Control apparatus for internal combustion engine

1. An internal combustion engine, comprising:

a turbo-supercharger including a compressor that is disposed in an intake passage and that supercharges intake air, and a turbine that is disposed in an exhaust passage and that operates by means of exhaust energy;

a throttle valve that is disposed in the intake passage and that adjusts an intake air amount;

an exhaust bypass passage that branches off from the exhaust passage on an upstream side of the turbine, and merges again with the exhaust passage on a downstream side of the turbine;

a waste gate valve that is positioned in the exhaust bypass passage and that adjusts opening and closing an exhaust gas amount in the exhaust bypass passage; and

a controller that is programmed and stored with non-transitory instructions therein being executable to:

(i) determine a steady-state characteristic that defines a relation between an engine load factor and a throttle opening degree in a steady state of the engine;

wherein the steady-state characteristic includes:

a high atmospheric pressure steady-state characteristic that is used under a high atmospheric pressure that is an atmospheric pressure that is higher than a predetermined value; and

a low atmospheric pressure steady-state characteristic that is used under a low atmospheric pressure that is an atmospheric pressure that is less than or equal to the predetermined value;

(ii) switch the steady-state characteristic between the high atmospheric pressure steady-state characteristic and the low atmospheric pressure steady-state characteristic in accordance with whether or not the atmospheric pressure is higher than the predetermined value;

(iii) control a throttle opening degree

a. to increase an intake air amount at a rate of change being less than a predetermined rate,

wherein the throttle opening degree becomes a target throttle opening degree that is obtained based on the high atmospheric pressure steady-state characteristic or the low atmospheric pressure steady-state characteristic that is selected and on a target engine load factor; and

b. to increase an intake air amount at a rate of change that is greater than or equal to the predetermined rate under the low atmospheric pressure,

wherein the throttle opening degree becomes a target throttle opening degree that is greater than a value obtained based on the low atmospheric pressure steady-state characteristic that is selected and on a target engine load factor,

wherein in the low atmospheric pressure steady-state characteristic,

a throttle opening degree corresponding to an identical engine load factor is set to a smaller value in comparison to the high atmospheric pressure steady-state characteristic in a medium load region, and

the throttle opening degree is set so as to increase as the engine load factor increases towards a full load in a region on a side of a higher load factor than the medium load region, and

wherein during the low atmospheric pressure steady-state characteristic, the controller controls the opening degree of the waste gate valve to a value on a closing side, in association with the throttle opening degree corresponding to an identical engine load factor being controlled to a smaller value in comparison to the high atmospheric pressure steady-state characteristic in the medium load region.

2. The internal combustion engine according to claim 1 , wherein when increasing the throttle opening degree, the controller further includes the non-transitory executable instructions to restrict an operating speed of the throttle valve so as not to exceed a predetermined upper speed limit value of the throttle valve to minimize or prevent a drop in outlet pressure of the compressor.

3. The internal combustion engine according to claim 1 , wherein the controller further includes the non-transitory executable instructions to decrease the throttle opening degree while increasing the engine load factor during the low atmospheric pressure steady-state characteristic being set in the medium load region.