Control device and control method for internal combustion engine

1. A control device for an internal combustion engine including: a variable intake valve timing mechanism configured to variably control a phase angle of an intake camshaft relative to a crankshaft; a variable exhaust valve timing mechanism configured to variably control a phase angle of an exhaust camshaft relative to the crankshaft; an intake cam sensor configured to output an intake cam signal at a predetermined rotational position of the intake camshaft; an exhaust cam sensor configured to output an exhaust cam signal at a predetermined rotational position of the exhaust camshaft; and a crank angle sensor configured to output a crank angle signal at a predetermined rotational position of the crankshaft, the internal combustion engine being configured such that each of the intake cam signal and the exhaust cam signal has a period longer than a period of the crank angle signal,

the control device comprising a control unit configured to:

control the variable intake valve timing mechanism based on the crank angle signal and the intake cam signal, when the crank angle signal is behaving normally; and

control the variable intake valve timing mechanism based on the intake cam signal and the exhaust cam signal while controlling the variable exhaust valve timing mechanism so as to set the relative phase angle of the exhaust camshaft to a reference phase angle, when the crank angle signal is behaving abnormally,

wherein a phase difference between the exhaust cam signal generated when the relative phase angle of the exhaust camshaft is set to the reference phase angle and the intake cam signal generated when the relative phase angle of the intake camshaft is set to a target value is greater after a start-up of the internal combustion engine than during the start-up, and wherein the phase difference during the start-up of the internal combustion engine is less than or equal to the period of the crank angle signal.

2. The control device for the internal combustion engine according to claim 1 , wherein the exhaust cam signal generated when the relative phase angle of the exhaust camshaft is set to the reference phase angle is in phase with the intake cam signal generated when the relative phase angle of the intake camshaft is set to a target value for during the start-up of the internal combustion engine.

3. The control device for the internal combustion engine according to claim 1 , wherein the reference phase angle of the exhaust camshaft is a relative phase angle of the exhaust camshaft that is set by mechanical positioning in the variable exhaust valve timing mechanism.

4. The control device for the internal combustion engine according to claim 1 ,

wherein the control unit calculates a rotation speed of the internal combustion engine based on the crank angle signal, when the crank angle signal is behaving normally, and based on the intake cam signal or the exhaust cam signal, when the crank angle signal is behaving abnormally, and

wherein the control unit converts time of phase difference into a crank angle based on the rotation speed of the internal combustion engine.

5. The control device for the internal combustion engine according to claim 4 ,

wherein, when the control unit calculates the rotation speed of the internal combustion engine based on the intake cam signal or the exhaust cam signal, one of the cam signals that is used for the calculation being a first cam signal, the other cam signal being a second cam signal,

the control unit measures time of phase difference from an output of the second cam signal to an output of the first cam signal, when the first cam signal is output immediately after the second cam signal, and

the control unit measures time of phase difference from an output of the first cam signal to an output of the second cam signal, when the first cam signal is output immediately before the second cam signal, and

wherein the control unit converts the measured time of phase difference into a crank angle based on the rotation speed of the internal combustion engine.

6. A control method for an internal combustion engine including: a variable intake valve timing mechanism configured to variably control a phase angle of an intake camshaft relative to a crankshaft; a variable exhaust valve timing mechanism configured to variably control a phase angle of an exhaust camshaft relative to the crankshaft; an intake cam sensor configured to output an intake cam signal at a predetermined rotational position of the intake camshaft; an exhaust cam sensor configured to output an exhaust cam signal at a predetermined rotational position of the exhaust camshaft; and a crank angle sensor configured to output a crank angle signal at a predetermined rotational position of the crankshaft, the internal combustion engine being configured such that each of the intake cam signal and the exhaust cam signal has a period longer than a period of the crank angle signal,

the control method comprising the steps of:

detecting whether the crank angle signal is behaving normally or abnormally;

controlling the variable intake valve timing mechanism based on the crank angle signal and the intake cam signal, when the crank angle signal is behaving normally;

controlling the variable exhaust valve timing mechanism based on the crank angle signal and the exhaust cam signal, when the crank angle signal is behaving normally;

controlling the variable exhaust valve timing mechanism so as to set the relative phase angle of the exhaust camshaft to a reference phase angle, when the crank angle signal is behaving abnormally; and

controlling the variable intake valve timing mechanism based on the intake cam signal and the exhaust cam signal, when the crank angle signal is behaving abnormally,

wherein a phase difference between the exhaust cam signal generated when the relative phase angle of the exhaust camshaft is set to the reference phase angle and the intake cam signal generated when the relative phase angle of the intake camshaft is set to a target value is greater after a start-up of the internal combustion engine than during the start-up, and

wherein the phase difference during the start-up of the internal combustion engine is less than or equal to the period of the crank angle signal.