Controller and control method for internal combustion engine

A controller for an internal combustion engine comprising at least one processor configured to implement:

• a knock signal calculator that calculates a knock signal based on an output signal of a combustion condition detection sensor which outputs a signal in accordance with a combustion condition of the internal combustion engine;
• a BGL calculator that calculates a background level based on the knock signal;
• a knock decision threshold calculator that calculates a knock decision threshold based on the background level;
• a knock intensity calculator that calculates a knock occurrence intensity based on the knock signal and the knock decision threshold;
• and
• a knock controller that changes a control parameter of the internal combustion engine so as to suppress occurrence of knocking in accordance with the knock occurrence intensity,
• wherein the BGL calculator calculates the background level by processing a low pass filter to the knock signal;
• and performs a low side frequency increase which makes a low side frequency, which is a cutoff frequency of the low pass filter in the case where the knock signal is smaller than an output value of the low pass filter, higher than a high side frequency, which is a cutoff frequency of the low pass filter in the case where the knock signal is larger than the output value of the low pass filter.