Unit_2 Sensors used in automobiles for Mechatronics Engineering

Sensors and Actuators

1. Sensors used in Automobiles Mass airflow sensor Engine Speed Sensor Oxygen Sensor Spark Knock Sensor Coolant Sensor Manifold Absolute Pressure Sensor Fuel Temperature Sensor Camshaft Position Sensor Throttle Position Sensor Vehicle Speed Sensor 2 3 6 9

2. Sensors used in Automobiles

3. Sensors used in Automobiles 1 Mass Airflow Sensor The Mass Air Flow sensor (MAF) is one of the key components of an electronic fuel injection system in your car. It is installed between the air filter and the intake manifold of the engine . The mass air flow sensor measures the amount of air entering the engine or the air flow. In modern cars, an intake air temperature or IAT sensor is built in the mass air flow sensor. The commonly used MAF hot-wire type.

4. Sensors used in Automobiles How a hot-wire air flow sensor works A hot-wire mass air flow sensor has a small electrically heated wire (hot wire). A temperature sensor installed close to the hot wire measures the temperature of the air near the hot wire. When the engine is idling, a small amount of air flows around the hot wire, so it takes a very low electric current to keep the wire hot. When you press the accelerator , the throttle opens allowing more air to flow over the hot wire. The passing air cools the wire down. The more air flows over the wire, the more electrical current is needed to keep it hot.

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6. Sensors used in Automobiles The electric current is proportional to the amount of air flow. A small electronic chip installed inside the air flow sensor translates the electric current into a digital signal and sends it to the engine computer (PCM). The PCM uses the air flow signal to calculate how much fuel to inject. The goal is to keep the air/fuel ratio at the optimal level. If the air flow sensor doesn’t work properly, the automatic transmission might shift differently too. A bad mass air flow sensor causes various driveability problems, including a no-start, stalling, lack of power, poor acceleration, Check Engine and Service Engine light indications on dashboard .

7. Sensors used in Automobiles MAF Sensor Problems : The sensor element could get contaminated or damaged. For example, in some engines, a failed mass air flow sensor could cause the engine to crank but not to start. An improperly installed or collapsed air filter and Over-soaking a washable air filter can also cause problems with the air flow sensor. MAF Sensor Testing : In modern cars, the only way to test the mass air flow sensor is with a scan tool. Mechanics measure the amount of air flow (mass air flow sensor readings) at different RPMs. They compare the readings to the specifications or to the readings of a known-good mass airflow sensor.

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9. Sensors used in Automobiles 2. Engine Speed Sensors / Crankshaft Speed Sensors Crankshaft speed sensors, also called speed sensors, are used to measure crankshaft speed; determine the position of the crankshaft (or even the position of the engine cylinder). The rotational speed is calculated by the time period of the sensor signals, following the passage of the gear teeth. The sensor is mounted directly opposite the ferromagnetic pulsed wheel (flywheel) fixed on the knee-shaft and is separated from it by an air gap ( about 2mm gap). The sensor contains a soft iron core (pole tip), which is surrounded by an inductor. The pole tip is connected to a permanent magnet .

10. Sensors used in Automobiles The magnetic field passes through the pole tip inside the pulse wheel. The intensity of the magnetic flux passing through the coil depends on what is opposite the sensor:The tooth or the gap between the teeth of the impulse wheel. Now the tooth causes amplification, and the gap, on the contrary, weakens the intensity of the magnetic flux. These changes induced in the coil an electromotive force(EMF) expressed in a sinusoidal (Sine/Analog) output voltage which is proportional to the rotational speed of the crankshaft. Figure: Engine Speed Sensor

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14. Sensors used in Automobile 3 3. Oxygen Sensor An oxygen sensor is available in the exhaust system of an automobile. The size and shape of this sensor look like a spark plug. Based on its arrangement in regard to the catalytic converter, this sensor can be arranged before (upstream) or after (downstream) the converter. The oxygen sensors used in automobiles are one sensor is arranged in front of the catalytic converter one is arranged in every exhaust manifold of the automobile. Most of the vehicles have 2 to 4-sensors

15. Sensors used in Automobiles Working Principle : The working principle of the o2 sensor is to check the oxygen amount within the exhaust. Firstly, this oxygen was added to the fuel for good ignition. The communication of this sensor can be done with the help of a voltage signal. So the oxygen status in the exhaust will be decided by the computer of the car. The computer regulates the mixture of fuel or oxygen delivered to the car engine. The arrangement of the sensor before after the catalytic converter. It permits to maintain the hygiene of the exhaust check the converter’s efficiency.

16. Sensors in Automobiles Signs of faulty sensor : Breakdown to exceed the emissions analysis Fuel mileage can be decreased . The engine light will be off . Performance is poor, stalling and rough idling Code checker recognizing sensor failure .

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18. Sensors used in Automobiles 4 4. Spark Knock Sensor The knock sensor is one kind of sensor used to detect the flash knock. This flash is the state within the engine of the automobile where the fuel starts burning because of the pre-ignition and detonation . The main function of this sensor is to monitor the ignition process inside the engine. Its indication assists the engine control to stop knocking ignition and thus guard the motor or engine control.

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20. Sensors used in Automobiles 4 Figure: Spark Knock Sensor

21. Sensors used in Automobiles Signs of faulty sensor Engine power can be reduced Fuel consumption can be increased Warning light of the engine will be ON Slow acceleration Causes Rust The short circuit inside the engine Damage of wiring Mechanical injury

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23. Sensors used in Automobiles 5 5. Coolant Sensor A coolant temperature sensor is confined to the engine of a vehicle and measures the temperature of the vehicle’s engine coolant. The sensor feeds this information back in the form of an electrical current to the engine control unit (ECU). The ECU then responds to a change in the temperature difference and readjusts the engine’s fuel injection .

24. Sensors used in Automobiles 5 Figure: Coolant Sensor

25. Sensors used in Automobiles Working: A coolant sensor is similar to a thermistor, based on the working principle that a change in electrical resistance will be the direct product of a change in the temperature of a wire carrying current. With a coolant temperature sensor, the full sensor is located in a coolant passage that sits before a thermostat and is connected to the engine control and monitoring unit. The coolant temperature sensor is fastened to the intake manifold of an engine coolant and is often referred to as a negative temperature coefficient type of sensor.

26. Sensors used in Automobiles In terms of resistance capacity, this coolant sensor has 20,000 ohms at 248 degrees Fahrenheit. There is an inverse relationship between the electrical resistance and the engine coolant i.e. when the engine coolant temperature increases, the electrical resistance decreases and this also causes a voltage drop in the sensor.

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28. Sensors used in Automobiles 6. Manifold Absolute Pressure Sensor (MAP Sensor) The sensor is used in electronic control systems for fuel consumption of an engine. The engines which use a MAP sensor are basically injected by fuel. The various pressure sensors provide instant pressure data to the electronic control unit (ECU) of an engine. The data can be used to evaluate air density decide the air mass flow rate of an engine that decides the necessary fuel metering for best combustion. An engine with fuel injected may use an alternate sensor name ly MAF sensor which is named as a mass airflow sensor for detecting the intake flow of air.

29. Sensors used in Automobiles Figure: Manifold Absolute Pressure Sensor

30. Sensors used in Automobiles Working Principle The MAP sensor is an input sensor which detects an engine load and provides a signal which is proportional to the sum of vacuum . After that, an engine computer utilizes this data to alter explosion timing fuel enhancement. Whenever the engine works hard, means the engine utilizes more air or more fuel to maintain the air or the fuel ratio instability. Once the computer examines a load signal from the sensor, it makes the blend of fuel go somewhat richer than regular thus the engine can generate extra power.

31. Sensors used in Automobiles Signs of faulty sensor Fuel ratio of lean air and rich air Surging (sudden power) The economy of Poor fuel Engine power problem Stalling or stop running Misfire Detonation

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33. Sensors used in Automobiles 7 7. Engine Temperature Sensor The engine temperature sensor is a type of sensor that changes its resistance with temperature. Many critical engine functions such as selection of air-fuel ratio, fuel injection timing, ignition timing etc. depend on the engine’s temperature. This is because a cold engine requires a rich air-fuel mixture; whereas the engine running at optimum operating temperature requires a lean mixture. The engine temperature sensor informs the engine’s ECU about the current ongoing variations in the engine temperature. ECU, in turn, adjusts and regulates the fuel quantity ignition timing. The data from the engine temperature sensor provides readings for engine temperature gauge on the dashboard. Based on this data, the ECU also controls the additional functions such as switching on / off the engine cooling fan .

34. Sensors used in Automobiles The engine temperature sensor connects either to the temperature gauge or to the temperature indicator in the dashboard. In modern cars, you will notice that there is no separate engine temperature gauge. Instead, there is a tiny ‘light’ symbolizing the engine temperature; which is integrated with rpm-meter/instrument cluster. Figure: Engine Temperature Sensor

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37. Sensors in Automobiles 8 8. Camshaft Position Sensor The camshaft position sensor monitors the rotation of the camshaft, specifically targeting when valves open and close. Most camshaft sensors are mounted just above a notched ring on the camshaft. It uses a magnet to produce or vary an AC electronic signal that is used in conjunction with a crankshaft position sensor to determine when a position approaches top dead center (TDC) on the compression stroke. This information will help to fine tune spark timing and injector pulse. In consecutive fuel injection systems, ECU must determine which cylinder to fire next. This information is provided from the cylinder identification sensor. During the engine rotation the sensor sends a signal to the onboard controller whenever the first cylinder is at the top dead center (TDC).

38. Sensors used in Automobiles Function of Camshaft position sensor To determine which cylinder is in its power stroke, while the car’s computer (for example) monitors the rotating position of the camshaft which is relative to the crankshaft position using a camshaft position (CMP) sensor. It will use this information to adjust the spark timing and the operation of the fuel injectors The CAM sensor or camshaft position sensor’s role is to signal the ECM the camshaft position. The crank and cam sensor operates in sync with eachother. The CAM sensor is frequently used in determining which injector to fire in a sequential system .

39. Sensors used in Automobiles Figure: Camshaft position sensor

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41. Sensors used in Automobiles 9. Throttle Position Sensor Throttle system present in the automobiles monitors and controls the fluid flow in the engine. The power of the vehicle engine can be controlled by changing the air-fuel ratio of the engine which is done by constrictions of the Throttle. The throttle is known as accelerator pedal in cars, thrust lever in aircraft, and as a regulator in steam-powered engines. In automobiles, the speed of the engine can be controlled by varying the amount of fuel and air supplied to the engine. For this throttle system is used.

42. Sensors used in Automobiles Working This sensor is usually mounted on the throttle body. It senses the position of the throttle valve or butterfly valve and transmits the information to the Engine control unit. This sensor monitors how far down the accelerometer pedal is pushed and gives the output current determining the position of the pedal. The position of the pedal controls the airflow of the engine. If the valve is wide opened, a large amount of air is supplied to the engine and vice-versa. The output given by this sensor, along with other sensors is transmitted to the engine control unit, which decides the amount of fuel to be injected into the engine accordingly.

43. Sensors used in Automobiles This sensor is a three wired potentiometer. Through the first wire, a 5V power is supplied to the sensors resistive layer. The second wire is used as ground whereas the third wire is connected to the potentiometer wiper and provides input to the Engine control system. Based on its construction, there are three types of throttle position sensors. Closed Throttle Position Sensor, the potentiometer type and the combination of both these types .

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45. Sensors used in Automobiles 10. Vehicle Speed Sensor The Vehicle Speed Sensor (VSS) is connected to a speedometer cable and positioned between the axle and the wheel of a vehicle. The most common types of VSS operate from a magnet connected at the back of the transmission housing . T he VSS senses the output of the transmission. Its opposite side is connected to a rotating magnet, which generates a voltage. This voltage is then transmitted to a computational device that calculates the speed proportional to the moving vehicle. During a vehicle’s movement, the VSS will generate four pulses in response to one rotation of the magnet.

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