Method and apparatus for shifting ranges in a continuously variable transmission

A transmission assembly comprising:

• a hydrostatic transmission having a variable displacement hydraulic device which controls a ratio of an input speed to an output speed of the hydrostatic transmission;
• a mechanical transmission coupled to the hydrostatic transmission and having a first range and a second range;
• and
• an output shaft driven by one or more of the hydrostatic transmission and the mechanical transmission which causes a work machine to move at a travel speed, wherein:
• a motor speed ratio is the ratio of the output speed to the input speed,
• a travel speed ratio is the ratio of the travel speed to the input speed,
• the torque through the hydrostatic transmission reverses when the mechanical transmission shifts from the first range to the second range,
• a synchronous travel speed ratio is the travel speed ratio which produces the same motor speed ratio in both the first gear range and the second gear range,
• an equal displacement travel speed ratio is the travel speed ratio at which a displacement of the variable displacement device in the second gear range is the same as the displacement in the first gear range,
• a travel speed ratio differential is a difference between the synchronous travel speed ratio and the equal displacement travel speed ratio, and
• the shift from the first range to the second range is initiated at a travel speed ratio which varies from the equal displacement travel speed ratio by less than eighty percent of the travel speed ratio differential.