DE19518089A1 - Fluid injector for gas- or hydrostatic-bearings having passive control - Google Patents

Abstract

An injector for a fluid bearing has a passive-control construction whose response is determined by the interaction of a spring spider (2, 3) whose centre (3) moves to regulate the control gap (5) with variable damping promoted by pressure differences.The fluid path during operation commences at the protective housing (9) in the chamber (7) from where it passes through the pierced apertures (8) in the spider (2, 3) to the ring channel (6), the control gap (5) and thence via the central bore (10) to the bearing gap (11).The dynamics of the system are such that a combined response to proportional, integral and differential components of change is obtained.

Description

The invention relates to a nozzle for a with a pressure medium (Fluid) supplied storage, usually aerostatic or called hydrostatic bearing.

The fluid is supplied to such bearings via nozzles or throttles, and relaxed in the nozzles to a pressure that is clearly below the supply pressure.

This results in a pressure increase in the gap when the gap is narrowed, because the throttling effect of the gap relative to the throttling effect of the Nozzle increases and the increase in pressure results in the stiffness of the Camp.

A number of different designs have proven themselves as nozzle shapes, (Capillary tubes, short nozzles with a conical inlet section and very short chokes, d. H. thin sheets with holes).

All of these nozzles typically have the disadvantage of small bores about 0.1 mm with the requirement for high uniformity of the Pressure-flow characteristic, which is difficult to achieve. The constant geometry creates further disadvantages because of changed ones and especially not dynamic loads or only can be counteracted insufficiently.

Elastic regulating nozzles have also been known for a long time, (more precisely it should read: with elastic deformations from the Pressure difference, the flow regulating nozzles), for hydrostatic Bearings that are installed in a supply line.

From now on, these are referred to as control nozzles.

Because of the large designs in the known control nozzles and because of the elasticity in the feed channels to the warehouse the known constructions work with hydrostatic Only limited storage, and only in the case of aerostatic bearings special cases.

Such a regulating throttle device is, for. B. in the Patent specification DE 35 33 037 described.

Due to their size, they are installed in a supply line for the fluid required with a clear distance to the camp, so that the  unavoidable elasticities of the flow spaces and the fluid still allow use in hydrostatic bearings, but make their dynamic behavior bad, while a Use in aerostatic bearings because of the occurring self-excited vibrations is hardly possible.

Another regulating throttle device is from DE 31 44 788 known.

Although this is intended for aerostatic applications, it has as well as the above-mentioned regulating throttle device serious disadvantage of a large design and a very large one Dead volume and thus the vibration risk of the bearing. This is the only reason why this vibration hazard does not apply because the masses in the described application in measuring machines very high and therefore the natural frequencies are very low.

Other regulating throttle devices are e.g. B. from open documents DE 34 11 625 and 31 44 788 and 31 50 117 and 28 29 787 and 24 56 032 and 32 15 972. These all have the serious disadvantage that they are for the rapid regulation are unsuitable because of their structure have large dead spaces which make fast regulation impossible make and a risk from instability vibrations produce.

Even the constructions built into the bearing body itself are still too far from the gap and much too large dead spaces for satisfactory behavior.

Furthermore, none of the known nozzles - neither the passive nor the elastically regulated -, properties as they are used to generate - Control engineering desired and for quick reactions necessary - integrating and differentiating reinforcements required are.

Regardless of the type of nozzles, fluid bearings are known Effect of low frequency instability due to dead volume before Nozzles at the transition into the gap, which is very precise Transition required. The permitted size of this dead volume is  in typical gas warehouses around 1 cubic millimeter per 20 cm² Storage area.

It is also known that when the bearing is loaded due to the strong non-linear flow characteristic of the increasing Gap share increases the fluid flow, so that the Supply units can be designed significantly more powerful than would be necessary for the unloaded case.

It is also known that the achievable stiffness is essentially is defined by the gap width, so that extreme requirements Dimensional accuracy and dimensional accuracy must be provided.

It is also known that because of the stiffness and the resulting small gap width the power loss Unacceptable even with gas storage in the case of extremely high speeds get high and because of the thermal strains generated from it the function and the quality is at risk.

It is also known that because of the high precision in nozzles and Gap manufacturing costs for fluid bearings are quite high.

It is also known that in a stepped version of the storage Area with different trench structures the damping of the Camp together with the associated connection units in one favorable frequency range, but often because of large dead volumes lead to instabilities which are optimal Prevent interpretation.

It is also known that fluid bearings speed limiting Have high-frequency instabilities, which are called half-frequency vortices be designated. This can be done through constructive measures shifted to high speeds, there was a general remedy but so far not.

All of these quality limiting characteristics apply to Unregulated and passively regulated pressure medium supply so far known design.  

In principle, a lot can be improved with actively controlled nozzles be, but the effort to be driven, not only for nozzles and Control amplifiers and controls, but also for Security expenditure is very large.

All of these serious limitations and disadvantages should be overcome optimal design can be overcome as far as possible.

According to the invention, this is achieved in that a passive Control mechanism is integrated into the nozzle itself, which in a meaningful combination proportional, integrating and contains differentiating proportions.

This control mechanism is operated by the pressure of supplied fluid and fluid in the gap and sets with fastest possible positioning speed the best flow and Throttle values.

This is caused by an in the nozzle in the extreme bearing gap integrated throttle gap, which is between a spring and creates a variable throttling effect on the nozzle body, one side of the supply pressure, the other side of the Bearing gap pressure is applied, so that the pressure difference the throttle gap between the supply line and the bearing gap is adjusted. The throttled fluid is such. B. through a hole in Nozzle base body fed to the bearing gap, the volume of the Fluids and the distance between the outlet of the throttle gap and Entrance of the bearing gap must be small, so that the throttle gap must be realized in the immediate vicinity of the warehouse gap.

This control mechanism offers the option of all of the above to influence the mentioned disadvantages extremely positively. According to the invention, this is an extremely small design in Combination with an extremely high natural frequency and an extreme Installation close to the gap required.

The static and dynamic dimensioning supports the achievable good properties and allows extremely high Realize positioning speed.  

For this, the use of the squeeze film damper effects is Control movement and, if necessary, the bearing gap for optimization of the dynamic properties required.

So far this has not been known with any passive construction possible because of the functionally similar looking control units passive nature for hydrostatic bearings because of the Elasticities mostly not as intended and in the case of gas storage at all not work, and extremely quick in regulating Failures fail.

The main advance of the control nozzle lies in the effects, from their small size and the proximity of the pressure consumer result, as well as from the use of differentiating and integrating mechanisms resulting from the use of the Squeeze film effects.

From the smallness it follows immediately that the moving masses in the Nozzle are very small and therefore the control mechanism up to very high frequencies is effective, and thus a possibility for the first time exists to passively regulate the high-frequency instabilities remove.

As long as the resonance frequency of the control nozzle or its first Cutoff frequency (resulting from stiffness and damping) is significantly above the speed at which the high-frequency instability occurs as long as regulates the Regulating nozzle the pressure fluctuations from that with unhindered The effect of instability fanning.

This design as a fast controller with natural frequencies far above the resonances of the stored system can only due to the extremely small size and the installation directly on the Realize gap.

From the proximity to the pressure consumer (this is the bearing gap) follows also immediately that somewhat larger dead volumes because of the Possibility to quickly and drastically increase the flow in are provided with target pressure in the shortest possible time and thus the Low frequency instability is also corrected. However, this does not go so far that the extreme  large dead volumes of the known controllers would be allowed. The delay time with which this occurs with classic nozzles Dead volumes are replenished (to their respective target pressure after a quick change in the gap width), this Delay time is one of the causes of instability.

Since the control nozzle in the "completely open" state is typically 10x has less resistance than in the nominal operating point (the at Gap setpoint is present), it can also the dead volumes fill up accordingly faster.

This should be ensured by designing the flow areas be that in the state "completely closed" the control gap is closed, but there is still sufficient flow, e.g. B. by engraved trenches.

The flow in the throttle and damper gap can be useful between parallel walls, this is special simple to manufacture, or slightly tapered so that the Flow rate remains approximately constant or over a Ring edge.

With targeted use of those permitted with this control nozzle larger dead volumes and the squeeze film damping effect on both sides The spring is the mentioned possibility of targeted influencing the damping of the natural vibration of the control nozzle and the stored one Rotor present.

Since the gap surface is defined from geometry and load capacity and the gap width from the stiffness remains conventional in one throttled camp little freedom in the design of the Damping film damping of the bearing.

In contrast, storage with the inventive control nozzle is in Considerable in terms of their damping in many other areas. This possibility can be further expanded if except regulated outlets on the inlet of the bearing can be provided with control nozzles.  

Compared to non-regulated bearings is a whole essential further characteristic of storage with the control nozzles described here also the possibility either increase the stiffness with the same gap width or to achieve the same stiffness with a larger gap width or something to benefit from both.

So far, there has been no possibility of this in gas warehouses.

As a desired, very important side effect in fast warehouses is also the power loss due to the larger gap width smaller, thus the heating is smaller and thus the storage more precise or the thermal speed limit is higher.

The bearing also has another important characteristic Control nozzles use less pressure medium so that the pressure supply can be designed weaker and the noticeably reduced costs for the operation of the warehouse become.

This positive characteristic results from the fact that the Control nozzle in the area of large gap of the bearing gap Resistance regulates so high that only a little pressure medium flows.

In contrast to the conventional bearing, which under load The stock with control nozzles has increased consumption Burden therefore a smaller consumption.

Another advantage of the control nozzle according to the invention is state that the cost of the nozzles themselves will not increase but rather lower because of the requirements for extreme tolerance and quality of the nozzle in the area of the flow cross-sections omitted and the quality requirements in the control gap of the nozzle a lot are easier to implement.

Since controllers generally try to achieve good control quality achieve, which requires a high control gain, are regulated structures at risk of instability if at higher frequencies phase rotations greater than 90 degrees and Reinforcements greater than 1 are present.  

It is therefore necessary to amplify at higher frequencies lower.

This is the case with passively regulated fluid bearings known to date not known and not possible, so that there Risk of instability small due to relatively small reinforcements must be kept.

With the control nozzle proposed here, the Lowering the gain at high frequencies both over the integrating effect of the volume of the outflow bore and achieve similarly acting pocket structures of the gap, and especially about the squeeze film damping effect of the Back of the spring.

The squeeze film effect of the back of the feather - on a small scale also the squeeze film effect of the spring front in the throttle gap reduces spring mobility at higher frequencies, thus acts as an integral gain of the controller.

In addition, it is extremely desirable to have a controller To give differential gain in a suitable Frequency range acts as a damper.

This can be done in the control nozzle proposed here the coupling of the fluid displacement in the bearing gap at gap change over the resulting from the squeeze film effect of the Bearing gap generated pressure increase and the resulting spring Reach bend.

With a clever design, the control nozzle can be purely passive as complete PID controller act, and thus optimal function with Combine secure stability and inexpensive construction. This is not possible with the known constructions, since the pressure created in the bearing gap via the squeeze film effect much too long or voluminous supply lines largely dismantled is and therefore cannot influence the regulator membrane in a meaningful way.

A typical embodiment of a control nozzle according to the invention consists of a spring and one by the spring directly or indirectly modified throttle.

The spring is typically a flat resilient element, e.g. B. from  Sheet etched, which is also a seal on one side takes over function.

The spring also serves as a pressure sensor, because on yours one side is under pressure and on the other side is Nip pressure, so that from the pressures and the associated areas an actuating force results, which deflects the spring and the Control gap changed in the desired way.

The spring also serves as a pressure surface for the design the squeeze film damping effect on both sides of the spring. Large damping effects can be achieved through large areas and through achieve small gap widths.

The sealing surfaces of the control gap are usefully with a defined roughness, curvature, skewness, waviness or with defined microscratches or trenches, in order also in total current state to achieve a flow.

The spring is usefully installed between the nozzle body and protective body, which both make sense largely rigid be formed.

The protective body serves to protect the spring from damage and if necessary or useful also as a filter.

Overall, the control nozzle according to the invention is a component of typically one to ten millimeters in diameter and becomes immediate used on the supply channel of the fluid to the bearing gap, just like it is known from passive gas storage nozzles.

A preferred embodiment of the control nozzle according to the invention is shown in FIG. 1.

The real diameter is typically in the range 1 to 10 mm Length is approximately equal to 1/2 to 1 times the diameter.

A plan view of a possible design of the spring is sketched in FIG .

Part ( 1 ) means the nozzle body, which is pressed, glued or screwed into a bore in the bearing.

Part ( 2 ) is the part of the spring that is firmly connected to part ( 1 ).

The spring, consisting of outer fixed part (2) and inner movable part (3) is changed upon movement of part (3), the gap (5) between the nozzle base body (1) and inner movable spring member (3).

The spring is attached to its fixed part ( 2 ) with the aid of a spacer ring ( 4 ) on part ( 1 ), for. B. glued. Of course, part ( 4 ) can also be realized as an adhesive gap of defined thickness.

The fluid first flows through the protective body ( 9 ) on the way to the bearing; this can be designed as a filter; after passing through the protective body ( 9 ), the fluid flows into the chamber ( 7 ) then through the openings ( 8 ) of the spring into the ring channel ( 6 ), in order to then pass through the control gap ( 5 ) and through the bore ( 10 ) the bearing gap ( 11 ) to be forwarded.

On the side of the spring facing away from the control gap there is a surface of the protective body ( 9 ) at a close distance in order to produce the squeeze film damper effect for damping the natural vibration of the spring.

The diameter of the basic nozzle body ( 1 ) or the protective body ( 9 ) is sensibly somewhat larger than the spring in order to protect the spring from tension.

The control gap ( 5 ) is not completely sealed by scratches or grooves or geometric structures that are at least partially oriented in the direction of the flow, even when the inner movable spring part ( 3 ) is in full contact with the nozzle body ( 1 ), but typically allows 20% of the nominal flow to flow through .

Another preferred embodiment also contains or only a filter on the downstream side of the control nozzle.

This eliminates the hole ( 10 ) and the downstream filter can take on additional throttling and damping functions.

Another preferred embodiment is outlined in FIG. 3. In this embodiment, the control nozzle consists only of spring ( 12 ) and protective body ( 13 ) and the control nozzle is installed in the bearing so that the spring is only slightly behind the surface of the bearing gap on the housing side.

In Fig. (4) the associated spring is shown. The very narrow gaps ( 14 ) take on the throttle function. They must be made significantly smaller than the spring thickness.

The holes ( 15 ) serve to reduce mechanical stresses and are not absolutely necessary.

The minimum flow is given by the length and width of the column ( 14 ), possibly supplemented by the flow through the bores ( 15 ).

The control effect is generated by changing the column ( 14 ) in the direction perpendicular to the spring surface with increasing pressure load on the spring on the bearing gap side.

This spring also consists of the clamping edge ( 16 ), the spring arms ( 17 ) and the inner movable part ( 18 ).

In the state of the bearing gap at maximum, the spring is flat, as shown in cross section in FIG. 5, so that the throttling effect through the gap ( 14 ) is at a maximum.

As the bearing gap becomes smaller and the bearing pressure rises, the spring deforms increasingly into the state as shown in FIG. 6. As a result, the gap length effective in the flow direction in the gaps ( 14 ) becomes shorter, the throttling effect decreases and the bearing pressure increases as desired.

The proportional gain of the control nozzle results from the Spring stiffness of the spring and the geometry of the nozzle gap and the storage gap.

The differential gain results from the pressure increase due to the squeeze film effect in the bearing gap and the spring stiffness the feather.

The integral gain results from the squeeze film effect of the Spring on the protective body.

The differential gain should be at low if possible Frequencies act to achieve effective damping.  

The integral gain should only be used at high frequencies use, but low enough to gain before reaching Stability-threatening phase shifts to a value smaller than lower 1.

Overall results when using the invention Control nozzle a better and cheaper bearing in all aspects.

Claims (14)

1.Control nozzle for a fluid bearing with spring and differential pressure controlled throttle effect characterized by a miniaturized design with a diameter of less than a quarter of the shaft diameter for radial bearings and less than a quarter of the bearing diameter for axial bearings and an installation instead of the usual fluid bearing nozzles passive bearings directly on Transition to the bearing gap. 2. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claim 1 marked by a proportional gain from spring action and throttle gap and a differential gain from the squeeze film effect of the Bearing gap with the spring action. 3. Control nozzle for a fluid bearing according to claim 1 or 2 characterized by a flat or almost flat spring with Breakthroughs which serve as flow channels. 4. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttling effect according to claims 1 to 3 marked by an integral gain from the squeeze film effect of the column one or both sides of the spring. 5. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claims 1 to 4 marked by a filter at the inlet and / or outlet of the control nozzle.   6. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttling effect according to claims 1 to 5 marked by a filter at the inlet and / or outlet of the control nozzle and with extremely small gap positioned adjacent to the spring. 7. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claims 1 to 6 marked by Use of a spring surface with the nozzle body as a throttle gap and the second spring surface with a further surface than Damper gap. 8. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claims 1 to 7 characterized by a version without bearing body and Use of the openings and column of the spring as a throttle column and installation of the bearing-side spring surface almost immediately flush with the bearing surface. 9. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claims 1 to 8 characterized by plane-parallel or slightly tapered or ring-shaped throttle gaps and / or damper gaps. 10. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claims 1 to 9 marked by an outflow without an outflow channel through a filter on the Outflow side.   11. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claim 10 marked by a filter made impermeable in the throttle gap area. 12. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claims 1 to 11 marked by a ratio of the stiffness of the spring to its moving mass by at least a factor of 2 higher than the stiffness of the bearing stored mass. 13. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claims 1 to 12 marked by an attachment in the bearing body with a clear axial distance of the feather. 14. Control nozzle for a fluid bearing with spring and differential pressure Controlled throttle effect according to claims 1 to 13 marked by a not completely sealed throttle gap due to Misalignment, scratches, ditches, scoring or ripples in the direction of the current or at an angle to it.