A transmission has an HMT which is in parallel with an HST both driving two planetaries
which are used for forward/reverse and for differential steer. A two or three mode
HMT is created by having a first HST in parallel with two or three mechanical power
paths defined by separate clutches. One clutch has a speed reversing gear to produce
reverse output speed. A four-element planetary sums the parallel flow and delivers
variable speed and torque to two output shafts. The differential steer is created
by two planetaries connected with the outputs of the HMT and a second HST. The
planetaries have a speed reversing gear on one power path connection. The second
HST controls the differential speed between the output shafts by adding speed to
one and subtracting speed from the other.