![Crankshaft sensor](https://upload.wikimedia.org/wikipedia/commons/7/7c/Crankshaft_sensor.png)
A crank sensor (CKP)
is an electronic device used in an
internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
, both petrol and diesel, to monitor the position or
rotational speed
Rotational frequency (also known as rotational speed or rate of rotation) of an object Rotation around a fixed axis, rotating around an axis is the frequency of rotation of the object. Its unit is revolution per minute (rpm), cycle per second ...
of the
crankshaft
A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting ...
. This information is used by
engine management systems to control the
fuel injection
Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of an injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines.
All comp ...
or the
ignition system
An ignition system generates a spark or heats an electrode to a high temperature to ignite a fuel-air mixture in spark ignition internal combustion engines, oil-fired and gas-fired boilers, rocket engines, etc. The widest application for spark i ...
timing and other engine parameters. Before electronic crank sensors were available, the
distributor
A distributor is an enclosed rotating switch used in spark-ignition internal combustion engines that have mechanically timed ignition. The distributor's main function is to route high voltage current from the ignition coil to the spark plugs ...
would have to be manually adjusted to a
timing mark
A timing mark is an indicator used for setting the timing of the ignition system of an engine, typically found on the crankshaft pulley (as pictured) or the flywheel, being the largest radius rotating at crankshaft speed and therefore the place w ...
on petrol engines.
The crank sensor can be used in combination with a similar
camshaft
A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...
position sensor (CMP)
to monitor the relationship between the
piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
s and
valves
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
in the engine, which is particularly important in engines with
variable valve timing
In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with varia ...
. This method is also used to "synchronise" a
four stroke
A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directi ...
engine upon starting, allowing the management system to know when to inject the fuel. It is also commonly used as the primary source for the measurement of engine speed in
revolutions per minute
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines.
Standards
ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
.
Common mounting locations include the main crank
pulley
A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that ...
, the
flywheel
A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, ass ...
, the
camshaft
A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...
or on the crankshaft itself. This sensor is one of the two most important sensors in modern-day engines, together with the camshaft position sensor. As the fuel injection (diesel engines) or spark ignition (petrol engines) is usually timed from the crank sensor position signal, failing sensor will cause an engine not to start or will cut out while running. Engine speed indicator takes speed indication also from this sensor.
Types of sensors
There are several types of sensors that can be used: the
inductive sensor
An inductive sensor is a device that uses the principle of electromagnetic induction to detect or measure objects. An inductor develops a magnetic field when a current flows through it; alternatively, a current will flow through a circuit contain ...
,
Hall Effect sensor
A Hall effect sensor (or simply Hall sensor) is a type of sensor which detects the presence and magnitude of a magnetic field using the Hall effect. The output voltage of a Hall sensor is directly proportional to the strength of the field. ...
, magnetoresistive sensor, and optical sensor. Inductive sensors have the simplest construction and are usually purely passive devices. Hall effect and magnetoresistive sensors have the advantage over inductive sensors in that they can detect static (non-changing) magnetic fields. Optical sensors do not have great resistance against fouling but are able to provide the most precise edge detection.
Some engines, such as
GM's Premium V family, use crank position sensors which read a
reluctor ring integral to the
harmonic balancer
A harmonic damper is a device fitted to the free (accessory drive) end of the crankshaft of an internal combustion engine to counter torsional and resonance vibrations from the crankshaft. This device must be interference fit to the crankshaft in ...
. This is a much more accurate method of determining the position of the crankshaft and allows the computer to determine, within a few degrees, the exact position of the crankshaft (and thereby all connected components) at any given time.
Function
The functional objective for the crankshaft position sensor is to determine the position and/or rotational speed (
RPM
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines.
Standards
ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
) of the crank.
Engine Control Units use the information transmitted by the sensor to control parameters such as ignition timing and fuel injection timing. In a diesel, the sensor will control the fuel injection. The sensor output may also be related to other sensor data including the cam position to derive the current combustion cycle, this is very important for the starting of a four-stroke engine.
Sometimes, the sensor may become burnt or worn out - or just die of old age at high mileage. One likely cause of crankshaft position sensor failure is exposure to extreme heat. Others are vibration causing a wire to fracture or corrosion on the pins of harness connectors. Many modern crankshaft sensors are sealed units and therefore will not be damaged by water or other fluids. When it goes wrong, it stops transmitting the signal which contains the vital data for the ignition and other parts in the system.
A bad crank position sensor can worsen the way the
engine idle
Idling refers to running a vehicle's engine when the vehicle is not in motion. This commonly occurs when drivers are stopped at a red light, waiting while parked outside a business or residence, or otherwise stationary with the engine running. Wh ...
s, or the acceleration behaviour. If the engine is revved up with a bad or faulty sensor, it may cause misfiring, motor vibration or backfires. Acceleration might be hesitant, and abnormal shaking during engine idle might occur. In the worst case, the car may not start.
The first sign of crankshaft sensor failure, usually, is the refusal of the engine to start when hot but will start again once the engine has cooled.
One detail of some designs is the "three-wire" inductive crank sensor whereby the third wire is actually just a co-axial shield around the two main sensor wires to prevent them from picking up stray electrical pulses from elsewhere in the vehicle engine bay.
Examples
Another type of crank sensor is used on
bicycle
A bicycle, also called a pedal cycle, bike or cycle, is a human-powered or motor-powered assisted, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A is called a cyclist, or bicyclist.
Bic ...
s to monitor the position of the
crankset
The crankset (in the US) or chainset (in the UK), is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain or belt, which in turn drives the rear wheel ...
, usually for the
cadence
In Western musical theory, a cadence (Latin ''cadentia'', "a falling") is the end of a phrase in which the melody or harmony creates a sense of full or partial resolution, especially in music of the 16th century onwards.Don Michael Randel (199 ...
readout of a
cyclocomputer
A cyclocomputer, cycle computer, cycling computer or cyclometer is a device mounted on a bicycle that calculates and displays trip information, similar to the instruments in the dashboard of a car. The computer with display, or ''head unit'', ...
. These are usually
reed switches mounted on the bicycle frame with a corresponding magnet attached to one of the pedals
crankset
The crankset (in the US) or chainset (in the UK), is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain or belt, which in turn drives the rear wheel ...
arms.
Notes
GMR (
giant magnetoresistance
Giant magnetoresistance (GMR) is a quantum mechanical magnetoresistance effect observed in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers. The 2007 Nobel Prize in Physics was awarded to Albert Fert and Peter ...
) technology is also used for Crank, Cam rotor sensing purpose. Mitsubishi is the first who used this technology in automotive application purpose.
References
External links
Crankshaft & Camshaft Position SensorsCrank Position Sensor
{{Automotive engine
Engine sensors
Gas sensors