Valve timing control system for internal combustion engine

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

1999-11-03

2001-09-04

Lo, Wellun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

C123S090170

Reexamination Certificate

active

06283074

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a valve timing control system for an internal combustion engine, which is for controlling the valve timing of the internal combustion engine.
2. Description of the Related Art
FIG. 12
is a conceptual illustration of a configuration of an internal combustion engine including a valve timing mechanism, disclosed in Japanese Patent Application Laid-open No. 6-299876.
As
FIG. 12
shows, an internal combustion engine
1
, including a conventional valve timing control system, is equipped with an air cleaner
2
, an air flow sensor
3
, a throttle valve
4
, a throttle sensor
5
, an intake pipe
6
, an injector
7
, an ignition plug
8
, an exhaust pipe
9
, an O
2
sensor
10
, a catalytic converter
11
, a sensor plate
12
, a crank angle sensor
13
, a sensor plate
14
, a cam angle sensor
15
, an oil control valve
16
, an ECU
17
and an ignition coil
18
.
Moreover, as shown in
FIG. 13
, a housing
21
, a rotor
22
, a retarding chamber
23
, and an advancing chamber
24
constitute a VVT (Variable Valve Timing) actuator
20
.
The air cleaner
2
is installed at an opening of the intake pipe
6
to clean the air the internal combustion engine
1
intakes. The air flow sensor
3
is installed on the downstream side of the air cleaner
2
to sense the air intake amount into the internal combustion engine
1
. The throttle valve
4
is opened and closed in connection with the accelerator pedal to adjust the air intake amount. The throttle sensor
5
detects the opening degree of the throttle valve
4
.
In such an internal combustion engine, when the driver steps on the accelerator pedal, the throttle valve
4
opens/closes, so that air is mixed with a fuel injected from the injector
7
and this air-fuel mixture is introduced into cylinders. The air-fuel mixture is then ignited by the ignition plug
8
to push the pistons downward by the combustion thereof, thereby causing the crank shaft to rotate. The rotation of the crank shaft is derived as the output of the internal combustion engine.
With this operation of the internal combustion engine, the O
2
sensor
10
detects the residual oxygen amount in the exhaust gas. The catalytic converter
11
simultaneously removes THC, CO and NOx which are harmful gases.
FIGS. 14 and 13
are enlarged illustrations of an essential portion of the VVT actuator.
In
FIG. 13
, the VVT (Variable Valve Timing) actuator
20
is situated on the intake side, and is composed of the housing
21
, the rotor
22
, the retarding chamber
23
and the advancing chamber
24
.
The rotor
22
is fixedly fitted on a cam shaft (not shown) to keep a constant positional relationship (for example, the positional relationship shown in
FIG. 13
) with respect to the housing
21
.
A timing belt, timing chain or the like (not shown) is set on the housing
21
. This timing belt or the like is also placed on a crank shaft (not shown).
With this structure, the rotation of the crank shaft causes the rotation of the cam shaft through the timing belt or the like.
Furthermore, the oil control valve
16
controls the oil pressure to be applied to the VVT actuator
20
fitted to the cam shaft.
Thus, in order to vary the valve timing in the internal combustion engine, the ECU
17
controls the VVT actuator
20
through the oil control valve
16
to adjust the amount of the lubricating oil to be supplied to the retarding chamber
23
and the advancing chamber
24
.
The ECU
17
shifts the relative position of the rotor
22
with respect to the housing
21
, for example, from the position shown in
FIG. 13
to the position shown in
FIG. 14
, thereby changing the valve timing.
FIG. 15
is a graph showing the characteristics of the relationship between valve timing and valve overlap. In this case, the term “valve overlap” signifies the overlap between the time period during which the intake valve is in the open condition and the time period during which the exhaust valve is in the open condition.
For instance, in order to retard the valve timing of the intake valve, the oil control valve
16
supplies the oil to the retarding chamber
23
. At this time, the rotor
22
is rotated counterclockwise with respect to the housing
21
, and the valve timing of the intake valve is retarded (in the direction indicated by arrow A in FIG.
15
), so that the valve overlap decreases.
On the other hand, if the valve timing of the intake valve is advanced (in the direction indicated by the arrow B in FIG.
15
), the valve overlap increases.
Furthermore, in the case of retarding the valve timing of the intake valve to a maximum, the housing
21
is brought into contact with the rotor
22
and is fixed at the position (see
FIG. 14
) where it stops mechanically, this being the position where the valve overlap assumes the minimum value.
In the following description, the advance amount in the case where the valve timing of the intake valve assumes this position will be referred to as a maximum retardation value, and in this case the valve timing of the intake valve is expressed as being at the maximum retardation position.
In the valve timing control for the internal combustion engine, the substantial advance amount (which will be referred to hereinafter as a VVT control variable) by the VVT mechanism is determined with the aforesaid maximum retardation value being employed as a reference. Moreover, this valve timing control is implemented by the ECU
17
. The optimal valve timing required for the internal combustion engine varies according to the operating conditions. Therefore, the ECU
17
always controls the valve timing according to the operational conditions.
For instance, a ROM of the ECU
17
retains a two-dimensional map for determining a required advance amount on the basis of the engine speed detected by the crank angle sensor
13
and the charging efficiency of the engine.
Thus, the ECU
17
controls the valve timing so that the VVT controlled amount (variable) coincides with the required advance amount obtained from the two-dimensional map on the basis of the engine speed and the intake amount.
As mentioned above, the required advance amount is stored in the form of a deviation of the advance amount from the maximum retardation value employed as a reference, and signifies a required VVT control variable. Accordingly, if the required advance amount is zero, the ECU
17
carries out control so that the VVT control variable assumes zero, with the valve timing being set to the maximum retardation side.
Next, a description will be made hereinbelow of a valve timing detecting device.
The sensor plate
12
and the sensor plate
14
are axially fixed on the crank shaft and the cam shaft, respectively. Projections are formed on outer circumferences of the sensor plates
12
,
14
.
Furthermore, in the vicinity of the sensor plates
12
,
14
, the crank angle sensor
13
and the cam angle sensor
15
are located facing the outer circumferences thereof, respectively. The crank angle sensor
13
and the cam angle sensor
15
detect as variations of magnetic fields, the variations in the distance between the crank angle sensor
13
and the sensor plate
12
and the variations in the distance between the cam angle sensor
15
and the sensor plate
14
, occurring with rotation of the sensor plates
12
,
14
respectively.
Thus, with the rotation of the crank shaft and the cam shaft, the sensor plates
12
,
14
rotate, and the crank angle sensor
13
and the cam angle sensor
15
sense the projections on the outer circumferences thereof to thereby detect a crank angle and a cam angle, respectively.
FIG. 16
is a flow chart showing the contents of the processing in a conventional valve timing control system for an internal combustion engine.
First, the operational flow starts at a step
1601
to check, on the basis of coolant temperature (cooling water temperature) in the internal combustion engine
1
, whether the warming-up of the internal combustion engine
1
has been completed or not. If a decision in this step

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