Engine control module or ECM is the brain of engine management system

The research and development in sensor technologies are 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 the Engine control unit (ECU) or Engine Control Module (ECM). It receives 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 the engine management system. So let’s discuss them all, one by on.

A plicture representing internal circuits of engine control module ecm

 

Engine control module or ECM is the brain of the 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.

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

The ECM is connected to the wire harness through the 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. ECM 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 ECM. The Engine control module has two kinds of memories i.e. permanent and volatile. The permanent memory stores the data permanently and can only be changed by external programming. The volatile memory stores the data which is lost if the battery is disconnected. 

Engine Sensors

Sensors actuators and engine control module (ecm) of engine management system
 

Engine sensors are small sensing units located at various positions in the 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

1. MAP Sensors

The Engine Management System requires to measure the load on the engine. This load can be determined by measuring the pressure drop in the intake manifold. This job is accomplished by the MAP sensors. Map sensors are located on the intake manifold. These engine sensors, sense the absolute pressure of the 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 the place. At a 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 ECM through the map sensors

Location Of MAP Sensor

The MAP sensor is generally located in intake manifold after the throttle body. It consists of two chambers separated by a flexible diaphragm. The first chamber is connected to the intake manifold while the second chamber has a sealed vacuum. It compares the pressure of intake manifold against the sealed vacuum.  

2. MAF Sensors

Mass air flow sensor wire mesh
 
MAP sensors measure the airflow indirectly through manifold pressure. To measure the airflow directly the Engine Management  System utilizes Mass Air Flow Sensor or MAF sensor. It is located just before the throttle body in the air intake system. It consists of platinum wire mesh which lies in the path of airflow. The platinum wires are heated by applying a constant voltage across them. As the air flows through these wires, it cools them down, decreasing their temperature and resistance. This causes more amount of current flow through the wire mesh. As more and more amount of airflow through the mesh, more cooling is done which causes furthermore the amount of current to flow. This change in current flow is measured by ECM and translated into Mass Flow rate of air.
 

Location Of MAF Sensor

MAF sensor is mounted in air intake system, between the air filter and the throttle body.  They consist of fine platinum while mesh which lies in the path of airflow. The wire mesh is kept heated by flowing current through them. This is done by applying a constant voltage across them.

3. Intake Air Temperature Sensor

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

4. Crankshaft Position Sensor

Crankshaft position sensor and the rotary wheel connected to crankshaft, engine Sensor
Crankshaft position sensor
The Engine Management  System requires to know the engine speed to control fuel metering, spark advance and shifting of electronic automatic transmissions. This speed is measured by the crankshaft position sensor.
Crankshaft position sensors may be based on magneto resistance or hall-effect. They detect the position of the crankshaft 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 the crankshaft. The rpm, temperature and absolute pressure data helps ECU in determining the mass flow rate 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.

5. Throttle position sensor

Throttle body houses the throttle position sensor
 
The Engine Management System must always know the position of the throttle valve. This helps it in determining fuel flow and spark advance.
The throttle body contains the throttle valve. The assembly usually mounts on the intake manifold. The throttle valve is connected by a linkage to the accelerator pedal in the driver’s compartment. Depressing the accelerator pedal opens the throttle valve. Then more air enters the engine.
Throttle Position Sensor continuously measures the throttle valve position. The ECM controls the fuel flow and spark duration depending upon the data of the TPS sensor. The ECM must match the fuel flow with airflow to feed engine the proper air-fuel mixture.

Location Of Throttle Position Sensors

The throttle position sensor is located inside the throttle body. It is mounted on the throttle valve spindle so it can monitor the position of moving valve. The rotating of valve spindle causes resistance to change in TPS which is transmitted to the ECM in the form of voltage signals. These voltage signals are then analysed by ECM to determine exact throttle position.

6.Oxygen  or lambda sensors

Oxygen sensor used in automobiles
The Oxygen sensors are called feedback sensors of Engine Management. They sense the amount of oxygen present in the exhaust gases. The presence of a higher amount of oxygen in exhaust gases suggests 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 ECM outputs more accurate and precise. Oxygen sensor voltage is between 1.3  and 0.15 volt. When the voltage is close to 0.45 volt, the air-fuel ratio is close to 14.7:1. If the voltage is higher, the oxygen content is low. If the voltage is less than 0.45 the oxygen content is high i.e mixture is lean. The varying voltage tells the ECM whether the air-fuel mixture is rich or lean. Based on this the ECM adjusts the duty cycle of fuel injectors. The Oxygen sensor required temperature of 200-800 degree celsius for working. It will not work if the engine is cold. During such conditions engine works in open loop condition or default mode.
 

Location Of Oxygen Sensors

The Oxygen sensors are located in the exhaust manifold or exhaust pipe. It is cylindrical in shape and about the size of a spark plug. It produces small voltage signals when exposed to Oxygen. These signals are carried to the ECM through cables. 

7. Coolant Temperature Sensor

Coolant temperature sensor senses the coolant temperature and helps engine management system in determining engine temperature
 
The Engine Management System requires the engine temperature to control the parameters such as air-fuel ratio, spark advance and canister duty cycle. The temperature of coolant represents the temperature of the engine as the coolant circulates all around the engine. This temperature is monitored by Engine Coolant Temperature Sensor. It is mounted somewhere in the coolant flow circuit. It transmits the coolant temperature data to ECM. The coolant temperature data helps ECM in determining the engine temperature. It can control it by varying the air-fuel ratio and spark advance. This data is also shown to the driver on the dashboard.
 

Location Of Coolant Temperature Sensors

Coolant Temperature Sensor is located in coolant passage of liquid-cooled engines.  It is also cylindrical in shape similar to the Oxygen sensor. It is connected to the ECM and the indicator light in the dashboard. It changes its resistance depending upon the engine temperature. This resistance change is analysed by ECM to determine the engine temperature.

8. 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 the 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 and helps the Engine Management System in running the engine smoothly and efficiently.

 

This was a brief overview of  Engine Management System and Engine sensors . We will discuss all these components in detail in future posts.

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