Installation Manual

Electrical & Electronic Application And Installation Manual
Production Release Version 1.0
Page 146
11.9 Engine Limp Home Speed
The engine limp home speed setting is a configurable default engine speed to
which the engine controls in the event of a throttle pedal failure. This limp
home speed is configurable using ET to a value between 800rpm and
1800rpm. The default value is set to 1200rpm. It is recommended that the
limp home speed is set to a different value than the engine low idle. This
ensures that in addition to an engine diagnostic code there is a clear
indication to the operator that the throttle signal has been lost. In addition the
limp home speed is usually set to allow the machine to be placed into a safe
condition / area for re-work to take place.
In the event of an engine throttle failure the engine is designed to behave as
follows;
If actual engine speed is above limp home speed when throttle fault occurs
the actual engine speed will default to the configured limp home speed.
If actual engine speed is below the limp home speed when throttle fault occurs
the actual engine speed will default to the configured low idle speed.
11.10 Throttle Calibration
The majority of throttle components have mechanical and electrical tolerances
that affect the final output of a device, for example two components of the
same design and part number may produce a different voltage output in the
open position. Also after a period of time throttle components can
mechanically wear, affecting/changing the output of a device. To
accommodate these differences and changes the engine ECM may be
configured to automatically calibrate to differing input values at the upper and
lower positions. The diagrams below give an example pedal design where the
open and closed position of the throttle pedal are set by adjusting the
manufacturing adjustment screws. With this type of arrangement the
mechanical accuracy is limited and therefore auto calibration may be used.
The calibration control logic needs a number of parameters specific to the
chosen device to allow auto calibration.
This feature is configurable for Analogue and PWM inputs. The algorithm
treats either a PWM or analogue input as a ‘raw signal’ in the range 0 to 100%
for example the analogue voltage range is 5V therefore 0.05V is treated as
1%.
Several parameters are used to:
• Define the boundaries for calibration in the open and closed positions
• Define the amount of ‘deadzone /play’ from the open and closed
positions
• Define the upper and lower diagnostic boundaries