FEM Analysis of the Pulser Coil in Motorcycle Ignition Systems

FEM Analysis of the Pulser Coil in Motorcycle Ignition Systems

In most modern engines with solid-state ignition, the pulser coil, also known as a pick-up coil or timing coil, provides the signal that initiates the spark to fire the plug.pulser coil Most motorcycles from the 1970’s and up use this type of system for reliable, accurate and easy to maintain ignition.

The pulser coil (TCI) has several key functions, the most important being to generate a voltage spike high enough to ignite the fuel/air mixture and jump the sparkplug gap.pulser coil It also has to know exactly when it’s time to do this, and that requires a precise control signal from the engine computer or the motorcycle’s distributor.

Basically, as the magnets in the rotor move past the primary windings of the TCI inside the stator and around its outside perimeter, a voltage is induced in them by Maxwell-Faraday law. The voltage builds until it reaches a peak when the current in the primary windings is at its maximum. At that point it triggers the transistor in the TCI and, like flipping an electronic switch, opens the circuit. That causes the secondary windings to energize, producing a huge voltage that jumps the sparkplug gap.

There are many different coil designs used in automotive applications. They all have a specific self-inductance value which increases with the number of turns and with increasing frequency. In order to achieve a high sensitivity for the fast operational amplifier (op-amp) constituting the integrator of the TCI, it is important to lower this value.

As the magnetic flux passes through the coil, a voltage is induced in it, but this is cancelled by an opposite eddy current in the conductor through which the magnetic flux is passing. Consequently, the ratio of the mutual inductance to the self-inductance decreases and a wider bandwidth can be achieved at a given measurement sensitivity.

To obtain these results, a FEM analysis was carried out with the software Ansoft Maxwell and Q3D Extractor (Canonsburg, PA, USA), on the vertical structure and horizontal structure coil models of the TCI. The results are shown in Figure 6 and Table 2.

As expected, the FEM results show that a higher Lc/M value is obtained in the case of a horizontal structure when compared to the vertical model. This is due to the fact that a larger area of the cross-over between the conductor and the coil is available for the mutual inductance to develop. The same result was obtained for the coupling capacitance between the conductor and the coil.

Tags:lighting coil | marine ignition coil