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Part 1:
by Julian Edgar
Race Car Data Logging
More information than you’d believe!
O
ptimising the engine and
suspension of racing cars has
always been a technologically
intensive pursuit but the ability to log
and then later analyse data has taken
the sport to a new level.
Australian motorsport specialist
MoTeC is at the forefront of racing car
electronics, producing digital dashboards, engine management systems
and data analysis software.
This month we’ll look at how racing car data is collected and then
next month, examine MoTeC’s i2 data
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analysis software.
So what sort of data is collected
from a racing car?
Engine
Collecting data on the engine status
is made simpler because the engine
management system’s Electronic
Control Unit (ECU) already uses many
sensors.
The outputs of these sensors can be
used not only by the engine management system but also logged and then
expressed in engineering units.
In addition, the ECU has available
internally calculated data, such as
injector duty cycle.
Engine Load
On naturally-aspirated race cars,
load is normally calculated by the
engine management ECU looking at
engine speed and throttle position.
(This is in contrast to road cars that
most often use an airflow meter to
directly measure the mass of ingested
air.)
Forced aspirated racing cars (that
is, those with turbo or supercharged
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or at the airfilter.
Air/fuel ratio
Previously, the air/fuel ratio was
measured by a zirconia oxygen sensor
such as the Bosch “four wire” design.
Based very much on the technology
of the oxygen sensors used in normal
passenger cars, this device outputs a
voltage of 0-1V, depending on mixture strength. However, the voltage
is non-linear with respect to air/fuel
ratio, with a sudden change in output
around 450 – 550mV (corresponding
to the air/fuel ratio passing through
stoichiometric) and also varies with
temperature. The Bosch unit has a
slightly flatter response than garden
variety oxygen sensors but still has
severe limitations in accuracy, especially at the rich end of the automotive
scale. Linearising it requires accurate
temperature and voltage compensation.
Replacing the Bosch “four wire”
unit is the Bosch LSU probe. This
probe works on a completely different principle and requires its own
control circuit. In short, a zirconiumdioxide/ceramic measuring cell is
used comprising a Nernst concentration cell and an oxygen pump cell,
with a small diffusion gap positioned
between them. Two porous platinum
electrodes are placed within this gap
– a Nernst measuring electrode and
an oxygen pump electrode. The gap
is connected to the exhaust gas via a
small passage.
On the other side, the Nernst cell
is connected to the atmosphere by a
reference air passage. By applying a
pump voltage across the electrodes,
oxygen is pumped from the exhaust
gas into or out of the diffusion gap.
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Fully configurable digital
electronic dashboards are used to
display sensed data and log it for later analysis.
In addition, output alarms can be set when certain combinations of parameters
are met. Data can also be scrolled through by the driver pushing a button.
engines) use a Manifold Absolute
Pressure (MAP) sensor that measures
manifold pressure. When this is combined with measurement of engine
speed, the ECU can again work out
load. So when engine load is logged,
the data is in the form of either throttle
position and engine speed, or manifold pressure and engine speed.
While it might first appear that this
is a complex way of logging engine
load, in fact in racing car applications
it is advantageous.
This is the case because engine
load is most often used in conjunction with the logged air/fuel ratio to
work out where in the load range the
engine is running richer or leaner
than desired.
Since the fuel injector outputs
are determined from an ECU map of
throttle angle (or MAP) versus engine
speed, having available throttle position and rpm (or MAP and rpm) allows
the engineer to quickly find the load
site at which the problem is and then
make the appropriate tuning change.
MAP sensors are calibrated in
absolute pressure and are most commonly available in 1 Bar (suitable for
naturally aspirated engines), 2 Bar (ie
suitable for 1 Bar of boost) and 3 Bar
(suitable for 2 Bar of boost) versions.
Interestingly enough, there is also
available a 1.05 Bar version which
takes into account the aerodynamic
air pressure build-up possible in the
airbox of a fast-moving car.
Most often used are Delco MAP
sensors which start at $80. These
conditioned sensors have a nominal
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0-5V output and are widely used in
production cars.
Coolant , Oil and Intake Air Temperature
Coolant and oil temperatures are
measured by NTC thermistors. The
Bosch 023 and 026 sensors are commonly used – at $17 they are cheap,
use a near universal 12 x 1.5mm thread
and are 2-wire designs (ie, no chassis
ground return) that use a standard fuel
injector plug.
Intake air temperature sensors
comprise a similar design but with
the thermistor exposed to the passing
airflow.
Intake air sensors can be used to sense
air temperature in an intake runner just
prior to entry into the engine (so measuring the temperature rise caused by the
air compression of a supercharger or
turbo, and intake manifold heat soak)
•
MoTeC’s
dashboard display
and logger uses surfacemount components, a military
spec connector and heavy-duty
aluminium construction.
July 2006 9
(Left): an infrared
receiver placed in the
car watches for the
output of a suitably
coded trackside
infrared transmitter.
In this way, accurate
lap times can be logged
and also displayed on
the in-car digital dash.
(Right): these
expansion units
allow a greater number
of inputs to be logged by the
digital dash or the engine
management ECU. The E816
has an additional 18 analog voltage
inputs and eight PWM outputs, while the
E888 has eight analog voltage inputs, eight
K-type compensated thermocouple inputs, four
digital inputs and eight PWM outputs.
The sensor controller varies this
voltage so that the composition of
the gas in the diffusion gap remains
at stoichiometric.
If the exhaust gas is lean, the pump
cell pumps the oxygen to the outside
(positive pump current). If the exhaust
gas is rich, the oxygen is pumped from
the exhaust gas into the diffusion gap
(negative pump current). The pump
current therefore reflects the actual
air/fuel ratio. Again, linearising is
required.
Other than the most recent
M400/600/800 series MoTeC engine
management systems and the PLM
air/fuel ratio meter, no MoTeC logging
device can accept a signal directly
from the LSU sensor. Instead they read
the data from the ECU or PLM via a
CAN bus communication, while the
PLM also has a configurable analog
Manifold
Absolute Pressure
(MAP) sensors made by Delco
are used in conjunction with RPM
and intake air temperature to measure
load. These sensors are available in 1,
1.05, 2, 3 and 4 Bar versions.
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output voltage that can be read by the
data logger.
Exhaust Gas Temperature
Exhaust gas temperature is measured with K-type thermocouples.
Again, an interface device is needed,
this time to amplify and cold junction
compensate the signal.
One example of such an interface is
the $1045 MoTeC E888 input/output
expander. Amongst other inputs and
outputs, this unit can accept eight
K-type thermocouple inputs and
then communicate this data to the
engine management ECU or digital
dash logger by means of a CAN bus
connection.
Exhaust gas temperature is most
often measured at individual exhaust
outlets near the engine, so explaining
the requirement for eight probes in
many race car applications. These give
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Individual cylinder exhaust gas
temperatures are often measured
and logged to indicate cylinder-tocylinder mixture consistency.
a guide to cylinder-to-cylinder mixture
consistency and are most commonly
used in drag racing.
Oil, Brake and Fuel Pressures
Two types of sensor are used in
these applications. The first is the
traditional Bourdon tube based potentiometer, as exemplified by the
large canister VDO units used as oil
gauge pressure sensors on countless
road cars.
However, the accuracy of these
sensors in race car applications is
suspect: when tested on the bench, a
light finger tap can sometimes change
the measured output by 5 psi!
Replacing these are Texas Instruments sensors that use a load cell
backed by a diaphragm. Available
up to 2000 psi maximum pressures,
these sensors have a conditioned 0-5V
output and are available in gauge and
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Bosch LSU sensors
are used to sense the
oxygen concentration of the
exhaust gas and from this, work
out the actual air/fuel ratio. These
new sensors replace the older
zirconia design and are faster and
have higher accuracy over a wider
measuring range.
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absolute pressure configurations.
Throttle Position
Throttle position sensors comprise
rotary potentiometers mounted on the
throttle shaft. They are available in a
wide range of physical designs to match
various shafts but a common one accepts a D-shaped shaft. As we will see
next month, knowing what the driver is
doing with the throttle is a vital component in race car data analysis.
Engine Speed
Engine speed is sensed from the
crankshaft position sensor. This normally comprises an inductive sensor
mounted on flywheel, although in
engines not specifically built for racing
but instead adapted from road cars, the
sensor can alternatively be optical or
use a Hall Effect device.
Other sensors that are sometimes
uses on the engine include infrared thermometers measuring block
temperature and pressure sensors in
the coolant system, the latter used
primarily to sense a catastrophic loss
of coolant.
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Fully programmable
engine management units like
this MoTeC design incorporate memory
for data logging. Engine sensor data is already
available to the unit and suspension data can be
communicated to it from the digital dashboard by CAN bus.
Suspension data requires the installation of specific sensors. Where the
behaviour of individual wheels needs
to be monitored, this involves four sets
of sensors.
Damper Movement
Damper movement is sensed by linear potentiometers. These are available
with different stroke lengths (for example: 75, 100, 125, 150 and 200mm) and
are mounted such that they move over
as much of their range as possible as
the suspension moves from full bump
to full droop.
These sensors cost about $400 each
but they are fully rebuildable, something often required as their vulnerable
positioning results in frequent damage
in racing incidents. Finding space for
the sensors and mounting them so that
no bending loads are placed on them
can be difficult; however, the logging
software can be easily configured to
show actual suspension deflection even
when the sensor is angled from the
vertical or is subjected to a non-linear
motion ratio.
Damper Temperature
The temperature of the oil within the
dampers is sensed indirectly, either by
the use of stick-on thermocouples or,
less commonly, by infra-red temperature sensors.
Lateral , Longitudinal and Vertical
Acceleration
One, two and three axis accelerometers are used to sense accelerations.
These sensors are conditioned with a
0-5V linear output and can be specified
to have maximum acceleration of 10g.
(In Top Fuel drag cars the previous
4g maxima were being exceeded in
longitudinal acceleration!) However,
in circuit racing cars, two-axis accelerometers with a maximum acceleration
of 4g are more normally used.
Cost varies from $360 for a single
axis 4g accelerometer to $688 for a
3-axis 4g sensor.
As we will cover next month, the
outputs of this sensor can be used by
the data analysis software to automatically construct a track map.
The accelerometer is normally
mounted at the roll and pitch centre of
the car. However, two accelerometers
can be individually mounted on the
front and rear axle lines and when
their outputs are compared to steering
angle, be used to assess the magnitude
of oversteer and understeer.
Yaw
Yaw is sensed by a Bosch yaw sensor, as normally fitted to the Subaru
STi model WRX that uses an active
Linear potentiometers
are used to sense
damper
movement.
Data interpretation software
allows damper speeds to be calculated from this displacement data,
allowing optimal bump and rebound
settings of the dampers to be set.
Hall Effect sensors
are used to sense engine
speed, a parameter
used by the engine
management ECU and
also logged for later
analysis.
Load-cellbased pressure
sensors are used
to measure oil, brake
and fuel pressures.
In some cars, even the coolant
pressure is measured!
Chassis and Suspension
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July 2006 11
mounted receiver. A configurable frequency signal is emitted by the beacon
and the car’s system is programmed to
respond to only this signal.
Lap times are logged and also displayed to the driver in terms of laps
to go or lap number. In addition, split
times can be gained by the use of
extra trackside beacons programmed
appropriately.
A dual axis accelerometer is used in
most data-logged racing cars to sense
lateral and longitudinal acceleration.
The unit is designed to work up to 4g
and outputs a conditioned 0-5V signal.
centre differential as part of its four
wheel drive system. In addition to
a yaw rate signal output, this sensor
also contains a lateral accelerometer.
Cost is $1014.
Tyre and Brake Temperatures
Tyre and brake temperatures are
monitored by infrared thermometers
aimed appropriately. In the case of Le
Mans racing cars, no less than three
infrared sensors are used per tyre –
quite a cost at $480 each sensor! Tyre
temperatures are amongst the most
useful of data in setting-up a car for
optimal lap times as the temperature
distribution shows how hard each
tyre – and each part of the tyre – is
working. The infrared thermometers
have a conditioned 0-5V output and
are available in 100°, 200° and 1000°
Celsius ranges – the latter being used
to measure brake temps.
Steering Angle
Steering angle is normally sensed
by a multi-turn rotary potentiometer
driven by a toothed rubber belt from a
pulley mounted on the steering shaft.
Road Speed
In road cars adapted for racing, the
ABS system is usually disconnected.
In these cases, one of the inductive
wheel speed sensors can then be
used for measuring road speed. The
logging software is configured for the
AC voltage levels of the sensor and
the frequency/speed relationship. In
purpose-built race cars, a new inductive sensor is fitted behind a wheel.
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Lap Time
Car racing is about going faster than
anyone else and so lap speed is a critically important parameter.
MoTeC use a trackside mounted
infrared transmitting beacon and a car
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Logging and Displaying
the Data
Given the number of channels and
the frequency at which many are collected, most teams choose to use in-car
logging rather than real time telemetry.
(Telemetry is still used but for slowchanging factors like fuel levels and
monitoring engine health.)
It is useful if the device that stores
the data can also display some of it for
the driver and so a common approach
is to use a customisable digital dashboard that can perform both functions.
MoTeC’s Advanced Data Logger (ADL2)
is such a unit.
The ADL2 can read 28 analog voltage inputs, 12 digital inputs and two
Bosch ‘four wire’ air/fuel ratio sensor
inputs.
And if even more logging capability
is required, another 22 inputs can be
added by means of an expansion unit!
The unit will also accept data communicated to it in RS232 (eg, from a
GPS unit) and CAN formats. A 16Mb
internal memory is incorporated and
the microprocessor is 32-bit. The fully
configurable backlit LCD can display
any of these inputs, shown in userselectable engineering units.
Conclusion
As we’ve seen, literally anything that
can be sensed on a race car is capable of
being logged. However, all the information in the world is of little use if no
sense can be made of it.
Next month, we’ll take a look at
the MoTeC i2 data analysis software
which has mind-boggling capabilities – not only can it display the data
in many different forms but it can
also make mathematical calculations
based on that data and then display
those calculations in relation to the
SC
collected data!
Contact:
MoTeC Pty Ltd 03 9761 5050
www.motec.com
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