Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2003-02-27
2004-06-29
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090160, C123S090150
Reexamination Certificate
active
06755165
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2002-051439 filed on Feb. 27, 2002, including its specification, drawings and abstract, is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a valve control apparatus and method for an internal combustion engine. More particularly, the invention relates to a valve control apparatus and method provided with means for changing a valve operating characteristic such as valve opening timing (i.e., valve timing), valve lift amount, and open valve period of one or both of an intake valve and an exhaust valve in each cylinder of an internal combustion engine.
2. Description of the Related Art
A valve control apparatus for an internal combustion engine is known that changes an operating characteristic of one or both of an intake valve and an exhaust valve of the internal combustion engine while it is running, so as to enable constant optimal engine performance regardless of the running state of the engine. One known example of this type of valve control apparatus controls one or more of a valve opening and closing timing (i.e., valve timing), a valve lift amount, and an open valve period, and the like of an intake valve and an exhaust valve according to the operating state of the internal combustion engine.
When changing the valve timing, for example, a method is used that changes a relative rotation phase of a camshaft with respect to a crankshaft using a hydraulic actuator or the like. Further, to change the valve lift amount, the open valve period and the like, various methods are used. One method aligns a plurality of cams having profiles with different cam lift amounts and cam operation angles in the axial direction on a camshaft, and switches the cam that drives the valve by moving the camshaft in the axial direction using a hydraulic actuator. Another method changes the valve lift amount and open valve period by providing a cam having a cam profile with a continuous change in the actuation angle and the like, instead of providing a plurality of cams, and moving the camshaft in the axial direction using a hydraulic actuator.
An example of this type of valve control apparatus is disclosed in Japanese Patent Laid-Open Publication No. 6-159021, for example.
The valve control apparatus in the foregoing publication controls the valve timing of an intake valve to an optimal value according to the operating state of the engine. This valve control apparatus is provided with a hydraulic actuator that rotates the camshaft relative to the crankshaft, and an oil control valve able to supply an oil pressure that actuates the hydraulic actuator in a direction to advance the valve timing and an oil pressure that actuates the hydraulic actuator in a direction to retard the valve timing.
Also, the valve control apparatus in the foregoing publication is provided with a cam position sensor that detects a rotation phase difference between the camshaft and the crankshaft. The valve control apparatus calculates the actual valve timing using the cam position detected by the sensor, obtains the difference between a target valve timing set from the operating state of the engine and the actual valve timing that was calculated, and performs feedback control on the oil control valve based on this difference.
For example, this feedback control is made PID control based on the difference, and the opening of the oil control valve is set as the sum of the difference and the components proportional to an integral value and a derivative value of the difference.
According to the apparatus in the publication, the proportional coefficient (i.e., gain) of each of the components of the PID control is set according to the engine speed. Ordinarily, because the oil pressure supplied to the actuator is supplied by an oil pump that is driven by the engine, the discharge pressure of the pump changes according to the engine speed. Therefore, if the gain of each of the components of the PID control are fixed, the response rate of the control may change according to a change in the pump discharge pressure (i.e., the engine speed). Therefore, because the output of the apparatus and the gain of each of the components of the PID control in the foregoing publication are not fixed, but set according to the engine speed, the pressure and amount of oil supplied to the hydraulic actuator can be controlled based on the ability (i.e., discharge pressure, discharge amount) of the engine driven oil pump. Accordingly, consistently stable valve timing control is able to be performed regardless of the engine speed.
By setting the gain of the PID control according to the engine speed, the apparatus disclosed in the aforementioned publication prevents the operation speed of the hydraulic actuator from decreasing by setting the gain large in the low speed region, in which the discharge pressure and discharge amount of the engine driven oil pump decrease, and prevents overshooting and hunting in the control by setting the gain low when the engine is running at high speeds, for example.
With the apparatus disclosed in Japanese Patent Laid-Open Publication No. 6-159021, however, even though control is performed according to the engine speed, there are times, such as when the oil temperature is low when the engine is cold, when the valve operating characteristic is unable to be controlled appropriately.
At times such as when the engine is running but is cold after starting, the temperature of the operating oil supplied to the hydraulic actuator has not risen sufficiently so the viscosity of that operating oil is high. Accordingly, an increase in flow resistance within the oil passages and an increase in friction resistance of the sliding portions, and the like, reduce the operating speed of the hydraulic actuator, thereby lowering the responsiveness in the control over the valve operating characteristic and narrowing the operating range of the hydraulic actuator.
The apparatus in the aforementioned publication compensates for the decrease in oil pressure and oil amount when the engine is running at low speeds by increasing the control gain. However, hydraulic systems and engine driven oil pumps and the like are ordinarily designed so that the discharge pressure and the discharge amount will not change much when the engine speed changes, so changes in the oil pressure and oil amount due to changes in the engine speed are kept comparatively small. In contrast, there are times when the increase in flow resistance and the increase in friction resistance due to increased oil viscosity at low temperatures may become far greater than the increase in flow resistance and the increase in friction resistance due to a change in the engine speed.
Therefore, when attempting to prevent a decrease in control responsiveness by only increasing the control gain when the oil temperature is low, there is a tendency for the increase in the gain to become quite large, which may result in overshooting or hunting or the like, making control unstable. Also, the deterioration in the control accuracy of the actuator due to the increased oil viscosity cannot be corrected by just increasing the gain. Just increasing the gain when the oil temperature is low results in the control becoming unstable, which in turn results in a delay in reaching the target valve operating characteristic, and the like, which ultimately leads to a deterioration in engine performance at low temperatures and a deterioration in the exhaust gas emissions, and the like.
SUMMARY OF THE INVENTION
In view of the foregoing problems, it is an object of the invention to provide a valve control apparatus and method that enables the responsiveness in valve control to be improved without losing stability in the control, even when the engine is cold.
According to a first aspect of the invention, a valve control apparatus is provided which changes a valve operating characteristic of an internal combustion engine, the valve operating characteristic including at l
Kondou Shinya
Koyama Hiroyasu
Denion Thomas
Oliff & Berridg,e PLC
Riddle Kyle
Toyota Jidosha & Kabushiki Kaisha
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