# Through Shaft Damper Update

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Following the small line in the Autosport International article, Race Tech has done two follow-up articles on Through Shaft Dampers (TSDs). One on the Penske example, and a further one on TSDs from Sachs Race Engineering.

## Conventional vs. Through

The operation of a standard gas pressurised, remote reservoir, mono tube damper is quite simple; the rod enters the body on compression and this displaces a volume of fluid that passes into the reservoir through an adjustable valve. Further valves are present in the piston itself. For those not clear on this subject, check out www.penskeshocks.com/technica.htm .

The problem is that the piston valve must be quite soft (with no low speed orifices) to prevent a large initial force being requires to compress the damper. As such the main compression damping (and adjustability) is provided by the reservoir valves that work on the displaced fluid. The problem that arises with this on modern formula cars is that short strokes and compact designs (i.e. small rod diameters) leads to very small fluid volumes with which to generate damping forces. This is a problem because damping is the conversion of kinetic to heat energy, and the less fluid you have the harder it will have to work, with all the obvious implications for the durability and consistency of the damper.

Recently dampers such as the Ohlins TT44 and the Sachs Formula have implemented twin tube designs that allow a larger flow volume though the valves, check out the Ohlins info here: www.ohlins.com/pdf/tt44.pdf . It is my belief that the through damper has the potential for the improved valve flow from the short strokes required in modern formula cars, while allowing very compact components.

The following diagram shows a mono tube damper and a through damper with an identically sized body and rod diameter. For the sake of argument I have set the rod diameter to 16mm and the id of the body to 36mm. For a stroke of 25mm this gives the following flows through the dominant valves in the respective dampers;

Conventional damper: $\small 25\pi8^2 = 201 mm^3$
Through damper: $\small 25\pi(18^2-8^2) = 20425mm^3$

This is a dramatic difference, admittedly a similar volume of fluid is flowing through the piston on the conventional damper, but this can’t be exploited to the same degree for the reasons mentioned.

It is clear from this that the through damper could allow much larger fluid volumes to be used to generate the primary damping forces for a given piston and rod combination. The simplicity of the design also appeals, as does the removal of the requirement for a large pressurised gas volume.

However some form of temperature compensation would probably be required, to deal with the reduced fluid density as the temperature increases.

## The ‘Fan’ Damper

Another fascinating development that Jeff Ryan alluded to is the development of what I’ve dubbed the ‘Fan Damper’. This apparently uses a piston with drilled orifices that contain tiny fans. The fans would spin as fluid was forced past them when the piston moves.

Apparently this will allow a very smooth progressive damping curve to be generated, but clearly posses some interesting manufacturing challenges.

## Penske

The Race Tech article on the Penske TSD appeared in the April/May issue and covers two pages. The following picture was also used.

As I suspected in my article, one of the key advantages to a TSD is the lack of nose pressure. Gas pressurisation is still employed to prevent cavitation of the damper oil, however when the temperature rises the pressure changes are equal across the piston and therefore the effective rate of the suspension isn't affected by this. Also because the gas pressure is only required to prevent cavitation it can be lower than a conventional damper and this reduces seal friction, but of course this benefit is offset by the addition of an extra shaft seal.

Another important feature of the TSD is that it is possible to add some form of spring between the end of the shaft and the damper body, this could act in the same way as a third spring and is an interesting set-up option for the users of TSDs.

I was lucky enough to spot a user of the Penske TSD at the recent British F3 meeting at Castle Combe. Avanti Motorsport is using the damper on it's pair of Dallaras. The following shot clearly shows the protruding damper shaft and the small nitrogen reservoir. What is also clear is that no additional spring or bump rubber has been fitted between the protruding shaft and the damper body. Clearly it is early in the development cycle for this configuration and the team either hasn't explored this option or didn't deem it suitable for the circuit.

## Sachs

The Sachs TSD article appeared in the June/July issue of Race Tech and covered 4 pages. The following picture was used.

The damper at the top of this shot is clearly the rear damper from a recent Ferrari F1 car. The key points to note are the non-adjustable nature of these units and the use of gas pressurisation to prevent cavitation.

The damper also has a flange for mounting an additional spring as mentioned in the section of the Penske TSD.

Sachs apparently has a development unit that uses a PEEK (polyetheretherketone – a polymer approximately 1/3 density of aluminium) piston and with some Sachs F1 dampers already in the region of 200g in mass, the potential would seem to be there for even lighter units.

## Conclusion

Since my article inspired by a comment in Race Tech, further articles appear to have confirmed my thoughts on the advantages of the TSD concept.

I have confirmed the use of these dampers in the British F3 championship and Race Tech has highlighted the use of TSDs from Sachs by Ferrari in the F1 arena. It will be interesting to see if the concept is taken up by other manufacturers and if the existing Penske unit gains any more customers.

By Ben Michell, 2002
Images from Race Tech Magazine