Trigger Systems Trigger Systems

Page 8Page 8

The optical pulse generator The optical pulse generator consists of a shutter (chopper), consists of a shutter (chopper),

which is connected to the which is connected to the distributor shaft cam. distributor shaft cam.

. Either side of the shutter is a . Either side of the shutter is a light emitting diode (LED) and a light emitting diode (LED) and a

photo transistor (a semi photo transistor (a semi conductor switch that is conductor switch that is

sensitive to light intensity). sensitive to light intensity).

When the distributor rotates, the When the distributor rotates, the shutter passes between the LED shutter passes between the LED and the photo transistor and the and the photo transistor and the

beam is interrupted. beam is interrupted.

The on and off signal voltage that is The on and off signal voltage that is produced by this action is passed to produced by this action is passed to

the control module to determine the control module to determine engine speed and position. engine speed and position.

Label the picture below Label the picture below Chopper plate (fitted to a conventional cam)

Infa-red light beam projected onto a silicon phototransistor

The output signals from each of The output signals from each of the switching systems we have the switching systems we have covered are a relatively small covered are a relatively small

one. Therefore a component is one. Therefore a component is required to amplify the signal. required to amplify the signal.

This is done by using a control This is done by using a control module. In addition to amplifying module. In addition to amplifying

and switching the primary and switching the primary signal, the module can also vary signal, the module can also vary

the dwell angle. the dwell angle.

The module can be located close to The module can be located close to the distributor; this can make the the distributor; this can make the

wiring layout simpler, and improve wiring layout simpler, and improve on reliability. on reliability.

The electronic ignition systems do The electronic ignition systems do away with the need for a away with the need for a

mechanical switching system such mechanical switching system such as the contact breaker points, name as the contact breaker points, name

advantages gained from this.advantages gained from this.

• Discuss in pairs and offer answers

• Electronic ignition offers the following advantages;

• Ignition timing stays accurately adjusted and doesn’t wear out, dwell angle is constant, less servicing required.

• No contact point bounce with electronic systems.

• Current in the primary circuit can be higher.

Questions Questions

1. Name three common types of trigger system.

2. What is the purpose of the trigger systems?

3. Why does the signals given out by the electronic ignition need to be amplified?

4. What is used to amplify the signal given off from the trigger system?

5. What is the name given to the transistor inside the optical trigger system?

Answers Answers

• Contact breaker points, optical, hall effect and inductive.

• To turn the ignition coil on and off

• To step up the current going into the coil

• A control module or ignition module

• A Phototransistor