DE102015120741B4 - Control device for internal combustion engine - Google Patents

Abstract

An internal combustion engine control device comprising a compressor (14) provided in an intake passage (10), a throttle (24) provided downstream of the compressor (14) in the intake passage (10), and one EGR valve (32) provided in an EGR passage (30) connecting a downstream side of the throttle (24) in the intake passage (10) to an exhaust passage (12), comprising: a surge predictor to detect the occurrence predicting a surge in the compressor (14); a target air quantity setting means for determining a target air quantity suitable for an operating state of the internal combustion engine and for correcting the target air quantity for an air quantity capable of the surge to be avoided when the occurrence of the surge is predicted by the surge prediction device; an EGR valve control device in order to control an opening degree of the EGR valve (32) so that an air quantity, which is introduced into a cylinder becomes the target air amount set by the target air amount setting means; and throttle control means for controlling a pressure difference between an upstream and a downstream side of the throttle (24) by controlling a degree of closing of the throttle (24) so that a pressure difference equal to or larger than a predetermined value between an upstream side and a downstream side of the EGR valve (32) occurs at least when the occurrence of the surge is predicted by the surge prediction device, the degree of closure of the throttle (24) being regulated by a control system in which the deviation is calculated Between a target pressure difference between the upstream side and the downstream side of the throttle (24) and an actual pressure difference between the upstream side and a downstream side of the throttle (24), a correction quantity of the degree of closure of the throttle (24) is calculated, whereby a new degree of closing of the throttle (24 ) is calculated by adding the calculated correction quantity to the existing degree of closure of the throttle (24).

Description

Background of the Invention

Field of the Invention

The present invention relates to a control device for an internal combustion engine installed in an automobile, more specifically, an internal combustion engine that includes a compressor provided in an intake passage, a throttle that is downstream of the Compressor is provided in the intake passage, and an EGR valve that is provided in an EGR passage that connects a downstream side of the throttle in the intake passage with an exhaust passage.

Explanation of the state of the art

In an internal combustion engine provided with a compressor in an intake passage, it is necessary to limit the occurrence of a surge or pressure surge in the compressor. This is because a blowback sound (slosh sound) like a sigh is generated by the intake system of the engine when the gush occurs, and this reduces the marketability of a vehicle. The surge occurs because a ratio of pressures on an upstream side and a downstream side of the compressor with respect to a flow rate of air passing through the compressor becomes too large. Therefore, the surge easily occurs when a throttle is quickly closed (for example, when the vehicle is decelerated when an automatic transmission upshift is performed).

One technique for limiting the occurrence of the surge is in JP 2013 - 249 739 A described as an example. The technique disclosed therein is a control technique that can be used for a diesel engine that includes a variable nozzle turbocharger. According to the technique, it is judged whether the compressor comes into a surge state when the vehicle decelerates. Then surge prevention control is performed when it is judged that the compressor is in the surge state. In the surge prevention control, a target opening degree of the variable nozzle based on an operating state and a throttle opening degree and a predetermined target opening degree to avoid the surge are compared. When the target opening degree based on the operating state and the throttle opening degree is equal to or larger than the target opening degree to prevent the surge, the variable nozzle is controlled in accordance with the target opening degree based on the operating state and the throttle opening degree. If the target opening degree is smaller than the target opening degree to avoid the surge based on the operating condition and the throttle opening degree, the variable nozzle is controlled in accordance with the target opening degree to avoid the surge.

The Indian JP 2013 - 249 739 A disclosed stand avoids the surge by reducing the boost pressure by opening the variable nozzle. However, if the boost pressure is reduced, an amount of gas introduced into a cylinder is also reduced. If the diesel engine in which the control technology is used is provided with an EGR device, the gas in the cylinder consists of air (fresh air) and EGR gas. Therefore, reducing an amount of gas in the cylinder means reducing either or both of an amount of air and an EGR amount of gas in the cylinder. When the EGR gas amount in the cylinder is decreased and when an EGR rate becomes insufficient with respect to an appropriate amount, an amount of NOx in the exhaust gas increases. On the other hand, smoke is generated, an amount of HC and CO in the exhaust gas increases, and misfire is caused when the amount of air in the cylinder becomes insufficient compared to an appropriate amount. That is, reducing the boost pressure causes deleterious effects such as deterioration in exhaust emission performance.

For the reason explained above, as a method of avoiding the surge, it is considered to increase the flow rate of the air passing through the compressor to a flow rate capable of avoiding the surge instead of reducing the boost pressure. The throttle can be opened to increase the air flow through the compressor. In the diesel engine, the throttle is normally operated in a closing direction when the vehicle is decelerated. However, if the throttle remains open, the surge can be avoided.

However, if the throttle just remains open, it is likely that an amount of air introduced into the cylinder is too large. When the combustion is started again after decelerating the vehicle, the amount of NOx exhaust gas becomes large when the amount of air in the cylinder is too large. Therefore, the amount of air in the cylinder must be controlled to the appropriate amount. In the case of the diesel engine provided with the EGR device, the flow rate of the air passing through the compressor decreases as a flow rate of the EGR gas introduced into the intake passage increases, while the flow rate of the air passing through the compressor increases when the flow rate of the EGR gas introduced into the intake passage decreases. The means that the flow rate of the air passing through the compressor is indirectly controlled by controlling the flow rate of the EGR gas through the EGR valve and indirectly controlling the amount of air in the cylinder.

However, control of the amount of air by the EGR valve sometimes does not work effectively depending on the throttle closed state. Flow of the EGR gas passing through the EGR valve is generated by a pressure difference between an upstream and a downstream side of the EGR valve, that is, a difference between the pressure in the exhaust passage and the pressure in the intake passage , When the throttle is opened and the pressure in the intake passage is high, the pressure difference between the upstream and the downstream side of the EGR valve is small especially when the fuel injection is stopped as at the time of the deceleration and the pressure in the intake passage is reduced , and you don't get a large flow rate. Therefore, the EGR valve is set to a fully open state when the pressure difference between the upstream side and the downstream side of the EGR valve is very small. In this state, the amount of air cannot be controlled by an opening degree of the EGR valve, and a suitable amount of air at which it is possible to maintain the emission performance cannot be obtained.

In the US 2014/0 041 384 A1 methods and systems for controlling air flow in a two-stage turbocharger are disclosed. In engines with highly variable EGR rates, air flow fluctuations may occur in response to changes in EGR, which may cause gushing or throttling under certain conditions. To ensure that air flow and pressure fluctuations do not cause turbocharger surge or throttling, the air flow can be controlled by a high pressure stage of the turbocharger via a turbine bypass valve. In addition, the engine's EGR rates can be controlled to provide the desired intake oxygen, and under selected conditions, the EGR rates can be controlled to avoid surge in a low pressure stage of the turbocharger.

Furthermore describes the JP 2001 - 280 202 A an exhaust gas recirculation system, which is equipped with a precise controllability for EGR, in that the EGR flow rate is taken exactly from the differential pressure between before and after an EGR valve and the degree of opening of the EGR valve. In this way, the EGR amount can be precisely measured even in a low load range in which the EGR requirement is high.

Further state of the art is still out JP 2002 - 221 050 A . JP 2006 - 183 558 A and JP 2003-097 298 A known.

Brief explanation of the invention

The present invention has been made in light of the problem explained above, and its object is to provide a control device for an internal combustion engine capable of preventing the occurrence of a surge while ensuring air volume controllability.

This object is achieved by a control device with the features of claim 1.

The control device according to the present invention controls the internal combustion engine comprising a compressor provided in an intake passage, a throttle provided downstream of the compressor in the intake passage, and an EGR valve provided in an EGR passage. that connects a downstream side of the throttle in the intake passage with an exhaust passage. The internal combustion engine to be controlled can be an internal combustion engine in which the control of the throttle is carried out, a fully open position being a basic position or starting position of the throttle, for example a diesel engine.

The control device according to the present invention comprises a surge prediction device for predicting the occurrence of a surge in the compressor. Predicting the occurrence of the gush does not mean detecting or estimating a fact that the gush occurs, but means sensing the occurrence of the gush in the near future based mainly on information regarding current and future operating conditions or operating conditions of the internal combustion engine in a situation where the gush has not yet occurred. A specific method for predicting the occurrence of the surge is not limited. One of the preferred methods is to calculate a surge amount of air based on a ratio of pressures upstream and downstream of the compressor or on an upstream and a downstream side of the compressor, and judge that the surge occurs when a target air amount (a setpoint one Air volume that is introduced into the cylinder) is smaller than the surge air volume.

The control device according to the present invention includes a target air amount setting device for setting the target air amount. The device for setting the target air volume is for this constructed to determine the target air quantity according to an operating condition of the internal combustion engine, and to correct the target air quantity to an air quantity capable of avoiding the surge when the surge prediction of the occurrence of the surge. The amount of air that is able to avoid the surge is determined by a relationship to a ratio of the pressure upstream and downstream of the compressor. The target air quantity can be corrected to the surge air quantity, which can be calculated based on the ratio of the pressure on the upstream side and the downstream side of the compressor. It is of course possible to correct the target air quantity to an air quantity with a limit range from the surge limit air quantity, but when considering the emission performance and the like, a corrected target air quantity is preferably as close as possible to the target air quantity is determined based on the operating condition.

The control device according to the present invention comprises an EGR valve control device for controlling the EGR valve. The EGR valve control device is designed to control an opening degree of the EGR valve so that the air quantity introduced into the cylinder becomes the target air quantity set by the target air quantity setting device or target air quantity setting device. Controlling the degree of opening of the EGR valve can be a regulation. In the control, the opening degree of the EGR valve is corrected based on the difference between a predetermined target value of a control quantity calculated on the basis of the target air quantity and an actual value of the control variable.

The control device according to the present invention includes a throttle control device for controlling the throttle. The throttle control device is configured to control a pressure difference between an upstream and a downstream side of the throttle by controlling a degree of closing of the throttle so that the pressure difference, which is equal to or larger than a predetermined value, between an upstream side and on a downstream side of the EGR valve occurs at least when the surge predictor predicts the occurrence of the surge. The control of the degree of closure of the throttle can be a control without feedback or a regulation. The throttle control device may be configured to control the pressure difference between the upstream side and the downstream side of the throttle by controlling the degree of closing of the throttle so that the pressure difference, which is equal to or larger than a predetermined value, between the upstream side and the downstream side of the EGR valve occurs while an amount of air is controlled by the control of the EGR valve by the EGR valve controller. The throttle control device may be configured to reduce pressure on the downstream side of the throttle by controlling the degree of closing of the throttle so that an amount of EGR gas necessary to achieve the target air amount is supplied to the intake passage without that the EGR valve is fully open.

According to the control device of the present invention, the target air amount is corrected to the amount of air capable of avoiding the surge, and the pressure difference between the upstream side and the downstream side of the throttle is so controlled by controlling the degree of closing of the throttle controlled that the pressure difference, equal to or greater than the predetermined value, occurs between the upstream and the downstream side of the EGR valve when a surge is predicted to occur in the compressor. The degree of opening of the EGR valve is then controlled so that the amount of air introduced into the cylinder becomes the corrected target amount of air. Because the pressure difference, which is equal to or larger than the predetermined value, is ensured between the upstream and the downstream side of the EGR valve, control of a flow rate of the EGR gas by the opening degree of the EGR valve is effective, and control of the amount of air in the cylinder is carried out indirectly by controlling the flow rate of the EGR gas. According to the control device of the present invention, the occurrence of the surge can be avoided while ensuring the controllability of the air amount in accordance with the above-mentioned operation.

list of figures

• 1 Fig. 12 is a diagram showing a construction of a machine system according to an embodiment of the present invention;
• 2 Fig. 12 is a diagram showing a control structure of a control device according to the embodiment of the present invention;
• 3 Fig. 12 is a diagram explaining a surge prediction and a target air quantity correction;
• 4 Fig. 14 is a flowchart showing the program of the surge prediction and the target air quantity setting;
• 5 Fig. 11 is a flowchart showing the EGR valve timing program;
• 6 Fig. 14 is a flowchart showing the throttle control program;
• 7 Fig. 12 is a time chart showing an operation realized in the embodiment of the present invention;
• 8th Fig. 11 is a flowchart showing another example of the EGR valve control program;
• 9 Fig. 11 is a flowchart showing another example of the throttle control program;
• 10 Fig. 11 is a flowchart showing another example of the throttle control program; and
• 11 Fig. 10 is a flowchart showing another example of the throttle control program.

Detailed explanation of the preferred embodiments

An embodiment of the present invention will be described below with reference to the figures. Note that the present invention is not limited to the numbers mentioned unless explicitly described otherwise, or when the invention is explicitly specified by the numbers in principle, even if numbers, amounts, sizes, ranges, and the like of the respective elements in FIG in the following embodiment. In addition, structures, steps and the like, which are described in the embodiment as shown below, are not always essential for the present invention, unless this has been explicitly stated otherwise, or unless the invention is explicitly specified in principle by them.

[Structure of the machine system]

1 Fig. 12 is a diagram showing a construction of a machine system according to the embodiment of the present invention. An internal combustion engine of the present embodiment is a diesel engine (which will be simply described as an engine hereinafter) equipped with a turbocharger. In the machine 2 four cylinders are provided in series, and one injection 8th is provided for each of the cylinders. The machine 2 includes an intake manifold 4 and an exhaust manifold 6 , An intake passage 10 , in the air (fresh air) flowing through an air filter 20 is introduced with the intake manifold 4 connected. A compressor 14 of the turbocharger is at the intake passage 4 intended. A thrush 24 is downstream of the compressor in the intake passage 10 intended. An intercooler 22 is between the compressor 14 and the throttle 24 in the intake passage 10 contain. An exhaust passage 12 to release exhaust gas into the atmosphere is with the exhaust manifold 6 connected. A turbine 16 of the turbocharger is in the exhaust passage 12 assembled. A variable nozzle 18 is on the turbine 16 intended. A catalyst device 26 for cleaning the exhaust gas is downstream of the turbine 16 in the exhaust passage 12 intended.

The machine 2 comprises an EGR device for recirculating the exhaust gas from the exhaust system into an intake system. The EGR device connects a downstream side of the throttle 24 in the intake passage 10 and the exhaust manifold 6 through an EGR passage 30 , An EGR valve 32 is in the EGR passage 30 intended. An EGR cooler 34 is on an exhaust side of the EGR valve 32 in the EGR passage 30 contain. In the EGR passage 30 is a bypass passage 36 provided the EGR cooler 34 bypasses. A bypass valve 38 that switches a direction in which the exhaust gas flows is provided at a point where the EGR passage 30 and the bypass passage 36 meet.

In the machine 2 sensors for obtaining information regarding an operating state of the machine 2 are attached at respective points. An air flow meter 58 for measuring a flow rate of air in the intake passage 10 is recorded, is downstream of the air filter 20 in the intake passage 10 appropriate. pressure sensors 62 and 64 are respectively downstream and upstream of the compressor 14 intended. A pressure sensor 56 and a temperature sensor 60 are between the intercooler 22 and the throttle 24 appropriate. A pressure sensor 54 is downstream of the throttle 24 appropriate. There is also a crankshaft angle sensor 52 that detects the rotation of a crankshaft, an accelerator position sensor or accelerator opening degree sensor 66 , which outputs a signal suitable for an opening degree of an accelerator pedal or a position of an accelerator pedal, and the like.

The various sensors and actuators as described above are electrical with the control device 100 connected. The control device 100 is an ECU (Electronic Control Unit). The control device 100 controls the entire system of the machine 2 through and consists mainly of a computer that has a CPU, ROM and RAM. Various types of control programs, which will be described later, are stored in the ROM. The program or programs are carried out by the control device 100 executed, and the actuators are actuated based on signals from the sensors, causing operation of the machine 2 is controlled.

[Control Structure of Control Device]

2 Fig. 10 is a block diagram showing a control structure of the control device 100 shows. The in 2 The control structure shown includes a target air quantity setting unit 102 as a target air quantity setting device, an EGR valve control unit 104 as EGR valve control device, a throttle control unit 106 as a throttle control device and a surge prediction unit 108 as a surge prediction device. These units that are in the control device 100 are included, corresponding to that in the ROM of the control device 100 stored control program, or correspond to a part of the control program. The control program is read out from the ROM and is executed in the CPU, whereby functions of these units by the control device 100 will be realized.

A function of the target air quantity setting unit 102 is described. The target air quantity setting unit 102 specifies a target air quantity that is a target value of an air quantity introduced into a cylinder. The target air quantity is an air quantity that can meet fuel efficiency performance and emission performance required for the engine 2 can be requested, and is adapted to information indicating an operating state of the machine 2 shows, more specifically, the engine speed and a fuel injection amount. In one in the ROM of the control device 100 stored target air quantity map, the target air quantity is linked to the engine speed and the fuel injection quantity. The target air quantity setting unit 102 searches the target air quantity map to match the engine speed and the fuel injection quantity, and sets an air quantity obtained by a search as the target air quantity. Note that the amount of fuel injected for the next time for injection 8th is used in the search.

The target air quantity setting unit 102 has a function of adding the correction to the target air quantity obtained from the target air quantity map. The correction is made after a request from the gush prediction unit 108 received, which will be described next. During a surge prediction flag in the surge prediction unit 108 is set to On, the target air quantity setting unit corrects 102 the target air volume to a surge limit air volume, which is provided by the surge prediction unit 108 is delivered.

Next, a function of the surge prediction unit 108 described. The surge prediction unit 108 says the appearance of a surge in the compressor 14 ahead. A condition under which the surge occurs can be determined by a relationship of a ratio between a pressure downstream of the compressor 14 and a pressure upstream of the compressor 14 (which will be described below as a compressor pressure ratio) and a flow rate of air flowing through the compressor 14 goes. The ratio between the pressure downstream of the compressor 14 and the pressure upstream of the compressor 14 (the compressor pressure ratio) is the ratio of the pressure downstream of the compressor 14 to the pressure upstream of the compressor 14 , A value of the ratio of the pressure becomes greater than 1 in a turbocharger area in which charging by the compressor 14 is carried out. The flow rate of air through the compressor 14 corresponds to an amount of air (an amount of air per cycle) that is introduced into the cylinder. In addition, the target air volume is also a future value of the air volume in the cylinder (an air volume that will be realized in the near future). As a result, whether or not the surge will occur in the very near future can be judged based on the relationship between the compressor pressure ratio and the target air amount.

Here shows 3 an area (a surge occurrence area) in which the surge occurs on a plane that spans the compressor pressure ratio and the amount of air as axes. An amount of air at a limit of the range of occurrence of the surge, that is, an amount of air that is the criterion of whether the surge occurs, is a surge limit amount of air. As in 3 shown, the surge air quantity has a one-to-one relationship or linear relationship to the compressor pressure ratio and is greater when the compressor pressure ratio is higher. The relationship between surge air quantity and compressor pressure ratio is examined in advance by an experiment and in the ROM of the control device 100 mapped and saved.

In 3 An example of a trajectory of the target air volume is drawn, on which a vehicle is accelerated and decelerated abruptly. Because the target air volume matches the operating status of the machine 2 (the engine speed and the fuel injection amount) is set, the target air amount increases at the time of acceleration and decreases at the time of deceleration. In the example, the target air quantity is reduced to the surge air quantity at the time of the delay. The trajectory that in 3 as the dotted line is shown, is a trajectory of the target air amount in a case where the target air amount is from the operating state of the engine 2 is determined even after the target air quantity is reduced to the surge air quantity. If the target air quantity is set as a trajectory, the probability of the surge occurring is extremely high. The surge prediction unit 108 predicts that the surge in the compressor 14 occurs when the target air volume becomes smaller than the surge air volume.

Back to 2 the explanation of the in 2 shown tax structure continued. The surge prediction unit 108 has a function of showing the surge prediction flag. The surge prediction flag or surge prediction flag is normally set to off. If the gush prediction unit 108 predicts the surge in the compressor 14 occurs, the surge prediction unit switches 108 the surge prediction flag from off to on. The surge prediction flag is held on until the target air quantity again becomes equal to or greater than the surge limit air quantity. With the surge prediction flag set to On, the surge prediction unit outputs 108 the surge air volume to the target air volume setting unit 102 from. In addition, the surge prediction flag also becomes the throttle control unit described later 106 shown or given to them.

Next, a function of the EGR valve control unit 104 described. The EGR valve control unit 104 takes the target air volume from the target air volume setting unit 102 on. The EGR valve control unit then controls 104 an opening degree of the EGR valve 32 so that the amount of air introduced into the cylinder becomes the target amount of air. The opening degree control by the EGR valve control unit 104 is carried out is a feedback control or regulation. However, there is no direct relationship between the degree of opening of the EGR valve 32 and the amount of air. Therefore, a control variable is directly related to the opening degree of the EGR valve 32 relates, more specifically, a target value of an EGR rate, calculated based on the target air quantity. The EGR valve control unit 104 determines a basic degree of opening of the EGR valve 32 based on the information indicating the operating status of the machine 2 displays, and calculates a correction amount for the basic opening degree based on a deviation between a target EGR rate and an actual EGR rate. The correction amount can be expressed, for example, as a sum of a proportional term and an integral term with respect to a deviation. The EGR valve control unit 104 gives a calculated EGR valve opening degree to the EGR valve 32 as a command value.

Next, a function of the throttle control unit 106 described. The throttle control unit 106 controls the throttle 24 matching a degree of closure with respect to a fully open position, the fully open position being a base position of the throttle 24 is. If that's from the gush prediction unit 108 The surge prediction flag shown is set to On, the throttle control unit takes 106 based on a target pressure difference map stored in the ROM, a target value of the pressure difference (a target pressure difference) that exists between an upstream and a downstream side of the throttle 24 is produced. The target pressure differential is set by adding to the information that indicates the operating status of the machine 2 (for example, the engine speed and the fuel injection amount) shows that the pressure difference, which is equal to or larger than a predetermined value, between the upstream side and the downstream side of the EGR valve 32 occurs.

When the vehicle decelerates or when the automatic transmission is shifted up, the surge occurs easily and the exhaust pressure drops because the fuel injection is stopped or the amount of fuel injected decreases. Accordingly, the pressure difference between the upstream side and the downstream side of the EGR valve tends 32 occurs, to be small. When the pressure difference is small, that between the upstream side and the downstream side of the EGR valve 32 occurs, the flow rate necessary to reach the target air volume cannot be achieved even if the EGR valve 32 is fully open. Hence the EGR valve 32 fully opened and the degree of opening of the EGR valve 32 established. If the EGR valve 32 is fully open and the degree of opening of the EGR valve 32 is set, the amount of air cannot be controlled and an appropriate amount of air cannot be obtained to maintain the emission performance. As a result, there must be a pressure difference between the upstream side and the downstream side of the EGR valve 32 generated that is equal to or greater than the minimum pressure difference required to control the amount of air. The pressure difference, which is the same as or larger than the predetermined value as described above, is a pressure difference which is the same as or larger than the minimum for the air flow control by the EGR valve 32 necessary pressure difference is. The target pressure difference described above is set so that it is capable of realizing the pressure difference. The throttle control unit 106 calculates a throttle closing degree based on the target pressure difference that is recorded and gives the throttle closing degree that for the throttle 24 is calculated as a command value.

Note that the air quantity control is an air quantity control by means of the throttle 24 and air flow control using the EGR valve 32 includes. Air flow control using the EGR valve 32 relates to the present invention. While controlling the air volume using the EGR valve 32 is carried out, controls the throttle control unit 106 the pressure difference between the upstream side and the downstream side of the throttle 24 by controlling the degree of closure of the throttle 24 so that the pressure difference between the upstream side and the downstream side of the EGR valve required for the air flow control 32 is produced. It also includes control in a situation where the surge prediction flag is set. However, a target pressure difference map used when the surge prediction flag is set to On may be prepared separately from the target pressure difference map normally used.

Next, a program for realizing the functions of respective units described above 102 . 104 . 106 and 108 in the control device 100 using a flowchart.

[Program of the surge prediction and determination of the target air volume]

4 is a flowchart showing a program for realizing the functions of the target air quantity setting unit 102 and the surge prediction unit described above 108 in the control device 100 shows. The control device 100 leads that in 4 shown program in a constant control cycle. Processes in the program are sequentially described step by step below.

In step S101 becomes pressure in an inlet of the compressor 14 (Pressure on the upstream side of the compressor) recorded based on a signal from the pressure sensor 62 is measured. There is also pressure in an outlet of the compressor 14 (the pressure downstream of the compressor) recorded based on a signal from the pressure sensor 64 is measured. Note that the control device 100 always receives signals from the respective sensors that the pressure sensors 62 and 64 and measures various state variables (which also include the pressure upstream of the compressor and the pressure downstream of the compressor as described above) on the basis of the signals from the respective sensors, which determine the operating state of the machine 2 Show.

In step S102 the compressor pressure ratio is calculated based on the ratio of the pressure on the downstream side of the compressor to the pressure on the upstream side.

In step S103 a surge limit air quantity map is recorded, which is stored in the ROM. The surge air quantity map is a map that specifies the relationship between the surge air quantity and the compressor pressure ratio.

In step S104 becomes the surge limit air quantity map that in step S103 is recorded based on the compressor pressure ratio searched in step S102 is calculated. This search calculates the surge air volume to match the current compressor pressure ratio.

In step S105 the target air volume is recorded. The target air quantity is determined by searching the target air quantity map for the engine speed and the fuel injection quantity in another program that is executed in parallel with this program.

In step S106 become the target air volume in step S105 is recorded, and the surge air volume that in step S104 is compared. If the target air quantity is equal to or larger than the surge limit air quantity, it can be judged that an operating range of the compressor 14 at least in a next control cycle does not come into a range of occurrence of the surge. If the target air volume is less than the surge air volume, it can be judged that the operating range of the compressor 14 comes into the surge area in the next control cycle. As a result, the following operation is performed depending on the comparison result.

If the target air quantity is equal to or greater than the surge air quantity, an operation in step S107 executed. In step S107 the surge prediction flag is set to off. In this case, the target air volume is not corrected. The target air quantity determined based on the engine speed and the fuel injection quantity is directly set as a final target air quantity.

If the target air amount is smaller than the surge limit air amount, operations in the step S108 and step S109 executed. In step S108 the surge prediction flag is set to on. The surge prediction flag is held on until the result of the step judgment S106 is confirmed and the process in step S107 is performed.

Then in step S109 corrected the target air volume. Instead of the target air quantity determined on the basis of the engine speed and the fuel injection quantity, the surge limit air quantity is set as a new target air quantity, which in step S104 is calculated.

[EGR valve timing program]

5 is a flowchart showing a program for realizing the function of the EGR valve control unit 104 shows the above in the control device 100 is described. The control device 100 leads that in 5 shown program in a constant control cycle. Processes in the program are sequentially described step by step below.

In step S201 the target air volume is recorded, which finally matches the in 4 shown program is set. When the surge prediction flag is set to off, the target air quantity that is taken in here is the target air quantity that is determined based on the engine speed and the fuel injection quantity. When the surge prediction flag is set to On, the target amount of air that is taken in is the surge amount of air.

In step S202 a total amount of gas is taken up in the cylinder. The total amount of gas in the cylinder is a sum of the amount of air and an EGR amount of gas. A calculation method of the total amount of gas in the cylinder is not limited. For example, the total amount of gas in the cylinder can be estimated based on the pressure in the cylinder measured by a pressure sensor (not shown) in the cylinder. In addition, the total amount of gas in the cylinder can be measured based on a signal from a flow rate sensor when the flow rate sensor is attached to an inlet port.

In step S203 the target EGR rate is calculated. Here, a ratio of a gas amount obtained by subtracting the target air amount from the total air amount in the cylinder to the total gas amount in the cylinder is calculated. A value obtained by this calculation is calculated as the target EGR rate.

In step S204 the actual EGR rate is recorded. A calculation method of the actual EGR rate is not restricted. For example, the actual EGR rate can be estimated based on the flow rate of the EGR gas, based on the opening degree of the EGR valve 32 and the pressure difference between the upstream and downstream sides of the EGR valve 32 and a flow rate of intake air calculated by the air flow meter 58 is measured.

In step S205 there will be a discrepancy between that in step S203 calculated target EGR rate and that in step S204 actual EGR rate calculated.

In step S206 A P gain or proportional gain and an I gain or integral gain for the feedback control are each recorded from a gain map stored in the ROM.

In step S207 becomes the basic opening degree of the EGR valve 32 while performing the air flow control through the EGR valve 32 from a basic opening degree map stored in the ROM. The basic opening degree is an adjustment value of the opening degree of the EGR valve 32 which is necessary to achieve the target air volume when the EGR valve 32 performs the air volume control. In the basic opening degree map, the basic opening degree is shown with the operating state of the machine 2 or the target air volume.

In step S208 are the proportional term (P term) and the integral term (I term) for the PI control due to the deviation of the in step S205 calculated EGR rate, and that in step S206 recorded P-gain and I-gain are calculated. Then the P term and the I term become in step S207 added basic opening degree added as correction quantities, whereby the EGR valve opening degree is calculated. The calculated EGR valve opening degree is given to the EGR valve as the command value.

[Throttle control program]

6 is a flowchart showing the program for realizing the function of the throttle control unit described above 106 in the control device 100 shows. The control device 100 leads that in 6 shown program in a constant control cycle. Processes in the program are sequentially described step by step below.

In step S301 the intake air flow rate is recorded based on a signal from the air flow meter 58 is measured. In addition, the temperature of the upstream side of the throttle 24 (the temperature upstream of the throttle) recorded based on a signal from the temperature sensor 60 is measured. In addition, the pressure on the upstream side of the throttle (pressure upstream of the throttle) 24 recorded based on a signal from the pressure sensor 56 is measured.

In step S302 becomes the target pressure difference between the upstream side and the downstream side of the throttle 24 recorded from a target pressure difference map. The target pressure difference is the minimum pressure difference required for the air volume control by the EGR valve 32 is necessary, and is more precisely determined in a range from 3 to 5 kPa.

In step S303 becomes a target value of the pressure on the downstream side of the throttle 24 (the target pressure on the downstream side of the throttle) by subtracting the in step S302 Recorded target pressure difference from the pressure upstream of the throttle calculated in the step S301 is recorded.

$$\varphi \left(\frac{Pds}{Pus}\right)=\{\begin{array}{lll}\sqrt{\frac{\kappa }{\kappa -1}\ast \left({\left(\frac{Pds}{Pus}\right)}^{\frac{2}{\kappa }}-{\left(\frac{Pds}{Pus}\right)}^{\frac{\kappa +1}{\kappa }}\right)}\hfill & falls\hfill & \frac{Pds}{Pus}\ge {\left(\frac{2}{\kappa +1}\right)}^{\frac{1}{\kappa -1}}\hfill \\ {\left(\frac{2}{\kappa +1}\right)}^{\frac{1}{\kappa -1}}\ast \sqrt{\frac{\kappa }{\kappa +1}}\hfill & falls\hfill & \frac{Pds}{Pus}<{\left(\frac{2}{\kappa +1}\right)}^{\frac{1}{\kappa -1}}\hfill \end{array}$$

In step S304 becomes an effective opening area or opening area of the throttle 24 using equation (1), which is a model equation of the throttle 24 is calculated for the throttle as follows. In equation (1) below, Ga represents the air flow rate [kg / sec], µA represents the effective opening area [m ² ], Pus represents the pressure [Pa] upstream of the throttle, Pds represents the pressure [Pa] downstream of the throttle again, Tus shows the temperature [K] upstream of the throttle, R shows a gas constant (J / K * kg) and κ shows the specific heat ratio. Respectively in the crotch S301 Measured values are read in for “Ga”, “Pus” and “Tus”, and the target pressure on the downstream side of the throttle, which in step S303 is calculated, is entered as "Pds".
[Mathematical equation 1] $$\mu A=\frac{Pus*\sqrt{\frac{2}{R*Tus}}*\phi \left(\frac{Pds}{Pus}\right)}{Ga}$$

$$\phi \left(\frac{Pds}{Pus}\right)=\{\begin{array}{lll}\sqrt{\frac{\kappa }{\kappa -1}*\left({\left(\frac{Pds}{Pus}\right)}^{\frac{2}{\kappa }}-{\left(\frac{Pds}{Pus}\right)}^{\frac{\kappa +1}{\kappa }}\right)}\hfill & falls\hfill & \frac{Pds}{Pus}\ge {\left(\frac{2}{\kappa +1}\right)}^{\frac{1}{\kappa -1}}\hfill \\ {\left(\frac{2}{\kappa +1}\right)}^{\frac{1}{\kappa -1}}*\sqrt{\frac{\kappa }{\kappa +1}}\hfill & falls\hfill & \frac{Pds}{Pus}<{\left(\frac{2}{\kappa +1}\right)}^{\frac{1}{\kappa -1}}\hfill \end{array}$$

In step S305 the degree of closure of the throttle 24 based on the effective opening area of the throttle 24 calculated that in step S304 is calculated using the characteristic map for the throttle closing degree stored in the ROM. There is a correlation between the degree of throttle closure and the effective opening area, which can be approximated by a linear equation. The relationship is set in the characteristic map for the degree of throttle closing. The calculated throttle closing degree is called the command value to the throttle 24 issued.

[Operation Realized by the Control Device]

7 Fig. 3 is a time chart showing the control device 100 realized operation shows. This in 7 The time chart shown shows respective changes in an accelerator opening degree over time, the fuel injection quantity, the target air quantity, an actual air quantity, the EGR valve opening degree, the throttle closing degree and the pressure difference between the upstream side and the downstream side of the throttle 24 in a case of performing abrupt acceleration and deceleration from an idling state in which the accelerator pedal is not depressed. A function and an effect of the machine control according to the present embodiment will be described below with reference to the time chart.

In the time chart, the accelerator opening degree is switched from a fully closed state at time t1 to a fully open state. The fuel injection amount is increased abruptly by changing the accelerator opening degree at time t1. Subsequently, the engine speed (not shown) increases due to an abrupt increase in the fuel injection quantity and the target air quantity, which is determined on the basis of the engine speed and the fuel injection quantity, also increases continuously from the time t1. The increase in the speed of the target air quantity at this time is the maximum realizable change speed, and in order to make the actual air quantity follow, the throttle 24 fully open while the EGR valve 32 is completely closed. The throttle 24 opens fully, creating the pressure difference between the upstream and downstream sides of the throttle 24 is reduced to a minimum value.

In the time diagram, the accelerator pedal actuation degree is switched over again from the completely open state at time t2 to the completely closed state. The fuel injection is stopped by changing the accelerator operation at time t2. The engine speed (not shown) is decreased by stopping fuel injection, and the target air amount determined based on the engine speed and the fuel injection amount is abruptly decreased at time t2. In the time chart, the target air amount, which is determined based on the engine speed and the fuel injection amount, is drawn in a dotted line after the time t2. After the control device 100 the correction of the target air quantity is carried out as drawn by a solid line in order to avoid the occurrence of the surge. The target amount of air after the correction is the surge threshold amount of air, which is a minimum amount of air, the minimum amount of air being able to avoid the surge.

In the time chart, the throttle closing degree in a case where the throttle is kept fully open to cope with the gush is plotted in a dotted line after the time t2, and the pressure difference between the upstream and the downstream side of the throttle is thereby is drawn in a dotted line. When the throttle is kept fully open, the pressure difference between the upstream side and the downstream side of the throttle 24 kept at the minimum value. After the time t2, the air volume control by means of the EGR valve 32 performed, however, when the pressure difference between the upstream side and the downstream side of the throttle 24 has the minimum value, the pressure difference between the upstream side and the downstream side of the EGR valve 32 also a minimum value. Hence the EGR valve 32 fully opened as shown in a dotted line, and the degree of opening of the EGR valve 32 is defined. In this case, the target air amount cannot be realized, and as shown in a dotted line, the actual air amount becomes larger than the target air amount. At the control device 100 however, as shown with a solid line, the degree of closure of the throttle is 24 controlled, and the pressure difference between the upstream side and the downstream side of the throttle 24 is controlled in such a way that it is possible to ensure the minimum pressure difference required for air volume control. Hence the opening degree of the EGR valve 32 not in a state with the EGR valve fully open 32 and the air volume control through the degree of opening of the EGR valve 32 becomes effective as shown with a solid line. As a result, the actual amount of air after the control device 100 follow the target air volume as drawn with a solid line.

In the time diagram, the fuel injection is started again at time t3. If the actual amount of air is too large compared to the target amount of air at time t3 as shown by the dotted line, the actual EGR rate is much smaller than an appropriate EGR rate, and a generated amount of NOx increases. After the control device 100 However, a deviation between the actual air amount and the target air amount can be restricted as shown by the solid line. In addition, the target air quantity at time t3 is the surge air quantity and is larger than an air quantity based on the operating state of the machine 2 is determined, but the difference is kept to a minimum, and therefore the increase in the amount of NOx generated is restricted.

As described above, after the control device 100 the occurrence of the surge can be avoided while the controllability of the air volume is ensured.

[Another example of EGR valve timing program]

8th FIG. 10 is a flowchart showing another example of a program for realizing the above-described function of the EGR valve control unit 104 in the control device 100 shows. In 8th have processes with the same content as in the program of in 5 EGR valve timing shown the same step numbers. In the in 8th The program shown is the process in step S203 in the in 5 shown program through operations in the steps S211 and S212 replaced.

In step S211 a basic target EGR rate is recorded from a basic target EGR rate map stored in the ROM. In this map is the basic target EGR rate with the operating state of the machine 2 or the target air volume.

In step S212 the target EGR rate is calculated. Here, a ratio of an amount of gas obtained by multiplying the basic target EGR rate by the total amount of gas in the cylinder is calculated to an amount of gas which is a sum of the amount of gas obtained by multiplying the basic target EGR rate with the total amount of gas in the cylinder and the target amount of air. A value obtained by this calculation is set as the target EGR rate.

[Another example 1 of the throttle control program]

9 10 is a flowchart showing another example 1 of the program for realizing the function of the throttle control unit described above 106 in the control device 100. In 9 operations that have the same content as in 6 have shown program for throttle control, assigned the same step numbers. In the in 9 shown program, the operations in the steps S304 and S305 in the in 6 shown program through the operations in the steps S311 and S312 replaced.

In step S311 a throttle closing degree map is recorded, which is stored in the ROM. The throttle closing degree map is a map in which the throttle closing degree is related to the flow rate of the intake air, the pressure upstream of the throttle, the pressure downstream of the throttle and the temperature upstream of the throttle. The map is formed on the basis of data obtained by adaptation.

In step S312 it will in step S311 Recorded map for the degree of throttle closing on the basis of corresponding measured values in the step S201 be included, and the step S303 The target pressure calculated downstream of the throttle is searched, and the throttle closing degree that matches a search condition is calculated. The calculated throttle closing degree is called the command value to the throttle 24 output.

[Another example 2 of a throttle control program]

10 Fig. 3 is a flowchart showing another example 2 of the program for realizing the function of the throttle control unit 106 as described above in the control device 100. During the throttle closing degree in the respective program as in 6 and 9 is calculated by a feed-forward control, the degree of throttle closing is in the 10 shown program calculated by the feedback scheme. Operations in the program are sequentially described step by step below.

In step S321 the pressure on the upstream side of the throttle 24 (the pressure upstream of the throttle) is recorded based on the signal from the pressure sensor 56 is measured. In addition, the pressure on the downstream side of the throttle 24 (the pressure downstream of the throttle) is recorded based on a signal from the pressure sensor 54 is measured.

In step S322 becomes the target pressure difference between the upstream side and the downstream side of the throttle 24 taken from the target pressure difference map.

In step S323 becomes the actual pressure difference between the upstream side and the downstream side of the throttle 24 by subtracting the pressure downstream of the throttle from the pressure upstream of the throttle in step S321 was recorded, calculated.

In step S324 there will be a deviation between the target pressure difference that you see in step S322 and the actual pressure difference that occurs in step S323 is calculated, calculated. A correction quantity of the throttle closing degree is then calculated by the feedback control (for example the PI control) in order to bring the deviation to zero.

In step S325 becomes a new throttle closing degree by adding the in step S324 calculated correction variable for the existing degree of throttle closing. The calculated throttle closing degree is called the command value to the throttle 24 issued.

[Another example 3 of the throttle control program]

11 Fig. 3 is a flowchart showing another example 3 of the program for realizing the function of the throttle control unit 106 as described above in the control device 100 shows. In the 11 receive operations that have the same content as the throttle control program as in 10 shown, assigned the same step numbers. In the in 11 shown program, the operations in the steps S323 and S324 in the in 10 shown program through the processes in the steps S331 and S332 replaced.

In step S331 the target pressure is downstream of the throttle by subtracting the step S322 Recorded target pressure difference from the pressure upstream of the throttle calculated in the step S321 is recorded.

In step S332 there will be a discrepancy between the actual pressure downstream of the throttle in step S321 is recorded, and the target pressure downstream of the throttle calculated in the step S331 is recorded. Then the correction quantity of the throttle closing degree, in order to make the deviation zero, is calculated by the feedback control (for example the PI control).

[Other modifications]

The compressor provided in the intake passage of the engine may be driven by the crankshaft or may be driven by an electric motor.

LIST OF REFERENCE NUMBERS

2

Machine or internal combustion engine

4

intake manifold

6

exhaust manifold

8th

injection

10

intake passage

12

Exhaust passage

14

compressor

16

turbine

24

throttle

30

EGR passage

32

EGR valve

52

Crank angle sensor

54, 56, 62, 64

pressure sensor

60

temperature sensor

66

Accelerator opening sensor or accelerator actuation sensor

100

control device

Claims (5)

An internal combustion engine control device comprising a compressor (14) provided in an intake passage (10), a throttle (24) provided downstream of the compressor (14) in the intake passage (10), and one EGR valve (32) provided in an EGR passage (30) connecting a downstream side of the throttle (24) in the intake passage (10) to an exhaust passage (12), with: a surge predictor to predict the occurrence of a surge in the compressor (14); target air quantity setting means for determining a target air quantity suitable for an operating state of the internal combustion engine and for correcting the target air quantity for an air quantity capable of avoiding the surge when the occurrence of the surge by the surge predictor is predicted; EGR valve control means for controlling an opening degree of the EGR valve (32) so that an amount of air introduced into a cylinder becomes the target air amount determined by the target air amount setting means; and throttle control means for controlling a pressure difference between an upstream and a downstream side of the throttle (24) by controlling a degree of closing of the throttle (24) so that a pressure difference equal to or larger than a predetermined value between an upstream side and a downstream side of the EGR valve (32) occurs at least when the occurrence of the surge is predicted by the surge predictor, wherein the degree of closure of the throttle (24) is regulated by a control in which, by calculating the deviation between a target pressure difference between the upstream and downstream sides of the throttle (24) and an actual pressure difference between the upstream side and one downstream of the throttle (24), a correction amount of the closing degree of the throttle (24) is calculated, whereby a new closing degree of the throttle (24) is calculated by adding the calculated correction amount to the present closing degree of the throttle (24). Control device for the machine with internal combustion after Claim 1 wherein the throttle controller controls the pressure difference between the upstream and downstream sides of the throttle (24) by controlling the degree of closing of the throttle (24) so that the pressure difference, which is equal to or greater than a predetermined value, between the upstream and downstream sides of the EGR valve (32) occurs while an amount of air is controlled by the control of the EGR valve (32) by the EGR valve controller. Control device for the machine with internal combustion after Claim 1 or 2 wherein the throttle control means reduces the pressure of the downstream side of the throttle (24) by controlling the degree of closing of the throttle (24) so that an amount of EGR gas necessary to reach the target air amount is supplied to the intake passage ( 10) is supplied without fully opening the EGR valve (32). Control device for the internal combustion engine according to one of the Claims 1 to 3 wherein the surge predictor calculates a surge threshold air amount based on a ratio between the pressure on a downstream side of the compressor (14) and the pressure on an upstream side of the compressor (14), and judges that the surge occurs when the target air amount is less than the surge air volume. Control device for the machine with internal combustion after Claim 4 wherein the target air amount setting means corrects the target air amount to the surge limit air amount when the occurrence of the surge is predicted by the surge prediction means.

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