Knock control apparatus for internal combustion engine

1. A knock control apparatus for an internal combustion engine, comprising:

a knock sensor that detects a vibration caused by a knock of the internal combustion engine;

a knock signal normalization unit that normalizes a knock signal extracted from an output signal of the knock sensor and obtains the normalized knock signal;

a knock determination threshold setting unit that sets a knock determination threshold on the basis of the normalized knock signal;

a knock intensity computation unit that calculates knock intensity on the basis of the normalized knock signal and the set knock determination threshold;

a knock determination unit that determines a presence or absence of a knock on the basis of the calculated knock intensity; and

a knock correction amount computation unit that calculates a knock correction amount to correct the calculated knock intensity in a case where an occurrence of a knock is determined by the knock determination unit,

wherein the knock signal normalization unit is configured to obtain the normalized knock signal by normalizing a standard deviation of the knock signal by dividing the extracted knock signal by an average value of the knock signal.

2. The knock control apparatus for an internal combustion engine according to claim 1 , wherein the knock signal normalization unit includes:

a standard deviation normalization unit that obtains the normalized knock signal by normalizing the standard deviation of the knock signal extracted from the output signal of the knock sensor; and

an average value normalization unit that normalizes the average value of the knock signal by linear mapping from the normalized knock signal obtained by the standard deviation normalization unit to a predetermined value.

3. The knock control apparatus for an internal combustion engine according to claim 2 , wherein processing of the linear mapping from the average value of the signal processed by the average value normalization unit to a predetermined value is repeated a predetermined number of times.

4. The knock control apparatus for an internal combustion engine according to claim 3 , wherein the standard deviation normalization unit normalizes the standard deviation of the knock signal using the average value of the knock signal immediately before execution of knock control is inhibited in a state where execution of the knock control is inhibited.

5. The knock control apparatus for an internal combustion engine according to claim 4 , wherein the knock correction amount calculated by the knock correction amount computation unit is an amount by which the knock intensity computed by the knock intensity computation unit has been corrected using the knock intensity calculated by the knock intensity computation unit and the knock signal before normalization by the knock signal normalization unit.

6. The knock control apparatus for an internal combustion engine according to claim 3 , wherein the knock correction amount calculated by the knock correction amount computation unit is an amount by which the knock intensity computed by the knock intensity computation unit has been corrected using the knock intensity calculated by the knock intensity computation unit and the knock signal before normalization by the knock signal normalization unit.

7. The knock control apparatus for an internal combustion engine according to claim 2 , wherein the standard deviation normalization unit normalizes the standard deviation of the knock signal using the average value of the knock signal immediately before execution of knock control is inhibited in a state where execution of the knock control is inhibited.

8. The knock control apparatus for an internal combustion engine according to claim 7 , wherein the knock correction amount calculated by the knock correction amount computation unit is an amount by which the knock intensity computed by the knock intensity computation unit has been corrected using the knock intensity calculated by the knock intensity computation unit and the knock signal before normalization by the knock signal normalization unit.

9. The knock control apparatus for an internal combustion engine according to claim 2 , wherein the knock correction amount calculated by the knock correction amount computation unit is an amount by which the knock intensity computed by the knock intensity computation unit has been corrected using the knock intensity calculated by the knock intensity computation unit and the knock signal before normalization by the knock signal normalization unit.

10. The knock control apparatus for an internal combustion engine according to claim 1 , wherein the knock correction amount calculated by the knock correction amount computation unit is an amount by which the knock intensity computed by the knock intensity computation unit has been corrected using the knock intensity calculated by the knock intensity computation unit and the knock signal before normalization by the knock signal normalization unit.

11. The knock control apparatus for an internal combustion engine according to claim 1 , wherein the knock signal normalization unit is configured to obtain the normalized knock signal by using an expression:

V NSGM [n]=V SIG [n]/V ASIG [n],

where V NSGM [n] is a value of the normalized knock signal,

V SIG [n] is a value of the knock signal,

V ASIG [n] is the average value of the knock signal, and

n is a number of interruption processing times.