Prodrive has developed a new system that can actively manipulate the toe angle of the rear wheels on front-wheel-drive cars so handling limits can be increased on the fly. The system, named "Active Toe Control," has the ability to make a standard twist beam rear suspension behave more like a complex multi-link arrangement by changing the wheel's angle relative to the longitudinal axis of the vehicle (i.e. toe). Prodrive is actively pursuing a partnership to develop the system and believes that it can increase safety and handling performance at a fraction of the cost of newer, more expensive multi-link setups.
All the details are available in Prodrive's press release after the jump.
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.
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Reader Comments (Page 1 of 2)
Franz @ Mar 13th 2008 4:02PM
Sounds really good in theory.
Farris @ Mar 13th 2008 4:04PM
This almost seems like it could be a form of rear wheel steering, the way some of it is worded.
TwinTurbo3000GT @ Mar 13th 2008 4:12PM
that's basically the way the rear steering on the 3000GT VR-4 workes. Yes, it does improve handling, but it's not worth the additional weight and cost, IMO. Back to the 90s we go...
SeattleJeremy @ Mar 13th 2008 4:35PM
The 4ws system on the 3000GT is differant. Rather than turn the wheels left or right, the active toe system will lean the top of the wheel left or right.
R @ Mar 13th 2008 4:54PM
Seattle, isn't that camber?
naggs @ Mar 13th 2008 4:56PM
leaning the top of the wheel left or right would change camber
we will see how simple this system is, my initial guess is that this is the last we will ever hear about it
Shotgunner @ Mar 13th 2008 4:56PM
"the active toe system will lean the top of the wheel left or right."
I think you're confusing toe with camber.
TwinTurbo3000GT @ Mar 13th 2008 5:17PM
Toe is the angle of the wheels in relation to pointing strait ahead, camber is the tilt of the wheels inward at the top (or outward).
The system on the 3000gt is speed sensitive and adjusts the rear toe so that, above 41mph, the rear wheels turn in phase with the front wheels up to 1.5*. circa 1991.
bbb @ Mar 13th 2008 4:18PM
I wonder if we can put "camel" in the name somewhere?
Franz @ Mar 13th 2008 4:50PM
lol
Zo @ Mar 13th 2008 4:50PM
Didn't the Eagle Talon AWD Tsi already have this at least in the 95 models? I could of sworn it was even in the brochure.
Jeff @ Mar 13th 2008 7:23PM
The Eagle Talon had one of those "complex multi-link arrangements" that the article mentions. One of the advantages of such a suspension design is that it has better toe characteristics under changing conditions like camber changes, lateral forces, etc. The disadvantage is that it's more expensive to design and produce.
What Prodrive is proposing is designed for simpler (and cheaper) suspension setups. i.e. what they call "twist beam".
I suppose "bolting on" better handling dynamics on a "twist beam" suspension would be nice, but I'd much rather the companies just spend more on a creating a better suspension design.
tdmain @ Mar 13th 2008 5:11PM
I'm pretty sure my 1991 VW Corrado had something like this to passively control rear toe on it's twist beam axle.
fm @ Mar 13th 2008 5:15PM
I'd love to have this on my base Pontiac Vibe since it uses the some what lame torsion beam setup. Make it an upgrade and I'll buy it.
Colin Smith @ Mar 13th 2008 5:34PM
The Honda something had this like a hundred years ago.
CEMan @ Mar 14th 2008 5:40AM
And Porsche before that. Way back on the 928.
antonio @ Mar 13th 2008 5:38PM
sounds good. I wonder how much quicker the rear tires will wear out though.
hashiryu @ Mar 13th 2008 5:50PM
There are quite a few (and very common) cars with passive toe-in systems.
This is pretty cool tho, and if it is much lighter than a 4WS and cost a fraction of a multi-link rear suspension, then it can be a pretty good thing.
mo @ Mar 13th 2008 6:10PM
saab 9-3 has had rear wheel steering like this since 03.
RockStoneSteel @ Mar 13th 2008 10:26PM
Great, one more excuse for manufacturers to continue using the lame torsion beam suspensions. Unfortunately, this article doesn't detail the typical cost of independent/multilink suspension or that of torsion/twist beam. If independent suspension is perhaps $200 compared to the torsion beam at $100, then that extra cost for the higher quality independent is a non-issue.
Fact is, torsion beam can never reach the potential handling quality and ride quality of an independent suspension since the motion of each wheel is not fully isolated. That's why I have to laugh when I read Autoblog articles such as that about the Chevy Cobalt being "tuned" on tracks in Germany. There is only so much tuning you can do to a torsion beam suspension.
Manufacturers need to quit thinking in terms of "cheap" small cars and start offering premium small cars with no compromise in drive trains or suspensions relative to mid and full size cars.