Internal-combustion engines – Poppet valve operating mechanism – Electrical system
Reexamination Certificate
2000-11-28
2001-12-25
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Electrical system
C251S129010, C251S129160
Reexamination Certificate
active
06332436
ABSTRACT:
The present invention relates to a method for the control of electromagnetic actuators for the actuation of intake and exhaust valves in internal combustion engines.
BACKGROUND OF THE INVENTION
As is known, drive units are currently being tested in which the actuation of the intake and exhaust valves is managed by using actuators of electromagnetic type that replace purely mechanical distribution systems (camshafts). While conventional distribution systems make it necessary to define a valve lift profile that represents an acceptable compromise between all the possible operating conditions of the engine, the use of an electromagnetically controlled distribution system makes it possible to vary the phasing as a function of the engine point in order to obtain an optimum performance in any operating condition.
The increase in efficiency and the actual savings resulting from the use of actuators of electromagnetic type are closely linked to the systems and methods used for the control of these actuators.
According to known methods, based for instance on open loop control systems, when each valve is opened or closed, the corresponding actuators are supplied with currents and/or voltages of a value such as to ensure that the valve, irrespective of the resistance opposing it, reaches the desired position within a predetermined time interval.
These methods have some drawbacks.
In the first place, the valves are subject to impacts each time that they come into contact with fixed members in the position of maximum opening (lower contact) or in the closed position (upper contact). This is particularly critical, since the valves are subject to an extremely high number of opening and closing cycles and therefore wear very rapidly.
The fact that the electrical power supplied must always be sufficient to overcome the maximum resistance that the valve may encounter, even though the operating conditions are such that the actual resistance opposing the valve is lower, is also a drawback. In this way, the overall efficiency of the drive unit is reduced as a result of the waste of electrical power.
It is also particularly important that a robust control is implemented so as to enable the intake and exhaust valves to be actuated according to desired movement and timing profiles, irrespective of the disturbances that take place and cause the actual operating conditions to deviate from the nominal conditions. The occurrence of a wide range of phenomena may make the actual operating conditions extremely variable.
For instance, engine temperature variations cause expansions and contractions of materials, as a result of which the friction encountered by the valves may change. Moreover, since the force applied to the ferromagnetic members on which the electromagnets act depends in a highly non-linear manner on the distance between these ferromagnetic members and the polar heads, it will be appreciated that the volume variations caused by heat gradients may have an adverse effect on the control. Further disturbances are due to the fact that the resistance encountered by the valves also depends on the pressure in the combustion chamber which varies depending, for instance, on the torque and power requirement of the consumer and on the engine control strategies implemented.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method for the control of electromagnetic actuators that is free from the above-described drawbacks and, in particular, has a reduced sensitivity to disturbances, making it possible to improve the overall efficiency of the drive unit.
The present invention therefore relates to a method for the control of electromagnetic actuators for the actuation of intake and exhaust valves in internal combustion engines, in which an actuator, connected to a control unit, is coupled to a respective valve and comprises a moving member actuated magnetically, by means of a net force, in order to control the movement of the valve between a closed position and a position of maximum opening and an elastic member adapted to maintain the valve in a rest position, which method comprises the stages of
a) detecting an actual position Z and an actual velocity V of the valve;
b) determining a reference position Z
R
and a reference velocity V
R
of this valve;
c) determining, by a feedback control action, an objective force value of this net force to be exerted on the moving ferromagnetic member as a function of the reference position Z
R
, the actual position Z, the reference velocity V
R
and the actual velocity V in order to minimise differences between the actual position Z and the reference position Z
R
and between the actual velocity V and the reference velocity V
R
, which method is characterised in that it comprises the stages of:
d) estimating disturbing forces acting on the valve,
e) calculating an actual force as a function of the objective force value and these disturbing forces,
f) implementing this actual force value F
E
.
REFERENCES:
patent: 5988123 (1999-11-01), Miyoshi et al.
patent: 6152094 (2000-11-01), Kirschbaum
patent: 6234122 (2001-05-01), Kirschbaum et al.
Burgio Gilberto
Di Lieto Nicola
Flora Roberto
Arent Fox Kintner & Plotkin & Kahn, PLLC
Lo Weilun
Magneti Marelli S.p.A.
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