Module no 6

Automobile Engineering

What is the purpose or function of knock sensors? Explain in details how the ECM uses the knock sensors to control timing Or Short notes on KNOCK SENSORS KNOCK SENSORS 1.

A knock sensor can be characterized as a tiny electronic microphone; it is

put in place to listen for pre-ignition knocks and then regulate the timing by retarding it at two degree intervals. 2. There are two types of pre-ignition; the first is when you get premature combustion in the cylinder before the piston reaches top dead center. 3. This can be caused by dirty gas, low octane fuel, timing issues with the engine, and also by the wrong spark plugs. 4. The second is engine run on, when the vehicle is turned off the engine still "rattles" as if it is on. 5. The cause for this type of pre-ignition is a spark plug that is too hot or an improper plug for application. 6. The knock sensor cannot help with this type of pre-ignition. Working :(The ECM uses the knock sensors to control timing ) 1. It detects the slightest noise in the engine and picks up on the "knock" of pre-ignition and sends the information to the ECM (Electronic Control Module). This 'ping' or 'knock' is caused when the mixture of air and gas does not burn smoothly or when it burns too soon. 2. When the timing is off, this can also cause the knocking of the engine. 3. The knock sensor is put in place to regulate these issues. 4. This sensor is usually mounted on the block by a threaded edge that is screwed directly into the block of the engine and is connected to the ECM by wires.

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Vaibhav Vithoba Naik

Automobile Engineering

5. When the knocking or pinging is detected, the sensor sends a signal to the ECM, and this in turn retards the engine spark timing at two degree intervals until it has corrected the issue. 6. The sensor's microphone is so sensitive it picks up the knocking when the human ear cannot detect it. 7. It will hear the slightest ping even when the engine is at its top speed. 8. Most vehicles are equipped with a knock sensor, although there are a few that aren't. 9. All production turbo charged high performance vehicles come equipped with this knock sensor, because these engines are prone to preignition issues.

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Vaibhav Vithoba Naik

Automobile Engineering

Explain in detail the operation of the Zirconium Oxygen sensors? Explain in detail how the PCM (ECM) uses the O2 sensor information? An oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed. The original sensing element is made with a thimble-shaped zirconium ceramic coated on both the exhaust and reference sides with a thin layer of platinum and comes in both heated and unheated forms. The planar-style sensor entered the market in 1998 (also pioneered by Robert Bosch GmbH) and significantly reduced the mass of the ceramic sensing element as well as incorporating the heater within the ceramic structure. This resulted in a sensor that both started operating sooner and responded faster. The most common application is to measure the exhaust gas concentration of oxygen for internal combustion engines in automobiles and other vehicles. Divers also use a similar device to measure the partial pressure of oxygen in their breathing gas.

Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. Oxygen sensors are used in oxygen analyzers which find a lot of use in medical applications such as anesthesia monitors, respirators and oxygen concentrators. There are many different ways of measuring oxygen and these include technologies such as zirconium, electrochemical (also known as Galvanic), infrared, ultrasonic and very recently laser. Each method has its own advantages and disadvantages. Automotive oxygen sensors, colloquially known as O2 sensors, make modern electronic emission control possible. They help determine, in real time, if the air fuel ratio of a combustion engine is rich or lean. Since oxygen sensors are located in the exhaust stream, they do not directly measure the air or

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Automobile Engineering

the fuel entering the engine. But when information from oxygen sensors is coupled with information from other sources, it can be used to indirectly determine the air-to-fuel ratio. Closed-loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with a predetermined (open-loop) fuel map. In addition to enabling electronic fuel injection to work efficiently, this emissions control technique can reduce the amounts of both unburnt fuel and oxides of nitrogen from entering the atmosphere. Unburnt fuel is pollution in the form of airborne hydrocarbons, while oxides of nitrogen (NOx

gases) are a result of

combustion chamber temperatures exceeding 1,300 Kelvin’s due to excess air in the fuel mixture and contribute to smog and acid rain. Volvo was the first automobile manufacturer to employ this technology in the late 1970s, along with the 3-way catalyst used in the catalytic converter. The sensor does not actually measure oxygen concentration, but rather the amount of oxygen needed to completely oxidize any remaining combustibles in the exhaust gas. Rich mixture causes an oxygen demand. This demand causes a voltage to build up, due to transportation of oxygen ions through the sensor layer. Lean mixture causes low voltage, since there is an oxygen excess. Modern spark-ignited combustion engines use oxygen sensors and catalytic converters in order to reduce exhaust emissions. Information on oxygen concentration is sent to the engine management computer or ECU, which adjusts the amount of fuel injected into the engine to compensate for excess air or excess fuel. The ECU attempts to maintain, on average, a certain air-fuel ratio by interpreting the information it gains from the oxygen sensor. The primary goal is a compromise between power, fuel economy, and emissions, and in most cases is achieved by an air-fuel-ratio close to stoichiometric. For spark-ignition engines(such as those that burn gasoline, as opposed to diesel), the three types of emissions modern systems are

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Automobile Engineering

concerned with are: hydrocarbons (which are released when the fuel is not burnt completely, such as when misfiring or running rich), carbon monoxide (which is the result of running slightly rich) and NOx (which dominate when the mixture is lean). Failure of these sensors, either through normal aging, the use of leaded fuels, or fuel contaminated with silicones or silicates, for example, can lead to damage of an automobile's catalytic converter and expensive repairs.

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Vaibhav Vithoba Naik

Automobile Engineering

Explain the Air Management System used in Modern Automotive? What is the role of the Catalytic Converter? Air Management System used in Modern Automotive 1. A charge air management system for an automotive engine includes a charge air-to-liquid coolant heat exchanger for receiving refrigerated liquid coolant from a reservoir. 2. The liquid coolant is refrigerated by means of an engine driven refrigerant system including a compressor, a condenser, and an evaporator mounted within the reservoir. Role of the Catalytic Converter 1. A catalytic converter (colloquially, "cat" or "cat-con") is a device used to reduce the toxicity of emissions from an internal combustion engine. 2. First widely introduced on series-production automobiles in the U.S. market for the 1975 model year to comply with tightening EPA regulations on auto exhaust, catalytic converters are still most commonly used in motor vehicle exhaust systems. 3. Catalytic converters are also used on generator sets, forklifts, mining equipment, trucks, buses, trains, and other engine-equipped machines. 4. A catalytic converter provides an environment for a chemical reaction wherein toxic combustion by- products are converted to less-toxic substances. Three-way catalytic converters have been used in vehicle emission control systems in North America and many other countries on road going vehicles. 5. A three-way catalytic converter has three simultaneous tasks: A. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2 B. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2 C. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2+ [(3x+1)/2]O2 → xCO2 + (x+1)H2O

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Vaibhav Vithoba Naik

Automobile Engineering

Short notes on ABS and TCS ANTI-LOCK BRAKING SYSTEM OR ABS 1. An anti-lock braking system, or ABS is a safety system which prevents the wheels on a motor vehicle from locking up (or ceasing to rotate) while braking. 2. A rotating road wheel allows the driver to maintain steering control under heavy braking by preventing a skid and allowing the wheel to continue interacting tractively with the road surface as directed by driver steering inputs. 3.

ABS offers improved vehicle control and decreases stopping distances on dry and especially slippery surfaces.

4. However, on loose surfaces like gravel and snow-on-pavement, it can slightly increase braking distance while still improving vehicle control. 5. Since initial widespread use in production cars, anti-lock braking systems have evolved considerably 6. A typical ABS is composed of a central electronic control unit (ECU), four wheel speed sensors — one for each wheel — and two or more hydraulic valves within the brake hydraulics. 7. The ECU constantly monitors the rotational speed of each wheel, and when it detects a wheel rotating significantly slower than the others —a condition indicative of impending wheel lock — it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel. 8. The wheel then turns faster; when the ECU detects it is turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied and the wheel slows. 9. This process is repeated continuously, and can be detected by the driver via brake pedal pulsation. 10. A typical anti-lock system can apply and release braking pressure up to 20 times a second

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Automobile Engineering

A TRACTION CONTROL SYSTEM (TCS) 1. A traction control system (TCS), also known as Anti-Slip Regulation (ASR), is typically (but not necessarily) an electro-hydraulic system on production vehicles designed to prevent loss of traction of the driven road wheels, and therefore maintain the control of the vehicle when excessive throttle is applied by the driver and the condition of the road surface (due to varying factors) is unable to cope with the torque applied. 2. Although similar to electronic stability control (ESC) systems, traction control systems do not have the same goal. 3. The intervention can consist of one or more of the following: 4. Retard or suppress the spark to one or more cylinders a. Reduce fuel supply to one or more cylinders b. Brake one or more wheels c.Close the throttle, if the vehicle is fitted with drive by wire throttle d. In turbo-charged vehicles, the boost control solenoid can be actuated to reduce boost and therefore engine power. 5. Typically, the traction control system shares the electro-hydraulic brake actuator 6. (but does not use the conventional master cylinder and servo), and the wheel speed sensors with the anti-lock braking system.

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Vaibhav Vithoba Naik