EP2157371B1 - Method and switching for temperature regulation in a vehicle headlamp - Google Patents

Description

The invention relates to a method for regulating the temperature in a motor vehicle headlight, which has in its headlight interior a number of LED light sources for generating one or more light functions.

Furthermore, the invention relates to a control device for temperature regulation in a motor vehicle headlight, which has in its headlight interior a number of LED light sources for generating one or more light functions.

In addition, the invention also relates to a vehicle headlight with an above-mentioned control unit.

Light-emitting diodes (LEDs) have gained in importance in recent years in the automotive industry as light sources for vehicle lights and for headlights, and LEDs are now increasingly used in headlights. However, the narrow thermal design limits of LED headlamps require active thermal management to prevent overheating of these headlamps.

Overheating of the headlamp interior has the consequence that the luminous flux emitted by the light-emitting diodes decreases. If a specified temperature is exceeded, the life of the LED is further reduced.

The DE 10 2004 011 939 B4 provides a solution to this problem. In the headlight described in this document, in order for the LEDs to properly emit their light, the current supplied to the LEDs is changed by means of a power control unit based on the speed of the vehicle. In detail, while the current is reduced, if the speed of the vehicle falls below a predetermined value, and the temperature of the vehicle lamp exceeds a predetermined temperature.

The DE 103 35 293 A1 shows the power control of a KF2 headlamp, taking into account the solar radiation.

The solution described in this document operates on the basis of limit values, and if these limits are exceeded or fallen below by changing the power supply, the heat emitted by the light-emitting diodes is reduced and, accordingly, care is taken that the headlight cools down or at least no longer heats up.

A disadvantage of this procedure, however, is that it is relatively difficult to define appropriate limits, which also can not be adapted to different external conditions. If the limit values are thus too generous, the current reduction may already be too late, or the limits are set too narrow, which often results in an unnecessary, too early current reduction and, accordingly, in a non-necessary deterioration of the light image.

It is an object of the invention to remedy the disadvantages described and to significantly improve the thermal management for LED headlights.

This object is achieved with a method mentioned in the fact that according to the invention in the operation of the headlight currently the headlight interior supplied power supply is determined, further continuously the currently possible power output from the headlight interior is determined from the determined supplied power supply and the a power balance is formed, and on the basis of the current account, a decision is made as to whether and which heat adjustment measures are to be carried out for the headlight interior.

Based on the power supplied and the currently possible power output, the decision is made according to the invention, which cooling strategy is active for the headlamp no active cooling, cooling fan, dimming the LEDs, cooling fan and additional dimming of the LEDs. The dimming can be done in one or more stages (also stepless), of course, accordingly, the fan can be operated with different cooling capacity.

In contrast to known methods, where on the basis of individual parameters, which are exceeded / fallen below, appropriate steps are initiated, in the present invention, the power balance is constantly monitored, so long before the headlight interior begins to overheat, appropriate cooling measures can be set. Overheating and damage to the LEDs is stifled with the invention already in the beginning, and accordingly, this measure can be much more moderate than in the case of exceeding / falling below limits, so that cooling measure according to the invention usually go without major impairment of the photograph in front of him ,

If the current reduction takes place only after exceeding a temperature limit, as is known from the prior art, this means that reacting only after the fact and does not prevent an increase in the temperature in advance, as is done in the present invention. The power reduction when exceeding a certain temperature limit has a negative effect on the photograph especially in the case when the power of the motor vehicle, the current can only be increased again when the headlamp has cooled far enough.

A particular objective is when heat regulation measures are carried out when the power balance is greater and / or greater than zero. A positive balance of power inevitably leads to a warming of the interior of the vehicle headlight; Accordingly, it makes sense in this case to set appropriate heat regulation measures for cooling the interior.

In the event that the interior of the headlamp already has a relatively high temperature, which is in the vicinity of the predetermined maximum temperature for the interior, it can also be provided that is cooled at a balanced power balance or even at a negative balance to the temperature to lower and thus get more scope for appropriate heat regulation measures.

It can be cooled in a particularly targeted manner if the decision whether and which heat regulation measures are to be carried out for the headlamp interior is also made dependent on the temperature in the interior of the headlamp and on the extent of the power balance.

Basically, it can be assumed that the headlight interior is cooled when the power balance is positive, so that the headlight has no way to heat up. Under certain circumstances, it may be expedient or (still) not necessary to cool, for example when the temperature in the interior is still far from the critical temperature and / or the power balance is only slightly positive. Also, as long as the temperature in the interior of the headlamp is below the operating temperature, cooling measures are not or only necessary if there is a strong positive power balance.

As a heat regulation measure, the activation of at least one fan for the interior of the vehicle headlight and the dimming of one, several or all LED light sources come into question.

It is favorable if at low temperatures with a positive power balance for the time being, the one or more fans is / are activated, before alternatively or additionally LED light sources be dimmed. Dimming the LED light sources leads to a deterioration of the light image; as long as this can be prevented with other cooling measures, just by activating a fan, these measures are set, and the light sources only additionally or alternatively dimmed, if absolutely necessary.

The current account can not be measured directly and must be calculated. For this computational determination of the power balance, therefore, a set of power supply parameters relevant to the power supply of the headlight is measured on the one hand to determine the power supply, and on the other hand a set of power output parameters relevant to the power output of the headlight is measured.

The set of power supply parameters comprises at least one parameter, which comes from the following quantity: power output of the light sources, temperature in the engine compartment of the motor vehicle, solar radiation (the energy radiated per surface). In modern passenger cars, solar radiation can usually be measured via the air conditioning system, these values can be used.

The set of power output parameters includes at least one parameter derived from the following: vehicle speed, engine compartment temperature of the vehicle, outside temperature, solar radiation, rainfall. The amount of precipitation may e.g. determined via a rain sensor for the windscreen wiper automatic and these data are used.

Based on the set of power supply parameters, the power supplied to the headlight interior is detected, and the set of power output parameters is used to determine the power output from the headlight interior.

The determination of the power supply and the power output is carried out by means of a mathematical model of the headlight. On the one hand, this mathematical model includes concrete calculation rules, on the other hand, a number of properties of the headlight are included in this model, such as material parameters such as heat conduction coefficients, the thickness of materials, the size and geometric shape of surfaces (windscreen, housing, ...), the special flow situation in SW (heat transfer coefficients), as well as the surfaces in the floodlight for absorbing solar radiation.

These parameters are summarized in the thermal contact resistance. While the rules of calculation between different headlamps do not change, of course, these contact resistances change.

The above-mentioned parameters or contact resistances for a headlight are determined empirically or in simulations, e.g. determined by finite element simulations.

To calculate the power supply and the power dissipated, a mathematical model is used, which consists of 2 parts, a part, with which the power supply and a part, with which the power dissipation is calculated.

If headlamps are the same, their thermal behavior within the tolerances will be the same. As far as the tolerances are concerned, the model should be designed for the "worst case", so that the theoretically possible power output does not exceed the actually achieved output.

In order to activate the fan or fans in critical temperature-critical situation, even when the headlamp is not in operation, it is still advantageous if the power balance is determined before the start-up and / or after the headlamp is taken out of service.

During operation of the headlamp, the current account is calculated on a regular basis. Typical time intervals for the determination are in the range of approx. 100 ms.

In general, not necessary, especially at small time intervals, but in principle it is still conceivable to adjust the time intervals, for example, the time intervals can be reduced at higher temperatures, thus in critical areas near the maximum temperature in the headlight interior higher resolution calculation of the current account.

• Fig.1 eine schematische Darstellung eines Fahrzeugscheinwerfers in einem Vertikalschnitt,
• Fig. 2 ein Flussdiagramm betreffend die Ermittlung der aus dem Scheinwerfer abgebbaren Leistung,
• Fig. 3 ein Flussdiagramm betreffend die Ermittlung der in dem Scheinwerfer zugeführten Leistung,
• Fig. 4 ein Flussdiagramm betreffend die Ermittlung der Leistungsbilanz,
• Fig. 5 ein Zustandsdiagramm der möglichen Kühlungsstufen, und
• Fig. 6 ein Temperaturschwellendiagramm.

In the following the invention is explained in more detail with reference to the drawing. In this shows

• Fig.1 a schematic representation of a vehicle headlamp in a vertical section,
• Fig. 2 a flowchart relating to the determination of the deliverable from the headlight power,
• Fig. 3 a flowchart relating to the determination of the power supplied in the headlight,
• Fig. 4 a flowchart concerning the determination of the current account,
• Fig. 5 a state diagram of the possible cooling stages, and
• Fig. 6 a temperature threshold diagram.

FIG. 1 schematically shows a motor vehicle headlight 1 with light emitting diodes 2, which are housed in a housing 5 of the headlamp. The light-emitting diodes 2 are mounted on a carrier element 4, which comprises a heat sink or is designed as such. The environment 5 towards the housing 5 is closed with a cover 6, to the rear of the engine compartment 7, the housing 5 has a corresponding wall section 6.

To carry out the method as described below, for example, a control unit 100 is provided, which makes a decision based on the relevant data, which cooling measures are to be taken and then causes the appropriate measures.

The temperature in the headlight interior 3 is denoted by Ti, those of the environment 8 by Tu, further Tm denotes the temperature in the engine compartment. 7

The thermal resistance of the housing is denoted by RB, that of the cover by RF.

Overheating of the headlamp interior has the consequence that the luminous flux emitted by the light-emitting diodes decreases. If a specified temperature is exceeded, the life of the LED is further reduced. Such overheating should be prevented by the method according to the invention.

For this purpose, the currently supplied to the headlight interior power supply is determined at least during operation of the headlamp, as shown schematically in FIG FIG. 2 is shown.

Furthermore, the currently possible power output from the headlight interior is continuously determined ( FIG. 3 ).

From the determined supplied power supply and the possible power output is accordingly FIG. 4 a current account is determined, and on the basis of the current account, a decision is made as to whether and which heat adjustment measures are to be carried out for the headlamp interior (3).

Based on the supplied power of the currently possible power output, the decision as to which cooling strategy is active for the headlight can then be made according to the invention: no active cooling, cooling via fan, dimming of the LEDs, cooling via fan and additional dimming of the LEDs. Furthermore, different dimming levels can be provided, for example, that at first only the main beam is dimmed, then the dipped beam is also dimmed, then the main beam is switched off completely; the transitions can also be stepless.

As FIG. 2 can be taken in detail, a set of relevant for the power supply to the interior of the headlight power supply parameters is measured for the computational determination of the power balance on the one hand to determine the power supply. The set of power consumption parameters comprises at least one parameter, which comes from the following quantity: power output of the light sources, temperature in the engine compartment of the motor vehicle, by means of which the power input from the engine compartment can be concluded, solar radiation (the energy radiated per surface). In modern passenger cars, solar radiation can usually be measured via the air conditioning system, these values can be used.

Using a mathematical model, the supplied power contributions are determined in the interior of the headlight and added up ( FIG. 2 ).

Furthermore, a set of power output parameters relevant to the power output of the headlight 1 is measured.

The set of power output parameters includes at least one parameter derived from the following quantity: vehicle speed, engine compartment temperature of the vehicle, outside temperature, solar radiation, precipitation (rain), the last three points in FIG. 3 summarized under the term "weather conditions". The amount of rainfall can be determined eg via a rain sensor for the windscreen wiper automatic and this data can be used.

On the basis of the set of power consumption parameters, the power supplied to the headlight interior 3 is determined by means of a mathematical model ( FIG. 3 ). The determination of the power supply and the power output is carried out by means of a mathematical model of the headlight. On the one hand, this mathematical model includes concrete calculation rules, on the other hand, a number of properties of the headlight are included in this model, such as material parameters such as heat conduction coefficients, the thickness of materials, the size and geometric shape of surfaces (windscreen, housing, ...), the special flow situation in SW (heat transfer coefficients), as well as the surfaces in the floodlight for absorbing solar radiation.

These parameters are summarized in the thermal contact resistances RB and RF. While the rules of calculation between different headlamps do not change, of course, these contact resistances change.

The above-mentioned parameters or contact resistances for a headlight are determined empirically or in simulations, e.g. determined by finite element simulations.

To calculate the power supply and the power dissipated, a mathematical model is used, which consists of 2 parts, a part, with which the power supply and a part, with which the power dissipation is calculated.

If headlamps are the same, their thermal behavior within the tolerances will be the same. As far as the tolerances are concerned, the model should be designed for the "worst case", so that the theoretically possible power output does not exceed the actually achieved output.

By determining the power supply in the headlight interior 3 can be determined how the current temperature will develop in the interior and it can be initiated appropriate countermeasures.

The temperature in the interior results in a simple approximation as follows: $$\mathrm{Ti}=\left(\mathrm{RF}\times \mathrm{TM}+\mathrm{RB}\times \mathrm{TU}+\mathrm{dQ}/\mathrm{dt}\times \mathrm{RF}\times \mathrm{RB}\right)/\left(\mathrm{RB}+\mathrm{RF}\right)\mathrm{,}$$

The power component is in the proportion dQ / dt, i. the amount of energy supplied or discharged per unit of time to the headlight interior (energy / time unit).

In contrast to known methods, where appropriate steps are initiated on the basis of individual parameters which are exceeded or fallen short of, in the present invention, the power balance is constantly monitored, so that long before the Headlight interior begins to overheat, appropriate cooling measures can be set. Overheating and damage to the LEDs is already stifled with the invention in the beginning, and accordingly, this measure can be much more moderate than in the case of exceeding / falling below of limits, so that cooling measure according to the invention usually go without major impairment of the photograph in front of him ,

A particular objective is when heat regulation measures are carried out when the power balance is greater and / or greater than zero. A positive balance of power inevitably leads to a warming of the interior of the vehicle headlight; Accordingly, it makes sense in this case to set appropriate heat regulation measures for cooling the interior.

FIG. 5 and FIG. 6 show which decision can be made regarding the cooling strategy to be chosen: Based on the power supplied and the possible power output as well as the current headlamp interior temperature, the decision is made which cooling strategy is active. There are 3 levels possible: No active cooling; Cooling via fan; Cooling via fan and additional dimming. The diagram FIG. 5 shows the state diagram for these 3 stages, FIG. 6 shows the relationships as a function of the temperature in the interior of the vehicle headlight.

• Ü1: Lüfter auf volle Leistung, wenn die Temperaturreserve (TiMax - Ti_akt) im Scheinwerfer einen 1. Grenzwert unterschreitet (TiMax - Ti_akt < dTL_Max) oder die Leistungsbilanz ohne Dimmung und ohne aktiviertem Lüfter größer Null ist (Pzu > Pab)
• Ü2: Lüfter auf reduzierte Leistung, wenn die Temperaturreserve im Scheinwerfer einen 2. Grenzwert überschreitet (TiMax-Ti_akt > dTL_MIN) und die Leistungsbilanz ohne Dimmung und ohne aktivierten Lüfter kleiner Null ist (Pzu < Pab)
• Ü3: Scheinwerfer dimmen, wenn die Temperaturreserve im Scheinwerfer einen 3. Grenzwert unterschreitet (TiMax - Ti_akt < dTD_MAX) und die Leistungsbilanz ohne Dimmung und ohne aktiviertem Lüfter größer oder gleich Null ist (Pzu >= Pab)
• Ü4: Scheinwerfer auf volle Leistung wenn die Temperaturreserve im Scheinwerfer einen 4. Grenzwert überschreitet (TiMax - Ti_akt > dTD_MIN) oder die Leistungsbilanz oh ne Dimmung und ohne aktiviertem Lüfter kleiner Null ist
• Ü5: Scheinwerfer auf volle Leistung, wenn die Temperaturreserve im Scheinwerfer einen 5. Grenzwert unterschreitet (TiMax - Ti_akt < dTD_MINHIGH) und die Leistungsbilanz bei aktiviertem Lüfter kleiner Null ist
• Ü6: Scheinwerfer auf volle Leistung, wenn die Temperaturreserve im Scheinwerfer den 5. Grenzwert überschreitet (TiMax - Ti_akt > dTD_MIN) und die Leistungsbilanz bei Dimmung kleiner Null (Pzu < Pab) und die Fahrzeuggeschwindigkeit größer einem festgelegten Wert ist.

The transitions are defined as follows:

• Ü1: Fan to full power, if the temperature reserve (TiMax - Ti_akt) in the headlamp falls below a 1st limit value (TiMax - Ti_akt <dTL_Max) or the power balance without dimming and without activated fan is greater than zero (Pzu> Pab)
• Ü2: Fan at reduced power if the temperature reserve in the headlight exceeds a second limit (TiMax-Ti_akt> dTL_MIN) and the power balance without dimming and without activated fan is less than zero (Pzu <Pab)
• Ü3: Dimming headlights if the temperature reserve in the headlamp falls below a 3rd limit (TiMax - Ti_akt <dTD_MAX) and the power balance without dimming and without activated fan is greater than or equal to zero (Pzu> = Pab)
• Ü4: Headlight on full power if the temperature reserve in the headlamp exceeds a 4th limit (TiMax - Ti_akt> dTD_MIN) or the power balance without dimming and without activated fan is less than zero
• Ü5: Headlight to full power, if the temperature reserve in the headlamp falls below a 5th limit (TiMax - Ti_akt <dTD_MINHIGH) and the power balance with activated fan is less than zero
• Ü6: Headlamps to full power when the temperature reserve in the headlamp exceeds the 5th limit (TiMax - Ti_akt> dTD_MIN) and the power balance at dimming is less than zero (Pzu <Pab) and the vehicle speed is greater than a specified value.

The temperature reserve is the difference between the maximum permissible (TIMax) and current (Ti_akt) temperature in the headlight interior. Pzu is the current power delivered and Pab is the power delivered.

TD_Min represents a difference to the maximum allowed temperature TiMax. This is important because the temperature limits are always seen relative to the maximum temperature, but the maximum temperature is constantly changing depending on the power in the LEDs. For example, at full light output, a TiMAX of 100 ° C and thus a TD_Min of 100 ° C-20 ° C = 80 ° C may be allowed, but with dimmed operation a TiMax of 110 °, corresponding to a TD_Min = 110 ° -20 ° = 90 ° would result (see FIG. 6 ).

In the event that the interior of the headlamp already has a relatively high temperature, which is in the vicinity of the predetermined maximum temperature for the interior, it can also be provided that is cooled at a balanced power balance or even at a negative balance to the temperature to lower and thus get more scope for appropriate heat regulation measures.

It can be cooled in a particularly targeted manner if the decision as to whether and which heat regulation measures are to be carried out for the headlight interior 3 is further made dependent on the temperature in the headlight interior 3 and on the extent of the power balance.

Basically, it can be assumed that the headlight interior is cooled when the power balance is positive, so that the headlight has no way to heat up. Under certain circumstances, it may be expedient or (still) not necessary to cool, for example when the temperature in the interior is still far from the critical temperature and / or the power balance is only slightly positive. Also, as long as the temperature in the interior of the headlamp is below the operating temperature, cooling measures are not or only necessary if there is a strong positive power balance.

It is advantageous if, at lower temperatures with a positive power balance for the time being, the fan (s) is / are activated before, alternatively or additionally, LED light sources are dimmed. Dimming the LED light sources leads to a deterioration of the light image; as long as this can be prevented with other cooling measures, just by activating a fan, these measures are set, and the light sources only additionally or alternatively dimmed, if absolutely necessary.

In order to activate the fan or fans in critical temperature-critical situation, even when the headlamp is not in operation, it is still advantageous if the power balance is determined before the start-up and / or after the headlamp is taken out of service.

During operation of the headlamp, the current account is calculated on a regular basis. Typical time intervals for the determination are in the range of about 100 ms.

It is also important in this context that the decision as to whether and which heat-regulating measures are to be carried out for the headlight interior 3 is likewise taken on an ongoing basis. That is, it is virtually permanently decided what measures to take, so that it can respond quickly to changing situations.

It is particularly quick to react when the decision regarding the cooling measures is taken for each calculated current account, ie that the decision regarding the cooling strategy is also "reconsidered" every 100 ms, for example at 100 ms for calculating the current account.

If the time intervals of the determination of the power balance are too short, it can also be provided that only for certain determined power balances, e.g. for every 10th current account, the decision is made new.

Finally, in the following table, the relationship between fan on, full power of the LEDs, and dimming (reduction by 1 or 2 stages) is shown purely by way of example purely by way of example in the following table. Shown in each case is the energy in watts, which is introduced into the headlight, a negative sign describes an energy dissipation from the headlight and provides a corresponding cooling effect: Full power Dimming level 1 Dimming level 2 Fan on wind -30 W -60 W -63 W Fan off wind +120 W +98 W +67 W Fan on no Fahrtw. +22 W +1 W -8 W Fan off no Fahrtw. +140 W +110 W +82 W

Claims (12)

1. A method for temperature regulation in a motor vehicle headlight (1), which in its headlight interior (3) has a number of LED light sources (2) for generating one or more light functions,
   characterised in that
   the power supply actually supplied to the headlight interior (3) is determined in an ongoing manner during operation of the headlight, the power output actually possible from the headlight interior (3) is also determined in an ongoing manner, a power balance is formed from the determined supplied power supply and the possible power output, and a decision is made on the basis of the power balance as to whether and which heat regulation measures are to be carried out for the headlight interior (3), wherein
   in order to determine the power supply, a set of power supply parameters relevant for the power supply of the headlight (1) is measured, wherein the set of parameters following power supply parameters comprises: power output of the light sources, temperature in the engine compartment of the motor vehicle, solar radiation,
   and wherein
   a set of power output parameters relevant for the power output of the headlight (1) is measured, wherein the set of parameters following the power output parameters comprises: vehicle speed, engine compartment temperature of the motor vehicle, external temperature, solar radiation,
   and wherein
   the power supply supplied to the headlight interior (3) is determined on the basis of the set of power supply parameters and the power output that can be output from the headlight interior (3) is determined on the basis of the set of power output parameters.
2. The method according to Claim 1, characterised in that, if the power balance is greater than and/or greater than or equal to zero, heat regulation measures are carried out.
3. The method according to Claim 1 or 2, characterised in that the decision as to whether and which heat regulation measures are to be carried out for the headlight interior (3) is also made depending on the temperature in the headlight interior (3) and on the magnitude of the power balance.
4. The method according to one of Claims 1 to 3, characterised in that the power supply and the power output are determined by means of a mathematical model of the headlight.
5. The method according to one of Claims 1 to 4, characterised in that the power balance is determined already before the headlight is commissioned and/or once the headlight has been decommissioned.
6. The method according to one of Claims 1 to 5, characterised in that the power balance is determined in an ongoing manner at regular intervals.
7. The method according to one of Claims 1 to 6, characterised in that the activation of at least one ventilator for the interior of the vehicle headlight is provided as heat regulation measure.
8. The method according to one of Claims 1 to 7, characterised in that the dimming of one, more, or all LED light sources is provided as heat regulation measure.
9. The method according to Claim 7 and 8, characterised in that, at low temperatures with a positive power balance, the ventilator or ventilators is/are activated for the time being before LED light sources are dimmed alternatively or additionally.
10. The method according to one of Claims 1 to 9, characterised in that the decision with regard to the question whether and which heat regulation measures are to be carried out for the headlight interior (3) is made in an ongoing manner.
11. The method according to Claim 10, characterised in that the decision is made anew for each determined power balance or for certain determined power balances.
12. The method according to one of Claims 1 to 11, characterised in that the set of power output parameters relevant for the power output of the headlight (1) also includes the parameter constituted by precipitation (rain).

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