AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Innovation Patent Applicant(s): D & D Group Pty Ltd Invention Title: LATCHES FOR GATES AND DOORS The following statement is a full description of this invention, including the best method for performing it known to me/us: -2 LATCHES FOR GATES AND DOORS The following is a divisional application of Australia Application No. 2007211833 which is incorporated herein by cross-reference. 5 FIELD OF THE INVENTION The present invention relates to latches for gates and doors and more particularly is concerned with a latch of the type wherein a displaceable latching element (usually 10 called a tongue) has a latching shoulder to engage with a striker arm with respect to which it is relatively moveable, the tongue having a striker surface adapted to engage with the striker arm to displace the tongue to permit engagement of the striker arm behind the latching shoulder. Typically, but not always, the biasing of the tongue will be under gravity, for example through a pivotal mounting and there is an arrangement to 15 permit the tongue to be displaced to release the striker arm whereby a gate or door is then released to be moved relative to a gate post or door post. The field of the invention extends to devices having spring biased tongues as well as gravity biased tongues and, in addition, extends to tongues which are both gravity and 20 spring biased. BACKGROUND TO THE INVENTION Various forms of latches and, in particular, gravity latches, have been previously 25 proposed such as US Patent No. 6,058,747 (Doyle) and US Patent No. 6,513,351 (Clark), both of which are assigned to the assignees of the present invention. These two US patents disclose specific developments in the field of latches for gates and doors. Other known prior latches in the field of those referred to as references in the printed specifications of the two US patents mentioned above. The prior art listed comprises: 30 204,267 Unger 4,691,541 McQuade et al 2,313,712 Jacobi 4,732,418 Crown et al 3833355_1 (GHMatters) P59410.AU.3 -3 2,953,916 Thomas 4,919,463 McQuade, Sr. 3,115,026 Moore 4,938,508 Thomas 3,433,518 Foltz 5,024,473 McQuade 3,593,547 Taylor 5,063,764 Amis et al 3,677,591 Waldo 5,103,658 McQuade 3,785,186 James et al 5,358,292 Van Wiebe et al 3,838,877 Hanson 6,058,747 Doyle et al 4,014,192 Dillon et al 6,347,819 Plaxco 4,378,684 Dugan et al US 6,058,747 (Doyle et al) has a disclosure of a gravity latch having an enshrouded tongue and the lock mounted to be accessible from the front face. The disclosure includes a rear actuator unit adapted to be mounted on the opposite or rear face of a gate 5 post so that, subject to any unlocking required of the rear unit, the tongue can be raised by the rear actuator to release the striker arm so that the gate may be opened from the rear side. US 6,513,351 (Clark) is a development with cylinder locks provided in front and rear 10 units and respectively key operated to rotate a locking element into and out of a locking position. In the locking position the gravity biased tongue is locked in a retaining position in which the associated striker arm is held in position. The prior published specifications referred to above are mentioned as an illustration of 15 the background but in doing so, no admission is made that any of the specifications form part of the common general knowledge in Australia or any other geographical region. In this specification, unless the context requires otherwise, the word "comprising" is 20 used in the non-exhaustive sense and further features may be present in the arrangement described. 3833355 1 (GHMatters) P59410 AU.3 -4 The present invention is directed to new and useful alternatives to known arrangements. SUMMARY OF THE INVENTION 5 According to a first aspect of the present invention, there is provided a latch for holding closed a gate (or door) is adapted to co-operate with a striker arm, the latch comprising: (a) a housing in which (b) a displaceable latching element is mounted to be displaceable from a latching position towards an open position in which the striker arm is 10 released for gate opening, and (c) the latching element having a latching shoulder to retain the striker arm when engaged behind the latching shoulder and having an engagement surface adapted to be engaged by the striker arm when the gate is moved towards a closed position to displace the latching 15 element and for permitting relative movement of the striker arm to adopt a position behind the latching shoulder (d) a key-operated lock in the form of a cylinder lock mounted in the housing and having a key operation for unlocking the latch; (e) a locking element for locking the latching element and adapted to be 20 displaced upon actuation of the key-operated lock between a locking position, in which movement of the latching element is restrained from moving, and a displaced position in which the latching element is free to be moved (f) the locking element being in the form of a rotor rotatably mounted in 25 the housing and movable about its axis between the locking position and the displaced position; (g) the housing lock and the rotor may be rotatable about a common axis; and (h) the rotor having a portion remote from the lock capable of being 30 engaged by a remote actuating unit which, in use, may be mounted on an opposite side of the gate post to the latch for remotely operating the latch via the rotor. 3942873_2 (GHMalters) P59410.AU.3 -5 The rotor may be capable of being displaced axially when in the displaced position to move the latching element towards the open position, such that the latch may be able to be locked and unlocked by rotation of the rotor and moved from the latching position by axial displacement of the rotor. 5 According to a second aspect a latch assembly is disclosed comprising a latch according to the first aspect; and a remote actuating unit, the remote actuating unit having a lock being in the form of a cylinder lock; and the housing lock, the rotor and the remote actuating unit lock are all rotatable about a common axis. 10 The latch assembly may further comprise a connector, wherein one end of the connector is received by the portion, and the other end of the connector is mounted to the remote actuating unit to enable the remote actuating unit to remotely operate the latch via the rotor. 15 The rotor may be able to be axially displaced and the remote actuating unit may be provided with a push button mounted to be depressed axially and to drive the connector to axially displace the rotor so as to cause the latching element to be displaced. 20 Usually the latching element will be partially enshrouded in the casing with a protruding portion extending out of a face slot so as to facilitate manual lifting of the tongue when a lock has been unlocked. The latching element may be located above the lock axis or below it and may simply be 25 biased by gravity to the latching position, but it could be arranged to be otherwise biased, e.g. magnetically or by springs. The shape of the latching element can be such that when a striker arm strikes the outer lower face of the latching element it is deflected pivotally upwardly, or strikes the outer 30 lower face of a spring biased latching element it is deflected pivotally downwards so that the striker arm can engage behind the latch and the latching shoulder prevents opening of the gate. However, usually the embodiments are designed so that manual locking through the front lock or, if provided, the rear lock is to take place in order to 3942e73.2 (GHMatters) P5941O.AU.3 - 5a lock the latch. Instead of having a cylinder lock operated by a key in a rear unit in order to unlock the gate, a further embodiment is one in which egress can be provided by having a push 394273_2 (GHMatter) P59410.AU.3 -6 button or a similar structure (such as an egress crash bar) mounted to be depressed axially and to drive a rack and pinion or worm and nut or similar mechanism to turn the locking element (or rotor) so that further action then causes the latching element to be displaced from the rear of the gate, thereby permitting opening, for example as might be 5 required for emergency purposes or to ensure there can be exit from e.g. a shed to which the latch has been fitted with a key lock arrangement on the outside. Embodiments include those in which the latching element is pivotally mounted and fully enshrouded in the housing apart from a striker arm retaining portion which extends 10 across an opening through which the striker arm moves upon gate closure. Embodiments include those in which the locking element is a rotor rotatably mounted for rotation by key operation of the lock, which can be a cylinder lock mounted in the housing and accessible at a front face of the housing, whereby the housing can be a slim line structure. The rotor may have an associated torsion spring for urging it from a 15 displaced position to a latching position. The latch can be adapted to be mounted on a gate post with the structure adapted to be coupled if desired with a rear actuation unit to be mounted on the opposite rear face of the gate post. By the use of a cylinder lock in such a rear unit with conventional 20 respective limited lost motion mechanisms in each cylinder lock, the latch unit can thus be formed such that unlocking can take place by either of the cylinder locks to rotate the locking element. Embodiments include those in which the locking element is mounted in a cartridge 25 holder which retains the components to facilitate removal and replacement of the cylinder lock, for example if the customer wishes to have the lock reset for common keying. A reassembly is thus facilitated without special tools or expertise. Furthermore, the arrangement can facilitate reassemble so that the device is configured for either left hand or right hand installation situations, for example, when the housing 30 has an L-shaped base plate for mounting on a post and a cover shroud mounted on the base plate. Thus embodiments of the invention, for the first time, provide a combination of features 3942573_1 (GHMatters) P5941OAU.3 -7 together which can be embodied in robust but simple componentry to provide a latch which can be purely gravity biased, spring biased, or gravity and spring biased to the locking position and/or can be self locking. Furthermore the latch can be of the form of having a front unit and rear unit for mounting on opposite sides of the gate post, such 5 that either lock may be turned to permit opening of a gate by displacement of the locking element to release the locking tongue which then moves to allow the striker bar to move out of engagement as the gate or door is opened. Although embodiments herein are described as key-actuated or manually actuated, 10 remote electrically operated embodiments may be provided as an alternative to key actuators or in addition. Thus the present invention lends itself to embodiments which provide a new combination of features. 15 BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described with reference to the accompanying drawings of which: 20 Fig. I is an exploded view of a front unit for a latch embodying the invention; Fig. 2 is an exploded view of a complementary latching arm intended to be fitting to a gate; Fig. 3 is an exploded view of a cartridge assembly for the lock unit of Fig. 1; Fig. 4 is an exploded view of a rear access unit for use with the embodiment of 25 Fig. 1; Fig. 5 is a cross-sectional view through the front unit showing the tongue in a latching position but prior to engagement with a striker bar; Fig. 6 is a front elevation of the front unit of Fig. 5; Fig. 7 is a view corresponding with Fig. 5 showing engagement by a striker bar 30 about to engage and rotate the latching tongues to release the rotor to lock the tongue in a down position (as shown in Figure 5); Fig. 8 is a part sectional rear of the body view on an enlarged scale taken in a plane at right angles to the axis of the cylinder lock and rotor showing inter-engagement 3942673_1 (GHMatlers) P5941O.AU.3 -8 between the tongue and the rotor prior to engagement of the striker bar, the rotor being held displaced from its final locking position; and Fig. 9 corresponds with Fig. 7 but shows the components when in the locked position. 5 Fig. 10 is an exploded view of a front unit for a latch of a second embodiment; Fig. I1 is a side elevation of the second embodiment; Fig. 12 is a front elevation of the second embodiment; Fig. 13 is a central cross-sectional side elevation of the second embodiment with an optional rear locking unit in position and; 10 Fig. 14 is a plan view of the embodiment of Fig. 13 positional on a gate post with a striker arm unit positioned on a gate. DETAILED DESCRIPTION OF THE DRAWINGS 15 Referring first to the exploded view of Fig. 1, the front unit for a latch assembly is illustrated and is in the form of self-locking assembly with automation opening when key actuation of a lock occurs. The front unit is adapted to cooperate in use with a striker arm assembly shown in Fig. 2 and optionally to be employed with a rear access unit shown in exploded view in Fig. 4. As shown in Fig. 1, the latch unit comprises a 20 housing 20 assembled from a base unit 22 and a front shell 24 within which is mounted a locking cartridge assembly 26 for cooperation with a pivotal latching element in the form of a tongue 28. The tongue is mounted in the shell 24 on a pivot pin 30 and the tongue is adapted to be biased upwardly to its open position by a helical extension spring 32 which, at its upper end, is mounted on a mounting pin 34 and, at its lower end, 25 is connected directly to the tongue. The base 22 is generally L-shaped in plan view and has a side leg 36 adapted to be engaged over the face of a gate post and secured to the gate post by screws 38. A main leg 39 of the base is symmetrical with two vertically spaced apertures 40A and 40B and 30 this leg is also adapted to be secured to the gate post by upper and lower screws 42. The shell 24, when the components are assembled inside, is fitted to the base by a series of four screws 44 from the rear of the base into the shell 24 with the cylinder lock 46 of the cartridge engaged in a corresponding aperture 48 in the shell and a rear barrel 3942673_1 (GHM-Trs) P59410 AU.3 -9 portion 50 of the cartridge engaged in the lower aperture 40A. So that the gate latch can be fitted to either left hand or right hand opening gates, the unit can be reassembled with the base 22 rotated through 180* so that the opening 40B 5 is lower and adapted to be engaged by the barrel 50. The striker pin unit of Fig. 2 is adapted to be fixed to an edge portion of a gate and for that purpose has an L-shaped striker bracket 60 with a side leg 62 adapted to be secured to a side face of the gate by two fixing screws 64 and the other leg of the bracket has an 10 integral upstanding body portion 66 also adapted to be secured to the gate but through a front face by two screws 68. The body portion mounts a steel striker pin 70. Fig. 3 shows details of the cartridge 26 which comprises a plastic moulded holder 72 having a cylindrical portion 73 at one end to accommodate the cylinder lock 46 and a 15 part cylindrical coaxial portion 74 for accommodating a locking element in the form of a rotor 76. A torsion spring 78 mounts over a rearwardly extending barrel 50, the barrel having a square-shaped axial aperture for accommodating a square actuation bar of a rear unit described below. Upon assembly, the torsion spring 78 is mounted to bias the rotor anti-clockwise as seen in Fig. 1 and Fig. 3 towards its locking position. The rotor 20 has a front barrel 80 with a rectangular axial slot accommodating a conventional flat operating bar 79 extending from the cylinder lock 46. The cylinder lock conventionally has a degree of lost motion so that initial turning by a key does not turn the bar 79 or the rotor but further action in a clockwise sense (as seen in Fig. I and Fig. 3) then turns the rotor against its spring biasing to disengage a tongue retaining finger 82 of the rotor to 25 release the tongue 28 to move upwardly under the biasing of spring 32, thereby releasing a striker arm so that the associated gate may be opened. The torsion spring 78 then acts to urge the rotor anti-clockwise (as seen in Fig. 1 and Fig. 3) until the side face of finger 82 inter-engages with a side face of the tongue 28 thereby holding the latch mechanism open and ready to be displaced by the striker pin when the gate is closed. 30 For this purpose, the tongue 28 has a protruding leg 84 (see Fig. 1) which interferes with the side of the finger 82 when the tongue is in the closed position. The profile of the tongue includes an abutment shoulder 86 configured such that when impacted by the 3942873_1 (GHMaeirs) P59410AU.3 - 10 striker arm 70, the tongue is rotated anticlockwise from the open position as seen in Fig. I to move the leg 84 rearwardly of the location of the finger 82, thereby releasing the rotor to turn under the force of the torsion spring 78 in an anticlockwise direction so that locking is automatically achieved. 5 More detail of assembly is shown in Fig. 5 in which, for ease of reading the drawings, the extension spring 32 is shown not engaged with the tongue so it has fallen under gravity the position it will have adopted when pushed in an anticlockwise direction by a striker bar. Fig. 5 is a section in a central plane and shows the space around the leg 84 10 of the tongue, the side face of the tongue acting as an interference element for a side face of the finger 82 of the rotor (which is visible in Fig. 5). Referring now to Fig. 4, the optional rear access unit has a housing 90 of general L-shape and having a side leg 92 adapted to be fixed by screws 93 to the side of a gate 15 and a casing 94 adapted to mount a lock 96 and an actuator assembly 98. The lock is mounted in a cap 100 which extends axially within a corresponding passage in the casing 94. The housing 90 also mounts a base element 102 to retain lock 96 in button 100. The actuating unit has a body portion 103 so that the lock and the button are biased to an outward position. The left hand end of the actuator comprises a barrel 105 20 having a rectangular slot into which the end of the operating bar 106 of the cylinder lock 96 engages for transmitting rotational force. The right hand end of the actuator 104 comprises a substantially square cross-section drive bar for engaging in the barrel 50 of the rotor 76. Thus, by virtue of the lock 96 being a left hand operating lock, a key is rotated anti-clockwise to take up initial lost motion and then further displaced to 25 rotate the bar 104 clockwise when seen in the view of Fig. 4, whereby the rotor is rotated towards its opening position and can release the latching tongue to more upwardly under its spring bias. In this embodiment the cap 100 is either not axially displaceable or, if axially 30 displaceable, it is so by virtue of the bar 104 not fully penetrating the cavity in the rotor. In either event, any movement of the button if possible does not cause any function whatsoever but the structure described above has useful design criteria so that the unit may be useable in a second embodiment or, at least, many components of Fig. 4 are 3942673_1 (GHMatters) P59410.AU.3 - 11 useable so that the manufacturer can cost effectively assemble and provide different embodiments for different market needs. For the purpose of this first embodiment with the self-locking front unit, there is no purpose in the cap 100 being axially displaceable. 5 In summary, the embodiment described above lends itself to efficient robust construction with relative simplicity in terms of the number of components and assembly. Furthermore, an important aspect is ease of fitting with hand tools and handheld drills to gates and gate posts. A single aperture is all that is needed to extend between the rear wall and front wall of a gate post in order to mount the optional rear 10 access unit to engage in alignment with the front latch assembly. By contrast, if drillings are required at spaced parallel locations for two operating actuators, there is a great difficulty in achieving on site precision with hand tools. Referring to the second embodiment with reference to Figs. 10-14, like parts have been 15 given like reference numerals, even though the specific configuration of certain parts may differ. In the case that a part is of a modified form compared with the first embodiment for different functionality, its reference numeral is 200 greater than the reference numeral used with reference to the first embodiment. 20 A significant difference in the second embodiment is that there is not automatic or self locking functionality but instead a lockable cylinder lock (46, 96) is provided in each of front and rear units and either may be actuated to unlock and leave unlocked the latch or manually to lock the latch. Either lock may be turned to unlock the latch and, in this embodiment, the tongue 228 has a projecting tab 229 having a finger engagement tip so 25 the tongue may be lifted manually. In this instance the tongue is profiled so as to have a leading nose portion 231 which is adapted to be impacted by the striker pin when a gate is closed so as to rotate the tongue than upwardly to permit the striker pin to engage behind the latching shoulder and the tongue drops down under gravity in this embodiment to perform the latching function. Adaptations of such an embodiment 30 include providing a lock in either or neither of the front or rear units but using interior components such as the rotor. Thus a suite of embodiments for different applications are based on the same interior rotor arrangements. 3942673_1 (GHMatters) P59410.AU.3 - 12 A key distinction of the rear operating unit in the illustrated embodiment is that the lock 96 is mounted in a depressible button 100 and the rotor 276 in the front unit has limited axial movement against the restoring force of a compression spring 223. The arrangement is such that opening the latch from the rear of the gate requires the button 5 100 to be pressed so that the actuating bar 104 moves forwardly and thereby pushes the rotor to a limited axial extent, providing it is in the unlocked position to engage a rear surface of the tongue to push it upwardly through a rotation about its pillet. In the locked position the rotor, however, has its upwardly projecting finger engaging in 10 front of the rear leg of the tongue thereby preventing it moving forward. 3942873_1 (GHMatters) P59410.AU.3