GB856573A - Improvements in or relating to hydraulic dynamometers - Google Patents

Abstract

856,573. Absorption dynamometers. HEENAN & FROUDE Ltd. May 2, 1958 [May 9, 1957], No. 14833/57. Class 106 (2). [Also in Groups XXIX and XXXIV] An hydraulic absorption dynamometer 1 is provided with a back-pressure valve 2 and means 13 responsive to the dynamometer speed for controlling the actuation of the valve 2 so that up to a selected predetermined speed the valve causes variable back pressure such that the power absorbed by the dynamometer varies with the cube of the speed and, upon the speed of the dynamometer exceeding that predetermined speed, the back pressure builds up rapidly so as to maintain the speed of the dynamometer substantially constant. The back pressure valve is shown in Fig. 2 and consists of a double mushroom valve a acting to open or close the water outlet 34 from the dynamometer casing 1. The valve a is mounted on a spindle b carrying a piston d, high-pressure oil from a pump 7, driven at a speed proportional to the speed of the dynamometer, being supplied to the left side of the piston through an inlet pipe 18, and low-pressure oil being supplied to the right side of the piston through an inlet 28. A spring n loads the spindle to the left to hold the valve a off its seatings under low load conditions. The speed-responsive means 13 is shown in Fig. 5 and consists of a piston c 6 loaded to the left by two adjustable tension springs h 6 . High-pressure oil from a pump 6 similar to the pump 7 is supplied to the left of the piston c 6 through an inlet 12, and the low-pressure oil being supplied to the backpressure valve 2 passes to the right of the piston c 6 between pipes 27 and 28, this path being cut-off if the piston c 6 moves to the right. Needle valves 15, 20 (Fig. 1), set by electric motors 21, 22, control the pressure of the oil in pipes 14, 19, upstream of these valves. The operation is as follows: If the speed is below the predetermined value, the pump 7 delivers oil through a filter 17 to the back-pressure valve 2 and by pressing its piston d to the right restricts the outflow of water through the outlet 34. For any one setting of the valve 20, the pressure set up behind the piston d will ensure that the back pressure against the water flowing through the outlet 34 will vary as the square of the speed, and hence the power absorbed will vary as the cube of the speed. Adjustment of the valve 20 regulates the factor of proportionality. Under these conditions, oil is supplied by the pump 6 through the valve 13 and the valve 15, which latter is partly closed, to the oil storage tank 3. When the speed of the dynamometer reaches the predetermined speed, the pressure to the left of the piston c 6 of the valve 13 rises sufficiently to move the piston over to the right, thus stopping the flow of oil through the pipes 27, 28 and this, overriding the action of the valve 20, causes an increase in pressure in the pipe 19. This in turn causes a sudden rise in the pressure applied to the piston d and hence a steep rise in the power absorbed. The speed at which this occurs is controlled by the adjustment of the springs h 6 and of the valve 15. If the tension in the springs h 6 is low, the valve 15 need only be closed slightly and the rate of movement of the piston c 6 is relatively low. If the tension in the springs h 6 is high, the valve 15 is closed further and the rate of movement of the piston c 6 is higher, thus ensuring that the speed stays more nearly constant as the power absorbed rises. In addition, a valve 23 controlling the rate of influx of water to the dynamometer is opened further by the rise of oil pressure in a pipe 26 caused by the closing of pipe 27. The Provisional Specification describes two further embodiments, in each of which the change from the cube law to constant speed absorption law is made manually, the apparatus operating to give substantially no power absorption up to a predetermined speed and then to operate on either of the above laws. Specifications 473,270 and 736,975 are referred to.