A hydromechanical transmission, comprising:
- means for producing first, second, third and fourth transmission ranges, said first range including a reverse gear range and said fourth range being an overdrive range;
- said means including an input shaft, an output shaft, first, second, third and fourth clutch means, and at least first, second, third and fourth planetary gearsets, each of said planetary gearsets including a respective sun gear means, planet gears rotatably mounted on a carrier means, and a ring gear means;
- said means further including a fixed displacement hydraulic unit hydraulically interconnected to a variable displacement hydraulic unit, said variable displacement unit being operably connected to said input shaft and including swash plate means variable from a first extreme position to a second extreme position through a central position, and said fixed displacement unit being operably connected to said output shaft;
- said reverse gear range of said first transmission range being defined when said first clutch means is engaged and said swash plate means is positioned between said first extreme position and said centered position, said centered position of said swash plate means in said first transmission range defining a neutral position, and a forward gear range of said first transmission range being defined when said swash plate means is positioned between said centered position and said second extreme position;
- an upward transition between said first and second transmission ranges defining a first shift point and being produced by sequentially engaging said second clutch means and disengaging said first clutch means while said swash plate means is positioned at said second extreme position and said second clutch means is nonrotating;
- an upward transition between said second and third transmission ranges defining a second shift point and being produced by sequentially engaging said third clutch means and disengaging said second clutch means while said swash plate means is positioned at said first extreme position and said third clutch means is nonrotating;
- an upward transition between said third and fourth transmission ranges defining a third shift point and being produced by sequentially engaging said fourth clutch means and disengaging said third clutch means while said swash plate means is positioned at said second extreme position and said fourth clutch means is nonrotating;
- said fourth overdrive transmission range being defined where said fourth clutch is engaged and said swash plate means is moved between said second extreme position where said input shaft and said output shaft rotate at an identical speed and said first extreme position where said output shaft rotates falter than said input shaft rotates.