Fluid handling – Line condition change responsive valves – Thermal responsive
Utility Patent
1998-11-03
2001-01-02
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Line condition change responsive valves
Thermal responsive
C137S501000
Utility Patent
active
06167904
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a hydraulic valve with a housing, having an inlet connection and an outlet connection with a hollow space between them, in which a valve slide is arranged to reciprocate, and, depending on its position, sets a flow cross section between the inlet connection and the outlet connection more or less free.
A hydraulic valve of this kind is known from DE 43 41 848 A1. A similar embodiment is found in DE 195 07 086 A1.
In such hydraulic valves the problem is to synchronise the valve slide correctly in relation to the surrounding wall in the hollow space. It would be ideal, if the valve slide could slide with practically no play in the housing, as then a very good sealing would be provided. However, such an embodiment can only be realised in theory. In practice, temperature and pressure fluctuations cause deformation of the valve slide, for example an increase in its diameter, which leads to a jamming. Then the valve slide cannot move any more. The valve loses its function. To avoid such a jamming, valves of this kind are dimensioned so that the valve slide is arranged in the housing with a relatively large play. A disadvantage in this connection is, however, that the valve is not “tight”, that is, relatively large amounts of hydraulic fluid can flow from the inlet connection past the valve slide to the outlet connection. Further, a certain hysteresis cannot be avoided, which is caused by the fact that in some cases the valve slide will get stuck anyway because of an expansion. Particularly in valves having a high control frequency, that is, in which the valve slide reciprocates relatively fast, the friction of the valve slide produces a relatively high heat load, which again involves the risk of a thermally conditioned expansion, which again can lead to a jamming. The same problem also occurs, when a relatively high pressure rules in the valve slide, in the state of the art defined to be a hollow cylinder, which pressure presses the valve slide outwards towards the wall of the hollow space.
SUMMARY OF THE INVENTION
It is the task of the invention to improve the operational behaviour of the valve.
In a hydraulic valve as mentioned in the introduction, this task is solved in that the valve slide is surrounded by a bush, which is arranged to be radially expandable in the hollow space.
Thus, the valve slide no longer bears direct on the housing. On the contrary, a bush is arranged between the housing and the valve slide in a way that the bush can expand radially without being obstructed by the housing. In this connection it is considered that a temperature increase, which causes an enlargement of the valve slide diameter, will also cause a similar enlargement of the bush diameter. As, however, the bush can expand, these mutual enlargements can relatively reliably prevent a jamming. The same applies for an expansion caused by an increased pressure in the hollow space, which can in many cases also influence the inside of the valve slide. Also here the diameter increase of valve slide and bush can be synchronous, so that this constructively relatively simple measure can prevent a jamming of the valve slide in the housing. Accordingly, the play between valve slide and bush can be made relatively small. Tests have shown that, all other conditions being unchanged, the leakage rate can be reduced to 20%, and additionally, the hysteresis inclination could be seen to be reduced.
Preferably, the housing has, at least in the area surrounding the bush, a larger flexibility than the bush, for example, it is softer or more resilient in this area. When the bush expands, for instance caused by a temperature increase, this is possible, as the housing cannot provide a sufficient resistance against this expansion. The same applies for expansions caused by an increased pressure inside the bush. Also here the bush can expand without being obstructed by the housing.
Alternatively or additionally, the bush can be floatingly supported in the housing. The “floating” support means that in the circumferential direction the bush is supported by a fluid cushion. If required, this cushion can be interrupted by sealings surrounding the bush in the circumferential direction and being arranged in one or several positions in the axial direction. The fluid cushion, which is normally subjected to a certain pressure, provides on the one hand that the bush is supported radially from the outside. On the other hand, however, it also permits a certain radial expansion, as long as the expansion forces are larger than the forces caused by the pressure, which is regularly the case.
Preferably, the housing is made of plastic. Most plastics can be dimensioned so that they have the desired flexibility. Additionally, plastics have the advantage, that they are relatively simply produced by moulding, particularly injection moulding, so that also complicated channel arrangements can be realised in the housing without causing drastic increases in the production costs. Further, a plastic housing can be made so that with little production effort and a high accuracy it can admit the bush, in a way that a play in the radial direction between bush and housing can to a large extent be prevented. This improves the operational behaviour of the valve.
In this connection it is particularly preferred that the bush is made of a metal. It is assumed that a metal has a lower resiliency than the plastic. With equal forces the metal bush will thus expand less than the plastic housing. However, this condition is what is wanted. As, during an expansion the metal bush will absorb most of the forces acting in it, be it pressure forces or expansion forces caused by a temperature increase, the load on the plastic of the housing will be kept relatively low.
Preferably, at least a part of the length of the housing surrounding the bush is surrounded by a reinforcement ring, inlet pressure acting between the reinforcement ring and the housing. A reinforcement ring of this kind will always be expedient, when the housing is made of plastic, as often a plastic does not have the required mechanical stability. Thus, the housing is additionally supported mechanically by the reinforcement ring, at least on part of the length, in which also the bush is arranged. Further, the support can be additionally improved when inlet pressure is ruling in this area, that is, between the housing and the reinforcement ring. Then the hydraulic fluid, which is submitted to inlet pressure, also supports the housing radially from the outside. This makes the valve particularly suited for the use of water as hydraulic fluid.
In this connection it is particularly preferred for a sealing to be arranged between the bush and the housing, which sealing separates an inlet pressure area from an outlet pressure area, the hollow space in the outlet pressure area having an inside diameter, which is increased in relation to the outside diameter of the bush. When hydraulic fluid under inlet pressure, which is normally higher than the outlet pressure, is ruling radially from the outside, the housing is in danger of getting deformed radially inwards in this area, as on the inside only the outlet pressure is ruling. A deformation of this kind can be permitted, if initially an increased hollow space has been provided to prevent such a choking of the housing from exerting a radially inwards acting force on the bush. In this case the pressure exerted on the housing radially from the outside is insignificant. This embodiment has the additional advantage that the bush gets even more free, so that the limits on its deformability are steadily getting wider, meaning that the behaviour of the bush in connection with an expansion is in fact practically determined exclusively by the bush itself.
Preferably, the sealing between the bush and the housing lies closer to an end of the bush than a sealing between the housing and the reinforcement ring. Thus, the inlet pressure can still act upon the housing. This gives rise to some sort of lever formed between the two sea
Nielsen Helge B.
Sand Hans Christian
Danfoss A/S
Hepperle Stephen M.
Lee Mann Smith McWilliams Sweeney & Ohlson
LandOfFree
Hydraulic valve does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydraulic valve, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydraulic valve will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2521021