Valve timing control apparatus for internal combustion engine

Details Valve timing control apparatus for internal combustion engine Valve timing control apparatus for internal combustion engine

2002-03-13

2003-09-30

Denion, Thomas (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

C123S090150, C123S090270, C123S090310, C464S002000, C464S160000

Reexamination Certificate

active

06626136

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a valve timing control apparatus for variably controlling at least one of intake valves and exhaust valves of an internal combustion engine, in accordance with an operation state of the engine.
2. Description of the Related Art
Various valve timing control apparatuses have been put into practice which change valve timings of intake valves and exhaust valves in accordance with an operation state of an internal combustion engine. Further, Japanese Patent Publication Laid-Open No. HEI 9-324613 discloses a valve timing control apparatus employing vanes equipped with a lock pin. The outline of the valve timing control apparatus disclosed in this publication will be described with reference to
FIGS. 11 and 12
.
FIG. 11
schematically shows the structure of the valve timing control apparatus. As shown in
FIG. 11
, the valve timing control apparatus is composed of a variable valve timing mechanism (VVT)
212
, an oil control valve (OCV)
240
, an engine control unit (not shown) and the like. The engine control unit drive-controls the OCV
240
in accordance with operation control of the engine, thereby variably controlling the VVT
212
.
FIG. 12
shows in cross section the structure of the VVT
212
. The VVT
212
is provided on an intake-side cam shaft
211
(FIG.
11
). The VVT
212
is composed of a housing
216
integrated with a sprocket
217
, a rotor
219
incorporated in the housing
216
and the sprocket
217
, a rear plate
214
(FIG.
11
), and a front cover
220
(
FIG. 11
) for covering a front face of the housing
216
. The rotor
219
, the rear plate
214
and the like are coupled to the intake-side cam shaft
211
by means of bolts or the like such that they can rotate integrally. Further, as shown in
FIG. 12
, the rotor
219
is provided with four vanes
224
that are arranged at equal intervals along an outer circumference thereof and project radially.
On the other hand, in the aforementioned VVT
212
, the sprocket
217
has a substantially cylindrical shape and is disposed on the outer circumference of the rear plate
214
. The sprocket
217
is supported such that it can rotate relative to the rear plate
214
and the intake-side cam shaft
211
. The sprocket
217
is drivingly coupled to a crank shaft (not shown). When the engine is started (comes into operation), the sprocket
217
rotates clockwise in
FIG. 12
in response to rotation of the crank shaft.
Further, the housing
216
, which is integrated with the sprocket
217
, is provided with four protruding portions
225
, which are arranged at equal intervals. Four concave portions
226
are provided to accommodate the vanes
224
of the rotor
219
, and each of the concave-portions
226
is formed between adjacent ones of the protruding portions
225
. With each of the vanes
224
being disposed in a corresponding one of the concave portions
226
, an advancement hydraulic chamber
230
and a retardation hydraulic chamber
231
are formed on opposite sides of each of the vanes
224
.
In a state where oil is supplied to both the hydraulic chambers
230
and
231
, the rotor
219
and the sprocket
217
are coupled to each other at a relative angle corresponding to a pressure balance of the oil. In response to rotation of the sprocket
217
, the rotor
219
and the cam shaft
211
are rotated.
If the pressure in the retardation hydraulic chamber
231
becomes higher than the pressure in the advancement hydraulic chamber
230
, the vanes
224
rotate counterclockwise in FIG.
12
. Then, each of the vanes
224
comes into abutment on one of the inner walls of a corresponding one of the protruding portions
225
. In this state, the cam shaft
211
is in its most receded position with respect to the crank shaft. At this moment, the valve timing of intake valves (not shown), which are driven in response to rotation of the cam shaft
211
, is also most retarded. Conversely, if the pressure in the advancement hydraulic chamber
230
becomes higher than the pressure in the retardation hydraulic chamber
231
, the vanes
224
rotate clockwise in FIG.
12
. Then, each of the vanes
224
comes into abutment on the other of the inner walls of a corresponding one of the protruding portions
225
. In this state, the cam shaft
211
is in its most advanced position with respect to the crank shaft. At this moment, the valve timing of the intake valves (not shown), which are driven in response to rotation of the cam shaft
211
, is also most advanced.
The VVT
212
is provided with a lock mechanism employing a lock pin. This lock mechanism will now be described.
As shown in
FIG. 12
, an accommodation hole
232
, which extends parallel to the axis of the cam shaft
211
, is formed in one of the protruding portions
225
within the housing
216
. A lock pin
233
is slidably accommodated in the accommodation hole
232
. A lock recess portion
234
(FIG.
11
), which is opposed to the accommodation hole
232
, is formed in the rear plate
214
.
Further, a ring-like hydraulic chamber
249
is formed in the accommodation hole
232
. The pressure of the oil supplied to the hydraulic chamber
249
acts on the lock pin
233
. For this purpose, the oil supplied to the advancement hydraulic chamber
230
or the retardation hydraulic chamber
231
is used. The lock pin
233
is constantly urged in such a direction as to engage the lock recess portion
234
by a spring
235
, which is interposed between the lock pin
233
and the front cover
220
.
Accordingly, in the case where the force acting on the lock pin
233
based on an oil pressure becomes smaller than an urging force of the spring
235
, for example, in stopping or starting the engine, the lock pin
233
engages the lock recess portion
234
of the rear plate
214
at a predetermined angle relative to the sprocket
217
. At this moment, the sprocket
217
is mechanically coupled to the rear plate
214
. Then, the rotor
219
and the sprocket
217
rotate integrally, for example, at a predetermined relative angle &bgr; as shown in FIG.
12
. That is, each of the vanes
224
is advanced from the most retarded position by the predetermined angle &bgr;.
On the contrary, in the case where the force acting on the lock pin
233
based on an oil pressure becomes greater than an urging force of the spring
235
, for example, during operation of the engine, the lock pin
233
is released from the lock recess portion
234
. Then, relative rotation between the sprocket
217
and the rear plate
214
, namely, between the sprocket
217
and the rotor
219
is permitted.
In this valve timing control apparatus, the relative angle between the rotor
219
and the sprocket
217
at the time of engagement of the lock pin
233
with the lock recess portion
234
is selected so as to correspond to a valve timing that does not adversely affect startability of the engine. By selecting the relative angle between the two members, as it were, as an intermediate phase, the variable valve timing zone can be enlarged in response to assurance of startability of the engine.
In this manner, by setting the phase between the rotor
219
and the sprocket
217
at the time of engagement of the lock pin
233
with the lock recess portion
234
to the aforementioned intermediate phase, desirable characteristics of the valve timing control apparatus such as assurance of startability of the engine, enlargement of the variable valve timing zone, and the like can be obtained. However, an apparatus that performs the aforementioned phase control or operation control of the lock pin
233
using a hydraulic pressure in the engine cannot avoid the following inconveniences.
That is, according to the aforementioned valve timing control apparatus, in a state where the hydraulic pressure is low in stopping or starting the engine, appropriate engagement of the lock pin
233
cannot be achieved. In other words, the controllability in the aforementioned intermediate phase deteriorates significantly.
SUMMARY OF THE INVENTION
It is an object o

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