Variable valve timing apparatus

Details Variable valve timing apparatus Variable valve timing apparatus

1999-02-16

2001-06-12

Lo, Weilun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

C123S090180

Reexamination Certificate

active

06244230

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to variable valve timing apparatuses that are employed in engines. More particularly, the present invention relates to a variable timing apparatus that includes a phase adjustor and a lift adjustor for controlling the valve timing of intake valves and exhaust valves with cams.
Engine variable valve timing apparatuses control the valve timing of intake valves and exhaust valves in accordance with the operating state of the engine. A variable valve timing apparatus generally includes a timing pulley and a sprocket, which synchronously rotate a camshaft with a crankshaft.
Japanese Unexamined Patent Publication No. 9-60508 describes a typical variable timing apparatus, which is represented by
FIGS. 18
,
19
, and
20
. The variable valve timing apparatus includes a phase adjustor, or first actuator, arranged on one end of a camshaft
1202
.
FIG. 18
is a cross-sectional view taken along line
18
—
18
in
FIG. 19
, while
FIG. 19
is a cross-sectional view taken along line
19
—
19
in FIG.
18
.
FIG. 20
is a cross-sectional view taken along line
20
—
20
in FIG.
19
.
A sprocket
1204
, which is driven by a crankshaft (not shown), is integrally coupled with a housing
1206
. A vane rotor
1208
is arranged in the center of the housing
1206
and secured to the end of the camshaft
1202
to rotate integrally with the camshaft
1202
.
Vanes
1210
project outward from the hub of the vane rotor
1208
to contact the inner wall of the housing
1206
. Partititions
1212
project inward from the housing
1206
to contact the hub surface of the vane rotor
1208
. Cavities
1214
are defined between the partitions
1212
. A first pressure chamber
1216
and a second pressure chamber
1218
are defined in each cavity
1214
between each vane
1210
and the partitions
1212
.
Hydraulic fluid is delivered to the first and second pressure chambers
1216
,
1218
to rotate the vane rotor
1208
relative to the housing
1206
. As a result, the rotational phase of the vane rotor
1208
relative to the housing
1206
is adjusted. This, in turn, adjusts the rotational phase of the camshaft
2102
relative to the crankshaft and varies the valve timing of the intake valves or exhaust valves.
The camshaft
1202
has a journal
1224
, which is supported by a bearing
1222
formed in a cylinder head of the engine. An oil channel, which is connected with a hydraulic unit
1220
, extends through the cylinder head and connects to an oil groove
1226
extending along the peripheral surface of the camshaft journal
1224
. The oil groove
1226
is connected to oil conduits
1227
,
1228
, which extend through the camshaft
1202
. The oil conduit
1228
is further connected to oil conduits
1230
,
1232
, which extend through the vane rotor
1208
and lead into the first pressure chambers
1216
. Accordingly, hydraulic fluid is forced from the hydraulic unit
1220
to the first pressure chambers
1216
through the oil channel, the oil groove
1226
and the oil conduits
1227
,
1228
,
1230
,
1232
. A further oil channel, which is connected with the hydraulic unit
1220
, extends through the cylinder head and connects to an oil groove
1236
, which extends along peripheral surface of the journal
1224
. The oil groove
1236
is connected to an oil conduit
1238
, which extends through the camshaft
1202
. The oil conduit
1238
is further connected to oil conduits
1240
,
1242
,
1244
, which extend through the vane rotor
1208
and lead into the second pressure chambers
1218
. Accordingly, hydraulic pressure is communicated between the hydraulic unit
1220
and the second pressure chambers
1218
through the oil channel, the oil groove
1236
, and the oil conduits
1238
,
1240
,
1242
,
1244
.
In addition to the first actuator, a lift adjustor, or second actuator, employed in a variable valve timing apparatus to change the lift amount and timing of intake or exhaust valves with a three-dimensional cam, is also known in the prior art. Japanese Unexamined Patent Publication No. 9-32519 describes a typical second actuator, which is represented by FIG.
21
. Three-dimensional cams
1302
are arranged on a camshaft
1304
. A timing pulley
1306
is arranged on one end of the camshaft
1304
. The timing pulley
1306
is supported such that it slides axially along and rotates integrally with the camshaft
1304
. A cylinder
1308
is arranged on one side of the timing pulley
1306
. A piston
1310
, secured to the end of the camshaft
1304
, is fitted into the cylinder
1308
. A pressure chamber
1312
is defined between one side of the piston
1310
and the inner wall of the cylinder
1308
. A compressed spring
1314
is arranged between the other side of the piston
1310
and the timing pulley
1306
. When the pressure in the pressure chamber
1312
is high, the piston
1310
urges the camshaft
304
against the force of the spring
1314
toward the right (as viewed in FIG.
21
). When the pressure in the pressure chamber
1312
is low, the spring
1314
pushes the piston
1310
and forces the camshaft
1304
toward the left.
Hydraulic fluid is delivered to the pressure chamber
1312
from an oil control valve
1318
through oil conduits
1322
,
1324
, which extend through a bearing
1320
, oil conduits
1326
,
1328
, which extend through the camshaft
1304
, and an oil conduit
1332
, which extends through a bolt
1330
. The bolt
1330
fastens the piston
1310
to the camshaft
1304
. A microcomputer
1316
controls the oil control valve
1318
to adjust the hydraulic pressure in the pressure chamber
1312
and change the axial position of the camshaft
1304
.
Accordingly, the position of contact between each three-dimensional cam
1302
and the associated valve lift mechanism is adjusted to vary the opening duration of a corresponding intake valve or exhaust valve in accordance with the profile of the cam
1302
. This varies the valve timing.
When changing the rotational phase of a camshaft relative to a crankshaft with the prior art first actuator to vary the valve timing, the opening and closing timing of the valves are both varied in the same manner. That is, if the opening timing is advanced, the closing timing is advanced accordingly, and if the opening timing is retarded, the closing timing is retarded accordingly. On the other hand, when changing the lift amount of the valves with the prior art second actuator to vary the valve timing, the opening timing and closing timing of the valves vary inversely at the same rate. That is, if the opening timing is retarded by a certain rate, the closing timing is advanced by the same rate, and if the opening timing is advanced by a certain rate, the closing timing is retarded by the same rate. Therefore, the opening and closing timing of the valves cannot be independently varied. This limits the control of the valve timing.
To solve this problem, the first actuator and the second actuator can be arranged together on a camshaft to adjust both the rotational phase of a camshaft relative to a crankshaft and the lift amount of the valves. This would reduce the limitations on the opening and closing timing control.
For example, as shown in
FIG. 22
, which illustrates an intake camshaft
1402
and an exhaust camshaft
1404
, a first actuator
1408
may be arranged on one end of the intake camshaft
1402
, and a second actuator
1410
may be arranged on the other end of the intake camshaft
1402
. The first actuator
1408
includes a timing sprocket
1406
.
However, the structure formed by installing the first actuator
1408
and the second actuator
1410
on the same intake camshaft
1402
results in a longer camshaft
1402
. This would also increase the size of the engine and occupy more space in the engine compartment, and space is very limited.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide a variable valve timing apparatus employing a phase adjustor and a lift adjustor that enables unlimited control of the valve timing without occupying additional spa

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