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As applied to a front drive or 4WD vehicle: at the inboard end of each front drive shaft is a simple disc clutch which, when engaged drives through gears to a high speed centrifuge fan. The fan is arranged to draw air from a hovercraft style skirt ('inside out' to contain vacuum) which occupies a space
between and immediatly behind the front wheels, exhausting into the front wheel arches. The skirt is normally supported off the ground, but is allowed to drop down on application of the brakes, creating a substantial area of low pressure under the car and pulling it down onto the road, increasing friction available at the front tyres for braking. The system would be self - balancing in that greater braking produces greater downforce. The clutches could have auxilliary brke pads to provide conventional braking at very low speeds. The clutches themselves could be much smaller than conventional brakes, as most of the braking energy will be dissapated in the accelleration of air.
Possible add-ons could include partial redirection of exhasut air to blast surface water from immediately ahead of the tyre contatct patches, or use of exhaust airflow in conjunction with a diffuser type undertray to create low pressure under the whole of the floorpan.
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||This is a grate idea and I think that the "exhaust air to blast surface water from immediately ahead of the tire contact patch" is a vary good add-on.
|| I drive and 1989 Cadillac and it hydroplanes when braking quite often.
||could such a system be of any real benefit. Your average fast stop in a car takes less than 2 seconds from start to finish, Your fan will not even be up to speed before the car is stopped.
||Initial calculation shows that the energy transfer to brake a 1.5 ton car at 1G (abot the limit of the tyres) would spin my fan up to speed in 0.03 seconds. The greatest delay would be in the rate of pressure drop in any duscting between the fan and the ground, but I think this could be kept very short and that would only account for 0.05 seconds to achieve 0.5 bar vacuum, which over 2 square feet of 'skirt' area gives over 1000 lbs of downforce. The fan would be a small, high speed aluminium or composite rotor. Air is light and easy to accelerate.