【正文】 structure and is axially supported on a series of load cells The friction force moves the liner axially and thus the force is measured directly For this method extensive engine modification is required Forbes and Taylor made the first attempt to measure the pistonassembly friction in a firing engine The experiment was carried out using an elastically mounted cylinder liner A very small amount of liner movement was allowed in the axial direction and the axial movement of the liner was recorded photographically Leary and Jovellanos and Livengood and Wallour later continued this work Furuhama and Takiguchi measured pistonassembly friction measurement using the floating liner method on a modified singlecylinder diesel engine Richez et al Parker et al Sherrington and Smith Cerrato et al Wakuri et al Kikuchi et al And Rogowski in their individual work used the floating liner method for pistonassembly friction measurements They all faced similar problems in their experiments such as gas sealing at the liner top end the effect of piston side force on the force sensor and vibration Cho et al used the floating liner method with a straingagetype load cell instead of the more normal piezoelectric type to determine absolute friction force under motored conditions The floating liner method requires extensive modification of the engine isolating the cylinder liner from the engine block This is carried out by having a special gassealing arrangement at the cylinder headliner interface and as a result may not give the true picture of an actual firing engine In the IMEP method the pistonassembly friction force is determined indirectly by measuring the forces acting on the piston assembly and the connecting rod That is measuring the connecting rod strain to determine the small end axial reaction force and subtracting this from the axial forces due to cylinder pressure and piston inertia thus subtracting large numbers to determine the friction force which is normally less than 05 of the imum pressure force As this method is liable to considerable potential inaccuracies a very accurate measurement system and sensors are required However the advantage of the IMEP method is that it requires almost no modification of the engine and therefore measures the true pistonassembly friction in a firing engine Uras and Patterson used the IMEP method for the first time to measure pistonassembly friction force A special device called a grasshopper linkage was used to lead the wires from the strain gages on the connecting rod to the side of the crankcase Although this method was successful in achieving results there was a limitation on the engine operating speed and load because at high speeds the wires broke Also the errors accumulated from various input data measurements and processing resulted in some inaccuracies As the IMEP method allows true measurement of pistonassembly friction without any major engine modification this method was adopted to study pistonassembly friction under different engine operating conditions 2 PistonAssembly Friction Force The forces acting on the piston assembly in a real firing engine in the direction along the central axis of the cylinder liner are the gas force acting on the piston crown pistonassembly inertial force connecting rod force weight of the piston assembly and the pistonassembly friction force Using the information from a 720 pulse per revolution encoder connected to the front end of the crankshaft and simple geometry the direction of all the above forces can be determined Thus if any of the three forces mentioned above are known the fourth can be calculated This is the basic principle of the IMEP method used for measuring pistonassembly friction loss To measure pistonassembly friction very accurate measurement of gas force and connecting rod force is required Normally the gas and connecting rod force are on the order of 100000000 N whereas the friction force is around 5000 N Thus any smal l error in measuring gas or connecting rod force will result in high inaccuracy for example an error of 01 in measuring gas or connecting rod force can result in a nearly 15 error in instantaneous pistonassembly friction force To measure instantaneous pistonassembly friction in a real firing engine experiments were carried out on a singlecylinder Ricardo Hydra gasoline engine the design of this being based on a real engine a GM 20 liter Cavalier engine The engine specification is given in the Appendix A detailed description of all the forces acting on the piston assembly and connecting rod is shown in Fig 1 21 Forces Acting on the Piston Assembly According to Fig 1 the sum of all the forces acting on the piston assembly in the axial direction is given by 厖 1 P 1P2 is the gas pressure acting on the piston assembly A is the calculated average cylinder bore area bore 8599 mm ao is the piston axial acceleration calculated every 05 deg crank angle mpg is the pistonassembly weight mp 5778 g CY is the force acting at the center of the small end bearing mpao is the pistonassembly inertial force and is calculated as Piston acceleration179。 102179。 n179。貝西設計了利用廢氣能量來壓縮進氣的廢氣渦輪增壓器并用于柴油機增壓柴油機的功 率大幅度增加其經(jīng)濟性也大大提高目前增壓已成為柴油機的重要發(fā)展趨勢 20世紀 70年代初由于石油危機導致原油價格成倍增長引起對發(fā)動機燃油經(jīng)濟性的重視為了減少內(nèi)燃機對日益短缺的石油基燃料的依賴各國正在加緊進行內(nèi)燃機代用燃料的研究工作以逐步減少汽油和柴油的用量 目前柴油機正朝著提高單機功率降低油耗污染和噪聲以及提高工作可靠性和延長使用壽命的方向不斷發(fā)展 本次課題研究的 CA498 柴油機屬于載重汽車用柴油機的一種這類柴油機的設計方面下列趨向值得注意 1．采用 V 型結(jié)構(gòu) 由于在中汽車噸位的日益增大和車速的普遍提高載重汽車用柴油機的功率也不斷增加從而發(fā)動機缸數(shù)就增多一般六缸以下的發(fā)動機均為直列式也是這類柴油機的主要形式由于 V 型結(jié)構(gòu)綜合了尺寸小和平衡好的優(yōu)點六缸以上的柴油機多采用 V 型 2．提高轉(zhuǎn)速 3．采用廢氣渦輪低增壓 多數(shù)汽車用柴油機采用低增壓發(fā)動機不需要在結(jié)構(gòu)上做大的改變就可以得到增壓和非增壓兩種機型使用相同的曲軸傳動系統(tǒng)而不致影響非增壓機型的摩擦損失和燃油消耗率因此采用低增壓是簡化柴油機系列的一個良好途徑 4．廢氣凈化和降低噪聲 柴油機排氣中的有害成分有氮氧化物 NOx 未燃碳氫化合物 HC一氧化碳 CO二氧化硫 SO2和碳煙等由于降低 NOx比降低其他有害氣體更為昆南因此當前廢氣凈化的主攻方向是降低 NOx目前降低 NOx的方