JP4527375B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly, to a control device for an internal combustion engine that can reduce exhaust temperature even during high-load operation and improve output and fuel consumption.

  In a normal gasoline engine, the air-fuel ratio is controlled to an output air-fuel ratio of about 12.5 to 12.7 in order to obtain a high output when the throttle is fully opened. However, on the high rotation side (for example, high rotation of about 4000 rpm or more), the exhaust temperature increases considerably, and the catalyst is damaged such as melting of the catalyst.

  This is because the combustion in the combustion chamber is slow in the high rotation range, the isovolume during combustion is small, and the rate at which the explosion energy is converted into axial work is small, so the energy discarded in the exhaust becomes large, This is because the exhaust temperature increases.

  Therefore, means for increasing the air-fuel ratio and lowering the exhaust temperature has been adopted. That is, a means for keeping the air-fuel ratio away from the stoichiometry having the highest combustion temperature has been adopted.

  As a related art, there has been proposed a technique for reducing the exhaust temperature by executing fuel increase correction when the exhaust temperature is in an overheated state (for example, Patent Document 1).

Japanese Patent Laid-Open No. 7-34924

  However, the conventional control device for an internal combustion engine has a problem that not only the maximum output cannot be increased but also the fuel consumption is deteriorated because the exhaust gas temperature is lowered by moving the air-fuel ratio away from the stoichiometry having the highest combustion temperature. .

  The present invention has been made in view of the above, and an object of the present invention is to provide a control device for an internal combustion engine that can lower the exhaust temperature even during high-load operation and can improve output and fuel consumption.

In order to solve the above-described problems and achieve the object, an internal combustion engine control apparatus according to claim 1 of the present invention is an internal combustion engine control apparatus capable of supplying main fuel and hydrogen to a combustion chamber. When the catalyst temperature, which is the temperature of the catalyst that is provided in the exhaust line and purifies exhaust from the combustion chamber, becomes higher than a reference temperature that is less than the temperature at which damage such as melting damage occurs in the catalyst during high load operation, the combustion chamber When hydrogen is supplied to the catalyst and the catalyst temperature is higher than the reference temperature , the hydrogen supply rate, which is the hydrogen supply rate, is increased by increasing the hydrogen addition rate, and feedback is performed so that the catalyst temperature becomes the reference temperature. During the control and feedback control, if the hydrogen supply amount exceeds the limit hydrogen supply amount, the hydrogen supply amount is set as the limit hydrogen supply amount, and if the catalyst temperature is higher than the reference temperature, the main fuel supply amount In By increasing the fuel supply amount, and is characterized in that a feedback control so that the catalyst temperature is a reference temperature.

By adding and supplying hydrogen during high-load operation, the combustion rate increases. Further, the amount of in-cylinder gas is increased by the injection of hydrogen, and combustion is promoted, so that the isovolume during explosion is increased. As a result, the shaft output increases and the energy loss to the exhaust decreases, so that the exhaust temperature decreases. Also, the main combustion is increased by increasing the fuel supply amount with the hydrogen supply amount as the limit hydrogen supply amount. However, only the main fuel is supplied because the exhaust temperature is lowered by adding hydrogen. Compared with the case where it does, the increase amount of gasoline for exhaust temperature fall may be small, and it can improve a fuel consumption as a whole.

According to a second aspect of the present invention, there is provided a control device for an internal combustion engine according to the first aspect, wherein the hydrogen is supplied when the catalyst temperature reaches a reference temperature , The fuel is injected between the theoretical air fuel ratio and the vicinity of the output air fuel ratio.

  Therefore, even if the gasoline as the main fuel is not increased, the catalyst is prevented from being overheated to a temperature at which it is damaged, and for example, the engine can be operated with the maximum output air-fuel ratio.

  According to the control device for an internal combustion engine according to the present invention (Claim 1), the exhaust temperature can be lowered even during high-load operation, and the output and fuel consumption can be improved.

  Further, according to the control device for an internal combustion engine according to the present invention (Claim 2), it is possible to suppress overheating to a temperature at which the catalyst is damaged without increasing the amount of gasoline as the main fuel. Operation is possible with the maximum output air-fuel ratio.

  Embodiments of an internal combustion engine control apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  First, a schematic configuration of an engine (internal combustion engine) to which the present invention is applied will be described with reference to FIG. Here, FIG. 1 is a cross-sectional view showing a schematic configuration of the engine according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the combustion chamber 10 a of the engine 10 is composed of a cylinder bore 11, a cylinder head 13, and a piston 12 that is reciprocally disposed in the cylinder bore 11. A spark plug 14 for igniting the air-fuel mixture is disposed substantially at the center of the combustion chamber 10a. An intake valve 16 is disposed at the intake port 15 facing the combustion chamber 10a, and an exhaust valve 20 is disposed at the exhaust port 18 facing the combustion chamber 10a.

  The engine 10 is configured such that gasoline as a main fuel can be injected into an intake port 15 by a gasoline port injection injector 25, and hydrogen as an auxiliary fuel is directly injected into a combustion chamber 10a by a hydrogen direct injection injector 23. It is configured to be jettable. This hydrogen direct injection injector 23 is disposed near the intake valve 16 of the combustion chamber 10a. In addition, the code | symbol 23a in a figure has shown the delivery pipe for hydrogen direct injection, and the code | symbol 25a has shown the delivery pipe for gasoline port injection.

  Further, the hydrogen injection pressure by the hydrogen direct injection injector 23 is set to be high so as to withstand the maximum in-cylinder pressure during combustion. Further, the hydrogen direct injection injector 23 is set so that hydrogen is uniformly injected into the cylinder, and can be configured, for example, to inject a substantially conical spray into the center of the combustion chamber 10a.

The hydrogen injection timing by the hydrogen direct injection injector 23 is after the intake valve 16 is closed (see steps S18 and S19 in FIG. 2). This is because if hydrogen is injected before the intake valve 16 is closed, the flow of fresh air to be sucked is hindered, the amount of air is reduced, and the output is reduced.

  The other components such as a catalyst device provided in an exhaust line (not shown) are the same as those of a known gasoline engine, and each component is controlled by an electronic control unit (ECU) (not shown).

  Next, a control method will be described with reference to FIG. Here, FIG. 2 is a flowchart showing a fuel injection control method. This control is premised on a high load operation such as a full load state (WOT).

  First, the engine speed Ne (rpm) and the throttle opening are detected (step S10). The initial gasoline injection amount Aa (cc / st) is calculated from the initial gasoline injector drive time τ0 (ms) when hydrogen is not added (hereinafter, “initial” is added to the code name in this case) (step) S11). The initial gasoline supply heat amount Fa (J / st) can be obtained as a product of the initial gasoline injection amount Aa and the known gasoline lower heating value Hg (Fa = Aa × Hg). That is, this initial gasoline supply heat amount Fa is the total supply heat amount before adding hydrogen.

  Next, the air / fuel mixing ratio A / F (for example, A / F = 12.5) at full load (WOT), MBT ignition timing IT0 (° BTDC) in the case of only the initial gasoline, a map, etc. The estimated value of the catalyst bed temperature is calculated based on this, and whether this catalyst bed temperature is higher than the reference catalyst bed temperature Tcat (° C.) defined as the reference temperature below the temperature at which damage such as melting damage occurs in the catalyst. Is determined (step S12).

  If the catalyst bed temperature is higher than the reference catalyst bed temperature Tcat (° C.) (Yes at Step S12), the process shifts to hydrogenation control (Step S13), and the catalyst bed temperature is not higher than the reference catalyst bed temperature Tcat (° C.). If so (No at Step S12), the catalyst is not damaged, and the control is terminated.

In the hydrogen addition control in step S13, the total supply heat amount Fa (J / st) calculated in step S11, the hydrogen supply heat amount Fh (J / st), and the gasoline supply heat amount Fg (J / st) at the time of hydrogen addition, Since there is a relationship shown in the following equations (1) and (2) between the hydrogen addition ratio RH2 (%) with respect to gasoline, hydrogen injection control and gasoline injection in the following step S14 are used using this relationship. Take control.
Fh + Fg = Fa (1)
Fh / Fg = RH2 (2)

  A hydrogen addition ratio RH2 (%) with respect to gasoline determined in advance by a map or the like according to the detected engine speed Ne and load is fixed (step S14). If the values of the total heat supply amount Fa and the hydrogen addition ratio RH2 are determined, the hydrogen supply heat amount Fh (J / st) and the gasoline supply heat amount Fg (J / st) at the time of hydrogen addition are obtained from the above equations (1) and (2). ) Can be calculated (step S15).

Next, since the lower hydrogen heating value Hh (J / cc) and the lower gasoline heating value Hg (J / cc) are known, the hydrogen supply heat amount Fh and the gasoline supply heat amount Fg calculated in step S15 are used, respectively. The hydrogen supply amount Ah (cc / st) is calculated from the following equation (3), and the gasoline supply amount Ag (cc / st) is calculated from the following equation (4) (step S16).
Ah = Fh / Hh (3)
Ag = Fg / Hg (4)

  Next, the driving time of the hydrogen direct injection injector 23 from a predetermined map based on the detected hydrogen line internal pressure Ph (MPa) in the hydrogen direct injection delivery pipe 23a and the engine speed Ne. The hydrogen injector driving time τh (ms) and the injection crank angle are calculated, and the injection end timing is calculated. For example, the injection start crank angle is calculated (step S17).

  Similarly, based on the detected gasoline line pressure Pg (KPa) in the gasoline port injection delivery pipe 25a and the engine speed Ne, the gasoline port injector 25 is determined from a predetermined map. The gasoline injector drive time τg (ms), which is the drive time, and the injection crank angle are calculated to calculate the injection end timing (for example, the injection start crank angle is calculated), and the gasoline port injection injector 25 is driven (step S17). ).

  Next, it is determined whether or not the intake valve 16 is closed (step S18), and after the intake valve 16 is closed, the hydrogen direct injection injector 23 is driven (Yes in step S18, step S19). This is because, as described above, if hydrogen is injected before the intake valve 16 is closed, the flow of fresh air to be sucked is hindered, the amount of air is reduced, and the output is reduced.

Subsequently, the MBT ignition timing IT _RH2 (° BTDC) when the hydrogen addition ratio RH2 to gasoline is set (step S20). The MBT ignition timing IT _RH2 can be obtained from a predetermined map as shown in FIG. 3 because the hydrogen addition ratio RH2 is fixed in step S14. Here, FIG. 3 is a map showing the relationship between the hydrogen addition ratio RH2 and the MBT ignition timing.

  Next, it is determined whether or not the catalyst bed temperature calculated under the above conditions is higher than the reference catalyst bed temperature Tcat (° C.) (step S21). If the catalyst bed temperature is higher than the reference catalyst bed temperature Tcat (° C.) (Yes at Step S21), a value obtained by multiplying the hydrogen addition ratio RH2 to gasoline by a predetermined hydrogen ratio increase coefficient α is set as a new hydrogen addition ratio RH2 ( Step S22) and the process proceeds to step S14. That is, when the catalyst bed temperature is higher than a predetermined value, the hydrogen supply amount is slightly increased and feedback control is performed so that the exhaust temperature is lowered. On the other hand, if the catalyst bed temperature is not higher than the reference catalyst bed temperature Tcat (° C.) (No at Step S21), the catalyst is not damaged and the control is terminated.

  By controlling by adding hydrogen as described above, the A / F, the exhaust temperature, and the generated torque have the relationship shown in FIG. Here, FIG. 4 is a graph showing the relationship between A / F, exhaust temperature, and generated torque when hydrogen is added.

  As shown in FIG. 4, in the case of a normal gasoline engine to which hydrogen is not added (a graph indicated by a thin line in the figure), the upper limit of the exhaust temperature (catalyst allowable exhaust temperature) is determined, and A / F is the output air-fuel ratio. As shown by point P, the catalyst allowable exhaust temperature is exceeded, so A / F is operated at point A. As a result, the exhaust temperature becomes point B, which is lower than the catalyst allowable exhaust temperature, but the torque obtained there becomes point C, which is lower than in the case of the output air-fuel ratio (point K).

  On the other hand, in the case of a gasoline engine to which hydrogen is added according to the present invention (a graph indicated by a thick line in the figure), the exhaust gas temperature decreases as the hydrogen addition rate increases as shown in FIG. The exhaust temperature is point D, which is below the catalyst allowable exhaust temperature. The torque at this time is point E. Here, FIG. 5 is a graph showing the relationship between the hydrogen addition ratio and the exhaust temperature.

As a result, while the exhaust gas temperature is kept lower than the allowable temperature, the torque can be operated at the output air-fuel ratio (torque at the point K−torque at the point C) and the improvement by the hydrogen addition (at the point E). Torque-torque at point K). That is, the torque is improved by (torque at point E−torque at point C).

  In addition, when hydrogen is added as shown in FIG. 6 (graph indicated by a thick line in FIG. 6), the MBT ignition timing is delayed as compared with the case where hydrogen is not added (graph indicated by a thin line in FIG. 6). It turns out that it shifts to the corner side and the generated torque is improved. Here, FIG. 6 is a graph showing how the torque is improved when hydrogen is added in the relationship between the MBT ignition timing and the generated torque.

  As described above, according to the control apparatus for an internal combustion engine according to the first embodiment, the combustion rate is increased by adding hydrogen during high-load operation. Further, the amount of in-cylinder gas is increased by the injection of hydrogen, and combustion is promoted, so that the isovolume during explosion is increased. As a result, the shaft output increases and the energy loss to the exhaust decreases, so that the exhaust temperature decreases. Accordingly, even if the gasoline fuel is not increased, the catalyst can be prevented from being overheated to a temperature at which it is damaged, and the operation can be performed with the maximum output A / F (output air-fuel ratio).

  In the first embodiment, the estimated value of the catalyst bed temperature is calculated as the hydrogenation start condition (high load condition). However, the present invention is not limited to this. It may be estimated that the bed temperature is equal to or higher than a reference value, and this may be used as the hydrogenation start condition, or the start condition may be determined by actually measuring the catalyst bed temperature.

  Further, in the first embodiment, it has been described that all the fuel (gasoline and hydrogen) is injected at the output air-fuel ratio while hydrogen is supplied. However, the present invention is not limited to this, and the stoichiometric air-fuel ratio ( Control may be performed so that the fuel is injected between the stoichiometric range and the vicinity of the output air-fuel ratio, whereby the same effect as described above can be expected.

  Moreover, in the said Example 1, although gasoline was made into the intake port injection and hydrogen was injected as direct in-cylinder injection, it is not limited to this, For example, it is good also as in-cylinder direct injection. In addition, although hydrogen may be intake port injection, in-cylinder direct injection is preferable.

  Further, the hydrogen direct injection injector 23 has been described as being disposed in the vicinity of the intake valve 16 of the combustion chamber 10a. However, the present invention is not limited thereto, and is disposed in the vicinity of the center of the combustion chamber 10a or in the vicinity of the exhaust valve 20. You can also.

  In the second embodiment, as shown in FIG. 7, steps S23 to S26 described later are added to the control of the first embodiment (see FIG. 2). Here, FIG. 7 is a flowchart showing a control method according to Embodiment 2 of the present invention.

By the way, the amount of hydrogen that can be actually mounted is limited, and it is not preferable to supply a certain amount or more of hydrogen into the cylinder from the viewpoint of cruising distance. Therefore, after step S22 for slightly increasing the hydrogen supply amount, when the hydrogen supply amount exceeds a predetermined limit amount, in other words, the limit hydrogen supply amount Fo (L / min) (Yes in step S23), hydrogen supply The amount is set to the limit hydrogen supply amount Fo (not shown), and the gasoline supply amount is increased by multiplying the gasoline supply heat amount Fg by a predetermined gasoline increase coefficient β (step S24).

  Then, the ignition timing is also optimized by setting the MBT ignition timing ITzou when the gasoline is increased (step S25). This MBT ignition timing ITzou can also be set based on a predetermined map.

  Next, it is determined whether or not the catalyst bed temperature calculated under the above conditions is higher than the reference catalyst bed temperature Tcat (° C.) (step S26). If the catalyst bed temperature is higher than the reference catalyst bed temperature Tcat (° C.) (Yes at Step S26), the process proceeds to Step S24, and the gasoline supply heat amount Fg is reset. That is, when the catalyst bed temperature is higher than a predetermined value, the gasoline supply amount is further slightly increased and feedback control is performed so that the exhaust gas temperature is lowered. Although the output is slightly reduced by the above control, the supplied hydrogen amount can be suppressed to a constant amount. On the other hand, if the catalyst bed temperature is not higher than the reference catalyst bed temperature Tcat (° C.) (No at Step S26), the catalyst is not damaged and the control is terminated.

  As described above, according to the control apparatus for an internal combustion engine according to the second embodiment, the amount of gasoline is increased, but since hydrogen is added to lower the exhaust temperature, only gasoline is supplied ( Compared with the conventional case), the increase amount of gasoline for lowering the exhaust gas temperature is small, and the overall fuel efficiency can be improved.

  As described above, the control device for an internal combustion engine according to the present invention is useful for an internal combustion engine that can lower the exhaust temperature even during high-load operation and can improve the output and fuel consumption. In particular, it increases the amount of gasoline fuel. Even if it is not, it is possible to suppress the catalyst from being overheated to a temperature at which it is damaged, and is suitable for an internal combustion engine that can be operated with the maximum output A / F (output air-fuel ratio).

It is sectional drawing which shows schematic structure of the engine which concerns on Example 1 of this invention. It is a flowchart which shows the fuel-injection control method. It is a map which shows the relationship between hydrogen addition ratio RH2 and MBT ignition timing. It is a graph which shows the relationship between A / F, exhaust temperature, and generated torque at the time of adding hydrogen. It is a graph which shows the relationship between a hydrogen addition ratio and exhaust temperature. It is a graph which shows a mode that a torque is improved when hydrogen is added in the relationship between MBT ignition timing and generated torque. It is a flowchart which shows the control method which concerns on Example 2 of this invention.

Explanation of symbols

10 Engine (Internal combustion engine)
DESCRIPTION OF SYMBOLS 10a Combustion chamber 11 Cylinder bore 12 Piston 13 Cylinder head 14 Spark plug 15 Intake port 16 Intake valve 18 Exhaust port 20 Exhaust valve 23 Hydrogen direct injection injector 23a Hydrogen direct injection delivery pipe 25 Gasoline port injection injector 25a Gasoline port injection delivery Pipe Ne Engine speed τ0 Initial gasoline injector drive time Aa Initial gasoline injection amount Fa Initial gasoline supply heat amount Hg Gasoline lower heating value Hh Hydrogen lower heating value Tcat Reference catalyst bed temperature IT0 MBT ignition timing for initial gasoline only Fh Hydrogen supply heat amount Fg Gasoline supply heat Fo Limit hydrogen supply rate RH2 Hydrogen addition ratio to gasoline Ah Hydrogen supply amount Ag Gasoline supply amount Ph Hydrogen line pressure Pg Gasoline line pressure τh Hydrogen indicator Injector drive time τg Gasoline injector drive time IT _RH2 MBT ignition timing when hydrogen addition ratio RH2 ITzou MBT ignition timing when gasoline is increased α Hydrogen ratio increase coefficient β Gasoline increase coefficient

Claims (2)

In a control device for an internal combustion engine capable of supplying main fuel and hydrogen to a combustion chamber,
During high load operation of the internal combustion engine, a catalyst temperature that is a temperature of a catalyst that is provided in an exhaust line and purifies exhaust from the combustion chamber is lower than a reference temperature that is less than a temperature at which damage such as melting damage occurs in the catalyst. Is higher, the hydrogen is supplied to the combustion chamber,
When the catalyst temperature is higher than the reference temperature, the hydrogen supply rate, which is the hydrogen supply amount, is increased by increasing the hydrogen addition rate, and feedback control is performed so that the catalyst temperature becomes the reference temperature. And
During the feedback control, if the hydrogen supply amount exceeds the critical hydrogen supply amount,
When the hydrogen supply amount is a critical hydrogen supply amount and the catalyst temperature is higher than the reference temperature, the fuel supply amount, which is the main fuel supply amount, is increased, and the catalyst temperature becomes the reference temperature. A control apparatus for an internal combustion engine, wherein feedback control is performed so that When the internal combustion engine is operating at a high load and the catalyst temperature reaches the reference temperature , the hydrogen is supplied. While the hydrogen is supplied, all fuel is between the stoichiometric air fuel ratio and the vicinity of the output air fuel ratio. The control apparatus for an internal combustion engine according to claim 1, wherein

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