The time required for the shifting elements in an automatic transmission to complete their engagements is an important indicator of the performance of both friction elements and automatic transmission fluids. The common method of measuring shifting time via analog (chart) recording techniques is somewhat time consuming; moreover, it is subject to interpretative error and does not lend itself to quick, accurate determinations. A shift timing device that has been designed and built utilizing digital techniques gives an automatic unattended digital readout of shift time. The details of this timer and applications of it to automatic transmission fluid testing are discussed.
THE TIME REQUIRED for the shifting elements in automatic transmissions to complete their engagements is an important indicator of transmission fluid and friction element performance and durability. Critical examination of shift time changes occurring during transmission life testing is an integral part of a number of test sequences used throughout the automotive and petroleum industries. The most common means of determining these engagement times is by recording certain of the more easily obtained operating parameters-engine speed, friction element (clutch) apply pressure, and sometimes transmission output torque-using analog strip chart recording techniques. A determination of the shift time is then made by direct measurement of the time interval between specific key points in the shift, or from a geometric construction based on these key parameters. Depending upon the timing points used, this type of determination may closely approximate the exact friction element engagement interval. However, shift time measurements made in this manner are time consuming and are subject to errors in interpretation. When large numbers of these determinations are necessary, manpower requirements are appreciable. An automatic timing device therefore becomes attractive.