Variable valve timing rocker arm arrangement for internal combustion engine

A main rocker arm which is pivotally mounted on a rocker shaft has one or more sub-rocker arms pivotally mounted thereon. The main rocker arm is arranged to synchronously open and close two poppet valves. Each of the sub-rocker arms can be selectively locked to the main one by way of hydraulically operated plunger arrangements. The main rocker arm is provided with a roller type cam follower which follows a low speed cam. The sub-rocker arms are provided with followers which engage high or very high speed cams. Lost motion springs which maintain the sub-rocker arms in contact with the cams are mounted on the main rocker arm.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a variable valve timing 
arrangement for an internal combustion engine and more specifically to a 
rocker arm construction for such an arrangement. 
2. Description of the Prior Art 
JP-A-63-167016 and JP-A-63-57805 disclosed rocker arm arrangements which 
include a first rocker arm which is arranged to cooperate with a low speed 
cam and a second rocker arm which cooperates with a high speed cam. The 
two rocker arms pivotally mounted on a common rocker arm shaft. 
A hydraulically operated connection device which enables the first and 
second rocker arms to be selectively locked together, comprises a set of 
plunger bores which are formed in the rocker arms in a manner to be 
parallel with and at a predetermined distance from the axis of the shaft 
about which the arms are commonly pivotal. By applying a hydraulic 
pressure to the end or ends of the plungers reciprocally disposed in the 
bores, the plungers can be induced to move axially within their bores and 
induce the situation wherein two of the plungers will partially enter an 
adjacent bore and lock the two arms together. 
However, this arrangement has suffered from the drawbacks that as the 
rocker arms are pivotally mounted on a rocker arm shaft minor variations 
in the rocker arm dimensions lead to variations in the opening and closing 
timing of the engine valves; and in that the rocker arms become relatively 
large and exhibit large moments. 
In addition to this, seats for the lost motion springs which are 
operatively connected with the high speed rocker arms must be provided on 
the cylinder head. This of course increases the complexity of forming and 
arranging the upper surface of the cylinder head. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a rocker arm 
arrangement which enables the construction of the cylinder head to be 
simplified and the assembly of the valve train on the cylinder head to be 
facilitated. 
In brief, the above objects are achieved by an arrangement wherein a main 
rocker arm which is pivotally mounted on a rocker shaft has one or more 
sub-rocker arms pivotally mounted thereon. The main rocker arm is arranged 
to synchronously open and close two poppet valves. Each of the sub-rocker 
arms can be selectively locked to the main one by way of hydraulically 
operated plunger arrangements. The main rocker arm is provided with a 
roller type cam follower which follows a low speed cam. The sub-rocker 
arms are provided with followers which engage high or very high speed 
cams. Lost motion springs which maintain the sub-rocker arms in contact 
with the cams are mounted on the main rocker arm. 
More specifically, a first aspect of the present invention comes in an 
internal combustion engine having a cylinder head and a poppet valve which 
is associated with the cylinder head and a rocker shaft and which 
features: a first rocker arm, the first rocker arm being pivotally mounted 
on the rocker shaft, arranged to engage a stem of the poppet valve and to 
engage a first cam having a profile suited for low speed engine operation; 
a second rocker arm, the second rocker arm being pivotally mounted on the 
first rocker arm arranged to engage a second cam having a profile suited 
for high speed engine operation; hydraulically operated engagement means 
for selectively connecting the first and second rocker arms in a manner 
wherein relative movement therebetween is prevented; and a lost motion 
spring mounted on the first rocker arm and arranged to engage the second 
rocker arm in a manner which biases the second rocker arm against the 
second cam. 
A second aspect of the present invention comes in a valve train for an 
internal combustion engine which features: a first rocker arm, the first 
rocker arm being motivated by a first cam having a profile suited for low 
speed engine operation, the first rocker arm being pivotally mounted on a 
rocker shaft; a second rocker arm, the second rocker arm being arranged to 
be motivated by a second cam having a profile suited for high speed engine 
operation, the second rocker shaft being pivotally mounted on the first 
rocker arm; a third rocker arm, the second rocker arm being arranged to be 
motivated by a third cam having a profile suited for high speed engine 
operation, the third rocker shaft being pivotally mounted on the first 
rocker arm; a first hydraulically operated interlocking device which 
selectively interconnects the first and second rocker arms in a manner 
wherein relative movement therebetween is prevented; a second 
hydraulically operated interlocking device which selectively interconnects 
the first and third rocker arms in a manner wherein relative movement 
therebetween is prevented; a first lost motion spring mounted on the first 
rocker arm and arranged to engage the second rocker arm in a manner which 
biases the second rocker arm against the second cam; and a second lost 
motion spring mounted on the first rocker arm and arranged to engage the 
third rocker arm in a manner which biases the third rocker arm against the 
third cam.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1-6 show a first embodiment of the present invention. This embodiment 
takes the form of a rocker arm which is arranged to synchronously open and 
close two poppet valve 9. These valves 9 may be either inlet or exhaust 
valves. 
A main rocker arm 1 is arranged so that one end there of engages both of 
the valves while the other is pivotally supported on the cylinder head by 
way of main rocker shaft 3. The ends of the main rocker arm which engages 
the valves are provided with adjust screws and locknuts 11. A roller 14 is 
rotatably mounted on the main rocker arm 1 by way of needle bearings 12. 
This roller is arranged to act as a follower which engages a low speed cam 
21 (viz., a cam which is configured for low speed engine operation). 
A will be appreciated from the plan view of FIG. 1 the main rocker arm 1 
has an essentially rectangular shape. A sub-rocker arm 2 is pivotally 
supported on the main rocker arm 1 by way of a sub-rocker arm shaft 16. 
The shaft 16 is received in a bore 17 formed in the sub-rocker arm 2 and a 
coaxial bore 18 formed in the main rocker arm 1. 
The sub-rocker arm 2 does not directly engage the valves 9 and is formed 
with a convexly shaped cam follower portion 23 which is arranged to engage 
a high speed cam 22. 
A lost motion spring 25 is received in a blind bore or recess 26 formed in 
the main rocker arm 1. In this embodiment the lost motion spring 25 is a 
coil spring. The lower end of the spring engages the blind end wall of the 
bore 26 while a retainer 27, which is reciprocatively disposed in the 
upper end of the bore 26, encloses the upper end of the same. A follower 
28 is formed on the underside of the sub-rocker arm 2 and arranged to 
engage the top of the retainer 27. 
An interlocking arrangement for selectively interconnecting the main and 
sub-rocker arms 1, 2 comprises a structure of the nature shown in FIGS. 4 
and 5. As shown, this structure includes a plunger 31 which is 
reciprocatively received in a though bore 32 formed in the sub-rocker arm 
2, and plungers 33, 34 which are respectively received in bores 35, 36 
formed in the main rocker arm 1. The plunger 33 defines a variable volume 
hydraulic fluid chamber 37 in the bore 35. On the other hand, a return 
spring 38 is disposed in the bore 36 between the plunger 34 and a plug 39 
in which an air vent bore 40 is formed. 
When the pressure prevailing in the hydraulic chamber 37 is below a level 
at which the bias of the return spring 38 is overcome, the plungers 31, 33 
and 34 assume the positions shown in FIG. 4. As will be appreciated, the 
plunger 33 and the bore are dimensioned so that when the hydraulic 
pressure is below the above mentioned level, the end face which engages 
one of the end faces of the plunger 31, lies flush with the wall surface 
of the main rocker arm 1 in which the bore 33 is formed. The plunger 31 is 
dimensioned so that under these conditions its end faces lie flush with 
the side walls of the sub-rocker arm 2. This of course maintains the 
plunger 34 in a state wherein its end face lies flush with the wall 
surface of the main rocker arm in which the bore 36 is formed. 
Under these conditions the sub-rocker arm 2 is rendered pivotal with 
respect to the main rocker arm 1 and thus can be driven down against the 
bias of the lost motion spring 25 under the influence of the high speed 
cam 22 engaging the cam follower 23. 
On the other hand, when hydraulic pressure is supplied into the hydraulic 
chamber 37 and produces a bias which overcomes the force of the return 
spring 38, the plungers 31, 33 and 34 move to the positions illustrated in 
FIG. 5. As will be appreciated this shift taken place when the cam 
followers 14, 23 engage the base circle portions of the low and high speed 
cams 21, 22 respectively. This shifting of the plungers locks the two 
rocker arms together. In this state the movement of the main rocker arm 1 
is determined by the engagement between the high speed cam 22 and the 
follower 23 formed on the sub-rocker arm. 
A hydraulic passage structure generally denoted by the numeral 41 in FIG. 1 
provides fluid communication between the hydraulic chamber 37 and a 
non-illustrated control source. As shown, this passage structure 
comprises: a passage 43 formed in the main rocker arm which leads from one 
end of the bore in which the hydraulic chamber 37 is defined to a 
horizontally large diameter bore 42 in which the rocker shaft 3 is 
disposed; an axial bore which defines an oil gallery 44 in the rocker 
shaft 3; an annular recess formed about the rocker shaft 3; and a radial 
bore 46 which provides fluid communication between the oil gallery 44 and 
the recess 47. Passage 43 communicates with the recess 47. A plug 45 
closes the drill hole produced when the passage 43 is formed in the main 
rocker arm. 
FIG. 6 shows the structure of the main rocker arm. In this figure, 48 
denote the threaded bores in which the adjust screws 10 are received, 49 
denotes the recess in which the roller 14 is disposed and 50 denotes the 
opening in which the sub-rocker arm 2 is received. 
The above mentioned control source comprises a switching valve (not shown) 
which is fluidly interposed between the chamber 37 and an oil pump. The 
valve is controlled by a control unit which receives data inputs 
indicative of engine speed, coolant temperature, lubricant oil 
temperature, supercharge pressure, engine throttle valve position. This 
control unit determines when it is necessary to switch between high and 
low cam lifting. 
The low and high speed cams 21, 22 are both formed integrally on a cam 
shaft and have profiles which are designed to produce the appropriate 
amount of lift and timing for low and high engine speed operation, 
respectively. Viz., the amount of lift and/or the length of time the valve 
is opened by the high speed cam 22 is greater than that induced the low 
speed one. 
OPERATION 
During low speed engine operation, the pressure in the hydraulic chamber 37 
is reduced to a level whereat the plungers 31, 33 and 34 assume the 
positions illustrated in FIG. 4. As a result the sub-rocker arm 3 is left 
unlocked from the main one 1 and is permitted to pivot relative to the 
main rocker arm 1 against the bias of the lost motion spring 25. The 
movement of the main rocker arm 1 and the lifting of the valves 9 is 
therefore determined by the low speed cam 21. 
When the engine operation changes to a high speed mode, the pressure which 
is supplied to the hydraulic chamber 37 is increased to a level whereat 
return spring 38 is overcome and the plungers are induced to assume the 
positions shown in FIG. 5. This locks the main and sub-rocker arm 1, 2 in 
a manner wherein the larger pivotal motion of the sub-rocker arm 2 is 
superimposed on the main one 1 and the valve 9 are subject to lifting 
control by the high speed cam 22. 
When the engine speed lowers to a low speed zone, the pressure in the 
hydraulic chamber 37 is reduced and the return spring 37 returns the three 
plungers to the positions shown in FIG. 4. This of course unlocks the main 
and sub-rocker arms and permits the valve lifting to be controlled by low 
speed cam 21. 
With the above described embodiment, the engine performance characteristics 
shown in FIG. 7 are obtained. That is to say, by switching between the 
high and low speed cams it is possible to maintain the level of torque 
produced by the engine at a much more uniform level than is possible using 
one one cam. 
As the sub-rocker arm 2 (high speed rocker arm) is pivotally supported on 
the main rocker arm 1 (low speed rocker arm) per se by way of the 
sub-rocker shaft 16 it is possible to greatly reduce the size and mass of 
the same. As a result, the mass of the sub-rocker arm is lower than that 
of the prior art discussed in the opening paragraphs of the instant 
disclosure. This enables the mass of the valve train to be reduced. 
Further, during high speed modes of operation when the two rocker arms are 
locked together so as to move as a single unit, as the mass of each unit 
is reduced as compared with said prior art the valve following 
characteristics are improved. 
On the other hand, during low speed modes of engine operation even though 
the mass of the sub-rocker arm 2 increases the oscillating mass of the 
main rocker arm 1, as the speed at which the valves are opened and closed 
is relatively low there is not detrimental effect on the valve following 
characteristics. 
In addition to the above, as the sub-rocker is relatively small and light, 
the lost motion spring can be relatively small and weak. This reduces the 
amount of friction which is produced between the high speed cam 22 and the 
follower 23 and thus reduces engine fuel consumption. 
Further, as the sub-rocker arm 2 is pivotally mounted on the main rocker 
arm 1 by way of sub-rocker shaft 16, it is possible to assembly the both 
to form a unit which can be then mounted on the rocker shaft. The 
precision with which the roller 14 and follower 23 are mounted on the 
respective rocker arms can be checked before the unit is actually mounted 
on the cylinder head. This reduces the amount of work which must be done 
in order to ensure uniform lift characteristics from cylinder to cylinder. 
That is to say, with the above mentioned prior art, these factors cannot 
be checked until both rocker arms are mounted on the cylinder head. 
The fact that the lost motion spring 25 does not require a seat to be 
formed on the cylinder head per se, reduces the amount of variation during 
assembly. 
In addition, as the plungers 31, 33 and 34 and the return spring can be 
assembled as a unit, the amount of time required for assembling valve 
train on the cylinder head is reduced. 
SECOND EMBODIMENT 
FIGS. 8 and 9 show a second embodiment of the present invention. In this 
embodiment three cams are provided on the cam shaft. A first low speed cam 
51, a second high speed cam 52 and a third very high speed cam 53. The 
rocker arm arrangement comprises a main rocker arm 1 on which a first cam 
follower (roller) 14 is mounted; and first and second sub-rocker arms 54, 
55 which are arranged to cooperate with the second and third cams 52, 53, 
respectively. 
The sub-rocker arms 54, 55 are pivotally mounted on the main rocker arm 1 
by way of a common sub-rocker shaft 56. 
Plungers 57, 58 and 59 and a return spring 60 are arranged to provide 
selective interlocking between the main and first sub-rocker arms 1, 54. 
The movement of the plungers is controlled by hydraulic pressure which is 
supplied through a control passage 61. 
Plungers 62, 63 and 64 and a return spring 65 are arranged to provide 
selective interlocking between the main and second sub-rocker arms 1, 55. 
The movement of these plungers is controlled by hydraulic pressure which 
is supplied through a control passage 66. 
The second sub-rocker arm 55 cooperates with a lost motion spring 
arrangement comprised of a spring 67, a retainer 68, and a stopper 69. As 
will be appreciated from FIG. 9, the bore in which the spring and the 
retainer are disposed is not blind and the stopper 69 is provided close 
one end of said bore. The first rocker arm is arranged to cooperate with a 
similar non-illustrated lost motion spring arrangement. 
The main rocker arm 1 is provided with hydraulic lash adjusters 71 which 
engage the tops of the valves 9. These devices are supplied with hydraulic 
fluid under pressure by way of passages 72, 74 as shown in FIG. 10. In 
this latter mentioned figure, numerals 75 and 76 generally denote the 
bores in which the plungers 62, 63 and 74 and 57, 58 and 59 are disposed. 
It should be further noted that in FIG. 10 the passage 72 is shown as 
passing below the bores 75 and 76; that 49 denotes the opening in which 
the roller 14 is disposed; 77 is the opening in which the first sub-rocker 
arm 54 is disposed; 78 is the bore in which the first lost motion spring 
arrangement is received; 79 is the opening in which the second rocker arm 
55 is received; and 80 is the bore in which the second lost motion spring 
arrangement is disposed. 
Passages 61, 66 and 72 are arranged to communicate with oil galleries 61', 
66' and 72' which are formed in the rocker shaft 3. 
This arrangement is such that the cams 51, 52 and 53 are used during low, 
high and very high engine speed operations, respectively. By appropriately 
configuring these cams, it is possible to achieve the torque output 
characteristics shown in FIG. 11. 
Further, by configuring the first cam 51 to provide a small low lift over a 
small crankangle range, it is possible to improve combustion 
characteristics during idling; and by configuring the cam 52 to provide 
appropriate lift for low speed/high load and cam 53 to provide the 
appropriate lift for high speed high load, the power output 
characteristics shown in FIG. 12 are rendered possible. 
THIRD EMBODIMENT 
FIGS. 13 and 14 show a third embodiment of the present invention. This 
embodiment is essentially similar to the second one and differs in that 
four cams and three sub-rocker arms are utilized. In this embodiment, cams 
81, 82, 83 and 84 are provided on the cam shaft. The first cam 81 
cooperates with the roller 14 of the main rocker arm 1, while cams 82-84 
cooperate with the three sub-rocker arms 85, 86 and 87. Cam 81 is 
configured for low speed engine operation while cams 82-84 are configured 
from sequentially increasing high speed operational modes. 
The three sub-rocker arms are respectively interlocked with the main rocker 
arm 1 by way of plunger sets 89, 90 and 91. Each of these are offset with 
respect to one another in essentially the same manner as the plunger sets 
of the second embodiment are. 
The plunger sets 89, 90 and 91 are supplied with control pressures via 
passage 92, 93 and 94 (formed in the rocker shaft). Passage 72' supplies 
hydraulic pressure to the hydraulic lash adjusters 61. The three 
sub-rocker arms cooperate with lost motion spring arrangements. In FIG. 14 
the lost motion spring arrangement which cooperates with sub-rocker arm 87 
is shown. This arrangement comprises a spring 95, a retainer 96 and a 
stopper 97. 
The engine torque output characteristics possible with the instant 
embodiment are shown in FIG. 15.