What role do automotive sensors play in modern vehicles?

A network of sensors is embedded throughout vehicles, serving as a critical type of “nervous system” that detects and measures different automotive parameters. This network is essential for a vehicle’s safety, performance, and efficiency. Several types of sensors are responsible for different roles, such as monitoring the temperature of engine components, the speed of the vehicle for traction control, or the proximity of objects for collision avoidance systems.

Data collected by these sensors is processed by the vehicle’s electronic control units (ECUs) to make real-time decisions and adjustments, ensuring optimal operation. In this article, we’ll cover the many different types of sensors in modern vehicles and their critical role in providing a safe and enjoyable driving experience.

The role of automotive sensors
Automotive sensors collectively contribute to the functioning of modern vehicles. Here are some of the attributes they offer.

Safety
A vehicle’s safety systems — such as its stability control, traction control, and anti-lock braking system (ABS) — depend heavily on sensors. These systems modify engine power and braking to avoid skids, loss of control, and potential collisions using sensor data, such as wheel speed, steering angle, etc. In milliseconds, impact sensors identify crashes and initiate airbag deployment, shielding occupants from severe injury. Similarly, camera sensors assist in locating vehicles in a driver’s blind area, which lowers the possibility of lane changes resulting in collisions.

Performance
Several sensors support automotive performance. For example, oxygen and mass airflow sensors are why a vehicle’s engine can run smoothly and burn fuel as efficiently as possible. These sensors monitor engine temperature and air-fuel combination, optimizing performance and reducing emissions by improving fuel economy. The sensors that measure road speed and engine revs also contribute to fuel savings and vehicle efficiency by ensuring the transmission shifts gears smoothly and effectively.

Additionally, radar and LiDAR sensors make fuel-efficient cruise control possible on highways while ensuring a safe distance from other vehicles.

Predictive maintenance
Some sensors detect minor anomalies in engine performance, tire pressure, and other systems, warning drivers of possible issues before they develop into more serious faults or failures. This often saves costs on repairs by enabling preventive maintenance.

Comfort and convenience
Enjoying the ideal temperature while driving is attributed to a vehicle’s temperature and humidity sensors, which regulate heat and air-conditioning systems to maintain a comfortable cabin environment. Parking sensors can help drivers navigate obstacles and guard against unintentional collisions. Light sensors improve safety and visibility at dawn and dusk by adjusting headlight brightness based on ambient light. Also, rain sensors automatically activate windshield wipers, enhancing visibility in wet conditions.

Self-driving
LiDAR, radar, cameras, and ultrasonic sensors support self-driving vehicles, gathering environmental data and making safe navigation decisions. By detecting lane markings, roadblocks, pedestrians, and other cars, these sensors help a vehicle make intelligent decisions and drive itself.

The sensors
Some of the most critical sensors are as follows.

1. Manifold absolute pressure (MAP) sensor
2. Oxygen sensor
3. Mass air-flow (MAF) sensor
4. Crankshaft position sensor (CKP)
5. Camshaft position sensor (CMP)
6. Engine coolant temperature sensor
7. Engine oil-pressure sensor
8. Throttle position sensor (TPS)
9. Knock sensor
10. Vehicle speed sensor (VSS)
11. Emission sensors
12. Steering angle sensor
13. Tire-pressure monitoring system (TPMS) sensors
14. Fuel-level sensor
15. Lane-departure warning system sensors
16. Voltage sensor
17. Convenience sensors

A manifold absolute pressure (MAP) sensor is a tiny yet essential part of a vehicle’s engine. It significantly impacts emissions, fuel economy, and maintaining smooth and efficient engine operation. The intake manifold is the chamber where fuel and air mix before reaching the engine cylinders. As the name implies, MAP sensors detect the absolute pressure inside the manifold.

The Engine Control Unit (ECU) uses this pressure reading to calculate the boost pressure, engine load, and air density. The ECU uses the pressure measurement to determine how much air enters the engine. This information is vital for figuring out how much fuel to inject for the proper combustion.

The intake manifold’s pressure varies depending on how hard a driver hits the gas pedal. A larger pressure corresponds to a larger engine load, and the ECU modifies ignition timing and fuel delivery correspondingly. A MAP sensor monitors the pressure boost produced by the turbo in vehicles equipped with turbochargers, enabling the ECU to regulate it for maximum efficiency and avoid over-boosting.

There are two main types of MAP sensors: piezoresistive and capacitive. The piezoresistive is the most common, and it uses a pressure-sensitive diaphragm that deflects slightly under pressure changes. This deflection alters the electrical resistance of a strain gauge on the diaphragm, which the ECU interprets as a pressure change.

Capacitive sensors use a small capacitor that detects capacitance changes depending on the pressure applied to its diaphragm. The ECU measures this capacitance to determine pressure.

MAP sensors have a sealed chamber with a reference (typically atmospheric) pressure. Depending on the sensor type, the intake manifold pressure acts on the diaphragm or capacitor plate. The diaphragm deflection or capacitance change alters the electrical signal sent to the ECU. The ECU interprets the signal and uses it to calculate air density, engine load, or boost pressure. The ECU adjusts fuel injection, ignition timing, and other engine parameters based on these calculations.

The oxygen sensor, sometimes called the O2 sensor, gauges how much oxygen remains in the exhaust gases following combustion. The ECU regulates the amount of fuel and air that enters the engine and depends on this data to stay in balance. The optimal air-fuel ratio is approximately 14.7:1, or 14.7 parts air to every 1-part fuel.

By ensuring full combustion, this ratio maximizes engine efficiency and reduces hazardous emissions. A key component in maintaining this delicate equilibrium is the oxygen sensor.

Vehicles have two types of oxygen sensors: narrow-band O2 sensors and wide-band O2 sensors. The narrow-band sensors are more common and less costly. When the exhaust is rich in oxygen (lean mixture), it produces a voltage signal that swings high (about 0.9 volts) and low (about 0.1 volts) when the exhaust is low in oxygen (rich mixture). They cannot, however, continuously offer feedback regarding the precise air-fuel ratio and have a restricted response range.

The wide-band sensors offer a greater range and quicker reaction than the narrow-band ones, providing more accurate fuel changes. This is because the ECU continually provides the exact air-fuel ratio over a more extensive range of oxygen concentrations. The results are better engine performance, less emissions, and increased fuel economy.

The O2 sensors are located in the exhaust manifold and are exposed to exhaust gases. So, these sensors have a porous zirconia electrolyte layer and a ceramic enclosure. A voltage differential is created between the inner and outer electrodes due to oxygen molecules from the exhaust diffusing through the electrolyte layer. The oxygen content of the exhaust determines the voltage differential.

A low voltage indicates a rich mixture (insufficient oxygen), whereas a high voltage indicates a lean mixture (too much oxygen). A reference voltage is sent to the sensor by the ECU. To obtain the optimal air-fuel ratio, the ECU compares the voltage signal from the sensor to the reference voltage and uses the difference to modify the fuel injection.

MAF Sensor

The mass air-flow (MAF) sensor measures the actual mass of air flowing into a vehicle’s engine per unit of time, regardless of pressure or temperature. The ECU uses this data to calculate how much fuel to inject for full vehicle combustion. For the maximum performance and lowest emissions, an engine requires the ideal air-fuel ratio, or around 14.7 parts air to 1-part fuel.

Where the MAF sensor measures the quantity of air, the MAP sensor measures the air pressure. The MAF sensor is located at the intake tube, before the throttle body, while MAP sensor is located at the intake manifold, after the throttle body. The MAF sensor determines fuel injection air intake, while the MAP sensor determines air density for fuel injection.

There are two types of MAF sensors: hot-wire and film. The hot-wire type uses a heated wire that cools down as air flows over it. The sensor monitors the current required to maintain the wire’s temperature, proportional to the mass of air flowing. The quantity of cooling is dependent upon the airflow rate.

The film type uses a thin-film heating element whose resistance varies according to the airflow rate. To determine the air mass, the ECU measures the voltage or current required to maintain this constant resistance.

The crankshaft position sensor (CKP). A vehicle’s up-and-down piston movements are converted into rotary action by the crankshaft, a steel-forged spinning shaft. A vehicle accelerates due to this rotational force, which is transferred to other parts like the flywheel and the wheels. The corresponding crank turns when each piston pushes and pulls on its connecting rod, adding to the total rotation of the crankshaft. The IC engine’s ability to generate power depends on this conversion of reciprocating motion to rotational motion.

The CKP sensor precisely tracks the crankshaft’s rotational position and speed. This information is essential so the ECU can accurately control various vital functions.

CKP sensors come in two types: magnetic and Hall effect. When using a magnetic type, a sensor coil and a magnet affixed to the crankshaft interact to provide a voltage signal that changes according to the magnet’s position. In the Hall effect type, a permanent magnet and a semiconductor chip work to detect changes in the magnetic field as the crankshaft turns, resulting in a voltage output that indicates the position of the sensor. Based on the CKP sensor, the ECU precisely controls fuel injection timing, idle speed control, and ignition timing.

The camshaft position sensor (CMP). The camshaft is a rotating shaft equipped with eccentric lobes (bumps). These lobes occasionally make contact with the rocker arms when the camshaft rotates. In turn, each rocker arm applies pressure to an appropriate valve (exhaust or intake) in the internal combustion engine. Exhaust gasses or air can enter or exit the cylinder by pushing open the valve.

The camshaft position sensor monitors the position and speed of the camshaft, aiding the ECM in controlling fuel injection and ignition timing. Just like the crankshaft position sensor (CKP) acts as the metronome for the engine, the CMP serves as the precise conductor of the valve dance.

The CMP sensor also comes in two types: magnetic and Hall effect. In the magnetic type, a sensor coil and a magnet on the camshaft interact to provide a voltage signal that varies according to the magnet’s location. When a camshaft rotates in the Hall effect type, a permanent magnet and semiconductor chip sense variations in the magnetic field, generating a voltage signal that indicates the camshaft’s position.

The engine coolant temperature sensor (ECT) acts as a guardian against overheating, continually measuring the temperature of the engine coolant flowing through the engine block. The coolant should be at or around 90° C (194° F) for most engines. It’s critical to strike a temperature balance between minimizing heat stress and enabling effective engine performance. The ECU, the engine’s brain, receives this crucial information from the ECT.

There are two types of ECT: thermistor and voltage sensor. A thermistor uses a semiconductor material, and its electrical resistance changes dramatically with temperature. As the coolant temperature rises, the resistance decreases, and the ECU interprets this change as a rise in temperature. Using a voltage divider circuit, the voltage sensor modifies the output voltage in response to coolant temperature. This voltage difference is measured by the ECU, which interprets it as a temperature reading.

The engine oil-pressure sensor monitors the oil pressure on the engine block or near the oil filter. If the pressure drops below a critical threshold, the sensor sends a warning signal to the ECU, vital in preventing engine damage and oil leaks.

There are two types of oil-pressure sensors: switch and analog sensors. The switch type functions similarly to a pressure switch. It completes a circuit and alerts the ECU when the oil pressure drops below a pre-determined level. The more advanced analog sensor sends a constant signal to the ECU proportional to the oil pressure. After that, the ECU decodes this signal to ascertain the precise pressure level and, if necessary, initiate the required action.

The throttle position sensor (TPS) monitors the position of the throttle valve, allowing the ECU to control the amount of air entering the engine precisely. This, in turn, dictates the engine’s power output.

There are two types of throttle position sensors: potentiometers and voltage dividers. Potentiometers have a variable resistor that changes based on the throttle valve position. As the valve opens, the wiper on the potentiometer moves, changing the resistance and sending a corresponding voltage signal to the ECU.

Voltage dividers have a fixed resistor and the variable resistance of the throttle valve to create a voltage divider circuit. The ECU measures the voltage output of this circuit to determine the throttle valve position.

The knock sensor. A vehicle’s engine combustion process must occur smoothly and effectively. However, premature detonation or knocking can occur under specific circumstances, leading to dangerous vibrations and possible engine damage.

The knock sensor, typically mounted on the engine block, picks up these dangerous vibrations. The engine’s vibrations are transformed into electrical signals via piezoelectric crystals. When the ECU detects “knocking,” it recognizes something is amiss and reacts quickly.

The vehicle speed sensor (VSS), also called the transmission speed or output shaft speed sensor, plays a crucial role in a vehicle’s operation by measuring the speed of the wheels or transmission. The speedometer uses the sensor data, which displays the vehicle’s current speed on the dashboard. It’s also used by cruise control to maintain a constant speed set by the driver.

In automatic transmission cars, the vehicle’s speed determines the appropriate gear. The traction control system uses this information to prevent wheel slip during acceleration and cornering. Based on this sensor’s data, the ABS optimizes the vehicle’s braking force to avoid wheel lockup.

There are two types of VSS: wheel speed sensor (WSS) and transmission speed sensor (TSS). The WSS is mounted on each wheel hub and typically uses magnetic or Hall effect technology to measure the speed of the rotating wheel. The TSS is mounted on the transmission output shaft and measures the rotational speed of the shaft, which is directly related to the vehicle’s speed.

Emission sensors help control a vehicle’s pollutants, ensuring it meets environmental regulations. The Nitrogen oxide (NOx) sensor measures the NOx in the exhaust, assisting the engine in reducing these emissions. The exhaust gas temperature (EGT) sensor monitors the temperature of the exhaust gases, ensuring they stay within safe limits.

The steering angle sensor (SAS) tracks the angle and speed of a vehicle’s steering wheel movements. This data informs the ECU exactly how much and quickly the driver moves or turns the wheel. The SAS relays this information, and it’s used for power steering, traction control, stability control, parking assistance, lane departure warning, and lane-keeping assistance. There are two steering angle sensors: potentiometer and magnetic types.

Tire-pressure monitoring system (TPMS) sensors track the air pressure of a vehicle’s tires, notifying the driver when it deviates from the suggested ranges. TMPS sensors come in two varieties: direct and indirect.

Every tire in the direct type comes with a sensor installed inside the wheel that’s powered by a battery. These sensors send pressure and temperature data in real-time to the vehicle’s onboard computer.

Indirect tire pressure monitoring uses a vehicle’s current wheel speed sensors. It analyzes each wheel’s rotating speed and looks for differences in pressure based on diameter changes. Although less precise than the direct TPMS, it’s less costly and requires no batteries.

The fuel-level sensor measures the amount of petrol left in the tank and provides the fuel gauge number on a vehicle’s dashboard. This sensor is inside the gas tank and measures the gasoline level using various technologies.

The conventional method uses a lightweight float connected to a lever that rises and falls in response to the fuel level. When a potentiometer (variable resistor) is positioned differently, the instrument cluster receives a voltage signal corresponding to the changed resistance.

However, most cars now have capacitive systems. Within the tank are two electrodes. The capacitance between these electrodes is influenced by the fuel level, which changes the voltage signal transmitted to the instrument cluster. Ultrasonic sensors are used in some sophisticated systems to measure the distance between the sensor and the fuel surface using ultrasonic waves. The ECU determines the fuel level based on this distance.

Lane-departure warning (LDW) system sensors continuously monitor and interpret the traffic markings. LDW systems use several technologies, including laser, radar, and cameras. The most common and efficient kind uses a front-mounted camera to detect lane markings. The camera detects lane edges and the vehicle by analyzing the images frame by frame. High-resolution cameras perform well in well-lit environments but may have intricate lane markings or low visibility challenges.

In some systems, radar sensors complement the camera or operate independently. They release radio waves, which are reflected by lane markers and then return to the sensor. By examining the return signal, the technology determines the position and distance between the lane edges. Radar can be less accurate than cameras on clear roads, but they perform better in low visibility conditions like fog or rain.

Laser sensors are sometimes used in high-tech systems for lane detection. They release laser beams that, like radar, reflect off-lane markings to reveal exact positional information. Currently, laser technology is the most expensive and least practical choice.

The voltage sensor measures the voltage of a vehicle’s battery and the entire electrical system, providing vital information to the ECU and other components to keep a car running smoothly and safely.

Convenience sensors. Several sensors are added to specific vehicle makes and models for a more comfortable driving experience. These can include a windshield’s automatic rain sensors or a headlight’s light sensors that automatically adjust depending on the ambient light conditions. There are many others.