Valve lash adjustment for overhead camshaft type engine

For an overhead camshaft type internal combustion engine, a valve lash adjustment system and apparatus using a sliding wedge for adjusting a bearing support for a journal of the camshaft thus moving the camshaft itself relative to a valve.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention concerns a selectively movable bearing support for a 
camshaft journal as utilized in an internal combustion engine's overhead 
camshaft type cylinder head. The support apparatus includes a member with 
a pair of spaced legs which extend upwardly from a top surface of a 
cylinder head. The legs extend along either side of a camshaft bearing 
assembly and guide vertical movements of the bearing assembly either 
towards or away from the top surface of the cylinder head. A selectively 
movable wedge is positioned between the bearing assembly and an end cap 
which extends across and is attached to the upper ends of the spaced legs. 
By adjusting the position of the wedge, the bearing assembly and thus the 
camshaft is moved towards or away from the cylinder head. 
2. Description of Related Art 
A pre-examination search of the subject apparatus has uncovered the 
following references. 
U.S. Pat. Nos. 4,205,634; 4,438,737; and 4,414,931 disclose use of a wedge 
or a movable fulcrum device to vary the timing and lift of a valve train 
with an overhead cam type engine. None of these patents disclose the wedge 
lash adjuster for a movable bearing journal in an overhead camshaft type 
of engine. 
U.S. Pat. No. 1,687,082 discloses a valve timing adjustment using a movable 
sleeve on a shaft. This patent does not disclose the wedge lash adjuster 
for a bearing journal in an overhead camshaft type of engine. 
U.S. Pat. Nos. 4,570,581 and 4,723,517 disclose various valve train timing 
changing mechanisms unlike the subject wedge lash adjuster for a bearing 
journal in an overhead camshaft type of engine. 
SUMMARY OF THE INVENTION 
This invention is directed to a selective adjustment apparatus for an 
overhead camshaft to establish desired valve lash adjustment. A movable 
wedge shaped adjuster is selectively positioned to locate a camshaft 
bearing assembly and the camshaft journal relative to the cylinder head 
and the valves themselves. The adjustment also alters the degree of 
overlap between intake valve and exhaust valve timing events. This may be 
desirable for improving emission characteristics and for increased engine 
performance. The subject adjusting apparatus is both simple and reliable. 
Other advantageous features will become more apparent from the following 
description.

DETAILED DESCRIPTION OF AN EMBODIMENT 
A portion 10 of an overhead camshaft type of cylinder head for an internal 
combustion engine is illustrated in FIG. 1. The cylinder head shown in 
FIG. 1 has an associated single camshaft 12 but the subject adjusting 
apparatus can also be utilized with a dual overhead type of cylinder head. 
Only a portion of camshaft 12 is shown with an axis extending generally 
parallel to the upper surface 14 of the cylinder head 10. 
As is known is the engine art, overhead type camshafts utilize lobe 
portions which periodically engage valve tappets as the camshaft is 
rotated. This engagement moves the valves from a normally closed operative 
position to a more opened operative position. Referring specifically to 
FIG. 4, the cylindrical body portion 16 of the camshaft 12 and an 
eccentric lobe portion 16' is illustrated. As camshaft 12 is rotated, the 
lobe portion 16' slides across surface 18 of a typical bucket type tappet 
member 20. This interaction generates a downward force on the tappet 
member 20 which is transferred to an associated valve 22. 
Specifically, a lower surface 24 of the tappet member 20 engages the upper 
end 26 of the cylinder head's valve stem portion 22. Resultantly, the 
valve stem 22 is forced downward to cause the associated valve to move to 
a more opened position. The generally downward force generated by camshaft 
lobe 16' against surface 18 is opposed by a force F created by a coil type 
valve spring 28. This force F generated by the spring 28 is applied 
upwardly which tends to move camshaft 12 away from cylinder head surface 
14 as shown in FIG. 4. 
Valve spring 28 is restrained axially and is operatively attached to valve 
stem 22 by a pair of half-round retainers 30, 32 which project into a 
groove 34 formed in valve stem 22. Retainers 30, 32 axially secure a valve 
spring keeper (annulus) 35 to valve stem 22. When camshaft 12 and tappet 
20 are removed away from the valve stem 22, such as during disassembly of 
the engine, the retainers 30, 32 maintain the valve spring keeper 35 to 
the upper end of valve stem 22. Resultantly, valve spring 28 is fixed to a 
closed valve operative position. 
Referring again to FIG. 1, camshaft 12 is supported for rotation relative 
to the surface 14 of the cylinder head 10 by a plurality of support 
assemblies, only one of which is shown in FIG. 1. This support assembly 
includes an upstanding member 36 extending from cylinder head surface 14. 
Specifically, member 36 has two leg portions 36' and 36" each extending 
upwards in spaced parallelism. A channel 38 is formed in each leg portion, 
specifically in its inwardly facing side surface. The channels 38 receive 
edge portions 40, 42 of a camshaft bearing assembly which includes a 
semi-circular lower part 44 and a semi-circular upper part 46. Together, 
parts 44, 46 define circular bearing 48 adapted to encircle and support a 
journal formed on camshaft 12. As seen in FIGS. 2 and 3, parts 40 and 42 
are secured together about the camshaft journal by fasteners 50. 
The support assembly permits the attached parts 44, 46 which support the 
camshaft 12 to slide in channels 38 up and down or toward and away from 
cylinder head surface 14. The upwards movement is limited by an end piece 
or cap 52 which is secured to leg portions 36', 36" by fasteners 54. 
The upper edge portion of part 46 has a channel 56 formed therein thus 
defining a bottom surface 58 aligned in an axial direction of camshaft 12. 
A wedge member 60 is positioned to extend over surface 58. Specifically, 
wedge 60 has an upper surface 62 and side surfaces 64 which guide movement 
of the wedge 60 through channel 56. Wedge 60 has a very slightly inclined 
bottom surface 66 which is adapted to slidingly engage surface 58 formed 
on part 46. As seen in FIGS. 2 and 3, an axial movement of the wedge 60 
into the channel 56 from the position shown in FIG. 1 will cause the parts 
44, 46 to move downward toward the cylinder head surface 14. This moves 
the whole camshaft downward towards tappet 20 and valve 22 shown in FIG. 
4. 
In FIG. 1, it can be seen that each camshaft support assembly (except the 
assembly located at the forward and rearward end of the cylinder head) is 
biased upwardly by a force F exerted upwardly on either side of the 
support assembly. These forces F are generated by the valve springs 28 
shown in FIG. 4. In a single camshaft engine with four cylinders to a bank 
(a four or eight cylinder engine), there would be eight separate forces F 
applied to the camshaft and tending to move it and its support parts 44, 
46 upward against the blocking action of wedge 60. 
In FIGS. 1-3, a relatively light coil spring 68 is provided between the 
lower part 44 and the base of the assembly 36. Spring 68 constantly urges 
parts 44, 46 upward against the wedge 60 to eliminate any clearances 
therebetween. 
A primary function of the above described apparatus is to establish a 
desirable small spacing between the circular portion of the camshaft lobe 
and the surface 18 of the tappet 20. This spacing is referred to as valve 
lash. Valve lash is greater at normal ambient temperatures such as 15 
degrees F. than at higher temperatures. As a engine approaches its 
operating temperature where the coolant temperature is about 220 degrees 
F., the valve lash becomes very small. Thus, the purpose of adjusting 
valve assemblies at a specified valve lash is to accommodate thermal 
expansion of engine parts, particularly exhaust valves. 
In FIG. 2, wedge 60 has positioned the camshaft (and its lobe) relatively 
higher or further from the surface 14 and valve stems 22 than as shown in 
FIG. 3. In FIG. 3, wedge 60 has been moved axially into channel 56 so as 
to move the camshaft and the lobes thereon downward towards surface 14 and 
valve stems 22. 
While a preferred embodiment of the subject valve lash adjusting system and 
apparatus has been illustrated and described, other embodiments will now 
become apparent to those skilled in the art and thus the invention is not 
necessarily limited to what is illustrated and described but by the 
following claims.