Control device and control method for variable valve timing mechanism

1. A control device for a variable valve timing mechanism of an internal combustion engine that includes: the variable valve timing mechanism configured to change a rotational phase of a camshaft relative to a crankshaft in the internal combustion engine by adjusting a rotation speed of a motor; a crank angle sensor configured to output a crank angle signal having pulses each generated for a predetermined crank angle degree; a cam angle sensor configured to output a cam angle signal having pulses each generated for a predetermined cam angle degree; and a motor angle sensor configured to output a motor angle signal in accordance with a rotation angle of the motor,

the control device comprising:

a first measuring unit configured to measure the rotational phase based on the cam angle signal and the crank angle signal upon each pulse of the cam angle signal;

a second measuring unit configured to measure an amount of change of the rotational phase over time within a period of the cam angle signal, based on the motor angle signal;

a control unit configured to adjust the rotation speed of the motor based on the measurements obtained by the first and second measuring units; and

a diagnosing unit configured to

determine whether or not at least one of the cam angle signal and the crank angle signal has a prescribed pulse pattern at a diagnostic timing that comes after a last pulse of the cam angle signal, and

when at least one of the cam angle signal and the crank angle signal has the prescribed pulse pattern, determine whether the motor angle sensor operates normally or abnormally based on the measurements that the first and second measuring units obtain when the last pulse of the cam angle signal is received before the diagnostic timing,

wherein the control unit is configured to control the motor in a normal state or an abnormal state based on the determination of whether the motor angle sensor operates normally or abnormally.

2. The control device according to claim 1 ,

wherein the crank angle sensor is configured to output the crank angle signal having pulses each generated for a unit crank angle degree with a pulse skipped for the predetermined crank angle degree,

wherein the first measuring unit detects a pulse skip position of the crank angle signal, and sets a reference crank angle position based on the pulse skip position, and measures, as the rotational phase, a crank angle from the reference crank angle position to a crank angle position corresponding to the last pulse of the cam angle signal, and

wherein the diagnosing unit determines the diagnostic timing is reached when the pulse skip position is detected after the last pulse of the cam angle signal, and

wherein, when a number of pulses of the crank angle signal between consecutive pulse skip positions matches a prescribed value at the diagnostic timing, the diagnosing unit determines whether the motor angle sensor operates normally or abnormally based on the measurements that the first and second measuring units obtain when the last pulse of the cam angle signal is received before the diagnostic timing.

3. The control device according to claim 1 ,

wherein the crank angle sensor is configured to output the crank angle signal having pulses adapted such that a number of pulses generated in rapid succession indicates which cylinder reaches a reference piston position,

wherein the first measuring unit measures the rotational phase based on a leading pulse of pulses generated in rapid succession of the cam angle signal,

wherein the diagnostic timing is set to coincide with a first timing for determining a number of pulses of the cam angle signal, the first timing coming after the leading pulse, and

wherein, when the number of pulses of the cam angle signal matches a prescribed value at the diagnostic timing, the diagnosing unit determines whether the motor angle sensor operates normally or abnormally based on the measurements that the first and second measuring units obtain when the leading pulse is received before the diagnostic timing.

4. The control device according to claim 1 ,

wherein the crank angle sensor is configured to output the crank angle signal having pulses each generated for a unit crank angle degree,

wherein the first measuring unit measures the rotational phase by measuring a time from a last pulse of the crank angle signal and the last pulse of the cam angle signal, and converts the time into a crank angle based on a period of the crank angle signal,

wherein the diagnosing unit determines the diagnostic timing is reached when a pulse of the crank angle signal is received after the last pulse of the cam angle signal, and

wherein, when a periodic change of the crank angle signal falls within a prescribed range at the diagnostic timing, the diagnosing unit determines whether the motor angle sensor operates normally or abnormally based on the measurements that the first and second measuring units obtain when the last pulse of the cam angle signal is received before the diagnostic timing.

5. A control method for a variable valve timing mechanism of an internal combustion engine that includes: the variable valve timing mechanism configured to change a rotational phase of a camshaft relative to a crankshaft in the internal combustion engine by adjusting a rotation speed of a motor; a crank angle sensor configured to output a crank angle signal having pulses each generated for a predetermined crank angle degree; a cam angle sensor configured to output a cam angle signal having pulses each generated for a predetermined cam angle degree; and a motor angle sensor configured to output a motor angle signal in accordance with a rotation angle of the motor,

the control method comprising:

measuring the rotational phase based on the cam angle signal and the crank angle signal upon receiving each pulse of the cam angle signal;

measuring an amount of change of the rotational phase over time within a period of the cam angle signal, based on the motor angle signal;

adjusting the rotation speed of the motor based on the measured rotational phase and the measured amount of change of the rotational phase; and

determining whether or not at least one of the cam angle signal and the crank angle signal has a prescribed pulse pattern at a diagnostic timing that comes after a last pulse of the cam angle signal, and

when at least one of the cam angle signal and the crank angle signal has the prescribed pulse pattern, determining whether the motor angle sensor operates normally or abnormally based on the rotational phase and the amount of change of the rotational phase that are measured when the last pulse of the cam angle signal is received before the diagnostic timing,

wherein the control unit is configured to control the motor in a normal state or an abnormal state based on the determination of whether the motor angle sensor operates normally or abnormally.