US 2811680 A
Description (OCR text may contain errors)
FERRARIS RELAY Filed May 10, 1955 ATTORNEYS ftilnited States Patent FERRARIS RELAY Josef Stoecklin, Ennetbaden, and Roland Braun, Nussbaumen, Switzerland, assignors to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Application May 10, 1955, Serial No. 507,374
Claims priority, application Switzerland February 22, 1955 7 Claims. (Cl. 317-167) The present invention relates to relays and more particularly to relays of the Ferraris type which include a disc that is set into rotation whenever the current being monitored reaches the predetermined response or threshold level. The disc is arranged to rotate through a maximum of one revolution as a function of the time the current remains above the responsive level, and the relay contacts, usually associated with the shaft on which the disc is mounted, are actuated after a predetermined angle of rotation of the disc.
In order to prevent the disc from rotating until the response level of the current has been reached, and also to start returning the disc towards its starting position whenever the current falls below the response level, a counter-torque device including a counter-acting spring is utilized. It is also necessary that the magnitude of current which will allow the disc to return be only a few percentage points below that magnitude of current which is just sufficient to start the disc to rotate in the contact actuating direction. Consequently it is essential that at the response level the torque of the counterspring equal the torque acting to turn the disc, throughout the entire turning range of the latter. One known way of effecting this result is by afiixing a helical spring to the axle of the disc, the other end of the spring being fixed or adjustable within a certain range. The spring is usually insulated at its end thus serving simultaneously as a conductor to the movable relay contact on the axle of the disc. This arrangement has two disadvantages. One disadvantage is that the torque of the spring does not remain constant but rather increases proportionally to the angle through which the disc is turned. As a remedy, it has been proposed to give the disc a spiral rather than a true circular configuration such as indicated by the broken line in Fig. 1. This arrangement has the effect that the disc, when its turning angle increases, will reach further and further into the air gap between the pole shoes of the associated magnetic core, and as a result the torque of the disc will be correspondingly increased thus constantly matching the increasing counter-torque exerted on the disc by the counterspring, regardless of the position of the disc. This balance is necessary with respect to the response current, that is, the current which will be just sufficient to start rotation of the disc. At this point a complication arises. Since for each time setting of the relay a corresponding angular travel of the disc is necessary, the extension of the disc periphery into the air gap between the pole shoes of the magnetic system will vary for each position of the disc. Since the forces of the magnetic system which serve to rotate the disc and the counter-spring are in balance only at the critical point of the response current, the characteristics of the relay can be plotted only by using a set of graphs, with the relay time as ordinates, the current as abcissa and the set time as the parameter. The other disadvantage of the helical spring arrangement is mechanical in character for when the disc Patented Oct. 29, 1957 is disassembled, it is always necessary to remove the soldered and sensitive helical counter-spring.
Another known arrangement for counter-balancing the disc torque comprises a small drum which is fastened to the horizontally arranged axle of the disc. A thread is wound on the drum and a weight is suspended at its end. This method has the disadvantage that the adjustment of the response current has to be made by adding or conversely removing weights, which is a cumbersome operation. Also there is always the possibility of entangling the thread, and the weights have the undesirable effect of adding mass which tends to cause overshoot, i. e. continued rotation of the disc after the current has ceased.
The present invention relates to an improved arrangement for effecting a constant counter-torque for the disc of the relay in every position of the disc. This objective is reached by using a spiral cam of uniformly decreasing radius in the direction of rotation of the disc from its starting position, the cam being mounted on the shaft on which the disc is mounted, and a taut flexible tape which is adapted to move longitudinally and wrap around the periphery of the earn as the disc rotates. The tape is connected to a counter-spring which is pulled progressively as the tape winds around the periphery of the cam. However since the effective radius of the cam, i. e. the moment arm, progressively decreases with a progressively increasing counter or restoring force in the spring, the counter-torque which is the product of these two factors will thereby remain constant. This condition will likewise hold true for rotation of the disc in the opposite or return direction for as the moment arm of the cam increases the counter-force of the spring correspondingly decreases.
The foregoing as well as other objects and advantages inherent in the invention will become more apparent from the following detailed description of a preferred embodiment thereof when considered with the accompanying drawings.
In the drawings, Fig. 1 is a view of a Ferraris relay in perspective showing the improved counter-torque arrangement according to the invention;
Fig. 2 is an enlarged view in perspective of the cam;
Fig. 3 is an enlarged perspective view illustrating the arrangement by which the tape member is secured to the spiral cam and the latter is secured upon the shaft; and
Fig. 4 is a transverse sectional View also showing the manner in which the cam and tape are secured in place.
With reference now to the drawings, the Ferraris relay is seen to be comprised of a rotatable disc 1 mounted at its center on a shaft 2, the rotation being about the axis of shaft 2. The relay contacts (not shown) are arranged in conventional manner in cooperation with the shaft 2 so as to be actuated after the disc 1 and shaft 2 have been turned through a predetermined angle which preferably has a maximum of 270 from the starting position shown in Fig. 1. Disc 1 is rotated whenever the current being monitored reaches a predetermined response or threshold level. In order to effect rotation of the disc, induction principles are utilized. To this end, a laminated magnetic core is provided, the core having one leg 3a around which is placed a coil 4 energized by the current being monitored. Two other legs 3b and 3c of this core extend laterally from the ends of core leg 30 and terminate in parallel pole shoes 5a, 5b located in confronting relation on opposite faces of the peripheral portion of disc 1 which is of uniform diameter. Each pole shoe is also provided with shortcircuited turns 6a, 6b, respectively, which is also conventional. All of the core legs are rectangular in cross section and the core legs 3b, 30 each taper convergingly in the direction of the pole shoes 50, 5b which is a feature more particularly disclosed and claimed in a copending application Serial No. 520,857 filed July 8, 1955 in the name of Roland Braun and assigned to the same assignee as is the present application.
As previously indicated, the construction is such that the disc 1 will not begin to rotate until the current in coil 4 and hence also the corresponding rotative effect i. e. torque at the periphery of the disc reaches a predetermined response or threshold level. To establish this condition, a counter-torque is applied to shaft 2, such torque being produced by means of a spirally shaped cam 7 secured upon the shaft, the radius of the cam changing uniformly as a function of its angle of rotation in order to effect a uniformly changing length of the moment arm by which the torque is produced. A flexible tape 8 has one end thereof secured to cam 7 in such manner that as the cam rotates, the tape 8 will Wind around the periphery of the cam. The tape 8 is preferably made from a material having great tensile strength and resistance to heat. Particularly suitable materials for this purpose are synthetics made of polyaethylen-terephthalat and polyamid.
Fig. 3 shows the manner in which the cam 7 is secured upon shaft 2 as well as the manner in which tape 8 is anchored to the cam 7. This view shows the position of the cam and tape after the cam has been rotated 270 from the starting position depicted in Fig. l. A sleeve 9 is secured upon shaft 2 and includes a lower axially extending slotted portion 9a on which cam 7 is mounted. The end of tape 8 is anchored in the slot 912 and, after making one complete turn around the sleeve portion 9a is carried out to the periphery of the cam through a radial slit 7a therein defining the junction between the greatest and smallest radii of the cam.
The end of tape 8 opposite that secured to cam 7 is secured to one end of a helical spring 10. The opposite end of spring 10 can be anchored to a fixed point if de sired but, in the illustrated embodiment of the invention, is attached to one end of a bimetallic spring leaf 11, the opposite end of spring leaf 11 being secured to an adjustable arm 12 mounted pivotally at 13. By adjusting arm 12 about it pivot in either direction there is thus effected a corresponding adjustment in position of the related end of the spring 10. Also, because of the presence of the bimetallic spring leaf 11, the position of the associated end of spring 10 will vary with changes in temperature and is thus self-compensating as regards temperature.
When the current in coil 4 has reached the response level so as to effect rotation of disc 1 in the direction indicated by the arrow, the position the-re shown being the starting position, the effective radius or moment arm of the spiral cam 7 i. e. at the tangent line of the contact of the tape 8 with the cam periphery, and which is greatest at the start of rotation of disc 1, will decrease progressively with increasing angle of rotation of the disc 1. As the tape 8 winds around cam 7 the pull on spring 19 and hence its restoring force will be correspondingly increased. The progressive increase in spring pull is such as to match the progressive decrease in effective cam radius with the result that their product, i. e. the countertorque exerted on the rotating disc will remain constant throughout the full range of rotation of disc 1.
In the case of a decrease in the current below the response value, the counter-torque system will effect rotation of the disc 1 in the opposite direction but the countertorque will remain constant because, as the effective radius of the cam 7 increases, the pull of spring 10 and tape 8 decreases by a corresponding degree. Consequently the torque tending to return the disc 1 to its starting position remains constant.
In conclusion it will be understood that various minor changes in the construction and arrangement of component parts may be made without, however, departing from the spirit and scope of the invention as defined in the appended claims.
1. In a Ferraris type relay including a circular disc mounted centrally on a rotatable shaft for rotation with said shaft and an electro-magnetic core structure including pole pieces in confronting relation on opposite faces of said disc at the peripheral portion thereof for effecting a torque upon said disc, means for applying a countertorque to said disc comprising a spiral cam mounted on said shaft, said cam being of uniformly decreasing radius in the direction of rotation of said disc and shaft from the starting position, a straight flexible tape arranged tangent to the periphery of said cam and having one end thereof secured to said cam and adapted to simultaneously shorten and wind around the cam periphery as said cam rotates, and spring means connected to the other end of said tape and exerting a uniformly changing counter pull on said tape which increases as the effective radius of said cam at the line of tangency with said tape decreases, and vice versa, thereby maintaining a uniform counter-torque on said shaft and disc throughout the range of angular travel thereof.
2. A Ferraris type relay as defined in claim 1 wherein said spring means includes a bimetallic spring connected therewith to effect automatic compensation in the pull of said spring means for changes in temperature.
3. A Ferraris type relay as defined in claim 1 and which includes a sleeve secured upon said shaft, said sleeve having a longitudinally extending slotted portion, said cam being secured upon said slotted portion and the end of said tape being anchored in said slotted portion and extending outwardly to the periphery of said cam through a radial slit therein coincident with its greatest and smallest radius.
4. A Ferraris type relay as defined in claim 1 wherein said spring means is constituted by a helical spring, one end of said spring being secured to said tape and the other end of said spring being anchored.
' 5. A Ferraris type relay as defined in claim 4 wherein the anchor for the other end of said helical spring is constituted by the free end of a bimetallic spring.
6. A Ferraris type relay as defined in claim 5 wherein said bimetallic spring is constituted by a bimetallic spring leaf, and which further includes means for adjusting the position of the end thereof to which said helical spring end is anchored.
7. A Ferrari s type relay a defined in claim 6 wherein said bimetallic spring leaf is mounted for pivotal movement.
France Mar. 20, 1923 43,882 Norway Mar. 28, 1927 511,675 Canada Apr. .5, 1955