VALVE DRIVING DEVICE FOR INTERNAL COMBUSTION ENGINE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a valve driving device for an internal

combustion engine, and more particularly to a valve driving device for an internal

combustion engine in which an oscillating member is interposed between a cam and a

valve to synchronize the oscillation of the valve with the rotation of a camshaft.

2. Description of the Related Art

[0002] A conventional variable valve driving device for an internal combustion

engine is described in, for example, Japanese Patent Application Publication No.

JP-A-2004-521235, that mechanically changes the duration and lift of a valve. This

type of conventional variable valve driving device includes a return spring (torsion coil

spring) that impels a pivot lever (oscillating member), interposed between a cam and a

valve, against the cam.

[0003] The variations in the shape of the torsion springs are inherent in the

production process. Li the variable valve driving device of the above related art, the

torsion spring impels the pivot lever to oscillate within a predefined oscillating range.

Therefore, such variations in shape of torsion springs can cause some torsion springs,

incorporated in the valve driving device, to generate a greater impelling force, and others

to generate a smaller impelling force, than the target value.

[0004] As a result, the torsion springs with an excessively large impelling force

may not be able to satisfy the allowable stress for the required fatigue strength, thus

providing only reduced durability. On the other hand, those torsion springs with an

excessively small spring force may not be able to provide sufficient impelling force for

the inertial force of valve driving components (such as the above oscillating member)

when the engine speed is high. Such an insufficient spring force at high engine speed

does not permit the valve driving components to maintain synchronous operation with

rotation of the cam (i.e., a so-called jump occurs), thus requiring the allowable speed of

the internal combustion engine to be reduced.

[0005] In the conventional variable valve driving device described above, the

length of one arm of the torsion spring for contacting the pivot lever is increased to

reduce its spring constant. According to such an approach, changes in spring force due

to variations in shape of torsion springs can be reduced. However, increasing the size of

the torsion spring, impairs the mountability of the variable valve driving device to the

internal combustion engine.

SUMMARY OF THE INVENTION

[0006] The present invention provides a valve driving device for an internal

combustion engine that allows for variations in shape of torsion springs as a result of

mass production, and that also improves mountability to the internal combustion engine.

[0007] A first aspect of the present invention provides a valve driving device for

an internal combustion engine, that includes an oscillating member interposed between a

cam and a valve to synchronize the oscillation of the valve with the cam, characterized by

including: a torsion spring, having a first portion and a second portion, that contacts the

oscillating member at the first portion end and impels the oscillating member toward the

cam; a support part that supports the second portion of the torsion spring; and a spring

position adjustment mechanism that adjusts a mounting position of the torsion spring

relative to the support part.

[0008] In the first aspect, the spring position adjustment mechanism may include

an adjustment member that includes a projection projecting from the support part, the

second portion of the torsion spring may surround the projection, the adjustment member

may be rotatably mounted on the support part, and the projection may have a cam-shaped

peripheral surface that contacts the second portion of the torsion spring.

[0009] In the first aspect, the spring position adjustment mechanism may include

an adjustment member having a projection projecting from the support part, the second

portion of the torsion spring may be formed to surround the projection, the projection

may include a cylindrical portion that contacts the second portion, and the spring position

adjustment mechanism adjusts the mounting position of the torsion spring relative to the

support part by using the adjustment member including the cylindrical portion, in contact

with the torsion spring, having a different outer diameter.

[0010] In the above aspects, the adjustment member may be mounted on the

support part in such an orientation that when a head cover of the internal combustion

engine removed, the adjustment member is accessible in a substantially axial direction of

the adjustment member.

[0011] According to the first aspect of the present invention, the orientation of the

first portion of a torsion spring that is mounted on the valve driving device may be

adjusted by adjusting the mounting position of the torsion spring relative to the support

part through the spring position adjustment mechanism. Thus, even if a torsion spring

with a larger spring constant is used, variations in spring force can be effectively reduced.

In this way, the first aspect of the present invention provides a valve driving device for an

internal combustion engine that allows for variations in shape of torsion springs as a

result of mass production, and that also provides excellent mountability to the internal

combustion engine.

[0012] In addition, the relative position of the second portion of the torsion spring

and the projection of the adjustment member may be changed by rotating the cam-shaped

projection of the adjustment member. In this way, the orientation of the first portion of

a torsion spring mounted on the valve driving device may be adjusted with a simple

construction by adjusting the mounting position of the torsion spring relative to the

support part through the spring position adjustment mechanism.

[0013] Further, the relative position of the second portion of the torsion spring

and the projection of the adjustment member can be changed by replacing the adjustment

member with one including a cylindrical portion having a different outer diameter. In

this way, the orientation of the first portion of a torsion spring mounted on the valve

driving device may be adjusted with a simple construction by adjusting the mounting

position of the torsion spring relative to the support part through the spring position

adjustment mechanism.

[0014] Furthermore, workability in adjusting the position of a torsion spring

mounted on the variable valve driving device is improved. In this way, variations

between a plurality of cylinders in spring force of the torsion spring can be easily

adjusted with the torsion spring mounted on the valve driving device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The foregoing and further objects, features and advantages of the

invention will become apparent from the following description of example embodiments

with reference to the accompanying drawings, wherein like numerals are used to

represent like elements and wherein:

FIG. 1 is a side view showing the construction of a variable valve driving device

according to a first embodiment of the present invention;

FIG. 2 is a perspective view of the variable valve driving device shown in FIG. 1 ;

FIGs. 3A to 3C illustrate the construction of a lost motion spring (for an oscillating

cam arm) shown in FIG. 2;

FIGs. 4A to 4C illustrate the construction of a lost motion spring (for a large lift

arm) shown in FIG. 2;

FIGs. 5A to 5C illustrate the construction of a spring position adjustment

mechanism;

FIG. 6 shows a cam-shaped head of an adjustment screw shown in FIGs. 5A to 5C as

viewed axially of the screw;

FIG. 7 shows the central position of the mount position of a first arm;

FIGs. 8 A to 8C show the lost motion spring mounted on a spring support shaft with

the first arm mounted at the central position shown in FIG. 7;

FIG. 9 illustrates an adjustment method to increase the spring force of the lost

motion spring;

FIG. 10 illustrates an adjustment method to reduce the spring force of the lost

motion spring;

FIG. 11 illustrates how the respective dimensions, etc., of a torsion coil spring are

defined;

FIGs. 12A and 12B illustrate the construction of a spring position adjustment

mechanism according to a second embodiment of the present invention;

FIGs. 13A and 13B illustrate a method to adjust the mounting position of a spring

with two narrow-angled arms;

FIGs. 14A and 14B illustrate a method to adjust the mounting position of a spring

with two wide-angled arms;- and

FIG. 15 illustrates the mounting direction of the spring position adjustment

mechanism relative to a cylinder head of an internal combustion engine.

• DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0016] Hereinafter, with reference to FIGs. 1 and 2, a valve driving device for an

internal combustion engine according to a first embodiment of the present invention will

be described. FIG. 1 is a side view of a variable valve driving device 1 according to the

first embodiment of the present invention. More specifically, FIG. 1 shows the cross

section of the variable valve driving device 1 taken along a plane passing through a first

1

driving cam 14 provided on a camshaft 12. FIG, 2 is a perspective view of the variable

valve driving device 1 shown in FIG. 1. Each cylinder of the internal combustion

engine includes two intake valves and two exhaust valves. The device shown in FIGs. 1

and 2 drives the two intake valves, or the two exhaust valves, provided for each cylinder.

[0017] The variable valve driving device 1 mechanically changes the valve

opening characteristics (such as lift and duration) of a valve 18. Specifically, the

variable valve driving device 1 includes a rocker arm type mechanical valve driving

mechanism, by which rotation of the camshaft 12 is converted into oscillating motion of

a rocker arm 16 by the first driving cam 14 provided on the camshaft 12, and then into

vertical lifting motion of the valve 18 supported by the rocker arm 16. The variable

valve driving device 1 drives the rocker arm 16 through a variable valve driving

mechanism 20 interposed between the first driving cam 14 and the rocker arm 16, rather

than directly through the first driving cam 14. The variable valve driving mechanism 20

may continuously change the oscillating motion of the rocker arm 16 in response to the

rotation of the first driving cam 14. The variable valve driving device 1 variably

controls the variable valve driving mechanism 20 to change the oscillating amount and

timing of the rocker arm 16, so as to continuously change the lift and duration of the

valve 18.

[0018] The variable valve driving mechanism 20 includes as its main constituent

parts a control shaft 22, a control arm 24, a link arm 26, an oscillating cam arm 28, a first

roller 30, and a second roller 32. The control shaft 22 is disposed parallel to the

camshaft 12. The rotational angle of the control shaft 22 may be controlled to an

arbitrary angle by an actuator (not shown) (such as motor, for example).

[0019] A retention part 28a of the oscillating cam arm 28 retains an end 34a of a

lost motion spring 34 (which may hereinafter be simply referred to as "spring 34"). The

spring 34 is a torsion coil spring that has a circular cross section. In the construction

shown in FIG. 2, one torsion coil spring as the spring 34 is used for two oscillating cam

arms 28.

[0020] A curved portion 34b is formed in the central portion of the spring 34.

The spring 34 is mounted on a cylinder head (not shown) (or on a support member such

as earn carrier) via a spring support shaft 62 (see FIGs. 5A to 5C). The mounting

position of the spring 34 to the variable valve driving device 1 is defined by the end 34a

retained by the retention part 28a and the curved portion 34b retained by the spring

support shaft 62.

[0021] An impelling force from the lost motion spring 34 impels a slide surface

36 formed on the oscillating cam arm 28 against the second roller 32, thereby the first

roller 30 against the first driving cam 14. The first and second rollers 30 and 32 are thus

positioned as interposed between the slide surface 36 and the peripheral surface of the

first driving cam 14 from both sides.

[0022] According to the variable valve driving mechanism 20 constructed as

described above, changing the rotational position of the control shaft 22 changes the

position of the second roller 32 on the slide surface 36, thus changing the oscillating

range of the oscillating cam arm 28 during lifting operation. Therefore, the lift and

duration of the valve 18 may be variably adjusted by controlling the rotational position of

the control shaft 22. The construction of the variable valve driving mechanism 20 for

variably controlling the valve opening characteristics of the valve 18 is similar to that

described in JP-A-2006-70738, for example, and thus will not be described in detail

herein.

[0023] The variable valve driving device 1 also includes a fixed valve driving

mechanism 40 for providing fixed valve opening characteristics to one (in FIG. 2, the

valve 18L on the left side) of the two valves 18 disposed side by side. The variable

valve driving device 1 includes a valve switching mechanism that selectively switches

operation of the valve 18L between the variable valve driving mechanism 29L or the

fixed valve driving mechanism 40.

[0024] In addition to the first driving cam 14, the camshaft 12 includes for each

cylinder a second driving cam 42 disposed adjacent to the first driving cam 14, as shown

in FIG. 1. The fixed valve driving mechanism 40 shown in FIG. 2 is interposed between

the second driving cam 42 and the oscillating cam arm 28L. The fixed valve driving

mechanism 40 allows the oscillating cam arm 28L to oscillate in conjunction with the

rotation of the second driving cam 42. The fixed valve driving mechanism 40 includes

a large lift arm 44 that is driven by the second driving cam 42.

[0025] The large lift arm 44 is disposed on the control shaft 22 next to the

oscillating cam arm 28L so as to oscillate independently of the oscillating cam arm 28L.

The large lift arm 44 rotatably supports an input roller 46 that contacts the peripheral

surface of the second driving cam 42. A retention part 44a of the large lift arm 44

retains a lost motion spring 48, as in the case with the oscillating cam arm 28. The

spring force of the lost motion spring 48 acts as an impelling force to press the input

roller 46 against the peripheral surface of the second driving cam 42.

[0026] The valve switching mechanism according to this embodiment is

constructed to couple and decouple the large lift arm 44 and the oscillating cam arm 28L.

The specific construction of the valve switching mechanism is unnecessary to understand

the present invention, and thus is not described in detail herein. By way of illustration,

the following construction may be used. One of the large lift arm 44 and the oscillating

cam arm 28L may be provided with a pin that is projected toward the other by, for

example, hydraulic pressure, while the other is provided with a pin hole that receives the

pin. The pin and the pin hole are aligned with each other when the oscillating cam arm

28L and the large lift arm 44 are in a predetermined relative positional relationship.

According to such a construction, when the oscillating cam arm 28L and the large lift arm

44 are coupled to each other via the pin, the pressing force of the second driving cam 42

is transmitted to the valve 18L via the large lift arm 44, the oscillating cam arm 28L and

the rocker arm 16. As a result, only the valve opening characteristics of the valve 18

will be controlled in a fixed manner, irrespective of the rotational position of the control

shaft 22.

[0027] FIGs. 3A to 3C illustrate the construction of the lost motion spring 34 (for

an oscillating cam arm) shown in FIG. 2. More specifically, FIG. 3 A illustrates the

spring 34 as viewed in the direction of an axis passing through the center of a coiled

portion 34c, FIG. 3B illustrates the spring 34 as viewed in the direction of the arrow B in

FIG. 3 A, and FIG. 3 C illustrates the spring 34 as viewed in the direction of the arrow C in

FIG. 3A.

[0028] FIGs. 3 A to 3C shows a spring 34 that is not loaded. Here, a portion of

the spring 34 that departs from the circumference of the coiled portion 34c on the curved

portion 34b side is referred to as a first arm 50a, while a portion of the spring 34 that

departs from the circumference of the coiled portion 34c on the other side, that is, on the

end 34a side is referred to as a second arm 50b. With the spring 34 mounted on the

variable valve driving device I ₃ the second arm 50b receives a load from the oscillating

cam arm 28, The spring 34 generates a spring force against the load from the oscillating

cam arm 28. Here, as shown in FIG. 3A ₅ the length of the line segment connecting the

center of the coiled portion 34c and the end 34a (load acting point) of the second arm 50b

is referred to as "load acting radius R2", and the direction perpendicular to the line

segment is defined as the acting direction of the spring force mentioned above.

[0029] The point where the outer line of the second arm 50b and the outer line of the circumference of the coiled portion 34c intersect is defined as "point P". With the spring 34 mounted on the variable valve driving device 1 (with the valve 18 closed), the spring 34 is twisted around the point P in FIG. 3 A by a torsion angle φl, compared to the free state, which narrows the angle between the two arms 50a and 50b. When the oscillating cam arm 28 receives the pressing force of the first driving cam 14 to start oscillating while the valve 18 is in lifting operation, the torsion angle φ increases. At this time, the torsion angle φ reaches an angle φ2 under maximum deflection (at the peak of the lift curve).

[0030] FIGs. 4A to 4C illustrate the construction of the lost motion spring 48 (for

a large lift arm) shown in FIG. 2. More specifically, FIGs. 4 A to 4C illustrate the spring

48 as viewed in the same directions as it is viewed in FIGs. 3A to 3C, respectively. The

construction of the spring 48 for the large lift arm 44 is similar to that of the spring 34

discussed above, except that the torsion coil spring is constructed independently for one

large lift arm 44. That is, the only difference of the spring 48 from the spring 34 is that

an end 48a of the spring 48 on the other side is formed as a curved portion 48b that is

retained by the spring support shaft 62.

[0031] Now, with reference to FIGs. 5 A to 5C and 6, the construction of a spring

position adjustment mechanism 60 (which may hereinafter be simply referred to as

"adjustment mechanism 60") for adjusting the mounting position of the lost motion

spring will be described. FIGs. 5A to 5C illustrate the construction of the spring

position adjustment mechanism 60. More specifically, FIG. 5 A illustrates the spring

position adjustment mechanism 60 as viewed along the axis of the spring support shaft 62,

FIG. 5B illustrates the spring position adjustment mechanism 60 as viewed from an

adjustment screw 64 side, and FIG. 5C illustrates the spring position adjustment

mechanism 60 as viewed from a fixation nut 66 side. FIGs. 5A to 5C illustrate the

adjustment screw 64 and the fixation nut 66 both before and after they are assembled to

the spring support shaft 62.

[0032] As shown in FIGs. 5 A to 5C, the lost motion spring 34 is wound to the

spring support shaft 62. The spring support shaft 62 is formed with a threaded hole 62a

in a direction perpendicular to the axis of the spring support shaft 62. The inner wall of

the threaded hole 62a is formed with female threads. The adjustment mechanism 60

includes an adjustment screw 64 for meshing the threaded hole 62a.

[0033] The adjustment screw 64 includes a male-threaded portion 64a formed on

its peripheral surface with male threads, and a cam-shaped head 64b. An end surface of

the adjustment screw 64 on the male-threaded portion 64a side is formed with a

hexagonal adjustment groove 64c (inner hexagonal groove) for adjusting the rotational

position of the screw 64.

[0034] The adjustment screw 64 is screwed into the spring support shaft 62 to a

position where the cam-shaped head 64b contacts the curved portion 34b of the spring 34.

The adjustment mechanism 60 includes a fixation nut 66 that fixes the rotational position

of the adjustment screw 64 relative to the spring support shaft 62. The adjustment

screw 64 is screwed into the spring support shaft 62 to a predetermined rotational

position with the male-threaded portion 64a projecting from the other side of the spring

support shaft 62. The fixation nut 66 is meshed with the male-threaded portion 64a on

the other side of the spring support shaft 62. The rotational position of the adjustment

screw 64 is fixed by the factional force between the spring support shaft 62 and the

fixation nut 66 when the fixation nut 66 is fastened.

[0035] FIG. 6 shows the cam-shaped head 64b of the adjustment screw 64 shown

in FIGs. 5 A to 5C as viewed along the axis of the screw 64. As shown in FIG. 6, the

cam-shaped head 64b includes a base circular portion 64b 1 that has smaller diameter than

and is concentric with the male-threaded portion 64a, and a cam nose portion 64b2 that

has the same diameter at its top as the male-threaded portion 64a. The spring position

adjustment mechanism 60 according to this embodiment includes the spring support shaft

62, the adjustment screw 64 and the fixation nut 66 described above.

[0036] Now, with reference to FIGs. 7 to 9, a method of adjusting the mounting

position of the lost motion spring 34 through the spring position adjustment mechanism

60 will be described. FIG. 7 shows the central position of the mounting position of the

first arm 50a. FIG. 7 shows the state where the cam-shaped head 64b contacts the

curved portion 34b at an intermediate position of the cam nose portion 64b2. Here, the

mounting position of the first arm 50a of the spring 34 to the variable valve driving

device 1 in such a state is defined as "central position".

[0037] FIGs. 8A to 8C show the lost motion spring 34 mounted on the spring

support shaft 62 with the first arm 50a mounted at the central position mentioned above.

In FIG. 8A, the second arm 50b of the spring 34 is in the same direction as the dot and

dash line, which indicates the target direction in design, when the spring 34 is mounted

on the spring support shaft 62 at the central position. In other words, the spring 34

shown in FIG. 8A is manufactured with no variation in shape from the design value.

[0038] The shape of the lost motion spring 34 may vary as a result of

manufacture. In FIG. 8B ₅ the second arm 50b of the spring 34 is directed more inwardly

than the dot and dash line. In other words, the spring shown in FIG. 8B is manufactured

with the angle between the first arm 50a and the second arm 50b narrower than the target

shape in design. Ih the case where such a spring is mounted on the variable valve

driving device 1, the spring force is insufficient because only a load below the design

target value acts on the spring. In FIG. 8C, the second arm 50b of the spring 34 is

directed more outwardly than the dot and dash line, opposite to the spring 34 shown in

FIG. 8B. In other words, the spring 34 shown in FIG. 8C is manufactured with the angle

between the first arm 50a and the second arm 50b wider than the target shape in design.

In the case where such a spring is mounted on the variable valve driving device 1, the

spring force is excessively large because a load above the design target value acts on the

spring.

[0039] In the variable valve driving device 1 including the spring position

adjustment mechanism 60 discussed above, the position of the first arm 50a of the lost

motion spring 34 assembled to the variable valve driving device 1 is determined by the

engagement between the curved portion 34b and the cam-shaped head 64b. Thus,

adjusting the rotational position of the adjustment screw 64 can change the positional

relationship between the curved portion 34b and the cam-shaped head 64b, which as a

result can change the mounting position of the first arm 50a.

[0040] FIG. 9 illustrates an adjustment method to increase the spring force of the

lost motion spring 34. When a spring with two narrow-angled arms, such as the spring

34 shown in FIG. 8B, is used, the fixation nut 66 is loosened, and the rotational position

of the adjustment screw 64 is adjusted such that the curved portion 34b is contacted by a

portion of the cam nose portion 64b2 more on the top side, as shown in FIG. 9. As a

result, the mounting position of the spring 34 is moved clockwise from the position

shown in FIG, 8B. This allows the second arm 50b to coincide in direction with the dot

and dash line.

[0041] FIG. 10 illustrates an adjustment method to reduce the spring force of the

lost motion spring 34. In the case where a spring with two wide-angled arms, such as

the spring 34 shown in FIG. 8C, is used, the fixation nut 66 is loosened, and the rotational

position of the adjustment screw 64 is adjusted such that the curved portion 34b is

contacted by a peripheral surface more on the base circular portion 64b 1 side, as shown

in FIG. 10. As a result, the mounting position of the spring 34 is moved

counterclockwise from the position shown in FIG. 8C. This allows the second arm 50b

to coincide in direction with the dot and dash line.

[0042] The adjustment of the spring position described above may be performed

by the following procedure. For example, with the spring 34 mounted on the spring

support shaft 62, the rotational position of the adjustment screw 64 is set at the central

position. Then, the assembly of the spring support shaft 62 and the spring 34 in this

state is set on a predetermined measurement jig to measure the position of the second arm

50b relative to the reference plane (see FIGs. 8A to 8C). At this time, if a variation is

found in position of the second arm 50b, the mounting position of the first arm 50a may

be adjusted by the methods shown in FIGs. 9 and 10. The spring 34 for each cylinder

may be adjusted in the manner described above.

[0043] The adjustment of the spring position may also be performed by the

following procedure, for example. The assembly in the above state is set on a

predetermined measurement jig with a small load acting on the spring 34. The spring

force generated at this time is measured to determine whether or not the spring force

satisfies the design value. If a difference is found between the measured spring force

and the design value, the mounting position of the first arm 50a is adjusted by the

methods shown in FIGs. 9 and 10 to obtain a spring force satisfying the design value.

The spring 34 for each cylinder may be adjusted in the manner described above.

[0044] As described above, according to the spring position adjustment

mechanism 60 according to this embodiment, adjusting the rotational position of the

adjustment screw 64 relative to the spring support shaft 62 changes the mounting angle of

the first arm 50a relative to the spring support shaft 62. This changes the direction of

the second arm 50b in the free state (where no load is acting on the spring 34). When

the direction of the second arm 50b in the free state is changed, the torsion angle ? (see

FIG. 8A) of a spring 34 mounted in the variable valve driving device 1 under maximum

deflection is also changed. As the torsion angle ? in the free state is reduced, the spring

force is reduced. Conversely, as the torsion angle ? in the free state is increased, the

spring force is increased. Therefore, the spring force of the lost motion spring 34

mounted on the spring support shaft 62 under maximum deflection may be uniformly set

to the design reference value, irrespective of variations in shape of the lost motion spring

34, by changing the direction of the second arm 50b through the spring position

adjustment mechanism 60.

[004S] As shown in FIGs. 5A to 5C ₅ the spring support shaft 62 is formed with a

threaded hole 62b, positioned adjacent to the threaded hole 62a, for adjusting the position

of the lost motion spring 48 for the large lift arm 44. The position of the spring 48 can

also be adjusted using similar adjustment screw 64 and fixation nut 66, which is not

described in detail herein.

[0046] Incorporating the spring position adjustment mechanism 60, constructed

as described above, into a valve driving device for an internal combustion engine

provides the effects as described below with a simple and convenient construction.

[0047] First, the mountability of a lost motion spring in the valve driving device

is improved. It is difficult to eliminate variations in shape and material of lost motion

springs in mass production. A spring with a larger spring constant generates a larger

spring force for variations in shape of springs.

[0048] The spring constant ktd of a torsion coil spring and the specifications of

the spring have a relationship represented by the equation (1) given below:

ktd = E - p . d ⁴ /(64 - (p - D - N + l/3 - (al + a2))) ^{■ • ■} (1)

where E represents the Young's modulus, d the diameter of the material, D the average

diameter of the coil, N the number of windings, al the length of the first arm, and a2 the

length of the second arm. FIG. 11 illustrates how the respective dimensions, etc., of a

torsion coil spring are defined.

[0049] The use of a spring with a smaller spring constant is conceivable in order

to reduce changes in spring force for variations in shape of springs. However, the use of

a spring with a smaller spring constant involves problems as follows. As indicated by

the equation (1), it is effective to increase the arm length al or a2, the coil average

diameter D or the number of windings N, in order to reduce the spring constant.

However, increasing the arm length al or a2 or the coil average diameter D increases the

size of the spring. Also, increasing the number of windings N increases the size of the

spring in the axial direction of the camshaft 12. Such attempts to reduce the spring

constant result in an increased size of the spring, which deteriorates the mountability of

the lost motion spring in the valve driving device. To avoid increasing the size of the

spring due to increasing the number of windings N, the use of a spring with a rectangular

coil cross section is conceivable, which, however, increases the manufacturing cost of the

spring.

[0050] To address the above problems, the valve driving device including the

spring position adjustment mechanism.60 according to this embodiment adjusts the

directions of the arms of a spring in the state of being assembled, thus allowing for the

use of a spring with a larger spring constant, that is, a spring of a smaller size. This can

favorably improve the mountability of a lost motion spring in a valve driving device, thus

achieving the compactness of an internal combustion engine as a whole,

[0051] Furthermore, variations between cylinders in spring force of the lost

motion spring 34, or the like, due to variations in position of the variable valve driving

mechanism 20 and fixed valve driving mechanism 40 side, may be reduced.

Specifically, taking the variable valve driving mechanism 20 for an example, variations

in shape, and positional deviation when assembled, of all the components of the variable

valve driving mechanism 20 and surrounding associated parts such as cylinder head may

cause variations between cylinders in lift and duration of the valve 18 when initially

assembled. Such variations between cylinders in lift, etc., may be reduced by a separate

adjustment mechanism provided to the variable valve driving mechanism 20. Therefore,

the position of the oscillating cam arm 28, which contacts the second arm 50b of the

spring 34, is determined after such adjustment of variations between cylinders in lift, etc.

That is, the position of the oscillating cam arm 28 with the spring 34 assembled thereto

may vary between cylinders. As a result, such variations between cylinders in position

of the oscillating cam arm 28 may cause variations between cylinders in spring force of

the spring 34. The spring position adjustment mechanism 60 according to this

embodiment may be used to adjust such variations between cylinders in spring force of

the spring 34.

[0052] Lastly, the spring force of the lost motion springs 34 for all the cylinders

may be made uniform, so as to allow for variations in inertial force of the oscillating cam

arm 28, the second roller 32, the large lift arm 44, or the like, while oscillating.

Specifically, the inertial force of those parts which synchronously oscillate with the

rotation of the camshaft 12, such as the oscillating cam arm 28, the second roller 32 and

the large lift arm 44, may vary between cylinders because of variations in shape of the

parts and positional deviation when assembled. Also, as already discussed, if the spring

force of a mounted spring 34 is larger because of variations in shape, the spring force is

also larger than the design value when the spring is under maximum deflection. A

combination of the spring 34 with a larger spring force and the variable valve driving

mechanism 20, or the like, with a larger inertial force cannot satisfy the allowable stress

for the required fatigue strength, and the spring 34 cannot secure sufficient durability.

Meanwhile, a combination of the spring 34 with a smaller spring force due to variations

in shape and the variable valve driving mechanism 20, or the like, with a larger inertial

force cannot permit valve driving components such as the oscillating cam arm 28 to

maintain synchronous operation with the rotation of the cam (i.e., a so-called jump

occurs) when the engine speed is high. In this case, it is necessary to reduce the

maximum allowable speed of the internal combustion engine. The spring position

adjustment mechanism 60 according to this embodiment can compensate variations

between cylinders in spring force due to variations in shape of the spring 34, or the like,

provided for each cylinder. Thus, it is possible to always satisfy the required durability

of the spring 34, or the like, even if combined with the variable valve driving mechanism

20, or the like, with a larger inertial force, and also to easily uniform the spring force of

the spring 34, or the like, for each cylinder to a proper range where a jump as described

above can always be prevented.

[0053] The oscillating cam arm 28 and the large lift arm 44 in the first

embodiment discussed above are embodiments of the "oscillating member" of the present

invention, the lost motion springs 34 and 48 embody the "torsion spring", the ends 34a

and 48a of the lost motion springs 34 and 48 embody the "first portion", the curved

portions 34b and 48b of the lost motion springs 34 and 48 are embodiments of the

"second portion", and the spring support shaft 62 is an embodiment of the "support part",

respectively. Also, the cam-shaped head 64b and the adjustment screw 64 are

embodiments of the "projection" and "adjustment member" in the present invention,

respectively. In addition, the peripheral surface of the cam-shaped head 64b (the base

circular portion 64b 1 and the cam nose portion 64b 2) embodies the "peripheral surface

that contacts the second portion" in the present invention.

[0054] Now, with reference to FIGs. 12A to HB ₅ a second embodiment of the

present invention will be described, FIGs. 12A and 12B illustrate the construction of a

spring position adjustment mechanism 70 according to the second embodiment of the

present invention. Here, the construction of the lost motion spring 34 for the oscillating

cam arm 28 is taken for an example. The construction of the lost motion spring 48 for

the large lift arm 44 is basically the same, and thus is not described in detail herein.

[0055] As shown in FIGs. 12A and 12B, the spring position adjustment

mechanism 70 according to this embodiment is characterized in that the construction of

the adjustment screw 74 to be inserted into the spring support shaft 72 is different.

More specifically, as shown in FIG. 12A, the spring support shaft 72 is formed with a

threaded hole 72a in a direction perpendicular to the axis of the spring support shaft 72.

The inner wall of the threaded hole 72a is formed with female threads. The spring

support shaft 72 is also formed with a threaded hole 72b, which is similar to the threaded

hole 72a, for the spring 48.

[0056] Meanwhile, as shown in FIG. 12B, a threaded portion 74a is formed on a

portion of the peripheral surface the adjustment screw 74 with male threads for meshing

the threaded hole 72a. The adjustment screw 74 also includes a cylindrical portion 74b

for contacting the curved portion 34b of the spring 34 when the adjustment screw 74 is

inserted into the threaded hole 72a. An end surface of the adjustment screw 74 on the

cylindrical portion 74b side is formed with a hexagonal adjustment groove 74c (inner

hexagonal groove) for screwing the adjustment screw 74 into the spring support shaft 72.

[0057] Here, the mounting position of the first arm 50a when the adjustment

screw 74 including the cylindrical portion 74b having such an outer diameter as shown in

FIGs. 12A and 12B is used is defined as the "central position" discussed above. In FIG.

12A ₉ the second arm 50b of the spring 34 is in the same direction as the dot and dash line,

which indicates the target direction in design, when the first arm 50a is at the central

position. In other words, the spring 34 shown in FIG. 12A is manufactured with the

target shape in design.

[0058] FIGs. 13A and 13B illustrate a method to adjust the mounting position of

the spring 34 with two narrow-angled arms. In the case where a spring with two

narrow-angled arms, such as the spring 34 shown in FIG. 13 A, is used, the adjustment

screw 74 is replaced by an adjustment screw 76 formed to include a cylindrical portion

76b having a larger outer diameter compared to the screw 74, as shown in FIG. 13B.

More specifically, the adjustment screw 76 includes a cylindrical portion 76b having a

larger outer diameter compared to the adjustment screw 74 including the cylindrical

portion 74b having an outer diameter achieving the central position. With such a

substitute adjustment screw 76, the mounting position of the first arm 50a of the spring

34 is changed from the state shown in FIG. 13 A in the clockwise direction in FIG. 13A.

This allows the second arm 50b to coincide in direction with the dot and dash line.

[0059] FIGs. 14A and 14B illustrate a method of adjusting the mounting position

of the spring 34 with two wide-angled arms. In the case where a spring with two

wide-angled arms, such as the spring 34 shown in FIG. 14A ₅ is used, the adjustment

screw 74 is replaced by an adjustment screw 78 that includes a cylindrical portion 78b

having a smaller outer diameter compared to the screw 74, as shown in FIG. 14B. More

specifically, the adjustment screw 78 includes a cylindrical portion 78b having a smaller

outer diameter compared to the adjustment screw 74 including the cylindrical portion 74b

having an outer diameter achieving the central position. With such a substitute

adjustment screw 78, the mounting position of the first arm 50a of the spring 34 is

changed from the state shown in FIG. 14A in the counterclockwise direction in FIG. 14A.

This allows the second arm 50b to coincide in direction with the dot and dash line.

[0060] The adjustment of the spring position described above may be performed

by the following procedure, for example. First, the spring 34 is mounted on the spring

support shaft 72 using the adjustment screw 74 achieving the central position. Then,

such an assembly of the spring support shaft 72 and the spring 34 is set on a

predetermined measurement jig to measure the position of the second arm 50b relative to

the reference plane (see FIGs. 12A to 12B). Then, if a variation is found in position of

the second arm 50b, the adjustment screw 74 is replaced by an adjustment screw that

includes a cylindrical portion that contacts the spring 34 with a different outer diameter,

thus allowing the mounting position of the first arm 50a to be adjusted by the methods

shown in FIGs. 13A to 14B. In this case, a plurality of adjustment screws may be

provided including a cylindrical portion having a different outer diameter by a

predetermined amount for every degree of torsion angle ?, for example. Adjustment

work described above is performed for the spring 34 for each cylinder.

[0061] As described above, the spring position adjustment mechanism 70

according to this embodiment can change the mounting angle of the first arm 50a relative

to the spring support shaft 72 by using an adjustment screw that has a cylindrical portion

in contact the spring 34 of a different outer diameter, thus allowing the direction of the

second arm 50b in the free state to be changed. Therefore, the spring force of the

mounted lost motion spring 34 under maximum deflection may be set to the design

reference value, irrespective of variations in shape of the lost motion spring 34, also by

changing the direction of the second arm 50b through the spring position adjustment

mechanism 70. In addition, the same effects as in the first embodiment discussed above

can be achieved.

[0062] In the second embodiment discussed above, the spring position is adjusted

by using an adjustment screw having a cylindrical portion with a different outer diameter.

However, the member for adjusting the spring position in the present invention is not

limited to a screw to be inserted into the spring support shaft, and may be an adjustment

pin to be press-fitted into the spring support shaft, for example. In such a case, a

plurality of adjustment pins including a cylindrical portion having different outer

diameters may be provided for adjusting the spring position.

[0063] The cylindrical portion 74b of the adjustment screw 74 in the second

embodiment discussed above is an embodiment of "cylindrical portion" in the present

invention.

[0064] Next, with reference to FIG. 15, a third embodiment of the present

invention will be described. FIG. 15 illustrates the mounting direction of a spring

position adjustment mechanism 90 relative to a cylinder head 80 of an internal

combustion engine. The construction of the spring position adjustment mechanism 90

shown in FIG. 15 is basically the same as that of the spring position adjustment

mechanism 60 discussed above, except for the mounting arrangement to the cylinder

head 80 via the spring support shaft 92, which will be described below.

[0065] As shown in FIG. 15, in this embodiment, the mounting position of the

spring position adjustment mechanism 90 relative to the cylinder head 8O ₅ and the

position of the retention part 92a, or the like, for the lost motion spring 34, or the like, in

the variable valve driving mechanism 20 and the fixed valve driving mechanism 40, are

determined such that the adjustment groove 64c in the adjustment screw 64 for rotational

position adjustment is oriented upwardly of the cylinder head 80. In other words, the

mounting position of the spring position adjustment mechanism 90 and the position of

the retention part 92a are oriented so that the adjustment groove 64c is accessible when

the head cover 82 is removed, and more specifically, is accessible in the substantially

axial direction of the adjustment screw 64 when the head cover 82 is removed.

[0066] According to the construction of the embodiment described above,

workability in adjusting the position of the spring 34, or the like, when the spring 34 is

mounted on the variable valve driving device 1 is improved. Specifically, variations

between cylinders in spring force of the spring 34, or the like, may be easily adjusted

while the torsion spring mounted on the variable valve driving device 1.

[0067] Ih the third embodiment discussed above, the mounting arrangement for

the spring position adjustment mechanism 90 that adjusts the spring position in the same

way as the spring position adjustment mechanism 60 in the first embodiment is described.

However, such a mounting arrangement may not necessarily be applied to a spring

position adjustment mechanism thus constructed, and may also be applied to a spring

position adjustment mechanism that adjusts the spring position in the same way as the

spring position adjustment mechanism 70 in the second embodiment. Specifically, the

mounting position of the spring position adjustment mechanism 70 relative to the

cylinder head 80, and the like, may be determined in such an orientation that as the

adjustment groove 74c is accessible in the substantially axial direction of the adjustment

screw 74 when the head cover 82 is removed.

[0068] In the first to third embodiments discussed above, the lost motion spring

34 is mounted on the spring support shaft 62 that is inserted into its coil portion 34c.

However, the support part for supporting the lost motion spring 34 is not limited to the

spring support shaft 62 or similar structures. Instead, the support part in the present

invention may be a stationary member such as cylinder head or another member fixed to

the stationary member, as long as it can support one arm of a torsion spring.

[0069] Also, in the first to third embodiments discussed above, the oscillating

cam arm 28 of the variable valve driving mechanism 20 and the large lift arm 44 of the

fixed valve driving mechanism 40 serve as examples of the oscillating member to be

impelled toward the driving cam 14 by the lost motion spring 34 for illustrative purposes.

However, the oscillating member that is impelled by a torsion spring in the present

invention is not limited thereto, as long as it needs to be impelled by a torsion spring

when it oscillates within a predetermined oscillating range in order to maintain contact

with a cam. For example, if a valve driving device for an internal combustion engine

includes a valve deactivating mechanism, the oscillating member may be interposed

between a deactivating valve and a cam that oscillates while maintaining contact with the

cam even when the valve is deactivated.