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55 3 Supplying the Power I’m not sure the buyer of a Buick LaCrosse would know or care if the engine was multivalve or pushrod. I don’t think a Camry buyer would know either, for that matter.1 “Powertrain” is the term the motor vehicle industry uses to encompass the systems responsible for providing power. The two principal powertrain systems are the engine and drivetrain. Components attached to the engine and drivetrain, as well as others closely related to the provision of power, can also be included in the powertrain designation. All but a handful of the world’s one billion motor vehicles produced during the twentieth century were powered by a four-stroke gasolineburning internal combustion engine. The heart of the engine is a piston moving back and forth inside a cylinder in four cycles or “strokes.” • On the first stroke—called the intake stroke—the piston descends , filling the cylinder with a mixture of gasoline and air drawn through an open intake valve. • On the second stroke—compression—the piston rises as the intake valve is closed, compressing the mixture. • On the third stroke—power—the piston descends again, driven down as the mixture is ignited and explodes. • On the fourth stroke—exhaust—the piston rises again, pushing the spent gases out through an open exhaust valve. Most gasoline engines have had four to eight cylinders. An eightcylinder engine typically had two rows of four cylinders set at a 90 degree angle to each other. Thus it was V-shaped and known as a V-8; if there were fewer than eight cylinders, they were more likely to be bored in a straight line. Displacement is the total volume displaced by all of the pistons in the engine block. Horsepower measures the rate at which the engine performs work. Before the motor vehicle age, one horsepower had been defined as the amount of power needed to lift 33,000 pounds one foot 56 Klier and Rubenstein in one minute. U.S. engines have typically displaced three to five liters and achieved 150 to 300 horsepower. Engines built elsewhere in the world have generally been smaller. The heart of the drivetrain is the transmission, which contains gears that are connected to the engine by means of an input shaft and to the axles by means of an output shaft. The purpose of the transmission gears is to adjust the input shaft to turn faster or slower than the output shaft, depending on conditions. The number of revolutions per minute that the input shaft—as well as the engine’s crankshaft to which it is attached—rotates is a factor of what is known as torque. Torque is a measure of force that produces rotation. At a high speed, the engine is capable of turning the crankshaft and input shaft more rapidly than is needed to keep the vehicle moving . In contrast, at a low speed the engine does not generate enough torque to move the vehicle except with some assistance. The transmission gears provide that assistance by increasing the torque delivered by the engine at low speed and decreasing it at high speed. The transmission adjusts torque by means of gears that mesh with each other. To move the vehicle at low speed or up a hill, the transmission increases torque by connecting the input shaft to a smaller gear and the output shaft to a larger gear. As a result, the input shaft turns several times before the output shaft makes one complete revolution. On the other hand, at high-speed driving or going downhill, gears are engaged to slow the rotation of the input shaft. Carmakers consider the powertrain to be one of their core competencies because it is vital to vehicle performance and character. A principal in-house activity is the assembly of engines and transmissions. Although carmakers put together most of their powertrains in-house, they purchase most of the parts from independent suppliers. Powertrain components add more value than any other system, an estimated $2,750 per vehicle in 2004, but only one-fifth of the value of the powertrain is estimated to be added by independent suppliers (Tomkins plc 2004, p. 4). Powertrain production is heavily clustered in the Midwest. Central to this distribution is the long-standing regional concentration of nearly all of the Detroit 3 facilities for assembling engines and transmissions. For manufacturers of powertrain components, a location in the Midwest has traditionally offered a compelling combination of proximity...

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Additional Information

ISBN
9780880994347
Print ISBN
9780880993333
MARC Record
OCLC
268995407
Pages
419
Launched on MUSE
2013-01-01
Language
English
Open Access
N
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