Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
1999-04-01
2001-02-06
Wolfe, Willis R. (Department: 3748)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
Reexamination Certificate
active
06182645
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of the priority document Japanese Patent Application No. HEI 10-165229 filed on Jun. 12, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas recirculation control apparatus for an internal combustion engine for adjusting an amount of exhaust gas recirculated to an intake passage through an exhaust gas recirculation passage of an internal combustion engine, and more particularly, to a preferable control structure employed to an apparatus having an outward opening type exhaust gas recirculation control valve which is opened by lifting a valve element from an intake passage side to an exhaust passage side of an exhaust gas recirculation passage.
2. Description of the Related Art
Conventionally, in order to satisfy emission control requirements or to enhance fuel efficiency, exhaust gas recirculation (EGR) control is conducted to recirculate to an intake passage a portion of exhaust gas discharged from an internal combustion engine to lower a temperature of combustion gas. In an internal combustion engine conducting EGR control, an EGR passage is provided for bringing the exhaust passage and the intake passage into communication, and an amount of recirculated exhaust gas is controlled based on adjustment of opening degree of an EGR control valve provided in the EGR passage.
One of such EGR control apparatuses is described in Japanese Patent Application Laid-open No. HEI 9-154299 in which an EGR control valve is driven for opening and closing by a stepping motor.
Normally, external force such as a pressure difference between intake negative pressure and exhaust gas pressure (back pressure) is applied to the EGR control valve. Therefore, the stress applied to the EGR control valve is different when the EGR control valve is driven in its opening direction than in it is when driven in its closing direction, and a required driving torque is also different. Further, a required response of the EGR control valve also differs depending on the driving direction.
For example, in the case of an outward opening type EGR control valve which is opened by lifting a valve element from an intake passage side to an exhaust passage side of an EGR passage, a pressure difference between the intake negative pressure and the back pressure, and the stress based on the flowing resistance of the exhaust gas flowing in the EGR passage act in the closing direction of the EGR control valve. Therefore, in such an outward opening type EGR control valve, a driving torque required when the valve is driven in its opening direction is higher than that required when it is driven in its closing direction because the valve must be driven against the pressure difference. Further, in the EGR control valve, in general, in order to suppress deterioration in emissions generated due to delay in EGR reduction at a time of acceleration, the response time required when the valve is closed is faster than that required when the valve is opened.
Therefore, the EGR control apparatus described in the aforementioned publication is controlled such that a driving speed of the EGR control valve is changed depending on whether the EGR control valve is being driven in the opening direction or the closing direction. That is, in the EGR control apparatus, the driving speed is decreased when a large driving torque is required and at the time of opening operation of the valve when a level of required response is low, and the driving speed is increased at the time of closing operation of the valve when the level of the required response is high.
An electric motor such as a stepping motor employed as a driving device of the EGR control valve in the EGR control apparatus generally has a characteristic that the driving torque generated and the driving speed (the number of revolution of the motor) are opposed to each other and therefore, if the driving speed is decreased, the generated driving torque is increased, and if the driving speed is increased, the generated driving torque is decreased. Therefore, by changing the driving speed depending on the driving direction as described above, the driving torque when the valve is driven for opening can be secured and the response speed when the valve is driven for closing can be increased, and it is possible to control the operation of the EGR control valve even with a small and inexpensive stepping motor for generating a small output.
Meanwhile, it has been confirmed that the magnitude of the external force like the pressure difference acting on the EGR control valve is not always constant, and the magnitude varies in accordance with a driving state of the internal combustion engine or the opening position of the EGR control valve. However, In the EGR control apparatus of the above publication, the driving speed is uniformly changed in accordance with the valve opening operation or the valve closing operation. Therefore, even when the external force actually acting on the EGR control valve is small and thus the driving torque required at that time is not so great, the driving speed may unnecessarily be decreased, and sufficient response of the EGR control apparatus may not be obtained.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the above circumstances, and it is an object of the invention to provide an exhaust gas recirculation control apparatus for an internal combustion engine capable of maintaining a required driving torque of an EGR valve, and maintaining a response at opening/closing of the EGR valve as high as possible.
To achieve the above object, according to a first aspect of the present invention, there is provided an exhaust gas recirculation control apparatus for an internal combustion engine including: an outward opening type control valve for adjusting a flow rate of an exhaust gas recirculated through an exhaust gas recirculation passage of the internal combustion engine, a pressure of the exhaust gas being exerted in a closing direction of the control valve; driving means having a characteristic that a driving speed is in inverse relation to a driving torque when the control valve is opened and closed, which drives the control valve for opening and closing; and control means for changing the driving speed of the driving means when the control valve is driven in its opening direction in accordance with a force external to the driving force of the driving means acting on the control valve.
In the outward opening type EGR control valve which is opened by lifting a valve element from an intake passage side to an exhaust passage side of an exhaust gas recirculation (EGR) passage, a force based on fluid resistance of an exhaust gas flowing through the EGR passage acts in a valve closing direction. Therefore, a large driving torque is required when the valve is opened. An electric motor such as a stepping motor may be used as the driving means for opening and closing the EGR control valve. The aforementioned electric motor has a characteristic that the driving speed inversely relates to the driving torque. That is, if the driving speed is increased, the driving torque is decreased, and if the driving speed is decreased, the driving torque is increased. The above structure makes it possible to maintain a required driving torque and to maintain the response as high as possible, by changing the driving speed in accordance with the external force acting on the control valve. Therefore, it is possible to maintain good control response, and to reliably open and close the EGR control valve, even with a small and inexpensive motor for generating a small output.
Further, in the exhaust gas recirculation control apparatus for the internal combustion engine of the first aspect, the control means changes a driving speed when the control valve is driven in its opening direction in accordance with a pressure difference between an exhaust gas pressure and an intake pressur
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
Wolfe Willis R.
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