EP1180778A1

EP1180778A1 - Tristable relay

Info

Publication number: EP1180778A1
Application number: EP00117309A
Authority: EP
Inventors: Graham Bailey
Original assignee: Ranco Inc of Delaware; Ranco Inc
Current assignee: Ranco Inc of Delaware; Robertshaw US Holding Corp
Priority date: 2000-08-18
Filing date: 2000-08-18
Publication date: 2002-02-20
Anticipated expiration: 2020-08-18
Also published as: DE60037017D1; DK1180778T3; EP1180778B1; DE60037017T2

Abstract

To achieve an energy effective switching between different loads at low cost there is provided a tristable relay using a core element (10) having a coil (12) for magnitisation of the core element (10). Further, a member (14) having at least one permanent magnet (16) defining a first and second magnetic pole region is arranged with respect to the core element (10) such that a relative movement between the member (14) and the core element (10) is possible. The relative movement is used to achieve switching in a tristable relay, e.g., for application within a no-frost refrigerator/freezer.

Description

FIELD OF THE INVENTION

The present invention relates to a tristable relay for the control, e.g., of applications having two loads which are switched in a mutually exclusive manner.

TECHNICAL BACKGROUND

One example for an application having two loads being switched in a mutually exclusive manner is a no-frost refrigerator or freezer where the compressor thereof is switched on and off to maintain a pre-defined temperature during normal operation. However, at some time during operation a defrost operation is carried out whereby the compressor is de-energized and the evaporator heater is energized so as to raise the temperature of the evaporator heater above 0°C hence removing accumulated ice. Here, it is not intended to energize both the compressor and the evaporator heater at the same time.
The mutually exclusive switching of the evaporator heater and the compressor may be achieved by use of two independently operator switch arrangements 100, 102, as shown in Fig. 1. Here, the switch arrangement 100 switches the compressor on and off while the switch arrangement 102 switches the heater evaporator on and off.
As shown in Fig. 1, typically during a normal operation the compressor is switched on and off in a cyclic fashion through the switch arrangement 100 until at a specific time t_d it is necessary to remove accumulated ice in the evaporator. Heretofore, the heater evaporator is switched on through the switch arrangement 102 to achieve a defrost operation. Hereafter, a drip time period follows in an optional way for further removal of accumulated ice and melt water. Then, the switch arrangement 100 activating and deactivating the compressor is again operated for further freezing operation.
One option to realize the switch arrangements is the use of an energy saving bistable relay that does not draw current except during the short transition stage to change the state of the switch arrangements 100, 102. However, a bistable relay is normally more expensive than a monostable relay so that this saving of energy is achieved only at the expense of higher system costs.
To overcome this deficiency, Fig. 2 illustrates the use of multi-position relay for the switching arrangements operating, e.g., on the basis of the ratchet mechanism. These multi-position relay are known and may be configured with any number of stable positions and contact arrangements. To achieve the next stable position, an energization pulse is applied to a single relay coil of the multi-position relay thus turning the ratchet mechanism always along the same direction.
As shown in Fig. 2, the use of such multi-position relay again for the no-frost refrigerator/freezer application has the disadvantage that these multi-position relay may only be operated in a cyclic fashion. For a two-position relay there exist four states 1 to 4 with the first switch arrangement 100 closed, the second switch arrangement 102 opened (state 1), both switch arrangements opened (state 2), the first switch arrangement 100 opened, the second switch arrangement 102 closed (state 3), and again both switch arrangements 100, 102 opened (state 4, optional).
As shown in Fig. 2, in case the compressor is to be switched on/off in a periodic manner during the freezer operation, it will be necessary to run through all states of the multi-position relay. Therefore, to reach state 1 again after the compressor has been switched off it is necessary to run through state 3 at time t_n, thus activating the heater evaporators while at the same time the defrost operation is necessary.
This has the disadvantage of creating unnecessary current transients in the mains and reduces life expectancy of the evaporator heater switch contacts.
Further, multi-position relays are inherently noisy when moving from one position to another via transient states which is a disadvantage in domestic appliances where audible noise is considered a disturbance.

SUMMARY OF THE INVENTION

In view of the above, the object of the invention is to achieve an energy-effective switching between different applications/loads at low cost and low noise.
According to the present invention, this object is achieved through a tristable relay having the features of claim 1.
Therefore, according to the present invention a tristable relay is implemented using a core element having a coil for magnetisation of the core element. Further, a member with at least one permanent magnet defining a first and second magnetic pole region is arranged with respect to the core element such that a relative movement between a member with the permanent magnet and the core element is possible.
In addition, the tristable relay comprises stopper means for limiting the relative movement of the core element and the member with the at least one permanent magnet between a first and a second limit stop position. According to the present invention different working positions in the tristable relay are maintained stable without further supply of energy to the coil in the core element which - in other words - is only energized to move the element with the at one least permanent magnet.
No energy supply is necessary to maintain this member in one of a plurality of working positions. According to the present invention this is achieved since in each of the different working positions the magnetic field flux of the permanent magnet closes over the core element which is therefore maintained in a stable state.
Further, the stopper means limits the relative movement of the core element and the member between a first and second limit stop position. In each stop position the member having at least one permanent magnet is moved slightly out of the related equilibrium position where its magnetic field flux fully closes over the core element. Therefore, there is the tendency of the member having the at least one permanent magnet to move into this equilibrium position. However, as the member with the at least one permanent magnet abuts to the stopper means there is generated a force or torque at either of the first and second limit stop position.
Operatively, the member with the permanent magnet is moved relative to the core element into the first limit stop position through supply of current pulse with a first appropriate polarity to the coil of the core element. Further, the member with the permanent magnet is moved operatively into the second limit stop position through supply of a current impulse with a polarity opposite to the polarity assigned for the first limit stop position. In case the member with the permanent magnet is to be moved into a third position lying between the first and the second limit stop position, this is achieved through supply of a sequence of impulses with alternating polarities to the coil.
In other words, the various working positions generally are selected by energizing the coil with short positive or negative pulses generated in a control unit to bring the tristable relay into the first to third working position. In particular, the third working position is obtained through supply of a short sequence of alternating pulses of calibrated energy to the coil. Here, the energy amount to achieve the third working position is determined as a function of the inertia and self-resonance characteristics of the tristable relay.
Further, according to the present invention it is proposed to use the thus achieved stable work positions being maintained without energy supply to turn on/off switch elements of the tristable relay through the relative movement of the core element and the member. In other words, contrary to the prior art only a single coil is used to achieve activation and/or deactivation of either switch arrangements.
Since it is possible to achieve a relative movement between the core element and the member such that a member having the at least one permanent magnet moves between the first limit stop position and the third relative position of the core element and further between the third relative position and the second limit stop position it is possible that the first switch element is turned on/off multiple times before the second switch element is turned on/off and then the first switch element is turned on/off again multiple times so as to avoid unnecessary transient states in the tristable relay.
Therefore, the tristable relay may be, e.g., ideally suited to the requirements of a relay for the no-frost refrigerator/ freezer application described above. However, it should be emphasized that according to the present invention any application requiring a switching between different load situations without continuous energy supply may be easily covered by the tristable relay according to the present invention.
According to a preferred embodiment of the present invention the member with the permanent magnet is provided with pole extensions in contact to the poles of the permanent magnet to achieve optimized interaction between the permanent magnet and the core element.
According to yet another preferred embodiment of the present invention, the tristable relay uses a rotor as member with a permanent magnet and core elements with two separate pole pieces face each other to form a rotor space for accommodation of the rotor. Preferably, the pole extensions in contact with the poles of the permanent magnet extend beyond the permanent magnet in a radial direction of the rotor.
This preferred embodiment of the invention allows to apply the basic principle outlined above to a rotary arrangement of a tristable relay. In particular, the geometry of the pole pieces and the pole extensions is important to determine the direction and the amount of torque generated on the rotor by the pole pieces under stationary conditions and in case the coil is energized.
According to yet another embodiment the switch elements are formed by a first fixed contact, a second fixed contact and a lever carrying a third contact. The lever may be moved between the first fixed contact and the second fixed contact. Also, through coupling of the rotor of the tristable relay the lever may be positioned between the first fixed contact and the second fixed contact or in abutment to each fixed contact in compliance with the relative movement of the core element and the member. This preferred embodiment of the present invention allows an implementation of the two switch elements with a minimized number of movable parts thus reducing the inherent inertia of the tristable relay and the necessary energy supply. In addition, the lower the number of movable parts within the tristable relay is the higher the switching frequency thereof may be.
According to yet another preferred embodiment of the present invention the member is implemented as sliding element adapted to carry out a reciprocal linear movement relative to the core element. Here, pole extensions of the sliding element comprise, e.g., a first U-shaped part and a second U-shaped part contained in the first U-shaped part and the U-shaped parts being arranged in contact with related pole faces of the permanent magnet.
Therefore, this further preferred embodiment of the present invention allows for a linear instead of a rotating movement within the tristable relay.
According to yet another preferred embodiment, irrespective of rotating or linear movement of the element with the permanent magnet this permanent magnet element is a sintered part made from Ne-Fe-B (Neodimium-Ferrous-Boron). Preferably, one could combine into only a single part the function of the permanent magnet, the pole extension, the rotor enabling the reduction of the number of parts from, e.g., three to one. This may be achieved using plastic material charged with ferrite being subsequently magnetized.
According to yet another preferred embodiment, suitable materials for the single part having a plurality of functions are, e.g., plastics of poly-oxy-methylene (POM) or poly-aryl-etherketone material families.
According to yet another preferred embodiment of the present invention it is proposed to mount the different parts of the tristable relay to a printed circuit board which may, e.g., be integrated into a moulded plastic housing. Therefore, according to the present invention it is possible to achieve a very compact realization of the tristable relay.
In the following, preferred embodiments of the present invention will be explained with reference to the drawings in which

Fig. 1: shows an application of two separated relay to an application with two loads, i.e. a no-frost refrigerator/freezer using a compressor and a heater evaporator;
Fig. 2: shows the application of a multi-position relay to the operation of a no-frost refrigerator/freezer where the heater evaporator is switched on with every compressor cycle;
Fig. 3: shows a schematic representation of an ideal relay having two change-over contacts;
Fig. 4: the application of the relay schematically shown in Fig. 3 to a no-frost refrigerator/freezer operation;
Fig. 5: shows the basic principle underlying different embodiments of the present invention;
Fig. 6: shows a tristable relay of the rotary type according to the present invention in a first stable working position;
Fig. 7: shows a tristable relay of the rotary type in a second stable working position;
Fig. 8: shows the tristable relay of the rotary type in a third stable working position;
Fig. 9: shows the use of the tristable relay of the rotary type for the actuation of switching arrangements;
Fig. 10: shows a tristable relay of the linear movement type according to the present invention in a first stable working position;
Fig. 11: shows the tristable relay of the linear movement type in a second stable working position;
Fig. 12: shows the tristable relay of the linear movement type in a third stable working position;
Fig. 13: shows the integration of a tristable relay as explained with respect to Figs. 5 to 12 on a printed circuit board PCB;
Fig. 14: shows a first circuit to provide the alternating pulse of calibrated energy for the activation of the tristable relay according to the present invention;
Fig. 15: shows a second control circuit for the supply of alternating currents for the activation of the tristable relay according to the present invention; and
Fig. 16: shows a third control circuit for the supply of alternating pulses for the activation of the tristable relay according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Fig. 3 shows a schematic representation of an ideal relay having two change-over contacts. As shown in Fig. 3, this relay has a left working position, a centre working position, and a right working position. In the left working position a first contact for supply of, e.g., energy to a load is achieved. To the contrary, in the right working position a second contact for supply of, e.g., energy to a further load is achieved. In the middle centre position no contact is established between an energy source and either load. An advantage of the relay illustrated with respect to Fig. 3 over previously discussed relay is that no intermediate states are necessary when switching to desired working positions.
In the following the use of the ideal relay shown in Fig. 3 will again be illustrated with respect to a no-frost refrigerator/freezer operation. Nevertheless, it should be noted that for those skilled in the art any other application for a mutual exclusive switching between, e.g., at least two loads and a common line is necessary and is as well covered by the different embodiments of the present invention as outlined in the following.
As shown in Fig. 4, during operation of the no-frost refrigerator/freezer using the ideal relay aligned for a mutual exclusive switching between the loads again the compressor is turned on/off by switching between the left working position and the centre working position in the relay. After a certain time of operation t_d it will be necessary to remove accumulated ice through activation of the heater evaporator by changing to the right working position. As soon as the desired defrost operation is finished, again a switch-back to the centre position occurs which allows to provide for a certain optional drip time period. Thereafter again the switching takes place between the left working position and the centre working position for the operation of the compressor.
In other words, the compressor may be cycled between the left working position and the centre working position, left working position, centre working position, ... to achieve the desired cooling performance. During the defrost phase the relay moves to the right working position to energize the heater evaporator and perform the defrost operation. In this working position the compressor contact pair remains open so that no cooling takes place.
Fig. 5 shows the basic principle underlying the tristable relay according to the different embodiments of the present invention; it should be noted that while Fig. 5 relates to a tristable relay of a rotary type the basic principle described with respect thereto may also be adapted to a tristable relay of the linear movement type, as will be outlined herein further below.
As shown in Fig. 5, the approach underlying the present invention relies on three stable positions or equilibrium states of an arrangement comprising at least a core element 10 having a coil 12 and a member 14 having a permanent magnet 16. The permanent magnet defines a first and second magnetic pole region N and S, respectively, of the member 14. In addition, the member 14 and the core element 10 are arranged such that a relative movement between the member 14 and the core element 10 is possible.
As shown in Fig. 5, this arrangement allows for three stable working positions. In the first position shown on the left side the magnetic field flux of the permanent magnet 16 is closed over the lower part of the core element 10 while the pole regions N and S of the permanent magnet are arranged symmetrically with respect to the center axis of the core element.
Further, in the second working position shown in the middle part of Fig. 5 the magnetic field flux of the permanent magnet 16 is closed such that it is again closed over the core element, however, with a first pole region, e.g., the N pole tending to align with the center axis of the core element 10.
Still further, in the third stable working position shown in the right part of Fig. 5 the magnetic field flux is also closed over the core element 10, however, this time with the other magnetic pole piece, e.g., the S pole tending to align with the center axis of the core element.
It is important to note that all these three working positions are maintained without continuous supply of energy to the coil 12. The reason for the coil 12 is to achieve a transition between the different working positions. Heretofore, it is necessary to temporarily excite the coil so as to achieve a magnetization of the core element 10 which is not maintained permanently.
One option would be, e.g., for a transition from the left working position to the middle working position that the pole piece of the core element 10 is temporarily changed to the S pole so that the N magnetic pole region of the permanent magnet 16 is attracted.
Equivalently, to achieve a transition between the left and the right working position shown in Fig. 5 the lower part of the core element 10 would temporarily be magnetized into a magnetic N pole so as to attract the magnetic pole region S of the permanent magnet 16.
Still further, it should be mentioned that the three different working positions shown in Fig. 5 have a natural tendency to achieve a stable position in which no further forces or torques are exerted onto the member with the permanent magnet.
Nevertheless, for some applications it might be necessary that in particular the left and right working position the member with the permanent magnet is not only maintained in a stable state but also exerts a certain force or torque onto other construction elements of the tristable relay.
For this reason, there may be provided a left or first stopper 18 and a right or second stopper 20. These stoppers 18, 20 allow to restrict the movement of the member 14 with the permanent magnet such that in the left and right working position the member 14 is not moved into the actual equilibrium state but is stopped shortly before reaching this state. Thus, there will remain a tendency of the member 14 to move further into the equilibrium state shown as left and right position in Fig. 5. This tendency to move further will result into a torque that is executed through the member 14 onto those construction elements being connected thereto.
As also shown in Fig. 5, the transition of the tristable relay between the first, second and third working position may be used to implement the ideal relay shown in Fig. 3. Heretofore, Fig. 5 shows in the left part schematically contact elements 22, 24 provided at the left and right side, respectively, of the permanent magnet 16. Also, the left stopper 18 is used as a first left contact area according to the left working position and the right stopper is used as a second right contact area 28 according to the right working position. Alternatively, at the left side and the right side the related stopper and contact area may be provided separately.
As shown in Fig. 5, in dependence of the working position the member 14 with the permanent magnet 16 either has no contact to the contact elements 22, 24 in the middle position or it achieves a contact between the first contact element 22 and the first contact area 18 in the left working position or a contact between the second contact element 24 and the second contact area 20 in the right working position.
It should be noted that the contact elements 22, 24 and the contact areas shown in Fig. 5 are only illustrative and that clearly the positioning thereof as well as the specific realization may be achieved in many different ways according to the requirements of the specific application. It is the relative movement between the member 14 and the core element 10 that allows to achieve the advantages according to the present invention.
In the following, the basic principle outlined with respect to Fig. 5 will be described in more detail for a tristable relay of the rotor type and the linear movement type. Throughout the following description those elements being related to the ones described with respect to Fig. 5 will be denoted using the same reference numerals for ease of explanation.
As shown in Fig. 6, the tristable relay of the rotor type comprises a core element 10 and the coil 12 for excitation of the core element 10. Further, there is provided the member 14 with the permanent magnet 16. To change the different working positions the core element is excited through the coil 12 through supply of current thereto via terminals 26, 28, respectively.
As shown in Fig. 6, for the tristable relay of the rotor type the core element 10 has a specific structure with two separate pole pieces 10-1, 10-2 facing each other to form a rotor space therebetween to accommodate the member 14 with the permanent magnet 16.
Here, the member 14 is a rotor comprising the permanent magnet 16. Further, the rotor 14 comprises pole extensions 30, 32 in contact with the poles of the permanent magnet 16 to achieve optimized interaction between the permanent magnet 16 and the core element 10. The pole extensions 30, 32 extend beyond the permanent magnet and have two concave recesses that are diametrically opposed. The form of the recesses and the pole extensions is chosen such that the tristable relay is optimized with respect to certain operation conditions, e.g., the torque that should be exerted on the contact elements to close either of the relay contacts.
Operatively, the tristable relay of the rotor type having the structure shown in Fig. 6 has three stable working positions shown in the Figs. 6 to 8. In particular, each of the working positions shown in Figs. 6 to 8 corresponds to the left, middle, and right working position shown in Fig. 5.
While in Fig. 5 the basic principle of the present invention has been explained with the core element having only one pole according to the tristable relay of the rotor type there are provided two pole pieces to increase the amount of torque that may be exerted through the member 14 with the permanent magnet 16.
As already outlined above with respect to Fig. 5, the different working positions shown in Figs. 6 to 8 differ in the way the magnetic field flux concatenates in the magnetic circuit. To better identify the various working positions a black dot has been added to one end of the permanent magnet 16.
The first working position shown in Fig. 6 is related to the middle working position shown in Fig. 5 where the magnetic flux of the permanent magnet 16 concatenates over the single poles of the core element, i.e. via 10-1 and 10-2.
Further, according to the right working position shown in Fig. 7, the member 14 has its clockwise rotation limited, e.g., through the left stopper or through contact areas abutting against each other. With the coil not energized the flux of the permanent magnet 16 flows from the lower to the upper side as shown by the arrows in Fig. 7, i.e. in the direction south/north.
Because the rotor is forced by contact areas to stop at an angle α1 with respect to the vertical axis the magnetic flux is somewhat distorted from the equilibrium point which will correspond to magnetic flux lines running along a straight line from the north to south.
This is a deliberate expedient to generate a clockwise torque to ensure that the contact elements maintain the related closed position with a given amount of force. Further, in case the coil is energized, e.g., by a current generating a upper pole piece with south polarity and a lower pole piece with north polarity, an even stronger clockwise torque may be generated maintaining the member 14 in the position as shown in Fig. 7.
Fig. 8 shows the left working position shown in Fig. 5. Here, the only difference is that the torque is generated in a counter-clockwise direction to close the other two contacts.
By inverting the current polarity in the coil 12, the upper and lower pole pieces of the core element 10 will also invert their magnetic polarity subjecting the element with the permanent magnet to a clockwise or counter-clockwise rotation due to the attractive/repulsive effect that the pole pieces 10-1, 10-2 exert on the contact pairs.
In consequence, the rotor 14 assumes the position illustrated either in Figs. 7 and 8 at which point the coil energization may be terminated. In both positions the contact elements and related contact areas rest against each other to stop the permanent magnet at an angle of either α1 or α2 relative to the vertical axis. In both positions an abutment force of the contact elements is achieved by deliberately keeping the flow of the magnetic flux lines distorted to generate a clockwise or counter-clockwise torque onto the contact elements.
Fig. 9 shows the use of the tristable relay of the rotary type being used together with external switching arrangements. In particular, Fig. 9 again shows the core element 10 and the coil 12 and also the movable member 14 with the permanent magnet, this time in a schematic way.
As shown in Fig. 9, the movable element 14 may be provided with actuator pins 34, 36 adapted to guide a lever 38 rotably supported by, e.g., a revolution joint. The lever carries a contact element 40. To the left side of the contact element 40 there is a left contact face 42 and to the right side of the contact element there is provided a right contact face 44.
As shown in Fig. 9, through operation of the tristable relay as explained with respect to Figs. 6 to 8 the actuator pins 34, 36 will turn the lever 38 either into the left or right working position thus achieving contact between the contact element 40 and the left contact face 42 or the right contact face 44. Further, in the middle position all circuits are open, in the left working position a first load is connected to the line being attached to the lever 38 and in the right working position a second load is connected to the line attached to the lever 38.
In the following, a tristable solenoid relay according to the linear movement type of the present invention will be explained with respect to Figs. 10 to 12. In these Figs. 10 to 12, functional units having the same function as outlined above are denoted using the same reference numerals.
As shown in Fig. 10, a sliding element 14 is adapted to carry out the reciprocal linear movement relative to the core element 10. For the tristable relay of the linear movement type the pole extension of the sliding element 14 comprises a first U-shaped part 46 and a second U-shaped part 48 protruding outside the first U-shaped part 46. The U-shaped parts 46, 48 are in contact with the pole faces of the permanent magnet 16. The core element 10 comprises a U-shaped yoke 10 carrying the coil 12.
As shown in Fig. 10, in the middle position of the tristable relay the magnetic flux generated through the permanent magnet 16 is guided to the pole piece of the yoke 10 via the U-shaped parts 46, 48, respectively, and closes via the single pole pieces 10-1, 10-2 of the yoke without supply of energy to the coil 12.
As shown in Fig. 11, to bring the tristable relay into the position with a closed left contact part, the yoke is magnetized such that the pole piece 10-1 has, e.g., S-polarity and the pole piece 10-2 has N-polarity. Therefore, at the left side there is exerted an attraction force onto the upper U-shaped part 46 and a repulsion force onto the lower U-shaped part 48. Accordingly, at the right side there is exerted a repulsion force between the pole piece 10-1 of the yoke 10 and the related upper U-shaped part 46 and further an attraction force to the lower U-shaped part 48. Once the left contact part is closed, no further energy will be supplied to the coil 12 and the magnetic flux will close along the dashed line shown in Fig. 11 so as to maintain this position as stable working position.
The same principles as outlined with respect to Fig. 11 apply to the Fig. 12 being related to the closed right contact part. The only difference is that here the pole pieces 10-1 and 10-2 have reversed magnetic polarities for movement of the member 14 to the righthand side.
Again, once the right contact part is closed, the magnetic field flux generated by the permanent magnet 16 closes along the dashed line shown in Fig. 9 so as to maintain the working position without further supply of the energy to the coil 12.
As illustrated in either Fig. 10 to 12, also with the tristable relay of the linear movement type there is achieved a coupling of the sliding element 14 to a lever 50 carrying a contact element 52 moving between a left contact face 54, a right contact face 56 and a middle position. Again, the operation is comparable to the one previously described with respect to Fig. 9 so that a repeated explanation is omitted.
Further, it should be noted that the swing angle α₃ and α₄ of the lever 50 shown in Figs. 10 to 12 is dependent on the sliding distance of the sliding element 14 and therefore may be easily modified and adjusted.
Fig. 13 shows an embodiment of the present invention where the tristable relay of the rotary type is provided with a printed circuit board and therefore may easily be inserted into a, e.g., plastic moulded housing.
As shown in Fig. 13, the tristable relay of the rotary type is assembled in a suitably designed moulded plastic box 58. The moulded plastic box 58 and the components of the tristable relay of the rotary type are designed such that the components are located and held after assembly without requiring any further fixing mechanism. Heretofore, the coil 12 may be inserted into a coil holder 60. Also, the member 14 with the permanent magnet and optional pole extensions in contact with the poles of the permanent magnet is supported by a cup type bearing 62. The design of the cup type bearing 62 is such that it allows free rotation of the member 14 but simultaneously prevents the member 14 from tilting under the magnetic attraction of the pole pieces 10-1, 10-2.
As also shown in Fig. 13, the two pole pieces 10-1, 10-2 are positioned using related pole piece locators of which only one 64 is shown. The curved ends of the pole pieces 10-1, 10-2 are brought into contact with the coil 12 through appropriate design of the coil holder 60 such that the pole pieces 10-1, 10-2 touch the pole piece locators 64 with slight pressure keeping them away from the member 14.
As also shown in Fig. 13, there are provided a first fixed contact 66 carrying the previously described left contact face 42, 54 and a second fixed contact 68 carrying the previously described right contact face 44, 56. Between the first fixed contact 66 and the second fixed contact 68 there is provided a moving contact 70 corresponding to the previously described lever 38, 50 and carrying the previously described contact element 40, 52. A fixed contact 66, 68 and the movable contact 70 are made from stamped material and double folded at the terminal end to form a flexible blade having a stiff contact element and contact face, respectively. The fixed contact 66, 68 and the movable contact 70 are located in the box through a labyrinth type of arrangement to secure the fixed and movable contacts. Further, in the moulded plastic housing 58 there are provided terminal access holes 74 for external access to the fixed and movable contacts, respectively.
As shown in Fig. 13, once the tristable relay components are assembled in the moulded plastic housing 58, a printed circuit board PCB 76 is mounted as a cover or lid on the moulded plastic housing. Here, the coil pins 78 and the terminal pins 80 protrude through the printed circuit board 76 so that they can be soldered to the printed circuit board 76. Hereby, the necessary electrical contact for the supply of the current to the coil 12 and to achieve the switching functionality described with respect to Fig. 4 may be achieved.
In the following, there will be explained different approaches to control the supply of pulses to the coil 12 for a transition of the member 14 between the different working positions, both for the tristable relay of the rotor type and the linear movement type.
An alternate current pulse is sent to the coil 12 to bring the member 14 with the permanent magnet 16 into the middle working position according to the lefthand side of Fig. 5 starting at one of these stable positions shown in the middle part and the right part of Fig. 5. The energy of the alternate pulse is calibrated such that it is strong enough to move the member 14 away from one of its stable positions shown in the middle and right side of Fig. 5 (or equivalently, in Fig. 7, 8 and Fig. 11, 12, respectively) but weak enough to exclude a full travel from the left to the right working position or vice versa. That means, the energy will be weak enough to allow an osciallation around the middle position at which point the supply of alternating pulses is terminated with the member 14 stabilizing in the middle position shown in Figs. 6 and 10.
Further, a duration of the power and energy of the alternating pulses is a function of the inertia of the member 14, i.e. the rotor or the sliding element and also of the self-resonance of the tristable relay. Because the rotor and the sliding element have the tendency to stabilize at the middle working position the parameters of the alternate pulses allow for fairly large tolerances.
Examples of calibrated energy alternate pulses and a related control circuit for their generation will be explained with respect to Figs. 14 to 16.
Fig. 14 shows a control circuit adapted to the provision of a conventional selector that allows to achieve progressively decreasing voltage or current pulses in full wave. In position A, a single positive pulse is guided over the diode D1 and goes through the capacitor C1 and further current pulses are precluded as the capacitor C1 is loaded. Further, in position B, a single negative pulse may go over diode D2 and then through the capacitor C2. Again, further current pulses are precluded as the capacitor C2 is loaded. Finally, in position C, alternate current pulses are sent to energize the coil. The damping of the amplitudes of the alternate current pulses is achieved through a PCT thermistor heating up and reducing the current to a negligible value after a short time. This results in a progressively reduced tendency to oscillate around the middle position.
Another option shown in Fig. 15 relates to an electronic controller wherein a coil L is driven with alternate current via thyristors T1 and T2. According to the position A, a single positive semi-wave is triggered by the control unit. In position B, a single negative semi-wave is triggered by a control unit. In a further position, alternate split semi-waves are sent by triggering the thyristors T1, T2 in sequence such that the energy is calibrated through selection of the timing at which the thyristors T1, T2 are triggered.
Another option for the electronic control is shown in Fig. 16 and relates to a coil L driven with direct current via a field effect transistor FET bridge. In position A, a positive pulse is generated by triggering the field effect transistors A and D. Here, the pulse length is selectively determined through the logic. Also, in position B, a negative pulse is generated by triggering the field effect transistors B and C. Again, the pulse length is selectively determined through the logic. Finally, in a further position alternative positive/negative pulses are triggered in sequence. Again, the pulse length, frequency and duration is determined by the logic so as to send a calibrated amount of energy.
Irrespective of the various embodiments outlined above, the permanent magnet may be a sintered part made, e.g, from Ne-Fe-B (Neodimium-Ferrous-Boron) or a single plastic part charged with ferrite combining the functions of the permanent magnet and associate magnetic pole extensions. Ferrite-charged materials known for their chemical stability are, e.g., plastics of the poly-oxy-methylene (POM) or poly-aryl-etherketone families.
Also, irrespective of the various embodiments outlined above, the operation of the tristable relay is effected by energizing the coil with short pulses of current whose positive, negative, alternative nature defines the position of the tristable relay once the coil is de-energized.

Claims

Tristable relay, comprising:

a core element (10) having a coil (12) for magnetising the core element (10); and

a member (14) having at least one permanent magnet (16) for defining a first and a second magnetic pole region of the member (14);

the member (14) and the core element (10) being arranged such that a relative movement between the member (14) and the core element (10) is possible;

stopper means (18, 20; 42, 44; 54, 56) for limiting the relative movement of the core element (10) and the member between a first and a second limit stop position (L, R) ; wherein

in the first limit stop position (L) a pole region of the core element (10) is located in the first magnetic pole region (N) of the member (14) which is urged towards the stopper means (18) for providing the first limit stop position (L) by the magnetisation of the permanent magnet (16), and

in the second limit stop position (R) the pole region of the core element (10) is located in the second magnetic pole region (S) of the member (14) which is urged towards the stopper means (20) for providing the second stopper position (R) by the magnetisation of the permanent magnet (16); and

the core element (10) and the member (14) are arranged such that there exists a third relative position (C) of the core element (10) and the member (14), in which third relative position the pole region of the core element (10) is located partially in the first magnetic pole region of the member (14) and partially in the second magnetic pole region of the member (14) such that the third relative position is stabilized by the magnetization of the permanent magnet (16);

at least two switch elements (18, 22; 20) turned on/off through the relative movement of the core element (10) and the member (14).
Tristable relay according to claim 1, characterized in that the two switch elements (18, 22; 20, 24) are turned on/off in a mutually exclusive manner.
Tristable relay according to claim 1 or 2, characterized in that the member (14) is further provided with pole extensions (30, 32) in contact with the poles of the permanent magnet (16) to achieve optimized interaction between the permanent magnet (16) and the core element (10).
Tristable relay according to one of claims 1 to 3, characterized in that the member (14) is a rotor.
Tristable relay according to claim 4, characterized in that the core element (10) has two separate pole pieces (10-1, 10-2) facing each other to form a rotor space therebetween to accommodate the rotor.
Tristable relay according to claim 5, characterized in that the pole extensions in contact with the poles of said permanent magnet (14) extend beyond the permanent magnet (16) in a radial direction of the rotor.
Tristable relay according to one of the claims 1 to 6, characterized in that the two switch elements are formed by

a first fixed contact (42);

a second fixed contact (44) being arranged opposite to the first fixed contact (42); and

a lever (38) carrying a third contact (40) and getting into contact with the first fixed contact (42) or with the second fixed contact (44) or being positioned between the first fixed contact (42) and the second fixed contact (44) according to the relative movement of the core element (10) and the member (14).
Tristable relay according to claim 7 dependent on claim 4 and claim 1, characterized in that the lever (38) is coupled to the rotor (14) by actuator pins (34, 36).
Tristable relay according to one of the claims 1 to 3, characterized in that the member (14) is a sliding element adapted to carry out a reciprocal linear movement relative to the core element (10).
Tristable relay according to claim 9, characterized in that the two switch elements are formed by

a first fixed contact (54);

a second fixed contact (56) being arranged opposite to the second fixed contact (54);

a lever (50) carrying a third contact (52) and getting into contact with the first fixed contact (54) or with the second fixed contact (56) or being positioned between the first fixed contact (54) and the second fixed contact (56) according to the reciprocal linear movement of the sliding element (14).
Tristable relay according to claim 10, characterized in that the lever (50) is coupled to the sliding element (14) by a revolute joint.
Tristable relay according to one of the claims 9 to 11, characterized in that the pole extensions of the sliding element (14) comprise a first U-shaped part (46) and a second U-shaped part (48) accommodated within the first U-shaped part, the U-shaped parts being arranged in contact with respective pole faces of the permanent magnet (16).
Tristable relay according to claim 12, characterized in that the core element (10) comprises a U-shaped yoke carrying the coil (12), the ends of the U-shaped yoke facing the ends of the U-shaped pole extensions of the permanent magnet (16).
Tristable relay according to one of the claims 1 to 13, characterized in that the permanent magnet (16) is formed of metal ceramic ferrite.
Tristable relay according to one of the claims 1 to 11, characterized in that the member (16) is formed of poly-oxy-methilene (POM).
Tristable relay according to one of the claims 1 to 13, characterized in that the member (16) is formed of poly-aryletherketone (PEKEKK).
Tristable relay according to one of the claims 1 to 16, characterized in that it is integrated as an assembly on a printed circuit board.
Method of operating a tristable relay according to any one of the preceding claims, comprising the steps:

a) moving the member (14) relative to the core element (10) into the first limit stop position (L) through supply of a current impulse with a first polarity to the coil (12);

b) moving the member (14) relative to the core element (10) into the second limit stop position (R) through supply of a current impulse with a polarity opposite to the first polarity to the coil (12); and

c) moving the member (14) relative to the core element (10) into the third position between the first and the second limit stop position through supply of a sequence of impulses with alternating polarity and calibrated amount of energy to the coil (12).
Method of operating a tristable relay according to claim 18, characterized in that the supply of a sequence of impulses with alternating polarity and calibrated amount of energy is achieved via a PTC-thermistor.