FR2602837A1 - DEVICE FOR INFLUENCING THE FLUID FLOW BEHAVIOR IN A FLOW SECTION, A DAMPER FOR EXAMPLE - Google Patents

Abstract

THIS DEVICE INCLUDES MEANS ALLOWING TO GENERATE, IN THE FLOW SECTION 8, VIBRATIONS WHICH ARE SUPERIMPOSED LIKE A GRADIENT OF AMPLITUDE SPEED DEFINED IN THE FLUID SPEED FIELD, IN WHICH IS LOCATED THE FLOW SECTION 8. DEVICE INCLUDES A VIBRATION GENERATOR, ESPECIALLY IN THE FORM OF A PIEZOELECTRIC OSCILLATOR 13 WHICH PRODUCES RADIAL OR AXIAL VIBRATIONS IN THE FLOW SECTION 8. THE VISCOSITY OF THE LIQUID IS THUS CHANGED, WHICH AT THE SAME TIME CHANGES THE DAMPER CHARACTERISTIC .

Description

The invention relates to a device for influencing the behavior of

  flow of fluids in a flow section located in a velocity field. Such a device is

known (GB-A 21 11 171).

  This known device is used with a rheological or liquid liquid with variable behavior, and an electrical device is provided in a passage passing through a piston, or in an annular space between a piston and the wall of the cylinder of a shock absorber, or apart from it, an electric device 10 which makes it possible to influence the rheological behavior of the liquid. We thus obtain the change of the characteristic

damping of the shock absorber.

  The disadvantage is that the electrorheological effects are too weak for most applications and there is still no rheological fluid which is thermally stable.

  For example, when the mechanical energy has to be dissipated in the damper, the rheological fluid heats up and becomes mechanically weaker. Changes in the external temperature also modify the behavior of the rheological fluid. The effective electrical power losses rise exponentially with the temperature and thus produce a further increase in temperature. The need for electrical power

  piloting becomes quickly prohibitive.

  The invention aims in particular to avoid the disadvantages mentioned above.

  According to the invention, a device for influencing the flow behavior of fluids in a flow section located in a speed field, is characterized by means

  for generating, in the flow section, vibrations which are superimposed as a defined amplitude velocity gradient at the velocity field of the fluid.

  One of the advantages of such a device is that variations in temperature have no influence on the stability of the liquid and sufficient liquids are available with sufficient dilatancy.

  Other characteristics and advantages of the invention will emerge more clearly from the following description of a nonlimiting exemplary embodiment, as well as from FIG.

  unique of the accompanying drawing, which is a schematic axial section of a damper. A damper 1, forming part of a vehicle suspension whose other elements are not represented,

  comprises a cylinder 2 in which a piston 3 can move.

  It is secured to a piston rod 4 whose free end 5 protrudes outside the cylinder 2. The end 5 of the piston rod and the cylinder 2 of the damper are fixed to parts of the vehicle moving relative to each other

  during movements of the suspension of the vehicle.

  The cylinder 2 contains two working chambers 6 and 7 which are separated by the piston 3 and are filled with a damping fluid with dilatancy. This fluid has a viscosity that can be changed with the flow section 8 between the outer lateral surface of the piston 3 and the inner wall of the cylinder 2. Preferably, the fluid has a viscosity which increases with the shear rate at which the fluid is subjected. The flow section 3 can be changed because the middle part 13 of the piston 3 is in the form of a planar piezoelectric oscillator, that is to say which oscillates in its own plane, radially with respect to the damper axis of this example. For this purpose, two end plates 9 and 10 of the piston are made as electrodes which are

  connected to an alternating current source 14, located on the outside, by two conductors 11 and 12 passing through the upright rod 4.

  The lower working chamber 7 is delimited at the bottom by a compensation volume 15, filled with gas, with the provision of a separation piston 16 between the working chamber 7 and this

compensation volume.

  During the operation of the damper 1, the fluid flows from a working chamber 6 or 7 into the other through the flow section 8. The latter constitutes a resistance to flow. This resistance can be modified by changing the diameter of the piston by means of the piezoelectric oscillator 13, which creates a shear gradient of small amplitude. This shear gradient is printed or superimposed on the fluid passing through the flow section 8, as a result of the movement of the piston 3 in the cylinder 2, in particular

at the speed of this fluid.

  It is also possible to use a sonic or ultrasonic field to change the flow section 8, directly or by means of the piezoelectric oscillator 13, and thus change the shear gradient accordingly. Unlike the exemplary embodiment shown, where the vibrations produced by the oscillator 13 are oriented radially, the shear gradient can also be created by a piezoelectric oscillator which oscillates in the direction of its thickness and which generates

  therefore vibrations in the axial direction.

  An important point is that, according to the invention, overall shear gradients are created, depending on the amplitude, in the range of high viscosity variations.

  fluid and that the damping characteristic of the damper 1 can thus be changed.

  Other examples of application of the invention are: 1. throttling flow rates in hydraulic systems, for example for controlling proportional control valves or servo valves; 2. controlled hydraulic couplings; and

3. controlled cylinders.

R E V E ND I C AT I 0 N S

  A device for influencing the flow behavior of fluids in a flow section located in a velocity field, characterized by means for generating, in the flow section (8), vibrations which are superimposed as a gradient of amplitude speed defined in the field

of fluid velocity.

  2. Device according to claim 1, characterized in that the means for generating the vibrations in the flow section (8) are constituted or controlled by a sound field

or ultrasound.

  Device according to Claim 1 or 2, characterized in that the means for generating the vibrations in the flow section (8) comprise a piezoelectric element, in particular in the form of a planar oscillator (13) or in the form of a planar oscillator (13).

  an oscillator that oscillates in the direction of its thickness.

  4. Device according to any one of claims 1 to 3, characterized in that the fluid used is a fluid

  with dilatancy, whose viscosity increases with the shear gradient.

  5. Apparatus according to any one of claims I to 4, characterized by its application in an annular slot (flow section-8) between a piston (3) and a cylinder (2) receiving the piston, the vibrations generated in the flow section (8) being oriented radially or axially.

  6. Device according to any one of claims 1 to 5, characterized by its application to a damper (I)

a vehicle suspension.