Fuel microinjection volume correction method and common-rail fuel injection control device

A fuel microinjection volume correction method in a common-rail fuel injection control device configured to correct deviations in a fuel injection volume resulting from deviations in an injection characteristic of a fuel injection valve and having a microcomputer that controls fuel injection, the fuel microinjection volume correction method comprising:

• performing, via the microcomputer, microinjection as fuel injection in a microinjection volume,
• acquiring, via the microcomputer, an energizing time for the microinjection on the basis of a fluctuation amount of an engine speed generated at the time,
• storing, via the microcomputer, a difference from a reference energizing time that is acquired in advance for the fuel injection valve as a learning value in an updatable manner in a non-injection state of the fuel injection valve,
• setting, via the microcomputer, a value that is acquired by correcting the reference energizing time by the learning value as the energizing time at the time of the microinjection, and
• correcting the fluctuation amount of the engine speed on the basis of a gear ratio and the engine speed so as to eliminate an unnecessary change that occurs to the fluctuation amount of the engine speed due to a gear shift operation of a transmission when acquiring the energizing time for the microinjection on the basis of the fluctuation amount of the engine speed.