GB2101408A

GB2101408A - Pressure or temperature responsive switch

Info

Publication number: GB2101408A
Application number: GB08216485A
Authority: GB
Inventors: Martin Junk
Original assignee: Juchheim & Co M K GmbH
Current assignee: Juchheim & Co M K GmbH
Priority date: 1981-07-07
Filing date: 1982-06-07
Publication date: 1983-01-12
Also published as: IT8221478A0; GB2101408B; FR2509519A1; IT1151241B; DE3126683C2; DE3126683A1; CH656483A5; FR2509519B1

Abstract

A pressure or temperature responsive electrical switch has a spindle 2 and a linkage for converting a rotation of the spindle into a linear motion parallel to the spindle for actuating a stationary microswitch 22. The linkage comprises a body part 4 fixed on the spindle 2 and a bistable sector 30 which is pivotable into one of two stable positions by means of a spigot 9 on the body part 4. When the sector 30 is pivoted a sleeve 16 is axially moved via a cam mechanism 33 to cause a lever 21 to be pivoted and actuate the microswitch 22. The body part 4 can be turned through more than 180 DEG with respect to the sector 30 in either of its positions without effecting a further switching action. The pivotable sector 30 is carried on a setting member 14 which is rotatable into a desired position, together with the sleeve 16, by means of an adjusting spindle 11. <IMAGE>

Description

SPECIFICATION Switch mechanism for pressure actuated electrical switch equipment having a spindle The invention relates to a switch mechanism for pressure actuated electrical switch equipment having a spindle and a linkage for converting a rotation of the spindle into a linear movement parallel to the spindle for actuating a fixed microswitch with at least two switch positions, a restoring spring and an actuating member capable of limited movement parallel to the spindle, which linkage comprises a body part fixed on the spindle and a sleeve displaceable with respect to the body part parallel to the spindle and which works the actuating member, which sleeve is relatively rotatable with respect to the body part by means of a connecting member by more than 3600 and whose displacement corresponds to the different switch states of the microswitch.

By the expression "pressure actuated electrical switch mechanism" is to be understood all switch mechanisms in which the expansion of a gas or liquid fluid medium enclosed in a sensor and in an actuator for the spindle effects a rotation of the spindle. This applied equally to temperature as well as pressure regulators.

As an actuator for the spindle will be found in general a single or multiple layer Bourdon spring, a metallic membrane, bellows or the like. It is only necessary that a displacement of the actuator element through pressure variation leads to a rotary movement of the spindle.

The invention can be used with particular advantage in switch equipment with indicating systems, which comprises an actual value pointer and a set value pointer, which overlie a scale of which the graduations extend over more than 1800. In such arrangement, the actual value pointer is fixed to the spindle, while the set value pointer is arranged on a coaxial adjusting spindle, which is also connected with the connecting member referred to above. Relative movement between spindle and adjusting spindle or between the body part and the connecting member or the sleeve leads on coincidence of the set and actual value pointers to a switching operation.

From Swiss Patent Specification No. 411,634 an electrical control is known with an actual value pointer and a plurality of set va[ue pointers, in which the set value pointer is physically connected to a plurality of bistable microswitches.

The microswitches are, for the purpose of adjusting a set value, displaceably arranged on the edge of the scale disc. The actuation of the microswitches is effected by switch arms fixed radially to the spindle which run through forkshaped rocker arms which form part of the switch mechanism.

The known switch drive -certainly works beyond the switching point in hysteresis-free manner, however bistable microswitches have a greater switching differential if an adequate assurance is to be given against unintended switching. On this account and because of the physical connection of the set value pointer, no commercially available microswitch with a push button can be used; it requires a specially produced one. Besides, adjustment of the set value requires bodily movement of the microswitch, so that flexible leads must be provided between the microswitches and the control housing, which involve substantial space requirements. The switch in the neighbourhood of the switching point has as a result a spacing which corresponds to the breadth of the switch in the circumferential direction of the scale disc.

From West German Patent Specification 16 23 850 are known two different versions of a switch mechanism for indicating~instruments with contact apparatus, that is to say for temperature controls, in which the switch body part is formed as a cam member. The linkage between the cam member and the microswitch comprises an angled lever which is connected to the microswitch and engages in a Z-shaped groove of a cam member. Here, too, the microswitch must be bodily moved relative to the cam member for the purpose of adjusting the set value, so that flexible leads are necessary for the microswitch.

The bodily movement of the microswitch and the engagement of the push button in the groove required thereby have the result that the switch pin always lies either side of the switch point on the edge of the groove of the cam member. This leads in every case to unavoidable friction forces which bring about a so-called hysteresis effect.

This peculiarity makes it necessary to have a correspondingly powerful form of the Bourdon spring that serves as the actuator, especially if several microswitches are to be operated by the same actuator.

From West German Patent Specification 29 52 474 is known a switch arrangement of the kind described above in which the switch body part has a surrounding circumferential rib to an angular extent of 3600 or less. The circumferential rib has two ends axially spaced apart, the spacing being greater than the dimension of the push button in the direction of the spindle axis, so that the push button can be passed through between the ends of the circumferential rib. In this way, the switch pin lies by its relative movement with respect to the switch body part, only ever on one side of the switch point of the circumferential rib, so that the hysteresis brought about by friction is substantially reduced.

The invention is based on the problem of providing a switch mechanism of the above mentioned kind, that is to say a switch mechanism with fixed microswitch, in which a connection between the body part and the linkage either side of the switch point is no longer required, and in which the switch body beyond the switch point is no longer loaded with the force of the restoring spring of the microswitch.

The invention comprises a switch mechanism for pressure actuated switches having a rotary spindle and a linkage that converts a spindle rotation to a linear motion for actuating a fixed position spring loaded microswitch comprising a sleeve slidable on the spindle and rotatable by more than 2600, the axial displacement of the sleeve corresponding to the different positions of the microswitch, and comprising a toggle that is rockable by rotating the spindle between stable positions beyond which the spindle can be further rotated by more than 1 800 without effecting another switching operation.

Such a bistable mechanical toggle exhibits assured freedom from the undesired switching of the microswitch beyond the switching point. The bistable mechanical toggle permits, by a suitable arrangement of its elements, the stabilisation of the switch position selected so that beyond the particular switching point or switching zone no braking forces are required of the switch shaft or the switch body for arresting sleeve in the axial direction, which as is known is acted on by the restoring spring of the microswitch. By this means, the switch mechanism works completely free of hysteresis on both sides of the switching point, so that the same actuator can be used without resort to a more powerful arrangement even for actuating two or more microswitches.In this way the use of a Bourdon spring as an actuator element is possible, which previously could only be contemplated for purely indicating instruments. The invention is of particular significance on this account, because it allows the fixed arrangement of one or more microswitches, in contrast, for example, to what is described in Swiss Patent Specification 411 634.

The switch mechanism may comprise a ramp arrangement for converting the rotary to the linear movement, the position and angle of the ramp being chosen so that the sleeve moves between the two switch positions of the microswitch.

The toggle may comprise a sector of a Maltese cross. Maltese crosses are, of course, known per se; they have however not previously been used as linkages for switch mechanisms of the kind here concerned and especially not arranged for bodily adjustment between body part and sleeve.

The use of a Maltese cross or a sector of one leads to completely defined switching positions of the toggle without the possibility of the switching position going beyond the switching point.

The sector of the Maltese cross is here particularly advantageously connected by a spindle carried in the connecting member by a ramp arrangement in the form of a helical cam track, which for its part acts directly or indirectly on the sleeve. By choice of the angle of the cam track it is possible to effect the switching forces and the switching differential independently of the microswitch within wide limits. It is in turn possible to adjust a damping action between the inclined plane and the point of contact which precludes a turning of the Maltese cross sector with respect to the switch body through reaction forces of the microswitch.

One embodiment of the invention will be further explained with reference to Figures 1 to 4.

These show: Figure 1: a side view of the switch mechanism according to the invention in conjunction with the measuring equipment of a two point controller with actual and set value pointers, and Figures 2 to 4: a plan view of the same switch mechanism proceeding from the plane X-X in Fig. 1.

In Fig. 1 is shown an actuator in the form of an enclosed Bourdon spiral, which is supported in known manner with its outer end fixed and connected by a capillary, not shown, with a sensor. The sensor, formed as a hollow body, the capillary and the Bourdon spiral are filled with a medium of which a pressure increase, for example by reason of a temperature rise, effects a change in the Bourdon spiral. The inner end of the Bourdon spiral is joined to a spindle 2 of the switch, to which an actual value pointer 3 is fixed.

Also on the spindle 2 a body part 4 is fastened by a screw 5. Every effect of the actuator 1 on the spindle 2 is expressed as an equal and similarly directed motion of the actual value pointer 3 and body part 4. The body part 4 comprises a boss 6, which has a cylindrical surface 7 on the major part of its periphery (Fig. 3) and also a flanged rim 8, in which a spigot 9 is fixed at a position at its periphery, in the neighbourhood of which the boss 6 is provided with a cylindrical recess 10 (Fig. 2).

The axes of the spigot 9 and recess 10 extend parallel to the spindle 2.

The spindle 2 is formed as a hollow sleeve and is fixedly supported on an adjusting spindle 11 which carries at its outer end an adjusting knob 12 and a set value pointer 13. The two pointers 3 and 1 3 are arranged above a scale plate, not shown, of which the graduations extend over an angle of for example 2700.

On the other side of the body part 4 a connecting member 14 is fixed, by means of a grub screw 15, on the adjusting spindle 11 so as to be fixed against rotation and against axial sliding.

On the adjusting spindle 11 a sleeve 16, which has a projection 17, is also carried so as to be axially slidable but only rotatable relative to the body part 4 together with the connecting member 14. In order that the sleeve 1 6 and the projection 1 7 should move together, the latter has a fork 1 8 into which a projection 19, fixedly mounted on the connecting member 14, fits, which allows axial displacement of the sleeve 1 6 with respect to the connecting member 14.

The sleeve 1 6 has a connection 20 radially of the adjusting spindle 11, on which a lever 21 abuts, which acts on a commercially available, fixed microswitch 22. The microswitch has two switch positions (ON-OFF), a restoring spring, not shown, and an actuating member 23, in the form of a push button, with limited movement parallel to the spindle 2. By this means, the spring loaded actuating member is pressed against the connection 20. The lever 21 is provided with a pivot at its other end which is fastened to a bearing member 25 adjustable parallel to the spindle 2. For the adjustment, an adjusting screw 26 is provided which is carried in the bearing member 24 and also in the housing 27 of the switch mechanism, of which only a small portion is shown.The possibility of adjusting the bearing member 25 serves to adjust the actuating point of the microswitch 22.

The connecting member 14 has a radial projection 28, on which a bistable toggle 1 9 is arranged. This comprises a sector 30 of a Maltese cross. As is seen in Figs. 2-4. The sector 30 is fixed for rotation with the end of the spindle 31 which runs parallel to the spindle 2. On the opposite end of the spindle 31 is secured, also fixed for rotation therewith, a boss 32 with a ramp arrangement 33, which is formed as a helical cam track. The projection 1 7 of the sleeve 1 6 contacts the ramp 33 from below. Rotation of the ramp 33 displaces the sleeve 1 6 by a particular amount which corresponds to the different switch positions of the microswitch. The sleeve acts by its connector 20 via the lever 21 on the actuating member 23 of the microswitch 22.

The shape of the sector 30 of the Maltese cross is shown in Figures 2-4. The sector has a bore 34 by means of which it is fixed to the spindle 31. A slit 35, of which the breadth corresponds to the diameter of the spigot 9, is directed radially of the spindle 31 and is of such depth that the spigot 9 does not reach the end of the slit as it passes through the middle position shown in Figure 3. On either side of the slit 35 the sector 30 is provided with two arcuate recesses 36 and 37, the radii of which are greater than the radius of the cylindrical surface of the body part 4. This assures that the sector 30 can take up two stable positions as shown in Figures 2 and 4, from which it cannot accidentally be moved when the spigot 9 is out of engagement with the slit 35.The presence of the slit 35 however enables the sector 9 to be switched over by the spigot 9 as shown in Fig. 3. The sector 30 has the form of a thin sheet and is desirably, as also is the spindle 31, made of metal while the hub 32 is desirably formed integrally together with the inclined plane 33 and for example made by injection moulding from plastics material. The body part 4 can be made of metal or plastics material, the spigot 9 being preferably of metal and inserted into the edge 8.

The illustrated switch mechanism works as follows: first the sector 30 is in a stable end position as shown in Figure 2, in which it has for example closed the microswitch by the corresponding spatial position of the inclined plane 33, for example for the purpose of increasing the temperature of a heating process.

By a given rotation to the left of the cam member 4, for example as a result of an increasing temperature and a corresponding change of condition of the drive 1, the spigot 9 engages in the slit 35. At the same time, the cylindrical surface 7 moves away from the region of the recess 37. Now the spigot 9 engages the sector 30 and moves it through the middle position shown in Figure 3 into the other stable end position shown in Figure 4, in which the cylindrical surface 7 arrests the sector 30 by virtue of its engaging with the recess 36. By a corresponding rotation therewith of the inclined plane 33 the sleeve 1 6 moves along into another axial position in which the lever 21 switches over the microswitch 22 at an adjustable switchingover point.

From the position shown in Figure 2, the body part can be rotated further by more than 1800, for example as much as more than 2700 in the clockwise direction, without causing a further switching operation or the contact between the cylindrical surface 7 and the recess 37 being broken. The body part 4 can likewise be turned in the reverse direction from the position shown in Figure 4 in the anticlockwise direction by more than 1 800, preferably by more than 2700, without causing a further switching action or the contact with the sector 30 being broken. The body part 4 can thus undergo a relative rotation, with respect to the connecting member 14 and the spindle 16, of more than 3600, preferably even more than 5400, without affecting more than one switching action of the microswitch.

Such a relatively large rotation angle is of importance, because first of all the body part 4 can have in reserve an angular rotation which corresponds to the full scale deflection of the actual value pointer 3. Additionally, however, the connecting member 14 and with it the set value can likewise be adjusted to the full scale deflection by means of the adjusting knob 12, so that as a result and in the extreme case, the deflections of the actual and set value pointers are added together.

In adjusting the set value, the kinematic switching movement occurs precisely at the moment the connecting member 14 is turned with the sector 30 from the position shown in Figure 2 with respect to the body part 4 in the clockwise direction, leading immediately to a switching over of the mechanical switch 29. Then the catch 14 is turned further up to about 2700 without any further switching action taking place.

from the position shown in Figure 2 the connecting member 14 can still be turned in the anticlockwise direction by about 2700, without a switching operation taking place.

It is clear that friction between the body part 4 and the sector 30, which must be overcome by the actuator 1, only occurs in the region of the switch over as seen in Figure 3. Outside this region and indeed on either side, the body part 4 and sector 30 are not in frictional contact with each other under an external force. It has already been explained that the effect of any reaction forces through the inclined plane 33 on the sector 30 can be excluded through a damping action.

Any insignificant contact that happens for all that between sector 30 and cylindrical surface 7 is negligible and in any event substantially smaller than for example happens with the arrangement of West German Patent Specification 29 52 474.

In this regard it is to be noted that the other drives for switch mechanisms can only generate extremely small turning moments and that the frictional forces therein lead to a marked hysteresis effect on the switch.

Claims

1. Switch mechanism for pressure actuated switches having a rotary spindle and a linkage that converts a spindle rotation to a linear motion for actuating a fixed position spring loaded microswitch comprising a sleeve slidable on the spindle and rotatable by more than 3600, the axial displacement of the sleeve corresponding to the different positions of the microswitch, and comprising a toggle that is rockable by rotating the spindle between stable positions beyond which the spindle can be further rotated by more than 1 800 without effecting another switching operation.

2. Switch mechanism according to claim 1 comprising a ramp arrangement for converting the rotary to the linear movement, the position and angle of the ramp being chosen so that the sleeve moves between the two switch positions of the microswitch.

3. Switch mechanism according to claim 1 or claim 2, in which the toggle comprises a sector of a Maltese cross.

4. Switch mechanism according to claim 3 in which the said sector has cylindrical faces either side of an actuating slot that cooperate with a cylindrical face or faces of a spindle-mounted body part to interlock the spindle and sector when the spindle is rotated beyond the actuating point for the sector.

5. Switch mechanism according to any one of the claims 1 to 4, in which the toggle mechanism is carried on an arm secured to the spindle and toggles about an axis parallel to the spindle.

6. Switch mechanism according to any one of claims 1 to 5, in which the linear motion of the sleeve is transmitted to the microswitch by a lever.

7. Switch mechanism according to claim 6, in which the said lever is pivoted on an adjustable block so that the position and throw of the microswitch actuating member can be accommodated.

8. Switch mechanism according to any one of claims 1 to 7, comprising an actuator for effecting rotation of the rotary spindle.

9. Switch mechanism according to claim 8, said actuator being connected to operate a plurality of microswitches.

1 0. Switch mechanism substantially as herein described with reference to the accompanying drawings.