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1、General comments of automobile engine Engine is the source of automotive.so far, automotive engines are all powered by heat except for a few of automotives drived by electricity.modern automotive engines are called internal combustion engines because fuel burns inside the engine .The engine conver

2、ts the burning fuel’s thermal energy to mechanical energy. By Cooling Systems Liquid-cooled engines and air-cooled engines are being used .Liquid-cooled engines are the most common in the diesel industry . By Fuel System Gasoline diesel and propane fuel systems are currently used in a wide vari

3、ety of engines . By Ignition Method Gas engines use the spark (electrical)ignition diesel engines use the heat fro BDC to TDC ;it varies with cylinder bore size ,length of piston stroke ,and numb system injection .The calory of diesel engine come from the fuel emblazed by the compressed air.The di

4、esel engine’compression ration is much bigger than the gas engine.Its sufficient calory is from the fuel burned by the pressed air. By valve Arrangement Four types of valve arrangements have been used in gasoline and diesel engines .Of the four types (L, T ,F ,and I heads ),the I head is commonly

5、 used on diesel engines . By Cylinder Arrangement Engine block configuration or cylinder arrangement depends on cylinder block design .Cylinders may be arranged in a straight line one behind the other .The most common in-line designs are the four-and six-cylinder engines .The V type of cylinder a

6、rrangement uses two banks of cylinders arranged in a 60°to 90°V design .The most common examples are those with two banks of three to eight cylinders each .The opposed engine uses two banks of cylinders opposite each other with the crankshaft in between . Engine’classification According to the dif

7、ferences of the piston’movement, the piston intenal combusition engine will be classified reciprocating intenal combusition engine and rotary piston intenal combusition engine.Then we will introduce working principle diagram of reciprocating internal combustion engine. Except for the wankel rotary

8、,engine ,all production automotive engines are the reciprocating ,or piston ,design . Reciprocating means “up and down “ or “back and forth “ .It is this up-and-down action of a piston in a cylinder that gives the reciprocating engine its name .Almost all engines of this type are built upon a cylind

9、er block ,or engine block .The block is an iron or aluminum casting that contains the engine cylinders .The top of the block is covered with the cylinder head ,which forms the combustion chambers .The bottom of the block is covered with an oil pan ,or oil sump .A major exception to this type of engi

10、ne on struction is the air-cooled Volkwagen engine .It is representative of the horizontally opposed air-cooled engines used by Porsche ,Chevrolet (Corvair ) ,and some other automobile manufacturers in years past . Power is produced by the inline motion of a piston in a cylinder .However ,this line

11、ar motion must be changed to rotating motion to turn the wheels of a car or truck .The piston is attached to the top of a connecting rod by a pin ,,called a piston pin or wristpin.The connecting rod transmits the up-and –down motion of the piston to the crankshaft ,which changes it to rotating motio

12、n .The connecting rod is mounted on the crankshaft with large bearings called rod bearings .Similar bearings , called main bearings ,are used to mount the crankshaft in the block. The crankshaft changes the reciprocating motion of the pistons to rotating motion . The combustible mixture of gasolin

13、e and air enters the cylinders through valves .Automotive engines use poppet valves .The valves can be in the cylinder head or in the block .The opening and closing of the valves is controlled by a camshaft .Lobes on the camshaft push the valves open as the camshaft rotates .A spring closes each val

14、ve when the lobe is not holding it open .The most common arrangements of engine cylinders and valves are discussed later .The basic single-cylinder engine consists of a cylinder (engine block ),a movable piston inside this cylinder ,a connecting rod attached at the top end to the piston and at the b

15、ottom to the offset portion of a crankshaft ,a camshaft to operate the two valves (intake and exhaust ), and a cylinder head .A flywheel is attached to one end of the crankshaft .The other end of the crankshaft has a gear to drive the camshaft gear .The camshaft gear is twice as large as the cranksh

16、aft gear .This drives the camshaft at half the speed of the crankshaft on four-stroke-cycle engines ,the crankshaft and camshaft run at the same speed . Energy Conversion The internal combustion diesel engine is a device used to convert the chemical energy of the fuel into heat energy and then con

17、vert this heat energy into usable mechanical energy .This is achieved by combining the appropriate amounts of air and fuel and burning them in an enclosed cylinder at a controlled rate .A movable piston in the cylinder is forced down by the expanding gases of combustion . The movable piston in cyli

18、nder is connected to the top of a connecting rod .The bottom of the connected rod is attached to the offset portion is transferred to the crankshaft ,As the piston is forced down ,this offset portion of a crankshaft ,to rotate .The reciprocating (back and forth or up and down )movement of the piston

19、 is converted to rotary (turning )motion of the crankshaft ,which supplies the power to drive the vehicle . In general an average air-fuel ratio for good combustion is about 15parts of air to 1 part of fuel by weight .However ,the diesel engine always takes in a full charge of air (since there is n

20、o throttle plate in most systems ) ,but only a small part of this air is used at low or idle engine speeds .Air consists of about 20 percent oxygen while the remaining 80 percent is mostly nitrogen .This means that ,for every gallon of fuel burned ,the oxygen in 9,000 to 10,000gallons of air is requ

21、ired . Four-Stroke Cycle Gasoline by itself will not burn ,it must be mixed with oxygen (air ) .This burning is called combustion and is a way of releasing the energy stored in the air-fuel mixture .To do any useful work in an engine ,the air-fuel mixture must be compressed and burned in a sealed

22、chamber .Here the combustion energy can work on the movable piston to produce mechanical energy .The combustion chamber must be sealed as tightly as possible for efficient engine operation .Any leakage from the combustion chamber allows part of the combustion energy to dissipate without adding to th

23、e mechanical energy developed by the piston movement . The 4-stroke engine is also called the Otto cycle engine ,in honor of the German engineer ,Dr. Nikolaus Otto ,who first applied the principle in 1876 .In the 4-stroke engine ,four strokes of the piston in the cylinder are required to complete o

24、ne full operating cycle :two strokes up and two strokes down .Each stroke is named after the action it performs-intake ,compression ,power ,and exhaust : 1、Intake Stroke As the piston moves down ,the vaporized ,mixture of fuel ;and air enters the cylinder past the open intake valve . 2、Compressio

25、n Stroke The piston returns up ,the intake valve closes ,the mixture is compressed within the combustion chamber ,and ignited by a spark . 3、Power Stroke The expanding gases of combustion force the piston down in the cylinder .The exhaust valve opens near the bottom of the stroke . 4、Exhaust

26、 Stroke The piston moves back up with the exhaust valve open ,and the burned gases are pushed out to prepare for the next intake stroke .The intake valve usually opens just before the top of the exhaust stroke . This 4-stroke cycle is continuously repeated in every cylinder as long as the engine r

27、emains running . Two-Stroke-Cycle The two-stroke-cycle diesel engine completes all four events:intake,compression, power ,and exhaust. in one revolution of the crankshaft or two strokes of the piston . A series of ports or openings is arranged around the cylinder in such a position that the ports

28、 are open when the piston is at the bottom of its stroke .A blower forces air into the cylinder through the open ports .expelling all remaining exhaust gases past the open exhaust valves and filling the cylinder with air .This is called scavenging . As the piston moves up ,the exhaust valves close

29、and the piston covers the ports .The air trapped above the piston is compressed ton covers the ports .The air trapped above the piston is compressed since the exhaust valve is closed .Just before the piston reaches top dead center ,the required amount of fuel is injected into the cylinder .The heat

30、generated by compressing the air ignites the fuel almost immediately .Combustion continues until the fuel injected has been burned .The pressure resulting from combustion forces the piston downward on the power stroke .When the piston is approximately falfway down ,the exhaust valves are opened ,all

31、owing the exhaust gases to escape .Further downward movement uncovers the inlet ports ,causing fresh air to enter the cylinder and expel the exhaust gases .The entire procedure is then repeated ,as the engine continues to run . The differences of the two intenal combustion engine It could be assum

32、ed that a two-cycle engine with the same number of cylinders ,the same displacement ,compression ratio ,and speed as a four-cycle engine would have twice the power since it has twice as many power .However ,this is not the case ,since both the power and compression strokes are shortened to allow sca

33、venging to take place .Thetwo-cycle engine also requires a blower ,which takes engine power to drive . About 160 degrees out of each 360 degrees of crankshaft rotation are required for exhaust gas expulsion and fresh air intake (scavenging )in a two-cycle engine .About 415 degrees of each 720 degre

34、es of crankshaft rotation in a four-cycle engine are required for intake and exhaust .These figures indicate that about 44.5% of crank rotation is used for the power producing events in the two-cycle engine ,while about 59% of crank rotation is used for these purposes in the four-cycle engine .Frict

35、ion losses are consequently greater in the four-cycle engine .Heat losses ,however ,are greater in the two-cycle engine though both the exhaust and the cooling systems .In spite of these differences ,both engine types enjoy prominent use worldwide . Engine construction Cylinder Block: The cylind

36、er block is cast in one piece. Usually, this is the largest and the most complicated single piece of metal in the automobile. The cylinder block is a complicated casting made of gray iron (cast iron ) or aluminum. It contains the cylinders and the water jackets that surround them. To make the cylin

37、der block, a sand form called a mold is made. Then molten metal is poured into the mold. When the metal has cooled the sand mold is broken up and removed. This leaves the tough cylinder-block casting. The casting. The casting is then cleaned and machined to make the finished block. Cylinder blocks

38、 for diesel engines are very similar to those for spark-ignition engines. The basic difference is that the diesel-engine cylinder block is heavier and stronger. This is because of the higher pressures developed in the diesel-engine cylinders. Several engines have aluminum cylinder blocks. Aluminum

39、is relatively light metal, weighing much less than cast iron. also ,aluminum conducts heat more rapidly than cast soft to use as cylinder wall material. It wears too rapidly. Therefore, aluminum cylinder blocks must have cast-iron cylinder liners or be cast from an aluminum alloy that has silicon pa

40、rticles in it. Some manufactures make an aluminum cylinder block that does not have cylinder liners, or sleeves. Instead ,the aluminum is loaded with silicon particles. Silicon is a very hard material. After the cylinder block is cast, the cylinders are honed. Then they are treated with a chemical

41、 that etches eats away, the surface aluminum. This leaves only the silicon particles exposed. the piston and rings slide on the silicon with minimum wear. Piston: The piston converts the potential energy of the fuel into the kinetic energy that turns the crankshaft. The piston is a cyl

42、indrical shaped hollow part that moves up and down inside the engine’s cylinder. It has grooves around its perimeter near the top where the ring are placed. The piston fits snugly in the cylinder. It has grooves around its perimeter near the top where the rings are placed. The piston fits snugly in

43、the cylinder. The pistons ate used to ensure a snug “air tight〞 fit. The piston in your engine’s cylinder are similar to your legs when you ride a bicycle. Think of your legs as pistons; they go up and down on the pedals, providing power. Pedals are like the connecting rods; they are “attached〞 to

44、your legs. The pedals are attached to the bicycle crank which is like the crank shaft, because it turns the wheels. To reverse this, the pistons (legs) are attached to the connecting rods ( pedals ) which are attached to the crankshaft (the bicycle rank). The power from the combustion in the cylin

45、ders powers the from the combustion rods to turn the crankshaft. Connecting rod： The connecting rod shown in is made of forged high strength steel. It transmits force and motion from the piston to the crank pin on the crankshaft. A steel piston pin, or “wrist pin〞, connects the small end of the co

46、nnecting rod. Some rods have a lock bolt in the small end. As the piston moves up and down in the cylinder, the pin rocks back and forth in the hole, or bore, in the piston. The big end of the connecting rod is attached to a crank pin by a rod bearing cap. Connecting rod and rod-bearing caps are as

47、sembled during manufacture. Then the hold for the bearing is bored with the cap in place. This is called line-bring. It make each rod and its cap a matched set. Usually, the same number is stamped on the rod and cap. This prevents the caps setting mixed during engine service. If the caps are mixed

48、, the bearing bore will not be round. An engine assembled with the rod bearing caps switched will probably lock the crankshaft. If the crankshaft turns, the bearing will probably have improper clearance and early bearing failure will result. Another reason for keeping the cap and rod matched is to

49、prevent engine unbalance and unwanted vibration. All connecting rods in an engine must be as light as possible. But they must all weigh the same. If one rod is heavier than the other, the engine will vibrate. This could damage the engine. Crankshaft： The crankshaft then main rotating member, or sh

50、aft, in the engine. It has crank-pins, to which the connecting rod from the pistons are attached. During the power strokes, the connecting rods force the crank-pins and therefore the crankshaft to rotate. The reciprocating motion of the pistons is changed to rotary motion as the crankshaft spins. Th

51、is rotary motion is transmitted through the power train to the car wheels. The crankshaft is a strong, one-piece casting, or forging, or heat-treated alloy steel. It must be strong to take the downward force of power strokes without excessive bending. It must be balanced so the engine will run with

52、out excessive vibration. Engine Displacement The frequently used engine specifications are engine displacement and compression ratio .Displacement and compression ration are related to each other ,as we will learn in the following paragraphs . By Displacement Engine displacement is the amoun

53、t of air displaced by the piston when it moves fro .The electrical ignition system causes a spark across the spark plug electrodes in the cylinder at the end of the compression stroke ,which ignites the vaporized fuel and air mixture .m compressing the air to ignite the fuel when it is injected into

54、 the cylinder at the end of the compression ratios are much higher than gasoline engine compression ratios ,sufficient heat is generated by compressing the air to ignite the fuer of cylinders .engines are classified as low ,medium ,high ,and super high speed . Commonly used to indicate engine size

55、,this specification is really a measurement of cylinder volume ..The number of cylinders is a factor in determining displacement ,but the arrangement of the cylinders or valves is not .Engine displacement is calculated by multiplying the number of cylinders in the engine by the total engine displace

56、ment is the volume displaced by all the pistons . The displacement of one cylinder is the space through which the piston’s top surface moves as it travels from the bottom of its stroke (bottom dead center )to the top of its stroke (top dead center ).It is the volume displaced by the cylinder by one

57、 piston stroke .Piston displacement can be calculated as follows : 1.Divide the bore (cylinder Diameter )by two.This gives you the radius of the bore . 2.Square the radius (multiply it by itself ). 3.Multiply the square of the radius by 3.1416 (pi or)to find the area of the cylinder cross section

58、 . 4.Multiply the area of the cylinder cross section by the length of the stroke . You now know the piston displacement for one cylinder .Multiply this by the number of cylinders to determine the total engine displaceme`nt .The formula for the complete procedure reads : **stroke*No.of cylinde

59、rs =displacement Compression Ratio This specification compares the total cylinder volume to the volume of only the combustion chamber.Total cylinder volume may seem to be the same as piston displacement ,but it is not .Total cylinder volume .The combustion chamber volume with the piston at top de

60、ad center is often called the clearance volume . Compression ratio is the total volume of a cylinder divided by its clearance volume .If the clearance volume is one-eighth of the total cylinder volume ,the compression ratio is 8 (8to1).The formula is as follows : =Compression ratio. In theory ,th

61、e higher the compression ratio ,the greater the efficiency of the engine ,and the more power an engine will develop from a given quantity of fuel .The reason for this is that combustion takes place faster because the fuel molecules are more tightly packed and the flame of combustion travels more rap

62、idly . But there are practical limits to how high a compression ratio can be .Because of the unavailability of high octane fuel ,most gasolineburning engines are restricted to a compression ratio no greater than 11.5 to 1.Ratios this high ,however ,create high combustion chamber temperatures .This

63、in turn creates oxides of nitrogen (NOx) ,a primary air pollutant .In the early 1970s ,compression ratios were lowered to around 8 to permit the use of lower octane low-lead or unleaded fuel ,and to reduce NOx formation .Advances in electronic engine control in the 1980s have allowed engineers to ra

64、ise compression ratios to the 9and 10 to 1 range for optimum performance and economy 發(fā)動機概述 發(fā)動機是汽車的動力源。迄今為止除為數不多的電動汽車外，汽車發(fā)動機都是熱能動力裝置。現(xiàn)代汽車發(fā)動機因為燃料發(fā)動機內部燃燒而被稱為內燃機。發(fā)動機將燃料燃燒產生的熱能變?yōu)闄C械能。 冷卻系統(tǒng)：水冷發(fā)動機和風冷發(fā)動機被應用，在柴油引擎制造業(yè)中，水冷發(fā)動機應用最廣泛。 燃料系統(tǒng)：汽油，柴油，丙烷燃料系統(tǒng)在各式各樣的發(fā)動機中廣泛應用。 點火方式：汽油機采用電子點火系統(tǒng)；電子點火系統(tǒng)在壓縮行程終了時通過氣缸內的火花塞高

65、壓電板產生火花，點燃霧化的燃油空氣混合物。柴油機的能量來源于當燃料被注入氣缸時壓縮空氣點燃燃料。柴油機的壓縮比遠遠大于汽油機的壓縮比。在注入燃料時靠壓縮空氣點燃燃料能產生足夠的熱量。 閥門裝置：已經有四種閥門配備被應用于汽油機和柴油機上。在這四種類型中〔I、T、F和I頭型〕，I型在柴油機中最常用。 氣缸排列方式：發(fā)動機的外形結構或氣缸排列方式取決于氣缸的設計，氣缸一個接一個地被排成直線，直線式最常用于四缸或六缸發(fā)動機；V型的氣缸排列方式是兩排氣缸成60°到90°角度。最常用的機型每排氣缸有三到八個。對置式發(fā)動機是指兩列氣缸水平相對曲軸位于二者之間 發(fā)動機的分類 按活塞運動方式的不同，活

66、塞式內燃機可分為往復活塞式和旋轉活塞式兩種，前者在現(xiàn)代車上被廣泛的運用，下面就以往復活塞式內燃機為例，介紹一下發(fā)動機的工作原理。 除了旋轉活塞式發(fā)動，所有生產的汽車發(fā)動機都是往復式的。往復的意思就是“上下運動〞或者“前后運動〞。正是由于活塞在氣缸內做上下運動而被稱為往復式發(fā)動機。幾乎所有的這種類型的發(fā)動機都是坐在氣缸上或發(fā)動機機體上的，機體是鑄有發(fā)動機氣缸的鐵或鋁的鑄造物。機體的上端被氣缸蓋住，形成燃燒室。機體的低部被油底殼或油箱覆蓋。對于這種類型的發(fā)動機在構造上有一個例外風冷的發(fā)動機，它是典型的水平對置式風冷發(fā)動機過去的幾年里被其他一些汽車廠商廣泛應用。 活塞在氣缸內的直線運動產生動力。然而，這種直線運動必須轉變成驅動轎車或卡車車輪轉動的旋轉運動?；钊灰粋€銷稱為活塞銷連接在連桿的頂端。連桿將活塞的上下運動傳遞給曲軸，曲軸將直線運動轉變?yōu)樾D運動。連桿由大軸承安裝在曲軸上。用類似的軸承稱為主軸承，將曲軸安裝在機體上。曲軸將活塞的往復運動轉變?yōu)樾D運動?？扇嫉钠秃涂諝饣旌衔锿ㄩy門進入氣缸。汽車發(fā)動機使用Poppet閥門。這種閥門可以安裝在機體或氣缸頭部。閥門的開啟與關閉被凸輪軸控