NZ528180A - Lighting system for motor vehicles - Google Patents

Abstract

A lighting system for motor vehicles, comprising a power source and a power monitoring circuit (4A) for controlling the function of at least one lamp, said lamps being filament lamps (1) and/or light-emitting diodes (2). In order to simulate a filament lamp, at least one electrical load (5) is provided in a power branch disposed in parallel to the lamps (1, 2) that can only be connected for a limited time window (T1). Said time window for connecting the load is synchronized with a control time window of the power monitoring circuit (4A).

Description

528180 Lighting system for motor vehicles The invention concerns a lighting system for motor vehicles, in particular a flashing light signal system, with a current source and a current monitoring circuit 5 for at least one lamp, wherein the lamps are filament lamps and/or light-emitting diodes (LEDs). The invention particularly concerns a parallel connection of two or more lamps. The purpose of the current monitoring circuit is the failure control the a lamp, whereby the total current, flowing through the parallel connection of the lamps, is measured. In the case of a lamp failing, the flow of the current through 10 one of the parallel current branches is interrupted, due to which the total current, that flows in the parallel connection, decreases. At the same time a current value below a predetermined threshold value indicated by the current monitoring circuit represents the failure of a lamp.

Since the current consumptions of filament lamps and light-emitting diodes are very different, the monitoring of current for a parallel circuit containing filament lamps and light-emitting diodes or only light-emitting diodes, presents a problem when the current monitoring circuit, particularly with regard to its threshold value, is designed to be used only for filament lamps.

When using light-emitting diodes as parallel connected lamps, with a current monitoring circuit that is designed for a row of parallel connected filament lamps, the total current flowing in the parallel connection will be below the threshold value, so that the current monitoring circuit would erroneously indicate a failure of 25 a lamp, although all lamps are in good order.

The problem is illustrated on the example of a flashing light signal system for a prime mover with a trailer. A flashing light signal system of this type has a flasher unit with an integrated current monitoring circuit, while the current monitoring 30 circuit, with regard to its threshold value, is designed for the operation of four parallel operating filament lamps as flashing lamps for each direction of travel (e.g. two flashing lamps on the prime mover and two flashing lamps on the trailer). The result of a failure of a filament lamp would result in a current that is 25 % below the threshold. If a trailer, having light-emitting diodes as flashing 2 lamps, is coupled to the prime mover, due to the lower current consumption, that is below the threshold, the current monitoring circuit would erroneously indicate the failure of a lamp.

From DE 196 1800 C1 a flashing light signal system is known, that is designed for a mixed operation of filament lamps and light-emitting diodes. In this conjunction the flasher unit has a voltage divider, that via an additional line is connected with a control circuit allocated to the light-emitting diodes. When the light-emitting diodes are in good order, the LED control circuit via the additional line and the voltage divider simulates the current consumption of a filament lamp for the current monitoring circuit during the entire duration of the flashing pulse. This flashing light signal system has, however, various disadvantages. First of all an additional lead is required between the flasher unit and the LED lights. This in turn necessitates additional connections to the LED lights and the flasher unit, i.e. when compared with a conventional flasher unit that is designed to operate purely with filament lamps, the flasher unit needs to be modified. Moreover, power will be dissipated in a disadvantageous manner since during the entire period of the flashing pulse additional power is generated to correspond with the filament light simulated.

Accordingly, the object of the invention is to produce a lighting system for motor vehicles, comprising at least one lamp and a current monitoring circuit allocated to it, that can be operated in a simple and current-saving manner with filament lamps and light-emitting diodes.

According to the invention this objective is achieved by that in a current branch provided parallel to the lamps at least one additionally connectable electric load is provided as current sink only for a predetermined time window, while the time window is synchronised with a control time window of the current monitoring 30 circuit for the additional connection of the load. In other words, when using light-emitting diodes during the time of monitoring, a load is additionally parallel connected as current sink for a short period in the lighting system according to the invention, that load simulating a current consumption that is at least similar to that of an operation using only filament lamps. In this case only the actual failure 3 of a filament lamp in a mixed operation comprising filament lamps and light-emitting diodes would lead to a fall of the current below the threshold value, by virtue of which the failure of a lamp will be correctly indicated. Thus it is possible to operate parallel connected lamps both with filament lamps and light-emitting 5 diodes, in fact with only a single current monitoring circuit. Since the load to simulate a filament lamp is switched on only for a short period, in an advantageous manner no unnecessary power dissipation is produced for simulation purposes. This in turn has the advantage of a reduced heating up, what is especially important since the additionally connectable load is arranged in 10 the spatial vicinity of the light-emitting diodes, because a heating up of the light-emitting diodes causes in a disadvantageous manner a degradation (impairment of the efficiency, i.e. lower yield of light) of the light-emitting diodes.

The additionally connectable load is preferably integrated in that light, e.g. in a 15 flashing light, in which the light-emitting diodes are also located.

The invention makes it possible, for example, to use a prime mover that is designed with a flasher unit (including the current monitoring circuit) for a trailer operation, alternately with trailers, the flashing lights of which have filament lamps 20 or light-emitting diodes. Thus the lighting system according to the invention has great flexibility. An additional lead between the flasher unit and the LED lights is not necessary.

The invention is explained below in detail based on the attached drawings. They 25 show in: Fig.1 - the circuit of a flashing light signal system according to the state-of-the-art, Fig.2 - the chronological progress of the flashing pulse (above) as well as the 30 progress of the current (below) in a flashing light signal system according to Fig.1, Fig.3 - a circuit for a flashing light signal system according to the invention, wherein the current monitoring circuit of the flasher unit is designed only 4 for filament lamp operations, however the parallel connection has both filament lamps and light-emitting diodes, Fig.4 - a circuit for a flashing light signal system, in which only light-emitting 5 diodes are provided, although the current monitoring circuit of the flasher unit is designed for a filament lamp operation, Fig.5 - a schematic illustration of a flashing light signal system with filament lamps and with flashing lights according to the invention fitted with light-emitting 10 diodes, Fig.6 - the chronological progress of the flashing pulse (above) as well as the progress of the current (below) in a flashing light signal system according to Fig.5, Fig.7 - a schematic circuit diagram for the additional connection of a resistor as load, Fig.8 - a schematic circuit diagram for the additional connection of a power 20 transistor as load.

Fig.1 shows the circuit of a flashing light signal system according to the state-of-the-art. In this case it comprises a parallel connection of four filament lamps (1) for each direction of travel, that are supplied by a common current source via a 25 flasher unit (4). In doing so a current monitoring circuit (4A) is integrated in the flasher unit (4). The supply of the filament lamps (1), which are provided in flashing lights (not illustrated), is carried out via the flasher unit (4) by means of a supply line (Vcc), that is cyclically charged by the flasher unit with the supply voltage of the motor vehicle. In addition, both the flasher unit (4) and the filament 30 lamp flashing lights are earthed (GND).

The current monitoring circuit (4A) measures the total current (I) flowing in the parallel connection and compares it with a threshold value (Is). The upper diagram of Fig.2 shows the flashing pulse. The duration of a flashing pulse is approx. 1 sec. The lower diagram of Fig.2 illustrates the corresponding progress of the current during the flashing pulse. Because the filament lamps are thermally controlled resistors, the starting current at the commencement of the flashing pulse is quite high. However, it quickly reaches a stable value. At the same time 5 the control time window (T|) for the current monitoring is so chosen, that the peak of the starting current is excluded. When current, that is below the threshold (Is), is detected within the control time window, a failure of a filament lamp (1) is noted.

If two filament lamps (1) are replaced by light-emitting diodes (2) (see Fig.3), the current would be in every case below the threshold illustrated in Fig.1, since the current consumption of the light-emitting diodes is considerable less than that of a filament lamp. The result of this would be that a lamp failure would be detected in every case although all lamps are operational.

Fig.3 shows a flashing light system in accordance with the invention, in which both filament lamps (1) and light-emitting diodes (2) are used. At the same time the light-emitting diodes are integrated in a flashing light (3), which, for example, may be arranged on a trailer. Just like a conventional flashing light, the LED flashing lights (3) according to the invention has merely two connections, in fact for the supply lead (Vcc) and the earth (GND).

For the purposes of clarity only two rows of light-emitting diodes (2) are shown, each of them comprising two light-emitting diodes. However, depending on the light intensity required, a plurality of parallel connected rows of light-emitting diodes, each with a plurality of light-emitting diodes, is conceivable. In each row a current-limiting resistance (1) is provided so that the light-emitting diodes would be operated in an optimum operating point.

According to the invention an additionally connectable load (5) is provided, that is additionally connected only for a predetermined time window (Ti), so that to generate an increased current consumption to simulate a filament lamp. In this conjunction this time window is synchronised with a control time window of the current monitoring circuit (4A) in the flasher unit (4). The additionally connectable 6 load (5) can be a resistor or a semi-conductor, e.g. a power transistor. As switching element (7) for the connection and disconnection of the load (5) a transistor, for example, may be used.

Fig.7 shows a parallel connection of a filament lamp (1) and of a light-emitting diode (2), while in a further current branch connected parallel to it a resistor (5) is provided as a load, that can be additionally connected via a switching element (7) (only symbolically illustrated). Above the supply line (Vcc) the flash pulse is symbolically illustrated. The actuation of the switching element (7) is carried out 10 via a time module (6), that may be a delay member or a timer. This time module (6) is triggered by the positive flank of the flashing pulse. The time module then actuates, with a delay, the switching element (7). In this conjunction in a preferred embodiment the time module (6) is so constructed, that it actuates the switching element (7) after a short period prior to the completion of the flashing pulse to 15 disconnect the load (5). The person skilled in the art is familiar with the electronic illustration of such a connection time window using commercially available components. In an alternative embodiment the time module (6) acts merely as a delay member (e.g. as an resistance-capacitance element), that connects the load (5) shortly prior to the end of the flashing pulse. The charging of the load (5) 20 with current of terminates automatically with the flashing pulse.

Fig.8 also shows a parallel connection of a filament lamp (1) and of a light-emitting diode (2). In this case as an additionally connectable load (5) a power transistor is used, that is triggered by an operation amplifier (10). A series 25 connection comprising a resistance (R2) and a Zener diode (Z) provided between the supply line (Vcc) and earth (GND) defines a reference voltage on the tap between the resistance (R2) and the cathode of the Zener diode (Z), this reference voltage directed to the positive input of the operation amplifier (10). To the negative input of the operation amplifier (10) that voltage is directed, which is 30 produced by the current flowing via the power transistor (5) to simulate the load of a filament lamp on a resistance (R3). The operation amplifier (10) compares the reference voltage generated by the Zener diode (Z) with the voltage on the resistance (R3), while the operation amplifier (10) triggers the power transistor (5) in a such manner, that the current produces a voltage drop over the resistance 7 (R3), said voltage drop corresponding to the reference voltage of the Zener diode (Z). In this conjunction the power transistor (5) is connected and disconnected via a transistor (7) as an additionally connectable load. When the transistor switches through, the cathode of the Zener diode (Z) is connected to earth. Thus the reference voltage of the operation amplifier (10) will also be zero, affecting a disconnection of the power transistor (5). In turn a timer component (6), to switch on and off the reference voltage, is connected upstream to the transistor (7), said timer component, triggered by the positive flank of the flashing pulse, switches on the reference voltage with delay for a short period.

In a particular embodiment of the invention the flashing light according to Fig.3 constructed in accordance with the invention comprises a failure control circuit (8) for the light-emitting diodes (2) in addition to the additionally connectable load (5) described above in detail. When a light-emitting diode (2) fails, this failure control 15 circuit (8) prevents, via a logic (9), the connection of the load (5). The result of this is that in this case the current threshold is not reached and the current monitoring circuit (4A) in the flasher unit (4) will indicate in an advantageous manner an error also when a light-emitting diode (2) fails.

The failure control circuit is only optional, since the failure of a light-emitting diode is less likely to occur than the failure of a filament lamp.

For the purpose of failure control the failure control circuit (8) measures the current in the parallel LED current branches and compares them with one 25 another. If the currents differ from one another by more than a certain tolerance value, the failure of an LED is signalled.

Fig.4 shows a version of the invention in which only light-emitting diodes (2) are used but not filament lamps, in conjunction with a flasher unit (4), the current 30 monitoring circuit (4A) of which is constructed for operation with filament lamps.

Fig.5 schematically shows a lighting system, in particular a flashing light signal system. This arrangement corresponds to the case of a prime mover with flashing lights containing two filament lamps for each direction of travel and a trailer with 8 flashing lights containing two LEDs f according to the invention for each direction of travel. The corresponding time diagram for the flashing pulse and the progress of the current is shown in Fig.6. It also shows the "simulation time window" that corresponds to the control time window of the current monitoring circuit (4A).

In a particularly advantageous embodiment of the invention the additionally connectable load, the switching element, the time module, and possibly the LED failure control circuit are integrated in the LED lights. This light has only two connections (supply line voltage and earth) and thus does not differ from a 10 filament lamp light. Consequently the LED lights according to the invention can replace a filament lamp light in a simple manner, without the necessity of modifying or replacing the current monitoring circuit of the lighting system.

When the lighting system is not a flashing light signal system, the switch-on 15 signal, for example, can be used as trigger signal for the time module.

Claims (1)

1. t 9 Patent claims 5 2. 15 3. 4. 5. 25 6. A lighting system for motor vehicles with a current source and a current monitoring circuit (4A) to control the function of at least one lamp, wherein the lamps are filament lamps (1) and/or light-emitting diodes (2), characterised in that in a current branch provided parallel to the lamps (1,2) at least one additionally connectable electric load (5) is provided only for a predetermined time window (Ti), while the time window is synchronised with a control time window of the current monitoring circuit (4A) for the additional connection of the load. A lighting system according to claim 1, characterised in that as additionally connectable load (5) a resistor is provided. A lighting system according to claim 1 or 2, wherein an additionally connectable load (5) in the form of a conducting device is provided. A lighting system according to any one of the preceding claims, characterised by a transistor as switching element (7) for the connection and disconnection of the load (5). A lighting system according to any one of the preceding claims, characterised in that a time module (6) is provided that receives a trigger pulse and switches on the load (5) for a predetermined period with a delay after this trigger pulse. A lighting system according to claim 5, characterised in that as time module (6) a combination of a resistance and a condenser (resistance-capacitance 10 element) is provided. A lighting system according to claim 5, characterised in that as time module (6) a timer is provided. A lighting system according to any one of the preceding claims, characterised in that a failure control circuit (8) is provided for the light-emitting diodes, that in the case of a failure of a light-emitting diode prevents the additional connection of the load. A lighting system according to claim 8, characterised by two or more parallel current branches, in which two or more parallel connected light-emitting diodes are provided, wherein the failure control circuit (8) measure the currents in these current branches and compares the current values measured with one another. A lighting system according to any one of the preceding claims, characterised in that it is a flashing light signal system, wherein the time window (T-i), during which the load (5) is additionally connected, is smaller than the duration of a flashing pulse. 11. A lighting system according to claim 9, characterised in that when switching on the flashing pulse the positive flank is used a trigger signal for the time module (6). 11 List of reference numerals 1) Filament lamp 5 2) Light-emitting diode 3) LED light 4) Flasher unit 4A) Current monitoring circuit Vcc) Supply line 10 GND) Earth 5) Additionally connectable load 6) Time module 7) Switching element 8) Failure control unit 15 9) Logic 10) Operation amplifier R1, R2, R3) Resistances Z) Zener diode Intellectual Propertv Office of N.Z. 24 DEC 2004 RECEIVED