Abstract:
An exhaust gas recirculation valve in which an impact element is spaced from a head on a valve rod, in order to develop kinetic energy when activated end produce impact on the head to free a valve member which may have become stuck to the valve seat due to deposits on the seat from the recirculating exhaust gas. The impact member is activated when the engine is started and after the valve disk is free, the exhaust gas recirculation valve operates conventionally.

Description:
FIELD OF THE INVENTION 
     The invention relates to an exhaust gas recirculation valve which controls flow of exhaust gas back to an internal combustion engine. 
     The invention relates in particular to such an exhaust gas recirculation valve in which the control of the flow of recirculated exhaust gas is obtained by moving a valve member off a valve seat by a regulated distance. 
     DESCRIPTION OF THE PRIOR ART 
     An exhaust gas recirculation valve is disclosed in DE 43 38 192 A 1 in which flow of engine exhaust gas back to a diesel engine is regulated as a function of operating conditions of the engine, in order to reduce NOx emissions and improve fuel consumption. For this purpose, the exhaust gas recirculation valve is arranged between the engine exhaust line and an air inlet line, preferably directly at the intake manifold. The exhaust gas recirculation valve can be actuated pneumatically or electrically. In the electrical actuator a magnetic field builds up when current is supplied to a coil to move an armature, which, in turn, acts on a valve rod to open the valve against a closing spring. In the pneumatically actuated exhaust gas recirculation valve, the valve is opened by applying suction pressure in a chamber to move a membrane connected to the valve rod. A reverse direction of operation is possible. 
     The valve which may be equipped with only one seat, preferably has two seats connected in series in the electrically actuated embodiment to reduce the required actuating force. For more precise flow control, which is dependent on the quantity of exhaust gas introduced into the inlet air of the engine, the valve is brought to a defined opening position by means of a potentiometer, of a positional regulation device, by an electromagnetic motor operator. In a pneumatic valve with positional feedback, the suction pressure is regulated appropriately in the operation chamber. 
     There occurs a deposition of carbon, lacquer and condensate in the exhaust gas recirculation valve due to the recirculation of exhaust gas, particularly when the recirculated exhaust gas is relatively cold, for example, under operating conditions in which the engine has not warmed up and in the case when the exhaust gas is cooled in heat exchangers for reduction of NOx emissions. 
     These residual deposits are applied to the sealing surfaces of the valve seat and the valve disk, and when the exhaust gas recirculation valve has been closed for a relatively long time, for example, during overnight parking of the vehicle, the valve disk becomes stuck to the valve seat. The adhesion of the disk to the seat exceeds by a multiple the maximum opening force of the electromagnetic or pneumatic actuator. 
     Thus, the valve can no longer open and its function is completely disrupted causing pollution of the environment and the need for repair. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide means to avoid this costly and environmentally undesirable disruption of the exhaust gas recirculation system. 
     This object is achieved according to the invention by an exhaust gas recirculation valve comprising an inlet for recirculated exhaust gas, an outlet for supplying recirculated exhaust gas to an internal combustion engine, valve means for controlling communication between said inlet and said outlet, said valve means comprising a valve member, a seat for said valve member, a valve rod connected to said valve member and a head on said valve rod, means for moving said valve rod to control the valve member and regulate flow of the exhaust gas from said inlet to said outlet, and a device for developing kinetic energy to impact against said head and free the valve member when stuck to the valve seat. 
     In further accordance with the invention, a method is provided for operating the exhaust gas recirculation valve to free a valve member stuck to the valve set, by the steps comprising controlling flow of exhaust gas from an inlet of the exhaust gas recirculation valve to an engine-connected outlet thereof by regulated movement of a valve member off a seat therefor, and developing kinetic energy in a drive member when the valve member is on said seat to produce impact of the drive member on the valve member to free the valve member when stuck to the valve seat. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING 
     FIG. 1 is a sectional view of an embodiment of an exhaust gas recirculation valve according to the invention in a rest or closed position; 
     FIG. 2 shows the exhaust gas recirculation valve in an intermediate position as the valve is being opened; 
     FIG. 3 shows the exhaust gas recirculation valve in the opened position; 
     FIG. 4 shows another embodiment of the exhaust gas recirculation valve according to the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an exhaust gas recirculation valve  1  which can be installed on a suction pipe (not shown) connected to the air inlet of an internal combustion engine. The valve  1  has an exhaust gas inlet  2  connected to a chamber to which is also connected an outlet  3  connected to the air inlet of the engine to recirculate exhaust gases thereto. Valve  1  is an electromagnetic valve and comprises a coil  4  in a head piece  5  and an armature  6  operated by energization of coil  4  to act on a valve rod  9  and displace valve disks  8  to open the valve against the action of a biassing spring  7 . 
     Armature  6  is connected to a positional feedback, device  10  connected to a computer ( 20 ) receiving other operating parameters, to determine the degree of opening of the exhaust gas recirculation valve and thus the quantity of exhaust gas recirculated to the engine. Valve disks  8  cooperate with two valve seats  11  but the exhaust gas recirculation valve may also be designed with one valve seat and one valve disk. Valve rod  9  is urged by a spring  12  to the closed position of the valve. In order to assure an opening of the exhaust gas recirculation valve even if there is sticking between the valve disk and the valve seat, the valve operates as described below. 
     In the rest position, a free space or clearance, x in FIG. 1, is provided between armature  6  and head  13  of valve rod  9  under the action of spring  7  between armature  6  and head  13 . If magnetic coil  4  is energized with full current instantaneously a magnetic field is rapidly produced and armature  6  is accelerated against the action of spring  7  to build up kinetic energy and impact against head  13  of the valve rod, by means of a striker  14  on armature  6 . When the current is turned off, the armature retracts under the action of spring  7 . By a single actuation of the armature or multiple repetitive actuations over brief intervals, the armature “hammers” the valve rod and any sticking between valve disk  8  and valve seat  11  is overcome. According to the computer program, the “hammering” can be effected continuously when the ignition is turned on, or only if it has been established that the determined position of the valve  1  has not been reached, for example, under normal, pulse width-modulated control of the electromagnet, by means of a comparison between the predetermined position of the armature and its actual position as determined by the positional feedback device  10 . 
     FIG. 4 shows another embodiment of the exhaust gas recirculation valve according to the invention. In this embodiment, a “hammering” of the valve disks  8  is effected by a separate additional plate magnet armature  6 ′ which is held at a distance from head  13  by spring  7 . The armature  6 ′ is actuated by a separate coil  15 . Because of the spacing of the plate armature  6 ′ from head  13 , when the coil  15  is energized, the armature  6 ′ is moved to produce kinetic energy and forceable impact with head  13  to free the disks  8  when they are stuck to the seats. 
     The regulated degree of opening of the valve disks to control the flow of the recirculated exhaust gas from the inlet  2  to the outlet  3  is effected by controlled displacement of head  13  by displacement of proportional magnetic armature  16  upon energization of coil  4 . The armature  16  is acted on by spring  17  to urge striker  14  against valve head  13 . Thereby, movement of armature  16  is directly followed by valve rod  9 . 
     This embodiment offers the advantage that the plate magnet  6 ′ opens the valve with high actuating forces over a short distance, whereafter control of the degree of opening of the valve is independently effected by the armature  16 . 
     Armature  16  is thus not subjected to development of high impact forces during very short periods of time therefore promoting service life and accuracy of flow control of the recirculated exhaust gas. 
     The positional feedback device  10  can determine the thickness of the depositions on the valve disk and valve seat from time to time in an adaptive process step in the computer. In this way, flow control accuracy is maintained due to a corresponding consideration in the valve stroke. 
     In another embodiment of the invention, which is not shown, drive head  5  can be constructed as a conventional pneumatic actuator, which is divided into two chambers by a membrane which carries out the function of armature  6  or  16 . In this regard the striker  14  is connected to the membrane and when the valve disks are on the seats the striker is spaced from the head  13  and when suction pressure is applied to an operating one of the chambers, the membrane deforms and causes the striker to accelerate and impact against the head  13  of the valve rod  9 . 
     When the operating chamber is returned to normal atmospheric pressure, the membrane returns to its initial position under the action of spring  7  arranged in the operating chamber, in readiness for the next operation. The operating chamber is arranged in the drive head  5  to face valve rod  9  and the other chamber is at atmospheric pressure. In the construction with the pneumatic actuator, the unsticking operation can be effected after buildup of suction pressure following the first engine revolutions after starting the internal combustion engine. The suction pressure, however, may also be produced by a vacuum pump driven mechanically or by an electrical motor. After the unsticking of the valve disks the exhaust gas recirculation valve, whether driven electromagnetically or pneumatically, operates as a conventional valve. Then the drive head is controlled by the computer in such a way that the free space x in FIG. 1 is taken up at conventional regulating speed against the action of spring  7  so that there is no impact, between striker  14  and head  13  and the device is in the position shown in FIG. 2, in which striker  14  is in contact with head  13  and the actual adjusting of valve disks  8  commences to open the exhaust gas recirculation valve  1  and provide regulated flow of exhaust gas from inlet  2  to outer  3 . 
     Although the invention has been described with reference to specific embodiments, it will be obvious to those skilled in the art that numerous modifications and variations can be made within the scope and spirit of the invention as defined in the attached claims.