Twist Lock Attachment for a Thermal Probe

This invention relates to apparatus for attaching a plastic shell of a thermal probe to a plastic structural member.

U.S. Pat. No. 5,046,857, issued 10 Sept. 1991 and assigned to the assignee of this invention, describes a thermal probe assembly having a premolded unitary one piece plastic shell which attaches to a structural member, e.g. a plastic intake manifold of an internal combustion engine, through male screw threads on the shell and female screw threads in a socket on the manifold. Manufacturing costs associated with fabricating male and female plastic screw threads are relatively high. A twist lock according to this invention for attaching a plastic shell of a thermal probe to a plastic structural member such as an internal combustion engine intake manifold is an improvement relative to the thermal probe attachment described in the aforesaid U.S. Pat. No. 5,046,857.

This invention is a new and improved twist lock for attaching a plastic shell of a thermal probe to a plastic structural member such as an internal combustion engine intake manifold. The twist lock according to this invention includes axial retention features on a cylindrical socket in the structural member and on the shell which cooperate when the shell is rotated in the socket from an unlocked position to a locked position to prevent dislodgement of the shell from the socket, and circumferential retention features on the socket and on the shell which cooperate to prevent reverse rotation of the shell from the locked position. The axial retention features include an annular shoulder at the bottom of the socket and a plurality of hooks on the shell which traverse the plane of the shoulder through notches therein when the shell is inserted in the socket and which are captured by the shoulder when the shell is rotated to the locked position. The circumferential retention features include a pair of radial lugs on the plastic shell and an annular lip around an open end of the socket having cam edges therein. When the shell is manually rotated toward the locked position, force reactions between the lugs and ramps of the cam edges effect progressively increasing resilient deflection of the lip and correspondingly increasing resistance to rotation of the shell so that an installer experiences tactile indication of the progress of the installation. The ramps are contiguous with seats of the cam edges which capture the lugs in the locked position of the shell. Sharp discontinuities of the cam edges between the ramps and seats afford tactile and audible indication of achievement of the locked position.

FIG. 1 is a partially broken-away elevational view of a thermal probe including a plastic shell having a twist lock according to this invention and showing the thermal probe prior to installation on a plastic structural member.

FIG. 2 is a sectional view taken generally along the plane indicated by lines 2--2 in FIG. 1;

FIG. 3 is a sectional view taken generally along the plane indicated by lines 3--3 in FIG. 1;

FIG. 4 is a sectional view taken generally along the plane indicated by lines 4--4 in FIG. 1; and

FIG. 5 is similar to FIG. 1 but showing the thermal probe after installation on the structural member.

Referring to FIGS. 1-3, a fragmentarily illustrated plastic structural member in the form of a plastic intake manifold 10 of an internal combustion engine, not shown, includes an internal chamber or induction passage 12 and a cylindrical socket 14. A one-piece, molded plastic shell 16 of a thermal probe 18 for monitoring the temperature of air in the induction passage 12 is disposed in the socket 14.

A thermistor 20 of the probe is supported below a tubular portion 22 of the shell 16 by a pair of elongated metal terminals 24 each having a pin end 26 in a receptacle portion 28 of the shell. A plastic premold 30 around the terminals is pressed into an appropriately configured passage 32 in the shell with a gas sealing elastomeric ring 34 therebetween whereby the terminals and the thermistor are attached to the shell. For a more complete description of the thermal probe 18, reference may be made to the aforesaid U.S. Pat. No. 5,046,857. The shell 16 is attached to the manifold 10 by a twist lock 36 according to this invention.

The twist lock 36 has axial retention features for preventing dislodgement of the shell 16 from the socket 14 including an annular shoulder 38 at the bottom of the socket 14, an annular flange 40 around the shell 16 between the tubular portion 22 and the receptacle portion 28, and a cage 42 at the distal end of the tubular portion 22. The annular shoulder 38 has an inside diameter 44 corresponding generally to the diameter of the tubular portion 22 and is pierced by an asymmetric array of notches 46 each open through the inside diameter 44.

The cage 42 surrounds the thermistor 20 and includes a plurality of radial legs 48 integral with the tubular portion 22 and defining an asymmetric array therearound, FIG. 3, corresponding in size and angular interval to the asymmetric array of notches 46 in the shoulder 38. Each of the legs 48 terminates at a flat hook 50 in a common plane perpendicular to a centerline 52 of the shell FIG. 1. The flat hooks 50 are separated from an annular surface 54 of the flange 40 in a plane perpendicular to the centerline 52 by a length dimension L1 of the shell, FIG. 1. The length dimension L1 of the shell corresponds to a length dimension L2, FIG. 1, of the socket 14 between an annular surface 56 of the shoulder 38 and an annular surface 58 defining the top of a reduced section annular lip 60 at the open end of the socket.

The shell 16 is inserted into the socket 14 with the tubular portion 22 first and has an unlocked position in the socket characterized by seating engagement of the surface 54 of the flange 40 against the surface 58 of the lip 60 and coincidence between the centerline 52 of the shell and a centerline 62 of the socket. Relative to the socket, the unlocked position of the shell is unique because the legs 48 can only traverse the plane of the shoulder 38 through the notches 46 when the asymmetric arrays of legs and notches are in angular registry. In the unlocked position of the shell, the hooks 50 on the legs 48 are closely adjacent but slightly below the plane of the annular surface 56 of the shoulder 38. An elastomeric seal ring 64 in a groove in the shell 16 seats against the cylindrical wall of the socket 14 to define a gas-tight seal between the shell and the socket.

The shell 16 has a locked position, FIG. 5, achieved by rotating or twisting the shell relative to the socket about the coincident centerlines 52,62 through an included angle of 60 degrees from the unlocked position. A pair of finger tabs 66, FIGS. 1-3, on the shell afford convenient manual grip for twisting the shell from the unlocked to the locked position. In the locked position of the shell, the asymmetric arrays of legs 48 and notches 46 are out of angular registry so that the surface 56 on the shoulder 38 captures the hooks 50 on the legs 48 to prevent dislodgement of the shell from the socket.

The twist lock 36 also has circumferential retention features for preventing reverse rotation of the shell 16 from the locked position thereof including a pair of radial lugs 68 integral with and located on opposite sides of the shell adjacent the annular flange 40 and a pair of cam edges 70 located diametrically opposite each other on an inside cylindrical wall 72 of the lip 60, FIG. 4. The cam edges 70 each include a ramp 74 and a seat 76 contiguous with the ramp. Each ramp has an outboard end radially outboard of the inside cylindrical wall 72 and an inboard end closer to the inside cylindrical wall. The junction of the inboard end of each ramp and the corresponding seat 76 is characterized by a sharp discontinuity or step 78, FIG. 4. The radial depth of the seats 76 corresponds generally to the radial depth of the outboard ends of the ramps.

The cam edges 70 are located relative to the notches 46 and the legs 48 such that in the aforesaid unlocked position of the shell 16, the lugs 68 are disposed at respective ones of the outboard ends of the ramps, and in the aforesaid locked position, the lugs are disposed in respective ones of the seats 76. When the shell is rotated about the coincident centerlines 52,62 from the unlocked position toward the locked position by application of manual effort at the finger tabs 66, the lugs 68 engage the ramps 74. The force reactions between the lugs and the ramps include radial forces on the inside cylindrical wall 72 effecting resilient outward deflection of the lip 60 and tangential forces on the lugs resisting rotation of the shell toward the locked position.

The radial and tangential force reactions increase as the lugs approach the seats 76 due to the increasing interference between the ramps 74 and the lugs 68 and afford an installer tactile indication of the progress of the installation of the thermal probe. At the instant the lugs traverse the discontinuities 78 between the ramps and the seats, the aforesaid radial and tangential force reactions are relieved and afforded both tactile and audible indications of achievement of the locked position. In addition, the discontinuities 78 block the lugs 68 in the opposite direction to prevent reverse rotation of the shell from the locked position toward the unlocked position except upon application of a high level of manual effort at the finger tabs 66 indicative of or corresponding to a conscious intent to remove the thermal probe from the socket.