Project 676: why Ferrari focused on reducing size of gearbox and differential

Ferrari is refining project 676 in its final details, in anticipation of the increasingly imminent 2024 racing campaign. In just over a month, the Sakhir circuit in Bahrain will put an end to all the rumors that characterize the winter break. In Maranello, the design phase is practically complete, entering the delicate assembly phase of the car, where every small detail can be crucial for the future.

The engineers are gathering valuable data from the simulator and test benches. The goal is to put a well-balanced car on the track, ready to extract the maximum from all the modifications made in recent months. The focal point of the transformations performed is the chassis. The new design of the “skeleton” has addressed some defects present in the SF-23, along with the restyling of the front suspension system and the revision of the undercut area.

The rear end has also undergone changes. The perspective with which shapes and geometries have varied aims to increase the rear diffuser’s exit area. The intention is to improve the volume of air extracted from the bottom and, consequently, produce higher aerodynamic downforce. The gearbox, transmission, and differential are the elements of the 2023 car that, due to their size, prevented an increase in the diffuser’s exit section.

These two components, “responsible” for the motion of the car, are located behind the thermal engine and are practically embedded in the rear of the chassis. The lower part of the monocoque curves around the transmission and gearbox, effectively starting the diffuser. However, the mechanical limitations with which the technicians, led by Enrico Cardile, worked are anything but negligible. The gearbox and transmission box mainly function thanks to gears that “mesh” with each other.

Reducing the size of the titanium box that encloses these components may have required reducing the size of these gears, with associated reliability issues that could arise. In addition to this, all “accessory” elements such as synchronizers, wheel engagement shafts, and linkages to move the gears when the driver gives input with the paddle, may have been similarly streamlined.

Ferrari project 676: new alloy steel for gears. Module and gear diameters reduced
According to regulations, it is known that within a season, each car has 8 gearbox sets available for use on the vehicle. Also, according to the technical regulations, article 9.5 allows a single opportunity for development related to transmission components between 2022 and 2025. The current regulatory framework states that the only reasons for which this element can be modified between seasons in these 4 years, only once, are reliability and cost reduction.

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These should be the reasons on which Ferrari leveraged, with the aim of reducing the size of the gearbox and transmission, with the consequent aerodynamic benefit on the diffuser. In theory, these measures must be carried out without producing performance advantages. The larger diffuser should therefore be judged as an “indirect consequence.” Going even more into technical detail, at the mechanical technology level, to reduce the gearbox’s size, the red team’s engineers may have done significant work in search of a new material.

We are talking about a metal alloy that ensures the same mechanical characteristics as the previous gearbox but with smaller dimensions. The analysis on the use of new steels with alloy components such as Nickel, Molybdenum, and Chromium was carried out with the aim of raising the material’s yield strength. Through this new alloy, Maranello technicians should have been able to reduce the volume of material required.

Moreover, this prerogative imposes a lower safety factor, which is applied as a divisor of the breaking load to ensure superior safety and reliability. Let’s take an example to understand the issue. If a material withstands a yield load of 1000 MPa, applying a safety factor of 2.5, it is imposed that the gears work with a maximum load of 1000/2.5 = 400 MPa. Lowering this coefficient to 2, the maximum safety load becomes 500 MPa, and consequently, with the same force to be transmitted, the volume of material required is lower.

In addition to the study on materials, for project 676, Italian technicians would have improved all the heat treatments performed on the gears. These are measures that, at high temperatures, allow enhancing some characteristics of the gear, such as external hardness through “cooking” at very high temperatures, immersing the element in a gas. Heating the gear to a temperature near 1000°C allows increasing the distance between the molecules of the high-alloy steel, allowing the insertion of more gas atoms into the gear’s crystalline structure.

Once the gas has entered the material’s crystals for a certain thickness, a rapid cooling is carried out to allow the gas atom to remain inside the crystalline lattice, thus improving its mere mechanical characteristics. Reducing the size by obtaining a more efficient material means having a lower gear modulus.

The modulus depends on the material’s breaking load, the number of teeth, and their thickness, fundamental aspects on which the sizing of the gears is based. The primitive (main) diameter is equal to the modulus multiplied by the number of teeth. A similar discussion could be made for the differential, which is located downstream of the gearbox, under the exhaust pipe of the combustion gas, a little further back than the wheel axis.

The significant difference compared to the gearbox is that these “rotisms” form two bevel gear pairs. We are talking about gears that allow transmitting motion to driven elements placed perpendicular to the driving element. These rotisms have a lower dependence on the module, therefore the reduction granted is proportionally less than what happens in the gearbox. The study conducted by materials engineers may have led to the reduction in the size of these two boxes, indirectly allowing Ferrari to increase the diffuser’s volume and, consequently, the air extracted from the bottom.

These changes also impose new attachment points for the suspension system, which, in general, should have a different geometry on the 2024 F1 car. The combination of suspension geometries and a greater amount of available downforce extracted from the bottom improves the overall behavior of the car. Widening the setup window to fine-tune the car optimally. This is a benefit to be put into practice with a large amount of fuel on board, reducing tire slip and overheating, weaknesses of the SF-23.