US2865624A

US2865624A - Devices sensitive to rotational speed

Info

Publication number: US2865624A
Application number: US631924A
Authority: US
Inventors: Skellern John
Original assignee: D Napier and Son Ltd
Current assignee: Napier Turbochargers Ltd
Priority date: 1956-01-13
Filing date: 1956-12-31
Publication date: 1958-12-23
Anticipated expiration: 1975-12-23
Also published as: GB832195A

Description

Dec. 23, 1958 J. SKELLERN 2,365,624

DEVICES SENSITIVE TO ROTATIONAL SPEED Filed Dec. 31, 1956 I ATTORNEYS United States Patent.

John Skellern 'Northolt England assignor a n. N ler a Son Limited, London, Englalid, a British compai l y- Application December 31, 1956, Serial No. 631,924

Claims priority, application Great Britain January 13, 1956 8 Claims. (Cl. 264-14) This invention relates to rotary speed sensitive devices of the kind which provide a fluid pressure or pressures which vary in accordance with the rotational speed of a member, which is hereinafter referred to for convenience as the rotary member.

For such purposes it is common practice to use a rotary pump; either of the positive displacement type in which case the volumetric output of the pump varies as a function of the rotational speed, and may be used to derive the required pressure signal by being passed through a valve or restriction; or of the centrifugal type in which case the fluid pressure derived from the pump itself varies approximately as the square of the speed of rotation. All such devices however suffer from the disadvantage that they are sensitive to the temperature, density, and viscosity of the fluid, and it is an object ofthe invention to provide an improved speed sensitive device which is substantially unaffected by changes in viscostiy, temperature or density.

A rotary speed sensitive device therefore according to the present invention comprises a centrifugal mass connected to a rotary member whose speed is to be measured to rotate therewith and having its centre of gravity displaced from the rotary axis of the rotary member with at least limited freedom of movement in a substantially radial direction, the radial outer and inner surfaces of the mass being arranged in separate fluid chambers, while the mass itself is arranged to operate valve mechanism controlling the pressure in at least one of said chambers automatically to balance the centrifugal forces acting on the mass, and including means for obtaining an indication of the differential fluid pressure acting on the mass between its 1 inner and outer surfaces respectively.

The device preferably includes pressure sensitive devices with pressure sensing heads arranged at approximately the same radial displacement from the rotary axis as the inner and outer surfaces of the centrifugal mass.

According to a preferred feature of the invention the valve mechanism comprises at least one valve port the effective opening of which is controlled by a part of the centrifugal mass itself, the port being of relatively narrow width in a radial direction but of relatively great length in a transverse direction so as to limit the range of radial movement of the mass in a radial direction.

Moreover the effective opening of the valve port as provided by the two cooperating parts is preferably of tapered form and of progressively decreasing length in relation to its width so as to provide a degree of damping on the movement of the centrifugal mass.

According to another preferred feature of the invention the centrifugal mass is mounted in a radial bore in a rotary support, and the port is formed in a wall of the bore closely adjacent to the periphery of the rotary support.

Thus the valve port may be conveniently of a shape formed by the intersection of a chord with a circumference of a circle, the chord being a machined flat On the periphery of the rotary support while the circumferential 2,865,624 Patented Dec. 23, 1958 ICC member subsequently attached to the support.

In any case the device preferably "includes means for providing a continuousfluid flow from the outer to the inner pressure chambers, and the valve mechanismacts as a variable restriction to control the dilferen tial'pressure acting between the inner and outer surfaces of the centrifugal m'ass.

It will be understood that theinner end of the mass preferably lies approximately on the rotary axis of the rotary member, and the device includes a central conduit on the axis of this member and means for sensing the pressure in this conduit. 7 3

Thus according to another aspect of the invention, a rotary speed sensitive device comprises a rotary support, preferably of cylindrical form, connected to rotate with the rotary member whose speed is to be measured, the support having one or more radial bores therein, each bore being opened at its outer end, and communicating at its inner end with a central small bore conduit coaxial with the support, a centrifugal mass forming a substantially fluid-tight seal with walls of each radial bore in the support, and free to move radially therein, the outer edge of each mass cooperating with a valve port formed in a side wall of the respective boreto control the flow of fluid therethrough, this port communicating with the central conduit, a cylindrical casing surrounding the rotary support, means for supplying fluid to said casing, and for withdrawing fluid continuously from the central conduit, and means for obtaining pressure signals responsive respectively to the pressures in the central conduit, and

edge of the port'is provided by a thin circular hoop-like in the casing at a radius substantially equal to the radial- Figure 3 is an enlarged detail scrap sectional view of the. valve port, as seen in Figure 2.

The present example is particularly applicable to hydraulic governor devices controlling the speed of a prime mover such as an internal combustion engine..

The device comprises a stationary casing 10 having substantially fluid tight seals 11, 12 in opposite end walls through which runs a rotor shaft 13 which is coupled at one end to the shaft of the prime mover (not shown). The shaft 13 is formed integral with a cylindrical rotor 14 which lies within the casing, the dimensions of the rotor being such as to provide a small clearance on both sides and around the periphery thereof. The rotor is formed with a diametral bore 15 of circular cross section, two

parallel bores

16, 17, and three

transverse bores

18, 19, 20. One end of the rotor shaft 13 is formed with a central drilling 21 which communicates with the midpoint of the diametral bore 15 in the rotor, and

this central drilling 21 communicates with a

pressureverse pins

32, 33, fixed to the rotor and passing through over-size holes in the masses. The outer surfaces of each of the centrifugal masses are each recessed to provide an upturned lip 34 at the edges thereof as seen in Figure 3. Fluid control ports 35 are provided closely adjacent to the outer periphery of the rotor at opposite sides of both ends of the diametral bore, and arranged to cooperate with the lips 34 formed on the centrifugal masses to constitute a fluid control valve. The two ports at each end of the diametral bore communicate through the

parallel bores

16, 17, and the transverse bore 19, with the central conduit 21 in the rotor shaft. Each port 35 is located as close as possible to the outer periphery of the rotor and conveniently therefore each port is formed by milling a flat 36 on the circumferential surface of the rotor, which is then surrounded by a hoop of thin sheet metal 37. The hoop is cut away at the ends of the diametral bore 15, to provide apertures in which the outer ends ofthe

masses

30, 31, can slide, and in which they are a substantially fluid tight fit. lt will be seen that this construction provides two control ports 35, at each end of the bore 15. Each port has somewhat greater radial dimensions at its centre and tapers at the edges to a narrow width slot, and

this construction automatically provides a degree of hydraulic damping as referred to below, and also provides that relative small radial movements of each

mass

30, 31 will alter the port opening from its fully closed to its fully open position.

Fluid is supplied continuously to the interior of the cylindrical casing through a conduit 40 from some suitable source such as a variable delivery pump (not shown) and means are provided for obtaining a high pressure signal from within the casing. To this end a small open mouthed pipe 41 extends through the outer circumferential wall of the easing into one of the clearance spaces between the rotor and the adjacent end wall of the casing, the pipe terminating in an open month which is spaced radially from the axis of the rotor by the same distance as the control ports 35 in the rotor 14. This pipe 41 passes through the wall of the easing and communicates with a high pressure signal line 42 leading to the second side of the pressure indicating device 24, which in this example is a differential pressure instrument indicating the diflerence in the pressures in the high and low signal lines 42 and 23.

The fluid pressure in the chamber 22 will act on the end of the shaft 13, and the fluid pressure forces in an axial direction on the rotor will be out-of-balance. To remedy this, the end of the shaft 13 within the chamber 22 is secured to dished flange 44 having a rim lying close to the adjacent end wall of the chamber. The space 45 between this flange 44 and the end wall is subject to a relatively high pressure from fluid which passes from the interior of the casing 10 along the shaft 13. A limited axial movement is allowed to the shaft, to provide for variations in the clearance between the rim of the flange 44 and the adjacent end wall, and this rim therefore acts as an automatic relief valve, controlling the pressure in the chamber 45 so as to balance automatically the end load caused by pressure in the chamber 22. i

In operation the fluid which is delivered continuously to the casing through conduit 40 passes through the control ports 35 into the central conduit 21 in the half shaft, and thence through the pressure chamber 22 and the restricted aperture 25 to relief. When the rotor is rotating the

centrifugal masses

30, 31 tend to fly outwards under centrifugal force and thus tend to restrict the cross section of the control ports 35 thereby restricting the flow of fluid to the central conduit 21 in the rotor shaft and so controlling the pressure acting on the inner end of the centrifugal masses. The outer surfaces of the centrifugal masses are subject to the pressures in the casing (which will also have a centrifugal component) while their inner surfaces are subject to the rela tively low pressure in the central conduit 21, and the control ports will be restricted progressively until the pressure acting on the outer surfaces of the centrifugal masses is balanced by the controlled pressure acting on the inner end of the centrifugal masses plus the centrifugal force acting on the masses. In practice the centrifugal masses will adopt a mean position in which the flow through the control ports is restricted to a value which will provide a differential pressure between their inner and outer surfaces which exactly counterbalances the effects of centrifugal force. The range of movement in a radial direction of the centrifugal masses is extremely small owing to the narrow width in a radial direction and relatively great length of the control ports. The fluid pressure on both the inner and outer faces of each centrifugal mass will of course itself vary with the radial speed owing to the centrifugal effect of the rotation on the fluid itself, but any such variations is minimised by the restriction on the radial movement of the mass, by the arrangement of the low pressure and high pressure signal lines, and also by the relatively low density of the fluid and consequent small force component in relation to that of the centrifugal masses. Thus the central conduit 21 in the rotor shaft which communicates with the centre of the diametral bore 15 in the rotor provides a low pressure signal at 23 which is in effect the mean of the pressures on the axis of rotation and on the wall of this conduit 21 and the centrifugal masses are so dimensioned that their inner surfaces lie closely adjacent to the rotational axis. Thus the pressure in this central conduit is substantially identical to the fluid pressure acting on the inner surfaces of the masses. Similarly the high pressure signal pipe 41 extending into the interior of the casing provides a high pressure signal which is substantially identical with the pressure acting on the outer surfaces of the masses, since the mouth of this pipe is at the same radial displacement from the radial axis. In order to ensure that the high pressure signal is identical to the high pressure acting on the outer surfaces of the masses in some cases the rotor may be provided with radial vanes to ensure that the whole of the fluid within the casing is rotating at the same speed. In some cases the whole casing may be made to rotate.

It will be understood that the centrifugal force acting on the centrifugal masses varies purely as the square of the speed of rotation, and since this centrifugal force is counterbalanced only by the differential pressure acting on each centrifugal mass the differential pressure between the low pressure and high pressure signals also varies purely as the square of the speed of rotation. Thus, at \any given rotational speed any change in the temperature, density or viscosity of the fluid will merely result in a change in the required opening in the control ports to maintain the required differential pressure. Any such change in the opening of the control ports, however, even a relatively great change in area, can be obtained by infinitely small radial movements of the masses, so that the differential pressure as derived from the high pressure and low pressure signal lines is substantially unaltered.

In the example described an unrestricted supply of fluid is fed to the rotor casing via conduit 40 at a pressure which may be constant or may be variable, while the flow from the low pressure chamber 22 takes place through a restriction 25. The valve mechanism controls the flow of fluid through the valve ports 35 so as to vary the pressure in the central conduit, that is to say in the low pressure side of the system, relative to a given fluid supply pressure substantially inversely as the square of the rotational speed.

In an alternative construction a restriction may be provided in the high pressure fluid supply line 40 to the casing, while the flow from the low pressure chamber will be unrestricted, for example connected direct to a fluid sump, or to atmospheric pressure. In this case with hydraulic liquid, for example engine oil, and may be supplied from the same oil presstire line which supplies lubricating oil to the prime mover. This is particularly convenient since the lubricating oil makes the device substantially self-lubricating. It will be understood however that the device may also be used withother fluid such as fuel oil or paraflin, and it is contemplated that itmay be used with gases such as compressed air. Where the same device is used with fluids of widely different densities and viscosities and it may be necessary to alter the dimensions of some of the parts, or it may be sufficient merely to alter the area of the restricted aperture between the low pressure receiving chamber and relief so as to reduce the total flow through the device for fluids of greater density.

What 1 claim as my invention and desire to secure by Letters Patent is:

l. A rotary speed sensitive device comprising a rotary support formed wtih a substantially radial guide, a centrifugal mass connected. to the support to rotate therewith, and having its centre of gravity displaced from the rotary axis of the Support, and having at least limited freedom of movement along said guide, the radial inner and outer surfaces of the mass lying in separate fluid chambers, and including valve mechanism operated by said centrifugal mass and controlling the pressure in one of said chambers automatically to balance the centrifugal forces acting on the mass, and including means sensitive to the differential fluid pressure between the inner and outer surfaces of said mass, including pressure sensitive devices with pressure sensing heads arranged at approximately the same radial displacement from the rotary axis as the inner and outer surfaces of the centrifugal mass.

2. A rotary speed sensitive device as claimed in claim 1 in which the valve mechanism comprises at least one valve port the effective opening of which is controlled by a part of the centrifugal mass itself, the port being of relatively narrow width in a radial direction but of relatively great length in a transverse direction so as to limit the range of radial movement of the mass in a radial direction.

3. A rotary speed sensitive device as claimed in claim 2 in which the profile of the valve port when viewed in a direction parallel to the axis of rotation is of tapered form and of progressively decreasing length at increasing radial displacement from the axis of rotation so as to provide a degree of damping on the movement of the centrifugal mass.

4. A rotary speed sensitive device as claimed in claim 3 in which the profile of the valve port is of a shape formed by the intersection of a chord with a circumference of a circle.

5. A rotary speed sensitive device as claimed in claim 4, in which the rotary support is of generally cylindrical external shape, and is provided with a flat, and including a thin circular hoop-like member attached to and surrounding the rotary support, and forming with the surface of the flat the said valve port.

6. A rotary speed sensitive device as claimed in claim 1 including means for providinga continuous flow of liquid from the outer to the inner pressure chambers, and in which the valve mechanism acts on a variable restriction in the flow path so as to control the differential pressure acting between the inner and outer surfaces of the centrifugal mass.

7. A rotary speed sensitive device as claimed in claim 1 in which the inner end ofthe mass lies approximately on the rptary axis of the rotary member and in which one of th ptgessure sensing heads also lies on the rotary axis and is connected to a central drilling on the axis of this the rotary member, and including means for sensing the pressure in this drilling.

83A rotary speed sensitive device comprising a rotary support connected to rotate with the rotary member whose speed is to be measured, the support having two or more radial bores therein, each bore being open at its outer end, and communicating at its inner end with a central small bore conduit coaxial with the support, a centrifugal mass in each radial bore forming a substantially fluid-tight seal with the walls of each radial bore, and free to move radially therein, the inner edge of each mass lying approximately on the axis of rotation and the outer edge of each mass co-operating with a valve port formed in a side wall of the respective bore to control the flow of fluid therethrough, this port communicating with the cen-' References Cited in the file of this patent UNITED STATES PATENTS 409,524 Thornycroft Aug. 20, 1889 1,791,028 Huff Feb. 3, 1931 2,324,191 Bowers July 13, 1943 2,416,110 Mallory Feb. 18, 1947 2,521,736 Mallory Sept. 12, 1950 i FOREIGN PATENTS 317,414 Great Britain Aug. 12, 1929