Method and apparatus for estimating temperature of exhaust system component of internal combustion engine

Abstract

To improve accuracy of a turbine inlet exhaust temperature which is a basis of temperature estimation of an exhaust system component.SOLUTION: The temperature estimation device includes a turbine-inlet exhaust-temperature map for stratified charge combustion 31 that outputs an exhaust temperature at an inlet of the turbine with respect to a rotational speed and a charging efficiency of the internal combustion engine on the assumption of stratified charge combustion, a turbine-inlet exhaust temperature map for homogeneous charge combustion 32 that outputs an exhaust temperature at the inlet of the turbine with respect to the rotational speed and the charging efficiency of the internal combustion engine on the assumption of homogeneous charge combustion, and a turbine-inlet exhaust temperature map for fuel cut 33 that outputs an exhaust temperature at the inlet of the turbine with respect to the rotational speed and the charging efficiency of the internal combustion engine on the assumption of a fuel cut state. The estimated temperature selected based on the stratified combustion determination flag and the fuel cut determination flag is given to a temperature estimation model for estimating the exhaust system component temperature.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an improvement in a technique for estimating the temperature of exhaust system components for protecting the exhaust system components of an internal combustion engine. [Background technology]

[0002] BACKGROUND ART In order to protect exhaust system components such as exhaust turbines and exhaust purification catalysts provided in the exhaust system of an internal combustion engine from excessive thermal load, a technique for estimating the temperature of exhaust system components from the operating conditions of the internal combustion engine is known.

[0003] Patent Document 1 discloses that in an internal combustion engine that can switch between intake manifold injection and in-cylinder injection, the temperature at which a certain exhaust system part will ultimately converge is estimated by switching between two characteristic convergence temperature maps depending on whether the injection is intake manifold injection or in-cylinder injection. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-37921 Summary of the Invention [Problem to be solved by the invention]

[0005] Even with the same direct-cylinder injection, some internal combustion engines can switch between stratified combustion and homogeneous combustion. In this case, the temperatures of exhaust system components differ between stratified combustion and homogeneous combustion, even at the same engine speed and load. Furthermore, internal combustion engines can enter a state in which the crankshaft rotates without combustion (a fuel-cut state). In such a fuel-cut state, the exhaust temperature is lower than during combustion operation. Patent Document 1 does not take into account the exhaust temperature in such a fuel-cut state, resulting in a lower accuracy in estimating the final temperature of exhaust system components.

[0006] Furthermore, in Patent Document 1, two types of convergence temperature maps are used for one exhaust system component, so if there are a large number of exhaust system components to be subjected to temperature estimation, it becomes necessary to prepare a large number of convergence temperature maps, which complicates the configuration. [Means for solving the problem]

[0007] The present invention provides an exhaust system component temperature estimation method for an internal combustion engine capable of switching between stratified charge combustion and homogeneous charge combustion, which estimates the temperature of exhaust system components based on the rotation speed and load of the internal combustion engine, comprising: a first exhaust temperature map that outputs the exhaust temperature at a reference position of the exhaust system for the rotation speed and the load on the assumption of stratified charge combustion; a second exhaust temperature map that outputs the exhaust temperature at the reference position for the rotation speed and the load on the assumption of homogeneous combustion; and a third exhaust temperature map that outputs the exhaust temperature at the reference position for the rotation speed and the load on the assumption of a fuel cut state, determining an exhaust gas temperature at the reference position using an exhaust gas temperature map corresponding to whether the control state of the internal combustion engine is stratified combustion, homogeneous combustion, or a fuel cut state; The temperature of each exhaust system component is estimated from the exhaust temperature at the reference position. [Effects of the Invention]

[0008] According to this invention, the exhaust temperature at the reference position is determined using an exhaust temperature map corresponding to each of the following conditions, taking into consideration whether stratified combustion or homogeneous combustion is being performed, and whether fuel is being cut off. This allows the exhaust temperature to be determined more accurately, thereby improving the accuracy of temperature estimation of exhaust system components. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram of the configuration of a series hybrid vehicle. [Figure 2] 1 is an explanatory diagram of an intake and exhaust system of an internal combustion engine according to an embodiment; [Figure 3] FIG. 1 is a functional block diagram of a temperature estimation device according to an embodiment. [Figure 4] 10 is a flowchart showing the flow of a temperature estimation process according to an embodiment. [Figure 5] 4 is a time chart showing the operation of an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment in which the present invention is applied to an internal combustion engine of a series hybrid vehicle will be described in detail below with reference to the drawings. FIG. 1 shows a schematic configuration of a series hybrid vehicle to which the present invention is applied. The series hybrid vehicle is configured to include a power-generating motor-generator 1 that operates primarily as a generator, an internal combustion engine 2 used as a power-generating internal combustion engine that drives the power-generating motor-generator 1 in response to power demands, a traction motor-generator 4 that operates primarily as a motor to drive drive wheels 3, and a battery 5 that stores the generated power. While the figure shows the internal combustion engine 2 driving the power-generating motor-generator 1 via a gear train, the internal combustion engine 2 and the power-generating motor-generator 1 may be arranged in series with each other so as to rotate at the same speed without a gear train (so-called direct connection).

[0011] The electric power obtained by the internal combustion engine 2 driving the power generation motor generator 1 is stored in the battery 5 via an inverter device (not shown). The driving of the traction motor generator 4 is controlled using the electric power of the battery 5. The electric power generated by the traction motor generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown).

[0012] The operation of the motor generators 1 and 4, the charging and discharging of the battery 5, and the operation of the internal combustion engine 2 are controlled by a controller 6. The controller 6 is composed of multiple controllers connected to each other so that they can communicate with each other, such as a motor controller 7 that controls the motor generators 1 and 4, an engine controller 8 that controls the internal combustion engine 2, and a battery controller 9 that manages the battery 5. Information such as an accelerator position signal (APO) generated by depression of an accelerator pedal (not shown) and vehicle speed (VSP) is input to the controller 6. The battery controller 9 also calculates the SOC of the battery 5 based on the voltage and current of the battery 5. When the SOC drops to a predetermined lower limit, the internal combustion engine 2 is started via the engine controller 8 to generate electricity. Such a series hybrid vehicle has two driving modes: an EV mode in which the vehicle runs on power from the battery 5 without combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle runs while generating electricity through combustion operation of the internal combustion engine 2. Even if the SOC is above the lower limit, the internal combustion engine 2 is driven and the vehicle runs in the HEV mode when the required driving force of the vehicle is relatively large. Therefore, the internal combustion engine 2 repeatedly operates in combustion mode and stops while the vehicle's main switch is on. Furthermore, the internal combustion engine 2 connected to the power-generating motor-generator 1 may be motored in reverse by the power running of the power-generating motor-generator 1. For example, when the internal combustion engine 2 is started, it is motored at a predetermined rotational speed and then switches to combustion mode.

[0013] 2 shows the configuration of the intake and exhaust systems of the internal combustion engine 2. This internal combustion engine 2 is a four-stroke, spark-ignition internal combustion engine (a so-called gasoline engine) equipped with a turbocharger 11 (turbine 11a and compressor 11b), and fuel is supplied directly into the cylinders via a fuel injection valve (not shown). The engine is configured to be able to switch between stratified charge combustion and homogeneous charge combustion by changing the number and timing of fuel injections, etc. The ignition timing of the spark plugs and the timing and amount of fuel injection by the fuel injection valve are controlled by an engine controller 8.

[0014] An electronically controlled throttle valve 13, the opening of which is controlled by a control signal from the engine controller 8, is provided in the intake passage 12. A compressor 11b of the turbocharger 11 is located upstream of the throttle valve 13, and an air flow meter 14, for example, of a hot wire type, that detects the amount of intake air, and an air cleaner 15 are disposed upstream of the compressor 11b. A water-cooled intercooler 16, for example, is provided between the compressor 11b and the throttle valve 13 to cool the high-temperature, high-pressure intake air.

[0015] A turbine 11a of a turbocharger 11 is located in the exhaust passage 20, and a pre-catalyst device 21 consisting of a three-way catalyst and a main catalyst device 22 consisting of a particulate filter carrying a three-way catalyst are disposed downstream of the turbine 11a. The main catalyst device 22 is disposed under the floor of the vehicle.

[0016] The exhaust gas recirculation passage 25 is also provided to recirculate a portion of the exhaust gas from the exhaust passage 20 to the intake passage 12. The exhaust gas recirculation passage 25 is provided with, for example, a water-cooled EGR gas cooler 27 and an EGR valve 28 whose opening is controlled by the engine controller 8. The tip of the exhaust gas recirculation passage 25 merges with the intake passage 12 at a position upstream of the compressor 11b, and the intake passage 12 is provided with a negative pressure generating valve 17 for generating negative pressure at a position upstream of this merger point. The opening of the negative pressure generating valve 17 is also controlled by the engine controller 8.

[0017] In addition to the air flow meter 14, detection signals from sensors such as an air-fuel ratio sensor in the exhaust passage 20 (not shown), a crank angle sensor for detecting the engine rotation speed, a water temperature sensor for detecting the coolant temperature, a boost pressure sensor for detecting the boost pressure, and an atmospheric pressure sensor for detecting the atmospheric pressure are input to the engine controller 8. Based on these detection signals and various signals input via other controllers (for example, the accelerator opening APO, vehicle speed VSP, etc.), the engine controller 8 optimally controls the fuel injection amount and injection timing, ignition timing, opening of the throttle valve 13, boost pressure, EGR rate, etc.

[0018] The engine controller 8 also estimates the temperatures of exhaust system components (for example, the turbine 11a and the pre-catalyst device 21) based on the rotation speed and load of the internal combustion engine 2, and performs protective control to prevent these exhaust system components from becoming excessively hot. One example of protective control is suppressing or reducing the exhaust temperature by increasing the fuel injection amount, i.e., enriching the air-fuel ratio, and another example is limiting the torque of the internal combustion engine 2 (for example, reducing the opening of the throttle valve 13).

[0019] The temperature estimation of exhaust system components is performed in two stages. In the first stage, the constantly changing exhaust gas temperature at a reference position in the exhaust system, such as the inlet of the turbine 11a, is estimated. In the second stage, the temperatures of the turbine 11a and the pre-catalyst device 21 are estimated from this exhaust gas temperature using a turbine temperature estimation model and a pre-catalyst temperature estimation model, which are previously created for each exhaust system component, namely the turbine 11a and the pre-catalyst device 21. These temperature estimation models take the constantly changing exhaust gas temperature at the inlet of the turbine 11a as input and basically output the current temperatures of the turbine 11a and the pre-catalyst device 21 based on heat balance. Note that the effects of several parameters, such as the air-fuel ratio, on the exhaust system component temperatures are corrected in the temperature estimation model. This invention mainly relates to the first-stage estimation of the exhaust gas temperature at the inlet of the turbine 11a; the second-stage temperature estimation model will not be described in detail.

[0020] FIG. 3 is a functional block diagram of a temperature estimation device for estimating the exhaust gas temperature at the inlet of the turbine 11a, which is the first step described above. Here, the charging efficiency is used as a parameter indicating the load on the internal combustion engine 2. The charging efficiency is basically determined by the relationship between the intake air mass detected by the air flow meter 14 and the cylinder volume, and corrections are made for the exhaust gas recirculation rate and response delay during transients. If the valve timing of the intake and exhaust valves is variable, corrections based on this valve timing can also be made. As shown in Figure 3, one embodiment of the temperature estimation device includes a turbine inlet exhaust temperature map 31 during stratified combustion that outputs the exhaust temperature at the inlet of the turbine 11a relative to the rotational speed and charging efficiency of the internal combustion engine 2, assuming stratified combustion; a turbine inlet exhaust temperature map 32 during homogeneous combustion that outputs the exhaust temperature at the inlet of the turbine 11a relative to the rotational speed and charging efficiency of the internal combustion engine 2, assuming homogeneous combustion; and a turbine inlet exhaust temperature map 33 during fuel cut that outputs the exhaust temperature at the inlet of the turbine 11a relative to the rotational speed and charging efficiency of the internal combustion engine 2, assuming a fuel cut state.

[0021] Each of the maps 31, 32, and 33 receives the rotation speed and the charging efficiency as inputs and outputs a corresponding exhaust temperature value. A first selection unit 34 selects and outputs either the output value of the turbine inlet exhaust temperature map 31 during stratified combustion or the output value of the turbine inlet exhaust temperature map 32 during homogeneous combustion, based on the on / off status of a stratified combustion determination flag indicating a stratified combustion state. A second selection unit 35 further selects and outputs either the output value of the first selection unit 34 or the output value of the turbine inlet exhaust temperature map 33 during fuel cut, based on the on / off status of a fuel cut determination flag indicating a fuel cut state. The output of the second selection unit 35 indicates the exhaust temperature at the inlet of the turbine 11a, and this estimated temperature is input to the turbine temperature estimation model and the pre-catalyst temperature estimation model, as described above.

[0022] The "fuel cut state" refers to a state in which the crankshaft rotates without combustion, rather than combustion operation involving fuel injection and ignition, and includes not only the motoring described above, but also a short period of idling when the internal combustion engine 2 is stopped, temporary fuel cut due to some request, etc.

[0023] FIG. 4 is a flowchart showing the process flow for estimating the exhaust gas temperature at the inlet of the turbine 11a in FIG. 3. In the first step 1, the stratified charge combustion determination flag is read, and in step 2, it is determined whether stratified charge combustion is occurring. If stratified charge combustion is occurring, the process proceeds to step 3, where the turbine inlet exhaust gas temperature map 31 during stratified charge combustion is used to determine the turbine inlet exhaust gas temperature. In step 4, the fuel cut determination flag is read, and in step 5, it is determined whether a fuel cut state is occurring. If a fuel cut state is not occurring, the process proceeds to step 6, where the turbine inlet exhaust gas temperature during stratified charge combustion is output to a turbine temperature estimation model and a pre-catalyst temperature estimation model (not shown). If a fuel cut state is occurring, the process proceeds to step 7, where the turbine inlet exhaust gas temperature during fuel cut is output to a turbine temperature estimation model and a pre-catalyst temperature estimation model (not shown).

[0024] If homogeneous combustion is in progress, the process proceeds to step 8, where the turbine inlet exhaust temperature is determined using the homogeneous combustion turbine inlet exhaust temperature map 32. Then, in step 9, the fuel cut determination flag is read, and in step 10, it is determined whether or not the fuel is cut. If the fuel is not cut, the process proceeds to step 11, where the turbine inlet exhaust temperature during homogeneous combustion is output to a turbine temperature estimation model and a pre-catalyst temperature estimation model (not shown). If the fuel is cut, the process proceeds to step 12, where the turbine inlet exhaust temperature during fuel cut is output to a turbine temperature estimation model and a pre-catalyst temperature estimation model (not shown).

[0025] FIG. 5 is a time chart showing the change in turbine inlet exhaust temperature during fuel cutoff and when switching between stratified and homogeneous combustion. From top to bottom, the chart shows: (a) accelerator pedal position, (b) engine speed, (c) charging efficiency, (d) combustion state (stratified, homogeneous, or fuel cutoff), and (e) turbine inlet exhaust temperature. In the (e) turbine inlet exhaust temperature column, the estimated exhaust temperature is shown by a phantom line and the actual exhaust temperature by a solid line. As shown, even with the same engine speed and charging efficiency, the exhaust temperature differs between stratified and homogeneous combustion. In the above embodiment, switching between the stratified combustion turbine inlet exhaust temperature map 31 and the homogeneous combustion turbine inlet exhaust temperature map 32 allows accurate estimation of the exhaust temperature based on the actual exhaust temperature. Furthermore, the turbine inlet exhaust temperature can also be accurately estimated when the crankshaft is rotating in a fuel cutoff state, improving the accuracy of the ultimately estimated temperatures of the turbine 11a and pre-catalyst device 21.

[0026] Furthermore, in the above embodiment, in the stage of estimating the exhaust gas temperature at the inlet of the turbine 11a (the first stage described above), exhaust gas temperature estimation is performed corresponding to each of stratified charge combustion, homogeneous charge combustion, and a fuel cut state, and these exhaust gas temperature values ​​are provided to the turbine temperature estimation model and the pre-catalyst temperature estimation model. Therefore, the turbine temperature estimation model and the pre-catalyst temperature estimation model do not require multiple models corresponding to stratified charge combustion, homogeneous charge combustion, or a fuel cut state, and this makes it possible to avoid complicating the temperature estimation model.

[0027] While one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be modified in various ways. For example, the present invention is not limited to an internal combustion engine for generating electricity in a series hybrid vehicle, but can also be applied to an internal combustion engine that serves as a mechanical driving source for the vehicle. For example, the exhaust temperature during fuel cut during vehicle deceleration can be accurately reflected in the exhaust system component temperature. Furthermore, the present invention may also be applied to a non-supercharged internal combustion engine that does not have a turbocharger. In this case, for example, the outlet of the exhaust manifold can be set as the reference position of the exhaust system. [Explanation of symbols]

[0028] 1...Power generating motor generator 2...Internal combustion engine 4...Traction motor generator 8...Engine controller 11...Turbocharger 11a...Turbine 14...Air flow meter 21...Pre-catalytic device 31...Turbine inlet exhaust temperature map during stratified charge combustion 32...Turbine inlet exhaust temperature map during homogeneous combustion 33...Turbine inlet exhaust temperature map when fuel is cut

Claims

1. A method for estimating the temperature of exhaust system components of an internal combustion engine that is capable of switching between stratified charge combustion and homogeneous charge combustion, the method estimating the temperature of exhaust system components based on the rotation speed and load of the internal combustion engine, a first exhaust gas temperature map that outputs the exhaust gas temperature at a reference position of the exhaust system for the rotation speed and the load on the assumption of stratified charge combustion; a second exhaust gas temperature map that outputs the exhaust gas temperature at the reference position for the rotation speed and the load on the assumption of homogeneous combustion; and a third exhaust gas temperature map that outputs the exhaust gas temperature at the reference position for the rotation speed and the load on the assumption of a fuel cut state, determining an exhaust gas temperature at the reference position using an exhaust gas temperature map corresponding to whether the control state of the internal combustion engine is stratified combustion, homogeneous combustion, or a fuel cut state; Estimating the temperatures of each exhaust system component from the exhaust temperature at the reference position; A method for estimating the temperature of exhaust system components in an internal combustion engine.

2. The charging efficiency of the internal combustion engine is used as a parameter indicating the load.

2. The method for estimating the temperature of an exhaust system component of an internal combustion engine according to claim 1.

3. the internal combustion engine is equipped with a turbocharger, and the exhaust gas temperature at a turbine inlet of the turbocharger is determined as the reference position using each exhaust gas temperature map; 2. The method for estimating the temperature of an exhaust system component of an internal combustion engine according to claim 1.

4. the internal combustion engine is a non-supercharged internal combustion engine, and the exhaust temperature at an outlet of an exhaust manifold is determined as the reference position using each exhaust temperature map.

2. The method for estimating the temperature of an exhaust system component of an internal combustion engine according to claim 1.

5. estimating the temperature of the exhaust purification catalyst using a catalyst temperature estimation model that estimates the temperature of the exhaust purification catalyst located downstream of the reference position from the exhaust temperature at the reference position; 2. The method for estimating the temperature of an exhaust system component of an internal combustion engine according to claim 1.

6. The internal combustion engine is an internal combustion engine for generating electricity that drives a generator in a series hybrid vehicle and is capable of motoring by powering the generator.

2. The method for estimating the temperature of an exhaust system component of an internal combustion engine according to claim 1.

7. an internal combustion engine capable of switching between stratified charge combustion and homogeneous charge combustion; a controller for switching between stratified charge combustion and homogeneous charge combustion in the internal combustion engine and for estimating the temperature of exhaust system components based on the rotational speed and load of the internal combustion engine; An exhaust system component temperature estimation device for an internal combustion engine, The above controller is a first exhaust gas temperature map that outputs the exhaust gas temperature at a reference position of the exhaust system for the rotation speed and the load on the assumption of stratified charge combustion; a second exhaust gas temperature map that outputs the exhaust gas temperature at the reference position for the rotation speed and the load on the assumption of homogeneous combustion; and a third exhaust gas temperature map that outputs the exhaust gas temperature at the reference position for the rotation speed and the load on the assumption of a fuel cut state, determining an exhaust gas temperature at the reference position using an exhaust gas temperature map corresponding to whether the control state of the internal combustion engine is stratified combustion, homogeneous combustion, or a fuel cut state; Estimating the temperatures of each exhaust system component from the exhaust temperature at the reference position; An exhaust system component temperature estimation device for internal combustion engines.

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