EP0795884A2 - Pressure switch - Google Patents

Abstract

A pressure switch for washing machines or dishwashers, for example, should be able to actuate at least one switch very precisely with high force at only low pressures. The membrane-operated pressure switch has a spider (12) with lever arms (12a), (12c) and (12d). A lever arm (12d) supports the spider (12) when the switch is actuated in a direction which is at least approximately opposite to the direction in which the spider (12) is pressed down by a force (M). <IMAGE>

Description

The invention relates to a pressure switch with at least one switch that can be actuated against a pretensioning force, a spider having two or more lever arms, into which a force is introduced in a first direction in order to use the lever arms to overcome the pretensioning force as a function of the switch or switches The magnitude of the force introduced and thus to be operated selectively depending on the pressure.

Such pressure switches, for example known from EP 0 347 904 B1, are also referred to as "pressure monitors". They serve to actuate at least one, usually two or more electrical switches depending on a pressure to be monitored. If the pressure to be monitored increases, the switches are operated selectively one after the other at certain, preselected pressures. Such multiple pressure switches are usually operated with a membrane, i.e. the pressure to be monitored generates a force on the membrane with which the switches are actuated.

Such membrane-operated switch arrangements, in which switches, in particular pretensioned mechanical snap switches, for electrical signals or load currents depending on one pressure applied to the membrane are used in many practical applications to control and regulate devices such as washing machines and dishwashers. The membrane is loaded with a pressure that is derived from the water level in the working area of the device. In this application, the pressure switch acts as a "pressure switch" and measures the height of the water column in the machine.

In technically advanced washing machines and dishwashers, relatively low water levels are set during a washing program to reduce water consumption. The consequence of this is that, with the same size of the pressure switch (and the same membrane area), only relatively small forces are available for switching the pressure switch. In addition, advanced washing machines or dishwashers or comparable devices to save energy and water consumption also require very precise switching points depending on the pressure, both when the pressure rises and when the pressure drops. Small hysteresis are also sought.

To explain the concept of the invention, the closest prior art will first be examined with reference to FIGS. 1 to 3 in order to derive the problem on which the invention is based.

1 shows an exploded view of individual components of a pressure switch, namely a lower housing part 10, a so-called spider 12, a plate 14, a membrane 16 and a cover 18. These components are mounted in or on the lower housing part 10 in the order mentioned. The membrane 16 together with the cover 18 forms a pressure chamber in which there is a pressure which is derived from the water level in the machine (when used in a washing machine, for example). In a manner known per se, the pressure derived from the water level is generated in the pressure chamber by means of an air trap. The pressure is transferred via a pressure port 20 into the pressure space between the membrane 16 and the cover 18.

Switches are arranged in the lower housing part 10 (the individual switches are also referred to in the prior art as "switching systems".

The pressure acting on the membrane 16 from above is transmitted via the plate 14 and its central pin 22 into a recess 24 which is formed centrally in the spider 12. The depression 24 is therefore the location of the spider 12 at which a force corresponding to the membrane pressure is introduced into the spider 12. The spider 12 is supported on its underside at its lever arm ends (see also FIG. 2). The spider 12 is supported on the individual switches it actuates via mandrels 28 which protrude upward at the free ends of the switch springs 26 and each engage in a recess 30 at the end of a lever arm of the spider 12. Instead of the trough, a surface or a trench, depending on the function, can also be provided. 1 shows a single switch I in the lower housing part 10 by way of example. FIG. 2 shows a top view of the lower housing part 10 with three switches I, II and III.

Each switch is biased into a position according to FIG. 1 by means of a spring 32. The spring 32 thus acts as a compression spring. It presses the free end 38 of the switch spring 26 in FIG. 1 upward against a nose formed on the lower housing part 10. The lower part of the housing is made of plastic.

The spreading force of the spring 32 is adjustable by means of a clamping screw 34. At the other end of the switch spring 26, the switch contacts 40 to be switched are arranged. The switch spring 26 is clamped approximately in the middle at a point 42 and is designed such that when the spring end 38 moves downward in FIG. 1 against a stop 36, a contact body 44 moves from the upper to the lower contact of the switch contacts 40 and thus either a signal or a load current is also switched directly. In the pressure switches in question, load currents flow with a considerable current (for example 12 A or greater).

In a manner known per se, protrusions 46, 48 projecting downward from the membrane 16 are formed, which engage in assigned recesses 50, 52 in the plate 14 in order to ensure a central force transmission by means of the pin 22 into the central recess 24 in the spider 12 .

Depending on the pressure acting on the membrane 16 and thus on the actuating force transmitted to the spider 12, forces are transmitted to the mandrels 28a, 28b and 28c of the three switches I, II and III according to FIG. 2. Each of the switches is biased into an open position (according to FIG. 1) by means of a spring 32.

The spider 12 distributes the force introduced centrally into the individual prestressed switches I, II and III via the mandrels 28a, 28b and 28c. Depending on the lever arms, the forces transmitted via the mandrels 28a, 28b and 28c are different. In the lever arms shown in FIG. 2, 43% of the force introduced into the spider 12 via the recess 24 is transmitted to the mandrel 28a of the switch I, while 33% of the force is applied to the mandrel 28b of the switch II and 24% of the force is applied to the Mandrel 28c of switch III are transmitted.

In the figures, corresponding or functionally similar components are provided with the same reference numerals, possibly distinguished from one another by an additional letter. Fig. 3 shows a pressure switch according to the prior art, in which only two switches I, III are provided instead of the three switches of FIG. 2. In the example shown in Fig. 3 above, the arm 12b of the spider does not operate a switch. Instead, the outer end of the arm 12b is supported on a stop 54 which is fixedly connected to the housing 10. This support of the spider 12 is necessary because the recess 24, in which the force is introduced into the spider 12, does not lie on the connecting line 56 of those points at which the force is transmitted to the switches via the arms 12a, 12c, ie the connecting line between the pins 28a, 28c of the switches I, III.

The force derived via the arm 12b is thus absorbed by the housing 10 and is not used to actuate a switch.

In the example of the prior art shown in FIG. 3, below, only the switches I and II are used, while the third arm 12c of the spider 12 is supported on a stop 54a which is fixedly connected to the housing 10, so that this pressure switch is also used much of the force introduced into the spider is uselessly lost.

Particularly in the case of the more advanced washing machines and dishwashers discussed above with very precise control in order to reduce water and energy consumption, low water levels must be detected and high currents switched in the process. The highest possible actuation forces for the switching systems are therefore required to maintain high contact forces when the switch is actuated and to be able to switch large load currents (e.g. 16 amperes). An increase in the membrane area to generate greater actuation forces for the switches would, however, have the disadvantage of increasing the pressure switch as a whole.

Starting from the prior art discussed above, the aim of the invention is to design the pressure switch described in the introduction in such a way that high actuation forces and the smallest hysteresis for the switches can be achieved without increasing the dimensions of the pressure switch even at relatively low pressures.

For this purpose, the spider is designed according to the invention so that it is supported when switching with at least one lever arm in a direction which is at least approximately opposite to the direction in which the force is introduced into the spider.

According to a preferred embodiment of the invention it is provided that, seen in the direction of the force introduction into the spider, the point of force application on one side of a connecting line between two points at which lever arms on switches act, lies and the point where the spider is supported with the other lever arm in the opposite direction, is on the other side of this connecting line.

Another preferred embodiment of the invention provides that the spider has at least one lever arm which, when the force is introduced into the spider after overcoming a free distance, meets a stop which is fixedly connected to the housing of the switch, and thus the spider during the subsequent actuation of switches supported on this stop.

A great versatility and adaptability of a given switch housing to different requirements with regard to the number and arrangement of the switches results in particular when the actuating force is introduced into the spider at a point which is at least approximately centric with respect to the force-generating, circular membrane.

Pressure switches of various structures can be realized with the inventive idea. The supporting lever arm of the spider and the switch-actuating further lever arms are preferably arranged in relation to one another and to the point of force introduction into the spider that one or more one-sided levers are formed and so the actuating forces for the switches are significantly greater than those in the spider initiated force.

The inventive concepts outlined above teach the use of a spider lever arm, with which the spider is supported in the opposite direction to the force application direction when actuating at least one switch. The geometry of the lever arms is chosen so that the above-mentioned goal of maximum force utilization is achieved. In the prior art, spiders of the type in question are known which have a lever arm which does not press a prestressed switch. The lever arms are not designed in the sense of the invention. They only serve to guide the spider and lift it immediately upon actuation of the spider, ie they do not absorb any forces in terms of supporting the spider according to the invention.

In the exemplary embodiment, the spider is designed so that the lever arm with which it is supported in the direction opposite to the force introduction direction is at least approximately at the location of the spider at which the actuating force is introduced into the spider. Other versions of the connection to the spider are possible.

If lever arms are mentioned above, this is to be understood functionally in relation to the acting force and torques and is not necessary in the sense of shaping elongated (thin) lever arms. The spider can also be a large, approximately plate-like structure. It is essential that the levers defined above are formed by the introduction of force into the spider on the one hand and the support points of the spider on the switches or the switch housing on the other hand.

Fig. 1 bis 3

oben erläuterte Druckschalter gemäß dem Stand der Technik;

Fig. 4

ein erstes Ausführunsbeispiel eines erfindungsgemäßen Druckschalters;

Fig. 5

ein weiteres Ausführungsbeispiel eines erfindungsgemäßen Druckschalters;

Fig. 6

drei Abwandlungen eines erfindungsgemäßen Druckschalters nach Fig. 4;

Fig. 7

drei Abwandlungen eines erfindungsgemäßen Druckschalters nach Fig. 5;

Fig. 8 und 9

weitere Ausführungsbeispiele von erfindungsgemäßen Druckschaltern.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawing. It shows or show:

1 to 3

Pressure switches according to the prior art explained above;

Fig. 4

a first exemplary embodiment of a pressure switch according to the invention;

Fig. 5

a further embodiment of a pressure switch according to the invention;

Fig. 6

three modifications of a pressure switch according to the invention according to FIG. 4;

Fig. 7

three modifications of a pressure switch according to the invention according to FIG. 5;

8 and 9

further embodiments of pressure switches according to the invention.

FIG. 4 shows a top view (corresponding to FIG. 2) of a first embodiment of a pressure switch according to the invention. In FIG. 4, the housing cover (FIG. 1, reference number 18), the membrane (FIG. 1, reference number 16) and the plate (FIG. 1, reference number 14) have been omitted, in order to look into the interior of the lower housing part 10 from above to release. The pressure switch is thus completed by adding a plate 14, a membrane 16 and a cover 18 according to FIG. 1.

In the exemplary embodiment according to FIG. 4, only two switches I and III are used, that is to say a so-called double pressure switch. In addition, overflow protection contacts known as such can be provided, but are not shown here in detail.

The pressure exerted on the membrane generates a force which is introduced into the central recess 24 of the spider 12 via a pin. In Fig. 4, this force is labeled "M". The force is perpendicular to the plane of the drawing. The force vector M points in the direction of observation (that is, from above into the drawing). Two arms 12a, 12c of the spider 12 extend approximately radially from the central force introduction point to spikes 28a and 28c of the two switches I, III. The spring-loaded mandrels 28a, 28c push the associated lever arms 12a and 12c in Fig. 4 axially upward, ie opposite to the direction of the force vector M. The resulting tilting moment on the spider 12 is absorbed by a further arm 12d, which deals with its supports radially outer end under a tab 58 protruding from the edge 10a of the lower housing part 10. In other words: in the top view according to FIG. 4 engages the radially outer end of the lever arm 12d under the tab 58 protruding radially inward from the housing edge 10a. The above-described tilting moment is thus absorbed on the spider 12 and the spider has a stable idle state in which no switch I, III has yet been actuated .

The spider 12 is therefore supported with the lever arm 12d in a direction on the tab 58 which is opposite (anti-parallel) to the direction of the force M. Therefore, on both sides of the connecting line 56 between the points at which the lever arms 12a, Press 12c on the assigned switch, two torques on the spider 12, which are in balance when the spider is not actuated.

ergibt. Da der zur Kraft M gehörende Hebelarm l₂ größer ist als der zur Kraft M₁ gehörende Hebelarm l₁, ergibt sich, daß die Kraft M₁, in Abhängigkeit von den gewählten Hebelarmen, deutlich größer ist als die Kraft M.Now increases the pressure across the membrane and correspondingly a greater force M is introduced at the point 24 into the spider 12 from above, so the levers 12a and 12c in Fig. 4 are pressed down (below the plane of the drawing) when the Forces of the springs (see FIG. 1, reference numeral 32) with which the switches I, III are biased are overcome. The spider 12 thus forms a one-sided lever, the lever forces acting on the mandrels 28a, 28c through the projections of the levers 12a and 12c on the connecting line 57 between the point at which the force M is introduced and the point at which the lever 12d is supported under the tab 58, are determined. A force M ₁ , which arises from the lever arms l ₂ and l ₁ shown in FIG. 4, acts (virtually) at the interface of the mentioned connecting lines 56, 57 ${\text{<figure-callout id="1" label="M" filenames="imgf0002.png" state="{{state}}">M</figure-callout>}}_{\text{1}}{\text{= M · l}}_{\text{2nd}}{\text{/ <figure-callout id="1" label="l" filenames="imgf0002.png" state="{{state}}">l</figure-callout>}}_{\text{1}}$

results. Since the lever arm belonging to the motor M L ₂ is greater than the force belonging to the lever arm ₁ M l _1, it follows that the force M _1, depending on the selected lever arms, is significantly greater than the force of M.

The force M ₁ is divided between the two switches I, III according to the lever arms a and b, the lever arms a and b each being the distance between the points at which the switches are pressed (mandrels 28a, 28c) from the connecting line 57 between the recess 24 and the tab 58 correspond. 4, the lever arm "a" is slightly longer than the lever arm "b". This means that, based on the dimensions shown in FIG. 4, the force acting on switch III is doubled and the force acting on switch II is approximately tripled. This makes it possible to influence the switching behavior and the switching sequence.

With the housing 10 remaining unchanged with the switches firmly positioned therein and the spider 12 remaining essentially the same, the force distribution can be varied simply by varying the point at which the lever arm 12d is supported on the tab 58.

4, very low switching values (low forces M) can be selected for both switches I and III, and the system as a whole has a very low hysteresis. The system is easy to adjust and very large load currents can be switched directly through the switches.

Fig. 5 shows a further embodiment of a pressure switch. In this exemplary embodiment as well, in accordance with the exemplary embodiment according to FIG. 4, the spider 12 is supported on the housing 10 with an arm 12d under the tab 58.

5 it is assumed that the switch III should switch at a very high water column (large force M). This could be achieved in that the pretensioning force of the switch III (cf. FIG. 1, spring 32) is chosen to be correspondingly strong. However, this leads to problems in the manufacture of switch III, in particular if it is a spring-loaded snap switch.

The principle of the invention explained in FIG. 4 enables the problem to be solved here in a simple manner to provide a very high switching force for the switch III. For switch I should apply that it should be operated with a relatively low switching force (as both switches according to FIG. 4).

5, a fourth lever arm 12e of the spider 12 is provided, which can be supported on a stop 60, which is fixedly connected to the housing 10. However, the radially outer end of the lever arm 12e is not supported in the rest position of the switch at the stop 60, but only when the spider 12 has already been depressed by the force M to such an extent that the switch I is closed. In the idle state, the arm 12e is still freely in the air without any support. Fig. 5 shows a section A-B at the bottom right. The radially outer end of the arm 12e is then at a distance "d" from the stop 60 in the idle state (depressurized). If the switch I is closed due to an increase in pressure and thus an increase in the force M and the pressure is increased further, the arm is supported 12e at the stop 60, and the spider 12 acts overall as a pressure switch according to the prior art described above with reference to FIG. 3, ie a part of the force M generated by the membrane is diverted into the housing via the stop 60 and only a relatively small part of the force is then available for depressing the lever arm 12c of the spider 12. This enables the desired high switching values (and correspondingly high water columns) to be achieved for switch III.

Fig. 6 shows three modifications of the embodiment of FIG. 4, wherein different pairs of switches are actuated in pairs, namely the switch pairs I-II, I-III and II-III. The examples in FIG. 6 are self-explanatory on the basis of the above description and the reference numerals.

FIG. 7 shows three modifications of the exemplary embodiment according to FIG. 5. In these exemplary embodiments, the switch combinations I-II, I-III and II-III are actuated selectively, a fourth arm 12e being provided, which follows Overcoming a free distance "d" is supported on a stop 60 so that a relatively large force (corresponding to a high water column) is required to actuate the open switch, which has not yet been actuated.

8 shows a further pressure switch according to the invention, which differs from the exemplary embodiments according to FIGS. 5 and 7 in that the stop 60 there is replaced by a switch. In the pressure switch according to FIG. 8, all three switches I, II and III are depressed by a respective associated arm 12a, 12b or 12c of the spider 12 against a biasing force, depending on the force "M". In this case, in the idle state of the spider 12, a spider arm, for example the arm 12b, is not yet supported on the associated mandrel 28b of the associated switch II. Rather, this arm must first overcome a distance "d" (analogue to FIG. 5, section A-B) until it strikes the mandrel 28b. This means that a very low switching force is effective for the switch I, so the advantage of supporting the spider 12 via the arm 12d under the tab 58 is fully given. With initially slowly increasing force M (and correspondingly low water column), switch I switches first and at the same time or shortly thereafter the previously free arm 12b is now supported on the associated mandrel 28b of switch II, so that switches II and III relatively high switching forces can be selected.

Fig. 9 shows that the invention can also be used with a 1-fold pressure switch. The arm 12e of the spider 12 is supported on a stop 60 fixed to the housing, and the arm 12d of the spider 12 is again threaded under a tab 58 on the housing edge 10a. The only switch I is actuated by the arm 12a, with a relatively large switching force. This enables a pressure switch that is very small in size, the point at which the switching force is introduced into the switch I does not have to be centered.

With the exemplary embodiments shown, the invention enables both selective and simultaneous switching of switching systems.

Claims (12)

Pressure switch with - at least one switch (I, II, III) which can be actuated against a pretensioning force, - A spider (12) having two or more lever arms (12a, 12b, 12c, 12d, 12e), into which a force is introduced in a first direction in order to use at least one of the lever arms to switch (s) (I, II, III) to be actuated selectively while overcoming the pretensioning force as a function of the magnitude of the force which is dependent on the pressure,
characterized in that
the spider (12) has at least one lever arm (12d) with which it is supported when the force is applied in a direction at least approximately opposite to the first direction. Pressure switch according to claim 1,
characterized in that
seen in the first direction, the point (24) of the introduction of force into the spider (12) on one side of a connecting line (56) between two points (28a, 28c) at which lever arms (12a, 12c) on switches (I, II, III) act, lies and the point (58) at which the spider (12) is supported with the further lever arm (12d) on the other side of the connecting line (56). Pressure switch according to one of claims 1 or 2,
characterized in that
the force in the first direction is introduced into the spider (12) from a pressure-actuated membrane (12) normal to the membrane surface. Pressure switch according to claim 3,
characterized in that the membrane (16) is circular and clamped at the edge in a housing (10) accommodating the switches (I, II, III). Pressure switch according to claim 4,
characterized in that
a force-transmitting plate (14) is arranged between the membrane (16) and the spider (12) and introduces the force into the spider (12) with a central pin (22). Pressure switch according to one of the preceding claims,
characterized in that
the spider (12) has at least one lever arm (12e) which, when the force is applied after overcoming a free distance (d), hits a stop (60) and thus supports the spider (12). Pressure switch according to one of claims 4 or 5,
characterized in that
the force is introduced into the spider (12) at a point (24) which lies at least approximately on the central axis of the circular area. Pressure switch according to one of the preceding claims,
characterized in that
the force with which at least one of the switches (I, II, III) is actuated is greater than the force which the spider (12) applies to the switching system, preferably at least 1.3 times greater. Pressure switch according to one of the preceding claims,
characterized in that
at least one switch (I, II, III) which can be actuated against a pretensioning force by means of arms (12a, 12b, 12c) extending from the force introduction point (24) of the spider (12) is provided. Pressure switch according to one of the preceding claims,
characterized in that
At least two switches (I, II, III) which can be actuated against a pretensioning force by means of arms (12a, 12b, 12c) extending from the force introduction point (24) of the spider (12) are provided. Pressure switch according to one of the preceding claims,
characterized in that
the further lever arm (12d), with which the spider (12) is supported in the direction opposite to the force introduction direction, is at least approximately from the point (24) of the spider (12) at which the actuating force is introduced into the spider. Pressure switch according to claim 6,
characterized in that
the stop is another switching system (Fig. 8).

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