introduction of electronically controlled diesel fuel injection system on several
heavy-duty high-speed truck engines has allowed the speed of the diesel engine to be
controlled electronically, rather than mechanically. The same type of balance condition in
a mechanical governor occurs in an electronic governor.
difference is that in the electronic governor, electric currents (amperes) and voltages
(pressure) are used together instead of mechanical weight and spring forces. This is
possible through the use of magnetic pickup sensor (MPS), which is, in effect, a
permanent-magnet single-pole device. This magnetic pickup concept is being used on all
existing electronic systems and its operation can be considered common to all of them. MPSs
are a vital communications link between the engine crankshaft speed and the onboard
computer (ECM). The MPS is installed next to a drive shaft gear made of a material that
reacts to a magnetic field. As each gear tooth passes the MPS, the gear interrupts the MPSs
magnetic field. This, in turn, produces an ac current signal, which corresponds to the rpm
of the engine. This signal is sent to the ECM to establish the amount of fuel that should
be injected into the combustion chambers of the engine. Electronic speed governing systems
are set up to provide six basic governing modes:
takeoff speed control
speed cruise control
speed cruise control
Each of the
control modes above is described in more detail below.
idle speed control provides fixed speed control over the entire torque capability of the
engine. Also, the idle speed set point is calculated as a function of the engine
temperature to provide an optional cold idle speed, which is usually several hundred rpm
higher than normal operating temperature.
engine maximum rpm setting can be programmed for different settings. This can improve fuel
economy by eliminating engine overspeed in all gear ranges.
power takeoff speed control setting can operate at any speed between idle and maximum. The
operator uses rotary control or a toggle switch in the cab to vary electronically the
engine power to the PTO from idle to the preset rpm.
and engine cruise control includes set, resume, and coast features similar to that of a
passenger car, as well as an accelerate (ACCEL) mode to provide a fixed speed increase
each time the control switch is activated.
road speed limiting function allows the organization assigned to determine what maximum
vehicle road speed they desire independent of the maximum governed speed setting of the
engine. Road speed governing provides the best method for ensuring ideal fuel economy.
advantage of the electronic governor over the mechanical governor lies in its ability to
modify speed reference easily by various means to control such things as acceleration and
deceleration, as well as load.