Dual clutch transmission with multiple range gearing

1. A multiple speed ratio power transmission mechanism for an engine powered vehicle having multiple gear ratio gearing, a mainshaft and range gearing with low and high ratio ranges;

two separate countershaft assemblies including separate countershafts, and multiple mainshaft gears on the mainshaft, each countershaft assembly having at least one countershaft gear element engageable with separate mainshaft gears;

two power input shafts;

each power input shaft being drivably geared to a separate one of the countershaft assemblies;

dual clutches for selectively establishing and disestablishing driving connections between an engine and each power input shaft; and

gear ratio change clutches for selectively establishing torque flow paths through the multiple gear ratio gearing;

one torque flow path from the engine to one countershaft assembly and through the multiple gear ratio gearing being established as another of the torque flow paths from the engine to the other countershaft assembly is preselected;

the dual clutches disestablishing the one torque flow path and establishing the other torque flow path as the dual clutches are respectively engaged and disengaged;

the range gearing including high and low range clutches for selectively establishing the low and high ratio ranges;

the low ratio range being established and the high ratio range being preselected during torque delivery through the multiple gear ratio gearing;

the low ratio range being disestablished and the high ratio range being established as the dual clutches are engaged and disengaged to condition the transmission mechanism for high range operation, the high and low range clutches being adapted to preselect high range operation during low range operation when torque delivery through range gearing for high ratio range operation is interrupted whereby a smooth transition from low ratio range operation to high ratio range operation is made during a change in torque delivery paths through the dual clutches.

2. A multiple speed ratio power transmission mechanism for an engine powered vehicle having multiple gear ratio gearing, a mainshaft and range gearing with low and high ratio ranges;

two separate countershaft assemblies including separate countershafts, and multiple mainshaft gears on the mainshaft, each countershaft assembly having at least one countershaft gear element engageable with separate mainshaft gears;

two power input shafts;

each power input shaft being drivably geared to a separate one of the countershaft assemblies;

dual clutches for selectively establishing and disestablishing driving connections between an engine and each power input shaft; and

gear ratio change clutches for selectively establishing torque flow paths through the multiple gear ratio gearing;

one torque flow path from the engine to one countershaft assembly and through the multiple gear ratio gearing being established as another of the torque flow paths from the engine to the other countershaft assembly is preselected;

the dual clutches disestablishing the one torque flow path and establishing the other torque flow path as the dual clutches are respectively engaged and disengaged;

the range gearing including high and low range clutches for selectively establishing the low and high ratio ranges;

the low ratio range being established and the high ratio range being preselected during torque delivery through the multiple gear ratio gearing;

the low ratio range being disestablished and the high ratio range being established as the dual clutches are engaged and disengaged to condition the transmission mechanism for high range operation, the lowest gear ratio in the high ratio range being established and highest gear ratio in the low ratio range being disestablished when the torque flow paths through the dual clutches are changed.

3. A multiple speed ratio power transmission mechanism for an engine powered vehicle having multiple gear ratio gearing, a mainshaft and range gearing with low and high ratio ranges;

multiple mainshaft gears on the mainshaft and two separate countershaft assemblies in torque flow paths from a torque input shaft assembly;

the mainshaft gears on the mainshaft and countershaft gear elements on each countershaft assembly being in driving engagement;

two power input clutches for separately establishing an engine power flow path to each of the countershaft assemblies;

gear ratio change clutches for selectively connecting the mainshaft gears to the mainshaft;

range gearing comprising a planetary gear unit having a sun gear connected to the mainshaft, a carrier connected to a torque output shaft and a ring gear;

a low range clutch for selectively braking the ring gear; and

a high range clutch for selectively locking together two elements of the planetary gear unit;

one gear ratio change clutch being adapted to selectively connect a mainshaft gear to the carrier during high ratio range operation and to connect the mainshaft gear to the sun gear during low ratio range operation.

4. The transmission mechanism set forth in claim 3 wherein the dual clutches are selectively engageable to effect a transition from operation in low ratio range to operation in high ratio range without torque delivery interruption.

5. The multiple speed ratio transmission set forth in claim 4 wherein the one mainshaft gear is selectively connected to the mainshaft in a torque delivery path during operation in highest gear ratio in the low ratio range and lowest gear ratio in the high ratio range as the dual clutches are engaged and disengaged.

6. The transmission mechanism set forth in claim 3 wherein operation in lowest gear ratio in the high ratio range is preselected during operation in highest gear ratio in the low ratio range, a power shift from the low ratio range to the high ratio range being effected when torque delivery paths through the dual clutches are exchanged.