

The legality of Toyota’s braking system has been challenged at Le Mans. Whilst there is no suggestion of cheating or underhand behaviour there has been some debate about the way its brakes are managed. ‘A clarification from the FIA was issued and that shows the others that our system is fully legal’ argues Pascal Vasselon.

The brake by wire layout on the TS040 has an automatic ‘brake migration’ system that sends the bias forwards or rearwards as the car travels deeper into the corner. In essence it is a form of active brake bias, as the electronic management system on the car manages it automatically.

If a driver hits the pedal and feels significant rear locking, the next time he arrives at that corner he would adjust the brake bias forwards to prevent it on a standard racing car. But sometimes as he starts to turn into the corner front locking can result as the wheels are unloaded. The Toyota system, which is in essence identical to those used in F1 mitigates this by using a brake migration tool to automatically send the bias rearwards again as the braking event continues. The drivers have control of how extreme this effect is by using rotary thumb switches on the steering wheel (below).



The technology is not unique to Toyota and features on most if not all Formula 1 cars and Toyota did not feel that the concept was especially confidential or indeed illegal as its implementation seems rather obvious on a hybrid competition car. However once rival manufacturers became aware of the system they complained to the FIA about its use suggesting it breaches two parts of the 2014 LMP1 technical regulations..

Article 14.1 states that:

The only connection allowed between the two circuits is a mechanical system for adjusting the brake force balance between the front and rear axles.

While article 14.7 states that

For vehicles with a Kinetic ERS, a specific braking system is allowed.

• Its function is to ensure the braking of the car strictly in

conformity with the order given by the driver.

• Its function cannot be, in any circumstances, to provide the driver with any additional support.

The system may be active.

In particular, this system must :

• Ensure balanced and stable braking, whatever the amount

of energy recovered. It must ensure a constant front / rear braking load distribution (sum of the electrical and hydraulic efforts) which can be adjusted only manually by the driver.

Following the requests for clarification from Toyota’s rivals the governing body issued a technical directive regarding brake bias control ahead of the first qualifying session at Le Mans which states

Following some questions about the ERS specific brake system, we feel important to clarify that in reference to articles 14.7.1 and 14.7.2:

1) a system that complies with LMP1 regulations cannot:

• Have any sort of balance adjustment to compensate automatically disc/pad wear or wheel locking.

2) a system that complies with LMP1 regulations can:

• Have a possibility of selection by the driver of the value of a nominal brake balance (selection made by an

HMI like a button/potentiometer, for example)

•Have a brake balance related to the brake pressure applied by the driver through a pre-definite law (which avoids any possibility of electronic anti-lock system), provided the relation pedal-pressure / brake balance is monotone and without any inflexion point (curvature always the same sign), like could be get from mechanical devices.

•Have a possibility of selection by the driver of the law defined above (relation pedal pressure/brake balance. Selection made by another HMI like a button, for example)

This guarantees that at any time, the brake balance is under the direct control of the driver through its selection and the pedal pressure he applies. For a definite set-up chosen by the driver, and a definite pedal pressure, the brake balance remains at a definite constant value, independently of the level of energy recovered or lock of the wheel.

Toyota has been very open about the use of the system on its cars and does not believe it to be illegal, indeed the layout has even been detailed in Racecar Engineering Magazine in the past!

Indeed the Toyota team seemed rather surprised that its rivals were not doing the same as they were!

Toyota technical boss Pascal Vasselon insists that the system is fully compliant with the regulations and that it has not changed its operation.

Further reading: What is brake by wire?