With ten years behind them, the turbo-hybrid power units continue to amaze. On the occasion of the last Italian Grand Prix, Ferrari showcased the power unit for the 2021 Formula 1 season. Enrico Gualtieri, Head of Power Unit Area, was there to reveal its secrets and characteristics, and he offered an intriguing discussion about the various ways the electric part is used. While the mapping for the thermal engine remains the same for qualifying and the race, the hybrid side features multiple modes that constantly change during the lap.
The power unit is used at its maximum power only for short moments, a precaution linked to reliability and, most importantly, battery charge. In these circumstances, the battery provides maximum electrical power without other components worrying about energy recovery. For instance, the turbine is bypassed through the wastegate valve, which remains open to reduce exhaust pressure losses and maximize the useful power of the combustion engine. However, with the wastegate open, the exhaust gas thrust on the turbine is limited.
It’s up to the MGU-H, the electric motor that rotates with the turbo unit, to push the compressor, drawing energy from the battery. “The MGU-H drives the turbocharger, transforming it into a mechanical compressor,” Enrico Gualtieri explains. The battery simultaneously powers the second electric motor, the MGU-K, whose thrust is directed straight to the wheels. Maximum power mapping is activated at low speeds when the driver needs all the thrust possible to regain speed. In terms of lap time, concentrating the power in the early stages of acceleration is more profitable than a spread delivery to the top speed.
Once a decent speed is reached, the power unit must strike the right balance between power output and energy savings. As it’s not externally rechargeable, the battery has to be managed through repeated charge and discharge cycles. In the continuous power mapping, the wastegate valve closes again, allowing the turbine to convert the thermal energy of the exhaust gases into mechanical energy by driving the compressor and MGU-H.
In these conditions, the MGU-H enters a recharge mode, recovering energy that is immediately redirected to power the MGU-K. As a result, the battery’s workload is substantially reduced. The mapping gradually evolves to completely preserve the battery charge. The MGU-K is then entirely powered by the MGU-H, still in recharge mode, leaving the remaining energy in the accumulator intact.
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In braking and deceleration phases when the driver doesn’t require thrust, the recharge mapping comes into play. All the thermal-mechanical energy converted from the exhaust gases through the turbine is used to drive the MGU-H and recharge the battery. The accumulator also receives energy recovered during braking from the MGU-K. This way, the battery charge is slowly restored and then delivers maximum thrust during the next corner exit.
Although presented as three distinct modes, the mappings have variable nuances, progressively transitioning from one to another. Usage times are also adaptable to external conditions. “The mappings constantly evolve in every part of the circuit and on every lap, depending on conditions, grip levels, and the driver’s style,” Enrico Gualtieri adds. It should be noted that in qualifying or during the hectic phases of a race, the maximum power mapping can be utilized for extended periods, but it comes at the cost of consuming the battery and subsequently requiring extensive use of the recharge mode. It’s a matter of strategy, whose complexity mirrors that of current power units.