10/11/12
TTEC 4848 Engine management system
Engine control unit
An engine management system is now very common or even required on both high end and regular vehicles. Its also common for people to use the term Engine Control Unit (ECU) in place of engine management system.
The engine management system is basically an electronic control unit (ECU) which receives signals from various sensors, make calculations and sends output signals to carry out various functions and operations within and around the engine.
The main reason for a proper engine management system is to reduce emissions and achieve better fuel economy.
4848
Vehicle Electrical & Electronic Controls
Sensors
and Switches (Off Car)
In this blog I will be covering some of the sensors and switches found in most of todays cars. These sensors are very vital to the normal operation of a vehicle.
Sensors and switches are used in most modern vehicles, their job is to relay such information as throttle position, engine temperature, coolant temperature, amount of air flow, etc. to the Electronic Control Unit (ECU). The ECU then uses it to determine how to best mentain optimum perfornace, fuel delivery (air/fuel ratio), reduce emissions etc..
Below is a summary, procedures, results and analasis of what each sensor outputs and likely causes of good and bad readings.
1. Throttle Position Sensor (TPS):
TPS: A TPS could either mean throttle postion sensor of throttle position switch. In this post we will be covering both.
Throttle Position Sensor (TPS): 4 Pin sensor
Fig 1. Throttle Position Sensor
A typical
TPS sensor generates 0.2V-4.5V. this voltages generated by throttle position is
relayed to the ECU to determine how long the fuel injectors stay open. At idle
the TPS produces a voltage of about 0.6V and it inreases proportionally as the
throttle angle increases. When throttle is fully open the voltage can go as high
as 4.5V.Test Procedure:
Fig 3. 4 pin TPS Schematic Diagram
This
type of TPS has 4 pins VS (VC)-------Power supply (5V)
VTA/VTA1---Signal Return to ECU
Idle-------------Idle position
E2--------------Ground
Before starting the test I carried out a visual inspection of the unit and after that I cheched to see the condition of the pins visually and I also connected them to my multimeter to check for continuity.
I connected the VS to my 5V power supply and E2 to ground. The signal pin (VTA) I connected it to my multimter red lead and black lead to ground. After wiring the sensor I started to measure voltage generated by sensor with respect to throttle angle position.
Test Result:
- Throttle Angle (Degrees)Voltage Output (Volts)00.16150.7301.2451.7602.3752.85903.4
This type of TPS a switch determines throttle position at idle or full throttle by connecting or disconnecting when throttle position changes.
This a 3 pin throttle position switch. It has 5V supply, signal, and ground.
While idling the throttle is almost closed and the resistance is high that is why the voltage reading is low about 0.4V. This is the available voltage between signal and source and as the throttle opens the resistance between arm and the variable resistor gets smaller and smaller and therefore the voltage increases.
From the graph we can see that at idle the resistance starts 0.4V and after opening the throttle about 5 degrees the resistance shoots up to OL (over limit) and stays that way till fully closed.
On the other hand, at PSW, the resistance when closed starts at OL till the throttle opens to about 40 degrees that is when it drop to 0.4V and stays there till fully closed.
3. Manifold Absolute Pressure
(MAP)
Fig 4.
MAP sensor
measures amount of pressure in the intake manifold and relays this information
to the ECU which uses it to monitor fuel delivery with regards to engine load,
speed, and valve timing so as to control air/fuel ratio for improved fuel
efficiency and emissions and overall vehicle performance.
Normally at idle, a MAP sensor should read high vacuum, low pressure but low voltage output. When it is throttle is fully open (WOT) it should read low vacuum, high pressure, and high voltage.
The MAP sensor has 3 pins. They VC (5V supply), ground, and signal. The sensor is connected to the 5V supply and then it is hooked up with a mity-vac in order to apply vacuum.
4. Mass Air Flow Sensor:
Hot wire type Mass Flow Air Sensor:
MAF measures
the amount in air going into the inlet valve and the ECU uses this input to
determine
aif/fuel
ratio and injector open/closed time.
A normal MAF sensor reads between 0.1V to 4.5. At idle it should be outputting about 1V to a peak voltage of about 4V-4.5V when accelerating. The more air going through the MAF sensor the higher the voltage signal it is relaying back to the ECU .
Hot wire type MAF sensor is made up of two wires which are placed inside the air flow passage , and closely placed is a temperature sensor which measures how hot the wires get. The wires are electrically connected and flows a small current which keeps is it hot. As air passes the two wires they cooler and this leads to an increase in the current flowing through then in order to maintain the wires hot.
5. Engine Coolant Temperature
Sensor (ECT):
Engine Coolant
Sensor
Theory:
ECT) tells
the ECU the coolant temperature and depending on how cold or hot the coolant is
to determine the amount of injector open time.
When the engine is cold the ECU opens the the injectors for longer time in order to compensate for the fuel that condenses in the combustion chamber therefore more fuel is required to stop the car from stalling. And as the coolant temperature increases the injector open time is shorter.
A normal ECT sensor voltage reading ranges between 0-5V. During cold starts the voltage reading is about 4.5V and as the engine reaches operating temperature this reading drops to about 0.5V.
When the engine is cold the ECT voltage is high (4.5V) thus the ECT tells the ECU the need for more fuel in order to run rich and as the engine warms up to operating temperature the reading goes down to 0.45-0.5V and now the sensor passes this data to the ECU in order for the engine runs close to Stoichiometric range.
For example, if we had warmed-up engine reading of 4.5V , this would mean that the engine is running rich and would result in burning more fuel and would cause engine to run rich and consequently impact fuel efficiency, bad emissins. On the other hand, a reading of 1.5V when engine is clod would mean the engine is running too lean, not enough fuel to facilitate combustion and cause engine stall, run rough or cause starting problems.
Therefore, precise balance of fuel and air ratio is important to achieve optimum performance, good fuel efficiency, and low emissions.
ECT sensor is a negative temperature coefficient (NTC) thermistor. That is as the the temperature of thermister increases the resistance of the sensor decreases and vice versa.
Test
Procedure:
Apparatus: Thermometer, pot, stove, water
Before putting the thermistor in the water I checked to make sure the internal resistance of the thermistor (sensor), it should normally read OL. This sensor has two wires, I connected the sensor with a multimeter polarity does not matter since we are measuring resistance. We then put the thermistor and the a thermometer in a pot of water and heating it slowly to near boiling temperature. The initial temperature of the water was 20 degrees.
Resistance Vs
Temperature
Water Temperature (ºC)
|
Resistance (Ώ)
|
20
|
2.5
|
30
|
1.76
|
40
|
1.25
|
50
|
0.88
|
60
|
0.6
|
70
|
0.45
|
80
|
0.33
|
90
|
0.24
|
Below is a summary and analysis of what each sensor outputs and likely causes of good and bad readings.
Reflection:
Coolant Temperature Sensor is negative
temperature coefficient (NTC). This means that temperature is inversly
proportional to temperature.
From the test reuslt we can see that when we raised the temperature of the thermister it is resistance decreased.
The Engine Coolant Temperature Sensor ("ECT" for short) measures the temperature of the coolant and feeds this data to the on-board computer. The computer then uses this data to maintain optimum drive-ability especially while the engine is warming up and until it reaches operating temperature.
From the test reuslt we can see that when we raised the temperature of the thermister it is resistance decreased.
The Engine Coolant Temperature Sensor ("ECT" for short) measures the temperature of the coolant and feeds this data to the on-board computer. The computer then uses this data to maintain optimum drive-ability especially while the engine is warming up and until it reaches operating temperature.
When the engine is cold the coolant temperature sensor tells the On-board computer (ECU) to run a rich fuel mixture until the engine warms up and reaches normal operating temperature.
The engine needs more fuel when the it is cold as the injector pintle sprays fuel into the combustion chamber for combustion to occur; some of the fuel from the injector pintle liquefies as it hits the cold walls of the combustion chamber, therefore there won't be enough fuel to allow combustion to take place. Hence, the sensor tells the ECU to provide more fuel during cold starts. Some of it will still liquefy but there would still be enough amounts of vaporous fuels to allow combustion to take place.
References:
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Ayob this is better than the previous version
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