汽车外文Engine Lubricating System

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Engine  Lubricating  System

There are a great many moving metal parts in the engine . These parts must be protected by lubricating oil so that there will be protected by lubricating oil so that there will be no actual metal-to-metal contact . The moving parts , in effect , float on films of oil .
Two types of lubricating systems have been used on four-cycle automotive engines , splash and combination splash and pressure feed .
In the splash lubricating system , oil is splashed up from the oil pan or oil trays in the lower part of the crankcase .The oil is thrown upward so droplets or fine mist and provides adequate lubrication to valve mechanisms , piston pins , cylinder walls , and piston rings .
In the splash lubricating system , oil is splashed up from the oil pan or oil trays in the lower part of the crankcase . The oil is thrown upward as droplets or fine mist and provides adequate lubrication to valve mechanisms , piston pins , cylinder walls , and piston rings .
In the combination splash and pressure feed lubricating system , an oil pump takes oil from the oil from the oil pan and forces it through holes drilled in the engine block and crankshaft .
This oil thereby reaches the various bearings that support rotating shafts and the different moving parts in the engine . It covers the surfaces of the moving parts to prevent metal-to-metal contact and undue wear of the parts .
In this system , cylinder walls are lubricated by splashing oil thrown off from the connecting –rod bearing .
The lubricating oil circulating through the engine to all moving parts requiring lubrication performs other jobs .
(1) Lubricate moving parts to minimize wear .
(2) Lubricate moving parts to minimize power loss from friction
(3) Remove heat from engine parts by acting as a cooling agent .
(4) Absorb shocks between bearings and other engine parts , thus reducing engine noise and extending engine life .
(5)   Form a good seal between piston rings and cylinder walls .
(6)   Act as a cleaning agent , washing the working surfaces free of chemical deposits , dust and dirt to protect them from corrosion .
A satisfactory engine lubricating oil must have certain characteristics , or properties . It must have proper viscosity (body and fluidity ) and must resist oxidation , carbon formation , corrosion , rust , extreme pressures , and foaming . Also , it must act as a good cleaning agent , must pour at low temperatures , and must have good viscosity at extremes of high and low temperature .
Any mineral oil , by itself , does not have all these properties . Lubricating-oil manufacturers therefore put a number of additives into the oil during the manufacturing process .A oil for severe service may have many additives , as follows :
(1)   usually a viscosity-index improver ;
(2)   pour-point depressants;
(3)   oxidation inhibitors ;
(4)   corrosion inhibitors ;
(5)   rust inhibitors ;
(6)   foam inhibitors ;
(7)   detergent-dispersants ;
(8)   extreme-pressure agents.           

Valves and Valves Train
Valves and Valve Train
There are two openings , or ports , in the enclosed end of the cylinder . One of the ports permits the mixture of air and gasoline vapor to enter the cylinder . The other port permits the burned gases , after combustion , to exhaust , or escape , from the cylinder . The two pores have valves assembled into them . These valves close off one or the other port , or both ports , during the various stages of engine operation . That is to say , each cylinder has two valves , an intake valve and exhaust valve . The cam lobes on the camshaft are so related to the crankshaft crankpins through the gears or sprockets and chain as to cause the valves to open and close with the correct relationship to the piston strokes .
The valves are nothing more than accurately machined metal plugs (on long stems ) that close the openings when they are seated ( have moved up into the openings ) . When the valve closes , it moves up so that the outer edge rests on the seat . In this position , the valve port is closed so that air or gas cannot escape from the cylinder .
A spring on the valve stem tends to hold the valve on its seat ( closed ) . The lower end of the spring rests against the cylinder head . The upper end rests against a flat washer , or spring retainer which is attached to the valve stem by a retainer lock ( also called a keeper ) . The spring is under compression , which means that it tries to expand and therefore spring-loads the valve in the closed position .
A valve-opening mechanism opens the valve , or lifts it off its seat , at certain times . On most engines , this mechanism , called the valve train , includes a cam on the camshaft , a valve lifter , a push rod ,and a rocker arm . As the camshaft turns , the cam lobe comes around under the value lifter . This raises the lifter , which in turn pushes upward on the push rod . The push rod , as it is lifted , causes the end of the rocker arm to move up . The rocker arm pivots around its supporting shaft so that the valve end of the rocker arm is forced downward . This downward movement forces the valve to move downward off its seat so that it opens . After the cam lobe moves out from under the valve lifter , the valve spring forces the valve up onto its seat again .
In the other kind of valve mechanism for an engine , the valves are located in the cylinder block instead of the head . With this arrangement , the camshaft is directly below the valve lifter , and no push rods or rocker arms are necessary . Although the valve-in-block arrangement is a simple design . Most automotive engines are the valve-in-head type . The valve-in-head engine has certain advantages .

Cam and Camshaft
A cam is a device that can change rotary motion into linear , or straight-line , motion . The cam has a high spot , or lobe ; a follower riding on the cam will move away from or toward the camshaft as the cam rotates . In the engine , cams on the camshaft cause the intake and exhaust valves to open . There is s cam on the camshaft for each valve , or two cams per cylinder . The camshaft is driven by gears , or by a chain , from the crankshaft . It turns at one-half crankshaft speed . In the four –cycle engine , every two revolutions of the crankshaft produce one revolution of the camshaft and one opening and closing . The cam lobes are so positioned on the camshaft as to cause the valves to open and close in the cylinders at the proper time with respect to the actions taking place in the cylinders .
In addition , the camshaft has an eccentric to operate the fuel pump and a gear to drive the ignition distributor and oil pump .

Piston Connecting Rod
Piston
The piston is essentially a cylindrical plug that moves up and down in the engine cylinder . it is equipped with piston rings to provide a good seal between the cylinder wall and piston . The piston absorbs heat from the gas , and this heat must be carried away if the metal temperature is to be held within safe limits . The constant reversal of the piston travel sets up inertia forces , which increase both with the weight of the piston and with its speed . For this reason , designers try to keep piston weight low , particularly in high-speed engines . As lower hood lines and over square engines became popular , the semi-slipper and full-slipper pistons came into use . On these pistons the number piston rings was reduced to three , two compression and one oil-control . One reason for the slipper piston is that , on the short-stroke , over square engine , the piston skirt had to be cut away to make room for the counterweights on the crankshaft . Also , the slipper piston , being shorter and having part of its skirt cut away , is lighter .        This reduces the inertia load on the engine bearings and , in addition , makes for a more responsive engine . The lighter the piston , the less the bearing load and the longer the bearings will last . Another way to lighten the piston is to make it lf light metal . The ideal piston material would be light and strong , conduct heat well , expand only slight when heated , resist wear ,and be low in cost .Thus , most automotive-engine pistons today are made of aluminum , which is less than half as heavy as iron . Iron pistons were common in the earlier engines . Aluminum expands more rapidly than iron with increasing temperature , however , and since the cylinder block is lf iron , special provisions must be made to maintain proper piston clearance at operating temperatures. To take care of it , the crown is machined on slight taper , the diameter being greatest where the crown meets the skirt and becoming less toward the top .

Piston Rings
A good seal must be maintained between the piston and cylinder wall to prevent blow-by . “ blow-by ” is the name that describes the escape of burned gases from the combustion chamber , past the piston , and into the crankcase . In other words , these gases “blow by ” the piston .It is not practical to fit the piston to the cylinder closely to prevent blow-by . Thus , piston rings must be used to provide the necessary seal . The rings are installed in grooves in the piston . Actually , there are two types of rings , compression rings and oil-control rings , The compression rings seal in the air-fuel mixture as it is compressed and also the combustion pressures as the mixture burns. The oil-control rings scrape off excessive oil from the cylinder wall and return it to the oil pan.
The rings have joints (they are split ) so that they can be expanded and slipped over the piston head and into the recessed grooves cut in the piston . Rings for automotive engines usually have butt joints , but in some heavy –duty engines , the joints may be angled ,lapped , or of the sealed type .
The rings are somewhat larger in diameter than they will be when en the cylinder . Then ,when they are installed , they are compressed so that the joints are nearly closed . Compressing the rings gives them an initial tension ; they press tightly against the cylinder wall .

Connecting Rod
The connecting rod is attached at one end to a crankpin on the crankshaft and at the other end to a piston , through a piston pin or wrist pin . The connecting rod must be very strong and rigid and also as light as possible . The connecting rod carries the power thrusts from the pioton to the crankpin . At the shame time , the rod is in eccentric motion . To minimize vibration and bearing loads , the rod must be light in weight . To maintain good engine balance , connecting rods and caps are individually matched to each other and usually carry identifying numbers so they will not be mixed if the engine is disassembled for service . They must mot be mixed during any service job , since this could result in poor bearing fit and bearing failure .

Crankshaft  Flywheel
Crankshaft
The crankshaft is a one-piece casting or forging of heat-treated alloy steel of considerable mechanical strength . The crankshaft must be strong enough to take the down ward thrusts of the pistons during the power strokes without excessive distortion . In addition , the crankshaft must be carefully balanced to eliminate undue vibration resulting from the weight of the offset cranks . To provide balance , crankshafts have counterweights opposite the cranks . Crankshafts have drilled oil passages through which oil can flow from the main to the connecting-rod bearings .
The front end of the crankshaft carries three devices , the gear or sprocket that drives the camshaft , the vibration damper , and the fan belt pulley . The camshaft , the vibration damper , and the fan belt pulley . The pulley drives the engine fan , water pump ,and generator with a V belt .

Flywheel
The flow of power from the engine cylinders is not smooth .Although the power impulses cylinders is not smooth . Although the power impulses overlap ( on six-and eight-cylinder engines ) , there are times when more power is being delivered than at other times . This tends to make the crankshaft speed up and then slow down . However , the flywheel combats the tendency . The flywheel is a comparatively heavy wheel bolted to the tear end of the crankshaft . The inertia of the flywheel tends to keep it turning at constant speed . Thus , the flywheel absorbs energy as the crankshaft tries to slow down . In effect , the flywheel absorbs power from the engine during the power stroke( or speedup time ) and then gives it back to the engine during the other three strokes ( or slowdown time ) of the cycle .

漫步云端

很实用的一篇汽车发动机方面的英文资料啊   就是没人顶 啊  顶一个

nwndsr

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tianhong0742

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chiyomei

很8错  不过要是有个中文翻译 就更完美了

zwz0517

我要引用这篇文章，请问原文的作者和出处是什么

为你依旧

有没有文章出出啊，作者、、