Mumbai: Volvo Cars research and development team says, power shift gearbox cuts fuel consumption by 8 per cent, which has prompted the German automaker to make new engine variants. The two-litre turbo diesel version of the Volvo C30, S40 and V50 is now also available with a fully-automatic transmission.
In all three models the power shift transmission is mated to the 2-litre four-cylinder turbo diesel, which delivers a power output of 136 hp and 320 Nm of torque. Fuel consumption (EU combined) is 5.9 l/100 km for the C30 and 6.0l/100 km for the S40 and V50.
The power shift transmission developed by Volvo Cars in cooperation with its transmission partner Getrag, is a six-speed unit and it significantly cuts fuel consumption compared with a conventional automatic transmission.
Power shift operates in principle as two parallel manual gearboxes. It has twin wet clutches that work independently of one another. One clutch controls the odd gears (1, 3, 5 and reverse) while the other handles the even gears (2, 4 and 6). The two clutches operate alternately, with one engaging while the other disengages.
This means that when the engine gets full power and maximum thrust in first gear, the second gear is already placed in readiness 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 gear changes while maintaining acceleration throughout the gear changing process.
The power shift 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.
Power shift gives the driver an automatic transmission that permits sequential gear changes, just like with Volvo's Geartronic transmission. The difference is that with power shift even manual gear changes take place without any time or power losses.
Since power shift, 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.
Thanks to the use of twin wet clutches, the power shift 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 power shift that Volvo is now launching is dimensioned to handle torque levels of up to 450 Nm.