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Traction Control
This system measures engine acceleration and if it exceeds previously determined limits acts to
limit engine power. The maximum permitted engine acceleration is dependant on the gear
selected, so this must also be determined by calculating the gear by comparing engine speed to
road speed. Use internal logging of Gear Ratio to find the usual spread for this parameter. Engine
acceleration is measured by comparing crank tooth segment times between successive crank
revolutions. Engine Accel raw is always calculated and may be used against the parameter
throttle position in normal gravel conditions to gauge surface grip.
17.1 Engine Acceleration
Engine Acceleration calculation, note only positive acceleration is measured all decelerations are
set to zero.
Engine Accel Raw = Crank Tooth period (latest) - Crank Tooth period (1 rev old)
Crank Tooth period (latest)
The option Engine Accel Cal gives the sampling interval and should represent either an engine
revolution or cylinder event (In Teeth)
Engine acceleration is scaled:
Engine Accel = (Engine Accel Raw × TC Accel Mod )/ TC Max
where TC Accel Mod = [TC sensitivity RPM/mph] × [TC Adjust Input]
If (Engine Accel Raw × TC Accel Mod ) > TC Max then the user must set this to 100.
TC Accel Mod may be selected using the TC Adjust Input option to modify either the TC
sensitivity RPM or TC sensitivity VSS tables. If none are selected then only the sensitivity table
is active. If TC vs Road Speed = On then TC sensitivity VSS is used instead of TC sensitivity
RPM.
17.2 Gear Determination
The Gear Ratio table is searched to see if the ratio is between the specified limits for the gear
starting with the low bound limit for Gear = 0, then the upper bound limit for
Gear = 0, and so on up to the maximum gear ratio for Gear = 7. Thus Gear is calculated. Typical
values: 68,86,44,51,29,38,22,28,18,21,8,10,0,0.
Gear is used to select a different Gear Spark mod, from Gear Spark mod table.
Gear is used to select a different Gear Accel mod, from Gear Accel mod table.
Gear is used to select a different Gear WG mod, from Gear WG mod table.
Gear is used to select a different Gear Boost mod, from Gear Boost mod table.
17.3 Preventing Loss Of Traction
This requires the reduction of engine power, often the best way is to retard the ignition advance,
but more drastic action my be required and will be taken by the cutting of sparks and fuel injection
pulses. The reduction method is invoked when the compensated engine acceleration exceeds the
trip value for the relevant gear.
If Engine Accel > [ TC Ign Cut Trip table value] for selected gear then an ignition cut set by TC
Ign Cut option is requested. When the acceleration returns to within limits the cut is restored
using TC Ign Cut Restore every engine revolution.
63 EM36 Manual
EM36 Manual © 2008 GEMS
If Engine Accel > [ TC Fuel Cut Trip table value] for selected gear then an injection cut set by TC
Fuel Cut option is requested. When the acceleration returns to within limits the cut is restored
using TC Fuel Cut Restore per engine revolution.
If Engine Accel > [ TC Ign Retard Trip] for selected gear then an ignition cut set by TC Ign
Retard option is requested. When the acceleration returns to within limits the
retard is restored using TC Ign Retard Restore per engine revolution.
VVS (Vehicle Speed), Road Speed must exceed TC min VSS.
17.4 TC Tuning
1. Log Engine Accel raw, and Gear ratio, in ideal conditions.
2. Select an appropriate TC max, set the Gear Ratio table if all gear ratios readily
distinguishable. Adjust the sensitivity table to compensate for the changing sensitivity with speed.
Log again with Engine Accel included in log This should be a flat line versus engine speed, if
traction maintained.
3. If last log is acceptable, say Engine Accel is 50% flat to ±10%, then set the TC trips with the
retard triggered first and fuel cut highest. Try a retard of 25degrees and a restore of 2 degrees,
30% cuts and 5% restores.
4. Log again and find a poor or slippery surface to confirm action.
Full Throttle Gear Shift
The full throttle gearshift is a switched ignition retard function. When the input for this function is
satisfied (normally by a physical input switch on the clutch pedal or gear stick), the ECU retards
the ignition at a rate, FTG Retard Rate, up to a maximum retard, FTG Retard Max (The
maximum retard is relative to the current map value, not absolute). When the input switch
changes to OFF, the ignition retard will be returned at a rate, FTG Restore Rate, until the normal
ignition timing is reached. If the input does not go to OFF, the timing will be returned after a time
set by FTG Time max. The retard rate is degrees per 4ms and would typically be very fast
(10-15) then the advance slower (2-3). The option FTG min RPM is the minimum engine RPM at
which a full throttle gearshift
retard can be performed. This prevents the engine RPM from dipping when depressing the clutch
whilst stationary.
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