TECHNICAL FIELD

The present disclosure relates to a wiper control device.

BACKGROUND ART

A wiper control device uses a controller such as a microcomputer to control a drive circuit configured by switching elements such as field effect transistors (FETs) in order to generate a voltage for application to a wiper motor that causes a wiper blade to perform a wiping operation.

In cases in which a wiper motor configuring a wiper system is, for example, configured by a brushed DC motor, potential issues that may arise include poor contact between the brush and the commutator, or circuit discontinuity in a coil of the wiper motor. Shorting may also occur in switching elements configuring a drive circuit.

The state of the wiper motor and the drive circuit are tested before shipping a wiper system product including a wiper control device. As a result of this testing, pieces that are deemed to be free of electrical connection issues inside the wiper motor, and also deemed to have normally-operating drive circuit switching elements, are shipped as products.

Such a wiper control device may be provided in advance with a test circuit such as that illustrated inFIG. 12. During pre-shipping testing, power supplied from the positive electrode (B terminal) of a vehicle battery through a terminal118is output from between a resistor R02and a resistor R03of a voltage divider circuit configured by the resistor R02and resistors R03and R04, and is supplied to a first terminal126A, this being a motor terminal on one side of a wiper motor18.

The power supplied to the first terminal126A passes through a first brush18B1, a commutator18C, a coil18D, the commutator18C, and a second brush18B2of the wiper motor, and is output to a second terminal126B, this being a motor terminal on the other side of the wiper motor18. The power output to the second terminal126B is then output from between a resistor R05and a resistor R06of a voltage divider circuit configured by the resistor R05and the resistor R06. The power output from between the resistor R05and the resistor R06passes through a terminal124B and is input to a microcomputer58as a signal indicating a voltage.

The power from the battery supplied through the terminal118is also output from between the resistor R03and the resistor R04of the voltage divider circuit configured by the resistor R02, R03and the resistor R04. The power output from between the resistor R03and the resistor R04passes through a terminal124A and is input to the microcomputer58as a signal indicating a voltage.

The microcomputer58computes microcomputer-detected voltages (hereafter simply referred to as detected voltages), these being respective voltages at the terminals124A,124B, from the signals input by the terminals124A,124B. The microcomputer58also computes a power source voltage, this being the voltage of the battery, and also computes motor terminal voltages, these being the respective voltages at the first terminal126A and the second terminal126B of the wiper motor18, based on the detected voltages. The respective states of the wiper motor18and a drive circuit56are determined based on conditions of the motor terminal voltages with respect to the power source voltage.

Japanese Patent Application Laid-Open (JP-A) No. 2017-34902 (Patent Document 1) discloses an invention relating to a motor that determines whether or not breaks or shorts are present in a circuit of the motor based on motor terminal voltages.

SUMMARY OF INVENTION

Technical Problem

However, testing of the motor disclosed in Patent Document 1 requires a complex circuit such as that illustrated inFIG. 12. Diodes D02, D03to protect the microcomputer58from high voltages need to be provided separately, in addition to the resistors R02to R06configuring the voltage divider circuits.

In consideration of the above circumstances, an object of the present disclosure is to provide a wiper control device capable of testing states of a wiper motor and a drive circuit using a simple configuration.

Solution to Problem

In order to address the above issue, a wiper control device of a first aspect includes a wiper motor that includes a first terminal and a second terminal, and that causes a wiper blade to perform a wiping operation by rotating in a specific direction in a state in which a positive voltage is supplied to the first terminal and the second terminal is grounded, and by rotating in the opposite direction to the specific direction in a state in which the first terminal is grounded and a positive voltage is supplied to the second terminal, a drive circuit that includes a first switching element with one end connected to a power source and another end connected to the first terminal, a second switching element with one end connected to the first terminal and another end grounded, a third switching element with one end connected to the power source and another end connected to the second terminal, and a fourth switching element with one end connected to the second terminal and another end grounded, the respective switching elements being switched ON/OFF so as to supply the positive voltage to the first terminal and ground the second terminal, or so as to ground the first terminal and supply the positive voltage to the second terminal, a voltage divider circuit that is configured by the second switching element and a resistor having one end connected to the power source and another end connected to the first terminal, and that is configured to lower a voltage of the power source to a test voltage that does not cause the wiper motor to rotate, a power source voltage detection section that is configured to detect the voltage of the power source, and a measurement section that is input with a detected voltage of a voltage output from the voltage divider circuit to the second terminal via the first terminal and the wiper motor in a state in which all the switching elements of the drive circuit are in an OFF state, and that is configured to compute a motor terminal voltage, this being a potential difference between the first terminal and the second terminal, from the detected voltage.

According to this wiper control device, the resistor connected to the power source and the second switching element configuring the drive circuit configure the voltage divider circuit that lowers the voltage of the power source. This enables the test voltage allowing states of the wiper motor and the drive circuit to be tested to be generated and supplied to the first terminal of the wiper motor using a simple configuration. Moreover, the motor terminal voltage, namely the potential difference between the first terminal and the second terminal of the wiper motor, is computed from the detected voltage output from the second terminal of the wiper motor when the test voltage is supplied to the first terminal of the wiper motor, thereby enabling the states of the wiper motor and the drive circuit to be tested.

A wiper control device according to a second aspect is the wiper control device according to the first aspect, wherein the measurement section determines states of the wiper motor and the drive circuit based on respective conditions of the detected voltage, the motor terminal voltage, and the power source voltage.

According to this wiper control device, states of the wiper motor and the drive circuit can be determined based on the respective conditions of the detected voltage, the motor terminal voltage, and the power source voltage when the test voltage generated using a simple configuration is supplied to the first terminal of the wiper motor.

A wiper control device according to a third aspect is the wiper control device according to the second aspect, wherein the measurement section determines that a break is present in circuitry of the wiper motor in cases in which the power source voltage is normal and the detected voltage and the motor terminal voltage each exhibit a gradually attenuating oscillating state converging on a constant low voltage.

According to this wiper control device, the presence of a break in the circuitry of the wiper motor can be determined using a simple configuration in cases in which both the detected voltage and the motor terminal voltage exhibit a gradually attenuating oscillating state converging on a constant low voltage when the test voltage is supplied to the first terminal of the wiper motor.

A wiper control device according to a fourth aspect is the wiper control device of the second aspect or the third aspect, wherein the measurement section determines that either the first switching element or the third switching element has shorted in cases in which the power source voltage is normal and the detected voltage and the motor terminal voltage each exhibit a gradually attenuating oscillating state converging on a constant high voltage.

According to this wiper control device, shorting of either the first switching element or the third switching element can be determined using a simple configuration in cases in which both the detected voltage and the motor terminal voltage exhibit a gradually attenuating oscillating state converging on a constant high voltage when the test voltage is supplied to the first terminal of the wiper motor.

A wiper control device according to a fifth aspect is the wiper control device of any one out of the second aspect to the fourth aspect, wherein the measurement section determines that either the second switching element or the fourth switching element has shorted in cases in which the power source voltage is normal and the detected voltage and the motor terminal voltage each indicate a constant low voltage without exhibiting an oscillating state.

According to this wiper control device, shorting of either the second switching element or the fourth switching element can be determined using a simple configuration in cases in which both the detected voltage and the motor terminal voltage indicate a constant low voltage without exhibiting an oscillating state when the test voltage is supplied to the first terminal of the wiper motor.

