BACKGROUND OF THE INVENTION
1. Field Of The Invention
The invention relates to a bistable electromagnetic valve (1) having a valve chamber arranged between two pole pieces and a valve body displaceable between two end pistons which is designed as a magnet armature for at least one permanent magnet and at least one control coil which novel valve includes a dirt filter (18,19).
2. Description of the Related Art Including Information Disclosed under 37 C.F.R. 1.97 and 1.98
Prior art valves of this type are used, for example, in refrigerant circuits of the kind described in publications DE 37 18 490 or EP 10 54 200.
In such valves, a bistable situation is achieved by arranging permanent magnets outside the valve housing, next to the valve chamber or next to the pole pieces, so that the valve body has two end positions at the pole pieces, in which it is held by these permanent magnets.
Stringent requirements are placed on such valves in terms of tightness and long-term stability. After manufactured at the production facility, the valves are generally incorporated into the refrigerant circuit at another facility, making it difficult to determine the cause of any malfunction.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is therefore to provide a valve, in particular for a refrigerant circuit, which is less susceptible to faults.
This object is achieved proceeding from a valve (1) having a valve chamber arranged between two pole pieces and a valve body displaceable between two end pistons which is designed as a magnet armature for at least one permanent magnet and at least one control filter which novel valve includes a dirt filter (18, 19).
The measures specified in the following description of the invention including drawings and dependent claims enable advantageous embodiments and further developments of the invention.
Accordingly, the invention is distinguished by the fact that the novel valve encompasses a dirt filter.
The invention is hence based on the knowledge that malfunctions are often caused by dirt that enters the valve after installation in the refrigerant circuit. According to the invention, the dirt filter prevents this dirt from reaching the critical locations of the valve, i.e., the area of the valve body and its seal seat.
The dirt filter is advantageously arranged on the inflow side of the valve chamber in the valve housing. In this way, dirt is reliably prevented from entering the critical components, i.e. the valve body and valve seats or the entire valve chamber containing the valve body, after the fluid circulation has been completed, since only cleansed fluid can get into the valve chamber.
The dirt filter is advantageously situated immediately adjacent to a pole piece for this purpose. This position represents the arrangement lying closest to the valve chamber for a dirt filter separate from the valve chamber, so that all fluid that gets into the valve chamber during startup of the fluid circuit is actually largely filtered.
A dirt filter according to the invention can be permanently installed into the valve casing, i.e., so that it only be replaced with the entire valve or not at all, provided the filter capacity is sufficient for a one-time cleansing of the fluid circuit.
Filters in fluid circuits are usually designed in such a way as to be replaceable or washable, since the filters become clogged over time. However, the invention is based on the additional knowledge that, when this type of valve is always used in circuits that generally remain closed for the life of the valve, the dirt filter can be permanently installed in the valve. However, this filter must here exhibit a filter capacity sufficient for a one-time cleansing of the entire fluid in the circuit.
Since no more dirt accumulates on the filter after this one-time cleansing, clogging can be prevented, so that the filter need not be replaced or cleaned.
In a further development of the invention, a magnetic dirt filter is provided. A magnetic dirt filter is able to retain magnetic or magnetizable dirt particles, such as those that are rinsed away from the inner wall of the tubes of the refrigerant circuit, or can get inside the circuit during assembly of the fluid circuit, e.g., via soldering. Precisely these magnetic or magnetizable dirt particles are especially critical with respect to malfunctions, however, since they stay behind in the valve chamber if no measures are taken to trap them in advance owing to the permanent magnets required for the bistable design, permanently impairing the tightness of the valve there, while at the same time increasing the wear.
A magnetic dirt filter is especially effective if in direct contact with fluid. For this reason, a permanent magnet is arranged inside the valve housing or inside its connecting line in a particularly advantageous embodiment of the invention.
In a further development of this embodiment, an annular magnet is provided as the dirt filter. Annular magnets are inexpensive to buy, and exhibit a large surface loadable with dirt particles while being readily mountable inside a circular tube, wherein a sufficiently high flow cross-section is simultaneously available for the fluid, e.g., refrigerant.
In another embodiment of the invention, a mechanical filter is provided, either alone or in combination with a magnetic filter. A mechanical filter is also able to retain nonmagnetic or non-magnetizable dirt particles, and hence provide for a more complete cleansing of the refrigerant.
It is particularly advantageous to combine a mechanical filter with magnet filter situated upstream relative to the direction of flow, since preliminarily filtering the magnetic or magnetizable dirt particles reduces the load on the mechanical filter, so that it can be given smaller dimensions.
In an advantageous embodiment, the magnet filter is simultaneously used as a mount for the mechanical filter, so that a separate mount need not be provided at the location of the magnet filter.
In particular when combined with an annular magnet, the mechanical filter is preferably designed as a tubular sieve. Such a tubular sieve can have attached to it an annular magnet, for example, which tightly abuts the inner wall of the inflow to the valve chamber. This fixes the tubular sieve in place on the one hand, and seals the inflow cross-section outside the tubular sieve via the annular magnets on the other, so that fluid can only flow into the tubular sieve.
In particular when combined with the aforementioned features, the interior space of the tubular sieve is connected with the inflow of fluid, e.g., the refrigerant, and the exterior space of the tubular sieve is connected with the valve chamber. The retained dirt particles here accumulate inside the tubular sieve, wherein magnetic or magnetizable particles are already retained at the permanent magnet, as indicated above.
The sieve holes of such a mechanical filter are designed with a diameter measuring between 50 μ and 80 μ, for example. Tests performed on valves in refrigerant circuits showed this type of magnetic filter configuration to be a particularly favorable design in terms of good filtering properties and sufficient flow.
In addition to enabling an arrangement (viewed in the direction of flow) in front of the valve chamber as described above, the use of a tubular sieve as the mechanical filter makes it possible to chose a high enough filter capacity by providing the tubular sieve with a corresponding axial length.
Further, the filter capacity of a tubular sieve can be improved by appropriately configuring the cross-section, specifically by making the cross-section larger. For example, such a tubular sieve can be designed with a corrugated or folded cross-section.
One particularly advantageous embodiment is a tubular sieve with a star-shaped cross-section, since a uniform all-around flow can be established here with a good surface enlargement.