Patent GB-1074592-A (GB)
Title: Improvements in or relating to systems employing hydraulic dynamometers of the hydrokinetic type
IPC: G01L3/20
Filed: 1964-02-06
Abstract: 1,074,592. Dynamometers. HEENAN & FROUDE Ltd., W.N. BATHURST, I.M. JARVIS and B.P. HOGAN. March 17, 1965 [Feb. 6, 1964], No. 5138/64. Headings G1N and G1W. [Also in Division G3] A dynamometer system for testing a prime mover such as a vehicle engine consists of an hydraulic dynamometer of which one of the parameters speed, torque and acceleration is measured electrically and in which an electric signal representative of the difference between the measured and a desired value of the selected parameter is made to control the fluid-pressure system of the dynamometer in such manner as to maintain that parameter at the desired value. Fig. 10 shows such a system in which all three parameters are measured electrically and any one of them can be made the controlling parameter. The prime mover 1 is coupled to the dynamometer 2. The latter's speed and torque are converted into corresponding electrical signals by suitable transducers 3, 4 and a differentiating circuit 6 derives an acceleration signal from the speed signal. One of these three signals, selected by a switch 13, is compared with a reference value derived from a potentiometer 8 in a controller 7. The controller output controls an electro-hydraulic valve 10 which varies the fluid pressure in the dynamometer casing so as to maintain the desired value of speed or torque or acceleration. The output of controller 7 need not be applied directly to the valve 10: a signal shaping network 9 may be interposed so that the valve responds not to changes in the selected parameter itself but to changes in a given function (e.g. the square) of that parameter. Also, to ensure stability, a further transducer 12 may sense the fluid-pressure and provide an electrical output which is then differentiated to provide a rate-ofa pressurechange signal which is used as a feedback signal. Instability arising from the mechanical hysteresis of the valve 10 may be overcome by superimposing a 100 c/s 'dither' on the D.C. supply to the circuitry. Preferably the circuitry includes an amplifier. Fig. 11 (not shown) depicts a suitable circuit in which transistor amplifiers (A1, A2 respectively) amplify the pressure rate feedback and measured-minus-desired value parameter signals, and which incorporates a 6 volt A.C. 'dither' input a selectable proportion of which may be superimposed on the 12 volt D.C. supply. The system can be used to test an engine under constant torque or speed or acceleration conditions. It may also be used to subject an engine to a simulated road trial. For this application Fig. 12 (not shown) the controller 7 is replaced by a programmer consisting of a tape recorded set of signals representing typical torque-speed changes in a road run. The measured speed output of the dynamometer is continuously compared with the tape recorded speeds and the dynamometer loading varied as described above to make the speed follow the taped values; the measured torque is also continuously compared with the programme torque, but in this case the difference is applied to means for varying the engine's throttle setting.