Controller and control method for internal combustion engine

1. A controller for an internal combustion engine, the internal combustion engine including:

a first forced induction device including a first compressor arranged on a first intake passage;

a second forced induction device including a second compressor arranged on a second intake passage;

a merge portion where intake air that has passed through the first compressor in the first intake passage merges with intake air that has passed through the second compressor in the second intake passage;

an intake manifold through which intake air is drawn into a cylinder in the first and second intake passages;

a merged intake air passage connecting the merge portion and the intake manifold in the first and second intake passages;

a throttle valve arranged on the merged intake air passage;

a first bypass connecting a portion upstream of the first compressor in the first intake passage and a portion downstream of the first compressor in the first intake passage;

a second bypass connecting a portion upstream of the second compressor in the second intake passage and a portion downstream of the second compressor in the second intake passage;

a first air bypass valve arranged on the first bypass; and

a second air bypass valve arranged on the second bypass, the controller comprising:

an intake air amount obtaining unit configured to obtain, using a target torque of the internal combustion engine, a target throttle passage amount as a target value of an amount of intake air drawn through the throttle valve;

an open-closed determination unit configured to determine whether a valve opening condition for the first and second air bypass valves is satisfied; and

an air bypass valve control unit configured to open the first and second air bypass valves when the valve opening condition is satisfied,

wherein the open-closed determination unit is configured to determine that the valve opening condition is satisfied when a decrease speed of the target throttle passage amount is greater than a specified determination speed.

2. The controller according to claim 1 , further comprising a pressure ratio obtaining unit configured to obtain a ratio of a boost pressure to an internal pressure as a pressure ratio, the internal pressure being a pressure in a portion upstream of the first compressor or a portion upstream of the second compressor in the first intake passage, the boost pressure being a pressure in a portion between the first compressor and the throttle valve in the first intake passage and a pressure in a portion between the second compressor and the throttle valve in the second intake passage, wherein

the open-closed determination unit is configured to execute:

a first process that determines whether the valve opening condition is satisfied; and

a second process that determines, with the valve opening condition referred to as a first valve opening condition, whether a second valve opening condition for the first and second air bypass valves is satisfied,

the open-closed determination unit is configured to determine, in the second process, that the second valve opening condition is satisfied when occurrence of surging is predicted from a relationship between the pressure ratio and the target throttle passage amount,

the air bypass valve control unit is configured to open the first and second air bypass valves when at least one of the first valve opening condition or the second valve opening condition is satisfied, and

the open-closed determination unit is configured to determine that the first valve opening condition is satisfied on condition that the pressure ratio is less than or equal to a specified determination pressure ratio.

3. The controller according to claim 2 , further comprising a throttle state determination unit configured to determine an open-closed state of the throttle valve,

wherein the open-closed determination unit is configured to determine, in the first process, that the first valve opening condition is satisfied on condition that the throttle valve is determined as being closed.

4. The controller according to claim 3 , wherein the throttle state determination unit is configured to determine that the throttle valve is closed when a pressure in the intake manifold is less than a specified determination pressure.

5. The controller according to claim 2 , wherein the open-closed determination unit is configured to determine, in the first process, that the first valve opening condition is satisfied on condition that the target throttle passage amount is less than or equal to a specified determination threshold value.

6. A control method for an internal combustion engine, the internal combustion engine including:

a first forced induction device including a first compressor arranged on a first intake passage;

a second forced induction device including a second compressor arranged on a second intake passage;

a merge portion where intake air that has passed through the first compressor in the first intake passage merges with intake air that has passed through the second compressor in the second intake passage;

an intake manifold through which intake air is drawn into a cylinder in the first and second intake passages;

a merged intake air passage connecting the merge portion and the intake manifold in the first and second intake passages;

a throttle valve arranged on the merged intake air passage;

a first bypass connecting a portion upstream of the first compressor in the first intake passage and a portion downstream of the first compressor in the first intake passage;

a second bypass connecting a portion upstream of the second compressor in the second intake passage and a portion downstream of the second compressor in the second intake passage;

a first air bypass valve arranged on the first bypass; and

a second air bypass valve arranged on the second bypass, the method comprising:

obtaining, using a target torque of the internal combustion engine, a target throttle passage amount as a target value of an amount of intake air drawn through the throttle valve;

determining whether a valve opening condition for the first and second air bypass valves is satisfied;

opening the first and second air bypass valves when the valve opening condition is satisfied; and

determining that the valve opening condition is satisfied when a decrease speed of the target throttle passage amount is greater than a specified determination speed.

7. A controller for an internal combustion engine, the internal combustion engine including:

a first forced induction device including a first compressor arranged on a first intake passage;

a second forced induction device including a second compressor arranged on a second intake passage;

a merge portion where intake air that has passed through the first compressor in the first intake passage merges with intake air that has passed through the second compressor in the second intake passage;

an intake manifold through which intake air is drawn into a cylinder in the first and second intake passages;

a merged intake air passage connecting the merge portion and the intake manifold in the first and second intake passages;

a throttle valve arranged on the merged intake air passage;

a first bypass connecting a portion upstream of the first compressor in the first intake passage and a portion downstream of the first compressor in the first intake passage;

a second bypass connecting a portion upstream of the second compressor in the second intake passage and a portion downstream of the second compressor in the second intake passage;

a first air bypass valve arranged on the first bypass;

a second air bypass valve arranged on the second bypass; and

a processor;

the processor is configured to:

obtain, using a target torque of the internal combustion engine, a target throttle passage amount as a target value of an amount of intake air drawn through the throttle valve;

determine whether a valve opening condition for the first and second air bypass valves is satisfied;

open the first and second air bypass valves when the valve opening condition is satisfied; and

determine that the valve opening condition is satisfied when a decrease speed of the target throttle passage amount is greater than a specified determination speed.