Engine Sensors

Cut section of an IC engine showing cylinder, piston, rings and valves

The research and development in sensor technologies is also influencing the way engines were working conventionally. The engine sensors are replacing the complex and heavy mechanical parts along with adding intelligence to the system. With these technologies the mileage and efficiency of engines have improved drastically. Engine management system refers to an electronic system consisting of different engine sensors, actuators and a central processing unit to manage them all. This central processing unit is called Engine control unit (ECU) or Engine Control Module (ECM). It receives the information using various  engine sensors and respond by varying injection and spark timing. The use of engine management systems is improving the performance of automobiles. In   this post we will look at different  engine sensors along with other components of engine management system. So lets discuss them all, one by one.

Engine Control Unit
Labeled digram of an engine control unit engine sensors, ecu ecm, epm

Engine control unit or ECU is the brain of Engine management system. It has four sections i.e. input, output, memory and processor. Input section receives the information through the different engine  sensors. The processor processes those signals based on the information stored in the memory section. Now it gives the final output through the output section.
The ECU is connected to the wire harness through these input and output sections. The ECU can  control the opening time for fuel injector to vary the air fuel ratio depending upon the data it receives through sensors. It can also vary the spark time depending upon the rpm and load requirements. ECU determines its outputs based on some pre-stored  data in its memory. This data consists of different  output parameters depending upon load , rpm, and throttle . This data can be changed according to our need by updating the software of ECU. 




Engine Sensors


Engine sensors are small sensing units located at various positions in vehicle. They sense a multitude of different parameters and supply the data to the engine control unit. They are vital for the proper functioning of the engine management system. Any malfunction in them may adversely affect the performance of the engine. The image below gives a brief description of some common engine sensors and their function. 



Different engine sensors and engine management
Different Engine Sensors

MAP sensors

Map sensors are located on the intake manifold. These engine sensors, sense the absolute pressure of air coming in, hence they are called Manifold absolute pressure sensors. Absolute pressure means the pressure measurement is done relative to absolute zero. The air pressure varies depending upon the altitude of place. At lower altitude the air pressure is high and at the higher altitudes the pressure decreases. The information regarding this pressure change is conveyed to the ECU through the map sensors

Intake Air Temperature Sensor


IAT sensor Or Intake Air Temperature Sensor is also located in intake manifold. It senses the temperature of the air coming in. The temperature and the pressure data from map sensor are used by ECU to calculate the density of the air coming in . This sensor must have capability to sense wide range of temperature depending upon the area in which automobile is being driven. 

Crankshaft Position Sensor



Crankshaft position sensor and the rotary wheel connected to crankshaft
Crankshaft position sensor

Crank shaft position sensors may be based on magneto resistance or hall effect. They detect the position of crank shaft and indirectly the position of the piston. The data regarding the position of piston helps ECU in knowing whether the piston is at TDC or not. It helps ECU in varying ignition timing. This sensor also calculates the engine rpm based on rotations of crank shaft. The rpm, temperature and the absolute pressure data helps ECU in determining the mass flow rat of air entering the engine. Based on this data the ECU determines the amount of fuel to be supplied in order to achieve the optimum air-fuel ratio. Accordingly the ECU varies the time for which the fuel injector will inject the fuel.

Throttle position sensor.


A gif showing overall combination process inside the engine


Throttle Position Sensor is mounted on the throttle body. This engine sensor measures the extent to which the throttle valve is opened. ECU controls the spark duration depending upon the data of TPS sensor. A higher valve opening means higher engine rpm. At higher engine rpm the air fuel mixture do not get sufficient time for combustion, which results in poor efficiency. In accordance to burn the mixture property the ECU increases the spark duration. So that the charge is burnt properly, increasing mileage and reducing the pollution.


Oxygen  or lambda sensors

Oxygen sensor used in automobiles

These engine sensors are located in exhaust manifold. They act as feedback sensors. They sense the amount of oxygen present in the exhaust gases. The presence of higher amount of oxygen in exhaust gases suggest that the charge burning inside the combustion chamber is lean. If the amount of oxygen present in exhaust gases is very low it means that the charge burning inside the combustion chamber is very rich. Based on the feedback of oxygen sensors the ECU again adjusts the air fuel ratio to obtain ideal mixture for combustion. The oxygen sensors make the ECU's outputs more accurate and precise.


Engine Temperature Sensor

The  temperature of coolant represents the temperature of the engine, since the coolant circulates all around the engine. The temperature sensor is mounted somewhere in the coolant flow circuit. The coolant temperature data helps ECU in determining the engine temperature . It can control it by varying the air-fuel ratio and spark duration. This data is also shown to the driver on dashboard.


Knock Sensor

Knock sensors sense the pre-ignition and detonation inside the engine by sensing the vibrations created by them. These engine sensors may be mounted in cylinder block, cylinder head or even on the intake manifolds. They send the signal to the ECU which reduces the spark duration in order  to prevent the pre-ignition. This reduces the  chances of knock inside the engine.

This was a brief overview of engine sensors and engine management system. We will discuss all these components in detain uin future posts.

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