Inputs
INPUTSThe Electronic Control Unit (ECU) receives information from the following inputs:
- Four Wheel Speed Sensors
- Boost Pressure Differential Switch
- Low Fluid Level Switch
- Proportioning Valve/Differential Pressure Switch
- Low Accumulator Pressure Switch
- Brake Switch
- Parking Brake Switch
- Ignition Switch
- Booster Pump and Motor
- Modulator
The ECU receives its input signals from various types of sensors. The types of sensors used by the Jeep Anti-Lock system are:
- Magnetic Inductive Pickups
- Switches
Fig. 6 Saw-Tooth Wave-Form:
MAGNETIC INDUCTIVE PICKUPS
Magnetic inductive pickup sensors operate using the following characteristics of magnetic fields:
A magnetic flux field is always present around and through a magnet.
When a material with low reluctance (low resistance to magnetic lines of force) and high permeability (high ability to provide a path for a magnetic field) moves into a magnetic field, the magnetic lines of force are concentrated and the strength of the field is increased.
When a low-reluctance, high-permeability material moves out of a magnetic field, the strength of the field decreases. In other words, the field collapses.
Magnetic inductive pickup sensors use permanent magnets to produce the magnetic field and a stator tip of permeable, lowreluctance material to concentrate the field near a rotating armature. The armature usually has evenly spaced teeth also made from a permeable, low reluctance material.
- When the stator tip is close to an armature tooth, the armature tooth strengthens the magnetic field.
- When the stator tip and an armature tooth are exactly adjacent, the magnetic field is at its strongest.
- When the stator tip is between two armature teeth, an air gap exists between the stator tip and armature. Because air is a highreluctance medium, the magnetic field is weakest with the armature in this position.
As the field strengthens and collapses, the change in the field induces a voltage in a pickup coil. The voltage varies from positive to negative in a sawtooth shaped wave-form similar to sine wave (fig. 6).
NOTE:
- Positive pulses occur as the field strength is increasing.
- Negative pulses occur as the field strength is decreasing (collapsing).
- The pulses DO NOT occur when the stator tooth and the armature tooth are exactly adjacent. The pulses occur when the field strength is increasing and decreasing at its most rapid rate.
- For example, when the armature tooth is approaching and when the armature tooth is leaving the stator tip.
- The wheel speed sensors are of a magnetic inductive type sensor design.
SWITCHES
Switch type sensors are two-position switches which allow a voltage signal to reach the ECU when they are closed. When the switch is opened, the circuit is broken and the ECU receives no voltage.
The opening and closing of the switch provides a voltage signal (yes) or no voltage signal (no) to the ECU.
The brake switch, low accumulator switch, and low fluid switch are all examples of switch type sensors.
Based on the information the ECU receives from the various input sensors the ECU provides a number of output signals. These include:
- Instrument Panel Warning Lights
- One Yellow
- One Red
- Relay
- Modulator Power Relay
- Solenoids (located in the pressure modulator).
- Isolation Solenoid Valves (3)
- Decay Solenoid Valves (3)
- Build Solenoid Valves (3)