Canadian Jacques Villeneuve is relishing the chance to help Renault overtake his former BAR team for second place in this year's Formula One constructors' championship.

"It's the reason I've been hired and I'll do all I can for that," Villeneuve said on Friday after Renault confirmed his comeback for the last three races of the season.

Villeneuve, the 1997 world champion with Renault-powered Williams, will not have raced for a year when he makes his comeback in next week's Chinese Grand Prix as team mate to Spaniard Fernando Alonso.

In October 2003, Villeneuve acrimoniously parted company from BAR after four frustrating years with the team.

Villeneuve's comeback promises to spice up the remainder of a season already being dismissed as one of the most boring of recent years.

Michael Schumacher has already secured a record seventh driver's championship and carried his Ferrari team to the constructors' title.

BAR overtook Renault into second spot in the constructors' ranking following last weekend's Italian Grand Prix and Villeneuve's return adds an element of suspense for the remainder of the season.

"That's exciting, but it will be very very difficult. BAR has made more points than Renault in the last few races and now we've got to turn that around," Villeneuve said.

The Canadian said he has put his split with BAR behind him and is focusing on the task ahead with Renault.

"The BAR episode ended in a negative manner and left me a bit bitter and that's not good memories to have," he said.

"Being away for a year cleaned all those problems and I think it will be much easier to be positive."

Villeneuve, the son of the late Ferrari favourite Gilles Villeneuve, began intensive physical training in February to get into shape for an F1 return.

"It won't be easy, I still have a lot to get used to and learn and I'll just look at the Fernando to get all the info I can," said the 33-year-old, who has won 11 races from 130 starts in his Formula One career.

This week, Villeneuve also signed a two-year contract with Sauber starting next season and the former champion said he was impressed with the team's progress in testing with its new wind tunnel.

"That doesn't mean we will take on the world and Ferrari but I was very impressed with the way they work," he said.

"There has never been a negative story coming out of the team, so I think it will be easier to be patient."