汽车专业英语课件-2 cha.ppt

复习,1.Discribe the main parts of a car ? 说明汽车的主要组成部件（系统）有哪些？ 2.Vehicle classificatin 汽车分类,提问,学习内容,本次课学习内容、目标和重点难点,学习目标,难点重点,Principle of Operation Classifications Main parts and systems,1.掌握内燃机的分类英文术语 2.掌握机体、曲柄连杆机构、配气机构的英文术语 2.了解各个系统的主要功能,1.重点为记忆分类和主要部件英文专业术语 2.难点需要记忆的生词偏多 3.准确汉译表达也是难点,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,2.1.1 New Words and Phrases,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,The rst internal-combustion engine to operate successfully on the four-stroke cycle used gas as a fuel and was built in 1876 by Nicolaus August Otto, a self-taught German engineer at the Gas-motoreufabrik Deutz factory near Cologne, for many years the largest manufacturer of internal-combustion engines in the world. It was one of Ottos associates Gottlieb Daimler who later developed an engine to run on petrol which was described in patent number 4315 of 1885. He also pioneered its application to the motor vehicle. Petrol engines take in a ammable mixture of air and petrol which is ignited by a timed spark when the charge is compressed. These engines are therefore sometimes called spark-ignition(S.I.)engines.,2.1.2 Text,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,These engines require four piston strokes to complete one cycle: an air-and-fuel intake stroke moving outward from the cylinder head, an inward movement towards the cylinder head compressing the charge, an outward power stroke, and an inward exhaust stroke. Induction stroke. The inlet valve is opened and the exhaust valve is closed. The piston descends, moving away from the cylinder head (Fig.2-1(a). The speed of the piston moving along the cylinder creates a pressure reduction or depression which reaches a maximum of about 0.3 bar below atmospheric pressure at one-third from the beginning of the stroke. The depression actually generated will depend on the speed and load experienced by the engine, but a typical average value might be 0.12 bar below atmospheric pressure.,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,This depression induces (sucks in) a fresh charge of air and atomised petrol in proportions ranging from 10 to 17 parts of air to one part of petrol by weight. An engine which induces fresh charge by means of a depression in the cylinder is said to be normally aspirated or naturally aspirated. Compression stroke. Both the inlet and the exhaust valves are closed. The piston begins to ascend towards the cylinder head (Fig.2-1(b). The induced air-and-petrol charge is progressively compressed to something of the order of one-eighth to one-tenth of the cylinders original volume at the pistons innermost position. This compression squeezes the air and atomised-petrol molecules closer together and not only increases the charge pressure in the cylinder but also raises the temperature.,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,Typical maximum cylinder compression pressures will range between 8 and 14 bars with the throttle open and the engine running under load. Power stroke. Both the inlet and the exhaust valves are closed and, just before the piston approaches the top of its stroke during compression, a spark-plug ignites the dense combustible charge (Fig.2-1(c). By the time the piston reaches the innermost point of its stroke, the charge mixture begins to burn, generates heat, and rapidly raises the pressure in the cylinder until the gas forces exceed the resisting load. The burning gases then expand and so change the pistons direction of motion and push it to its outermost position. The cylinder pressure then drops from a peak value of about 60 bars under full load down to maybe 4 bar near the outermost movement of the piston.,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,Exhaust stroke. At the end of the power stroke the inlet valve remains closed but the exhaust valve is opened. The piston changes its direction of motion and now moves from the outermost to the innermost position (Fig.2-1(d). Most of the burnt gases will be expelled by the existing pressure energy of the gas, but the returning piston will push the last of the spent gases out of the cylinder through the exhaust-valve port and to the atmosphere.,Chapter 2 Internal Combustion Engine 2.1 Principle of Operation,Fig 2-1 Four-stroke-cycle petrol engine,Chapter 2 Internal Combustion Engine 2.2 Engine Classifications,Fig 2-1 Four-stroke-cycle petrol engine,Chapter 2 Internal Combustion Engine 2.2 Engine Classifications,2.2.1 New Words and Phrases,Chapter 2 Internal Combustion Engine 2.2 Engine Classifications,Chapter 2 Internal Combustion Engine 2.2 Engine Classifications,Todays automotive engines can be classified in several ways depending on the following design features: Operational cycles. There are two-stroke and four-stroke cycles. Four-stroke-cycle engines are widely used on road vehicles. However, a few older cars have used and some cars in the future will use a two-stroke engine. Number of cylinders. Current engine designs include 3-, 4-, 5-, 6-, 8-, 10-, and 12-cylinder engines. Cylinder arrangement. An engine can be flat (horizontal-opposed), inline, or V-type. Other more complicated designs have also been used. See figure 2-2.,2.2.2 Text,Fig. 2-2 Cylinder arrangements,Chapter 2 Internal Combustion Engine 2.2 Engine Classifications,Valvetrain type. Engine valvetrains can be either the overhead camshaft (OHC) type or the camshaft in-block overhead valve (OHV) type (Figure 2-3). Some engines separate camshafts for the intake and exhaust valves. These are based on the OHC design and are called double overhead camshaft (DOHC) engines.V-type DOHC engines have four camshaftstwo on each side.,Figure 2-3 (a) Overhead camshaft（OHC）,Chapter 2 Internal Combustion Engine 2.2 Engine Classifications,Valvetrain type. Engine valvetrains can be either the overhead camshaft (OHC) type or the camshaft in-block overhead valve (OHV) type (Figure 2-3). Some engines separate camshafts for the intake and exhaust valves. These are based on the OHC design and are called double overhead camshaft (DOHC) engines. V-type DOHC engines have four camshaftstwo on each side.,Figure 2-3 (b) Overhead valve (OHV) engines,Chapter 2 Internal Combustion Engine 2.2 Engine Classifications,Ignition type. There are two types of ignition systems: spark ignition and compression ignition. Gasoline engines use a spark ignition system and are sorted to spark ignition engines. In a spark ignition engine, the air-fuel mixture is ignited by an electrical spark. Diesel engines, or compression ignition engines, have no spark plugs. An automotive diesel engine relies on the heat generated as air is compressed to ignite the air-fuel mixture for the power stroke. Cooling systems. There are both air-cooled and liquid-cooled engines in use. Nearly all of todays engines have liquid-cooling systems. Fuel type. Several types of fuel currently used in automobile engines include gasoline, natural gas, methanol, diesel, and propane. The most commonly used is gasoline although new fuels are being tested.,Chapter 2 Internal Combustion Engine 2.2 Engine Classifications,Chapter 2 Internal Combustion Engine 2.3 Engine block and head,2.3.1 New Words and Phrases,Chapter 2 Internal Combustion Engine 2.3 Engine block and head,Chapter 2 Internal Combustion Engine 2.3 Engine block and head,2.3.1 Engine block The engine block (or cylinder block) serves as a rigid metal foundation for all parts of an engine (Fig.2-4). It contains the cylinders and supports the crankshaft and camshaft. Accessory units and the clutch housing are bolted to it. Blocks are made of either cast iron or aluminum.,2.3.2 Text,Chapter 2 Internal Combustion Engine 2.3 Engine block and head,The cylinder is a round hole formed in the block. It forms a guide for the piston and acts as a container for taking in, compressing, firing, and exhausting the air-fuel charge. Cylinders have been made of both steel and cast iron. Cast iron is by far the most popular. When steel cylinders are desi