PROBLEM TO BE SOLVED: To optimize injection processes and injection jet shapes at appreciably small structural cost and with the best possible functional precision from a durability-based point of view by adapting the phase of the cross-sectional area of an injection hole to every operating condition on a time basis. SOLUTION: On an inner needle 12 within a hollow needle 10, a control piston 13 is disposed having a stop surface 14 cooperating with the upper end of the inner needle 12 and a first stop shoulder 23 cooperating with the hollow needle 10. The hollow needle 10 internally defines a chamber 16 encircling the stop surface 14 and energized with a control liquid. The inner needle 12 has a very narrow pressure shoulder.
