CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

Abstract

A control device for an internal combustion engine which does not require fitting of a feed forward term on an occasion of calculation of a fuel amount to be supplied at a time of temperature raising control is provided. According to the present embodiment, by feed forward control using a steady-state DPF model and a steady-state CCO model, a basic amount (feed forward term) of a fuel amount Qinj that is added from a fuel injector 20 in the temperature raising control can be calculated. Namely, the feed forward term can be calculated without depending on a control map. If the feed forward term can be calculated without depending on the control map, fitting of the feed forward term with use of the controlling map is not required.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control device for an internal combustion engine. More particularly, the present invention relates to a control device for an internal combustion engine including a device that supplies fuel as means that purifies an exhaust gas.

2. Background Art

There has been conventionally known to public an internal combustion engine that includes a catalyst (CCO) that oxidizes HC, CO and NO in an exhaust gas, and a diesel particulate filter (DPF) that traps particulate matters (PM) in the exhaust gas. Further, in order to burn and remove PM that is trapped in the DPF in the internal combustion engine like this, performing control that forcefully raises the temperature of the DPF is known to public. Temperature raising control is generally performed by delay of fuel injection timing, and post injection. For raising the temperature of the DPF, heat that is generated with oxidation of the injection fuel in the CCO is used.

As an example of the internal combustion engine which performs temperature raising control, Japanese Patent Laid-Open No. 2012-072666 as follows can be cited. In Japanese Patent Laid-Open No. 2012-072666, the post injection amount at the time of temperature raising control is calculated by adding the basic injection amount calculated by feed forward control and the correction amount calculated by feedback control. More specifically, in the second embodiment of Japanese Patent Laid-Open No. 2012-072666, a control gain is obtained by applying the exhaust flow rate to a gain map, and the basic injection amount is calculated by the relational expression of the linear transfer function including the control gain. The correction amount is calculated by PID operation with the target temperature and the actual temperature of the DPF as inputs.

• Patent Literature 1: Japanese Patent Laid-Open No. 2012-072666
• Patent Literature 2: Japanese Patent Laid-Open No. 2011-157893
• Patent Literature 3: Japanese Patent Laid-Open No. 2009-243398
• Patent Literature 4: Japanese Patent Laid-Open No. 2011-117394

SUMMARY OF THE INVENTION

Technical Problem

However, since the gain map is set by test data or simulation calculation, adjustment by trials and errors is indispensable. Further, since fitting of control gains (feed forward terms) is required, the load of the feedback terms becomes large in the operation region in which the control gains cannot be fitted, and accumulation in the integrator is likely to occur frequently.

The present invention is made in the light of the aforementioned problem. Namely, an object of the present invention is to provide a control device for an internal combustion engine which does not require fitting of feed forward items on an occasion of calculation of an amount of fuel to be supplied at a time of temperature raising control.

Means for Solving the Problem

To achieve the above mentioned purpose, a first aspect of the present invention is a control device for an internal combustion engine, comprising:

a first purifying device that is provided in an exhaust passage of the internal combustion engine and has an oxidation catalyst function;

a second purifying device that is provided downstream of the first purifying device, in the exhaust passage;

a fuel supply device that supplies fuel to upstream of the first purifying device; and

a control device that controls a temperature of the second purifying device to a target temperature by controlling a fuel supply amount from the fuel supply device,

wherein the control device comprises a first model that is constructed based on a relation of a heat balance established in the first purifying device, and a second model that is constructed based on a relation of a heat balance established in the second purifying device,

the first model and the second model are constructed on a precondition that all of the fuel supplied from the fuel supply device is converted into heat in the first purifying device, and all of the converted heat contributes to raising a temperature of the first purifying device, and

the control device is configured to calculate the temperature of the first purifying device by inputting the target temperature into the second model and calculate the fuel supply amount by inputting the calculated temperature into the first model.

A second aspect of the present invention is the control device for an internal combustion engine according to the first aspect of the present invention, wherein the first model is expressed by expression (1), and the second model is expressed by expression (2).

Q*_inj=H_v⁻¹[K_atm,1st(T*_1st−T_atm)+h_1stA_1st(T*_1st−T_1st,us)]  (1)

In expression (1), Q_inj* represents the fuel supply amount that is supplied from the fuel supply device in a predetermined steady state, H_v represents a low heating value of HC, K_atm,1st represents a heat transfer coefficient to an atmosphere in the first purifying device, T_1st* represents a temperature of the first purifying device in a predetermined steady state, T_atm represents an atmospheric temperature, h_1st represents a heat conversion coefficient per channel unit area of the first purifying device, A_1st represents a channel area of the first purifying device, and T_1st,us represents an inlet temperature of the first purifying device.

T*_1st=T^ref_2nd−(h_2ndA_2nd)⁻¹[Q_exo,2nd,pm(T^ref_2nd,m_pm)−K_atm,2nd(T^ref_2nd−T_atm)]  (2)

In expression (2), T_1st* represents the temperature of the first purifying device in a predetermined steady state, T_2nd^ref represents the target temperature of the second purifying device, h_2nd represents a heat conversion coefficient per channel unit area of the second purifying device, A_2nd represents a channel area of the second purifying device, Q_exo,2nd,pm represents a heat flow that moves to the second purifying device by heat generation accompanying PM combustion in an exhaust gas, m_pm represents an accumulation amount of PM, K_atm,2nd represents a heat transfer coefficient to an atmosphere in the second purifying device, and T_atm represents an atmospheric temperature.

A third aspect of the present invention is the control device for an internal combustion engine according to the first aspect or the second aspect of the present invention,

wherein the control device is configured to correct a fuel supply amount calculated from the first and the second models by increasing and decreasing the fuel supply amount based on a deviation of an actual temperature of the second purifying device and the target temperature.

A fourth aspect of the present invention is the control device for an internal combustion engine according to any one of the first aspect to the third aspect of the present invention,

wherein the control device is configured to correct the fuel supply amount so that the fuel supply amount is an upper limit value or less, which is set based on an exhaust air-fuel ratio, or less.

A fifth aspect of the present invention is the control device for an internal combustion engine according to any one of the first aspect to the fourth aspect of the present invention,

wherein the control device is configured to correct the fuel supply amount so that the fuel supply amount is an upper limit value or less, which is set based on an allowable amount of hydrocarbon in the exhaust gas, or less.

Effects of the Invention

According to the first aspect, the temperature of the first purifying device is calculated by inputting the target temperature of the second purifying device into the second model, and by inputting the calculated temperature into the first model, the amount of the fuel to be supplied from the fuel supply device can be calculated. Namely, the fuel supply amount can be calculated without using a control map. Therefore, the feed forward terms can be calculated without performing fitting by a control map.

According to the second aspect, the amount of the fuel to be supplied from the fuel supply device can be calculated according to the first model expressed by expression (1) and the second model expressed by expression (2).

According to the third aspect, the fuel supply amount calculated from the first and the second models can be corrected by increasing and decreasing the fuel supply amount based on the deviation of the actual temperature and the target temperature of the second purifying device, and therefore, the target temperature can be followed.

According to the fourth aspect, the fuel supply amount can be corrected to be the upper limit value or less, which is set based on the exhaust air-fuel ratio, or less. Namely, the fuel supply amount can be determined with the constraint based on the exhaust air-fuel ratio taken into consideration.

According to the fifth aspect, the fuel supply amount can be corrected to be the upper limit value or less, which is set based on the allowable amount of hydrocarbon in the exhaust gas, or less. Namely, the fuel supply amount can be determined with the constraint based on the hydrocarbon amount taken into consideration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing a configuration of the after-treatment system of the diesel engine.

FIG. 2 is a functional block diagram of the ECU 30 for executing the temperature raising control.

BEST MODE OF CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1 and FIG. 2.

A control target of a control device according to the present embodiment is an after-treatment system of a diesel engine to be loaded on an automobile. FIG. 1 is a schematic view showing a configuration of the after-treatment system of the diesel engine. The after-treatment system includes a CCO (diesel oxidation catalyst) 14 and a DPF (diesel particulate filter) 16 in an exhaust passage 12 of an engine 10, and includes a fuel injector 20 in an exhaust port 18 of a cylinder head. A temperature sensor 22 for measuring an inlet temperature T_coo,us of the CCO 14 is attached upstream of the CCO 14. A temperature sensor 24 for measuring an actual temperature T_dpf^real of the DPF 16 is attached in a vicinity of the DPF 16.

The after-treatment system further includes an ECU (Electronic Control Unit) 30 as the control device. The temperature sensors 22 and 24 are connected to an input side of the ECU 30. A sensor (not illustrated) for measuring an atmospheric temperature T_atm is also connected to the input side of the ECU 30. The fuel injector 20 is connected to an output side of the ECU 30. The ECU 30 is configured to execute control that raises the temperature of the DPF 16 to a target temperature (approximately 650° C.) by adding fuel from the fuel injector 20 when an accumulation amount of PM that is accumulated in the DPF 16 exceeds a predetermined value. By executing temperature raising control, the PM accumulated in the DPF 16 is burned and removed.

FIG. 2 is a functional block diagram of the ECU 30 for executing the temperature raising control. The ECU 30 includes arithmetic operation units 32 and 34 for calculating a steady-state addition amount Q_inj* corresponding to a basic amount of a fuel amount Q_inj which is added from the fuel injector 20 by feed forward (F/F) control. The arithmetic operation unit 32 includes a steady-state DPF model which is inversely calculated from a relational expression of a heat balance which the temperature of the DPF 16 satisfies when the temperature of the DPF 16 converges to the target temperature. The steady-state DPF model is a model which outputs a temperature of the CCO 14 when the DPF 16 is in a steady state in which the temperature of the DPF 16 converges to the target temperature, as will be described later. Further, the arithmetic operation unit 34 includes a steady-state CCO model which is inversely calculated from a relational expression of a heat balance when the temperature of the CCO 14 converges to a predetermined temperature when fuel is supplied at a predetermined fuel supply amount from upstream of the CCO 14. The steady-state CCO model is a model that outputs the supply amount of the fuel that is supplied from upstream of the CCO 14 at the time of converging the temperature of the CCO 14 to the predetermined temperature as will be described later.

The steady-state DPF model is configured to output a steady-state CCO temperature T_cco* when a temperature target value T_dpf^ref of the DPF 16 is given. More specifically, the steady-state DPF model is expressed by expression (3) as follows. Note that definitions other than T_dpf^ref and T_cco* will be described later.

T*_cco=T^ref_dpf−(h_dpfA_dpf)⁻¹[Q_exo,dpf,pm(T^ref_dpf,m_pm)−K_atm,dpf(T^ref_dpf−T_atm)]  (3)

Expression (3) is derived based on an updated expression of the temperature of the DPF 16. The expression is expressed by expression (4) as follows. In expression (4), T_dpf represents a temperature (K) of the DPF 16, and σ_md1 represents a sample time (sec) of model discretization time, C_dpf represents a heat capacity (J/(kg·K)) of the DPF 16, and M_dpf represents a mass (kg) of the DPF 16. Further, k expresses a discrete time step.

$\begin{array}{cc}{T}_{\mathrm{dpf}}\left(k\right)=T_{\mathrm{dpf}}\left(k-1\right)+{\delta }_{\mathrm{mdl}}\frac{1}{C_{\mathrm{dpf}}M_{\mathrm{dpf}}}\left[Q_{\mathrm{exo},\mathrm{dpf}}-Q_{\mathrm{air},\mathrm{dpf}}-Q_{\mathrm{exh},\mathrm{dpf}}\right]& \left(4\right)\end{array}$

Further, in expression (4), Q_exo,dpf represents a heat flow (W=J/sec) that moves to the DPF 16 by generation of heat in an exhaust gas, Q_air,dpf represents a heat flow (W) that moves to an atmosphere from the DPF 16, and Q_exh,dpf represents a heat flow (W) that moves to the exhaust gas from the DPF 16. They are expressed by expressions (5) to (7) as follows.

Q_exo,dpf=Q_exo,dpf,pm(T_dpf,m_pm)+{1−η_exo,cco(T_cco,W)}H_vQ_inj  (5)

Q_air,dpf=K_atm,dpf(T_dpf−T_atm)  (6)

Q_exh,dpf=h_dpfA_dpf(t_dpf−T_cco)  (7)

In expression (5), Q_exo,dpf,pm represents a heat flow (W) that moves to the DPF 16 by generation of heat accompanying PM combustion in the exhaust gas, m_pm represents an accumulation amount (kg) of PM, η_exo,cco represents a heat conversion efficiency of the addition fuel in the CCO 14, T_cco represents a temperature (K) of the CCO 14, W represents an exhaust flow (kg/sec), and H_v represents a low heating value (J/kg) of HC.

In expression (6), K_atm,dpf represents a heat transfer coefficient (W/K) to the atmosphere in the DPF 16, and T_atm represents an atmospheric temperature (K).

In expression (7), h_dpf represents a heat conversion coefficient (W/(m²·K)) of the DPF 16 per channel unit area, and A_dpf represents a channel area (m²) of the DPF 16.

The first term of the right side of expression (5) expresses heat generated by PM combustion in the DPF 16. The second term of the same side expresses heat that is generated by oxidation of the addition fuel in the CCO 14, and flows into the DPF 16 without contributing to raising the temperature of the CCO 14.

In the present embodiment, in a steady state in which a sufficient time period elapses after start of temperature raising control and the temperature T_dpf of the DPF 16 converges to the temperature target value T_dpf^ref, it is the precondition that all of the addition fuel is oxidized in the CCO 14, and all of the heat generated by oxidation contributes to raising the temperature of the CCO 14. Under the precondition, the second term of the right side of expression (5) becomes zero. Namely, expression (8) as follows is established.

η_exo,cco(T_cco,W)=1  (8)

When expression (8) is applied to expression (5), and expression (4) is organized with respect to the temperature T_cco of the CCO 14, expression (9) as follows is derived.

T_cco=T_dpf−(h_dpfA_dpf)−1[Q_exo,dpf,pm(T_dpf,m_pm)−K_atm,dpf(T_dpf−T_atm)]  (9)

When the temperature T_dpf in expression (9) is set as the temperature target value T_dpf^ref, expression (3) which expresses the steady-state CCO temperature T_cco* is derived. In this manner, by assigning the aforementioned precondition, the second term of the right side of expression (5), from which T_cco needs to be obtained by convergence calculation with the steady-state DPF model, becomes zero, and the temperature of the CCO 14 can be derived by a simple arithmetic operation.

The steady-state CCO model is configured to output the steady-state addition amount Q_inj* when the steady-state CCO temperature T_cco* is given. More specifically, the steady-state CCO model is expressed by expression (10) as follows.

Q*_inj=H_v⁻¹[K_atm,cco(T*_cco−T_atm)+h_ccoA_cco(T*_cco−T_cco,us)]  (10)

Expression (10) is derived based on the updated expression of the temperature of the CCO 14. The expression is expressed by expression (11) as follows. In expression (11), T_cco represents the temperature (K) of the CCO 14, σ_md1 represents the sample time (sec) for model discretization time, C_cco represents the heat capacity (J/(kg·K)) of the CCO 14, and M_cco represents the mass (kg) of the CCO 14. Further, k expresses the discrete time step.

$\begin{array}{cc}{T}_{\mathrm{cco}}\left(k\right)=T_{\mathrm{cco}}\left(k-1\right)+{\delta }_{\mathrm{mdl}}\frac{1}{C_{\mathrm{cco}}M_{\mathrm{cco}}}\left[Q_{\mathrm{exo},\mathrm{cco}}-Q_{\mathrm{air},\mathrm{cco}}-Q_{\mathrm{exh},\mathrm{cco}}\right]& \left(11\right)\end{array}$

In expression (11), Q_exo,cco represents a heat flow (W=J/sec) that moves to the CCO 14 by heat generation of the addition fuel, Q_air,cco represents a heat flow (W) that moves to an atmosphere from the CCO 14, and Q_exh,cco represents a heat flow (W) that moves to the exhaust gas from the CCO 14. They are expressed by expressions (12) to (14) as follows.

Q_exo,cco=η_exo,cco(T_cco,W)H_vQ_inj  (12)

Q_air,cco=K_atm,cco(T_cco−T_atm)  (13)

Q_exh,cco=h_ccoA_cco(t_cco−T_cco,us)  (14)

In expression (13), K_atm,cco represents a heat transfer coefficient (W/K) to an atmosphere in the CCO 14.

In expression (14), h_cco represents a heat conversion coefficient (W/(m²·K)) of the CCO 14 per channel unit area, and A_cco represents a channel area (m²) of the CCO 14.

As described above, in the present embodiment, establishment of expression (8) is the precondition. When expression (8) is applied to expression (12), and expression (11) is organized with respect to the fuel amount Q_inj, expression (15) as follows is derived.

Q_inj=H⁻¹_v[K_atm,cco(T_cco−T_atm)+h_ccoA_cco(T_cco−T_cco,us)]  (15)

When the temperature T_cco of expression (15) is set to be the steady-state CCO temperature T_cco*, expression (10) that expresses the steady-state addition amount Q_inj* is derived.

Returning to FIG. 2, explanation of the function of the ECU 30 will be continued. The ECU 30 includes a structure for causing the temperature of the DPF 16 to follow the target temperature by feedback (F/B) control. The feedback structure includes an adder-subtractor 36, an integrator 38 and an adder 40. When a deviation of the temperature target value T_dpf^ref of the DPF 16 and the actual temperature T_dpf^real of the DPF 16 is given to the feedback structure, the feedback structure outputs a request correction amount Q_inj^cor corresponding to a correction amount of the steady-state addition amount Q_inj*. Note that a control algorithm in the feedback structure is not limited to a proportional integration operation, and an optional control algorithm can be adopted.

The steady-state addition amount Q_inj* calculated by feed forward control and the request addition amount Q_inj^cor calculated by feedback control are inputted into an adder 42, and a base request addition amount Q_inj^base is outputted.

Subsequently, in a limiter 44, the base request addition amount Q_inj^base is adjusted not to exceed a maximum allowable value calculated under a constraint on an exhaust air-fuel ratio (A/F), and a maximum allowable value calculated under a constraint on hydrocarbon (HC) that flows upstream of the CCO 14. Thereby, a final request addition amount (namely, the fuel amount Q_inj) is determined. Note that the above described two maximum allowable values are assumed to be set by a simulation or the like and stored in the ECU 30 in advance.

As above, according to the present embodiment, a feed forward term (namely, the steady-state addition amount Q_inj*) can be calculated by the two steady-state models. Namely, the feed forward term can be calculated without depending on the control map. If the feed forward term can be calculated without depending on the control map, fitting of the feed forward term with use of the controlling map is not required as a matter of course. Further, according to the present embodiment, the feed forward term can be calculated with high precision. Accordingly, the load of the feedback term (namely, the request correction amount Q_inj^cor) can be reduced, and therefore, influence by accumulation in the integrator 38 can be prevented. In addition, according to the present embodiment, an A/F constraint and an HC constraint can be incorporated. Accordingly, temperature raising control with these constraints satisfied can be realized.

Incidentally, in the above described embodiment, the temperature raising control of the DPF 16 is described as an example, in the after-treatment system including the CCO 14 and the DPF 16. However, the temperature raising control is not limited to the DPF 16, and also can be applied to devices installed at a subsequent stage of the CCO 14, for example, an NSR catalyst (NOx Storage Reduction catalyst) and a SCR catalyst (Selective Catalytic Reduction catalyst).

Further, while in the above described embodiment, so-called exhaust pipe injection which adds fuel by using the fuel injector 20 is performed, the fuel may be added by delay of fuel injection timing and post injection by using a fuel injection valve which is attached to a combustion chamber of the engine 10. Namely, as long as fuel can be added to upstream of the CCO 14, the addition of the fuel by such a fuel injection valve can be applied as a modification of the present embodiment.

Further, in the above described embodiment, the inlet temperature T_cco,us of the CCO 14, the actual temperature T_dpf^real of the DPF 16 and the atmosphere temperature T_atm are measured by the sensors, but may be acquired or estimated by other means known to public.

Note that in the above described embodiment, the CCO 14 corresponds to “a first purifying device” of the above described first aspect, the DPF 16 corresponds to “a second purifying device” of the same invention, the fuel injector 20 corresponds to “a fuel supply device” of the same invention, the ECU 30 corresponds to “a control device” of the same invention, the steady-state CCO model corresponds to “a first model” of the same invention, and the steady-state DPF model corresponds to “a second model” of the same invention, respectively.

DESCRIPTION OF REFERENCE NUMERALS

• 10 engine
• 12 exhaust passage
• 14 CCO
• 16 DPF
• 20 fuel injector
• 30 ECU
• 32, 34 arithmetic operation unit

Claims

1. A control device for an internal combustion engine, comprising:

a first purifying device that is provided in an exhaust passage of the internal combustion engine and has an oxidation catalyst function;

a second purifying device that is provided downstream of the first purifying device, in the exhaust passage;

a fuel supply device that supplies fuel to upstream of the first purifying device; and

a control device that controls a temperature of the second purifying device to a target temperature by controlling a fuel supply amount from the fuel supply device,

wherein the control device comprises a first model that is constructed based on a relation of a heat balance established in the first purifying device, and a second model that is constructed based on a relation of a heat balance established in the second purifying device,

the first model and the second model are constructed on a precondition that all of the fuel supplied from the fuel supply device is converted into heat in the first purifying device, and all of the converted heat contributes to raising a temperature of the first purifying device, and

the control device is configured to calculate the temperature of the first purifying device by inputting the target temperature into the second model and calculate the fuel supply amount by inputting the calculated temperature into the first model.

2. The control device for an internal combustion engine according to claim 1,

wherein the first model is expressed by expression: (1) Q*inj=Hv−1[Katm,1st(T*1st−Tatm)+h1stA1st(T*1st−T1st,us)]  (1)

wherein Qinj* represents the fuel supply amount that is supplied from the fuel supply device in a predetermined steady state, Hv represents a low heating value of HC, Katm,1st represents a heat transfer coefficient to an atmosphere in the first purifying device, T1st* represents a temperature of the first purifying device in a predetermined steady state, Tatm represents an atmospheric temperature, h1st represents a heat conversion coefficient per channel unit area of the first purifying device, A1st represents a channel area of the first purifying device, and T1st,us represents an inlet temperature of the first purifying device;

wherein the second model is expressed by expression: (2), T*1st=Tref2nd−(h2ndA2nd)−1[Qexo,2nd,pm(Tref2nd,mpm)−Katm,2nd(Tref2nd−Tatm)]  (2)

wherein T1st* represents the temperature of the first purifying device in a predetermined steady state, T22ndref represents the target temperature of the second purifying device, h2nd represents a heat conversion coefficient per channel unit area of the second purifying device, A2nd represents a channel area of the second purifying device, Qexo,2nd,pm represents a heat flow that moves to the second purifying device by heat generation accompanying PM combustion in an exhaust gas, mpm represents an accumulation amount of PM, Katm,2nd represents a heat transfer coefficient to an atmosphere in the second purifying device, and Tatm represents an atmospheric temperature.

3. The control device for an internal combustion engine according to claim 1,

wherein the control device is configured to correct a fuel supply amount calculated from the first and the second models by increasing and decreasing the fuel supply amount based on a deviation of an actual temperature of the second purifying device and the target temperature.

4. The control device for an internal combustion engine according to claim 1,

wherein the control device is configured to correct the fuel supply amount so that the fuel supply amount is an upper limit value or less, which is set based on an exhaust air-fuel ratio, or less.

5. The control device for an internal combustion engine according to claim 1,

wherein the control device is configured to correct the fuel supply amount so that the fuel supply amount is an upper limit value or less, which is set based on an allowable amount of hydrocarbon in the exhaust gas, or less.