Control device and method for variable valve mechanism

Abstract

A control device for a variable valve mechanism that avoids the overheating an actuator while reducing adverse effects on the driveability of a vehicle. The actuator adjusts the lift of an intake valve by moving a drive element, and a sensor is used to determine whether the actuator will overheat. A control unit stops the drive element if the lift adjusted by the actuator is equal to or larger than a first predetermined value, when the control unit determines that the actuator will overheat. The actuator may be an electric actuator. In this case, the actuator maintains the drive element in a fixed position when supply of electric power to the actuator is interrupted. The control unit stops the drive element, and interrupts the supply of electric power to the actuator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a diagram showing the configuration of an engine according to an embodiment of the invention;

FIG. 2 is a diagram showing the relation between a valve lift and a crank angle in a variable valve mechanism;

FIG. 3 is a front view showing a VVL mechanism that controls the lift and duration of an intake valve;

FIG. 4 is a cutaway view partially showing the VVL mechanism;

FIG. 5 is a sectional view showing an actuator that linearly moves the drive shaft of the VVL mechanism in an axial direction;

FIG. 6 is an enlarged view showing the detail of the VI portion of the actuator in FIG. 5;

FIG. 7 is a waveform diagram explaining the operation for avoiding the overheating of the actuator;

FIG. 8 is a flowchart explaining the control of the actuator, which is executed by a control unit; and

FIG. 9 is a flowchart showing a modified example of the control shown by the flowchart in FIG. 8.

Claims

1. A control device for a variable valve mechanism comprising: a drive element, provided in the variable valve mechanism that determines a lift of at least one of an intake valve and an exhaust valve in an internal combustion engine;an actuator that adjusts the lift of the at least one of an intake valve and an exhaust valve by moving the drive element in a variable valve control;a sensor used to determine whether the actuator will overheat; anda control unit that ends the variable valve control and stops the drive element if the lift adjusted by the actuator is equal to or larger than a first predetermined value, when the control unit determines that the actuator will overheat.

2. The control device for the variable valve mechanism according to claim 1, wherein the actuator is an electric actuator;the actuator maintains the drive element in a fixed position when supply of electric power to the actuator is interrupted; andwherein the control unit further interrupts the supply of electric power to the actuator.

3. The control device for the variable valve mechanism according to claim 2, further comprising: a sensor, provided in the variable valve mechanism, that detects changes in the position of the drive element; andwherein the sensor outputs signals indicating the position of the drive element, and the control unit restarts the supply of electric power to the actuator when the position of the drive element deviates from the fixed position by at least a second predetermined value during the supply of electric power to the actuator is interrupted.

4. The control device for the variable valve mechanism according to claim 2, wherein the control unit restarts the supply of electric power to the actuator when the variable valve mechanism satisfies a condition for restarting operation of the actuator; wherein operation of the actuator restarts when the temperature of the actuator has decreased to a temperature that is equal to or below a threshold temperature at which the operation of the actuator is stopped.

5. The control device for the variable valve mechanism according to claim 2, wherein the control unit executes a control to fix the position of the drive element, immediately after the supply of electric power to the actuator restarts.

6. The control device for the variable valve mechanism according to claim 5, wherein the control unit executes the control to fix the position of the drive element during the supply of electric power to the actuator restarts, andthe control unit executes the variable valve control to change the position of the drive element using the actuator when a request relating to an operation of an internal combustion engine satisfies a condition for resuming the variable valve control.

7. The control device for the variable valve mechanism according to claim 6, wherein the condition for resuming the variable valve control is satisfied when a driver requests acceleration.

8. The control device for the variable valve mechanism according to claim 6, wherein the condition for resuming the variable valve control is satisfied when a difference between a position of the drive element, which is estimated on an assumption that the variable valve control is executed, and the fixed position of the drive element is equal to or smaller than a predetermined amount.

9. The control device for the variable valve mechanism according to claim 1, wherein the variable valve mechanism increases the lift, and a duration that represents a period in which the at least one of the intake valve and the exhaust valve is held open in terms of crank angle, by moving the drive element.

10. A method of controlling a variable valve mechanism comprising: determining whether a lift of at least one of an intake valve and an exhaust valve in an internal combustion engine, determined by a drive element provided in the variable valve mechanism, is equal to or larger than a first predetermined value;monitoring the temperature of an actuator, which adjusts the lift of the at least one of the intake valve and the exhaust valve by moving a drive element; andstopping the drive element if the temperature of the actuator indicates the actuator may overheat and the lift adjusted by the actuator is equal to or larger than the first predetermined value.