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 comb ...

, both petrol and diesel, to monitor the position or

rotational speed Rotational frequency, also known as rotational speed or rate of rotation (symbols ''ν'', lowercase Greek nu, and also ''n''), is the frequency of rotation of an object around an axis. Its SI unit is the reciprocal seconds (s−1); other com ...

of the

crankshaft A crankshaft is a mechanical component used in a reciprocating engine, piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating Shaft (mechanical engineering), shaft containing one or more crankpins, ...

. This information is used by

engine management system An engine control unit (ECU), also called an engine control module (ECM), is a device that controls various subsystems of an internal combustion engine. Systems commonly controlled by an ECU include the fuel injection and ignition systems. The ...

s 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 a fuel injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All c ...

or the

ignition system Ignition systems are used by heat engines to initiate combustion by igniting the fuel-air mixture. In a spark ignition versions of the internal combustion engine (such as petrol engines), the ignition system creates a spark to ignite the fuel-ai ...

timing and other engine parameters. Before electronic crank sensors were available, the

distributor A distributor is an electric and mechanical device used in the ignition system of older spark-ignition engines. The distributor's main function is to route electricity from the ignition coil to each spark plug at the correct time. Design ...

would have to be manually adjusted to a timing mark 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 syst ...

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 (engine), cylinder a ...

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 fittings, ...

in the engine, which is particularly important in engines with

variable valve timing Variable valve timing (VVT) is the process of altering the timing of a Poppet valve, valve lift event in an internal combustion engine, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combina ...

. 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 r⋅min−1) is a unit of rotational speed (or rotational frequency) for rotating machines. One revolution per minute is equivalent to hertz. Standards ISO 80000-3:2019 de ...

. Common mounting locations include the main crank

pulley Sheave without a rope A pulley is a wheel on an axle or shaft enabling a taut cable or belt passing over the wheel to move and change direction, or transfer power between itself and a shaft. A pulley may have a groove or grooves between flan ...

, the

flywheel A flywheel is a mechanical device that 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, a ...

, the

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

Types of crank sensor include: the

inductive sensor An inductive sensor is an electronic device that operates based on the principle of electromagnetic induction to detect or measure nearby metallic objects. An inductor develops a magnetic field when an electric current flows through it; alternat ...

Hall Effect sensor A Hall effect sensor (also known as a Hall sensor or Hall probe) is any sensor incorporating one or more Hall elements, each of which produces a voltage proportional to one axial component of the Magnetic field#The B-field, magnetic field vector ...

, 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. 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 r⋅min−1) is a unit of rotational speed (or rotational frequency) for rotating machines. One revolution per minute is equivalent to hertz. Standards ISO 80000-3:2019 def ...

) of the crank.

Engine Control Unit An engine control unit (ECU), also called an engine control module (ECM), is a device that controls various subsystems of an internal combustion engine. Systems commonly controlled by an ECU include the fuel injection and ignition systems. The ...

s 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 An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ge ...

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, push-bike or cycle, is a human-powered transport, human-powered or motorized bicycle, motor-assisted, bicycle pedal, pedal-driven, single-track vehicle, with two bicycle wheel, wheels attached to a ...

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 Classical music, Western musical theory, a cadence () is the end of a Phrase (music), phrase in which the melody or harmony creates a sense of full or partial resolution (music), resolution, especially in music of the 16th century onwards.Don ...

readout of a cyclocomputer. These are usually

reed switch The reed switch is an Electromechanics, electromechanical switch operated by an applied magnetic field. It was invented in 1922 by professor Valentin Kovalenkov at the Peter the Great St. Petersburg Polytechnic University#Soviet era, Petrogra ...

es mounted on the bicycle frame with a corresponding magnet attached to one of the pedals

arms.

Notes

GMR (

giant magnetoresistance Giant magnetoresistance (GMR) is a quantum mechanics, 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 Alb ...

) 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