United States Patent 1 Prouty et al.
[1 l1 3,848,206 [451 Nov. 12, 1974 ELECTROMAGNETIC SOLENOID WITH IMPROVED CONTACT ANTIBOUNCE MEANS Inventors: Robert E. Prouty; James J. Smith, both of Logansport, 1nd.
Assignee: Essex International, Inc., Fort Wayne, 1nd.
Filed: July 18, 1973 Appl. No.: 380,502
US. Cl 335/193, 200/286, 200/288, 335/194 Int. Cl. HOlh 3/60 Field of Search 335/193, 194, 131, 255, 335/133, 156, 257, 258; 200/166 H, 166 M; 324/28 CH References Cited UNITED STATES PATENTS 1/1947 Mason ct al. 335/194 Beardow 335/258 Lundberg 335/194 OTHER PUBLICATIONS Measuring Relay Contact Bounce, by George E. Morris, Electronic Design, Vol. 6, 10/1/58.
Primary ExaminerHarold Broome Attorney, Agent, or Firm-Robert D. Sommer  ABSTRACT An electromagnetic switch having improved means to minimize contact bounce. The improved contact bounce minimizing means includes an adjustable stop member which prevents substantial overtravel of a plunger type armature and a contact assembly connected thereto. I
2 Claims, 5 Drawing Figures PATENIEL 713V 1 21974 @N izgzw on W 1.\w u
PATENTEL WV 1 3.848.206
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lob |o,4 OPEN w Hos CLOSED 71 j MTIME OPEN CLOSED TIME ELECTROMAGNETIC SOLENOID WITH IMPROVED CONTACT ANTIBOUNCE MEANS BACKGROUND OF THE INVENTION This invention relates to electrical solenoids and, in particular, to a method and apparatus for minimizing contact bounce in these devices.
In the electrical contact art, particularly where related to electromagnetically operated switches, the life and current carrying capacity of these contacts are to a great degree dependent on the elimination of bounce of the contacts. Bounce creates an arcing condition that causes deterioration of the contacts and possibly welding of the contact members in a closed condition. It has long been recognized that when the moving contact of a pair of contact members strikes a fixed or stationary contact, the two contact members tend to bounce away from one another causing an arcing condition between the contacts.
Many methods have been proposed to help overcome this problem. For example, there have been numerous proposals on a specific contact structure which eliminates contact bounce. In general these contact structures have been complex and required precise assembly and alignment. This increases production costs and results in an expensive final product.
Thus, it is an object of this invention to provide a method and apparatus to minimize the problem of contact bounce in solenoids.
SUMMARY OF THE INVENTION Briefly, the present invention provides an adjustable stop member which minimizes contact bounce in an electromagnetic switch having a plunger type armature and bridging contacts connected thereto. The stop member is threaded through the switch housing so that it is in alignment with the end of an armature extension. Then, the stop is adjusted properly so that the kinetic energy imparted to the armature and the contact assembly connected thereto is absorbed by the stop member. Normally, this kinetic energy results in contact bounce.
It has been found that the adjustment of the stop member is a critical procedure. Preferably, the stop should be adjusted so that a small amount of overtravel is permitted after the normally closed bridging contacts make. It has been found thatthe best method for adjusting this stop member is by observing the contact action on an oscilloscope. By doing this, the stop can be adjusted to minimize contact bounce.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in connection with the drawing figures in which:
FIG. 1 is an external plan view of an electromagnetic switch constructed in accordance with the invention;
FIG. 2 is an external end view of the electromagnetic switch shown in FIG. 1;
FIG. 3 is an enlarged sectional view taken along line 3-3 of FIG. 2;
FIG. 4 is a graphical view of an oscilloscope trace displaying the action of the normally closed bridging contacts of a switch constructed as shown in FIG. 3, but not having the adjustable stop member 30; and
FIG. 5 is a graphical view of an oscilloscope trace displaying the action of the normally closed bridging contacts of a switch constructed as shown in FIG. 3 and having the adjustable stop member 30 adjusted properly.
DESCRIPTION OF THE PREFERRED EMBODIMENT Shown in FIGS. 1 and 2 is an electromagnetic switch constructed in accordance with the present invention. The switch housing may include a tubular central portion 10 formed from cold rolled steel or other suitable magnetizable material. The central portion 10 has a plurality of tabs 12 which are bent over to hold the as sembly together. Fixed to the central portion 10 by any suitable means is a mounting bracket 14. A first washer 16, formed of suitable magnetizable material, is disposed between the central portion 10 and a first end closure 18 made from a suitable insulating material such as a phenol plastic. A second washer 20, also made of a suitable magnetizable material, is disposed between a second end closure 22, made from electrical insulating material, and the other end of the central portion 10. At this point it should be noted that the type of housing is not part of the invention and that other housing types may be used.
The switch as shown in the drawings consists of two single pole single throw bridging contacts, one normally open and one normally closed. Conventional threaded terminals 24 and 25 are adapted to be bridged by normally closed bridging contacts and terminals 26 and 27 are adapted to be bridged by normally open bridging contacts. An electromagnetic coil is connected to terminals 28 and 29 such that when the proper voltage is applied to these terminals, the coil will be energized and the switch actuated. Protruding axially from end closure 18 is a threaded adjustable stop member 30 constructed in accordance with the invention.
Referring now to FIG. 3, a coil bobbin 32 is disposed axially within the central portion 10. Electrically connected to terminals 28 and 29 (not shown in FIG. 3) is a plurality of conductive turns 34 which are wound upon the coil bobin 32. A circular aperture 35 at the center of washer 16 accommodates movement of a cylindrical plunger type armature 36. The armature 36 is, of course, made from suitable magnetizable material. A small notch 37 within first washer l6 and a slightly offset portion 39 on second washer 20 act conjointly to hold bobbin 32 in place while assembled. Offset portion 39 also acts as a pole piece to which armature 36 is attracted. Thus, it can be seen that when the electromagnetic coil 34 is energized, a magnetic flux path will be created from armature 36, through pole piece 39 and washer 20, through tubular central portion 10 of the housing, through washer l6 and back to armature 36. Thus armature 36 will be attracted to pole piece 39.
A central aperture 40 extends through washer 20 and accommodates movement of a tubular bushing 42 which has a bore extending therethrough. The bushing 42 is disposed in axial alignment with, and between, the armature 36 and a first contact assembly. The first contact assembly includes two nested contact carrying members 44 and 46 which are made from an insulating material such as nylon. Member 44 has a hub 45 which is adapted to fit inside hub 47 of member 46. Both members 44 and 46 have a bore through which a bolt 48 extends. Bolt 48 has a head 56 which fits flush against member 44 to hold the assembly together.
The first contact assembly also includes a generally C-shaped spring member 50 as viewed in FIG. 3. Spring member 50 exerts a force on a contact carrying strip 52 which has contacts 54 and 55 mounted at each end thereof. Both spring member 50 and contact strip 52 are disposed on hub 47 of member 46 and as viewed in FIG. 3 are free to slide thereon. Mounted at each end of contact strip 52 are conventional contacts 54 and 55 which are adapted to bridge fixed contacts 58 and 59- which are connected directly to threaded terminals 27 and 26 respectively.
A second contact assembly, identical to the first contact assembly, is disposed axially adjacent to the other end of armature 36. This second contact assembly includes nested contact carrying members 61 and 62 identical to members 44 and 46 respectively. Also, a spring member 63 identical to member 50 and a contact strip 64 identical-to strip 52 are disposed on the hub of member 62. Contacts 65 and 66 are mounted at each end of contact strip 64 and are adapted to bridge contacts 67 and 68 fixed to threaded terminals 25 and 24 respectively. It can be seen from FIG. 3 that bolt 48 passes through members 44 and 46, bushing 42, armature 36, members 62 and 61, a washer 70 and finally a nut 72. Finally, a compression spring 71 exerts a force on member 44 in a rightward direction as viewed in FIG. 3.
The switch as shown in FIG. 3 is shown in its deenergized position. When the electromagnetic coil 34 is energized, however, the armature 36 will be attracted to the offset portion or pole piece 39. Referring to FIG. 3 it can be seen that when a force of attraction between the armature 36 and pole piece 39 overcomes the force exerted by spring 71, the armature and contact assemblies move to the leftrThus it can be seen that when the armature 36 has moved to its full leftward position, a circuit will be completed from terminal 26 to terminal 27 through contacts 59 and 55, contact carrying strip 50 and contacts 54 and 58.
It should be noted that the particular type of contact arrangement shown in FIG. 3 has the inherent problem that the armature is allowed to overtravel. And it is believed that overtravel and contact bounce are closely related in this type of contact structure. For example, referring to the normally closed bridging contacts in FIG. 3, it can be seen that whenever the electromagnetic coil 34 is energized, armature 36 will be in its full leftward position and contacts 65 and 66 will be disengaged. Also, spring member 63 will be bowed slightly. However, as soon as the coil 34 is deenergized compression spring 71 will force the armature 36 to its deenergized position. It can be seen that as soon as contact 65 engages contact 67 and contact 66 engages contact 68 contact carrying strip 64 willslide to the left on the hub of member 62. At that point if the armature 36 still-has enough kinetic energy, it is possible for the armature and contact assembly to overtravel slightly. This overtravel actually creates a force which directly opposes the force of spring 71. Thus the contacts bounce out of engagement and then quickly reestablish the electrical connection.
By threading the adjustable stop member 30 through the end of the housing and adjusting it properly overtravel can be minimized, thus minimizing contact bounce. It is believed that the stop member 30 actually absorbs the kinetic energy which would result in this overtravel.
It has been found that the adjustment of the stop member 30 is a fairly critical procedure and that the best method for doing this utilizes an oscilloscope. Terminals 24 and 25 may be connected to a voltage source through a resistor and the oscilloscope used to measure the voltage change across the resistor as the normally closed bridging contacts and 66 close.
FIGS. 4 and 5 represent oscilloscope traces which illustrate the first and the last step in the adjustment of the stop member 30. FIG. 4 illustrates the type of trace which is obtained when the stop member 30 is threaded out as far as possible. Line represents an open condition between terminals 24 and 25. Then when the electromagnetic coil 34 is deenergized and spring 71 forces the switch to its deenergized position, bridging contacts 65 and 66 will bridge fixed contacts 67 and 68 and a circuit will be completed from terminal 24 to terminal 25. This is illustrated by the short wavy line 102. However, since the stop member is screwed out as far as possible the armature and contact assembly will be allowed to overtravel and the circuit from terminal 24 to terminal 25 will be opened as illustrated by the transition from the line 102 to line 104 in FIG. 4. Then after a short time interval 108 the bridging contacts will remake as illustrated by line 106.
In order to adjust the stop member 30 properly, it may be threaded farther into the switch housing permitting less and less overtravel and reducing the time interval 108. Eventually when the stop is threaded in far enough a trace similar to that shown in FIG. 5 will be obtained. It can be seen in FIG. 5 that the normally closed bridging contacts associated'with terminals 24 and 25 are either open or closed and there is no appreciable time interval'during which the contacts are open due to bounce.
It is believed that the invention allows for many modifications without departing from the true spirit of the invention. The scope of the invention is defined in the claims.
What is claimed is:
1. In an electromagnetic switch having a housing, an electromagnetic actuator including a coil with a central bore, a plunger armature reciprocable within said coil bore between actuated and unactuated positions in response to energization and deenergization of said coil, a pair of spaced fixed contacts in said housing, contact carrier means rigidly connected to and movable conjointly with said plunger armature, flexible bridging contact means slidably carried by said contact carrier means for limited relative movement thereon and arranged to engage said fixed contacts when said plunger armature is at the unactuated position, a spring member carried by said contact carrier means and biasing said bridging contact means toward said fixed contacts, and spring means biasing said plunger armature and contact carrier means to said unactuated position, wherein the improvement comprises in combination therewith:
an adjustable stop member on said housing disposed adjacent one end of said plunger armature to effectively limit the extent of movement of said plunger armature in the direction toward said unactuated position; and
said stop member being adjusted to allow movement of said plunger armature and said contact carrier means from said actuated position to said unactuated position until said fixed contacts are engaged by said flexible bridging contact means and thereafter an additional predetermined distance which limits the sliding and flexing movement of said flexible bridging contact means to a value that results in minimum bounce of the flexible contact means upon deenergization of said coil.
2. In an electromagnetic switch having a housing, an electromagnetic actuator including a coil with a central bore, a plunger armature reciprocable within said coil bore between actuated and unactuated positions in response to energization and deenergization of said coil, a pair of spaced fixed contacts in said housing, a spoollike insulating member fixed to said armature, said spool-like insulating member having a central hub portion and spaced end walls, a flexible elongated bridging conductor slidable on the hub of said spool-like insulating member, said elongated bridging conductor being adapted to engage said fixed contacts when said plunger armature is at the unactuated position, a generally C-shaped leaf spring slidable upon the hub of said spool-like insulating member, said leaf spring engaging one end wall of said spool-like insulating member and biasing said elongated bridging conductor toward said fixed contacts relative to said spool-like insulating member, a pair of electrical contacts attached to said elongated bridging condutor in spaced relationship, and spring means biasing said plunger armature and said spool-like insulating member to said unactuated position, wherein the improvement comprises in combination therewith:
an adjustable stop member on said housing disposed adjacent one end of said plunger armature to effectively limit the extent of movement of said plunger armature in the direction toward said unactuated position; and said stop member being adjusted to allow movement of said plunger armature and said spool-like insulating member from said actuated position to said unactuated position until said fixed contacts are engaged by said elongated bridging conductor and thereafter an adtional predetermined distance which limits the sliding and flexing movement of said elongated bridging conductor to a value that results in minimum bounce of said elongated bridging conductor upon deenergization of said coil.