Internal combustion engine
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to improvements in an internal combustion engine of the split type which will operate on less than all of its cylinders with the remaining cylinders being supplied with exhaust gases reintroduced thereinto under normal or light load conditions. 
     2. Description of the Prior Art 
     It is generally known that engine operation is more economical if each cylinder of the engine is run under relatively high loads. However, under most vehicle operating conditions the engine is operating under relatively light loads resulting in uneconomical fuel consumption. Accordingly, it is desired to shift engine operation into a split or part cylinder engine mode wherein the engine operates on less than all of its cylinders such as by cutting off air and fuel flow to the remaining cylinders during normal or light load operation with the remaining cylinders being brought into operation only after the load on the engine exceeds a given value. In this way it is possible to increase the load on each of the active cylinders, which results in greater overall operating economies for the engine. 
     For the purpose of reducing pumping losses in the inactive cylinders thereby making engine operation more economical, it is common practice to re-introduce exhaust gases into the inactive cylinders so as to maintain them at substantially atmospheric pressure. 
     In introducing blow-by gases into the intake passage of the split engine in such a manner as is done in normal internal combustion engines, a particularly difficult problem occurs in that the intake system associated with the inactive cylinders is soiled greatly with solid carbon. Blow-by gases, unburned air-fuel mixture leaking from the combustion chamber to the crankcase past the piston rings fitted between the piston and the cylinder wall, include a great amount of oil. The oil sticks to the wall of the intake system associated with the inactive cylinders and combines with soot included in re-introduced exhaust gases to form a pile of solid carbon thereon. 
     SUMMARY OF THE INVENTION 
     It is therefore one object of the present invention to provide an improved split type internal combustion engine operable on less than all of its cylinders with the remaining cylinders being supplied with exhaust gases re-introduced thereinto at low load conditions which will be substantially free from formation of solid carbon on the intake system associated with the inactive cylinders. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention will be described in greater detail by reference to the following description taken in connection with the accompanying drawing, in which: 
     The single FIGURE is a schematic sectional view showing one embodiment of a split engine made in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the single FIGURE, the reference numeral 10 designates an engine block shown as containing therein a first group of cylinders #1 to #3 being always active and a second group of cylinders #4 to #6 being normally inactive and activated only after the engine load exceeds a predetermined value. The invention is described and illustrated with reference to a six cylinder internal combustion engine, although it is apparent that the invention could be applied to engines having any number of cylinders. 
     Air or air-fuel mixture to the engine is supplied through an intake passage 12 which has therein a throttle valve 14 drivingly connected to the accelerator pedal (not shown) for controlling air or air-fuel mixture flow to the engine. The intake passage 12 is divided downstream of the throttle valve 14 into first and second branches 12a and 12b, the first branch 12a leading to the first group of cylinders #1 to #3 and the second branch 12b leading to the second group of cylinders #4 to #6. In the FIGURE, the letter A designates the point from which the first and second branches 12a and 12b extend separately toward their associated cylinders. Provided at the entrance of the second branch 12b is a stop valve 16 which is normally closed and open to allow the flow of air or air-fuel mixture to the second group of cylinders #4 to #6 only when the engine load exceeds a predetermined value. 
     An exhaust gas recirculation (EGR) passage 20 is provided which has its one end opening into the exhaust passage 18 of the engine and the other end thereof opening into the second intake passage branch 12b. The EGR passage 20 has therein an EGR valve 22 which is open only during a split engine mode of operation to allow recirculation of exhaust gases through the EGR passage 20 into the second intake passage branch 12b so as to maintain it at substantially atmospheric pressure. This is effective to minimize pumping losses in the inactive cylinders #4 to #6, making engine operation more economical. 
     A blow-by gas passage 24 is provided which has one end opening into the crankcase (not shown) and the other end opening into the first intake passage branch 12a for re-introducing thereinto unburned air-fuel mixture leaking from the combustion chambers to the crankcase past the piston rings for re-combustion. The blow-by gas passage 24 has therein a check valve 26 which allows flow only toward the first intake passage branch 12a. 
     The operation of the present invention is as follows: When the engine operates at low load conditions, the stop valve 16 is in its closed position to cut off the flow of air or air-fuel mixture to the second intake passage branch 12b so as to bring the second group of cylinders #4 to #6 out of operation. In which case, the EGR valve is open to allow recirculation of exhaust gases into the second intake passage branch 12b. Blow-by gases flow through the blow-by gas passage 24 into the first intake branch 12a under a suction vacuum appearing therein and hence flow into the first group of cylinders #1 to #3 along with the flow of air or air-fuel mixture from the intake passage 12. 
     When the engine load exceeds a given value, the stop valve 16 opens to allow the flow of air or air-fuel mixture through the second intake passage branch 12b to the second group of cylinders #4 to #6 with the EGR valve 22 closing to stop the exhaust gas recirculation into the second group of cylinders #4 to #6. In this way, engine operation is shifted from a split engine mode to a full engine mode wherein the engine operates all of its cylinders. In which case, the blow-by gases introduced through the blow-by gas passage 24 into the first intake passage branch 12a is driven into the first group of cylinders #1 to #3 by the flow of air or air-fuel mixture from the intake passage 12 thereto. As a result, there occurs a great reduction in the amount of blow-by gases flowing into the second intake passage branch 12b and thus in the amount of oil sticking to the wall of the second intake passage branch 12b. 
     If the blow-by gas passage 24 is opened at its one end into the intake passage 12 upstream of the point A as found in conventional arrangements, then a great amount of blow-by gases will flow through the opened stop valve 16 into the second intake passage branch 12b and a great amount of oil included in the blow-by gases will stick to the wall of the second intake passage branch 12b. The attached oil combines with soot included in the exhaust gases recirculated during a split engine mode of operation to form a pile of solid carbon. 
     According to the present invention, the blow-by gas passage 24 is opened into the first intake passage branch 12a downstream of the point A from which the first and second branches 12a and 12b extend individually to their associated cylinders. The arrangement is effective to greatly reduce the amount of blow-by gases flowing through the second intake passage branch 12b into the second group of cylinders #4 to #6 during a full engine mode of operation. Thus, the amount of oil sticking to the wall of the intake system associated with the second group of cylinders #4 to #6 can be greatly reduced. In this way, it is possible to minimize formation of solid carbon on the wall of the intake system associated with the second group of cylinders #4 to #6 caused by the combination of the oil sticking on the wall of the intake system and soot included in the exhaust gases re-introduced into the second intake passage branch 12b during a split engine mode of operation. 
     It is to be noted that the particular engine shown is only for illustrative purposes and the structure of this invention could be readily applied to any split engine structure including carburetor type engines. While the present invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.