crank shaft sensor.docx

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Introduction The Trigger Wheel mode is designed to support most combinations of regular missing tooth wheels with or without a cam signal. Other ignition modes are used to support irregular or OEM specific wheel patterns. The table below lists all of the valid combinations for trigger wheel. However some of the modes will rarely be used. The most common are: 36-1 on crank - many Fords 36-1 on crank plus single tooth cam sensor - same 60-2 on crank - many vehicles with Bosch ECU, BMW, VW, Audi, Volvo, Vauxhall, Opel, Peugeot etc. 60-2 on crank plus single tooth cam sensor - same 24 tooth on cam - many Japanese originated vehicles use the Nippondenso 24 tooth CAS with differing numbers of 2nd trigger teeth and sensors. Note - this table is for four-stroke piston engines. Two stroke or rotaries only need 360 degrees of information for full sequential and COP. Commonly used modes have detailed sections on how to set them up. Unusual modes are not documented in detail at this time. For initial setup and determining tooth#1 angle on uncommon setups having timing marks or tape on your crank pulley/damper covering the full 360 degrees will be greatly helpful. Speed shops sell timing tape for a variety of damper diameters. If your engine has no timing marks you do need to add them. Just guessing at timing is a great way to damage an engine. Running excessive timing under load will almost always cause severe engine damage e.g. broken pistons It is essential that timing is confirmed with a timing- light on EVERY install.

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crank shaft sensor

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IntroductionThe Trigger Wheel mode is designed to support most combinations of regular missing tooth wheels with or without a cam signal. Other ignition modes are used to support irregular or OEM specific wheel patterns.The table below lists all of the valid combinations for trigger wheel. However some of the modes will rarely be used.The most common are:36-1 on crank - many Fords36-1 on crank plus single tooth cam sensor - same60-2 on crank - many vehicles with Bosch ECU, BMW, VW, Audi, Volvo, Vauxhall, Opel, Peugeot etc.60-2 on crank plus single tooth cam sensor - same24 tooth on cam - many Japanese originated vehicles use the Nippondenso 24 tooth CAS with differing numbers of 2nd trigger teeth and sensors.Note - this table is for four-stroke piston engines. Two stroke or rotaries only need 360 degrees of information for full sequential and COP.Commonly used modes have detailed sections on how to set them up. Unusual modes are not documented in detail at this time.For initial setup and determining tooth#1 angle on uncommon setups having timing marks or tape on your crank pulley/damper covering the full 360 degrees will be greatly helpful. Speed shops sell timing tape for a variety of damper diameters. If your engine has no timing marks you do need to add them. Just guessing at timing is a great way to damage an engine.Running excessive timing under load will almost always cause severe engine damage e.g. broken pistonsIt is essential that timing is confirmed with a timing-light on EVERY install.Physical wheelsSupportsSettings

Main wheelSecondary wheelSingle coilWasted sparkWasted-COPCOPBatch/bank fireSemi-sequentialSequentialTrigger wheel arrangementMain wheel speed2nd trig every rotation of

Missing tooth on crankNoneYYYNYYNSingle wheel with missing toothCrankn/a

Missing tooth on camNoneYYYYYYYSingle wheel with missing toothCamn/a

Missing tooth on crankSingle tooth on camYYYYYYYDual wheel with missing toothCrankn/a

Missing tooth on crankLS2 4X, VW 2 wide/narrow or half-moon on camYYYYYYYDual wheel with missing toothCrankn/a

Non-missing tooth on crankSingle tooth on crankYYYNYYNDual wheelCrankCrank

Non-missing tooth on crankSingle tooth on camYYYYYYYDual wheelCrankCam

Non-missing tooth on crankCam wheel with tooth per cylinderYNNNYNNDual wheelCrankEvery Cylinder

Non-missing tooth on camSingle tooth on camYYYYYYYDual wheelCamCam

Non-missing tooth on camSingle tooth on crankor two opposite teeth on camYYYNYYNDual wheelCamCrank

Non-missing tooth on camCam wheel with tooth per cylinderYNNNYNNDual wheelCamEvery Cylinder

Terminology notesMissing tooth- This is a regular wheel with a group of "missing" teeth e.g. 12-1, 36-1, 36-2, 60-2on crank- the wheel is rotating at crank speed, normally directly attached to the crank pulley or flywheelon cam- the wheel is rotating at camshaft or distributor speedSingle coil- a single coil and distributorWasted spark- double ended coils (or a pair of coils) that fire twice per cycleWasted-COP- a single coil per cylinder, but firing twice per cycleCOP- a single coil per cylinder that fires once per cycleBatch/bank fire- groups of injector fired at once, not timed to a specific cylinder eventSemi-sequential- injectors fired twice per cycle timed to cylinder eventsSequential- each injector fires once per engine cycle timed to a specific cylinder eventWheel namingThere does not appear to be universal agreement on the way to name wheels, however in the Megasquirt world, they will be named like the following examples.36-1. This means a single wheel with place for 36 teeth and a single tooth omitted. i.e. 35 teeth at 10 (360/36) degree spacing.36-2. This means a single wheel with place for 36 teeth and a two adjacent tooth omitted. i.e. 34 teeth at 10 (360/36) degree spacing.36-1-1. This means a single wheel with place for 36 teeth and a two non-adjacent single tooth omitted. This type of wheel is not supported by this generic wheel decoder. It is supported as Rover#136-2-2-2. This means a single wheel with place for 36 teeth and a three sets of double missing teeth. This type of wheel is not supported by this generic wheel decoder. It is supported as 36-2-2-2 with the specific OEM pattern required.24/1. This means 24 teeth (non-missing) on one wheel and a single tooth on a second wheel.36-1/1. This means a one 36-1 wheel and a single tooth on a second wheel.3+1. This means one wheel with 3 equally spaced teeth and an additional tooth to indicate sync. (Supported somewhat as Daihatsu 3cyl)

SettingsThe settings are inIgnition Options->Ignition options/wheel decoder

Spark Mode- set to "Toothed Wheel"Trigger Angle/Offset- always zeroAngle between main and return- n/aOddfire small angle- for oddfire engines this specifies the smallest of the crank angles between ignition eventsGM HEI/DIS options- n/a420A/NGC alternate cam- n/aUse cam signal if available- n/aOddfire phasing- usually "Alternate" but for Vmax use "Paired"Skip pulses- number of input pulses at startup that are ignored before decoding begins. Safe to leave at 3.Ignition Input Capture- see ignition pageSpark output- see ignition pageNumber of coils- see ignition pageSpark hardware in use- see ignition pageCam input- see ignition pageTrigger wheel arrangement- see table above for correct settingsTrigger wheel teeth- the number of effective teeth, counting the missing teeth as if they existed. i.e. a 36-1 wheel has 35 physical teeth, but enter 36.Missing Teeth- the number of missing teeth. Common are1for 36-1, or2for 60-2 or 36-2Tooth #1 angle- definition depends on whether main wheel is missing or non-missing type. See sections below.Main wheel speed- Does the main wheel rotate at crankshaft speed or camshaft (distributor) speed.Second trigger active on- Like ignition input capture above, specifies which voltage level is considered "active"Level for phase 1- only applies in "Poll level" mode. See Dual+Missing section.and every rotation of- how often are second trigger input pulses received. See Dual Wheel sectionAll of the settings on the right hand side of the page are general and will be covered in the Ignition manual.

There are two main categories of install -ExistingandRetrofit.ExistingIn this cases where you are fitting Megasquirt to an engine already fitted with a trigger wheel, your main task is to wire up the sensor(s), determine the tooth #1 angle and wire up your coil(s). It should not normally be necessary to alter the engine.RetrofitIf you have an engine that did not originally come equipped with a trigger wheel (e.g. a distributor based, pre-EFI engine) then you have to mount a wheel and sensor and set the phasing correctly.For a typical car engine - go for a 36-1 wheel on the crank for non-sequential.or a 36-1 wheel on the crank and a 50/50 cam tooth with gear-tooth hall sensor for full sequential60-2 works great on most engines too, but is not advised for very high rpms.For very high revving engines (such as motorcycle engines) due to the number of teeth per second, 36-1, 24-1 or 12-1 are preferred.While the code can cope with any sensor/tooth phasing, during cranking the rpms vary up and down greatly as the engine rotates. It is desireable to place the missing tooth such that it passes the sensor when the engine is somewhat stable. The OEMs have found that certain tooth#1 angles work well and it is worth following their lead.It is suggested to align your wheel and sensor to arrive at the following tooth #1 angles. (See later for explanation of tooth#1.)4 cylinders ~90-120 deg6 cylinders ~50 deg8 cylinders ~40 degTake a look at the EDIS pages for places to source used trigger wheels, sensors and coilpacks. Note that you do NOT need the EDIS module, so later ('internal-EDIS') cars are useful donors too.Mounting the wheel is quite critical in that itMUSTbe mounted so it rotates without moving up, down, left or right as the sensor needs to see all of the teeth with a gap of 0.75 - 1.0mm.Having mounted the wheel and sensor, you can proceed for an existing install.

Sensors and wiringRefer to theignition pageandbuild manualfor how to connect your crank and/or cam sensors.Spark outputsRefer to theignition pagefor how to connect up your ignition module and coils.

Missing tooth crank wheelThis is a very common configuration for wasted spark with the most typical wheels being 36-1 (Ford) and 60-2 (Bosch.) Note that the missing teeth are in a single group - if your wheel has multiple groups then you need a special wheel decoder. Many custom decoders already exist e.g. 36-2-2-2 and the one matching your wheel must be used instead of the 'generic' trigger wheel mode.The Megasquirt-3 code benefits from a reasonable number of teeth (hence 36 or 60) for best ignition timing accuracy. Low tooth count wheels such as 4-1 are not advised.What is Tooth #1Make sure you understand this!With the engine rotating in the normal direction...

Tooth #1 is the first tooth to pass the sensor after the missing tooth gap.We use the term "tooth#1" as it is consistent across wheels with one, two, three or four missing teeth in the group.Once the code knows the tooth#1 angle it automatically calculates other needed information internally. (No need to manually enter trigger teeth or delay teeth etc.)Clockwise rotation (normal) - method aSet your engine at TDC, then count the number of GAPS to tooth#1 in the direction of rotation (clockwise here) and multiply by the angular size of the tooth.e.g. 8 teeth * 10 deg per tooth = 80 deg36-1 wheels are 10 deg per tooth (360 deg / 36 teeth)60-2 wheels are 6 deg per tooth (360 deg / 60 teeth)24-2 wheels are 15 deg per tooth (360 deg / 24 teeth)

Clockwise rotation (normal) - method bA different way of looking at the SAME phasing.Turn your engine so that tooth #1 aligns with the sensor. Read off the tooth#1 angle from timing marks/tape on the crank pulley.

Critical tuning software settings are inIgnition Options->Ignition options/wheel decoder

Typical settings:Ford 4 cyl = 36-1, 80deg tooth #1Ford 6 cyl = 36-1, 50deg tooth #1Ford 8 cyl = 36-1, 40deg tooth #1Bosch 4 cyl (Peugeot, Vauxhall) = 60-2, 114 deg tooth #1

Missing tooth cam wheelThis arrangement is not commonly used by OEMs but does support full sequential with a single wheel and sensor. Cam triggering is less accurate than crank triggering due to timing belt or chain stretch.The Megasquirt-3 code benefits from a reasonable number of teeth (hence 36 or 60) for best ignition timing accuracy. Low tooth count wheels such as 8-1 are not advised.The previous section on missing tooth crank wheel generally applies when the wheel is mounted to the cam, but remember that one rotation of the cam is 720 crank degrees. The settings are in crank degrees. So a tooth#1 that is 8 gaps earlier than the sensor on a 36-1 wheel would give a 160deg tooth#1 angle (8 * 10 * 2 [for cam] )Critical tuning software settings are inIgnition Options->Ignition options/wheel decoder

Missing tooth crank wheel and single tooth cam wheelThis is an very common arrangement that supports full sequential and coil on plug. (For 50/50 half-moon or 4-window wide/narrow or other polled cam wheels seethe next sub-section.)

The definition of tooth#1 is the same as the basic missing tooth crank wheel and should be phased in the same way. Ensure you also read thesection above. The cam input tells the code which engine cycle/phase it is on. From the crank wheel alone the code knows when cylinder one is at TDC, but it cannot distinguish TDC compression or TDC exhaust. The cam sensor adds this information which is why it needs to be one pulse only per engine cycle.The cam signal is a single pulse usually generated by a narrow tooth, vane or window. Technically it is edge triggered. For VR type sensors, the edge setting will depend on the wiring you use (typically Rising) as the signal is a very short pulse. For a hall type sensors you need to ensure that the edge you choose matches up with the phasing as below. (*Needs more explanation on how*)To confirm correct cam sensor phasing proceed as follows.First, set your engine at TDC compression #1

Now rotate the engine backwards to tooth#1The angle read off the damper is the tooth#1 angle

Now rotate the engine backwards some more - this is the best place for the cam tooth to pass the sensor.

The settings are inIgnition Options->Ignition options/wheel decoder

Missing tooth crank wheel and polled (50/50 or half moon) cam wheelThis is an fairly common arrangement that supports full sequential and coil on plug. Here a missing tooth wheel is used on the crank in the common way and a hall-effect or geartooth sensor is used on the cam with a long tooth or window or vane. This gives you the ability to have full sequential, but the engine syncs up as fast as a regular missing tooth crank wheel.Different OEM implementations exist - some engines use a 50/50 cam pattern, Vauxhall red-top engines use a window in the distributor rotor that spans the missing tooth region. Many newer engines with Bosch ECUs utilise a 4 tooth wide/narrow cam trigger, this is used on some VW, GM LS2 and some Mercedes. As far as the code is concerned these are equivalent because it only 'looks at' (polls) the cam just after the missing tooth.Typical polled cam triggers:4 tooth wide/narrow type

e.g. GM LS2 4X / VW / Mercedes

Vane cup with single window

e.g. 1 window Bosch dizzy in Vauxhall red-top.

Half moon type

General arrangement

The missing tooth code uses the teeth of the missing tooth crank wheel to create 'tach teeth'. That is, it creates a tach signal from a particular tooth, then skips a number of teeth before declaring another tooth a tach signal. This means that all the tach teeth must correspond to real teeth. For a four stroke cycle engine, this means that the total number of teeth, including missing ones, must be evenly divisible by the number of cylinders (or by the number of cylinders for a 2-stroke).In later versions of the code (2.883+), the 'tach teeth' are still created for injection events, etc., but instead of the ignition timing advance signal being based entirely on the time after the last tach tooth (with intervening teeth ignored), the timing is set by the counting number of teeth, with only the amount between the last tooth and the desired timing estimated.For example, if the engine had a 36-1 wheel, and 4 ignition events per revolution (i.e., a V8 with 90 intervals), then if this desired timing was 36 BTDC, the calculation would look like:2.883+:timing calc=int*[(90-36)/90 (36 teeth/ 4 events)] + (mod**[(90-36)/90 9 teeth/event] last individual tooth interval)***

=int[54/90 9 teeth/event] + (mod[54/90 9 teeth/event] last tooth interval)

=int[5.4] + (0.4 teeth last tooth interval)

= 5 teeth + (0.4 last individual tooth interval)

old code:timing calc= [(90-36)/90] last tach tooth interval***

= 54/90 last tach tooth interval

= 0.60 last tach tooth interval

*'int[...]' means truncate to in integer ("whole number"),**'mod[...]' (short for 'modulus') means take the remainder after dividing (i.e., the fractional portion),***interval adjusted for , , prediction results.The net result is that the new code estimates the timing interval over a much shorter period (1 tooth versus 9 teeth in the above example), making it more accurate.

To set the Trigger wheel settings, go to 'Settings/Trigger Wheel Settings' in MegaTune. There you will find: Trigger Wheel Teeth(M): is the nominal (include missing) teeth for wheel decoding. (0=no wheel decoding). Missing Teeth(N): Number of consecutive missing teeth. Skip Teeth: Skip tooth is the number of teeth between "tach" triggers. (It is the number of teeth skipped after the last tach signal before MS-II calls a tooth a tach signal.) What you need to have happen is for MegaSquirt-II to 'skip' a certain number of teeth so the only the right number of teeth are counted as 'tach signals' per revolution. In general, this is: 4-strokes:skip_teeth = (2 M) / #cylinders 2-strokes:skip_teeth = (M) / #cylindersSome permissible combinations are:Skip Teeth Setting

Wheel12-124-236-160-2

cylinders(4-stroke)

212243660

46121830

6481220

836915

10n/an/an/a12

1224610

n/a - cannot be used Delay Teeth: Number of teeth to delay after 1st tooth after the missing teeth before 1st tach synch declared. You get synch as soon as you detect "first real tooth after the missing tooth". If the piston for cylinder #1 is at TDC when that 'first' tooth is detected, then there is 0 delay. If TDC doesn't occur until the next tooth is detected, then there is a delay of one tooth, and so forth.

Thetrigger offsetis 0, if that tooth lies up perfectly with the sensor at TDC.The best way to think about this is the delay teeth is the 'coarse' setting, and the trigger offset is for fine adjustment (less than one tooth) to account for minor sensor misalignment. If the sensor is misaligned by more then one tooth, the number of delay teeth should be changed, and the trigger offset used to calibrate the advance as seen on a timing light with that seen in MegaTune.For another example, with a 60-2 wheel, you would have for settings: Trigger wheel teeth = 60, Missing teeth = 2, Skip teeth = On a four cylinder four stroke engine, we want is two tach events per revolution. Since we have determined the number of tach signals we want is 2, we need to skip 60/2 = 30 teeth. For a eight cylinder 60-2, we need 4 ignition events per revolution, so we set skip teeth to 60/4 = 15. And for an eight cylinder 36-1 wheel, we would set skip teeth = 36/4 = 9. Delay teeth = depends on the position of the sensor relative to the missing teeth at TDC for cylinder #1.Note that you should change these parameters only with the engine OFF (or the stim rpm at no more than 300 rpm).The missing tooth wheel decoder has been tested up to at least 18000 rpm for 36-1 and 60-2 wheels (yes, 18 thousand rpm) on the bench, and works fine.For testing the missing tooth decoder on the bench, you may wish to use the crank wheel pulser. There is information on that here:crank wheel pulser.Note that you must get the sensor polarity correct for the missing tooth code. This is even more important than with regular triggers, because if you get the signal polarity reversed you will get two (n+1)*t missing tooth 'gaps', instead of the desired one (n+1)*t gap (and the engine might not run at all).

Theblue lineis the VR sensor output, thered lineis the output from the VR input circuit to the processor.Note that the VR circuit used in MicroSquirtand the MS-II/Sequencer controllers performs an additional inversion on the VR signal before passing it to the processor. The net result is that you have to use the opposite edge to trigger off, compared to a MS-II controller with the V3 main board. So where MS-II uses 'rising edge', you would use 'falling edge' with MicroSquirtor the MS-II/Sequencer, and vice-versa.In this case, an input capture setting of 'rising edge' is correct ('falling edge' for MicroSquirt/MS-II Sequencer).The proper polarity will depend on the way you wire your VR sensor (swapping the two leads to DB37 pin 24 and ground inverts the signal as seen by the VR input circuit), as well as your input capture setting. You may have to experiment to get them right if you don't have an oscilloscope.In the code are two input variables to control the interrupt masking to prevent false triggers:1. Time Mask, (ICISR_tmask)time (msx10) after tach input capture during which further interrupts are inhibited to mask coil ring or VR noise, and2. Percentage Mask, (ICISR_pmask)percentage of the predicted interval before the next tooth (dtpred) after tach input capture during which further interrupts are inhibited to mask coil ring or VR sensor noise.These are called thetime maskandpercentage mask, respectively, in the ignition options dialog of MegaTune. For wheel decoding you must use values close to 0.2 ms and 10%. However, to not break any existing setups, the default values are 0 and 50%, the same values hardwired into pre-v2.5 code.Be sure to adjust these values when you set up for a trigger wheel(note that they are in a separate dialog from the trigger wheel settings).In addition to the above settings, you should set: Predictor Algorithmto last interval, and Predictor Gainto zero.These are not needed because the teeth are much closer together than 1 signal/cylinder, and having them enabled only adds to the processor overhead.