汽车构造英文-Chapter 1 The engine assembly

The engine assembly Engine components V—type engine assembly Engine systemsEngine configurations Cylinder arrangements Engine design features Automotive engines Technical terms Review questionsThis in an introductory chapter on engines. It reviews the various engine components and sub assemblies and looks at some representative engine arrangements. These things wi11 be introduced in this chapter and will be covered in more detail in the chapters that follow.Rotary engines are not included here, but they are covered later in a separate chapter. The engine assemblyThe complete engine assembly consists of the mechanical components that make up the engine itself and also a number of associated systems. These are the systems that are needed to start the engine and also to control it and keep it running.The mechanical parts of the engine assembly can be broken down into a number of sub-assemblies, or groups of associated components．although these are usually referred to merely as assemblies-example, cylinder-head assembly and piston assembly.An engine assembly is shown in Figure 1.1 .There are two side views of a four-cylinder engine which has two overhead camshafts. Some parts of an engine are internal, other parts are external – this illustration identifies a number of external parts.Modern engines often have top covers that are also used as sound barriers to reduce engine noise. With the engine installed in the vehicle, it is not easy to identify the components as many are partly hidden by covers or shields.In both views of the engine, there are components that can be identified at the front of the engine and also at each side of the engine. The flywheel at the rear of the engine is the only major part that is not shown.Front of the engineThe following parts located at the front of the engine：1. Crankshaft pulley. This is attached to the end of the crankshaft. It drives the ribbed belt for the alternator.2. Timing cover. This is attached to the front of the cylinder block and covers the toothed timing belt.3. Oil pump. The pump is mounted on the front of the crankcase and driven directly by the crankshaft.4. Toothed sensor ring. This rotates with the crankshaft. It is used, in conjunction with the sensor, to produce engine rpm and timing signals for the eng ine’s electronic control unit. Right-hand side of the engineParts to be seen on the right-hand side of the engine are:1. Intake manifold.There are upper and lower parts of the assembly. They are designed to facilitate the air flow into the engine.2. Throttle body assembly. This is part of the electronic fuel injection system.3. Fuel rail. This carries the injectors. The fuel rail has pressurized fuel and the injectors are timed to spray it into the engine.4. Engine electronic control unit. This controls the electronic fuel injection system and also many other engine functions.Left-hand side of the engineParts to be seen on the left-hand side of the engine are：1. Exhaust manifold. The manifold is covered by a metal heat shield that prevents heat from radiating to other parts of the engine compartment.2. Oil pan. Located on the underside of the engine, it encloses the crankcase and holds the engine oil.3. Oil filter. This is at the rear of the crankcase.4. Oil dipstick. This is also located at the rear of the crankcase.Other parts of the engine1. Top cover. This fits over the top of the engine and also helps with sound deadening2. Flywheel. This cannot be seen, but it is mounted to the rear of the crankshaft.3. Mounting flange. A mounting flange is provided at the rear of the crankcase for the transmission.Engine componentsThe various components of an engine are assembled together during manufacture and most of these are secured by means of bolts, nuts and other types of fasteners. Some parts are internal and others are attached to the outside of the engine.The following are the main mechanical components of an engineCylinder block：The cylinder block (Figure 1.2) is the largest part of the engine. The other parts are either fitted into theLTDFigure 1.2 Bare engine block for a four-cylinder engine HOLDEN LTDblock or attached to it. As its name suggests, it is basically a block of case metal, usually cast iron. but it can be aluminium alloy with cast iron or steel liners. Aluminium is used to reduce the weight.The cylinder block has accurately bored cy1inders to take the pistons. The lower part of the block is known as die crankcase and this has bearings that carrythe crankshaft. The water-jacket that surround the cylinders are filled with coolant.The top of the cylinder block has a machined surface for the cylinder bead and the bottom of the cylinder block is machined to provide a mounting for the oil pan. or sump.The cylinder can be arranged in the block so that they are in line, as shown, or they can be set at an angle (V-type engine).CrankshaftThe crankshaft (Figure 1.3) is mounted in bearings in the lower part of the cylinder block (the crankcase). The connecting rods connect the pistons to the crankshaft, which is rotated by the power strokes of the piston when tile engine is running. The up-and-down, or reciprocating, motion of the pistons is changed to rotary motion by the combined action of the connecting rods and the cranks of the crankshaft.The term crankshaft comes from the word cranked ,which also means bent. It is a shaft with a number of cranks or bends.■With in-line engines, there is a crank for each cy1inder but with some V-type engines, there is only one crank for each pair of cylinders.FlywheelThe flywheel (Figure 1.4) is a heavy cast iron wheel attached to the rear of the crankshaft. It reduced engine vibrations by smoothing out the power impulses of the pistons. The flywheel absorbs energy during the power stroke and gives up energy during the other strokes and this helps to keep the engine running smoothly.A ring gear is fitted to the rim of the flywheel so that the engine can be rotated by the starter pinion when starting the engine.With automatic transmissions, a drive plate and torque converter take the place of the flywheel and perform the same functions as a flywheel, as far as the running of the engine is concerned.Pistons and connecting rodsThe parts, of a piston and connecting rod assembly are shown in Figure 1.5.The piston has grooves that carry the piston rings and these provide a seal between the piston and the cylinder wall. Compression rings are used as a gas seal and the oil ring is used to prevent excess oil from finding its way up past the piston into the combustion chamber.The connecting rod has a removable cap and a split bearing at its lower end where it is connected to the crankshaft. Its upper end has a piston pin that provides a wrist-type of action with the piston.■Because of its action, the piston pin is sometimes referred to as wrist pin.Cylinder headThe cylinder head (Figure 1.6) is made of cast aluminium alloy. It is bolted to the top of the cy1inder block so that it encloses the cylinders. It has combustion chambers above the cylinders in which the air-fuel mixture is burnt.Cylinder heads can be made of cast iron. which is more resistant to corrosion, but aluminium alloy is used for petrol engines because it has advantage of better heat transfer and lighter weight.The cylinder head has intake ports and exhaustports. The intake valves open the intake ports to admit the fuel charge into the cylinder during the intake stroke. The exhaust valves open the exhaust ports to allow the burnt gases to leave the cylinder following the exhaust stroke.■The cylinder head shown has two overhead-camshaft, one for the exhaust valves and one for the intake valves.Camshaft and valvesThe camshaft and the valve mechanism are used to open and close the valves at the correct time. The camshaft is driven from the crankshaft at half the crankshaft speed.The cylinder-head assembly that was shown in Figure 1.6 is for an overhead camshaft engine. The two camshafts are carried in bearings on top of the cylinder head.The valve cover. also called the cy1inder-head cover, is fitted to the top of the cylinder head. This encloses the valve mechanism. An additional cover on top of the engine cover the ignition coils.This cylinder-head arrangement, for a four-cylinder engine, has two camshafts andsixteen valves. 0ther four-cylinder engines can have two camshafts and twelve valves, orone camshaft and eight valves.■There are a number of different arrangements for operating the valve and these are covered in the next chapter.Timing belt and pulleysThe timing belt and pulleys, shown in Figure 1.7,drive the camshaft at half the crankshaft speed (engine speed). A toothed drive belt is shown. but gears and chains are also used-in some instances a belt and chain are both used.On some engines, the timing chain is used to drive the oil pump. On diesel engines, a timing chain or a timing gear is used to drive tile injection pump as well as the camshaft.The lubrication diagram in Figure 1.10 shows how the four camshafts of a V-type engine are driven by a belt and gears. The timing belt drives the intake camshafts and gears drive the exhaust camshafts.Oil pan or sumpThe oil pan, or sump, holds the oil for the engine-lubricating system. The oil pan shown in Figure 1.8 isTiming belt and pulleys at the front of an overhead-camshaft engineOil pan and oil strainer HOLDEN LTDthat has been cast to shape.The oil pan is bolted to the underside of the engine so that it closes off the crankcase. Only the ends of the crankshaft that extend beyond the cylinder block are exposed. Gaskets, seals and small partsVarious forms of gaskets and seals are used between the surfaces where the parts are bolted together. Some of these are used to seal against oil, some against coolant and some against heat and pressure. Some provide a seal on flat surfaces, others seal against rotating shafts.As well as the larger parts of an engine, there are numerous small parts. These include bolts, nuts, washers, retainers, springs and brackets which go to make up the mechanical components of the engine.V-type engine assemblyThe parts covered previously are the main mechanical parts that are needed for a bare engine. However, for a V-type engine assembly, such as the one shown in Figure 1.9, there arc parts that are attached externally. Parts that can be identified in the illustration are:1. Crankshaft balancer-at the front of the engine(this is pan of the crankshaft pulley ).2. Flywheel-at the rear of the engine.3. Oil pan and oil filter - at the underside of the engine.4. Exhaust manifold - on tile left side of the engine(there is also one on tile right side).5. Intake manifold - located in the valley between the cylinders.6. Throttle body assembly - at the front of the intake manifold.7. Water pump and pulley - at the front of the engine.8. Fuel rails - on each side 0f the intake manifold.9. Ignition coils - on top of the valve cover (there are four coils on each side).10. Spark plugs - at the side of each bank of cylinders.Engine systemsThe engine systems that enable the engine to start and to continue to operate are as follows:1. starting system2. fuel system3. ignition system4. cooling system5. lubricating system6. intake system7. exhaust system8. charging system9. engine electronic control system.There are the systems for petrol engines. Diesel engines have similar systems except for the fuel and ignition systems. Some parts of the systems are built into the engine, some parts are attached to tile engine and other parts are located on the body panels in the engine compartment.The function of these systems are summarisedExternal components of a V-8 engine HOLDEN LTD below. Some already been covered in V olume 1 and others are covered in detail in later chapters of this volume.Starting systemThe starter is used to rotate the engine during starting. It consists of an electric motor and a drive. The drive has a small pinion that meshes with the ring gear on the flywheel during starting. The battery supplies the electrical energy to operate the starter and rotate the engine until it fires and runs on its own.Fuel systemThere are four basic types of fuel systems:1. carburettor systems for petrol engines2. fuel injection systems for petrol engines3. gas fuel systems (LPG or NGV)4. diesel injection systems.All these systems operate in different ways, but they all have somewhere to store fuel (a fuel tank or a cylinder) and a way of supplying the engine with the fuel. They also have a way of supplying air and fuel mixed in the correct proportions so that it can be effectively burnt in the combustion chambers.■Automotive gas fuels are liquefied petroleum gas (LPG) and natural gas for vehicles(NGV).Ignition systemPetrol engines and engines operating on gas require an ignition system. This is needed to provide the sparks that fire the charges in the combustion chambers. For this reason, petrol engines are sometimes referred to as spark-ignition engines. This distinguishes them from diesel engines that do not need a spark because they use compression ignition.Combustion in a diesel occurs when the fuel is sprayed into the combustion chamber. The air in the cylinder is at a high temperature from being compressed- high enough Io ignite tile fuel that is sprayed from the injector.Cooling systemA considerable amount of heat is produced in an engine by the burning air-fuel mixture. Some of the heat is used to do useful work, some is transferred to other parts of the engine and some is carried away with the exhaust gases.However, there is still enough heat to cause damage unless it is removed. This is the function of the cooling system which remove about one-third of the heat that is produced.The cooling system does not just remove heat; it maintains the engine at a desirable operating temperature. In a liquid-cooled engine, this is done by circulating coolant through the water jackets. In an air-cooled engine, cooling is by air blown over cooling fins. Lubricating systemThe engine-lubricating system consists of an oil pump, a relief valve and a filter; also pipes, passages and drillings in various parts of the engine through which the oil can flow.A quantity of oil is held in the oil pan. From this, oil is taken by the oil pump and circulated throughout the engine before returning to the oil pan. The oil lubricates all the moving parts and this not only reduces friction, but it prevents wear and damage.The oil flow through an engine is shown in Figure 1.10; the oil pump is driven directlyby the crankshaft. This system has an oil cooler, Located at the filter mounting under the filter.■The illustration below shows the camshaft and valve arrangements for a V-type engine with four camshafts.Intake systemIn petrol engine with electronic fuel injection, the intake system includes the air cleaner, ducting, the throttle valve assembly and the intake manifold. The intake system provides clean air and carries it into the engine through the intake manifold. Nozzles of the fuel injectors spray fuel into the air passing from the intake manifold into the intake ports.With carburettor fuel systems, a mixture of air and fuel is carried from the carburetor, through the intake manifold and into the engine through the intake ports.For engines that operate on gas, a mixture of air and gas is carried into the engine by the intake manifold.TOYOTAthe intake system.Exhaust systemThe exhaust system carries the burnt gases away from the engine and also reduces noise. The system consists of the exhaust manifold, exhaust pipes, a catalytic converter and a muffler. Arrangements vary with different engines - there may be more than one muffler and more than one catalytic converter. Engines that run on lead replacement petrol (LRP) do not have a catalytic converter, neither do diesel engines.Charging systemThe alternator, which is driven from the engine. converts mechanical energy to electrical energy.The battery supplies energy for the starter, the ignition system and the electric fuel pump during the starting period (petrol engine), but once the engine is running, the alternator supplies all the electrical energy. It also recharges the battery to replace the energy used during starting.Engine electronic control systemThe engine's electronic control system consists of sensor, a control unit and actuators. The control unit receives signals from the sensors and then sends signals to various actuators.There are sensor on the engine, in the intake system and in the exhaust system. The injectors are actuators that adjust the spray of fuel. There are also actuators in the ignition system that advance and retard the spark. These are just two examples of where electronic control is used.■A sensor and sensor ring can be seen at the front of the engine in Figure l. 1.Engine configurationsThe term engine configuration refers to the way that the cylinders of an engine are arranged. The basic arrangements are shown in Figure 1.11. The cylinders can be in-line, opposed, or at an angle (V-type). While three basic arrangements are shown, there are a number of variations.■Configuration means shape, and it is the arrangement of the cylinders that has a large bearing on the shape of an engine.In-line enginesWith in-line engines, the cylinders are arranged in a straight line, one behind the other. Most in-line engines have their cylinder vertical, but some are slanted. That is, the engine is tilted at an angle to reduce the overall height. These engines are sometimes referred to as slanted engines.Some in-line engines have their cylinders horizontal, so that the engine is more or less on its side. This reduces the overall height of the engine. This arrangement is used mainly in larger commercial vehicle with the engine mounted under part of the cab.The mechanical arrangement of a four - cylinder in line engine for a passenger car is shown in Figure 1.12. This has a single camshaft and sixteen valves operated by rocker arms. It has electronic fuel injection. The cut-away view enables the various parts to beidentified.cover, 2 camshaft pulley, 3 camshaft, 4 air chamber, 5 throttle, 6 valve cover, 7 distributor, 8 spark plug cabbies, 9 exhaust valve, 10 cylinder, 1l piston, 12 cylinder block, 13 connecting rod, 14 crankshaft, 15 screen,16 oil pan, 17 oil pump,18 crankshaft pulley,19 timing belt, 20 alternator MAZDAHorizontally opposed engineA sectional view of a horizontally opposed engine is shown in Figure 1.19( at the end of the chapter) .This has its cylinder arranged in two flat banks with the crankshaft between them. The engine shown has a short rigid crankshaft with five bearings. A horizontally opposed engine has even firing impulses and good balance. Movement of a piston in one direction is opposed by movement of a piston in the opposite direction.Horizontally opposed engines, with their fiat design, give the engine a low height and also help to keep the centre of gravity of the vehicle low. A low centre of gravity gives the vehicle stability.■The centre of gravity, stated simply, is the point at which the mass of the vehicle canbe considered t be concentrated.V-type enginesWith V-type engines, the cylinders are arranged in two banks at an angle. This reduces the length of the engine and makes it more compact. This also reduces the length of the crankshaft, which can be designed to be more rigid than a long shaft.A section through a V-type engine with eight cylinders is shown in Figure 1.13. V-8 engines with their cylinders at an angle need only four crankpins the connecting rods of opposite cylinders are connected side-by-side to the same crankpin.Sectional view of a V-8 engine, looking from the front-the banks of°FORDThe engine shown is an overhead-valve engine. It has a camshaft in the V of the cylinder block and pushrods to operate the valve mechanism on the cylinder head. The cylinders are at an angle of 90°.V-6 enginevA V-type engine with a different arrangement is shown in Figure 1.14. This is a sectional views of a V-6 engine with two banks of three cylinders set at an angle of 60°.It is a double overhead-camshaft (DOHC) engine. with two camshafts on each bank of cylinders. One camshaft on each bank operates the intake valves andthe other operates the exhaust valves.The intake camshafts on both banks are driven by a single timing belt from the crankshaft pulley. The exhaust camshafts are then driven by gear from the intake camshaft.The crankshaft of this engine is supported in four main bearings and it has a separate crankpin for each connecting rod bearing.■The internal arrangement fof this engine is shown in the lubrication diagram in Figure1.10.Cylinder numberingFigure 1.15 shows a number of different cylinder arrangements that are commonly used for in-line and V-type engines. The firing orders for the engines are also shown.There are also other arrangements including: in-line engines with two cylinders, five cylinders and eight cylinders: V-type engines with two cylinders and twelve cylinders; and horizontally opposed engines with four and six cylinders.Cylinder numberingWith in-line engines, the cylinders are numbered in order from front to rear, as shown in the diagrams (a) to (c) in Figure 1.15.V-type engines are designed with one bank of cylinders a little in front of the other. This is necessary because the connecting rods are side by side on the crankshaft. The front cylinder is usually designated No. 1. This can be the front cylinder on either the right or left bank, depending on the design of the particular engine.In the diagrams (d) and (f) the front cylinder is onSectional view of a V-6 engine: the cylinders of the right-hand bank areTOYOTAarc numbered across tile engine from bank to bank.The diagram in Figure 1.1 6 is an alternative arrangement for the cylinders of a V-6 engine. No. 1 cylinder is on the right bank because the cylinders on the right bank are set ahead of the cylinders of the left bank. Cylinder 1,3 and 5 are on the right bank and 2,4 and6 are on the left bank.Cylinder numbering and firing order for a V-6 engine TOYOTA Firing orderThe firing order is the order, or sequence, in which the cylinders of an engine fire or deliver their power strokes. The firing order is part of engine design and is determined by the design of both the crankshaft and the camshaft.The arrangement of the cranks, or throws, of the crankshaft determines the movement of the pistons and the arrangement of the cams on the camshaft determines when the valves open and close. The crankshaft and camshaft are designed and timed so that the valves open correctly in relation to the piston atl'oke~.For petrol and gas engines, the ignition system is also timed so that it provides the spark at the right time and in the correct firing order. For a diesel, the injection pump is timed so that fuel is injected in the correct firing order.Firing orders are shown in the diagrams in Figures 1.15 and 1.16.Other firing ordersThere are a number of other firing orders. For example, a four-cy1inder engine can be 1-3-4-2 or 1-2-4 3.A particular V-8 engine has a firing order of 1-8-7-2-6-5 4 3. With this engine, No. 1 cylinder is the front cylinder on the left bank, with No. 2 on the opposite bank, and so on. In all sequences, the firing order of the cylinders is staggered so that the power impulses are spaced as evenly as possible.There are a couple of instances where engines fire in the sequence of the cy1inder numbers. One is a three-cylinder engine, where the cylinders must fire one after the other. Changing the firing order from 1-2-3 does not stagger the sequence because the cylinders will always fire consecutively.The V-6 cylinders in Figure 1.16 are another example of how cylinders can fire in sequence. The firing order here is 1-2-3-4-5-6. Again, the firing order depends on the design of the crankshaft, which controls piston movement, and tile design of the camshaft, which controls the opening and closing of the valves.■As well as knowing the firing order for the engine, the method of numbering the cylinders must also be known.Engine design featuresEngines are classified or described by their design features. These are as follows:1. Number of cylinders. This has already been discussed. The number of cylinders can range from two to twelve. There can be an odd number of cylinders, or an even number.2. Cylinder arrangement. An engine can have cylinders which are in-line, horizontally opposed, or V- type.3. Cubic capacity. This is also referred to as piston displacement. It is the size of the engine, being the total volume, in litres, of all the cylinders. A small passenger-car engine could have a capacity of 1.5 litres, while a large passenger or light commercial vehicle engine could have a capacity of 4 litres or more.4. Valve mechanism. This relate to whether the engine is an overhead valve(OHV) or anoverhead-camshaft (OHC) engine. It can also relate to the number of valves. Some four -cylinder engines in particular have four valves per cy1inder and so are referred to as sixteen-valve engines.5. Number of camshaft. Some in-line engines have a single overhead camshaft (SOHC). Other in-line engines have two overhead camshafts and are referred to as double overhead-camshaft engines(DOHC). V-type engines have two overhead camshafts; they can also be designed with four overhead camshafts.■Four overhead camshafts are referred to as quad-cams.6. Type of cooling. Engines can be liquid-cooled or air-cooled. Almost all passenger vehicles and light commercial vehicles are liquid-cooled.7. Operating cycle. The operating cycle of an engine can be a four-stroke cycle or a two-stroke cycle. Passenger and light commercial vehicles have four stroke engines, but some larger diesel engines are two-strokes.8. Type of fuel or fuel system. Engines are designed to run on a particular fuel. This can be petrol, distillate, liquefied petroleum gas (LPG) or natural gas for vehicles (NGV). Dual -fuel engines can run on petrol or gas.Petrol engines fitted with electronic fuel injection systems are often called EFI engines and those with a carburettor are called carburettor engines.9. Turbocharging and supercharging. Some engines are fitted with an exhaust-driven turbocharger, and so are referred to as turbocharged engines. Other engines have a supercharger that is engine driven. Turbocharging and supercharging enable air to be forced into the cylinders and this increases engine performance.General arrangement of the power units of a hybrid-powered vehicle TOYOTARotary enginesOnly some of the features above apply to rotary engines. Rotary engines do not have cylinders or valve mechanisms. They have a rotor or rotors instead of pistons and they have their own operating cycle. They operate on petrol and can be turbocharged.■Rotary engines are the subject of Chapter 10.Hybrid powered vehicles have been developed to provide transport with a low fuel consumption and low exhaust emission.The hybrid power for the vehicle is provided by a combination of a petrol engine and an electric motor. Vehicles with hybrid power can operate on the petrol engine only, on the electric motor only, or on a combination of both. When operating on electricity, the petrol engine is closed down so that there are no engine emission.A general arrangement of the hybrid power unit is shown in Figure 1.17. The engine compartment contains the petrol engine and the special electric motor. These are connected through a hybrid transmission to the front driving wheels. Electric power is provided by a bank of special batteries located in the boot of the vehicle. The batteries are charged by the petrol engine while it is running and there is also some regenerative charging by the electric motor when it is not driving and being used for braking.Automotive enginesThe engines and components described so far are representative of those used in passenger and light commercial vehicles, but there are others. All manufacturers have a wide range of engines, and while the basic engine construction and principles remain the same, there are many changes in design that occur as a result of advances in technology.Representative engines can be seen in Figures 1.18 and 1.19. These can be used to identify engine design features.。