Method for controlling a coupling system of a summation mechanical transmission which is configured to couple a first drive shaft and a second drive shaft during coupling, the coupling system comprising an hydraulic coupling with two releasable coupling sections (28, 30), wherein a first coupling section is connected to the first drive shaft and a second coupling section is connected to the second drive shaft, the coupling system further comprising an hydraulic cylinder which is connected to one of the first and the second coupling sections (28, 30) and is configured to engage and to disengage said first coupling section with said second coupling section based on a pressure inside said hydraulic cylinder, wherein the pressure inside said hydraulic cylinder can be regulated by means of a pressure regulating device, wherein said pressure regulating device comprises activating means, which are configured to regulate the pressure inside said hydraulic cylinder based on a current (i C) provided to said activating means; the method comprising the following steps: a. Proving said activating means with a current (i C) for a first time interval (t 1) such that said first coupling section and said second coupling section are approached to each other but the kiss point has still not be reached; b. After said first time interval (t 1) providing said activating means for a modulation time interval (t 2, t 3) with a current (i C) such that the approaching speed of said first coupling section and said second coupling section is slowed down with respect to the approaching during said first time interval (t 1), wherein during said modulation time interval (t 2, t 3) the kiss point is reached; said method being characterized in that said modulation time interval (t 2, t 3) is divided into a second time interval (t 2) and a third time interval (t 3), wherein both in said second time interval (t 2) and said third time interval (t 3) the current (i C) provided to said activating means is gradually increased or decreased with a predetermined slope, wherein the slope of the current (i C) during said second time interval (t 2) is different with respect to the slope of the current (i C) during said third time interval (t 3). wherein said pressure regulating device comprises activating means, which are configured to regulate the pressure inside said hydraulic cylinder based on a current (i C) provided to said activating means; the method comprising the following steps: a. Proving said activating means with a current (i C) for a first time interval (t 1) such that said first coupling section and said second coupling section are approached to each other but the kiss point has still not be reached; b. After said first time interval (t 1) providing said activating means for a modulation time interval (t 2, t 3) with a current (i C) such that the approaching speed of said first coupling section and said second coupling section is slowed down with respect to the approaching during said first time interval (t 1), wherein during said modulation time interval (t 2, t 3) the kiss point is reached; a. Proving said activating means with a current (i C) for a first time interval (t 1) such that said first coupling section and said second coupling section are approached to each other but the kiss point has still not be reached; b. After said first time interval (t 1) providing said activating means for a modulation time interval (t 2, t 3) with a current (i C) such that the approaching speed of said first coupling section and said second coupling section is slowed down with respect to the approaching during said first time interval (t 1), wherein during said modulation time interval (t 2, t 3) the kiss point is reached; said method being characterized in that said modulation time interval (t 2, t 3) is divided into a second time interval (t 2) and a third time interval (t 3), wherein both in said second time interval (t 2) and said third time interval (t 3) the current (i C) provided to said activating means is gradually increased or decreased with a predetermined slope, wherein the slope of the current (i C) during said second time interval (t 2) is different with respect to the slope of the current (i C) during said third time interval (t 3).