汽车专业英语课件-3 cha.ppt

复习,提问（教师说发动机汉语部件名称，同学回答英文名称） 用英语说明内燃机分类方式和类别 What are four strokes in a four-stroke-cycle engine?,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,2.4 Pistons, Connecting Rods and Crankshaft 2.5 Valve System,1.掌握曲柄连杆机构主要组成、零件英文名称； 2.了解VVT系统的主要功能,1.重点为记忆曲柄连杆机构主要组成、零件英文专业术语 2.难点需要记忆的生词偏多 3.汉译准确表达也是难点,Chapter 2 Internal Combustion Engine 2.4 Pistons, Connecting Rods and Crankshaft,2.4.1 New Words and Phrases,2.4.1 Piston and connecting rod The piston must move down through the cylinder to produce a vacuum to draw a fuel charge into the cylinder. It then travels up in the cylinder and compresses the mixture. When the mixture is fired, the pressure of the expanding gas is transmitted to the top of the piston. This drives the piston back down through the cylinder with great force, transmitting the energy of the expanding gas to the crankshaft. The piston then travels up through the cylinder and exhausts the burned fuel charge. Pistons are usually made of aluminum. Often, aluminum pistons are tin-plated to allow proper break-in when the engine is started. Aluminum pistons can be forged, but they are more commonly cast. Cast iron is a good material for pistons used in a slow-speed engine. It has excellent wear characteristics and will provide good performance.,Chapter 2 Internal Combustion Engine 2.4 Pistons, Connecting Rods and Crankshaft,2.4.2 Text,Fig.2-5 Pistons, connecting rods and crankshaft,As the name implies, connecting rods are used to connect pistons to the crankshaft (Fig.2-5). The upper end of the rod has a hole through it for the piston pin. The bottom of the large end of the connecting rod (Fig.2-6) must be removed so the rod can be installed on the crankshaft journal. The section that is removed is called the connecting rod cap. Connecting rods are normally made of alloy steel. They are drop-forged to shape and then machined.,Fig.2-6 Connecting rod,Chapter 2 Internal Combustion Engine 2.4 Pistons, Connecting Rods and Crankshaft,2.4.2 Crankshaft The engine crankshaft (Fig.2-7) provides a constant turning force to the wheels. It has throws to which connecting rods are attached, and its function is to change the reciprocating motion of the piston to a rotary motion to drive the wheels. Crankshafts are made of alloy steel or cast iron. The crankshaft is held in position by a series of main bearings. The maximum number of main bearings for a crankshaft is one more than the number of cylinders. It may have fewer main bearings than cylinders.,Chapter 2 Internal Combustion Engine 2.4 Pistons, Connecting Rods and Crankshaft,Most engines use precision insert bearings that are constructed like the connecting rod bearings, but are somewhat larger. In addition to supporting the crankshaft, one of the main bearings must control the forward and backward movement.,Fig.2-7 Crankshaft,Chapter 2 Internal Combustion Engine 2.5 Valve System,2.5.1 New Words and Phrases,The camshaft must turn at one-half crankshaft speed. The camshaft is linked with crankshaft by one of three ways: belt drive, chain drive and gear drive. The main components of the valve system are: Camshaft. It is used to open and close the valves. Generally only one camshaft is used in most engines. Newer engines are increasingly equipped with two or more camshafts (Figure 2-8). Valves. Each engine cylinder ordinarily has two valves. However, modern engines often use four valves per cylinder (two intake valves and two exhaust valves). In order to prevent burning, the valve must give off heat to the valve seat and to the valve guide. The valve must make good contact with the seat and must run with minimum clearance in the guide.,Chapter 2 Internal Combustion Engine 2.5 Valve System,2.5.2 Text,Valve lifters. Mechanical valve lifters were used in older engines. Most valve trains that contain mechanical lifters have some provision for adjusting clearance. Hydraulic valve lifters perform the same job as mechanical lifters. However, hydraulic lifters are self-adjusting, operate with no lifter-to-rocker arm clearance, and uses engine oil under pressure to operate. Hydraulic lifters are quiet in operation.,Chapter 2 Internal Combustion Engine 2.5 Valve System,Fig.2-8 Dual overhead camshaft（DOHC）,补充： Three types of camshaft drive,凸轮轴三种传动方式： Belt drive 带传动 Gear drive 齿轮传动 Chain drive 链传动,variable valve timing system eliminates the compromise of conventional valve timing with the introduction of VVT. By continuously varying intake valve timing (up to 60 crank angle degrees), Toyota optimizes low- to mid-speed torque, improves fuel economy and lowers emissions without having a negative impact on idle. In essence, the system controls valve overlap, which means it can eliminate it completely for a glass smooth idle, or maximize it to boost volumetric efficiency and reduce pumping lossesthis translates into power, economy and cleaner running at all engine speeds.,补充： Continuously Variable Valve Timing （CVVT）,The heart of the system is the intake cam pulley, which consists of an inner and outer section. The inner portion is fixed to the camshaft and nests inside the belt-driven outer pulley via helical spline gears. An electronically controlled hydraulic piston moves the pulley halves relative to one another