Apparatus for shifting phase between shafts in internal combustion engine

Disclosed is an apparatus for shifting a phase between shafts in an internal combustion engine. A phase shifting device for shifting a rotational phase of the driven shaft to the drive shaft and an amplifying gear mechanism having a plurality of gears are disposed between the drive shaft and driven shaft. The amplifying gear mechanism amplifies the amount of phase shifting when the phase shifting is made by the phase shifting device and rotates all the gears integrally when no phase shifting is made.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus for shifting the phase 
between shafts (hereinafter referred to as intershaft phase shifting 
apparatus). More specifically, this invention pertains to an intershaft 
phase shifting apparatus for a valve timing control device or the like 
which shifts the rotational phase of a cam shaft to a crank shaft and 
varying the amount of the phase shift in order to control the 
opening/closing timing of intake and exhaust valves in an internal 
combustion engine in accordance with the running state of the engine. 
2. Description of the Related Art 
As a phase shifting apparatus of this type, a phase shifting apparatus (cam 
shaft driving apparatus) using a planetary gear mechanism is disclosed in, 
for example, Japanese Unexamined Utility Model Publication No. 59-156102. 
According to this technique, a cam shaft 61 is divided into an input-side 
shaft 61a for driving a crank shaft 62 and an output-side shaft 61b having 
a cam 63 as shown in FIG. 10. A planetary gear mechanism 64 intervenes 
between these shafts 61a and 61b. In the planetary gear mechanism 64, a 
carrier 65 is attached to the end of the input-side shaft 61a. On the 
carrier 65 are rotatably supported a plurality of planetary gears 66 whose 
outer peripheral portions are engaged with a ring gear 67. A sun gear 68 
is attached to the end of the output-side shaft 61b, and it is engaged 
with the inner peripheral portions of the planetary gears 66. The ring 
gear 67 is rotated by a piston 70 which is thrust forward and backward 
from a cylinder 69. 
According to this apparatus, as the ring gear 67 rotates due to the 
forward/backward movement of the piston 70, the carrier 65 and sun gear 68 
rotate by different angles. This causes the rotational phase of the crank 
shaft 62 to deviate from that of the output-side shaft 61b, thus changing 
the opening/closing timing of the intake and exhaust valves during engine 
running. The amount of a phase shift is varied by an amount corresponding 
to the ratio of the diameter of the sun gear 68 to that of the planetary 
gears 66. 
According to the conventional phase shifting apparatus, however, when no 
phase shift is performed, the piston 70 will not be activated and the ring 
gear 67 stays unmoved. It is therefore necessary to always rotate the 
planetary gears 66 and the sun gear 68. The backlash between those gears 
66, 67 and 68 may cause gearing noise or wear out the gears. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an intershaft 
phase shifting apparatus capable of preventing individual gears from 
producing gearing noise or from wearing out or the like when no phase 
shift between two shafts in an internal combustion engine is performed. 
To achieve this object, an intershaft phase shifting apparatus of this 
invention comprises a drive shaft; a driven shaft; a phase shifting 
mechanism for shifting a rotational phase of the driven shaft to the drive 
shaft between the drive shaft and driven shaft; and an amplifying gear 
mechanism having a plurality of gears, for amplifying an amount of a phase 
shift when the phase shift is made by the phase shifting mechanism and 
rotating all the gears integrally when no phase shift is made.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first preferred embodiment where an intershaft phase shifting apparatus 
according to the present invention is embodied in a valve timing 
controller in an internal combustion engine will now be described 
referring to FIGS. 1 to 5. 
In FIG. 1, the valve timing controller has a timing pulley 6 on the intake 
side, a timing pulley 101 on the exhaust side, and a timing pulley 102 and 
a timing belt 7 on the crank shaft side; these components of the 
controller are coupled to each other by the timing belt 7 to which a 
tensioner 104 applies a tension. This valve timing controller controls the 
timing for opening and closing of an intake valve in accordance with the 
running status of the engine. The valve timing controller therefore is 
designed to shift the rotational phase of a crank shaft 105 to a cam shaft 
1. 
A cylinder 5 is attached to the front end (or the left end) of the cam 
shaft 1 in FIG. 2. A timing pulley 6 is formed around the outer surface of 
the front end of the cylinder 5. An annular wall 3 having a small diameter 
is concentrically provided in the cylinder 5. The cam shaft 1 is fitted in 
the annular wall 3. As a crank shaft 100 rotates, this movement is 
transmitted to the cylinder 5 by the timing belt 7. 
Between the cam shaft 1 and the cylinder 5 lie a phase shifting mechanism 
10 for shifting the rotational phase of the cam shaft 1 to the cylinder 5, 
and a planetary gear mechanism 9 for amplifying the angle of the 
rotational phase. The planetary gear mechanism 9 serves as a differential 
gear mechanism which amplifies the operation of gears. 
The planetary gear mechanism 9 includes a ring gear 11, a sun gear 12, a 
carrier 13 and planetary gears 14. The ring gear 11 is fixed on the inner 
surface of the front end of the timing pulley 6. The sun gear 12 is 
secured at the front end of the cam shaft 1 with a volt 20. At the 
immediately rear end of the sun gear 12, the almost ring-shaped carrier 13 
is placed and held between thrust washers 13' and 13", and is fitted 
rotatable on the outer surface of the cam shaft 1. A cylindrical portion 
15 is placed on the rear portion of the carrier 13, and the outer surface 
of the cylindrical portion 15 touches a bearing 16 on the inner surface of 
the front end of the cylinder 5. The carrier 13 therefore rotates while 
sliding in contact with the cam shaft 1, the thrust washers 13' and 13", 
and the bearing 16. 
Three support shafts 17 are protruded from the front outer surface of the 
carrier 13, and the planetary gears 14 are supported rotatable around the 
respective support shafts 17. Each planetary gear 14 is engaged with the 
ring gear 11 and the sun gear 12 to transmit the rotation of the timing 
pulley 6 to the cam shaft 1. A stopper ring 18 is securely attached to the 
front end of the support shaft 17 to prevent the planetary gear 14 from 
falling from the support shaft 17. 
The phase shifting mechanism 10 will now be explained. An approximately 
cylindrical piston 8 is provided in the space defined by the cylinder 5, 
the annular wall 3 and the carrier 13. Helical splines 8a and 8b which 
extend in the opposite directions are formed respectively on the inner and 
outer surfaces of the front end of the piston 8. The helical splines 8a 
and 8b are respectively engaged with the helical spline 3a formed on the 
outer surface of the annular wall 3 and the helical spline 15a formed on 
the inner surface of the cylindrical portion 15 of the carrier 13. 
Accordingly, the piston 8 is forced to reciprocate while rotating. A 
pressure chamber 19 is defined between the piston 8 and the inner bottom 
of the cylinder 5 so that working fluid may be supplied to the pressure 
chamber 19. More specifically, a fluid path 21 which communicates with the 
pressure chamber 19 is formed in the cam shaft 1 and the cylinder 5. The 
working fluid, after sucked by an oil pump (not shown), is controlled by a 
solenoid-operated hydraulic control valve 22 and is supplied to the 
pressure chamber 19 through the fluid path 21. The pressure of the 
supplied working fluid forces the piston 8 to move forward. 
An engaging ring 23 is fitted in the inner surface of the front end of the 
cylinder 5, and a return spring 24 is placed in the space between the 
engaging ring 23 and the outer surface of the rear end of the piston 8. 
The engaging ring 23 and the return spring 24 always urge the piston 8 
backward. 
When the working fluid is not supplied to the pressure chamber 19 (at the 
advance angle timing), the piston 8 is forced to position at the rear end 
by the return spring 24 as shown in FIG. 1. When the fluid oil is supplied 
to the pressure chamber 19, however, the piston 8 is moved rotating 
forward against the force of the return spring 24. At this time, the 
helical splines 3a, 8a, 8b and 15a shift the rotational phase of the 
cylinder 5 to the carrier 13, both coupled to the piston 8. In association 
with this phase shift, the rotational phase of the cam shaft 1 to the 
crank shaft 105 are also shifted to the delay angle side. 
The opening of the control valve 22 is controlled by an electronic control 
unit (ECU) 25. More specifically, a throttle sensor 26 which detects the 
opening of the throttle valve 22 is connected as an engine load to the 
input side of the ECU 25. Further, a rotational speed sensor 27 is 
connected to the input side of the ECU 25. The sensor 27 detects the 
number of rotations of the engine in the unit time from the rotations of 
the rotor of a distributor. The control valve 22 is connected to the 
output side of the ECU 25. 
First to third regions A, B and C as shown in FIG. 5 are previously stored 
in the ECU 25, indicating the relationship between the engine speed and 
the engine load. The first region A is selected when the engine is running 
at a low or middle speed with a high load, the second region B is selected 
when the engine is running at a low speed with a low load, and the third 
region C is selected when the engine is running at a middle or high speed 
regardless of the load. Based on detection signals from the throttle 
sensor 26 and the rotation speed sensor 27, the ECU 25 determined in which 
one of the first to third regions A to C the current engine status is, and 
outputs a control signal for controlling the opening of the hydraulic 
control valve 22. 
The action and effect of the valve timing controller in this embodiment as 
structured above will now be described. 
When the engine starts running, the rotation of the crank shaft 105 is 
transmitted to the cylinder 5 by the timing belt 7. The ECU 25 receives 
detection signals from the throttle sensor 26 and the rotation speed 
sensor 27 to detect the engine load and the engine running speed. The ECU 
25 then determines which of the regions A to C the current engine state 
belongs to. The ECU 25 sends a control signal to the control valve 22 to 
change the rotational phase of the cam shaft 1 with respect to the crank 
shaft 105 to a rotational phase corresponding to the determined region A, 
B or C. 
FIG. 2 illustrates the valve timing controller when the ECU 25 has judged 
that the engine state is in the region A. In this condition, the valve 22 
is closed and the working fluid is not supplied to the pressure chamber 
19. The piston 8 is therefore forced back by the return spring 24 to stay 
at the rear end of the cylinder 5. 
When the piston 8 stays at the rear end in the cylinder 5 and will not move 
back and forth, the cam shaft 1, the planetary gear mechanism 9, the 
piston 8 and the cylinder 5 rotate integrally. This is because the piston 
8 is coupled respectively to the annular wall 3 and the carrier 13 while 
the planetary gears 14 on the carrier 13 mesh with the ring gear 11 and 
the sun gear 12. A this time, rotational torque which is transmitted to 
the cylinder 5 by the timing belt 7 is to be sent to the cam shaft 1 via 
either of the following two routes: a path leading to the cam shaft 1 
through the helical splines 8a and 8b, and the planetary gear mechanism 9, 
and a path leading to the cam shaft 1 directly through the planetary gear 
mechanism 9 from the ring gear 11 secured to the timing pulley 6. 
If the piston 8 stays at the rear end of the cylinder 5 as described above, 
the timing for closing the intake valve is quickened, and a fluid-air 
mixture fed into an intake cylinder will not easily be returned. This 
causes the air filling efficiency higher to provide a high output. 
FIG. 3 shows the valve timing controller when the ECU 25 has judged that 
the state of the engine is changed from the first region A to the second 
region B. Under these circumstances, the ECU 25 outputs a control signal 
to open the control valve 22. If the opening of the control valve 22 
reaches a predetermined level, the pressure of the working fluid is 
controlled by the control valve 22, and the working fluid is supplied to 
the pressure chamber 19 through the fluid path 21. The pressure of the 
supplied working fluid acts on the rear surface of the piston 8 to push 
the piston 8 forward against the force of the return spring 24. Then, the 
piston 8 is moved forward while rotating by the action of the helical 
splines 3a, 8a, 8b and 15a. The movement of the piston 8 applies twisting 
force to the cylinder 5 and the carrier 13, which rotate separately. The 
piston 8 stops moving forward when contacting the rear surface of the 
carrier 13. 
The amount of the shifted rotational phase is increased by the planetary 
gear mechanism 9. To describe more specifically, the rotational phase of 
the sun gear 12 to the ring gear 11 can be understood from the following 
equation. 
EQU (1+.lambda.)Cn=Rn+.lambda..multidot.Sn (1) 
where .lambda. is the ratio of the diameter of the sun gear 12 to that of 
the ring gear 11, Cn is the number of rotations of the carrier 13, Rn is 
the number of rotations of the ring gear 11, and Sn is the number of 
rotations of the sun gear 12. 
To simplify the explanation, it is assumed that the ring gear 11 is fixed, 
and the rotational force of the crank shaft is received by the carrier 13 
and is output from the sun gear 12, as shown in FIGS. 3 and 4. This 
assumption is made because, with the ring gear 11 fixed so, the phase 
difference between the ring gear 11 and the carrier 13 can be considered 
in terms of the rotation of the carrier 13. 
Because the ring gear 11 is fixed as mentioned above, Rn=0, Substituting 
Rn=0 into the equation (1) yields an equation (2) below. 
EQU {(1+.lambda.)/.lambda.}Cn=Sn (2) 
The sun gear 12 therefore rotates (1+.lambda.)/.lambda. times more than the 
carrier 13. The additional provision of the planetary gear mechanism 9 can 
increase the rotational phase caused by the rotation of the piston 8 by a 
factor of {(1+.lambda.)/.lambda.}. 
This will be discussed in more detail with specific values substituted in 
the equation (2). Suppose that the phase difference (phase angle) of 
10.degree. has appeared between the cylinder 5 and the carrier 13 by the 
rotation of the piston 8, and that the ratio .lambda. of the diameter of 
the sun gear 12 to that of the ring gear 11 is 0.5. Substituting these 
values into the equation (2) yields: 
EQU Sn={(1+0.5)/0.5}.multidot.10=3.multidot.10=30 
The phase difference between the sun gear 12 and the ring gear 11 is 
30.degree. three times more than that (10.degree.) of the cylinder 5 and 
the carrier 13. The preferable diameter ratio .lambda. ranges from 0.3 to 
0.6. A phase angle to be transmitted to the sun gear 12 is preferably 
about 2.6 to 4.4 times greater than a phase angle to be transmitted to the 
carrier 13. 
As the phase angle becomes greater, the timing for closing the intake valve 
is significantly delayed in the region where both the engine load and the 
engine speed are low. The volume of the cylinder is therefore reduced in 
appearance so as to decrease the pumping loss. The "pumping loss" means an 
intake loss occurring when the engine takes in the necessary amount of air 
to impart its working power to the outside. 
If the engine state shifts from the first region A or the second region B 
to the third region C, though not shown, the ECU 25 outputs a control 
signal to slightly open the control valve 22. As the control valve 22 is 
opened, the piston 8 moves to the position where the hydraulic pressure 
applied to the rear end of the piston 8 balances with the urging force of 
the return spring 24. 
The amount of the displacement of the piston 8 and the amount of the 
rotation of the cam shaft 1 at this time are smaller than those in the 
case where the engine running state shifts to the second region B from the 
first region A. Naturally the timing for closing the intake valve is later 
than that in the case of the first region A, and earlier than that in the 
case of the second region B, making the amount of the valve overlapping 
smaller. Consequently, the intake inertia permits more amount of mixture 
to be fed into the cylinder. It is to be noted that the magnitude of the 
hydraulic pressure acting on the piston 8 at this time can be adjusted by 
altering the opening of the control valve 22. 
As described above, according to this embodiment, the piston 8 and the 
planetary gear mechanism 9 intervene between the cylinder 5 having the 
timing pulley 6 and the cam shaft 1. The piston 8 and cylinder 5 are 
coupled together by means of the helical splines 8a and 3a, and the piston 
8 and carrier 13 by means of the helical splines 8b and 15a. Further, the 
ring gear 11 is secured to the cylinder 5, and the sun gear 12 to the cam 
shaft 1. With this design, when the engine is in a steady state (no phase 
shifting made) which belongs to any of the first to third regions A to C, 
all the components of the valve timing controller rotate integrally. This 
embodiment can therefore prevent gearing noise from occurring and the 
individual gears from wearing out due to the backlash between the gears 
when no phase shift is made. When the engine running state shifts from one 
of the first to third regions A to C to another, the phase shifting 
mechanism 10 alters the rotational phase of the cam shaft 1 to the carrier 
13. In addition, the phase angle can be amplified by the planetary gear 
mechanism 9, providing a large displacement angle for the cam shaft 1. The 
amount of the displacement angle can be set variably by changing properly 
the twisting angles of the helical splines 3a, 8a, 8b and 15a and/or the 
ratio of the diameter of the sun gear 12 to that of the ring gear 11. 
This embodiment provides the following action and effect in addition to 
those described above. 
For instance, in the case where the planetary gear mechanism 9 is 
eliminated and only the mechanism which moves the piston having helical 
splines in the axial direction to shift the rotational phase of the 
housing to the cam shaft is employed, the phase angle is determined by the 
amount of the axial movement of the piston. To increase the phase angle, 
therefore, the amount of the piston movement or the twisting angle of the 
helical splines should be increased, reducing the degree of design 
freedom. According to this embodiment, by way of contrast, the additional 
provision of the planetary gear mechanism 9 can not only easily increase 
the phase angle, but also it will give the rate of the increase in the 
phase angle by proper selection of the ratio of the diameter of the sun 
gear 12 to that of the ring gear 11. As a result, the degree of design 
freedom can be improved. 
A second embodiment of the present invention will now be described 
referring to FIGS. 6 to 8. 
This embodiment uses a step motor 35 as a means for moving the piston 8 
forward and backward. 
FIG. 6 illustrates the valve timing controller in an advanced angle state, 
and FIG. 7 illustrates it in a delayed angle state. As shown in both 
diagrams, a cylinder 5 with an open rear end is supported rotatable to the 
front end portion of a cam shaft 1. Between the cam shaft 1 and the 
cylinder 5 are disposed a phase shifting mechanism 10 for shifting the 
rotational phase of the cam shaft 1 to the cylinder 5, and a planetary 
gear mechanism 9 for amplifying the angle of the rotational phase. 
As shown in FIG. 8, the piston 8 of the phase shifting mechanism 10 is 
provided with a ring-shaped body 30 having helical splines 8a and 8b. 
Three link pieces 31 protrude forward at equal angles from the front end 
of the body 30. These link pieces 31 penetrate through a hole 2b provided 
at the deepest portion of the cylinder 5. A coupling ring 32 is fixed to 
the front inner surfaces of the link pieces 31. 
As shown in FIG. 6, a cylindrical portion 34 protrudes rearward on a timing 
belt cover 33 located at the front of the cam shaft 1. The step motor 35 
is attached to the front of the cover 33. The motor 35 has a rotary shaft 
36 penetrating the cylindrical portion 34 and rotatably supported on the 
front end portion of the cam shaft 1. The motor 35 rotates the rotary 
shaft 36 by an angle corresponding to the number of pulse signals output 
from an ECU 25. A feed screw 37 is formed on the outer surface of the 
rotary shaft 36, with a nut 38 fastened on the screw 37. The outer surface 
of the nut 38 and the inner surface of the cylindrical portion 34 are 
coupled by means of splines. As the rotary shaft 36 of the motor 35 
rotates, the nut 38 is moved forward or backward. 
A thrust bushing 39 is attached to the rear outer surface of the nut 38, 
and the coupling ring 32 is coupled rotatable to the thrust bushing 39. 
The reason why the thrust bushing 39 is used here is to reduce the 
frictional resistance originated from the difference between the 
rotational speeds of the nut 38 and the coupling ring 32. The thrust 
bushing 39 may be replaced with a thrust bearing. The other structure of 
this embodiment is the same as that of the first embodiment. 
According to this embodiment, when no phase shift is made as shown in FIGS. 
6 and 7, the rotary shaft 36 of the motor 35 does not rotate based on the 
control signal from the ECU 25, and the components of the valve timing 
controller, such as the planetary gear mechanism 9 and phase shifting 
mechanism 10, rotate integrally. It is therefore possible to prevent the 
occurrence of gearing noise or the wear-out of the individual gears caused 
by the backlash between the gears. 
When a phase shift is to be made, the rotary shaft 36 of the motor 35 
rotates based on the control signal from the ECU 25, moving the nut 38 on 
the rotary shaft 36 forward or backward. As the piston 8 is coupled 
through the thrust bushing 39 to the nut 38, the piston 8 moves rotating 
with respect to the cylinder 5. Consequently, the rotational phase of the 
piston 8 to the cylinder 5 is shifted and its phase angle is increased by 
the planetary gear mechanism 9. 
Further, the use of the step motor 35 in this embodiment also brings about 
the following effect. 
In the case where hydraulic power and a return spring 24 are used as a 
means to move the piston 8, to attain continuous or multi-stage phase 
shifting, the piston 8 should be stopped where the hydraulic pressure 
acting on the piston 8 is balanced with the urging force of the return 
spring 24. The stop position of the piston 8 may be affected by the 
hydraulic pressure and the precision of the return spring 24. It is 
therefore necessary to apply the hydraulic pressure as designed to the 
piston 8 in the light of the fluid temperature, the hysteresis of the 
control valve 22, etc. To accomplish this, another sensor to detect the 
position of the piston 8 may be provided so that the hydraulic pressure, 
etc. can be controlled to position the piston 8 to a predetermined point. 
When the piston 8 is moved to the determined position, it is in an unstable 
state balanced by the hydraulic pressure and the return spring 24. If the 
position of the piston 8 is unstable, the piston 8 may be deviated from 
the set position due to external factors, such as a change in torque 
caused by the rotation of the cam shaft 1. In this respect, it is 
desirable to provide another mechanism to hold the piston 8 in position. 
According to this embodiment, on the contrary, the forward and backward 
positions of the piston 8 are determined by the rotational angle of the 
rotary shaft 36 of the step motor 35. This ensures the accurate positional 
control of the piston 8 without requiring a special sensor. Further, as 
the step motor 35 has self-holding torque, the piston 8 can be stably held 
at a predetermined position without requiring a special holding mechanism. 
Furthermore, this embodiment does not utilize the hydraulic pressure to 
move the piston 8, thus eliminating the need to form a fluid path in the 
cam shaft 1 or cylinder 5. 
A third embodiment of this invention will now be explained referring to 
FIG. 9. 
This embodiment differs from the first and second embodiments considerably 
in that the planetary gear mechanism 9 is replaced with a differential 
gear mechanism 41 as the accelerating gear mechanism. In FIG. 9 a timing 
belt 7 is located at the back (on the right-hand side in the diagram). 
A cam shaft 1 is separated into an input-side shaft 42 and an output-side 
shaft 43, which are coupled together by the differential gear mechanism 
41. The differential gear mechanism 41 includes a case 44, which covers 
end portions of both shafts 42 and 43 and has a cylindrical portion 44a 
provided at its rear end. In the case 44 are disposed input-side and 
output-side level gears 45 and 46 secured to the end portions of the 
shafts 42 and 43, and level gears 47 and 48 which supported rotatable by 
the case 44 and mesh with the former gears 45 and 46. The output-side 
level gear 46 is formed smaller than the input-side level gear 45. 
A cylinder 5 is supported rotatable on the input-side shaft 42 between a 
timing pulley 6 and the differential gear mechanism 41. A cylindrical 
piston 8 is disposed in the cylinder 5. The piston 8 is coupled by means 
of helical splines 49 and 50 to a cylindrical portion 44a and the 
input-side shaft 42. In the shaft 42 is formed a fluid path 21 through 
which a working fluid is fed into the cylinder 5 with the delayed phase 
angle and is not supplied thereto with the advanced phase angle. 
According to the valve timing controller constituted in the above manner, 
when no phase shift is made, the piston 8 neither moves forward nor 
backward, and the input-side shaft 42, piston 8, case 44, all the level 
gears 45 to 48, and output-side shaft 43 rotate integrally. Therefore, the 
rotational phase of the input-side shaft 42 to the output-side shaft 43 
does not change. 
When supplying a working fluid in the cylinder 5 starts or stops, the 
piston 8 moves forward or backward while rotating. Since the case 44 is 
coupled to the piston 8 by the helical spline 49, the case 44 rotates 
integrally with the piston 8. Consequently, the level gears 47 and 48 
rotate both around the input-side level gear 45 and on their own axes. The 
rotation around the level gear 45 accelerates the rotation of the 
output-side level gear 46. The rotational phase therefore becomes larger 
by the differential gear mechanism 41, thus providing a large displacement 
angle of the output-side shaft 43. 
This embodiment apparently has the same action and same effect as the first 
and second embodiments. 
The present invention is not limited to the structures of the 
above-described embodiments, but may be modified in various other manners 
as desired within the scope and spirit of the invention. 
(1) The timing pulley 6 in the individual embodiments may be replaced with 
a sprocket which is coupled in a drivable manner to the crank shaft by a 
chain. 
(2) The valve timing controller of each described embodiment may be applied 
to an engine which has an intake cam shaft coupled in a drivable manner to 
an exhaust cam shaft by a scissors gear. In this case the valve timing 
controller should be disposed between the scissors gear and the cam shaft. 
(3) One of the helical splines 8a and 8b on the inner and outer surfaces of 
the piston 8 may be changed to a spline. 
(4) The same valve timing controller as used in each embodiment described 
above may be attached to the exhaust cam shaft.