US3697049A

US3697049A - Winch drum drive and control

Info

Publication number: US3697049A
Application number: US136324A
Authority: US
Inventors: David B Wallace
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-04-22
Filing date: 1971-04-22
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10

Abstract

There is provided in a winch structure, rotational speed reduction gearing in a fixed housing supporting an hydraulic actuator piston housed in an extension of the rotational speed reduction gearing, the piston being centrally open through inner and outer relatively rotatably connected members thereof, through which central opening a power output shaft of a rotational speed reduction worm gear extends and is connected to rotate with a power input casing component of a selectively slip, normally nonslip coupling, and a power output component of the casing is connected relatively rotatably with the power input casing component and to rotate with a drum of the winch, there being discs in the casing in sets connected respectively to rotate with the casing components and biased by spring-loaded means in the casing to maintain non-slip conditions between the sets and be actuated by lugs on the outer member of the hydraulic piston through apertures in the power input casing component against the bias of the spring-loaded means for slip to occur between the sets of discs when the piston is hydraulically energized.

Description

United States Patent Wallace [54] WINCH DRUM DRIVE AND CONTROL [72] Inventor: David B. Wallace, 630 Camp Circle,

Birmingham, Ala. 35215 [22] Filed: April 22, 1971 [21] Appl.No.: 136,324

[52] US. Cl. ..254/187 R, 192/91 A [51] Int. Cl. ..B66d l/00 [58] Field of Search.254/187, 185; 192/85 AA, 91 A [56] References Cited UNITED STATES PATENTS 3,107,899 10/1963 Henneman ..254/187 3,373,972 3/1968 Peterson ..254/187 3,016,121 1/1962 Mosbacher ..192/91 A FOREIGN PATENTS OR APPLICATIONS 16,155 8/1956 Germany ..2S4/l87 1,119,483 12/1961 Germany ..254/187 Primary Examiner-Harvey C. Hornsby Attorney-John B. Armentrout [151 3,697,049 [451 Oct. 10, 1972 ABSTRACT There is provided in a winch structure, rotational speed reduction gearing in a fixed housing supporting an hydraulic actuator piston housed in an extension of the rotational speed reduction gearing, the piston being centrally open through inner and outer relatively rotatably connected members thereof, through which central opening a power output shaft of a rotational speed reduction worm gear extends and is connected to rotate with a power input casing component of a selectively slip, normally non-slip coupling, and a power output component of the casing is connected relatively rotatably with the power input casing component and to rotate with a drum of the winch, there being discs in the casing in sets connected respectively to rotate with the casing components and biased by spring-loaded means in the casing to maintain non-slip conditions between the sets and be actuated by lugs on the outer member of the hydraulic piston through apertures in the power input casing component against the bias of the spring-loaded means for slip to occur between the sets of discs when the piston is hydraulically energized.

5 Claim, 5 Drawing Figures PATENTEDHN 10 I972 SHEET 1 BF 2 J INVENTOR /c/ 5. Wa//ace ATTORNEY v v m nmmm i kwvm M mm WINCH DRUM DRIVE AND CONTROL The present invention relates to improvementsin power operated winches and is more particularly concerned with rotary power transmission and control toward controlling winch drum operations.

Among the objects of this invention is to provide compact, durable and reliable mechanism which equips a winch drum, and through which mechanism the drum may be driven rotationally through self-locking speed reduction gearing on power supplied from a source of rotary power represented by a motor and yet be counteracted by the gearing against effecting back drive through the gearing while holding a load suspended on a cable having convolutions wound on the drum and furthermore be prevented from overdriving the motor while the gearing is being motor operated having the drum paying out cable lowering a load, all with the mechanism moreover having a selectively slip, normally non-slip coupling serving controllably between the gearing and the drum for braking or clutching the drum to an extent based upon amount of slip desired to be introduced ranging from substantially zero slip up to substantially full slip, the latter condition being useful for such purposes as for enabling free fall of a load on the drum to occur with the load being on a cable paying out from the drum.

Other objects of the present invention will in part be obvious and in part pointed out more fully hereinafter.

In accordance with the present invention, a winch drum power transmission is provided having a selectively slip, normally non-slip coupling between rotational speed reduction gearing and the winch drum, which gearing is characterized by being self-locking against torque supplied back from the winch drum through the selectively slip, normally non-slip coupling such as under non-slip conditions in the coupling. The self-locking rotational speed reduction gearing nevertheless is available for being operated to have rotary power output in either rotary direction to the selectively slip, normally non-slip coupling and the coupling may be controlled to transmit normally rotary full power in either rotary direction through itself, accordingly received, for operating the winch drum, or be controlled to achieve power operation of the winch drum under conditions of slip either for delivering power to the winch drum or for absorbing backdrive from the winch drum on slip up to being controllable for accomplishing substantially full slip and free fall of a load backdriving.

The foregoing features, moreover, ally with the fact that the selectively slip, normally non-slip coupling includes first and relatively rotatably connected second casing components, the first casing component being connected for rotating with the winch drum, and the second casing component being connected for rotating with the power output shaft of the self-locking rotational speed reduction gearing. The coupling has first and second sets of discs, and thrust application means, all within the rotary casing, the discs in the sets being in a side by side alternating relationship with one another, this with the thrust applicator means being constructed having contact and presser structure and spring biasing means. In the contact and presser structure there are contactand presser members carried on the second casing component of the coupling for the presser member to be moved forward longitudinally of the to tary casing against the sets of discs, which for abutment are opposed by the first casing component, and the contact and presser structure as mounted carrying the presser member forward against the sets of discs is adapted to carry the contact member forward simultaneously toward apertures in the second housing component, thus for the contact and presser structure eventually, as may be desired, to be reversely actuated by force applied to the contact member through those apertures.

The forward movement of the contact and presser structure is urged, and reversely is opposed, by the aforementioned spring means, the latter being supported to the second casing component and against the contact member so as compressively to maintain nonslip conditions between the sets of discs at least up to a rated maximum load under which the winch drum is to operate.

The foregoing features also are allied with introduction of fixed housing structure wherein the self-locking rotational speed reduction gearing is housed, and with introduction of an extension of the fixed housing structure having that extension provide a chamber closed off by an hydraulically controllable piston for hydraulic control of the thrust applicator means in the selectively slip, normally non-slip coupling to produce slip ranging up to substantially full slip in the coupling while the actuator piston acts against bias of the aforementioned spring biasing means in the thrust applicator means. The piston includes relatively rotatably connected inner and outer piston members each having a central aperture therein accommodating the power output shaft of the self-locking rotational speed reduction gearing. There is at least one port communicating with the piston chamber within the fixed housing extension and the inner piston member is slidably movably sealed closing off that chamber for the piston to respond slidably to the pressure of hydraulic fluid introduced into the chamber through the port. The outer piston member is provided with lugs at the outer end thereof and the lugs extend through the aforementioned apertures in 'the second casing component of the selectively slip, normally non-slip coupling, accordingly locking the outer piston member and the second casing component together rotationally and relatively movably longitudinally of the rotary casing. Reach of the lugs is sufficient for the piston to maintain contact with the contact member of the thrust applicator means in the selectively slip, normally non-slip coupling and shuttle according to bias of the thrust applicator means 'and the pressure of fluid admitted into the piston chamber, the amount of slip between the discs in the coupling thus being prescribably according to pressure of the fluid in the chamber and the normally non-slip conditions being arrived at by demand of the spring means in the thrust applicator means, with hydraulic pressure in the chamber being sufficiently reduced.

In the accompanying drawings there is represented for purposes of illustration a form which the invention may assume in practice; in which drawings:

FIG. 1 represents in a winch, a winch drum, and as further components of the winch, in longitudinal central vertical section, a selectively slip, normally non-slip rotary coupling in association with the drum, and selflocking rotary speed reduction gearing housed along with an hydraulic piston for operating the selectively slip, normally non-slip rotary coupling;

FIG. 2 is a transverse vertical section taken in the apparatus through the selectively slip, normally non-slip rotary coupling in the plane of line 2-2 in FIG. 1;

FIG. 3 also is a transverse vertical section taken in the apparatus through the selectively slip, normally non-slip rotary coupling, but is in the plane of line 33 in FIG. 1;

FIG. 4 represents details of the hydraulic actuator piston as viewed in vertical transverse cross section in the plane of line 4-.-4 in FIG. 1; and

FIG. 5 is a view in transverse vertical cross section in the plane of line 5-5 in FIG. 1, representing further details concerning the actuator piston, particularly in relation to the actuator housing member which extends from the housing of the rotational speed reduction gearing.

Like reference characters are intended to have like designation throughout the several figures of the drawmg.

Referring now more particularly to the accompanying drawings, a power operated winch designated in general by reference numeral is represented in FIG. 1 to the extent that in the mechanism of the winch a rotary drum 11 is provided such as for hoisting or lowering a load by cable 12 attached to the winch drum and to the load. Drum 11 is secured for rotating unitarily with the drum shaft 13 having the latter journaled in uprights 14 of a supporting framework which further comprises a base 15 securely mounted upon a support 16 which, for example, is offered either on a vehicle or in a static location, and in either instance such as in a warehouse, a factory, or at a site of engineering construction. For transmitting power to the winch drum 11 and controlling the same, in the present embodiment, a unit comprising a selectively slip, normally non-slip coupling 17 is attached to the winch drum shaft 13, and the unit referred to further has an hydraulically controllable power actuator 18 for controlling the selectively slip, normally non-slip coupling 17, and also has rotational speed reduction worm gearing 19 connected with the selectively slip, normally non-slip coupling for supplying power to the coupling. The unit as installed is fixedly connected to the support 16 by suitable fasteners through apertures in an external flange 21 of the housing 20, the latter accommodating therein the rotational speed reduction worm gearing 19.

A power input helical worm gear 23 of the speed reduction gearing 19 is connected driven with a power input drive shaft 22 of the speed reduction gearing, having the power input drive shaft suitably journaled within housing and introduced in a manner through an aperture in the housing and driven by any suitable motor not shown, for operating the winch 10. A power output toothed annular gear 24 meshing with the power input helical worm gear 23 is splined at 26 to the speed reduction gearing power output shaft which in supporting the annular gear is journaled in the housing 20 and extends through aperture 27 in the housing.

The selectively slip, normally non-slip coupling 17 in the present embodiment is characterized by having a rotary casing formed including a hollow annular first casing component 28 providing a generally cylindrical wall 29 closed off at one end by a first end wall 30 integral centrally with a hub 31 which is splined at 36 to shaft 13 of the winch drum 1]. At opposite end, the cylindrical side wall 29 is closed off by a second end wall 32, the latter centrally having an aperture 34 therein. A circular second casing component 35 coaxial with the power output shaft 25 of the speed reduction worm gearing 19 is splined to that shaft and is joined relatively rotatably with the first casing component 28 through an anti-friction bearing and seal 37, the bearing and seal joint being annularly between the generally cylindrical side wall 39 of a dished member 38 secured to rotate with the second casing component 35 and be interiorly of the rotary casing formed including the aforementioned first and

second casing components

28 and 35 with which components the cylindrical side wall 39 is coaxial. At inner end, the dished member 38 is provided with a transverse end wall 40 integral with the dished member cylindrical wall 39.

A first set of discs 41, and a second set of discs 42, are in side by'side alternating relationship with one another in the sets, and each of the discs is in the form of a flat ring preferably metallic, such as of steel. The discs 41 in the first set are annularly exteriorly toothed and the discs 42 in the second set are annularly interiorly toothed. Further, the generally cylindrical side wall 29 of the first casing component 28 integrally has splines 43 interiorly with the splines leading longitudinally of the rotary casing and engaging with the exterior teeth of the first set of discs 41, and the generally cylindrical side wall 39 of the dished member 38 integrally has exterior splines 44 with the splines leading longitudinally of the rotary casing and engaging with the second set of discs 42. Advantageously, the annular trough formed in the first casing component 28 by the cylindrical side wall 29 and the

opposite side walls

30 and 32 contains oil in which the lower portions of the sets of

discs

41 and 42 are immersed.

Thrust applicator means generally designated by the reference numeral 45 receives support and guidance slidably on the transverse end wall 40 of the dished member 38. In the thrust applicator means, there is an outer or forward circular contact plate 46, and an inner or rearward presser plate 47 wherein an annular presser foot 48 is provided for transmitting force to the

discs

41 and 42. An inner face of the contact plate 46 carries bosses 49 which are uniformly annularly spaced apart and are threadly engaged with ends of headed studs 50 which are inserted through openings in the pressure plate 47 and in transverse end wall 40 of the dished member 38, having these openings aligned with the bosses and the stud heads disposed rearwardly of the inner face of the presser plate. Thrust applicator means 45 further includes on each of the shanks of the studs 50 a helical spring 51 convoluted around the shank and compressed through having opposite ends bearing upon the forward face of the presser plate 47 and the rearward face of the contact plate 46. The springs 51 accordingly urge the contact plate 46 into a forward position and concurrently apply force through the studs 50 which act slidably through the openings in transverse end wall 39 of the dished member 38 and apply their heads forcefully upon the presser plate which in turn applies its force through the annular presser foot 48 to the

discs

41 and 42. The thrust on the

discs

41 and 42 is opposed by the forward end wall 32 of the first housing component 28. Springs Slam of a strength for the

discs

41 and 42 to maintain non-slip conditions with reference to each other at least up to a rated maximum load under which the winch drum 1 1 is to operate when the discs are receiving full force of the springs 51 from the annular presser foot 48. Accordingly, power delivered from the power output shaft 25 in either of opposite directions of rotation to the second casing component 35 causes that component to rotate with the dished member 38, and with the

discs

41 and 42 under non-slip, and with the first housing component 28 as well, having the hub 31 rotate the winch drum 11 with shaft 13. Otherwise, any slip introduced between the sets of

discs

41 and 42 enables relative rotation between the first and

second housing components

28 and 35 to occur as tolerated by the anti-friction bearing and seal 37.

It will be recalled that under non-slip conditions between the sets of

discs

41 and 42, the contact plate 46 occupies a forward position within the rotary casing of the selectively slip, normally non-slip coupling 17. There are annularly uniformly spaced apart apertures 54 in the second casing component 35 at equal distances out from shaft 25 for the contact plate 35 to be actuated by the hydraulically controllable actuator 18, to which reference in further detail now will be had.

Housing 20 fixed on the support 16 and containing the rotational speed reduction worm gearing 19 carries securely projecting outwardly from a side thereof a housing extension 56 which is a component of the hydraulically controllable actuator 18. Leading coaxially with the power output shaft 25, the housing extension 56 is cylindrically hollow from outer end to inner end, first being cylindrical on a relatively large diameter on the interior surface for a distance inwardly from the outer end and then being annularly stepped and thence cylindrical on a relatively small diameter on the interior surface leading to the inner end, so as to receive slidably in the hollow a companion, similarly externally shaped male inner end member 60 of a piston 58 of the hydraulically controllable actuator 18. Accordingly, there are

annular seals

63 and 64 in the hollow of the housing extension respectively between the surfaces of the relatively large and small diameter portions of the piston member 60 and housing extension 56 and the relatively small diameter portions of the piston member and the housing extension and closing off a chamber 65 for hydraulic fluid to be contained in the chamber under control through a port 66 leading from the outside through the wall of the housing extension. An outer member 59 of the piston 58 is relatively rotatably connected through annular anti-friction bearing 70 with the inner piston member 60 and for being moved longitudinally in either of opposite directions with the inner piston member. Outer piston member 59 is idle on the power output shaft 25 having a central opening accommodating that shaft and the outer piston member has lugs 62 on the outer end thereof inserted through the apertures 54 in the second casing component 35 of the selectively slip, normally non-slip coupling 17 for the outer piston member to rotate on the annular anti-friction bearing 70 interlocked by the lugs with the second casing component on power received by the second casing component from the power output shaft 25 and to move the lugs 62 longitudinally in either of opposite directions through the apertures 54, pressing against the contact plate 46 according to pressure of hydraulic fluid in chamber 65 and the oppositely directed pressure-of springs 51.

Thus it will be appreciated that as the hydraulic pressure of fluid admitted into chamber 65 through port 66 is increased beyond the normally non-slip force produced upon the

discs

41 and 42 in the sets from the springs 51, the springs will be further compressed under thrust transmitted to the contact plate 46 from the lugs 62, thereby causing the presser plate 47 commensurately to relieve thrust upon the sets of

discs

41 and 42 for the sets to slip rotationally relativelyto each other. As this amount of slip is increased with increase in hydraulic pressure in the chamber 65, the amount of rotary power transmitted from shaft 25 through the second housing component 35, the dished member 38, the sets of

discs

41 and 42 and the first casing com ponent 28 to the winch drum shaft 13 is diminished and accordingly slip may be increased up to and including substantially full slip under which latter conditions a load suspended from cable 12 having convolutions wound on the drum will back drive the drum and fall freely. On diminishing the hydraulic pressure in chamber 65 gradually, or otherwise, springs 51 take over, forcefully driving the contact plate 46 and the piston 58 through lugs 62, and for the presser plate 47 to increase pressure upon the

discs

41 and 42 and reduce slip between the discs by an amount ranging back to the normally non-slip condition. Any suitable hydraulic fluid supply and control system 69 is connected with the chamber port 66 for accomplishing the foregoing functions.

As the invention lends itself to many possible embodiments and as many possible changes may be made in the embodiment hereinbefore set forth it will be distinctly understood that all matter described herein is to be interpreted as illustrative and not as a limitation.

lclaim:

1. In a winch equipped with a rotary drum, the combination which includes, rotational speed reduction gearing and fixed housing structure, said rotational speed reduction gearing comprising a power input helical worm gear and a power output toothed annular gear in said fixed housing structure, said power output toothed annular gear having a power output shaft journaled in said fixed housing structure and said power output shaft extending through said fixed housing structure, and said power input helical worm gear being journaled and meshing with said power output toothed annular gear in said fixed housing structure and accessible through said fixed housing structure for said power input helical gear to be driven on drive of a rotary power output motor and said power output toothed annular gear to have power output on said power output shaft and interlock with said power input helical worm gear against overdriving said worm gear and against backdriving said worm gear; a selectively slip, normally non-slip coupling comprising, a rotary casing having first and second relatively rotatably interrelated casing components, said first casing component being connected with said winch drum for rotating with said drum, and said second casing component being connected with said power output shaft for rotating with said power output shaft, first and second sets of 7 discs within said rotary casing and in side by side alternating relationship with one another in said sets, said first set of discs being connected to rotate with said first casing component and to be moved toward and away from one another longitudinally of said rotary casing, and said second set of discs being connected to rotate with said second casing component and to be moved toward and away from one another longitudinally of said rotary casing, and thrust applicator means including contact and presser structure and spring means, within said rotary casing, said contact and presser structure being connected with said second casing component for being moved in either of opposite directions longitudinally of said rotary casing, a presser member of said contact and presser structure being disposed interposing said sets of discs between itself and said first casing component, and a contact member of said contact and presser structure being adjacent to apertures in said second casing component for said contact and presser structure to be actuated through said apertures in inward and outward directions longitudinally of said rotary casing, and said spring means being supported to said second casing component and biasing said contact and presser structure to move longitudinally of said rotary casing in said outward direction and force said presser member onto said sets of discs having said discs opposed by said first casing component and thereby retractibly establish an antislip condition between said sets of discs and thus between said power output shaft and said drum; and actuator structure including a piston comprising inner and outer relatively rotatably interconnected piston members each having a central aperture accommodating said power output shaft, said outer piston member having lugs introduced into said apertures in said second casing component and contacting said contact member, and said inner piston member being slidably movably sealed closing off a chamber in an extension of said fixed housing structure, and being responsive to fluid under pressure through at least one fluid port communicating with said chamber, for said piston to be hydraulically controlled having said lugs acting upon said contact member of said contact and presser structure against bias of said spring means for said piston hydraulically energized to move said contact and presser structure longitudinally of said rotary casing in said inward direction and select slip between said sets of discs and said spring means to select non-slip between said sets of discs on said piston being hydraulically deenergized.

- 2. In a winch equipped with a rotary drum, the com bination as set forth in claim 1 wherein said discs in said first set are characterized by being exteriorly annularly toothed disc rings and said discs in said second set by being interiorly annularly toothed disc rings, this with said first casing component including an annular wall interiorly provided with splines leading longitudinally of said rotary casing in engagement with said exterior teeth of said first set of discs, and there being a dished member interiorly of said rotary casing and comprising a generally cylindrical wall member connected at an outer end portion with said second casing component and integrally having exteriorly a set of splines leading longitudinally of said rotary casing in engagementwith said interior teeth of said second set of discs, and a transverse wal leading from an mner endportlon of said generally cylindrical wall and provided with a plurality of annularly spaced apart openings, said contact and presser structure having studs extending slidably through said openings in said transverse wall and said studs interconnecting said contact member and said presser member, and said spring means including springs helically convoluted around said studs and compressed against said transverse wall and said contact member.

3. In a winch equipped with a rotary drum, the combination as set forth in claim 1 wherein said rotary casing is formed having an annular reservoir therein for containing a liquid lubricant having said sets of discs partially immersed in the lubricant.

4. In a winch equipped with a rotary drum, the combination as set forth in claim 3 wherein said first casing component has a hollow hub accommodating within said hollow the end of a power input shaft of said drum and connected to rotate with said drum shaft.

5. In a winch equipped with a rotary drum, the combination as set forth in claim 2 wherein said discs in said sets are metallic and said rotary casing is formed having an annular reservoir therein for containing a liquid lubricant having said sets of metallic discs partially immersed in the lubricant.

Claims

1. In a winch equipped with a rotary drum, the combination which includes, rotational speed reduction gearing and fixed housing structure, said rotational speed reduction gearing comprising a power input helical worm gear and a power output toothed annular gear in said fixed housing structure, said power output toothed annular gear having a power output shaft journaled in said fixed housing structure and said power output shaft extending through said fixed housing structure, and said power input helical worm gear being journaled and meshing with said power output toothed annular gear in said fixed housing structure and accessible through said fixed housing structure for said power input helical gear to be driven on drive of a rotary power output motor and said power output toothed annular gear to have power output on said power output shaft and interlock with said power input helical worm gear against overdriving said worm gear and against backdriving said worm gear; a selectively slip, normally non-slip coupling comprising, a rotary casing having first and second relatively rotatably interrelated casing components, said first casing component being connected with said winch drum for rotating with said drum, and said second casing component being connected with said power output shaft for rotating with said power output shaft, first and second sets of discs within said rotary casing and in side by side alternating relationship with one another in said sets, said first set of discs being connected to rotate with said first casing component and to be moved toward and away from one another longitudinally of said rotary casing, and said second set of discs being connected to rotate with said second casing component and to be moved toward and away from one another longitudinally of said rotary casing, and thrust applicator means including contact and presser structure and spring means, within said rotary casing, said contact and presser structure being connected with said second casing component for being moved in either of opposite directions longitudinally of said rotary casing, a presser member of said contact and presser structure being disposed interposing said sets of discs between itself and said first casing component, and a contact member of said contact and presser structure being adjacent to apertures in said second casing component for said contact and presser structure to be actuated through said apertures in inward and outward directions longitudinally of said rotary casing, and said spring means being supported to said second casing component and biasing said contact and presser structure to move longitudinally of said rotary casing in said outward direction and force said presser member onto said sets of discs having said discs opposed by said first casing component and thereby retractibly establish an anti-slip condition between said sets of discs and thus between said power output shaft and said drum; and actuator structure including a piston comprising inner and outer relatively rotatably interconnected piston members each having a central aperture accommodating said power output shaft, said outer piston member having lugs introduced into said apertures in said second casing component and contacting said contact member, and said inner piston member being slidably movably sealed closing off a chamber in an extension of said fixed hOusing structure, and being responsive to fluid under pressure through at least one fluid port communicating with said chamber, for said piston to be hydraulically controlled having said lugs acting upon said contact member of said contact and presser structure against bias of said spring means for said piston hydraulically energized to move said contact and presser structure longitudinally of said rotary casing in said inward direction and select slip between said sets of discs and said spring means to select non-slip between said sets of discs on said piston being hydraulically deenergized.

2. In a winch equipped with a rotary drum, the combination as set forth in claim 1 wherein said discs in said first set are characterized by being exteriorly annularly toothed disc rings and said discs in said second set by being interiorly annularly toothed disc rings, this with said first casing component including an annular wall interiorly provided with splines leading longitudinally of said rotary casing in engagement with said exterior teeth of said first set of discs, and there being a dished member interiorly of said rotary casing and comprising a generally cylindrical wall member connected at an outer end portion with said second casing component and integrally having exteriorly a set of splines leading longitudinally of said rotary casing in engagement with said interior teeth of said second set of discs, and a transverse wall leading from an inner end portion of said generally cylindrical wall and provided with a plurality of annularly spaced apart openings, said contact and presser structure having studs extending slidably through said openings in said transverse wall and said studs interconnecting said contact member and said presser member, and said spring means including springs helically convoluted around said studs and compressed against said transverse wall and said contact member.