MotoHawk:Encoder

Overview

MotoHawk™ has features specially designed to synchronize to rotating machinery, such as the crankshaft of an internal combustion engine. It does this by monitoring electronic signals from a crank sensor and/or a cam sensor. A crank sensor is mounted near a crank encoder wheel, which has teeth like a gear, but usually has a pattern encoded into the teeth. This pattern allows MotoHawk™ to calculate not only how fast the engine crankshaft is spinning, but to also decipher instantaneous crank angle engine position.

The Encoder Definition block configures ControlCore so that it may perform such engine synchronization tasks for all the Supported Encoders. Other MotoHawk™ blocks in the Encoder Blocks group allow access to engine speed, the current engine position, the encoder synchronization state, notification of an encoder fault and what encoder fault occurred. Other blocks can adjust the top-dead-center (TDC) offset or the phase at runtime. Crank synchronous triggers are also made available via the MotoHawk ™ Trigger block.

Missed or False Extra Teeth

Once initially synchronized, pulses are scheduled on the assumption that the teeth correspond to the defined pattern. The failure to detect a tooth would make all pulses scheduled between that missed tooth and the missing tooth pair to be late. The instantaneous RPM at the point where the tooth was missed would be in error as would average RPM. A synchronization error would be flagged when the key (double missing) was detected if the tooth were truly missed because the tracked position would not equate to the calculated position defined by the key.

In a pattern where two missing teeth is the 'key' on the crank wheel, if two teeth in a row were missed a a synchronization error would be flagged because a false key was detected and the tracked position wouldn’t likely match the calculated position defined for the detected key. Tracked position is always updated with a synchronization event so pulses would schedule using the new calculated position. Therefore the pulses would not occur where required. Another synchronization error would result when the real key was detected and pulses would operate correctly soon after that.

If an exta pulse is sensed the operation would be similar to 1 except the pulses would occur earlier than expected rather than later. The system would recover once the real key is detected.

In the case of an extra or missing tooth, the encoder state would not change. It would continue to report synchronized. In some encoders, the position of the cam is ratified by the crank encoder so the state could change to cam unknown.

The encoder expects the tooth period to be no more than 1.5 times the tooth period of the previous tooth. If an extra or missing pulse occured and this ratio was violated then an encoder error would be flagged as well. Rapid acceleration or deceleration (for example if a starter motor is undersized resulting in large deceleration during compression) could also cause a syncronization error.

The encoder system attempts to always schedule pulses once synchronized. Tracked tooth position is used to schedule and so the insertion of a tooth or lack of a tooth will displace all pulses until the encoder re-synchronizes. False synchronization will step change pulse generation until a subsequent synchronization event occurs. The occurrence of false teeth (extra) or not observing a tooth (missing) will be flagged by seeing a synchronization error when the key is detected (so some point after the abnormal encoder event). An absent key error can sometimes occur before the synchronization error and could be flagged without a synchronization error if conditions are preventing the key from ever being detected. For example, continuous false detection of a tooth during the missing tooth region would result in an absent key error without a synchronization error (because there is no key being detected).