Analysis: 2014 – Braking

Although it has not cropped up extensively in the media, braking (in particular brake bias and control) will be an important design consideration for 2014. This is down to the introduction of the new power units, which – due to the additional recovery power of the MGU-K – makes the bias difficult to adjust and control.

Current Braking System and KERS

In this section of this post I am going to break (pardon the pun) down the key characteristics of the current (2009-2013) braking system and how each component affects each other.

Since 2009 (excluding 2010), Formula 1 has utilised the Kinetic Energy Recovery System (KERS) that increases the efficiency of the braking system, transferring the previously lost energy to a battery. This energy can then be used to provide an additional boost of power at the driver’s disposal for 6.67 seconds per lap. The KERS harvests 60kW of power, which equates to about 80bhp – about the same power as a small family hatchback car.

It does this via a Motor Generator Unit (MGU). As the driver brakes, the engine drives the generator of the MGU which acts as a resistive force to the driveshaft connected to the wheels. The MGU transfers the energy recovered from the generator to the battery. When the driver pushes the KERS button the energy is sent back to the motor of the MGU, adding power to the engine.

Image via racecar-engineering.com

Image via racecar-engineering.com

It is under braking that the KERS is difficult to manage. We often hear the engineers asking the driver to select a KERS harvest setting on the steering wheel. The harvest level is important because not only does the driver have to recover enough energy to supply the engine with additional power each lap, but it also controls the braking characteristics of the car. The driver will probably be asked to change the harvest level multiple times throughout the race as the fuel load decreases, even during each stint as tyre degradation occurs.

Although the KERS is connected to the rear braking system, the harvest level can have a huge influence on the front braking and therefore brake bias as a whole. At the beginning of 2011 – when KERS was formerly introduced – we saw lots of lock-ups and braking errors. This was down to the harvest levels either being too high or low and the brake bias incorrectly set. If the harvest level is set quite aggressively you may want to shift the brake bias forward as more work is being done on the rear brakes by the MGU, and vice versa.

Ultimately, if the braking system is not managed correctly it can lead to driver error and also increase the wear rate of the tyres. The former could well be very common for 2014…

ERS and Rear Brake Control Systems

For 2014, KERS has been kicked up a notch. The Energy Recovery System (ERS) is comprised of two MGUs: the MGU-K and the MGU-H. As covered in my 2014 power units analysis, these two units will provide an additional 161bhp (for 33.3 seconds per lap) on top of the 600bhp V6 turbo engine. The MGU-K (Motor Generator Unit – Kinetic) is the MGU in charge of recovering energy from the braking system. It is essentially a bigger KERS unit.

The MGU-K must only harvest up to a maximum capacity of 2MJ per lap. However, the MGU-H (Motor Generator Unit – Heat, which harvests energy normally lost from the turbo unit) has unlimited harvesting capabilities, making the overall capacity over 4MJ. Compare this to the maximum capacity of the KERS unit (400kJ per lap), there is a lot more energy being recovered under braking and from the turbo unit. Because the MGU-K has to harvest a lot more energy, it acts as a greater resistive force to the wheels under braking than the KERS. As the two MGUs are linked together, there is also the potential for spikes to occur in the harvesting of each MGU. Therefore there is also the likelihood that the braking system in the 2014 cars could be unpredictable and cause the driver to spin.

However the FIA were informed of this issue and addressed it by adding a further article to the 2014 technical regulations. Article 11.7 reads:

Rear brake control system :

The pressure in the rear braking circuit may be provided by a powered control system
provided that :
a) The driver brake pedal is connected to a hydraulic master cylinder that generates a
pressure source that can be applied to the rear braking circuit if the powered system is
disabled.
b) The powered system is controlled by the control electronics described in Article 8.2.

The article refers to a “powered control system” with a back up braking system in the form of a traditional hydraulic master cylinder connected to the rear brakes via hydraulic brake lines.

The “powered control system” is commonly known as Brake by Wire (BBW). In very modern road cars (such as the new Porsche 918 Spyder) we are seeing the installation of electronic power steering rather than hydraulic. This is primarily used to save weight, removing pumps, hoses and fluid from the system. It is also cheaper to manufacture and removes the need for a fluid replacement, potential pump and hose failure. It works by using a torque sensor connected to the steering column, sending the information to the ECU, translating this information to a motor which in turn moves the steering rack and therefore the wheels.

The same principles apply with BBW except that the brake pedal position is monitored by a sensor. The reason why we are not seeing BBW in road cars yet is because it is deemed to be too risky to have for public use, as failure of the system could lead to large accidents!

The reason why the FIA elected to allow teams to use BBW is because it is a system that can be easily tuned via the ECU (when the article refers to Article 8.2, it means that the control system must be linked to the SECU and no other external ECU). The ECU can detect spikes in the harvesting of the MGU-K and therefore modulate brake pressure accordingly without the driver noticing too much. The 2014 rear braking system effectively becomes a live system that has endless complications and capabilities. It is up to the engineers to be able to tune the system accordingly to fully realise the potential of the MGU-K.

Other than BBW, there are other ways in which teams can create a braking control system. The rear brake circuit could be composed of a traditional hydraulic system featuring a hydraulic/pneumatic control valve (monitored by the SECU) to distribute brake pressure accordingly. This set up does not have the technical freedom that BBW has but the technology is already well known.

The word ‘reliability’ has been pinged around a lot in the build up to 2014 so I wonder if we will see some conservative systems for the coming season before something more adventurous for 2015 – if there is an advantage to be had.

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5 thoughts on “Analysis: 2014 – Braking

    1. thewptformula Post author

      Cheers, Michael.

      Yes, if the ERS harvest level is more aggressive it acts as a greater resistive force to the wheels under braking. Generally the resistance will be higher so the brake discs will be a lot smaller at the rear which could lead to some more complex brake duct designs as there’s a bit more space to play with.

      Reply
  1. Morris Dancer

    Interesting stuff, especially as (as you said) we haven’t heard too much about brakes, with the focus being on changes to the engines/power units.

    Reply
    1. thewptformula Post author

      That is correct, yes. 2MJ from the MGU-K and the rest comes from the MGU-H.

      This is why the battery capacity will probably more than 4MJ because, although the maximum amount of energy the MGU-K can use per lap is 4MJ, the MGU-K transfers additional energy to the MGU-H to spool up the turbo electronically.

      Apologies for the mistakes, thanks for pointing it out.

      Reply

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