Control device for internal combustion engine

Abstract

To provide a device for controlling an internal combustion engine that is applied to an internal combustion engine, in which two superchargers including actuators capable of controlling rotational speeds of turbines are connected in parallel, and can sufficiently exert supercharging capability of both superchargers while avoiding generation of surging in the two compressors.SOLUTION: A device for controlling an internal combustion engine, when surging is less likely to be generated in both compressors, controls actuators so as to make amounts of air flowing into two compressors equal to each other, and when it is predicted that surging is likely to be generated in one of the compressors, acquires an off-set value, raises a parameter of the actuator corresponding to the one of the compressors by the off-set value, and lowers a parameter of the other actuator by the off-set value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control device for an internal combustion engine, for example, to a control device for an internal combustion engine including two superchargers arranged in parallel with each other. [Background technology]

[0002] There is known an internal combustion engine having two turbochargers arranged in parallel with each other. The operating states of the two turbochargers are generally switched between a single turbo state in which only one turbocharger (first turbocharger) operates, and a parallel turbo state in which the other turbocharger (second turbocharger) also operates.

[0003] When the turbocharger is in a parallel turbo operating state, a portion of the exhaust gas (combustion gas) discharged from the combustion chamber of the internal combustion engine flows into the turbine (first turbine) of the first turbocharger, and the other exhaust gas flows into the turbine (second turbine) of the second turbocharger. Meanwhile, a portion of the air (intake air) flowing through the intake path flows into the compressor (first compressor) of the first turbocharger, and the other intake air flows into the compressor (second compressor) of the second turbocharger. Both the intake air compressed from the first compressor and the intake air compressed from the second compressor flow into the combustion chamber.

[0004] For example, in the supercharging system described in Patent Document 1, either a single turbo state or a parallel turbo state is selected based on the amount of intake air flowing into the first compressor and the compression pressure ratio, which is the ratio of the outlet pressure (i.e., supercharging pressure) to the inlet pressure of the first compressor. As a result, when the amount of energy obtained from the exhaust (exhaust energy amount) is relatively small, the single turbo state is selected, improving the responsiveness of the pressure of the intake air introduced into the internal combustion engine (i.e., supercharging pressure). In other words, the so-called turbo lag is prevented from becoming large. On the other hand, when the amount of exhaust energy is relatively large, the parallel turbo state is selected, making it possible to increase the amount of intake air introduced into the combustion chamber of the internal combustion engine by using two superchargers.

[0005] Additionally, in the turbocharging system, each of the first turbine and the second turbine is equipped with a variable nozzle mechanism. The variable nozzle mechanism includes a plurality of nozzle vanes, and the nozzle closure degree (i.e., the degree to which the nozzle vanes close the exhaust path) changes according to the rotation angle of each nozzle vane. As the nozzle closure degree increases, the exhaust path is narrowed and the flow velocity of the exhaust gas introduced into the turbine increases, so that the rotation speed of the turbine increases. In other words, the amount of exhaust energy supplied to the turbine increases. Therefore, the operating states of the first compressor and the second compressor can be controlled by controlling the nozzle closure degrees of the first turbine and the second turbine. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-122467 A Summary of the Invention [Problem to be solved by the invention]

[0007] When the intake air pumped from the first compressor and the second compressor join together and flow into the combustion chamber, the outlet pressures of the two compressors are approximately equal to each other. In addition, the inlet pressures of the first compressor and the second compressor are approximately equal to atmospheric pressure. Therefore, the compression pressure ratios of the two compressors are approximately equal to each other.

[0008] In addition, if the nozzle closure degrees of the first turbine and the second turbine are equal to each other, the flow velocities of the exhaust gas introduced into the two turbines (i.e., the amount of exhaust energy supplied to the turbines) will be approximately equal to each other. Therefore, the rotation speeds of the two turbines will be approximately equal to each other, and as a result, the intake air amounts of the two compressors will be approximately equal to each other. That is, in this case, the combinations of the intake air amounts and compression pressure ratios of the first compressor and the second compressor (i.e., the operating points of the compressors) will be approximately equal to each other. The process of setting the nozzle closure degrees of the first turbine and the second turbine to equal values ​​will hereinafter be referred to as "air amount equalization process."

[0009] However, when the intake air amount of the compressor is smaller than the required air amount determined for the compression pressure ratio, the possibility of so-called surging occurring increases. In addition, when the first and second turbochargers are operating in a parallel turbo state, the required air amount of the first compressor and the required air amount of the second compressor may differ from each other. That is, the conditions for surging occurring may differ between the first compressor and the second compressor. In other words, the surge line, which is a set of combinations of the intake air amount and the compression pressure ratio (i.e., the operating points of the compressors) at which surging is highly likely to occur, may differ between the first compressor and the second compressor.

[0010] For example, even if two compressors of the same type and size are arranged in parallel to an internal combustion engine, if the intake passage leading to the first compressor and the intake passage leading to the second compressor are different, the surge lines of the two compressors may be different. Specifically, if the intake path branches into two to reach the first compressor and the second compressor, and the number of curved parts and the length of the straight sections included in the two branched paths are different, the surge lines may be different.

[0011] When the surge lines of the first compressor and the second compressor are different from each other, if the operating points of the two compressors are approximately equal to each other, a situation may occur in which surging is highly likely to occur in only one compressor. In other words, when the air amount equalization process is being performed, a situation may occur in which surging is highly likely to occur in one compressor and is unlikely to occur in the other compressor.

[0012] When the operating state of one compressor is also controlled so that surging does not occur in the other compressor, an unused operating region occurs on the compressor map for the other compressor. Specifically, this operating region is a region that is above the surge line of one compressor and below the surge line of the other compressor. Therefore, if the air amount equalization process is always performed in the parallel turbo state, the two turbochargers are controlled so that the operating point of the other compressor is not included in this operating region, and as a result, there is a risk that the turbocharging capacity of the other compressor cannot be fully utilized.

[0013] However, in the supercharging system described in Patent Document 1, even if the surge lines of the two compressors are different from each other, no consideration is given to allowing each of the two compressors to fully exert its supercharging capacity.

[0014] The present invention has been devised in consideration of the above points, and has an object to provide a control device for an internal combustion engine that enables two compressors, each of which has a different surge line and is equipped with two turbochargers in a parallel turbo state, to fully exert their turbocharging capacity. [Means for solving the problem]

[0015] In order to solve the above problems, a control device for an internal combustion engine according to a first aspect of the present invention is applied to an internal combustion engine, a first supercharger, and a second supercharger. The internal combustion engine burns fuel in a combustion chamber using intake air flowing in from an intake path, and discharges exhaust gas generated in the combustion chamber to an exhaust path. The first supercharger has a first turbine interposed in the exhaust path, a first compressor interposed in the intake path and rotating in conjunction with the first turbine, and a first turbine actuator for increasing a first control parameter when increasing the rotation speed of the first turbine. The second supercharger is of the same type and size as the first supercharger, and has a second turbine interposed in the exhaust path, a second compressor interposed in the intake path and rotating in conjunction with the second turbine, and a second turbine actuator for increasing a second control parameter when increasing the rotation speed of the second turbine.

[0016] The control device for an internal combustion engine executes an air amount equalization process, which acquires a target parameter value that is a value determined according to a target value of a pressure of the compressed air, and sets the first control parameter and the second control parameter to the target parameter value, when a parallel turbo condition is established, which is established when the intake path is configured so that intake air that has flowed into the intake path flows into each of the first compressor and the second compressor, and compressed air compressed by the first compressor and the second compressor join and flow into the combustion chamber, and the exhaust path is configured so that the exhaust gas discharged from the combustion chamber flows into each of the first turbine and the second turbine. and a control unit that, when the parallel turbo condition is satisfied and it is predicted that the amount of air flowing into one of the first compressor and the second compressor will be smaller than a required air amount determined for a compression pressure ratio, which is a ratio of the pressure of the compressed air to the pressure of the intake air, executes air amount difference processing to acquire the target parameter value and an offset value, and set a parameter corresponding to the one of the first control parameter and the second control parameter to a value larger than the target parameter value by the offset value, and set the other parameter of the first control parameter and the second control parameter to a value smaller than the target parameter value by the offset value.

[0017] A second aspect of the present invention is a control device for an internal combustion engine according to the first aspect of the present invention, wherein the control unit sets the offset value to a larger value as the rotational speed of the internal combustion engine is higher, and sets the offset value to a larger value as the amount of fuel injected into the combustion chamber is larger.

[0018] A third aspect of the present invention is a control device for an internal combustion engine according to the first or second aspect of the present invention, wherein each of the first turbine actuator and the second turbine actuator is a variable nozzle device having a nozzle vane that controls the degree of closure of a flow path that leads the exhaust gas to the first turbine or the second turbine, and each of the first control parameter and the second control parameter is a parameter that increases as the state of the nozzle vane approaches a fully closed state from a fully open state. Effect of the Invention

[0019] The control device for an internal combustion engine according to the first aspect of the present invention, when it is predicted (determined) that surging is highly likely to occur only in one of the first compressor and the second compressor, increases the intake air amount of the one compressor while decreasing the intake air amount of the other compressor. This makes it possible to avoid the occurrence of surging in the one compressor while utilizing the supercharging capacity of the other compressor. Therefore, according to the first aspect of the present invention, it is highly likely that the supercharging capacity of each of the two compressors having different surge lines can be fully utilized.

[0020] In the second invention, when it is predicted that surging is highly likely to occur in only one of the compressors, a target parameter value required to avoid surging in the one of the compressors is determined based on the engine speed and the fuel injection amount. In other words, according to the second invention, it is possible to obtain, by simple processing, a target parameter value that corresponds to an increase in the amount of exhaust energy supplied to the turbine linked to the one of the compressors, which is required to avoid surging.

[0021] According to the third invention, by adjusting the first control parameter and the second control parameter to a value (nozzle closure degree) that increases as the nozzle vanes close, it is possible to control the amount of exhaust energy supplied to the first turbine and the second turbine. [Brief description of the drawings]

[0022] [Figure 1] 1 is a schematic configuration diagram of an engine system to which a control device for an internal combustion engine according to the present invention is applied; [Diagram 2] 4 is a compressor map showing the operating point of a compressor provided in the turbocharger. [Diagram 3] 4 is a map for determining a nozzle offset amount based on an engine rotation speed and an injection amount. [Figure 4] 4 is a time chart showing changes in the air amount and pressure ratio of a compressor, and the nozzle closure degree of a turbine. [Diagram 5] 3 is a flowchart showing a "supercharger control processing routine" executed by a control device for an internal combustion engine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] An embodiment of the present invention will be described with reference to Figs. 1 to 5. The same reference numbers in the description refer to the same elements having the same functions without duplicate description. An internal combustion engine control device according to the present invention is applied to an engine system 1 shown in Fig. 1. The engine system 1 includes an internal combustion engine 2, a first supercharger 3, a second supercharger 4, an intake system 5, an exhaust system 6, and an ECU 7 which is a control unit.

[0024] The internal combustion engine 2 in this embodiment is a multi-cylinder diesel engine mounted on a vehicle (not shown) as a driving force source. The internal combustion engine 2 includes a plurality of fuel injection valves 21. Each of the fuel injection valves 21 injects high-pressure fuel supplied from an accumulator chamber of a common rail device (not shown) into a combustion chamber (cylinder) in response to an instruction from an ECU 7.

[0025] The first turbocharger 3 includes a first turbine 31, a first variable nozzle mechanism 32, and a first compressor 33. The first turbine 31 is operated (rotated) by the pressure of exhaust gas (combustion gas) discharged from the combustion chamber of the internal combustion engine 2. The first variable nozzle mechanism 32 is equipped with a nozzle vane which is a throttling mechanism for the exhaust gas flowing into the first turbine 31.

[0026] Specifically, the degree of closure of the exhaust flow passage in the first turbine 31 (i.e., the degree to which the exhaust flow passage is closed) changes according to a first nozzle closure degree Vn1, which is a rotational position of a nozzle vane provided in the first variable nozzle mechanism 32. The first variable nozzle mechanism 32 includes an actuator, and changes the first nozzle closure degree Vn1 between a predetermined fully open position (fully open state) and a fully closed position (fully closed state) according to an instruction from the ECU 7. The first compressor 33 operates (rotates) in conjunction with the first turbine 31, and pressurizes the air (intake air) that is drawn into the combustion chamber of the internal combustion engine 2. For convenience, the first variable nozzle mechanism 32 and the first nozzle closure degree Vn1 are also referred to as a "first turbine actuator" and a "first control parameter", respectively.

[0027] The second turbocharger 4 is a turbocharger of the same type and size as the first turbocharger 3. The second turbocharger 4 includes a second turbine 41, a second variable nozzle mechanism 42, and a second compressor 43. The second turbine 41 is operated by the pressure of the exhaust gas from the internal combustion engine 2. The degree of closure of the exhaust passage in the second turbine 41 changes according to a second nozzle closure degree Vn2, which is a rotational position of a nozzle vane provided in the second variable nozzle mechanism 42. The second variable nozzle mechanism 42 includes an actuator, and changes the second nozzle closure degree Vn2 between a fully open position and a fully closed position according to an instruction from the ECU 7. The second compressor 43 operates in conjunction with the second turbine 41, and pressurizes the air to be taken into the combustion chamber of the internal combustion engine 2. For convenience, the second variable nozzle mechanism 42 and the second nozzle closure degree Vn2 are also referred to as a "second turbine actuator" and a "second control parameter", respectively.

[0028] The intake system 5 includes intake pipes 51a-51g, which form an intake path, an intake manifold 52, an intake switching valve 53, and an intake bypass valve 54. The intake pipe 51a introduces intake air (fresh air) drawn in from the outside (outside the vehicle) to the intake pipes 51b and 51c. The intake pipe 51b introduces the intake air flowing in from the intake pipe 51a to the first compressor 33. The intake pipe 51c introduces the intake air flowing in from the intake pipe 51a to the second compressor 43. The intake pipe 51d introduces the intake air discharged from the first compressor 33 to the intake pipe 51f. The intake pipe 51e introduces the intake air discharged from the second compressor 43 to the intake pipe 51f.

[0029] The intake pipe 51f introduces the intake air flowing in from the intake pipes 51d and 51e to the intake manifold 52. The intake pipe 51g connects the branched portion of the intake pipe 51b to the branched portion of the intake pipe 51e. The intake manifold 52 introduces the intake air flowing in from the intake pipe 51f to the combustion chamber of the internal combustion engine 2.

[0030] The intake changeover valve 53 is disposed in the intake pipe 51e between a branch point with the intake pipe 51g (i.e., one end of the intake pipe 51g) and a junction point with the intake pipes 51d and 51f (i.e., one end of the intake pipe 51e). The intake changeover valve 53 is switched between a closed state and an open state in response to an instruction from the ECU 7. The intake bypass valve 54 is disposed in the intake pipe 51g. The intake bypass valve 54 is switched between a closed state and an open state in response to an instruction from the ECU 7.

[0031] The exhaust system 6 includes exhaust manifolds 61a-61b, exhaust pipes 62a-62e forming exhaust paths, an exhaust switching valve 63, and an exhaust gas purification device 64. The exhaust manifold 61a introduces a portion of the exhaust (combustion gas) discharged from a portion of the combustion chambers of the internal combustion engine 2 into the exhaust pipe 62a. The exhaust manifold 61b introduces exhaust gas discharged from the other combustion chambers of the internal combustion engine 2 into the exhaust pipe 62b.

[0032] The exhaust pipe 62a introduces exhaust gas to the first turbine 31. The exhaust pipe 62b introduces exhaust gas to the second turbine 41. The exhaust pipe 62c connects the exhaust pipe 62a and the exhaust pipe 62b. The exhaust pipe 62d exhausts the exhaust gas discharged from the first turbine 31 and the exhaust gas flowing in from the exhaust pipe 62e to the outside (outside the vehicle). The exhaust pipe 62e introduces the exhaust gas discharged from the second turbine 41 into the exhaust pipe 62d.

[0033] The exhaust switching valve 63 is disposed in the exhaust pipe 62b at a position between the second turbine 41 and a branch portion of the exhaust pipe 62c (i.e., one end portion of the exhaust pipe 62c). The exhaust switching valve 63 is switched between a closed state and an open state in response to an instruction from the ECU 7.

[0034] The exhaust gas purification device 64 is disposed in the exhaust pipe 62d downstream of the junction with the exhaust pipe 62e. The exhaust gas purification device 64 includes a well-known oxidation catalyst, a DPF (Diesel Particulate Filter), and an SCR (Selective Catalytic Reduction) and purifies the exhaust gas.

[0035] The ECU 7 is an electronic control unit including a CPU, a ROM, a RAM, and an EEPROM. The CPU sequentially executes a predetermined program to read data, perform numerical calculations, and output the calculation results. The ROM stores the programs executed by the CPU and maps (lookup tables), etc. The RAM temporarily stores data referenced by the CPU. The EEPROM stores data referenced by the CPU, and furthermore, retains the stored data even when the ECU 7 stops operating.

[0036] The ECU 7 is connected to a crank angle sensor 71, a cam position sensor 72, an airflow sensor 73, vane closure sensors 74a-74b, pressure sensors 75a-75c, temperature sensors 76a-76b, and an accelerator opening sensor 77. The crank angle sensor 71 outputs a pulse signal to the ECU 7 every time a crankshaft (not shown) of the internal combustion engine 2 rotates by a predetermined angle. The cam position sensor 72 outputs a signal corresponding to the rotational position of a camshaft (not shown) of the internal combustion engine 2 to the ECU 7.

[0037] The ECU 7 acquires the engine speed NE of the internal combustion engine 2 based on a signal input from the crank angle sensor 71. The ECU 7 acquires the crank angle CA of a specific combustion chamber provided in the internal combustion engine 2 based on signals input from the crank angle sensor 71 and the cam position sensor 72.

[0038] The airflow sensor 73 is disposed in the intake pipe 51a. The airflow sensor 73 detects an air amount Ga, which is the amount of intake air (intake air) flowing through the intake pipe 51a, and outputs a signal indicative of the air amount Ga to the ECU 7. The vane closure sensor 74a detects a first nozzle closure degree Vn1, and outputs a signal indicative of the first nozzle closure degree Vn1 to the ECU 7. The vane closure sensor 74b detects a second nozzle closure degree Vn2, and outputs a signal indicative of the second nozzle closure degree Vn2 to the ECU 7.

[0039] The pressure sensor 75a detects atmospheric pressure P1, which is the pressure of outside air (i.e., the pressure of the intake air flowing into the first compressor 33 and the second compressor 43), and outputs a signal representing the atmospheric pressure P1 to the ECU 7. The pressure sensor 75b is disposed in the intake pipe 51d near the joining position of the intake pipes 51e and 51f (i.e., one end of the intake pipe 51d). The pressure sensor 75b detects boost pressure P3, which is the pressure of the intake air (compressed air) flowing into the combustion chamber of the internal combustion engine 2, and outputs a signal representing the boost pressure P3 to the ECU 7. The pressure sensor 75c is disposed in the intake pipe 51a. The pressure sensor 75c detects exhaust pressure P4, which is the pressure of the exhaust gas flowing out from the combustion chamber of the internal combustion engine 2, and outputs a signal representing the exhaust pressure P4 to the ECU 7.

[0040] The temperature sensor 76a is disposed in the intake pipe 51a. The temperature sensor 76a detects an intake temperature δ0, which is the temperature of the intake air flowing into the first compressor 33 and the second compressor 43, and outputs a signal indicative of the intake temperature δ0 to the ECU 7. The temperature sensor 76b is disposed in the exhaust pipe 62a. The temperature sensor 76b detects an exhaust temperature T4, which is the temperature of the exhaust gas flowing out from the combustion chamber of the internal combustion engine 2, and outputs a signal indicative of the exhaust temperature T4 to the ECU 7.

[0041] The accelerator opening sensor 77 detects the accelerator pedal opening Ap, which is the opening of the accelerator pedal (not shown) that is operated by the driver of the vehicle equipped with the internal combustion engine 2 to accelerate the vehicle, and outputs a signal representing the accelerator pedal opening Ap to the ECU 7.

[0042] The ECU 7 controls the engine speed NE based on the accelerator pedal opening degree Ap. When increasing the engine speed NE, the ECU 7 increases the injection amount Qi, which is the amount of fuel injected from the fuel injection valve 21. Furthermore, the ECU 7 increases the supercharging pressure P3 by operating the first supercharger 3 and the second supercharger 4 as described below, thereby increasing the pressure and amount of intake air flowing into the combustion chamber of the internal combustion engine 2.

[0043] When the injection amount Qi is determined, the ECU 7 determines a fuel injection pattern including (a plurality of) combinations of the timing of fuel injection represented by the crank angle CA and the fuel injection amount at that timing, according to the injection amount Qi. The ECU 7 causes the fuel injection valve 21 of each combustion chamber to inject fuel in accordance with the fuel injection pattern.

[0044] In order to control the supercharging pressure P3, the ECU 7 determines a target supercharging pressure Ptgt. The ECU 7 controls the first supercharger 3 and the second supercharger 4 so that the supercharging pressure P3 approaches the target supercharging pressure Ptgt. Specifically, the ECU 7 switches the operating state (hereinafter also referred to as the "supercharging state") of the first supercharger 3 and the second supercharger 4 between a "single turbo state" and a "parallel turbo state". For convenience, the target supercharging pressure Ptgt is also referred to as the "target parameter value".

[0045] The single turbo state is a state in which only the first turbocharger 3 pressurizes the intake air flowing into the combustion chamber of the internal combustion engine 2. The parallel turbo state is a state in which both the first turbocharger 3 and the second turbocharger 4 pressurize the intake air flowing into the combustion chamber of the internal combustion engine 2. When the supercharging state is the single turbo state, the intake changeover valve 53, the exhaust changeover valve 63, and the intake bypass valve 54 are each in a "closed state". When the supercharging state is the parallel turbo state, the intake changeover valve 53 and the exhaust changeover valve 63 are in an "open state", and the intake bypass valve 54 is in a "closed state". For convenience, the conditions that are met when the supercharging state is the parallel turbo state are also referred to as "parallel turbo conditions".

[0046] When the supercharging state is the single turbo state and a predetermined parallel turbo switching condition is satisfied, the ECU 7 switches the supercharging state to the parallel turbo state. When the supercharging state is the parallel turbo state and a predetermined single turbo switching condition is satisfied, the ECU 7 switches the supercharging state to the single turbo state. In general, the ECU 7 sets the supercharging state to the parallel turbo state when the target supercharging pressure Ptgt is relatively large.

[0047] When switching the supercharging state from the single turbo state to the parallel turbo state, the ECU 7 first switches the exhaust switching valve 63 and the intake bypass valve 54 to the "open state". Then, after a predetermined switching time Tc has elapsed, the ECU 7 switches the intake bypass valve 54 to the "closed state" and switches the intake switching valve 53 to the "open state".

[0048] When the supercharging state is a single turbo state, the ECU 7 determines a target closure degree V1tgt, which is a target value of the first nozzle closure degree Vn1, based on parameters such as the target supercharging pressure Ptgt, the exhaust temperature T4, the exhaust pressure P4, the air amount Ga, and the injection amount Qi (hereinafter collectively referred to as "turbine parameters"). The target closure degree V1tgt increases as the target supercharging pressure Ptgt (one of the turbine parameters) increases. The target closure degree V1tgt decreases as each of the exhaust temperature T4 and the exhaust pressure P4 increases. Furthermore, the ECU 7 controls the first variable nozzle mechanism 32 so that the actual first nozzle closure degree Vn1 approaches the target closure degree V1tgt.

[0049] On the other hand, when the supercharging state is a parallel turbo state, the ECU 7 acquires the target closure degree V1tgt and the target closure degree V2tgt which is a target value of the second nozzle closure degree Vn2 based on the turbine parameters. The target closure degree V1tgt and the target closure degree V2tgt increase as the target supercharging pressure Ptgt increases. In addition, the ECU 7 controls the first variable nozzle mechanism 32 and the second variable nozzle mechanism 42 so that the actual first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 approach the target closure degree V1tgt and the target closure degree V2tgt, respectively.

[0050] If the "nearby condition" described later is not satisfied, the ECU 7 sets the target closure degree V1tgt and the target closure degree V2tgt to values ​​equal to each other, and therefore the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 become substantially equal to each other. In this case, the first air amount Ga1, which is the amount of air flowing into the first compressor 33, and the second air amount Ga2, which is the amount of air flowing into the second compressor 43, become substantially equal to each other.

[0051] The air amount Ga detected by the air flow sensor 73 is equal to the sum of the first air amount Ga1 and the second air amount Ga2 (i.e., Ga=Ga1+Ga2). When the supercharging state is a single turbo state, the second air amount Ga2 is "0." The engine system 1 according to this embodiment does not include a sensor that directly detects each of the first air amount Ga1 and the second air amount Ga2.

[0052] The process of making the first air amount Ga1 and the second air amount Ga2 substantially equal to each other, which is executed when the supercharging state is the parallel turbo state and the vicinity condition is not satisfied, is also called the “air amount equalization process.” On the other hand, when the supercharging state is the parallel turbo state and the vicinity condition is satisfied, the ECU 7 executes the “air amount difference process” of making the second air amount Ga2 larger than the first air amount Ga1.

[0053] The air amount difference processing and the proximity condition will be described with reference to Fig. 2 to Fig. 4. Fig. 2 shows a part of a so-called compressor map showing the operating points (operating conditions) of the first compressor 33 and the second compressor 43. The operating point of the first compressor 33 in Fig. 2 is determined by a combination of the first corrected air amount Gam1 and the pressure ratio Pr.

[0054] The first corrected air amount Gam1 is a value obtained by multiplying the first air amount Ga1 by a correction coefficient K (i.e., Gam1=K×Ga1). The correction coefficient K is the square root of a value obtained by dividing a predetermined reference temperature θ0 (in this embodiment, θ0=288.215K (=15°C)) by an intake temperature δ0 expressed in absolute temperature (i.e., K=(θ0 / δ0) 1 / 2 The pressure ratio Pr is the ratio of the boost pressure P3 to the atmospheric pressure P1 (i.e., Pr=P3 / P1). For convenience, the pressure ratio Pr is also called the "compression pressure ratio."

[0055] 2 is determined by a combination of the second corrected air amount Gam2 and the pressure ratio Pr. The second corrected air amount Gam2 is a value obtained by multiplying the second air amount Ga2 by a correction coefficient K (i.e., Gam2=K×Ga2).

[0056] The curve La shown in Fig. 2 is part of the surge line of the first compressor 33. That is, if the operating point of the first compressor 33 moves above the curve La in Fig. 2, the possibility of surging occurring in the first compressor 33 increases. On the other hand, the curve Lb shown in Fig. 2 is part of the surge line of the second compressor 43. That is, if the operating point of the second compressor 43 moves above the curve Lb in Fig. 2, the possibility of surging occurring in the second compressor 43 increases.

[0057] In other words, the curve La shows the first corrected air amount Gam1, which is determined for the pressure ratio Pr and is necessary to prevent surging in the first compressor 33. Similarly, the curve Lb shows the second corrected air amount Gam2, which is determined for the pressure ratio Pr and is necessary to prevent surging in the second compressor 43.

[0058] As described above, the first compressor 33 and the second compressor 43 are compressors of the same type and size. However, the intake path from the intake pipe 51a to the first compressor 33 does not match the intake path from the intake pipe 51a to the second compressor 43. Specifically, the first compressor 33 and the second compressor 43 differ from each other in the number and positions of curved portions included in the intake paths, and the lengths of straight sections. Therefore, the surge lines (i.e., the curves La and Lb) of the first compressor 33 and the second compressor 43 are different from each other.

[0059] Here, it is assumed that the air amount difference processing is not executed (i.e., the air amount equal processing is continued) when the supercharging state is the parallel turbo state, and the operating points of both the first compressor 33 and the second compressor 43 move from point Pa to point Pf via points Pb and Pe on the curve Lc. In this example, the first corrected air amount Gam1, the second corrected air amount Gam2, and the pressure ratio Pr increase with time. Therefore, in this case, the engine speed NE increases.

[0060] Since point Pc is an operating point on curve Lb, when the operating point of the second compressor 43 reaches point Pc, there is a high possibility that surging will occur in the second compressor 43. On the other hand, even if the operating point of the first compressor 33 reaches point Pc, there is a low possibility that surging will occur in the first compressor 33.

[0061] The proximity condition is thus met when continued execution of the air amount equalization process increases the possibility of surging occurring only in the second compressor 43. In this embodiment, the proximity condition is met when the following (Condition A) and (Condition B) are both met. (Condition A): The corrected air amount Gam is included in the range from the predetermined air amount g1 to the predetermined air amount g2 shown in FIG. (Condition B): The operating point obtained by the combination of the corrected air amount Gam and the pressure ratio Pr is located above the dashed line Ld shown in FIG.

[0062] The corrected air amount Gam when the supercharging state is a parallel turbo state is a value obtained by multiplying half the air amount Ga by the correction coefficient K (i.e., Gam = 0.5 x K x Ga). On the other hand, the corrected air amount Gam when the supercharging state is a single turbo state is a value obtained by multiplying the air amount Ga by the correction coefficient K (i.e., Gam = K x Ga). The dashed line Ld is a curve obtained by shifting the curve Lb in Figure 2 downward by a predetermined pressure ratio difference Δr.

[0063] In the example of Fig. 2, when the operating point on the curve Lc (i.e., the combination of the corrected air amount Gam and the pressure ratio Pr) moves from point Pa to point Pe on the curve Lc, the vicinity condition is satisfied. Therefore, the air amount difference process is executed during this period, and as a result, the actual operating point of the first compressor 33 moves from point Pa to point Pf via points Pb1 and Pe1 on the dashed line Le. In addition, the actual operating point of the second compressor 43 moves from point Pa to point Pf via points Pb2 and Pe2 on the dashed line Lf.

[0064] More specifically, when the air amount difference process is executed, the ECU 7 increases the second corrected air amount Gam2 by a predetermined air amount difference Δg and decreases the first corrected air amount Gam1 by the air amount difference Δg. Therefore, the ECU 7 increases the second nozzle closure degree Vn2 by the nozzle offset amount Vf and decreases the first nozzle closure degree Vn1 by the nozzle offset amount Vf. For convenience, the nozzle offset amount Vf is also referred to as the "offset value."

[0065] The ECU 7 determines the nozzle offset amount Vf by applying the engine speed NE and the injection amount Qi to the relationship between the engine speed NE, the injection amount Qi, and the nozzle offset amount Vf shown in Fig. 3. As can be seen from Fig. 3, the nozzle offset amount Vf increases as the engine speed NE increases and increases as the injection amount Qi increases.

[0066] In other words, the nozzle offset amount Vf required to increase the second corrected air amount Gam2 by the air amount difference Δg (and decrease the first corrected air amount Gam1 by the air amount difference Δg) increases as the engine speed NE and the injection amount Qi increase. When the engine speed NE and the injection amount Qi are high, the exhaust pressure P4, the exhaust temperature T4, and the amount of exhaust air, etc. increase, so that the amount of energy (amount of exhaust energy) supplied from the exhaust of the internal combustion engine 2 to the second turbine 41 increases. Therefore, the increase in the amount of exhaust energy supplied to the second turbine 41, which is required to increase the second corrected air amount Gam2 by the air amount difference Δg, increases.

[0067] The relationship between the engine speed NE and the injection amount Qi, and the nozzle offset amount Vf, which is shown in Fig. 3, is also called an "offset amount map." The offset amount map is stored in the ROM of the ECU 7 in the form of a look-up table.

[0068] FIG. 4 shows the changes in the first corrected air amount Gam1, the second corrected air amount Gam2, the corrected air amount Gam, the first pressure ratio Pr1, the second pressure ratio Pr2, the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 in the situation shown by the curve Lc in FIG. 2.

[0069] The first pressure ratio Pr1 is a ratio of the intake pressure at the outlet (i.e., one end of the intake pipe 51d) of the first compressor 33 to the intake pressure at the inlet (i.e., one end of the intake pipe 51b) of the first compressor 33. Similarly, the second pressure ratio Pr2 is a ratio of the intake pressure at the outlet (i.e., one end of the intake pipe 51e) of the first compressor 33 to the intake pressure at the inlet (i.e., one end of the intake pipe 51c) of the second compressor 43. Except for a transitional period when the supercharging state is switched between the single turbo state and the parallel turbo state, the first pressure ratio Pr1 and the second pressure ratio Pr2 are approximately equal to the pressure ratio Pr.

[0070] 4, the solid line Lg, the dashed line Lh, and the dashed line Li respectively indicate the first corrected air amount Gam1, the second corrected air amount Gam2, and the corrected air amount Gam. The solid line Lj and the dashed line Lk respectively indicate the first pressure ratio Pr1 and the second pressure ratio Pr2. The solid line Lm and the dashed line Ln respectively indicate the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2.

[0071] In the example of Fig. 4, the supercharging state is a single turbo state until time t1. Therefore, the second corrected air amount Gam2 is "0", while the first corrected air amount Gam1 is equal to the corrected air amount Gam. At time t1, the parallel turbo switching condition is met, the supercharging state is switched from the single turbo state to the parallel turbo state, and as a result, the second corrected air amount Gam2 starts to increase.

[0072] When the switching time Tc has elapsed from time t1 to time t2, the first corrected air amount Gam1 and the second corrected air amount Gam2 are substantially equal to each other. The corrected air amount Gam indicated by the dashed dotted line Li is equal to the sum of the first corrected air amount Gam1 and the second corrected air amount Gam2.

[0073] After that, at time t3, the operating points of the first compressor 33 and the second compressor 43 in Fig. 2 become equal to the state represented by point Pa in Fig. 2, and the vicinity condition is established. Therefore, the air amount difference process is started at time t3. That is, the nozzle offset amount Vf is acquired based on the offset amount map in Fig. 3.

[0074] In addition, the first variable nozzle mechanism 32 is controlled so that the first nozzle closure degree Vn1 is decreased by the nozzle offset amount Vf as shown by the solid line Lm. Furthermore, the second variable nozzle mechanism 42 is controlled so that the second nozzle closure degree Vn2 is increased by the nozzle offset amount Vf as shown by the dashed line Ln. As a result, the second corrected air amount Gam2 starts to increase as shown by the dashed line Lh, and the first corrected air amount Gam1 starts to decrease as shown by the solid line Lg.

[0075] 2, the operating point of the first compressor 33 becomes the state represented by point Pb1, and the operating point of the second compressor 43 becomes the state represented by point Pb2. Specifically, compared to the case where the air amount equalization process is continued, the second corrected air amount Gam2 becomes larger by the air amount difference Δg, and the first corrected air amount Gam1 becomes smaller by the air amount difference Δg. That is, the difference between the second corrected air amount Gam2 and the first corrected air amount Gam1 becomes equal to twice the value of the air amount difference Δg.

[0076] As a result, the actual operating point of the second compressor 43 moves to a region below the curve Lb in Fig. 2 (see dashed line Lf in Fig. 2), thereby avoiding an increased possibility of surging occurring in the second compressor 43. Note that the period from time t3 to time t4 is the time (time lag) until the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 change by the nozzle offset amount Vf and the first corrected air amount Gam1 and the second corrected air amount Gam2 actually change by the air amount difference Δg.

[0077] At time t5, the operating point in FIG. 2 (specifically, the combination of the corrected air amount Gam and the pressure ratio Pr) becomes the state indicated by point Pe, and the vicinity condition is no longer satisfied. Therefore, instead of the air amount difference processing, the air amount equalization processing is executed. That is, the first variable nozzle mechanism 32 and the second variable nozzle mechanism 42 are controlled so that the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 become equal to each other. As a result, when time t6 arrives and the operating point in FIG. 2 becomes the state indicated by point Pf, the first corrected air amount Gam1 and the second corrected air amount Gam2 become approximately equal to each other.

[0078] During the period from time t3 to time t5 (that is, when the air amount difference processing is being executed), the engine speed NE and the injection amount Qi increase, and accordingly, the nozzle offset amount Vf increases.

[0079] (Specific operation) Next, a specific operation of the ECU 7 will be described with reference to Fig. 5. The CPU of the ECU 7 (hereinafter also referred to as "CPU") executes a "supercharger control processing routine" shown in the flowchart of Fig. 5 every time a predetermined time period elapses.

[0080] When an appropriate timing arrives, the CPU starts the process from step 500 in Fig. 5, proceeds to step 505, and determines the injection amount Qi. Specifically, the CPU sets the injection amount Qi to a larger value as the accelerator pedal opening degree Ap increases.

[0081] Next, the CPU proceeds to step 510 and determines the target boost pressure Ptgt. Specifically, the CPU sets the target boost pressure Ptgt to a larger value as the engine speed NE increases. In addition, the CPU sets the target boost pressure Ptgt to a larger value as the injection amount Qi increases.

[0082] Next, the CPU proceeds to step 515 and determines whether the operating state (i.e., the supercharging state) of the first supercharger 3 and the second supercharger 4 is a parallel turbo state. If the supercharging state is a single turbo state, the CPU determines "No" in step 515 and proceeds to step 555, where it determines the target nozzle closure degree Vtgts in the single turbo state based on the turbine parameters. The target nozzle closure degree Vtgts is a value of the first nozzle closure degree Vn1 that is adapted in advance to the turbine parameters so that the supercharging pressure P3 becomes equal to the target supercharging pressure Ptgt when the supercharging state is a single turbo state.

[0083] Next, the CPU proceeds to step 565 and sets the target closure degree V1tgt of the first supercharger 3 to a value equal to the target nozzle closure degree Vtgts. Furthermore, the CPU proceeds to step 550 and controls the first supercharger 3 based on the target closure degree V1tgt. Specifically, the CPU controls the first variable nozzle mechanism 32 so that the first nozzle closure degree Vn1 approaches the target closure degree V1tgt. Next, the CPU proceeds to step 595 and ends the processing of this routine.

[0084] On the other hand, if the supercharging state is a parallel turbo state, the CPU judges "Yes" in step 515 and proceeds to step 520, where it determines the target nozzle closure degree Vtgtt in the parallel turbo state based on the turbine parameters. The target nozzle closure degree Vtgtt is the value of the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 that are adapted in advance to the turbine parameters so that the supercharging pressure P3 becomes equal to the target supercharging pressure Ptgt when the supercharging state is a parallel turbo state.

[0085] Next, the CPU proceeds to step 525 and determines whether or not the vicinity condition is satisfied. That is, the CPU determines whether or not both of the above-mentioned (Condition A) and (Condition B) are satisfied. If the vicinity condition is satisfied, the CPU determines "Yes" in step 525 and sequentially executes the processes of steps 530 to 545 described below, and proceeds to step 550. In this case, air amount difference processing is executed.

[0086] Step 530: The CPU determines the nozzle offset amount Vf based on the engine speed NE and the injection amount Qi. That is, the CPU determines the nozzle offset amount Vf by applying the engine speed NE and the injection amount Qi to the offset amount map in FIG. Step 535: The CPU sets the target closure degree V2tgt of the second turbocharger 4 to a value obtained by adding the nozzle offset amount Vf to the target nozzle closure degree Vtgtt.

[0087] Step 540: The CPU controls the second supercharger 4 based on the target closure degree V2tgt. Specifically, the CPU controls the second variable nozzle mechanism 42 so that the second nozzle closure degree Vn2 approaches the target closure degree V2tgt. Step 545: The CPU sets the target closure degree V1tgt of the first turbocharger 3 to a value obtained by subtracting the nozzle offset amount Vf from the target nozzle closure degree Vtgtt.

[0088] If the vicinity condition is not satisfied, the CPU determines "No" in step 525 and proceeds to step 560, where it sets the nozzle offset amount Vf to "0." Next, the CPU proceeds to step 535. That is, in this case, the air amount equalization process is executed.

[0089] As described above, when the ECU 7 determines (predicts) that the possibility of surging occurring only in the second compressor 43 increases if the air amount equalization process is continued, the ECU 7 executes the air amount difference process. This increases the possibility of fully utilizing the supercharging capabilities of the first compressor 33 and the second compressor 43 while avoiding the occurrence of surging. In addition, the ECU 7 can acquire the nozzle offset amount Vf required to increase the second corrected air amount Gam2 by the air amount difference Δg and decrease the first corrected air amount Gam1 by the air amount difference Δg when the air amount difference process is executed, by simple processing based on the offset amount map.

[0090] In addition, the ECU 7 switches between an air amount equalization process in which the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 are set to equal values, and an air amount difference process in which the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 are each changed by the nozzle offset amount Vf, depending on whether the proximity condition is satisfied. Therefore, even if the engine system 1 does not have two airflow sensors, it is highly likely that the supercharging capabilities of the first compressor 33 and the second compressor 43 can be fully exerted while avoiding the occurrence of surging by using these simple processes.

[0091] Furthermore, the ECU 7 starts the air amount difference processing before the operating point of the second compressor 43 reaches the curve Lb (at the time when the proximity condition is established). Therefore, it is possible to reduce the occurrence of surging in the second compressor 43 compared to a case where the air amount difference processing is started when the operating point of the second compressor 43 reaches the curve Lb. Specifically, the occurrence of an event in which surging occurs in the second compressor 43 due to the period from the start of the air amount difference processing to the time when the second corrected air amount Gam2 actually increases by the air amount difference Δg (for example, the period from time t3 to time t4 in FIG. 4) is avoided.

[0092] Although the embodiment of the present invention has been described with reference to the above structure, it will be apparent to those skilled in the art that many modifications, improvements, and variations are possible without departing from the scope of the present invention. Accordingly, the present invention includes all modifications, improvements, and variations that do not depart from the spirit and scope of the appended claims. The present invention is not limited to the specific structure described above, and can be modified, for example, as follows:

[0093] When the vicinity condition is satisfied (i.e., when it is determined that the possibility of surging occurring only in the second compressor 43 is high), the ECU 7 executes a process of increasing the second nozzle closure degree Vn2 by the nozzle offset amount Vf while decreasing the first nozzle closure degree Vn1 by the nozzle offset amount Vf. In addition, when it is determined that the possibility of surging occurring only in the first compressor 33 is high, the ECU 7 may execute a process of increasing the first nozzle closure degree Vn1 by the nozzle offset amount Vf while decreasing the second nozzle closure degree Vn2 by the nozzle offset amount Vf. In this case, the nozzle offset amount Vf may be determined based on an offset amount map different from the offset amount map of FIG. 3.

[0094] The ECU 7 determines that the vicinity condition is satisfied when both of the above-mentioned (Condition A) and (Condition B) are satisfied. Alternatively, the ECU 7 may determine that the vicinity condition is satisfied when the distance between the operating point of the first compressor 33 and the curve La in the compressor map of Fig. 2 is greater than a predetermined first threshold value and the distance between the operating point of the second compressor 43 and the curve Lb is smaller than a predetermined second threshold value.

[0095] The ECU 7 obtains the target nozzle closure degree Vtgts and the target nozzle closure degree Vtgtt based on the turbine parameters. That is, the ECU 7 obtains the target values ​​of the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 such that the boost pressure P3 becomes close to the target boost pressure Ptgt by feedforward processing. Alternatively, the ECU 7 may obtain the change amounts of the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2 such that the boost pressure P3 becomes close to the target boost pressure Ptgt by feedback processing.

[0096] The first turbine actuator and the second turbine actuator were the first variable nozzle mechanism 32 and the second variable nozzle mechanism 42. In addition, the first control parameter and the second control parameter were the first nozzle closure degree Vn1 and the second nozzle closure degree Vn2. Alternatively, each of the first turbine actuator and the second turbine actuator may be a wastegate valve that adjusts the amount of exhaust gas flowing into the first turbine 31 and the second turbine 41. In this case, each of the first control parameter and the second control parameter may be a parameter that has a value according to the opening degree of the wastegate valve and increases the boost pressure P3 as the first control parameter and the second control parameter increase. [Explanation of symbols]

[0097] 1. Engine system 2. Internal combustion engine 3...First turbocharger 4...Second turbocharger 5…Intake system 6…Exhaust system 7…ECU 21...Fuel injector 31…First turbine 32...First variable nozzle mechanism (variable nozzle device) 33…First compressor 41…Second turbine 42...Second variable nozzle mechanism (variable nozzle device) 43…Second compressor 51a~51g…Intake pipe 52…Intake manifold 53...Intake switching valve 54…Intake bypass valve 61a, 61b...Exhaust manifold 62a~62e…Exhaust pipe 63...Exhaust switching valve 64...Exhaust gas purification equipment 71...Crank angle sensor 72...Camera position sensor 73...Air flow sensor 74a, 74b...Vane closure sensor 75a~75c...Pressure sensors 76a, 76b...Temperature sensor 77...Accelerator opening sensor

Claims

1. an internal combustion engine that burns fuel in a combustion chamber using intake air flowing in through an intake path and discharges exhaust gas generated in the combustion chamber into an exhaust path; a first turbocharger including a first turbine disposed in the exhaust path, a first compressor disposed in the intake path and rotating in conjunction with the first turbine, and a first turbine actuator for increasing a first control parameter when increasing a rotation speed of the first turbine; a second turbocharger of the same type and size as the first turbocharger, the second turbocharger including a second turbine disposed in the exhaust path, a second compressor disposed in the intake path and rotating in conjunction with the second turbine, and a second turbine actuator for increasing a second control parameter when increasing a rotation speed of the second turbine; A control device for an internal combustion engine, When a parallel turbo condition is satisfied, the intake path is configured so that intake air flowing into the intake path flows into each of the first compressor and the second compressor, and compressed air compressed by the first compressor and the second compressor join and flow into the combustion chamber, and the exhaust path is configured so that the exhaust gas discharged from the combustion chamber flows into each of the first turbine and the second turbine, acquiring a target parameter value, which is a value determined according to a target value of the pressure of the pressurized air, and executing an air amount equalization process for setting the first control parameter and the second control parameter to the target parameter value; When the parallel turbo condition is satisfied and it is predicted that the amount of air flowing into one of the first compressor and the second compressor will be smaller than a required amount of air determined for a compression pressure ratio that is a ratio of the pressure of the compressed air to the pressure of the intake air, an air amount difference process is executed to acquire the target parameter value and an offset value, set a parameter corresponding to one of the first control parameter and the second control parameter to a value larger than the target parameter value by the offset value, and set the other parameter of the first control parameter and the second control parameter to a value smaller than the target parameter value by the offset value; A control device for an internal combustion engine comprising a control unit.

2. 2. The control device for an internal combustion engine according to claim 1, The control unit is the offset value is set to a larger value as the rotation speed of the internal combustion engine increases, and the offset value is set to a larger value as the amount of the fuel injected into the combustion chamber increases. A control device for an internal combustion engine.

3. The control device for an internal combustion engine according to claim 1 or 2, Each of the first turbine actuator and the second turbine actuator has a variable nozzle device having a nozzle vane that controls a degree of closure of a flow passage that guides the exhaust gas to the first turbine or the second turbine, Each of the first control parameter and the second control parameter is a parameter that increases as the state of the nozzle vane approaches a fully closed state from a fully open state, A control device for an internal combustion engine.

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