With the shift toward pull rod rear suspension, the teams’ mechanics are faced with a maintenance issue. As the pull rod reaches down into the gearbox casing, access to the transmission is hindered by the inboard suspension inside the gear casing. Most teams maintain their transmission by first having to remove parts of the inboard suspension. However the Ferrari engined teams have each found a neater solution to this problem. Sauber use the Ferrari gearbox and also follow a similar practice of using a separate module to mount the entire inboard suspension in between the engine and gearbox.
Pull rod suspension runs the pull rod from the outer end of the top wishbone down the bottom corner of the chassis. For the rear suspension, the inner end of the pull rod set up is on the gearbox casing. This mounts the inboard elements of the system low down on the gearbox, either inside entirely contained within the casing (which is more aerodynamic), or splits the elements inside and outside of the gearcase. Both however will have heave and anti roll elements passing from one side of the gearbox to the other. These parts sit ahead of the transmission inside the gear casing and will hinder access to it.
The inboard suspension is made up of: torsion bar springs, side dampers, anti roll bar and heave elements. While the transmission consists of: gear cluster, clutch and hydraulics. Although teams do not normally need to maintain the transmission or inboard suspension over the course of a race weekend, the transmission is regularly inspected in between sessions and this require access through the front of the gear casing. With the inboard suspension in the way, most teams simply unbolt the heave elements, anti roll bar and if required the side dampers. This is complex and takes time, which the teams can do without.
Toro Rosso Gearcase
For the Ferrari engined teams (Ferrari, Sauber and Toro Rosso) the inboard suspension is mounted in a separate assembly. Although Toro Rosso do not use the Ferrari gearbox, they were in fact the innovators in this area. Toro Rosso shifted towards pull rod suspension before Ferrari and have evolved a split gearbox casing with the transmission inside a short metal casing. This is then bolted to a separate carbon fibre casing, which contains the inboard suspension. Bolting to the back of the engine, this suspension case is akin to a separate bell housing. When the team need access to the transmission, they unbolt the front legs of the wishbones and pull rods, then split the metal gear casing from the carbon suspension case. This allows the gearbox and outer rear suspension to be wheeled away, with the carbon suspension case remaining undisturbed and still bolted to the back of the engine. To keep the unbolted wishbone legs and pull rods supported, the team fit temporary mounts to the metal gearcase.
This split case design will have an inherent stiffness\weight penalty, although teams are able to simulate the assemblies stiffness against known load cases, so the Toro Rosso split case design does not imply that is any less stiff. With the weight distribution now fixed and more rearwards biased than in previous times, any weight penalty to recover stiffness is not a problem. No doubt making the suspension case a carbon fibre part helps with lowering the total weight of the design. One further benefit is the suspension case and the inboard suspension are all made by the team itself, unlike a cast gearbox case, which has to be outsourced to an outside supplier. This means any changes to the suspension case or inboard suspension can be competed quickly and reliably by the team. With suspension being a primary factor in tyre management, this equates to a strategic advantage for the team.
Ferrari shifted to Rear Pull Rod suspension for 2012, this necessitated a new gearbox casing. No doubt the Toro Rosso solution inspired Ferrari approach to their powertrain design. They were perhaps also mindful of the stiffness\weight challenge of split case, so their design is a progression from Toro Rosso’s. With the access benefits of a separate inboard suspension module, but not by employing a split case.
The Ferrari gearbox case is made from carbon fibre and as is conventional, it is a single structure from the rear of the engine back to the differential. This makes the structure as efficient as possible from a stiffness perspective. But if otherwise conventional, this would present the same access issues. So Ferrari have cutaway a small section at the bottom front of the casing (yellow). This allows the pullrod to reach the inboard suspension, but rather than the springs and dampers being mounted to a bellhousing-like separate case, or mounted directly inside the case, Ferrari have mounted everything on a separate plate.
The other design difference to the Toro Rosso is that the wishbones remain bolted to the gearcase and do not have to be disturbed, which makes splitting the gearcase from the suspension module even easier.
Sauber Suspension module
I have been lucky enough to have a photo of the Sauber Suspension module sent to me, by a ScarbsF1 fan at the 2012 Airtel Indian GP. In this image we can see the machined metal module, which mounts the entire inboard suspension. This assembly bolts to the back of the engine, with the clutch passing through the opening in the middle of the module. As with the Toro Rosso solution the gearbox can be removed, by unbolting the pull rod ends and the gearcase from the engine. This leaves the suspension still bolted to the engine and the outer rear suspension attached to the gearcase. The potential for the engine\gearcase interface to lose is possible as the apparently unbridged gap at the lower front of the case appears to be left open. But the gearcase bolts through the suspension module and into the back of the engine, restoring stiffness to the unbridged section. As with the Toro Rosso split case solution, this makes revisions to the inboard suspension easier. However for Ferrari the suspension module is far simpler than Toro Rosso’s casing, so Ferrari\Sauber would find altering their suspension module even easier.
As Sauber use the entire Ferrari powertrain (Engine\Gearbox\KERS), they also employ the unique Ferrari gearcase shape. Although they do not necessarily employ exactly the same layout on the suspension module, as each team is responsible for their own suspension design.
Unfortunately the Sauber suspension module photo does not include the dampers, so we will have to speculate on the position and purposes for each bell crank on the rockers. Each Rocker (grey) is operated by the pullrod, which pulls on the lowest of the bell cranks emerging from the rocker. Inside the rockers are the torsion bars (yellow) which are mounted in a near vertical position and act as the side springs for each wheel. There appears to be three other bell cranks mounted to the rocker. I’d suggest the lower pair are used for the Heave spring (blue), while the middle pair operate the Anti roll Bar (ARB) by a set of connecting links. Barely visible behind the anti roll bar, are the last pair of bell cranks, which probably operate the side dampers (red) with their inner ends mount to the structure supporting the ARB. In the Sauber set up, there does not appear to be a separate roll damper or interlinked heave element. I know that many teams do run separate roll dampers, Ferrari had one included as part of their 2011 rear suspension. While the front and rear suspensions could still be linked, if the heave element was a hydraulic device, as well as a sprung device.
Ferrari 2013 Rear inboard supension module
With these set ups, all three teams appear to have found a small operational advantage and perhaps even a strategic benefit as they can alter the inboard suspension layout with resorting to a completely new gearcase. It’s strange it’s solely the Ferrari engine teams that have found this solution, no other gearcase I have seen powered by another engine manufacturer have seen this as a solution, despite some teams having run rear pull rod suspension since 2009. Perhaps we will see some different solutions from the other teams in 2013?