In the first of a two-part insight into brake-by-wire use in the ABB FIA Formula E Championship, e-racing365 speaks to a company behind one of the most crucial parts of Gen 2 Formula E technology.
There has been no stopping the ABB FIA Formula E Championship since its second season when Jaguar triggered an avalanche of manufacturer interest in the all-electric series.
Yet, from a technical perspective, one of the key topics and points of interest as it ventures in to its new era of Gen 2 hardware and a new race format is now actually getting the cars stopped!
The new Gen 2 cars are quicker, and given their natural habitat on some seriously sinuous street circuits, braking is as critical as it has ever been in Formula E.
Brembo, which won the contract to supply some of the hardware, has majored on shifting every possible gram of weight from its callipers.
With the front and rear callipers weighing in at 1.2 and 1 kg, the products are significantly lighter than any F1 equivalent.
But it is all about the rear brakes in the new-look Formula E cars where the brains and the intrigue lie for the engineers and the fans watching at the track and on TV.
The previous generation of cars, used between 2014 and 2018, used driver-managed regenerative braking systems, with no active function to control brake bias.
This is why we often saw drivers locking up or losing control completely, because the state-of-charge in the battery and the drop-off in regeneration unbalanced the car.
This season, brake-by-wire systems are allowed in the all-electric championship, which should make life easier for drivers who can now fully control their front brakes.
The regulations limit the power accessible to the teams at 52 kWh (the equivalent of only 6 liters of gas) per race.
In order to race with such little energy at a good pace, energy management and regeneration is key.
Proper recuperation of energy needs a BBW system to keep the car stable and predictable, and a lot of systems and control units have to interact, which calls for a lot of arbitration work.
The BBW system now largely takes care of the rear callipers, and manufacturers tested their systems and rear braking architecture during their allocated test days over the summer months.
This is where the secrecy of the software and overall BBW systems gets interesting, and also where e-racing365’s newshound reflexes have been pricked.
After some intensive detective work, we can reveal that all except two of the 11 teams are using the IBSe system, conceived by LSP.
DS Techeetah and Mahindra Racing are the two teams that have developed their own in-house systems.
Both have been reticent to discuss details but are known to have been working on their respective packages since early 2017.
But, thanks to LSP GmbH speaking to e-racing365, we can at least get some understanding of how and why BBW will be so important for the 2018-19 Formula E season.
How BBW Works on the Gen 2 Formula E Car
In a brake-by-wire system, the brakes are not directly actuated by the driver, but through software and eventually the brake actuator.
This is a simple enough solution but why is it necessary?
“For electric [or hybrid] cars, recuperation acts as an additional brake torque on the axle/wheels,” LSP’s Simon Zollitsch told e-racing365.
“The amount of the brake torque coming from the electric motor is strongly variable and influenced by things like charging status of the battery (full is full but if the battery is almost empty, the power for recuperations needs to be reduced too), battery temperature or the status of the inverter.”
The old approach in Formula E was to set the recuperation to fixed levels and then to coach the driver to handle the switching of the levels.
“With a BBW the driver is completely decoupled from the actual brake, so if the control software is working properly, the brake torque requested by the driver can be split into electric and hydraulic braking torque without the driver even noticing this,” says Zollitsch.
Other assistances that are possible via a BBW system are: online diagnosis of the brakes, online arbitration of brake balance (according to vehicle speed, aerodynamics, race situation) and launch control functions among many others.
Internally the IBSe is made of three main parts. One of these is an electric PMSM motor, which was developed in-house at LSP, especially for this use.
This electric motor drives a ball screw which transfers the rotation of the motor into forward and backward movement of a hydraulic plunger.
The in-house-developed electronics enables the pressure to be controlled in a range of 0 to 110 bars precisely and quickly.
Moreover several safety functions are performed online and diagnose the status of the BBW and also the brakes at all times.
“The third, and a very important part of the IBSe is the valve block, with which the BBW can be coupled into the brake circuit, but also, which is a key benefit of our system, decoupled from the hydraulic brake circuit in case of an unexpected situation or failure,” said Zollitsch.
“Like this, the vehicles brakes work like a normal brake with the driver’s pedal being connected directly to the brake callipers.
“Since race cars are always prototypes, this is a crucial part of the IBSe. It ensures that the car can be stopped safely, even if our customer’s vehicle control unit brakes down, power is lost, or other things happen which lead to a malfunction of the BBW.”
Click here to read Part 2 of e-racing365’s look into brake-by-wire technology, published on Sunday, Dec. 23.