Fully-automatic and sequential six-speed transmission
Twin wet clutches give extremely fast and smooth changes
About 8% lower fuel consumption than conventional automatic transmission
Optimised for powerful diesel engines
The new Powershift gearbox that is now offered as the transmission in the two-litre turbodiesel versions of the Volvo S40 and V50 has not only improved the driving experience in these models of Volvo Car South Africa, but it also offers exceptional fuel economy and performance which one would expect from a manual gearbox.
The new Powershift transmission launched in the Volvo S40 and V50 2.0D models is a six-speed unit which features twin wet clutches that provide gear changing comfort on a par with that of a fully-automatic transmission.
And, as with Volvo’s fully automatic Geartronic transmission, the driver has a choice of moving the gear lever manually, or leaving it in automatic mode. But with the Powershift, viewed as the transmission of the future, there is no torque converter as with a conventional automatic gearbox, and thus no power loss.
The Powershift transmission has been developed by Volvo Cars in cooperation with its transmission partner Getrag. Powershift operates in principle as two parallel manual gearboxes, with two shafts –one running inside the other – which each operates a different set of gears. It has twin wet clutches that work independently of one another. One clutch controls the odd gears on the one shaft (1, 3, 5 and reverse) while the other handles the even ratios on the other shaft (2, 4 and 6).
The two clutches operate alternately, with one engaging while the other disengages. This means that at the same time as the engine gets full power and maximum thrust in first gear on the one shaft, second gear is placed in readiness on the other shaft to be engaged. And when second gear has been engaged, third gear is readied, and so on.
This promotes a continuous flood of power without any disruption in power delivery or any torque loss, resulting in extremely fast and silky-smooth gearchanges while maintaining acceleration throughout the process of gear changing.
Eight percent lower fuel consumption than a conventional automatic transmission Apart from gearchanging comfort and high performance, the Powershift transmission contributes to noticeably lower fuel consumption.
“According to our measurements, Powershift contributes to a fuel consumption saving of about 8% compared with a conventional automatic transmission,” says Magnus Jonsson, senior vice president for research and development at the Volvo Car Corporation. “And that is an important benefit in the hunt to keep lowering the negative impact on the environment.”
The Powershift function is based on the technology used in a manual gearbox but with the difference that the two wet clutches are each linked with their own input shaft. One shaft spins inside the other. The inner shaft regulates the output shaft for first, third, fifth and reverse gears, while the outer shaft controls second, fourth and sixth gears. The clutch function is operated by an electro-hydraulic control unit that ensures that one clutch is shut while the other is open, and vice versa.
Each clutch functions like a slip clutch. A piston pushes a number of clutch plates against each other and locks them together through the resultant friction.
A Transmission Control Module (TCM) determines the optimum time for a gear change in automatic mode. The TCM, through solenoids and hydraulic oil pressure in cylinders, then controls the shifting forks to move the drive gears into position – just as would happen through a manual gearshift in the previous S40 and V50 2.0D model.
Automatic or sequential gearchanging without any loss in torque
Powershift gives the driver an automatic transmission that permits sequential gearchanges, just like with Volvo’s Geartronic transmission. The difference is that with Powershift even manual gearchanges take place without any time or power losses.
Since Powershift, unlike a conventional automatic transmission, does not need a torque converter, planetary gears or multiple wet clutches, there is also none of the added torque losses that these features bring.
Optimal choice for powerful diesel engines
Thanks to the use of twin wet clutches, the Powershift transmission can handle high torque levels and in principle has no limitations on choice of ratio. This makes it an ideal partner for today’s modern, powerful diesel engines.
The version of Powershift that Volvo is now launching is dimensioned to handle torque levels up to 450 Nm. In the versions of the Volvo S40 and V50 in which it is fitted, Powershift is mated to the 2-litre four-cylinder turbodiesel which delivers a power output of 136 hp and 320 Nm of torque.
“With Powershift we can now offer automatic transmission with our two-litre diesel engine,” says Jonsson. “And it’s not just any old automatic transmission: lower fuel consumption coupled with increased comfort and higher performance sounds like an impossible equation. But with Powershift we have shown this is perfectly possible.”