GB2028734A - An improved latch mechanism - Google Patents

Abstract

A latch mechanism is provided whereby a spring biassed sleeve (25) is held in a latched position by balls (28) in bores (27) in the sleeve engaging a step (30) in a housing so long as a shoulder (31) on a displaceable member (21) remains aligned with the bores (27). If the shoulder (31) moves out of alignment with the bores (27) the balls (28) can cam over the step (30) to release the sleeve (25), which can only be relatched when the member (21) returns to the position shown. In preferred embodiments movement of the displaceable member (21) in the unlatching direction is caused by variation of a fluid pressure being monitored, the sleeve (25) providing a visual signal indicating loss of air pressure in a tyre or alternatively closing a liquid supply line. <IMAGE>

Description

SPECIFICATION An improved latch mechanism This invention relates to an improved latch mechanism of widespread utility where a spring or otherwise biassed member is to be reliably released under given conditions, and where it is desired that the said member cannot be re-latched against its bias so long as the said conditions prevail.

Non-exclusive examples of the application of the latch mechanism of the invention are to a low pressure warning device for pneumatic tyres and an hydraulic fuse. in both cases a spring-biassed member is to be actuated (unlatched) in response to a variation of fluid pressure detected by the device and in both cases it is undesirable that the spring-biassed member will re-latch so long as the detected pressure condition prevails - in the case of the air pressure signalling device so long as air pressure in a tyre remains below a predetermined value and in the case of an hydraulic fuse so long as fluid pressure in a pipeline controlled by the fuse remains above a predetermined value.

In the air pressure warning device the movement of the unlatched member under its spring bias can be used to activate an audible or electronic signal, or in a particularly simple example the unlatched member, which may be brightly coloured, is exposed from the device housing to provide a visual signal.

In the hydraulic fuse the unlatched member moves under its spring bias to close the fluid passage in which an excess pressure has been detected.

Many prior art proposals have been made for utilising a latched, spring-loaded member to signal a pressure variation, e.g. in a pneumatic tyre, but none is fully satisfactory in terms of simplicity of construction, reliability of operation and versatility of application. U.K. Patent Specification No. 193,791 may be mentioned as one example of a prior art proposal for an analogous purpose, but here the member (bell 15) which performs the latching function has very limited movement and is incapable of further movement beyond the latching position, and there is furthermore no way in which the position at which latching takes place could readily be varied.

By constrast, the present invention provides an arrangement in which the latch elements are captive in bores in the biassed member and are held in the latching position by a shoulder on the displaceable member such that the latter can travel beyond the latched position of the biassed member. The camming action of exposed ends of the latch elements over a step on the fixed member provides a more reliable release of the biassed member than will occur in the prior art example given, where to disengage the striker 17 the balls 16 must move radially outwardly therefrom against a fixed surface which deflects them axially. The possibility is therefore apparent that a given ball 16 might become wedged between its recess in the striker and the deflecting surface so that the striker 17 will not be reliably released.

In accordance with the present invention there is provided a latch mechanism for maintaining an intermediate member in a latched position against a biassing force acting thereon to tend to displace it longitudinally relative to inner and outer members between which the intermediate member is disposed, one of said inner and outer members being longitudinally displaceable relative to the other to effect latching and unlatching of the intermediate member, wherein the intermediate member is penetrated by at least one transverse bore in which a latching element is freely movably located, the dimension of the latching element axially of the bore being greater than the length ofthe bore, and wherein the inner and outer members have respective shoulder formations toward the intermediate member defining respective steps which are mutually opposed longitudinally of the members, the intermediate member being latched when the shoulder of the displaceable member is aligned with the bore to cause the latching element to engage the step of said other member.

The advantages of this arrangement are manifold.

The greater proportion of the latching element is guided in a bore and only opposite end portions are exposed from the bore for camming actions over the steps. Since the intermediate member remains latched so long as the shoulder of the displaceable member is aligned with the bore the displaceable member can travel beyond the latching position a distance determined by the length of the shoulder.

Furthermore the position at which latching takes place can itself be made adjustable by varying the position along the non-displaceable member of the step thereon without requiring any modification of the other two members or their associated biassing means.

Preferably the katching element is a ball of diameter greater than the length of the bore, and the intermediate member is a sleeve spring biassed in the unlatching direction, the wall of the sleeve being penetrated by a plurality of circumferentially spaced bores and the inner and outer members are tubular, the outer member being comprised in a fixed housing and the inner member being displaceable relative to the outer member.

The inner member may be spring biassed in the unlatching direction and may be arranged to be subject to a fluid pressure tending to maintain it against said bias in the latching position, the arrangement being such that the sleeve will be unlatched if said fluid pressure becomes less than said spring bias. In this arrangement the sleeve and the inner member may be oppositely spring biassed by a common compression spring located therebetween. The housing may be adapted for connection to the air chamber of a pneumatic tyre and wheel assembly so that said fluid pressure will be air pressure in. the tyre and so that movement of the sleeve under the spring bias thereof will give an indication of a predetermined drop in the air pressure of the tyre.

The housing may be adapted for connection to the inflation valve of a wheel and tyre assembly by the provision of an internally screw-threaded bore having at its inner end a metal nozzle with a frusto conical shoulder surrounded by a ring of deformable but incompressible material, the arrangement being such that when the housing is fully screwed onto the inflation valve the rim of the valve will deform said ring so that the nozzle is projected against the pip of the inflation valve to open the same, thereby placing an air chamber in communication with said inner member.A rocker member may be mounted in the housing to be pivotable about an axis transverse to the direction of movement of the sleeve, one end of the rocker member being contactable solely with the axially inner end of the sleeve and the other end of the rocker member being contactable solely with the axially inner end of the inner member, the arrangement being such that during movement of the sleeve from its unlatched to its latched position it will contact the rocker member to cause the latter to displace the inner member against the spring bias thereof towards its latched position.

In an alternative embodiment of the invention the inner member may be spring biassed in the latching direction and arranged to be subject to a fluid pressure ten.ding to displace it against such bias in the unlatching direction, the arrangement being such thatthe sleeve will be unlatched if said fluid pressure exceeds the counter-pressure of the spring, the inner member may be hollow and may be included in a passageway for fluid controlled by the sleeve, said fluid pressure being produced by a restrictor in the inner member and the arrangement being such that if fluid pressure in said passageway exceeds the spring bias of the inner member the unlatched sleeve will close said passageway.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure l is a sectional elevation of a first device incorporating a latch mechanism in accordance with the invention; Figure 2 is a partial cross-sectional view taken on the line ll-ll of Figure 1, Figure 3 is a partial sectional elevation taken on the line Ill-Ill of Figure 2, and Figure 4 is a side sectional elevation of a second device incorporating a latch mechanism in accordance with the invention.

The device 10 illustrated in Figures 1-3 comprises a tubular housing 11 into which an annular core 12 is screw-threaded, the core having an internal screw thread 13 to engage the external screw thread of a pneumatic tyre inflation valve housing (not shown).

Integral with the core 12 is a coaxial, hollow stem 14 within the housing on which a hollow piston assembly 15 is reciprocably mounted, an O-ring 16 in an annular recess near the free end of the stem 14 forming with the piston 15 a seal whereby an air chamber 17 of variable volume is formed between the stem 14 and piston 15 communicable through the stem 14 with the air chamber of the pneumatic tyre.

When the device is screwed onto the inflation valve housing of a pneumatic tyre the pip or stem of the inflation valve must be depressed to permit air from the tyre to discharge into the chamber 17 of the device. However, it is undesirable that the device should depress the pip of the inflation valve unless and until it is screwed fully and firmly onto the valve housing as otherwise there is a danger that air from the tyre might escape along the thread 13.To avoid any danger of leakage of air from the inflation valve along the thread 13 there is provided at the bottom end of the bore in the stem 14a metal nozzle 18 the end surface 20 of which, arranged to contact and depress the pip of an inflation valve, is recessed into a frusto-conical extension 19 of the nozzle surrounded by a correspondingly shaped, annular rubber washer 37 at the blind end of the bore of the core 12.

To prevent premature depression of the pip of the inflation valve the surface 20 is so positioned that it will not contact the pip so long as the washer 37 remains undeformed, i.e. retains the shape shown.

When the core 12 is screwed fully onto the inflation valve housing of the tyre the end of the inflation valve housing abuts the washer 37. As the rubber is substantially incompressible it must deform away from the fixed metal surfaces by which it is surrounded and by acting on the frusto-conical surface of the projection 19 it will tend to displace the nozzle 18 out of the bore of the stem 14 toward the inflation valve until the surface 20 contacts and depresses the pip of the inflation valve and places the air chamber 17 in communication with the air chamber of the pneumatic tyre.

For convenience of manufacture the piston 15 comprises parts 21 and 22 which together form an annular recess in which a compression spring 23 is located, the spring 23 being in compression between the piston 15 and a closed end 24 of a hollow plunger 25 displaceable by the spring from the limit position in which it is shown in Figure 1 to a second limit position extended out of the housing 11, in which a shoulder 26 of the plunger engages a shoulder 38 of the housing 11.

The shoulder 26 is at the top end of a thickened part of the wall of the plunger 25 in which radial bores, such as 27, 27' are formed at circumferentially spaced intervals around the plunger 25. In each bore 27, 27' is a respective ball 28, 28' which in the position shown in Figure 1 serves to hold the plunger 25 in its limit position retracted into the housing 11, against the action of the spring 23, by engaging under an annular step 30 in the housing 11. In the position of Figure 1 the balls 28, 28' are engaged under the step 30 because they are pushed radially outward of their bores 27,27' by an increased diameter portion 31 at the bottom end of the piston 15. However, if the piston 15 moves from the position of Figure 1 so that its increased diameter portion 31 no longer bears on the balls 28, 28' the balls are able to roll radially inward by a cam action against the step 30, enabling the plunger 25 to extend out of the housing 11 to its second limit position where the shoulder 26 engages the second step 38.

It will be appreciated that to enable the balls 28,28' to travel between the internal wall of the housing 11 and the external wall of the part 21 of the piston 15 the gap between these surfaces is not less than the diameter of each ball.

It will thus be seen that so long as the piston 15 is in the position shown, i.e. where its increased diameter portion 31 will tend to push the balls, 28, 28' under the step 30, the plunger 25 will be held in the position shown. If it is moved to the position shown from its other limit position it will be latched and held because the balls 28,28' will tend to depress the piston 15 from the position shown toward the core 12 when they engage the shoulder between the increased diameter portion 31 and the remainder of the part 21 of the piston until the balls are able to cam radially outward under the step 30, whereupon the piston 15 can move back to the position shown in Figure 1.

However, the piston 15 only remains in the position shown in Figure 1 as long as air pressure in the tyre and in the chamber 17 overcomes the force of the spring 23. If air pressure in the chamber 17 falis below a value predetermined by the setting of the spring 23 the latter is able to displace the piston 15 toward the core 12 that the increased diameter portion 31 of the piston moves out of radial alignment with the balls 28,28', enabling the latter to cam over the step 30 so that the plunger 25 can be projected by the spring 23 to its other limit position extended from the housing 11.

Projection of the plunger 25 from the housing 11 wl. thus give a visual indication that air pressure in th tyre is below the predetermined value.

Preferably the plunger 25, or at least that part of it which is concealed within the housing 11 when it is retracted into the housing, is given a bright colour different from that of the housing 11 so that the fact that the plunger 25 as extended from the housing 11 is conspicuous to the observer even from a distance.

Furthermore, so long as the piston is in its limit position nearer the core 12 to which it is displaced by the spring 23 the plunger 25 cannot be re-set in its retracted limit position because the balls 28,28' will not engage under the step 30 if the portion 31 of the piston 15 is not in the position shown in Figure 1.

Thus the device cannot be prevented from continuing to give its warning until the low pressure state is remedied. If the plunger 25 is depressed into the housing 11 after it has actuated to give its warning it will not stay depressed unless pressure in the tyre is now sufficient to displace the piston 15 to its limit position shown in Figure 1.Thus if the device, having actuated, is taken off an inflation valve, the tyre is inflated and then the device is re-mounted, whether or not the plunger 25 will now stay in its depressed position serves as a check that the tyre has now been inflated to a pressure above that determined by the setting of the spring 23.

Although the device as so far described will function as described the refusai of the plunger 25 to relatch in the depressed position may not give a sufficiently precise indication of the inflation pressure of the tyre if this is similar to the setting of the spring 23 because the differential of pressures acting on the piston 15 may be inadequate to overcome friction forces involved in the latching. To avoid any error due to failure of the piston 15 to move back to the position shown in Figure 1 a rocker 33 is provided in a transverse slot in the core 12 and pivotable relative thereto about an axis 34. The rocker 33 has at one end a flange 35 which is shaped so that the plunger 25 can contact it but the piston 15 cannot.However, the other end of the rocker 33 is positioned to engage under and abut the piston 15 when the rocker 33 is pivoted about its axis 34 from the position shown by abutment of the plunger 25.

When the plunger 25 is manually depressed it causes the rocker 33 to kick up the piston 15 to the position shown in Figure 1 against the action of the spring 23 assuming air pressure in the chamber 17 has failed already to do so; and prevents the balls 28, 28' displacing the piston 15 downward from the position shown in Figure 1 as the plunger 25 is latched. With the device now latched as shown in Figure 1 it remains for the spring 23 to unlatch it if it can overcome air pressure in the chamber 17. This gives a more precise indication that air pressure in the tyre exceeds the setting of the spring 23 than is obtained if the rocker 33 is omitted so that the differential of pressures must be great enough to withstand the latching action as well as to overcome the spring 23.

The alternative embodiment of the invention illustrated in Figure 4 is an hydraulic fuse 40 whereby flow of a liquid from an inlet 41 to an outlet 42 of the device is controlled by a seal 43 which will abut a seat 44 to close the liquid passageway if pressure in the passageway exceeds a value predetermined by the setting of a compression spring 51.

The seal 43 is a frusto-conical surface of an intermediate member or sleeve 45 which is axially moveable in a housing 46 provided with the inlet and outlet openings 41 and 42. The sleeve 45 is biassed toward the right, as viewed, by a compression spring 47 acting between a collar 48 on the sleeve and the bottom of a recess in the housing formed by an integral member 49 which surrounds the sleeve 45.

Within the sleeve 45 is a relatively axially moveable, hollow inner member 50 biassed to the right, as viewed, by the compression spring 51. The sleeve has apertures 52 in advance of the seal 43 whereby the interior of the inner member 50 can be communicated with the inlet 41 via an annular recess 53 and bores 54 in the inner member, and liquid discharges therefrom to the outlet 42 via a restrictor 55 at the opening of the blind bore in the inner member 50.

The sleeve 45 h as i has circumferentially-spaced bores 56 in which respective balls 57 are a sliding fit, the diameter of each ball 57 being greater than the length of the associated bore 56 so that the ball must project to one side or the other of the wall of the sleeve 45. The member 49 has a shoulder 58 terminating in a step 59 and the inner member 50 has a shoulder 60 terminating in a step 61, the steps 59 and 61 being mutually opposed longitudinally of the assembly.

In the position shown, the spring 51 holds the inner member 50 to the right, where its shoulder 60 is aligned with the bores 56, causing the balls 57 to engage the step 59 so that the sleeve 45 is held latched to the outer member 49 against the bias exerted on the sleeve by the spring 47. If, however, there is an undesired increase in the pressure of fluid flowing between the inlet 41 and outlet 42 such as to urge the restrictor 55, and therefore the inner member 50, to the left as viewed against the action of the spring 51, the step 61 will move over the bores 56, enabling the balls 57 to move radially inward, camming over the step 59 through the action ofthe spring 47 which then moves the sleeve 45 to the right until the seal 43 closes the liquid passageway.

Resetting of the fuse to the latched position shown is effected by pressing a plunger 62 integral with the sleeve 45 into the housing 46, but unless pressure in the liquid passageway has dropped sufficiently to enable the spring 51 to restore the inner member 50 to the position shown, where its shoulder 60 is aligned with the bores 56, the balls 57 will not engage the step 59 to retain the sleeve 45 against the action of the spring 47. Thus the fuse can only be re-set after the pre-set operating pressure for the pipe line controlled by the fuse has been re established.

Claims (12)

1. A latch mechanism for maintaining an inter mediate member in a latched position against a biassing force acting thereon to tend to displace it longitudinally relative to inner and outer members between which the intermediate member is dis posed, one of said inner and outer members being longitudinally displaceable relative to the other to effect latching and unlatching of the intermediate member, wherein the intermediate member is penetrated by at least one transverse bore in which a latch ig element is freely movably located, the dimension of the latching element axially of the bore being greater than the length of the bore, and wherein the inner and outer members have respective shoulder formations toward the intermediate member defining respective steps which are mutual ly opposed longitudinally of the members, the intermediate member being latched when the shoulder of the displaceable member is aligned with the bore to cause the latching element to engage the step of said other member.

2. A latch mechanism as claimed in claim 1 wherein said latching element is a ball of diameter greater than the length of the bore.

3. A latch mechanism as claimed in either preceding claim, wherein the intermediate member is a sleeve spring biassed in the unlatching direction, the wall of the sleeve being penetrated by a plurality of circumferentially spaced bores and wherein the inner and outer members are tubular, the outer member being comprised in a fixed housing and the inner member being displaceable relative to the outer member.

4. A latch mechanism as claimed in claim 3 wherein the inner member is arranged to be subject to a fluid pressure tending to maintain it against said bias in the latching position, the arrangement being such that the sleeve will be unlatched if said fluid pressure becomes less than said spring bias.

5. A latch mechanism as claimed in claim 4, wherein the sleeve and the inner member are oppositely spring biassed by a common compress ion spring located therebetween.

6. A latch mechanism as claimed in claim 4 or claim 5, wherein the housing is adapted for connection to the air chamber of a pneumatic tyre and wheel assembly so that said fluid pressure will be air pressure in the tyre and so that movement of the sleeve under the spring bias thereof will give an indication of a predetermined drop in the air press ure of the tyre.

7. A latch mechanism as claimed in claim 6, wherein the housing is adapted for connection to the inflation valve of a wheel and tyre assembly by the provision of an internally screw-threaded bore having at its inner end a metal nozzle with a frustoconical shoulder surrounded by a ring of deformable but incompressible material, the arrangement being such that when the housing is fully screwed into the inflation valve the rim of the valve will deform said ring so that the nozzle is projected against the pip of the inflation valve to open the same, thereby placing the air chamber in communication with said inner member.

8. A latch mechanism as claimed in any one of claims 4-7 and comprising a rocker member mounted in the housing to be pivotable about an axis transverse to the direction of movement of the sleeve, one end of the rocker member being contactable solely with the axially inner end of the sleeve and the other end of the rocker member being contactable solely with the axially inner end of the inner member, the arrangement being such that during movement of the sleeve from its unlatched to its latched position it will contact the rocker member to cause the latter to displace the inner member against the spring bias thereof toward its latched position.

9. A latch mechanism as claimed in claim 3, wherein the inner member is spring biassed in the latching direction and is arranged to be subject to a fluid pressure tending to displace it against said bias in the unlatching direction, the arrangement being such that the sleeve will be unlatched if said fluid pressure exceeds the counter-pressure of the spring.

10. A latch mechanism as claimed in claim 9 wherein the inner member is hollow and is included in a passageway for fluid controlled by the sleeve, said fluid pressure being produced by a restrictor in the inner member and the arrangement being such that if fluid pressure in said passageway exceeds the spring bias of the inner member the unlatched sleeve will close said passageway.

11. A latch mechanism included in a device for indicating variation of tyre pressure substantially as herein described with reference to and as shown in Figures 1-3 ofthe accompanying drawings.

12. A latch mechanism included in an hydraulic fuse substantially as herein described with reference to and as shown in Figure 4 of the accompanying drawings.