GB2233824A - A solenoid actuated relay - Google Patents

Abstract

A solenoid actuated relay providing very low contact bounce in which the contacts 15, 16 are arranged to close in response to the linear movement of the solenoid armature 4 has low contact bounce. A pivotally-mounted member 7 translates the linear motion of the armature 4 into non-linear motion and produces a rotary cam action on a contact holder 8 to operate the relay contacts 15, 16. The camming surface is profiled so that the moving contact 15 decelerates as it approaches the fixed contact 16, reducing contact bounce. The cam 7 additionally provides a locking action by virtue of its continued rotary movement after contact closure. Contact bounce can be further reduced by an extending arm forming part of the cam 7 and exerting pressure on the contacts. The relay can achieve the standard 3mm contact gap and contact movement using a relatively small wound bobbin. The relay may incorporate a flag which indicates whether the contacts are open or closed and may further include a mechanical lever to prevent the contacts closing or prevent them opening unless the lever has been moved to a predetermined position. <IMAGE>

Description

Design of a Solenoid Actuated Relay The present invention relates to a relay intended to be used in devices such as but not exclusively, portable R C D's and similar products.

The relay will find application in any product where low contact bounce and immunity to contact welding under conditions of heavy short circuit currents is required. It is also economical to produce having a minimum of piece parts which are easily assembled.

Most British and International Standards require a contact gap of 3 mm or more to provide electrical isolation and devices such as R C D's and similar products, although not necessarily intended to perform an isolation function in the strict meaning of the term, are often required to provide a minimum contact gap of 3 mm. The provision of a contact gap with a relatively small operating coil requires the relay to operate with high initial pull-in power and relatively low hold-in power while maintaining the low contact bounce, necessary to provide immunity to short circuit contact welding.

It is customary in conventional relay design for the contacts to be operated directly from the relay armature, this is achieved by rigidly fixing the contacts via a contact lifting arm or lifting card which is itself rigidly fixed to the relay armature.

With these types of arrangement the contacts are moved at the same speed as the relay armature or at a faster speed due to the amplification of the lifting arm or lifting card, and since the attractive force on the relay armature increases as it approaches the relay pole piece the contact are moving fastest at the end of their movement. It is at this point that the contacts close and accelerate away from the lifting arm or card causing excessive contact bounce with the consequent danger of contacts welding when closing on to high current and voltage.

The present invention provides a relay comprising a solenoid having a linearly moveable member, contacts arranged to be closed in response to movement of the moveable member, and coupling means for translating the linear movement of the moveable means to non-linear motion whereby the contacts are closed with low contact bounce.

The preferred embodiment provides a relay in which a small solenoid produces a rotary can action to operate the relay contacts which are at right angles and substantially independent to the linear motion of solenoid armature. The can additionally provides a locking action by virtue of its continuing rotary movement after contact closure, reduces contact bounce which can be further reduced by an extending arm forming part of the can and exerting pressure at the contact points.

As a result of the continued rotary movement after contact closure, very little magnetic force is required to complete the linear motion of the solenoid armature and hold it in the closed position while at the same time maintaining relatively high contact pressure.

It is an advantage of this invention that the required 3 mm contact gap and contact movement can be achieved with the utilization of a relatively small wound bobbin, providing the solenoid with the necessary linear motion to achieve this contact travel.

Incorporated in the design is provision for a flag indicator which is preferably integral to the contact position and indicates whether the contacts are open or closed.

A further feature is the provision of a mechanical lever to prevent the contacts closing unless the said lever has been moved to a predetermined position.

The complete design consists of two basic assemblies the linear solenoid actuator and the rotary contact section.

The solenoid actuator comprises a wound plastics materials bobbin, a ferrous material frame, a ferrous metal pole piece, a ferrous metal armature (Plunger) and a compression return spring.

The rotary contact section comprises a plastic material body, a plastic material cam operator, a plastic material contact carrier, moving contact blade assemblies and two pivot pins.

The solenoid actuator is coupled to the rotary contact section by being housed in the body of this latter section and arranged such that its armature couples with the can operator, the cam can be profiled so as to de-accelerate the movement of the contacts as the armature of the solenoid itself accelerates towards the end of its travel, this results in a minimum of contact bounce.

This method of cam operation has the effect of allowing overtravel of the solenoid armature to be transmitted through the cam operator to the contact carrier without necessarily increasing the contact follow through beyond a required amount, locking the contacts into the closed position and easing assembly such that little or no contact adjustment is required to obtain contact follow through and contact pressure.

In order that the present invention be more readily understood, embodiments thereof will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a sectional view of a solenoid; Figure 2 shows a side view of a relay according to the present invention in a first position but with some parts removed for clarity; Figure 3 shows the relay of Figure 2 in a second position; Figure 4A shows a side view of a further embodiment of the present invention; and Figure 4B shows a top plan view of a further embodiment; and Figure 5 shows a circuit diagram of a circuit arrangement incorporating the embodiment shown in Figs.

4A and 4B.

Figure 5 shows a solenoid actuator comprising a wound bobbin 1, a ferrous frame 2, to which is rivetted a ferrous pole piece 3, a ferrous armature 4 is free to move towards the pole piece 3 and is tensioned away from the pole piece 3 by a compression spring 5 shown in Figure 2. When the wound bobbin 1 is energised, the armature 4 will move towards and meet the pole piece 3 and when the power is removed will revert to the rest position.

Figure 2 shows the solenoid actuator in position with a movable, this case rotary contact section 6 from which it can be seen that as the armature 4 is attracted to the pole piece 3 the rotary cam 7 is pulled by the armature 4 causing it to rotate around the pivot 11 and its cam face 14 bears on a movable contact carrier 8 which also rotates about a second pivot 12 resulting in movement of a contact blade 9 closing contact 15 on to a fixed contact 16.

The contacts may be duplicated on the opposite side of the relay providing a 2-pole normally open relay, suitable for making and breaking the live and neutral lines in a supply.

The body of the rotary contact section 6 is of an insulating material and extends between the contacts to provide a natural barrier between them preventing flashover or breakdown particularly during breaking operations.

It is apparent that contacts 15 and 16 do not provide a "dead stop" and that the cam 7 can be profiled as required to give a de-acceleration of the contacts as they approach each other and also provide over travel of the contacts for the purposes of exterting contact pressure between them. In addition the cam can itself accommodate overtravel providing both locking action to the contacts and freedom for the solenoid armature to bounce off the pole piece without transmitting such bounce to the contacts.

A wiping action between contacts 15 and 16 is achieved by the positioning of the contact carrier pivot 12 and the cam 14. These are so arranged that contact 15 travels in an arc about pivot 12 and this motion continues after contact between 15 and 16 is made providing a sliding action between the two contacts.

This sliding or wiping action ensures that the contact faces are "Cleaned" each time they close, providing good contact without introducing contact bounce.

The objective of simple assembly and relatively few piece parts is achieved and the cam over travel and locking action result in little or not adjustment being required while the contact gap and travel is automatically obtained by the moving contacts 15 bearing upon the body 6.

The relay can be mounted on a printed circuit board by means of the foot or projection 17 being inserted through a slot in the PCB and engaging with the underside of the board and one fixing screw into a tapped hole 18 of the relay body 6.

The fixed contacts 16 can form part of a contact assembly part 10 of the relay by being held in the relay body 6. Alternatively, the contacts 16 may conveniently by fixed to the PCB at the same time as the electronic components prior to flow soldering of the PCB. The solenoid relay can then be assembled to the PCB after the flow soldering procedure.

Figure 3 shows in greater detail the method of assembling the solenoid actuator to the rotary contact section the solenoid actuator being held in the rotary contact section body 6 by means of a clip assembly 20 which covers the relay spring 5 and its guide pin 21.

The spring 5 and pin 21 are more conventionally fitted to the clip assembly 20 prior to assembly to the solenoid actuator and rotary contact section.

The clip assembly 20 clips on the body 6 as shown and holds the solenoid in place and at the same time enables the spring 5 which is held in place by guide pin 21 to bear on the cam 7 thus providing the return force required to enable the contacts to achieve the open position. This is achieved by a projection 25 on cam 7 which projects under each moving contact blade 9 thus lifting it as the cam 7 returns to its rest position and the contacts thus revert to the open position.

Cam 7 may include a projection 31 as shown in Figure 3 which can be arranged to bear on the moving blade assembly 9 just at the moment of contact between contacts 15 and 16 to further reduce contact bounce if required. This projection may be moulded as a part of cam 7 or may be an adjustably flexible member subsequently assembled to cam 7.

The armature 4 of the solenoid assembly is retained in position by an extension 8A of the contact carrier 8 which is moulded as part of carrier 8. The extension 8A acts as a stop for armature 4 when the carrier 8 is in the rest position and cam 7 and armature 4 are also in the rest position.

For some applications a mechanical indication of the contact positions, such as a flag 13, may be required, this flag can form part of either the cam 7 or the contact carrier 8 but is preferably part of cam 7 which has greater movement.

Both cam 7 and carrier 8 rotate about their own pivots 11 and 12 respectively and are therefore ideal for this purpose in that neither can change position unless the contacts also change position. A typical indicator or flag 13 shown as part of cam 7, such an indicator can also form part or carrier 8 and can be positioned anywhere on either cam 7 on carrier 8 which will take advantage of their rotary motion and be made to appear or disappear in a window which may form part of an enclosure. The indicator may comprise of two colours such that only one of the two colours appears in the window of the enclosure for each of the two possible contact positions.

Figure 4 shows two possibilities of providing means of preventing the contact closing when the solenoid is energised, this may required for some applications where the insertion of an external plug, pin, key or other external into an enclosure is required before the contacts can be closed. Conversely it may be required to prevent contact closure while a plug, pin, key or other external means is inserted into an enclosure and until it has been removed.

In Figure 4A, an arm 27 is biased by spring 30 and pivoted at 22 so that a projection 29 prevents the contact carrier 8 from moving.

In a similar manner, arm 28 in Figure 4B is biased by spring 24 and pivoted at 23 so that it prevents the movement of cam 7.

In both the above cases contact closure cannot take place unless an external means has been used to remove the relevant arm from the position in which it prevents movement of either carrier 8 or cam 7. It is only necessary to use either the arm 27 or 28 for any one application whichever may be the most suitable.

Conversely means can be used to remove the arm from its position of preventing contact movement, allowing the relay to energise. An external means can then be inserted so as to free the arm which will then be forced on to either the side of cam 7 or carrier 8 by spring 24 or 30 such that should the relay be deengerised the arm 28 or 27 will be free of the side of cam 7 or carrier 8 and spring 24 or 30 will move arm 28 or 27 so as to impeded the movement of cam 7 or carrier 8.

The relay cannot then be re-energised until the external means has been removed after which the relay can be re-engerised and the external means reinserted.

For completeness, reference is now made to Figure 5 which shows a diagram of a circuit for use with the relay constructions as described above. To enable the desired linear motion to be achieved the solenoid may be energised from an electronic circuit devised from that used in our previous patent no. 1585826 and as shown in figure 5, whereby a thyristor SCR1 has its gate connected to a potentionmeter chain R4 and R5. The purpose of SCR1 is to ensure that the relay RLA is provided with adequate power to enable the solenoid armature to complete its travel at which time the holding voltage across the solenoid coil and R6 reduces to a low value, this is achieved by virtue of the capacitor resistor parallel circuit R1.C1 which is itself in series with the bridge rectifier BR1 from the ac input supply.The efficiency of the solenoid coupling to the contacts via the rotary cam and its locking action ensure that adequate contact pressure is maintained in the hold condition.

If required a normally open push button PB1 can be inserted at position X between the bridge rectifier BR1 and resistor R4 such that the relay RLA will not energise unit the push button PB1 is closed.

Push button PB1 can be replaced by a normally closed contact which can be opened by inserting an external plug, key, or other external means, thus the relay will not operate until the external means has been removed and the contacts closed.

The relay RLA is de-energised by SCR2 shorting its coil, and dropping the whole of the holding voltage across R6, SCR2 responds to a signal on its gate which can be generated in the case of an R C D by a fault current to earth or by any other means in the case of the other products.

Relay RLA will therefore remain in the deenergised condition when the signal to the gate of SCR2 has been removed and will not be capable of being reenergised until the ac input to the bridge rectifier has been removed and reconnected interrupting the hold current of SCR1 and SCR2 which otherwise maintains both SCR1 and SCR2 latched.

In the event of a signal being present at the gate of SCR2, the relay RLA will close momentarily when SCR1 conducts but will be de-energised when SCR2 conducts.

In the case of the ac input being interrupted for any reason the relay RLA will re-energise when the ac input is restored provided the circuit is such that resistor R4 is permanently connected to the bridge rectifier BR1.

In the case of a push button PB1 being in circuit the relay will energise when the input is restored and PB1 is closed.

In the case of a normally closed contact replacing PB1, the relay will energise when the ac input is restored provided that the external plug, key or other external means is removed.

Claims (14)

Claims:

1. A relay comprising a solenoid having a linearly moveable member, contacts arranged to be closed in response to movement of the moveable member, and coupling means for translating the linear movement of the moveable member to non-linear motion whereby th-e contacts are closed with low contact bounce.

2. A relay according to claim 1, wherein the nonlinear motion comprises rotary motion about an axis which is perpendicular to the axis of the solenoid of the relay.

3. A relay according to claim 1 or 2, wherein the motion of the coupling member between a first position and a second position causes the contacts to move from an open condition to a closed condition.

4. A relay according to claim 1, 2 or 3, wherein the contacts are fixed to a pivotally mounted holder member.

5. A relay according to claim 4, wherein the coupling members have co-operating camming surfaces.

6. A relay according to claim 5, wherein the camming surfaces are profiled such that the contacts decelerate towards the closed condition.

7. A relay according to claims 5 or 6, wherein the camming surfaces are profiled such that motion of the contacts continues after the contacts first touch each other.

8. A relay according to any of claims 5 to 7, wherein the camminy surfaces are profiled such that when the coupling member reaches the second position the contacts lock in a closed condition.

9. A relay according to any of the preceding claims, wherein the coupling member includes an elongate arm and the contacts move under the action of the free end of the arm.

10. A relay according to any of the preceding claims, further including a lever member which prevents the contacts from closing or prevents the contacts from opening unless the lever has been moved to a predetermined position.

11. A relay according to claim 10 wherein the lever member is moveable to and from the predetermined position by external means.

12. A relay according to any of the receding claims, further including a flag indicator which indicates whether the contacts are open or closed.

13. A relay substantially as hereinbefore described with reference to Figures 1 to 3, 4A and 5 of the accompanying drawings.

14. A relay substantially as hereinbefore described with reference to Figures 1 to 3, 4B and 5 of the accompanying drawings.