ABSTRACT As vehicle fuel economy continues to grow in importance, the ability to accurately measure the level of parasitic losses on all driveline components is required. A standardized comparison procedure enables manufacturers and suppliers to measure component losses consistently, in addition to offering a reliable process to assess enablers for efficiency improvements. This paper reviews the development of a comprehensive test procedure to measure transfer case speed- dependent parasitic losses at key speed, load, and environmental conditions. This procedure was validated for repeatability considering variations in soak time, temperature measurement positions on the transfer case, and test operating conditions. Additional assessments of spin loss at low ambient temperatures, and the effect of component break-in on spin loss were also conducted. The resultant procedure is proposed as a new SAE J-standard (Surface Vehicle Recommended Practice J2985) for release by the All Wheel Drive (AWD) Standards Committee. This project was undertaken and financially supported by the Transmission Working Group of the United States Council of Automotive Research (USCAR) for the SAE AWD Standards Committee. INTRODUCTION The purpose of this project was to develop a test procedure which could form the basis of an SAE J-standard for measurement of parasitic losses (spin losses) of transfer cases used in passenger car and light duty truck applications [ 1]. The standard is intended to cover transfer case designs including chain/gear drives as well as manual/electronic shift systems [ 2]. At the start of the program, initial parasitic loss testing focused on the use of ‘traditional methods’ for measurement of test unit temperature during data acquisition. The ‘traditional method’ of temperature control is measurement of the transfer case temperature via a thermocouple installed in the sump of the test unit. Upon review of the initial parasitic losses data acquired using traditional temperature monitoring/ control methods at low temperature (i.e., −7°C), it was clear that the repeatability was not acceptable and another procedure would need to be developed. This paper outlines the steps taken to develop a new test procedure and compares the results of ‘traditional’ methods to the newly developed method. Development of a Standard Spin Loss Test Procedure for 4WD Transfer Cases2012-01-0306 Published 04/16/2012 Michael Kirk and Syed M. Ilyas Chrysler Group LLC Thomas D'Anna FEV Inc Andreas E. Perakes Ford Motor Co. Craig S. Ross General Motors Company Copyright © 2012 SAE International doi:10.4271/2012-01-0306Downloaded from SAE International by Univ of California Berkeley, Thursday, July 26, 2018TRANSFER CASE PARASITIC LOSS TESTING The traditional method for assessing the losses of transmission and driveline components is to use a single dynamometer to measure the torque needed to spin the unit under test at a typical (warm) operating temperature (as measured at the sump). It is important to utilize a process that can consistently and accurately measure such losses across a range of operating temperatures (cold to hot) as well as input speeds. As mentioned previously, the traditional method (for spin loss testing on transfer cases) was noted to fall short of meeting this objective, necessitating the development of a refined test process [ 3]. This paper discusses the development of such a process (focused on transfer cases), the details of which are advanced in the following sections. PROJECT OBJECTIVES The project had several objectives, the most important of which was to develop a standardized procedure (SAE J- standard) to facilitate comparison of parasitic loss measurements. The primary objective of the project (and ultimately the focus of the J-standard) was to provide a procedure that met the following criteria: • Works for multiple test temperatures (−7°C, 21°C, & 65°C) • Covers a range of test speeds (250 - 3500 rpm) • Can be