【正文】 transmissions (used local delivery trucks), all these measures have resulted in an inerease in the power weight ratio of 38%with in 9 years 38% (F ).As in the past, more performance is requiredof heavyduty represents a challenge for ZF: to also be able to supply transmissions perfect for vehicles with 600 bhp engines and to rque levels of up to 2700 areas of application for these transmissions are both long distance travel and well as harsh off road operations and heavyduty tran sportation vehicles, in which the ZFTran smatic, a bination of the ZFEco split transmission and a to rque converter clutch (W SK), are used.System aticoptimization steps by means of FEM calculations, ponent and test riginvestigatons, special gear grinding procedures, gear conrections to contend with hig to rque levels together with high quality materials for gears and bearings as well as improved lubricants have resulted in the ZFEcosplit 16 S 251(F ), the world’s most powerful synchromesh length and weight only had to be increased slightly as a result of the up graded technology.When pared with the first generation of the Eco split range, we have managed to increase the powerweight ratio of the Eco sp lit t ran sm ission by %.(F ).F also shows the new fully automatic A S T ronic transmission (F ), which has once again brought about an inerease in the powerweight ratio.The A ST ronic transmission is an automatically shifted transmission system based on a robust, mechanical basic transmission is engagedusing constant mesh and does not have synchromesh, the engine /transmission shaft speeds are a ligned in the main transmission during shift s with input from the EDC engine and transmission very good powerweight ratio is achieved not least thanks to the plete in tegration of the clutchplate, the shift module with in tegrated transmission electronics and the ZFintarder.If required the transmission can also be operated in semiautomatic mode (manual gear slection).Extremely costeffective driving is however available, especially to the average driver, through the use of the fully automatic mode together with the ZF shift strategy.In addition to the fuel saving (on average 3%) in automatic mode, the A ST ronic transmission results in another sign ificant operating cost saving since driver training is no longer required and as clutch service is no longer required due to a shifting method which conserves the clutch and other advantages resulting from the long service life(F ):Sign ificant progress has also recently been made in the development of oil (F ).Where a sat the start of the 1980s, an oil changemade in Eco split transmissions every 80000km, acurrent mileage of 300 000 and in the future 500000 km can be attained thanks to the progressive formulation and add it ives used in the lubricants.A t the same time, the object ive for E at bus transmissions is to use synthetic A T F to extend the oil change in terva ls from 30 000 to 1200000 total cost for the operator can be halved despite the fact that the lub ricant is expensive since savings can be made in the filter, disposal of used oil and payroll costs(F )No iseSince the introduction of the ZFEcosplit transmission, the housing and the gears of the basic transmission and splitter group have been designed in a noise optimized gears are now state of the arttechnology in the spur gear stages of modern truck transmissions used to reduce the level of transmission has therefore contributed neither subjectively nor inameasurable manner to the vehicle noises in gears 9 to order to provide the driver and environ ment with the same level of fortable noise, even in the lower gears, in which the planetary g roup(GP)increases the ratio,a techn ical vibration optimized helical gear was even developed for the GP.Another milestone in the reduction of noise in the ZFEcosplit family was attained with the introduction of the helical multi ratio on the operating conditions, the pure GP noise has been reduced by up to 18 dB and the transmission noise in the low ratio range by up to 10 here is hardly any scatter in the noise level thanks to the high quality of the ground gears.As is shown in the noise parison measured on testrig (F ), the ZFEco split transmission now has the same positive noise characteristics in the lower gears as it already had in the upper transmission no longer makes any sign ificant contribution in the vehicle to the overall noise clarifies this by displaying the measurement for drive by noise for transmissions of the Ecosplit range and the newly developed A ST had to betedronic transmissions.ComfortAn increasing level of fort, similar to that to which car drivers are accustomed, is also expected in mercial approaches are pursued here for the different transmission types.In the past, emphasis was placed on significantly reducing the shift forces in manual transmissions (synch romesh) by means of continual further developments to the synchronizer units, such as short stroke and dualcone further increase in fort was attained through the development of a shift aid,the integrated ZFServoshift(F ):A parison between ZFEco split transmissions with and without Servo shift shows the success of this development (F ).When without the Servo shift:there is a very small difference in shift forces between the various shiftsthe force required is usually halvedthe shift stroke is reduced from mm to 80 mmthe air in the servo cylinder smoothes peak power ratings。 since there is nomechanical connection between them anual and sliding sleeve, this results inavery uniform shift process which feels subjectively pleasantother shifting principles can be retained Car shift force levels can therefore be attained in trucks and the driver enjoys considerable shifting relief and increased fort.In the future, transmissions in long distance buses and coaches will also be equipped exclusively with shift servos to enabl