The invention relates to multicylinder internal combustion engines having several cylinders or cylinder groups which are associated with a respective fuel-air mixture supply means and fuel-air supply process therefor. 
More particularly, the invention relates to the type of internal combustion engine disclosed in commonly assigned U.S. patent application Ser.  No.  90,613, filed Nov. 2, 1979 with respect to which the present inventor is a co-inventor, wherein the activation and the deactivation of a second cylinder group takes place, in the condition warmed up for operation, in an essentially jerk-free fashion.  However, this prior system does not make special adjustments to its operation in the warming-up phase of the internal combustion engine. 
DAS [German Published Application] No.  1,109,947 disclosed a multicylinder internal combustion engine wherein individual cylinder groups or all cylinder groups are supplied with fuel, depending on the torque requirement, this internal combustion engine operating in the warming-up phase in all operating ranges with all cylinders.  There is nothing disclosed in this DAS No.  1,109,947 to the effect that the feeding of the fuel-air mixture to the cylinders of the individual cylinder groups takes place differently in dependence on the load on the internal combustion engine. 
It is an object of the invention to provide an internal combustion engine comprising various cylinders or cylinder groups, especially two cylinder groups, wherein the operating characteristic of the second cylinder group is optimized in a predetermined partial load range during the warming-up phase of the internal combustion engine and with the internal combustion engine having been warmed-up for operation. 
According to the present invention, this object has been attained in accordance with preferred embodiments disclosed therein, whereby the fuel-air supply to the second cylinder group is controlled differently when the engine is warmed-up than when it is not. 
The advantages obtained by the invention reside especially in that, when the internal combustion engine is warmed-up for operation, the driving comfort of the automotive vehicle is increased by a completely smooth activation and deactivation of the second cylinder group.  In the warming-up phase of the internal combustion engine, the starting procedure of the internal combustion engine and the starting-up process of the automotive vehicle are improved, and the warming-up phase is considerably shortened, whereby fuel comsumption is reduced and exhaust gas emission is improved. 
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.