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Diesel & Gas: Part 10 pages
DIESEL AND GAS
ENGINES
ENGINES
Sensors for cam and crank shaft position
General Characteristics
The sensors are all sealed in robust stainless steel
housings with blind front ends and are available in
various sizes (diameter and length). They are fitted
either with a cable or an integrated connector.
All JAQUET speed sensors for diesel and gas engines
are fully GL certified meaning that they passed
environmental tests required to prove their suitability
for use on large engines.
Introduction
For modern injection and ignition
systems used in diesel and gas engines
it is crucial to know the exact
crankshaft position at all times. In order
to gain this information, two sensors
are mounted on the engine. The first
sensor monitors the camshaft position
delivering one pulse per revolution
which corresponds to the top-deadcentre (TDC) position of one of the
pistons. The second sensor is placed in
the vicinity of the flywheel where a
toothed wheel is mounted as a target.
Depending on the requirements of the
control system, the number of teeth on
the cog wheel is defined to allow a
resolution of approximately one pulse
per degree of crankshaft revolution. For
this task, JAQUET AG – a sensor
specialist manufacturing more than one
million sensors per year for engines and
turbochargers – offers a set of reliable
and robust speed sensors which are
particularly suited for the use in large
diesel and gas engines.
JAQUET AG provides three different sensor
concepts:
•
Variable reluctance sensor
Variable reluctance (VR) speed sensors consist of an iron core, an inductive coil,
and a permanent magnet. A metal pole wheel passing the sensor face changes
the magnetic field strength, resulting in an AC voltage being induced in the coil.
The frequency of the output signal is proportional to the speed of the moving
target. VR sensors, also known as passive or electromagnetic sensors, do not
require an external supply.
•
Hall effect sensors
Hall effect speed sensors measure the distortion of magnetic field created by a
ferrous pole wheel. They provide a digital output signal proportional to the
rotary speed and can have a static behaviour meaning that pulse generation is
guaranteed down to a speed corresponding to a frequency of 0 Hz.
•
Eddy current sensors
Eddy current sensors use a high-frequency oscillator as the sensing element. A
metallic pole wheel influences the oscillator behaviour. This modulation is
converted to a square wave output signal proportional to the rotary speed by an
amplifier with trigger characteristics.
The different sensor concepts can be combined with a choice of signal output
configurations:
•
Single output
The single speed signal output is the standard configuration. Depending on
the sensor concept (see above) the output signal is either analogue or
digital.
•
Redundant output
The sensor provides two galvanically isolated output signals which can be
used for two independent applications, e.g. one signal for the governor and
the second for the over-speed protection system.
•
Speed signal plus inverted output
In addition to the standard single output the sensors also provides an
inverted signal which can be used in diagnostic applications.
D&G SpeedPackage 1.4
www.jaquet.com
Tel.: +41 61 306 88 22
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