Figure 1: A throttle position sensor in the car.
The throttle Position Sensor (TPS), located on the butterfly spindle, is operated by the throttle, and its installation varies according to the structure. For a traditional mechanical cable throttle, the throttle position sensor is usually installed on the side of the throttle body in the form of an independent component. And its rotation openness is driven by the throttle shaft, as shown in figure 2. For the commonly used electronic throttle, the throttle position sensor is integrated into the electronic throttle control component, as shown in figure 3.
Figure 2: A traditional mechanical cable throttle.
The throttle position sensor, also known as the throttle opening angle sensor or throttle valve switch, is used to detect the engine state of the device. Its main function is to detect whether the starter is in idle or load condition, whether the accelerating or decelerating condition. It is essentially a variable resistor and switches mounted on the throttle body.
The rotor of the resistor is connected to the throttle and it has two contacts, full open contact and idle contact. When the throttle is in an idle position, the idle contact is closed and an idle working signal is the output to the computer.
When the throttle is in other positions, the idle contact opens, output voltage signal relative to different throttle angles, the computer will identify the load of the engine according to the signal voltage value. The computer can identify the acceleration or deceleration condition according to the change rate of signal voltage in a certain time. According to these working conditions, the computer can correct the oil injection amount or cut off the oil.
Figure 3: An electronic throttle.
The throttle position sensor is one of the most important sensors in the Engine Control Module (ECM). It is used to detect the opening angle of the engine throttle and input the signal to the Engine Control Module. Its role mainly has the following 8 aspects.
The throttle position sensor signal, as well as the intake volume signal measured by the airflow meter and the absolute pressure sensor signal of the intake manifold, are the main parameters used by ECM to calculate the engine load. And they can monitor each other for signal consistency to see if any sensor is faulty.
ECM calculates the engine load according to the throttle position sensor signal, based on which, the fuel injection quantity is corrected and controlled.
When starting the engine, the fuel system supplies a thick mixture to the engine to ensure the smooth starting of the vehicle. If you are unable to start the car many times in a row, the fuel vapor that accumulates in the cylinder will saturate the spark plug, making it even harder to start the engine.
At present, most electronically controlled engines have a clearance control function for this fault. The basic principle is that when the throttle is fully opened during the start of the engine, ECM will reduce fuel supply to the engine or even stop its supply according to the signal from the throttle position sensor. As a result, this helps clear the fuel vapor in the cylinder, dry the spark plug, and ensure the spark plug jumps normally.
Three conditions are required for ECM to execute the control.
The ignition switch is in the start position.
Engine speed is low, usually less than 300r/min.
Throttle opening angle larger than 80% or fully open.
Therefore, when starting the electronically controlled engine, you should not press the accelerator pedal, otherwise, it may enter the clearance control procedure, resulting in the close of the engine.
Slow down and cut off oil control. When the vehicle stops the fuel at high speed or acceleration driving (throttle opening angle is very large), the throttle will close rapidly.
At this time, the engine intake gas sharply reduces and fuel injection continues, which is easy to occur extremely thick mixture, causing engine flameout, and poor fuel economy and emissions. For this reason, ECM will timely cut off oil to prevent engine stalls based on the throttle opening angle changes.
Figure 4: The engine control module.
The throttle position sensor signal directly reflects the load of the engine, and the ignition timing will be adjusted due to the change of the engine load. Therefore, a TPS is one of the main sensors for ECM ignition timing control.
ECM determines whether the engine is in idle condition according to the throttle position sensor opening angle signal (%). If the signal shows that it is idle, the ECM maintains the set idle speed through an idle air control and ignition control. If the signal is not in idle condition, the fuel supply system and ignition system will perform an acceleration operation.
Throttle position sensor signals are also used for traction control and air conditioner compressor control. If the ECM detects that the throttle position is in or towards the fully open position, the air conditioner compressor will be withdrawn to meet the vehicle's traction requirements.
The throttle position sensor signal and speed signal are the two most important parameters to determine the automatic transmission up and down gear.
If the throttle opening angle is very large, it indicates that the driving force of the vehicle needs to increase, the power control module (PCM) or automatic transmission control module (TCM) will reduce or delay the shift. So the transmission runs in the low gear, so as to achieve the effect of deceleration and torque increase.
If the throttle opening angle is small, the shift time will be at the designed minimum speed to achieve a good economy of the fuel.
Throttle position sensor signals are used for engine control. In addition, the automatic transmission control module (TCM) will share throttle position sensor signals with ECM via the data bus.
If the TCM detects sudden acceleration, it will release the lock clutch in the hydraulic torque converter, and make full use of the torque increase of the torque converter to increase the input torque of the transmission, helping the transmission to achieve large torque output.
Figure 5: An intake manifold absolute pressure sensor.
When ECM detects an airflow meter or intake manifold absolute pressure sensor failure, the throttle position sensor signal will be used as a backup signal to replace the MAF and MAP. At this point, ECM uses engine speed and throttle position to calculate ignition timing and fuel requirements so that the engine can continue running.