Racing on a budget

Original de pe Automotive Ingineering

From the dust of Spain to the snow of Finland, the World Rally Championship (WRC) races cars across the globe, forcing them to endure some of the most inhospitable conditions imaginable. In the past, teams would have spent tens of millions of euros to develop, test and race vehicles in the series, using technologies specifically designed for the task.

But that model wasn’t sustainable. The high  costs limited the number of teams participating, so world motorsport’s governing body, the FIA, changed the regulations.

Today’s World Rally cars have more in common with the passenger vehicles seen on public roads, but they’ve lost none of their performance.

Downsized, turbocharged, direct-injection engines are used to power the vehicles over the rugged terrain everyone associates with the sport.

Each vehicle now costs no more than €180,000, and this has brought more manufacturers to the arena. As well as Ford and Citroën, Mini will begin racing a variant of its Countryman SUV next year, and from 2013 Volkswagen will enter a rally-spec version of its B-segment Polo.

The more competitive series should challenge even the teams that have long been associated with the sport to remain at the top of the leaderboard. Ford runs its WRC programme with M-Sport, whose chief engineer, Tim Jackson, has worked with the previous Ford Focus rally car and the current Fiesta-based vehicles. He says the new regulations have had a huge impact: “The technical regulations underwent a complete overhaul, and they are much more restrictive in almost all areas of the car. Whereas in the past we could make many evolutive steps of the design for many of the main components – such as suspension linkages – now we are only allowed two options. And many of these options had to be nominated before the car could achieve its initial homologation and be allowed to compete.”

It’s likely that the new regulations concerning the powertrain will have the biggest effect on the series. Downsized 1.6-litre turbocharged gasoline engines with direct injection are being used for the first time, so teams are having to learn quickly how to get the most from the technology.

Jackson says: “While the engine used in the Ford Fiesta RS WRC is based on the technology used in Ford’s EcoBoost production car engine, it has been extensively modified to increase its performance over the road-going version – it produces 223kW of power and 450Nm of torque. Among the changes are a new head design and lightweight machining to the engine block as well as changes to many of the internal components.

“While the layout of the engine has been kept similar to the road-going version, significant design and development from Ford, M-Sport and our partner Pipo Moteurs has ensured that the engine is capable of withstanding the rigours of WRC, providing the much increased power and torque required of an engine designed with motorsport in mind.”

One requirement that is a challenge whether you are developing a rally or a road car is minimising weight. Regulations state that the minimum weight for a WRC car is 1,200kg, but reaching this target is difficult as exotic materials such as titanium and magnesium are banned unless already used on the original passenger vehicle.

“We want to keep weight to a minimum to increase performance. While we don’t have most of the components that make modern road cars heavy, such as the multiple airbags, air-conditioning units and sound insulation, we do add a roll-cage for increased safety. But the new regulations mean we have to use much more of the original road car bodywork,” says Jackson.

In the past, teams would substitute a steel bonnet for an aluminium version, so now there’s  an advantage to be gained if the starting point for the rally car is a road car with a lightweight body.

The task of fielding a competitive car while staying within the laws of the sport is just as difficult for the new teams. Mini is working with Prodrive to develop its WRC Countryman, which will compete in selected rally stages this season before entering its first full season next year.

Prodrive previously worked with Subaru, but Paul Eastman, head of rally engineering at the motorsport company, is enthusiastic about working with a new OEM: “The 1.6-litre gasoline engine in the standard Countryman produces 135kW of power – we’re targeting 220kW. The base car produces 300Nm of torque and we’re targeting 420Nm,” he says. There are restrictions on power output: vehicles are fitted with a 33mm air restrictor to the turbocharger. And teams are also limited to 2.5bar boost pressure. “Gone are the days where we used to run 4bar and we could produce up to 700Nm of torque. Some cars only needed four gears because they had so much torque,” he says.

The introduction of direct-injection technology is helping teams to overcome the performance restrictions placed on other areas of the powertrain. It’s a new technology to the sport, and one that was too costly before the regulations came into force. As direct injection is widely used in series production vehicles, it’s easier now for teams to adopt it.

Eastman says: “It’s a great technology to explore. Without the production car development we would never have used it, because the investment required is just extraordinary, with 300bar pumps and injectors to withstand the sort of cylinder pressures we run. But the road car technology is robust enough to use in rallying.” 

The Mini Countryman will run the injectors at 250bar on the main line, with a low-pressure feed to a high-pressure fuel pump – a standard system developed by Bosch.

Direct injection’s main benefit is in the amount of control it gives over the combustion process. “With a restrictor there’s only a certain amount of air, and you want to use it efficiently. So being able to control the burn through the injector is incredibly useful,” says Eastman. Feeding that power to the all-wheel drive system of a rally car is also highly restricted by the sport’s regulations.

Vehicles can only use transmissions approved by the FIA. Ford and Mini use an Xtrac sequential gearbox, though the deployment is slightly different.

“Although we share a transmission, we have a slightly different arrangement, developed for  efficiency and reducing weight. We’ve racked up over 2,000km on a single gearbox, without any troubles whatsoever,” he says.

And durability is key to winning races in the WRC, which is why not all the technologies in the road cars will migrate to the rally vehicles.

Electric power-assisted steering can’t meet the rigours of a rally, according to Eastman: “At this point, the electric systems don’t offer the same level of performance as the hydraulic systems. Steering rates average around 700° per second, peaking at about 1,500° per second during a rally. The electric systems can’t keep up with that. If you try and develop a system that can, it requires more electrical power and the alternator becomes larger. At the moment it’s just not efficient enough compared to a finely tuned hydraulic system,” he says.

Motorsport has often been criticised for not having a definite link between what races on the circuit and what consumers drive on public roads. But the changes to the WRC regulations mean that passenger vehicle technologies will power one of the teams to the title.

Volkswagen team gears up for the 2013 race season

The changes to the WRC regulations have opened the door to manufacturers that  previously shied away from the expense of developing and running a rally team. From 2013, VW will enter the championship with its WRC Polo R. The OEM is testing the technology and collecting data in preparation for its entry. Volkswagen Motorsport’s technical director Andreas Lautner explains the challenges in developing a WRC car.

“We’re waiting until the 2013 season to enter the competition so we can close the experience gap between us and the other teams. We’re designing a completely new rally car. We’re in the test phase at the moment.

“The power and torque of the WRC Polo R are 240kW and 450Nm. The Polo GTI, which the rally car is based on, has 135kW and 250Nm.

“The biggest restriction we face is in the drivetrain concept, which doesn’t allow active differentials any more, but there is more freedom in reducing friction. Bringing together the  different interests of the engine and chassis departments under one roof is challenging, because it means a lot of compromises need to be made.

“We have had to find compromises between the lowest possible engine position versus driveshaft angle. The suspension is completely different as we need to develop a system that is easily serviceable and strong. We also have to live with the homologated sequential gearbox, which leaves only the layout and the housings free for us to develop. And while electric power-assisted steering is an option – we use it in our Golf GT24 – the systems aren’t reliable enough for the rally programme yet.

“It’s always a challenge to save weight, especially as alternative material use – magnesium, titanium, ceramics and composites – is prohibited.

“The bodyshell has to come from the standard production vehicle. You can remove all the  unnecessary brackets and you can change the bottom and tunnel to change the platform from a front-wheel driven concept to install the all-wheel drive system, but for stiffness you can only work on the roll-cage construction.

“The materials used for the braking systems have changed little and ABS is forbidden. We’ve focused on optimisation of the calipers to reduce the mass.

“We’re using CFD to design all our body and cooling concepts before going into the wind tunnel.”