Inside the VFR1200F Dual Clutch Transmission
This schematic shows the separate...
This schematic shows the separate clutches and input shafts for even- and odd-numbered gears in the VFR's dual clutch transmission. Some automobile applications use completely separate shafts and clutches rather than the concentric setup used here, adding significantly more space than would be available on a motorcycle.
While dual clutch transmissions have been in use in the automotive world for many years - and currently available on several production models - the VFR1200F is the first production motorcycle application. To fit in a motorcycle's relatively confined space, the Honda's transmission differs from the typical automotive DCT in several ways and the company has applied for more than 100 related patents.
In a conventional motorcycle transmission, the actual teeth of each gearset are always engaged and dogs on one of the gears mate with slots in a neighboring gear to engage or disengage that particular gearset. The various gears must slide along their shafts, and for that to happen power must be removed from the input shaft so that its speed can match that of the output shaft and the dogs can properly mesh. A good rider can complete the process fairly smoothly in a few tenths of a second; with a quickshifer mechanism, this can be reduced to about a tenth of a second.
A dual clutch transmission has two input shafts and two clutches, one each for the even-numbered gears and one each for the odd-numbered gears. When you are in first gear, for example, the even-numbered clutch and input shaft are engaged and operating, while the other clutch and input shaft are disengaged. Because power is not being applied to the even-numbered gears, second gear can be activated at any time while first gear is still engaged and powering the motorcycle - the even-numbered clutch and shaft are still disengaged. Transferring power from first to second gear is then a matter of disengaging the odd-numbered clutch and then engaging the even-numbered clutch, a simple matter that can be accomplished in milliseconds. Now that power is being transmitted through second gear and not the odd-numbered gears, first gear can be disengaged and third gear engaged, all at a relatively leisurely pace, in preparation for the next shift.
The cutaway engine shows the...
The cutaway engine shows the separate clutches occupying not much more room than the standard model's single clutch. Note also the two hydraulic solenoids on the upper right of the engine cover, one to operate each clutch.
In most automobile applications, the two input shafts are separate, adding considerable size to the transmission. In the VFR's case, Honda made the two shafts co-axial, with the odd-numbered input shaft passing through the even-numbered shaft. Ironically, most standard-transmission automobiles have a single-plate clutch, requiring significant changes for a dual clutch model; The VFR's DCT splits what is almost a standard clutch in half, with one clutch behind the other and stacked on the input shafts. Making all this happen requires hydraulics and servomotors activated by computer, and the rest of the VFR's package is just as innovative in this respect. A servomotor rotates the shift shaft directly, while the clutches are controlled hydraulically with solenoids mounted on the engine's sidecover; there are two separate controllers, one for each clutch.
Once some computing power is brought into the equation, more benefits can be realized. In addition to completing a shift much quicker than the rider could, the DCT is much smoother as the machine can disengage and engage the clutches quickly but gradually. An ECU-controlled ride-by-wire throttle can be blipped so that revs are matched exactly on each downshift, further smoothing the process. And various automatic modes can be added for fuel economy or performance, as Honda has done with the VFR. -AT