Valve operating device for internal combustion engine

A valve operating device for an internal combustion engine, including a plurality of cams or a camshaft having different cam profiles corresponding to operating conditions of the engine for opening and closing the intake valves according to the operating conditions of the engine. The high-speed cam has a cam lobe which projects from a base-circle portion of the cam by a distance smaller than the distance by which the cam lobe of a low-speed cam projects from the base-circle portion. The cam lobe of the high-speed cam also subtends a larger angle on the base circle of the camshaft than the cam lobe of the low-speed cam.

The present invention relates to a valve operating device for an internal 
combustion engine, including a camshaft with a plurality of cams having 
cam profiles for opening and closing intake valves according to the 
operating conditions of the engine. 
In a conventional valve operating device, as disclosed in Japanese 
Laid-Open Patent Publication No. 59-85408, for example, the degree to 
which an intake valve is lifted and the time period in which it is open 
during high-speed operation of the engine are generally larger than those 
during low-speed operation of the engine. 
In the high-speed operation range of the internal combustion engine, it is 
preferable for the intake valve to be opened earlier and closed later than 
in the low-speed operation range in order to supply a sufficient amount of 
air into a combustion chamber. This demand cannot however be met by the 
aforesaid conventional valve operating device. 
According to the present invention, the cam lobe of a high-speed cam 
corresponding to high-speed operation of the engine projects from a 
base-circle portion coaxial with the axis of rotation thereof by a 
distance smaller than the distance by which the cam lobe of a low-speed 
cam corresponding to low-speed operation of the engine projects from the 
base-circle portion, and the cam lobe of the high-speed cam subtends a 
larger angle at the base-circle portion than the cam lobe of the low-speed 
cam does. 
With the above arrangements of this invention, in the high-speed operation 
range of the engine, the intake valve is opened earlier and closed later 
than in the low-speed operation range of the engine for supplying a 
sufficient amount of air. The degree to which the intake valve is lifted 
can be reduced thereby preventing the intake valve from jumping or 
bouncing due to its inertia during high-speed operation. In the low-speed 
operation range, the degree of lifting of the intake valve can be made 
larger than that in the high-speed operation range to supply a required 
amount of air.

The first embodiment of the present invention will hereinafter be described 
with reference to FIGS. 1 through 5 of the drawings which illustrate the 
valve operating mechanism for a single intake valve 1 for one cylinder of 
an engine but it will be understood that there may be multiple cylinders 
in the engine and multiple intake valves for each cylinder. In FIGS. 1, 2 
and 3, an intake valve 1 disposed in an engine body E is opened and closed 
by valve operating mechanism including a low-speed cam 3, a raised portion 
4, and a 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 with 
respect to the speed of rotation of the engine, by first, second and third 
rocker arms 7, 8, 9, respectively, pivotally supported on a rocker shaft 6 
extending parallel to the camshaft 2, and by selective coupling mechanisms 
10a, 10b disposed between the first and second rocker arms 7, 8 and the 
second and third rocker arms 8, 9, respectively. 
The camshaft 2 is rotatably disposed above the engine body E. The low-speed 
cam 3, the raised portion 4, and the high-speed cam 5 are axially 
successively arranged in adjacent relation and integrally formed with the 
camshaft 2. The low-speed cam 3 has a cam profile corresponding to 
low-speed operation of the engine and includes a base circle portion 3a 
coaxial with the camshaft 2 and a cam lobe 3b projecting radially 
outwardly from the base circle portion 3a. The raised portion 4 is of a 
circular shape coaxial with the camshaft 2 and of the substantially the 
same diameter as base circle portion 3a. The high-speed cam 5 has a cam 
profile corresponding to a high-speed operation of the engine and includes 
a base circle portion 5a coaxial with the camshaft 2 and a cam lobe 5b 
projecting radially outwardly from the base circle portion 5a. The cam 
lobe 5b of the high-speed cam 5 subtends a larger angle .alpha.1 from the 
center of the camshaft 2 along the base circle portion 5a than the cam 
lobe 3b of the low-speed cam 3 which subtends an angle .alpha.2 from the 
center of the camshaft 2 along the circumference of the base circle 
portion 3a. The distance d1 by which the cam lobe 5b of the high-speed cam 
5 projects from the base circle portion 5a is smaller than the distance d2 
by which the cam lobe 3b of the low-speed cam 3 projects from the base 
circle portion 3a. 
The rocker shaft 6 is fixedly positioned below the camshaft 2. 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 raised portion 
4, and the third rocker arm 9 has on its upper surface a cam slipper 13 
held in slidable contact with the high-speed cam 5. The rocker arms 7, 8 
and 9 are pivotally supported on the rocker shaft 6 in axially adjacent 
relation. 
The intake valve 1 is operatively associated with the second rocker arm 8. 
A flange 14 is attached to the upper end of the intake valve 1. The intake 
valve 1 is normally urged in a closing direction, i.e., upwardly, by a 
valve spring 15 disposed between the flange 14 and the engine body E. A 
tappet screw 16 is adjustably threaded in the distal end of the second 
rocker arm 8 in abutting engagement with the upper end of the intake valve 
1 (a gap is shown for clarity of illustration only). 
The first rocker arm 7 is normally urged resiliently in a direction to 
cause the cam slipper 11 to slidably contact the low-speed cam 3 by 
resilient urging means 17 disposed between the first rocker arm 7 and the 
engine body E. The resilient urging means 17 comprises a cylindrical 
bottomed lifter 18 with its closed end held against the lower surface of 
the first rocker arm 7, and a lifter spring 19 disposed between the lifter 
18 and the engine body E. The lifter 18 is slidably fitted in a bottomed 
hole 20 defined in the engine body E. 
Resilient urging means (not shown) similar to the resilient urging means 17 
is also disposed between the third rocker arm 9 and the engine body E for 
normally urging the third rocker arm 9 upwardly to hold the cam slipper 13 
slidably against the high-speed cam 5 at all times. 
As shown in FIG. 4, the selective coupling mechanism 10a comprises a piston 
22a movable between a position in which the first and second rocker arms 
7, 8 are connected and a position in which they are disconnected, a 
stopper 23a for limiting the movement of the piston 22a, and a return 
spring 24a for urging the piston 22a in a direction to disconnect the 
rocker arms 7, 8. 
The second rocker arm 8 has a first bottomed guide hole 25a opening toward 
the first rocker arm 7 and parallel to the rocker shaft 6, with a 
smaller-diameter hole 27a being defined at the closed end of the first 
guide hole 25a with a step 26a therebetween. The piston 22a is slidably 
fitted in the first guide hole 25a, with a hydraulic chamber 28a being 
defined between the piston 22a and the closed end of the smaller-diameter 
hole 27a. 
The first rocker arm 7 has a second bottomed guide hole 29a opening toward 
the second rocker arm 8 and parallel to the rocker shaft 6 for 
registration with the first guide hole 25a. The disc-shaped stopper 23a is 
slidably fitted in the second guide hole 29a. A smaller-diameter hole 31a 
is defined at the closed end of the second guide hole 29a with a limiting 
step 30a therebetween. An insertion hole 32a is also defined at the closed 
end of the smaller-diameter hole 31a coaxially therewith. A guide rod 33a 
coaxial and integral with the stopper 23a extends through the insertion 
hole 32a. The return coil spring 24a is disposed between the stopper 23a 
and the closed end of the smaller-diameter hole 31a around the guide rod 
33a. 
The piston 22a has an axial length such that when one end thereof abuts 
against the step 26a, the other end thereof is positioned between the 
first and second rocker arms 7, 8, and when the piston 22a is urged by 
hydraulic pressure to enter the second guide hole 29a to the extent that 
the stopper 23a abuts against the limiting step 30a, said one end of the 
piston 22a remains positioned in the first guide hole 25a. 
The rocker shaft 6 has an interior hollow space divided into two oil 
passages 34a, 34b by an axially extending partition 37. The oil passages 
34a, 34b are selectively supplied with hydraulic pressure from a hydraulic 
pressure supply source (not shown). 
The rocker shaft 6 has defined therein a communication hole 35a in 
communication with the oil passage 34a and a communication hole 35b in 
communication with the oil passage 34b. The communication holes 35a, 35b 
are axially spaced from each other. The second rocker arm 8 has defined 
therein a communication passage 36a and a communication passage 36b. The 
communication passage 36a and the communication hole 35a are held in 
communication with each other at all times, irrespective of how the second 
rocker arm 8 may be angularly moved, by a circumferential groove 
(unnumbered) and the communication passage 36b and the communication hole 
35b are held in communication with each other at all times, irrespective 
of how the second rocker arm 8 may be angularly moved, by a separate 
circumferential groove (unnumbered). The communication passage 36a 
communicates with the hydraulic chamber 28a. 
The selective coupling mechanism 10b disposed between the second and third 
rocker arms 8, 9 is basically of the same construction as that of the 
selective coupling mechanism 10a. Those components of the selective 
coupling mechanism 10b which are identical to those of the selective 
coupling mechanism 10a are denoted by identical reference numerals with a 
suffix b, and will not be described in detail. The hydraulic chamber 28b 
of the selective coupling mechanisms 10b communicates with the oil passage 
34b through the communication passage 36b and the communication hole 35b. 
Operation of the above-described embodiment now will be described. During 
low-speed operation of the engine, hydraulic pressure is supplied to the 
oil passage 34a whereas the other oil passage 34b is released of any 
hydraulic pressure. Therefore, the piston 22a of the selective coupling 
mechanism 10a is moved toward the first rocker arm 7 against the 
resiliency of the return spring 24a and into the second guide hole 29a to 
connect the first and second rocker arms 7, 8. In the other selective 
coupling mechanism 10b, the mutually sliding surfaces of the piston 22b 
and the stopper 23b are positioned between the second and third rocker 
arms 8, 9, which are thus disconnected from each other. Therefore, the 
second rocker arm 8 swings to open and close the intake valve 1 at the 
timing and lift according to the profile of the low-speed cam 3, as 
indicated by the solid line L in FIG. 5. 
During high-speed operation of the engine, hydraulic pressure is supplied 
to the oil passage 34b whereas the oil passage 34a is released of any 
hydraulic pressure. In the selective coupling mechanism 10a, the mutually 
sliding surfaces of the piston 22a and the stopper 23a are positioned 
between the first and second rocker arms 7, 8, which are thus disconnected 
from each other. The piston 22b of the selective coupling mechanism 10b is 
moved toward and into guide hole 29b of the third rocker arm 9 against the 
resiliency of the return spring 24b to connect the second and third rocker 
arms 8, 9. Accordingly, the second rocker arm 8 swings to open and close 
the intake valve 1 at the timing and lift according to the profile of the 
high-speed cam 5, as indicated by the dotted line H in FIG. 5. 
Since the angle .alpha.1 subtended at the basic circle of the camshaft 2 by 
the cam lobe 5b of the high-speed cam 5 is larger than the angle .alpha.2 
subtended at the basic circle of the camshaft 2 by the cam lobe 3b of the 
low-speed cam 3, the intake valve 1 is opened earlier during high-speed 
operation than during low-speed operation and is closed later during 
high-speed operation than during low-speed operation. Consequently, during 
high-speed operation, the intake valve 1 remains open for a relatively 
long time, so that a sufficient amount of air can be supplied into the 
combustion chamber. Moreover, since the distance which the intake valve 1 
is lifted during high-speed operation is relatively small, the intake 
valve 1 is prevented from jumping or bouncing due to its inertia upon 
high-speed operation. During low-speed operation, the period of time in 
which the intake valve 1 is open is relatively short. However, since the 
distance which the intake valve 1 is lifted is larger during low-speed 
operation than during high-speed operation, a required amount of air can 
be supplied. 
It is preferable that the cams 3, 5 be dimensioned to substantially 
equalize the areas surrounded by the lift curves H, L for the intake valve 
1. 
FIGS. 6 and 7 show another embodiment of the present invention. Those parts 
which are identical to those of the previous embodiment are denoted by 
identical reference numerals. First, second, and third rocker arms 7, 8', 
9 are pivotally supported on a rocker shaft 6, with a pair of intake 
valves 1a, 1b being operatively associated with the second rocker arm 8'. 
Integrally formed with the camshaft 2 are a low-speed cam 3 held in 
slidable contact with the first rocker arm 7, and a very low-speed cam 3' 
held in slidable contact with the second rocker arm 8', and a high-speed 
cam 5 held in slidable contact with the third rocker arm 9. 
The rocker arms 7, 8', 9 have selective coupling mechanisms capable of 
selecting one of three conditions, namely, a condition in which all of the 
rocker arms 7, 8', 9 are disconnected, a condition in which the first and 
second rocker arms 7, 8' are connected, and a condition in which the 
second and third rocker arms 8', 9 are connected. Thus, the three 
selective operating conditions are (1) a condition in which the intake 
valves 1a, 1b are opened and closed by the very low-speed cam 3', (2) a 
condition in which the intake valves 1a, 1b are opened and closed by the 
low-speed cam 3, and (3) a condition in which the intake valves 1a, 1b are 
opened and closed by the high-speed cam 5. 
The very low-speed cam 3' is of a shape to provide a valve opening profile 
as indicated by the solid line L1 in FIG. 7. The low-speed cam 3 is of a 
shape to provide a valve opening profile as indicated by the dot-and-dash 
line L2 in FIG. 7. The high-speed cam 5 is of a shape to provide a valve 
opening profile as indicated by the dotted line H in FIG. 7. 
In this embodiment of FIGS. 6 and 7, the intake valves 1a, 1b are opened 
earlier and closed later during high-speed operation to supply a 
sufficient amount of air. During low-speed operation in which the 
low-speed cam 3 operates, the distance which the intake valves 1a, 1b are 
lifted is relatively large to supply a required amount of air. In very 
low-speed operation by cam 3', the valve lift and duration are less to 
enhance the air flow rate and turbulence for maintaining a good air-fuel 
mixture. 
The present invention is not limited to the valve operating device in which 
the rocker arms are selectively connected and disconnected by the pistons, 
but also to a valve operating device in which rocker arms are movable 
axially of a camshaft into slidable contact with different cams or any 
other mechanism for selectively operating intake valves by different cam 
profiles. 
With the present invention, as described above, a high-speed cam 
corresponding to high-speed operation of an engine has a cam lobe which 
projects from a base circle portion coaxial with the axis of rotation of 
the high-speed cam by a distance smaller than the distance which the cam 
lobe of a low-speed cam corresponding to low-speed operation of the engine 
projects from the base-circle portion, and the cam lobe of the high-speed 
cam subtends a larger angle on the camshaft than the cam lobe of the 
low-speed cam does. During high-speed operation of the engine, an intake 
valve is opened earlier and closed later than during low-speed operation 
to supply a sufficient amount of air, and the intake valve is prevented 
from jumping or bouncing due to its inertia upon high-speed operation. 
During low-speed operation, the distance which the intake valve is lifted 
is increased to supply a required amount of air.