Engine Cycle Sync (Camshaft)

Overview

On 4 stroke engines where sequential injection and/or ignition is required, the ECU must synchronize to the correct revolution of the engine cycle so that the correct fuel and spark events are generated.

The crank wheel typically rotates once per revolution and therefore does not provide the ECU with enough information on its own.

However, the camshaft rotates once per cycle (2 revolutions of the crankshaft) and a sync signal from the camshaft can be used to determine the engine cycle.

Camshaft Sync

The ECU counts the occurrence of rising or falling (or both) edges from the cam sensor.

The counter, typically T2R counter (rising) or T2F counter (falling), is captured at an actual crank tooth Sync Test A Tooth and is reset to zero to begin counting again; the counter will be reset every crank revolution at the specified tooth.

Example:

In this example with a 8-1 crank wheel, there are 2 rising edges in the 1st crank revolution and 1 rising edge in the 2nd crank revolution.

The synchronization test point may be adjusted using the Sync Test A Tooth option.

Sync Test A Tooth is the actual crank tooth number (i.e. not an internal tooth number) at which the camshaft counter is captured and reset to zero on every crank revolution. The value is captured into the Cam Tooth Count channel.

Sync Teeth is the number of Cam teeth expected at Sync Test A Tooth when testing for synchronization if the engine is within the expected half of the 4-stroke cycle.

If Sync Test A Tooth were set to 6 in this example (corresponding to the 7th tooth of the crank wheel, counting from 0), then the counter would be set to 2 in the first revolution and 1 in the second revolution.

Setting Sync Teeth to 2 would result in synchronization to be achieved on the 1st crank revolution. If set to 1 then synchronization would be achieved on the 2nd crank revolution.

During the ‘synchronization’ portion of the tooth control table, the captured counter value is tested against the Sync Teeth value.

Variable Valve Control Systems

On variable cam control systems, the timing of the camshaft signal varies with respect to the crankshaft signal.

Considering the example diagram again, if the camshaft was in its most retarded position at that point then the ‘Cam’ signal could shift to the left by up to 80 degrees (almost 2 Actual Teeth in this example).

The original example with Sync Test A Tooth set to 6 would still be correct, when counting rising edges, for either cycle 1 or cycle 2 if the cam signal were shifted to the left by as far as 2 teeth.

However, suppose Sync Test A Tooth was set to 4. There would be multiple issues:

• In the first revolution, the ECU would detect either 1 or 2 teeth, depending on whether the camshaft position was advanced by VVC.
• In the second revolution, Sync Test A Tooth closely coincides with the cam signal, and there is a race between the crank signal and cam signal - small timing variations could cause unreliable detection of the cam signal.

In both cases, the cycle detection would be highly unreliable.

Edge Selection

Depending upon the cam sensor configuration, the ECU could be counting rising edges, falling edges or both.

The cam sensor edge direction may be selected by a combination of T2 Rising Edge, T2 Falling Edge and Sync Channel T.

It is possible to use timers other than T2 for cam synchronization, but T2 is the most common.

Engines with Variable Valve Control (VVC / VVT) would typically require both edges to be enabled with Sync Channel T set to either “T2 Rise” or “T2 Fall” so that only the rising or falling edge of the cam signal is used for engine cycle synchronization.

The edge selection may require adjustment to improve engine cycle detection.

If you are using a VR (Variable Reluctance) sensor for the Cam sensor then there may only be 1 valid edge due to the nature of signals from VR sensors - see Crank Sensor.

Sync 2 (Reliably Synchronize Within 1 Revolution)

An optional feature is available to support synchronization within a single crank revolution.

If Sync 2 Active is set to ON, then the cycle shall also be matched using Sync 2 Teeth.

If Cam Tooth Count matches Sync 2 Teeth then synchronization will be achieved (Stat Sync'd will be set to ON) and the value of Sync 2 Fuel Tooth will be placed into Fuel Tooth and the value of Sync 2 Spark Tooth will be placed into Spark Tooth to ‘jump’ these important clocks to the next half of the cycle.

Considering the example again:

For sequential injection + ignition with 4 internal teeth per revolution, this example ECU could be configured with:

Option	Value
Sync Teeth	2
Sync Test A Tooth	6
Sync 2 Active	ON
Sync 2 Teeth	1
Sync 2 Fuel Tooth	4
Sync 2 Spark Tooth	4
Fuel Teeth	8
Spark Teeth	8

Options / Channels

Option	Description
Start No Cam Sync	The ECU will not attempt to synchronize to the camshaft while cranking (starting) the engine.
Sync Channel T	Selects Cam synchronization input timer (e.g T2 Rise)
Sync Teeth	Number of teeth expected to unambiguously identify 1 revolution in the engine cycle. Must be set to 0 if not using a Cam Sync input.
Sync Test A Tooth	The actual crank tooth number at which the camshaft counter is captured and reset to zero. This is the actual crank tooth (A Tooth) number, not the internal tooth number. Care should be taken, particularly with systems using VVC, to ensure reliable detection across the range from most retarded to most advanced camshaft positions.
Cam Tooth Count	Value of the sync channel (e.g. T2R counter) when A Tooth reaches Sync Test A Tooth
Cam Tooth MX	Value of Cam Tooth Count when ‘MX’ (Missing / Extra tooth) synchronization tested.
Sync 2 Active	Enabled Sync 2 feature.
Sync 2 Teeth	Number of teeth to identify 2nd revolution in the engine cycle.
Sync 2 Fuel Tooth	Value to set in Fuel Tooth if Sync 2 is achieved. Jumps the injection ‘clock’ to the next half of the cycle. Should be set to the number of internal teeth per revolution, if sequential injection is required.
Sync 2 Spark Tooth	Value to set in Spark Tooth if Sync 2 is achieved. Jumps the ignition ‘clock’ to the next half of the cycle. Should be set to the number of internal teeth per revolution, if sequential ignition is required.