Vehicles are the most common transportation facilities in our lives. They are very important to us. The ECU controls many parts in the engine. Sensors and the ECU work together to keep the vehicle in the optimum working state. New drivers may not know much about engine sensors. Let's take a look.
2.6 Intake air temperature sensor
2.9 Crankshaft position sensor
The car contains various systems, such as the engine, transmission, suspension, braking, air conditioning, body control system, etc. To control these systems, the ECU must get the correct information to confirm the working state. It issues the proper commands to control various operations, which carries out the driver's intentions and ensures smooth driving.
These messages, which reflect systems conditions, are detected and converted by sensors. The ECU cannot directly read the information such as water temperature, oil temperature, vehicle speed, intake air pressure, gear position, etc. The sensors convert them into electrical signals that the computer can recognize. This process keeps the car running properly.
Even an ordinary car has dozens of sensors on it. Sensors on the advanced vehicle are more than one hundred.
When determining the fault in a sensor, we shouldn't test the sensor itself but rather the entire circuit. Therefore, besides the sensor, the wiring harness, plug, and relevant circuit between the sensor and the ECU should also be checked when looking for defects.
The water temperature sensor has a semiconductor thermistor inside. The lower the temperature, the larger the resistance, and vice versa. This sensor settles on the water jacket of the cylinder block or head. It directly contacts the cooling water and measures the temperature. We know the car's operating condition through the engine water temperature.
There are generally two oxygen sensors, one is behind the exhaust manifold. The other settles behind the three-way catalytic converter. The former is known as the front oxygen sensor and the latter is known as the rear oxygen sensor. The oxygen sensor determines whether the fuel is burning properly by detecting the amount of oxygen in the exhaust. it provides the ECU with important information to control the air-fuel ratio in the engine.
Engine knocking is a problem that many people have encountered. The knock sensor collects the messages and sends them to the ECU. Those messages are the essential basis for identifying the engine knocking. After detecting the knocks, the ECU adjusts the ignition advance angle to resolve the issue.
When the car is under emergency braking, the ABS wheel speed sensor constantly detects changes in the wheel speed. It adjusts the wheel cylinder braking pressure through solenoid valves so that the wheels obtain the best braking efficiency. At the same time, the wheels do not get held up. The car won't go into a skid. The automobile maintains good driving stability and directional maneuverability in the braking process.
The vehicle speed sensor is a crucial sensor that provides data to the speedometer on the dashboard. The electronic control unit identifies the information and changes transmission gears. The vehicle speed sensor has many functions. It adjusts the transmission torque converter, engine idle speed, cooling fan and cruise control, etc.
2.6 Intake air temperature sensor
The intake air temperature sensor measures the temperature of the gas entering the intake manifold. It has an NTC thermistor. The resistance value is inversely proportional to the temperature. The voltage changes accordingly with the resistance in the circuit, which generates a different voltage signal to carry out the automatic operation in the control system.
The mass air flow sensor is related to the petrol injection system. In order to obtain the optimum concentration of gas mixture under all operating conditions, the amount of air drawn into the engine at each instant must be correctly measured. The information is the primary basis for the ECU to calculate (control) the injection volume. If there is a fault in the mass air flow sensor, it causes too rich or too thin gas mixture, making the engine run abnormally.
The throttle position sensor is essentially a variable resistor and a couple of switches. It monitors the throttling threshold. In most cases, when we step on the accelerator pedal, we increases the throttling threshold.
When the throttling threshold increases, the sensor recognizes the information and transmits the signal to the engine control unit. The ECU receives the messages, then corrects the fuel injection and ignition timing. This process causes acceleration or deceleration.
2.9 Crankshaft position sensor
The crankshaft rotation is the key factor to drive the pistons up and down. Its rotation speed directly reflects the engine speed. The sensor is one of the most critical sensors to the ignition system. It detects the top dead center pulse signal, the crankshaft angle signal and the speed signal. The ECU makes the correct ignition commands according to the cylinder's ignition sequence.
The camshaft position sensor collects the position information of the camshaft. It inputs the signal to the ECU so that the ECU identifies the top dead center of the cylinder compression. It controls the sequential injection, ignition moment and combustion.
In addition, the camshaft position signal is used to identify the moment of the first ignition when the engine starts. The camshaft position sensor identifies which cylinder piston is about to reach the top dead center. So it is also called the cylinder recognition sensor.
The oil pressure sensor installs in the main oil duct of the engine. It detects the oil pressure when the machine is working. Its function is to detect how much oil remains inside the engine. The driver knows the condition through the warning light on the dashboard. If the oil is not much, put the refueling on the plan.
We have introduced some basic types of sensors inside the engine. Of course, there are far more than these 11 sensors installed in the car. Thanks to the proper functioning of these sensors, the vehicle provides a safe driving environment for drivers.
The vintage oil pressure and water temperature sensors were independent of each other. They had defined maximum or minimum values. Some of the sensors actually functioned as switches in the old days.
As the features of sensors move towards electronic and digitized, these output values are more relevant in the application. Intensive competition in the market also improves the development of engine components. Micro-electro-mechanical system ( MEMS) plays the big role.
Nowadays, people focus on functionality, energy efficiency, environmental protection and safety when choosing a car. These demands are constantly increasing. As a result, electronic control systems are widely popular in automotive applications.
With the continuous development of the electronic control system, sensors play prominent roles in the engine. The market prospect of intelligent, multi-functional, miniaturized, integrated sensors is promising.
In recent years, micro-electro-mechanical systems (MEMS) have become more and more mature. Sensors with this technology measure mechanical, magnetic, thermal, chemical and biological quantities. They are ideal for vehicles.
Lauritz Carolsfeld 
July 21, 2021