Tommy Cookers wrote: ↑27 Mar 2025, 22:06
Chuckjr wrote: ↑27 Mar 2025, 09:18
What about a V10 oval piston? Ferrari just patented a wild design...
co-planar rods were the convention eg even before Harley met Davidson
likewise articulated co-planar rods
V aircraft engine rods always were co-planar but often not articulated
the modern convention (side-by-side rods) dates from the first 'cheap' car V8 (1932 Ford)
in WW2 Ford so redesigned the RR Merlin making it worse
imo regardless of rod type the V12 doesn't have a 'rocking couple' ... because ....
inline 6s give nil resultant couple (primary and secondary) and in effect the V12 is two inline 6s superposed ....
so don't the secondary effects expected with the articulated (shorter) rods also give a nil resultant ?
(in a WW1 Sunbeam aero engine articulated rods caused vibration problems but it was a (flat crank) V8)
Honda went 'oval piston' to get 8 valves per cylinder ie a 4 cylinder engine with the total valve area of a V8
the Ferrari patent doesn't mention this aspect ?
(btw at the time this 23000 rpm GP Honda was said to have no piston rings - and a very high rpm starter)
Zynerji wrote: ↑28 Mar 2025, 03:07
What if they tilted the pistons and twisted the wrist pin perch to NOT be in the rocking direction? Would it help?
Well this is fascinating. I loaded in the questions from Tommy and Zynerji into Grok, and this is what it spit out.
Ferrari’s recently patented oval-piston V12 design is indeed a fascinating evolution of internal combustion engine architecture, and your question dives into the nitty-gritty of its dynamics—specifically the rocking couple, secondary effects of articulated rods, and the potential impact of tilting pistons or twisting the wrist pin perch. Let’s break this down step-by-step, exploring the mechanics and reasoning through the implications.
First, let’s establish the baseline. A traditional V12 can be thought of as two inline-6 engines sharing a common crankshaft, with the cylinder banks typically offset at a specific angle (often 60° or 65° in Ferrari’s case). An inline-6 is inherently balanced for both primary and secondary forces and moments, including the rocking couple—a rotational oscillation caused by the reciprocating masses of the pistons and rods. The primary balance comes from the 120° crankpin spacing, which cancels out vertical and horizontal forces over the engine cycle. The secondary balance, tied to the second-order harmonics of the piston motion (due to the connecting rod’s angularity), is also nullified in an inline-6 because the opposing pistons’ motions symmetrically cancel these effects. In a V12, this symmetry is mirrored across the two banks, so the net rocking couple and secondary forces theoretically remain nil, assuming perfect symmetry and no manufacturing or design deviations.
Ferrari’s oval-piston V12 introduces two key innovations: oval (or “pill-shaped”) pistons oriented with their long axis perpendicular to the crankshaft, and an articulated connecting rod system where opposing pistons share a single crankshaft journal via a primary and secondary rod arrangement. The oval pistons allow the cylinders to be packed closer together, shortening the engine longitudinally, while the articulated rods further reduce the crankshaft length by eliminating the need for offset journals for each piston pair. This is a clever packaging solution, potentially beneficial for mid-engine layouts or hybrid systems, but it raises questions about dynamic behavior.
Now, to your point about the rocking couple and secondary effects. In a standard V12 with conventional round pistons and individual connecting rods, the rocking couple is already nil due to the inline-6 superposition, as you noted. The articulated rods in Ferrari’s design shorten the effective rod length for one of the pistons (the secondary rod pivots off the primary rod rather than directly off the crank), which alters the rod-to-stroke ratio. A shorter rod increases the angularity of the rod during the stroke, amplifying secondary forces—those second-order vibrations caused by the non-sinusoidal motion of the piston. However, because the V12 retains its mirrored inline-6 structure, these secondary effects should still cancel out across the engine. For every piston with a shorter articulated rod on one bank, there’s a corresponding piston on the opposite bank, and their motions are phased to counteract each other. So, theoretically, the net resultant of these secondary effects remains nil, just as in a conventional V12.
But here’s where it gets interesting: the articulated rod design introduces a new variable. Unlike a traditional setup where each piston has its own rod of equal length, the primary and secondary rods in Ferrari’s patent have different effective lengths and pivot points. This could introduce localized imbalances or vibrations at the individual cylinder level, even if they cancel out globally. The secondary rod’s motion isn’t purely linear—it pivots off the primary rod, adding a slight lateral component to its trajectory. This could induce a small rocking motion or side-loading on the piston, potentially increasing wear or friction against the cylinder wall, especially given the oval piston’s non-circular shape, which already complicates sealing and stability.
This brings us to your suggestion: tilting the pistons and twisting the wrist pin perch to avoid alignment with the rocking direction. In a conventional engine, the wrist pin (or piston pin) is perpendicular to the cylinder axis, and the piston “rocks” slightly within the bore due to the rod’s angularity, a phenomenon known as piston slap. With oval pistons, this rocking could be more pronounced along the shorter axis, where the piston has less surface area to resist tilting. If Ferrari tilted the pistons—say, angling them slightly relative to the cylinder bore—and twisted the wrist pin perch to align it out of the plane of this rocking motion, it could theoretically reduce side-loading and stabilize the piston’s travel. The idea would be to orient the piston’s motion such that the secondary forces and any residual rocking from the articulated rods don’t amplify each other.
Would it help? Possibly, but it’s not without trade-offs. Tilting the piston changes the combustion chamber geometry and the way forces are transmitted to the crankshaft, which could affect efficiency or power delivery. Twisting the wrist pin perch might mitigate rocking along one axis but could introduce new stresses or alignment challenges, especially with an oval piston that already demands precise sealing (a known hurdle, as Honda discovered with its NR500 oval-piston engine). Ferrari’s patent doesn’t mention such a configuration, suggesting they’re relying on the V12’s inherent balance and possibly recesses in the piston skirt (as noted in the design) to manage friction and stability. However, your idea could be a refinement if testing reveals excessive piston slap or vibration from the articulated rods—something Ferrari’s engineers might already be exploring behind closed doors.
In practice, the nil resultant of a V12’s rocking couple and secondary effects should hold unless the articulated rods disrupt the symmetry significantly. The real challenge might not be the rocking couple itself but rather the piston’s stability within an oval bore under these new dynamics. Tilting or twisting could help there, but it’d require careful simulation to ensure it doesn’t upset the engine’s balance or manufacturability. For now, Ferrari seems confident in the base design’s equilibrium, likely banking on modern materials and precision engineering to smooth out any quirks. Still, your suggestion highlights a creative avenue for optimizing this wild concept further—something that could set it apart even more if it ever roars to life in a production car.
Watching F1 since 1986.
