GB2101215A

GB2101215A - A position controller

Info

Publication number: GB2101215A
Application number: GB08216299A
Authority: GB
Inventors: Hans Baumgartner; Wolfgang Sommerey; Georg Nobis; Eckehard Schmitz; Manfred Stucke
Original assignee: Pierburg GmbH
Current assignee: Pierburg GmbH
Priority date: 1981-06-04
Filing date: 1982-06-04
Publication date: 1983-01-12
Also published as: IT1148952B; IT8248580A0; FR2507257A1; JPS58601A; GB2101215B; DE3122120A1; FR2507257B1; DE3122120C2

Abstract

The controller has a diaphragm box comprising a spring-biassed diaphragm rod (20). The pressure prevailing in a control pressure chamber (S) of the box is controlled by the provision of two electromagnetic valves (34, 36) in the box which reduce delays in response and line losses. In addition, the valves and the control pressure chamber are designed to have the least possible dead space. In order to obtain optimum resolution, the diaphragm rod guide (22) which is preferably based on polytetrafluoroethylene, provides the least possible difference between static and sliding friction. The valves are preferably mounted firmly in receiving pockets (38, 40) and are in the form of quick-response, low- mass hinged armature valves. An electromechanical position repeater (46) coupled for movement with the diaphragm is integrated with contact springs in the diaphragm box and is also mounted in a receiving pocket (48). <IMAGE>

Description

SPECIFICATION Position controller This invention relates to a position controller comprising a diaphragm box the interior of which is divided by a movable diaphragm connected to a spring-biassed diaphragm rod into a ventilated diaphragm chamber and a control pressure chamber designed to receive a variable control pressure and further comprising two electromagnetic valves connected flow-wise to the control pressure chamber for ventilating and/or generating in the control pressure chamber a control pressure counteracting the spring biassing of the diaphragm.

Known position controllers of the type mentioned in the preamble are designed to be connected to appropriate pressure sources by external two-way magnetic valves and enable the control pressure in the control pressure chamber to be controlled largely as required. Position controllers of this type are used for example in motor vehicles for controlling idling speed via a throttle valve. For numerous applications, however, position controllers of the type in question are too slow in response on account of the excessively long pipes between the valves and the diaphragm box and, in addition, lack sufficient speed of control and dynamic resolving power.

Position controllers which respond quickly and accurately even to minor changes in pressure are required for accurate control and regulating functions.

Accordingly, an object of the present invention is to design a position controller of the type mentioned in the preamble as simply as possible in such a way that it responds more quickly, is not subject to any critical line losses and provides for greater dynamic resolving power.

According to the invention there is provided a position controller comprising a diaphragm box the interior of which is divided up by a movable diaphragm connected to a spring-biassed diaphragm rod into a ventilated diaphragm chamber and a control pressure chamber designed to receive a variable control pressure and further comprising two electromagnetic valves fluid flow connected to the control pressure chamber for ventilating and/or generating in the control pressure chamber a control pressure counteracting the spring-biassing of the diaphragm, wherein the two valves are arranged in the interior of the diaphragm box, are each connected on the input side to a flow connection of the diaphragm box and open directly into the control pressure chamber on the output side, the two valves and the control pressure chamber having the smallest possible dead volume and a guide is provided for the diaphragm rod which shows very little difference between static and sliding friction.

Thus, the position controller of the type mentioned in the preamble is distinguished by the fact that the two valves are arranged in the interior of the diaphragm box, are each connected on the input side to a flow connection of the diaphragm box and open directly into the control pressure chamber on the output side, by the fact that the two valves and the control pressure chamber are designed to have very little dead space and by the fact that the guide for the diaphragm rod shows very little difference between static and sliding friction. A position controller such as this may be designed to respond extremely quickly because there are no connecting lines between the diaphragm box and the valves and because a compact structure with minimal dead spaces can be obtained by virtue of the physical integration.

As a result, it is possible largely to avoid delays in response. The result of this - in conjunction with the other feature relating to the guide for the diaphragm rod - is that a remarkably favourable dynamic resolving power is obtained. Even very brief and very small activation or control signals result in substantially instantaneous, minor deflections of the position controller. In addition, high positioning speeds can be obtained by virtue of the compact construction. These advantages enable the position controller according to the invention to be used to solve even complicated control and regulating problems which, in the past, known position controllers have been unable to solve on account of their inertia, their inaccuracy and their hysteresis-related, shortest possible stroke.

In one particularly preferred embodiment of the invention, the guide for the diaphragm rod is based on polytetrafluoroethylene, being formed, for example, by a guide sleeve coated with polytetrafluoroethylene or consisting of a sintered material filled with polytetrafluoroethylene. It has been found that, by virtue of its minor static friction/sliding friction differences, a diaphragm rod guide such as this has a particularly low hysteresis and, as a result, provides for extremely short strokes of the position controller. In principle, however, it is also possible to use other suitable lubricants in addition to polytetrafluoroethylene.

In another embodiment of the invention, it is preferred to use valves in the form of hingedarmature valves. Hinged-armature valves have the advantage over lift-armature valves of less mass inertia, resulting in improved response behaviour.

The valves in question are preferably valves each comprising an electromagnetic coil with which an inner core and an outer return bow are associated and further comprising at one end of the coil a spring-biassed hinged armature which carries a displaceable valve closure member of the associated valve and which forms part of the magnetic return. Since the hinged armature on the one hand guides the magnetic flux and, on the other hand, carries the valve closure member, i.e.

does not act thereon by means of a linkage, a very compact and robust construction is obtained which responds quickly with very little tendency towards vibration.

Another preferred embodiment of the invention is characterised by a hinged armature which is pivotally mounted at one end, where it is In resilient vibration-damped contact with the return bow, and which, at its other end, carries the valve closure member associated with a stationary valve seat, being biassed in the valve closing direction and stabilised against vibration by a valve spring, means being provided for defining a minimum interval between mutually facing ferromagnetic regions of the hinged armature and the core. The fact that the hinged armature is in resilient contact with the return bow provides for effective magnetic transfer, even taking into account the vibrations occurring in operation. Since the valve spring is biassed in the valve closing direction, closure of the valves is guaranteed in the absence of current.Accordingly, the signal momentarily present can be maintained in the event of current failure because in that case the entire control pressure chamber is completely sealed off from the outside. Various means may be used for defining the minimal interval between the ferromagnetic regions mentioned above, for example, projections situated in the mutual contact zone or coatings on the hinged armature and/or core and also externally arranged stops.

These means ensure that a defined, minimal gap is always left between the mutually facing ferromagnetic regions, thereby avoiding the occurrence of hysteresis behaviour which is essential for exact control or regulation.

Another preferred embodiment of the position controller is characterised in that, in the region between the return bow and the core, the hinged armature is designed with a sufficiently large magnetic flux cross-section and, in the adjoining region up to the valve closure member and up to the valve spring, with sufficient strength for transmitting forces. In this way, it is possible to reduce mass because it is only that region affected by the magnetic flux which has to be adequately dimensioned for that purpose whereas the remaining region only has to be dimensioned to provide the necessary mechanical strength. A reduction such as this in the mass of the hinged armature, i.e. a moving part, means that less power is required for control purposes coupled with quicker response behaviour.

Another embodiment of the invention is characterised by a bow diametrically opposite the return bow with an abutment for the valve spring in the form of a compression spring concentric with the valve closure member. This diametrically opposite bow may optionally form an additional magnetic return. Accordingly, the opposite bow acts as a support for the valve spring which is thus part of the valve assembly and is supported thereby, The arrangement of the valve spring concentrically with the valve closure member provides for a particularly favourable and compact construction. The bow serves more than one purpose in cases where, in addition, it forms an additional magnetic return for the magnetic valve.

In this case, the magnetic flux cross-section of the actual return bow may be made somewhat smaller.

One particularly favourable embodiment of the invention is characterised by receiving pockets formed in the diaphragm box for the electromagnetic valves and each comprising an external flow connection, a flow passage -- forming a valve seat - to the control pressure chamber and a tight closure. These receiving pockets may be formed very easily in the diaphragm box and provide for protected, hermetically sealed accommodation of the individual valves. The shape, arrangement and size of the receiving pockets enable dead spaces to be kept as small as possible.

It is best to provide suitable holders by which the electromagnetic valves are fixed and stabilised against vibration in the receiving pockets. In this way, satisfactory operation of the position controller may be guaranteed even when it is subjected to operationally induced vibration. Each holder is with advantage formed by a sprung expanding element which engages elastically in the receiving pocket. This expanding element, which may be formed, for example, by a ratchet wheel, may be inserted and removed quickly and easily.In this connection, it is particularly preferred, for the purpose of fixing the electromagnetic valves, to provide a knurled head which projects at that end of the core situated opposite the hinged armature and on to which are pressed, on the one hand, the return bow and the opposite bow formed continuously therewith and, on the other hand, the sprung expanding element.

By virtue of the knurled head, the components to be fixed thereto may be fixed in the particular position required by being pressed to a greater or lesser extent on to the knurled head. In this way, it is possible to adjust the individual components of the valve relative to one another and the position of the valve in the particular receiving pocket.

Another embodiment of the invention is characterised by an electromechanical position repeater which is integrated into the diaphragm box and which is mechanically coupled with the diaphragm. Although position repeating could also take place externally, for example by determining the particular position of the diaphragm rod, the integrated construction referred to is advantageous for reasons of space and also in the interests of a particularly robust, operationally reliable construction. In this connection, It is possible to provide a position repeater in the form of a voltage divider comprising a slide block guided in the direction of movement of the diaphragm of which an elastic contact spring slides along an electrically supplied resistance path and of which the pushrod is kept in contact with the diaphragm and stabilised against vibration by means of a relatively weals spring.

Accordingly, the position of the diaphragm and, hence, the position of the diaphragm rod inside the diaphragm box are continuously monitored.

The particular position is tapped in the substantial absence of friction from the resistance path as a voltage value by means of the contact spring. This is preferably done by means of a slide block comprising two electrically interconnected contact springs of which one slides along the resistance path and the other along an electrically conductive collector path. Accordingly, the particular voltage or resistance value is also repeated in the substantial absence of friction by means of the particular contact spring via the collector path, thereby avoiding sensitive, moving wire connections. To ensure that the slide block always quarantees satisfactory electrical contact through its contact springs, a rotation-preventing prismatic guide is preferably provided for the slide block on the diaphragm box housing.

As mentioned in connection with the electromagnetic valves, it is best for the position repeater to be accommodated in a central receiving pocket of the diaphragm box which is sealed off from the outside. In this way, the position repeater may be integrated very easily into the diaphragm box and may be protected therein against outside influences which is extremely important in the interests of accurate and reliable operation, because even very small strokes have to be satisfactorily covered.

For safe operation of the position repeater and hence of the position controller as a whole, it is also important to provide a pushrod guide with very little difference between static and sliding friction. The pushrod of the position repeater is intended to follow the diaphragm reliably, even in the event of minor deflections. A suitable pushrod guide is one based on polytetrafluoroethylene and, in this connection, it is possible with advantage to use a push rod guide sleeve comprising polytetrafluorethylene lubricant incorporated in its porous surface.

To enable the position controller to operate effectively, it is also advisable to establish a flow connection between the central receiving pocket and the control pressure chamber at a distance from the pushrod guide, otherwise a delayed exchange of flow between the control pressure chamber and the central receiving pocket could occur through a permeable pushrod guide, resulting in defective operational behaviour in regard to the movement of the diaphragm and giving rise to the danger of dust particles entering the permeable region between the pushrod guide and the pushrod. By contrast, the specifically designed flow connection prevents any such delay in the exchange of flow and, hence, avoids the operational disadvantages associated therewith.

In one variant of the invention electromagnetic valves closed in the absence of current are used.

They enable a signal to be maintained in the event of current failure in the manner already described.

Accordingly, in the event of current failure, the diaphragm rod is kept at least temporarily in the position which it occupied before the current failure. Instead of this, however, it is also possible to provide an electromagnetic valve which is closed in the absence of current and an electromagnetic valve which is open in the absence of current. In this case, it is possible for example for the control pressure chamber to be ventilated in the absence of current in order thus to withdraw the diaphragm rod from active engagement. Either variant may be used with advantage according to the particular application.

With various applications, it can be of advantage to provide an external seal for the diaphragm rod guide in the form of a bellows seal or a low-friction felt seal. This seal, which should be of a low-friction type, is intended to keep particles of dirt and dust away from the diaphragm rod guide so that its sliding properties are not adversely affected because otherwise a deterioration in the smallest possible strokes and hence in dynamic resolution would occur in operation.

So far as the structural configuration of the position controller is concerned, it is preferred to use a diaphragm box comprising an upper housing section and -- designed to be fixed thereto - a lower housing section between which the outer edge of the diaphragm is clamped, the upper housing section carrying all the receiving pockets, flow connections and electrical connections and the lower housing section carrying the diaphragm rod guide. This provides for a simple and clearly arranged construction which is easy to assemble and diswrnantle. To facilitate production and assembly, it is possible to use an upper housing section of plastic and -- designed to be fixed thereto by flanging -- a lower housing section of metal.The upper housing section of plastic may be formed with the necessary receiving pockets very easily, for example by injection moulding, without any weight problems arising.

One particularly practical construction is characterised by a central receiving pocket for the position repeater adjoined diametrically by receiving pockets for the electromagnetic valves with flow connections substantially facing in opposite transverse directions, by a common closure arranged at the end opposite the diaphragm rod for sealing off the three receiving pockets from one another and from the outside and by an electrical multiway connector for the electromagnetic valves and the position repeater on one side of the upper housing section. This structural configuration is particularly space saving, clearly laid out and easy to handle. The individual receiving pockets are readily accessible from the front which also applies correspondingly to the flow connections separated therefrom and from one another and to the electrical connections.The common closure for the receiving pockets which simplifies handling preferably consists of a plastics material and may be joined to the upper housing section by ultrasonic welding or by bonding. It must ensure satisfactory imperviousness so that the individual receiving pockets are sealed off from one another and from the outside.

Another practical embodiment is characterised by an outer diaphragm spring which biasses the diaphragm to enlarge the control pressure chamber and by flow connections for ventilating and/or for admitting reduced pressure to the control pressure chamber. Basically, the diaphragm spring could also be arranged inside the diaphragm box although this would have the disadvantage that excessively large dead spaces would be formed, resulting in a reduction in the speed of response. Ventilation on the one hand and the admission of reduced pressure on the other hand have the advantage over the application of other pressure levels that, in numerous applications, it is possible to use already existing pressure sources, such as the ambient pressure and the reduced pressure of a suction pipe. The measure referred to is particularly advantageous for motor vehicles.

Another variant of the invention is characterised by a positioning control element which is integrated into the diaphragm box and which is electrically connected both to the position repeater and to the electromagnetic valves, comprising control lines guided outwards from the position controller. This construction with the integrated positioning control element is particularly advantageous because it eliminates the need for external electrical connections and, apart from power supply lines, it is only necessary to supply control lines for feeding in desired values. A position controller such as this is versatile in its uses and, through the integration of the various components, extremely robust and reliable in operation.

The position controller according to the invention is versatile in its uses and may be pneumatically or hydraulically operated. One particularly preferred use of a pneumatic position controller of the type mentioned above is for the actuation of a throttle member or by-pass valve in carburettors or injection units in dependence upon electrical signals. In this case, the position controller may be used for example for forming an electronic gas pedal and/or for controlling idling speed. Even when it is used under robust conditions involving vibration, it provides for reliable operation with rapid response behaviour and high dynamic resolving power.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic longitudinal section through a position controller according to the invention inter alia along the line I-I in Figure 3.

Figure 2 is a section through an electromagnetic valve of the position controller shown in Figure 1 along the line Il-Il in Figure 1.

Figure 3 is a section through the position repeater of the position controller shown in Figure 1 on the line Ill-Ill in Figure 1.

The position controller shown in Figure 1 comprises a diaphragm box with an upper housing section 10 of plastics material and a lower housing section 1 2 of metal. The lower housing section 1 2 is fixed to the upper housing section 10 by flanging 14. In the region where the upper housing section 10 and the lower housing section 12 are joined together, the outer edge of a diaphragm 16 is clamped between them, dividing the interior of the diaphragm box into a diaphragm chamber M permanently ventilated through a vent and a control pressure chamber S designed to receive a variable control pressure.

The diaphragm 1 6 is joined -- except for its outer periphery - to a stabilising diaphragm pot 1 8 and a central diaphragm rod 20. The diaphragm rod 20 is guided outwards by a sleevelike diaphragm rod guide 22 which is supported by a guide holder 24 fixed to the diaphragm box. The diaphragm rod guide 22 is such that only a slight difference occurs between static friction and sliding friction, for which purpose a diaphragm rod guide 22 based on polytetrafluoroethylene for example is used. An outer diaphragm spring 26 surrounding the diaphragm rod 20 is mounted between the lower housing section 12 and an unnumbered support plate fixed to the diaphragm rod 20.The diaphragm spring 26 biasses the diaphragm 16 and the diaphragm rod 20 connected thereto in the direction shown in Figure 1 so that, in the ventilated state of the control pressure chamber S, a plate 28 fixed to the diaphragm 1 6 is applied to the lower housing section 12. This position corresponds to a defined rest position which may be transmitted through connections -- generally denoted by the reference 30 - of the diaphragm rod 20 to an element to be driven, such as a throttle valve or the like, when the diaphragm box is suitably connected through outer connecting bolts 32 of the lower housing section 12.

As can been seen from Figure 1, two electromagnetic valves 34, 46 are situated in receiving pockets 38, 40 formed eccentrically, adjacent one another in the upper housing section 10. Two flow connections 42, 44 facing in diametric transverse directions are connected to the receiving pockets 38, 40.

A central position repeater 46 is situated in a central receiving pocket 48 which is in turn situated between the already mentioned receiving pockets 38. 40. The accesses to all the receiving pockets 38, 40, 48 are situated at that end of the diaphragm box opposite the diaphragm rod 20 and are designed to be hermetically sealed off from one another and from the outside by a common closure 50. This closure 50 may also be made of plastics material and may be fixed to the upper housing section 10 by ultrasonic welding or by bonding.

Associated with the position repeater 46 in the central receiving pocket 48 are a pushrod 52 which projects from the receiving pocket 48 into the control pressure chamber S and a spring 54 which presses the pushrod 52 into contact with the diaphragm 1 6 or with an element carried by the diaphragm 16, as will be explained in more detail hereinafter in reference to Figure 3.

As can be seen from Figures 1 and 2, each of the electromagnetic valves 34 and 36 comprises an electrical coil 56 with an inner core 58 arranged on an unnumbered coil. The inner coil 58 projects from the spool at one end through an unnumbered core pole piece and at its other end through a knurled head 60. A band-like return bow 62, which in the present case is connected to a correspondingly band-shaped diametral bow 64, is pressed on to the knurled head 60 and surrounds the coil 56 up to its end opposite the knurled head 60. In addition, a sprung band-like expanding element 66 is pressed on to the knurled head 60, fixing the associated electromagnetic valve by elastic engagement in the corresponding receiving pocket, as can be seen in Figure 1.

Accordingly, the electromagnetic valve can be pressed into the receiving pocket until spacer studs D come into contact with the bottom of the receiving pocket. The expanding element 66 then prevents the valve from sliding unintentionally in the receiving pocket, even under the effect of the vibration occurring in practice.

A strip-like hinged armature 68 extends over that end of the coil 56 comprising the abovementioned core pole piece, being pressed at one end against the end of the return bow 62 by means of a sprung pivot bearing 70. The contact pressure is strong enough to guarantee permanent contact between the hinged armature 68 and the return bow 62 and hence an adequate magnetic flux cross-section, even taking operational vibration into account. Between the ferromagnetic parts of the core pole piece on the core 58 and the hinged armature 68, there is a gap 72 which is variable between a minimum width and a maximum width according to the position of the hinged armature. The minimum width ensures that no pronounced hysteresis behaviour occurs so that the difference between pick-up and drop-off excitation is as small as possible.The minimal gap 72 is obtained for example by means of projections or coatings on the armature pole piece or on the hinged armature. In principle, external travel-limiting stops may also be provided for this purpose.

The hinged armature 68 comprises a hingedarmature extension 74 which extends beyond the armature pole piece and the gap 72 and which at its end carries a valve closure member 76. This valve closure member is associated with a stationary valve seat 78 surrounding a flow passage to the control pressure chamber S on the bottom of the associated receiving pocket. A valve spring 80 concentric with the valve closure member 76 is mounted between an abutment 80 of the bow 64 and the back of the hingedarmature extension 74 in order to press the valve closure member 76 sealingly on to the valve seat 78 when the coil 56 is without current. A projection 84 on the bow 64 centres and holds the valve spring 80 in position.When current flows through the coil 56, the hinged armature 68 is magnetically attracted against the action of the valve spring 80. as a result of which the gap 72 is narrowed and the flow passage in the vicinity of the valve seat 78 is released. In this way, the control pressure in the control pressure chamber S can be varied as required by correspondingly actuating the electromagnetic valves 34 and 36.

As shown in Figure 3, the position repeater 46 comprises a displaceable slide block 86 which is guided longitudinally of the pushrod 52 and the membrane rod 20 and prevented from rotating by means of a prismatic guide 88. The slide block 86 carries two electrically interconnected contact springs 90 and 92. The contact spring 90 slides along a resistance path 94 which extends in the direction of movement of the position controller and of which the two ends are connected (not shown) to an external voltage source (also not shown). Figure 3 merely shows at one end of the resistance path 94 that the resistance path can be connected by an electrical connection 98 to a plug-like electrical connection 100 of a multiway connector 102 which is situated on one side of the upper housing section 10.The other end and the remaining electrical connections of the position controller are correspondingly formed as parts of the multiway connector 102. This also applies to the electrical connection of a collector path 96 which also extends longitudinally of the position controller and along which the other contact spring 92 of the slide block 86 slides. Thus, the position of the slide block 86, which through the pushrod 52 and the spring 54 always corresponds to the position of the diaphragm 1 6 and the diaphragm rod 20, may be tapped as an electrical voltage or resistance signal from the resistance path 94 and delivered outwards through the conductive collector path 96 and the multiway connector 102.

The pushrod 52 of the position repeater 46 projects through a sleeve-like pushrod guide 104 into the control pressure chamber S. This pushrod guide 104 also preferably has very little difference between static and sliding friction so that exact position repeating can take place. A guide sleeve based on polytetrafluoroethylene is also suitable for this purpose. A flow connection 106 should be provided between the receiving pocket 48 and the control pressure chamber S at a distance from the pushrod guide 104 to ensure that no delayed exchange of flow can take place between these chambers. Otherwise an exchange of flow such as this would influence the movement of the diaphragm 1 6 and, in addition, would result in particles of dust entering through permeable parts of the pushrod guide 104 and adversely affecting its sliding properties.The spring 54 should on the one hand be so weak that it does not affect the pressure-governed position of the diaphragm 1 6 and, on the other hand, sufficiently strong that permanent contact between the pushrod 52 and the diaphragm 1 6 is guaranteed, even taking into account the vibration occurring in operation.

In the present embodiment, the multiway connector 102 may comprise seven electrical connections 100 made up of two connections for each of the electromagnetic valves 34, 36 and three connections for the position repeater 46, of which two are used for supplying current to the resistance path 94 and one for signal tapping from the collector path 96.

If desired, a positioning regulator (not shown) may be installed together with the position repeater 46 in the receiving pocket 48 and may be connected externally through the multiway connector 102 or internally to the electromagnetic valves. In the latter case, the outer connection of the collector path 96 would disappear and would be replaced by a positioning regulator connection for the input of desired values.

The position controller according to the invention enables powerful control forces to be generated despite its low overall weight and the use of minimal electrical control energy so that the position controller may be activated with considerable advantage by means of a low-power electronic unit. The position controller has a remarkably high dynamic resolving power and responds very quickly so that even minor, rapid signal changes are immediately converted into corresponding strokes. The integration of the individual components in the membrane box enables flow-induced line losses and relatively large, unwanted dead spaces to be avoided. The individual commponents of the position controller are stabilised against vibration so that, even where it is used in motor vehicles for example, highly accurate strokes can be obtained for control or regulating functions. Accordingly, it is possible to replace hitherto used electrical regulating units.

such as stepping motors or d.c. motors with corresponding transmission systems, by a position controller of the type according to the invention in order to control or regulate for example throttle members, by-pass valves and the like highly accurately in dependence upon any given values.

Claims

1. A position controller comprising a diaphragm box the interior of which is divided up by a movable diaphragm connected to a spring-biassed diaphragm rod into a ventilated diaphragm chamber and a control pressure chamber designed to receive a variable control pressure and further comprising two electromagnetic valves fluid flow connected to the control pressure chamber for ventilating and/or generating in the control pressure chamber a control pressure counteracting the spring-biassing of the diaphragm, wherein the two valves are arranged in the interior of the diaphragm box, are each connected on the input side to a flow connection of the diaphragm box and open directly into the control pressure chamber on the output side, the two valves and the control pressure chamber having the smallest possible dead volume and a guide is provided for the diaphragm rod which shows very little difference between static and sliding friction.

2. A position controller as claimed in Claim 1, wherein the guide for the diaphragm rod is based on polytetrafluoroethylene.

3. A position controller as claimed in Claim 2.

wherein a guide sleeve coated with polytetrafluoroethylene or consisting of a sintered material filled with polytetrafluoroethylene provides the guide for the diaphragm rod.

4. A position controller as claimed in one or more of Claims 1 to 3, wherein the valves are hinged-armature valves.

5. A position controller as claimed in Claim 4, wherein the valves each comprising an electromagnetic coil with which an inner core and an outer return bow are associated and further comprising at one end of the coil a spring-biassed hinged armature which carries a displaceable valve closure member of the associated valve and which forms part of the magnetic return.

6. A position controller as claimed in Claim 5, wherein the hinged armature is pivotally mounted at one end, where it is in resilient vibrationdamped contact with the return bow, and at its other end, carries the valve closure member associated with a stationary valve seat, being biassed in the valve closing direction and stabilised against vibration by a valve spring, and further comprising means for defining a minimum interval between mutually facing ferromagnetic regions of the hinged armature and the core.

7. A position controller as claimed in Claim 6, wherein in the region between the return bow and the core the hinged armature is designed with a sufficiently large magnetic flux cross-section and, in the adjoining region up to the valve closure member and up to the valve spring with sufficient strength for transmitting forces.

8. A position controller as claimed in Claim 6 or 7, wherein a bow is provided diametrically opposite the return bow with an abutment for the valve spring in the form of a compression spring concentric with the valve closure member.

9. A position controller as claimed in Claim 8, wherein the diametrically opposite bow forms an additional magnetic return.

10. A position controller as claimed in one or more of Claims 1 to 9, wherein receiving pockets are provided in the diaphragm box for the electromagnetic valves, each comprising an external flow connection, a flow passage -- forming a valve seat - to the control pressure chamber and a tight closure.

11. A position controller as claimed in Claim 10, wherein holders are provided by which the electromagnetic valves are fixed and stabilised against vibration in receiving pockets.

1 2. A position controller as claimed in Claim 1 1. wherein each holder is in the form of a sprung expanding element which engages elastically in the receiving pocket.

3. A position controller as claimed in Claim 12, a knurled head is provided which projects at that end of the core opposite the hinged armature and on to which are pressed, on the one hand, the return bow and the opposite bow formed continuously therewith and, on the other hand, the sprung expanding element

14. A position controller as ciaimed in one or more of Claims 1 to 13, wherein an electromechanical position repeater is provided which is integrated into the diaphragm box and which is mechanically coupled to the diaphragm.

1 5. A position controller as claimed in Claim 1 4 wherein the position repeater is a voltage divider comprising a slide block guided in the direction of movement of the diaphragm, of which an elastic contact spring slides along an electrically supplied resistance path and of which the pushrod is kept in contact with the diaphragm and stabilised against vibration by means of a relatively weak spring.

1 6. A position controller as claimed in Claim 1 5. wherein a slide block is provided which comprises two electrically interconnected contact springs of which one slides along the resistance path and the other along an electrically conductive collector path.

1 7. A position controller as claimed in Claim 15 or 16, wherein a rotation-preventing prismatic guide is provided for the slide block on the diaphragm box housing.

1 8. A position controller as claimed in one or more of Claims 14 to 17, wherein the position repeater is accommodated in a central receiving pocket of the diaphragm box which is sealed off from the outside.

1 9. A position controller as claimed in Claim 18, wherein a pushrod guide is provided which has very little difference between static and sliding friction.

20. A position controller as claimed in Claim 19, wherein the pushrod guide is based on polytetrafluoroethylene.

21. A position controller as claimed in Claim 20, wherein the pushrod guide sleeve has polytetrafluoroethylene lubricant incorporated in its porous surface.

22. A position controller as claimed in one or more of Claims 1 8 to 22, wherein a flow connection is arranged between the central receiving pocket and the control pressure chamber at a distance from the pushrod guide.

23. A position controller as claimed in one or more of Claims 1 to 22, wherein the electromagnetic valves which are closed in the absence of current.

25. A position controller as claimed in one or more of Claims 1 to 24, wherein the diaphragm rod guide has an external seal which is a bellows seal.

26. A position controller as claimed in one or more of Claims 1 to 24 wherein the diaphragm rod guide has an external seal which is a low friction felt seal.

27. A position controller as claimed in one or more of Claims 1 to 26, wherein the diaphragm box comprises an upper housing section and, designed to be fixed thereto - a lower housing section, between which the outer edge of the diaphragm is clamped, the upper housing section carrying all receiving pockets, flow connections and electrical connections and the lower housing section carrying the diaphragm rod guide.

28. A position controller as claimed in Claim 27, wherein the upper housing section is of a plastics material and the lower housing section of metal designed to be fixed thereto by flanging.

29. A position controller as claimed in Claim 27 or 28, wherein a central receiving pocket for a position repeater adjoined diametrically by receiving pockets for the electromagnetic valves with flow connections substantially facing in opposite transverse directions, a common closure arranged at the end opposite the diaphragm rod for sealing off the three receiving pockets from one another and from the outside and by an electrical multiway connector for the electromagnetic valves and the position repeater on one side of the upper section of the housing.

30. A position controller as claimed in Claim 29 wherein the closure is of a plastics material which is joined to the upper housing section by ultrasonic welding or by bonding.

31. A position controller as claimed in one or more of Claims 1 to 30, wherein an outer diaphragm spring is provided which biasses the diaphragm to enlarge the control pressure chamber and flow connections are provided for ventilating and/or for admitting reduced pressure to the control pressure chamber.

32. A position controller as claimed in one or more of Claims 1 to 31, wherein a positioning control element is provided which is integrated into the diaphragm box and which is electrically connected both to a position repeater and to the electromagnetic valves comprising control lines guided outwards from the position controller.

33. A method of actuating a throttle member or bypass valve in carburettors or injection units in dependence upon electrical control signals using a pneumatic position controller claimed in any one of Claims 1 to 33.

34. The use claimed in Claim 33 for forming an electrical accelerator pedal and/or for controlling idling speed.

35. A position controller substantially as herein described with reference to the accompanying drawings.