Fluid-control System Comprising A Viscosity Compensating Device

Abstract

Fluid-control system comprising fluid-control means having a positive viscosity-resistance characteristic the flow resistance of which increases with an increase in viscosity, and further comprising vortex means having a negative viscosity-resistance characteristic the flow resistance of which increases with a decrease in viscosity to compensate for changes in the flow resistance of the fluid-control means due to changes in fluid viscosity. The vortex means is provided with a circular hollow chamber, a tangential nozzle connected to a source of incompressible and viscous pressure fluid, and a central output port connected to the fluid control means.

Description

This invention relates to a fluid-control system, comprising a viscosity compensating device adapted to compensate for changes in the viscosity of a viscous fluid flowing through the control system, so that the operative characteristics of the system may be kept constant.

Generally, since the viscosity of a viscous fluid, and in particular of an incompressible fluid such as oil, flowing in a fluid-control system, is affected by changes in temperature, the flow rate in the control system, and particularly in constricted portions of fluid passages, is affected, and therefore pressure in the system is changed. Thus, there is danger that the control system may not operate correctly and reliably. In particular, fluid-control systems comprising a plurality of pure fluid control elements are greatly influenced by changes in the viscosity of the viscous fluids used as operative fluids. A "pure fluid control element," as used herein, comprises a chamber enclosed by sidewalls, and a main nozzle from which the fluid, hereinafter referred to as a "main jet," is introduced, at high speed, into the chamber. Output ports in the chamber receive the main jet. Control nozzles deflect the main jet, so that the output ports are supplied with the main jet in different proportions. Pure fluid control elements of this kind may be classified as belonging to one or the other of two types, depending on the conditions controlling the deflection. One type is an element deflecting the main jet proportionally to the input to the control nozzle, and is called a jet deflection proportional amplifier. The other type is a wall-attachment amplifier wherein the deflected condition is maintained stable by the wall-attachment or Coanada effect. In both types the jet speed and flow rate of the main jet are affected by changes in the viscosity, if constant fluid pressure is supplied to the main nozzle. Thus, the pressure and flow rate in the output port are changed. Consequently, in a jet deflection proportional amplifier, the gain is changed. As a result there is danger not only of incorrect operation in the fluid-control system but also of lowering the reliability of the operation. In the wall-attachment amplifier, substantially the same characteristic change as in the jet-deflection proportional amplifier is produced, so that the main jet is not always deflected by the same constant control input. In order to avoid such conditions it is desirable that the temperature of the operative fluid be maintained constant so that the viscosity remains unchanged. However in this case an additional thermostat is required at the pressure fluid supply source, which results in volume and weight increases and complication in the control system. Particularly for vehicles, small size and light weight in the control system are strongly required. Therefore it is difficult to keep the temperature of the operative fluid constant. Thus, a simple viscosity compensating device is required, which has no undesirable effects on the operative characteristics of the control system, even when the viscosity of the operative fluid is changed by changes in the temperature thereof.

The primary object of this invention is to provide a fluid-control system comprising a simple and effective viscosity compensating device.

Another object of the invention is to provide a fluid-control system comprising fluid control means having a positive viscosity-resistance characteristic and vortex means having a negative viscosity-resistance characteristic which compensates for changes in the viscosity of the fluid in the fluid control means.

The foregoing and other objects of the present invention will become fully apparent from the following description of a preferred embodiment of said invention with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of the plate 1 of a viscosity compensating device connected to a wall-attachment element according to the present invention as seen from the left of FIG. 2, with the plate 2 removed;

FIG. 2 is a side elevation of the device shown in FIG. 1; and

FIG. 3 is a cross-sectional view showing a vortex-type element used to describe its theoretical operation.

DESCRIPTION OF THE INVENTION

Generally, a pure fluid control element such as a wall-attachment element utilizing two dimensional flow is not actuated until the Reynolds number in its main nozzle becomes larger than a specified value.

Now the Reynolds number in substantially two dimensional flow is as follows.

Re =2V. Ws. t/.nu.(Ws +t) (1) where

Re=Reynolds number

Ws=Width of main nozzle

t=height of main nozzle

v=average flow speed in main nozzle

.nu.=coefficient of kinetic viscosity.

As is apparent from the above equation (1), Re becomes a function of v, that is, Re becomes larger with an increase in v, when the main nozzle of the identical size and the identical operative fluid are used. It is, however, uneconomical to increase Re more than required to increase the quantity of fluid used in fluid control system. Thus, it is desirable to set Re within a preferable range, but as previously mentioned, the viscosity of the fluid changes considerably with changes in temperature, and thus Re is influenced by .nu.. Re changes with a change in .nu., even if v is constant. Thus, in order to keep Re constant, it is preferable to change v in direct proportion to the change in .nu..

Flow rate in two dimensional flow is as follows:

Q=Ws. t.sup.3 .DELTA.p/12..mu.. l (2) where

i Q=flow rate

Ws=width of main nozzle

t=height of main nozzle

.DELTA.p=pressure difference across the nozzle

.mu. =coefficient of viscosity

l =length of the nozzle. Thus, flow rate Q changes with a change in pressure difference .DELTA.p. In a pure fluid control element, the pressure downstream of the main nozzle is approximately constant, and thus the change in flow rate Q is substantially equal to the change in pressure upstream of the main nozzle. Therefore, in order to keep the Reynolds number Re constant, the pressure upstream of the main nozzle may be changed in direct proportion to the change in viscosity.

If the fluid flow in the main nozzle is a steady flow, the flow resistance is as follows.

R=.DELTA.p/Q where

R=flow resistance

.DELTA.p=pressure difference across the main nozzle

Q=flow rate from equation (2) Thus, the flow resistance R increases with an increase in the coefficient of viscosity .mu., and vice versa. This positive viscosity-resistance characteristic is hereinafter referred to as a positive characteristic.

As shown in FIG. 3, a vortex amplifier comprises a cylindrical vortex chamber, a tangential supply port, and a central output port. When fluid is introduced from the supply port into the vortex chamber, fluid issues from the output port following a vortex path in the vortex chamber. The pressure drop in the vortex chamber is given as a function of the radial distance from the center of the vortex chamber.

Generally, vortex flow may be characterized by the tangential velocity-radial distance relationship

v.phi.r.sup.n=constant= K.sub.2

or v.phi.=K.sub.2 r.sup.-.sup.n (5) where n is a parameter determined by the viscosity of the fluid and practically

-1<n<+1 from equations (4) (5) For an incompressible fluid, .rho. is constant and equation (6) integrates to the general form where C.sub.1 is a constant of integration. If the pressure at r=0 is P.sub.1, C.sub.1 =P.sub.1 equation (8) gives the pressure drop in the vortex chamber. Further

P-P.sub.1= QR (9) where

Q=flow rate in the vortex chamber

R=flow resistance in the vortex chamber. Substituting equation (8) into equation (9) gives When n=-1, that is, viscosity is zero, flow resistance R.sub.1 is as follows. When n=+1, that is, viscosity is infinite, flow resistance R.sub.2 is as follows. As is apparent from the above equations (11) (12), R.sub.1 >R.sub.2. Thus, the flow resistance increases with a decrease in viscosity, and vice versa.

This negative viscosity-resistance characteristic is hereinafter referred to as a negative characteristic.

Thus, the connection of the vortex-type element to the pure fluid control element causes the vortex element to automatically regulate the supply pressure or flow rate to the pure fluid element to keep the Reynolds number in the main nozzle of the pure fluid element constant, even if the viscosity of the fluid in the pure fluid element is changed.

Referring now to FIGS. 1 and 2, a wall-attachment element 20 is illustrated as a representative pure fluid control element. A vortex type element 10 is connected to the wall-attachment element 20 upstream thereof. The vortex-type element compensates for changes in the viscosity of fluid in the wall-attachment element. A flat plate 1 is recessed to form both the wall-attachment element and the vortex-type element, and is tightly sealed to a flat plate 2.

The vortex type element 10 comprises a circular chamber 12, a tangential nozzle 14 and a central output port 15. The nozzle 14 is connected to a pressure fluid supply source (not shown) through a supply port 11.

The wall-attachment element 20 is provided with a main nozzle 23, a pair of control nozzles 24 and 25, a chamber 22 and a pair of ducts 28 and 29. The main nozzle 23 extends at one end into the chamber 22 and communicates at the other end with a supply port 21 connected to the output port 15 of the vortex-type element 10. The control nozzles 24 and 25 extend from opposite sides into the chamber 22 at substantially right angles to the main nozzle 23, and are respectively connected to control ports 33 and 34. The chamber 22 is divided into the two ducts 28 and 29 by a divider 30. A pair of vent passages 31 and 32 open respectively into the ducts 28 and 29 downstream of the chamber 22. The ducts 28 and 29 are respectively connected to output ports 26 and 27.

Operative fluid having a certain viscosity, for example, an incompressible fluid such as oil, and supplied through the supply port 11, enters along the wall 13 into the chamber 12 through the nozzle 14, following a vortex path. This vortex flow decreases the pressure in the center of the chamber 12 and this pressure decreases as the radial distance from the center decreases. The higher the flow speed in the nozzle is, the stronger the vortex flow becomes, and the pressure in the central output port 15 therefore becomes lower and the flow resistance in the chamber 12 is increased. When the viscosity of the fluid is decreased, the viscous resistance of the fluid is decreased, so that the vortex flow in the chamber 12 increases to increase the flow resistance. Inversely, the viscous resistance of the fluid increases with an increase in the viscosity thereof, so that the vortex flow in the chamber is decreased to reduce the flow resistance. Thus, the connection of a vortex-type element to a pure fluid control element such as the wall-attachment element permits the vortex-type element to compensate for changes in the viscosity of the fluid in the wall-attachment element.

The fluid from the output port 15 of the vortex type element 10 issues into the chamber 22 through the supply port 21 and the main nozzle 23. This main jet adheres to one of walls 35 and 36 in the chamber 22. This phenomenon is called the wall-attachment effect or Coanda effect, by which deflected condition is maintained stable. Assuming that the main jet issues initially from the left output port 26, if a control flow is introduced into the control nozzle 24, the main jet is deflected to the right and then adheres to the wall 36 in the chamber 22. Thus the main jet continues to leave from the right output port 27 until a control flow is introduced into the control nozzle 25. Under one stable condition, the greater part of the main jet is supplied to the next device to be operated through the left output port 26, while under the other stable condition, the greater part of the main jet is supplied to the next device through the right output port 27. The next device is operated in response to the difference in momentum between the control flows supplied to the control nozzles 24 and 25.

Vent passages are required to maintain the deflected condition stable even when the loads exerted on the output ports 26 and 27 are increased.

The main jet, when in a stable condition, is responsive to jet speed in the main nozzle, the shape and size of the main nozzle, and the viscosity of the main jet and is usually designed to that the Reynolds number in the main nozzle is more than 4.times.10.sup.3 . The Reynolds number Re is given by equation (1) and changes with any change in the viscous resistance in the hydraulic circuit without compensation for such change. Thus, the entrainment characteristic of the main jet is changed, which causes a change in the time required for switching between deflected conditions. Consequently, the flow rates and pressures in the output ports 26 and 27 are changed. However, as previously described in detail, the vortex element 10 connected to the main nozzle 14 serves to compensate for such conditions, in response to changes in fluid viscosity, and thus automatically regulates the pressure and flow rate of fluid supplied to the main nozzle.

Thus the vortex element serves to maintain the Reynolds number in the main nozzle constant. Consequently, the operative characteristic of the hydraulic circuit is kept stable, and is unaffected by changes in fluid viscosity, which results in increased accuracy and reliability in the control of the hydraulic circuit.

While the vortex element is connected to a wall-attachment element in the above embodiment, the vortex element may be applied to a jet deflection proportional element or like element, and almost the same effect may be obtained. Further while the vortex element is applied to one pure fluid control element in the above embodiment, the vortex element may be applied to a plurality of pure fluid control elements. In this case, the vortex chamber and tangential nozzle of the vortex element are designed to compensate for the viscosity changes of all the pure fluid elements.

It is desirable to provide suitable means such as an enlarged passage portion or foraminous screen in the connecting passage between the output port of the vortex element and the supply port of the pure fluid element for dissipating the vortex flow in the connecting passage.

While the invention has been described in terms of one specific embodiment, it should be understood that the novel characteristics of the invention may be incorporated into other structural forms without thereby departing from the spirit and scope of the invention, as defined in the following claims.

Claims

What is claimed is:

1. A fluid-control system comprising fluid control means having a positive viscosity-resistance characteristic, and vortex means having a negative viscosity-resistance characteristic connected in series, said vortex means comprising a circular chamber, a single tangential nozzle adapted to be connected to a source of incompressible and viscous pressure fluid and a single central output port connected to said fluid control means, whereby any change in the viscosity of the fluid flowing in said system which causes a change in the flow resistance of said fluid control means produces a compensating change in the flow resistance of said vortex means.

2. A fluid-control system as claimed in claim 1, wherein said fluid control means comprises at least one pure fluid control element.

3. A fluid-control system as claimed in claim 2, wherein said pure fluid control element is a wall-attachment element comprising a main nozzle connected to the output port of the vortex means to deliver a main jet, control nozzles downstream of said main nozzle on opposite sides of said main jet for deflecting the path of said main jet and output ports positioned to receive the deflected jet.

4. A fluid-control system as claimed in claim 2, wherein said pure fluid control element is a jet deflection proportional element comprising a main nozzle connected to said output port of the vortex means to deliver a main jet, control nozzles downstream of said main nozzle on opposite sides of said main jet for deflecting the path of said main jet, and output ports positioned to receive the deflected main jet.