Control system and method for an internal combustion engine

A control method for an internal combustion engine having a variable valve operating mechanism capable of varying at least one of a valve lift and an operation angle continuously, the method comprising:

• detecting an operating condition of the variable valve operating mechanism and producing a signal representative thereof by means of a detecting device;
• and
• controlling the operating condition of the variable valve operating mechanism in response to the signal from the detecting device;
• the controlling including determining whether an operation responsiveness of the variable valve operating mechanism is lowered based on the signal from the detecting device and varying operational characteristics of the variable valve operating mechanism when the operation responsiveness of the variable valve operating mechanism is lowered;
• wherein the variable valve operating mechanism includes an actuator and a control shaft that is driven by the actuator so as to vary in a rotational angle thereof and thereby variably control one of the valve lift and the operation angle, and the controlling comprises determining whether the operation responsiveness of the variable valve operating mechanism is lowered based on a holding energy of the actuator for holding the control shaft at a target rotational angle when a target rotational angle of the control shaft is held constant for a predetermined period of time.

A control system for an internal combustion engine having a variable valve operating mechanism which is driven by an electric motor to vary valve lift characteristics, comprising:

• a detecting device which detects an electric energy consumed by the electric motor;
• and
• a controller programmed to:
• determine a target of the valve lift characteristics in accordance with an engine operating condition;
• control the electric motor so as to achieve the target;
• determine whether an operation responsiveness of the variable valve operating mechanism is lowered based on the electric energy for holding actual valve lift characteristics at the target;
• and
• vary the target when the operation responsiveness is lowered.