Active Brake Balance Control in F1

Some time ago I designed an active brake balance control system for the Prost F1 car, from memory it was for AP04. The idea was that aerodynamic load builds up differently front to rear with respect to speed and therefore when a driver brakes into a corner and slows the car the load on the tyres and therefore the amount of grip front to rear changes as the car slows. The front wing is far more efficient than the rear, and so as the car slows the brake balance should shift progressively to the front.

Also what we found is that the difference in brake hose length between the front and rear mean't that the rear brakes take fractionally longer to come up to pressure on rapid application of the brake pedal, than the fronts do. So very briefly you have a lot more front bias than you would ideally want.

So our answer was to develop an active brake balance control system. It's hard to know what the other teams were doing at the time, but, we were pretty confident that we were the only ones using it. It never actually got raced because the rules were changed to ban it as soon as we were ready to race it. It seems that 2014's regulation might require this kind of system and that the rules may have been changed to allow it once more.

The heart of any active system is the Moog valve. This is a servo hydraulic control valve that F1 cars use to control the throttles, gear change, and in the early 90's active suspension systems. It's a very sensitive and rapidly responding valve with a built in feedback system that allows you to control the pressure in a system very accurately, and extremely quickly.

The active brake balance system was in essence very simple. All we had to do we 'T' off of the rear brake hose and put in a hydraulic piston. On one side of the piston was the brake fluid and on the other side was the hydraulic fluid controlled by the Moog valve. The hydraulic fluid circuit also included an accumulator and obviously a high pressure pump (the same pump is used for the gear change and throttles). The Moog valve was controlled by software that had the cars speed, front brake pressure and rear brake pressure as inputs. The software did the calculations to compare the front to rear brake pressure split to the nominal selected balance with respect to speed, so in essence we had a 2D map of what brake balance we wanted for each particular speed. The Moog valve then regulated the pressure of the rear brake line increasing or lowering the pressure many thousands of times a second to maintain the optimum balance.

For 2014 with the addition of extra KERS harvesting and therefore variation in the amount of braking that the rear of the car sees during this harvest, this active balance system would be able to reduce rear brake line pressure during harvesting to keep the balance stable.

The simplicity of this system mean't that if there was a failure in the active system the rear brakes would still function as normal because the separator piston had limited travel and if the hydraulic pressure were to fail then the piston would move back against a hard stop allowing the brake master cylinder to build pressure as in a normal system.