Autotest of Volvo

Since previous tests of the car the engine capacity has been in­creased from 1.778 to 1.986 c.c.

Earlier Volvos had some real difference in appearance but the current series have international look, but with considerably more space for passengers and baggage than the earlier models. Technically, they are conventional, with the 2-litre 4-cylinder engine mounted in front, and rear-wheels drive through a 4-speed gearbox and coil-spring live axle.

Brakes are servo-assisted discs, the rear brakes incorporating small drums for the parking brake. Twin hydraulic circuits unite both front brakes to one rear brake, so that when one circuit fails only one brake is lost.

The synchromesh gearbox is satisfactory. In average conditions the car rides well.

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Finding a Fault in the Car

If your car doesn't start in the morning, you should check three things first: the battery, the fuel level and the spark plugs. It is easy to repair these faults. If the battery is flat, you should recharge it. If this doesn't work, you should replace it. If the petrol tank is empty, fill it up. If the spark plugs are dirty, clean them, and if the gap in a spark plug is too narrow or too wide, adjust it to the correct width.

Section 12

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Let's look closer at the engine components that operate together to generate power. The basic unit of the engine is the piston which moves up and down inside a cylinder. As air is compressed in the cylinder, fuel is injected on top of the piston. Under high pressure the fuel mixes with the hot air end self-ignites causing combustion. The force of the combustion pushes the piston and connecting rod down turning the crankshaft and flywheel which drive other components.

During engine operation the piston goes through four strokes: in­take, compression, power and exhaust. During the four strokes, the piston moves down and up to complete cycles.

Intake: During the intake stroke the piston moves down in the cylinder pulling air past an open intake valve into the combustion cham­ber.

Compression: During the compression stroke all valves are closed, and piston moves up in the cylinder compressing the air. As the air molecules are compressed the air temperature increases dramatically to about 1000° F (537° C). As the piston nears the top of its stroke, fuel is injected into the combustion chamber on top of the piston. The fuel mixes with the hot compressed air and causes combustion.

Power: During the power stroke the valves are closed as the forces from combustion push the piston and connecting rod down, thereby turning the crankshaft. The heat energy has now been converted into mechanical power.

Exhaust: During the exhaust stroke the inertial force of the turn­ing flywheel helps continue the rotation of the crankshaft to push the piston up again in the cylinder forcing the burned gases out the open exhaust valve. This completes the four strokes of the piston. These four strokes are repeated over and over as the engine operates.

Diesel engine offers the following advantages over automotive-type gasoline engines:

Fuel economy

Diesel engines have higher compression ratios and therefore burn fuel more completely and efficiently.

Reliability

Diesel engines have no electrical ignition system to fail or be main­tained. They are built with heavy-duty parts to withstand the higher compression ratios and to operate for long periods with minimum breakdown. In on-highway trucks for instance, diesel engines have a projected service life of many hundreds of thousands of miles.

Power

It depends on engine size, but diesel engines generally produce more torque and power output than gasoline engines.

Date: 2015-12-13; view: 1391; Нарушение авторских прав