source: diariomotor.com
We know that throtle, use to maintain amount of air that flow into the cylinder. This component will affect on engine RPM. But, how throtle do that ?. Inside of throtle, there is a component like a coin. It will close and open the air flow.
Why the coin inside of throtle can open and close ?. There is a connection between throtle and accelerator pedal. When the driver moving the accelerator pedal, throtle will move too.
Several years ago, steel cable was use to connecting throtle and pedal. But nowdays, the technology is growing. Most car, replace the steel cable with a system, which computerized integration. This system called Throtle Actuator Control (TAC) or Electronic Throtle Control (ETC). It was first used by BMW on 1988.
TAC using electrical curent to connecting between Throtle and pedal. A couple of wire use to replace the the steel cable. This system will handling idle RPM. So, the idle speed control is no more needed on this system.
What is the advantages
- More fuel economy
- Smooth acceleration
- Safety increase.
What is the disadvantages
- Need more cost
- Extra treatment needed
The component of TAC
APP sensor
source: ricksfreeautorepairadvice.com
This sensor is fungcionaly as input device that detect the accelerator pedal depnest when it pressed. This sensor will read the depnest of pedal using variable resistor. Similar with Throtle position sensor, the value of resistor will change when a force applied on a pedal. Most car have two or three APP sensor to detect acurately.
ECM/PCM
source: m5board.com
As a controller unit, Engine control mudule will receive all data from the sensor. This module have a lot of IC. So, ECM could calculate all data from sensor to determain the right action.
Throtle Body
source: tunersport.com
Throtle body fungcionaly as an actuator in this system. It will execute the command from ECM. On a unit throtle body, there is three part
- Throtle modulator
This modul, will translate the command from ECM to the right voltage and the right direction. That voltage using to energize throtle motor.
- Throtle motor
This is a DC elektrik motor. The value of voltage will determain the angle of open/closed throtle.
- Throtle position sensor
The sensor mount inside of throtle body. It fungcionaly as feedback signal of throtle movement. This sensor will give the information about throtle open/closed angle to ECM.
How TAC work ?
The IG "ON"
When the Ignition switches to ON position, main relay will active. It will connecting the curent from positive battery to all control module. Engine control module will give reference voltage to each sensor. APP sensor is one of them. Each car have different specification of reference voltage. But in general, the value of reference voltage is 5 V. APP sensor will send the value of voltage. The value of voltage is dependent on condition of Accelerator pedal. If there is no force pressing the pedal, the value is near bottom limit voltage (0,1/0,2 V).
The Engine "Start"
When the engine is starting, ECM give a command to open the throtle. The result, Engine RPM will step up on first engine running. And slowly down. We know to start an engine there is much curent needed for starter motor. This system designed to decrease the load on first start up.
Acceleration and decceleration
source: picoauto.com
Both acceleration and decceleration have same princip. When the force applied on accelerator pedal, APP sensor will send this information via a value of voltage depending pedal depnest. Range of value is between 0,1 V to 4,9 V. if the value is outside of the range, the fault indicator signal will raise on dasboard. ECM calculate this information and determine the right output signal. The output signal use as command to move the throtle.
Throtle movement is corrected by throtle position sensor. When the movement is correct, the system is okay. But if there is miss data, fault indicator signal will raise on dasboard. So if you see this fault indicator on your dasboard, check your engine.
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