Lotus Renault GP: Fluid Inerter

Lotus Renault GP (LRGP) have been on one of the teams most innovative with their suspension over the past decade. As RenaultF1 They introduced the Tuned Mass Damper (TMD) back in 2006 and have since raced conventional Inerters. Inerters are a special component in the suspension to counteract spring effect of the TyresSuspension, using a spinning mass on a threaded rod to control these loads.

LRGP have also been one of the teams racing hydraulically interlinked suspension and have looked at other ways to legally alter the suspensions performance. It seems this work has lead to the discovery of a new form of Inerter, primarily using fluid for the Inerter effect. This new development has been termed by the team a “Fluid Inerter”.

A cross section of the patented Fluid Inerter

The intellectual property rights to this development have been safeguarded by Patent, allowing the details to be freely accessible in the pubic domain (the source for the picture at the top of this article). My attention was drawn to this development by Italian Mechanical Engineer Rodolfo De Vita, a specialist in Torsional Dampers and Dual Mass Flywheels (DMF).

Background
Becoming ever more complex the suspension in an F1 car has a number of devices to counter loads fed into the chassis, in order to maintain the ideal conditions at the tyre contact patch. We understand the role of springs and dampers, but there remain other spring effects within the suspension system, not least from the high profile tyres. Their spring effect goes undamped and hence is largely out of the control of the teams in setting up the car. Being able to counteract these uncontrolled forces in a suspension will allow the tyre to main better contact with the ground for more consistent grip. In 2003 Cambridge Universities, Dr Malcolm Smith proposed a mechanical method of controlling these loads via the Inerter. McLaren took up this idea and tested the idea in 2004 then went on to race an Inerter in 2005.
In size and construction the Inerter looks like any other damper. Being placed in the same position as a Heave Damper it was well hidden and unknown to most people. Until the “Spygate” saga in 2007, when the design was referenced as both the “J-Damper” and “a Damper with a Spinning Mass”. It wasn’t until May 2008 that I was able to understand and expose the details of the Inerter concept, publishing its details in Autosport.com (subscribers only http://www.autosport.com/journal/article.php/id/1554 ). Co-incidentally this article is cited in the patent documentation!

A Mechanical Interter

An Inerter can be configured in two ways: a linear and a rotary format. In both guises the device uses a toothed drive to spin a mass. Likened to the same effect as a bicycle bell, the load fed into the bells lever is dissipated by the spinning element. In F1 teams use a cylindrical mass screwed onto a threaded rod inside a damper body. One end of the rod is affixed to one side of the suspension and the damper body to the other side of the suspension. Reacting to the acceleration of the suspension, the Inerter absorbs the loads that would otherwise not be controlled by the velocity sensitive conventional dampers.

The Renault 2006 Front Tuned Mass Damper (TMD) - Copyight: Craig Scarborough

The Inerter predates Renaults TMD, which aimed to achieve the same effect. With the TMD a weight is suspended on spring to offset the same forces being fed into the chassis as the Inerter. Renault first raced the TMD in 2005, its discovery by Giorgio Piola around Monaco of that year; both forced a development race and an enquiry by the FIA. It was subsequently banned on what proved to be false grounds. The FIA citing a movable aerodynamic effect as the reason for its ban.
Unaware of its effect on the contact patch, I initially saw the device as a means to prevent the front wing pitching downwards when braking. The inertia of the suspended mass keeping the nose from pitching downwards during the initial braking phase. This I thought would prevent the car from being pitch sensitive. Despite a lengthy court room case, this “aero” function was upheld as the reason for the ban of the device.
Ironically the McLaren was using the Inerter at the time, and despite it being used for the same function was not banned and remains legal and in universal use to this day.

LRGP’s Fluid Inerter Concept
Reading the detail of the LRGP patent, it’s clear this was at least partly a surprise discovery. The Patent states the discovery was “based on lab testing of another hydraulic suspension device”, when it was found that the effect of the fluid within the system “has a very significant inertia effect”.
I would suspect this discovery was made during the development of the linked suspension system. Where fluid lines are used to link the suspension in a similar manner to the Mercedes system I detailed earlier this year (http://scarbsf1.wordpress.com/2011/10/17/mercedes-innovative-linked-rear-suspension/). Perhaps the longer fluid lines to link front and rear suspension provided the discovery, rather than the very short left to right linking pipework. I understand Renault have had hydraulically linked suspension on the car since at least 2009.
With this insight LRGP have proposed a Fluid Inerter using both the inertia of the fluid and a spinning mass. By making the Inerter device more like a damper, where by a damper rod displaces fluid; this fluid is then piped into a circuit to spin the mass. There by both effects can be created. It is the inertance of the fluid that differentiates the LRGP patent to the conventional Inerter proposed by Dr Malcolm Smith.
Inertance is a new term and I’ll quote the patent for LRGP’s explanation of the effect.
“Hydraulic fluid inertance means” concerns an arrangement in which the presence of a hydraulic fluid provides an inertance, where inertance is a measure of the fluid pressure which is required to bring about a change in fluid flow rate in a system. Between the terminals this translates to an inertial force which resists acceleration.
LRGP found that the fluid used was critical to the efficiency of the design. In particular to make it effective for the lightweight and small packaging volume required to make the device work within the tight confines of an F1 footwell or gearbox. Needing to be incompressible and low viscosity, they have proposed several fluids, such as water and oil, but the preference appears to be for Mercury. Although a metal, it’s liquid at ambient temperatures and very dense. This means smaller fluid lines filled with mercury will provide the necessary inertance, compared to larger amounts of less dense fluids. Passing from one chamber in the damper body via the fluid line to the other chamber, the detail design of the length and diameter of the fluid lines are key in creating the correct tuned inertance effect. Just “1 to 50g” of fluid is required to get the desired effect. The range of inertial reaction is quoted as “10 to 500kg, which is a typical range required in Formula One racing cars”.
As a side note McLaren decouple this inertial reaction force into different measured units. Rather than Kg of Inertial force, McLaren use the term “Zog”, this allows them to hide the actual units set up on their Inerter.
Renault suggests winding the lines around the damper body as one solution for the packaging of the fluid circuit. Additionally a valve or shim stack in the damper rod would also alter the amount of fluid displaced, to further tailor the Inerters effect.
With Mercury having a high coefficient of thermal expansion, the patent suggests using a relief valve emptying into another chamber is used to ensure the system has a constant volume of fluid.
Clearly the emphasis is on the fluid to provide the inertance effect, the patent citing a minimum 50%, up to as much as 90% of the inertance coming from the fluid.

In Detail

The device uses the left hand casing as the fluid cylinder & the right hand casing for bump rubbers

Not only does the Patent contain the conceptual information on the Inerter, but also detailed cross sections. I have simplified these to explain the Inerters construction. LRGP have been able to condense the entire solution into a single self contained component, which fits into the same volume as the conventional Inerter.
The device is made up of a main body and a damper rod. The main body split into left and right sections bolted together. The left hand casing forms the cylinder, not only contains the fluid, but also channels machined in the outer casing form the fluid lines. Such that no external pipework is required. The right hand casing allows the damper rod to pass through and also houses bump stops to prevent the device bottoming at the end of its 16mm of bump travel or 23mm of droop travel. In total the device is just 220mm long (eye to eye).
In cross section we can see the casing is a complex machined part. With the right hand chamber formed with bushes, seals and endplates to create the cylinder for the damper rods to pass through. The damper rod along with its shim stack valve pass through the cylinder like piston as the suspension compresses and rebounds. The mercury within is displaced and passes through channels into the channels machined into the wall of the body.

Installation

The Inerter (yellow) is mounted between the rockers

LRGP provide a diagram for the Inerters mounting. This being a typical position between the pushrod rockers. No doubt a similar mounting is found between the rear pull rod rockers. Externally it would be hard distinguish the Fluid Inerter from a Mechanical version. Albeit the Renault front bulkhead design shows almost nothing of the Inerter inside the footwell. The steering rack and anti roll bar getting in the way of the small aperture inside the front of the monocoque. Thus we cannot be clear if the device has raced.

Benefits
One benefit is the technology is proprietary to LRGP and not used under license via Penske or Dr Malcolm Smith. Thus LRGP are free to use and develop this technology freely.
I couldn’t state whether the Fluid Inerter has any compliance benefits over a mechanical one. Perhaps it’s easier to tune via the shim stack in the damper rod, rather than the fixed specification of the mechanical Inerter. Equally it may be easier to maintain, teams needing to strip clean and re-grease their Mechanical Inerters frequently to maintain their smooth operation.
It seems one advantage to this device might be lightweight. The tiny amount of fluid required would be lighter than an equivalent spinning mass. As Inerters tend to be mounted relatively high a weight saving will aid CofG height, as well as ballast placement.
One negative issue is that Mercury is a hazardous material. Considering the unit is positioned ahead of the driver’s legs, any mercury leakage as a result of a major accident will only complicate the health issues for the Driver and Marshalls. I am not aware of Mercury being specifically restricted by the FIA approved material list. Although with just a few CC’s of the liquid contained within the cylinder, this might not be regarded as an issue by the FIA.

Conclusion
However the team came across this solution, it is a new direction for Inerter development. The solution is totally legal, as set by the precedent of the mechanical Inerter being allowed to race, even when the TMD wasn’t
It will be interesting other teams come forward with new Inerter or linked suspension solutions. The only problem is few teams patent their design to allow us such insight to their design.

A view of the outer casing

A cross section of the Inerter

An exploded view of the parts

More references on Inerters

http://www.montefiore.ulg.ac.be/doc/smith09.pdf

http://www.ieeecss.org/sites/ieeecss.org/files/documents/IoCT-Part2-14FormulaOne-HR.pdf

Williams Jerez Development

Williams: this inlet blanking panel (arrowed) reduces the cooling airflow to the radiators

One last development spotted from Jerez was this inlet stuffer on the Williams.  Normally teams add tape or blanking plates over the radiator itself to tune cooling to the ambient conditions.  This more sophisticated solution suggests the Cosworth does not need the full cooling provided by the initial FW32 spec.  So this stuffer not only reduces the cooling airflow to the radiator but also imroves the airflow around the sidepods, reducing drag.

Heated Fog Free Visor

Wires on the visor provide a fog free view via a heated film inside the visor

SebastianVettel wearing an Arai helmet was seen in the wet Jerez tests with this heated Visor.  Not new to F1, as Schuberth Helmet wearers raced a similar solution a few years ago.  The wires leading into the visor, pass a current to a heated film inside the visor to prevent fogging in the cold and wet conditions.

Quote from my 2008 Monaco GP technical review on Autosport.com

“One feature not seen in a race before was a novel anti-fog visor used by the Schuberth-helmeted drivers (including the Ferrari drivers and Nico Rosberg). We have seen drivers struggling to stop the inside of the visor from misting during previous wet races, as the hot breath from the drivers’ exertion condenses on the cold visor.

Some drivers prop open the visor a little to let air pass inside, or use a double-glazing like inner visor. Schuberth’s solution was to place an electric element inside the visor, to heat the visor slightly.

Much like the demisting element in car windscreen, this prevents the breath forming a mist inside the visor. At the moment the visor is an add-on to the standard RF1 helmet, so the electric cable feeding the element runs exposed down the side of the driver’s element to connect via a plug into the car’s electrical loom.”

http://www.autosport.com/journal/article.php/id/1592

Schuberth heated visor Monaco 2008

Sauber: Jerez Developments

Sauber: The slotted 2009 rear wing made a reappearance, the inlet in the mainplane expands inside the wing to a full width slot

Sauber introduced a number of developments Late in the Jerez test.
These include the blown rear wing based on the 2009 design, new turning vanes some cockpit fins and cooling outlets.
The rear wing uses the moulded inlet on the front of the mainplane to feed a full width slot exiting behind the wing, just below the slot created between the main plane and flap. This is similar to the wing used at Monaco in 2009.

Sauber: the blown slot is below the normal slot in the rear wing

Meanwhile the cockpit gained a pair of serated fins placed where the mirrors would normally be placed. These sit inside a wedge shape space ahead of the sidepods that allow bodywork. they send a vortex over the fronts of the sidepods, although it cannot be ascertained if this goes into the sidepod inlet or over the top of the sidepod.

Sauber: Small fins are fitted where the mirrors would normally be placed

Then just by the side of the cockpit on the sidepods are two new cooling outlets. unlike other teams Sauber choose to fully expose the vents, so they sit proud of the sidepods top. Other teams have these joined to the cockpit side. Cooling outlets in this area are allowed as they sit just inboard of the controlled sidepods surface. additional cooling is provided by long thin louvered panel (not visible in these pics) moulded  the floor in the narrow coke bottle area. Again this sits below the controlled area for the sidepods surface.
Under the raised chassis at the frotn fo the car are a pair of new turning vanes, not especially clear in the photo, they curve down and outwards, just behind the wishbones.

Sauber: New cooling outlets and turnign vanes appeared on the car

McLaren: Jerez Developments

Continuing their fight back from the MP4-24, McLaren are working hard with the aggressive looking MP4-25.  Several aero tests were run during the last test, with some new details becoming apparent.  

Their 2009 public testing of flow vis, the fluorescent paint used for surface flow visualisation, was unheard by the average fan before last year.  Although this is in fact a common practice for teams.  Used mainly in straight-line testing, but it has even been used in public testing.

Also using arrays of pressure taps is another common aero testing tool made public by McLaren last year.  Again this year McLaren have used these tools in recent tests, the flow-vis being tried several times and the pressure taps early one morning in last weeks tests.  

These are not necessarily the sign of a problem, as the tests are aimed at proving the simulation results (wind tunnel or CFD) are borne out on track.  

Another tool commonly used and rarely seen are the tyre temperature sensors used in testing and often in Friday practice.  McLaren have long since used tiny infrared cameras to measure the temperature signature across the full width of the tyre.  In previous years these have been fitted in pods to the side of the cockpit or to the rear floor of the car.  Now the cameras are so small land their range sufficient that McLaren fit theirs inside the wing mirror shells, pointing to each front tyre.

Small infrared cameras in the mirrors measure the temperature accross the full tread of the tyre

Details of IR cameras used in motorsport can be found at thermoteknix.co.uk

McLaren: Innovative rear wing and shark fin

McLaren blown rear wing: The black line is fed by air fed through the airbox inlet and sharkfin

Still at the ‘unproven theory’ stage is the potential function of the supplementary air intake above the drivers head.  This had been presumed to be purely to feed an oil cooler, but closer inspection suggests there may be another primary function for this inlet.  Allied with the shark fin, the inlet appears to provide airflow to inside the rear wing.  Creating a ‘blown slot’ to make the rear wing more effective.  Similar to a concept used by BMW Sauber last year.

It looks like McLaren have opened up a slot in the back of the rear wing, this is visible as a blackline above the normal slot between the wing and flap.  This slot is fed with air from the inlet and routed inside the shark fin and rear wing flap.  The high pressure air exits through the slot and effectively makes the two element rear wing into a three element device.  This allows the rear wing to angled more steeply without fear of stalling, thus creating more downforce.

Clues to support this theory is the way McLaren have closed off the inlet, an access hatch inside the shark fin, as well as the bulbous shape of the fin leading towards the rear wing.

As BMW Sauber set a precedent last year with a flap blown by an inlet in the front of the wing, this is a legal approach to circumventing the restriction on the number of elements allowed in the rear wing.

Red Bull: Jerez developments

Red Bull: Revised front wing endplates, with a slotted side and new cascades

Following their evolutionary theme for the RB6, last week their car appeared with a logical development to the RB5 front wing.  As with much of the aero on the Newey designed car, the approach is unique.  Red Bull have a wing highly integrated into the endplates, with the flap and two slots hard to distinguish from the endplate and main plane.  

One feature common to many cars is the Brawn style upright-less endplate, Red bull have not followed this path and the endplate still features a large upstand along its upper edge.  The upright-less design directs more flow low around the wheel, to replicate this Newey has followed some other teams and vented the side of the endplate to accelerate the flow inside the endplate, creating the more powerful flow around the front tyre. 

Allied to the vented endplate the new front wing also sports revised cascades, still split into two span-wise sections,.  But the two sections are now more aggressive and flanked by endplates.

Mercedes: Jerez Developments

Ross Brawn was open following the opening test in Valencia, which uncovered a few problems with the car.  One being the cars weight distribution, which is reportedly too far forward.   With the narrower front tyres and revised rears most teams are playing with this setting.  Brawn were one of the team that learnt early last year how a forwards weight bias would work well with the new slick tyres.  This year the tendency is to shift the distribution back 1-2%.  Which is a relatively simple case of taking ballast from the front wing and splitter and placing it around the gearbox area.

One more visual change is the unique roll structureairbox, which has been subtly revised.  The sculpting behind the roll structure feeding the oil cooler has gained a side panel to enclose the duct, forming a more distinct entrance either side of the main inlet.  

Then having had problems with cracking exhausts and the question over the original exposed exhaust design not meeting the R75 bodywork regulations, the car sported new exhausts, twisted near their exits and with slash cuts to make them flush with the bodywork.

Mercedes: a side panel for the oil cooler inlet and new exhausts have been tested in the past weeks at Jerez

Jerez Updates

Jerez testing has proven a wash out with few teams running any new developments.  This is not totally due to the weather, as most teams are now in the first phases of setting up the cars, trying different weight distribution and learning the new tyres.  Which requires a good baseline to work from and not complicating the picture by adding untested aero parts.