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Air control device including air switching valve driven by motorRelated Patent Categories: Power Plants, Internal Combustion Engine With Treatment Or Handling Of Exhaust Gas, By Means Producing A Chemical Reaction Of A Component Of The Exhaust Gas, Condition Responsive Control Of Reactor Feed, Pressure, Or By-pass, Air Feed To Reactor Modulated Or Diverted By ControlAir control device including air switching valve driven by motor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070017217, Air control device including air switching valve driven by motor. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is based upon and claims benefit of priority of Japanese Patent Application No. 2005-209613 filed on Jul. 20, 2005, the content of which is incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a valve for switching a fluid flow such as airflow, the valve being driven by a driving mechanism including a driving motor. [0004] 2. Description of Related Art [0005] An airflow control valve for controlling an amount of air flowing through an air passage connected to an exhaust pipe of an internal combustion engine has been known. The airflow control valve is driven in an on-off fashion by a driving mechanism including an electric motor and a speed reduction mechanism having plural gears. A final gear in the speed reduction mechanism is engaged with a rack formed on a valve shaft which is reciprocated to open or close a valve port. Examples of this kind of airflow control valve are disclosed in JP-A-6-173783 and JP-A-11-62724. [0006] A coil spring for biasing the valve head toward an open position or a closed position of the airflow control valve is disposed around the valve shaft. Since the coil spring is disposed around the valve shaft, it is unavoidable to make the valve shaft longer by a length of the coil spring to secure a space for the coil spring. Accordingly, the airflow control valve becomes large in size, requiring a large mounting space. [0007] Some of the airflow control valves such as EGR (Exhaust Gas Recirculation) valves are connected in a cantilever fashion to an air passage communicating with a combustion chamber of an internal combustion engine. More particularly, a housing containing a motor, a speed reduction mechanism and a valve therein is connected to the air passage at a position opposite to the motor in a cantilever fashion. If the valve shaft is long in its axial direction, a distance from the mounting portion of the housing to the motor becomes long, and the housing has to be made stronger to endure vibration of the engine. When the speed reduction mechanism is severely vibrated, a relative movement between a rack of the valve shaft and a final gear of the speed reduction mechanism engaging with the rack is generated, and thereby abrasion wear occurs in the rack and the final gear. SUMMARY OF THE INVENTION [0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved air control device including an air switching valve, which is made compact in size by making the valve shaft short. Another object of the present invention is to improve its mechanical strength against vibration and to suppress the abrasion wear of the rack and the final gear. [0009] The air control device of the present invention is advantageously used as a secondary air control device for an internal combustion engine mounted in an automotive vehicle. The air control device supplies secondary air sent from an air pump to a catalyzer, such as three-way catalyzer, disposed in an exhaust pipe for purifying exhaust gas. The secondary air is supplied to the catalyzer to warm it up to thereby activate it when a temperature of the catalyzer is low. [0010] The air control device includes a housing having a valve port formed therein, an electric motor, a speed reduction mechanism having plural gears for transmitting a rotational torque of the motor at a reduced speed, a valve for opening or closing a valve port, and a biasing spring for biasing the valve in a direction to close the valve port. The valve is composed of a valve head sitting on a valve seat and a valve shaft connected to the valve head. The valve shaft includes a rack engaging with a final gear of the speed reduction mechanism. A rotational movement of the final gear is converted to a linear movement of the valve shaft. The biasing spring is disposed around an axis of the final gear. When the electric motor is energized, the valve shaft of the valve is driven in a direction to open the valve port against the biasing force of the biasing spring, and thereby the valve port is open to supply the secondary air to the catalyzer. [0011] The housing containing components of the air control device therein is connected to an air passage communicating with the valve port in a cantilever fashion. The valve may be biased in a direction to open the valve port so that the valve port is closed when driven by the electric motor. The electric motor may be replaced with other drivers such as an electromagnetic solenoid. The air control device may be used for re-circulating exhaust gas into an engine in a controlled manner. Preferably, the biasing spring is a torsion spring wound around a flange connected to the axis of the final gear. [0012] Since the biasing spring is disposed around the axis of the final gear, instead of disposing it around the valve shaft, a length of the valve shaft can be made shorter. Accordingly, the air control device can be made compact, and its mechanical strength against engine vibration can be improved when the housing is mounted on the air passage in a cantilever fashion. Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0013] FIG. 1 is a perspective view showing a structure of a valve-driving mechanism used in an air control device of the present invention; [0014] FIG. 2 is a cross-sectional view showing an entire structure of a secondary air control device for an internal combustion engine; [0015] FIG. 3 is a cross-sectional view showing the valve-driving mechanism; and [0016] FIG. 4 is a plan view showing a speed reduction mechanism of the secondary air control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0017] A preferred embodiment of the present invention will be described with reference to accompanying drawings. The present invention is applied to a secondary air control device for an internal combustion engine mounted on an automotive vehicle. The secondary air control device is used in a system for supplying secondary air to a three-way catalizer in an exhaust pipe to warm up and quickly activate it when a temperature of the exhaust gas is low at a starting up of the engine, for example. An air pump is connected to the secondary air control device through a secondary air passage. [0018] Referring to FIG. 2, an entire structure of the secondary air control device will be described. The secondary air control device includes an air switching valve 1 for opening or closing an air passage, a one-way valve 2 for permitting airflow only in one direction and an electric motor 3 for driving the air switching valve 1. A driving force of the electric motor 3 is transmitted through a valve driving mechanism (shown in FIG. 1) to a poppet valve 4 of the air switching valve 1. All of these components of the secondary air control device are contained in a housing composed of a valve case 11, an outlet case 13 and case cover 12 (shown in FIG. 3). [0019] An air pump for supplying the secondary air to an inlet port 17 of the air switching valve 1 and the electric motor 3 are controlled by an ECU (Electronic Control Unit) according to driving conditions of the engine. The ECU is a known microcomputer including a CPU (Central Processing Unit) and memories (ROM, RAM) for storing programs and data. A temperature of the three-way catalizer is detected and inputted to the ECU. When the catalizer temperature is lower than a predetermined level, at a starting up of the engine, the air pump and the electric motor 3 are driven to supply the secondary air to the three-way catalizer. Continue reading about Air control device including air switching valve driven by motor... 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