Internal combustion engine provided with double system of fuel injection

A double system of fuel injection type internal combustion engine includes: a direct injection injector and a port fuel injection injector; a control unit for changing a fuel injection distribution ratio of fuels injected from these injectors; a delivery pipe for the direct injection injector; a high pressure fuel pump; a fuel pressure sensor and a fuel temperature sensor for detecting a fuel pressure and a fuel temperature in the delivery pipe; and a fuel regulating unit for regulating the fuel pressure and fuel temperature in the delivery pipe. The control unit can control the fuel regulating unit so as to lower the exceeding value thereof when the fuel injection distribution ratio of the port fuel injection injector is higher than that of the direct injection injector and at least one of the fuel pressure value and fuel temperature value exceeds an aimed value.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-080697 filed on Mar. 18, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an internal combustion engine provided with double system of fuel injection including a direct injection (DI) system and a port fuel injection (PFI) system.

2. Related Art

In a conventional art, there is known, in a fuel supply system for supplying a high pressure fuel to an injector through a delivery pipe from a high pressure fuel pump, a fuel supply device adapted to connect a mechanical pressure control valve to the delivery pipe. In such fuel supply device, when the fuel pressure in the delivery pipe exceeds over a predetermined pressure, the pressure control valve is opened to thereby discharge the fuel from the delivery pipe to reduce the fuel pressure in the delivery pipe to be less than the predetermined pressure.

However, in such a mechanical pressure control valve as mentioned above, in order to remove, in a short time, the fuel in the form of vapor generated in a fuel supply line, it was necessary to reduce the pressure in the delivery pipe through the fuel injection of the injector, which requires an unnecessary fuel injection for the pressure reduction.

Because of this reason, it is considered that the pressure in the delivery pipe is reduced by forcibly opening the pressure control valve. Such technology is, for example, disclosed in Japanese Laid-open patent (KOKAI) Publication No. HEI 10-054318 concerning a double system of fuel injection type internal combustion engine.

In this publication, there is disclosed a fuel injection type internal combustion engine for reducing a pressure by means of an electromagnetic high pressure regulator (relief valve), which is to be opened by an input signal at a time of requiring a pressure reduction in the delivery pipe or for avoiding a pressure increase in the delivery pipe.

It is also disclosed in this publication that the pressure in the delivery pipe can be promptly made to a reduced pressure state from the high pressure state at a time of requiring no fuel injection such as at a shift-up time of a vehicle mounted with an automatic speed-variable transmission or at an accelerator pedal releasing time.

However, such fuel injection type internal combustion engine is an engine in which the fuel in the delivery pipe is discharged for reducing the fuel pressure, and accordingly, it may be said to be related to a single system fuel injection type internal combustion engine equipped only with either one of the direct injection injector and port fuel injection injector. In this meaning, the above prior art publication does not consider the characteristics of a double system of fuel injection equipped with both the direct injection injector and the port fuel injection injector.

Here, if the structure in which valve portion in such conventional fuel injection type internal combustion engine is driven by the electromagnetic drive is applied as it is to the direct fuel injection injector of the double system of the fuel injection, there may cause a problem at a time when the fuel injected from the port fuel injection injector is fully (100%) used, and on the other hand, the fuel injected from the direct injection injector is not (0%) used (that is, in a state that the direct injection injector is not operated). For example, in an event that the fuel stays without being injected in the direct injection delivery pipe for supplying the fuel in the direct injection injector, the fuel is apt to be highly pressurized and highly heated through the heat transfer from the internal combustion engine. At this time, although the pressure in the delivery pipe may be reduced by the operation of the relief valve, the fuel expands because of the heat increase and the fuel density becomes lower, and if such a low density fuel is injected from the direct injection injector, there is a fear of injection of lean mixed fuel.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a double system of fuel injection type internal combustion engine capable of always ensuring an optimum pressure and temperature of a fuel in a direct injection injector and improving air/fuel mixture performance at the time of fuel injection through the direct injection injector.

This and other objects can be achieved according to the present invention by providing a double system of fuel injection type internal combustion engine comprising:

a direct injection injector;

a port fuel injection injector;

a control unit for changing an fuel injection distribution ratio of fuels injected from the direct injection injector and port fuel injection injector in accordance with an operating condition of the engine;

a delivery pipe connected to the direct injection injector so as to supply the fuel to the direct injection injector;

a high pressure fuel pump for supplying the fuel under pressure to the direct injection injector through the delivery pipe;

a fuel pressure sensor for detecting a fuel pressure in the delivery pipe;

a fuel temperature sensor for detecting a fuel temperature in the delivery pipe; and

a fuel regulating unit for regulating the fuel pressure and fuel temperature in the delivery pipe,

wherein at a time when the fuel injection distribution ratio of the port fuel injection injector is higher than that of the direct injection injector and at least one of the fuel pressure value and fuel temperature value detected respectively by the fuel pressure sensor and the fuel temperature sensor exceeds over an aimed value, the control unit controls the fuel regulating unit so as to lower the exceeding value thereof.

In a preferred embodiment of the above aspect of the present invention, the control unit will judge that the port fuel injection injector has the fuel injection distribution ratio higher than that of the direct injection injector and control the fuel regulating unit at a time when the fuel injection distribution ratio of the port fuel injection injector is of 100% or near.

The fuel regulating unit may be incorporated with a first flow control valve disposed to a fuel supply line for supplying the fuel in a fuel tank of the engine to the delivery pipe of the direct injection injector and a second flow control valve disposed to a fuel return line for returning the fuel from the direct injection delivery pipe to the fuel tank.

The high pressure fuel pump may be operated in an event of the fuel injection distribution ratio of 100% of the port fuel injection injector, in which the first flow control valve is operated so as to stop the fuel supply to the direct injection delivery pipe, and on the other hand, when either one of the fuel pressure or the fuel temperature in the direct injection delivery pipe exceeds over the aimed value, the second flow control valve is operated as well as the first flow control valve so as to circulate the fuel in the direct injection delivery pipe.

It is desired that the second flow control valve is an electromagnetic relief valve.

According to the above characters of the present invention, the control units control the fuel regulation unit so as to lower the fuel pressure value and/or fuel temperature value at a time when the fuel injection distribution ratio of the port fuel injection injector is higher than that of the direct injection injector and at least one of the fuel pressure value and fuel temperature value detected respectively by the fuel pressure sensor and the fuel temperature sensor exceeds over an aimed value. Accordingly, at the time when the fuel is mainly injected from the port fuel injection injector, the fuel staying in the direct injection delivery pipe is heated by the heat from the internal combustion engine, and when the detected fuel pressure exceeds over the aimed value, the fuel will leak through the injection port of the direct injection injector or through the seal portion to the delivery pipe, and on the other hand, when the detected fuel temperature exceeds over the aimed value, the fuel expands and the fuel density is excessively lowered, so that the fuel regulating unit serves to lower the fuel pressure and/or fuel temperature to the steady and stable state. Thus, the fuel pressure and the fuel temperature in the direct injection delivery pipe can be always ensured to be steady and stable, thus improving the air/fuel mixture performance at the injection time of the direct injection injector.

According to the preferred embodiment, the control unit controls the fuel regulating unit at a time when the fuel injection distribution ratio of the port fuel injection injector is of 100% or near. Accordingly, in the case where the fuel is mainly injected through the port fuel injection injector and is less injected through the direct injection injector, the control unit controls the fuel regulation unit. Thus, for example, an event such that the fuel stays in the direct injection delivery pipe and is highly pressurized and highly heated therein can be avoided.

Moreover, in another preferred embodiment in which the flow regulating unit is incorporated with a first and second flow control valve. The fuel staying in the direct injection delivery pipe can be prevented from being highly pressurized and heated by the heat transfer from the internal combustion engine by opening the first and second flow control valves to circulate the fuel in the direct injection delivery pipe. Accordingly, the fuel in the direct injection delivery pipe can be always maintained at appropriate pressure and temperature.

Furthermore, in still another preferred embodiment, in an event of the fuel injection distribution ratio of 100% of the port fuel injection injector, the first flow control valve is operated so as to stop the fuel supply to the direct injection delivery pipe, and on the other hand, when either one of the fuel pressure or the fuel temperature in the direct injection delivery pipe exceeds over the aimed value, the second flow control valve is operated. Therefore, in an event of the fuel injection distribution ratio of 100% of the port fuel injection injector, the first flow control value is closed so as to stop circulation of the fuel in the direct injection delivery pipe. In an event that either one of fuel pressure or fuel temperature exceeds over the aimed value, the fuel in the direct injection delivery pipe circulates so that fresh fuel flows into there. Accordingly, the fuel can be always surely maintained in the direct injection delivery pipe to be stable and steady.

In addition, in another preferred embodiment, an electromagnetic relief valve may be utilized as the second flow control valve. Accordingly, in comparison with a mechanical relief valve, the electromagnetic relief valve can be easily opened or closed precisely. Then, in the opened state of the electromagnetic relief valve, the highly pressurized and heated fuel in the direct injection delivery pipe is discharged and in the closed state, the fresh stable fuel is introduced into the direct injection delivery pipe and then stays therein.

Moreover, when such electromagnetic relief valve is subjected to the open/close control by a PWM (Pulse Width Modulation) controlling, the duty ratio is regulated and the flow amount of the fuel due to the repeated open/close operation of the electromagnetic relief valve is made equal to the flow amount of the fuel in the half-opened state between fully opened state and fully closed state. Therefore, the fuel amount in the direct injection delivery pipe can be finely adjusted.

DESCRIPTION OF THE PREFERRED EMBODIMENT

One preferred embodiment according to the present invention will be described hereunder.

With reference toFIGS. 1 to 6, reference numeral11denotes a 6-cylinder engine as a double system of fuel injection type internal combustion engine (which may be called hereinlater merely “engine”) of the present invention, in which an intake port13and an exhaust port14are connected to each of the cylinders12, which is in addition provided with a direct injection-type injector (DI injector)15and a port fuel injection-type injector (PFI injector)16.

The fuel is directly injected into the cylinder, i.e., combustion chamber,12from the DI injector15and is then mixed with air in the cylinder12, and in addition, the fuel is injected into the intake port13through the PFI injector16and is then mixed with air passing in the intake port13. The thus mixed fuel is sucked in the cylinder12and burnt therein by an ignition of an ignition plug, not shown, at a predetermined timing.

Further, each of the cylinders12is also provided with an intake valve18for opening or closing the intake port and an exhaust valve19for opening or closing the exhaust port, and by opening the intake valve18, a clean air is introduced into the cylinder12, i.e. combustion chamber, from a serge tank20through the intake port13.

As shown inFIGS. 1 to 4, the respective DI injectors15arranged for the respective cylinders12are coupled with each other through direct injection delivery pipes (DI delivery pipes)23, and the respective PFI injectors16are also coupled with each other through port fuel injection delivery pipes (PFI delivery pipes)24. The DI delivery pipes23are connected through a direct injection conduit (DI conduit)26so that the injected fuel circulates to a fuel tank28, and the PFI delivery pipes24are connected to the fuel tank28through an intake pipe injection conduit (PFI conduit)27.

As shown inFIG. 4, the fuel is delivered, at a predetermined high pressure, to the DI delivery pipe23by means of a fuel pump31and a high pressure pump32, and the fuel is also delivered, at a pressure lower than that of the DI delivery pipe side, to the PFI delivery pipe24by means of the fuel pump31. For the DI injector15, in order to directly inject the fuel in the highly pressurized cylinder12, a high pressure is required.

These injectors15and16inject the fuel, at a predetermined amount, delivered at the predetermined fuel pressure by the fuel pumps31and32by valves, not shown, by a predetermined injecting time period.

These injectors15and16are connected to an engine control unit (ECU)35as control means so as to control opening (or closing) timing and opening (or closing) time interval of the valves. According to this arrangement, the fuel is injected from both the injectors15and16at a fuel injection distribution (divided) ratio. The fuel injection distribution ratio of the fuel from the injectors15and16can be changed in accordance with the engine operating condition. The fuel injection distribution ratio is a ratio of fuel injected from each injector15,16to the total fuel injected from both DI injector15and PFI injector16. For example, if the fuel injection distribution ratio of the PFI injector16is 80%, the fuel injection distribution ratio of the DI injector is 20%.

A fuel pressure sensor36arranged to the DI delivery pipe23as fuel pressure detection means and a fuel temperature sensor37arranged thereto as fuel temperature detection means are connected to the ECU35. An engine revolution speed (number) sensor38for detecting the revolution of six-cylinder engine and an engine load sensor39for detecting the engine load are also connected to the ECU35. According to this arrangement, the fuel pressure in the DI delivery pipe23is detected by the fuel pressure sensor36, and the fuel temperature therein is detected by the fuel temperature sensor37. The operating condition of the engine, i.e. six-cylinder engine, is also detected by the engine revolution sensor38and the engine load sensor39.

As the engine load sensor39, a sensor for detecting intake air amount will be utilized, and in an alternation, a sensor for detecting an accelerator opening or a sensor for detecting an intake negative pressure may be utilized.

Various kinds of actuators41may be incorporated for the ECU35so as to be controlled or regulated by signals from the ECU35.

A high pressure fuel pump flow (flow rate) control valve43(first flow control valve) as fuel adjusting means is disposed on the inlet side of the DI delivery pipe23in the DI conduit26as a fuel feed line from the fuel tank28to the DI delivery pipe23. On the other hand, an electromagnetic relief valve44(second flow control valve) as fuel adjusting means is disposed on the outlet side of the DI delivery pipe23in the DI conduit26as a fuel return line for returning the fuel in the DI delivery pipe23to the fuel tank28.

The ECU35hence operates to change the fuel pressure in accordance with the engine operating condition and control the fuel injection amount as well.

The six-cylinder engine11of this embodiment will operate in the following manner.

FIG. 4is a block diagram showing the fuel feed or supply line in the six-cylinder engine, andFIG. 5is a flowchart representing the controlling of the high pressure fuel pump flow control valve43and electromagnetic relief valve44.

With reference toFIGS. 4 and 5, the ECU35reads in detection data detected by the engine revolution sensor38and the engine load sensor39in connection with the engine revolution speed and engine intake air amount, respectively (step S101).

Next, the ECU35reads in the fuel injection distribution ratio of the DI injector15and the PFI injector16(step S102) after calculates them. Although the high pressure fuel pump32is operated at both the fuel injection distribution ratio of the PFI injector16of 100% and less, the high pressure fuel pump32operates, at the fuel injection distribution ratio of 100%, such that the flow control valve43of the high pressure fuel pump is closed so as to stop the fuel supply to the DI delivery pipe23.

The ECU35also serves to judge whether the fuel injection distribution ratio of the PFI injector16is within a preliminarily predetermined range from N % to 100% (step S103). In the described embodiment, in the case of N=80%, for example, the ECU35judges that the fuel injection distribution ratio of the PFI injector16is high. On the other hand, in the case of “NO” in the judgment, the operation returns to the step S101, and in the case of “YES” in the judgment, the fuel pressure for the DI detected by the fuel pressure sensor36and the fuel temperature for the DI detected by the fuel temperature sensor37are read in (step S104).

Then, the ECU35judges whether an actual pressure of the fuel staying in the DI delivery pipe23is larger than an aimed fuel pressure for DI (step S105). In this judgment, in the case of “YES”, the electromagnetic relief valve44is operated to be opened by the PWM (Pulse Width Modulation) control through the regulation of the duty ratio in response to the degree of the fuel pressure (step S107), and moreover, the flow rate control valve43of the high pressure fuel pump32is operated to be opened by the PWM control through the regulation of the duty ratio (step S108) to thereby circulate the fuel in the DI delivery pipe23and flow in the fuel in the steady condition to thereby return the step S101. On the contrary, in the case of “NO” in this judgment, it is judged whether the actual fuel temperature is larger than an aimed fuel temperature for the DI (step S106).

Thus, the ECU35judges whether the actual temperature of the fuel staying in the DI delivery pipe23is higher than the aimed fuel temperature for the DI (step S106). In this judgment, in the case of “YES”, the step returns to the step S101through the steps S107and S108, and on the contrary, in the case of “NO”, the controlling process is ended.

That is, the ECU35serves to open the high pressure fuel pump flow (rate) control valve43and the electromagnetic relief valve44(steps S107and S108) and then to circulate the fuel in the case where the port fuel injection injector16has a high fuel injection distribution ratio (“YES” in the step S103) and either one of the fuel pressure detected by the fuel pressure sensor36and the fuel temperature detected by the fuel temperature sensor37exceeds over the aimed value (“YES” in the step S105and “YES” in the step S106).

The open/close control of the electromagnetic relief valve44is performed by the PWM control to thereby finely adjust stepwise the degree of opening of the electromagnetic relief valve44.

Further, in the manner such that the electromagnetic relief valve44is controlled to be opened or closed through the PWM control so that opening amount of the electromagnetic relief valve44is finely adjusted in a phased manner.

For example, as shown inFIG. 6A, when opening or closing of the electromagnetic relief valve44is controlled by PWM control and by conducting a current of the duty ratio of 50%, the fuel in the DI delivery pipe23is gently guided to the DI conduit26so as not to rapidly lower the fuel pressure in the DI delivery pipe23as shown inFIG. 6B. On the contrary, in the case where the electromagnetic relief valve44is subjected to the PWM control and a current passes as shown inFIG. 6C, the fuel pressure is rapidly lowered as shown inFIG. 6D.

According to the six-cylinder engine11of the characters mentioned above, in the case where the fuel injection distribution ratio of the port fuel injection injector16is high (high value) and the fuel pressure detected by the fuel pressure sensor36and the fuel temperature detected by the fuel temperature sensor37are high (high values), the ECU35serves to operate the electromagnetic relief valve44to lower these values. Because of this reason, in the case where the fuel is injected through the PFI injector16, the fuel staying in the DI delivery pipe23is heated by the heat transferred from the six-cylinder engine11and the fuel pressure detected by the fuel pressure sensor36becomes higher than the aimed value of the fuel pressure. In such a case, the fuel may leak through the injection port of the DI injector15and the sealed portion to the DI delivery pipe23. When the fuel temperature detected by the fuel temperature sensor37becomes higher than the aimed value of the fuel temperature, the fuel expands and the fuel density will become excessively lowered. Then, the electromagnetic relief valve44operates to make the high fuel pressure and high fuel temperature stable and steady, and the fuel returns to the fuel tank28so as to be again usable in the steady state. Thus, according to the present embodiment, the fuel can be always maintained at its suitable pressure and temperature in the DI delivery pipe23and the air/fuel mixture performance at the fuel injection time in the DI system can be hence improved.

Furthermore, the ECU35serves to control the electromagnetic relief valve44in the case where the fuel injection distribution ratio of the PFI injector16is 100% or near. Thus, the fuel is mainly injected through the PFI injector16and is substantially less injected through the DI injector15, the ECU35controls the electromagnetic relief valve44. Therefore, for example, the ECU35serves to prevent the fuel from staying in the DI delivery pipe23and from being highly pressurized and highly heated therein in the case where the PFI injector16is mainly driven and the DI injector is substantially not driven.

Moreover, the six-cylinder engine11of the present embodiment is provided with the high pressure fuel pump flow rate control valve43and the electromagnetic relief valve44. Accordingly, it can be possible to prevent the fuel staying in the DI delivery pipe23from being highly pressurized and highly heated by the heat transfer from the six-cylinder engine11by circulating the fuel in the DI delivery pipe23by opening the high pressure fuel pump flow rate control valve43and the electromagnetic relief valve44. Thus, the fuel can be always kept in the Dl delivery pipe23at the suitable pressure and temperature.

In addition, the ECU35serves to operate the flow rate control valve43of the high pressure fuel pump32so as to stop the supply of the fuel to the DI delivery pipe23at the fuel injection distribution ratio of 100% of the PFI injector16, and also serves to operate the electromagnetic relief valve44so as to circulate the fuel in the DI delivery pipe23at the time when at least one of the fuel pressure and the fuel temperature in the DI delivery pipe23exceeds over the aimed value. Because of this reason, at the time when the fuel injection distribution ratio of 100% of the PFI injector16, the high pressure fuel pump flow rate control valve43is closed to thereby stop the circulation of the fuel in the DI delivery pipe23, and on the other hand, at the time when either one of the fuel pressure and the fuel temperature exceeds over the aimed value, the fuel in the DI delivery pipe23circulates and fresh fuel is introduced, thus always ensuring the fuel in the steady and stable state.

Further, the open/close operation of the electromagnetic relief valve44is apt to be carried out more easily than in the use of a mechanical relief valve, and accordingly, in the opened state of the electromagnetic relief valve44, the fuel highly pressurized and heated in the DI delivery pipe23is released, and in the closed state thereof, the fresh fuel in the steady state is introduced into the DI delivery pipe23and stays there.

When the open/close control of the electromagnetic relief valve44is performed through the PWM control, the flow rate of the fuel in the repeated open/close control thereof can be made equal to the fuel flow rate in the half-opened state between the full opened and full closed states. Therefore, the fuel amount in the DI delivery pipe23can be finely regulated, and the fuel can be returned little by little to the fuel tank28.

For example, although in the described embodiment of the internal combustion engine, one DI injector15and one PFI injector16are provided for each cylinder12, the present invention is not limited to this embodiment and may provide a modification in which one DI injector15is provided for each cylinder12, a plurality of cylinders are connected to one intake pipe to supply air thereto, and one PFI injector16is connected to this intake pipe to thereby introduce the air/fuel mixture injected from the one PFI injector15to the cylinders12, respectively.