Internal-combustion engines – Vibration compensating device – Balancing arrangement
Reexamination Certificate
2001-06-22
2003-09-30
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Vibration compensating device
Balancing arrangement
C464S180000
Reexamination Certificate
active
06626139
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gear mechanism of a power transmitting system that is favorably used as a balancer apparatus of an internal combustion engine.
2. Discussion of Related Art
As well known in the art, in a balancer apparatus of an internal combustion engine, a balance shaft provided with an unbalance weight is operatively coupled with a crankshaft via a gear mechanism, whereby rotational force of the crankshaft is transmitted to the balance shaft. In the balancer apparatus, the balance shaft rotates in synchronization with the crankshaft, whereby inertial force generated by reciprocation of an engine piston is cancelled, and vibration of the engine is accordingly reduced.
Since explosive combustion in the internal combustion engine takes place intermittently, the magnitude of the rotational force transmitted from the crankshaft to the balance shaft is not constant or fixed, but rather is always fluctuating.
The inventors have confirmed that, among frequency components included in the fluctuations of the rotational force, a secondary component of a fundamental frequency that results from engine combustion occurring once in every two rotations of the crankshaft, and a sextic component that is amplified by torsional resonance of the crankshaft are relatively large compared to a component (primary component) of the fundamental frequency that is determined according to the speed of rotation of the crankshaft.
The balancer apparatus receives the rotational force including the vibration components of different frequencies as described above, and therefore vibration occurs in the gear mechanism, in particular, in a meshing portion(s) of the gears. Such vibration may result in generation of noise and reduction in the durability of the gears.
Thus, a balancer apparatus has been proposed wherein a damping mechanism formed by, for example, a spring or springs is inserted in a rotational-force transmission path from the crankshaft to the balance shaft so as to damp the vibration components of the rotational force.
In order to effectively damp a high-frequency component of the fluctuations in the rotational force, such as the sextic component of the fundamental frequency, by using the damping mechanism, the spring constant of the spring(s) must be set to a sufficiently low value so as to reduce the natural frequency of a vibration system formed by the balancer apparatus. However, if the spring constant is merely set to a low value, the spring(s) may be excessively deformed in response to a rapid increase in the rotational force transmitted from the crankshaft upon, for example, acceleration of the engine. Thus, the damping mechanism may be damaged due to the deformation. Moreover, characteristics of the spring may be substantially lost by so-called bottoming or the like, whereby the damping mechanism may cease to function properly.
In view of the above situation, a balancer apparatus in which a damping mechanism provides non-linear spring characteristics has been proposed in, for example, Japanese Laid-Open Patent Publication No. 60-192145.
FIG. 22
shows a cross-sectional structure of a main part of one example of the balancer apparatus. As shown in
FIG. 22
, the balancer apparatus includes a rotary shaft
100
operatively coupled with a balance shaft (not shown), and a generally cylindrical gear
110
that surrounds the outer periphery of the rotary shaft
100
and operatively coupled with a crankshaft (not shown). The rotary shaft
100
has a plurality of radially protruding driving pieces
102
formed on its outer periphery. The gear
110
also has a plurality of radially protruding driving pieces
112
formed on its inner periphery so as to be located between the corresponding driving pieces
102
of the rotary shaft
100
.
Damper chambers
120
are formed between the respective driving pieces
102
of the rotary shaft
100
and the corresponding driving pieces
112
of the gear
110
, and an elastic member
130
is disposed in each damper chamber
120
. Moreover, clearances
132
are formed between each elastic member
130
and the corresponding driving pieces
102
and
112
. In the balancer apparatus thus constructed, the driving pieces
102
and
112
and the elastic members
130
form the damping mechanism.
The operation of the damping mechanism will be now described. As the rotary shaft
100
rotates relative to the gear
110
, the clearances
132
are reduced, and the driving pieces
102
and
112
then abut on the respective elastic members
130
. As the rotary shaft
100
further rotates relative to the gear
110
, the elastic members
130
are elastically deformed, thereby generating elastic force according to the amount of relative rotation. This elastic force (more specifically, torque based on this elastic force) acts against the relative rotation between the rotary shaft
100
and the gear
110
.
Referring to
FIG. 23
, the solid line indicates the relationship between the angle &thgr;r of the relative rotation between the rotary shaft
100
and the gear
110
and the elastic force (torque) T. The two-dot chain line indicates the relationship between the relative rotational angle &thgr;r and the elastic force T in a comparative example. In the comparative example, the clearances
132
are not formed, and the natural frequency of the vibration system is reduced merely by setting the spring constant of the elastic members
130
to a low value.
As indicated by the solid line of
FIG. 23
, when the relative rotational angle &thgr;r is within a predetermined rotational phase range or angle (&thgr;r<&thgr;
1
), the elastic members
130
are not elastically deformed, whereby the elastic force T is “zero”. Thus, by forming the clearances
132
between each driving piece
102
,
112
and the corresponding elastic members
130
so as to provide a relative rotational phase range in which the elastic force T is not produced, the natural frequency of the vibration system formed by the balancer apparatus can be reduced without significantly reducing the spring constant of the elastic members
130
.
When the rotary shaft
100
and the gear
110
rotate relative to each other beyond the predetermined rotational angle (&thgr;r>&thgr;
1
), the elastic force T increases with the relative rotational angle &thgr;r. As compared with the comparative example, the relative rotational angle &thgr;r is limited to a relatively small value even when the elastic force T becomes extremely large (T=Tmax), that is, when the rotational force transmitted from the crankshaft to the balancer apparatus becomes extremely large (&thgr;max
1
<&thgr;max
2
). Thus, the elastic members
130
are not excessively deformed.
Thus, according to the balancer apparatus, a high-frequency component of the fluctuation in rotational force can be damped without causing any damage and deterioration in the function of the damping mechanism when the rotational force from the crankshaft rapidly increases upon, for example, acceleration of the engine.
Such a damping mechanism having a non-linear spring characteristic can certainly reduce the natural frequency of the vibration system formed by the balancer apparatus, and damp the high-frequency component of the fluctuations in the rotational force, while avoiding any damage and deterioration in the function of the damping mechanism.
However, the reduction in the natural frequency of the vibration system may cause a problem as follows: the natural frequency is reduced to be equal to a frequency that is close to that of a low-frequency component, such as the secondary component of the fundamental frequency of the engine, which is included in the fluctuations in the rotational force. As a result, a resonance phenomenon occurs in the balancer apparatus due to the low-frequency component of the fluctuations in rotational force. Thus, vibration resulting from the resonance phenomenon cannot be prevented.
The aforementioned problem occurs not only in the above-described balancer apparatus of the interna
Hori Kouhei
Horita Yuji
Hosoi Hiroshi
Ishikawa Makoto
Kamen Noah P.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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