SE539826C2

SE539826C2 - Compensation unit configured to be connected between a control unit and at least one LED lamp

Info

Publication number: SE539826C2
Application number: SE1451288A
Authority: SE
Inventors: Österlund Henrik
Original assignee: Scania Cv Ab
Priority date: 2014-10-29
Filing date: 2014-10-29
Publication date: 2017-12-12
Also published as: SE1451288A1; DE102015013309B4; DE102015013309A1; BR102015026375A2

Abstract

16 Abstract A compensation unit (2) configured to be connected between a control unit (4) forlamp failure status detection using test pulses (6) and at least one LED lamp (8)including at least one light emitting diode (LED). The compensation unit (2)includes a housing (10) and is provided with one input connection line (12) forconnection to an electrical line (14) connected to the control unit (4), and oneoutput connection line (16) for connection to an electrical line (18) connected tothe LED lamp (8). The components comprises one capacitor unit (28) having acapacitor value G1 and one resistor unit (30) having a resistor value R1, thecapacitor unit and the resistor unit are connected in parallel between the inputconnection line (12) and the earth connection point (26), and that the inputconnection line (12) is connected to said output connection line (16). The valuesG1, R1 are chosen in dependence of characteristics of the control unit (4) andcharacteristics of the LED lamp (8), and of a time period T between test pulses(6), such that said control unit (4) correctly detects the failure status of said LEDlamp (8). (Figure 4)

Description

Compensation unit costfioured to be connected betmfeen a controi tinit and at leastone LED lamp Field of the inventionThe present invention relates to a compensation unit, and a method in relation to the compensation unit, according to the preambles of the independent claims. ln particular the present invention relates to the use of a compensation unit thatenables control units configured for a specific type of detection of an electronicload to determine the working status of a light emitting diode (LED) (i.e. if it isbroken or not) even if it is connected to an output of the control unit configured for detection of the status of an incandescent filament lamp.

Background of the invention lt is a known problem that the large difference in current consumption between aLED and a filament lamp with corresponding luminance makes it difficult toconstruct driver electronics adapted to discover failures related to an electricbreakdown, e.g. related to a damaged electrical cable or a non-working lamp(LED lamp or filament lamp). ln the present application the term LED lamp is used to designate a unitcomprising one or many light emitting diodes (LEDs) arranged together as asingle unit. ln the unit one or many resistors may be included to support thefunction of the LED(s).

More specifically, the above problem may arise at vehicles, e.g. busses, trucks orcars, where the directional indicators traditionally included filament lamps but nowinstead use LED lamps. For indicators at certain positions, e.g. a lower directionalindicator at a bus, there are legal requirements that the driver should receive anindication when a lamp is out of order. lf a control unit for the indicators isconfigured for use in connection with filament lamps, but if instead LED lamps areused, the control unit probably will not work as required.

There are different methods to determine if there is a failure along the circuitincluding the control unit- the lamp - earth, i.e. if the electric cable or the lamp isbroken. One common method includes that the control unit applies a currentthrough a measurement resistor within the control unit and then through the lampto earth. The voltage at the output of the control unit is measured and if thevoltage is above a predefined threshold it is determined that a failure is detected.The measurement is performed during a very short initial test pulse preferablyapplied before each flashing pulse of the directional indicator. After the test pulsethe full operational current is applied to the lamp.

During the test pulse a fully functional filament lamp displays a considerablysmaller resistance than a fully functional LED lamp, i.e. there is a much smallervoltage over the filament lamp than over the LED lamp during the test pulse.Therefore, the control unit may detect the presence of a fully functional LED lampas a failure, which is not correct.

This problem may be solved in many different ways.

One solution that is commonly used is to arrange one or more external resistorsconnected in parallel in order to increase the load so much that the control unit willconsider it (the LED lamp and the resistors) as a filament lamp. However, thissolution has high energy consumption, generates heat and it is often difficult todimension the resistors, which is dependent e.g. upon the construction of the LEDlamp, the structure of the control unit, and the used voltages.

Another way is to arrange a more advanced electronic circuit between the controlunit and the LED lamp in order to measure the current and create a higher loadfor the control unit in order to simulate that it is connected to a filament lamp. lt isthen possible to exactly dimension and adapt the electronic circuit to the LEDlamp. This solution is relatively complex and expensive, and may have similarproblems as the resistor solution above (high energy consumption and heatgeneration).

The following documents disclose various aspects of the technical field.

EP-2000359 relates to a connection unit provided with a semiconductor switch forcontrolling a trailer light including e.g. a light emitting diode and being switchableby a control device, where the control device communicates with a data networkof a drawing vehicle.

US-2004/0061450 relates to a vehicular lamp including a break detection unit fordetecting breaking of a light source and notifying the outside of the lamp body ofthe detection result.

EP-2685789 discloses a directional LED indicator system including capabilities ofdetecting a failure of an LED.

EP-1458222 relates to a lamp failure warning device for an LED comprising aswitch means for connecting one or many load resistors in parallel with the LED in order to simulate a conventional filament lamp. l\/lany of the known solutions discussed above include complex circuitry and maynot be applicable in connection with control systems using short test pulses inorder to determine the status of the LED lamp.

Thus, the object of the present invention is to remove the above stated drawbacksof the presently used solutions in relation to detection of failure of a LED lampwhen connected to a control unit configured to detect failures of conventionalfilament lamps. The drawbacks with the presently used technique are e.g. thatthey are often technically complex and therefore expensive, they have highenergy consumption, and in addition they are not applicable for working inconnection with control systems using short test pulses.

One further object is to provide for failure detection using existing control units invehicles, i.e. it should not be necessary to exchange the existing control unit ifLED lamps are used instead of filament lamps.

Summarv of the inventionThe above-mentioned objects are achieved, or at least mitigated, by the present invention according to the independent claims.

Preferred embodiments are set forth in the dependent claims.

The present invention relates to a compensation unit that facilitates for controlunits configured for a specific type of detection of an electronic load to determinethe working status of a LED lamp (i.e. if it is broken or not) even if it is connectedto an output of a control unit configured for detection of the status of an incandescent filament lamp.

According to the present invention a compensation unit is provided which isconfigured to be arranged between the control unit and the LED lamp (adirectional indicator or other lights). The compensation unit is a very simpleelectronic circuit that includes only two or three cheap standard components. ln particular the compensation unit includes a housing configured to enclose,protect and seal the components as the compensation unit is mounted in a roughenvironment.

The compensation unit is provided with one input connection line for connection toan electrical line connected to the control unit, and one output connection line forconnection to an electrical line connected to the LED lamp. The input and outputconnection lines pass through the wall of the housing in sealed feed throughopenings.

During the test pulse, that preferably occurs just before each flash pulse for thedirectional indicator, the compensation unit will simulate a filament lamp bycreating a load that corresponds to the load of a filament lamp, but after a shortperiod of time, when the test pulse has terminated, it will have very little influence of the control unit and a very low current consumption. lf there is a failure of the LED lamp the load simulation capability of thecompensation unit will cease and the control unit will detect the failure. Thecompensation unit will preferably be located close to the LED lamp.

According to one embodiment the compensation unit comprises a capacitor unitand a resistor unit being connected in parallel to earth. These are dimensionedsuch that the measurement during the test pulse will result in a measurementvoltage being below the failure detection threshold when the LED lamp is workingnormally, and above the failure detection threshold when the LED lamp is broken.Generally, the specific values of the components of the compensation unit mustbe adapted to each specific application because the characteristics of the differentcontrol units and LEDs differ.

The capacitor unit loads the output of the control unit when it is charged during thetest pulse enough for the measurement voltage over the measurement resistor inthe control unit to be below the detection threshold and the control unit willtherefore consider that a sufficiently large load being connected. When theflashing pulse has terminated the capacitor is discharged through the resistor ofthe compensation unit and through the LED lamp. All this provided that the LED lamp is working normally. lf the LED lamp ””disappears”” the capacitor will not be sufficiently dischargedbetween the flashings because the discharge must be through the resistor in thecompensation unit which is dimensioned such that the capacitor cannot bedischarged during the time period between the test pulses and this will keep upthe measurement voltage over the measurement resistor. This results in that onlya small amount of current is required in order to recharge it during next test pulseand the control unit will then consider it as the load is too low and a failure will bedetected. 6 The solution according the invention is applicable for a LED lamp of a typeincluding resistors and the actual light emitting diode, but the solution is applicablealso for other types.

The present invention is advantageous at least in the following aspects: lt is simple, robust and considerably cheap. lt is easy to be applied on vehicles designed for conventional filament lamps. - lt is adaptable to different control units and LED lamps. One possibleembodiment would be to use variable components in the compensationunit.

- A further advantage is that it suppresses the flashes that might occur in LEDs caused by specific control units continuously sending out short current pulses to detect if a trailer has been coupled to the vehicle.

Short description of the appended drawinqs Figure 1 is a diagram illustrating test pulses for failure detection of a lamp where alamp failure is detected.

Figure 2 is a diagram illustrating test pulses for failure detection of a lamp where afunctional lamp is detected.

Figure 3 is a schematic block diagram of a known failure detection system.

Figure 4 is a schematic block diagram illustrating a failure detection systemincluding a compensation unit according to the present invention.

Figure 5 is a schematic block diagram illustrating a failure detection systemincluding a compensation unit according to an embodiment of the presentinvenﬁon.

Figure 6 illustrates different views of the compensation unit according to anembodiment of the present invention.

Figure 7 is a schematic flow diagram illustrating the method according to the present invention.

Detailed description of preferred embodiments of the invention 7 The present invention will now be described in detail with references to theappended figures. Throughout the figures the same or similar item has the same reference sign. ln figure 3 is illustrated a schematic block diagram of a known lamp failuredetection system. A control unit 4 is provided configured to apply a test pulse 6 tothe lamp 3 to be tested. The lamp could be a filament lamp or a LED lamp. Thetest pulse 6 is applied via a measurement resistor 32 within the control unit 4.Preferably, the control unit 4 also comprises circuitry to generate and apply pulsesapplicable for controlling directional indicators of a vehicle. The circuitry comprisese.g. an amplifying unit 34 configured to amplify an applied voltage to a requiredvoltage level. The directional indicator pulses 7 are illustrated in figures 1 and 2and occur normally immediately after each test pulse.

The test pulse may have a duration of approximately 20 ms and a voltage of 24Volt. They are generated at a regular frequency of 1/T, where T is the time periodbetween two consecutive test pulses. T is normally in the range of 0.5 - 1.5seconds. The voltage U at the output of the control unit 4 is measured during thetest pulse and the voltage U is compared to a threshold value UT, see figures 1and 2. The threshold value UT is naturally determined in dependence of thevoltage amplitude of the test pulse. According to one typical example UT is in therange of 13-17 Volt, e.g. 15 Volt.

Figure 1 is a diagram illustrating test pulses for failure detection of a lamp where alamp failure is detected, i.e. if the filament of a lamp is broken the voltagemeasured at the output of control unit 4 would be close to the voltage amplitude ofthe test pulse which is above UT and a lamp failure is detected by the control unit.However, as discussed in the background section this situation may also occurwhen the lamp is a fully functional LED lamp because a LED lamp corresponds toa small load in comparison to a filament lamp that does not lower the voltage asmuch as a filament lamp during the test pulse. Therefore, the control unit maydetect the presence of a fully functional LED lamp as a failure, which is notcorrect. 8 Figure 2 is a diagram illustrating test pulses for failure detection of a lamp where aworking lamp is detected.

Thus, the intention of the present invention is to enable correct failure detectionirrespectively if a filament lamp or a LED lamp is used, and in particular tocorrectly detect a fully functional LED lamp such that the diagram in that case is as in figure 2.

A compensation unit 2 is provided configured to be connected between a controlunit 4 for lamp failure status detection using test pulses 6 and at least one LEDlamp 8 including at least one light emitting diode (LED).

The compensation unit 2 includes a housing 10 configured to enclose and protectcomponents mounted within the housing 8, as the compensation unit may bemounted at a vehicle in a rough environment.

The compensation unit 2 is provided with one input connection line 12, e.g. aninsulated electrical cable, for connection to an electrical line 14 connected to thecontrol unit 4, and one output connection line 16, e.g. an insulated electrical cable,for connection to an electrical line 18 connected to the LED lamp 8.

The input and output connection lines (12, 18) pass through the wall 20 (se figure6) of the housing 10 in one or two sealed feed through openings (22, 24) (sefigure 6). ln addition the housing 10 is provided with an earth connection point 26configured to be connected to earth potential. The earth potential may be commonto the earth potential of the LED lamp.

The components comprise one capacitor unit 28 having a capacitor value G1 andone resistor unit 30 having a resistor value F11.

Preferably, each of the capacitor unit and the resistor unit comprises onecapacitor component and resistor component, respectively. However, each unitmay be embodied by a plurality of components, e.g. the resistor unit may 9 comprise two or more resistor components connected such that the compoundresistor value is F11.

The capacitor unit and the resistor unit are connected in parallel between the inputconnection line 12 and the earth connection point 26, and that the inputconnection line 12 is connected to the output connection line 16. The values G1,Fïi are chosen in dependence of characteristics of the control unit 4 andcharacteristics of the LED lamp 8, and of a time period T between test pulses 6,such that the control unit 4 correctly detects the failure status of said LED lamp 8.According to one embodiment the capacitor value is in the range of 100-200 uFand the resistor value is in the range of 6.0 - 8.0 kQ, and advantageously thecapacitor value is approximately 150 uF and the resistor value is approximately6.8 kQ.

The characteristics of the LED lamp include the internal resistance of the LED(s)and also of resistor values of resistors, if any, arranged within the LED lamp.According to one embodiment the characteristics of the control unit includes aresistor value R, e.g. in the range of 500-800 Q, and approximatively 700 Q, of ameasurement resistor and a failure detection voltage threshold UT, which may bein the range of 13-17 Volt, e.g. 15 Volt, provided a test pulse amplitude of 24 Volt.The time period T is preferably in the range of 0.5 - 1.5 seconds. ln the case where a LED lamp includes a number of individual LEDs, e.g. 20LEDs, the compensation unit may be set to result in a failure detection when allindividual LEDs fail, or when a predetermined number, e.g. half of the LEDs fail.

The capacitance and resistance values of the components of the compensationunit are chosen such that the accumulated charge of the capacitor unit is kept at alevel where a subsequent test pulse will result in a clear indication of themeasurement voltage U measured at the output of the control unit, i.e. themeasured voltage level should be well below the voltage threshold UT when theLED lamp is working.

The purpose of the resistor is to set the thresholds with/without LED including a margin around the threshold. ln addition it also allows the capacitor to continue lO discharging between the test pulses, e.g. in connection with the flashings of thedirectional indicators, but also prevents that the capacitor remains charged if no lamp is connected.

According to one alternative the resistor unit and capacitor unit may be variablecomponents that may be adapted to different control units and LED lamps. lf many LED lamps are connected to the same output of the control unit it isnecessary, irrespectively if all LED lamps should be failure-monitored or not, toinclude a diode to insulate the lamps from each other and to prevent the capacitorfrom being discharged through the wrong lamp. One such embodiment isillustrated in figure 5. Thus, according to this embodiment the componentscomprise a diode 36 connected in its forward direction between the inputconnection line and the capacitor unit and resistor unit. ln the set-up illustrated infigure 5, only the lower LED lamp is monitored by the control unit.

As the compensation unit should be robust it comprises only few different parts;according to one embodiment the components of the unit comprise not more than three electrical components.

Figure 6 illustrates different views of the compensation unit according to oneembodiment of the present invention.

As described above the input and output connection lines (12, 16) pass throughthe wall 20 of the housing 10 in one or two sealed feed through openings (22, 24).ln addition the housing 10 is provided with an earth connection point 26configured to be connected to earth potential. ln this embodiment the connectionpoint includes a hole for attaching the unit to e.g. the chassis of the vehicle.

The compensation unit may have a size of approximately 50x35x3O mm and maybe made from a suitable plastic and sealed by an epoxy resin. Each of the inputand output connection lines 12, 16 are provided, at their respective ends, with acontact member configured to, respectively, be connected to the electrical line 14connected to the control unit 4, and to the electrical line 18 connected to the LED lamp8. ll The present invention also relates to a method which now will be described withreferences to figure 7.

Thus, the method is intended to be applied in relation to a compensation unit 2configured to be connected between a control unit 4 for lamp failure statusdetection using test pulses 6 and at least one LED lamp 8 including at least onelight emitting diode (LED). The compensation unit 2 includes a housing 10configured to enclose and protect components mounted within the housing 8. Thecompensation unit 2 is provided with one input connection line 12, for connectionto an electrical line 14 connected to the control unit 4, and one output connectionline 16, for connection to an electrical line 18 connected to the LED lamp 8. Theinput and output connection lines (12, 18) pass through the wall 20 of the housing10 in one or two sealed feed through openings (22, 24). The housing 10 isprovided with an earth connection point 26 configured to be connected to earthpotential. The input connection line 12 is connected to the output connection line16. Further features of the compensation unit are discussed above whendescribing the compensation unit.

The method comprises the steps of: -Connecting a compensation unit between the control unit and the LED lamp.The compensation unit comprises one capacitor unit having a capacitor value G1and one resistor unit having a resistor value F11, the capacitor unit and the resistorunit are connected in parallel between the input connection line and an earthconnection point. The values G1, Fši are chosen in dependence of characteristicsof the control unit 4 and characteristics of the LED lamp 8, and of a time period Tbetween test pulses 6.

-Applying consecutive test pulses to the LED lamp via the compensation unit.-Charging the capacitor unit, -Determining a measurement voltage to be used by the control unit 4 to correctlydetect the failure status of said LED lamp 8.

-Discharging the capacitor unit. 12 According to one embodiment, Characteristics of the control unit include a resistorvalue R of a measurement resistor and a failure detection voltage threshold UT.These features are further discussed above. ln a further embodiment the method comprises providing a diode to be connectedin its forward direction between the input connection line and the capacitor unit and resistor unit.

The present invention is not limited to the above-described preferredembodiments. Various alternatives, modifications and equivalents may be used.Therefore, the above embodiments should not be taken as limiting the scope ofthe invention, which is defined by the appending claims.

Claims

13 Claims

1. A compensation unit (2) configured to be connected between acontrol unit (4) for lamp failure status detection using test pulses (6) and at leastone LED lamp (8) including at least one light emitting diode (LED), the compensation unit (2) includes a housing (1 O) configured to enclose andprotect components mounted within the housing (_1_Q_8), the compensation unit (2) is provided with one input connection line (12) forconnection to an electrical line (14) connected to the control unit (4), and oneoutput connection line (16) for connection to an electrical line (18) connected tothe LED lamp (8), and that the input and output connection lines (12, 1648) passthrough the wall (20) of the housing (10) in one or two feed through openings (22,24), the housing (10) is provided with an earth connection point (26) configured to beconnected to earth potential, c h a r a c t e r i z e d in that said components comprises one capacitor unit (28)having a capacitor value G1 and one resistor unit (30) having a resistor value Fh,the capacitor unit and the resistor unit are connected in parallel between the inputconnection line (12) and said earth connection point (26), and that said inputconnection line (12) is connected to said output connection line (16), wherein saidvalues G1, Fh are chosen in dependence of characteristics of the control unit (4)and characteristics of the LED lamp (8), and of a time period T between testpulses (6), such that said control unit (4) correctly detects the failure status of saidLED lamp (8).

2. The compensation unit according to claim 1, wherein saidcharacteristics of the control unit includes a resistor value R of a measurementresistor and a failure detection voltage threshold UT.

3. The compensation unit according to claim 1 or 2, wherein saidcomponents comprise a diode (36) connected in its forward direction between theinput connection line and said capacitor unit and resistor unit. 14

4. The compensation unit according to any of claims 1-3, wherein saidtime period T is in the range of 0.5 - 1.5 seconds.

5. The compensation unit according to any of claims 1-4, wherein saidcapacitor value is in the range of 100-200 uF and said resistor value is in therange of 6.0 - 8.0 kQ.

6. The compensation unit according to any of claims 1-5, wherein saidcapacitor value is approximately 150 uF and said resistor value is approximately6.8 kQ.

7. The compensation unit according to any of claims 1-6, wherein saidLED lamp is a directional indicator of a vehicle.

8. The compensation unit according to any of claims 1-7, wherein saidcomponents comprise not more than three electrical components.

9. A method in relation to a compensation unit (2) configured to beconnected between a control unit (4) for lamp failure status detection using testpulses (6) and at least one LED lamp (8) including at least one light emitting diode(LED), the compensation unit (2) includes a housing (10) configured to enclose andprotect components mounted within the housing (108), the compensation unit (2) is provided with one input connection line (12), forconnection to an electrical line (14) connected to the control unit (4), and oneoutput connection line (16), for connection to an electrical line (18) connected tothe LED lamp (8), and that the input and output connection lines (12, 1818) passthrough the wall (20) of the housing (10) in one or two sealed feed throughopenings (22, 24), the housing (10) is provided with an earth connection point (26) configured to beconnected to earth potential, c h a r a c t e r i z e d in that said input connection line (12) is connected to said output connection line (16), wherein the method comprises the steps of: -connecting a compensation unit between said control unit and said LED lamp,wherein said compensation unit comprises one capacitor unit having a capacitorvalue G1 and one resistor unit having a resistor value Ri, the capacitor unit andthe resistor unit are connected in parallel between the input connection line andan earth connection point, wherein said values G1, Fïi are chosen in dependenceof characteristics of the control unit (4) and characteristics of the LED lamp (8),and of a time period T between test pulses (6), -applying consecutive test pulses to said LED lamp via said compensation unit,-charging said capacitor unit, -determining a measurement voltage to be used by said control unit (4) tocorrectly detect the failure status of said LED lamp (8), -discharging said capacitor unit.

10. The method according to claim 9, wherein said characteristics of thecontrol unit includes a resistor value R of a measurement resistor and a failure detection voltage threshold UT.

11. The method to claim 9 or 10, wherein said method comprisesproviding a diode to be connected in its forward direction between the input connection line and said capacitor unit and resistor unit.