Sash latch

A latch device for securely locking a keeper mounted on a window within a latch housing located on a window frame. The latch includes a locking bolt which is biased into an open position by a spring. The handle is coupled to the bolt through links. Rotation of the handle causes rotation of the bolt which captures and may lift the keeper to accommodate keeper misalignment.

TECHNICAL FIELD 
The present invention relates generally to window latch hardware and more 
particularly to a sash latch for use with movable windows of the type 
found in houses. 
BACKGROUND ART 
It is conventional to mount many windows in homes so that they can be 
opened for ventilation. Windows mounted on vertically oriented hinges are 
generally referred to as "casement" windows. Windows mounted on horizontal 
hinges are referred to as "awning" type windows. It is conventional to 
provide a hand cranked winder to move the window through its range of 
motion from the opened to the closed position. As the window approaches 
the closed position a latch is usually provided to seat the window and to 
lock it in the closed position. Typically, a keeper attached to the window 
sash mates with a latch assembly which is attached to the window frame or 
sill. The latch captures the keeper and operation of the latch draws the 
window into the closed position where it is locked. In the closed position 
the window is seated in the frame and compresses weather stripping to seal 
the window assembly. 
In many applications the window may sag and alignment between the keeper 
and the latch may vary over time. In these applications it is difficult 
for the latch to capture the keeper and effectively close the window. 
DISCLOSURE OF THE INVENTION 
The present invention discloses a latch assembly which is tolerant of 
keeper misalignment and which, in a preferred embodiment, may be mounted 
for use with either right or left handed windows. 
The latch assembly includes a handle or lever which is pivotally mounted in 
a latch housing. A bolt is pivotally mounted in the housing as well. The 
handle is coupled to the bolt through a pair of links which transfer 
motion from the handle to the bolt. The bolt itself has a complex shape 
and includes several specialized surfaces. Some surfaces are adapted to 
mate with the keeper and to lift it to compensate for window sag. Other 
surfaces catch or capture the keeper to draw the keeper into the latch 
housing during bolt rotation. Another surface serves to "kick-out" the 
keeper during extreme bolt rotation in the unlock direction. 
A spring is included in the latch assembly. In the "unlocked" position the 
spring biases the bolt into an open position which effectively increases 
the reach of the latch and which makes the latch tolerant of keeper 
misalignment. In the "locked" position the spring helps to prevent 
rattling of the handle and the keeper. 
When the handle is moved to rotate the bolt, the bolt captures, lifts and 
draws the keeper into the latch housing. When the handle is moved to its 
extreme position the latch assumes a "locked" position. In the "locked" 
position the linkage between the bolt and handle is tensioned and forms an 
over-center toggle to retain the window in the closed position.

MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 shows a perspective view of the latch assembly 10 and the 
complimentary keeper 12. In a typical application, the keeper 12 will be 
mounted on a window casement by the placement of mounting screws through 
mounting aperture 26 and mounting aperture 28. The latch assembly 10 will 
be mounted on a window frame or sill through the use of mounting aperture 
22 and mounting aperture 24. In use, the window is hinged so that the 
keeper 12 can move along a closure path 30 toward the latch assembly 10 as 
the window is closed. 
When the keeper 12 is adjacent the latch assembly 10, the latch handle 14 
can be rotated about handle axis 20 into a "locked" position 15 shown in 
phantom outline in FIG. 1, from the "open" position 18 shown in phantom 
outline in FIG. 1. Movement of the handle 14 from the "open" position to 
the "locked" position causes the so called "bolt" to rotate and to capture 
the keeper 12. This process causes the keeper 12 to be lifted in the 
vertical direction indicated by the lifting path arrow 32 and to be pulled 
into the latch housing 11 as indicated by the closure path arrow 30. This 
movement of the bolt closes the window and supplies sufficient force to 
the window to provide a good seal against weather stripping. 
In a similar fashion, movement of the handle 14 from the "locked" position 
15 to the "open" or unlocked position 18 releases the keeper 12. A 
kick-out surface on the bolt interacts with the keeper hook 13 and forces 
the keeper 12 out of the latch. 
In the preferred embodiment both the latch assembly 10 and the keeper 12 
are symmetrical and they may be mounted for use with right handed or left 
handed windows. However in order to economize on the cost of production it 
is possible to eliminate one of the two links forming complimentary right 
and left handled latch assemblies. It is common to die cast latch 
components out of zinc or aluminum, although certain components may be 
stamped from mild steel or the like. In general, materials choices are not 
critical to the operation of the latch. The optimum material choice will 
depend upon balancing durability and cost considerations. 
FIG. 2 is an exploded view of the latch assembly 10. This view shows an 
outer latch housing 11 and an inner latch housing plate 21. The interior 
portion of the handle 14 is visible in the figure. This portion of the 
handle 14 is mounted for pivotal rotation around a handle axis 20. The 
bolt 34 is also shown and it is mounted for pivotal rotation about a bolt 
axis 36. First link 38 and second link 40 are also shown. These links 
connect the handle 14 to the bolt 34. First link 38 has a journal 39, 
which mates with a corresponding journal aperture 41, located in the 
handle 14. An upper link pin 42 is fitted in the first link 38, to 
communicate with an arcuate first link pin slot 50, located in the bolt 
34. In a similar fashion, the second link 40 carries a link pin 44, which 
mates with an arcuate second link pin slot 52, formed in bolt 34. The 
outer housing 11 carries a pair of spring retention features, one of which 
can be seen in FIG. 2 and is identified by reference numeral 51. The leaf 
spring 48 is shown nested in the retention features. 
FIG. 3, FIG. 4 and FIG. 5 should be considered together. These figures show 
the handle 14, the bolt 34 and one of the links 38 in a variety of 
positions. For clarity the housing and lower link are not shown in these 
views. 
FIG. 3 corresponds to the handle 14 in the unlocked position 19. In this 
view the bolt 34 is fully rotated in the counterclockwise direction to the 
"open" position to capture the keeper 12. The bolt 34 includes a hook 
shaped pulling surface 35 which is positioned beneath the keeper hook 13 
in the figure. In this position the spring 48 is in its minimum energy 
state and it biases the bolt 34 in the fully counterclockwise direction. 
As shown in the figure the bolt 34 includes a cam surface 33 which abuts 
the spring 48. In this unlocked position 19 the spring 48 provides a force 
to maintain the bolt 34 in the fully rotated position. This permits 
substantially more bolt 34 rotation than would be possible with the links 
alone. This increases the capture range of the bolt and thus contributes 
to the ability of the latch to accommodate a misaligned keeper. FIG. 3 
also depicts the kick-out surface 43 which is located on the bolt 34. If 
the window sticks, the handle 14 and link 38 move the kick-out surface 
into abutment with the keeper hook 13 and force the keeper 12 away from 
the latch. 
FIG. 4 shows the handle 14 rotated to the intermediate position 17. In this 
position the cam surface 33 has deflected the spring in to its maximum 
energy state and the spring is resting on a cam nose detent surface 29. 
During manufacture this handle position is used as an aid to painting the 
latch assembly. In use, the handle 14 lever pulls on the first link 38 
which in turn causes the first link pin 42 to abut the end of the first 
link pin slot 50 to rotate the bolt 34 into this intermediate position. It 
is important to note that the bolt 34 includes a keeper lifting surface 37 
which will bottom out on a sagging keeper hook as the keeper 12 is drawn 
into the latch housing 11. In FIG. 3 this keeper lift surface 37 lies 
somewhat below the bolt axis 36, while in FIG. 4 the surface 37 lies above 
the bolt axis. Consequently if the keeper hook 13 has sagged it will be 
lifted during bolt 34 rotation which typically facilitates window closure. 
FIG. 5 shows the latch assembly in locked position 15. In this figure the 
keeper 12 is drawn into the locked position 15 by bolt 34 rotation. The 
handle 14 is connected to the bolt 34 through the first link 38. As seen 
in the figure the centerline 31 of the first link 38 is located below the 
handle axis 20 in this locked position. By positioning the centerline 31 
below the handle axis 20 results in an over-center toggle action and 
forces supplied to the bolt 34 which tend to force the bolt 34 to rotate 
in the counterclockwise direction tend to move the handle 14 in the 
clockwise direction. This action causes the latch assembly to latch firmly 
and to resist being pried open.