CN107620641B

CN107620641B - ECU for motor vehicle engine

Info

Publication number: CN107620641B
Application number: CN201610561070.3A
Authority: CN
Inventors: 俞吉; 安部元幸; 于广
Original assignee: Hitachi Astemo Ltd
Current assignee: Hitachi Astemo Ltd
Priority date: 2016-07-15
Filing date: 2016-07-15
Publication date: 2022-04-01
Anticipated expiration: 2036-07-15
Also published as: CN107620641A

Abstract

The ECU for the motor vehicle engine is characterized by comprising a rotating speed monitoring unit, a control unit and a control unit, wherein the rotating speed monitoring unit is used for monitoring the rotating speed value of the engine; the air inlet passage pressure monitoring unit is used for monitoring the pressure value behind an air throttle valve of the air inlet passage; a storage unit that stores a correspondence relationship between an engine speed, an intake passage pressure, and an opening/closing angle of a corresponding intake valve and/or exhaust valve in a state where EGR can be activated; and an intake valve timing control unit and/or an exhaust valve timing control unit that controls the intake valve and/or the exhaust valve to open or close at a specified time stored in the storage unit. According to the invention, the emission reduction of NOx can be realized, and the fuel economy is improved.

Description

ECU for motor vehicle engine

Technical Field

The present invention relates to an ECU for a motor vehicle engine, and more particularly, to an ECU for a motor vehicle engine capable of implementing EGR control.

Background

Under the background that the current environmental pollution problem is more and more emphasized by people, automobile manufacturers will adopt various technical means to realize the reduction of emission. Among them, the control of NOx (nitrogen oxide) emissions is a very important technical goal.

In the existing engine control technology, the emission reduction of NOx is generally realized by using an EGR (Exhaust Gas Recirculation) starting mode. When the engine is under certain load conditions, the ECU controls the engine to turn EGR on. The operating principle of EGR is to reduce the temperature of the combusted gases by the high heat capacity of the exhaust gases, thereby reducing NOx emissions. In addition, since the temperature of the burned gas is low, the heat loss of the engine is also reduced accordingly. However, an excessively high EGR amount causes unstable combustion, and an excessively low EGR amount does not sufficiently exhibit the effect of reducing emissions, and is therefore very important for controlling the EGR amount.

EGR can be divided into two categories, external EGR and internal EGR, according to different implementations. External EGR is a method in which a part of gas in an exhaust passage is drawn into an intake passage by an external device. By using the EGR valve, the ECU can accurately control the flow of EGR, thereby controlling the EGR rate in the cylinder. However, this method is expensive because an additional external device needs to be installed, and the required structure is complicated. Internal EGR traps part of the exhaust gas in the cylinder by closing the exhaust valve early in the exhaust stroke; or in the intake stroke, the exhaust valve is opened again to suck part of the exhaust gas into the cylinder. This method does not require an additional device, but cannot control the flow rate of EGR quantitatively, and cannot fully utilize EGR to achieve the effect of reducing emissions.

In patent CN204851353U, a dual-peak intake camshaft is applied to the implementation of EGR. On the intake camshaft, there are provided an intake cam for intake of the engine and an EGR cam for achieving internal exhaust gas circulation. When the cylinder is on the exhaust stroke, the EGR cam opens the intake valve, allowing exhaust gas to enter the intake passage, thereby achieving internal EGR. However, this method still does not essentially solve the problem of quantitatively controlling EGR, but adds an additional mechanical structure, affecting mechanical efficiency.

The existing internal EGR realization method is mainly realized by a method of closing an exhaust valve in advance through an exhaust stroke or closing the exhaust valve in a delay mode through an intake stroke, and the advance angle or the delay angle is fixed for all working conditions in which EGR can be applied. This is detrimental to fully exploiting the potential of EGR for reducing NOx emissions, and does not meet increasingly stringent emission regulations, so that other approaches to achieve more accurate control of internal EGR are desirable to achieve lower NOx emissions.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object of the present invention is to provide an ECU for a motor vehicle engine, including: the rotating speed monitoring unit is used for monitoring the rotating speed value of the engine; the air inlet passage pressure monitoring unit is used for monitoring the pressure value behind an air throttle valve of the air inlet passage; a storage unit that stores a correspondence relationship between an engine speed, an intake passage pressure, and an opening/closing angle of a corresponding intake valve and/or exhaust valve in a state where EGR can be activated; and an intake valve timing control unit and/or an exhaust valve timing control unit that controls the intake valve and/or the exhaust valve to open or close at a specified time stored in the storage unit.

According to the ECU for the motor vehicle engine, the opening and closing angles of the air inlet valve and/or the exhaust valve under each working condition of enabling EGR are determined in the calibration stage, so that the effect of EGR can be effectively utilized, the emission reduction of NOx is realized, and the fuel economy is improved.

In addition, the ECU for a motor vehicle engine of the present invention, preferably, an oxygen content monitoring unit for monitoring an oxygen content in exhaust gas; the throttle valve opening control unit controls the throttle valve to adjust the opening according to the monitoring result of the oxygen content monitoring unit; and when the oxygen content in the exhaust gas does not reach the specified range, adjusting the opening of the throttle valve until the oxygen content in the exhaust gas reaches the specified range. Thereby, safe discharge of the exhaust gas can be ensured.

Further, the ECU for a motor vehicle engine of the present invention preferably stores the correspondence relationship between the engine speed, the intake passage pressure, and the opening/closing angle of the corresponding intake valve and/or exhaust valve at the time when the coefficient of variation (COV) of the mean indicated effective pressure reaches or approaches the limit value under different operating conditions of the engine in the EGR enabled state. Therefore, the opening and closing angles of the air inlet valve and/or the exhaust valve under various working conditions are determined by taking the COV as a target value, so that the effect of EGR is effectively utilized, the emission reduction of NOx is realized, the fuel economy is improved, and meanwhile, the combustion stability of the engine can be ensured.

Further, in the ECU for a motor vehicle engine of the present invention, it is preferable that the intake valve timing control unit drives the intake valve to open according to the earliest allowable intake valve opening angle recorded in the storage unit when the monitored values of the rotation speed monitoring unit and the intake passage pressure monitoring unit are within the stored data range of the storage unit, and the exhaust valve timing control unit opens and closes the exhaust valve according to a normal setting. Optimal control in the EGR mode can be achieved by controlling only the intake valve opening angle, thereby simplifying control of the ECU.

Further, the ECU for a motor vehicle engine of the present invention preferably has the earliest allowable intake valve opening angle in each operating condition corresponding to the intake valve opening angle at which the EGR amount is the maximum value of the allowable EGR in that operating condition. Thus, NOx reduction can be achieved by EGR as much as possible while ensuring engine stability.

Further, in the ECU for a motor vehicle engine of the present invention, it is preferable that the exhaust valve timing control unit drives the exhaust valve to open according to the latest allowable exhaust valve closing angle recorded in the storage unit and the intake valve timing control unit opens and closes according to a normal setting when the monitored values of the rotation speed monitoring unit and the intake passage pressure monitoring unit are within the stored data range of the storage unit. Thus, the optimal control in the EGR mode can be achieved by controlling only the exhaust valve closing angle, and the control of the ECU is simplified.

Further, the ECU for a motor vehicle engine of the present invention preferably has the latest allowable exhaust valve closing angle in each operating condition corresponding to the exhaust valve closing angle at which the EGR amount in that operating condition is the maximum value of the allowable EGR. Thus, NOx reduction can be achieved by EGR as much as possible while ensuring engine stability.

Further, the ECU for a motor vehicle engine of the present invention preferably further comprises an intake valve timing control unit and an exhaust valve timing control unit that drive the intake valve and the exhaust valve to open respectively according to a combination of the allowable earliest intake valve opening angle and the latest exhaust valve opening angle recorded in the storage unit when the monitored values of the rotation speed monitoring unit and the intake passage pressure monitoring unit are within the stored data range of the storage unit. Thereby, the optimization control in the EGR mode can be more accurately achieved.

Further, the ECU for a motor vehicle engine of the present invention preferably has the earliest allowable intake valve opening angle and the latest allowable exhaust valve closing angle for each operating condition corresponding to the combination of the intake valve opening angle and the exhaust valve closing angle at which the EGR amount is the maximum of the allowable EGR for that operating condition. Thus, NOx reduction can be achieved by EGR as much as possible while ensuring engine stability.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the ECU for the motor vehicle engine, the emission reduction of NOx can be realized and the fuel economy can be improved under the condition of ensuring the stability of the engine.

Drawings

Fig. 1 is a schematic diagram of an engine structure to which an ECU of the present invention is applied.

Fig. 2 is a logic flow diagram of the calibration phase of embodiment 1 of the present invention.

Fig. 3 is a control logic flow diagram of embodiment 1 of the present invention.

FIG. 4 is a schematic exhaust stroke exhaust gas flow diagram achieved by the present invention.

Fig. 5 is a lift variation diagram of the intake valve in different working conditions according to the embodiment 1 of the invention.

Fig. 6 is a logic flow diagram of the calibration phase of embodiment 2 of the present invention.

Fig. 7 is a control logic flow diagram of embodiment 2 of the present invention.

Fig. 8 is a graph of the exhaust valve lift according to embodiment 2 of the present invention.

Fig. 9 is a logic flow diagram of the calibration phase of embodiment 3 of the present invention.

Fig. 10 is a control logic flow diagram of embodiment 3 of the present invention.

FIG. 11 is a graph of exhaust valve lift for different operating conditions according to embodiment 3 of the present invention.

Detailed Description

The invention is explained in more detail below with reference to the figures and examples.

Preferred embodiments of an ECU for a motor vehicle engine according to the present invention will be described in detail below with reference to the accompanying drawings. In the description of the drawings, the same or corresponding portions are denoted by the same reference numerals, and redundant description is omitted.

< embodiment 1 >

Fig. 1 is a schematic structural view of an engine and an ECU thereof to which embodiment 1 of the present invention is applied. Specifically, as shown in fig. 1, the engine is constituted by an engine main body and an intake line and an exhaust line connected thereto. An air flow meter 1 is disposed in the intake pipe, and a gas temperature sensor is incorporated in the air flow meter 1. A pressure sensor 2 is disposed downstream of the air flow meter 1. A compressor 3 is arranged downstream of the pressure sensor 2. An air throttle 4 for controlling the amount of air taken into the cylinder is disposed downstream of the compressor 3. The throttle valve 4 is an electronic throttle valve whose valve opening degree can be controlled independently of the opening degree of the accelerator pedal. A gas pressure sensor 5 is disposed downstream of the throttle valve 4 and thereafter connected to the intake manifold. In the engine body, an injector 6 is disposed inside the cylinder. An ignition plug 7 for igniting a mixture of fuel and air, and a timing mechanism 8 for controlling opening and closing of intake and exhaust valves are disposed at the top of the cylinder. A rotation speed sensor 9 is disposed on a crankshaft connected to a piston of a cylinder via a connecting rod, and the rotation speed of the engine can be obtained based on a signal of the rotation speed sensor 9. A gas pressure sensor 10 is disposed in an engine cylinder. A turbine 11 is arranged in the exhaust line. The turbine 11 is coaxially connected to the compressor 3 and converts part of the internal energy of the exhaust gas into mechanical work to compress the air. An oxygen sensor 12 is disposed downstream of the turbine 11, and the fuel injection amount is adjusted to a target air-fuel ratio based on the detection result of the oxygen sensor 12. A catalytic converter 13 is disposed downstream of the oxygen sensor 12, and can purify the exhaust gas of carbon monoxide, nitrogen oxides, and hydrocarbons. All monitoring mechanisms and actuators are connected to the ECU 14.

Embodiment 1 of the present invention is directed to implementing internal EGR by adjusting the opening time of an intake valve under different operating conditions. And when the cylinder is in the later period of the exhaust stroke, controlling the air inlet valve to open in advance, introducing part of the exhaust gas into the air inlet channel, and then re-sucking the part of the exhaust gas into the cylinder in the air inlet stroke to realize internal EGR. This implementation requires the use of an intake valve timing control unit, with the corresponding valve opening time being the earliest opening angle of the intake valve recorded by the ECU 14.

During the calibration phase, the earliest intake valve opening angle is calibrated for all operating points where EGR may be employed and recorded to the ECU 14. Fig. 2 is a logic flow diagram of the calibration phase of this implementation. Firstly, when the working condition changes (201), recording the engine rotating speed value monitored by a rotating speed sensor 9 and the pressure of an air inlet channel monitored by a gas pressure sensor 5 (202); secondly, if the engine is in a working condition that EGR can be started (203), adjusting the opening angle of an air inlet valve, and calculating a coefficient of variation (COV) of average indicated effective pressure according to a pressure value returned by the gas pressure sensor 10 (204); when the COV reaches a limit value, namely when the combustion stability of the engine is in a critical state (205), recording a corresponding opening angle of an air inlet valve, namely the earliest opening angle of the air inlet valve (206); finally, the correspondence between the opening angle of the intake valve and the engine speed value and the intake passage pressure is recorded to the ECU 14, thereby ending the calibration of the operating condition (207). It should be noted that, in the most preferred embodiment, the earliest intake valve opening angle corresponds to the case where the COV reaches the limit value, but the earliest intake valve opening angle may be set to correspond to the case where the COV approaches the limit value, so as to ensure the engine combustion stability, and such setting may obtain substantially the same effect as the most preferred embodiment. Here, in consideration of the difference between individual engines, the COV limit value criterion may be set to 95% or even 90% or even 80% of the calibrated limit value during actual operation, depending on the engine operating conditions.

Fig. 3 is a control logic flow chart of embodiment 1. The control flow starts to be effective when the engine is started and is terminated when the engine is shut down. In the control of the ECU of the present invention, when a change in the state of the accelerator pedal 15 is monitored (301, 302), the ECU 14 will determine whether EGR can be used or not based on the engine speed value monitored by the speed sensor 9 and the intake passage pressure monitored by the gas pressure sensor 5 (303, 304). If EGR is available, the ECU 14 will select the corresponding earliest intake valve opening angle based on the calibration (305) and control the intake valve to open on time. Thereafter, the ECU 14 also monitors the signal from the oxygen sensor 12 (306), and if the oxygen content in the exhaust gas does not meet the requirement, the ECU 14 controls the throttle opening control mechanism to adjust the opening of the throttle valve 4 (307) until the oxygen content in the exhaust gas monitored by the oxygen sensor 12 meets the requirement. After the engine is turned off, the control is terminated (308).

FIG. 4 is a schematic exhaust stroke exhaust gas flow diagram achieved by the present invention. During the exhaust stroke, exhaust gas flows into the exhaust passage primarily through the exhaust valve. If the opening time of the intake valve is adjusted so that the intake valve is opened in the exhaust stroke, part of the exhaust gas can flow into the intake passage, and internal EGR is realized.

Fig. 5 is a graph showing the change in lift of the intake and exhaust valves according to this embodiment. The allowable maximum EGR value is different for different operating conditions, and thus, it is desirable to calibrate its corresponding allowable maximum EGR value for each operating condition. By advancing the opening time of the air inlet valve, the waste gas in the cylinder can be discharged to the air inlet valve and completely enters the cylinder in the following air inlet stroke; the amount of exhaust gas discharged, and the length of time the intake valve is opened prematurely, is positively correlated, and therefore will have a correspondingly different earliest intake valve opening angle for different operating conditions (as shown by the dashed and dotted lines). During this process, the closing angle of the exhaust valve remains unchanged.

According to embodiment 1 of the present invention, the earliest intake valve opening angle for each operating condition in the EGR state is predetermined, whereby the maximum COV can be achieved in each EGR state. Therefore, the optimization of EGR can be realized only by modifying the opening angle of the air inlet valve in different EGR states without improving the existing engine structure, thereby reducing NOx and realizing fuel economy.

< embodiment 2 >

Embodiment 2 of the present invention differs from embodiment 1 in that the internal EGR is realized by adjusting the closing time of the exhaust valve under different operating conditions, without changing the opening time of the intake valve. Further, embodiment 2 may be applied to an engine for a vehicle in which fuel injection is performed in an intake passage. The method for adjusting the closing time of the exhaust valve is a common method for realizing internal EGR at present, and the internal EGR is realized by controlling the exhaust valve to be closed in a delayed manner at the early stage of an intake stroke and sucking part of exhaust gas into a cylinder again from an exhaust passage; this method, however, also cannot achieve precise control of the EGR amount. However, by using the method set forth in the present invention, the following method is used for calibration, and the maximum utilization of the EGR effect under different working conditions can be realized. In contrast, this implementation requires the use of an exhaust valve timing control unit, with the corresponding valve closing time being the latest exhaust valve closing angle recorded by the ECU 14.

During the calibration phase, the latest exhaust valve closing angle is calibrated for all operating points where EGR may be employed and recorded to the ECU 14. Fig. 6 is a logic flow diagram of the calibration phase of embodiment 2. Firstly, when the working condition changes (601), recording the engine rotating speed value monitored by the rotating speed sensor 9 and the pressure of an air inlet channel monitored by the air pressure sensor 5 (602); secondly, if the engine is under the working condition that EGR can be started (603), adjusting the closing angle of an exhaust valve, and calculating a coefficient of variation (COV) of the average indicated effective pressure according to the pressure value returned by the gas pressure sensor 10 (604); when the COV reaches a limit value, i.e. engine combustion stability is in a critical state (605), recording a corresponding exhaust valve closing angle, i.e. a latest exhaust valve closing angle (606); finally, the correspondence of the exhaust valve closing angle to the engine speed value and the intake passage pressure is recorded to the ECU 14, thereby ending the calibration of the operating condition (607). It should be noted that, in the most preferred embodiment, the latest exhaust valve closing angle corresponds to the case where the COV reaches the limit value, but the latest exhaust valve closing angle may be set to correspond to the case where the COV approaches the limit value, so that the engine combustion stability is ensured, and such setting can obtain substantially the same effect as the most preferred embodiment. Here, in consideration of the difference between individual engines, the COV limit value criterion may be set to 95% or even 90% or even 80% of the calibrated limit value during actual operation, depending on the engine operating conditions.

Fig. 7 is a control logic flow chart of embodiment 2. The control flow starts to be effective when the engine is started and is terminated when the engine is shut down. In the control of the ECU of the present invention, when a change in the state of the accelerator pedal 15 is monitored (701, 702), the ECU 14 determines whether EGR can be used or not based on the engine speed value monitored by the speed sensor 9 and the intake passage pressure monitored by the gas pressure sensor 5 (703, 704). If EGR is available, the ECU 14 will select the corresponding latest exhaust valve closing angle based on the calibration results (705) and control the exhaust valve to close on time. Thereafter, the ECU 14 also monitors the signal from the oxygen sensor 12 (706), and if the oxygen content in the exhaust gas does not meet the requirement, the ECU 14 controls the throttle opening control mechanism to adjust the opening of the throttle valve 4 (707) until the oxygen content in the exhaust gas monitored by the oxygen sensor 12 meets the requirement. After the engine is shut down, control terminates (708).

Fig. 8 is a lift change diagram of intake and exhaust valves according to embodiment 2. The waste gas in the exhaust passage can be sucked back into the cylinder by delaying the opening time of the exhaust valve; the amount of exhaust gas that is drawn is positively correlated to the length of time the exhaust valve is delayed to close, and thus will have a corresponding different latest exhaust valve closing angle for different operating conditions (as shown by the dashed and dotted lines). During this process, the opening angle of the intake valve remains unchanged.

According to embodiment 2 of the present invention, the latest exhaust valve closing angle for each operating condition in the EGR state is predetermined, whereby the maximum COV can be achieved in each EGR state. Thus, without modifying the existing engine structure, the optimization of EGR can be realized by only modifying the closing angle of the exhaust valve in different EGR states, thereby reducing NOx and realizing fuel economy.

< embodiment 3 >

Embodiment 3 of the present invention is different from

embodiments

1 and 2 in that the opening and closing times of the intake and exhaust valves are adjusted simultaneously in different conditions to realize internal EGR. When the cylinder is in the later period of the exhaust stroke, controlling the air inlet valve to open in advance, introducing part of waste gas into the air inlet channel, and then re-sucking the part of waste gas into the cylinder in the air inlet stroke; meanwhile, in the early stage of the intake stroke, the exhaust valve is controlled to be closed in a delayed mode, and partial exhaust gas is sucked into the cylinder again from the exhaust passage, so that internal EGR is achieved. This implementation requires the simultaneous use of intake and exhaust valve timing control units, and the corresponding valve opening times, which are different from the corresponding values of the two implementations described above, need to be determined by calibration.

During the calibration phase, the combination of the earliest intake valve opening angle and the latest exhaust valve closing angle is calibrated for all operating points where EGR may be employed and recorded to the ECU 14. FIG. 9 is a logic flow diagram of a calibration phase of this method. Firstly, when the working condition changes (901), recording the engine rotating speed value monitored by a rotating speed sensor 9 and the pressure of an air inlet channel monitored by a gas pressure sensor 5 (902); secondly, if the engine is in a working condition that EGR can be started (903), adjusting the opening angle of an air inlet valve and the closing angle of an exhaust valve, and calculating a coefficient of variation (COV) of average indicated effective pressure according to a pressure value returned by the gas pressure sensor 10 (904); when the COV reaches a limit value, i.e. when engine combustion stability is in a critical state (905), recording corresponding intake valve opening angles and exhaust valve closing angles (906), i.e. a combination of the earliest intake valve opening angle and the latest exhaust valve closing angle; finally, the correspondence between the intake valve opening angle and the exhaust valve closing angle, and the engine speed value and the intake passage pressure is recorded to the ECU 14, thereby ending the calibration of the operating condition (907). It should be noted that, in the most preferred embodiment, the earliest intake valve opening angle and the latest exhaust valve closing angle correspond to the case where the COV reaches the limit value, but the earliest intake valve opening angle and the latest exhaust valve closing angle may be set to correspond to the case where the COV approaches the limit value, so that the engine combustion stability is ensured, and such setting may obtain substantially the same effect as the most preferred embodiment. Here, in consideration of the difference between individual engines, the COV limit value criterion may be set to 95% or even 90% or even 80% of the calibrated limit value during actual operation, depending on the engine operating conditions.

Fig. 10 is a control logic flowchart of embodiment 3. The control flow starts to be effective when the engine is started and is terminated when the engine is shut down. In the control of the ECU of the present invention, when a change in the state of the accelerator pedal 15 is monitored (1001, 1002), the ECU 14 determines whether EGR can be used or not based on the engine speed value monitored by the speed sensor 9 and the intake passage pressure monitored by the gas pressure sensor 5 (1003, 1004). If EGR is available, the ECU 14 will select the corresponding combination of the earliest intake valve opening angle and the latest exhaust valve closing angle based on the calibration (1005), and will control the intake valve to open and the exhaust valve to close on time. Thereafter, the ECU 14 also needs to monitor the signal of the oxygen sensor 12 (1006), and if the oxygen content in the exhaust gas does not meet the requirement, the ECU 14 controls the throttle opening control mechanism to adjust the opening of the throttle valve 4 (1007) until the oxygen content in the exhaust gas monitored by the oxygen sensor 12 meets the requirement. After the engine is turned off, the control is terminated (1008).

Fig. 11 is a lift change diagram of intake and exhaust valves according to embodiment 3. By advancing the opening time of the air inlet valve, the waste gas in the cylinder can be discharged to the air inlet valve and completely enters the cylinder in the following air inlet stroke; and the amount of exhaust gas discharged is positively correlated with the length of time the intake valve is opened in advance. By delaying the closing time of the exhaust valve, the exhaust gas in the exhaust passage can be sucked back into the cylinder; and the amount of exhaust gas drawn is positively correlated with the length of time the exhaust valve is delayed to close (as shown by the dashed and dotted lines). There will be correspondingly different combinations of the earliest intake valve opening angle and the latest exhaust valve closing angle for different operating conditions.

According to embodiment 3 of the present invention, by combining embodiment 1 and embodiment 2, EGR can be optimized more favorably, NOx can be reduced, and fuel economy can be achieved.

The ECU of the present invention is not limited to the above-described embodiment, and various other modifications are possible. While the invention has been specifically described above in connection with the drawings and examples, it will be understood that the above description is not intended to limit the invention in any way. Those skilled in the art can make modifications and variations to the present invention as needed without departing from the true spirit and scope of the invention, and such modifications and variations are within the scope of the invention.

Claims

1. An ECU of an engine for a motor vehicle,

the disclosed device is provided with:

the rotating speed monitoring unit is used for monitoring the rotating speed value of the engine;

the air inlet passage pressure monitoring unit is used for monitoring the pressure value behind an air throttle valve of the air inlet passage;

a storage unit that stores a correspondence relationship between an engine speed, an intake passage pressure, and an opening/closing angle of a corresponding intake valve and/or exhaust valve in a state where EGR can be activated;

an intake valve timing control unit and/or an exhaust valve timing control unit that controls an intake valve and/or an exhaust valve to open or close at a specified time stored in the storage unit, the engine enabling the EGR only through the intake valve and/or the exhaust valve;

the oxygen content monitoring unit is used for monitoring the oxygen content in the waste gas;

a throttle valve opening control unit for controlling the throttle valve to adjust the opening according to the monitoring result of the oxygen content monitoring unit,

and after the air inlet valve and/or the exhaust valve are opened or closed according to the specified time stored in the storage unit, when the oxygen content in the exhaust gas detected by the oxygen content detection unit does not reach the specified range, the opening degree of the throttle valve is adjusted until the oxygen content in the exhaust gas reaches the specified range.

2. The ECU of claim 1,

the storage unit stores correspondence relationships between engine speeds, intake passage pressures, and opening/closing angles of respective intake valves and/or exhaust valves at different operating conditions of the engine in a state where EGR is enabled, when a coefficient of variation (COV) indicating an effective pressure on average reaches or approaches a limit value.

3. The ECU of claim 1 or 2,

and the intake valve timing control unit drives the intake valve to open according to the allowable earliest opening angle of the intake valve recorded in the storage unit and the exhaust valve timing control unit opens and closes the exhaust valve according to the conventional setting when the monitoring values of the rotation speed monitoring unit and the intake passage pressure monitoring unit are within the storage data range of the storage unit.

4. The ECU of claim 3,

the earliest allowable intake valve opening angle under each condition corresponds to the intake valve opening angle at which the amount of EGR is at the maximum of the allowable EGR for that condition.

5. The ECU of claim 1 or 2,

and the exhaust valve timing control unit drives the exhaust valve to open according to the latest allowable exhaust valve closing angle recorded in the storage unit when the monitoring values of the rotation speed monitoring unit and the intake passage pressure monitoring unit are within the storage data range of the storage unit, and the intake valve timing control unit sets the opening and closing according to the convention.

6. The ECU of claim 5,

the latest allowable exhaust valve closing angle at each operating condition corresponds to the exhaust valve closing angle at which the amount of EGR at that operating condition is the maximum value of allowable EGR.

7. The ECU of claim 1 or 2,

and when the monitoring values of the rotating speed monitoring unit and the air inlet channel pressure monitoring unit are within the storage data range of the storage unit, the air inlet valve and the air outlet valve are driven to be opened according to the allowable combination of the earliest opening angle and the latest opening angle of the air inlet valve recorded in the storage unit respectively.

8. The ECU of claim 7,

the earliest allowable intake valve opening angle and the latest exhaust valve closing angle for each operating condition correspond to the combination of the intake valve opening angle and the exhaust valve closing angle at which the amount of EGR is at the maximum of the allowable EGR for that operating condition.