Engine Control Device

Abstract

An object of the present invention is to optimally control a recirculation amount of exhaust gas flowing to an engine that includes an exhaust heat recovery device in a main exhaust pipe thereof and performs exhaust gas recirculation from downstream of the exhaust heat recovery device. An engine control device includes an exhaust heat recovery device, an exhaust gas recirculation pipe, an exhaust gas temperature acquisition unit, and an exhaust gas recirculation amount control unit. The exhaust heat recovery device is provided in a main exhaust pipe of an engine and recovers heat from exhaust gas. The exhaust gas recirculation pipe is branched from the main exhaust pipe downstream of the exhaust heat recovery device and recirculates exhaust gas to the engine. The exhaust gas temperature acquisition unit acquires an exhaust gas temperature downstream of the exhaust heat recovery device. The exhaust gas recirculation amount control unit controls a recirculation amount of exhaust gas flowing through the exhaust gas recirculation pipe based on at least the exhaust gas temperature.

Claims

1. An engine control device, comprising: an exhaust heat recovery device provided in a main exhaust pipe of an engine and configured to recover heat from exhaust gas; an exhaust gas recirculation pipe branched from the main exhaust pipe downstream of the exhaust heat recovery device and configured to recirculate exhaust gas to the engine; an exhaust gas temperature acquisition unit configured to acquire as exhaust gas temperature downstream of the exhaust heat recovery device; and an exhaust gas recirculation amount control unit configured to control a recirculation amount of exhaust gas flowing through the exhaust gas recirculation pipe based on at least the exhaust gas temperature.

2. The engine control device according to claim 1, wherein the exhaust gas temperature acquisition unit configured to acquire as exhaust gas temperature downstream of the exhaust heat recovery device is an exhaust temperature sensor disposed downstream of the exhaust heat recovery device or the exhaust gas recirculation pipe.

3. The engine control device according to claim 1, wherein the exhaust gas temperature acquisition unit configured to acquire an exhaust gas temperature downstream of the exhaust heat recovery device estimates the exhaust gas temperature based on at least a recovery heat amount or recovery efficiency of the exhaust heat recovery device.

4. The engine control device according to claim 1, wherein the exhaust gas recirculation amount control unit configured to control the exhaust gas recirculation amount is an EGR valve provided in the exhaust gas recirculation pipe.

5. The engine control device according to claim 1, wherein the exhaust gas recirculation amount control unit configured to control the recirculation amount of exhaust gas flowing through the exhaust gas recirculation pipe controls the exhaust gas recirculation amount such that an EGR rate is within a predetermined range.

6. The engine control device according to claim 1, wherein the exhaust gas recirculation amount control unit configured to control the recirculation amount of exhaust gas flowing through the exhaust gas recirculation pipe controls such that a temperatures of mixed gas of the exhaust gas recirculation amount and an intake air amount is within a predetermined range.

7. The engine control device according to claim 1, wherein the exhaust gas recirculation amount control unit configured to control the recirculation amount of exhaust gas flowing through the exhaust gas recirculation amount controls such that combustion stability is within a predetermined range.

8. The engine control device according to claim 1, wherein the ignition timing is corrected to an advance angle side in accordance with increase in the exhaust gas recirculation amount.

9. The engine control device according to claim 1, further comprising: abnormality determination unit configured to determine an abnormality of the exhaust heat recovery device based on the exhaust gas temperature downstream of the exhaust heat recovery device, wherein when the exhaust heat recovery device is determined to be abnormal, the engine control device corrects the exhaust gas recirculation amount by a predetermined amount.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is a diagram of an engine control system according to first to third, fifth, and sixth embodiments.

[0027] FIG. 2 is a diagram indicating the interior of a control unit according to the first to third, fifth, and sixth embodiments.

[0028] FIG. 3 is a block diagram indicating overall control according to the first to third embodiments.

[0029] FIG. 4 is a block diagram indicating a target EGR rate calculation unit according to the first to fifth embodiments.

[0030] FIG. 5 is a block diagram illustrating a target EGR valve opening calculation unit according to the first and fifth embodiments.

[0031] FIG. 6 is a block diagram indicating a target EGR valve opening calculation unit according to the second embodiment.

[0032] FIG. 7 is a block diagram illustrating a target EGR valve opening calculation unit according to the third embodiment.

[0033] FIG. 8 is a diagram indicating an engine control system according to a fourth embodiment.

[0034] FIG. 9 is a diagram indicating the interior of a control unit according to the fourth embodiment.

[0035] FIG. 10 is a block diagram indicating overall control according to the fourth embodiment.

[0036] FIG. 11 is a block diagram indicating an estimated exhaust gas temperature calculation unit according to the fourth embodiment.

[0037] FIG. 12 is a block diagram indicating a target EGR valve opening calculation unit according to the fourth embodiment.

[0038] FIG. 13 is a block diagram indicating overall control according to the fifth embodiment.

[0039] FIG. 14 is a block diagram indicating an ignition timing correction value calculation unit according to the fifth embodiment

[0040] FIG. 15 is a block diagram indicating overall control according to the sixth embodiment.

[0041] FIG. 16 is a block diagram indicating an exhaust heat recovery device abnormality determination unit according to the sixth embodiment.

[0042] FIG. 17 is a block diagram indicating a target EGR valve opening calculation unit according to the sixth embodiment.

DESCRIPTION OF EMBODIMENTS

[0043] Embodiments will be described below with reference to the drawings.

First Embodiment

[0044] A first embodiment describes that an exhaust gas recirculation amount is controlled by using an EGR valve so as to achieve a target EGR rate, based on as output value of a temperature sensor downstream of an exhaust heat recovery device.

[0045] FIG. 1 is a system diagram illustrating the embodiment. In an engine 9 including multiple cylinders (four cylinders in this case), air from the outside passes through an air cleaner 1 and flows into the cylinders via an intake manifold 4 and a collector 5. The amount of inflow air is adjusted by an electronic throttle 3. An air flow sensor 2 detects an inflow air amount. In addition, an intake air temperature sensor 29 detects an intake air temperature. A crank angle sensor 15 outputs a signal for every 10 rotation angle of a crankshaft and a signal for each combustion cycle. A water temperature sensor 14 detects a cooling water temperature of an engine. In addition, an accelerator opening sensor 13 detects a depression amount of an accelerator 6, and accordingly detects a torque requested by a driver.

[0046] Each signal of a throttle opening sensor 17, a crank angle sensor 15, and a water temperature sensor 14 attached to the accelerator opening sensor 13, the air flow sensor 2, the intake air temperature sensor 29, and the electronic throttle 3 is sent to a control unit 16 to be described later. After an operation state of the engine is obtained from these sensor outputs, an air amount, a fuel injection amount, an ignition timing, and a main operation amount of an engine for an EGR amount are optimally calculated.

[0047] A target air amount calculated in the control unit 16 is converted from a target throttle opening degree into an electronic throttle driving signal and sent to the electronic throttle 3. A fuel injection amount is converted into a valve opening pulse signal and sent to a fuel injection valve (injector) 7. A drive signal is sent to an ignition plug 8 so as to be ignited at an ignition timing calculated by the control unit 16. A drive signal is sent to an EGR valve 19 so as to realize a target EGR amount calculated by the control unit 16.

[0048] The injected fuel is mixed with air from an intake manifold and flows into a cylinder of the engine 9 to form an air-fuel mixture. The air-fuel mixture is exploded by sparks generated from the ignition plug 8 at a predetermined ignition timing, and a piston is pushed down by a combustion pressure by the explosion and becomes a driving force of an engine. Exhaust air after the explosion passes through an exhaust manifold 10 and passes through an exhaust heat recovery device 11. After the exhaust heat recovery device recovers heat (energy) possessed by the exhaust air recovers, a part of the exhaust air is returned to an intake side through an exhaust gas recirculation pipe 18. A recirculation amount is controlled by the EGR valve (valve) 19.

[0049] A catalyst upstream. air-fuel ratio sensor 12 is mounted between the engine 9 and the exhaust heat recovery device 11. In addition, in the embodiment, an exhaust temperature sensor 20 is provided as an exhaust temperature acquisition unit for acquiring an exhaust temperature downstream of the exhaust heat recovery device 11. The exhaust temperature sensor 20 is attached downstream of the exhaust heat recovery device 11.

[0050] FIG. 2 illustrates the interior of the control unit 16. Each sensor output value of the air flow sensor 2, the catalyst upstream air-fuel ratio sensor 12, the accelerator opening sensor 13, the water temperature sensor 14, the crank angle sensor 15, the throttle valve opening sensor 17, the exhaust temperature sensor 20, the intake air temperature sensor 29, a vehicle speed sensor 30 is input to ECU 16. After an input circuit 24 performs signal processing, such as removal of noise, the value is sent to an input/output port 25. The value of the input port is stored in a RAM 23 and processed in the CPU 21. A control program in which calculation process contents are written is preliminary written in ROM 22. A value representing each actuator operation amount calculated according to a control program is stored in the RAM 23 and then sent to the input/output port 25. As an operation signal of an ignition plug, an ON/OFF signal is set which is turned on when the signal can flow in a primary side coil in an ignition output circuit and turned off when the signal cannot flow therein. The ignition timing is a time from ON to OFF. A signal for the ignition plug set at an output port is amplified to sufficient energy necessary for combustion in the ignition output circuit 26 and supplied to the ignition plug. Further, the ON/OFF signal is set such that a drive signal of a fuel injection valve is turned on when a valve is opened and turned off when the valve is closed. The signal is amplified to energy sufficient for opening the fuel injection valve by a fuel injection valve drive circuit 27 and sent to the fuel injection valve 7. The drive signal for realizing a target opening of the electronic throttle 3 is sent to the electronic throttle 3 via an electronic throttle drive circuit 28. The drive signal for realizing a target opening of the EGR valve 19 is sent to the EGR valve 19 via an EGR valve drive circuit 30.

[0051] Hereinafter, the control program written in the ROM 22 will be described. FIG. 3 is a block diagram illustrating overall control. The overall control includes the following calculation units. [0052] Target EGR rate calculation unit (FIG. 4) [0053] Target EGR valve opening calculation unit (FIG. 5)

[0054] The target EGR rate calculation unit calculates a target EGR rate (TgEGR). The target EGR valve opening calculation unit calculates a target EGR valve opening (TgEVO) based on EGR and an exhaust gas temperature (Tex).

[0055] In the present embodiment, the exhaust gas temperature (Tex) downstream of the exhaust heat recovery device 11 is detected, and the exhaust gas recirculation amount (EGR valve opening) is controlled so as to optimize combustion performance in accordance with the detected exhaust gas temperature. As a result, fuel efficiency/exhaust performance/stability performance of an engine improve. Details of each calculation unit will be described below.

[0056] <Target EGR Rate Calculation Unit (FIG. 4)>

[0057] In this calculation unit, TgEGR (target EGR rate) is calculated. FIG. 4 specifically describes.

[0058] A value obtained by referring to a map M_TgEGR by using TP (cylinder inflow air amount equivalent value) and Ne (rotational speed) is set to the TgEGR.

[0059] A set value of the map M_TgEGR is preferably determined from such as an actuary machine test so as to achieve the desired fuel consumption performance/exhaust performance based on the engine (combustion) performance. An exhaust gas temperature that is a premise of a setting value of the map is set at a specific exhaust gas temperature, for example, set in a state where an exhaust heat recovery device is not functioning.

[0060] <Target EGR Valve Opening Calculation Unit (FIG. 5)>

[0061] The calculation unit calculates TgEVO (target EGR valve opening). FIG. 5 specifically describes. [0062] A value obtained by referring to a map M_TgEVO_0 by using TgEGR and Tp is set to TgEVO_0 (target EGR valve basic opening). [0063] A value obtained by referring to a map M_Hos_Tex by using Tex is set to Hos_Tex (exhaust gas temperature correction coefficient). [0064] A value obtained by multiplying TgEVO_0 by Hos_Tsx is TgEVO.

[0065] The setting value of the map M_TgEVO_0 sets an EGR valve opening for realizing Tg_EGR under each operating condition. The exhaust gas temperature that is a premise of a set value of the map is a value set when M_TgEGR indicated in FIG. 4 is set. In addition, the engine speed (Ne) may also be referred to improve accuracy.

[0066] As a setting value of the map M_Hos_Tex, a correction value for TgEVO_0 is set such that TgEVO realizes TgEGR at an actual exhaust gas temperature (Tex). Generally, as an exhaust gas temperature decreases, the value of Hos_Tex decreases, and as the exhaust gas temperature increases, the value of Hos_Tex increases.

[0067] In the present embodiment, the exhaust temperature sensor is disposed directly under the exhaust heat recovery device. However, it may be disposed in an exhaust pipe flow pipe.

Second Embodiment

[0068] The present embodiment describes that an exhaust gas recirculation amount is controlled by using an EGR valve so as to achieve a target EGR rate based on an output value of a temperature sensor downstream of an exhaust heat recovery device and also controlled such that the exhaust gas recirculation amount (inflow gas in a combustion chamber) is limited within a predetermined range.

[0069] FIG. 1 is a system diagram illustrating the embodiment. The system diagram is the same as that of the first embodiment (FIG. 1), and therefore details will not be described.

[0070] FIG. 2 indicates the interior of a control unit 16, which is the same as that of the first embodiment (FIG. 5), and therefore details will not be described.

[0071] Hereinafter, a control program written in ROM 22 will be described. FIG. 3 is a block diagram illustrating overall control. The overall control includes the following calculation units. [0072] Target EGR rate calculation unit (FIG. 4) [0073] Target EGR valve opening calculation unit (FIG. 6)

[0074] The target EGR rate calculation unit calculates a target EGR rate (TgEGR). The target EGR valve opening calculation unit calculates a target FOR valve opening (TgEVO) based on TgEGR and an exhaust gas temperature (Tex). However, under each operating condition, the exhaust gas recirculation amount (EGR valve opening) is limited such that Tex does not excessively rise or fall as it adversely affects engine performance.

[0075] In the present embodiment, the exhaust gas temperature (Tex) downstream of an exhaust heat recovery device is detected, and an exhaust gas recirculation amount (EGR valve opening) is controlled so as to optimize combustion performance in accordance with the detected exhaust gas temperature. On the other hand, since the exhaust gas recirculation amount (EGR valve opening) is limited such that Tex does not excessively rise or fall as it adversely affects the engine performance, knock limit and NOx emissions of combustion are optimized, and the fuel consumption and exhaust performance of an engine improve. Details of each calculation unit will be described below.

[0076] <Target FOR Rate Calculation Unit (FIG. 4)>

[0077] The calculation unit calculates TgEGR (target EGR rate). Specifically, although illustrated in FIG. 4, the calculation unit is the same as that of the first embodiment and therefore will not be described in detail.

[0078] <Target EGR Valve Opening Calculation Unit (FIG. 6)>

[0079] The calculation unit calculates TgEVO (target EGR valve opening) FIG. 6 specifically describes. [0080] A value obtained by referring to a map M_TgEVO_0 by using TgEGR and Tp is set to TgEVO_0 (target EGR valve basic opening) [0081] A value obtained by referring to a map M_Hos_Tex by using Tex is set to Hos_Tex (exhaust gas temperature correction coefficient). [0082] A value obtained by multiplying TgEVO_0 by Hos_Tex is set to TgEVO_1 (target EGR valve opening 1). [0083] A value obtained by referring to a map M_K1_Tex by using TP and Ne is set as K1_Tex (exhaust gas temperature upper limit value). [0084] A value obtained by referring to a map M_K2_Tex by using TP and Ne is set as K2_Tex (exhaust gas temperature lower limit value). [0085] i) When TexK1_Tex, TgEVO=TgEVO_z+K1_TgEVO [0086] ii) When TexK2_Tex, TgEVO=TgEVO_z+K2_TgEVO

[0087] Here, TgEVO_z is the previous calculated value of TgEVO.

[0088] As a setting value of the map M_TgEVO_0, an EGR valve opening for realizing Tg_EGR under each operating coy condition as in the first embodiment is set. The exhaust gas temperature that is a premise of a set value of the map is a value set when M_TgEGR indicated in FIG. 4 is set. In addition, the engine speed (Ne) may also be referred to improve accuracy.

[0089] As a setting value of the map M_Hos_Tex, as in the first embodiment, a correction value for TgEVO_0 is set such that TgEVO realizes TgEGR at an actual exhaust gas temperature (Tex). Generally, as an exhaust gas temperature decreases, the value of Hos_Tex decreases, and as the exhaust gas temperature increases, the value of Hos_Tex increases.

[0090] The set values of the maps M_K1_TgEVO and M_K2_TgEVO are set based on the combustion performance such that the fuel consumption performance (for example, knock limit) and the exhaust performance (for example, NOx) do not deviate from desired ranges.

[0091] In the present embodiment, the exhaust temperature sensor is disposed directly under the exhaust heat recovery device. However, it may be disposed in an exhaust pipe flow

Third Embodiment

[0092] The present embodiment describes that an exhaust gas recirculation amount is controlled by using an EGR valve so as to achieve a target EGR rate based on an output value of a temperature sensor downstream of an exhaust heat recovery device and also controlled such that fuel stability is within a predetermined range.

[0093] FIG. 1 is a system diagram illustrating the embodiment. The system diagram is the same as that of the first embodiment (FIG. 1), and therefore details will not be described. FIG. 2 indicates the interior of a control unit 16, which is the same as that of the first embodiment (FIG. 2, and therefore, details will not be described.

[0094] Hereinafter, the control program written in the ROM 22 will be described. FIG. 3 is a block diagram illustrating overall control. The overall control includes the following calculation units. [0095] Target EGR rate calculation unit (FIG. 4) [0096] Target EGR valve opening calculation unit (FIG. 7)

[0097] The target EGR rate calculation unit calculates a target EGR rate (TgEGR). The target EGR valve opening calculation unit calculates a target EGR valve opening (TgEVO) based on TgEGR and an exhaust gas temperature (Tex). However, under each operating condition, the exhaust gas recirculation amount (EGR valve opening) is limited such that the stability of an engine (combustion) is not excessively deteriorated.

[0098] In the present embodiment, the exhaust gas temperature (Tex) downstream of the exhaust heat recovery device is detected, and the exhaust gas recirculation amount (EGR valve opening) is controlled so as to optimize combustion performance in accordance with the detected exhaust gas temperature. On the other hand, an exhaust gas recirculation amount (EGR valve opening) is limited so as not to excessively deteriorate combustion stability, and therefore engine robustness is improved. Details of each calculation unit will be described below.

[0099] <Target EGR Rate Calculation Unit (FIG. 4)>

[0100] In this calculation unit, TgEGR (target EGR rate) is calculated. Specifically, although illustrated in FIG. 4, the calculation unit is the same as that of the first embodiment and therefore will not be described in detail.

[0101] <Target EGR Valve Opening Calculation Unit (FIG. 7)>

[0102] The calculation snit calculates TgEVO (target EGR valve opening). FIG. 6 specifically describes. [0103] A value obtained by referring to a map M_TgEVO_0 by using TgEGR and Tp is set to TgEVO_0 (target EGR valve basic opening). [0104] A value obtained by referring to a map M_Hos_Tex by using Tex is set to Hos_Tex (exhaust gas temperature correction coefficient). [0105] A value obtained by multiplying TgEVO_0 by Hos_Tex is set to TgEVO_1 (target EGR valve opening 1). [0106] A value obtained by referring to a map M_K1_IndSta by using TP and Ne is set to K1_IndSta (stability threshold). [0107] When IndStaK1_IndSta, TgEVO=TgEVO_zK1_TgEVO

[0108] Here, TgEVO_z is the previous calculated value of TgEVO. IndSta is a stability index which is a value correlated with combustion stability. For example, such as the magnitude of rotational fluctuation, the degree of variation in engine rotation angle acceleration, and the degree of variation in an in-cylinder pressure are considered. These calculation methods include many known techniques and therefore will not be described here in detail.

[0109] As a setting value of the map M_TgEVO_0, an EGR valve opening for realizing Tg_EGR under each operating condition as in the first embodiment is set. The exhaust gas temperature that is a premise of a set value of the map is a value set when M_TgEGR indicated in FIG. 4 is set. In addition, the engine speed (Ne) may also be referred to improve accuracy.

[0110] As a setting value of the map M_Hos_Tex, as in the first embodiment, a correction value for TgEVO_0 is set such that TgEVO realizes TgEGR at an actual exhaust gas temperature (Tex). Generally, as an exhaust gas temperature decreases, the value of Hos_Tex decreases, and as the exhaust gas temperature increases, the value of Hos_Tex increases.

[0111] A set value of the map M_K1_IndSta is set such that combustion stability does not deviate from the desired range.

[0112] In the present embodiment, an exhaust temperature sensor is disposed directly under the exhaust heat recovery device. However, it may be disposed in an exhaust pipe flow pipe.

Fourth Embodiment

[0113] In the present embodiment, an exhaust gas temperature acquisition unit for acquiring an exhaust gas temperature downstream of an exhaust heat recovery device estimates an exhaust gas temperature based on a recovered heat amount (recovery efficiency) of the exhaust heat recovery device and acquires the estimated exhaust gas temperature. The present embodiment describes that an exhaust gas recirculation amount is controlled by using an EGR valve so as to achieve a target EGR rate based on the estimated temperature.

[0114] FIG. 8 is a system diagram illustrating the embodiment. A heat recovery amount/recovery efficiency detector 31 is disposed in an exhaust heat recovery device 11. In the first embodiment, the exhaust temperature sensor 20 is attached downstream of the exhaust heat recovery device 11. However, in the present embodiment, the heat recovery amount/recovery efficiency detector 31 is disposed in the exhaust heat recovery device 11. The heat recovery amount/recovery efficiency detector also depends on the recovery principle of the exhaust heat recovery device. However, for example, a current value and a voltage value generated at the tame of heat recovery and a temperature of a heat medium is considered. Other than the above, the present embodiment is the same as the first embodiment and therefore will not be described in detail.

[0115] FIG. 9 illustrates the interior of a control unit 16. An output value of the heat recovery amount/recovery efficiency detector 31 is input into the ECU 16, and signal processing such as noise removal is performed in an input circuit 24. Then, the value is sent to an input/output port 25. Other than the above, the present embodiment is the same as the first embodiment and therefore will not be described in detail.

[0116] Hereinafter, the control program written in the ROM 22 will be described. FIG. 10 is a block diagram illustrating overall control. The overall control includes the following calculation units. [0117] Estimated exhaust gas temperature calculation unit (FIG. 11) [0118] Target EGR rate calculation unit (FIG. 4) [0119] Target EGR valve opening calculation unit (FIG. 12)

[0120] The estimated exhaust gas temperature calculation unit calculates Tex_est (estimated exhaust gas temperature) based on Ind_Eff (heat recovery amount (recovery efficiency) index) The target EGR rate calculation unit calculates a target EGR rate (TgEGR). The target EGR valve opening calculation unit calculates a target EGR valve opening (TgEVO) based on TgEGR and an exhaust gas temperature (Tex).

[0121] In the present embodiment, the exhaust gas temperature (Tex) downstream of the exhaust heat recovery device is estimated based on the detected value by the heat recovery amount/recovery efficiency detector 31 disposed in the exhaust heat recovery device 11, and the exhaust gas recirculation amount (EGR valve opening) is controlled so as to optimize combustion performance in accordance with the estimated exhaust gas temperature. Therefore, fuel efficiency/exhaust performance/stability performance of an engine improve. Details of each calculation unit will be described below.

[0122] <Estimated Exhaust Gas Temperature Calculation Unit (FIG. 11)>

[0123] In this calculation unit, Tex_est (estimated exhaust gas temperature) is calculated. FIG. 11 specifically describes. [0124] A value obtained by referring to a map M_Tex_est_0 by using TgEGR and Tp is set to Tex_est_0 (basic estimated exhaust gas temperature). [0125] A value obtained by referring to a map M_Hos_Tex_est by using Ind_Eff (heat recovery amount (recovery efficiency) index) is set to Hos_Tex_est (estimated exhaust gas temperature correction value). [0126] A value obtained by multiplying Tex_est_0 by Hos_Tex_est is set as Tex_est (estimated exhaust gas temperature).

[0127] A set value of the map M_Tex_est is set at a specific exhaust gas temperature, for example, set at an exhaust gas temperature at the time when the exhaust heat recovery device is not functioning. A setting value of the map M_Tex_est_0 is set such that the actual exhaust gas temperature corresponding to the value of Ind_Eff and Tex_est coincide. Generally, when Ind_Eff increases, the exhaust gas temperature decreases, and therefore the value of Hos_Tex_est decreases, and as Ind_Eff decreases, the exhaust gas temperature increases, and the value of Hos_Tex_est increases. Incidentally, as described above, Ind_Eff is, for example, a value obtained by indexing such as a current value, a voltage value generated at the time of heat recovery, or the temperature of a heating medium.

[0128] <Target EGR Rate Calculation Unit (FIG. 4)

[0129] The calculation unit calculates TgEGR (target EGR rate). Specifically, although illustrated in FIG. 4, the calculation unit is the same as that of the first embodiment and therefore will not be described in detail.

[0130] <Target EGR Valve Opening Calculation Unit (FIG. 12)>

[0131] The calculation unit calculates TgEVO (target EGR valve opening). FIG. 12 specifically describes. [0132] A value obtained by referring to a map M_TgEVO_0 by using TgEGR and Tp is set to TgEVO_0 (target EGR valve basic opening). [0133] A value obtained by referring to a map M_Hos_Tex by using Tex_est is set to Hos_Tex (exhaust gas temperature correction coefficient). [0134] A value obtained by multiplying TgEVO_0 by Hos_Tsx is TgEVO.

[0135] The setting value of the map M_TgEVO_0 sets an EGR valve opening for realizing Tg_EGR under each operating condition. The exhaust gas temperature that is a premise of a set value of the map is a value set when M_TgEGR indicated in FIG. 4 is set. In addition, the engine speed (Ne) may also be referred to improve accuracy.

[0136] As a setting value of the map M_Hos_Tex, a correction value for TgEVO_0 is set such that TgEVO realizes TgEGR at the estimated exhaust gas temperature (Tex_est) or an actual exhaust gas temperature. Generally, as an exhaust gas temperature decreases, the value of Hos_Tex decreases, and as the exhaust gas temperature increases, the value of Hos_Tex increases.

Fifth Embodiment

[0137] The present embodiment describes that, based on an output value of a temperature sensor downstream of an exhaust heat recovery device, an exhaust gas recirculation amount is controlled by using an EGR valve so as to achieve a target EGR rate, and in accordance with increase in the exhaust gas recirculation amount, an ignition timing is corrected in an advance angle.

[0138] FIG. 1 is a system diagram illustrating the embodiment. The system diagram is the same as that of the first embodiment (FIG. 1), and therefore details will not be described. FIG. 2 indicates the interior of a control unit 16, which is the same as that of the first embodiment (FIG. 5), and therefore details will not be described.

[0139] Hereinafter, the control program written in the ROM 22 will be described. FIG. 13 is a block diagram illustrating overall control. The overall control includes the following calculation units. [0140] Target EGR rate calculation unit (FIG. 4) [0141] Target EGR valve opening calculation unit (FIG. 5) [0142] Ignition timing correction value calculation unit (FIG. 14)

[0143] The target EGR rate calculation unit calculates a target EGR rate (TgEGR). The target EGR valve opening calculation unit calculates a target EGR valve opening (TgEVO) based on TgEGR and an exhaust gas temperature (Tex). The ignition timing correction value calculation unit calculates the ignition timing correction value (ADV_HOS) based on TgEGR and Tex. A value obtained by adding ADV_HOS to the basic ignition timing (ADV_0) is set as the final ignition timing (ADV). A calculation method of the basic ignition timing (ADV_0) includes known techniques and therefore will not be described here in detail.

[0144] In the present embodiment, the exhaust gas temperature (Tex) downstream of the exhaust heat recovery device 11 is detected, and the exhaust gas recirculation amount (EGR valve opening) is controlled so as to optimize combustion performance in accordance with the detected exhaust gas temperature. On the other hand, when the exhaust gas recirculation amount changes, the knock limit may change, and therefore the ignition timing is corrected to an advance angle side accordingly, and the fuel consumption performance/robustness of an engine improves. Details of each calculation unit will be described below.

[0145] <Target EGR Rate Calculation Unit (FIG. 4)>

[0146] In this calculation unit, TgEGR (target EGR rate) is calculated. Specifically, although illustrated in FIG. 4, the calculation unit is the same as that of the first embodiment and therefore will not be described in detail.

[0147] <Target EGR Valve Opening Calculation Unit (FIG. 5)>

[0148] The calculation unit calculates TgEVO (target EGR valve opening). Specifically, although illustrated in FIG. 5, the unit is the same as that of the first embodiment, and therefore will not be described in detail.

[0149] <Ignition Timing Correction Value Calculation Unit (FIG. 14)>

[0150] This calculation unit calculates ADV_HOS (ignition timing calculation unit correction value). FIG. 12 specifically describes. [0151] A value obtained by referring to a map M_ADV_HOS by using TgEGR and Tex is set as ADV_HOS.

[0152] As a setting value of the map M_ADV_HOS, a correction value for the basic ignition timing (ADV_0) is set such that the ignition timing is optimized in accordance with a change in an EGR rate (TgEGR). Furthermore, if the exhaust gas temperature (Tex) is different even at an equal EGR rate, the optimal ignition timing may change, and therefore the setting value is determined such that the ignition timing is optimized in accordance with Tex under equal TgEGR. Generally, when the recirculated exhaust gas temperature drops, the knock limit extends, and therefore, under the equal TgEGR, the ADV_HOS is set to increase (advance) when Tex decreases, and the knock limit is shortened when the recirculated exhaust gas temperature increases. Therefore, under the equal TgEGR, when Tex decreases, ADV_HOS is set so as to be small (close).

Sixth Embodiment

[0153] The present embodiment describes that an abnormality of an exhaust heat recovery device is determined based on an output value of an temperature sensor downstream of an exhaust heat recovery device, and when it is determined to be abnormal, an exhaust gas recirculation amount is corrected by a predetermined amount by using an EGR valve.

[0154] FIG. 1 is a system diagram di lustrating the embodiment. The system diagram is the same as that of the first embodiment (FIG. 1), and therefore details will not be described. FIG. 2 indicates the interior of a control unit 16, which is the same as that of the first embodiment (FIG. 5), and therefore details will not be described.

[0155] Hereinafter, the control program written in the ROM 22 will be described. FIG. 15 is a block diagram illustrating overall control. The overall control includes the following calculation units. [0156] Exhaust heat recovery device abnormality determination unit (FIG. 16) [0157] Target EGR rate calculation unit (FIG. 4) [0158] Target EGR valve opening calculation unit (FIG. 17)

[0159] The exhaust heat recovery device abnormality determination unit calculates an abnormality flag (f_MUL) based on an exhaust gas temperature (Tex). The target EGR rate calculation unit calculates a target EGR rate (TgEGR). The target EGR valve opening calculation unit calculates a target EGR valve opening (TgEVO) based on f_MUL, TgEGR, and Tex. When the exhaust heat recovery device is abnormal, the target EGR valve opening is controlled to a specific opening.

[0160] In the present embodiment, the exhaust gas temperature (Tex) downstream of an exhaust heat recovery device 11 is detected, and when it is determined from the detected exhaust gas temperature that the exhaust heat recovery device is not functioning normally, to avoid an adverse effect on combustion accompanying a temperature rise of recirculated exhaust, gas and a decrease in a mass flow rate per unit volume, an exhaust gas recirculation amount is corrected, and robustness of an engine is improved. Details of each calculation unit will be described below.

[0161] <Exhaust Heat Recovery Device Abnormality Determination Unit (FIG. 16)>

[0162] This calculation unit calculates f_MUL (abnormality flag). FIG. 16 specifically described. [0163] A value obtained by referring to a map M_Ka_Tex by using TP and Ne is set as Ka_Tex (abnormality determination threshold a). [0164] A value obtained by referring to a map M_Kb_Tex by using TP and Ne is set as Kb_Tex (abnormality determination threshold b). [0165] i) When TexKa_Tex or TexKb_Tex, f_MUL=1 [0166] ii) Otherwise, f_MUL=0

[0167] As setting values of the maps M_Ka_Tex and M_Kb_Tex, a temperature not to be reached when the exhaust heat recovery device is functioning normally, that is, a temperature in an abnormal state, is set.

[0168] <Target EGR Rate Calculation Unit (FIG. 1)>

[0169] In this calculation unit, TgEGR (target EGR rate) is calculated. Specifically, although illustrated in FIG. 4, the calculation unit is the same as that of the first embodiment and therefore will not be described in detail.

[0170] <Target EGR Valve Opening Calculation Unit (FIG. 17)

[0171] The calculation unit calculates TgEVO (target EGR valve opening). FIG. 17 specifically described. [0172] A value obtained by referring to a map M_TgEVO_0 by using TgEGR and Tp is set to TgEVO_0 (target EGR valve basic opening). [0173] A value obtained by referring to a map M_Hos_Tex by using Tex is set to Hos_Tex (exhaust gas temperature correction coefficient). [0174] A value obtained by multiplying TgEVO_0 by Hos_Tsx is set to TgEVO2 (target EGR valve opening 2). [0175] A value obtained by referring to a map M_TgEVO_MUL by using TP and Ne is set as TgEVO_MUL (EGR valve opening at abnormality). [0176] When f_MUL=0, TgEVO=TgEVO2 [0177] When f_MUL=1, TgEVO=TgEVO_MUL

[0178] As a setting value of the map M_TgEVO_0, the EGR valve opening for realizing TgEGR under each operating condition is set. The exhaust gas temperature that is a premise of the setting value of the map is a value set when M_TgEGR indicated in FIG. 4 is set. In addition, the engine speed (Ne) may also be referred to improve accuracy.

[0179] As a setting value of the map M_Hos_Tex, a correction value for TgEVO_0 is set such that TgEVO2 realizes TgEGR at an actual exhaust gas temperature (Tex). Generally, as an exhaust gas temperature decreases, the value of Hos_Tex decreases, and as the exhaust gas temperature increases, the value of Hos_Tex increases.

[0180] A set value of the map M_TgEVO_MUL is set to an EGR valve opening at which a recirculation amount does not adversely affect on an engine even when the exhaust heat recovery device is operating abnormally.

[0181] In the present embodiment, the exhaust temperature sensor is disposed directly under the exhaust heat recovery device. However, it may be disposed in an exhaust pipe flow pipe.

REFERENCE SIGNS LIST

[0182] 1 air cleaner [0183] 2 air flow sensor [0184] 3 electronic throttle [0185] 4 intake pipe [0186] 5 collector [0187] 6 accelerator [0188] 7 fuel injection valve [0189] 8 ignition plug [0190] 9 engine [0191] 10 exhaust pipe [0192] 11 exhaust heat recovery device [0193] 12 A/F sensor [0194] 13 accelerator opening sensor [0195] 14 water temperature sensor [0196] 15 engine speed sensor [0197] 16 control unit [0198] 17 throttle opening sensor [0199] 18 exhaust gas recirculation pipe [0200] 19 exhaust gas recirculation flow control valve [0201] 20 exhaust temperature sensor [0202] 21 CPU mounted in control unit [0203] 22 ROM mounted in control unit [0204] 23 RAM mounted in control unit [0205] 24 input circuits of various sensors mounted in control unit [0206] 25 input of various sensor signals, port outputting actuator operation signal [0207] 26 ignition output circuit for outputting drive signal to spark plug at appropriate timing [0208] 27 fuel injection valve drive circuit for outputting appropriate pulse to fuel injection valve [0209] 28 electronic throttle drive circuit [0210] 29 intake air temperature sensor [0211] 30 exhaust gas recirculation flow control valve drive circuit [0212] 31 heat recovery amount/recovery efficiency detector