Arrangement and process for operating a fail safe braking system in a continuously variable driving unit of a motor vehicle

An arrangement for operating a continuously variable drive unit of a motor vehicle comprising:

• a regulatable internal combustion engine (2);
• a hydrostatic mechanical power-distribution transmission (6), with a continuously variable gear ratio, having a rotatable input shaft (18), connected to the engine, and a rotatable output shaft (10),
• a mechanical branch (19) of the hydrostatic mechanical power-distribution transmission (6) being at least driven by said input shaft and having a plurality of gear ratios and a plurality of hydraulically actuated multi-disc clutches,
• a hydrostatic branch (17) of the hydrostatic mechanical power-distribution transmission (6) having a primary unit (15) connected to said input shaft and a secondary unit (16) for a continuous change of a gear ratio, said secondary unit (16) being connected to said mechanical branch (19),
• at least two coupling shafts (23, 24) each being connectable with the output shaft (10) of said transmission (6) via one of said plurality of hydraulically actuated multi-disc clutches (25, 26), and each of said at least two coupling shafts being coordinated with a gear ratio of said mechanical branch,
• wherein a control device is connected with an input shaft sensor for sensing the speed of said input shaft and with an output shaft sensor for sensing the speed of said output shaft, and said control device (3) actuates a monitoring device (29), said plurality of multi-disc clutches (25, 26) and a brake of the motorvehicle (43) in accordance with the ratio of said sensed speeds, a pump (30) conveys pressurized fluid to actuation devices for said multi-disc clutches (25, 26) via a first line (32), a second line (33) branches off from said first line (32) and a third line (34) branches off from said second line (33), said third line (34) divides into parallel fourth and fifth lines (37, 38), and a sixth line (42) connects an actuation device of said brake (43) with said fourth and fifth lines (37, 38), said fourth line (37) contains a value (39), control by pressure in said second line (33), which controls the flow of pressurized fluid through said fourth line (37), and an electrically actuated valve (40), connected with the control device (3), controls the flow of pressurized fluid through said fifth line (38).