ABSTRACT The objective of this investigation is to characterize the torsional characteristics of the hydrodynamic torque converter. Analytical and experimental techniques are used to quantify the relationship between torsional oscillations imposed on the pump to those at the turbine as a function of frequency, operating point and design. A detailed model of the hydrodynamic torque converter based upon one- dimensional flow theory is used to establish fundamental torsional behavior independent of the downstream mechanical system. A simplified linear spring-mass-damper representation of the hydrodynamic torque converter is derived whose coefficients are proportional to pump speed for a particular design. A transmission dynamometer test cell with the capability to produce torsional oscillations was used to develop frequency response functions for various torque converters in a transmission, operating at steady state conditions. It was found that the torque converter behaves like a low pass filter with a cutoff frequency dependent upon operating speed, torque and design. Angular vibrations below 20 Hz were found to pass through the torque converter with sufficient energy to excite natural frequencies of downstream drivetrain components. INTRODUCTION A significant amount of published literature exists on torque converter operation, design optimization, analysis or testing of internal flow and cavitation, which the reader is referred to [1, 2, 3, 4] for more detail. There is also substantial published work on torque converter modeling to assess the complete drivetrain for low frequency dynamic behavior, typically less than 10 Hz, see [ 5, 6, 7, 8, 9, 10]. However, a survey of the literature revealed little if any discussion on the characteristics of the torque converter represented as a spring,mass, damper torsional element. More specifically limited published information exists about how the torque converter behaves as a function of frequency in coupling with the upstream and downstream components. The objective of this paper is to quantify its frequency response function using analytical models and test measurements obtained using a transmission dynamometer test cell. The most fundamental relationship for any torque converter is its K-factor, given by, (1) which states that for an operating condition the ratio of pump speed to the square root of pump torque is a constant. The K- factor relationship is not a constant over an entire engine - transmission input (turbine) speed range, but is a function of the ratio of turbine to pump speed, referred to speed ratio, SR. From the definition of damping for a torsional system, it can be seen that K-factor can be rearranged and differentiated on speed to become a steady state damper rating for the torque converter, as noted in equation 2: (2) The steady state damper rating from equation 2 is simply the tangent of the pump torque - pump speed curve, as shown in Figure 1 for three speed ratios typical of positive engine torque operation. A couple of things to note from Figure 1 are that as pump (engine) speed increases, damping increases and as SR increases, damping decreases. Both of these observations are fundamentally expected. Dynamic Torque Characteristics of the Hydrodynamic Torque Converter2011-01-1540 Published 05/17/2011 Darrell Robinette, Michael Grimmer and Randall Beikmann General Motors Company Copyright © 2011 SAE International doi:10.4271/2011-01-1540 SAE Int. J. Passeng. Cars - Mech. Syst. | Volume 4 | Issue 2 1023Downloaded from SAE International by University of Michigan, Sunday, July 29, 2018The conventional notion is that fluids in shear cannot transfer high frequency torsional vibration. As engine speed increases so too does engine firing frequency, leading to higher damping. At SR's above the coupling point, pump and turbine speeds are nearly equivalent, and torque is no longer multiplied, the flow velocity within the converter torus decreases sharply. A