Inductive Distributor
This type of distributor is an AC (alternating current) generator. When rotating the distributor genrates an AC voltage which increases in frequency and amplitude with an increase in the speed of rotation. The number of tips on the pole pieces equals the number of cylinders of the engine.This system uses magnetic principles coupled together with an inductor winding commonly known as the pickup winding. Magnetic inductive devices can be found in many shapes and and forms. The single most important aspect of the their operation is that they need some kind of movement between the conductor coil and the magnetic field. In a normal situation we would think of induction taking place by the moving of a conductor across a stationary conductor. With this system the conductor coil and the magnet remain stationary. Theonly moving component is the reluctor wheel.
(A) In order to generate any voltage, the reluctor wheel needs to move at around 75-150 rpm. As the reluctor wheel approaches the trigger assembly, the air gap begins to get smaller and the reluctance to magnetic flow is now diminishing.(B) The magnetic lines are now starting to appear across the trigger coil winding inducing a voltage into the winding. When the trigger wheel is at the point where the air gap is the smallest, full magnetic saturation of the pickup coil has now been reached, the induced voltage is now at its peak.
(C) As the reluctor wheel pickup moves away, the air gap increases causing a reluctance to magnetic field flow resulting in the magnetic lines of force collapsing across the trigger coil and inducing a voltage in the opposite direction. This is the principle of alternating current (AC) generator using increasing and decreasing air gaps to create magnetic field movement. This concept allows movement of the magnetic field across the stationary conductor. The voltage output pattern when displayed on an oscilloscope would look similar to the following.
We used an oscilloscope and spun the shaft with a drill to get the graph. The only thing different about this graph is that we spun it a different way to graph on the left. As the shaft rotates, a tip connected to a reluctor wheel mounted on the shaft, rotates with it. A pickup-coil is places on the outside of the shaft and is stationary. As the tip rotates, a magnetic field is created, As the air gap gets smaller the coil charges which is referred to dwell time. When the tip is at it's closest point to the distributor, the coil gets saturated, which results in the voltage spike. When the tip moves away from the coil, the voltage suddenly drops down. The whole process gets repeated over and over until the shaft stops moving.
Optical Distributor
A optical distributor has two LED's and two photo diodes. A thin plate attached to the distributor shaft rotates between the LEDs above the plate, and the photo diodes below the plate. This plate contains slots, which rotate directly below the inner LED and the photo diode. The inner LED and photo diode act as a pickup. As in Hall-Effect pickup systems (which will be discussed later), the reference pickup in the optical distributor provides a crankshaft position and speed signal to the ECU. When the ignition switch is on, the ECU supplies voltage to the optical pickup, which causes the LEDs to emit light. If a solid part of the plate is under the reference LED, this light does not shine on the photo diode. Under this condition, the photo diode does not conduct current and the reference voltage signal to the ECU is 5v. As a reference slot moves under the LED, the light shines on the photo diode. The diode then conducts current and the reference voltage to the ECU is 0v. The outer LED, photo diode and row of slots on the
outer plate all function in the similar way to Hall-Effect pickups. The row of slots are very closely spaced, and the width between each slot represents 2 degrees of crankshaft rotation. On the inner edge of the plate, there are 5 slots, and 1 unique slot. When this unique slot rotates under the LED, a signal is sent to the ECU informing that the distributor is now at the number one piston position. As the outer row of slots on the plate rotate under the outer LED, a voltage signal to the ECU cycles from 0v to 5v. The reference pickup signal informs the ECU when each piston is a specific number of degrees before TDC on the compression stroke. A= The plate is interfering with the signal and the infared beam has been broken.
B= After 10ms, the distributor has rotated enough for the infared beam to send a signal through to the photo electric cell via the outer holes on the interrupter blade. This gives a output voltage of 12v as shown in the graph. C= The infared beam is about to be cut from the interruptor blade rotating. D= The beam has been cut from the interrupter blade, and this has prevented the signal from reaching the photo electric cell which will drop the voltage back to 0V. Hall Effect Distributors
A stationary permanent magnet and semiconductor Hall effect chip are mounted next to each other seperated by an air gap, forming the Hall Effect sensor. A metal rotor consisting of windows and tabs is mounted to a shaft and arranged so that during shaft rotaton, th windows and tabs pass through the air gap between the permanent magnet and the hall effect chip. This effectively shields and exposes the Hall chip to the permanent magnets field respective to whether a tab or window is passing through the Hall sensor. For ignition timing purposes, the metal rotor will have a number of equal-sized tabs and windows matching the number of engine cylinders. This produces a uniform square wave output since the on/off (shielding and exposure) time is equal. This signal is used by the ECU to control ignition timing. Many automotive Hall effect sensors have a built in internal NPN transistor, meaning that rather then a voltage being produced at the Hall sensor signal output wire, transisor is turned on providing a circuit to ground through te signal output wire.Summing up, Hall effect, Optical and Inductive distributors have all different ways of operating. Inductive distributors use an AC voltage created by a magnetic field and spinning reluctor wheel attached to the shaft. On the reluctor weel is a tip that passes a magnetic coil. A Magnetic field is created by the reluctor tip approaching the magnet, this creates a magnetic field that discharges when the tip passes by the magnet. Hall Effect and Optical Distributors both produce a DC voltage, but work in different ways. Optical distributors use a Photo Diode and LED. When voltage is supplied, the LED emits a infared beam to the Photo diode. A interrupter blade connected to the shaft seperates this beam as it passes through, interupting the connection, dropping the voltage to 0V. Hall Effect Distributors use a permanent magnet and semiconductor chip. When the shaft rotates a magnetic field is created. The shaft have tabs and windows connected around it, which forms a uniform square wave. This magnetic field collapses very fast and switches on and off creating a digital waveform.
