Friday, March 11, 2011

Electric Engine-Cooling Fans

Electric engine-cooling fans are used on all transversely and some longitudinally mounted engines. Small, permanent-magnet, high-torque motors are used for this application. They are able to move large amounts of air independent of engine speed. Conventional electric cooling fan circuits incorporate a relay and engine-coolant temperature switch.

When engine coolant temperature increases above 230*F or 100*C, the cooling fan switch closes to energize the relay coil and switch the cooling fan motor ON. The coil is also energized to switch the cooling fan motor ON any time the air conditioning unit is ON. On some vehicles the temperature-switch circuit is hot at all times, allowing the fan to continue to cool the engine compartment and the radiator coolant even if the ignition switch is OFF. For this reason, you should always disconnect the fan motor when working under the hood near it in case it comes on without warning.

Cooling fan motors are also controlled by on-board computer-based electronic control module. A temperature sensor provides the input information used by the computer to determine the exact coolant temperature. Based on this information and other instructions programmed into it, the computer outputs signal that switches the fan circuit ON and OFF.

One advantage of this type of control circuit is that the computer may be programmed to turn the fan OFF. Automatically when the car is traveling at speeds above approximately 35 mi/h. This puts less load on the alternator. The fan is not normally needed when the car travels at road speeds because of forced air flowing across the radiator.

Electronic Variable-Assist Power Steering

The power steering unit is designed to reduce the mount of effort required to turn the steering wheel. Conventional Power steering system operate by means of hydraulic pump driven by abelt from the crankshaft pulley. This pump provides the fluid pressure and flow needed to operate the system. Maximum pressure line and return line connect the pump to the system. the hydraulic pressure provides most of the force needed for steering. The remaining steering effort provides needed driver feel for googd steering control.
The basic purpose of an electronic variable assist power steering system is to provide maximum power assist for light steering effort during low-speed vehicle maneuvering, such as parking, and minimum power assist for firm steering wheel control and directional stability at higher speeds.

Essendtially, the system is made up of microprosessor-based control modul the recives information on vehicle speed sensor. The control modul prosesses this information and signal an electrically controlled actuator valve in regard to annamount of assist required. During parking and low-speed operation, the control module sends a signal to actuator valve steeper motor, positioning the valve spool to allow for maximum power assist. As vehicle speed increases, the control module signals the actuator valve spool to open gradually, diverting an increased amount af fluid, therefore providing lass power assist. At cruising speeds, maksimum power assist is supplied, providing better road feel.

Motor Blower of AC

An most cases, the blower motor moves air inside a vehicle for air conditioning, heating and defrosting. A blower switch(in dashboard) is used in conjunction swith resistor block to control fan speeds. The resistor block consists of two coil-wound wire resistors connected to terminals. These resistors drop the voltage and reduce the current to the motor, causing it to turn more slowly. The blower switchs directs current through one resistor to run the motor at low speed, through one resistor to run the motor at medium speed, and directly to the motor to run the motor at high speed.

Some computer-controlled blower motor system have eliminated the blower motor resistors. Instead of varying current through the motor with resistors, the current is pulsed trhough the motor. The speed of the motor is hanged by veryingthe amount of ON time as compared with OFF time. This has the same effect as using a resistor to change the current through the motor. This type of control is easy for computers to perform and reduces current draw on alternator due the ON-OFF pulse instead of continous current flow

Oxygen (O2) Sensor

The exhaust gas or oxygen (O2) sensor is a device used by the vehicle's engine computer to measure the amount of oxygen present in the exhaust stream after combustion has taken place. This information is used by the computer to maintain the ideal air/fuel ratio.
The heart of oxygen sensor is a hollow cone-shaped piece of ceramic material called zirconium dioxide that is platinum coated on the inside and outside. This platinum coating provides the electrodes, as in a battery. During engine operation, exhaust gases are forced to pass over the outside of the sensor element while the inside is exposed to outside air (also referred to as reference gas). When the amount of oxygen in the exhaust differs from the reference gas, a voltage is produced.
A lean air/fuel ratio mixture has higher oxygen content in the exhaust gas. In this condition, the amount of oxygen ions present on both the inner and outer sensor surface are nearly equal, creating a lower output voltage. When the mixture gets too rich, however, there is a high amount of hydrocarbons in the exhaust as well as a low amount of oxygen. This condition causes an unequal amount of oxygen ions present on the exhaust side of the sensor tip compared to the inside, which causes a proportionately higher sensor voltage to be generated. The voltage output of a normal operating oxygen sensor will fluctuate rapidly back and forth between approximately 100mV (0.1V) and 1000mV (1V) at approximately 1200 to 155 RPM with a warm engine. The sensor switch point is the voltage value at which a radical change in output voltage occurs at around the ideal mixture ratio. Voltages above or below the switch point indicate that the air fuel ratio is rich or lean, respectively. The microcomputer tries to keep the sensor voltage at the ideal switch point by controlling fuel input to the engine.

Ignition Module And Coil Driver

An ignitions module houses integrated circuits that contai transistor, diodes, resistor and capacitor. A power within the module is used to switch primary current ON and OFF. It works much like a mechanical switch, except that it has no moving part and is turned ON and OFF by timed electrical pulses.

Ignitions module uses a transistor to switch primary current ON and OFF Although many different type of ignition modules are used, they all perform basically the same function: switch primary current On and Off. That image Shows an ignitions module that uses a singgle transistor to control primary current to ignition coil of a distributor-type ignitions system.

The image shows an ignition module that uses

The modern ignition coil driver power IC, One chip, small and....

Tuesday, February 8, 2011

Car Ignition System Works

The ignition system in your car ignites the fuel inside the engine's combustion chamber at the optimal time in the piston stroke to produce the most power while emitting the least amount of emissions as possible. There are many configurations of ignition systems but all operate on the same principle, create a low energy field and collapse it onto a high energy coil and that transfers the electrical energy into the secondary ignition system, coil wire, distributor cap and rotor (if equipped) plug wires and finally the spark plug.

Typical Ignition System in Operation

This system is triggered by the primary ignition system, this system varies depending on manufacturer but all operate on the same principle, use some kind of low voltage trigger system i.e. crankshaft position sensor, camshaft position sensor. This low voltage system (1.5 to 3.0 volts) is amplified to 12 volts by using a ignition module (amplifier) and then transferred to the primary side of the ignition coil. The ECM (engine control module) controls the engine ignition timing by advancing and retarding the primary trigger signal. In old cars a points, condenser and a vacuum advance unit performed this job.

This ignition coil is a pulse-type it consists, in part, of two coils of wire. These wires are wrapped around two iron cores. Because this is a step-up transformer, the secondary coil has far more turns of wire than the primary coil. The secondary coil has several thousand turns of thin wire, while the primary coil has just a few hundred raps. This allows 40,000 volts or more of voltage to be generated by a car battery.

This electrical signal is generated by the crankshaft position sensor, camshaft position sensor. The ECM calculates spark timing by using the computer system.

Some ignition systems have a coil for each spark plug. This is called Direct Ignition (DI) system, there are no plug wires in this system just individually controlled ignition coils. The amount of coils or spark plugs depend on the number of cylinders the engine is designed with.

The initial power supplied to the ignition system is generated from the battery. All vehicles use an alternator to recharge the battery during normal operation. A low battery can cause an engine not to start even if the engine is cranking over slowly. This is because the vehicle voltage has dropped below 12 volts. If any component of the ignition system is not functioning properly, it can cause an entire ignition system failure. Proper maintenance such as a tune up can help ensure that the vehicle's ignition system operates at peak performance.

Spark Plug in Operation

When an engine misfires under power it is typically caused by the ignition system. To troubleshoot the cause of the ignition system failure scan the ECM for trouble codes and repair as needed. Maintenance to the ignition system includes changing the spark plugs and distributor cap and spark plug wires if equipped. Changing the spark plugs and wires usually is a simple task that most people can perform themselves.

Monday, February 7, 2011

Handling The ECU (Electronic Control Unit)

ECU (Electronic Control Unit) contains electronic component that are extremely sensitivy to power surges, static, electricity, and phisical shock. Whenever working on or around microcomputer-based system, the following procedures should be used to avoid damaged to electronic component.

* Power must always be OFF wen removing or installing Ecu wiring harness connector. Make sure the ignitions is turned off and the ECu Fuse Removed.
* To get rid of any static charge buildup, frequently touch a known good ground with your hands or use statistic protection kit during installation of a ECu. This is especially important if you are moving your feet on a carpet or sliding across a seat.
* Jumper cable should be connected and disconnected with the ignition OFF to avoid possible power surges. You should avoid both giving and getting jump starts.
* Always remove the battery cable before charging the battery in car.
* Hande the ECu unit with extreme care. Dropping it from about waist height onto a concrete floor can do permanent damage.

* never apply 12V directly to any components of an ECu control System unless intructed specifically to do so. Some components are designed to operate at much lower voltage levels and can be destroyed almost instantly by this higher voltage.
* When measureing microcomputer-controlled components, suplay voltage with multimeter and separate ane test probe lead from other. If the two test probe leads accidentally make contact with each other during measurement, the circuit will be stored, resuting in damage to the control unit’s power transistor.
* When connecting disconnecting pin connectors into or from the microprosessor port, take care not to damage pin terminals.
* When installing a replacement engine computer or other electronic module, take the unit out of its protective antistatic bag at the last possible minute.

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