Valve operating device for internal combustion engine

A valve operating device for the intake or exhaust valves of an internal combustion engine wherein a plurality of cam followers are disposed adjacent to each other for operation by different cams in mutually different modes dependent on the speed of rotation of a camshaft. A selective coupling mechanism disposed in and between the cam followers has switching pins movable between a connecting position in which the cam followers are interconnected and a disconnecting position in which the cam followers are disconnected. An oil passage is provided in one or more of the cam followers and the switching pin therein is arranged to control the rate of flow of oil through the oil passage defined in that cam follower in response to movement of the switching pin between the connecting and disconnecting positions. The oil supplied through the oil passage is used for lubricating the cam and cam following sliding surfaces in one embodiment and for operating hydraulic valve lash adjusters in another embodiment.

The present invention relates to a valve operating device for an internal 
combustion engine of the type having a plurality of cam followers disposed 
adjacent to each other for operating the intake or exhaust valves in 
different modes dependent on engine speed by means of a selective coupling 
mechanism for connecting and disconnecting the cam followers and, in 
particular, to an arrangement for controlling oil flow through a passage 
in a cam follower by means of the coupling mechanism. 
Heretofore, valve operating devices of this general type have been known, 
for example, as disclosed in U.S. Pat. Nos. 4,537,164, 4,537,165, 
4,5453342, 4,536,732, 4,656,927, 4,612,884, 4,526,128 and 4,587,936 owned 
by the assignee of this application. 
In the valve operating mechanism, the cam followers may have oil passages 
for supplying lubricating oil to the surfaces of the cam followers which 
are slidably held against the camshaft or for supplying oil to the 
hydraulic lash adjusters. It is desirable that the amount of lubricating 
oil supplied be controlled according to the operating conditions of the 
engine. If the control of the amount of supplied lubricating oil, and/or 
hydraulic lash adjuster oil can be, accomplished by the selective coupling 
mechanism, then no special control device is necessary for such control, 
and hence the number of parts required and the cost of manufacture can be 
reduced. 
It is an object of the present invention to provide a valve operating 
device for an internal combustion engine, which includes a selective 
coupling mechanism having a switching pin capable of controlling the 
amount of flow of oil in an oil passage defined in the cam follower.

As shown in FIGS. 1 and 2, a part of intake valves 1a, 1b disposed in a 
engine body E is opened and closed by two low-speed cams 3 and one 
high-speed cam 5 which are integrally formed on a camshaft 2 rotatable by 
the crankshaft of the engine at a speed ratio of 1/2 the speed of rotation 
of the crankshaft, by first, second, and third rocker arms 7,8,9, 
pivotally supported on a rocker shaft 6 extending parallel to the camshaft 
2. A selective coupling mechanism 10 is provided in the rocker arms 7 
through 9 for selectively connecting and disconnecting the rocker arms. 
The camshaft 2 is rotatably disposed above the engine body E. The two 
low-speed cams 3 are integrally formed with the camshaft 2 in alignment 
with the intake valves 1a, 1b, respectively. The high-speed cam 5 is 
integrally formed with the camshaft 2 in an intermediate position between 
the low-speed cams 3. Each of the low-speed cams 3 has a cam lobe 3a 
projecting radially outwardly to a relatively small extent and a base 
circle portion 3b. The high-speed cam 5 has a base circle portion 5b and a 
cam lobe 5a projecting radially outwardly to an extent larger than that of 
the cam lobe 3a and having a larger angular extent than that of the cam 
lobe 3a. 
The rocker shaft 6 is fixed below the camshaft 2. The first rocker arm 7 is 
operatively associated with the intake valve 1a, the second rocker arm 8, 
is operatively associated with the intake valve 1b, and the third rocker 
arm 9 is disposed between the first and second rocker arms 7,8, and all 
three rocker arms are pivotally supported on the rocker shaft 6 in 
mutually adjacent relation to each other. The first rocker arm 7 has on 
its upper surface a cam slipper 11 held in slidable contact with the 
low-speed cam 3. The second rocker arm 8 has on its upper surface a cam 
slipper 12 held in slidable contact with the low-speed cam 3. The third 
rocker arm 9 has on its upper surface a cam slipper 13 held in slidable 
contact with the high- o speed cam 5. Thus, the rocker arms 7,8,9 serve as 
cam followers. The rocker arms 7 through 9 have ejector holes 14a, 14b; 
15a, 15b; 16a, 16b defined in the cam slippers 11 through 13 respectively, 
and opening on opposite sides of their surfaces slidably held against the 
cams 3, 5 for supplying lubricating oil to these sliding surfaces. 
Flanges 17 are attached to the upper ends of the intake valves 1a, 1b. The 
intake valves 1a, 1b are normally urged in a closing direction, i.e., 
upwardly, by valve springs S disposed between the flanges 17 and the 
engine body E. Tappet screws 18 are adjustable threaded in the distal ends 
of the first and second rocker arcs 7, 8, respectively, and held against 
the upper ends of the intake valves 1a, 1b, respectively. 
As also shown in FIG. 3, the third rocker arm 9 extends from the rocker 
shaft 6 toward a position between the intake valves 1a, 1b. The third 
rocker 9 is normally urged resiliently in a direction to slidably contact 
the high-speed cam 5 by resilient urging means 19 disposed between the 
third rocker arm 9 and the engine body E. The resilient urging means 19 
comprises a cylindrical bottomed lifter 20 with its closed end held 
against the third rocker arm 9, and a lifter spring 21 disposed between 
the lifter 20 and the engine body E. The lifter 20 is slidably fitted in a 
bottomed hole 22 defined in the engine body E. 
As illustrated in FIG. 4, the selective coupling mechanism 10 for 
connecting and disconnecting the rocker arms 7 through 9 are disposed in 
and between these rocker arms 7 through 9. The selective coupling 
mechanism 10 comprises a first switching pin 23 capable of coupling the 
second and third rocker arms 8, 9 to each other, a second switching pin 24 
capable of coupling the third and first rocker arms 9, 7 to each other, a 
third switching pin 25 for limiting movement of the first and second 
switching pins 23, 24, and a return spring 26 for urging the switching 
pins 23 through 25 in a direction to disconnect the rocker arms. 
The second rocker arm 8 has a first guide hole 27 parallel to the rocker 
shaft 6 and having an end closed by a closure member 28 remote from the 
third rocker arm 9. The first switching pin 23 is slidably fitted in the 
first guide hole 27, with a hydraulic chamber 29 being defined between the 
closure member 28 and the first switching pin 23. The second rocker arm 8 
also has a communication passage 30 defined therein in communication with 
the hydraulic chamber 29. The rocker shaft 6 has an oil pressure supply 
passage 31 defined herein and connected to an oil pressure supply source 
(not shown). The communication passage 30 and the oil pressure supply 
passage 31 are in communication with each other at all times through a 
communication hole 32 defined in a side wall of the rocker shaft 6, 
irrespective of the angular position of the second rocker arm 8. 
The third rocker arm 9 has a second guide hole 33 extending between its 
opposite surfaces parallel to the rocker shaft 6 in registration with the 
first guide hole 27, and the second guide hole 33 has the same diameter as 
has the first guide hole 27. The second switching pin 24 has a length 
equal to the entire length of the second guide hole 33 and is slidably 
fitted therein. 
The first rocker arm 7 has a third guide hole 34 extending parallel to the 
rocker shaft 6 in registration with the second guide hole 33, and the 
third guide hole 34 has the same diameter as the second guide hole 33. The 
end of the third guide hole 34 remote from the third rocker arm 9 is 
closed by a closure member 35. The third switching pin 25 is slidably 
fitted in the third guide hole 34 and has a coaxial shaft 36 movably 
inserted through a guide hole 37 defined in the closure member 35. The 
return spring 26 is disposed around the shaft 36 between the closure 
member 35 and the third switching pin 25 for normally urging the abutting 
switching pins 23 through 25 in the direction to disconnect the rocker 
arms, i.e., toward the hydraulic chamber 29. 
With no high oil pressure supplied to the hydraulic chamber 29, the 
switching pins 23 through 25 are in the position shown in FIG. 4 where the 
rocker arms are disconnected under the bias of the return spring 26. In 
this position, the abutting surfaces of the first and second switching 
pins 23, 24 lie between the second and third rocker arms 8, 9, and the 
abutting surfaces of the second and third switching pins 24, 24 lie 
between the third and first rocker arms 9, 7, whereby the rocker arms 7 
through 9 are disconnected from each other. When high oil pressure is 
supplied to the hydraulic chamber 29, the switching pins 23 through 25 are 
moved in direction away from the hydraulic chamber 29 against the force of 
the return spring 26 until the first switching pin 23 is slidably inserted 
into the second guider hole 33, and the second switching pin 24 is 
slidably inserted into the third guide hold 34 for thereby connecting the 
rocker arms 7 through 9, as shown in FIG. 5. 
The third switching pin 25 has an annular groove 40 defined in its outer 
peripheral surface. The inner peripheral surface of the first rocker arm 7 
which defines the third guide hold 34 has an annular recess 41 defined 
therein. The annular recess 41 is held in registry with the annular groove 
40 when the third switching pin 25 is in the position to disconnect the 
rocker arms. The widths of the annular groove 40 and the annular recess 41 
along the axis of the third switching pin 25 are selected such that when 
the third switching pin 25 is moved from the rocker arm disconnecting 
position to the rocker arm connecting position, the annular groove 40 and 
the annular recess 41 are positionally displaced from each other. The 
first rocker arm 7 has an oil passage 42 defined therein with one end 
communicating with the ejector holes 14a, 14b and the other end 
communicating with the annular recess 41. Another oil passage 43 in first 
rocker arm 7 has one end communicating with the annular recess 41 and the 
other end communicating, at all times, with the oil pressure supply 
passage 31 through a communication hole 44 defined in the side wall of the 
rocker shaft 6. Therefore, the oil passageway formed by the oil passages 
42, 43 is open in the rocker arm disconnecting position of the coupling 
mechanism 10 but is restricted when the third switching pin 25 is moved 
into the rocker arm connecting position. 
The first switching pin 23 has an annular groove 45 defined in its outer 
peripheral surface. The inner peripheral surface of the second rocker arm 
8 which defines the first guide hole 27 has an annular recess 46 defined 
therein. The annular recess 46 is held in registry with the annular groove 
45 when the first switching pin 23 is in the position to disconnect the 
rocker arms. The widths of the annular groove 45 and the annular recess 46 
along the axis of the first switching pin 23 ar selected such that when 
the first switching pin 23 is moved from the rocker arm disconnecting 
position to the rocker arm connecting position, the annular groove 45 and 
the annular recess 46 are positionally displaced from each other. The 
second rocker arm 8 has an oil passage 47 defined therein with one end 
communicating with the ejector holes 15a, 15b and the other end 
communicating with the annular recess 46. Another oil passage 48 in the 
second rocker arm 8 has one end communicating with the communication hole 
30. Therefore, the oil passageway formed by the oil passages 47, 48 is 
open in the rocker arm disconnecting position but is restricted when the 
first switching pin 23 in moved into the rocker arm connecting position. 
An annular groove 49 is defined in the outer peripheral surface of the 
second switching pin 24. The third rocker arm 9 has an oil passage 50 
defined therein with one end opening at the inner peripheral surface of 
the second guide hole 33 so that the oil passage 50 will communicate with 
the annular groove 49 when the second switching pin 24 is in the rocker 
arm connecting position. The other end of the oil passage 50 communicate 
with the ejector holes 16a, 16b. The third rocker arm 9 also has an oil 
passage 51 defined therein with one end opening at the inner peripheral 
surface of the second guide hole 33 so that the oil passage 51 will 
communicate with the annular groove 49 when the second switching pin 24 is 
in the rocker arm connecting position. The other end of oil passage 51 
always communicates with the oil pressure supply passage 31 through a 
communication hole 52 defined in the side wall of the rocker shaft 6. 
Operation of the valve operating device is as follows. During low-speed 
operation of the engine, the hydraulic chamber 29 is supplied with a 
relatively low oil pressure, and the switching pins 23 through 25 are 
positioned at the maximum stroke toward the hydraulic chamber 29, i.e., 
into the rocker arm disconnecting position, under the force of the return 
spring 26. In this position, the abutting surfaces of the first and second 
switching pins 23, 24 lie between the second and third rocker arms 8, 9, 
and the abutting surfaces of the second and third switching pins 24,25 lie 
between the third and first rocker arms 9, 7. Therefore, the rocker arms 7 
through 9 are angularly displaceable with respect to each other. 
While the rocker arms 7 through 9 are thus disconnected, the first and 
second rocker arms 7, 8 are angularly moved in sliding contact with the 
respective low-speed cams 3 in response to rotation of the camshaft 2. 
Therefore, the intake valves 1a, 1b are opened and closed at the timing 
and lift according to the profile of the low-speed cams 3. At this time, 
the third rocker arm 9 is angularly moved in sliding contact with the 
high-speed cam 5, but such angular movement does not affect operation of 
the first and second rocker arms 7, 8 in any way. 
In the rocker arm disconnecting position, the annular groove 40 and the 
annular recess 41, and the annular groove 45 and the annular recess 46 are 
registered with each other, and the relatively low oil pressure from the 
oil pressure supply passage 31 is supplied via the oil passages 42, 43, 
and 47, 48 to the ejector holes 14a, 14b and 15a, 15b without being 
restricted. 
During high-speed operation of the engine, a relatively high oil pressure 
is supplied to the hydraulic chamber 29. As shown in FIG. 5, the switching 
pins 23 through 25 are moved into a position to connect the rocker arms 
against the spring bias of the return spring 26 for thereby inserting the 
first switching pin 23 slidably into the second guide hole 33 and 
inserting the second switching pin 24 slidably into the third guide hole 
34. The rocker arms 7 through 9 are thus interconnected. At this time, 
since the third rocker arm 9 slidingly contacting the high-speed cam 5 
swings to the maximum extent, the first and second rocker arms 7, 8 swing 
in unison with the third rocker arm 9, and hence the intake valves 1a, 1b 
are opened and closed at the timing and lift according to the profile of 
the high-speed cam 5. 
When the selective coupling mechanism 10 is thus operated to connect the 
rocker arms, the oil passageways formed the oil passages 42, 43 and the 
oil passages 47, 48 are restricted by the first and third switching pins 
23, 25. Therefore, only a small amount of lubricating oil is supplied to 
the sliding surfaces of the low-speed cams 3 and the cam slippers 11, 12. 
With the second switching pin 42 moved to the rocker arm connecting 
position, the oil passages 50, 51 communicate with each other through the 
annular groove 49 whereupon lubricating oil from the oil supply passage 31 
is supplied to the ejector holes 16a, 16b for lubricating the sliding 
surfaces of the high-speed cam 5 and the cam slipper 13. 
Thus, when the engine operates in a low-speed range, a relatively large 
amount of lubricating oil is supplied between the low-speed cams 3 and the 
cam slippers 11, 12 which are subjected to a relatively large load during 
sliding movement. When the engine operates in a high-speed range, a 
relatively large amount of lubricating oil is supplied between the high 
speed cam 5 and the cam slipper 13 which are subjected to a relatively 
large load during sliding movement. Consequently, the necessary amount of 
lubricating oil to be supplied to the above sliding surfaces can be 
minimized dependent on the operating conditions of the engine. Therefore, 
the pump which is required to feed the lubricating oil can be smaller in 
size and the power expended for circulating the oil can be lowered. Such 
lubricating oil flow control can be performed by the selective coupling 
mechanism 10 without providing any special control device. 
While the present invention has been described as being applied to intake 
valves, the invention is also applicable to a valve operating mechanism 
for exhaust valves. Further, although the low-speed cams 3 have been 
described as each having a cam lobe 3a of a profile to lift the respective 
valves 1a, and 1b, it is also possible to provide one cam 3 with only a 
base circle 3b so that it does not cause lifting of the associated valve 
during low speed operation or even provide one cam 3 with a slightly 
different cam lobe 3a than the other cam 3 for different operation of the 
two valves at low-speed. 
With the present invention, as described above, with respect to the first 
embodiment, a switching pin is arranged to control the rate of flow of oil 
in an oil passage defined in at least one o the cam followers in response 
to movement of the switching pin between cam follower connecting and 
disconnecting position. Therefore, the rate of flow of oil passage can be 
controlled in response to movement of the switching pin of the selective 
coupling mechanism. No special control device for effecting such oil flow 
control is required. Therefore the number of parts and the cost of 
manufacture are reduced. 
Referring now to the second embodiment of the present invention shown in 
FIGS. 6-10, those elements which are substantially the same as the first 
embodiment will be numbered the same and may not be described again in 
detail. For example, the cams rotate to pivot the rocker arms and actuate 
the valves in the same manner and the coupling mechanism 10 functions in 
the same manner to connect or disconnect the rocker arms 7, 8 and 9. As 
shown in FIGS. 6 and 8, for purposes of this embodiment, one of the low 
speed cams 3 is depicted as a base-circle raised portion without a cam 
lobe whereas the other low-speed cam 4 has a cam lobe 4a suitable for 
low-speed engine operation. The first rocker arm 7 has on its upper 
surface a cam slipper 11 held in slidable contact with the low-speed cam 
4. The second rocker arm 8 has on its upper surface a cam slipper 12 held 
in slidable contact with the raised portion 3. The third rocker arm 9 has 
on its upper surface a cam slipper 13 held in slidable contact with the 
high-speed cam 5. 
Flanges 17 are attached to the upper ends of the intake valves 1a, 1b. The 
intake valves 1a, 1b are normally urged in a closing direction, i.e., 
upwardly, by valve springs S disclosed between the flanges 14, 15 and the 
engine body E. Hydraulic lash adjusters T1, T2 having discharge holes H 
defined in the upper eends thereof are disposed in the distal ends of the 
first and second rocker arms 7, 8 respectively. The first and second 
rocker arms 7, 8 are held against the intake valves 1a, 1b through the 
respective hydraulic lash adjusters T1, T2. 
As described with respect to the first embodiment, the coupling mechanism 
10 functions to connect the rocker arms 8, 9 for high speed operation and 
disconnect the rocker arms for low-speed operation. With no high oil 
pressure supplied to the hydraulic chamber 29, for low-speed operation the 
switching pins 23 through 25 are in the position where the rocker arms are 
disconnected under the bias of the return spring 26. In this position, the 
abutting surfaces of the first and second switching pins 23, 24 lie 
between the second and third rocker arms 8, 9, and the abutting surfaces 
of the second and third switching pins 24,25 lie between the third and 
first rocker arms 9, 7, with the rocker arms 7 through 9 being 
disconnected from each other. When high oil pressure is supplied to the 
hydraulic chamber 29 for high-speed operation of the engine, the switching 
pins 23 through 25 are moved in a direction away from the hydraulic 
chamber 29 against the force of the return spring 26 until the first 
switching pin 23 in slidably inserted into the second guide hole 33, and 
the second switching pin 24 is slidably inserted into the third guide hole 
34 for thereby connecting the rocker arms 7 through 9. 
The third switching pin 25 has an annular groove 40 defined in its outer 
peripheral surface. The inner peripheral surface of the first rocker arm 7 
which defines the third guide hole 34 has an annular recess 41 defined 
therein. The annular recess 41 is held in registry with the annular groove 
40 when the third switching pin 25 is in the position to disconnect the 
rocker arms. The widths of the annular groove 40 and the annular recess 41 
along the axis of the third switching pin 25 are selected such that when 
the third switching pin 25 is moved from the rocker arm disconnecting 
position to the rocker arm connecting position, the annular groove 40 and 
the annular recess 41 are positionally displaced from each other. The 
first rocker arm 7 has an oil passage 42a defined therein with one end 
communicating with the hydraulic lash adjuster T1 and the other end 
communicating with the annular recess 41 and another oil passage 43 with 
one end communicating with the annular recess 41 and the other end 
communicating, at all times, with the oil pressure supply passage 31 
through a communication hole 44 defined in the side wall of the rocker 
shaft 6. Therefore, the oil passageway formed by the oil passages 42, 43 
is open in the rocker arm disconnecting position but is restricted when 
the third switching pin 25 is moved into the rocker arm connecting 
position. 
The first switching pin 23 has an annular groove 45 defined in its outer 
peripheral surface. The inner peripheral surface of the second rocker arm 
8 which defines the first guide hole 27 has an annular recess 46a, defined 
therein. The annular recess 46a is held in registry with the annular 
groove 45 when the first switching pin 23 is in the position to disconnect 
the rocker arms. The widths of the annular groove 45 and the annular 
recess 46a along the axis of the first switching pin 23 are selected such 
that when the first switching pin 23 is moved from the rocker arm 
disconnecting position to the rocker arm connecting position, the annular 
groove 45 and the annular recess 46a are positionally displaced from each 
other. The second rocker arm 8 has an oil passage 47a defined therein with 
one end communicating with the hydraulic lash adjuster T2 and the other 
end communicating with the annular recess 46a, and another oil passage 48 
with one end communicating with the annular recess 46a and the other end 
communicating with the communication hole 30. Therefore, the oil 
passageway formed by the oil passages 47a, 48 is open in the rocker arm 
disconnecting position but restricted when the first switching pin 23 is 
moved into the rocker arm connecting position. 
Operation of the valve operating device is as follows. During low-speed 
operation of the engine, the hydraulic chamber 29 is supplied with a 
relatively low oil pressure, and the switching pins 23 through 25 are 
positioned in the maximum stroke toward the hydraulic chamber 29, i.e., 
into the rocker arm disconnecting position, under the force of the return 
spring 26. In this position, the abutting surfaces of the first and second 
switching pins 23, 24 lie between the second and third rocker arms 8, 9, 
and the abutting surfaces of the second and third switching pins 24, 25 
lie between the third and first rocker arms 9, 7. Therefore, the rocker 
arms 7 through 9 are angularly displaceable with respect to each other. 
While the rocker arms 7 through 9 are thus disconnected, the first rocker 
arm 7 is angularly moved in sliding contact with the low-speed cam 4 in 
response to rotation of the camshaft 2, whereas the second rocker arm 8 is 
held at rest in sliding contact with the circular raised portion 8. 
Therefore, the intake valve 1a is opened and closed at the timing and lift 
according to the profile of the low-speed cam 4, and the other intake 
valve 1b remains closed. At this time, the third rocker arm 9 is angularly 
moved in sliding contact with the high-speed cam 5, but such angular 
movement does not affect operation of the first and second rocker arms 7, 
8 in any way. 
In the rocker arm disconnecting position, the annular groove 40 nd the 
annular recess 41, and the annular groove 45 and the annular recess 46a 
are registered with each other and the relatively low oil pressure from 
the oil pressure supply passage 31 is supplied via the oil passages 42a, 
43, and 47a, 48 to the hydraulic lash adjusters T1, T2 without being 
restricted. 
During high-speed operation of the engine, a relatively high oil pressure 
is supplied to the hydraulic chamber 29. As shown in FIG. 5, the switching 
pins 23 through 25 are moved into a position to connect the rocker arms 
against the spring bias of the return spring 26 for thereby inserting the 
first switching pin 23 slidably into the second guide hole 33 and 
inserting the second switching pin 24 slidably into the third guide hole 
34. The rocker arms 7 through 9 are thus interconnected. At this time, 
since the third rocker arm 9 slidingly contacting the high-speed cam 5 
swings to the maximum extent, the first and second rocker arms 7, 8 swing 
in unison with the third rocker arm 9, and hence the intake valves 1a, 1b 
are opened and closed at the timing and lift according to the profile of 
the high-speed cam 5. 
When the selective coupling mechanism 10 is thus operated to connect the 
rocker arms, the oil passageways between the oil passages 42a, 43 and the 
oil passages 47a, 48 are restricted by the first and third switching pins 
23, 25. Oil is discharged from the discharge holes H of the hydraulic lash 
adjusters T1, T2. Therefore, under the condition in which the flowing 
amount of oil discharge from the discharge holes H and the flowing amount 
of oil-restricted by the switching pins 23, 25 are balanced, the high oil 
pressure from the oil pressure supply passage 31 does not directly act on 
the hydraulic lash adjusters T1, T2, but a relatively low oil pressure is 
imposed on the hydraulic lash adjusters T1, T2. Accordingly, the hydraulic 
lash adjusters T1, T2 are presented from being operated undesirably in 
error under high oil pressure which would otherwise be applied. 
With the present invention, as described above, with respect to this second 
embodiment, the cam followers associated with the hydraulic lash adjusters 
have oil passages joining the oil pressure supply passage and th hydraulic 
lash adjusters, and the switching pins of the selective coupling mechanism 
are disposed across the oil passages in the cam followers. The switching 
pins can restrict the oil passages when the switching pins are moved from 
the cam follower connecting position. Therefore, when the selective 
coupling mechanism is operated to connect the cam followers under high oil 
pressure supplied to the oil pressure supply passage, the oil pressure to 
be supplied to the hydraulic lash adjusters is restricted to prevent high 
oil pressure from acting on the hydraulic lash adjusters. Consequently, 
the hydraulic lash adjusters are prevented from undesirable abnormal 
operation.