Laboratory Durability Testing Heavy Duty Powershift Transmissions Under Simulated Field Conditions F.Blair,Jr. Allison Division General Motors Corp. In general, laboratory testing of trans­ missions has been concerned mainly with running each gear range of the unit in pro­ portion to the percentage of its use required by a particular type of application such as working, hauling, and military vehicles. It has been also confined to other phases of operation - insuring proper functioning, im­ proving performance and efficiency, and test­ ing areas redesigned because of field prob­ lems. Consequently, durability testingof this nature has been limited mostly to steady state conditions. However, as applied to Torque Converters and power shift transmissions, which have become a requirement in heavy duty vehicles, this mode of testing is not adequate. Allison's experience with these products has indicated that steady state testing alone does not com­ plete the endurance picture because it ignores dynamic or transient conditions. It is appar­ ent that these factors, rather than steady state durability, are the real obstacle to transmis­ sion reliability. An added variable may result from the principle of using interchangeable components. For example, a scraper, a rear dump truck, crawler tractor or tank have different duty cycles. This means that if certain basic parts are to be used for all applications they must be capable of meeting these extreme variations. Laboratory testing of full torque shifting transmissions under simulated field conditions should provide a more reliable unit. To ac­ complish a program of this nature requires the following approach: . Accurate work cycle information relating to different classes of applications. . Quick and simple means of reduc­ ing the field data acquired. . Durability testing facility. In other words, the requirements may be summed up as "bringing the field into the laboratory". Downloaded from SAE International by University of British Columbia, Tuesday, September 25, 2018The method chosen by Allison is briefly outlined in Figure 1. Field data or work cycle information is measured at the work site by using a magnetic data recorder. The taped data are brought back to the laboratory where it may be fed either directly into an analog computer for a quick analysis of the transmis­ sion's performance (component life, fuel con­ sumption, etc.) or converted to digital form by a data reduction center. With this conver­ ted data (digitized) the performance character­ istics of the transmission may be more ac­ curately estimated and a duty cycle may be defined in order to establish an equivalent durability cycle for the laboratory set-up. A check system is also provided to com­ pare this established cycle with the field infor­ mation. By feeding the digitized information into a digital computer, the dynamometer pro­ gram maybe compared with the acquired work cycle. This is done to assure that the labora­ tory test simulates the field cycle as closely as possible within the physical limitations of the test equipment. It is easily seen that this plan has followed the requirements of a laboratory testing pro­ gram that includes, not only steady state but transient or dynamic conditions as well. It provides the work cycle, the means to reduce it, and the laboratory facilities. The purpose of this paper is to explain and describe in de­ tail the Allison program. WORK CYCLE DATA Allison's experience gained by field test­ ing with oscillograph recorders indicated that the best way to obtain work or duty cycle in­ formation would be to design a mobile data lab­ oratory that could be dispatched to any work site where such a record could be made. A vehicle duty cycle may be defined by knowing the torque and speed required for it to perform its job. For example, to define the work cy