Chapter 13

[object Object],[object Object],[object Object],[object Object],[object Object],OBJECTIVES: After studying Chapter 13, the reader should be able to:

[object Object],KEY TERMS: Continued

SCIENTIFIC METHOD ,[object Object],Step #1 Observe the conditions or problem; define or describe. Step #2 Formulate an explanation that could be the cause. Step #3 Use the explanation ( hypothesis ) to see if it matches the existing problem. If not, return to step 2. Step #4 After the explanation has proved to be a possible solution to a problem, additional tests should verify the method. Continued

[object Object],[object Object],[object Object],Continued

[object Object],[object Object],[object Object]

ENERGY PRINCIPLES ,[object Object],Energy is called kinetic energy if it is in the form of a moving object. An example is a moving vehicle. Potential energy is capable of being changed to useful energy, such as energy stored in a battery or a vehicle at the top of a hill. In both of these cases, there is no energy being released. Figure 13–1 Energy, the ability to perform work, exists in many forms.

TORQUE ,[object Object],The metric unit for torque is Newton-meters. 1 pound-foot = 1.3558 Newton-meters 1 Newton-meter = 0.7376 pound-foot Figure 13–2 Torque is a twisting force equal to the distance from the pivot point times the force applied expressed in units called pound-feet (lb-ft) or Newton-meters (N-m). See a conversion chart on Page 97 of your textbook

WORK ,[object Object],Figure 13–3 Work is calculated by multiplying force times distance. If you push 100 pounds 10 feet, you have done 1,000 foot-pounds of work.

The designations for torque and work are often confusing. Torque is expressed in pound-feet because it represents a force exerted a certain distance from the object and acts as a lever. Work, however, is expressed in foot-pounds because work is the movement over a certain distance (feet) multiplied by the force applied (pounds). Engines produce torque and service technicians exert torque represented by the unit pound-feet. What is the Difference Between Torque and Work? Continued

POWER AND HORSEPOWER ,[object Object],An engine produces horsepower ( hp ). One horsepower is the power required to move 550 pounds one foot in one second, or 33,000 pounds one foot in one minute (550 lb 60 sec 33,000 lb). This is expressed as 500 foot-pounds (ft-lb) per second or 33,000 foot-pounds per minute. Continued Horsepower = torque times RPM divided by 525 2

Figure 13–4 One horsepower is equal to 33,000 foot-pounds (200 lbs 165 ft) of work per minute. The actual horsepower produced by an engine is measured with a dynamometer , (abbreviated as dyno or dyn ). It places a load on the engine and measures the twisting force the crankshaft places against the load. The load holds the engine speed, so it is called a brake. The horse power derived is called brake horsepower (bhp) and calculated from torque readings at various engine speeds (in revolutions per minute or RPM).

NEWTON’S LAWS OF MOTION ,[object Object],[object Object],Continued

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KINETIC ENERGY ,[object Object],Engineers calculate kinetic energy using this formula: Another way to calculate this: Continued

[object Object],Figure 13–5 Kinetic energy increases in direct proportion to the weight of the vehicle. Results show that when vehicle weight doubles from 3,000 to 6,000 pounds, kinetic energy also doubles from 90,301 to 180,602 foot-pounds. In mathematical terms, kinetic energy increases proportionally as weight increases. If weight quadruples, so will kinetic energy.

[object Object],Figure 13–6 Kinetic energy increases as the square of any increase in vehicle speed. The vehicle traveling at 30 mph has over 90,000 foot-pounds of kinetic energy. At 60 mph the figure increases to over 350,000 foot-pounds. Continued

Mass is the amount of matter in an object. One of the properties of mass is inertia. Inertia is the resistance to being put in motion and the tendency to remain in motion once it is set in motion. The weight of an object is the force of gravity on the object and may be defined as the mass times the acceleration of gravity. Therefore, mass means the property of an object and weight is a force. What is the Difference Between Mass and Weight? Continued

INERTIA ,[object Object],No vehicle can stop on a dime. The energy required to slow or stop a vehicle must be absorbed by the braking system. All drivers should be aware of this fact and drive at a reasonable speed for the road and traffic conditions. Brakes Cannot Overcome the Laws of Physics

MECHANICAL PRINCIPLES ,[object Object],Continued

[object Object],Figure 13–7 A first-class lever increases force and changes the direction of the force. Continued

[object Object],Figure 13–8 A second-class lever increases force in the same direction as it is applied. Continued

[object Object],Figure 13–9 A third-class lever reduces force but increases the speed and travel of the work. Continued

[object Object],Figure 13–10 This brake pedal assembly provides a 5:1 mechanical advantage because a 10-lb force input results in a 50-lb force into the master cylinder. The force applied to the master cylinder by the pedal pushrod is much greater than the force applied at the pedal pad, but the pushrod does not travel as far. Leverage creates a mechanical advantage at the brake pedal, called the pedal ratio , and is used at many points in service and parking brake systems Continued

HEAT AND TEMPERATURE ,[object Object],Heat Is measured in British Thermal Units , ( BTUs .) One BTU is the amount of heat needed to raise the temperature of one pound of water one degree Fahrenheit. Room heaters and air conditioners are rated in how many BTUs per hour can be added (heater) or removed (air conditioner) from a space. Continued

[object Object],Heat energy can be transferred by three ways, including: Metals are good conductors of heat, whereas plastic, rubber, and ceramics are poor conductors of heat and are called insulators . If a material is a good conductor of heat, it is also a good conductor of electricity. Most conductors are metals, such as steel, copper, aluminum, and brass. Most insulators are nonmetals, such as plastic and rubber. Therefore, if a material does not conduct heat, it usually will not conduct electricity. Conductors and Insulator

[object Object],[object Object],A coat is worn in cold weather to keep warm. Does it keep the cold out or the heat in? Actually, both, but because heat travels from a warm object (human body) to a colder object (outside cold air), the primary purpose of a coat is to keep the body heat from escaping into the cold air. How Does a Coat Keep You Warm? Continued

[object Object],Figure 13–11 A typical outdoor thermometer which is used to measure temperature, not heat. Temperature is measured using two scales: Celsius (centigrade) and Fahrenheit. The Celsius scale was devised by taking the difference between the freezing and boiling points of water and dividing it into 100 equal parts. See a quick and easy temperature conversion chart on Page 101 of your textbook.

Thermodynamics is the study of the relationship among temperature, pressure, and volume changes. The laws of thermodynamics help engineers design and develop engines with higher efficiency. Thermodynamics is therefore used in the design of the cooling system, as well as in the engine, because the more heat created by the burning of fuel in the engine, the more power the engine can develop using the same or less amount of fuel. What is Thermodynamics?

ACIDS AND BASES ,[object Object],Bases Substances that can also burn if strong enough. Also referred to as alkaline . Common bases are generally not harmful unless eaten and have a bitter taste, including baking soda, soap, and antacid, such as Milk of Magnesia . Stronger bases, which can burn the skin include lye (sodium hydroxide), bleach and drain cleaner. ® CAUTION: Whenever working with chemicals, eye protection is a must. Continued

Acids have a very strong affinity for water and as a result, if water is poured into acid, the resulting reaction would be extremely violent and acid would be forced outward in all directions. Always pour acid into water, never water into acid. Technicians seldom need to work with acids because even battery electrolytes from the water and acid are premixed to help prevent the possibility of a technician creating a harmful reaction. Can Water and Acid be Mixed Together?

GAS LAWS ,[object Object],Boyle’s Law Written in 1662 by Robert Boyle (1627–1691) and describes the relationship between volume and pressure of a gas in a closed container. States that the volume of a gas varies inversely (opposite) with the pressure exerted against it in a closed container. Therefore, if a closed container is compressed, the volume of the gas inside is reduced but the pressure is increased. Charles’s Law 1787 by French scientist, Jacque Charles (1746–1823). States that as the temperature of a gas increases, the volume increases. As temperature decreases, volume decreases.

SOUND AND ACCOUSTICS ,[object Object],Frequency Called the pitch, and measured in Hertz or cycles per second. Normal hearing ranges from as low as 20 Hertz to 20,000 Hertz. Very low frequencies and very high frequencies over 20,000 Hertz cannot be detected by humans. Intensity Intensity of sound, called loudness, is measured in decibels (dB), named for Alexander Graham Bell (1847–1922), inventor of the telephone. Continued

[object Object],[object Object],[object Object],[object Object],[object Object],Acoustics Is the study of sound and how it is generated and transmitted. Acoustic engineers are employed by manufacturers to help reduce noise and design methods to reduce or noise from being transmitted into the passenger compartment. According to acoustic engineers, about 80% of noise created by the movement of the tires on the road is transmitted through the chassis and body of the vehicle. Continued

According to audiologists (hearing and speech doctors), a person should wear ear protection if the level of sound requires that your voice be raised in order to be heard. Any level that exceeds 90 dB requires the use of ear protection to avoid hearing loss. This means that ear protection should be worn when using a power mower or using an air tool, such as an air impact wrench or air ratchet. Wear Hearing Protection

PLASTIC ,[object Object],Thermoset Plastic This type of plastic is changed chemically when cured and shaped. It cannot be reheated or reformed. Rubber an example of a thermoset plastic material that cannot be remelted and reformed after curing. Other examples of thermoset plastics include: ,[object Object],[object Object],[object Object],Continued

[object Object],Thermoplastic Flexible at room temperature. Thermoplastic can be recycled by grinding it into pieces and remolding it into another shape. Examples of thermoplastics include: ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Continued

[object Object],[object Object],[object Object],Most large plastic pieces are labeled on the inside with letters, such as PP or PE. If no marking is visible, it is still possible to identify the type of plastic using a simple basic test. Often replacement plastic parts are available in only one color and must be painted to match the original. A burn test is used to test if the plastic part. • No visible smoke means that the plastic is polypropylene. • Visible black smoke means that the plastic is ABS. Continued

[object Object],Figure 13–12 This interior plastic part is labeled PE-HD, which means polyethylene-high density. After the plastic has been identified, check service information and paint literature to determine the proper paint and preparations needed to refinish the plastic part.

IRON AND STEEL ,[object Object],Cast Iron Contains 2% to 4% carbon, usually in the shape of flakes of graphite 0.001 to 0.004 inches long. Cast iron is used in engine blocks, rear axle assemblies, and suspension components. Ductile Cast Iron In ductile iron, the carbon in the alloy with silicon are small ball-shapes called spheroidols. Ductile iron is also called malleable iron and is used to make crankshafts. Continued

Gray Cast Iron Gray cast iron is cast iron that has silicon in the alloy giving the metal a gray color. Gray cast iron is used for engine blocks. NOTE: Cast iron contains graphite, which acts as a lubricant when being machined. As a result, cooling oil or water is not needed when making cast iron brake rotors or brake drums.

SAE STEEL DESIGNATIONS ,[object Object],[object Object],[object Object],Continued

[object Object],CAUTION: Both medium carbon and high carbon steel can be hardened by heating and then cooling, using water or oil to rapidly cool the metal. Therefore, if heating any metal, always allow it to cool slowly to avoid changing the hardness of the steel. Continued

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],A common alloy for forged crankshafts is SAE 4340. The analysis of this designation is: 4340—An alloy containing 1.82% nickel, 0.5% to 0.8% chromium, 0.25% molybdenum, 40 parts of carbon.

ALUMINUM AND ALUMINUM ALLOYS ,[object Object]

SUMMARY ,[object Object],[object Object],[object Object],[object Object],Continued

SUMMARY ,[object Object],[object Object],[object Object],[object Object],[object Object],( cont. )

Chapter 13

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Chapter 13