A transmission protection system and an electronic transmission control unit for the transmission protection system

The subject of the invention provides a transmission protection system (1) for motor vehicles equipped with low range of ratios and high range of ratios, comprising a device for shifting gears LCR (2) operating in "H" letter array. Selection of gear is effected by means of the gear selection shaft (5) connected with the gear change lever (3) equipped with the preselective switch (4) to select low or high range of ratios, and the low range of ratios is equipped with at least four ratios 1, 2, 3, 4 and the high range of ratios is equipped with at least four ratios 5, 6, 7 and 8, the transmission being equipped with pneumatic installation used to select the ratios range by means of the preselective switch and vehicle speed sensor (6). The gear selection shaft (5) is connected to an electro-pneumatic actuator EPV acting axially on the gear selection shaft (5) so that it counteracts accidental positioning of the gear selection shaft (5) in position of the gears 1-2 within the low range of ratios or in position of the gears 5-6 within the high range of ratios, and the electro-pneumatic actuator EPV is controlled by means of the electronic transmission control unit TCU depending on the difference between the vehicle speed S v and the first assumed speed S 1 for the low range of ratios of the difference between the vehicle speed S v and the second assumed speed S 2 for the high range of ratios.