JP6194591B2 - Vehicle lighting - Google Patents

Description

  The present invention relates to a vehicular lamp.

  Conventionally, a drive circuit that drives a load, which is a light source, is mounted on a vehicular lamp. In a vehicular lamp provided with this drive circuit, in order to protect the drive circuit during high temperature driving, the ambient temperature of the drive circuit is detected, and the output current is suppressed on the condition that the ambient temperature has reached a specified temperature. It has been proposed to perform control (output current suppression control).

  For example, Patent Document 1 discloses a vehicular lamp including a lighting circuit that controls an output current to a load according to temperature so that the temperature of a junction portion of the LED does not exceed a rated temperature. In this vehicle lamp, in order to detect the temperature of the LED, a temperature detection unit is disposed in the vicinity of the LED.

JP 2012-160277 A

  By the way, since the load also varies from individual to individual, the output voltage from the drive circuit for the load also varies. Since the drive circuit generates heat in accordance with the output voltage and self-heats up, a situation may occur in which the ambient temperature of the drive circuit is erroneously detected due to the heat of the drive circuit itself. For this reason, there is a problem that the suppression control of the output current cannot be appropriately performed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to appropriately perform output current suppression control according to the ambient temperature regardless of variations in output voltage with respect to the load.

In order to solve this problem, the present invention outputs a load, a current output unit to which a power supply voltage is applied and outputs a current supplied to the load, and a correction signal for suppressing the output current to the current output unit. Provided is a vehicle lamp having a correction calculation unit, a temperature detection unit that detects a temperature around a drive circuit including a current output unit and a correction calculation unit as an ambient temperature , and a voltage detection unit that detects an output voltage with respect to a load. To do. In this vehicle lamp, the correction calculation unit corrects the ambient temperature detected by the temperature detection unit based on the output voltage detected by the voltage detection unit, and outputs a correction signal based on the corrected ambient temperature.

  Here, in the present invention, the correction calculation unit outputs a predetermined constant current from the current output unit until the ambient temperature reaches the start temperature, and increases the ambient temperature after the ambient temperature reaches the start temperature. Accordingly, it is preferable to output the correction signal so that the output current is suppressed.

  According to the present invention, by correcting the ambient temperature detected by the temperature detection unit according to the output voltage, it is possible to consider the temperature rise variation of the current output unit according to the output voltage variation. Can be grasped correctly. Thereby, the target output current characteristic in the current output unit can be matched with the actual output current characteristic. As a result, regardless of the magnitude of the output voltage, that is, the magnitude of heat generation in the current output unit, the output current suppression control can be appropriately performed according to the ambient temperature.

Explanatory drawing which shows the structure of a vehicle lamp typically Explanatory diagram of ambient temperature correction processing using output voltage Explanatory drawing which shows the operation | movement concept of the correction process of ambient temperature by output voltage Explanatory drawing which shows the output current characteristic of the drive circuit which concerns on this embodiment Explanatory drawing showing an operation concept when ambient temperature correction processing is not performed Explanatory diagram showing the output current characteristics of the drive circuit when ambient temperature correction processing is not performed

(First embodiment)
FIG. 1 is an explanatory diagram schematically showing the configuration of a vehicular lamp 1 according to the present embodiment. The vehicular lamp 1 is used as a headlamp for a vehicle such as an automobile, and forms a predetermined light distribution pattern in front of the vehicle. The vehicular lamp 1 is mainly composed of a load 10 and a drive circuit 20, and is supplied with electric power from a battery mounted on the vehicle.

  The load 10 functions as a light source, and is configured by, for example, a single light emitting diode (LED) or a plurality of LEDs connected in series. In addition, since the load 10 has a variation in resistance value or the like for each individual, even when a predetermined constant current is supplied to the load 10 as will be described later, the generated voltage is different for each individual. Can occur.

  The drive circuit 20 is a circuit that supplies current to the load 10 to drive the load 10, and includes a current output circuit 22 and a correction circuit 24.

  The current output circuit 22 is a current output unit that receives a power supply voltage (+ V) from a power source (not shown) such as a battery and outputs a current supplied to the load 10. In the present embodiment, the current output circuit 22 is a constant current circuit, and for example, a DC-DC converter can be used. The current output circuit 22 operates so as to supply a constant current to the load 10, and supplies a predetermined constant current even if the resistance value of the load 10 varies or the input voltage varies. Adjust the output voltage.

  The correction circuit 24 is a circuit that corrects the output current from the drive circuit 20 (current output circuit 22) in order to protect the drive circuit 20 during high temperature driving. The correction circuit 24 includes a correction calculation unit 26. As the correction calculation unit 26, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an I / O interface can be used.

  The correction calculation unit 26 performs suppression control of the output current, and suppresses the output current based on the ambient temperature that is the ambient temperature of the drive circuit 2. The output current is suppressed by outputting a correction signal to the current output circuit 22. Specifically, the correction calculation unit 26 outputs a predetermined constant current from the current output circuit 22 until the ambient temperature reaches a predetermined start temperature T1. On the other hand, when the ambient temperature reaches the predetermined start temperature T1, the correction calculation unit 26 starts suppressing the output current and outputs a correction signal so that the output current is suppressed as the ambient temperature increases. To do. This correction signal functions as a signal indicating the output current after suppression or a signal indicating the amount of suppression. When the correction signal is input to the power output circuit 22, the current output circuit 22 converts the output current to the output current after suppression. In response, current is output.

  Detection signals from the voltage detection unit 30 and the temperature detection unit 32 are input to the correction calculation unit 26. The voltage detection unit 30 detects an output voltage with respect to the load 10. The temperature detection unit 32 has a function of detecting the ambient temperature, and for example, an NTC thermistor can be used. This NTC thermistor has a resistance that decreases with increasing temperature. Therefore, temperature detection is performed by connecting a fixed resistor and an NTC thermistor in series, applying a constant voltage (Vi) to the circuit, and monitoring a voltage change at a connection point between the fixed resistor and the NTC thermistor. Can do.

  As one of the features of this embodiment, the correction calculation unit 26 corrects the ambient temperature based on the output voltage, and outputs a correction signal based on the corrected ambient temperature. Hereinafter, the ambient temperature correction process using the output voltage will be described with reference to FIGS. Here, FIG. 2 is an explanatory diagram of the correction process of the ambient temperature by the output voltage, (a) illustrates the contents of the correction process as specific numerical values, and (b) shows the output voltage and the correction value. Shows the relationship. FIG. 3 is an explanatory diagram showing an operation concept of an ambient temperature correction process using an output voltage.

  In FIG. 2A, “Case 1” indicates a state in which the standard load 10, that is, the load 10 having a standard output voltage with respect to a predetermined output current is connected to the drive circuit 20. “Case 2” indicates a state in which a load 10 that varies downward, that is, a load 10 having an output voltage lower than a standard output voltage with respect to a predetermined output current is connected to the drive circuit 20. . “Case 3” indicates a state in which the load 10 that varies upward, that is, the load 10 having an output voltage higher than the standard output voltage with respect to a predetermined output current is connected to the drive circuit 20.

  The drive circuit 20 generates heat according to the output voltage. Therefore, as shown in FIG. 3A, when the output voltage Va is low, the temperature of the drive circuit 20 is low because the self-temperature rise of the drive circuit 20 is small, and conversely, the output voltage Va is low. If it is high, the self-temperature rise of the drive circuit 20 is correspondingly increased, and the temperature Tu of the drive circuit 20 is also increased accordingly.

  Therefore, even when the ambient temperature of the drive circuit 20 is the same, when the self-temperature rise of the drive circuit 20 acts and the output voltage Va is low, the ambient temperature detected by the temperature detector 32 is relative. Conversely, when the output voltage Va is high, the ambient temperature detected by the temperature detector 32 is relatively high. Here, an alternate long and two short dashes line a in FIG. 3B indicates the detection signal St from the temperature detection unit 32 configured by an NTC thermistor.

  For example, as shown in FIG. 2A, even if the ambient temperature of the drive circuit 20 is the same, the ambient temperature before correction, that is, the ambient temperature detected by the temperature detection unit 32 is higher than Case 1. Case2 is lower. This is because the drive circuit 20 has a lower self-temperature rise than the load 10 having the standard output voltage because the load 10 having a low output voltage is connected. Similarly, even in the situation where the ambient temperature of the drive circuit 20 is the same, the ambient temperature before correction is higher in Case 3 than in Case 1. This is because the drive circuit 20 has a higher self-temperature rise than the load 10 having a standard output voltage because the load 10 having a higher output voltage is connected.

  Thus, the variation in the load 10, that is, the difference in self-temperature rise due to the variation in the output voltage appears as an error in the ambient temperature detected by the temperature detection unit 32. Therefore, the correction calculation unit 26 corrects the ambient temperature detected by the temperature detection unit 32 with the correction value.

  As shown in FIG. 2B, the correction value is determined according to the voltage difference between the standard output voltage as the reference value and the output voltage of each load 10. For example, in Case 1, the voltage difference is “± 0”, and the correction value is set to a value (“0.0”) that sets the ambient temperature after correction to the same value as that before correction. On the other hand, in Case 2, the voltage difference is “−10”, and the correction value is set to a value (“+ Y.Y”) that increases the corrected ambient temperature more than that before the correction. In Case 3, the voltage difference is “+10”, and the correction value is set to a value (“−X.X”) that reduces the ambient temperature after correction more than that before correction.

  The relationship between the voltage difference and the correction value is set in advance through simulations and experiments, and the correction calculation unit 26 holds a map and an arithmetic expression that define this relationship. And the correction | amendment calculating part 26 can obtain | require the correction value according to a voltage difference by calculating | requiring a voltage difference from an output voltage and the preset reference value (standard output voltage). Even if the voltage difference is not obtained, the correction value may be obtained directly from the output voltage in consideration of the voltage difference. A two-dot chain line b in FIG. 3B shows a correction value for the ambient temperature as an image.

  The correction calculation unit 26 corrects the ambient temperature detected by the temperature detection unit 32 based on the correction value, and obtains the corrected ambient temperature. An example of the correction is to add the correction value and the ambient temperature before correction. For example, in Case 1, the ambient temperature after correction is the same as that before correction. In Case 2, the ambient temperature after correction is higher than that before correction, and is the same temperature as Case 1, that is, the actual ambient temperature. In Case 3, the ambient temperature after correction is lower than that before correction, and is the same temperature as Case 1, that is, the actual ambient temperature.

  Then, as shown in FIG. 2A, in Case 1, when the corrected ambient temperature (= the ambient temperature before correction) reaches 60 ° C., the correction calculation unit 26 starts to suppress the output current, and the unit The output current is suppressed at a predetermined suppression rate k with respect to the temperature rise. On the other hand, in Case 2, even if the ambient temperature before correction is 50 ° C., it is assumed that the ambient temperature after correction has reached 60 ° C., and suppression of the output current is started. The output current is suppressed at the suppression rate k. In Case 3, at the timing when the ambient temperature before correction reaches 70 ° C., it is assumed that the ambient temperature after correction has reached 60 ° C., and suppression of output current is started. The output current is suppressed at the suppression rate k.

  With this correction process, as shown in FIG. 3C, the suppression of the output current can be started at a constant start temperature T1 regardless of the variation in the output voltage. Further, as shown in FIG. 3D, the suppression rate k can be kept constant regardless of variations in the output voltage.

  Thus, in the present embodiment, the correction calculation unit 26 corrects the ambient temperature detected by the temperature detection unit 32 based on the output voltage detected by the voltage detection unit 30, and based on the corrected ambient temperature. A correction signal is output.

  According to such a configuration, by correcting the ambient temperature detected by the temperature detection unit 32 according to the output voltage, it is possible to consider the temperature rise variation of the drive circuit 20 according to the output voltage variation. The temperature can be grasped correctly. As a result, the target output current characteristics (relative characteristics between the ambient temperature Ta and the output current Ia (see FIG. 4A)) in the drive circuit 20 and the actual output current characteristics (the ambient temperature Ta and the output current Ia Can be matched with the relative characteristics (FIG. 4B). As a result, regardless of the output voltage variation, that is, the heat generation variation of the drive circuit 20, the output current suppression control can be appropriately performed according to the ambient temperature.

  Here, a case where the ambient temperature correction process is not performed will be described with reference to FIG. 5A to 5D correspond to FIGS. 3A to 3D, respectively. As shown in FIG. 5A, when the output voltage Va is low, the self-temperature rise of the drive circuit 20 is small accordingly, so the temperature Tu of the drive circuit 20 is low, and conversely, the output voltage Va is high. Therefore, since the self-temperature rise of the drive circuit 20 is large, the temperature Tu of the drive circuit 20 is also increased. Therefore, even when the ambient temperature of the drive circuit 20 is the same, when the output voltage Va is low, the ambient temperature detected by the temperature detection unit 32 is low, and conversely, when the output voltage Va is high. Accordingly, the ambient temperature detected by the temperature detection unit 32 also increases. The solid line in FIG. 5B indicates a detection signal from the temperature detection unit 32 configured with an NTC thermistor.

  In this case, as shown in FIG. 5C, when the output voltage is low, the correction calculation unit 26 reaches the start temperature T1 when the actual ambient temperature becomes higher than the start temperature T1. It will be recognized that. On the other hand, when the output voltage is high, the correction calculation unit 26 recognizes that the actual ambient temperature has reached the start temperature T1 when the actual temperature is lower than the start temperature T1 ″.

  Therefore, the start temperature for suppressing the output current has a width (variation) such as T1, T ′, T ″. Along with this, the suppression rate k has a width (k, k ′, k ″). End up. This phenomenon is caused by the fact that the actual output current characteristics (relative characteristics between the ambient temperature Ta and the output current Ia (FIG. 6B)) are the target output current characteristics in the drive circuit (the ambient temperature Ta and the output current Ia). It means that it deviates from a relative characteristic (FIG. 6 (a)).

  Further, according to the present embodiment, the correction calculation unit 26 outputs a predetermined constant current from the current output circuit 22 until the ambient temperature reaches the start temperature T1, and after the start temperature T1 has reached, The correction signal is determined so that the output current is suppressed according to a predetermined suppression rate k, that is, an increase in the ambient temperature.

  According to such a configuration, regardless of variations in the self-temperature rise of the drive circuit 20, the output current suppression control can be appropriately started at the timing when the actual ambient temperature reaches the start temperature T1. Accordingly, the output current can be suppressed at a predetermined suppression rate k.

  In the present invention, the temperature detection unit 32 detects the ambient temperature of the drive circuit 20 including the current output circuit 22 and the correction calculation unit 26 as the ambient temperature.

  With this configuration, it is possible to appropriately detect the ambient temperature for protecting the drive circuit 20.

  As mentioned above, although the vehicle lamp concerning embodiment of this invention was demonstrated, it cannot be overemphasized that a various deformation | transformation is possible within the scope of the invention, without this invention being limited to embodiment mentioned above. .

DESCRIPTION OF SYMBOLS 1 Vehicle lamp 10 Load 20 Drive circuit 22 Current output circuit 24 Correction circuit 26 Correction calculation part 30 Voltage detection part 32 Temperature detection part

Claims (2)

Load,
A current output unit to which a power supply voltage is applied and outputs a current supplied to the load;
A correction calculation unit that outputs a correction signal for suppressing an output current to the current output unit;
A temperature detection unit that detects the ambient temperature of the drive circuit including the current output unit and the correction calculation unit as an ambient temperature;
A voltage detection unit for detecting an output voltage with respect to the load,
The correction calculator corrects the ambient temperature detected by the temperature detector based on the output voltage detected by the voltage detector, and outputs the correction signal based on the corrected ambient temperature. A vehicular lamp characterized by the above.   The correction calculation unit outputs a predetermined constant current from the current output unit until the ambient temperature reaches the start temperature, and responds to an increase in the ambient temperature after the ambient temperature reaches the start temperature. The vehicle lamp according to claim 1, wherein the correction signal is output so that an output current is suppressed.

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