Installation Manual

Electrical & Electronic Application And Installation Manual
Production Release Version 1.0
Page 227
17.0 Engine Governor
17.1 Min / Max Governing
17.1.1 Min / Max Governing Operation
The min/max engine speed governor will provide an approximate amount of
power for a given throttle position. Engine speed is allowed to vary between
the low idle and high idle engine speed settings. This governor essentially
only ‘governs’ engine speed when at the minimum or maximum allowed
engine speed. In between these limits, the throttle position will cause the
engine to produce power proportional to its value. The benefit of this type of
governor is smoother shifting for engines with electronic automatic/automated
transmissions. The Min/Max governor is also known as the ‘limiting speed’ or
‘power throttle’ governor.
The Min/Max engine speed governor control strategy uses the isochronous
speed governor to control the engine speed when operating at the minimum
(low idle) and maximum (high idle) speeds. This is the same control strategy
used by the full range engine speed governor, but with a fixed desired engine
speed input of low idle and high idle. The governor control strategy does not
try to control fuel delivery and engine speed at the operating speeds between
low idle and high idle.
The Min/Max engine speed governor will attempt to maintain a constant
engine power output based on the throttle position. This design provides
optimised shift quality with automatic transmissions and offers excellent power
modulation, which allows the operator to adjust the engine power output to
match typical vehicle operating conditions. The engine will accelerate or
decelerate to ‘find’ a vehicle load level that matches the engine output
command by the throttle. If the throttle is commanding more power than the
vehicle load will offer, the engine will accelerate to the high idle speed.
Machines that are lightly loaded will achieve a desired acceleration at a lower
throttle position than machines that are heavily loaded. Machines with very
high power/weight ratios will accelerate at very low throttle positions.
Figure 17.1 illustrates the Min/Max engine speed governor operation across
the engine operating speed range. The curve is bounded by the rating torque
curve between LI and Rated engine speed (RS) once above rated speed the
HSG limit curve takes over. For a fixed throttle position, the Min/Max
governor will deliver a constant amount of power proportional to the throttle
position, the engine power output will remain fairly constant, and engine
speed will vary with engine load.
Min/Max governing above the configured Rated speed (RS) is limited by the
HSG limit curve. This region of operation is often referred to as the overrun
region (shown in figure 17.1 as the High Speed Governor operating area).
The HSG limit curve is always below the rated torque curve. This curve is
linear and the slope of the line is determined by the configured Rated speed
point (RS) and HI engine speeds (run out line).