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Engine Torque

Engine Torque

The rotating or turning effort of the that range, torque is no longer increased. engine’s crankshaft is called engine torque. Engine torque is measured in foot-pounds ( ft.-lbs. ) or the metric measurement Newton-meters (N-m). engine produce a maximum amount of torque when operating within a narrow range of engine speeds. When an engine reaches the maximum speed within

The amount of torque produced in relation to engine speed is called the engine’s torque curve. Ideally, the engine should always be run when it is providing a maximum amount of torque. This allows the engine to provide the required amount of power while using a minimum amount of fuel.

As a car is climbing up steep hill, its driving wheels slow down because of the increased amount of work it must do; this causes engine speed to decrease as well as a reduce the engine’s torque. The driver must downshift the transmission or press down harder on gas pedal, which increases engine speed and allows the engine to produce more torque. When the car reaches the top of the hill and begins to go down, its speed and the speed of the engine rapidly increase. The driver can now up shift or let up on the gas pedal, which allows the engine’s speed to decrease and places it back into its peak within the torque curve.

Torque Multiplication

Measurements of horsepower indicate the amount of work being performed and the rate at which it being done. The drive line transmit power and multiply torque, but it cannot multiply power. When power flows through one gear to another, the torque is multiplied in proportion to the different gear sizes. Torque is multiplied, but the power remains the same, as the torque is multiplied at the expense of rotational speed. Maximum horsepower occurs when the engine is operating at high speed and producing close to its maximum torque. Engine horsepower can be calculated by using a mathematical formula :

Hp = T X rpm / 5252

Where hp = horsepower; T= the amount of torque produced by an engine, rpm = the speed of the engine when it is producing the torque, and 5252 being a mathematical constant.

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Although the engine is major system by itself (figure 1-3), its output should be considered a component of the drive train. The engine provides the power to drive the wheels of the vehicle. An engine develops a rotary motion or torque that, when multiplied by the transmission gears, will move the car under a variety of conditions. The engine produces power by burning a mixture of fuel and air in its combustion chambers. Combustion cases a high pressure in the cylinders, which forces the pistons downward. Connecting rods transfer the downward movement of the pistons to the crankshaft, which rotates by the force on the pistons.

All automobile engines, both gasoline and diesel, are classified  as internal combustion engines because the combustion or burning that creates energy takes place inside the engine. Combustion is the burning of an air and fuel mixture. As a result of combustion, large amounts of pressure are generated in the engine. This pressure or energy is used to power the car. The engine must be built strong enough to hold the pressure and temperatures formed by combustion.

Diesel engines have been around a long time and are mostly found in big heavy-duty trucks. However, they are also used in some pick-up trucks and will become more common in automobiles in the future ( figure 1-4). Although the construction of a gasoline and diesel engine are similar, their operation is quite different.

A gasoline engine relies on a mixture of fuel and air that is ignited by a spark to produce power. A diesel engine also uses fuel and air, but does not need a spark to cause ignition. Diesel engines are often called compression ignition engines. This is because its incoming air is tightly compresses air. The heat of the compressed air ignites the fuel and combustion takes place. The following sections cover the basic parts and the major systems of a gasoline engine.

Most automotive engines are four-stroke cycle engines. The opening and closing of the intake and exhaust valves are timed to the movement of the piston. As a result, the engine passes through four different events or strokes during one combustion cycle. These four the intake, compression, power, and exhaust strokes.

One the intake stroke, the piston moves downward, and charge of air/fuel mixture is introduced into cylinder. As the piston travels upward, the air/fuel mixture is compressed in preparation for burning. Just before the piston reaches the top of the cylinder, ignition occurs and combustion starts. The pressure of expanding gases forces the piston downward on its power stroke. When it reciprocates, or moves upward again, the piston is on the exhaust stroke. During the exhaust stroke, the piston pushes the burned gases out of the cylinder. As long as the engine is running, the cycle of event repeats itself, resulting in the production of engine torque.

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Fundamental Technology

 Manual Drive Trains and Axles


An automobile can be divided into four major systems or basic components : 1 the engine, which serves as source of power: 2) the power train, or drive, which transmits the engine’s power to the car’s wheels ; 3) the chassis, which supports the engine and body and includes the brake, steering, and suspension system; and 4) the car’s body, interior, and accessories, which include the seats, heater and air conditioner, lights, windshield wipers, and other comport and safety features.

Basically, the drive train has four primary purposes: to connect and disconnect the engine’s power to the wheels, to select different speed rations, to provide a way to move the car in reverse, and to control the power to drive wheel for safe turning of the automobile. The main components of the manual drive train are the : clutch, transmission, differential, and drive axles ( figure 1-1). The exact components used in vehicle’s drive train depend on whether the vehicle is equipped with front-wheel drive, rear-wheel drive, or four-wheel drive.

Today, most cars are front-wheel drive ( FWD). Power flow through the drive train of  FWD vehicles passes though the clutch or torque converter, through the transmission, and then moves to front differential, the driving axles, and onto the front wheels. The transmission and differential are housed in a single unit ( figure 1-2) called a trans axle.

Some large and many performance cars are rear-wheel drive (RWD). Most pick-up trucks and many SUV’s are also RWD vehicles.  Power flow in a RWD vehicle passes through the clutch or torque converter, transmission, and the drive line ( drive shaft assembly ). Then it goes through the rear differential, the rear-driving axles, and onto the rear wheels.

Four-wheel drive ( 4WD ) or all-wheel drive (AWD) vehicles combine features of both rear- and front-wheel drive systems so power can be delivered to all wheel all the time or when the conditions or driver selects two-wheel or four-wheel drive. Normally, a 4WD pi Normally, a 4WD pi Normally, a 4WD pickup or full-size SUV has 4WD; the drive train is based on a RWD vehicle modified to include a  front drive axle and transfer case.  When a smaller SUV or car has AWD or 4WD, the drive train is modified system. Modification include a rear drive axle and assembly that transfers some of the engine’s power to the rear drive axle.

There are two sets of gear in the drive train: the transmission and the differential. The transmission allows the gear ratio to change and the differential unit changes the power output from the transmission and allows the drive wheels to rotate at different speeds during turns; this prevents tire scuffing. Through the use of different gear ratios, torques is multiplied.