Prodrive improves handling with Active Toe Control

[rev]

Motorsports company Prodrive is developing a new vehicle dynamics system that actively adjusts toe angle (the symmetric angle that each wheel makes with the longitudinal axis of the vehicle) to improve vehicle handling. Dubbed ‘Active Toe Control,’ it works on the rear axle of front wheel drive cars to optimise the toe angle, depending on the speed of the vehicle. This helps overcome the static toe compromise of either giving a vehicle agile handling at lower speeds or making it more stable and predictable at high speed.

To give a vehicle additional low speed agility, the wheels usually have a certain degree of toe at the rear axle, while to make a car more stable at higher speeds, for emergency manoeuvres like a lane change, then toe-in is preferred. Because of this there’s always a compromise between low and high speed handling.

Prodrive claims its new system can match the handling of a vehicle with a complex multi-link rear suspension using just a traditional twist beam set-up. “Active Toe Control, fitted to an existing twist beam axle, can give many of the dynamic benefits of a multi-link system, but at less than half the cost,” Prodrive engineer Matt Taylor explains.

Officials are now looking for a hardware partner to take the project to a working prototype.


Source: Motor Authority Prodrive improves handling with Active Toe Control

[Monster]

So which is more effective, active toe or active rear steering ? I guess this solution is less complex, cheaper and lighter than active steering, but it will still be a massive pain in the backside for the engineers to make sure the entire structure will be strong enough to perform under the normal cornering loads applied by the car.

[coolraoul]

Reminds me of the Merceds F400 Carving, with active toe control on evary wheel and special tyres!


DaimlerChrysler is exhibiting a special concept study at the 35th Tokyo Motor Show: the F 400 Carving is a research vehicle packed with dynamic systems designed to give the cars of tomorrow and beyond substantially enhanced active safety, dynamic handling control and driving pleasure.
Like a number of other manufacturers, Mercedes is researching the viability of a new system that varies the camber angle on the outer wheels between 0 and 20 degrees, depending on the road situation. Used in conjunction with newly-developed tyres, the Mercedes implementation provides 30 percent more lateral stability than a conventional system with a fixed camber setting and standard tyres.
Active camber control boosts the research vehicle's maximum lateral acceleration to 1.28 g, meaning that the concept study outperforms current sports cars by some 28 percent.

Asymmetrical Tyres

The active camber control in the F 400 Carving also paves the way for an equally new asymmetrical-tread tyre concept. When the two-seater car is cornering, the outer wheels tilt inwards, leaving only the inner area of these tyres in contact with the road. This area of the tread is slightly rounded off. Meanwhile both the tread pattern and the rubber blend have been specially selected to ensure highly dynamic and extremely safe cornering. When driving straight ahead, however, it is the outer areas of the tyres that are in contact with the road. These areas have a tried-and-tested car tread pattern, offering excellent high-speed and low-noise performance. Two different concepts can be combined thanks to the active camber control.
The F 400 Carving is something of a mobile research laboratory for the Stuttgart-based automotive engineers. They will be using it to investigate the further potential of this new chassis technology: besides offering excellent directional stability during cornering, the new technology ensures a much higher level of active safety in the event of an emergency. By way of example, if there is a risk of skidding, the wheel camber is increased by an appropriate degree. The resultant gain in lateral stability significantly enhances the effect of the Electronic Stability Program. If the research car needs to be braked in an emergency, all four of its wheels can be tilted in next to no time, thus shortening the stopping distance from 100 km/h by a good five metres.

Other Stuff

In addition to active camber control, the F 400 Carving research car is fitted with other futuristic elements including a steer-by-wire system. Sensors pick up the driver’s steering inputs and send this information to two microcomputers which, in turn, control an electrically driven steering gear.
The F 400 Carving is also the showcase for a totally new form of lighting technology developed by the Stuttgart-based researchers: fibre-optic lines are used to transmit light from xenon lamps beneath the bonnet to the main headlamps. This technology stands out by virtue of its high performance and extremely space-saving design. Additional headlamps positioned on the sides also come on when the car is cornering. It's an idea that will transform the frontal design of cars in years to come.
Whilst it's a pretty wacky looking car, the technologies being explored by Mercedes are exciting and will no doubt be present in the most mundane of cars in ten years time. It's also good to see clever thinking applied to the basics rather than just throwing computing power in to make up for shortcomings in mechanical design.

(text found on pistonhead.com)

Wonder if MB is still working on that. I assume yes.

[Monster]

Originally Posted by coolraoul

Reminds me of the Merceds F400 Carving, with active toe control on evary wheel and special tyres!

I think you have mistaken between toe and camber. The toe angle is the angle between the wheel and the center line when view from the top of the car. The camber angle is the angle between the wheel and the line perpendicular to a flat surface. A diagram will explain it instantly, I will try to find some now.

[Monster]

Originally Posted by monster

I think you have mistaken between toe and camber. The toe angle is the angle between the wheel and the center line when view from the top of the car. The camber angle is the angle between the wheel and the line perpendicular to a flat surface. A diagram will explain it instantly, I will try to find some now.

Camber angle


Toe angle

[coolraoul]

Whooops my bad...
Thanks for the explanation...

So it's more an alternative to a rear-wheel steering, right? I know some carmakers are developping such steerings. Renault for the new Laguna has announced for 2009 I think.

Sounds interesting BTW.

[Monster]

Originally Posted by coolraoul

Whooops my bad...
Thanks for the explanation...

So it's more an alternative to a rear-wheel steering, right? I know some carmakers are developping such steerings. Renault for the new Laguna has announced for 2009 I think.

Sounds interesting BTW.

Yeah it is more an alternative to rear wheel steering, but less dramatic. Car with wheels toe angle set outwards will be less stable as a toe in angle (just in general). So by adjusting the toe angle at the back end of the car, it can effect the car's handling characteristics.

You can see it here from the F2008. The front wheels are at an toe out angle for more responsive turn in while the rear are set at an toe in angle for bettet stability and traction out of the corner.

[rev]

PRESS RELEASE

Vehicle dynamics that actively toe the line

Motorsport and vehicle technology specialist, Prodrive, is developing a vehicle dynamics system that actively adjusts toe angle to improve vehicle handling.

Known as Active Toe Control, it works on the rear axle of front wheel drive cars to optimise the toe angle, depending on the speed of the vehicle. This helps overcome the static toe compromise of either giving a vehicle agile handling at lower speeds or making it more stable and predictable at high speed.

Advances in tyre technology and suspension, mean that the dynamic capability of modern cars is now so good, that it is rare for drivers to ever reach a vehicle's limits. "Typically most drivers stay well within 60-70 per cent of their car's capabilities," said Matt Taylor, Prodrive chief dynamics specialist. "This means vehicle manufacturers are increasingly focusing on making their cars feel more sporty in this region, without necessarily increasing their outright performance."

Once the chassis and suspension designs have been completed on a new model, the final adjustment to refine the dynamic characteristics is typically to set the static toe angles. To give a vehicle additional low speed agility, the wheels usually have up to a degree of toe‑out at the rear axle, while to make a car more stable at higher speeds, for emergency manoeuvres like a lane change, then toe-in is preferred. This makes any fixed toe setting a compromise and one that has contributed to the increasing use of complex multi-link rear suspensions in mid-size hatchbacks; a design previously reserved for high end vehicles. Ford set the trend with the Focus and others have since followed suit. However, while they work extremely well, such rear axles are far more expensive than the traditional twist beams they replace.

"Vehicle manufacturers really want ways to reduce the production cost of their cars. Replacing simple twist beam axles with more expensive multi-link systems goes against the grain, but as they all strive for class leading handling, it is direction they are being forced to take," said Taylor. "Active Toe Control, fitted to an existing twist beam axle, can give many of the dynamic benefits of a multi-link system, but at less than half the cost."

Handling characteristics are increasingly becoming attributes of vehicle brands. A BMW drives differently to a Renault, which is different to a Ford and in different markets there are differing expectations on how a car should handle.

The German market tends to like the handling characteristics typical of a rear wheel drive car where the vehicle's yaw rate and lateral acceleration build at the same time.

"You don't get the feeling of the car rotating, rather that the car is being pushed sideways. People often describe this as if the rear wheels are following the front wheels, with the car turning around the rear axle," said Taylor.

Cars with this tight lateral acceleration and yaw rate phasing tend to turn in well and it is a typical set up for competition cars.

Markets, like France, which have been dominated by front wheel drive cars, favour different characteristics. Here they are used to cars where the lateral acceleration lags behind the yaw rate gain, a common characteristic of twist beam suspensions where the suspension flexibility allows the rear wheels to move sideways before 'pushing' the rear of the car.

"This gives the driver the sensation that the car is momentarily turning on the spot around its centre of gravity, as the nose tucks in and the back kicks out, giving an agile feeling," said Taylor. "Neither approach is right or wrong, it's a matter of preference. With Active Toe Control you have the added benefit of refining the handling simply by changing the control algorithms on the production line or at the dealer, to give the characteristics favoured by whichever market the car is to be sold."

Prodrive has identified a preferred mechanism design to adjust the toe angle and is looking for a hardware partner to take the project to a working prototype.


Source: Prodrive develops active toe control - Autoblog