The ACO, which organises the Le Mans 24 hour race and sets
the technical regulations that are also used by the European
Le Mans Series (ELMS) and the American Le Mans Series
(ALMS), attempts to equalise performance between different
types of engine within each of its various LMP and LM GT divisions. It
does this by means of intake air restrictors and also a cap on plenum
pressure in the case of turbo-supercharged engines (see sidebar: LE
MANS ENGINE RESTRICTIONS). In theory the ACO could cap plenum
pressure by means of a mechanical Ôpop-offÕ valve, as has been used
in Indy Car racing, for example. In practice, it has put the onus on the
individual competitor and rather than introduce some form of control
device, instead it monitors the plenum pressure of each turbocharged
car to ensure that it does not transgress the limit.

Stack supplies the Le Mans scrutineering system

 

These days all turbocharged Le Mans engines have wastegate control
as part of a sophisticated engine management system. For example,
in Race Engine Technology 010/ Grid, we looked at a contemporary
Nissan system. That system, in effect, added controllable pneumatic
springing to the action of the wastegate diaphragmÕs normal wire coil
spring. Control was effected by metering the pneumatic system using
a pintle-type solenoid air valve under the command of the engine
management system.

Clearly the engine management system will constantly monitor
plenum pressure and will be programmed to ensure that the maximum
permitted level is not exceeded. However, it is equally clear that,
rather than rely upon competitor honesty, the ACO needs its own
independent monitoring system to ensure that the limit is enforced at
all times. Thus the ACO needs a system whereby it can monitor each
and every turbocharged carÕs plenum pressure throughout all practice
sessions and the 24-hour race itself: a somewhat tall order!
On top of that, the ACOÕs requirement is to monitor intake air
pressure of the naturally aspirated cars as well. Placing an air pressure
sensor between the intake air restrictor(s) and the throttle bodies
enables the operation of the restrictors to be monitored, to check
that they have not been tampered with, or perhaps somehow been
inadvertently circumvented. For example, on one occasion a Porsche
GT2 competitor started lapping suspiciously quickly after an accident
and the ACOÕs scrutineering system identified the fact that a restrictor
had been knocked off!

To attain sufficient resolution to properly monitor restrictor
operation, the ACO requires a highly sophisticated scrutineering
system, one that has the capability to monitor all 50 cars at the Le
Mans 24 Hour race. The system must monitor one or two intake air
pressure sensors on each car (vee-engined turbo cars sometimes have
two plenums, one for each bank). In addition, the ACO nowadays
requires each car to be further monitored by a throttle sensor feed and
a Hall-effect wheel speed sensor feed into its scrutineering system.
These are not for regulatory purpose. Rather, the requirement follows
concern over the relative speeds between the various divisions.
This year, there was also added a cockpit ambient temperature
sensor for all of the GT cars. This again followed safety concerns but
it does allow the ACO to check that air conditioning is functioning
in the case of those competitors who accept to run it in return for air
restrictor size concessions.

Not only does the ACOÕs scrutineering system have to collect all
of this data from 50 cars throughout a twice around the clock event,
it has to be clever enough to ensure that it cannot be tampered with.
Consider the number of highly qualified engineers running the 50-odd
cars at Le Mans and one can appreciate that making a tamper-proof
system is another considerable challenge!

The Peugeot coupe is one of many cars that in 2007 will have
to conform to Le Mans engine regulations through the Stack system

 

SYSTEM DEVELOPMENT
Stack Ltd of Bicester, Oxfordshire, England, well known to the global
racing industry for its data logging and display products, is the ACOÕs
partner in development of this complex scrutineering system. Technical
Director of Stack, Trevor Tapping remarks that his company has worked
with the ACO for more than a decade now, initially supplying a system
that logged only plenum pressure data for download at each pit stop.
While this system proved 100% reliable over a ten-year period, it did
require a scrutineer to physically download data from each car at each
stop so from a logistical point of view it put quite a burden on the
ACOÕs officials.

This year the ACO introduced a new Stack developed scrutineering
system and at the 24 Hour race meeting Tapping took Race Engine
Technology through it. The key to it is wireless connectivity, so that there
is no longer a need for an individual scrutineer to physically download
data from each car. Instead the relevant data is transmitted from each car
to the ACOÕs computer system via a telemetry-type system.
The 2006 system saw each car fitted with one or two intake air
pressure sensors and in the case of GT cars a cockpit air temperature
sensor, all these sensors supplied by Stack through the ACO. In
addition, each competitor had to supply data from approved throttle
and wheel speed sensors and from a lap trigger. The lap trigger data
helps the system operator navigate the data.

The boost and temperature sensors are sealed into a carbonfibre
enclosure, the ÔACO trayÕ, which the competitor fits permanently
into his carÕs cockpit. The boost sensor is then linked to the plenum
by a pipe and the ACO checks the integrity of this connection. The
tray also carries a recorder module, which can be easily unplugged
and removed from the car. This module is a modified version of the
normal Stack ÔSRÕ Sensor Recorder module. This Stack technology has
been carefully developed to ensure that it has the heat and vibration
resistance needed to operate reliably in the racing car environment.

The ACO recorder module is known as the WSR: WiFi Sensor
Recorder. It has four channels accepting analogue or pulse signals,
four reading 0-5 volts plus a lap time channel. At its heart is a 25 MHz
Motorola processor, of the type normally used in high-end engine
control units. The module has up to 64 MB of data storage capacity,
which for the ACO provides 14 hours of recording capability. In theory
therefore the data could be downloaded just once during the course of
the 24 Hour race but in practice the ACO wants to keep a much closer
eye on things!

The ACO has 40 of these recorder modules, which incorporate
wireless connectivity, enough for all the cars at an ELMS race (the
ALMS organiser makes its own arrangements) but 10 short at the 24
Hours, where modules are rotated on regular basis. They are allocated
at random and can be switched around even during the race, so a
competitor never knows in advance when they are going to be running
without one. Of course, once 10 cars have retired the remaining field
is fully covered!

The ACO tray is linked by a 13-way Autosport connector to the
carÕs own harness, to accept the signals provided by the teamÕs own
throttle and wheel speed sensors and lap trigger. It contains an internal
battery, which will keep it running for up to three hours in the event of
the carÕs own power system stopping. This means that while the carÕs
ignition is switched off the ACO can still access data wirelessly from
the recorder module. Once data has been taken from the module its
memory is automatically cleared.

While the module is normally accessed by a wireless link, data can
be retrieved by manual download. This is particularly useful in the
event of the carÕs dedicated aerial getting broken off!

The new scrutineering system can collect data wirelessly from any car
carrying a module while that car is in the region of the pit lane. It can
connect while the car is in its garage provided the garage door is open,
which is a requirement during the race. The system recognises the car in
question and can accept data from it not only while stationary but also
as it passes the pits on track and as it runs through the pit lane.
In fact normally data is only downloaded when the car slows
to less than the pit lane speed limit. The system is programmed to
automatically download from each car that it senses travelling within
the speed limit. It takes no more than four or five seconds to download
all the relevant data since the last download, which might have been
up to an hour earlier.

Cars passing at speed are normally ignored while the system can
be programmed to only take data after a certain minimum period of
time has elapsed. This stops data being downloaded at inappropriately
frequent intervals in the event of a car only travelling a lap or so
between pit stops. In principle, the ACO wants data once an hour from
each car, so as not to overload its system operators. However, if a car
becomes of concern to the scrutineers they can monitor its data each
time it passes through the start/finish area in front of the pits.
The ACO scrutineers have a screen that shows the status of each car Ð
whether of not it is connected and when data was last downloaded from
it. The system operators are located away from the garages and this allows
them to keep an eye on the status of each car that they are monitoring.

LE MANS ENGINE RESTRICTIONS

The ACO, which organises the Le Mans 24 Hour race, accepts cars in a number of divisions (currently LMP1 and LMP2 for prototypes plus GT1 and GT2 for production-derived cars) and aims to equalise performance within each. In the Group C era (which ran from the early eighties to the early nineties) this was done by allocating a certain amount of fuel to each division for the race and leaving it up to the individual competitor how that fuel was used. Group C gave us some memorable battles, including those between naturally aspirated 7.0 litre Jaguar V12 and turbosupercharged 5.0 litre Mercedes V8 (as recounted in my recently published book ÔSauber-Mercedes C9, The Return of the Silver ArrowsÕ Ð Crowood Press ISBN 1-86126-836-X). It also gave us 1000 bhp pole attempts by Nissan and Toyota turbo cars for fuel was restricted for the race, not for qualifying! On the whole Group C favoured the flexibility afforded by turbocharging and perhaps mindful of this the ACO these days restricts air as well as fuel. Today fuel is restricted only indirectly, via a maximum permitted tank capacity and a limit on refuelling rate. The competitor still has to use organiser-supplied fuel and making a car more fuel efficient will no longer make it faster around the lap but will allow it to go further between refuelling stops, reducing the amount of time spent in the pits. The reason it will not go faster around the lap is the air restriction that is at the heart of the current equalisation of engine performance within each division. These days all cars at Le Mans have to be fitted with one or two intake air restrictors, the size of which reflects the type of engine. Thus, for example, a 3.0 litre naturally aspirated LMP1 gasoline engine with four valves per cylinder has to be fitted with a 47.8 mm restrictor (or a pair at 34.1 mm) while a 6.0 litre naturally aspirated gasoline engine with two valves per cylinder has to be fitted with a 46.3 mm restrictor (or a pair at 33.1 mm). On top of this the ACO caps the plenum pressure of turbocharged cars. It does this by setting a maximum figure for the various types of engine and then monitoring each car throughout the race meeting to ensure that it is in conformability with the rules, as is described in the main article.

HOW IT WORKS
The wireless technology uses a WiFi ÔengineÕ in the module of the type
found these days in most laptop computers. This converts the data to
radio frequency and it is connected by a lead to an aerial on the car. In
turn the aerial transmits to panel antennas, a pair of which are located
in the pit lane. These are directional antennas, located a couple of
metres apart back to back so that one faces south, the other north. The
south antenna picks up signals down to the final chicane while the
north has visibility up as far as the Dunlop Bridge.

The system uses a high radio frequency, so as not to interfere with
the teamsÕ own telemetry signals. Underneath the pit lane antennas
is a grey box that receives the signals from them. At this Ôaccess
pointÕ the signals are converted from RF and are fed into an Ethernet
connection, which ÔwiresÕ them to the ACO headquarters. The system
operators are located in the ACO building opposite the pits and
the wire goes through the tunnel under the track. The data can be
accessed anywhere on the network in the ACO building.

A PC is used as a server, to store and process the data fed to the
ACO building network. This PC controls the data that is collected and
it wires the relevant data back to the access point, from which it can
be accessed remotely by wireless laptop-equipped ACO scrutineers
operating in the pit lane. The system allows the access point to accept
data from up to five modules concurrently and to transmit data (again
through the pit lane antenna panels) concurrently to as many as 10
laptop computers.

In the event of there being more than five cars to download in pit
lane, the system will automatically work its way through all of the
available modules.

THE SPY IN THE PLENUM
Once the latest data has been collected from a given car, the first
check is that the plenum pressure has remained within the allowable
limit. In the event that there has been a transgression there is an
automatic alarm display on the relevant screen. This highlights the
Ôalarm eventÕ and the system operator can double click on it, thereby
to access the underlying data. The operator will then interrogate
the data, to see exactly by how much and for how long the plenum
pressure was excessive.

The alarm event might indicate a fault with the car rather than a
deliberate attempt to transgress the rules. In the case of a fault, the
excess pressure may or may not have benefited the car. The ACO
scrutineers will make a judgement of the situation and will apply
a penalty or ultimately exclude the car, as they see fit. In general,
competitors do not blatantly flout the rules and normally the action of
bringing in the car to fix a fault that has led to over-boost is considered
sufficient penalty in itself.

In the event that there appears to have been a deliberate attempt
to break the rules, the ACO has the data it needs to make a case
against the competitor. Over the last ten years there have only
been two such instances. In both, upon inspection of the car the
scrutineers found a mechanism designed specifically to circumvent
the boost restriction!

 

This article from race engine magazine was published by permission.