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Description  |
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BACKGROUND
The present invention relates to pushbutton switches for use in electrical circuits; for example, an ON-OFF switch in which electrical contact is made when the plunger of the switch is pressed once and contact is broken when the plunger is
pressed a second time. It may also be useful for an ON-ON-OFF switch, where there are two different ON positions and an OFF position. It might also be useful for a single pole, double throw switch, where there are two different ON positions and one OFF
position. A switch may be an ON-ON switch, where electrical contacts are switched between a common lead and either of two alternate other leads. etc.
A variety of electrical pushbutton switches are well known, with quite a variety of internal operating mechanisms. Small pushbutton switches are desirable for automotive applications, for example, and many of such switches are somewhat noisier
than desired. It is preferable to have a pushbutton switch that is quieter than most that are presently available. Many switches have wiping or sliding contact between terminals as the switch is opened or closed. It is desirable to minimize friction
in such a wiping contact, if for nothing else but to minimize wear. Light wiping contact pressure is therefore desirable.
It is also desirable that the change of state of the switch does not occur when the plunger of the switch is depressed, but only commences when the plunger is released and moves upwardly. This is known as a "stable-ON feature," which avoids a
problem of intermittent contact (e.g., a flickering light bulb) when the plunger of the switch is partly depressed or vibrated.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment, the pushbutton switch comprises a body or housing with two or three electrical terminals, for example. A pushbutton plunger is mounted for reciprocation in the housing for operating the switch. There is a rotatable
contact member for contacting the terminals, depending on the rotational position of the contact member for making or breaking an external circuit. A shaft engages the plunger so that it is moved downwardly upon downward depression of the plunger and
rotates in response to movement of the plunger. A ratchet rotates the contact member in response to rotation of the shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features and advantages of this invention will be appreciated from the following description of presently preferred embodiments when considered in connection with the accompanying drawings in which:
FIG. 1 is an exploded perspective view of a pushbutton switch, looking somewhat downwardly toward the switch;
FIG. 2 is another exploded perspective view looking somewhat upwardly toward the switch;
FIG. 3 is an additional perspective view of a plunger insert which forms a part of the plunger of the switch;
FIG. 4 is a longitudinal cross-section of the outer portion of the plunger;
FIG. 5 is a bottom end view of a shaft that fits into the plunger;
FIG. 6 is a view of the face of an electrical contact member;
FIG. 7 is a side view of the contact member illustrated in FIG. 6;
FIG. 8 is a face view of electrical terminals in the switch housing;
FIG. 9 is a semi-schematic illustration of the switching positions for an ON-ON-OFF switch;
FIG. 10 is a partial longitudinal cross-section through the switch when the plunger is depressed;
FIG. 11 is a partial longitudinal cross-section through the switch when the plunger is released or retracted;
FIG. 12 is an end view of another embodiment of shaft for a pushbutton switch;
FIG. 13 is a view of the face of a second embodiment of electrical contact member for a pushbutton switch; and
FIG. 14 is a side view of the contact member illustrated in FIG. 13.
DESCRIPTION
A pushbutton switch has a housing formed of a switch body 10 and a cover 11. The housing is assembled and kept together by pressing pins 12 on the cover into holes 13 in the body with an interference fit. In the illustrated embodiment, three
electrical terminals 14, 15 and 16 fit into the cover. The electrical terminals provide means for connecting the switch to external leads. No additional description is needed for the body, cover and terminals, since they are nearly conventional, and no
additional information is needed for an understanding of this invention.
It may be kept in mind that such a pushbutton switch is actually quite small, not nearly as large as suggested by the drawings. Thus, a typical switch may have a housing that is only 13 by 18 millimeters.
As a matter of convention for this specification, the body is considered to be the top of the switch and the cover is considered to be the bottom. For example, when the plunger of the switch is pressed, it moves downwardly. Similarly, the view
of FIG. 1 looks generally downwardly toward the switch, and FIG. 2 looks generally upwardly toward the switch. The switch may, of course, be used in any orientation.
There are three keys 17 on the outer part of the plunger 18 of the switch. These keys fit into matching keyways 19 in the housing to permit the plunger to reciprocate without rotation. The plunger includes a hollow insert 20, which fits into
the outer part 18. This is illustrated separately herein, since it is manufactured in a separate piece from the balance of the plunger, so that the internal structure of the plunger can be injection molded. The insert is pressed into the plunger with
an interference fit so that, when assembled, it becomes a permanent part of the plunger. A key 21 on the insert fits into a longitudinal slot 25 inside the plunger to assure appropriate alignment of the insert within the plunger.
The insert includes two slots 22. Each of the slots has a lower portion 22A extending longitudinally and connecting to an upper portion 22B that extends diagonally or spirally upwardly and circumferentially (FIG. 3).
A shaft 23 fits into the assembled plunger, i.e., within the hollow insert portion of the plunger. A pair of opposite pins 24 extend laterally from the side of the shaft somewhere near the middle of its length. These two pins fit into the two
slots respectively in the plunger insert. The pins and slots serve as guides or cams for relative movement of the shaft upwardly within the plunger and diagonally upwardly, as described below. The shaft is kept centered in the housing by the hollow
plunger and a short axial pin 35 which fits into a cavity in the cover 11.
At the lower end of the shaft, there is a small flange with a plurality of teeth 26 radiating from the shaft. In the illustrated embodiment, there are nine teeth (FIG. 5). In this embodiment, one of the pins on the shaft and its corresponding
slot in the plunger are relatively wide. The opposite slot and pin are relatively narrow. The reason for doing this is that this permits assembly of the shaft into the plunger in only one rotational position. In an embodiment with an odd number of
teeth on the shaft, it is desirable that the leading edge of a tooth lies at a known location, for example, on a centerline of the switch. This can be seen, for example, in the illustration of FIG. 9. Having a structure that permits assembly of the
shaft into the plunger in only one position, assures correct alignment of the teeth on the shaft with the housing of the switch, hence with the terminals.
An electrical contact member 27 fits over the shaft 23 so that the center portion of the contact member lies above the toothed flange at the lower end of the shaft. There is a generally conical raised lip around the center hole of the contact
member which engages the flange at the lower end of the shaft to keep the contact member centered. In this embodiment, there are three circumferentially extending fingers 29 on the contact member, which are bent downwardly far enough that the ends of
the fingers extend below the teeth on the shaft so as to make electrical contact with the terminals fixed in the housing. It will be apparent that the fingers are radially further from the center of the shaft than are the ends of the teeth. Preferably,
the electrical contact member is made of beryllium copper so that the contact fingers are only slightly bendable, only enough to assure good wiping electrical contact with the respective terminals.
There is a smaller finger 31 which is also bent downwardly on the electrical contact member. This finger is bent downwardly only enough that the end can engage the leading edge of a tooth to act as a pawl with the teeth acting like a rachet.
This pawl finger is narrower and hence more easily flexible than the contact fingers.
As mentioned above, there are three electrical contact terminals 14, 15 and 16 placed in the cover and held there by the body of the housing. Each of the terminals has a pair of shallow raised and widened areas 32 spanning an opening 33. These
raised areas provide for electrical contact with external leads plugged into the housing of the switch from either an end or the bottom of the switch. Further toward the center of the switch, each of the terminals has an electrical contact pad 34 for
electrical contact with fingers on the rotatable contact member 27. The center terminal has a somewhat larger contact pad (i.e., extending further circumferentially) than the outer two terminals. The circular holes 30 illustrated through the outer
terminals are clearance for pins between the cover and body which also help position the terminals.
As described below, the contact member rotates 40.degree. (with a nine tooth shaft) each time the plunger of the switch is depressed and released. The contact member is rotated 40.degree. upon each actuation of the switch by the leading edge
of a tooth engaging the pawl 31 extending downwardly from the contact member.
FIG. 9 illustrates contact positions for the contact member on the respective terminals. This is a schematic illustration with small diameter circles labeled A1, B1, etc., representing the contact location for the respective fingers on the
contact member as the switch is operated. The arrangement is suitable for a three-state, ON-ON-OFF, switch. Thus, in one state of the switch, finger A1 is in electrical contact with terminal 16 (referred to as the upper terminal, as illustrated in FIG.
9). The second finger A2 is in electrical contact with the center terminal. The third finger A3, is not in electrical contact with any terminal. Thus, in this state the switch is ON with an electrical circuit completed between the upper and central
terminals.
Upon one actuation of the switch, the fingers advance 40.degree. to the B positions. As seen in this illustration, none of the fingers B1, B2 or B3 is in electrical contact with any of the contact pads on the terminals. Thus, the switch is
OFF.
Upon an additional actuation of the switch, the fingers advance another 40.degree. to the C positions. Now, one of the fingers C1 is in contact with the center terminal, a finger C2 is in contact with the lower terminal and the third finger C3
is not in electrical contact with any terminal. As in this state, there is a completed electrical circuit between the center and lower terminals and the switch is ON in a second state.
It will be apparent that upon an additional actuation of the switch, the fingers advance another 40.degree. (e.g. with the contact C1, then the position of A2 is illustrated in FIG. 9) and the switch is advanced to its initial ON state.
FIG. 10 illustrates in longitudinal cross section the state of the switch when the plunger is depressed. FIG. 11 is similar, but with the plunger released. These illustrations are semi-schematic since the vertical positions of the plunger,
etc., are shown without rotation being shown.
As the plunger is depressed, it commences compressing a coil spring 36, one end of which is in an annular channel in the plunger outside the insert. The other end of the spring bears against the electrical contact member 27 biasing it toward the
terminals for good electrical contact. The spring also serves as a return spring for the plunger when pressure on the plunger is released.
As the plunger is depressed, a longitudinal portion of the slots 22 travels along the pins 24 extending laterally from the shaft. As the plunger reciprocates further, the pins enter the diagonal or spiral portion of the slots which causes the
shaft to rotate. Furthermore, the upper face or camming surface of the slots moves the shaft downwardly, reducing and eliminating engagement between the teeth on the shaft and the pawl extending downwardly from the contact member. The spacing between
teeth (i.e., circumferential width of the teeth) can be such that there is very little, if any contact, between the pawl and the tooth during this rotation of the shaft. Even if there is some contact, the angles and flexibility of the pawl finger are
such that the pawl can ride over the trailing edge of a tooth. At the end of a depression stroke of the plunger, as illustrated in FIG. 10, the pawl is completely disengaged from the teeth.
When the plunger is released, the lower edge or camming surface of the slots engages the pins on the shaft and simultaneously lift the shaft toward the contact member and rotate the shaft so that the leading edge of a tooth engages the pawl.
Thus, the tooth causes rotation of the contact member. The tooth engaged with the pawl advances the contact member 40.degree. (for the nine tooth embodiment illustrated) causing a change of state of the switch (from ON-to-OFF, for example) as the
plunger reciprocates towards its released position.
It will be noted that as the plunger is depressed, the teeth do not engage the pawl to change the state of the switch. This is desirable for a more stable switch.
The length and/or the angle of the spiral slots acting on the pins, determine the angles through which the shaft oscillates in rotation. As a matter of practice, it is desirable to rotate the shaft more than 40.degree. during the depression
stroke. Thus, when the shaft returns during release, there is some free travel before a tooth engages the pawl and commences rotation of the contact member. Thus, the length of the diagonal portion of the slots preferably extends more than 40.degree.
around the insert.
The pins enter the longitudinal portion of the slot toward the end of the release stroke and the wall of this portion of the slot determines the final position of the tooth relative to the switch housing, and hence the rotational position of the
pawl and electrical contact fingers on the terminals. The various keys used during assembly of the switch assure appropriate alignment of all of the parts so that the contact fingers engage the terminals in the appropriate location.
In a simple ON-OFF switch, it is appropriate to use an even number of teeth on the shaft, such as the embodiment of FIG. 12 wherein there are six-teeth 41 radiating from the lower end of the shaft. In such an embodiment, the length and/or angle
of the spiral slot in the plunger is sufficiently longer that the shaft oscillates in rotation somewhat more than 60.degree.. This is enough that in the ON state of the switch all three contact fingers on the contact member are in electrical contact
with a respective terminal. Upon 60.degree. rotation of the contact member, none of the contact fingers are in contact with any of the terminals and it switches OFF.
Other variations of design are quite feasible in such a pushbutton switch. For example, instead of a plurality of more or less square teeth radiating from a flange at the lower end of the shaft, one may use teeth that are more typical of a
rachet. In such an embodiment, which is not illustrated, there is a circular flange and more or less triangular teeth radiate above the upper surface of the flange. Such a shaft operates similarly, but is somewhat more difficult to injection mold.
The shaft in the illustrated embodiment has two laterally extending pins with different diameters. This is merely an aid for correct assembly when there are an odd number of teeth on the shaft. The pins and slots may have the same size if other
means are employed for assuring correct assembly, or if the number of teeth is even, such as in the six tooth embodiment illustrated. A second pin as also not necessary, it simply balances the loading. A switch is operable when only one set of pin and
slot is used.
Another variation is illustrated in FIGS. 13 and 14, which show a somewhat different structure of the electrical contact member. In this embodiment, instead of circumferentially extending fingers (such as illustrated in the embodiment in FIGS. 6
and 7) there are three circumferentially spaced apart "bumps" 46 on the bottom on the contact member for electrical contact with terminals in the housing. The contact member is basically a circular disk with a central hole 47 through which a pin on the
end of the shaft fits to engage a hole in the cover. There are three circumferentially extending slits 48 through the face of the disk. Each of the bumps is stamped or coined out of the plane of the disk in a generally U-shape between the outer edge of
such a slit and the perimeter of the disk.
Two of the slits 48 are short circumferential arcs. A third slit 49 has an elongated U-shape to nearly surround a finger 51. At least the end of the finger is bent downwardly to form a pawl 52 extending below the plane of the disk. The pawl
finger can be stamped or coined thinner than the balance of the contact member for enhanced flexibility. Thus, although structurally different from the embodiment illustrated in FIGS. 6 and 7, this contact member is functionally equivalent.
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