JP4136555B2 - Fuel supply device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel supply device for an internal combustion engine, and more particularly to a fuel supply device that switches between two types of fuel, a high-octane fuel and a low-octane fuel, and supplies the fuel to the engine.
[0002]
[Prior art]
The demand for the fuel octane number of an internal combustion engine varies depending on the engine operating condition. For example, in order to prevent knocking and obtain a high engine output in a low-rotation and high-load engine operating state, a higher fuel octane number is preferable, while in a high-rotation and low-load engine operating state, to maintain a good combustion state The fuel octane number is preferably lower. For this reason, the high-octane fuel and the low-octane fuel are simultaneously supplied to the engine combustion chamber, and the fuel octane number is changed by changing the mixing ratio of both fuels according to the engine operating state, or the engine operating state In response to this, there is known a fuel supply device that switches the fuel supplied to the engine combustion chamber to only the high-octane fuel or only the low-octane fuel. In this way, by supplying fuel with different octane numbers to the engine at the same time or switching, the engine can be operated using the required octane number fuel according to the engine operating conditions. Can always be maintained in good condition.
[0003]
For example, an example of such a fuel supply device is described in Patent Document 1. The fuel supply system of this document generates a high-octane fuel having a higher octane number than that of the raw material fuel and a low-octane fuel having a lower octane number than that of the raw material fuel by fractionating the raw material fuel. It is mixed at a mixing ratio according to the state and supplied to the engine.
[0004]
In the apparatus of Patent Document 1, the high-octane fuel and the low-octane fuel generated by fractionating the raw fuel are temporarily stored in separate sub-fuel tanks, and the high-octane fuel and the low-octane fuel are separately stored from these sub-fuel tanks. It is taken out, mixed at a predetermined ratio, and supplied to the engine. Thereby, it is possible to adjust the octane number of the fuel supplied to the engine according to the operating state.
[0005]
In the apparatus of Patent Document 1, since the high octane fuel and the low octane fuel are generated by fractionation of the raw material fuel, the ratio of the generated amounts of both fuels is fixed within a certain range. For this reason, a problem arises when an operation state in which only one fuel is consumed (or an operation state in which one fuel consumption is large) continues for a long time.
[0006]
For example, in the apparatus of Patent Document 1, when the engine is operated at a relatively low load, the engine is operated by self-ignition combustion by mainly supplying low-octane fuel to the engine. For this reason, the high-octane fuel is hardly consumed in the self-ignition combustion operation, and only the low-octane fuel is consumed, and the balance of consumption of both fuels cannot be maintained.
[0007]
On the other hand, since the apparatus of Patent Document 1 generates high-octane fuel and low-octane fuel by fractionating raw material fuel, it is not possible to generate only one fuel. Therefore, during the self-ignition operation of the engine, the amount of high octane fuel stored in the sub fuel tank increases and the amount of low octane fuel decreases.
[0008]
If a state in which a large difference in the consumption amounts of both fuels continues as described above, for example, the low-octane fuel amount in the sub-fuel tank becomes insufficient or the high-octane fuel amount in the sub-fuel tank increases. A case where the upper limit of the capacity of the tank is reached is not preferable.
[0009]
In the apparatus of Patent Document 1, for example, when the operation of self-ignition combustion continues for a long time and the remaining amount of low octane fuel in the tank decreases below the lower limit value, or the remaining amount of high octane fuel in the tank exceeds the upper limit value. When the engine combustion mode is increased, the combustion mode of the engine is switched from self-ignition combustion to spark ignition combustion, and the supply ratio of high octane fuel to the engine is increased. This adjusts the fuel consumption balance between the high-octane fuel and the low-octane fuel.
[0010]
That is, in the device of Patent Document 1, an operation state in which one fuel consumption is large continues and the remaining amount of one fuel becomes excessive or the remaining amount of the other fuel becomes excessive. In order to balance the consumption amounts of both fuels, the engine is operated in an operation mode in which a larger amount of fuel is used by switching the operation mode of the engine.
[0011]
[Patent Document 1]
JP 2001-5070 A
[0012]
[Problems to be solved by the invention]
In the device of Patent Document 1, when it is necessary to adjust the balance of consumption of both fuels by continuing the engine operation under the condition that only the consumption of one fuel is increased, The fuel consumption balance is adjusted by switching the operation state from a combustion mode in which a large amount of fuel is used (that is, from self-ignition combustion to spark ignition combustion).
[0013]
However, there is a problem in changing the combustion mode only for the purpose of adjusting the fuel consumption balance. For example, in the case of the device of Patent Document 1, when the remaining amount of high-octane fuel decreases or the remaining amount of low-octane fuel increases, the low-octane fuel in a region other than the operation region where spark ignition combustion is originally performed Although self-ignition combustion is performed using a gas, if it is forcibly operated with self-ignition combustion in an operation state that is not originally suitable for self-ignition combustion, the combustion state deteriorates and the exhaust properties deteriorate significantly. become.
[0014]
Also, for example, in a low load region of an engine, a combustible air-fuel ratio mixture is stratified in a part of the combustion chamber, and the combustion chamber as a whole performs combustion at a very high (lean) air-fuel ratio. In the case of an engine that operates in a homogeneous combustion mode in which a uniform air-fuel mixture is formed in the entire combustion chamber in the middle and high load regions and performs combustion, for example, low-octane fuel is used for stratified combustion mode operation. High octane fuel is used for homogeneous combustion mode operation. However, there is a limit to the region in which the operation in the stratified combustion mode can be performed. If the stratified combustion mode operation is performed in the region where the homogeneous combustion mode operation is originally performed, the engine performance and the exhaust property may be greatly affected. Therefore, in these engines, it is difficult to efficiently adjust the consumption balance between the high-octane fuel and the low-octane fuel by switching the combustion mode.
[0015]
In view of the above problems, the present invention effectively balances the consumption of both fuels without significantly degrading engine performance or exhaust properties when both high-octane fuel and low-octane fuel are supplied to the engine. An object of the present invention is to provide a fuel supply device for an internal combustion engine that can be used.
[0016]
[Means for Solving the Problems]
According to the first aspect of the present invention, when the air-fuel ratio of the inflowing exhaust gas is lean, the NO in the exhaust gas _X Is selectively occluded and held by adsorption, absorption or both, and when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich air-fuel ratio, the occluded NO is stored. _X NO is reduced and purified using reducing components in exhaust gas _X An NOx storage reduction catalyst is provided in the exhaust system, and the NO _X NO stored in the storage reduction catalyst _X When the engine is to be reduced and purified, an internal combustion engine that performs a rich spike operation that temporarily operates the engine at the stoichiometric air-fuel ratio or rich air-fuel ratio is supplied to either the high octane fuel or the low octane fuel depending on the engine load condition. A fuel supply device for an internal combustion engine that selectively supplies one of them, and increases the consumption of one of the high-octane fuel and the low-octane fuel for adjusting the balance of the consumption of both fuels. In the case where the engine should be operated, the internal combustion engine supplies the one fuel to the engine during a rich spike operation during the lean air-fuel ratio operation using the other of the high octane fuel and the low octane fuel. A fuel supply apparatus is provided.
[0017]
That is, in the invention of claim 1, the engine has NO. _X A NOx stored in the catalyst during lean air-fuel ratio operation is provided. _X In order to reduce and purify the fuel, it is necessary to periodically perform a rich spike operation in which the engine is operated at a stoichiometric air-fuel ratio or a rich air-fuel ratio for a short time. During the rich spike operation, the engine performs homogeneous combustion in which a uniform stoichiometric air-fuel ratio or rich air-fuel ratio mixture is formed in the combustion chamber and burned. In homogeneous combustion, that is, homogeneous combustion at a stoichiometric or rich air-fuel ratio, the influence of the fuel octane number on the combustion is small compared to combustion at a lean air-fuel ratio or combustion in a stratified combustion mode. Further, at the time of rich spike operation, the stoichiometric air-fuel ratio or rich air-fuel ratio operation is always performed, and the amount of fuel supplied to the engine is increased compared to normal operation (for example, lean air-fuel ratio operation). For this reason, by using the fuel whose consumption should be increased during the rich spike operation, it becomes possible to efficiently adjust the fuel consumption balance without affecting the engine performance and the exhaust properties.
In addition, when the engine is operated with the fuel whose consumption should be increased before the rich spike operation, the use of the fuel whose consumption should be increased for the rich spike operation naturally without switching the fuel. Will continue.
[0018]
According to the second aspect of the present invention, when the consumption of the high octane fuel is to be increased and when the engine is accelerated following the rich spike operation, the acceleration operation is further completed. The fuel supply apparatus for an internal combustion engine according to claim 1, wherein the high octane fuel is supplied to the engine.
[0019]
That is, in the invention of claim 2, when the consumption of the high octane fuel is to be increased and the engine is accelerated following the rich spike during the operation with the low octane fuel, the acceleration is performed not only during the rich spike. Use high octane fuel until the end. In high-load operation of the engine such as during acceleration, the homogeneous combustion of the stoichiometric air-fuel ratio or rich air-fuel ratio is normally performed, the engine load increases, and it is in a state suitable for the use of high octane fuel. For this reason, when accelerating after a rich spike, the high-octane fuel consumption can be increased without affecting the engine performance and exhaust properties by continuing to use the high-octane fuel until the acceleration is completed. Therefore, it is possible to adjust the fuel consumption balance.
[0020]
According to the third aspect of the present invention, when the consumption of the low octane fuel is to be increased and the engine is accelerated following the rich spike operation, after the rich spike operation is completed, 2. A fuel supply apparatus for an internal combustion engine according to claim 1, wherein the low octane fuel is supplied to the engine until the engine reaches a predetermined load state during acceleration.
[0021]
That is, in the invention of claim 3, in order to increase the consumption of the low octane fuel, the low octane number is used during the rich spike during the lean air-fuel ratio operation with the high octane fuel. During operation at rich spike, homogeneous combustion at the stoichiometric air-fuel ratio or rich air-fuel ratio is performed, so there is no problem even if low octane fuel is used. However, when the engine is continuously accelerated after the lean air-fuel ratio operation, if the low-octane fuel is continuously used until the acceleration operation is completed, knocking may occur when the engine load increases. In the present invention, a load state in which knocking occurs is obtained in advance by experiments, etc., and low-octane fuel is used until the engine operating state reaches this load state. When this load state is reached, low-octane fuel is used. And resume operation with high-octane fuel.
Thereby, in the present invention, it is possible to efficiently adjust the balance of the amounts of use of both fuels without affecting the engine performance even during acceleration or the like.
[0022]
According to the invention described in claim 4, further comprising a fuel tank for storing the high-octane fuel and the low-octane fuel supplied to the engine, respectively, one of the high-octane fuel and the low-octane fuel. When the ratio between the remaining amount in the tank and the remaining amount in the tank of the other fuel exceeds a predetermined upper limit, the consumption amount of the one fuel should be increased to adjust the fuel consumption balance The fuel supply device for an internal combustion engine according to any one of claims 1 to 3, wherein the fuel supply device for the internal combustion engine is determined.
[0023]
That is, in the invention of claim 4, it is determined whether or not the consumption of one fuel is to be increased based on the ratio of the remaining amount of the fuel tank that stores the high-octane fuel and the low-octane fuel.
For example, assuming that the remaining amount of high octane fuel in the tank is RH and the remaining amount of low octane fuel in the tank is RL, if the ratio RL / RH reaches a predetermined upper limit α, the low octane fuel It is determined that the consumption should be increased.
Similarly, when the ratio, RH / RL value reaches a predetermined upper limit value β (β may be the same value as α or a different value), the consumption of high octane fuel is increased. Judge that it is the state to be.
[0024]
In this case, for example, when the value of RL / RH becomes equal to or lower than the lower limit value (1 / β or less), it may be determined that the consumption amount of the high octane fuel should be increased.
This makes it possible to accurately determine when the consumption of one fuel should be increased, and to appropriately adjust the balance of consumption of both fuels.
[0025]
According to a fifth aspect of the present invention, the upper limit value is further changed based on the consumption rate of the high octane fuel and the consumption rate of the low octane fuel so that the consumption rates of both fuels approach each other. The fuel supply device for an internal combustion engine according to claim 4, wherein a learning operation is performed.
[0026]
That is, in the fifth aspect of the invention, the determination values α and β in a state where the consumption amount of one fuel of the fourth aspect should be increased are changed according to the consumption rates of both fuels. For example, when the engine is operated in an operation pattern in which there are many opportunities to use high-octane fuel, the consumption rate of high-octane fuel (for example, m ^Three / Hr) is greater than the consumption rate of the low octane fuel. In this case, if the frequency of increasing the consumption of the low-octane fuel is increased, the consumption rate of the low-octane fuel will increase and the consumption rates of both fuels will approach each other. Large differences in quantity are prevented. Therefore, in this case, for example, by reducing the upper limit α of the ratio RL / RH, the frequency of the low octane number fuel consumption increasing operation is increased, and the consumption rate of the low octane number fuel is increased. On the other hand, when the engine is operated in an operation pattern in which there are many opportunities to use a low octane number, conversely, by reducing the upper limit value of the ratio RH / RL, the frequency of operations for increasing the consumption of high octane fuel is increased. Thus, the consumption rates of both fuels can be made closer to each other.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram schematically showing a schematic configuration of an embodiment when the fuel supply device of the present invention is applied to an internal combustion engine for a vehicle.
[0028]
In FIG. 1, reference numeral 100 denotes a vehicle internal combustion engine, and 110H and 110L denote fuel injection valves that directly inject fuel into each cylinder of the internal combustion engine 1. In this embodiment, one fuel injection valve 110H and 110L is provided for each cylinder. That is, in the example of FIG. 1, since a four-cylinder gasoline engine is used, four fuel injection valves 110H and 110L are provided, and a total of eight fuel injection valves are provided.
[0029]
As will be described later, the fuel injection valve 110H is a high-octane fuel injection valve that injects high-octane fuel into each cylinder, and 110L is a low-octane fuel injection valve that injects low-octane fuel into each cylinder. The high-octane fuel injection valve 110H and the low-octane fuel injection valve 110L are connected to a high-octane fuel delivery pipe 20H and a low-octane fuel delivery pipe 20L, which will be described later, respectively, and the fuel in the delivery pipes 20H and 20L Each is injected into the cylinder.
[0030]
In FIG. 1, the fuel tanks of the engine 1 are indicated by 11H and 11L. In this embodiment, in order to inject two fuel oils having different octane numbers into the engine from the fuel injection valves 110H and 110L, each fuel tank is provided separately. In this embodiment, two fuels having different octane numbers, such as high octane gasoline and low octane gasoline, gasoline and other types of liquid fuel (for example, DME (dimethyl ether)), or liquid fuels having different octane numbers other than gasoline are used. However, the example of FIG. 1 shows a case where high-octane gasoline and low-octane gasoline are used.
[0031]
In the present embodiment, high octane gasoline is stored in the fuel tank 11H, and low octane gasoline is stored in 11L. The high-octane gasoline and the low-octane gasoline may be replenished separately to the tanks 11H and 11L from the outside, respectively. For example, as in the device of Patent Document 1 described above, fractional distillation or the like is appropriately performed on the vehicle. It is also possible to produce by separating commercially available gasoline into gasoline containing many high octane components and gasoline containing many low octane components using such means.
[0032]
The fuel stored in the fuel tanks 11H and 11L is supplied to the high-pressure fuel pumps 21H and 21L via the low-pressure supply pipes 15H and 15L by the low-pressure feed pumps 11Ha and 11La provided in the tanks, respectively.
The high-pressure fuel pumps 21H and 21L are, for example, plunger-type high-pressure pumps, and each have a discharge amount control mechanism that adjusts the pump discharge amount. High-pressure fuel pumps 21H and 21L are connected to delivery pipes 20H and 20L via high-pressure supply pipes 25H and 25L, respectively.
[0033]
As shown in FIG. 1, high-octane gasoline is supplied from a fuel tank 11H to a high-pressure fuel pump 21H by a low-pressure feed pump 11Ha, boosted by a high-pressure fuel pump 21H, and supplied from a high-pressure supply pipe 25H to a delivery pipe 20H. The fuel is injected into each cylinder from the valve 110H. Further, the low octane gasoline is supplied from the fuel tank 11L to the delivery pipe 20L through the low pressure feed pump 11La, the high pressure fuel pump 21L, and the high pressure supply pipe 25L, and is injected from the fuel injection valve 110L to each cylinder. That is, in the present embodiment, high-octane gasoline and low-octane gasoline are supplied from the mutually independent supply sources to the respective fuel injection valves through the mutually independent supply paths, and therefore, from one fuel to the other fuel. Can be switched in an extremely short time.
[0034]
An electronic control unit (ECU) of the engine 100 is indicated by 30 in FIG. In the present embodiment, the ECU 30 is configured as a microcomputer having a known configuration in which a read only memory (ROM), a random access memory (RAM), an arithmetic unit (CPU), and an input / output port are connected by a bidirectional bus. In addition to performing basic control such as the ignition timing of each cylinder of the engine and the fuel injection amount to each cylinder, in this embodiment, switching of the combustion mode of the engine, which will be described later, and the type of fuel supplied to each cylinder (octane number) Switching, NO _X NO stored in the NOx storage reduction catalyst _X Various controls such as a rich spike operation for reducing and purifying the water are performed.
[0035]
For these controls, the output port of the ECU 30 is connected to the fuel injection valves 110H and 110L of each cylinder via a drive circuit (not shown) and controls the fuel injection amount of each fuel injection valve. It is connected to an ignition plug (not shown) of each cylinder through a circuit to control the ignition timing of the engine. Further, the input ports of the ECU 30 include fuel remaining amounts sensors 12H and 12L provided in the fuel tanks 11H and 11L, respectively, a remaining amount of high octane gasoline in the tank 11H and a remaining amount of low octane gasoline in the tank 11L. In addition, the number of revolutions of the engine 1, the amount of depression of the accelerator pedal of the driver, and the like are input from respective sensors (not shown).
[0036]
In the present embodiment, the exhaust port of each cylinder of the engine 100 is connected to a common exhaust pipe 50 via an exhaust manifold 50a. In FIG. 1, 70 indicates NO disposed in the exhaust pipe 50. _X It is an occlusion reduction catalyst.
NO _X The occlusion reduction catalyst 70 is configured to detect NO in the exhaust when the air-fuel ratio of the inflowing exhaust is lean. _X Is selectively retained (occluded) by adsorption, absorption, or both, and when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric or rich air-fuel ratio, the stored NO _X Is reduced and purified using a reducing component in the exhaust gas.
[0037]
As will be described later, in the present embodiment, the engine 100 is operated at a lean air-fuel ratio in most of its operating range. For this reason, NO _X A lean air-fuel ratio exhaust gas flows into the storage reduction catalyst 70, and NO in the exhaust gas _X Is NO _X Occluded in the occlusion reduction catalyst 70. However, if the engine's lean air-fuel ratio operation continues for a long time, NO _X NO stored in the storage reduction catalyst 70 _X The amount increases, NO _X NO stored by the storage reduction catalyst 70 _X Saturates and no more _X The storage reduction catalyst may not be stored. Therefore, in the present embodiment, the ECU 30 is NO. _X NO stored in the NOx storage reduction catalyst _X When it is determined that the amount has increased, the engine 100 is operated at a rich air-fuel ratio for a short time and NO. _X A rich spike operation is performed for supplying the rich air-fuel ratio exhaust gas to the storage reduction catalyst.
By performing rich spike operation, NO _X NO stored in the storage reduction catalyst 70 _X Is reduced and purified, NO _X NO of storage reduction catalyst 70 _X Saturation due to is prevented.
[0038]
NO _X NO of storage reduction catalyst 70 _X Whether or not the amount of occlusion has increased, that is, whether or not the rich spike operation should be performed is determined by, for example, whether a certain driving time has elapsed since the previous rich spike operation or whether the vehicle travel distance has reached a certain value Or the NO per unit time based on a predetermined relationship from the operating state of the engine. _X Calculate the generated amount, and this NO _X A predetermined ratio to the amount generated (NO in exhaust _X NO _X The integrated value of the value multiplied by the ratio of the occlusion in the occlusion reduction catalyst (that is, NO of the catalyst 70) _X The determination may be made based on whether or not (occlusion amount) has reached a predetermined value.
[0039]
Next, a method for using high-octane gasoline and low-octane gasoline in this embodiment will be described.
In this embodiment, the engine 100 is a lean combustion engine that can be operated by switching between two operation modes of a stratified combustion mode and a homogeneous combustion mode.
In the homogeneous combustion mode of the engine, fuel is directly injected into the engine combustion chamber from the fuel injection valves 110H and 110L in the first half of the intake stroke to form a uniform mixture in the combustion chamber, and this mixture is ignited by a spark plug. Burn. In the homogeneous combustion mode, the air-fuel ratio of the entire air-fuel mixture in the combustion chamber must be within the flammable range, so the air-fuel ratio of the air-fuel mixture cannot be made significantly high (lean), but from fuel injection to ignition Therefore, a relatively large amount of fuel can be supplied to the engine.
For this reason, in this embodiment, the homogeneous combustion mode operation is performed in an operation region where the engine shaft torque is large or in a high engine rotation region.
[0040]
On the other hand, in stratified combustion, fuel is injected into the combustion chamber in the late stage of the compression stroke of the cylinder, so that a mixture of a combustible air-fuel ratio is stratified only in the vicinity of the spark plug. By stratifying the injected fuel only around the spark plug in this way, stable combustion can be performed while maintaining the air-fuel ratio as a whole cylinder is significantly higher (lean) than in the case of homogeneous mixture combustion. It becomes possible.
In stratified combustion, the combustion air-fuel ratio of the entire cylinder is set sufficiently high, and exhaust properties (especially NO) _X Although the time from the start of fuel injection to ignition is relatively short and only a relatively small amount of combustion can be supplied to the engine, there is a problem that it is difficult to increase the engine output.
In this embodiment, the engine is operated in the stratified combustion mode in an operation region where the engine output is relatively small and the engine speed is low.
[0041]
FIG. 2 shows an operation in which the stratified combustion mode operation and the homogeneous combustion mode operation of the engine 100 are represented with the engine axis torque T (or the accelerator pedal depression amount of the driver) on the vertical axis and the rotational speed N on the horizontal axis. It is a figure which shows an area | region.
As shown in FIG. 2, in this embodiment, the engine shaft torque is small and the engine speed is low (the shaft torque T in FIG. ₀ And the engine speed N is N ₀ (Below) In the operation region, stratified combustion mode operation is performed, and either or both of the engine shaft torque and the engine speed are large (T> T in FIG. 2) ₀ And N> N ₀ The homogeneous combustion mode operation is performed when one or both of the above are established.
[0042]
As described above, in this embodiment, the fuel injection valve 110H that injects high-octane gasoline into each cylinder and the fuel injection valve 110H that injects low-octane gasoline are individually provided, and the fuel injection amount from each valve is determined. By adjusting, the octane number of the fuel supplied to the engine as a whole can be changed.
[0043]
In the embodiment described below, a case where fuel injection is performed from only one of the fuel injection valves 110H and 110L, that is, a case where only high-octane gasoline or only low-octane gasoline is switched and supplied to the engine will be described.
[0044]
The octane number required for the fuel is preferably as low as possible without causing knock. This is because the lower the octane number, the better the ignitability of the fuel and the better the combustion state of the fuel. On the other hand, as the fuel octane number decreases, the flame propagation speed at the time of combustion increases, so knocking occurs when the ignition timing is advanced. For this reason, if the fuel octane number is low, the ignition timing cannot be advanced to the optimum timing, and the engine output cannot be increased sufficiently.
[0045]
In the present embodiment, in consideration of the above requirement for the octane number, optimum combustion is obtained in each load state by switching the octane number of the fuel to be used in accordance with the engine load in addition to the switching of the combustion mode. That is, in this embodiment, when the engine output is higher than a certain switching determination value, high-octane gasoline is supplied from the fuel injection valve 110H to each cylinder, and when low, low-octane gasoline is supplied from the fuel injection valve 110L to the cylinder. Spray.
[0046]
A straight line A shown in FIG. 2 is a determination value of the fuel switching load in the present embodiment. As shown in FIG. 2, the load determination value is set to increase as the engine speed increases. That is, knocking is likely to occur even with a small load as the engine speed is low. In this embodiment, the engine is operated with high octane number gasoline up to a small load area as the engine speed is low, and the load area is high as the engine speed is high. To low-octane gasoline.
As can be seen from FIG. 2, in the present embodiment, even when the engine is operated in the stratified combustion mode, the fuel is switched from the low octane gasoline to the high octane gasoline when the engine load becomes higher than the straight line A in FIG.
[0047]
Further, as shown in FIG. 2, since the low-octane fuel is used in a region where the load is relatively low, the operation with the low-octane gasoline is frequently performed in the normal operation state of the engine. However, when operating with low-octane gasoline, the engine output is relatively low, so the fuel consumption per unit time is small. On the other hand, since the region where high-octane gasoline operation is performed is a region where the load is relatively high, the frequency of operation with high-octane gasoline is smaller than the frequency of operation with low-octane gasoline. However, since the engine output is relatively large when operating with high octane gasoline, the fuel consumption per unit time is large.
[0048]
For this reason, in normal operation, the overall consumption of high-octane gasoline and low-octane gasoline is substantially equal and balanced.
However, depending on the operating condition, the balance of the above fuel consumption may be lost, and one fuel may be consumed more than the other fuel.
[0049]
For example, when only low-load operation continues for a long time and the consumption of low-octane gasoline becomes extremely large compared to the consumption of high-octane gasoline, the fuel level in the high-octane gasoline tank 11H is high. Regardless, the fuel level in the low octane gasoline tank 11L may decrease. In such a case, although there is a sufficient amount of high-octane gasoline in the tank, the operation cannot be continued unless low-octane gasoline is supplied.
[0050]
In such a case, if you increase the consumption of high-octane gasoline, that is, if you use high-octane gasoline even in operation that originally uses low-octane gasoline, the consumption of high-octane and low-octane gasoline You should be able to adjust the balance.
[0051]
However, in actuality, depending on the combustion mode, if the octane number of the gasoline used changes, the combustion may be greatly affected. For example, in the low load operation region in the stratified charge combustion mode, the amount of fuel stratified in the combustion chamber is extremely small, so the air-fuel ratio of the stratified mixture becomes considerably low. For this reason, when high octane gasoline having a relatively low ignitability is used in the low load operation region in the stratified combustion mode, there is a possibility that problems such as misfire and defective combustion occur.
[0052]
On the other hand, the homogeneous combustion mode is relatively less susceptible to changes in the octane number of the fuel than the stratified combustion mode. For this reason, in the homogeneous combustion mode, in a region that is originally operated with low-octane gasoline, even if operation with high-octane gasoline is performed regardless of the load, no major problem occurs.
In this embodiment, the engine exhaust passage 50 is NO. _X The NOx storage reduction catalyst 70 is provided. _X NO stored in the storage reduction catalyst _X In order to reduce and purify the engine, it is necessary to periodically perform a rich spike operation in which the engine 100 is operated at a rich air-fuel ratio for a short time. Usually, in the rich air-fuel ratio operation, it is necessary to increase the amount of fuel supplied to the cylinder, so the combustion mode is switched to homogeneous combustion even during the stratified combustion mode operation.
[0053]
Normally, at the time of rich spike operation, the same fuel as that used at the previous lean air-fuel ratio operation is used. That is, when the rich spike operation is executed during the stratified combustion mode operation using the low octane gasoline, the low octane gasoline is also used during the rich spike operation.
[0054]
Therefore, in the present embodiment, for example, when the consumption of high octane gasoline is to be increased for fuel consumption balance adjustment, high spike operation performed during lean air-fuel ratio operation using low octane gasoline is high. Use octane gasoline. As described above, the combustion mode is switched to the homogeneous combustion mode that is not easily affected by the fuel octane number during the rich spike operation, and the fuel injection amount to the cylinder is increased in order to shift the air-fuel ratio to rich. For this reason, by using a high octane fuel during a rich spike, the consumption of high octane gasoline can be increased without significantly affecting combustion.
[0055]
Similarly, if the consumption of low-octane gasoline should be increased, the use of high-octane gasoline during the rich spike operation during lean air-fuel ratio operation using low-octane gasoline will have a significant impact on combustion. Without increasing the consumption of low octane gasoline.
[0056]
FIG. 3 is a flowchart for explaining the consumption balance control operation.
This operation is performed as a routine executed by the ECU 30 at regular intervals.
In the operation of FIG. 3, step 301 shows a determination of which gasoline is currently being used in which region the engine is operating. Which gasoline is currently used is determined from the relationship shown in FIG. 2 based on the engine shaft torque (or the accelerator pedal depression amount) and the engine speed.
[0057]
That is, in step 301, it is determined whether or not the current operation region is low octane gasoline. ("LRON" in step 301 is a low octane number (LOW
Means RESEARCH OCTANE NUMBER))
If it is determined in step 301 that the operation region is low-octane gasoline, the process proceeds to step 303 to determine whether the value of the flag XH is set to 1. XH is a flag indicating whether or not the consumption of high-octane gasoline should be increased for the current fuel consumption balance adjustment. In this embodiment, the value of the flag XH is set to XH = 1 (necessary to increase the consumption of high-octane gasoline) or XL = 0 (not necessary to increase the consumption) by the ECU 30 separately by a method described later.
[0058]
If XH = 1 in step 303, it is a region where the engine should be operated with low-octane gasoline at present, and the consumption of high-octane gasoline should be increased. _X NO stored by the storage reduction catalyst 70 _X When a rich spike operation is performed for reduction and purification of gasoline, high-octane gasoline is used to increase consumption of high-octane gasoline.
[0059]
That is, in step 307, it is determined whether or not the rich spike is currently being executed. XRS in step 307 is a flag indicating whether or not rich spike is being executed. When the value of XRS is set to 1, the ECU 30 is switched to the homogeneous combustion mode by the ECU 30 and the fuel injection amount is separately set. Is increased and the stoichiometric air-fuel ratio or rich air-fuel ratio is operated.
[0060]
If XRS = 1 in step 307, that is, if the rich spike is currently being executed, there is no risk of combustion deterioration even if high-octane gasoline is used, so the routine proceeds to step 309, where the fuel injection valve 110H increases from cylinder to cylinder. Inject octane gasoline. ("HRON" in step 309 represents a high octane number (HIGH RESEARCH OCCTENE NUMBER).) This increases the consumption of high octane number gasoline without deteriorating combustion.
[0061]
If it is not currently necessary to increase the consumption of high octane gasoline in step 303 at step 303, or if XRS ≠ 1, that is, no rich spike is currently being performed in step 307, the routine proceeds to step 305, where fuel injection is performed. Low-octane gasoline is injected from the valve 110L, and low-octane gasoline is supplied to the engine regardless of whether rich spike is being executed.
[0062]
On the other hand, if it is not the current low-octane gasoline operating region in step 301, that is, if the engine is currently operating in the high-octane gasoline operating region, the operations of steps 311 to 317 are performed.
The operation from step 311 to step 317 is almost the same as the operation from step 303 to 309. In this case, however, it is time to increase the consumption of low-octane gasoline (XL = 1 in step 311). The difference is that low octane gasoline is supplied to the engine only when the spike is being executed (step 315) (step 317), and high octane gasoline is supplied to the engine in other cases (step 313).
[0063]
When the consumption of the low octane gasoline is to be increased by the operations of steps 311 to 317, the fuel is switched to the low octane gasoline during the rich spike, and the consumption of the low octane gasoline increases without deteriorating the combustion.
[0064]
Next, another embodiment of the present invention will be described.
In the embodiment of FIG. 3, the fuel on the side whose consumption is to be increased only during the rich spike operation is used. However, in actual operation, a rich spike may be first performed at the start of engine acceleration. In order to increase the engine output during engine acceleration, switching to the lean or rich air-fuel ratio homogeneous combustion mode occurs when the engine load increases to a predetermined value even during acceleration from lean air-fuel ratio stratified combustion operation To do. For this reason, the engine air-fuel ratio may become a rich air-fuel ratio during acceleration, and NO _X NO stored in the storage reduction catalyst 70 _X May be released from the catalyst.
[0065]
Therefore, in this embodiment, the normal (NO) of FIG. _X NO stored in the storage reduction catalyst 70 _X (Based on the amount) In addition to the rich spike operation, when the engine starts acceleration, the rich spike operation is performed at the initial stage of acceleration, and NO _X NO stored in the storage reduction catalyst 70 _X Rich spike during acceleration to reduce and purify. Even when the engine operating air-fuel ratio becomes a rich air-fuel ratio during acceleration by performing a rich spike during acceleration, NO _X NO from the storage reduction catalyst 70 _X Is prevented from being released into the atmosphere.
[0066]
In the present embodiment, even when a rich spike operation during acceleration is performed, the fuel on the side whose consumption should be increased during the rich spike is used as in the embodiment of FIG. However, in the embodiment of FIG. 3, when the rich spike ends (when XRS ≠ 1), the used fuel is immediately returned to the fuel used before the start of the rich spike. The embodiment is different in that the use of the fuel whose consumption is to be increased is continued until the end of acceleration or until a predetermined condition is satisfied during acceleration. During engine acceleration operation, the load is higher than in normal operation and the fuel injection amount is increased. Therefore, fuel consumption can be effectively increased by using the fuel whose consumption should be increased during acceleration after the end of rich spike. The balance can be adjusted.
[0067]
If the consumption of high-octane gasoline should be increased, high-octane gasoline is used during the rich spike, but the engine output increases during subsequent acceleration, rather than returning to using low-octane gasoline after the rich spike operation. If you continue to use high-octane gasoline, you can get higher output and acceleration performance will improve. Therefore, in this case, it is preferable from the viewpoint of fuel consumption balance adjustment and engine output that the use of high-octane gasoline is continued until the acceleration is completed.
[0068]
Conversely, if the consumption of low-octane gasoline is to be increased, low-octane gasoline is used during rich spikes. Moreover, since the engine combustion mode is switched to homogeneous combustion during acceleration, low-octane gasoline can be used to some extent even during acceleration after a rich spike. Also, since the engine load increases during acceleration, it is preferable to return to the use of high-octane gasoline in order to suppress knocking, but in this case as well, combustion does not occur even if the use of low-octane gasoline is continued. The above problem does not occur.
[0069]
Therefore, in this embodiment, in order to increase the consumption of low-octane gasoline, if low-octane gasoline is used during rich spike operation before starting acceleration, the engine load increases during acceleration even after the rich spike ends. The use of low-octane gasoline is continued until the knock generation limit is reached.
[0070]
FIG. 4 is a flowchart similar to FIG. 3 for explaining the present embodiment. This operation is also performed as a routine executed by the ECU 30 at regular intervals.
FIG. 4, step 401 shows a determination as to which operation region currently uses high-octane gasoline or low-octane gasoline. This step is the same as step 301 in FIG. Also in this embodiment, for example, when the engine is operating in the operation region where low octane gasoline is currently used in step 401, whether or not the current use of high octane gasoline is to be increased in step 403 is determined. If it is not time to increase (XH ≠ 1), the low-octane gasoline is continued to be used regardless of the presence or absence of the rich spike (step 405).
[0071]
In step 403, when XH = 1, that is, when it is time to increase the use of high-octane gasoline, the routine proceeds to step 407, where it is determined whether a rich spike is currently being executed (XRS = 1). If it is during rich spike, high octane gasoline is supplied to the engine at step 409. If it is determined in step 407 that the rich spike is not currently being executed, the process proceeds to step 411, where it is determined whether the acceleration after the rich spike has ended or not. If the acceleration after the rich spike is still continuing, Step 409 is executed and high octane gasoline is continuously supplied to the engine.
[0072]
If both the rich spike and the subsequent acceleration are completed in step 411, low-octane gasoline is supplied to the engine according to the determination result in step 401 (step 405).
Next, when the engine is operating in the region where the high octane gasoline is currently used in step 401, the routine proceeds to step 413, where it is determined whether or not the current consumption of the low octane gasoline should be increased.
[0073]
Also in this case, when there is no need to increase the consumption of the low-octane gasoline, the high-octane gasoline is supplied to the engine at step 415.
If it is time to increase the consumption of low-octane gasoline at step 417, the presence or absence of rich spike is determined at step 417. If rich spike is being executed (XRS = 1), the amount is reduced at step 419. Octane gasoline is supplied to the engine.
[0074]
When the rich spike is not executed in step 417 (XRS ≠ 1), the process proceeds to step 421, where it is determined whether or not the acceleration after the rich spike is currently being executed. If the operation has been completed), the process proceeds to step 415 to return to operation with high-octane gasoline.
[0075]
If acceleration is currently being executed in step 421, the process proceeds to step 423, and whether or not the current load state is a region where low octane number gasoline can be used, that is, the engine load condition is low octane number gasoline. It is determined whether or not the knock generation limit when used is reached.
[0076]
Here, for example, as shown by a dotted line B in FIG. 2, the knock occurrence limit is a value that is slightly larger than the upper limit load at which normal low-octane gasoline can be used. If the engine load is lower than the dotted line B in FIG. 2 in step 423, knocking does not occur even if low octane gasoline is used, so the low octane gasoline continues to be used during acceleration. Thereby, it becomes possible to increase the consumption of low octane gasoline and to efficiently adjust the balance of fuel consumption.
[0077]
Note that the use of low-octane gasoline ends when acceleration ends in step 421 or when it is determined in step 423 that the engine load has reached the knock limit indicated by the dotted line in FIG. Fuel is supplied to the engine (step 415).
[0078]
Next, the setting of the flags XH and XL in FIGS. 3 and 4, that is, the determination of whether or not the consumption amount of either high octane gasoline or low octane gasoline should be increased will be described.
In the present embodiment, the low octane gasoline remaining amount RL and the high octane gasoline remaining in the tank detected by the fuel remaining amount sensors 12L and 12H provided in the low octane gasoline tank 11L and the high octane gasoline tank 11H, respectively. Based on the value of the ratio RL / RH with respect to the amount RH, the determination of the fuel consumption balance, that is, whether or not the current consumption amount of any one of the fuels should be increased is determined.
[0079]
FIG. 5 is a flowchart for explaining the fuel consumption balance determination operation of the present embodiment. This operation is performed as a routine executed by the ECU 30 at regular intervals.
In the operation of FIG. 5, first, in step 501, the remaining amount RL in the low octane number gasoline tank 11L and the remaining amount RH in the high octane number gasoline tank 11H are read from the outputs of the fuel remaining amount sensors 12L and 12H.
[0080]
In step 503, the value of the ratio RL / RH between RL and RH is calculated, and whether or not the ratio RL / RH exceeds a predetermined upper limit value α (α is a constant larger than 1 in this embodiment). Determined.
If RL / RH> α in step 503, the remaining amount of low-octane gasoline is greater than the remaining amount of high-octane gasoline. It is necessary to balance.
Therefore, in this case, the process proceeds to step 505, the value of the low octane gasoline consumption increase flag XL is set to 1, and the process proceeds to step 509.
[0081]
On the other hand, if RL / RH ≦ α in step 503, it is not necessary to increase the consumption of low-octane gasoline. Therefore, after setting the value of the flag XL to 0 in step 507, the process proceeds to step 509.
In steps 509 to 513, it is determined whether or not the value of the ratio RL / RH has reached a predetermined lower limit value β (in this embodiment, β = 1 / α is set). If RL / RH <1 / α in step 509, that is, the remaining amount of low-octane gasoline is smaller than the remaining amount of high-octane gasoline, the consumption of high-octane gasoline is increased and both It is necessary to balance consumption.
[0082]
In this case, the process proceeds to step 511, where the value of the high octane gasoline consumption increase flag XH is set to 1, and the operation is terminated. If RL / RH ≧ 1 / α, the value of XH is set to 0 in step 513.
That is, in the operation of FIG. 5, when the value of the ratio RL / RH is larger than the upper limit α, the flag XL value is set to 1 and the XH value is set to 0 to increase the consumption of low-octane gasoline. When the operation is performed and the value of RL / RH is smaller than the lower limit value 1 / α, the value of flag XH is set to 1 and the value of XL is set to 0 to increase the consumption of high-octane gasoline. Is called.
[0083]
When the value of the ratio RL / RH is 1 / α ≦ RL / RH ≦ α, the flags XL and XH are both set to 0, and the fuel consumption increase operation is not performed.
In the embodiment of FIG. 5, the upper limit value α and the lower limit value α are fixed, but the value of α can be corrected by learning the operation pattern of the engine 1. For example, when the engine 1 is operated in an operation pattern that uses a large amount of high-octane gasoline, the frequency of operations for increasing the consumption of low-octane gasoline is executed in order to maintain a good balance between the consumption of both fuels. It is preferable to increase the number.
[0084]
Therefore, for example, from the change in the remaining amount of fuel in the tank detected by the remaining fuel amount sensors 12H and 12L, the consumption rate of high octane gasoline (m ^Three / Hr) and the consumption rate of low-octane gasoline is greater than a predetermined value, that is, when the consumption rate of high-octane gasoline is greater than the consumption rate of low-octane gasoline, α is decreased by a certain amount. It can also be done. As a result, the frequency at which RL / RH> α is established in step 503 in FIG. 5 increases, and the frequency of operations for increasing the consumption of low-octane gasoline increases, so the consumption rate of low-octane gasoline increases and both The difference in fuel consumption is reduced. Therefore, by reducing the value of α by a certain amount until the difference between the consumption rates of both fuels falls within a predetermined allowable range, it is possible to maintain a good balance between the consumption rates of both fuels.
[0085]
If the consumption rate of low-octane gasoline is greater than that of low-octane gasoline, the consumption rate is similarly increased by increasing the lower limit value 1 / α (that is, by reducing α in this case as well). Good balance can be maintained.
[0086]
In the above-described embodiment, as shown in FIG. 1, the high-octane gasoline injection valve 110H and the low-octane gasoline injection valve 110L that inject fuel directly into each cylinder are provided. It is also possible to configure one or both of them as a port injection valve that injects fuel into each cylinder intake port.
[0087]
In the above-described embodiment, the fuel injection valve 110H that injects high-octane gasoline and the fuel injection valve 110L that injects low-octane gasoline are individually provided. However, the type of fuel to be injected includes a plurality of fuel systems. It is also possible to provide a single fuel injection valve capable of switching between the cylinders.
[0088]
【The invention's effect】
According to the invention described in each claim, when high-octane fuel and low-octane fuel are supplied to the engine according to the engine operating conditions, the engine performance and the exhaust properties are not significantly deteriorated, but efficiently. There is a common effect that it is possible to maintain a good balance between the consumption amounts of both fuels.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an internal combustion engine for a vehicle.
FIG. 2 is a diagram showing an example of switching between a fuel to be used and a combustion mode according to a load condition of the engine of FIG. 1;
FIG. 3 is a flowchart illustrating an embodiment of a fuel consumption balance control operation.
FIG. 4 is a flowchart illustrating an embodiment different from FIG. 3 of the fuel consumption balance control operation.
FIG. 5 is a flowchart illustrating an embodiment of a fuel consumption balance determination operation.
[Explanation of symbols]
11H… High octane gasoline tank
11L ... Tank for low octane gasoline
12H, 12L ... Fuel level sensor
30 ... Electronic control unit (ECU)
70 ... NO _X Occlusion reduction catalyst
100 ... Internal combustion engine body
110H, 110L ... Fuel injection valve

Claims (5)

When the air-fuel ratio of the exhaust gas flowing into the NO _X in the exhaust gas adsorption, which selectively absorbing held by absorption, or both at the time of the lean air-fuel ratio of the exhaust flowing becomes stoichiometric or rich air-fuel ratio , the occluded NO _X and provided with _the NO _X storage reduction catalyst to reduce and purify using reducing components in the exhaust gas in the exhaust system, reducing the _the NO _X storage reduction catalyst occluded the NO _X during the lean air-fuel ratio operation purification Select one of high-octane fuel and low-octane fuel according to the engine load conditions for an internal combustion engine that performs a rich spike operation that temporarily operates the engine at the stoichiometric or rich air-fuel ratio. A fuel supply device for an internal combustion engine,
When the consumption of one of the high-octane fuel and the low-octane fuel should be increased in order to adjust the consumption balance of both the fuels, the engine may use the high-octane fuel and the low-octane fuel. During the rich spike operation during the lean air-fuel ratio operation using the other fuel, the one fuel is supplied to the engine.
A fuel supply device for an internal combustion engine. When the consumption of high-octane fuel is to be increased and the engine is accelerated following the rich spike operation, the high-octane fuel is supplied to the engine until the acceleration operation is completed. Item 2. A fuel supply device for an internal combustion engine according to Item 1. When the consumption of low-octane fuel is to be increased and the engine is accelerated following the rich spike operation, the engine is brought into a predetermined load state during acceleration after the rich spike operation is completed. The fuel supply device for an internal combustion engine according to claim 1, wherein the low-octane fuel is supplied to the engine until it reaches. And a fuel tank for storing the high-octane fuel and the low-octane fuel supplied to the engine, respectively. When the ratio to the remaining amount is equal to or greater than a predetermined upper limit value, it is determined that the consumption amount of the one fuel should be increased in order to adjust the fuel consumption balance. Item 4. The fuel supply device for an internal combustion engine according to any one of Items 3 to 3. 5. The learning operation according to claim 4, further comprising: performing a learning operation for changing the upper limit value so that the consumption rates of both fuels approach each other based on the consumption rate of the high-octane fuel and the consumption rate of the low-octane fuel. A fuel supply device for an internal combustion engine.

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