On Tue, 28 Oct 2014 11:27:11 +0000, Neil Williams
wrote:

On 2014-10-28 09:39:29 +0000, Roland Perry said:

Is ASC also controlling the throttle?

In some cases yes. However even in traditional traction control where
it isn't, it still works.

If I'm driving a car with both wheels *just* about to start spinning
and I floor the accelerator, what prevents them starting to spin?

If *both* wheels spin, what is needed is to reduce the throttle. The
braking works where *one* wheel is spinning, to divert power from one
side to the other. If you braked *both* wheels, you would be fighting
the engine and burning off the excess in the brakes, but that's where
the option of controlling power comes in. Of course cars are only
fitted with one engine, so reducing power is a far blunter instrument.

FWIW the brakes on modern cars are perfectly strong enough to fight
against the accelerator - try pulling off against the handbrake and see
how far you get. Though I can see that if used for extended periods
they might overheat.

In my 2007 model car, the system is called DSC, and I've found this
description of how it works in an online forum:

"The Dynamic Stability Control (DSC) system includes the:

- anti-lock brake system.
- yaw/lateral control.
- full speed traction control.

The DSC system manages the braking system to enhance the driver
control of the vehicle.

The DSC system continually monitors the steering wheel angle, master
cylinder brake pressure, front and rear wheel speeds, vehicle yaw and
lateral rate acceleration.

The yaw/lateral rate sensor supplies a signal to the DSC module, via a
serial link, which monitors the vehicle's rate of acceleration from
its central axis in a sideways direction, and also the vehicle's
angular rotation around its central axis.

The driver input parameters are continually monitored via the brake
master cylinder dynamic stability control sensor, the brake pedal
travel sensor and the steering wheel angle sensor.

DSC is enabled/disabled via the traction control ON/OFF switch.

Self-diagnosis of the DSC system is provided via the instrument
cluster message centre.

Traction control is an additional function added to the ABS/DSC
system. The vehicle's driven wheels are continually monitored for
wheel spin relative to the calculated reference speed and to each
other. If wheel spin is detected, the traction control function
intervenes independently of the driver, applying brake pressure to the
slipping wheel and reducing the engine drive torque supply. Meanwhile,
brake pressure is modulated by the traction control until traction is
re-established. Traction control brake actuation is diminished above
40 km/h (25 mph). Above this speed traction control relies primarily
on engine torque reduction.

Traction control is enabled/disabled via the traction control ON/OFF
switch. When the switch is in the (OFF) position, the amber traction
control warning lamp solidly illuminates within the instrument cluster
message centre. The traction control is automatically activated when
the ignition is switched on. Self-diagnosis of the traction control
system is also provided via the instrument cluster message centre.

The traction control brake intervention is automatically disabled
whenever the brakes exceed a temperature limit. The traction brake
intervention will remain disabled until the brakes have cooled,
irrespective of ignition switch position or ignition switch cycling."

From
http://www.jaguarforums.com/forum/ge...ow-works-3853/

I dare say more modern cars than mine have more sophisticated systems,
including features like torque vectoring.