JP6323263B2 - Control device and control method for variable compression ratio internal combustion engine - Google Patents

Description

  The present invention relates to a control device and a control method for an internal combustion engine including a variable compression ratio mechanism that changes a mechanical compression ratio and an exhaust gas recirculation device that recirculates a part of exhaust gas to an intake passage.

  Various types of variable compression ratio mechanisms for changing the mechanical compression ratio of an internal combustion engine have been known. For example, as disclosed in Patent Document 1, the applicants have proposed many variable compression ratio mechanisms in which the piston top dead center position is displaced up and down by changing the link geometry of a multi-link type piston crank mechanism. Has been.

  In such a variable compression ratio mechanism, it is basically desirable that the compression ratio be as high as possible without causing abnormal combustion such as knocking. Therefore, as a general tendency of the target compression ratio, the load is The lower the value, the higher the compression ratio.

  On the other hand, exhaust gas recirculation devices that recirculate a part of exhaust gas to the intake passage are known, and recently, more exhaust gas recirculation tends to be performed to improve fuel efficiency. Since this exhaust gas recirculation contributes to the suppression of knocking, the target compression ratio is set as a value considering the target EGR rate (target exhaust gas recirculation rate) under each operating condition. That is, even when the load and rotation speed are the same, when exhaust gas recirculation is performed, a relatively high target compression ratio is given.

JP 2010-285873 A

  The flow rate of the recirculated exhaust gas is controlled so as to achieve a target EGR rate corresponding to the operating conditions by opening control of an exhaust recirculation control valve provided in an exhaust recirculation passage extending from the exhaust system to the intake system. Therefore, when the acceleration or deceleration of the internal combustion engine is transited, the actual change in the EGR rate in the cylinder is delayed, and as a result, knocking occurs transiently, or conversely, the compression ratio becomes temporarily too low. Therefore, there is a concern that fuel consumption will deteriorate.

  More specifically, based on FIGS. 4, 9, and 10, for example, FIG. 9 is operated from the point P1 outside the EGR region to the point P2 within the EGR region as shown as “transient scene 1” in FIG. The change of the EGR rate and the target compression ratio at the time of acceleration where conditions change is shown. The target EGR rate indicated by the broken line changes in accordance with the same EGR rate map as that in the steady state, and exhaust gas recirculation is started as acceleration starts. However, the in-cylinder EGR rate is actually shown by the solid line. It rises late. On the other hand, the target compression ratio is, for example, a high compression ratio of about “14” regardless of the increase in load on the premise of the EGR rate given at point P2, as shown as a “comparative example” in FIG. Therefore, knocking occurs transiently until the in-cylinder EGR rate actually increases.

  Conversely, at the time of deceleration when the driving condition changes from the point P3 in the EGR region to the point P4 outside the EGR region as shown as “transient scene 2” in FIG. 4, as shown in FIG. 10, the target EGR rate However, the actual decrease in the EGR rate in the cylinder is delayed as shown by the solid line. Therefore, the target compression ratio is temporarily controlled to an unnecessarily low compression ratio as shown as a “comparative example” indicated by a broken line, resulting in deterioration of fuel consumption.

  In particular, in the configuration in which the exhaust gas is recirculated to the upstream side of the throttle valve via the exhaust gas recirculation passage, the difference between the EGR rate value based on the EGR rate map and the actual in-cylinder EGR rate becomes large during the transition, and the compression ratio Proper control is not possible. Although Patent Document 1 describes the delay in exhaust gas recirculation at the time of transition, it does not disclose specific means for recirculating exhaust gas upstream of the throttle valve.

A control apparatus for a variable compression ratio internal combustion engine according to the present invention includes:
In an internal combustion engine having a variable compression ratio mechanism and an exhaust gas recirculation device that recirculates part of the exhaust gas from the exhaust passage to the upstream side of the throttle valve of the intake passage through the exhaust gas recirculation passage.
Target compression ratio setting means for setting a target compression ratio of the variable compression ratio mechanism according to the operating conditions of the internal combustion engine;
Throttle valve upstream side EGR rate estimating means for estimating an EGR rate in the intake passage volume between the junction with the exhaust gas recirculation passage and the throttle valve during a transition of the internal combustion engine;
An in-intake port EGR rate estimating means for obtaining an EGR rate at the intake port from an EGR rate at the upstream side of the throttle valve using a transfer function corresponding to a transport delay in the intake passage from the throttle valve to the intake port;
Compression ratio correction means for correcting the target compression ratio based on the estimated EGR rate at the intake port ;
It is configured with.
The compression ratio correction means corrects the target compression ratio to the high compression ratio side when the estimated EGR rate at the intake port is higher than the target EGR rate in a steady state.

  In other words, the EGR rate upstream of the throttle valve (EGR rate in the intake passage volume between the junction with the exhaust gas recirculation passage and the throttle valve) on the upstream side of the throttle valve is estimated by the throttle valve upstream EGR rate estimation means, and this estimated EGR rate Further, by giving a delay using a transfer function corresponding to a transport delay in the intake passage from the throttle valve to the intake port, the EGR rate at the intake port at the time of transition is estimated. The EGR rate in the cylinder is substantially equal to the EGR rate at the intake port. Then, the target compression ratio is corrected based on the EGR rate at the intake port.

According to the present invention, the EGR rate of the gas sucked into the cylinder is correctly estimated even during the transition, and the target compression ratio is corrected to the high compression ratio side when the estimated EGR rate is higher than the target EGR rate in the steady state. Therefore , it is possible to avoid a deterioration in fuel consumption due to an unnecessarily low compression ratio.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows typically the structure of the control apparatus of the variable compression ratio internal combustion engine which concerns on this invention. Configuration explanatory drawing of a variable compression ratio mechanism. The functional block diagram of compression ratio control. Explanatory drawing which shows the characteristic of the map of steady compression ratio setting. The functional block diagram which shows the detail of a transient EGR rate estimation means. The functional block diagram which shows the detail of the EGR rate estimation means in an intake port. The characteristic view which showed the relationship between EGR flow volume / (total flow volume-throttle gas flow volume) and an EGR rate. The characteristic view which showed the relationship of the compression ratio correction amount with respect to the deviation of the EGR rate at the time of transition. 3 is a time chart showing an operation in a transient scene 1; 4 is a time chart showing an operation in a transient scene 2;

  FIG. 1 is an explanatory diagram schematically showing the configuration of a control device for a variable compression ratio internal combustion engine according to the present invention. The internal combustion engine 1 includes a variable compression ratio mechanism 2 that changes a mechanical compression ratio as will be described later, and the target compression ratio of the variable compression ratio mechanism 2 is variably controlled by a control unit 3.

  In FIG. 1, 5 schematically shows an intake passage of the internal combustion engine 1, and 6 schematically shows an exhaust passage of the internal combustion engine 1. In the intake passage 5, an air cleaner 7, a turbocharger compressor 8, an intercooler 9 for cooling the supercharged intake air, and a throttle valve 10 are arranged in this order from the upstream side. Between the air cleaner 7 and the compressor 8, an air flow meter 11 for detecting an intake air amount (fresh air amount) Qa is provided. Further, before and after the throttle valve 10, a first pressure sensor 12 that detects a boost pressure PA upstream of the throttle valve 10 and a second pressure sensor 13 that detects a collector internal pressure PB downstream of the throttle valve 10 are provided. Is provided. Reference numeral 14 denotes a recirculation valve that opens supercharged intake air from the downstream side to the upstream side of the compressor 8 at the time of deceleration, for example.

  In the exhaust passage 6, a turbocharger turbine 16, a pre-catalytic converter 17, a main catalytic converter 18, and a silencer 19 are provided in order from the upstream side. The turbine 16 includes a waste gate valve 20 that allows part of the exhaust to escape for supercharging pressure control.

  As an exhaust gas recirculation device, an exhaust gas recirculation passage 21 branches from the pre-catalyst converter 17 and the main catalytic converter 18 in the exhaust passage 6, and the tip of the exhaust gas recirculation passage 21 is connected to the air intake passage 5. The merging point 22 is located between the meter 11 and the compressor 8. The exhaust gas recirculation passage 21 is provided with an EGR gas cooler 23 that cools the recirculated exhaust gas, and an EGR valve 24 that controls the exhaust gas recirculation amount in accordance with a target EGR rate (exhaust gas recirculation rate). The EGR valve 24 includes, for example, a flow rate detection sensor 25 that detects an actual EGR gas flow rate Qegr from a pressure difference before and after the EGR valve 24.

  All the detection signals of the above-described sensors such as the flow rate detection sensor 25 are input to the control unit 3.

  The variable compression ratio mechanism 2 of the internal combustion engine 1 uses a known multi-link type piston crank mechanism described in Japanese Patent Application Laid-Open No. 2004-116434 and the like. As shown in FIG. A lower link 32 rotatably supported by the pin 31a, an upper link 35 that connects the upper pin 33 at one end of the lower link 32 and the piston pin 34a of the piston 34, and a control at the other end of the lower link 32 A control link 37 having one end connected to the pin 36 and a control shaft 38 that pivotally supports the other end of the control link 37 are mainly configured. The control shaft 38 has an eccentric shaft portion 38a whose position changes as the control shaft 38 rotates. Specifically, the end portion of the control link 37 is rotatably fitted to the eccentric shaft portion 38a. Match. The rotational position of the control shaft 38 is controlled by an actuator 39 such as an electric motor. In the variable compression ratio mechanism 2 described above, the top dead center position of the piston 34 is displaced up and down in accordance with the rotational position of the control shaft 38, so that the mechanical compression ratio changes.

  FIG. 3 is a functional block diagram showing compression ratio control in the control unit 3. The steady compression ratio setting means 41 is based on the engine rotational speed Ne detected by a crank angle sensor (not shown) and the intake air amount (fresh air amount) Qa detected by the air flow meter 11, and the steady-state target corresponding to the engine operating conditions. Output the compression ratio. Although the details of the transient EGR rate estimating means 42 will be described later, the actually detected EGR gas flow rate Qegr, the supercharging pressure PA by the first pressure sensor 12, the collector internal pressure PB by the second pressure sensor 13, and the air flow meter 11 is used to estimate the EGR rate at the intake port during transition (which is substantially equal to the in-cylinder EGR rate). The steady EGR rate estimating means 43 outputs a target EGR rate at a steady time determined from a predetermined map, for example, based on the engine operating condition, that is, the engine rotational speed Ne and the intake air amount Qa. The transient EGR compression ratio correcting unit 44 outputs a necessary compression ratio correction amount based on the difference between the EGR rate at the transient intake port output by the transient EGR rate estimating unit 42 and the target EGR rate at the steady state. By adding this compression ratio correction amount to the steady target compression ratio at the addition point 45, the final target compression ratio is obtained.

  FIG. 4 shows the characteristic of the target compression ratio at the steady state by the steady compression ratio setting means 41. The steady compression ratio setting means 41 sets a steady target compression ratio based on, for example, a map using the engine speed Ne and the intake air amount Qa as parameters. FIG. 4 also shows an exhaust gas recirculation region in which exhaust gas recirculation is performed via the exhaust gas recirculation passage 21, but the target compression ratio in a steady state takes this exhaust gas recirculation into consideration.

  FIG. 5 is a functional block diagram showing details of the transient EGR rate estimating means 42. The throttle flow rate estimating means 51 outputs the throttle gas flow rate Qth passing through the throttle valve 10 based on the supercharging pressure PA upstream of the throttle valve 10 and the collector internal pressure PB downstream of the throttle valve 10. Further, the EGR gas flow rate Qegr and the fresh air amount Qa by the air flow meter 11 are added at the addition point 52, so that the total flow rate Qtt flowing into the intake passage volume between the junction 22 of the intake passage 5 and the throttle valve 10 is added. Ask for. Then, at the subtraction point 53, the difference gas flow rate Qg is obtained by subtracting the throttle gas flow rate Qth from the total flow rate Qtt. The throttle gas flow rate Qth corresponds to the amount of gas flowing out from the intake passage volume between the junction 22 of the intake passage 5 and the throttle valve 10. The intake port EGR rate estimating means 54 outputs an intake port EGR rate estimated value from the differential gas flow rate Qg and the EGR gas flow rate Qegr.

  FIG. 6 shows details of the EGR rate estimating means 54 in the intake port. The EGR rate estimating means 54 in the intake port includes a throttle valve upstream EGR rate map 61 and a gas from the throttle valve 10 to the intake port 10. And an intake pipe internal model 62 having a transfer function corresponding to the transport delay. The EGR ratio map 61 on the upstream side of the throttle valve is based on the difference gas flow rate Qg of “total flow rate Qtt−throttle gas flow rate Qth” and the EGR gas flow rate Qegr, and the EGR in the intake passage volume between the junction 22 and the throttle valve 10. The rate, that is, the EGR rate upstream of the throttle valve 10 is obtained. FIG. 7 shows the characteristics of the throttle valve upstream EGR rate map 61. The intake pipe internal model 62 can be simply configured as a first-order lag element, and gives a delay corresponding to a transport delay to the EGR rate upstream of the throttle valve 10 obtained from the throttle valve upstream EGR rate map 61. The estimated EGR rate in the intake port is output.

  With such a configuration, the EGR rate in the intake port corresponding to the EGR rate of the gas sucked into the cylinder can be accurately estimated during the transition.

  At the time of transition, a necessary compression ratio correction amount is output from the transient EGR compression ratio correction means 44 in accordance with the difference between the estimated intake port EGR rate and the steady-state target EGR rate. FIG. 8 shows the characteristics of the compression ratio correction amount output by the transient EGR compression ratio correction means 44, and the difference between “the steady-state target EGR rate−the estimated EGR rate in the intake port” is a negative value. For example, the compression ratio correction amount is output as a positive value, and if the difference is a positive value, the compression ratio correction amount is output as a negative value. That is, when the EGR rate at the intake port estimated at the time of transition is higher than the target EGR rate at the time of steady state, the target compression ratio at the time of steady state is corrected to the high compression ratio side, and the EGR rate at the intake port estimated at the time of transition is When the target EGR rate is lower than the steady-state target EGR rate, the steady target compression ratio is corrected to the low compression ratio side.

  FIG. 9 shows changes in the EGR rate and the target compression ratio in the above-described transient scene 1 (during acceleration in which the operating conditions change from point P1 outside the EGR region to point P2 in the EGR region). As described above, the target EGR rate indicated by the broken line changes according to the same EGR rate map as that in the steady state, but the in-cylinder EGR rate rises with a delay as indicated by the solid line. In the configuration of the above embodiment, the estimated EGR rate in the intake port is obtained with the characteristic along the solid line. For this reason, the target compression ratio is temporarily corrected to the low compression ratio side with respect to the steady-state characteristics, as shown as a solid line “Example” in the figure. Therefore, the occurrence of transient knocking is suppressed.

  FIG. 10 shows changes in the EGR rate and the target compression ratio in the above-described transient scene 2 (during deceleration where the operating condition changes from point P3 in the EGR region to point P4 outside the EGR region). As described above, the target EGR rate indicated by the broken line changes according to the same EGR rate map as that in the steady state, but the in-cylinder EGR rate decreases with a delay as indicated by the solid line. In the configuration of the above embodiment, the estimated EGR rate in the intake port is obtained with the characteristic along the solid line. Therefore, the target compression ratio becomes a higher compression ratio at an earlier stage than the steady-state characteristic, as shown as a solid line “Example” in the figure. Therefore, temporary deterioration of fuel consumption is suppressed.

  As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, A various change is possible. For example, in the above embodiment, a multi-link variable compression ratio mechanism that changes the compression ratio by vertically moving the top dead center position of the piston 34 is used. Even if it exists, this invention is applicable similarly.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Variable compression ratio mechanism 3 ... Control unit 41 ... Steady compression ratio setting means 42 ... Transient EGR rate estimation means 43 ... Steady EGR rate estimation means 44 ... Transient EGR compression ratio correction means 44
62 ... Intake pipe model (transfer function)

Claims (6)

In an internal combustion engine having a variable compression ratio mechanism and an exhaust gas recirculation device that recirculates part of the exhaust gas from the exhaust passage to the upstream side of the throttle valve of the intake passage through the exhaust gas recirculation passage.
Target compression ratio setting means for setting a target compression ratio of the variable compression ratio mechanism according to the operating conditions of the internal combustion engine;
Throttle valve upstream side EGR rate estimating means for estimating an EGR rate in the intake passage volume between the junction with the exhaust gas recirculation passage and the throttle valve during a transition of the internal combustion engine;
An in-intake port EGR rate estimating means for obtaining an EGR rate at the intake port from an EGR rate at the upstream side of the throttle valve using a transfer function corresponding to a transport delay in the intake passage from the throttle valve to the intake port;
Compression ratio correction means for correcting the target compression ratio based on the estimated EGR rate at the intake port ;
Equipped with a,
The control apparatus for a variable compression ratio internal combustion engine, wherein the compression ratio correction means corrects the target compression ratio to the high compression ratio side when the estimated EGR rate at the intake port is higher than the target EGR rate in a steady state . EGR gas flow rate detection means for detecting the flow rate of EGR gas flowing through the exhaust gas recirculation passage,
2. The control of a variable compression ratio internal combustion engine according to claim 1, wherein the throttle valve upstream side EGR rate estimating means estimates an EGR rate in the intake passage volume using the EGR gas flow rate. 3. apparatus. The throttle valve upstream side EGR rate estimating means includes:
A total flow rate that flows into the intake passage volume is obtained from the fresh air flow rate and the EGR gas flow rate, and a differential gas flow rate obtained by subtracting a gas flow rate that passes through the throttle valve from the total flow rate is obtained. 3. The control apparatus for a variable compression ratio internal combustion engine according to claim 1, wherein an EGR rate in the intake passage volume is obtained from a gas flow rate. The compression ratio correcting means, claim estimated EGR rate in the intake port to correct the target compression ratio to the low compression ratio side when lower than the target EGR rate during steady, characterized in that 1-3 The control apparatus of the variable compression ratio internal combustion engine according to any one of the above. The internal combustion engine includes a turbocharger, the exhaust gas recirculation device, either from the turbine downstream side of the exhaust passage for recirculating the exhaust to the compressor upstream of the intake passage, according to claim 1-4, characterized in that A control apparatus for a variable compression ratio internal combustion engine according to claim 1. In an internal combustion engine having a variable compression ratio mechanism and an exhaust gas recirculation device that recirculates part of the exhaust gas from the exhaust passage to the upstream side of the throttle valve of the intake passage through the exhaust gas recirculation passage.
Set the target compression ratio of the variable compression ratio mechanism according to the operating conditions of the internal combustion engine,
During the transition of the internal combustion engine, the EGR rate in the intake passage volume between the junction with the exhaust gas recirculation passage and the throttle valve is estimated,
A delay corresponding to the transport delay in the intake passage from the throttle valve to the intake port is given to the EGR rate upstream of the throttle valve to estimate the EGR rate at the intake port,
A control method for a variable compression ratio internal combustion engine , wherein , based on the estimated EGR rate at the intake port, the target compression ratio is corrected to a high compression ratio side when the EGR rate is higher than a target EGR rate in a steady state .

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