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一、一、 题目及专题题目及专题1、题目 车床主轴传动系统设计 2、专题 单主轴变速机构设计 二、二、 课题来源及选题依据课题来源及选题依据 课题来源为无锡某机械有限公司。通过毕业设计是为了培养学生开发和创新机械产品的能力，要求学生能够针对实际使用过程中存在的机床选择问题，综合所学的机械理论设计与方法、专用机床设计方法，在机床基础型系的基础上，设计一个简单的主传动变速系统，从而达到解决实际工程问题的能力。在设计传动件时，在满足产品工作要求的情况下，应尽可能多的采用标准件，提高其互换性要求，以减少产品的设计生产成本。三、三、 本设计（论文或其他）应达到的要求本设计（论文或其他）应达到的要求1、该部件工作时，能运转正常；2、拟定工作机构和驱动系统的运动方案，并进行多方案对比分析； 3、根据车床的加工要求，设计出机床主传动系统的原理及绘制主传动系 统的装配图；4、 对所设计的主传动系统进行必要的验算和推导；5、 绘制车床的主传动轴的零件图；6、 绘制车床主传动系转速图和变速传动系图；7、 编制设计说明书 1 份。四、 接受任务学生接受任务学生：I摘要摘要车床主要是为了进行车外圆、车端面和镗孔等项工作而设计的机床。车削很少在其他种类的机床上进行，而且任何一种其他机床都不能像车床那样方便地进行车削加工。由于车床还可以用来钻孔和铰孔，车床的多功能性可以使工件在一次安装中完成几种加工。因此，在生产中使用的各种车床比任何其他种类的机床都多。车床的基本部件有：床身、主轴箱组件、尾座组件、溜板组件、丝杠和光杠。主轴箱安装在内侧导轨的固定位置上，一般在床身的左端。它提供动力，并可使工件在各种速度下回转。它基本上由一个安装在精密轴承中的空心主轴和一系列变速齿轮(类似于卡车变速箱)所组成。通过变速齿轮，主轴可以在许多种转速下旋转。大多数车床有 812 种转速，一般按等比级数排列。而且在现代机床上只需扳动 24 个手柄，就能得到全部转速。一种正在不断增长的趋势是通过电气的或者机械的装置进行无级变速。由于机床的精度在很大程度上取决于主轴，因此，主轴的结构尺寸较大，通常安装在预紧后的重型圆锥滚子轴承或球轴承中。主轴中有一个贯穿全长的通孔，长棒料可以通过该孔送料。主轴孔的大小是车床的一个重要尺寸，因此当工件必须通过主轴孔供料时，它确定了能够加工的棒料毛坯的最大尺寸。 关键字关键字：车床；主轴箱组件；主轴；无级变速IIAbstractLathes are machine tools designed primarily to do turning, facing and boring, Very little turning is done on other types of machine tools, and none can do it with equal facility. Because lathes also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the work piece. Consequently, more lathes of various types are used in manufacturing than any other machine tool.The essential components of a lathe are the bed, headstock assembly, tailstock assembly, and the leads crew and feed rod.The headstock is mounted in a foxed position on the inner ways, usually at the left end of the bed. It provides a powered means of rotating the word at various speeds . Essentially, it consists of a hollow spindle, mounted in accurate bearings, and a set of transmission gears-similar to a truck transmissionthrough which the spindle can be rotated at a number of speeds. Most lathes provide from 8 to 18 speeds, usually in a geometric ratio, and on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives.Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings, usually preloaded tapered roller or ball types. The spindle has a hole extending through its length, through which long bar stock can be fed. The size of maximum size of bar stock that can be machined when the material must be fed through spindle. Key words: Lathes; headstock assembly; variable speed;目录目录摘要 .IIIABSTRACT .IV1 绪论 .11.1 毕业设计的目的 .11.2 机床主传动系统设计要求 .12 车床参数的拟定 .22.1 车床主参数和基本参数 .22.1.1 极限切削速度 Vmax、Vmin 的确定 .22.1.2 主轴的极限转速的确定 .22.1.3 主轴转速级数和公比的确定 .32.1.4 主电机的选择 .33 主传动系统设计 .63.1 传动结构式、结构网、转速图的确定 .63.1.1 传动形式的确定 .63.1.2 传动组及各传动组中传动副的数目 .63.1.3 传动系统扩大顺序的安排.73.1.4 绘制转速图.73.1.5 转速图的拟定 .73.1.6 分配降速比 .83.2 齿轮齿数的确定及传动系统图的绘制.103.2.1 带轮确定 .103.2.2 齿轮齿数的确定的要求 .144 强度计算和结构草图设计 .174.1 确定计算转速.174.1.1 各轴、齿轮的计算转速.174.2 轴的估算和验算 .194.2.1 主轴的设计与计算.194.2.2 传动轴直径的估算 .224.3 齿轮模数的估算和计算.244.3.1 齿轮模数的估算 .244.3.2 齿轮模数的验算.26I4.4 轴承的选择与校核.314.4.1 一般传动轴上的轴承选择 .314.4.2 主轴轴承的类型 .314.4.3 轴承间隙调整和预紧.334.4.4 轴承的较核 .344.4.5 轴承的密封和润滑.364.5 片式摩擦离合器的选择与验算.364.5.1 按扭矩选择 .364.5.2 片式离合器的计算 .364.5.3 计算摩擦面的对数 Z.375 主轴箱的箱体设计 .396 结论与展望 .406.1 结论.406.2 展望.40致 谢 .41参考文献 .42 01 绪论绪论1.1 毕业设计的目的毕业设计的目的 通过机床主运动机械变速传动系统的结构设计，在拟定传动和变速的结构方案过程中，得到设计构思、分析方案、结构工艺性、机械制图、零件计算、编写技术要求文件和查阅级数资料等方面的综合训练，树立正确的设计思想，掌握机床设计的过程和方法，使原有的知识有了进一步的加深。（1） 课程设计属于机械系统设计课程的延续，通过设计实践，进一步学习掌握机械系统的一般方法。（2） 培养综合运用机械制图、机械设计基础、精度设计、金属工艺学、材料热处理及结构工艺等相关知识，进行工程设计的能力。（3） 培养使用手册、图册、有关资料及设计标准规范的能力。（4） 提高技术总结及编制技术文件的能力。（5） 为进入工厂打下基础。1.2 机床主传动系统设计要求机床主传动系统设计要求（1） 、主轴具有一定的转速和足够的转速范围、转速级别，能够实现运动的开停、变速、换向和制动等，以满足机床的运动要求。（2） 、主电动机具有足够的功率，全部机构和元件具有足够的强度和刚度，以满足机床的传动要求。（3） 、主运动的有关机构，特别是主轴组件有足够的精度、抗振性、温升小和噪音小，传动效率高，以满足机床的工作性能要求。（4） 、操作灵活可靠，调整维修方便，润滑密封良好，以满足机床的使用要求。（5） 、结构紧凑简单、工艺性好、成本低、以满足经济要求。三、车床主要参数（规格尺寸）最大工件回转直径 D（mm） 400 刀架上最大回转直径 D1 200 主轴通孔直径d 50 主轴头号（JB2521-79） 6 最大工件长度 L 750-2000外文翻译1 SummarizeOutline uses a more compact design along with the engine and has in a big way, the engine produces the waste heat density also obviously increases along with it. Some essential regions, if around a row of tyre valve radiates the question to have first to consider, the cooling system even if appears the small breakdown also possibly to create the disaster in such region consequence. The engine cooling system radiation ability generally should satisfy when the engine full load radiation demand, because this time engine produces the quantity of heat is biggest. However, when partial loads, the current capacity which the cooling system can have the power loss, which the water pumping station provides the refrigerant current capacity surpasses needs. We hoped starts the starting time to be as far as possible short. Because engine time discharges pollutant more, the oil consumption is also big. The cooling system structure has a more tremendous influence to the engine cold starting time. 2 Characteristics of modern engine cooling systemModern engines series characteristic tradition cooling system function reliably protects the engine, but also should have the function which the improvement fuel economy and reduces discharges. Therefore, the modern cooling system must synthesize under the consideration the factor: Engine interior friction loss; Cooling system water pump power; Burning boundary condition, like combustion chamber temperature, complete density, complete temperature. The advanced cooling system uses systematized, the modular design method, the overall plan considered each influence factor, causes the cooling system both to guarantee the engine normal work, and enhances the engine efficiency and the reduction discharges. 2.1 The temperatures set point Temperatures hypotheses firing in bursts motive operating temperature limit value are decided by a row of tire valve the peripheral region maximum temperature. The most ideal situation is according to the metal temperature but is not the refrigerant temperature control cooling system, like this can protect the engine well. Because the cooling system hypothesis cooling temperature is by the full load time most is big is the foundation, therefore, engine and cooling system in partial loads time is at not too the perfect condition, when urban district travel and low speed travel, can have the high oil consumption and discharge. Supposes the fixed point through the change refrigerant temperature to be possible to improve the engine and the cooling system in partial loads time performance. According to a row of tyre valve the peripheral region temperature limit value, may elevate either reduce the refrigerant or the metal temperature supposes the fixed point. Elevates or reduced temperature all respectively has the characteristic, this is decided the goal which achieved to the hope. 2.2 Enhances the temperatureEnhances the temperature to suppose the fixed-point enhancement operating temperature to suppose the fixed point is one kind of comparison the method which welcome. Enhances the temperature to have many merits, it directly affects the engine loss and the cooling system effect as well as the engine discharging formation. Will enhance the operating temperature to enhance the engine Mac reduce the engine to rub wears, reduces the engine fuel oil consumption. The research indicated that, the engine operating temperature to rubs the loss to have the very tremendous influence. Discharges the temperature the refrigerant to enhance to 150 , causes the cylinder temperature to elevate to 195 , the oil consumption drops 4%-6%. Maintains the refrigerant temperature in 90-115 scope, causes the engine machine oil the maximum temperature is 140 , then oil consumption in partial loads time drops 10%. Enhances the operating temperature also obvious influence cooling system the potency. Enhances the refrigerant or the metal temperature can improve the engine and disperse the steam heat transfer transmission the effect, reduces the refrigerant the speed of flow, reduces the water pump the rated power, thus reduces the engine the power dissipation. In addition, may select the different method, further reduces the refrigerant the speed of flow.2.3 Reduce the temperatures set point Reduced temperatures suppose the fixed point to reduce the cooling system the operating temperature to be possible to enhance the engine charge efficiency, reduces the inlet temperature. This to the combustion process, the fuel oil efficiency and discharges advantageously. The reduced temperature supposes the fixed point to be allowed to save the engine movement cost, enhances the part service life. The research indicated, if the cylinder head temperature reduces to 50 , the ignition angle of advance may 3 A but not have the engine knock ahead of time, the charge efficiency enhances 2%, the engine operational factor improvement, is helpful to the optimized compression ratio and the parameter choice, obtains the better fuel oil efficiency and discharges the performance. 2.4 Precise cooling system Precise cooling systems precise cooling system mainly manifests in the cooling jacket structural design and in the refrigerant speed of flow design. In precise cooling system, hot essential area, if around a row of tyre valve, the refrigerant has an greater speed of flow, the heat transfer efficiency is high, the refrigerant gradient of temperature changes slightly. Such effect comes from to reduce these place refrigerant channels the lateral section, enhances the speed of flow, reduces the current capacity. The precise cooling system design key lies in the determination cooling jacket the size, the choice match cooling water pump, guaranteed the system the radiation ability can satisfy when the low speed big load essential region operating temperature demand. The engine refrigerant speed of flow range of variation is quite big, from time 1 m/s to maximum work rate time 5 m/s. Therefore should considered the cooling jacket and the cooling system whole that, mutually supplemented, display biggest potential. The research indicated that, uses the precise cooling system, in the engine entire work rotational speed scope, the refrigerant current capacity may drop 40%. Covers the cooling jacket to the air cylinder the precise design, may make the ordinary speed of flow to enhance from 1.4m/s to 4 m/s, greatly enhances the cylinder cover or cap thermal conductivity, cylinder cover or cap metal temperature drop to 60 . 2.5 Divergences types cooling systemDivergences types cooling system divergence type cooling system for other one kind of cooling system. In this kind of cooling system, the hine oil temperature, will cylinder cover or cap friendly cylinder body cools by respective return route, the cylinder cover or cap friendly cylinder body has the different temperature. The divergence -like cooling system has the unique superiority, may cause engine each part to suppose the fixed-point work at the most superior temperature. The cooling system overall efficiency achieves in a big way. Each cooling return route will suppose under the fixed point or the speed of flow in the different cooling temperature works, will create the ideal engine temperature distribution. The ideal engine hot active status is the cylinder head temperature lower but the air cylinder body temperature relative is higher. The cylinder head temperature is lower may enhance the charge efficiency, increases. The temperature is low also greatly may promote completely to burn, reduces CO, HC and the NOx formation, also enhances the output. The higher air cylinder body temperature can reduce the friction to lose, directly improves the fuel oil efficiency, indirectly reduces in the cylinder the peak value pressure and the temperature. The divergence type cooling system may cause the cylinder cover and the cylinder body temperature differs 100 . The cylinder temperature may reach as high as 150 , but the cylinder cover temperature may reduce 50 , reduces the cylinder body to rub loses, reduces the oil consumption. The higher cylinder body temperature causes the oil consumption to reduce 4%-6%, when partial loads HC reduces 20%-35%. When the damper all opens, the cylinder cover and the cylinder body temperature supposes the definite value to be possible to move to 50 and 90 , improves the fuel oil consumption, the power output from the whole and discharges. 2.6 Controllable cooling systemControllable engine cooling system tradition engine cooling system belongs to the passive form, the structure simple or the cost is low. The controllable cooling system may make up at present cooling system the insufficiency. Now the cooling system design standard solves time the full load radiation problem, thus partially shoulders time the oversized radiation ability will cause the engine power waste. This to the light vehicle said especially obvious, these vehicles majority time all under the partial loads go in the urban district, only uses the partial engine power, causes a cooling system higher loss. In order to solve the engine to get down the hot question in the peculiar circumstance, the present cooling system volume was bigger, causes the evaporation efficiency to reduce, has increased the cooling system power demand, lengthened the engine during warm machine-hour. The controllable engine cooling system generally includes the sensor, the execution and the electrically controlled module. The controllable cooling system can act according to the engine working condition adjustment cooling quantity, reduces the engine power loss. In the controllable cooling system, the execution for the cooling water pump and the thermostat, generally and the control valve is composed by the electrically operated water pump, may act according to requests to adjust the cooling quantity. Temperature sensor for a system part, but rapidly bequeaths the engine hot condition the controller. Controllable installment, if the electrically operated water pump, may suppose the temperature the fixed point from 90 to enhance to 110 , saves 2%-5% fuel oil, CO reduces 20%, HC reduces 10%. When steady state, the metal temperature ratio tradition cooling system is high 10 , the controllable cooling system has the quicker response ability, may cool the temperature to maintain is supposing the fixed point 2 the scope. From 110 drops to 100 only needs 2 s. The engine during warm machine-hour reduces 200s, the cooling system operating region draws close to the work limit region, can reduce the engine cooling temperature and the metal temperature undulation scope, reduces circulates the fatigue of metal which the hot load creates, lengthens the component life.3 ConclusionIn front of 3 conclusions introduced several kind of advanced cooling systems have the improvement cooling system performance the potential, can enhance the fuel oil efficiency and discharge the performance. The cooling system can control the nature is improves the cooling system the key, can the controlling expression to the engine structure protection essential parameter, like the metal temperature, the refrigerant temperature and the machine oil temperature and so on can control, guarantees the engine to work in the safety margin scope. The cooling system can make the rapid reaction to the different operating mode, the most earth saves the fuel, reduces discharges, but does not affect the engine overall performance. Looked from the design and the operational performance angle that, divergence type cooling and precise cooling unifies has the very good prospects for development, both can provide the ideal engine protection, and can enhance the fuel oil efficiency and discharge the nature. This kind of structure is advantageous to forming the engine ideal temperature distribution. Directly to a cylinder cover or cap row of tyre valve around the supplies refrigerant, reduced the cylinder head temperature change, causes the cylinder cover temperature distribution to be evener, also can maintains the machine oil and the cylinder body temperature at the design operating region, has a lower friction to damage the pollution withdrawal. cooling system function and maintenance maintenance method as follows: 1st, the cooling system function, is part of quantity of heats which absorbs the engine part carries off, guaranteed the diesel engine various components maintain in the normal temperature range. 2nd, the cooling water should be does not contain dissolves the Xie salt the soft water, like clean river water, rain water and so on. Do not use hard water and so on the well water, water seepage or sea water, guards against produces, causes the engine to radiate not good, question occurrence and so on air cylinder heat. 3rd, with the funnel when joins the cooling water the water tank, must prevent the water splashes to on the engine and the radiator, prevented on the radiator fin and the organism accumulates the dust, smears, affects the cooling effect.4th, if when the engine lacks the water causes the hyperpyrexia, cannot immediately add water, should cause the engine idling speed to revolve 10 15 minutes, after the uniform temperature slightly reduces, slowly does not join the cooling water in the engine situation. 5th, the winter, the water tank planted agent adds the hot water. After the start should surpass 40 degree-hour the slow revolution to the water temperature to be able to work. After the work had ended, must put the completely cooling water. 6th, must regularly eliminate in the water tank, must frequently scour the sludge to the forced-air cooling engine radiator fin, dirty is filthy. The radiator fin cannot damage, after if damages must promptly replace, in order to avoid influence radiation effect.4 LathesLathes are machine tools designed primarily to do turning, facing and boring, Very little turning is done on other types of machine tools, and none can do it with equal facility. Because lathes also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the work piece. Consequently, more lathes of various types are used in manufacturing than any other machine tool.The essential components of a lathe are the bed, headstock assembly, tailstock assembly, and the leads crew and feed rod.The bed is the backbone of a lathe. It usually is made of well normalized or aged gray or nodular cast iron and provides s heavy, rigid frame on which all the other basic components are mounted. Two sets of parallel, longitudinal ways, inner and outer, are contained on the bed, usually on the upper side. Some makers use an inverted V-shape for all four ways, whereas others utilize one inverted V and one flat way in one or both sets, They are precision-machined to assure accuracy of alignment. On most modern lathes the way are surface-hardened to resist wear and abrasion, but precaution should be taken in operating a lathe to assure that the ways are not damaged. Any inaccuracy in them usually means that the accuracy of the entire lathe is destroyed.The headstock is mounted in a foxed position on the inner ways, usually at the left end of the bed. It provides a powered means of rotating the word at various speeds . Essentially, it consists of a hollow spindle, mounted in accurate bearings, and a set of transmission gears-similar to a truck transmissionthrough which the spindle can be rotated at a number of speeds. Most lathes provide from 8 to 18 speeds, usually in a geometric ratio, and on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives.Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings, usually preloaded tapered roller or ball types. The spindle has a hole extending through its length, through which long bar stock can be fed. The size of maximum size of bar stock that can be machined when the material must be fed through spindle.The tailsticd assembly consists, essentially, of three parts. A lower casting fits on the inner ways of the bed and can slide longitudinally thereon, with a means for clamping the entire assembly in any desired location, An upper casting fits on the lower one and can be moved transversely upon it, on some type of keyed ways, to permit aligning the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 51 to 76mm(2to 3 inches) in diameter, that can be moved several inches longitudinally in and out of the upper casting by means of a hand wheel and screw.The size of a lathe is designated by two dimensions. The first is known as the swing. This is the maximum diameter of work that can be rotated on a lathe. It is approximately twice the distance between the line connecting the lathe centers and the nearest point on the ways, The second size dimension is the maximum distance between centers. The swing thus indicates the maximum work piece diameter that can be turned in the lathe, while the distance between centers indicates the maximum length of work piece that can be mounted between centers.Engine lathes are the type most frequently used in manufacturing. They are heavy-duty machine tools with all the components described previously and have power drive for all tool movements except on the compound rest. They commonly range in size from 305 to 610 mm(12 to 24 inches)swing and from 610 to 1219 mm(24 to 48 inches) center distances, but swings up to 1270 mm(50 inches) and center distances up to 3658mm(12 feet) are not uncommon. Most have chip pans and a built-in coolant circulating system. Smaller engine lathes-with swings usually not over 330 mm (13 inches ) also are available in bench type, designed for the bed to be mounted on a bench on a bench or cabinet. Although engine lathes are versatile and very useful, because of the time required for changing and setting tools and for making measurements on the work piece, thy are not suitable for quantity production. Often the actual chip-production tine is less than 30% of the total cycle time. In addition, a skilled machinist is required for all the operations, and such persons are costly and often in short supply. However, much of the operators time is consumed by simple, repetitious adjustments and in watching chips being made. Consequently, to reduce or eliminate the amount of skilled labor that is required, turret lathes, screw machines, and other types of semiautomatic and automatic lathes have been highly developed and are widely used in manufacturing.5 Limits and Tolerances Machine parts are manufactured so they are interchangeable. In other words, each part of a machine or mechanism is made to a certain size and shape so will fit into any other machine or mechanism of the same type. To make the part interchangeable, each individual part must be made to a size that will fit the mating part in the correct way. It is not only impossible, but also impractical to make many parts to an exact size. This is because machines are not perfect, and the tools become worn. A slight variation from the exact size is always allowed. The amount of this variation depends on the kind of part being manufactured. For examples part might be made 6 in. long with a variation allowed of 0.003 (three-thousandths) in. above and below this size. Therefore, the part could be 5.997 to 6.003 in. and still be the correct size. These are known as the limits. The difference between upper and lower limits is called the tolerance. 1 概述 随着发动机采用更加紧凑的设计和具有更大的比功率，发动机产生的废热密度也随之明显增大。一些关键区域，如排气门周围散热问题需优先考虑，冷却系统即便出现小的故障也可能在这样的区域造成灾难性的后果。发动机冷却系统的散热能力一般应满足发动机满负荷时的散热需求，因为此时发动机产生的热量最大。然而，在部分负荷时，冷却系统会发生功率损失，水泵所提供的冷却液流量超过所需的流量。我们希望发动机冷启动时间尽可能短。因为发动机怠速时排放的污染物较多，油耗也大。冷却系统的结构对发动机的冷启动时间有较大的影响。 2 现代发动机冷却系统的特点 传统冷却系统的作用是可靠地保护发动机，而还应具有改善燃料经济性和降低排放的作用。为此，现代冷却系统要综合考虑下面的因素：发动机内部的摩擦损失；冷却系统水泵的功率；燃烧边界条件，如燃烧室温度、充量密度、充量温度。 先进的冷却系统采用系统化、模块化设计方法，统筹考虑每项影响因素，使冷却系统既保证发动机正常工作，又提高发动机效率和减少排放。 2.1 温度设定点 发动机工作温度的极限值取决于排气门周围区域最高温度。最理想的情况是按金属温度而不是冷却液温度控制冷却系统，这样才能更好地保护发动机。由于冷却系统设定的冷却温度是以满负荷时最大散热率为基础，因此，发动机和冷却系统在部分负荷时处于不太理想状态，如市区行驶和低速行驶时，会产生高油耗和排放。 通过改变冷却液温度设定点可改善发动机和冷却系统在部分负荷时的性能。根据排气门周围区域温度极限值，可升高或降低冷却液或金属温度设定点。升高或降低温度点都各有特点，这取决于希望达到的目的。 2.2 提高温度设定点 提高工作温度设定点是一种比较受欢迎的方法。提高温度有许多优点，它直接影响发动机损耗和冷却系统的效果以及发动机排放物的形成。提高工作温度将提高发动机机油温度，降低发动机摩擦磨损，降低发动机燃油消耗。 研究表明，发动机工作温度对摩擦损失有很大影响。将冷却液排出温度提高到150，使气缸温度升高到195，油耗则下降4%-6%。将冷却液温度保持在90-115范围内，使发动机机油的最高温度为140，则油耗在部分负荷时下降10%。 提高工作温度也明显影响冷却系统的效能。提高冷却液或金属温度会改善发动机和散热气热传递传递的效果，降低冷却液的流速，减小水泵的额定功率，从而降低发动机的功率消耗。此外，可采用不同的方式，进一步减小冷却液的流速。 2.3 降低温度设定点 降低冷却系统的工作温度可提高发动机充气效率，降低进气温度。这对燃烧过程、燃油效率及排放有利。降低温度设定点可以节省发动机运行成本，提高部件使用寿命。 研究表明，若气缸盖温度降低到50，点火提前角可提前3A而不发生爆震，充气效率提高2%，发动机工作特性改善，有助于优化压缩比和参数选择，取得更好的燃油效率和排放性能。 2.4 精确冷却系统 精确冷却系统主要体现在冷却水套的结构设计与冷却液流速的设计中。在精确冷却系统中，热关键区，如排气门周围，冷却液有较大的流速，热传递效率高，冷却液的温度梯度变化小。这样的效果来自缩小这些地方冷却液通道的横截面，提高流速，减少流量。 精确冷却系统的设计关键在于确定冷却水套的尺寸，选择匹配的冷却水泵，保证系统的散热能力能够满足低速大负荷时关键区域工作温度的需求。 发动机冷却液流速的变化范围相当大，从怠速时的1 m/s到最大功率时的5 m/s。故应将冷却水套和冷却系统整体考虑，相互补充，发挥最大潜力。 研究表明，采用精确冷却系统，在发动机整个工作转速范围，冷却液流量可下降40%。对气缸盖上冷却水套的精确设计，可使普通冷却道的流速从1.4m/s提高到4 m/s，大大提高气缸盖传热性，将气缸盖的金属温度降低到60。 2.5 分流式冷却系统 分流式冷却系统为另外一种冷却系统。在这种冷却系统中，气缸盖和气缸体由各自的液流回路冷却，气缸盖和气缸体具有不同的温度。分流式的冷却系统具备特有的优势，可使发动机各部分在最优的温度设定点工作。冷却系统的整体效率达到最大。每个冷却回路将在不同冷却温度设定点或流速下工作，创造理想的发动机温度分布。 理想的发动机热工作状态是气缸盖温度较低而气缸体温度相对较高。气缸盖温度较低可提高充气效率，增大进气量。温度低且进气量大可促进完全燃烧，降低CO，HC和NOx的形成，也提高输出功率。较高气缸体温度会减小摩擦损失，直接改善燃油效率，间接地降低缸内峰值压力和温度。分流式冷却系统可使缸盖和缸体温度相差100。气缸温度可高达150，而缸盖温度可降低50，减少缸体摩擦损失，降低油耗。较高的缸体温度使油耗降低4%-6%，在部分负荷时HC降低20%-35%。节气门全开时，缸盖和缸体温度设定值可调到50和90，从整体上改善燃油消耗、功率输出和排放。 2.6 可控式发动机冷却系统 传统的发动机冷却系统属于被动式的，结构简单或成本低。可控式冷却系统可弥补目前冷却系统的不足。现在冷却系统的设计标准是解决满负荷时的散热问题，因而部分负荷时过大的散热能力将导致发动机功率浪费。这对轻型车辆来说尤为明显，这些车辆大多数时间都在市区内部分负荷下行驶，只利用部分发动机功率，引起冷却系统较高损耗。为解决发动机在特殊情况下过热的问题，现在的冷却系统体积较大，导致冷却效率降低，增大了冷却系统的功率需求，延长了发动机暖机时间。可控式发动机冷却系统一般包括传感器、执行器和电控模块。可控式冷却系统能够根据发动机工作状况调整冷却量，降低发动机功率损耗。在可控式冷却系统中，执行器为冷却水泵和节温器，一般由电动水泵和液流控制阀组成，可根据要求调整冷却量。温度传感器为系统的一部分，可迅速把发动机的热状态传给控