To Slip, or Not to Slip

In recent years, the number of cars equipped with systems like ABS, ESC and traction control has shot up – to the point that fitment of these so-called “driver-assist” electronic gizmos is practically standard on new cars. Everyone knows that using ABS’ clever pulsating braking, for example, means that skidding on dry roads is now virtually a thing of the past, but what have tyre manufacturers done to incorporate operational differences like this into tyre design? As 2007 drew to a close, Tyres & Accessories visited Continental AG’s Arvidsjaur, Sweden proving ground in order to learn more about how the automotive systems supplier designs tyres that work in conjunction with increasing electronic cars.

After first being launched in 1978, it took about 20 years for ABS to be represented in 40 per cent of all new cars. The ESC stability system, introduced in 1995, has already exceeded a 40 per cent share of all newly registered cars – ranging from vehicles like the Audi TT to right down the Ford Fiesta. Being a manufacturer of both auto-electronics like ESC and vehicle tyres puts Continental in a unique position to exploit its know-how to the benefit of each connecting product. The aim to make tyres that are safer and electronic systems that are more “interactive” than constrictive, allowing the room for a “fun”, but safe driving.

According to Continental, one of the main benefits of passenger vehicles equipped with winter tyres that are designed to be used in conjunction with driver assist systems is that they promise shortened braking distances and improved features for handling cures on wet, snowy or icy roads. Arvidsjaur in December has an average temperature of -10’C, but Lapland obviously knew T&A was coming because the actual temperature was a much more temperature 3-5’C. This significantly increased the slipperiness of the test centre’s driving surfaces, but also made it more comparable with mild British and European winters.

Tyre developers at Continental told T&A they have been conducting exhaustive tests analysing different kinds of tyre treads and the way they respond to ABS and ESC systems on winter roads. The result is a what the company calls a holistic integrated design for tyres and driver assist systems that promises considerable advances in helping to prevent accidents, and to help drivers feel more secure while driving in typical winter weather.

According to Continental research, an accident is six times more likely to occur during the winter months than during the summer, and more than half of all accidents occur during the winter. “Despite new winter tyres and driver assist systems, hardly anything has changed in this regard,” stated Dr Burkhard Wies, Continental’s director of passenger vehicle tyre development for the replacement market. “On the one hand, the number of vehicles has increased, but on the other hand, we have to rely on integrated system networks if we want to make any significant strides in dealing with hazardous wintry road conditions.” And what’s more, the positive effect of driver assist systems increases proportional as the friction co-efficient decreases. Or in others words, ESC, ABS and traction control have the greatest potential to increase overall grip in slippery conditions.

Likewise, fears of the dangers associated with winter driving remain similarly stable. Research conducted by the University of Cologne, found that 62 per cent of drivers were fearful when braking (especially braking on a curve) during wintry weather. The research into subjective fear potential also found that 46 per cent of drivers were scared of downhill driving in these conditions, with 41 per cent feeling the same on a wintry uphill road.

“The question for us as leaders in the European winter tyre market is how to mitigate fears of driving during the winter by adapting tyres and driver-assist systems,” Dr Wies points out. “Our new holistic design for winter tyres and the electronic stability control (ESC) guarantees considerable advances, an area in which, we as system suppliers of tyres and chassis, have a great deal of expertise,” Dr Wies explained.

Winter tyre tread design affects braking distance and cornering performance differently. This is due to driver assistance systems such as ABS and ESC, which are most effective with different tyre designs. Continental engineers have been testing each of these for optimum tyre design. As a result they advise coordinating driver assistance systems and tyres to master this conflict in objectives, and to shorten braking distances and enhance cornering.

Depending on the tread design, winter tyres have different centres of gravity that driver assistance systems can either partially mitigate of amplify. This means that on a snow-covered road, a longitudinal tread pattern without ABS will have a longer braking distance than a lateral tread pattern. “During braking tests using ABS, the difference is almost obliterated, since the electronics minimize the differences between the tyre systems in favour of a more secure, optimal vehicle stability,” explains Dr Wies, adding: “Cornering using a lateral tread pattern without ESP would…supply us subjectively and objectively with significantly better values than we would get using a longitudinal tread pattern.” Switching on driver assist evens both of these results out at a high level.

Don’t slip…too much

The results of these tests are expected to go into production “soon” and “in the near future” Continental reports that it will introduce a winter tyre whose tread design will be customized to vehicles equipped with ABS and ESC systems. And by optimising the development of both driver assistance systems and winter tyres, engineers at Continenatl expect significant progress in reducing braking distances on snow-covered roads. The development of so-called “high-slip ABS” promises to create great potential for taking advantage of braking forces that, up till now, have not been fully exploited. The theory is that “significantly higher” traction can be transferred by adjusting brake slip to be high – comfortably exceeding the usual 10 per cent.

Continental engineers have already put the theory into practice and report it has already been possible to reduce braking distances by 10 per cent. The loss of cornering ability that is encountered by doing this is counteracted by making use of the ESC sensor system and by activating the standard ABS mode when vehicle instability has been detected or during cornering.

This example speaks volumes about the future direction of Continental AG as an automotive supplier, particularly after the recent takeover of Siemens VDO. As described above, the high-slip ABS system requires interaction with on-board ESC in order to function effectively. The logical next step for inclusion in this “information loop” is the tyres. So while what Continental is describing here sees the advances in driver assist systems influencing tyre design. It is only a question of time before there of parts of the vehicle technology (such as the active steering and hill-start break technology Conti also showcased in Lapland) are also brought into the loop.

This is something that he newly created Continental Chassis & Safety Division (formerly Conti Automotive Systems) will spearhead the development of. During the Arvidsjaur visit, Continental AG revealed some of the strategy associated with this continuous development from being a tyre manufacturer into an automotive supplier. It is centred on the company’s vision of developing a so-called “global chassis system” that could be branded as ContiSafe and potentially become a selling point for new cars and by all accounts it is not far away.