Method for operating a multiple direct injection internal combustion engine and mass-based switching of the number of injections

A method for operating an internal combustion engine of a motor vehicle, in which fuel is injected in a fuel injection device directly into a combustion chamber of the internal combustion engine in a plurality of time-spaced partial injections per duty cycle, the method comprising:

• determining a total injection mass per duty cycle into the combustion chamber as a function of an output requirement for the internal combustion engine as a function of an air mass supplied into the combustion chamber;
• and
• producing a fuel/air mixture, taking into account a predetermined air-fuel ratio, via the steps of:
• verifying a maximum possible number of partial injections per duty cycle as a function of a critical mass threshold of a fuel injector assigned to the respective combustion chamber, in which the fuel mass per partial injection is not undercut, and of the desired determined total fuel mass per duty cycle to be injected;
• determining a verified mass-based target injection number as a function of the verified maximum possible number of partial injections and distribution of the total fuel mass to the verified mass-based target injection number;
• and
• injecting the total fuel mass per duty cycle according to the verified mass-based target injection number with the fuel masses distributed to the partial injections,
• wherein a mass-based switching of the verified mass-based target injection number to a lower maximum possible verified target injection number is carried out due to an undercutting of the critical mass threshold, which is defined dependent on the rail pressure at a minimum possible opening time of the fuel injector, and determining a distribution of the total fuel mass over the lower maximum possible verified target injection number, and
• wherein a mass-based switching of the verified mass-based target injection number to a maximum possible verified target injection number is carried out due to an undercutting of the critical mass threshold, which is defined dependent on the rail pressure at a minimum possible opening time of the fuel injector, and determining a distribution of the total fuel mass over the maximum possible verified target injection number.