceding claim, wherein the circuitry is arranged to signal a fault to the vehicle by providing a high resistance path to ground or open circuit on detection of a fault in the trailer lighting circuit.
9. A lighting interface (21) for a vehicle (1) and trailer (2) combination, wherein the trailer has a plurality of lighting circuits (22, 23, 24) including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect a path to ground through at least one of the lighting circuits, wherein the interface further comprises circuitry (52) arranged to signal a fault to the vehicle by providing a high resistance path to ground or open circuit on detection of a fault in the trailer lighting circuit.
10. The interface of any preceding claim, comprising circuitry (100, 63) arranged to disconnect a path to ground for a trailer detection signal from the vehicle, optionally wherein the circuitry (100, 63) comprises a depletion mode transistor (63) in series with a current load (100), whereby the transistor is configured to open if a filament bulb is detected.
11. The interface of any one of claims 8 or 9, arranged not to connect said further load (100) if a filament bulb is detected in the trailer lighting circuit.
12. A lighting interface (21) for a vehicle (1) and trailer (2) combination, wherein the trailer has a plurality of lighting circuits (22, 24) including indicator to be flashed by spaced apart power pulses provided by the vehicle, wherein the vehicle is arranged to detect a path to ground through at least one of -29 -the lighting circuits, wherein the interface comprises: energy storage circuitry (53) for storing energy provided by the power pulses, for a time period at least equal to the expected spacing between adjacent power pulses, and latching circuitry (70) arranged, on detection of a fault during a first pulse of power from the vehicle, to signal the detected fault to the vehicle by providing a high resistance path to ground or open circuit at the next pulse of power.
13. The interface of claim 12, wherein the energy storage circuitry (53) is arranged for storing energy for a time period sufficient to power the latching circuitry (70) in order to signal the detected fault at the next pulse of power, such as for at least two seconds.
14. A lighting interface (21) for a vehicle (1) and trailer (2) combination, wherein the trailer has a plurality of lighting circuits (22, 23, 24) including at least a stop signal circuit (23) and a tail signal circuit (26, 27) which are interconnected, to detect a path to ground through at least one of the lighting circuits, wherein the interface comprises circuitry (65) arranged to detect a fault condition in the stop circuit, irrespective of whether the tail circuit is powered.
15. The interface of claim 14, comprising circuitry (46, 47) providing a voltage drop between the stop signal circuit (23) and the tail signal circuit (26. 27), in order to facilitate discrimination of the power voltage of the stop signal circuit (23) and the tail signal circuit (26, 27) for the fault detection.
16. The interface of any one of claims 8 to 15, wherein the fault comprises an open circuit or failure of an LED light, based on an LED light current threshold.
17. The interface of any one of claims 8 to 16, wherein the fault comprises an open circuit or failure of a filament light.
18. The interface of any one of claims 8 to 17, wherein the fault comprises an overload or short circuit based on an overload current threshold.

-30 -
19. The interface of any one of the preceding claim, arranged to disconnect the trailer lighting circuit (22, 23, 24) in an overload condition, optionally comprising an enhancement mode transistor (52) arranged to be in series with the lighting circuits (22, 23, 24), whereby the transistor is configured not to conduct if an overload condition is detected.
20. A lighting interface (21) for a vehicle (1) and trailer (2) combination, wherein the trailer has a plurality of lighting circuits (22, 23, 24) including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect the presence of the trailer by detecting a path to ground through a bulb of at least one of the lighting circuits, the interface comprising circuitry (100, 63) comprising a depletion mode transistor (63) in series with a current load comprising a resistor (100), whereby the transistor is configured to remain in a conducting state if insufficient power is applied to power logic controlling said transistor; wherein the circuitry (100, 63) is arranged for providing, for at least one circuit: a path to ground through the resistor (100), when a short duration pulse or a low voltage insufficient to power the lighting circuits (22, 23, 24) significantly is applied to the interface, irrespective of the condition of the lighting circuit, to enable trailer detection by the vehicle; and a current load through the resistor (100) in order to simulate a filament bulb when the trailer light circuit is powered by the vehicle and comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb.
21. The interface of claim 20, wherein the transistor is configured to open if a filament bulb is detected and/or if a fault in the trailer lighting circuit is detected.
22. A lighting interface (21) for a vehicle (1) and trailer (2) combination, wherein the trailer has a plurality of lighting circuits (22, 24) including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to provide power supply to the interface and to detect the presence of a path to ground through at least one of the lighting circuits; -31 -the interface comprising circuitry (100, 63) comprising a depletion mode transistor (63) in series with a resistor (100), whereby the transistor is configured to remain in a conducting state if insufficient power is applied to power logic controlling said transistor; wherein the circuitry (100. 63) is arranged for providing a current load through the resistor (100) in order to simulate a filament bulb when the trailer light cirGuit Gomprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb; and wherein the interface is arranged, on detection of a power supply voltage drop below a predetermined threshold, to keep the transistor in series with the resistor (100) for at least a predetermined time period, such as at least two seconds, in order to avoid detection of a fault in the trailer lighting circuit due to short term transient voltage drops.
23. The interface of claim 22, wherein the power supply is comprised in a predetermined nominal voltage supply range of[+18V; +32V], and the predetermined threshold is +18V.
24. A lighting interface (21) for a vehicle (1) and trailer (2) combination, wherein the trailer has a plurality of lighting circuits (22, 24) including at least one of a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect a path to ground in at least one of the lighting circuits; wherein the interface further comprises circuitry (100, 63) arranged to provide a load (100) to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb; wherein the interface further comprises circuitry (62, 52) arranged to, on detection of a current draw of the light emitting element below a predetermined LED light current threshold, signal a fault in the light emitting element of the trailer lighting circuit to the vehicle by providing a high resistance path to ground or open circuit, irrespective of the current draw in other elements of the interface.
25. The interface of any one of claims 1 to 24, connected to each of the stop and two direction indicator circuits.

-32 -
26. A lighting interface (21) for a vehicle (1) and trailer (2) combination, wherein the trailer has a plurality of lighting circuits (22, 23, 24) including at least a stop signal and direction indicator signals to be powered by the vehicle, wherein the vehicle is arranged to detect the presence of the trailer by detecting a path to ground through a bulb of at least one of the lighting circuits; the interface comprising circuitry (100, 63) for providing a path to ground for the or each circuit within a predetermined resistance range, irrespective of the condition of the lighting circuit, and a load (100) to simulate a filament bulb when the trailer light circuit comprises a light emitting element with a lower current draw, such as an LED light, to enable bulb detection logic in the vehicle to detect a bulb, whilst not providing a further load if a filament bulb is detected in the lighting circuit; wherein the circuitry (100, 63) optionally comprises a depletion mode transistor (63) in series with a resistor (100), whereby the transistor is configured to remain in a conducting state if insufficient voltage is applied to power logic controlling said transistor and arranged to disconnect a path to ground for a trailer detection signal from the vehicle, and to open if a filament bulb is detected; the interface further comprising circuitry (52) arranged to signal fault to the vehicle by providing a high resistance path to ground or open circuit on detection of a fault in the trailer lighting circuit; wherein the trailer has a plurality of lighting circuits (22, 24) including indicator to be flashed by spaced apart power pulses provided by the vehicle; wherein the interface comprises: energy storage circuitry (53) for storing energy provided by the power pulses, for a time period at least equal to the expected spacing between adjacent power pulses, and latching circuitry (70) arranged, on detection of a fault during a first pulse of power from the vehicle, to signal the detected fault to the vehicle by providing a high resistance path to ground or open circuit at the next pulse of power.
27. The lighting interface (21) of claim 26, wherein the trailer has a plurality of lighting circuits (22, 23, 24) including at least a stop signal circuit (23) and a tail signal circuit (26, 27) which are interconnected, -33 -wherein the vehicle is arranged to detect the presence of a bulb in at least one of the lighting circuits, wherein the interface comprises circuitry (65) arranged to detect a fault condition in the stop circuit, irrespective of whether the tail circuit is powered.
28. The interface of any one of claims 3, 4, 20 or 26, wherein the current load is equivalent to a cold bulb resistance.
29. The interface of any one of claims 5, 10, 20, 22 or 26, wherein the depletion mode transistor (63) is a MOSFET.
30. The interface of any one of claims 6, 7, 20, 22, 24 or 26, wherein the load is equivalent to a 21W filament lamp powered by nominal 24V, preferably comprising a resistor (100) having a resistance of about 30Q ±50%.
31. The interface of claim 16, wherein the LED light current threshold is comprised between 2mA and 500mA.
32. The interface of any one of claims 18 or 19, wherein the overload current threshold is comprised between 2.5A and 7.5A, preferably 4.2A.
33. The interface of any one of claims 10 or 11 or 26, wherein a filament bulb is detected in the trailer lighting circuit on detection of a current draw superior or equal to a current representative of a filament bulb through the lighting circuits (22, 24), the current draw being comprised between USA and 2A, preferably 0.8A.
34. The interface of any preceding claim, comprising a logic arranged on a Printed Circuit Board placed in a housing (216).
35. The interface of any preceding claim, comprising a heat sink (213), the heat sink (213), preferably comprising radiating fins (2131) and preferably fitted on a housing (216) of the unit using an elastomer 0-ring.

-34 -
36. The interface of any preceding claim, comprising a housing (216) comprising: an input (214) from the at least one lamp circuit (22, 23, 24) of the trailer (2); and an output (215) to the controller (11) adapted to be fitted on the vehicle (1), wherein the housing is filled with potting compound to seal the input (214) and the output (215).
37. The interface of any preceding claim, comprising a housing (216) adapted to be fitted on the trailer (2).
38. The interface of any one of claims 6, 7, 10, 11 or 26, wherein the load (100) has a variable resistance, whereby the load is arranged to be configurable with a plurality of sets of lighting circuits (22, 23, 24), the load being configured to a specific set of lighting circuits (22, 23, 24) by setting the resistance of the load (100).
39. The interface of claim 38, wherein the load is arranged to be manually configured.
40. The interface of claim 38, comprising logic adapted to measure a level of a working current of the plurality of lighting circuits (22, 23, 24) of the trailer when powered by the vehicle and to automatically configure the load.
41. The interface of any preceding claim, wherein the interface is built-in with the lighting circuits (22, 23, 24) of the trailer.