Split engine operation of closed loop controlled multi-cylinder internal combustion engine with air-admission valve

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BACKGROUND OF THE INVENTION

This invention relates to an engine control system and, in particular, to a charge forming device to effect split engine operation of a closed loop controlled multi-cylinder internal combustion engine.

Closed loop or feed back control of a multi-cylinder internal combustion engine is known in which the quantity of fuel fed to the engine is controlled in response to the output from an oxygen sensor, which detects the oxygen concentration of the exhaust gases discharged from all cylinders of the engine, in order to maintain the air fuel ratio of the mixture to be supplied to the engine at stoichiometry to cause a three-way catalytic converter, in the engine exhaust system, to operate most efficiently.

It is also known to operate a multi-cylinder internal combustion engine by suspending the supply of fuel to selected cylinders, less than the total number, to render them inactive and by increasing the load on the remaining active cylinders to operate them efficiently under high load conditions to improve the fuel economy of the engine.

This is known as split engine operation. Applying this split engine operation to a closed loop controlled internal combustion engine provided with a three-way catalytic converter will cause the air fuel ratio of the exhaust gases to deviate considerably from stoichiometry toward the lean side when the engine is shifted into split engine operation mode because at this engine operation mode the exhaust gases discharged from the active cylinders will be diluted with air discharged from the remaining inactive cylnders.

As a result, the quantity of fuel to the active cylinders will be increased excessively in accordance with the output from the oxygen sensor which represents the oxygen concentration of the exhaust gases containing oxygen from the air discharged from the inactive cylinders, thereby to deteriorate the driveability, thus worsening the fuel economy of the engine.

In order to prevent this, it is known to maintain the intake and exhaust valves for the inactive cylinders in their closed conditions to prevent air induction and air discharge by these cylinders. With this, overenrichment of the air fuel mixture charge to the active cylinders will be prevented and the pumping loss by the inactive cylinders will be reduced. The problem encountered in this known system is that since the inactive cylinders operate with their intake and exhaust valves in closed conditions, the pistons are likely to suffer from compression loss.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an engine control system with a charge forming device adapted to effect split engine operation by preventing supply of fresh air to the inactive cylinders and by recirculating substantially all of the exhaust gases discharged from these inactive cylinders back into these inactive cylinders, thereby to prevent dilution of the exhaust gases discharged from the remaining active cylinders with gases discharged from the inactive cylinders and thereby to prevent the compression loss of the inactive cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a first preferred embodiment of an engine control system according to the invention;

FIG. 2 is a schematic view of the air admission valve, the exhaust gas recirculation (EGR) valve and their control diagram in the system shown in FIG. 1;

FIG. 3 is a schematic view of another example of the induction system with another example of the air admission valve;

FIG. 4 is a schematic view of the induction system similar to that of FIG. 2 showing still another example of the air admission valve;

FIG. 5 is a schematic view of a second preferred embodiment of an engine control system according to the invention showing the air admission valve, two EGR valves and their control diagram in this system; and

FIG. 6 is a schematic view of a third preferred embodiment in an engine control system according to the invention showing the air admission valve, the EGR valve, the shut off valve and their control diagram of this system .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, the first preferred embodiment will be described. In this embodiment, a multi-cylinder internal combustion engine 1 is employed which has six cylinders divided into two groups, one group consisting of three cylinders #1 to #3 and the other group consisting of the remaining three cylinders #4 to 6. These cylinders #1 to #6 are supplied by separate fuel injectors 2a to 2f, respectively.

An induction system 3 has a common chamber divided by a partition 5 into a first sub-chamber 3a and a secnd sub-chamber 3b. The first sub-chamber 3a has three runner passages 4a, 4b and 4c extending toward the cylnders #1, #2 and #3 and communicating with an air induction passage in which a throttle valve 3c is rotatably mounted. The second sub-chamber 3b has three runner passages 4d, 4e and 4f extending toward the cylinders #4, #5 and #6. The partition 5 is formed with an opening 6 which establishes air flow communication between the two sub-chambers 3a and 3b. An air admission valve 7 is provided to open or close the opening 6.

Under the control of fuel injection control unit 8, the three fuel injectors 2a, 2b and 2c are operated to discharge fuel to the corresponding three cylinders #1, #2 and #3 through the whole engine operating condition, but, the remaining three fuel injectors 2d, 2e and 2f are rendered inoperable to suspend supply of fuel to the corresponding remaining three cylinders #4, #5 and #6 during a predetermined engine operating condition.

An exhaust system 10 includes a first exhaust passage 10b leading from the three cylinders #1, #2 and #3 and a second exhaust passage 10b leading from the remaining three cylinders #4, #5 and #6. The first exhaust passage 10a joins the second exhaust passage 10a.

An oxygen sensor 11 is mounted in the exhaust system 10 at a location preferably downstream of the junction at which the first exhaust passage 10b joins the second exhaust passage 10a. A three-way catalytic converter 12 is connected to the exhaust system 10 at a location downstream of the oxygen sensor 11. Output from the oxygen sensor 11, which represents the oxygen concentration of the exhaust gases within the exhaust systen 10 at the location downstream of the junction, is fed to an air fuel ratio control unit 13 which compares the output from the oxygen sensor 11 with a target value to provide a deviation signal. The deviation signal is fed to the fuel injection control unit 8 where the quantity of fuel to be injected per each injection is determined so as to reduce the deviation signal to zero.

The fuel injection control unit 8 includes a circuit means responsive to engine load for providing a 3-cylinder mode operation command signal when the engine operates under light load. When the 3-cylinder mode operation command signal appears, supply of a fuel injection pulse signal to the three fuel injectors 2d, 2e and 2f will be cut off, thereby to render the cylinders #4, #5 and #6 inactive.

An exhaust gas recirculation (EGR) system 14 includes an exhaust gas recirculation (EGR) passage 14a leading from the second exhaust passage 10a to the sub-chamber 3b to recirculate the exhaust gases discharged from the three cylinders #4, #5 and #6 to the sub-chamber 3b. An exhaust gas recirculation (EGR) valve 15 is provided to control flow of exhaust gases through the exhaust gas recirculation passage 14a.

An actuator means 9 is provided for urging the air admission valve 7 to take a closed condition and the EGR valve 15 to take a fully open condition when the 3-cylinder mode operation command signal appears.

As best seen in FIG. 2, the actuator means 9 includes a diaphragm device 16 for the air admission valve 7, a diaphragm device 17 for the EGR valve 15, and a solenoid operable valve 18 responsive to the 3-cylinder mode operation command signal. FIG. 2 shows the closed condition of the air admission valve 7 and the fully open condition of the EGR valve 15.

The air admission valve 7 has a poppet valve member 7a and a valve stem 19 slidably extending through a guide 20. The valve stem 19 has one end fixed to the valve member 7a and an opposite end linked to one end of an arm 21 whose other end is fixedly connected to one end of a rotatable shaft 22 for rotation therewith. The rotatable shaft 22 is rotatable by a plunger 23 of the diaphragm device 16 via an arm 24. The arm 24 is fixedly mounted at one end thereof to the rotatable shaft 22 and is linked at its opposite end to the plunger 23. The plunger 23 is fixed at one end thereof to a diaphragm 25 which separates a power or vacuum chamber 26 from an atmospheric chamber 27. A spring 28 is mounted with the vacuum chamber 26 to urge the plunger 23 and the arm 24 toward the phantom line illustrated positions in which the valve member 7a is in an open position to permit air flow communication through the opening 6. When a vacuum is applied to the vacuum chamber 26, the diaphragm 25 is deflected toward the left, viewing in FIG. 2, against the bias of the spring 28 to pull the plunger 23 to the left, thereby to rotate the rotatable shaft 22 clockwise, viewing in FIG. 2. This clockwise rotation of the rotatable shaft 22 will urge the valve member 7a to take the illustrated closed position in which air flow communication through the opening 6 is prevented.

The EGR valve 15 has a valve member 15a cooperating with a valve port 15b. The valve member 15a is fixedly connected to one end of a plunger 30 which is fixed at its opposite end to a diaphragm 31. The diaphragm 31 separates a power or vacuum chamber 32 from an atmospheric chamber 33. A spring 34 is disposed in the vacuum chamber 32 to urge the valve member 15a upwardly, viewing in FIG. 2, toward the valve port 15b. When the atmospheric pressure is applied to the vacuum chamber 32, the spring 34 urges the valve member 15a toward the valve port 15b to take a closed position in which the valve member 15a closes the valve port 15b to prevent admission of exhaust gases into the sub-chamber 3b. When the vacuum is applied to the vacuum chamber 32, the diaphragm 31 is deflected downwardly against the bias of the spring 34 to move the valve member 15a downwardly toward the illustrated fully open position in which the admission of the exhaust gases into the sub-chamber 3b is permitted.

The solenoid valve 18 is a so-called "three-way" solenoid valve which has a vacuum port 40 connected to a vacuum tank 41 via a vacuum line 42, an air bleed port 43 communicating directly with the atmosphere, and a control port 44 connected to the vacuum chamber 26 via a vacuum line 45 and also connected to the vacuum chamber 32 via a vacuum line 46 branching from the vacuum line 45. The vacuum tank 41 is connected to the induction system through a vacuum line 47 via a check valve 48. With this check valve 48, the vacuum within the vacuum tank 41 will be maintained at a sufficiently high level.

Referring to FIG. 3, a more simple operative connection between a valve member 7a and a diaphragm 16 for an air admission valve 7 is shown, in which the valve member 7a is fixedly connected to a plunger 23 of the diaphragm device 16 which extends transversely with respect to the longitudinal direction of an induction system 3. In this example, a partition 5 is provided with a check valve 50 which is designed to be opened to permit air flow communicating therethrough between sub-chambers 3a and 3b when vacuum within the sub-chamber 3b is higher than that in sub-chamber 3a.

Referring to FIG. 4, this example differs from that of FIG. 3 only in that a plunger 23 having a valve member 7a fixedly connected thereto extends along the longitudinal direction of the sub-chamber 3b and is slidably guided through a guide 51.

The operation of the engine control system shown in FIGS. 1 and 2 will be described.

When the engine 1 operates under any load condition except for a light load, the fuel injection signal is supplied to all of the fuel injectors 2a to 2f to effect full cylinder or 6-cylinder operation of the engine. Under this condition, the 3-cylinder operation mode command signal does not appear. Then, the solenoid valve 18 is in a state in which air flow communication between the control port 44 and the air bleed port 43 only is permitted, while, air flow communication between the control port 44 and the vacuum port 40 is prevented, thereby to apply atmospheric pressure to the vacuum chambers 26 and 32, thus causing the air admission valve 7 to be opened and the EGR valve 15 to be closed. Since the air admission valve 7 is opened to permit air flow communication between the two sub-chambers 3a and 3b, air will be supplied to all of the cylinders #1 to #6.

When a light load condition of the engine 1 is detected, the 3-cylinder operation mode command signal appears. In response to this command signal the fuel injection control unit 8 will prevent the supply of a fuel injection signal to the three fuel injectors 2d, 2e and 2f to render the corresponding three cylinders #4, #5 and #6 inactive. Then, the solenoid valve 18 is shifted into a second state in which the air flow communication between the control port 44 and the air bleed port 43 is prevented, while, the air flow communication between the control port 44 and the vacuum port 40 is permitted, thereby to apply the vacuum within the vacuum tank 41 to the vacuum chambers 26 and the vacuum chamber 32, thus causing the air admission valve 7 to be closed and the EGR valve to be fully opened, as illustrated in FIG. 2. Since no fuel or fresh air is supplied to the inactive cylinders #4, #5 and #6, these inactive cylinders #4, #5 and #6 will induct exhaust gases recirculated into the sub-chamber 3a from the exhaust passage 10a during their induction strokes and will discharge the same exhaust gases into the exhaust passage 10a during their exhaust strokes. When vacuum within the sub-chamber 3b has been reduced to a predetermined level, the amount of the exhaust gas drawn in by the inactive cylinders and the amount of exhaust gas discharged from these inactive cylinders will balance. In this manner substantially all of the exhaust gases discharged from the inactive cylinders will be recirculated through the EGR passage 14, the sub-chamber 3b, the inactive cylinders #4, #5 and #6, and the exhaust passage 10a cyclically when the engine 1 operates at 3-cylinder mode.

As a result, since there occurs little pumping loss by the inactive cylinders #4, #5 and #6 and no fresh charge is discharged from them, only the exhaust gases discharged from the active cylinders #1, #2 and #3 will flow past the junction, at which the exhaust passage 10a joins the exhaust passage 10b, toward the oxygen sensor 11. Since the oxygen sensor 11 detects the oxygen concentration of the exhasut gases discharged from the active cylinders #1, #2 and #3, the three-way catalytic converter 12 will operate efficiently and excessive enrichment of the air the fuel mixture to the active cylinders #1, #2 and #3 will be prevented.

At split engine operation mode, since the active cylinders #1, #2 and #3 operate under heavy or high load, the fuel economy of the engine is good.

Since the exhaust gases are recirculated into the sub-chamber 3b at split engine operation mode, any change in oil level when the engine 1 is shifted between full cylinder mode and split cylinder mode is made small.

Referring to FIG. 5, this embodiment differs from the previously described embodiment in connection with FIGS. 1 and 2 in that although, in the previously described embodiment, the atmospheric pressure is applied to the vacuum chamber 32 of the diaphragm device 17 at 6-cylinder mode engine operation to close the EGR valve 15, in this embodiment a control vacuum, such as an amplified venturi vacuum, is applied to a vacuum chamber 32 of a diaphragm device 17 of an EGR valve 15 at 6-cylinder mode engine operation so that exhaust gas recirculation is effected through an EGR passage 14a into a sub-chamber 3b under the control of the EGR valve 15 at 6-cylinder mode engine operation.

Another difference is in that another independent EGR passage 14b leads from an exhaust system 10 to a sub-chamber 3a and another EGR valve 55 for controlling flow of exhaust gases through the EGR passage 14b is provided, as shown in FIG. 5.

To a vacuum chamber 56 of a diaphragm device 57 for the EGR valve 55, a vacuum line 58 leads from a vacuum control device(not shown) which provides the amplified venturi vacuum. Another solenoid operable three-way valve 60 is provided which has a control port 62 connected to the vacuum chamber 32 of the diaphragm device 17 via a vacuum line 64, a first vacuum port 66 connected to the vacuum tank 41 via a vacuum line 68 and the vacuum line 42, and a second vacuum port connected to the vacuum line 58.

When the engine operates at 3-cylinder mode, the solenoid operable three-way valves 18 and 60 are in the states illustrated by the solid line so that the vacuum from the vacuum tank 41 is applied to the vacuum chambers 26 and 32. Under this condition, the exhaust gas recirculation is effected through the EGR passage 14b under the control of the EGR valve 55, the air admission valve 7 is closed and the EGR valve 15 is fully opened to recirculate substantially all of the exhaust gases discharged from inactive cylinders #4, #5 and #6 into these cylinders.

When the engine is shifted into 6-cylinder mode from 3-cylinder mode, the solenoid operable three-way valves 18 and 60 will take the state illustrated by the dotted lines so that the atmospheric pressure is applied to the vacuum chamber 26 and the control vacuum is applied to the vacuum chamber 32. Under this cndition, therefore, the air admission valve 7 is opened and the exhaust gas recirculation is effected through the exhaust passage 14a under the control of the EGR valve 15.

Referring to the fuel injection control in each of the previously described embodiments, an air flow meter (not shown) is disposed upstream of the throttle valve 3c and the fuel injection amount or pulse width of the fuel injection command signal is controlled in accordance with the amount of intake air detected by the air flow meter, in the same manner known in the conventional fuel injection control system.

The amount of air passing through the intake manifold at an area where the throttle valve 3c is disposed will remain unchanged when the engine operating condition has switched from 6-cylinder mode to 3-cylinder mode as long as the throttle valve 3c is in a partial load position. Thus, if the fuel injection amount is unchanged upon shifting from 6-cylinder mode into 3-cylinder mode the air fuel charge within each of the disabled cylinders will become excessively lean. In order to avoid this problem the fuel injection pulse width should be increased generally to double the amount when the engine operates at the previous 6-cylinder mode.

Referring to FIG. 6, this embodiment differs from the FIG. 5 embodiment in that instead of two independent EGR passages 14a and 14b provided with separate EGR valves 15 and 55, a passage 75 branches from an EGR passage 14a at a junction disposed downstream of an EGR valve 15 and a shut off valve 77 is provided to close the passage 75.

At 6-cylinder mode engine operation, the shut off valve 77 opens the passage 75 so that the exhaust gas will be recirculated into both sub-chambers 3a and 3b under the control of the EGR valve 15.

At 3-cylinder mode engine operation, the shut off valve 77 closes the passage 75 and the EGR valve 15 is fully opened, so that substantially all of the exhaust gases discharged from the inactive cylinders will be recirculated into the sub-chamber 3b to be drawn in by these inactive cylinders.

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