JP2008034141A - Heater device, and vehicular liquid crystal display device equipped with heater device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heater drive device capable of accurately determining a failure of a drive circuit. <P>SOLUTION: By determining the relationship between a voltage signal V transmitted from a meter ECU 50 and a voltage level of a divided voltage Vb of a heater 30, it is determined to be normal when the relationship of both of them is consistent, and it is determined to be a failure when the relationship between both of them is inconsistent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heater device having a heater that keeps an object to be kept warm, and a liquid crystal display device for a vehicle including the heater device.

  As this type of heater device, for example, one described in Patent Document 1 is known. In this case, the temperature of the liquid crystal display element, which is a heat retaining object, is detected by a temperature sensor, and the switching control (drive circuit) in which the CPU switches the operation state of the heater based on the detected temperature is controlled. Specifically, the switching state of the switching circuit is controlled so that the heater is turned on when the detected temperature is 0 ° C. or lower and the heater is turned off when the detected temperature is 5 ° C. or higher.

  By the way, when the switching circuit fails for some reason, it is conceivable that the heater is kept on while ignoring the control command from the control means. Therefore, it is necessary to add a configuration capable of detecting the switching circuit failure.

Therefore, it is conceivable to detect a failure of the switching circuit based on the temperature of the liquid crystal display element obtained by the temperature sensor. In this case, it can be determined that the switching circuit is faulty when the detected temperature is equal to or higher than the predetermined temperature.
Japanese Patent Laid-Open No. 2004-207771

  By the way, the detected temperature obtained by the temperature sensor is affected by the ambient temperature of the liquid crystal display element. Therefore, when the ambient temperature is low, it cannot be determined that the switching circuit is faulty even though the switching circuit is faulty. When the temperature is high, even if the switching circuit operates normally, there may be a problem that it is erroneously determined as a failure.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a heater device that can accurately determine a failure of a switching circuit that switches the operating state of the heater and a liquid crystal display for a vehicle including the heater device. Is to provide a device.

  In order to achieve the above object, according to the first aspect of the present invention, there are provided an electric heater for keeping an object to be kept warm, a switching circuit for switching a power supply state to the electric heater, and a control signal for switching the switching state of the switching circuit. The control means for outputting, the detection means for detecting the operation state of the electric heater, the relationship between the control signal output from the control means and the operation state detected by the detection means is determined, and the relationship is determined to be inconsistent In this case, a failure determination means for determining that the switching circuit is in failure is provided.

  According to the first aspect of the present invention, when the switching circuit is normal, the relationship between the output control signal and the operating state of the electric heater coincides, and when the switching circuit is faulty, the transmitted control signal The relationship with the operating state of the electric heater is inconsistent. Therefore, the failure of the switching circuit can be detected by determining the relationship between the two.

  If a failure of the switching circuit is judged based on the temperature detection result of the electric heater or the object to be kept warm, the temperature of the heater itself cannot be detected due to the ambient temperature of the heater, so an accurate failure is not possible. Judgment becomes difficult. On the other hand, in this configuration, since the relationship between the control signal and the operation state is not disturbed by the surrounding situation, accurate failure determination can be performed.

  According to a second aspect of the present invention, the failure determination means indicates that the operation state is a non-energized state when the control signal is an on signal for turning on the switching state, or the control signal indicates the switching state. It is characterized in that it is determined that the relationship is inconsistent on condition that the operation state is an energized state when the signal is an off signal for turning off.

  When the operating state is off when the control signal is an on signal, the switching circuit has an open failure, and when the operating state is on when the control signal is an off signal, the switching circuit is short-circuited. It is considered a failure. Therefore, in these cases, the failure of the switching circuit can be detected by performing the failure determination.

  According to a third aspect of the present invention, the control means includes a connection portion for connecting the electric heater to the power source when the off signal is transmitted, and the failure determination means operates when the control means transmits the off signal. When the state is a non-energized state, it is determined that the relationship is inconsistent and it is determined that the electric heater is in failure.

  When the electric heater is in a non-energized state despite being connected to the power source, an open failure of this electric heater can be considered. Judgment can be made.

  The invention according to claim 4 is characterized in that the detecting means detects an applied voltage of the electric heater and determines an operating state based on the applied voltage.

  As in the fourth aspect of the invention, when detecting a failure of the switching circuit and the electric heater, the operating state of the electric heater can be determined by detecting the applied voltage of the electric heater.

  The invention according to claim 5 is characterized in that the control means outputs a control signal at the time of activation. In this way, when a failure occurs in the switching circuit or the electric heater, it can be quickly detected.

  According to a sixth aspect of the present invention, there is provided a liquid crystal display device for a vehicle including the heater device according to any one of the first to fifth aspects, wherein a liquid crystal panel that displays vehicle information as a heat retaining object is kept warm. It is characterized by. According to this, since the liquid crystal display element can be stably operated even when the ambient temperature is constant temperature, the vehicle information can be always displayed in a good state.

<First Embodiment>
An embodiment in which the heater driving device according to the present invention is applied to a liquid crystal display device used in a vehicle instrument will be described. In the present embodiment, the operation state of the heater 30 (electric heater) is switched based on the temperature of the liquid crystal panel 10 (insulation object) that displays various vehicle information, and the liquid crystal panel 10 is kept warm.

  FIG. 1 shows the overall configuration of the liquid crystal display device. The liquid crystal panel 10 is attached to a meter panel, for example, and displays various vehicle information to a driver or the like. The liquid crystal panel 10 is of a dot matrix type, for example, and is transmitted and illuminated by a backlight (not shown) disposed rearward.

  The liquid crystal drive circuit 20 drives the liquid crystal panel 10 based on a control command from a meter ECU 50 described later. Specifically, each pixel of the liquid crystal panel 10 is switched on and off to display predetermined vehicle information, and the backlight output is adjusted so that the illuminance of the liquid crystal panel 10 is set to the predetermined illuminance.

  The heater 30 is for keeping the temperature of the liquid crystal panel 10 in a stable operation. The heater 30 is constituted by a PTC heater, for example, and the power supply state is switched by the heater drive circuit 40.

  The heater drive circuit 40 switches the power supply state to the heater 30 based on a voltage signal V (control signal) from the meter ECU 50 described later, detects the applied voltage Va of the heater 30, and corresponds to the applied voltage Va. Divided voltage Vb is output to meter ECU 50.

  The meter ECU 50 receives sensor signals from various sensors directly or through communication with other ECUs, and outputs a control command to the liquid crystal drive circuit 20 to display predetermined information on the liquid crystal panel 10 based on the sensor signals. To do. The meter ECU 50 receives a detection signal from a temperature sensor 60 that detects the temperature of the liquid crystal panel 10 (panel temperature Ta), and outputs a voltage signal V corresponding to the panel temperature Ta to the heater drive circuit 40.

  FIG. 2 is a circuit diagram showing a specific configuration of the heater drive circuit 40. This heater drive circuit 40 detects a switching circuit 410 for switching the power supply state to the heater 30 and an applied voltage Va of the heater 30 and detects a divided voltage Vb corresponding to the applied voltage Va to the meter ECU 50. Circuit 420. The switching circuit 410 mainly includes an input transistor 411 that inputs a voltage signal V from the meter ECU 50 and an output transistor 412 that switches the power supply state of the heater 30 according to the switching state of the input transistor 411.

  The input transistor 411 is an NPN bipolar transistor. The collector terminal of the input transistor 411 is connected to the first power supply Vcc1 via a resistor element pair 413 connected in series, and the voltage signal V from the meter ECU 50 is input to the base terminal. . When the voltage signal V input to the base terminal is the on signal VH, the transistor 411 is turned on, and when the voltage signal V is the off signal VL, the transistor 411 is turned off. The signals VH and VL will be described later.

  The output transistor 412 is configured by a P-channel type MOSFET. The gate terminal of the output transistor 412 is connected to the intermediate connection point of the resistor element pair 413, the source terminal is connected to the first power supply Vcc1, and the heater 30 is connected in series to the drain terminal.

  Therefore, when the input transistor 411 is turned on, the transistor 412 is also turned on accordingly, and the heater 30 is energized in response to power supply from the first power supply Vcc1. Further, when the input transistor 411 is turned off, the transistor 412 is also turned off accordingly, the power supply is cut off, and the heater 30 is turned off.

  The detection circuit 420 includes voltage dividing resistors 421 and 422 composed of two resistance elements connected in series. The voltage dividing resistors 421 and 422 are connected to the drain terminal of the output transistor 412. That is, the voltage dividing resistors 421 and 422 are connected in parallel to the heater 30. An input terminal of the meter ECU 50 is connected to an intermediate connection point between the voltage dividing resistors 421 and 422 via a current limiting resistor 423. Therefore, the applied voltage Va of the heater 30 is divided by the voltage dividing resistors 421 and 422, and the divided voltage Vb is input to the meter ECU 50.

  Further, the heater 30 is connected to a second power supply Vcc2 that is a system different from the first power supply Vcc1 via a resistance element 511 (connecting portion), and the heater 30 is provided even when the switching circuit 410 is in an OFF state. Is in an energized state. In order to prevent current from flowing from the first power supply Vcc1, a backflow prevention diode 512 is connected to the second power supply Vcc2.

  The meter ECU 50 outputs the voltage signal V to the heater drive circuit 40 and the divided voltage Vb output from the detection circuit 420. The voltage signal V transmitted from the meter ECU 50 to the heater drive circuit 40 is a two-level signal level of a high level voltage signal VH (on signal VH) and a low level voltage signal VL (off signal VL). The signals VH and VL are selectively output based on the panel temperature Ta. Further, the input divided voltage Vb is compared with the reference voltage Vth, the voltage level of the divided voltage Vb exceeding the reference voltage Vth is high level (Hi), and the voltage level of the divided voltage Vb lower than the reference voltage Vth is low level. (Low) is binarized.

  The configuration of the present embodiment is as described above, and the operation will be described next. For example, when the ignition switch is turned on or communication with another ECU is established, the meter ECU 50 alternately switches the signals VH and VL to determine a failure of the switching circuit 410 and the heater 30. Normality / failure is determined based on the correspondence table shown in FIG. FIG. 3 shows the voltage level of the divided voltage Vb corresponding to the voltage signal V (VH, VL) for each state of the switching circuit 410 or the heater 30. Hereinafter, the operation and effect in each state will be described.

"Normal"
When the meter ECU 50 outputs the on signal VH, the transistors 411 and 412 in the switching circuit 410 are turned on, and the operation state of the heater 30 is turned on. Thereby, the divided voltage Vb exceeds the reference voltage Vth, and the meter ECU 50 determines that the voltage level of the input shared voltage Vb is a high level (Hi).

  On the other hand, when the meter ECU 50 outputs the off signal VL, the transistors 411 and 412 in the switching circuit 410 are turned off. Here, the power supply from the first power supply Vcc1 is cut off, but the heater 30 is energized in response to the power supply from the second power supply Vcc2. However, since the resistance value of the resistance element 511 is sufficiently higher than the resistance value of the heater 30, the divided voltage Vb corresponding to the applied voltage Va of the heater 30 is lower than the reference voltage Vth. Thereby, the divided voltage Vb is lower than the reference voltage Vth, and the meter ECU 50 determines that the voltage level of the inputted divided voltage Vb is a low level (Low).

  Accordingly, when the output voltage signal V is the on signal VH, the divided voltage Vb is at a high level (Hi), and when the voltage signal V is an off signal VL, the divided voltage Vb is at a low level (Low). It is said that. As shown in FIG. 3, it is determined that the relationship between the voltage signal V transmitted with this relationship and the operating state of the heater 30 matches, and it is determined that both the switching circuit 410 and the heater 30 are normal.

"Output transistor short circuit fault"
Even when the meter ECU 50 outputs either the on signal VH or the off signal VL, the output transistor 412 in the switching circuit 410 is in a short circuit state, so that the heater 30 is energized. As a result, the divided voltage Vb exceeds the reference voltage Vth regardless of the signals VH and VL, and the meter ECU 50 determines that the voltage level of the input divided voltage Vb is a high level (Hi).

  When the output voltage signal V is the off signal VL and the divided voltage Vb is at the high level (Hi), the relationship between the voltage signal V and the operating state of the heater 30 does not match as shown in FIG. It is determined that it is a failure.

"Output transistor open failure"
Even when the meter ECU 50 outputs either the on signal VH or the off signal VL, the output transistor 412 in the switching circuit 410 is in an open state, so that the heater 30 is in a non-energized state. Thus, the divided voltage Vb is lower than the reference voltage Vth regardless of the signals VH and VL, and the meter ECU 50 determines that the voltage level of the input divided voltage Vb is the low level (Low).

When the output voltage signal V is the on signal VH and the divided voltage Vb is at a low level (Low), the relationship between the voltage signal V and the operating state of the heater 30 does not match as shown in FIG. It is determined that it is a failure.
"Heater open failure"
When the meter ECU 50 outputs the on signal VH, the transistors 411 and 412 in the switching circuit 410 are turned on, but the heater 30 is in an open state and remains in a non-energized state. However, since the voltage of the first power supply Vcc1 is applied to the voltage dividing resistors 421 and 422, the divided voltage Vb exceeds the reference voltage Vth, and the voltage level of the input divided voltage Vb is high in the meter ECU 50. Judged to be level (Hi).

  On the other hand, when the meter ECU 50 outputs the off signal VL, the heater 30 should be in the energized state upon receiving the power supply of the second power source Vcc2, but is in the non-energized state because of an open failure. Here, since the resistance values of the voltage dividing resistors 421 and 422 are larger than the resistance value of the resistance element 511, the divided voltage Vb exceeds the reference voltage Vth. Therefore, the meter ECU 50 determines that the voltage level of the divided voltage Vb is a high level (Hi).

  Since the relationship between the voltage signal V and the operating state of the heater 30 is the same as that in the case of the short circuit failure of the transistor 412, it is determined that there is a failure.

  For example, when a failure (short circuit failure or open failure) of the output transistor 412 and an open failure of the heater 30 occur at the same time, the divided voltage Vb is at a high level (Hi) when the off signal VL is transmitted. Because it becomes. As a result, the relationship between the voltage signal V and the operating state of the heater 30 becomes inconsistent, and it is determined that there is a failure.

  From the above description, it is clear that the meter ECU 50 has the functions of “control means” and “failure determination means” described in the claims, and the function of “detection means” by the meter ECU 50 and the detection circuit 420. is there.

  According to the present embodiment, when the switching circuit 410 is normal, the relationship between the output voltage signal V and the operating state of the heater 30 (voltage level of the divided voltage Vb) matches, and the switching circuit 410 When there is a failure, the relationship between the transmitted voltage signal V and the operating state of the heater 30 is inconsistent. Therefore, a failure of the switching circuit 410 can be detected by determining the relationship between the two.

  If the failure of the switching circuit 410 is determined based on the panel temperature Ta, the ambient temperature of the liquid crystal panel 10 becomes a disturbance factor and the temperature of the liquid crystal panel 10 itself cannot be detected. It becomes. On the other hand, in this configuration, since the relationship between the voltage signal V and the divided voltage Vb is not disturbed by the surrounding conditions, accurate failure determination can be performed.

  When the output transistor 412 has an open failure, the divided voltage Vb is low when the voltage signal V is the ON signal VH, and when the output transistor 412 has a short-circuit failure, the voltage signal When V is the off signal VL, the divided voltage Vb becomes low level (Low). Therefore, it is possible to reliably detect these problems.

  Further, when the off signal VL is output, the heater 30 is supplied with power by the second power source Vcc2 and the divided voltage Vb is detected. it can.

  Further, since the meter ECU 50 makes a failure determination when the ignition switch is turned on, when the failure occurs, the meter ECU 50 can quickly detect this.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.

  In the above-described embodiment, the configuration in which power is supplied to the heater 30 using the two power sources Vcc1 and Vcc2 has been described, but these may be configured by a common power source.

  Further, in the above-described embodiment, the configuration in which the resistance element 511 that energizes the heater 30 with the second power source Vcc2 is provided in order to detect the opening failure of the heater 30 has been described. When omitted, the second power supply Vcc2, the resistance element 511, and the backflow blocking diode 512 can be omitted.

  The transistors 411 and 412 may be either bipolar transistors or FETs.

1 is a block diagram showing an overall configuration of a vehicle display device showing an embodiment of the present invention. It is the circuit diagram which showed the specific structure of the heater drive circuit. It is the correspondence table which showed the voltage level of the divided voltage corresponding to the output voltage signal in each state of a switching circuit and a heater.

Explanation of symbols

11 ... Liquid crystal panel (insulation object)
30 ... Heater (electric heater)
40 ... heater drive circuit 50 ... meter ECU (control means, detection means, failure determination means)
410 ... switching circuit 411 ... input transistor 412 ... output transistor 420 ... detection circuit (detection means)
421, 422 ... Voltage dividing resistor 511 ... Resistance element (connection part)
V ... Voltage signal VH ... On signal VL ... Off signal Va ... Applied voltage Vb ... Divided voltage

Claims (6)

An electric heater for keeping the object to be kept warm;
A switching circuit for switching a power supply state to the electric heater;
Control means for outputting a control signal for switching the switching state of the switching circuit;
Detecting means for detecting an operating state of the electric heater;
The relationship between the control signal output from the control means and the operation state detected by the detection means is determined, and when the relationship is determined to be inconsistent, the switching circuit is determined to be faulty. And a failure determination means.   The failure determination means is configured such that the operation state is a non-energized state when the control signal is an on signal for turning on the switching state, or the control signal turns off the switching state. 2. The heater device according to claim 1, wherein the relationship is determined to be inconsistent on condition that the operation state is an energized state when the signal is an off signal for setting a state. 3. When the control means is transmitting the off signal, comprising a connection portion for connecting the electric heater to a power source,
The failure determination means determines that the relationship is inconsistent when the operation state when the control means transmits the off signal is the non-energized state, and the electric heater is in failure. The heater device according to claim 2, wherein the heater device is determined.   5. The heater device according to claim 1, wherein the detection unit detects an applied voltage of the electric heater and determines the operation state based on the applied voltage. 6.   The heater device according to any one of claims 1 to 4, wherein the control means outputs the control signal at startup. A vehicle liquid crystal display device comprising the heater device according to any one of claims 1 to 5,
A liquid crystal display device for a vehicle, wherein a liquid crystal panel displaying vehicle information is kept warm as the heat retaining object.

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