Locking door latch

A locking entry door latch equipped with a positive locking dead bolt and a latch bolt. The latch includes a housing, a sliding latch bolt mechanism, a sliding dead bolt mechanism, a center bolt to resist longitudinal loading, a strike assembly with a precatch that holds the door latched when it is not completely closed and a final catch for the latch bolt and dead bolt, a locking mechanism and inside and outside operating handles. Both the locking mechanism and the operating handles are independently operable from inside or outside the vehicle.

BACKGROUND OF THE INVENTION 
Typically on motor homes and travel trailers the main entrance door leading 
into the living quarters and other restricted areas is secured with a 
latch equipped with a locking mechanism that can be operated from inside 
or outside the vehicle. 
It is common practice to have large numbers of these locks all keyed alike. 
The reason for this is to reduce the number of different keys the 
manufacturer and dealer have to contend with while the vehicle is in their 
possession. It is more convenient for a dealer to unlock a number of 
vehicles with one master key when showing to customers than to locate and 
carry around a separate set of keys for each vehicle on the lot. 
Unfortunately this practice offers very little security against 
unauthorized entrance into the motor home, so in addition to the locking 
door latch a separate dead bolt is installed in each door. The dead bolt 
is designed to be keyed to a higher number of key configurations, to 
reduce the chance of a key from one motor home being able to unlock the 
dead bolt of the door of another. 
The dead bolt can be kept unlocked while on the dealers lot so he can enter 
any vehicle with a master key, yet the additional security is available 
for the final owner when required. 
This arrangement of a latch bolt lock and a separate dead bolt lock appears 
to offer the easy access needed by the dealer and the security and peace 
of mind required by the final owner of the vehicle, but creates other 
problems in the way of added costs for the additional security. 
Having to install two separate units in each door means higher costs, due 
to the additional labor and materials required for the additional 
inventory, door preparation and installation, all of which is paid for by 
the customer in the way of higher product cost. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a door latch with 
improved security features, thus eliminating the need for additional 
locking devices beyond the primary latch assembly. 
Another object of the invention is to provide a latch of the above stated 
character that is strong enought to meet the requirements of automotive, 
architectural and industrial applications, yet is compact enough to offer 
styling and functional advantages over the latches in use today. 
A particular object is to provide an entrance door latch with no need for a 
separate dead bolt assembly to be installed in the door, rather 
incorporating a positive locking, sliding dead bolt arrangement as an 
integral part of the latch assembly. 
The latch of the invention not only fulfills the easy access and additional 
security requirements in one small package, but offers the motor home 
industry needed functional and styling features. 
The low profile compact design of the outside housing and handle of the 
latch of the invention offers very little interruption to the smooth 
styling lines of today's modern motor home and industrial architecture, 
with the low profile design of the outside housing and handle resulting in 
a flush mounting latch. A dished outside housing incorporates a flat 
paddle handle for operation of the latch from the outside of the vehicle. 
The latch is primarily intended for an industry such as motor homes and 
trailers and other vehicles that are required to meet the Motor Vehicle 
Safety Standard No. 206, but it's use is not restricted to these vehicles 
alone, as there is a general need for this type of latch on other vehicles 
and for numerous stationary applications as well, and it is also an object 
of the invention to provide such a latch which has general application to 
all types of closures.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The latch includes a housing with an outer cover 21 and an inner cover 22 
joined by screws 23. A latch bolt 24, a dead bolt 25 and a center bolt 26 
are carried in the housing. The center bolt has a center section 27 of 
lesser diameter than an end section 28. The latch bolt and dead bolt may 
each be a unitary piece or may be a two piece construction with a hardened 
rod or bar carried in the body and extending outward for engaging the 
strike. 
Control means are provided for the latch bolt and include a spring 31, a 
latch cam plate 32 and a stop 33. Control means are provided for the dead 
bolt and include a dead bolt cam plate 34 and a dead bolt cam 35. 
A strike or keeper has an inner plate 38 and an outer plate 39, with 
openings 40, 41, 42 and 43, and slots 44, 45. 
The latch bolt is moved between locked and unlocked conditions by a latch 
key lock 51 and the dead bolt is moved between locked and unlocked 
positions by a dead bolt key lock 52. The latch bolt and the dead bolt are 
locked in place by locking handles 53, 54, respectively, and the latch 
bolt is moved to the unlocked position by an outside handle 55 and an 
inside handle 56. The inside handle is centered by detent means including 
a ball 58, spring 59, and notched detent cam 60. 
The two key actuated lock cylinders 51, 52 are accessed through openings in 
the outside handle 55 for operation of the dead bolt 25 and the latch bolt 
24. 
Two small locking handles 53, 54 are rotatably attached to the inner cover 
for operation of the latch bolt and the dead bolt, respectively, from 
inside the vehicle. 
A turn handle 56 is also rotably attached to the inner cover of the 
housing, and can be rotated in either direction to operate the latch. This 
symmetrical handle operation means the latch can be mounted in either left 
or right hand doors without any sacrifice in convenience of operation. 
The inner and outer strike plates or strikes 38, 39 are mounted in the door 
frame and have rectangular openings positioned to receive the latch bolt 
and the dead bolt when the door is closed. 
The opening 42 for the latch bolt 24 in the inner strike 38 is positioned 
to receive the latch bolt slightly prior to the door being in the fully 
closed position. This is known as the precatch position and offers a 
margin of safety by holding the door latched in the event it is not 
completely closed, or it becomes unlatched from the fully closed position. 
The portion of the inner strike 38 with the latch bolt opening 42 
preferably is made out of the plane of the remainder of the strike, as 
seen in FIG. 2, spacing the opening 42 from the opening 43 in the outer 
strike 39. 
An angled surface on the back of the outboard end of the latch bolt 24 
creates a ramp effect which causes the bolt to longitudinally travel 
inboard when it makes contact with the curved outer surface of the flange 
37 on the inner strike 38 as the door is closed. 
The spring loaded cam plate 32 is attached to the inboard end of the latch 
bolt and causes the bolt to longitudinally travel in an outboard direction 
from the housing when it comes in line with the precatch opening 42 in the 
inner strike 38. 
As the door is closed further the latch bolt comes in line with and extends 
into the opening 43 in the outer strike 39. This is known as the final 
catch position. 
In this door position the dead bolt 25 is in line with openings 40, 41 in 
both the inner and outer strikes and can be extended into these openings 
to the locked position by operating the dead bolt locking handle 54 inside 
the vehicle or the dead bolt key lock 52 from the outside. 
The center bolt 26 has a cylindrical shape, with the flange 28 at one end 
and a threaded portion at the other end for attachment to the latch in a 
location between the dead bolt and the latch bolt. A back plate 64 is 
positioned in the housing between the outer and inner covers. The center 
bolt may be attached directly to the back plate or to a backup block 65 
which in turn is attached to the back plate. A front plate 66 may be 
attached to the back plate 64 when additional strength is desired. 
When the latch is installed in the door, the center bolt protrudes through 
a clearance hole in the edge of the door and bridges the gap between the 
door and frame. An open sided slot 44 in the inner strike 38 is positioned 
to accept the neck portion 27 of the center bolt when the door is closed. 
The flange 28 on the center bolt being outboard of the inner strike and 
having a larger diameter than the width of the slot 44 prevents the 
separation of the latch from the keeper when a longitudinal load is 
applied between the door and the door frame. This construction prevents 
the door from becoming unlatched due to the latch bolt and dead bolt being 
separated from the keeper. 
The need for this feature comes into play when the vehicle is in an 
accident or simply when doors and frame structures come under greater 
loads than they were designed for. 
The outer strike 39 has a similar open ended slot 45 that is slightly 
larger than the outside diameter of the center bolt flange 28. This is 
done to create a clearance to the center bolt flange so it can be kept 
short and the overall package compact, but if more strength is needed to 
resist higher longitudinal loads, both slots could be the same size and 
the center bolt neck could be long enough to accommodate the thickness of 
both strikes. Such a design would increase the holding power of the center 
bolt to the strength of both strikes instead of just one. 
The entrance to the slots in both strikes is wider than the slot itself, 
and is angled into the slot to provide ramps to guide the center bolt into 
the slot. The ramps act as a guide for vertical alignment between the door 
and the frame. 
The center bolt is threaded into the back plate 64 and bottoms out against 
a shoulder 68 located on the center bolt shank near the end of the thread. 
Tightening the center bolt against the shoulder 68 holds it in place and 
prevents it from becoming loose. 
If adjustment to the length of the center bolt is necessary due to an 
application having a wider or narrower gap between the door edge and door 
frame, spacers could be added beneath the shoulder 68 or the shoulder 
could be adjustable by making it separate from the center bolt, in the 
form of a threaded ring or lock nut. The position of such a ring on the 
thread would determine the extended length of the center bolt. 
As is the case with the latch bolt, a sliding cam plate 34 is attached to 
the inboard end of the dead bolt 25. Both the dead bolt locking handle 54 
and the dead bolt key lock 52 are mechanically attached to the cam 35 that 
pushes against the dead bolt cam plate 34 to move the dead bolt into the 
locked or unlocked position when the lock handle or key lock is rotated in 
the appropriate direction. 
When the dead bolt is in either the locked or unlocked position a spring 
loaded ball 69 located in a blind hole in the housing outer cover is in 
line with a small hole or detent in the dead bolt cam 35. The spring 70 
forces the ball partially into the hole, which holds the cam in that 
position until the force of the spring holding the ball in the hole is 
overcome by turning the dead bolt key lock or locking handle. The size of 
the hole in the cam, relative to the size of the ball determines how far 
the ball will enter the hole and how strong the detent will be. The larger 
the hole, the further the ball will enter it and the higher the holding 
power of the detent will be. 
When the dead bolt is in the locked position a perpendicular leg 72 that 
connects the two parallel legs of the "U" shaped cam 35 is in a position 
against the edge of a slot 83 in the cam plate as to prevent movement of 
the dead bolt into the unlocked position without physically rotating the 
key lock or locking handle. This positive lock prevents the dead bolt from 
being pried open from outside the vehicle. 
The lock mechanism for the latch bolt works in the same way, except the 
mechanism rotates the latch bolt stop 33 instead of a cam. The stop 33 
rotates to an over center, detented position in the path of the latch bolt 
travel, preventing latch bolt movement and making the latch inoperative. 
When the lock mechanism is rotated in the opposite direction, the latch 
bolt stop 33 moves to a detented position out of the way of the latch bolt 
travel and the latch can be operated. 
In both the dead bolt lock mechanism and the latch bolt lock mechanism, the 
attachment between the key lock cylinder and the cam or stop has 
sufficient rotary clearance or play to allow the cam or stop to be rotated 
between the locked and unlocked positions via the inside locking handles 
without turning the key lock cylinders. 
This function is desirable because when the key is removed from the lock 
cylinder, spring loaded wafers in the lock cylinder extend radially 
outward into an axial groove in the cylinder lock bore in the outside 
housing. This prevents rotational movement of the lock cylinder. A second 
axial groove 180 degrees away from the first groove is in the bore because 
as the key is being inserted or removed, the wafers ride against the 
contour of the key which causes them to travel back and forth and 
alternately extend from both sides of the lock cylinder. 
When the key is inserted all the way into the lock cylinder the wafers are 
completely retracted and rotational movement is not limited, so the lock 
cylinder can be rotated until the play between the lock cylinder and 
cam/stop is overcome and it moves the cam/stop into the locked or unlocked 
(detented) position. The ball detent arrangement holds the cam/stop in 
this position while the key lock cylinder is rotated back to the original 
position where the wafers line up with the grooves and the key can be 
removed. 
The inside locking handles 54, 53 are connected to their related cam/stop 
35/33 with a rod 74 having a square cross section. One end of this rod is 
inserted into a square hole in the inboard end of the cylindrical shaft 
portion of the locking handle. The other end is inserted in a square hole 
in one leg of the cam/stop. 
Both the dead bolt cam and the latch bolt stop are made from thin pieces 
bent or formed into a "U" shape. One leg of the "U" has the appropriate 
hole for attachment to the lock cylinder while the opposite leg has the 
square hole for connection to the rod. Both holes are located on the same 
centerline, which becomes the pivot point for the cam/stop when it is 
rotated. Being rigidly connected to the cam/stop via the rod, the locking 
handles follow the rotary movement of the cam/stop, and act as pointers to 
indicate whether the latch bolt and dead bolt are locked or unlocked. The 
length of the rods can vary, relative to the thickness of the door being 
used. 
When the latch is installed in the door the rods become captured between 
the lock cylinders and the bottom of the square holes in the locking 
handles. The rod length is sized to prevent it from sliding far enough in 
an axial direction to become disconnected from the locking handle or the 
cam/stop. The locking handles are held into the housing inner cover by 
snap rings. The lock cylinders are held into the housing outer cover with 
"E" rings. These methods of attachment are only two of numerous methods 
that could be used and work equally as well. 
The back plate 64 has multiple bends and cutouts and is attached to the 
inboard side of the housing outer cover. The back plate has rectangular 
openings that support and guide the linear travel of the latch bolt and 
the dead bolt and their respective cam plates. 
A compression spring 31 positioned on a tang 76 on the latch bolt cam plate 
32 pushes against the flat surface of a tab or flange 78 on the backplate 
64 to hold the latch bolt in the extended position, until the spring force 
is overcome when the door is closed or one of the handles is operated to 
open the door. 
Attached to the inboard end of the shaft portion of the inside handle 56 is 
one leg of the "L" shaped cam 60, while the other leg extends inboard 
adjacent to lips or flanges 78, 81 on the latch bolt cam plate 32. When 
the inside handle 56 is rotated in either direction the cam 60 pushes 
against the lip 78 or 81 and moves the cam plate 32 and latch bolt 24 in a 
linear direction against the pressure of the spring 31. When the handle is 
released the force of the spring returns the cam plate and latch bolt to 
the extended or locked position. 
A recess or detent 79 is formed on the cam leg that attaches to the handle, 
and is positioned over a blind hole in the housing inner cover, which 
contains the spring 59 and ball 58. This detent arrangement holds the cam 
and inside handle in a neutral position and prevents handle rattle when it 
is not in use. 
The outside handle 55 is attached to the housing outer cover with vertical 
hinge pins 80 located near the edge of the handle closest to the free edge 
of the door. The handle pivots on the hinge pins when operated. A tang 82 
extending from the inboard surface of the handle protrudes through an 
opening in the outer cover and into the area where the latch bolt cam 
plate 32 is located. A tab 84 (FIG. 5) formed on the latch bolt cam plate 
32 is in contact with the end portion of the tang 82 and the force of the 
cam plate spring 31 pushing the cam plate against the tang holds the 
handle in a position flush with the outboard surface of the housing outer 
cover. 
When the outside handle 55 is operated, it pivots outward on the hinge pins 
and the tang pushes against the cam plate. As the force of the cam plate 
spring is overcome, the cam plate and latch bolt move longitudinally in a 
direction to retract the bolt from the strike and unlatch the door. When 
the handle is released, the force of the spring returns the cam plate, 
bolt and handle back to the original position. 
The front plate 66 has somewhat of a "U" cross section and is attached to 
the back plate 64. The front plate has holes and cutouts positioned to 
line up with the mounting holes and cutouts in the back plate. The front 
plate functions to give additional stiffness and support to the back plate 
when the latch bolt and center bolt come under heavy loads (as described 
in Safety Standard No. 206). For some applications the front plate might 
not be required, or it could be manufactured as an integral part of the 
back plate or of the housing outer cover. 
The back plate along with the attached components is mounted to the inboard 
side of the housing outer cover and held in place with screws 85 threaded 
into bosses in the cover. 
An opening cut through the door close to the free edge is sized to accept 
the latch assembly. The inner and outer covers, along with the attached 
components, are installed into the opening from opposite sides of the 
door, and held together with the screws 23 inserted through holes in the 
inner cover and into threaded bosses in the outer cover. Flanges on all 
four sides of both covers are sized slightly larger than the door opening, 
thus creating a sandwich affect that holds the latch into the door. In 
addition to the housing screws, there are mounting holes available on the 
backplate that can be accessed through holes in the door edge.