JP6551317B2 - Exhaust temperature estimation device for internal combustion engine - Google Patents

Description

  The present invention relates to an apparatus for estimating the exhaust temperature of an internal combustion engine.

  2. Description of the Related Art Conventionally, it has been known that a temperature sensor is provided in an exhaust passage of an internal combustion engine, a catalytic converter, or the like to detect the temperature of exhaust gas and reflect it in various controls. In addition, in order to avoid an increase in cost, it has also been proposed to estimate the exhaust temperature without providing a temperature sensor. For example, in the internal combustion engine described in Patent Document 1, when a heater is provided in the air-fuel ratio sensor, the heater is temporarily interrupted while the heater is energized, and the exhaust temperature is estimated from the change in element impedance. It is like that.

Unexamined-Japanese-Patent No. 2000-227364

  However, if the energization of the heater is temporarily interrupted as in Patent Document 1, the activation state of the air-fuel ratio sensor changes accordingly, and the detection accuracy of the air-fuel ratio is reduced, and the activation of the air-fuel ratio sensor is reduced. As a result, there is a risk that the air-fuel ratio control of the internal combustion engine will be adversely affected.

  In view of this point, an object of the present invention is to enable estimation of an exhaust gas temperature without interrupting energization of a heater of an air-fuel ratio sensor.

  In order to achieve the above object, the present invention focuses on the fact that the exhaust temperature of the internal combustion engine can be estimated mainly by the engine load factor, the engine speed, etc., and is influenced by the air-fuel ratio and the ignition timing.

  That is, the present invention is directed to an apparatus (exhaust temperature estimation apparatus) that estimates the temperature of exhaust gas from an internal combustion engine. First, based on at least the engine load factor and the engine speed, the stoichiometric air-fuel ratio and the reference exhaust temperature in MBT are determined. A reference exhaust temperature calculation means for calculating is provided. In addition, first correction coefficient calculation means for calculating a first correction coefficient representing the influence of the air-fuel ratio on the exhaust temperature based on the air-fuel ratio detected by the air-fuel ratio sensor and the reference exhaust temperature is also provided.

  Further, the present invention relates to a combustion center of gravity calculating means for calculating the current combustion center of gravity and the combustion center of gravity in MBT based on at least the engine load factor, the engine speed and the detected air-fuel ratio, and the difference between these combustion centers of gravity. Based on the second correction coefficient calculating means for calculating the second correction coefficient representing the influence of the combustion center of gravity on the exhaust temperature, and using the first and second correction coefficients and the reference exhaust temperature, the exhaust temperature is calculated. And an estimation operation means for estimating.

  With the above configuration, first, the exhaust temperature that changes depending on the operating state of the internal combustion engine is based on at least the engine load factor and the engine speed (other than that, valve timing, EGR rate, etc.), for example, a preset map or calculation It is calculated by the reference exhaust gas temperature calculating means using the equation. At this time, assuming that the air-fuel ratio is the stoichiometric air-fuel ratio and the ignition timing is MBT (Minimum Advance for Best Torque), the reference exhaust temperature (reference exhaust temperature) is calculated.

  The first correction coefficient representing the influence of the air-fuel ratio on the exhaust temperature is calculated based on the current air-fuel ratio and the reference exhaust temperature using, for example, a preset map or arithmetic expression. Calculated by means. The influence of the air-fuel ratio tends to be lower than the stoichiometric air-fuel ratio on either the rich side or the lean side, and the exhaust temperature can be determined by examination in advance.

  Further, regarding the influence of the ignition timing, a second correction coefficient representing the influence of the combustion center of gravity on the exhaust temperature is calculated by the second correction coefficient calculation means. That is, based on at least the engine load factor, the engine speed, and the air-fuel ratio, the combustion center of gravity and the combustion center of gravity in MBT are calculated by the combustion center of gravity calculating means, for example, using a preset map and arithmetic expression. The center of gravity of combustion changes not only by the ignition timing but also by the combustion speed, etc., but this can be set by investigating in advance through experiments or the like.

  Then, based on the difference between the current combustion gravity center and the combustion gravity center at the MBT, a second correction coefficient is calculated using, for example, a preset map or an arithmetic expression. During the operation of the internal combustion engine, the ignition timing is usually retarded from the MBT, and as the retard is on the retarded side, the combustion center of gravity is also retarded and the conversion efficiency of the combustion pressure into torque decreases. Therefore, the exhaust temperature tends to rise. Also about this, it should just examine and set by experiment etc. beforehand.

  When the reference exhaust gas temperature and the first and second correction coefficients are thus calculated, the exhaust gas temperature is estimated by the estimation calculation means using them. Since this estimated value appropriately reflects the influence of the air-fuel ratio and the influence of the combustion center of gravity on the temperature of the exhaust determined roughly by the load factor and the rotational speed of the internal combustion engine, it is possible to accurately estimate the exhaust temperature. it can.

  As described above, according to the exhaust gas temperature estimation device for an internal combustion engine according to the present invention, the air-fuel ratio and the ignition timing are set to the reference exhaust temperature that takes into account the influence of the operating state of the internal combustion engine such as the engine load factor and the engine speed. The exhaust temperature can be accurately estimated by appropriately reflecting the influence of the change. There is no need to interrupt the energization of the heater of the air-fuel ratio sensor for the estimation.

It is a figure showing roughly the composition of the engine concerning an embodiment. It is explanatory drawing shown about a heat release rate waveform and a combustion gravity center. It is a graph which shows an example about the influence on the exhaust temperature of an air fuel ratio. It is a graph which shows an example of the relationship between a combustion gravity center and torque conversion efficiency. It is a graph which shows an example about the influence on the exhaust temperature of a combustion gravity center. It is a flowchart which shows an example of the estimation routine of exhaust temperature. It is explanatory drawing which shows an example of the model of a heat release rate waveform.

  Hereinafter, an embodiment in which an exhaust gas temperature estimating device according to the present invention is applied to a gasoline engine (an internal combustion engine) mounted on a vehicle will be described. The engine 1 according to this embodiment has a plurality of cylinders 2, although only one is shown in FIG. 1, and a piston 12 is accommodated so as to define a combustion chamber 11, and a crankshaft is connected by a connecting rod 14. It is linked with 13. A signal rotor 13a is attached to the end of the crankshaft 13, and a crank angle sensor 61 is disposed below the cylinder block 17 so as to detect its rotation angle (crank angle θ).

  On the other hand, the cylinder head 18 is fastened to the upper end of the cylinder block 17 to close the upper end of each cylinder 2. The cylinder head 18 is provided with a spark plug 20 so as to face the inside of the cylinder 2. When a high voltage is supplied from an igniter 21 controlled by the ECU 100, spark discharge occurs. A water temperature sensor 62 that detects the cooling water temperature of the engine 1 is disposed on the upper side wall of the cylinder block 17.

  Further, an intake passage 3 and an exhaust passage 4 are provided in communication with the combustion chamber 11 of each cylinder 2. A portion on the downstream side of the intake passage 3 (downstream side of the intake flow) is an intake port formed in the cylinder head 18, and an intake valve 31 is disposed at an opening facing the combustion chamber 11. Similarly, the upstream side of the exhaust passage 4 (upstream side of the exhaust flow) is an exhaust port, and an exhaust valve 41 is disposed at the opening thereof. A valve system 5 for operating the intake valve 31 and the exhaust valve 41 is provided to the cylinder head 18.

  As an example, the valve system 5 of the present embodiment includes an intake camshaft 51 that drives the intake valve 31 and an exhaust camshaft 52 that drives the exhaust valve 41. The two camshafts 51 and 52 are driven by the crankshaft 13 via a timing chain (not shown), so that the intake valve 31 and the exhaust valve 41 are opened and closed at a predetermined timing.

  In addition, an electric VVT 53 is interposed between the intake camshaft 51 and a sprocket around which the timing chain is wound, and both are relatively rotated. The operation of the VVT 53 is controlled by the ECU 100, whereby the timing of opening and closing the intake valve 31 can be changed by continuously changing the rotation phase of the intake camshaft 51 with respect to the rotation of the crankshaft 13.

  An air cleaner 32, an air flow meter 63, an intake air temperature sensor 64 (built in the air flow meter 63), and an electronically controlled throttle valve 33 are disposed in the intake passage 3 in this order from the upstream side. The throttle valve 33 is driven by a throttle motor 34 to adjust the intake air amount of the engine 1 by restricting the flow of intake air, and the opening degree (throttle opening degree) is controlled by the ECU 100.

  Further, an injector 35 for fuel injection is also disposed in the intake passage 3 for each cylinder 2 and is connected to a common delivery pipe 36, and although not shown, fuel is discharged from a fuel tank via a fuel supply pipe. It is supposed to be supplied. When the injector 35 is controlled by the ECU 100 and fuel is injected into the intake passage 3, the fuel spray is sucked into the cylinder 2 while being mixed with the intake air, and forms an air-fuel mixture in the combustion chamber 11.

  Then, when the air-fuel mixture compressed by the rise of the piston 12 is ignited and burned by the spark plug 20 in the compression stroke of the cylinder 2, the piston 12 shifted to the expansion stroke beyond the compression top dead center (TDC) is burned at high pressure. The gas is pushed down, and the crankshaft 13 is rotated via the connecting rod 14. That is, the combustion pressure in the cylinder 2 is converted into the torque of the engine 1 by the crank mechanism.

  Such a combustion state of the air-fuel mixture is generally represented by a heat release rate waveform as shown in FIG. The horizontal axis of the graph shown is the crank angle θ, and the vertical axis is the heat release rate dQ / dθ. As shown in this graph, the heat release rate dQ / dθ rises due to the combustion of the air-fuel mixture, and after reaching a peak, it falls to the end of the combustion. The area of the lower part of the graph of the heat generation rate waveform is the total heat generation amount Qall (total amount of heat generation by combustion), and the crank angle θ that is the center of the area is the combustion center of gravity CA50.

  In FIG. 2, the broken line graph is a waveform when MBT, the peak of the heat generation rate dQ / dθ is high, and the combustion period is short. For this reason, the conversion efficiency of combustion pressure into torque tends to be high, and the temperature of exhaust gas tends to be low. On the other hand, when the ignition timing is retarded, the peak of the heat generation rate dQ / dθ is lowered and moved to the retarded side as shown by the solid line graph. The period will be longer. Therefore, the torque conversion efficiency is lowered and the exhaust temperature is raised.

  The burned gas that has generated a torque by pushing down the piston 12 as described above flows into the exhaust passage 4 when the exhaust valve 41 is opened thereafter, and is purified by the catalytic converter 42 shown in FIG. become. An air-fuel ratio sensor 65 is disposed upstream of the catalytic converter 42 and outputs a signal corresponding to the oxygen concentration in the exhaust to the ECU 100. Although not shown, the air-fuel ratio sensor 65 is provided with a heater for promoting activation, and is controlled to be energized by the ECU 100.

  Further, although not shown, an EGR passage is provided for returning a part of the exhaust from the exhaust passage 4 to the intake passage 3 and recirculating it to the combustion chamber 11 of each cylinder 2. The EGR passage is provided with an EGR valve 54 for adjusting the flow rate of exhaust gas (EGR gas) flowing to the intake side, and the opening degree thereof is controlled by the ECU 100 to obtain an EGR rate Control) is performed.

-ECU-
The ECU 100 is a microcomputer that includes a known electronic control unit and includes a CPU, a RAM, a ROM, an input / output interface, and the like. The ROM stores a control program of the engine 1 and the like, and the RAM is a memory that temporarily stores calculation results of the CPU, data input from each sensor, and the like. In addition, the backup RAM records data etc. to be saved when the engine 1 is stopped.

  As described above with reference to FIG. 1, the ECU 100 is connected with the crank angle sensor 61, the water temperature sensor 62, the air flow meter 63, the intake air temperature sensor 64, the air-fuel ratio sensor 65, and the like. The ECU 100 is also connected to an accelerator opening sensor 66 that detects an operation amount (accelerator opening) of an accelerator pedal 7 provided in the vehicle interior. Further, although not shown, the ECU 100 is used for operation control of the engine 1. Other sensors and switches are also connected.

  The ECU 100 executes various control programs based on signals input from the various sensors, switches, and the like, so that the ECU 100 transmits the engine 1 to the engine 1 based on the accelerator opening, the load and rotation speed of the engine 1, or the vehicle speed. The control of the ignition timing by the igniter 21, the control of the throttle opening by the throttle motor 34 (that is, the control of the intake amount), the control of the fuel injection by the injector 35, etc. Do.

  The ECU 100 also performs control of the valve timing by the VVT 53 and control of the EGR rate by the EGR valve 54, and further, for example, control of raising the exhaust temperature for early activation of the catalytic converter 42 at cold start of the engine 1. Or control to lower the exhaust temperature to suppress an excessive temperature rise of the catalytic converter 42 when the high load operation is continued. For this purpose, the ECU 100 estimates the exhaust temperature as follows.

-Estimation of exhaust temperature-
The exhaust temperature of the engine 1 varies greatly depending on its operating condition. In the present embodiment, the ECU 100 controls the air fuel ratio, the ignition timing, the valve timing, the EGR rate, etc. in association with the load factor of the engine 1 and the engine speed, so that the load factor and engine speed An approximate exhaust temperature can be estimated on the basis of this.

  That is, first, an exhaust gas temperature map (which may be an arithmetic expression) in which a reference exhaust gas temperature (reference exhaust gas temperature Texst) is set based on the load factor of the engine 1 and the engine speed is provided. This is set in advance by experiments, etc., and assumes that the air-fuel ratio is the stoichiometric air-fuel ratio and the ignition timing is MBT (Minimum Advance for Best Torque). The valve timing and EGR rate are control values corresponding to the load factor and the engine speed.

  However, even if the load factor of the engine 1 and the engine speed are the same, the air-fuel ratio and ignition timing may vary depending on the vehicle running state, the temperature of the catalytic converter 42, etc. Make corrections to reflect the effects of time. For example, as shown in FIG. 3, the influence of the air-fuel ratio tends to decrease even when the stoichiometric air-fuel ratio shifts to either the rich side or the lean side, and this is examined in advance by experiments or the like. In the present embodiment, a function of the reference exhaust gas temperature Texst and the air-fuel ratio A / F: f (Texst, A / F) is set so as to approximate the graph of FIG. Calculate Kt.

  Further, as described above with reference to FIG. 2 regarding the influence of the ignition timing, as the ignition timing is retarded from the MBT, the combustion center of gravity CA50 is also retarded, and the conversion efficiency of the combustion pressure into torque decreases. As a result, the temperature of the exhaust tends to increase. However, normally, the MBT cannot always be traced during operation, and is often controlled to the retard side, so that the combustion center of gravity CA50 is also retarded accordingly. As the combustion center of gravity CA50 is retarded, the torque conversion efficiency gradually decreases as shown in FIG. 4 as an example, so that the temperature of the exhaust gas gradually increases.

  Focusing on the correlation between the combustion center of gravity CA50 and the exhaust gas temperature, in this embodiment, based on the load factor, the engine speed, the air-fuel ratio, and the like, a preset arithmetic expression (to be described later with reference to FIG. 7). The combustion center of gravity CA50now at present and the combustion center of gravity CA50mbt at MBT are calculated respectively. Then, based on the difference ΔCA50, a second correction coefficient Kca for correcting the exhaust temperature is calculated.

  As an example, as shown in FIG. 5, the value of the second correction coefficient Kca is set to Kca = 1 corresponding to the combustion gravity center CA50 mbt in the MBT (combustion gravity center difference ΔCA50 = 0), and from this, the ignition timing is retarded. Accordingly, as the combustion center of gravity CA50 is retarded, that is, as the combustion center of gravity difference ΔCA50 increases, it increases in a quadratic curve. This relationship has been examined in advance by experiments and the like. In this embodiment, the combustion gravity center difference ΔCA50: g (ΔCA50) is set so as to approximate the graph of FIG. Calculate the coefficient Kca.

  Hereinafter, the exhaust temperature estimation routine of the engine 1 will be specifically described with reference to the flowchart shown in FIG. This routine is executed at a predetermined timing (for example, a predetermined timing synchronized with one combustion cycle for each cylinder 2) during operation of the engine 1.

  First, in step S101 after the start in FIG. 6, the load factor and the engine speed representing the operating state of the engine 1 are detected. These are all calculated for example from signals of the crank angle sensor 61 and the air flow meter 63 and stored in the RAM of the ECU 100 for normal control of the engine 1, so that the values may be read in step S101. Subsequently, in step S102, the reference exhaust gas temperature Texst at the stoichiometric air-fuel ratio and MBT is calculated with reference to the exhaust gas temperature map.

  In step S103, the current air-fuel ratio is detected. Since this is also calculated from the signal of the air-fuel ratio sensor 65 and stored in the RAM of the ECU 100 for normal control of the engine 1, the value may be read in step S103. In step S104, the first correction coefficient Kt is calculated by substituting the reference exhaust gas temperature Texst and the air-fuel ratio A / F into the arithmetic expression: Kt = f (Texst, A / F).

  Subsequently, in step S105, the first correction coefficient Kt is multiplied by the reference exhaust temperature Texst to calculate the current air-fuel ratio and the exhaust temperature at MBT, that is, the MBT exhaust temperature Texmbt. In step S106, the combustion center of gravity CA50mbt of the MBT is calculated using a preset arithmetic expression based on the values of necessary parameters in addition to the load factor, engine speed, and air-fuel ratio.

  This arithmetic expression is derived from a model that approximates a heat release rate waveform to a triangular waveform as shown in FIG. 7 as an example. That is, the waveform of heat release rate dQ / dθ described above with reference to FIG. 2 has four characteristic values (ignition delay τ, first half combustion period a, heat release rate gradient b / a, and heat release amount Qall) ) To approximate a triangular waveform as shown in FIG. And these four characteristic values are respectively represented by the following formulas (1) to (4).

τ = C ₁ × ρ ₁ α × Neβ (1)
a = C ₂ × V ₁ γ × Neδ (2)
b / a = C ₃ × ρ ₂ × Neε (3)
Qall = Q _1- Q ₂ (4)
In the equations (1) to (4), ρ ₁ and ρ ₂ represent the fuel density at the ignition timing and the fuel density at the combustion peak, respectively, and these are calculated from the fuel injection amount and the cylinder volume. Further, Ne represents the engine speed, V ₁ represents the cylinder volume at the combustion peak, and Q ₁ and Q ₂ represent the amount of heat generated corresponding to the amount of fuel supplied and the amount of unburned fuel, respectively. Furthermore, C _{1 to} C ₃ , α, β, γ, δ, and ε are coefficients set by experiments or the like.

  Substituting the parameter values representing the current operating state of the engine 1 into the equations (1) to (4), calculating the triangular waveform with the ignition timing as MBT and the air-fuel ratio as the stoichiometric air-fuel ratio, The crank angle θ, which is the center of the area, can be calculated as the combustion center of gravity CA50mbt of the MBT. Similarly, in step S107, the combustion gravity center CA50now at the current ignition timing can be calculated.

  Subsequently, in step S108, a combustion gravity center difference ΔCA50 is calculated. Since the current combustion center of gravity should be retarded from the MBT, the combustion center CA50mbt of the MBT is subtracted from the current combustion center of gravity CA50now with the retard side as positive. In step S109, based on the combustion gravity center difference ΔCA50 calculated in this way, the combustion gravity center difference ΔCA50 is substituted into the above-mentioned arithmetic expression: Kca = g (ΔCA50) to calculate a second correction coefficient Kca, and the process proceeds to step S110.

  In step S110, the MBT exhaust temperature Texmbt calculated in step S105 is multiplied by the second correction coefficient Kca to calculate the current air fuel ratio and the exhaust temperature Tex (estimated value) at the ignition timing, and the routine is ended. To (end). That is, in the present embodiment, the exhaust gas temperature is estimated by multiplying the reference exhaust gas temperature Texst by the first correction coefficient Kt and the second correction coefficient Kca.

  By executing step S102 of the flow of FIG. 6, the ECU 100 constitutes a reference exhaust temperature calculation means for calculating the reference exhaust temperature Texst at the stoichiometric air-fuel ratio and MBT based on the engine load factor and the engine speed. By executing S104, based on the air-fuel ratio detected by the air-fuel ratio sensor 65 and the reference exhaust temperature Texst, a first correction coefficient calculation that calculates the first correction coefficient Kt that represents the effect of the air-fuel ratio on the exhaust temperature is calculated. Configure the means.

  Further, by executing steps S106 and S107 of the flow, the ECU 100 calculates combustion center of gravity CA50now at present combustion center of gravity CA50now and combustion center of gravity CA50mbt at MBT respectively based on at least load factor, engine speed and air fuel ratio. The second correction coefficient calculation means is configured to calculate the second correction coefficient Kca representing the influence of the combustion gravity center CA50 on the exhaust temperature based on the combustion gravity center difference ΔCA50mbt by configuring the step S108 and S109. Do.

  Further, by executing steps S105 and S110 of the flow, the ECU 100 calculates (estimates) the exhaust temperature Tec using the reference exhaust temperature Texst and the first and second correction coefficients Kt and Kca. Configure

  As described above, according to the exhaust gas temperature estimation device according to the present embodiment, the influence of changes in the air-fuel ratio and the ignition timing is affected on the reference exhaust gas temperature estimated from the operating state such as the load factor of the engine 1 and the engine speed. The exhaust gas temperature can be accurately estimated with appropriate reflection. At this time, conventionally, it is not necessary to interrupt energization of the heater to the air-fuel ratio sensor 65 as in a known method (Patent Document 1).

-Other embodiment-
The description of the embodiment described above is merely an example, and is not intended to limit the configuration or use of the present invention. For example, in the above embodiment, in steps S106 and S107 of the flow of FIG. 6, the combustion gravity center CA50 is calculated using an arithmetic expression derived from a heat release rate waveform model, but the invention is not limited thereto. For example, when an in-cylinder pressure sensor is provided in the engine 1, the combustion center of gravity can be calculated from the detected value by a known method.

  Further, in the above embodiment, the exhaust temperature Tex estimated by the flow of FIG. 6 may be further corrected according to the water temperature and the oil temperature of the engine 1.

  Furthermore, although the case where the present invention is applied to the gasoline engine 1 mounted on the vehicle has been described in the above embodiment, the present invention is not limited thereto, and the present invention is not limited to a gasoline engine such as an alcohol engine or a gas engine. It is also possible to apply this to a spark ignition engine, and of course, a hybrid powertrain provided with an electric motor may be used. The present invention is also applicable to engines other than vehicles.

  The present invention can estimate the exhaust gas temperature without arranging a temperature sensor in the exhaust system of the engine, and is highly effective when applied to a spark ignition engine mounted on a vehicle.

1 Engine (internal combustion engine)
65 air-fuel ratio sensor 100 ECU (reference exhaust temperature calculation means, first correction coefficient calculation means, combustion gravity center calculation means, second correction coefficient calculation means, estimation calculation means)

Claims (1)

An apparatus for estimating the temperature of exhaust gas from an internal combustion engine,
A reference exhaust gas temperature calculating means for calculating a reference air temperature at a theoretical air-fuel ratio and MBT based on at least the engine load factor and the engine speed;
First correction coefficient calculating means for calculating a first correction coefficient representing the influence of the air-fuel ratio on the exhaust temperature based on the air-fuel ratio detected by the air-fuel ratio sensor and the reference exhaust temperature;
Combustion center of gravity calculation means for calculating the current combustion center of gravity and the combustion center of gravity in MBT based on at least the engine load factor, the engine speed and the detected air-fuel ratio,
Second correction coefficient calculating means for calculating a second correction coefficient representing the influence of the combustion center of gravity on the exhaust temperature based on the current ignition timing and the difference of the combustion center of gravity in MBT;
An exhaust gas temperature estimation device for an internal combustion engine, comprising: an estimation calculation means for estimating an exhaust gas temperature using the reference exhaust gas temperature and the first and second correction coefficients.

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