JP2013221445A - Gas temperature estimating device of internal combustion engine and failure diagnosis apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas temperature estimating device capable of estimating a gas temperature at an EGR inlet using a versatile estimating equation.SOLUTION: Using a water temperature T4 of an exhaust gas discharged from a combustion chamber and the function (3): Tegr=T4-f(T4-water temperature), in which using T4 and the function f(T4-water temperature) an EGR inlet gas temperature Tegr is estimated by the function (3), cooling water temperature of an internal combustion engine appear as parameters. Use of this estimating equation which uses only T4 and the function f (T4-water temperature) appear, allows estimating the EGR inlet gas temperature regardless of the type of the internal combustion engine. When a difference between the estimated value of the EGR inlet gas temperature and the actually measured value by a temperature sensor is larger than the prescribed determination value, it is determined that a failure is generated in the temperature sensor.

Description

  The present invention relates to a gas temperature estimation device for an internal combustion engine, and more particularly to a gas temperature estimation device for estimating the temperature of EGR gas recirculated from an exhaust system to an intake system, and a failure diagnosis device for a temperature sensor.

  2. Description of the Related Art An internal combustion engine (hereinafter also referred to as an engine) mounted on a vehicle or the like has an EGR (Exhaust Gas Recirculation) device that recirculates a part of exhaust gas to an intake system for the purpose of improving exhaust emission. It has been. Such an EGR device includes, for example, an EGR passage (exhaust gas recirculation passage) connecting an exhaust system and an intake system of an internal combustion engine, and an EGR valve provided in the EGR passage, and the opening degree of the EGR valve is set. By adjusting, the amount of EGR gas recirculated from the exhaust passage to the intake passage through the EGR passage (EGR amount) is adjusted. When a part of the exhaust gas is returned to the intake passage by such an EGR device, the combustion temperature is lowered by the EGR gas, the generation of nitrogen oxide (NOx) in the combustion chamber is suppressed, and the exhaust emission is improved.

  As an EGR device, there is a system (a pipe system in the head) in which a part of exhaust gas exhausted from the combustion chamber is returned to the intake system through a pipe (passage) in the cylinder head and the EGR passage from the exhaust manifold. There is a system (external head piping system) in which a part of the exhaust gas exhausted from the combustion chamber is recirculated from the exhaust manifold to the intake system through the piping (passage) outside the cylinder head and the EGR passage.

  Here, in an internal combustion engine such as a diesel engine mounted on a vehicle or the like, in order to appropriately control the combustion state, for example, it is necessary to estimate the temperature of the intake air sucked into the combustion chamber. In the case of an internal combustion engine equipped with an EGR device, it is necessary to consider the EGR gas temperature when estimating the intake air temperature to the combustion chamber. As a method of acquiring the EGR gas temperature, for example, there are a method of arranging an EGR gas sensor in the EGR passage and detecting it from the sensor output, and a method of estimating the EGR gas temperature. Moreover, as a method for estimating the EGR gas temperature, there are methods described in Patent Documents 1 and 2 below. In the techniques described in Patent Documents 1 and 2, the EGR gas temperature is estimated using a mathematical formula (estimation formula).

Japanese Patent Laid-Open No. 2004-21560 JP 2005-133601 A

  By the way, when estimating the EGR gas temperature, the EGR gas temperature is estimated using the above-described estimation formula or map, but it is difficult to generalize these estimation formulas and maps. For this reason, conventionally, estimation formulas and maps are individually adapted for each engine model (for example, for each displacement) by experiments or the like, resulting in complicated operations and high costs.

  The present invention has been made in consideration of such a situation, and it is possible to estimate a gas temperature at an EGR passage inlet using a generalized estimation equation, and a temperature sensor for an internal combustion engine and a temperature sensor. An object is to provide a fault diagnosis apparatus.

-Solution principle of the invention-
The solution principle of the invention devised to achieve the above object is to use a generalized estimation formula based on the temperature of the exhaust gas discharged from the combustion chamber and the amount of heat released from the exhaust manifold to the EGR passage inlet. Thus, the gas temperature at the EGR passage inlet can be estimated. Further, a failure diagnosis of the gas temperature sensor is performed using the EGR inlet gas temperature estimated as described above.

-Solution-
Specifically, the present invention is applied to an internal combustion engine including an EGR device that recirculates a part of exhaust gas discharged from a combustion chamber to an intake system through piping and an EGR passage in the cylinder head from an exhaust manifold. A gas temperature estimation device for estimating the gas temperature at the passage inlet is assumed. In such a gas temperature estimation device, the temperature of the exhaust gas discharged from the combustion chamber T4 and the temperature of the cooling water of the internal combustion engine are used to calculate the EGR passage inlet by the following equation (3). It is characterized by estimating the gas temperature Tegr.

Tegr = T4-f (T4-water temperature) (3)
However, f (T4-water temperature): a function obtained by experiment or simulation. The present invention is an invention applied to an internal combustion engine having an in-head piping type EGR device, and exhaust gas discharged from a combustion chamber Focusing on the temperature T4 and the amount of heat released from the exhaust manifold to the EGR passage inlet (the amount of heat released correlates with the function f (T4-water temperature)), and only the exhaust gas temperature T4 and the function f (T4-water temperature) are used. By using the estimated equation, the EGR passage inlet gas temperature can be estimated regardless of the model of the internal combustion engine. Moreover, by estimating the heat radiation amount from the exhaust manifold to the EGR passage inlet (the heat radiation amount correlates with the function f (T4-water temperature)), the EGR passage inlet gas temperature can be estimated with higher accuracy than in the conventional control. I have to.

  Further, the present invention is applied to an internal combustion engine having an EGR device that recirculates a part of exhaust gas discharged from a combustion chamber to an intake system through a pipe outside the cylinder head and an EGR passage from an exhaust manifold, and the EGR passage inlet In the gas temperature estimation device for estimating the gas temperature of the EGR, the EGR passage inlet gas temperature Tegr is estimated by the following equation (6) using the temperature T4 of the exhaust gas discharged from the combustion chamber and the outside air temperature. It is a feature.

Tegr = T4-g (T4-outside temperature) (6)
However, g (T4-outside air temperature): a function obtained by experiment or simulation. The present invention is an invention applied to an internal combustion engine equipped with an EGR device of an outside head piping system, and is exhausted from a combustion chamber. Focusing on the gas temperature T4 and the amount of heat released from the exhaust manifold to the EGR passage inlet (the amount of heat released correlates with the function g (T4-outside temperature)), the exhaust gas temperature T4 and the function g (T4-outside temperature). By using the estimation formula using only the EGR passage inlet gas temperature can be estimated regardless of the model of the internal combustion engine. Moreover, by estimating the amount of heat released from the exhaust manifold to the EGR passage inlet (the amount of heat released correlates with g (T4−outside temperature)), the EGR passage inlet gas temperature can be estimated with higher accuracy than in the conventional control. I have to.

  In the present invention, when a temperature sensor for measuring the EGR passage inlet gas temperature is provided, the EGR passage inlet gas temperature (estimated value) estimated using the above equation (3) or the above equation (6) is used. The temperature sensor failure diagnosis apparatus may be configured. In this case, specifically, the measured value of the EGR passage inlet gas temperature detected by the temperature sensor and the EGR passage inlet gas temperature (estimated value) estimated using the above formula (3) or the above formula (6). The absolute value of the temperature difference between the two is calculated, and if the absolute value of the temperature difference is larger than a predetermined determination value (normal determination reference value), it is determined that a failure has occurred in the temperature sensor. be able to.

  According to the present invention, since the estimation formula for estimating the gas temperature at the EGR passage inlet is generalized, it is possible to simplify the operation for creating the estimation formula and achieve cost reduction.

It is a figure which shows schematic structure of the engine and its control system to which this invention is applied. It is sectional drawing which shows the combustion chamber of a diesel engine, and its peripheral part. It is a block diagram which shows the structure of control systems, such as ECU. It is a model figure which shows an example (example of piping system in a head) of a thermal system from an exhaust manifold to an EGR passage entrance. It is a graph which shows the relationship between EGR gas flow volume and exhaust-gas temperature T4, and the thermal radiation amount Qc. It is a graph which shows the relationship between [exhaust gas temperature T4-water temperature] and [Qc / EGR gas flow rate]. It is a figure which shows the relationship between the estimated value of EGR inlet gas temperature, and the measured value of EGR inlet gas temperature. It is a model figure which shows the other example (example of a piping system outside a head) from the exhaust manifold to an EGR channel | path entrance. It is a graph which shows the relationship between [exhaust gas temperature T4-outside temperature] and [Qc / EGR gas flow rate]. It is a flowchart which shows an example of the failure diagnosis process of an EGR gas temperature sensor. It is a graph which shows the relationship between [exhaust gas temperature T4-water temperature] and [Qc / EGR gas flow rate]. It is a graph which shows the relationship between [exhaust gas temperature T4-outside temperature] and [Qc / EGR gas flow rate].

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In this embodiment, a case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (for example, in-line 4-cylinder) diesel engine (compression self-ignition internal combustion engine) mounted on a vehicle will be described.

-Engine configuration-
First, a schematic configuration of a diesel engine (hereinafter simply referred to as an engine) according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram of an engine 1 and its control system according to the present embodiment. FIG. 2 is a cross-sectional view showing the combustion chamber 3 of the diesel engine 1 and its periphery.

  As shown in FIG. 1, the engine 1 according to the present embodiment is configured as a diesel engine system having a fuel supply system 2, a combustion chamber 3, an intake system 6, an exhaust system 7 and the like as main parts.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, an injector (fuel injection valve) 23, an engine fuel passage 27, and the like.

  The supply pump 21 pumps fuel from the fuel tank, makes the pumped fuel high pressure, and supplies it to the common rail 22 via the engine fuel passage 27. The common rail 22 has a function as a pressure accumulating chamber that holds (accumulates) high-pressure fuel at a predetermined pressure, and distributes the accumulated fuel to the injectors 23. The injector 23 includes a piezoelectric element (piezo element) therein, and is configured by a piezo injector that is appropriately opened to supply fuel into the combustion chamber 3.

  The intake system 6 includes an intake manifold 63 connected to an intake port 15a formed in the cylinder head 15 (see FIG. 2), and an intake pipe 64 is connected to the intake manifold 63. The intake port 15a, intake An intake passage is constituted by the manifold 63, the intake pipe 64, and the like. In this intake passage, an air cleaner 65, an air flow meter 43, an intake air temperature sensor 31, a compressor impeller 53 of a turbocharger 5 to be described later, an intake throttle valve (diesel throttle) 62, and the like are arranged in this order from the upstream side. The air flow meter 43 outputs an electrical signal corresponding to the amount of air flowing into the intake passage via the air cleaner 65. The intake air temperature sensor 31 outputs an electrical signal corresponding to the temperature of the air that has passed through the air cleaner 65 (corresponding to the outside air temperature).

  The exhaust system 7 includes an exhaust manifold 72 connected to an exhaust port 71 formed in the cylinder head 15, and an exhaust pipe 73 is connected to the exhaust manifold 72. The exhaust port 71 and the exhaust manifold 72 are connected to the exhaust manifold 72. An exhaust passage is constituted by the exhaust pipe 73 and the like. In the exhaust passage, a turbine wheel 52 of the turbocharger 5 described later, an exhaust purification unit 77, and the like are disposed.

  The exhaust purification unit 77 includes an NSR catalyst (exhaust purification catalyst) 75 and a DPF (Diesel Particulate Filter) 76 as NOx storage reduction catalysts. A DPNR catalyst may be applied as the exhaust purification unit 77.

The NSR catalyst 75 stores NOx in a state where a large amount of oxygen is present in the exhaust gas, has a low oxygen concentration in the exhaust gas, and a large amount of reducing component (for example, an unburned component (HC) of fuel). In the existing state, NOx is reduced to NO ₂ or NO and released. NO NOx released as NO ₂ or NO, the N ₂ is further reduced due to quickly reacting with HC or CO in the exhaust. Further, HC and CO are oxidized to H ₂ O and CO ₂ by reducing NO ₂ and NO. That is, by appropriately adjusting the oxygen concentration and HC component in the exhaust gas introduced into the NSR catalyst 75, HC, CO, and NOx in the exhaust gas can be purified. In the present embodiment, the oxygen concentration and HC component in the exhaust gas are adjusted by the fuel injection operation (post injection) from the injector 23 and the opening degree control of the intake throttle valve 62.

  The DPF 76 is made of, for example, a porous ceramic structure, and collects PM (Pattern Matter) contained in the exhaust gas when the exhaust gas passes through the porous wall. . The DPF 76 carries a catalyst (for example, an oxidation catalyst mainly composed of a noble metal such as platinum) for oxidizing and burning the collected PM during the DPF regeneration operation.

  Here, the structure of the combustion chamber 3 of the engine 1 and its peripheral part will be described with reference to FIG. As shown in FIG. 2, a cylinder block 11 constituting a part of the engine body is formed with a cylindrical cylinder bore 12 for each cylinder (four cylinders), and a piston 13 is formed inside each cylinder bore 12. Is accommodated so as to be slidable in the vertical direction.

  The combustion chamber 3 is formed above the top surface 13 a of the piston 13. That is, the combustion chamber 3 is defined by the lower surface of the cylinder head 15 attached to the upper portion of the cylinder block 11, the inner wall surface of the cylinder bore 12, and the top surface 13 a of the piston 13. A cavity (concave portion) 13 b is formed in a substantially central portion of the top surface 13 a of the piston 13, and this cavity 13 b also constitutes a part of the combustion chamber 3.

  The piston 13 is connected to a crankshaft, which is an engine output shaft, by a connecting rod 18. As a result, the reciprocating movement of the piston 13 in the cylinder bore 12 is transmitted to the crankshaft via the connecting rod 18, and the engine output is obtained by rotating the crankshaft.

  Further, a glow plug 19 is disposed toward the combustion chamber 3. The glow plug 19 functions as a start-up assisting device that is heated red when an electric current is applied immediately before the engine 1 is started and a part of the fuel spray is blown onto the glow plug 19 to promote ignition and combustion.

  The cylinder head 15 is formed with the intake port 15a and the exhaust port 71, respectively, and an intake valve 16 for opening and closing the intake port 15a and an exhaust valve 17 for opening and closing the exhaust port 71 are disposed. The cylinder head 15 is provided with the injector 23 that directly injects fuel into the combustion chamber 3. The injector 23 is disposed at a substantially upper center of the combustion chamber 3 in a standing posture along the cylinder center line P, and injects fuel introduced from the common rail 22 toward the combustion chamber 3 at a predetermined timing.

-Turbocharger-
Further, as shown in FIG. 1, the engine 1 is provided with a turbocharger (supercharger) 5. The turbocharger 5 includes a turbine wheel 52 and a compressor impeller 53 that are connected via a turbine shaft 51. The compressor impeller 53 is arranged facing the inside of the intake pipe (intake passage) 64, and the turbine wheel 52 is arranged facing the inside of the exhaust pipe (exhaust passage) 73. Therefore, the turbocharger 5 performs a so-called supercharging operation in which the compressor impeller 53 is rotated using the exhaust flow (exhaust pressure) received by the turbine wheel 52 to increase the intake pressure. The turbocharger 5 in the present embodiment is a variable nozzle type turbocharger, and a variable nozzle vane mechanism (not shown) is provided on the turbine wheel 52 side. By adjusting the opening of the variable nozzle vane mechanism, the engine 1 supercharging pressure can be adjusted.

  The turbine wheel 52 of the turbocharger 5 is accommodated in the turbine housing 52a, and the compressor impeller 53 is accommodated in the compressor housing 53a. The turbine 520 is configured by the turbine wheel 52, the turbine housing 52a, the variable nozzle vane mechanism, and the like, and the compressor 530 is configured by the compressor impeller 53, the compressor housing 53a, and the like.

  An intake pipe 64 of the intake system 6 (an intake passage on the downstream side of the intake air flow of the compressor 530) is provided with an intercooler 61 for forcibly cooling intake air whose temperature has been raised by supercharging in the turbocharger 5. .

-EGR device-
Further, the engine 1 is provided with an EGR passage (exhaust gas recirculation passage) 80 that connects the intake system 6 and the exhaust system 7. The EGR passage 80 is configured to reduce a combustion temperature by recirculating a part of the exhaust gas to the intake system 6 and supplying the exhaust gas to the combustion chamber 3 again, thereby reducing the NOx generation amount. Further, the EGR passage 80 is opened and closed steplessly by electronic control, and an exhaust gas flowing through the EGR passage 80 (refluxing) is cooled by an EGR valve 81 that can freely adjust an exhaust flow rate flowing through the EGR passage 80. An EGR cooler 82 is provided. The EGR passage 80, the EGR valve 81, the EGR cooler 82, and the like constitute an EGR device (exhaust gas recirculation device) 8. The EGR device 8 may have a configuration that does not include the EGR cooler 82.

  Here, as the EGR device 8, for example, a part of the exhaust gas exhausted from the combustion chamber 3 of the engine 1 is sucked from the exhaust manifold 72 through a pipe (passage) outside the cylinder head 15 (see FIG. 2) and the EGR passage. A system that recirculates to the system (piping system outside the head) (the one shown in FIG. 1) and a part of the exhaust gas exhausted from the combustion chamber 3 of the engine 1 from the exhaust manifold 72 to the pipe in the cylinder head 15 (Passage) and a method of returning to the intake system through the EGR passage (in-head piping method).

-Sensors-
Various sensors are attached to each part of the engine 1, and signals related to environmental conditions of each part and the operating state of the engine 1 are output.

  For example, the air flow meter 43 outputs a detection signal corresponding to the flow rate (intake air amount) of intake air upstream of the intake throttle valve 62 in the intake system 6. The rail pressure sensor 41 outputs a detection signal corresponding to the fuel pressure stored in the common rail 22. The throttle opening sensor 42 detects the opening of the intake throttle valve 62.

  The intake air temperature sensor 31 is arranged on the upstream side of the intake air flow of the compressor 530 of the turbocharger 5, and the temperature of the air that has passed through the air cleaner 65 (the temperature of the air flowing into the inlet of the compressor 530 (corresponding to the outside air temperature)). A corresponding detection signal is output.

  The intake pressure sensor 48 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air pressure. The intake manifold temperature sensor (intake air temperature sensor) 49 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the temperature of the intake air. The exhaust gas temperature sensor 32 outputs a detection signal corresponding to the temperature of the exhaust gas discharged from the combustion chamber 3 (the temperature in the exhaust manifold 72).

  The A / F (air-fuel ratio) sensors 44a and 44b are arranged on the upstream side and the downstream side of the NSR catalyst 75, respectively, and output detection signals that change continuously according to the oxygen concentration in the exhaust gas. The A / F sensor may be disposed only on the upstream side of the NSR catalyst 75 or only on the downstream side of the NSR catalyst 75. Similarly, the exhaust temperature sensors 45a and 45b are disposed on the upstream side and the downstream side of the NSR catalyst 75, respectively, and output detection signals corresponding to the exhaust gas temperature (exhaust temperature). The exhaust temperature sensor may be disposed only on the upstream side of the NSR catalyst 75 or only on the downstream side of the NSR catalyst 75.

-ECU-
The ECU 100 includes a microcomputer including an unillustrated CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and an input / output circuit.

  As shown in FIG. 3, the input circuit of the ECU 100 includes the rail pressure sensor 41, the throttle opening sensor 42, the air flow meter 43, the A / F sensors 44a and 44b, the exhaust temperature sensors 45a and 45b, the intake pressure sensor 48, An intake manifold temperature sensor 49, an intake air temperature sensor 31, and an exhaust gas temperature sensor 32 are connected. Further, the input circuit includes a water temperature sensor 46 that outputs a detection signal corresponding to the cooling water temperature of the engine 1, an accelerator opening sensor 47 that outputs a detection signal corresponding to the depression amount of the accelerator pedal, and an output shaft (crank) of the engine 1. A crank position sensor 40 that outputs a detection signal (pulse) each time the shaft rotates a certain angle is connected.

  On the other hand, the supply pump 21, the injector 23, the intake throttle valve 62, the EGR valve 81, and the variable nozzle vane mechanism (actuator for adjusting the opening degree of the variable nozzle vane) 54 of the turbocharger 5 are connected to the output circuit of the ECU 100. Has been.

  Then, the ECU 100 executes various controls of the engine 1 based on outputs from the various sensors described above, calculated values obtained by arithmetic expressions using the output values, or various maps stored in the ROM. .

  For example, the ECU 100 executes pilot injection (sub-injection) and main injection (main injection) as fuel injection control of the injector 23.

  The pilot injection is an operation for injecting a small amount of fuel in advance prior to the main injection from the injector 23. The pilot injection is an injection operation for suppressing the ignition delay of fuel due to the main injection and leading to stable diffusion combustion, and is also referred to as sub-injection.

  The main injection is an injection operation (torque generation fuel supply operation) for generating torque of the engine 1. The injection amount in the main injection is basically determined so that the required torque can be obtained according to the operating state such as the engine speed (engine speed), the accelerator operation amount, the coolant temperature, the intake air temperature, and the like. . For example, as the engine speed (engine speed calculated based on the detection value of the crank position sensor 40; engine speed) increases, the accelerator operation amount (depressing the accelerator pedal detected by the accelerator opening sensor 47) increases. The larger the (amount) (the greater the accelerator opening), the higher the required torque value of the engine 1, and the greater the fuel injection amount in the main injection.

  As an example of a specific fuel injection mode, the pilot injection (fuel injection from a plurality of injection holes formed in the injector 23) is performed before the piston 13 reaches the compression top dead center, and the fuel injection is temporarily stopped. After that, the main injection is executed when the piston 13 reaches the vicinity of the compression top dead center after a predetermined interval. As a result, the fuel is combusted by self-ignition, and energy generated by this combustion is kinetic energy for pushing the piston 13 toward the bottom dead center (energy serving as engine output), and heat energy for raising the temperature in the combustion chamber 3. The heat energy is radiated to the outside (for example, cooling water) through the cylinder block 11 and the cylinder head 15.

  The fuel injection pressure when executing the fuel injection is determined by the internal pressure of the common rail 22. As the common rail internal pressure, generally, the target value of the fuel pressure supplied from the common rail 22 to the injector 23, that is, the target rail pressure, increases as the engine load (engine load) increases and the engine speed (engine speed) increases. It will be expensive. This target rail pressure is set according to a fuel pressure setting map stored in the ROM, for example. In the present embodiment, the fuel pressure is adjusted between 30 MPa and 200 MPa according to the engine load and the like.

  In addition to the pilot injection and the main injection described above, after injection and post injection are performed as necessary. The function of these injections is well known. In particular, the post injection is used for NOx reduction processing, S poison recovery control, and DPF regeneration processing.

  Further, the ECU 100 controls the opening degree of the EGR valve 81 (including the case where the opening degree = 0 (closed)) according to the operating state of the engine 1, and the exhaust gas recirculation amount (EGR amount) toward the intake manifold 63. Adjust. This EGR amount is set in accordance with an EGR map that is created in advance by experiments, simulations, or the like and stored in the ROM. This EGR map is a map for determining the EGR amount (EGR rate) using the engine speed and the engine load as parameters.

  Further, the ECU 100 estimates an EGR passage inlet gas temperature (hereinafter also referred to as an EGR inlet temperature) described later. Further, based on the estimated EGR inlet gas temperature, a failure diagnosis of an EGR gas temperature sensor described later is performed.

  The gas temperature estimation device and the failure diagnosis device of the present invention are realized by the program executed by the ECU 100 described above.

-EGR inlet gas temperature-
Next, a method for estimating the EGR inlet gas temperature, which is a characteristic part of the present embodiment, will be described. Here, a method for estimating the EGR inlet gas temperature in each of the engine having the above-in-head piping type EGR device and the engine having the outside-head piping type EGR device will be described.

<Piping system in the head>
First, in the case of the in-head piping system, the system shown in FIG. 4 is considered, and the exhaust gas temperature T4 exhausted from the combustion chamber 3 and the EGR inlet gas temperature Tegr are taken from the exhaust manifold 72 to the passage of the cylinder head. The heat radiation amount Qc (up to the entrance of the EGR passage 80) can be expressed by the following formula (1).

Qc = EGR gas amount × specific heat × (T4-Tegr) (1)
Here, the heat release amount Qc is proportional to the EGR gas amount, and the temperature difference between the inside and outside of the pipe in the head increases as the exhaust gas temperature T4 increases. Therefore, as shown in FIG. The amount of heat Qc increases. FIG. 5 is a graph depicting an approximate line obtained by linearly approximating a result obtained by experiment / simulation or the like regarding the relationship between the EGR gas amount and the exhaust gas temperature T4 and the heat release amount Qc.

  Next, the temperature of the piping in the head is defined as the water temperature (engine cooling water temperature), and the heat dissipation amount Qc (inclination of each approximate line in FIG. 5) per unit mass is arranged based on the water temperature, as shown in FIG. In addition, it was found that there is a correlation between [T4-water temperature] and the heat release amount Qc per unit mass (inclination in FIG. 5 = Qc / EGR gas flow rate). In other words, the relationship between [T4-water temperature] and [heat dissipation amount Qc / EGR gas flow rate] can be uniquely defined regardless of the model of engine 1 (hard configuration such as displacement). There was found. When the solid line (secondary curve) in FIG. 6 is converted into an empirical formula, it can be expressed by the following formula (2).

Qc / EGR gas amount = f (T4−water temperature) (2)
From this equation (2) and the above equation (1), the EGR inlet gas temperature Tegr can be expressed by the following equation (3), and the estimated value of the EGR inlet gas temperature Tegr can be calculated by this equation (3). Can do.

Tegr = T4-f (T4-water temperature) (3)
However, the gas specific heat is included in the function f (T4-water temperature). Further, the function f (T4−water temperature) of the equation (3), that is, the quadratic function of FIG. 6 is determined by experiment or simulation. Further, the above equation (3) including this function f (T4-water temperature) is stored in the ROM of the ECU 100.

  When the engine 1 is in operation, the ECU 100 calculates the exhaust gas temperature T4 from the output signal of the exhaust gas temperature sensor 32, calculates the water temperature from the output signal of the water temperature sensor 46, and calculates the exhaust gas temperature T4 and the water temperature. Using this, the EGR inlet gas temperature Tegr is calculated (estimated) from the above equation (3).

  As for the exhaust gas temperature T4, the exhaust gas is referred to a map created in advance through experiments and simulations based on the engine speed and the required torque determined from the engine speed and the accelerator opening (depression amount). You may use the estimated value which estimated temperature.

  Here, the above equation (3) is an estimation equation obtained from the relationship between [T4−water temperature] and [Qc / EGR gas flow rate] shown in FIG. 6, and is based only on the exhaust gas temperature T4 and the water temperature of the engine 1. Since it is an equation for calculating the EGR inlet temperature Tegr, it can be used regardless of the model of the engine 1 (hard configuration such as displacement) and is versatile (in the range of practical EGR piping) Versatile). Moreover, since the amount of heat released from the exhaust manifold 72 to the inlet of the EGR passage 80 is estimated (since the amount of heat released is subtracted from the exhaust gas temperature T4), the EGR inlet temperature Tegr is estimated with higher accuracy than in the prior art. can do.

  In order to confirm the versatility of the above formula (3), the inventors of the present invention can use the above formula (for example, a large number of engines having different displacements in the range of 2 to 3 L). 3) was used to estimate the EGR inlet temperature Tegr. Moreover, the EGR inlet temperature was measured with the sensor about the engine of each model. FIG. 7 shows the relationship between the estimated value and the actually measured value of the EGR inlet temperature Tegr. As is apparent from FIG. 7, the estimated value of the EGR inlet temperature Tegr and the measured value of the EGR inlet temperature substantially coincide with each other. Thus, in the practical EGR piping range, the above formula (3) Can be used as a general-purpose equation for estimating the EGR inlet gas temperature.

<External piping system>
Next, an outside-head piping EGR apparatus will be described.

  First, in the case of the piping system outside the head, if the system as shown in FIG. 8 is considered and the exhaust gas temperature T4 exhausted from the combustion chamber 3 is assumed to be the EGR inlet gas temperature Tegr, the exhaust manifold 72 to the inlet of the EGR passage 80 The heat dissipation amount Qc up to can be expressed by the following equation (4).

Qc = EGR gas amount × specific heat × (T4-Tegr) (4)
Here, also in the case of the piping system outside the head, as in the case of the piping system in the head described above, the heat radiation amount Qc is proportional to the EGR gas amount, and the heat radiation amount Qc increases as the exhaust gas temperature T4 increases. .

  Next, the temperature of the pipe outside the head is defined as the outside air temperature, and the heat radiation amount Qc per unit mass (corresponding to the slope of the approximate line in FIG. 5) is arranged at the outside air temperature. As shown in FIG. It was found that there is a correlation between [T4-outside air temperature] and the heat release amount Qc per unit mass (slope = Qc / EGR gas flow rate). That is, the relationship between [T4-outside air temperature] and [heat radiation amount Qc / EGR gas flow rate] can be uniquely defined regardless of the model of engine 1 (hard configuration such as displacement). It has been found. Then, when the solid line (secondary curve) in FIG. 9 is empirically expressed, it can be expressed by the following expression (5).

Qc / EGR gas amount = g (T4−outside temperature) (5)
From this equation (5) and the above equation (4), the EGR inlet gas temperature Tegr can be expressed by the following equation (6), and the estimated value of the EGR inlet gas temperature Tegr can be calculated by this equation (6). Can do.

Tegr = T4-g (T4-outside temperature) (6)
However, the gas specific heat is included in the function g (T4-outside air temperature). Further, the function g (T4−outside air temperature) in Expression (6), that is, the quadratic function in FIG. 9 is determined by experiment or simulation. Further, the above equation (6) including this function g (T4-outside air temperature) is stored in the ROM of the ECU 100.

  When the engine 1 is in operation, the ECU 100 calculates the exhaust gas temperature T4 from the output signal of the exhaust gas temperature sensor 32, calculates the outside air temperature from the output signal of the intake air temperature sensor 31, and the exhaust gas temperature T4. Then, the EGR inlet gas temperature Tegr is calculated (estimated) from the above equation (6) using the outside air temperature.

  As for the exhaust gas temperature T4, the exhaust gas is referred to a map created in advance through experiments and simulations based on the engine speed and the required torque determined from the engine speed and the accelerator opening (depression amount). You may use the estimated value which estimated temperature. As for the outside air temperature, a sensor detection value or an estimated value of the engine room internal temperature (engine compartment internal temperature) may be used.

  Also in this example, the above equation (6) is an estimation equation obtained from the relationship between [T4−outside air temperature] and [Qc / EGR gas flow rate], and the EGR inlet temperature is obtained only from the exhaust gas temperature T4 and the outside air temperature. Since it is a formula for calculating Tegr, it can be used regardless of the model of the engine 1 (hard configuration such as displacement) and is versatile (in the range of practical EGR piping) is there). Moreover, since the amount of heat released from the exhaust manifold 72 to the inlet of the EGR passage 80 is estimated (since the amount of heat released is subtracted from the exhaust gas temperature T4), the EGR inlet temperature Tegr is estimated with higher accuracy than in the prior art. can do.

  In order to confirm the versatility of the above formula (6), the inventors of the present invention have described the above formula (for a large number of engines with different displacements in the range of 2 to 3 L, for example) 6) was used to estimate the EGR inlet temperature Tegr. Moreover, the EGR inlet temperature was measured with the sensor about the engine of each model. When the relationship between the estimated value of the EGR inlet temperature Tegr and the actually measured value was examined, the same result as in the above-described FIG. 7 was obtained. Thus, it was confirmed that the above formula (6) can be used as a general-purpose formula for estimating the EGR inlet gas temperature in the practical EGR piping handling range.

-EGR gas temperature sensor fault diagnosis-
As described above, according to the present embodiment, the EGR gas inlet temperature can be estimated. Therefore, when the EGR gas temperature sensor is provided, a failure diagnosis of the EGR gas temperature sensor can be performed. .

  An example of the specific process (EGR gas temperature sensor failure diagnosis process) will be described with reference to the flowchart of FIG. The processing routine of FIG. 10 is repeatedly executed by the ECU 100 every predetermined time (for example, several msec).

  First, in step ST101, the EGR inlet gas temperature Tegr is estimated. Specifically, the exhaust gas temperature T4 is calculated from the output signal of the exhaust gas temperature sensor 32, the water temperature is calculated from the output signal of the water temperature sensor 46, and the above equation (3) is calculated using the exhaust gas temperature T4 and the water temperature. To estimate the EGR inlet gas temperature Tegr.

  An estimated value may be used for the exhaust gas temperature. For example, based on the engine speed and the required torque determined from the engine speed and the accelerator opening (depression amount), the exhaust gas temperature is estimated with reference to an estimation map created in advance through experiments, simulations, etc. The EGR inlet gas temperature Tegr may be estimated using the estimated value of the exhaust gas temperature.

  Next, in step ST102, the EGR inlet gas temperature (actually measured value) is detected from the output signal of the EGR gas temperature sensor.

  In step ST103, a temperature difference (absolute value) ΔT between the EGR inlet gas temperature (actual value) detected in step ST102 and the EGR inlet gas temperature Tegr (estimated value) estimated in step ST101 is calculated (ΔT = | EGR inlet gas temperature-estimated Tegr |).

  In step ST104, it is determined whether or not the temperature difference (absolute value) ΔT calculated in step ST103 is equal to or less than a predetermined normal determination reference value Tref. Regarding the normal determination reference value Tref used in the determination process of step ST104, for example, the allowable range (normal range) of the temperature difference ΔT (| EGR inlet gas temperature−estimated Tegr |) when the EGR gas temperature sensor is normal. Is obtained by experiment / simulation in consideration of sensor variation and the like, and a suitable value is set based on the result.

  If the determination result in step ST104 is affirmative (YES) (when [ΔT ≦ Tref]), it is determined that the EGR gas temperature sensor is normal (step ST105).

  On the other hand, if the determination result in step ST104 is negative (NO), that is, the temperature difference ΔT between the EGR inlet gas temperature (actually measured value) and the estimated EGR inlet gas Tegr is larger than the normal determination reference value Tref (ΔT> In the case of (Tref), it is determined (diagnostic) that a failure has occurred in the EGR gas temperature sensor (step ST106). In this case, for example, a MIL (Malfunction Indicator Lamp; warning lamp) on the meter panel in the passenger compartment is turned on to prompt the user (driver) to warn, and the abnormality information is written in the diagnosis provided in the ECU 100.

  In the above-described failure diagnosis processing, the case where the above-described equation (3) is used (in the case of the in-head piping method) has been described. However, when the EGR device 8 is the outside-head piping method, the above equation (6) ) To perform fault diagnosis.

  In this case, in step ST101 of FIG. 10, the exhaust gas temperature T4 is calculated from the output signal of the exhaust gas temperature sensor 32, the outside air temperature is calculated from the output signal of the intake air temperature sensor 31, and the exhaust gas temperature T4 and The EGR inlet gas temperature Tegr is calculated (estimated) from the above equation (6) using the outside air temperature. Then, processing equivalent to steps ST102 to ST106 in FIG. 10 may be performed to determine normality / failure of the EGR gas temperature sensor.

(Modification 1)
The vertical axis (Qc / EGR gas flow rate) in FIG. 6 is a difference between the inlet temperature and the outlet temperature of the system shown in FIG. 4, and the horizontal axis (T4-water temperature) in FIG. 6 is the inlet of the system shown in FIG. Since this is the difference between the temperature and the temperature of the cooling medium (engine cooling water), FIG. 6 is considered to be a diagram showing the heat dissipation efficiency in the system of FIG. Here, FIG. 6 can be handled as a quadratic function, but if the range is limited, it can be regarded as a linear function (constant efficiency) as shown by the broken line in FIG. Therefore, the above equation (3) may be obtained by obtaining the slope and intercept (function f (T4−water temperature)) of FIG. 11 by experiment or simulation.

(Modification 2)
The vertical axis (Qc / EGR gas flow rate) in FIG. 9 is a difference between the inlet temperature and the outlet temperature of the system shown in FIG. 8, and the horizontal axis (T4-outside air temperature) is the inlet temperature of the system shown in FIG. Since this is the difference from the outside air temperature, FIG. 9 is considered to be a diagram showing the heat radiation efficiency in the system of FIG. Here, FIG. 9 can also be handled as a quadratic function, but if the range is limited, it can be regarded as a linear function (constant efficiency) as shown by a broken line in FIG. Therefore, the above equation (6) may be obtained by obtaining the slope and intercept (function g (T4−outside air temperature)) of FIG. 12 by experiment or simulation.

(Modification 3)
As described above, in the present embodiment, since the EGR inlet gas temperature Tegr can be estimated, the EGR outlet gas temperature can also be estimated. Specifically, the EGR inlet gas temperature (estimated value) calculated by the above formula (3) or (6) is used for the heat dissipation efficiency of the system from the EGR passage inlet to the outlet (including the cooling efficiency of the EGR cooler 82). , The EGR outlet gas temperature can be calculated (estimated).

-Other embodiments-
In the above example, the case where the present invention is applied to temperature estimation and temperature sensor failure diagnosis of an in-line four-cylinder diesel engine mounted on a vehicle has been described. The present invention is not limited to vehicles, but can be applied to engine temperature estimation and temperature sensor failure diagnosis used for other purposes. Further, the number of cylinders and the engine type (separate type engine, V-type engine, horizontally opposed engine, etc.) are not particularly limited.

  In the above example, the engine 1 to which the piezo injector 23 that changes the fuel injection rate by changing to the fully open valve state only during the energization period has been described. However, the present invention relates to an engine to which the variable injection rate injector is applied. Application to temperature estimation and temperature sensor failure diagnosis is also possible.

  Further, the present invention is not limited to a diesel engine, but can also be applied to temperature estimation and temperature sensor failure diagnosis of a gasoline engine.

  INDUSTRIAL APPLICABILITY The present invention can be used for a gas temperature estimation device and a failure diagnosis device for an internal combustion engine, and more specifically, for a gas temperature estimation device and a failure diagnosis device that estimate the temperature of EGR gas that is recirculated from an exhaust system to an intake system. can do.

1 Engine 31 Intake Air Temperature Sensor 32 Exhaust Gas Temperature Sensor 6 Intake System 63 Intake Manifold 64 Intake Pipe (Intake Passage)
7 Exhaust system 72 Exhaust manifold 73 Exhaust pipe (exhaust passage)
8 EGR device 80 EGR passage 81 EGR valve 100 ECU

Claims (3)

A gas temperature estimation device applied to an internal combustion engine including an EGR device that recirculates a part of exhaust gas discharged from a combustion chamber to an intake system through a pipe in an cylinder head and an EGR passage from an exhaust manifold,
The gas temperature Tegr at the EGR passage inlet is estimated by the following equation (3) using the temperature T4 of the exhaust gas discharged from the combustion chamber and the temperature of the cooling water of the internal combustion engine. A gas temperature estimating device for an internal combustion engine.
Tegr = T4-f (T4-water temperature) (3)
However, f (T4-water temperature): function obtained by experiment or simulation A gas temperature estimation device applied to an internal combustion engine equipped with an EGR device that recirculates a part of exhaust gas discharged from a combustion chamber to an intake system through a pipe outside the cylinder head and an EGR passage from an exhaust manifold,
The gas temperature estimation of the internal combustion engine, wherein the gas temperature Tegr at the EGR passage inlet is estimated by the following equation (6) using the temperature T4 of the exhaust gas discharged from the combustion chamber and the outside air temperature. apparatus.
Tegr = T4-g (T4-outside temperature) (6)
However, g (T4-outside temperature): function obtained by experiment or simulation Failure diagnosis applied to an internal combustion engine including an EGR device that recirculates a part of exhaust gas discharged from the combustion chamber to the intake system through the EGR passage from the exhaust manifold, and a temperature sensor that detects the temperature of the EGR passage inlet A device,
The actual measured value detected by the temperature sensor and the EGR passage inlet gas temperature estimated by the internal combustion engine gas temperature estimation device according to claim 1 or the internal combustion engine gas temperature estimation device according to claim 2. A failure diagnosis device characterized in that, when the absolute value of the temperature difference from the EGR passage inlet gas temperature is larger than a predetermined determination value, it is determined that a failure has occurred in the temperature sensor.

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