Sash locks used for securing double or single hung sash windows are known. These locks are generally of a type which include a rotating'cam'with a fixed rotational axis positioned on the top edge of the bottom window sash slidingly mounted in a window frame in a double or single hung sash arrangement. When rotated the cam turns so the unsymmetrical edge protrudes to engage in a receiving member positioned on the lower edge of the top window sash.

When the cam is engaged the window sashes are effectively locked together. Thus the upper sash cannot freely slide downward and likewise the lower sash cannot freely slide upward.

Existing sash locks provide varying security value due to the simple constructions known. It may be possible to pry the cam member out of the receiving member from the outside of the building due to the sash locks not providing lateral locking of the window sashes.

Lateral location lugs are previously known which act to stop the sash lock from sliding in the vertical plane, however, they do not actually lock the cam and receiving members together.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sash lock which provides additional strength and security over previously known sash lock constructions.

In one broad aspect of the invention there is provided a sash lock to provide a locking effect to prevent relative sliding movement between first and second elements the sash lock including a mounting adapted for mounting with the first element and a keep adapted for mounting with the second element, a first cam member coupled with said mounting and movable from a non locking position to a locking position where the cam member interengages with said keep and a second cam member coupled with said mounting and movable with said first cam member from a non-locking position to a locking position where the second cam member also interengages with said keep, the first and second cams in use and when in the locking positions preventing relative sliding movement between the first and second elements.

In a preferred form of the invention the first and second cam members are pivotally coupled to the mounting to be rotatable about a common axis of rotation. Preferably the first and second cams are coupled together and to the mounting by a rivet.

According to one form of the invention the first cam member is provided with operating handle means. Also in a preferred form the first cam member engages with stop means which limits relative movement between the mounting and the keep in a direction other than the direction in which the first and second elements are capable of relative movement.

In a preferred form of the invention the sash lock includes limit means which limits relative movement between the mounting and the keep in a direction other than the direction in which the first and second elements are capable of relative movement.

The other direction is preferably transverse to the direction of relative sliding movement.

The limit means can be a notched finger which projects from one of the mounting or keep and a tab which engages in the notch of the finger said tab being provided with the respect other of the keep or mounting.

According to the preferred form of the invention the keep includes a ledge which separates the first and second cam members when they are in the locking positions.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a general view of the sash lock according to the invention, in use on a window section, Figure 2 is a cross section general view across the centre of the sash lock of Figure 1, Figure 3 is an underneath general view of the sash lock according to the invention, Figure 4 is a perspective view of a further form of the sash lock according to the present invention, Figure 5 is an underside plan view of the embodiment of the invention shown in Figure 4, Figure 6 is a view similar to Figure 5 but with the second cam removed,

Figure 7 is a sectioned view of the form of the invention shown in Figures 4-7, Figure 8 is a perspective view of a third form of the invention shown in use with window sash sections, Figure 9 is a cross-sectional view of the third form of the invention, and Figure 10 is an exploded view of the third form of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In Figure 1 the sash lock 10 is illustrated as it would appear in use, upon extruded window frame sections V and L (the first and second elements referred to in the claims).

These frame sections can form the glass frame of respective sashes in a double hung sash window or one can form a sash and the other a fixed frame.

The principle components of the sash lock (as visible in Figure 1) are: a base member 11, a first cam element 12, a fastener 13 (more particularly a rivet) to secure the cam element 12 to the base member 11 and provide an axis of rotation for cam 12, a receiving member or keep 14 and

optionally an interlocking means 17/17a between the base 11 and the keep 14.

Both base 11 and keep 14 are provided with apertures lla/14a to accommodate mechanical fasteners for fastening to the frame sections L and V respectively. Apertures lla and 14a are arranged on the outward peripheral edge of base 11 and keep 14 for convenient access.

Cam 12 (which in a preferred form is formed from a plastics material such as acetyl) is located for rotational movement by rivet 13. Engagement with the adjacent keep 14 is possible by virtue of the engagement edge 12a which effectively increases the radius of the cam relative to the basic circular cam body 12b.

Figure 1 illustrates the full locking position. The sash lock 10 may be unlocked by rotating the cam 12 counter clockwise using the handle or tab 12c. Handle 12c extends from cam 12 substantially perpendicular to the cam body 12b and may be operated by the simple flick of a finger. When the cam is rotated substantially 180° the engagement edge 12a is completely removed from the keep 14 due to the lesser radius of body 12b.

The actual locking method is based not only on the engagement edge 12a'overlapping'into the cavity 14b of keep 14 but

also on the interlocking feature of the engagement edge 12a with a protruding tongue 14c extending downward from the roof of cavity 14b.

The interlocking feature of engagement edge 12a with tongue 14c is best seen by the section view of Figure 2. Figure 2 illustrates the full locking position of the sash lock 10.

It will be apparent that no lateral or vertical relative movement between the base 11, cam 12 and the keep 14 will be possible.

Figure 2 also illustrates the feature of a second cam 15 located underneath base 11 (and hence not visible when the sash lock is installed). The second cam 15 (which in a preferred form is of metal construction) moves dependently with cam 12 as it is actioned by handle 12c.

The eccentric shape of cam 15 is illustrated by Figure 3 which also displays the sash lock in full locking position.

An eccentric engagement edge 15a increases the effective radius of cam 15 from the basically circular body. The engagement edge 15a overlaps into the cavity 14b where a keeper insert 16 is located within cavity 14b. The insert 16 includes a protruding ledge 16a which overlaps with engagement edge 15a to fulfil a secondary locking function of the sash lock.

The secondary cam 15 provides additional strength to the locking function and is hidden beneath base 11 so it does not detract from the aesthetics of the overall sash lock.

Also providing an additional security feature is the interlocking of a finger 17 on the base 11 and a tab 17a on the keep 14.

Figure 1 best illustrates the notched finger member 17 extending from and integrally formed with base 11. The tab 17a formed with keep 14 is'captured'by the notch in member 17 as window frame members V and L align during relative movement between frame member V and frame L. Further vertical movement is prevented by the interlocking means 17/17a.

Notched finger member 17 and tab 17a also provide a guide for the locking movement of cams 12/15 into cavity 14b of keep 14.

As with the interlocking feature of engagement edge 12a and tongue 14c, the notched finger member 17 and tab 17a also secures against lateral movement (eg. when an intruder attempts to pry the window frames apart from outside the building).

A modified form of the invention is shown in Figures 4-7. According to this form of the invention there is provided a locking arrangement whereby the lock is automatically latched when it reaches its locking position. As a result the operator of the lock must physically actuate or release the latching mechanism so as to enable the sash lock to be operated.

In the form of the invention as illustrated the latching arrangement is actuated by a"push to release"button 18 which is conveniently located at the front edge of the base 11. The button 18 has a connecting piece 19 which extends through an opening 20 in the wall of the base.

This connecting piece 19 is coupled to (in the preferred form of the invention it is integral with) an annular member 22 which extends about the turret 21 of second cam 15.

Projecting from the annular part 22 is at least one (as shown more preferably two) spring or biasing elements 23. In the illustrated form the spring elements 23 are effectively cantilevers with the free ends thereof engaging with projections 25 extending inwardly from the inner wall surface of base 11. The spring elements provide a biasing effect which biases the button 18 to its outer position.

A nib or lug 26 extends inwardly from within the annular member 22. This lug 26 engages in an opening or recess 27 in

the turret 21 of the second cam 15 when the sash lock is in the locking position. Such an arrangement is shown in Figure 7.

To release the sash lock for operation the user applies a pushing action on the button 18 which causes the annular portion 22 to move against the biasing effect of the spring elements 23. This movement releases the lug 26 from the recess 27 thereby freeing the second cam 15 (and hence also first cam 12) so that the cams can be rotated to release the lock. As the cams 12 and 15 rotate the end of the lug 26 rides on the surface of the turret 21 of the second cam 15.

However, when the cams 12 and 15 are moved back to the locking position the lug 26 becomes aligned with the opening or recess 27 so that it moves into engagement therewith under the action of the biasing effect of the spring elements 23.

The lock therefore is automatically latched into the locked position and is not able to be moved therefrom until the pushed or released button 18 is activated.

This modified form of the invention therefore provides all of the advantages of the first embodiment but with the added security of the automatic latching of the lock in its locked position.

Figures 8-10 show a third form of the invention. In these Figures, the same reference numerals are used for like parts.

As can be seen in Figure 8, this form of the invention includes a cover llb which is formed integrally with the base member 11. The handle 12c projects through an elongate slot llc in the cover llb.

In this form of the invention, the fastener 13 is formed integrally with the cover llb. As can be seen from Figure 9, the first cam element 12 and second cam element 15 are located on the fastener 13, the tail 13a thereof then being swaged over (though this is not shown in Figure 9) in a like manner to that shown in eg Figure 7. This swaging over of the distal or free end of the fastener 13 retains the components together and rotatable within the housing formed by base 11 and cover llb.

Unlike the previous forms of the invention described herein, the handle 12c is not formed integrally with the first cam element 12. The handle 12c thus has a mounting portion 28 which is insertable through the elongate slot llb to engage in a shaped recess which is the same as recess 29 shown in Figure 10 but on the reverse side of the first cam element 12.

The first cam element 12 has a first opening 30 which, when cam 12 is installed, fits over the fastener 13. Adjacent to this is a second opening 31. Once the first cam element 12 has been located on the fastener 13, the mounting portion 28 of the handle 12c can be inserted through slot llb so that the distal end 32 of the mounting portion 28 engages within recess 29. The distal end 32 is bifurcated and thus engages about a part of the peripheral surface of fastener 13. A spigot 33 on the mounting portion 28 engages in opening 31.

With the mounting portion 28 in position, the second cam element 15 can be located onto the fastener 13 and then the tail of the fastener 13 swaged over into recess 34 in the second cam element 15 to lock all of the components together.

Because the mounting portion 28 of the handle 12c is effectively sandwiched within the confines of the housing formed by cover lla, lateral movement of the handle is not possible because of the interengagement of the spigot in opening 31.

It will be noted that first cam 12 is symmetrical about a mid plane. Thus, due to the duplicate recesses 29 the first cam 12 can be placed on fastener 13 in two different orientations with the result that handle 12c when mounted to the cam will extend in line with the orientation of recess 29. Thus the sash lock can be"handed"by selecting the direction in which handle 12c will protrude from housing ll/llb.

While not shown in the drawings, this third form of the invention can include the interlocking means 17/17a as well as the locking arrangement described in relation to the second form of the invention as shown in Figures 4-7.

The sash lock of the present invention thus provides a sturdy and secure method of internally locking sliding window members.

It will be appreciated that the general construction of the sash lock may be relevant to a number of applications where two members are in a relative sliding arrangement (other than use for single or double hung windows).