The present invention relates to a switching device for an electric lighting unit for use in a motor vehicle that is equipped for a lighting unit of a different kind.

Lighting units such as low-high beam, front fog lights, for motor vehicles such as cars, lorries, trucks, busses and motorcycles are undergoing continuous development. New lighting units with lesser power consumption and higher light output regularly appear on the market. Presently the majority of cars is being equipped with a halogen lighting unit, notably for the head lamps, which consume ^' considerably less power and have a considerably higher light 'Output than lamp units that were in common use before. Certain types of motor vehicles can today be equipped with so called xenon lighting units which again do consume considerably less power than the halogen lighting units and also have a better light output. Motor vehicles are being offered equipped with xenon lighting units as delivered from the factory at a considerable additional cost. This has led to a rather lively replacement market in which motor vehicles, that from the factory were equipped with halogen lighting units, could be retrofitted with xenon lighting units.

Until some years ago this could be done without problems, however since some time manufacturers of cars, trucks and motorcycles have introduced (on) board computers in a vehicle, in which the board computers in addition to other tasks also control the lighting units. One possibility that was introduced with the board computers is to safeguard the lamps to overload voltage, since e.g. a voltage higher than 12V reduces the life of halogen lamps considerably. This is then being done by controlling the lighting units through a duty cycle signal using Pulse Width Modulation (PWM) . By reducing the pulse rate, the effective voltage can be reduced and kept to a maximum of 12 Veff, even if the momentary battery voltage is higher. Another advantage of the board computer is that functioning of the lamps in each lighting unit can be checked. If a lamp is defect then this is noticed by the board computer and is reported to the driver by providing a signal at the dashboard, so that the driver can replace the defected lighting unit as soon as possible. Now when halogen lighting units of a motor vehicle are replaced by a xenon lighting unit or a led lighting unit, this can lead to certain types of failures when the lighting units are being controlled by a board computer. The board computer is designed and programmed to control a halogen lighting unit. If the board computer detects an anomaly, for instance that the lamp has failed or a wrong lamp has been placed, the computer can report this to the driver and may in some cases cut off the power signal to the lamp. Since the signals are controlled to increasingly tighter tol ^¬ erances, it has become almost impossible to retrofit xenon or led lighting units in motor vehicles that are controlled by a board computer that is designed and programmed to control halogen lamps . For instance in case of replacing the halogen lamp with a xenon lighting unit, the PWM-signal can get into conflict with the xenon ballast. This may lead to a defected ballast or even a defected board computer after a certain amount of time. It may also lead to the board computer giving erroneous loss-of-f nction signals to the driver.

German Patent DE 10 2009 052 690 B3 describes a system for retrofitting led lights to motor vehicles that originally have been fitted with light bulbs. The system comprises a current measuring device that measures the current fed towards a lamp and when that current is lower than what may be expected, a control signal is sent to a DC/DC booster that controls a supplementary load such, that the current measured equals the value expected. The supplementary load is trans- ferred to the battery. This system has the drawback that it cannot make use of state of the art controls and checks that are found in today's motor vehicles. The effective voltage control by a PWM signal e.g. cannot properly be adjusted to the new lamp unit and may cause damage to a retrofitted Xenon lamp system or to the board computer or both. Also in case the system is used for simulating Xenon lamps, a cold lamp check will issue flashes to the headlights, which is an undesirable effect that can be disturbing for the traffic.

The barrier, mentioned above by retrofitting a motor vehicle with a lighting unit for which the motor vehicle was not equipped originally, for instance because the board computer of the motor vehicle was programmed to control a lighting unit of a different kind, as well as the drawbacks found with a system according to DE 10 2009 052 690 B3 are completely overcome by using a switching device according to. claim 1 of the present invention. When for instance a car that originally was equipped with halogen lighting units and a board computer controlling the lighting units is retrofitted with xenon lighting units and a switching device according to the invention, then the circuitry of the switching device according to the invention will consume a predetermined amount of electric power from the power supply cable. This predetermined amount of power has been determined so as to correspond to the power used by a lighting unit for which the motor vehicle has been laid out. Consequently to the motor vehicle concerned, the switching device according to the invention simu ^¬ lates that the motor vehicle is still equipped with the lighting unit the motor vehicle, and in particular the board computer of the motor vehicle expects to be present. In addition the switching device according to the invention establishes an electrical connection between its connection terminal to the battery of the motor vehicle and the connection terminal to the lighting unit. Thus in the vehicle an electrical connec ^¬ tion is then made between the battery and the lighting unit that is actually installed in the motor vehicle. In the lighting unit according to the invention, the switching device comprises a step up circuit to lead the power consumed from the power supply cable back to the battery, so that no power is lost unnecessary and also is not transformed into heat.

When the headlights on this motor vehicle are being switched on., the board computer provides power to the lighting unit concerned and this is being detected by the detection circuit of the first switching unit of the switching device according to the invention. If the detection circuit detects a predefined voltage level offered by the power supply cable controlled by the board computer, where this predefined voltage level is the voltage level required by the halogen lamp unit, then the detection circuit supplies a control signal to the power circuit as well as a control signal to the second switching unit. Upon receipt of the control signal from the detection circuit, the control circuit is equipped to connect the voltage offered by the power supply cable to the power circuit of the first switching unit, which controls the power being consumed from this power supply cable in such a way, that the power consumed coincides with the power that is normally consumed by e.g. a halogen lighting unit. The second switching unit, upon receipt of the control signal from the detection circuit, connects the battery to the lighting unit to switch on the lighting unit. In this way the board computer from the motor vehicle experiences a power consumption that is in conformance with the power consumption of a halogen lighting unit, whereas the retrofitted lighting unit, e.g. a xenon lighting unit including its ballast, will receive its power directly from the vehicle battery, however only at the time that the board computer provides the proper power to the no longer existing halogen lighting unit, meaning that the lighting unit is to be in the Switched on' condition. Because the voltage offered by the board computer is fed back to the battery and the power taken by the retrofitted lighting unit is taken separately from the battery under control of the second switching unit, it is possible with the switching device according to the invention to retrofit modern lamp units in motor vehicles that originally were not equipped with these, and still make full use of modern control systems as cold lamp checks and PWM control of the supply voltage without damage to the replacement parts or to the board computer and without un- desired effects such as head light flashing, etc. In this way it is possible to retrofit a motor vehicle that originally was equipped for one type of lighting unit, with another, more modern type of lighting unit that for instance exhibits reduced power consumption and increased light output, such as xenon lighting units or led lighting units. Although mention is made of halogen lighting units, xenon lighting units and led lighting units, the switching device according to the invention is certainly not limited to one or two of the kinds of lighting units mentioned, but will equally well function in any combination of these. According to a preferred embodiment of the switching device according to the invention, the second switching unit comprises a current sensing circuit that is arranged to give a control signal to the power circuit of the first switching unit, if the current through the lighting unit lies below a predefined threshold value. The power circuit of the first switching unit, upon receipt of the control signal from the current sensing circuit as mentioned before, is arranged to switch off the power consumption from the power supply cable. This means that when the retrofitted lamp unit fails, the power consumption from the power supply cable as controlled by the board computer of the vehicle will also be switched off and thus be reduced to zero. This will be noticed by the board computer which will give a notification to the driver on the dash board that the lamp has failed. This means that also with the retrofitted lighting unit this possibility of notifying the driver about a failed lighting unit remains fully intact due to the switching device according to the invention.

In another preferred embodiment of the invention the second switching unit comprises a voltage sensing circuit that is arranged to disconnect the connection from the battery to the lighting unit, if the voltage supplied by the battery lies below a predefined threshold value. This means that when the battery voltage for one reason or another has dropped below that predefined threshold value, the battery is no longer used to power the switching device according to the invention and thus also the lighting unit, which under circumstances can be desirable to avoid possible damage to the switching device caused by too low operating voltage.

Another option that is easily possible with a switch ^¬ ing device according to the invention is to detect loss of voltage to the lamp unit e.g. because of a loose battery contact. In that case the first switching unit may still transfer the voltage offered by the power supply cable to the lighting unit to keep the lights functioning. Of course this would be an emergency solution and the broken connection would require repair .

In further advantageous embodiments of the invention the switching device can be equipped with a number of signal- ling units that produce a visible signal if certain conditions have been fulfilled. For instance a first signalling unit producing a first visible signal may be comprised by the switch ^¬ ing device if the detection circuit detects that the prede- fined voltage level is supplied by the power supply cable. This will make visible that the required power supply is available, which might be convenient for a mechanic during maintenance activities. A second signalling unit giving a second visible signal is incorporated in a preferred embodiment of the switching device if voltage is supplied to the lighting unit. Again this visible signal may be of interest for maintenance personnel. Likewise in a preferred embodiment of the switching device according to the invention the detection circuit is arranged to detect if the voltage level supplied by the power supply cable comprises a PWM-signal and the switch ^¬ ing device comprises a third signalling unit arranged to give a third visible signal if the detection device detects that the voltage level offered by the supply cable comprises a PWM- signal. In preferred embodiments of the switching device ac- cording to the invention the signalling units each comprise a led for forming the visible signal.

Preferably the switching device according to the invention is accommodated in a preferably metal housing. The metal housing giving good protection and also is dissipating the heat generated by the switching device. The protecting properties as well as the heat dissipating properties in a preferred embodiment are enhanced when the switching device in the housing is moulded in a resin with good heat transfer properties. For use in motor vehicles such as cars, trucks and buses, the housing may accommodate two or more switching devices according to the invention to serve two headlights and possibly also fog lights, whereas for motor cycles the housing may accommodate a single switching device according to the invention .

The invention will now further be explained by the description of a preferred example of an embodiment of the switching device according to the invention with reference to the enclosed drawing in which:

Fig. 1 shows schematic representation of part of a vehicle equipped with a retrofitted lighting unit according to the invention;

Fig. 2 shows a switching device according to Fig. 1 in more detail.

Fig. 1 shows a schematic representation of a vehicle that originally has been equipped for halogen headlights and been retrofitted with xenon headlights according to the inven ^¬ tion. Shown is a battery 12 of the motor vehicle connected to a board computer 11 from which a power supply cable 3 origi- nally led to the halogen lighting unit but is now connected to a switching device 1 according to the invention. Switching device 1 is also connected to battery unit 12 on one hand and on the other hand also to a xenon lighting unit 2. Xenon lighting unit 2 comprises a xenon lamp 15 as well as a xenon lamp bal- last 14. Power supply cable 3 connects the board computer 11 with the retrofitted switching device 1. Schematic representa ^¬ tion of electrical connections is indicated as a single line. Obviously connections also comprise connection to common vehicle ground that from various places have been indicated with reference number 13 in figure 1. Usually a motor vehicle comprises one common ground, but this is not necessarily always the case. Clearly the switching device according to the invention should be laid out in correspondence with the grounding method used.

Fig. 2 shows switching device 1 in more detail and

, connected to lighting unit 2 as well as vehicle battery 12, as well as power supply cable 3 coming from the vehicle board computer. Switching device 1 comprises first switching unit 4 and second switching unit 5. First switching unit 4 comprises detection circuit 6 and power circuit 7. When the lighting unit 2 of the vehicle is to be switched on, the on board computer 11 will supply via power supply cable 3 power of a suitable voltage intended for a halogen lighting unit. Power supply cable 3 is connected to detection circuit 6 and power cir- cuit 7 of switching device 1. Detection circuit 6 is arranged to detect if power supply cable 3 is supplying a voltage of a predefined level. The predefined voltage is a voltage of a level suitable for supplying power to a halogen lighting unit. If voltage of the predefined suitable level is detected, de- tection unit 6 will send a control signal 16 to second switching unit 5 as well as control signal 17 to power circuit 7. Upon receipt of control signal 16 second switching unit 5, which closes connection between a vehicle battery 12 to light- ing unit 2, and thus supplying lighting unit 2 with a suitable power from the battery 2, which will cause lighting unit 2 to light up. As long as on board computer 11 supplies proper power to switching device 1 via power supply cable ^" 3, switching device 1, via second switching unit 5 will keep xenon lighting unit 2 connected with vehicle battery 12. So as long as lighting unit 2 has not failed it will continue to emit light as long as the proper signal is coming from the board computer 11. At the same time as long as a proper voltage is being supplied by a power supply cable 3, detection circuit 6 will send control signal 17 to power circuit 7. Upon receipt of control signal 17, power circuit 7 will arrange power of a predefined level to be drawn from power supply cable 3, and via a step up circuit will reroute this power back to battery 2, so that no power is wasted and turned into harmful heat. The predefined amount of power consumption is such that it is the same amount of power required for lighting a halogen lighting unit, as will be expected by the board computer 11. As such a switching device 1 will simulate towards the board computer that the board computer is delivering its power to a halogen lighting unit whereas the xenon lighting unit 2 is be ^¬ ing fed by the battery 12 of the vehicle without passing through the board computer 11. Thus in practice the xenon lighting unit 2 is fed simultaneously with the switching as regulated by the on board computer 11 but the actual feeding of electric power is separated from the on board computer 11 and is directly from the vehicle battery as controlled by second switching unit 5 of switching device 1. Power circuit 7 is arranged to accept the predefined amount of power from the on board computer 11 via a supply cable 3 and returns this amount of power to the vehicle battery 12. Second switching unit 5 of switching device 1 also comprises a current sensing circuit 9. When second switching unit 5 has connected vehicle battery 12 to lighting unit 2, current sensing circuit 9 senses the cur ^¬ rent going through lighting unit 2 and is arranged to send a control signal 18 to power circuit 7 if the current detected by current sensing circuit 9 falls below a predefined threshold. Upon receipt of control signal 18, power circuit 7 will stop drawing power from power supply cable 3 and thus from the on board computer 11. This means that if lighting unit 2 brakes down, and consequently current through lighting unit 2 stops, the on board computer will also detect that power no longer is being consumed and thus will stop power supply via power supply cable 3 and subsequently will arrange for a mes- sage that the lighting unit 2 concerned has failed and needs to be replaced.

Second switching unit 5 also comprises a voltage

• sensing circuit 10. Voltage sensing circuit 10 senses a voltage level coming from vehicle battery 12 and control signal 16 indicates that lighting unit 2 should be switched on. If however voltage sensing circuit 10 senses a voltage from vehicle battery 12 that is below a predefined threshold value, voltage sensing circuit 10 is arranged such that second switching unit 5 is prevented from connecting vehicle battery 12 to lighting unit 2. This will for instance prevent vehicle battery 12 from the delivering power to lighting unit 2 if the voltage level is to low and the power probably is better used for other critical purposes in the vehicle such as starting up the engine. If the voltage level from the vehicle battery 12 is rather low, but the power supplied is sufficient to start the vehicle engine, then once the vehicle engine is running, the voltage coming from the vehicle battery 12 will increase due to loading by an alternator and thus lighting unit 2 will be ignited .

List of reference numbers

1 switching device

2 lighting unit

3 power supply cable to original lighting

4 first switching unit

5 second switching unit

6 detection circuit

7 power circuit not used

current sensing circuit voltage sensing circuit vehicle board computer vehicle battery vehicle ground

xenon ballast

xenon lamp

control signal

control signal

control signal

fuse