JP2005351199A - Engine control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an engine control system capable of making intake pressure/EGR ratio follow a target value more quickly in most operating states in which hunting is not generated and prioritizing EGR control over intake pressure control only when the hunting is generated. <P>SOLUTION: Only when the hunting which gives a negative impact on exhaust gas is generated, the opening of a variable nozzle 33 is fixed and the opening of an EGR control valve 42 is controlled to be the target value. Then, the opening of the EGR control valve 42 is fixed and the opening of the variable nozzle 33 is controlled to be the target value. Thereby, in the most operating states in which the hunting is not generated or the hunting gives no negative impact on the exhaust gas, the variable nozzle 33 and the EGR control valve 42 are independently controlled, which makes it possible for a high drivability to be compatible with a high exhaust gas purification capability in the most operating states. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an engine control system including a variable nozzle turbocharger (hereinafter referred to as VNT) and an EGR device (exhaust gas recirculation device), and in particular, a variable nozzle in the VNT and an EGR control valve in the EGR device. It is related with the technique of avoiding the malfunction by hunting.
In the present invention, the simple term “exhaust pressure” refers to the exhaust pressure upstream of the variable nozzle.
In the present invention, “open” of the variable nozzle and the EGR control valve means that the opening degree is displaced in the opening direction, and “closed” of the variable nozzle and the EGR control valve is that the opening degree is displaced in the closing direction. It means to do.

The VNT includes a variable nozzle that adjusts the intake pressure (supercharging pressure) of the engine by adjusting the opening of a nozzle (which forms part of the exhaust passage) that blows exhaust gas to the exhaust turbine.
On the other hand, the EGR device includes an EGR control valve that adjusts the EGR rate of the exhaust gas with respect to the intake air by adjusting the opening degree of the EGR path for returning a part of the exhaust gas upstream of the variable nozzle to the intake side. .

Thus, since the variable nozzle of the VNT adjusts the opening degree of the nozzle that forms a part of the exhaust passage, the exhaust pressure increases when the variable nozzle closes (opening degree, small) (variable nozzle: closed → If the variable nozzle opens (opening, large), the exhaust pressure decreases (variable nozzle: open → exhaust pressure: lower).
Further, the EGR control valve of the EGR device adjusts the opening degree of the EGR path that connects the exhaust upstream side and the intake side of the variable nozzle. Therefore, when the EGR control valve closes (opening degree, small), the exhaust pressure Increases (EGR control valve: closed → exhaust pressure: increased), conversely, when the EGR control valve opens (opening, large), the exhaust pressure decreases (EGR control valve: open → exhaust pressure: decreased).

In this way, the exhaust pressure changes when the opening of the variable nozzle changes, and the exhaust pressure changes even when the opening of the EGR control valve changes. Therefore, controlling either one will affect the other. It will occur.
For this reason, if the opening degrees of the variable nozzle and the EGR control valve are controlled simultaneously, hunting may occur in the opening changes of the variable nozzle and the EGR control valve due to mutual influences.

A specific example will be described with reference to FIG.
(1a) The target intake pressure rises due to a change in the operating state, and the control means for controlling the opening of the variable nozzle rapidly reduces the opening of the variable nozzle (variable nozzle: closed).
(1b) When the variable nozzle is closed, the exhaust pressure in the “A region” increases.
(1c) When the exhaust pressure in the “A region” increases, the EGR amount (exhaust amount returned to the intake side) increases and the actual fresh air amount decreases.
(1d) The control means for controlling the opening degree of the EGR control valve reduces the opening degree of the EGR control valve in order to increase the actual fresh air amount when the actual fresh air amount detected by the airflow sensor decreases (EGR control Valve: closed).

(2a) When the EGR control valve is closed, the exhaust pressure in the “A region” increases.
(2b) When the exhaust pressure in the “A region” increases, the rotational speed of the exhaust turbine increases and the actual intake pressure increases.
(2c) The control means for controlling the opening degree of the variable valve increases the opening degree of the variable valve to reduce the actual intake pressure when the actual intake pressure detected by the intake pressure sensor increases (variable valve: open). .
(2d) When the variable valve is opened, the exhaust pressure in the “A region” decreases.
(2e) When the exhaust pressure in the “A region” decreases, the EGR amount decreases and the actual fresh air amount increases.
(2f) The control means for controlling the opening degree of the EGR control valve increases the opening degree of the EGR control valve in order to reduce the actual fresh air amount when the actual fresh air amount detected by the airflow sensor increases (EGR control Valve: Open).

(3a) When the EGR control valve opens, the exhaust pressure in the “A region” decreases.
(3b) When the exhaust pressure in the “A region” decreases, the rotational speed of the exhaust turbine decreases and the actual intake pressure decreases.
(3c) The control means for controlling the opening of the variable valve reduces the opening of the variable valve to increase the actual intake pressure when the actual intake pressure detected by the intake pressure sensor decreases (variable valve: closed). .
Next, returning to (1b) above, hunting is repeated to repeat the above.

Thus, when hunting occurs in the opening change of the variable nozzle and the EGR control valve, the control for converging the intake pressure to the target intake pressure is disturbed by the EGR control, and the control for converging the EGR rate to the target EGR rate is performed. Control will be disturbed.
That is, due to the occurrence of hunting, the intake pressure control and the EGR control are disturbed with each other, and it takes a long time for both the intake pressure and the EGR rate to converge to the target value.

When hunting occurs, as described above, it takes a long time for both the intake pressure and the EGR rate to converge to the target value. Therefore, there is a technology that always prioritizes EGR control and preferentially prevents exhaust deterioration. It has been proposed (see, for example, Patent Document 1).
However, the technology that always gives priority to the EGR control is a technology that controls the intake pressure to the target intake pressure after controlling the EGR rate to the target EGR rate, so that the intake pressure and the EGR rate immediately after the operating state fluctuates. When it is necessary to change both of these, even if hunting does not occur, the follow-up performance of the intake pressure is always delayed.
JP 2001-329901 A

  The present invention has been made in view of the above problems, and its purpose is to give priority to EGR control over intake pressure control only when hunting occurs, and in most operating states where hunting does not occur, The object is to provide an engine control system capable of causing the EGR rate to follow the target value earlier.

[Means of claim 1]
When the engine control system adopting the means of claim 1 determines that the hunting determination means determines that hunting has occurred in the change in opening of the variable nozzle and the EGR control valve, the hunting countermeasure means controls the opening of the variable nozzle ( The opening degree control (EGR control) of the EGR control valve is prioritized over the intake pressure control).
As a result, only when hunting occurs, the EGR rate can be made to follow the appropriate value earlier, and deterioration of exhaust gas due to hunting can be suppressed.
On the other hand, in most operating states in which hunting does not occur, the nozzle opening degree control means and the EGR opening degree control means independently control the intake pressure and the EGR rate, so that the intake pressure and the EGR rate can be set to the target values earlier. (Target intake pressure, target EGR rate) can be followed.

[Means of claim 2]
The engine control system employing the means of claim 2 does not activate the hunting countermeasure means when the exhaust deterioration judging means does not judge exhaust deterioration.
That is, since the hunting countermeasure means is activated only when it is determined that the exhaust gas has deteriorated, the frequency of delay in intake pressure control can be reduced.

[Means of claim 3]
The engine control system employing the means of claim 3 is a preset hunting determination start condition (for example, when exhaust deterioration is determined, when the opening of the variable nozzle and the EGR control valve is changed simultaneously, or is set in advance. Hunting determination means determines whether or not the variable nozzle and the EGR control valve are hunted.

[Means of claim 4]
The hunting determination means of the engine control system adopting the means of claim 4 has a predetermined number of inversions in the opening and closing direction of the variable nozzle within a predetermined time and a predetermined number of inversions in the opening and closing direction of the EGR control valve. When the number of times is equal to or greater than the number of times, hunting is determined.
The predetermined time may be a predetermined time set in advance, or may be set in length according to the driving state.

[Means of claim 5]
The hunting countermeasure means of the engine control system adopting the means of claim 5, when the hunting determination means determines hunting, (1) the opening of the variable nozzle is fixed, the target fresh air amount according to the operating state, The opening degree of the EGR control valve is controlled so that the actual fresh air amount detected by the airflow sensor substantially matches. (2) When the actual fresh air amount is substantially converged to the target fresh air amount, the EGR control valve The opening of the variable nozzle is controlled so that the target intake pressure corresponding to the operating state and the actual intake pressure detected by the intake pressure sensor are substantially the same, and (3) the actual intake pressure is the target When the convergence control is performed to the intake pressure, the fixed opening of the EGR control valve is released and the nozzle opening control means and the EGR opening control means are returned to the normal control.

The engine control system of the best mode includes a variable nozzle turbocharger, an EGR device, a nozzle opening control means, an EGR opening control means, a hunting determination means, and a hunting countermeasure means.
The variable nozzle turbocharger includes a variable nozzle that adjusts the intake pressure of the engine by adjusting the opening of a nozzle that blows exhaust gas to the exhaust turbine.
The EGR device includes an EGR control valve that adjusts the EGR rate of the exhaust gas with respect to the intake air by adjusting the opening degree of the EGR path for returning a part of the exhaust gas upstream of the variable nozzle to the intake side of the engine. .
The nozzle opening control means controls the opening of the variable nozzle so as to obtain a target intake pressure corresponding to the operating state.
The EGR opening degree control means controls the opening degree of the EGR control valve so that the target EGR rate corresponding to the operating state is obtained.
The hunting determination means determines whether or not hunting has occurred in the opening changes of the variable nozzle and the EGR control valve.
The hunting countermeasure means gives priority to the opening control of the EGR control valve over the opening control of the variable nozzle when the hunting determination means determines hunting.

(Configuration of Example 1)
A first embodiment to which the present invention is applied will be described with reference to FIGS. 1 is an overall configuration diagram of the engine control system, and FIG. 2 is a schematic configuration diagram of a control system of the engine control system.

  An engine control system according to the present embodiment includes an accumulator fuel injection device that injects high-pressure fuel into a combustion chamber 2 of each cylinder of an internal combustion engine (hereinafter referred to as an engine) 1 such as a diesel engine mounted on a vehicle such as an automobile. The VNT 3 for supercharging the intake air of the engine 1, the EGR device 4 for recirculating a part of the exhaust gas of the engine 1 to the intake side, the accumulator fuel injection device, the VNT 3 and the EGR device 4 actuators are electronically connected. An engine control unit (hereinafter referred to as ECU) 5 is provided.

In each cylinder (cylinder) of the engine 1, a piston 11 connected to a crankshaft via a connecting rod is slidably disposed. The cylinder head of the engine 1 is provided with an intake valve 13 that opens and closes an intake port 12 of the engine 1 and an exhaust valve 15 that opens and closes an exhaust port 14 of the engine 1.
The intake port 12 of the engine 1 is configured so that new intake air (hereinafter, fresh air) is supplied through the intake passage of the intake pipe 16 of the engine 1. Further, the exhaust port 14 of the engine 1 is configured to discharge exhaust gas into the exhaust passage of the exhaust pipe 17.
Here, an air cleaner case 18 is disposed on the upstream side of the intake pipe 16, and a filter element (air filter) 19 for filtering fresh air supplied to the engine 1 is accommodated in the air cleaner case 18. .

The accumulator fuel injection device includes a common rail (not shown), a supply pump (not shown), and an injector 21 provided for each cylinder.
The common rail is a pressure accumulation container that accumulates high-pressure fuel corresponding to the injection pressure.
The supply pump is a fuel pump that pumps high-pressure fuel to the common rail. A feed pump that sucks fuel from a fuel tank (not shown) to the supply pump, and compresses the fuel sucked up by the feed pump to high pressure to the common rail. It is equipped with a high-pressure pump for pumping. The feed pump and the high-pressure pump are driven by a common cam shaft, and the common cam shaft is driven by the engine 1. An intake metering valve (hereinafter referred to as SCV) 22 for adjusting the amount of fuel sucked into the pressurizing chamber is mounted in the middle of the fuel path from the feed pump to the pressurizing chamber of the high pressure pump. The common rail pressure is adjusted by adjusting the SCV 22 by the ECU 5.

The injector 21 is attached to the cylinder head of the engine 1 corresponding to each cylinder individually, and injects and supplies high-pressure fuel accumulated in the common rail into the combustion chamber 2 of each cylinder. In this embodiment, an electromagnetic (two-valve type) injector 21 will be described as an example.
When an injection command (injection signal ON) is given from the ECU 5 to the electromagnetic valve 23 of the injector 21, the injector 21 opens the outlet orifice of the pressure control chamber, and the pressure in the pressure control chamber is reduced by the inlet orifice. Lowering starts, the needle urging force due to the pressure in the pressure control chamber decreases, the needle starts to rise, the needle moves away from the nozzle seat, and fuel injection starts. When the injection command given to the electromagnetic valve 23 from the ECU 5 stops (injection signal OFF), the electromagnetic valve 23 closes the outlet orifice, the pressure in the pressure control chamber rises, and the needle biasing force due to the pressure in the pressure control chamber increases. Then, the needle starts to descend, the needle is seated on the nozzle seat, and the fuel injection is stopped.

The VNT 3 includes an exhaust turbine 31, an intake compressor 32, and a variable nozzle 33.
The exhaust turbine 31 is an impeller that is surrounded by a turbine housing 34 that spirally surrounds the exhaust turbine 31 and is rotationally driven by an exhaust gas flow that passes through the turbine housing 34.
The intake compressor 32 is an impeller that is connected to the exhaust turbine 31 via a shaft 35 and rotates integrally with the exhaust turbine 31. The intake compressor 32 is surrounded by a compressor housing 36 that spirally surrounds the exhaust turbine 31, and rotates the exhaust turbine 31. In response, the air in the intake pipe 16 is pressurized and supplied toward the engine 1.

The variable nozzle 33 adjusts the intake pressure (the intake pressure pressurized by the intake compressor 32) by adjusting the opening degree of the nozzle 37 that blows the exhaust gas to the exhaust turbine 31.
Specifically, the variable nozzle 33 includes a nozzle 37 that blows exhaust gas to the exhaust turbine 31 and a nozzle actuator 38 that changes the opening degree (exhaust gas flow area) of the nozzle 37. By changing by the nozzle actuator 38, the flow rate of the exhaust gas blown to the exhaust turbine 31 is adjusted to control the rotational speed of the exhaust turbine 31, that is, the rotational speed of the intake compressor 32, thereby controlling the intake pressure. When the opening degree of the variable nozzle 33 is close, the flow velocity blown to the exhaust turbine 31 becomes large, and the intake pressure increases. Conversely, when the opening of the variable nozzle 33 is on the opening side, the flow velocity blown to the exhaust turbine 31 becomes small, and the intake pressure decreases.

The EGR device 4 includes an EGR path 41 and an EGR control valve 42.
The EGR path 41 is an exhaust gas return path for returning a part of the exhaust gas upstream of the variable nozzle 33 to the intake side of the engine 1. The EGR path 41 has an upstream end branched from the exhaust pipe 17 on the exhaust upstream side of the variable nozzle 33, and a downstream end connected to the intake pipe 16 on the intake downstream side of the intake compressor 32.
The EGR control valve 42 adjusts the EGR rate of the exhaust gas with respect to fresh air by adjusting the amount of the exhaust gas recirculated to the intake side by the EGR path 41. The EGR control valve 42 is disposed in the EGR path 41, and a valve (valve element) 43 that changes the flow area of the exhaust gas in the EGR path 41 and an electromagnetic that drives the valve 43 in the valve opening direction. Or an electric EGR actuator 44 and a return spring (not shown) for urging the valve 43 in the valve closing direction.

The ECU 5 includes functions such as a CPU that performs control processing and arithmetic processing, a storage device (ROM, standby RAM or EEPROM, memory such as RAM) that stores various programs and data, an input circuit, an output circuit, a power supply circuit, and the like. It consists of a microcomputer having a known structure.
The ECU 5 also includes a pump drive circuit that applies an SCV drive current (for example, a PWM signal) to the SCV 22 of the supply pump, and an injector drive circuit that applies an injector drive current (for example, a drive pulse) to the electromagnetic valve 23 of the injector 21. , A variable nozzle drive circuit that applies a VNT drive current (for example, PWM signal) to the nozzle actuator 38 of the variable nozzle 33, and an EGR drive that applies an EGR drive current (for example, PWM signal) to the EGR actuator 44 of the EGR control valve 42 Circuit.

The ECU 5 performs various arithmetic processes based on the read sensor signals (engine parameters: signals corresponding to the operating state of the engine 1 including the driving state of the occupant and the driving state of the vehicle).
A crank angle sensor 51, an accelerator opening sensor 52, a cooling water temperature sensor 53, an intake pressure sensor 54, an airflow sensor 55, and the like are connected to the ECU 5 as means for detecting the operating state of the engine 1.

  The crank angle sensor 51 detects the rotation angle of the crankshaft of the engine 1 and comprises an electromagnetic pickup coil attached so as to face the outer periphery of the NE timing rotor attached to the crankshaft of the engine 1. The NE timing rotor has a plurality of convex teeth arranged on the outer peripheral surface for each predetermined rotation angle. The crank angle sensor 51 outputs a pulsed rotational position signal (NE signal pulse) by electromagnetic induction as each convex tooth of the NE timing rotor repeatedly approaches and separates from the crank angle sensor 51. The ECU 5 also functions as a rotational speed detection means for detecting the engine rotational speed (engine rotational speed: NE) by measuring the interval time of the NE signal pulse output from the crank angle sensor 51.

The accelerator opening sensor 52 detects an accelerator opening (ACCP) that is a depression amount of an accelerator pedal.
The coolant temperature sensor 53 detects the engine coolant temperature (THW).
The intake pressure sensor 54 detects the pressure of fresh air (hereinafter referred to as actual intake pressure) in the intake pipe 16 on the intake downstream side of the intake compressor 32.
The air flow sensor 55 detects a flow rate of fresh air (hereinafter referred to as actual fresh air amount) flowing through the intake pipe 16 that has passed through the filter element 19.

(Control method of Example 1)
Next, calculation control of the ECU 5 will be described.
The ECU 5 includes, as means for controlling the injector 21, functions of an injection amount determining means, an injection timing determining means, an injection period determining means, and an injector driving means.
The injection amount determining means adds an injection correction amount considering the engine coolant temperature (THW) and the like to the basic injection amount (Q) set corresponding to the engine speed (NE) and the accelerator opening (ACCP). Thus, the command injection amount (QFIN) is calculated.
The injection timing determining means calculates a command injection timing (TFIN) for each cylinder of the engine 1 based on the command injection amount (QFIN) and the engine speed (NE).
The injection period determining means determines the energization time of the injector 21 (command injection period: TQ) from the command injection quantity (QFIN) and the common rail pressure (fuel pressure in the common rail: PC) read from the common rail pressure sensor (not shown). ) Is calculated.
The injector drive means controls the injector drive circuit based on the command injection timing (TFIN) and the command injection period (TQ), and from the injector drive circuit to the injector 21 from the command injection timing (TFIN) to the command injection period (TQ). To output an INJ drive current.

The ECU 5 has functions of a fuel pressure determining means and a discharge amount controlling means as means for controlling the SCV 22 of the supply pump.
The fuel pressure determining means calculates a target common rail pressure (PFIN) based on the engine speed (NE) and the accelerator opening (ACCP).
The discharge amount control means feedback-controls the SCV drive current value applied to the SCV 22 of the supply pump based on the deviation (ΔP) between the common rail pressure (PC) and the target common rail pressure (PFIN).

The ECU 5 has a function of nozzle opening control means for controlling the intake pressure by controlling the opening of the variable nozzle 33 of the VNT 3.
The nozzle opening degree control means controls the opening degree of the variable nozzle 33 so that the target intake pressure corresponding to the operating state of the engine 1 is obtained. The target intake pressure determining means 61, the intake pressure feedback means 62, the nozzle Drive means 63 is provided.

The target intake pressure determination means 61 calculates a target intake pressure (T) corresponding to the operating state of the engine 1.
The intake pressure feedback means 62 performs a corrected intake pressure (Tf) by known PID control or PI control based on a deviation (ΔT) between the target intake pressure (T) and the actual intake pressure (Tj) read from the intake pressure sensor 54. ) Is calculated.
The nozzle driving means 63 controls the variable nozzle driving circuit with a value obtained by correcting the target intake pressure (T) with the corrected intake pressure (Tf), and sets the target intake pressure (T) to a value corrected with the corrected intake pressure (Tf). A corresponding VNT drive current is output to the nozzle actuator 38 of the variable nozzle 33.

The ECU 5 has a function of EGR opening degree control means for controlling the EGR rate by controlling the opening degree of the EGR control valve 42 of the EGR device 4.
The EGR opening degree control means controls the opening degree of the EGR control valve 42 so that a target EGR rate corresponding to the operating state of the engine 1 is obtained. The target EGR rate determining means 64, the EGR feedback means 65, EGR driving means 66 is provided.

The target EGR rate determining unit 64 calculates a target EGR rate (G) corresponding to the operating state of the engine 1.
The EGR feedback means 65 is a known type based on a deviation (ΔE) between a target fresh air amount (E) set corresponding to the operating state of the engine 1 and an actual fresh air amount (Ej) read from the airflow sensor 55. The corrected EGR rate (Gf) is calculated by PID control or PI control.
The EGR drive means 66 controls the EGR drive circuit with a value obtained by correcting the target EGR rate (G) with the corrected EGR rate (Gf), and corresponds to the value obtained by correcting the target EGR rate (G) with the corrected EGR rate (Gf). The EGR drive current is output to the EGR actuator 44 of the EGR control valve 42.

(Characteristics of Example 1)
Next, features of the present embodiment will be described.
Since the variable nozzle 33 of the VNT 3 adjusts the opening degree of the nozzle 37 that forms part of the exhaust passage, when the variable nozzle 33 is closed, the exhaust pressure in the “A region” in FIG. When 33 opens, the exhaust pressure of “A region” decreases.
Further, since the EGR control valve 42 of the EGR device 4 adjusts the opening degree of the EGR path 41 that connects the exhaust upstream side and the intake side of the variable nozzle 33, when the EGR control valve 42 is closed, the "A region" When the EGR control valve 42 is opened and the EGR control valve 42 is opened, the exhaust pressure in the “A region” is decreased.
As described above, when the opening of the variable nozzle 33 is changed, the exhaust pressure in the “A region” is changed, and even if the opening of the EGR control valve 42 is changed, the exhaust pressure in the “A region” is changed. If one of them is controlled, the other is affected.
For this reason, if the opening degrees of the variable nozzle 33 and the EGR control valve 42 are controlled simultaneously, hunting may occur in changes in the opening degrees of the variable nozzle 33 and the EGR control valve 42 due to mutual influences.

When hunting occurs in the opening change of the variable nozzle 33 and the EGR control valve 42, the control for converging the intake pressure to the target intake pressure is disturbed by the EGR control, and the control for converging the EGR rate to the target EGR rate is performed. It will be disturbed.
That is, due to the occurrence of hunting, the intake pressure control and the EGR control are disturbed with each other, and it takes a long time for both the intake pressure and the EGR rate to converge to the target value.

(Control for hunting)
In order to solve the above problem, the ECU 5 of this embodiment includes functions of a hunting determination unit 71 and a hunting countermeasure unit 72. The functions of the hunting determination means 71 and the hunting countermeasure means 72 will be described with reference to FIGS.

(Description of hunting determination means 71)
The hunting determination means 71 is a program for determining whether or not hunting has occurred in the opening changes of the variable nozzle 33 and the EGR control valve 42.
The hunting determination means 71 of this embodiment starts determining whether or not the variable nozzle 33 and the EGR control valve 42 are hunting when a preset hunting determination start condition is satisfied.
As an example of the hunting determination start condition, in the present embodiment, only when the operating state of the engine 1 is in a steady operation (for example, not during rapid acceleration or deceleration) and exhaust deterioration more than a predetermined value is estimated. , Programmed to start hunting determination (control of steps S1 and S2 described later).
The ECU 5 determines whether or not the operating state of the engine 1 is a steady operation, and whether or not the deterioration of exhaust gas is greater than or equal to a predetermined value from the operating state of the engine 1. And an exhaust deterioration judging means.
The exhaust deterioration judging means of this embodiment includes an intake pressure deviation detecting means 74 for estimating exhaust deterioration when a deviation (ΔT) between the target intake pressure (T) and the actual intake pressure (Tj) is a predetermined value or more, and a target new The EGR deviation detecting means 75 estimates the deterioration of exhaust gas when the deviation (ΔE) between the air volume (E) and the actual fresh air volume (Ej) is equal to or greater than a predetermined value.

  As an example of determining hunting between the variable nozzle 33 and the EGR control valve 42, the hunting determination means 71 of the present embodiment is the number of times the variable nozzle 33 is reversed in the opening / closing direction within a predetermined time after the hunting determination start condition is satisfied. Is equal to or greater than a predetermined number (for example, 3 times), and the occurrence of hunting is determined when the number of inversions in the opening / closing direction of the EGR control valve 42 is equal to or greater than the predetermined number (for example, 3 times) (described later). Steps S4 to S8, S10, and S11). Further, the hunting determination means 71 of the present embodiment is configured to detect the exhaust gas estimated by the exhaust deterioration determination means (the intake pressure deviation detection means 74 and the EGR deviation detection means 75) within a predetermined time after the hunting determination start condition is satisfied. When the deterioration state is not equal to or greater than a predetermined value, the hunting determination is finished and the hunting countermeasure means 72 is not operated (control in step S9 described later).

The ECU 5 has a function of the turbo change detecting means 76 as a means for detecting the number of reversals in the opening / closing direction of the variable nozzle 33, and an EGR change detecting means 77 as a means for detecting the number of reversals in the opening / closing direction of the EGR control valve 42. Is provided.
The turbo change detection means 76 includes a previous value T (i−1) of the target intake pressure (T: or actual intake pressure, target opening of the variable nozzle 33, actual variable nozzle opening) and the target intake pressure (T: or A difference ΔT (i) = T (i−1) −T (i) from the actual intake pressure, the target opening degree of the variable nozzle 33, and the actual variable nozzle opening degree) T (i) is obtained. The difference ΔT (i) is multiplied by the previous difference ΔT (i−1), and when the multiplied value becomes smaller than 0 (zero), the reversal of the opening / closing direction of the variable nozzle 33 is detected.
The EGR change detection means 77 includes a previous value E (i−1) of the target fresh air amount (E: or actual fresh air amount, target EGR rate, actual EGR valve opening) and target fresh air amount (E: or actual A difference ΔE (i) = E (i−1) −E (i) from the current value E (i) of the fresh air amount, the target EGR rate, and the actual EGR valve opening is obtained. The difference ΔE (i) is multiplied by the previous difference ΔE (i−1), and when the multiplied value becomes smaller than 0 (zero), the reversal of the opening / closing direction of the EGR control valve 42 is detected. .

Next, hunting determination control by the hunting determination means 71 will be described with reference to the flowchart of FIG.
If this determination routine is entered during the operation of the engine 1 (start), it is first determined in step S1 whether or not the operation state is a steady operation.
If the determination result in step S1 is NO, it is determined that the driving state for determining hunting is not in effect, and the process proceeds to step S2. In step S2, the hunting determination flag indicating that hunting is not detected is turned OFF, and this determination routine is ended (END).
If the decision result in the step S1 is YES, in a step S3, it is judged whether or not the estimated exhaust deterioration state is a predetermined value or more. Specifically, the deviation (ΔT) between the target intake pressure (T) and the actual intake pressure (Tj) is equal to or greater than a predetermined value (a value at which exhaust deterioration is estimated), or the target fresh air amount (E) It is determined whether the deviation (ΔE) of the actual fresh air amount (Ej) is equal to or greater than a predetermined value (a value at which exhaust deterioration is estimated).
If the determination result in step S3 is NO, it is determined that the exhaust has not deteriorated and it is not necessary to implement hunting countermeasures, and the process proceeds to step S2.

When the determination result in step S3 is YES (satisfaction of the hunting determination start condition), in steps S4 to S8, the number of inversions in the opening / closing direction of the variable nozzle 33 within a predetermined time after the hunting determination start condition is satisfied, and The number of inversions in the opening / closing direction of the EGR control valve 42 is counted.
In step S4, after the hunting determination start condition is satisfied, it is determined whether or not it is within a predetermined time set in advance.
If the determination result of step S4 is YES, the next calculation and determination are performed in step S5.
The previous value T (i-1) of the target intake pressure (T: or actual intake pressure, target opening of variable nozzle 33, actual variable nozzle opening) and target intake pressure (T: or actual intake pressure, variable nozzle 33). A difference ΔT (i) = T (i−1) −T (i) from the current value T (i) of the target opening and the actual variable nozzle opening) is obtained.
Then, the difference ΔT (i) is multiplied by the previous difference ΔT (i−1), and it is determined whether or not the multiplied value is smaller than 0 (zero).
If the determination result in step S5 is YES, it is determined that the variable nozzle 33 has been reversed in the opening / closing direction, and the number of reversals of the variable nozzle 33 is counted up in step S6.

If the determination result in step S5 is NO, or after execution of step S6, the next calculation is determined in step S7.
The previous value E (i-1) of the target fresh air amount (E: or actual fresh air amount, target EGR rate, actual EGR valve opening) and the target fresh air amount (E: or actual fresh air amount, target EGR rate) The difference ΔE (i) = E (i−1) −E (i) from the current value E (i) of the actual EGR valve opening) is obtained.
Then, the difference ΔE (i) is multiplied by the previous difference ΔE (i−1), and it is determined whether or not the multiplied value is smaller than 0 (zero).
If the determination result in step S7 is YES, it is determined that the EGR control valve 42 has been reversed in the opening / closing direction, and the number of inversions of the EGR control valve 42 is counted up in step S8.

  When the determination result of step S4 is NO, when the determination result of step S7 is NO, or after execution of step S8, in step S9, it is determined whether or not the estimated exhaust deterioration state is equal to or greater than a predetermined value. I do. Specifically, the deviation (ΔT) between the target intake pressure (T) and the actual intake pressure (Tj) is equal to or greater than a predetermined value (a value at which exhaust deterioration is estimated), or the target fresh air amount (E) It is determined whether the deviation (ΔE) of the actual fresh air amount (Ej) is equal to or greater than a predetermined value (a value at which exhaust deterioration is estimated). If the determination result of this step S9 is NO, this determination routine is ended (end).

If the determination result in step S9 is YES, in step S10, the value counted in step S6 (the number of inversions of the variable nozzle 33) is a predetermined number (for example, 3 times) or more, and the value counted in step S8. It is determined whether (the number of times the EGR control valve 42 is reversed) is a predetermined number (for example, three times) or more. If the determination result of this step S10 is NO, this determination routine is ended (end).
If the determination result in step S10 is YES, it is determined that the exhaust is affected within a predetermined time after starting the hunting determination, and that the hunting has occurred in the variable nozzle 33 and the EGR control valve 42, In step S11, a hunting determination flag indicating that hunting has been detected is turned ON, and this determination routine is ended (END).

(Description of hunting countermeasure means 72)
The hunting countermeasure means 72 gives priority to the opening degree control of the EGR control valve 42 over the opening degree control of the variable nozzle 33 when the hunting judgment means 71 determines hunting (hunting determination flag ON), and subsequently the EGR control valve. The opening control of the variable nozzle 33 is given priority over the opening control of 42. Specifically, in this embodiment, when the hunting determination means 71 determines hunting, the opening control of the EGR control valve 42 is performed with the opening of the variable nozzle 33 fixed, and then the EGR control valve 42 is opened. The degree of opening of the variable nozzle 33 is controlled with the degree fixed.

Therefore, the hunting countermeasure means 72 includes a VNT opening degree fixing means 78 for fixing the opening degree of the variable nozzle 33 to the previous value, and an EGR valve opening degree for fixing the opening degree of the EGR control valve 42 to the previous value. And fixing means 79.
As described above, the opening of the variable nozzle 33 in this embodiment is controlled by a value obtained by correcting the target intake pressure (T) with the corrected intake pressure (Tf). Therefore, the variable nozzle 33 in this embodiment is used. Is the previous value obtained by correcting the target intake pressure (T) with the corrected intake pressure (Tf).
As described above, the opening degree of the EGR control valve 42 in this embodiment is controlled by a value obtained by correcting the target EGR rate (G) with the correction EGR rate (Gf). Therefore, the EGR control in this embodiment is performed. The previous value of the opening degree of the valve 42 is the previous value obtained by correcting the target EGR rate (G) with the corrected EGR rate (Gf).

When the hunting determination means 71 determines hunting, the hunting countermeasure means 72 first fixes the opening degree of the variable nozzle 33, and the EGR opening degree control means causes the target fresh air amount (E) and the actual fresh air amount (Ej). ) Is controlled so that the opening degree of the EGR control valve 42 substantially matches.
If it is determined that the actual fresh air amount (Ej) has been substantially converged to the target fresh air amount (E), then the opening of the EGR control valve 42 is fixed, and the target intake pressure ( The opening degree of the variable nozzle 33 is controlled so that T) and the actual intake pressure (Tj) substantially coincide.
When it is determined that the actual intake pressure (Tj) has been substantially converged to the target intake pressure (T), the fixed opening of the EGR control valve 42 is released, and the nozzle opening control means and the EGR opening control means are switched to normal control. Implement control to return.

(Description of operation)
The operation of the hunting determination means 71 and the hunting countermeasure means 72 will be described with reference to the time chart of FIG. FIG. 6A is a time chart for comparison when hunting measures are not taken. This time chart shows an example in which hunting occurs during steady operation immediately after acceleration so that the command injection amount (QFIN) stabilizes after a rapid increase.
(1) During steady operation immediately after acceleration, if the deviation (ΔE) between the target fresh air amount (E) and the actual fresh air amount (Ej) is equal to or greater than a predetermined value and exhaust gas deterioration is estimated, the hunting determination means 71 Hunting determination is started (t1).

(2) The hunting determination means 71 has the number of reversals in the opening / closing direction of the variable nozzle 33 within a predetermined time (t1 to t2), and the number of reversals in the opening / closing direction of the EGR control valve 42 is also a predetermined number of times or more. In addition, if the deviation (ΔE) or the deviation (ΔT) is greater than or equal to a predetermined value within a predetermined time (t1 to t2) and exhaust gas deterioration is estimated, occurrence of hunting is determined. (3) When the hunting determination means 71 determines hunting (t2), the hunting countermeasure means 72 fixes the opening of the variable nozzle 33 by the VNT opening fixing means 78 and at the same time the target fresh air amount by the EGR opening control means. The opening degree of the EGR control valve 42 is feedback-controlled so that (E) and the actual fresh air amount (Ej) substantially coincide.

(4) When the actual fresh air amount (Ej) is substantially converged to the target fresh air amount (E) by the EGR opening degree control means (t3), the opening degree of the EGR control valve 42 is set by the EGR valve opening degree fixing means 79. At the same time, the opening degree of the variable nozzle 33 is released by the VNT opening degree fixing means 78, and the target intake pressure (T) and the actual intake pressure (Tj) are made substantially equal by the nozzle opening degree control means. The opening degree of the nozzle 33 is feedback-controlled.
(5) When the actual intake pressure (Tj) is substantially converged to the target intake pressure (T) by the nozzle opening control means (t4), the EGR control valve 42 is fixed by the EGR valve opening fixing means 79. The control is performed to cancel and return the nozzle opening degree control means and the EGR opening degree control means to the normal control.

(Effect of Example 1)
In the engine control system of the first embodiment, as described above, only when hunting that adversely affects exhaust occurs, (1) the opening of the variable nozzle 33 is fixed, and the target fresh air amount is controlled by the EGR opening control means. The opening degree of the EGR control valve 42 is feedback-controlled so that (E) and the actual fresh air amount (Ej) substantially coincide, and (2) the actual fresh air amount (Ej) substantially converges to the target fresh air amount (E). Then, the opening degree of the EGR control valve 42 is fixed, and the opening degree of the variable nozzle 33 is feedback-controlled by the nozzle opening degree control means so that the target intake pressure (T) and the actual intake pressure (Tj) substantially coincide with each other. 3) When the actual intake pressure (Tj) substantially converges to the target intake pressure (T), the nozzle opening degree control means and the EGR opening degree control means are returned to the normal control.
By this control, only when hunting that adversely affects exhaust occurs, the EGR rate can be made to follow the appropriate value more quickly, and exhaust gas deterioration (smoke, etc.) due to hunting can be suppressed.

Further, when hunting has not occurred or when hunting has occurred so as not to adversely affect the exhaust, the nozzle opening control means and the EGR opening control means independently control the intake pressure and the EGR rate. Therefore, the intake pressure and the EGR rate can be made to follow the target intake pressure and the target EGR rate earlier.
That is, in most operating states where hunting does not occur or when hunting occurs to such an extent that the exhaust gas is not adversely affected, the variable nozzle 33 and the EGR control valve 42 are independently controlled. Both performance and high exhaust gas purification properties can be achieved.

[Modification]
In the above-described embodiment, an example is shown in which exhaust gas deterioration is estimated during steady operation and hunting determination is started when exhaust gas deterioration is determined.
On the other hand, the hunting determination may be started when the preset operating state of the engine 1 is established.
In the above-described embodiment, an example in which the predetermined time for determining hunting is fixed is shown.
On the other hand, you may provide so that the length of the predetermined time which determines hunting according to the specification of the engine 1, etc. may be changed.

In the above embodiment, as an example in which the opening degree control of the EGR control valve 42 is prioritized over the opening degree control of the variable nozzle 33, the example in which the opening degree of the variable nozzle 33 is fixed is shown.
On the other hand, you may provide so that the change speed of the opening degree of the variable nozzle 33 may become slow. As a specific example, the change speed of the corrected intake pressure (Tf) by the intake pressure feedback means 62 may be slowed.
In the above embodiment, an example in which the opening degree of the EGR control valve 42 is fixed as an example of giving priority to the opening degree control of the variable nozzle 33 after the priority control of the EGR control valve 42 has been shown.
On the other hand, the EGR control valve 42 may be provided so that the rate of change of the opening degree becomes slow. As a specific example, the EGR feedback means 65 may be provided so as to slow down the changing speed of the corrected EGR rate (Gf).

In the above-described embodiment, an example in which the two-valve type injector 21 equipped with the electromagnetic valve 23 is used has been described.
On the other hand, a linear solenoid (piezo actuator or the like) may be mounted with an injector 21 that directly drives the needle.
In said Example, the example using a pressure accumulation type fuel-injection apparatus was shown.
On the other hand, a fuel injection device that does not use a common rail may be used. Of course, the present invention is not limited to an engine control system using a diesel engine, and the present invention can be applied to all engine control systems including the VNT 3 and the EGR device 4.

1 is an overall configuration diagram of an engine control system. It is a schematic block diagram of the control system of an engine control system. It is explanatory drawing of the control logic of a hunting determination means and a hunting countermeasure means. It is explanatory drawing of the control logic of a hunting determination means. It is a control flowchart of a hunting determination means. It is a time chart explaining the action | operation of a hunting determination means and a hunting countermeasure means.

Explanation of symbols

1 Engine 3 VNT (Variable nozzle turbocharger)
4 EGR device 5 ECU (nozzle opening control means, EGR opening control means)
31 Exhaust turbine 33 Variable nozzle 37 Nozzle 41 EGR path 42 EGR control valve 54 Intake pressure sensor 55 Airflow sensor 71 Hunting determination means 72 Hunting countermeasure means 74 Intake pressure deviation detection means (exhaust deterioration determination means)
75 EGR deviation detecting means (exhaust deterioration judging means)

Claims (5)

(A) a variable nozzle turbocharger having a variable nozzle that adjusts the intake pressure of the engine by adjusting the opening of the nozzle that blows exhaust gas to the exhaust turbine;
(B) An EGR control valve that adjusts the EGR rate of the exhaust gas with respect to the intake air by adjusting the opening degree of the EGR path for returning a part of the exhaust gas upstream of the variable nozzle to the intake side of the engine. EGR device equipped with,
(C) nozzle opening degree control means for controlling the opening degree of the variable nozzle so as to obtain a target intake pressure corresponding to the operating state;
(D) EGR opening degree control means for controlling the opening degree of the EGR control valve so that a target EGR rate corresponding to the operating state is obtained;
(E) hunting determination means for determining whether or not hunting has occurred in the opening change of the variable nozzle and the EGR control valve;
(F) hunting countermeasure means for giving priority to the opening control of the EGR control valve over the opening control of the variable nozzle when the hunting determination means determines hunting;
An engine control system comprising: The engine control system according to claim 1,
An engine comprising exhaust deterioration determining means for measuring or estimating exhaust deterioration and determining exhaust deterioration, and when the exhaust deterioration determining means does not determine exhaust deterioration, the hunting countermeasure means is not operated. Control system. The engine control system according to claim 1 or 2,
The engine control system, wherein the hunting determination means determines whether or not hunting occurs between the variable nozzle and the EGR control valve when a preset hunting determination start condition is satisfied. The engine control system according to any one of claims 1 to 3,
The hunting determination means determines hunting when the number of inversions in the opening / closing direction of the variable nozzle is not less than a predetermined number and the number of inversions in the opening / closing direction of the EGR control valve is not less than a predetermined number within a predetermined time. An engine control system. The engine control system according to any one of claims 1 to 4,
The hunting countermeasure means is:
When the hunting determination means determines hunting, the opening degree of the variable nozzle is fixed and the EGR so that the target fresh air amount according to the operating state and the actual fresh air amount detected by the airflow sensor substantially coincide. Control the opening of the control valve,
When the actual fresh air amount is approximately converged to the target fresh air amount, the opening degree of the EGR control valve is fixed, and the target intake pressure according to the operating state and the actual intake pressure detected by the intake pressure sensor are Controlling the opening of the variable nozzle so as to substantially match,
When the actual intake pressure is controlled to substantially converge to the target intake pressure, the fixed opening of the EGR control valve is released, and the nozzle opening control means and the EGR opening control means are returned to normal control. Engine control system.

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