GB2060909A - Hydrodynamometers - Google Patents

Abstract

A hydrodynamometer comprising a rotating blade wheel (6) driven through a shaft (8) by a prime mover whose power is to be measured while water flows between vaned plates (5) in a casing (3) has a valve (37, 38) under the control of a bellows (41) subjected internally to the total pressure in the casing (3) and externally to the static pressure in the casing. The valve (37, 38) controls the rate of discharge of water from the casing, the static pressure being maintained proportional to the square of the speed of the blade wheel (6) by this arrangement to stabilize the measurement of the power of prime movers liable to vary in speed. <IMAGE>

Description

SPECIFICATION Improvements in hydrodynamometers This invention relates to hydrodynamometers and concerns a braking-torque control means for use with a hydrodynamometer.

Where power of a prime mover is measured which is liable to vary its revolving speed, such as with a reciprocating engine the output torque of which is almost kept constat regardless of its speed, the power measurement can stably be performed by a hydrodynamometer if the torque of the hydrodynamometer is kept proportional to the square of the revolving speed, since the hydrodynamometer acts to suppress variation in revolving speed when an engine tends to change its speed for some reason. Thus, a hydrodynamometer is normally designed to effect its braking-torque in a manner proportional to the square of the revolving speed X of its rotating shaft or blade wheel.

However, the mechanism for making the braking-torque proportional to the square of revolving speed X of its rotating blade wheel is complex in conventional hydrodynamometers.

For example, the Froude hydrodynamometer in the U.K. uses an impeller of a centrifugal pump mounted on the shaft of the rotating blade wheel in the hydrodynamometer casing and is adapted to increase or reduce feed water pressure to the blade wheel proportionally to the square of its revolving speed while keeping the sectional area of the exit port unchanged, thus maintaining a constant circulating water flow.

In another example, the ZBllner hydrodynamometer of West Germany, while keeping the sectional area of the water feed port and pressure of feed water constant, controls a pressure regulator valve installed in an exit port by water pressure from a centrifugal pump, the pressure being proportional to the square of the revolving speed of the pump which is installed outside the casing and beltdriven by the rotating shaft of the dynamometer. The dynamometer thus maintains the circulating water flow constant regardless of its revolving speed and controls the brakingtorque by regulating the output flow (consequently the output pressure) of the centrifugal pump similarly to the aforementioned Froude dynamometer.

Thus, the braking-torque has been made proportional to the square of revolving speed of the rotating blade wheel in prior art dynamometers, but these devices have been complex and costly to produce.

The present invention provides a hydrodynamometer having a rotatable blade wheel mounted between vanes fixed in a restrained, rotatably mounted casing to be driven against the action of a load generated on the wheel by a flow of liquid through the blade wheel casing wherein a valve means is provided to control the rate of discharge of the liquid from the blade wheel casing in proportion to the square of the revolving speed of the blade wheel.

The braking-torque control means for use with a hydrodynamometer according to the present invention does not need to use such complex mechanisms as conventional hydrodynamometers, but very simple constructions in which the sum of static and dynamic pressures and the static pressure are introduced respectively to the inside and outside of a pressure sensing means, thereby actuating a control valve and thus, the static pressure in the blade wheel casing is made proportional to the square of the revolving speed of a blade wheel, permitting the stable operation of a hydrodynamometer and bringing great benefit to industry.

A specific embodiment of the present invention will now be described by way of example and not by way of limitation with reference to the accompanying drawings in which: Figure 1 is a sectional elevation of a hydrodynamometer according to the present invention, and Figure 2 is a section taken on line X-X in Fig. 1.

With reference now to the accompanying drawings, reference numeral 1 represents the base portion of the hydrodynamometer, which is formed with a tank therein and rotatably receives through bearings 4 a casing 3 two supports 2, 2 vertically extending therefrom.

Inside the casing 3 are secured two opposing stationary vane plates 5, and 5 and the casing is rotatably provided with a rotating blade wheel 6 between, and in close proximity to, the two vane plates 5, 5.

The blade wheel 6 is mounted on a rotating shaft 8 which is supported by the casing 3 through the bearings 4 and formed with fins 6a which are slightly extended radially from their peripheral portions. Each of the opposing surfaces of the vane plates 5, 5 and the blade wheel 6 are formed with circulation chambers a,bwhich are defined by dividing, with a plurality of radial partitions, annular channels which are concentric to the rotating shaft 8. A water feed port 9 of the base portion 1 and a water inlet port 10 of the casing 3 communicate via a tube 1 2 through 0 ring seals 11, 11 so that water can be fed without obstruction even though the casing 3 is angularly displaced about the axis of rotation of the shaft 8 in use of the hydrodynamometer.

Water, for instance tap water, supplied through the water feed port 9 flows through the pipe 1 2 and a water inlet port 10, into a passage 1 3 in the left hand vane plate, as seen in Fig. 1, whereas part of the water flows, through a passage 14, into the center portion of the circulation chamber a on the left, and other portions of the water flow, through a hole 1 5, a passage 16, a hole 17 and passages 8 and 1 9 on the righthand side, through the latter into the center portion of the circulation chamber b on that side. The water proceeds from the peripheral portion of the rotating blade wheel 6 into a radially extending tube 26, to be described later and is thereafter discharged.Gas generated in the circulation chambers a, b flows through other passages 20, 21 in the vane plates respectively and through discharge ports 22, 23 into the tank in the base portion 1 and is discharged from the dynamometer through a discharge port 48. An arm 24 extends from the outer surface of the casing 3 to permit measurements of torque being exerted on the casing 3.

A control valve 27 is provided in the lower portion of the casing 3, having a valve opening in the wall of the tube 26. The tube 26 has its upper end opening 25 disposed opposite the periphery of the rotating blade wheel 6 so that the pressure of water in the tube 26 is about equal to the static pressure Ps of the water in the casing 3.

A valve case 28 of the control valve 27 has one side opening 29 connected through a tube 31 to a opening 30 (Fig. 2) provided radially on the periphery of the casing 3 and another side opening 32 connected through a flexible tube 34 to a valve 33 which is vented to atmosphere.

The valve has a valve stem, the root of which is enclosed by a bellows 41 in the case 28, the bellows being attached to a closure 35 at one end and to a plate secured to the valve stem 39 at its other end. In the closure 35 are formed passages 42, 43 communicating the inside of the bellows 41, the passage 42 being connected through a tube 44 to a duct 45 which is attached to the casing 3 tangentially to the rotating blade wheel and opening at the position where it intersects at right angles with a radius, and the passage 43 being connected through a flexible tube 46 to a valve 47 which is vented to atmosphere.

When the valves 33, 47 are closed, the flow of feed water through the tube 1 2 is kept constant and the shaft 8 is driven by a reciprocating engine for instance. Then water is agitated between the vane plates 5, 5 and the blade wheel 6, and torque is exerted on the casing 3 and measured by means of the arm 24. In the steady-state operation, water supplied through the feed port 10 enters the tank in the base portion 1 through the valve opening between the valve seat 37 and the valve 38 in the valve seat tube 26 and is discharged from the discharge port 48. The amount of fed water and the amount of discharged water are the same and the amount of water being agitated between the vane plates 5, 5 and the blade wheel 6 is kept constant.Water in the periphery of the blade wheel enters the valve seat tube 26 through the opening 25 and discharges into the base portion 1 through the opening of the valve 38, with the pressure in the tube 36 being kept equal to the static pressure Ps in the casing 3. If the valve 38 is pressed against the valve seat 37, stopping the water flow through the valve opening, the static pressure Ps increases, while if the valve 38 is moved apart from the valve seat 37 discharging more water into the base portion 1 than that during the steady-state operation, then the static pressure Ps decreases.

The total pressure made up of the dynamic pressure Which is generated by the fins 6a of the rotating wheel 6 pushing water in the casing 3 and the static pressure Psw is applied inside the bellows 41 through the tubes 45, 44 and the passage 42. Thus, if the effective actuating area of the valve 38 is represented by A,, and that of the plate 40 by A2, then the force F1 which urges the valve stem 39 to move to the right in the drawing, F,= PsA, The force F2 which acts to move the valve stem 39 to the left, F2 = (Pd+ P)A2 - P,A2 = PdA2 y And,= -a'2R2 = Kw2 2g where Y: density of water g : acceleration of gravity w: : revolving speed of the rotating blade wheel R : mean radius of fins 6a K: constant Since F, = F2 in the steady operating condition, Pisa, = P,,,A2 A2 Ps = A1 ax2 Then the amount of feed water supplied through the tube 1 2 equals the amount of water discharged through the discharge port 23 and the opening 36 and thus the operating flow of the water is kept constant.

If the revolving speed w increases while the dynamometer is operated under this condition, the dynamic pressure Pd increases in proportion to (52, the force pushing the valve .38 to the left in Fig. 1 of the drawings through the valve stem 39 also increasing in proportion to 62 whereby the valve 38 is moved to the left to define a smaller opening for the gushing water due to the static pres sure P5. This causes a reduction of the water flow from the opening 36 and an increase in the volume of water in the casing 3 and consequently, the valve 38 is pushed to open against the force which is proportional to (z2, to move the valve stem 39, thereby increasing the static pressure-Ps in proportion to 02.

When the engine speed returns to the original speed, the force tending to move the valve stem 39 to the left is weakened, and the valve 38 moves again to the open position, increasing the discharge of water from the opening 36, the static pressure P5 regaining its original value. Similarly, when the revolving speed X of the shaft 8 decreases, the static pressure P5 reduces in proportion to Ce)2.

By changing its opening, the valve 47 is used to adjust the dynamic pressure Pud which is applied inside the bellows 41 and thereby adjust the static pressure Pus and the torque of the dynamometer, while the valve 33 is used to change the characteristic of the dynamometer such as the rate of change of the static pressure P5 in relation to co and time. The fins 6a of the rotating blade wheel 6 are effective in creating a large dynamic pressure, but a smaller dynamic pressure can be created without those fins such as to actuate control valve 27, for instance, by making the diameter of the bellows 41 larger.

The braking-torque control means for a hydrodynamometer as described is intended to increase or reduce the static pressure P5 in the casing 3 in proportion to the square of the revolving speed co of the rotating blade wheel by actuating a control valve 27 when the speed X changes, the control valve consisting simply of a valve seat tube 26, bellows 41 enclosed by a case 28, and a valve and valve stem, wherein the static pressure Pus and the dynamic pressure Pd are applied, respectively, to the inside and outside of the bellows, causing the static pressure Pus to change in proportion to the square of the shaft speed w as soon as U changes, thus accomplishing stable operation of the hydrodynamometer by using a simple construction to control the static pressure in proportion to the square of the revolving speed a).

The drawing show an example in which the control valve 27 is installed in the casing 3 but it will be readily understood that the valve can be placed in any location where it can control the discharge of water by sensing the static and dynamic pressure of the water.

Claims (8)

1. A hydrodynamometer comprising a rotatable blade wheel mounted between vanes fixed in a restrained, rotatably mounted casing to be driven against the action of a load generated on the wheel by a flow of liquid through the blade wheel casing wherein a valve means is provided to control the rate of discharge of the liquid from the blade wheel casing in proportion to the square of the revolving speed of the blade wheel.

2. A hydrodynamometer comprising a rotatable blade wheel mounted vanes fixed in a restrained, rotatably mounted casing, to be driven against the action of a load generated on the wheel by a flow of liquid through the blade wheel casing wherein a valve means is provided to control the rate of discharge of the liquid from the blade wheel casing in proportion to the dynamic pressure of liquid in the blade wheel casing.

3. A hydrodynamometer as claimed in claim 1 or 2 in which the liquid is discharged via an opening in the the blade wheel casing at the periphery of the blade wheel and through a passage disposed radially with respect to the blade wheel, the valve means being disposed downstream of said opening and connected with said opening by said passage.

4. A hydrodynamometer as claimed in claim 3 in which the valve means comprises a valve member having a valve slidable in a valve case to contract and expand a bellow mounted in the case, the valve case is communicated with the blade wheel casing via a radial passage opening into the periphery of the blade wheel casing and the interior of the bellows is communicated with the blade wheel casing via a tangential passage opening into the periphery of the blade wheel casing.

5. A hydrodynamometer as claimed in Claim 4 in which the blade wheel has peripheral fins which extend radially on each side of the opening to said tangential passage.

6. A hydrodynamometer as claimed in claim 4 or 5 in which said valve casing is vented to atmosphere via an adjustable flow control valve.

7. A hydrodynamometer as claimed in claim 4, 5 or 6 in which the interior of said bellows is vented to atmosphere via an adjustable flow control valve.

8. A hydrodynamometer substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.