Rotary potentiometer with molded terminal package

A rotary potentiometer (10) having an insert molded thermoplastic resin body (12) with an annular groove (14) disposed therein about a central post (19) having an aperture (16) therethrough. A resistive element (26) is disposed about the periphery of the groove (14), an actuator arm (20) is attached to one end of a metallic shaft (18) journalled in said aperture (16) in the central post (19), and a return spring (28) has one end (29) captured within a drop slot (13) at the perimeter of the groove and the other end (31) secured in slot (11) of the shaft (18) for returning the actuator arm (20) and drive arm (22) to their initial position. A drive arm (22) has a rake type contactor (33), the drive arm (22) being secured to the operating end of the shaft (18). A terminal coupling subassembly (65) is positioned within a receiving well (40 ) in the potentiometer body (12), and is captured within the body by securing a cover (80) over the receiving well (40). The plurality of terminals (60-62) in the coupling subassembly (65) have angled ends (72) for resilient contact with terminations of the resistive element (26) and terminal connection ends (55) molded within the potentiometer body (12).

DESCRIPTION 
1. Technical Field 
This invention relates to rotary potentiometers. 
2. Background Art 
A wide variety of variable resistor and potentiometer constructions are 
presently available. These constructions utilize well known prior art 
techniques for the fabrication and assembly of the piece parts. Usually 
the terminals are fabricated as separate piece parts, and then 
individually secured to the housing or a portion of the construction, or 
the terminal piece parts may become part of the housing when the housing 
is formed by insert molding. There are many methods and structures 
utilized for assembling the terminals as part of a variable resistor or 
potentiometer construction. This is illustrated by the following patents: 
Marsten U.S. Pat. No. 2,240,565 entitled "Volume Control," issued May 6, 
1941; Douglas U.S. Pat. No. 3,004,233 entitled "Potentiometer," issued 
Oct. 10, 1961; Hardison et al. U.S. Pat. No. 3,069,646 entitled "Variable 
Resistor Device," issued Dec. 18, 1962; Beaver et al. U.S. Pat. No. 
3,518,604 entitled "Electrical Component," issued June 30, 1970; Casey et 
al. U.S. Pat. No. 3,533,042 entitled "Subminiature Trimmer Potentiometer," 
issued Oct. 6, 1970; and Hildreth et al. U.S. Pat. No. 4,081,782 entitled 
"Combined Rotary Potentiometer and Switch," issued Mar. 28, 1978. 
The development of electronic controls for utilization in the automotive 
industry has resulted in a demand for devices able to a transduce rotary 
position to an electrical output received by a microprocessor. 
Potentiometers are most often utilized to transduce a change in rotational 
position to an electrical output. In order that a potentiometer 
construction be useable with an automotive engine, it is often necessary 
to utilize a thermoplastic resin housing, such a material being resistant 
to many of the contaminants and corosive materials present about an 
automotive engine. When utilizing an insert molding process, it is 
important that the metallic parts be of a standard configuration so that 
the insert molding process can be completed in one step. Otherwise, if the 
parts to be integrally molded within the housing are of an irregular 
shape, this will require more than one insert molding step. Therefore, it 
is desirable to produce a potentiometer construction useable with an 
automotive engine, wherein the body is insert molded about standard shaped 
terminal connections so that the insert molding process may be completed 
in one step. It is also desirable that this potentiometer construction be 
comprised of a number of parts which are easily assembled. 
DISCLOSURE OF THE INVENTION 
The present invention comprises a rotary potentiometer having an insert 
molded thermoplastic resin housing. Disposed within the housing is an 
annular groove disposed about a central post having an aperture 
therethrough. A resistive element is mounted about the outer peripheral 
wall of the groove, and a metallic shaft is journalled within the aperture 
in the post, the shaft having an actuator arm connected to the exterior 
end of the shaft and a drive arm connected to the interior end of the 
shaft. A cylindrically shaped return spring is mounted within the groove 
and about the post by having one end received by a drop slot at the outer 
peripheral wall of the groove, and the other end of the spring received 
within a slot in the end of the shaft. A rake type contactor is secured to 
the drive arm for wipable engagement with the flexible resistive element. 
A terminal subassembly is comprised of three terminals coupled together in 
an insert molded subassembly package. The potentiometer housing has three 
identically shaped terminal projections and connectors insert molded 
within one end of the housing. Each of the ends of the terminals contained 
in the terminal subassembly package are angled for resilient engagement 
with a termination of the resistive element at one end and a terminal 
projection at the other end. The terminal coupling subassembly may be 
drop-fitted in a receiving well within the potentiometer housing. The 
terminal coupling subassembly is captured within the potentiometer housing 
by ultrasonically welding a cover over the terminal receiving well.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings, the potentiometer of the present invention 
is designated generally by reference numeral 10. The body 12 is comprised 
of a thermoplastic resin formed by insert molding techniques well known in 
the art. Formed within body 12 during the insert molding operation, is a 
groove 14 disposed about an interior post 19. The interior post 19 has a 
sintered bronze bushing 15 fitted therein, the bushing 15 having a through 
aperture 16 located therein. The groove 14 includes exterior peripheral 
wall 30 having at one end a drop slot 13. The body 12 includes fastening 
ears 50 for securement of one end of the housing 12, and at the other end 
of the housing is plug fitting 63 for accepting a plug connection with 
terminal connections 70. Located within the body 12 is a terminal 
receiving well or opening 40 and at one end of the receiving well 40 are 
exposed terminal connection ends 55 of terminal connections 70. Also 
located within the receiving well 40 is positioning slot or opening 42. 
A metal shaft 18 is journalled within the aperture 16, with an exterior 
actuator arm 20 secured to the exterior end of shaft 18 and a drive arm 22 
secured to the interior end of the shaft. A "Kapton.RTM." film washer 24 
is positioned about the interior end of the shaft 18 and rests upon the 
bushing surface 25. 
A resistive element 26 comprises a flexible Kapton.RTM. film having 
resistive tracks disposed thereon and element 26 is mounted along the 
peripheral wall 30 of the groove 14. Housing shoulders 32 are disposed at 
an angle of 20.degree. with the wall 30 so that each end of the flexible 
film is captured within the corner of a shoulder. A resilient cylindrical 
spring 28 is located about the post 19. End 29 of the spring 28 protrudes 
radially outwardly and is captured within the drop slot 13 to fix the 
position of the spring relative to the body 12. The other end 31 of the 
spring is fitted within the transverse shaft slot 11, thereby providing a 
return force when the shaft is rotated via the actuator arm 20. 
The slot 17 of the drive arm 22 receives the interior end of the shaft 18 
so that the drive arm rotates with the shaft. Affixed to the drive arm is 
a metallic contactor 33 having a plurality of rake fingers 27, the 
contactor 33 secured by heat staking. The drive arm 22 is positioned 
within groove 14 provided by the body 12 so that contactor 33 wipably 
engages the resistive tracks on the resistance element 26. 
In order to complete the electrical circuit across the contactor 33 and 
resistive tracks of the element strip 26, to the terminal connection ends 
55, three terminals 60, 61, and 62 are affixed together in a terminal 
coupling subassembly 65. The terminals 60-62 are bound together by an 
insert molded thermoplastic body 66. This enables terminals 60-62 to be 
simultaneously fitted within the receiving well 40. The terminal coupling 
subassembly 65 has a downwardly protruding post (not shown) and opening 
68, the post being received by well opening 42 of well 40, and the opening 
68 receiving the protruding posts 46 forming the top portion of drop slot 
13, and thereby position the subassembly 65 within the well 40. The 
terminals 60-62 each have angled ends 72 designed for resilient contact 
with either a terminal end 55 or a resistive track on the element strip 
26. Thus, the entire coupling assembly 65 may be simply drop fitted into 
the receiving well 40 and thereby complete the circuit connections between 
the contactor 33, resistive element 26, and the terminal ends 55. The 
terminal coupling subassembly 65 is captured within the body 12 by 
securing a cover 80 over the receiving well 40. The cover 80 may be 
secured by any suitable adhesive, but preferably secured by ultrasonic 
welding. 
OPERATION 
The potentiometer 10 is assembled by inserting the resistive element 26 
along the peripheral wall 30 of the groove 19, the ends of the element 26 
being secured by the angled shoulders 32. The actuator arm 20 is affixed 
to the exterior end of shaft 18, and the shaft journalled within aperture 
16. The return spring 28 is fitted about the post 19, with end 29 being 
captured by slot 13, and end 31 being secured within transverse shaft slot 
11. The washer 24 is mounted over the interior end of the shaft 18 prior 
to the positioning of spring end 31 within the slot 11. 
Contactor 33 is mounted on the drive arm 22 by heat staking methods well 
known in the art, and the drive arm then secured to the interior end of 
the shaft 18. The shaft 18 may be rotated by angular displacement of the 
actuator arm 20, and the shaft will be returned to its initial position by 
the return spring when the displacement force upon the actuator is 
released. A body housing stop 57 positions the actuator arm 20 and shaft 
in their initial position. Assembly is completed by fitting the terminal 
coupling subassembly 65 within the well 40 so that the downwardly 
protruding (not shown) post is received by the well opening 42 and the 
opening 68 receives the posts 46. The terminal coupling subassembly 65 is 
captured and secured within the potentiometer housing by ultrasonically 
welding the cover 80 over the receiving well 40. 
Rotation of the actuator arm 20 rotates the shaft 18 and effects wipable 
engagement of the contactor rake fingers 27 with the resistive tracks on 
the element 26. The electrical circuit of the potentiometer is completed 
through the terminals 60-62 whose respective angled ends 72 engage 
termination of the resistive tracks and terminal ends 55. 
The flexible resistive element 26 can be readily mounted upon the exterior 
wall 30 of the groove 14. Because the terminal coupling subassembly 65 
allows for the drop-in fitting of a plurality of differently shaped 
terminals into the potentiometer housing, three identically shaped 
terminal connections are insert molded in a single step. Thus, the housing 
is formed in one insert molding step rather than several which would be 
required if the terminals 60-62 were not shaped the same. The angled ends 
72 of the terminals 60-62 are designed specifically for resilient 
engagement with either respective terminal ends 55 or terminations of a 
resistive element 26. The potentiometer of the present invention enables 
the fabrication of piece parts and the assembly of those parts in a 
minimal number of steps, and produces a potentiometer suitable for use in 
an automobile engine environment where there are corrosives and 
contaminants present about the engine. The potentiometer is attached via 
the fastening ears 50, and the plug fitting 63 receives a plug attachment 
to electrically communicate the unit with a microprocessor. 
INDUSTRIAL APPLICATION 
The potentiometer of the present invention may be utilized in automotive 
applications. 
CONCLUSION 
Although the present invention has been illustrated and described in 
connection with example embodiments, it will be understood that this is 
illustrative of the invention, and it is by no means restrictive thereof. 
It is reasonably to be expected that those skilled in the art can make 
numerous revisions and additions to the invention and it is intended that 
such revisions and additions will be included within the scope of the 
following claims as equivalents of the invention.