Controller for internal combustion engine

A controller for an internal combustion engine using hydrogen as fuel, the internal combustion engine including a variable valve mechanism configured to change a valve timing of an exhaust valve, and a turbocharger arranged in an exhaust passage, the turbocharger including an adjustment mechanism configured to adjust an amount of exhaust gas supplied to a turbine wheel, the controller comprising:

• processing circuitry, wherein:
• the processing circuitry is configured to execute
• an acquisition process that acquires a parameter correlated with a back pressure, the back pressure including a pressure of the exhaust passage located upstream of the turbine wheel,
• a determination process that determines, based on the parameter, whether the back pressure is higher than or equal to a predetermined pressure, and
• an overlap limitation process that limits a valve overlap amount between an intake valve and the exhaust valve of the internal combustion engine when the back pressure is determined as being higher than or equal to the predetermined pressure;
• and
• the overlap limitation process changes a valve closing time of the exhaust valve, so that the valve overlap amount becomes smaller than the valve overlap amount before execution of the overlap limitation process.