Method and device for estimating maximum charging efficiency of an internal combustion engine

Abstract

To accurately estimate a maximum filling efficiency obtainable under a present engine revolution speed, considering an intake air density influencing a turbocharger.SOLUTION: An internal combustion engine has a turbocharger. A maximum filling efficiency obtainable under a present engine revolution speed for engine torque control is calculated on the basis of the engine revolution speed and a maximum intake air density. The maximum intake air density is obtained from a table defining a relationship between the engine revolution speed and maximum filling efficiency for every intake air density. In a characteristic L1 of a standard intake air density, an increase rate of the maximum filling efficiency increases at a point P1 corresponding to a turbo intercept revolution speed N1. In a low intake air density, the turbo intercept revolution speed changes to a high revolution speed side, that is, toward N2, hence, in a maximum filling efficiency characteristic L2, an increase rate increasingly changes at a point P2. Therefore, an estimation accuracy is better than a characteristic L3 that does not take a change in the intercept revolution speed into consideration.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for estimating maximum charging efficiency in an internal combustion engine equipped with a turbocharger, for example, for torque control of the internal combustion engine, which estimates the maximum charging efficiency that can be obtained at the engine speed based on the engine speed. [Background technology]

[0002] The intake air density changes when the engine is at high altitude or when the intake air temperature is high. The maximum charging efficiency that can be achieved at a certain engine speed is affected by the intake air density. Patent Document 1 describes a method for calculating the maximum basic torque of an engine based on the engine speed and atmospheric pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-137435 Summary of the Invention [Problem to be solved by the invention]

[0004] In an internal combustion engine equipped with a turbocharger, for example, as the engine speed gradually increases and the maximum charging efficiency gradually increases, there is a tendency for the maximum charging efficiency to begin to increase relatively suddenly at a certain point. The engine speed at which the rate of increase in the maximum charging efficiency changes corresponds to the engine speed at which supercharging by the turbocharger can be obtained.

[0005] According to the inventor's new findings, the engine speed at which the rate of increase in maximum charging efficiency changes in relation to this supercharging action varies depending on the intake air density. For example, if the intake air density is lower than in a standard state, assuming the throttle valve is fully open, the rotational speed of the turbocharger driven by exhaust energy tends to decrease. As a result, the engine speed at which supercharging action by the turbocharger can be obtained becomes relatively higher.

[0006] It is generally known that different intake density results in different charging efficiencies even when the volumetric efficiency is the same. However, it has not been considered that the engine speed at which the turbocharger's supercharging effect can be obtained varies depending on the intake density. This results in low accuracy in estimating the maximum charging efficiency based on the engine speed. Patent Document 1 does not mention this issue. [Means for solving the problem]

[0007] This invention provides a method for estimating the maximum charging efficiency of an internal combustion engine equipped with a turbocharger, which estimates the maximum charging efficiency achievable at a given engine speed based on the engine speed, by acquiring the intake air density and calculating the maximum charging efficiency according to a predetermined characteristic using the engine speed and the intake air density as parameters. Here, the characteristic is set so that the engine speed at which the rate of increase in the maximum charging efficiency with respect to an increase in engine speed increases becomes higher as the intake air density decreases. [Effects of the Invention]

[0008] According to this invention, it is possible to more accurately estimate the maximum filling efficiency based on the engine speed of an internal combustion engine equipped with a turbocharger when the intake air density differs from the standard value, for example, in high altitudes, extremely cold regions, or tropical regions. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a structural explanatory diagram showing an example of an internal combustion engine to which the present invention is applied; [Figure 2] FIG. 2 is a functional block diagram of engine torque control. [Figure 3] FIG. 4 is a more detailed functional block diagram of the maximum engine torque calculation unit. [Figure 4] 10 is a flowchart showing the flow of a process for calculating the maximum charging efficiency. [Figure 5] FIG. 10 is a characteristic diagram showing the characteristics of intercept rotation speed. [Figure 6] FIG. 4 is a characteristic diagram showing the characteristics of maximum filling efficiency with respect to engine speed and intake air density. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0011] FIG. 1 shows the system configuration of an automotive internal combustion engine 1 to which the present invention is applied. This internal combustion engine 1 is a four-stroke, spark-ignition internal combustion engine equipped with a turbocharger 2. A pair of intake valves 4 and a pair of exhaust valves 5 are arranged on the ceiling wall of each cylinder 3, and an ignition plug 6 is arranged in the center surrounded by these intake valves 4 and exhaust valve 5. A fuel injection valve 7 that supplies fuel into the cylinder 3 is provided below the intake valve 4. The ignition timing of the spark plug 6 and the injection timing and injection amount of fuel by the fuel injection valve 7 are controlled by an engine controller 9. The type of fuel injection device is not limited to direct injection into the cylinder, and may be a port injection type.

[0012] The intake valve 4 and the exhaust valve 5 are equipped with variable valve timing mechanisms 18, 19 that can change the opening and closing timings of the valves, respectively. These variable valve timing mechanisms 18, 19 may be of any type, but for example, a mechanism that retards the phase of the camshaft relative to the phase of the crankshaft can be used. Note that the variable valve timing mechanisms 18, 19 are not essential components of the present invention.

[0013] An intake passage 11 connected to a combustion chamber 10 via an intake valve 4 has an intake collector 11a. An electronically controlled throttle valve 12, the opening of which is controlled by a control signal from an engine controller 9, is provided upstream of the intake collector 11a. A compressor 2a of a turbocharger 2 is located upstream of the throttle valve 12, and an air flow meter 14 for detecting the amount of intake air and an air cleaner 15 are provided upstream of the compressor 2a. A water-cooled intercooler 16, for example, is provided between the compressor 2a and the throttle valve 12. A recirculation valve 17 is provided to communicate the discharge side and intake side of the compressor 2a. The recirculation valve 17 opens during deceleration when the throttle valve 12 is closed.

[0014] A turbine 2b of the turbocharger 2 is installed in an exhaust passage 20 connected to the combustion chamber 10 via the exhaust valve 5, and a pre-catalyst device 21 consisting of a three-way catalyst and an exhaust particulate filter (GPF) 22 coated with a three-way catalyst are disposed downstream of the turbine 2b. An air-fuel ratio sensor 23 for detecting the air-fuel ratio is disposed upstream of the turbine 2b in the exhaust passage 20. The turbine 2b is equipped with a wastegate valve 24 that bypasses part of the exhaust gas in accordance with the boost pressure in order to control the boost pressure. The wastegate valve 24 is an electrically operated valve whose opening is controlled by the engine controller 9.

[0015] An exhaust gas recirculation passage 25 is also provided as an exhaust gas recirculation device, which recirculates a portion of the exhaust gas from the exhaust passage 20 to the intake passage 11. For example, one end of the exhaust gas recirculation passage 25 is connected to the exhaust passage 20 between the pre-catalyst device 21 and the exhaust particulate filter 22, and the other end of the exhaust gas recirculation passage 25 is connected to the intake passage 11 at a position upstream of the compressor 2a. The exhaust gas recirculation passage 25 is equipped with, for example, a water-cooled EGR gas cooler 27 that cools the recirculated exhaust gas, and an EGR valve 28 that controls the amount of recirculated exhaust gas. The opening degree of the EGR valve 28 is controlled by the engine controller 9.

[0016] In addition to the air flow meter 14 and air-fuel ratio sensor 23, the engine controller 9 receives detection signals from various sensors, such as a crank angle sensor 31 for detecting engine speed, a water temperature sensor 32 for detecting coolant temperature, an accelerator pedal position sensor 33 for detecting the amount of depression of the accelerator pedal operated by the driver, a vehicle speed sensor 34 for directly or indirectly detecting vehicle speed, an atmospheric pressure sensor 35 for detecting atmospheric pressure, an intake air temperature sensor 36 for detecting intake air temperature (in other words, outside air temperature), and a boost pressure sensor 37 for detecting boost pressure. Based on these detection signals, the engine controller 9 optimally controls the fuel injection amount and injection timing, ignition timing, the opening of the throttle valve 12, the opening of the wastegate valve 24, the valve timing by the variable valve timing mechanisms 18 and 19, the opening of the EGR valve 28, and the like.

[0017] Next, engine torque control, which is a main part of the present invention, and maximum charging efficiency estimation, which is the basis for the control, will be described.

[0018] 2 is a functional block diagram showing the engine torque control function realized by the engine controller 9. As shown in the figure, the engine torque control function includes a maximum engine torque calculation unit 41, a target engine torque calculation unit 42, and an engine torque control unit 43.

[0019] The maximum engine torque calculation unit 41 estimates the maximum engine torque that can be output by the internal combustion engine 1 under the current environment, and as will be described later, it estimates the maximum filling efficiency that can be obtained under the current engine speed, and then calculates the maximum engine torque that can be output by the internal combustion engine 1 based on this maximum filling efficiency.

[0020] The target engine torque calculation unit 42 determines the target engine torque by arbitrating various requests, such as the torque required by the driver based on the accelerator pedal depression amount by the driver, the torque required by other controllers of the vehicle, the torque required by an automatic driving function (for example, cruise control that follows the vehicle in front), etc. The target engine torque output here is restricted to within the maximum engine torque that can be output by the internal combustion engine 1 at that time, as estimated or calculated by the maximum engine torque calculation unit 41.

[0021] The engine torque control unit 43 determines and operates target values ​​of engine torque control devices (e.g., throttle valve 12, wastegate valve 24, fuel injector, ignition device, variable valve timing mechanisms 18, 19, EGR valve 28, etc.) involved in engine torque in order to realize the target engine torque determined by the target engine torque calculation unit 42.

[0022] That is, the output of the internal combustion engine 1 is controlled on a torque basis, and by determining in advance the maximum engine torque that can be output at that time, appropriate torque control that does not cause any discomfort can be achieved.

[0023] 3 shows a more detailed functional block diagram of the maximum engine torque calculation unit 41. The maximum engine torque calculation unit 41 includes a maximum charging efficiency calculation unit 51, an indicated torque calculation unit 52, and an engine friction correction unit 53, and further has an intake density calculation unit 54.

[0024] The intake air density calculation unit 54 receives the intake air temperature and atmospheric pressure as inputs and calculates the intake air density at that time. Alternatively, altitude obtained from map information in a car navigation system may be used instead of atmospheric pressure. Alternatively, intake air density may be calculated simply by regarding one of the intake air temperature and atmospheric pressure as a fixed value.

[0025] The maximum charging efficiency calculation unit 51 estimates or calculates the maximum charging efficiency that can be achieved at the engine speed using the current engine speed and intake air density as inputs. In the illustrated example, the maximum charging efficiency is corrected based on the engine system operating conditions. The engine system operating conditions refer to various engine system conditions that affect the charging efficiency, such as the operating conditions of the variable valve timing mechanisms 18 and 19, the particulate accumulation state of the exhaust particulate filter 22, and the like.

[0026] The indicated torque calculation unit 52 calculates the maximum indicated engine torque from the maximum charging efficiency estimated by the maximum charging efficiency calculation unit 51 and the ignition efficiency. An engine protection required torque provided for protecting the internal combustion engine 1 is also input to the indicated torque calculation unit 52, and the maximum indicated engine torque is limited by this engine protection required torque.

[0027] The engine friction correction unit 53 applies a correction based on the engine friction to the maximum indicated engine torque. By subtracting the torque due to the friction from the maximum indicated engine torque, the maximum engine torque that the internal combustion engine 1 can output is obtained.

[0028] In one embodiment, the maximum filling efficiency calculation unit 51 calculates the maximum filling efficiency using a three-dimensional map in which the maximum filling efficiency corresponding to the engine speed and the intake air density are assigned as parameters. More specifically, the maximum filling efficiency calculation unit 51 has a table for each intake air density in which the maximum filling efficiency corresponding to the engine speed is assigned to each intake air density, and calculates the maximum filling efficiency corresponding to the engine speed and intake air density at that time by appropriate interpolation calculation or the like.

[0029] FIG. 4 is a flowchart showing the processing in the maximum charging efficiency calculation unit 51 and the intake air density calculation unit 54. In step 1, the current engine speed is read, and in step 2, the engine system operating conditions that affect the charging efficiency, such as the operating conditions of the variable valve timing mechanisms 18 and 19 and the particulate accumulation state of the exhaust particulate filter 22, are read. Next, in step 3, the atmospheric pressure and intake air temperature detected by the atmospheric pressure sensor 35 and the intake air temperature sensor 36, respectively, are read, and in step 4, the intake air density is calculated based on the atmospheric pressure and intake air temperature. Next, in step 5, a table corresponding to the intake air density is selected, and in step 6, a value of the maximum charging efficiency corresponding to the engine speed is obtained based on this table. Then, in step 7, corrections or modifications are made according to the engine system operating conditions, and the corrected value is output as the maximum charging efficiency that can be obtained at the current engine speed.

[0030] Here, the relationship between engine speed and maximum charging efficiency in each table for each intake density is determined, for example, by simulation, and the characteristics are determined taking into consideration the influence that the mass of the same volume of air in the cylinder 3 changes depending on the intake density, and also that the engine speed at which the supercharging effect of the turbocharger 2 can be obtained (in other words, the engine speed at which the supercharging effect begins to occur assuming that the throttle valve 12 is fully open) changes depending on the intake density.

[0031] 5 is a characteristic diagram showing the relationship between the engine speed at which the turbocharger 2 can provide a supercharging effect (hereinafter referred to as the turbo intercept speed for convenience) and the intake air density. As shown in the figure, the turbo intercept speed (rpm) increases as the intake air density decreases, and changes linearly. For example, if the intake air density is lower than in a standard state when the throttle valve is fully open, the rotational speed of the turbocharger 2, which is driven by exhaust energy, tends to decrease, and the engine speed at which the turbocharger 2 can provide a supercharging effect becomes relatively higher.

[0032] Fig. 6 shows the characteristics of a three-dimensional map using engine speed, intake air density, and maximum filling efficiency as parameters, and more specifically, shows the relationship between engine speed and maximum filling efficiency in each table for each intake air density. Line L1 shows the characteristics of maximum filling efficiency at a standard intake air density (for example, intake air density at an air temperature of 15°C and an altitude of 0m). As shown in the figure, the overall trend is that as the engine speed increases from a low speed equivalent to idle speed, the maximum filling efficiency increases, and after reaching a peak at a certain engine speed, the maximum filling efficiency decreases as the engine speed increases.

[0033] Here, if we focus on the first half of the characteristics showing an increasing trend, the rate of increase in maximum charging efficiency increases at a certain point P1. In other words, the characteristic line L1 showing an increasing trend has a singular point P1, and the gradient of line L1, which corresponds to the amount of change in maximum charging efficiency, becomes relatively abruptly large at point P1. This point P1 corresponds to the turbo intercept speed described above. In other words, because it is possible to obtain the supercharging effect of the turbocharger 2 on the rotational speed side higher than this turbo intercept speed, the maximum charging efficiency becomes relatively abruptly large at the turbo intercept speed as a boundary.

[0034] Line L2 shows the maximum charging efficiency characteristic when the intake air density is low, such as at high altitudes. Here, because the mass of the same volume of air decreases depending on the intake air density, the overall tendency is for the maximum charging efficiency to be lower than the maximum charging efficiency characteristic shown by line L1 by an amount corresponding to the intake air density. Furthermore, the present invention further takes into consideration the fact that the turbo intercept speed described above becomes a relatively high engine speed at low intake air density. For example, the turbo intercept speed, which is N1 at a standard intake air density, becomes a relatively high engine speed shown as N2 due to the low intake air density. Therefore, on characteristic line L2, the increase in the maximum charging efficiency with increasing engine speed is relatively gradual up to point P2, which corresponds to turbo intercept speed N2. At point P2, where supercharging by the turbocharger 2 can be achieved, the rate of increase in the maximum charging efficiency increases relatively significantly.

[0035] Line L3, shown for reference, represents the maximum charging efficiency characteristic (characteristic determined by simulation) at low intake density when the change in turbo intercept speed according to intake density is not considered. Here, it is assumed that the turbo intercept speed remains N1 even at low intake density, resulting in a characteristic where the rate of increase in maximum charging efficiency increases at point P3. In other words, the characteristic is set as if the characteristic of line L1 on the diagram were shifted downward in parallel. Therefore, if the maximum charging efficiency based on the engine speed is estimated along such characteristic line L3, the estimation accuracy will be low. In the engine speed range where line L3 deviates from line L2, the maximum charging efficiency and therefore the maximum outputtable engine torque will be overestimated. This can result in a situation where, for example, when the driver presses the accelerator pedal heavily, the expected engine torque is not obtained, causing the driver to feel uncomfortable.

[0036] In this way, in the above embodiment, the maximum filling efficiency is estimated based on the engine speed taking into account changes in the turbo intercept speed according to the intake air density, so the estimation accuracy is improved and more appropriate engine torque control can be achieved.

[0037] Although one embodiment of the present invention has been described above in detail, the present invention is not limited to the above embodiment and can be modified in various ways. For example, the above embodiment has been described as having a table specifying the relationship between engine speed and maximum charging efficiency for each intake air density. However, any type of calculation means that inputs engine speed and intake air density and outputs maximum charging efficiency may be used, as long as it takes into account that the engine speed at which supercharging by the turbocharger 2 can be varied depending on the intake air density. Furthermore, the internal combustion engine to which the present invention is applied is not limited to the configuration exemplified in FIG. 1. [Explanation of symbols]

[0038] 1...Internal combustion engine 2...Turbocharger 9...Engine controller 12...Throttle valve 33...Accelerator opening sensor 35...Atmospheric pressure sensor 36...Intake air temperature sensor 41...Maximum engine torque calculation unit 42...Target engine torque calculation unit 43...Engine torque control unit 51...Maximum filling efficiency calculation section 52...Indicated torque calculation section 53...Engine friction compensation section 54...Intake density calculation unit

Claims

1. A method for estimating a maximum charging efficiency of an internal combustion engine equipped with a turbocharger, which estimates a maximum charging efficiency that can be obtained at an engine speed based on the engine speed, comprising: Obtain the intake density, The maximum charging efficiency is calculated according to predetermined characteristics using engine speed and intake density as parameters. Here, the above characteristics are set so that the engine speed at which the rate of increase in maximum charging efficiency increases with increasing engine speed becomes higher as the intake density decreases. A method for estimating the maximum charging efficiency of an internal combustion engine.

2. The intake air density is obtained based on at least one of the air pressure and the intake air temperature. The method for estimating the maximum charging efficiency of an internal combustion engine according to claim 1.

3. Obtains information on the system status that affects the intake air volume and corrects the maximum charging efficiency according to this system status. The method for estimating the maximum charging efficiency of an internal combustion engine according to claim 1.

4. 1. A maximum charging efficiency estimation device for an internal combustion engine equipped with a turbocharger, which estimates a maximum charging efficiency that can be obtained at an engine speed based on the engine speed, an intake density acquisition unit that acquires an intake density; a maximum charging efficiency calculation unit that calculates the maximum charging efficiency according to predetermined characteristics using engine speed and intake air density as parameters; Equipped with The above characteristics are set so that the engine speed at which the rate of increase in maximum charging efficiency increases with increasing engine speed becomes higher as the intake density decreases. A device for estimating the maximum charging efficiency of an internal combustion engine.

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