J-Dampers in Formula One
One of the key technologies emerging from F1 this year has been the so called J-Damper. Acting as an alternative to the banned Tuned Mass Damper (TMD), pioneered by Renault to reduce variations in contact patch load between the tyre and the ground. The systems first existence was revealed in the McLaren/Renault F1 spy case when the device was noted as one of the drawings taken to Renault when Phil Mackereth left McLaren. It now emerges that McLaren have run their J-Damper since early 2005, pre dating Renaults adoption of the Mass Damper later that year. It’s now believed many teams run a J-Damper more correctly termed an Inerter, as explained by Malcolm Smith of Cambridge University back in 2003. Smiths Inerter solution absorbs energy from the Tyres/suspension providing an "equal and opposite force applied at the nodes, proportional to the relative acceleration between the nodes". When tuned for the tyres natural frequency an Inerter will offset the tyres deflection from upsetting the suspension behaviour.
Tuned Mass Dampers
Mass Dampers were first raced at the Brazilian GP in September 2005 by Renault and subsequently adopted by several teams in 2006. Using a sprung/damped mass mounted inside the nose cone the ~9Kg helped offset the large sidewall deflections of the high aspect ratio F1 tyres. Particularly aiding Michelin runners whose vertical stiffness was lower than the rival Bridgestone tyres. With the head start on the technology, Renault had also repackaged their gearbox to fit a TMD above the gear cluster for 2006. Technical Director Bob Bell commented on the rear TMD at the time "It’s less effective by virtue of the fact that the physics of the situation dictate you get more benefit from one at the front than at the rear, but it’s still there and worth having".
Alleged to be worth a couple of tenths per lap, once exposed at Monaco 2006, the FIA soon stepped in to ban the devices on a technicality. There placement inside the detachable nose cone and considerable weight, sparked both safety fears and issues surrounding the use of moveable ballast. However the FIA felt their potential aerodynamic effect of stabilising ride height and hence diffuser and front wing efficiency was the best legal course to take.
Even before Renault had adopted the TMD, McLaren had picked up on work completed by Malcolm C. Smith at the University of Cambridge, His lecture to the Society of Instrument and Control Engineers (SICE) in August 2003, explained the systems principles, making the mechanical system analogous a passive electrical system. His proposal was a dual flywheel set inside a damper body operated by a rack\pinion. As force is applied to the endpoints of the device, the flywheels accelerate producing an opposite and equal force. In this layout the Inerter is akin to a bicycle bell, the force from your finger is opposed by the spinning of the bells ringer. Smith also put forward alternative embodiments with a flywheel concentric to a threaded damper rod and also a hydraulic solution.
|Cross section of the J-damper, showing the eyes for mounting the casing to one suspension rocker and the threaded rod to the other. The flywheel (in red) spins in the bearings (yellow) to absorb and release kinetic energy||Mounted between the suspension rockers, the J-damper is inactive in body roll and only operates in vertical movement or jounce, hence its name|
Adoption in F1
It is believed the solution was then picked up by McLaren and developed in associated with Smith during 2004. This reached maturity when the system raced for the first time at San Marino in late April 2005.
Packaging the system on a Formula1 car precluded the rack and pinion ‘Bicycle bell’ from Smiths Lab tests and the concentric version has been adopted. The Inerter is mounted in place of the usual heave damper, thus the set up is decoupled from roll. As the system is relatively light (~3Kg) and easy to package it can be fitted front and rear. At the front on the McLaren the inerter is hidden inside the footwell of the monocoque, while at the rear being mounted high above the gearbox the device is in clearer view. McLarens long running practice of using large diameter hollow Titanium heave spring hides the detail of the device, making its existence hard to spot.
With TMDs being banned in August 2006, many teams were left without the benefit of an alternative solution. With Smiths work being public and nothing in F1 being secret for very long, the Inerter solution has been adopted by other teams. Exactly who is a matter of conjecture, Williams technical director feels "Most teams have been using them for a couple of seasons now".
Ferrari are believed to be the first of the other teams to race Inerters. As an ex-TMD user, the team were struggling against McLarens better mechanical grip through out 2007. Late in the year the team raced their solution in Monza, the tell-tale large heave damper fitted to the rear of the car, certainly improved their grip. But the system caused a race retirement for Felipe Massa, when the inerter failed after 10 laps.
Recent comments from Renault's director of engineering, Pat Symonds suggests Renault have now adopted the technology. Their debut being delayed by the need for Renault to be transparent, in not using any of McLaren’s intellectual property in their interpretation of the solution. Although not confirmed by Renault they are understood to have raced their solution at this years Spanish GP.
As with TMDs the Inerter is said to be worth two tenths per lap and a sizable advantage for any team in what is now a tyre controlled formula.
As the Inerter becomes more common place in F1, its long served covert use at McLaren, raises the issue that the device, which ostensibly is the same as the TMD, was not banned by the same interpretation of the rules. While the FIA’s banning of TMDs on aerodynamic grounds was tenuous, but matched common understanding of the system at the time, was more related to fears that ever heavier and complex TMDs would be fitted creating a safety fear should they break loose. The Inerters advantage is that they are lighter and a recognisable part of the suspension, thus are well contained within chassis in the event of an accident. Again Sam Michael explains "These are different to mass dampers and fully legal because they are part of the suspension system". Thus it appears that the Inerter is likely to remain within the sport and perhaps be expanded into other high aspect tyre ratio formulae, where vertical tyre deflection produces unwanted disturbance to the suspensions work.
As published in Racecar Engineering magazine
Text and illustrations by Craig Scarborough
Image by Ian Harris