Field of the Invention
The present invention relates to a CVT transmission having an input drive, a continuously variable variator, a sub-transmission to achieve at least two operating ranges (low and high) with continuously variable gear ratios, and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high) with continuously variable gear ratios.  In addition, the present invention relates to a method for operating such a CVT transmission. 
Description of the Related Art
The term CVT refers to a stepless transmission; the letters CVT stand for continuously variable transmission.  To increase the transmission ratio range of a stepless transmission—its gear ratio spread—it is known from European published application EP 2 275 709 A1 to position a planetary gear set after the stepless transmission.  The controllable planetary gear set enables two-range shifting and shifting into reverse.  In addition, it is known from German published unexamined application DE 102 61 900 A1 to provide a multi-range CVT with fixed engageable gears, for example for moving off or for top speed; however, when these fixed transmission ratios are in operation, the variator is uncoupled.  Consequently there is only one stepless range; stepless operation is not possible in all driving ranges. 
An object of the present invention is to simplify the operation of a CVT transmission having an input drive, a continuously variable variator, and a sub-transmission to achieve at least two operating ranges (low and high) having continuously variable gear ratios and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high) with continuously variable gear ratios.