Crankshaft position sensor
Typical inductive crankshaft position sensor A crank sensor is an electronic device used in an internal combustion engine, engine , both petrol and diesel, to monitor the position or rotational or rotational speed of the crankshaft crankshaft.. This information is used by engine management systems to control the fuel injection or the ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor distributor would would have to be manually adjusted to a timing mark on on petrol engines. The crank sensor can be used in combination with a simil ar ar camshaft camshaft position position sensor to monitor the relationship between the pistons the pistons and valves in the engine, which is particularly important in engines with variable valve timing. timing. This method is also used to "s ynchronise" a four stroke engine upon starting, allowing the management system to know when to inject the fuel. It is also commonly used as the t he primary source for the measurement of engine speed in revolutions per minute. minute . Common mounting locations include the main crank pulley crank pulley,, the flywheel flywheel,, the camshaft or on the crankshaft itself. This sensor is the 2nd most important sensor in modern-day engines after the camshaft position sensor. When it fails, there is a probability the engine e ngine will not [citation needed ] start, or cut out while running. Contents
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1Types of sensor 2Function 3Bicycles 4 Notes 5External links Types of sensor [edit edit]] There are three main types t ypes of sensor commonly in use. The Hall Effect sensor , Optical sensor or the Inductive sensor . Hall effect sensors have the advantage over inductive sensors in that they can detect static (non-changing) magnetic fields.
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 wit hin a few degrees the exact position of the crankshaft (and thereby all connected components) at any given time. Function[edit] The functional objective for the crankshaft position sensor is to determine the position and/or rotational speed (RPM) 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 th erefore 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 idles, 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 t hem from picking up stray electrical pulses from elsewhere in the vehicle engine bay. Bicycles[edit] Another type of crank sensor is used on bicycles to monitor the position of the crankset, usually for the cadence readout of a cyclocomputer . These are usually reed switches mounted on the bicycle frame with a corresponding magnet attached to one of the pedal crankset arms. Notes[edit] GMR (giant magnetoresistance) technology is also used for Crank, Cam rotor sensing purpose. Mitsubishi is the first who used this technology in automotive application purpose. External links[edit]
Crankshaft & Camshaft Position Sensors Crank Position Sensor Hall effect sensor From Wikipedia, the free encyclopedia
A wheel containing two magnets passing by a Hall effect sensor
The magnetic piston (1) in this pneumatic cylinder will cause the Hall effect sensors (2 and 3) mounted on its outer wall to activate when it is fully retracted or extended.
Engine fan with Hall effect sensor
Commonly used circuit symbol A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effectsensors are used for proximity switching, positioning, speed detection, and current sensing applications.[1] In a Hall effect sensor a thin strip of metal has a current applied along it, in the presence of a magnetic field the electrons are deflected towards one edge of the metal strip, producing a voltage gradient across the short-side of the strip (perpendicular to the feed current). Inductive sensors are just a coil of wire, in the presence of a changing magnetic field a current will be induced in the coil, producing a voltage at its output. Hall effect sensors have the advantage that they can detect static (nonchanging) magnetic fields. In its simplest form, the sensor operates as an analog transducer, directly returning a voltage. With a known magnetic field, its distance from the Hall plate can be determined. Using groups of sensors, the relative position of the magnet can be deduced. Frequently, a Hall sensor is combined with threshold detection so that it acts as and is called a switch. Commonly seen in industrial applications such as the pictured pneumatic cylinder , they are also used in consumer equipment; for example some computer printers use them to detect missing paper and open covers. They can also be used in computer keyboards applications that require ultra-high reliability. Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. In the pictured wheel with two equally spaced magnets, the voltage from the sensor will peak twice for each revolution. This arrangement is commonly used to regulate the speed of disk drives.
Working principle[edit] When a beam of charged particles passes through a magnetic field, forces act on the particles and the beam is deflected from a straight path. The flow of electrons through a conductor is known as a beam of charged carriers. When a conductor is placed in a magnetic field perpendicular to the direction of the electrons, they will be deflected from a straight path. As a consequence, one plane of the conductor will become negatively charged and the opposite side will become positively charged. The voltage between these planes is called the Hall voltage.[2] When the force on the charged particles from the electric field balances the force produced by magnetic field, the separation of them will stop. If the current is not changing, then the Hall voltage is a measure of the magnetic flux density. Basically, there are two kinds of Hall effect sensors. One is linear which means the output of voltage linearly depends on magnetic flux density; the other is called threshold which means there will be a sharp decrease of output voltage at each magnetic flux density.
Crankshaft & Camshaft Position Sensors Copyright AA1Car
Distributorless ignition systems require a crankshaft position sensor (CKP), and sometimes also a camshaft position sensor (CMP). These sensors serve essentially the same purpose as the ignition pickup and trigger wheel in an electronic distri butor, the only difference being that the basic timing signal is read off the crankshaft or harmonic balancer instead of the distributor shaft. This eliminates ignition timing variations that can result from wear and backlash in the timing chain and distributor gear. It also does away timing adjustments (or misadjustments as the case may be).
On 1996 vehicles with Onboard Diagnostics II (OBD II), the crankshaft position sensor i s also used to detect variations in crank speed caused by ignition misfire. If the computer senses enough of these, it will illuminate or flash the Check Engine or Service Engine Soon light to signal the driver he has a problem.
DIFFERENT TYPES OF CRANKSHAFT POSITION SENSORS
There are a variety of different t ypes of crankshaft position sensors. One is a Hall eff ect crank position sensor that reads a notched metal "interrupter" ring on the back of the harmonic
balancer. This was first used on the early GM 3.8L V6 Buick Sequential Fuel Injection (SFI) engines (and turbos) with distributorless Computer Controlled Coil Ignition (C3I). The crank position sensor provides an on-off signal to the Powertrain Control Module (PCM) that the computer uses to monitor engine rpm and crank position. The system also uses a separate cam position sensor in place of the original distributor to inform the PCM about valve timing. This enables the PCM to determine the correct firing sequence which it then uses to control both injector and ignition timing. Ford uses a similar setup on its 5.0L V8 with distributorless ignition. Another type of crankshaft position sensor GM uses is t he "combination sensor" which you'll find mounted on the front of the 3.0L and 3300 V6. GM calls it a combination sensor because the crank position sensor contains a pair of hall effect switches that generate two separate signals. There are two notched interrupter rings on the back of the harmonic balancer. One ring has three notches which causes one of the hall effect switches to generate three crank position signals every revolution. The other ring has only one notch, which causes the other hall effect switch to generate a single "sync-pulse" signal that the ECM uses to calculate rpm and ignition timing. Another variation of the combination sensor is the "fast start" system used on GM's 3800 engine. A pair of Hall effect switches are mounted by the crank pulley while a cam sensor is mounted over the timing gear. One crank signal generates 3 pulses per r evolution while the other generates 18. This allows the coil module to "s ync" with the engine more quickly so the engine will start almost instantly. The third type of crankshaft position sensor is a magnetic pic kup that reads slots machined in a "reluctor" ring in the center of the crankshaft, on the harmonic balancer or flywheel. This setup is used on GM engines with the Direct Ignition Systems (DIS) on the 2.0L, 2.5L and 2.8L engines, and the Integrated Distributorless Ignition (IDI) on the 2.3L Quad 4, and also many Ford, Chrysler and import engines. On the GM applications, the crank reluctor ring has six equally spaced slots 60 degrees apart. A seventh slot is spaced 10 degrees from one of the others so the crank sensor will generate an extra "sync-pulse" every revolution. The PCM then uses the information to calc ulate proper ignition and injector timing. This type of sensor must be carefully positioned so the air gap is within .050 in. of the crankshaft reluctor ring.
CKP & CMP SENSOR DIAGNOSIS
The fastest way to check the crank and/or camshaft sensors on a 1995 or newer vehicle with OBD II is to plug in your scan tool and check for any fault codes. P0335....Crankshaft Position Sensor A Circuit P0336....Crankshaft Position Sensor A Circuit Range/Performance P0337....Crankshaft Position Sensor A Circuit Low Input P0338....Crankshaft Position Sensor A Circuit High Input P0339....Crankshaft Position Sensor A Circuit Intermittent P0340....Camshaft Position Sensor 'A' Circuit (Bank 1 or Single Sensor) P0341....Camshaft Position Sensor 'A' Circuit Range/Performance (Bank 1) P0342....Camshaft Position Sensor 'A' Circuit Low Input (Bank 1) P0343....Camshaft Position Sensor 'A' Circuit High Input (Bank 1) P0344....Camshaft Position Sensor 'A' Circuit Intermittent (Bank 1) P0345....Camshaft Position Sensor 'A' Circuit (Bank 2) P0346....Camshaft Position Sensor 'A' Circuit Range/Performance (Bank 2) P0347....Camshaft Position Sensor 'A' Circuit Low Input (Bank 2) P0348....Camshaft Position Sensor 'A' Circuit High Input (Bank 2) P0349....Camshaft Position Sensor 'A' Circuit Intermittent (Bank 2) You can also use your scan tool to check for the presenc e of a cranking rpm signal if an engine is cranking but is not starting because there is no spark (which is often a clue that the crankshaft position sensor is not working). On pre-OBD II vehicles, you can use a scan tool t o check for codes, or use a manual flash code procedure to read out codes. On a pre-OBD II GM application, a t rouble Code 12 while cranking would indicate no reference signal being generated. On pre-OBD II Ford applications, a Code 14 would indicate a problem with the crank position sensor signal, which Ford calls a "PIP" (Profile Ignition Pick-up) signal.
CRANK POSITION SENSOR CHECKS
Whether a crankshaft position sensor is the magnetic type or a hall effect switch, most problems can be traced to faults in the wiring harness. A disruption of the sensor supply voltage, ground or return circuits can cause a loss of the all-important timing signal resulting in an engine that cranks but won't start. Also, on some vehicles, damage to the notched sensor ring on the crankshaft, harmonic balancer or flywheel can cause an erratic crankshaft sensor signal. When troubleshooting a suspected crankshaft position sensor problem, you should follow the diagnostic flow charts in the vehicle manufacturer's service literature to isolate the faulty component when a fault code is present, otherwise there is no way to know if a no-spark starting problem is a bad ignition module, coil, computer, wiring fault or ignition switc h. Magnetic sensors can be checked by unplugging the electrical connector and checking resistance between the appropriate terminals. On a GM 2.3L Quad 4, for example, the sensor should read between 500 and 900 ohms. Always refer to the vehicle manufacturers test specifications when testing these sensors. Obviously, if you see a zero resistance reading (shorted) or an infinite (open) reading, the sensor has fai led and needs to be replaced. If viewed on an oscilloscope, a magnetic crank sensor will produce a waveform similar to that below:
Digital and analog crank sensor waveforms as they would appear on a DSO scope.
A good magnetic crank position sensor should produce an alternating current when the engine is cranked, so a voltage output check while cranking is another test that can be performed. With the sensor connected, read the output voltage across the appropriate terminals while cranking the engine. If you see at l east 20 mV on the AC scale, the sensor is good, meaning the fault is probably in the module, coil, wiring or computer.
Hall effect crankshaft position sensors typically have three terminals; one for current feed, one for ground and one for the output signal. The sensor must have voltage and ground to produce a signal, so check these terminals first with an analog voltmeter. Sensor output can be checked by disconnecting the coil and cranking the engine to see if the sensor produces a voltage signal. The voltmeter needle should jump each time a shutter blade passes through the Hall effect switch. If observed on an oscilloscope, you should see a square wave form (see above) that changes in frequency. If your diagnosis reveals a faulty crank sensor, the only option is to replace it. With Hall effect sensors, the sensor must be properly aligned with the interrupter ring to generate a clean signal. Any rubbing or interference could cause idle problems as well as sensor damage. Magnetic crankshaft position sensors must be installed with the proper air gap, which is usually within .050 in. of the reluctor wheel on the crankshaft. CAMSHAFT POSITION SENSORS
On many engines with distributorless ignition systems and sequential fuel injection, a camshaft position sensor is used to keep the engine's control module informed about the position of the camshaft relative to the crankshaft. By monitoring cam position (which allows the control module to determine when the intake and exhaust valves are opening and closing), the control module can use the cam position sensor's input along with that from the crankshaft position sensor to determine which cylinder in the engine's firing sequence is approaching top dead center. This information is then used by the engine control module to synchronize the pulsing of sequential fuel injectors so they match the firing order of the engine. On some applications, input from the camshaft position sensor is also required for ignition timing. The camshaft position sensor may be magnetic or Hall effect, and mounted on the timing cover over the camshaft gear, on the end of the cylinder head in an overhead cam application, or in a special housing that replaces the distributor (in the case of some of the GM applications). Operation and diagnosis is essentially the same as that for a crankshaft position sensor.
