845115 A Regenerative Road Load Simulator Ian A. Stringer, Keith J. Bullock ABSTRACT The design, control and performance of a versatile regenerative road load simulator for laboratory use is described. The arrangement of the unit provides two separate controllable dynamometers for testing a wide range of conventional, electrical and hybrid propulsion systems and transmission components. A hydro­ static pump-motor set forms one dynamometer; this will absorb or supply a maximum torque of 410 N.m, and up to 70 kW of tailshaft power at speeds from zero to 3000 r/min. The second dynamometer, which can also simulate the behaviour of small to medium sized IC engines, is a Ward Leonard motor-generator set capable of absorbing or supplying up to 150 N.m to 3000 r/min, then 56 kW up to 6000 r/min. Components of this dynamometer can also be set up as a battery simulator to supply or absorb power for electrical components of any hybrid or electric transmission system under test. In this mode the mechanical power is absorbed or supplied by the hydrostatic dynamometer. The two dyna­ mometers can be used concurrently to evaluate such components as axle differentials and epicyclic gear boxes, in which case a separate prime mover is required. Regenerative capabil­ ities in this mode will depend on the power absorbing capacity of the prime mover chosen. The performance of the simulator with a test automatic transmission fitted, when evaluated using the Federal DHEW Urban Driving Schedule velocity-time history, was found to be satisfactory. INTRODUCTION During the last fifteen years the major world automobile manufacturers have striven to improve the fuel economy and reduce emissions of motor vehicles. Many alternative vehicle propulsion systems, including those with on-board energy storage, have been proposed and analysed. Such systems can be built up from a wide variety of energy converting and power transmitting compon­ ents and the performance of the final system will depend on the selection of components, their ratings and the way they are combined. Analog, digital and hybrid computational modelling techniques used to evaluate such systems require accurate specification of all components and sophisticated, time consuming computation while road testing of prototype vehicles is expensive. Thus many research workers have resorted to laboratory evaluation of their ideas (1-6)*. Computer analysis can aid selection of components (7), which can then be assembled on a test bed and coupled to a dynamometer programmed to provide the necessary load. Such "breadboard" propulsion and trans­ mission systems can be subjected to comparative testing so that alternative concepts can. be evaluated. For this type of testing, a repres­ entative driving cycle is adequate and the road load characteristic is not critical; provided the same driving cycle and hypothetical vehicle parameters are used between tests, the results should indicate which is the superior system. The recovery of vehicle kinetic energy during stopping is important if overall fuel economy is to be improved, and the dynamometer must be capable of operating in a regenerative mode. This paper describes a versatile laboratory regenerative road load simulator based on a unique approach to the problem of measuring the performance of propulsion systems and their components. OBJECTIVES The stochastic road load on a vehicle can be represented by simultaneous traction force-time *Numbers in brackets designate references at end of paper. 4.58 Downloaded from SAE International by University of British Columbia, Tuesday, September 25, 2018and speed-time histories. Figure 1 depicts the typical relationship between wheel torque and road speed for various road gradients and vehicle accelerations. Curves of constant road power are also shown. Much higher torques are required for acceleration and hill climbing than for cruising, w