【正文】 transfer efficiency of the drive train η 178。low costs The transmissions have a sign ificant influence on the vehicle glance at F indicates the great number of requirem entsplaced on the you look at the different a ssessment criteria for road vehicles, it beesclear that all systems produced, including thealvehicle drivehe drive train is of transmission a recertainly always depicted with a weighted optimization because some criteria require conflicting solutions. In parison to passenger cars, the absolute priority for mercial vehicles is to earn money. A s a very general rule, you can say tha t the requirements of modern vehicles 北京工商大學(xué)畢業(yè)論文（設(shè)計） 28 are increasing and that fort requirements are directing them selves more and more towards the standards usually applied in cars. Commercial vehicles have very different tasks and areas of application (F ).When considering buses, city and line buses should be mentioned on the one hand as should (longdistance) coaches on the other area of application for trucks extends from the lightduty class (local delivery trucks) through mediumduty classes to heavyduty longdistance haulage ructioinsite and special vehicles or even municipal vehicles can also be added to this all these types of application are bined with the engine rating installed and the special customer requests, they characterize the requirements placed on the tranSmission. Anumber of tranSmission variants are currently available for road vehicles. According to , aninitial dist inction can be made between multiratio transmissions and continuously variable dealing with multiratio transmissions, one should consider the group of manually shifted transm issions with constantmesh, synchromesh or servo shift system as well as the group of automatic transmissions, where a dist inction is made between powershift automatic units and automated shift continuously variable transmissions extend from mechanically continuously variable transmissions (chain/belt and /orto raidal transmissions) through hydrostatic units to electrical drive trains with various n additional dist inction can be made with mutliratio transmissions as to the type of shift system, where gear shifts are either undertaken with or w ithout an interruption to traction. All continuously variable transmissions have one mon feature: the ratio can be adju without any noticeable interruption to traction. The requirements placed on the transmission in the various areas of applicatio indiffer differentiated prioritization of criteria (refer to ) thereby results in an individual preference for certain transmissions types in the individual the whole, you can say that as in the past, manual transmissions continue to dominate in trucks where emphasisis placed on 北京工商大學(xué)畢業(yè)論文（設(shè)計） 29 costsavings, fuel consumpt ion and efficiency rather than in stances where fort plays a decisive role, such as in city buses with frequent stopping and starting operations, preference is given to powershift automatic automatic transmissions,which stemfrom manual transmissions,at tempt to bine the advan tages of favourable efficiency with a satisfactory degree of shifting fort. The requirement for fort and easyer operation is however currently being increasingly important (refer to F ).A s far as the transmission is concerned, this means both areduction and harmonization of shift forces in manually shifted transmission as well as an increasing interest in automated transmissions with in the drive train with an optimumadaptation to the bustion engine. Furthermore, a reduction in the number of gears (from 16 to 12 o r 10 gears) can also be seen, in particular in drive train concepts with engine management. Wherea selectrical drive concepts remain the preferred option in all special applications in trucks, important activities should be noted in the bus field, especially with regard to city generally introduced low floor technology is not the sole initiator of this work consists of finding a lternatives to the standardm echanical drive train by means of a characteristics curveoptimized method of operating the diesel engine using hybrid , alternative sources of energy such as batteries,catenary wire operation,but also fuel cells are also a lready being tested. The follwing information uses selected examples to indicate the extent to which thesvarious approaches affect fuel consumption, noise level and fort. Fuel consumption The general formula for calculating the fuel consumption is well known from analysis of the lognitudinal dynamics of road vehicles taking into account the different levels of drive resistance and engine and /or drive train characteristics: The transmission with in the drive train directly and indirectly influences the 北京工商大學(xué)畢業(yè)論文（設(shè)計） 30 fuel consumptionvia 178。high levels of reliability 178。pact dimensions 178。simple operation 178。Electrical and electronic units used more in all drive train areas 178。Economic viability through use of light const ruct ion, drive train optimization and improved efficiency as well as reduction in maintenance costs 178。Technologies, inparticular transmission technology In addition to the key engine developments with the object ive of satisfying the exhaust gas standards defined in EU Euro and EU Euro IV, the optmium configuration of the drive train is of → Diesel engines remain predom inant ● Wider consumption characteristics curves ● Torque levels of up to 3000Nm in the future → Comfort requirements as in passenger car ● Reduction and harmonization of shift forces ● Increased: automatic transmissions with optimum adaption to the bust on engine ● M inmi ization of fuel consumption,emissions 北京工商大學(xué)畢業(yè)論文（設(shè)計） 26 ● Reductionin number of gears from 16 to 12 or less→ Electrical drive technology in city buses ● A lternatives to mechanical driv